Citric Acid Industry

After 1922 shipments of Italian calcium citrate and citric acid to the United States, formerly thebest market, began to decline. This decline must be ...
3 downloads 0 Views 2MB Size
Download PDF
CITRIC ACID INDUSTRY,

,,

P. A. WELLS A N D H. T. HERRICK Industrial Farm Products Research Division, Bureau of Chemistry and Soils, Washington, D. C.

HE development of the fermentation citric acid industry during the past decade has aroused a great deal of interest throughout this country and in Europe. The successful commercial production of this acid from sugar by a mold fermentation process, both in this country and abroad, has brought about a n entirely new situation with respect to world trade in this commodity. Formerly, the raw material, calcium citrate, was produced almost entirely from citrus products, Italy being by far the largest producer. The bulk of the Italian production of calcium citrate was formerly shipped to England, France, and the United States. Because of the development of the fermentation process in this country and our increased output of citrous materials, imports of citric acid and calcium citrate into the United States have practically ceased since 1927. The fermentation process has also been developed in Europe to a large extent. Large quantities of the fermentation acid are produced in England, Belgium, Czechoslovakia, and probably Russia, although complete production figures are not available. The former dominant position occupied by the Italian producers of this commodity has thus been lost through new methods introduced by scientific research. The development of the fermentation process for citric acid and the various factors which stimulated and brought about the substantial displacement of the natural product are interesting.

T

TYPICAL SURFACE MOLD GROWTHSOBTAINEDIN SHALLOW PANSAND THE SEVEN-PAN INSTALLATION FOR THE PRODUCTION OF CALCIUM GLUCONATEFROM GLUCOSEBY MOLD FERMENTATION

in Table I. Production of citric acid in the United States from 1914 to 1935 is shown in Table 11. The latter figures show the total production of citric acid for sale which includes that manufactured from domestic and imported calcium citrate, imported concentrated lemon juice, and that produced from sugar by fermentation. Separate production figures for the fermentation citric acid are not available since the manufacture is limited to one company. The rapid increase in acid production in 1923 and 1925 was not entirely due to our increased output of citrus materials and production of fermentation acid; during this time large quantities of concentrated lemon juice were imported for acid manufacture, since this item remained duty-free under the Tariff Act of 1922. The import figures shown in Table I do not include shipments of concentrated lemon juice. The 1929 revision of the Tariff Act imposes a duty of 5 cents per pound on such concentrated juices unfit for beverage purposes so that these imports are now negligible. The first successful commercial development of the fermentation citric acid process was achieved in the United States and as later events proved it came a t a n opportyne time. Although some acid was probably produced by this method in the United States as early as 1919, production in amounts sufficient to meet a n appreciable portion of the domestic demand did not occur until 1923. I n 1927 the Italian Government, in order to encourage greater home production of citric acid, placed an embargo on exports of calcium citrate to all manufacturers outside of Italy. The principal citric

Fermentation Citric Acid in World Trade A number of factors were responsible for the changes which have taken place with respect to foreign trade in citric acid. I n 1922 Italy produced about 90 per cent of the world supply of calcium citrate, the raw material for citric acid production. Other countries, including the United States, were largely dependent on the Italian producers for their supplies of this material. Sales of calcium citrate in Italy for both the domestic and foreign markets were controlled b y the Camera Agrumaria of Messina, a central sales organization formed in 1908 by the Italian Government to protect the small producers by maintenance of a profitable and fixed price. Various schemes of price fixing, export taxes, and methods of payment to the producers were used to regulate and control the market, but none met with any degree of success. After 1922 shipments of Italian calcium citrate and citric acid to the United States, formerly the best market, began t o decline. This decline must be attributed in part to the Tariff Act of 1922 which increased the duty on citric acid from 5 to 17 cents per pound and on calcium citrate from 1 to 7 cents per pound, the large increase in acreage of bearing lemon trees in California, our increased imports of concentrated lemon juice, and last, but not least, the large-scale manufacture of fermentation citric acid which began in 1923. The change which took place can be seen from the import figures for citric acid and calcium citrate 255

INDUSTRIAL AND ENGINEERING CHEMISTRY

256

TABLE I. U. S. IMPORTS OF CALCIUM CITRATE AND CITRIC ACID FOR CONSUMPTION, 1910-36 (Figures from U. S. Bureau of Foreign Commerce and Navigation) -Calcium Citrate-Citria AcidDuty Duty Year per pound Pounds Value per pound Pounds Value 4,114,256 $ 568,175 $0.07 142,001 $ 40,967 1910a Free 447,131 6,242,244 1,109,629 0.05 722,434 1915a $0.01 3,865,294 1,583,806 0 . 0 5 1,224,591 1,187,267 0.01 1919 0.05 1,317,467 1,142,842 1920 0 . 0 1 12,490,196 3,027,823 0.05 490,084 988,969 151,811 922,737 1921 0.01 0.05 1,325,366 1922b 477,568 0 . 0 1 16,000,692 2,223,506 0.17 233,665 757 864 1923 200,143 0.07 1,672,604 0.17 673:114 186,512 199,620 1,938,647 1924 0.07 0.17 288,574 376,694 3,475,964 1925 0.07 79 634 0.17 284,897 77:525 3,039,319 1926 0.07 347,073 0.17 71,291 18,515 46,865 416,045 1927 0.07 1,338 524 .... 0 . 1 7 1928 0.07 0.17 None hone None None 1929 0.07 0.17 None 6,726 1930 0.07 1,987 None 0.17 19,641 None None 90,850 1931 0.07 0.17 134,521 19,746 704 1932 0.07 34 0.17 55,272 9,784 1,213 2,367 1933 0.07 0.17 None None 1934 5,275 0.07 748 0.17 None None 1935 575 79 0.07 0.17 12 None 1936 40 0.07 None a Figures for 1910-15 are for the fiscal year: 1919-36 figures are for the calendar year. b New law went into effect Sept. 22, 1922.

