Pathways in particle assembly by ultrasound-assisted spray-drying of kaolin/SAPO-34 as a fluidized bed catalyst for methanol to light olefins

摘要

Fluidized bed reactor and continuous catalyst regeneration system was proposed to overcome the effects of exothermic methanol to light olefins (MTO) reaction and achieve longer lifetime. The proper catalysts for fluidized bed reactor were usually prepared via spray drying method. The shaping of SAPO-34 with the matrix of kaolin and alumina sol binder was selected to prepare in spray dryer and test in fixed and fluidized bed reactor. The main properties of spray dried catalysts such as attrition resistance and micro-spherical morphology are necessary as well as good catalytic performance. The effects of ultrasound power on solid-liquid slurries were examined by the consideration of structural and catalytic properties of the spray dried catalysts. Ultrasound application for the slurries prior to spray drying leads to different particle size distributions and dispersion. Various models of particles assembly were obtained and discussed by XRD, FESEM, NH3-TPD, EDX, BET-BJH and FTIR techniques. Pore volume was increased by the application of lower ultrasound power. Its detailed analysis showed that 22 and 78% of the pore volume increase comes from the micro and mesopores, respectively. Ultrasound application prior to spray drying mostly have influence on the arrangement of particles resulted in mesopore volume enhancement. Formation of spherical and symmetric shaped particles is enhanced at the lower power of 45 W but it was not acceptable for the higher power of 90 W. The catalyst which was sonicated at the optimized power demonstrates improvement in physiochemical characteristics but showed higher attrition rate (30% increase compared to non-sonicated one). The catalyst experienced ultrasound irradiation prior to spray showed lower MTO reaction life time (432 min) as it was reported to be 850 min for non sonicated catalyst. Shorter life time of KSAPO-HU (P = 45) can be attributed to its lower mechanical strength.