CHESTER PLACEK, Associate Editor in collaboration with
BRUCE J. BUHMANN and RICHARD
T.
GALGANSKI
Marathon, A Division of American Can Co., Rothschild, Wis.
THE
PROBLEM of what to do with spent sulfite liquor is as old and as widespread as the pulping industry itself. One solution is to dump the liquor into a stream. But disposing it this way results in stream pollution and endangers aquatic life. Pulp liquor's effects are due almost entirely to wood sugars and other related agents in the liquor. Overloading the stream's natural capacity for using these sugars to the advantage of its fish life
can occur. Sugars wind up as fish food only up to a point. One effect of overloading is to increase the food supply of small organisms already in the stream. 'These then multiply, and their life processes CUI: down the water's dissolved oxygen supply. The second way of handling sulfite liquor is to use it-as a source of chemicals (which is Marathon's way), yeast ( 4 ) , fuel, road bindei and other applications.
Here i s raw material for process. Logs made into wood chips are pressure-cooked in a cooking liquor of calcium bisulfite and sulfur dioxide. The spent cooking liquor is then processed
Spent sulfite liquor contains mainly lignin, and smaller or greater amounts of carbohydrates and other constituents ( 7 7). Actual amounts of these products depend on the type of wood and the cooking procedure used. The lignin is sulfonated, thus is water soluble. The lignosulfonic acids contain about one sulfonic acid group per two C C - C ~ units (two methoxyl groups) (70). Solids content of calcium based sulfite liquor breaks down this way (5):
% Lignin (as sulfonate) Sugars Sugar sulfonic acids Ca (as CaO) SuIfur (as SO%)
50-65 15-22 5-8 7-10
8-12
Until about 1927, almost all approaches to sulfite liquor utilization involved finding uses for the whole liquor. But then, different fractions of the liquor were found useful. To capitalize on these uses, Marathon built a plant for fractionating the liquor, using the Howard process ( 3 ) of lime precipitation of lignosulfonates followed by metallic ion addition and desulfonation.
History of Marathon Process First pilot plant work was started in 1929, and showed that the lignin products produced had value as tanning agents. Commercial quantities of lignosulfonates were made by 1932. Economics of the lignosulfonate tans were good enough to enable partial replacement of imported tanning agents like quebracho. At about the same time, other lignosulfonate uses such as binders in ceramics were found. During this early pilot plant work. a vanillin process (6, 8, 9) from alkaline lignosulfonates was developed. The technique was licensed to Salvo Chemical Co. (now a division of Sterling Drug) and the main lignosulfonic acid and vanillin plants were built a t the Same time in 1936. Simultaneously, other companies were looking into lignosulfonate utilization. Some of them did come up with crude lignosulfonate materials which were sold a t give-away prices. Because the Marathon products were fractionated, the company had to put higher prices on its various lignosulfonate compounds. So from 1937 through 1941 sales were relatively poor. But with the onset of World War 11, imports of tanning agents dropped, and consequently Marathon’s lignosulfonate tan’s sales rose. Also during the war, Marathon developed a lignin impregnated plastic sheet. This was followed by a plastic (Lignolite) based on lignosulfonates. Although the plastic gained acceptance during the early forties because of wartime shortages, manufacturing costs were too high to meet postwar competi-
Basic calcium lignosulfonate-part of which goes on to vanillin processing-is separated here
tion ; and early in 1946 plastics production was dropped. After the war, when all familiar foreign materials began arriving in quantity once more, Marathon recognized that its tanning agents needed additional research. And more technical information had to be furnished to tanners. In 1947, a program to study the behavior of lignosulfonate products toward hide substances was started. This work improved the products, produced a lot of technical information for tanners, and prompted acceptance of Marathon’s tanning materials. In 1949, a new oxidation process to yield substantially more vanillin was developed. The Salvo plant took up the process, and now supplies more than 50% of the nation’s vanillin requirements. The process converts about 10% of the lignin in spent liquor to vanillin. The rest of it is returned to Marathon’s chemical plant as a highly alkaline material for processing further.
