CN1178213A - Manufacture of bisphenol-A - Google Patents

Abstract

An integrated process for the preparation and recovery of BPA in pure form utilizes a series of steps to crystallize pure BPA of improved color stability and recycle separated impurities to improve overall yields. The principal impurity recycled to the process is Omicron, Rho-BPA which functions as a color stabilizer in the product and in polycarbonate resins prepared from the BPA.

Description

Preparation of bisphenol A

The invention relates to a preparation method of bisphenol A.

Dihydric phenol, 2,2-bis-p-hydroxyphenylpropane (often referred to as "bisphenol A", "BPA" or "pp-BPA") is produced industrially by making 2 moles of phenol Condensed with 1 mole of acetone. In the reaction, phenol was used in an amount exceeding the stoichiometric requirement by 1 mole. During the condensation reaction, some impurities, which are considered to be the desired product BPA, are formed, such as by-products of isomeric forms of BPA. These impurities are carried over into the product stream from the condensation reaction zone and include water, traces of acidic species derived from the catalyst, unreacted phenol and acetone. In general, the purification of the desired product BPA is a costly and multi-step process.

The main use of BPA is as a monomer for polymerization to obtain polycarbonate and polyester carbonate resins. With many of these polymeric resins, color, lack of color, and color stability are important for their end uses, such as clear lenses. Recently, it has been discovered that one of the isomers of BPA, 2-(4-hydroxy-phenyl)-2-(2-hydroxyphenyl)propane (also known as o,p-BPA, is used as impurities) as a color stabilizer in resins prepared by polymerization of BPA. Its recent studies have shown that o,p-BPA at a concentration of at least about 100 ppm in the BPA monomer during polymerization can produce polycarbonate resins with improved color (as measured by yellowness index).

The present invention utilizes the above recent discovery by improving the preparation of monomeric BPA so as to increase the content of o,p-BPA impurities in the product, thereby increasing its value as a color stable polycarbonate resin precursor. An advantage of the improved process of the present invention is that it avoids increasing the concentration of other impurities associated with BPA production, such as BPX-II, BPX-I, dimers, and the like.

There are two important methods commonly used in the industrial synthesis of BPA. One is the method associated with the acid catalyst (hydrogen chloride) used, sometimes referred to as the "HCl" method.

The second industrial synthesis reaction involves the use of active ion exchange catalysts and is sometimes referred to as the "IER" method. Both synthesis methods involve passing phenol, acetone, and recycled by-products through a reactor containing an acidic catalyst, followed by a BPA purification process. The "IER method" can be accomplished in one of two ways: the first way is until substantially all the acetone is consumed; the second way and the most ideal way is "partial acetone conversion". This technique is described in US Patent No. 5,315,042, which is incorporated herein by reference. The BPA reaction can optionally be accelerated in the presence of a free mercaptan such as 3-mercaptopropionic acid or with or without a promoter chemically or covalently bonded to the EIR resin. These resins are generally known compositions, as are methods for their preparation. For example, its preparation method can be found in US Patent No. 3,037,052, which is incorporated herein by reference.

The reaction effluent of the IER process contains unreacted acetone, phenol, BPA, adducts of BPA and phenol, and BPA isomer by-products and accelerators (when used). This effluent (or HCl process reaction effluent) can be fed to a stripping process to remove reaction moisture, residual acetone and phenol.

A more detailed description of the above methods for condensing phenol with acetone to obtain BPA can be found in U.S. Patent Nos. 4,346,247, 4,396,728, 4,400,555, 4,424,283, 4,584,416, 4,766,254, and 4,847,433, incorporated herein. Invention as a reference. Common to all these known methods and processes is the need to purify and recover the BPA product in a post-condensation step. Another auxiliary process commonly used in both HCl or IER BPA production processes is the "recovery process" for recovery of useful species from the effluent stream. It can be produced and recovered by catalytic cracking of said effluents (for example as described in U.S. Patent No. 4,131,749), by adduct crystallization (U.S. Patent No. 5,210,329) or by distillation (for example, see U.S. Patent No. 5,300,702 or European Patent (U.K.) No. 055251A published on September 13, 1995).

The present invention is an improved process for the production of pure BPA in a fully integrated industrial process starting with condensation reaction products.

