An Experimental Study of the Performance of a Small Reformer for Hydrogen Generation
Date Issued
2007
Date
2007
Author(s)
Huang, Chih-Yung
DOI
zh-TW
Abstract
This study details the design and fabrication of a small reformer for the generation of hydrogen gas from a solution of methanol and water. The catalysts used for the methanol steam reforming process were CuO-ZnO-Al2O3, CuO-ZnO-Al2O3-Pt-Rh and Pt-Rh. The solution of methanol and water, when passed through the reformer, produced H2, CO, CO2, and small amounts of O2. As the CO in the products can induce degradation of the electrode in a proton exchange membrane fuel cell, the concentration of CO must be reduced to an acceptable level by preferential oxidation. The purification process used different contents of catalysts Ru and Pt; moreover, Co, Fe or water were also added in order to study the effect on the CO conversion rate and methane yield.
In general, the reformer system can be divided into two parts: one for the production of hydrogen and the other for the removal of carbon monoxide. The first experimental investigation produced hydrogen in the methanol reformer unit. The results show that both the methanol conversion and the hydrogen yield rates increase with temperature. Of the three catalysts tested, CuO-ZnO-Al2O3 provides the best performance at temperatures lower than 320℃; however, at higher temperatures, the performance of this catalyst deteriorates, while that of CuO-ZnO-Al2O3-Pt-Rh and Pt-Rh continues to improve. This suggests that the addition of Pt and Rh to the original CuO-ZnO-Al2O3 catalyst has a stabilizing effect upon the reforming process under higher temperature conditions. The results also show that a higher methanol feed rate reduces the methanol conversion rate but increases the hydrogen yield rate. It was found that both the methanol conversion and the hydrogen yield rates reduce as the steam-to-methanol ratio is increased. Finally, the performance can be significantly improved by introducing a turbulence inducer upstream of the catalyst carrier and by increasing both the length and the cell density of the honeycomb structure of the catalysts.
The purification of hydrogen involves a preferential oxidation (PROX) reaction. When the content of Pt in the base catalyst r-A12O3 was increased from 1wt% to 5wt%, the CO conversion rate was increased significantly at lower temperatures; however, the methane yield was lower at higher temperatures. When the Ru content was increased from 0.5wt% to 5wt%, the CO conversion rate was increased at lower temperatures and the methane yield increased with increasing temperature. As the cell densities of catalysts Pt and Ru were increased from 300 to 400CPSI, the ranges of the high CO conversion rates were similar, while the methane yields decreased. The effect of addition of Fe can increase the range of the high CO conversion rate and can also slightly suppress methane production. The CO conversion rate for the addition of a Co catalyst was increased at higher temperatures, while the methane yield was higher than that found upon addition of Fe. Finally, catalysts 5wt%Pt/r-A12O3 and 1wt%Ru-1wt%Fe/r-A12O3 remained stable throughout the 12-hour stability test.
The existence of water in preferential oxidation reactions can increase the CO conversion, especially with the 5%Pt catalyst; it can also reduce the methanation phenomenon of all catalysts used in the experiment at high temperatures, especially in the series of Ru catalysts. At a temperature of 220℃ and a water flow rate of 1 ml/min, the 1wt%Ru/r-A12O3 catalyst can reduce the methane concentration to 1414ppm. Therefore, it can decrease the loss of hydrogen and improved the efficiency of the reformer system.
Subjects
重組器
觸媒
甲醇轉化率
氫氣產生率
優先氧化反應
CO轉化率
甲烷產量
Reformer
Catalyst
Methanol Conversion
Hydrogen Yield
Preferential Oxidation
CO Conversion
Methane yield
Type
thesis
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