483
Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, 483-489
Additional difficulties with this fermentation include the need for strict anaerobic conditions, delicate culture maintenance and propagation, and a tendency for bacteriophage infection and Lactobacilli contamination. If improved upon, however, the acetone-butanol fermentation has the potential of becoming a major source of highly valuable chemicals and fuels in future years. Acknowledgment
The authors gratefully acknowledge partial support received for this project from the Solar Energy Research Institute (SERI), Golden, Colo. Nomenclature
AMP = adenosine monophosphate ADP = adenosine diphosphate ATP = adenosine triphosphate CoA = coenzyme A NAD+ = nicotinamide adenine dinucleotide (oxidized form) NADH = nicotinamide adenine dinucleotide (reduced form) PPi = inorganic pyrophosphate TPP = thiamine pyrophosphate L i t e r a t u r e Cited Beesch, S. C. Ind. €ng. Chem. 1852, 44(7), 1677-1662. Bernsteln. S.; Tzeng. C. H.; Sisson, D. Biotechnol. Bioeng. Symp. 1877, 7, 1-9. Buchanan. R. E.; Glbbons, N. E., Ed., ”Bergey’s Manual of Determinative Bacteriology”, 8th ed.;Williams and Wlikins Co.; Baitlmore, 1974.
Doelle, H. W. “Bacterlal Metabolism”, 2nd ed.;Academic Press: New York, 1975. Falth, W. L.; Keys, D. 6.; Clark, R. L. “Industrial Chemlceis”, 3rd ed.; Wlley: New York, 1965; pp 181-188. Graf, T. F. ”Economics of the Whey Roblem”, paper 114 presented at the Whey Products Conference, Atlantlc Cky, NJ, 1976. Krahn. L., Agricultural Statlstlcian,Wisconein D q m M of Agiculhre, prlvate communication, 1979. Landy, T., Publlcker, Inc., Phliadelphla, private communications, 1979. Laugh, H. W. ”Truck Transportatlon Costs of Bulk MIW, Report AOERS-33 (NTIS), Economic Research Service. U S . Department of Agiculture, 1977. Unsley, J. Chem. €ng. May 21, 1878, 86, 201. O’Sulllvan. D. A. Chem. €ng. News Apr 23, 1878, 11. Pace, G. W.; Oddsteln, D. J. "Economic Analysis of UltraflbationFermentation Plants Produdng Whey Proteinand SCP hom cheese Whey”, In “SI@ Cell Roteh. II”, S. Tannenbaum end D.I. C. Wang. Ed.; MIT Press: Cambridge, Mass., 1975. Perlman, D., CH€MEC/-/July, 1877, 434-443. Peters, M. S.; Tlmmwbus, K. D. “Plant Deslgn and Economlcs for Chemlcal Englneers”, 3rd ed.; McGraw-HIik New York, 1980. Reesen, L.; Strube, L. Recess Blochem. 1878, 13, No. 11. Shreve, R. N. "Chemical Process IndWies”, 3rd ed.;MCGrawHIk New York, 1967. Sobmons, G. L. Process Blochem. 1876, 11(4), 32-37. Stank, R. Y.; Adelberg, E. A,; Ingraham, J. “The Mlcroblai World”, 4th ed.; PrentlceHall: Englewood Cliffs, NJ, 1976. Webb, L., IMC (Formerly Commercial Solvents Corp.), Tene Haute, IN, private communication, 1979.
Received for review May 5 , 1980 Accepted September 15, 1980
This paper was presented in part at the 179th National Meeting, of the American Chemical Society, Houston, Texas, Mar 23-28, 1980, Division of Industrial and Engineering Chemistry.
11. Symposium on Fuels and Chemical Feedstocks from Renewable Resources E. S. Lipinski, Chairman 11th Central Regional Meeting of the American Chemical Society Columbus, Ohio, May 1979
Economics of Ethanol and D-Glucose Derived from Corn Carroll R. Kelm 50 Glenbrook Road, Stamford, Connecticut 06902
As a renewable source of chemicals, corn offers a number of advantages: ready avallabllity In large quantities, established processing technologies, and low product costs. Subjected to the “wet-milling’’ process, it provides corn oil and hgh-protein animal feeds as valuable byproducts which reduce significantly the effective cost of products made from the corn’s starch content. Operations are in place for the production of high-purity wlucose solution with low ash and light color at low enough cost to merit its consideration as a potential replacement for some nonrenewable chemical materials. By comblnlng the technologies of corn wet-milling, enzymatic starch hydrolysis, and petrochemical distillation, fermentation ethanol may already be highly competitive with synthetic alcohol produced from ethylene: its costs are significantly less than alcohol produced by traditional methods.
