Carbohydrate Raw Materials useful products. The manufacture of Dextran from sucrose is now a familiar story. The manufacture of cyclic acetals of sucrose, glucose, and fructose by treating sugar with aldehydes in the presence of sulfuric acid was developed in the laboratories of the Xational Sugar Refining Co. ( 2 ) . Olin Mathieson Chemical Co. is a t present in pilot plant production of these agricultural sticking agents which cause insecticides and herbicide8 to adhere to the leaves of plants. A paper by Skell, Crist, and Micich (8) describes a new general method of going from soluble carbohydrates t o diamines by catalytic hydrogenation in the presence of ammonia or an amine. At the recent Meeting-in-Miniature of the New York Section, York (17) of Foster D. Snell, Inc., reported the excellent surface active properties of sucrose monoesters of fatty acids. These discoveries are representative of what Can be done with Rugar as an organic starting material. A question frequently asked by nonchemical friends is why chemists never seem to think of using sugar as a starting material for organic synthesis. I t is cheap and plentiful, and will remain so while the sun shines and fields are fertile. The principal functional groups-primary and secondary hydroxyls-have been thoroughly studied and their reactions are well known. Sometimes all that is necessary to start a new but obviously logical trend is for some one company to break the ice and show that it can be done. But although Atlas Powder Co. has made an outstanding commercial success of mannitol and sorbitol and their derivatives and their proposed $I 0,000,000 plant to go from sorbitol to glycerol has been announced, sucrose ii: still being neglected. There is no simple answer. Part of the reason is the failure of most sugar companies to carry out the type of use research which any chemical company would automatically do on a product so little explored as sugar. The recognition of the potentials in sucrochemistry was one of the reasons for the establishment of Sugar Research Foundation, Inc., by the leaders of the sucrose industry. There is evidence that research moves in surges almost analagous to fashions. I n industrial organic chemistry first there was the chemistry of coal tar constituents culminating in Worltl War 11, which can be oversimplified as a struggle between picric wid and TNT. Beginning about 1920 the petrochemicals age began. This has not yet reached its zenith but a recent survey by Ayres indicates that not many decades hence petroleum and natural gas will be x declining source of raw materials ( I ) . Then there is the complexity of the Nucro6e molecule and the
ease with which it comes apart in the presence of a trace of acid. There is one cyanoethylation product obtainable with ethanol and acrylonitrile. Sugar can yield 255 or 28 - 1. Of these, there are 8 each of mono- and hepta-substitution products, 2s each of di- and hexa-, 56 each of tri- and penta-, 70 tetra-, and 1 octa-substitution product. Therefore, a chemist studying a new reaction will use a simple alcoh.ol and avoid the complexities of a highly intricate reaction mixture whose separation to pure products other than the completely substituted one would be difficult. The advent of chromatography has minimized this problem but has not eliminated it. It is high time that, the energy applied to the fascinating industrial chemistry of sucrosc is brought more nearly in line with its possibilities. The movement of sucrochemistry from imagination to laboratory to manufacturing plant should be accelerated. It is safe to predict that this will happen. LITERATURE CITED (1) byres, E., Chem. Eng. News., 32,,2876 (1954). (2) Bray, D. F., Agr. Exp. Sta., Univ. of Delaware, Bull. 304 (June 1954) . (3) Calvin, M., and Benson, A. A., Science, 109, 140 (1949). (4) Chem. Eng., 60, No. 7, 136 (1953). (5) Chem. W e e k , 69, No. 25, 23 (1951). (6) Foreign Crops and Markets, 69, No. 22, U. S. Dept. Agr. (Nov. 29,1954). (7) Rabinowitch, I. M., Am. J . Digest. Diseases, 14,315 (1947). (8) Skell, P. S., Crist, I. G., and Micich, T. J., Division of Industrial
and Engineering Chemistry, 126th Meeting ACS, New York, September 1964. (9) Snyder, H., Agr. Expt. Sta., Univ. Minn., 12th AnnualRept., p. 225 (1904).
(IO) Stallings, J. W., U. 9. Patent 2,473,308(June 14, 1949). (11) “Statistical Abstract of the United States,” pp. 650-2, U. S. Department of Commerce, Washington 25, D. C., 1953. (12) Stiles, H. R., Ibid.,2,603,567 (July 15, 1952). (13) Sugar, 49,No. 1 , 2 8 (1954). (14) “Sugar Manual,” p. 16, Hawaiian Sugar Planters’ Association, Honolulu, 1954. (15) Through the Leaves, Great Western Sugar Co., Denver, Colo., 42, No. 1 and 2 , l O (Spring 1954). (16) Walker, G. L., “Industrial Molasses-An Annual Market Review,” p. 9, U. S. Department of Agriculture, Washington 25, D. C., November 1954. (17) York, W. C., New York Meeting-in-Miniature, ACS, February 1954. RECEIVED for review October 22, 1954.
ACCEPTED April 21, 1955.
Wood Industries as a Source of Carbohydrates AVERILL J. W-ILEY Sulfite Pulp Manufacturers Research League, Appleton,
Wis.
JOHN F. HARRIS, JEROME F. SAEMAN, AND EDWARD G. LOCKE Forest Products Laboratory, Forest Service, U . S . Department of Agriculture, Madison, Wis.
