- Email: [email protected]
Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels
Chemosphere xxx (2013) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels Xingmin Xu, Changsen Zhang, Yonggang Liu, Yunpu Zhai, Ruiqin Zhang ⇑ The College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, China Research Academy of Environmental Science, Zhengzhou University, Zhengzhou 450001, China
h i g h l i g h t s Two-step catalytic HDO process used for translating bio-oil to transportation grade hydrocarbon fuel. First step to overcome coke formation with better biofuel quality. Second step upgrading biofuel. 1
Final products similar to fossil fuels with HHV of 46 MJ kg
a r t i c l e
i n f o
Article history: Received 1 April 2013 Received in revised form 14 June 2013 Accepted 17 June 2013 Available online xxxx Keywords: Fast pyrolysis oil Two-step catalytic hydrogenation Mild HDO Deep HDO Organic solvent
and <1% O content.
a b s t r a c t Two-step catalytic hydrodeoxygenation (HDO) of fast pyrolysis oil was investigated for translating pyrolysis oil to transportation grade hydrocarbon liquid fuels. At the first mild HDO step, various organic solvents were employed to promote HDO of bio-oil to overcome coke formation using noble catalyst (Ru/C) under mild conditions (300 °C, 10 MPa). At the second deep HDO step, conventional hydrogenation setup and catalyst (NiMo/Al2O3) were used under severe conditions (400 °C, 13 MPa) for obtaining hydrocarbon fuel. Results show that the phenomenon of coke formation is effectively eliminated, and the properties of products have been significantly improved, such as oxygen content decreases from 48 to 0.5 wt% and high heating value increases from 17 to 46 MJ kg1. GC–MS analysis indicates that the final products include C11AC27 aliphatic hydrocarbons and aromatic hydrocarbons. In short, the fast pyrolysis oils were successfully translated to hydrocarbon liquid fuels using a two-step catalytic HDO process. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction The fast pyrolysis oil (bio-oil) is a promising second-generation liquid fuel which can be obtained from lignocellulosic biomass by fast pyrolysis with the yield up to 75 wt% (Czernik and Bridgwater, 2004; Huber et al., 2006). The bio-oil, which has been produced in the demonstration and semi-commercial scales, is one of a most potential renewable energy to replace fossil fuel (Bridgwater, 2012). However, the bio-oil includes abundant oxygenated compounds such as carboxylic acids, aldehydes, ketones, alcohols and phenols as well as water (Lu et al., 2009; Oasmaa et al., 2012). These undesirable properties render bio-oil less useful; for example lower heating value due to high oxygen content and high moisture content, serious corrosivity because of abun-
⇑ Corresponding author at: The College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, China. Tel.: +86 371 67781284; fax: +86 371 67781163. E-mail address: [email protected] (R. Zhang).
dant acids, instability attributed to the activity of oxygenated chemicals (especially aldehydes, ketones and furans) and easy blockages in nozzles due to formation of coke (Wildschut, 2009). Consequently, the application of bio-oil for direct use as hydrocarbon fuels is limited. It is essential to upgrade bio-oil with different approaches, including catalytic cracking (Adjaye and Bakhshi, 1995; Hew et al., 2010), catalytic hydrogenation (Czernik and Bridgwater, 2004; Elliott, 2007), supercritical technology (Tang et al., 2009; Zhang et al., 2012) and emulsification (Bridgwater, 2012). Among these processes, catalytic hydrogenation has been demonstrated to be a promising alternative. However, it is difficult for bio-oil simply translated to hydrocarbon fuel by directly catalytic hydrodeoxygenation (HDO) using noble catalysts (Ru, Pd, and Pt). This is mainly due to the fact that the instability of active oxygenated compounds easily leads to coke formation during the catalytic hydrogenation of bio-oil, even under the mild conditions. The polymerization reaction generates a large amount of asphalt-like materials resulting in coke formation, which ultimately leads to catalyst deactivation (Wildschut et al., 2009, 2010). Thus, searching for
0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
2
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx
Table 1 Experiment results of mild HDO using Ru/C catalyst with several solvents under different conditions. Parameter
Value
Cases
A
B
C
D
Solvent Additive amount (g) Hydrogen consumption (kg kg1 feedstock)
Processing conditions Tetraline 30 0.04
Decalin 30 0.03
Diesel 30 0.03
Diesel/isopropanol 20/10 0.03
Density (kg L1) Viscosity (at 25 °C, cst) HHV (MJ kg1) Moisture (wt%) TAN (mg KOH g1)
Properties (oil phase) 0.91 10.4 38.0 1.2 25.7
0.88 11.0 39.5 1.4 25.2
0.88 (L)–1.12 (H) 6.5 (L) 43.1 (L)–33.9 (H) 0.4 (L)–4.4 (H) 8.7 (L)–43.6 (H)
0.93 11.2 38.7 1.5 24.2
C H O Feedstocks oxygen (wt%) Degree of deoxygenation (wt%)
Elemental analysis (oil phase, wt%) 80.8 78.9 9.4 11.4 9.4 9.3 36.9 36.9 75 75
83.1 (L)–73.0 (H) 12.9 (L)–9.5 (H) 3.7 (L)–18.4 (H) 36.9 90 (L)–50 (H)
78.2 11.0 9.3 35.6 74
Note: All data were the average value of three samples; feedstocks oxygen contents were calculated based on oxygen contents of bio-oil and solvents; L – Light component, H – Heavy component; all experiments were carried out using 100 g bio-oil and 10 g Ru/C catalyst at 300 °C, 10 MPa, 3 h.
other alternatives such as employing a two-step catalytic HDO for upgrading of bio-oil to hydrocarbon fuel is needed. In the two-step process, the partial oxygenated groups can be eliminated especially like aldehydes, ketones and furans, which are easily causing coke formation, to obtain stable oil-phase products with lower oxygen content under relatively mild conditions in the 1st step. The 2nd step is then performed at severe conditions to obtain hydrocarbon fuels. In fact, Elliott and Baker (1989) have initially conducted a two-step catalytic hydrotreating of bio-oil for obtaining hydrocarbon fuel at low temperatures (250–300 °C), and then hydrogenation of bio-oil under higher temperature conditions using conventional hydrotreating catalyst (CoMo/Al2O3). However, the results showed that coking phenomenon was still severe and oxygen content of products remained extremely high (30 wt%). The subsequent studies by several investigators using two-step process employing NiMo/Al2O3 and CoMo/Al2O3 catalysts (Samolada et al., 1998) or using noble catalysts (Wildschut et al., 2009; Venderbosch et al., 2010) still faced coke formation problems as well as high oxygen content in the final products (6– 11 wt%). It is well known that solvent (usually considered to be a hydrogen donor solvent) can restrain coke formation and improve bio-oil upgrading (Zhang et al., 2005; Elliott, 2007). However, the improvement of the quality of the products was only limited to single step HDO process with oxygen content of 3 wt%, which cannot meet the standards for transportation liquid fuel. In this paper, we evaluated a two-step catalytic hydrogenation method. In the first step, various organic solvents were employed to improve HDO of bio-oil using Ru/C catalyst under mild conditions to avoid coke formation and obtained stable intermediate products for the subsequent deep HDO. In the second step, experiments were performed at conventional hydrogenation setup and with catalyst (NiMo/Al2O3) under relatively severe conditions for the production of hydrocarbon biofuels. Four different solvents (tetraline, decalin, diesel and diesel/isopropanol) were used and result comparisons could be made as to the effectiveness of each solvent. Since information for a comprehensive analysis of obtained biofuel is almost non-existent, this study was undertaken to analyze organics from oil phase, gas phase composition as well as oil properties for both products from 1st and 2nd step HDO process. To the best of our knowledge, the oxygen content in the final oil products achieved is one of the lowest (0.5%) among all upgraded bio-oils.
2. Materials and methods 2.1. Materials Bio-oil was supplied by the fast pyrolysis of pine sawdust at 500 °C in a Bench-Scale Fluidized-Bed reactor at Zhengzhou University. The typical properties of the bio-oil, with 48% oxygen content, are given in Supplementary Material (SM), Table SM-1. The commercial noble catalyst Ru/C was obtained from Shanxi Rock New Materials for mild HDO of bio-oil. Note that Ru catalyst has been commonly used in hydrotreatment of bio-oil (e.g., Wildschut et al., 2009, 2010; Venderbosch et al., 2010). The Ru content was 5 wt% with the total surface area of 800 m2 g1 and the average particle size of 74 lm. The traditional petroleum hydrogenation catalyst NiMo/Al2O3 was provided by Shenyang Chemical Industry Research Institute for deep HDO. Hydrogen, argon (carrier gas) and calibration gases all were purchased from Beijing Ruizhx Technology. All reagents used are analytical grade. Tetraline, decalin and isopropanol were obtained from Sinopharm Chemical Reagent and the diesel oil from a nearby gas station. Tetraline and decalin were selected as organic solvents because they are known to be hydrogen donor with respect to hydrogenation and HDO (Sheu et al., 1988; Zhang et al., 2005). Diesel was chosen because it has capacity to dissolve hydrogen. Unfortunately, diesel is immiscible with bio-oil because of polarity diversity. Therefore, the mixture of diesel and isopropanol was also used as organic solvent, because isopropanol is easy to blend with bio-oil as cosolvent to promote the intermiscibility between diesel and bio-oil.
2.2. Experiments The first so called mild step hydrogenation was performed at pressure of 10 MPa and temperature of 300 °C. The mild conditions are in comparison with the severe conditions used in the single step of hydrotreatment of bio-oil, or temperature up to 400 °C and pressure 20 MPa (Wildschut et al., 2009, 2010; Venderbosch et al., 2010). The reactants were stirred at 650 rpm with a magnetic stirrer in a 500 mL autoclave (Weihai Automatic Control). The temperature was controlled using an electric jacket combined with a thermocouple thermometer and the pressure regulated by the back pressure valve. The second step hydrogenation setup is a
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
3
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx
continuous fixed bed reactor (Luoyang Kaimeisheng Petrochemical Equipment) with a maximum pressure of 25 MPa and at a temperature of 500 °C. Temperature and pressure were controlled as in the first step. A schematic representation of the system setup is given in Fig. SM-1. The overall experimental conditions are summarized in Table 1 and the detailed description of each step is as follows: For the first step hydrogenation experiment, the reactor was filled with 100 g bio-oil, 30 g organic solvents (tetraline, decalin, diesel or diesel/isopropanol) and 10 g Ru/C catalyst. Subsequently, the reactor was flushed with N2 gas and then purging with 2 MPa H2 (replacing nitrogen) three times, and eventually pressurized with 8.0 MPa H2 at room temperature. The reactor was heated to the intended reaction temperature (300 °C) with a heating rate of 3.0 °C min1 and kept at that temperature for 3 h at stirring speed 650 rpm. The pressure in the reactor was set to the predetermined value (10 MPa) controlled by the back pressure valve. The volume of off-gas was metered by a wet type gas meter, and off-gas was collected using a gas bag after the reaction for the detection of gaseous composition by GC (Gas Chromatograph). After completion of the reaction, the reactor content was cooled to ambient temperature. The catalysts were separated from the liquid phase by filtration. The liquid phase was then separated via a separatory funnel into 2- or 3-phase (light/heavy oil and water phase). The second step hydrogenation experiment employed a typical conventional petroleum hydrogenation technology (fixed bed reactor) and catalyst (NiMo/Al2O3), which has been employed as the most frequently tested catalysts for the HDO reaction (Sheu et al., 1988; Baldauf et al., 1994). At first, the fixed bed reactor was filled with 10 mL Al2O3 (protection zone, or 18 g) at the bottom, 20 mL (about 19.2 g) NiMo/Al2O3 catalyst (reaction zone) in the middle and 40 mL Al2O3 (preheating zone, or 70 g) at the top. Afterward the NiMo/Al2O3 catalyst was sulfurized using 1.5% CS2 kerosene solution at 320 °C and 13 MPa H2 for 10 h, The stabilized intermediate oil (termed as HDO-biofuel) from the 1st step was then fed to reactor by a high pressure pump at 20 mL h1 at 400 °C with a liquid hourly space velocity (LHSV) of 1.0 h1. Hydrogen was continuously fed to the reactor through mass flow meter with the H2/oil ratio (v/v) 400 or 800 (or 0.04–0.08 kg kg1). Temperature and pressure measurement and control were the same as in the first step. The refined products were cooled and then separated by a primary and secondary liquid-vapor separator, with liquid phase (lesser extent of water) collected (Fig. SM-1). The resultant from this deep HDO product is called hydrocarbon biofuel (HC-biofuel). The off-gas was collected just like the first step experiment.
