DE1812720C3 - Process for the purification of crude bis (ß-hydroxyethyl) terephthalate - Google Patents

Description

characterized in that (1) the raw Bis (0-hydrosethylethyl) terephthalate in benzene. toluene or xylene as a solvent at a temperature higher than the apparent melting point of the crude BHET is in the solvent - where the apparent melting point is that in the description given definition - and with a higher concentration than the saturation solubility of the crude bis (j? -hydroxyethyl) terephthalate in the Solvent is dissolved at the temperature corresponding to the apparent melting point, and (2) the solution is rapidly cooled to a temperature below this apparent melting point.

.1 °

The invention relates to a process for the purification of crude bis (j3-hydroxyethyl) terephthalate.

Bis (j3-hydroxyethyl) terephthalate, hereinafter Abbreviated as »BHET«, it is used in large quantities as an intermediate in the manufacture of Polyethylene terephthalate obtained and has a high technical value.

40 BHET is usually made by ester interchange between dimethyl terephthalate and ethylene glycol or produced by direct esterification of terephthalic acid with ethylene glycol Operation commonly referred to as the ethylene oxide process, a considerable technical interest whereby terephthalic acid is reacted directly with ethylene oxide.

Raw bis (/? - hydroxyethyl) terephthalate, which is produced by the above procedure is obtained contains various impurities, e.g. B. those contained in the starting sterephthalic acid, the catalyst used in the BHET formation reaction, additives and as a by-product of the reaction formed impurities. Some of these impurities are prone to staining or Lowering of the melting point of the polyester, or they are detrimental to the polymerization reaction. It is therefore essential to avoid such impurities from the BHET to the maximum possible degree in order to use it as a starting material for Use high quality polyester.

In particular, the impurities in crude bis (j? -Hydroxyethyl) terephthalate comprise a reaction product of the impurities carried along by the starting terephthalic acid, e.g. B. 4-carboxybenzaldehyde with ethylene glycol or ethylene oxide

[HIGH ₂ CH ₂ OOC-

CHO

hereinafter abbreviated as HE-4CBA); a reaction product of p-toluic acid with ethylene glycol or Ethylene oxide

.15 (HIGH ₁ CH ₂ OOC-

CH ₃

hereinafter abbreviated as HE-PTA); low condensation products of the above compounds with BHET; Addition products of BHET and ethylene oxide obtained as by-products of the reaction of terephthalic acid with ethylene glycol or with ethylene oxide will

(HOCH ₂ CH ₂ OCh ₂ CH ₂ OOC - <^ V-COOCH ₂ CH ₂ OH HOCH ₂ CH ₂ OCH ₂ CH ₂ -OOc- / V-COOCH ₂ CH ₂ OCH ₂ CH ₂ Oh),

and lower condensation products between the above or those of the above with BHET. (Such impurities that contain ether bonds are abbreviated as DEG below.) Such impurities cause the following disadvantageous phenomena during Polyester manufacture: HE-4CBA creates a dyeing of the polyesters; HE-PTA delays the extent or the Rate of polymerization reaction of polyester; and DEG lowers the melting point of the Pclyester product.

So far, various cleaning procedures for crude bis (0-hydroxyethyl) terephthalate have been indicated ben. A typical example of such procedures is solvent recrystallization. As useful Solvents in this procedure are, for. Am U.S. Patent 3,062,862 water and in the U.S. Patents 3,120,560 and 3,268,575 polar organic solvents such as chlorinated hydrocarbons, aliphatic or cycloaliphatic alcohols or the like. Proposed. The solubility of bis (/? - hydroxyethyl) terephthalate (BHET) in these solvents is extremely high and even low Temperatures, the solubility is still considerable. Therefore, when the solvent solution is set to low Temperatures are cooled to recover BHET from solution, substantial amounts of remain BHET dissolved in the solution. Therefore, in order to regain this BHET, the solution must be either very low temperatures must be cooled, or the solvent must be completely evaporated or almost completely removed. Also is

the cleaning effect achieved is often unsatisfactory. Hence, they are recrystallization solvents hardly suitable for large-scale use

Also the use of non-polar solvents, for example aliphatic or cycloaliphatic Hydrocarbons as recrystallization solvents for BHET is known. However, the solubility of BHET in such solvents is too low to be to justify their use on a technically feasible scale.

The object of the invention is therefore to create a process for the purification of crude bis (/? - hydroxyethyl) terephthalate, which was obtained by reacting terephthalic acid with ethylene oxide, the undesired impurities of the type indicated above can be satisfactorily removed and a bis (/? - hydroxyethyl) terephthalate of high Purity, which is suitable as polyester starting material, and can be recovered to a high degree of recovery.

Experiments have been carried out and it has been found that when using aromatic compounds, which are liquid at room temperature, e.g. B. benzene, toluene and xylene as recrystallization solvents, the solubility of BHET in these aromatic compounds at relatively low temperatures, for example room temperature is very low, but at higher temperatures, for example 100 ° C and above it is very high. Therefore, in terms of solubility of BHET, only those are aromatic Compounds suitable recrystallization solvents.

Attempting to recrystallize crude BHET by a common recrystallization process using the However, purifying the aromatic compounds mentioned above did not give a BHET of more satisfactory Purity. In contrast, it has now been found that when using the special cleaning process according to the invention to the recrystallization with such aromatic compounds detrimental impurities can be removed very effectively and that a BHET used as a starting material is very satisfactory for polyester can be obtained.

According to the invention, a method for the purification of crude bis (j? -Hydroxyäihyl) terephthalate, which was obtained by reacting terephthalic acid with ethylene oxide, where

(a) Crude bis (jJ-hydroxyethyl) terephthalate with heating in an aromatic compound as a solvent, which is liquid at room temperature, is solved,

(b) the heated solution is cooled and

(c) the precipitated bis (/ I-hydroxyethyl) terephthalate is separated,

which is characterized in that (1) the crude bis (/ I-hydroxyethyl) terephthalate in benzene, toluene or xylene as a solvent at a temperature higher than the apparent melting point of the crude BHET is in the solvent - the apparent melting point being that in the description below given definition - and with a higher concentration than the saturation solubility of the crude bis (j9-hydroxyethyl) terephthalate in the solvent at the temperature corresponding to the apparent melting point, and (2) the solution rapidly to a temperature below that apparent melting point is cooled

When carrying out the method according to the invention the precipitate can be granular or blocky Solids from BHET should be avoided.

As stated above, the solubility of crude BHET in the said aromatic compounds, which are liquid at room temperature, relatively low at low temperatures, whereby

However, it increases rapidly with increasing temperature. For example, the solubility of a ^{BHET of high purity melting at 110 0} C in benzene is shown at different temperatures in the graph of the figure, with similar results also when investigating the solubility using toluene or Xylene can be obtained.

