Methods for increasing yield and improving quality of petroleum pitches

Abstract

In the work reported here, electrode pitches were obtained from a vacuum-reduced cracked resid (VCR) with an aromatic additive -- a heavy pyrolysis tar (HPT). A mixed charge with the required ratio of these components was heated at atmospheric pressure in a batch still unit. Timing of the run was started at the time initial decomposition (ffactionation) was observed, and the run was continued up to the formation of 50% distillate. The physicochemical characteristics of the components of the charge are listed in Table 1. The resuhs obtained in thermal processing of VCR, HPT, and blends of the two stocks are presented in Table 2. When the low-boiling aromatic additive is not present, the process is typical for cracked tars of this type. With increasing content of the HPT, the time corresponding to 50% distillate recovery becomes shorter. The longer time of 120 min that is observed for the blend with 5 % HPT can be explained by a "retardation effect" of thermocondensation processes that is observed in the thermal processing of cracked tars in mixture with a small amount of pyrolysis tar [4]. In the present series of experiments, the charge with 10% HPT proved to be optimal. From such a mixture, under otherwise equal conditions, a pitch with higher plasticity is obtained, with a greater yield. This pitch has a higher yield of coke residue and hence a higher pitch index (PI), which determines the processing and economic indexes of pitch production: