Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor(s)

Sohrab Rohani

Abstract

This thesis is focused on the synthesis of nano-size (50-100nm) NaY zeolite crystals inside the micro/meso pores of preshaped amorphous silica particles of size 50 micrometer using a dry process, which reduced several operational steps and the zeolite synthesis time that are generally required for current in-practice processes. Three types of reactors namely; polypropylene bottles, a stainless steel tubular reactor, and a novel vibrated baffles fluidized bed (VBFB) reactor coupled with infrared radiation emitters were used to evaluate the effects of different operating parameters on the synthesis of NaY zeolite. The synthesis process took place without using any structure directing agent and, due to using a dry synthesis technique, no significant chemical waste was generated. A parametric study revealed that an silica/alumina ratios above 6.6 did not produce any appreciable zeolite within the time frame of 24 h at 100C. The optimal silica/alumina ratio was found to be 6.1 for 16 h of synthesis at 100C in polypropylene bottles. The use of a stainless steel tubular reactor reduced the synthesis time to 8 h owing to its higher thermal conductivity as compared to polypropylene. Synthesis in the stainless steel tubular reactor reduced the synthesis time to 15 min while operating at 170C without any zeolite phase transformation. An operating temperature beyond 170C was not recommended due to NaY zeolite phase transformation to analcime. The effects of different concentrations of NaOH revealed that concentrations below 20wt% retarded the synthesis process whereas higher concentrations up to 32wt%, not only accelerated the synthesis but also resulted in the production of smaller crystals, less than 50nm in size. An NaOH concentration beyond 32wt% was not recommended due to dissolution and loss of structure of silica particles. The novel VBFB reactor produced single crystals in the size range of 300-600nm at 100C in 5 min. Using IR radiation for fast heat transfer accelerated the surface integration mechanism and led to the growth of crystals in 5 min. The synthesized NaY zeolite was tested for FCC reaction in a riser simulator after an ion-exchange with ammonium nitrate. A high conversion of 1,3,5-tri-isopropylbenzene in the range of 55-65% was obtained with a loss in conversion by 10% after regeneration. The as-synthesized NaY zeolite within silica particles was also tested for desulfurization of model hydrocarbons containing thiophene. The desulfurization through adsorption was achieved by removing thiophene from 500 ppmw to less than 15 ppmw in hexanes and a mixture of p-xylene in hexanes. The removal of 500 ppmw thiophene could not be achieved below 300 ppmw while using the mixture of toluene in hexanes. The as-synthesized NaY zeolite performed better for thiophene removal as compared to other adsorbents like silica, commercial NaX and NaY pellets, and commercial NaY fine powder.


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