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
82
system. This profile corresponds to the 2000 pounds per square inch absolute curve of Figure 6. It is apparent that a large amount of information is necessary in order to describe in reasonable detail the volumetric properties of a ternary system throughout extended ranges of pressure and temperature. Data for a number of other profiles suitably spaced across the figure are needed. Later papers of this series will present such information. EXPERIMENTAL ACCURhCY
The sensitivity and precision of the measuring inqtruments which were mentioned earlier in this paper do not necessarily indicate the accuracy of the experimental results. Uncertainties related to the skill of the experimenter, the reliability of the calibrations, the density and distribution of the observations, and the validity of the graphical methods employed in the interpolation and correlation of the data render the exact estimation of over-all experimental accuracy very difficult. Probably the most reliable estimates of accuracy may be derived from comparisons of results from similar studies by several investigators. Wherever such comparisons are not possible, as in the present case, statements of experimental accuracy necessarily represent merely estimates based upon extended experience with the apparatus and techniques during their development and improvement, and upon those comparisons which have been possible in similar cases. The following estimates of the uncertainties in the accuracy of measurements reported here are believed to be valid :
Pressure Volume Temperature Composition
Vol. 39, No. 1 *0.1% *0.25% *0.05’ F.
*0.002 mole fraction
ACKNOWLEDGMENT
This work was carried out as a part of the activities of Research Project 37 of the dmerican Petroleum Institute. Assistance from R. H. Olds and J. A. Irwin in calculations, graphical treatment of the data, and their preparation in final form R i gratefully acknowledged. H. A. Taylor gave valuable aid in the operation of the labohtory equipment and in graphical smoothing operations. LITERATURE CITED (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Beattie, Stockmayer,and Ingersoll, J . Chem. Phys., 9, 871 (1941). Bridgeman, J . Am. Chem. SOC.,49, 1174 (1927). Calingaert and Soroos, Ibid., 58, 635 (1936). Lavender, Sage, and Lacey, Oil Gas J., 39, No. 9 , 4 8 (1940). Marker and Oakwood, J . Am. Chem. Xoc., 60,2598 (1938). Olds, Reamer, Sage, and Lacey, IND. ENG.CHEM.,35, 922 (1943).
Ibid., 36, 282 (1944). Reamer, Olds, Sage, and Lacey, Ibid., 34, 1526 (1942). Sage, Budenholzer, and Lacey, Ibid., 32, 1262 (1940). Sage, Hicks, and Lacey, “Drilling and Production Practice, 1938”, p. 402, New York, Am. Petroleum Inst., 1939. (11) Sage, Hicks, and Lacey, IND.ENG.CHEM.,32, 1085 (1940). (12) Sage and Lacey, “Drilling and Production Practice, 1939”, p. 641, New York, Am. Petroleum Inst., 1940. (13) Sage and Lacey, Trans. Am. Inst. Mining Met. Engrs., 136, 136 (1940). (14) Sage, Lavender, and Lacey, IND. ENO.CHEM.,32,743 (1940). (15) Shepard, Henne, and Midgley,J.Am. Chem.Xoc., 53,1948 (1931). (16) Young, Proc. Roy. Irish Acad., B38, 65 (1928). PAPER 47 in the series “Phase Equilibria in Hydrocarbon Systems”. Previous articles have appeared during 1934-40 and 1942-46.
Recovery of Lactic Acid from Dilute Solutions ALBERT A. DIETZl WITH ED. F. DEGERING
H. H. SCHOPMEYER
Purdue University, Lafayette, Znd.
American Maize-Products Company, Roby, Znd.
I
N T H E manufacture of lactic acid by the fermentation of glucose, lactose, or other carbohydrates, the acid is obtained in
dilute solution. Difficulties due to the properties of lactic acid are encountered in its purification. Because of the relative high solubility of its salts, lactic acid cannot be precipitated quantitatively, and it cannot be rectified without decomposition because it undergoes autoesterification on heating. The difficulties involved in the manufacture of pure lactic acid are indicated by the fact that, until 1930, only commercial grades of lactic acid were manufactured in the United States (3). Smith and Claborn (9) described the preparation of a pure lactic acid by the hydrolysis of an ester. The commercial manufacture of lactic acid and the difficulties encountered in its purification were reviewed by Peckham (6) and Smith and Claborn (9). Several methods are used at present for the removal of lactic acid directly from dilute fermentation liquors. Small amounts of lactic acid volatilize with steam a t atmospheric pressure, but the distillation is not complete unless superheated steam 47) or high vacuum is used. Methodsinvolving the extraction of the acid with isopropyl ether are used, but, because of the impurities that are extracted a t the same time, i t is necessary to start with a pure 1 Present
6, Ohio.
