In this study, a series of Ni, Co mono and bimetallic catalyst supported by Mg and Al were prepared and evaluated for hydrogen production from various model /waste biomass samples via SCWG process. The SCWG tests were conducted at 650 °C, 26 MPa and water to biomass ratio of five. It was found that for catalyst preparation, coprecipitation technique is better than impregnation, and the best catalyst in terms of hydrogen yield is CopCat-2Ni4Co4. The hydrogen yield from different biomass with this catalyst was found to be in the order of: Canola meal \u3e Timothy grass \u3e Wheat straw ~ Lignin \u3e Cellulose. Canola meal was identified as a promising feedstock for hydrogen production from SCWG. Also, the effect of catalyst loading on hydrogen yield was investigated.It was confirmed that high catalyst loading up to 50 wt% is desirable for hydrogen production.
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Azargohar, Ramin

Dalai, Ajay K.

Kang, Kang

Shakouri, Mohsen

Wang, Hui

English

Engineering Conferences International

DEVELOPMENT OF NI-CO BIMETALLIC CATALYST FOR HYDROGEN GENERATION VIA SUPERCRITICAL WATER GASIFICATION OF LIGNIN AND WASTE BIOMASS  Kang Kang, University of Saskatchewan ajay.dalai@usask.ca Mohsen Shakouri, University of Saskatchewan Ramin Azargohar, University of Saskatchewan Ajay K. Dalai *, University of Saskatchewan Hui Wang *, University of Saskatchewan  Key words:  Supercritical water gasification (SCWG), hydrogen, biomass, catalyst, lignin  Abstract  In this study, a series of Ni, Co mono and bimetallic catalyst supported by Mg and Al were prepared and evaluated for hydrogen production from various model /waste biomass samples via SCWG process. The SCWG tests were conducted at 650 °C, 26 MPa and water to biomass ratio of five. It was found that for catalyst preparation, coprecipitation technique is better than impregnation, and the best catalyst in terms of hydrogen yield is CopCat-2Ni4Co4. The hydrogen yield from different biomass with this catalyst was found to be in the order of: Canola meal > Timothy grass > Wheat straw ~ Lignin > Cellulose. Canola meal was identified as a promising feedstock for hydrogen production from SCWG. Also, the effect of catalyst loading on hydrogen yield was investigated.It was confirmed that high catalyst loading up to 50 wt% is desirable for hydrogen production.  1. Introduction  For future, a sustainable hydrogen orientated energy system could be an ultimate solution for the world energy crisis, global warming and the atmospheric contamination caused by fossil fuel utilization [1, 2]. Waste biomass could be considered as a reliable precursor as it is abundant and carbon neutral. Supercritical water gasification (SCWG) is an attractive process for hydrogen production from biomass. As a main advantage, this process can directly handle wet biomass therefore reduces the high cost introduced by the drying process required for thermochemical processes [3]. Secondly, under supercritical water (SCW) condition which is: T ≥ 374 °C, P ≥ 22.1 MPa, rate of hydrolysis as well as gasification reactions are boosted which lead to fast generation of gaseous product  at relatively low temperatures as compared to conventional gasification process [4]. Catalysis is important for hydrogen production from SCWG. Specifically, without catalysts, reactions in SCWG suffer from high activation energy. Therefore, use of catalysts can potentially achieve promising conversion of biomass at lower temperature, which is crucial for reducing the cost of this process [5]. To fully evaluate the performance of catalyst used in this study, lignin (Lig), cellulose (Cel) as well as three types of waste biomass such as canola meal (CM), wheat straw (WS), and timothy grass (TG) were chosen. Wheat straw and Timothy grass are all abundant biomass in the province of Saskatchewan. Canola meal is the by-product of biodiesel industry and is generally used for animal feed, however, the issue of oversupply drives the need to utilize canola meal as renewable energy source [6].  2. Experimental section  2.1 Materials The catalysts used in this study were prepared as two groups using both impregnation and co-precipitation method. The co-precipitation (Cop) catalysts, which are noted as CopCat, was made by precipitating Ni and/or Co, Mg and Al from their nitrate salt solutions via aqueous ammonia solution titration. The impregnation (Imp) catalysts are noted as ImpCat. For these catalysts, firstly, the support of Mg and Al oxide was made by the co-precipitation procedure as depicted above. Then Ni and/or Co were loaded onto the support by incipient wetness impregnation using solution of Ni and/or Co nitrates. For all catalysts, drying was performed at 120 °C for overnight and the calcination was performed at 850 °C in air for 6 h. More details could be found in our earlier publication [7].   