Rapidly increasing prices and diminishing supplies of petroleum products underscore the urgent need for solutions to fuel and raw material problems-immediate as well as long-range. The mushrooming demand for ethanol from renewable resources to supply the gasohol program makes it imperative to start producing the largest possible quantities in the shortest possible time and at the lowest possible cost. The only possible solution, at least for the near to medium
term, is through fermentation of agricultural products, especially corn, since technologies and infra-structures for other processes are far from being in place. Questions about the economic and other implications of using grains for this purpose are many, and they are not susceptible to easy general answers. However, this paper is intended to help answer the questions by providing background information and some technical detail on the nation’s agricultural system’s ability to support an inten0 1980 American Chemical Society
484
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980
Table I. U.S. Corn Production and Yields (Source : U.S.D.A. ) bu per acre 1930 1940 1950 1960 1970 1975 76 77 78 79
20.5 28.9 38.2 54.7 72.4 86.3 87.9 90.7
100.8 109.4
billions bu 2.08 2.46 2.76 3.91 4.15 5.83 6.27 6.43 7.09 7.76
Table 11. Use of Corn Crop (Millions of Bushels; Source: U.S.D.A.) man-hours/ 100 bu 108 53 20 7
flop Ye? ending alcoSept 30 fooda holb seed 1976 1977 1978 1979
399 419 462 488
71 74 70 69
1976 1977 1978 1979
6.4 6.5 6.5 6.9
1.1 1.2 1.0 1.0
20 20 18 18 percent of
4
a Although “bushel” should really be a volume measurement, in grain it means weight. For corn, a bushel is defined as 56 lb irrespective of its bulk density.
sive corn-alcohol program and on the economics of certain alternate processing technologies. Processes and economics of making high-purity corn starch and D-glucose are also given. Corn as a Raw Material Corn is an immediately available raw material for industry. It is currently produced in such large volume that it is a problem for the Government, and still greater quantities can easily be grown. Furthermore, extremely efficient systems are already in place for commercially handling corn from the seed through culture, harvest, collection, storage, grading, transport, marketing, and shipping, all at a very low cost. Corn availability, both present and future, is very great. Today there are some 1 200OOO OOO bushels being withheld from the market under government programs. This is enough to make more than 3000000000 gallons of fuelgrade alcohol, and as more is needed there is plenty of land waiting to be cultivated-land that is being kept idle under government programs to reduce production. As will be seen in Table I, the American farming complex has established an outstanding record of constantly improving its results. Since 1950,corn production per acre nearly tripled from 38 to 102,the total crop increased by more than 4000000000 bushels and the labor input dropped from 53 man-hours per 100 bushels to a mere 4! If this had happened in a factory with $8 per hour labor costs, this would represent a savings of some $4 per bushel, against a present market price of some $2.50. The actual cost of growing corn not only varies from crop to crop and region to region and farm to farm, but also with how the accounting is done, especially as to how the factors of management cost and land usage charges are handled. Nevertheless, it is important to note that, except for aberrations such as the Russian grain purchase and corn blight scare, in constant dollars the market prices of corn have constantly tended downward. Present uses of the corn crop (Table 11) leave great opportunity for its use as a raw material for fuels and chemicals, since less than 8% of the crop is processed for human consumption and one-third of this is byproducts used to enrich the protein in animal feeds. The remaining 92+% of the corn crop goes for animal and poultry feed, for export, and into surplus storage. As for export, these markets are interested primarily in protein, not the starch content. Thus it should be possible to use the starch in the US. as a raw material and export the remaining one-third to supply export needs for protein. Thus as a raw material, corn offers a great many important advantages: immediate availability, possibility of increased supplies, and reasonable prices. Even so, our
Primarily wet-milling.
feed
export
total
3592 3587 3710 4198 crop
1711 1684 1948 2133
5793 5784 6208 6906
57.3 55.8 52.4 59.2
27.3 26.2 27.5 30.1
92.4 90.0 87.7 97.5
0.3 0.3 0.3 0.3
Includes beer.
