DEVELOPMENT OF THE SCHOLlER PROCESS IN THE UNITED STATES W. L. FAITH Office of Production Research and Development,
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War Productiori Board, Washington
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The history of the Scholler process in the United Stdtes during the present war i s outlined. In December, 1949, a proposal to prepare an engineering report on the design and construction of a wood-saccharification plant was made to the Office of Production Research and Development by the American Wood Sugar Company. This proposal was referred to the Chemical Referee Board, which recommended that a study be made in existing pilot-plant facilities at Marquette, Mich., by the Forest Products Laboratory. A contract was subsequently made with the Laboratory to operate this pilot plant for the purpose OF securing adequate design data using American wood species and techniques. Vulcan Copper and Supply Company was requested to follow the pilot-plant operation and to prepare a process report which could serve as a basis for the engineering design of a commercial plsnt. Upon completion of these reports, the Board recommended to the Chemicals Bureau of. WPB that a commercial plant using the modified Scholler process be constructed and operated as insurance against possible future grain shortages. This was subsequently approved, and a plant i s n o w under construction. This paper compares the Scholler process as operated in Germany with the modified process developed in the pilot plant. Factors affecting the economic evaluation of the process are discussed.
of 2000-3000 gallons of 0.5% sulfuric acid were forced through the wood waste beginning at 165 and reaching 180 pounds per square inch in the final batch. Each batch remained in the percolator approximately 45 minutes. At the end of this time a dilute sugar solution was removed from the percolator, cooled in heat exchangers, neutralized, and otherwise prepared for fermentation. Several difficulties were inherent in the Scholler process as practiced in Germany. German economy demands high yields regardless of conversion time and labor requirements. Accordingly the German process was directed virtually to squeezing the last drop of sugar from the wood. The converters in the first plant at Tornesch were ceramic-lined, and it was not unusual to send men into shutdown converters to reset bricks and test each one for leaks. Lignin plugs were not unusual and often had to be removed by hand labor armed with picks and crowbars. Resin deposits fouled the heat-transfer surfaces of the heat exchangers and had to be removed by reaming each tube. At times plant operation had to await this operation even though extra exchangers were at hand. The first commercial Scholler plant was built at Tornesch, Germany, in 1931. I n 1941 it was estimated that at least twenty such plants were in operation in the Reich. I n addition to alcohol, these plants are believed to be producing glycerol and feed yeast from the sugar solutions produced. A plant was built in Manchuria in 1936,and a t least one other is supposedly in operation in Korea. -4t least three were also built in Italy beginning in 1938. Several American companies reviewed and evaluated the Scholler process before the war and even attempted i t on a pilotplant scale. I n every case it appeared to be uneconomical. The American Wood Sugar Company was aware that the German process was not adapted to American peacetime conditions, and based their proposal on the possibility of future grain shortages and the lack of other raw materials. Accordingly, their proposal was presented to the Chemical Referee Board of the Office of Production Research and Development on January 10, 1943. The Board voted to postpone consideration of the proposal until January 30. I n the meantime it resolved to advise the Department of Agriculture that the Board would consider from the Forest Products Laboratory a proposal for study of the Scholler process on a pilot-plant scale. The Board's thought was that the proposal should cover primarily pilot-plant investigations of the Scholler process as adapted to American conditions and species. On January 30 the U. S. Forest Service submitted to OPRD a proposal for the conduct of pilot-plant experimental work at an existing pilot plant owned by the Dow Chemical Company at Marquette, Mich. It was recommended by the Forest Products Laboratory that this experimental work should be undertaken ahead of plant design in order t o obtain satisfactory basic date as to yields, liquid volumes, and times of cycle in order that the process might be successfully applied to American woods. The Chemical Referee Board then adopted the following resolution:
URING World War I1 one of the major increases in chemicals production has been that of ethanol which has been occasioned principally by demands for butadiene manufacture. I n 1939 approximately 150,000,000 gallons of alcohol were produced in the United States; during the present year, goals have been set for over 600,000,000gallons. Prior to the war the chief raw material was imported blackstrap molasses although a small quantity was made from ethylene derived from petroleum gases. Limitations of the availability of these materials made i t apparent early in the war that other raw materials would have to be utilized. Accordingly, about 60% of 1943 alcohol production was based on the use of cereal grains, chiefly wheat. Corn, rye, and grain sorghums were also used. Various proposals for the use of other raw materials were made to the War Production Board from time to time. Among these was a proposal submitted to the Office of Production Research and Development in December, 1942, by the American Wood Sugar Company. This proposal requested Government funds to finance the preparation of plans and operating specifications for an alcohol-wood sugar plant of approximately 1,000,000gallons annual capacity based on the Scholler process; as a corollary, certain investigations adapting the procedures to American species should be financed by the Government; and the Government should finance a survey to determine a proper site for a plant. The Scholler process as carried out in Germany was described rerently by Collins (1). Wood waste consisting of sawdust and chips was compressed in brick-lined steel percolators (45 X 8 feet) to approximately 11 pounds per cubic foot by low-pressure steam (3045 pounds per square inch) and then preheated with live steam to 265' F. Successive batches (as high as twenty-four)