.....

TABLE 11. CNITED STATESPRODUCTION OF CITRIC ACIDFOR SALE,1914-35 (From the U. S. Bureau of the Census) Av. Price per Year Pounds Value Pounda 2,657,840 $1,516,326 1914 $0.53 3 047 371 3,163,676 1919 1.10 1:913:774 3 849 789 1921 0.49 2,829,306 5:689:473 1923 0.50 3,469,740 7,589,213 0.46 1925 7,058,215 0.44 3,150,976 1927 4,832,984 10,755,789 1929 0.46 3,060,185 8,361,441 1931 0.36 1,795,382 5,695,793 1933 0.32 2,768,377 10,493,068 1935 0.28 Current price, $0.24 per pound; average price figures from trade journals. Q

acid producing countries at that time, England, France, and the United States, were suddenly cut off from supplies of raw material; if it had not been for the development of the new process, consumers in this country would have been placed in a difficult situation and forced to pay much higher prices for citric acid. Despite the fact that no calcium citrate was imported during 1928 and 1929, our domestic production of citric acid rose to over 10,000,000 pounds in 1929. Production of the natural product during this year probably did not exceed 3,500,000 pounds, so that the fermentation industry furnished about two-thirds of the total or approximately 7,000,000 pounds. The United States thus became independent of foreign citrate supplies and, for a few years after 1927, exported large quantities of calcium citrate, chiefly to England (44). I n 1933 exports of calcium citrate totaled 8,035,957 pounds ($496,521) of which 8,025,467 pounds ($496,083) were shipped to England. Exports since 1935 have fallen off sharply, largely because of the development of the fermentation process in England, our increased domestic consumption, and the International Citric Acid agreement between Italy, England, France, Belgium, and Czechoslovakia. This agreement which is valid until 1939 was established to regulate exports and strengthen prices and, according to consular reports, has successfully achieved its objectives. The details of the pact are not generally known, but Italy is reported to have an export quota of 38 per cent of the total figure set for exports. The figures in Table I1 show production of citric acid for sale in this country only, so that the decreased production in 1931 and 1933 is only apparent, because during these years large amounts of the fermentation acid produced were converted to calcium citrate for export.

VOL. 30,NO. 3

European Situation since 1928 ITALY.The Italian citric acid industry was reorganized entirely during 1928 in order to bring about more satisfactory conditions and to increase home production of citric acid (45, 48)- A common sales organization, known as the C. I. F. A. C. (Consorzio Italian0 Fabbriche Acido Citrica), was formed to control production and sales. Under the agreement citric acid manufacture was centered under two concerns, the Arenella a t Palermo and the Sada-Bosurgi a t Messina. The agreement, likewise, covered the distribution of calcium citrate, controlled by the Camera Agrumaria of Messina. The C. I. F. A. C. obtained first call on all supplies of the raw material held by the Camera Agrumaria, and only when its needs were satisfied was any surplus exported. Italian exports of citric acid thus rose to an alltime high in 1928 as a result of increased production but declined rapidly in the following years because of increased foreign competition resulting from the development of the fermentation process in the United States and in Europe. Table I11 shows Italian production and exports of citric acid and calcium citrate for the period 1920-36. For a number of reasons the Italian citric acid industry is a t present in a state of flux. The introduction of improved methods of -production has been deferred; and because of a recent crop shortage which necessitated imports of biological calcium citrate, there have been reports that manufacture of fermentation acid would be undertaken. The severe competition introduced by commercial development of the fermentation process may spell the eventual doom of the natural citric acid industry in Italy. The sharp curtailment of exports of calcium citrate from Italy as a result of the 1928 reorganization agreement seemed to stimulate efforts in other countries in the development of the fermentation process. Perhaps this would have taken place regardless of the Italian situation, but the rapid development in the United States, Belgium, Czechoslovakia, and Great Britain about this time was undoubtedly influenced a great deal by the rigid control of raw material supplies by Italy. TABLE 111. ITALIANPRODUCTION AND EXPORTS OF CITRIC ACIDAND CALCIUM CITRATEO Year

-Calcium Production 7

1920 1922 1924 1926 1928 1930 1932 1934 1935 1936

12,449 16,733 15,789 11,003 10,018 b b b b

--

CitrateCitric AcidExports Production Exports Thousands of pounds 19,350 3847 3371 19,879 4158 3479 0063 4257 8,322 4299 10,132 4544 3,587 7358 400.5 5,036 1,455 4,150 2,660 2,200

Production figures are for the Italian calcium citrate season, Nov. 1 t o Oat. 30. Export figures are for the calendar year. b Figures not available. Q

BELGIUM. One of the early attempts to produce citric acid was made a t Tirlemont, Belgium, in 1914, but until 1927 the amount of acid produced in this plant was insignificant. The firm, LaCitrique Belge S. A., is a member of the European citric acid cartel. Citric acid was not produced in quantities sufficient to become a factor in export trade until 1927. The present production capacity is not known, but in 1931 it was estimated a t 1,650,000 pounds, and 1933 over 2,000,000 pounds were exported. Export data are shown in Table IV. It has been reported (45) that the Italian producer, Arenella, owns an 80 per cent interest in the Tirlemont Company.

