The first generation biofuels are those that are characterized by mature commercial markets and well understood technologies3. Some examples are sugarcane ethanol in Brazil, corn ethanol in the United States, oilseed rape biodiesel in Germany, and palm oil biodiesel in Malaysia. The development and use of first generation biofuels are encouraged by the desire to attain energy security by reducing oil and coal imports, support the rural economy and agricultural industries, and mitigate the accumulation of greenhouse gases. Bioethanol from sugar cane has a positive net energy balance and provides an effective means of reducing greenhouse gas emissions. However, the commercial production of ethanol and biodiesel in some of the developed countries has zero or negative energy balance if upstream energy and chemical inputs are accounted for. For example, fertilizers used to grow biomass feedstocks for fuel can produce nitrous oxide, which is an extremely potent greenhouse gas. This therefore offsets some of the climate benefits associated with avoided fossil fuel use. The use of fossil fuels during the production and processing of some biofuels can also significantly reduce the performance of such fuels from a climate mitigation perspective.
Most of the evaluation studies and life cycle analyses done on first generation biofuels show that there is still a net benefit in terms of greenhouse gas emissions and energy balance. Nevertheless, first generation biofuels continue to draw a number of concerns, whether completely valid or not, as follows: (a) they contribute to higher food prices due to competition with food crops; (b) since biofuels production normally receive government grants and subsidies, it is an expensive option for attaining energy security; (c) with the exception of sugar cane ethanol, most biofuels provide only limited greenhouse gas reduction benefits; (d) since the production of biomass feedstock may not always be done in a sustainable manner, biofuels do not meet the claimed environmental benefits; (e) they have potentially negative impact on biodiversity, for example, through mono-culture cultivation of large tracts of land; and (f) they compete for already
scarce water resources in some areas.
The second generation biofuels address many of the problems and concerns associated with first generation biofuels. Table 7.1 presents a classification of second generation biofuels. Since most second generation biofuels are still relatively immature technologically, there is therefore great potential for cost reductions and increased efficiency levels as the technologies develop and experience in using them accumulate. The current biofuels industry is primarily based on the production of ethanol via the fermentation of sugars or starches and on the production of biodiesel derived from plant oils. To develop second generation biofuels, research and development work has been directed towards advanced technologies such as ethanol hydrolysis and fermentation, biodiesel enzymes, higher carbon fixation in roots, and improved oil recovery. Through advances in genetic engineering, it has become possible to develop crops that: (a) are disease-resistant, (b) viable even in degraded lands previously considered not suitable for cultivation, and (c) require much lower inputs of chemicals and water. New cutting-edge technologies are also being developed for the processing of lignocellulosic materials for the production of both industrial chemicals and biofuels, with overall conversion efficiencies of up to 70-90 percent. For this purpose, low-cost crops and forest residues, wood process wastes, and municipal solid wastes can all be used as feedstocks.
The other examples of second generation biofuel technologies that show a great deal of promise for eventual commercialization include gasification processes that incorporate the co-production of multiple valuable outputs, including electricity, industrial chemicals and liquid transportation fuels. These processes are capable of handling multiple feedstocks such as energy crops, animal wastes, and a wide range of organic materials. In general, gasification processes involve two-steps: firstly, the production of a synthesis gas, comprising primarily of carbon monoxide and hydrogen, from any carbon-containing and/ or hydrogen-containing material; and secondly, the use of this synthesis gas to drive highly efficient turbines for power production and as a feedstock for the production of a variety of synthetic chemicals or fuels.
The use of lignocellulosic biomass materials (as second generation biofuels technology) – as opposed to starches or sugars (as first generation biofuels technology) – offers the greatest potential for maximizing the efficient conversion of sunlight, water and nutrients into biofuels. The currently available methods of producing ethanol from cellulosic feedstock involve three steps: first, the thermochemical pretreatment of raw biomass to make complex cellulose and hemicellulose polymers more accessible to enzymatic breakdown; second, the use of a mixture of special enzymes that can hydrolyze plant cell-wall polysaccharides into a mixture of simple sugars; and third, the fermentation of sugars into ethanol in the presence of bacteria or yeast. These unit operations and processes are complex and energy-intensive and special enzymes are expensive. For this reason, there is need for further research and development work to make these technologies commercially viable.