Condensation process for recovery of bisphenol A and phenol

Abstract: A gaseous mixture of steam, phenol and bisphenol A, such as is obtained in the manufacture of bisphenol A, is treated for recovery of bisphenol A and phenol by the steps of: (a) introducing the gaseous mixture into a first cooling zone maintained at a pressure of 30 Torr or less and such a temperature that the steam is prevented from condensing while a portion of the phenol is condensed, wherein the gas is brought into counter-current contact with a first liquid cooling medium to condense substantially all of the bisphenol A and part of the phenol and thereby obtain a mixed gas containing uncondensed steam and uncondensed phenol, the first liquid cooling medium being phenol or bisphenol A-containing phenol; and introducing the mixed gas into a second cooling zone maintained at a pressure of 30 Torr or less and such a temperature that substantially all of the mixed gas is condensed, wherein the gas is brought into counter-current contact with a second liquid cooling medium to condense substantially all of the mixed gas and thereby obtain a condensate-containing liquid, the second liquid cooling medium being an aqueous solution of phenol.

Description: This invention relates to a process for condensing a gaseous mixture of steam, phenol and bisphenol A, such as is obtained as a by-product in the manufacture of bisphenol A, in order to recover bisphenol A and phenol. Our European Patent Application No. 92306380.4 (Publication No. EP-A-0523931), from which the present application is divided, discloses a process of producing bisphenol A (2,2-bis(4-hydroxyphenyl)propane, hereinafter referred to as BPA for brevity), which comprises the steps of: liquefying a crystalline adduct of bisphenol A and phenol to obtain a liquefied adduct containing bisphenol A and phenol; feeding said liquefied adduct to an evaporating zone and forming said liquefied adduct into a downwardly flowing liquid film while maintaining said evaporating zone at a temperature of 160-185°C and a pressure of 15-60 Torr to vaporize and remove phenol from said liquefied adduct and thereby obtain a first product containing bisphenol A and 1-5% by weight of phenol; introducing said first product into a first stripping zone and forming said first product into a downwardly flowing liquid film while feeding a stripping gas to said first stripping zone, wherein said liquid film of said first product is brought into counter-current contact with said stripping gas at a temperature of 170-185°C and a pressure of not higher than 15 Torr to strip phenol and to obtain a second product; introducing said second product into a second stripping zone and forming said second product into a downwardly flowing liquid film while feeding steam to said second stripping zone, wherein said liquid film of said second product is brought into counter-current contact with said steam at a temperature of 170-185°C and a pressure of not higher than 15 Torr to strip phenol and thereby obtain a bisphenol A product and phenol-entraining steam; and feeding said phenol-entraining steam to said first stripping zone as said stripping gas. In this process the stripping gas which is discharged from the first stripping zone as a by-product of the process is composed of steam, phenol and BPA, and it would be desirable to be able to recover the BPA and phenol from this stripping gas. The present invention provides a condensation process whereby such recovery may be effected. More generally, the present invention provides a process for condensing a gaseous mixture of steam, phenol and bisphenol A maintained at a pressure of 40 x 10 2 N/m 2 (30 Torr) or less, comprising the steps of: introducing said gaseous mixture into a first cooling zone maintained at a pressure of 40 x 10 2 N/m 2 (30 Torr) or less and such a temperature that said steam is prevented from condensing while a portion of said phenol is condensed, wherein said gas is brought into counter-current contact with a first liquid cooling medium to condense substantially all of said bisphenol A and part of said phenol and thereby obtain a mixed gas containing uncondensed steam and uncondensed phenol, said first liquid cooling medium being phenol or bisphenol A-containing phenol; and introducing said mixed gas into a second cooling zone maintained at a pressure of 40 x 10 2 N/m 2 (30 Torr) or less and such a temperature that substantially all of said mixed gas is condensed, wherein said gas is brought into counter-current contact with a second liquid cooling medium to condense substantially all of said mixed gas and thereby obtain a condensate-containing liquid, said second liquid cooling medium being an aqueous solution of phenol. Fig. 1 is a schematic diagram showing an apparatus for carrying out a two-stage condensation process of the present invention; and Fig. 2 is a schematic diagram showing another embodiment of the two-stage condensation process. In this invention, a gaseous mixture of steam, phenol and BPA maintained at a pressure of 40 x 10 2 N/m 2 (30 Torr) or less is treated to recover the phenol and BPA. Such a gaseous mixture may be obtained as an overhead gas by stripping phenol-containing BPA liquid with steam. The gas discharged from the second evaporator 2 through the line 13 of the BPA-producing apparatus of Fig. 1 of the parent Application No. 92306380.4 (Publication No. EP-A-0523931) is the typical example of such a gaseous mixture to be treated in accordance with this invention. The gaseous mixture is introduced into a first cooling zone maintained at a reduced pressure, where the gas is brought into counter-current contact with a first, liquid