(30 m 0.53 mm 0.25 lm) with a TCD was used to detect CO2, C2H4, and C2H6. Helium (99.9999%) was used as the carrier gas, and the oven temperature was kept at 80 °C for 13 min. Both Instruments were calibrated by calibration gas for quantification of all gas components. GC–MS analyses were performed for analysis of different organic compositions in oil phase in an Agilent 7890A-5975C GC equipped with a DB-FFAP capillary column (30 m 0.25 mm 0.25 lm). The GC split was 1:100 and the injector temperature was set at 250 °C with an injection volume of 1 lL. The oven temperature was kept at 50 °C for 3 min, increased to 200 °C at a rate of 3 °C min1, and then held at 200 °C for 50 min. Helium was used as the carrier gas with a constant flow rate of 1 mL min1. The mass spectrum employed Electron Impact ionization source at 70 eV. The compositions of bio-oil and HDO products were identified by NIST08 spectrogram depot. The FTIR spectra of HDO products were recorded in a Bruker Alpha Class 1 instrument. The typical Quality Assurance/Quality Control procedures were closely followed to ensure data adequacy. 2.4. Performance evaluation In practice it is not possible to evaluate the conversion of each individual component in the bio-oil. Thus, several important gross parameters were used for evaluating the oil yield (Yobs) and the degree of deoxygenation (DOD) as:
Y obs ¼
mproduct 100% mfeed
DOD ¼
ð1Þ
wt% Oproduct 100% 1 wt% Ofeed
ð2Þ
Here mproduct and mfeed are the mass of product and feedstock, respectively; and wt% Oproduct as well as wt% Ofeed are the percentage of oxygen in product and feedstock, respectively (Mortensen et al., 2011). The energy efficiency was estimated as (Milne et al., 1990):
energy efficiencyð%Þ ¼
! yproduct HHVproduct 100% HHVfeed þ yH2 HHVH2
ð3Þ
where yproduct is defined as the kg yield of biofuel produced per kg raw pyrolysis oil, HHVproduct and HHVfeed are the high heating value of product and feedstock, respectively. yH2 is kg hydrogen used per kg of pyrolysis oil. 3. Results and discussion
2.3. Analytical methods 3.1. Mild HDO The elemental compositions of the both HDO and HC biofuels were determined using a Thermo Electron Corporation Flash EA 1112 analyzer (Delft, the Netherlands). The heating values of the samples were measured by a ZDHW-6000 automatic calorimeter (Hebi Instrument, Henan). The water content in the samples was determined by a Karl Fischer KF-1A automatic titration (Shanghai Baoshan Fine Working Electronic Instrument). The viscosities of the oil and products were determined at 25 °C with a kinematic viscosity instrument (TimePower Measure and Control Equipment, Beijing). The total acid number (TAN) for the bio-oil and upgraded products were determined using the ASTM D66 standard method. GC analyses of H2, CO and CH4 were preformed on a Varian CP3380 GC equipped with a thermal conductivity detector (TCD) using a 5 Å molecular sieve column. The injector, oven and detector temperatures were kept at 50, 80 and 130 °C, respectively. Argon (99.9999%) was used as the carrier gas. Another Varian CP-3800 GC equipped with a RT-QPLOT capillary column
3.1.1. HDO-biofuel composition Four types of organic solvents including tetraline, decalin, diesel and diesel/isopropanol were used and compared under the same operating conditions with the same catalyst (Ru/C) for choosing the best solvent for the subsequent deep HDO process study; these cases are defined as A to D (Fig. 1), and the corresponding oil-phase products are called HDO-biofuel A to D, respectively (Table 1). The composition for different components of HDO products is illustrated in Fig. 1a. Through mass balance (90–99 wt%), the unaccountable loss fraction is apparently due to viscous compounds that tend to stick to reactor wall and tubing. Clearly, the compositions for each component under different solvent conditions are varied, particularly for off-gas and oil distribution. Nonetheless, light oil and water fractions constitute a major portion of HDObyproducts. All different solvents used exhibited yellowish transparent aqueous phase and yielded insignificant fraction of solid,
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
4
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx
3.1.3. Gas composition The gas-phase compositions are given in Fig. 1b. As could be expected, the main component was un-reacted hydrogen. In addition, CO2 was present in amounts between 2.5 and 5 mol%. A likely pathway for the formation of CO2 was thermal decarboxylation of organic acids (Venderbosch et al., 2010; Wang et al., 2012). For each case, small amounts of CO were formed as well (1– 2 mol%), probably as a result of decarbonylation reactions (Choudhary and Phillips, 2011; Wang et al., 2012), with insignificant amount of CH4 detected (<1 mol%) due to demethylation of phenolic derivatives (Bykova et al., 2012). Some C2H4 and C2H6 were also formed resulting from thermal cracking of hydrocarbon present in the solvent. The unknowns of total gas compositions (1–3 mol%) were within experimental errors. To sum up, if the goal was to achieve higher oil yields and higher DOD under mild reaction conditions, tetraline and diesel/isopropanol appeared to be efficient at studied reaction conditions of 300 °C, 10 MPa and 3 h. Thus, HDO-biofuel A with tetraline as solvent and HDO-biofuel D with diesel/isopropanol were selected for intermiscibility and stability evaluation. HDO-biofuels were easy to blend with bio-oil and diesel resulting in the homogeneous state. In addition, the stability was evaluated by determining viscosity of HDO-biofuels stored after a period of time (up to 12 months) at 25 °C. The relativity constant viscosity values even after 12-month storage (<7% difference) clearly indicate their stable properties (Table SM-2). Fig. 1. Mild HDO of bio-oil using various solvents under the same operating conditions (Ru/C catalyst at 300 °C, 10 MPa, 3 h). (a) Product composition, (b) gasphase composition (Note: A-tetraline as solvent, B-decalin as solvent, C-diesel as solvent, D-diesel/isopropanol as solvent).
indicating less coke formation. One of the main ideas of the 1st step process is to reduce coke formation and results of solid composition (<2%) are much less than those of the previous studies using the Ru/C catalysts without any solvent addition (Wildschut et al., 2009, 2010). Use of diesel alone yields increased fraction of heavy oil and less light oil, due to the fact that bio-oil which has high polarity is difficult to blend with petroleum-based hydrocarbons. On the other hand, with the blend of isopropanol into diesel, the composition changes dramatically with high oil yield (38%) and least amount of solid (<1%) along with higher gas composition (17%).
3.1.2. Properties of mild HDO products Several properties of upgraded bio-oil are shown in Table 1. Except for case C with diesel alone, all solvents and co-solvent used exhibit similar characteristics. Data comparison with those of feedstock (Table SM-1) clearly indicates better improved properties after mild hydrogenation reactions promoted by organic solvents, e.g., density was reduced from 1.2 to approximately 0.9 kg L1, viscosity from 19 down to 10 cst (25 °C), moisture content from 24 to 1–1.5 wt%, and the HHV increased by more than double. In particular, TANs have all been significantly reduced from 118 to about 25 mg KOH g1. Furthermore, elemental analysis showed that C element content of the oil phase after mild HDO was increased from 45 to about 78–81 wt%, H elements from 7 to 9–13 wt%, while O contents have all significantly been reduced from 48 to less than 10 wt%. The DOD reached almost 75 wt% with the highest up to 90 wt% in the light oil of HDO-biofuel C. For comparison, Venderbosch et al. (2010) investigated mild HDO using Ru/C catalyst at different temperatures (175–400 °C) with the DOD only 54 wt%. Clearly, the benefit of solvent addition is apparent in terms of lesser solid formation, lower oxygen content and much higher DOD efficiency.
3.1.4. Organic composition in oil phase GC/MS was applied to gain insight into the composition of the HDO-biofuels produced at 300 °C, 10 MPa and 3 h using Ru/C catalyst. The various components present in the original bio-oil were also analyzed for comparison. The compositions were classified into different categories: acids, aldehydes, ketones, alcohols, phenols, furans, esters and hydrocarbons (Table 2). The results showed that unused tetraline accounted for major peak area for the HDObiofuel A. In order to investigate composition change/formation of HDO-biofuel in comparison with bio-oil, the tetraline content was excluded in Table 2 data. It is noted that data in Table 2 are in area% and the following qualitative discussion must be made with care because of solvent effect on the measured organic composition. In general, the type and number of organic components for feedstock bio-oil are in agreement with those reported by others (Lu et al., 2009; Mortensen et al., 2011), e.g., more than 300 different compounds have been identified in bio-oil. However, the notable differences of pine sawdust produced bio-oil is its higher acetic acid content (15%), no detected carbohydrate due to its further decompose to aldehydes, ketones and alcohols, as well as extremely high phenols (25%) from lignin decomposition (Zhang et al., 2011). The organic compositions after mild HDO process are completely changed. The results for each category are briefly discussed below: After reaction, the content of acids was significantly decreased, e.g., acetic acid reduction from 15 to 2–3%. The acid translation likely includes three pathways: (1) CO2 formation because of decarboxylation as discussed before, (2) ester formation due to esterification with alcohols (e.g. formation of acetic acid butyl ester shown in Table 2), and (3) transfer to aqueous phase (Zhang et al., 2011). Nonetheless, the content of carboxylic acids is one order of magnitude lower than those (2–5%) reported by others (zhang et al., 2011; Ardiyanti et al., 2012) for hydrogenation of bio-oil, apparently due to their partition into oil phase. Aldehydes including aromatic vanillin were translated completely to 2-methoxy-phenol or other phenols derivates (shown in Table 2) through hydrogenation and decarbonylation (Crossley et al., 2009). 2-Butenal might be hydrogenated and saturated to form butanol, and then esterification with acetic acid to form butyl
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
5
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx Table 2 Selected components of bio-oil and HDO-biofuels by GC/MS. Bio-oil
Area (%)
HDO-biofuel A (excluding 85% tetraline)
Area (%)
HDO-biofuel D
Area (%)
Acids Acetic acid Propanoic acid Butanoic acid
16.1 15.3 0.6 0.2
Acids Acetic acid Propanoic acid Butanoic acid
5.5 3.3 0.0 2.2
Acids Acetic acid Propanoic acid Butanoic acid
3.1 1.8 0.4 0.9
Aldehydes Vanillin 2-Butenal
4.0 3.8 0.2
Aldehydes Vanillin 2-Butenal
0.0 0.0 0.0
Aldehydes Vanillin 2-Butenal
0.0 0.0 0.0
Ketones 1-Hydroxy-2-propanone 1,2-Cyclopentanedione 2-Cyclopenten-1-one 1-Hydroxy-2-butanone
15.2 11.4 1.8 1.1 0.9
Ketones 2-Methyl-cyclopentanone 3-Hexanone 2-Ethyl-cyclopentanone 2-Hexanone
5.6 3.0 1.0 1.0 0.6
Ketones 2-Methyl-cyclopentanone 3-Hexanone 2-Hexanone 2-Ethyl-cyclohexanone
3.3 2.2 0.7 0.2 0.2
Alcohols 1-Propanol 2-Cyclohexen-1-ol 3-Methyl-2-hexanol
1.9 1.0 0.8 0.1
Alcohols 1-Propanol Cyclohexanol 2-Methyl-cyclopentanol
1.6 0.5 0.7 0.4
Alcohols 1-Propanol Cyclohexanol 2-Methyl-cyclopentanol
0.0 0.0 0.0 0.0
Phenols 2,6-Dimethoxy-phenol 2-Methoxy-phenol 2-Methoxy-4-propenyl-phenol 2-Methoxy-4-methyl-phenol Phenol
24.5 7.1 5.9 5.3 4.1 2.1
Phenols 2,6-Dimethoxy-phenol 2-Methoxy-phenol 2-Methoxy-4-propyl-phenol 2-Methoxy-4-methyl-phenol Phenol
28.9 2.5 6.4 9.3 6.7 4.0
Phenols 3,4-Dimethyl-phenol 2-Methoxy-phenol 2-Methoxy-4-propyl-phenol 2-Methoxy-4-ethyl-phenol 4-Propyl-phenol
13.8 4.5 2.6 1.1 3.2 2.4
Furans Furfural 2(5H)-Furanone 2-Furanmethanol
5.8 3.0 2.4 0.4
Furans Furfural 2(5H)-Furanone 2-Furanmethanol
0.0 0.0 0.0 0.0
Furans Furfural 2(5H)-Furanone 2-Furanmethanol
0.0 0.0 0.0 0.0
Esters Butyrolactone Acetic acid, butyl ester
0.4 0.4 0.0
Esters Butyrolactone Acetic acid, butyl ester
0.7 0.4 0.3
Esters Butyrolactone Acetic acid, butyl ester
0.2 0.0 0.2
Hydrocarbons Naphthalene Decahydro-naphthalene Toluene
2.0 1.8 0.2 0.0
Hydrocarbons Naphthalene Decahydro-naphthalene Toluene
28.7 23.9 3.4 0.6
Hydrocarbons 1,6-Dimethyl-Naphthalene 2-Methyl-naphthalene Tetradecane
24 7.9 6.2 2.4
o-Xylene 1,3-Dimethyl-benzene 1-Methyl-indan
0.0 0.0 0.0
o-Xylene 1,3-Dimethyl-benzene, 1-Methyl-indan
0.2 0.2 0.4
Undecane 1-Methyl-naphthalene Heptadecane
2.0 3.3 2.2
Note: A: tetraline as solvent, D: diesel/isopronal as solvent, using Ru/C catalyst, at 300 °C, 10 MPa, 3 h.
