Process conditions of preparing methanol from cornstalk gas

Available online at www.sciencedirect.comJOURNAL OF..ENVIRONMENTAL .。ScienceDirectJESISN 1001-0742. 000Journal of Environmental Sciences 19<207) 628 632www.jesc.ac.cnProcess conditions for preparing methanol from cornstalk gasZHU Ling-feng*, DU Lei, LI Xin-bao, LI Guo-ting, ZHANG JieDepartment of Environmental Engineering, North China Institute of Water Conservancy and Hydroeletric Power,Thengzhou 450011, China. E-mail: Ufthu. yrc@yahoo.com.cnReceived 17 March 2006; revised 24 May 2006; accepted 25 December 2006AbstractThe low-heat- value cornstalk gas produced in the down-flow fixed bed gasifier was tentatively used for methanol synthesis. Thecornstalk gas was purified and the technical procedures such as deoxygenation, desulfurization, catalytic cracking of tar, purificationand hydrogenation were studied. The catalytic experiments of methanol synthesis with cornstalk syogas were carried out in a tubular-flow integral and isothermal reactor. The efect of reaction temperature, pressure, catalyst types, catalyst particle size, syngas flow atentering end and composition of syngas was investigated. The optimum process conditions and yield of metbanol from cornstalk syngaswere obtained. The experimental results indicated that the proper catalyst for the synthetic reaction was C301 and the optimum catalystsize was 0.833 mm x 0.351 mm. The optimum operating temperature and pressure were found to be 235°C and 5 MPa, respectively.The suitable syngas fow 0.9-1.10 mol/h at entering end was selected and the best composition of syngas were CO 10.49%, CO2 8.8%,N2 37.32%, CHm 0.95% and H2 40.49%. The best methanol yield was 0.418 g/g coristalk. This study provided the technical supportfor the industrial test of methanol production from biomass cornstalk) gas.Key words: cornstalk syngas; fuel gas; purification; catalyst; methanol; synthesisIntroductionThe technology of methanol catalytic synthesis frombiomass is an effective approach for the utilization of agri-Biomass is a kind of renewable energy resource andcultural residues. Meanwhile, methanol is mainly madeits utilization has caused so much attention all over thefrom fossil fuel such as natural gas, oil and coal, andworld. China is one of the largest agricultural countriesthe technology for methanol synthesis from biomass haswith extremely rich biomass resources and a great amountnot been developed till now. In fact, methanol can beof agricultural residues are produced every year, in whichproduced from the original biomass. Some countries suchthe cornstalk amounts to about 100 million tons (Gaoeral, as America and Japan began to study the technology more2003). However, most of the cornstalks are discarded orthan twenty years ago (Baker et al, 1983; Beenackersburnt easily and only a small portion is utilized. It leads toand van Swaaji, 1984; Baker and Brow, 1984; Borgwardt,serious environmental pollution and wastes a large amount1998; Demirbas, 2000; Tsutomu, 2000; Goudeau et al,of resources. Therefore, the utilization of biomass becomes1983; Helena and Ralph, 2001; Hirano et al, 1998; Palmer,an urgent need and biomass gasifying is selected till1984) and many methanol factories are running now.now. The commercial equipments of biomass gasifying areHowever, expensive equipments are always employed inclassified as the up-flow and down-flow fixed bed gasifierthe methanol factory, which hinders the development ofto produce low-heat-value fuel gas (4 6 MJ/nm3), whichmethanol synthesis in China. The equipments for biomasswas mainly used for cooking and heating in the countrysidegasifying are relatively cheap enough to be used in mostor the outskirts of town. Most of the biomass gasiferpart of China but the resulted fuel gas is always directlyruns only 3- 4 h every day because of the low utilizationused without any treatment. In this research, the low-ratio of biomass fuel gas. In addition, the fuel gas leadsheat-value fuel gas was made from cornstalk in a cheapto pollution of the underground water due to its highdcwn-flow fixed bed gasifier and is firstly utilized tocontent of tar and block of the fuel gas installation whichproduce methanol after purification through the fuel gas,involves higher cost of maintenance. It is necessary torntont of nitrogen. This