N-Butanol Production from S. Cerevisiae

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Introduction
The energy consumption grows year by year with the economical development of the countries such as China and Japan despite the boisterous events. With the ‘Arab Spring’ in 2011, energy market was shook in terms of both production and consumption of the oil with the loss of one of the suppliers, also the massive earthquake and tsunami that hit Japan coast caused immediate action for nuclear power and other fuels around the world. Due to those events, oil prices reached an all-time record high [BP Statistical Review of World Energy, 2012]. When the situation, which revolves around mostly economical, environmental and geopolitical issues, in fuel industry is like this, the consumers head towards to renewable energy such as biotechnology. An entire branch of biotechnology embraces the bioproduction of fuels and chemicals from renewable sources. These technologies use living cells and enzymes to synthesize products that are easily (bio)degradable, require less energy and create less waste during their production or use than those produced from fossil resources [Dellomonaco et al, 2010]. However fossil fuels still dominate energy consumption, with a market share of 87%. Renewable energy continues to gain but today accounts for only 2% of energy consumption globally. Meanwhile, the fossil fuel mix is changing as well. Oil, still the leading fuel, has lost market share for 12 consecutive years. Coal was once again the fastest growing fossil fuel, with predictable consequences for carbon emissions [BP Statistical Review of World Energy, 2012]. Ethanol fuel is the most common biofuel worldwide, particularly in Brazil and USA which is produced from several biomass feedstocks and different technologies [].The ethanol production methods are respectively, enzyme digestion (to release sugars from stored starches), fermentation of the sugars, distillation and drying. The distillation process requires significant energy input for heat, often unsustainable natural gas fossil fuel, but cellulosic biomass such as bagasse, the waste left after sugar cane is pressed to extract its juice, can also be used more sustainably [Knothe and Gerhard,2010]. Bioethanol has relatively large octane rating with 116 while ordinary petrol has 91, which allows an increase of an engine's compression ratio for increased thermal efficiency. Yet the energy yield is nearly four times smaller than usual petrol which makes it inefficient. The other disadvantage of the ethanol is cannot be piped which makes it hard to be processed and transported. Along with the many advantages of biofuels there are still some disadvantages exist, thus second generation biofuels are developed from the simple biomass consuming biofuels. Biomass is a wide-ranging term meaning any source of organic carbon that is renewed rapidly as part of the carbon cycle. First generation biofuels are made from the sugars and vegetable oils found in arable crops, which can be easily extracted using conventional technology but limited in most cases such as threatening the food supplies and biodiversity. In comparison, second generation biofuels are made from lingo-cellulosic biomass or woody crops, agricultural residues or waste, which makes it harder to extract the required fuel. Second generation biofuel technologies have been developed because first generation biofuels manufacture has important limitations [Evans, 2008]. Butanol has a 4-carbon structure and the carbon atoms can form either a straight-chain or a branched structure, resulting in different properties. The molecular structure and the main applications of butanol isomers are listed in Table 1. 1-butanol, also better known as n-butanol, has a straight-chain structure with the –OH at the terminal carbon. 2-butanol, also known as sec-butanol, is also a straight-chain alcohol but with the -OH group at an internal carbon. Iso-butanol is a branched isomer with the -OH group at the terminal carbon and tert-butanol refers to the...
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