acetate (shown in Table 2). Ketone content was reduced because of its micromolecule decomposition through decarbonylation and decarboxylation to form CO, CO2 and hydrocarbons, e.g., 1-hydroxy-2-propanone was not detected in product; the finding is consistent with others (Gayubo et al., 2004b). On the other hand, macromolecule ketones were translated to other ketones, e.g., 1,2-cyclopentanedione to 2-methyl-cyclopentanone (shown in Table 2). In short, the content of those compounds (carboxylic acid, aldehydes, and ketones) responsible for coke formation (Liu et al., 2012) has been significantly reduced. Alcohols were easily translated by HDO forming hydrocarbons and water and this pathway was reported by others (Gayubo et al., 2004a). Phenols are difficult to be translated to hydrocarbons due to Ru/C catalyst selectivity and steric effect of phenolic macromolecule resulting in abundant phenolic derivates present in HDObiofuels – in fact, phenolic content has been increased (total form 25% to 43%, Fig. SM-2). Furans are very active functional groups and their completely complex translation includes ring cleavage, hydrogenation, hydrocracking, dehydration and isomerization (Yu et al., 2011). Hydrocarbon levels were increased in the products because of solvent and nature products of HDO of oxygenated organic compounds. To better compare different solvent effects on the organic composition, the composition profiles for two different solvents of HDO biofuel are shown in Fig. SM-2 which indicates the completely different compositions. For example, HDO-biofuel A (excluding sol-
vent) mainly included 43% phenols and 35% hydrocarbons, as well as 7% acids, 9% ketones and 3% alcohols with the corresponding percentages of 18%, 70%, 3%, 5% and 1% in HDO-biofuel D. Again, it must be noted that abundant hydrocarbons certainly come from diesel solvent, thus, if the area% is excluded for diesel, then areas in other components would increase. Therefore, the conversion process of the mild HDO is practically similar for both solvents. The FTIR spectra of typical functional groups of mild HDO-biofuels are shown in Fig. 2. Both solvents exhibit a similar pattern. The major difference lies in the region of 1500–600 cm1, especially at 744 cm1 with no strong peaks due to CAH groups of aromatic hydrocarbon (Fig. 2b), because of the solvent diesel/ isopropanol used rather than tetraline. There are strong CH2, CH3 stretching of aliphatic and aromatic hydrocarbons at 2860, 2929 and 3016 cm1 (Chen et al., 2010; Agblevor et al., 2012). The broadband peak at 3300 cm1 belongs to OH groups of the oxygenated groups associated with phenols and other acidic groups (Zhang et al., 2005; Yang et al., 2009) and, to lesser extent, water interference. The peak at 1707 cm1 is due to C@O groups of carboxylic acid and ketones groups (Chen et al., 2010) with the peaks at 1603, 1494 and 1453 cm1 due to aromatic compounds and their derivatives (Agblevor et al., 2012). Carboxylic acids and phenols are identified in HDO-biofuels in combination with the peak of OH group at 3300 cm1. No peak due to CHO groups in the 2850–2720 cm1 region is observed, due to the absence of aldehydes. The 1300–1000 cm1 region with
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
6
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx Table 3 Properties of deep HDO products. Properties (oil phase) Density (kg L1) Viscosity (at 25 °C, cst) HHV (MJ kg1) Moisture (wt%) TAN (mg KOH g1)
HC-biofuel A H2/oil (v/ v) 400
HC-biofuel A H2/oil (v/ v) 800
HC-biofuel D H2/oil (v/ v) 400
HC-biofuel D H2/oil (v/ v) 800
0.84 2.8
0.85 2.5
0.82 3.3
0.83 3.6
44.9 0.02 0.02
44.8 0.02 0.03
45.7 0.02 0.02
45.6 0.02 0.03
85.6 12.8 0.6 9.3
84.8 12.4 0.8 9.3
94
92
Elemental analysis (organic phase, wt%) C 88.0 87.5 H 11.5 11.8 O 0.5 0.7 Feedstocks oxgen 9.4 9.4 (wt%) 94 93 Degree of deoxygenation (wt%)
Note: All tests were run using NiMo/Al2O3 (dry 19.2 g) at 400 °C, 13 MPa, 1 h1. HC-biofuel A: feedstok was HDO-biofuel A, HC-biofuel D: feedstock was HDO-biofuel D.
Fig. 2. FTIR spectra of functional group of HDO-biofuels using Ru/C catalyst at 300 °C, 10 MPa, 3 h. (a) HDO-biofuel A (tetraline as solvent) and (b) HDO-biofuel D (diesel/isoproponal as solvent).
peaks at 1267 and 1211 cm1 is due to CAO and CAOAC group stretching vibrations of phenols and esters (Yang et al., 2009), respectively. The CAH stretching vibrations of aromatic hydrocarbon are detected at 944, 863, 806 and 785 cm1, as evident by the abundance of aromatic hydrocarbon presented in HDO-biofuel A. The FTIR spectral data corroborated well with the GC/MS data (Fig. SM-2) as well as other biofuel property evaluation. The compositions of mild HDO products mainly contain aliphatic/aromatic hydrocarbons and phenols with less oxygenated compounds like acetic acids, ketones and esters. All in all, the properties of bio-oils have been improved dramatically through mild HDO process. The oxygen content of products is decreased from nearly 48 to less than 10 wt% (Table 1). Due to reduction of oxygenated compounds and solid, oil-water is easily separated. The stability of products had been remarkably ameliorated and easy to mix with fossil fuels (Table SM-2). At last, the corrosivity has been decreased dramatically with the TAN from 118 (bio-oil) to about 25 mg KOH g1. In short, the HDO-biofuel provides a better source for further upgrading to hydrocarbon fuels using the existing refining technology and facility. 3.2. Deep HDO Deep HDO experiments were carried out in a catalytic hydrogenation setup under severe reaction conditions (400 °C, 13 MPa) with conventional hydrogenation catalyst (NiMo/Al2O3) for two different feedstocks (HDO-biofuel A and D). The effect of different H2/oil ratio was investigated with a constant LHSV (1 h1). The major objective was to obtain hydrocarbon liquid fuels with negligible oxygen content and with high HHV which may be potentially used as transportation fuels. 3.2.1. Effect of feedstocks and H2/oil The effect of H2/HDO-biofuels on the properties of deep HDO derived oils for both feedstocks is insignificant as shown in Table 3. Some subtle differences may be due to change in gas hourly space velocity although LHSV (1 h1) is the same. Nevertheless, some
slight changes can be observed between feedstocks, notably lower C and higher H content for HDO-biofuel D due to higher content in aliphatic and lower composition in aromatic hydrocarbons (Fig. SM-2). 3.2.2. Properties of deep HDO products To better comprehend the improved properties of HC-biofuels, one needs to compare data in Table 3 with those of mild HDO products in Table 1. The density of final products is decreased to 0.83 kg L1 with the HHV enhancing to 45 MJ kg1. In addition, the reductions in viscosity (>70% reduction to about 3 cst), moisture (1.2–0.02%), and TAN (25–0.02 mg KOH g1) all exhibit remarkable improvement. In fact, these parameters are similar to the characteristics of fossil refinery fuels. From elemental analysis data, the C, H and O contents are 85–88%, 12–13%, and <1%, respectively, with DOD about 93%. The O/C ratio (Fig. SM-3), an excellent indicator as the extent of deoxygenation, illustrates its one order of magnitude reduction for each step of HDO from original bio-oil (0.8) to HDO-biofuels (0.09) to final HC-biofuels (0.004). For the product to be useful as a transportation fuel, the O/C molar ratio should preferably be less than 0.02 and the H/C ratio between 1.8 and 2.0 (Kersten et al., 2007); for comparison our final products are 0.004 and 1.8, for O/C and H/C ratio, respectively. 3.2.3. Composition of the deep HDO products The composition of deep HDO-products is classified into alkanes, cycloparaffin, monocyclic aromatic hydrocarbons, indan derivates and bicyclical aromatics which include decalin, tetraline and naphthalene and its derivates (Fig. 3), with some representative compounds listed in Table SM-3. The two types of mild HDO products yield a similar pattern (Fig. 3) but with different area percentages. Bicyclical aromatic hydrocarbons are dominant in HCbiofuel A, e.g., peaks at 5.9, 7.6, 16.9 and 22.9 min represent trans-decalin, cis-decalin, tetraline and naphthalene, respectively. The low intensity peaks (before 5 min) represent cycloparaffin. The peaks of benzene series derivatives are detected at 8–15 min with peaks at 17–19 min representing indan derivants and peaks after 25 min as alkanes. On the other hand, for product D, the alkanes are major components with C11AC27 distributing homogeneously in chromatogram. For example, peaks at 4.8, 10.3, 16.6, 25.02, 29.9, 34.5 38.7 and 42.9 min represent undecane, tridecane, pentadecane, octadecane, eicosane, docosane, tetracosane and heptacosane, respectively. Aromatic hydrocarbons and its deriva-
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx
7
Fig. 3. Comparison of the GC–MS chromatograms of deep HDO biofuel (at 400 °C, 13 MPa, 1 h1 and 400 H2/oil with NiMoSx/Al2O3). (a) HC-biofuel A. (b) HC-biofuel D.
