JPS6326735B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously crystallizing an adduct of 2,2-bis(4-hydroxyphenyl)propane and phenol with high purity.

2,2-Bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A) is important as a raw material for polycarbonate resins and epoxy resins, and is particularly suitable for polycarbonate resins as a highly pure and colorless material. of bisphenol A is required. To meet this requirement, crude bisphenol A is purified by various methods such as extraction, distillation, and recrystallization.

One method for such purpose is to use a crude mixture obtained from the reaction of phenol and acetone,
Alternatively, bisphenol can be obtained by crystallizing an adduct consisting of a 1:1 molar ratio of bisphenol A and phenol from a phenolic solution of crude bisphenol A, separating this crystal from the mother liquor, and removing the phenol component from the adduct. It is to manufacture A. A specific example is Japanese Patent No. 800709
12428) or, as seen in Japanese Patent Publication No. 52-46946, crude bisphenol A is dissolved in aqueous phenol at high temperature prior to cooling, or water is added to a phenolic solution of crude bisphenol A to form a single phase. A (homogeneous phase) liquid mixture is formed, which is then fed to a crystallization tank and cooled to crystallize an adduct of bisphenol A and phenol. In both cases, prior to cooling, it is essential to form a single-phase liquid mixture containing water;
% of water is specified, and it has been shown that a high purity adduct cannot be obtained below the lower limit of the water content mentioned above.

However, in the conventional method, prior to crystallization, a homogeneous aqueous phenol solution of bisphenol A must first be prepared, which is very complicated to carry out industrially. Furthermore, it was difficult to keep the crystallization conditions constant due to fluctuations in the concentration and temperature of the aqueous phenol solution supplied. Furthermore, the obtained crystals had a relatively small particle size, did not necessarily have good permeability, and were not satisfactory in terms of purity and hue.

The present invention has been made in view of the above points, and its gist is that an adduct of 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A) and phenol is prepared by adding the phenol of bisphenol A to the phenol of bisphenol A. In the method of crystallizing from a solution, the above-mentioned phenol solution of bisphenol A is added under a pressure of 20 to 100 mmHg while supplying 2 to 20% by weight of water to the solution.
A method for crystallizing an adduct of bisphenol A and phenol, which comprises crystallizing an adduct of pure bisphenol A and phenol by cooling to a temperature in the range of 35 to 70°C.

It is.

The present invention will be explained in detail below.

In the present invention, aqueous phenol, which is a crystallization solvent, is separately supplied to the crystallization system in the form of phenol accompanying a phenolic solution of bisphenol A and water for cooling purposes, and the aqueous phenol is A solvent is created.

That is, a phenolic solution of crude bisphenol A is sent into a crystallization tank operated at a constant pressure and temperature, and is gently stirred and cooled at a temperature in the range of 35 to 70°C. This results in crystallization of the adduct of pure bisphenol A and phenol. The cooling is performed by removing heat by evaporating water or phenol-containing water that is sent to the crystallization tank separately from the phenol solution of crude bisphenol A. The distilled vapor phase consists mainly of water and small amounts of phenol and can be condensed and recycled for cooling.

The amount of water added to keep the internal temperature of the crystallization tank constant is the amount necessary to cool the phenol solution of crude bisphenol A and to remove the heat of crystallization generated during adduct crystal formation by evaporation. is sufficient.
This corresponds to 2-20% relative to the phenolic solution. Note that the water content in the liquid phase in the crystallization tank is about 1.0 to 8%. Excessive addition of water remains in the crystallization mother liquor, increases the solubility of the adduct, and reduces the crystal yield, which is undesirable.

Water or phenol water is added to the slurry in the crystallizer through a different route than the phenol solution of bisphenol A. When water is sent as a single liquid phase mixture with a phenol solution of crude bisphenol A to a crystallization tank operated under reduced pressure, water vaporizes in the crystallization solution, causing bumping, blow-through, etc. Especially when the amount of water is large and the operating pressure is low,
It has an unfavorable disturbing effect on crystal growth, resulting in a decrease in crystal purity and crystal grain size.

In the present invention, the crude bisphenol A phenolic solution sent to the crystallization tank may contain 20-50% bisphenol A. Such a phenolic solution can be prepared by a condensation reaction of a stoichiometric excess of phenol with acetone under the action of an acid catalyst. Furthermore, bisphenol A containing impurities and which cannot be obtained in sufficient purity by other purification methods may be produced by dissolving it in phenol.

