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Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase
Applied Energy xxx (2014) xxx–xxx
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Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase Tiejun Wang ⇑, Kai Li, Qiying Liu, Qing Zhang, Songbai Qiu, Jinxing Long, Lungang Chen, Longlong Ma ⇑, Qi Zhang CAS Key Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, PR China
h i g h l i g h t s A new route for hemicellulose derived aviation fuel production was proposed. This route follows hydrolysis/dehydration, hydrogenation, coupling and HDO steps. The effective hydrogenation and hydrodeoxygenation catalysts were prepared. The high yield of C8AC15 alkanes and catalytic stability were obtained.
a r t i c l e
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Article history: Received 31 October 2013 Received in revised form 5 June 2014 Accepted 18 June 2014 Available online xxxx Keywords: Aviation fuel Aqueous phase Catalytic conversion Biomass hydrolysate
a b s t r a c t This paper presents a new route for biomass derived aviation fuel synthesis by catalytic conversion in aqueous phase. Furfural with the yield of 71% was produced by acid hydrolysis of raw corncob, and hydrogenated to 2-methylfuran with obtaining the yield of 89% over Raney Ni catalyst, both of which were implemented under mild reaction conditions. The hydroxyalkylation/alkylation condensation of 2-methylfuran and furfural to C15 intermediate was conducted by using organic and inorganic acid as the catalyst under the reaction condition of 328 K and atmospheric pressure. The maximal 95% of the C15 intermediate was gained when using sulfuric acid as the catalyst. 83% of liquid alkanes (C8AC15) yield and more than 90% of C14/C15 selectivity were produced by hydrodeoxygenation of the C15 intermediate over 10 wt%Ni/ZrO2–SiO2 catalyst. During the hydrodeoxygenation process, the catalyst showed excellent stability depended on the 110 h of time-on-stream test, due to its significantly decreased carbon deposition. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Overuse of fossil resources and increasing concern of environmental problem urge people to develop new pathways for producing biomass derived fuels and chemicals [1–3]. Alternative fuel for aviation received more attention in recent years. Some potential alternatives (e.g. alcohols and esters) contain oxygen and have lower energy content than the petroleum based hydrocarbon fuels, which lead to the reduced power and flight range [4]. Hydrocarbon fuels for aviation can also be produced by biomass gasification/Fischer–Tropsch (FT) synthesis and/or hydrogenation of bio-diesels [5,6]. For the former technology, the additional process for upgrading crude syngas from biomass gasification is
⇑ Corresponding authors. Tel.: +86 20 87057751; fax: +86 20 87057737 (T. Wang). Tel./fax: +86 20 87057673 (L. Ma). E-mail addresses: [email protected] (T. Wang), [email protected] (L. Ma).
necessary to meet with the requirement of FT synthesis [7]. Moreover, FT synthesis fuels are mainly straight chain hydrocarbons, which must be further processed by cracking and isomerizing to the desired properties for aviation fuel. This technology has not been commercialized because of the lengthy processes and high production cost. Bio-diesels, which are produced from a variety of materials containing vegetable oil, animal fat and algae, have been considered as the aviation fuel. However, bio-diesel has freezing point of near 273 K, which is much higher than the conventional aviation fuel of 233 K. Hydrodeoxygenation of bio-diesel should be used to the hydrocarbon fuels with low freezing point. The expensive grease resources prohibits its commercialization [8], and the additional isomerization process of the oxygen removed hydrocarbons is also necessary [9]. Furfural, which can be obtained from hemi-cellulose, is presented as a key platform to synthesize downstream fuels and chemicals. It has been produced in industry for decades by hydro-
http://dx.doi.org/10.1016/j.apenergy.2014.06.035 0306-2619/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Wang T et al. Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy (2014), http://dx.doi.org/10.1016/j.apenergy.2014.06.035
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Nomenclature Abbreviation 2MF 2-methylfuran HAA hydroxyalkylation/alkylation HMF 5-hydroxymethylfurfural LA levulinic acid TG thermogravimetric analysis
lysis/dehydration of agricultural and forest waste [10]. Recently, Dumesic and co-workers proposed a new pathway of aviation fuel by aldol condensation of furfural and acetone [11]. In the process, the long carbon chain intermediates of C8AC16 could be synthesized. The hydrodeoxygenation was followed to remove the oxygen atoms from these oxygen-containing intermediates and the branched alkanes with high thermal stability and energy density could be used as the alternative aviation fuel [12]. However, this process needs acetone as the reactant, which is expensive and cannot be produced economically from renewable biomass. Many researchers strived to investigate CAC coupling reaction without acetone [13,14]. Chheda and Dumesic proposed a rout for long hydrocarbons production by self-aldol condensation of tetrahydrofurfural which can be synthesized by hydrogenation of furfural [15]. Chheda et al. found that trifurylmethane (oxygenated C13 intermediate) could be produced by the hydroxyalkylation/ alkylation (HAA) of furan and furfural [16]. However, these processes only produce the intermediates with straight carbon chain. After hydrodeoxygenation for saturating C@C and C@O bonds and removing oxygen atoms, the obtained alkanes were mainly composed of straight carbon chain hydrocarbons, which is only used as the high quality substitutes for diesel [17]. For the application of aviation fuel, the hydrocarbons with branched carbon chains are preferable to keep the low freezing points. 2-Methylfuran (2MF) is produced in industry by selective hydrogenation of furfural. Recently, Corma et al. proposed a process to produce branch hydrocarbons starting from 2MF, due to its high reactivity and selectivity for alkylation reactions [8]. However, limited researches are addressed the conversion of hemi-cellulose to aviation fuel. In this work, biomass derived aviation fuel was synthesized by coupling acid hydrolysis hemicellulose followed by the catalytic conversion in aqueous phase. 2MF production by hydrogenation of distilled furfural from hemicellulose hydrolysates was investigated. Then, HAA condensation of 2MF and furfural was explored. Finally, the aviation fuel synthesis by hydrodeoxygenation of HAA products was studied. With using hemicellulose as the feedstock, the whole process and the performance of catalysts involved in each step were shown in Fig. 1.
