The process of the present invention comprises a first step in which crude molten bisphenol A containing phenol is supplied to a flash evaporator and separated into a gaseous phase comprising phenol and a liquid phase comprising bisphenol A and residual phenol, and a second step in which the liquid phase obtained in the first step is heated by a thin film evaporator and separated into a gaseous phase comprising phenol and a liquid phase comprising concentrated bisphenol A and residual phenol, part of the liquid phase obtained in the second step being circulated to the first step and supplied to the flash evaporator along with crude molten bisphenol A. It is possible with this process to obtain high-quality bisphenol A stably from phenol-containing bisphenol A.
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1. A process for purifying phenol-containing bisphenol A comprising
a first step in which crude molten bisphenol A containing phenol is supplied to a flash evaporator and separated into a gaseous phase comprising phenol and a liquid phase comprising bisphenol A and residual phenol, and
a second step in which the liquid phase obtained in the first step is heated by a thin film evaporator and separated into a gaseous phase comprising phenol and a liquid phase comprising concentrated bisphenol A and residual phenol,
wherein part of the liquid phase obtained in the first second step being circulated to the first step and supplied to the flash evaporator along with crude molten bisphenol A, and further comprising
a purification step with water vapor in which the concentrated liquid phase of bisphenol A obtained in the second step is supplied to the top of a packed column to let it flow down in the column while water vapor is blown into the column from its bottom to let it rise in the column so that phenol in the concentrated liquid phase of bisphenol A is removed entrained by water vapor.
10. A process for purifying phenol-containing bisphenol A comprising the steps of:
supplying a melt of an adduct of bisphenol A and phenol to a natural falling-thin film evaporator maintained under reduced pressure and a pressure of not less than 100 Torr,
heating said melt to 160° C. to 220° C. to evaporate light ends including phenol to yield crude molten bisphenol A comprising bisphenol A and residual phenol,
supplying said melt of adduct of bisphenol A and phenol to a flash evaporator maintained under a pressure of not more than 60 Torr to separate it into a liquid phase and a gaseous phase by flash evaporation,
supplying said liquid phase to a natural falling-thin film evaporator maintained under a pressure of not more than 60 Torr,
heating said liquid phase to 170° C. to 200° C. and evaporating phenol to obtain a concentrated liquid phase of bisphenol A,
mixing part of said concentrated liquid phase of bisphenol A with said crude molten bisphenol A and supplying it to a flash evaporator to be subject to flash evaporation, and supplying the rest of the liquid phase to the top of a packed column to let if flow down in the column into which water vapor is being blown from the bottom so that residual phenol is entrained by water vapor and removed.
2. The process according to
3. The process according to
4. The process according to
5. The process according to any one of
6. The process according to any one of
7. The process according to any one of
8. The process according to any one of
0. 9. The process according to any one of
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This application is a more than 60 Torr, preferably between 60 and 400 Torr, especially between 100 and 300 Torr. The heating tubes are maintained at 160 to 220° C., preferably at 170 to 200° C. by steam heating. In order to control thermal decomposition of bisphenol A, the heating temperature is preferably set at not higher than 200° C., especially not higher than 190° C. For expediting evaporation on the other hand, the heating temperature is preferably set at not less than 170° C., especially not les less than 180° C. It is possible to let the vapor of light ends and the concentrated liquid effuse separately from each other from the thin film evaporator but preferably they are discharged as parallel flows and led into a gas/liquid separator, and after sufficient gas/liquid separation, the liquid phase is supplied to the first step. If desired, part of the liquid phase which has passed through the thin film evaporator may be mixed with the melt of the bisphenol A/phenol adduct and sent back to the thin film evaporator.
Flash evaporation in the first step is naturally conducted under a pressure lower than the operating pressure of the said thin film evaporator, usually under a pressure of not higher than 100 Torr, preferably not higher than 60 Torr, especially 10 to 60 Torr. A large amount of phenol is contained in the phenol-containing crude molten bisphenol A yielded from the thin film evaporator. Therefore, if this melt is supplied as is to the flash evaporator, temperature drops acutely with evaporation of phenol, which may cause generation of the crystals of bisphenol A in the flash evaporator. In the present invention, in order to avoid such generation of crystals of bisphenol A, the said phenol-containing crude molten bisphenol A is mixed with a concentrated solution of bisphenol A prepared in the second step to raise the concentration of bisphenol A and then supplied to the flash evaporator. This can lessen the drop of temperature in the flash evaporator. Since the melting point of bisphenol A is 156 to 157° C., the mixing rate of the concentrated solution of bisphenol A supplied from the second step in the phenol-containing crude molten bisphenol A is preferably decided so that the temperature in the evaporator will not become lower than the above-shown melting point of bisphenol A even if a desired amount of phenol has been evaporated by flash evaporation.
