GB628403A - Improvements in or relating to the purification of naphthalene - Google Patents

Abstract

Naphthalene containing oily impurities is crystallized and purified on introducing in the molten or vapour state into a cold or cool aliphatic alcohol having not more than four carbon atoms or a mixture of such alcohols, the alcohol being substantially anhydrous, maintained cold or cool if necessary, and present in an amount such that the greater part of the naphthalene crystallizes substantially instantaneously on contact with the alcohol while the impurities are dissolved together with only a small amount of impure naphthalene. The resultant crystals of naphthalene are preferably maintained in motion in the alcohol so as to wash them and prevent the occlusion of impurities in crystal aggregates. Methyl alcohol is the preferred alcohol and when it is used a temperature within the range of 20 DEG to 45 DEG C. is preferred. An anhydrous alcohol is stated to be one with less than 1 per cent of water. Crude naphthalene should have a naphthalene content of at least 25 per cent, preferably 55 per cent, and molten naphthalene derived from a fractional distillation of coal tar may be treated. The process may be made continuous by recycling the alcohol until it is nearly saturated with impurities, or by withdrawing a portion of impure alcohol and adding fresh alcohol for make-up purposes. In an illustration 100 parts by weight of crude naphthalene derived from vertical retort tar and with a boiling range of 211 DEG to 220 DEG C. is fed at 100 DEG C. into 140 parts by weight of cold anhydrous methyl alcohol, the crystals formed being agitated and air-dried after collection. The methyl alcohol is recycled and maintained at 35 DEG C. at the point of naphthalene entry. In a further illustration a similar naphthalene fraction is treated as above after initial refrigeration. According to the Provisional Specification solid naphthalene may also be treated.