Outlook for the future
Irving S. Goldstein
IRVING, S. GOLDSTEIN is a professor in the Department of Wood and Paper Science North Carolina State University, USA. This article was a paper which was presented to the Eighth World Forestry Congress, Djakarta, October 1978.
There are two future uses, for wood in chemicals. One is by extending and expanding present practices. The other is to convert cell wall components into chemical feedstocks. These cell wall polymers, which constitute the major portion of wood, have the potential for meeting all of our chemical needs in place of petrochemicals.
Projections of future demand for some commodities can be based on population growth or past trends. In projecting the future demand for chemicals from wood, however, simple extrapolation from present data is not reliable. At present, the industrial societies depend almost entirely an petrochemicals derived from fossil liquid and gaseous hydrocarbons as the raw materials for fibres, plastics, rubbers, adhesives, etc. As petroleum and natural gas become more expensive and more scarce, it is obvious that other carbon sources, such as coal or wood, may begin to serve as alternative raw materials. However, even though the conversion of wood into chemicals is conceptually and technologically feasible, it does not necessarily follow that wood will be used for this purpose.
Before exploring the factors-which are mainly beyond the control of the forest industries-that will ultimately determine the kind and volume of chemicals that will be derived from wood in the future, it would be helpful to understand the potential contribution of wood in this area. This background is presented here in a brief discussion of the chemical composition of wood and in a short description of past, present and potential future chemicals derived from wood.
Although in theory a chemist can convert the components of wood into any desired chemical, the chemicals which can be in practice derived from wood depend greatly on its inherent chemical composition. Wood is a mixture of three natural polymers -- cellulose, lignin and hemicelluloses -- in an approximate ratio of 50:25:25, depending on species, biological variations such as genetic differences within species, and growing conditions. Cellulose and hemicelluloses are carbohydrate polymers built up from molecules of simple sugars, and lignin is a polymer of phenylpropane units (Browing, 1963).
Cellulose is a long-chain polymer of glucose which differs from starch, also a glucose polymer, only in the configuration of the glucose molecules. The fibrous nature of the wood cells is the result of the linear, oriented, crystalline arrangement of their most abundant component, cellulose.
Hemicelluloses are shorter, or 'branched polymers of five-carbon sugars (pentoses), such as xylose, or six-carbon sugars (hexoses) other than glucose. They are amorphous in nature and serve with the lignin to form the matrix :in which the cellulose fibrils are embedded. Although the cellulose structure is the same in different species, the hemicelluloses vary considerably among species and especially between hardwoods and soft-woods. Hardwood hemicelluloses are generally richer in pentoses while softwood hemicelluloses generally contain more hexoses.
Lignin, the third cell wall component, is a three-dimensional polymer formed from phenylpropane units which have randomly grown into a complicated large molecule with many different kinds of linkages between the building blocks. Lignin structure also varies between hardwoods and softwoods. The phenyl groups in hardwood lignins are more highly substituted with methoxyl groups than those in softwood lignins. One consequence of this difference is that hardwood lignins are less cross-linked and more easily dissolved in pulping.
A FOREST IN CANADA chemical factory
Lignin acts as a cement between the wood fibres and as a stiffening agent within the fibres. In the production of chemical wood pulps, it is dissolved by various chemical processes, leaving the cellulose and hemicelluloses behind in fibrous form. Some hemicelluloses are lost in the process because of their lower molecular weight, greater solubility and easier hydrolysis.
In addition to the polymeric cell wall components which make up the major portion of the wood, different species contain varying amounts and kinds of extraneous materials collectively called extractives. In softwoods, we often find considerable amounts of resins consisting of both fatty acids and so-called resin acids which are derived from the simple terpenes such as turpentine and pine oil. Tannins are polyhydroxylic phenols which are found in the heartwood and bark of many species. Rubber is obtained from the inner bark of certain trees in the form of a latex. Aromatic oils and water-soluble sugars may also be obtained from various species. Cedar oil and maple sugar are familiar examples.