The liquid phase produced by flash evaporation in the first step is then heated by a thin film evaporator in the second step and separated into a gaseous phase comprising phenol and a liquid phase comprising bisphenol A and residual phenol. As the thin film evaporator, it is preferable to use a natural falling-thin film type as in the case where the light ends are evaporated from the melt of the bisphenol A/phenol adduct. The pressure in this evaporator is maintained equal to or higher than the pressure in the flash evaporator in the first step. The heating temperature is usually 170° C. to 200° C., preferably 180° C. to 190° C. It is possible to let vapor and liquid effuse separately from each other from the thin film evaporator in the second step, but preferably they are discharged out together and supplied to a gas/liquid separator to effect sufficient separation of gas and liquid. Part of the liquid phase formed by this gas/liquid separation is circulated to the first step in the same way as described above and mixed with the phenol-containing crude molten bisphenol A supplied to the first step. This liquid circulation has the effect of flash-evaporating, along with phenol, the thermal decomposition products formed by heating in the second step, in addition to its above-mentioned function to lessen the drop of temperature in flash evaporation in the first step.
The concentrated liquid of bisphenol A obtained in the second step is preferably further purified by steam stripping. Steam stripping is an operation in which the concentrated liquid of bisphenol A is supplied to a packed column from its top while steam is supplied from the bottom of the column to effect countercurrent contact between the falling liquid and the rising steam to remove phenol entrained by the steam effused from the column top. This operation is preferably conducted under the same pressure as or a lower pressure than used in the second step, usually with the column top pressure of 10 to 60 Torr. The temperature is preferably selected such that purified bisphenol A yielded from the column bottom will have a temperature of 160° C. to 220° C., preferably 170° C. to 190° C. A high temperature may induce thermal decomposition of bisphenol A. The ratio of steam to the concentrated liquid of bisphenol A supplied to the packed column is usually 2 to 8% (by weight). Steam stripping makes it possible to obtain bisphenol A with very high purity and excellent hue.
The present invention will be explained in further detail with reference to the examples thereof.
A melt of an adduct of bisphenol A with phenol (56% by weight of bisphenol A, 44% by weight of phenol and 0% by weight of isopropenylphenol) was purified according to the process shown by the flow sheet of FIG. 1.
23.4 parts by weight/hr of a melt (150° C.) of a bisphenol A/phenol adduct supplied via conduit 1 and 15 parts by weight/hr of a liquid circulated from a gas/liquid separator 3 via conduit 4 were mixed and led into a natural falling-thin film evaporator 2 maintained under an internal pressure of 300 Torr. Evaporator 2 was heated with steam so that the effluent liquid would have a temperature of 180° C. The liquid and gas effusing from evaporator 2 were guided into a gas/liquid separator 3 and thereby separated into gas and liquid under 300 Torr. The concentration of bisphenol A in the effluent liquid from evaporator 2 was 73.6% by weight, and the concentration of bisphenol A in the liquid extracted from gas/liquid separator 3 was 74.5% by weight, with the concentration of isopropenylphenol being 5 ppm (by weight).
A portion (15 parts by weight/hr) of the liquid extracted from gas/liquid separator was circulated and the rest thereof was mixed with the liquid (20 parts by weight/hr) sent from a gas/liquid separator 8 and supplied to a flash evaporator 6 maintained under 15 Torr for carrying out flash evaporation. The liquid (bisphenol A concentration: 97.5% by weight, temperature: 156.7° C.) discharged from flash evaporator 6 was led as is into a natural falling-thin film evaporator 7. Evaporator 7 was heated with steam so that the effluent liquid would have a temperature of 180° C. The liquid and gas effusing from evaporator 7 were led into gas/liquid separator 8 and separated into gas and liquid. The section from flash evaporator 6 to gas/liquid separator 8 in the system was kept under the same pressure.
The concentration of bisphenol A in the liquid extracted from gas/liquid separator 8 was 98.8% by weight, with the concentration of ispropenylphenol being 6 ppm (by weight). Thus, the rise of concentration of bisphenol A of the liquid phase in evaporator 7 was 1.3% by weight. This liquid, save 20 parts by weight/hr thereof circulated, was supplied to a packed column 9. 0.5 part by weight/hr of steam was supplied to the column bottom through conduit 10 to carry out steam stripping. The phenol concentration in bisphenol A yielded from the column bottom was 10 ppm (by weight), and the hue of this product was determined to be APHA<5, indicating very high quality of the product. The results are shown in Table 1.
