Process for converting a hydroxycarboxylic acid, or salts thereof, to an unsaturated carboxylic acid and/or its esters
First Claim
1. A process for preparing an unsaturated carboxylic acid, and esters thereof, from an ammonium salt of a hydroxycarboxylic acid, said process comprising:
- a) providing an aqueous solution comprising the ammonium salt of a hydroxycarboxylic acid;
b) converting the ammonium salt of a hydroxycarboxylic acid to a corresponding hydroxycarboxylic acid and ammonium cation in aqueous solution; and
c) separating the ammonium cation from the aqueous solution, leaving the hydroxycarboxylic acid in aqueous solution;
wherein said converting and separating steps b) and c) are accomplished by a technique selected from the group consisting of;
(1) adding a solution comprising a hydrophobic acid and, optionally, an organic solvent, to the aqueous solution, wherein the hydrophobic acid comprises a proton and a conjugate base, is immiscible in water, is capable of forming an ammonium salt which is also immiscible in water, and has an acid dissociation constant (pKa) which is at least 0.5 less than the acid dissociation constant of the hydroxycarboxylic acid, to form a multi-phase solution which comprises an aqueous phase comprising the hydroxycarboxylic acid, which comprises the carboxylic anion and the proton, and a non-aqueous phase comprising a neutralized acid, which comprises the ammonium cation and the conjugate base of the hydrophobic acid, and(2) contacting the aqueous solution comprising the ammonium salt of hydroxycarboxylic acid with an acid ion exchange resin having an acid dissociation constant (pKa) which is at least 0.5 less than the acid dissociation constant of the hydroxycarboxylic acid, to form an aqueous solution comprising the corresponding hydroxycarboxylic acid and a non-aqueous ammonium cation-containing exchange resin.
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Abstract
A process for converting a salt of a hydroxycarboxylic acid to an unsaturated carboxylic acid, or esters thereof. The process involves converting an ammonium salt of a hydroxycarboxylic acid in aqueous solution to a corresponding hydroxycarboxylic acid and ammonium cation in aqueous solution; and separating the ammonium cation from the aqueous solution, leaving the hydroxycarboxylic acid in aqueous solution. The converting and separating steps may be accomplished by employing a hydrophobic acid or an acid ion exchange resin, each of which must have an acid dissociation constant, i.e., pKa, at least 0.5 less that that of the salt of the hydroxycarboxylic acid. Where a hydrophobic acid is used, it must be immiscible in water, and its salt must also be immiscible in water, and the resulting multi-phase solution comprises an aqueous phase comprising the corresponding hydroxycarboxylic acid, as well as a non-aqueous phase comprising a neutralized acid. Alternatively, where the ion exchange resin is used, the aqueous solution of the ammonium salt of a hydroxycarboxylic acid is contacted with the resin, thereby converting the salt to a hydroxycarboxylic acid and capturing the ammonium cations on the resin. In either case, the aqueous solution is treated, such as by heating, to separate and recover the hydroxycarboxylic acid. The non-aqueous phase or resin is treated to separate and recover ammonia useful for preparing additional ammonium salt of a hydroxycarboxylic acid.
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Citations
13 Claims
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1. A process for preparing an unsaturated carboxylic acid, and esters thereof, from an ammonium salt of a hydroxycarboxylic acid, said process comprising:
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a) providing an aqueous solution comprising the ammonium salt of a hydroxycarboxylic acid; b) converting the ammonium salt of a hydroxycarboxylic acid to a corresponding hydroxycarboxylic acid and ammonium cation in aqueous solution; and c) separating the ammonium cation from the aqueous solution, leaving the hydroxycarboxylic acid in aqueous solution; wherein said converting and separating steps b) and c) are accomplished by a technique selected from the group consisting of; (1) adding a solution comprising a hydrophobic acid and, optionally, an organic solvent, to the aqueous solution, wherein the hydrophobic acid comprises a proton and a conjugate base, is immiscible in water, is capable of forming an ammonium salt which is also immiscible in water, and has an acid dissociation constant (pKa) which is at least 0.5 less than the acid dissociation constant of the hydroxycarboxylic acid, to form a multi-phase solution which comprises an aqueous phase comprising the hydroxycarboxylic acid, which comprises the carboxylic anion and the proton, and a non-aqueous phase comprising a neutralized acid, which comprises the ammonium cation and the conjugate base of the hydrophobic acid, and (2) contacting the aqueous solution comprising the ammonium salt of hydroxycarboxylic acid with an acid ion exchange resin having an acid dissociation constant (pKa) which is at least 0.5 less than the acid dissociation constant of the hydroxycarboxylic acid, to form an aqueous solution comprising the corresponding hydroxycarboxylic acid and a non-aqueous ammonium cation-containing exchange resin. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification