Inhibition of Diolefin Hydrogenation by Quinohne

摘要

This study addresses the hydrogenation of olefins as related to their removal from thermally cracked bitumen. The inhibition effect of a nitrogen base is evaluated on the model feed comprising a conjugated diolefin 2,5-dimethyl-2,4-hexadiene (0.5 wt % in decalin), quinoline Q(0-250 ppm of N), and dibenzothiophene DBT (5.8 wt %). The reactions were performed with a Ni catalyst at 10 bar H-2 pressure and in a temperature range of 125-150 degrees C. The diolefin is converted to equal amounts of alkenes 2,5-dimethyl-2-hexene and trans-2,5-dimethyl-3-hexene, Qis hydrogenated to 1,2,3,4-tetrahydroquinoline, and DBT remains intact. The Qaddition was found to inhibit the hydrogenation rate, but not the product distribution. The Qfree diolefin hydrogenation follows first order to diolefin. When Qis present, the diolefin hydrogenation order to diolefin changes to 0 with the negative first order to the total concentration of nitrogen bases. The Qhydrogenation follows the zeroth order to the Q The activation energies of the diolefin and Qhydrogenation in the presence of 100 ppm of N were found to be 123 and 82 kJ/mol, respectively. A Langmuir-Hinshelwood mechanism was suggested to explain the shifting reaction orders. It is likely that there are at least two types of active sites that interact with diolefin and quinoline differently. This study indicates that higher temperatures are preferable for diolefin hydrogenation and that the rational design of active sites, which are less susceptible to nitrogen poisoning, is warranted.