Purification of bisphenol A was conducted under the same operating conditions as in Example 1 except that the pressure of flash evaporator 6 was raised from 15 Torr to 60 Torr. The results are shown in Table 1.
Purification of bisphenol A was conducted under the same operating conditions as in Example 1 except that the pressure of flash evaporator was raised from 15 Torr to 60 Torr while the liquid temperature at the outlet of evaporator 7 was elevated from 180° C. to 200° C. The results are shown in Table 1.
Purification of bisphenol A was conducted under the same operating conditions as in Example 1 except that the pressure of flash evaporator was raised from 15 Torr to 60 Torr, that the liquid temperature at the outlet of evaporator 7 was elevated from 180° C. to 200° C., and that the circulation of part of the liquid extracted from gas/liquid separator 8 to flash evaporator 6 was suspended. The results are shown in Table 1.
Purification of bisphenol A was conducted under the same operating conditions as in Example 1 except that the circulation of part of the liquid extracted from gas/liquid separator 8 to flash evaporator 6 was suspended. The results are shown in Table 1. In this operation, after a while, the liquid distributor of evaporator 7 was blocked with the crystals of bisphenol A to check the flow of the liquid from flash evaporator 6 to evaporator 7. The bisphenol A concentration of the liquid at the outlet of flash evaporator 6 was 93.9% by weight and the temperature was 131.7° C.
A melt of a bisphenol A/phenol adduct (56% by weight of bisphenol A, 44% by weight of phenol and 0% by weight of isopropenylphenol) was purified according to the process illustrated by the flow sheet of FIG. 2.
23.4 parts by weight/hr of a melt (150° C.) of a bisphenol A/phenol adduct supplied through conduit 1 and 15 parts by weight/hr of a liquid circulated from a gas/liquid separator 3 via conduit 4 were mixed and supplied to a natural falling-thin film evaporator 2 maintained under an internal pressure of 300 Torr. Evaporator 2 was heated with steam so that the effluent liquid would have a temperature of 180° C. The liquid and gas released from evaporator 2 were led into a gas/liquid separator 3 and separated into liquid and gas under a pressure of 300 Torr. The bisphenol A concentration of the effluent liquid from evaporator 2 was 73.6% by weight and the bisphenol A concentration of the liquid extracted from gas/liquid separator 3 was 74.5% by weight, with the concentration of isopropenylphenol being 5 ppm (by weight).
The liquid extracted from gas/liquid separator 3, save 15 parts by weight/hr thereof circulated, was mixed with a liquid circulated from heater 5 at a rate of 20 parts by weight/hr and supplied to a flash evaporator 6 maintained under 60 Torr for conducting flash evaporation. Part (20 parts by weight/hr) of the effluent liquid (bisphenol A concentration: 97.5% by weight; temperature: 156.7° C.) from flash evaporator 6 was passed through heater 5 to raise the liquid temperature to 249° C. and then circulated back to gas/liquid separator 3. The rest of the liquid was supplied to a packed column 9. Steam was supplied (0.5 part by weight/hr) to the bottom of the packed column through conduit 10 to carry out steam stripping. As a result, the temperature of flash evaporator rose to 200° C., the bisphenol A concentration reached 97.2%, the IPP concentration in the liquid supplied to packed column 9 rose to 91 ppm by weight, and APHA of bisphenol A at the bottom of packed column 9 hiked to 50, verifying bad quality of the product.
TABLE 1
Example
Comp. Example
1
2
3
1
2
Pressure of flash
15
60
60
60
15
evaporator (6) (Torr)
Liquid temperature at
180
180
200
200
180
the outlet of thin
film evaporator (7)
(° C.)
Rate of circulation
20
20
97.2
0
0
from gas/liquid
separator (8) to flash
evaporator (6)
(parts by weight/hr)
Concentration of
98.8
95
97.2
97.2
98.8
bisphenol A extracted
from gas/liquid
separator (8)
(% by weight)
Concentration
6
6
21
32
10
isopropenylphenol in
bisphenol A extracted
from gas/liquid
separator (8)
(% by weight)
Phenol concentration
10
100
12
12
10
in bisphenol A
obtained from the
bottom of packed
column (9)
(% by weight)
Hue of bisphenol A
5>
5>
10
20
5>
obtained from the
bottom of packed
column (9) (APHA)
Operation
Stable
Stable
Stable
Stable
Blocked
According to the present invention, it is possible to obtain high-quality bisphenol A stably from phenol-containing bisphenol A.
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