Energy Fuels 2010, 24, 6456–6462 Published on Web 11/12/2010
: DOI:10.1021/ef1010995
Hydrogen Production via Catalytic Steam Reforming of Fast Pyrolysis Bio-oil in a Fluidized-Bed Reactor Qingli Xu,*,† Ping Lan,†,‡ Baozhen Zhang,† Zhizhong Ren,† and Yongjie Yan† † Research Center for Biomass Energy, East China University of Science and Technology, Shanghai 200237, China, and ‡School of Chemistry and Ecoengineering, Guangxi University for Nationalities, Nanning 530006, China
Received August 17, 2010. Revised Manuscript Received October 27, 2010
Bio-oil reforming to produce hydrogen could be an attractive option for sustainable hydrogen. Hydrogen production via catalytic steam reforming of bio-oil in a fluidized-bed reactor was studied in this paper. The optimum conditions on hydrogen production were obtained at 700 °C, steam/carbon mole ratio (S/C) of 17, and weight hourly space velocity (WHSV) of 0.4 h-1. In addition, the reason for catalyst deactivation in a fluidized-bed reactor was investigated. The fresh and deactivation catalysts were analyzed by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), which showed that the carbon deposition is not the main reason for catalyst deactivation. The main reason for fresh catalyst deactivation was the NiO grain sintered on the supporter surface.
technology, already mature,4-7 is predicted to be the most economic way to produce hydrogen from biomass on an industrial scale. Hydrogen produced from bio-oil provides a new route for use of bio-oil. Studies on steam reforming of bio-oil or bio-oil model component showed promising results.8-12 Bio-oil was reformed in a fixed-bed reactor.13-17 Although the reaction was run at a high steam/carbon mole ratio (S/C), rapid carbon deposition still took place on the catalyst, which limited the reforming time to 3-4 h, and then the catalyst regeneration was required. Some researchers believe that the fixed-bed reactor is not suitable for thermally unstable bio-oil reforming
1. Introduction Hydrogen is not only an ideal energy carrier for the future but also a fundamental raw material and feedstock in petroleum, chemical engineering, chemical fertilizer, and metallurgical industries. Currently, hydrogen is primarily produced by catalytic steam reforming of natural gas, light hydrocarbon, or naphtha. However, with the depletion of world’s fossil fuel reserves, the serious environmental problems have gained more attention, focusing on hydrogen production from renewable energy sources. In that respect, hydrogen production from renewable biomass is particularly adapted to sustainable development concerns. Biomass, a kind of renewable resource that adsorbs CO2 during its growth, contributes net zero carbon emissions when used to produce hydrogen. Hydrogen can be produced by direct gasification of biomass into syngas.1-3 However, the biomass is difficult to collect and store, and the energetic density of it is low, which leads to high transportation and store costs. An alternative method is its primary conversion into bio-oil by fast pyrolysis. This
(8) Wang, Z.; Pan, Y.; Dong, T.; Zhu, X.; Kan, T.; Yuan, L.; Torimoto, Y.; Sadakata, M.; Li., Q. Production of hydrogen from catalytic steam reforming of bio-oil using C12A7-O--based catalysts. Appl. Catal., A 2007, 320, 24–34. (9) Wang, D.; Czernik, S.; Chornet, E. Production of hydrogen from biomass by catalytic steam reforming of fast pyrolysis oils. Energy Fuels 1998, 12, 19–24. (10) Bimbela, F.; Oliva, M.; Ruiz, J.; Garcı´ a, L.; Arauzo, J. Hydrogen production by catalytic steam reforming of acetic acid, a model compound of biomass pyrolysis liquids. J. Anal. Appl. Pyrolysis 2007, 79, 112–120. (11) Czernik, S.; Evans, R.; French, R. Hydrogen from biomassproduction by steam reforming of biomass pyrolysis oil. Catal. Today 2007, 129, 265–268. (12) Wu, C.; Huang, Q.; Sui, M.; Yan, Y.; Wang, F. Hydrogen production via catalytic steam reforming of fast pyrolysis bio-oil in a two-stage fixed bed reactor system. Fuel Process. Technol. 2008, 89, 1306–1316. (13) Kinoshita, C. M.; Turn, S. Q. Production of hydrogen from biooil using CaO as a CO2 sorbent. Int. J. Hydrogen Energy 2003, 28, 1065– 1071. (14) Basagiannis, A. C.; Verykios, X. E. Catalytic steam reforming of acetic acid for hydrogen production. Int. J. Hydrogen Energy 2007, 32, 3343–3355. (15) Wu, C.; Sui, M.; Yan, Y. A comparison of steam reforming of two model bio-oil fractions. Chem. Eng. Technol. 2008, 31, 1748– 1753. (16) Takanabe, K.; Aika, K.-i.; Seshan, K.; Lefferts, L. Sustainable hydrogen from bio-oil;Steam reforming of acetic acid as a model oxygenate. J. Catal. 2004, 227, 101–108. (17) Zhang, R.; Wang, Y.; Brown, R. C. Steam reforming of tar compounds over Ni/olivine catalysts doped with CeO2. Energy Convers. Manage. 2007, 48, 68–77.
