Ind. Eng. Chem. Prod. M. A. Chesters, B. J. Hopkins. A. R. Jones, and R. Nathan, Surf. S a . . 45. 740 (1974). J. M. White, R. R. Rye, and J. E. Houston. Chem. Phys. Lett.. 46,146
(1977). R. R. Rye. T. E. Madey. J. E. Houston, and P. H. Holloway, J. Chem. Phys.. 69, 1504 (1978). R. L. Gerlachand 0. W. Tipping. Rev. Sci. Instrum., 42. 1519 (1971). D. R. Jennison, Chem. Phys. Len., in press. W. N. Asaad and E. H. S. Burhop, Proc. Phys. SOC. London 72. 369 ,.oc*3 I /I"U,. D. A. Shirley, Phys. Rev. A . 7 , 1520 (1973). H. Siegbahn. L. Asplund. and P. Kelfve, C k m . Php. Len., 35, 330 (1975). 0.R. Jennison, Phys. Rev. Len.. 40,807(1978);J. A. D. Matthew and Y. Komninos. Surf. SO., 53. 716 (1975). (13) See P. Oooffenhartr, "Atomic and Molecular Orbital T h e q " , p 292, McGraw-Hili, New York. N.Y., (1970).or any basic molecular theory text. (14) H. Agren. S . Suensson, and U. 1. Wahlgren, Chem. Phys. Len., 35. 336 11975) I._._,. 1151 0.R. Jennison. wivate commtmirAion . ii6i K. Siegbahn. G. Norms. G. Johansson,J. Hedman. P. F. ~eden.K. Hamsin, U. Geiius. T. Bergmark, L. 0. Werme, R. Manne, and T. Baer, "ESCA Applied to Free Molecules". American Elsevier. New York. N.Y.. 1969. ~~~
Res.
Dev.. Vol. 18. No. 1,
1979
7
W. E. Moddeman, T. A. Carlson. M. 0. Krawe, B. P. Pullen, W. E. Bull, and G. K. Schweilrer, J. Chem. Phys.. 5 5 , 2317 (1971). R. Spohr. T. Bergmark, N. Magnusson. L. 0. Werme, C. Nordiing, and K. Siegbahn. Phys. Scr.. 2. 31 (1970). K. Faegre and R. Manna. Mol. Phys. 31, 1037 (1976). 1. H. Hillier and J. Kendrick. Mol. Phys.. 31. 849 (1976). 1. B. Ortenburger and P. S. Bagus. Phis. Rev. A , 11. 1501 (1975). H. H. Madden and J. E. Houston, J. Appi. Phys.. 47, 3071 (1976). J. E. Houston, J. Vac. Sci. Technoi., 12. 255 (1975). J. E. Houston, G. Moore. and M. G. Lagally, Soiid State Commun., 21,
679 (1977). L. Pauling, "The Nature of the Chemical Bond. Cornell Universiw Press. Ithaca. N.Y., 1952. B. Kamb. "Structures of Ices in Water and Aqueous Solutions", R. A. Home. Ed., Wiley-lnterscience, New York. N.Y., 1972.
~~
Received for reuiew October 9, 1978 Accepted December 5, 1978
TECHNICAL REVIEW Selective Oxidation of C, Hydrocarbons to Maleic Anhydride R. L. Varma' and D. N. Saraf * Depamnent of Chemical Engineering, Indian Institute of Technology, Kanpur-2080 16, India
Recent developments in the C, process for making maleic anhydride have been critically reviewed. Major work in this field deals with the development of catalysts for.this reaction. V-P-0 catalysts often containing activating agents have been widely described in the patent literature to give good yields of maleic anhydride. Some important characteristics of vanadiumphosphorus catalysts have been discussed. Kinetics and mechanisms of butene and butane oxidation reactions to maleic anhydride have also been presented.
Introduction The heterogeneous selective oxidation of hydrocarbons to a wide range of useful intermediates in the petrochemical industry has been of interest to numerous industrial and research organizations. Extensive reviews on this subject have appeared (1-9). A widely employed example of this class of reactions is the manufacture of maleic anhvdride bv. vauor . .uhase catalvtic oxidation of benzene (10-12). The ever-increasing application of maleic anhydride as a versatile chemical for the Droduction of alkvd resins. polyesters, fumaric acid and bther food addit&, insec: ticides, etc. is well known (llJ3-18). The more recent process that uses maleic anhydride as the raw material is the production of tetrahydrofuran. The increasing demand for maleic anhydride and the use of benzene as the most suitable raw material for the production of a wide range of important organic chemicals, coupled with its limited resources, have made it imperative to search for more progressive feed stocks for producing maleic anhydride, The low cost C4 hydrocarbon stream obtained from naphtha cracker is a very attractive source as an alternative raw material for producing maleic anhydride on a large scale. The predominantly C4hydrocarbon stream produced in 'H. B. Technological Institute, Kanpur India.
