WO2017201664A1

WO2017201664A1 - Method for purifiying sorbate

Info

Publication number: WO2017201664A1
Application number: PCT/CN2016/083102
Authority: WO
Inventors: Selvanathan Arumugam; John ELL; Wei Wang; Steven Zhang
Original assignee: Rohm And Haas Company; Dow Global Technologies Llc
Priority date: 2016-05-24
Filing date: 2016-05-24
Publication date: 2017-11-30

Abstract

Disclosed is a method of removing residual sorbic acid from a crude mixture containing a sorbate and sorbic acid comprising the steps of contacting a mixture comprising sorbic acid and a sorbate with a macroporous ion exchange resin functionalized with ammonium hydroxide groups at a concentration of at least 1.01 equivalents based on the equivalents of acids in the mixture to reduce the concentration of the sorbic acid in the mixture by at least 50％; then separating the ion exchange resin from the mixture to forma purified disorbate with a reduced concentration of sorbic acid. The method provides an efficient way of purifying and recovering sorbates, which are useful as low VOC coalescents for coatings formulations.

Description

METHOD FOR PURIFIYING A SORBATE

Sorbic acid esters, with boiling points above 350℃ have been found to be effective reactive coalescents for ultra-low volatile organic content (VOC) architectural coatings. Diesters of sorbic acid (disorbates) are ordinarily prepared by reacting sorbic acid and a diol using a stoichiometric excess of sorbic acid to drive the reaction to quantitative conversion. The residual unreacted sorbic acid present in the crude sorbate product adversely impacts the storage stability of the disorbate, thereby requiring free radical inhibitor to maintain product stability. However, the presence of residual free radical inhibitor slows down the cure rate of the coated material； moreover, the presence of residual sorbic acid adds unwanted color and results in gelation of the paint formulation. The complexities associated with excess sorbic acid warrant a removal step. Traditional workup approaches such as an aqueous base wash result in loss of valuable product； separation by vacuum distillation are impractical due to the high boiling points of the disorbate. Accordingly, it would be desirable to find a way to efficiently remove excess sorbic acid from a disorbate and the sorbic acid without impacting yield of the purified disorbate.

Summary of the Invention

The present invention addresses a need in the art by providing a method comprising the steps of a) contacting a mixture comprising sorbic acid and a sorbate with a macroporous ion exchange resin functionalized with ammonium hydroxide groups at a concentration of at least 1.01 equivalents based on the equivalents of acids in the mixture to reduce the concentration of the sorbic acid in the mixture by at least 50％； then b) separating the ion exchange resin from the mixture to form a purified sorbate with a reduced concentration of sorbic acid. The method of the present invention addresses a need by providing a simple and cost effective way of substantially reducing levels of sorbic acid from a mixture containing a sorbate, preferably a disorbate, and sorbic acid without substantially impacting the recovery of the desired sorbate.

Detailed Description of the Invention

The present invention is a method comprising the steps of a) contacting a mixture comprising sorbic acid and a sorbate with a macroporous ion exchange resin functionalized with ammonium hydroxide groups at a concentration of at least 1.01 equivalents based on the equivalents of acids in the mixture to reduce the concentration of the sorbic acid in the mixture by at least 50％； then b) separating the ion exchange resin from the mixture to form a purified sorbate with a reduced concentration of sorbic acid.

The macroporous ion exchange resin functionalized with ammonium hydroxide groups can be obtained commercially, for example, as AMBERJET^TM 9000 OH Ion Exchange Resin or DOWEX^TM 550A Ion Exchange Resin (Trademarks of The Dow Chemical Company or its Affiliates) . Preferably the concentration of the ammonium cations in the ion exchange resin is from 1.10, more preferably from 1.15 equivalents, to preferably 2.5, more preferably to 2.0, and most preferably to 1.5 equivalents, based on the equivalents of acids in the mixture. As used herein “equivalents of acids” refers to residual sorbic acid and any residual acid catalyst present in the crude mixture.