*To whom correspondence should be addressed. E-mail: xuqingli2001@ 163.com. (1) Acharya, B.; Dutta, A.; Basu, P. An investigation into steam gasification of biomass for hydrogen enriched gas production in presence of CaO. Int. J. Hydrogen Energy 2010, 35, 1582–1589. (2) Onwudili, J. A.; Williams, P. T. Role of sodium hydroxide in the production of hydrogen gas from the hydrothermal gasification of biomass. Int. J. Hydrogen Energy 2009, 34, 5645–5656. (3) Gao, N.; Li, A.; Quan, C. A novel reforming method for hydrogen production from biomass steam gasification. Bioresour. Technol. 2009, 100, 4271–4277. (4) Lede, J.; Broust, F.; Ndiaye, F.-T.; Ferrer, M. Properties of biooils produced by biomass fast pyrolysis in a cyclone reactor. Fuel 2007, 86, 1800–1810. (5) Ertas, M.; Alma, M. H. Pyrolysis of laurel (Laurus nobilis L.) extraction residues in a fixed-bed reactor: Characterization of bio-oil and bio-char. J. Anal. Appl. Pyrolysis 2010, 88, 22–29. (6) Garcia-Perez, M.; Chaala, A.; Pakdel, H.; Kretschmer, D.; Roy, C. Vacuum pyrolysis of softwood and hardwood biomass: Comparison between product yields and bio-oil properties. J. Anal. Appl. Pyrolysis 2007, 78, 104–116. (7) Gercel, H. F. The production and evaluation of bio-oils from the pyrolysis of sunflower-oil cake. Biomass Bioenergy 2002, 23, 307–314. r 2010 American Chemical Society
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Energy Fuels 2010, 24, 6456–6462
: DOI:10.1021/ef1010995
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Table 1. Physical Properties and Ultimate Analysis of Fast Pyrolysis Bio-oil ultimate analysis (%, dry basis) content of viscosity at water (%) 40 °C (mm2 s-1) bio-oil
40.71
6.45
[C]
[H]
[O]
[N]
[S]
56.64 7.968 33.064 1.691 0.637
hydrogen production,11 and eventually, it will be replaced by the fluidized-bed reactor, which can overcome the carbon deposition.18-20 Besides, its isothermal environment is really favorable for the reaction. At present, a fixed-bed technology has been developed, but the development of the fluidized-bed process is still slow; therefore, it is urgent to develop the fluidizedbed process. In this work, a fluidized-bed reactor operated at atmospheric pressure was set up with fast pyrolysis bio-oil as feedstock. The nickel-based catalyst (Ni/MgO) was chosen as the reforming catalyst. Influential parameters, such as the reaction temperature, S/C, and weight hourly space velocity (WHSV), were investigated. In the end, the reason for catalyst deactivation in a fluidized-bed reactor was investigated.
Figure 1. Schematic of the fluidized-bed reactor system: 1, cylinder; 2, valve; 3, steam generator; 4, pressure gauge; 5, steam flow meter; 6, gas flow meter; 7, nozzle; 8, heater; 9, thermocouple; 10, fluidized-bed reactor; 11, temperature controller; 12, cyclone separator; 13, condensor; 14, liquid collector; 15, metering pump; 16, gas chromatograph; 17, bio-oil; and 18, thermostatic bath.