R . L . Varma is a lecturer in the Department of Chemical Engineering at H.B. Technological Institute, Kanpur, India. He receiued his E.&. (Chem. Eng.) from Kanpur Uniuersity i n 1968 and his M.Sc. (Chem. Eng.) from Banaras Hindu University in 1970. In 1976 he receiued the degree of Ph.D. i n Chemical Engineering from Indian Institute of Technology, Kanpur, where he worked on selective oxidation of C, hydrocarbons to maleic anhydride. His research interests deal with modeling of fixed and fluidized bed catalytic reaction, computer simulation, and enuironmental engineering. He has coauthored nine papers. D . N . Saraf is a Professor i n the Department of Chemical Engineering at the Indian Institute of Technology, Kanpur, India. He received his B S c . (Hons.) degree i n Petroleum Engineering from the Indian School of Mines, Dhanbad, in 1961, and the M.S. and Ph.D. in Engineering from the Uniuersity of California, Berkeley, in 1963 and 1966, respectively. He joined the Indian Institute o f Technolopv. K a n m r . i n 79fi7 as ~~Assistant Professor. He was named Department Head from 1975 to 1977. His research interests deal with the simulation of chemical process systems, process deuelopment and design, petroleum processing, and interfacial phenomena. He has guided several Master's and Doctoral theses and authored a number of technical papers.
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8
Ind. Eng. Chem Prod. Res Dev., Vol. 18, No 1, 1979
the processing of petroleum may often comprise a complex mixture of butenes together with n-butane, butadiene, isobutene, isobutane, etc. The selective catalytic oxidation of C4 hydrocarbons yields a number of commercially desirable products. The vast literature dealing with the processes involved is compiled by several reviewers (2,4,7,19-21). The C4 fraction primarily containing butenes was tried as a feed stock for making maleic anhydride almost a decade ago by Petro-Tex Chemical Corporation, but the process was dropped in favor of benzene-based production, probably for economic considerations. Since 1971, however, renewed interest and excitement has prevailed in the chemical world looking a t successful commercial production of 20000 tons per year of maleic anhydride by Mitsubishi Chemical Industries Ikd., using the C4 fraction from naphtha cracker as feed stock (22). Recently, Amoco has started operating a 60 million pound per year maleic anhydride plant, based on butane, at Joliet, Ill. The recent developments regarding the maleic anhydride process from C4 fractions have been emphasized by Japanese manufacturers (23-26a). The C4 process is believed to be under active development by Kuraray, Mitsubishi, Ube, BASF, Chevron, Monsanto, Petro-Tex, Mobil Oil, Standard Oil, and other organizations. It should be noted that the catalysts compositions and the optimum process conditions may differ significantly for different C4 feed compositions, and in general more severe conditions are required for oxidation as the degree of unsaturation of feed stock decreases. The existing Amoco process is based on n-butane as feedstock while the Mitsubishi process employs C4 cut from the naphtha cracker which mainly contains butenes and butadiene. The small amount of butane present in feed is essentially unreacted under the conditions of the process and the isobutylene present oxidizes to carbon oxides. Some organizations, particularly BASF and Bayer in Germany (26b),have explored the concentrated but not pure butene streams derived from the crude C4 naphtha cuts after extraction of butadiene and isobutylene. The process economics of the two routes (benzene add C4 as feed stocks) for making maleic anhydride has been examined and reported (22,27,28-30). With almost similar capital cost for both the processes, the principal factor governing the selection depends on the price equation of the two feed stocks. In view of relative differences in prices of benzene and C4 hydrocarbons, which is believed to persist regardless of the base price, it appears that the C4 process is very attractive. On the other hand, the highpriced butadiene content of the C4 cut seems to affect its commercial exploitation. Nevertheless, oxidation of hydrocarbons containing four carbon atoms is probably the best method to produce maleic anhydride, as it utilizes all four available carbon atoms of a molecule, whereas benzene oxidation utilizes only four out of six. Recently numerous patents have been issued on the C4 process, adding the bulk of information to the literature. However, little information on kinetics and choice of reactor operating conditions is available. The purpose of the present paper is to review and analyze the recent developments in the process and to discuss the kinetics of C4 hydrocarbons oxidation to maleic anhydride. Process Details Catalysts. It has been a continuing objective in this field to provide a catalyst which gives improved yield, permits the use of higher hydrocarbon concentration in the feed, and possesses longer life. As a result, a large
