Synthesis of mesoporous ZSM-5 from rice husk ash with ultrasound assisted alkali-treatment method used in catalytic cracking of light naphtha

A series of mesoporous ZSM-5 zeolite was synthesized with ultrasonic assisted alkali-treatment technique and their catalytic activity was investigated in catalytic cracking of light naphtha. ZSM-5 zeolite was synthesized from rice husk ash without using any organic template. Effect of alkali-treatment conditions on physicochemical properties of synthesized zeolite was investigated with XRD, FESEM, TEM, N2 adsorption-desorption isotherm, NH3-TPD and TGA technique. It was found that ultrasound energy facilitates the creation of hierarchical structure of ZSM-5 during alkali-treatment. According to XRD analysis, zeolite structure was preserved after 20 min ultrasonic assisted alkaline treatment. However, prolonged dessilication time led to the destruction of MFI zeolite structure. The synthesized ZSM-5 represented highly ordered hexagonal-shape morphology. With increasing alkali-treatment time, the plough land roughness appeared on the surface of zeolite. Comparison of the textural properties samples revealed that the mesopore surface area of alkali-treated samples increased considerably with the increase of ultrasonic assisted alkali-treatment time. Results from catalytic activity tests showed that ultrasound energy has great influence on the activity of ZSM-5. The sample had the highest activity after alkali-treated for 20 min in presence of ultrasound energy which was due to their appropriate hierarchical structure.     

碱处理对江蓠琼胶出胶率、性质和化学组成影响的研究

本文通过对在华南沿海采集到的１５种江蓠样品用两种优化碱处理工艺条件处理，分析了碱处理前后江蓠琼胶在凝胶强度、出胶率、琼胶分子组成及流变特性的变化规律和内在联系。研究结果表明，“硬质型”江蓠最佳碱处理工艺条件为８％ＮａＯＨ８５℃处理２ｈ；“软质型”江蓠为１０％ＮａＯＨ８０℃处理２ｈ。琼胶凝胶强度主要与江蓠琼胶的化学结构与组成（即硫酸基的含量与分布、单糖的组成与含量、琼胶的分子量等）有关。琼胶凝胶强度与硫酸基含量呈显著的负相关，与３，６－ＡＧ（３，６－内醚半乳糖）的含量、碱处理前后３，６－ＡＧ增加幅度、硫酸基含量减少幅度呈显著的正相关；与琼胶的绝对粘度、碱处理前的粘度呈显著正相关，与出胶率也有较显著的正相关。碱处理前后琼胶凝胶强度提高倍数与琼胶融点、凝固点提高幅度大小呈较显著的相关关系。     

Alkali-treatment of ZSM-5 zeolites with different SiO2/Al2O3 ratios and light olefin production by heavy oil cracking

Four kinds of ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios are alkali-treated in 0.2 M NaOH solution for 300 min at 363 K. Changes to the compositions, morphologies, pore sizes, and distributions of the zeolites are compared before and after alkali-treatment. The changes observed are largely influenced by the SiO₂/Al₂O₃ ratios with which the zeolites are synthesized. A possible mechanism of desilication during alkali-treatment is proposed. The SiO₂/Al₂O₃ ratio of zeolites is found to influence the yield of light olefins that use heavy oil as feedstock. Alkali-treated ZSM-5 zeolites produce higher yields of light olefins compared to either untreated zeolites or the industry catalyst CEP-1. It is believed that alkali-treatment introduces mesopores to the zeolites and improves their catalytic cracking ability. ZSM-5 zeolites with SiO₂/Al₂O₃ ratios of 50 also present superior selectivity toward light olefins because of their optimized hierarchical pores.     

Structure and apatite formation of microarc oxidized TiO2-based films before and after alkali-treatment by various alkali concentrations

Alkali-treatment was performed to modify the surface of the TiO₂-based film containing Ca and P prepared by microarc oxidation (MAO) technique for improving the apatite-forming ability of the MAO film. Before alkali-treatment, in the MAO film amorphous and crystalline regions with main composition of Ti, Ca, P and Al both were observed; and in the latter TiO₂ nanocrystals were randomly distributed in Ca- and P-doped matrix. After alkali-treatment, the surfaces of the MAO films become rough, and the Ca and P concentrations decrease with increasing the concentration of NaOH solution (1, 3 and 5 mol/L). When 5 mol/L NaOH solution was used, amorphous calcium titanate hydrogel was formed on the surface, showing a nanoflake-like morphology. In vitro experiment indicates that the ability to induce apatite formation of the alkali-treated MAO films increase with increasing the concentration of NaOH solution, which is associated with the formation of Ti-OH groups during the incubation process in a simulated body fluid.