GB804221A - Separating naphthalene from hydrocarbon oils by azeotropic distillation - Google Patents

Abstract

Naphthalene is separated from hydrocarbon oils by distilling the oil in the presence of an amino-hydroxy organic compound, such as monoethanolamine or 4-amino-2-butanol, which forms azeotropes of minimum boiling point with those components of the oil having boiling points close to that of naphthalene whereby the azeotropes distil over before the purified naphthalene. A second azeotropic entrainer for the impurities, e.g. ethylene glycol, may be added to the distilland, so as to cause the amino-hydroxy compound to concentrate in the upper part of the distillation column thereby <FORM:0804221/III/1> obviating thermal decomposition of the aminocompound in the hotter lower sections. Alternatively the distillation may be operated at a lowered base temperature by carrying it out in the presence of an excess of ethanolamine and by introducing an inert gas, such as nitrogen. In an example, a coal tar fraction having a boiling range of 180-240 DEG C. was washed with alkali and with acid to give a neutral oil containing 62 per cent of naphthalene. This oil was mixed with a third of its weight of monoethanolamine, and distilled through a packed column. The first fraction of the distillate boiling between 160 DEG and 168 DEG C. contained about equal amounts of ethanolamine and nonaromatic hydrocarbons. This distillate separated into two phases, the lower ethanolamine-rich phase containing 10 per cent of hydrocarbon oil, and the upper hydrocarbon-rich layer containing 3.5 per cent ethanolamine. This first distillate was followed by a naphthalene fraction distilling at 218-220 DEG C. and having a crystallizing-point of 75-76 DEG C. In the apparatus shown, crude naphthalene oil is first fractionated in column I and solvent naphtha passes overhead. The topped crude is further fractionated in column II, from which crude methyl naphthalene is withdrawn as bottoms. The impure naphthalene obtained at the overhead product from column II is submitted to azeotropic distillation with monoethanolamine in column III. Purified naphthalene is withdrawn from the base of column III. The condensed distillate from this column is passed to decanter IV, where naphtha separates from ethanolamine. The latter is returned to column III via line 8 or line 11.