Technology
Cellulose-to-elhanoi prolects losing momentum onstration plants from private sources. They're finding that it's a lot harder to persuade individuals and corporations to risk their own money on unproved technology than it was (until recently) to persuade the government to part with taxpayers' money. Still, some private support has been forthcoming. It appears that one demonstration plant may be in operation within a couple of years— Ward Worthy but it probably will be in Canada, not C&EN, Chicago the U.S. There's nothing new about the idea The Reagan Administration's deci- of converting cellulose to sugars for sion not to support commercial de- making alcohol or something else. velopment of synthetic fuels tech- The old (1920's) Bergius process did nology was a hard blow to several it with concentrated hydrochloric promoters of cellulose-to-ethanol acid. The not-quite-so-old (1930's) projects. These projects have been Scholler process does it, using dilute carried through the pilot-plant stage, sulfuric acid to catalyze the hydrolywith encouraging results. Now they sis. A number of plants based on the need to be proved in larger demon- Scholler process are in operation stration-scale plants before com- today, notably in the U.S.S.R., turnmercial plants are attempted. As late ing out a variety of products. as last January, it appeared that these Brazil has embarked on a large demonstration plants would be project to make ethanol from eucafunded in large part by the govern- lyptus trees and other cellulosic ment. Now it seems they won't. feedstocks using Soviet technology. The processes' promoters are That technology may be successful in trying to get funding for their dem- those countries, given their particular economics and needs. The process is inherently messy and inefficient, however, and it's generally accepted that plants of that sort can't succeed in the U.S. or in other highly industrialized countries. In the 1940's, scientists at the U.S. Forest Products Laboratory in Madison, Wis., developed a continuous percolation acid hydrolysis process that was quite an improvement over the Scholler process. A commercialscale plant, with a hoped-for capacity of 4 million to 6 million gal of ethanol per year, was built in Oregon, close to an ample supply of wood wastes. It worked, after a fashion, but there were problems and it never reached full capacity. More to the point, postwar petrochemical developments made the process hopelessly uncompetitive, so the plant was closed. With the advent of cheap petrochemicals, including ethanol from ethylene, cellulose-to-ethanol technology pretty much stagnated. But in the aftermath of the energy crunches of the 1970's, there was a flurry of Lehlgh researchers monitor fermentationrenewed interest in fuel production In blomass conversion project processes that, by employing locally
Although results have been encouraging at pilot-plant stage, promoters are finding it tough to secure funds for demonstration plants
Stake Technology's digester uses steam to pretreat llgnocellulosic feedstocks
abundant energy sources, could reduce U.S. dependence on imported petroleum. Those processes included making ethanol from cellulosic feedstocks, which certainly are abundant, at least in principle. It was only one approach to the energy problem. But the idea of taking something like cornstalks or sawdust or rubbish and turning it into ethanol seemed so thrifty, so noble, so ecologically sound, somehow, that it aroused a great deal of public enthusiasm and support, perhaps out of proportion to its relative importance. The idea does have merit, so government support of the synfuels program has included modest amounts for development of cellulose-to-ethanol processes. Under the current arrangement, the Department of Energy oversees projects aimed at developing large-scale industrial systems. The Department of Agriculture concentrates on projects that could lead to smaller celluloseto-ethanol plants, suited to individual farms or agricultural cooperatives with limited but handy supplies of feedstocks. DOE has delegated management of the cellulose-to-ethanol program to Dec. 7, 1981 C&EN
35
