JPS587633B2 - Purification method of maleic anhydride - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for purifying maleic anhydride.

Specifically, the present invention relates to a method of purifying crude maleic anhydride to obtain maleic anhydride with good thermal stability.

Maleic anhydride is produced by partially oxidizing unsaturated hydrocarbons having 4 or more carbon atoms, such as benzene and butene, or hydrocarbon mixtures containing these, with air in the presence of a vanadium catalyst.

To collect the generated crude maleic anhydride, there are two methods: cool the generated gas and collect the crude maleic anhydride in liquid form, or absorb the generated gas into water and collect the maleic anhydride as an aqueous maleic acid solution. Then, the aqueous solution is concentrated and dehydrated to obtain crude maleic anhydride.

In any of the above methods, the crude maleic anhydride obtained contains organic acids such as acrylic acid, methacrylic acid, and benzoic acid, aldehydes such as acuolein and tolualdehyde,
Contains other high-boiling colored substances.

In addition to its purity and degree of coloration, the product specifications for maleic anhydride strongly require its thermal stability, that is, not to be colored when heated.

This thermal stability test is called HST and is usually carried out by the following method.

Place maleic anhydride in a quartz test tube with an inner diameter of 20 mm.
Heated at 182°C for 13 minutes, and the degree of coloration was determined by APHA N.
Display on 6i.

APHA Ni. The smaller the value, the better the thermal stability of maleic anhydride.Hereinafter, HST APHA No. Convert maleic anhydride with a small amount of
PHA No. Maleic anhydride with a high HST is called maleic anhydride with a bad HST.

The mechanism of thermal stability of maleic anhydride is complex;
Although it has not been fully investigated yet, if an unsaturated organic acid or aldehyde exists as an impurity in maleic anhydride, even if the amount is minute, the HST of maleic anhydride will deteriorate and the product will be rejected. There is.

Therefore, in order to obtain product maleic anhydride, it is necessary to purify crude maleic anhydride by some method, but it is difficult to obtain maleic anhydride with a good HAT by ordinary distillation purification.

That is, during the distillation process, impurities such as aldehydes polymerize in the distillation pot, and this polymer gradually decomposes to produce a substance with a boiling point lower than that of maleic anhydride, which is the main distillate of maleic anhydride. This is because they also get mixed in.

Therefore, in order to obtain maleic anhydride with a good HST by distillation, the above aldehydes must be completely decomposed or
Alternatively, in order to prevent decomposition during the distillation process, it is necessary to sufficiently polymerize aldehydes in advance to form a harz.

Conventionally, a method of carrying out the above-mentioned halving using concentrated sulfuric acid is known, but since concentrated sulfuric acid is highly corrosive, the material of the distillation column that can be used is limited, and the halving progresses too much. The viscosity of Harz increases, making Harz separation difficult.

Alternatively, in order to effectively carry out the above-mentioned Harzification, concentrated sulfuric acid must be contained in the crude maleic anhydride in an amount of about 0.1 to 10%, so it is necessary to add concentrated sulfuric acid to the crude maleic anhydride. There is a drawback that a large amount of sulfuric acid remains in the residue, and the maleic anhydride in the residue cannot be recovered and must be discarded.

As a result of our research on all possible methods for solving these drawbacks and obtaining maleic anhydride with a good HST by distillation, we found that by heating crude maleic anhydride in the presence of an extremely small amount of reducing substances. It was discovered that maleic anhydride with good HST can be obtained by distillation purification after treatment, and the present invention was achieved based on this finding.

That is, the purpose of the present invention is to advantageously produce maleic anhydride with a good HST, and this purpose is to oxidize an unsaturated hydrocarbon having 4 or more carbon atoms or a hydrocarbon mixture containing the same. In purifying the crude maleic anhydride obtained by , achieved by distillation purification.

Next, to explain the present invention in detail, in the method of the present invention, when purifying crude maleic anhydride obtained by oxidizing hydrocarbons such as benzene and butene, or hydrocarbon mixtures containing these hydrocarbons, the above-mentioned crude maleic anhydride is purified. It is necessary to heat-treat maleic anhydride in the presence of a reducing substance.

