Patent ID: 7989667

Claim:
A process for the continuous crystallization of a mixture comprising cis-2,2,4,4-tetramethylcyclobutanediol and trans-2,2,4,4-tetramethylcyclobutanediol dissolved in a solvent, the process comprising: (a) crystallizing cis-2,2,4,4-tetramethylcyclobutanediol in a first crystallization stage operated at a temperature such that the concentration of trans-2,2,4,4-tetramethylcyclobutanediol in solution is below the saturated concentration of trans-2,2,4,4-tetramethylcyclobutanediol at the operating temperature of the first stage; (b) transferring a slurry of crystallized cis-2,2,4,4-tetramethylcyclobutanediol and the corresponding mother liquor from the first crystallization stage to a second crystallization stage; (c) crystallizing both cis-2,2,4,4-tetramethylcyclobutanediol and trans-2,2,4,4-tetramethylcyclobutanediol in the second crystallization stage; and (d) separating the crystals of cis-2,2,4,4-tetramethylcyclobutanediol and trans-2,2,4,4-tetramethylcyclobutanediol from the mother liquor present in the second crystallization stage to yield a mixture of crystallized cis-2,2,4,4-tetramethylcyclobutanediol and crystallized trans-2,2,4,4-tetramethylcyclobutanediol, wherein the solvent is isobutyl isobutyrate.