The present invention comprises a method of preparing BPA comprising:

(a) Condensation of phenol and acetone in the reaction zone in the presence of a stoichiometric excess of phenol and a catalytic ratio of acidic catalyst, thus obtaining the reaction zone effluent of by-products comprising o,p-BPA in admixture with the desired BPA adducted with phenol;

(b) crystallizing the BPA/phenol adduct from the effluent, leaving the mother liquor;

(c) releasing at least a portion of said mother liquor from the process;

(d) recrystallizing the separated BPA/phenol adduct crystals;

(e) dehydrating and distilling the discharged mother liquor to obtain a light fraction comprising o,p-BPA; and

(f) adding at least a portion of the light fraction to the BPA/phenol adduct crystals separated from the mother liquor prior to the recrystallization step (d) above, in order to adjust the o,p-bisphenol content therein to a color-stabilizing ratio .

The accompanying drawing is a schematic flow chart showing the method of the embodiment of the present invention.

An industrially important process for the preparation of BPA involves the condensation of 2 moles of phenol with 1 mole of acetone in the presence of an acidic catalyst and a stoichiometric excess of the phenol reactant, see for example the aforementioned US patent. This reaction is the starting point of the process of the present invention as shown in the figures used to illustrate the example process of the present invention. Any of the aforementioned reaction conditions and catalysts may be used in order to obtain a reaction zone effluent for subsequent treatment according to the process of the present invention.

Preferred is the condensation method described in US Patent No. 5,315,042, incorporated herein by reference.

The condensation reaction can generally be carried out in the reaction zone (12), as described in the figure. Typically the reaction effluent comprising crude BPA phenol, BPA isomers [comprising 0-5% by weight of o,p-BPA], water, acetone and other reaction by-products is carried into a multi-step crystallization process wherein at least A crystallization (unit 14) and a recrystallization (unit 16) are performed to crystallize out the BPA/phenol adduct. After each crystallization, a solid/liquid separation (filtration or centrifugation) is carried out in units 18, 20 in order to separate off the mother liquor. After the crystallization and filtration process, the phenol in the pure adduct is removed in a phenol recovery unit 22 in order to obtain the BPA product.

The molten pure BPA product from recovery unit 22 can be reconstituted in various forms, including "flakes" from solidifying the melt on a rotating cooling drum or "pellets" from a pelletizing process.

Typically the first portion of the mother liquor separated from the crystallization of the precipitated BPA/phenol adduct is dehydrated in unit 24 and recycled back to reaction zone 12 to recover a portion of the phenol and BPA values contained in the mother liquor. Additionally, water (and unreacted acetone, if present) can be removed prior to crystallization of the adduct. In addition to moisture, this first mother liquor generally contains a high proportion of o,p-BPA, which will be isomerized in reaction zone 12 during subsequent reactions. In order to avoid increasing the undesired impurities to BPA, the remaining part of the dehydrated first part mother liquor has been discharged to the recovery treatment stage from the above-mentioned processing pipeline through the exhaust pipeline 25, so as to transfer the first cut containing phenol (stripping device 26 ). The product of the extracted phenol in stripper 26 is then distilled through distillation column 30 (or multiple stages) to separate p,p-BPA, chroman, and other valuable components of BPA synthesis. By-product light fractions. This light fraction collected in vessel 32 contains a high proportion of o,p-BPA which can be used to adjust the o,p-BPA content of the first crystals of BPA/phenol adduct obtained from unit 18. Said adjustment is accomplished by adding at least a portion of the light fraction from vessel 32 prior to unit 16 to the first adduct crystallization in a proportion sufficient to provide color stability. Color stabilization ratios generally range from about 0.01 to about 3% by weight of pp-BPA, preferably from 0.01 to 0.3% by weight, more preferably from about 0.015 to about 0.1% by weight, most preferably from about 0.02 to about 0.08 %(weight). Additions to the product of unit 18 are in process conduit 34 via conduit 36 (shown in phantom) before entering unit 16 .

The distilled phenol from strip column 26 as a mixture comprising some water and some acetone may be recovered in a pure, substantially anhydrous state by further distillation for further condensation in reaction zone 12 using known methods.

The following examples illustrate the manner and method of carrying out the invention and provide the best forms of carrying out the invention contemplated by the inventors, but are not intended to be limiting.

Example

The feed liquid (residual crystallization solution) is obtained from the industrial production of BPA after the first crystallization and isolation process of the BPA/phenol adduct from the condensation reactor effluent. Analysis of an aliquot of the feed solution revealed the composition shown in Table 1 below.

