Date of Publication

2006

Document Type

Master's Thesis

Degree Name

Master of Science in Chemical Engineering

Subject Categories

Chemical Engineering

College

Gokongwei College of Engineering

Department/Unit

Chemical Engineering

Thesis Adviser

Leonila C. Abella

Defense Panel Chair

Luis F. Razon

Defense Panel Member

Pag-asa D. Gaspillo
Elaine N. Tolentino

Abstract/Summary

Methane reforming reactions are important routes for the production of synthesis gas (H2 and CO). In the Philippines, natural gas is found in abundant supply and its primary component is methane (CH4). The reforming of methane using steam is typically operated in the industry at temperatures beyond 700oC. These high temperature conditions favor the formation of CO, but more particularly H2 gas. Carbon formation and deposition on the catalysts are likewise minimized at the said operating temperatures. Decreasing the temperature up to 500oC can potentially reduce energy expenditures. However, this may affect conversion and catalyst activity. Utilizing the right support material for nickel-based catalysts may lead to higher percentage conversions and catalytic activities even at relatively low operating temperatures.

In this study, the effect of low operating temperatures on the catalytic activity of nickel using various support materials was investigated in the methane steam reforming process. The support materials considered in this study included g-Al2O3, SiO2, TiO2, and ZrO2. The catalysts used were prepared by loading nickel at 5% on the various support materials using both the wet impregnation and dry impregnation methods as applicable. Information regarding the surface morphology of the test catalysts was determined using the SEM-EDX. The pore size and surface area were also determined using the BET Analyzer.

In all the trials that involved the investigation of the catalytic activity of the various catalysts included in the study, methane was injected into a U-tube plug-flow micro-reactor made of quartz. This methane was made to react with steam at a H2O/CH4 ratio of 4.0 by using helium as the carrier gas. Utilizing steam, delivered by the carrier gas Helium as it went through a saturator, methane was converted at 500, 600, and 700oC. Time course activity tests were conducted at 30-minute time intervals to capture possible catalyst deactivation due to carbon deposition.

Among all the catalysts tested, Ni/ZrO2 delivered the highest average methane conversion rate of 68.42% at the steam reforming reaction temperature of 500oC. This was attributed to the high mobility of oxygen atoms found in the crystal lattice of zirconia, similar to what was reported by other researchers in the past. The average methane conversion rates for Ni/g-Al2O3 and Ni/TiO2 at 500oC were 55.18% and 52.27% respectively. Ni/SiO2 performed the poorest among the group with an average methane conversion rate of 42.46%

In terms of catalyst stability, Ni/SiO2 was the only one that exhibited a noticeable downtrend in methane conversion rate within an 8-hour continuous cycle both at 600oC and 500oC. This confirmed the incompatibility of silica with the steam reforming process because of the presence of steam. It was mentioned in past researches that water tends to attack the surface bonds between silicon and oxygen atoms to form silanol species that are acidic in nature. This, in turn, encourages the formation of carbon deposits that deactivate the catalyst.

In general, percent (%) methane conversion increased with increasing steam reforming reaction temperature for all the catalysts tested. There was a significant increase in percent (%) methane conversion moving from 500oC to 600oC for Ni/g- Al2O3, Ni/SiO2, and Ni/ZrO2. However, further increasing the temperature to 700oC did not produce much difference anymore in percent (%) methane conversion, most likely since conversion values were already close to 100%. Ni/TiO2, on the other hand did not show as much increase in percent (%) methane conversion as the other catalysts did. This may be because of the phase transformation of anatase titania to the rutile form that may have affected the surface structure of the catalyst.

H2/CH4 Yield also increased with the increase in temperature from 500 to 600oC for all the catalysts except for Ni/TiO2. Consistent with methane conversion results, Ni/TiO2 performed as well as Ni/g-Al2O3 at 500oC but lost the performance at higher temperatures.

Abstract Format

html

Language

English

Format

Electronic

Accession Number

CDTG004063

Shelf Location

Archives, The Learning Commons, 12F Henry Sy Sr. Hall

Physical Description

1 computer optical disc ; 4 3/4 in.

Keywords

Catalysts; Nickel catalysts; Methane; Catalytic reforming

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