workfurther study the exploitation of the biomass resources for was中国煤化工: methanol from low-high- grade products and to utilize the renewable resourcesheat-|YHC N M H Gn approach would bemore reasonably and effectively.preferaulc luruculuIass u auisiun mation into methanol.Project suppored by the Foundation of Science and Technology of HenanProvince (NO. 0324210047). *Corresponding author.E-mail: lfzhu_yrcc@yahoo.com.cn.No.5Process conditions for preparing methanol from cornstalk gas6291 Experiments and methodswere used in these experiments. The cylindrical catalystwas ground into particles with the size of 0.991 mm x1.1 Preparation of biomass feedstock gas and syngas0.833 mm, 0.833 mm x 0.351 mm, 0.351 mm x 0.246mm, 0.246 mm X 0.175 mm, dried over heat and cooled1.1.1 Preparation of biomass feedstock gasto the room temperature. The same size quartz sand wasThe feedstock of cornstalks was gathered from themixed evenly after weighed. A proper thin layer of quartzfarms of Xinzheng, Henan Province, China. The averagesand (particle size is 0.833 mm X 0.351 mm) was ftteddiameter of the cormnstalks is about 3 cm and the corstalksin catalytic reaction pipe, then experimental catalyst withwere processed in XFF- 1000 Biomass Gasifier producingdifferent size was added slowly. Finally, the quartz sandthe biomass gas of low heat value (LHV). The analysis datawith particle size of 0.833 mm x 0.351 mm, china ringof feedstock gas from cornstalks are given as follows: COof 0.991 mm x 0.833 mm and thin copper wire were15.80%, CO2 12.50%, H2 12.60%, CH4 1.40%, O2 2.07%,put into orderly and pressed solid. The catalytic reductionC2H4 0.50%, CzH6 0.10%, C2H2 0.03%, N2 55.00%, LHVcondition was the same as that of industrial catalyst (Fang5873 kJ/m, tar 24.6 mg/m', and sulfides 3.48 mg/L.et al., 1990). The synthetic experiment could not be done1.1.2 Preparation of biomass syngasunless the catalyst activity was stable by test after reducedThere are still a small amount of oxygen, sulfide, andfor 86 h.tar in feedstock and they can destroy the catalytic activity 1.2.2 Experimental processesof catalyst. There is a great need to remove them fromFig.1 presents the experimental circuit. It shows that thethe fdstock gas before use. In addtion, the content of biomass syngas entered the reaction vesel afer it cameH2 is too low to satisfy the theoretic ratio required byout from steel bottle, then flowed through control valvecarbon and hydrogen in synthetic process. Therefore, thewhich control the pressure to be the same as the mainfeedstock gas was pretreated for desulfurization, deoxy,reaction. Methanol and water were separated when thecatalytic cracking of tar, purification and hydrogenation.gas flowed through condenser at the end of reaction. ThTR catalyst made by authors themselves was used forremaining gas was reduced to atmospheric pressure bytar cracking. Active carbon and thin copper wire acted aspressure reducer valve. One part of the gas measured bydeoxidizer and ZnO power was used for desulphurization.flowmeter was tapped. The other part flowed into gas chro-The following experiments were conducted between 600-matograph where automatic collection and data processing800°C in a 623-1.3 Type tubular electric stove using ZK-1were finished by chromatographic working station (Zhu etsilicon voltage regulator. It was proved that the contental, 2003).of sulfide was about 1.2x10 3 mg/L and oxygen and tarThe biomass syngas contained eight chemical compo-were not determined in the pretreated feedstock gas. Thenents (CO, CO2, H2, N2, CH4, C2H2, C2H6, C2H4) amongbiomass syngas was prepared by adding a definite amountwhich three reactions occurred over the Cu-supportedof high pure hydrogen in the pretreated feedstock gas.catalyst:Then the biomass syngas was compressed into a highpressure steel bottle through compressor and reserved for CO + 2H2= = CH:OH(1)two months before use. The components of biomass syngas CO2+3H2= CH3OH + H2O(2treated from feedstock gas are presented in Table 1.CO2+H2= CO+ H20(3Table 1 Components of biomass syngas treated from feedstock gasThe Reactions (1) and (2) are exothermic, so themolecular number becomes less after reaction. ReactionH2 (%)CO(%)CHm*(%) Nz (%)(3) absorbs heat and the molecular number is unchanged30.4-75.775.85-13.16 3.23-10.55 0.37-1.3517.7-45.38 before and after reaction. The theory of chemical reactions*CnHm=CH, C2H2, C2H4, C2H.