Study Of Fluidized Bed Propylene-Hydrogen Peroxide Gas-Phase Epoxidation And TS-1 Zeolite Catalysts Preparation

The new route of propylene-H2O2 gas-phase epoxidation to synthesize PO(G-HPPO),has been proposed and studied by our Laboratory since 2003.This solvent-free route exhibits great potential to completely overcome the shortcomings of propylene-H2O2 liquid-phase epoxidation.But it suffers from fast decompostion of H2O2 at high reaction temperature.To overcome this major challenge,previous studies were mainly focused on TS-1 zeolite modification and fixed-bed G-HPPO performance.Based on literature investigation,this dissertation,however,chooses to attempt a fluidized bed propylene-H2O2 gas-phase epoxidation with the aim to further improve the utilization of H2O2 of G-HPPO.The main research contents and results are shown as follows:Firstly,according to the particularity of G-HPPO,efforts were made to access a special laboratory-scale fluidized bed reactor and suitable microspheric TS-1 catalyst.Fortunately,a quartz fluidized bed reactor was finally developed.It had a double-pipe structure for the evaporation of H2O2,and worked in a fluidized state of bubbling bed under typical reaction conditions of G-HPPO.Besides,a microspheric TS-1 catalyst matrix was also developed by using nitric acid hydrolysate of ethyl osilicate as binder,which had good sphericity and mechanical strength.The microspheric TS-1 catalyst matrix contained 50?60 wt.%TS-1 zeolite(dry basis)and had an average volume particle size of 63?64 ?m.In order to enhance the catalytic performance of the microspheric TS-1 catalyst matrix,the hydrothermal modification method with alkali metal hydroxide solution established previously for TS-1 zeolite by our laboratory,was employed herein.After that,systematical fluidized bed G-HPPO studies were carried out by using the above-mentioned reactor and microspheric TS-1 catalyst.Results show that,the self-developed laboratory bubbling bed reactor and the microspheric TS-1 catalyst are usable for G-HPPO study.And that,the hydrothermal modification method with alkali metal hydroxide solution established previously for TS-1 zeolite by our laboratory,is also suitable for the modification of microspheric TS-1 catalyst matrix.It is worth mentioning that,the hydrothermal modification method would not notably modify the shape and particle size distribution of the microspheric matrix,but could enhance its mechanical strength.On this basis,a microspheric catalyst matrix containing 50 wt.%TS-1 zeolite(dry base)was employed to prepare the hydrothermally modified microspheric TS-1 catalyst GPO-1,by using an alkaline solution containing potassium ion and tetrapropyl amonium(TPA+)ion.The modification was conducted with different scale(0.1 L?10 L).Then,a comparison was made under the same reaction conditions by using the same catalyst(GPO-1)and reactor,in order to know which one is superior,the fluidized bed G-HPPO(the microspheric GPO-1 catalyst was used as-prepared)and the fixed bed G-HPPO(the GPO-1 catalyst was tabletting,crushed and then sieved for 40-60 mesh granulles for fixed bed reactor).Furthermore,blank experiments were conceived to understand the formation paths of some of the by-products in the fluidized bed G-HPPO.Results show that,the catalytic performance of microspheric GPO-1 catalyst prepared by carrying out the hydrothermal modification at different scales exhibited good reproducibility.Compared with fixed bed reaction mode,the fluidized bed reaction mode allows the G-HPPO to have clearly higher H2O2 utilization.When the fluidized bed G-HPPO was conducted in the presence of 10 ppm methylamine,and the following conditions,i.e.,reaction temperature=155? and n(C3H6)/n(H2O2)?6/1,were provided,the average values of propylene conversion,PO selectivity,H2O2 utilization and PO productivity of GPO-1 catalyst were seen to arrive at 14.1%,97.0%,85.3%and 7.7 kgpo·kgcat-1·h-1,respectively.These are the best results of G-HPPO ever obtained so far.In addition,the preparation of TS-1 zeolite via the chemical vapor deposition of TiCl4 on defective S-1 zeolite parent synthesized by conventional hydrothermal method was also attempted for the G-HPPO.So far,this work has an encouraging beginning.