330
Ind. Eng. Chem. Prod. Res. Dev.
V.
Symposium on World-Wide Progress of the Petro, Organic, and Polymer Chemical Industries N. Platzer and S. Inoue, Chairmen ACSKSJ Chemical Congress, Honolulu, Hawaii, April 1979 (Continued from December 1979 issue)
Hydrocarboxymethylation-an Acid Esters?
1980, 19, 330-334
Attractive Route from Olefins to Fatty
Peter Hofmann, Kurt Kosswig, and Wolfgang Schaefer Chernische Werke Huls Aktiengesellschaft, Zentralbereich Forschung und Entwicklung, 0-4370 Marl, West Germany
Three hundred combinations of nonnoble metals of group 8A and halogen-free promotors were examined as catalysts for the hydrocarboxymethylation. Using the apparent optimal catalyst system cobaWpyridine or y-picoline and a-octene and a mixture of isomeric internal ndodecenes a s olefins, the influence of various reaction parameters on hydrocarboxymethylation was examined. We have found that for both types of olefins under optimal reaction conditions fatty acid esters of high linearity (175%) can be obtained with space-time yields between 300 and 500 g/L.h and selectivities of 195% . A comparison between hydrocarboxymethylation and two different hydroformylation processes shows that hydrocarboxymethylation can be an economic alternative to the conventional route to fatty alcohols and acids.
Introduction While tallow and palm oil provide an adequate low-cost natural base for soaps chiefly consisting of the salts of C16 and C18fatty acids, the natural base for detergent alcohols is insufficient. Coconut oil and palm-kernel oil are practically the only natural raw materials for detergent alcohols in the C12-C15range which are in the greatest demand. Since the annual production of 2.7 million tons of coconut oil and 0.5 million tons of palm-kernel oil (1977) mainly goes to the food industry, other raw materials must be used for the production of detergent alcohols. Of the fatty alcohol world capacity of 861 000 tonslyear, only 25% is based on natural materials (Table I). By 1990, fatty alcohol production is forecast to reach 1.6 million tons/year (Haupt and Schwin, 1978) and it seems doubtful whether the present percentage can be maintained. T o provide a secure basis for fatty alcohols in the future, petrochemical raw materials-despite rising oil prices-cannot be abandoned. Today, ethylene and paraffins form the exclusive raw material basis for the production of synthetic fatty alcohols. In comparison to the K. Ziegler Alfol synthesis and to the hydrogenation of synthetic fatty acid esters obtained by paraffin oxidation (mainly practiced in the East bloc countries) which can only be carried out on the basis of one particular raw material, production of fatty type alcohols by hydroformylation is more flexible regarding feedstock. The olefins of the detergent range required for hydroformylation can be obtained from ethylene as well as from paraffins (a-olefins can be produced by poly-reaction from ethylene according to K. Ziegler and by pyrolysis of wax; olefins with internal double bonds are available by dehydrogenation or by partial chlorination and 0196-4321/80/1219-0330$01 .OO/O
subsequent dehydrochlorination of paraffins). While today more than 50% of the synthetic fatty alcohols are produced by conventional cobalt-catalyzed hydroformylation or by the cobalt/ phosphine-catalyzed Shell oxo process, another carbonylation process, namely hydrocarboximethylation, which is closely related to hydroformylation, has to this date not been used for the production of fatty alcohols. olefin + CO + CH30H fatty acid methyl ester (hydrocarboxymethylation) --+
fatty acid methyl ester
+ H2
-
fatty alcohol (hydrogenation) This process variant leading from olefins via fatty acid methyl esters to fatty alcohols should not have been neglected. The raw material bases for hydroformylation and hydrocarboxymethylation are identical. Moreover, the fatty acid methyl esters obtained by hydrocarboxymethylation are versatile and therefore attractive intermediate products. This has induced us to reconsider this reaction which was discovered by Reppe in the laboratories of BASF as early as 1938-1945. Experimental Part Experiments to examine the effectiveness of various catalyst systems were carried out in a 2-L stainless steel autoclave at 170 "C and a carbon monoxide pressure of 130 bar. The carbon monoxide contained 3% by volume of hydrogen; 4 mol of methanol, 0.015 g-atom of catalyst metal in the form of fatty acid salts or the respective carbonyls, and 0.55 mol of promotor were used in relation to 1 mol of olefin. 1980 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 3, 1980 331 Table I. World Capacity of Fatty Type Alcohols > C,, in 1978
USA West Europe Japan other countries
cap. of natural fatty alc., tons
total cap.
