Kinetics of the hydro-deoxygenation of stearic acid over palladium on carbon catalyst in fixed-bed reactor for the production of renewable diesel

Date of Award

2013

Degree Name

M.S. in Chemical Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Advisor: Kevin J. Myers

Abstract

Biological oils are potential sources of liquid transportation fuels. In the presence of a precious metal catalyst under reducing conditions, the transformation of biological oils to liquid fuels proceeds sequentially. First, any double bond is quickly saturated. The double bond saturation is followed by the hydrogenolysis of the ester linkages which releases the saturated fatty acids from the propane backbone. The fatty acids are then deoxygenated producing n-alkanes. Typically, the n-alkanes are further treated to meet the required physical properties of a particular fuel fraction. Although important, the deoxygenation of the fatty acid had not yet been studied in production-like conditions. For this reason, in this study, a comprehensive investigation of the deoxygenation of a representative fatty acid was carried out by studying stearic acid (S.A.) diluted in a highly isomerized C24 solvent. The deoxygenation of stearic acid was studied in the presence of hydrogen, in a trickle-bed reactor by using a 3 wt % carbon-supported palladium catalyst. In order to simplify the study of the kinetics of the S.A. deoxygenation, a uniform S.A. concentration across the catalyst bed was desired. For this reason, the entire study was conducted under differential conditions, by limiting the S.A. conversion to 10 percent. The limited conversion allowed me to assume uniform S.A. concentration across the catalyst bed. The liquid products were identified early on as n-heptadecane, n-octadecane, and stearyl stearate. The rate of formation for each liquid product was examined over wide-ranging sets of temperature, initial S.A. concentration and hydrogen pressure. Kinetic data for the different products were graphically derived and rate expressions were developed and presented. The S.A. deoxygenation reaction network in the presence of hydrogen was found to be rather complex. The observed rate of n-heptadecane production was a combined rate of two reactions, the stearic acid decarboxylation and the octadecanal decarbonylation. Likewise, the observed rate of n-octadecane production was the sum of the rates of octadecanol reduction and stearyl stearate hydrogenolysis. In order to estimate the contribution of each of the rates of S.A. decarboxylation and octadecanal decarbonylation to the total rate of n-heptadecane production, the relative rate of CO/CO2 production was studied over a range of temperature and hydrogen pressure. And, in order to estimate the contribution of the rate of alcohol reduction and the rate of stearyl stearate hydrogenolysis to the total observed rate of n-octadecane production, a complete study of palmityl stearate hydrogenolysis was carried out to estimate the stearyl stearate hydrogenolysis partial contribution to the overall rate of n-octadecane production.

Keywords

Stearic acid Deoxidizing, Biomass energy Research, Renewable energy sources Research, Alternative energy; chemical engineering; chemistry; energy; materials science; organic chemistry; physical chemistry; deoxygenation; Pd on C; stearic acid; renewable diesel fuel; green diesel; fatty acids; hydrogenation of fatty acids; palladium catalyst; decarboxylation of fatty acid; decarbonylation; hydrocarbons production; algae oil refining

Rights Statement

Copyright © 2013, author

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