JPS585898B2 - Continuous production method of trimellitic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous process for producing trimellitic acid, and more specifically, the present invention relates to a continuous process for producing trimellitic acid, and more specifically, when pseudocumene is oxidized in a liquid phase using cobalt, manganese, and bromine as catalysts, a limited catalyst concentration is used, and a two-stage tank is used. This method is characterized by performing oxidation by changing the reaction temperatures in the first and second stages in a complete mixing type continuous reactor.

Trimellitic acid is an aromatic tribasic acid and has a market as a raw material for high-grade plasticizers as well as a raw material for heat-resistant plastics.

Pseudocumene is C9 in catalytically reformed oil or pyrolysis residual oil.
It exists in distillates and has a different boiling point from other components, so it can be easily separated by distillation.

Air oxidation and nitric acid oxidation are methods for liquid-phase oxidation of pseudocumene to produce trimellitic acid, but the latter has drawbacks such as oxidizing agent cost and by-products, so the former is preferred for mass production.

Air oxidation of pseudocumene is carried out in the presence of a heavy metal catalyst like other alkyl aromatic compounds, but because the two carboxyl groups of the product trimellitic acid have an ortho-position structure, they form a complex with the heavy metal catalyst and oxidize the catalyst. It is said that the yield of pseudocumene in liquid phase oxidation is lower than that of alkyl aromatic compounds that do not have such a structure.

Focusing on this point, various improvements in catalyst systems have been made,
For example, cobalt, manganese, and
A method of sequentially adding catalyst components of cerium and bromine, and a method of coexisting cobalt, manganese, and bromine in JP-A-50-18434 have been proposed.

Although these improved methods for catalysts have improved oxidation yields, the complex catalyst systems have left a new problem in that it is difficult to recover and reuse the catalysts.

Since liquid-phase air oxidation requires mass transfer between gas and liquid and is accompanied by large heat generation, completely mixed tank reactors are widely used in industry, and are able to safely produce products of stable quality. being produced.

This can be seen, for example, in the continuation of terephthalic acid, isophthalic acid and acetic acid.

However, in the production of trimellitic acid, the previously known techniques, including the improved catalyst method mentioned above, were carried out only in a batch or semi-continuous manner, and the production of trimellitic acid was carried out only in a batch or semi-continuous manner; There were hopes for the development of a continuous production method for mellitic acid.

To further clarify this point, if we refer to the conventional trimellitic acid liquid phase air technology, Japanese Patent Publication No. 41-742 provides semi-continuous reaction conditions, and Japanese Patent Publication No. 41-5-2
3 7 3 2 discloses a batch or semi-continuous operation using an improved catalyst, and JP-A-46-7173 discloses an example of stepwise addition of catalyst in a batch and semi-continuous manner. It is difficult to say that this method is industrially advantageous either.

It is generally known that those capable of batchwise operation can be directly applied to continuous operation using a tubular reactor.

However, even if it can be carried out batchwise, it may not be applicable to continuous operation using a complete mixing reactor if side reactions are involved, and the production of trimellitic acid from pseudocumene is one such method. The inventors' study revealed that this is an example.

That is, it was found that the yield of trimellitic acid was extremely reduced when side reactions occurred.

In light of the above, we recognized the importance of continuously producing trimellitic acid using a completely mixed reactor, and after intensive study, we decided to use a two-stage tank system to increase the reaction temperature and limit the concentration of heavy metals. As a result, they found that pseudocumene can be continuously oxidized using a complete mixing reactor to obtain trimellitic acid in high yield, and the present invention has been achieved.

That is, the present invention provides liquid-phase air oxidation of pseudocumene in acetic acid using a simple catalyst system of cobalt, manganese, and bromine, with a total concentration of cobalt and manganese of 0.05 to 0.5 wt% based on acetic acid; In the stage tank complete mixing type continuous reactor, the reaction temperatures in the first stage tank and second stage tank were set at 110 to 170°C and 180 to 240°C, respectively.
This is a continuous process for producing trimellitic acid characterized by oxidation at ℃.

According to the method of the present invention, the final trimellitic acid yield is 65
It reaches ~80 mo1%, and moreover, the catalyst can be easily recovered and reused, and stable continuous operation is possible.

The reasons for the good results achieved by the present invention are not entirely clear.

However, according to the inventor's speculation, there is an extremely large difference in oxidizability between the raw material pseudocumene and the reaction intermediates methyl phthalic acid and dimethyl-benzoic acid. All the components coexist in the process, and many side reactions occur.

However, in the method of the present invention, there are two reaction vessels and different reaction conditions are set for each, so side reactions are suppressed as much as possible, resulting in a high yield of trimellitic acid. .

The catalyst used in the process of the invention is a combination system of two heavy metals, cobalt and manganese, and bromine.

Heavy metals other than cobalt and manganese can also be used, but
It is not advantageous from the point of view of catalyst cost.

The amount of cobalt and manganese used needs to be 0.05 to 0.5 wt% in total concentration based on acetic acid as a solvent.

If the concentration is lower than this, the smooth progress of the reaction will be inhibited, and steady oxidation may not be possible, or the yield of trimellitic acid will be greatly reduced.

