Synthesis Gas Cleanup with Nonthermal Plasma

Plasma processes are very useful in industry because plasma has the unique characteristic of producing active species in large numbers of energetic species than conventional chemical processes. Nonthermal plasma (NTP), such as corona or glow discharge plasmas, is widely used for generating such active species. Synthesis gas produced from coal gasification requires cleanup for further application. To elucidate the possible reactions, including side reactions, in syngas cleanup with nonthermal plasma, a series of simulated gases were fed into a noncatalytic nonthermal plasma tubular reactor, and the results were summarized as follows:

1) Under nonthermal plasma conditions, no reaction was observed between CO and H₂O;

2) The reaction of CO₂, water, and dilute gas N₂ gave only 1 mol% of CO₂ conversion;

3) For the reaction of SO₂ with water and dilute gas N₂, the highest SO₂ conversion rate was 21.1 mol% at 15.3 kV; Water vapor facilitated the reactions since the hydroxyl radicals generated from water molecules are active oxidant;

4) For the water-gas shift reaction (CO + H₂O ? CO₂ + H₂), the highest conversion rate for the reaction of CO with H₂O was only 0.34 mol% at 200°C;

5) For the reaction of CO₂ with water and diluent gas N₂, the CO₂ conversion extent was only ~1 mol%;

6) For the reaction of CO₂ with hydrogen and diluent gas N₂, the highest conversion rate for CO₂ was 8.9 mol%, and 0.6 mol% of CH₄ was produced. It was also observed that, without NTP, the reaction of CO₂ and H₂ was extremely temperature dependent, and 0.85% of CO₂ conversion was obtained at 550°C in the preheater;

7) For the reaction CO with H₂, no significant reaction was observed for the reaction of CO with H₂ under NTP condition.