中国纤维素乙醇技术的研究进展

第19卷第7/8期化学进展Vol. 19 No. 7/82007年8月PROGRESS IN CHEMISTRYAug.,2007Advancing Cellulosic Ethanol Technology in ChinaBin Yang Charles E. WymanBourns College of Engineering-Center for Environmental Research and TechnologyUniversity of California, Riverside, CA, USA 92507)now faces very serious energy shortages and environmental pollution problems. Thus, the Chinesegovermment is encouraging ethanol use as an altemative transportation fuel by introducing fuel ethanol production anddistribution within several provinces. Although the current emphasis is on ethanol production from com and other grainsChina has huge quantities of low cost cellulosic biomass that could significantly expand ethanol production volume andduce feedstock costs. Over the last 20 years, a number of technical advances have dropped the cost of making cellulosicethanol from more than $4.00/ gallon to only about $1. 20-1. 50/ gallon for biomass costing about $44 per ton. At thiscost,ethanol is competitive for blending with gasoline, and several companies are working to build the first commercialcellulosic ethanol plants. Although these initial facilities will be relatively small to capitalize on niche opportunities andmanage risk, economies of scale appear to favor larger plants even though delivered biomass costs increase with demandand co-production of ethanol, chemicals, and electric power can provide important synergies. Advances in overcalcitrance of cellulosics are still needed to achieve competitive costs without subsidies, and strategic opportunities havebeen defined to reduce the cost of cellulosic ethanol sufficiently to become a low-cost pure liquid transportation fuelKey words cellulosic ethanol; research and development; commercialization; China中图分类号:TK6;S216.2文献标识码:A文章编号:1005-281X(2007)07/8-107204中国纤维素乙醇技术的研究进展杨斌 Charles e. WymanBoums College of Engineering-Center for Environmental Research and TechnologyUniversity of Califomia, Riverside, CA, USA 92507)摘要中囯面临着严重的能源短缺和环境污染问题,中国政府正在局部几个省份内政策性鼓励燃料乙醇生产和使用。尽管当前主要是用玉米和谷物作为生产乙醇的原料,然而中国具有大量潜在的低成本的纤维素生物质原料,可以极大地扩大乙醇的产量,降低原料成本。近20年来,由于技术的革命性进步,已使得纤维素乙醇的生产成本从4美元/加仑以上,降低至约1.2-15美元/加仑。其中,每吨生物质约44美元因此,目前乙醇掺汽油具有十分强的市场竞争力。已有几个公司正在建造首批商业纤维素乙醇工厂,虽然这些刚起步的小型设施在合理利用和管理上风险较小,但规模经济需要较大型工厂。尽管配送生物质原料的成本会随需求的增加而增加,但在乙醇生产基础上的生物精炼技术的发展,尤其是化工产品和动力的协同生将会使全过程的经济可行性大大提高。进一步深入的基础研究,将解决低成本下实现纤维素的完全利用,以确保在无政策性补贴的前提下,真正使纤维素乙醇成为具有市场竞争力的低成本纯液体燃料。关键词纤维素乙醇研究与开发商业化中国中国煤化工CNMHG收稿:2007年6月通讯联系人 e-mail: binyang@cert, ucr. edu第78期Bin Yang et al. Advancing Cellulosic Ethanol Technology in China1073Increased energy consumption is leading to serious five-carbon sugars arabilpetroleum shortages and environmental pollution problems high yields, new developments in genetic engineering nowin China. As the fastest growing economy with the largest make it possible to efficiently ferment both to ethanolpulation in the world, China has an interest in A portion of the pretreated solids, and possibly some ofadvancing and promoting the use of technologies and the liquid hydrostrategies for sustainable energy productionproduction step where an organism such as the fungusconversion of cellulosic biomass into ethanol being aTrichoderma reesei makes cellulase enzyme. Thisopportunity to address oil demands". Cellulosic biomass cellulase is then added back to the bulk of the pretreatedis abundant with prominent examples including solids to catalyze breakdown of cellulose to glucose, whichmany organisms, including common yeast, can ferment tosolid waste; and grasses and wood grown as dedicated ethanol. Next, the broth from both hemicellulose andenergy crops that may use non-arable land with low fossil cellulose fermentations is transferred to distillation andinputs, possibly reducing potential conflicts between land dehydration to recover ethanol. The lignin, enzymesuses for food versus fuel and also enhancing organisms, residual cellulose and hemicellulose, andFurthermore, cellulosic biomass is verery other unutilized solids are bumed to provide all of the heatexpensiveample, cellulosic biomass at about and electricity needed for the entire process with excess$44/dry ton