2. Experimental Section
experimental data can be regarded as effective when the relative error between them is lower than 3%. 2.3. Catalyst. Nickel-based catalysts are widely used for steam reforming of hydrocarbons. In this work, the nickel-based catalyst was purchased from Wuxi Qiangya Company. The catalyst NiO/MgO (7.2 wt % NiO) was first crushed and sieved to a particle size range of 0.15-0.30 mm, and then the grain was reduced in H2/N2 (5 vol % H2) gas flow at the temperature of 700 °C for 5 h. The experiments were carried out in a fluidized-bed reactor. The temperature, S/C, and WHSV were investigated with hydrogen yield as the index. The fresh and deactivation catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), thermogravimetry analysis (TGA), and scanning electron microscopy (SEM). 2.4. Chemical Reaction. Because the components of bio-oil are numerous and complex, CnHmOk is used to represent their basic chemical formula. Given that the reaction has completed, the steam reforming of bio-oil can be expressed in the following reaction:
2.1. Preparation of Fast Pyrolysis Bio-oil. The bio-oil obtained by fast pyrolysis of rice husk was provided by the University of Science and Technology of China. The physical properties and ultimate analysis are shown as Table 1. It was demonstrated that bio-oil has high water and oxygen contents, while sulfur and nitrogen contents were rather low. 2.2. Apparatus and Experimental Procedures. The experimental installation that was designed by the East China University of Science and Technology is shown in Figure 1. The fluidized bed, with dimensions of 700 mm in height and 50 mm in diameter, was manufactured from stainless steel, which can stand high temperatures up to 1000 °C. A 3 kW electric heater and a temperature controller are on the reactor. The experimental system was operated at atmospheric pressure. The reactor bed contained a catalyst with a bed of 2 cm in height. The particle size of the catalyst used was 0.15-0.30 mm. The catalyst tiled on a single perforated plate. Bio-oil is kept in a constant temperature bath at the temperature of 50 °C for the convenience of feeding. The feeding rate of bio-oil was controlled by a metering pump, and the feed rate of steam from the steam generator was controlled by a steam flow meter. Nitrogen from the cylinder is regulated at the flow rate of 0.5 L/min, while the reactor was preheated. Both bio-oil (about 50 °C) and steam (about 240 °C) were mixed in a nozzle and then fed into the bottom of the reactor when the temperature reaches the setting value. Reaction tail gas was condensed, and the condensation was collected in a liquid receiver. The noncondensed components of tail gases were sampled, and their contents were analyzed by an Agilent 6820 micro gas chromatograph (GC) equipped with thermal conductivity (TC) detectors. The following gases were measured: H2, CO2, CO, and CH4. To reduce the influence of accidental error on experimental results, five groups of a parallel experiment were carried out. The
Cn Hm Ok þ ð2n - kÞH2 O f nCO2 þ ð2n þ m=2 - kÞH2
ð1Þ
However, actually, bio-oil components are in general thermally unstable at the typical temperatures of the fluidized-bed reactor. Therefore, a mixture of gases (H2, CO, CO2, CH4, unsaturated hydrocarbon, etc.) will form as primary products because of thermal decomposition of bio-oil. In addition, if the reaction has not reached completion, the main reactions involved on the catalyst bed are listed as follows: Cn Hm Ok þ ðn - kÞH2 O f nCO þ ðn þ m=2 - kÞH2
ð2Þ
Steam reforming is an endothermic reaction, and high temperatures can favor the reaction proceeding. Some decomposition reactions may occur because of the high temperature. Cn Hm Ok T Cx Hy Oz þ gases ðH2 , H2 O, CO, CO2 , CH4 , etc:Þ þ coke
ð3Þ (18) Medrano, J. A.; Oliva, M.; Ruiz, J.; Garcı´ a, L.; Arauzo, J. Hydrogen from aqueous fraction of biomass pyrolysis liquids by catalytic steam reforming in fluidized bed. Energy 2010, DOI: 10.1016/ j.energy.2010.03.059. (19) Kechagiopoulos, P. N.; Voutetakis, S. S.; Lemonidou, A. A.; Vasalos, I. A. Hydrogen production via steam reforming of the aqueous phase of bio-oil in a fixed bed reactor. Energy Fuels 2006, 20, 2155–2163. (20) Czernik, S.; French, R.; Feik, C.; Chornet, E. Hydrogen by catalytic steam reforming of liquid byproducts from biomass thermoconversion processes. Ind. Eng. Chem. Res. 2002, 41, 4209–4215.