2. Experimental section 2.1. Catalyst preparation and characterization Raney Ni preparation. With constant magnetic stirring, 160 g deionized water and 40 g NaOH were added into a 500 mL threenecked flask to gain a 20 wt% NaOH solution, 30 g NiAAl alloy (Dalian Toyounger Chemical Co., Ltd.) was slowly added at the temperature of 323 (±2) K. After 1.5 h, the supernatant was dumped, the solid collected was washed by distilled water until the pH of 8–9 and further washed by ethanol for 5–6 times. The prepared Raney Ni catalyst was stored in ethanol. Ni/SiO2–ZrO2 preparation. Appropriate amounts of Na2SiO3 9H2O and ZrOCl28H2O were dissolved in distilled water, respec-
DTG LHSV
differential thermogravimetric analysis liquid hourly space velocity
Symbols T temperature [K]
tively. Under continuously stirring, the solution of ammonium nitrate was dropped gradually into the solution of Na2SiO3 until the pH of 8.0 was reached, obtaining the Si(OH)4 precipitate. According to the similar procedure, the solution of ammonia was dropped into the solution of ZrOCl2 until the pH of 8.0 was reached and the Zr(OH)4 precipitate was obtained. The two precipitates were mixed and aged for 12 h at 348 K under constant stirring. Subsequently, the precipitate was filtered and washed with distilled water to completely remove chloride ions. The solid obtained was dried overnight at 393 K and calcined at 773 K for 5 h. An appropriate amount of nickel nitrate was dissolved in a predetermined volume of distilled water based on the amount of the SiO2–ZrO2 support. The solution was evaporated and the residues were dried in air at 393 K overnight and then calcined at 773 K for 5 h. The catalysts were designated as Ni/SiO2–ZrO2. The surface area and pore size distribution of catalyst were measured on a Quantachrome instrument at 77 K. The catalyst was degassed at 523 K for 10 h prior to measurement. Its surface area was calculated by the Brunauer–Emmett–Teller (BET) method and the average pore diameter and pore volume were calculated with the Barret–Joyner–Halenda (BJH) model. X-ray powder diffraction (XRD) patterns were obtained on a RigakuD/max-rCX-ray diffractometer at 40 kV and 40 mA using Cu Ka radiation, and the data were collected at steps of 0.02° in the 2h range of 5°–80°. The chemical composition of Raney Ni was identified by inductively coupled plasma-atomic emission spectrometry (ICP-AES, OPTIMA 8000). TG analysis of spent catalyst was implemented on a NETZSCHSTA 409PC DSC-SP Thermal analyzer by increasing the temperature from 313 K to 1123 K at 10 K/min under an air flow of 30 ml/min. 2.2. Catalytic performance in aqueous phase and product analysis Degradation of hemi-cellulose to furfural was carried out in a 100 ml stainless steel reactor at 433 K with corncob as the feedstock. In a typical experiment, 1.0 g corncob, 10 ml deionized water and 10 ml 5 wt% sulfuric acid were loaded into the reactor. N2 was used to purge the air inside the reactor and pressurized to 1.0 MPa. Then the reactor was heated to 433 K with steam. The produced furfural was stripped out of the reactor with flowing steam. When the reaction stopped, the liquid products were collected by filtration with a 0.45 lm film and analyzed by GC–MS and HPLC. Hydrogenation of furfural to 2MF was carried out on a fixed bed by using Raney Ni catalyst. 2 g of freshly prepared Raney Ni catalyst was loaded in a tubular stainless steel reactor with the inner diameter of 10 mm and the length of 300 mm. After the system was heated to a certain reaction temperature in a H2 flow of 50 ml/min, furfural was fed with 0.05 ml/min by a syringe pump. The mixture of furfural and hydrogen was introduced into the reactor via a preheater of 423 K at the liquid hourly space velocity (LHSV) of 1.0 h 1. The H2 pressure was controlled at 0.3 MPa by a backpressure valve. The reaction temperature was measured by a thermocouple in the catalyst bed and controlled by a temperature controller. After the time-on-stream of 5 h, the liquid product was
Please cite this article in press as: Wang T et al. Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy (2014), http://dx.doi.org/10.1016/j.apenergy.2014.06.035
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O O
H2SO4
Hemicellulose
Hydrolysis/ dehydration
O O
Raney Ni
(1) Furfural O
Hydrogenation
(2) 2MF
Furfural
O
O
O
O +
Formic acid
O
O
2 HAA
Furfural
(3)
2MF C15 intermediate
O O
O
Ni/ZrO2-SiO2
(4)
Hydrodeoxygenation
C15 alkane
C15 intermediate
Fig. 1. Processes involved in the new route for biomass derived aviation fuel production.
collected via a condenser and a gas-liquid separator. The products were analyzed by a GC (Shimazu 2014C) equipped with a FID detector and a Carbowax capillary column. HAA condensation was conducted in a 250 ml glass reactor with magnetic stirring and reflux system. The distilled furfural (4.8 g, 0.05 mol) and 2MF (5.8 g, 0.1 mol) were charged into the reactor together with 50 vol% of water/ethanol (95.4 g). The presence of ethanol favors the dissolution of condensation product due to the poor dissolution ability in water. When a given temperature was reached, the formic acid was added into the reactor to catalyze HAA reaction. After 16 h, the resulting mixture was automatically separated into two phases. The upper oil phase contained C15 intermediate was collected for HPLC analysis and was directly hydrodeoxygenated to aviation fuel. Hydrodeoxygenation of C15 intermediate from HAA condensation was carried out over 10 wt%Ni/SiO2–ZrO2 catalyst on the same apparatus to hydrogenation of furfural to 2MF. The reaction condition was kept at 523 K, 5 MPa of H2 pressure and LHSV of 0.75 h 1. Before reaction, the catalyst was reduced at 773 K for 3 h in the presence of H2 flow. The alkane products were analyzed by a GC (Shimazu 2010) instrument equipped with a FID detector and a HP-5 capillary column.
3. Results and discussion 3.1. Degradation of hemi-cellulose to furfural The weight percentage of glucan, xylan and lignin in corncob was determined according to the laboratory analytical procedure (LAP), which was exploited by the US National Renewable Energy Laboratory (NREL). The total sugars in the pretreatment liquor were calculated after a secondary hydrolysis of oligosaccharide into mono-saccharides with 4 wt% sulfuric acid at 121 °C for 45 min [18]. Sugars and other degradation products were quantitatively determined by HPLC instrument. The results showed that the hemi-cellulose, cellulose and lignin units were 27.6%, 29.3% and 12.6%, respectively. This indicates that nearly 30% of species including ash, moisture and unidentified compounds are involved in the raw corncob.
