Catalyst evaluation and kinetic study for ethylene production

Abstract

The need to produce olefins via catalytic cracking has attracted increased attention in recent years. In this paper results are presented with catalysts composed of two or more of the following metal oxides: CaO, A1203, SrO, MgO, Ti02, Mn02, Zr02, and K20. A fixed bed reactor system was used to evaluate the catalysts with n-hexane as feedstock. The best results were obtained with calcium aluminate based catalysts. The higher olefins yields obtained with the new catalysts compared with a-Al203 are explained by the higher conversion obtained at the same process conditions. The kinetics of the pyrolysis of n-hexane was also studied. The overall decomposition reaction is first order both for thermal cracking and for cracking in the presence of catalyst 12CaO7Al203. The kinetic parameters estimated in the presence of the catalyst are kov/ = 4.57 X 106 cm3/(g-s) and Ew = 26130 cal/mol. Literature ReviewThe most commonly used method for manufacturing light olefins is introducing streams rich in paraffinic hydrocarbons, such as ethane, propane, and naphtha, into externally heated tubes. In this thermal decomposition process, the cracking reactions are controlled by varying the composition of the feed materials, the reaction temperature, and the residence time in the reaction tube.This method has some drawbacks, such as the high temperature required for cracking reactions, the deposition of coke in the tubes, and especially low selectivity in ethylene and other desired products (Nowak and Gunsehell, 1983).To overcome these problems, a serious effort started a few years ago to introduce catalysts in the process. Various catalytic processes for the preparation of olefins have been reported, but these processes have not yet been applied commercially because of various difficulties.

Steam Cracking of Naphtha in Packed Bed Reactors

“…The experiments carried out show that the yield of ethylene as a main product of steam cracking of naphtha does not change for some of the catalysts and for some catalysts it decreases compared to that for a packed bed reactor with inert material. This result is in contradiction to results published by others. − Figure compares the yield of ethylene over the metal oxide catalysts with the yield of ethylene in a ceramic packed bed reactor at different cracking severities. The catalysts 12CaO·7Al 2 O 3 , SrO·Al 2 O 3 , and Cr 2 O 3 ·Al 2 O 3 do not affect the yield of ethylene, but the catalysts MgO·Al 2 O 3 , MnO·Al 2 O 3 , and Ti 2 O 3 ·Al 2 O 3 reduce the yield of ethylene.…”

“…Lemonidou et al , proposed several types of catalysts consisting of different phases of calcium aluminate and other complexes of various metal oxides such as Mg, Mn, Ti, In, and Zr which have been tested in steam cracking of n -hexane. The selectivity ratio, defined as the weight of the target product (ethylene or propylene) to the weight of reacted n -hexane, is 10−18% higher than the selectivity ratio over α-alumina.…”

Molecular Simulation of the Catalytic Cracking of Hexadecane on ZSM-5 Catalysts Based on Reactive Force Field (ReaxFF)

“…Great efforts have been made with the catalysts used in FCC processes. − Early in 1915, an aluminum chloride catalyst was developed for FCC, and then an activated clay catalyst and silica/aluminum catalyst were produced subsequently. In 1945, the first commercial FCC catalyst was developed by Davision Company.…”

Downer Catalytic Pyrolysis (DCP): A Novel Process for Light Olefins Production

“…For example, raising the operating temperature will strengthen the thermal effect and produce more ethylene. During our experiments, the yield of ethylene was observed to increase from 9.17 wt.-% to 16.06 wt.-% when the cracking temperature increases from 637 C to 659 C. This is also a reason for the high ethylene yield in the HCC process at 700 C.…”