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Finished Lactic Acid Is Piped to Specially Lined Tank Cars for Large Volume Users of the Product
GORDON C. INSKEEP Associate Editor
G. G. TAYLOR AND W. C. BREITZKE
in collaboration with
L
ACTIC acid as an unnamed component of sour milk had been known for ages, but it was not until 1780 that it was first isolated and identified by Scheele. Even after its identification, lactic acid was only a laboratory' curiosity for 100 years. The commercial development dates from 1881, when Charles E. Avery built the f i s t lactic acid plant in Littleton, Mass. One of today's important commercial units is operated by American Maize-Products Co. as a part of its Hammond, Ind., plant. Other producers of lactic acid today are Clinton Foods Inc., Clinton, Ia.; E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.; and Sheffield Farms Go., Inc., Norwich, N. Y. The total United States production of lactic acid in recent years is shown graphically in Figure 1. Early production figures were 10,000 pounds in 1894; 400,000 pounds in 1897; and 1,000,000 pounds in 1917. The commercial manufacture and chief uses for lactic acid have been developed by Americans and the industry was well established in the United States before it was undertaken in foreign countries (11 ). Dextrose, Whey, or Molasses May Be Used for Lactic Acid Fermentations The important raw materials for a lactic acid fermentation are starch or dextrose, whey, or molasses. American-Maize, Clinton Foods, and D u Pont use hydrolyzed starch or dextrose
American Maim-Products Co., H a m m o n d , Znd.
as the principal raw material. Sheffield Farms, producing a number of milk by-products (16),uses whey as the starting material for lactic acid. Olive ( $ 1 ) and Burton (8)have described the whey process in detail. The process used by Clinton Foods for edible acid is almost the same as for its technical grade. However, a more highly refined sugar is used as the substrate and the purification steps are more intensive. Peckham, in his survey of the lactic acid industry ( 2 2 ) ,has pointed out that the crude acids are largely characterized by the starting substrates and methods of processing. Leonard, Peterson, and Johnson (19) have shown that the production of lactic acid from sulfite waste liquor by fermentation is possible. They used Lactobacillus pentosus as the inoculum and malt sprouts and blackstrap molasses in the medium. Cordon et al. (S), using fungal amylases to convert the starch to sugar, showed that potatoes could be used as raw materials for the lactic acid fermentation. Commercially, ~ t l a c t i cacid is being produced by bacteria. However, D-lactic acid can be produced by selected strains of molds in a rotary fermentor (31). A lactic acid free from color and of high purity may be produced in this manner. I n general, lactic acid is formed in a relatively high temperature bacterial fermentation, using such organisms as L.delbruckzi. It is neutralized with calcium carbonate to form calcium lactate 1955
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
1956
during the fermentation. The calcium lactate is converted to lactic acid by sulfuric acid. Purification is by repeated carbon bleaches. This is the process used by American Maize. Acid May Be Purified by Several Methods Including Crystallization, Esterification, Extraction, or Distillation There are several other methods that may be used in purifying lactic acid. These have been outlined by Smith and Claborn {SO). For example, calcium lactate may be converted to zinc lactate which is then purified by repeated crystallizations. Hydrogen sulfide is added to the zinc lactate to liberate lactic acid, and zinc sulfide is precipitated. 5
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Vol. 44, No. 9
to the esterifier continuously, and feeding a lactic acid solution into the esterifier continuously. American Maize has not found a large enough market for National Formulary ( S . F . ) lactic acid to operate this process on a commercial basis.
I t Is Marketed in Four Different Grades Lactic acid is widely distributed in nature. It is found in the blood and muscle tissues of animals and in yeast fermentation. I t is found in sauerkraut, pickles, beer, cheese, buttermilk, silage, and corn steep liquor (34). Commercially it is marketed in four different grades: technical, edible, plastics, and National Formulary (N.F). These are sold in solutions of various concentrations from 22 to 85%. Recent price levels are shown in Table I. All the manufacturers produce the technical and edible grades, but only Du Pont is currently producing the costly N.F. product.
