Waste Product Use elps P As a consequence of enlightened R&Dprograms for many years, the pulp and paper industry has found that one effective way to achieve pollution abatement is through the chemical utilization of waste products n the chemical pulping of wood by the acid sulfite process, traditionally w w d chips have been digested with a solution of calcium bisulfite and sulfurous acid at elevated temperatures under pressure. During this process the lignin is dissolved as calcium lignosulfonate, and the hemicelluloses are hydrolyzed to soluble carbohydrates or simple sugars leaving approximately 50% of the dry weight of the wood as cellulosic pulp. The effluent from this process, the so-called spent sulfite liquor, therefore, contains approximately one half of the solids of the original wood, together with the chemicals employed in the pulping process. As the liquor leaves the digester, it contains approximately 10% solids, of which 50-60% is calcium lignosulfonate and 25-30% is caTbohydrate material. Unlike the alkaline pulping processes, in which the cooking chemicals are recovered from the spent liquors by evaporation and burning, the calcium-base sulfite process yields spent liquors which must be disposed of by other means. Usually, the spent sulfite liquor is disposed of by dumping the material into the waterway upon which the mill is situated. From the beginning of the sulfite pulping industry in the latter part of the 19th century, the spent liquor from this industry bas been sewered into adjoining waterways, and has constituted a public nuisance. Pressures for the abatement of these pollutional effluents were responsible for most of the research on lignin and ligno-
sulfonates, important constituents of spent sulfite liquor. After World War 11, two important factors added new incentives for research toward more complete utilization of the wastes from all pulping and wood-using industries: The need for conservation to mea expanding raw material requirements. - T h e urge for more economical production in the face of higher o p erating costs. The 2.5 million tons of spent sulfite liquor solids generated in the U. S. alone offered tremendous carbohydrate and aromatic chemical raw material for chemical utilization. Inasmuch as the carbohydrate content of spent sulfite liquor could be fermented ewnomically to produce ethanol or Torula yeast, the lignosulfonate content of the spent sulfite liquor became the organic raw material of interest The enormous quantity of wasted lignin offered a chemical raw material which potentially could rival coal tar and petroleum as a source of synthetic organic chemicals. Also, the use of lignin for such a purpose was in line with the increased necessity of wnserving our dwindling supply of re maining natural resources and with the axiom that we should employ raw materials which are being replenished constantly by nature, rather than those. accumulated slowly over geologic ages. In an industry of constantly cbanging technology, pulp mills with large capital investments in particular locations needed to find revenue-producing byproducts from their wastes to com-
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pete with other mills that were situated better or that employed less costly processes. With this background, and more important, with the anticipation of increased pressure from regulatory agencies, a group of midwestern sulfite pulp producers recognized, before World War 11, that the time might come when they would be forced to remove all spent liquor solids from their adjoining waterways. Complete removal of spent liquor solids from the waterway suggested evaporation and disposal of the solids on land. Because of the corrosiveness of the strongly acid spent s a t e liquor, stainless steel evaporators and auxiliary equipment are required for its evaporation. Iu many of the small midwestem mills, the capital investment required
FEATURE
Irwin A. Pearl
The Znsfifufe of Paper Chemistry Appleton, Wis. 54911
for such an evaporating plant was as great as that for the existkg mia Under such conditions, these mills could not afford to evaporate their spent liquor and dispose of tbe core ceutrated liquor by with IB wvery of only heat Evapnration d d be aSorded only if profitable utilization of the amcenimted liquor d d be achieved. During the past decade, mewed and augmented inin both water and air poUution and the more acnte anticipatiou of specific pressores fmu regulatory agencies for the abatement of both types of pouution have led to lacreased &oxt w the palt of the industry to 6nd economic values in its waste pmdmts. In this manner the ilk dustry hopes either to remove powing material entirely or to make pos-