In the figure, the temperatures ("C) are indicated on the abscissa, and the maximum amount of BHET that can be dissolved in 100 g of benzene is recorded on the ordinate. The point B in the figure indicates the apparent melting point (about 90 ⁰ C) of the crude BHET in benzene.

In the hatched area on the right side of curve A of the figure, the crude BHET completely dissolves in benzene and forms a homogeneous solution. On the other hand, in the hatched area on the left-hand side of curve A of the figure, which is delimited by the vertical line B ' extending above point B , lies molten crude BHET and the solution in which BHET is dissolved in benzene, together before. The point P \ corresponds e.g. B. a state as it is obtained when carrying out Example 2 described below, wherein 7 kg of crude bis (0-hydroxyethyl) terephthalate and 32 kg of benzene at 110 ⁰ C for 30 minutes under a pressure of 4 kg / cm ² (nitrogen) are heated.

The area on the left side of the vertical line B ' in the figure is the zone in which BHET in solid form coexists with the benzene solution of BHET or benzene.

If the above discussed 2-phase mixture of the molten crude BHET and benzene solution of BHET, indicated by the point Pi, are present together, the undissolved material, ie the molten crude BHET, is first removed, the state indicated by the point P2 in the figure being reached .

The benzene solution is then quickly quenched until it reaches a temperature corresponding to point Pj .

This point Pi is at a lower temperature than the apparent melting point in benzene of crude BHET, the above quenching causing the precipitation of purified BHET in the substantial amount from Qz to Qi as shown on the ordinate of the figure. The purified BHET precipitated in this way is separated and recovered.

It is essential that the point Pj is lower than the point B. Thus, namely, purified BHET corresponding to Q2 to Qj is precipitated in the temperature range from point Pz-Pj , and also the amount of purified BHET corresponding to Qi to Qj is far greater than the amount of purified BHET which precipitates when the temperature from point B to Room temperature would be cooled.

(, 5 According to the invention, the rapid cooling of the temperature from point P2 down to a temperature (point Pj) below the apparent melting point (point B) is essential.

Of course, the temperature can finally be lowered from point Pi to any desired temperature, for example room temperature, after the temperature has been lowered from P2 to P) . The temperature below the point Ps can be cooled gradually or rapidly.

As can be seen, the solubility of BHET in the aromatic compounds decreases with increasing temperature quickly to. Therefore, it is for the practical execution of cleaning with high effectiveness advantageous, the maximum possible amount of raw BHKT at considerably high temperatures, for example 100 ° C or above to dissolve in these solvents and bring this solution to a selected temperature, z. B. room temperature, or to cool above, so that the maximum possible amount of purified BHET can be obtained by a single cleaning operation.

Investigations showed that the melting point of BHET is of high purity at RO to 1 ITC, where however, the apparent melting point of the same BHET in the system in which the aromatic Compound is simultaneously present to about 5 to 20 ° C lower than the temperature indicated above is. For example, the apparent melting points of BHET are in the typical aromatic Compounds used according to the invention at temperatures as set out in the following Table I are given.

Table I.

Melting point of BHET in the simultaneous presence of various aromatic compounds (Solvent)

Aromatic compound

Apparent melting point of BHET

("Q

benzene
toluene
Xylene

90 to 98

91 to 100
93 to 102

The apparent melting points of crude BHET, the minor amounts of those described above Contains impurities, in the simultaneous presence of aromatic compounds, as above are also somewhat lower than the temperatures given in Table I above.

The apparent melting points of BHET in the liquid aromatic compounds can e.g. Am can be measured as follows: 1 g of a BHET sample and 5 g of solvent (an aromatic Compound) are placed in a sealed tube and gradually heated in an oil bath Temperature at which the BHET sample has melted (if it is softer in the sealed tube, two liquid phases are formed) is measured as the apparent melting point.

Investigations showed that when a heated solution containing the crude BHET is gradually cooled becomes, as practically carried out in the common recrystallization process, the purity of the precipitated BHET is still unsatisfactory. Namely, the BHET thus precipitated and separated retains the back larger proportions of the impurities, and that obtained by polymerizing this BHET Polyethylene terephthalate is yellow to brown in color and its melting point is about 1 to 5 ° C lower than

S that of high purity polyethylene terephthalate.

Further studies were therefore made into the mechanism of precipitation of purified BHET and it has been found that if the heated solution is rapidly cooled or quenched, at least from said high temperature to a selected temperature below the apparent The melting point of the crude BHET in the solvent to essentially precipitate the BHET instantly, the precipitated BHET has a very high purity and that polymerized from this BHET Polyethylene terephthalate is completely free of coloration, or if it is colored, no more than this is to an essentially negligible degree. In addition, the polyethylene terephthalate has such a high melting point like that of commercially available polyethylene terephthalate or even higher than this.

When the solution obtained by dissolving crude BHET in the aromatic compound as a solvent

2s tel which is liquid at room temperature such as benzene, toluene or xylene obtained with heating is gradually cooled, a blocky or granular solid BHET is precipitated when the solution is crude BHET in a uniformly dissolved state in an amount greater than that according to its solubility at the apparent melting point.
In contrast, if, for example, the heated solution described above is discharged into a low pressure zone so that the sludge system, which results from the rapid evaporation of part or most of the solvent in the heated solution and the partial precipitation of the BHET dissolved therein, rapidly results is quenched to a temperature below said apparent melting point of the crude BHET in the same solvent, a BHET precipitate consisting mainly of flaky or needle-like crystals is obtained. In this case, however, if the pressure in the low pressure zone is not sufficiently low and furthermore the cooling is not carried out sufficiently quickly, a granular or blocky solid BHET may be precipitated together with the flaky or needle-like crystals.
The phenomena related to the purity of the precipitated BHET were examined, whereby the following was found:

(A) In the case of the precipitation of BHET by cooling the solution of crude BHET which is at a higher level Temperature is heated as the apparent melting point of the BHET, when using cooling is performed insufficiently quickly, a granular or blocky solid BHET is precipitated

(B) The analytical results of such grains or blocks of solid BHET show that these still considerable amounts of impurities, e.g. B. HE-4CBA and DEG included.

(C) On the other hand, if the cooling is sufficiently rapid, the BHET precipitate becomes main in the form of flaky or needle-like crystals mixed with smaller amounts of amorphous BHET obtained but not including any granular or blocky BHET

(D) The BHET precipitate that is not granular or contains blocky bhet shows an extremely low level of impurities, and if so this is polymerized, a substantially color-free polyethylene terephthalate of high Melting point can be obtained.