WOODS PYROLYSIS. Before the advent of cheap fossil fuels such as coal, petroleum and natural gas, the destructive distillation of wood to produce charcoal was an important industry (Stamm, 1953). Only vestiges of the industry remain in the United States, providing briquettes for outdoor recreational cooking.
The gas produced in wood carbonization can be used as a low Btu fuel. It was occasionally used during World War II to power internal combustion engines when gasoline was unavailable. A number of volatile organic chemicals can be recovered from the distillate of wood pyrolysis. Acetic acid, methyl alcohol and acetone were formerly obtained exclusively from wood distillation, leading to the common name, "wood alcohol," for methanol. In addition, various wood tar oil fractions used for medicinals, smoking meats, disinfectants and weed-killers were isolated.
EXTRACTIVES. The resinous exudates from pine trees provided the raw material for the naval stores industry, the oldest chemical industry in North America. First used for tarring of ropes and caulking of seams in wooden ships, these crude exudates were latter distilled to provide turpentine and rosin which have a great variety of industrial uses.
The latex tapped from rubber trees was for many years the only source of rubber. For many applications, natural rubber is still preferred today over tile synthetic rubbers. Extracts of the heartwood of certain hardwoods as well as the bark of various species provided tannins which, as their name indicates, were important in tanning leather.
In addition to cellulose, the most widely used polymer today, which is primarily used in its natural fibrous state after extraction from the wood, considerable quantities of chemicals called "silvichemicals" are still in use today (Goheen, 1972) despite the overwhelming preponderance of petroleum-based chemicals called "petrochemicals."
PULPING LIQUORS. The chemical fragments of the cell wall polymers which end up in solution after pulping can often be isolated from the pulping liquors and used. In general, alkaline pulping liquors are burned in the recovery of the pulping chemicals, but sulphite pulping liquors are frequently treated to yield useful by-products.
The sulphonated lignin can be precipitated as lignin sulphonates and used as tanning agents, adhesives, binders, dispersants, etc. The sugars in spent sulphite liquor can be fermented with yeast to produce ethyl alcohol and fodder and food supplements. By mild alkaline oxidation of lignin sulphonates, vanillin can be obtained for flavouring and odorant applications
Alkali lignin from sulphate or kraft black liquor may be precipitated and used as an extender for resins, for rubber reinforcement and in emulsion stabilization. Volatile products from kraft black liquor include dimethyl sulphide, dimethyl sulphoxide, and dimethyl sulphone useful as solvents and chemical reactants.
TALL OIL. The gum naval stores industry has for the most part been replaced by the recovery of oleoresinous wood components from the kraft pulping process (Uprichard, 1978; Zinkel, 1975). Volatiles such as turpentine are recovered from the digester relief gases. The alkaline pulping liquor converts the fatty acids and resin acids to sodium salts which can be skimmed off the concentrated black liquor and acidified to yield crude tall oil.
WOOD HYDROLYSIS. Wood hydrolysis, the conversion of the carbohydrate polymers in wood to simple sugars by chemical reaction with water in the presence of acid catalysts, has been known for 150 years and has been practiced on a commercial scale in the United States during World War I, in Germany during World War II, and at present in the USSR. Glucose is the principal product and can be further converted to ethanol or yeast.
CELLULOSIC POLYMERS. High-purity, chemical cellulose or dissolving pulp is the starting material for such polymeric cellulose derivatives as rayon and cellophane (both regenerated cellulose), cellulose esters such as the: acetate and butyrate for fibre, film and moulding applications, and cellulose ethers such as carboxymethylcellulose, ethylcellulose and hydroxyethylcellulose for use as gums.
EXTRACTIVES. Some turpentine and rosin are still obtained by steam distillation or extraction of pine stumps. Arabinogalactan, a hemicellulose gum extracted from larch, is used in place of gum arable. Phenolic acids extracted from the bark of various conifers are used as extenders for synthetic resin adhesives, and as binders and dispersants. Waxes extracted from Douglas fir bark can be used for general wax applications, and natural rubber remains an important :material.
