what is second generation biofuels?

Second generation biofuel technologies have been developed because first generation biofuels manufacture has important limitations. 

First generation bio fuel processes are useful, but limited in most cases: there is a threshold above which they cannot produce enough biofuel without threatening food supplies and biodiversity. Second generation biofuels can help solve these problems and can supply a larger proportion of our fuel supply sustainably, affordably, and with greater environmental benefits.First generation bio ethanol is produced by fermenting plant-derived sugars to ethanol, using a similar process to that used in beer and wine-making . This requires the use of 'food' crops such as sugar cane, corn, wheat, and sugar beet. These crops are required for food, so if too much bio fuel is made from them, food prices could rise and shortages might be experienced in some countries. Corn, wheat and sugar beet also require high agricultural inputs in the form of fertilizers, which limit the green-house gas reductions that can be achieved.

The goal of second generation biofuel processes is to extend the amount of biofuel that can be produced sustainably by using biomass consisting of the residual non-foodparts of current crops, such as stems, leaves and husks that are left behind once the food crop has been extracted, as well as other crops that are not used for food purposes such as switchgrass, jatropha, miscanthus and cereals that bear little grain, and also industry waste such as woodchips, skins and pulp from fruit pressing, etc.

The problem that second generation biofuel processes are addressing is to extract useful feedstocks from this woody or fibrous biomass, where the useful sugars are locked in by lignin and cellulose. All plants contain cellulose and lignin. These are complex carbohydrates (molecules based on sugar). Lignocellulosic ethanol is made by freeing the sugar molecules from cellulose using enzymes, steam heating, or other pre-treatments. These sugars can then be fermented to produce ethanol in the same way as first generation bioethanol production. The by-product of this process is lignin. Lignin can be burned as a carbon neutralfuel to produce heat and power for the processing plant and possibly for surrounding homes and businesses.