Distillation: processes – separatory – With disparate physical separation – Utilizing removing solid from liquid
Reexamination Certificate
2001-02-08
2002-12-10
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
With disparate physical separation
Utilizing removing solid from liquid
C203S091000, C203S100000, C203SDIG001, C203S038000, C023S29500G, C023S300000, C560S106000, C562S494000, C568S810000
Reexamination Certificate
active
06491795
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for recovering high-purity benzyl benzoate from a reaction mixture obtained by the oxidation of toluene by molecular oxygen.
DESCRIPTION OF THE RELATED ART
Benzyl benzoate is an important compound useful as raw material for perfumes and pharmaceuticals and applicable to other industries and a large number of processes for its manufacture have been reported. For example, Japan Kokai Tokkyo Koho Sho 56-39045 (1981) reports the recovery of benzyl benzoate by distillation of benzyl benzoate under reduced pressure from a reaction mixture produced by the oxidation of toluene by molecular oxygen. However, distillation alone has not yielded benzyl benzoate with such high purity as to be acceptable for use in perfumes. Likewise, Japan Kokai Tokkyo Koho Sho 53-95934 (1978) reports the recovery of benzyl benzoate by distillation from a reaction mixture produced by the oxidation of toluene by molecular oxygen, but high-purity benzyl benzoate is not obtained on account of the difficulty of separating fluorenone whose boiling point is close to that of BZB.
Japan Kokai Tokkyo Koho Sho 53-31639 (1978) describes a process for synthesizing benzyl benzoate by the transesterification of methyl benzoate with benzyl alcohol and an article in Industrial and Engineering Chemistry, Vol. 39, No. 10, pp.1300-1302 (1947) describes the synthesis of benzyl benzoate by the reaction of sodium benzoate with benzyl alcohol. Although these processes yield high-purity benzyl benzoate, they face a problem of high manufacturing cost because of the use of expensive catalysts and raw materials.
SUMMARY OF THE INVENTION
An object of this invention is to provide a process, free from the aforementioned shortcomings, for recovering benzyl benzoate in high purity at low cost.
This invention relates to a process for recovering benzyl benzoate which comprises distilling the residue remaining after removal of unreacted toluene and benzoic acid from a reaction mixture produced by the oxidation of toluene by molecular oxygen in the presence of a metal catalyst thereby separating a fraction of benzyl benzoate containing 80% by weight or more benzyl benzoate and simultaneously 10% by weight or less benzoic acid and 10% by weight or less fluorenone, purifying the fraction of benzyl benzoate by crystallization and recovering high-purity benzyl benzoate.
DETAILED DESCRIPTION OF THE INVENTION
Benzyl benzoate (BZB) is known to be present as by-product in a reaction mixture produced by the oxidation of toluene by molecular oxygen in the presence of a catalyst. In general, the oxidation of toluene is carried out for the purpose of manufacturing benzoic acid and those catalysts which are commonly used for the reaction are based on heavy metals such as cobalt and manganese. As for the normal operating conditions inside the reactor, the temperature is 120-170° C., the pressure is normal to 1 MPa and air is frequently used as molecular oxygen. A reaction mixture produced under any conditions, not limited to the aforementioned conditions or the purpose, may be used in this invention as long as it contains BZB and benzoic acid.
Either a continuous process or a batch process may be chosen for the oxidation reaction, though a continuous process is more economical. The main product to be produced by the oxidation of toluene is benzoic acid, but the following by-products besides unreacted toluene have been identified in the reaction mixture: water, formic acid, acetic acid, propionic acid, acetone, benzene, biphenyl, methylbiphenyl, dimethylbiphenyl, fluorene, fluorenone, toluic acid, phthalic acid, isophthalic acid, terephthalic acid, biphenylcarboxylic acid, methylbiphenylcarboxylic acid, biphenyldicarboxylic acid, and phenylbenzyl alcohol, compounds occurring as intermediates in the oxidation of toluene to benzoic acid such as benzaldehyde and benzyl alcohol, and esters formed by the esterification of benzyl alcohol or phenylbenzyl alcohol with a variety of carboxylic acids inside the reactor such as benzyl benzoate (BZB), benzyl acetate (BZA), benzyl toluate and benzyl biphenylcarb oxylate.