number of catalysts have been reported essentially in the patent literature. An extensive review dealing with catalysts involved based on literature available up to 1972 has been given by Hucknall (7). Only the recent catalysts claims described in the patent literature are given in Table I for feed stocks primarily containing C4 olefins. A few patents based on butane-rich feed, available in the literature, are given in Table 11. It is seen from Tables I and I1 that a majority of the investigators have disclosed catalysts containing oxides of vanadium and phosphorus alone or often mixed with some activating compounds, though other catalyst configurations have also been reported. Numerous other patent claims regarding V205-P205catalysts may be found in previous reviews (4, 7). In view of their wide acceptance, a brief discussion of their salient features is in order. The activity and selectivity of vanadium-phosphorus catalysts depend markedly on methods of their preparation. According to a preferred procedure of preparation, a vanadium compound such as ammonium metavanadate is dissolved in a suitable reducing agent to obtain a clear blue solution of V02+ ions and thereafter a phosphorus compound such as phosphoric acid is added. The mixture is refluxed to obtain a deep blue solution of a vanadium-phosphorus complex. This complex is uniformly deposited onto a carrier from the solution, without a precipitation step, by evaporation of the water content of the solution along with continuous agitation. The coated catalyst is then dried and calcined. This procedure is reported to provide a catalyst giving higher yields of maleic anhydride as compared to a method wherein the catalyst is prepared by mixing ammonium metavanadate and phosphoric acid in the presence of a carrier followed by precipitation of the active components on the carrier (71). The reducing agent for vanadium may be either organic such as oxalic acid or inorganic such as hydrochloric acid. Oxalic acid has been frequently used for the purpose. Recently, improved activity and selectivity has been reported from catalysts made using d-tartaric acid as the reducing agent in place of oxalic acid by Nakamura et al. (35). In a subsequent paper, Nakamura e t al. (72)have pointed out the structural difference between vanadyl phosphate catalysts made using oxalic acid and those made using a-hydroxycarboxylic acids such as maleic acid, tartaric acid, and citric acid. Indeed, the yield of maleic anhydride depends significantly on the valence of vanadium ions in the catalyst (72,731. It has been reported (71,72)that higher yields of maleic anhydride result when the vanadium has an average valence of less than + 5 (4.0-4.6). The valence of vanadium ions can be controlled by (i) the method of preparation of the catalyst (711, (ii) the composition of the catalyst (72), and (iii) the operating conditions, particularly the hydrocarbon concentration in the feed (73). The preferred atomic ratio of phosphorus and vanadium in V-P-0 catalysts is usually about 1.1to 1.6. The effect of phosphorus addition to the vanadium catalyst during oxidation of butene has been studied by Ai (74) and Ostraushko et al. (75). The addition of phosphorus was found to decrease the activity of the catalyst, yet the V205-P205catalyst showed increased selectivity to maleic anhydride. Kerr (76) found that the catalysts comprising oxides of vanadium and phosphorus lose their activity after about 300 h of operation due to the loss of phosphorus. It was also found that phosphorus may be stabilized by the addition of suitable amounts of alkali metal compounds such as potassium chloride or lithium hydroxide. This
Ind. Eng. Chem. Prod. Res. Dev., Vol. 18, No. 1,
1979 9
Table I. Some Patented Catalysts for the Oxidation of C, Unsaturated Hydrocarbons t o Maleic Anhydride cat. compn V-P-0 on silica carrier. P/V= 2 v-P-0
feed-gas compn 1-butene-air mixture
temp, "C -
contact timelspace vel. -
yield, %a
lit. ref
35-45
31
38
32
45.7
33
4 % alkane-olefin mixture in air (mixture: 31.4% butadiene, 18.4% 1-butene, 13.0% 2-butene, 29.0% isobutene, 7.0% butane, 1.2% others) mixture: 31.5% butadiene, 16.8% 1-butene, 11.7% butene butylenes
-
-
0.5% butene in air
450
40% butadiene, 25% butene, 25% isobutene, 10% in air C, fraction (165 gth) 67.5% butenes and butadiene + air ( 5 Llh) through 1380 g catalyst hydrocarbons of 4-10 C atoms 0.05-0.1% in air 1-butene-air mixture
-
5700ih ( 0 " C and 1a t m ) -
-
36
-
-
105.3 gth
37
37 5
0.1-2 s
94 (d)
38
-
-
32.8
39
1-butene, cyclopentadiene, butadiene (C 2 4 unsaturated hydrocarbons), 0.5% in air 2-butene in air
-
61.8
40
480
87 ( w t )
41
0.7 mol ?%
446
84 (wt)
42
1%2-butene in air
511
55.2
43a
1%2-butene in air 0.6% butene, butadiene in air
516 400
35 35.5
43b,c 44
1.2% butene mixture in air (mixture = 63% 1-butene, 12% trans-2-butene, 25% cis-2-butene) 1.0% butene in air 1-butene in air 1-butene in air
465-505
0.5 s
58
45
408 450 460
-
45501h
62.3 53 67
46 4 7a 47b
1-butene in air 4% 1-butene in air 4% 1-butene in air > C, unsaturated hydrocarbon 1:26 mol % 2-butene-0 mixture 0.5% 1-butene in air 1-butene and air 1%butene in air 4 vol % 1-butene in air (>C, unsaturated hydrocarbons) air contg. 0.5 vol % 1-butene 0.5 vol % butadiene in air
410 400 405
-
4 7c 48a 48b 49 50
480
5000 h'' 3000 h-'
64 30.5 37.8 56 18.8 conv. 94.5 sel. 34 70 ( w t ) 58 30.5
450 360
0.6 s 0.6 s
55.2 69.1
55a 55b
0.5 mol % 1-butene in air
360
0.6 s
57.5
55c
4.0 vol % 1-butene in air 4.0 vol % 1-butene in air
350 350
2500 h-' 2500 h-'
35.0 37.5
56a 56b
4.0 vol % 1-butene in air 400 2000 h-l Mo-Sn-Te-W (12:12: 4% butene in air 38 7 1000 h-' 1:4) The yield is in mole percent based o n hydrocarbon fed unless otherwise stated.