W
one of the most important sources of carbomaterial that is actually or potentially available ::a $: on a world-wide basis. Most woods and wood residues average about 50% cellulose and about 20% hemicellulose, The carbohydrate products that are or can be derived from the cellulose or from the hemicelluloses of wood are the principal subject of this paper. Cellulose itself, as used by the structural wood, the July 1955
fiber, the paper, and the chemical cellulose industries, is a polymer beyond the scope of this paper. Much research has been directed toward utilization of wood wastes. The more fruitful of those wood utilization methods finding actual commercial application today use the structural and fibrous properties of the wood. Apart from cellulose and fiber products, the utilization of individual wood components such
INDUSTRIAL AND ENGINEERING CHEMISTRY
1397
as the carbohydrates has been discouraging when judged in the decisive stage of practical application. Because technology and the economic situations change constantly, one should not be too much impressed by the negative experience of the past. Periodically, i t is well to review the part that wood residues can play as a raw material for the carbohydrate using industries. Three years ago at a symposium of the Sugar Division of the AMBRICAN CHEMICAL SOCIETY,Moyer (34) stated his conviction that cellulose will become one of man’s most useful raw materials, that the production of simple carbohydrates by hydrolysis of cellulose will become a dominant economic factor, and that cellulosic products will find increased utilization as raw materials for the production of simple aliphatic chemicals. Many others hold such views. It is almost certain that cellulosic materials will become increasingly important, but it is not clear how quickly they will acquire this new importance. What is needed most is long range planning by the larger operators. Integration is needed to recover wood residues in suitable form for subsequent processing, and processes are needed that recover from the residues a maximum of the chemical values that they contain. This paper presents the actualities and a few of the potentialities that arise from revised thinking on wood as a source of carbohydrates from integrated operations. WOOD RESIDUES
The primary product of the forest is a fairly expensive raw material. The better grades of pulp or of softwood lumber, for example, are comparable to refined sugar in cost per pound. For this reason consideration of wood as a source of carbohydrate is almost necessarily limited to processing residues. These residues differ in chemical nature because of the species involved. They differ physically because of the operations by which they are produced. Their concentrations and the amounts available show extreme regional variation. These facts make broad generalizations meaningless. Before the problem can be discussed, information must be at hand on the quantity, location, and character of available waste. While statistics on specific commercial products are readily available, data on the total product of the nation’s forests are gathered infrequently, a t high cost. A new report on the subject
200
-
’”’
is in preparation and will be available within a year. The most recent data at hand are those collected in 1946-46. Changes in the wood industry since that time are of minor consequence in this paper. One phase of the earlier study (58) goes into unusual detail on the kind and amount of waste resulting from logging and manufacture in the various wood industries and in the various regions. The term “hardwoods” is commonly used for deciduous woods, regardless of density. The term “softwoods” refers to coniferous woods. Wood waste is defined as wood material from the forest that does not appear finally in marketable products. Neither bark nor wood cut for fuel is considered waste. Other wood residues that are burned for fuel are classified as waste. The term includes all substances lost in processing, such as the solubles produced in pulping. Classification of Waste. Wood waste is subdivided into two main classes-logging waste and primary manufacturing waste. Secondary manufacturing waste is a minor item. Logging and other woods operations left behind more than 49,000,000 tons of mood accounting for 45% of the wasted product of our forests. Only 6.6% of this quantity mas used at all, and that as fuel. Included in the estimate are unutilized stems 5 inches in diameter and more a t breast height, tops, and limbs (tops only in softwoods) to a 4-inch minimum diameter inside the bark, and trees destroyed during logging and slash disposal. Of the total logging waste, 7201, was accounted for by cutting of lumber logs (58). Primary manufacturing waste includes coarse material like slabs, edgings, and trimmings; fine material like sawdust and shavings; and pulping residues. This amounted to 44,300,000 tons of wood and 8,600,000 tons of pulping waste, accounting for 49% of the total waste. The pulping residues, while small in quantity, have an important place in this discussion because of their ready availability Secondary manufacturing waste, generated in final woodworking operations, accounts for only 6% of the total waste and is unimportant as a source of carbohydrates. Use and Waste of All Timber Products. The over-all national picture of the use and waste of wood is given in Figure 1 (58). This shows graphically the disposition of the total commodity drain of standing timber; 63% of the primary manufacturing waste was burned for fuel. This is in marked contrast with the 6.6% of logging waste so used. The portion of logging waste not used for fuel was not removed from the woods, hence i t is not PERCL NT OF COMMODITY DRAIN AND WOOD IMPORTS
WOOD IMPORTS 2.5
loo-
IW -
lea
43.0
140-
m8000-
40 20OL
22.5
34.5 Figure 1. Use and waste in logging and manufacture of all timber products (58)
1398
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 45, No. 1
.
Carbohydrate Raw Materials Data are presented on the quantity, location, and character of wood and pulping residues in the United States. Methods for processing such residues are reviewed and the possibilities of further industrial utilization are discussed. Increasing quantities of wood residues have been moving into pulp and coarse fiber production. There is increasing chemical utilization of pulping residues. Solid wood residues for chemical utilization are limited mainly to material unsuitable for fiber production. An interesting potential use for wood is its hydrolysis to produce furfural, acetic acid, levulinic acid, and formic acid.
immediately accessible for further processing, but i t remains as a future potential supply, especially in an integrated operation. The unburned portion of primary manufacturing waste amounted to 20,000,000 tons. I n addition to this supply, the burned portion is available a t a price equivalent to its fuel value. Primary manufacturing waste is far more accessible for chemical processing than is the logging waste. Use and Waste of Timber Cut for Lumber. Figure 1 shows that 80% of the primary manufacturing waste came from the manufacture of lumber. I n Figure 2 (68) are shown data on the use and waste of timber cut for lumber. Manufacturing wastes from lumbering operations are the most attractive source for chemical conversion because they are concentrated and produced in a continuing supply. Location of Wood Waste in the United States. Figure 3 (1)shows a map of the forested areas of the United States with a rough breakdown as to type of forest. The area and amount of timber in these areas is shown in Table I (66). I n Figure 3, areas are outlined corresponding to regions used by Winters, Chidester, and Hall (68)in their tabulations of waste available in the United States.