Future use of wood for chemicals can be divided into two major categories, the first being chiefly an extension and expansion of present practices and the second involving conversion of the cell wall polymers into low molecular weight chemical feed-stocks.
EXPANSION OF PRESENT PRACTICE. Involved here is not merely the physical expansion of existing operations, but also an extension to related opportunities in by-product and extractives utilization. The examples cited are illustrative, not limiting.
Extractives from bark and wood have much more potential than their present use represents (Hillis, 1978; Laver, 1978). Cellulosic polymers could become more important if energy costs can be reduced and properties improved (Allen, 1978; Goldstein, 1977). Oleoresin production in pines can be stimulated by the application of herbicides (Roberts, 1973). Hydrocarbon polymers can be obtained by cultivation of new plants as commercial crops (Galvin, 1978). Low molecular weight phenols can be obtained from byproduct lignin in pulping liquors (Goheen, 1971; Benigni and Goldstein, 1971). Saccharinic acids could be recovered from kraft black liquor (Sarkanen, 1976). Foliage can yield essential oils, chlorophyll and protein (Barton, 1978).
CONVERSION OF CELL WALL POLYMERS. The major portion of the wood consists of the cell wall components. This source of raw material far exceeds the extractive components or the chemical by-products in volume and represents a potential resource for meeting all of our chemical needs in place of petrochemicals. Large-scale production of industrially important chemicals from lignocellulose can be accomplished by various routes (Goldstein, 1976a). These tonnage quantities could provide the basic chemical building blocks for conversion to synthetic polymers (Goldstein, 1975a).
TOTAL WOOD. The cell wall polymers in their natural mixed state can be broken down into simpler compounds by drastic processes involving high temperatures and in some cases high pressures as well. These processes are inherently non-selective and are the same as those useful for the conversion of organic solid wastes or coal into chemicals.
In gasification, the wood is heated at temperatures up to 1 000°C to form a mixture of carbon monoxide and hydrogen as the major products (Prahacs, 1971). Low yields of ethylene, acetylene, propylene, benzene and toluene are formed as by-products. The carbon monoxide and hydrogen formed as in coal gasification may be (a) further processed to provide hydrogen for ammonia production, (b) catalytically converted to methanol, (c) enriched with hydrogen and reacted to form methane, or (d) catalytically converted to a mixture of aliphatic hydrocarbons by the Fisher-Tropsch process.
Wood may be liquefied by reaction with carbon monoxide and water at 350400°C and 4 000 lbf/in² pressure in the presence of various catalysts (Appel, 1971). A viscous oil is produced in 4050 % yield which might be further processed to chemicals in the same way petrochemicals are derived from petroleum.
Pyrolysis or thermal degradation of wood in the absence of air or oxygen converts the wood to charcoal, gas and oil (Soltes, 1978; Wender, 1974). The relative yields of the products depend on the pyrolysis conditions and substrate composition, but typical values at 900°C might be: 25-35 percent charcoal, 30-45 percent gas and up to 8 percent tar and oil. The gas consists chiefly of hydrogen, carbon monoxide and methane, while the tar and oil contain such light oil components as benzene and toluene as well as mixtures of higher boiling compounds.
CELLULOSE. Selective conversion of the glucose polymer cellulose to monomeric glucose can be accomplished by a number of routes. Hydrolysis to glucose can be catalyzed by either acids or enzymes, but neither way is as facile as the hydrolysis of starch because of the crystalline nature of cellulose. Acid hydrolysis is not inhibited by lignin content, but cellulose with a high lignin content is resistant to enzymatic hydrolysis, so wood would have to be partially delignified or finely ground to undergo hydrolysis by enzymes.
Coal or wood will be the alternatives to oil as the chemical feedstock of the future. It will' of course, depend upon which one a country has. But only wood is renewable.
Acid hydrolysis by dilute acid at high temperatures causes decomposition of some of the glucose formed to hydroxymethylfurfural (Harris, 1975), limiting net sugar yield to about 50 percent. Strong acid hydrolysis at lower temperatures can provide almost quantitative yields of glucose (Kusama, 1960).