tives are distributed all over the alkane range. No peaks of oxygenated compounds (acids, ketones and phenols) are found in Fig. 3a and b. For HC-biofuel A, alkanes (25%) mainly includes C11AC27 which maybe from solvent components and HDO of oxygenated compounds. Cycloparaffin was about 3% which comes from hydrosaturation of aromatic components (Zhao et al., 2009). Monocyclic aromatic hydrocarbons occupied 11% mainly including benzene derivates with branched chains which mainly came from the HDO and hydrocracking of phenolic derivates (Mortensen et al., 2011). Indan derivates are about 4% which maybe from demethylation of tetraline and the cyclization reaction of aromatic derivates, with octahydro-indene derived from hydrogenation of indan derivates. The same pathways may also explain the accumulation/formation/changes of these constituents for HC-biofuel D. However, HC-biofuel D include large amount of alkanes (48%, C11AC27). Cycloparaffin is about 4% including of five-ring and six-ring derivates resulting from hydrogenation of aromatic hydrocarbons. Monocyclic aromatic hydrocarbons are nearly 20% which mainly come from phenols. Bicyclical aromatic hydrocarbons and Indian derivates are about 17.6% (naphthalene derivates). In summary, the products of deep HDO are constituted by various hydrocarbons with negligible oxygenated compounds. The FTIR spectra of HC-biofuel A and D are shown in Fig. 4. The spectra show CAH stretching of alkanes and aromatic hydrocarbons at 2924 and 2867 cm1 and no peak due to OH groups in the 3300 cm1 region (see Fig. 2 for comparison). The absence of OH groups suggests that the oxygenated groups associated with phenols and other acidic groups in the bio-oil and HDO-biofuels have been eliminated during the two-step HDO; this was corroborated with the GC/MS data (Fig. 3). The spectra also show a
Fig. 4. FTIR spectra of functional group of deep HDO biofuel (at 400 °C, 13 MPa, 1 h1 and 400 H2/oil with NiMoSx/Al2O3). (a) HC-biofuel A. (b) HC-biofuel D.
medium intensity peak at 1611, 1608 and 1458 cm1 due to aromatic benzene ring breathing motion, indicating the presence of aromatic groups in the deep HDO biofuels. The peaks at 1458
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
8
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx
and 1376 cm1 are due to CH2 and CH3 vibrations of aliphatic hydrocarbons. The carbonyl carbon peaks (between 1700 and 1730 cm1 due to C@O stretching in ketones, carboxylic acids, and aldehydes) are not detected. The peaks of phenols and other carbohydrate compound due to CAO stretching vibrations between 1300 and 1000 cm1 (Agblevor et al., 2012) are also not observed. Thus, it appears that the composition of biofuels is the mixture of aliphatic and aromatic hydrocarbons and/or alkylated aromatic hydrocarbons. 3.3. Mass balance and energy efficiency In the first step, the HDO reaction primarily generated abundant aqueous phase in addition to water originally present in bio-oil and less gas phase of CO, CO2, CH4, and C23. The average yields for both oil- and water phase were about 40% with gas phase 12% (Fig. 1a). In the second step, the yields (base on HDO-biofuel) were 87% oilphase with 5% gas phase and 8% aqueous phase. Therefore, the total yield of oil-phase was about 35 wt% based on the feed oil. In determining energy efficiency, the energy level of solvent should be included. With the HHV of bio-oil (including 30% solvent), hydrogen, HDO-biofuel and HC-biofuel typically 19, 143, 39 and 46 MJ kg1, respectively, the energy efficiency of 73% for mild HDO and 96% for deep HDO can be achieved. Thus, approximately the overall 70% of the energy present in the bio-oil feedstock is transferred to the final product oil under two-step HDO process. Losses were due to the formation of gas-phase components and solids as well residual amounts of organics in the aqueous phase. 4. Conclusions Bio-oils were successfully translated to hydrocarbons liquid fuels by two-step catalytic HDO process which included mild HDO and deep HDO. In the mild HDO process, the organic solvents were employed to improve quality HDO of bio-oils resulting in less coke formation. For the deep HDO process, the conventional hydrogenation technology (fixed bed reactor) and catalyst (NiMo/Al2O3) were employed for translating HDO-biofuels to hydrocarbon liquid fuels. The properties of final products are similar to fossil fuels which include aliphatic and aromatic hydrocarbons with HHV of 46 MJ kg1 and negligible oxygenated compounds. However, the final hydrocarbon product is a mixture of upgraded bio-oil with solvents and the extent of contribution of solvent to excellent properties of final products along with mechanisms of coke removal through solvent addition awaits further study. Also, the cost of two-step hydrotreatment of bio-oil for transportation hydrocarbon fuel is relatively high at the present time, but the cost should be eventually decreased with the development of technology in the future. Acknowledgments The authors sincerely acknowledge the financial support by the key programs of science and technology of Henan province and Zhengzhou city (Project 10ZDGG121 and Project 111PCXTD165). The authors also thank Miss Zhichao Tan and Mr. Songling Li for their assistance in laboratory analysis. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.chemosphere. 2013.06.060.
References Adjaye, J.D., Bakhshi, N.N., 1995. Production of hydrocarbons by catalytic upgrading of a fast pyrolysis bio-oil. Part I: Conversion over various catalysts. Fuel Process. Technol. 45, 161–183. Agblevor, F.A., Mante, O., Mcclung, R., Oyama, S.T., 2012. Co-processing of standard gas oil and biocrude oil to hydrocarbon fuels. Biomass Bioenergy 45, 130–137. Ardiyanti, A.R., Khromova, S.A., Venderbosch, R.H., Yakovlev, V.A., Melián-Cabrera, I.V., Heeres, H.J., 2012. Catalytic hydrotreatment of fast pyrolysis oil using bimetallic Ni–Cu catalysts on various supports. Appl. Catal., A 449, 121–130. Baldauf, W., Balfanz, U., Rupp, M., 1994. Upgrading of flash pyrolysis oil and utilization in refineries. Biomass Bioenergy 7, 237–244. Bridgwater, A.V., 2012. Review of fast pyrolysis of biomass and product upgrading. Biomass Bioenergy 38, 68–94. Bykova, M.V., Ermakov, D.Y., Kaichev, V.V., Bulavchenko, O.A., Saraev, A.A., Lebedev, M.Y., Yakovlev, V.A., 2012. Ni-based sol–gel catalysts as promising systems for crude bio-oil upgrading: Guaiacol hydrodeoxygenation study. Appl. Catal., B 113–114, 296–307. Chen, Y., Wang, C., Lu, W., Yang, Z., 2010. Study of the co-deoxy-liquefaction of biomass and vegetable oil for hydrocarbon oil production. Bioresour. Technol. 101, 4600–4607. Choudhary, T.V., Phillips, C.B., 2011. Renewable fuels via catalytic hydrodeoxygenation. Appl. Catal., A 397, 1–12. Crossley, S., Faria, J., Shen, M., Resasco, D.E., 2009. Solid nanoparticles that catalyze biofuel upgrade reactions at the water/oil interface. Science 327, 68–72. Czernik, S., Bridgwater, A.V., 2004. Overview of applications of biomass fast pyrolysis oil. Energy Fuels 18, 590–598. Elliott, D.C., 2007. Historical developments in hydroprocessing bio-oils. Energy Fuels 21, 1792–1815. Elliott, D.C., Baker, E.G., 1989. Process for Upgrading Biomass Pyrolyzates. US Patent, 4 795 841. Gayubo, A.G., Aguayo, A.T., Atutxa, A., Aguado, R., Olazar, M., Bilbao, J., 2004a. Transformation of oxygenate components of biomass pyrolysis oil on a HZSM-5 zeolite. I. Alcohols and phenols. Ind. Eng. Chem. Res. 43, 2610–2618. Gayubo, A.G., Aguayo, A.T., Atutxa, A., Aguado, R., Olazar, M., Bilbao, J., 2004b. Transformation of oxygenate components of biomass pyrolysis oil on a HZSM5 zeolite. II. Aldehydes, ketones, and acids. Ind. Eng. Chem. Res. 43, 2619– 2626. Hew, K.L., Tamidi, A.M., Yusup, S., Lee, K.T., Ahmad, M.M., 2010. Catalytic cracking of bio-oil to organic liquid product (OLP). Bioresour. Technol. 101, 8855–8858. Huber, G.W., Iborra, S., Corma, A., 2006. Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering. Chem. Rev. 106, 4044–4098. Kersten, S.R.A., van Swaaij, W.P.M., Lefferts, L., Seshan, K., 2007. Options for catalysis in the thermochemical conversion of biomass into fuels. In: Centi, G., van Santen, R.A. (Eds.), Catalysis for Renewables: From Feedstock to Energy Production. Wiley-VCH, Chichester, pp. 119–141. Liu, W.J., Zhang, X.S., Qv, Y.C., Jiang, H., Yu, H.Q., 2012. Bio-oil upgrading at ambient pressure and temperature using zero valent metals. Green Chem. 14, 2226– 2233. Lu, Q., Li, W.Z., Zhu, X.F., 2009. Overview of fuel properties of biomass fast pyrolysis oils. Energy Convers. Manage. 50, 1376–1383. Milne, T.A., Brennan, A.H., Glenn, B.H., 1990. Source Book of Methods of Analysis for Biomass and Biomass Conversion Processes. Elsevier, London. Mortensen, P.M., Grunwaldt, J.D., Jensen, P.A., Knudsen, K.G., Jensen, A.D., 2011. A review of catalytic upgrading of bio-oil to engine fuels. Appl. Catal., A 407, 1–19. Oasmaa, A., Kuoppala, E., Elliott, D.C., 2012. Development of the basis for an analytical protocol for feeds and products of bio-oil hydrotreatment. Energy Fuels 26, 2454–2460. Samolada, M.C., Baldauf, W., Vasalos, I.A., 1998. Production of a bio-gasoline by ugrading biomass flash pyrolysis liquids via hydrogen processing and catalytic cracking. Fuel 77, 1667–1675. Sheu, Y.H.E., Anthony, R.G., Soltes, E.J., 1988. Kinetic-studies of upgrading pine pyrolytic oil by hydrotreatment. Fuel Process. Technol. 19, 31. Tang, Z., Lu, Q., Zhang, Y., Zhu, X., Guo, Q., 2009. One step bio-oil upgrading through hydrotreatment, esterification, and cracking. Ind. Eng. Chem. Res. 48, 6923– 6929. Venderbosch, R.H., Ardiyanti, A.R., Wildschut, J., Oasmaac, A., Heeres, H.J., 2010. Stabilization of biomass-derived pyrolysis oils. J. Chem. Technol. Biotechnol. 85, 674–686. Wang, S.R., Guo, Z.G., Cai, Q.J., Guo, L., 2012. Catalytic conversion of carboxylic acids in bio-oil for liquid hydrocarbons production. Biomass Bioenergy 45, 138–143. Wildschut, J., 2009. Pyrolysis Oil Upgrading to Transportation Fuels by Catalytic Hydrotreatment. PhD Thesis, University of Groningen, The Netherland. Wildschut, J., Cabrera, I.M., Heeres, H.J., 2010. Catalyst studies on the hydrotreatment of fast pyrolysis oil. Appl. Catal., B 99, 298–306. Wildschut, J., Mahfud, F.H., Venderbosch, R.H., Heeres, H.J., 2009. Hydrotreatment of fast pyrolysis oil using heterogeneous noble-metal catalysts. Ind. Eng. Chem. Res. 48, 10324–10334. Yang, Y., Gilbert, A., Xu, C., 2009. Hydrodeoxygenation of bio-crude in supercritical hexane with sulfided CoMo and CoMoP catalysts supported on MgO: a model compound study using phenol. Appl. Catal. 360, 242–249. Yu, W., Tang, Y., Mo, L., Chen, P., Lou, H., Zheng, X., 2011. One-step hydrogenation– esterification of furfural and acetic acid over bifunctional Pd catalysts for bio-oil upgrading. Bioresour. Technol. 102, 824–8246.
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx Zhang, J., Luo, Z., Dang, Q., Wang, J., Chen, W., 2012. Upgrading of bio-oil over bifunctional catalysts in supercritical monoalcohols. Energy Fuels 26, 2990– 2995. Zhang, S., Yan, Y., Li, T., Ren, Z., 2005. Upgrading of liquid fuel from the pyrolysis of biomass. Bioresour. Technol. 96, 545–550.
9
Zhang, Z.J., Wang, Q.W., Tripathi, P., Pittman, J.C.U., 2011. Catalytic upgrading of biooil using 1-octene and 1-butanol over sulfonic acid resin catalysts. Green Chem. 13, 940–949. Zhao, C., Kou, Y., Angeliki, A.L., Li, X., Johannes, A.L., 2009. Highly selective catalytic conversion of phenolic bio-oil to alkanes. Angew. Chem., Int. Ed. 48, 3987–3990.