Table I. Forest Northern Central Southern Western West Coast
Timbered Regions of United State6 Millions of Awes
Billions of Board Feet Hardwood Softwood 108 48 144
123 48
183
202 34
1 4
Figure 4 (67) shows graphically the logging and manufacturing waste by the regions defined in Figure 3. Figure 4 provides an estimate of the total potential quantity of waste and its location. Figure 5 (67) shows similar data for primary manufacturing w a s t e o n l y . This is the more accessible type of wood residue, and i t is the type that should be the first to be utilized. The main species used in lumber production in the United States in 1947 are shown in Table 11, together with their percentage contribution to the total lumber supply. There was nearly four times as much softwood lumber used as hardwood. I n both the softwoods and the hardwoods, a few species account for most of the lumber supply. In conjunction with this information i t is important to consider the large variations in sawmilling practices over the country; these practices have an important effect on the quantity and disJuly 1955
62
3
194 490 546
tribution of waste. The New England and Middle Atlantic regions are characterized by small sawmills. Concentration yards for drying and surfacing lumber are uncommon. The waste is widely scattered. The South Atlantic region is characterized by portable sawmills, and by concentration yards. The waste a t concentration yards holds real promise as a raw material for chemical processing. I n the Southeast and West Gulf regions sawmill practices are similar to those of the South Atlantic region: With the establishment of markets for wood residues, many mills could convert to gas or oil, increasing the available supply of wood residues. The days of the large lumber operations in the Lake States region are past. The wood residues are scattered and small in quantity. The Northern Rocky Mountain region has a moderate amount of wood residues, and the mills are sufficiently large to hold some promise for utilization. The market situation is relatively unfavorable. The Pacific Northwest region offers the most promising Iocation for the utilization of primary manufacturing waste. The sawmills are very large; waste is concentrated. There is increasing industrial activity in the area and a rapidly rising population. I n addition to primary manufacturing wastes, there is a very large amount of logging waste in high concentration. Wood Sources Other Than Logging and Manufacturing Residues. I n addition to the waste generated in lumbering operations, certain areas give promise of providing large quantities of another form of wood for chemical conversion. This is the wood logged from forests for the purpose of upgrading the forest stand and establishing better forest management practices. In certain areas this source of wood has attractive possibilities. This discussion of wood raw material for chemical conversion Billion
Cu.Ft.
2.I
I .6
3.0 Figure 2.
Use and waste of timber cut for lumber (58)
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1399
has presented only the broad view. Other sources give additional information, and a detailed breakdown is available from state and federal agencies
Table 11.
Lumber Production by Important Species (U.S. Bureau of Census data, 1947) %
of Total
POLYSACCHARIDES OF WOOD
The amount and nature of the sugars obtainable from wood and the processes required t o effect the necessary hydrolysis are determined by the polysaccharides of the wood. The main polysaccharide in all woody plant materials is cellulose. This cellulose is chemically and physically similar to cotton in that it is fibrous, has a high resistance to alkali, and is hydrolyzed only with much difficulty to yield glucose. The other main carbohydrate portion of woody plants is hemicellulose. The differentiation between the two is indistinct and arbitrary and depends on the higher alkali solubility of hemicellulose. I n addition to its higher alkali solubility, hemicellulose is hydrolyzed much more rapidly than is the resistant true cellulose. If the total carbohydrate of wood were hydrolyzed as easily as is hemicellulose, there would be no question about the immediate widespread industrial usefulness of wood saccharification as a source of sugar and materials derived from sugar. The total carbohydrate fraction of wood has been named holocellulose by Ritter. The composition of various woods is given by Van Becltum and Ritter (61). The reducing sugars and fermentable sugars obtainable from wood and other cellulosic materials can be evaluated by quantitative saccharification, followed by a determination of the sugar fermented by Saccharomyces cerevisiae. The results of such analyses on a number of woods are available ( 4 1 ) . There is a large variation in the amount of sugar obtainable from the
Southern pine Douglas fir Ponderosa pine Hemlock Eastern and northern white pine White fir Redwood Spruce Cedar Suear nine Larch Idaho white pine Cypress Lodgepole pine Balsam fir Other softwoods Total softwoods Oak Sweet gum Poplar Maple Tupelo Cottonwood and aspen Beech Birch Other hardwoods Total hardwoods All species ~
26,76 25.54 10.84 3,51 3.16 1.90 1.50 1.10 1.03 0.97 0.83 0.71 0.68 0.28 0.08 0.02 78.91 9.02 2.27 1.80 1.78 1.15
1.08 0.93 0.49 2.57
21.09 100.00
various species. Hardwoods, because of their lower lignin content, have a higher content of total potential sugar. The higher pentosan content, however, causes the hardwood hydrolyzates to have a lower fermentability than the softwood hydrolyzates. Aspen wood has the very high potential sugar content of 75%.
PAC. N.
,TL. GAL
L.
ROCKY
WEST COAST FOREST WESTE.RN FOREST NORTHERN
HARDWOOD FOREST SOUTHERN FOREST
FOREST
Figure 3,
1400
fWJ CENTRAL
Principal timbered regions of the United States
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. ?