Table 1 Furfural production by direct degradation of corncob catalyzed with sulfuric acid. Sulfuric acid (mmol)
0 0.45 0.9 1.8
Yield of products (mol%) Furfural
HMF
LA
0 46 71 68
0 0.3 1.5 2.8
0 0 2.6 4.7
Degradation of hemi-cellulose fraction of corncob to furfural involves the sequential hydrolysis and dehydration processes, both of which are catalyzed by sulfuric acid. As shown in Table 1, the blank experiment revealed that no product was detected without sulfuric acid, indicating its essential catalysis in this process. By using sulfuric acid, the detectable products mainly contain 5-hydroxymethylfurfural (HMF), levulinic acid (LA), furfural and trace amount of glucose by HPLC measurement. The furfural yield was increased with increasing the sulfuric acid amount and the maximal yield was reached to 71% at 0.9 mmol of sulfuric acid. However, as the sulfuric acid was further increased to 1.8 mmol, the furfural yield slightly reduced to 68% while with the significantly increased HMF and LA. The formation of HMF is attributed to the C6 sugar dehydration, while LA is responsible for rehydration of furfural and HMF intermediates, implying that the high concentration of sulfuric acid leads to side products [19]. After
Table 2 Chemical composition and textural properties of Raney Ni and Ni–Al alloy. Item
Raney Ni
Ni–Al alloy
Ni/(mol%) Al/(mol%) BET/(m2/g) Vp/(cm3/g) PD/(nm)
87.00 13.00 11.23 0.015 4.10
30.40 69.60 0.33 – –
Vp, mesoporous volume; PD, Ni particle size.
Please cite this article in press as: Wang T et al. Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy (2014), http://dx.doi.org/10.1016/j.apenergy.2014.06.035
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B Al3Ni2 Al3Ni
Intensity (a.u.)
Intensity (a.u.)
A
Ni-Al
111 200
220
Raney Ni
10
20
30
40
50
60
70
80
o
10
20
30
40
50
60
70
80
o
2−Τheta/ ( )
2-Theta/ ( )
Fig. 2. XRD patterns of Raney Ni and Ni–Al alloy (A), and 10 wt%Ni/SiO2–ZrO2 (B).
distillation, the purity of furfural was 99%, which is suitable for 2MF synthesis by the downstream hydrogenation process. 3.2. Hydrogenation of furfural to 2MF Raney Ni catalyst was prepared and used for hydrogenation of furfural to 2MF. Its chemical composition and XRD pattern were shown in Table 2 and Fig. 2, respectively. After dissolution of Al component, the surface of Raney Ni was significantly increased to 11.23 m2/g and the mesoporous volume of 0.015 cm3/g was created. The XRD patterns of the NiAAl alloy indicated that it contains the two kinds of Ni3Al1 and Ni3Al2 domains. After dissolving Al component by NaOH, the diffractions relative to metallic Ni were observed with the Al residue (13%, from Table 2) as amorphous nature. The effect of reaction temperature on furfural hydrogenation to 2 MF was listed in Table 3. The furfural conversion of 72% and the 2MF yield of 65% were obtained at 453 K and 0.3 MPa of H2 pressure. Both furfural conversion and 2MF yield increased with increasing the temperature, and the highest furfural conversion and 2MF yield were obtained with 100% and 89%, respectively, at the temperature of 523 K. As the temperature was further increased to 543 K, however, the 2MF yield was decreased to 83% although the furfural conversion was kept at 100%, which indicates that side reactions occurred due to 2MF transformation in the presence of H2. These results demonstrate that Raney Ni catalyst in this preparation is highly active for 2MF production from furfural hydrogenation. This is possibly due to that the Ni particle size of about 4 nm (as indicated in Table 2) exposes more metal sites for this transformation and obtained as high as 89% of 2MF yield at the relatively low temperature of 523 K. 3.3. HAA condensation of 2MF and furfural HAA condensation of 2MF and furfural was carried out by using formic acid as the catalyst under the reaction condition of 328 K,
2MF/furfural molar ratio of 2 and reaction time of 16 h. The effect of acid concentration was listed in Table 4. Product analysis showed that the condensation products mainly contained the C15 intermediate, indicating that 2MF and furfural can be effectively transferred into the goal product in the presence of formic acid. As increasing the formic acid concentration, the 2MF/furfural conversion and the C15 intermediate yield increased. As comparing with 2MF, furfural was relatively easy to be converted and got the higher conversions at the same acid concentration. At 4 mol/l of formic acid, the highest C15 intermediate yield of 69% can be obtained. The effect of reaction temperature on HAA condensation was investigated under 4 mol/l of formic acid concentration, 2MF/furfural molar ratio of 2 and reaction time of 16 h. The results in Table 5 indicated that the reaction temperature had evident influence on the yield of C15 intermediate. The higher reaction temperature leads to the higher conversions of 2MF/furfural and the yields of the C15 intermediate. At 338 K, the maximal C15 intermediate yield of 89% was obtained. HAA condensation was studied with using different acids under the condition of 328 K, 2MF/furfural molar ratio of 2, acid concentration of 2.5 mol/l and reaction time of 16 h. As shown in Table 6, the sulfuric acid showed excellent activity in HAA process. Both the 2MF/furfural conversion of 100% and the C15 intermediate yield of 95% were obtained. For formic acid catalyst, furfural conversion was kept at 100% but the 2MF conversion decreased to 84%, obtaining the significantly reduced C15 intermediate yield of 43%. As the same concentration of acetic acid was used, the conversion of 2MF and furfural was changed a little, but the yield of C15 intermediate further decreased to 32%. Obviously, the yield of C15 intermediate produced by CAC coupling is mainly depended on the acidity of the employed acids and the strongest sulfuric acid showed the maximal C15 intermediate yield of 95%. However, formic acid is an organic acid which can be produced from cellulose, showing the renewable and friendly environmental feature. Acetic acid showed the inferior catalytic performance for HAA condensation and its low C15 intermediate yield may be resulted from the side reaction.