The sorbate is either a monosorbate or a disorbate. An example of a preferred monosorbate is tripropylene glycol n-butyl ether sorbate (TPnB-monosorbate) , as illustrated:

An example of a preferred disorbate is triethylene glycol disorbate (TEG-disorbate) , as illustrated:

The sorbate can be prepared in a variety of ways. For example, sorbic acid can be contacted with an alcohol or diol at an elevated temperature, preferably in the range of from 60℃ to 160℃, and in the presence of a solvent and an acid catalyst for a sufficient time (typically from 1 h to 24 h) to produce the desired sorbate. Examples of suitable acids include sulfuric acid, hydrochloric acid, and toluene sulfonic acid； preferred solvents include those that are immiscible with water and preferably have a density of less than that of water. Examples of preferred solvents include toluene, xylene, chlorobenzene, ethyl benzene, and dibutyl ether, with toluene and xylene being preferred.

Where the desired product is a disorbate, some amount of incompletely reacted monosorbate byproduct is typically formed during the process, and it is also often desirable to remove this byproduct without impacting the recovery of the disorbate. Fortuitously, it has been discovered that the ion exchange resin functionalized with ammonium hydroxide groups achieves these goals. Accordingly, in another aspect, the present invention is a method for increasing the purity of a disorbate from a mixture containing the disorbate, a monosorbate of the disorbate, and sorbic acid comprising the steps of contacting the mixture with a macroporous ion exchange resin functionalized with ammonium hydroxide groups at a concentration of at least 1.01 equivalents based on the equivalents of acids in the mixture to reduce the concentration of the sorbic acid and monosorbate in the mixture by at least 50％； then b) separating the ion exchange resin from the mixture to form a purified disorbate with a reduced concentration of sorbic acid and monosorbate of the disorbate.

As used herein, “monosorbate of the disorbate” refers to an incompletely reacted glycol. Thus, the monosorbate of TEG-disorbate is TEG-monosorbate, as illustrated:

The amount of residual acid is preferably reduced by at least 75％, more preferably by at least 90％, more preferably by at least 95％, and most preferably by at least 99％. The amount of the desired sorbate recovered (disorbate in the case of TEG-disorbate, monosorbate in the case of TPnB-monosorbate) is preferably at least 90％, more preferably at least 95％, and most preferably at least 99％.

The process of the present invention provides a simple way to improve the purity of the disorbate and achieve almost total recovery of this desired product.

Intermediate Example 1–Preparation of a Crude Triethylene Glycol Disorbate

To a 500-mL three-neck flask equipped with a Dean Stark apparatus was added sorbic acid, triethylene glycol, and toluene. The reaction mixture was carried under N₂ and the contents of the flask were heated to ～80℃ with stirring until the sorbic acid dissolved. Concentrated H₂SO₄ premixed with toluene was then added drop-wise to the flask and the mixture was heated to an internal kettle temperature of 120℃ to 130℃. The reaction proceeded until no additional water was observed to condense in the Dean-Stark apparatus from the toluene/water heterogeneous azeotrope. The contents were cooled to room temperature and the mixture was analyzed to reveal a mixture of triethylene glycol disorbate (TEG-disorbate) , which also contained triethylene glycol monosorbate (TEG-monosorbate) and unreacted sorbic acid.

Example 1–Purification of Crude TEG-disorbate with Ammonium Hydroxide Functionalized Ion Exchange Resin

A portion of the crude TEG-disorbate (1 g) prepared as described in Intermediate Example 1 was dissolved in acetone (20 mL) followed by addition of AMBERJET^TM 9000 OH Ion Exchange Resin (4.24 g, 1.2 equivalents based on residual acid) . The mixture was stirred for 30 min at room temperature after which time the ion exchange resin was filtered out and washed twice with acetone (5 mL) . The dissolved fractions were combined and the solvent removed in vacuo.