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The Board feels strongly that the Scholler Process for utilizing wood waste, under American conditions, should be thoroughly and quickly ex lored and made ready fgr use when, as, and if needed. The Joard feels that by far the quickest way to attain this end is for OPRD t o arrange a research contract with the Forest Products Laboratory to carry on pilot-plant o erations on a reasonably large scale in the Marquette plant of thebow Chemical Company where a material part of the necessary apparatus is already available, in addition to some previous experience gained in the operation under a Scholler license. The Board urges that thetechnicalassistance of Mr. LevyofLondon and any others familiar with the technical aspects of the process as practiced in Germany be secured on appropriate terms, in addition to such technical information as mav be available in the U. S. Patent Office. The Board suggests that the American Wood Sugar Company and any others interested be given access to information on all stawes of progress so that they ma be in a position to engineer anlmanage a commercial plant, wgenever the erection of such a plant seems justified. The Board urges great expedition in the prosecution of this ilot-plant project and su gests that the contract provide that a taison officer, named by t%eBoard, be assigned to the project. However, the Board believed that the Scholler process would require a more expensive plant from the standpoint of critical materials than any plant in operation in this country, and that it also could not compete on a peacetime basis with alcohol from cheap molasses or from refinery gases. The Board felt, however, that the process should be examined to determine its applicability to American conditions as insurance against a future grain shortage. Shortly thereafter work was begun both a t Marquette and at Madison, Wis. Subsequently, OPRD requested the Vulcan Copper and Supply Company to follow the pilot-plant work at Marquette and the laboratory work at Madison and to prepare a n engineering report which could serve as the basis for the design of a commercial plant suitable for the manufacture of alcohol from wood waste. The Board was kept informed of the progress of the work and on December 6, 1943, in anticipation of the final reports adopted the following resolution: Resolved that in view of the critical ethyl alcohol situation and the dedrability of obtaining information (1) about all methods of producing alcohol commercially and (2) about procedures for the more effective utilization of wood as a raw material, the Referee Board of OPRD approves in principle the erection of a commercial size plant for the production of “wood sugar” from waste by the Scholler process and the production of alcohol from the ‘‘wood sugar”‘ provided that the report to be submitted on the Marquette dot-plant operation indicates that the erection and operation ofsuch a proposed full-scale plant will be feasible; and with the understanding that i t is fully recognized b the Referee Board that the cost of alcohol from wood by the Scgoller process at the outset will probably not be so low as that of alcohol produced by the most efficient known processes, but that there are reasonable prospects that the cost may ultimately be materially lowered when profitable outlets are found for the by-product lignin. Subsequently the reports were issued, and have been summarized by the author (2). Based on the reports and the resolution of the Board, OPRD recommended to the Chemicals Bureau of WPB the erection of a wood sugar plant. On May 15, 1944, WPB approval of the $2,247,000 project of the Willamette Valley Wood Chemical Company for a plant near Eugene, Oreg., to produce industrial alcohol by the hydrolysis of wood wastes was announced by WPB Chairman Nelson: “The plant has been approved on (the basis of its exploratory value. Successful development of a method for large-scale industrial alcohol production from wood wastes would represent a form of national insurance against any future raw materials shortages. Feed and food grains, sugars from the subtropics, and petroleum form the basis of the Nation’s record 611,000,000 gallon alcohol program.” Plant capacity was estimated as 4,100,000 gallons of alcohol per year. The process to be used has already been described (1, 2 ) . Even though the modified Scholler plant at Springfield, Oreg., was authorized on the basis that it was an insurance plant made
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necessary by war conditions, a great many inquiries have been made of WPB concerning the feasibility of this and similar plants in the postwar period. Actually such queries can be answered only after the plant has been in operation for a sufficient time to gather production data. Prior to that time we can make only estimates which, in turn, must be based on a number of assump tions. Unfortunately in many cases that have come to the author’s attention, these assumptions have not been well founded. For instance, it is foolish to say that, since sound estimates show the annual wood waste of the United States to be approximately 80,000,000 tons, by means of the Scholler process we can produce 4,000,000,000 gallons of ethanol annually. Wood availability and other considerations reduce these figures to a much smaller quantity Let us examine the various factors that enter into the price of a gallon of wood sugar alcohol delivered to th,e consumer. The major costs of any chemical may be divided into four categories: raw material cost, processing cost, investment cost, and distribution cost.
