Hydrorefining Of Coking Crude Benzol Over NiMo And CoMoP/TiO₂-Al₂O₃ Catalysts

Coking crude benzene is the byproduct of coking industry, the composition of whichis very complicated , and the content of benzene, toluene, xylene can even reach 90percent. Crude benzene can't be directly used in the production of chemical productsuntil it is refined firstly to remove impurities, especially the high content of thiophene.As the environment protection is more valued today, the refining method of crudebenzene is transformed from the traditional sulfur acid washing technology to catalytichydrorefining technology. Among these hydrorefining methods, the low temperaturehydrorefining process, with low investment, simple operation and possibility to belocalization, is much more suitable for our country. Many plants for hydrorefining crudebenzene is being built these years, so to study and develop our own hydrorefiningcatalysts is becoming more important.TiO₂-Al₂O₃ composite oxide was selected as the support by comparison with otherAl2O3 supports. NiMo/TiO₂-Al₂O₃ and CoMoP/TiO₂-Al₂O₃ catalysts were prepared bymulti-step impregnation method. The effects of Ni(Co)/Mo mole ratio and phosphoruscontent on performances of these catalysts for hydrorefining of coking crude benzolwere evaluated in a fixed-bed microreactor, and reaction conditions for two-stagehydrorefining process of coking crude benzol were also determined.2Ni8Mo/TiO₂-Al₂O₃ and 2Co8Mo1P/TiO₂-Al₂O₃ were found as the two best catalystsfor pre-hydrogenation and main hydrogenation reaction of coking crude benzol, forwhich mole ratio of Ni to (Ni+Mo) and Co to (Co+Mo) were 0.325 and 0.324, and massfractions of NiO, CoO, MoO₃ and P₂O₅ were 2%, 2%, 8% and 1%, respectively.Thiophenic sulfur content of liquid product was zero and total recovery of benzene,toluene and xylene was kept over 99% , when the optimized reaction conditions were asfollows: first-stage temperature 190℃²30℃, second-stage temperature 310℃³60℃, pressure 2.0MPa³.5MPa, liquid hourly space velocity 2.0h-1³.5h-1 and volume ratioof H2 to Oil 350⁸00. The two kinds of catalysts exhibited good stability in a 160-hourlife test.The results of H2-TPR experiments showed that, the reduction performance of thecatalyst could be promoted by addition of TiO₂ ,as the content of octahedral Mo speciesthat can be reduced at low temperature increased. The interactions between the supportand Mo species decreased with addition of proper content of phosphorus. Excessivephosphorous may bring down the activity of catalysts for hydrodesulfurization.