Technology stage yields a beer slurry containing about 3.5% ethanol—well below Smith's suggested 12%—which is recovered by distillation. Stillage would be concentrated to a 60% syrup for animal feed. Solid residues from the process, mostly lignin and unconverted cellulose, would be used as fuel for the plant. Gulf carried the process to the point of building and operating a 1 ton-per-day (dry feedstock) pilot plant at Pittsburg, Kan. Then, Emert says, the company decided to concentrate its R&D efforts elsewhere. So it gave the patents, know-how, and $500,000 seed money to the University of Arkansas—retaining, however, a 22.5% interest in any eventual profits. Emert and some key associates moved from Merriam to USDA scientist at Peoria, III., research center adds solution of xylose (available from Fayetteville, Ark., where Emert bepaper mill waste) to fermentor that uses yeast to make ethanol came the director of a newly estabits Solar Energy Research Institute Gulfs Merriam, Kan., laboratories, lished Biomass Research Center. (SERI), in Golden, Colo. Midwest that produce enzymes that can hySince coming to Fayetteville, the Research Institute operates SERI for drolyze cellulose to glucose in the former Gulf crew has accomplished presence of lignin with satisfactory detailed process and engineering deDOE under contract. Clayton S. Smith, manager of yields. Because of the tolerance to sign and site-specific engineering for SERFs chemical and biological divi- lignin, some feedstocks, such as mu- a 50 ton-per-day demonstration sion, says that some of the processes nicipal solid wastes and pulp mill plant, to use two thirds municipal being worked on could indeed be wastes, need only minimal pretreat- solid wastes and one third pulp mill commercially competitive within a ment before hydrolysis. wastes as feedstocks, and to be built few years. However, he comments, Emert and his coworkers developed at Pine Bluff. Several Arkansas "I've been managing and supervising a continuous enzyme production companies joined forces to form a new process R&D for 12 years, and I've method that, compared to batch firm, Cellulose Alcohol Development never seen anything with more po- methods, offers economies in terms of Co. (Cadco), which was licensed to use tential for improvement than these more efficient use of reaction vessels. the process and which undertook to cellulose-to-alcohol processes." Retention time in the enzyme reac- obtain financial support for the For example, Smith says, digesters tors is about 48 hours. It isn't neces- demonstration plant. and fermenters still need to be able to sary to separate the enzyme from the "Before Reagan took over," Emert handle higher concentrations of broth; the broth can be used directly says, "we had an FHA loan guarantee feedstock. Fermentation time needs in the next stage of the process. for construction money and written In a working system, about 15% of approval from DOE for a $10 million to be cut to about 12 hours, compared to the currently typical two days or so, the feedstock would be sterilized and grant for the first couple of years of and the fermentation process should used as the growth medium for the operation." After Reagan took over, yield ethanol in at least 12% concen- enzyme-producing fungus. The rest however, both the loan guarantee and tration. In addition, commercial of the feedstock would be pasteurized, the grant were "suspended." Since success, at least for the first plants, cooled, and mixed with the enzyme then, Cadco has turned to private will depend not only on efficient broth and with yeast for the sacchar- enterprise for the money. ethanol production but on a supply of ification/fermentation stage. Com"To date," Emert says, "we've good marketable coproducts, such as bining saccharification and fermen- aroused a lot of interest, but we aren't animal feeds and high-grade lignins. tation provides some important ad- near the $30 million we need. Right According to DOE, the cellulose- vantages, Emert says. For one thing, now, we can project economic feasito-ethanol process that is farthest it saves time. For another, the yeast bility at commercial scale. But it's an along in terms of overall technical and removes the glucose about as fast as uncommercialized technique, there's economic development is a method it's produced. That prevents the a lot of unsureness in the marketknown variously as the Emert process "end-product inhibition" of the cel- place, and people aren't yet willing." (for its inventor, George H. Emert), lulase system that otherwise would Nevertheless, Emert adds, it's "inthe Gulf process (because it was in- occur as the glucose concentration evitable" that cellulose-to-ethanol vented at Gulf Oil Chemicals in the increased. So yields and conversion technology eventually will be com1970's), the University of Arkansas efficiencies are higher. Emert notes mercialized. process (because Gulf donated most that the enzyme broth contains Meanwhile, a Richmond, Va., rights to that school in 1979), or the i8-glucosidase