CATALYTIC SYNTHESIS OF LACTIC ACID FROM ACETALDEHYDE, CARBON MONOXIDE, AND WATER S .
K .
BHATTACHARYYA, 5 .
K .
PALIT, A N D A.
R .
DAS'
Department of Applied Chemistry, Indian Institute of Technology, Kharagpur, India High pressure synthesis of lactic acid from acetaldehyde, carbon monoxide, and water was attempted in the presence of various iron( II), cobalt( II), and nickel( II) iodides supported on silica gel catalysts (metal to Si02 = 50 to 50). With the nickel(l1) iodide supported on silica gel ( t h e catalyst exhibiting the highest activity), a maximum conversion of 44.4% of acetaldehyde to lactic acid was obtained under the optimum experimental conditions of 23OoC., 5 100 p.s.i.g., 3 hours of residence period, and a mole ratio of CO:CH3CHO:H20 = 2:0.124:0.72.
LACTIC acid,
which has various important industrial applications, is manufactured by the bacterial fermentation of starch or other agricultural products. Because of shortage of agricultural commodities in some parts of the world, attempts are being made to discover methods for its manufacture from other raw materials. One such method of synthesis of aliphatic hydroxy acids (Loder, 1941) involves the use of an aldehyde, carbon monoxide, and water as reactants under pressure. Recently a thorough investigation was carried out on the synthesis of glycollic acid from formaldehyde, carbon monoxide, and water under pressure in the presence of various catalysts (Bhattacharyya and Vir, 1967). In view of the promising results obtained, the present work on the synthesis of lactic acid from acetaldehyde, carbon monoxide, and water under pressure was undertaken. I n our investigations, selected salts of iron(II), cobalt(II), and nickel(I1) supported on silica gel, at a metal to silica ratio of 50 to 50 (w./w.), were used as catalysts. This particular metalsilica ratio was observed by Bhattacharyya and Lahiri (1963) to have optimum activity in other similar synthetic reactions under pressure. Thermodynamics of Reaction
The thermodynamic feasibility of Reaction 1 and the influence of temperature on the equilibrium constant were calculated (Table I ) .
Table I . Variation in Values of Equilibrium Constant with Change in Temperature Temp
,
100 150 210 230 250 300
C
K,(at 1 Atm ) 2.4 x 3.1 x 1.5 x 1.9 x 8.4 x 7.1 x
10 10
lo-' 10 10 * lo-'
Present address, Department of Chemistry, State University of New York at Stony Brook, N. Y. 11790
92
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9,No. 1, March 1970
CH3CHO (g)
+ H20 (g) + CO
(g) =
C H , C H ( O H ) C O O H (g)
(1)
Some of the thermochemical data, such as entropy of lactic acid and the values of virial coefficients in specific heat expressions, were not available in the literature, and were calculated by the group contribution methods of Watson et al., (Hougen et al. 1954). Experimental
A high pressure rocking autoclave (designed and fabricated a t our workshop) of 270-ml. capacity at 25°C. and 1 atm. of pressure with an angular play of 15" and 45 oscillations per minute, was used. Pressure valves were supplied by Aminco. The experiments were carried out under shaking conditions, because while taking trial runs it was found that the yields in the rocking autoclaves were better than in the static autoclaves. A calculated amount of carbon monoxide gas was fed in, until the desired gage pressure was attained. The operating pressure was built up by inert nitrogen gas from a cylinder of nitrogen a t high pressure. The temperature was gradually raised and maintained a t a desired value as recorded by a calibrated millivoltmeter. With the increase of temperature, the pressure of the gas increased gradually and attained a maximum value, described here as the operating pressure of the reaction. The product release assembly and other experimental setup were similar to those described by Bhattacharyya and Vir (1959). Reactants used were distilled water and extra pure grade acetaldehyde, redistilled and assayed as 99.8%. Very pure carbon monoxide as prepared by Bhattacharyya and Sen (1964) in the laboratory was used. The catalysts used were salts of iron(II), cobalt(II), and nickel(I1) supported on silica gel. The catalysts had a metal-silica ratio of 50 to 50. The methods of preparing silica gel and most of these catalysts have been discussed by Bhattacharyya (1961, 1963). NICKEL(II)SULFIDE CATALYST. Nickel(I1) sulfide was precipitated with hydrogen sulfide, from an ammoniacal solution of nickel(I1) nitrate, then washed with water
and carbon disulfide. Pure nickel(I1) sulfide, so obtained, was impregnated with silica gel and dried a t 60' C. COPPER(I) IODIDE-MANGANESE (11) IODIDE BINARY CATALYST. Copper(1) iodide was prepared by adding alkali iodide solution to copper(I1) sulfate solution. A green precipitate of copper(1 [) iodide decomposed into brownish gray cuprous(1) iodide a t room temperature (30" C.). Copper(1) iodide so prepared was mixed with pure manganese(I1) iodide, and later impregnated with silica gel. Manganese( 11) iodide was prepared by dissolving manganese(I1) carbonate in hydriodic acid.
