acid mixture comprising about 70 to about 90 weight per› cent glycolic acid, based on the total weight of the aqueous glycolic acid mixture, and about 1 to about 10 weight percent of the acid catalyst; 

(B) extracting the aqueous glycolic acid mixture with an extraction solvent, comprising 

(i) about 5 to about 45 weight percent, based on the total weight of the extraction solvent, of a tertiary amine comprising tris(2-ethylhexyl)amine, tris(2-ethylbutyl) amine, trioctylamine, triisooctylamine, triisodecyl amine, tridodecylamine, tridecylamine, dioctyldecy› lamine, didecyloctylamine, or a combination thereof; 

(ii) about 5 to about 45 weight percent, based on the total weight of the extraction solvent, of a modifier compris- ing 2-ethylhexanoic acid, !auric acid, bis(2-ethylhexyl) hydrogen phosphate, perfluorooctanoic acid, or a com› bination thereof, wherein the weight ratio of the modifier to the tertiary amine is about 1: 1 to about 5: 1; and 

(iii) about 10 to about 90 weight percent of a diluent, based on the total weight of the extraction solvent, comprising hexane, heptane, decane, methylcyclohexane, benzene, toluene, xylene, isoparaffinic mixed hydrocarbons hav› ing a boiling range between 90 and 325° C., or a com› bination thereof; 

to form an aqueous raffinate phase comprising a major amount of the glycolic acid contained in the aqueous glycolic acid mixture and an organic extract phase com› prising a major amount of the acid catalyst contained in the aqueous glycolic acid mixture; 

(C) separating the aqueous raffinate and organic extract phases; and 

(D) extracting the organic extract phase from step ( C) with an aqueous formaldehyde solution, comprising about 35 to about 85 weight percent formaldehyde, based on the total weight of the aqueous formaldehyde solution, to form an aqueous formaldehyde extract comprising a major amount of the acid catalyst contained in the organic extract phase from step (C) and an organic raffinate phase comprising a minor amount of the acid catalyst contained in the organic extract phase. 

It is understood that the above process can include the various embodiments of the hydrocarboxylation process, formalde› hyde and carbon monoxide reactants, aqueous glycolic acid mixture, the sulfonic acid catalysts, reactor formats and con› figurations, reaction conditions of time, temperature, and pressures, extraction solvents, tertiary amines, modifiers, diluents, and wash steps as described hereinabove and in any combination. For example, as described previously, the acid catalyst can comprise methanetrisulfonic acid. 

The invention also includes the following embodiments 1-34 set forth below. Embodiment 1 is a process for recover› ing an acid catalyst from aqueous glycolic acid, comprising: 

(A) extracting an aqueous glycolic acid mixture, comprising 55 

(i) about 50 to about 95 weight percent glycolic acid, based on the total weight of the aqueous glycolic acid mixture, and 

(ii) about 0.2 to about 12 weight percent, based on the total weight of the aqueous glycolic acid mixture, of an acid 60 catalyst comprising sulfuric acid, an alkyl sulfonic acid containing from 1 to 5 carbon atoms, a fluoroalkyl sul› fonic acid containing from 1 to 5 carbon atoms, or a combination thereof; 

with an extraction solvent, comprising 

(i) about 5 to about 45 weight percent, based on the total weight of the extraction solvent, of at least one tertiary 

amine containing from 12 to 40 carbon atoms, at least one onium carboxylate compound, or a combination thereof; 

(ii) about 5 to about 45 weight percent of at least one modifier comprising an aliphatic carboxylic acid con› taining from 5 to 16 carbon atoms, a fluoroalkyl car› boxylic acid containing 5 to 16 carbon atoms, an orga› nophosphorus acid containing from 5 to 16 carbon atoms, or a combination thereof; and 

(iii) about 10 to about 90 weight percent of at least one diluent comprising carbon dioxide, an aliphatic hydro› carbon containing from 3 to 25 carbon atoms, an aro› matic hydrocarbon containing 6 to 25 carbon atom, a halogenated hydrocarbon containing 6 to 25 carbon atoms, or a combination thereof; 

to form an aqueous raffinate phase comprising a major amount of the glycolic acid contained in the aqueous glycolic acid mixture and an organic extract phase com› prising a major amount of the acid catalyst contained in the aqueous glycolic acid mixture; 

(B) separating the aqueous raffinate and organic extract phases; and 

(C) extracting the organic extract phase from step (B) with an aqueous formaldehyde solution to form an aqueous form› aldehyde extract comprising a major amount of the acid catalyst contained in the organic extract phase from step (B) and an organic raffinate phase comprising a minor amount of the acid catalyst contained in the organic extract phase. 

Embodiment 2 is a process that includes the features of embodiment 1 in which the aqueous glycolic acid mixture comprises about 70 to about 90 weight percent glycolic acid and is produced by contacting aqueous formaldehyde with carbon monoxide in the presence of an acid catalyst. 

Embodiment 3 is a process that includes the features of any one of embodiments 1 and 2, in which the acid catalyst comprises sulfuric acid, trifluoromethanesulfonic acid, meth› anesulfonic acid, methanedisulfonic acid, methanetrisulfonic acid, bis(methylsulfonyl)methanesulfonic acid, 1,1,2,2-tet- rafluoroethanesulfonic acid, or a combination thereof. 

Embodiment 4 is a process that includes the features of any one of embodiments 1-3, in which the tertiary amine com› prises tris(2-ethylhexyl)amine, tris(2-ethylbutyl)amine, trio› ctylamine, triisooctylamine, triisodecyl amine, tridodecy- !amine, tridecylamine, dioctyldecylamine, didecyloctylamine, or a combination thereof. 

Embodiment 5 is a process that includes the features of any one of embodiments 1-4, in which the modifier comprises n-pentanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, hexanoic acid, 2-ethylbutanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, pelargonic acid, nonanoic acid, decanoic acid, !auric acid, palmitic acid, bis (2-ethylhexyl)hydrogen phosphate, perfluorooctanoic acid, or a combination thereof. 

Embodiment 6 is a process that includes the features of any one of embodiments 1-5, in which the diluent comprises pentane, hexane, heptane, decane, methylcyclohexane, meth› ylene chloride, chlorobenzene, dichlorobenzene, 1,2-dichlo› roethane, benzene, toluene, xylene, or a combination thereof. 

Embodiment 7 is a process that includes the features of any one of embodiments 1-6, in which the aqueous formaldehyde solution comprises about 35 to about 85 weight percent form› aldehyde, the aqueous formaldehyde extract comprises about 0.5 to about 10 weight percent, based on the total weight of the aqueous formaldehyde extract, of the acid catalyst, and the weight ratio of the aqueous formaldehyde solution to the organic extract phase is about 0.1: 1 to about 1: 1. 