Material
-
STARCH
C6H10G5
WATEZ
H20
1
D-GLUCOSE
I ETHANOL
CAREON
DIOXIDE
Molecular
I
Weisht 162
18
1
C6H120b
I ZC2H jGH
92
2CG2
88
Figure 1. Conversion of starch to ethanol.
needs are so large that corn alone cannot solve the total US.energy problem-but it can be a very important help. Traditional Ethanol Fermentation Until the end of World War 11,ethanol in the US.was made by fermentation, primarily of molasses, corn, and other grains. After the war, the higher quality and lower price of synthetic alcohol made from ethylene derived from petroleum or natural gas permitted it to gain the market for all uses except beverages, which is largely a legal question. As shown in Figure 1, the starch in corn, or from any other source, combines chemically with water to form Dgluccee and gains 11.1% weight in so doing. The glucose then may be fermented to ethanol and carbon dioxide in a ratio of about 51:49. Based on the starch, alcohol yield is theoretically 56.8% and C02 is 54.3%, but actual yields of alcohol were usually well below 90% of theoretical, and the COPwas not often recovered. The dry basis composition of U.S. corn averages about 72% starch, 10% protein, and 4.5% oil. The rest includes cellulose, pentosans, ash, sugars, fats, vitamins, and other materials. For the D-glucose and ethanol, the starch component is the starting material and the others are treated as byproducts. The traditional process for making fermentation alcohol from corn is shown in block outline in Figure 2. In this process, shelled corn is dry-milled, suspended in water, and heated to the boiling point with steam in order to gelatinize or “cook” the starch. In this step, the starch granules first absorb water and then burst, freeing the starch molecules for easy reaction in subsequent steps. After cooking, the solution is cooled to about 60 OC and “malt” is added. This malt is simply barley grain which has been allowed to sprout, thereby releasing the enzymes that turn starch into sugar for the benefit of the growing seedling. The principal enzymes are a-amylase, which reduces the length of starch molecules by randomly cutting
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980 485
cor
CORN
* 1
WATER
STEAM
1
1
-
coz
D ALCOHOL
HYDROCLONES
EVAPORATOR
PRIME
I
7 DRYER
I ,GRAINS AND SOLUBLES
Figure 2. Distillery process.
them, and &amylase, which splits off successive molecules of maltose, a disaccharide. These enzymes attack the corn starch just as if it were barley, converting it to maltose. However, before the reaction has proceeded to completion, the mash is cooled to below 30 “C, its pH is adjusted, and it is transferred to the fermentors where yeast is added. This yeast is of the same class as that used in bakeries and breweries, but especially selected for useful characteristics, primarily its ability to tolerate high concentrations of alcohol. The yeast is usually grown to its final volume on mash that has been by-passed from the fermentors. The fermentation reaction is strongly exothermic, proceeding rapidly at first but then slowing down as the carbohydrate is consumed and the alcohol concentration increases. Yeasts perform best at temperatures under 30 OC, so substantial cooling is required to counteract the generated heat. After the sugars are consumed, which may take up to 72 h in a conventional unit, the dilute solution of alcohol, called “beer”, passes to the beer still which strips alcohol from the fermented mash and concentrates to some 60 to 70% by volume, after which it is further refined. After the alcohol has been removed, the material remaining at the bottom of the beer still includes the yeast and all of the solubles and insolubles from the corn including protein, oil, fiber, unfermented carbohydrates, etc. These are recovered by dewatering the insolubles and concentrating the solubles in a multi-effect evaporator, after which the two are mixed and dried together to produce “distillers dried grains and solubles”, which is used as an ingredient by the mixers of animal feeds. As shown in Figure 2, some of the liquid from the bottom of the still is recycled to the fermentors in order to reduce the total amount of fresh water entering the system and thus the amount that has to be evaporated. In this process there are inherent problems which lead to high operating cost. (a) When the cooked starch is cooled before adding the malt, some of it sets back, or retrogrades, so that it can no longer by hydrolyzed. (b) The cooking method used requires large amounts of water and thus large equipment and extra steam. (c) The liquid in the still bottom contains high amounts of solubles and
I
FRESH WATER
Figure 3. Basic corn wet-milling process.
