312. No country has yet been successful in developing an industrial process for the enzymatic conversion of cellulose to sugars or alcohol. Several countries have, however, designed and built pilot or pre-pilot scale solid waste treatment plants. Outlines for proposed commercial processes and comparison of these technologies to highlight their advantages and disadvantages are as follows:


1.   Gulf Oil Chemicals Company

313. Gulf Oil Chemicals' cellulose alcohol technology appears to be the most advanced from both technical and economic viewpoints. Based on extensive research begun in the early 1970s at Gulf's Merriam Laboratories and on the one ton/day pilot plant operation in Jayhawk Works near Pittsburg, Kansas, their process has developed into four major stages: (1) pretreatment of feedstocks, (2) in-house production of required yeasts and enzymes, (3) the simultaneous saccharification of feedstocks and fermentation of the resultant sugars into ethanol, and (4) distillation of the alcohol. This process was evaluated as technically feasible by the Ralph Katzen Association. In addition, available information indicates that the economic potential of other US enzymatic technologies is not as promising as the Gulf approach.

314. Gulf's proposed commercial process is based on processing 2,000 tons/day (dry basis) of cellulosic waste material, containing approximately 57% cellulose. A typical mixed feedstock ($15.75/ton avg.) composed of 2/3 municipal solid wastes (MSW, the air-classified fraction) and 1/3 pulp mill waste (PMW, primary sludge and digester rejects), is used as the basis for cost estimates. One ton/day of the mixed feedstock yields approximately 300 liters/d of 95% alcohol. According to available data, the 2,000 tons/day cellulosic wastes will yield 150,000 gallons per day of industrial (190°) ethanol. The study assumes that the processing facility is located imediately adjacent to a municipal solid waste treatment plant. MSW is air-conveyed to the cellulose alcohol facility while PMW is transported to the facility by either road or rail.

315. In the raw material preparation section, the feedstock is split between two separate pretreatment steps. Approximately 15% of the MSW is mechanically pretreated and sterilized prior to use as feedstock in continuous enzyme production. The remaining MSW is mechanically pretreated and mixed with incoming PMW, after which the mixture is pasteurized and becomes the feedstock for simultaneous saccharification and fermentation (SSF).

316. Enzyme production is a continuous process of T. reesei cultivation with a 48-hour total retention time. This process is much faster than conventional long-term batch processes (one to two weeks). The enzymes need not be extracted from the enzyme broth; they can be used directly in the next stage.

317. The next stage is simultaneous saccharification and fermentation, which can also yield reduced time requirements compared to other processes, most of which have separate steps for saccharification (2-6 days) and fermentation (two more days). The SSF process is carried out continuously in a series of fermenter trains with a total retention time of 24 hours. The multitrain fermenter concept permits the operator to shut down and sterilize one train while maintaining operations in the remaining trains.

318. The beer slurry, with a 3.5% ethanol content, from the SSF stage is neutralized prior to distillation. The alcohol recovery section is designed for maximum heat recovery and heat reuse. The stillage from the alcohol recovery section is evaporated to produce a syrup animal feed by-product in the amount of 534 tons/day (60% solids content composed of protein, carbohydrates, inorganics and trace vitamins).

319. The Gulf process minimizes external fuel requirements through separation of insoluble solids, the organic content of which - primarily lignin and unconverted cellulose - serves as basic fuel for the plant, essentially providing all the thermal energy and most of the turbine drive energy.

320. Importantly, the Gulf process does not utilize any acids or solvents, thereby minimizing corrosion and eliminating problems with solvent recovery. While the investment base and related operating charges are currently substantial (see below), a 50 tons/day demonstration plant, which was in its planning stage in the early 1980s and was to be built in Pine Bluff, Arkansas, may eventually lead to reduced costs.

321. As indicated below, the production cost on a 100% investor equity capital basis is $0.70 per gallon (18.5 cents per liter) of alcohol. After credit is taken for the animal feed by-product and allowances made for investment tax credit and a 15% after-tax return-on-investment for a 10-year plant life, the projected selling price during the first year of production (1983 dollars) was expected to be $1.44 per gallon (38 cents per liter).

322. The estimated cost of one gallon of ethanol will almost double if a smaller plant producing 10 million gallons per year alcohol (400 tons/day cellulosic wastes) is constructed.

323. Provided below are figures that allow an analyst to compare the cost of producing one gallon of alcohol in a 50-million-gallons-per-year plant by any of three methods: (1) through SSF of cellulose, (2) through corn fermentation or (3) through synthesis. Each method allows for a 15% after-tax return on investment. Clearly, if all the technical and economic assumptions can be proved valid, the cellulose alcohol process will be competitive in the alcohol market.

324. In August 1979 the technology for the conversion of cellulose to ethanol that was developed at Gulf Oil as a proprietary package was donated to the University of Arkansas Foundation. The University then established the Biomass Research Center with the objectives of continued research and development in biomass utilization and scale-up to a demonstration level with funding from private sources and the US Department of Energy (DOE). Through the efforts of the Biomass Research Center and representatives from the Cellulose Alcohol Development Company (CADCO), financing had been arranged for a 50 ton/day plant to be built in Pine Bluff, Arkansas. Feedstock for the facility was projected to be 37.5 tons/day of air-classified MSW plus 12.5 tons/day of primary clarifier sludge from a local paper pulp mill, with additional plans to use rice hulls, cotton gin waste, bagasse and straws. The plant was to produce 5 million liters of ethanol per year and the cost of the plant was expected to be $26 million. It was assumed that the plant would operate for a minimum of 2.5 years prior to commercial scale-up. In 1981 the DOE planned to finance the construction of the plant partially by a grant of $10.5 million but the action was postponed.

