Common processes for producing 2 nd generation biofuels. 

Context in source publication

Context 1

... availability of modern transportation vehicles and fuels has driven rapid economic growth and greatly improved our daily life with needed and new materials. The fuels have been overwhelmingly obtained from fossil resources, particularly petroleum, through sophisticated refining processes. Due to ever increasing demand in products and improving technology in exploration and production, the easy-access conventional petroleum resources have been rapidly depleted. The situation has become even more serious in recent years as a result of the rapid growth of developing countries having large populations, such as China, India, Brazil and Russia. Research and development of refining technology have shifted to heavy oils that have high contents of sulfur, nitrogen and metals that are harmful to refining processes and the environment. Because of dwindling fossil resources and increasing evidence of carbon dioxide as a main culprit for global warming, fuels from biological resources are now explored and have achieved some success. Biofuels cover biogas, liquid fuels and solid biomass. Methane is the main component of biogases produced by anaerobic digestion. Solid biomass includes wood, saw dusts, agricultural wastes, dry manure, non-food crops, etc. Some of them are also the feedstock for 2 nd generation transportation biofuels. Liquid products are for transportation, mainly gasoline, diesel and jet fuels. The development of liquid biofuels is being considered as in three generations. The first generation biofuels are produced by using conventional technology, such as fermentation and trans- esterification, to convert sugar, starch, vegetable oils and animal fats into ethanol and biodisels. Ethanol is usually used as a gasoline additive because it cannot completely replace gasoline without a modification of existing internal combustion engine. Biobutanol, on the other hand, can be used in existing engine as a gasoline substitute, having advantages of high Reed vapor pressure and less water solubility. Common biodiesels are mainly methyl or ethyl esters of fatty acids. The biggest disadvantage of first generation biofuels is competition with food sources using the same crops. The second generation biofuels use non-food sources as lignocellulosic biomass feedstock. These include non-edible portion of food crops, bark, wood, nuts and seeds, forestry residue such as saw dusts, agricultural wastes/residues, cellulose and lignin, etc. There are many processes being used for the conversion of lignocellulosic biomass into biofuels, including (1) acid hydrolysis/enzyme pre-treatment followed by conventional fermentation/dehydration, (2) pyrolysis to produce bio-oil, or pyrolysis oil, followed by hydrotreating to convert oxygenates into hydrocarbons as green gasoline, diesel and jet fuel, and (3) gasification to produce synthetic gas with additional hydrogen from water-shift reaction to produce green diesel/gasoline or alcohols. Figure 1 summarizes common reactions used for producing 2 nd generation biofuels. The bio-oils, such as vegetable oils, grease and pyrolysis oils, can be mixed with petro-oils to undergo co- processing, such as hydrotreating or catalytically cracking, to produce diesel, gasoline and light olefins, as shown in Figure 2. The co-hydrotreating process remove sulfur, nitrogen from diesel to form environmental friendly diesel and oxygenates from bio-oils to form green diesel. Unlike the 1 and 2 generation biofuels, the 3 generation biofuels involve genetically modified the feedstock to improve the efficiency of fuel production. The most commonly used feedstock is genetically modified, or engineered, algae for increasing the lipid yields to reduce the cost of water removal in the extraction process. Two of the 3 rd generation biofuel companies are used as examples for different approaches of producing algae oils for further processing. Sapphire Energy produces genetically modified algae that feeds on carbon dioxide and sunlight in open ponds. The algae are designed to yield oil that is easily processed into liquid transportation fuel. Solazyme, on the other hand, feeds its algae various cellulosic and other waste materials rather than CO 2 and sunlight. The genetically engineered algae sugar is fermented in dark beer brewing ...