address, Toledo Hospital Institute of Medical Research, Toledo
fermentation mash (6). Extraction methods using an alcohol to extract the lactic acid (IO)have also been tried. If the alcohol is soluble in water, a solvent immiscible with water can be used to extract the lactic acid, which is then esterified in the extraction mixture. I n the present investigation a method was sought whereby it would be possible to recover the lactic acid as an alkyl lactate after its esterification in dilute solutions. Two methods were tried. First a study was made of the distill&ion of the binary and ternary mixtures of the esterification ingredients. The esters and the corresponding alcohols do not distill azeotropically. The esters and water distill azeotropically to give a distillate containing 20 to 3001, ester. This distillation has since been studied fully (2, 6), and several patents for the purification of lactic acid are based on it (8, 11, 12). I n the reported methods an alcohol is passed through a tower containing partly concentrated lactic acid, and the vapors are collected without reflux. Since no reflux is used, impurities are also carried into the distillate, and considerable hydrolysis of the ester may take place before the ester can be obtained free of aathr. I n the second method tried by the present authors, the dilute lactic acid solution (5 to 6%) is esterified and the ester extracted with a solvent in which it is preferentially soluble, The chlori-
January 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
A t present there appears to be no best method for the isolation of pure lactic acid from fermentation liquors. Acid of varying degrees of purity is obtained by solvent extraction, steam distillation, and crystallization of its salts. The recovery of lactic acid by passing vapors of an alcohol through a partly concentrated lactic acid solution has been reported. A pure grade of acid may be prepared by the hydrolysis of an alkyl lactate. In the present investigation a study was made of the recovery of lactic acid as an ester directly from dilute solutions. In the method evolved the acid is converted to an ester and is extracted with a solvent in which it is preferentially soluble. Certain chlorinated hydrocarbons were found to be selective solvents. Using 1,2-dichloroethane as the solvent, the preparation of ethyl and propyl lactates is described. The esters can be purified to any desired degree by distillation.
nated hydrocarbons act as selective solvents for the esters in the presence of the other ingredients constituting the esterification mixtures. Using 1,2-dichloroethane, the esters are extracted a t such a rate that only a small amount of impurities are removed. The esters can be recovered from the solvents and purified t o any desired degree by rectification. A correspondingly pure grade of lactic acid could then be prepared by the method of Smith and Claborn (9). The esterification mixture need not be cooled toseparate the chlorinated hydrocarbon solvent, since the latter is immiscible at the boiling point of the former. This property makes it possible to operate a continuous, countercurrent esterificationextraction, but working out the process is beyond the scope of this investigation. The method studied is one of continuous esterification a t the boiling point and intermittent extraction. The use of chlorinated hydrocarbons as solvents has a further advantage in that only a little water is removed urith the ester. The extracted water is removed during the recovery of the first portion of the solvent, so that hydrolysis of the ester is prevented. I n order that a method of esterification and extraction be feasible, it is necessary that the equilibrium constant be favorable and that the ester be preferentially soluble in the solvent. A study was therefore made of the equilibrium constant of the esterification mixture under the experimental conditions and of the preferential solubility of the ingredients.
83
tions were made had a concentration of 9.78% as lactic acid and contained 0.6% polymers. The ingredients used in these experiments were weighed separately into iodine flasks, mixed, and rapidly heated to boiling. As catalyst, 0.1823 gram of hydrogen chloride was used per 250 grams of esterification mixture. Samples were withdrawn at intervals, rapidly cooled, weighed, and diluted with carbon dioxide-free water, and the acid and ester contents determined. The lactic acid concentration was determined by direct titration (with corrections for the hydrochloric acid present), and the esters by back titration after hydrolysis had occurred in the presence of excess alkali. The analysis of the known mixtures a t zero time showed that this method gave accurate values. The results of the determination of the equilibrium conditions are shown in Table I and Figure 1, and the rate of esterification in Table I1 and Figure 2. The boiling points given are only approximate, since they vary slightly with changes in concentrations of the ingredients and with barometric pressure. Xeglecting the three low values in Table I, the average value for K is 2.71 * 0.06. EXTRACTION OF ETHYL LACTATE.I n order to be useful in an esterification-extraction procedure, the solvent should preferentially dissolve the ester in the presence of the other ingredients. It should have a density significantly different from that of the esterification mixture and be but slightly miscible with it.