According to the invention, it has been found that when the solvent solution, the crude BHET in a uniformly dissolved state at a higher concentration ι ο than the saturation solubility of the BHET in the solvent at the apparent melting point of the BHET contained in the solvent, the solution being at a higher temperature than said apparent Melting point is heated from this temperature to a desired temperature, which is at the most at a Temperature is below the apparent melting point, is cooled sufficiently quickly to cause the precipitation of granular or blocky solid BHET to avoid precipitation of high purity BHET, free of the granular or blocky solid of BHET can be obtained, such as this described in (C) and (D) above even if thereafter the resulting slurry is gradually cooled.

It is believed that if the cooling of the solution from the initial high temperature to a temperature which is at most below the temperature at point B is not carried out at a sufficiently high rate or to a sufficiently high degree, during the cooling of Point A at point β the molten BHET is separated from the solution to form a separate phase, and this molten BHET is solidified into a granular or blocky shape upon cooling to a temperature below point B. Since such a solidified BHET still contains considerably large amounts of impurities, particularly HE-4CBA, it becomes a poor polyethylene terephthalate when polymerized.

The quenching or rapid cooling of the solution from point P2 to below point B can be done to any extent and in any way.

For example, the heated benzene solution of crude BHET (1) is formed with a temperature of 120 ° C in a pressure vessel because the boiling point of benzene at 8O ⁰ C. In order to quench or rapidly cool this solution to a temperature below the Sin point in the figure, the pressure vessel can be opened to rapidly reduce its internal pressure to atmospheric pressure. However, the pressure to which the vessel is opened need not be atmospheric pressure, but may also be higher as long as the temperature of the BHET sludge in benzene, which is formed when the pressure is released, becomes lower than the point B. In addition, the pressure can also be lower than atmospheric pressure.

(2) It is also permissible to add a large amount of cooling liquid or cooling sludge containing purified BHET to the heated solution in order to rapidly cool or quench the latter to a temperature below point B.

(3) On the other hand, said heated solution can be mixed in a large amount of cooling liquid or the be introduced sludge described above.

The cooling liquid to be used in the above-described cooling methods (2) and (3) or the Sludge to be used therein is not limited to specific substances as long as they are opposed to BHET are not reactive. For reasons of convenience, for example in terms of easy recovery of solvent and higher heat output, it is preferred to use the same solvent as it was used in the solution, applied, d. that is, in the case of the heated solution A, benzene or a becomes Sludge formed from purified BHET suspended in benzene is preferred.

(4) A preferred system for rapid cooling or quenching according to the invention comprises dispensing the heated solution, e.g. apparent melting point of the crude BHET is formed in this solvent. The heated solution is rapidly cooled or quenched from the high temperature to a selected temperature below the apparent melting point. In such a procedure, it is possible to rapidly cool or quench the heated solution to the desired temperature, for example in the case of the aforementioned heated solution A, to a temperature below the point B using a very simple procedure.

In the operation (4) described above, the heated solution can be immediately discharged into a vapor phase under a pressure lower than the above pressure or into a liquid phase under such a low pressure. The vapor phase can consist of air, an inert gas, e.g. B. nitrogen or carbon dioxide, or consist of the vapor of the solvent used. Any liquid which is inert to BHET can again be used as the liquid phase, but for the reasons already mentioned above the same solvent as was used in the heated solution, or a solution or suspension thereof containing BHET is preferred. The solvent can of course be cooled to a suitable temperature in advance. The low pressure zone can be suitably pressurized or left at atmospheric pressure or it can be at a reduced pressure. The essential requirement in this case is that the pressure of the low pressure zone must be kept lower than the saturated vapor pressure of the mixture of the BHET and solvent, this mixture being formed upon cooling the heated solution to the apparent melting point of the crude BHET in the same solvent will. In addition, the pressure at the low altitude must be maintained during the period of dispensing of the heated solution into the low pressure zone. This z. B. the heated solution A from the point P ₂ , ie 120 ⁰ C, rapidly to a temperature below the point ^ ie. about 90 ° C, chilled without causing any granular or flaky BHET to precipitate. In addition, the sludge obtained by releasing the heated solution into the low pressure zone can be further cooled by any means, if desired.

Even if, in the above-described cooling operation (3), the pressure under which the heated solution is mixed with the cooling liquid or the cooling sludge, either the same or

slightly higher than the saturation vapor pressure of the mixture of the same composition as that is the heated solution that is formed when the heated solution reaches the apparent melting point of the raw BHET cooled in the solvent can be essentially equivalent and the same satisfactory results as in the procedure (4) can be easily obtained.

After rapidly cooling the heated solution using any one of the procedures (1) through (4) As described above, it is advantageous to keep the quenched liquid generally during Allow one minute to 10 hours, preferably 20 minutes to 3 hours, to complete the BHET to fail.

The cleaning solvent used in the invention has a low resolving power for BHET at low temperature, but a high resolution at higher temperatures, e.g. B. 100 ° C or above, and is moreover heat stable. for For the purposes of the invention, benzene is particularly preferred. Mixtures of Benzene, toluene and / or xylene are used, but this is of no particular advantage is obtained.

According to the invention, a heated solution of the above-mentioned crude BHET and the aromatic solvent produced. In doing so, it is important to form a solution that the raw BHET in uniformly or homogeneously dissolved state at a higher concentration than the saturation solubility of the crude BHET in the solvent at the temperature corresponding to the apparent melting point of the to containing detergent BHET in the same solvent, and the temperature of the solution to a higher Bring temperature than the apparent melting point.

The procedure for preparing such a heated solution is not critical. Some useful Working methods are given below, for example:

(1) The total amount of the fed crude BHET is completely dissolved in the solvent by heating to make the solution of
Forming temperature;

(2) Crude BHET is dissolved in the solvent by heating, and the insoluble part becomes removed to form a homogeneous solution of high temperature; or

(3) Raw BHET is mixed with the raw BHET at a temperature above the melting point Solvent to form a homogeneous solution that does not contain any insoluble matter in Brought in touch

According to the method according to the invention, the heated solution of crude BHET is in one of the specified solvents as described above, a treatment for rapid cooling or Subjected to quenching and then a desired further cooling, with precipitated BHET is separated. This BHET that on a very high purity can be obtained using simple procedures.

According to a preferred embodiment of the invention, if, for example, S benzene is used as the solvent, a homogeneous solution, heated to at least 96 ° C. and consisting of 8 to 60 parts by weight of crude BHET and 100 parts by weight of benzene, is directly converted into Benzene or a solution or suspension formed from benzene and BHET from a pressure

ic of not above 2 kg / cm ² abs., preferably below 1.3 kg / cm ² and from a temperature of not above 90 ⁰ C, and the precipitated BHET is either directly from the resulting system or after further cooling of the Systems separated and

won. In this way, a BHET of high purity can be obtained very smoothly.

