ETHANOL ELECTRICITY

Overview of Biomass to Ethanol

Ethanol, with the chemical formula, CH3CH2OH, can be produced by chemical synthesis through direct hydration of ethylene (ethylene derived from petroleum), or by biological fermentation using microorganisms. Production of ethanol has been limited to using sources of soluble sugar or starch, primarily in the Midwest, U.S. using corn. Ethanol production grew from 175 million gallons in 1980 to 1.4 billion gallons in 1998, with support from Federal and state ethanol tax subsidies and the mandated use of high-oxygen gasoline. Currently, over 1.5 billion gallons of ethanol is produced in the US. California ethanol production is limited, a modest amount of 6 million gallons per year from food processing wastes and other liquid products, such as cheese whey. Demand for ethanol could increase further if methyl tertiary butyl ether (MTBE) is eliminated from gasoline. In March 1999, Governor Gray Davis announced the phase out of the use of MTBE in gasoline by 2002 in California, which uses 25 percent of the global production of MTBE. It is unclear, however, whether the U.S. Congress will eliminate the minimum oxygen requirement in reformulated gasoline (RFG), an action that would reduce the need for ethanol. If the oxygen requirement is eliminated, ethanol will still be as valuable as an octane booster and could make up some of the lost MTBE volume.

Extending the volume of conventional gasoline is a significant end use for ethanol, as is its use as an oxygenate. To succeed in these markets, the cost of ethanol must be close to the wholesale price of gasoline, currently made possible by the Federal ethanol subsidy. However, the subsidy is due to expire in 2007, and although the incentive has been extended in the past, in order for ethanol to compete on its own merits the cost of producing it must be reduced substantially. The production of ethanol from corn is a mature technology that is not likely to see significant reduction in production costs. Substantial reductions must be possible, however, if lignocellulosic-based feedstocks are used instead of corn. The ability to produce ethanol from low-cost biomass will be key to making ethanol competitive with gasoline. In addition, if an ethanol production system was co-located with biomass power plant certain synergies could occur. In particular, lignin from the ethanol plant could be utilized by the power plant, while steam and electricity from the power plant could be utilized by the ethanol facility. Also, it is likely that the ethanol plant could utilize other existing utilities at the biomass power plant, such as sewage handling, cooling water and other buildings. It is also likely that the ethanol Although lignocellulosic feedstock are less expensive than corn, today they are more costly to convert to ethanol because of extensive processing required.

Ethanol fermentaion pathway
Ethanol Production from Ligno-Cellulosic Conversion Technologies

Cellulosic biomass is a complex mixture of carbohydrate polymers known as cellulose, hemi-cellulose, lignin, and a small of amount of compounds known as extractives. Examples of cellulosic biomass include agricultural and forestry residues, municipal solid waste (MSW), herbaceous and woody plants, and underused standing forests. Cellulose is composed of glucose molecules bonded together in long chains that form a crystalline structure. Cellulose is a fibrous, tough, water-insoluble substance. Hemi-cellulose is not soluble in water. It is a mixture of polymers made up from xylose, mannose, galactose, or arabinose. Hemi-cellulose is much less stable than cellulose. Lignin is a complex aromatic polymer of phenylpropane building blocks. Lignin is resistant to biological degradation.

For production of ethanol, the cellulosic feedstock is first pretreated to convert hemi- cellulose into soluble sugars such as xylose sugars. The cellulose fraction is hydrolyzed by acids or enzymes to produce glucose, which is subsequently fermented to ethanol. The soluble xylose sugars derived from hemi-cellulose are also fermented to ethanol. Lignin, which cannot be fermented into ethanol, can be used as fuel to produce heat or electricity. Pathways to produce ethanol using cellulosic feedstock are described below.
General Pathways for Ethanol Production from Cellulosic Feedstock

* Enzymatic hydrolysis :simultaneous saccharification and co-fermentation (SSCF): The steps in the conversion of cellulosic materials to ethanol in processes featuring enzymatic hydrolysis includes pretreatment, biological conversion, product recovery, and utilities and waste treatment. SSCF is an adaptation to the process, which combines hydrolysis and fermentation in one vessel. Sugars produced during hydrolysis are immediately fermented into ethanol. By fermenting the sugars as soon as they form, eliminates problems associated with sugar accumulation and enzyme inhibition.
* Dilute acid hydrolysis : This process uses low concentration acids and high temperatures to process the cellulosic biomass. Lignocellulose biomass is pretreated with approximately 0.5% acid in liquid at up to 200ºC to hydrolyze the hemicellulose and expose the cellulose for hydrolysis. The hemicellulose hydrolysis yields most pentose (C5) sugars, principally xylose and arabinose, which are fermented to ethanol and distilled. The remaining solids, cellulose and lignin, enter the second stage hydrolyzer where cellulose is converted to glucose with approximately 2% acid in liquid at up to 240ºC. The resulting sugars are then fermented to ethanol and distilled.
* Concentrated acid hydrolysis : This process uses high concentration halogen acids and near ambient temperatures to convert cellulosic biomass to sugars. The decrystalization and hydrolysis of cellulose with nearly 100% yields may be accomplished with 40 wt% hydrochloric acid, 60 wt% sulfuric acid, or 90 wt% hydrofluoric acid. The liquid phase hydrochloric acid process is the only halogen process to have reached commercial development.
The feedstock is pretreated with approximately 10 wt% acid liquid stream which is recycled from cellulose hydrolysis. Pretreatment hydrolyzes the hemicellulose into C5 and C6 sugars and exposes the cellulose for hydrolysis. The subsequent liquid acid and sugar stream is separated from the solids, neutralized, fermented and distilled. The solids mostly cellulose and lignin, enter the second stage hydrolyzer and are mixed with 40-90 wt% acid (the concentration depends on acid type). Cellulose is converted into C6 glucose sugars. After another liquid-solid separation step, the liquid containing about 10% acid and 10% glucose is recycled to the hemicellulose hydrolysis / pretreatment vessel. The remaining solids are washed, dried and used as fuel source for power production.
* Biomass Gasification and Fermentation

