Citric Acid
M a r k e t scramble looms as Bzura Chemical bows in with its highly touted processcitric acid from blackstrap molasses
T A K E ONE NEW PRODUCER boasting a new low-cost process, an already balanced supply and demand for the product, and you have the combustibles for a hotly competitive business scramble. This, with some modification, is the present situation in citric acid. Providing the spark: newcomer Bzura Chemical and its highly touted new route to citric via fermentation of blackstrap molasses. Bzura appears to have embarked on an ambitious undertaking. I n Chas. Pfizer, it faces a formidable competitor who not only pioneered commercial production of citric acid in the U.S., but, until the entry of Miles Chemical in 1950, was the sole domestic supplier. Pfizer owns some 80 million pounds of citric capacity against Bzura’s 16 million pounds. And many citric customers are also customers for many other Pfizer products, thus affording Pfizer the opportunity to offer price reductions on citric through mixed truckload orders. Although its citric capacity stands at only some 15 million pounds, Miles holds a pretty strong hand, too. Perhaps 50% of its citric production is captive, being used in its seltzer product. To push the remainder, Miles has a well oiled sales force, plus a vast network of distributors. Another advantage, according to Miles, is its strategic plant location (at Elkhart, Ind.), near a major outlet for citric-the heavy concentration of food industry in the Midwest.
Cost Cutting Features Yet Bzura is brimming with confidence, and for good reason. If the
LOUIS A. AGNELLO, Associate Editor in collaboration with
.
R. J. KIEBER; Bzura Chemical Co., Inc., Keyport, N. J.
promised economies of its new process prove out after extensive commercial trial, the company would have the competitive edge in the all-important cost column. It’s the first process capable of using crude blackstrap molassesa very low-cost sugar source. Its cycle time, which Bzura says is considerably shorter than competitive processes, means additional cost savings. And, being deep fermentation, handling, maintenance, and labor costs are much lower than in shallow pan processes. With these and other cost-saving process ramifications working for it, Bzura feels certain it can carve out a good chunk of the citric market. Miles also uses a deep fermentation process. Pfizer reportedly has made the switch from shallow pan to deep fermentation. However, both require more refined, hence more expensive, starting materials. For Miles, it’s deionized high-test molasses; for Pfizerbeet molasses. Blackstrap molasses, a by-product of cane sugar manufacture, is perhaps the most inexpensive form of carbohydrate available. As the name implies, it is the black, viscous liquid remaining after the various cuts of sugar are crystallized out. Blackstrap molasses contains some 52y0 sugar, plus various sugar crystallizing inhibitors and other impurities. I t is used in the U. S. primarily as a livestock feed, and in the production of fermentation products. Although subject to some fluctuation, the price of blackstrap molasses delivered in the New York area currently runs about 13 cents per gallon. Thus, figuring 12 pounds of blackstrap to the gallon and 52% sugar content, Bzura’s
actual sugar costs work out to roughly 2 cents a pound. I n comparison, beet molasses goes for about 3 cents a pound, approximately the same price as that for the high-test molasses required by Miles. Miles must also bear the additional expense of deionizing its molasses, which adds about a cent a pound to its raw material costs. But a cost comparison of starting materials is of little value without a similar comparison of process efficiencies-cycle times, the amount of citric acid produced per mole of sugar, and the like. Obviously, no such comparison has heen made available. Bzura’s initial pricing schedule for citric acid is in line with that of the other two producers. And its initial marketing plans do not call for any price decrease. Rather the company’s sales strategy stresses Bzura as a basic second source of citric acid. Markets Citric acid-a hydroxytricarboxylic acid, C6H807-is sold commercially both in the anhydrous and the monohydrate form. At 27 cents per pound for the monohydrate (291/2 cents for the anhydrous form), the acid occupies a middle ground between low cost, large-scale fermentation products, such as ethyl and butyl alcohols, and high cost, low yield products such as vitamins and antibiotics. The food and beverage industries together probably account for better than 6070 of citric acid sales. Here, the acid is a real work horse, performing a batch of different jobs. For example, it’s an acidulating and flavor enhancing agent for soft drinks, fruit juices, hard candies, and desserts. It works as a VOL. 53,
