JPS6113711B2 - - 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 ortho-xylene. Specifically, the present invention relates to a method for producing highly pure phthalic anhydride by efficiently removing impurities, mainly phthalides, which are contained in the crude phthalic anhydride and are difficult to separate. . Generally, catalytic gas phase oxidation of orthoxylene 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,
By-product phthalide is mixed in as the main impurity,
It is difficult to separate the phthalic anhydride sufficiently using the distillation equipment commonly used in industry, and thus a non-negligible amount of phthalide and other impurities remain in the purified phthalic anhydride, which may impair the quality of the product. It is well known that there is a tendency to decrease Therefore, in the production process of phthalic anhydride, it is required to reduce the amount of phthalide, which is the main impurity in crude phthalic anhydride, as much as possible and operate the catalytic gas phase oxidation reaction of ortho-xylene to maintain it at a low level. be done. In other words, in order to suppress the decrease in the conversion rate of ortho-xylene and the increase in the amount of intermediate by-product phthalide due to the decrease in the activity of the catalyst, it is necessary to gradually raise the reaction temperature. leading to a decrease in Even if this is not the case, the presence of by-product phthalide as an impurity is unavoidable in crude phthalic anhydride, and various methods for removing this phthalide have been proposed in the industrial production process of phthalic anhydride. For example, according to the specification of Japanese Patent Publication No. 45-10333, crude phthalic anhydride is produced using a sulfur-containing alkali metal compound such as potassium hydrogen sulfite (KHSO ₃ ) or potassium pyrosulfite (K ₂ S ₂ O ₅ ). A method of treatment is disclosed, and US Pat. No. 4,165,324 discloses a treatment method using an alkali metal hydroxide such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). but,
It is pointed out that these methods have the following drawbacks and are difficult to be advantageously employed industrially. First, in the former method, sulfur compounds also coexist in the residue during the phthalic anhydride purification process, so a large amount of sulfur oxides are generated during the treatment of this residue (for example, incineration), causing a pollution problem. In addition, the sulfur compounds themselves tend to cause corrosion of distillation equipment, which is a drawback that requires a large amount of cost to solve or avoid these problems. Furthermore, in the latter method, since the alkali metal hydroxide itself has high reactivity, it can be extremely dangerous depending on the crude phthalic anhydride to be added. That is, for example, when potassium hydroxide is added to liquid crude phthalic anhydride,
The maleic anhydride contained therein polymerizes explosively to form a coke-like polymer. This reaction is extremely rapid and poses a non-negligible obstacle to the stable operation of phthalic anhydride production equipment, as well as piping and piping caused by the coke-like polymer generated.
It can also cause blockage of valves, distillation column trays, etc. Furthermore, the rapid reaction between potassium hydroxide and maleic anhydride also leads to decomposition reactions of phthalic anhydride and other impurities, which react with phthalic anhydride and generate tar-like polymers.
It is also pointed out that this results in a significant decrease in the yield of purified phthalic anhydride. Furthermore, a method has been proposed in which phthalide is oxidized using an oxidation catalyst to obtain highly pure phthalic anhydride. For example, in US Pat. No. 3,208,423, heavy metal bromides such as cobalt bromide and manganese bromide are converted into crude phthalic anhydride and brought into contact with molecular oxygen gas. However, this method cannot be adopted industrially because bromide as a catalyst is expensive and it is extremely difficult to recover and reuse it. Furthermore, in order to achieve the same objective, West German Patent Publication No. 1935008 discloses that a catalyst in which vanadium oxide is supported on a carrier is packed in a packed bed, and crude phthalic anhydride is passed through this bed while air is passed through it. A method for carrying out the oxidation of However, it has been found that when this method is adopted, tar-like substances present in the crude phthalic anhydride adhere to the surface of the supported catalyst, resulting in a decrease in catalytic activity within a very short period of time. Originally, a supported catalyst is a catalyst in which a catalytically active substance is effectively dispersed and supported on the surface of a carrier, and it is well known that the preparation method and calcination conditions greatly affect the catalytic activity. Therefore, it must be said that it is difficult to stably use the method of filling such a supported catalyst inside a packed column and using it as a fixed bed on an industrial scale. The purpose of the present invention is to eliminate the above-mentioned drawbacks,
The object of the present invention is to provide a method for oxidizing phthalide to obtain high-purity phthalic anhydride using a catalyst that is extremely easy to operate and maintain. The invention is specified as follows. (1) Crude phthalic anhydride obtained by catalytic gas phase oxidation of ortho-xylene is treated with an alkali metal salt of at least one carboxylic acid selected from the group consisting of maleic acid, succinic acid and benzoic acid, manganese, 1. A method for producing high-purity phthalic anhydride, which comprises contacting it with a molecular oxygen-containing gas at high temperature in the presence of an alloy composition containing chromium and iron, and then subjecting it to a distillation operation. (2) At least 1 x 10 ^-4 molecular oxygen-containing gas converted to oxygen gas per 1 kg of crude phthalic anhydride.
(1) above, characterized by contacting for mol/hour;
Method described. (3) The above characterized in that the contact treatment is performed at a temperature range of 150°C to 300°C and a treatment time of 0.5 to 30 hours.
The method described in (1) or (2). (4) The amount of alkali metal salt added is 10 to 10% as alkali metal atoms to crude phthalic anhydride.
