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Full Name:[Saheed Adewale Lateef]
Thesis Title:[Development of SSZ-54 catalysts for catalytic cracking of alkanes for production of light olefins]
Major Field:[Chemical Engineering]
Date of Degree:[June 2017]

 

A detailed study of the preparation of SSZ-54, an intergrowth of MTT and TON frameworks using a novel mixture of two templates; isopropyl amine (IPA) and 1,6-hexane diamine (DAH), was carried out with hydrothermal and microwave reactors. The characterization of the products done using X-ray diffraction (XRD), scanning electron microscopy (SEM) and aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM) unveil assemblies of needles with spans of about 1 micron and 20-30 nm in thickness, confirms the formation of SSZ-54. The amount of the structure directing agents, synthesis time and temperature were pivotal in the synthesis of SSZ-54 zeolite. Furthermore, we observed that the higher molecular weighted molecule (DAH) has more influence on the control of the metamorphosis of the SSZ-54 phase.

Catalytic evaluation of SSZ-54 zeolite with cracking of n-hexane reveals high activity, good selectivity to olefins and minimal paraffin. Also, SSZ-54 displays better catalytic performance than either of its component frameworks (MTT and TON frameworks) in offering better stability, slower resistance to coking and improved yield to olefins.

 

Investigation of the effects of alkali (NaOH + TEAOH) and acid (nitric acid) treatments on the properties and catalytic performance of proton-type SSZ-54 zeolite reveals no structural collapse, improvement in physicochemical properties and ultimately, better catalytic activity, selectivity to olefins with prolonged catalyst life than the parent samples.

 

Catalytic behavior towards change in reaction temperature reveals considerable drop in activity and overall olefin selectivity as temperature drops. Selectivity data shows increase in ethylene selectivity as temperature increases and more propylene at lower reaction temperatures.

 

Considering the methods of sample synthesis, microwave-assisted synthesis offers faster route than hydrothermal method. Also, microwave- assisted synthesized samples show better activities than hydrothermally-produced samples because of better structural and acidity characteristics.

In addition, the shape selective property of SZZ-54 zeolite to mainly olefins owing to its unique innate pore structure was demonstrated as the selectivity to BTX on SSZ-54 was minimized to ca. 1 % over 10 h time on stream in all the samples.

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