JPH10237063A - Production of high-purity phthalic anhydride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient method for treating a crude phthalic anhydride by which the product purity and economical efficiency are satisfied in order to obtain a high-purity phthalic anhydride from the crude phthalic anhydride prepared by the catalytic vaor-phase oxidation of naphthalene or a mixture thereof with o-xylene. SOLUTION: High-purity phthalic anhydride can efficiently be produced by heat-treating a crude phthalic anhydride in the presence of phthalimide, maleic anhydride and an alkali metallic compound while blowing molecular oxygen into the reactional mixture, then purifying and distilling the heat-treated mixture and regulating the total content of the phthalimide and maleic anhydride in the crude phthalic anhydride at the time of heat treatment to 0.4-5.0 ratio expressed in terms of molar ratio to naphthoquinone in the crude phthalic anhydride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a technique for purifying phthalic anhydride. In particular, the present invention relates to a method for producing high-purity phthalic anhydride by purifying crude phthalic anhydride obtained by catalytic vapor phase oxidation from naphthalene alone or a mixed raw material of naphthalene and orthoxylene.

[0002]

2. Description of the Related Art The production of phthalic anhydride is widely and industrially carried out generally by a method of catalytic gas-phase oxidation using naphthalene and / or orthoxylene as a raw material and a vanadium-titanium catalyst.

In recent years, a method has been proposed in which two types of raw materials are mixed and reacted.

[0004] Naphthoquinone, which is an intermediate oxide of phthalic anhydride, is mixed into crude phthalic anhydride produced from naphthalene as a raw material.
In the reaction using naphthalene alone, 0.2 to 1% of naphthoquinone is produced as a by-product. When naphthalene is mixed with orthoxylene, the amount of naphthoquinone by-product generally decreases as the mixing ratio increases.

[0005] Since naphthoquinone has a vapor pressure close to that of phthalic anhydride, it is difficult to remove it by a simple distillation operation, and even if a few ppm remain in the purified phthalic anhydride, the color tone and thermal stability of the product quality deteriorate. It is well known that these are very problematic compounds. The product phthalic anhydride is a colorless liquid or white crystal. The presence of naphthoquinone causes the product to be colored yellow. This alone reduces the value of the product.

In the case of crude phthalic anhydride obtained from a raw material of ortho-xylene alone, 250-270
High-purity phthalic anhydride can be obtained by performing a heat treatment at a temperature of several hours and then distilling. On the other hand, when a raw material containing naphthalene is used, naphthoquinone is by-produced, and naphthoquinone cannot be removed only by heating the crude phthalic anhydride in the same manner as described above. In general, naphthoquinone is removed as a residue by subjecting crude phthalic anhydride to polycondensation by some treatment or converting it to a high-boiling substance. Therefore, many methods have been proposed to treat crude phthalic anhydride to prevent naphthoquinone from being mixed into products.

[0007] The treatment method is as follows:
No. 6937 proposes a method of reacting an unsaturated compound such as maleic anhydride with naphthoquinone, and (b) Japanese Patent Publication No. 60-28834 proposes a method of reacting tetrahydroanthraquinone with naphthoquinone.

As another method, (c) Japanese Patent Publication No. 60-56149 discloses a method in which an alkali metal compound and molecular oxygen are used in combination.

(D) Japanese Patent Publication No. 5-8194 discloses a method of treating with a polydiene compound, and (e) Japanese Patent Application Laid-Open No.
-A method of treating with a compound such as cyclododecatriene or a combination thereof with an alkali metal compound has been proposed.

[0010]

However, these methods have problems in practice.

As for (a), naphthoquinone is originally known to be susceptible to substitution and addition reactions at the 2 and 3 positions due to its chemical structure, and is unsaturated such as maleic anhydride having a double bond. Although the reaction with the compound is naturally presumed, in reality, the reaction hardly proceeds in the crude phthalic anhydride, so that a sufficient treatment effect cannot be expected by the method using only maleic anhydride.

In the method (b), a large amount of a treating agent is required to achieve a sufficient treating effect, and there is a problem in cost.

