Title : High performance HZSM-5 zeolite catalysts for catalytic cracking of hydrocracking diesel to produce light olefins
Abstract:
A series of HZSM-5 zeolite catalysts were prepared for catalytic cracking of hydrocracking diesel to produce light olefins such as ethylene and propylene. The physiochemical features of HZSM-5 catalysts were characterized by various means of XRD, BET, XRF, NH3-TPD, SEM, TEM, OH-IR, Py-IR, 27Al-NMR, 29Si-NMR, etc. Their catalytic performances were evaluated and compared with those of the previously published or commercialized ones of similar kind. HZSM-5 zeolite catalysts with SiO2/Al2O3 ratio of 26 (20-50 nm) were treated with NaOH of various concentrations under a variety of treatment temperatures and duration, to elucidate the effects of treatment conditions on catalyst characteristics. The catalytic cracking experiments were conducted in a fixed-bed microreactor over HZSM-5 catalysts, by using hydrocracking diesel as reactant to produce light olefins. A batch of experiments were carried out to investigate the effects of reaction temperature, pressure and space velocity on the reaction yield. Accordingly, the optimal reaction conditions were identified to produce the most ethylene and propylene, which are ideal products by catalytic cracking. The NaOH treatment results showed that the BET surface areas of the zeolite samples first increased and then decreased, with the increase of the [OH]/[SiO2] ratio. A maximum value for BET surface area, which suggests the formation of mesopores, could exist when the [OH]/[SiO2] ratio was in a range of 0.19-0.57. It was also found that mesopores were most effectively formed in the zeolite samples when they were treated at temperatures between 60 oC and 80 oC for 5 hours. HZSM-5 zeolite catalysts, which were obtained under the determined optimal treatment conditions, were then applied for catalytic cracking of hydrocracking diesel to produce light olefins, e.g. ethylene and propylene, and to enhance the selectivity to ethylene in particular. The results showed that, with the reaction temperature being 650 oC and the weight space velocity being above 0.5 h-1, maximum yields of ethylene and propylene were achieved at 33% and 15%, respectively. These yields are effectively higher than those obtained with published or commercially available catalysts, whose ethylene yields are generally below 30%, with propylene being the favored product. The benefits of this work include: first, high performance HZSM-5 zeolite catalysts were obtained, outperforming the other competitive ones in producing more ethylene and propylene from hydrocracking diesel by catalytic cracking reaction; second, effects of treatment conditions on catalyst characteristics, as well as those of reaction conditions on product yields, were systematically investigated and well explained, providing researchers with useful guidance on achieving optimal conditions for relevant applications.
Audience Take Away
- The audience will be able to understand the mechanisms of catalytic cracking of hydrocracking diesel to light olefins over zeolite catalysts.
- The audience will improve their experimental skills and gain analyzing ability in their job.
- Other faculty could apply the methodology used in this research to develop catalysts, which meet their research demands.
- This provides an efficient optimizing method for experimentalists to simplify their work.