DILUTE ETHYL LACTATE ESTERIFICATION
EQUILIBRIUM CONSTANT.Several results are recorded in the literature for the equilibrium constant of the esterification but none for the conditions of these experiments. I n the following discussion the equilibrium constant will always be given for the alcohol ester f water. equation written as follows: acid Williams, Gabriel, and Andrews (13) found the equilibrium constant of the ethyl lactate system to be 2.64 a t 100' C. They established the equilibrium in sealed tubes without the aid of additional catalysts and indicated that the above equation does not represent the true equilibrium conditions because of the presence of lactic acid polymers which analyze as esters. The concentration of these polymers is very small in the 5 to 770 lactic acid used in the present investigation (6). Berger (1) found the equilibrium constant of the same system at 40.5' C. to be 1.61. Palomaa (4) gives the constants for the rate of hydrolysis of methyl and ethyl lactates in 0.1 and 0.2 N hydrochloric acid at 25' C. In view of the above differences the equilibrium constant for the ethyl lactate esterification was determined for the conditions of these experiments. It was determined both by hydrolysis of ethyl lactate and by the esterification of lactic acid. The ethyl lactate was carefully rectified at requced pressure, the lactic acid was C.P. grade, and the alcohol was obtained by distilling absolute alcohol over sodium. The lactic acid from which the final dilu-
+
+
Figure 1. Ethyl Lactate in Equilibrium Mixtures
The selective solvent action was determined by adding 5 ml. of the esterification ingredients (ethyl lactate, absolute ethyl alcohol, and 102% lactic acid) to 40 ml. of water. This mixture was then heated to boiling under reflux and poured into 50-ml. graduated cylinders. The volumes of the solvent layers at two temperatures and the indices of refraction of both layers at 25" C. mere used as criteria for the preferential solvent action. The results are summarized in Table 111. In the absence of water all other ingredients were completely miscible. The ethyl lactate was more soluble in the solvent layer than was the alcohol or acid. Table I11 indicates that 1,1,2,2-tetrachloroethane is a better solvent for ethyl lactate than is 1,2-
INDUSTRIAL AND ENGINEERING CHEMISTRY
84
Vol. 39, No. 1
TABLE I. ETHYL LACTATE PRESENT IN EQUILIBRIUM MIXTURES % Ester5 at Equil. &fole Ratio ~ ~ i as l Determined i ~ ~ by: K of Acid:Alc. : Temp., Hydroly- Estqri- . Hydroly- EsteriExpt. Water c. sis fication 81s fication A
1:1:98 1:2:97 1:4:95
B
C D E
1:8:91
1:16:83 1:32:67
F
2.5 4.0 9.9 19.1 33.5 50.4
100.0 95.5 94.3 89.0 86.3 84.0
2.7
2.60 2.12 2.64 2.78 2.70 2.18
l0:l 33:6 52.0
2.80 2:i4
2:fO 2.32
I, Per cent of total possible ester.
TABLE 11. RATSOF ETHYL LACTATE ESTERIFICATION
a
% Esterificationa
Time, Hr.
A
0.5 1.0 5.0 24.0 30.0 48.0
1.7 2.8 3.0 3.0 2.6 2.6
c .
5.3 9.6 10.5 10.0 10.4 10.0
E
F
13.4 22.8 33.4 33.6 33.6 33.6
17.0 26.6 49.2 52.0 51.8 62.2
Per cent of total possible ester.
dichloroethane, but the former aho dissolves more alcohol and acid. Furthermore, the boiling point of the former is too high and too close to that of ethyl lactate to be used most effectively. 1,1,2-Trichloroethane could perhaps be used to advantage. Isopropyl ether and 0- and p-dichlorobenzenes were also tried, but their selective solvent action was insufficient. Figure 2. ESTERIFICATION AND EXTRACTION PROCEDURES
A 1-liter distilling flask was connected through a condenser to
a 2- or 5-liter three-necked flask. Reflux condensers were used in' the latter, and a glass tube ran from the bottom of it to the top of the distilling flask. The esterification was carried out in the threenecked flask with 1,2dichloroethane as the solvent. The solvent was transferred to the distilling flask a t intervals by the use of suction, and the solvent, alcohol, and water distilled back into the esterification flask. The ester is thus obtained in anhydrous form, The esterification mixture was allowed to run overnight before the first extraction was made, and the following day the extractions were carried out a t 30- t o 60-minute intervals. A long period of heating a t the start was used to obtain an initial equilibrium mixture, Since all the ester was not extracted, subsequent maximum ester concentrations were reached in shorter periods, especially as the lactic acid concentration decreased (Figure 2). The 30- to 60-minute interval was estimated to give sufficient esterification to make extraction prefitable. A more detailed investigation of the optimum intervals for extraction is desirable. When a number of extractions had been made, the anhydrous extract was transferred to the distilling flask of a Podbielniak column, from which the ester was distilled under reduced pressure.