Lactic acid, along with the unreacted acetaldehyde and water, and traces of formic acid (in a few cases only), were identified in the liquid product. The presence of these compounds and the absence of any other acid or ester were confirmed by usual analytical tests, the preparation of suitable derivatives, and paper and gas chromatography. The lactic acid was optically inactive. I t was determined by simple alkalimetry. The gaseous product consisted of unreacted carbon monoxide, carbon dioxide, methane, and hydrogen. The gaseous mixture was analyzed with a standard Orsat gas analyzer. Results and Discussion
The catalysts tried varied widely in their activity (Table 11). The gaseous products were formed as a result of the decomposition of carbon monoxide, acetaldehyde, and lactic acid, as is evident from the decomposition studies discussed below. Catalysts favoring the main reaction of acid formation also favored decomposition (not recorded in the table). As nickel(I1) iodide supported on silica gel (Ki:SiO?, 50 to 50) exhibited the highest activity among all catalysts in this study, it was thought worthwhile to study the influence of the different operational parameters on the yield of lactic acid to find the optimum conditions for the highest yield of acid with this catalyst (Figures 1 to 5). I n these studies, other variables were kept constant. Influence of Temperaiture. The yield of lactic acid was maximum a t 230°C. (Figure 1). The yield of carbon dioxide increased steadily with temperature, whereas yields Table 11. Activity of Catalysts 2
0.124 0.72
0
a
crl
>
Z
0 0
bc
5:z
I
w
0 J
4
bli U
Analysis of Products
Moles of carbon. monoxide. Moles of acetaldehyde Moles ~i water
z Q
3 hr. 5100 p.s.i.g. 230" C. 12-13 grams
Residence period. Reaction pressure. Reaction temperature. Catalyst weight.
of
Cataijsts Hydriodic acid on silica gel Nickel bromide on silica gel (Ni:SiOL= 50:50) Nickel iodide on silica gel (Ni:SiO>= 50:50) Cobalt iodide on silica gel (Co:Si02= 50:50) Iron iodide on silica gel (Fe:SiO>= 50:50) Nickel acetate on silica gel(Si:SiO?= 50:50) Nickel phosphate on silica gel(Ni:SiO? = 50:50) Nickel sulfide on silica gel(Ni:Si02= 50:50) Cobalt naphthenate on silica gel(Co:Si02= 50:503 Copper iodide and manganese iodide on silica gel (Cu + Mn:SiO, = 50,501
Comerston Aceta1deh)de to Lact1c AcLd, '( 7.79 18.33 44.36 18.33 20.69 32.36 14.33 7.59 9.63 22.71
4
I
190
I
210
230
250 TEMP.
270
OC
Figure 1 . Influence of temperature on conversion of acetaldehyde to lactic acid Nickel(l1) iodide (84.16%). silica gel( 15.84%) catalyst(Ni:SiO? = 5060) A Cobalt (11) iodide(84.1 Yo), silica gel( 15.9%) catalyst(CO:Si02 = 5060) 0 Iron(ll) iodide (84.7%), silica gel(l5.3Yo) catalyst(Fe:SiO2 = 5030) Operational conditions Pressure range. 4800 to 5600 p.s.i. Catalyst. 10 ml. (approx. 13 grams) Moles of reactant Co. 2.0 Acetaldehyde. 0.177 Residence period. 3 hours Water. 0.56 X
of methane and hydrogen were not much affected in the temperature range studied. Influence of Pressure. The pressure was gradually increased with gaseous nitrogen, keeping the mole ratio of the reactants fixed a t CO:CH3CHO:H20::2:0.124:0.72, temperature a t 230" C., and residence period a t 3 hours. Process conversion of input acetaldehyde to lactic acid increased with increasing pressure (Figure 2 ) , and decreased after reaching the optimum pressure of 5100 p.s.i.g. The formation of carbon dioxide increased a t higher pressures (not shown in the figure). Influence of Residence Period. Though 3 hours of residence period was optimum, variations had little influence on the yield of acid (Figure 3). However, increase in residence period resulted in increase of gaseous products. Influence of Mole Ratio of Reactants. Keeping the input amount of carbon monoxide fixed a t 2 moles! the mole ratio of water to acetaldehyde was varied (Figure 4 ) . The optimum mole ratio, in all cases, was carbon monoxide to acetaldehyde to water, 2:0.124:0.72, corresponding to approximately 15 mole 5 of acetaldehyde in the input aldehyde water mixture. With the increase of mole per cent of water in the mixture, the yield of hydrogen increased (not shown in the figure). Influence of Amount of Catalyst. As seen in Figure 5, the ratio of catalyst had a definite effect on the yield of acid in the case of the nickel(I1) catalyst, whereas with others the effect was not prominent. This is probably due to the increasing amount of water, one of the reactants, taking part in the reaction. This water comes from the catalyst itself, since the catalyst, made of silica gel and aqueous nickel salt solution, contains water (about 40'; by weight). The catalyst is particularly interesting in Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 1, March 1970
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30-
I
20
-
10
-
I
0
I
2000
')OM)
4000
60M
5000
PRESSURE.