The amount of bisphenol A in the above solution can be arbitrarily selected within the above range, but since bisphenol A has a slight solubility in phenol, the higher the concentration of bisphenol A, the higher the crystallization yield. increases. The temperature of the phenol solution must be controlled within the above bisphenol A concentration range so that crystals of the adduct are not formed. Specifically, when the bisphenol A concentration is 20%, the temperature is 70°C or higher, and when the bisphenol A concentration is 50%, the temperature is 95°C.
That's all. Preferably 5-10℃ from this lower limit
It is better to control it above. The phenolic solution of crude bisphenol A may contain water or may contain no water at all.

According to the invention, the crystallizer is operated under constant pressure. The operating pressure is preferably 20 to 100 mmHg. At pressures below 20 mmHg, special measures are required to condense the evaporating vapor phase, and at operating pressures above 100 mmHg, the added water is not effectively evaporated, resulting in relatively high temperatures and high residual concentrations in the mother liquor. Moisture is introduced, which also increases the solubility of bisphenol A and reduces the crystallization yield.

The internal temperature of the crystallizer is controlled by the amount of water added to the crystallizer under constant pressure. The water evaporates until the vapor pressure of the remaining mother liquor reaches the above-mentioned constant pressure, and takes away the sensible heat difference of the supplied liquid, the amount of heat given to the crystallization tank, and the heat of crystallization accompanying crystal formation. As a result, when the amount of water is small, the temperature obtained is high;
An increase in the amount of water results in a decrease in the temperature of the slurry.
The heat of crystal formation is naturally proportional to the amount of crystals obtained, which indicates that the amount of water required to obtain the same temperature varies depending on the concentration of bisphenol A in the phenol solution sent to the crystallization tank. The internal temperature of the crystallization tank is preferably maintained at 35 to 70°C, and the amount of water required at this time is 2 to 20% by weight based on the phenol solution.

As described above, in the present invention, the phenol solution and water are added through separate routes without preparing a homogeneous solution of bisphenol aqueous phenol in advance. Crystallization conditions can be easily kept constant by controlling the amount of water added (specifically, setting the operating temperature and operating pressure, and controlling the amount of water supplied using TiC to match the set conditions). can be kept.

Although the crystallization according to the present invention is carried out continuously,
This may be carried out using one crystallization tank, or two or more crystallization tanks installed in series may be used. When two or more crystallizers are used, the water added to the second and subsequent crystallizers for cooling may be added by the method already described in the present invention, or the slurry containing adduct crystals may be added to the second and subsequent crystallizers for cooling. It is also possible to utilize the water contained in the effluent from the previous crystallizer, which is supplied as If no additional cooling water is added, the second and subsequent crystallizers are operated at a lower pressure than the previous crystallizer. As a result, the slurry is further cooled and the bisphenol A dissolved in the mother liquor is
crystallization becomes more complete.

Additional advantages of the invention are obtained by adding water or phenolic water from the top of the crystallizer, especially along the inner wall surface. Generally, in a vacuum evaporation type crystallizer, crystals adhere and grow near the gas-liquid interface, then fall.
Since continuous operation of the crystallizer is difficult, cleaning is required at regular intervals. By adding water, especially water as phenolic water, along the walls, crystal adhesion is effectively prevented and the crystallizer can be operated continuously without adhesion even for several months. Continuous and stable operation is necessary for the continuous production of high purity crystals and is one of the advantageous features of the present invention.

In the crystallization method according to the present invention, the average residence time can be arbitrarily selected, but is preferably 2 hours to 5 hours. 1
If the residence time is less than 1 hour, the boiling of water will be too rapid, depending on the content of bisphenol, and it will be difficult to obtain crystals of uniform particle size. Moreover, if it takes more than 10 hours, it becomes industrially disadvantageous.

The slurry containing the growing crystals in the crystallizer is preferably gently stirred. This forms larger crystals that are extremely pure. Larger crystals make the separation process of crystals and mother liquor easier. That is, the mother liquor adhering to the crystals can be completely removed with a very small amount of washing liquid, and in some cases, high purity bisphenol A can be separated from the crystals without washing at all. Therefore, by obtaining larger crystals, a decrease in crystal yield due to washing can be avoided.

