Effect of Steam Deactivation Severity of ZSM-5 Additives on LPG Olefins Production in the FCC Process

Abstract

ZSM-5-containing catalytic additives are widely used in oil refineries to boost light olefin production and improve gasoline octanes in the Fluid Catalytic Cracking (FCC) process. Under the hydrothermal conditions present in the FCC regenerator (typically >700 °C and >8% steam), FCC catalysts and additives are subject to deactivation. Zeolites (e.g., Rare Earth USY in the base catalyst and ZSM-5 in Olefins boosting additives) are prone to dealumination and partial structural collapse, thereby losing activity, micropore surface area, and undergoing changes in selectivity. Fresh catalyst and additives are added at appropriate respective levels to the FCC unit on a daily basis to maintain overall targeted steady-state (equilibrated) activity and selectivity. To mimic this process under accelerated laboratory conditions, a commercial P/ZSM-5 additive was hydrothermally equilibrated via a steaming process at two temperatures: 788 °C and 815 °C to simulate moderate and more severe equilibration industrial conditions, respectively. n-Dodecane was used as probe molecule and feed for micro-activity cracking testing at 560 °C to determine the activity and product selectivity of fresh and equilibrated P-doped ZSM-5 additives. The fresh/calcined P/ZSM-5 additive was very active in C12 cracking while steaming limited its activity, i.e., at catalyst-to-feed (C/F) ratio of 1, about 70% and 30% conversion was obtained with the fresh and steamed additives, respectively. A greater activity drop was observed upon increasing the hydrothermal deactivation severity due to gradual decrease of total acidity and microporosity of the additives. However, this change in severity did not result in any selectivity changes for the LPG (liquefied petroleum gas) olefins as the nature (Brønsted-to-Lewis ratio) of the acid/active sites was not significantly altered upon steaming. Steam deactivation of ZSM-5 had also no significant effect on aromatics formation which was enhanced at higher conversion levels. Coke remained low with both fresh and steam-deactivated P/ZSM-5 additives.

Valorization of Hazardous Organic Solid Wastes towards Fuels and Chemicals via Fast (Catalytic) Pyrolysis

“…The pyrolysis oil (12.6 wt.%) obtained by the use of ZSM-5 (40) zeolite catalyst has a very low organic content and contains mainly water due to deoxygenation/dehydration reaction of impurities of oxygenated compounds and fatty acids. The strongly acidic ZSM-5 zeolite induces cracking reactions of the paraffinic molecules formed via the initial thermal decomposition of the heavy oil waste towards small alkenes, which can be further converted to BTX monoaromatics via oligomerization/cyclization and dehydrogenation reactions on the Brønsted acid sites of ZSM-5, as discussed above for the Py/GC-MS catalytic pyrolysis results [11,71]. This mechanism is also supported by the increased content of ethylene and propylene in the gases, both being typical hydrocarbon catalytic cracking products, and can serve as a basis for the aromatization reactions.…”

Converting the Surplus of Low-Quality Naphtha into More Valuable Products by Feeding It to a Fluid Catalytic Cracking Unit

“…The fact that thermal effect has a bigger impact than the properties of the catalyst is in concordance with the essential role of the thermal cracking in the formation of the dry gas lump. 32,33 The composition of the dry gas lump has been also determined. Overall, ethylene is the main compound both for ECat-1 and ECat-2 (with average concentrations of 50 and 45%, respectively), but some trends have been observed.…”

Effect of steam de-alumination on the interactions of propene with H-ZSM-5 zeolites

“…Further reactions or isomerisations within the zeolite may lead to the formation of a molecule which is too large to move freely through the network leading to pore blockage and eventual catalyst deactivation. 6,13 However, while the zeolite's acid site density and the mean diffusion path within the zeolite are the most important contributors to the propene-zeolite interactions, these properties do not remain constant throughout the catalyst's useful lifetime. Hydrothermal conditions in catalytic use result in partial de-alumination of the zeolite framework with a corresponding reduction in the number of acid sites, since removing an aluminium atom also removes its associated Brønsted O-H acid group, and increases mesoporosity due to removal of portions of the framework.…”

“…15 Effects of this loss of acidity can be dramatic, with numerous studies reporting improved selectivity, stability and even activity in steamed zeolites relative to studies performed using fresh materials. 13,16,17 Knowledge of how these framework changes affect fundamental properties like propene diffusion and acid site bonding in the zeolite is therefore key to improved understanding of the catalytic activity and the mechanism behind these improvements. Changes due to de-alumination from catalytic use can be simulated by the steam treatment of fresh zeolite, allowing the generation of model zeolite materials whose properties closely match those of used or partially-deactivated catalysts.…”

“…Changes due to de-alumination from catalytic use can be simulated by the steam treatment of fresh zeolite, allowing the generation of model zeolite materials whose properties closely match those of used or partially-deactivated catalysts. 14,15,18 The low temperature oligomersiation of olens in HZSM-5 has been previously studied by 13 C NMR spectroscopy 19 and infrared spectroscopy. [20][21][22] These studies agree that at low temperatures olens such as ethene and propene readily form oligomeric species, and that the rates of oligomer formation vary with the Al content of the zeolite 21 and the distribution of acid sites within the zeolite crystals.…”