Carbohydrate Raw Materials ment of new evaporation methods has renewed interest in the actual recovery of hemicellulose products. The pentose sugars from sulfite pulping of hardwoods are being evaluated as a raw material for furfural production. The available sources of dissolved carbohydrates are outlined in Figure 6, which shows the two hydrolysis processes used in pulping. Steam hydrolysis or prehydrolysis of wood chips is used to produce hardboard and chemical (alpha) cellulose from the prehydrolysis kraft process. The amounts that might be commercially available and the composition of the particular hydrolytic products are not definitely known. The procedure involves a pressure steaming of the chips. Considerable quanti' ENG NEW MID LAKE CENT SOUTH SOUTH WEST ROCKY ROCKY PAC GAL. ATL ATL EAST GULF M T IN) MT (S) NW ties of acetic and formic acids result from such steaming, and these prehydrolysis Figure 4. Logging and manufacturing wood waste by geographic regions operations actually involve a dilute acid hy(57) drolysis rather than a simple hot water reaction and extraction. Laboratory and pilot tests of prehydrolysis liquors have shown the presence Large variations Can occur within a species. Douglas fir samples of some free sugars and appreciable amounts of nonreducing vary from 61.7 to 71,4$7,, potential sugar. carbohydrates that can be efficiently hydrolyzed to the free sugars. The component sugars of the total hydrolyzate of 20 different Large industrial operations are a potential source of large tonspecies of woods have been determined by Gustafsson and conages of carbohydrate derivatives. workers (16). According to these workers, all the wood species The acid sulfite pulping process converts the wood hemicelluloses investigated contain glucosan, galactan, mannan, araban, and to free sugars with yields approaching 400 pounds in the dilute xylan. The amount of galactan based on the total sugar prospent liquor from each ton of pulp production, of which perhaps duced by the hydrolysis of softwoods varies from 6.0 to 17.5%, 300 pounds or 75% can be recovered. and that of mannan between 7.5 and 16.0%. The corresponding The two alkaline pulping processes in present practice normally values for hardwood are 1.0 to 4.0% and 0.5 to 4.0%, respectively. break down the hemicelluloses to saccharinic acid end products The xylan content of softwood hydrolyzates varies between 9.0 in a spent liquor that is routinely collected for evaporation and and 13.0%, and that of hardwood hydrolyzates, between 19.5 burning to recover the pulp cooking chemicals. These sacand 39.0%. The araban content is low throughout and exceeds charinic acids are a large volume carbohydrate product. Klason 3% only for three of the softwood species. The carbohydrate composition of a given species is not strictly constant, but the (26, 97') reported early studies on these acids a t the turn of the century, but there has been no further incentive for complete variation8 that exist are not sufficient to obscure the characteristic characterization and utilization of these compounds because of differences between hardwoods and softwoods. the established practice of burning the spent liquor. Additional UTILIZATION OF PULPING RESIDUES study of these materials can be expected in the future.
e
Bugsrs and other disaolved wood carbohydrates, substantially all of which are derived from the hemicellulose fraction of wood, are present in the hydrolysis spent liquors of the wood pulping industry. The availability of these dissolved carbohydrates has long been known, but recovery and use has been handicapped by the necessity for dealing with large volumes of dilute solutions. Immoved techniques for recovery or utilization of these dissolved carbohydrates have become available since World War 11, and these have improved the possibilities considerably. The recent general trend of thinking of people in the wood industries toward greater use of the wasted half of the tree has been of similar concern to those in the pulping industry, and much research and development on new processes and products have been an evident result. The first two wood carbohydrate utilizing processes dasigned for full commercial production during recent years in the United States are based on fermentation methods. These include two torula yeast plants in Wisconsin (23, 66)and one alcohol plant (7, 32) in Washington for recovering values from the wood sugars of spent sulfite liquor. More recently the developiuly 1955
P(D
PI(
c *a
3
'€4
s2 I
OC
81
4,
Figure 5.
Primary manufacturing waste by type and geographic regions
INDUSTRIAL AND ENGINEERING CHEMISTRY
1401
Tonnage production figures in recent years for the various chemical pulping processes are shown in Figure 7. The production for chemical pulps has been subject to steady increase from 9,000,000 tons in 1949 to 12,860,000 tons in 1953. Production has about doubled in the past 20 years, and the expected demand for the next 20 years forecasts that production may be doubled again. The kraft pulping process has been subject to great expansion and, indeed, accounts for most of the expansion noted. The so-called semichemical processes for high yield pulping are also undergoing expansion, but these processes are specifically designed to minimize hydrolysis of carbohydrates and for that reason are not considered in this report. Table I11 summarizes the potentially available volume of carbohydrate products that are or could be made available by the chemical wood pulp industry. The calculations for the potentially available carbohydrates are based on a total hydrolysis product amounting to 20% of the pulp yields, and 75% recovery of such hydrolyzed product.
Table 111. Potential Volume of Dissolved Carbohydrates Carbohydrate Potential a t 75% Recovery, Tons U. s. Standard With preShort Tons process hydrolysis 2,300,000 346,000 9,435,000 ,. i,4ii:ooo 428,000 ... 64,000
1953 pulp Production, Process Acid sulfitea Alkaline krafta Alkaline soda Special alpha (sulfite and kraft) Total chemical pulps
.
677,000 12,840,000
.....
