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Al2O3 catalyst
Fuel Processing Technology 128 (2014) 191–198
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Hydrorefining of oil from rapeseed cake pyrolysis over NiMo/Al2O3 catalyst Katarzyna Pstrowska ⁎, Jerzy Walendziewski, Marek Stolarski Wroclaw University of Technology, Faculty of Chemistry, Fuels Chemistry and Technology Division, Gdańska 7/9, 50-344 Wroclaw, Poland
a r t i c l e
i n f o
Article history: Received 28 February 2014 Received in revised form 23 July 2014 Accepted 23 July 2014 Available online xxxx Keywords: Biomass Bio-oil Biofuel Hydro-treating Hydrodeoxygenation Upgrading
a b s t r a c t Bio-oil from rapeseed cake pyrolysis, bio-oil fraction boiling over 120 °C and bio-oil blended with light gas oil fraction were submitted to the hydrorefining studies. The usability of NiMo/Al2O3 catalyst for pyrolytic oil hydrorefining was tested at the following parameters: temperature (290–350 °C), LHSV (0.5–2.0 h−1) and 3 MPa hydrogen pressure. The influence of hydrorefining parameters on the physicochemical properties and chemical composition of the obtained products was evaluated. Hydrorefining of raw bio-oil at the temperature of 350 °C, 2.0 h−1 and 3 MPa of H2 resulted in unsatisfactory level of refining. Removal of low boiling fraction and LHSV until the value of 0.5 h−1 was reached allowed to deepen the degree of hydrorefining up to the levels of 71.4% of HDS, 29.0% of HDN and 78.8% of HDO. These hydrorefining products cannot be used as internal combustion engine liquid fuels or as their components. Blending of the biooil (20% v/v) with petroleum-derived oil fraction and subjecting it to a hydrorefining process made it possible to obtain a fuel component of relatively good quality. © 2014 Elsevier B.V. All rights reserved.
1. Introduction World energy consumption relies mainly on the use of non-renewable energy sources such as coal, natural gas and crude oil. The transportation sector is responsible for the largest energy consumption, mainly in the form of liquid fuels. According to the Netherlands Environmental Assessment Agency, transport sector is also responsible for nearly one-quarter of global energy-related CO2 emissions [1]. In order to reduce the consumption of non-renewable energy sources and to reduce CO2 emissions, alternative, renewable sources of transport fuels are diligently sought. Successfully, during the last decades, numerous studies have been focusing on fuels derived from agricultural biomass fully compatible with conventional ones. The main sources of liquid alternative internal combustion engine fuels are vegetable oils, e.g. soybean, rapeseed and sunflower oil, typical liquid triglycerides, esters of glycerol and unsaturated fatty acids. Triglycerides converted in the transesterification process can be used to obtain diesel oil-like products [2]. Nowadays esters produced from vegetable oils are worldwide used as diesel oil components in various portions blended with petroleum derived oils. Similarly as transesterificated vegetable oils, raw vegetable oils and pyrolytic vegetable oils blended with petroleum fractions are used to produce liquid fuels for self-ignition engines [3]. Recent increase in biodiesel production resulted in developing of agricultural production, including rapeseed. Rapeseed oil cake, the solid waste from the rapeseed oil ⁎ Corresponding author at: Wroclaw University of Technology, Division of Fuels Chemistry and Technology, 50-344 Wroclaw, Gdańska 7/9, Poland. Tel./fax: +48 71 320 65 92. E-mail address: [email protected] (K. Pstrowska).
http://dx.doi.org/10.1016/j.fuproc.2014.07.035 0378-3820/© 2014 Elsevier B.V. All rights reserved.
pressing process, seems to be potentially an attractive feedstock for liquid fuel production originating from biomass [4]. Agricultural residue energy recovery has focused on the thermochemical processes such as direct combustion, gasification, and pyrolysis [5,6]. Simplicity of pyrolysis process and accessibility to raw material increase the interest in using rapeseed oil cake for bio-oil production both as a potential liquid biofuel or as a biofuel component. Regardless of pyrolysis process conditions, e.g. bed type, heating rate or process temperature, bio-oil (pyrolysis liquid products) physical and chemical characteristics present challenges that need to be overcome before they can be used as pure liquid fuels. Bio-oils are highly viscous (high molecular weight particles) and relatively unstable products (e.g. high olefins content). Elemental analysis of bio-oils obtained in rapeseed oil cake pyrolysis indicates large concentration of heteroatoms (14.8–23.8 wt.% of oxygen, 3.6–9.1 wt.% of nitrogen and to a lesser extent sulphur—0.1–0.6 wt.%) [7–9]. Sulphur and nitrogen are bonded in proteins, which are the main components of the remained rapeseed oil in oil cake structure. High oxygen content lowering heating value of the pyrolysis liquids is a result of depolymerisation and fragmentation of three key biomass building blocks: cellulose, hemicellulose and lignin. Oxygen in bio-oils from biomass pyrolysis is bonded in various groups, such as acids, aldehydes, ketones, alcohols, esters, ethers and phenols [10]. Hence, pyrolytic bio-oils cannot be used directly as liquid fuels and require further upgrading. The main group of bio-oil upgrading processes takes into account physical upgrading such as solvent addition, filtration, and catalytic upgrading as hydrotreating, zeolite cracking, and other chemical methods, e.g. steam reforming, esterification, and mild hydrocracking
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[6,11]. Zeolite cracking, emulsification of pyrolysis bio-oil with diesel oil and hydrorefining were found as the most effective in bio-oil upgrading for fuel purposes [11,12]. Complex mixture (as pyrolysis bio-oils) hydroprocessing for fuel purposes requires hydrogenolysis of organic hetero compounds, hydrodesulphurisation (HDS), hydrodenitrification (HDN), hydrodeoxygenation (HDO) and hydrogenation of unstable olefins. Nitrogen, sulphur, and oxygen compounds undergo hydrogenolysis split out to ammonia, hydrogen sulphide and water respectively. Olefins and other unstable compounds, such as diolefins, which might lead to the formation of gums or insoluble materials, should be converted to more stable saturated compounds. Hydrodeoxygenation (HDO), which is the most effective in case of bio-derived pyrolysis liquids hydrorefining, improves product stability and compatibility with conventional fuels. The efficiency of hydrorefining kinetic parameters (temperature, hydrogen pressure, LHSV, catalyst type) and influence of water content for bio-oil HDO was widely described by Furimsky [12], Elliott [13] and Al-Sabawi [14]. Several papers describe hydrorefining studies with the use of commercially produced catalysts, including model compounds and real bio-oil feeds (mainly wood pyrolysis bio-oils, e.g. from poplar wood) [13]. The effectiveness of commercial catalysts in HDO of raw rapeseed oil over NiMo/ Al2O3, CoMo/Al2O3 and NiW/Al2O3 was evaluated at a mild process temperature of 250–270 °C by Horacek et al. [15]. These studies indicate the highest activity of NiMo catalyst comparing to the other two tested catalysts. High activity for oxygen removal in case of NiMo/Al2O3 catalyst was also confirmed in the hydrorefining of rapeseed grain pyrolysis oil [16]. Stable hydrorefining activity of NiMo/Al2O3 catalyst requires the presence of sulphur compounds (hydrogen sulphide) in the reaction space. Because contents of sulphur in pyrolytic bio-oils are relatively low, it is profitable to co-refine bio-oils with sulphur containing petroleum fractions such as light gas oil [17] or search for new non-sulphide catalysts [18]. According to the author's knowledge, there are not many papers comparing results of hydrorefining of raw pyrolytic bio-oil, dehydrated bio-oil and bio-oil blends with petroleum fraction. These studies are particularly important due to the large production of biodiesel components obtained e.g. from rapeseed oil which is accompanied by increased rapeseed waste creation. Application of this waste as raw material for liquid fuel production should also help to solve partially the problem deriving from its use as a source for bio-oil production in the first place. In this paper the catalytic hydrorefining efficiency of bio-oil from rapeseed oil cake pyrolysis was investigated, dewatered bio-oil fraction boiling at temperature over 120 °C, and bio-oil blend with non-desulphurized light gas oil fraction. The hydrorefining process was realized under mild process parameters (temperature in the range of 260–350 °C) to prevent high conversion of the feed to gasphase products, which reduces liquid product yield. Moreover, relatively low hydrogen pressure (3 MPa) and moderate or low liquid hour space velocity (LHSV at the level of 0.5–2.0 h−1) was applied in order to reduce hydrogen consumption and hydrorefining costs.
