Process for the production of benzaldehyde by the catalytic...

Details Process for the production of benzaldehyde by the catalytic... Process for the production of benzaldehyde by the catalytic...

1999-10-07

2002-12-17

Padmanabhan, Sreeni (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S426000, C568S432000

Reexamination Certificate

active

06495726

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for the production of benzaldehyde by catalytic liquid phase air oxidation of toluene, preferably with 40-50% selectivity.
The N.F./F.C.C. grade of benzaldehyde is widely used in flavors such as almond and cherry and in various fragrances for soap and toiletries. Benzaldehyde is a F.D.A. sanctioned synthetic flavoring substance generally recognized as safe for food. The technical grade is a versatile chemical intermediate in the manufacture of pharmaceuticals, dyes, perfume and flavoring chemicals. The technical grade of benzoic acid is used as an intermediate in the manufacture of chemicals, alkyd resins, polyesters, plasticizers, dyestuffs, preservatives, rubber activators and retardants. Benzoic acid, industrial grade, is used as a chemical intermediate and as a diverting agent in crude oil recovery applications.
BACKGROUND OF THE INVENTION
Benzaldehyde is currently produced by the hydrolysis of the corresponding side chain halogenated toluene compound. U.S. Pat. No. 4,229,379, Oct. 21, 1980 describes the preparation of benzaldehyde by hydrolysis of benzyl chloride at 100-200° C. at normal or under increased pressures in the presence of an excessive aqueous hydrochloric acid. U.S. Pat. 4,450,298, May 22, 1994, discloses vapour phase catalytic hydrolysis of benzyl chloride to form benzaldehyde by using activated carbon treated with H
2
SO
4
or impregnated with a metal chloride such as FeCl
3
or a metal sulphate such as cupric sulphate. The drawbacks in the above processes are generation of large excess of effluents and the benzaldehyde produced does not meet food grade specifications.
Air oxidation of toluene and its derivatives offers green technology path, provided the desired selectivities are realised for market driven products and minimisation of halogenated and unwanted by-products causing effluents is achieved. Several patents and or applications describe innovation in air oxidation of toluene and its derivatives both in liquid and vapour phase.
One of the prevalent industrial practices for the vapour phase oxidation of toluene to benzaldehyde involves a uranium oxide/molybdenum oxide catalyst at 500-600° C. (W. L. Faith, D. B. Keyes and R. L. Clark, Industrial Chemicals, 3
rd
Ed., John Wiley & Sons, Inc., New York, 1965); (U.S. Pat. No. 3,579,589). U.S. Pat. 3,946,067 discloses a process for the preparation of aromatic aldehydes such as benzaldehyde or substituted benzaldehydes by the vapour-phase oxidation of aralkyl compounds, such as toluene or substituted toluenes, respectively, at temperatures of less than ~250° C. in the presence of a catalyst composition containing phosphoric acid and a catalytically effective amount of palladium metal. The aromatic aldehydes are produced in a single reaction step. The drawbacks in this process are that the conversion of toluene has to be kept very low <4% to attain high selectivity (>70%) of benzaldehyde and significant amount of carbon dioxide is also formed in this process.
U.S. Pat. No. 3,989,674, Nov. 2, 1976 describes a process wherein a mixture of toluene, oxygen and a helium diluent in molar ratio 1:2:8 is passed over the Cu—Au-silica catalyst at atmospheric pressure and temperatures in the range of 450-600° F. with 200-1000 volumes of gas/h/volume of catalyst. The selectivity of benzaldehyde is 75-80% at conversion levels 15-30%. U.S. Pat. No. 4,137,259, Jan. 30, 1979, describes a process for the vapour phase catalytic oxidation of toluene to benzaldehyde and benzoic acid at a temperature ranging from 300-500° C. in the presence of a silver-iron vanadate on silica with conversion 21%. A selectivity to aldehyde of 33% is described. U.S. Pat. No. 4,390,728, Jun. 28, 1983, describes a process wherein benzaldehyde is formed by the oxidation of toluene in the presence of a catalyst composed of the oxides of Cu, Fe, Pb, U, Mo, and P, and optionally including some other promoter elements. The reaction conditions are 475-550° C., 0-10 atm. pressure, per pass conversion is 35-50%, and selectivity to benzaldehyde 40-70%. Ray et al, Ind. J. Technol., 21(4), 137, 1983, reported a process for the oxidation of toluene to benzaldehyde. But, the conversion per pass is restricted to ~15% and the yield of benzaldehyde is generally not more than 70%, with CO
