Exploratory investigation on conversion behaviors and coking tendency during coal-based asphaltene hydrogenation processes

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Coking is an urgent problem to be solved in direct coal liquefaction（DCL）industry, and coal-based asphaltene is considered as the main source of coking. Therefore，in this manuscript, the effects of solvent/asphaltene ratio, temperature and hydrogen pressure on conversion behaviors of asphaltene were investigated, and coking propensity of asphaltene in relatively high temperature and hydrogen-deficient systems was focused. The results show that in the hydrogen-deficient system, temperature significantly affects asphaltene conversion and coke yield, which reaches 82.91% and 6.31% at 470°C. And moreover, with hydrogen pressure increases from 2MPa to 4MPa, oil yield increases from 65.28% to 71.16% while coke yield decreases significantly from 8.85% to 2.90%, which indicates that relatively increase hydrogen pressure can effectively stabilize the free radicals to produce oil and restrict the generation of coke at 470°C. With increasing temperature or decreasing hydrogen pressure, H/C atom ratio of hydrogenated asphaltene decreases to 0.54–0.82 at the temperatures of 430–470°C and 0.45–0.66 at hydrogen pressures of 2.0–6.0MPa, while the H/C atom ratio of asphaltene is 1.02. Besides, methyl and methylene carbons are easily cleaved, and protonated aromatic carbons are converted to bridgehead aromatic carbons during hydrogenation process, which increases the aromaticity of asphaltene from 61.43% to 83.90% at 470°C.

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