On the other hand, when toluene is used as a solvent, it becomes 40 to 60 parts by weight of crude BHET per 100 parts by weight of toluene used, and one

homogeneous solution is obtained by heating the two components at a temperature not less than 98 ° C formed. The solution is immediately in toluene or a solution formed from toluene and BHET or Suspension with a pressure not above

1.5 kg / cm ² abs., Preferably not above 500 mm Hg and a temperature of below 91 ⁰ C, and the precipitated BHET is either separated directly from the resulting suspension or from the suspension that has been cooled further

won. In this way, too, a BHET of high purity using smooth Procedural measures received.

The dissolution of crude BHET in the solvent is carried out with heating to a temperature of preferred

wise not higher than 200 ° C. especially not higher executed as 180 ° C. This can cause the deterioration in the quality of BHET during manufacture of the heated solution can be effectively prevented.

According to the invention, the cleaning method described above can be carried out two or more times be repeated. In addition, the cleaning can be carried out continuously or batchwise.

For the production of an essentially high-color free polyethylene terephthalate with a high melting point by polymerizing purified BHET, it is generally desirable that the HE-4CBA, HE-PTA and DEG content of the BHET is as low as possible. Research has shown that this is satisfactory

Polyethylene terephthalate can be obtained when the HE-4-CBA content does not exceed 600 parts each Million and the HE-PTA content is not more than 0.6% by weight. It is possible to have a purified BHET to produce its content of impurities

is less than the values given above, this by properly executing the cleaning process can be easily achieved according to the invention.

The cleaning performance of the recrystallization

driving using a solvent can be influenced by the distribution coefficient of the impurity, expressed by the equation below can be evaluated:

Partition coefficient =

Impurity concentration in the precipitated BHET
Impurity concentration in the filtrate

According to the invention, the above partition coefficient is not more than 2.5 with respect to HE-4CBA, not more than 1.0 with respect to HE-PTA and not more than 8 with respect to DEG.

Thus, in general, those impurities are effectively carried over to the filtrate phase and removed. Accordingly, the cleaning method according to the invention has a very high removal performance Regarding these impurities.

The invention is explained in more detail below with the aid of examples.

example 1

A glass pressure flask with a capacity of 200 cm ¹ , which was equipped with an electromagnetic rotary stirrer, was charged with 25.1 g of crude BHET, which had been obtained by reacting terephthalic acid with ethylene oxide, and 170 cm ^{3 of} benzene, and the internal pressure of the The flask was raised to 4 kg / cm ² overpressure by supplying nitrogen. This pressure flask was connected in advance to a glass flask having a capacity of 500 cm ³ and equipped with a vacuum jacket, reflux condenser and stirrer (hereinafter referred to as "expansion tank") by means of a valve-attached stainless steel pipe that connected the bottom of the plunger to the side of the flash tank. The flash tank was in advance with 150 cm ³ of a BHET-benzene slurry boiled under atmospheric pressure (1.94 g BHET / 100 g benzene) were charged, and the entire assembly of the apparatus including the pressure piston and the flash tank was oil bath in a of 115 ° C to dissolve the filled BHET. The contents of the plunger were agitated, and after the complete dissolution of the BHET charge was determined, the valve on the tube connecting the bottom of the plunger to the bottle container was opened so that the benzene solution of the BHET in the plunger into the boiling slurry in was transferred to the flash tank under atmospheric pressure.

Meanwhile, the temperature in the container was 80.7 ° C and the pressure was atmospheric pressure held. When the solution in the plunger had been completely transferred, the valve opened closed and the device removed from the oil bath. The plunger was again with the same raw BHET and benzene charged under the same conditions, and the slurry in the Expansion vessel of an amount corresponding to that of the operation described above increased amount was withdrawn from the system as a sample. The device was then reinserted into the immersed in oil bath. In this way, the same operation was repeated seven times. With everyone The slurry obtained as a sample was immediately filtered and the cake was mixed with washed in cold benzene and dried. The purified BHET obtained did not contain any blocky or granular solid BHET, but mainly consisted of flaky crystals. The analysis results of the sample made uniform and the contents and distribution coefficients of impurities as follows:

Content of impurities in the raw starting BHET HE ^ tCBA: 2820 parts / mill.
HE-PTA: 355 parts / mill.
DEG: 1.24% by weight

Number of attempts
1 2 4

Concentration of the sludge in the expansion tank (% by weight) 8.45 10.1

Contaminant content of the purified BHET
HE-4CBA (parts / mill.)

HE-PTA (parts / mill.)
DEG (% by weight)

Partition coefficient
HE ^ iCBA

HE-PTA
DEG

11.5

11.2

11.4

115 126 216 246 212 = 0 = 0 = 0 = 0 = 0 0.337 0.402 0.412 0.432 0.405 0.264 0.315 0.484 0.538 0.439 = 0 = 0 Φ0 = 0 = 0 2.86 3.59 2.88 3.40 3.05

In the experiment described above, the recovery rate was that of the purified one BHET about 76%.

Flaky crystalline BHET was obtained.

The determination of the DET content in the BHET was carried out in this example as follows: 0.010 g of tetraethylene glycol dimethyl ether were placed in a sealed tube with 0.500 g of BHET and 1.0 g ml of dehydrated and distilled ethanol (internal standard substances). The decomposed product with ethanol, which was obtained by heating for 8 hours at 230 ⁰ C, was gas chromatography using a PEG (Polyäthylengly-

Ao

fts kol) 20 M column with a height of 1 m quantitative analyzed The same procedure was used in the following examples and control experiments

Example 2

A stainless steel pressure vessel with a capacity of 501, which is equipped with a stirrer, A heating mantle and sight glass were used with 7 kg of the crude BHET, which was prepared in a similar manner prepared as in Example 1, and charged 32 kg of benzene, and its internal pressure was increased to 4 atm increased by introducing nitrogen gas. After that

the system was ^{heated to 110 °} C. and stirred for 30 minutes. The undissolved material in the system which settled when the stirring was interrupted was then removed. Then, the solution was introduced into the liquid phase portion in a stainless steel flash tank equipped with a reflux condenser and a stirrer, which had been previously charged with 71 of boiling benzene. The sludge formed in the bottle container was continuously withdrawn from the system while the temperature was maintained within the flash tank at 80.7 ⁰ C in the meantime. The thus obtained sludge was separated into solid and liquid, and the cake was washed with cold benzene and dried. The thus purified BHET contained absolutely no blocky or granular solid BHET.

