Aromatic hydrogenation and sulfur removal via the water gas shift reaction using dispersed catalysts

Abstract

The purpose of this thesis is to investigate the hydrogenation of aromatic compounds and sulfur removal present in diesel fuel through in situ hydrogenation via the water gas shift reaction (WGSR). Naphthalene (NAPH) and benzothiophene (BTH) are the model compounds to represent the aromatic and sulfur contents of diesel fuel, respectively. The H2 generated in situ via the WGSR is utilized in the hydrogenation reaction by employing dispersed catalysts at the temperature of 340*C. The activity of the in situ H2 using an individual model compounds and binary mixtures of the model compounds will be compared. In addition, the activity differences among four types of MO catalysts (phosphomolybdic acid, molybdic acid ammonium-heptamolybdate-tetrahydrate and ammonium-tetrathio-molybdate), and four different catalyst concentrations based on Mo metals available in the phosphomolybdic acid catalyst (500, 1000, 1500, and 3000 ppm), will be addressed.

CO conversions in the presence of BTH or NAPH were found to be in the range of 92 - 94 % at 340*C using phosphomolybdic acid as a dispersed catalyst with a concentration of 1500 ppm of the Mo metal. Under the same operating conditions, a slightly higher CO conversion for the binary mixture (BTH + NAPH) of 95.5% is observed. The presence of benzothiophene and phosphomolybdic acid dispersed catalysts seems to be very effective in activating the water gas shift reaction.

Benzothiophene and naphthalene conversions were found to be 100% and 67.57% respectively in their mixture, under 600 psi CO/(2.5% H2S) initial loading pressure, with NAPH: BTH ratio of 3.2 mol/mol at 340*C and 1500 ppm Mo-metal concentration of the phosphomolybdic acid (PMA) catalyst. Variations of the CO loading pressure have more significant effects on NAPH conversions than the variation of water contents. Moreover, different Mo concentration produced even greater effects in the NAPH conversions. When the Mo concentration is 3000 ppm 82.3% NAPH conversion is obtained. Different Mo catalysts at the same Mo concentration (1500 ppm) produce essentially the same conversions of CO, BTH and NAPH for reaction duration of 4 hours.

The measured kinetics, based on sampling from a batch autoclave, were found to follow a pseudo first order reaction. The rate constant calculated for CO, NAPH and BTH, is 4.88 x 10-4, 7.33 x 10-5, and 7.87 x 10-4 (s-1), respectively. Ion chromatograph analyses of the aqueous solution indicated the presence of very small quantities of sulfate. This study demonstrates that the dispersed catalyst based on Mo and utilizing H2 in situ is highly efficient for aromatic hydrogenation and hydrodesulfurization reactions.