I
W. A. SKINNER and DALE TIESZEN Department of Chemistry, Stanford Research Institute, Menlo Park, Calif.
Production of Maleic Acid
. . . by
O x i d i z i n g Butenes
Higher yields were obtained in vapor phase air oxidation of butenes through
4 an improved catalyst system
v'
improved reaction conditions
N INCREASED DEMAND for maleic anhydride for use in polyester resins has led to the construction of many new plants for its manufacture in recent years. All of the maleic anhydride currently being produced in this country is manufactured either by the partial air oxidation of benzene in the vapor phase or as a by-product in phthalic anhydride synthesis via naphthalene oxidation. Approximately 90% of the maleic anhydride produced is from the benzene oxidation process. This process is carried out by contacting benzene vapors a t 400' to 450' C. with a vanadium pentoxide on alumina catalyst. T h e reactor effluent passes through heat exchangers and the products are absorbed in water which is evaporated, yielding maleic acid. This is dehydrated to afford maleic anhydride in yields of 50 to 60% of theory. This article reports studies of the vapor phase air oxidation of butenes over several catalyst systems in a fixed bed reactor. T h e catalyst system studied in detail was a phosphomolybdate catalyst on a silica gel support. Some mixed phosphomolybdate- p h o s p h o v a n a d a t e catalysts were also evaluated. Yields of maleic acid u p to 5 5 wt.% (27% of theory) based on the butene fed were achieved by developing a new catalyst system, variation of reaction con-
A
Background LiteratureMaleic Acid-Maleic Anhydride Production
Subject Production of maleic anhydride by vapor phase oxidation of crotonaldehyde Production of maleic acid-maleic anhydride by the vapor phase oxidation of butenes Analysis of maleic acid
Reference (1, 3,
4)
(6-7, 9, 10) (3, 8)
ditions, and the use of a rapid water quench of the hot exit gases. Experimental Reactor Design. T h e air oxidations were carried out in a 0.75-inch stainless steel annular tube reactor (below) over fixed bed catalysts. A butene (Phillips, 99 mole yo Z-butene)-air mixture was introduced at the top of the reactor, using the main portion of the tube as a preheat section. Exit gases containing the products were condensed by a series of traps and water scrubbers. Typical Oxidation Procedure. T h e volume concentrations of 1-butene or 2-butene oxidized were 1 or 2y0 in air. A typical oxidation procedure was as follows: T h e catalyst bed was heated in air to near the desired temperature and the butene was added to the extent of 1% by volume. Air flow was regulated -e.g., at 6000 ml. per minute, and butene flow at 60 ml. per minute, corresponding to a contract time of 0.50 second. A large rise in bed temperature accompanied the introduction of butene into the system, so the heat input had to be adjusted in order to attain the desired temperature. The time needed for attaining temperature equilibrium varied from 30 to 90 minutes. When the desired bed temperature, measured a t the point of maximum heat in the reactor, was attained, the exit gases leaving the reactor were first scrubbed through several hundred mil-. Miters of water a t 0' C. T h e gases then passed through several traps a t dry ice-acetone temperatures. This system was capable of trapping any acids produced by the oxidation. Over a period of 2 hours, at a contact time of 0.50 second, the bed temperature ranged from 409' to 424" C. At the end of 2 hours, the cold traps and water scrubbers were disconnected from the system, the contents diluted to 500 ml., and an aliquot titrated with 0.10N sodium hydroxide. Analytical Procedures. To a 10ml. portion of the acidic solution was added 10 ml. of 5% BaC12.2HzO solution. This was made alkaline with litmus, using concentrated NHdOH, and diluted to 60 ml. with 95% ethyl alcohol. T h e precipitate was centrifuged, dried to a constant weight at 110" C., and weighed as barium maleate monohydrate (8). T h e yield of maleic acid was
calculated from this result, knowing the amount of butene fed as determined from the flow rate. T h e yields were calculated as weight per cent of the butene fed. I t was felt that weight per cent of the butene fed is a more economically significant way of presenting the data due to the fact that it would be uneconomical to recycle the butene in such a dilute air stream. T h e remaining acid from the titration was calculated as acetic acid. A polarographic method of analysis of maleic acid was developed. I n order to eliminate interference from aldehydes such as crotonaldehyde, formaldehyde, and acetaldehyde, also produced during the oxidations, formation of Girard "T" derivatives of the aldehydes was followed by their separation
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A stainless steel reactor was used for the vapor phase oxidation of butene over a fixed bed catalyst
Table 1. Comparison of Analytical Methods for Maleic Acid Determination Maleic Acid, Grams Barium Maleate Polarographic 0.93 2.75 5.93 3.92 4.25
VOL. 53. NO. 7
0.83 2.85 6.00 3.25 4.12
JULY 1961
557
Table II.