The analysis results of the raw raw BHET and the purified product thereof were as follows:

Raw starting BHET 1750 parts / mill HE-4CBA content: 0.130 optical density: Purified BHET 150 parts / mill. HE-4CBA content: 0.030 optical density: 0.66 HE-4CBA partition coefficient:

Extent of recovery of purified BHET

86.20%

Example 4

In the above and subsequent examples, the optical density was determined with respect to 25 cm ^{3 of} a solution formed by dissolving 1 g of the BHET sample in 14% aqueous ammonia and placing it in a 5 cm long cell, measured at a wavelength of 380 ιημ.

Example 3

The slurry as obtained in Example 2 80.7 VCN ⁰ C was allowed to stand to cool them in this form to about 25 "C, and the slurry thus obtained was treated in the same manner as in Example. 1, the results obtained were ' as follows:

Purified BHET HE-4CBA content: 150 parts / mill.

optical density: 0.045

HE-4CBA partition coefficient: 0.66 Extent of recovery

of purified BHET 98.17%

The slurry as obtained in Example 2 of 80.7 ⁰ C was continuously introduced into benzene of 37 ° C and the slurry was indirectly cooled with a cooling medium so that the inside of the low-temperature crystallization vessel was maintained at 37 ° C. The resulting slurry was treated in the same manner as in Example 1 ίο with the following results:

Purified ßHET HE-4CBA content: 290 parts / mill.

optical density: 0.068

Partition coefficient: HE-4CBA: 132 Extent of recovery

of purified BHET: 98.09%

Example 5

In this example the same apparatus as used in Example I was used. The pressure vessel was charged with 25.1 g of crude BHET and 170 cm ^{3 of} toluene, and nitrogen gas was introduced therein to to give a pressure of 4 atm. The bottle was charged with 150 g of it) ³ of a slurry (1.94 formed of BHET and toluene BHET / lOOg toluene) and the pressure therein was controlled so that it always abs 310 mm Hg. fraud. The slurry was boiled under this pressure at 85 ° C. The overall arrangement of the apparatus including the pressure vessel and the flash tank was immersed in an oil bath at 147 ⁰ C. Thereafter, stirring was started in the pressure vessel, and gradually complete dissolution of BHET in the toluene in The pressure vessel was the valve on the tube that connects the bottom of the pressure vessel to the bottle container connected, opened The toluene solution of BHET was poured into the boiling slurry while reducing tem pressure transferred into the expansion tank. Here, the pressure and the temperature inside the bottle container were essentially at 310 mm Hg abs. or 85 "C. When the solution in the pressure vessel had been completely transferred, the following treatments as in Example 1 were repeated.

The purified BHET thus obtained did not contain a blocky or granular solid BHET but consisted of it mainly of crystalline flakes thereof. the Analysis results of the sample made uniform of these and the contents as well as the distribution coefficient of the impurities were as follows:

Content of impurities in the raw starting BHET HE ^ CBA: 1980 parts / mill. HE-PTA: 250 parts / mill. DEG: 1.05% by weight

Number of attempts 12 3 4

Concentrations of the sludge in the flash tank

(Wt .-%)

Contaminant content of the purified BHET HE4CBA (parts / mill.) HE-PTA (parts / mill.)

DEG (% by weight)

7.21 7.30 9.26 10.7

391 425 540 567 537

2.10 15.4 9.49 17.1 6.32

0.470 0.485 0.622 0.594 0.5 3f

I-'orlselzunii

Number of attempts 12 4 6

Distribution coefficient HE-4CBA HE-PTA DEG

The recovery rate from the purified BH ET was 75.5%.

Example 6

Example 1 was repeated with the modification that the flash tank was left empty and the benzene solution of BHET in the pressure tank into the Flash tank was transferred by a vapor phase, which is below the boiling point of benzene atmospheric pressure. The following results were obtained: HE-4-CBA content of raw BHET starting material: HE-4CBA content of the purified BHET: HE-4-CBA partition coefficient: Extraction rate of purified BHET:

3190 parts / mill.

606 parts / mill. 1.63

77%

Example 7

The same device as used in Example 1, in which a glass pressure vessel with a capacity of 200 cm ³ and an expansion vessel with a capacity of 500 cm ^{3 were} connected, was used. The pressure vessel was charged with 39.1 g of crude BHET and 135 g of benzene (BHET concentration: 22.5% by weight), and the flash tank was charged with 120 g of benzene alone ° C was maintained and that in the expansion tank was kept at 80 ⁰ C, ie the boiling point of benzene. After the crude BHET had completely dissolved in benzene in the pressure glass container, the homogeneous solution was poured into the flash container in the manner described in Example 1. The working pressure in the pressure vessel was 5 atmospheres and in the expansion vessel the working pressure was at atmospheric pressure. The crystalline precipitate-containing slurry in the flash tank was stirred at 80.5 ⁰ C for 30 minutes, filtered at the same temperature, and the recovered cake was washed immediately with cold benzene. The following results were obtained in this experiment:

Raw BHET starting material HE-4CBA housing: HE-PTA content: DEG content:

Crystalline cake HE-4CBA content: HE-PTA content:

DEG content:

2660 parts / mill.

480 parts / mill.

1,250 wt%

280 parts / mill. = 0 (below perceptible concentration or density) 0.463 wt%

1.64

0.1

3.98

0.7 4.10

2 ^ 0

0.4

6.54

Partition coefficient HE-4CBA: HE-PTA: ■ 5 DEG:

2.23 2.00 0.6 0.3

6.27 5.90

0.749

= 0

4.28

Example 8 Using the same device as in

Example 1 was used using the glass pressure vessel 54.0 g of BHET and 120 g of benzene (BHET concentration 31.0% by weight) are charged and the expansion tank was charged with 350 g of benzene alone. The temperature in the pressure vessel was at 134 ° C and that of the expansion tank was kept at 80 ° C. After homogeneously dissolving the crude BHET in benzene in the pressure vessel the homogeneous solution was converted into the benzene in the expansion vessel according to the in Example 1 poured procedure described. the Working pressure in the pressure vessel was 5 atm and in the pressure relief tank was the working pressure at atmospheric pressure. The the crystalline precipitate containing slurry was stirred for 30 minutes at 80.5 ° C and then at the same Temperature filtered. The cake was immediately washed with cold benzene. The one in this attempt results obtained were as follows:

Raw output BHET HE-4CBA content: HE-PTA content: DEG content:

Crystalline cake

HE-4CBA content: ♦ 5 HE-PTA content: DEG content:

Partition coefficient HE-4CBA: HE-PTA: DEG:

