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Trends in biotechnological production of fuel ethanol from different feedstocksIntroductionEthanol from sugarsBatch and semicontinuous processesContinuous processesEthanol from starchHydrolysis of starchEthanol production from cornEthanol production from wheatEthanol production from cassavaEthanol production from other starchy materialsEthanol from lignocellulosic biomassPretreatment of lignocellulosic biomassPhysical methodsPhysical-chemical methodsChemical methodsBiological methodsDetoxification of lignocellulosic hydrolyzatesHydrolysis of celluloseFermentation of biomass hydrolyzatesSeparate hydrolysis and fermentationSimultaneous saccharification and fermentationFermentation of pentosesComparison of the main types of feedstockConclusionsAcknowledgementsReferencesThis paper contains a lot of good information on ethanol production from both sugar sources (grain, sugar cane, etc.) and cellulosic material. Please use only the information pertaining to cellulosic sources as we will cover sugar ethanol earlier in the semester.ReviewTrends in biotechnological production of fuel ethanolfrom different feedstocksO´scar J. Sa´ncheza,b, Carlos A. Cardonaa,*aDepartment of Chemical Engineering, National University of Colombia at Manizales, Cra. 27 No. 64–60 Of. F-505, Manizales, Caldas, ColombiabDepartment of Engineering, University of Caldas, Calle 65 No. 26–10, Manizales, Caldas, ColombiaReceived 12 July 2006; received in revised form 4 November 2007; accepted 6 November 2007Available online 26 December 2007AbstractPresent work deals with the biotechnological production of fuel ethanol from different raw materials. The different technologies forproducing fuel ethanol from sucrose-containing feedstocks (mainly sugar cane), starchy materials and lignocellulosic biomass aredescribed along with the major research trends for improving them. The complexity of the biomass processing is recognized throughthe analysis of the different stages involved in the conversion of lignocellulosic complex into fermentable sugars. The features of fermen-tation processes for the three groups of studied feedstocks are discussed. Comparative indexes for the three major types of feedstocks forfuel ethanol production are presented. Finally, some concluding considerations on current research and future tendencies in the produc-tion of fuel ethanol regarding the pretreatment and biological conversion of the feedstocks are presented.Ó 2007 Published by Elsevier Ltd.Keywords: Bioethanol; Sugars; Starch; Lignocellulosic biomass; Ethanolic fermentation1. IntroductionWorld faces the progressive depletion of its energeticresources mainly based on non-renewable fuels. At thesame time, energy consumption grows at rising rates. TheUSA is the first oil consumer, but China’s spectacular eco-nomic growth has imposed serious pressure on the oil mar-ket. Global panorama in that market is dark. Permanentcrises in the Middle East and the speculation in the stockexchange, among other factors, have caused the oil priceto reach such elevated values of 100 dollars per barrel.World economy could experience stagnation if the oilmaintains these high prices. In addition, the intensive utili-zation of fossil fuels has led to the increase in the genera-tion of polluting gases released into the atmosphere,which have caused changes in the global climate. The solu-tion to this problematic dep ends on how the developmentand implementation of technologies based on alternativesources of energy will be undertaken. Through the use ofrenewable energetic resources, humankind can find partof the solution to their energy requirements in an environ-mentally friendly way.One renewable solution is the use of solar energy in formof biomass (bioenergy). Global potential of bioenergy isrepresented in energy crops an d lignocellulosic residues.Conversion of these feedstocks into biofuels is an impor-tant choice for the exploitation of alternative energysources and reduction of polluting gases. In addition, theutilization of biofuels has important economic and socialeffects. For instance, Sheehan and Himmel (1999) pointout that the diversification of fuel portfolio would bringmoney and jobs back into the USA economy. Moreover,the development of energy crops dedicated to the biofuelsproduction would imply a boost to agricultural sector. Thisanalysis is also valid for developing countries, especially inLatin Ame rica, considering the perspective of drasticreduction of proven oil reserves in the mid term. In addi-tion, agricultural products from developing countries have0960-8524/$ - see front matter Ó 2007 Published by Elsevier Ltd.doi:10.1016/j.biortech.2007.11.013*Corresponding author. Tel.: +57 6 8810000x50417; fax: +57 6 8810000x50193.E-mail address: [email protected] (C.A. Cardona).Available online at www.sciencedirect.comBioresource Technology 99 (2008) 5270–5295to face a fierce competition from rich countries that granthuge subsidies for their agricultural production.Ethanol (ethyl alcohol, bioethanol) is the mostemployed liquid biofuel either as a fuel or as a gasolineenhancer. Ethanol has some advantages when it is usedas an oxygenate. Firstly, it has a higher oxygen co ntent thatimplies a less amount of required additive. The increasedpercentage of oxygen allows a better oxidation of the gas-oline hydrocarbons with the consequent reduction in theemission of CO and aromatic compounds. Related toMTBE, ethanol has greater octane booster properties, itis not toxic, and does not contaminate water sources. Nev-ertheless, ethanol production costs are higher than those ofMTBE, gasoline mixed with alcohol conduces the electric-ity, and Reid vapor pressure is higher that entails a greatervolatilization, which can contribute to ozone and smog for-mation (Thomas and Kwong, 2001). Many countries haveimplemented or are implementing programs for ad dition ofethanol to gasoline (see Table 1). Fuel ethanol productionhas increased remarkably because many countries look forreducing oil imports, boosting rural economies andimproving air quality. The world ethyl alcohol productionhas reached about 51,000 mill liters (Renewable FuelsAssociation, 2007), being the USA and Brazil the first pro-ducers (see Table 2). In average, 73% of produced ethanolworldwide corresponds to fuel ethanol, 17% to beverageethanol and 10% to industrial ethanol.The fuel ethanol can be obtained from energy crops andlignocellulosic biomass. The complexity of the


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