Oil content in the material was determined as 14.3 wt.% with hexane extraction method (EN ISO 734–1:2006). Additionally thermogravimetric (TG) analysis of rapeseed oil cake was carried out with Perkin Elmer TGA7 analyser. The TG experiment was performed under argon flow rate (60 cm3/min) up to the temperature of 800 °C with a heating rate of 5 °C/min. Analysis of the thermogravimetric curve (TG—Fig. 1) implies significant loss of the rapeseed cake mass up to the temperature range of 450–500 °C (ca. 68 wt.% at 500 °C). Derivative thermogravimetric curve (DTG—Fig. 1) implies two major peaks of thermal degradation. The first one at the temperature below 100 °C is connected mainly to the moisture removal. The biggest peak at the DTG curve detected at the temperature of 281 °C is connected to the maximum devolatilization of the rapeseed cake sample. Devolatilization of the sample was completed at about 550 °C (DTG—Fig. 1). 2.2. Rapeseed cake pyrolysis Pyrolysis experiments were carried out in a fixed bed reactor up to the final temperature of 500 °C. In the typical experiment, 2000 g of the rapeseed cake material was loaded to the batch reactor and then the reactor temperature was increased at the steady rate of 5 °C/min till desired final temperature was reached. At this point, the experiment was held at a constant (final) temperature for 30 min till the process was completed. Before the start of the experiment, the reactor was purged with argon for 15 min at a flow rate of 20 l/h to remove air from the apparatus system. The gaseous pyrolysis products were flowing through a water condenser, where they were condensed and cooled in a water jacket and next in a cold trap maintained at temperature ~ − 5 °C. The liquid products were separated to aqueous and oil fractions. Oil fractions (bio-oil) were additionally dried over molecular sieves 4A. The hermetically closed glass bottles with oils were stored at reduced temperature (~3–5 °C). The material balance of pyrolysis experiments (5 °C/min heating rate, final temperature of 500 °C) showed the following average product yields: solid pyrolysis residue (biochar): 32.9 wt.%, bio-oil: 25.9 wt.%, water fraction: 25.3 wt.%, and gas fraction: 15.9 wt.%. 2.3. Hydroprocessing Three series of pyrolytic bio-oil hydroprocessing experiments were carried out. The reactor feed was composed of the following raw materials: first series—raw bio-oil, second series—bio-oil fraction boiling over 120 °C, third series—20% (v/v) bio-oil and 80% (v/v) nonrefined light gas oil fraction mixture. The experiments were performed in the laboratory “continuous flow apparatus” previously described by Walendziewski et al. [17]. The applied series parameters are presented
2. Materials and methods 2.1. Material The rapeseed cake, used for pyrolysis experiments, is a solid biomass residual after cold pressing of rapeseed grain (Brassica napus L.). Samples were taken from the oil producing plant in Malczewo located in the west region of Poland. Samples were used as received (average particle size b 2 mm). Rapeseed oil cake is rich in carbon (52.9 wt.%), hydrogen (7.9 wt.%), and oxygen (31.9 wt.%). High values of nitrogen and sulphur contents 6.7 wt.% and 0.6 wt.%, respectively were found in the feed. Proximate analysis indicates high volatile matter content (81.8 wt.%), relatively high heat of combustion value (18.7 MJ/kg) and 6.1 wt.% of ash content.
Fig. 1. Thermogravimetric curve of rapeseed oil cake.
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in Table 1. A commercial hydrorefining NiMo/Al2O3 catalyst was used in the fixed bed reactor (50 cm3 of the catalyst, total reactor volume 300 cm3). Basic properties and composition of the catalyst are presented in Table 2. The catalyst was activated with sulphiding process (3 MPa of H2, temperature 320 °C, LHSV = 2 h−1, sulphiding time—12 h) with diethyl sulphide, S(C2H5)2 solution in diesel fuel. Fig. 2 presents the schematic view of hydrorefining continuous flow apparatus used in these experiments.
193
Table 2 Hydrorefining catalyst properties. NiMo/Al2O3 Chemical composition, [wt.%] NiO MoO3 Bulk density, [g/cm3] SBET, [m2/g]
3.0 15.0 0.72 270
2.4. Bio-oil and hydrorefining products analyses The following analyses of the obtained products were carried out according to the suitable standards: − − − − − −
product density at 15 °C according to EN ISO 3675, EN ISO 12185, fractional composition according to EN ISO 3405, bromine number according to ASTM D1159-07, kinematical viscosity at 20 and 40 °C according to EN ISO 3104, freezing point according to ASTM D2386-06, heat of combustion according to ASTM D4809.
Elemental analysis of raw materials and obtained hydrorefining products was carried out using the CHNS EA 1110 CE Instruments analyser. Sulphur content was measured with Varian-ICP-AES Liberty 220 analyser, and oxygen content was calculated from the difference. NMR Bruker DRX 300 Spectrometer with a 5 mm broad band probe was used to record the 1H NMR and 13C NMR spectra. The 1H NMR spectra of the oils (200 μl of bio-oils was mixed with 300 μl CDCl3) were obtained at a H frequency of 300.12 MHz, measured in a range of −3.838–16.137 ppm (16 scans, delay: 1 s, acquisition time: 5.46 s). The 13C spectra, at C frequency of 75.45 MHz, were measured in the range of 10–230 ppm (1024 scans, delay: 30 s, acquisition time: 3.62 s). The percentage of protons and carbon atoms in different groups was determined according to the method proposed by Mullen et al. [19] using spectra of equimolar solution (1:1:1:1) of 1-hexene, isooctane, m-cresol and 4-methyl-2-pentanone. Differences in relaxation time of the obtained spectra were corrected using the standard mixture correlations. Chemical shifts in the 1HNMR spectra correspond to the following proton assignments: − − − − − −
0.5–1.5 ppm—alkanes; 1.5–3.0 ppm—aliphatics-α to unsaturated or heteroatom; 3.0–4.4 ppm—alcohols, methylene-dibenzene, ethers; 4.4–6.0 ppm—methoxy, carbohydrates; 6.0–8.5 ppm—(hetero-) aromatics; 9.5–10.0 ppm—aldehydes, carboxylic acids.
Chemical shifts in the 13CNMR spectra correspond to the following carbon assignments: − 13–15 ppm—peripheral CH3-olefins; − 15–20 ppm—peripheral, CH3-aliphatics;
Table 1 Hydroprocessing parameters. Feed
Series/ exp. no.
Temp., [°C]
Hydrogen pressure, [MPa]
LHSV, [h−1]
Raw rapeseed cake pyrolysis bio-oil
I/1 I/2 I/3 II/1 II/2 II/3 III/1 III/2 III/3
290 320 350 350 350 350 290 320 350
3 3 3 3 3 3 3 3 3
2.0 2.0 2.0 0.5 1.0 2.0 2.0 2.0 2.0
Rapeseed cake pyrolysis bio-oil fraction boiling over 120 °C 20% v/v raw rapeseed cake pyrolysis bio-oil and 80% v/v light gas oil fraction blend
− − − − − −
20–30 ppm—aliphatic inside chain-CH2; 30–34 ppm—unsaturated inside chain-CH; 35–55 ppm—chain branching carbon; 100–115 ppm—olefins; 116–165 ppm—aromatics; 180–215 ppm—ketones, aldehydes.
3. Results and discussion 3.1. Raw rapeseed cake bio-oil hydroprocessing Table 3 presents results of raw bio-oil hydroprocessing at constant LHSV (2.0 h−1) and 3.0 MPa hydrogen pressure over NiMo/Al2O3 catalyst. For the series I, process temperature in the range of 290–350 °C was the variable parameter (Table 1). Elemental composition of the raw bio-oil from rapeseed cake pyrolysis indicates relatively low hydrogen content (10.20 wt.%), high oxygen (10.62 wt.%), nitrogen (7.05 wt.%) and sulphur (0.63 wt.%) content. Distillation profile of the bio-oil indicates a fairly large amount of low boiling fraction (10 wt.% of the material boiling below 105 °C), which includes water and low boiling hydrocarbons. Initial boiling point (IBP) was measured at the temperature of 82 °C. Up to the temperature of 297 °C (EBP—end/final boiling point) distilled 65% (v/v) of the bio-oil. Further heating of the product in the course of distillation results in its thermal decomposition. 1HNMR calculations point the saturated hydrocarbons as the dominant state in the bio-oil (44.7%—Fig. 3), which was confirmed by 13CNMR spectra analysis (47.6% of inside-chain carbon—Fig. 4). Despite the predominant share of aliphatic, rapeseed oil cake pyrolysis oil contains a large quantity of unsaturated compounds, which was confirmed by bromine number (81.0 g Br2/100 g) as well as (hetero-) aromatic protons and carbons content, calculated from NMR spectra. In order to use the refined bio-oils as internal combustion engine fuels or fuel oils, a considerable part of heteroatoms (particularly nitrogen and sulphur) must be removed. It is also necessary to partially reduce the unsaturated hydrocarbons content (hydrogenation of the most unstable olefins) and improve the physical properties of the product. In the applied temperature range, an increase in the process temperature causes higher gas production (up to 12 wt.% at 350 °C hydrorefining temperature—Table 3). Higher process temperature caused the higher conversion-rate of the feed, including intensification of heteroatoms hydrogenolysis and limited hydrocracking reaction of bio-oil components to light gaseous products. Increasing of the hydrorefining temperature leads to H/C ratio grow (up to the value of 1.94—I/3 product) which is caused mainly by oxygen removal and olefin hydrogenation. Partial decrease in bromine number together with process temperature increase (81.0–41.4 gBr2/100 g—product I/3—Table 3) certifies unsaturated hydrocarbon resistance to the applied process parameters, which was also confirmed by slight decrease of olefin carbons content in 13CNMR spectra analysis (Fig. 4). Hydrogenation of unsaturated hydrocarbons causes an increase in alkane type carbon content (44.7–57.7%—Fig. 4), which is the main reason of both the improvement (mainly viscosity) of the hydrorefining products physical properties and the undesirable increase of freezing point. Freezing point temperature rises from −11 °C (raw bio-oil) up to 0 °C for the product obtained at the hydrorefining temperature of 320 °C, which is a result of increase
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Fig. 2. Schematic view of hydrorefining apparatus [18]. (1) Gasmeter, (2) pump, (3) feed tank, (4) reactor, (5) temperature controllers, (6) water cooler, (7) pressure gas–liquid separator, and (8) atmospheric separator.
in alkane content. Further increase in hydrorefining temperature slightly lowers the freezing point temperature up to − 4 °C (I/3—Table 3), which was caused by isomerisation of alkanes formed in lower temperatures (2.1% increase in chain branching carbon type comparing to the raw bio-oil—hydrorefining product I/3—Fig. 4). The higher content of i-alkanes is advantageous from the fuel-use point of view because it improves the low temperature properties of the product. As a result of changes in the chemical structure, heating value increases from
Table 3 Hydroprocessing results of the raw rapeseed cake pyrolysis bio-oil—series I—properties of the raw material and hydrorefining products. Raw material
Sample no. I/1
I/2
I/3
Temperature, [°C]
290
320
350
Hydrogen pressure, [MPa]
3
3
3
LHSV, [h−1] Liquid product yield, [wt.%] Density at 15 °C, [g/cm3] Elemental composition, [wt.%] C H N S Oa) Atomic ratio H/C Distillation IBP, [°C] 10%, [°C] 50%, [°C] 80%, [°C] EBP, [°C] % distilled fraction Bromine number, [gBr2/100 g] Viscosity at 20 °C, [cSt] 40 °C, [cSt] Freezing point, [°C] Heat of combustion, [MJ/kg] a)
Calculated by difference.