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buffer, a p H stabilizer, and a fat antioxidant in a variety of processed foods. Its sodium salt also finds use in foods. Some l6Y0 of citric business is in pharmaceuticals. Seltzer - type effervescent tablets and powders make up the bulk of this business. But the acid also goes into sirups, elixirs, astringents, spermicides, and other drug preparations. Industrial uses are a relatively small (about 5%) but growing outlet for citric, primarily as a sequestrant. I t is used to tie up iron during secondary recovery from oil wells by water flooding, in water conditioning, and in metal pickling baths. Esters, such as triethyl and tributyl citrate, are gaining favor as plasticizers and foam inhibitors for vinyl sheeting and polyester resins. Probably about 2% of citric sales are to the cosmetic and toiletries industry. Plodding Development Citric acid occurs naturally in many fruits. But development of commercial processes for its production has been painstakingly slow. In 1893, the German microbiologist Carl Wehmer discovered that certain species of penicillia would produce citric acid from sugar. However, an attempt to utilize Wehmer's process commercially was abandoned in 1903. Currie's work with Aspergillus niger, reported in 1917, ushered in the modern period in the investigation of citric acid formation by molds ( 7 ) . H e found that many strains of A. niger-when grown at low p H in surface culture on concentrated (up to 15%) sucrose solutions, in inorganic media containing certain nutrients-gave respectable yields of citric acid. His incubation time for the conversion ran about 8 days at 28" C. Subsequent work by other researchers agree that the Aspergilli are the best citric acid producers. Generally, special strains of A. niger are used. But others, such as A. awamori ( 4 ) and A. wentii (3, 70) also have been used. Best stored as dry spores without periodic transfer, the mold can be grown either on a growth medium, then made to produce citric acid on a replacement medium, or it can be made to produce citric in the original medium. The best incubation temperature varies with the particular mold strain and the medium used. But generally 28" to 30" C. is reported best for A . niger fermentations. With submerged-culture fermentations: about 25" C. Although sugar concentrations of more than 20% have been reported, probably the 10 to Z070 sugar range is best for shallow pan operations. However, concentrations of 2670 reportedly are not too high when working with submergedculture fermentations (8). There is evidence that the use of high sugar con-
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centrations is more successful when the citric acid is partially neutralized with calcium carbonate or other agents. Selecting the right medium is another critical factor. A medium that gives the best growth of the fungus will not give good yields of citric acid, since carbon converted to mycelium is not available to form the citric. Therefore, since carbon dioxide is the normal end product of carbohydrate utilization, conditions favorable for citric acid are abnormal and considered to be the result of nutritive deficiencies in the medium or metabolic deficiencies in the organism. Among the nutrients of apparent importance in this respect are: phosphate, manganese, iron, zinc, and probably copper. Most workers have used media deficient in either phosphate or metals. The media used by many are similar in that they contain chiefly ammonium nitrate, monopotassium phosphate, and magnesium sulfate. Hydrochloric acid is another common ingredient for p H control. Some add metal ions (usually iron, zinc, and manganese). However, there is no general agreement among citric researchers on the best amounrs of some of these constituents.
agitation problems. And, while the relatively heavy growth shortens fermentation time, it also eats into citric yield due to the large amount of sugar carbon which is converted to mycelium. Miles' submerged-culture process (7, 9, 77) uses a medium deficient in iron. Manganese, too, may be deficient. One patent claims that adding morpholine to the medium aids citric acid production ( 7 ) . The latest patent claims that the cellular metabolism of the Asbergillus niger can be controlled by adding ionic copper to the medium before the end of the organism's initial growth period (6). The company is able to use invert molasses after pretreating it with a cation exchanger. However, the fermentation period specified in one patent-9 days-is long. According to observers, the actual plant fermentation period is considerably shorter.