Further, the method (c) has a disadvantage that the polymerization rate is slow and the treatment time is long. When a large amount of an alkali metal compound is used to make up for the disadvantage, the deposition in the treatment tank and the blockage of the piping are prevented. There are drawbacks to invite.

In the methods (d) and (e), it is necessary to increase the amount of addition in order to enhance the effect. For this reason, the distillation yield is increased due to an increase in side reactions during the heat treatment and an increase in distillation residue. This is practically disadvantageous in that the rate decreases and the cost increases.

The problem to be solved by the present invention is to reduce the product purity and economical efficiency of obtaining high-purity phthalic anhydride from crude phthalic anhydride obtained by catalytic gas-phase oxidation of naphthalene or a mixture of naphthalene and orthoxylene. It is an object of the present invention to provide a method for treating crude phthalic anhydride that is satisfactory and efficient.

[0016]

DISCLOSURE OF THE INVENTION As a means for obtaining high-purity phthalic anhydride from crude phthalic anhydride obtained by catalytic gas phase oxidation of naphthalene or a mixture of naphthalene and orthoxylene, the present inventors have proposed a method for obtaining crude phthalic anhydride. The treatment method of acid was studied diligently.

As a result, the crude phthalic anhydride is converted into a solution in the presence of maleic anhydride, phthalimide and an alkali metal compound.
After a heat treatment while blowing in molecular oxygen, a method for purifying and distilling was found, and the present invention was completed.

In order to solve the above-mentioned problems, the method for producing high-purity phthalic anhydride according to the first aspect of the present invention provides a method for producing crude phthalic anhydride in the presence of maleic anhydride, phthalimide and an alkali metal compound. After heating while blowing, purifying and distillation, and the total content of maleic anhydride and phthalimide in the crude phthalic anhydride at the time of the heat treatment with respect to naphthoquinone which is a by-product during the production of the crude phthalic anhydride In a molar ratio of 0.4 to 5.0.

According to a second aspect of the present invention, in the method for producing high-purity phthalic anhydride according to the first aspect, the molar ratio of maleic anhydride to phthalimide is 2: 8 to 8: 2.

The method for producing high-purity phthalic anhydride of the invention according to claim 3 is characterized in that the alkali metal compound is Li, Na, K,
It is characterized in that it is at least one selected from the group consisting of carbonate, bicarbonate, nitrate, hydroxide, and organic acid salt of at least one alkali metal element selected from the group consisting of Rb and Cs. .

The method for producing high-purity phthalic anhydride of the invention according to claim 4 is characterized in that the crude phthalic anhydride at the time of heat treatment contains 0.0001 to 0.5% by weight of an alkali metal compound.

The method for producing high-purity phthalic anhydride according to the fifth aspect of the present invention is characterized in that the heat treatment temperature is 200 to 300 ° C. and the heat treatment time is 1 to 50 hours.

In the method for producing high-purity phthalic anhydride according to the present invention, the amount of molecular oxygen blown during the heat treatment is 5 × 10 ^{-5 to} 5 × 10 ^-3 mol / hour per kg of crude phthalic anhydride. It is characterized by being.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The crude phthalic anhydride used in the present invention is preferably produced by catalytic gas-phase oxidation using naphthalene or a mixture of naphthalene and orthoxylene as a raw material. If the raw material contains 0.01% by weight of naphthalene, the crude phthalic anhydride obtained by subjecting it to catalytic gas phase oxidation contains
There is a risk of by-products longer than pm. Therefore, the composition of the raw material mixture for producing crude phthalic anhydride used in the present invention is 0.01 wt%.
≦ naphthalene / (naphthalene + orthoxylene) × 100 wt%.

The catalytic gas phase oxidation catalyst used in the present invention is a catalyst containing vanadium and titanium.
One example is vanadium pentoxide and titanium dioxide. These are preferably used supported on an inert carrier. Examples of the inert carrier include silica gel and SiC.

The reaction conditions for the catalytic gas phase oxidation in the present invention are as follows: raw material gas concentration: 50 to 80 g / Nm ³ , space velocity: 1,000 to 4,000 H
r ⁻¹ , the reaction temperature is 330 to 400 ° C. More preferable reaction conditions include a raw material gas concentration of 60 to 70 g / Nm ³ and a space velocity of 2,000.
3,0003,000 Hr ⁻¹ , reaction temperature 350350400 ° C.