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
Contents lists available at SciVerse ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels Xingmin Xu, Changsen Zhang, Yonggang Liu, Yunpu Zhai, Ruiqin Zhang ⇑ The College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, China Research Academy of Environmental Science, Zhengzhou University, Zhengzhou 450001, China
h i g h l i g h t s Two-step catalytic HDO process used for translating bio-oil to transportation grade hydrocarbon fuel. First step to overcome coke formation with better biofuel quality. Second step upgrading biofuel. 1
Final products similar to fossil fuels with HHV of 46 MJ kg
a r t i c l e
i n f o
Article history: Received 1 April 2013 Received in revised form 14 June 2013 Accepted 17 June 2013 Available online xxxx Keywords: Fast pyrolysis oil Two-step catalytic hydrogenation Mild HDO Deep HDO Organic solvent
and <1% O content.
a b s t r a c t Two-step catalytic hydrodeoxygenation (HDO) of fast pyrolysis oil was investigated for translating pyrolysis oil to transportation grade hydrocarbon liquid fuels. At the first mild HDO step, various organic solvents were employed to promote HDO of bio-oil to overcome coke formation using noble catalyst (Ru/C) under mild conditions (300 °C, 10 MPa). At the second deep HDO step, conventional hydrogenation setup and catalyst (NiMo/Al2O3) were used under severe conditions (400 °C, 13 MPa) for obtaining hydrocarbon fuel. Results show that the phenomenon of coke formation is effectively eliminated, and the properties of products have been significantly improved, such as oxygen content decreases from 48 to 0.5 wt% and high heating value increases from 17 to 46 MJ kg1. GC–MS analysis indicates that the final products include C11AC27 aliphatic hydrocarbons and aromatic hydrocarbons. In short, the fast pyrolysis oils were successfully translated to hydrocarbon liquid fuels using a two-step catalytic HDO process. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction The fast pyrolysis oil (bio-oil) is a promising second-generation liquid fuel which can be obtained from lignocellulosic biomass by fast pyrolysis with the yield up to 75 wt% (Czernik and Bridgwater, 2004; Huber et al., 2006). The bio-oil, which has been produced in the demonstration and semi-commercial scales, is one of a most potential renewable energy to replace fossil fuel (Bridgwater, 2012). However, the bio-oil includes abundant oxygenated compounds such as carboxylic acids, aldehydes, ketones, alcohols and phenols as well as water (Lu et al., 2009; Oasmaa et al., 2012). These undesirable properties render bio-oil less useful; for example lower heating value due to high oxygen content and high moisture content, serious corrosivity because of abun-
⇑ Corresponding author at: The College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, China. Tel.: +86 371 67781284; fax: +86 371 67781163. E-mail address: [email protected] (R. Zhang).
dant acids, instability attributed to the activity of oxygenated chemicals (especially aldehydes, ketones and furans) and easy blockages in nozzles due to formation of coke (Wildschut, 2009). Consequently, the application of bio-oil for direct use as hydrocarbon fuels is limited. It is essential to upgrade bio-oil with different approaches, including catalytic cracking (Adjaye and Bakhshi, 1995; Hew et al., 2010), catalytic hydrogenation (Czernik and Bridgwater, 2004; Elliott, 2007), supercritical technology (Tang et al., 2009; Zhang et al., 2012) and emulsification (Bridgwater, 2012). Among these processes, catalytic hydrogenation has been demonstrated to be a promising alternative. However, it is difficult for bio-oil simply translated to hydrocarbon fuel by directly catalytic hydrodeoxygenation (HDO) using noble catalysts (Ru, Pd, and Pt). This is mainly due to the fact that the instability of active oxygenated compounds easily leads to coke formation during the catalytic hydrogenation of bio-oil, even under the mild conditions. The polymerization reaction generates a large amount of asphalt-like materials resulting in coke formation, which ultimately leads to catalyst deactivation (Wildschut et al., 2009, 2010). Thus, searching for
0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
2
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx
Table 1 Experiment results of mild HDO using Ru/C catalyst with several solvents under different conditions. Parameter
Value
Cases
A
B
C
D
Solvent Additive amount (g) Hydrogen consumption (kg kg1 feedstock)
Processing conditions Tetraline 30 0.04
Decalin 30 0.03
Diesel 30 0.03
Diesel/isopropanol 20/10 0.03
Density (kg L1) Viscosity (at 25 °C, cst) HHV (MJ kg1) Moisture (wt%) TAN (mg KOH g1)
Properties (oil phase) 0.91 10.4 38.0 1.2 25.7
0.88 11.0 39.5 1.4 25.2
0.88 (L)–1.12 (H) 6.5 (L) 43.1 (L)–33.9 (H) 0.4 (L)–4.4 (H) 8.7 (L)–43.6 (H)
0.93 11.2 38.7 1.5 24.2
C H O Feedstocks oxygen (wt%) Degree of deoxygenation (wt%)
Elemental analysis (oil phase, wt%) 80.8 78.9 9.4 11.4 9.4 9.3 36.9 36.9 75 75
83.1 (L)–73.0 (H) 12.9 (L)–9.5 (H) 3.7 (L)–18.4 (H) 36.9 90 (L)–50 (H)
78.2 11.0 9.3 35.6 74
Note: All data were the average value of three samples; feedstocks oxygen contents were calculated based on oxygen contents of bio-oil and solvents; L – Light component, H – Heavy component; all experiments were carried out using 100 g bio-oil and 10 g Ru/C catalyst at 300 °C, 10 MPa, 3 h.
other alternatives such as employing a two-step catalytic HDO for upgrading of bio-oil to hydrocarbon fuel is needed. In the two-step process, the partial oxygenated groups can be eliminated especially like aldehydes, ketones and furans, which are easily causing coke formation, to obtain stable oil-phase products with lower oxygen content under relatively mild conditions in the 1st step. The 2nd step is then performed at severe conditions to obtain hydrocarbon fuels. In fact, Elliott and Baker (1989) have initially conducted a two-step catalytic hydrotreating of bio-oil for obtaining hydrocarbon fuel at low temperatures (250–300 °C), and then hydrogenation of bio-oil under higher temperature conditions using conventional hydrotreating catalyst (CoMo/Al2O3). However, the results showed that coking phenomenon was still severe and oxygen content of products remained extremely high (30 wt%). The subsequent studies by several investigators using two-step process employing NiMo/Al2O3 and CoMo/Al2O3 catalysts (Samolada et al., 1998) or using noble catalysts (Wildschut et al., 2009; Venderbosch et al., 2010) still faced coke formation problems as well as high oxygen content in the final products (6– 11 wt%). It is well known that solvent (usually considered to be a hydrogen donor solvent) can restrain coke formation and improve bio-oil upgrading (Zhang et al., 2005; Elliott, 2007). However, the improvement of the quality of the products was only limited to single step HDO process with oxygen content of 3 wt%, which cannot meet the standards for transportation liquid fuel. In this paper, we evaluated a two-step catalytic hydrogenation method. In the first step, various organic solvents were employed to improve HDO of bio-oil using Ru/C catalyst under mild conditions to avoid coke formation and obtained stable intermediate products for the subsequent deep HDO. In the second step, experiments were performed at conventional hydrogenation setup and with catalyst (NiMo/Al2O3) under relatively severe conditions for the production of hydrocarbon biofuels. Four different solvents (tetraline, decalin, diesel and diesel/isopropanol) were used and result comparisons could be made as to the effectiveness of each solvent. Since information for a comprehensive analysis of obtained biofuel is almost non-existent, this study was undertaken to analyze organics from oil phase, gas phase composition as well as oil properties for both products from 1st and 2nd step HDO process. To the best of our knowledge, the oxygen content in the final oil products achieved is one of the lowest (0.5%) among all upgraded bio-oils.
2. Materials and methods 2.1. Materials Bio-oil was supplied by the fast pyrolysis of pine sawdust at 500 °C in a Bench-Scale Fluidized-Bed reactor at Zhengzhou University. The typical properties of the bio-oil, with 48% oxygen content, are given in Supplementary Material (SM), Table SM-1. The commercial noble catalyst Ru/C was obtained from Shanxi Rock New Materials for mild HDO of bio-oil. Note that Ru catalyst has been commonly used in hydrotreatment of bio-oil (e.g., Wildschut et al., 2009, 2010; Venderbosch et al., 2010). The Ru content was 5 wt% with the total surface area of 800 m2 g1 and the average particle size of 74 lm. The traditional petroleum hydrogenation catalyst NiMo/Al2O3 was provided by Shenyang Chemical Industry Research Institute for deep HDO. Hydrogen, argon (carrier gas) and calibration gases all were purchased from Beijing Ruizhx Technology. All reagents used are analytical grade. Tetraline, decalin and isopropanol were obtained from Sinopharm Chemical Reagent and the diesel oil from a nearby gas station. Tetraline and decalin were selected as organic solvents because they are known to be hydrogen donor with respect to hydrogenation and HDO (Sheu et al., 1988; Zhang et al., 2005). Diesel was chosen because it has capacity to dissolve hydrogen. Unfortunately, diesel is immiscible with bio-oil because of polarity diversity. Therefore, the mixture of diesel and isopropanol was also used as organic solvent, because isopropanol is easy to blend with bio-oil as cosolvent to promote the intermiscibility between diesel and bio-oil.
2.2. Experiments The first so called mild step hydrogenation was performed at pressure of 10 MPa and temperature of 300 °C. The mild conditions are in comparison with the severe conditions used in the single step of hydrotreatment of bio-oil, or temperature up to 400 °C and pressure 20 MPa (Wildschut et al., 2009, 2010; Venderbosch et al., 2010). The reactants were stirred at 650 rpm with a magnetic stirrer in a 500 mL autoclave (Weihai Automatic Control). The temperature was controlled using an electric jacket combined with a thermocouple thermometer and the pressure regulated by the back pressure valve. The second step hydrogenation setup is a
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
3
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx
continuous fixed bed reactor (Luoyang Kaimeisheng Petrochemical Equipment) with a maximum pressure of 25 MPa and at a temperature of 500 °C. Temperature and pressure were controlled as in the first step. A schematic representation of the system setup is given in Fig. SM-1. The overall experimental conditions are summarized in Table 1 and the detailed description of each step is as follows: For the first step hydrogenation experiment, the reactor was filled with 100 g bio-oil, 30 g organic solvents (tetraline, decalin, diesel or diesel/isopropanol) and 10 g Ru/C catalyst. Subsequently, the reactor was flushed with N2 gas and then purging with 2 MPa H2 (replacing nitrogen) three times, and eventually pressurized with 8.0 MPa H2 at room temperature. The reactor was heated to the intended reaction temperature (300 °C) with a heating rate of 3.0 °C min1 and kept at that temperature for 3 h at stirring speed 650 rpm. The pressure in the reactor was set to the predetermined value (10 MPa) controlled by the back pressure valve. The volume of off-gas was metered by a wet type gas meter, and off-gas was collected using a gas bag after the reaction for the detection of gaseous composition by GC (Gas Chromatograph). After completion of the reaction, the reactor content was cooled to ambient temperature. The catalysts were separated from the liquid phase by filtration. The liquid phase was then separated via a separatory funnel into 2- or 3-phase (light/heavy oil and water phase). The second step hydrogenation experiment employed a typical conventional petroleum hydrogenation technology (fixed bed reactor) and catalyst (NiMo/Al2O3), which has been employed as the most frequently tested catalysts for the HDO reaction (Sheu et al., 1988; Baldauf et al., 1994). At first, the fixed bed reactor was filled with 10 mL Al2O3 (protection zone, or 18 g) at the bottom, 20 mL (about 19.2 g) NiMo/Al2O3 catalyst (reaction zone) in the middle and 40 mL Al2O3 (preheating zone, or 70 g) at the top. Afterward the NiMo/Al2O3 catalyst was sulfurized using 1.5% CS2 kerosene solution at 320 °C and 13 MPa H2 for 10 h, The stabilized intermediate oil (termed as HDO-biofuel) from the 1st step was then fed to reactor by a high pressure pump at 20 mL h1 at 400 °C with a liquid hourly space velocity (LHSV) of 1.0 h1. Hydrogen was continuously fed to the reactor through mass flow meter with the H2/oil ratio (v/v) 400 or 800 (or 0.04–0.08 kg kg1). Temperature and pressure measurement and control were the same as in the first step. The refined products were cooled and then separated by a primary and secondary liquid-vapor separator, with liquid phase (lesser extent of water) collected (Fig. SM-1). The resultant from this deep HDO product is called hydrocarbon biofuel (HC-biofuel). The off-gas was collected just like the first step experiment.
