Process for cleaning bisphenol crystallizer

Details Process for cleaning bisphenol crystallizer Process for cleaning bisphenol crystallizer

2000-03-30

2001-03-20

Kunemund, Robert (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Processes of growth from liquid or supercritical state

Having growth from a solution comprising a solvent which is...

C117S073000, C117S078000, C117S925000, C117S927000, C568S724000, C568S727000, C568S728000, C023S29500G

Reexamination Certificate

active

06203612

ABSTRACT:

FIELD OF THE INVENTION
This application relates to a process for cleaning a crystallizer used in the recovery of bisphenols, such as bisphenol A.
BACKGROUND OF THE INVENTION
Bisphenols, and in particular bisphenol A (2,2 bis(p-hydroxyphenyl) propane), 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 HC
1
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.
The crystallization of bisphenol from the reactant stream is generally carried out in a crystallizer which is designed for continuous or semi-continuous operation. The crystallization coolers have a complex interior structure to provide significant surface area for heat exchange between the bisphenol reaction stream and a circulating coolant. Over time, adduct precipitates out on the cooling surfaces on the interior crystallizer, reducing the efficiency of cooling and in some cases plugging orifices in the crystallizer and restricting flow of materials into and out of the crystallizer. When this happens, the crystallizer must be taken off-line for a period of time for cleaning. This interruption of the manufacturing process is costly, and it is therefore desirable to perform the cleaning as infrequently as possible, and with maximum effectiveness.
One method for cleaning the crystallizer and associated coolers is by increasing the temperature on the inside of the crystallizer to melt out deposits of crystals that may have formed. This can be accomplished by increasing the temperature of the heat exchange fluid, or by introducing hot phenol into the interior of the crystallizer. This method, however, is not always effective, and generally requires about 24 hours of down time to complete the cleaning procedure. In addition, this type of process suffers from poor reproducibility, and requires delicate control of the start-up procedure to return the crystallizer to the efficient production of the desired crystallized bisphenol adduct. U.S. Pat. No. 5,856,589 discloses an alternative approach in which phenol containing from 3 to 40 weight percent of water is used to dissolve deposited bisphenol adduct from the cooling and crystallization surfaces. The use of combinations of phenol and water reduces the time required for a melt out and the frequency of required melt outs. Nevertheless, there remains a need for further improvements in cleaning procedures, to further reduce the process down-time associated with such cleaning.
SUMMARY OF THE INVENTION
The present invention provides an alternative and improved method for cleaning cooling and/or crystallization surfaces of a crystallizer fouled with a crystallized bisphenol as a result of processing a slurry derived from the production of bisphenol. The method comprises the steps of:
(a) draining from 20 to 80%, and preferably about 50% of the slurry from the crystallizer;
(b) replacing the drained slurry with a solvent comprising phenol, thereby forming a diluted slurry;
(c) increasing the temperature in the crystallizer to a temperature at which the crystallized bisphenol is dissolved in the diluted slurry, and then rapidly cooling the diluted slurry to a temperature of 45 to 55° C.; and
(d) adding a seed slurry containing solid bisphenol at a concentration of 5 to 30%, said seed slurry having a temperature of 45 to 55° C., until conditions are established at which bisphenol crystals added to the crystallizer do not redissolve.


REFERENCES:
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patent: 5210329 (1993-05-01), Gomes De Matos et al.
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patent: 5874644 (1999-02-01), Gammill
patent: 718267 (1996-06-01), None

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