41.8 40.0
56c 57
V-P-silica gel V-P-SiO, (P/V = 1, 20-80% SiO,) V-P-0 on alumina (PtV > 0.6) V,O,-P,O,-TiO, ( 4 : 10:86) 3.7% V,O,, 13.3% P,O,, 83.0% TiO, on steatite balls V-P-mixed oxide V-P-0-Ag-silica sol. (VIPlAg = 1:1.6:0.025) V-P-Zr (1:3.0 :9.8) V-P-Li, V-P-Cu + alkali metal (P/V = 1.0:1.6) V-P-Cu-Nb oxides (1:1.35:0.082:0.021) 20% catalyst on alundum VU Dhosohate f 24% v,o,, vtu = 0.9) u-P mixed oxides of V, P, Mo, Ni, Fe, Bi, Mg, or Co V-P-MQ (1:1.2:0.05) V-P-WxFe-Ti (1:7,9:0.1: 3.5:3.1) V-P-Li (1:1.5:0.5) P-W (1:6.3) P-W + optionally Li, Na etc. (PIW = 1:6.3) W-P-Ti (3.2: 1:0.5) MoO,-P,O, Mo-P-CU (12: 1:0.36) Mo-Sn (1: 1) Sbo.9,Mo9O28.6 Mo-Sb/Al,O, ( 9 : l ) Mo-Bi-V-Fe-Co P-W-Ga (1:3.2:0.1) Mo-P-Bi (12:1:0.36) on a-alumina V-P-Ti VPuZrbMn,Od ( a = 3, b = 1 0 , c = 0.1) V,I,Zr,BidO, (a: b:c:d = 1:3:10:@.5)
400
1200/h
200-420
-
460 355
88 g of b u t e n e l l of cat./h
-
2500th 2500lh 0.3 s 3.2 s
-
-
62.4
34 35
51 52 53 54
"40.0 P1Mol~Bi0.;6Mn0.52040.1
10
Ind. Eng. Chem. Prod. Res. Dev., Vol. 18, No. 1, 1979
Table 11. Some Patented Catalysts for Oxidation of Normal C, Hydrocarbons to Maleic Anhydride cat. compn p2°5-v205
feed gas compn
temp, " C
1.5% butane in air
410
3 mol % butane in air
contact timelspace vel. 780 h-'
yield, %a
lit. ref
90 (conv.) 90 (sel.)
58
440
39
59
bu tane-air
-
-
60
1vol % butane in air
500
72 ( w t )
61
1:25 butane-air mixture
400
6 2a
bu tane-air butane-air mixture
450 450
68 63.2 (conv.) 62.0 (sel.) 92.4 ( w t )
butane-air 1.591 mol % butane in air 1.5% butane in air
495
1203 h-'
25.7
64 65
450
1156ih
53.0
66a
1.46% butane in air
460
1198/h
46.5
66b
butane-air
400
3050 mL/mL h
32.5
6 7a
3 mol % butane in air
446
1500 cm3/cm3h
42.5
67b
0.5-1.8 mol % butane in
450
-
35.22
68a
-
-
58.0
68b
482
-
47-50
69
402
0.46 s
36 (conv.) 30 (sel.)
70
v2°,(p205)1.2
( n = 4.1-4.5) 2°5-p205
(P/V a t 1-1.2) V-P-0 (contg. tetravalent V and pentavalent P ) P-V-Zn
0.4 s
(1.15:1.0:0.19) ZnC1, as activator
V-P-Zr ( 1 :1.2: 0.13)
V-P-Zr-0 v-P-co
62b 63
(1:1.14:0.19)
CoCl, as activator MOO3-V,05-P205 V-P-Fe (13.71:64.35:21.94)
P-V-Fe-Cr-Ba (62.0:8.0:20.0: 8.0:Z.O)
P-V-Fe-Cr (62.0:9.0:20.0:9.0)
V-P-Ti (Ti/P = 0.08:l) V-P-Mg (1: 1.1:0.05) vp 1.leuQ.026Te 0.026Li0,0390X
vp 1.5zn0.19si0.~
67
V-U oxide Sb-Ni-Mo
OX
air 0.5-1.8 mol % butane in
air 1: l o 0 butane-air mixture 0.8 mol % butane in air
(1:0.24:0.14) a
The yield is in mole percent based on hydrocarbon fed unless otherwise stated.