2.0
2.0
2.0
– 1.003
90.8 0.999
88.5 0.979
88.0 0.977
71.50 10.20 7.05 0.63 10.62 1.71
74.91 10.68 6.75 0.53 7.13 1.71
75.62 10.90 6.50 0.42 6.66 1.73
74.90 12.10 6.42 0.33 6.25 1.94
82 103 273 – 297 65 81.0 117.2 47.3 −11 32.5
89 106 254 – 280 70 75.6 95.4 33.8 −4 34.5
72 104 275 – 307 75 75.6 80.8 23.2 0 35.2
74 107 280 – 310 78 41.4 75.6 21.2 −4 36.4
32.5 for raw bio-oil up to 36.4 MJ/kg for the product obtained at 350 °C of the hydrorefining process (Table 3). Maximum removal of nitrogen (HDN), sulphur (HDS) and oxygen (HDO) was observed at the highest applied hydrorefining temperature (350 °C): 8.9%, 47.6% and 41.1% respectively. Incomplete oxygen removal may be caused by the presence of less reactive aromatic oxygen compounds, e.g. phenols, where C\O bonding is more durable (dissociation energy at the level of 422–468 kJ/mol) than in aliphatic compounds (339–385 kJ/mol). Moreover, high nitrogen content in raw bio-oil and H2O presence cause lowering of HDO efficiency [12]. With the increase in hydrorefining temperature, the degree of HDS increases up to the value of 47.6% (I/3). Product I/3, obtained at the hydrorefining temperature of 350 °C, is characterized with 0.33 wt.% sulphur content (Table 3), which precludes direct use of the liquid as internal combustion engine fuel or fuel oil. Since NiMo catalysts are commercially used for HDS processes, unsatisfactory level of sulphur removal may be caused by many factors, e.g. too high LHSV (too short contact time of the feed with the catalyst), and too low hydrogen pressure (the degree of HDS process increases with the partial pressure of hydrogen increase). Applied catalyst and process parameters poorly promote nitrogen compounds hydrogenation (Table 3). Maximum HDN efficiency was observed at the process temperature of 350 °C (8.9% for the I/3 product). Low degree of nitrogen removal implies hydrogenation of aliphatic nitrogen-containing compounds in which nitrogen is present in the substituent (e.g. amines, nitriles), since these are much easier to remove than heterocyclics and aromatics, in which nitrogen is embedded in the ring. From this point of view, it is highly possible that the majority of nitrogen compounds are heterocyclic or aromatic types, in which nitrogen is embedded in the ring. Such conclusion may be partly confirmed by 1HNMR analysis, confirming high heteroaromatics content (including N, S and O bonded in the aromatic ring) in the case of raw rapeseed cake bio-oil (17.4% of protons) and in the I/3 product (7.1% of protons—Fig. 3). Hydrorefining transformation of raw rapeseed cake pyrolysis oil obtained in the I series of the experiment was moderate. Unsatisfactory level of hydrorefining may be caused by many factors, e.g. high content of low boiling fraction, including water (catalyst deactivation), presence of the water fraction forming in the hydrodeoxygenation process (catalyst deactivation), too high LHSV or too low hydrogen pressure. In order
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195
Fig. 3. Results of 1HNMR spectra calculations.
to improve HDS, HDN and HDO processes, as well as saturation of olefin type hydrocarbons, LHSV in the range of 0.5–2.0 h−1 was lowered. Additionally, low boiling fraction of the bio-oil (b120 °C) was removed from the hydroprocessing feed with vacuum distillation (to avoid biooil components polymerization processes). 3.2. Hydroprocessing of dewatered bio-oil fraction boiling over 120 °C Series II of the hydrorefining studies was realized using the bio-oil fraction boiling over 120 °C as the process feed. Variable parameter of the series II was the liquid hour space velocity (LHSV) in the range of 0.5–2.0 h−1 (Table 1). Removal of low boiling fraction strongly influences bio-oil primary properties, as density (increase up to the value of 1.105 g/cm3 at
15 °C) and viscosity (an increase of 70 cSt at 20 °C comparing to the raw bio-oil). A decrease in oxygen content (to the value of 9.9 wt.%) was caused by partial water fraction removal. Water removal caused also a slight increase in H/C ratio up to the value of 1.77. Raw material for series II hydrorefining distills in the amount of 68% (v/v) up to the temperature of 305 °C. As in case of the raw bio-oil, series II feed is characterized by large share alkane and (hetero-) aromatic type protons: 52% and 14.8% respectively (Fig. 3). 13CNMR analysis points large share of olefin type carbon atoms (Fig. 4), which was confirmed by bromine number determination (79.9 gBr2/100 g in the hydroprocessing series II feed—Table 4). Table 4 presents the properties of the feed and hydrorefining products of the hydroprocessing series II. Removal of low boiling fraction strongly influences hydroprocessing product yield. Comparing
Fig. 4. Results of 13CNMR spectra calculations.
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Table 4 Hydroprocessing results of the raw rapeseed cake pyrolysis bio-oil fraction boiling over 120 °C—series II—properties of the feed and hydrorefining products. Raw material
Sample no. II/1
II/2
Temperature, [°C]
350
350
350
Hydrogen pressure, [MPa]
3
3
3
LHSV, [h−1]
0.5
1.0
2.0
Liquid product yield, [wt.%] Density at 15 °C, [g/cm3] Elemental composition, [wt.%] C H N S Oa) Atomic ratio H/C Distillation IBP, [°C] 10%, [°C] 50%, [°C] 80%, [°C] EBP, [°C] % distilled fraction Bromine number, [gBr2/100 g] Viscosity at 20 °C, [cSt] 40 °C, [cSt] Freezing point, [°C] Heat of combustion, [MJ/kg] a)
II/3
1.105
92.0 0.915
92.3 0.918
93.0 0.985
71.80 10.60 7.07 0.63 9.90 1.77
80.40 12.30 5.02 0.18 2.10 1.84
78.30 12.10 5.53 0.25 3.82 1.89
77.10 12.30 6.39 0.30 3.91 1.91
120 170 287 – 305 68 79.9 190.2 60.9 −2 32.1
85 95 283 320 322 90 44.3 14.3 8.2 −8 40.5
85 95 295 318 320 88 46.1 17.6 11.0 −4 39.2
84 96 295 316 316 88 53.4 24.5 14.5 −6 38.5
Calculated by difference.
to the product I/3, obtained at the same process parameters (350 °C, LHSV = 2 h−1, 3 MPa of H2), product II/3 showed 5 wt.% higher yield (93.0 wt.%—Table 4). This is associated with the reduction of lowboiling hydrocarbon hydrocracking reactions in case of the series II feed, where low boiling fraction (b120 °C) was removed. Fourfold prolonged contact of the catalyst with the feedstock (decrease in LHSV from the value of 2.0 h−1 to 0.5 h−1) did not significantly affect product yield, but significantly affected the degree of heteroatoms hydrogenolysis and overall physicochemical properties of the obtained products.
The primary properties of the products obtained in the series II are more diversified than in the series I. The characteristic of the products properties is presented in Table 4. Lowering the level of LHSV to 0.5 h−1 causes similar olefin hydrogenation level as in case of series I (bromine number varies from 79.9 gBr2/100 g in the raw material of series II to 44.3 gBr2/100 g—product II/1). Olefin hydrogenation was confirmed by 13CNMR spectra analysis (Fig. 4), e.g. reduction of inside chain olefin carbon content (from 3.1% in the raw material of series II to the value of 2.4% in the II/1 product—30–34 ppm), and reduction of peripheral olefin carbon content (from 11.2% at the raw material to the value of 8.4% in II/1 product—13–14 ppm). The final content of the olefins in the II/1 product is unacceptably high in the case of use of this product as a pure liquid fuel. Increase in alkane content considerably improves the physical properties of the hydrorefining products. Together with LHSV value lowering, distillation efficiency increases, up to the 90% (v/v) of the product at the final distillation temperature of 322 °C. Comparing to the series I raw material—distillation efficiency was increased by 22%. Together with LHSV lowering, increase in i-alkane content was observed. As consequence, the freezing point of the product obtained at 0.5 h− 1 LHSV was lowered up to the value of − 8 °C (from the value of − 2 °C for series II feed material). This observation was confirmed by an increase in chain branching carbon content (from 3.9 in raw material, up to 6.4% for the product II/1—35–55 ppm, Fig. 4). Sample II/1 obtained at 0.5 h−1 LHSV is characterized by 78.8% HDO, 71.4% HDS and 29.0% HDN efficiency. It was the maximum effectiveness of heteroatoms removal obtained in the series II. Comparing to the raw bio-oil hydrorefining results (Table 3), a significant increase in the hydrogenation process may be caused mainly by two reasons—fourfold prolonged contact time of the raw material with catalyst and lower water content in the reaction zone (raw material distillation starts at 120 °C, which significantly reduces water content in the feed, still in the reaction zone remains water formed in HDO). Despite the large increase in heteroatom removal, nitrogen (5.02 wt.%) and sulphur (0.18 wt.%) are still present in high concentration, which limits direct use of the II/1 product as a fuel component. As in case of series I, a significant decrease of heteroatoms was also observed in 1HNMR spectra (Fig. 3), where e.g. heteroaromatic (6.0–8.5 ppm), carbohydrate, or
Table 5 Hydroprocessing results of 20% (v/v) rapeseed cake pyrolysis bio-oil and 80% (v/v) light gas oil fraction blend—properties of the feed and hydrorefining products. Light gas oil fraction
Raw material
Sample no. III/1
III/2
III/3
Temperature, [°C]
290
320
350
Hydrogen pressure, [MPa]
3
3
3
LHSV, [h−1]
2.0
Liquid product yield, [wt.%] Density at 15 °C, [g/cm3] Elemental composition, [wt.%] C H N S Oa) Atomic ratio H/C Distillation IBP, [°C] 10%, [°C] 50%, [°C] 80%, [°C] EBP, [°C] % distilled fraction Bromine number, [gBr2/100 g] Viscosity at 20 °C, [cSt] 40 °C, [cSt] Freezing point, [°C] Heat of combustion, [MJ/kg] a)
Calculated by difference.