In terms of model biomass, the Kraft lignin sample and cellulose sample were purchased from Sigma Aldrich (Oakville, ON, Canada). Regarding waste biomass samples, wheat straw and timothy grass were provided by a local farm (Saskatoon, SK, Canada) and canola meal sample was provided by Milligan Biofuels Inc. (Foam Lake, SK, CANADA). The solvents used in this study included distilled water and HPLC grade acetone, which was supplied by Fisher Scientific (Ottawa, ON, Canada). The compressed nitrogen gas (N2) with high purity (> 99.998%) was purchased from Praxair Canada Inc. (Saskatoon, SK, Canada).  2.2 SCWG reactor, test procedure All the SCWG tests were performed using a batch type supercritical water reactor. Schematics of reactor and SCWG test procedure are depicted in detail in our previous publication [8]. The catalyst screening tests were performed at 650 °C, 26 MPa, with 0.65 g of lignin sample and 3.25 ml water. For each catalytic SCWG test, after sample loading, the reactor was sealed, and the leak test was performed before each experiment. Air in the reactor was then removed by using the vacuum pump. Then, the reactor was purged with N2 to provide a certain initial pressure to reach the final pressure of 26 MPa. During each run, the reactor was heated by the electrical furnace with a fixed heating rate of 30 °C/min and a fixed 50min residence time. It should be mentioned that the residence time include the time used for reactor heating up and reaction time at the desired temperature. The temperature of the furnace was controlled by the temperature controller and monitored/calibrated by a k type thermocouple.  Other experiments were performed at the same temperature, pressure and water loading but with different biomass and catalyst loading. Figure 1 shows the configuration of the SCW reactor used in this study. The reactor was made from 316 stainless steel tubing, with an O.D. of 0.95 cm and wall thickness of 0.17 cm. All parts were purchased from Swagelok Canada (Winnipeg, MB, Canada). The vacuum pump (Buchi V-700) was supplied by BUCHI Corporation (New Castle, USA). The laboratory tube furnace was supplied by Carbolite (Hope Valley, UK). Both the temperature controller (CN7500) and the K-type thermocouple were supplied by Omega Engineering Inc. (Stamford, USA).  For product collection, after each run, the furnace was immediately removed from the reactor, and the reactor was quickly cooled down using cold water spray. Then the gas phase products were released to the condenser and the fully stabilized gas phase products were collected from the vent line using a Tedlar bag. A desiccator was used to remove the moisture. Then, the reactor was disassembled from the setup. The liquid and solid products were collected from the reactor by sequentially rinsing with distilled water and HPLC grade acetone into clean beakers namely water phase and acetone phase products. All liquid and solid phase products (SCWG char) were filtered through filter paper (Whatman No. 2) for the separation of the solid phase products. Then by drying in the oven for 8h at 105 °C, the SCWG char was obtained. For some tests, spent catalyst were sorted out manually from the solid phase for analysis.   Figure 1 Schematic of the batch type SCW reactor  (Figure reproduced from reference [8], with permission from Elsevier)  FurnaceReactorV-2V-1CondenserV-5V-3V-4 Temperature ControllerFilterN2 InletDesiccatorTGas CollectionThermalcoupleVaccum Pump2.3 Characterization of SCWG product and biomass samples Analysis of the gas phase products was performed using an Agilent GC 7890A gas chromatograph (GC). The GC was equipped with a flame ionization detector (FID) and two thermal conductivity detectors (TCD). For all tests, a DB-1 column was used. Helium was used as carrier gas and column pressure was maintained at 22 kPa. Compounds were separated by a linear temperature program of 50 –280 °C (10 °C/min) and then at 280 °C for 10 min. The molar percentage composition of the gas phase was calculated using peak normalization method and the molar amount of N2 gas was used as reference.  