this limits the amount that can be recycled, so the remaining large amounts must be evaporated. (d) Even though the “dried grains and solubles” contain all the noncarbohydrates from the original grain, the proteiP percentage is so low that the market value is not outstanding. These deficiences may be largely overcome by using several of the procedures that were developed in the corn wet-milling process for producing starch and in the enzymatic process for converting starch into D-g1UCOSe. Corn Wet-Milling Figure 3 shows the basic steps of the corn wet-milling process for obtaining from corn not only starch but also commercial yields of corn oil and concentrated protein. In this figure the dotted lines represent water and the solid ones represent dry matter. Corn is steeped in a warm sulfurous acid solution for some 25 to 40 h in order to toughen the hull and germ, to soften the protein matrix that holds the starch granules, and to leach out soluble ash, protein, and carbohydrates. This solution leaves the process as “light steepwater” and is concentrated in a multi-effect evaporator to about 50% solids for sale as a fermentation nutrient or liquid animal feed, or it may be dried together with fiber as described below. The germ which contains riiost of the valuable corn oil is recovered by coarse milling, followed by hydroclone separation, countercurrent washing, dewatering, and drying. It is then expelled or extracted yielding about 1.6 to 1.75 lb of oil per bushel of corn. The degermed slurry is further milled, the fiber removed by screening, countercurrent washing, dewatering, and drying-usually together with steepwater to produce “corn gluten feed (21 5% protein)”. Next the insoluble protein is removed centrifugally, concentrated, and dried. This product is called “corn gluten meal (60% protein)” and is sold at attractive prices. Finally, the remaining slurry is washed countercurrently with fresh water to remove solubles and protein, and it leaves the system as a sluny of refined starch at about 40% dry substance. Important features of this process are its economical use of water and the high value of the byproducts. It will be
486
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980
Table 111. Byproduct Values and Net Corn Costa
STARCH SLURRY
distillery wet-milling compn, % moisture protein oil other
lbper bu dperlb dper Bu gross corn
oil
feed
meal
grains total and credit solubles credit
0 11 10 0 22.5 62 100 2.5 2.5 0 -64 25.5 100 100 100 oil 1.7 36 61
feed meal 11.2 3.3 6 14 67 46
8 27 9
AMYLASE
GLUCO-AMY LASE
+ 9
u-
56 100
FILTER
DDGS 16.8 7 $1.74
(1
RESIDUE
EVAPORATE
$1.18
2.50
2.50
$0.76
$1.32
CARBON
a
Clean corn basis.
noted that the only entry point for water is at the starch washing station and that no water is sewered: it only goes out with the products and is evaporated. The high byproduct value comes from the high yield of corn oil and the high protein content of the corn gluten meal. Table 111shows how the value of these byproducts compares with that of distillers dried grains and solubles. In this table, the yields shown are approximate commercial averages, and the prices are recent ones on the appropriate commodity market. Using these data, it is seen that distillers dried grains and solubles sold for about $450/ton or 7t/lb, so the 16.8 lb produced per bushel give a return of $1.18. The byproducts from wet-milling come out at $1.74/ bushel or 58e more than this. Oil alone returns some 61e, meal another 46t, and feed, 67e. If corn had cost $2.50/bushel, then the real net cost after byproduct credit is only 76e. About 32 lb of dry substance starch is produced per bushel, so the net cost of the corn used in that starch is only about 2.38t/lb. This of course is only an example. Actual figures change continually and depend upon a great many market variables. After this millhouse process, many things may be done with the starch. I t may be modified, dried, blended, dextrinized, hydrolyzed into malto-dextrins, glucose