US 8,927,766 B2  16  15  The present invention provides in a second embodiment a  process for the preparation of glycolic acid, comprising  The examples of the first embodiment regarding methylene  dipropionate, homogeneous acid catalyst, propionic acid,  molar ratio of propionic acid to methylene dipropionate,  molar ratio of homogeneous acid catalyst to methylene dipro› pionate, molar ratio of water to methylene dipropionate, car› bon monoxide, hydrocarboxylation reaction zone process  conditions, esters of glycolic and propionic acids, hydrolyz› ing and hydrolyzed mixture composition, extraction, first and  second hydrophobic solvent and first and second hydrophilic  solvent, as well as feed ratios of each solvent to the effluent  and hydrolyzed mixture on a weight basis, separation of the  first and second extracts and first and second raffinates, sepa› ration of the homogenous acid catalyst from the effluent and  recycle of the homogeneous acid catalyst to the hydrocar- boxylation reaction zone, separation and recycle of the pro› pionic acid and second hydrophobic solvent, esterification of  the glycolic acid and hydrogenation of the glycolate ester  oligomers and glycolic acid oligomers to produce ethylene  glycol apply to the second embodiment.  For example, the process of the invention includes an  aspect wherein the feeding of the propionic acid, homoge› neous acid catalyst, methylene dipropionate in step (A)  occurs at a molar ratio of propionic acid:methylene dipropi› onate of from 0.5:1 to 4:1 or 0.5:1 to 2.5:1, a molar ratio of  homogenous acid catalyst:methylene dipropionate of from  0.01: 1 to 0.07: 1, and a molar ratio of water:methylene dipro› pionate of from 0.25:1 to 2:1 or 0.5:1 to 1.5:1. In another  example the extraction occurs with a first hydrophobic sol› vent selected from at least one of the group consisting of  hexane, heptane, toluene, xylene, and methyl tertiary-butyl  ether.  In another example, greater than 90 weight percent of the  esters of glycolic and propionic acids are recovered in the first  organic raffinate phase and greater than 95 weight percent of  The compounds and abbreviations given in Table 1 are  used throughout the Examples section. Structures for each  compound are also given.  The invention can be further illustrated by the following  examples of preferred embodiments thereof, although it will  be understood that these examples are included merely for  purposes of illustration and are not intended to limit the scope  of the invention.  In yet another example, the above process further com› prises  (I)  reacting a first ethylene glycol with the second  aqueous raffinate phase while simultaneously removing  water to produce an esterification effluent comprising glyco› late ester oligomers and glycolic acid oligomers and an over- head stream comprising water; and (J) reacting hydrogen  with the esterification effluent to produce a second ethylene  glycol, separating the second ethylene glycol into a product  ethylene glycol and the first ethylene glycol, recycling the  first ethylene glycol to step  (I).  In yet another example, the above process further com› prises (E) hydrolyzing the first organic raffinate phase to  produce a hydrolyzed mixture comprising glycolic acid and  propionic acid; (F) recovering the propionic acid from the  hydrolyzed mixture by extracting the hydrolyzed mixture  with a second hydrophobic solvent selected from at least one  of the group consisting ofn-propyl acetate, i-propyl acetate,  n-butyl acetate, i-butyl acetate, s-butyl acetate, methyl propi› onate, ethyl propionate, i-propyl propionate, methyl tertiary› butyl ether, methyl i-butyl ketone, methyl i-propyl ketone,  methyl propyl ketone, and toluene to form a second aqueous  raffinate phase comprising a major amount of the glycolic  acid contained in said hydrolyzed mixture and a second  organic extract phase comprising a major amount of the pro› pionic acid contained in the hydrolyzed mixture; (G) separat- ing the second aqueous raffinate phase and the second organic  extract phase; and (H) separating the second organic extract  phase into the second hydrophobic solvent and the propionic  acid, recycling the second hydrophobic solvent to step (F),  and recycling the propionic acid to step (A).  In another example of the process of the present invention,  the molar ratio of carbon monoxide to methylene dipropi› onate ranges from 1:1 to 10:1, and the hydrocarboxylation  reaction zone is operated at a pressure of from 35 bar gauge to  200 bar gauge and a temperature of from 80°  C. to 220°  C.  the homogenous acid catalyst is recovered in the first aqueous  extract phase. In another example, the extracting of step (B)  occurs in a continuous counter-current extractor, wherein the  first aqueous extract phase exits the bottom of the extractor  and the first organic raffinate phase exits the top of the extrac- tor, the first hydrophilic solvent is fed to the extractor above  the effluent, and the feed ratio of the first hydrophilic solvent  to the effluent ranges from 0.5:1 to 4:1 on a weight basis.  Additionally, a first hydrophobic solvent can be fed to the  extractor below the effluent, wherein the feed ratio of the first  hydrophobic solvent to the effluent ranges from 0.01 :1 to 5:1  on a weight basis, and the feed ratio of the first hydrophilic  solvent to the effluent ranges from 0.5:1 to 4:1 on a weight  basis.  (A) feeding carbon monoxide, methylene dipropionate, a  homogeneous acid catalyst, propionic acid, and water to  a hydrocarboxylation reaction zone to produce an efflu› ent comprising the homogeneous catalyst and esters of  glycolic and propionic acids;  (B) recovering the homogeneous acid catalyst from the  effluent by extracting the effluent with a hydrophilic  solvent comprising 15 weight percent to 100 weight  percent water and 0 weight percent to 85 weight percent  of glycolic acid, each on a total hydrophilic solvent  weight basis, and with a first hydrophobic solvent  selected from at least one of the group consisting of  n-propyl acetate, i-propyl acetate, n-butyl acetate, i-bu- tyl acetate, s-butyl acetate, methyl propionate, ethyl pro› pionate, i-propyl propionate, methyl tertiary-butyl ether,  methyl i-butyl ketone, methyl i-propyl ketone, methyl  propyl ketone, hexane, heptane, and toluene to form a  first aqueous extract phase comprising a major amount  of the homogeneous acid catalyst contained in the efflu› ent and a first organic raffinate phase comprising a major  amount of the esters of glycolic and propionic acids  contained in the effluent;  (C) separating the first organic raffinate phase and the first  aqueous extract phase; and  (D) recycling the first aqueous extract phase to step (A).  EXAMPLES 