cap. of synth. fatty alc., tons
total cap.
total cap. of natural and synth. fatty alc., tons
57.000 100.000 27.000 30.000
15 39 24 29
330.000 158.000 85.000 74.000
85 61 76 71
387.000 258.000 112.000 104.000
214.000
25
64 7.000
75
861.000
% of
Experiments to examine the influence of the reaction conditions on space-time yield, selectivity, and linearity of the cobalt-catalyzed hydrocarboxymethylation were carried out in a 5-L stainless steel autoclave equipped with an agitator and with temperature and pressure controls. In order to be able to determine the exact starting point of the reaction, CO and Hzwere not pressured until the reaction temperature had been reached. Since the active catalyst species was prepared in situ, the reaction did not begin until after an induction period of approximately 0.5 h. (For the graphic evaluation of the experiments, this induction period was not included.) The reaction conditions of the various experiments are shown in the respective diagrams. Samples taken by means of a steel capillary tube during the reaction at intervals of between 10 min and 1h were analyzed by gas-liquid chromatography in the presence of an internal standard to determine conversion rate and distribution of products. When using a-olefins, the degree of isomerization of the unreacted olefin was determined by 'H NMR spectroscopy. The chemicals used were of commercial quality. The mixture of isomeric linear dodecenes which served as an example for olefins with an internal double bond was obtained from a-dodecene by isomerization with a Na/AlZ0, catalyst at 110 "C and contained less than 1%a-dodecene. All other isomers were present according to the thermodynamic equilibrium.
Experimental Results and Discussion Selection of Catalyst. As in the case of hydroformylation, hydrocarboxymethylation is catalyzed by metals of group 8A (Reppe, 1949, 1953; Bird, 1962; Falbe, 1967; Knifton, 1976, 1978) and can in the same way be greatly influenced by catalyst ligands. We felt that it was not only our task to select an effective catalyst; in accordance with the raw material situation referred to at the beginning, such a catalyst should also be able to produce chiefly linear products irrespective of the position of the double bond in the olefin. From the start, noble metals were excluded from our investigation in order to avoid the inevitable problems of quantitative catalyst recycling. As ligands, exclusively halogen-free compounds were used in order to eliminate any corrosion problems. Included in the promotor screening were 130 compounds containing N, P, As, Sb, 0, and S which were tested together with iron, cobalt, and nickel salts as well as with the three possible binary combinations of these metals in 300 autoclave runs under standardized conditions. Of the great number of catalystlligand combinations only cobalt/pyridine and nonortho-substituted pyridine derivatives, such as 4-picoline, met the aformentioned requirement (Matsuda, 1965; Seide, 1969). In 1951, BASF (v. Kutepow and Bille, 1951) in Germany and in 1966 Shell (Hearne et al., 1966) in the USA obtained patents on these catalyst systems. The reason for the unique effect of pyridine as a promotor has not been investigated experimentally and we should like to abstain
-
1
-
% of
1
-
2
1
3
L
r e a c ~ # '8rie c~
;hrl
Figure 1. Conversion rate as a function of reaction time for different molar ratios of pyridine/cobalt. spcce-tlme y i e l d Ig~am/l~terxhoLrl
1-octene methono!
mol
pressure, CO pressure, H2
0.015 150 atm 2.5 "
temperalure
1EC
CO-so!l
I
1
1
OC
I
20
LO
6C
80 '00 mami rat o p y r i C o
Figure 2. Space-time yield as a function of the molar ratio of pyridine/cobalt for different conversion rates.