costs about the same as petroleum at $6/leftbarrel based on an equal mass basis or about $13/barrel anaerobic and aerobic waste treatment process, with thefor equivalent energy content. Making ethanol from clean water discharged from the plant or recycled to thecellulosic biomass can be critical in meeting the growing procese, the sludge disposed of, and the methane fed toenergy demand in China as well as other developing the boiler. The ash from the boiler is landfilled[9countries as living standards are improved for more andCellulosic ethanol bioprocess technology was initiallyFurthermore, cellulosic ethanol is judged to be too expensive for industry to pursue butbecause it canpower of biotechnology to achieve close to theoretical application of the emerging field of bichnology thatyields with very low costs vital to commercial success, could dramatically reduce costs % to l. Through govemmentwith unparalleled environmental, economic, and strategic support over the last 25 years, a number of technical7advances in biological conversion dramatically reduced theTypically, biological conversion of cellulosic production cost from over $4.00/ gallon to be competitivebiomass to ethanol begins with biomass collection and with com ethanol now). However, although operatingtransportation operations that bring feedstock into the costs are low and the technology is readyplant, where it is stored and prepared for processing. commercialization of cellulosic ethanol faces importantNext, biomass is conveyed into the process where it is challenges. First, the technology is still not proven at afirst milled and then pretreated to open up its structure commercial scale, and investors are reluctant to take theand overcome its natural resistance to biological risk of first applications. In addition, capital costs aredegradation. In one pretreatment approach, dilute acid is high, particularly for the first commercial plants, andused to release sugars from hemicellulose into the liquid margins for commodity products such as ethanol are lowand prepare the cellulose in the remaining solids for Although the cost of cellulosic ethanol production hasenzymatic hydrolysis. The liquid hydrolysate containing potential to be competitive without tax incentives,themost of the hemicellulose sugars is conditioned to remove challen中国煤化工 wards has slowedor deactivate any compounds naturally released from the developtry throughmaterial or formed by degradation of biomass which inhibit privatCNMHGit pcuochemical industryorganisms and sent to a fermentation step to produce grew as a result of government imperatives during Worldethanol. Although natural organisms cannotferment the War I, government policy could serve a vital role in1074化学进展第19卷accelerating the emergence of a new cellulosic ethanol major cost element is also associated with overcoming thedustry. However, private investors tend to not trust recalcitrance of cellulosic biomass in the operations ofgovernment subsides that are vulnin enzyme production and enzymatic hydrolysis of biomass topolicy for capital intensive projects, and assurances must sugars. Thus, research targeted at advancing organisms toill not be stranded. For simplify the process and improve yields has great potentialexample, in light of the important economic, societal, for dramatically reducing costs, with the concept ofand strategic long term benefits of cellulosic ethanol, the consolidated bioprocessing(CBP)in which one anaerobicgovernment could provide a significant portion, say 40%or consortium of anaerobic organisms proof the capital costs of the first few projects to corenzymes to release sugars from hemicellulose and cellulosefor initial commercialization riskand ferment those sugars to ethanol. Although firstbstacle that has stalled build up of a cellulosic ethanol commercial plants will likely use residues or other low toindustry. Other govemment contributions such aszero cost feedstocks, ultimately research is needed toof research to improve the quality of performance datdevelop a new generation of energy crops with enhancedenhance the ability to predict large scalermancesustainability, yields, and reduced fertilizer demandscommerciization of the cellulosic grown on the non-arable land with ecological benefits andthat avoid potential conflicts between production of fuelTechnical opportunities have been identified to and food 3, i5. 