JPS6056149B2 - Production method of high purity phthalic anhydride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing highly pure phthalic anhydride by purifying crude phthalic anhydride obtained by catalytic gas phase oxidation of naphthalene.

Specifically, the present invention relates to a method for producing high-purity phthalic anhydride by removing fractions contained in the above-mentioned crude phthalic acid.

Generally, catalytic gas phase oxidation of naphthalene as a raw material using a vanadium catalyst to obtain phthalic anhydride is widely practiced industrially.

In the crude phthalic anhydride obtained by this method, naphthoquinone, which is an intermediate oxide from naphthalene, is present as an impurity in an amount of 0.5 to 5% by weight. It is well known that a non-negligible amount (several ppm) of naphthoquinone is mixed into phthalic acid, and that this mixed naphthoquinone is an extremely inconvenient compound as it reduces the color tone and thermal stability of the product. ing. The product phthalic anhydride is a colorless liquid or white crystal, but naphthoquinone is contained in O, 5pp.
When m (weight) is also present, the product is colored yellow.

This alone reduces the value of the product. Many methods have been proposed to prevent naphthoquinone from being mixed into the conventional phthalic anhydride product. They can be broadly classified as follows. (a) By reacting the naphthoquinone in the crude phthalic anhydride with another compound, a compound with a higher boiling point than phthalic anhydride is formed and separated by distillation.

For example, an unsaturated compound such as maleic anhydride is reacted with naphthoquinone (see Japanese Patent Publication No. 45-16937), or tetrahydroanthraquinone is reacted with naphthoquinone and phthalic anhydride is separated by distillation (Japanese Patent Publication No. 16-16937). 6874 Ginko) method.

(CF) A method of polymerizing naphthoquinone in crude phthalic anhydride with an oxide such as sulfuric acid (Ullmann, Erl
cycleOpediaOfChemicalTechr
(Refer to IOLO edition, Vol. 13, pp. 720-721).

(c) A method of polymerizing naphthoquinone in crude phthalic anhydride by adding an alkali metal compound such as potassium phthalate (see US Pat. No. 3,155,688).

By the way, in the method (a), the processing agent added for the purpose of reducing naphthoquinone requires a large amount because the amount is equivalent to or close to the molar amount of naphthoquinone.

Moreover, these processing agents are quite expensive, and the cost of separating and removing naphthoquinone cannot help but increase significantly. Also(
Regarding method C7), the polymerization rate of naphthoquinone is high and the processing agent is available at low cost, so it is often used industrially in comparison to (a).

However, after the naphthoquinone is polymerized at high temperatures, the remaining sulfuric acid must be neutralized and removed.
Generally, it is neutralized with a basic alkali metal salt such as sodium carbonate, but as a result, two treatment operations using two types of treatment agents are required, which complicates the process itself. Furthermore, sulfuric acid itself is a chemical that tends to corrode equipment, and sulfur oxides are generated during heat treatment, and the treatment of sulfur compounds that are mixed into the residue after distillation is expensive in terms of pollution prevention. There are some drawbacks. The method (c) is advantageous compared to the methods (a) and (c) because the processing agent used is inexpensive and the operation is simple, and there is relatively little corrosion on the equipment.

However, the polymerization rate of naphthoquinone is extremely slow, and it is necessary to take a long treatment time. Otherwise, a large amount of alkali metal compounds must be added, and since these compounds themselves are insoluble in phthalic anhydride, they may accumulate in the processing tank or clog the pipes or trays of the distillation column. has. Certainly, there have been attempts to increase the polymerization rate of naphthoquinone and reduce the amount of processing agent. For example, a method of using an alkali metal compound and a peroxide in combination is disclosed in US Pat. No. 3,338,924. However, according to the description in the patent specification, the method of using sodium carbonate and hydrogen peroxide in combination is applicable only to crude phthalic anhydride containing 25% by weight or more of phthalic anhydride produced from ortho-xylene. (i.e., a mixture of phthalic anhydride produced from naphthalene and phthalic anhydride produced from ortho-xylene), but it is not an advantageous method for only the crude phthalic anhydride produced from naphthalene. In fact, the patented invention does not describe anything regarding the polymerization treatment of naphthoquinone. Moreover, adding a dangerous peroxide to the high-temperature heat treatment of crude phthalic anhydride, as in the US patent invention, would require overcoming great difficulties in maintaining safety; For example, when hydrogen peroxide is used as a substance, the water produced converts phthalic anhydride to hydrated phthalic acid, and this phthalic acid undergoes a decarboxylation reaction due to the catalytic action of an alkali metal, changing to benzoic acid. There are also drawbacks that may lead to a decrease in the yield and quality of purified phthalic anhydride. Furthermore, peroxide decomposes in a short time at the high temperatures at which it is heat treated, and its effectiveness is not maintained for a long period of time, making it difficult to control the process.
The object of the present invention is to provide an industrially safe and effective method for obtaining high purity phthalic anhydride substantially free of naphthoquinone from crude phthalic anhydride containing naphthoquinone obtained by catalytic gas phase oxidation of naphthalene. The purpose of the present invention is to provide a method for treating crude phthalic anhydride, which significantly increases the rate of naphthoquinone reduction, does not cause any unnecessary side reactions, does not leave any excess decomposition products, and substantially eliminates phthalic anhydride. The objective is to produce high quality phthalic anhydride without reducing the yield of phthalic anhydride.

That is, the present invention is specified as follows.

