Biofuels: Where We Stand

14 Apr 2008 Biofuels: Where we stand? Energy resources have the largest influence on the decisions that people and governments make. Energy is one of the fundamental elements in any economy of any nation. Today, crude petroleum represents the dominant raw material for the energy worldwide. Energy consumption is increasing dramatically and there is no sign that this growth in demand will abate. Global energy consumption is projected to increase by 57% from 435 trillion MJ in 2002 to 681 trillion MJ in 2025. Global petroleum demand in 2004 was 82 million bbl/day, with a projected increase to 111 million bbl/day in 2025. Biofuels are derived from non-depleted resources. They include production of bioethanol, biogas, biodiesel, as well as hydrogen production by microorganisms. Raw materials could be energy crops, algae and water plants, and various organic wastes. Bioethanol was introduced into the transportation fuel supply chain as early as the 1970s in Brazil. Nowadays, several countries have adapted the bioethanol concept. Bioethanol is produced commercially by fermenting sugars with yeast or bacteria. Cellulosic and starch containing raw materials are also used after hydrolyzing them. The process needs media sterilization and adjustment, sterilization, and later special distillation of the resulting broth to obtain fuel-grade ethanol. Although yeast (Sacharomyces sp.) yields higher amount of ethanol than bacteria (Zymomonas sp.), but it usually does not ferment pentose sugars found on many lingo-cellulosic materials. Recent advancement in biotechnology allowed the introduction of non-native metabolic pathways. Natural ethanol producing bacterium Zymomonas mobilis has been metabolically engineered to ferment xylose and arabinose as preferred carbon sources via introduction/expression of E. coli pathway genes. Xylose utilization by S. cerevisiae has been optimized via introduction of a Piromyces sp. xylose isomerase. Moreover, osmotolerant stains that contain the hydrolytic enzymes genes were recently announced. Biogas generation is a unique technique for converting waste to energy. The gas formed is mainly methane mixed with CO2. It is common in many countries to use waste materials for biogas production. In the UK for instance, methane produced from sewage works is used to run “Combined Heat and Power” engines, producing heat for the digestion process, and electricity used either at the works or sold to the National Grid. In Sweden, the remaining biogas is used as fuel in public transport vehicles. Another option for biofuels is the biodiesel, which is made from virgin vegetable oils, from waste fryer oils, or from waste animal fats and oils. It can be used alone or blended with petroleum diesel in any percentage without major modifications to the engine. Biodiesel includes fuel derived from corn, soybeans, sunflower seed, cottonseed, canola and rapeseed, and others. Transesterification is used to transform the raw vegetable oil into biodiesel and glycerin. This process is not complicated and uses methanol and sodium hydroxide as a catalyst. There is another impressive way of producing energy using the hydrogen-producing bacterium Halobacterium halobium which is still under intensive research. Bacteriorhodopsin, a protein found in the purple membrane of the bacterium, is known to pump protons across the membrane upon illumination, which creates an electrochemical gradient across the plasma membrane of the intact cell. The purple membrane is oriented in such a manner that the release of protons will occur into the surrounding medium. Thus hydrogen can be collected and stored. Egypt’s biomass potential is approximately 23 million tons of agricultural residues and 4.88 million tons of animal waste. One-third and one-tenth of the fuel requirements of rural Egypt are met from crop residues and animal droppings, respectively. If proper technology is applied to convert biomass into biofuel, energy requirement could be met. Salah Hassouna
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