16). Crops might also be engineered to befurther advance cellulosic ethanol technologies(), and more compatible with conversion technologwell targeted govemment support for advanced research enzyme and pretreatment costs while improving yieldswould dramatically lower costs. In particular, cellulosic Furthermore, production of fuels, chemicals, and powerbiomass has developed a natural resistance to release of its in the same facility has important economic synergiesconstituent sugars, and particular focus is needed on Thus, advances in the production of valuable co-productsovercoming the recalcitrance of biomass to conversion. In and power from residues left after cellulosic ethanolline with this, economic projections show that production can greatly enhance the impact of the cellulosicpretreatment is the single most expensive process step and ethanol industryhas a major impact on the cost and performance of thThe keyze currententire bioprocess system n, 1), Over the years, various technologies and develop next-gernerationbiological, chemical, and physical pretreatment enzymatic hydrolysis operations that can substantiallyapproaches have been studied in an attempt to increase reduce the cost of biomass processing to ethanol. Severalthe susceptibility of cellulose to attack by enzymes, and companies in the United States and elsewhere are strivingseveral chemical technologies appear particularlyto build the cellulosic ethanol manufacturing facilities buteverthe choice ofmust overcome the risk of initial applications. Faced withtechnology is not trivial and must take into account sugar critical natural resource, energy, and environmentalrelease patterns and solids concentrations for each issues, it is timely for China to consider commercializingpretreatment in conjunction with their compatibility with cellulosic ethanol to support its rapidly developingthe overall process, enzymes, and microorganisms to beeconomyapplied. Although interesting technologies are emergingReferencesour limited[1]Yang B,Launderstanding of pretreatment and related celluloseBiotechnology,2007,82(1):6-10hydrolysis. On this basis, a concerted effort is needed to [2]中国煤化工006,314(5805)better understand chemical and enzymaticechanisms and their interplay and apply that ki[3]CNMHG0,25(4):13-157[4] Farra E. Science,2006,312(5781):1748-1748to lower pretreatment and subsequent cellulose hydrolysis [s] wyman C E. Encyclopedia dfEnerry(ed. Cutler E).Scosts and expedite their commercialization. The secondLouis, MO: Elsevier, 2004. 541--555第7/8期Bin Yang et al. Advancing Cellulosic Ethanol Technology in China1075[6] Beck R J. Worldwide Petroleum Industry Outlook: 1998-200226157, 1999. National Renewable Energy LaboratoryProjections to 2007. 14th ed. Tulsa, Oklahoma: Penwell Books[11] Yang B, WymanCE. Asia Pacific Biotech New, 2007, 11(9):[7] Lynd LR, Cushman J H, NicholsR J, Wyman CE.Science1991,251(499):1318-1323[12] Lynd L R, Elander R T, Wyman C E. Applied Biochemstry and8]Ingram L O, Aldrich H C, Borges A CC, Causey T B, MartinezBiotechnology,1996,57/58:741-761A, Morales F, Saleh A, Underwood S A, Yomano L P, York S[13] Mosier N, Wyman C E, Dale B E, Elander R T, Lee YY,W, Zaldivar J, Zhou S D. Biotechnology Progress,1999, 15Holtzapple M R, Ladisch M. Bioresource Technology, 2005, 96(6):673-686[9] Wyman C E. Applied Biochemistry and Biotechnology, 2001, 91/ [14] Wyman CE, Dale B E, Elander rt, Holzapple M, Ladisch M93:5-21R, Lee YY. Bioresource Technology, 2005, 96(18): 2026-[10] Wooley R, Ruth M, Sheehan J, Ibsen K, Majeski H, Galve Acellulosic Biome to Ethanol process Design and Economics[15] Somerville C. Science,2006,312(57):1277-127Utilizing Co-Current Dilute AcidEnrymatie [16] Wyman C E. Biotechnology Progress, 2003, 19(2):254-262drolysis: Current and Futuristic Scenarios. NREL/TP-580中国煤化工CNMHG