3.4. Hydrodeoxygenation of C15 intermediate to alkanes Table 3 Effect of temperature on hydrogenation of furfural to 2MF. t/(K)
Furfural conversion (%)
2MF yield (%)
453 473 493 523 543
72 89 95 100 100
65 81 85 89 83
The surface area, pore volume and mesoporous diameter of 10 wt%Ni/SiO2–ZrO2 were determined by isothermal adsorption– desorption of N2 at 77 K. The surface of 230 m2/g, the pore volume of 0.71 cm3/g and the average pore diameter of 12.3 nm were observed on this catalyst. The XRD pattern of 10 wt%Ni/SiO2– ZrO2 was presented in Fig. 2B. The significant diffractions at 2h = 37.3°, 43.3° and 62.9° indicate the existence of aggregated
Please cite this article in press as: Wang T et al. Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy (2014), http://dx.doi.org/10.1016/j.apenergy.2014.06.035
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T. Wang et al. / Applied Energy xxx (2014) xxx–xxx Table 4 Effect of acid concentration on HAA condensation of furfural and 2MF. Acid concentration (mol/l)
2MF conversion (%)
Furfural conversion (%)
Condensation C15 products yield (%)
2 3 4
84.4 87.0 92.9
88.7 100.0 100.0
51.1 62.6 68.8
Table 5 Effect of temperature on HAA condensation of furfural and 2MF. Temperature (K)
2MF conversion (%)
Furfural conversion (%)
Condensation C15 products yield (%)
328 338 348
92.9 100.0 100.0
100.0 90.5 94.2
68.8 88.9 84.7
the intrinsic branched nature and the further isomerization process is avoided, which shows the priority for the direct application as aviation fuel. Fig. 4 shows the stability of 10 wt%Ni/ZrO2–SiO2 at the same reaction condition to Fig. 3, except for the LHSV of 0.5 h 1. The stable yield for the liquid alkanes was about 90% and no distinct deactivation was observed during the time on stream of 110 h, indicating that this catalyst is highly stable in this hydrodeoxygenation process. After 110 h of reaction, the TG curve of the spent 10 wt%Ni/ZrO2–SiO2 in Fig. 5 showed that only 3.8% of carbon deposition was obtained, demonstrates its excellent anti-coking ability in this process. The photo of produced liquid alkanes was displayed in Fig. 6. The colorless top liquid phase was composed of alkanes with carbon chains of C5AC15. The main components were focused on the C14/C15 alkanes with the high selectivity of 77%. Depended on the weight percentage (27.6%) of hemi-cellulose in the raw corncob and the respective yields of goal products involved in corncob hydrolysis/dehydration to furfural, furfural hydrogenation to 2MF, HAA condensation of furfural and 2MF to C15 intermediate, and hydrodeoxygenation of C15 intermediate to
Table 6 Effect of catalyst on HAA condensation of furfural and 2MF. 2MF conversion (%)
Furfural conversion (%)
Condensation C15 products yield (%)
H2SO4 Formic acid Acetic acid
100.0 83.7
100.0 100.0
94.6 42.8
85.0
100.0
31.8
NiO crystallites on SiO2–ZrO2. The average particle size of NiO was calculated with 29 nm by using Scherrer equation. The HAA condensation product (C15 intermediate) was subjected to hydrodeoxygenation on a fixed bed by using 10 wt%Ni/ SiO2–ZrO2 as catalyst. The composition of liquid alkanes was shown in Fig. 3. The C14 and C15 alkanes were the main products. The selectivity of these two alkanes reached to 92% and the other alkanes by CAC cracking were significantly suppressed aside from CH4. These results showed that the C15 intermediate can be efficiently converted into the long chain alkanes and obtained the highest 83% of liquid alkanes yield under the reaction condition of 553 K, 5 MPa of H2 pressure and LHSV of 0.75 h 1. It is noted that the C15 alkane by hydrodeoxygenation of C15 intermediate presents
100
80
Yield of liquid alkane /%
Catalyst
60
40
20
0 0
10
20
30
40
50
60
70
80
90
100 110 120
Time on stream /h Fig. 4. Stability test in hydrodeoxygenation of C15 intermediate over 10 wt%Ni/ ZrO2–SiO2.
DTG
Remaining weight: 98.07%
Exothermic
Relative weight
100%
TG Remaining weight: 96.24%
200
400
600
800
1000
1200
Temperature / K Fig. 3. Composition of liquid alkanes produced by hydrodeoxygenation of C15 intermediate in fixed bed.
Fig. 5. TG and DTG profiles of spent 10 wt%Ni/ZrO2–SiO2 after 110 h of time-onstream.
Please cite this article in press as: Wang T et al. Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy (2014), http://dx.doi.org/10.1016/j.apenergy.2014.06.035
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fuel. The hydrodeoxygenation catalyst showed excellent stability after 110 h of time-on-stream test, indicating its essential application in this process. Acknowledgements This work was supported by the National Natural Science Foundation of China (NSFC, No. 51161140331), the National Key Basic Research Program (973 Plan, No. 2012CB215304) and the National High Technology Research and Development Program (863 Plan, No. 2012AA101806). References Fig. 6. Photo image of liquid alkanes produced by hydrodeoxygenation of C15 intermediate.
aviation fuel, we calculated that one ton of corncob can produce 0.149 ton of aviation fuel. Although only hemi-cellulose component is presently used for aviation fuel production, however, if the possible utilization of cellulose and lignin units (bioethanol and/or HMF by biochemical/chemical transformations of cellulose and heat by lignin combustion [20]) was considered, the comprehensive efficiency of biomass can be further improved. 3.5. Energy conversion efficiency analysis Lignocellulosic biomass is produced by photosynthesis in nature. Here, we used corncob as the feedstock to produce aviation fuel. Due to the fact that the involved four steps were conducted in aqueous phase at the mild temperatures of no more than 523 K and the hydrophobic hydrocarbons can be automatically separated from aqueous phase (the energy intense distillation is avoided), the energy input in our cases is proposed to be lower than that obtained by biomass gasification (the high temperature is necessary) followed by FT synthesis [21]. It is calculated that the energy efficiency of biomass derived hydrocarbon fuels from aqueous phase catalysis is about two times higher than the cellulosic ethanol produced from biomass hydrolysis and fermentation (the energy consumption for ethanol distillation is composed of about 40% of total energy input) [22]. Moreover, the calorific value of C8AC15 hydrocarbons (46 MJ/Kg) is more than three times of the raw corncob (14.4 MJ/Kg) owing to oxygen removal, indicating the significant energy output in our new technology. 4. Conclusions Aviation fuel was produced from raw corncob by a new route. The pathway involved the sequential steps of corncob hydrolysis/ dehydration to furfural, furfural hydrogenation to 2MF, HAA condensation of furfural and 2MF to C15 intermediate and hydrodeoxygenation of C15 intermediate to the final C8AC15 alkanes. The maximal furfural yield of 71 mol% was achieved via degradation of hemicellulose fraction of corncob and the highest 89% of 2MF yield can be produced from hydrogenation of furfural by Raney Ni. Under the optimal condition with using H2SO4 as the catalyst, 95% of C15 intermediate yield was obtained. More than 90% of liquid alkanes yield was obtained by hydrodeoxygenation of C15 intermediate over 10 wt%Ni/ZrO2–SiO2. In the liquid alkanes, the selectivity of iso-alkanes was 82.9% and the main carbon chain was in the range of C8AC15, both of which are suitable for aviation
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Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase Tiejun Wang ⇑, Kai Li, Qiying Liu, Qing Zhang, Songbai Qiu, Jinxing Long, Lungang Chen, Longlong Ma ⇑, Qi Zhang CAS Key Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, PR China
h i g h l i g h t s A new route for hemicellulose derived aviation fuel production was proposed. This route follows hydrolysis/dehydration, hydrogenation, coupling and HDO steps. The effective hydrogenation and hydrodeoxygenation catalysts were prepared. The high yield of C8AC15 alkanes and catalytic stability were obtained.
