KR100846316B1 - Apparatus for separation dimethylterephthalate from polyester methanolysis gas - Google Patents

Abstract

An apparatus for separating dimethylterephthalate from polyester methanolysis gas is provided to simplify a partial condenser and a spray tower or spray zone, and to save energy by using the heat of methanolysis gas as distillation energy. An apparatus for separating dimethylterephthalate from methanolysis gas comprising dimethylterephthalate, methyl-2-hydroxyethylterephthalate, ethyleneglycol, and methanol as depolymerization products of polyethyleneterephthalate includes: a liquid storage tank(10) in which an inflow of methanolysis gas is condensed; a methanol distillation column(20) provided in the upper part of the liquid storage tank; an ethyleneglycol distillation column(30) provided in the lower part of the liquid storage tank; and a dimethylterephthalate storage tank(40) provided in the lower part of the ethyleneglycol distillation column.

Description

Apparatus for separation dimethylterephthalate from polyester methanolysis gas}

1 is a cross-sectional view of a device according to the invention.

Description of the main parts of the drawings

10 liquid storage tank 11: chimney

11a: hollow part 11b: height

20: methanol distillation unit 21: condenser

22: storage tank 30: ethylene glycol distillation unit

31 side flow outlet 40 dimethyl phthalate storage tank

The present invention relates to a methanolysis gas comprising dimethylterephthalate (DMT), methyl-2-hydroxyethylterephthalate (MHET), ethylene glycol and methanol, which is discharged from a low pressure methanolysis reactor as a depolymerization product of polyethylene terephthalate. The present invention relates to an apparatus for efficiently separating dimethyl terephthalate. The MHET is discharged with DMT and converted to terephthalic acid (TPA) in the subsequent process, DMT hydrolysis.

Methanolissis is a process of depolymerizing polyester using methanol. At this time, the reactant is discharged in a gaseous state, which is mainly composed of excess methanol, dimethyl terephthalate (DMT), methyl-2-hydroxyethylterephthalate (MHET) and ethylene glycol. It is. The present invention needs to be separated and purified into methanol, ethylene glycol (EG), dimethyl terephthalate (DMT), which are the main components of this gas. The separated methanol can be reused in the methanolysis process.

For this purpose, conventionally, a partial condensation heat exchanger and a distillation column have been used. The cooling medium of such a heat exchanger should be kept above the freezing point of the DMT and at a low temperature so that gas can condense. This prevents the DMT from becoming solid or contaminating the heat exchanger. That is, the tubes of the heat exchanger should not be blocked with DMT solids, but the temperature between the DMT's freezing point and melting point (140 ° C.) is narrow, so that the DMT tends to sublimate to form a solid deposit. Therefore, in order to prevent DMT from depositing on the pipe wall, the temperature of the refrigerant should be well maintained in an appropriate region.

In addition, the DMT gas becomes a solid on a dry surface that is below the DMT freezing point, causing problems such as clogging.To prevent this, US Patent No. 5,578,173 sprays the DMT saturated condensate on the inner wall of the distillation column to prevent the DMT on the dry surface. The gas was not contacted and in addition, methanol was injected into the stages of the distillation column. However, it was confirmed that it is difficult to completely recover the DMT gas in the gas from the methanolysis reactor through injection. That is, it is difficult to condense the DMT even when a very large amount of methanol is injected, and thus there is a problem in that the DMT becomes solid at the top of the column, causing problems in the operation of the distillation column.

It is an object of the present invention to provide a device that overcomes these difficulties and simplifies the partial condenser and spray tower or spray area.

This allows the gas discharged from the methanolissis reactor to be in direct contact with the liquid storage tank to condense high-boiling materials such as DMT and EG, and utilize the sensible and condensation heat of the gas to evaporate the methanol in the liquid storage tank to separate the energy of the distillation column. It was used.

The present invention for achieving the object as described above is connected to a depolymerization reactor that decomposes polyester, that is, polyethylene terephthalate, and efficiently removes dimethyl terephthalate, ethylene glycol and methanol in the gaseous raw materials produced through depolymerization. An apparatus for separation recovery is presented.

That is, the present invention is installed at the end of the depolymerization reactor of polyethylene terephthalate, the depolymerization is composed of a glycolissis reaction using ethylene glycol and methanolysis reaction using methanol, usually methane after the glycolysis reaction Since the olissis reaction is taking place, the apparatus of the present invention can be installed at the rear end of the methanolysis reactor.

The present invention is a device for efficiently separating the gaseous reaction product discharged from the methanolysis reactor, particularly difficult to separate because the temperature between the freezing point and the melting point (140 ℃), that is, the liquid phase temperature range is narrow It is intended to provide a device for efficiently separating known dimethylterephthalates.

Hereinafter, a detailed description will be given with reference to FIG. 1.