0.858 86.50 13.10 0.20 0.10 0.10 1.82 231 261 289 310 336 99 0.4 4.8 3.5 n/a 44.7
0.888 83.50 12.52 1.57 0.21 2.20 1.80 82 145 282 308 322 94 13.0 13.1 11.3 −13 42.6
2.0
2.0
93.2 0.877
93.0 0.873
92.3 0.862
84.40 13.80 1.18 0.17 0.45 1.96
84.80 13.50 1.22 0.12 0.36 1.91
85.30 13.47 1.01 0.06 0.16 1.89
80 195 280 305 322 94 12.3 5.9 4.3 −12 44.4
80 200 285 300 325 95 11.7 5.6 4.2 −11 43.9
74 250 285 302 332 97 10.5 5.3 3.7 −11 45.5
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methoxy- (4.4–6.0 ppm) proton content is lower than in the case of the raw material. As in case of series I, it is highly possible that nitrogen and sulphur atoms are bonded in heterocyclic or aromatic type compounds, which are characterized by much higher bond dissociation energy, than nitrogen in the aliphatic compounds. Low sulphur removal level from bio-oil in this series may be the result of the presence of hydrogenolysis resistant thiophene-ring containing compounds. Potentially, the hydrorefining product II/1 could be applied as a fuel oil component in a mixture with a suitable petroleum fraction.
view a higher hydrogenolysis level of oxygen and sulphur containing compounds can be a result of diminished content of nitrogen containing compounds. Nitrogen compounds in larger concentrations and ammonia, products of their hydrogenolysis, are poison for the acid centres of NiMo catalyst. As a consequence basic nitrogen compounds in higher concentration lower catalysts activity. Therefore a low level of hydrogenolysis in the hydrorefining process of raw bio-oil and bio-oil fraction boiling over 120 °C (Tables 3 and 4) in comparison to hydrorefining of lower nitrogen containing feed was observed (Table 5).
3.3. Hydroprocessing of rapeseed cake pyrolysis bio-oil and non-desulphurized light gas oil fraction blend
4. Conclusions
Series III raw material was the blend composed of raw bio-oil from rapeseed oil cake pyrolysis—20% (v/v) and non-refined light gas oil petroleum fraction—80% (v/v) (Table 5). The blended material feed for hydrorefining series III was characterized by the lowest heteroatom content of all feeds applied in these studies: S, N and O content was 0.21 wt.%, 1.57 wt.% and 1.80 wt.% level respectively. Comparing to the hydroprocessing series I and II feeds, elemental composition and relatively low olefin content (bromine number at the level of 13.0 g Br2/100 g) in the series III feed indicate the blended material as much easier feed for hydrorefining process. Variable parameter of the series III was the process temperature in the range of 290–350 °C (Table 1). The yield of hydrorefining products varies in the series III from 92.3 (III/3) to 93.3 wt.% (III/1). An increase in the process temperature slightly results in higher gas production up to the yield of 7.7 wt. at the hydroprocessing temperature of 350 °C, which was caused mainly by higher hydrogenolysis levels at the applied process temperature. An increase in hydrorefining temperature causes significant improvement of hydrorefining product properties (Table 5). Products distill up to 94% (v/v) (III/1)–97% (v/v) (III/3) at the final temperature boiling range of 322 °C (III/1)–332 °C (III/3). Sample III/3 obtained at the highest hydrorefining temperature of 350 °C is characterized by 92.7% HDO, 71.4% HDS and 35.7% HDN level, the maximal effectiveness of heteroatom removal. This level is the highest found amongst all applied hydrorefining parameters and all the studied (series I–III). The product obtained at the final hydrorefining temperature of 350 °C was characterized by the following heteroatom content: S: 0.06 wt.%, N: 1.01 wt.%, and O: 0.16 wt.%. At the applied process parameters higher hydrogen consumption was observed for heteroatom removal (mainly oxygen), than hydrogenation of unsaturated hydrocarbons. Whilst appreciable increase in heteroatoms hydrogenolysis of the series III feed was observed, diminishing of olefin content in series III was rather small (reduction of olefin content up to the bromine number of 10.5 g Br2/100 g at the hydrorefining temperature of 350 °C—Table 5, confirmed by low reduction of olefin type carbons calculated with 13 CNMR—Fig. 4). Partial hydrogenation of unsaturated hydrocarbons and heteroatom removal improve the physical properties of products obtained in the series III experiments. A low increase in freezing point was observed (from − 13 °C for the series III feed, up to the value of −11 °C for the III/3 product), which was caused by an increase in n-alkane type hydrocarbon content; heat of combustion value increased up to the value of 45.5 MJ/kg for the product obtained at the hydrorefining temperature of 350 °C (III/3—Table 5). The product obtained at the hydrorefining temperature of 350 °C (III/3) partly meets regulatory requirements established for fuel oils (according to ASTM D396). The required level of hydrorefining (to the “ready-to-use” fuel) could be possibly achieved with the second step of hydrorefining or with higher hydrogen pressure at the applied process parameters. Relatively satisfying hydrorefining results, low content of oxygen, sulphur and nitrogen containing compounds in the hydrorefining products of this series is mainly the result of much lower concentration of hetero compounds in the feed as a result of dilution of a large amount of heteroatom compounds containing raw bio-oil with low heteroatoms containing light gas oil–petroleum fraction. From the other point of
One-step hydrorefining of raw and partially dewatered bio-oil obtained in pyrolysis of rapeseed cake does not result in a satisfactory hydrorefining level. It is a result of high heteroatom containing compounds and olefins as well as water fraction in bio-oils—catalyst poisons (in case of raw bio-oil). The highest heteroatom removal in case of raw bio-oil was obtained with the hydrorefining at the temperature of 350 °C (at LHSV 2.0 h−1, 3 MPa of H2): 47.6% of HDS, 8.9% of HDN and 41.1% of HDO. Removal of low boiling fraction and LHSV lowering to the value of 0.5 h−1 (at the process temperature of 350 °C and 3 MPa of H2) allowed to increase the degree of hydrorefining up to the levels of 71.4% of HDS, 29.0% of HDN and 78.8% of HDO. The obtained hydrorefining products do not meet the normalized requirements for light commercial fuel oil. The application of the blend consisting of 20% (v/v) of the raw bio-oil and 80% (v/v) of light gas oil as the feed considerably improves hydrorefining process results. It is connected with the relatively lower heteroatom concentration in the feed. At high LHSV (2.0 h−1), hydrorefining temperature of 350 °C temperature and 3 MPa hydrogen pressure, hydrorefining products fulfil majority of light commercial fuel oil requirements. However, the best product of hydrorefining still contains too large quantity of sulphur and nitrogen (0.06 wt.% and 1.01 wt.% respectively). It means that severity of the hydrorefining process should be distinctly higher or the obtained product should be mixed with proper petroleum fraction for fuel purposes. Acknowledgements This work was financed by statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wroclaw University of Technology, project number S 30063. The authors would like to gratefully acknowledge Mr. Paweł Dąbrowski from Wroclaw University of Technology NMR Laboratory, for his support in NMR analysis. References [1] J.G.J. Olivier, G. Janssens-Maenhout, J.A.H.W. Peters, Trends in global CO2 emissions, 2012 Report, PBL Netherlands Environmental Assessment Agency, The Hague/ Bilthoven, 2013, pp. 8–11. [2] T. Issariyakul, A.K. Dali, Biodiesel from vegetable oils, Renewable and Sustainable Energy Reviews 31 (2014) 446–471. [3] F. Ma, M.A. Hanna, Biodiesel production: a review, Bioresource Technology 70 (1999) 1–15. [4] E. David, Valorization of residual biomass by thermochemical processing, Journal of Analytical and Applied Pyrolysis 104 (2013) 260–268. [5] M. Demirbas, M. Balat, H. Balat, Biowastes-to-biofuels, Energy Conversion and Management 52 (2011) 1815–1828. [6] A.V. Bridgwater, Thermochemical processing of biomass, in: R.C. Brown (Ed.), Conversion into Fuels, Chemicals and Power, first ed., Wiley, West Sussex, United Kingdom, 2011, pp. 157–188. [7] E. Culcuoglu, E. Unay, F. Karaosmanoglu, D. Angin, S. Sensoz, Characterization of the bio-oil of rapeseed cake, Energy Sources 27 (2005) 1217–1223. [8] K. Smets, A. Roukaerts, J. Czech, G. Reggers, S. Schreurs, R. Carleer, J. Yperman, Slow catalytic pyrolysis of rapeseed cake: product yield and characterization of the pyrolysis liquid, Biomass and Bioenergy 57 (2013) 180–190. [9] S. Ucar, A.R. Ozkan, Characterization of products from the pyrolysis of rapeseed oil cake, Bioresource Technology 99 (2008) 8771–8776. [10] J.H. Marsman, J. Wildschut, F. Mahfud, H.J. Heeres, Identification of components in fast pyrolysis oil and upgraded products by comprehensive two-dimensional gas
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[15] J. Horacek, Z. Tisler, V. Rubas, D. Kubicka, HDO catalysis triglycerides conversion into pyrolysis and isomerization feedstock, Fuel 121 (2014) 57–64. [16] K. Pstrowska, J. Walendziewski, R. Łużny, M. Stolarski, Hydroprocessing of rapeseed pyrolysis bio-oil over NiMo/Al2O3 catalyst, Catalysis Today 223 (2014) 54–65. [17] J. Walendziewski, M. Stolarski, R. Łużny, B. Klimek, Hydroprocessing of light gas oil– rape oil mixtures, Fuel Processing Technology 90 (2009) 686–691. [18] E. Furimsky, Hydroprocessing challenges in biofuels production, Catalysis Today 217 (2013) 13–56. [19] C.A. Mullen, G.D. Strahan, A.A. Boateng, Characterization of various fast-pyrolysis bio-oils by NMR spectroscopy, Energy & Fuels 23 (2009) 2707–2718.