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CO þ H2 O T CO2 þ H2
ð4Þ
2CO T CO2 þ C
ð5Þ
C þ H2 O T CO þ H2
ð6Þ
CH4 þ 2H2 O T CO2 þ 4H2
ð7Þ
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2.5. Data Treatment. Hydrogen was the desirable product in steam reforming of bio-oil along with the byproducts of CO2, CO, and CH4. The purpose of this work is to investigate the gas product yield in a fluidized-bed reactor under different operation conditions. The equations used in this paper can be shown as follows:
3.1. Effect of the Temperature and S/C. As shown in Figure 2, it was demonstrated that the reaction temperature and S/C have an important impact on the H2 yield as well as other data for catalytic steam reforming of bio-oil. In Figure 2a, with the increase of the temperature, the hydrogen yield increases rapidly but the increase rate will be slowed when the temperature exceeds 700 °C. At the same temperature, the hydrogen yield increases with S/C as a whole. At higher temperatures of 700, 750, and 800 °C, S/C shows a slight effect on the hydrogen yield when S/C is more than 17. The maximum hydrogen yield at 56.3% is obtained at S/C of 20 and temperature of 800 °C. In Figure 2b, with the increase of the temperature, the CO yield increases gradually when the temperature is lower than 650 °C but the increase rate will be accelerated when the temperature exceeds 650 °C. When the temperature is over 700 °C, the increase rate reduced. In addition, S/C does not show an obvious effect on the CO yield, and the results are almost at the same level. The CO yield increases with S/C at the same temperature in the experiment. However, at lower temperatures of 500, 550, 600, and 650 °C, S/C does not show an obvious effect on the CO yield and the results are almost at the same level. At higher temperatures of 650, 700, 750, and 800 °C, the CO yield shows a decrease tendency with S/C. It is indicated that higher S/C favors the WGS reaction of CO under higher temperature (>650 °C) conditions. The effect of the temperature as well as S/C on the CO2 yield, carbon selectivity of gas products, and potential H2 yield were similar to that of H2. In addition, the CH4 yield increases slowly when the temperature is lower than 700 °C, but the increase rate rapidly increased when the temperature is more than 700 °C. Therefore, the optimum temperature is 700 °C. 3.2. Effect of the Temperature and WHSV. In this part, the reaction was carried out in the temperature range of 500-800 °C and S/C of 17 for the fluidized-bed reactor. Effects of the WHSV on results were shown in Figure 3. The results shown in panels a, d, and f of Figure 3 indicated H2 yields, CO2 yields, and potential H2 yields increased with the increase of the WHSV at first and then decreased when the WHSV is more then 0.4 h-1. That is to say, at the same temperature, the H2 and potential H2 yields achieved a maximum. In the panels b, c, and e of Figure 3, CO yields, CH4 yields, and carbon selectivity of the gas product decreased with the WHSV increasing. The reason could be due to the low fluidized efficiency caused by the low steam flow rate. The heat and mass transfers were limited under a low steam feeding rate. The higher WHSV caused a high bio-oil feeding rate, and some bio-oil components reacted inefficiently. Some unreacted bio-oil components were condensed in the liquid collector, and the H2 yield decreased. 3.3. Blank Experiment and Catalyst Deactivation. 3.3.1. Blank Experiment. In this section, the blank experiment was carried out for 1 h, under the same conditions of 700 °C, S/C of 17, WHSV of 0.4 h-1, and quartz sand of 200.0 g, to compare to the catalytic reforming experiment. The results shown in Figure 4 indicated that H2 yields, potential hydrogen yields, and the mole fractions of H2, CO, CO2, and CH4 changed little with the time on stream, which means that the thermal cracking of bio-oil was relatively stable in the blank experiment. 3.3.2. Catalyst Deactivation. In this section, the reactions were carried out over a long-term duration, i.e., 12 h, under the same conditions of 700 °C, S/C of 17, WHSV of 0.4 h-1, and catalyst of 200.0 g, to investigate the variation of the
H2 yield % moles of H2 obtained 100% ð8Þ ¼ ð2n þ m=2 - kÞ moles of carbon in the feed=n
CO ðor CH4 or CO2 Þ yield % ¼
moles of CO ðor CH4 or CO2 Þ obtained 100% moles of carbon in the feed
ð9Þ
The carbon element takes up 56.64% of the bio-oil weight on a dry basis, and the increase of the carbon element in the gas product means the decrease of carbon loss in the form of coke and unconverted reactant itself. We defined carbon selectivity of the gas product as follows: carbon selectivity of gas production % ¼
moles of CO, CH4 , and CO2 obtained 100% moles of carbon in the feed
ð10Þ
