Graduation Year

2019

Document Type

Thesis

Degree

M.S.C.H.

Degree Name

MS in Chemical Engineering (M.S.C.H.)

Degree Granting Department

Chemical Engineering

Major Professor

Babu Joseph, Ph.D.

Co-Major Professor

John Kuhn, Ph.D.

Committee Member

Scott Campbell, Ph.D.

Keywords

Synthetic Fuel, Biofuel, Heterogeneous Catalysis, Syngas

Abstract

Development of an effective High Temperature Fischer-Tropsch Synthesis (HTFTS) catalyst is of interest in process intensification that combines methane reforming with long chain hydrocarbon production. Literature indicates iron catalysts supported on mesoporous silica performed relatively well in high temperature applications. In this work, we investigated the effect of manganese promoter on iron catalysts for FTS at 430 °C as it was known from previous studies that manganese promotion could enhance the CO conversion with higher hydrocarbon yields. Also, the effect of temperature on FTS activity was evaluated by testing the base and promoted Fe/SBA-15 catalysts for temperature ranging from 370 to 430 °C.

Incipient wetness impregnation method was used to prepare the catalysts. The catalysts used in this work were un-promoted iron (15 wt%) and Mn promoted (1.4, 2.8, 4.2, 5.6, 11.2 wt%) iron (15 wt%) catalysts supported on SBA-15. The catalysts were characterized using XRD, TPR, N2 Physisorption, and SEM. These catalysts were first activated in synthesis gas (H2: CO = 2:1) at 430 °C and then tested for their catalytic performance at the same temperature and atmospheric pressure. Prior work with SBA-15 supported iron catalysts showed that manganese promotion could improve the CO conversion when compared to copper and potassium.

The main goal of this work was to study the effect of varying the manganese content on SBA-15 supported iron catalysts to determine the optimum loading of Mn along with the effect of temperature. It was found that CO conversion increases from 27% to74% with increasing the amount of manganese. The yield of CO2 increased substantially with higher Mn loadings. When different Mn promoted iron catalysts were compared, the catalysts with 2.8 wt% Mn loading showed the best performance in terms of the CO conversion and yield of C2+ hydrocarbons. Catalyst with 2.8 wt% of manganese loading yielded a CO conversion of 54%, with a methane yield of 17%, 32% (carbon) yield of C2- C4 and 9%(carbon) yields of C5+ hydrocarbon products, respectively.

The effect of operating temperature on the catalytic performance of both the base catalyst 15Fe/SBA-15 and the promoted 2.8Mn/15Fe/SBA-15 catalyst was also examined. The unpromoted iron catalyst showed an improved catalytic activity at 400 °C with the total CO conversion of 38% and a higher yields of C5+ hydrocarbons. A significant decrease was also observed in the yields of CH4 and CO2. The methane and carbon dioxide yield increased from 11% and 8% to 25% and 40%, respectively, as the temperature increased from 400 to 450 °C. The catalyst with 2.8 wt% of manganese promotion gave better CO conversion and hydrocarbon product yields at 430 °C. Lower temperature showed negative effect on hydrocarbon product yield for manganese promoted catalysts.

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