Lishan Cui

The transformation of acid leached metakaolin to zeolite beta

Abstract Well-crystallized zeolite beta was synthesized by using acid leached metakaolin and tetraethylammonium hydroxide (TEAOH) respectively as the silica-alumina source and the structure-directing agent. The acid leached metakaolin was prepared by first calcining kaolin at 993 K to obtain metakaolin and then hydrothermally treating the metakaolin with 20 wt% HCl solution at 367 K. The change process from kaolin to metakaolin, then to acid leached metakaolin and finally to the beta product was monitored by means of XRD, SEM, FTIR and N2 adsorption techniques. The result reveals the formation of zeolite beta from acid leached metakaolin. Interestingly, the as-made beta product possesses a bimodal pore system composed of microporous structure of zeolite beta and mesopores inherited from acid leached metakaolin.

In-situ growth of ZSM-5 zeolite on acid-activated metakaolin

Abstract A series of acid-activated metakaolins overgrown with ZSM-5 crystals have been prepared by in situ crystallization of zeolite ZSM-5 on the acid-activated metakaolins with tetraethylammonium hydroxide (TEAOH) as the templating agent. The acid-activated metakaolin was obtained by first calcining China kaolin at 993 K and then treating the calcined kaolin, metakaolin, with 20 wt% HCl solution at 367 K. The composites synthesized were characterized by XRD, SEM, IR spectra and N 2 adsorption. It is found that the relative amount of ZSM-5 in the composite can be controlled by varying the reactant composition and by tuning the crystallization conditions. The results of N 2 adsorption indicate that the composites possess a bimodal pore system comprising mesopores inherited from acid-activated metakaolin and microporous structure of zeolite ZSM-5. Furthermore, the catalytic activity of the composite was tested by means of light diesel oil cracking reaction and compared with that of the mechanical mixture composed of ZSM-5 and acid-activated metakaolin. Interestingly, the composite-based catalyst exhibits better catalytic activity than the mechanical mixture.

ANIONIC EMULSION-MEDIATED SYNTHESIS OF ZEOLITE BETA

Well-crystallized zeolite beta is first synthesized in the anionic emulsion systems of cyclohexane/sodium dodecylbenzenesulfonate(SDBS)/pentanol/zeolite synthesis mixture. Beta materials are then characterized by XRD, SEM, and N2-adsorption techniques. Compared to beta samples grown using the same synthesis mixture in the absence of the anionic emulsion, the as-synthesized beta presents uniform and well-defined larger crystals. Interestingly, N2-adsorption results show that such beta sample possesses both ordered mesopores at 3.9 nm and macropores centered at 60.5 nm. These pores combined with the intricate micropores of the Beta crystal comprise the hierarchical porosity. The hierarchical pore-structured zeolite beta may have potential catalysis application in reactions involving large molecules. Additionally, control experiments are also performed to ascertain the effects of the individual emulsion components. Further synthesis study finds the transformation of zeolite beta to ZSM-5 through increasing oil contents, crystallization temperature and time.

Properties of oxide films grown on 25Cr20Ni alloy in air-H2O and H2-H2O atmospheres

The oxidation kinetics, surface morphology and phase structure of oxide films grown on 25Cr20Ni alloy in air-H2O and H2-H2O atmospheres at 900 °C for 20 h were investigated. The anti-coking performance and resistance to carburization of the two oxide films were compared using 25Cr20Ni alloy tubes with an inner diameter of 10 mm and a length of 850 mm in a bench scale naphtha steam pyrolysis unit. The oxidation kinetics followed a parabolic law in an air-H2O atmosphere and a logarithm law in a H2-H20 atmosphere in the steady-state stage. The oxide film grown in the air-H2O atmosphere had cracks where the elements Fe and Ni were enriched and the un-cracked area was covered with octahedral-shaped MnCr2O4 spinels and Cr1,3Fe0.7O3 oxide clusters, while the oxide film grown in the H2-H2O atmosphere was intact and completely covered with dense standing blade MnCr2O4 spinels. In the pyrolysis tests, the anti-coking performance and resistance to carburization of the oxide film grown in the H2-H2O atmosphere were far better than that in the air-H20 atmosphere. The mass of coke formed in the oxide film grown in the H2-H2O atmosphere was less than 10% of that in the air-H2O atmosphere. The Cr1.3Fe0.7O3 oxide clusters converted into Cr23C6 carbides and the cracks were filled with carbon in the oxide film grown in the air-H2O atmosphere after repeated coking and decoking tests, while the dense standing blade MnCr2O4 spinels remained unchanged in the oxide film grown in the H2-H2O atmosphere. The ethylene, propylene and butadiene yields in the pyrolysis tests were almost the same for the two oxide films.

Formation mechanism of micro-flows in aqueous poly(ethylene oxide) droplets on a substrate at different temperatures

The drying of aqueous poly(ethylene oxide) (PEO) droplet on a substrate at different temperatures was studied. It was found that the contact line receded when the substrate was at a temperature above 60 °C. Different nucleation behavior and surface profiles of PEO films were found in different droplets drying processes. The rheological properties of aqueous PEO solutions were studied to understand the mechanism of contact line recession and micro-flow in drying aqueous PEO droplets. It was found that at low temperature, the contact line was static because of great viscous stress; while at high temperature, it receded because of great Marangoni force and the decrease of viscous stress. It was indicated that Marangoni convection was inhibited by the outward capillary flow and viscous stress at low temperature, whereas it became dominant at high temperature. Two types of mechanism for surface profiles and nucleation of PEO film from drying droplets are proposed, providing a theoretical guide for polymer solution application in oil and gas foam flooding technology.