MARCH, 1938

INDUSTRIAL AND ENGINEERING CHEMISTRY

GERMANY.Production of citric acid in Germany is centered in two firms, C. K. Boehringer & Soehne G. m. b. H. a t Nieder-Ingelheim a m Rhein, and Chemische Fabrik J. A. Benclriser G. m. b. H. a t Ludwigshafen am Rhein. According to recent consular reports, neither of these firms manufactures citric acid by fermentation. The entire production of acid is due to conversion of imported biological and natural calciurn citrate. Imports of citric acid declined from 770 metric tons in 1932 to 119 in 1935; exports rose from 16 metric tons in 1933 to 204 in 1934, but declined to 75 in 1935. Germany does not participate directly in the European citric acid cartel. TABLE IV.

EUROPEAN EXPORTS OF CITRICACID 1927 7

Italy England Belgium Czechoslovakia Germany France a Figures not available.

1908 439 26 None a

229

1929

1931

1933

Metric tons 2803 1821 1960 1069 1391 1711 20 874 1217 None 370 518 39 17 l6 93 130 (1

1935 >

16iO a

577 75 a

CZECHOSLOVAKIA. Production of citric acid from molasses by fermentation in Czechoslovakia was started in 1930. According to reports of the Department of Commerce (45), the production capacity of the original plant was 240 metric tons annually, but this has increased rapidly. I n 1936 production totaled 911 metric tons or approximately 2,000,000 pounds; 729 metric tons were exported. Imports of citric acid which totaled 44 metric tons in 1929 are now negligible. T h e sole producer of citric acid in Czechoslovakia, Montan und Industrialwerke (vorm. J. D. Starck) of Prague,. participates in the European Citric Acid Agreement, but information regarding the export quota assigned is not available. One of the five countries participating in the FRANCE. European citric acid cartel is France, although no citric acid is produced by the fermentation process. Manufacture of citric acid from imported calcium citrate (9) is carried on by the Anciens etablissements Mante & Cie a t Marseilles. Formerly large quantities of calcium citrate and citric acid were imported from Italy. I n 1930 France became the principal Italian outlet for calcium citrate owing to the loss of the American and British markets for this product, but after 1931 imports of the raw material from Italy declined rapidly. Imports of citric acid from Italy totaled 520 metric tons in 1928, but in 1933 had declined to 112. Export data in Table I V for the period 1927-31 show that during those years French exports were not appreciable. GREATBRITAIN. Up to 1928 Great Britain was one of t h e chief markets for Italian calcium citrate, but, owing to t h e uncertainty regarding citrate supplies, American calcium citrate largely replaced the Italian product during the period 1928-36. However, the loss to Italy of this important market was largely compensated for by increased exports of citric acid to England. British imports of citric acid and calcium citrate have declined rapidly during the past few years owing to the greatly increased domestic production of the fermentation product. Two companies, Kemball,+Bishop and Company Ltd., a t London, and John and E. Sturge Ltd., a t Birmingham, now produce citric acid by the tation process, and it is believed that the production is sufficient to meet the domestic demand. T h s quota assigned to these producers under the European ic Acid Agreement has not been announced. ER COUNTRIES. An intensive study of the citric fermentation process has been made during the past years in Russia (29, 31, 40). The reported semiplant-

257

scale work there indicates that commercial operation is in pogress, although the production capacity is not known. Production of the fermentation acid on a small scale in Japan has been carried on for some time, and recent reports indicate that an expansion of existing fecilities for the production of a million pounds annually is contemplated.

Mycological Production of Citric Acid The production of citric acid from sugars by mold fermentation was first discovered by Wehmer (60) about 1893. Since that time the process has been intensively studied, particularly with respect to citric acid formation by various species of fungi, the various factors which influence the fermentation, and the highly interesting mechanism of the conversion from sugar to citric acid in which a branchedchain structure exists. It is not intended here to mention all of the vast amount of work which has been done on the mycological production of citric acid but to point out some of the more important contributions to the subject. More complete references will be found in the bibliography of Fulmer and Werkman (26) and in the works of Bernhauer ( 5 ) . The production of citric acid from sugars was believed by Wehmer (60) to be characteristic of a particular group of Penicillium-like fungi which he appropriately termed “Citromyces.” He, likewise, believed that the formation of oxalic acid was characteristic of the Aspergilli. The separation of the two groups of fungi based on this physiological difference was later abandoned after Zahorski (66) and Thom and Currie (47) had shown that citric acid was readily produced by many different strains of Aspergillus niger. Numerous other fungi have since been studied which produce citric acid from sugars. The citric acid process has been studied in great detail, and in much of this work Aspergillus niger has been employed. Thom and Church (46) pointed out that the term “Aspergillus niger does not designate a definite strain or species” but is used to designate ‘ia whole group of black Aspergilli with fundamental characters in common.” The great variations in acid production by different Aspergillus niger strains which have been recorded is, therefore, not a t all surprising. The activity of individual strains frequently varies so much that the stabilization or maintenance of a high acid-producing capacity of the organism is recognized as one of the most difficult problems encountered in dealing 6 t &the process. Doelger and Prescott (20) recently carried out studies with the object of determining methods for maintaining uniformity of conditions which would result in consistent yields of acid in successive fermentations. The influence of various factors which affect the citric acid fermentation has been studied by many workers. I n 1917 Currie (19) made a thorough investigation of the production of citric acid by selected strains of Aspergillus niger and showed that, by properly controlling the p H and the concentrations of the inorganic nutrient salts, the proportion of citric and oxalic acids could be varied almost a t will. H e found that oxalic acid formation was almost completely suppressed under conditions which were most favorable for the formation of citric acid. The importance of a preliminary acidification with hydrochloric acid to p H 3.5 for suppressing oxalic acid formation, preventing undesirable spore formation and minimizing the danger of infection by other organisms, was clearly demonstrated. It is known that contamination difficulties were at least partially responsible for the failure of early attempts made in Europe to establish the fermentation process on a commercial scale. This was undoubtedly due in part to the practice of neutralizing the acid formed with calcium carbonate. Acid sterilization has without

