Method for the Enrichment of 4,4'-Dihydroxydiphenylmethane in Isomer Mixtures

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority of U.S. Provisional Patent Application No. 60/951,888, filed July 25, 2007, the entire disclosure whereof is expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] This invention relates generally to the enrichment of isomer mixtures so as to increase the concentration of preferred constituents, and in particular for the treatment of mixtures which comprise 4,4'-dihydroxydiphenylmethane and other isomers of dihydroxy- diphenylmethane so as to produce a product or mixture which is enriched in 4,4'-dihydroxy- diphenylmethane .

2. Discussion of Background Information

[0003] Bisphenol F is widely used in industry, for example, in the production of polycarbonates, polyesters, and epoxy resins. It is produced commercially by the reaction of phenol and formaldehyde, and is obtained in the form of a mixture of a number of species, including 4,4'-dihydroxydiphenylmethane, 2,4'-dihydroxydiphenylmethane, 2,2'-di- hydroxydiphenylmethane, and various trimeric and higher oligomeric species. Isomers of dihydroxydiphenylmethane can make up more than 90% of all species (based on area % in a HPLC). Typically isomeric mixtures can vary from about 25 wt. % to about 40 wt. % of 4,4' -dihydroxydiphenylmethane; from about 40 wt. % to about 60 wt .% of 2,4' -dihydroxydiphenylmethane; and from about 10 wt. % to about 25 wt. % of 2,2'- dihydroxydiphenylmethane .

[0004] The industry demand for 4,4' -dihydroxydiphenylmethane has increased in recent times, for example, as a raw material in so-called "high end" (i.e., high-value) coating applications, composites and in electronics. As a result, there has been significant activity in recent years in attempting to produce bisphenol F with a higher content of 4,4'-di- hydroxydiphenylmethane, and in attempting to produce that isomer in substantially pure form.

[0005] The quantity of trimeric and higher molecular weight species in bisphenol F is generally reduced by the use of high phenol/formaldehyde (PfF) ratios, and increased by the use of lower P/F ratios. The excess phenol in the reaction mixture is removed by distillation, and further distillation is also used to separate the mixture of di-functional bisphenol F isomers, and achieve an isomer mixture with a higher content of the di-functional species.

[0006] Most attempts have focussed on seeking to influence the isomer content and the isomer distribution during the formation reaction. Other methods seek to separate 4,4'-di- hydroxydiphenylmethane from the other components of the bisphenol F product. Existing separation methods require the use of organic solvents, typically chlorinated organic solvents, or are based on steam-distillation, and are therefore highly energy intensive.

[0007] GB-A-1182260, the entire disclosure of which is incorporated by reference herein, teaches the separation of a mixture of 2,4'-dihydroxydiphenylmethane and 4,4'-dihydroxy- diphenylmethane from bisphenol F reaction mixtures by using steam distillation at temperatures greater than 100 ⁰ C followed by further separation by fractional crystallization from boiling water. No further details regarding the separation are given.

[0008] EP-A-331173, the entire disclosure of which is incorporated by reference herein, describes the use of aromatic hydrocarbons as solvents to separate 4,4'- dihydroxydiphenylmethane from reaction mixtures containing the bisphenol F isomers in good yields and purity. EP-A-331173 describes further in a Comparative Example that bisphenol F isomeric mixtures do not dissolve completely in water even under reflux and that 4,4'-dihydroxydiphenylmethane can be separated only in small yields (14.8%) after decanting the aqueous phase from the bisphenol F oil phase. The residue (85.2%) still contains almost all of the 4,4'-dihydroxydiphenylmethane at 35.2% of the starting material (which starting material contained 38.8% of 4,4'-dihydroxydiphenylmethane). EP-A- 331173 also describes that the content of trimer and higher oligomers can be 8.1% at a P/F ratio of 25 and 22.6% at a P/F ratio of 8.

[0009] JP-A-48038694, the entire disclosure of which is incorporated by reference herein, describes the use of DMSO and DMF to separate 4,4'-dihydroxydiphenylmethane from reaction mixtures containing the bisphenol F isomers.

[0010] US Patent No. 6,492,566, the entire disclosure of which is incorporated by reference herein, describes the use of zeolites in the presence of 1,2-dichloroethane, CHCl ₃ , CCl ₄ , benzonitrile, nitrobenzene, acetonitrile, methylethylketone, or 1,2-dichlorobenzene to prepare bisphenol F isomeric mixtures with a high content of 4,4'-dihydroxydiphenyl- methane.

[0011] SU-A-245799, the entire disclosure of which is incorporated by reference herein, describes the use of a 2-phase solvent mixture of water and either THF, dichloroethane, tetrachloroethane or their mixtures with CCl ₄ to separate 4,4'-dihydroxydiphenylmethane from mixtures containing the bisphenol-F isomers.

