JPS5829207B2 - Recovery method of polyethylene terephthalate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering powdered polyethylene terephthalate from pure material products.

The present invention also relates to polyethylene terephthalate (hereinafter PET).
The present invention relates to a method for recovering PETP in powder form from scrap, in particular textile scrap, which may also contain other synthetic or natural polymers or both in addition to P (abbreviated as P).

Polyesters, especially PETP, are suitable for example l, 1°1.3,
It is already known that scales are soluble in solvents such as 3,3-hexafluoropropanol, for example mixed solvents such as trichloroacetic acid-chloroform or phenol-tetrachloroethane.

However, industrial processing techniques and economic considerations limit the use of these solvents and mixed solvents.

Its use is only important for analytical tests. Furthermore, in the utilization of scrap of pure PETP, this scrap can be decomposed and decondensed to become the starting material for PETP production, and then recondensed and spun. Make polyester possible.

It is also known that it is possible to make unsaturated polyester resins or to agglomerate and extrude scrap into pellets again.

This method is not used for scrap of mixtures containing polyethylene terephthalate.

One method for purifying impure PETP is known from US Pat. No. 3,701,741.

In this method, impure PETP is dissolved in aliphatic alcohol under pressure at about 170-200 °C, the resulting solution is filtered under pressure to separate undissolved impurities, and then the solution is Cooling precipitates PETP in powder form.

This method is equally applicable when using as starting material a non-quality PETP which melts at about 170°C.

Approximately 200° C. is required for dissolution of partially or fully crystalline PETP.

At this temperature, undesirable decondensation of PETP occurs, depending on the type of alcohol used as a solvent.

When separating and recovering PETP from fiber scrap containing other fibers in addition to PETP fibers, the recovery method using aliphatic alcohol cannot be applied because the other fibers are damaged by the high temperatures used.

At the same time, if PETP is successfully separated, there is also interest in reusing this fibrous material.

Another critical drawback that limits the application of this method of separating and recovering PETP from textile scrap is that other coexisting materials, such as polyamides, are equally soluble under the given conditions and precipitate in powder form upon cooling. It is to be.

The production of PETP powder from a starting pure PETP product has to date been successful by mechanical methods.

In this method, a milling process using an impact milling frame machine is applied.

This milling process is very energy consuming and complex.

Another disadvantage is that the yield is low, the particle size distribution is unusually wide, and sieving has to be carried out many times in succession.

It is also known to embrittle PETP to obtain a starting material that is easily pulverized.

This embrittlement can be prevented by treatment at a low temperature below 0℃, or by
Obtained by heat treatment at temperatures exceeding 'C.

Although embrittlement can improve the efficiency of the pulverization process, the above-mentioned drawbacks such as too broad particle size distribution, laborious sieving, etc. still remain.

The cost of producing low temperatures or high temperatures exceeding 250°C is added.

To embrittle PETP by heat treatment, the starting material must be dried for two days, for example at 150-170°C, and then slowly and continuously raised to a temperature above 270°C, without further treatment at that temperature. No.

A gradual and continuous temperature increase increases the degree of polymerization of PETP and thus its melting point.

Thereby, PETP can be efficiently pulverized in the impact pulverizer.

A known possible method of embrittling thermoplastic polymers is to embed them in a highly crystalline and highly brittle organic matrix material.

After the resulting mixture is subjected to a mechanical grinding process, the matrix material is removed by melting, dissolving or sublimation.

In this case, due to the large proportion of matrix material in the mixture, the disadvantage was that only a small amount of the target polymer powder was present in the precipitate.

In addition, recovering the matrix material is expensive;
The solvent must be recovered by distillation.

The present invention aims to recover PETP in powder form in a method that does not have the disadvantages and difficulties mentioned above.

The object of the present invention is to process a starting pure PETP product as well as multicomponent scrap, in particular scrap of fiber polymers, into a wet process.
The purpose of the present invention is to develop and provide a method for recovering PETP in powder form.

Surprisingly, selectively acting solvents belonging to the halogenated hydrocarbon group, in particular those with boiling points below 100'C at standard pressure and molecular weights below 200, or mixed solvents containing such solvents, usually Below °C, PET
Pure PET in the form of granules, fibers or films, since non-solvents of P dissolve PETP under the corresponding steam pressure at temperatures up to 200°C.
It has been found that PETP is suitable for melting and recovering in powder form from P products or from multi-component scrap.