from making any speculations in this respect. Influence of Reaction Conditions on Space-Time Yield, Selectivity, and Linearity of Hydrocarboxymethylation. After selection of the catalyst the following parameters were examined: (1) space-time yield (conversion); (2) selectivity (side reactions); (3) linearity (nliso ratio of resulting fatty acid methyl esters) as a function of: (a) molar ratio of pyridine/cobalt or 4-picoline/cobalt, (b) cobalt concentration, (c) reaction temperature, (d) carbon monoxide pressure, (e) partial pressure of hydrogen, (0 methanol concentration, and (g) mass transfer (agitation speed). 1-Octene served as a model olefin for a-olefins and a mixture of all possible double bond isomeric linear dodecenes with an a-portion under 1% as a model for internal olefins. Influence of Ligand/Cobalt Molar Ratio. The variations of the ligand/catalyst molar ratio may serve as an example for the systematic experimental method employed
332 Ind. Eng. Chem. Prod. Res. Dev., Vol. 19, No. 3, 1980 100
w n v e r s i o n rate ,
100,
z
-
YO
/ I
1
A
L
1
98
j
. 96-
'
~
LO'
I()'(''
- aldehydes
11'1
__
pyr I C 0
/
u n i d e n t i f i e d products
molar rat o
I n t e r n a l octenes
u
,
20 acetals
acld esters
.c
i A
80.
-
molar ratlo pyr IC0
1
acld e s t e r s
901
I
i
-pyr IC0 L 0
4
35
15
70
100
Figure 3. Selectivity of the formation of pelargonic acid methyl esters from l-octene as a function of the molar ratio pyridine/cobalt (conversion rate: 60%).
c-c-c-c-e-c -e-c
C-C-C-C-C-C-C-C-COOCH3
I
L------I 80 00 _ L
20
l-octene
LO
-
60
60
1
molar i n t e r n a l octenes pyrlCo
I
Figure 5. Formation of esters and isomerization of l-octene for different molar ratios of pyridine/cobalt.
c-c-c-c-c-c-c-c
60
80
,
3
molar ratlo pyrICo
Figure 4. Yield of linear and branched pelargonic acid methyl esters as a function of the molar ratio pyridine/cobalt (conversion rate: 60%).
by us. On the basis of the gas chromatographic analysis of the samples taken during the reaction, conversion curves were plotted. They are shown in Figure 1 for the pyridine/cobalt molar ratios 0,15,35,70, and 100 with respect to l-octene. Accordingly, the optimum reactivity occurs at a molar ratio of pyridine/cobalt of approximately 15 to 35. With increasing conversion the curves level off; in other words, the space-time yields decrease. In Figure 2, the space-time yields are plotted against the pyridine/cobalt ratio for various conversion rates. The curves run through a maximum at a molar ratio of pyridine/cobalt of 30-35. From the selectivity curve shown in Figure 3 it appears that above a pyridine/cobalt ratio of 35 the total amount of byproducts (viz., octane, acetals, aldehydes, high-boiling and unidentified products) decreases from 12 70to approximately 2%. The percentage of byproducts remains
constant at approximately 2% even if three times the amount of pyridine is added. An analysis of the isomeric esters (Figure 4) shows that primarily linear reaction products are formed and that there is no appreciable change in this respect above a pyridine/cobalt ratio of approximately 35. The pyridine-complexed hydridocobalt carbonyl is, therefore, in most cases forced to add to the terminal double bond analogous to an anti-Markovnikov addition and the tendency toward such an addition rises with increasing pyridine concentration. From Figure 5, a further reason for the increase in linearity with increasing pyridine concentration becomes evident. Pyridine suppresses the (l-octene) double bond isomerization which takes place parallel to the hydrocarboxymethylation. In the absence of pyridine, the entire l-octene is isomerized to internal octenes at a conversion rate to esters of approximately 12%. At a pyridine/cobalt ratio of 35, isomerization will not be completed until a conversion rate of 75% has been reached, and a t a still higher pyridine concentration, isomerizatin is practically completely supressed. Figure 6 shows space-time yield, selectivity, and linearity as a function of the ligand/cobalt molar ratio: at a pyridine/cobalt ratio of 35 the space-time yield runs through a maximum of approximately 420 g of ester/L.h. At this ratio, maximum values are obtained also for the selectivity with approximately 98% and the linearity of the ester with approximately 85%; contrary to the space-time yield, these values are maintained at higher pyridine concentrations. In Figure 6, the results for l-octene as representative of a-olefins are compared with those for olefins with internal double bonds. It appears that even in the case of dodecene with almost exclusively internal double bonds mainly linear products are formed at a yield of 75%. This can only be understood if apart from the tendency toward an anti-
Ind. Eng. Chem. Prod. Res. m i dodecene
1 mol
methanol
2 mol 0 OL mol 180 aim 2 . 5 atm !70 O C
Co-salt press press
CO
ti2
temp
Dev., Vol. 19, No. 3, 1980 333
TEMPERATURE I
f i fi I-
H2 PRESSURE
~
,,'--,,
\O IN'L'JEhCE
N3 'hFLLENCE
80; 75' 95-98; 95" methyl ester
CY-;
F o r internal olefins.
