All plants convert solar energy into strongly linked chains of sugar known as cellulose. Anyone who has ever made beer knows that yeast can make ethanol from sugar. Yeast, however, cannot easily convert the sugar in cellulose to ethanol without the chains first being broken down into simple sugars. There are two principle approaches to breaking the cellulose chains into sugars.
Thermochemical conversion involves the breaking down of biomass into a mixture of gases and then converting the gasses into ethanol. Although thermochemical conversional is a simpler and relatively mature technology, it requires significant capital and energy expenses.
Biochemical methods rely on the use of enzymes to break down the cellulose into sugar. Where do these enzymes come from? In Nature, organisms such as termites live on sugars derived from cellulose. Similar to humans, the digestive system of a termite requires bacteria to digest food. But in the case of termites, the resident bacteria produce special enzymes that can break down cellulose into simple sugars that are used to fuel the termite’s body. In industry, the enzymes used to break down the cellulose into sugars come from yeast and bacteria which then also ferment the sugar into ethanol.
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