GB942015A - A process for separating naphthoquinone from mixtures containing it - Google Patents

Abstract

<PICT:0942015/C2/1> In a process for separating naphthoquinone from mixtures which contain naphthalene preferably amounting to not less than half the quantity of naphthoquinone, in addition to a substantial amount of naphthoquinone, and also containing phthalic anhydride, the mixture is treated with water at an elevated temperature until the phthalic anhydride has undergone hydrolysis, the naphthalene phase and the aqueous phase are separated from each other at a temperature at which the two phases are liquid, and then at least the naphthalene liquid phase, which contains a large proportion of a naphthoquinone, is subjected to fractional counter current extraction to separate the naphthoquinone from the naphthalene. The fractional counter current extraction is carried out with the use of a polar water-miscible organic liquid of low molecular weight e.g. an aliphatic oxygen-containing compound such as methanol, which is advantageously aqueous as solvent for the naphthoquinone, and of an organic liquid of very low polarity e.g. an aliphatic hydrocarbon containing 4 to 10 carbon atoms such as heptane, as solvent for the naphthalene. The aqueous phase which has been separated from the naphthalene phase and contains phthalic acid and a small proportion of the naphthoquinone is subjected to counter current extraction to extract the naphthoquinone from the aqueous phase. Preferably the substantially water-imiscible organic solvent of low polarity used for extracting naphthoquinone from the aqueous phase is the same as the solvent used for extracting the naphthalene from the naphthalene phase, and the solvent containing the naphthoquinone from the aqueous phase is transferred to the extraction system in which the naphthoquinone is extracted from the naphthalene phase. In an example a mixture obtained from the catalytic oxidation of naphthalene and consisting of 5 parts each of naphthoquinone, napthalene and phthalic anhydride, is mixed with 100 parts of water having a temperature of 82 DEG C., which hydrolyses the phthalic anhydride and melts the naphthalene which dissolves the naphthoquinone. On standing two layers form and are separated in the separator 1, the lower layer, consisting of 5 parts of naphthalene, 4.5 parts of naphthoquinone and traces of phthalic acid, is subjected to fractional extraction at 55 DEG C. in the column II with the use of a solvent system consisting of heptane and aqueous methanol of 85% strength and the point of introduction of the naphthalene phase may be located at the centre of the extraction system. From the upper aqueous layer, containing substantially all the phthalic acid and about 0.5 part of naphthoquinone, the naphthoquinone is extracted in the column III at 80 DEG C. with heptane under a slightly superatmospheric pressure. The heptane phase may be introduced into column II at a suitable point, for example approximately at the lower third.