2660 parts / mill. «EOTeile / Mill. 1.250 wt%

186 parts / mill. 3.5 parts / mill. 0.441 wt%

0.845
= 0.1
5.53

Example 9

Using the same apparatus as used in Example 1, the glass pressure vessel was charged with 35.2 g of crude BHET and 52.5 g of benzene (BHET concentration: 40.2% by weight), and the flash vessel was charged with 250 g Charged with benzene. The interior of the plunger was at 140 ° C and held for 5 atm, and the interior of the flash tank was held at 8O ⁰ C under atmospheric pressure. After the BHET had been homogeneously dissolved in benzene in the pressure vessel, the homogeneous solution was poured into the benzene in the flash vessel by opening the valve between the pressure vessel and the flash vessel as described in Example 1. The slurry containing the crystalline precipitate in the flash tank

was stirred for 30 minutes and then nitrided at 80.5 ⁰ C. The cake was washed with cold benzene. The following results were obtained in this experiment:

Raw starting BHET HE-4CBA content: HE-PTA content: DEG content:

Crystalline cake HE-4CBA content: HE-PTA content: DEG content:

Partition coefficient HE-4CBA: HE-PTA: DEG:

2660 parts / mill. 480parts / mil 1.250 wt%

183TeHeZMiIl. 8.0TeHeZMiIL 0.438 wt%

0389 = 0.2 536

10

■ 25

.1 °

example

In the same apparatus as used in Example 1, the glass pressure vessel was charged with 25.1 g of BHET and 150 g of benzene (BHET concentration: 143% by weight), and the expansion vessel was charged with 250 g of benzene atm at 4 and held 123 ° C and that of the flash tank was maintained at a reduced pressure (380 mm Hg) and at 60 ⁰ C. After the crude BHET in benzene had completely dissolved in the pressure vessel, the homogeneous solution was poured into the benzene in the flash vessel by opening the valve on the pipe connecting the pressure vessel to the flash vessel as described in Example 1. The slurry thus formed containing the crystalline precipitate was stirred for 20 minutes. Thereafter, the pressure in the expansion vessel was returned to atmospheric pressure and at the same time the device, including the glass pressure vessel and the expansion vessel, was removed from the oil bath. The slurry was filtered at 60 ° C and the solid cake was immediately washed with cold benzene. In this experiment, the following results were obtained.

Raw output BHET HE-4CBA content: HE-PTA content: DEG content:

Crystalline cake HE-4CBA content: HE-PTA content: DEG content:

Partition coefficient HE-4CBA: HE-PTA: DEG:

45

1980TeHeZMiIl. 380 parts / mill. 1.154 wt%

190TeHeZMiIl. 9.3 parts / mill. 0.489 wt%

1.57

= 0.4

12.1

250 g of benzene charged. The inside of the metal ^{pressure vessel was kept at 6 atm and 150 0} C, and the inside of the flash tank (flash evaporator was cured at atmospheric pressure of 80 ° C. It was determined in advance that the crude BHET of the same composition as that in the pressure vessel was homogeneously soluble in benzene at 150 ° C. by an experiment in a sealed tube the flash tank by opening the valve between the metal pressure vessel and the EntspannungsbehMter poured. the resulting slurry containing the crystalline precipitate was stirred in the flash tank for 30 minutes and then filtered at 80.5 ⁰ C. the cake was washed with cold benzene. In this experiment, the following result was obtained.

Example 11

The glass pressure vessel in the apparatus used in Example 1 was replaced by a metal pressure vessel with a capacity of 200 cm ¹ , similarly equipped with a stirrer and connected to the expansion vessel by a pipe. The pressure vessel was filled with 25.1 g of crude BHET and 150 g of benzene (BHET concentration: 14.3% by weight) and the flash vessel was filled with

fts

Raw starting BHET Example 12 4440 parts / mill HE-4CBA content: 843 parts / mill. HE-PTA content: 1.286 wt. O / o DEG content: Crystalline cake 161 parts / mill. HE-4CBA content: 3 parts / mill. HE-PTA content: 0.280 wt% DEG content: Distribution coef f izien t 0.775 HE-4CBA: = 0.1 HE-PTA: 5.24 DEG:

In the same device as used in Example 11, the metal pressure vessel was 25,! g of crude BHET and 150 g of benzene (BHET concentration: 14.3% by weight) and the flash tank was charged with 250 g of benzene. The interior of the pressure vessel was atm at 10 and held for 170 ⁰ C, and the interior of the flash tank was maintained at atmospheric pressure and 8O ⁰ C. It was determined in advance that the material introduced into the pressure vessel respective BHET in benzene at 170 ⁰ C was soluble homogeneous. After a long period of dissolution, the resulting homogeneous solution was poured into the flash tank by opening the valve between the metal pressure vessel and the flash tank. The slurry thus formed containing the crystalline precipitate was stirred for 30 minutes and then filtered. The cake was washed with cold benzene. The following results were obtained in this experiment:

5: 5 Raw output BHET HE-4CBA content: HE-PTA content: DEG content:

Crystalline cake HE-4CBA content: HE-PTA content: DEG content:

Partition coefficient HE-4CBA: HE-PTA: DEG:

4440 parts / mill. 843 parts / mill. 1.286 wt. O / o

183 parts / mill. 3.5 parts / m ill. 0.326 wt%

0.855 = 0.1 6.18

Example 13

7.2 parts by weight of crude BHET which has an HE-4CBA content 1980 parts / million have been completely dissolved in 100 parts by weight Teüen Xy-lol at 130 ⁰ C 100 g of this solution were continuously fed into a with a stirrer equipped Ent ^ annungsbehälter introduced, which had been charged in advance with 50 g of xylene of 60 ⁰ C. In this case, xylene was pft of normal temperature continuously from the system so zugetr ^ to an exceeding of 80 ⁰ C of the temperature to prevent in the container. In the period in which the continuous supply of 100 g of the xylene solution of BHET was completed, 60 g of the normal temperature xylene was dropped therein. The resulting slurry was separated into solid and liquid, and the cake was washed with cold xylene. The subsequently dried and purified BHET had an HE-4CBA content of 160 parts / MM and the HE-iCBA partition coefficient was 2.3.

pressure in the vessel was gradually decreased to not higher than 1 mm Hg, which took 30 minutes. the Polymerization in vacuo was continued for an additional 60 minutes, 2 hours after immersion in the In the oil bath, the polymerization was terminated by the introduction of nitrogen gas into the vessel The resulting polymer had excellent properties as shown below (ij): 0.651