syrups, or D-glucose solution, and the latter in turn may be crystallized (standard commercial “dextrose”), converted into sorbitol and ascorbic acid, isomerized into high fructose syrup, etc. D-Glucose By using the process shown in Figure 4 the conversion of starch to D-glucose is nearly quantitative. The starch slurry at 35-40% dry substance is treated with thermophilic a-amylase and cooked to a temperature above 100 “C, followed by retention at a slightly lower temperature. This produces a solution that does not set-back on cooling to 55 to 60 “C as required for saccharification which is carried out by glucoamylase (amyloglucosidase) over a period of 36 to 48 h. The hydrolysate is refined by filtration to remove intreatment with granular activated solubles (less than l%), carbon to remove color bodies and their precursors, and by ion exchange to remove ash. The resulting crystal-clear, water-white solution contains 97% or more pure D-glUCOSe and has a “dextrose equivalent” of 98 to 99%. Pro-forma costs for producing this sugar are shown in Table IV. These figures refer to a plant which grinds 35000 bushels of corn per day and converts all of it to D-glucose solution. The battery limits cost of the processing sections are about $20 million for the millhouse and $15 million for the glucose section. Steam and power are
v ION EXCHANGE
POLUCOSE SOLUTION
Figure 4. Process for D-glucose. Table IV. D - G ~ U C O Solution. S~ Cost of Production ($ per 100 lb of Dry Substance)
starch battery limits plant cost ($ millions)a variable costs raw material steam (at 3.50) power (at 5$) supplies total variable fixed costs dep., maint., ins. (15%) salaries and wages plant overheadtotal fixed total plant cost
D-ghCOSe
20.0
14.8
$2.3Bb 0.39 0.94 0.06 3.77
$4.52c 0.28 0.10 0.82d 5.72
0.78 0.39 0.08 1.25 $5.02
0.51 0.04
0.55 $6.27
a First quarter 1979 costs of process only-excluding site, boilers, services, corn storage-stimated by author for 35 000 bushel per day units. Net corn, $0.76 bu; starch yield, 32 lb/bu. Starch cost, $5.02/100 lb; Includes carbon and ion glucose yield, 111 lb/100 lb. exchange.
costed at $3.50/1000 lb and 5e/kWh, respectively; depreciation, maintenance, and insurance are taken at 10, 4, and 1% of the plant investment per year. All expenses except those directly attributable to D-glucose are charged to starch. Using the $2.38 per cwt net raw material cost derived earlier (Table 111 and text), the plant cost of starch in the slurry form is a little over $5.00/100 lb of dry substances. To make 100 Ib of D-glucose, 90 Ib of starch ($4.52) is required. When all the variable and fixed department costs are added in, the total plant cost of D-glucose in solution is about 6.25@/1bof dry substance. Improved Ethanol Process The deficiencies of the traditional distillery process can be largely overcome by making use of the wet-milling and glucose technologies, and Figure 5 shows one of various process designs for doing this. The first part of the process is like wet-milling-removal of the solubles followed by recovery of corn oil-and although fine milling is omitted, the protein is recovered as corn gluten meal (60%). A
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980 487 Table V.
CORN
.1
traditional wet-mill -with and difenzyme alcohol ference battery limits plant cost ($ millions)a variable costs raw material steam (process) steam (distillation) power supplies and enzyme total variable fixed costs dep., maint., ins. salaries and wages plant overhead total fixed total-ex-battery limits 20% return on plant Cost total
t
01L
OLUTEN
L--r--A
I
?
STARCH
c$iE STEM
Fuel Alcohol Pro-Forma Costs ( $ per Gallon)
UWEFY
FERMENT
20.9 0.51 0.12 0.12 0.06 0.05 0.86
30.2 0.29 0.06 0.12 0.11 0.06 0.64
0.10 0.13 0.04 0.05 0.01 _ _ -0.01 0.15 .19 $1.01 0.83 0.13
0.19
+9.3 -0.22 -0.06 +0.05
+0.01 -0.22
+0.03 +0.01 t .04
-0.18 +0.06
- - $1.14
1.02
-0.12
ALCOHOL WATER
1
t
DEUIWTIR
J
a DRYER
I
FEED
Figure 5. Wet-milling process for alcohol.
