Patent GB-662783-A (GB)
Title: Purification of alkyl phenols
IPC: C07C37/84
Filed: 1949-02-23
Abstract: A process of separating a polyalkyl phenol from a mixture of the same with one or more other alkyl phenols having a lower melting point, the mixture containing a major proportion of the higher melting polyalkyl phenol to be separated, comprises crystallizing a major proportion of the higher melting polyalkyl phenol from the mixture at a temperature at which substantially only the higher melting polyalkyl phenol but not more than about 90 per cent thereof crystallizes from the mixture to form a slurry which is readily filterable, separating the crystals of polyalkyl phenol from the resulting slurry, crystallizing the separated mother liquor at a substantially lower temperature than the first crystallizing temperature to form a second slurry which is readily filterable, separating a second crystalline product from the resulting second slurry, and recrystallizing the second crystalline product at a temperature substantially above the temperature of the second crystallization.  In particular, di-(tertiary butyl)-cresol may be recovered from the mixture obtained by alkylating cresol with a tertiary olefin or alcohol. The last stage may be effected by mixing the second portion of crystals with another portion of the original mixture, and crystallizing at the first crystallization temperature, and it is then preferable to choose the crystallization temperatures so that a product of desired purity is obtained by the first crystallization and the second crystal product corresponds to the original charge in content of the polyalkyl phenol to be recovered. A variant of the process is to start with a feed charge containing from about 40 per cent to about 60 per cent by weight (based upon total alkylphenol content) of the higher melting polyalkyl phenol to be separated, crystallizing the mixture at a temperature (e.g. 30 DEG C.) such as to produce a readily filterable slurry of a crude crystalline product which has an increased content of the higher melting polyalkyl phenol and which contains a major proportion thereof, separating this crude product from the mother liquor, melting it and recrystallizing it at a temperature higher than the temperature of the first crystallization and at which a readily filterable slurry of the higher melting polyalkyl phenol is obtained, separating the resulting crystals, mixing the mother liquor with a further portion of the original mixture and reprocessing as before. The crystallizations may be effected from solution.  Examples of suitable starting mixtures are 2,6-ditertiary butyl-4-methyl phenol and 2-tertiary butyl-4-methyl phenol; 2-tertiary butyl-4-methyl phenol and o- or p-cresol; 2,4-ditertiary butyl-6-methyl phenol, 2-methyl-4-tertiary butyl phenol and/or 2-methyl-6-tertiary butyl phenol; 2,4-dimethyl-6-alkyl phenol wherein the alkyl group is preferably secondary or tertiary and contains from 3 to 12 carbon atoms and 2,4-dimethyl phenol; dialkyl-metacresols and monoalkyl metacresols; monoalkyl metacresols and m-cresol; 2,4,6-trialkyl metacresol and corresponding dialkyl metacresols; 2-, 4-, or 6-tertiary amyl 3,4-dimethyl phenol and 3,4-dimethyl phenol.  An example describes the crystallization of a mixture containing about 80 mol. per cent of 2,6-ditertiary butyl-4-methyl phenol obtained when p-cresol is alkylated with isobutylene or tertiary butyl alcohol in the presence, e.g. of sulphuric acid.  The first crystallization is performed at 95 DEG  F., and the product washed with isopropyl alcohol.  The mother liquor is crystallized at about 30 DEG  F., and the separated crystals containing about 80 per cent of 2,6-ditertiary butyl-4-methyl phenol are recycled for p  recrystallization at 95 DEG F. with further crude stock.  The mother liquor from the second stage may be crystallized at a still lower temperature, and the separated crystals melted and recrystallized at 30 DEG  F. along with mother liquor from the first crystallization.ALSO:A process of separating a polyalkyl phenol from a mixture of the same with one or more other alkyl phenols having a lower melting point, the mixture containing a major proportion of the higher melting polyalkyl phenol to be separated, comprises crystallizing a major proportion of the higher melting polyalkyl phenol from the mixture at a temperature at which substantially only the higher melting polyalkyl phenol but not more than about 90 per cent thereof crystallizes from the mixture to form a slurry which is readily filterable, separating the crystals of polyalkyl phenol from the resulting slurry, crystallizing the separated mother liquor at a substantially lower temperature than the first crystallizing temperature to form a second slurry which is readily filterable, separating a second crystalline product from the resulting second slurry, and recrystallizing the second crystalline product at a temperature substantially above the temperature of the second crystallization.  The last stage may be effected by mixing the second portion of crystals with another portion of the original mixture and crystallizing at the first crystallizing temperature, and it is then preferable to choose the crystallization temperatures so that a product of desired purity is obtained by the first crystallization, and so that the second crystal product corresponds to the original charge in content of the polyalkyl phenol to be recovered.  A variant of the process is to start with a feed charge containing from about 40 per cent to about 60 per cent by weight (based upon total alkyl phenol content) of the higher melting polyalkyl phenol to be separated, crystallizing the mixture at a temperature (e.g. 30 DEG C.) such as to produce a readily filterable slurry of a crude crystalline product which has an increased content of the higher melting phenol and which contains a major proportion thereof, separating this crude product from the mother liquor, melting it and recrystallizing it at a temperature higher than the temperature of the first crystallization and at which a readily filterable slurry of the higher melting polyalkyl phenol is obtained, separating the resulting crystals, mixing the mother liquor with a further portion of the original mixture, and processing as before. The crystallizations may be effected from solution.  Suitable starting mixtures are, e.g. 2, 6-ditertiary butyl-4-methyl phenol and 2-tertiary butyl-4-methyl phenol; 2-tertiary butyl-4-methyl phenyl and o-or p-cresol; 2, 4-ditertiary butyl-6-methyl phenol, 2-methyl-4-tertiary butyl phenol, and/or 2-methyl-6-tertiary butyl phenol; 2, 4-dimethyl-6-alkyl phenol wherein the alkyl group is preferably secondary or tertiary and contains from 3 to 12 carbon atoms and 2, 4-dimethyl phenol; dialkyl metacresols and monoalkyl metacresols; monoalkyl metacresols and m-cresol; 2, 4, 6-trialkyl metacresol and corresponding dialkyl metacresols; 2-, 4-, or 6-tertiary amyl 3, 4-dimethyl phenol and 3, 4-dimethyl phenol.  An example describes the crystallization of a mixture containing about 80 mol per cent of 2, 6-ditertiary butyl-4-methyl phenol obtained when p-cresol is alkylated with isobutylene or tertiary butyl alcohol in the presence, e.g. of sulphuric acid.  The first crystallization is performed at 95 DEG F. and the product washed with isopropyl alcohol.  The mother liquor is crystallized at about 30 DEG F. and the separated crystals containing about 80 per cent of 2, 6-ditertiary butyl-4-methyl phenol are recycled for recrystallization at 95 DEG  with further crude stock.  The mother liquor from the second stage may be crystallized at a still lower temperature, and the separated crystals melted and recrystallized at 30 DEG F. along with mother liquor from the first crystallization.