2.4 Data interpretation For the results from SCWG tests, the hydrogen and gas yield, and hydrogen selectivity are defined as: (1) Hydrogen/Methane yield (mmol/g) = (Millimoles of hydrogen/methane produced per run)/(Grams of dry lignin sample used per run)                                                                                                        (2) Gas yield (wt %) = (Milligrams of gas produced per run)/(Milligrams of dry lignin sample used per run)                                                                                                                                                  (3) Hydrogen selectivity= (Hydrogen yield )/(2×Methane yield)                                                                               3.  Result and discussion  3.1 Catalyst screening 3.1.1 Effects of preparation method In total, two groups of catalysts were screened in this study, the results of SCWG test on lignin as well as the composition of the catalysts is given in Table 1, the ICP results are obtained from our previous work [7]. From the results, it is clear that in terms of preparation method, Cop is better than Imp for hydrogen yield. Generally, when only Ni or Co was used, Cop catalysts showed higher gas yield, however, the trend is not as clear when it comes to bimetallic catalysts. For example, the gas yield of ImpCat-3Ni3Co is a bit higher than that of the CopCat-2Ni4Co, but the difference is not significant. Also, as per the composition of these two catalyst, the Cop catalyst contains less Ni as active phase, which means other than preparation method, the difference of active metal also plays a role in the process, and this will be discussed later in this paper. In terms of hydrogen yield, the CopCat-2Ni4Co showed the highest value of 2.36 mmol/g, which is almost 2 times higher than that for the Imp Catalysts.  Table 1 Results of catalyst screening and composition by ICP              3.1.2 Catalyst Composition by ICP (%)  Gas yield （wt%） Hydrogen yield (mmol/g) Metane yield (mmol/g) Imp. Group Ni Co Mg Al       ImpCat-5Ni 5 0 65 30 8.2 ± 0.4 0.75 ± 0.02 0.78 ± 0.05 ImpCat-5Co 0 5 65 30 5.1 ± 0.3 0.81 ± 0.03 0.88 ± 0.04 ImpCat-3Ni3Co 3 3 67 27 14.2 ± 0.8 0.89 ± 0.08 0.90 ± 0.08 Cop. Group               CopCat-4Ni 4 0 69 27 10.5 ± 0.2 1.53 ± 0.09 0.93 ± 0.03 CopCat-6Co 0 6 69 26 5.6 ± 0.4 0.65 ± 0.02 1.79 ± 0.07 CopCat-2Ni4Co 2 4 68 26 12.9 ± 0.5 2.36 ± 0.13 1.36 ± 0.04 MgAlOx support 0 0 69 31 9.7 ± 0.4 0.59 ± 0.05 0.87 ± 0.06 Effects of active metal The effect of different active metals could also be understood from results in Table 1.First of all, no matter what is the preparation method, with single active metal, Ni always gave higher gas yield than Co. For example, the ImpCat-5Ni and CopCat-4Ni catalysts are given gas yield of 8.5 and 10.2 wt%, respectively, which are higher than that of the ImpCat-5Co (5.05 wt%) and CopCat-6Co catalysts (5.57 wt%).  In terms of hydrogen yield, a dependency on both preparation method and active metal was observed. Specifically, interestingly, within the Imp group, no matter how the composition changes, the hydrogen yield stays consistent. On the other hand, when Cop method was used, the hydrogen yield was in the order of: NiCo ˃ Ni ˃ Co. Hence, Ni is more active than Co for hydrogen production.  As undesired product, methane yield seems to also depend on both preparation method and active metal. On one hand, when Impregnation method was applied, no significant difference was found in methane yield by using different active metals. On the other hand, when Coprecipitation method was applied, the methane yield was in the order of Co ˃ Ni-Co ˃ Ni.   Based on the results, it could be concluded that the interaction between Ni and Co plays a role in both hydrogen and methane yield for both preparation methods. Generally, under SCW conditions, Ni is better than Co for hydrogen production. To obtain the highest hydrogen yield, however, Ni and Co should be both used as active phases and coprecipitation method should be applied for catalyst preparation.  3.2 Optimization of catalyst loading and biomass type 3.2.1 Effect of biomass type on gas/hydrogen yield and composition from waste biomass The SCWG test results of best catalyst (CopCat-2Ni4Co) using different biomass samples are listed in Table 2. According to the results, the gas yield from different biomass were in the order of: TG ~ CM > Cel > WS > Lig. Whereas the hydrogen yield from different biomass samples were in the order of: CM > TG > WS ~ Lig > Cel. The highest hydrogen yield was observed with CM as the feedstock, which is 3.94 mmol/g, therefore, in this study CM is the best biomass for hydrogen production.   