JP3202325B2 - Purification method of dialkyl aromatic dicarboxylate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to dimethyl terephthalate (hereinafter abbreviated as DMT), 2,6
-Dimethyl naphthalenedicarboxylate (hereinafter referred to as 2,6-N
(May be abbreviated as DM) by recrystallization to produce a high-purity dialkyl aromatic dicarboxylate.

[0002] DMT, along with terephthalic acid, comprises fibers,
It is a very industrially useful compound as a raw material for producing films or resins. Similarly, for 2,6-NDM,
Fibers, films or resins made from it are
Due to its high Young's modulus and excellent gas barrier properties, its use has recently been expanding.

[0003] Therefore, if sufficiently purified DMT and 2,6-NDM can be efficiently produced, their industrial value is extremely large.

[0004]

2. Description of the Related Art Hitherto, as a method for producing high-purity DMT for, for example, fibers or plastics, a method has been used in which methylated paraxylene oxidation product is esterified to obtain a crude DMT.
There is known a method for purifying the compound by recrystallization with methanol or, if necessary, by combining it with distillation.

When recrystallizing crude DMT with methanol,
First, a predetermined amount of each of methanol and crude DMT is charged into the recrystallization tank, and then, if necessary, heating is performed so that the temperature in the tank reaches a predetermined heating end temperature. Further, the inside of the tank at the end of heating is usually in a pressurized state.

In the next cooling step, first, the pressure control valve is opened, and methanol and nitrogen gas in the tank are vented to atmospheric pressure via a condenser to a vent system (vent cooling), and further reduced to cool to a predetermined temperature. At the start of vent cooling, since the inside of the crystallization tank is in a boiling state, forming starts to occur in the tank as the pressure decreases. When the forming becomes severe, the vent condenser is closed, and as a result, the recrystallization operation becomes impossible.

Therefore, it is common to adjust the pressure drop rate in the tank by the opening of the pressure control valve and perform vent cooling while suppressing forming as much as possible, but the time cycle (cooling time) becomes longer and the production efficiency becomes longer. Is a bad cause.

Further, heating a large amount of methanol and DMT,
There is also a disadvantage that energy consumption is large because cooling is repeated.

[0009] Regarding the above problems, 2,6-NDM
The manufacturing process is exactly the same as the DMT manufacturing process.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for purifying a crude dialkyl aromatic dicarboxylate by recrystallization, which minimizes forming during cooling, shortens cooling time, and reduces recrystallization. It is an object of the present invention to provide an industrially superior method in which the device efficiency of the tank is increased and the energy load during heating and cooling is small.

[0011]

According to the method of the present invention, a crude dialkyl aromatic dicarboxylate is recrystallized and purified to produce a high-purity dialkyl aromatic dicarboxylate. Consists of

The crude dialkyl aromatic dicarboxylate used in the present invention is crude DMT or crude 2,6-NDM, which is usually oxidized with para-xylene, 2,6-dialkylnaphthalene or a derivative thereof, and treated with methanol. It is manufactured by esterification. Examples of the dialkylnaphthalene include dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene and the like, and derivatives thereof include an oxidation intermediate of the dialkylnaphthalene such as formylnaphthoic acid and acetylnaphthoic acid, or methylacetylnaphthalene and methylbutyrylnaphthalene. Examples thereof include alkylacylnaphthalene and diacylnaphthalene.

The recrystallization solvent used in the present invention is a solvent having a boiling point at normal pressure lower than the heating end temperature at the time of recrystallization,
An example is methanol. The total charge amount is the larger of the amount necessary for improving the sufficient refining effect and the amount necessary for slurry handling.

In the method of the present invention, the recrystallization solvent is divided and fed, and the first charging is carried out simultaneously with, immediately before or immediately after the charging of the dialkyl crude aromatic dicarboxylate. Often done right before.

The first charge of the recrystallization solvent in the method of the present invention is suitably 10 to 90% of the total charge. In particular, the heating end temperature scent Te, a quantity can almost all dissolved charged aromatic dicarboxylic acid dialkyl, and as little as possible the amount is preferable. By keeping the first charging amount as small as possible and keeping the liquid level in the tank at the time of vent cooling as low as possible, it becomes possible to prevent the vent condenser from being clogged even if forming occurs, and to reduce the cooling rate. It is possible to take large.

Further, it is preferable that the recrystallization solvent charged in the first time is fed after being preheated with low energy such as low pressure steam. As a result, the time cycle is shortened, and the energy load and cost during heating are also reduced.

The remaining recrystallization solvent may be fed in several parts, but usually the whole amount is fed in the second preparation without division.

In the method of the present invention, the second charging of the recrystallization solvent is started at the time when the forming is most intense at the time of vent cooling.
Within minutes. Further, the temperature of the recrystallization solvent to be charged in the second time is preferably as low as possible within a range in which there is no problem in handling or a range in which no special equipment is required. Thus, forming is suppressed, the cooling rate is increased, the time cycle can be shortened, and the energy load can be reduced.

