Abstract
LPG olefins (propene and butenes) are key building blocks in the petrochemical industry whose demand has been expanding steadily in recent years. The use of FCC (fluid catalytic cracking) units for conversion of triglycerides is a promising option for the future to boost production of LPG olefins. However, a need for innovative cracking catalysts is rising due to the different nature between petroleum and biomass-derived feedstocks. In this study, series of hierarchical ZSM-5 materials, namely, mesoporous ZSM-5, nanosized ZSM-5, and composite ZSM-5 were prepared, aiming to enhance the production of LPG olefins along with transportation fuels. Mesoporous ZSM-5 materials were synthesized by the postsynthetic modifications involving base treatment and subsequent acid washing, whereas nanosized ZSM-5 and composite ZSM-5 were synthesized by the direct-synthetic routes for a comparative purpose. The obtained materials were characterized by XRD, FTIR, N2 sorption, TEM, AAS, ICP-AES, and NH3-TPD, and their catalytic performance was assessed in the cracking of triolein as a representative of triglycerides under FCC conditions. It was found that the subsequent strong acid washing step of alkaline treated ZSM-5 for removal of aluminum debris and external acid sites is needed to improve the catalytic performance. The resulting mesoporous ZSM-5 material shows higher yields of the desired products, i.e., gasoline and LPG olefins than its parent, commercial ZSM-5 at the almost complete conversion (ca. 90 wt.%). The selectivity toward LPG olefins is also enhanced over all the hierarchical ZSM-5 materials, particularly high for composite ZSM-5 (ca. 94 wt.%). The improved diffusion and lowered acidity of the hierarchical ZSM-5 materials might be responsible for their superior catalytic performance.
Highlights
liquefied petroleum gas (LPG) olefins including propene and butenes are important raw materials for the petrochemical industry to produce various valuable products such as PP, acrylonitrile, propene oxide, MTBE ETBE, etc. [1, 2]
ZSM-5 zeolites have been extensively investigated for the catalytic cracking of triglyceridebased feedstocks [5,6,7,8,9,10]. e medium pore zeolite ZSM-5 has been found to be very selective to C5-C10 hydrocarbons which correspond to gasoline fraction [9, 10]
Mesoporous ZSM-5 materials were prepared by the alkaline and subsequent acid treatments of the parent, commercial ZSM-5 (Zeocat PZ-2/25, Zeochem AG) as previously reported [20], but with some modifications. e parent ZSM-5, coded as parent ZSM5 (P-Z), was first treated in the optimized NaOH aqueous solution (0.5 M) to generate mesopores. en, the alkalinetreated sample, coded as M-Z-AT, was further treated in a stronger HCl aqueous solution (1.0 M) to completely remove aluminum debris, which was formed and deposited on the external surface during the base treatment. e resulting mesoporous ZSM-5 material upon alkaline and acid treatments is labelled as M-Z-AAT
Summary
LPG (liquefied petroleum gas) olefins including propene and butenes are important raw materials for the petrochemical industry to produce various valuable products such as PP (polypropene), acrylonitrile, propene oxide, MTBE (methyl tert-butyl ether) ETBE (ethyl tert-butyl ether), etc. [1, 2]. Steam crackers and FCC units have accounted for the majority of LPG olefins, which are coproducts in the production of ethene and gasoline, respectively. The shale gas revolution has made ethane as a preferred feedstock for steam crackers, lowering the yield of LPG olefins by an order of magnitude [2, 3]. Us, for application of ZSM-5 as cracking catalysts for efficient conversion of triglycerides to liquid fuels and LPG olefins, a high demand for research occurs due to the different nature of fossil and biogenic. Most of available studies have performed on a single type of hierarchical ZSM-5 materials with the focus on production of fuels, gasoline
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