325. United Biofuels Industries, Inc. (Richmond, Virginia) later announced plans to commercialize the Gulf - University of Arkansas process by building a 50 million gallon per year plant that would use 2,000 tons/day of waste wood pulp and Trichoderma reesei enzymes. Foster-Wheeler Corporation was the overall project manager with Raphael Katzen Associates as designer. The plant, with four individually-built modules, each with a capacity of 12.5 million gallons per year, would burn lignin and heavy combustibles to generate steam for a condensing steam turbine able to produce 40,000 kW electricity. The cost of the plant was estimated at $130 million and $160 million by two independent sources.

2.   United States Army - Natick Laboratories

326. One of the primary goals of the enzymatic hydrolysis program at Natick was the development of technology for producing low-cost, high-quality cellulase complex enzymes. As a result of this work, T. reesei mutant enzyme productivity was raised from 8 filter paper international units (I.U.)/l/hr to 167 I.U./l/hr. Additionally, more than 100 different cellulosic materials from sources all over the world and including a wide spectrum of native and processed cellulose and lignocellulose were evaluated with respect to enzymatic attack.

327. Of the many different types of pretreatments, including milling (attritor, ball, colloid, hammer two roll), hydropulping, disc refining, acid, solvents, chemical and steam, two are the most promising: steam and compression (two roll) milling. For example, in prepilot plant studies, a 20% slurry of compression (two roll) milled newspaper was hydrolyzed yielding an 8% reducing-sugar syrup in 24 hours. However, both methods have been tested only on a laboratory scale and there is no information available as to whether they are practical or economical on a large scale.

328. The research efforts of the Natick group were directed also toward integrating and optimizing ethanol production with other parts of the process. This program included the development and characterization of coupled/uncoupled batch and continuous saccharification and fermentation systems with emphasis on product removal and optimization of the physical process parameters including pH, temperature, time, and concentrations of cellulase, cellulosic substrate and yeast (Candida utilis and Saccharomyces cerevisiae). The fermentation produced 4% to 5% (v/v) ethanol solutions with no apparent adverse effects on the fermentation from urban waste or newspaper-derived components. The yield of ethanol was approximately 45% based on the initial glucose concentration in the syrup.

329. A solid waste treatment prepilot plant was designed and built by the Natick group in conjunction with the New Brunswick Scientific Company, Inc., New Jersey, to convert cellulose wastes to sugars and alcohol. A mutant strain of T. reesei is cultivated in a 400-liter fermenter for the production of cellulase in submerged culture. The cellulase is transferred to a 250-liter enzyme reactor where a substrate is converted to carbohydrates and ethanol. Extensive analysis and excellent control of the physical process parameters in this enzyme hydrolysis facility, made possible by extensive instrumentation, resulted in the determination of specific rates and yield factors allowing for the evaluation of the economic feasibility of the process.

330. The cost analysis was based on a plant with a manufacturing capacity of 25 million gallons per year of 190° fuel grade ethanol. A material balance calculation for the plant shows that 495,000 tons of urban waste containing 375,000 tons of enzyme hydrolyzable cellulosics should be supplied each year. Using 5 x 1012 I.U. of cellulase, or 1 million m3 of culture fluid with an activity of 5 I.U./ml, 45% of this substrate is hydrolyzed to fermentable sugars (10% syrups) which in turn are converted by yeast to ethanol in 40% yields. The plant operates 24 hours per day, for 330 days per year with an on-stream factor of 0.9. Other figures are as follows:
    - Cellulase productivity of 125 l.U./liter/h;
    - The enzyme is used for only one hydrolysis period of 24 hours due to economic considerations;
    - Initial substrate solids' charge of 20% is increased to an effective 30% level by the addition of         substrate during the first few hours of hydrolysis;
    - The ratio of enzyme to urban waste-derived substrate is 10 I.U./gm;
    - Energy required for ethanol distillation is 25,000 Btuh/gallon based on the 1979 commercial plant         designs for the production of fuel grade ethanol from corn;
    - Pretreatment of the substrate is compression (two roll) milling with 0.225 Kwh/lb of cellulosic         material.

331. Economic analysis (see below) demonstrates that the factory cost of ethanol from urban waste is $1.60 per gallon (in 1983 dollars) including $0.17 per gallon for the purchase of substrate from urban waste. Enzyme production contributes the most (38%) to the factory cost followed by ethanol production (23%), pretreatment (18%), substrate (11%) and hydrolysis (11%).

332. This factory cost of ethanol ($1.60 per gallon) is higher than in the Gulf cellulose alcohol process ($1.07 per gallon) (see paragraphs 321 and 323). If credits are taken for process steam (enzymatic hydrolysis residue from the ethanol facility can be returned to the utility for use as fuel) and cellular biomass ($200/ton), factory cost could be substantially reduced. It is anticipated that cellular biomass would be used as animal feed and/or fertilizer. By taking both credits, ethanol factory costs are reduced from $1.60 per gallon to $1.23 per gallon.