Rate of Ethyl Lactate Esterification
A typical experiment is as follows: 345 grams of 11.24% lactic acid, 317.4grams of absolute ethyl alcohol, and 337.6 grams of water (mole ratio 1:16:83) were used as the esterification mixture. This corresponds to starting with a 5.7% lactic acid solution. Two ml. of hydrochloric acid were added as the catalyst, and 250 ml. of dichloroethane as the solvent. The reflux temperature of the mixture is 69' C., which is the boiling point of the ternary constant boiling mixture, ethyl alcohol-dichloroethane-water. After twelve extractions, 15.6 grams of ethyl lactate were recovered following distillation (30.6% yield). I n another experiment using only 200 ml. of dichloroethane, twelve extractions gave a 24.4% recovery of ethyl lactate. An additional twelve extractions brought the yield t o 45.2%, and the third set of twelve extractions increased the yield to 59.6%. A more concentrated solution of lactic acid can perhaps be used to advantage. PROPYL LACTATE. An experiment was run using crude fermentation lactic acid, with a mole ratio of lactic acid t o propyl alcohol to water of 1:10:89. This is equivalent to starting with a 5.3% solution of lactic acid by weight. For this 81.0 grams of 48.4% crude lactic acid, 262 grams of propyl alcohol, 657 grams of water, and 5 ml. of concentrated hydrochloric acid were used.
\
TABLE 111. EXTRACTION OF ESTER~FICATION INGREDIENTS5 MI. CHClz.CHCln (1.4911)0
Solvent layer Additional Ingredients, 6 MI. None Eahyl alcohol
before Addp. of Chlorinated solvent nD
At
ml.
At
1.3329 1.3381
Ethyllactate
1.3438
7.0
6.8
1.4649
Lactic acid
1.3452
5.3
5.0
1.4856
Ethylalcohol, ethyl laotate, lactic acid
1.3570
8.0
7.4
1.4591
(1.4107)''
(1.4368)"
6
Values in parentheses are for
ng
2 5 ' ~ 4.2 4.8
a%' 1.4913 1.4897
5 MI. CHzC1.CHzCl (1.4425)'
Aqueous layer n.D,
'
750 C . 4.5 5.1
(1.3595)a
+ 40 MI. HIO
difference from pure solvent,
x
Solvent layer
x
Volume* ml. At At 65' C. 25O C.
ng
104
nY
3:
1.3329 1.3373
-8
4.3 4.8
4.0 4.1
1.4421 1.4413
-262
1.3395
-43
6.6
6.0
1.4300
-56
1.3449
-3
4.2
4.0
1.4413
-320
1.3424
-146
6.2
5.9
1.4287
of the pure ingredients.
2,
104 0
Aqueous layer nD,
nD,
difference from value in column
+ 40 M1. H10 n D3
difference from pure solvent,
difference from value in column
x
104 -4 -12
2,
x
1.3330 1.3380
+1 -1
-125
1,3404
-34
-12
1.8453
+1
-138
1.3650
-20
104
,
I
January 1947
I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
1,2-Dichloroethane (250 ml.) was added as the solvent and the mixture refluxed a t 74' C. A total of thirty-six extractions a t 30to 60-minute intervals were made and a yield of 70.5% obtained after two rectifications (boiling point, 164.2" C.; nail1.4147). SUMMARY
The equilibrium constant for ethyl lactate esterification mixtures was found to be 2.71 * 0.06 a t the boiling point. Ethyl lactate may be preferentially dissolved from esterification mixtures by the use of chlorinated hydrocarbon solvents. Symmetrical di- and tetrachloroethanes were found to serve this purpose, but the latter cannot be used satisfactorily b.ecause its boiling point is too near that of ethyl lactate. By a method of continuous esterification and intermittent extraction with 1,2-dichloroethane, it was found that the lactic acid may be recovered as ethyl or propyl lactate from solutions containing as little as 5.3% lactic acid. LITERATURE CITED
(1) Berger, G.,Rec. ~ T Uchim., V . 43,163 (1924). (2) Filachione, E.M., and Fisher, c. H., IND.ENG.C H E M . , 38,228 (1946).