To obtain high-purity hydrogen production, hydrogen-rich syngas via steam reforming of bio-oil must be purified. In consideration of the following purification process, the watergas shift (WGS) reaction for CO is exothermic and can be carried out at relatively lower temperatures. However, for CH4, it is much more difficult than that for CO. For the endothermic reaction system, a high temperature and the presence of the catalyst are necessary to achieve the efficient conversion of CH4. At the same time, CO2 can be removed from the gas product easily by the alkali liquor absorption method. Therefore, the total content of H2 and CO can be regarded as the desirable potential H2 yield % moles of H2 and CO obtained 100% ¼ ð2n þ m=2 - kÞ moles of carbon in the feed=n
ð11Þ
When the mole flow rate of water in the feed (including steam and bio-oil) was designated as S and that of bio-oil in the feed was designated as C, the S/C in percentage was denoted as S=C ¼
moles of water in the feed of steam þ moles of water in the feed of bio-oil moles of carbon in the feed of bio-oil
ð12Þ The WHSV was defined as a ratio of the bio-oil feed weight flow rate and the weight of the loaded catalyst. WHSV ¼
weight flow rate of bio-oil feed weight of catalyst
ð13Þ
The experiments were carried out at u/umf = 31.2 (u/umf defined as the ratio between the superficial gas velocity and the velocity for minimum fluidization).
3. Results and Discussion In this part, the reaction proceeded in the presence of the nickel-based catalyst in the temperature range of 500-800 °C. The reaction is based on the same total bio-oil feeding content and fresh catalyst for every single investigation point. Three important influential parameters, which were the reaction temperature, S/C, and WHSV that had an effect on the hydrogen yield, as well as other data were investigated. 6458
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Figure 2. Steam reforming of the bio-oil effect of S/C on the (a) H2 yield, (b) CO yield, (c) CH4 yield, (d) CO2 yield, (e) carbon selectivity of the gas product, and (f) potential H2 yield. Experimental conditions: mass of catalyst, 200.0 g; particle diameter, 0.15-0.30 mm; bio-oil feed rate, 100 g/h; reaction time, 3 h; and WHSV, 0.5 h-1.
catalyst activity and the reason for catalyst deactivation with the time on stream. Figure 5 showed the effect of the time on stream on the gas product mole fraction and yield. The H2 and potential H2 yields decreased slightly with the time on stream, which means that the catalyst activity gradually reduced. However, the yield decreased rapidly when the reaction time was 8 h, and finally, the yield reached a plateau. The values of the H2 and potential H2 yields were almost the same with the blank test, which means that the catalytic activity may be completely lost, and then only the thermal cracking reaction but no catalytic cracking occurred. 3.3.3. BET Analysis of the Catalyst. The specific surface areas of the fresh and deactivated catalysts were measured with the instrument ASAP2420 through nitrogen adsorption. The results shown in Table 2 indicated that the BET surface area and average pore diameter of the deactivated catalyst are smaller than those of the fresh catalyst. This may be due to carbon deposition on the catalyst surface or pores or catalyst sintering at higher temperatures, which is one of the reasons for catalyst deactivation.
3.3.4. TGA Characterization of the Catalyst. TGA was carried out to quantify the carbon deposition content of reacted catalysts. The reacted catalyst was first ground to a powder, and a 30 mg sample was placed in the analyzer (Netzsch, STA 409 PC). The sample was initially heated to 100 °C under argon to outgas water. Then, a temperature ramp (10 °C/min from 100 to 1000 °C) was applied under atmosphere. A fresh catalyst sample was run under the same conditions as the blank test to revise the weight loss of reacted catalysts. Table 3 showed the effect of the time on stream on the carbon content of deactivated catalysts. From the results shown in Table 3, the carbon content of the deactivated catalyst is slightly higher than that of the fresh catalyst. This could be due to excessive water, causing eq 6 to move to the right side. That is to say, the higher S/C can favor the reaction of carbon elimination. The results indicated that, for steam reforming of bio-oil in a fluidized-bed reactor, carbon deposition is not a main reason for catalyst deactivation. This result was not the same as the results by Medrano et al.18 3.3.5. XRD Analysis of the Catalyst. The XRD spectra of the catalyst were obtained through diffractive analysis on 6459
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Figure 3. Steam reforming of the bio-oil effect of the WHSV on the (a) H2 yield, (b) CO yield, (c) CH4 yield, (d) CO2 yield, (e) carbon selectivity of the gas product, and (f) potential H2 yield. Experimental conditions: mass of catalyst, 200.0 g; particle diameter, 0.15-0.30 mm; reaction time, 3 h; and S/C, 17.
