Coal Hydrocoprocessing with Tires and Tire Components

摘要

This paper shows that the addition of rubber from old tires to dry coal hydrogenation always has a positive effect and promotes the formation of oils. This is the first time that components from tire rubber have been coprocessed with coal in order to gain knowledge of the specific role played by each in coal—tire hydrocoprocessing. A subbituminous coal, typical of the northeast of Spain, which shows good conversions in dry hydrogenation at nonsevere conditions because it reaches 75% at 400℃ and 10 MPa for 30 min without a catalyst, was hydrocoprocessed with rubber from old tires, and the results are reported in this paper. The rubber used came from a mixture of old tires, which had been ground and from which the steel thread and the textile netting had previously been removed. The coprocessing of both materials was batch run at 350, 375, and 400℃, keeping constant the initial hydrogen pressure, 10 MPa, and the residence time, 30 min, but varying the ratio between both materials (1/0, 4/1, 2/1, 1/1, 1/2, 1/4, and 0/1) in the feed mixture. The influence of the feed composition was also studied for the first time. Despite the fact that total conversions and gas formation do not undergo significant variations in comparison with the ones when only coal is processed, oils conversion (43% at 350℃ and 45% at 400℃ with 20% coal-40% rubber feed) and oils selectivity (93% at 350℃ and 85% at 400℃ with 20% coal-40% rubber feed) show important increases, mostly when rubber-rich feeds are processed. Furthermore, asphalthenes formation decreases with increasing rubber percentages in the feed mixture. Results obtained show that the addition of rubber from old tires to coal hydrogenation always promotes the percentage of oils formation. To enter into the coal—tire interactions, three main components from the same tire rubber, carbon black (CB), polybutadiene (PB), and styrene-butadiene (SBR) were processed alone and with coal. In addition, polystyrene (PS) was coprocessed with coal. Conclusions show that CB catalyzes the process by promoting hydrocracking reactions, and secondary reactions, by breaking the hydrogenation products from direct hydrogenation, primary reactions, into smaller and lighter molecules leading to gas formation. PB addition has no affect at 350℃, but at 400℃ it significantly improves total conversions (from 75% to 88%) and oils conversion (from 12% to 36%), giving intermediate conversions at 375℃. With regard to SBR, significant improvements on results are already reached at 375℃. Model compounds were not used in this work, but from the bulk of results obtained from the 29 different experiments carried throughout this research, it appears that from all the possible interactions between radicals involved in the coal—rubber hydrocoprocessing, those implying the alkylation of the aromatic radicals from rubber by all the radicals involved in the process are promoted.