a
m
TABLE I. RECENT PRICE LEVELS"
0 3
0
Lactic Acid Technical
22%, bbl. 44%, carload lots 50%, bbl. 8 0 9 bhl. 5 0 8 : bbl. SO%,
Edible Plastics
___._ TECHNICAL
- EDIBLE tI
I
1940 41
I
42
1
43
I
44
I
45
I
46
I
47
a
I
48
I
49
I
I j
50 51
YEAR
Figure 1. U . S. Production of Lactic Acid-1940-51
A procedure described by Jeiiemann { l o ' ) involves extraction of lactic acid from crude solution by isopropyl ether, followed by re-extraction of the lactic acid from the ether with water. A continuous extraction tower is used. The process results in somewhat higher purity acid than is required for edible grade and frequently enters the market as plastics-grade acid (4). Another method of purifying lactic acid is by esterification with a low molecular weight aliphatic alcohol, preferably methyl, as described by Wenker ( 3 2 ) and Schopmeyer and Arnold (29) and modified by Filachione and Fisher (6, 7 ) , to the extent of passing the alcohol vapor up through a packed column countercurrent t o the crude acid fed a t the top. The vapors from these processes contain a mixture of methanol, methyl lactate, and water from which methyl lactate can be recovered or hydrolyzed to obtain a purified acid. hlore recent work ( 2 5 ) suggests that it is commercially possible to extract the lactic acid from the aqueous fermentation liquor by neutralizing the acid with an organic, tertiary amine and then extracting the lactic acid-amine salt with an organic solvent. Semicommercial production of a distilled lactic acid has been carried out by American l\laize by direct vacuum distillation. The acid produced by this method did not have the desired quality; it was costly and the production rate low. Later, a semicommercial process by American Maize was based on the method developed by Schopmeyer and Arnold ( 2 9 ) . Essentially the process comprises esterifying lactic acid with methanol in the presence of a strong acid catalyst. After an initial esterification time the process is carried on continuously by heating the esterifier to drive off the ester and water as an azeotropic mixture of boiling point 209-210" F., hydrolyzing the ester to lactic acid and methanol in a fractionating column with the purified acid leaving the column at the bottom and a rectified alcohol leaving the top of column, returning the alcohol
100%
As Sold, per Lb.
per Lb
$0.0630
SO 2864
Bam,
0.1145 0.1850 0.3320 0.2175 0.3815 0.8680
85yG.carboys N.F. Representative prices a8 of J u n e 1952.
0 0 0 0 0 1
2602 3700 4150 4350
4760 6176
I n Commercial Practice Yields of 85% of Fermentable Hexose Are Normal
Lactic acid, or a-hydroxypropionic acid, occurs in thrcr fornib: levorotatory lactic acid, dextrorotatory lactic acid (known also as sarcolactic acid), and the optically inactive racemic mixture. The commercial bacterial fermentations produce the racemic mixture. COOH
COOII
I I
HO-C-€1
H-c-OH 1
CH, D(
CHI L( +)-Lactjc
- )-Lactic acid
acid
l'rescott and Dunn ( 2 4 ) point out that lactic acid may arise through methylglyoxal by a mechanism similar to that of the alcoholic fermentation
+
CsH1206 --+ 2CHjCOCHO 2HzO Dextrose hle thylgl yoxal CIIjCOCHO
+ H20 +CHzCHOHCOOH Lactic acid
The theoretical yield of lactic acid is therefore 100% of the JT-eight of fermentable hexose sugar. I n actual practice, of coume, this yield is never obtained. I n typical plant operation, yields of about 85% are normal. It is presumed that a portion of the carbohydrate is utilized by the organism in its metabolism, and additional losses occur during subsequent processing ( 1 2 ) . During the normal commercial fermentation the lactic acid produced is neutralized by calcium carbonate t o form calcium lactate 2CH,CHOHCOOII Lactir acid
+ CaC03 --+ Calcium carbonate
+
(CH3CHOHC00)&a HzO Calcium lactate
+ COL
September 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
1957
Lactic acid is extremely soluble in both water and watermiscible organic solvents but insoluble in other organic solvents. The physical constants of the DL form of lactic acid as given by Lange (18) are: Specific gravity, 15'/4' Melting C. Boiling point, C.
1.249 16.8 122.0 (14 mm.)
