Chinese Journal of Chemical Physics  2016, Vol. 29 Issue (5): 635-643

The article information

Jiang Pei-wen, Wu Xiao-ping, Liu Jun-xu, Li Quan-xin
姜沛汶, 吴小平, 刘俊旭, 李全新
Preparation of Bio-hydrogen and Bio-fuels from Lignocellulosic Biomass Pyrolysis-Oil
生物油制备生物质氢气和生物质燃料
Chinese Journal of Chemical Physics, 2016, 29(5): 635-643
化学物理学报, 2016, 29(5): 635-643
http://dx.doi.org/10.1063/1674-0068/29/cjcp1603056

Article history

Received on: March 24, 2016
Accepted on: May 6, 2016
Preparation of Bio-hydrogen and Bio-fuels from Lignocellulosic Biomass Pyrolysis-Oil
Jiang Pei-wen, Wu Xiao-ping, Liu Jun-xu, Li Quan-xin     
Dated: Received on March 24, 2016; Accepted on May 6, 2016
Department of Chemical Physics, Anhui Key Laboratory of Biomass Clean Energy, Key Laboratory of Urban Pollutant Conversion, Chinese Academy of Sciences, University of Science and Technology of China, Hefei 230026, China
Abstract: In recent years, production of engine fuels and energy from biomass has drawn much interest. In this work, we conducted a novel integrated process for the preparation of bio-hydrogen and bio-fuels using lignocellulosic biomass pyrolysis-oil (bio-oil). The process includes (i) the production of bio-hydrogen or bio-syngas by the catalytic cracking of bio-oil, (ii) the adjustment of bio-syngas, and (iii) the production of bio-fuels by ole nic polymerization (OP) together with Fischer-Tropsch synthesis (FTS). Under the optimal conditions, the yield of bio-hydrogen was 120.9 g H2/(kg bio-oil). The yield of hydrocarbon bio-fuels reached 526.1 g/(kg bio-syngas) by the coupling of OP and FTS. The main reaction pathways (or chemical processes) were discussed based on the products observed and the catalyst property.
Key words: Biomass pyrolysis-oil     Bio-hydrogen     Ole ns polymerization     Fischer-Tropsch synthesis     Bio-fuels    
I. INTRODUCTION

Biomass, as a carbon-containing resource in the earth, has attracted great attention in the world due to its potential applications for producing energy and fuels [1-4]. Lignocellulosic biomass pyrolysis-oil (named as bio-oil) is a black oxygenated organic liquid, which was produced from fast pyrolysis of lignocellulosic biomass. Nowadays, bio-oil has been proved to be an important renewable feedstock for the production of bio-fuels and chemicals [5-7]. As compared with solid biomass, bio-oil can be stored and transported readily, together with the advantage of equipment sharing by using already existent petroleum refining infrastructures. However, the raw bio-oil has high viscosity and acidity, low stability and low heating value due to its high oxygen content. As a result, bio-oil cannot be directly used as engine fuels [8, 9]. Up to now, the upgrading of bio-oil into high grade bio-fuels and chemicals has been widely investigated, especially, the hydrodeoxygenation and the catalytic cracking of bio-oil [8-20]. The bio-oil hydrodeoxygenation can obtain high yield of hydrocarbon bio-fuels. Alternatively, the catalytic cracking of bio-oil seems to be a cheaper route for producing hydrocarbon bio-fuels or chemicals, since such processes are typically operated using cheaper zeolites under the atmospheric pressure, along with free of external hydrogen consumption [19, 20]. Unfortunately, the upgrading of bio-oil by the hydrodeoxygenation or the catalytic cracking of bio-oil often contains part of oxygenated compounds.

Another important route for the transformation of bio-oil into clean bio-energy is the production of hydrogen for fuel cell applications. The production of hydrogen from bio-oil can be realized by the reforming reactions of oxygenated organic compounds and the water-shift reaction. Various catalysts have been investigated for production of hydrogen via the reforming of bio-oil or its model oxygenates [21-24]. One of the major problems for the catalytic reforming of bio-oil is the deactivation of catalysts due to coke or oligomer deposition even in the presence of an excess of steam. For the production of pure hydrogen from bio-oil, another hindering is that the gas products generally contain a certain amount of methane, carbon monoxide, carbon dioxide, and other gaseous compounds, which increase the difficulty of hydrogen purification and its cost.