宫291.2 Experimental equipments and processes-下6661.2.1 Main experimental equipments and catalyst re-2|ductionThe following experimental devices in methanol syn-thesis were used: JA-Five troughs direct-fow isothermnalintegral reactor (the size of reaction pipe is 14 mm X 292:mm and 110 mm long; homothermic region is about 5 cm;中国煤化工’the difference in temperature is in the range from +0.5 to-0.59C); TCS-A itellectual temperature contoller; ZK- Fig. 1sMYHCN M H G (1) bomss syegs; (2)50 silicon voltage regulator; YF-2 pressure control valve;methanol synthesis reactor; (3) pressure control valve; (4) productGC-900C gas chromatograph; HW-2000 chromatographiccollector, (5) condenser; (6) rotor flow meter; (7) compressor, (8)temperature controller; (9) power and control board; (10) temperatureworking station; precision pressure gauge, rotor flowmeter.programmer, (1) gas chomalograph; (2)arrner gas;(13) data counter,Homemade Cu-supported catalysts (C301, C302, NC306)(14) computer.630ZHU Ling-feng et al.Vol. 19 .shows that the increase of pressure and the decrease oftemperature are beneficial to the two synthesis reactions(1) and (2). By changing one of the six technologicalparameters- temperature, pressure, catalyst, catalyst size,2:composition of syngas, and syngas flow at entrance (the62other five parameters remained constant), the seeking ofthe optimum experimental parameters were accomplished(every experiment was repeated three times), and better10technological conditions of methanol synthesis were ac-Pressure (MPa)cordingly obtained.Fig. 3 Infuence of reaction pressure time-space yield of CHjOH. Tem-perature:. 2359C; catalyst C301 with size: 0.991 mm x 0.833 mm;2 Results and discussioncomposition of entrance syngas (%): CO 12.95, CO2 10.55, N2 43.82,C.Hm 1.35, H2 31.48.2.1 Reaction temperature and pressurevaried from 5-7 MPa. It was proved that the ratio of time-The conditional experiments for reaction temperaturespace yield of methanol to pressure is the highest at 5 MPa.were caried out with C301 calysty by changing tem- So 5 MPa was chosen in the flowin experiments.perature between 220°C and 261°C to find out the effectof temperature on time-space yield of CHzOH under the2.2 Catalyst and size of the particlepressure 5 MPa when the other conditions of the reactionSelection of low pressure catalyst for methanol synthesisremained constant values. The experimental results pre-is regarded as a key solution to reduce the productionsented in Fig.2 indicate that reaction temperature exertscost of methanol. Cu-supported catalyst is commerciallya tremendous influence on the chemical equilibrium andavailable and characterized as high activity and selectivity.reaction rate of reactants. The time-space yield of methanolIt is industrially used in methanol production from coal bychanged in parabola pattern with the increased tempera-many factories in China. Three kinds of low pressure Cu-ture. The optimum temperature under the given conditionsupported catalyst: C301, C302, NC306 were employedwas at 235°C with CH3OH yield of 25%.The effect of reaction pressure of cornstalk syngas werein the experiments. The experiments were carried out atinvestigated by changing reaction pressure between 4 and 8235°C and 5 MPa pressure for each kind of Catalyst bychanging the entrance syngas-flow. The results presentedMPa when the other conditions remained constant. The ex-in Fig.4 ilustrates that the time-space yield of methanolperimental results are presented in Fig.3 and it is observedis the highest using catalyst C301, while the lowest withthat the time- space yield of methanol increased graduallycatalyst NC306 under the other identical conditions. Al-with the increasing reaction pressure. The changing ratiothough the experimental results indicate that all these threeof time -space yield to pressure (slope of the curve) is lowkinds of catalyst can be used to synthesize methanol withat the pressure of 4 and 8 MPa, and comparatively higher atcormstalk syngas, it is obvious that C301 is the best one5, 6 and 7 MPa. Subsequent experiments were conductedfor methanol synthesis. The composition of C301 Cu-under other identical conditions and the reaction pressuresupported catalyst are CuO (58.1%), ZnO (31.7%), Al2O3(30.06%) and H2O (4.0%).5「The optimum catalyst particle size was also investigated.0上Catalyst C301 was employed and the related experimentswere conducted with different particle sizes of catalyst15 十under above- mentioned conditions and the results arepresented in Table 2.Table 2 indicates that both the conversion of carbonmonoxide and time-space yield of methanol increased withthe decrease of particle size of catalyst. However, the210220 230 240 250 260 270conversion of carbon dioxide changed in the same trendTempernture(C )as that of carbon monoxide and methanol except when theFig. 