258

INDUSTRIAL AND ENGINEERING CHEMISTRY

doubt played an important part in the successful coriunercialscale development of the process, both in this country and in Europe. The work of Currie (19), which was carried out in the United States Department of Agriculture, later formed the basis for the timely commercial development of the process in the laboratories of the Charles Pfizer Company, of Brooklyn. The process is usuaUy carried out between 2.5" and 35" C., although temperatures as low as 20" and as high as 40' C. have been employed. The optimum temperature probably depends somewhat on the organism used. Aeration is undoubtedly an important factor, although little information concerning it is available. We may assume that relatively small amounts of air are required to supply the necessary oxygen for the life processes of the organism, since Porges (S9) and Doelger and Prescott ($0) have observed that large amounts of air adversely affected acid yields. It is impossible to make any general conclusions regardiiig the kind and amount of inorganic nutrients that ndl in all cases yield the best results for citric acid production. From the vast amount of work reported, it appears that the nutrient requirements depend to some extent on the individnal characteristics of the organism nsed. Aside from the carbon and nitrogen sources, the only essential elements are potassium, phosphorus, magnesium, and sulfur as shown by Currie (19) and by Doelger and Prescott (20). Nonever, many investigators claim that small amounts of zinc and iron am essential for the best growth of the organism, and in some instances it seems fairly well established that these elements exert a beneficial effect on acid prodnetion. The essential elements, aside from carbon, oxygen, and nitrogen, are conveniently snpplied as KNJQ in amounts varying from 0.03 to 0.1 per cent and as MgS01.7Hz0 in amounts from 0.01 to 0.05 pep cent. The highest yields of acid have nsnally been obtained from sucrose and fructose as the carbon source (3, 4, SG); in some instances glucose appears to serve about as well ( I # , 53). Sugar concentrations of 15 to 20 per cent are necessary for high yields of citric acid. Kitragen is supplied either as ammonium salts or as nitrates. In most cases ammonium nitrate in concentrations of 0.16 to 0.32 per cent has been reported to give the higliest yields of acid. Porges ($9)found that sodium nitrate was superior to either ammonium nitrate or ammonium sulfate as a nibrogen source in a concentration of 0.4 Der cent. and

VOL. 30, NO. 3

acid was roughly proportional to this ratio. Doelger and Prescott (20) found a similar relation in studies on the production of citric acid.

Large-Scale Operation In present industrial practice shallow aluminum pans are used for the prodnetion of citric acid from sugars by mold fermentation. The pans must be constructed with highpurity aluminum t.o prevent corrosion and to avoid the harmful effect of other metals such as copper,iron, etc. Theprocess consists essentially in tile inoculation with spores of a suitable organism of the sterile sugar solution contained in the aluminum culture vessels. A continuous felt of mycelium forms over the entire surface of the solution within 2 days, and formation of citric acid occurs rapidly aft.er the fourth day. The fermentation is usually complete in 7 to 10 days after inoculation. The solution is then drained off, the myeelium is pressed to remove any acid present in the tissues, and the acid is either crystallized directly after a yeast fermentation of the residual carbohydrate or first separated from the solution as the calcium salt from which the acid may be recovered by crystallization after treatment with sulfuric acid. The yield of citric acid obtained is approximately 60 per cent by weight of the sugar taken, Little is known regarding the actual details of industrial operation of the fermentation, but the difficulties involved rnnst be enormous. May et al. (S4), in semiplant-scale st.ndies on the production of gluconic acid, used aluminum pans 43 X 43 X 2 inches (109 X 109 X 5 em.) which had an optimum charge capacity of 48 liters of culture solution. Based on a 7-day process and a 50 per cent weight yield of acid from 20 per cent sucrose solutions, it is calculated that from 12,000 to 16,000 pans of this capacity would be required to manufacture the estimated 7,000,000 pounds of fermentation citric acid produced annually in the United States. It is not surprising that the details of such a process are kept secret. MIICHAXISMSTUDIES. Most of the recent literature dealing with citric acid has been concerned with efforts to explain the mechanism of the reactions involved in the conversion of glucose and other sugars to citric acid. Cliallrnger ( 1 4 ) and May and Herrick (3s) summarized the