gives a marked increase in catalyst life. The effect of alkali metal addition on activity and selectivity has been studied by Ai (77). It was reported that the addition of less than 10% Li showed no remarkable effect, but traces of Na or K (Na or K-V = 0.02) considerably lowered the oxidation activity. The addition of suitable activator(s) to V-P-0 catalyst is reported to give an improved yield of maleic anhydride by several patent claims (46,61,63,67b). For example, increased yields (62.3 mol 70)were reported by Ikawa and Yamamoto (46) using a catalyst containing P-V-Li (1.5:1:0.5),as compared to 49.8% maleic anhydride obtained under similar conditions without LiOH. After about 15W5600 h of use of vanadium-phosphorus catalysts, the yield of maleic anhydride decreases and the yield of CO and COS increases. Reactivation of used catalyst is carried out by treating the catalyst with a phosphorus compound (78,791. Ai and Suzuki (80) have compared the oxidation activities of 1-butene and butadiene over various V-P-0 catalysts with the dehydration activity for isopropyl alcohol, which was used as a measure of the acidity of the catalysts. It was found that the introduction of P205to Vz05causes a decrease in surface area and acidity as well as basicity of the V205catalyst. Thus, the addition of Pz05 to V205-basedcatalysts lowers the acid strength to a proper extent and consequently suppresses the C-C fission of butene and increases the selectivity in the step of allylic oxidation: C4H8 C4Hs. Systems other than vanadium-phosphorus which have been studied include Mo03-P205,Mo03-V205, Co-Mooxide, Bi203-Mo03-P205,etc. (4 7). Ai (81) studied ox-
-
idation of butene using VS05-MOO,catalysts with different compositions and concluded that no satisfactory maleic anhydride yield can be expected by the use of V205-Mo03 catalyst. Akimoto and Echigoya (82) investigated butadiene oxidation over supported molybdena catalysts with reference to the nature of oxygen and adsorbed butadiene species selective for maleic anhydride formation. It was found that maleic anhydride is formed from butadiene species adsorbed on Mo5+and double bond type lattice oxygen Mo6+=0 plays an important role as a selective oxygen species. Trifiro et al. (81-83) investigated the behavior of a series of molybdenum-based catalysts such as MnMoO, which gave satisfactory yields of maleic anhydride although lower than those obtained with other known catalysts. Recently, butene has been oxidized to maleic anhydride using two different catalysts; the one, viz. K-Ni-Co-Fe-Bi-P-Mo-0, converted at least part of the butane or butene to butadiene, and the other, viz. V-Fe-Sb-Mo-W-0, converted a t least part of the butadiene to maleic anhydride in a fixed (84) and fluidized-bed (85) reactor. Design of Catalytic Reactor. An equally important aspect of the development of this process is the choice between two fluid-solid catalytic reactors, viz. fixed and fluidized beds. Fixed-bed catalyst systems, surrounded by suitable heat transfer medium, have been frequently described both in patent as well as in published literature. Mitsubishi's recent process consists of treating the mixture of C4 unsaturated hydrocarbons and air in contact with the fluidized catalyst (22,32). This technique avoids catalyst deactivation and gas explosion (86) and allows
Ind. Eng. Chem. Prod. Res. Dev., Vol. 18, No. 1, 1979
higher hydrocarbon concentrations in the feed. The reactor is said to consist of cooling coils in order to remove large amounts of heat of reaction and generate high pressure steam (22). Laguerie and Angelino (87) have studied the oxidation of commercial butane over V205Pz06catalyst in a fluidized or a fixed bed a t 345-460 "C. The selectivities of maleic anhydride in the two beds were compared. It was observed that in the fixed bed, the selectivity of maleic anhydride decreased with increase in contact time, while in the fluidized bed, the variation of selectivity with contact time passed through a maximum, giving an optimum contact time for the operation. The variations in selectivity were explained on the basis of a bubble phenomenon in the fluidized bed. Product Recovery and Purification. The dicarboxylic acid anhydride contained in the reacted gas may be recovered by direct condensation or adsorption of water so as to form an aqueous solution of maleic acid. This is followed by well-known dehydration and purification schemes. According to a patent to Mitsubishi (88),the crude gaseous product obtained from hydrocarbon oxidation was cooled to >97 "C (dew point of maleic anhydride) by passing through a cooling tube containing alumina to remove high boiling (>97 "C) impurities and then introduced into an absorption tower containing water. This procedure was claimed to give colorless maleic anhydride.
Kinetics and Reaction Mechanism Oxidation of Butenes to Maleic Anhydride. The mechanism of this reaction has been proposed by Sampson and Shooter (41, Ostroushko et al. (89),and Ai et al. (90). It is suggested that over V-P-0 catalysts, maleic anhydride is formed from butenes via 1,3-butadiene and furan (89,W). Crotonaldehyde has also been postulated to be an intermediate product during step by step oxidation (91,92). However, the possibility of maleic anhydride formation from butenes via crotonaldehyde has been ruled out by Ostroushko et al. (89). Thus, the catalytic oxidation of butenes to maleic anhydride may be represented by the kinetic mechanism in Scheme I. The side products include CO, C 0 2 , acetic acid, and aldehydes (acrolein, acetaldehyde, crotonaldehyde, butyraldehyde, etc.). Butadiene may be considered as the primary intermediate product (74). Butene-1 and butene-2 show similar oxidation behavior and oxidation of butene-2 is accompanied by some isomerization to butene-1 (4,91). Sunderland (93)has recently studied the kinetics of this reaction in a laboratory scale recycle reactor over a V205-P205catalyst under isothermal conditions in the temperature range 300 to 350 "C. Butene-2 was found to be oxidized by two competing routes, one leading initially Scheme I CH2=CHCH2CH3
11 CH3CH=CHCH3
-
-
-
CH2 =CHCH=CH2
1 side p r o d u c t s
-
HC-CH
II CH II
HC
\0 i
/
11
to maleic anhydride and water and the other to a mixture of carbon monoxide, carbon dioxide, and water. The carbon monoxide was then further oxidized to carbon dioxide and the maleic anhydride to carbon dioxide and water.