2 Infuence of reacton temperature on time space yield of CH3OH. catalyst particle size of 0.833 mmx0351 mm was selected.Pressure 5 MPa; catalyst C301 with size: 0.833 mm x0.351 mm;catalyst It is also observed that the yield of methanol varied inweight: 5.1532 g; composition of entrance syngas (%): CO 11.41, CO2a small range. In addition, the power consumption will8.96, Nz 37.63, C.Hm 1.03, H2 42.9.increase rapidly due to the sharp pressure drawdown usingTable 2 Eftet of calyst particle sizes on the conversion of (中国煤化工-OHParticle size of catalyst (mm)0.991 x 0.833THC NMH G_0.246 x 0.175Conversion of CO (%)12.3716.9818.7920.23Conversion of CO2 (%)0.300.270.872.01Time-space yield of CH3OH (102 kg/(kg cath))10.0213.3614.3916.10Pressure: 5 MPa; temperature: 235*C; catalyst: C301; composition of entrance syngas (%): CO 13.16, CO2 9.84, N2 45.38, CnHm 1.16. H230.4.No.5.Process conditions for preparing methanol from comnstalk gas63140+*、0.09卜 b-- C301会36|。二C2020.08 F王3-中- C302-- NC3060.07 F32-825 F2120-.05 t”2604-24i 15十22200.81.21.62.02.42.83.2Plow of cttaoce syngas (mol/h)Flow of entrance syogs (molh)Flow of entrance syngas (mol/b)Fig.4 Efet of dferet calyt on CO covesion () CO2 corversion (b)and CHgOH time space yield (e), rsecively Pessue: 5 MPa; empeatur:2359C; catalyst: C301, C302 and NC306 with size: 0.991 mm x 0.833 mm, composition of entrance syngas (%): co 11.2, CO2 5.98, N2 32.73, CnHm0.76, H2 46.61.the small size of catalyst particle. Therefore, the optimum 40.49%.particle size of catalyst is 0.833 mmx0.351 mm.2.4 Flow of entrance syngas2.3 Cornstalk syngas ratioThe fow velocity of entrance syngas is also regard-The composition of the cornstalk syngas is also aned as a key parameter which would influence the yieldimportant parameter to be investigated during methanolof methanol greatly. The experiment was conducted byproduction. Five kinds of cormstalk syngas with differentchanging the fow velocity of entrance syngas under otherproportion of components were prepared according to theidentical conditions.designed reaction condition. The effect of the content ofFig.5 ilustrates the efct of flow of the entrance syngas.each component in syngas on the yield of CHzOH underIt was observed in Fig.5a that the conversion of CO de-the other identical conitions was determined experimen- creased gradually with the continuous increase of entrancetally by keeping the other parameters constant. The resultssyngas flow. Fig.5b demonstrates that the conversions ofare presented in Table 3.CO2 increased at first, then came to a drop, and subse-The experimental results show that the conversionsquently came to a rise and a drop again. When the flowof Co and CO2 are the highest when hydrogen-carbonvelocity of entrance syngas is 1.1 mol/h, the conversion ofratio (mol) value is 7.08, but the concentration of themCO2 reached the maximum value 6.85%. Fig.5c indicateswas lower in reaction system. The time-space yield ofthat time-space yield of CH3OH also increase at first, thenCHgOH gained by test was not the highest yet, because thedrop. The changing slope of time-space yield of CH3OHinverse alternation reaction of CO2 strongly restrained theis relatively small and the entrance syngas flow velocityconversion from CO2 to methanol in high concentration ofis in the range of 0.49-1.62 mol/h. When the syngas flowH2. The time space yield of CH2OH is the highest whenvelocity is 1.10 mol/h, the time space yield of CH3OHM value is 1.71 and thereater the proper composition of reached the maximum. Based on all the above results, thecornstalk syngas under the experimental condition are COentrance syngas flow velocity in the range of 0.9-1.1010.49%, CO2 8.8%, N2 37.32%, CjHm 0.95%, and H2mol/h was selected.10「b0.51.01.52.0253.08。