Shafizadeh (1978) has shown that dry distillation of cellulose at 400 500°C gives about 80 percent of a tar that contains mainly levoglucosan and may be converted to glucose in 50 per
cent yield based on cellulose. Cellulose free from other cell wall components would be required to avoid contamination and reaction with other decomposition products.
The conversion of cellulose to glucose is the first step in the potential large-scale chemical utilization of cellulose. Of greatest potential importance is the fermentation of glucose to ethanol by commercially proved techniques with high yields. Ethanol is an important industrial chemical now produced by hydration of ethylene. It also could have wide application as a fuel for internal combustion engines.
The dehydration of ethanol to ethylene, the reverse reaction to present ethanol formation from ethylene from petroleum, also results in high yields. Similarly, butadiene can be readily obtained from ethanol by processes which were proved commercially, but made obsolete by cheap petroleum. The conversion of glucose via ethanol to ethylene and butadiene represents the greatest potential utilization of cellulose for chemicals because of the importance of ethylene both as the largest volume organic chemical and as a building block for petrochemicals and plastics, and of butadiene as an agent in the production of synthetic rubber.
Glucose may also be converted into chemicals which are not now important industrially, but which could become so under the proper economic conditions. One such process is the production of hydroxymethylfurfural and its further conversion into levulinic acid by the action of hot mineral acids on glucose (Harris, 1975). The use of glucose as a general fermentation substrate would allow the production of a wide assortment of antibiotics, chemicals, vitamins and enzymes from wood (Seeley, 1976). Lactic acid, for example, could be converted to acrylic acid and acrylates.
HEMICELLULOSES . The hemicelluloses are more readily hydrolysed by acid than cellulose and, consequently, are easily converted into simple sugars under mild conditions in high yield. The xylans, which are more abundant in deciduous trees, yield principally xylose, while the glucomannans found in larger quantities in conifers yield mannose.
Mannose and other hexoses can be combined with glucose for fermentation to ethanol. Xylose and other pentoses can be converted to furfural, or alternatively xylose could be reduced to xylitol. Furfural is now produced commercially by acid treatment of the xylan in corn-cobs and sugarcane bagasse. Since it would be available in much greater quantity from wood hydrolysis, new applications would be needed. However, since furfural once served as the raw material for nylon until displaced by butadiene, an abundance of furfural at a reasonable cost should stimulate new uses.
LIGNIN. The features of lignin important for chemical utilization are its aromatic character (in the chemical sense of phenyl group content) and the covalent carbon-carbon bonding which prevents reversion to monomers by mild processing. By more severe conditions of pyrolysis, hydrogenation, and hydrolysis, yields of phenols of up to 50 percent have been reported (Goheen, 1971, Goldstein, 1975b; Schweers, 1978), and, in addition, projected yields of 35 percent pure phenol have been suggested. Benzene has been isolated as a component from lignin hydrocracking and could be obtained in 25 percent yield on lignin by dehydroxylation of phenol.
FUTURE CHEMICAL PLANT. It is apparent from the preceding discussion that the various components of the wood can be converted into specific chemicals: cellulose, for example, to ethanol and the hemicelluloses to furfural. Although such single product plants have been considered from time to time, they do not represent the most efficient and economical utilization of the wood harvested and collected as raw material. The wood chemicals plant of the future should convert all the components of the wood into useful products just as petroleum refineries and meat-packing plant utilize all their raw materials.
An example of such a scheme (Goldstein, 1975a), but not the only one which can be envisaged, would involve prehydrolysis of the wood by weak acids to convert the hemicelluloses into xylose or mannose-rich streams, leaving a solid residue of cellulose and lignin behind. The xylose could be converted into furfural or xylitol and the mannose combined with glucose for fermentation. Strong acid hydrolysis of the cellulose-lignin substrate would yield a glucose solution fermentable to ethanol or other chemicals and a solid lignin residue. The lignin could then be hydrogenated to phenols or otherwise processed l resins. By further processing the ethanol to ethylene and butadiene, such a plant could produce the chemicals required for the production of molt of the synthetic plastics, fibres and rubbers indispensable to industrial society.