in amounts high enough firm—United Bio-Fuel Industries SSF process (for simultaneous sac- to prevent cellobiose inhibition. Also, (UBFI)—also has bought an option to charification and fermentation, a key Emert says, the growing yeast rapidly license the Arkansas SSF technology. creates an anaerobic environment, The newly formed company has amfeature of the process). By whatever name, the process which eliminates the need for strict bitious plans to build a 50 million gal-per-year ethanol plant adjaent to relies on mutant strains of the fungus aseptic conditions. Trichoderma reesei, developed at The saccharification/fermentation the Petersburg, Va., landfill, where 36 C&EN Dec. 7, 1981
municipal solid wastes would provide the bulk of the feedstock. UBFI is hedging its bets, however. The cellulose-to-ethanol plant is to be the second phase of a two-phase project. Phase one is to consist of a 3000 ton-per-day waste sorting and recovery plant, a 52.5-MW cogenerator (using solid waste and sludge as fuel) to supply power to run the plant and also to sell to utilities, and— maybe—a 12.5 million gal-per-year distillery to make ethanol from corn. Total costs are projected to be $240 million, including $140 million for the optional distillery. If the necessary financing can be arranged, construc tion will start in the spring of 1982. Completion of the first phase would require 24 to 30 months. If all goes well, construction of the cellulose-to-ethanol plant could begin in 1983 and be completed in 1985. UBFI estimates that total investment for the second phase would be about $130 million. Francis B. Richerson, UBFFs di rector of engineering, stresses that making ethanol from cellulosic feed stocks is the firm's ultimate goal. "But first," he says, "we have to tie up our feedstock." The "front end," where the cellulose is separated from the balance of the waste, must be in place and in operation to support the second phase of the project. Also, the decision to license the SSF technology
was based on pilot-plant work. "A few improvements might be in order," Richerson comments, noting that UBFI expects that such improve ments will be made before construc tion begins. The stepwise approach to construction also will make it easier to finance the project, he adds. The company says it has engaged three firms—Teledyne National, Raphael Katzen Associates Interna tional, and Foster Wheeler Synfuels Corp.—to design the project, and that E. F. Hutton is assisting in financial development. Although the package is designed for the Petersburg site, UBFI points out that the system can be adapted, with only minor modifi cations, to any site with an available waste stream. According to Richerson, UBFI already has received "feelers" from other parts of the U.S. Another enzyme-based cellulose conversion process that may be nearing commercialization is the Penn/GE process. That process was so named because the enzyme-pro ducing microorganism was discovered at General Electric laboratories in Fairfield, Conn., and because most of the process development work has been carried out at the University of Pennsylvania, Philadelphia. GE has provided financial support for the work, as has DOE. Other contribu tions to the project have come from
Hahnemann Medical College and lately, from Lehigh University. The GE microorganism, a propri etary species of Thermomonospora, is a thermophilic bacterium that can hydrolyze cellulose rapidly at tem peratures up to 60 °C. In the process conceived at Penn by E. Kendall Pye, Arthur E. Humphrey (now at Lehigh), and associates, wood chips from aspens or hybrid poplars are the primary feedstocks. The method involves pretreatment of the chips with hot aqueous ethanol to yield cellulose, partially degraded hemicellulose, and lignin; the solvent ethanol is recycled. The cellulose can go to a combined, high-temperature saccharification/ fermentation stage, where Thermo monospora enzymes hydrolyze it, mainly to cellobiose, while another thermophilic bacterium, Clostridium thermocellum, ferments the cello biose to ethanol (preventing the cel lobiose buildup that otherwise would inhibit the hydrolysis). Ethanol is removed continuously by mild vacu um. The high temperature minimizes the likelihood of contamination by unwanted organisms. Another possibility involves sac charification without fermentation. In that case, with no C. thermocellum present, it's necessary to add jS-glucosidase (such as solid culture mix ture) to prevent inhibition by cello-
Fermentation isn't the only way to make alcohols from biomass Bioconversion processes Sugars
Starches.