The method according to (1), (2) or (3) above, characterized in that the amount is in the range of 10,000 ppm (by weight). (5) The above (1) and (2) characterized in that the contact area of the alloy composition containing manganese, chromium and iron with respect to 1 kg of crude phthalic anhydride is at least 1×10 ^-3 m ² , (3) or (4). (6) The above (1), (2), (3), and (4) characterized in that the manganese content in the alloy composition containing manganese, chromium, and iron is at least 0.05% by weight.
or the method described in (5). The present invention will be further explained in detail below. Crude phthalic anhydride obtained by catalytic gas phase oxidation of orthoxylene usually contains 0.05 to 1.0% by weight of phthalide. In the present invention, crude phthalic anhydride containing a phthalide is coexisted with an alkali metal salt of a carboxylic acid and an alloy composition containing manganese, chromium, and iron (hereinafter referred to as a manganese-containing alloy composition), with a 0.5 to
Contact treatment with a molecular oxygen-containing gas at a temperature of 150-300°C, preferably 200-300°C for 30 hours, preferably 1-20 hours, to oxidize most of the phthalide content, followed by conventional distillation. By subjecting it to the operation, purified phthalic anhydride with a significantly reduced phthalide content is obtained. This purified product not only has a significantly reduced phthalide content, but also removes other impurities that degrade quality, such as thermal stability, thereby preventing quality deterioration caused solely by phthalide. It has been found that this product has more than just this effect. The manganese-containing alloy composition used in the present invention is preferably one in the form of a wire mesh, through which molecular oxygen-containing gas can easily pass, and which causes almost no pressure loss. In particular, by filling the gas-liquid contact device with a net-like layered material,
A method in which crude phthalic anhydride and the alkali metal salt of the above-mentioned carboxylic acid are introduced into the mixture, and bubbles of molecular oxygen-containing gas are generated from below under stirring and heat treatment is the simplest and most convenient method for carrying out the present invention. This is a convenient method. The composition of the manganese-containing alloy composition used in the present invention is such that it contains at least 0.05% by weight of manganese, and it is particularly preferable that the content of manganese and chromium is 10% by weight or more. The surface area used is at least 1×10 ^-3 m ² , preferably 5×10 ^-3 m ² or more per kg of crude phthalic anhydride to be treated. Increasing the surface area is preferable because it leads to a reduction in processing time, but increasing the surface area too much may have disadvantages such as increased pressure loss. The amount of molecular oxygen blown into the crude phthalic anhydride depends on the amount of phthalide impurities contained in the crude phthalic anhydride, but at least
The amount is 0.0001 mol/hour, preferably 0.0005 mol/hour or more, particularly preferably 0.001 to 0.01 mol/hour. In the carboxylic acid alkali metal salts of the present invention, examples of the alkali metal include sodium, potassium, lithium, cesium, rubidium, etc., but potassium is most preferred. The most preferred carboxylic acid is maleic acid. The amount of the carboxylic acid alkali metal salts used in the present invention depends on the amount of phthalide contained in the crude phthalic anhydride, but is 10 to 10,000 ppm (by weight), preferably 20 to 10,000 ppm (by weight) based on the crude phthalic anhydride.
2000ppm (by weight), more preferably 50-1000ppm
(weight) range. Furthermore, according to the findings of the present inventors, organic acid salts other than the alkali metal salts of carboxylic acids, such as alkali metal salts of toluic acid, phthalic acid, and fumaric acid, all have a certain degree of effect in reducing impurity phthalide. Although some of them are less effective than the carboxylic acid salts mentioned above. The reason for this is not clear, but it is presumed that it is because the reaction affinity for phthalides, such as oxidation activity, is inferior to that of the compounds according to the present invention. Furthermore, according to the findings of the present inventors, the method of the present invention is even more effective than the levels achieved by the combinations of manganese-containing alloy compositions and oxygen, and alkali metal carboxylates and oxygen, respectively. I found out something. In other words, it has become clear that there is a very significant improvement in terms of both temperature and time. Although the reason for this is not clear, it is presumed that it is due to the additive effect of the alkali metal salt of carboxylic acid, the manganese-containing alloy composition, and molecular oxygen. As described above, by using the present invention, the phthalide in crude phthalic anhydride is reduced to 1/10 to 1/1000 in a very short time, and purified phthalic anhydride obtained by distillation is no longer phthalide. amount
A high quality of 0.01% by weight or less can be achieved. What is even more surprising is that the thermal stability of the phthalic anhydride obtained by the method of the invention is incomparably better than that obtained by conventional methods. The present invention will be explained in more detail below with reference to Examples. Example 1 Catalytic gas phase oxidation using orthoxylene as a raw material,
Crude phthalic anhydride having the following composition was obtained. Phthalic anhydride 99.3 (weight% and below are the same) Benzoic acid 0.05 Maleic acid 0.07 Phthalic acid 0.03 Phthalide 0.50 Put 1 kg of the above crude phthalic anhydride and 0.1 g of potassium maleate (equivalent to 100 ppm) in a flask, and add 5% by volume of oxygen and nitrogen from the bottom. 95% volume gas mixture
3000 ml/hour (oxygen amount: 6×10 ⁻³ mol/hour) was blown into the reactor, and the treatment was carried out at a temperature of 270° C. for 10 hours. 20 g of an iron-chromium-manganese alloy wire having the following composition and structure was previously formed into a disk shape and fixed in the flask. The iron-chromium-manganese alloy has the following composition and structure.