0051.01.52.0253.0日60°051.01.520253.0Synags flow (mol/b)Synags fnow (mo/h)Synags flow (mol/h)Fig. 5 Infuoence of syngas flow (entrance) on CO conversion (a), CO2 conversion (b) and time space yield of CHsOH. Pressur: 5 MPa; temperaure:2359C; catalyst C301 with size: 0.246 mm x0.175 mm; composition of entrance syngas (%): CO 9.36, CO2 6.85, N2 32.92, CjHm 0.81, H2 50.81.Table 3 Efet of syngas composition on time space yield of CHzOHSyngas composition (%)Ratio ofConversionTime- space yield of CHzOHCOCO2N2CnHmHH2/(CO+ 1.5CO2)中国煤化工-102 k/(kg cath)13.099.842.631.1231.461.13F.9810.4937.320.9540.491.71CHCNMHGo.819.226.8531.9951.12.6215.889.2314.758.64 .5.0327.690.6561.853.8219.465.3912.375.853.230.3775.777.0822.6226.4016.43Pressure: 5 MPa; temperature: 2359C catalyst: C301 with size: 0.246 mm x 0.175 mm.63ZHU Ling-feng et al.Vol. 19Under the optimum experimental conditions examinedReferencesabove, 0.418 g methanol could be obtained from 1 gof cornstalk. Some reports suggest that 0.283- 0.487 gBaker E G, Elliott D C, Stevens D J, 1983. Transportation fuclsof methanol are yielded from 1 g of woody biomassfrom wood[J]. Altern Energy Sources, 3(3): 363- 376.(including wood chips, pine bark, straw and bagasseBaker E G, Brow M D, 1984. Catalytic steam gasification ofpellets, etc.) by optimizing the gasification and synthesisbagasse for the production of methanol[J]. Energy Biomassconditions (Beenackers and van Swajj, 1984; Baker andWastes, 8: 651-674.Brow, 1984; Borgwardt, 1998; Demirbas, 2000; Tsutomu,Beenackers A A C M, van Swaaji W P M, 1984. Methanol from2000; Goudeau et al, 1983; Helena and Ralph, 2001;wood[]. Sol Energy, 2(5); 349 -367.Hirano et al, 1998; Palmer, 1984). It is also reported thatBorgwardt R H, 1998. Methanol production from biomass and0.64 g of methanol is yielded theoretically from 1 g ofnatural gas as transportation fuel[J]. Ind Eng Chem Res,microalgal biomass (Hirano et al, 1998). The methanol37(9): 3760- 3767.yield from comnstalks in experiments was in accord withDemirbas A, 2000. Biomass resources for energy and chemicalthe above cases of woody biomass and was lower than theindustry[J]. Energy Educ Sci Technol, 5(1): 21 45.theoretical value from microalgal biomass. The microal-FangD Y, YaoP F, Zhu B C, 1990. Production technology ofgal biomass did not need purification due to small andmethanol and procceding[M]. Shanghai: Publishing Houseuniform particles and thus the complete gasification andof Hua Dong Chemical-Industrial College. 167-170.the optimum process conditions are explored to get higherGaoZJ, LiXJ, Yang D Y et al, 2003. Anaerobic digestionmethanol yield.of cornstalk for biogas production: ambient Vs. mesophilictemperature[J]. Transactions of the CSAE, 19(5): 214 -217.3 ConclusionsGoudeau J C, Bourreau A, Souil F, 1983. An investigation onMethanol was creatively designed to produce from themethanol catalytic synthesis from biomass gases[J]. Energylow-heat-value cornstalk gas in a comparatively cheapRes, 3: 191-202.down-flow fixed bed gasifier. The optimum experimentalHelena L C, Ralph P O, 2001. Biomass and renewable fucls[].conditions for methanol synthesis with cornstalk syngasFuel Processing Techunology, 71: 187-195.were examined in order to lower the production cost.Hirano A, Hon-Nami K, Kunito S et al, 1998. TemperatureIt was proved that the yield of CH3OH reached 0.418effect on continuous gasification of microalgal biomass[D].g/g cornstalk under the optimum experimental conditionCatalysis Today, 45(1-4): 399- 404.examined. The optimum experimental condition in thisPalmer E R, 1984. Gasifcation of wood for methanol produc-research is selected as the follows. The temperature andtion[]. Energy Agric, 3(4): 363 -375.pressure of synthetic system are controlled at 2359C andTsutomu S, 2000. Catalyst technology used in biomass conver-5 MPa; C301 catalyst with particle size of 0.833 mmsion into liquid and gaseous fuels[]. Appl Catal, 42(7):x 0.351 mm is employed in the synthetic reaction; th521-525.suitable syngas flow at entering end is 0.9-1.10 mol/h; theZhu L F, Zhang B L, Liang G B et al, 2003. Methanol synthesisbest composition of syngas is CO 10.49%, CO2 8.8%, N2from cormstalk by the thermochemical method[J]. Joumal37.32%, C.Hm 0.95% and H240.49%.of Henan Agricultural University, 37(4): 400- 405.中国煤化工MYHCNMHG