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RAW MATERIALS
The chief raw materials for the Scholler process are wood, sulfuric acid, lime, water, and miscellaneous fermentation chemicals. Pilot-plant results indicate that the quantities of major raw materials needed for one gallon of 190-proof ethanol are: Wood (Dou las fir, dry basis), Ib. Hn804 (76%7, lb. Chemical lime lb. Water for periolation and neutreliaetion, gal.
38.4 2.8
2.2
121
The costs of these materials may vary considerably, depending upon circumstances. %w material cost for wood will depend chiefly on its quality, quantity, and location. Wood waste usually includes not only sawdust, slabs, edgings, and. culls produced in milling lumber but also the tops, limbs, and breakage left in the woods. At most mills approximately one third of the total waste is sawdust which needs no further processing before being charged to the percolators. Small mills usually produce a larger quantity of sawdust than larger ones. On the other hand, the actual quantity that may be charged along with chips for optimum percolator operation can be determined only by actual plant operation. Scrap other than sawdust must be hogged into chips, which adds further costs for raw material. This also holds true for woods waste, for which a gathering cost must be added. However, the most important wood quality factor affecting the final cost of the alcohol is species. Pilot-plant results indicate that 52 gallons of 190-proof alcohol may be obtained from a ton of Douglas fir but only 35 gallons from certain hardwoods. The proportion of bark and rotten wood is also an important factor. I n the Douglas fir region about 25% of the mill waste is bark. The quantity of wood available at the site of the wood saccharification plant obviously governs the size of the plant that may be built. This quantity depends on the size of the milling operation being carried out, although wood can be hauled from surrounding territory for a price. Mill operators usually figure on one ton of waste from each thousand feet of lumber cut. If a wood saccharification plant were built at the site of the mill, no hauling charge need be counted. Hauling charges for additional waste vary with transportation facilities, type of terrain, and distance of haul. I t has been estimated that woods waste can be hauled within a 30-mile radius in the Pacific Northwest a t a cost of 10 cents per ton-mile. I n the South more favorable terrain may reduce this cost. The effect of plant location on raw material costs governs somewhat the quality and quantity of wood available. I t introduces a further factor in the form of competition for wood waste for use as fuel, I n certain sections of the Northwest, particularly in the Puget Sound and Columbia River territories of the Douglas fir region, practically all mill waste not used as fuel at the mill it-
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self (generally 25% of the waste) is used as domestic fuel. Current prices for this waste run as high as $6.50 per dry ton at the mill. I n more sparsely settled regions, wood waste is also used for domestic fuel but in much smaller quantities. Another wood supply factor that must be considered is the amount needed for boiler fuel in the wood saccharification plant. The Springfield, Oreg., factory will use the by-product lignin from the percolators for boiler fuel and augment this fuel supply with waste wood amounting to 10% of that needed for raw material, or 3.84 pounds of wood per gallon of alcohol. If lignin were disposed of in some other manner, wood requirements for fuel would be increased by 6.5 pounds per gallon of alcohol produced. I n the South, particularly in Texas, the possibility of using low-cost natural gas or other fuels would alter this situation. A final effect of location on wood costs is the permanence of wood supply. A hydrolysis plant can be built only a t a site where operations are comparatively constant, and where wood may be acquired within a predetermined area during the life of the plant. At $3.00 per ton of delivered dry wood substance, the wood itself represents about 75% of the raw material cost. Accordingly, no attempt a t locating a wood saccharification plant should be undertaken without tl?e advice of an expert with broad knowledge of forestry, lumber mill operation, and the wood hydrolysis process. It should also be kept in mind that, although sulfuric acid and chemical lime are reasonably constant in price, they are lowbulk-value chemicals and delivery costs can be appreciable if long hauls are involved. PROCESSING
The chief items entering into processing costs in any chemical operation are material services, labor and supervision, and maintenance. The material services per gallon of 190-proof alcohol per day for a wood saccharification plant of the size under consideration are: Water for distn. and miscellaneous uses), gal. Steam {190 lb./sq. in.), Ib Electric power (440-3-60) (connected load), h.p. Compressed air, cu. ft.
