JPS588074A - Preparation of high purity phthalic anhydride - Google Patents

Abstract

PURPOSE:To prepare a high purity phthalic anhydride free from naphthoquinone, by adding an alkali metal compound to crude phthalic anhydride obtained by the vapor-phase catalytic oxidation of naphthalene, heat-treating the mixture introducing an oxygen-containing gas, and distilling the product. CONSTITUTION:Crude phthalic anhydride is incorporated with 0.0001-0.5wt% alkali metal compund (preferably carbonate or bicarbonate of Na, K, etc.), and heat-treated at 150-300 deg.C for 1-15hr while introducing a gas containing molecular oxygen at a rate of at least 1X10<-4> mole/hour per 1kg of the crude raw material. Naphthoquiinone existing in the crude raw material as impurity is polymetized to a high-boiling material by the heat treatment. A high purity phthalic anhydride can be prepared by removing the polumerized naphthoqinone by distillation. The gas containing molecular oxygen is prepared usually by adding N2 gas to air to reduce the oxygen concentration to 1-10vol% (preferably 3-8vol%).

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 efficiently removing naphthoquinone, an impurity contained in the crude phthalic acid and difficult to separate.

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 heptallic 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 acids, and that this mixed naphthoquinone is an extremely inconvenient compound because it reduces the color tone and thermal stability of the product quality. There is. The product phthalic anhydride is a colorless liquid or white crystal, and naphthoquinone is present in o, s pp
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 naphthoquinone in crude phthalic anhydride with another compound.1. A compound with a higher boiling point than phthalic anhydride is formed and separated by distillation. For example, by reacting an unsaturated compound such as maleic anhydride with naphthoquinone (see Japanese Patent Publication No. 45-16937),
Tetrahydranthraquinone is reacted with naphthoquinone and phthalic anhydride is separated by distillation (Japanese Patent Application Laid-Open No. 53-68
740) method.

(O) A method of polymerizing naphthoquinone in crude phthalic anhydride with an acid compound such as sulfuric acid (Ullmann).

j- Encyclopedia & Chemical Te
(See Chno1ology 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.

Regarding method (1), the polymerization rate of naphthoquinone is high and the processing agent is available at low cost, so it is more commonly used commercially than (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 corrodes 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.

(Compared to methods (a) and (b), the method of → is advantageous because the processing agent used is cheaper and the operation is easier, and there is relatively less corrosion on the equipment.However, the polymerization rate of naphthoquinone is It is extremely slow and requires a long treatment time.Otherwise, a large amount of alkali metal compounds must be added, and these compounds themselves are insoluble in 7-talic anhydride, so they may accumulate in the treatment tank. However, it has drawbacks such as clogging the pipes and trays of the distillation column.It is true that there are attempts to increase the polymerization rate of naphthoquinone and reduce the amount of processing agent.For example, using a combination of an alkali metal compound and a peroxide. A method for doing so 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 crude phthalic anhydride produced from naphthalene. In fact, the patented invention does not describe anything regarding the polymerization treatment of naphthoquinone.

Moreover, it is not possible to add dangerous peroxides to the high-temperature heat treatment of crude phthalic anhydride as in the US patent invention.
Great difficulties must be overcome to maintain its safety, and when hydrogen peroxide, for example, is used as the peroxide, the water produced converts phthalic anhydride into hydrated phthalic acid. There is also the drawback that phthalic acid undergoes a decarboxylation reaction due to the catalytic action of an alkali metal and changes to benzoic acid, which may lead to a decrease in the yield and quality of purified phthalic anhydride. Additionally, peroxides are heat treated at high temperatures,
It is also pointed out that it is difficult to control its operation because it decomposes in a short period of time and its effectiveness is not maintained for a long time.

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 reduction of synaphthoquinone, does not cause any unnecessary side reactions, does not leave any excess decomposition products, and is substantially anhydrous. The objective is to produce high quality phthalic anhydride without reducing the yield of phthalic acid.

That is, the present invention is specified as follows.

High-purity phthalic anhydride is produced 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. Production method.

(2) The temperature of heat treatment is 150-300℃, preferably 2
50 to 280°C, treatment time is 1 to 15 hours, and the amount of molecular oxygen blown is 1 kgM of crude phthalic anhydride, at least 1X10' mol/hour, preferably 2X10' to
The above (1
) method described.