TCA Cycle
Deep Fermentation Miles was first to solve the riddle of commercial production of citric acid via the submerged culture, or deep fermentation route. I n many aerobic fermentations the submerged-culture approach offers many advantages over surface culture, or shallow pan, operations. Among them: lower labor costs, higher yields, shorter time cycle, simpler operation, and easier maintenance of asepsis under industrial conditions. But it also presents a host of problems. I n the case of citric acid, it requires the development of an organism which can convert high concentrations of relatively crude carbohydrate sources rapidly into
I t was not until 1937 that H. Krebs, in England, proposed a theory to explain the mechanism of citric acid formation by molds (5). His renowned tricarboxylic acid cycle (called the TCA cycle) shows that the products of fat, sugar, amino acid metabolism are eventually burned to carbon dioxide and water, and the chemical energy released in the oxidation of these substances is captured in part as chemical bonds of higher energy content. And it defines the steps by which citric acid, isocitric acid, alpha-ketoglutaric acid, succinic acid, fumaric acid, malic acid, and oxalacetic acid are synthesized and degraded. The citric mechanism generally recognized is that pyruvic acid and carbon dioxide condense to give oxalacetic acid. This, in turn, condenses with acetic acid, or a derivative, to yield citric acid. This may proceed as follows (2):
Glucose 1 2CH3.C0.COOH Pyruvic acid
A c o k - \ HOOC~CHZCO~COOH Oxalacetic acid
---_i--- + ;COz1
CH3COOH
.____
k acid
HOOC.CH,.C(OH) .CH,.COOH I COOH Citric acid
citric acid. This probably means either an induced mutant with extremely high metal requirements to produce deficiencies in the media, or an organism with a defective enzyme system which can accumulate citric even in a complete medium. I t introduces aeration and
INDUSTRIAL AND ENGINEERING CHEMISTRY
Bzura's Route With any fermentation process, the key to success depends almost wholly on the development, isolation, and growth of the fermentation organism. I n Bzura's case, it involves a particularly elusive strain or mutant of Aspergillus
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TU!E SLANT
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ROTARY DRUM FILTER
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SEED TANK (IO%/VOL.OF INOCCULUM)
FERMENTOR (17) 30,000 GALLON
MIX TANK 30 GALLON
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Flowsheet for the manufacture of citric acid from blackstrap molasses, Bzura Chemical Co., Inc., Keyport, N. J. VOL. 53, NO. 4
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4 Continuous sterilizer-a
Bzura innovation-sterilizes crude blackstrap molasses before the molasses-water solution i s transferred to the 30,000-gallon fermentors
Inside a fermentor. Position and pitch of the impeller blades can b e varied. Note also the heating coil, running the depth o f the vessel
v
A Fermentation area. lnocculum and sterilized molasses are reacted in these giant fermentors to form crude citric acid
b Lime handIing system. A bucket elevator i s used t o charge the lime hopper. Slaked lime i s f e d t o calcium citrate precipitation tank
nzzer. Since the term A . niger embraces several hundred different strains, the trick here is to find and cultivate the one that gives the most econcmical yield of citric acid. This means one that not only works on untreated blackstrap molasses to produce citric piedominantly with little or no by-products, but also works fast and in a submergedculture operation. And this trick. as well as the organism, Ezura is keeping
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under wraps-saying only that the mold \vas “chemically adapted” speciall3- for citric acid. It points out, however, that the organism is very sturdy and can be maintained under standard conditions and laboratory procedures with no evidence of mutation. Patents are now pending on the Bzura route. The actual process begins in the laboratory with a stock test tube slant of the organism. T h e spores are ‘.har-
lNDUSTRlAL AND ENGINEERING CHEMISTRY
vested” by mechanically shaking the slant with a liquid, such as molasses solution, saline lvater, nutrient media, or the like. The spores break away from the culture medium and are held in the liquid. The liquid is adjusted to a predetermined spore count. or concenrration. The transfer of the spores to nutrient media is the start of the “seed run-up”-a series of similar steps to establish proper metabolic activity of the
Staff-Industry
String filter. Stainless steel rotary filters are used to separate mycelium from crude citric acid after fermentation and calcium citrate after the initial purification step
