JPS60199855A - Production of benzoic acid - Google Patents

Abstract

PURPOSE:To convert phthalic anhydride in a mixture of phthalic anhydride and benzoic acid to benzoic acid in high yield without affecting the benzoic acid in the mixture, by reacting the mixture with steam in combination with a decarbonation catalyst. CONSTITUTION:Phthalic anhydride is produced by the catalytic vapor-phase oxidation of o-xylene or naphthalene. A mixture of mainly phthalic anhydride and benzoic acid obtained from the purification process is used as a raw material, and is made to react with steam in the presence of a decarbonation catalyst containing zinc oxide and/or lead oxide at 300-500 deg.C to obtain the objective compound. The weight ratio of phthalic anhydride to benzoic acid is 1/10-10/1, and >=1mol of steam based on 1mol of phthalic anhydride in the reaction system is supplied as a mixture with a gas such as air, nitrogen, oxygen, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing benzoic acid. At the same time, the present invention relates to a method for effectively utilizing by-product-containing mixtures of low industrial value found in the phthalic anhydride production process. To be more specific, the present invention deals with the production of phthalic anhydride by oxidizing ortho-xylene or naphthalene to produce phthalic anhydride.
The present invention relates to a method for industrially advantageously producing mainly benzoic acid from a mixture using a raw material (hereinafter referred to as the first distillate) and contacting the mixture as it is with steam and a decarboxylation catalyst.

Benzoic acid is an industrially useful substance and is currently more expensive than phthalic anhydride. Therefore, by converting only phthalic anhydride into benzoic acid in a high yield without changing the benzoic acid in the mixture of 7-talic anhydride and benzoic acid, the first fraction is effective as a raw material for benzoic acid. If it can be used for this purpose, it can be said to have industrial significance.

Currently, phthalic anhydride is mainly produced by a catalytic gas phase oxidation method using orthoxylene or naphthalene as raw materials, but it is known that benzoic acid is produced as a by-product in addition to the main product phthalic anhydride during the oxidation process. . Benzoic acid mixed into phthalic anhydride in the collection step following the oxidation step is usually separated by black part as an initial fraction containing benzoic acid with a low boiling point in the next purification step. At this time, in order to completely remove the benzoic acid in the phthalic anhydride, it is necessary to drive out the benzoic acid vapor with the phthalic anhydride vapor. Thus, the first distillate inevitably contains a portion of phthalic anhydride along with benzoic acid.

Traditionally, the initial distillate of and is incinerated as having low utility value, or in some cases it is added to alkaline water, and the benzoic acid content is obtained as a useful by-product by isolating the benzoic acid component using the difference in solubility with water. However, in this case, it is not an economical method because the recovery treatment of phthalic acid, which is dissolved in water and hydrated, is expensive.

Therefore, although the above first distillate contains industrially useful benzoic acid and phthalic anhydride, it is a complex mixture that is difficult to separate, so it has no industrial value, and at best it cannot be evaluated as a fuel. The reality is that it has become something that will remain.

As a result of intensive research into economically effective ways to use the first distillate, the present inventors discovered an industrially effective method for producing benzoic acid using it as a raw material with a high yield. The present invention has now been completed.

fixed That is, the present invention is specifically adapted as follows.

(1) When producing phthalic anhydride by oxidizing naphthalene or ortho-xylene, a mixture mainly consisting of phthalic anhydride and benzoic acid found in the purification process is used as a raw material, and the mixture is decarboxylated together with steam. 1. A method for producing benzoic acid, which comprises producing mainly benzoic acid from the mixture by contacting the mixture with a catalyst for use in the production of benzoic acid.

(2) The method of (1) above, wherein the decarboxylation catalyst contains zinc oxide and/or lead oxide.

The present invention will be explained in more detail below.

Originally, a method for producing benzoic acid by using phthalic anhydride as a raw material and bringing it into contact with a decarboxylation catalyst in the presence of water vapor is known (Da Organic Chemistry Vol. 9, p. 368, published by Asakura Shoten). However, by using the first distillate in the 7-thalic anhydride production process, that is, mainly a mixture of phthalic anhydride and benzoic acid, as a raw material, these active ingredients can be converted into benzoic acid in a good yield, thereby increasing the added value of the first distillate. No attempt has been made to increase this. The inventors initially predicted that if a decarboxylation reaction was carried out using the mixture as a raw material, the benzoic acid in the raw material would also be decarboxylated, and as a result, the yield of benzoic acid would deteriorate. Chiru.

However, as a result of various studies, it was surprisingly discovered that benzoic acid hardly decomposes, and phthalic anhydride is converted into benzoic acid with good yield, and the present invention was completed.

The content ratio of 7-talic anhydride and benzoic acid in the initial distillate used as raw materials in the present invention naturally varies depending on the purification process in the phthalic anhydride production process described above, especially the black part conditions for separating benzoic acid from phthalic anhydride. do. Usually phthalic anhydride/benzoic acid =
7.0 to 1 oA (weight ratio), and any value within this range can be used as a raw material. In some cases, the initial distillate may contain maleic acid and phthalide, which are by-produced in the phthalic anhydride manufacturing process, but their content ratio has little effect on the method of the present invention. In particular, even if maleic acid is contained, in the method of the present invention, by allowing molecular oxygen to coexist in the decarboxylation reaction system, most of the maleic acid is decomposed to carbon dioxide gas, and separation and removal from the produced benzoic acid is not necessary. It was also found that the operation is very simple.