cooling medium to condense substantially all of the BPA and part of the phenol and thereby obtain a first gas phase composed of uncondensed steam and uncondensed phenol and a first liquid phase containing BPA and phenol inclusive of those condensed during the counter-current contact. The first cooling medium is phenol or BPA-containing phenol. The first cooling zone is maintained at such a temperature that the steam is prevented from condensing while a portion of the phenol is condensed, generally at a temperature higher by 1-50°C than the solidifying point of phenol. More particularly, the temperature of the first cooling zone is maintained at 42-90°C, preferably 45-55°C. The pressure within the first cooling zone is maintained at 40 x 10 2 N/m 2 (30 Torr) or less, preferably 6.67 x 10 2 - 26.7 x 10 2 N/m 2 (5-20 Torr), and can be the same as that used in the second evaporator 2 in Fig. 1 of EP-A-0523931, supra . In the first cooling zone, at least 70% by weight, preferably at least 85% by weight of the phenol in the gaseous mixture feed is condensed and recovered. A part of the first liquid phase may be recycled to the first cooling zone as at least part of the first cooling medium. The first cooling medium is used in the first cooling zone in an amount sufficient to cool the gaseous mixture to a predetermined temperature and generally in an amount of 5-10 parts by weight, preferably 5-6 parts by weight per part by weight of the gaseous mixture. The weight ratio of the BPA to the phenol in the liquid contained in bottom in the first cooling tower is generally adjusted to 0.05-0.20, preferably 0.08-0.14. Since phenol is present in large excess relative to BPA, BPA/phenol adduct crystals are not formed in the first cooling zone even though the temperature therein is lower than the solidifying point of BPA. The first gas phase containing uncondensed phenol is fed to a second cooling zone wherein the gas is brought into counter-current contact with a second, liquid cooling medium, which is an aqueous solution of phenol, to condense substantially all of the gas and thereby obtain a condensate-containing liquid, namely an aqueous phenol solution. Part of the aqueous phenol solution thus obtained may be recycled to the second cooling zone as at least part of the second cooling medium. The concentration of the phenol in the second cooling medium is suitably selected with the consideration of the composition of the first gas phase to be treated and the conditions employed in the first cooling zone and, generally, 55-75% by weight. The pressure within the second cooling zone is maintained at 40 x 10 2 N/m 2 (30 Torr) or less, preferably 6.67 x 10 2 - 26.7 x 10 2 N/m 2 (5-20 Torr), and may be the same as in the first cooling zone. The second cooling zone is maintained at such a temperature that substantially all of the first gas phase is condensed, generally at a temperature lower by 1-10°C than the condensation point of steam. The second cooling medium is used in the second cooling zone in an amount sufficient to condense substantially all of the first gas phase and generally in an amount of 100-300 parts by weight, preferably 190-250 parts per part by weight of the first gas phase introduced into the second cooling zone. The first and second cooling zones may be any gas-liquid contact apparatus, such as a packed tower or a spray tower. As the packing material to be used in the packed tower, there may be suitably used Raschig rings, pall rings and perforated plates, which are low in pressure loss. Fig. 1 depicts one preferred apparatus useful for carrying out the above process. The reference numerals 21 and 22 designate first and second cooling towers, respectively. Designated as 23 is a line through which a feed of a gaseous mixture to be treated is introduced into the first cooling tower 21 and which may be connected to the line 13 of the apparatus for producing BPA which is shown in Fig. 1 of EP-A-0523931 supra . An evacuation line 24 leading to a vacuum pump (not shown) through a cooler (not shown) is connected to the second cooling tower 22 to maintain the whole apparatus in a reduced pressure. The gaseous mixture feed introduced into through the line 23 into the first cooling tower 21 is brought into counter-current contact with a first cooling medium (phenol or BPA-containing phenol) fed from the top of the tower 21 through a line 25 to condense part of the phenol and substantially entire BPA contained in the gaseous mixture feed. The resulting cooling medium in which the condensed BPA and phenol have been dissolved is discharged from the bottom of the tower 21 through a line 26 by the action of a pump 27. A portion of the liquid discharged through the line 26 may be recycled, after being cooled to a predetermined temperature, to the line 25 as at least part of the first cooling medium, if desired. The gas mixture from which BPA and part of phenol have been removed is discharged from the top of the first cooling tower 21 through a line 28 and is introduced into the second cooling tower 22 where it is brought into counter-current contact with a second cooling medium (an aqueous solution of phenol) supplied through a line 29 and is substantially entirely condensed. The condensate is discharged together with the second cooling medium from the bottom of the tower 22 through a line 30 by the operation of a pump 31. A portion of the liquid in the line 30 is cooled in a cooler 34 by indirect heat exchange with a cooling medium, supplied through a line 40 and exhausted through a line 41, and is recycled through the line 29 to the second cooling tower 22 as the second cooling medium. The remainder portion of