(3) The amount of the alkali metal compound added is 0.0001 to 0.5% by weight, preferably 0.001 to 01% by weight, more preferably 0.005% by weight, based on the crude phthalic anhydride.
The above (characterized in that it is in the range of ~0.05
1) or the method described in (2).

(4) The above (1) and (2), wherein 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.
Or the method described in (3).

The method of the present invention will be explained in more detail below.

Crude phthalic anhydride obtained by catalytic gas phase oxidation of naphthalene usually contains about 0.5 to 5 wt % naphthoquinone. 200% of this crude phthalic anhydride
An industrially advantageous method is to add additives and heat treatment at ~300°C, preferably 250-280°C, to polymerize the impurity naphthoquinone and convert it to a high-boiling point substance, which is then distilled. .

The alkali metal compounds used include basic inorganic acid salts of lithium, sodium, potassium, rubidium, and senlum, such as carbonates, bicarbonates, and nitrates, as well as organic acid salts, such as maleic acid, fumaric acid, and chloride. Monosalts of phosphoric acid, adipic acid, benzoic acid, phthalic acid, etc.
Specific examples include di-salts, and their hydroxides. Among these, particularly preferred are carbonates such as sodium and potassium, bicarbonates, salanimaleic acid,
Mono- and di-salts of 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 10 volumes, preferably 3 to 8 volumes. The effect of the addition is exhibited by dispersing and blowing into the crude phthalic anhydride solution. .

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.

Phthalic anhydride 97.9% by weight Benzoic acid 0.05 p Maleic acid 0.05 p Naphthoquinone 2.0 #Put 1 kg of this crude phthalic anhydride into a flask and add 270% by weight under nitrogen atmosphere.
Heat to ℃, add sodium carbonate, 0.19 (l OOp
pm) was added. Regarding this, add 5 volumes of oxygen,
120 cc/hour of mixed gas of 95 volumes of nitrogen (2.5 x 10' as oxygen gas for 1 kg of crude phthalic anhydride)
The heat treatment was carried out for 10 hours.

The thus obtained phthalic anhydride was heated under a pressure of 55 mmHg (absolute pressure) using a distillation column (inner diameter 32 mm, height 500 mm) having a perforated plate with actual IO stages at a reflux ratio of 0.
Distilled at 5. As a result, APIA was 10, and freezing point was 131.
Purified phthalic anhydride was obtained at 12°C. The thermal stability obtained by heating at 250° C. for 2 hours was APIA 10, which was of high quality, and the color of the crystals was white. Naphthoquinone in this purified product is 0.1 ppm or less, benzoic acid 0.07% by weight,
The phthalic anhydride content was 99.93% by weight. The purification yield was 97.5% by weight.

Comparative Example 1 Crude phthalic anhydride 1k with the same composition as used in Example 1
g was heated to 270°C in a nitrogen atmosphere in a flask,
0.1 g of sodium carbonate was added.

Further, hydrogen peroxide solution (30% by weight) was added in an amount of 0.7% by weight based on phthalic anhydride, and the mixture was then heated for 10 hours. Note that hydrogen peroxide was violently decomposed upon addition. The obtained phthalic anhydride was then distilled in the same manner as in Example 1 to obtain phthalic anhydride with a yellowish crystal appearance.

APHA 200, freezing point 1309℃, naphthoquinone in purified product 500ppm1 benzoic acid 03% by weight,
Phthalic anhydride content: 99.6'5% by weight, purification yield: 97. O
He was in charge of weight.

Examples 2 to 17 and Comparative Examples 2 to 4 1 kg of crude phthalic anhydride having the same composition as that used in Example 1 was placed in a flask, and the treatment agents and amounts used were changed as shown in Table 1 below, and then blown. The amount of naphthoquinone in purified phthalic anhydride was measured in the same manner as in Example 1, except that the amount of oxygen incorporated, the heat treatment temperature, and the treatment time were changed. The results are shown in Table 1.

Claims (4)

[Claims] (1) After adding an alkali metal compound to crude phthalic anhydride obtained by catalytic gas phase oxidation of naphthalene and heat-treating it while blowing molecular oxygen-containing gas,
A method for producing high-purity phthalic anhydride, which comprises subjecting it to distillation. (2) Heat treatment temperature is 150-300℃, treatment time is 1
15 hours and the amount of molecular oxygen blown in is at least I x 10' mol/h per kg of crude phthalic anhydride. (3) Claim (1) or (2) characterized in that 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.
Method described. (4) Claim (1) characterized in that 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.
, (2) or (3).