(1) High purity, characterized by adding an alkali metal compound to crude phthalic anhydride obtained by catalytic gas phase oxidation of naphthalene, heat-treating it while blowing molecular oxygen-containing gas, and then subjecting it to distillation. Method for producing phthalic anhydride. (2) The heat treatment temperature is 150 to 3000C, preferably 250 to 280C, and the treatment time is 1 to 1 hour;
Crude phthalic anhydride 1K9 as the amount of molecular oxygen injected
at least 1 x 10-4 mol/hour, preferably 2 moles per hour
-4 to 1×10 −3 mol/hour, the method described in (1) above.

(3) The amount of the alkali metal compound added is 0.0001 to 0.5% by weight, preferably 0.0001 to 0.5% by weight, based on the crude phthalic anhydride.
．． 0001-0.1% by weight, more preferably 0.005
0.05% by weight of the above (
1) or the method described in (2).

(4) The alkali metal compound is at least one selected from the group consisting of basic inorganic acid salts and organic acid salts of alkali metals (1), (2) or (3) above. ) method described.

The method of the present invention will be explained in more detail below. In the crude phthalic anhydride obtained by catalytic gas phase oxidation of naphthalene,
Usually about 0.5-5% by weight of naphthoquinone is included. This crude phthalic anhydride was heated at 200 to 300°C.
Preferably, an industrially advantageous method is to add additives and heat treat at 250 to 2,800 C, polymerize impurity naphthoquinone, convert it to a high boiling point product, and then distill it. The alkali metal compounds used include basic inorganic acid salts of lithium, sodium, potassium, rubidium, cesium, such as carbonates, bicarbonates, nitrates, as well as organic acid salts, such as maleic acid, fumaric acid, succinic acid, etc. Specific examples include monosalts and di-salts of acids, adipic acid, benzoic acid, phthalic acid, and other hydroxides. Particularly preferred among these are sodium,
Carbonates and bicarbonates such as potassium, and mono- and di-salts of maleic acid, fumaric acid, benzoic acid, and phthalic acid. The molecular oxygen-containing gas to be blown is usually air mixed with nitrogen gas to give an oxygen concentration of 1 to 1% by volume, preferably 3 to 8% by volume.

The effect of its addition is exhibited by dispersing it in crude phthalic anhydride and blowing it into it. As is clear from the following comparative examples, if the amount of oxygen supplied is small, the effect is not sufficient, and the treatment agent must be used in a large amount. On the other hand, increasing the amount of oxygen has a corresponding effect, but due to the high temperature treatment, it is necessary to avoid dispersing and supplying too much oxygen to prevent danger and pollution. The present invention will be specifically described below using examples.

Example 1 Crude phthalic anhydride having the following composition was obtained by catalytic gas phase oxidation of naphthalene.

1k9 of this crude phthalic anhydride was placed in a flask, heated to 270°C under a nitrogen atmosphere, and 0.1y (1k9) of sodium carbonate was added to the flask.
00 ppm) was added.

Next, a mixed gas of 5% by volume of oxygen and 95% by volume of nitrogen was blown into the mixture at 120cc/hour (equivalent to 2.5×10-4 mol/hour of oxygen gas per 1kg of crude phthalic anhydride) and heat-treated for 10 hours. Ivy. The thus obtained phthalic anhydride was distilled into a distillation column (with an inner diameter of 32 m) having a single-stage perforated plate.
φ, height 500 m) under a pressure of 55 mHg (absolute pressure) and a reflux ratio of 0.5.

As a result, APHAlO, a crude phthalic anhydride with a freezing point of 131.17C, was obtained. Thermal stability after heating at 250° C. for 2 hours was also high quality for APHAlO, and the color of the crystals was also white.

The purified product contained 0.1 ppm or less of naphthoquinone, 0.07% by weight of benzoic acid, and 99.93% by weight of phthalic anhydride. The purification yield was 97.5% by weight. Comparative Example 1 Crude phthalic anhydride 1k9 with the same composition as used in Example 1
was heated in a flask to 270° C. under a nitrogen atmosphere, and 0.1y of sodium carbonate was added.

Furthermore, hydrogen peroxide solution (3% amount) was added to phthalic anhydride.
0.7% by weight was added, and then heated for 1 minute.
Note that hydrogen peroxide was violently decomposed upon addition. Then,
The obtained phthalic anhydride was distilled in the same manner as in Example 1 to obtain phthalic anhydride with a yellowish crystal appearance. The starting point is APHA2OO, the freezing point is 130J℃, and the naphthoquinone in the purified product is 500ppm1 benzoic acid 0. Weight %, phthalic anhydride content 99.61% by weight, purification yield 97. The amount was %. Examples 2 to 17 and Comparative Examples 2 to 4 1k9 of each crude phthalic anhydride acid having the same composition as that used in Example 1 was placed in a flask, and the treatment agent and its usage amount were changed as shown in Table 1 below. The amount of naphthoquinone in the crude phthalic anhydride was measured in the same manner as in Example 1 except that the amount of oxygen blown, the heat treatment temperature, and the treatment time were changed.

Claims (1)

[Claims] 1. A method characterized by adding an alkali metal compound to crude phthalic anhydride obtained by catalytic gas-phase oxidation of naphthalene, heat-treating it while blowing molecular oxygen-containing gas, and then subjecting it to distillation. A method for producing high-purity phthalic anhydride. 2 Heat treatment temperature is 150-300℃, treatment time is 1-300℃
15 hours, and the amount of molecular oxygen injected is at least 1 x 10^-^4 mol/kg of crude phthalic anhydride.
2. The method according to claim 1, wherein the method is: 3. The method according to claim 1 or 2, wherein the amount of the alkali metal compound added is in the range of 0.0001 to 0.5% by weight based on the crude phthalic anhydride. 4. The alkali metal compound is at least one selected from the group consisting of basic inorganic acid salts and organic acid salts of alkali metals.
4. The method according to claim 1, 2 or 3, wherein the method is a species.