Contents lists available at ScienceDirect
Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc
Hydrorefining of oil from rapeseed cake pyrolysis over NiMo/Al2O3 catalyst Katarzyna Pstrowska ⁎, Jerzy Walendziewski, Marek Stolarski Wroclaw University of Technology, Faculty of Chemistry, Fuels Chemistry and Technology Division, Gdańska 7/9, 50-344 Wroclaw, Poland
a r t i c l e
i n f o
Article history: Received 28 February 2014 Received in revised form 23 July 2014 Accepted 23 July 2014 Available online xxxx Keywords: Biomass Bio-oil Biofuel Hydro-treating Hydrodeoxygenation Upgrading
a b s t r a c t Bio-oil from rapeseed cake pyrolysis, bio-oil fraction boiling over 120 °C and bio-oil blended with light gas oil fraction were submitted to the hydrorefining studies. The usability of NiMo/Al2O3 catalyst for pyrolytic oil hydrorefining was tested at the following parameters: temperature (290–350 °C), LHSV (0.5–2.0 h−1) and 3 MPa hydrogen pressure. The influence of hydrorefining parameters on the physicochemical properties and chemical composition of the obtained products was evaluated. Hydrorefining of raw bio-oil at the temperature of 350 °C, 2.0 h−1 and 3 MPa of H2 resulted in unsatisfactory level of refining. Removal of low boiling fraction and LHSV until the value of 0.5 h−1 was reached allowed to deepen the degree of hydrorefining up to the levels of 71.4% of HDS, 29.0% of HDN and 78.8% of HDO. These hydrorefining products cannot be used as internal combustion engine liquid fuels or as their components. Blending of the biooil (20% v/v) with petroleum-derived oil fraction and subjecting it to a hydrorefining process made it possible to obtain a fuel component of relatively good quality. © 2014 Elsevier B.V. All rights reserved.
1. Introduction World energy consumption relies mainly on the use of non-renewable energy sources such as coal, natural gas and crude oil. The transportation sector is responsible for the largest energy consumption, mainly in the form of liquid fuels. According to the Netherlands Environmental Assessment Agency, transport sector is also responsible for nearly one-quarter of global energy-related CO2 emissions [1]. In order to reduce the consumption of non-renewable energy sources and to reduce CO2 emissions, alternative, renewable sources of transport fuels are diligently sought. Successfully, during the last decades, numerous studies have been focusing on fuels derived from agricultural biomass fully compatible with conventional ones. The main sources of liquid alternative internal combustion engine fuels are vegetable oils, e.g. soybean, rapeseed and sunflower oil, typical liquid triglycerides, esters of glycerol and unsaturated fatty acids. Triglycerides converted in the transesterification process can be used to obtain diesel oil-like products [2]. Nowadays esters produced from vegetable oils are worldwide used as diesel oil components in various portions blended with petroleum derived oils. Similarly as transesterificated vegetable oils, raw vegetable oils and pyrolytic vegetable oils blended with petroleum fractions are used to produce liquid fuels for self-ignition engines [3]. Recent increase in biodiesel production resulted in developing of agricultural production, including rapeseed. Rapeseed oil cake, the solid waste from the rapeseed oil ⁎ Corresponding author at: Wroclaw University of Technology, Division of Fuels Chemistry and Technology, 50-344 Wroclaw, Gdańska 7/9, Poland. Tel./fax: +48 71 320 65 92. E-mail address: [email protected] (K. Pstrowska).
http://dx.doi.org/10.1016/j.fuproc.2014.07.035 0378-3820/© 2014 Elsevier B.V. All rights reserved.
pressing process, seems to be potentially an attractive feedstock for liquid fuel production originating from biomass [4]. Agricultural residue energy recovery has focused on the thermochemical processes such as direct combustion, gasification, and pyrolysis [5,6]. Simplicity of pyrolysis process and accessibility to raw material increase the interest in using rapeseed oil cake for bio-oil production both as a potential liquid biofuel or as a biofuel component. Regardless of pyrolysis process conditions, e.g. bed type, heating rate or process temperature, bio-oil (pyrolysis liquid products) physical and chemical characteristics present challenges that need to be overcome before they can be used as pure liquid fuels. Bio-oils are highly viscous (high molecular weight particles) and relatively unstable products (e.g. high olefins content). Elemental analysis of bio-oils obtained in rapeseed oil cake pyrolysis indicates large concentration of heteroatoms (14.8–23.8 wt.% of oxygen, 3.6–9.1 wt.% of nitrogen and to a lesser extent sulphur—0.1–0.6 wt.%) [7–9]. Sulphur and nitrogen are bonded in proteins, which are the main components of the remained rapeseed oil in oil cake structure. High oxygen content lowering heating value of the pyrolysis liquids is a result of depolymerisation and fragmentation of three key biomass building blocks: cellulose, hemicellulose and lignin. Oxygen in bio-oils from biomass pyrolysis is bonded in various groups, such as acids, aldehydes, ketones, alcohols, esters, ethers and phenols [10]. Hence, pyrolytic bio-oils cannot be used directly as liquid fuels and require further upgrading. The main group of bio-oil upgrading processes takes into account physical upgrading such as solvent addition, filtration, and catalytic upgrading as hydrotreating, zeolite cracking, and other chemical methods, e.g. steam reforming, esterification, and mild hydrocracking
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[6,11]. Zeolite cracking, emulsification of pyrolysis bio-oil with diesel oil and hydrorefining were found as the most effective in bio-oil upgrading for fuel purposes [11,12]. Complex mixture (as pyrolysis bio-oils) hydroprocessing for fuel purposes requires hydrogenolysis of organic hetero compounds, hydrodesulphurisation (HDS), hydrodenitrification (HDN), hydrodeoxygenation (HDO) and hydrogenation of unstable olefins. Nitrogen, sulphur, and oxygen compounds undergo hydrogenolysis split out to ammonia, hydrogen sulphide and water respectively. Olefins and other unstable compounds, such as diolefins, which might lead to the formation of gums or insoluble materials, should be converted to more stable saturated compounds. Hydrodeoxygenation (HDO), which is the most effective in case of bio-derived pyrolysis liquids hydrorefining, improves product stability and compatibility with conventional fuels. The efficiency of hydrorefining kinetic parameters (temperature, hydrogen pressure, LHSV, catalyst type) and influence of water content for bio-oil HDO was widely described by Furimsky [12], Elliott [13] and Al-Sabawi [14]. Several papers describe hydrorefining studies with the use of commercially produced catalysts, including model compounds and real bio-oil feeds (mainly wood pyrolysis bio-oils, e.g. from poplar wood) [13]. The effectiveness of commercial catalysts in HDO of raw rapeseed oil over NiMo/ Al2O3, CoMo/Al2O3 and NiW/Al2O3 was evaluated at a mild process temperature of 250–270 °C by Horacek et al. [15]. These studies indicate the highest activity of NiMo catalyst comparing to the other two tested catalysts. High activity for oxygen removal in case of NiMo/Al2O3 catalyst was also confirmed in the hydrorefining of rapeseed grain pyrolysis oil [16]. Stable hydrorefining activity of NiMo/Al2O3 catalyst requires the presence of sulphur compounds (hydrogen sulphide) in the reaction space. Because contents of sulphur in pyrolytic bio-oils are relatively low, it is profitable to co-refine bio-oils with sulphur containing petroleum fractions such as light gas oil [17] or search for new non-sulphide catalysts [18]. According to the author's knowledge, there are not many papers comparing results of hydrorefining of raw pyrolytic bio-oil, dehydrated bio-oil and bio-oil blends with petroleum fraction. These studies are particularly important due to the large production of biodiesel components obtained e.g. from rapeseed oil which is accompanied by increased rapeseed waste creation. Application of this waste as raw material for liquid fuel production should also help to solve partially the problem deriving from its use as a source for bio-oil production in the first place. In this paper the catalytic hydrorefining efficiency of bio-oil from rapeseed oil cake pyrolysis was investigated, dewatered bio-oil fraction boiling at temperature over 120 °C, and bio-oil blend with non-desulphurized light gas oil fraction. The hydrorefining process was realized under mild process parameters (temperature in the range of 260–350 °C) to prevent high conversion of the feed to gasphase products, which reduces liquid product yield. Moreover, relatively low hydrogen pressure (3 MPa) and moderate or low liquid hour space velocity (LHSV at the level of 0.5–2.0 h−1) was applied in order to reduce hydrogen consumption and hydrorefining costs.