Vapor Phase Oxidation of 2-Butene and 1 -Butene
Table 111.
Fixed-bed, Stainless Steel Annular Reactor; Phosphomolybdate Catalysta o n Silica Gel (Ethyl Orthosilicate)
Vapor Phase Oxidation of 2-Butene in Fixed-Bed Stainless Steel Annular Reactor -Maleic Acid
Maleic Acid
Yield.
Contact Time, Run No.
Flow, Ml./Min.
Sec.
Bed Temp., C.
wt.-%-'of
Butene Fed
2-Butene Air 37-1 38-1 39-1
40
43-2 42-1 43-1
40
4000
0.74
440-85 405-52 356-67
25.2 31.5 21.7
I-Butene Air 4000
0.74
444-67 25.6 406-42 27.4 327-404 18.8 a Catalyst prepared according t o British Patent 693,604 (6) except t h a t ethyl orthosilicate was used for the preparation of the support.
o n a cation exchange resin. T h e maleic acid produced was not adsorbed on the column and could be determined polarographically by the method of Elving (2). A comparison of the polarographic method with the barium precipitation method for several earlier runs is shown in Table I. Also, gas chromatographic analyses o n the oxidation products showed the presence of acetaldehyde, formaldehyde, acrolein, crotonaldehyde, and formic acid in addition to acetic and maleic acids. Typical Catalyst Preparation. T o 41 grams of (KH4)6M0702d.4 H 2 0 was added 9 grams of and 1.7 ml. of 85% H3P04 in 250 ml. of HzO. Silica gel prepared from ethyl orthosilicate was added to the above solution. T h e silica gel was prepared as follows: 61 ml. of ethyl alcohol and 43 ml. of water were added to 121 ml. of ethyl orthosilicate (Union Carbide Chemical Co.). T h e solution was heated over a steam bath to hasten formation of a gel and the supernatant was decanted. After the silica gel was added to the molybdena-vanadia-phosphate solution, the solution was heated over a steam bath with constant stirring until dry. T h e catalyst was then pressed into wafers, using a Carver press a t 10,000 to 15,000 p.s.i.g. and a die 1 inch in diameter. T h e wafers were approximately l/8 inch thick and were broken into pellets of inch X '/8 inch in size. For activation of the catalyst, 50 ml. of the pellets were introduced into the reactor. Air was passed over the catalyst a t a rate of 400 ml. per min. for a period of 16 hours and the bed temperature was maintained at 420' C. Results and Discussion
T h e use of ethyl orthosilicate in place of sodium metasilicate for preparation of the silica gel support resulted in cata-
558
R~~ h-0." 31-1 31-2 32-1 32-2 36-lb 36-2b 37-lb 33-1 33-2b
Flow, ~ U I . / M ~ I L 2-Butene Air
INDUSTRIAL AND ENGINEERING CHEMISTRY
Time, See.
