Synthesis Of L Zeolites And Their Applications In The Selective Chlorination Of Toluene

Para-chlorotoluene is widely used in many industries such as the pharmaceutical, dye, pesticides, and so on. The research and development of para-chlorotoluene and its down-stream product plays an important role in the global economy. However, in the state-of-art chlorination of toluene, the selectivity for para-chlorotoluene is rather low and a large amount of ortho-chlorotoluene is produced, resulting in low atom economy. Zeolite L with one-dimension twelve-ring pore channel structure has been largly investigated in many fields such as adsorption-seperation, isomerization of normal alkanes, membrance separation, optical materials. Additionally, zeolite L shows a good prespect in the chlorination of toluene with high selectivity for para-chlorotoluene.In this thesis, we systematically investigated the chlorination of toluene on zeolite L with emphasis on the synthesis of zeolite L, post-treatment by ion-exchange, and improvement of the Si/Al ratio of zeolite L. This thesis mainly consists of four parts as follows:1. Zeolite L was synthesized by the hydrothermal method. XRD, SEM, N2adsorption-desorption, NH3-TPD and ICP measurements were used to characterize crystallinity, morphology, textural properties, acidity and Si/Al ratio of the samples. The effects of Al source, gel composition, crystallization temperature, crystallization time, additives on the crystallinity and morphology of the samples were investigated. Zeolite L with morphology in hexagonal columnar shape, disc-shape and ellipsoid shape were successfully synthesized. Finally, zeolite L with small crystal size of500nm was obtained. 2. Zeolite K-L with small crystal size was used in chlorination of toluene by sulfuryl chloride. The effects of catalyst amount, mole ratio of toluene to sulfuryl chloride, reaction temperature, and the protection gas on the reaction as well as the recycle of catalyst were investigated. Small-sized Zeolite K-L showed an exellent activity and selectivity for para-chlorotoluene, achieving para to ortho ratios (p/o) as high as3.3. After two-cycle used, the activity of the K type zeolite L decreased to a great extent. The possible reasons might be the destruction of zeolite L, confirmed by the significant reduction of BET specific surface area.3. An ion-exchange method with Na+or Li+was used to modify zeolite K-L. The modified samples were characterized by means of XRD, SEM, N2adsorption-desorption, NH3-TPD, AAS and n-butane adsorption measurements. The chlorination of toluene by sulfuryl chloride on the modified samples indicated that both the modified zeolite K8Na1-L and zeolite KLi-L show an improved catalytic activity and selectivity for para-chlorotoluene. Para to ortho ratios (p/o) as high as3.76can be obtained on zeolite K8Na1-L and3.9on zeolite KLi-L. The modified catalyst shows an improved stability. Nevetheless, after three-cycle used, the activity of the chlorination on the modified catalyst still decreased.4. To improve the stability of zeolite L, two methods were used to increase the Si/Al ratio of zeolite L. One is to add KF into the synthesis system and zeolite L with Si/Al of3.06was obtained, which was slightly increased compared to the one without KF (Si/Al=2.96). The other is to modify the obtained K-L by post-treatment, however, the crystallinity greatly decreased.