802 + 2C4H8
-
+02
4H20 + 2C02 + 2CO
-
3 H 2 0 + C4H203
H20
2C02
+202
+ 2C02 + 2CO
i-02
2C02 (11)
Rate expressions were fitted to each step in the overall reaction scheme. Butene-2 oxidation rate data indicated that a reaction between adsorbed oxygen and gaseous butene-2 was controlling. Further oxidation of maleic anhydride apparently involved the anhydride and oxygen, both in the adsorbed state, whereas in carbon monoxide oxidation, only oxygen was adsorbed. Rate expressions developed by Sunderland based on Hougen-Watson models are rather complicated and may not be suitable for the purpose of routine design of catalytic reactors. Moreover, the temperature range covered in his investigation (300-350 "C) is appreciably below the usual operating range adopted by industrial units (see Tables I and 11),and the published literature (72,77,91). In fact, the yield of undesirable organic side products, particularly acetic acid, would be appreciable at temperatures below 350 "C, and therefore a higher temperature is considered essential for favorable yield of maleic anhydride (73). More recently, Varma (94) studied the kinetics of this reaction in a quasi-isothermal integral reactor (immersed in a molten salt bath) at atmospheric pressure between 350 and 400 "C over a vanadyl phosphate catalyst (PI V = 1.6). Oxidation of butene was found to follow a two-stage redox model proposed by Mars and van Krevelen (95). For a reaction of the following stoichiometry hydrocarbon + a,Oz products
-
The rate of hydrocarbon oxidation according to this model is
where Ph and poare partial pressures of a hydrocarbon and oxygen, respectively, and CY,, is the stoichiometric number. The validity of the redox model implies that the reaction takes place between the butene in the gas phase and the oxygen ion of the oxide lattice. It is interesting to note that this mechanism is not very different from the findings of Sunderland that the reaction between gaseous butene and adsorbed oxygen was controlling. Varma (94) also reported that below 1 mol % concentration of butene in the feed, its disappearance can be represented by firstorder kinetics. Similar results have been reported by Ai (74) and Ostroushko et al. (89). For the purpose of kinetic analysis, the following reaction scheme (111)has been found to be satisfactory (94). butene
4
ki
butadiene
5maleic
anhydride
/kq
side p r o d u c t s (mainly c a r b o n oxides)
The results of parameter estimation revealed that further destruction of maleic anhydride to carbon oxides is insignificant within the reaction conditions studied. This conclusion is in agreement with the findings of Ai et al.
12
Ind. Eng. Chem. Prod. Res. Dev., Vol. 18, No. 1, 1979
(74,90,9l) which were of a qualitative nature. They found that the addition of phosphorus to vanadium oxide inhibits further destruction of maleic anhydride. Interestingly, studies of butadiene oxidation over a Mo03-Ti02 catalyst by Akimoto and Echigoya (96) also revealed that successive oxidation of maleic anhydride does not occur; rather, the anhydride and carbon dioxide are formed through different reaction paths. The oxidation of butene over a vanadium-based catalyst is one of those heterogeneous reactions where fast chemical steps of high exothermicity are observed. This necessitated a careful examination of heat- and mass-transfer effects. Varma (94) studied these effects by formulating a mathematical model of the catalyst pellet for reaction I11 and combining the same with the differential equations for the fluid field to obtain the heterogeneous model of the packed-bed reactor. It was found that the intrapellet mass transfer and interphase heat transfer resistances could be significant enough to influence conversion and product distribution. Dente et al. (97) examined the oxidation of butene and butadiene to maleic anhydride and formaldehyde on a Fe-Mo-oxide catalyst. A kinetic model was developed based upon the analysis of experimental results obtained in a nonisothermal integral reactor. Oxidation of Butane to Maleic Anhydride. Escardino et al. (98)have studied the mechanism of kinetics of this reaction over a 55.5% v205-44.5% P205catalyst a t reaction temperatures of 400 to 480 "C. It has been found that the oxidation rate is controlled by both the oxygen chemisorption and the surface oxygen reaction with butane gas. The chemisorption apparent activation energy is larger than the surface reaction activation energy. At large butane pressure (20 torr a t 400 "C),the rate-determining step is the oxygen chemisorption, whereas at low butane pressure (below 7 torr) the reaction step is rate controlling. A t partial pressures of butane less than 7.5 mmHg, the behavior of the butane oxidation reaction may be predicted with three single pseudo-first-order reactions butane
I
m o l e i c anhydride
J3
4 GO.
coz,
H20
(IV)
The estimated reaction velocity constants (g-mol/ kg of cat. h atm) are k l = (1.44 X lo5) exp(-7180/T) (2) k 2 = (7.20 X lo6) exp(-9301/T) (3)
k3 = (2.53 X lo4) exp(-5558/T)
(4) where T is the reaction temperature in K. Bissot and Benson (99) found that the kinetics of this reaction over a Co-MOO, catalyst is controlled by two consecutive first-order reactions: dehydrogenation of butane and decomposition of maleic anhydride. The intermediate oxidation of butene to maleic anhydride is so rapid that it has no influence on the kinetics of the overall reaction. The kinetics of butane oxidation to maleic anhydride over a Co-Mo catalyst has been studied by Agasiev and Shakhtakhtinskii (100). The oxidation reaction was found to be first order with an activation energy of 19.5 kcal/mol. The dependence of the logarithm of the reaction velocity constant on the inverse temperature (1/T) was linear.
