Study On Catalysts For Selective Ring Opening Reaction Of Heavy Diesel Aromatics

Selective ring-opening（SRO）technology is the most effective way to improve the cetane number of diesel and reduce the density of diesel under the premise of minimizing the loss of diesel oil.The development of catalysts with high selectivity for ring opening has become a focus of research.In this thesis,the effect of low-content noble metal Pt-based catalyst on the ring opening reaction of pretreated diesel oil was studied,including the Selection of molecular sieves,modification of molecular sieve,and hierarchical pore structure of carrier.the effects of different catalyst supports on the performance of hydrogenation and diesel combustion were investigated.In the case of the same low precious metal Pt content,ZSM-5,Beta,USY and SBA-15 zeolite sieves were selected.The USY molecular sieve showed the best hydrogenation and cracking activity due to its proper pore structure.The effects of different doping amounts on the FCC reaction were investigated by adjusting the acidity and pore size of USY zeolite carrier with Al₂O₃doping.The results show that with the increase of Al₂O₃doping content,the composite zeolite mixes evenly,the dispersity of Pt particles is high,and there is no agglomeration phenomenon.The particle size conforms to the normal distribution and the average particle size is about4.4 nm.The total acid content of the composite zeolite remains unchanged,the L acid content decreases slightly,the B acid content decreases slightly,the weak acid strength basically remains unchanged,and the strength of strong acid position and medium-strong acid position decreases.The specific surface area of the composite zeolite decreases,pore volume and pore size increase,the ring opening activity of the composite zeolite decreases,and the hydrogenation activity increases.When the doping content ofγ-Al₂O₃reaches 40%,the aromatics content decreases to 3.4%.the effect of Pt_0.4/40%Al₂O₃+60%USY catalyst on the ring opening selectivity of tetrahydronaphthalene was investigated in a fixed bed micro reactor under different reaction conditions,and the stability of Pt_0.4/40%Al₂O₃+60%USY catalyst was tested for more than 200 hours.The results showed that the catalyst exhibited the best catalytic activity when the reaction temperature was 300℃,the pressure was 6 Mpa,the ratio of hydrogen to oil was 750,and the liquid-space velocity was 2 h^-1.The content of aromatics remained at 3-6%within 200 h,and the cetane index increased steadily by 10 units.