Double effect evaporator and continuous crystallizer. Pure, dilute citric acid solution is concentrated in the evaporator and citric acid product i s crystallized in a continuous, closed system
organism. This procedure moves stepwise from the original test tube slant, to a shake flask, on to a carboy, and finally to a seed tank-each time building u p the activity of the inoculum. Run-up on seed takes from 36 to 48 hours. Continuous Sterilization Crude blackstrap molasses-straight from Bzura's 3 million-gallon storage
tank-and water are pumped to a 30gallon mixing tank, and the resulting molasses-water mix moves on through a continuous sterilizer. The sterilizera company innovation to the art of fermentation processing, says Bzura-is essentially a continuous three-stage plate and frame-type heat exchanger. The molasses slurry is flashed to sterilization temperature 100' to 150' C. in the second stage, passes through a retention
coil, and then flows back through the shell of the first stage to preheat the incoming feed. I t then passes through the cooling stage and is charged into the sterilized fermentor. Continuous sterilization, says Bzura, gives better control of the sterilization cycle, faster turn around time, and more efficient use of heat. A battery of 12 giant fermentors, each with a 30,000-gallon capacity, makes VOL. 53, NO. 4
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up the heart of the citric operation. The fermentors, as well as the contacting surfaces of all process equipment, are of stainless steel. Another Bzura innovation on two of the fermentors-impellers that can be varied both in speed and length-allows the company to test new process modifications on a commercial scale, thus avoiding many scale-up problems. I n the fermentor, the sterile media is inoculated from the seed tank, and sterilized air is let in a t a controlled rate through special, Bzura-designed sparging rings. In all aerobic fermentations, the rate of air admitted is a critical factor and must be carefully controlled. I t varies with the particular organism used and the job it is to perform. Bzura is carefully guarding this information.
lncubation Cyclle The normal fermentation cycle for citric reportedly runs from 7 to 11 days. Bzura claims that its cycle time is considerably shorter than this minimum, but it will not say how much shorter. During the fermentation, the organism dissimilates carbohydrates in blackstrap molasses to pyruvic acid. In the presence of acetyl coenzyme A, the acid then enters the Krebs cycle. By selective control of metabolic conditions, citric acid can be made to pile up as the end product. And, according to Bzura, the process gives remarkably few byproducts. and thus presents no product separation problems. At the end of the fermentation period, the product is a dark brown, dilute solution of citric acid which contains the mycelium and the various contaminants -caramelized products from the sugar cane, such as phenols, aconitic acid, and nitrogenous materials. This solution runs through a string discharge rotary drum filter to remove the mycelium and then on to a holding tank. Here, slaked lime is added to precipitate calcium citrate. This is another critical operation. says Bzura, because the crystal size of calcium citrate controls the amount of contaminants that will be carried over to the next step in the process. Rate of addition, time, and temperature are the three deciding factors which must be carefully governed. The calcium citrate crystals are separated from the waste liquor in a string discharge rotary filter, and then dropped directly to a weigh tank. When the charge is built up sufficiently, 60 Bt sulfuric acid is added at a controlled rate to hydrolyze calcium citrate to citric acid. Passing through another rotary drum filter to remove the calcium sulfate, the dilute citric acid solution moves to another holding tank. Washing operations in the preceding three steps must be handled carefully to avoid the loss of product.
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Treating with activated carbon decolorizes the solution and it passes through a leaf-type filter to remove the carbon. Now purified, the dilute citric solution is evaporated under vacuum in a double effect evaporator and sent to a hold tank. From here, the concentrated solution moves to a continuous crystallizer-pulling out of a vacuum system-and on to an automatic batch centrifuge. The crystallizer and the centrifuge are linked together in a closed loop liquor recycle system. Liquor from the crystallizer is pumped to a head tank which supplies a constant feed source for the centrifuge. Separated in the centrifuge, the pure crystals of citric acid are dropped to a rotary dryer. A bucket elevator picks u p the dried crystals and dumps them on a vibrating screen, where they are sized and sent to a compartmented hopper. From here, they pass through a bagging, or drum off device and are ready for market.
