Studies On The Catalysts Of Catalytic Pyrolysis For Maximizing Propylene Yield

Propylene is an important basic feedstock of petrochemical industry. ZSM-5 is the active component of LTB-2, which is supporting catalyst of two-stage riser catalytic cracking pyrolysis for maximizing propylene yield (TMP) technology and which hydrothermal stability and heavy oil conversion need to be improved. In this paper, we have modified the zeolite and carrier respectively, carried out two studies: one is modifing ZSM-5 with rare earth and phosphorus to improve the hydrothermal stability of zeolite; the other is adding mesoporous acidic material to the catalyst to improve heavy oil conversion.We found that the optimal case for rare earth-phosphorus modifition is impregnating Ce in ZSM-5 and then impregnating phosphorus under the conditions of pH = 6.0. Impregnating Ce, P or Ce-P have little effect on the zeolite framework structure. There are some particles on the surface of Ce-Modified ZSM-5, which lead to crystallinity reduced and the amount of acid have the smallest increase. A small amount of P-modified ZSM-5 crystal gathered, and which acid amount have the biggest increase. Phosphorus can also inhibit the change of crystalline phase during the hydrothermal treatment. The surface of Ce-P modified ZSM-5 has no significant change and which acid amount increased medium. For modified ZSM-5, the downtrend of crystallinity was slower than that of base ZSM-5 with the aging time extending. Laboratory and industrial test results have proved: the catalysts which active component is Ce-P modified ZSM-5 has a substantial increase in hydrothermal stability, and its catalytic cracking activity has also been enhanced.Modified vermiculites have larger specific surface area, suitable pore volume and poresize. Acid-modified vermiculite has a tiny amount B acid; layer-pillared vermiculite has large quantities of B acid and a small amount of L acid. Pillared-layer can not be used in harsh reaction conditions of catalytic cracking process due to its poor structure stability. Acid-modified vermiculite was more stable, it can be used in catalytic cracking catalysts for improving the conversion of heavy oil. With the increasing of acid-modified vermiculite added, magnesium dissolution from acid-modified vermiculite neutralized the acid sites of ZSM-5, propylene and LPG yield were reduced. Acid-modified vermiculites were unsuitable to acting as activity carrier of catalytic cracking catalyst for maximizing propylene yield.The best preparation conditions of Mg-Al spinel materials are: preparing aluminum gel with hydrochloric acid; Mg-Al atomic ratio in the raw materials is equal to stoichiometric ratio of MgAl2O4; roasting mixed slurry at 800oC after dried. Modified spinel materials prepared by impregnation only have weak L acid, but modified spinel materials prepared by hydrothermal synthesis have a strong B acid and a small amount of strong L acid. After hydrothermal treatment, modified spinel materials prepared by hydrothermal synthesis showed better catalytic activity for cracking heavy oil. It could partially substitute for kaolin to improve the performance of catalysts for heavy oil catalytic cracking.