Oil content in the material was determined as 14.3 wt.% with hexane extraction method (EN ISO 734–1:2006). Additionally thermogravimetric (TG) analysis of rapeseed oil cake was carried out with Perkin Elmer TGA7 analyser. The TG experiment was performed under argon flow rate (60 cm3/min) up to the temperature of 800 °C with a heating rate of 5 °C/min. Analysis of the thermogravimetric curve (TG—Fig. 1) implies significant loss of the rapeseed cake mass up to the temperature range of 450–500 °C (ca. 68 wt.% at 500 °C). Derivative thermogravimetric curve (DTG—Fig. 1) implies two major peaks of thermal degradation. The first one at the temperature below 100 °C is connected mainly to the moisture removal. The biggest peak at the DTG curve detected at the temperature of 281 °C is connected to the maximum devolatilization of the rapeseed cake sample. Devolatilization of the sample was completed at about 550 °C (DTG—Fig. 1). 2.2. Rapeseed cake pyrolysis Pyrolysis experiments were carried out in a fixed bed reactor up to the final temperature of 500 °C. In the typical experiment, 2000 g of the rapeseed cake material was loaded to the batch reactor and then the reactor temperature was increased at the steady rate of 5 °C/min till desired final temperature was reached. At this point, the experiment was held at a constant (final) temperature for 30 min till the process was completed. Before the start of the experiment, the reactor was purged with argon for 15 min at a flow rate of 20 l/h to remove air from the apparatus system. The gaseous pyrolysis products were flowing through a water condenser, where they were condensed and cooled in a water jacket and next in a cold trap maintained at temperature ~ − 5 °C. The liquid products were separated to aqueous and oil fractions. Oil fractions (bio-oil) were additionally dried over molecular sieves 4A. The hermetically closed glass bottles with oils were stored at reduced temperature (~3–5 °C). The material balance of pyrolysis experiments (5 °C/min heating rate, final temperature of 500 °C) showed the following average product yields: solid pyrolysis residue (biochar): 32.9 wt.%, bio-oil: 25.9 wt.%, water fraction: 25.3 wt.%, and gas fraction: 15.9 wt.%. 2.3. Hydroprocessing Three series of pyrolytic bio-oil hydroprocessing experiments were carried out. The reactor feed was composed of the following raw materials: first series—raw bio-oil, second series—bio-oil fraction boiling over 120 °C, third series—20% (v/v) bio-oil and 80% (v/v) nonrefined light gas oil fraction mixture. The experiments were performed in the laboratory “continuous flow apparatus” previously described by Walendziewski et al. [17]. The applied series parameters are presented
2. Materials and methods 2.1. Material The rapeseed cake, used for pyrolysis experiments, is a solid biomass residual after cold pressing of rapeseed grain (Brassica napus L.). Samples were taken from the oil producing plant in Malczewo located in the west region of Poland. Samples were used as received (average particle size b 2 mm). Rapeseed oil cake is rich in carbon (52.9 wt.%), hydrogen (7.9 wt.%), and oxygen (31.9 wt.%). High values of nitrogen and sulphur contents 6.7 wt.% and 0.6 wt.%, respectively were found in the feed. Proximate analysis indicates high volatile matter content (81.8 wt.%), relatively high heat of combustion value (18.7 MJ/kg) and 6.1 wt.% of ash content.
Fig. 1. Thermogravimetric curve of rapeseed oil cake.
K. Pstrowska et al. / Fuel Processing Technology 128 (2014) 191–198
in Table 1. A commercial hydrorefining NiMo/Al2O3 catalyst was used in the fixed bed reactor (50 cm3 of the catalyst, total reactor volume 300 cm3). Basic properties and composition of the catalyst are presented in Table 2. The catalyst was activated with sulphiding process (3 MPa of H2, temperature 320 °C, LHSV = 2 h−1, sulphiding time—12 h) with diethyl sulphide, S(C2H5)2 solution in diesel fuel. Fig. 2 presents the schematic view of hydrorefining continuous flow apparatus used in these experiments.
193
Table 2 Hydrorefining catalyst properties. NiMo/Al2O3 Chemical composition, [wt.%] NiO MoO3 Bulk density, [g/cm3] SBET, [m2/g]
3.0 15.0 0.72 270
2.4. Bio-oil and hydrorefining products analyses The following analyses of the obtained products were carried out according to the suitable standards: − − − − − −
product density at 15 °C according to EN ISO 3675, EN ISO 12185, fractional composition according to EN ISO 3405, bromine number according to ASTM D1159-07, kinematical viscosity at 20 and 40 °C according to EN ISO 3104, freezing point according to ASTM D2386-06, heat of combustion according to ASTM D4809.
Elemental analysis of raw materials and obtained hydrorefining products was carried out using the CHNS EA 1110 CE Instruments analyser. Sulphur content was measured with Varian-ICP-AES Liberty 220 analyser, and oxygen content was calculated from the difference. NMR Bruker DRX 300 Spectrometer with a 5 mm broad band probe was used to record the 1H NMR and 13C NMR spectra. The 1H NMR spectra of the oils (200 μl of bio-oils was mixed with 300 μl CDCl3) were obtained at a H frequency of 300.12 MHz, measured in a range of −3.838–16.137 ppm (16 scans, delay: 1 s, acquisition time: 5.46 s). The 13C spectra, at C frequency of 75.45 MHz, were measured in the range of 10–230 ppm (1024 scans, delay: 30 s, acquisition time: 3.62 s). The percentage of protons and carbon atoms in different groups was determined according to the method proposed by Mullen et al. [19] using spectra of equimolar solution (1:1:1:1) of 1-hexene, isooctane, m-cresol and 4-methyl-2-pentanone. Differences in relaxation time of the obtained spectra were corrected using the standard mixture correlations. Chemical shifts in the 1HNMR spectra correspond to the following proton assignments: − − − − − −
0.5–1.5 ppm—alkanes; 1.5–3.0 ppm—aliphatics-α to unsaturated or heteroatom; 3.0–4.4 ppm—alcohols, methylene-dibenzene, ethers; 4.4–6.0 ppm—methoxy, carbohydrates; 6.0–8.5 ppm—(hetero-) aromatics; 9.5–10.0 ppm—aldehydes, carboxylic acids.
Chemical shifts in the 13CNMR spectra correspond to the following carbon assignments: − 13–15 ppm—peripheral CH3-olefins; − 15–20 ppm—peripheral, CH3-aliphatics;
Table 1 Hydroprocessing parameters. Feed
Series/ exp. no.
Temp., [°C]
Hydrogen pressure, [MPa]
LHSV, [h−1]
Raw rapeseed cake pyrolysis bio-oil
I/1 I/2 I/3 II/1 II/2 II/3 III/1 III/2 III/3
290 320 350 350 350 350 290 320 350
3 3 3 3 3 3 3 3 3
2.0 2.0 2.0 0.5 1.0 2.0 2.0 2.0 2.0
Rapeseed cake pyrolysis bio-oil fraction boiling over 120 °C 20% v/v raw rapeseed cake pyrolysis bio-oil and 80% v/v light gas oil fraction blend
− − − − − −
20–30 ppm—aliphatic inside chain-CH2; 30–34 ppm—unsaturated inside chain-CH; 35–55 ppm—chain branching carbon; 100–115 ppm—olefins; 116–165 ppm—aromatics; 180–215 ppm—ketones, aldehydes.
3. Results and discussion 3.1. Raw rapeseed cake bio-oil hydroprocessing Table 3 presents results of raw bio-oil hydroprocessing at constant LHSV (2.0 h−1) and 3.0 MPa hydrogen pressure over NiMo/Al2O3 catalyst. For the series I, process temperature in the range of 290–350 °C was the variable parameter (Table 1). Elemental composition of the raw bio-oil from rapeseed cake pyrolysis indicates relatively low hydrogen content (10.20 wt.%), high oxygen (10.62 wt.%), nitrogen (7.05 wt.%) and sulphur (0.63 wt.%) content. Distillation profile of the bio-oil indicates a fairly large amount of low boiling fraction (10 wt.% of the material boiling below 105 °C), which includes water and low boiling hydrocarbons. Initial boiling point (IBP) was measured at the temperature of 82 °C. Up to the temperature of 297 °C (EBP—end/final boiling point) distilled 65% (v/v) of the bio-oil. Further heating of the product in the course of distillation results in its thermal decomposition. 1HNMR calculations point the saturated hydrocarbons as the dominant state in the bio-oil (44.7%—Fig. 3), which was confirmed by 13CNMR spectra analysis (47.6% of inside-chain carbon—Fig. 4). Despite the predominant share of aliphatic, rapeseed oil cake pyrolysis oil contains a large quantity of unsaturated compounds, which was confirmed by bromine number (81.0 g Br2/100 g) as well as (hetero-) aromatic protons and carbons content, calculated from NMR spectra. In order to use the refined bio-oils as internal combustion engine fuels or fuel oils, a considerable part of heteroatoms (particularly nitrogen and sulphur) must be removed. It is also necessary to partially reduce the unsaturated hydrocarbons content (hydrogenation of the most unstable olefins) and improve the physical properties of the product. In the applied temperature range, an increase in the process temperature causes higher gas production (up to 12 wt.% at 350 °C hydrorefining temperature—Table 3). Higher process temperature caused the higher conversion-rate of the feed, including intensification of heteroatoms hydrogenolysis and limited hydrocracking reaction of bio-oil components to light gaseous products. Increasing of the hydrorefining temperature leads to H/C ratio grow (up to the value of 1.94—I/3 product) which is caused mainly by oxygen removal and olefin hydrogenation. Partial decrease in bromine number together with process temperature increase (81.0–41.4 gBr2/100 g—product I/3—Table 3) certifies unsaturated hydrocarbon resistance to the applied process parameters, which was also confirmed by slight decrease of olefin carbons content in 13CNMR spectra analysis (Fig. 4). Hydrogenation of unsaturated hydrocarbons causes an increase in alkane type carbon content (44.7–57.7%—Fig. 4), which is the main reason of both the improvement (mainly viscosity) of the hydrorefining products physical properties and the undesirable increase of freezing point. Freezing point temperature rises from −11 °C (raw bio-oil) up to 0 °C for the product obtained at the hydrorefining temperature of 320 °C, which is a result of increase
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Fig. 2. Schematic view of hydrorefining apparatus [18]. (1) Gasmeter, (2) pump, (3) feed tank, (4) reactor, (5) temperature controllers, (6) water cooler, (7) pressure gas–liquid separator, and (8) atmospheric separator.
in alkane content. Further increase in hydrorefining temperature slightly lowers the freezing point temperature up to − 4 °C (I/3—Table 3), which was caused by isomerisation of alkanes formed in lower temperatures (2.1% increase in chain branching carbon type comparing to the raw bio-oil—hydrorefining product I/3—Fig. 4). The higher content of i-alkanes is advantageous from the fuel-use point of view because it improves the low temperature properties of the product. As a result of changes in the chemical structure, heating value increases from
Table 3 Hydroprocessing results of the raw rapeseed cake pyrolysis bio-oil—series I—properties of the raw material and hydrorefining products. Raw material
Sample no. I/1
I/2
I/3
Temperature, [°C]
290
320
350
Hydrogen pressure, [MPa]
3
3
3
LHSV, [h−1] Liquid product yield, [wt.%] Density at 15 °C, [g/cm3] Elemental composition, [wt.%] C H N S Oa) Atomic ratio H/C Distillation IBP, [°C] 10%, [°C] 50%, [°C] 80%, [°C] EBP, [°C] % distilled fraction Bromine number, [gBr2/100 g] Viscosity at 20 °C, [cSt] 40 °C, [cSt] Freezing point, [°C] Heat of combustion, [MJ/kg] a)
Calculated by difference.