a r t i c l e
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Article history: Received 31 October 2013 Received in revised form 5 June 2014 Accepted 18 June 2014 Available online xxxx Keywords: Aviation fuel Aqueous phase Catalytic conversion Biomass hydrolysate
a b s t r a c t This paper presents a new route for biomass derived aviation fuel synthesis by catalytic conversion in aqueous phase. Furfural with the yield of 71% was produced by acid hydrolysis of raw corncob, and hydrogenated to 2-methylfuran with obtaining the yield of 89% over Raney Ni catalyst, both of which were implemented under mild reaction conditions. The hydroxyalkylation/alkylation condensation of 2-methylfuran and furfural to C15 intermediate was conducted by using organic and inorganic acid as the catalyst under the reaction condition of 328 K and atmospheric pressure. The maximal 95% of the C15 intermediate was gained when using sulfuric acid as the catalyst. 83% of liquid alkanes (C8AC15) yield and more than 90% of C14/C15 selectivity were produced by hydrodeoxygenation of the C15 intermediate over 10 wt%Ni/ZrO2–SiO2 catalyst. During the hydrodeoxygenation process, the catalyst showed excellent stability depended on the 110 h of time-on-stream test, due to its significantly decreased carbon deposition. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Overuse of fossil resources and increasing concern of environmental problem urge people to develop new pathways for producing biomass derived fuels and chemicals [1–3]. Alternative fuel for aviation received more attention in recent years. Some potential alternatives (e.g. alcohols and esters) contain oxygen and have lower energy content than the petroleum based hydrocarbon fuels, which lead to the reduced power and flight range [4]. Hydrocarbon fuels for aviation can also be produced by biomass gasification/Fischer–Tropsch (FT) synthesis and/or hydrogenation of bio-diesels [5,6]. For the former technology, the additional process for upgrading crude syngas from biomass gasification is
⇑ Corresponding authors. Tel.: +86 20 87057751; fax: +86 20 87057737 (T. Wang). Tel./fax: +86 20 87057673 (L. Ma). E-mail addresses: [email protected] (T. Wang), [email protected] (L. Ma).
necessary to meet with the requirement of FT synthesis [7]. Moreover, FT synthesis fuels are mainly straight chain hydrocarbons, which must be further processed by cracking and isomerizing to the desired properties for aviation fuel. This technology has not been commercialized because of the lengthy processes and high production cost. Bio-diesels, which are produced from a variety of materials containing vegetable oil, animal fat and algae, have been considered as the aviation fuel. However, bio-diesel has freezing point of near 273 K, which is much higher than the conventional aviation fuel of 233 K. Hydrodeoxygenation of bio-diesel should be used to the hydrocarbon fuels with low freezing point. The expensive grease resources prohibits its commercialization [8], and the additional isomerization process of the oxygen removed hydrocarbons is also necessary [9]. Furfural, which can be obtained from hemi-cellulose, is presented as a key platform to synthesize downstream fuels and chemicals. It has been produced in industry for decades by hydro-
http://dx.doi.org/10.1016/j.apenergy.2014.06.035 0306-2619/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Wang T et al. Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy (2014), http://dx.doi.org/10.1016/j.apenergy.2014.06.035
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Nomenclature Abbreviation 2MF 2-methylfuran HAA hydroxyalkylation/alkylation HMF 5-hydroxymethylfurfural LA levulinic acid TG thermogravimetric analysis
lysis/dehydration of agricultural and forest waste [10]. Recently, Dumesic and co-workers proposed a new pathway of aviation fuel by aldol condensation of furfural and acetone [11]. In the process, the long carbon chain intermediates of C8AC16 could be synthesized. The hydrodeoxygenation was followed to remove the oxygen atoms from these oxygen-containing intermediates and the branched alkanes with high thermal stability and energy density could be used as the alternative aviation fuel [12]. However, this process needs acetone as the reactant, which is expensive and cannot be produced economically from renewable biomass. Many researchers strived to investigate CAC coupling reaction without acetone [13,14]. Chheda and Dumesic proposed a rout for long hydrocarbons production by self-aldol condensation of tetrahydrofurfural which can be synthesized by hydrogenation of furfural [15]. Chheda et al. found that trifurylmethane (oxygenated C13 intermediate) could be produced by the hydroxyalkylation/ alkylation (HAA) of furan and furfural [16]. However, these processes only produce the intermediates with straight carbon chain. After hydrodeoxygenation for saturating C@C and C@O bonds and removing oxygen atoms, the obtained alkanes were mainly composed of straight carbon chain hydrocarbons, which is only used as the high quality substitutes for diesel [17]. For the application of aviation fuel, the hydrocarbons with branched carbon chains are preferable to keep the low freezing points. 2-Methylfuran (2MF) is produced in industry by selective hydrogenation of furfural. Recently, Corma et al. proposed a process to produce branch hydrocarbons starting from 2MF, due to its high reactivity and selectivity for alkylation reactions [8]. However, limited researches are addressed the conversion of hemi-cellulose to aviation fuel. In this work, biomass derived aviation fuel was synthesized by coupling acid hydrolysis hemicellulose followed by the catalytic conversion in aqueous phase. 2MF production by hydrogenation of distilled furfural from hemicellulose hydrolysates was investigated. Then, HAA condensation of 2MF and furfural was explored. Finally, the aviation fuel synthesis by hydrodeoxygenation of HAA products was studied. With using hemicellulose as the feedstock, the whole process and the performance of catalysts involved in each step were shown in Fig. 1.