Softening Point (SP): 262.4 ° C
Hue: / = 844; a = -0.4; 6 = -34
(COOH): 15.1

Example 14

In the extraction apparatus consisted of a recovery section (mixer-settler 3-containers), cleaning portion (mixer-settler 8-tank), a condenser and a reflux vessel, the recovery and purification sections at 105 ⁰ C and the reflux vessel were added at Held at 100 ° C. From one end of the recovery section, 100 parts by weight per unit of time of preheated toluene were continuously fed, and from the other end of the recovery section, molten crude BHET, which had been obtained by reacting crude terephthalic acid with ethylene oxide, was continuously supplied ( HE-4CBA content: 2900 parts / mill .; HE-PTA content: 480 parts / mill .; DEG content: 1.3% by weight; optical density: 0.195), at a level of 7.5% by weight . -Parts supplied per unit of time. The toluene solution was dissolved in which the BHET at '05 ° C when obtained in the purification section, was cooled to 100 ⁰ C by the condenser was resulting in a part of melted BHET and separated. This molten BHET phase separated from the toluene phase in the reflux tank and was returned to the purge section and refluxed. In this way, the toluene phase and the molten BHET phase were continuously brought into countercurrent contact in the cleaning section. The toluene phase separated from the molten BHET phase at the reflux vessel was continuously withdrawn from the system. Thereafter, all of the toluene was removed and the resulting dry cake was treated in the same manner as in Example 1.

The yield of dry cake was 5 parts per 100 parts of toluene used, the parts being up By weight.

This purified BHET was HC-4CBA content of 240 parts / mil!., HE-PTA content of 5.4 parts / mil., DEG content of 0.408% by weight and a optical density of 0.021.

This BHET and 0.027 mol%, based on it, of antimony trioxide were placed in a polymerization vessel, and after replacing its internal atmosphere with nitrogen, the vessel was immersed in an oil bath at 285 ° C. After 30 minutes of polymerization under atmospheric pressure, the inside of the above data was (η) the intrinsic molar viscosity of the polyester, measured at 35 ° C using o-chlorophenol as the solvent; SP means the softening point of the polyester; and the symbols /, a and b, which have been used as the standards for the hue, are the readings on a color difference meter according to the indication method according to ASTM 1482-57T.

Comparative experiment 1

The experiments described below were carried out using the method according to the invention to compare the operation described in US-PS 32 68 575.

It was the solvent used in US-PS 32 68 575 in the only example, namely hexyl alcohol, with benzene as the solvent used in the present invention, as the recrystallization solvent compared using both solvents under the same conditions and the cleaning effects achieved were determined.

It was determined with what purity BHET when recrystallizing crude bis (/? - hydroxyethyl) terephthalate when using hexyl alcohol or benzene as recrystallization solvent (A) below gradual cooling or (B) rapid cooling according to the method according to the invention could be obtained. The experimental procedure is explained in detail below.

Attempt 1

7.5 g of crude BHET and 42.5 g of benzene were placed in a pressure-resistant vessel with an inner capacity of 100 cm ^{3 and equipped with a rotary stirrer.} N2 was introduced up to an overpressure of 4 kg / cm ² . The vessel was immersed in an oil bath kept at 120 ° C. and kept therein for 10 minutes. After the BHET had completely dissolved, the oil bath was gradually cooled to 40 ° C at a rate of 2 ° C / min. The mixture was ^{stirred at 40 °} C. for 30 minutes and then filtered as such. The solids thus separated were cleaned with cold benzene and dried. The analysis results of the purified BHET thus obtained are shown in the table below.

Attempt Il

The same procedure was carried out as indicated above in Experiment I, with the modification that n-hexyl alcohol is used in place of benzene f> 5 became. The solids separated at 40 ° C were washed with cold benzene and dried. The analytical results of the purified, so obtained BHET are shown in the table below

Try IH

The procedure of Experiment II was repeated with the modification that the mixture was gradually cooled to 10 ⁰ C at a rate of 2 ° C / min after complete dissolution of the introduced BHET. The analysis results of the purified BHET obtained in this way are summarized in the table below.

Experiment IV

In a pressure-resistant vessel with an ^{internal capacity of 100 cm 3} equipped with a rotary stirrer, 7.5 g of crude BHET and 42.5 g of benzene as used in Experiment I were placed. N2 was introduced up to an overpressure of 4 kg / cm ² . The bottom of the pressure-resistant vessel was (flash tank) by means of a valved tube of stainless steel connected in advance with a 300 cm ³ glass bulb equipped with a vacuum jacket, reflux condenser and stirrer. 60 cm ³ of benzene were introduced in advance in the flash tank, the inside of the system was subjected to a vacuum pump to a pressure reduction and maintained at 40 ⁰ C in the boiling state. The apparatus set including the pressure-resistant vessel and the flash container was immersed in an oil bath of 12O ⁰ C. After it was found that the crude BHET was completely dissolved, the valve of the pipe through which the pressure-resistant vessel was connected to the expansion tank was opened to pour the benzene solution of BHET in the pressure-resistant vessel into the boiling benzene under reduced pressure to introduce into the expansion tank.

In the meantime, the internal temperature of the expansion vessel was kept at 40 ^° C. under reduced pressure. When the solution in the pressure resistant vessel disappeared, the valve was closed and the set of equipment was removed from the oil bath. The pressure-resistant vessel was charged again with the same BHET and benzene under the same conditions. A slurry was sampled from the system from the flash tank in an amount corresponding to the volume increased by this operation. Thereafter, the set of equipment was again immersed in the oil bath and the same

table

Work stages were repeated seven times. The slurry obtained as a sample became immediately filtered. The filter cake was then cleaned with cold benzene and then dried. In that way the purified BHET obtained, a massive or spherical solid-like BHET was not perceived. The purified BHET consisted primarily of flake-like crystals. The analysis results of the the sixth sample taken are shown in the table below.

Experiment V

The procedure of Experiment IV was repeated except that n-hexyl alcohol was used in place of benzene was used. The filter cake separated off at 40 ° C. was washed with cold benzo! cleaned and dried. The analytical results of the purified BHET obtained in this way are shown in the table below listed. The purity of BHET was determined by determining the impurities it contains HE-4CBA, HE-PTA and DEG determined

The method by which HE-4CBA, HE-PTA and DEG are analyzed is given below:

Determination of the HE-4CBA content

0.5 g of BHET was dissolved in concentrated sulfuric acid in such an amount that 25 cm ^{3 of} the solution were obtained. In the solution prepared in this way, color development was brought about by means of thymol (5 g of thymol, dissolved in benzene, up to a solution volume of 25 cm ^3). After 30 min, the absorption capacity was measured at a wavelength of 400 μm in a cell 1 cm in length and the HE-4CBA content was read from the calibration curve.

Determination of the HE-PTA content

0.2 g of BHET, 2 cm ³ of ethanol and 0.4 mg of diphenyl were added to a closed, held at 260 ⁰ C tube for five hours followed by cooling. This solution was concentrated to 1/3. The content was measured as the ethyl ester of PTA by gas chromatography and then converted into the content of HE-PTA.