2.0
2.0
2.0
– 1.003
90.8 0.999
88.5 0.979
88.0 0.977
71.50 10.20 7.05 0.63 10.62 1.71
74.91 10.68 6.75 0.53 7.13 1.71
75.62 10.90 6.50 0.42 6.66 1.73
74.90 12.10 6.42 0.33 6.25 1.94
82 103 273 – 297 65 81.0 117.2 47.3 −11 32.5
89 106 254 – 280 70 75.6 95.4 33.8 −4 34.5
72 104 275 – 307 75 75.6 80.8 23.2 0 35.2
74 107 280 – 310 78 41.4 75.6 21.2 −4 36.4
32.5 for raw bio-oil up to 36.4 MJ/kg for the product obtained at 350 °C of the hydrorefining process (Table 3). Maximum removal of nitrogen (HDN), sulphur (HDS) and oxygen (HDO) was observed at the highest applied hydrorefining temperature (350 °C): 8.9%, 47.6% and 41.1% respectively. Incomplete oxygen removal may be caused by the presence of less reactive aromatic oxygen compounds, e.g. phenols, where C\O bonding is more durable (dissociation energy at the level of 422–468 kJ/mol) than in aliphatic compounds (339–385 kJ/mol). Moreover, high nitrogen content in raw bio-oil and H2O presence cause lowering of HDO efficiency [12]. With the increase in hydrorefining temperature, the degree of HDS increases up to the value of 47.6% (I/3). Product I/3, obtained at the hydrorefining temperature of 350 °C, is characterized with 0.33 wt.% sulphur content (Table 3), which precludes direct use of the liquid as internal combustion engine fuel or fuel oil. Since NiMo catalysts are commercially used for HDS processes, unsatisfactory level of sulphur removal may be caused by many factors, e.g. too high LHSV (too short contact time of the feed with the catalyst), and too low hydrogen pressure (the degree of HDS process increases with the partial pressure of hydrogen increase). Applied catalyst and process parameters poorly promote nitrogen compounds hydrogenation (Table 3). Maximum HDN efficiency was observed at the process temperature of 350 °C (8.9% for the I/3 product). Low degree of nitrogen removal implies hydrogenation of aliphatic nitrogen-containing compounds in which nitrogen is present in the substituent (e.g. amines, nitriles), since these are much easier to remove than heterocyclics and aromatics, in which nitrogen is embedded in the ring. From this point of view, it is highly possible that the majority of nitrogen compounds are heterocyclic or aromatic types, in which nitrogen is embedded in the ring. Such conclusion may be partly confirmed by 1HNMR analysis, confirming high heteroaromatics content (including N, S and O bonded in the aromatic ring) in the case of raw rapeseed cake bio-oil (17.4% of protons) and in the I/3 product (7.1% of protons—Fig. 3). Hydrorefining transformation of raw rapeseed cake pyrolysis oil obtained in the I series of the experiment was moderate. Unsatisfactory level of hydrorefining may be caused by many factors, e.g. high content of low boiling fraction, including water (catalyst deactivation), presence of the water fraction forming in the hydrodeoxygenation process (catalyst deactivation), too high LHSV or too low hydrogen pressure. In order
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Fig. 3. Results of 1HNMR spectra calculations.
to improve HDS, HDN and HDO processes, as well as saturation of olefin type hydrocarbons, LHSV in the range of 0.5–2.0 h−1 was lowered. Additionally, low boiling fraction of the bio-oil (b120 °C) was removed from the hydroprocessing feed with vacuum distillation (to avoid biooil components polymerization processes). 3.2. Hydroprocessing of dewatered bio-oil fraction boiling over 120 °C Series II of the hydrorefining studies was realized using the bio-oil fraction boiling over 120 °C as the process feed. Variable parameter of the series II was the liquid hour space velocity (LHSV) in the range of 0.5–2.0 h−1 (Table 1). Removal of low boiling fraction strongly influences bio-oil primary properties, as density (increase up to the value of 1.105 g/cm3 at
15 °C) and viscosity (an increase of 70 cSt at 20 °C comparing to the raw bio-oil). A decrease in oxygen content (to the value of 9.9 wt.%) was caused by partial water fraction removal. Water removal caused also a slight increase in H/C ratio up to the value of 1.77. Raw material for series II hydrorefining distills in the amount of 68% (v/v) up to the temperature of 305 °C. As in case of the raw bio-oil, series II feed is characterized by large share alkane and (hetero-) aromatic type protons: 52% and 14.8% respectively (Fig. 3). 13CNMR analysis points large share of olefin type carbon atoms (Fig. 4), which was confirmed by bromine number determination (79.9 gBr2/100 g in the hydroprocessing series II feed—Table 4). Table 4 presents the properties of the feed and hydrorefining products of the hydroprocessing series II. Removal of low boiling fraction strongly influences hydroprocessing product yield. Comparing
Fig. 4. Results of 13CNMR spectra calculations.
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Table 4 Hydroprocessing results of the raw rapeseed cake pyrolysis bio-oil fraction boiling over 120 °C—series II—properties of the feed and hydrorefining products. Raw material
Sample no. II/1
II/2
Temperature, [°C]
350
350
350
Hydrogen pressure, [MPa]
3
3
3
LHSV, [h−1]
0.5
1.0
2.0
Liquid product yield, [wt.%] Density at 15 °C, [g/cm3] Elemental composition, [wt.%] C H N S Oa) Atomic ratio H/C Distillation IBP, [°C] 10%, [°C] 50%, [°C] 80%, [°C] EBP, [°C] % distilled fraction Bromine number, [gBr2/100 g] Viscosity at 20 °C, [cSt] 40 °C, [cSt] Freezing point, [°C] Heat of combustion, [MJ/kg] a)
II/3
1.105
92.0 0.915
92.3 0.918
93.0 0.985
71.80 10.60 7.07 0.63 9.90 1.77
80.40 12.30 5.02 0.18 2.10 1.84
78.30 12.10 5.53 0.25 3.82 1.89
77.10 12.30 6.39 0.30 3.91 1.91
120 170 287 – 305 68 79.9 190.2 60.9 −2 32.1
85 95 283 320 322 90 44.3 14.3 8.2 −8 40.5
85 95 295 318 320 88 46.1 17.6 11.0 −4 39.2
84 96 295 316 316 88 53.4 24.5 14.5 −6 38.5
Calculated by difference.
to the product I/3, obtained at the same process parameters (350 °C, LHSV = 2 h−1, 3 MPa of H2), product II/3 showed 5 wt.% higher yield (93.0 wt.%—Table 4). This is associated with the reduction of lowboiling hydrocarbon hydrocracking reactions in case of the series II feed, where low boiling fraction (b120 °C) was removed. Fourfold prolonged contact of the catalyst with the feedstock (decrease in LHSV from the value of 2.0 h−1 to 0.5 h−1) did not significantly affect product yield, but significantly affected the degree of heteroatoms hydrogenolysis and overall physicochemical properties of the obtained products.
The primary properties of the products obtained in the series II are more diversified than in the series I. The characteristic of the products properties is presented in Table 4. Lowering the level of LHSV to 0.5 h−1 causes similar olefin hydrogenation level as in case of series I (bromine number varies from 79.9 gBr2/100 g in the raw material of series II to 44.3 gBr2/100 g—product II/1). Olefin hydrogenation was confirmed by 13CNMR spectra analysis (Fig. 4), e.g. reduction of inside chain olefin carbon content (from 3.1% in the raw material of series II to the value of 2.4% in the II/1 product—30–34 ppm), and reduction of peripheral olefin carbon content (from 11.2% at the raw material to the value of 8.4% in II/1 product—13–14 ppm). The final content of the olefins in the II/1 product is unacceptably high in the case of use of this product as a pure liquid fuel. Increase in alkane content considerably improves the physical properties of the hydrorefining products. Together with LHSV value lowering, distillation efficiency increases, up to the 90% (v/v) of the product at the final distillation temperature of 322 °C. Comparing to the series I raw material—distillation efficiency was increased by 22%. Together with LHSV lowering, increase in i-alkane content was observed. As consequence, the freezing point of the product obtained at 0.5 h− 1 LHSV was lowered up to the value of − 8 °C (from the value of − 2 °C for series II feed material). This observation was confirmed by an increase in chain branching carbon content (from 3.9 in raw material, up to 6.4% for the product II/1—35–55 ppm, Fig. 4). Sample II/1 obtained at 0.5 h−1 LHSV is characterized by 78.8% HDO, 71.4% HDS and 29.0% HDN efficiency. It was the maximum effectiveness of heteroatoms removal obtained in the series II. Comparing to the raw bio-oil hydrorefining results (Table 3), a significant increase in the hydrogenation process may be caused mainly by two reasons—fourfold prolonged contact time of the raw material with catalyst and lower water content in the reaction zone (raw material distillation starts at 120 °C, which significantly reduces water content in the feed, still in the reaction zone remains water formed in HDO). Despite the large increase in heteroatom removal, nitrogen (5.02 wt.%) and sulphur (0.18 wt.%) are still present in high concentration, which limits direct use of the II/1 product as a fuel component. As in case of series I, a significant decrease of heteroatoms was also observed in 1HNMR spectra (Fig. 3), where e.g. heteroaromatic (6.0–8.5 ppm), carbohydrate, or
Table 5 Hydroprocessing results of 20% (v/v) rapeseed cake pyrolysis bio-oil and 80% (v/v) light gas oil fraction blend—properties of the feed and hydrorefining products. Light gas oil fraction
Raw material
Sample no. III/1
III/2
III/3
Temperature, [°C]
290
320
350
Hydrogen pressure, [MPa]
3
3
3
LHSV, [h−1]
2.0
Liquid product yield, [wt.%] Density at 15 °C, [g/cm3] Elemental composition, [wt.%] C H N S Oa) Atomic ratio H/C Distillation IBP, [°C] 10%, [°C] 50%, [°C] 80%, [°C] EBP, [°C] % distilled fraction Bromine number, [gBr2/100 g] Viscosity at 20 °C, [cSt] 40 °C, [cSt] Freezing point, [°C] Heat of combustion, [MJ/kg] a)
Calculated by difference.
