Date of Award

January 2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Brian Tande

Second Advisor

Wayne Seames

Abstract

A two-step process was developed for the production of aromatic hydrocarbons from triacyl glyceride (TG) oils such as crop oils, algae oils, and microbial oils. In the first step, TG (soybean) oil was non-catalytically cracked to produce an organic liquid product (OLP). The resulting OLP was then converted into aromatic compounds in a second reaction using a zeolite catalyst, HZSM-5. In this second reaction three main factors were found to influence the yield of aromatic hydrocarbons, namely the SiO2:Al2O3 ratio in the HZSM-5, the reaction temperature and the OLP-to-catalyst ratio. Upon optimization, up to 58 wt% aromatics were obtained. Detailed analyses revealed that most of the alkenes and carboxylic acids, and even many of the unidentified/unresolved compounds which are characteristic products of non-catalytic TG cracking, were reformed into aromatic hydrocarbons and n-alkanes. Instead of BTEX compounds that are the common products of alkene reforming with HZSM-5, longer-chain alkylbenzenes dominated the reformate (along with medium-size n-alkanes). Another novel feature of the two-step process was a sizable (up to 13 wt%) yield of alicyclic hydrocarbons, both cyclohexanes and cyclopentanes. At optimum conditions, the yields of coke (5 wt%) and gaseous products (14 wt%) were found to be lower than those in a corresponding one-step catalytic cracking/aromatization process. Thus this novel two-step process may provide a new route for the production of renewable aromatic hydrocarbons.

Aromatization of propylene was performed in a continuous reactor over HZSM-5 catalysts. A full-factorial design of experiments (DOE) methodology identified the effects of temperature (400-500 °C), Si:Al ratio (50-80), propylene feed concentration (8.9-12.5 mol%), and catalyst amount (0.2-1.0 g) on propylene conversion as well as the yields of benzene, toluene, p-xylene, o-xylene (BTX), and total BTX. The Si:Al ratio and amount of the HZSM-5 catalyst influenced all of the responses, while temperature impacted all the responses except the yield of p-xylene. An increase in feed concentration significantly increased the yields of benzene, toluene, and total BTX. An interaction between propylene feed concentration and catalyst amount influenced the yields of benzene, toluene, and total BTX. This interaction indicated that a higher feed concentration promotes aromatization at higher catalyst concentrations. By contrast, the interaction of Si:Al ratio with propylene feed concentration was found significant for p-xylene and o-xylene yields, but not for benzene and toluene, suggesting that xylenes are synthesized on different sites than those for benzene and toluene. These interaction effects demonstrate how the use of DOE can uncover significant information generally missed using traditional experimental strategies.

The catalytic conversion of propylene to BTX (benzene, toluene, xylenes) over nanoscale HZSM-5 zeolite was studied. A full-factorial design of experiments (DOE) methodology identified three factors which significantly affected the aromatization process: temperature (400-500 °C), propylene feed concentration (8.9-12.5 mol%), and catalyst amount (0.2-1.0 g). An increase in all three factors significantly increased the yields of benzene, toluene, and total BTX but decreased the yield of xylene. A DOE method was used to determine significant interaction effects which may be missed using parametric experimental strategies. The observed effects showed that nanoscale HZSM-5 catalyst is better suited for facilitating cracking rather than aromatization reactions presumably due to the smaller pore availability compared to micro-sized zeolites. Select experiments in a batch reactor with soybean oil as a feedstock showed that the nanoscale zeolite strongly retained large amounts of water, presumably within its pores, despite prior high temperature calcinations.

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