As the method for collecting phthalic anhydride in the present invention, solvent collection, cooling solid collection, etc. are used, but cooling solid collection is preferably used. 55-75 ° C inside the collection tower,
Preferably, the temperature is controlled at 65 to 75 ° C., and the crystals are collected.

Examples of the alkali metal compound used in the present invention include carbonate, bicarbonate, nitrate, hydroxide of at least one alkali metal element selected from the group consisting of Li, Na, K, Rb and Cs. It is at least one selected from the group consisting of organic acid salts. Specific examples of the organic acid salts include mono- and di-salts such as maleic acid, fumaric acid, succinic acid, adipic acid, benzoic acid and phthalic acid. Among them, preferred are sodium and potassium carbonates, bicarbonates, hydroxides, and mono- and di-salts of maleic acid, fumaric acid, benzoic acid and phthalic acid of sodium and potassium as organic bases. Among them, sodium carbonate and potassium hydroxide are particularly preferred.

The heat treatment method of the crude naphthalene of the present invention is more effective than the method of blowing oxygen in the presence of phthalimide and sodium carbonate or blowing oxygen in the presence of maleic anhydride and sodium carbonate. Process can be performed. That is, in the method of the present invention, due to the synergistic effect of phthalimide and maleic anhydride, the treatment can be performed sufficiently even with a small amount of phthalimide and maleic anhydride compared to the above two methods. In the present invention, the total content of maleic anhydride and phthalimide in the crude phthalic anhydride at the time of the heat treatment is 0.0 in molar ratio to the content of naphthoquinone in the crude phthalic anhydride.
4 or more has a sufficient effect. However, unnecessarily increasing the addition amount of maleic anhydride or phthalimide is not preferable because it significantly increases the purification cost. The total addition amount of maleic anhydride and phthalimide is preferably not more than 5 times mol of naphthoquinone.

The amounts of maleic anhydride and phthalimide added are such that the molar ratio of maleic anhydride to phthalimide is 2: 8 to
A ratio of 8: 2 is preferable for exhibiting a sufficient synergistic effect.

The amount of the alkali metal compound added is 0.0001 to 0.5% by weight, preferably 0.0001% by weight, based on the crude phthalic anhydride.
It may be in the range of 0.1 to 0.1% by weight, more preferably 0.005 to 0.05% by weight.

The heat treatment temperature is 200 to 300 ° C., preferably 25
0-270 ° C. If the heat treatment temperature is low, the treatment becomes insufficient, and if the heat treatment temperature is too high, the production of benzoic acid due to the decarboxylation reaction increases, leading to a decrease in yield, which is not preferable. The heat treatment time is 1 to 50 hours, preferably 10 to 20 hours.
Time.

As the molecular oxygen-containing gas, pure oxygen or a gas obtained by mixing nitrogen gas with air to have an oxygen concentration of 1 to 10% by volume, preferably 3 to 8% by volume is used. Preferably, the molecular oxygen-containing gas is dispersed and blown into crude phthalic anhydride by various methods.

There are various methods for dispersing the molecular oxygen-containing gas. As an example, a ring-shaped tube provided with a large number of pores is placed at the bottom of the heat treatment tank, and the molten crude phthalic acid is dispersed. There is a method of releasing gas from pores while stirring with a stirrer.

The amount of oxygen blown is 5 × 10 ^{-5 to} 5 × 10 ^-3 mol / hour, preferably 2 × 10 ^-4 to 1 × 10 5 / kg of crude phthalic anhydride.
^What is necessary is ^{just -3} mol / hour.

As a method of supplying maleic anhydride, a method of adding maleic anhydride at the time of heat treatment is preferable. As another supply method, by selecting the reaction conditions and the collection conditions of the catalytic gas phase oxidation, it is possible to increase or decrease the production amount of maleic anhydride which is a by-product, and it is necessary to heat the crude phthalic anhydride. There is also a method in which part or all of the amount is contained, and only the insufficient amount is added during the heat treatment.