2. Experimental section 2.1. Catalyst preparation and characterization Raney Ni preparation. With constant magnetic stirring, 160 g deionized water and 40 g NaOH were added into a 500 mL threenecked flask to gain a 20 wt% NaOH solution, 30 g NiAAl alloy (Dalian Toyounger Chemical Co., Ltd.) was slowly added at the temperature of 323 (±2) K. After 1.5 h, the supernatant was dumped, the solid collected was washed by distilled water until the pH of 8–9 and further washed by ethanol for 5–6 times. The prepared Raney Ni catalyst was stored in ethanol. Ni/SiO2–ZrO2 preparation. Appropriate amounts of Na2SiO3 9H2O and ZrOCl28H2O were dissolved in distilled water, respec-
DTG LHSV
differential thermogravimetric analysis liquid hourly space velocity
Symbols T temperature [K]
tively. Under continuously stirring, the solution of ammonium nitrate was dropped gradually into the solution of Na2SiO3 until the pH of 8.0 was reached, obtaining the Si(OH)4 precipitate. According to the similar procedure, the solution of ammonia was dropped into the solution of ZrOCl2 until the pH of 8.0 was reached and the Zr(OH)4 precipitate was obtained. The two precipitates were mixed and aged for 12 h at 348 K under constant stirring. Subsequently, the precipitate was filtered and washed with distilled water to completely remove chloride ions. The solid obtained was dried overnight at 393 K and calcined at 773 K for 5 h. An appropriate amount of nickel nitrate was dissolved in a predetermined volume of distilled water based on the amount of the SiO2–ZrO2 support. The solution was evaporated and the residues were dried in air at 393 K overnight and then calcined at 773 K for 5 h. The catalysts were designated as Ni/SiO2–ZrO2. The surface area and pore size distribution of catalyst were measured on a Quantachrome instrument at 77 K. The catalyst was degassed at 523 K for 10 h prior to measurement. Its surface area was calculated by the Brunauer–Emmett–Teller (BET) method and the average pore diameter and pore volume were calculated with the Barret–Joyner–Halenda (BJH) model. X-ray powder diffraction (XRD) patterns were obtained on a RigakuD/max-rCX-ray diffractometer at 40 kV and 40 mA using Cu Ka radiation, and the data were collected at steps of 0.02° in the 2h range of 5°–80°. The chemical composition of Raney Ni was identified by inductively coupled plasma-atomic emission spectrometry (ICP-AES, OPTIMA 8000). TG analysis of spent catalyst was implemented on a NETZSCHSTA 409PC DSC-SP Thermal analyzer by increasing the temperature from 313 K to 1123 K at 10 K/min under an air flow of 30 ml/min. 2.2. Catalytic performance in aqueous phase and product analysis Degradation of hemi-cellulose to furfural was carried out in a 100 ml stainless steel reactor at 433 K with corncob as the feedstock. In a typical experiment, 1.0 g corncob, 10 ml deionized water and 10 ml 5 wt% sulfuric acid were loaded into the reactor. N2 was used to purge the air inside the reactor and pressurized to 1.0 MPa. Then the reactor was heated to 433 K with steam. The produced furfural was stripped out of the reactor with flowing steam. When the reaction stopped, the liquid products were collected by filtration with a 0.45 lm film and analyzed by GC–MS and HPLC. Hydrogenation of furfural to 2MF was carried out on a fixed bed by using Raney Ni catalyst. 2 g of freshly prepared Raney Ni catalyst was loaded in a tubular stainless steel reactor with the inner diameter of 10 mm and the length of 300 mm. After the system was heated to a certain reaction temperature in a H2 flow of 50 ml/min, furfural was fed with 0.05 ml/min by a syringe pump. The mixture of furfural and hydrogen was introduced into the reactor via a preheater of 423 K at the liquid hourly space velocity (LHSV) of 1.0 h 1. The H2 pressure was controlled at 0.3 MPa by a backpressure valve. The reaction temperature was measured by a thermocouple in the catalyst bed and controlled by a temperature controller. After the time-on-stream of 5 h, the liquid product was
Please cite this article in press as: Wang T et al. Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy (2014), http://dx.doi.org/10.1016/j.apenergy.2014.06.035
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O O
H2SO4
Hemicellulose
Hydrolysis/ dehydration
O O
Raney Ni
(1) Furfural O
Hydrogenation
(2) 2MF
Furfural
O
O
O
O +
Formic acid
O
O
2 HAA
Furfural
(3)
2MF C15 intermediate
O O
O
Ni/ZrO2-SiO2
(4)
Hydrodeoxygenation
C15 alkane
C15 intermediate
Fig. 1. Processes involved in the new route for biomass derived aviation fuel production.
collected via a condenser and a gas-liquid separator. The products were analyzed by a GC (Shimazu 2014C) equipped with a FID detector and a Carbowax capillary column. HAA condensation was conducted in a 250 ml glass reactor with magnetic stirring and reflux system. The distilled furfural (4.8 g, 0.05 mol) and 2MF (5.8 g, 0.1 mol) were charged into the reactor together with 50 vol% of water/ethanol (95.4 g). The presence of ethanol favors the dissolution of condensation product due to the poor dissolution ability in water. When a given temperature was reached, the formic acid was added into the reactor to catalyze HAA reaction. After 16 h, the resulting mixture was automatically separated into two phases. The upper oil phase contained C15 intermediate was collected for HPLC analysis and was directly hydrodeoxygenated to aviation fuel. Hydrodeoxygenation of C15 intermediate from HAA condensation was carried out over 10 wt%Ni/SiO2–ZrO2 catalyst on the same apparatus to hydrogenation of furfural to 2MF. The reaction condition was kept at 523 K, 5 MPa of H2 pressure and LHSV of 0.75 h 1. Before reaction, the catalyst was reduced at 773 K for 3 h in the presence of H2 flow. The alkane products were analyzed by a GC (Shimazu 2010) instrument equipped with a FID detector and a HP-5 capillary column.
3. Results and discussion 3.1. Degradation of hemi-cellulose to furfural The weight percentage of glucan, xylan and lignin in corncob was determined according to the laboratory analytical procedure (LAP), which was exploited by the US National Renewable Energy Laboratory (NREL). The total sugars in the pretreatment liquor were calculated after a secondary hydrolysis of oligosaccharide into mono-saccharides with 4 wt% sulfuric acid at 121 °C for 45 min [18]. Sugars and other degradation products were quantitatively determined by HPLC instrument. The results showed that the hemi-cellulose, cellulose and lignin units were 27.6%, 29.3% and 12.6%, respectively. This indicates that nearly 30% of species including ash, moisture and unidentified compounds are involved in the raw corncob.
Table 1 Furfural production by direct degradation of corncob catalyzed with sulfuric acid. Sulfuric acid (mmol)
0 0.45 0.9 1.8
Yield of products (mol%) Furfural
HMF
LA
0 46 71 68
0 0.3 1.5 2.8
0 0 2.6 4.7
Degradation of hemi-cellulose fraction of corncob to furfural involves the sequential hydrolysis and dehydration processes, both of which are catalyzed by sulfuric acid. As shown in Table 1, the blank experiment revealed that no product was detected without sulfuric acid, indicating its essential catalysis in this process. By using sulfuric acid, the detectable products mainly contain 5-hydroxymethylfurfural (HMF), levulinic acid (LA), furfural and trace amount of glucose by HPLC measurement. The furfural yield was increased with increasing the sulfuric acid amount and the maximal yield was reached to 71% at 0.9 mmol of sulfuric acid. However, as the sulfuric acid was further increased to 1.8 mmol, the furfural yield slightly reduced to 68% while with the significantly increased HMF and LA. The formation of HMF is attributed to the C6 sugar dehydration, while LA is responsible for rehydration of furfural and HMF intermediates, implying that the high concentration of sulfuric acid leads to side products [19]. After
Table 2 Chemical composition and textural properties of Raney Ni and Ni–Al alloy. Item
Raney Ni
Ni–Al alloy
Ni/(mol%) Al/(mol%) BET/(m2/g) Vp/(cm3/g) PD/(nm)
87.00 13.00 11.23 0.015 4.10
30.40 69.60 0.33 – –
Vp, mesoporous volume; PD, Ni particle size.
Please cite this article in press as: Wang T et al. Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy (2014), http://dx.doi.org/10.1016/j.apenergy.2014.06.035
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B Al3Ni2 Al3Ni
Intensity (a.u.)
Intensity (a.u.)
A
Ni-Al
111 200
220
Raney Ni
10
20
30
40
50
60
70
80
o
10
20
30
40
50
60
70
80
o
2−Τheta/ ( )
2-Theta/ ( )
Fig. 2. XRD patterns of Raney Ni and Ni–Al alloy (A), and 10 wt%Ni/SiO2–ZrO2 (B).
distillation, the purity of furfural was 99%, which is suitable for 2MF synthesis by the downstream hydrogenation process. 3.2. Hydrogenation of furfural to 2MF Raney Ni catalyst was prepared and used for hydrogenation of furfural to 2MF. Its chemical composition and XRD pattern were shown in Table 2 and Fig. 2, respectively. After dissolution of Al component, the surface of Raney Ni was significantly increased to 11.23 m2/g and the mesoporous volume of 0.015 cm3/g was created. The XRD patterns of the NiAAl alloy indicated that it contains the two kinds of Ni3Al1 and Ni3Al2 domains. After dissolving Al component by NaOH, the diffractions relative to metallic Ni were observed with the Al residue (13%, from Table 2) as amorphous nature. The effect of reaction temperature on furfural hydrogenation to 2 MF was listed in Table 3. The furfural conversion of 72% and the 2MF yield of 65% were obtained at 453 K and 0.3 MPa of H2 pressure. Both furfural conversion and 2MF yield increased with increasing the temperature, and the highest furfural conversion and 2MF yield were obtained with 100% and 89%, respectively, at the temperature of 523 K. As the temperature was further increased to 543 K, however, the 2MF yield was decreased to 83% although the furfural conversion was kept at 100%, which indicates that side reactions occurred due to 2MF transformation in the presence of H2. These results demonstrate that Raney Ni catalyst in this preparation is highly active for 2MF production from furfural hydrogenation. This is possibly due to that the Ni particle size of about 4 nm (as indicated in Table 2) exposes more metal sites for this transformation and obtained as high as 89% of 2MF yield at the relatively low temperature of 523 K. 3.3. HAA condensation of 2MF and furfural HAA condensation of 2MF and furfural was carried out by using formic acid as the catalyst under the reaction condition of 328 K,
2MF/furfural molar ratio of 2 and reaction time of 16 h. The effect of acid concentration was listed in Table 4. Product analysis showed that the condensation products mainly contained the C15 intermediate, indicating that 2MF and furfural can be effectively transferred into the goal product in the presence of formic acid. As increasing the formic acid concentration, the 2MF/furfural conversion and the C15 intermediate yield increased. As comparing with 2MF, furfural was relatively easy to be converted and got the higher conversions at the same acid concentration. At 4 mol/l of formic acid, the highest C15 intermediate yield of 69% can be obtained. The effect of reaction temperature on HAA condensation was investigated under 4 mol/l of formic acid concentration, 2MF/furfural molar ratio of 2 and reaction time of 16 h. The results in Table 5 indicated that the reaction temperature had evident influence on the yield of C15 intermediate. The higher reaction temperature leads to the higher conversions of 2MF/furfural and the yields of the C15 intermediate. At 338 K, the maximal C15 intermediate yield of 89% was obtained. HAA condensation was studied with using different acids under the condition of 328 K, 2MF/furfural molar ratio of 2, acid concentration of 2.5 mol/l and reaction time of 16 h. As shown in Table 6, the sulfuric acid showed excellent activity in HAA process. Both the 2MF/furfural conversion of 100% and the C15 intermediate yield of 95% were obtained. For formic acid catalyst, furfural conversion was kept at 100% but the 2MF conversion decreased to 84%, obtaining the significantly reduced C15 intermediate yield of 43%. As the same concentration of acetic acid was used, the conversion of 2MF and furfural was changed a little, but the yield of C15 intermediate further decreased to 32%. Obviously, the yield of C15 intermediate produced by CAC coupling is mainly depended on the acidity of the employed acids and the strongest sulfuric acid showed the maximal C15 intermediate yield of 95%. However, formic acid is an organic acid which can be produced from cellulose, showing the renewable and friendly environmental feature. Acetic acid showed the inferior catalytic performance for HAA condensation and its low C15 intermediate yield may be resulted from the side reaction.