Effluent from the vanillin process was the material from which Lignolite was made. But after giving up the plastic venture, Marathon researchers tried to find other uses for the effluent. During their work they noticed that the material had exceptional dispersing characteristics. Therefore, a number of modifications were prepared and a succession of applications developed. One of these was a scale-inhibiting boiler compound ( 7 ) which has since been adopted in the treatment of feed waters for many of the nation’s steam generators. At about the same time, rubber companies were starting a new method of compounding synthetic rubbers; incorporating carbon black powder into a latex emulsion before coagulation. An effective dispersant is required for this, and none of the available dispersants was satisfactory a t the time. Marathon developed a lignin material to fill the need, and it has proved so effective that the government requisitioned it for all
Gypsum, obtained after acidifying the ot.ganic precipitate, is separated on a rotary filter, then sewered
c
PROCESS L I M E
SOLUTION OF SALTS OF , ORGANIC ACIDS TO F U R T H E R PROCESSING
PLANT PROCESS SERIES
of its butadiene-styrene rubber plants. Still another lignosulfonate material is a component of the paste used in lead storage batteries (2: 7). Lignin’s function here is to slow down formation of dense lead sulfate crystals on the surfaces of negative plates, giving better service and longer battery life. About 80% of all automotive batteries made in the United States contain the material. As research and application studies pointed to even more uses, Marathon
(ORGANIC PRECIPITATE) FOR PROCESSING AT MARATHON
decided to try developing a new series of dispersant products by modifying the basic lignosulfonate. These dispersants are used today in ceramics, concrete, gypsum board, and other building materials. They are also employed LO give better distribution of dyes and insecticide sprays. Several other lignin compositions now go in to deep oil well drilling, ore flotation and beneficiation, industrial cleaners, emulsions, and even into certain types of animal feeds.
Bottom half of triple effect evaporator for concentrating process liquors before drying
572
INDUSTRIAL AND ENGINEERING CHEMISTRY
Flowsheet 1. Three-stage lime precipitation process, Marathon, A Division of American Can Co., Rothschild,
Wis.
TO VANILLIN PROCESS AT SALVO
Chemistry of Marathon’s Lignosulfonates
Xfarathon’s lignosulfonates-sold under various trade names-are heterodispersed polymers whose molecular weights vary between 1000 and 20,000. The organic structure of lignosulfonates isn’t certain yet, but it is known that the basic lignin monomer unit is the substituted phenyl propane. Lignosulfonates can be partially de-
STAFF-INDUSTRY REPORT sulfonated by heating with alkalies. Heating with alkali beyond the point needed for desulfonation causes cleavages in the lignin and enables the vanillin molecule to form. During the process for making lignosulfonates, various metallic salts (like calcium, magnesium, aluminum) are added to impart properties needed for the many applications. Spent Liquor from 50,000 Tons of Pulp
The first’ step in obtaining the lignosulfonate fractions is, of course, the manufacture of pulp for paper. Marathon operates a sulfite pulp mill at Rothschild, Wis., on the Wisconsin River (the state’s largest). Here, annual production of sulfite pulp is about 50,000 tons, and the output of organic solids in the spent sulfite liquor is about the same. The chemical manufacturing area is also located here. In Marathon’s sulfite process, wood chips are pressure-cooked in an acid cooking liquor of calcium bisulfite and sulfur dioxide. Cellulose fibers are freed during cooking, while lignin and wood sugars dissolve in the cooking liquor. Cellulose is separated from the sulfite liquor and made into paper, and the spent sulfite liquor is recovered from the pulp mill blowpits. For storage before entering the chemical process plant, the liquor is screened to remove solid residues, mostly pulp fibers, and sent to outside wood storage tanksstored liquor usually contains from 9 to 10% total solids.
