رسائل ماجيستير
English
2014
DEVELOPMENT OF NANOSIZED ZEOLITES FOR CONVERTING METHANOL TO OLEFINS
Adnan M. Jarallah Al-Amer, Oki Muraza, أنس كرار جميل عبد الرحمن
كلية الهندسة-جامعة الملك فهد للبترول والمعادن · السعودية
Commercial zeolites used for methanol to olefins (MTO) reaction suffer from serious problems of fast deactivation and poor selectivity. One of the effective methods to overcome these problems is by fabrication of nanoscale high selective catalysts.To reduce the diffusion limitation in the MTO reaction, nanoscale crystal sizes of one-dimensional pore ZSM-22 zeolite has been developed. The prepared catalysts were characterized and tested in a model reaction with mass-transfer limitation, namely the methanol to olefins (MTO) conversion reaction.Nanocrystalline zeolite ZSM-22 with TON frameworks have been synthesized using conventional autoclave and microwave assisted hydrothermal methods. The effect of different synthesis parameters, such as crystallization temperature, time, and water content on the crystal size, surface area has been studied. The effect of adding surfactant and co-solvent on the ZSM-22 crystal size, morphology and crystallinity had been studied in details. The synthesized zeolites used in this work were characterized using a variety of methods, including powder X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), N2 adsorption–desorption measurements (BET measurement), temperature programmed desorption (TPD) and infra-red Spectroscopy (FT-IR).The prepared ZSM-22 zeolite was tested for the methanol to olefins reaction (MTO), Weight hourly space velocity (WHSV) of 1.03 g. g-1.h-1 was found to be suitable in the MTO reaction, temperature range of 350 - 450 oC was used; most of the experiments were done at 450 oC. MTO reaction over ZSM-22 nanocrystals exhibited a high selectivity for propylene and light olefins. At 100% methanol conversion, the selectivity to C2= - C4= olefins was 87% with 53% selectivity of propylene. Very low amounts of heavier compounds, paraffin’s 4% and heavier olefins 6%, were detected. By reducing the crystal size of ZSM-22 zeolite, deactivation rate can be reduced and high selectivity to propylene can be maintained. ZSM-22 crystal size of 100 nm was almost free of diffusion resistance, 300 nm was in the transition period, while 1000 nm was suffering from serious diffusional problems resulted in high deactivation rates.