JPH02304078A - Method for recovering phthalic anhydride from distillation residue of phthalic anhydride - Google Patents

Abstract

PURPOSE:To readily and efficiently recover phthalic acid anhydride in distillation residue hitherto disposed or burned by adding a phthalic acid ester to distillation residue of phthalic anhydride and then re-distilling the mixture. CONSTITUTION:A phthalic acid ester, e.g. dimethyl, diethyl, dibutyl, diheptyl, di-n-octyl, di-2-ethylhexyl, diisononyl, diisodecyl, dilaulyl, dicyclohexyl, diundecyl or butylbenzyl ester of phthalic acid or di-n-octyl, di-2-ethylhexyl or diisodecyl ester of tetrahydrophthalic acid is added to distillation residue of phthalic anhydride at an amount of 0.1 to 50wt.% and the mixture is re-distilled to efficiently recover high purity phthalic anhydride from the abovementioned distillation residue and contrive increase of unit in production of phthalic anhydride and lowering of cost.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for treating a distillation residue of phthalic anhydride. More specifically, the present invention relates to a treatment method for efficiently recovering phthalic anhydride from a distillation residue containing phthalic anhydride as a main component by adding a phthalic acid ester and performing a distillation operation.

<Prior art> Naphthalene is catalytically oxidized with a gas containing oxygen in the presence of a vanadium catalyst, and the oxidation reaction product is cooled and collected to obtain crude phthalic anhydride, which is then thermally polymerized to form quinones. The residue after producing phthalic anhydride by distillation contains a considerable amount of phthalic anhydride, but it is usually extracted from the system and disposed of or incinerated. Other processing methods include the following.

(1) The distillation residue liquid is sent to a thin film evaporator, and phthalic anhydride, which is a light fraction, is evaporated and recovered by heating. On the other hand, the heavy fraction is passed through a small-diameter column, and water is sprayed onto the distillate stream at the bottom of the column to cool the resulting solidified granules, which are then precipitated (Japanese Patent Laid-Open No. 50-29526).

(2) After recovering phthalic anhydride from the distillation residue liquid in a thin film evaporator to the extent that the phthalic anhydride concentration in the residue maintains 50% by weight or more, the concentrated residual liquid was taken out from each thin film evaporator. The entire amount of phthalic anhydride is recovered by batchwise vacuum distillation of Method of discharging outside (Unexamined Japanese Patent Publication No. 53-1
No. 37926).

(3) Recovering phthalic anhydride contained in the distillation residue by batchwise vacuum distillation of the distillation residue;
A method of lowering the freezing point and viscosity of the residue by mixing a fraction with a boiling point lower than that of phthalic anhydride with the residue after recovering the phthalic anhydride, and extracting the residue from the distillation vessel (JP-A-Sho) 59-1
No. 16280).

(4) Pour the distillation residue into the kneading I/J1 outlet, evaporate the phthalic anhydride contained in the distillation residue under reduced pressure while heating, and remove the remaining phthalic anhydride from the kneading ↑ J1 outlet. A method for discharging distillation residue with a concentration of 5% by weight or more (Unexamined Japanese Patent Publication No. 6)
No. 2-114984).

However, these methods have the following problems.

In (1), when the recovery rate of phthalic anhydride is increased, troubles often occur in the small-diameter column outlet pipe due to decreased fluidity of the residue after the thin film evaporator. Furthermore, since a large amount of water is required to solidify and granulate the residue, a large amount of contaminated wastewater containing phthalic anhydride, which is highly corrosive, is generated, and its treatment requires a large amount of cost.

In (2), two distillation devices for residue treatment are required,
The amount of heat required for distillation is wasted. In addition, since the residue remaining in the can during batch vacuum distillation is stored for several batches and then cooled, it takes a long time to solidify.
In this case, the lag in water usage also incurs wastewater treatment costs.

In (3), the proportion of low boiling point fraction mixed in the residue is
Since the amount is 0.81 to 2 parts by weight per 1 part by weight of the residue, the amount of residue ultimately generated increases and the processing cost also increases. In addition, since low boiling point fractions are directly added and mixed in the distillation pot, low boiling point fractions are added and mixed together with phthalic anhydride during distillation in the distillation pot.
, the purity of the recovered phthalic anhydride is reduced.

In (4), if the concentration of phthalic anhydride in the weight residue in the kneading and discharging machine is 5% by weight or less, clogging occurs inside the kneading and discharging machine due to a decrease in the viscosity of the residue. Moreover,
Since it is not easy to control the concentration of phthalic anhydride in the residue in the kneading and discharging machine, the above-mentioned operational troubles are likely to occur.