sible the satisfactory evaporation or burning of these wastes without added costtothemill. Over the years, many important pmcesses have evolved, and commercial exploitatiou of these processes has permitted a few selected mills not only to eliminate stream pollution, but also to lower considerably the P ~ U G tion cost of their pulps. This article dkcuses new commercial processes and modi6catious of old processes which have been initiated in both the SUlMe and kraft pulping industries, together with important research now mder way. Although essentially aU develop ments in the pulping and wood-using indushies have been covered recently in detailed reviews, I will note here some of the most important achieve me&. Furihemore, although the chief purpose of this article is to discuss the use of the pulp and paper ind w s wastes as sources of chemicals, the article will also mentiou some of the important developments in the gene& utilization of the industry's most important waste product4pent s u l h liquor. R m b directed at the utilization of spent sulfite liquor and its lignsulfooate content resulted in many important developments. The dispersant properties of the lignosulfonates, combind with their ability to sequester many metallic ions, have contributed to their success as additives for the preparation of oilwell drilling muds. This use in drilling mud compositions constitutes the largest single use for p d e d lignosulfonates, and accounts for a market currently estimated at
90 million pounds per year. Unfortunately, this market is enjoyed by only a few producers of spent sulfite liquor. But these few have been successful in deriving cousiderahle profit on the basis of their capital investment for byproduct recovery. In some instances, primary producers of lignosulfonate materials cannot meet market demands with theu own lignosulfouate and must purchase spent sulfite liquor from other less fortunate producers of spent sulfite liquor. Two other largescale uses of spent sulfite liquor actually utilize the crude liquor without any fractionation. The relatively low-grade utilization scheme of roadbinding is the largest user of crude spent sulfite liquor, accoUnting for an estimated 125 million pounds of spent sulfite liquor solids annually. This use for speut liquor solids is a splendid method for disposal of the potential polluting agent during the warm weather months. However it accounts for very little, if any, monetary rehm to the mill. Furthemore, the high cost of transporting the dilute liquor in stainless steel tank trucks precludes the use of spent sulfiteliqnor on secondary mads distant from producing mills. The other largescale use of crude spent sulfite liquor is that of binder for animal feed pellets. Concentrated spent mllite liquors and spent sulfite liquor solids from the calcium, magnesium, ammonium, and sodium-based procepses have found exceptional BCceptance as pelletizing agents for the produclion of animal and poultry feeds and are used in amounts up to 4% of the finishedpellets.
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In addition to the nutritional values of the carbohydrate and inorganic constituents, the lignosulfonates in the liquors are said to lubricate the pellet die and to reduce power consumption during pellet formation. Stronger, denser pellets with less tendency to break are produced, and the amount of fines that must be recycled is greatly reduced. This market for spent sulfite liquor solids is approximately 65 million pounds annually. Other important uses of lignosulfonate materials are for concrete additives (30 million pounds per year) ;and water treatment (15 million pounds per year). About 100 million pounds of lignosulfonate materials are sold for a host of miscellaneous uses based upon both the physical and the chemical properties ot' these spent sulfite liquorderived products. Notable uses are for dispersing agents for carbon black in rubber applications, vat dyestuffs in the textile industry, pesticides in agricultural sprays, ore flotation, and various special applications in the cement and ceramic industry. Many of these dispersant uses are made possible also by the sequestering action of lignosulfonates toward many metallic ions. an important chemical property utilized in other important processes such as the prevention of unwanted chemical reactions. precipitations, discolorations. and even biochemical reactions of trace elements in agricultural applications. Metal complexes
The ability of lignosulfonates to complex with metals is utilized in still another agricultural application of iron in the control of lime-caused iron chlorosis in fruit trees. The specific chemical reaction of lignosulfonates with proteins is made use of in removing contaminating proteins from emuents of canneries or fish-processing plants. and for the production of casein-lignosulfonate binders. Lignosulfonates are also used to a considerable extent in the tanning industry along with vegetable and chrome tans. Lignosulfonates react with phenolformaldehyde resins to give condensation products with special properties which have found a variety of uses based upon either their relatively lowcost or their specific properties. This brings us to the utilization of the components of spent sulfite liquor