100,000
1,924,000
Except alpha grade.
large bibliographies. Practical success in the field has been limited by economic and technological problems stemming from the difficulty of hydrolyzing the cellulose, the unfavorable ratio of the hydrolysis rate of the cellulose t o the decomposition rate of the sugar, and the fact that the wood hydrolyzes to both pentose and hexose sugars. Wood sugar plants have been characterized by rather low yields and impure product, much of the contaminant being products of the decomposition of the sugars. Industrial wood hydrolysis has been carried out by the following basic types of processes. The simplest method, and the first to be used on an industrial scale, is the batchwise hydrolysis (68). This method has the disadvantages of low yield and poor quality because the sugar is left in the reactor during the entire hydrolysis period. These disadvantages are somewhat compensated for by the simplicity of equipment and ease of operation. Recent research by Plow and coworkers (56) has shown the possibility of making important improvements in the process. These improvements are the result of much more rapid hydrolysis, and the possible use of a second or third batch hydrolysis of the residue. A continuoJs wood hydrolysis process has been described in which a slurry consisting of 8 t o 10 parts of dilute acid to 1 of sawdust is pumped through a heat exchanger ($4, 25, 35, 36). The purpose was the production of a lignocellulose plastic. Because of the high liquid to solid ratio the sugar solution was dilute. The Bergius process of wood saccharification involves a primary extraction and hydrolysis with strong hydrochloric acid, followed by the removal and recovery of the acid, then dilution and secondary hydrolysis to produce the monosaccharides. The demonstration pilot plant for this process was built a t Rheinau, and it was followed by a full scale plant a t Regensberg, Germany. The industrial application of this process has been an engineering achievement that involved overcoming very serious obstacles, Drimarilv the recoverv. evaDoration, and concentration of fuminn hydrochioric acid. The Bergius process has been described by Bergius ( 3 ) ; technical aspects are described by Hagglund ( l 7 ) , and operational information was obtained following World War I1 by Saeman, Locke, and Dickerman (42). On the basis of available information the Bergius process requires a very high capita1 investment; theprocess is difficult, and production costs are high. Recently Schoeneman has reviewed this process and made some suggestions for decreasing production costs and upgrading product; with these improvements it is claimed that the process could compete in the United States With corn as a Source of dextrose (6198). Currently, the most important type of industrial wood hydrolysis process is the Scholler percolation method. Fresh acid is introduced in the top of the percolator and the sugar solution is withdrawn from the bottom. Sugar decomposition is reduced by
The chemical pulping industry has an estimated total potential amounting to 1,925,000 tons of carbohydrates a t current rates of production, of which about 500,000 tons are actually being produced and the balance of which could be produced by introducing the prehydrolysis step in the kraft process. Presently, the most active research and development on utilization of these carbohydrates is supported by the sulfite pulp industry. The in the statesof wisconsin and Washingthree fermentation ton are specifically designed to utilize the sugars in the dilute liquor for production of food and feed yeast and of alcoho1. Several other United States sulfite mills have recently installed evaporation plants to concentrate their spent liquor. The concentrated product a t 50 to 60% solids contains between 5 and 10% carbohydrates, and it probably averages about 7.5% as contrasted to about 1.5 t o 2% carbohydrates in the dilute liquor a t blow-pit strength. T h e s e e v a p o r a t i o n plants are producing the carbohydrates in a form more readily available for utilization and recovery processes. The prospects for obtaining these sugars a t low cost are BASIC PROCESS promising when considered within the framework of integrated utilization.
PRIMARY PRODUCTS HARDBOARD FIBER
C
UTILIZATION OF SOLID WOOD RESIDUES
Direct Conversion to Sugar. The discovery, more than 130 years ago, that the carbohydrate constituents of plants can be converted to sugars was considered to be of great practical importance and has been followed by considerable work on the subject. The books by Stamin and Harris (@), Hiigglund ( l 7 ) , and Wise (69) have sections devoted to the subject that include 1402
SACCHAR[NIC ACIDS
Figure 6.
Available sources of dissolved carbohydrates
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 7
Carbohydrate Raw Materials carrying out hydrolysis and removing the sugar solution as it is formed. The process was originally intended to make use of a battery of percolators arranged for countercurrent extraction, but these plans were later discarded in favor of percolators operated separately. The industrial development of the Scholler process has been described by Schaal (44),Fritzweiler and Rochstroh (11), Luers ( S I ) , Scholler (46, 46), and Fritzweiler and Karsch (10). These sources do not give detailed information on the process, but in 1945 operating details of two German plants were obtained (15, 4%). A Scholler plant a t Ems, Switzerland (50), has proved very successful. It has apparently operated a t better than design capacity and probably represents the best industrial success t o date. Recent work on wood sugar production in the United States has been described (8, 9, 15, 14, 19, BO, 38, 42, 4 7 ) ; in general these processes have been modifications of the Scholler percolation process. All the dilute acid industrial processes employed until the present time have operated under conditions where the relative rates of formation and destruction of the sugars are unfavorable, resulting in low yields and a low quality product. Yields on dry wood are 20% in the simple batch operation and 45 to 50% in the Scholler percolation process. The sugar solution from wood hydrolysis is comparable in value to blackstrap molasses and, in most cases, can be used similarly. The chief difference is the presence of appreciable amounts of acetic and other organic acids. It has been used as a cattle food with good results. I n this application the presence of acetic acid is actually beneficial. The production of yeast has been successfully demonstrated (48) with yields of product comparable to those from blackstrap; the organism employed in this case is Torulopsis utilis, which utilizes both the pentose and hexose sugars. The fermentation