dewatering step is included before mash cooking in order to keep solubles for going forward. The same process as for D-glucose is used to liquefy and saccharify the starch, but shorter saccharification time is used, since maximum conversion is not required for the fermentation. Fermentation may be carried out by traditional means, but new short-time and continuous methods may be used to advantage. The beer still bottom material is dewatered as in the distillery, but since this liquid is low in solubles, it can be recycled to the fermentors and back through to the beginning of the process. This reuse reduces the amount of water put into the process and thus the amount to be finally evaporated (at the steepwater evaporator). With this system, the difficulties of the traditional distillery are greatly alleviated. (a) Higher value byproducts are produced, and this reduces the cost of alcohol. (b) Less water is used, so there is less to evaporate, reducing the energy consumption as steam. (c) Enzymes convert more starch to fermentables than malt does, so alcohol yield is higher and its cost lower. (Note that cost comparisons in Table V are based on use of enzyme in both processes.) (d) Yeast recycle is also possible. This increases the alcohol yield by substantially reducing the amount of fermentables consumed in the propagation department and in the fermentors for growing yeast instead of producing alcohol. This also lowers the cost of the alcohol. With slight modification, the process can be used to make starch as a product along with the alcohol. This would be attractive to a company wishing to produce both alcohol and starch or its products as chemical raw materials, or it could be beneficial to an alcohol producer to be able supply starch or sweeteners to a regional market. In both cases, the larger volumes reduce costs through economies of scale, and the two products work smoothly together in the process. Alcohol Before it can be used commercially, the alcohol product
See Table IV.
from the beer still must be further processed according to market demands. For beverages, as a chemical intermediate and for many solvent uses, impurities must be removed as completely as possible, but for use as a fuel the impurities may remain. Furthermore, permissible water content varies with the use. For chemical purposes, the alcohol must be anhydrous, but up to 0.5% water is allowed when it is to be mixed with gasoline for fuel, and 4-5% is normal for beverage-grade spirits and most solvents. To produce these different product grades, process engineers and still designers have developed a great many different column designs and configurations. In addition, with today’s major interest in saving energy, considerable effort is being directed toward the reduction in the amount of steam used in distillation. Here substantial progress is being made through reducing the number of columns, using different solvents for dehydrating, operating under pressure or vacuum, using reboilers, mechanical or thermal recompression, etc. Product Costs The cost advantage of a combined process is shown in Table V by comparing it with a traditional process which has been improved by using enzymes instead of malt. If malt had been used, the cost of alcohol would have been significantly higher. In examining these figures, it should be borne in mind that the reported “cost” of any product will vary with the values used for a very great number of inputs and with assumptions and policy decisions made by the accountants and system that produced the figure. No costs of different products or of products from different sources should eker be compared without being sure that the underlying data are comparable and are being treated in the same fashion. In this table, grain cost, byproduct values, steam cost ($3.50) and power (5&)and annual rates for depreciation, maintenance, and insurance (15%), etc. were the same as used in the previous example (Tables I11 and IV). These and all other factors were applied consistently to both sets, and both plants produce 90000 gal per day of 99.5% alcohol for the gasohol program. Under these conditions, the cost of producing alcohol in the wet-milling process would be some 18g/gal lower
488
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 4, 1980
Table VI. Bases for Calculation
Table VII. Calculation Details
Common to Both Processes minimum possible water usage in cooking liquefaction with a-amylase saccharification with glucoamylase 95%of theoretical yield of alcohol from glucose feed byproducts dried to 10%moisture solubles evaporated to 50%moisture before drying dryer uses 1.36 lb of steam to remove 1 lb of water evaporator uses 0.237 l b of steam/lb of water annual depreciation, maintenance and insurance, respectively, l o % , 4%, and 1%on fixed assets
Byproduct Return ( $ per Bushel) distillery
1975 1976 1977 1978 1979 1980a
Distillery 3%of the mash is diverted t o propagate yeast still bottoms dewatered to 35%solids one-fourth of the overflow is recycled, remainder evaporated yields per bushed of corn: 99.5%fuel alcohol 2.60 gal D.D.G.S. 17.3 lb
1975 1976 1977 1978 1979 1980b
DDGS 110.58 317.08 129.58 122.42 134.42 134.33
feed 86.01 100.15 101.43 96.75 126.22 133.12
meal 215.60 249.09 252.52 234.60 274.48 245.92
oil, dllb 32.53 25.63 29.63 36.62 33.67 27.50
Prices for Distillers Dried Grains and Solubles (DDGS) from “Feed Situation” USDA, various tissues, averages by author. All other prices from “Sugar and Sweetener Report”, USDA Vol. 5, No. 5, May 1980, p 20. First quarter 1980.