Enzymes
Acid hydrolysis
Cellulosic materials"
Pretreatment
Mid-temperature enzymic hydrolysis
Alcohol
Fermentation
Separation
High-temperature enzymic hydrolysis
By-products
Thermal conversion processes Wood_
Wood.
Gasification
Fast pyrolysis
Synthesis gas
-•
CO + H,
φ. Olefins
Methanol synthesis
Hydration
t Methanol
. Mixed alcohols
Source: Solar Energy Research Institute
Dec. 7, 1981 C&EN
37
Technology Pye notes, however, that research on the integrated cellulose-to-ethanol process continues at Penn and Lehigh, with DOE assistance. Depending on market conditions and feedstock availability, the Penn/GE approach could yet lead to commercial ethanol production, he says. Pye adds that the option of producing high-concentration glucose syrups makes the process well suited to retrofit—that is, to rovide cellulose-conversion capailities for existing ethanol plants. Pretreatment also plays a major role in the cellulose conversion plans of a Canadian company, Ottawabased Iotech. Iotech uses a steam explosion device that, it says, is somewhat similar to the old Masonite gun. Biomass is heated at high pressure with steam, to the point of structural softening. Then the pressure is released quickly, exploding the material and making the cellulose fibers more accessible to hydrolysis. The Iotech process resembles the Emert process in that it uses enzymes from T. reesei (a different strain) to hydrolyze the cellulose and it uses part of the feedstock to culture the enzyme-producing microorganisms. It differs in that hydrolysis and fermentation are separate steps, with the lignin removed from the hydrolysate before fermentation. Iotech asserts that hydrolysis efficiency is so high with the process— 90% conversion of cellulose to glucose and 80% conversion of hemicellulose to xylose—that the lignin "literally falls out the bottom." (Actually, it's removed by filtration.) The lignin is said to be of high quality, suitable for making phenolic resins or other chemicals. The company has carried out pilot-plant operations at the Gulf facility in Kansas, using poplar chips as feedstock. There, Iotech says, the system was able to handle wood concentrations as high as 20 to 25%, and to achieve ethanol concentrations of 6%, high enough for cost-effective distillation. Like the Penn/GE process, the Iotech process offers various product options. However, it appears that the first sizable installation will indeed produce ethanol as its major product. Iotech has a fairly firm agreement with Canada's Mohawk Oil to add a cellulose-converting "front end" to the latter's recently completed fuel ethanol plant in Manitoba. The plant now uses barley as feedstock. The Iotech addition would use poplar and straw, both of which are plentiful and cheap in that part of Canada. According to Iotech vice president Peter
E
Cellulose-to-ethanol production had a slow start in U.S. The history of cellulose-to-ethanol production in the U.S. so far hasn't been a glorious one. In 1943 the War Production Board asked the Department of Agriculture's Forest Products Laboratory to study the German Scholler wood hydrolysis process with a view to using wood wastes to make ethanol. The ethanol was needed to make butadiene, which was vitally needed for production of synthetic rubber. At the same time, Vulcan Copper & Supply (now Vulcan Cincinnati) was requested to follow the pilot-plant work and to prepare an engineering report as the basis for a commercial-scale plant. FPL scientists built a pilot plant at Marquette, Mich., but it soon was moved to Madison, Wis. There, by 1944, FPL had developed a rapid percolation process that was a marked improvement over the original Scholler process, with its batchwise addition of acid. Hydrolysis could be carried out in about three
biose. The process yields glucose syrups at concentrations of nearly 20%, Pye says. The syrup can be used for fermentation to ethanol, for enzymic conversion to high-fructose sweeteners, or whatever. GE has had enough confidence in the work so far that it recently formed a new subsidiary, Biological Energy Corp., headquartered in Philadelphia, to advance the technology further. GE has given the new company a couple of million dollars and a couple of years to come up with something that would merit additional investment by GE and others. Pye has taken a leave of absence from Penn to become president of the new firm. The original idea was to commercialize the cellulose-to-ethanol tech38
C&ENDec. 7, 1981
hours, compared to 16 to 20 hours for the older process, and conversion efficiency was higher. Design and construction of a government-financed industrial plant in Springfield, Ore. (shown above), began in 1944, but the plant wasn't finished until May 1947. Meanwhile, of course, the war had ended; the project was transferred to USDA. The plant made its first shipment—8000 gal of ethanol—in late May, confirming that the plant could be made to function. Details of subsequent production are hazy. The plant was leased, first to Willamette Valley Wood Chemicals Co. and later to Weyerhaeuser, but apparently neither of them could run it at a profit. By the mid-1950's, according to FPL, "it was gone." Nevertheless, it made a valuable contribution to the technology; several modem processes now being developed can trace their ancestry back to the old "Madison process."