to alcohol (21) is straightforward and offers no difficulty. Recently the fermentation of wood sugar to glycerol has been studied a t the Forest Products Laboratory. Upgrading of the product is possible by partial separation of the pentose and hexose sugars. This can be done in the Scholler process where the first hydrolyzate is rich in pentose sugars. No cheap effective purification process has been devised for the sugar solution. Ion exchange purification is available to bring the quality to any desired level, but this is expensive. Chief impurities in the solution appear to be acetic acid from the original wood and products of sugar and lignin decomposition. These present storage and handling problems because of polymerization. The commercial aspects of producing sugars directly from wood carbohydrates are unfavorable in the United States. Recent estimated costs (14) of producing wood sugar molasses by a percolation process show that i t could compete with blackstrap molasses for only a portion of the time from 1940 to 1951. I n analyzing the economics of wood sugar production, it becomes apparent that capital costs are very high in relation to the maximum market value of the product. A major reason for the high capital cost of the plant is that the hydrolysis must be carried out in a more elaborate manner than by the simple methods suitable for starch. Cellulose is more difficult to hydrolyze by a factor of perhaps a hundredfold than other familiar Carbohydrates. This fact in itself does not add much to processing cost but the difficulty of hydrolysis results in a situation whereby in dilute acid hydrolysis the rate of glucose formation is equal t o its rate of decomposition. The difficulty is overcome in part by the use of strong acids in the Bergiue process, and by the use of percolation technique in the Scholler process. Both methods are too elaborate in relation to the value of the crude sugar solution. Work a t the Forest Products Laboratory (BO) has shown that the hydrolysis reaction has a higher heat of activation than the decomposition reaction, hence increasing temperature of hydrolysis has a favorable effect. July 1955
Irradiation of cellulose or wood with cathode rays increases its rate of hydrolysis (49) and hence results in a more favorable ratio of sugar production to destruction. Important improvements in the saccharification process can result only from inexpensive techniques that effect an increase in the rate of the hydrolysis reaction relative to the decomposition reaction. Production of Carbohydrate Derivatives from Wood Residues. It is possible to make use of the carbohydrate components of wood without the intermediate production of sugar. Western larchwood contains a hot water-soluble polymer consisting of 1 molecule of arabinose to 6 of galactose. Borgin ( 4 ) found the material consists of two components with molecular weights of 16,000 and 100,000, respectively. Mitchell and Ritter (33) report that virgin growth butt logs contain about 14% of the material. Pilot plant preparations have been made ( 2 ) .
-
12 v)
z
IO
.....--*
......**. ....---
8 6
TOTAL SULPHATE .*......... .................-.......-.
a-....
.***
4 TOTAL
----_-_________
SULPHITE
--------’-------___________.._-_-
1949
1950 Figure 7. U. S. pulp production by types Bureau of Census
Cellulose for feeding ruminants is another example of the direct use of wood polysaccharide. Chemical hydrolysis is not necessary, but delignification is required. I n Scandinavian countries, 1,000,000 tons of fodder cellulose were produced in 1942. The product was expensive, and warranted only by World War I1 emergency conditions. I n reviewing the subject, Risi states that a kilogram of fodder cellulose is equivalent t o 0.80 to 0.87 kilogram of oats. An inexpensive delignification of wood residues would be useful to produce fodder (39). Examples of biological or chemical conversion of wood residues include thermophilic fermentation to organic acids, the alkaline degradation to organic acids, and the acid degradation to furfural, hydroxymethyl furfural, levulinic, formic, and acetic acids. Virtanen and coworkers have found that finely ground sawdust can be fermented by thermophilic bacteria (55). I n fermentation times of 3 to 4 weeks as much as 68% of the cellulose and 87% of the pentosans in the wood were consumed. Additional work on this subject was carried out a t the Forest Products Laboratory by Hajny and coworkers (18). Hajny reports that the main products of the fermentation are acetic, butyric, and lactic acids in yields approximately 50Yo of the carbohydrates consumed. Untreated sweet gum wood produced organic acids in yields of 15.9% calculated as acetic, based on the weight of dry wood. Wood fermentations are characteristically slow. Wood ferments much more slowly than delignified cellulose. The close association between cellulose and lignin must be disturbed physically or chemically in order to increase the susceptibility of the wood to bacterial action.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1403
Previous to its synthesis by treating carbon monoxide with sodium hydroxide, oxalic acid was produced exclusively by the caustic fusion of wood. The literature on the preparation of oxalic acid from wood is reviewed by Hagglund (17). Fusion of sawdust with mixtures of sodium and potassium hydroxide yields about i’oyOof its weight of oxalic acid. Acetic acid and formic acid are produced simultaneously. WOOD I
ACETYL
PENTOSAN
HEXOSAJV
ACE TIC ACID
PEN JOSE
HEXOSE
/ FURFURAL
+ \\
LIGNIN
LIGNIN
Any industry based on residues from forest and lumbering operations is assured of a very favorable raw material situation. It is the nature of forest operations t o be stable, and the increasing attention given to proper forest management practices will result in a supply that will have no abrupt variations in quality, quantity, and price (29, SO, 40,54, 55). The need for industries making effective use of wood residues is such that excellent cooperation can be anticipated from forest and lumber operators and from public agencies. The unfavorable past history of attempts a t the chemical utilization of wood residues results in prejudice against proper consideration of its possibilities. Earlier operations were characterized b y relatively poor integration with the residue suppliers, a n undue interest in a single unstable commodity (alcohol), and ignoring completely the chemical values contained in wood residues other than the hexosans. Successful development of an economic chemical utilization process must not only take full advantage of all the chemical values in the wood residues but also its product must find a large market in stable fields.
) .
HYDROXYMETHYFURFURAL LITERATURE CITED
Figure 8.
