GB789709A - A process for the separation of mixtures of solid and liquid substances occurring intars - Google Patents

Abstract

Mixtures of liquid and solid crystallizable substances occurring in coal tars are separated by producing a dispersion in an aqueous phase by means of a wetting, emulsifying or dispersing agent, the specific gravity of the aqueous phase of which is above that of the solid constituents present in the mixture, and separating the dispersion so obtained into two phases of different specific gravity in an imperforate wall centrifuge. In particular, naphthalene, phenanthrene and anthracene may be separated from tars by crystallization. The tars are preferably first distilled to give a fraction boiling between 170 DEG and 300 DEG C. at atmospheric pressure. The wetting agents may be alkylbenzene sulphonates, alcohol sulphates, alkyl sulphonates, sulphated fatty acid mono-glycerides, mono-, di-, and tri-ethanolamine, alkylpyridinium salts, polyglycol ethers of fatty alcohols or alkylphenols, polyglycol esters of fatty acids, partial ethers of higher alcohols, partial esters of fatty acids with polyhydroxy alcohols, and fatty acid esters of sorbitol. The specific gravity of the aqueous phase may be increased by means of chlorides, sulphates or nitrates of the alkali metals, alkaline earth metals such as of sodium, potassium, magnesium, calcium, and aluminium, or water-soluble organic substances including glycols, polyglycols, glycerine and water-soluble ethers. The aqueous phase may be stabilized by a protective colloid such as salts of polymeric phosphoric acids, glues, gelatine, tragacanth, pectins, alginates, high molecular weight polyglycol ethers, polyacrylates, and water-soluble cellulose derivatives, especially those containing glycol ether residues. In a typical example, crude naphthalene was mixed at 18-25 DEG C. with an aqueous solution of magnesium sulphate, sodium cellulose glycollate and an alkyl sulphonate and centrifuged in a continuously operating imperforate wall centrifuge at a throughput of 20 kgs./hour. Naphthalene of M.P. 78 DEG C. was isolated.