I
I
1
I
I
IO
20
30
40
50
ACETALDEHYDE MOLE
"/.
IN THE A C E T A L D E H Y D E
WATER M I X T U R E
LBS/INC"L
Figure 2. Influence of pressure on conversion of acetaldehyde to lactic acid
Figure 4. Influence of mole ratio on conversion of acetaldehyde to lactic acid
Legends same as Figure 1 Temperature. 230" C. Moles of CO:CH3CHO:H?O. 2.0:0.124:0.72 Other conditions same as Figure 1
Legends same os Figure 1 Residence period. 3 hours Moles of CO. 2.0 Other conditions same as Figure 3
9
< 3
2
1 5
5
4
R E S I D E N C E PERIOD, HR.
I
I
I
I
K)
15
20
25
CATALYST V O L U M E
Figure 3. Influence of residence period on conversion of acetaldehyde to lactic acid
I
ML
Figure 5 . Influence of amount of catalyst on conversion of acetaldehyde to lactic acid Legends same as Figure 1 Pressure. 5100 p.s.i. Other conditions same os Figure 1
Legends same as Figure 1 Pressure. 5100 p.s.i. Temperature. 230" C. Other conditions same as Figure 1
Table 111. Influence of Temperature on Decomposition of Acetaldehyde and lactic Acid under Pressure Catalyst. 13 grams of nickel(I1) iodide (84.16%) supported on silica gel (15.84'2) (Ki:SiO, = 50:50) Residence period. 3 hours. Pressure built up by nitrogen gas. Substance Undergoing Decomposition
Initial Pressure, P S . I .
Acetaldehyde
3000
Lactic acid
94
3000
Temp., C.
Final Pressure, P.S.I.
200 230 250
5500 5700 6000
200 230 250
5200 5500 5700
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 1, March 1970
$1 Conversion
co
CH,
H2
8.6 18.3
2.20 3.7 4.6
9.4 21.8 23.8
Trace Trace Trace
14.5 15.9 25.0
5.4 3.9 3.2
7.0 12.5 16.6
Trace Trace Trace
CO2 1.82
this respect, because the increase of the direct ratio of water in the reactants did not favor the higher yield of lactic acid. Considering the formation of carbon dioxide, methane, and hydrogen, use of 10 ml. (13 grams, as 1 ml. weighed 1.3 grams) of the catalyst seemed to be optimum. Studies on Decomposition
The decomposition of acetaldehyde a t 200” to 300” C. and a pressure of about 5000 p.s.i.g. to methane and carbon monoxide is a well recognized phenomenon (Hinshelwood and Hutchison, 1926). Bhattacharyya and Sourirajan (1959) studied the decomposition of carbon monoxide under temperature and pressure in the presence of nickel(I1) iodide supported on silica gel. Fisher and Filachione (1950) earlib observed that the decomposition products of lactic acid are actaldehyde, carbon monoxide, and water. Our decomposition studies on acetaldehyde and lactic acid revealed the formation of carbon dioxide, carbon monoxide, and methane (Table 111). I n all cases, nitrogen was used to build up pressure.
Bhattacharyya, S. K., “Physics and Chemistry of High Pressures,” Proceedings of symposium a t Olympia, London, 1962, p. 202, Society of Chemical Industry, London, 1963. Bhattacharyya, S. K., Lahiri, C. R., J . A p p l . Chem. (London) 13, 544 (1963). Bhattacharyya, S. K., Sen, A. K., IND.ENG.CHEM.PROCESS DESIGNDEVELOP. 3, 169 (1964). Bhattacharyya, S. K., Sourirajan, S., J . A p p l . Chem. (London) 9, 126 (1959). Bhattacharyya, S. K., Vir, D., Aduan. Catalysis 9, 625 (1967). Bhattacharyya, S. K., Vir, D., I n d . Eng. Chem. 51, 139 (1959). Fisher, C. H., Filachione, E. M., U. S. Dept. Agr., Bur. Agr. Ind. Chem., AIc-279 (October 1950). Hinshelwood, C. N., Hutchison, W. K., Proc. Roy. Sac. A 111, 380 (1926). Hougen, 0. A., Watson, K. M., Ragatz, R . A., “Chemical Process Principles,” Part 11, 2nd ed., p. 1004, Wiley, New York, 1954. Loder, D. J., U. S. Patent 2,265,945 (1941).
Literature Cited
Bhattacharyya, S. K . , Actes de Deuxieme Congress, International Congress on Catalysis, Paris, 1960, Vol. 2, p. 2401, Editions Technip, Paris, 1961.
RECEIVED for review April 18, 1969 ACCEPTED September 3, 1969
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9,No. 1, March 1970
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