(30 m 0.53 mm 0.25 lm) with a TCD was used to detect CO2, C2H4, and C2H6. Helium (99.9999%) was used as the carrier gas, and the oven temperature was kept at 80 °C for 13 min. Both Instruments were calibrated by calibration gas for quantification of all gas components. GC–MS analyses were performed for analysis of different organic compositions in oil phase in an Agilent 7890A-5975C GC equipped with a DB-FFAP capillary column (30 m 0.25 mm 0.25 lm). The GC split was 1:100 and the injector temperature was set at 250 °C with an injection volume of 1 lL. The oven temperature was kept at 50 °C for 3 min, increased to 200 °C at a rate of 3 °C min1, and then held at 200 °C for 50 min. Helium was used as the carrier gas with a constant flow rate of 1 mL min1. The mass spectrum employed Electron Impact ionization source at 70 eV. The compositions of bio-oil and HDO products were identified by NIST08 spectrogram depot. The FTIR spectra of HDO products were recorded in a Bruker Alpha Class 1 instrument. The typical Quality Assurance/Quality Control procedures were closely followed to ensure data adequacy. 2.4. Performance evaluation In practice it is not possible to evaluate the conversion of each individual component in the bio-oil. Thus, several important gross parameters were used for evaluating the oil yield (Yobs) and the degree of deoxygenation (DOD) as:
Y obs ¼
mproduct 100% mfeed
DOD ¼
ð1Þ
wt% Oproduct 100% 1 wt% Ofeed
ð2Þ
Here mproduct and mfeed are the mass of product and feedstock, respectively; and wt% Oproduct as well as wt% Ofeed are the percentage of oxygen in product and feedstock, respectively (Mortensen et al., 2011). The energy efficiency was estimated as (Milne et al., 1990):
energy efficiencyð%Þ ¼
! yproduct HHVproduct 100% HHVfeed þ yH2 HHVH2
ð3Þ
where yproduct is defined as the kg yield of biofuel produced per kg raw pyrolysis oil, HHVproduct and HHVfeed are the high heating value of product and feedstock, respectively. yH2 is kg hydrogen used per kg of pyrolysis oil. 3. Results and discussion
2.3. Analytical methods 3.1. Mild HDO The elemental compositions of the both HDO and HC biofuels were determined using a Thermo Electron Corporation Flash EA 1112 analyzer (Delft, the Netherlands). The heating values of the samples were measured by a ZDHW-6000 automatic calorimeter (Hebi Instrument, Henan). The water content in the samples was determined by a Karl Fischer KF-1A automatic titration (Shanghai Baoshan Fine Working Electronic Instrument). The viscosities of the oil and products were determined at 25 °C with a kinematic viscosity instrument (TimePower Measure and Control Equipment, Beijing). The total acid number (TAN) for the bio-oil and upgraded products were determined using the ASTM D66 standard method. GC analyses of H2, CO and CH4 were preformed on a Varian CP3380 GC equipped with a thermal conductivity detector (TCD) using a 5 Å molecular sieve column. The injector, oven and detector temperatures were kept at 50, 80 and 130 °C, respectively. Argon (99.9999%) was used as the carrier gas. Another Varian CP-3800 GC equipped with a RT-QPLOT capillary column
3.1.1. HDO-biofuel composition Four types of organic solvents including tetraline, decalin, diesel and diesel/isopropanol were used and compared under the same operating conditions with the same catalyst (Ru/C) for choosing the best solvent for the subsequent deep HDO process study; these cases are defined as A to D (Fig. 1), and the corresponding oil-phase products are called HDO-biofuel A to D, respectively (Table 1). The composition for different components of HDO products is illustrated in Fig. 1a. Through mass balance (90–99 wt%), the unaccountable loss fraction is apparently due to viscous compounds that tend to stick to reactor wall and tubing. Clearly, the compositions for each component under different solvent conditions are varied, particularly for off-gas and oil distribution. Nonetheless, light oil and water fractions constitute a major portion of HDObyproducts. All different solvents used exhibited yellowish transparent aqueous phase and yielded insignificant fraction of solid,
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
4
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx
3.1.3. Gas composition The gas-phase compositions are given in Fig. 1b. As could be expected, the main component was un-reacted hydrogen. In addition, CO2 was present in amounts between 2.5 and 5 mol%. A likely pathway for the formation of CO2 was thermal decarboxylation of organic acids (Venderbosch et al., 2010; Wang et al., 2012). For each case, small amounts of CO were formed as well (1– 2 mol%), probably as a result of decarbonylation reactions (Choudhary and Phillips, 2011; Wang et al., 2012), with insignificant amount of CH4 detected (<1 mol%) due to demethylation of phenolic derivatives (Bykova et al., 2012). Some C2H4 and C2H6 were also formed resulting from thermal cracking of hydrocarbon present in the solvent. The unknowns of total gas compositions (1–3 mol%) were within experimental errors. To sum up, if the goal was to achieve higher oil yields and higher DOD under mild reaction conditions, tetraline and diesel/isopropanol appeared to be efficient at studied reaction conditions of 300 °C, 10 MPa and 3 h. Thus, HDO-biofuel A with tetraline as solvent and HDO-biofuel D with diesel/isopropanol were selected for intermiscibility and stability evaluation. HDO-biofuels were easy to blend with bio-oil and diesel resulting in the homogeneous state. In addition, the stability was evaluated by determining viscosity of HDO-biofuels stored after a period of time (up to 12 months) at 25 °C. The relativity constant viscosity values even after 12-month storage (<7% difference) clearly indicate their stable properties (Table SM-2). Fig. 1. Mild HDO of bio-oil using various solvents under the same operating conditions (Ru/C catalyst at 300 °C, 10 MPa, 3 h). (a) Product composition, (b) gasphase composition (Note: A-tetraline as solvent, B-decalin as solvent, C-diesel as solvent, D-diesel/isopropanol as solvent).
indicating less coke formation. One of the main ideas of the 1st step process is to reduce coke formation and results of solid composition (<2%) are much less than those of the previous studies using the Ru/C catalysts without any solvent addition (Wildschut et al., 2009, 2010). Use of diesel alone yields increased fraction of heavy oil and less light oil, due to the fact that bio-oil which has high polarity is difficult to blend with petroleum-based hydrocarbons. On the other hand, with the blend of isopropanol into diesel, the composition changes dramatically with high oil yield (38%) and least amount of solid (<1%) along with higher gas composition (17%).
3.1.2. Properties of mild HDO products Several properties of upgraded bio-oil are shown in Table 1. Except for case C with diesel alone, all solvents and co-solvent used exhibit similar characteristics. Data comparison with those of feedstock (Table SM-1) clearly indicates better improved properties after mild hydrogenation reactions promoted by organic solvents, e.g., density was reduced from 1.2 to approximately 0.9 kg L1, viscosity from 19 down to 10 cst (25 °C), moisture content from 24 to 1–1.5 wt%, and the HHV increased by more than double. In particular, TANs have all been significantly reduced from 118 to about 25 mg KOH g1. Furthermore, elemental analysis showed that C element content of the oil phase after mild HDO was increased from 45 to about 78–81 wt%, H elements from 7 to 9–13 wt%, while O contents have all significantly been reduced from 48 to less than 10 wt%. The DOD reached almost 75 wt% with the highest up to 90 wt% in the light oil of HDO-biofuel C. For comparison, Venderbosch et al. (2010) investigated mild HDO using Ru/C catalyst at different temperatures (175–400 °C) with the DOD only 54 wt%. Clearly, the benefit of solvent addition is apparent in terms of lesser solid formation, lower oxygen content and much higher DOD efficiency.
3.1.4. Organic composition in oil phase GC/MS was applied to gain insight into the composition of the HDO-biofuels produced at 300 °C, 10 MPa and 3 h using Ru/C catalyst. The various components present in the original bio-oil were also analyzed for comparison. The compositions were classified into different categories: acids, aldehydes, ketones, alcohols, phenols, furans, esters and hydrocarbons (Table 2). The results showed that unused tetraline accounted for major peak area for the HDObiofuel A. In order to investigate composition change/formation of HDO-biofuel in comparison with bio-oil, the tetraline content was excluded in Table 2 data. It is noted that data in Table 2 are in area% and the following qualitative discussion must be made with care because of solvent effect on the measured organic composition. In general, the type and number of organic components for feedstock bio-oil are in agreement with those reported by others (Lu et al., 2009; Mortensen et al., 2011), e.g., more than 300 different compounds have been identified in bio-oil. However, the notable differences of pine sawdust produced bio-oil is its higher acetic acid content (15%), no detected carbohydrate due to its further decompose to aldehydes, ketones and alcohols, as well as extremely high phenols (25%) from lignin decomposition (Zhang et al., 2011). The organic compositions after mild HDO process are completely changed. The results for each category are briefly discussed below: After reaction, the content of acids was significantly decreased, e.g., acetic acid reduction from 15 to 2–3%. The acid translation likely includes three pathways: (1) CO2 formation because of decarboxylation as discussed before, (2) ester formation due to esterification with alcohols (e.g. formation of acetic acid butyl ester shown in Table 2), and (3) transfer to aqueous phase (Zhang et al., 2011). Nonetheless, the content of carboxylic acids is one order of magnitude lower than those (2–5%) reported by others (zhang et al., 2011; Ardiyanti et al., 2012) for hydrogenation of bio-oil, apparently due to their partition into oil phase. Aldehydes including aromatic vanillin were translated completely to 2-methoxy-phenol or other phenols derivates (shown in Table 2) through hydrogenation and decarbonylation (Crossley et al., 2009). 2-Butenal might be hydrogenated and saturated to form butanol, and then esterification with acetic acid to form butyl
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
5
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx Table 2 Selected components of bio-oil and HDO-biofuels by GC/MS. Bio-oil
Area (%)
HDO-biofuel A (excluding 85% tetraline)
Area (%)
HDO-biofuel D
Area (%)
Acids Acetic acid Propanoic acid Butanoic acid
16.1 15.3 0.6 0.2
Acids Acetic acid Propanoic acid Butanoic acid
5.5 3.3 0.0 2.2
Acids Acetic acid Propanoic acid Butanoic acid
3.1 1.8 0.4 0.9
Aldehydes Vanillin 2-Butenal
4.0 3.8 0.2
Aldehydes Vanillin 2-Butenal
0.0 0.0 0.0
Aldehydes Vanillin 2-Butenal
0.0 0.0 0.0
Ketones 1-Hydroxy-2-propanone 1,2-Cyclopentanedione 2-Cyclopenten-1-one 1-Hydroxy-2-butanone
15.2 11.4 1.8 1.1 0.9
Ketones 2-Methyl-cyclopentanone 3-Hexanone 2-Ethyl-cyclopentanone 2-Hexanone
5.6 3.0 1.0 1.0 0.6
Ketones 2-Methyl-cyclopentanone 3-Hexanone 2-Hexanone 2-Ethyl-cyclohexanone
3.3 2.2 0.7 0.2 0.2
Alcohols 1-Propanol 2-Cyclohexen-1-ol 3-Methyl-2-hexanol
1.9 1.0 0.8 0.1
Alcohols 1-Propanol Cyclohexanol 2-Methyl-cyclopentanol
1.6 0.5 0.7 0.4
Alcohols 1-Propanol Cyclohexanol 2-Methyl-cyclopentanol
0.0 0.0 0.0 0.0
Phenols 2,6-Dimethoxy-phenol 2-Methoxy-phenol 2-Methoxy-4-propenyl-phenol 2-Methoxy-4-methyl-phenol Phenol
24.5 7.1 5.9 5.3 4.1 2.1
Phenols 2,6-Dimethoxy-phenol 2-Methoxy-phenol 2-Methoxy-4-propyl-phenol 2-Methoxy-4-methyl-phenol Phenol
28.9 2.5 6.4 9.3 6.7 4.0
Phenols 3,4-Dimethyl-phenol 2-Methoxy-phenol 2-Methoxy-4-propyl-phenol 2-Methoxy-4-ethyl-phenol 4-Propyl-phenol
13.8 4.5 2.6 1.1 3.2 2.4
Furans Furfural 2(5H)-Furanone 2-Furanmethanol
5.8 3.0 2.4 0.4
Furans Furfural 2(5H)-Furanone 2-Furanmethanol
0.0 0.0 0.0 0.0
Furans Furfural 2(5H)-Furanone 2-Furanmethanol
0.0 0.0 0.0 0.0
Esters Butyrolactone Acetic acid, butyl ester
0.4 0.4 0.0
Esters Butyrolactone Acetic acid, butyl ester
0.7 0.4 0.3
Esters Butyrolactone Acetic acid, butyl ester
0.2 0.0 0.2
Hydrocarbons Naphthalene Decahydro-naphthalene Toluene
2.0 1.8 0.2 0.0
Hydrocarbons Naphthalene Decahydro-naphthalene Toluene
28.7 23.9 3.4 0.6
Hydrocarbons 1,6-Dimethyl-Naphthalene 2-Methyl-naphthalene Tetradecane
24 7.9 6.2 2.4
o-Xylene 1,3-Dimethyl-benzene 1-Methyl-indan
0.0 0.0 0.0
o-Xylene 1,3-Dimethyl-benzene, 1-Methyl-indan
0.2 0.2 0.4
Undecane 1-Methyl-naphthalene Heptadecane
2.0 3.3 2.2
Note: A: tetraline as solvent, D: diesel/isopronal as solvent, using Ru/C catalyst, at 300 °C, 10 MPa, 3 h.
