Semester

Summer

Date of Graduation

2001

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Edwin L. Kugler.

Abstract

The performance of fluid catalytic cracking (FCC) catalyst decreases due to the severe negative effects of metal contaminants (e.g., nickel, vanadium and iron) deposited on the catalyst from the hydrocarbon feed. The metal contaminants cause an increase in the production of gas and coke at the expense of gasoline.;In this work the effect of pretreatment with hydrogen and methane gases on the performance of commercial, metal-contaminated, FCC equilibrium catalysts was investigated. Cracking reactions of both sour imported heavy gas oil (SIHGO) and n-hexadecane were carried out in a microactivity test (MAT) unit using three commercial equilibrium catalysts with different metals concentrations. These catalysts were also characterized by temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), surface area measurements (BET/T-Plot), atomic force microscopy (AFM), and scanning electron microscopy in combination of elemental analysis by EDX (SEM-EDX). The characterization data were used in the interpretation of the MAT results.;MAT results have shown that pretreatment of catalysts with hydrogen and methane prior to cracking reactions decreases the yields of hydrogen and coke from gas oil cracking with a significant increase in gasoline yield. The decrease in hydrogen and coke yields with pretreatment was attributed to the lower dehydrogenation activity of reduced vanadium compared to oxidized vanadium.;In TPR spectrum the metal oxide represented by the peak at around 690°C was found to be active in dehydrogenation during cracking reactions. TPO experiments were carried out to determine the nature, and composition of the coke on the spent catalysts. TPO profiles were deconvoluted into four peaks (Peak K, L, M and N). The location of TPO peaks shifted to lower temperatures with increasing metal concentrations due to the catalytic effects of metals on the oxidation reaction. Peak L was assigned to the "contaminant" coke in the vicinity of metals. Surface area measurements indicated that the coke preferentially deposits in the micropores of the catalyst. AFM images have shown that roughness of surface decreased with increasing metal concentrations on the catalyst. These images also revealed the presence of debris on the catalyst surface. Iron was detected in some of these debris using SEM-EDX analysis.

Download

Share

COinS