Catalytic Cracking Of Supercritical N-dodecane Over Zeolite Catalysts

Micro-zeolites depending on its strong acid, high thermal and hydrothermalstability, have been widely used in the field of catalytic. However, the pore size of themicroporous limits the macromolecules adsorption and diffusion in the zeolite, whichaffects its catalytic activity. Increasing the intragranular mesoporous or externalsurface area of the molecular sieve, is an effective way to strengthen its diffusionproperties. This paper systematically studied the influence of alkali-treatment anddelamination processing on pore structure and acid nature of the cage-based MCM-22zeolite and the channel-base ZSM-11zeolite. Finally, using the cracking ofn-dodecane as a model reaction, a comparative study was taken on catalyticperformance of the two types of molecular sieve in structured reactor.First of all, mesoporous MCM-22zeolites were prepared using alkali-treatment.It was found that the super-cage structure in MCM-22zeolite was not affected withNaOH solution treatment, and the templating agent in MCM-22zeolite channelswould affect the alkali-treatment results greatly. Alkali treatment of MCM-22zeolitewith the templating agent existing only made the lamellar structure crush andproduced some accumulation mesoporous, leading to an increase in external surfacearea and the total acid amount which improvd the catalytic activity. For the samplewithout the templating agent existing, alkali treatment would generate muchintragranular mesoporous, but the degree of crystallinity decreased significantly tolead to a worse catalytic activity.Furthermore, a sequential swelling using cetyltrimethylammonium bromide andtetrapropylammonium hydroxide solution as a swelling agent and ultrasonicdelamination were processed on precursor MCM-22. It was found that pH=13.25,swelling temperature80oC,3h ultrasound treatment and the amount of CTMABradded in8.4times to the precursor would receive the largest stripped degree. And theXRD confirmed the sample after delamination was ITQ-2zeolite. Compared withMCM-22zeolite, ITQ-2gave the specific surface area more than700m2g-1andgreater strong Lewis acid amount, and exhibited more excellent activity and stabilityin the catalytic cracking of n-dodecane.Finally, the paper studied the pore structure change and catalytic cracking performance of alkali treatment on the channel-base ZSM-11zeolite. The samplesafter alkali treatment would generate4-15nm intragranular mesoporous withoutdamaging the microporous structure of the molecular sieve. The increase in externalsurface area and the amount of acid would greatly enhance the catalytic crackingactivity.