acetate (shown in Table 2). Ketone content was reduced because of its micromolecule decomposition through decarbonylation and decarboxylation to form CO, CO2 and hydrocarbons, e.g., 1-hydroxy-2-propanone was not detected in product; the finding is consistent with others (Gayubo et al., 2004b). On the other hand, macromolecule ketones were translated to other ketones, e.g., 1,2-cyclopentanedione to 2-methyl-cyclopentanone (shown in Table 2). In short, the content of those compounds (carboxylic acid, aldehydes, and ketones) responsible for coke formation (Liu et al., 2012) has been significantly reduced. Alcohols were easily translated by HDO forming hydrocarbons and water and this pathway was reported by others (Gayubo et al., 2004a). Phenols are difficult to be translated to hydrocarbons due to Ru/C catalyst selectivity and steric effect of phenolic macromolecule resulting in abundant phenolic derivates present in HDObiofuels – in fact, phenolic content has been increased (total form 25% to 43%, Fig. SM-2). Furans are very active functional groups and their completely complex translation includes ring cleavage, hydrogenation, hydrocracking, dehydration and isomerization (Yu et al., 2011). Hydrocarbon levels were increased in the products because of solvent and nature products of HDO of oxygenated organic compounds. To better compare different solvent effects on the organic composition, the composition profiles for two different solvents of HDO biofuel are shown in Fig. SM-2 which indicates the completely different compositions. For example, HDO-biofuel A (excluding sol-
vent) mainly included 43% phenols and 35% hydrocarbons, as well as 7% acids, 9% ketones and 3% alcohols with the corresponding percentages of 18%, 70%, 3%, 5% and 1% in HDO-biofuel D. Again, it must be noted that abundant hydrocarbons certainly come from diesel solvent, thus, if the area% is excluded for diesel, then areas in other components would increase. Therefore, the conversion process of the mild HDO is practically similar for both solvents. The FTIR spectra of typical functional groups of mild HDO-biofuels are shown in Fig. 2. Both solvents exhibit a similar pattern. The major difference lies in the region of 1500–600 cm1, especially at 744 cm1 with no strong peaks due to CAH groups of aromatic hydrocarbon (Fig. 2b), because of the solvent diesel/ isopropanol used rather than tetraline. There are strong CH2, CH3 stretching of aliphatic and aromatic hydrocarbons at 2860, 2929 and 3016 cm1 (Chen et al., 2010; Agblevor et al., 2012). The broadband peak at 3300 cm1 belongs to OH groups of the oxygenated groups associated with phenols and other acidic groups (Zhang et al., 2005; Yang et al., 2009) and, to lesser extent, water interference. The peak at 1707 cm1 is due to C@O groups of carboxylic acid and ketones groups (Chen et al., 2010) with the peaks at 1603, 1494 and 1453 cm1 due to aromatic compounds and their derivatives (Agblevor et al., 2012). Carboxylic acids and phenols are identified in HDO-biofuels in combination with the peak of OH group at 3300 cm1. No peak due to CHO groups in the 2850–2720 cm1 region is observed, due to the absence of aldehydes. The 1300–1000 cm1 region with
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
6
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx Table 3 Properties of deep HDO products. Properties (oil phase) Density (kg L1) Viscosity (at 25 °C, cst) HHV (MJ kg1) Moisture (wt%) TAN (mg KOH g1)
HC-biofuel A H2/oil (v/ v) 400
HC-biofuel A H2/oil (v/ v) 800
HC-biofuel D H2/oil (v/ v) 400
HC-biofuel D H2/oil (v/ v) 800
0.84 2.8
0.85 2.5
0.82 3.3
0.83 3.6
44.9 0.02 0.02
44.8 0.02 0.03
45.7 0.02 0.02
45.6 0.02 0.03
85.6 12.8 0.6 9.3
84.8 12.4 0.8 9.3
94
92
Elemental analysis (organic phase, wt%) C 88.0 87.5 H 11.5 11.8 O 0.5 0.7 Feedstocks oxgen 9.4 9.4 (wt%) 94 93 Degree of deoxygenation (wt%)
Note: All tests were run using NiMo/Al2O3 (dry 19.2 g) at 400 °C, 13 MPa, 1 h1. HC-biofuel A: feedstok was HDO-biofuel A, HC-biofuel D: feedstock was HDO-biofuel D.
Fig. 2. FTIR spectra of functional group of HDO-biofuels using Ru/C catalyst at 300 °C, 10 MPa, 3 h. (a) HDO-biofuel A (tetraline as solvent) and (b) HDO-biofuel D (diesel/isoproponal as solvent).
peaks at 1267 and 1211 cm1 is due to CAO and CAOAC group stretching vibrations of phenols and esters (Yang et al., 2009), respectively. The CAH stretching vibrations of aromatic hydrocarbon are detected at 944, 863, 806 and 785 cm1, as evident by the abundance of aromatic hydrocarbon presented in HDO-biofuel A. The FTIR spectral data corroborated well with the GC/MS data (Fig. SM-2) as well as other biofuel property evaluation. The compositions of mild HDO products mainly contain aliphatic/aromatic hydrocarbons and phenols with less oxygenated compounds like acetic acids, ketones and esters. All in all, the properties of bio-oils have been improved dramatically through mild HDO process. The oxygen content of products is decreased from nearly 48 to less than 10 wt% (Table 1). Due to reduction of oxygenated compounds and solid, oil-water is easily separated. The stability of products had been remarkably ameliorated and easy to mix with fossil fuels (Table SM-2). At last, the corrosivity has been decreased dramatically with the TAN from 118 (bio-oil) to about 25 mg KOH g1. In short, the HDO-biofuel provides a better source for further upgrading to hydrocarbon fuels using the existing refining technology and facility. 3.2. Deep HDO Deep HDO experiments were carried out in a catalytic hydrogenation setup under severe reaction conditions (400 °C, 13 MPa) with conventional hydrogenation catalyst (NiMo/Al2O3) for two different feedstocks (HDO-biofuel A and D). The effect of different H2/oil ratio was investigated with a constant LHSV (1 h1). The major objective was to obtain hydrocarbon liquid fuels with negligible oxygen content and with high HHV which may be potentially used as transportation fuels. 3.2.1. Effect of feedstocks and H2/oil The effect of H2/HDO-biofuels on the properties of deep HDO derived oils for both feedstocks is insignificant as shown in Table 3. Some subtle differences may be due to change in gas hourly space velocity although LHSV (1 h1) is the same. Nevertheless, some
slight changes can be observed between feedstocks, notably lower C and higher H content for HDO-biofuel D due to higher content in aliphatic and lower composition in aromatic hydrocarbons (Fig. SM-2). 3.2.2. Properties of deep HDO products To better comprehend the improved properties of HC-biofuels, one needs to compare data in Table 3 with those of mild HDO products in Table 1. The density of final products is decreased to 0.83 kg L1 with the HHV enhancing to 45 MJ kg1. In addition, the reductions in viscosity (>70% reduction to about 3 cst), moisture (1.2–0.02%), and TAN (25–0.02 mg KOH g1) all exhibit remarkable improvement. In fact, these parameters are similar to the characteristics of fossil refinery fuels. From elemental analysis data, the C, H and O contents are 85–88%, 12–13%, and <1%, respectively, with DOD about 93%. The O/C ratio (Fig. SM-3), an excellent indicator as the extent of deoxygenation, illustrates its one order of magnitude reduction for each step of HDO from original bio-oil (0.8) to HDO-biofuels (0.09) to final HC-biofuels (0.004). For the product to be useful as a transportation fuel, the O/C molar ratio should preferably be less than 0.02 and the H/C ratio between 1.8 and 2.0 (Kersten et al., 2007); for comparison our final products are 0.004 and 1.8, for O/C and H/C ratio, respectively. 3.2.3. Composition of the deep HDO products The composition of deep HDO-products is classified into alkanes, cycloparaffin, monocyclic aromatic hydrocarbons, indan derivates and bicyclical aromatics which include decalin, tetraline and naphthalene and its derivates (Fig. 3), with some representative compounds listed in Table SM-3. The two types of mild HDO products yield a similar pattern (Fig. 3) but with different area percentages. Bicyclical aromatic hydrocarbons are dominant in HCbiofuel A, e.g., peaks at 5.9, 7.6, 16.9 and 22.9 min represent trans-decalin, cis-decalin, tetraline and naphthalene, respectively. The low intensity peaks (before 5 min) represent cycloparaffin. The peaks of benzene series derivatives are detected at 8–15 min with peaks at 17–19 min representing indan derivants and peaks after 25 min as alkanes. On the other hand, for product D, the alkanes are major components with C11AC27 distributing homogeneously in chromatogram. For example, peaks at 4.8, 10.3, 16.6, 25.02, 29.9, 34.5 38.7 and 42.9 min represent undecane, tridecane, pentadecane, octadecane, eicosane, docosane, tetracosane and heptacosane, respectively. Aromatic hydrocarbons and its deriva-
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx
7
Fig. 3. Comparison of the GC–MS chromatograms of deep HDO biofuel (at 400 °C, 13 MPa, 1 h1 and 400 H2/oil with NiMoSx/Al2O3). (a) HC-biofuel A. (b) HC-biofuel D.
tives are distributed all over the alkane range. No peaks of oxygenated compounds (acids, ketones and phenols) are found in Fig. 3a and b. For HC-biofuel A, alkanes (25%) mainly includes C11AC27 which maybe from solvent components and HDO of oxygenated compounds. Cycloparaffin was about 3% which comes from hydrosaturation of aromatic components (Zhao et al., 2009). Monocyclic aromatic hydrocarbons occupied 11% mainly including benzene derivates with branched chains which mainly came from the HDO and hydrocracking of phenolic derivates (Mortensen et al., 2011). Indan derivates are about 4% which maybe from demethylation of tetraline and the cyclization reaction of aromatic derivates, with octahydro-indene derived from hydrogenation of indan derivates. The same pathways may also explain the accumulation/formation/changes of these constituents for HC-biofuel D. However, HC-biofuel D include large amount of alkanes (48%, C11AC27). Cycloparaffin is about 4% including of five-ring and six-ring derivates resulting from hydrogenation of aromatic hydrocarbons. Monocyclic aromatic hydrocarbons are nearly 20% which mainly come from phenols. Bicyclical aromatic hydrocarbons and Indian derivates are about 17.6% (naphthalene derivates). In summary, the products of deep HDO are constituted by various hydrocarbons with negligible oxygenated compounds. The FTIR spectra of HC-biofuel A and D are shown in Fig. 4. The spectra show CAH stretching of alkanes and aromatic hydrocarbons at 2924 and 2867 cm1 and no peak due to OH groups in the 3300 cm1 region (see Fig. 2 for comparison). The absence of OH groups suggests that the oxygenated groups associated with phenols and other acidic groups in the bio-oil and HDO-biofuels have been eliminated during the two-step HDO; this was corroborated with the GC/MS data (Fig. 3). The spectra also show a
Fig. 4. FTIR spectra of functional group of deep HDO biofuel (at 400 °C, 13 MPa, 1 h1 and 400 H2/oil with NiMoSx/Al2O3). (a) HC-biofuel A. (b) HC-biofuel D.
