The Pilot Studies On The Synthesis Of Zeolite L And Its Application In FCC Catalyst

Zeolite L possesses a LTL type framework topology and hexagonal crystalline structure with pores bounded by 12 rings. It was mostly used in the process such as dehydrogenation, reforming and other applications, howerver, there is previously scarce report but desired catalytic properties about zeolite L when used in hydrocarbon cracking reaction. For this reason, on the basis of previous laboratory work, the synthesis condition of zeolite L including ion-exchange, ultra stabilization and rare earth modified method were optimized further. Thus, zeolite L was successfully synthesized in 5 liters and 1000 liters autoclave, and modified zeolite L was used as an additive component of the fluid catalytic cracking (FCC) catalysts, which was investigated in the distributions and qualities of the products from micro-activity testing(MAT), fixed fluid bed(FFB) and riser reation.For increasing the ion-exchanged rate, the dynamic drip washing method was applied in the process, decreasing the K₂O content in zeolite L(less than 2.5 wt%). In order to prepare ultra stable zeolite L(USL), it is optimized through using the dynamic hydrothermal treatment and self-steam calcined method with rotating material in a close furnace substitute for the static self-steam calcined method. The zeolite USL was modified by composite rare earth (RE, contaning La and Ce) substituted for single rare earth (La or Ce). The results showed that the performances of FCC catalyst added zeolite USL modified by proper amount of composite rare earth were superior to zeolite USL modified by single one. In addition, zeolite L mixed with zeolite W was introduced in the FCC catalyst, the effect of zeolite W on the catalytic activity and the quality of the product was firstly investigated. The results suggested that the proper amount of zeolite W added to FCC catalyst was effective to the catalytic activity and product distributions of catalyst.The phase structure, crystal morphology, surface area, pore diameter distribution, framework structure and acid properties of zeolite L synthesized in the 5 liters and 1000 liters autoclaves were characterized by XRD, SEM, N₂-sorptiom FT-IR,Py-FTIR and NH3-TPD techniques. The results showed that the relative crystallinities of as-sythesized L were more than 90%, morphology was regular, average crystal partical size was about 1μm. After hydrothermal treatment, the framework SiO₂/Al₂O₃ (mole ratio) of ultra stable zeolite L was 20-30, which relative crysallinity, BET surface area and pore volume were more than 65%, 300 m²g^-1 and 0.2cm³g^-1, respectively. Zeolite USL exhibited higher L/B value (the ratio of L acid amount to B acid amount) of 0.61 to 0.85 and hydrothermal stabilization (the crystallinity retetion is more than 70%). The catalysts obtained from 5 liters scale-up zeolite L were evaluated by the FFB with the different feed stock, compared with reference catalyst, the conversion increased by 2.9-5.2%, the iso-paraffms increased by 1.0-2.2 wt%, the aromatics increased by 1.0-2.1 wt%, the content of olefins decreased by 1.3-2.8 wt%, and research octane number(RON) increased by 1.0～1.4 units in gasoline product.In the pilot sythesis of zeolite L with 1000 liters, the relative crystallinity of as-synthesized L was more than 80%, the framework SiO₂/Al₂O₃ of zeolite USL is 20-30. The catalytic cracking performances were excellent when used the RE-USL as active component. The total liquid yield increased by 1.0-2.5 wt%, the total content of iso- paraffins and aromatics in result product increased by 4.0-7.0 wt%, the content of olefins decreased by 2.0-5.0 wt%, while the octane number increased 1-2 units.In summary, the pilot synthesis of zeolite L was successfully carried out, and as a novel active additive of FCC catalysts it could advance the cracking activity of the heavy oil, the product distribution and the gasoline quality. The zeolite L is a novel type of catalytic material for the deep processing of the heavy oil.