SUMMARY OF THE INVENTION [0012] None of the above documents disclose that bisphenol F isomeric mixtures are miscible with (soluble in) small amounts of water or that crystals may be precipitated from such mixtures which contain 4,4'-dihydroxydiphenylmethane at good purity and at high yield, with only relatively small quantities of 4,4'-dihydroxydiphenylmethane being left in the remainder of the treated product.

[0013] The present invention provides a method of preparing a product which is enriched in 4,4'-dihydroxydiphenylmethane from a starting material which comprises 4,4'-dihydroxy- diphenylmethane in combination with one or more other isomers of dihydroxydiphenyl- methane and/or one or more polycondensation products which are obtainable from a reaction of phenol and formaldehyde (e.g., trimeric and higher oligomeric and/or polymeric species). The method comprises (a) forming a (liquid) mixed phase comprising the starting material and water, and (b) allowing a product that is enriched in 4,4'-dihydroxydiphenyl- methane to crystallize from the mixed phase.

[0014] In one aspect of the method of the present invention, the mixed phase may comprise not more than about 30 wt. %, e.g., not more than about 25 wt. %, not more than about 20 wt. %, not more than about 15 wt. %, or not more than about 10 wt. % of water, based on the total weight of the mixed phase.

[0015] In another aspect, the mixed phase may comprise at least about 5 wt. %, e.g., at least about 7 wt. %, or at least about 8 wt. % of water, based on the total weight of the mixed phase.

[0016] In yet another aspect of the instant method, the product enriched in 4,4'-dihydroxy- diphenylmethane may be allowed to crystallize from the mixed phase at a temperature which is not lower than 40 ⁰ C and not higher than 88 ⁰ C. For example, the temperature may be not lower than about 45 ⁰ C, e.g., not lower than about 50°C, not lower than about 55 ⁰ C, or not lower than about 60°C, and/or the temperature may be not higher than about 85°C, e.g., not higher than about 8O ⁰ C, not higher than about 75°C, or not higher than about 70°C.

[0017] In a still further aspect of the method of the present invention, the starting material may comprise commercially produced bisphenol F. For example, the starting material may comprise from about 25 wt. % to about 40 wt. % by weight of 4,4'-dihydroxydiphenyl- methane and/or from about 40 wt. % to about 60 wt. % of 2,4'-dihydroxydiphenylmethane and/or from about 10 wt. % to about 25 wt. % of 2,2'-dihydroxydiphenylmethane, each based on the total weight of the starting material.

[0018] In another aspect of the instant method, the concentration of 4,4'-dihydroxy- diphenylmethane in the enriched product may be at least about 5 %, e.g., at least about 10 % higher than the concentration of 4,4'-dihydroxydiphenylmethane in the starting material.

[0019] In a still further aspect of the method of the present invention, the mixed phase may comprise not more than about 5 wt. %, e.g., not more than about 2 wt. %, or not more than about 1 wt. %, or not more than about 0.5 wt. % of added organic solvent (i.e., organic solvent, if any, that is not already present in the starting material), based on the total weight of water and added organic solvent. For example, the mixed phase may be substantially free of added organic solvent.

[0020] In another aspect, the method of the present invention may further comprise recovering the enriched product (e.g., by filtration) and subjecting the enriched product to one or more further enrichment treatments to further increase the concentration of 4,4'-di- hydroxydiphenylmethane in the product. For example, the one or more further enrichment treatments may comprise the method of the present invention as set forth above (including the various aspects thereof).

[0021] The present invention also provides a method of decreasing the concentration of 4,4'-dihydroxydiphenylmethane by-product in an oligomeric and/or polymeric product which has been obtained by the reaction of phenol and formaldehyde. The method comprises (a) forming a mixed phase comprising the product and water, and (b) allowing a material which is enriched in 4,4'-dihydroxydiphenylmethane to crystallize from the mixed phase. The various aspects of this method may be the same as those which are set forth above.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0022] Unless otherwise stated, a reference to a compound or component includes the compound or component by itself, as well as in combination with other compounds or components, such as mixtures of compounds.

[0023] As used herein, the singular forms "a," "an," and "the" include the plural reference unless the context clearly dictates otherwise.

[0024] Except where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not to be considered as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding conventions.

[0025] Additionally, the recitation of numerical ranges within this specification is considered to be a disclosure of all numerical values and ranges within that range. For example, if a range is from about 1 to about 50, it is deemed to include, for example, 1, 7, 34, 46.1, 23.7, or any other value or range within the range.