as raw materials for the productiou of chemicals. Over the years, many attempts have been made to create an industry based upon these spent liquors, but efforts along this line were only partially successful for several important reasons. In addition to the very competitive nature of the chemical market and the fact that the market potential for byproduct chemicals is so small compared with available raw material, the great dilution of solids in spent sulfite liquor and the presence in quantity in this liquor of two such chemically different types of materials presented substantial obstacles to commercial utilization of spent sulfite liquor as a source of chemical byproducts. Still, there have been some marked commercial successes. The dilution and vaned chemical obstacles were obviated by the Howard Process which was instituted at Rothschild. Wis.. by the Marathon Corp. (now the American Can Co.) in 1936. In this process. calcium-based spent sulfite liquor from the pulping of coniferous wood was precipitated fractionally with lime. and the lignosulfonate was ilated as a basic calcium salt free from nonlignin materials. In 1937. on the Marathon lot in a separate plant operated by the Salvo Chemical Corp.. a subsidiary of Sterling Drug Co.. this lignosulfonate salt was treated with sodium hydroxide under pressure. The resulting alkaline solution was extracted directly with butanol to obtain vanillin, an important flavoring agent (Figure 1). Within a few years this plant was supplying approximately 40% of the vanillin requirements of the U. S. In the late 1940's the commercial operation at Rothschild was modified by introducing gaseous oxygen under pressure into the lignosulfonate-alkaline reaction mixture. thereby increasing the yield of vanillin on the lignin basis. During World War 11, the Ontario Paper Co., Ltd.. of Thorold, Ontario. and the Puget Sound Pulp and Timber Co. (now a Division of Georgia-Pacific C o p ) of Bellingham. Wash., began the fermentation of the sugars of coniferous spent sulfite liquor to ethanol. and have continued production ever since. The residual spent liquors from the ethanol fermentation are desugared to the extent of 65-702. and thus become another type of relatively
pure lignosulfonate materid avai!able tor chemical utikation. Y e a t -re#?
M e r the war, plants for the production of Torula yeast by the termentation of both coniferous and deciduous spent s a t e liquors with Torulopsis urilir were placed in operation by Lake States Yeast Corp. (now a Division of St. Regis Paper Co.) and by Charmin Paper Products Co. (now a Division of Procter and Gamble Co.) at Rhinelander, Wis., and at Green Bay, Wis., respectively. These yeasts have found extensive use as animal f d and human tood supplements and as a source Lor nucleic acids. Because Torulopsis rrfilis uses both hexose and pentose sugars, the residual liquors from this fermentation are desugared to the extent of 90-95%. which leaves a lignosulfonate solution almost free of carbohydrate materials. Although the market for Torula yeast has increased tremendously since its production was commenced. and it is continuing to grow, the Charmin plant in Green Bay has shut down its yeast plant recently because! a complete change in its pulping process has produced a spent sulfite liquor with a sugar content below that which can be fermented economically. As a result, other yeast production probably will be initiated to supply the market that is now going unfilled 0 U
C-H
After the war, two important chemicals from spent sulfite liquor operations came into being. Both of these developments utilized carbohydratepoor residual liquors from the ethanol fermentation of spent sulfite liquor. The Ontario Paper Co. began the production of vanillin by a modified process employing lime as makeup alkali in the presence of oxygen. After a few years of operation, this plant, with a reported production of 3 million pounds per year, supplied the vanillin requirements of most of the British Commonwealth and was even successful in competing in the U. S. market. The Ontario vanillin process produces acetovanillone and vanillil (Figure 1) as coproducts. These two aromatic fine chemicals are available in pilot-plant quantities from the producer. As a final product of its oxidation process, Ontario Paper produces oxalic acid (Figure I ) in an amount of 2 million pounds per year. Very recent increased demand for both vanillin and oxalic acid has prompted Ontario Paper to double its production of these two chemicals. Vanillin manufacture