MARCH, 1938

INDUSTRIAL AND ENGINEERING CHEMISTRY

various theories which had been proposed up to about 1930. The more recent theories have been concerned with mechanisms involving acetic acid as one of the important intermediate substances. The acceptance of this acid as an intermediate in the process naturally led to the assumption that its formation was preceded by a breakdown of glucose similar to that encountered in the alcoholic fermentation of yeast. Chrzaszcz and Tiukow (16) proposed that citric acid is formed from acetic acid through the following steps: acetic acid -+ succinic acid 3 fumaric acid -+ malic acid. The latter by condensation with another molecule of acetic acid then forms citric acid, according to their view. Bernhauer (6) proposed a similar scheme in which succinic acid reacts with acetic acid to form tricarballylic acid which, on oxidation, yields aconitic and finally citric acid. However, in spite of all the favorable evidence to support these views, it has been shown that mechanisms involving acetic acid as an intermediate in the citric acid process, in which it is assumed that the initial reactions leading to its formation follow the general chemical equation which represents the alcoholic fermentation, can be ruled out on purely quantitative evidence. Butkevich and Galvskaya ( l a ) , Chrzaszcz and Peyros (15), Bernhauer and Iglauer (Y), and Wells, Moyer, and May (52) reported results in which the citric acid yields obtained from glucose and sucrose greatly exceeded the highest yields obtainable from these sugars if the initial reactions followed those of the usual alcoholic fermentation of yeast. The mechanism recently proposed by Emde (ag),in which quinic acid was suggested as an intermediate, can likewise be ruled out since both the yield of citric acid and carbon dioxide production required by that theory do not agree with experimental data. Any satisfactory theory for the mechanisms of citric acid formation by fungi must take into account the quantitative data which have been accumulated, and the fact that citric acid formation by fungi from 2-, 3-, 4-, 5-, 6-, 7-, and 12carbon compounds has been well established. I n spite of all the work done on this problem, the mechanism of the mycological production of citric acid is still obscure, and no theory so far proposed accounts for all of the observed facts. PATENTS. The mycological production of citric acid has been widely patented both in the United States and in Europe. However, the one successful commercial process in this country was developed only after years of intensive biochemical and engineering research; consequently the actual details of operation have been closely guarded as trade secrets. The process undoubtedly consists of a shallow-pan fermentation of pure sucrose or of blackstrap molasses by a strain of A. niger; the reaction is probably completed in less than 9 days. The patent literature dates back to 1893 when Wehmer (51) secured broad patents ewering the process which he had discovered. The industrial application of Wehmer’s patent was attempted in Germany (28) about forty years ago, but, because of the numerous difficulties encountered, it was soon abandoned. In 1913 Zahorski (56) was granted a patent for the production of citric acid from sugars by the fungus Xterigmatocystis nigra. A preliminary acclimatization of the organism to high concentrations of citric acid was claimed to result in higher yields of acid than had previously been obtained. Falck (23) patented a process for the production of acids based on the use of solid starchy substrate and organisms of the Aspergillus, Penicillium, or Citromyces groups. The production of citric, malic, tartaric, and succinic acid is claimed,

259

but no details as to methods of recovery or individual yields of the acids are given. The patent of Bleyer (8) specifies a preliminary acidification to pH 3.3 and the use of an abundant supply of air to maintain temperature control and to remove carbon dioxide. The patent granted to Szucs (49) in 1928 claimed the production of citric acid from molasses by fungi of the Citromyces, Mucor, Aspergillus, or Penicillium groups. With a strain of Aspergillus it was claimed that a temperature around 20 O C. suppressed oxalic acid formation, inhibited infections, and gave high yields of citric acid. Fernbach and Yuill (24) patented a process in which the novel feature lies chiefly in the elimination of sterilization by heat through the addition of sufficient hydrochloric or sulfuric acid to the sugar solutions to give a p H of 1.2 to 2.5. Kanhauser (30) was granted a patent for the production of citric acid in which it is claimed that improvements in the process are effected by cultivating the organisms in alternating stages on solid agar media, on media corresponding to those used industrially, and on vegetable media containing organic acids and vitamins. It is further claimed that the presence of substances which form complexes of high molecular weight with citric acid is beneficial. According to patent specifications, Cahn (13) succeeded in producing citric acid in good yields in a short fermentation period by mold fermentation of sections of sugar-containing plants, such as sugar beets and artichokes; by fermentation of plant residues, such as sugar cane bagasse and spent sugar beet cossettes, impregnated with sugar solutions; and from sections of starch-containing material such as potato dices. It was further claimed that the fermentation may take place in closed tanks or vats. This feature would be a distinct advantage over the shallow-pan process in reducing the cost and amount of equipment required and in simplifying manipulation procedures. Lilly (32) was granted a patent on an apparatus and method for the production of citric acid. The apparatus consists of a number of long, porous, flat, hollow tubes suspended within a closed outer casing. The outer surface of the porous tube is inoculated with a suitable organism, and a regulated stream of nutrient sugar solution is allowed to flow by gravity through the tubes. Oxygen is supplied to the organism by passing sterile air through the outer casing. Since no yield figures are given, it is not possible to determine how effectively this method operates. The patent of Frey (26) describes an apparatus for citric acid production in which a number of superimposed shallow pans are so arranged that the nutrient solution may be drawn off to a large vessel, the citric acid removed by treating with calcium carbonate, and the solution recirculated through the pans. A yield of 40 per cent citric acid in a period of 15 days is reported. In 1936 Nussbaum (37) obtained a patent for producing citric acid in which mixed cultures, especially A . niger and Mucor piriformic, are employed. The addition of mineral salts of uranium, manganese, and zinc in the proportion of 0.001 to 0.005 per cent is claimed to stimulate acid production. It is further claimed that addition of 1 to 15 per cent of citric acid favors the rapid development of the citric acid enzymes. A highly interesting process for the conversion of acetic acid and acetates to citric acid by yeast was patented by Boehringer (10). This process is based on the original discovery of Wieland and Sonderhoff (53) who found that aerated yeast cultures produced both succinic and citric acids from acetates. A dilute solution (0.2 N ) of sodium or calcium acetate is fermented with yeast under highly aerobic conditions maintained by stirring the solution vigorously in the presence of air or oxygen. Eight hundred and B t y grams

260

INDUSTRIAL AND ENGINEERING CHEMISTRY

of citric acid and 230 grams of succinic acid were obtained from 6000 grams of acetic acid during a fermentation period of 12 hours. The chief importance of this discovery lies in the fact that a submerged yeast growth is employed for the process, making possible the use of tanks or vats as culture vessels. The reported yield of citric acid is low, but further research might reveal conditions that would lead to improvements in this respect.

