Patent GB-712835-A (GB)
Title: Improvements in or relating to process for isolating low molecular weight phenolic compounds
IPC: C10G21/20
Filed: 1951-07-16
Abstract: Phenol, cresols, ethylphenols and xylenols are isolated from crude aromatic mixtures containing them by contacting such a mixture with hexamethylenetetramine at a temperature below 180 DEG  F., separating a complex phase, consisting mainly of complexes of hexamethylenetetramine with the phenolic compounds, from the resulting mixture in the presence of an anti-solvent (i.e. a paraffinic or naphthenic hydrocarbon or mixture thereof in which the complex phase is insoluble), decomposing the complex phase into its components by extraction, at a temperature below 180 DEG  F., with water or an oxygenated hydrocarbon solvent having high solvent power for tar acids and low solvent power for hexamethylenetetramine and water, whereby the phenols are liberated from the complex phrase. Aliphatic hydrocarbons containing 3 to 10 carbon atoms are suitable anti-solvents.  A pentane fraction or hexanes are preferred.  Propane and butane (in a pressure system) and naphthenes such as cyclohexane and cyclopentane are also mentioned.  The hexamethylene tetramine may be used in solid powder form or as an aqueous saturated or nearsaturated solution or as a slurry, a slurry containing 2 to 5 volumes of water per volume of solid hexamethylene tetramine being preferred.  Contact of the aromatic oil and anti-solvent with aqueous hexamethylene tetramine may be effected in a countercurrent extraction system or batchwise.  Two or three phases may be formed following the contacting of the mixtures; in each case the top layer comprises anti-solvent solution of aromatic mixture from which low molecular weight phenols have been substantially removed.  Underneath is a layer mainly of liquid complex below which is an aqueous solution or suspension of hexamethylene tetramine containing dissolved complex.  Where a large excess of hexamethylene tetramine is used, the separate layer of complex is not formed.  Volume ratios of anti-solvent to crude aromatic mixture between 0.5 and 5 are referred to. Decomposition of the complex may be effected by a counter-current extraction process, e.g. the combined complex and aqueous phases are contacted countercurrently with ether in which the liberated phenols dissolve.  Water is suitable for decomposing the complex only when the latter comprises substantially water-insoluble phenols, e.g. xylenols and ethylphenols.  Preferred solvents are ether and tetrahydrofurane.  Usual decomposition temperatures are between 50 DEG  and 120 DEG  F.  The extract phase and the anti-solvent solution after separation may be water washed to recover hexamethylene tetramine which may be used in a pre-treatment of the aromatic oil.  A flow sheet is given for a continuous process in which an anti-solvent solution of feed oil which has been treated with hexamethylene tetramine-containing wash solution is contacted with an aqueous slurry of hexamethylene tetramine in a contact tower and the resulting composite of complex phase and aqueous slurry is extracted with ether to recover the phenols.  In examples, tar-oil is used as starting material, pentane as anti-solvent and ether as decomposing agent.  In examples: (1) and (2) three phases are formed, the phenols being extracted in (1) from the combined complex and aqueous phases, and in (2) from the separated complex phase; (3) sufficient hexamethylene tetramine slurry is used to produce only two phases, the phenols being extracted from the aqueous phase; (4) water washings of the separated oil-rich phase and ether extract of complex are mixed, and after stripping free of ether the solution (containing 2.5 per cent by weight of hexamethylene tetramine) is used to treat raw tar acid oil as a preliminary step; (5) the hexamethylene tetramine is used in solid form.  In each example neutral tar oil containing tar acids is recovered from the separated oil phase.