As a method of supplying phthalimide, a method of adding phthalimide at the time of heat treatment is preferable. As another supply method, phthalimide is also generated by the oxidation of quinoline, which is one of the impurities in the raw material naphthalene. There is also a method in which the amount of production is increased or decreased, and a part or all of the amount necessary for the heat treatment of the crude phthalic anhydride is contained, and only the insufficient amount is added during the heat treatment.

The content of naphthoquinone is determined by adding a small amount of activated carbon to methyl alcohol, dissolving and decolorizing, filtering, adding a malononitrile solution to the filtrate to form a color, and measuring the absorbance.

According to JIS (K-4128), the melting color is determined by taking a measurement sample in a colorimetric tube made of hard glass, heating and dissolving in a heat block, and comparing with the color number of the Hazen standard solution.

The freezing point is determined according to JIS (K-4128) by placing a measurement sample in a hard glass test tube, setting a standard thermometer, melting in a glycerin bath, and lowering the temperature.

FIG. 1 shows that naphthoquinone was added to purified phthalic anhydride.
5% by weight was added to produce simulated crude phthalic anhydride, which was melted and subjected to a heat treatment under the following conditions.

[Heat treatment conditions] ・ Heat treatment temperature 270 ° C. ・ Sodium carbonate 200 ppm ・ Gas blowing O ₂ 8% gas 200 ml / kg ・ hour (O ₂ 7.14 × 10 ^-4 mol / kg ・ hour) ・ Stirring speed 400 rpm [ Additives] (1) Sodium carbonate alone (2) Maleic anhydride alone (1.0) (3) Phthalimide alone (1.0) (4) Phthalimide (0.4) + sodium carbonate (5) Maleic anhydride (0.4) + Carbonic acid Sodium (6) phthalimide (0.2) + maleic anhydride (0.2) + sodium carbonate * () indicates the molar ratio to naphthoquinone.

As can be seen from FIG. 1, compared to the conditions of (4) phthalimide + sodium carbonate or (5) maleic anhydride + sodium carbonate, these two were combined.
(6) phthalimide + maleic anhydride + sodium carbonate,
According to the method described above, a remarkable synergistic effect is shown.

[0044]

EXAMPLES Examples and comparative examples of the present invention will be shown below, but the present invention is not limited to these examples.

Example 1 A crude phthalic anhydride mainly containing the following impurities was obtained by a catalytic gas phase oxidation reaction of naphthalene.

Naphthoquinone 0.67% by weight Phthalimide 0.16% by weight Maleic anhydride 0.10% by weight The total content of maleic anhydride and phthalimide was 0.49 in molar ratio with respect to the content of naphthoquinone in the crude phthalic anhydride. . 1 kg of this crude phthalic anhydride is placed in a flask, heated to 270 ° C. under a nitrogen atmosphere,
0.2 g (corresponding to 200 ppm) was added. Then add 8 oxygen
The mixture was heated at a rate of 200 ml / hour (corresponding to 7.14 × 10 ^-4 mol / hour) with a mixed gas containing 92% by volume of nitrogen and 92% by volume.

The phthalic anhydride thus obtained was distilled at a reflux ratio of 0.7 under a reduced pressure of 7 K pascal using a distillation column (inner diameter 32 mmφ, height 500 mm) having 10 perforated plates.

The quality of the purified product is such that the crystal appearance is white and the freezing point is 13
APHA5, naphthoquinone 0.1 ppm or less, melting temperature APHA5 or more, and high-quality APHA10 with heat stability of 250 ° C for 90 minutes were obtained.

Example 2 A crude phthalic anhydride having an impurity composition shown in Table 1 was obtained in the same manner as in Example 1 except that naphthalene / orthoxylene = 50/50 (weight ratio) was used as a raw material. This was subjected to heat treatment and purification in the same manner as in Example 1. The results were as shown in Table 1.

Example 3 Phthalimide was added to crude phthalic anhydride obtained by the catalytic gas phase oxidation reaction of naphthalene to obtain crude phthalic anhydride having the impurity composition shown in Table 1. This was subjected to heat treatment and purification in the same manner as in Example 1. The results were as shown in Table 1.