Other integrated systems of wood utilization can be designed which include alternative production of energy, food, and materials as well as chemicals (Lipinsky, 1978). These systems can have more or less of a chemical component and to that extent contribute to the chemical needs of the people of the world.
Wood for making chemicals does not compete with wood for lumber' panels or pulp. Form is unimportant Species and size do not matter.
A major substitution of chemicals from wood for the petrochemicals now in use will depend upon a number of technical, economic, political and social factors. The conceptual feasibility of chemicals from wood developed in the preceding sections will be tempered by the reality of the factors discussed below.
A NEW ERA. The chemical industry has grown rapidly during the past 50 years in both volume and sophistication of products. Stimulated by abundant and inexpensive supplies of petroleum as a raw material, synthetic organic materials have become so pervasive that the standard of living of industrial societies is inextricably bound to these materials.
Davies (1978) has pointed out that industrial chemistry has known three eras during these 50 years. In the first, free science led the way. The results of good and relevant research led to inventions that were useful and profitable. In the second era' after World War II, market forces set the pace. Identification of market needs allowed ingenuity and science to meet them in new ways. It was especially in this era that inexpensive petroleum permitted rapid growth. The third era, which we are now entering, is -termed by Davies "the resource and husbandry period." Now the imperatives are to improve, cheapen and assure supplies of desired products by materials economy and substitution of more abundant feedstocks.
According to this analysis, the chemical industry must turn toward the resource base to continue to thrive. Just as there was an earlier change from a coal tar base to a petroleum base, a change now to coal and cellulose could be needed for future chemical feedstocks. Chemicals from wood will probably not have to face an institutional barrier to their acceptance. The historic adaptability of the chemical industry would seem to provide a receptive climate.
IMPROVED TECHNOLOGY. The timing and rate at which chemicals from wood might displace petrochemicals would ultimately depend on their relative cost. The price of petroleum is beyond the control of the forest industries, but changing technology in wood chemistry could act to reduce these costs.
At present prices, chemicals from wood such as ethanol, methanol, etc. cannot compete with petrochemicals. The one possible exception might be an integrated plant producing ethanol, furfural, and phenol (Katzen, 1978; USDA Forest Service, 1976). Process improvements in wood gasification and wood hydrolysis to increase yields and reduce capital costs could make this price gap smaller, especially if there were significant improvements over the 50 percent net yield of glucose in weak acid hydrolysis.
The isolation of chemical cellulose (dissolving pulp) and its conversion into fabricated fibres, films, plastics or gums are areas where technological improvements could bring about improvements in the competitive position of cellulosic polymers, not only with respect to synthetic polymers from petroleum, but also in competition with synthetic polymers from feedstocks obtained from cellulose breakdown.
Other areas where improved technology can favourably influence the cost of chemicals from wood are the hydrolysis of cellulose to glucose by enzymes and the conversion of lignin to phenols.
Research on the chemical utilization of wood has been relatively meagre in comparison with the effort expended on petrochemicals during the past 50 years. As a percentage of sales, it represents only about 10 percent of that devoted to chemicals and synthetic polymers generally. In fact, when petroleum prices were declining, research on chemicals from wood was virtually discontinued. An increase in the scale of wood research could be expected to provide significant new and improved technology to exploit the full potential of wood as a feed-stock for chemicals.
Ethanol can serve as engine fuel, as an industrial chemical in its own right, and as a raw material for ethylene production. The market for each is different' but the price of ethanol probably would be set by the market for its use as fuel.
COST AND AVAILABILITY. This factor is the most important consideration affecting chemicals from wood and one of the most imponderable. Reaction to the increasing cost of petroleum and recognition of its ultimate depletion have stimulated many analyses of alternative energy sources and alter native chemical feedstocks of which this article is yet another example. There is wide disagreement among the experts about how fast oil prices will continue to rise and how soon supplies will become exhausted. These matters are beyond the control of the forest industries. Advocates of wood as an alternative chemical feedstock can do little beyond improving their technology while they wait.
