问题：甲苯生产苯甲酸？？？
类型：求助 (悬赏分:3分)
提问：langy
等级：▲
版块：一般性化工问题(qixie,dingshx,wangnc3,)
信誉：33%
回复：3
阅读：1005
时间：2005-11-03 00:10:55 编辑加入/取消收藏订制/取消短消息举报该贴

求助：以甲苯为原料到底是怎样生产苯甲酸的，现在的生产工艺评价如何（优缺点）谢谢！！

回复人：pccs,★ (知之为知之, 不知Google之...) 时间：2005-11-03 14:33:46 编辑

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Production of Benzoic Acid

Liquid-Phase Oxidation of Toluene with Molecular Oxygen. This process was developed by I.G. Farbenindustrie in Germany during World War II and was operated until the end of the war [8]. The plant consisted of a bubble-column oxidation reactor made of aluminum-lined steel and equipped with an air inlet tube, a separator, and an absorber to recover toluene. The reactor contained heat-exchange coils to remove the great amount of heat generated in the reaction. The purity of the toluene was critical because sulfur compounds, nitrogen compounds, phenols, and olefins inhibit the oxidation reaction. The reaction was carried out at 140 °C and ca. 0.2 MPa with a cobalt naphthenate catalyst (0.1 %) for 30 h. About 50 % conversion of toluene was achieved, 80 % of which formed benzoic acid. Other oil-soluble cobalt salts were also used as catalysts. The crude oxidation product was neutralized with sodium carbonate to produce sodium benzoate. Unreacted toluene was recovered from the spent oil phase by distillation.

The elemental mechanism of this oxidation is a free-radical chain process [9]. The cobalt catalyst shortens the induction period of the reaction and retards the accumulation of inhibitors. Peroxides are reaction intermediates. Manganese behaves similarly to cobalt as a catalyst, but its performance is weaker. Copper adversely affects the oxidation. High pressures retard the reaction, especially at lower catalyst concentrations. Above 130 °C, the reaction rate is determined by the diffusion of oxygen. Phenolic compounds gradually accumulate during the reaction and eventually inhibit it.

In a typical modern process the oxidation is conducted at 165 °C and 0.9 MPa. The reaction heat is removed by external circulation of the contents of the reactor. The pressure of the liquid discharged form the reactor is reduced to atmospheric, and unreacted toluene is recovered. Benzoic acid is purified by rectification. The bottom residue is extracted to recover the cobalt catalyst. The exhaust gas is cooled to recover most of the toluene, purified, and vented. The oxidation reactor can be a bubble column or a stirred tank. Stainless steel is generally used as the construction material. Heat removal is still a serious problem, and air distribution within the reactor is critical to prevent a runaway reaction. The oxygen content of the exhaust gas should be strictly monitored to avoid an explosion.

The oxidation produces several byproducts. Benzaldehyde is formed in fairly large amounts, especially at lower conversions. It can be recovered by distillation. A limited amount of benzyl alcohol is formed, but its recovery is impractical because of the unavoidable esterification with benzoic acid. Benzyl benzoate can be recovered from the bottoms of the benzoic acid column [10]. Other esters, including benzyl formate and benzyl acetate, are also present. Biphenyl and methylbiphenyls are formed in smaller amounts. Because their vapor pressures are close to that of benzoic acid, they play a role in the rectification of benzoic acid. The product is contaminated by small amounts of phthalic acid. Carbon monoxide and carbon dioxide are detected in the exhaust gas. The yield of benzoic acid is about 90 %, but it varies with toluene conversion. At lower conversions, the selectivity for benzaldehyde and benzyl alcohol exceeds 10 %.

Conventional technical-grade benzoic acid is usually of as-rectified quality. Further processing is necessary for higher grade products. Sublimation, recrystallization, and neutralization processes have been proposed. Thermal treatment in an inert atmosphere is attempted [11]. To remove phthalic acid, whose presence is not allowed for food or pharmaceutical uses, treatment with amines [32] and rinsing [33] methods have been reported. Methylbiphenyls are responsible for the odor of the product. For their removal, extraction [34] and treatment in an inert gas stream [35] have been proposed.