the liquid in the line 30 is discharged through a line 32 for recovery. In Fig. 1, designated as 51-54 are flow control valves for controlling the flow rates of respective liquids in response to detection signals from temperature sensors 55 and 58 or liquid level sensors 56 and 57. Fig. 2 illustrates another embodiment of an apparatus for carrying out the condensation treatment according to the present invention. In Fig. 2, the same reference numerals as in Fig. 1 designate similar component parts and flow rate controlling members are omitted. Designated generally as 60 is a cooling zone composed of vertically aligned first and second cooling towers 21 and 22. The first and second towers 21 and 22 are partitioned from each other by a partition plate 45 having an opening 44. A vertically upwardly extending cylinder 43 is connected to the opening 44 to define an annular, liquid collecting chamber above the partition plate 45 between the cylinder 43 and the inside wall of the cooling zone 60. The first and second towers are in fluid communication with each other through the opening 44. Designated as 42 is a guide plate to guide a liquid in the second cooling tower 22 into the liquid collecting chamber. A gaseous mixture feed is introduced through a line 23 into the first cooling tower 21 and is brought into counter-current contact with a first cooling medium fed through a line 25 to condense part of the phenol and substantially entire BPA contained in the gaseous mixture feed. The resulting cooling medium is discharged through a line 26. The gas mixture from which BPA and part of phenol have been removed is passed through the opening 44 to the second cooling tower 22 where it is brought into counter-current contact with a second cooling medium supplied through a line 29 and is condensed. The condensate is collected together with the second cooling medium in the annular chamber above the partition plate 45 and is discharged through a line 30 by the operation of a pump 31. A portion of the liquid in the line 30 is cooled in a cooler 34 by indirect heat exchange with a cooling medium, supplied through a line 40 and exhausted through a line 41, and is recycled through the line 29 to the second cooling tower 22 as the second cooling medium. The remainder portion of the liquid in the line 30 is discharged through a line 32 for recovery. An evacuation line 24 is connected to the top of the cooling zone 60 to maintain the first and second towers 21 and 22 in vacuum. According to the process of the present invention, the gaseous mixture of steam, phenol and BPA maintained in a reduced pressure 40 x 10 2 N/m 2 (30 Torr) or less can be condensed without increasing the pressure. Though the condensation is carried out at a low pressure of 40 x 10 2 N/m 2 (30 Torr) or less and a low steam condensation temperature, no crystals of BPA or phenol are formed. Thus, the condensation treatment can be performed without bringing about reduction of cooling efficiency of the coolers or clogging thereof by deposition of solids. Further, the condensation treatment can condense all of the components of the gaseous mixture so that substantially no vapors of these components are passed to the vacuum pump. This is advantageous from the standpoint of installation costs and energy consumption because it is not necessary to use a vacuum pump with a large displacement capacity. The gas mixture to be treated in accordance with this invention may additionally contain phenol derivatives such as isopropenyl phenol. Such phenol derivatives are recovered together with phenol.

Claims: A process for condensing a gaseous mixture of steam, phenol and bisphenol A maintained at a pressure of 40 x 10 2 N/m 2 (30 Torr) or less, comprising the steps of: introducing said gaseous mixture into a first cooling zone maintained at a pressure of 40 x 10 2 N/m 2 (30 Torr) or less and such a temperature that said steam is prevented from condensing while a portion of said phenol is condensed, wherein said gas is brought into counter-current contact with a first liquid cooling medium to condense substantially all of said bisphenol A and part of said phenol and thereby obtain a mixed gas containing uncondensed steam and uncondensed phenol, said first liquid cooling medium being phenol or bisphenol A-containing phenol; and introducing said mixed gas into a second cooling zone maintained at a pressure of 40 x 10 2 N/m 2 (30 Torr) or less and such a temperature that substantially all of said mixed gas is condensed, wherein said gas is brought into counter-current contact with a second liquid cooling medium to condense substantially all of said mixed gas and thereby obtain a condensate-containing liquid, said second liquid cooling medium being an aqueous solution of phenol. A process as claimed in Claim 1, further comprising recycling a portion of said condensate-containing liquid to said second cooling zone as at least part of said second liquid cooling medium. A process as claimed in Claim 1 or Claim 2, wherein said first cooling zone is maintained at a temperature of 42-90°C.

Inventors: ASAOKA SACHIO, IMAZEKI TAKASHI, INABA RYUCHI, KUKIDOME ATHUMI, MAEJIMA TETSUO, MORIYA KOBUO, NISHIJIMA HIROAKI, ONDA NOBUHIRO, SAKASHITA KOUJI, SHIMOGAWARA KAORU, SHINDO AKIO, WATANABE TSUNEO, YASUI MAKOTO, YONEDA NORIYUKI, ASAOKA, SACHIO, IMAZEKI, TAKASHI, INABA, RYUCHI, KUKIDOME, ATHUMI, MAEJIMA, TETSUO, MORIYA, KOBUO, NISHIJIMA, HIROAKI, ONDA, NOBUHIRO, SAKASHITA, KOUJI, SHIMOGAWARA, KAORU, SHINDO, AKIO, WATANABE, TSUNEO, YASUI, MAKOTO, YONEDA, NORIYUKI
Applicants: CHIYODA CHEM ENG CONSTRUCT CO, CHIYODA CORPORATION
Application year: 1992
Main classification: C07C39
IPC codes: C07C37