VOL. 30. NO. 3

citrates, 15 per cent in foods, 9 per cent in candy, and smaller amounts in silvering, engraving, as an ink ingredient, and in dyeing and calico printing. Recent research on synthetic resins of the alkyd type revealed the importance of citraconic and itaconic acids and their anhydrides as raw materials. Substantially better yields of these products from citric acid were obtained recently; a n enormous potential use of this acid (9) is thus indicated. The use of citric acid in the manufacture of edible synthetic ester resins which may be employed as substitutes for chicle was suggested by Ellis (21). The use of citric acid in Italy in the manufacture of 1-phenyl-3-methylpyrazolone which is used as an intermediate in the production of antipyrine and certain azo colors was reported by Corbellini (17).

Natural Citric Acid Industry

LABORATORY METHODSOF CULTURING SURFACE MOLDSIN TUBESAND FLASKS Zender (56) recently patented a process for the production of citric acid by mold fermentation in which the acid may be crystallized directly from the culture solution, thus eliminating the usual step of first separating the acid as the calcium salt. The mold-fermented culture solution is fermented with yeast in the presence of a soluble calcium compound to remove the residual carbohydrate, the calcium is removed with oxalic acid, and the citric acid is then recovered by crystallization.

Properties and Uses of Citric Acid Citric acid was first isolated in the solid state by Scheele in 1784 from lemon juice. It crystallizes in large rhombic prisms containing one molecule of water of crystallization and has the formula CsHg07,H20. The anhydrous form of the acid, which is now commercially available, crystallizes in monoclinic prisms. It is readily soluble in water, moderate:y in alcohol, but only sparingly in ether. The water of crystallization of the hydrated form is entirely lost at 130"; it melts a t 153" and, on further heating above 175", decomposes into aconitic and itaconic acids, citraconic anhydride, carbon dioxide, and acetone, Chemically, citric acid is a tribasic acid forming three series of salts which are well defined. The alkali salts are soluble in water, the others are mostly insoluble. Citric acid is used in the manufacture of citrates, flavoring extracts, confectionery, soft drinks, effervescent salts, as a silvering agent and as an ink ingredient in engraving, in dyeing and calico printing, and in medicine. According to the United States Department of Commerce, about 65 per cent of the domestic consumption was recently reported to be used for medicinal purposes, including the manufacture of

Citric acid occurs in many plant tissues, especially those of the citrus variety. I n citrus fruits and in sloes, cranberries, etc., it occurs free and with very little malic acid; in fruits such as the cherry, strawberry, and raspberry it occurs with an approximately equal proportion of malic acid. The chief commercial sources for the natural variety of acid are lemons, limes, and pineapples. Another potential source of large quantities of citric acid is tobacco waste but, so far as is known, no commercial development of a process making use of this material has yet occurred, although several patents have been granted to Shmuk (62). Italy still produces the largest quantity of natural citric acid; the only other important sources are California, the West Indies, and Hawaii. The Sicilian citrus by-products industry was described in detail by Cruess ( I @ , Molinari (Sti), and Galeano (b7), so that only the more important features of this industry will be mentioned here. The larger part of the citrus fruit grown in Sicily is primarily for export in the fresh state. The normal annual production of lemons in Sicily is 300,000 tons, but, unless the fresh fruit market is unfavorable, little normal fruit goes into the by-product industry. However, the proportion of inferior fruit grown in Italy is very high (30 to 50 per cent) so that large quantities are available for the production of lemon oil and calcium citrate. Most of the Italian calcium citrate was formerly exported, but since 1921 large quantities of this raw material have been consumed for the manufacture of citric acid in the domestic citric acid industry. The manufacture of citric acid in Italy is now centered mainly in two large modern factories located a t Palermo and Messina. Although crystallization of citric acid direct from lemon juice is apparently feasible (I, 4 l ) , the usual practice in Italy is first to separate it as the calcium salt which, on decomposition with sulfuric acid, yields the free acid in crystallizable form. The method of preparing crude calcium citrate is briefly as follows: The clarified lemon juice, which contains from 4.5 to G per cent citric acid, is heated to boiling and then neutralized with lime and calcium carbonate with constant stirring. The insoluble tricalcium citrate is filtered and washed thoroughly with hot water until the washings remain colorless. The dried salt, which usually contains from 67 to 70 per cent citric acid, is sold on a 64 per cent citric acid basis; a premium is paid for percentages in excess of that figure. Molinari (36) states that approximately 100,000 lemons are required to produce 300 kg. of calcium citrate of this strength, or about 150 lemons per pound. Citric acid is prepared from the crude calcium citrate by adding gradually a slight excess of sulfuric acid to the suspension of the salt which is stirred continuously. The mixture is boiled, and the calcium sulfate which separates is filtered off and washed. The acid liquors are then concentrated in vacuum evaporators in two stages; in the first