The reaction mixture is successively distilled to recover unreacted toluene and the main product benzoic acid. Simultaneously distilled in this step are components boiling lower than toluene such as water, formic acid, acetic acid, propionic acid, acetone and benzene and an intermediate fraction with a boiling point between those of toluene and benzoic acid such as benzaldehyde and benzyl alcohol. The unreacted raw material toluene and the intermediates benzaldehyde and benzyl alcohol are returned to the reactor for conversion to benzoic acid. Components boiling higher than benzoic acid, for example, biphenyl, methylbiphenyl, dimethylbiphenyl, fluorene, fluorenone, toluic acid, phthalic acid, isophthalic acid, terephthalic acid, biphenylcarboxylic acid, methylbiphenylcarboxylic acid, biphenyldicarboxylic acid, benzyl benzoate (BZB), benzyl acetate (BZA), and benzyl toluate are contained in the residue after the distillation of benzoic acid. Although the composition of the high-boiling components contained in the residue varies with the conditions for reaction and distillation, any residue containing at least a given amount, preferably 5% by weight or more, of BZB is acceptable for use in this invention. The residue may contain heavy metals such as cobalt or manganese originating from the oxidation catalyst, but it is advantageous to extract such heavy metals by hot water.
The BZB contained in the residue is distilled again and recovered as a BZB fraction. Either a continuous process or a batch process may be chosen for the distillation, though a continuous process is preferable economically. The BZB fraction obtained here is purified in the recrystallization step. Economical recovery of high-purity BZB, however, makes it necessary to maximize the recovery and the concentration of the BZB fraction in the distillation step.
The distillation in question is carried out below 270° C., preferably below 250° C., in order to prevent benzoate esters from thermally decomposing to benzoic acid as much as possible when the temperature at the bottom of the distillation column becomes too high and also to prevent benzoic acid from corroding the apparatus. As the boiling point of BZB is 323° C., it is desirable to carry out the distillation under reduced pressure while keeping the pressure at the top of the distillation column preferably at 4.0 Kpa or less.
The number of plates for a distillation column used for the recovery of BZB from the residue will be 5 or more for satisfactory operation and the concentration of the BZB fraction can be controlled by reflux ratio. Providing the distillation column with an unnecessarily larger number of plates will raise the temperature at the bottom of the column on account of the pressure difference inside the column and occasionally cause such problems as formation of by-product benzoic acid and corrosion of the apparatus. The concentration of BZB in the BZB fraction to be obtained by this distillation is preferably 80% by weight or more, more preferably 90% by weight or more, in consideration of the recovery and purity in the following crystallization step. For this reason, the BZB fraction is obtained by carrying out the distillation preferably at 180-220° C., more preferably at 190-210° C., in case the pressure at the top of the distillation column is kept at 2.6 KPa.
The BZB fraction contains, in addition to BZB, such compounds as benzoic acid and fluorenone whose boiling point is close to that of BZB. In case the concentration of BZB in the BZB fraction is less than 80% by weight, the recovery of BZB in the following recrystallization step falls and, at the same time, benzoic acid and fluorenone crystallize together with BZB to lower the purity of the recovered BZB. The presence of less than 10% by weight of benzoic acid in the BZB fraction allows economical recovery of BZB while the presence of benzoic acid in excess of 10% by weight decreases the recovery of BZB i
Akamine Ryouji
Daitou Noboru
Horibe Kazuyoshi
Sakura Katsuhiko
Ueda Shingo
Manoharan Virginia
Nippon Steel Chemical Co. Ltd.
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