85
Garrett, J. F., Ibid., 22, 1153 (1930). Palomaa, M. H.,Ann. Acud. Sci. Fennicue ( A ) ,4 , 1-104 (1913); Chern. Zentr., 1913,11, 1956. Peckham, G.T.,Jr., Chem. Eng. News, 22,440(1944). Rehberg, C.E.,Faucette, W. A,, and Fisher, C . H., IND. ENQ. CHEM.,36, 469 (1944). Rozhdestvenskii, A. A., Trans. T7I Mendeleev congr. TheoTet. Applied Chern., 1.932,2,Pt. 2. 166 (1935). Schopmeyer, H. H.,and Arnold, C . R. (to American MaizeProducts Co.), U.9. Patent 2,350,370(June 6, 1944). Smith, L. T.,and Claborn, H. V.,
[email protected].,NEWSED., 17, 641 (1939). SOC. anon des distilleries des Deux-Shes, French Patent 711,175 (May 16,1930). Weisberg, 8. M., and Stimpson, E. G . (to Sealtest, Inc.), U.S. Patent 2,290,926(July 28,1942). Wenker, H.(to Apex Chemical Go., Inc.), Ibid., 2,334,524(Nov. 16, 1943).
Williams, R. S., Gabriel, A,, and Andrew, R. C., J. Am. Chem. SOC.,50, 1267 (1928). ABSTRACTED from a portion of a thesis submitted by A. A. Dietz t o the faoulty of Purdue University in partial fulfillment of the requirements for the degree of doctor of philosophy. This work was sponsored by t h e American Maize-Products Company.
Extending Phenolic Resin Plywood Glues with Proteinaceous Materials GLEN E. BABCOCB AND ALLmT K. SMITH Northern Regional Research Laboratory, U. S . Department of Agriculture, Peoria, 111. F o r the first time data are presented showing that vegetable proteinaceous materials, such as corn gluten and soybean meal, can be used in substantial amounts as extenders for phenolic resin plywood glues. To attain the best results in this combination, it is necessary to use a resin of low molecular weight and proteinaceous materials low in water-soluble constituents. Formulas containing resin and protein materials in the ratio of 6:4 give rapidcuring glue lines which meet the established standards for exterior-grade plywood with a considerable saving in glue cost.
P
REVIOUS investigations on modifying phenolicplasticswith soybean meal performed at this laboratory ( I ) led to the suggestion that soybean meal or other proteinaceous materials could be used to extend phenolic resin plywood glues. The addition of substantial amounts of inexpensive proteinaceous materials to phenolic resin would materially lower the glue cost and broaden the field of usefulness of plywood, provided no substantial loss resulted in glue quality and handling properties. The proteinaceous materials are a Combination primarily of proteins and insoluble carbohydrates. The proteins are excellent glue materials in themselves, and the carbohydrates can function as a filler material to substitute for the commonly used walnut-shell flour. Earlier work with plastics ( 1 ) demonstrated that the incorporation of 30 to 40% resin in a molding powder was sufficient to give excellent water resistance to the resulting plastic product; this suggested that an extension of the plywood resin could be effected without serious loss in plywood quality. Preliminary experiments in which glued joints were prepared, using mechanical mixtures of commercial phenolic resin plywood glues and soybean meal, gave very poor bonding properties. An examination of the results indicated that the failure was due to insufficient plastic flow of the glue, which resulted in poor contact between the glue and the veneer. These preliminary results
showed that the preparation of a successful combination of proteinaceous material and resin appeared to depend primarily on securing high plastic flow properties in the glue without, at the same time, producing starved joints. Several methods are available for improving the flow properties of a combination of resin and protein mixtures: (a) addition of a plasticizer, ( 6 ) modification of the protein by hydrolytic treatment, ( c ) use of a resin of low molecular weight, and ( d ) a combination of the suggested methods. Although some work was done toward increasing the flow of soybean meal by hydrolytic treatment, it was found that the third method, the use of low molecular weight resin, was essential to the process and was the best method of attaining the desired flow properties. I n addition to describing the proper type of resins for use in combination with protein materials for making plywood glues, the present paper presents information on the characteristics of corn gluten, soybean meal, and linseed meal which are important in their glue formulation, the proper conditions for using the glue, and test results for both hard and soft woods. PREPARATION OF RESIN
Since the preliminary studies had indicated that the available commercial plywood resins would be unsuitable for combination with proteinaceous materials, the problem resolved itself into the preparation of the correct type of phenolic resin. The studies on resin preparation which followed eventually led to two. general formulations of low molecular weight products which may be further characterized by their phenol and formaldehyde ratios. Resin 1 contains phenol and formaldehyde in the mole ratios 1:1.5, with 6 grams of sodium hydroxide per mole of phenol as catalyst. Resin 2 contains phenol and formaldehyde in the ratio 1:2.5, with 9 grams of sodium hydroxide per mole of phenol as catalyst. Resin 2 is the more rapid-curing resin, and its curing rate is further increased by the use of ammonia as an acceler-
