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Ethanol

Cellulosic Ethanol Production

Cellulosic ethanol has not yet been produced commercially. However, several commercial cellulosic ethanol production plants are under construction, and intensive research and development is rapidly advancing the state of cellulosic ethanol technology, including biochemical and thermochemical conversion processes.

Biochemical Conversion

Because cellulosic feedstocks are more difficult to break down into fermentable sugars than starch- and sugar-based feedstocks, the cellulosic biochemical conversion process requires additional steps (see diagram below). Two key steps are biomass pretreatment and cellulose hydrolysis. During pretreatment, the hemicellulose part of the biomass is broken down into simple sugars and removed for fermentation. During cellulose hydrolysis, the cellulose part of the biomass is broken down into the simple sugar glucose. For a description of all the cellulosic ethanol production steps, see the U.S. Department of Energy (DOE) Biomass Program's Bioethanol Production.

Block diagram describing the cellulosic ethanol production process. It starts with Biomass Handling and then can go either to Biomass Pretreatment or Enzyme Production. Each of those feed into Cellulose Hydrolysis, then goes to Glucose Fermentation, then goes to Ethanol Recovery, which feeds into either Lignin Utilization or the final Ethanol Fuel Product. An additional route can also stem from the Biomass Pretreatment phase which feeds into Pentose Fermentation, which goes to Ethanol Recovery.

Source: DOE Biomass Program

Thermochemical Conversion

Ethanol can also be produced using thermochemical processes. In this approach, heat and chemicals are used to break biomass into syngas (a mixture of carbon monoxide and hydrogen) and reassemble it into products such as ethanol. To learn more, see the DOE Biomass Program's Thermochemical Conversion. Also see Research Advances—Cellulosic Ethanol (PDF 1.7 MB) to learn more about biochemical and thermochemical conversion technologies. Download Adobe Reader.

This is a simplified schematic of a thermo chemical conversion model that shows the many steps that can be manipulated to optimize efficiency and cost. Basically, Biomass goes into a dryer, then into an indirect gasifier, which goes into a tar reformer, then Syngas Cleanup and Compression, then Mixed Alcohol Synthesis.

Source: Research Advances—Cellulosic Ethanol (PDF 1.7 MB) Download Adobe Reader.

Cellulosic Ethanol Production Facilities

DOE and industry partners are deploying commercial and pre-commercial cellulosic ethanol production technologies. Visit the DOE Biomass Program's Deployment page to learn about DOE-supported cellulosic ethanol biorefinery projects and view a project map.

DOE is also supporting development of integrated biorefineries, which produce both high-volume liquid transportation fuels such as ethanol and high-value chemicals or products. See the Biomass Program's Integrated Biorefineries page for more information and descriptions of projects.