At a recent conference on chemical feedstock alternatives (Van Antwerper, 1977), one group of participants predicted that the petrochemical industry would begin its decline about 1990, with 50 percent or more of the new feedstocks being added to the system coming from non-petroleum sources. At the other end of the prediction scale, the middle of the next century was cited as the approximate date for the depletion of world oil reserves. Somewhere in the intervening period, crude oil prices will be so high that the production of ethylene by dehydration of ethanol will probably become economically feasible (Sarkanen, 1976). This, of course, presumes that crude oil prices will continue to climb at a faster rate than wood costs.
Some people contend that petroleum is more valuable as a chemical raw material than as a fuel and should therefore be conserved for preferential use as a chemical feedstock. However, if the users of petroleum feedstocks have to compete with energy users, those who demand gasoline and heating oil will be willing to pay more, thus improving the competitive position of alternative raw materials.
COAL AND WOOD. The chemical feedstocks now derived from petroleum can be alternatively derived from coal or wood. Coal is also a finite resource and will ultimately be consumed, leaving only wood as a renewable resource in perpetuity. But in the near future coal will probably play an important role in chemicals because the development work is further advanced than with wood and because the massive use of coal to produce synthetic liquid fuels will also produce chemicals. In fact, coal gasification plant are now in operation, notably in South Africa.
The actual price of such chemicals from coal would depend on whether they were bargain priced as by-products or reflected a fair share of the cost of production. Plant investment costs are much greater for coal than for petroleum, as are extraction costs and transportation costs. The cost of coal itself has not reflected environmental damage, just as the cost of oil before 1973 did not reflect the depletion of the resource. It has been predicted that chemicals from coal will be competitive with petrochemicals when the price of low-sulphur crude oil doubles (Richards, 1976).
With these uncertainties, there are insufficient hard facts to state categorically that either wood or coal will predominate as an alternative feedstock for chemicals. Of course, in countries which have had an ample supply of wood and no coal or vice versa, the choice would be obvious.
The procurement of wood for chemical processing would not compete with wood for lumber, plywood and pulp since it would rely on sources not at present used. Neither the form nor the nature of wood for conversion into chemicals is of importance. Species and size do not matter. For example, low-grade hardwoods in the southern United States which are suitable neither for structural nor for pulping purposes because of size, species, defects or bark content would be ideal for this application (Goldstein, 1978). Similar resources, at present non-commercial, are abundant all over the world.
The present delivered cost of such wood harvested by whole-tree chipping can be well below the cost of pulpwood chips. However, if it were used for direct combustion to provide energy, its cost could be lower than the cost of obtaining the same heat content from alternative fuels.
ENERGY AND CHEMICALS. The cost of chemicals derivable from raw materials cannot be divorced from energy considerations. The major products of petroleum refineries, for example, are gasoline and fuel oil rather than petrochemicals. Petrochemical prices are affected by internal accounting and would be much higher if most of the overhead were not borne by the major products.
Similarly, coal conversion plants are being planned to meet the need for synthetic liquid fuels. Chemicals will be only by-products. The economics for coal conversion plant devoted solely to chemical production would be much :less favourable.
Turning to chemicals from wood, ethanol can serve as fuel for internal combustion engines, as an industrial chemical in its own right, and as a raw material for ethylene production. The market for each is different, but it seems reasonable to suppose that the price of ethanol would be set largely by its potential market as fuel.
If pulping by-products such as lignin, phenols and saccharinic acids are to be recovered from kraft black liquor, they will have to be replaced in the energy economy of the pulp-mill by an equivalent amount of energy from another source. Since one of the functions of the recovery boiler is to provide a reducing atmosphere for the inorganic pulping chemicals, another source of carbon compounds would be needed. Hydrogen would require redesign of the recovery system and process-steam generated externally would not suffice, even though it satisfied the energy deficit. This constraint, combined with the separation problems, places serious economic limits on large quantities of by-product chemicals from this source.