than with the improved traditional process. Furthermore, although the wet-milling process requires a larger capital investment, the per gallon profit is still 12&/galhigher even after taking a 20% return on the the extra investment. In a plant this size, the advantage would add some $4 OOO OOO to the profits, above that of the other plant. Of course actual figures will vary from these examples. Total investment will be higher when land and improvements, corn storage and cleaning, product storage, and other similar costs are added. Total product costs will also be increased by charges such as general and administrative overhead, selling expenses, and financial charges if they are allocated. Nevertheless, since alcohol for gasohol sells today at about $1.50 per gallon, the profit opportunity is very attractive. Summary 1. As a raw material, corn can make a valuable contribution to our economy since it is a renewable source for chemicals and ethanol. It is already grown in very large quantities and delivered to the consumer at attractive prices. It can be easily stored, transported, and processed using infra-structure and processes that already exist. If greater quantities are needed, much more could be produced if governmental policies were altered. 2. The introduction of cheap synthetic alcohol nearly caused the demise of the U S . fermentation alcohol industry. It had little money or incentive to invest in im-
oil, 1.61b
feed, 9.9 lb
meal, 3.61b
total
0.96 1.01 1.12 1.06 1.16 1.16
0.52 0.41 0.47 0.59 0.54 0.44
0.42 0.49 0.50 0.48 0.62 0.66
0.39 0.45 0.46 0.42 0.49 0.44
1.33 1.35 1.43 1.49 1.65 1.54
distillery 1975 1976 1977 1978 1979 1980a
bu
gal
1.95 1.69 1.10 1.25 1.48 1.43
0.75 0.65 0.42 0.48 0.57 0.55
wet-milling difference, bu gal $/gal 1.58 0.58 -0.17 1.35 0.50 -0.15 0.79 0.29 -0.13 0.82 0.30 -0.18 0.99 0.37 -0.20 1.05 0.39 -0.16
Byproduct Drying
Corn and Bytwoduct Pricesa dollars per ton
17.3 lb DDGS
Net Raw Material Cost (Dollars) (Corn minus Byproduct Return)
Wet-Milling water flows countercurrently, with internal recycles, and is removed with dewatered byproducts and as steepwater yields per bushel of corn: 99.5%fuel alcohol 2.71 gal 1.6 lb corn oil 9.9 lb feed (21%protein) meal (60%protein) 3.6 lb
corn, $/bu 2.91 2.70 2.22 2.31 2.64 2.59
wet-milling process
process
lb of water/ gal of alcohol
distillery dryers evaporator
__ 57.5
9.1
factor
lb of steam/ gal of alcohol
1.36 0.231
13.6
66.6 wet-milling dryers evaporator
11.8
difference
18.0 48.6
6.2
12.4 26.0
1.36 0.237
8.4
2.8 11.2 14.8
Total At average unit cost rates, the total difference resulting from these major items would be some 15d/gal in favor of the modified wet-milling process over the distillery process: 1. raw material cost - 16.6dlgal 2. depreciation, etc. +4.2 3. steam (at $3.50) -5.3 4. power (at 0.05) t 2.0 5. labor (at $8.00) +0.4 -15.3dlgal a
First quarter 1980.
proving its high-energy, low yield, low byproduct return process. 3. Nevertheless, major advances which are applicable to alcohol production were being made in other industries, notably in the process and equipment for corn wet-milling, enzyme technology, fermentation techniques, and distillation design. As a result, the efficiency of producing ethanol from corn and the cost of doing so, are much lower than the literature indicates. 4. Furthermore, using modern technology, D-glucose of high purity can be produced at a battery limits plant cost today at about 6.25t/lb of dry substance. The cost would be still lower if carbon and/or ion-exchange treatments were omitted. 5. With a combined wet-milling and alcohol process, ethanol may be produced at a much lower cost than with the modern distillery process. In the example, this advantage was 12t-after a 20% return on the investment. This process may easily be adapted to produce starch or starch sweeteners in addition to the alcohol to give added flexibility and marketing capabilities.
