Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-10-12
2001-06-12
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S727000
Reexamination Certificate
active
06245951
ABSTRACT:
FIELD OF THE INVENTION
This application relates to a process for reducing fouling of cooling surfaces of pre-reactors used in the production of bisphenols, such as bisphenol A.
BACKGROUND OF THE INVENTION
Bisphenols, and in particular bisphenol A (2,2 bis(p-hydroxyphenyl) propane, “BPA”), have become industrially significant reactants for a number of processes including the preparation of polycarbonates. Bisphenols are prepared on an industrial scale by one of two processes: an acid-catalyzed or HCI process and an ion exchange process, in which an acidic ion exchange resin such as sulfonic acid-substituted polystyrene is employed.
The bisphenol is prepared by condensation of two moles of phenol with one mole of a ketone or aldehyde, for example acetone, in the presence of an acidic catalyst. In addition to the bisphenol, however, the product stream from the reaction includes unreacted phenol, which is included in excess over the stoichiometric requirement, and various isomers of the desired bisphenol and other by-products. Because these by-products can compromise the properties of products made using the bisphenol, they need to be separated. One technique for accomplishing this separation involves cooling the product stream to induce crystallization of a 1:1 bisphenol:phenol adduct which can then be further processed by washing, distillation, extraction and/or steam stripping to produce a purified bisphenol product. Processes for the production and purification of bisphenols are well known, and are described inter alia in U.S. Pat. Nos. 4,107,218; 4,294,994; 5,210,329; 5,243,093; 5,245,088; 5,288,926; 5,368,827; 5,786,522; and 5,874,644.
In some semicontinuous procedures for the preparation of bisphenols, phenol and acetone are mixed and partially reacted in a pre-reactor. The partial reaction is allowed to proceed through 10 to 70% conversion, and the resulting product is then transferred to a batch reaction in which full conversion of the starting materials is achieved. The temperature in the pre-reactor is selected so that a little, BPA is precipitated. These crystals serve as seed crystals in the batch reactor. However, crystallization of BPA tends also to form a layer on interior surface of the pre-reactor, particularly the cooling surfaces which are used to maintain the temperature in the pre-reactor. This layer hinders heat transfer between these cooling surfaces and the reaction mixture. This reduced heat transfer can cause lower production rates and/or reduced purity of the finished product and is therefore undesirable.
To prevent these side effects, it is conventional to clean the pre-reactor periodically. This is done by either filling the pure phenol or with a normal charge where extra water or acid is added. These procedures increases the solubility of BPA and the removal of the BPA layer from the cooling surfaces, but the product produced during these cleaning procedures does not meet product specification. Thus, the time spent cleaning is wasted from a productivity point-of-view, and there is a need for an improved method for manufacture of bisphenols, in which this disruption is reduced or eliminated.
SUMMARY OF THE INVENTION
The present invention provides a semicontinuous method for manufacturing bisphenols with reduced fouling in the pre-reactor. In accordance with this method, two or more prereactors are used to continuously condense the dihydric phenol and the ketone or aldehyde to produce a partial reaction product in which the reaction of the dihydric phenol and the ketone or aldehyde is 10 to 70% complete. This partial reaction product is continuously removed from the pre-reactors, combined and introduced to a batchwise completion reactor. A stream of water or aqueous hydrochloric acid is added in alternating intervals to the pre-reactors, such that one is being cleaned by shifting the solubility of the bisphenol product at the same time that the other(s) continue to product a normal product stream which includes seed crystals for enhancing the performance of the batchwise completion reactor.
REFERENCES:
patent: 4107218 (1978-08-01), Konrad et al.
patent: 4294994 (1981-10-01), Li
patent: 5210329 (1993-05-01), Gomes de Matos et al.
patent: 5243093 (1993-09-01), Kissinger et al.
patent: 5245088 (1993-09-01), Fimuro et al.
patent: 5288926 (1994-02-01), Patrascu et al.
patent: 5368827 (1994-11-01), Moriya et al.
patent: 5786522 (1998-07-01), Cipullo
patent: 5874644 (1999-02-01), Gammill
patent: 197 57 570 (1999-06-01), None
patent: 0 323 831 (1989-07-01), None
Caré Hendrik Herman
Peemans Rudy
Van Der Schuit Edwin
Visser Jan-Peter
Vos Robbert
General Electric Company
Oppedahl & LarsonLLP
Shippen Michael L.
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