333. Total capital investment for the plant is projected to be $85,330,000, as shown below:

334. Researchers at Natick intended to develop the process for commercial use in two steps. Urban waste was to be used as the primary substrate, and fuel grade ethanol as the end-product. First, a one to two ton/day pilot plant facility was expected to be leased for four to six months to develop process refinements and collect the necessary design data for a 50 ton/day pilot plant. The next step was to build a 50 ton/day pilot plant and conduct a two-year program to establish the engineering baseline for the design and construction of subsequent full scale plants. Apparently, those plans were postponed.

3.   Purdue Process

335. The overall process developed at the Laboratory of Renewable Resources Engineering, Purdue University, West Lafayette, Indiana, includes six procedures: hydrolysis of hemicellulose; fermentation of hemicellulose hydrolyzate; hydrolysis of cellulose; fermentation of cellulose hydrolyzate; recovery of alcohol and other products; and treatment of waste liquors in methane generation. According to data supplied by the principal investigators, the program succeeded in raising $440,000 in funds during 1979 - 1980. Some pilot plant equipment was installed.

336. The principal advantage of the Purdue process is the great improvement in the solvent pretreatment of cellulosics so that good yields are obtained by acid or enzymatic hydrolysis. The cellulose solvents used for this step are Cadoxen, 70% sulfuric acid (at 100°C) or zinc chloride solution, although researchers believe that other solvents including organic bases such as amines (e.g. ethylene diamine) may also be useful. For reasons of economics and/or safety, sulfuric acid seems to be the solvent of choice at this stage of development with corn stover as the preferred substrate.

337. The process starts with hemicellulose hydrolysis by dilute sulfuric acid at 80 - 100°C to yield xylose and other soluble products, mainly pentoses. A technique known as "roasting and leaching" was developed involving the use of a minimum amount of water so that a sugar concentration of about 15% (w/v) can be achieved. The pentose solution, or part of it, is then converted to butanediol at 90% theoretical yield in concentrations of approximately 100 grams per liter.

338. In the next step of the process, the cellulose content in the lignocellulosic residue from the pretreatment operation is hydrolyzed to yield glucose by a number of different techniques including the classical dilute acid process under severe conditions or the new solvent method (paragraph 336), followed by acid or enzymatic hydrolysis. A 50 to 90% yield of glucose can be obtained. The dilute glucose solution is recycled upstream to hemicellulose hydrolysis. For every kilogram of sulfuric acid consumed it is possible to produce 3 - 3.5 kg of fermentable sugars. The ratio between glucose and xylose varies depending upon the raw material but averages about 2:1. The combined glucose and xylose is fermented to ethanol and the solid residue consisting of residual cellulose and lignin can be dried and burned to generate steam. With a 50 to 70% hydrolysis of available cellulose, enough residue is produced during operations to support the energy requirements of the entire process.

339. Other advantages of the Purdue process are the development of better dehydration methods for ethanol with the successful use of cracked corn, corn starch and other materials as dehydrating agents. Further, a new bacterial strain can produce ethanol or butanediol or both from pentoses thereby increasing the alcohol yield by nearly 300%. Enough moisture is adsorbed by passing 180 - 190 proof alcohol vapor through very dry ground corn (1-2% moisture) to give 199 proof alcohol with corn being dried and reused as many as 20 times.

340. This process was being scaled-up to larger size laboratory operations. According to the developers of the process, the estimates for producing 40 gallons of ethanol per ton of dry residues appeared conservative; between 70 and 75 gallons per ton is economically feasible and 100 gallons per ton is possible. The investigators were designing a plant based on overall biomass utilization, including cellulose, hemicellulose and lignin.

4.   Berkeley Process

341. Studies undertaken at Lawrence Berkeley Laboratory, University of California, resulted in several tentative processing schemes. However, the proposals of the Berkeley group, even though developed for a large plant, are based on small-scale laboratory checks of key process steps coupled with engineering assumptions as yet untested and are therefore conjectural; reported flows, balances and costs should be considered in this context.

342. The Berkeley group investigated dilute acid pretreatment of corn stover and wheat straw, which removes hemicelluloses and opens up the cellulose for enzyme hydrolysis. Batch hydrolyses were conducted on the acid treated material with cellulase from batch cultures of T. reesei Rut C-30, for substrate concentrations of 5 to 25% by weight. After 48 hours of hydrolysis a maximum conversion of approximately 52% of the pretreated corn stover was obtained for the 5% substrate case at enzyme activities above 1 I.U./ml.

343. An enzyme recycle stage was developed whereby part of the enzyme was recovered from the product stream by adsorbing cellulases countercurrently on pretreated cellulose solids. Hence a continuous hydrolysis stage is coupled with an enzyme recovery stage, thereby reducing the amount of makeup enzyme required. The cellulose solids, after adsorbing as much of the enzyme as possible, are then passed on to the enzymatic hydrolysis stage.

344. As a result of this research, a multi-stage continuous countercurrent adsorption process for enzyme recovery was developed. In such a system the cellulose solids remain stationary in each tank and are brought into contact, by means of vigorous stirring, with the enzyme-sugar solution. The wetted solids are then filtered and brought into contact with fresh enzyme sugar solution, while the filtrate is brought into contact with fresh solids.

345. Preliminary data indicated that in an eight-stage system, it would be necessary to supplement the recycled enzyme with 35% of the enzyme added to the initial charge. Approximately 87% of the filter paper activity leaving the first stage is present in the exit stream from the eighth stage, and thus available for recycling to the first hydrolysis stage. With this type of process approximately 8% glucose is recovered in the reaction mixture; reducing sugars, calculated as glucose, make up approximately 16% of the reaction mixture.