SCALE OF OPERATIONS. In contrast to the thousands of millions of dollars in capital investment required for individual world-scale petrochemical plants and the large coal conversion plant considered to be necessary for economy of scale, a large wood chemicals industry would require neither concentration nor large individual installations. The need to procure: a wood supply within a reasonable hauling radius would lead to plant of relatively modest size widely dispersed throughout the forest resource. A compromise between economy of scale and wood procurement limitations would be in the range of about 2 000 tons per day, dry-wood basil. This has proved to be a convenient size for many pulp mills. Estimated capital investment would be in the range of $100 million (USDA Forest Service, 1976).
INCREMENT CAPITAL INVESTMENT. Because existing capital investment in petroleum-based facilities is enormous, substitution would have to be gradual unless a sudden unavailability of petrochemical feedstocks required a crash programme to replace them. The relatively small size of wood chemicals plant and the corresponding relatively small capital investment required could influence: a decision in favour of chemicals from wood for incremental capacity. Offsetting this would be the uncertainty of new processes compared to known petrochemical technology.
POLITICAL CONSIDERATIONS. In all probability, decisions whether or not to build plant for the conversion of wood into chemicals will not be based entirely on technical feasibility and traditional laissez-faire economics of supply, demand and profitability. Government incentives and disincentives will surely influence these decisions, especially since chemicals and energy are so interrelated. These could take the form of subsidies, price supports, favourable tax treatment, or taxation of unfavoured alternative feed-stocks. Social decisions varying from country to country will play an important role, in some instances the determining role in the future growth of chemicals from wood.
ENVIRONMENTAL CONSIDERATIONS. The increased use of wood for conversion to chemicals will cause an increase in harvesting activity with its resultant impact on soils, watersheds and wildlife. Since these same concerns already exist in harvesting for conventional wood uses, there should be no special technical problems in extending the practices already in use.
However, a preservationist attitude by the public toward the forest environment could limit the availability of the additional wood which would be needed. An affluent society might choose to allow a, major portion of the wood which grows each year to be recycled by natural agents rather than permitting the harvest of this annual growth as a chemical raw material.
PSYCHOLOGICAL BARRIERS. Chemical engineers find liquids and gases easier to handle than solids, and both the petroleum industry and the sector of the chemical industry involved in organic feedstocks are accustomed to handling liquid raw materials by tanker or pipeline. The prospect of collecting a solid raw material over thousands of square kilometres could be so foreign a concept for them that its very feasibility has been questioned.
In addition, the forest products industries, which regularly assemble even larger quantities of wood in their operations, are equally uncomfortable with the idea of producing chemicals alongside their familiar products.
Barriers of this kind will fall when incentives become great enough, but they do slow the conversion process.
Having considered the factors involved, it is apparent that predictions about the future of chemicals from wood can be made only in the most general terms, and even then will be fraught with uncertainty. Nevertheless, I will venture to present my opinion, biased as it might be by my personal involvement in research on chemicals from wood.
Our present reliance on fossil hydrocarbons for organic chemicals and polymers cannot continue any longer than the availability of this finite depletable resource. Even before the total exhaustion of the world's oil and gas supplies, the cost of these resources will increase to a level at which chemicals from alternative resources such as coal and wood will be able to compete with petrochemicals. This point will be reached sooner in some countries than in others because of local availability of alternative resources and favourable government policy decisions affecting their economics. It is likely that chemicals from both coal and wood will replace petrochemicals.
Where coal is available, wood gasification to produce ammonia, methanol and hydrocarbons will not be practiced, but in the absence of coal this technology can be effective. Wood hydrolysis to sugars for further conversion to chemicals such as ethanol, furfural, lactic acid and the polymerizable monomers obtainable therefrom will be prevalent. Even now an integrated plant producing ethanol, phenol and furfural from hardwoods would be economically feasible at current prices.
Although there will be no single answer to the problem of organic chemicals supply which will be caused by increasing petroleum prices, I believe that wood will make a significant contribution to its resolution.
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