American Forest Products Industries, Inc., “Facts About the Nation’s Lumber Industry,” 15, Washington, D. C. (1953). Austin, G. T., J . Forest Products Research Soc., 4, No. 1, 7 Cleavage products from acid degradation of wood
Acid degradation presents a n interesting comparison with alkaline degradation. I n the latter, the reagent is consumed and chemical costs are high. T h e reactions brought about by acid are catalytic. By going t o high temperatures, rapid rates of reaction can be achieved with low chemical requirements. The high temperature hydrolysis of wood using dilute mineral acid as a catalyst results in the products shown in Figure 8. The pentosans of wood are converted t o furfural ( 6 ) ,and the hexosans are converted to hydroxymethyl furfural, which in turn is conand formic acid. These comverted t o levulinic acid ( I d , 3’) pounds represent only the main products of decomposition and are formed by many consecutive and simultaneous reactions; yields of any compound are dependent on the conditions and duration of hydrolysis. Using a high temperature to promote rapid hydrolysis and permitting complete conversion of the sugars t o furfural and levulinic acid, the anticipated yields from hardwoods are approximately Pounds per
Acetic acid Formip acid Levulinic acid Furfural Lignin
100 Pounds of Dry Wood 5 4 14
7
30 60
T h e use of furfural as a nylon intermediate has opened a potential demand that is several times the current output, which is approaching the limit of production from available agricultural residues a t present price levels. Wood and wood residues are the only readily available source for a large increase in the domestic furfural supply. Levulinic acid is a n exceptionally interesting substance, because its several reactive groups adapt i t in a unique manner for synthesis of heterocyclic compounds. It has been available only in pilot plant quantities at a high price, but its potential consumption is enormous if i t can be produced a t low cost. Lignin will be produced in yields of 20 to 30% of the weight of wood and could be used as fuel. However, i t is possible that i t may find uses in glues and plastics or as a n intermediate in the production of phenols, cyclohexanol, and substituted cyclohexanols.
1404
(1954).
Bergius, F., IND.ENQ.CEIEM., 29, 247 (1937). Borgin, G . L., J. Am. Chem. Soc., 71, 2247 (1949). Chern. Eng., 61, No. 2, 138 (1954). Dunlop, A. P., and Peters, F. N., “Furans,” Reinhold, New York, 1953. Ericsaon, E. O., Chem. Eng. Progr., 43, 165 (1947). Faith, W. I,., IND.ENQ.CHEM.,37, 9 (1945). Faith, W. L., and Hall, J. A., Chem. Eng. News, 22, 525 (1945). Friteweiler, R., and Kapch, W., 2. Spiritusind, 61, No. 28, 207 (1938).
Friteweiler. R., and Roohstroh, Ibid., 59, No. 28, 229 (1936). Frost. T. R.. and Kurth. E. F.. T a o o i . 34. No. 2. 80 (19511. Gilbert, N., Hobbs, I. A:, and Le&e,’J. D., IND:EN;. CHEM., 44, 1712 (1952).
Gilbert, N., Hobbs, I. A., and Sandberg, W . D., J . Forest Products Research Soc., 2, No. 5, 43 (1952). Greaves, C., U. S. Dept. Comm. Off. Pub. Bd. Rept. PB18941, December 1945. Gustafsson, Ch., Sundman, J., Pettersson, S., and Linclh, T., Paper a n d Timber, 3, No. 10, 300 (1951). Hagglund, E., “Chemistry of Wood,” Academic, New York, 1951.
Hajny, G. J., Gardner, C. H., and Ritter, G. J., IND. ENQ. CHEM.,43, 1384 (1951). Harris, E. E., in “Advances in Carbohydrate Chemistry,” Pigman, W. W., and Wolfrom, M. L. (editors), Vol. IV, p. 154, Academic, New York, 1949. IND.ENQ.CHEM..37. 5-54 11945). Harris, E. E., Hannan, M. L., Marquardt, R. R., and Bubl, J. L., Ibid., 40, 1216 (1948). Ibid., 46, No. 3, 13 A (1954). Inskeep, G. C., Wiley, A. G., Holderby, J. M.. and Hughes, L. P.. Ibid., 43, 1702 (1951). Katzen, R., Aries, R. S., and Othmer, D. F., Ibid., 37,442 (1945). Katzen, R., and Othmer, D. F., Ibid., 34, 314 (1942). Klason, P., Tek. Tidskr. Kemi. Metall, 17, 33 (1893). Klason, P., and Segerfelt, B., Arkiv. Kcmi, Mineral. G w l . 4, No. 6, 1 (1911). Kressman, E”. W., U. S. Dept. Agr. Bull. 983 (1922). Locke, E. G., J . Forest Products Research SOC.,4, No. 1, 10 (1954). Locke, E. G., and Johnson, K. G., IND. ENQ. CHEM.,46, 478 (1954). Ltlers, H., Hotz Roh-u. Werlcstoff, 1, 35 (1937). MoCarthy, J. L., in “Industrial Fermentations,” Underkofier, L. A., and Hickey, R. J. (editors), Vol. I, Chap. 4, Chemical Publishing Co., New York, 1954. Mitchell, R. L., and Ritter, G. J., U. S. Degt. Agr., Forest Service, Forest Products Lab., Rept. R1771, 1950. Moyer, W. W., Chem. Eng. News, 30, 510 (1952). Olson, E. T., Kateen, R., and Plow, R. H., Ibid., 2,156,159 (1939). Olson, E. T., and Plow, R. H., U. S. Patent 2,156,160 (1939). Ploete, Th., Naturwissenschajten, 29, 707 (1941).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
~
Val. 47, No. 2
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Carbohydrate Raw Materials (38) Plow, R. H., Saeman, J. F., Turner, H. D., and Sherrard, E. C., IND.ENG.CHEM.,37, 36 (1945). (39) Risi, J., P u l p & Paper M a g . Can.,46, No. 8, 611 (1945). (40) Saeman, J. F., J . Foresf Products Research SOC.,2, No. 5, 50 (I 952). (41) Saeman, J. F., and .4ndreasen, A. A., in “Industrial Fermentations,” Underkofler, L. 4.,and Hickey, R. J. (editors), Vol. I, Chap. 5, Chemical Publishing Co., New York, 1954. (42) Saeman, J. F., Locke, E. G., and Dickerman, G. K., U. S. Dept. Comm. Pub Bd. Rept. 7736,Washington 25, D.C., 1945. (43) Saeman, J. F., Millett, M. A , , and Lawton, E. J., IND.ENG. CHEM.,44, 2848 (1952). (44) Schaal, 0.. Cellulose C h a . , 16, 7 (1935). (45) Soholler, H., C h e m A t g . , 63, 737 (1939). (46) Scholler, H., and Siedel, .M., C. S. Patent 2,188,192 (1937). (47) Sherrard, E. C., Chemical A g e , 29, 76 (1921). (48) Stamm, A. J., Proc. Am. Phzl. SOC.,95, No. 1, 68 (1951). (49) Stamm, A. J., and Harris, E. E., “Chemical Processing of Wood,” Chemical Publishing Co., New York (1953). (60) Trechsel, M. A , , Neuen Ziircher Zeztung, Beilage Technik, June 12, 1946.