346. According to the author's estimates of the cost of a 10% glucose solution (excluding raw material costs), production of the enzyme costs approximately 60 cents per equivalent US gallon of alcohol, using a continuous process with cell recycling. The hydrolysis and recycling add a further cost of 60 - 80 cents, resulting in a cost of $1.40 per gallon. Addition of raw material costs increases the total to well over $2.50 per gallon.

5.   M.I.T. Process

347. The essence of the M.I.T. process is that carefully selected mixed cultures are added directly to coarsely ground cellulosics. Enzymes hydrolyze both the cellulose and the hemicellulose while the organisms convert the resulting sugars to ethanol. The remarkable feature of this approach is that only a small investment is required in preparing feedstocks and the process is not overly dependent on a high efficiency of feedstock utilization. The residue can be burned to supply energy for the factory. Other advantages include the development of microbial cultures with improved performance as a result of increasing the microorganism's ability to tolerate ethanol; continuous removal of butanol from the acetone/butanol process of bioconversion of biomass by extraction with a water-immiscible solvent during the reaction; and producing acrylic acid (an important intermediate in the manufacture of plastics and resins).

348. For the direct production of ethanol from agricultural cellulosics, mutant strains of the anaerobic, thermophilic bacteria Clostridium thermocellum and Clostridium thermosaccharolyticum (see paragraphs 86-88) are used. Through strain improvements for increased ethanol tolerance and catabolite selectivity, alcohol yields of 85% of the theoretical maximum were obtained with mixed culture. According to the principal investigators, however, the project was postponed.

6.   Lehigh/Pennsylvania/General Electric

349. The collaboration of groups at Lehigh University and the University of Pennsylvania in conjunction with the General Electric Company, Hahnemann Medical College and the Biology Energy Corporation led to the development of a promising process based on solvent pretreatment in which aqueous solutions of either butanol or ethanol and a catalytic agent remove lignin from the lignocellulosic feedstock, thereby improving substrate susceptibility to hydrolysis. A new thermophilic culture, Thermomonospora, is used for production of the cellulases. In addition, significant economic gain is realized by such measures as utilizing lignin by-products in diesel fuels.

350. The research group paid considerable attention to feedstock costs because they represent a substantial fraction of the total cost of alcohol produced. Accordingly, nurseries in Pennsylvania have developed short-harvest cycle, high-yield poplars resulting in feedstock costs of under $15 per dry ton. Interestingly, the material produced from harvesting two to three year old trees has about 20% of fines that can be separated easily by air classification. This fraction has 24 - 27% protein and an estimated price of $150 to $200 per ton for animal feed. Two specific process alternatives being investigated by the research team were: combined saccharification-fermentation with cellulases from Thermomonospora and the thermophilic, anaerobic noncellulolytic bacterium C. thermohydrosulfuricum for ethanol production and extractive fermentation for both ethanol (S. cerevisiae) and butanol (C. acetobutylicum) production.

7.   EG & G Idaho, Inc./Colorado State University

351. The group planned to design and construct a pilot plant in Idaho Falls, Idaho, for the enzymatic conversion of lignocellulose, primarily from wheat or barley straw, into ethanol. The autohydrolysis process was optimized for wheat straw, and work was in progress to optimize the autohydrolysis of hemicellulose and "organosolv" extraction of lignin from pinewood chips and corn stover. Batch or continuous digester technology from the paper industry was to be used for the autohydrolysis step. Other advances included an improved enzyme cycle system, advanced fermentation work, incorporation of vapor recompression distillation techniques, and the conversion of hemicellulose-based pentose sugars into butanol or another product.

8.   University of Lowell, Massachusetts

352. This group was interested in a practical process for producing alcohol fuel from waste paper. On the pilot plant level, the process combines modern pulp and paper technology with the use of commercial enzymes from T. reesei. Mechanical reduction is accomplished by combining waste paper or mill effluent solids with either water or recycled enzyme solution in a Jones system hydropulper. To enhance the enzymatic hydrolysis, the hydropulper breaks down the paper structure into individual fibers or fiber fragments, which are further reduced to 150 mesh size or less. Enzymatic conversion takes place in a 600 gallon, temperature-controlled, agitated tank. The saccharification stage is 90% efficient. Ethanol is recovered after final distillation as a 180° (90% alcohol) product.

9.   Alternative Fuels Division, National Renewable Energy Laboratory (NREL), Solar Energy Research Institute (SERI), Golden, Colorado

353. The Solar Energy Research Institute and its National Renewable Energy Laboratory is developing enzyme-based technology for conversion of lignocellulosic biomass into fuel ethanol. NREL is pursuing research on SHF (separate hydrolysis and fermentation) and SSF (simultaneous saccharification and fermentation). SSF is currently favored over SHF processes by SERI (Philippidis et al., 1993). The SSF techniques integrate enzymatic hydrolysis of cellulose to glucose with fermentative synthesis of ethanol. A recent economic analysis of ethanol production from biomass (Hinman et al., 1992) identifies the SSF unit operation as the major contributor to the cost of ethanol (>20%). Thus the SSF performance procedure still requires optimization.