To make chemicals from sulfite liquor, a three-stage lime precipitation, yielding inorganic and organic solids and an effluent, is used. Spent sulfite liquor from storage is treated with a lime water suspension to precipitate inorganicsmainly calcium sulfite-from solution. Throughput is approximately 250 to 300 gallons per minute, and the stirred mixture is kept on the alkaline side. Precipitate is removed on a vacuum rotary filter (6E) and is returned to the cooking acid making plant. T h e filtrate is pumped into another reaction tank. Here, more process lime is added to precipitate calcium lignosulfonate. Separation of this organic fraction is by a rotary vacuum filter (77E), and the filter goes on to a third fractionation step. The process lime in tank 3, added under the same conditions as in the first two steps, strips the filtrate of any other lignin solids. Contents from the third tank are‘ pumped into a settling tank (8E),and the enriched lignin slurry that settles out then pumped again into reactor number 2 in place of the milk of lime slurry. There it helps in the calcium lignosulfonate precipitation step, and is filtered on the rotary filter between steps 2 and 3. Since the process is continuous, flow between, into, and out of each reaction tank is at the same rate. Recycling the filtrate from step 3 back into the second tank ensures almost complete removal of all lignin in the original liquor. The effluent, which remains in the settling tank after the lignin slurry, is recycled to the second fractionation
,
Sacking of finished product. Marathon’s control of fines here ensures 99% recovery of dried product
tank and is then processed for sale as salts of organic acids. Calcium lignosulfonate which was filtered off after the second lime addition goes in two directions : 1. Directly into processing for lignosulfonates a t Marathon, or 2. Pumped to Salvo for vanillin production, the effluent from which comes back into Marathon for further processing into partially desulfonated sodium lignosulfonates. Fate of Calcium lignosulfonate (Organic Precipitate)
Double drum dryer handles neutral or alkaline producfs (as does the spray dryer). Right, part of dust recovery system 0
Depending upon production schedules, the precipitated calcium lignosulfonate from the rotary vacuum filter is processed either directly a t Marathon, or after it returns from the vanillin production set-up a t Salvo. This filter cake contains about 30 to 32y0 solids (organic precipitate, or OP) and will eventually result in the company’s main product line. When processed a t Marathon, the material is sent to a wood reaction tank equipped with an agitator consisting of a stainless steel impeller and shaft. The organic precipitate filter cake is acidified with sulfuric acid here. Acid concentration is about 30%. and is made U D from 98% acid via ;’dilution tank ‘(TOE). Addition is continuous and flow rate is VOL. 50, NO. 4
APRIL 1958
573
m Q
E
METALLIC SULFATES b g .AI. M g , N o 1
;;m~
$ 2 8
y 4
Flowsheet 2. Organic acids salts solution and calcium lignosulfonate process at Marathon
e s ATMOSPHERIC
GYPSUM TO SEWER
DOUBLE DRUM
+--
DRYER
TANK CAR SHIPMENT OF ORGANIC ACID SALTS SOLUTION
controlled by pH tests. During acidification, various dry metallic sulfate salts-such as sodium, magnesium, aluminum, or any combination of these-are added from paper bags to make the various corresponding metallic lignosulfonates. The salt used depends on eventual marketing. The precipitated salt mixture, or slurry, is pumped to a stainless steel, continuous rotary filter (9E). Gypsum which is removed is piped to a sewer. The filtrate, checked for clarity, is held in a n iron storage tank until called for. These different metallic salts of lignosulfonic acid are pumped from the storage tank to a triple-effect evaporator ( I E ) . In here, the solution is evaporated to a solids content of about 45%.
Capacity of the evaporator is approximately 3000 gallons per hour. From the evaporator, the product goes into one of these drying units :
b
Spray dryer (76E). b Vacuum dryer (3E).
b
The pH of the material decides the choice of dryer. For example, low p H products are dried on the copperbronze vacuum dryer; neutral or alkaline products on the other dryers. Marathon believes that its No. 2 spray dryer is one of the largest ever built. Its drying chamber has a diameter of 20 feet, and the vertical furnace that supplies the heat has four tangential
Roof top view of duct work for cyclone separator's air system
574
Atmospheric double drum dryer
@E).
INDUSTRIAL AND ENGINEERING CHEMISTRY
vertical burners. The equipment can handle up to 50,000 pounds of powder per day. The drum dryers are hooked into a unique system, designed by Marathon engineers, which works this way. When the product is dry, it is put into the plant's own air pick-up system. As the solids come off the drum (originally sprayed on), they go through a rebuilt cyclone separator for first separation. The bulk of the product goes to the bagger (45) while the fines are blown free through a bag filter (73E) and recovered into the cyclone separators' discharge. This way, Marathon claims 997' recovery of dry material. When drying on drums or on the spray dryer, the powdered material is