Moreover, the catalytic cracking of bio-oil can produce bio-syngas, mainly containing light olefins, CO, CO$_2$, CH$_4$, and other gas alkanes [25-27]. This bio-syngas, in general, is able to prepare the liquid hydrocarbon fuels through the olefin oligomerization or Fischer-Tropsch synthesis (FTS). However, the H$_2$/CO ratio in the bio-oil-derived crude syngas typically is lower than 2, which is required for common requirement for the FTS. A large amount of CO$_2$ in the crude syngas also reduces the FTS efficiency. Generally, the bio-syngas formed from the catalytic cracking of bio-oil include two types of useful compositions (light olefins and H$_2$/CO). So far, there are some reports about the production of the liquid fuels by FTS and olefinic polymerization alone [28-33]. However, the coupling of FTS and olefinic polymerization seems to improve the yield of the liquid fuels, which has not been investigated as far as we know.

In this work, an integrated catalytic transformation for producing bio-fuels using the bio-oil was demonstrated, which included the catalytic cracking of the bio-oil to bio-hydrogen or bio-syngas, the bio-syngas conditioning, and the synthesis of liquid bio-fuels via the oligomerization of olefins with Fischer-Tropsch synthesis. This integrated catalytic transformation potentially provides a new and useful route for the production of hydrocarbon bio-fuels from lignocellulosic biomass-derived bio-oil.

II. EXPERIMENTS A. Feedstocks

The crude bio-oil used for this research was obtained by fast pyrolysis in a circulating fluidized bed with a capacity of 120 kg/h of oil in our lab. The bio-oil was produced using rice husk which included 44.12wt % cellulose, 25.74wt % lignin, and 21.93wt % hemicelluloses, along with 44.90wt % C, 6.35wt % H, and 48.30wt % O.

In this work, the light bio-oil with a boiling point of 105_115 ℃ was used. The chemical compositions, elemental composition, and water content of the light bio-oil used are given in Table I. The use of the light bio-oil can reduce the coke deposition and improve the yield of light olefins during the catalytic cracking of bio-oil, as proved in our previous work [11, 25].

Table I Properties of the bio-oil used$^{\rm{a}}$. Comp. anal.=composition analysis. Ele. anal.= Elemental analysis.
B. Catalyst preparation and characterization

HZSM-5(25) zeolite obtained from Nankai University Catalyst Co., Ltd. (Tianjin, China) was calcined in nitrogen atmosphere at 550 ℃ for 4 h prior to use. The 5wt % Ce/HZSM-5 catalyst was prepared by impregnation method. A certain amount of HZSM-5 zeolite was impregnated in cerium nitrate solution at room temperature overnight, followed by rotary-evaporation at 60 ℃, drying at 80 ℃ for 6 h, and calcinating at 550 ℃ for 5 h. The incipient wetness impregnation method was adopted to load the cobalt into the SiO$_2$ (supplied by Qingdao Haiyang Chem Co., Ltd., China). The details were described elsewhere [34]. The 20wt %Ni/Al$_2$O$_3$ catalyst and CuZnAl catalyst (containing 61.2wt % CuO, 33.8wt % ZnO, and 5.0wt % Al$_2$O$_3$) were supplied by Jingjiang Co., Ltd. in China. The LTG-0 catalyst was kindly provided by Beijing Huiersanji Green Chem. Co., Ltd., China.

The elemental content in the catalysts was measured by inductively coupled plasma and atomic emission spectroscopy (ICP-AES, Atomscan Advantage, Thermo Jarrell Ash Co., USA). The catalysts were also investigated by NH$_3$-TPD (temperature programmed desorption of ammonia), N$_2$ adsorption/desorption isotherms and X-ray diffraction (XRD). For the NH$_3$-TPD tests, the catalyst was pretreated at 500 ℃ under helium flow (ultrahigh purity, 100 mL/min) for 2 h, and adsorption of ammonia was carried out at 120 ℃ for 1 h. After the catalyst was flushed with He at 120 ℃ for 1 h, the programmed-desorption of NH$_3$ was run from 120 ℃ to 700 ℃ with a heating rate of 10 ℃/min. The catalyst acid strength was obtained by the adsorption-desorption of NH$_3$, which was detected on-line with a gas chromatograph (GC-SP6890, Shandong Lunan Ruihong Chemical Instrument Co., Ltd., Tengzhou, China). The N$_2$ adsorption/desorption isotherms of the catalysts were measured at _196 ℃ using the COULTER SA 3100 analyzer.