Structurally lactic acid is a three-carbon organic acid: one terminal carbon atom is part of an acid or carboxyl group; the other terminal carbon atom is part of a methyl or hydrocarbon group; and a central carbon atom having an alcohol carbon group is attached. Fisher and Filachione (12) have summarized the various reactions characteristic of an alcohol which lactic acid (or its esters or amides) may undergo, Among those listed are: xanthation with carbon bisulfide; esterification with organic acids; and dehydrogenation or oxidation to form pyruvic acid or its derivatives. The acid reactions of lactic acid have also been summarized (4,12). Probably the most important acid reactions are those that form salts. As pointed out in a later section on uses of lactic acid, a number of these salts are of commercial interest. Lactic acid undergoes esterification readily with various alcohols. A very complete bibliography on the chemical and industrial aspects of lactic acid and its derivatives has been prepared by n7orkei-s a t the Eastern Regional Research Laboratory (10). Almost 1400 references are included in this bibliography. American Maize-Products Co. Produces Calcium Lactate and Edible and Technical Acid at Hammond, Ind. American Maize started in the lactic acid business in 1928 in an effort ta utilize a n important by-product of its corn wet-milling process. This by-product was the dextrose which formed pills during the dextrose drying operation and was rejected by the screen in the classifier. The original plan was to produce calcium lactate rather than lactic acid as an end product. The first equipment was of a decidedly makeshift nature; 3000-gallon fermentors were secured from a defunct brewery. The fermentation a t that time required approximately 2 weeks but has since been reduced to 4 to 6 days. Originally, all the filtrations were on plate-and-frame presses. I n the early days it required 16 hours of filter press operations to accumulate sufficient calcium lactate to operate the spray dryer for 2 hours. Eventually this method of filtration was replaced by an American filter, and the drying operation then assumed a more-or-less continuous aspect. I n 1930 the idea of using the sodium salt of lactic acid as an antifreeze was suggested. The company investigated this but decided the idea was impractical. The production of sodium lactate was therefore discontinued until late in the 1930's, when other uses became apparent. At that time it was used in the textile and paper industries as a sizing or a substitute for glycerol. The production of copper lactate (to be used as a mordant in dyeing) was also investigated, and a small quantity was produced from lactic acid and copper oxide. Since 1932 American Maize has been actively engaged in the production of calcium lactate and both technical and edible grades of lactic acid.
L. delbruckii Is Culture Used; Corn Sugar Is Principal Fermentation Medium American Maize is using Lactobacillus delbruckii, which produces the racemic mixture of the D- and L-lactic acid. The original culture was obtained from the Department of Agriculture. The inoculum is cultured successively in a test tube, a 500-ml.
Initial Transfers of the Producing Microorganism Are Made Using Sterile Technique by a Trained Bacteriologist
flask, and finally a 6-liter flask containing 3 liters of media. After 24 hours incubation, the 6-liter flasks are used to inoculate stainless steel-jacketed culture tanks equipped with vertical agitators. The culture tanks, shown in the flow sheet, Figure 2, are previously charged with 375 gallons of aqueous media using as substrate: 15% corn sugar; 0.375% malt sprouts and 0.2570 diammonium phosphate as nutrients; and 10% calcium carbonate as a buffer to maintain a p H in the optimum range of 5.8 to 6.0. After 24 hours a t 120" F., the culture tanks are used to inoculate fermentors which have been charged with medium of the same composition. One culture tank is used for inoculating the 6600-gallon fermentors or three are used to inoculate the 30,000gallon fermentors. The small fermentors are filled to a volume of 4600 gallons and the larger fermentors to a volume of 24,000 gallons. The agitators in the small fermentors consist of two cross arm timbers on a wooden vertical shaft. The drive is by a commonline shaft with a clutch for each fermentor. The large fermentors are each equipped with stainless steel side-entering propellertype agitators (7E). There are eight small fermentors and two large ones. The temperature in the smaller fermentors is controlled by circulating water from a central supply tank through internal coils. These coils are made up of 2-inch stainless steel pipe with a heat transfer surface of approximately 60 square feet. The water temperature in the supply tank is automatically controlled (12E) t o maintain a temperature of 120' F. The temperature of the larger fermentors is individually and automatically controlled by means of circulating hot water through the coils. The coils in the large fermentors have approximately 180 square feet of heat transfer surface. The large fermentors are also equipped with circulating pumps ( I E ) taking liquor from the bottom and discharging i t back into the top to assist in mixing. The operating temperature of 120' F. is wellabove theoptimum fermentation temperature for most bacteria or yeast which might appear as contaminants. Because of this high fermentation temperature, it is not necessary to heat the media for the culture
1968
INDUSTRIAL A N D ENGINEERING CHEMISTRY
September 1952
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1959
tanks or the fermentors even to pasfeurizing temperature. After each batch, the tanks are washed out with hot water, then filled with water and heated to boiling temperature before refilling.