Examples 4 to 6 Naphthoquinone and phthalimide were added to purified phthalic anhydride to obtain simulated crude phthalic anhydride having the impurity composition shown in Table 1. This was subjected to heat treatment and purification in the same manner as in Example 1. The results were as shown in Table 1.

Example 7 Example 1 was repeated except that sodium carbonate was changed to potassium hydroxide and the added amount was equivalent to 100 ppm.
The same was done. The results were as shown in Table 1.

Comparative Example 1 Crude phthalic anhydride having the impurity composition shown in Table 1 was obtained by catalytic gas phase oxidation reaction of naphthalene. The obtained crude phthalic anhydride was subjected to heat treatment and purification in the same manner as in Example 1. The results were as shown in Table 1.

[Comparative Example 2] Naphthoquinone, phthalimide and maleic anhydride were added to purified phthalic anhydride.
A simulated crude phthalic anhydride having the impurity composition shown in the following was obtained. This was subjected to heat treatment and purification in the same manner as in Example 1. The results were as shown in Table 1.

Comparative Example 3 Naphthoquinone and maleic anhydride were added to purified phthalic anhydride to obtain a simulated crude phthalic anhydride having the impurity composition shown in Table 1. This was subjected to heat treatment and purification in the same manner as in Example 1. The results were as shown in Table 1.

Comparative Example 4 Naphthoquinone and phthalimide were added to purified phthalic anhydride to obtain a simulated crude phthalic anhydride having the impurity composition shown in Table 1. This was subjected to heat treatment and purification in the same manner as in Example 1. The results were as shown in Table 1.

Comparative Example 5 Naphthoquinone, phthalimide and maleic anhydride were added to purified phthalic anhydride.
A simulated crude phthalic anhydride having the impurity composition shown in the following was obtained. This was subjected to heat treatment and purification in the same manner as in Example 1 except that sodium carbonate was not added. The results were as shown in Table 1.

[0058]

[Table 1]

[0059]

The crude phthalic anhydride obtained by the catalytic gas phase oxidation of naphthalene or a mixture of naphthalene and ortho-xylene is subjected to the heat treatment according to the present invention, followed by purification and distillation, whereby high-purity phthalic anhydride can be efficiently produced. can get.

[Brief description of the drawings]

FIG. 1 shows a comparison of the change in naphthoquinone content in crude naphthalene with heat treatment time under various additive conditions.

Claims (6)

[Claims] 1. A method for producing high-purity phthalic anhydride by purifying and distilling crude phthalic anhydride, wherein the crude phthalic anhydride is blown with molecular oxygen in the presence of maleic anhydride, phthalimide and an alkali metal compound. After performing a heat treatment while mixing, purifying and distilling, and the total content of maleic anhydride and phthalimide in the crude phthalic anhydride at the time of the heat treatment is a mole relative to the content of naphthoquinone in the crude phthalic anhydride. A method for producing high-purity phthalic anhydride, wherein the ratio is 0.4 to 5.0. (2) The molar ratio of maleic anhydride to phthalimide is
The method for producing high-purity phthalic anhydride according to claim 1, wherein the ratio is 2: 8 to 8: 2. 3. The method according to claim 1, wherein the alkali metal compound is Li, Na, K, R
b, and at least one selected from the group consisting of carbonates, bicarbonates, nitrates, hydroxides, and organic acid salts of at least one alkali metal element selected from the group consisting of Cs. 2. The method for producing high-purity phthalic anhydride according to 1. 4. The method for producing high-purity phthalic anhydride according to claim 1, wherein the crude phthalic anhydride at the time of the heat treatment contains 0.0001 to 0.5% by weight of an alkali metal compound. 5. The heat treatment temperature is 200 to 300 ° C. and the heat treatment time is 1 to 50 hours.
Or the method for producing high-purity phthalic anhydride according to any of 3. 6. The method according to claim 1, wherein the amount of molecular oxygen blown during the heat treatment is 5 × 10 ^{-5 to} 5 × 10 ^-3 mol / hour per kg of crude phthalic anhydride. Or the method for producing high-purity phthalic anhydride according to any of 4.