medium intensity peak at 1611, 1608 and 1458 cm1 due to aromatic benzene ring breathing motion, indicating the presence of aromatic groups in the deep HDO biofuels. The peaks at 1458
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
8
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx
and 1376 cm1 are due to CH2 and CH3 vibrations of aliphatic hydrocarbons. The carbonyl carbon peaks (between 1700 and 1730 cm1 due to C@O stretching in ketones, carboxylic acids, and aldehydes) are not detected. The peaks of phenols and other carbohydrate compound due to CAO stretching vibrations between 1300 and 1000 cm1 (Agblevor et al., 2012) are also not observed. Thus, it appears that the composition of biofuels is the mixture of aliphatic and aromatic hydrocarbons and/or alkylated aromatic hydrocarbons. 3.3. Mass balance and energy efficiency In the first step, the HDO reaction primarily generated abundant aqueous phase in addition to water originally present in bio-oil and less gas phase of CO, CO2, CH4, and C23. The average yields for both oil- and water phase were about 40% with gas phase 12% (Fig. 1a). In the second step, the yields (base on HDO-biofuel) were 87% oilphase with 5% gas phase and 8% aqueous phase. Therefore, the total yield of oil-phase was about 35 wt% based on the feed oil. In determining energy efficiency, the energy level of solvent should be included. With the HHV of bio-oil (including 30% solvent), hydrogen, HDO-biofuel and HC-biofuel typically 19, 143, 39 and 46 MJ kg1, respectively, the energy efficiency of 73% for mild HDO and 96% for deep HDO can be achieved. Thus, approximately the overall 70% of the energy present in the bio-oil feedstock is transferred to the final product oil under two-step HDO process. Losses were due to the formation of gas-phase components and solids as well residual amounts of organics in the aqueous phase. 4. Conclusions Bio-oils were successfully translated to hydrocarbons liquid fuels by two-step catalytic HDO process which included mild HDO and deep HDO. In the mild HDO process, the organic solvents were employed to improve quality HDO of bio-oils resulting in less coke formation. For the deep HDO process, the conventional hydrogenation technology (fixed bed reactor) and catalyst (NiMo/Al2O3) were employed for translating HDO-biofuels to hydrocarbon liquid fuels. The properties of final products are similar to fossil fuels which include aliphatic and aromatic hydrocarbons with HHV of 46 MJ kg1 and negligible oxygenated compounds. However, the final hydrocarbon product is a mixture of upgraded bio-oil with solvents and the extent of contribution of solvent to excellent properties of final products along with mechanisms of coke removal through solvent addition awaits further study. Also, the cost of two-step hydrotreatment of bio-oil for transportation hydrocarbon fuel is relatively high at the present time, but the cost should be eventually decreased with the development of technology in the future. Acknowledgments The authors sincerely acknowledge the financial support by the key programs of science and technology of Henan province and Zhengzhou city (Project 10ZDGG121 and Project 111PCXTD165). The authors also thank Miss Zhichao Tan and Mr. Songling Li for their assistance in laboratory analysis. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.chemosphere. 2013.06.060.
References Adjaye, J.D., Bakhshi, N.N., 1995. Production of hydrocarbons by catalytic upgrading of a fast pyrolysis bio-oil. Part I: Conversion over various catalysts. Fuel Process. Technol. 45, 161–183. Agblevor, F.A., Mante, O., Mcclung, R., Oyama, S.T., 2012. Co-processing of standard gas oil and biocrude oil to hydrocarbon fuels. Biomass Bioenergy 45, 130–137. Ardiyanti, A.R., Khromova, S.A., Venderbosch, R.H., Yakovlev, V.A., Melián-Cabrera, I.V., Heeres, H.J., 2012. Catalytic hydrotreatment of fast pyrolysis oil using bimetallic Ni–Cu catalysts on various supports. Appl. Catal., A 449, 121–130. Baldauf, W., Balfanz, U., Rupp, M., 1994. Upgrading of flash pyrolysis oil and utilization in refineries. Biomass Bioenergy 7, 237–244. Bridgwater, A.V., 2012. Review of fast pyrolysis of biomass and product upgrading. Biomass Bioenergy 38, 68–94. Bykova, M.V., Ermakov, D.Y., Kaichev, V.V., Bulavchenko, O.A., Saraev, A.A., Lebedev, M.Y., Yakovlev, V.A., 2012. Ni-based sol–gel catalysts as promising systems for crude bio-oil upgrading: Guaiacol hydrodeoxygenation study. Appl. Catal., B 113–114, 296–307. Chen, Y., Wang, C., Lu, W., Yang, Z., 2010. Study of the co-deoxy-liquefaction of biomass and vegetable oil for hydrocarbon oil production. Bioresour. Technol. 101, 4600–4607. Choudhary, T.V., Phillips, C.B., 2011. Renewable fuels via catalytic hydrodeoxygenation. Appl. Catal., A 397, 1–12. Crossley, S., Faria, J., Shen, M., Resasco, D.E., 2009. Solid nanoparticles that catalyze biofuel upgrade reactions at the water/oil interface. Science 327, 68–72. Czernik, S., Bridgwater, A.V., 2004. Overview of applications of biomass fast pyrolysis oil. Energy Fuels 18, 590–598. Elliott, D.C., 2007. Historical developments in hydroprocessing bio-oils. Energy Fuels 21, 1792–1815. Elliott, D.C., Baker, E.G., 1989. Process for Upgrading Biomass Pyrolyzates. US Patent, 4 795 841. Gayubo, A.G., Aguayo, A.T., Atutxa, A., Aguado, R., Olazar, M., Bilbao, J., 2004a. Transformation of oxygenate components of biomass pyrolysis oil on a HZSM-5 zeolite. I. Alcohols and phenols. Ind. Eng. Chem. Res. 43, 2610–2618. Gayubo, A.G., Aguayo, A.T., Atutxa, A., Aguado, R., Olazar, M., Bilbao, J., 2004b. Transformation of oxygenate components of biomass pyrolysis oil on a HZSM5 zeolite. II. Aldehydes, ketones, and acids. Ind. Eng. Chem. Res. 43, 2619– 2626. Hew, K.L., Tamidi, A.M., Yusup, S., Lee, K.T., Ahmad, M.M., 2010. Catalytic cracking of bio-oil to organic liquid product (OLP). Bioresour. Technol. 101, 8855–8858. Huber, G.W., Iborra, S., Corma, A., 2006. Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering. Chem. Rev. 106, 4044–4098. Kersten, S.R.A., van Swaaij, W.P.M., Lefferts, L., Seshan, K., 2007. Options for catalysis in the thermochemical conversion of biomass into fuels. In: Centi, G., van Santen, R.A. (Eds.), Catalysis for Renewables: From Feedstock to Energy Production. Wiley-VCH, Chichester, pp. 119–141. Liu, W.J., Zhang, X.S., Qv, Y.C., Jiang, H., Yu, H.Q., 2012. Bio-oil upgrading at ambient pressure and temperature using zero valent metals. Green Chem. 14, 2226– 2233. Lu, Q., Li, W.Z., Zhu, X.F., 2009. Overview of fuel properties of biomass fast pyrolysis oils. Energy Convers. Manage. 50, 1376–1383. Milne, T.A., Brennan, A.H., Glenn, B.H., 1990. Source Book of Methods of Analysis for Biomass and Biomass Conversion Processes. Elsevier, London. Mortensen, P.M., Grunwaldt, J.D., Jensen, P.A., Knudsen, K.G., Jensen, A.D., 2011. A review of catalytic upgrading of bio-oil to engine fuels. Appl. Catal., A 407, 1–19. Oasmaa, A., Kuoppala, E., Elliott, D.C., 2012. Development of the basis for an analytical protocol for feeds and products of bio-oil hydrotreatment. Energy Fuels 26, 2454–2460. Samolada, M.C., Baldauf, W., Vasalos, I.A., 1998. Production of a bio-gasoline by ugrading biomass flash pyrolysis liquids via hydrogen processing and catalytic cracking. Fuel 77, 1667–1675. Sheu, Y.H.E., Anthony, R.G., Soltes, E.J., 1988. Kinetic-studies of upgrading pine pyrolytic oil by hydrotreatment. Fuel Process. Technol. 19, 31. Tang, Z., Lu, Q., Zhang, Y., Zhu, X., Guo, Q., 2009. One step bio-oil upgrading through hydrotreatment, esterification, and cracking. Ind. Eng. Chem. Res. 48, 6923– 6929. Venderbosch, R.H., Ardiyanti, A.R., Wildschut, J., Oasmaac, A., Heeres, H.J., 2010. Stabilization of biomass-derived pyrolysis oils. J. Chem. Technol. Biotechnol. 85, 674–686. Wang, S.R., Guo, Z.G., Cai, Q.J., Guo, L., 2012. Catalytic conversion of carboxylic acids in bio-oil for liquid hydrocarbons production. Biomass Bioenergy 45, 138–143. Wildschut, J., 2009. Pyrolysis Oil Upgrading to Transportation Fuels by Catalytic Hydrotreatment. PhD Thesis, University of Groningen, The Netherland. Wildschut, J., Cabrera, I.M., Heeres, H.J., 2010. Catalyst studies on the hydrotreatment of fast pyrolysis oil. Appl. Catal., B 99, 298–306. Wildschut, J., Mahfud, F.H., Venderbosch, R.H., Heeres, H.J., 2009. Hydrotreatment of fast pyrolysis oil using heterogeneous noble-metal catalysts. Ind. Eng. Chem. Res. 48, 10324–10334. Yang, Y., Gilbert, A., Xu, C., 2009. Hydrodeoxygenation of bio-crude in supercritical hexane with sulfided CoMo and CoMoP catalysts supported on MgO: a model compound study using phenol. Appl. Catal. 360, 242–249. Yu, W., Tang, Y., Mo, L., Chen, P., Lou, H., Zheng, X., 2011. One-step hydrogenation– esterification of furfural and acetic acid over bifunctional Pd catalysts for bio-oil upgrading. Bioresour. Technol. 102, 824–8246.
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060
X. Xu et al. / Chemosphere xxx (2013) xxx–xxx Zhang, J., Luo, Z., Dang, Q., Wang, J., Chen, W., 2012. Upgrading of bio-oil over bifunctional catalysts in supercritical monoalcohols. Energy Fuels 26, 2990– 2995. Zhang, S., Yan, Y., Li, T., Ren, Z., 2005. Upgrading of liquid fuel from the pyrolysis of biomass. Bioresour. Technol. 96, 545–550.
9
Zhang, Z.J., Wang, Q.W., Tripathi, P., Pittman, J.C.U., 2011. Catalytic upgrading of biooil using 1-octene and 1-butanol over sulfonic acid resin catalysts. Green Chem. 13, 940–949. Zhao, C., Kou, Y., Angeliki, A.L., Li, X., Johannes, A.L., 2009. Highly selective catalytic conversion of phenolic bio-oil to alkanes. Angew. Chem., Int. Ed. 48, 3987–3990.
Please cite this article in press as: Xu, X., et al. Two-step catalytic hydrodeoxygenation of fast pyrolysis oil to hydrocarbon liquid fuels. Chemosphere (2013), http://dx.doi.org/10.1016/j.chemosphere.2013.06.060