The typical NH$_3$-TPD spectra of Ce/HZSM-5 and LTG-0 catalysts are shown in Fig. 1. Two ammonia desorption peaks were observed, assigned to the weak acid sites at 230 ℃ and the strong acid sites at 450 ℃. The ratios of strong to weak acid sites for Ce/HZSM-5 and LTG-0 were 0.79 and 0.93 respectively. As shown in Fig. 2, Ce/HZSM-5 and the LTG-0 belong to the ZSM-5 zeolite catalyst. The XRD pattern of 20wt %Ni/Al$_2$O$_3$ catalyst present the NiO phase (at 37.5$^\circ$, 43.3$^\circ$, and 62.9$^\circ$) and the Al$_2$O$_3$ phase at 2$\theta$=25.4$^\circ$. The XRD spectrum for CuZnAl indicates that the Cu and Zn element appeared as CuO and ZnO. Co$_3$O$_4$ was also observed in Co/SiO$_2$ catalyst. The main physical and chemical properties of the catalysts are summarized in Table II.

Table II Main physical and chemical properties of the catalysts.
FIG. 1 Typical NH$_3$-TPD spectra of (a) the fresh Ce/HZSM-5 catalyst and (b) the fresh LTG-0 catalyst
FIG. 2 Typical XRD spectra of the catalysts.
C. Product analysis 1. Production of bio-hydrogen or bio-syngas from bio-oil

For production of bio-syngas from bio-oil, an integrated catalytic transformation process by coupling the catalytic cracking reactions, the water gas reaction and the CO$_2$ adsorption were designed and operated under atmospheric pressure. The system consists of three units: one for the production of hydrogen or bio-syngas by the catalytic cracking of the bio-oil, together with the water gas reaction unit for the increase of hydrogen proportion, and the CO$_2$ removal unit via the CO$_2$ adsorbents.

For the catalytic cracking of bio-oil to bio-hydrogen or crude bio-syngas, 10 g of 20wt % Ni/Al$_2$O$_3$ or 5wt % Ce/HZSM-5 catalyst was filled in the catalyst bed, which was held in the reactor by quartz wool. The mixture of bio-oil and water (oil/water mass ratio of about 1:3) was fed into the reactor through a multisyringe pump (TS2-60, Baoding Longer Precision Pump) at a given feeding rate. Before each run, the reactor was flushed with nitrogen at a flow rate of 200 cm$^3$/min for 1 h, and was externally heated to a given temperature by the carborundum heater with a programmed temperature controller. The gaseous products were on-line analyzed using a gas chromatograph (GC-SP6890, Shandong Lunan Ruihong Chemical Instrument Co., Ltd., Tengzhou, China) with two detectors: a TCD (thermal conductivity detector) for analysis of H$_2$, CO, CO$_2$ and CH$_4$ separated on the TDX-01 column, and a FID (flame ionization detector) for gas hydrocarbons separated on the Porapak Q column.

The water gas shift reaction was conducted in the second unit of the reaction system. 3.0 g of the CuZnAl catalyst was typically loaded in the reactor. Before the reaction, the reactor were externally heated to the given temperature. The off-gas of the catalytic cracking process was fed into the WGS reactor. The analysis procedures of the products obtained from the water gas shift reaction unit were the same as the steps for the catalytic cracking, as mentioned above. Then, the CO$_2$ removal by the 15wt % NaOH solution was conducted in the third unit. Typically, 1 L of the 15wt % NaOH solution was loaded in the absorption bottle.