Some of the purified lignosulfonates are dried in this vacuum dryer, some in double drum dryers, and the rest in spray dryers. Drying method depends on type of product and uses
STAFF-INDUSTRY REPORT smothered with carbon dioxide or nitrogen. Carbon dioxide comes from the stacks in the boiler house, and nitrogen from the vanillin plant’s exhaust gases. The idea is to keep atmospheric oxygen down to less than 14% as a safety measure. Because of the fineness of the powder being handled, an explosion hazard exists when powder is air conveyed, unless oxygen content is controlled. The product is packaged in 50-lb. multiwalled paper bags. Vanillin Process Effluent
When the basic calcium lignosulfonate is earmarked for Salvo’s vanillin plant, the material is first made heavily alkaline. This is done a t the Marathon plant in another reaction tank, and the alkaline material then pumped to Salvo’s plant. Salvo’s effluent re-enters Marathon’s system and is pumped to a rotary precoat filter (7E) to remove finely divided solids which are formed during the vanillin making. The solids are discarded and effluent goes into either a storage tank to hold before concentrating, cooking, and drying, (vanillin effluent A) or to still further processing (vanillin effluent B). Vanillin Effluent A. From the storage tank, the filtered vanillin effluent is pumped into the triple-effect evaporator. In the storage tank stage after filtration, the solution runs about 20 to 22y0solids, and the evaporator takes it up to 45 to 50%. From the evaporator, the viscous solution is pumped into a Dowtherm cooker (74E), then dried on one of the different dryers. The cooker is made of stainless steel. Heating medium is Dowtherm A, to
Partially desulfonated, purified lignosulfonates are isolated on this rotary precoat filter
effect a high temperature cook. The boiler is bricked in, and the operation partially demethylates and desulfonates the lignosulfonates. This cooking step makes the materials suitable for water treatment compounds. Vanillin Effluent B. This portion goes directly from the filter to a reaction tank similar to the others used earlier in the process. Here, the liquor is acidified with sulfuric acid to precipitate lignin. From this tank, the slurry flows into a
plate and frame filter (72E). Filtrate is discarded and the lignin goes into an iron reaction tank, stainless steel-lined, and treated with 46y0sodium hydroxide solution to form sodium lignosulfonate, followed by drying and bagging.
Salts of Organic Acids The solution of salts of organic acids which results from the initial threestage fractionation step followed by
20-22.h SOLIDS
TRIPLE EFFECT
PARTIALLY DESULFONATED SODIUM UGNOSULFONPTES TO DRYERS AND BAGGING
Flowsheet 3. Vanillin plant effluent process at Marathon 46% N4OH
LIGNOSULFONIC ACID
I
(DRYERS SHOWN ON FLOWSHEET “ 2 )
PARTIALLY DESULFONATED SODIUM LIGNOSULFONATES TO DRYERS AND BAGGING
FILTRATE
TO SEWER ~
~~
~
VOL. 50, NO. 4
APRIL 1958
575
Future Developments Lignosulfonate Products, Their Make-up, and Outlets
Morabond Partially purified calcium lignosulfonate, used in oil-well cement retarders, foundry supplies, and ceramics. Maratans Tannins. High puritv magnesium and sodium lignosulfonates. Maracell E Partially desulfonated sodium lignosulfonate, used by water-treating compound formulators to inhibit carbonate and phosphate scale formation in boiler tubes and fred lines. Norlig Unrefined calcium lignosulfonate, having about 20% reducing sugars, for uses that need hygroscopicity and/or limited dispersion. Maracarbs Complex mixtures of the salts of the alkaline reversion products of hexoses and pentoses, and low7rr molecular weight lignosulfonic acids; sugar to acid ratio is about 2 to 1. [A lot of sugar is destroyed during the original sulfite digestion (I 7). Bisulfite is reduced to thiosulfate, and sugar is oxidized to aldonic acid. Thiosulfate later reacts with lignosulfonic acid. In addition to this oxidationreduction other sulfonic acids of unknoivn structures are formed.] The Maracarbs have found a place among agricultural chemicals, metal cleaners, bordeaux mixes, and possibly in sequestering copper and iron. Maracon Water reducing admixtures, used in ready-mixed concrete and concrete products. Marasperses Dispersants. The main group is made u p of four lignosulfonate salts; three sodium and one calcium. Some special ones are made for specific fields like dyestuffs and oil-well drilling. Some are partially desulfonated. They are completely water soluble, but complex structure makes them insoluble in oils and most or anic solvents. Aqueous solutions of the Marasperses, containing 33 to 4 0 k Marasperse by weight, can be made. Higher solids contents form extremely viscous solutions. Marasperse action is largely electrokinetic in nature. i f h e n adsorbed by the particles of solids in suspension, they impart negative charges to the particle. These charges cause them to repel one another. Adsorption of the Marasperses on a suspended particle might also form a polymolecular layer, or film, which then acts as a physical barrier to prevent direct contact between the particle and other particles-or between the particle and surrounding media.
