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The purpose of this study was to increase light olefins yield and selectivity in catalytic cracking of propane. Pretreatment of ZSM-5 zeolite was performed during calcination. First, lanthanum was loaded on the catalyst by wet impregnation method and then the effect of parameters, such as temperature(400–800 oC), time(120–480 min) and type of stream, on La-ZSM-5 zeolite was examined during calcination using central composite design(CCD) method. Based on the proposed models, the optimized condition for maximizing selectivity of light olefins for air stream was 680 oC and 310 min and for the nitrogen stream was 735 oC and 173 min that under these conditions, selectivity amount increased 24% for nitrogen stream and 19% for air stream as compared with H-ZSM-5 catalyst. The synthesized catalysts were characterized by X-ray diffraction(XRD) and temperature-programmed desorption(TPD) techniques. According to the results of NH_3-TPD, as the temperature increased, the number of strong acid sites(specially Bronsted acid sites) reduced and resulted in increased production of light olefins as well as catalyst stability. Accordingly, stability of the samples calcined with nitrogen stream was higher than the samples calcined with the air stream.
The purpose of this study was to increase light olefins yield and selectivity in catalytic cracking of propane. Pretreatment of ZSM-5 zeolite was performed during calcination. First, lanthanum was loaded on the catalyst by wet impregnation method and then the effect of parameters, such on temperature (400-800 oC), time (120-480 min) and type of stream, on La-ZSM-5 zeolite was examined during calcination using central composite design (CCD) method. Based on the proposed models, the optimized condition for maximizing the selectivity of light olefins for air stream was 680 oC and 310 min and for the nitrogen stream was 735 oC and 173 min that under these conditions, The synthesis catalysts were characterized by X-ray diffraction (XRD) and temperature-programmed desorption (TPD) techniques. According to the results of NH3-TPD, as the temperature increased, the number of strong acid reduced, resulted in increased production of light olefins as well as catalyst stability. of, stability of the samples calcined with nitrogen stream was higher than the samples calcined with the air stream.