354. The following table presents economic data for the SHF and SSF process designs according to SERI. SSF has an 88 cent/gal cost advantage over SHF, primarily because the amount of enzyme required is reduced as a consequence of less inhibition by hydrolysis products (Wright, 1988a,b; Lynd, 1990). Although xylose conversion systems are not yet well developed, there is a strong economic incentive to utilize xylose in order to obtain useful byproducts (Hinman et al., 1989). Utilizing xylose, the SSF production cost was $1.35/gal. According to the most recent data (Wyman, 1992), however, the cost of ethanol production has been reduced from about $3.60/gallon in 1980 to $1.27/gallon at present through advances in technology. According to the researchers, areas have been identified to further reduce the cost of ethanol to $0.67/gallon, a price competitive with gasoline produced from oil costing $25/barrel. SERI estimates that technology consistent with this price can be developed at the pilot-scale level by the year 2000 if aggressive research and development is continued (Lynd, 1990). According to SERI, a selling price of $0.60/gal would very likely be competitive with gasoline prices anticipated in the year 2000. An interim stage of process development having an ethanol selling price of $0.75/gal is itemized in the following table with respect to costs for wood, other operating expenses, and capital.

SSF + xylose

355. The above table also shows that the biological steps dominate the cost of production and that reduced overall costs correlate with their reduced costs. The economic importance of the poorly defined biological steps makes them a logical priority for future research (Lynd, 1990). Improvement of these procedures is likely to result from both engineering and enzymological (cellulases) and microbiological (fermentation) approaches. A process development unit is being put into place at NREL to establish a fully-integrated process operation at the pilot side.


1.   Iotech Process

356. The Iotech Corporation Limited, Ottawa, Ontario, a Canadian-owned company founded in 1975, has underway a multidisciplinary program to investigate the conversion of cellulosic feedstocks to ethanol, chemicals and feed, and to commercialize the process. According to available data, the work was financed with $1 million (U.S.) per year from private investors and government grants with the DOE providing $397,000.

357. The Iotech process uses steam explosion for the pretreatment of lignocellulosics (see paragraphs 66-70), producing as an essential component a high quality lignin suitable for chemical production. The lignin is a sterilized powder that can be converted to resins, plastics, detergents and petrochemicals. A one ton/day pilot plant, designed and built by Iotech, used aspen chips as feedstock and converted 90% of cellulose and 80% of hemicellulose into sugars. The glucose obtained was converted into ethanol at 95% of the theoretical yield. A yield of 68 gallons of ethanol per ton of wood was achieved. If a feasible technology for xylose fermentation is developed by Iotech, the yield is likely to approach 90 gallons per ton.

358. A detailed design of a 250 ton/day (7.5 million gallons per year) demonstration plant and a preliminary design for a 1,000 ton/day (30 million gallons per year) commercial plant has been prepared. The 1980 market price of $1.70 per gallon (1983, $2.08 per gallon) of ethanol was projected as achievable assuming lignin is burned as fuel. A 250 ton/day demonstration plant was scheduled for construction in the United States by the mid-1980s; a similar one was planned for Canada. These plans have apparently been postponed.

2.    Stake Process

359. Stake Technology Limited, Ottawa, Ontario, has become well known following the disclosure of its efficient, low-cost conversion of waste lignocellulosics biomass through continuous "autohydrolysis". The Company's patented process and equipment accepts waste biomass, such as hardwood chips, sugarcane bagasse or straw, without using any chemicals or other additives. Raw materials are fed continuously via a plug-forming feeder into a steam-pressurized cylindrical vessel, which contains a helical screw conveyor, with steam pressures of 500 psi or more. Autohydrolized materials are discharged intermittently to atmospheric pressure through an orifice. The product is then subjected to an aqueous extraction, followed by an alkaline extraction, resulting in the recovery of a raw material containing three major components: cellulose, hemicellulose, and lignin. The cellulose fraction is further saccharified by acid or enzymatic hydrolysis to glucose which is fermented to ethanol. The pentose-rich hemicellulose fraction can be converted to furfural or xylitol, or may undergo a specific fermentation to ethanol. The lignin fraction has high fuel value or it may be used as a starting material for producing chemicals. Alcohol yields greater than 80% of theoretical have been achieved.

360. A joint venture was formed between Stake and Technip (France's largest engineering and construction firm) to integrate engineering, construction and marketing activities for alcohol plants outside North America. Vulcan Cincinnati had an exclusive license for the use of Stake's technology within North America.

361. According to the latest information (Yu et al., 1992), the Company's major research interests include biomass chemicals, high yield pulping and wastepaper recycling. In the area of biomass chemicals, StakeTech's Biomass Conversion Process emphasized process and product flexibility. StakeTech has been collaborating with the University of Sherbrooke to achieve effective fractionation of hardwood and softwood residues based on steam-explosion technology. It has also carried out technology development for the co-production of alcohol/furfural/lignin from various wood and agricultural residues. StakeTech is currently in the process of jointly evaluating steam-explosion technology for the conversion of waste paperboard to ethanol. In the production of alcohol, the Company has been involved in the evaluation of commercial and developmental cellulase preparations for the economically effective enzymatic hydrolysis of steam-exploded material to produce fermentable sugars (Yu et al., 1992). Two new integrated pilot plant facilities using StakeTech's continuous steam-explosion reactors were scheduled to be in operation in Trisaia, Italy and Ohio, USA, in the summer of 1992.