The present invention provides a method for efficiently separating dimethyl terephthalate from a methanolysis gas containing dimethyl terephthalate (DMT), methyl-2-hydroxyethyl terephthalate (MHET), ethylene glycol and methanol as a depolymerization product of polyethylene terephthalate. In the apparatus,

A liquid storage tank 10 into which the methanolissis gas is introduced and condensed;

A methanol distillation unit 20 provided on an upper portion of the liquid storage tank 10;

Ethylene glycol distillation unit 30 provided in the lower portion of the liquid storage tank 10;

Dimethyl terephthalate storage tank 40 provided in the lower portion of the ethylene glycol distillation column (30);

It proposes a dimethyl terephthalate separation device comprising a.

In particular, the center of the liquid reservoir 10 in the present invention is provided with a hollow portion (11a) therein, the lower end is connected to the upper portion of the ethylene glycol distillation tower 30 and protrudes to a predetermined height (11b) inside the liquid reservoir It is preferable that the tubular chimney 11 is further formed so that the liquid ethylene glycol and dimethyl terephthalate rise to a certain height and then overflow. Multiple chimneys can be installed as needed.

In addition, the upper part of the methanol distillation tower 20 is preferably provided with a condenser 21 and a storage tank 22 for condensing methanol in a gaseous state and recovering it in a liquid state.

In addition, the ethylene glycol distillation column 30 is preferably further provided with a side flow outlet 31 so that the vaporized ethylene glycol is discharged.

In the present invention, the liquid reservoir 10 is maintained at a temperature at which the methanolissis gas can be condensed into the liquid phase, and the methanolissis gas is in direct contact with the liquid of the liquid reservoir. In other words, the methanolissis gas passes through the liquid while pushing the liquid out of the liquid reservoir. Therefore, the liquid level of the outer cylinder portion is kept lower than that of the inner cylinder portion. In this process, the methanolissis gas is condensed while contacting the liquid, and methanol in the liquid reservoir 10 is vaporized due to the sensible and latent heat of the methanolissis gas. At this time, the pressure of the distillation column is preferably maintained at 10 atm, preferably at 5 atm. At this time, the liquid storage tank 10 is maintained at a temperature of 120 ℃ to 200 ℃. This is because at low pressure, the DMT sublimates and rises to the top of the column, which solidifies in each part of the distillation column, causing the distillation column to be blocked by the solid DMT.

The methanol distillation unit 20 is composed of a tray or a packing, and methanol is discharged to the top of the column by separation and purification in this part, and a mixture of some methanol, ethylene glycol and dimethyl terephthalate, which cannot be vaporized Is condensed into the liquid phase and flows back to the liquid reservoir (10). That is, in contact with the liquid stream refluxed down from the column and the vaporized stream from the liquid reservoir and the gas stream rising from the EG refining unit, the purified methanol is discharged to the upper part of the column, and the methanol and the ethylene glycol and dimethyl terephthalate mixture are To flow back into the liquid reservoir (10). At this time, the temperature on the column is maintained at about 100 ° C. at 70 ° C. which is the boiling point of methanol at the distillation column operating pressure.

In the ethylene glycol distillation unit 30, ethylene glycol is vaporized, and dimethyl terephthalate is condensed in the liquid phase and flows down to the dimethyl terephthalate storage tank 40. Therefore, the EG discharge part 31 maintains the boiling point temperature of EG at the distillation column operating pressure, and the dimethyl terephthalate storage tank 40 maintains the boiling point temperature at this distillation column operating pressure.

That is, the present invention is the gas introduced through the methanolysis reaction is condensed in contact with the liquid methanol, ethylene glycol and dimethyl terephthalate mixture stored in the liquid reservoir 10, at this time evaporated due to the latent heat of the incoming gas The gas is raised to the upper portion of the methanol distillation unit 20, condensed in the condenser 21, stored 22, and part of the reflux is accumulated in the liquid storage tank 10 via the methanol distillation unit 20.

The liquid methanol, ethylene glycol, and dimethyl terephthalate accumulated in the liquid storage tank 10 overflow the tubular chimney and then descend into the ethylene glycol distillation unit 30 through the hollow part 11a. This liquid stream is separated and purified in contact with the rising gas from the reboiler at the bottom of the distillation column so that a gas stream having a high methanol concentration bypasses the liquid storage tank 10 and rises, and ethylene glycol is a side draw in the gas state. The highest boiling point material, DMT, is obtained from the bottom of the tower. At this time, the obtained ethylene glycol contains a small amount of DMT and methanol, DMT will contain a high boiling point materials such as a small amount of MHET.

The whole distillation column proposed by the present invention separates the methanolysis gas stream into three components. Methanol is separated and purified to the top of the tower and the ethylene glycol is vented in the gaseous state in the center of the tower, i.e. obtained as a side draw. In addition, DMT is obtained under the tower. Methanol obtained from the column top, that is, methanol distillation unit 20 can be recycled to the methanolysis reactor and reused. Some EG may be included at the top of the column but this is not a problem in the methanolysis reactor. The ethylene glycol distilled off flows into a subsequent distillation column (not shown) to obtain an EG containing a small amount of methanol in the upper part of the column, and an EG containing a small amount of DMT in the lower part of the column. Since EG containing traces of methanol has a large boiling point difference between the two substances, pure EG can be obtained using a simple distillation apparatus. EG, including DMT, can also be recycled and reused in the previous process for use in the dissolution of spent polyesters and glycolissis reactions.

