Polymerization in narrow fractions of coal tar wash-oil

Certain changes take place in coal tar wash-oil as it is circulated through the benzol hydrocarbons recovery and distillation cycle. It undergoes condensation, loses much of its light distillates content and attains a higher cp. One major problem with coal tar wash-oil is its tendency to form polymers as it circulates through the processing cycle and comes into contact with coke-oven gas. The polymerization rate is affected by a number of factors relating to the composition of the wash-oil, the concentrations in the coke-oven gas of components capable of promoting condensation and the operating conditions in the processing cycle. It has been shown that H/sub 2/S and O/sub 2/ in the coke-oven gas greatly accelerate polymerization processes in the wash-oil. Cyanide compounds and oxides of nitrogen also impair the quality of coal tar wash-oil.The deterioration of wash-oil in circulation leads to a serious rise in its cp and the rapid build-up of deposits on the scrubber packings, with serious effects on the performances of the benzol recovery and distillation sections. We have attempted to evaluate the polymerization tendencies of individual narrow wash-oil fractions. The tests were planned to simulate the conditions under which wash-oil can condense and polymerize. The resultsmore » show that polymerization proceeds most rapidly in the fractions boiling at 280 to 285 and 285 to 295/sup 0/C. They rapidly increase in density and viscosity and lower the quality of the entire oil. The most stable fractions in respect of polymerization are those boiling up to 270/sup 0/C and up to 280/sup 0/C. These tests have shown that wash-oil boiling up to 280/sup 0/C is the least liable to polymerization; its processing quality is superior and the specific consumption can thus be reduced.« less