Example 2–Purification of Crude TEG-disorbate with Ammonium Hydroxide Functionalized Ion Exchange Resin

The method of Example 1 was repeated except that DOWEX^TM 550A OH Ion Exchange Resin was used as the ion exchange resin.

Comparative Examples 1-6

The method of Examples 1 was repeated except using other ion exchange resins or bases for removing residual sorbic acids. The results are shown in Table 1.

In each instance, 1.2 equivalents of ion exchange resin or base was used based on total acids in the crude mixture, except for silica gel, which was used at 50 wt％based on residual acids. The w/w ratio of the TEG-disorbate to the sorbic acid to the TEG-monosorbate (Disorbate: SA: Monosorbate) prior to the purification procedure was 73.6: 25.3: 1.1.

Table 1–Purification of TEG-Disorbate

As the data show, the treatment of the crude mixture with the ion exchange resin functionalized with ammonium hydroxide groups (Examples 1 and 2) resulted in complete removal of sorbic acid and nearly complete removal of the monosorbate, with quantitative or nearly quantitative recovery of the disorbate. In contrast, the other methods of purifying the disorbate were significantly less effective for removing the impurities and all suffered substantial recovery loss.

Intermediate Example 2–Preparation of Tripropylene Glycol n-Butyl Sorbate

Tripropylene glycol n-butyl monosorbate was prepared by contacting DOWANOL^TM TPnB Glycol Ether (A Trademark of The Dow Chemical Company) under conditions substantially as described in Intermediate Example 1. The resulting product contained a mixture of the desired Tripropylene glycol n-butyl monosorbate (TPnB monosorbate) and unreacted sorbic acid at a w/w ratio of 72: 28.

Example 3–Purification of Crude TPnB Monosorbate

The crude TPnB monosorbate was purified using AMBERJET 9000 OH substantially as described in Example 1. The resulting purified product was free of sorbic acid with quantitative recovery of the purified monosorbate.

Claims

A method comprising the steps of a) contacting a mixture comprising sorbic acid and a sorbate with a macroporous ion exchange resin functionalized with ammonium hydroxide groups at a concentration of at least 1.01 equivalents based on the equivalents of acids in the mixture to reduce the concentration of the sorbic acid in the mixture by at least 50％； then b) separating the ion exchange resin from the mixture to form a purified disorbate with a reduced concentration of sorbic acid.
The method of Claim 1 wherein the concentration of the ammonium hydroxide groups in the ion exchange resin is from 1.10 to preferably 2.5 equivalents of acids in the mixture.
The method of Claim 2 wherein the concentration of the ammonium hydroxide groups in the ion exchange resin is from 1.10 to preferably 2.0 equivalents of acids in the mixture.
The method of Claim 3 wherein the concentration of the sorbic acid in the mixture is reduced by at least 90％ after contact with the ion exchange resin.
The method of any of Claims 4 wherein the sorbate is a disorbate and the mixture further comprises a monosorbate of the disorbate.
The method of Claim 5 wherein the disorbate is triethylene glycol disorbate and the monosorbate is triethylene glycol monosorbate, wherein the amount of disorbate recovered is at least 90％ after contact with the ion exchange resin.
The method of Claim 4 wherein the sorbate is tripropylene glycol n-butyl ether monosorbate.
A method for increasing the purity of a disorbate from a mixture containing the disorbate, a monosorbate of the disorbate, and sorbic acid comprising the steps of contacting the mixture with a macroporous ion exchange resin functionalized with ammonium hydroxide groups at a concentration of at least 1.01 equivalents based on the equivalents of acids in the mixture to reduce the concentration of the sorbic acid and monosorbate in the mixture by at least 50％； then b) separating the ion exchange resin from the mixture to form a purified disorbate with a reduced concentration of sorbic acid and monosorbate.
The method of Claim 8 wherein the disorbate is triethylene glycol disorbate and the monosorbate is triethylene glycol monosorbate.