2. Production of hydrocarbon bio-fuels

According to the composition of the adjusted bio-syngas, the model gas with H$_2$/CO/C$_2$H$_4$/C$_3$H$_6$/C$_4$H$_8$/N$_2$=30.6/14.7/15.0/20.1/4.9/14.7 (in volume ratio) was employed for the production of liquid hydrocarbon fuels. As shown in Fig. 3(a), the olefinic polymerization was carried out in a high pressure micro-reactor unit of 10 mm internal diameter, 40 cm in length. 2.0 g of the LTG-0 catalyst was loaded in the center of the reactor. Before the reaction, the reactor was flushed with argon at a flow rate of 200 cm$^3$/min for 30 min, and then was externally heated to the given temperature by the carborundum heaters. The model gas was then fed into the reactor. The reaction conditions were $T$=300 ℃, $P$=3.0 MPa, and GHSV=1200 h$^{-1}$. The liquid products were collected in an ice trap immersed in the ice/salt bath, and then analyzed using GC-MS (Thermo Trace DSQ (I)) with a TR-5MS fused-silica capillary column. The stream leaving the ice trap was depressurized and periodically analyzed on line in a gas chromatograph with TCD and FID detectors, as detailed above.

FIG. 3 Schematic diagram of the synthesis of bio-fuels from bio-syngas. (a) the synthesis of bio-fuels by olefinic polymerization or Fischer-Tropsch synthesis, (b) the synthesis of bio-fuels by the coupling of olefinic polymerization and Fischer-Tropsch synthesis. MG=model gas, MFC=mass flow controller, PIC=pressure indicator controller, FD=flow detector, TCD=thermal conductivity detector, FTD= flame ionization detector.

The Fischer-Tropsch synthesis (FTS) was carried out over 2.0 g of the 15wt %Co/SiO$_2$ catalyst in the same reactor. The system was first purged by an argon flow at the rate of 200 cm$^3$/min for 30 min, followed by pre-reducing stage with a 10 %vol H$_2$/Ar mixture at 400 ℃ for 8 h, then model gas was fed into the system until reaching the desired pressure by slowly adjusting the system to the desired temperature. The reaction was operated under the following conditions: $T$=270 ℃, $P$=3.0 MPa, and GHSV=1200 h$^{-1}$. The liquid products were condensed in two consecutive traps located at the reactor outlet and kept, respectively, at 393 and 268 K. Gas products leaving the ice trap were on-line sampled every 30 min and analyzed using the on-line gas chromatograph with two detectors, as detailed above. Products collected in the traps were mixed and analyzed using GC-MS (Thermo Trace DSQ (I)) with a TR-5MS fused-silica capillary column.

As shown in Fig. 3(b), the olefinic polymerization combined with Fischer-Tropsch synthesis (OP-FTS) reaction was operated in the same stainless tube. Two types of catalysts were loaded in the reactor: 2.0 g of the LTG-0 catalyst in the front part and 2.0 g of the 15wt % Co/SiO$_2$ catalyst in the back part. The two parts were externally heated by short furnace and heat tape, respectively. The operation steps and the products analysis procedures were the same as that for Fischer-Tropsch synthesis, as mentioned above.

Finally, the conversion, product yield and the resulting product distribution were calculated according to the method reported in Ref.[35-37]. All the tests were repeated three times and the reported data are the mean values of three trials.

III. RESULTS AND DISCUSSION A. Routes for production of bio-hydrogen and bio-syngas from bio-oil

To produce hydrocarbon bio-fuels from bio-oil, the catalytic transformation of oxygenated organic compounds in bio-oil into hydrogen-containing bio-syngas is required. Thus, we first performed the comparative tests for the catalytic cracking of bio-oil over different characteristic catalysts and the pyrolysis of bio-oil with SiO$_2$.

As shown in Table III, the gas products produced by the pyrolysis of bio-oil with SiO$_2$ consist of CO, CO$_2$, gas alkanes (mainly CH$_4$), with small amount of desired products of hydrogen and C2$^=-$C4$^=$ light olefins. The pyrolysis of bio-oil also formed the organic liquid products (OLPs) mainly including small molecule oxygenated organics, which were caused by the thermal decomposition of heavier oxygenated organic compounds in bio-oil.

Table III Results of different preparation routes of bio-hydrogen and bio-syngas from bio-oil$^{\rm{a}}$.

On the contrary, the catalytic cracking of bio-oil significantly enhanced the bio-oil conversion as well as the yield of the gas products as compared with the pyrolysis of bio-oil. For the catalytic cracking of bio-oil over the 20wt % Ni/Al$_2$O$_3$ catalyst at the typical temperature of 550 ℃, the bio-oil conversion reached about 91.1 % along with a hydrogen yield of 120.9 (g/kg bio-oil). The gas products was dominant during the catalytic cracking of bio-oil, which mainly included 66.0vol % hydrogen and 31.7vol % carbon dioxide together with trace amount of methane and carbon monoxide. In this sense, the steam reforming of bio-oil reactions and the water gas shift reaction were main reaction pathways, and the Ni-based catalyst like the Ni/Al$_2$O$_3$ catalyst can be employed for the production of bio-hydrogen.

On the other hand, the catalytic cracking of bio-oil over the 5wt %Ce/HZSM-5 catalyst also shows a high bio-oil conversion (about 88.6 %). However, the resulting products using 5wt %Ce/HZSM-5 catalyst were quite different from the catalytic conversion of bio-oil with the Ni-based catalyst. The catalytic cracking of bio-oil over Ce/HZSM-5 was mainly converted into H$_2$/CO/CO$_2$ and C$_2$_C$_4$ light olefins over the acidic sites of the zeolite. As shown in Table III, the gas products produced by the catalytic cracking of bio-oil over Ce/HZSM-5 mainly consist of the desired 24.6 % CO, 8.1 % H$_2$ and light olefins (15.3 % C$_2$H$_4$, 16.7 % C$_3$H$_6$, 2.8 % C$_4$H$_8$), which can be comprehensively utilized as the bio-syngas for the subsequent synthesis of hydrocarbons bio-fuels.

B. Influence of temperature on the preparation of bio-syngas from bio-oil

Table IV shows the influence of temperature on the preparation of bio-syngas from bio-oil by the catalytic cracking of bio-oil over 5wt %Ce/HZSM-5 catalyst. The conversion of bio-oil increased with increasing temperature, and was close to complete conversion near 650 ℃. In the investigated temperature range, the products formed from the catalytic cracking of bio-oil mainly included gas olefins, hydrogen, CO and CO$_2$, together with small amount of gas alkanes, liquid products (mainly C$_6$_C$_8$ aromatics) and coke/tar. The yield of total effective gas (like H$_2$, CO, C$_2$_C$_4$ alkenes) reached 370.8 g/(kg bio-oil) at 550 ℃. Further increasing temperature caused an increase of the total effective gas, while a decrease of the light olefins yield due to the increase of gas alkanes (especially methane). The above results indicate that high temperatures will facilitate the deoxygenation of the bio-oil, and at the same time, enhance the deep cracking of the heavier intermediates.

Table IV Effect of temperature on the production of bio-syngas by the catalytic pyrolysis of bio-oil under the conditions: 500_650 ℃, S/C=5.0 and WHSV of 0.4 h$^{-1}$.

As shown in Table IV, based on the main compounds identified in this work and the previous studies [11, 25], the reaction pathways for the catalytic cracking of bio-oil over an acid molecular sieve catalyst mainly include: (i) the formation of lighter intermediates via breaking the C_C and/or C_O bonds in the oxygenated organic compounds in bio-oil; (ii) the formation of olefin compounds via the deoxygenation (decarboxylation, decarbonylation and dehydration) and catalytic cracking of intermediates; and (iii) formations of low-carbon aromatics by further cyclization and aromatization of light olefins over the acidic sites of the zeolites. Hydrogen should come from the direct decomposition of the oxygenated organic compounds in bio-oil along with the sencond catalytic cracking of intermediates. Gaseous small molecule products (mainly C$_2$_C$_4$ light olefins and gas alkanes) were formed by further decomposition of intermediates. The oxygen in the bio-oil was removed by the decarbonylation, decarboxylation and dehydration processes, since oxygenated chemicals observed in the catalytic cracking of bio-oil mainly contain CO$_2$, CO and H$_2$O.