MARCH, 1938

INDUSTRIAL AND ENGINEERING CHEMISTRY

stage the remaining calcium sulfate is separated after concentration to about 28’ BB., and in the second stage it is concentrated further to 48-50’ BB. The concentrated liquors are then discharged and allowed to crystallize. The crude citric acid thus obtained is redissolved and treated to remove metallic impurities and coloring matter; then the purified liquors are concentrated in vacuum a t 60’ to 65” C. The pure acid was formerly crystallized in lead-lined or wooden containers, but in modern practice crystallizers constructed with stainless steel, aluminum alloys, or rubber are used. The formation of normal crystals usually required from 4 to 5 days. The crystals are separated from the mother liquors by centrifuging and washing in the centrifuge with pure citric acid solution. The yield of acid from lemons varies from 15 to 50 pounds per ton of fresh fruit, depending chiefly on the time of harvest. The methods employed in the California citrate industry were completely described by Wilson (64), and a description of the process used in the West Indies was given by Browne (11) and by Warneford and Hardy (49). I n addition to the citric acid from lemons in California, some is also produced from pineapple waste from the canning industry. According to Pilhasky (38), about 250,000 pounds of calcium citrate were produced in 1926 from this source. The Hawaiian citric acid industry is a comparatively recent development, although for a number of years about 100,000 pounds of calcium citrate were annually shipped to the United States. However, all of the available citrate from pineapple waste is now converted to citric acid in a modern plant erected in Hawaii during 1930 (45). The total annual production capacity is estimated a t 750,000 to 1,000,000 pounds, Shipments of citric acid from Hawaii to the United States have increased steadily since 1930 and in 1935 amounted to approximately 1,000,000 pounds, or about 10 per cent of the total production in the United States during that year.

Future of the Industry The fermentation citric acid industry is now well established. Manufacturers consuming this acid are assured of adequate supplies, regardless of crop failures and other conditions. The price trend since the first commercial development in the United States has been steadily downward, despite the fact that producers are protected by an almost insurmountable tariff barrier to foreign competition. The present low price of citric acid has undoubtedly been responsible for t,he increased domestic consumption of this product which has taken place during the past few years. Important new developments in the industry can be expected shortly. The use of citric acid in the synthesis of certain types of plastics and other products has been indicated previously. Such uses would provide an outlet for large quantities of this acid. It is probable that expansion of existing production facilities in the fermentation citric acid industry will take place in the near future. The use of cheap carbohydrate materials for citric acid manufacture and lower operating costs, due to improved technic, may make possible further price reductions which will probably lead to greater demand and consumption of this product. Although citric acid production by a true submerged growth process in yields high enough t o be of practical importance has not been accomplished, the possibility still remains that this problem may be solved. Amelung (2) reported that 19 per cent yields of citric acid from sugar were obtained in a period of 40 days by employing submerged growths of A . niger. The commercial development of such a process would revolutionize present methods of manufacture.

261

Producers of the naturally occurring citric acid may, therefore, in the future be subjected to competition more severe than that which now exists. Satural citric acid production in the United States is definitely limited to the amount of cull citrus fruit available and probably seldom exceeds 3,500,000 pounds annually. It is not known whether the manufacture of citric acid from cull citrus fruits and other wastes could be operated profitably if prices were further reduced. Improved methods of manufacture to reduce operating costs may be necessary to compete successfully with the fermentation citric acid industry.

Literature Cited (1) Ajon, G., Ann. merceol. siciliuna, 1, 33 pp. (1933). (2) Amelung, H., Chem.-Ztg., 54, 118 (1930). (3) Amelung, H., Z. phvsiol. Chem., 166, 161-209 (1927). (4) Bernhauer, K., Biochem. Z., 197,309-42 (1928). (5) Bernhauer, K., “Die oxydativen Garungen,” pp. 78-103. Berlin, Julius Springer, 1932; “Garungschemisches Praktikum,” pp. 199-202, Berlin, Julius Springer, 1936. (6) Bernhauer, K., Ergeb. Enzymforsch., 3,185-227 (1934). (7) Bernhauer, K., and Iglauer, A.,Biochem. Z . , 286,45 (1936). (8) Bleyer, B., German Patent 434,729 (Oct. 6, 1926). (9) Boehringer, C. F., & Soehne, G. m. b. H., British Patent 452,460 (Aug. 24, 1936). (10) Boehringer, C. F., & Soehne, G. m. b. H., German Patent 636,135 (Oct. 2, 1936). (11) Browne, C. A., J. IND. ENG.CHEM.,13, 81 (1921). (12) Butkevich, V. S., and Galvskaya, M. S., Compt. rend. mad. sci. U . S. S . R., [N. S.] 3,405-8 (1935). (13) Cahn, F. J., U. S.Patents 1,809,797 (June 9, 1931), 1,812,136 (June 30, 1931), and 2,047,669 (July 14, 1936); French Patents 675,236 and 675,237 (Oct. 29, 1929). (14) Challenger, F., I n d . Chemist, 5 , 181-4 (1929). (15) Chreaszcz, T., and Peyros, E., Biochem. Z., 280,327-36 (1935). (16) Chrzasecz, T., and Tiukow, D., Ibid., 229,343 (1930). (17) Corbellini, Arnaldo, “L’utilizzaeione dell’acido citric0 alla sintesi dell’ 1-fenil 3-metil 5-piraeolone e derivati,” Palermo, Ires, 1935. (18) Cruess, TV. V., Chem. & Met. Eng., 32,313-15 (1925). (19) Currie, J . N., J . Rid. Chem., 31,15-37 (1917). (20) Dodger, W. P., and Prescott, S. C., IND. ENG.CHEM.,26, 1142 (1934). (21) Ellis, Carleton, U. S. Patent 2,007,965 (July 16, 1935). 275,373 (1935). (22) Emde, H., Biochem. Z., (23) Falck, R., German Patent 426,926 (-March 29, 1926). (24) Fernbach, A,, and Yuill, J. L., U. S. Patents 1,691,965 and 1,691,966 (Nov. 20, 1928); British Patents 266,414 and 266,415 (Feb. 28, 3927); French Patents 610,121 and 610,122 (Mag 29, 1926). (25) Frey, A., German Patent 567,071 (Sept. 13, 1930). (26) Fulmer, E. I., and Werkman, C. H., “Index to the Chemical Action of Microorganisms on the Non-Nitrogenous Organic Compounds,” Springfield, Ill., Chas. C. Thomas, 1930. (27) Galeano, S., Ann. merced. siciliuna, 2, 59-101 (1934). (28) Henneberg, W., Handbuch der Garungsbakteriologie, 1‘01. I, p. 557, Berlin, Paul Parey, 1926. (29) Ivanov, N. N., and associates, Proc. Inst. Sci. Research Food Ind. (U. S . S.R.), 3, 3-153 (1935); 3,1-167 (1936). (30) Kanhauser, F., U. S. Patent 1,779,001 (Oct. 21, 1930). (31) Kostuichev, S., and Berg, V., Bull. State Inst. Agr. Microbiol. (U. S.S.R.),5 , 8-27 (1933). (32) Lilly, C. H., U. 9. Patent 1,936,983 (Nov. 28, 1933). (33) May, 0. E., and Herrick, H. T., U. S. Dept. Agr., C k . 216 (May, 1932). (34) May, 0. E., Herrick, H. T., Moyer, A. J., and Hellbach, R., IXD. EXG.CHEM.,21,1198-1203 (1929). (35) Molinari, Ettore, “Treatise on General and Industrial Chemistry,’’ 2nd ed., Part I, pp. 412-19, London, J . and A. Churchill, 1920. (36) Molliard, M., Compt. rend. soc. biol., 90, 1395-7 (1924). (37) Nussbaum, J., French Patent 801,273 (July 31, 1936). (38) Pilhasky, B. M., Chem. & Met. Eng., 33,559 (1926). (39) Porges, Nandor, Am. J. Botanu, 19, 559-67 (1932). (401 . , Protod’yakonov, 0 . P., Bull. State Inst. Agr. Microbiol. (U. S . S . R.), 5, 231-58 (1933). (411 Ricevuto. A,. and Bennett, A. H., U. S. Patent 2,072,530 (March 2, 1937). (42) Shmuk, A. A., Russian Patents 30,272 (July 31, 1933) and 35,187 (March 31, 1934). ~~~I