Bzura Sefs Rapid Development Pace Bzura got its chemical start about 10 years ago through the determination and frustration of its founder and president, Hyman Bzura. Earlier, as a bench chemist for a small New Jersey organic chemicals producer, Mr. Bzura was hampered by the shortage of fumaric brought about by the crisis in Korea. Looking further into the fumaric supply picture, he decided to enter the field, and, on a shoe-string, formed familyowned (with brother Albert and brotherin-law Irving Weiss) Bzura, Inc., in 1951, Initial chemical assets: one garage-type fumaric operation in Keyport, hT.J. The venture took hold immediately, and the company began its climb to a position of reckoning among producers of fermentation organic chemicals. Capping the rise in 1957 was the development of the company’s new route to citric via blackstrap molasses. To exploit the new process, Bzura set up publicly-owned Bzura Chemical and built the $2.5 million citric plant a t Fieldsboro, hT.J. Now-under terms of a recent $3.7 million public stock issue-Bzura Chemical has acquired Bzura, Inc., which includes domestic and foreign sales outlets and real estate holdings, as well as the fumaric acid operation. Bzura is in the midst of another expansion-go-around. A 7.5 millionpound fumaric expansion, now nearly c.ompleted, will double the company’s capacity and, Bzura claims, make it the top domestic producer of the acid. “Over the past 2 years,” Mr. Bzura explains, “fumaric acid has been in such short supply that we have been forced to cut way back on our production of succinic acid and dibutyl fumarate.
INDUSTRIAL AND ENGINEERING CHEMISTRY
But with the added capacity, we now can shift new emphasis on strengthening this business. And we probably will venture into other esters-including those of citric acid.” Itaconic acid will be Bzura’s next commercial venture. Slated to go onstream late this year, a new itaconic semiworks will have an initial production of 2 to 3 million pounds a year. Marketing prospects for itaconic acid took a turn upward last spring with the announcement of two new itaconic-styrene copolymers with excellent heat resistance by Ledoga S.p.A., Milan, Italy. Bzura pegs current demand for itaconic at some 5 million pounds a year. Here, Bzura again will lock horns with Pfizer-currently the sole commercial supplier of this acid. But Miles reportedly also plans to enter the itaconic acid picture shortly.
Blackstrap Booster Master plan for the company’s future is keyed to Bzura’s unshakable faith in blackstrap molasses as a versatile, lowcost, and abundant chemical raw material. Research chemists are probing the commercial prospects of the entire range of organics based on blackstrap molasses-lactic, gluconic, glutamic, and the like. Amino acids and derivatives, and enzyme systems are also top items on the research docket. As countries mark economic progress. one of the first signs is an increase in sugar consumption. This means more by-product blackstrap molasses. It js an ever-growing, virtually unlimited raw material that, in many areas, is considered a waste disposal problem. Thus. Bzura has mapped its future around an over-abundant, extremely low-cost source of carbohydrate with enormous chemical possibilities.
literature Cited (1) Curie, J. N., J . B i d . Chem. 31, 15 (1917). (2) Johnson, M. J., in “Industrial Fermentation” (L. A. Underkofler, R. J. Hickey, ed.), Vol. 1, chap. 13, p. 420, Chemical Publishing, New York, 1954. (3) Karow, E. O., Waksman, S. A., IND. ENG. CHEM.39, 821 (1947). (4) Nakezawa, R., Takeda, Y., Nakano, M., J . Agr. Chem. SOC.Japan 13, 52 (1937). (5) Neilands, 3. B., Stumpf, P. K.: “Outlines of Enzyme Chemistry,” 2nd ed., p. 333, Wiley, New York, 1958. (6) Schweiger, L. B. (to Miles Laboratory, Inc.), U. S. Patent 2,970,084 (Jan. 31, 1961). (7) Schweiger, L. B., Snell. R. L. (to Miles Laboratories, Inc.), Ibid., 2,476,159 (July 12, 1949). (8) Shu, P., Johnson, M: J., IND.ENC. CHEM.40, 1202 (1948). (9) Snell, R. L., Schweiger, L. B. (to Miles Laboratories, Inc.), U. S. Patent 2,492,667 (Dec. 27, 1949). (IO) Waksman, S. .4.(to Merck & Co., Inc.), Ibid., 2,400,143 (May 14, 1946). (11) Woodward, J. C., Snell, R. L., Nicholls, R. S. (to Miles Laboratories, Inc.), Ibid., 2,492,673 (Dec. 27, 1949).