On the other hand, if the concentration is higher than this, not only will it not lead to an improvement in the reaction surface, but the combustion reaction of the solvent will increase, and there will be no benefit.

The atomic ratio of cobalt and manganese is most preferably 1:1, but there is no major problem if it is in the range of 1:4 to 4:1.

The atomic ratio of bromine to cobalt and manganese is 2.
Although 0 is most preferred, it can be implemented within the range of 1.5 to 2.5.

The composition of these catalysts can be changed between the first low-temperature oxidation step and the second high-temperature oxidation step.

However, in order to carry out a catalyst recovery method in which the mother liquor from which trimerisotonic acid has been separated is dehydrated and purified to concentrate the catalyst components and recycled to the oxidation step again, it is particularly preferable that the catalyst composition is not changed.

Cobalt and manganese are organic salts such as acetate, propionate, nanthenate, octanoate, halides,
It can be used as inorganic salts such as borates and nitrates and as organic complexes.

Bromine can be used not only as bromine but also as an inorganic bromide, hydrobromic acid, or an organic bromide.

Cobalt bromide, manganese bromide, etc. can be used as containing two catalyst components.

The solvent for the method of the invention is acetic acid.

Aliphatic carboxylic acids other than acetic acid can also be used, but are not practical.

It is better for the acetic acid used to have a lower water content, but 95% acetic acid (5% water content) is used industrially due to the relationship with the acetic acid purification process.

The amount of solvent acetic acid used is 1.0 to 5 of the raw material pseudocumene.
,0 times the weight.

2. From the space-time yield (S.T.Y.) in the reactor.
A particularly preferred range is 0 to 3.0.

If it is below this range, steady scale response may be impaired or it may become impossible to slurry the product.

If it exceeds this range, the yield at ripening will decrease and it will not be economical.

The oxidation reaction temperature in the method of the present invention is 110 to 170°C in the first-stage low-temperature oxidation step, and 110 to 170°C in the second-stage high-temperature oxidation step.
in the range of 80 to 240°C, preferably 12
0-150°C and 195-225°C.

Further, it is preferable that the temperature difference between the first stage and the second stage is 50°C or more.

Operation outside these temperature ranges results in increased by-products and decreased trimellitic acid yield.

The residence time of the reaction liquid in the low-temperature oxidation step (amount of liquid retained in the tank/flow rate of liquid) varies depending on the set conditions and cannot be unambiguously determined, but is selected from a range of 30 minutes to 3 hours.

The primary requirement for selecting the residence time in the low temperature oxidation step is the amount of unreacted pseudocumene in the effluent of the oxidation step.

That is, under the set catalyst and temperature conditions, it is necessary to reduce the pseudocumene in the effluent from the low-temperature oxidation step to 10% or less based on the charged pseudocumene.

If the amount of unreacted pseudocumene is 10% or more, the effluent is introduced into a high temperature oxidation step, and even if oxidized, the yield of trimellitic acid will not exceed 65%.

Usually, in order to reduce unreacted pseudocumene to 10% or less, 2.
More than 0 mole of oxygen is absorbed.

The effluent from the low temperature oxidation process is directly introduced into the high temperature oxidation process.

The residence time in the high temperature oxidation step ranges from 30 minutes to 3 hours.

The residence time here is preferably selected so that the residual amount of dimethylbenzoic acid and methylphthalic acid is 15 mo1% or less.

If a large amount of these oxidized intermediates remain, the burden on subsequent steps will increase.

The method of the present invention will be explained in the following comparative examples and examples.

Comparative Examples 1 to 4 A titanium oxidation reactor having an inner diameter of 56 mm and an internal volume of 2 liters was used.

The oxidation reactor has a reflux condenser, a reaction liquid charging nozzle,
It is equipped with an air blowing nozzle and a nozzle for extracting the contents, and is stirred by a rotary agitator equipped with four turbine blades.

Heating and cooling are performed by a jacket.

Charge the raw material solution into the reactor, raise the temperature, and then ventilate to start the reaction.

A predetermined flow rate of raw material liquid is charged, and the reactants are extracted so as to keep the liquid level in the reactor constant.

After the composition of the reactant stabilizes, it is sampled and analyzed.

The reaction conditions and results are shown in Table 1. Examples 1 to 3 Two oxidation reactors similar to those in the comparative example were connected in series, and the product oxidized under low temperature oxidation conditions in the first stage reactor was then transferred to the second stage set under high temperature oxidation conditions. The reaction was carried out by introducing the reactor into a stage reactor.

The reaction conditions and results are shown in Table 2.

Claims (1)

[Claims] 1. When pseudocumene is subjected to liquid phase air oxidation in acetic acid using cobalt, manganese, and bromine as catalysts, the total concentration of cobalt and manganese is set to 0.05 to 0.05 in acetic acid standard.
5 wt%, and the atomic ratio of cobalt and manganese is 1:4 ~
4:1, and the atomic ratio of bromine to cobalt and manganese is in the range of 1.5 to 2.5, and the reaction temperature is 110 to 1.
The amount of unreacted pseudocumene in the reaction solution was reduced to 10 at 70°C.
% or less, and reaction temperature 18
1. A continuous method for producing trimellitic acid, which comprises continuous oxidation in a two-stage reaction in which the reaction is carried out at 0 to 240°C.