3.4. Hydrodeoxygenation of C15 intermediate to alkanes Table 3 Effect of temperature on hydrogenation of furfural to 2MF. t/(K)
Furfural conversion (%)
2MF yield (%)
453 473 493 523 543
72 89 95 100 100
65 81 85 89 83
The surface area, pore volume and mesoporous diameter of 10 wt%Ni/SiO2–ZrO2 were determined by isothermal adsorption– desorption of N2 at 77 K. The surface of 230 m2/g, the pore volume of 0.71 cm3/g and the average pore diameter of 12.3 nm were observed on this catalyst. The XRD pattern of 10 wt%Ni/SiO2– ZrO2 was presented in Fig. 2B. The significant diffractions at 2h = 37.3°, 43.3° and 62.9° indicate the existence of aggregated
Please cite this article in press as: Wang T et al. Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy (2014), http://dx.doi.org/10.1016/j.apenergy.2014.06.035
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T. Wang et al. / Applied Energy xxx (2014) xxx–xxx Table 4 Effect of acid concentration on HAA condensation of furfural and 2MF. Acid concentration (mol/l)
2MF conversion (%)
Furfural conversion (%)
Condensation C15 products yield (%)
2 3 4
84.4 87.0 92.9
88.7 100.0 100.0
51.1 62.6 68.8
Table 5 Effect of temperature on HAA condensation of furfural and 2MF. Temperature (K)
2MF conversion (%)
Furfural conversion (%)
Condensation C15 products yield (%)
328 338 348
92.9 100.0 100.0
100.0 90.5 94.2
68.8 88.9 84.7
the intrinsic branched nature and the further isomerization process is avoided, which shows the priority for the direct application as aviation fuel. Fig. 4 shows the stability of 10 wt%Ni/ZrO2–SiO2 at the same reaction condition to Fig. 3, except for the LHSV of 0.5 h 1. The stable yield for the liquid alkanes was about 90% and no distinct deactivation was observed during the time on stream of 110 h, indicating that this catalyst is highly stable in this hydrodeoxygenation process. After 110 h of reaction, the TG curve of the spent 10 wt%Ni/ZrO2–SiO2 in Fig. 5 showed that only 3.8% of carbon deposition was obtained, demonstrates its excellent anti-coking ability in this process. The photo of produced liquid alkanes was displayed in Fig. 6. The colorless top liquid phase was composed of alkanes with carbon chains of C5AC15. The main components were focused on the C14/C15 alkanes with the high selectivity of 77%. Depended on the weight percentage (27.6%) of hemi-cellulose in the raw corncob and the respective yields of goal products involved in corncob hydrolysis/dehydration to furfural, furfural hydrogenation to 2MF, HAA condensation of furfural and 2MF to C15 intermediate, and hydrodeoxygenation of C15 intermediate to
Table 6 Effect of catalyst on HAA condensation of furfural and 2MF. 2MF conversion (%)
Furfural conversion (%)
Condensation C15 products yield (%)
H2SO4 Formic acid Acetic acid
100.0 83.7
100.0 100.0
94.6 42.8
85.0
100.0
31.8
NiO crystallites on SiO2–ZrO2. The average particle size of NiO was calculated with 29 nm by using Scherrer equation. The HAA condensation product (C15 intermediate) was subjected to hydrodeoxygenation on a fixed bed by using 10 wt%Ni/ SiO2–ZrO2 as catalyst. The composition of liquid alkanes was shown in Fig. 3. The C14 and C15 alkanes were the main products. The selectivity of these two alkanes reached to 92% and the other alkanes by CAC cracking were significantly suppressed aside from CH4. These results showed that the C15 intermediate can be efficiently converted into the long chain alkanes and obtained the highest 83% of liquid alkanes yield under the reaction condition of 553 K, 5 MPa of H2 pressure and LHSV of 0.75 h 1. It is noted that the C15 alkane by hydrodeoxygenation of C15 intermediate presents
100
80
Yield of liquid alkane /%
Catalyst
60
40
20
0 0
10
20
30
40
50
60
70
80
90
100 110 120
Time on stream /h Fig. 4. Stability test in hydrodeoxygenation of C15 intermediate over 10 wt%Ni/ ZrO2–SiO2.
DTG
Remaining weight: 98.07%
Exothermic
Relative weight
100%
TG Remaining weight: 96.24%
200
400
600
800
1000
1200
Temperature / K Fig. 3. Composition of liquid alkanes produced by hydrodeoxygenation of C15 intermediate in fixed bed.
Fig. 5. TG and DTG profiles of spent 10 wt%Ni/ZrO2–SiO2 after 110 h of time-onstream.
Please cite this article in press as: Wang T et al. Aviation fuel synthesis by catalytic conversion of biomass hydrolysate in aqueous phase. Appl Energy (2014), http://dx.doi.org/10.1016/j.apenergy.2014.06.035
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fuel. The hydrodeoxygenation catalyst showed excellent stability after 110 h of time-on-stream test, indicating its essential application in this process. Acknowledgements This work was supported by the National Natural Science Foundation of China (NSFC, No. 51161140331), the National Key Basic Research Program (973 Plan, No. 2012CB215304) and the National High Technology Research and Development Program (863 Plan, No. 2012AA101806). References Fig. 6. Photo image of liquid alkanes produced by hydrodeoxygenation of C15 intermediate.
aviation fuel, we calculated that one ton of corncob can produce 0.149 ton of aviation fuel. Although only hemi-cellulose component is presently used for aviation fuel production, however, if the possible utilization of cellulose and lignin units (bioethanol and/or HMF by biochemical/chemical transformations of cellulose and heat by lignin combustion [20]) was considered, the comprehensive efficiency of biomass can be further improved. 3.5. Energy conversion efficiency analysis Lignocellulosic biomass is produced by photosynthesis in nature. Here, we used corncob as the feedstock to produce aviation fuel. Due to the fact that the involved four steps were conducted in aqueous phase at the mild temperatures of no more than 523 K and the hydrophobic hydrocarbons can be automatically separated from aqueous phase (the energy intense distillation is avoided), the energy input in our cases is proposed to be lower than that obtained by biomass gasification (the high temperature is necessary) followed by FT synthesis [21]. It is calculated that the energy efficiency of biomass derived hydrocarbon fuels from aqueous phase catalysis is about two times higher than the cellulosic ethanol produced from biomass hydrolysis and fermentation (the energy consumption for ethanol distillation is composed of about 40% of total energy input) [22]. Moreover, the calorific value of C8AC15 hydrocarbons (46 MJ/Kg) is more than three times of the raw corncob (14.4 MJ/Kg) owing to oxygen removal, indicating the significant energy output in our new technology. 4. Conclusions Aviation fuel was produced from raw corncob by a new route. The pathway involved the sequential steps of corncob hydrolysis/ dehydration to furfural, furfural hydrogenation to 2MF, HAA condensation of furfural and 2MF to C15 intermediate and hydrodeoxygenation of C15 intermediate to the final C8AC15 alkanes. The maximal furfural yield of 71 mol% was achieved via degradation of hemicellulose fraction of corncob and the highest 89% of 2MF yield can be produced from hydrogenation of furfural by Raney Ni. Under the optimal condition with using H2SO4 as the catalyst, 95% of C15 intermediate yield was obtained. More than 90% of liquid alkanes yield was obtained by hydrodeoxygenation of C15 intermediate over 10 wt%Ni/ZrO2–SiO2. In the liquid alkanes, the selectivity of iso-alkanes was 82.9% and the main carbon chain was in the range of C8AC15, both of which are suitable for aviation
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