Sepiolite In Situ Crystallization Of Y Zeolite And Its Raw Oil Hydrocracking Performance

Sepiolitic FCC catalysts were successfully synthesized via an in situ crystallization method. Feedstock oil was catalytically cracked on the fixed fluid bed (FFB) using the as-prepared catalysts, and the reaction mechanism of catalytic cracking as well as the physicochemical properties of the feedstock oil were analyzed. The as-synthesized Y zeolite was characterized by XRD, SEM, FT-IR, N2 adsorption-desorption and solid NMR. The formation mechanism of zeolite NaY was studied by a kinetic model.(1) The microporous NaY zeolite has been hydrothermally synthesized by in-situ crystallization using sepiolite as silica source and kaolin as aluminum source, and characterized by XRD and SEM. The effects of molar ratios of starting materials and crystallization temperatures on the relative crystallinity of the products were particularly investigated. The research results showed that the crystallization temperature is the most important factor for the synthesis of zeolite NaY. The relative crystallinity of the samples markedly increase with raising the crystallization temperature. When the crystallization temperature reaches 100℃, excellent zeolite crystals with high relative crystallinity were obtained. The relative crystallinity of NaY zeolite enhances with the molar ratio of SiO2/Al2O3 declining. The increase of the molar ratio of Na2O/SiO2 and decrease of the molar ratio of H2O/Na2O in the reaction system favor the formation of NaY zeolite. It was found that the molar ratio of SiO2/Al2O3 played a dominant role in the molar ratios of starting materials. The optimizing crystallization conditions were obtained with the crystallization temperature of 100℃, crystallization time of 24 h, SiO2/Al2O3 of 4.7, Na2O/SiO2 of 0.60 and H2O/Na2O of 39.2, under which the relative crystallinity of the as-synthesized product was 60%.(2) The changes of solid phase or liquid phase components were investigated at different crystallization times with all starting materials were mixed and reacting in an autoclave at 100℃. In the solid phase, SiO2 content decreases first followed by increasing. The increase of SiO2 content is accelerated after 4 h and tends to stop after 8 h. The content of Al2O3 becomes stable after 2 h, while the content of Na2O increases with prolonging the crystallization time. Certain amount of silica-alumina gel phase exists in the solid phase. The content of SiO2 increases firstly and then decreases in the liquid. The content of A12O3 decreases rapidly at the beginning of the reaction and becomes stable after 10 h, while the Na2O content decreases with prolonging the crystallization time. The crystallization induction periods vary with the crystallization temperatures. The crystallization induction periods are 2,7 and 8.5 h at 100,90 and 85℃, respectively. NaY zeolite crystals start to grow at the induction period and the growth rate reaches the highest at 24 h. The molecular sieve content increases with elevating the crystallization temperature at the same crystallization time. Sepiolite in-situ crystallization belongs to spontaneous nucleation system, and the activation energies of nucleation, transition state and crystal growth are 115.9 KJ/mol,123.5 KJ/mol and 29.47 KJ/mol, respectively.(3) The alkaline solution, sodium silicate, directing reagent, sepiolite and metakaolin microspheres were put into a autoclave to prepare NaY zeolite by in-situ crystallization. Sepiolitic catalysts were obtained after modifications. The mechanism of catalytic cracking and properties of feedstock oil were analysed. Atmospheric residue (AR) as well as different proportion VR-mixed wax oil were evaluated on the FFB. At the same time, the acidities and pore structures of the sepiolitic catalysts were also analyzed. Catalytic cracking reaction is conducted as follows: the carbon cations are formed behind the reaction of hydrocarbon molecules with the acid centres, resulting in many reactions. Both of the properties of feedstock oil and the physicochemical properties of catalysts have the influence on the percent conversion of feedstock oil and the distribution as well as the yields of products in the cracking reaction. Sepiolitic catalysts have moderate acid strength and density, relatively big BET and mesoporous volume, benefiting the cracking reaction of heavy oil.