[0026] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard,

no attempt is made to show embodiments of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

[0027] The present invention provides a method for enriching 4,4'-dihydroxydiphenyl- methane in an isomer and/or oligomer mixture, particularly in commercially available bisphenol F, substantially without the drawbacks of existing methods.

[0028] The (preferably clear) mixed phase of the method of the present invention preferably comprises from about 5 wt. % to about 30 wt. %, e.g., from about 5 wt. % to about 20 wt. %, more preferably from about 5 wt. % to about 10 wt. % of water, based on the total weight of the mixed phase.

[0029] The crystallization may be carried out at any temperature up to the melting point of the starting material containing the 4,4'-dihydroxydiphenylmethane, but is preferably carried out at a temperature of above 4O ⁰ C and below 88 ⁰ C, preferably from about 5O ⁰ C to about 80°C, more preferably from about 6O ⁰ C to about 70°C. The yield of the crystallization process depends on the equilibrium temperature of the reaction mixture. The closer the temperature is to the actual crystallization temperature of the reaction mixture, the higher the yield.

[0030] The oily residue that is usually obtained after the method of the present invention has been carried out is enriched in products which are different from 4,4'-dihydroxy- diphenylmethane such as, e.g., 2,4'-dihydroxydiphenylmethane and 2,2'- dihydroxydiphenylmethane and in the tri-functional and higher oligomers and polymers and other undesired products (impurities).

[0031] In one aspect of the method of the present invention, the starting material may be a raw mixture resulting from the reaction of phenol and formaldehyde, typically containing, for example, from about 25 wt. % to about 40 wt. % of 4,4'-dihydroxydiphenylmethane, from about 40 wt. % to about 60 wt. % of 2,4'-dihydroxydiphenylmethane, and from about 10 wt. % to about 25 wt. % of 2,2'-dihydroxydiphenylmethane.

[0032] In another aspect, the starting mixture may be an isomeric mixture which has been pre-enriched in 4,4'-dihydroxydiphenylmethane, for example, by a previous treatment in

accordance with the method of the present invention and/or by one of the alternative enrichment methods known from the prior art. In a particularly preferred embodiment, the fraction enriched in 4,4'-dihydroxydiphenylmethane resulting from a treatment in accordance with the method of the present invention is subjected to at least one further treatment in accordance with the method of the present invention in order to obtain a product which is further enriched in 4,4'-dihydroxydiphenylmethane. Such a treatment may, for example, be an additional crystallization step according to an embodiment of the method of this invention or another method of crystallization using organic solvents. Other methods of purification such as, e.g., distillation may, of course, be used as well.

[0033] The method of the present invention renders the use of additional (organic) solvent(s) (i.e., in addition to water) dispensable. The less solvent is used the less there are issues with respect to separating the enriched product from solvents and disposal of the organic solvent waste. The method of the present invention can even be carried out without the use of any additional (organic) solvent. If employed, the added organic solvent is preferably water-miscible, such as, e.g., one or more of methanol, ethanol, n- and i- propanol, acetone and butanone. Both the resulting 4,4'-dihydroxydiphenylmethane enriched product and the residue (e.g., filtrate) can easily be dried and used separately. In this regard, it is noted that the enriched product and the residue can be separated by any method that is suitable for separating solids from liquids, e.g., by filtration, decantation, centrifugation, etc. Filtration is a preferred method.

[0034] The sequence of combining the starting material with the aqueous liquid is not critical for the success of the method of the present invention. Accordingly, the crude bisphenol F containing starting material may be added to the aqueous liquid (e.g., substantially undiluted water) or vice versa, or the aqueous liquid and the starting material may be fed to a treatment vessel together. Also the temperature of the aqueous liquid is not critical. The (bisphenol F) starting material can be employed in solid or liquid (e.g., molten) form.

[0035] The method of the present invention makes it possible to separate bisphenol F species from trimer and higher molecular weight species and also to separate 4,4'- dihydroxydiphenylmethane from other di-functional isomers and higher molecular weight species, in a manner which is convenient, and inexpensive. Because the method preferably

uses only a small quantity of water, does not require the use of additional (organic) solvent, and allows separation (e.g., filtration) temperatures of below about 100 ⁰ C, the method is also environmentally friendly, and does not require the use of large reactor volumes or tanks that contain large volumes of filtrate solutions.

[0036] As indicated above, the product enriched in 4,4'-dihydroxydiphenylmethane may be utilized in a variety of applications, for example, as a raw material in high-end coating applications, composites and in electronics. The remaining mixture (residue) may be used, for example, as starting material in other applications, e.g., to make lower viscosity bisphenol F liquid epoxy resins.

[0037] The principles of the present method may also be applied in order to extract bisphenol F species from higher molecular weight phenol-formaldehyde reaction products such as novolac resins to increase the (overall) functionality of the product. The resulting (bisphenol F depleted) products are particularly useful for making other intermediates such as epoxy novolac resins of high functionality for use in, for example, coatings, composites and electronics.