3.   University of Toronto

362. The objective of the group at the Department of Chemical Engineering, University of Toronto, was to develop and optimize an autohydrolysis extraction process in order to use under-utilized woods and agricultural residues to produce alcohol. Steps in the basic process are: autohydrolysis; hemicellulose extraction; lignin extraction; hydrolysis, with clarification of the wood sugar solution; and fermentation and distillation. According to the research group, acid hydrolysis is preferred in most cases. Some aspects of the process have been tested at the pilot stage.

363. The Toronto University program was concerned specifically with the problem of sugar survival in acid hydrolysis. Partial acid hydrolysis was studied with as low as 20% conversion of glucose with the remainder being recycled. Using this process, glucose yields of 70 - 80% are possible. Enzymatic hydrolysis was another method under study. To overcome the problem of glucose inhibition, a partial hydrolysis-recycle process has been investigated, similar to that proposed for acid hydrolysis. It was concluded that this recycle reaction will become practical when immobilized enzymes become available.

4.   Canertech Inc.

364. The interests of the Canadian Crown Corporation Canertech Inc. lie in energy conservation and in renewable energy development. Part of the latter interest was its Ethanol-From-Cellulose Program, which was a special project within the National Energy Program. Initially, the Program aimed to complete a 1 - 5 ton/day pilot plant by April 1984 and a 50 - 100 ton/day demonstration plant in 1986/1987. The estimated cost of the overall program was $21 million, of which $7 million was allocated for the pilot plant. The need for extensive process technology development apparently delayed the construction of the pilot plant.

365. A detailed comparative assessment of five alternative acid hydrolysis processes was undertaken with the aim of producing ethanol fuel that was competitive in price with gasoline. In regard to the economics, the Company found that by using aspen feedstock, assuming reasonable process development and allowing no commercial credit for lignin, three of the five processes could have led to a competitively-priced fuel in Canada by 1990-1995. Two of the processes, though in early stages of development, appeared technically promising. One of these may have an economic edge and is, therefore, likely to be selected for pilot scale development. However, proprietary complexities associated with one of these two processes has delayed action and probably eliminated one of the alternatives from further consideration.


1.   Celloglucose Process (A.N. Bach Institute of Biochemistry/Moscow State University/Research Institute of Bioengineering)

366. The National Program in Biotechnology, started at the end of 1981, called for the large-scale production of glucose in the form of glucose syrups and crystalline glucose by means of enzymatic hydrolysis of cellulosic wastes. The development of an appropriate industrial level process should have been attained by the end of the 1980s. Work along this line was coordinated by the Commission of Biotechnology of Cellulose at the USSR Academy of Sciences and by the National Council on Biotechnology.

367. The Program's initial goals were to complete two prepilot plants capable of producing 100 kilos of crystalline glucose per day by 1984 and two demonstration plants producing 1 - 5 tons/day of crystalline glucose by 1985/1986. A continuous prepilot plant was running at the A.N. Bach Institute of Biochemistry, USSR Academy of Sciences, in 1984-1988, producing glucose and ethanol from cellulosic wastes (USSR Program, that is Utilization of Sugar Syrups from Refuse). Some raw materials were used directly and included cotton stalks and sawdust; others required chemical pretreatment. Among the materials were cotton linters and other cotton ginning residues, and also under-utilized slurries from paper-making consisting of tiny cellulose particles. The source of enzymes used by the prepilot plant was solutions regularly donated by the nearest industrial biochemical unit which produced 600 m3 per year of cellulase culture in the form of a non-concentrated microbial culture fluid with a filter paper activity of 1 I.U./ml.

368. The original hydrolyzer unit was a countercurrent continuous reactor with an average glucose productivity of 2 - 5 g/liter/h. The productivity of the reactor can be increased, according to bench-scale experimental results, up to 15 g/liter/h, which corresponds to approximately 24,000 tons per year of glucose per industrial 200 m3 reactor. The cost structure shows that the three major components (raw materials with their pretreatment, enzyme production and use, and the purification and crystallization of glucose) contribute approximately equally to the cost of crystalline glucose production.

369. The high-efficiency, continuous process of enzymatic conversion of cellulose to glucose was made possible as a result of detailed investigation into cellulases' adsorption on cellulose. As a result, optimal conditions were determined for the adsorption of the enzymes on pretreated cellulosics. The adsorption was found to be so strong that researchers could use a column-type reactor for scaling-up the process. Other accomplishments include:

- The development of specific methods for determining activity (in absolute units) for all four principal components of the cellulase complexes (see paragraphs 24-28, 71-77) without their resolution;

- The development of a kinetic theory of action of a multi-enzyme cellulase system on cellulose useful for prediction of the kinetic behavior of glucose formation from cellulose while taking into account the activity of individual components of the cellulase complex;

- An increased understanding of adsorption of different cellulases (from different microbial and other sources) to cellulose and the quantitative evaluation of the availability of the enzymes for effective hydrolytic action toward cellulosics;

- Clarification of the role of adsorption in the effectiveness and conversion of amorphous crystalline cellulose to glucose;

- The development of a formula relating the quantitative relationships between the major physicochemical and structural factors of cellulose and the effectiveness of its conversion into glucose.

370. These approaches allowed researchers to properly select the microbial source of cellulases and cellulosic materials for practical conversion of cellulose into glucose. In 1988 the prepilot testing was transferred to a Privolzhsky Biochemical Plant near Moscow, where the T. viride liquid culture was produced and where a larger pilot plant was under construction. Turmoil in the USSR microbiological industry with regard to safety issues resulted in reorganization of the entire industry in general and the Biochemical Plant in particular, and the ensuing political and economical crises in the country led to a complete cessation of work at the plant in 1990-1991.


