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. 7/8200年8月PROGRESS IN CHEMISTRYAug.,2007Advancing Cellulosic Ethanol Technology in ChinaBin Yang Charles E. ymanBoums College of Engineering-Center for Environmental Research and TechnologyUniversity of California, Riverside, CA, USA 92507)Abstract China 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 andreduce 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 thisost,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 overcoming therecalcitrance 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)07/8-1072-04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 technoloUniversity 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,巳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产,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收稿:2007年6月通讯联系人 e-mail: binyang@cert, ucr.ed第7/8期Yang et al. Advancing Cellulosic Ethanol Technology in ChinaIncreased energy consumption is leading to serious five-carbon sugars arabinose and xylose to ethanol within China. As the fastest growing economy with the largest make it possible to efficiently ferment both to ethano/&pulation in the world, China has an interest in A portion of the pretreated solids, and possibly some ofproduction step where an organism such as the fungusconversion of cellulosic biomass into ethanol beiTrichodermareeset nakesopportunity 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, andecosystems=-4. Furthermore, cellulosic biomass is very other unutilized solids are burmed to provide all of the heatinexpensive: for example, cellulosic biomass at about and electricity needed for the entire process with excess$44/dry ton costs about the same as petroleum at $6/ left to sell. The liquid is processed through a combinedbarrel based on an equal mass basis or about $13/barrelanaerobic 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 process, the sludge disposed of, and the methane fed tomergy demand in China as well as other developing the boiler. The ash from the boiler is landfilled 9)countries as living standards are improved for more andCellulosic ethanol bioprocess technology was initiallymore people. Furthermore, cellulosic ethanol is judged to be too expensive for industry to pursue butparticularly promising because it can capitoffered thevances tpower of biotechnology to achieve close to theoretical application of the emerging field of biotechnology thatyields with very low costs vital to commercial success, could dramatically reduce costs 9. oJwith unparalleled environmental, economic, and strategic support over the last 25 years, a number of technicaladvances in biological conversion dramatically reduced theTypically, biological conversion of cellulosic production cost from over $4. 00/ gallon to be competitiveethanol begins with biomass collection and with com ethanol now ttransportation 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 challenge of high capital risk us. rewards has slowedor deactivate any compounds naturally released from the development of a cellulosic ethanol industry throughmaterial or formed by degradation of biomass which inhibit private investment. Justorganisms and sent to a fermentation step to produce grew as a result of government imperatives during Worldethanol. Although natural organisms cannot ferment the War I, government policy could serve a vital role in化学进展第19卷accelerating the emergence of a new cellulosic ethanol major cost element is also associated with overcoming theindustry. However, private investors tend to not trust recalcitrance of cellulosic biomagovemment subsides that are vulnerable to changes in enzyme production and enzymatic hydrolysis of biomass topolicy for capital intensive projects, and assurances must sugars. Thus, research targeted at advancing organisms tobe made that the capital will 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%, organism or consortium of anaerobic organisms produceof the capital costs of the first few projects to compensate enzymes to release sugars from hemicellulose and cellulosefor initial commercialization risk, overcoming the major and 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 as support zero cost feedstocks, ultimately research is needed toof research to improve the quality of performance data and develop a new generation of energy crops with enhancedenhance the ability to predict large scale performance sustainability, yields, and reduced fertilizer demandswould also speed commercialization of the cellulosic grown on the non-arable land with ecological benefits and9that avoid potential conflicts between production of fuelTechnical opportunities have been identified to and food. Crops might also be engineered to befurther advance cellulosic ethanol technologies(), and more compatible with conversion technologies, reducingwell 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 orThus, advances in the production of valuable co-productovercoming the recalcitrance of biomass to conversion. In and power from residues left after cellulosic ethanolline with this, economic projections show that production can greatly enhanceact of the cellulosicpretreatment is the single most expensive process stephas a major impact on the cost and performance ofThe key now is to successfully commercialize currentprocess systerOver the years. varioustechnologies and develop next-generation pretreatment andbiological,chemical, and physical pretreatment enzymatic hydrolysis operations that can substantiallypaches have been studied in an attempt toIncreasereduce 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 particularly to build the cellulosic ethanol manufacturing facilities butHowever, the choice of pretreatmentmust overcome the risk of initial applications. Faced withtechnology is not trivial and must take into account sugarritical natural resource, energy, and environmentalrelease pattems and solids concentrations for each issues, it is timely for China to consider commercializingpretreatment in conjunction with their compatibility with cellulosic ethanolsupport its rapidly developingthe overall process, enzymes, and microorganisms to be conomypplied. Although interesting technologies are emerginghas slowed, in part dueour limited[1] Yang B, La Y. Joumal of Chemical Technology anunderstanding of pretreatment and related celluloseBiotechnology,2007,82(1):6-10hydrolysis. 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