[Table] The thus obtained treated phthalic anhydride contained 0.01% by weight of phthalide. This treated phthalic anhydride was distilled using a distillation column (inner diameter 32 mmφ, height 500 mm) equipped with 10 perforated plates.
Distilled under Hg (absolute) pressure with a reflux ratio of 0.5. As a result, purified phthalic anhydride with APHA10 and freezing point of 131.12℃ was obtained. APHA10 thermal stability by heating at 250℃ for 2 hours
It was of high quality. Note that this purified phthalic anhydride contained 0.008% by weight of phthalide. Example 2 1Kg of the same crude phthalic anhydride used in Example 1
and potassium benzoate 0.2g (equivalent to 200ppm) were placed in a flask, and a mixed gas of 5% by volume of oxygen and 95% by volume of nitrogen was poured from the bottom at 4500ml/hour (9.4× as the amount of oxygen).
10 ⁻³ mol/hour) and treated at a temperature of 280° C. for 5 hours. A wire 5 of an iron-chromium-manganese alloy having the composition and structure shown below is placed in the flask in advance.
g (corresponding to a contact area of 75×10 ⁻³ m ² ) was added.

[Table] The thus obtained treated phthalic anhydride contained 0.005% by weight of phthalide. This treated phthalic anhydride was distilled into a distillation column (inner diameter 32 mmφ, height 500 mm) equipped with 10 perforated plates.
Distilled under mmHg (absolute) pressure with a reflux ratio of 0.5.
As a result, purified phthalic anhydride with APHA10 and freezing point of 131.12℃ was obtained. Thermal stability after heating at 250℃ for 2 hours is also APHA10.
It was of high quality. Note that this purified phthalic anhydride contained 0.003% by weight of phthalide. Example 3 Crude phthalic anhydride 500 same as used in Example 1
Kg was placed in a vertical treatment tank with an inner diameter of 80 cmφ and a height of 120 cm. A dispersion plate for blowing a mixed gas of 5% by volume of oxygen and 95% by volume of nitrogen is installed at the bottom, and a stirrer is installed on top of the dispersion plate for blowing a mixed gas of 5% by volume of oxygen and 95% by volume of nitrogen. thing 1250
g (corresponding to a contact area of 10×10 ^-3 m ² per kg of phthalic anhydride).