Conclusions I t is evident from the above discussion that in view of the advantages of the C4 process for maleic anhydride,
considerable effort has been devoted to the development of this process in recent years. Although catalysts for oxidation of C4 hydrocarbons to maleic anhydride were known even a decade ago, the yields of the product until recently were below the desired economic level. Catalysts containing oxides of vanadium and phosphorus often mixed with activating compounds have been most widely used for this reaction. Most of the information in this field is contained in the patent literature, and published studies are scanty. Although numerous catalysts have been suggested, meager information on kinetics and reactor design is available. Oxidation of butene over a V-P-0 catalyst probably proceeds through a V4+-V5+ redox mechanism. At low hydrocarbon pressures, oxidation of both butene and butane may be described by pseudofirst-order kinetics.
Literature Cited (1) Marek, L. F., Hohn, D. A., "The Catalytic Oxidation of Organic Compounds in the Vapor Phase", Chemical Catalog Co., New York, N.Y., 1932. (2) Dixon, J. K., Longfield, J. E., Catalysis, 17, 183-280 (1960). (3) Margolis, L. Ya., Adv. Catal., 14. 429 (1963). (4) Sampson, R. J., Shooter, D.. Oxid. Combust. Rev., 1, 225 (1965). (5) Voge, H. H., Adams, C. R., Adv. Catal., 17, 151 (1967). (6) Sachtler, V. M., Catal. Rev., 4, 27 (1970). (7) Hucknall, D. J., "Selective Oxidation of Hydrocarbons", Academic Press, London, 1974. (8) Margoiis. L. Ya., Catai. Rev., 8, 241 (1974). (9) Sit@, M., "Combine Hydrocarbonsand Oxygen for Profit", Noyes Develop. Corp., Park Ridge, N.J., 1968. (10) Vaidyanathan, K., Cbem. Age India, 19(5), 363 (1968). (1 1) Kerr, R. 0. in "Benzene and Its Industrial Derivatives", pp 524-45, E. G. Hancock, Ed., Wiley, New York, N.Y., 1975. (12) Sherwood, P. W., Aust. Chem. Process Eng., 21(9), 211 (1968). (13) Kawatra, D. P., Indian Cbem. J . , 9(8), 531 (1975). (14) Dmuchovskv. B., Franz, J. E.. Kirk-Othmer Encvcl. Cbem. Techno/.. ZndEd., 12, 819-37 (1967). (15) Luskln, L. S.,Funct. Manomers. Their Prop., Polymn , Appl, 2, 357 (1974). (16) Pietsch, H., Ropa Ublie, 15(4), 175 (1973); Cbem. Abstr., 79, 54095j (1973). (17) Klosowicz, R., Pajda, E.. Chemik, 27(9), 339 (1974). (18) Sittig, M., Cbem. Process Monograph No. 18, 17-30 (1966). (19) Bailey, W. J., High Polym., 24, 757 (1971). (20) Kaneko, K., Wada, S., Sekiya Gakkai Sbi, 15(2), 97 (1972); Cbem. Abstr., 78, 427912 (1973). (21) Lenz, G., Chem. Analgen Verfahren, (7), 27 (1976). (22) Ushio, S.,Chem. Eng. ( N . Y . ) ,78(21), 107 (1971). (23) Ueno, S., Kamimura, S.,Sekiyu Gakkai Sbi, 16(8). 632 (1973); Cbem. Abstr., 78, 14588b (1973). (24) Ueno, S., Kamimura, S., Nikkakyo Geppo, 26(6), 278 (1973); Chem. Abstr., 80, 3011s(1974). (25) Kamimura, S., Kagaku Kogaku, 31(11), 1082 (1973). (26) (a) Ito, M., Yuki &sei Kagaku Kyokai Sbi, 34(7), 505 (1976); (b) Heller, H., Lenz, G., Thiel, R., I . Cbem. E. Symp. Ser., No. 50, 121 (1977). (27) (a) Sherwin, M., CHEMTECH, 225 (Apr 1974); (b) Cbem. Eng., 129 (March 1976). (28) Wurzbacher, G., Cbem. Ing. Tech., 45(22), 1297 (1973). (29) Eur. Cbem. News.. 23, 28 (1973). (30) Veprek, J., Ropa UMe, 13(4), 201 (1971); Cbem. Abstr., 75, 350789 (1 , 97 .. 1). .,. Minota, N., Miyajima, S.,Ito, M., Terabata, T., Tazawa, S. (to Mitsubish Chemical Industries Co., Ltd.,), Japanese Patent 7140926 (1971). Tokio, T., Shigeo, T., Toshikatsu, K., Shigehiko, M., Makoto, M., Masao, I., Haruo, I., Toshiteru, K. (to Mitsubishi Chemical Industries Co. Ltd.), French Patent 2 121 130 (1972). Mitsubishi Chemical Industries Co., Ltd., Japanese Patent 7 424 899 (1974); Cbem. Abstr., 83, 59754r(1975). Serebryakov, B. R., Akimova, L. S.,U.S.S.R. Patent 342854 (1972). Nakamura, M., Kawai, K., Fujiwara, Y. (to Kuraray Co., Ltd.), Japanese Kokai 7441 291 (1974); Chem. Abstr., 83, 59938d(1975). BASF-A.G., German Offen. 