After the vent cooling, the pressure is usually further reduced by a steam ejector or the like to cool to a predetermined temperature. After cooling is completed, the pressure is returned to normal pressure with an inert gas, then dumped, and the next cycle is started.

[0020]

According to the method of the present invention, in the purification by recrystallization of the dialkyl crude aromatic dicarboxylate, the vent condenser is clogged by the forming at the time of vent cooling as compared with the conventional method of charging all the recrystallization solvent at once. Since the risk is greatly reduced, the time cycle can be shortened, and the equipment efficiency of the recrystallization system is improved. Further, since the energy load during heating and cooling is greatly reduced, it is industrially very advantageous.

Hereinafter, the present invention will be described in detail with reference to examples.

[0022]

Comparative Example 1 First, the entire amount of methanol (90 to 100 ° C.) as a solvent was charged into a recrystallization tank including a recrystallization tank main body, a circulation pump, a heat exchanger, an ejector, and the like.
Next, in order to facilitate handling, a crude Molton DMT set so that the solid content of the slurry is 30 to 40% by weight is charged, and a heating cycle is performed while circulating to heat to a predetermined temperature to dissolve the DMT. did. In the next cooling cycle, cooling was performed in a very short time without controlling the pressure in the tank during vent cooling. As a result, as shown in Table 1, forming at the time of vent cooling was severe, and methanol slurry of DMT flowed out of the vent system, and eventually the vent condenser was clogged, and operation became impossible.

[0023]

Comparative Example 2 As in Comparative Example 1, methanol and crude Molton DMT were charged and a heating cycle was performed. In the next cooling cycle, when the most intense forming occurred (tank pressure 2.0 to 1.5 kg / cm ² G), the opening of the tank internal pressure control valve was adjusted to perform very gentle vent cooling. As a result, as shown in Table 1, it was possible to suppress the forming at the time of vent cooling, and it was possible to continue the operation, but the time cycle was significantly lengthened and the production capacity was reduced.

[0024]

Example 1 In the same recrystallization tank as in Comparative Example 1, an amount of methanol required for dissolving DMT (charge temperature: 90 to 100)
C.) only, then crude Molton DMT was charged, and a heating cycle was performed while circulating together to dissolve DMT. In the next cooling cycle, when the most intense forming occurs during vent cooling, the remaining methanol (45
６５65 ° C.) as the second charge. The total charged methanol was the same as in Comparative Example 1, and the second charged methanol was about 75% of the whole. As a result, as shown in Table 1, forming at the time of vent cooling was suppressed, and clogging and the like due to inflow of DMT into the vent system could be prevented. In addition, the vent cooling rate could be increased, and the recrystallization system could be improved. Processing capacity could be greatly improved.

[0025]

[Table 1]

[0026]

Comparative Example 3 Recrystallization purification was carried out under the same conditions as in Comparative Example 2, except that DMT was changed to 2,6-NDM and the amount of slurry was changed so that the slurry concentration became about 15% by weight. There was no blockage of the vent condenser, and the required time for vent cooling was 70 minutes.

[0027]

Example 2 Example 1 was repeated except that DMT was changed to 2,6-NDM, the total amount of methanol charged was the same as in Comparative Example 3, and the amount of methanol charged in the second time was about 50% of the whole. Recrystallization purification was performed under the same conditions. There is no blockage of the vent condenser, and the required time for vent cooling is 4
9 minutes.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Akio Nakuten 77, Kitayoshida-cho, Matsuyama-shi, Ehime Prefecture Teijin Limited Matsuyama Office (56) References JP-A-4-54152 (JP, A) JP-A-3-3 223234 (JP, A) JP-A-3-11040 (JP, A) JP-A-49-45030 (JP, A) JP-B-58-20950 (JP, B2) "Chemical Dictionary 3 (Vol. 3)" (Showa 35.9.30, published by Kyoritsu Shuppan Co., Ltd.) Page 781 ("Recrystallization" section) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07C 69/76 C07C 67/52 C07C 69 / 82

Claims (5)

(57) [Claims] 1. A method for purifying a crude dialkyl aromatic dicarboxylate by recrystallization, wherein a recrystallization solvent is divided and fed. 2. The purification method according to claim 1, wherein the first charge of the recrystallization solvent is 10 to 90% of the total charge. Wherein the recrystallization solvent charge of the first time is, in the heating end temperature, purifying method according to claim 1 which is a solvent charged amount capable of dissolving the entire amount of charged aromatic dicarboxylic acid dialkyl. 4. The purification method according to claim 1, wherein a recrystallization solvent having a boiling point lower than the heating end temperature is used. 5. The method according to claim 1, wherein the dialkyl aromatic dicarboxylate is dimethyl terephthalate or dimethyl 2,6-naphthalenedicarboxylate.