Figure 4. Effect of the time on efficiency of bio-oil to produce hydrogen (blank test). Reaction conditions: S/C, 20; temperature, 700 °C; WHSV, 0.4 h-1; quartz sand, 200.0 g; particle diameter, 0.15-0.30 mm; and bio-oil feed rate, 80 g/min.
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Figure 5. Effect of the time on the efficiency of bio-oil to produce hydrogen. Reaction conditions: S/C, 17; tempereture, 700 °C; WHSV, 0.4 h-1; catalyst, 200.0 g; particle diameter, 0.15-0.30 mm; and bio-oil feed rate, 80 g/min. Table 2. Pore Structure of Catalysts catalyst
BET surface area (m2 g-1)
average pore diameter (nm)
fresh catalyst deactivated catalyst
2.69 1.53
10.94 5.03
Table 3. Carbon Content of Fresh and Deactivated Catalysts catalyst
carbon content (wt %)
fresh catalyst deactivated catalyst
0.96 1.71
Figure 7. SEM images of fresh and deactivated catalysts: (a) fresh catalyst and (b) deactivated catalyst.
than those of the fresh catalyst, caused by the increasing of NiO grains, and catalyst sintering is the main reason for NiO grain growth. Therefore, NiO sintering is one of the reasons for catalyst deactivation. 3.3.6. SEM Analysis of the Catalyst. The SEM analyses were shown in Figure 7. From the results shown in Figure 7, the SEM image of the fresh catalyst looks like many leafshaped sheets, while the SEM image of the deactivated catalyst looks like scattered small balls. The surface of the deactivated catalyst did not find the carbon grains, which means that the catalyst crystal grains were growing up together. This result is the same as that of XRD. That is to say, the main reason for catalyst deactivation is that the active component of the catalyst was sintered in the carrier surface.
Figure 6. XRD spectra of fresh and deactivated catalysts: (a) fresh catalyst and (b) deactivated catalyst.
4. Conclusions a D/max-2500 X-ray diffraction instrument, equipped with a graphite monochromator and Cu KR as the radiation source, operated under the following conditions: tunnel voltage, 40 kV; current, 80 mA; and scanning scope (2θ), 10-80°. The XRD analyses of fresh and deactivated catalysts were shown in Figure 6. From the results shown in Figure 6, the diffraction peak is sharp, which indicated that the crystallization of the catalyst is in a good condition. The fresh and deactivated catalysts have a similar characteristic structure, which reveals that the skeleton structure of the catalyst does not change; however, the active composition of the nickel oxide peak and the area of the deactivated catalyst are more
The temperature is an important parameter in the process of bio-oil reforming to produce hydrogen. With the increase of the temperature, hydrogen production, potential hydrogen yield, and carbon selectivity of gas products also increased. The experimental results showed that the suitable reaction temperature was more than 700 °C. S/C is a key factor for increasing the hydrogen yield in the process of bio-oil reforming to produce hydrogen. The higher S/C is very favorable to improve the heat and mass transfers and leads eq 6 to the right side in the fluidized-bed reactor. That is to say, the higher S/C can favor the reaction of carbon 6461
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elimination but will increase the cost of producing hydrogen. The suitable S/C is 17 in the process of producing hydrogen. WHSV has a great role in the process of producing hydrogen. The lower WHSV decreased the heat and mass transfers and led to the decrease of the hydrogen yield. The higher WHSV increases the bio-oil feeding rate, and some bio-oil components reacted inefficiently. Some unreacted bio-oil components were condensed in the liquid collector, and the hydrogen yield decreased. The suitable WHSV is 0.4 h-1 in the process of producing hydrogen.
The results of BET, TGA, XRD, and SEM analyses showed that carbon deposition is not the main reason for catalyst deactivation. The main reason for fresh catalyst deactivation was the NiO grain sintered on the supporter surface. Acknowledgment. Financial support was provided by the “973” State Key Fundamental Research Development Program of China (2007CB210206) and the East China University of Science and Technology Outstanding Young Teachers’ Scientific Research Funds (YB0157109).
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