2 150690 (1973); Cbem. Abstr., 79, 323856 (1973). BASF-A.G., German Offen. 2352314 (1975); Cbem. Abstr., 83, 983499 (1975). Schneider. R. A. (to Chevron Research Co.1. German Offen. 2 328 755 (19 74). Otaki, T., Hishida, T., Hatano, M. (to Mitsubishi Chemical Industries Co. Ltd.), Japanese Kokai 7344 213 (1973). Sakai, F. (to Ube Industries Ltd.), Japanese Kokai 7562 930 (1975). Kerr, R. 0. (to Petro-Tex Chemical Corp.), U.S. Patents 3366648; 3 385 796 (1968). Kerr, R. 0. (to Petro-Tex Chemical Corp.), US. Patent 3484384 (1969). (a) Kobylinski, T. P., Taylor, B. W. (to Gulf Research and Develop. Co.), German Offen. 2219603 119721: Ib) German Offen. 2219604 (1972); (c) U.S. Patent 3 907 835'(1975).' ' Shiraishi, T., Komiy, T., Yoshika, T., Shimizu, S.. Honmaru. S. (to Sumitomo Chemical Co., Ltd.), Japanese Patent 7 300 685 (1973).
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Kerr, R. 0. (to Petro-Tex Chemical Corp.), U.S. Patent 3 156707 (1964). Nakamura, M., Kawai, K., Fujiwara, Y., J. Catal., 34, 345 (1974). Varma, R. L., Saraf, D. N., Ind. Chem. Eng., 20, T44 (1976). Ai, M., Bull. Chem. SOC. Jpn., 43(11), 3490 (1970). Ostroushko, V. I., Kernos, Yu. D., Khim. Prom. (Moscow), 48(2), 93 (1972); Chem. Absb., 76, 152942r (1972). (76) Kerr, R. 0. (to Petro-Tex Chemical Corp.), U.S. Patent 3288721 (1966). (77) Ai, M., Sekiya GakkaiShi, 14(5),324 (1971); Chem. Abstr., 75, 1 1 7 9 1 8 ~ (1 97 1). (78) Ken, R. 0. (to Petro-Tex Chemical Corp.), French Patent 1451 364 (1966); Belgian Patent 666 273 (1966);Neth. Appl. 6 507 591 (1966); British Patent 1 088 696 (1967). (79) Ohtaki, T., Koike, S., Hishida, T., Hatano, M. (to Mitsubishi Chemical Industries Co. Ltd.), Japanese Patent 7510714 (1975). (80)Ai, M., Suzuki, S., Bull. Chem. SOC. Jpn., 47(12), 3074 (1974). (81) Ai, M., Bull. Chem. SOC.Jpn., 44, 761 (1971). (82) Akimoto, M., Echigoya, E., J . Catal., 31, 278 (1973); 29, 191 (1973). (83) (a) Trifiro, F., Banfi, C., Caputo, G., Forzatti, P., Pasquon, I., J. Catal., 30(3),393 (1973); (b) Trifiro, I., Caputo, G., Villa, P. L., J. Less-Common Met., 36, 305 (1974); (c) Trifiro, F., Caputo, G., Forzatti, P.. Ind. Eng. Chem. Prod. Res. Dev., 14, 22 (1975). (84) Milberger, E. C., Dolhyj, S.R., Miko, S.J. (to Standard Oil Co., Ohio), U.S. Patent 3919257 (1975). (85) Milberger, E. C., Zagata, R. J. (to Standard Oil Co., Ohio), German Offen.
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Received for re2ieu February 7, 1978 Accepted October 25, 1978
POLYMER COATINGS SECTION Electrochemical Techniques to Monitor Performance of Polymer Coatings in Corrosion Protection J6zsef DBvay, * Lajos Miszlros, and Ferenc Janlszik Electrochemistry Research Group, Hungarian Academy of Sciences, 8200 Veszprgm, Hungary
The determination of permittivity and activation energy of the dielectric relaxation of polymer coatings provides useful information on the effects of aging and deterioration. Measurement of polarization resistance was useful in studying the anticorrosive protection of steel.
Painting is the least expensive, the most frequently used, and a relatively durable corrosion preventive method; therefore it is of special importance to study the properties of paint coatings and the corrosion processes taking place under them. 0019-7890/79/1218-0013$01.00/0
Since results are obtained slowly in exposure tests, accelerated investigations utilizing electrochemical methods are desirable. Corrosion is an electrochemical phenomenon taking place at the interface of the metal in contact with the coating system. Thus all information 'C
1979 American Chemical Society