nology. But according to Pye, a funny thing has happened on the way to commercialization. Although it appeared that the process could be used to make ethanol at a profit, it soon became equally apparent, he says, that it would be foolish to take highquality cellulose pulp, worth 20 cents a lb, and turn it into glucose, worth maybe 3 cents a lb, for fermentation to alcohol. So, at least initially, the new venture will concentrate its development efforts on the pretreatment phase of the process, with cellulose pulp, lignins, and molasses as the main marketable products. In other words, Pye says, Biological Energy Corp. has no current intention of going into the alcohol business.
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Technology V. Smith, capacity will be about 50 tons per day of dry feedstock, yielding 1 million to 2 million gal of ethanol per year. The plant could be ready for startup within a year, Smith says. Meanwhile, a U.S. licensee, Moter Energy Corp., St. Louis, is trying to arrange financing for a 150 ton-perday plant based on the Iotech tech nology. Molasses and lignin would be the primary products from this plant, however. Moter says Hohenwald, Tenn., is a possible site for the plant. The city is about to build a steam generation plant and could furnish process steam to the proposed mo lasses plant. With the ability to pur chase steam, capital costs for the plant could be reduced to about $10 million, Moter says, adding that the site is also attractive because it's close to cheap feedstocks and to river transportation. In another U.S.-Canadian venture, Stake Technology of Toronto and Vulcan Cincinnati have joined forces to design and build integrated cellulose-to-ethanol plants based on technology from both companies. Vulcan, whose business is the devel opment of chemical process technol
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ogy, has a long history of involvement in the design of alcohol plants (in cluding the Oregon plant based on the Madison process) and other biomass conversion processes. Stake's contribution is the devel opment of continuous digestion technology for pretreatment of lignocellulosic feedstocks. Stake calls the process autohydrolysis; however, it's not talking about the hydrolysis of cellulose to glucose but rather the conversion of hemicellulose and lignin to more easily recoverable forms. In the Stake digester, biomass is fed via a plug-forming feeder into a steam-pressurized cylinder contain ing a screw conveyor. In the vessel, the steam treatment renders the hemicellulose highly soluble in water and the lignin soluble in alkali, Stake says. The material passes through a discharge section that intermittently densifies the product and ejects it to atmospheric pressure. The product then is washed with water to remove the hemicellulose and with alkali so lution to remove the lignin. This leaves the solid cellulose available for saccharification and fermentation, while the xylans and lignin go to their own further processing. Stake notes that the digester sys tem is already in commercial opera tion at two locations, producing cattle feed from aspen chips in Maine and from bagasse in Florida. Three other plants are under construction, the company adds. Vulcan Cincinnati president Don ald R. Miller says the two companies have completed an overall feasibility study and economic analysis for a commercial plant, using wood chips to produce fuel-grade alcohol and other salable coproducts. As a step toward that goal, they hope to attract "multiclient support" for the design and construction of a smaller dem onstration plant. If the money turns up, the plant could be in operation within a year, Miller says. Stake also has contributed to a cellulose-to-ethanol project at Geor gia Institute of Technology. The Georgia Tech approach has been to assemble what it considers the best available technologies for each step of the conversion and to combine them in an integrated process. Those technologies include the Stake pretreatment system and also a Stake-developed acid hydrolysis reactor. According to Alton R. Colcord, Georgia Tech's senior research scientist for the program, the reactor converts cellulose to glucose at ef ficiencies up to 80%, compared to about 55% for other dilute-acid hy-