with respect to linearity show characteristic differences. This illustrates the different significance of olefin isomerization for the formation of linear products from CY- and internal olefins. Comparison between Conventional Hydroformylation, the Shell Oxo Process and Hydrocarboxymethylation. Figure 8 shows the flow scheme of a plant for the production of esters according to the hydrocarboxymethylation process. The mode of the reaction and the catalyst cycle do not differ fundamentally from other oxo processes. As compared with competitive processes, the presence of methanol as a reactant as well as larger quantities of a promotor requires, however, larger distillation facilities. A comparison (Table 11) between the results obtained for hydrocarboxylation and hydroformylation shows that the process investigated by us may be an alternative to conventional oxo processes. The linearity of the products obtained by hydrocarboxymethylation is approximately on a level with that of the modified oxo process and thus exceeds the values of conventional oxo processes. While the selectivity obtained in hydroformylation processes does not exceed 85% due to the formation of high-boiling products and/or paraffin, 95% are attained by hydrocarboxymethylation. Unlike aldehydes, the esters obtained by hydrocarboxymethylation are almost inert under reaction conditions and do, therefore, not tend to form byproducts. Only minimal quantities of hydrogenation products such as aldehydes or paraffins are produced since carbon monoxide almost completely free from hydrogen is used. Contrary to conventional hydroformylation solely employing cobalt catalyst, the use of promotors in the two other processes entails a decrease in reactivity. For the same output, larger reactors are, therefore, required. Moreover, the increase in linearity achieved by the use of promotors must be paid for by the disadvantage of having
to recover the promotors. The use of methanol and high-purity CO favoring selectivity requires, as mentioned earlier, larger distillation facilities and an additional CO plant. For this, technical processes are available, such as the gas low-temperature separation, the pressure swing process (molecular sieve process), or the COSORB process. While pressure and temperature conditions during hydrocarboxymethylation are comparable to those of the conventional oxo synthesis, the modified oxo process can be operated at a lower pressure. An essential advantage of hydrocarboxymethylation is the fact that it combines the flexibility of the modified oxo process with respect to olefin feedstock and of the conventional oxo process with respect to the primary reaction product. Irrespective of the olefin used, a product of high linearity is obtained, as in the case of the Shell hydroformylation process, which can further be processed into fatty acids, fatty alcohols, or other secondary products similar to the conventional oxo process.
Literature Cited Bird, C. W., Chem. Rev., 62, 283 (1962). Falbe, J., "Synthesen mit Kohienmonoxid", Springer-Veriag, Berlin, 1967. 55, 28 (1978). Haupt, D. E., Schwin, P. B., J. Am. Oil. Chem. SOC., Hearne, G. W., Furman, K. E., Rupert, C. M., Van Winkle, J. L., (to Shell 011 Co.), U S . Patent 3 5 0 7 8 9 1 (Apr 21, 1970). Knifton, J. F., J . Org. Chem., 41, 793 (1976). Knifton, J. F., J . Org. Chem., 41, 2885 (1976). Knifton, J. F., J . Am. 01 Chem. Soc.. 55, 496 (1978). v. Kutepow, N., Bille, H., (to BASF), German Patent 921 988 (Apr 28, 1951). Matsuda, A,, Uchida, H., Bull. Chem. SOC. Jpn., 38, 710 (1965). Reppe, W., "Neue Entwickiungen auf dem Gebiet der Chemie des Acetylens und Kohlenoxids", Springer-Verlag, Berlin, 1949. Reppe, W., Justus Liebigs Ann. Chem., 582, 1 (1953). Selde, W., Thesis, Rheinisch-Westfalische Technische Hochschule Aachen, 1969.
Receiued for review April 10, 1979 Resubmitted March 5, 1980 Presented a t the ACS/CSJ Chemical Congress, Honolulu, Hawaii, April 14,1979, Division of Industrial and Engineering Chemistry.