Calcium Lactate Ia Produced during
4- to 6-Day Fermentation Period
The course of the fermentation is followed by checking the p H and reducing sugar content each day in the plant control laboratory. Figure 3 shows the production of calcium lactate and decrease in reducing sugar during the fermentation. When the reducing sugar has been lowered from the initial 15 to 0.10% the fermentation is considered complete. The organism is inactivated by heating to 180' F. The time for the fermentation varies from 4 to 6 days. The effect of continuously controlled p H on the lactic acid fermentation has been the subject of some investigations a t the University of Minnesota (9, 17'). Using dextrose solutions and also xheat and grit mashes it was found that the rate of acid production was sensitive to even small changes in pH. Research a t Minnesota on the lactic acid fermentation at controlled pH is being extended a t the present time to an investigation of a continuous operation (d.3). The raw materials and product flow continuously into and out of a stirred tank. In 1943 and 1944, American Maize maintained continuous control over pH during the fermentation process by automatically adding a hydrated lime slurry through the use of a pH
The Microorganism L. delbruckii Is Cultured in Successively Larger Glass Containers in the Laboratory; Finally, a 6-Liter Florence Flask Containing 3 Liters of Media Is Used to Inoculate Stainless Steel Culture Tanks controller, This was discontinued because line voltage variations and fouling of electrodes made close pH control impossible. The lactic acid produced reacts with the calcium carbonate forming calcium lactate as the fermentation proceeds. The inhibition of bacterial action by increased acidity is thus avoided. The solubility of calcium lactate a t the fermentation temperature is in the range 12 to 15%, and this of course limits the final soluble concentration obtainable (34). Recycled Calcium Sulfate Added to Aid Filtration
Figure 3. Production of Calcium Lactate and Decrease in Reducing Sugar during Fermentation
From the fermentor, the liquor is pumped to a settling and decanting tank, where hydrated lime is added to a p H of 10.0, and the temperature is held a t 180' F. The elevated temperature and pH serve to coagulate the protein present, making the settling more complete and subsequent filtration easier. After final p H adjustment, the slurry is agitated for 30 minutes and then allowed to settle from 2 to 6 hours. The clear liquor is decanted from the top and pumped to the first bleach tank. The sludge from the bottom is transferred by gravity to a mud slurry tank. Calcium sulfate mud from subsequent processing, limed to pH 10, is added to the fermentor sludge to act as a filter aid. The combined slurries are filtered on a string vacuum filter (2%) constructed with rubber-covered carbon steel and Type 316 stainless steel. Vacuum is supplied by a single-stage porcelain steam jet ejector. The filtrate goes to the first bleach tank, combining with the liquor from the decanting tank. The filter cake is slurried with water in a tank and pumped to another part of the plant for by-product recovery. Activated vegetable carbon ( I @ ) is added to the calcium lactate solution in first bleach tanks in the ratio of 3 pounds of
+
U U CAKE TO ACID BLEACH
Figure 4.
Flow Shest for the Production
of calcium Lactate at the Aammond, Ind., Plant of American Maize-Pmduota CQ.
carbon to 40 gallons of 14% average concentration calcium lactate. The carbon-calcium lactate slurry is filtered in a wood plate-and-frame press (9E). The filtrate goes to an evaporator supply tank and the carbon is held for use in the second bleach. The bleached calcium lactate liquor is concentrated in a singleeffect vacuum evaporator (6E, BE) to 32% concentration. The evaporator is operated a t a pressme of 17 inches of mercury with the reaultii temperature of 160' F., SuEciently high to prevent crystallhation. The evaporator tubes are %inch copper, and the vapor head is of bronze alloy construction. The average evaporation rate is 4000 pounds of water per hour.
filtered on the a t r i i filter. The lactic acid filtrate goes to a second bleach tank, where carbon from the first, third, and fourth bleach is added. The filter cake is slurried in a tank with the addition of enough lime to raise the pH to 10. The calcium sulfate slurry is then pumped to the mud slurry tank to act as a filter aid for the fermentor sludge. The lactic acid-carbon slurry in the acid bleach tank is checked for free sulfuric acid or soluble cslcium and adjustments made by adding either Sulfuric acid or lime. The elurry is then filtered on a plate-and-frame filter press ( 9 E ) ; the cake is dincarded and the filtrate collected in a wooden acid evuporator supply tank.