Table 1 Table 2 Table 3 Table 4

Wt% Wt% Wt% Wt%

Phenol 67.81 0.4 0.01 0.01

pp-BPA 25.81 23.3 99.91 99.94

op-BPA 2.38 40.3 0.041 0.007

Dimer 2.04 2.0 0.000 0.000

Chromene 0.61 22.3 0.000 0.000

Spiro 0.25 0.1 0.000 0.000

BPX-I 0.56 0.0 0.001 0.002

BPX-II 0.54 1.0 0.02 0.028

The above mother liquor was dehydrated, filtered and distilled at about 410°F under reduced pressure of 35 mm Hg (abs.) to remove phenol. Secondary distillation at about 450-470°F at a pressure of less than about 1 mmHg produced a light fraction, which was analyzed in the amounts shown in Table 2 above.

Part of said "light" fraction is added to the crystallization of the separated BPA/phenol adduct in the form of a melt and recrystallized. After desorption by phenol, the analysis results of the recrystallized product are shown in Table 3 above. Table 4 provides a typical composition that did not utilize the present invention (ie, the recrystallization of the materials in Table 1 did not add the materials in Table 2).

Those skilled in the art will appreciate that the amount of o,p-BPA added in the product will depend on the composition of the first adduct, the distillation conditions selected, the composition of the light fraction produced and the choice of feed to the second adduct. The amount of said light ends in the distillation stage. The present invention provides a method for recovery and reuse of useful low boiling point species (o,p-BPA and pp-BPA) and removal of "heavies" (BPX-I, BPX-II, dimers, etc.). The "heavy fraction" by-products can be a source of color, can induce polymerization branching, or have adverse effects on other physical properties. The composition of the light effluent can be varied to provide by-products of various compositions, depending on the desired concentration. In the light effluent, the concentration of o,p-BPA may range from about 10% by weight to about 80% by weight. Under the conditions most commonly used, the light effluent has an o,p-BPA content of from about 20% by weight to about 70% by weight.

This principle is also applicable to other industrial BPA processes using multi-step purification systems, such as melt recrystallization (see eg US Pat. No. 5,243,093). In this case, the o,p-BPA-enriched process effluent can be added to the crystallization in an amount that increases the concentration of o,p-BPA in the product without appreciably affecting the concentration of other impurities in the product. a certain stage of the process.

Said US patent is hereby incorporated by reference into the present invention.

Claims (2)

1. The method for preparing BPA, it comprises: (a) Condensing phenol with acetone in the reaction zone in the presence of a stoichiometric excess of phenol and a catalytically proportioned acidic catalyst, thereby obtaining Reaction zone effluent of BPA isomer by-products of BPA; (b) crystallizing the BPA/phenol adduct from the effluent, leaving the mother liquor; (c) releasing at least a portion of said mother liquor from the process; (d) recrystallizing the separated BPA/phenol adduct crystals; (e) dehydrating and distilling said vented mother liquor or by-product effluent to obtain a light fraction comprising o,p-BPA; and (f) adding at least a portion of said light fraction to said BPA/phenol adduct crystals separated from the mother liquor before said recrystallization step (d) in order to adjust the o,p-BPA content therein to such that Color stable ratio. 2. A method for preparing BPA, comprising: (a) Condensing phenol with acetone in the reaction zone in the presence of a stoichiometric excess of phenol and a catalytically proportioned acidic catalyst, thereby obtaining Reaction zone effluent of BPA isomer by-products of BPA; (b) crystallizing the BPA/phenol adduct from the effluent, leaving the mother liquor; (c) removing moisture from said mother liquor or reactor and effluent prior to crystallization; (d) circulating the first part of the dehydrated mother liquor to the reaction zone for further reaction; (e) releasing a second portion of dehydration mother liquor from said process; (f) recrystallize the isolated BPA/phenol adduct crystals; (g) removing phenol from the recrystallized adduct; (h) extracting phenol from the second part of dehydration mother liquor released; (i) distilling said phenol-free vented liquid in order to divert the light fraction comprising o,p-BPA; and (j) before the above recrystallization step (f), adding at least a portion of said light fraction to the BPA/phenol adduct crystals separated from said mother liquor in order to adjust its o,p-BPA content to such that Color stable ratio.

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