Study On Mesoporous Modification Of Catalytic Cracking Catalysts

Fluid catalytic cracking is an important mean to make heavy oil lighter,and fluid catalytic cracking unit is the main device for the production of 70%of gasoline,35%of diesel and 30%of propylene in petrochemical industry.The selectivity of the device affects the national economy and people's livelihood.With the intense trend of heavy feedstock oil,the rigid requirements of environmental protection regulations on carbon emission and the device's pursuit of long period operation,energy saving and consumption reduction,the existing fluid catalytic cracking catalysts have shown some problems of insufficient conversion capacity of heavy oil and poor coke selectivity.It is urgent to improve the conversion of heavy oil through improving the accessibility of active centers of heavy oil macromolecules and to inhibit the over-cracking coking reaction through improving the diffusion performance.The mesoporosity of catalysts is an efficient method to solve the above-mentioned problems and has aroused widespread concerns in academia.In the thesis,the mesoporous modification of FCC catalysts was investigated from catalyst preparation technology and active component zeolite,respectively.On the one hand,a FCC catalyst with good mesoporous structure and high wear resistance was prepared by modification with phosphate and mesoporous recovery technology under the condition of low cost and low pollution.On the other hand,Y zeolite with rich mesoporous and high crystallinity was prepared by mesoporous modification using hydrothermal-chemical acid treatment of industrial grade Y zeolite to reduce industrial amplification effect.Using a catalyst with low binder content,poor abrasion strength and rich mesopores as a raw material and a phosphate as a modifier,a new low-cost catalyst molding method which can flexibly control the wear index,pore structure and abrasion strength was developed.The effects of modification conditions on the catalyst were explored.The modified catalyst was analyzed and characterized.The reaction performance evaluation and reaction mechanism were also explored.The results showed that the best modification conditions were:using 3.2%?calculated with P₂O₅?of?NH₄?₃PO₄ as impregnating modifier and calcinating at 550 ^oC for 2.0h,then washing with ammonium salt.Compared with traditional catalyst,phosphorus-modified catalyst showed well characteristics.The wear index of phosphorus-modified catalyst decreased by 50.0%,the total pore volume and mesopore volume increased by 8.0%and 16.7%,respectively;the yields of dry gas and coke reduced by 0.10 and 0.72 percentage points,respectively;moreover,the total liquid yield and gasoline yield increased by 0.11 and 0.91 percentage points,respectively.It was found that the H₃PO₄ generated by phosphate hydrolysis interacted with the tetracentric aluminum produced by calcining kaolin matrix at high temperature to form the new phase of AlPO₄,and P–O–Al scaffold could stabilize the structure of the catalyst.To reduce the industrial amplification effect,industrial NH₄NaY zeolite was modified by hydrothermal-chemical acid treatment.Under the consideration of mesoporous volume and crystallinity,the optimal conditions were determined,i.e.,calcinating at 650 ^oC for 2.5 h with medium steam dosage,then reacting with citric acid under stirring at 80 ^oC for 1.0 h.Compared with USY zeolite,the total pore volume and mesopore volume of hydrothermal-chemical acid treated zeolite increased by 10.2%and 23.8%,respectively;the total B acid amount and the ratio of B and L acid amount increased,whereas the total L acid amount decreased.