0.858 86.50 13.10 0.20 0.10 0.10 1.82 231 261 289 310 336 99 0.4 4.8 3.5 n/a 44.7
0.888 83.50 12.52 1.57 0.21 2.20 1.80 82 145 282 308 322 94 13.0 13.1 11.3 −13 42.6
2.0
2.0
93.2 0.877
93.0 0.873
92.3 0.862
84.40 13.80 1.18 0.17 0.45 1.96
84.80 13.50 1.22 0.12 0.36 1.91
85.30 13.47 1.01 0.06 0.16 1.89
80 195 280 305 322 94 12.3 5.9 4.3 −12 44.4
80 200 285 300 325 95 11.7 5.6 4.2 −11 43.9
74 250 285 302 332 97 10.5 5.3 3.7 −11 45.5
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methoxy- (4.4–6.0 ppm) proton content is lower than in the case of the raw material. As in case of series I, it is highly possible that nitrogen and sulphur atoms are bonded in heterocyclic or aromatic type compounds, which are characterized by much higher bond dissociation energy, than nitrogen in the aliphatic compounds. Low sulphur removal level from bio-oil in this series may be the result of the presence of hydrogenolysis resistant thiophene-ring containing compounds. Potentially, the hydrorefining product II/1 could be applied as a fuel oil component in a mixture with a suitable petroleum fraction.
view a higher hydrogenolysis level of oxygen and sulphur containing compounds can be a result of diminished content of nitrogen containing compounds. Nitrogen compounds in larger concentrations and ammonia, products of their hydrogenolysis, are poison for the acid centres of NiMo catalyst. As a consequence basic nitrogen compounds in higher concentration lower catalysts activity. Therefore a low level of hydrogenolysis in the hydrorefining process of raw bio-oil and bio-oil fraction boiling over 120 °C (Tables 3 and 4) in comparison to hydrorefining of lower nitrogen containing feed was observed (Table 5).
3.3. Hydroprocessing of rapeseed cake pyrolysis bio-oil and non-desulphurized light gas oil fraction blend
4. Conclusions
Series III raw material was the blend composed of raw bio-oil from rapeseed oil cake pyrolysis—20% (v/v) and non-refined light gas oil petroleum fraction—80% (v/v) (Table 5). The blended material feed for hydrorefining series III was characterized by the lowest heteroatom content of all feeds applied in these studies: S, N and O content was 0.21 wt.%, 1.57 wt.% and 1.80 wt.% level respectively. Comparing to the hydroprocessing series I and II feeds, elemental composition and relatively low olefin content (bromine number at the level of 13.0 g Br2/100 g) in the series III feed indicate the blended material as much easier feed for hydrorefining process. Variable parameter of the series III was the process temperature in the range of 290–350 °C (Table 1). The yield of hydrorefining products varies in the series III from 92.3 (III/3) to 93.3 wt.% (III/1). An increase in the process temperature slightly results in higher gas production up to the yield of 7.7 wt. at the hydroprocessing temperature of 350 °C, which was caused mainly by higher hydrogenolysis levels at the applied process temperature. An increase in hydrorefining temperature causes significant improvement of hydrorefining product properties (Table 5). Products distill up to 94% (v/v) (III/1)–97% (v/v) (III/3) at the final temperature boiling range of 322 °C (III/1)–332 °C (III/3). Sample III/3 obtained at the highest hydrorefining temperature of 350 °C is characterized by 92.7% HDO, 71.4% HDS and 35.7% HDN level, the maximal effectiveness of heteroatom removal. This level is the highest found amongst all applied hydrorefining parameters and all the studied (series I–III). The product obtained at the final hydrorefining temperature of 350 °C was characterized by the following heteroatom content: S: 0.06 wt.%, N: 1.01 wt.%, and O: 0.16 wt.%. At the applied process parameters higher hydrogen consumption was observed for heteroatom removal (mainly oxygen), than hydrogenation of unsaturated hydrocarbons. Whilst appreciable increase in heteroatoms hydrogenolysis of the series III feed was observed, diminishing of olefin content in series III was rather small (reduction of olefin content up to the bromine number of 10.5 g Br2/100 g at the hydrorefining temperature of 350 °C—Table 5, confirmed by low reduction of olefin type carbons calculated with 13 CNMR—Fig. 4). Partial hydrogenation of unsaturated hydrocarbons and heteroatom removal improve the physical properties of products obtained in the series III experiments. A low increase in freezing point was observed (from − 13 °C for the series III feed, up to the value of −11 °C for the III/3 product), which was caused by an increase in n-alkane type hydrocarbon content; heat of combustion value increased up to the value of 45.5 MJ/kg for the product obtained at the hydrorefining temperature of 350 °C (III/3—Table 5). The product obtained at the hydrorefining temperature of 350 °C (III/3) partly meets regulatory requirements established for fuel oils (according to ASTM D396). The required level of hydrorefining (to the “ready-to-use” fuel) could be possibly achieved with the second step of hydrorefining or with higher hydrogen pressure at the applied process parameters. Relatively satisfying hydrorefining results, low content of oxygen, sulphur and nitrogen containing compounds in the hydrorefining products of this series is mainly the result of much lower concentration of hetero compounds in the feed as a result of dilution of a large amount of heteroatom compounds containing raw bio-oil with low heteroatoms containing light gas oil–petroleum fraction. From the other point of
One-step hydrorefining of raw and partially dewatered bio-oil obtained in pyrolysis of rapeseed cake does not result in a satisfactory hydrorefining level. It is a result of high heteroatom containing compounds and olefins as well as water fraction in bio-oils—catalyst poisons (in case of raw bio-oil). The highest heteroatom removal in case of raw bio-oil was obtained with the hydrorefining at the temperature of 350 °C (at LHSV 2.0 h−1, 3 MPa of H2): 47.6% of HDS, 8.9% of HDN and 41.1% of HDO. Removal of low boiling fraction and LHSV lowering to the value of 0.5 h−1 (at the process temperature of 350 °C and 3 MPa of H2) allowed to increase the degree of hydrorefining up to the levels of 71.4% of HDS, 29.0% of HDN and 78.8% of HDO. The obtained hydrorefining products do not meet the normalized requirements for light commercial fuel oil. The application of the blend consisting of 20% (v/v) of the raw bio-oil and 80% (v/v) of light gas oil as the feed considerably improves hydrorefining process results. It is connected with the relatively lower heteroatom concentration in the feed. At high LHSV (2.0 h−1), hydrorefining temperature of 350 °C temperature and 3 MPa hydrogen pressure, hydrorefining products fulfil majority of light commercial fuel oil requirements. However, the best product of hydrorefining still contains too large quantity of sulphur and nitrogen (0.06 wt.% and 1.01 wt.% respectively). It means that severity of the hydrorefining process should be distinctly higher or the obtained product should be mixed with proper petroleum fraction for fuel purposes. Acknowledgements This work was financed by statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wroclaw University of Technology, project number S 30063. The authors would like to gratefully acknowledge Mr. Paweł Dąbrowski from Wroclaw University of Technology NMR Laboratory, for his support in NMR analysis. References [1] J.G.J. Olivier, G. Janssens-Maenhout, J.A.H.W. Peters, Trends in global CO2 emissions, 2012 Report, PBL Netherlands Environmental Assessment Agency, The Hague/ Bilthoven, 2013, pp. 8–11. [2] T. Issariyakul, A.K. Dali, Biodiesel from vegetable oils, Renewable and Sustainable Energy Reviews 31 (2014) 446–471. [3] F. Ma, M.A. Hanna, Biodiesel production: a review, Bioresource Technology 70 (1999) 1–15. [4] E. David, Valorization of residual biomass by thermochemical processing, Journal of Analytical and Applied Pyrolysis 104 (2013) 260–268. [5] M. Demirbas, M. Balat, H. Balat, Biowastes-to-biofuels, Energy Conversion and Management 52 (2011) 1815–1828. [6] A.V. Bridgwater, Thermochemical processing of biomass, in: R.C. Brown (Ed.), Conversion into Fuels, Chemicals and Power, first ed., Wiley, West Sussex, United Kingdom, 2011, pp. 157–188. [7] E. Culcuoglu, E. Unay, F. Karaosmanoglu, D. Angin, S. Sensoz, Characterization of the bio-oil of rapeseed cake, Energy Sources 27 (2005) 1217–1223. [8] K. Smets, A. Roukaerts, J. Czech, G. Reggers, S. Schreurs, R. Carleer, J. Yperman, Slow catalytic pyrolysis of rapeseed cake: product yield and characterization of the pyrolysis liquid, Biomass and Bioenergy 57 (2013) 180–190. [9] S. Ucar, A.R. Ozkan, Characterization of products from the pyrolysis of rapeseed oil cake, Bioresource Technology 99 (2008) 8771–8776. [10] J.H. Marsman, J. Wildschut, F. Mahfud, H.J. Heeres, Identification of components in fast pyrolysis oil and upgraded products by comprehensive two-dimensional gas
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