Wood chips from hybrid poplars are a primary feedstock of Penn /GE process
drolysis processes. He adds that it also should be superior to proposed concentrated-acid hydrolysis pro cesses that would require premium construction materials and expensive acid recovery systems. The high conversion efficiency derives from recycling unconverted cellulose through the multiple-pass plug-flow reactor. Furthermore, Colcord says, the Georgia Tech process can convert cellulose to sugar about an order of magnitude faster than enzyme pro cesses. The preliminary separation of lignin prevents the degradation that otherwise would occur during the acid treatment, so it can be sold for use in molding compounds or for other purposes. Georgia Tech has designed—and had planned to build, with DOE and private support—a 3 ton-per-day unit to demonstrate the process. Execu tion of that plan, like some others, has been delayed by the new DOE policy on demonstration plants; the uni versity still hopes to arrange enough private financing to carry out the project. Another modern approach to dilute acid hydrolysis has been brought to a reasonably advanced state of devel opment with an assist from plastics technology. In a method devised by Barry A. Rugg, Walter Brenner, and coworkers at New York University, cellulosic wastes—wood chips, saw dust, or agricultural residues—are fed
continuously into a twin-screw ex truder of the type used for plastics fabrication. The extruder's design creates a "dynamic seal" that allows the ma terial to be compressed to about 500 psi. In the extruder's process section, sulfuric acid and steam are added to and mixed intimately with the cellulosic mass. The acid-catalyzed hy drolysis requires only about 20 sec onds' residence time in the extruder. That's long enough to convert 50 to 60% of the cellulose to glucose, Rugg notes, but short enough to minimize subsequent thermal degradation of the sugar. The product is discharged to a flash tank for recovery of steam and other volatiles. The glucose-containing slurry that remains is neutralized with lime and extracted with water to yield a syrup that's fed to a conven tional alcohol distillery. Residues are used as boiler fuel to furnish process steam and energy. The process—at least, the cellu lose-to-glucose part of it—has been tested in a 1 ton-per-day pilot plant at NYU laboratories on Long Island. The main piece of equipment is a Werner & Pfleiderer twin-screw ex truder modified by the addition of acid- and steam-feeding and dis charge accessories. In addition, there are the necessary pumps, plumbing, utilities, and process control instru ments. Tests have shown that energy consumption is only about 1200 Btu per lb of feedstock, Rugg says. A company, Alcohol Fuels of Mis sissippi, was formed to advance the project to the stage of building a 4 million gal-per-year demonstration module. Contributors to the program were Vulcan Cincinnati, Werner & Pfleiderer, and Riverside Energy Technology (which is Rugg's con sulting firm). DOE provided funds for a detailed study which showed that the process was feasible. Plans were made to construct the demonstration unit near Vicksburg. Again, the new DOE policy put those plans on hold. Alcohol Fuels of Mississippi has "sort of fallen by the wayside," Rugg says. Meanwhile, development continues at the Long Island pilot plant, with funding mostly from DOE and the state of New York, and Rugg says that private investors may yet be found to support the larger project. Although the processes described probably are the ones farthest along in terms of overall development, it's by no means certain that any of them finally will prove to be the method of choice. They're just the tip of the
iceberg compared to the total alcohol A IN