20
2000
1.5
40
4000
0.75
+
Bed Temp.,
Yield. Wt. of Butene
304-9 340-8 371-81 334-58 311-33 335-51 333-47 414-27 413-24
Fed 19.6 40.0 31.6 55.0 50.0 58.5 53.1 32.3 43.7
c.
a Catalyst was (9hlo 3 V ) / P on a silica gel support. quench of exit gases used.
lysts with increased activity. Using such a support with a phosphomolybdate catalyst, yields of maleic acid of 32 wt.% ( l G % of theory) based on the 2-butene fed were obtained. Substitution of 1-butene for 2-butene as a feed material had little effect on the maleic acid yield when a typical phosphomolybdate catalyst was used (Table 11). Under conditions of oxidation such that maleic acid yields of 32 wt.% were being obtained-i.e., a phosphomolybdate catalyst on silica gel from ethyl orthosilicate at 400' to 440' C . and 0.74 second contact time-9.0 wt.% acetic acid, 6.4 wt.% acetaldehyde, and 5.2 wt.%l, formaldehyde were also obtained, based on the 2-butene fed. Variations of the molybdenum to phosphorus atomic ratios indicated that a 12:l molybdenum to phosphorus ratio gave optimum maleic acid yields from 2-butene oxidation. Mixed phosphomolybdate and phosphovanadate catalysts were also prepared, and a catalyst containing a M o : V : P ratio of 9: 3: 1 gave a 40 wt.% (20y0 of theory) yield of maleic acid and a 17.5 wt.% yield of other acids calculated as acetic acid when the temperature of oxidation was 348' C. and the contact time 1.5 seconds. Using a water quench of the exit gases by means of a spray installed in the exit of the reactor, this same catalyst system and reaction conditions gave a 53 wt.70 (27yc of theory) yield of maleic acid (Table 111). T h e effect of the activation temperature on the catalytic activity of the mixed phosphomolybdate and phosphovanadate catalyst with atomic ratios of (9 Mo 3V)/P was studied in some detail. Catalyst preparations were activated by heating a t 390°, 420°, and 450' C. overnight. From the yields of maleic acid obtained from these three catalysts under identical conditions of oxidation of 2-butene, it was found tha1
+
Contact
Water
390' C. was too low an activation temperature. Optimum yields of maleic acid were obtained from the use of the catalyst activated a t 450' C. Acknowledgment
The authors wish to acknowledge the support of this research by the PetroTex Chemical Corp. Many helpful suggestions were received from Marshall Welch of Petro-Tex Chemical Corpand C. M. Himel of Stanford Research Institute during the course of the research. Dale Coulson and W. C. Crawford of the Institute's analytical section contributed to certain analytical aspects of this problem. literature
Cited
(1) Bludworth, J. E., Pearson, P. C., Jr., U. S. Patent 2,462,938 (March 1, 1949) ; British Celanese, Brit. Patent 6 1 3 , 7 7 5 (Dec. 2: 1949). (2) Elving. P. J., Teitelbaum, Charles, J . Am. Chem. SOC. 71. 3916 (1949): Elving. P. J., Martin, A. J., Rosenthal, I.: Anal. Chem. 25, 1082 (1953). ( 3 ) Faith. W.L.. Schaible. A. M.. J . Am. Chem. Soc. 60, 52 (1938). ' (4) Goldstein, R. F., "The Petroleum. Chemicals Industry," p. 341-2, Wiley, New York, 1950; C.I.O.S. 27-85; B.I.O.S. 739. (5) Hadley. D. J., Jacobs, D. I. H., Brit. Patent 693,604 (July 8, 1953); Hadley,. D. J.. Heap. R.. Jacobs, D. I. H., Zbid., 677,624' (Aug. 20, 1952) ; Zbid.; 688,033 (Feb. 25, 1953); Hadley, D. J., Heap, R.. Jacobs, D. I. H., U. S. Patent Ibid.,2,649,477 (Aug. 18, 1953). (6) Hartig, M. J. P., U. S. Patent 2,625,519 (Jan. 13, 1953); Zbid.,2,691,660 (Oct. 12, 1954). (7) Krantz, K. W., Zbid., 2,605,238 (July 29, 1952). (8) Milas, N. A,, Walsh, W. L., J . Am. Chem. SOC.57, 1398 (1935). (9) Morrell, C. E., Beach, L. K., Cunningham, M. E., U. S. Patent 2,504,034 (April 11, 1950); Slotterbeck, 0. C., Zbid..2,260,409 (Oct. 28, 1941). (10) Walters, C. H., Zbid., 2,097,904 (Nov. 2, 1937). \
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RECEIVED for review October 1I , 196@ ACCEPTED April 5, 1961