EXAMPLES

Example 1

[0038] A total of 200 g of commercial grade bisphenol F containing 32.99 % of 4,4'- dihydroxydiphenylmethane, 42.26 %of 2,4'-dihydroxydiphenylmethane and 17.01 % of 2,2'-dihydroxydiphenylmethane was melted in a beaker at 12O ⁰ C, and 20 g of water of room temperature were added thereto. The components were mixed and the mixture was allowed to cool, resulting in the formation of a slurry. After the temperature of the slurry had reached 62 ⁰ C the slurry was kept at this temperature for about 30 minutes. Thereafter the resultant mixture was filtered through a filter which had been preheated to about 74 ⁰ C. A total of 120 g of crystals was collected in the filter, corresponding to a yield of 60 %. The crystals were air dried. The crystals contained 44.28 wt. % of 4,4'- dihydroxydiphenylmethane, 34.63 wt. % of 2,4'-dihydroxydiphenylmethane and 13.93 wt. % of 2,2'-dihydroxydiphenylmethane. All data are based on area-% in the HPLC chromatogram.

[0039] The filtrate contained 15.47 wt. % of 4,4'-dihydroxydiphenylmethane, 54.11 wt. % of 2,4'-dihydroxydiphenylmethane and 21.79 wt. % of 2,2'-dihydroxy-diphenylmethane. All data are based on area-% of a HPLC chromatogram.

[0040] HPLC analysis was done by dissolving 50 +/- 5 mg of a sample to the nearest 0.1 mg in 5.00 rnL of acetonitrile. 3.0 μL of the solution was injected into an HPLC apparatus using a RP- 18 reversed phased column. A gradient of water/ acetonitrile was used at a flow rate of 1.0 niL/min, and detection was carried out spectroscopically at 254 nm. The LC traces were evaluated by area-%.

Example 2

[0041] 30 kg of commercial grade bisphenol F as described in Example 1 and 3 kg of water of room temperature were charged into a reactor and heated to 8O ⁰ C within 2 hours with mixing. After additional 30 minutes at 8O ⁰ C of mixing the bisphenol F containing solid was completely dissolved. The reactor was cooled to about 69 ⁰ C within 30 minutes with the oil in the reactor mantle set to 44 ⁰ C. After the temperature had reached 69 ⁰ C, the mixture was slowly cooled to 6O ⁰ C within 2 hours. The resultant mixture was discharged from the reactor and was filtered using a 25 μm filter using nitrogen pressure. A total of 12 kg of colorless graphite like crystals was obtained. Analysis of the crystals showed 53.7 % of 4,4'-dihydroxydiphenylmethane, 30.3 % of 2,4'- dihydroxydiphenylmethane, 10.9 % of 2,2'- dihydroxydiphenylmethane and 5.1 % of tri- and higher functional species and other impurities. The filtrate contained 19.2 % of 4,4' -dihydroxydiphenylmethane, 49.9 % of 2,4' -dihydroxydiphenylmethane, 20.9 % of 2,2' -dihydroxydiphenylmethane and 10.0 % of tri- and higher functional and species and other impurities. All data are based on area-% determined by the HPLC method described above.

[0042] The crystals enriched in 4,4'-dihydroxydiphenylmethane from Examples 1 or 2 may be subjected to further treatment in order to further increase the concentration of 4,4'- dihydroxydiphenylmethane. For example, the crystals enriched in 4,4'-dihydroxydiphenyl- methane may be subjected to another treatment in accordance with the method of this invention. Alternatively, also other methods such as, e.g., any of those described in the prior art set forth above may be used to further enrich 4,4'-dihydroxydiphenylmethane.

Comparative Example

[0043] A mixture of 10 grams of commercial grade bisphenol F and 20 ml of water was heated to about 8O ⁰ C. The bisphenol F material melted to form an oil in the water. Upon filtration both the oil and the water passed through the filter with no crystals being left in the filter. Also upon cooling no crystals were formed.

[0044] Although the present invention has been described in considerable detail with regard to certain versions thereof, other versions are possible, and alterations, permutations, and equivalents of the version shown will become apparent to those skilled in the art upon a reading of the specification and study of the drawings. Also, the various features of the versions herein can be combined in various ways to provide additional versions of the present invention. Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the present invention. Therefore, any appended claims should not be limited to the description of the preferred versions contained herein and should include all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.

[0045] Having now fully described this invention, it will be understood to those of ordinary skill in the art that the methods of the present invention can be carried out with a wide and equivalent range of conditions, formulations, and other parameters without departing from the scope of the invention or any embodiments thereof.