(51) Van Beckum, W. G., and Ritter, G. J., Paper T r a d e J . , 108, No. 7, 27 (1939). (52) Varossieau, W. W., “Forest Products Research and Industries in the United States,” Meulenhoff, Amsterdam, 1954. (53) Virtanen, A. I., and Nikkila, 0. E., Suomen Kemistilehti, 19B, 3 (1946). (54) Walton, A. T., J. Forest Products Research Soc., 2, No. 2, 57 (1952). (55) Wiesehuegel, E. G., Ibid., 3 , No. 2, 62 (1953). (56) Wilev. A. J.. in “Industrial Fermentations.” Underkofler. L. A. anx Hickey, R. J. (editors), Vol. I, Chap. 10, Chemical Publishing Co., New York, 1954. (57) Winters, R. K., Proc. Forest Products Research SOC.,2, 15 (1948). (58) Winters, R. K., Chidester, G. H., and Hall, J. A., Reappraisal of the Forest Situation, Rept. 4, U.S. Dept. Agr., Forest Service, 1947. (59) Wise, L. E., and Jahn, E. C., “Wood Chemistry,” Reinhold, New York, 1952. RECEIVED for review October 2 2 , 1954. ACCEPTEDMay 5 , 1965. ~I
Forest Products Laboratory is maintained a t Madison, Wis., in cooperation with the University of Wisconsin.
Starch: Raw Material Sources and Economics NORMAN F. KENNEDY Corn Industries Research Foundation, 270 Park Ave., New York, N . Y .
The major sources of starch as industrial and organic raw materials, the availability of supply from the standpoint of domestic and world production, and starch consumption and its future trends are discussed. The economic factors influencing the present contribution of each major raw material source to the industrial supply of starch are reviewed. The effect of differences in chemical, physical, and polymeric properties of starches from various sources and the effect of cost factors in the selection of certain types of starches for specific end uses are analyzed. The future of starch in general as a chemical raw material is appraised and the areas in which starch could reasonably compete on an econoniic basis with nonstarch materials such as petroleum and cellulose are delineated.
T
HE total supply of starch, and the various sources of this
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commodity within the United States, present certain economic and qualitative aspects interesting to research chemists and to the many industries whose manufacturing processes depend partly on starch. As shown in Figure 1, the annual supply of all starches, domestic and foreign, has increased threefold in the years 1922 to 1953; 1954 shows a slight recession from the peak, the total supply declining to 2,258,000,000. This annual supply total approximates the annual consumption. Figure 1 shows, also, that the annual supply of foreign grown starches available t o U. S. manufacturers through import was about 5% of the total available starches in 1954. Figure 2 demonstrates that U. S. starch consumers have come to rely more and more on domestic sources. Among domestic starches, cornstarch is in far greater supply than all others combined, as shown in Figure 3. There have been periods in the past 30 gears when cornstarch has constituted as much as 92% of t h e total supply. I n recent years this proportion has dropped to about 87 to 9 0 % because of increased use of domestically produced potato and wheat starch. A breakdown showing the supply of starches from domestic sources, other than corn, is charted in Figure 4. Among these, July 1955
potato starch is the most important. While wheat, rice, and sorghum starches are considered collectively on the chart, i t should be pointed out that starch from wheat constitutes the major portion of these three. COMMERCIAL DOMINANCE O F CORNSTARCH
Because of several economic factors, the dominant position of cornstarch can never be challenged in a free market. Chief among these factors is the stability of the raw material sourcet h e annual corn harvest. T h e corn refining industry, producing most of the domestic cornstarch, uses only about 401, of the total production of corn. Long the principal grain of t h e United States, because of its a d v a n t a a s as a stock feed, corn is handled commercially through well-established markets and channels of distribution. The availability of terminal and country elevators and other storage facilities enables the corn refiners t o bring their own supply of corn t o their plants at minimum cost; all of which contributes to the economic production of cornstarch. Yield per acre is another economic factor on the side of cornstarch. I n the corn belt, where most commercial corn is grown, the average yield from the yellow grain is about 1500 pounds of starch per acre. Wheat yields only about 500 pounds of starch per acre, and costs much more than corn per unit of starch.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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