In order to obtain maleic anhydride with a particularly good HST by the subsequent distillation process, it is necessary to use sodium metabisulfite, sulfurous acid and phosphorous acid as the reducing substances.

These reducing substances are added to the crude maleic anhydride before distillation.

The forms of addition of these substances are: Sodium metabisulfite is usually a solid, phosphorous acid is a solid or an aqueous solution, and sulfite is an aqueous solution.

The amount of reducing substance added is between 1 and
It is appropriately selected from the range of 1000 ppm, preferably 5 to 100 ppm.

After adding the reducing substance, the crude maleic anhydride is heat-treated, but if the heating temperature is too low, the maleic anhydride will solidify and the maleic anhydride and the reducing substance will not be able to mix sufficiently. If the temperature is too high, maleic anhydride will be half-formed and there will be a corresponding loss, so heat treatment is usually
It is carried out at a temperature of 0 to 200°C, preferably 80 to 160°C.

Moreover, the time of the heat treatment is also appropriately selected from the range of 0.5 to 10 hours, preferably 0.5 to 2 hours.

This heat treatment can be carried out in a batchwise or continuous stirring tank or the like.

It is known that when an alkali metal is mixed into maleic anhydride, this becomes a radical initiator, causing an explosive condensation reaction of maleic anhydride.

However, if the amount of sodium metabisulfite added is within the above range, the heat treatment can be carried out without causing any reaction.

In addition, in the distillation process following heat treatment, if there is a risk of a condensation reaction occurring due to the high temperature, sulfuric acid etc. may be added to convert the soda content of sodium metabisulfite into a non-volatile salt such as mirabilite. The condensation reaction can be suppressed by distilling from

The maleic anhydride heat-treated in the presence of a reducing substance is then purified by distillation, and this distillation purification can be carried out according to a conventional method.

For example, one rectification column may be used to separate high-boiling components and low-boiling components at the same time, or two rectification columns may be used, and the second rectification column separates light-boiling components. , the high-boiling components may be separated in a subsequent second rectification column.

Maleic anhydride with a good HST can be obtained by directly distilling and purifying the maleic anhydride that has been subjected to the heat treatment in the presence of a reducing substance.

In the method of the present invention, a very small amount of a reducing substance is added to crude maleic anhydride, heat treated, and then purified by distillation, so there is no risk of corrosion of the equipment due to additives, and maleic anhydride in the bottom of the pot is also effective. This is a very advantageous method compared to the treatment method using sulfuric acid addition described above.

Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

The crude maleic anhydride used in the following Examples and Comparative Examples is obtained by air oxidizing an unsaturated hydrocarbon having 4 carbon atoms in the presence of a vanadium-based catalyst, and absorbing the reaction product gas in water to obtain maleic anhydride. The acid was collected as maleic acid, concentrated and dehydrated, and then charged into a Harz separator to separate about 2% by weight of high-boiling components including Harz.

Example 1 700 g of crude maleic anhydride was placed in a 14-piece removable flask equipped with a stirrer, a nitrogen gas inlet, and a thermometer, and 211n9 (equivalent to 30 ppm) of sodium metabisulfite was added thereto, and the mixture was heated while passing nitrogen through the flask. , 2 at 135°C in an oil bath.
Heat treatment was performed while stirring for hours.

Next, the heat-treated crude maleic anhydride was heated to a height of 50 cm.
1 Using a Witsdomer distillation column with an inner diameter of 1 cm, the top temperature of the column was 1.
Batch distillation was carried out at 18°C and an internal pressure of 60 mmHk to yield 530 g.
A distillate was obtained, which was further subjected to batch distillation under the same conditions.

APHA Nc. of HST of the obtained maleic anhydride. The first distillate 85g is 20, the main distillate 170g is 30g, and the rear distillate is 130g.
was 40.