262

VOL. 30, NO. 3

INDUSTRIAL AND ENGINEERING CHEMISTRY

(43) Sziice, J., U. S. Patent 1,679,186 (July 31, 1 9 2 8 ) ; German Patent 4 6 1 , 3 5 6 (June 13, 1928) ; Austrian Patent 101,009 (Sept. 25, 1925); Canadian Patent 251,180 (June 30, 1925). (44) Taylor, J. N., and Boyd, R. G., Commerce Rept., pp. 227-8 (Jan. 26, 1931). (45) Taylor, J. N., and Lord, R. A., Ibid., pp. 38-41 (July 6, 1931). (46) Thom, C . , abd Church, M. B., “The Aspergilli,” p. 168, Baltimore, Williams and Wilkins Co., 1926. (47) Thom, C., and Currie, J. N., J. Agr. Research, 7 , 1-15 (1916). (48) U. S. Tariff Comm., Summary of Tariff Information, 1929, on Tariff Act of 1922, Schedule I, pp. 6-9 (1929). (49) Warneford, F. H. S.,and Hardy, F., IND. ENO.CHEM.,17, 1283 (1925).

(50) Wehmer, C., BUZZ. sac. chim., 9, 728 (1893); Compt. Tend., 117, 332 (1893). (51) Wehmer, C., U. S. Patent 515,033 (Feb. 20, 1 8 9 4 ) ; German Patent 7 2 , 9 5 7 (Feb. 20, 1894) ; British Patent 5 , 6 2 0 (Dee. 9, 1893); French Patent 2 2 8 , 5 5 4 (March 11, 1893). (52) Wells, P. A., Moyer, A. J., and May, 0. E., J . Am. Chem. Soc., 58, 565 (1936). (53) Wieland, H., and Sonderhoff, R., Ann., 499, 213-28 (1932). (54) Wilson, C. P., Chem. & M e t . Eng., 29, 787-92 (1923). (55) Zahorski, Boleslas, U. S. Patent 1,066,358 (July 1, 1913). (56) Bender, J., Ibid., 2 , 0 7 2 , 9 1 9 (March 9 , 1937).

RECEIVED November 1 1 , 1937.

Solubilities of

Natural R e s i n s in Solvents and W a x e s c. L. MANTELL AND R. W. ALLAN American Gum Importers Association, Inc., Brooklyn, N. Y.

T

HIS paper is a correlation of data on the solubilities of the commercially important natural resins in paint, varnish, and lacquer solvents determined to date in the laboratory of the American Gum Importers Association, Inc. The results were obtained for a large number of commercial solvents representative of t h o s e i n c o m m o n use. These data are recorded, and the effects of the various classes of solvents on the individual gums are discussed.

Solvents The solvents used represent those c o m m o n 1y available (Tables I and 11). The following types are included: alcohols, chlorinated compounds, c o a 1- t B r hydrocarbons, petroleum hydrocarbons, esters, ethers, ketones, alcohol ethers, and various miscellaneous types. One hundred grams of ground resin were put in a narrow screw-cap jar, and ( T o p ) NOTCHAND DOME 100 grams of solvent were OF AND added. The sealed jars were placed on an end-overShores end mixing machine and rojavanaca tated . -..- at, .. . 35 .. r. D. m. at room temperature Tor 15 to 18 (Left) TAPPING AND hours, The bottles were COLLECTING LOBA MAnever more than two-thirds NILA G m FROM Agathis to three-quarters full;hence, alba efficient mixing resulted.