Monsanto Chemical Co., which for many years had been supplying approximately one half the vanillin requirements of the U. s. with synthetic vanillin, ceased the production of synthetic vanillin in the early 1950's and began the production of vanillin from lignosulfonates. The Monsanto plant at Seattle, Wash., utilizes concentrated ethanol-fermented spent sulfite liquor from the mill of the Puget Sound Division of Georgia-Pacific COT. at Bellingham, Wash., and converts it to vanillin by a modified sodium hydroxide-oxygen process. This lignosulfonate-derived vanillin from the Seattle plant now supplies all of Monsanto's vanillin markets. Unfortunately, the requirements for flavoring vanillin are so small that the amount of spent sulfite liquor utilized in its production represents only a negligible percentage of the available spent sulfite liquor. With the philosophy that a fundamental study of the chemistry of vanillin and subsequent development of new chemical uses for vanillin would result in the wider utilization of waste lignosulfonates, such a project was initiated more
than 25 years ago in my laboratory at the Institute of Paper Chemistry. This fundamental research program was sponsored by the Sulphite Pulp Manutacturer's Research League. Processes were evolved for the simple conversion of vanillin to its derived acid, vanillic acid (Figure 2 ) , which had been a laboratory curiosity until that time. Many new esters, amides, ethers, and other derivatives of vanillic acid were prepared and evaluated for a variety of uses. For example, ethyl vanillate was found to be less toxic to humans than sodium benzoate, but very toxic to specific microorganisms. As such, it found usefulness in the treatment of human diseases and as a preservative in foodstuffs. At present, it is manufactured commercially for the specific treatment of the progressive disseminated form of the two mycotic diseases, histoplasmosis and coccidioidomycosis (valley fever). Similarly, in Europe, the diethylamide of vanillic acid has found widespread use as an analeptic agent for the control of respiration and blood pressure. The ultraviolet absorption characteristics of ethyl vanillate make it useful in sunburn preparations, and its specific antimycotic properties indicate its use for the topical treatment of skin fungus infections. Vanillin, itself, has also been converted to hundreds of compounds, and most of these have also been evaluated
OH
for different end uses, especially medicinal uses. In addition, many have been found useful as intermediates in the preparation of already known medicinal agents. In other laboratories, vanillic acid has been converted to its hydroxyethyl ether, and the resulting product polymerized to a linear polyester that could be extruded in the form of fibers or filaments, molded in a press, or cast from a melt-products similar to those prepared from polyesters of terephthalic acid. Although no use of this process has been made as yet in this country, there is limited commercial production in Japan. More than conifers
At this point, we should remember that the discussion so far has been concerned with the lignin and lignosulfonates of only coniferous woodswoods which traditionally made up the furnish for pulp mill operations. In the early 1950's, several economic factors caused a number of mills around the country to cease cooking spruce, balsam, hemlock, and other conifers, and to cook in their stead readily available aspen, cottonwood, alder, birch, and other deciduous woods. The spent liquor from the pulping of these deciduous woods is not satisfactory for the production of vanillin or its derivatives because commercial vanillin processes, when applied to these li-
J
Figure 2
Volume 2, Number 9, September 1968 679
quors, yield equal or greater amounts 01 syringaldehyde and other similarly suostituted compounds (Figure 3). Cnemical utilization of these deciduOLIS wood spent liquors must await a greater knowledge of the chemistry of syringaldehyde and other syringyl compounds. A comprehensive program on this subject is under way in the institute's laboratory, and encouraging results have been reported already. Hydrogenation of lignobulicnates and lignins to desirable low-molecular weight compounds has received considerable attention by investigators. Several years ago, the Noguchi Institute of Japan revealed a commercially practical procedure for the hydrogenation of waste lignin materials to phenolic compounds of interest, but commercial evaluation of the process by the Crown Zellerbach Corp. demonstrated that the process could not compete on the American market under existing conditions. Glacial acetic acid