The oxidation reactions of alkylaromatic hydrocarbons are dramatically enhanced by adding bromine compounds to the cobalt catalyst in acetic acid [12]. This method is now widely used in the production of terephthalic acid and is also applicable to the benzoic acid process. Under certain conditions, benzoic acid itself can be used as a solvent. Manganese has synergistic effect on the cobalt catalyst. This process can realize high reaction rates and better toluene conversion, as well as eliminating reaction inhibition. However, to avoid corrosion, the equipment must be constructed of expensive titanium.

Another type of cobalt catalyst activator is a readily oxidizable carbonyl compound such as methyl ethyl ketone or acetaldehyde. These additives permit a considerable reduction in reaction temperature, but because of the high consumption of these activators, this technology does not seem to be practical.

The catalytic oxidation of toluene in aqueous sodium hydroxide directly affords sodium benzoate. This process has been tried since 1940s, but satisfactory yields have not been achieved.

Vapor-phase oxidation of toluene at higher temperatures is another potential process. Various catalysts (vanadium, tungsten, uranium, molybdenum, silver, etc.) have been investigated, but yields were not comparable to those of the liquid-phase process. However, a patent claims a significant improvement in yield by using complex vanadia catalysts [36].

References
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8. BIOS 1786; BIOS (Misc.) 112.
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10. Mitsubishi Chem. Ind., JP-Kokai 56-39045, 1981.
11. Bayer, JP-Kokai 51-88934, 1976.
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13. I. P. Tharp, H. A. Nottorf, Ind. Eng. Chem. 39 (1947) 1300. Link
14. Org. Synth. 2 (1922) 5. Link
15. SU 56 693, 1936 (Uwarov, Stepanov).
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19. T. Ohara, Z. Iwao, M. Ninomiya, Y. Nakagawa, Yuki Gosei Kagaku Kyokaishi 26 (1968) 213. Link
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23. Org. Synth. 33 (1953) 13. Link
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27. Akzo, DE 2313580, 1973.
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29. J. A. Bigot, P. L. Kerkhoffs, Recl. Trav. Chim. Pays-Bas 82 (1963) 677. Link
30. Mitsubishi Chem. Ind., JP 55-37532, 1980; JP 55-50928, 1980.
31. T. Yokoyama, T. Setoyama, N. Fujita, M. Nakajima, T. Maki, K. Fujii, Appl. Catal. A 88 (1992) 149. Link
32. Bayer, DE 3 420 111, 1984 (W. Schulte-Huermann). Stamicarbon, EP-A 453 022, 1990 (U. F. Kragten, M. K. Frohn-Schloesser).
33. Mitsubishi Chem. Ind., JP-Kokai 4-69357, 1990 (K. Fujii, M. Nakamura).
34. Stamicarbon, EP-A 183 318, 183 319, 1984 (J. J. P. M. Goorden, A. J. F. Simons, L. A. L. Kleintjens).
35. Stamicarbon, EP-A 188 298, 1985 (S. M. P. Mutsers, M. H. Willems, W. P. Wolvers).
36. Nippon Kokan, JP-Kokai 5-255 181, 1991 (I. Osada, A. Imai, A. Miki).
37. European Parliament Council, Official Journal, no. L061 (1995) 0001 – 0040.
38. Iowa State University, material safety data sheets, see http://avogadro.chem.iastate.edu/msds/msds.html
39. Safety Information on the Internet, see http://siri.org/index.html
40. C. Barron: “Benzoic acid” in SRI International Chemical Economics Handbook, 1995, 618, 8000A.
41. 21 CFR 184. 1733 (Report no. 88, US Dept. of Agriculture).
42. Chemical Market Reporter Sept. 29, 1997. Link

[该帖子已被pccs在2005-11-3 14:34:18编辑过]

回复人：langy,▲ () 时间：2005-11-04 01:18:11 编辑	2楼
没有中文文献吗，看英文有点费劲阿

回复人：rarinbow,▲ (化学工艺的学生) 时间：2005-11-04 08:30:10 编辑	3楼
甲苯与空气在环烷酸钴存在下生产，目前石家庄化纤有限责任公司利用改工艺

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