C. Conditioning of bio-syngas by water gas reaction and CO$_2$ adsorption

To improve the synthesis efficiency of bio-fuels, the conditioning of bio-syngas was conducted by the increase of the H$_2$/CO ratio and the removal of CO$_2$. Table V shows the composition distribution of three typical bio-syngas before and after the conditioning of bio-syngas. For the raw bio-syngas from the catalytic pyrolysis of bio-oil at 550 ℃ over 5wt % Ce/HZSM-5 catalyst, the H$_2$/CO ratio was very low (about 0.33). To increase the H$_2$/CO ratio in the bio-syngas, the raw bio-syngas was first adjusted on-line by the low-temperature water gas reaction over the CuZnAl catalyst (named as adjusted syngas-I). The H$_2$/CO ratio in the adjusted syngas-I was about 1.9, which basically met the requirement of the Fischer-Tropsch synthesis (corresponding to the H$_2$/CO ratio of 2). However, the content of CO$_2$ also remarkably increased to 33.5vol % due to the water gas reaction. To increase the effective composition of bio-syngas (H$_2$, CO, C$_2$_C$_4$ alkenes) in the bio-syngas, the adjusted syngas-I was further tuned by the removal of CO$_2$ with the CO$_2$ absorption (named as adjusted syngas-II). As can be seen from Table V, the amount of carbon dioxide was reduced near zero (trace), and the final adjusted syngas-II contained 28.7vol % H$_2$, 14.6vol % CO, 11.4vol % CH$_4$, 17.0vol % C$_2$H$_4$, 21.4vol % C$_3$H$_6$, 3.9vol % C$_4$H$_8$ and 3.0vol % C$_2$_C$_4$ alkanes. The above results indicate that the effective conditioning of bio-syngas was able to simply be realized through the water gas reaction and the CO$_2$ adsorption.

Table V The gas composition (vol %) of bio-syngas produced by different ways.
D. Synthesis of hydrocarbon bio-fuels by olefinic polymerization and Fischer-Tropsch process

Considering that the bio-syngas derived from the catalytic cracking of bio-oil and the conditioning are essentially composed of C$_2$_C$_4$ light olefins and H$_2$/CO, the synthesis of bio-fuel using the adjusted syngas-II was tested by means of three routes: olefinic polymerizations (OP), Fischer-Tropsch synthesis (FTS), OP-FTS process.

As show in Table VI, the olefinic polymerization over the modified zeolite (LTG-0) can convert the compositions of C$_2$_C$_4$ light olefins into liquid hydrocarbon fuels. The main products from the olefinic polymerization mainly included chain hydrocarbons (C$_5$$^+$ olefins and C$_5$$^+$ paraffins) together with small amount of C$_6$$^+$ aromatics. The olefinic polymerization mainly involve the oligomerization of light olefins, the hetero-oligomerization and the cracking of heavier oligomers. The C$_6$ olefins were formed by the dimerization of propylene and/or the hetero-oligomerization between ethylene and butenes. The C$_8$ and C$_9$ olefins were mainly produced through the dimerization of butenes and the trimerization of propylene respectively. The formation of light odd number alkenes like C$_5$ and C$_7$ olefins may originate from the hetero-oligomerization and/or the cracking of heavier oligomers. The paraffins products observed could be formed through the oligomerization of olefins followed by hydrogen transfer, cyclization and isomerization. The C$_6$$^+$ aromatic hydrocarbons should be derived from the aromatization of olefins and the hydrogen transfer reactions.

As shown in Table VI, on the other hand, the Fischer-Tropsch synthesis (FTS) over the 15wt % Co/SiO$_2$ catalyst can convert the compositions of H$_2$/CO into liquid hydrocarbon fuels. The main products derived from the FTS mainly included chain hydrocarbons (C$_5$$^+$ paraffins and C$_5$$^+$ olefins). The FTS reaction produces hydrocarbons of variable chain length from a gas mixture of carbon monoxide and hydrogen (bio-oil-derived syngas). The FTS reaction is a building stone (CH$_2$) by the CO hydrogenation for longer hydro-carbons. The liquid hydrocarbon distributions by FTS depend on the chain growth probability (described as the Anderson-Schulz-Flory (ASF) distribution). As shown in Fig. 4, compared with olefinic polymerizations (OP), FTS produced more long-chain hydrocarbons. It was noticed that FTS using the 15wt % Co/SiO$_2$ catalyst can also convert C$_2$_C$_4$ light olefins. However, the main products derived from C$_2$_C$_4$ light olefins by FTS were C$_2$_C$_4$ gas paraffins, which were formed through the hydrogenation of light olefins.