1.   The Indian Institute of Technology

371. At this Institute an integrated approach to the bioconversion of lignocellulosics to sugars, organic feedstock and liquid fuels was developed. Within the framework of this objective, two pretreatment processes for lignocellulosics were used. The first, a two-step process, involves dilute alkali treatment followed by steam treatment at 120°C in the presence of alkali. The second process employs treatment with butanol as a catalytic solvent (see paragraph 339) for effective delignification. It was shown that hemicellulose, the solvent, and lignin can be recovered to the extent of 95, 96, and 80%, respectively, by using steam distillation and solvent extraction.

372. Furthermore, a process of simultaneous saccharification and fermentation was also developed. Using cellulase and Pichia etchelsii at 40°C, ethanol yields of up to 32 grams per liter are obtained at 140 grams per liter of bagasse concentration. The direct conversion of cellulose into ethanol and other chemicals by C. thermocellum is also being studied. Ethanol yields of 0.20 and 0.25 g/g substrate degraded are observed using raw and mild alkali pretreated bagasse. A process to utilize the xylose component in bagasse (about 30%) via enzymatic isomerization to xylose and subsequent conversion of both glucose and xylose into ethanol is being developed. The energy requirements for producing 190 proof (95%) from a feed concentration of 4% have been estimated to be nearly half that of the distillation process.


1.   Technical Research Center/Helsinki University of Technology/State Alcohol Monopoly

373. A project was undertaken to develop an industrial process for producing ethanol from wood and other cellulosic materials based on enzymatic hydrolysis. Areas of research include the development of mutants of T. reesei for the production of cellulases, cellobiases and hemicellulases; pretreatment of cellulosic materials; hydrolysis of pretreated cellulosic materials; enzyme recycling; fermentation of glucose to ethanol by yeasts or bacteria (mainly Zymomonas sp.) in a separate process or simultaneously with hydrolysis of cellulose, fermentation of pentose to ethanol by molds (Fusarium sp.); and process design. The production of cellulolytic enzymes was investigated at pilot scale and tested at an industrial fermentation plant. According to the investigators, the economic feasibility of the processes based on enzymatic hydrolysis of cellulosic materials is as yet uncertain.


374. The work of the Swedish Forest Products Research Laboratory, Stockholm, focused on enzyme mechanisms involved in fungal cellulose and lignin degradation. For the fungi Phanerochaete sp. and T. reesei, the pattern of attack on cellulose was elucidated in some detail. In addition, a group at the Biomedical Center, University of Uppsala, focused for a long time on studying cellulases from Trichoderma strains with the general aim of obtaining information of the greatest possible value to applied research. In recent years, amino acid sequence determination of the individual cellulolytic components as well as their X-ray crystallographic studies were begun by the Uppsala group. Currently the Swedish Forest Products group in co-operation with a major Swedish company is trying to develop a process for ethanol production based on biomass. This project has only recently begun and is still at an investigative stage.


1.   Comitato Nazionale Energia Nucleare, Rome

375. The development of advanced biological technologies for the conversion of cellulosic wastes, including textile wastes, paper pulp, wheat straw, corn cobs, and olive shoots to ethanol was the primary objective. Pretreatment utilized sodium hydroxide at low temperatures. The saccharification of cellulosics was performed by a mixture of commercial T. viride and A. niger cellulases, the latter being immobilized in gelled alginate beads. An improvement in conventional batch fermentation was achieved by continuous fermentation with immobilized living cells packed in a column reactor; S. cerevisiae cells are immobilized with a 10% (w/v) suspension in 3% sodium alginate. Ethanol is produced continuously from a medium containing 15% (w/v) glucose with a yield of 90% of the theoretically determined maximum amount. The work has thus far been performed on a bench scale.


376. The Council for Scientific and Industrial Research in Pretoria coordinates a national program for converting cellulose and hemicellulose from bagasse to liquid fuels and chemicals. Of the three million tons of bagasse (with cellulose contents of 43 - 45%), 1,300,000 tons per year of cellulosic fraction could be recovered. The conversion of this material to ethanol could contribute 10% of the country's liquid fuel needs. The following research organizations in South Africa are involved in the part of the bagasse program dealing with the bioconversion of cellulosics to alcohol:

- National Food Research Institute, Pretoria: Isolation and improvement of aerobic cellulolytic organisms; optimization of cellulase production on a pilot scale and the development of large-scale enzyme production process technology; a promising technology using T. reesei QM 9414 or MCG 77 is planned for transfer to a pilot scale 150-liter fermenter;

- University of Natal, Pietermaritzburg: Hydrolysis of untreated and pretreated bagasse by using T. reesei or mutant strains of locally isolated microorganisms; fermentation of the resulting glucose and pentoses to ethanol;

- Sugar Milling Research Institute, Durban: Pretreatment of bagasse to enhance enzymatic hydrolysis;

- University of Orange Free State, Bloemfontain: Enzymatic saccharification of acid extracted bagasse; fermentation of glucose and pentose to ethanol;

- University of Fort Hare, Alice: The study of the cellulase complex of T. reesei;

- University of Cape Town: Ethanol fermentation from bagasse hydrolysate.