Table 2 Effect of catalyst loading on hydrogen yield from SCWG of lignin  The gas phase                  composition of product from different biomass is given in Figure 2. It was found that in terms of model biomass, lignin tends to produce gas with higher hydrogen and methane proportion whereas for cellulose, CO2 is the dominant component, which contributes more than 50 mol% of the gas phase. In terms of real biomass, TG and WS showed similar composition for the gas phase, whereas CM showed higher hydrogen proportion and lower proportion of CO2. Biomass  Catalyst Gas yield (wt%) Hydrogen yield (mmol/g) Cel CopCat-2Ni4Co 16.5 ± 0.5 1.45 ± 0.08 WS CopCat-2Ni4Co 14.7 ± 0.8 2.2 ± 0.07 TG CopCat-2Ni4Co 20.5 ± 1.2 3.02 ± 0.09 CM CopCat-2Ni4Co 18.5 ± 0.8 3.94 ± 0.16 CM-Blank MgAlOx support 7.7 ± 0.5 1.13 ± 0.07  Figure 2 Effect of biomass type on gas phase composition  3.2.1 Effects of catalyst loading on gas yield/hydrogen yield from lignin   The effects of catalyst loading were also studied and the results are provided in Table 3. According to the result, the gas yield increased from 9.7 wt% to 12.4 with increase in catalyst loading from 0% to 75%.However, further increase in catalyst loading did not improve the gas yield.   The hydrogen yield increased from 0.6mmol/g to 2.14 mmol/g when catalyst loading increased from 0 to 50 wt%, no further increase was observed with increase in catalyst loading. Therefore, for hydrogen production, higher catalyst loading is desirable, but considering the cost, 50 wt% loading is adequate.    Table 3 Effect of catalyst loading on hydrogen yield from SCWG of lignin     0102030405060CH4 H2 CO2 C2-C4mol%TGCMWSLigCelCatalyst loading (wt%) Catalyst Gas yield （wt%） Hydrogen yield (mmol/g) 0 MgAlOx support 9.7 ± 0.4 0.59 ± 0.05 25 CopCat-2Ni4Co 11.1 ± 0.3 1.6 ± 0.03 50 CopCat-2Ni4Co 11.0 ± 0.7 2.14 ± 0.05 75 CopCat-2Ni4Co 12.4 ± 0.5 2.18 ± 0.10 100 CopCat-2Ni4Co 12.9 ± 0.5 2.36 ±0.13 4.Conclusion In this study, several catalysts were prepared and evaluated for hydrogen production from SCWG of biomass. During this study, it was understood that for Ni-Co bimetallic catalyst, coprecipitation method is better than impregnation method. In addition, Canola meal is identified as a promising feedstock for hydrogen production via this process.   Acknowledgement The authors gratefully acknowledge the financial support from the Natural Science and Engineering Research Council of Canada (NSERC), BioFuelNet Canada and China Scholarship Council (CSC).   References [1] D. Teichmann, W. Arlt, P. Wasserscheid, R. Freymann. A future energy supply based on liquid organic hydrogen carriers (LOHC). Energy & Environmental Science. 4 (2011) 2767-73. [2] S. Dunn. Hydrogen futures: toward a sustainable energy system. International Journal of Hydrogen Energy. 27 (2002) 235-64. [3] L.J. Guo, Y.J. Lu, X.M. Zhang, C.M. Ji, Y. Guan, A.X. Pei. Hydrogen production by biomass gasification in supercritical water: A systematic experimental and analytical study. Catalysis Today. 129 (2007) 275-86. [4] A. Kruse. Hydrothermal biomass gasification. The Journal of Supercritical Fluids. 47 (2009) 391-9. [5] Y. Guo, S.Z. Wang, D.H. Xu, Y.M. Gong, H.H. Ma, X.Y. Tang. Review of catalytic supercritical water gasification for hydrogen production from biomass. Renewable and Sustainable Energy Reviews. 14 (2010) 334-43. [6] R. Azargohar, S. Nanda, B.V.S.K. Rao, A.K. Dalai. Slow Pyrolysis of Deoiled Canola Meal: Product Yields and Characterization. Energy & Fuels. 27 (2013) 5268-79. [7] H. Wang, J.T. Miller, M. Shakouri, C. Xi, T. Wu, H. Zhao, et al. XANES and EXAFS studies on metal nanoparticle growth and bimetallic interaction of Ni-based catalysts for CO2 reforming of CH4. Catalysis Today. 207 (2013) 3-12. [8] K. Kang, R. Azargohar, A.K. Dalai, H. Wang. Systematic screening and modification of Ni based catalysts for hydrogen generation from supercritical water gasification of lignin. Chemical Engineering Journal. 283 (2016) 1019-32.   

Development of ni-co bimetallic catalyst for hydrogen generation via supercritical water gasification of lignin and waste biomass

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Development of ni-co bimetallic catalyst for hydrogen generation via supercritical water gasification of lignin and waste biomass

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