Existing R&D Status on Cellulosic Biomass to Ethanol

The technology behind converting cellulosic biomass to ethanol has yet to pass the most important test of being demonstrated in a commercially viable facility. Despite there being many different technologies available i.e.: dilute acid, concentrated acid, enzyme based hydrolysis, none are in use in a commercial facility in the United States. There are many plans for future facilities at sites all over the United States and Canada, some much more viable than others.

In North America there are seven facilities that we at the California Energy Commission found to be in various stages of planning and or construction. These are listed in the table below.
Site Location Developer Feedstock
Sacramento, CA Arkenol Agricultural residue
Mission Viejo, CA Arkenol Cellulosic biomass
Jennings, LA Collins Pine, BCI Wood waste
Gridley, CA BCI Rice Straw/Wood waste
Middletown, NY Masada Cellulosic biomass
Ottawa, Canada IOGEN Cellulosic biomass

The Sacramento (actually Rio Linda, slightly to the north), CA sites were in the planning stages and have now been abandoned. It is unclear whether Arkenol still owns the site or if it has changed hands, but the important permits that were granted for the site have expired. The site was planned as a joint operation with SMUD (Sacramento Municipal Utilities District) that would use rice straw and other local agricultural residues as feedstock for a 20-MM gal/yr. biomass to ethanol facility.

Arkenol also owns the cellulosic biomass to ethanol facility in Mission Viejo and it is also not a commercial facility. The facility is used as the pilot plant demonstrator of their proprietary hydrolysis and fermentation technology. The plant uses concentrated acid hydrolysis and unknown type of yeast in its fermentation facilities. The small scale (less than 100 gals/batch) of the plant has lead to the use of a batch process system rather than a continuous operating facility. It is also unclear whether or not the facility is still being used at this time.

The Jennings LA project is to determine the technical and economic feasibility of integrating a new biomass-to-ethanol production facility in Jennings LA with an existing biomass power plant, located Chester, California. If feasible, these two facilities would be operate together and become customers for each other's products. The planned facility In Chester, California is to be co-located with the wood waste burning thermal plant at their sawmill. The specifics of the hydrolysis and fermentation are yet to be determined as they are relying on the research being done in Jennings, LA to determine the feasibility of enzymatic or dilute acid hydrolysis. The sawmill in Chester shipped wood waste (forgest thinnings) to Jennings for testing and hydrolysis. So far, no information shows if the pilot tests on ethanol production using forest thinnings have been performed. A stop work order was issued by the California Energy Commission due to the lack of with regards to lack of deliverables due from Subcontractor. A critical project review meeting was held at the Commission on Dec. 20, 2001. The purpose of the meeting was to review the status of the Collins Pine project and the quality of work that had been conducted. The ultimate goal is to find a way to proceed with this project in a way that successfully accomplishes the original intention and objectives.

Gridley, CA project was initial planned to evaluate the technical and economic feasibility of a cellulase technology proved to be promising during the Gridley Phase I study using a feedstock mix consisting of 75000 bdt/yr of rice straw and 175000 bdt/yr of wood waste. By January 1999, it was concluded that the commercial readiness of cellulase enzyme and microorganisms remains a key technical issue. A decision was made by BCI to switch the cellulase technology to the two stage dilute acid hydrolysis process. It was concluded that production of fuel grade ethanol is viable after evaluation of various two-stage hydrolysis scenarios by BCI. It is unclear on current status of the BCI Gridley project.

Masada Corporation is planning the cellulosic biomass to ethanol facility in Middletown, NY. Masada uses concentrated acid hydrolysis of MSW based cellulosic biomass then conventional fermentation for the ethanol portion of its comprehensive MSW mitigation package. The facility is planning on using MSW from several local municipalities and is currently under going environmental review and permitting by the local governments. This facility is still several years away from commercial ethanol production.

In Ottawa, Canada the company IOGEN has been pursuing enzymatic hydrolysis for 25 years. The ethanol production facility in Ottawa is co-located with IOGEN1s industrial enzyme production facility. The cellulosic biomass to ethanol facility is currently under construction and is nearing completion; IOGEN is reporting 3-6 months before plant is operational. The technology in use at IOGEN1s facility is steam explosion then enzymatic hydrolysis and a mix of yeast and microbes to ferment the different sugars. Microbes that will allow for SSCF are in testing, but not currently operational. The facility is expected to process approximately 40 tons per day of cellulosic biomass.