[Table] Additionally, 25g of potassium succinate
(equivalent to 50 ppm) was added. Afterwards, a mixed gas was passed through at 840/hour (equivalent to 3.5×10 ^-3 mol/hour Kg) and treated for 15 hours while heating to 275°C.
After treatment, the distillation column (inner diameter
Distilled at a reflux ratio of 0.5 under a pressure of 55 mmHg (absolute pressure) at a diameter of 3.2 cmφ and a height of 50 cm, with an APHA of 10 and a freezing point of 131.11.
℃, high purity phthalic anhydride with a phthalide content of 0.05% by weight was obtained. The thermal stability of this product after heating at 250°C for 2 hours was APHA20. Example 4 Crude phthalic anhydride 500 same as used in Example 1
Kg was placed in a vertical treatment tank with an inner diameter of 80 cmφ and a height of 120 cm. A dispersion plate for blowing gas is installed at the bottom, and a stirrer is installed above it. In the middle part of the treatment tank, 300g of chromium and manganese alloy mesh having the composition and structure shown below (contact area: 2.7g per 1kg of phthalic anhydride,
×10 ^-3 m ² ).

[Table] And 150g of sodium succinate
(equivalent to 300 ppm) was added. However, later on,
A mixed gas of 5% by volume oxygen and 95% by volume nitrogen.
1200/hour (equivalent to 5 x 10 ^-3 mol/hour of oxygen per 1 kg of phthalic anhydride), heated to 265°C and treated for 12 hours, and after the treatment, a distillation column equipped with a perforated plate with 10 plates ( Inner diameter 3.2cmφ, height 50cm)
Distilled at a reflux ratio of 0.5 under 55 mmHg (absolute pressure) pressure,
APHA10, freezing point 131.12℃, phthalide content 0.01
% by weight of high purity phthalic anhydride was obtained. of this
Thermal stability after heating at 250°C for 2 hours was APHA20. Comparative Example 1 The same procedure as in Example 1 was carried out except that potassium maleate and the chromium-manganese alloy composition were not added, and the sample was colored yellow with APHA50. freezing point
Obtained phthalic anhydride at 130.5℃. The phthalide content in this phthalic anhydride is 0.48% by weight, and 250
Thermal stability when heated at ℃ for 2 hours was APHA500 or higher. Examples 5 to 25 and Comparative Examples 2 to 3 1 kg of each crude phthalic anhydride having the same composition as used in Example 4 was taken, and in a flask, the additives and amounts used in Example 4 were added as shown in Table 1. The amount of phthalide in the phthalic anhydride after the treatment was measured by varying the same amount of alloy used, heat treatment temperature, and treatment time, and the results shown in Table 1 were obtained.

【table】

Claims (1)

[Scope of Claims] 1. Crude phthalic anhydride obtained by catalytic gas phase oxidation of ortho-xylene is treated with at least one alkali metal carboxylic acid selected from the group consisting of maleic acid, succinic acid and benzoic acid. 1. A method for producing high-purity phthalic anhydride, which comprises contacting it with a molecular oxygen-containing gas at high temperature in the presence of a salt and an alloy composition containing manganese, chromium, and iron, and then subjecting it to a distillation operation. 2. The method according to claim 1, wherein 1 kg of crude phthalic anhydride is contacted with a molecular oxygen-containing gas for at least 1×10 ^-4 mol/hour in terms of oxygen gas. 3. The method according to claim 1 or 2, wherein the contact treatment is performed at a temperature range of 150°C to 300°C and for a treatment time of 0.5 to 30 hours. 4 The amount of alkali metal salt added is 10 to 10,000 ppm as alkali metal atoms relative to crude phthalic anhydride.
4. The method according to claim 1, 2 or 3, wherein the weight is within a range of (weight). 5. Claims 1, 2, 3 or 5, characterized in that the contact area of the alloy composition containing manganese, chromium and iron with respect to 1 kg of crude phthalic anhydride is at least 1×10 ^-3 m ² . The method described in 4. 6 Manganese content in the alloy composition containing manganese, chromium and iron is at least 0.05% by weight
Claims 1, 2,
3. The method described in 4 or 5.