In addition, the DMT obtained in the dimethylphthalate storage tank 40 may be sent to a hydrolysis tank, which is a subsequent process, to be used as a raw material for producing terephthalic acid (TPA). Thus, impurities contained in trace elements in DMT, including MHET, are removed in subsequent hydrolysis and crystallization processes.

The advantage of the present invention is that the three components are separated in one tower, which greatly simplifies the process and greatly reduces the separation energy. In addition, since the gas discharged from the center of the tower can operate a distillation column with low separation at atmospheric pressure, low equipment cost is required. In the conventional methanolless gas distillation purification system, two distillation columns are used to separate the three components mentioned (US Pat. No. 5,051,528, US Pat. No. 5,672,780). Methanol is separated from DMT and EG in the first column and DMT and EG in the second column. Accordingly, as the ethylene glycol and DMT stay together for a long time in the reboiling of the first tower and the bottom of the tower, the polymerization reaction proceeds under the influence of a catalyst with methanolis gas, forming an oligomer and contaminating the distillation column. A problem occurred. However, in the present invention, since the EG and the DMT stay together very short, that is, the DMT concentration is high at the bottom of the tower and the EG concentration is high at the center of the tower, so that the reaction between the two components is difficult to occur, thereby preventing oligomer formation. .

The present invention can greatly reduce the device cost by the simplification of the process, and since the heat of the methanolic gas is directly used as distillation energy, the energy can be greatly saved. In addition, the conventional subcondenser and spray tower used to effectively condense and effectively condense the highly sublimable DMT in the methanolissis gas can be replaced by a simple gas-liquid contact system. In addition, it is possible to solve the problem of oligomer formation by the polymerization of DMT and EG, which is a problem of conventional gas separation and purification of methanol.

Claims (8)

In an apparatus for efficiently separating dimethyl terephthalate from a methanolysis gas containing dimethyl terephthalate (DMT), methyl-2-hydroxyethyl terephthalate (MHET), ethylene glycol and methanol as a depolymerization product of polyethylene terephthalate. , A liquid storage tank 10 into which the methanolissis gas is introduced and condensed; A methanol distillation tower 20 provided above the liquid storage tank 10; An ethylene glycol distillation tower 30 provided below the liquid storage tank 10; Dimethyl terephthalate storage tank 40 provided in the lower portion of the ethylene glycol distillation column (30); Dimethyl terephthalate separation apparatus comprising a. The method of claim 1, The center of the liquid reservoir (10) is provided with a hollow portion (11a) therein, the lower end is connected to the upper portion of the ethylene glycol distillation tower 30 and formed to protrude to a predetermined height (11b) in the liquid reservoir to form a liquid ethylene Dimethyl terephthalate separation device further comprises a tubular chimney (Chimney, 11) to allow the glycol and dimethyl terephthalate to rise after rising to a certain height. The method of claim 2, Dimethyl terephthalate separation device, characterized in that the upper part of the methanol distillation tower 20 is further provided with a condenser 21 and the storage tank 22 for condensing the methanol in the gas state to recover in the liquid state. The method of claim 3, wherein The ethylene glycol distillation tower 30 is a dimethyl terephthalate separation device, characterized in that the side flow outlet 31 is further provided to discharge the ethylene glycol vaporized. The method of claim 4, wherein The liquid reservoir 10 is maintained at a temperature at which the methanolissis gas can be condensed into the liquid phase by adjusting the operating pressure of the distillation column, and the methanolissis gas is condensed by direct contact between the methanolissis gas and the liquid in the liquid reservoir. And dimethyl terephthalate separation device, wherein methanol is vaporized due to sensible and latent heat of methanolysis gas in this process. The method of claim 5, The methanol distillation unit 20 is composed of a tray or a packing, and methanol is discharged to the top of the column by separation and purification in this part, and a mixture of some methanol, ethylene glycol and dimethyl terephthalate, which cannot be vaporized Dimethyl terephthalate separation device characterized in that the condensed to the liquid phase to flow back to the liquid reservoir (10). The method of claim 6, The ethylene glycol distillation unit 30 is ethylene glycol is vaporized, dimethyl terephthalate is dimethyl terephthalate separation device characterized in that the separation and purification to occur to flow down into the dimethyl terephthalate reservoir (40). The method of claim 7, wherein The dimethyl terephthalate storage tank 40 is a dimethyl terephthalate separation device, characterized in that the dimethyl phthalate is stored in the liquid phase, the temperature is maintained so that ethylene glycol is vaporized.

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