settling is pumped into a reaction tank of 10,000-gallon capacity. Here, solid sodium carbonate may be added to change the cation from calcium to sodium. The slurry is pumped through another rotary precoat filter. The calcium carbonate from this step is also discarded, and the filtrate sent to the triple-effect evaporator for evaporation to a solids content of 50 to 52%. The solution can be dried or transferred to tank car for shipment. Operating Technology Marathon operates its chemical plant over 4 shifts of 6 hours, 7 days a weekexcept for holidays. Total operating personnel number 58, not including those engaged in control analysis. When the process is stopped, it is usually at a stage where all in-process liquors can be held in storage tanks. Stopping operations and holding the liquors a t any
576
stage does not affect product quality in any way. Equipment is cleaned whenever a product change is involved. This happens once or twice a week. During vacation periods, the entire plant is shut down and cleaned. Large tanks are completely cleaned twice a year, usually by scrubbing down. T o clean evaporators and the high pressure cooker, dilute caustic is used. Water is used on the dryers. The cooker itself is cleaned with dilute hydrochloric acid when solids build up. Fuel used for the whole process is industrial No. 2 oil, and consumption runs about 110 gallons per hour. A 30,000-gallon-storage system for fuel is on the company grounds. T o maintain fresh air, the plant depends on exhaust fans, and an air tempering unit (75E) for constant temperature.
INDUSTRIAL AND ENGINEERING CHEMISTRY
hIarathon has a large research group, which spends part of the time developing new products from spent sulfite liquors. Several new developments are currently being pilot planted. The goal here is to derive new, pure products from spent liquors, which was once thought of as “waste” material. Literature Cited (1) Bird, B. G. (to h-ational Aluminate), U. S. Patent 2,505,457 (April 25, 1950); 2,576,386 (Kov. 27, 1951). (2) Harmon, Carlyle (to Marathon Corp.), Zbid. 2,371,136 (March 13.1945). (3) Howard, G. C., Ibid., 1,699,845 (Jac. 22, 1929); reissue 18,268 (Dec. 1, 1931): 1,856,558 (May 3, i932); ‘1,924,361 29, 1933); 1,981,176 (Nov. 20, 1934). (4) Inskeep, G. C., Wiley, A. J., Holderly, J. M., Hughes, C. P., IXD.ENG. CHEM.43, 1702-11 (1951). (5) Kirk, R. E., Othmer, D. F., “Encyclopedia of Chemical Technology,” Vol. 8, p. 331, Interscience, Sew York, 1952. (6) Zbid.,Vol. 14, p. 606, 1955. (7) Orsino, J. A. (to Kational Lead Go.), Harmon! Carlyle (to Marathon Corp.), U. S. Patent 2,371,137 (March 13, 1945). (8) Sandborn, L. T. (to Marathon Corp. and G. C. Howard Co.), Ibid., 2,104,701 (Jan. 4, 1938). (9) Sandborn, L. T., Salvesen, J. R. (to Marathon Corp.), Howard, G. C. (to G. C. Howard Co.), Z6id.,2,057,117 (Oct. 13, 1936). (10) Wise, L. E., Jahn, E. C., “Wood Chemistry,” Vol. 2, p. 1004, ACS Monograph, Reinhold, New York, 1952. (11) Zbid.,p. 1019.
.(hi.
Processing Equipment (1E) Buflovak Equipment Div., BlawKnox Co., Buffalo, N. Y., tripleeffect evaporator. (2E) Z6id., atmospheric double drum dryer. (3E) Zbid.,copper-bronze vacuum dryer. (4E) E. Coddington Mfg. Co., Milwaukee 9, Wis., valve-type bag packer. (5E) Dorr-Oliver, Inc., Stamford, Conn., lime classifier. (6E)Ibid.,modified vacuum rotary filter. (7E) Ibid.,rotary precoat filter. (8E) Zbid., settling tank (two tray thickener j . (9E) Zbid.,stainless steel continuous rotary filter. (10E: Haveg Corp., Wilmington 8, Del., sulfuric acid dilution tank. (11E) Improved Machinery, Inc., Nashua, N. H., rotary vacuum filter for separating organic precipitate. (12E) T. Shriver & Co., Harrison, N. J., plate and frame filter. (13E) W. W. Sly Manufacturing Co., Cleveland 1, Ohio, bag filter. (14E) A. 0. Smith Corp., Milwaukee 1, Wis., Dowtherm cooker (BlawKnox design). (15E) The Trane Go., La Crosse, Wis., air tempering unit. (16E) Western Precipitation Corp., LOS Angeles 15, Calif., spray dryer.