Ind. Eng. Chem. Prod. Res. Dev. W 0 Q , 19, 489-496
Acknowledgment This paper was orginally presented at the 11th Central Regional Meeting of the American Chemical Society, Columbus, Ohio, on May 9,1979, at the Chemical Economics Section, chaired by E. S. Lipinsky. Appendix Cost Differences Resulting from Different Processes. The cost figures in Table V are calculated for total plants operating with modern distillery and wet-milling processes using prices of early May, 1979. It is assumed that fermentation and distillation processes are the same, so that the cost differences are the result of differences in the processes for milling the corn and producing the byproducts. This Appendix is intended to enlarge on the practical differences by examining the background of the costs and how the total product cost varies with changes in the costs and values of the different cost elements. The major assumptions used in these calculations are shown in Table VI and the calculations in Table VII. This significant cost differences between a distillery process using enzyme hydrolysis and a modified wetmilling process also using enzyme hydrolysis are the following. 1. Raw Material Cost. Over the past several years, the net corn cost per gallon of alcohol has been from 13 to 196/gal lower using the wet-milling process, with an average advantage of 15.9&/gal. 2. Capital Investment. For a plant producing 33 million gal of fuel alcohol per year, the investment would be higher for the wet-milling process to the extent of about $9.3 million. This translates into a higher cost of 4.2@/gal for depreciation, maintenance, and insurance. 3. Byproduct Drying. Less fresh water is used in the wet-milling process so that there is nearly 50 lb of water
480
less to be removed per gallon of alcohol. This results in using a total of 14.8 lb of steam less per gallon. The monetary difference depends upon the cost of fuel, type of system, energy-saving installations, etc. At different costs of steam, the savings are Steam,
$/lo00Ib 2.50 3.50 5.00 7.50
savings, dlgd 3.8 5.3 7.5 11.2
4. Power. The webmilling process uses about 0.41 kWh of power per gallon of alcohol, primarily in steeping, byproduct washing, and oil expelling. At different power rates, the added cost is 2.5 3.5 5.0 7.5
1.0 1.4 2.0 3.1
5. Operating Labor. Wet-milling may require up to two more operators per shift of 16800 man-hours per year. At 33 million gallons per year, the additional cost per gallon is, at different labor rates !j /k
dleal
4.00 6.00 8.00 10.00
0.2 0.3 0.4 0.5
Received f o r review June 20, 1979 Accepted June 9, 1980
Multi-Use Botanochemical Crops, an Economic Analysis and Feasibility Study Russell A. Buchanan, Fellx H. Otey,’ and 0. Earle Hamerstrand Northern Regional Research Center, Agricultural Research, Science and Education Adminlstratlon, U S . Department of Agriculture, Peoria, Illinois 6 1604
Dwindling reserves and increasing costs of petroleum have brought the realization that agricultural production of substitutes may be both feasible and the best long-term alternative. Multi-use oil- and hydrocarbon-producing (botanochemical)crops, specially designed for an adaptive agricultural system, appear to offer potential for combining the production of both food and industrial raw materials with increased overall productivity. Processing methods are being developed for extraction of prlmary botanochemicals, Le., soluble polyphenols, wholegiant oils, and isoprene polymers that could serve as chemical feedstocks. The extractive-free residues are promising raw materials for papermaking fibers, animal feeds, fermentation substrates, chemical feedstocks, fuels, and soil amendments. Preliminary cost assessments of crop production, collection, and processing compared wlth projected produce values suggest that a new and radically different agricultural system would be economically attractive.
Introduction New crops specially designed for “integrated adaptive agricultural systems” (Lipinsky, 1978a) offer much promise and have been designated “multi-use botanochemical crops” (Figure 1). A scenario has been developed for their
introduction into the U.S.agricultural scene (Buchanan and Otey, 1979). Besides the major social and economic achievement of allowing agricultural production of fuels and industrial feedstocks without necessarily decreasing food production,
This article not subject to U.S. Copyright. Published 1980 by the American Chemical Society