For several years, the Sonoco Products Co. of Hartsville, S. C., has been manufacturing close to 8 million pounds per year of glacial acetic acid and about one half million pounds per year of 90% formic acid from their spent liquor from the neutral sulfite pulping of mixed southern hardwoods. In 1966, Weyerhaeuser C o . began producing acetic acid from spent sulfite liquor at Cosmopolis, Wash., in a plant with an annual capacity of more than 6 million pounds. In the alkaline processes for producing chemical pulps (both kraft and soda), economics require that the organic matter in the spent liquor be evaporated and 'burned for pulping chemical and heat recovery. In the recovery of heat, the kraft and soda mills of this country consume some 4 million tons of lignin and other organic materials. Although this transformation of organic materials into heat is an economic method of disposing of the spent liquor as far as the mill operation is concerned, it might not be the most profitable manner of treating such potentially valuable chemical raw materials. That the alkaline pulp industry is well aware of this fact is demonstrated by several important developments. The rags to riches story of tall oil is an example. In this case, the need 680
Environmental Science and Technolog>-
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C- H
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ducers of tall oil chemicals are seeking urgently additional sources. Accordingly, even kraft pulp producers employing marginal wood species are turning to tall oil recovery. Thus, the kraft industry has converted a waste product into a valuable byproduct with a market value many times that of its value as fuel.
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C-OH
Figure 3
for product development was impressed upon the industry in the beginning. Before World War 11, tall oil skimmings from the concentrated black liquors of our kraft mills was usually burned for fuel because its desirable components could not compete on the American market with these same materials derived from oils and fats imported from the Far East. War with Japan cut off this supply of fats and oils needed in so many phases of our economy, and the separation of substitute fats and oils from tall oil became an economic necessity. After the war, the instability, due to political changes, of sources of supply of vegetable oils from the Far East, the population explosion in this country, and the marked changeover from solid fats to liquid oils in the eating habits of the American public placed a heavy demand on our own supplies of vegetable oils for food purposes. The outlet for tall oil fatty acids to fill nonfood markets, coupled with the expanded market for the resin acids of tall oil due to new developments in the rosir and modified rosin industries and the decreased production of gum rosin, led several kraft pulp manufacturers to enter the tall oil chemical field. These manufacturers, along with other independent tall oil chemical producers, now process the skimmings from every kraft mill capable of producing tall oil. At present, the demand is so great that more and more kraft pulp producers are entering the tall oil chemical business, and all pro-
Turpentine production
Along with the tall oil development, the kraft pulp industry has entered the turpentine industry, so that now the turpentine production in the U. S. from kraft pulping is greater than production from all other sources combined. In the past several years, individual pulp mills employing unique pulpwood furnishes have found that their kraft turpentine contained high percentages of desirable individual components such as delta-3-carene or beta-pinene. In addition, the high profits associated with purified turpentines and their components have appealed to many kraft pulp producers. As a result, in the past few years a number of the kraft pulp producers have initiated their own turpentine purification and fractionation plants. Although most producers of alkaline process pulps still believe that the best way to utilize their most plentiful waste product, alkali lignin, is as a source of heat, a few of the more enterprising producers are convinced that the values in alkali lignin are much greater than that of fuel. Accordingly, several soda and kraft mills in this country and Canada already are isolating and marketing alkali lignins in commercial quantities. Research on these isolated lignins will lead to new uses for them and to larger-scale participation in alkali lignin use on the part of the entire alkaline pulping industry. Alkali lignins have found uses in industry because their physical and chemical properties are similar to those of lignosulfonates. But many of these uses have been circumscribed by the fact that these lignins are water-soluble only in alkaline solutions. This water-solubility problem has been overcome by the West Virginia Pulp and Paper Co. Their process sulfonates alkali lignin to produce a series of synthetic lignosulfonates with sodium sulfonate groups comprising from 6 3 3 % of the products.
