GB573111A - Improvements in and relating to the treatment of coal tar distillates and the like - Google Patents

Abstract

Aromatic hydrocarbons having a non-aromatic double bond such as styrene and indene are separated from light coal tar distillates and like hydrocarbon mixtures containing also saturated aromatic hydrocarbons by adding a solvent containing formic acid, a polyhydric alcohol or its ester or any admixture thereof to form a solution containing an increased ratio of said unsaturated to saturated hydrocarbons and an immiscible residue, rendered immiscible if necessary by addition of a liquid or a salting-out agent. Suitable solvents are propylene and diethylene glycols, mono-and di-acetin or mixed solvents such as 80 per cent formic acid and 20 per cent acetone. The hydrocarbons can be recovered from the solvent by adding a further solvent such as water which causes precipitation or by salting-out as by addition of sodium formate to a formic acid extract. The concentration of unsaturated hydrocarbons, for example styrene, in the solvent phase can be increased by repeated extraction with the same or a different solvent or by extraction with a liquid which is a solvent for the hydrocarbons, but immiscible with the first solvent, preferably a petroleum fraction boiling below styrene, e.g. below 100 DEG C. Alternatively, the solvent phase may be extracted with a styrene solution of the concentration desired. The process may be effected using a counter-current extraction with reflux. In examples: (1) coal tar naphtha boiling at 130-160 DEG C. is treated in a packed column with propylene glycol in counter-current. A refined naphtha layer is withdrawn at the top while the solution drawn off at the base is diluted with water causing separation of a hydrocarbon layer containing 15 per cent unsaturateds, mainly styrene; (2) the product of dehydrogenation of ethyl benzene is treated similarly with diethylene glycol, the hydrocarbon layer being removed from the glycol by vacuum distillation and recycled, while the glycol layer is vacuum distilled to recover hydrocarbons containing 50 per cent or more of styrene; (3) aromatic hydrocarbons, 40 per cent styrene, are dissolved in diacetin and passed countercurrent to petroleum ether, B.P. 70 DEG C., yielding a diacetin solution of hydrocarbons which are 80 per cent styrene; (4) a diethylene glycol solution obtained in (2) containing 20 per cent hydrocarbons of which 50 per cent is styrene is treated with a mixture of 80 per cent styrene with 20 per cent saturated aromatic hydrocarbons. A solution containing 25 per cent hydrocarbons of which 80 per cent is styrene is obtained, in addition to a hydrocarbon layer containing some dissolved glycol and only 5 per cent styrene which may be further treated as in (1) or (2).