Determination of the DEG content

The DEG content was determined in the manner indicated above.

Experiment no.

Crystallization Crystalline content of impurities system sations- in purified BHET

temperature _HEj , _cba HE-PTA DEG

Extent of recovery
of purified BHET

/ " Weight on ger. BHET _χ
V weight to added BHET

CQ

(Parts / mill.) (Parts / mill.) (Wt .-%) (%)

Initial - - 2126 227 0.80 - BHET Attempt I. gradual 40 885 78 0.63 98.5 (Benzene) Cool Experiment II the same 40 142 15th 0.28 70.5 (Hexyl alcohol) Experiment III the same 10 159 17th 0.34 89.3 (Hexyl alcohol

l-'orlsct / uni;
Search no.

Crystallization crystallization content of impurities system salions- in purified HI HiT

temperature | ,,: _{4 (ΒΛ} ,,, .-. ,, ^

quick (() (Icilc / Mill.) (Tci Experiment IV Cool 40 67 = 0 (Benzene) the same Experiment V 40 352 72 (Hexyl alcohol) the same Attempt Vl 10 405 86 (Hexyi- alcohol) Test results

1. In experiment I, BHET can be recrystallized and purified with gradual cooling in benzene can be obtained with a recovery rate as high as 98.5%, but its purity is far too high leaves something to be desired. On the other hand, when hexyl alcohol is used as the solvent (Experiment II) BHET with a relatively high purity can be obtained.

In this case, however, the recovery rate of BHET is reduced to 70.5%.

2. If, on the other hand, in experiment II, in which cooling down to 40 ° C has been performed, cooling is continued down to 10 ° C (experiment III) the recovery rate of BHET is improved up to 89.3%, but the amount of the in the BHET contained impurities increases.

3. If in experiment V the recrystallization with rapid cooling and using hexyl alcohol is effected, a BHET of high purity cannot be obtained. In addition, that too Recovery rate of BHET as low as 70.1%.

4. Since the recovery rate of BHET in the experiment given above V is as low as Was 70.1%, the cooling temperature was further increased to 10 ° C decreased in experiment VI and also carried out rapid cooling. As a result, the recovery rate became of purified BHET increased up to 89%, but the content of impurities in the purified BHET increased so that it was difficult to obtain a highly purified BHET.

5. In contrast, rapid cooling in benzene can produce a purified BHET of high purity and high quality with a greatly reduced content of impurities are obtained in experiment IV, also the recovery rate is as high as 98.7%.

6. When comparing experiment II and experiment V or between experiment III and experiment VI it can be seen that when the recrystallization is carried out in hexyl alcohol, better cleaning effects are obtained can be used when gradual cooling is used as when rapid cooling is used is performed.

7. When comparing Experiment I and Experiment IV, however, it is found that if the recrystallization run in benzene, a highly purified BHET with superior properties when run rapid cooling is obtained according to the invention, but not when performing a gradual one Cooling.

I) IiCi

(Wt .-%)
0.16

0.47
0.51

Rückgewi η nungsausinaU of purified envelope

/ Weight at ger. HIIIiT \ Ciew. on reins.

ι reins. BIIIiT

98.7
70.1

89.0

8. From the above results, it follows that when recrystallization of BHET by rapid cooling is carried out using benzene as the solvent according to the invention, a more highly purified Superior quality BHETs can be obtained at a much greater rate of recovery as in the case of any cooling procedure using hexyl alcohol as a solvent according to US-PS 32 68 575.

The following comparative tests show that if the conditions of the method according to the invention are not met, a BHET of good purity and quality cannot be obtained.

Comparative experiment 2

Crude BHET and benzene were placed in the glass pressure vessel under the same conditions as used in Example 1, and immersed in an oil bath at 115 ° C. The contents were stirred to cause complete dissolution of the BHET in benzene. After formation of a homogeneous solution, the system was kept at a constant temperature for 5 minutes with stirring. Thereafter, the stirring was stopped and the oil bath was cooled at a rate of 2 ° C per minute. When it reached 8O ⁰ C, the cooling was stopped and the content in the pressure vessel was maintained at this temperature for 30 min and then removed from the vessel and treated in a similar manner as in Example. 1 The results obtained are shown below.

Raw starting BHET
HE-4CBA content:
HE-PTA content:
DEG content:

Purified BHET
HE-4CBA content:
HE-PTA content:
DEG content:

Partition coefficient
HE-4CBA:
HE-PTA:
DEG:

2820Parts / Mill.

610Parts / MiII.

1.24% by weight

1330 parts / ml. 232Parts / Mill. 1.074 wt%

4.8 3.4 21.2

Control attempt 3

70 g benzene and 12 g crude BHET made in a manner similar to Example 1 (HE-4CBA content: 2800 parts / milL: HE-PTA content:

510 parts / mill .; DEG content: 1.3 wt .-%) were introduced into the glass pressure vessel and heated at 120 ⁰ C in an oil bath with stirring, was completely dissolved until the BHET in benzene. Then, the temperature of the system was reduced to an extent of 2 ° C per minute up to 50 ⁰ C. The contents were then removed from the pressure vessel and separated into solid and liquid. The cake was washed with cold benzene. The cake consisted of blocky BHET, which solidified via a molten state when the solution was cooled, and flaky crystals which immediately precipitated out of the solution at a temperature below the melting point. When the two were separated after drying the cake, 7 g of blocky solid BHET and 4.5 g of flaky crystalline BHET were obtained. The impurity content of the two products was as follows:

Form of purified BUKT

Blocky BHET
Flaky BHET

IIE-4CBA
(Parts / mill.)

1600
450

HE-PTA

(Parts / mill.)

DEG

(Wt .-%)

240 13

Control attempt

Control experiment 1 was repeated with the modification that the cooling with stirring the contents in the pressure vessel was carried out. The product consisted of granular BHET and flaky, crystalline BHET. The mixture was separated into the two types of products, each of which was analyzed. The results are shown in the table below:

Form of purified BHET

HE-4CBA content

HE-PTA content

1.19 0.62

DEG-Gchalt

(Parts / mill.) (Parts / mill.) (% By weight)

Royal BHET
Flaky BHET

1180
490

160 16

1.08 0.71

1 sheet of drawings

Claims (1)

Claim: Process for the purification of crude bis (8-hydroxyethyl) terephthalate, which is obtained by reacting Terephthalic acid was obtained with ethylene oxide, with (a) crude bis - {/? - hydroxyethyl) terephthalate under Heating in an aromatic compound as ι ο solvent that is liquid at room temperature is, is solved, (b) the heated solution is cooled and (c) the precipitated bis (0-hydroxyethyl) terephthalate is separated off,