Table VI Products of different ways to synthesize hydrocarbon bio-fuels.
FIG. 5 Typical GC-MS spectra (a) the sample from the olefinic polymerization of the bio-oil-derived bio-syngas catalyzed by LTG-0 at 300 ℃. (b) the sample from the Fischer-Tropsch synthesis catalyzed by 15wt %Co/SiO$_2$ catalyst. (c) the sample from the olefinic polymerization and Fischer-Tropsch synthesis coupling reaction. Note: C$_n$ means alkenes and alkanes with $n$ carbon atoms, C$_n$$^0$ means normal-alkanes with $n$ carbon atoms.

Moreover, the olefinic polymerization combined with Fischer-Tropsch synthesis process (OP-FTS) can convert both C$_2$_C$_4$ light olefins and H$_2$/CO in the bio-syngas. As a result, the yield of the liquid fuels by OP-FTS was obviously higher than the levels from OP or FTS alone. The main products from OP-FTS also included chain hydrocarbons (C$_5$$^+$ olefins and C$_5$$^+$ paraffins) together with small amounts of C$_6$$^+$ aromatics. This suggests that the coupling of olefinic polymerization and Fischer-Tropsch synthesis could be a high efficiency way for the synthesis of bio-fuels with the bio-oil derived bio-syngas.

E. Catalysts stability during transformation of bio-oil to bio-fuels

As shown in Fig. 5(a), the stability of Ce/HZSM-5 catalyst during the catalytic cracking of bio-oil was measured by the conversion of bio-oil and the yield of light olefins. After the catalyst was continuously used for 15 h, the conversion of bio-oil and the yields of light olefins were obviously decreased. For the olefinic polymerization step performed at 300 ℃, after the LTG-0 catalyst was used for 15 h, the conversion of light olefins degraded by 25 %, accompanied with an significantly decrease in the yield of bio-fuel (Fig. 5(b)).

FIG. 5 Catalyst stability during (a) the catalytic cracking of bio-oil to light olefins over the Ce/HZSM-5 catalyst at 550 ℃ and (b) the synthesis of bio-fuel from bio-syngas over the LTG-0 catalyst at 300 ℃.
IV. CONCLUSION

We studied a novel integrated process for the preparation of bio-hydrogen and bio-fuels using biomass pyrolysis-oil. The Ni-based catalyst was suitable for the production of bio-hydrogen. On the other hand, the catalytic cracking of bio-oil over Ce/HZSM-5 mainly formed the crude bio-syngas containing light olefins and H$_2$/CO/CO$_2$. The H$_2$/CO ratio and the efficient composition of bio-syngas were much improved by the water gas reaction and CO$_2$ adsorption. Especially, the yield of the liquid fuels through the coupling of Fischer-Tropsch synthesis and olefinic polymerization was obviously higher than the levels from OP or FTS alone.

V. ACKNOWLEDGMENTS

This work is supported by the National Sci-Tech Support Plan (No.2014BAD02B03), the Program for Changjiang Scholars and Innovative Research Team in University and the Fundamental Research Funds for the Central Universities (No.wk2060190040).

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生物油制备生物质氢气和生物质燃料
姜沛汶, 吴小平, 刘俊旭, 李全新     
中国科学技术大学化学物理系, 安徽省生物质洁净能源重点实验室, 中国科学院城市污染物转化重点实验室, 合肥 230026
摘要: 研究了一种以生物质裂解油为原料制备氢气和生物燃料的催化转化过程。该过程包括生物油催化裂解制备氢气和生物合成气,合成气的调变,烯烃聚合和费脱合成耦合制备生物燃料。在优化反应条件下,氢气产率达到120.9 g H2/(kg bio-oil),烯烃聚合-费脱合成耦合反应形成的生物燃料产率达到526.1 g/(kg bio-syngas)。基于产物分析和催化剂特性表征,探讨了生物燃料合成过程中的反应路径和化学反应过程.
关键词: 生物油     生物质氢气     烯烃聚合     费脱合成     生物燃料