These syuthetic lignosulfonates from alkali ligains are useful under all the conditions found for purified lignsulfonates from spent sulfite liquor. Furthermore, because of possible changes in sulfonic acid Eontent, the synthetic lignosulfonates can he made to order for specificend uses One of the most importaut and exciting developments in the utilization ot alkali lignins is their use in the production of aliphatic sulfur chemicals. Recently, the Cmwu Zelle*acb Corp., at its Bogalusa, La, mill has initiated the commercial production of dimethyl s m d e by the reaction of alkali lignin in kraft black liquor with excess sulfur at elevated temperature (Figure 4). The capacity of this plant is 10 million pounds of dimethyl dfide per year. A potential production of more than 400,WO tons per year of dimethyl sulfide could be produced by this process from the alkali lignin available from the kraft mills of the U. S . Concurrently with the dimethyl sulfide. a smaller amount of methyl mercaptan is also produced and isolated from the crude dimethyl sulfide. By a modification of the process, he obtained as methyl mercaptan the chief product of the reaction between kraft lignin and sulfur. Starting materials
Dimethyl sulfide and methyl mercaptan can then act as startiug materials for a host of sulfur derivatives. The principal one, dimethyl sulfoxide, is produced on a large scale for use as a solvent and as a reaction m e dium. Dimethyl sulfoxide has also demonstrated remarkable therapeutic propenies. Dimethyl &de has been converted more recently on a large scale into methylthio phenols such as &(methylthio)-mcresol aod 4 (methy1thio)phenol which have found widespread utility as intermediates in the manufacture of pesticides. The overall chemical composition of the methylthiophenols also suggests their use for synthesis of pharmacenticals and antioxidants. as well as chemids for the ruhher and polymer fields Dimethyl sulfide also has been converted commercially to dimethyl sdfone, and methyl mercaptau has been converted to dimethyl disulfide. These sulfur compounds have fouud uses as odorants. solvents, reaction intermediates. dispersants, and plaslicizing agents.
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CH-J-2 - a i 3
cHj-S-S-CH3
F-4 The production of dimethyl sulfide from lignin accounts for the n t i l i t i o n of only a very small part of the entire lignin molecule. Still, the production of dimethyl sulfide from all the l i e produced in the world's pulping o p erations would he larger than today's production of polyethylene. Ohvionsly, the further exploitation of this process depends only on the development of suitable markets. Although the pmhlem of cracking lignin to valuable aromatic materials has been the subject of intemive investigation since the turn of the century with no large-scale results, it is still possible that through new techniques a process might he devised that would he attractive economically. T h e approaches suggssted for investigation are microorganisms and the use of modem intense energy sources, such as intense light h e m s from lasers, intense microwave beams from masers, higher-pwered sources of ultrasonic energy, and intense sources of radiant energy from radioactive materials. These, coupled with conventional cracking processes, might produce lignin fragments in good yields. It has been pointed out that the mnversion of lignin into useful products should he no more difficult than the problems of similar conversion of coal or petroleum raw materials, provided an equal amount of time and effort is applied to lignin utilization. The increased incentive for pollution abatement may provide the required effort, and workers in the &Id are looking forward with great interest to developments which should be forthcomins in the next few years.
Jrwin A. Pearl i ssenior reseanzh essai-
ate and group leader of the lignin chemimp group at the Irmiiure of Paper Chemistry, Appleton, Wir.. a position he has held since 1955. He received his B S . (19341,M S . (1935), and P h B . (I9371from the University of Washington, Seanle. After several at the Uniyems as r e x m h --ate verJity of Washingam, Dr. Pearl joined the std at the I n d m f e of Paper Chemimy m 1941. Ee is the mathor of l%e chemigtry of Lignin, as well as papers on m h topicx as pulp mill pollntion, chemimp of vanillin and in derivatives, and chenrinry of hardwoods, and he is a conmiburor to mkruificjournds. He is (I member of ACS, AAAS, Phytmhemiml Society of Norrh A m e r i q TAPPI. N.Y. Acad. emy of Science, ~ e c ~ h e m i m Sol &ty. Sigma Xi, and Phi Lambda Upsilon.