The decarboxylation catalyst used in the present invention may be any catalyst that completely decarboxylates phthalic acid to produce benzoic acid, but from the viewpoint of obtaining benzoic acid in a good yield, zinc oxide and/or zinc oxide are preferably used.
Alternatively, a catalyst containing lead oxide may be used. In this case, the decomposition rate of benzoic acid in the raw material can be kept low, and the selectivity from phthalic anhydride to benzoic acid is high, thus maintaining a high yield of benzoic acid from the first fraction. Furthermore, even when the initial distillate, which is a raw material, contains maleic acid, it has the ability to increase the decomposition rate, which is advantageous in subsequent purification.

The catalytically active components may be used alone or together with a carrier such as titanium oxide, silicon carbide, alumina, or silica. In particular, it is preferable to use silicon carbide or titanium oxide. The catalyst may be in any commonly used form such as a powder or a molded body. The amount of water vapor to be added is not limited as long as it is sufficient to hydrate phthalic anhydride in the raw material, that is, at least 1 mol or more per 1 mol of phthalic anhydride in the reaction system. It may be supplied together with a conductive gas such as air, nitrogen, or oxygen.

As for the reaction mode, it is preferable to carry out the reaction using a gas phase flow system.

As a specific embodiment, for example, a reaction tube filled with a catalyst is
The reaction temperature is increased to 00 to 500° C., and the raw material gas and steam are passed through the catalyst layer together with the above-mentioned conduction gas as the case may be. The raw material gas concentration at that time can be set arbitrarily, but preferably 0.1
~50 capacity chi, space velocity (SV) 100~10,
The range is 000 shi' (STP).

However, the reaction format is merely a specific example and is not limited to the above method.

The present invention will be explained in more detail with reference to Examples below. However, in the examples, the yield of benzoic acid was expressed by the following formula.

Example 1 (a) Production of catalyst Zinc oxide powder 501 was added and dissolved in soo ml of water to which concentrated nitric acid was added. Silicon carbide powder 5ofP (average particle size 0.3μ, B
ET surface area of 12,7 g/i was added and suspended. This suspension was sprayed onto a heated and rotating spherical silicon carbide carrier (average diameter 3 mm) and then calcined at 520°C to produce a catalyst other than ZnO. The carrying amount at this time is 41111P/100mA! It is a carrier.

(b) Reaction The catalyst 959 obtained in Example 1(a) was filled into a tubular reaction tube with an inner diameter of 21 mm, and the tube wall temperature was set at 440°C.

Next, the mixture was passed through the first distillate catalyst prepared in the phthalic anhydride manufacturing process (8V-1,000Hr'). The composition of the raw materials at this time was 40% by weight of benzoic acid and 60% by weight of phthalic anhydride.
The raw material gas concentration in the conduction gas was 1.1 volume. Moreover, water/phthalic anhydride=83 (molar ratio).

The reaction tube outlet gas was cooled and collected, dissolved in acetone, and unreacted phthalic anhydride and total benzoic acid were quantified by gas chromatography, and the following results were obtained.

Benzoic acid yield: 82.9% Residual phthalic anhydride in product: 3.8% by weight Example 2 (a) Production of catalyst In Example 1(a), titanium oxide powder (anatase type, BET) was used instead of silicon carbide powder. surface area zoi
/r) was carried out in the same manner except that ZnO-TiO2 (Z
A catalyst consisting of nO/Ti01 = 1/1 dissolution ratio) was produced. The amount of support at this time is 2s, sr/100m1
It is a carrier.

(b) In Reaction Example 1 (b), the first distillate from the phthalic anhydride production process was used as a raw material (composition: 30% by weight of benzoic acid, 55% by weight of phthalic anhydride, containing 15% by weight of impurities such as maleic anhydride). ) and using air as the conduction gas, the same procedure was carried out, and the results shown in Table 1 below were obtained. Note that no impurities such as maleic anhydride were observed in the outlet gas.

Example 3 (,) Preparation of catalyst Instead of preparing the aqueous solution of zinc nitrate in Example 1 (a), lead nitrate 509 was added to 500 m/! of water! A catalyst called pbo was produced in the same manner except that it was dissolved in a homogeneous solution. The amount supported at this time was 34.5f/100ml carrier.

(b) 10% by weight of benzoic acid as a raw material in Reaction Example 1(b)
The same procedure was carried out except that a mixture of phthalic anhydride and phthalic anhydride (90% by weight) was used, and the results shown in Table 1 below were obtained.

Table-1

Claims (2)

[Claims] (1) When producing phthalic anhydride by oxidizing naphthalene or orthoxylene, a mixture mainly consisting of phthalic anhydride and benzoic acid found in the refining process is used as a raw material, and the mixture is used together with steam for decarboxylation. 1. A method for producing benzoic acid, which comprises producing mainly benzoic acid from the mixture by contacting it with a catalyst. (2) Claims (11) characterized in that the decarboxylation catalyst contains zinc oxide and/or lead oxide
The method described in section.