377. Ethanol production from cellulosic materials has been established in Japan since 1980 as a national project of the Ministry of International Trade and Industry. Twelve companies belonging to the Research Association for Petroleum Alternatives Development that worked on this project have payed particular attention to the development of a practical delignifying process, physical or chemical pretreatment of cellulosics, isolation of active cellulolytic microorganisms, economical production of cellulase, and innovative ethanol separation methods as well as the selection of new cellulosic biomass and its cultivation in large quantities.

378. Japanese researchers attempted to devise a very simple procedure for enzymatic saccharification of cellulosic materials with the intent to produce sugar and ethanol at low cost with considerable savings in fuel. They claim that the production of 10 - 20% sugar solutions, comparable to extracts of sugar cane and sugar beet, is now feasible from cellulosic resources such as rice straw, grass, bagasse, sawdust, corrugated paper and newspaper, by saccharification with T. viride cellulase preparations. Cellulases are recycled during the course of hydrolysis by means of ultrafiltration or by the locally developed tannic acid-polyethylene glycol method. The simultaneous saccharification-fermentation at temperatures of 15 - 30°C in open tanks in the presence of citric or lactic acids to prevent microbial contamination, i.e. the Oriental brewing method, gives 5 - 7% ethanol solutions after a 7-day incubation. According to the researchers this is now a practical way of using sugar solutions from cellulosics. The experiments have apparently been performed on a laboratory scale.

379. On a relatively larger scale, the chemical delignification (by boiling with a 1% sodium hydroxide solution for 3 hours or by autoclaving at 120°C with 1% NaOH for one hour) of eight tons of air-dried rice straw usually yields four tons of holocellulose. After enzymatic saccharification of the holocellulose, one ton of Candida utilis yeasts or a corresponding amount of ethanol is obtained while providing 50% saccharification. On the other hand, the nonhydrolyzable residue provides two tons of a mixture consisting mainly of lignin. This mixture, when further mixed with two tons of the residual root and stump of rice plant, is useful as new compost.

380. For the saccharification of delignified Carpinus shavings or delignified sawdust the economic substrate concentration was estimated to be 9 - 10%. After four days of incubation with 1 - 3% T. viride cellulase solution at 45°C the sugar concentration was 8.6%, and the degree of saccharification 77%. In another series of experiments, 25% shredded tissue paper, delignified rice straw, or delignified bagasse incubated with 1 - 3% T. viride cellulases at 45°C for four to eight days yielded 13 - 22% sugar solutions with a 40-66% degree of saccharification. These experiments have been performed on a laboratory scale. Whether scale-up technologies have been developed and assessed economically is not clear from the available sources. lt seems, however, that the high enzyme concentrations and the long incubation time would not result in an economically feasible process.


381. The shortage of food and fuel has become increasingly serious in many developing countries as a result of increased population density. From this point of view the enzymatic saccharification of cellulosic materials, primarily renewable agricultural residues, presents a possible partial solution to this problem, especially given the extremely large quantity of cellulosic resources being produced each year in subtropical and tropical developing countries.

382. In those developing countries where the technique of microbial technology is not fully established, enzymatic hydrolysis of cellulosic materials and fermentation of the resulting sugars into ethanol should be performed on a relatively small scale with facilities that are already available.

383. In some cases, existing branches of industry typical for developing countries can produce cellulosic material as wastes that are ready for bioconversion and could, when utilized, be beneficial for the industry. For example, in the manufacture of tobacco substantial amounts of waste filter material and cigarette paper are generated. Such waste materials generally find no use in cigarette manufacture, but instead are typically disposed of by burning after separation from tobacco components. On the other hand, sugars, particularly glucose, are employed in a number of tobacco treatment processes. Sugars are used as a carbon source during tobacco fermentations and as tobacco casing materials or in the production of tobacco flavorants.

384. Of the numerous cellulosic residues, rice straw is one of the most promising renewable resources in many developing countries. Cotton and sugar cane residues are also promising materials since they have been studied extensively and the findings have been published widely. With the data accumulated in the literature it is easier to select an appropriate approach to processing the material. The biological pretreatment that uses lignin utilizing microorganisms (paragraphs 60-62) should then be considered a highly promising means for pretreatment of lignocellulosics, particularly in developing countries. The potential of this approach is far from exhausted even in industrial countries which can utilize highly instrumented, capital-intensive equipment for the pretreatment of lignocellulosics. Of course new and more efficient lignin-utilizing microorganisms lacking cellulose should be discovered, thereby increasing the efficiency of the biotechnological processing of lignocellulose.

385. Clearly, commercial cellulase preparations, such as T. reesei cellulases, are too expensive for developing countries to purchase on large scale for the saccharification of their cellulosic resources. The cellulases produced by solid culture using, for example, wheat bran or rice straw, as well as solid culture methods rather than submerged cultivations are recommended for fungal cellulase production in developing countries, at least during the initial period of transition to modern biotechnology. Such cultures have been successfully developed in Japan and the Soviet Union and are suitable in terms of both enzymatic activity and costs.

386. It appears likely that the enzymatic saccharification of cellulose to glucose followed by its refinement or conversion to edible sugars (e.g., fructose) or its fermentation into liquid fuels, or its conversion to fodder, will gradually become a new rural industry in developing countries. From a practical standpoint, uncomplicated equipment together with manual labor to provide employment to a large number of rural people should be used. Hopefully, renewable cellulosic resources will be used as industrial raw material for producing sugar, yeast, and liquid fuel in the near future. Importantly, education may well prove to be the critical determinant for the future developments foreseen in this treatise.


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