JPS6050179B2 - Benzyl benzoate recovery method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering benzyl penzoate (hereinafter abbreviated as BZ). This relates to a method for recovering.

Conventionally, in order to produce benzoic acid (hereinafter abbreviated as BA) and benzaldehyde (hereinafter abbreviated as BZ, A), for example, a method is known in which toluene is oxidized with molecular oxygen in the presence of a heavy metal catalyst. There is. In this method, the mixture obtained by the oxidation reaction is distilled to sequentially recover the active ingredients. Usually, first, unreacted toluene is separated from the mixture, and then BZA and BA are separated and recovered. After these are separated, the residue contains various by-products such as BZB and catalysts. If BZ and B contained in this residue are of high purity and can be well separated and recovered, they can be used, for example, as an odor retention agent or a carrier agent for dyeing, which is preferable. However, since the boiling point of BZB is 323°C, BZB should be recovered well if the residue is distilled at high temperature.
Normally, BZB cannot be efficiently recovered by distillation.

That is, pressure B causes decomposition due to heat during distillation, and therefore BZ and B in the residue cannot be efficiently recovered.
This phenomenon is not a problem when recovering ZB from a mixture that does not contain heavy metal catalysts, but is a problem specific to said residues that contain heavy metal catalysts. In view of the above circumstances, the inventors have
As a result of various studies on methods for distilling and separating BZB from the residue obtained by removing unreacted toluene, BZA and BA from a mixture obtained by oxidizing toluene in the presence of a heavy metal catalyst,
By performing distillation below a certain temperature, BZ,
The present invention was completed after learning that the decomposition of B was significantly suppressed.

That is, the gist of the present invention is to oxidize toluene with molecular oxygen in the presence of heavy metal catalyst J to obtain a reaction mixture containing benzoic acid, and to successively distill the reaction mixture to remove low-boiling substances such as unreacted toluene and A method for recovering benzyl penzoate, which comprises recovering benzoic acid by distillation, and then further distilling the distillation residue at a bottom temperature of 120 to 220°C to recover benzyl penzoate as a distillate fraction. exists in

The present invention will be explained in detail below.

The method for producing BZA and BA, which is the object of the present invention, is a method in which toluene is oxidized with molecular oxygen in the presence of a heavy metal catalyst.

Usually, a catalyst such as cobalt or manganese is added to toluene at 10 to 500 ppm, preferably 50 to 200 ppm.
The oxidation reaction can be carried out using pm (as metal) with air at a temperature of 140-200 DEG C., preferably 150-170 DEG C., and a pressure of 4-20 k91 dG1, preferably 8-12 kg1 cdG. The composition of the mixture obtained in this oxidation reaction varies somewhat depending on the oxidation conditions, but usually
77.5-86.5% by weight of unreacted toluene, BZAl.
5-2. Saliva volume %, BAlO~2 saliva volume%, others 1.0~
It is 1.5% by weight. Distilling the mixture as described above,
Unreacted toluene? A and BA are separated and recovered, and the distillation conditions are, for example, the separation of unreacted toluene is at normal pressure of 105 to 110, and the separation of temperature and pressure of A is about 10 to 110.
Temperature of 105 to 115°C on shore (10Tn:1nHg),
Moreover, the separation of BA was approximately 40 tons. 0rr(407177!
Hg) at a temperature of 158-167C.

The composition of the residue after separating each component is usually 10 to 3% by weight of BA, 80 to 55% by weight of pressure B, and 10 to 15% by weight of catalyst and others. In the present invention, the above-mentioned residue is further distilled. B is recovered, but the bottom temperature during distillation is 120 to 220°C, preferably 150°C.
There is an essential requirement to maintain the temperature below ~210°C.

That is, if the temperature is higher than the above, ? This is not preferable because B causes decomposition and the recovery rate decreases significantly. this is. Due to the influence of heavy metal catalysts present in the residue? B is thermally decomposed, and as is clear from the reference examples described later, decomposition does not occur even if pressure B, which does not contain heavy metals, is heated to a high temperature. Also, at 120℃? Is the vapor pressure of B about 0.5? H
g, and B small at less than 120°C! To carry out distillation, the distillation column must be maintained at a high degree of vacuum, which is not practical for industrial operation. In order to carry out the distillation at the above-mentioned temperature, it is necessary to carry out the distillation under a reduced pressure of usually 40 tons or less (Hg) or less, preferably 300rr (30?Hg) or less. ? In order to obtain B with high purity, it is usually preferable to distill the residue in advance to remove the remaining BA. This pre-distillation to remove remaining BA is usually carried out at a temperature of 30-100 t0 at a temperature of 160-190°C.
It is carried out under a reduction of rr (30-10-Hg). Through such treatment, B2l3 can be recovered as a fraction with high purity and high yield without decomposing pressure B. For example, small B with a purity of 90 to 95% can be obtained with a recovery rate of about 80% or more. ) Further, the residue from which KB is separated is sent to a heavy metal catalyst recovery process and treated according to a conventional method.

As mentioned above, according to the present invention, below a certain temperature? By distilling B, ? Since the decomposition of B can be significantly suppressed, B2'B can be obtained with a high recovery rate. can be done.

Next, the present invention will be explained in detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

Example Cobalt naphthenate 14 was placed in a stirred tank reactor having a raw material supply port, an air supply port, a reaction liquid outlet, and an exhaust gas outlet.
Toluene containing 0ppm (as CO metal) was charged, and 02
Air is supplied and the reaction is carried out three times so that the concentration is 3V01% or less, and then toluene containing the same amount of cobalt is continuously supplied to the reactor so that the residence time is 30 minutes, On the other hand, the same amount of the reaction mixture was continuously taken out to perform an oxidation reaction.

The mixture obtained in the oxidation reaction (toluene 82.5Wt%, BZ
Al. 9wt%, BAl4. OWt% content) was distilled at a top temperature of 110°C and normal pressure to recover toluene, and then BZA was distilled at a top temperature of 110°C and 100 TIUrLHg
and BA were further distilled and recovered at a tower top temperature of 160° C. and 40 w0 nHg.

The above residue (containing ?B68.Owt%, BA 2l.?t%) was heated to a temperature of 16rC at the top of the column and a temperature of 178°C at the bottom of the column at 1307°C.
077! After distillation was performed using Hg to separate residual BA, BZB was recovered by distillation under the conditions shown in Table 1.

The purity and recovery rate of the obtained BA were as shown in Table 1.
Reference Example 200y of B-7B (not containing cobalt catalyst) recovered in Example 1 above was heated to a temperature of 255C under a pressure of 10-Hg and held for 5 hours, and then the decomposition rate of BZB was measured. ,? B was not decomposed at all.

Claims (1)

[Claims] 1. Toluene is oxidized with molecular oxygen in the presence of a heavy metal catalyst to obtain a reaction mixture containing benzoic acid, and the reaction mixture is successively distilled to distill and recover low-boiling substances such as unreacted toluene and benzoic acid, The distillation residue is then heated to 120-220
A method for recovering benzyl penzoate, which comprises further distilling at a bottom temperature of °C to recover benzyl penzoate as a fraction.