In particular, methods (1), (2), and (4) cannot be implemented easily on existing equipment because they require construction or major modification of equipment for distillation residue treatment. Furthermore, since the recovered phthalic anhydride has an increased high boiling point content compared to purified phthalic anhydride, it is necessary to purify it by distillation or the like.

<Problems to be Solved by the Invention> Crude phthalic anhydride obtained by a one-step oxidation reaction of naphthalene with oxygen-containing gas in the presence of a vanadium catalyst is converted into a high-purity product through purification steps such as polymerization and distillation. do.

However, until phthalic anhydride is finally obtained, the crude phthalic anhydride is exposed to heating during the polymerization step of quinones and the separation step of components with lower boiling points and higher boiling points than phthalic anhydride. Therefore, the residue after rectifying phthalic anhydride contains a considerable amount of polymers in addition to high-boiling impurities produced by the reaction. Therefore, if the distillation rate (distillation amount/supply amount) of phthalic anhydride is made too high, the purity of phthalic anhydride will decrease, the liquid viscosity of the residue will increase, and the thermal efficiency of the reboiler will deteriorate. . Furthermore, it results in promoting the polymerization of phthalic anhydride and the like.

Therefore, the distillation rate of phthalic anhydride is necessarily kept below a certain range, and a considerable amount of phthalic anhydride is present in the residue together with high-boiling components such as polymers. Therefore, if the residue is disposed of or incinerated, it will lead to a loss of phthalic anhydride, which will lead to a deterioration of the unit consumption and an increase in costs, so it is necessary to try to recover phthalic anhydride by some method.

Means for Solving the Problems> The present inventors have focused on the above-mentioned problems and have devised a method for effectively recovering phthalic anhydride from a polymer and a residue containing high-boiling components after distilling phthalic anhydride. As a result of intensive study on the method, it was found that high-purity phthalic anhydride could be efficiently recovered by adding phthalic acid ester to the residue containing impurities specific to the present invention and carrying out a distillation operation. completed.

That is, the present invention provides a method for recovering phthalic anhydride from a distillation residue of phthalic anhydride, which is characterized by adding a phthalic acid ester to the distillation residue of phthalic anhydride and then redistilling.

Phthalate ester is a distillation residue of phthalic anhydride.
It is preferable to use it in an amount of 0.1 to 50% by weight.

Hereinafter, the method for recovering phthalic anhydride from distillation residue according to the present invention will be specifically explained.

The residue to which the method of the present invention can be applied may be any distillation residue of phthalic anhydride, but it can be catalytically oxidized with an oxygen-containing gas in the presence of a vanadium catalyst, and the oxidized product is collected by cooling. An example in which the resulting crude phthalic anhydride is treated with quinones by thermal polymerization and purified into phthalic anhydride by distillation, and the resulting residue is used will be described below.

The composition of this residue is usually 40-60% by weight of phthalic anhydride and 40-60% by weight of high boilers and polymers.
The high boiling point substance in the residue is a polymer of naphthoquinone and phthalic anhydride or dimer to tetramer of phthalic anhydride.

By adding the phthalic acid ester according to the method of the present invention to the above-mentioned distillation residue of phthalic anhydride and distilling it, a useful substance such as highly purified phthalic anhydride can be obtained.

The phthalate esters used in the present invention include dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisodecyl phthalate, and phthalate. Representative examples include dilauryl acid, dicyclohexyl phthalate, diundecyl phthalate, butylbenzyl phthalate, di-n-octyl tetrahydrophthalate, di-2-ethylhexyl tetrahydrophthalate, diisodecyl tetrahydrophthalate, and the like.

Since the vapor pressure of phthalic acid ester is significantly lower than that of phthalic anhydride, it is not distilled out together with phthalic anhydride in the distillation operation, and the viscosity-lowering effect of the residue can be maintained. By adding the phthalic acid ester and distilling it in this way, it is possible to prevent an increase in the viscosity of the residue and to efficiently recover phthalic anhydride without distilling off most high-boiling point impurities.

The amount of phthalate used in the present invention is usually 0.1 to 50% by weight, preferably 2 to 50% by weight based on the residue.
25% by weight, and with such an amount used, highly purified phthalic anhydride can be obtained at a high recovery rate. If the amount of phthalic acid ester used in the distillation operation is less than 0.1% by weight, the viscosity-lowering effect will be significantly reduced, and recovery of high-purity phthalic anhydride cannot be expected. Also, 2
If it exceeds 5% by weight, no difference is observed in the viscosity-reducing effect and the cost of the phthalate ester increases, which is not very desirable from an industrial perspective.

The distillation operation method may be either a commonly used batch method or a continuous method, and the distillation apparatus does not need to be a special one. Further, the operating pressure when performing distillation may be normal pressure, increased pressure, or reduced pressure, but when energy costs are taken into account, it is desirable to perform distillation under reduced pressure.

The distillate obtained by distillation is phthalic anhydride that contains almost no high-boiling components, and can be used as a product as it is, but if further purification is required, a step is taken to produce purified phthalic anhydride from crude phthalic anhydride. It may be distilled in an appropriate place, for example, in the distillation process of crude phthalic anhydride, together with the crude phthalic anhydride after thermal polymerization.

The addition of the phthalic acid ester is not limited to the distillation residue as described above, and in some cases, it may be added in advance during the purification distillation of crude phthalic anhydride after the thermal polymerization treatment without causing any problems.

<Examples> Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited in any way by these Examples.

(Examples 1 to 8) Naphthalene was catalytically oxidized with a gas containing 21% oxygen in the presence of a vanadium catalyst, and 125 tons of crude phthalic anhydride obtained by cooling and collecting the oxidation product was placed in a polymerization kettle at 270 tons.
After processing the quinones by thermal polymerization for 8 hours at ℃, the bottom pressure was 120 mmHg and the bottom temperature was 210 mmHg in a batch distillation column.
By purifying phthalic anhydride at a temperature of 1.5 °C and a reflux ratio of 1.5, 120 tons of phthalic anhydride with a purity of 99.95 wt% or higher was obtained. The distillation pot contains 41.7% by weight of phthalic anhydride, 573% by weight of high boilers and polymers, and 1.0% by weight of non-volatile substances.
Five tons of distillation residue remained.

Di-2-ethylhexyl phthalate was added to this residue in a proportion not shown in Table 1, and the bottom pressure was 120 mmHg and the reflux ratio was 5.0.
The final distillation temperature was set to 300°C, and distillation was carried out in a batch-type residue distillation pot. The results are shown in Table 1. The distillation residues showed no increase in viscosity except in Example 8 (no additives) and could be easily discharged from the residue distillation pot.

(Example 9.10) The same conditions as Examples 1 to 8 were used, except that other phthalate esters shown in Table 2 were used instead of di-2-ethylhexyl phthalate, and the amount added was limited to 2.5% by weight. I went there. The results are shown in Table 2.

The distillation residue did not increase in viscosity and could be easily discharged from the residue distillation vessel in the same manner as in Examples 1 to 7.

(Comparative Examples 1 to 3) It was carried out under the same conditions as Examples 1 to 8, except that the additives shown in Table 3 were used instead of di-2-ethylhexyl phthalate, and the amount added was 2.5% by weight. . The results are shown in Table 3.

As in Example 8 (no additives), the viscosity of the distillation residue increased, making it difficult to discharge the residue from the still.

Note that the recovery rate of phthalic anhydride was determined by the following formula.

<Effects of the Invention> According to the present invention, phthalic anhydride in the distillation residue, which was conventionally disposed of or incinerated, can be easily and efficiently recovered with high purity.

Therefore, the unit consumption during the production of phthalic anhydride increases and the cost decreases.

Claims (3)

[Claims] (1) A method for recovering phthalic anhydride from a distillation residue of phthalic anhydride, which comprises adding a phthalic acid ester to the distillation residue and then redistilling the residue. (2) The method for recovering phthalic anhydride from a distillation residue of phthalic anhydride according to claim 1, wherein the phthalic acid ester is used in an amount of 0.1 to 50% by weight based on the distillation residue of phthalic anhydride. (3) The phthalate ester is dimethyl phthalate (DMP
), diethyl phthalate (DEP), dibutyl phthalate (D
BP), diheptyl phthalate (DHP), diphthalate n
-Octyl (nDOP), di-2-ethylhexyl phthalate (DOP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), dilauryl phthalate (DLP), dicyclohexyl phthalate (DCHP),
Claim 1: Diundecyl phthalate (DUP), butylbenzyl phthalate (BBP), di-n-octyl tetrahydrophthalate (nDOTP), di-2-ethylhexyl tetrahydrophthalate (DOTP), or diisodecyl tetrahydrophthalate (DIDTP). or 2. The method for recovering phthalic anhydride from the distillation residue of phthalic anhydride according to 2.