There are two ways of producing alcohol from cellulose:

1. Cellulolysis processes which consist of hydrolysis on pretreated lignocellulosic materials, using enzymes to break complex cellulose into simple sugars such as glucose and followed by fermentation and distillation.

Gasification that transforms the lignocellulosic raw material into gaseous carbon monoxide and hydrogen. These gases can be converted to ethanol by fermentation or chemical catalysis.

2. They both include distillation as the final step to isolate the pure ethanol. Cellulolysis (biological approach)There are four or five stages to produce ethanol using a biological approach:

A "pretreatment" phase, to make the lignocellulosic material such as wood or straw amenable to hydrolysis,

Cellulose hydrolysis (cellulolysis), to break down the molecules into sugars;

Separation of the sugar solution from the residual materials, notably lignin;

Microbial fermentation of the sugar solution;

Distillation to produce 99.5% pure alcohol.

 

From Biomass to Cellulosic Ethanol:

Ethanol from cellulosic biomass—the most abundant biological material on the planet— has the potential to revolutionize the fuel ethanol industry and decrease U.S. dependence on imported oil. Despite its abundance, cellulosic biomass is a complex feedstock that requires more extensive processing than corn grain, the primary feedstock for conventional fuel ethanol production in the United States. Several scientific breakthroughs are needed to make cellulosic ethanol production cost-efficient enough to operate at a commercial scale.

This figure highlights some key processing steps in an artist's conception of a future large-scale, cellulosic ethanol production facility. (1) Cellulosic biomass from trees, grasses, or agricultural wastes is harvested and delivered to the biorefinery. (2) Biomass is ground into small, uniform particles. Thermal or chemical pretreatment separates cellulose, a tough polymer of tightly bound sugar chains, from other biomass materials and opens up the cellulose surface to enzymatic attack. (3) A mix of enzymes is added to break down cellulose into simple sugars. (4) Microbes produce ethanol by fermenting sugars from cellulose and other biomass carbohydrates. (5) Ethanol is separated from water and other components of the fermentation broth and purified through distillation. To bring down costs, continued progress is needed in the development of energy crops dedicated to biofuel production, biomass-collection technologies, pretreatment methods that minimize the release of inhibitory by-products, and more efficient enzymes and microbes robust enough to withstand the stresses of industrial processing.