Calcium Lactam a n d Sulfuric Acid R-t to Form LaotJo Acid
Stdnlcss Steel Is U d for Acid Evaporators Two aoid evapratom are available and are used alternately to
Concentrate from the evaporator is pumped to w d e n acid conversion tsnka,where 50' BB. sulfuric acid is added aimultaneously. The rate of acid additiou is manually controlled to obtain complete reaction with the calcium lactate as it enters the bnk. The slurry is checked periodically for exoeea ofeither acid or soluble calcium. A rough check for soluble calcium is made by the plant operatom by adding sulfuric acid to a filtered sample. For a closer check, a sample is filtered, diluted 1to 5 with denatured alcohol, and heated to boiling, Sample is then filtered and divided into two portions. To one, barium chloride is added to test for excess d a t e . To the other, sulfuric aoid in added to check for soluble calcium. The alcohol treatment precipitates any calcium sulfate in the originalsample. The calcium sulfate urecipitated in the conversion tank is
concentrate the acid from 8 to approximately 50%. Both evsporatom are constructed throughout of Type 316 stainless steel. One evaporator (IlE) is a single4ect with an evaporation rate varying from 2OOO to 6000 pounds of water per hour, depending on the condition of the tubes; the second ia a modified doubleeffect (SE). The evaporators are boiled out a t least once a week with a caustic solution. It has not been necessary to rod out the tubes. The liquor goes from the 6rst effect to the second, but low presaure steam (6 pounds per square inch gage) is supplied to each effect, and the same vacuum is pulled on each effect. The vacuum is supplied by means of a barometric condenser and douhle-ste-ge steam jet ejector with inter-condenser @E). The total evaporation rate varies from 2ooo to 8ooo per hour.
c
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September 1952
” presented at Kational Farm Chemurgic Conference, 1948, (34) TVoodward, C . F., Chemur&eUigest, 9 , 9 (June 1950) 7 - - -
\ - - -
I
Processing Equipment (1E) Allis Chalmers Mfg. Co., Milwaukee, \Vis., stainless steel centrifugal circulating pumpa, (2E) Filtration Engineering, h e . , Newark 4, N. J., string filtea, diameter 5 ft., drum face 6 ft., supplied with Reeves variable speed drive. (3E) Coslin-Birmingham Mfg. Co., Birmingham, Ala., doubleeffect acid evaporator; healing surface of each steam chest, 216 sq. ft. (4E) Hills-McCanna Co.. Chicago, Ill*, Baunders Type diaphragm valves. (5E) Tngersoll-Rand Co., New York 4, N. Y., steam j e t ejectors. (6E) Leader Iron Works, Decatur, IlL9evaporator heat exchanger: heating surface, 410 sq. ft. (7E) Mixing Equipment Co., Rochester, N. Y . , side-entering, propeller-type agitator. (8E) Pfaudler Co., Rochester, N. Y., glass-lined finished acid tank; capacity, 2500 gal. (9E) Shriver. T., and Co., Harrison, K, J., 32 X 32 inch wood plate-and-frame filter presses. (IOE) Socony-Vacuum Oil Co., New York, N. Y., Sovawax D. (11E) Struthers-Wells Corp., Titusville, Pa., single-effect acid evaporator; heating surface, 399 sq. ft. (12E) Taylor Instrument Co., Rochester, N. Y . ,automatic temgerature control equipment. (13E) Wellington, Sears Co., New York, N. Y., cotton palma twill filter cloth, Style 69. (14E) West Virginia Pulp & Paper Co., lndustiial Chemical Sales Div.. Covington, Va., Nu-Char C-190-A. (15E) Wilfley, A. R , and Sons, Denver, Colo., stainless steel processing pumps RECEIVED for review dune 27, 1952,
Impure Lactic Aeld 11Treated with Activated Carbon i s later
Yo1. 44, No. 9
rmerea by a ~ ~ a t e - 61~ter~press ~ ~ r ~ ~ e
Accr:rl’n,, .l,,ly 17, 1!2.52.
