Access Type

Open Access Dissertation

Date of Award

January 2014

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemical Engineering and Materials Science

First Advisor

Simon Ng

Second Advisor

Steven Salley

Abstract

The purpose of this research is to minimize the gap between the production of biofuels and the production of petroleum-based fuels by developing catalysts that can utilize renewable non-food based feedstocks (waste vegetable oils, algal oil, brown grease, etc.) and have great performance under low operation conditions. In particular, green diesel has become an attractive biofuel due to its superior properties that are quite similar to petroleum diesel. Therefore, no modifications are required to existing infrastructures. Three distinct experimental phases have been identified in order to achieve the objective of this work as follow:

First, the hydrocracking of distillers dried grains with solubles (DDGS) corn oil over bimetallic carbide catalysts was explored for green diesel production. A catalyst composed of nickel−tungsten (Ni−W) carbide supported on Al-SBA-15 was designed based on the ability of nickel to adsorb and activate hydrogen and the potential of tungsten for hydrogenation reactions. Four different Ni−W ratios (1:9, 1:1, 2:1, and 9:1) were prepared by the impregnation method to study the effect of metal ratio on the catalyst structure, activity, and selectivity. Catalyst activity was evaluated in a fixed bed reactor at 400 °C and 650 psi (4.48 MPa) with a hydrogen flow rate of 30 mL min-1 and DDGS corn oil flow rate of 0.08 mL min-1. The catalysts showed significant differences in activity and selectivity, with the catalyst having a Ni−W ratio of 9:1 achieving 100% conversion of corn oil and 100% selectivity to diesel for 2 days. Results indicate that by minimizing metal alloy formation and enhancement of the metal dispersion leads to higher activity, selectivity, and durability of the catalysts. A dendrimer-encapsulated nanoparticle (DENP) method was employed to minimize alloy formation and increase the metal dispersion on the support. The catalysts prepared by the DENP method showed activity greater than that of the catalyst prepared by the impregnation method for the hydrocracking of DDGS corn oil.

Second, Nickel-based carbide catalysts combined with four different metals (Mo, Nb, W, and Zr) and supported on Al-SBA-15 were investigated for the hydrocracking of DDGS corn oil to produce biofuels under mild reaction conditions. The effects of the fractional sums of the electronegativities of the transition metals on the catalyst activities, selectivities, and stabilities were investigated. The closer the fractional sum of the transition metal electronegativities was to the electronegativity range of the noble catalysts (2.0-2.2), the better was the catalyst performance. The highest diesel selectivity was obtained from NiWC/Al-SBA-15, with a fractional sum of electronegativity of 2.06. The effects of doping a promoter (Ce) on the catalyst electronegativity and activity were studied. Adding Ce generally improved the catalyst performance, by adjusting the combined electronegativities nearer to 2.0-2.2. However, other parameters affected by Ce addition, such as textural properties, or the performance of individual metals could also impact catalyst performance. The NiNbC/Al-SBA-15 catalyst promoted with 5% Ce maintained stable activity for 168 h at 400 ◦ C and 4.48 MPa H2 .

Third, several Ni-based transition metal carbide catalysts supported on Al-SBA-15 were studied for the hydrothermal decarboxylation of oleic acid and soybean oil to produce diesel range hydrocarbons with no added H2. The effect of pre-reduction, sub-critical and super-critical water conditions on the catalyst activity and selectivity was investigated. Both the conversion of oleic acid and selectivity of decarboxylation products under super-critical conditions for each catalyst were about 2-times greater than at sub-critical conditions. In addition, the potential of these catalysts for utilizing aqueous phase reforming (APR) of glycerol for in situ H2 production to meet process demands was demonstrated. The performance of the catalysts increases with the addition of glycerol, especially for the NiWC/Al-SBA-15 catalyst. With the addition of glycerol, the NiWC/Al-SBA-15 catalyst showed greater conversion of oleic acid and selectivity to heptadecane; however, most of the oleic acid was hydrogenated to produce stearic acid. The highest conversion of oleic acid and selectivity for heptadecane was 97.3% and 5.2%, respectively. Furthermore, the NiWC/Al-SBA-15 catalyst exhibited good potential for hydrolyzing triglycerides (soybean oil) to produce fatty acids and glycerol, and then generating H2 in situ from the APR of the glycerol produced. A complete conversion of soybean oil and hydrogenation of produced oleic acid were obtained over the NiWC/Al-SBA-15 at super-critical conditions.

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