Example 2 In the same manner as in Example 1, 21 μm of sodium metabisulfite (equivalent to 30 ppm) was added to crude maleic anhydride, and the mixture was heated at 135°C.
Heat treatment was performed for 2 hours.

Next, 8.4■ (
Concentrated sulfuric acid (equivalent to 12 ppm) was added, and this was subjected to batch distillation using a Windmar distillation column to obtain 520 g of distillate, which was further batch distilled under the same conditions.

APHA No. of HST of the obtained maleic anhydride. The first distillate 75g is 10, the main distillate 190I is 20, and the rear distillate is 150p.
was 30.

Example 3 In the same manner as in Example 1, 14 to 14 (equivalent to 20 ppm) of sulfite was added to 700 g of crude maleic anhydride, and heat treatment was performed at 90° C. for 1 hour.

Next, the heat-treated crude maleic anhydride was subjected to batch distillation using a Windmar distillation column to obtain 490 g of distillate, which was further batch distilled under the same conditions.

APHA No. of HST of the obtained maleic anhydride. The first distillation 80g is 20, the main distillation 200y is 30, and the rear distillation is 165I.
was 50.

Example 4 In the same manner as in Example 1, 17.5 mg (equivalent to 25 ppm) of phosphorous acid was added to 700 g of crude maleic anhydride, and the mixture was heated at 135°C.
Heat treatment was performed for 1 hour.

Next, the heat-treated crude maleic anhydride was batch distilled using a Widmer distillation column to obtain 510 g of distillate, which was further batch distilled under the same conditions.

The HST APHA Na of the obtained maleic anhydride was 20 for 95 g of the first distillate, 20 for 195 g of the main distillate, and 3 for 90 g of the latter distillate.
It was 0.

Example 5 In the same manner as in Example 1, 10.5 μm (equivalent to 15 ppm) of phosphorous acid was added to 700 g of crude maleic anhydride, and heat treatment was performed at 135° C. for 1 hour.

Next, the heat-treated crude maleic anhydride was subjected to batch distillation using a Windmar distillation column to obtain 580 g of distillate.5 This was then subjected to batch distillation under the same conditions.

APHA Nu of HST of the obtained maleic anhydride was 20 in the first distillation 110g, 30 in the main distillation 210g, and 150g in the rear distillation.
was 50.

Comparative Example l Same as Example l, 700 g of crude maleic anhydride was mixed with 1 part of concentrated sulfuric acid.
．． 05g (equivalent to 0.15% by weight) was added and heated to 150°C.
Heat treatment was performed for 2 hours.

Next, the heat-treated crude maleic anhydride was subjected to batch distillation using a Widmer distillation column to obtain 500 g of distillate, which was further subjected to batch distillation under the same conditions.

APRA No. of the obtained maleic anhydride. is Hatsutome 90
g is 100, main distillate 240g is 30, rear distillate 190I is 5
It was 0.

Comparative Example 2 In the same manner as in Example 1, 700 g of crude maleic anhydride was heat-treated at 150° C. for 2 hours without adding any additives.

Next, the heat-treated maleic anhydride was subjected to batch distillation using a Widmer distillation column to obtain 540 g of distillate, which was further subjected to batch distillation under the same conditions.

The HST APHA of the obtained maleic anhydride is the first distillation 1.
10g is 300 or more, main distillation 245g is 250, rear distillation 10
0g was 300 or more.

Claims (1)

[Claims] 1. In purifying crude maleic anhydride obtained by oxidizing an unsaturated hydrocarbon having 4 or more carbon atoms or a hydrocarbon mixture containing the same, the crude maleic anhydride is treated with sodium metabisulfite. A method for purifying maleic anhydride, which comprises heating in the presence of at least one reducing substance selected from the group consisting of sulfurous acid and phosphorous acid, followed by distillation purification. 2. A method for purifying maleic anhydride according to claim 1, characterized in that the temperature of the heat treatment is 60 to 200°C. 3. A method for purifying maleic anhydride according to claim 1 or 2, characterized in that the amount of the reducing substance present in the crude maleic anhydride is 1-1000 pPm.