The crystals thus obtained are separated from the mother liquor by conventional separation methods, such as filtration and centrifugation. The mother liquor can be dehydrated if necessary, further concentrated if necessary, and can be used as a raw material for the production of new bisphenol A according to the method of the present invention.

The separated crystals are washed, if necessary, and then the phenol is removed from the crystals. Phenol can be removed by conventional methods including extraction, distillation, steam stripping, bisphenol A recrystallization, and the like. The bisphenol A thus obtained is highly pure and pure white and can be used directly in applications requiring high purity bisphenol A, including the production of polycarbonate resins.

The present invention has been described below, and embodiments of the present invention will be specifically illustrated by the following examples.

Example 1 Phenol and acetone were mixed and a condensation reaction was carried out at 55° C. for 8 hours while blowing hydrogen chloride into the mixture. The reaction mixture was heated under reduced pressure to remove hydrochloric acid and water produced by the reaction. This dehydrochloric acid solution was a phenol solution of crude bisphenol A and had the following composition.

Bisphenol A 30% O, P'-isomer (isomer) 0.8% Other impurities 1.0% Phenol 68.2% (Contains only traces of hydrogen chloride and water.) This phenol solution was heated to 90°C at a flow rate of 400 kg/hour. , the liquid was sent to a crystallization tank operated at 50 mmHg. Water was added to the crystallizer using a separate route at a rate of 30 Kg per hour. The temperature inside the crystallization tank was kept constant at 55°C. Note that the residence time was 2 hours. Slurry was continuously withdrawn from the crystallization tank at a rate of 150 kg/hour (slurry concentration 40%) and filtered continuously. The obtained crystals had an average grain size of 0.4 mm and had the following composition.

Bisphenol A 69.9% O, P'-isomer (isomer) 0.02% Other impurities 0.02% The remainder was phenol 30.06% The color tone of the 50% ethanol liquid was APHA5 and was essentially colorless.

Example 2 A phenolic solution of crude bisphenol A was prepared in the same manner as in Example 1, and the solution was fed to a crystallization tank at a rate of 600 kg/hour. Phenol water containing 6% phenol that had been evaporated and condensed from the crystallization tank was added to the crystallization tank at a rate of 52 kg/hour. The slurry in the crystallizer contained 30% crystals and 5% water. The slurry was continuously sent to a second crystallizer operated at 20 mmHg. The temperature inside the second crystallization tank can be adjusted without adding water.
Cooled to 45°C. The slurry is continuously withdrawn from the second crystallizer and filtered to remove 0.5 adduct crystals.
Washed with double phenol, average particle size at 250Kg/hour
A crystal of 0.4 mm was obtained. (The residence time is in the first tank,
The adduct crystals obtained were melted and the phenol was removed under reduced pressure. The freezing point of the obtained bisphenol A was 156.7°C, and the proportion of impurities was as follows.

Phenol 0.01% O, P'-form (isomer) 0.03% Other impurities 0.04% The color tone of the 50% ethanol solution was APHA10 and colorless.

Comparative Example 1 A phenol solution of crude bisphenol A was prepared in the same manner as in Example 1. The composition of the phenolic solution is the same as described in Example 1. 10% by weight of water was added to this phenol solution to form a homogeneous mixed solution at 90° C., and the solution was sent to a crystallization tank operated at 50 mmHg at a flow rate of 400 kg/hour.
Water violently boiled in the liquid, disrupting stirring. The slurry that was continuously extracted contained many fine crystals, and the average grain size of the crystals was 0.2 mm. The composition of the crystals obtained by continuous filtering and washing was as follows.

Bisphenol A 69.8% O, P'-form (isomer) 0.1% Other impurities 0.1% The color tone of the 50% ethanol solution was APHA20.

Claims (1)

[Claims] 1 In a method for crystallizing an adduct of 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A) and phenol from a phenolic solution of bisphenol A, the phenolic solution of bisphenol A is The adduct of pure bisphenol A and phenol was crystallized by cooling to a range of 35-70°C while supplying 2-20% water by weight to the solution under a pressure of ~100 mmHg. A characterized method for crystallizing an adduct of bisphenol A and phenol.