2
as main product. Further, the low concentration of toluene in the toluene-air feed mixture poses problems of recovery. The drawbacks in the above processes are the use of higher reaction temperatures, generation of carbon dioxide in large amounts contributing to global warming. Therefore, these processes do not appear to be attractive.
U.S. Pat. No. 5,476,827, Dec. 19, 1995, discloses the preparation of aldehydes by the reduction of acids and esters in vapour phase in the presence of a bimetallic catalyst. The drawback is the two-step process of oxidation of toluene, a desired raw material, to benzoic acid and reduction of benzoic acid to benzaldehyde with hydrogen. Eventually, this process becomes uneconomical, when compared to a process of selective oxidation of toluene to benzaldehyde conceived.
Morimoto et al (J. Chem. Soc. Sect. B, 62, 1967), Fields et al (Adv. Chem. Ser., No. 76 (2), 395) and Kamiya (Adv. Chem. Ser., No. 76 (2), 193, 1968) have reported that liquid phase air oxidation provides high yield of benzaldehyde when oxidation is carried out in acetic acid medium with cobalt acetate as catalyst and sodium bromide as promoter. The drawbacks are that this process suffers from the disadvantages of relatively low yield. U.S. Pat. No. 2,959,613, describes a process wherein the liquid phase oxidation of toluene or its nucleus substituted materials, such as xylene, is carried out by oxygen under the presence of a catalyser containing a bromine compound and a heavy metallic compound (such as a cobalt compound or manganese compound) along with a zinc compound or an alkaline earth metallic compound or an alkaline metallic compound. The drawbacks in this method are that the main product is the corresponding aromatic carbonic acid and either there is absolutely no production of the corresponding aromatic aldehyde or it is produced in a very small quantity as a by-product.
Japanese Patent No. SHO-53-5132 discloses a process wherein in order to increase the selectivity of benzaldehyde or its nucleus substituted material, a large quantity of catalyser containing a cobalt compound and bromine compound is used. Japanese Patent No. SHO-56-108728, Aug. 28, 1981, describes a process wherein the liquid phase air oxidation of toluene is carried out by a catalyst comprising a heavy metallic compound, zinc and bromine compound at 30-180° C. and a small pressure. The transformation percentage of toluene is maintained within a specific range with the advantage of the execution of the reaction employing carboxylic acid as solvent in the range 0.5-2.0 times with respect to toluene or its substituted material. By this method, the selectivity of benzaldehyde is increased while formation of benzyl bromide is reduced to 2 mol %. However, the turnover number is 3-50 in these air oxidation reactions. The drawback in the above processes are that low turnover numbers render the process uneconomical; the use of higher catalyst concentration hasten corrosion of reactors and excessive production of benzyl bromide is detrimental to achieve the desired quality of the product. U.S. Pat. No. 3,969,405 wherein the oxidation of toluene in the presence of cobalt acetate, acid activator and molecular oxygen oxidant giving high yield of benzoic acid with selectivity to benzaldehyde 35% is disclosed. U.S. Pat. No. 5,473,101 describes a process wherein the oxidation of toluene is carried out in the presence of cobalt acetate, sodium bromide and hydrogen peroxide disclosing conversion of 90.6%, benzaldehyde yield of 29.0%, benzoic acid yield of 55.6%. There are drawbacks in the above processes due to excessive production of benzyl bromide or its nucleus substituted material. Therefore, such a method cannot be said to be a satisfactory one fr

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