Identifier

etd-0924102-205423

Degree

Master of Science in Chemical Engineering (MSChE)

Department

Chemical Engineering

Document Type

Thesis

Abstract

New catalysts were prepared and studied for: (1) a model amidation with a hindered amine, diethylamine (DEA), to N,N¡¯-diethyltoluamide (DEET); (2) the oxidation of m-xylene (MX) to DEET¡¯s alkylaromatic precursor, m-toluic acid (MTA). In both cases the goal was to reduce waste associated with current processes. Thermodynamic analyses showed that the amidation to produce DEET from MTA and DEA was an equilibrium limited reaction with equilibrium constants (Ke) less than 41 at temperatures below 320¡ÆC. The kinetics on silica-supported titanium (¥³) (triethanolaminato)-isopropoxide (Tyzor TE), calcium hydroxyapatites and silica supported tungsten heteropolyacids were studied using a continuous reactor. Both porous hydroxyapatites and heteropolyacids on silica proved to be superior to merely supporting the Ti-amine complexes currently used as homogeneous catalysts. These acidic catalysts were more active, more stable in the presence of a gas phase, and, unlike previous heterogeneous catalysts examined for this reaction, could be used with near stoichiometric feeds. The best results (about 65-70% MTA conversion and 93-97% DEET selectivity) were obtained using supported tungsten heteropolyacids at a WHSV of 3-9 h-1 using a feed of molar ratio DEA/MTA/DEET = 1/1/0.4 at 300¨¬C and low pressure. The catalysts maintained activity for a few days. Deactivation was easily reversed by air regeneration. The kinetics of soluble Co, Co/Mn, Co/Mn/Br, and Co/Mn/Ce catalysts for m-xylene oxidation were studied using two kinds of semi-batch reactors. Xylene oxidation was also tested in supercritical-CO2 solution using a supported Co-imide complex as a catalyst. When the oxidation was performed in a large stirred autoclave at PO2 = 0.51 MPa and 170¨¬C, using Co/Mn/Ce as catalysts, and in the presence of recycle aldehyde/alcohol mixture, the best results (68% MX conversion, 76% MTA selectivity) were obtained in 15 h. A Ce-salt promoter can effectively substitute for corrosive bromide salts, and recycle alcohol/aldehyde mixture can substitute for an acetic acid solvent.

Date

2002

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

F. Carl Knopf

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