Chapter 23 - Biological conversion into liquid fuels

Abstract

This chapter presents several processes converting biomass into liquid fuels that are easy to store. There is also a possibility of direct production of liquid fuels by photosynthesis. Oil from the seeds of many plants, such as rape, olive, groundnut, corn, palm, soy bean, and sunflower, is used as food or in the preparation of food. Many of these oils will burn readily in diesel engines and can be used directly or mixed with diesel oil of fossil origin, as they are indeed in several pilot projects around the world. Much interest is concentrated on plants that yield hydrocarbons and that, at the same time, are capable of growing on land unsuited for food crops such as Euphorbia lathyris (gopher plant), Simmondsia chinensis (jojoba), Cucurdia foetidissima (buffalo gourd) and Parthenium argentatum (guayule). The glucose molecules in most sugar-containing plant material exist in polymerized form such as starch or cellulose. Starch or hemicellulose is degraded to glucose by hydrolysis, while lignocellulose resists degradation owing to its lignin content. Lignin glues the cellulosic material together to keep its structure rigid, whether it is crystalline or amorphous. Several methods of hydrolysis have been developed, based on enzymatic intervention. Bacterial such as Trichoderma or fungal such as Sporotrichum pulverulentum enzymes have proved capable of converting cellulosic material, at near ambient temperatures, to some 80% glucose and a remainder of cellodextrins. The residue left behind after the fermentation process can be washed and dried to give a solid product suitable as fertilizer or as animal feed. The composition depends on the original material, in particular with respect to lignin content.