Upon cooling, PETP precipitates in powder form. When recovering PETP from multi-component scrap, filtering the solution under pressure to separate it from the residue and cooling it produces PETP.
precipitates in powder form.

Separation of the PEPT powder, drying and recovery of the solvent are carried out according to known methods.

It is convenient to carry out the dissolution process by stirring in an inert gas atmosphere.

Temperature and pressure conditions vary according to the solvent used and its solubility.

The dissolution process requires 0.25 to 4 hours including temperature rise time.

By the method of the present invention, PETP, which is usually considered to be poorly soluble, can be
It became possible to dissolve the above-mentioned solvent and a mixed solvent containing the above-mentioned solvent.

Unexpectedly, the method of the present invention is characterized in that PETP can be recovered in high yield, and PETP is obtained in high purity with virtually no decomposition.

Another important and decisive advantage of the process according to the invention is that the polyamides, e.g.
Does not dissolve base polymers and/or natural polymers such as polyacrylonitrile, viscose, cotton, wool, silk or special latexes, and in addition does not damage these polymers, so they can be reused There is a point.

Example 1 200ml of PETP grains! of dichloromethane and heated to about 150°C in a pressure vessel.

After maintaining this temperature for 30 minutes, the solution was cooled and approximately 19.1 g of the PETP used was recovered in powder form by precipitation.

Example 2 20 g of PETP film was treated with 200 g of a mixed solvent consisting of 90 volumes of dichloromethane and 10 volumes of acetone.
and heated to about 165° C. in a pressurized vessel.

After maintaining this temperature for 30 minutes and cooling the solution, at least 96 φ of the PETP used precipitated out and was entrained in powder form.

Example 3 20g of PETP scrap was dissolved in dichloromethane 200g
mA? and heated to approximately 150°C in a pressurized vessel.

After maintaining this temperature for 30 minutes, the solution was cooled and at least 95% of the PETP used precipitated and was recovered in powder form.

Example 4 30 g scrap of PETP-polyurethane-polyamide mixture was mixed with 200 m dichloromethane and heated to about 150<0>C in a pressurized vessel.

After maintaining this temperature for 30 minutes, the solution was pressure filtered to separate undissolved residue.

The filtrate was then cooled. At least 95 pieces of PETP that were present in the mixture were recovered in powder form.

Neither polyurethane nor polyamide dissolved.

Example 5 The procedure of Example 4 was repeated using 30 g each of scrap of PETP-cotton mixture and scrap of PIETP viscose mixture.

95% of the PETP present in each mixture was recovered in powder form.

Neither cotton nor viscose was dissolved.

Example 6 A 55% PETP-45% wool mixture 3 (Bi') was processed according to the procedure of Example 4.

16 g of powdered PETP was obtained.

This corresponds to a yield of 97. The wool component was not dissolved.

Example 7 30 g of a heterophasic mixture of PETP, silk and special latex
was processed according to the procedure of Example 4.

More than 95 strips of the PETP used were recovered in powder form.

Other components of the starting mixture, namely silk and special latex, did not dissolve.

Example 8 20 g of PETP scrap was mixed with 200 rnl of trichloromethane and heated to about 170'C in a pressurized vessel.

After maintaining this temperature for 30 minutes, the solution was cooled and at least 85% of the PETP used was recovered in powder form by precipitation.

Claims (1)

[Claims] 1. Polyethylene terephthalate from a pure polyethylene terephthalate product or scrap is dissolved in the solvent at a temperature exceeding the boiling point of the solvent and under a vapor pressure corresponding to the temperature, and then cooled to form a powdery precipitate. In the method of recovering polyethylene terephthalate in powder form by scaling, the solvent is a halogenated hydrocarbon having a boiling point lower than 100°C at standard pressure and a molecular weight lower than 200, or the halogenated hydrocarbon is used as the solvent. A method for recovering the powdered polyethylene terephthalate, characterized in that a mixed solvent containing the above is used. 2. Claim 1, characterized in that when polyethylene terephthalate is recovered from the scrap, the precipitate is filtered to separate undissolved polymers and reused. the method of. 3. Process according to claim 1, characterized in that the dissolution step is carried out at temperatures up to 200'C and under the vapor pressure that the solvent or solvent mixture used has at this temperature.