Return to the process flow of the fuel processing system
Osaka Gas has developed its unique high-performance PROX (preferential oxidization) catalyst for ENE・FARM.
- CO is reduced through preferential oxidization process: in this process, air is added to the CO shift converter outlet gas, and carbon monoxide (CO) reacts with oxygen (O2) on a catalyst, which is made of a noble metal, such as Pt (platinum) or Ru (ruthenium), and eventually is converted into carbon dioxide.
CO preferential oxidation reaction
* The molar ratio of O2 in the air added for preferential oxidation to CO in the CO shift converter outlet gas is referred to as the [O2]/[CO] ratio.
- In the low temperature region, insufficient activity prevents the CO from being removed completely. In the high temperature region, the effect of a decrease in selectivity and side reactions such as reverse shift reactions causes the CO concentration to increase. (See the illustration.)
- Osaka Gas’ new catalyst (Ru-based) is capable of removing CO to less than 1 ppm level. In addition, it has a very wide temperature range, allowing it to be used between 85 and 170˚C (optimum temperatures: 100 to 130˚C). For this reason, the new catalyst is highly robust and easy-to-use for the reactor design.
- A conventional catalyst cannot remove CO down to a level of less than 10 ppm without increasing the [O2]/[CO] ratio to 3. For this reason, in general practice a CO preferential oxidizer is designed in two stages, the first of which roughly removes CO with the [O2]/[CO] ratio set at about 1 and the second of which removes the CO down to a level of less than 10 ppm with the ratio set at about 3.
- Osaka Gas’ catalyst is capable of removing CO to a level of less than 10 ppm even when the [O2]/[CO] ratio is equal to 1. Since CO is removed to a level of less than 1 ppm with the [O2]/[CO] ratio equal to 1.5, CO is removed using a one-stage reactor. With the fluctuation in control and the catalyst performance after deterioration taken into consideration, an [O2]/[CO] ratio equal to 1.5 is used normally. This enables the efficiency of the fuel processing system to be kept high.