42.3
96 0.08
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The largest item in this list is steam, which depends largely on the source of fuel. This cost may vary considerably from one location to another and can be calculated only for a specific site. Labor requirements can be determined only after a commercial plant has been in operation for some time. I n German practice, the wood saccharification plant was often integrated with other operations, so labor requirements were indefinite. It has been estimated that the total labor requirement for the Springfield, Oreg., plant excluding supervision will be about 700 man-hours per 24-hour day, or 0.06 man-hour per gallon of 190-proof alcohol. Maintenance requirements are difficult to estimate accurately in advance of plant operation, and depend to a large extent on proper selection of materials and adequate design. By breaking the process down into its component parts, some idea of the variation of maintenance problems can be obtained. Equipment for such a plant can be roughly divided into three parts-wood preparation equipment, hydrolysis equipment, and fermentation and distilling equipment. Although maintenance in an alcohol plant is often estimated a t 4y0of the selling price of the alcohol, this may not apply closely to a wood hydrolysis plant. Wood preparation equipment, such as mills and conveyors, has many moving parts subject to considerable shock and will demand higher maintenance costs than fermenters and stills. Likewise, the handling of acids in the hydrolysis equipment may also alter the usual maintenance rate. INVESMENT
The fixed charges in any plant are generally divided into amortization, depreciation, taxes, and insurance. Of special significance in 8 wood sugar plant are the first two items. Experience to date indicates that a wood saccharification plant is the most expensive
of all types of alcohol plant, with the possible exception of one based on petroleum gases. Accordingly, a plant must be of high capacity in order to keep fixed charges at a minimum. Unfortunately, the'cost of various sized Scholler plants is not known, The actual investment cost is known only for the Springfield, Oreg., plant which is $2,247,000 for a capacity of 11,500 gallons per day. Amortization of this plant over varioua periods would reflect alcohol costs as follows: Centa per gal. of Alcohol
Years of Amortisation
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5 10 15 20
5.6 3.7 2.8
These figures do not appear so high in themselves, but they do not include interest on the investment or replacement of those pieces of equipment which may have to be discarded before the plant is fully amortized. Undoubtedly depreciation will be a key factor. The average life of the wood handling equipment will probably be fifteen years; certain equipment subject to acidic solutions can rewonably be given a life of only five years. On the other hand, filters, stills, fermentation equipment, and the like may have a life expectancy of twenty years. These factors will undoubtedly increase fixed charges. A smaller plant would have even higher fixed charges. For instance, if we assume that a plant of half the capacity would cost three fourths as much as the one under consideration, the figures for amortization (neglecting interest and depreciation) would be 16.6 cents per gallon for a five-year amortization and 4.2 cents for a twenty-year amortization. On the other hand, we must realize that the above figures are based on the assumption that the actual capacity of the plant under consideration is the same as its design capacity. This may be approximately true, but only actual operation can give the true capacity upon which costs must be based. DISTRIBUTION
The most important factor in distribution costs, as far as a Scholler plant is concerned, is the necessity for building the plant near a wood supply which may often be far removed from large alcohol markets. Therefore, in many cases distribution costs may limit the size of a plant by limiting the favorable market area. Actually an adequate market survey should precede selection of a plant location. EFFECT O F BY-PRODUCTS
One factor which may greatly alter all cost estimates of alcohol from wood is disposition of the by-products. For each gallon of alcohol 13 pounds of lignin are produced on the dry basis. Under the present circumstances this can be credited with its fuel value alone. Possible other uses are the subject of considerable research which may increase its value. Each cent per pound increase in value over the fuel value alone will reduce alcohol costs by approximately 10 cents per gallon. Obviously, then, an adequate market for lignin can effect great economies in alcohol production. A further factor of importance is the alternate use of a portion of the wood sugar solutions not needed for alcohol production. Production of butanol and acetone, yeast, butylene glycol, and other fermentation products may alter the economic situation markedly. Taking all of the above factors into consideration, two conclusions are preeminent: (a) Until commercial operation of a Scholler plant has been carried out for a t least a year, adequate operations cost data cannot be determined; (b) for a new plant of given capacity, plant location will play a great part in cost determination. LITERATURE CITED
(1) Collins, Chapin, Chem. & Met. Enu., 51, No. 7,100-1(July, 1944). (2) Faith, W. L., and Hall, J. A.. Chem. Eng. News, 22,525-6 (1944).
