The effect of methanol in the first catalytic converter of the Claus sulfur recovery unit

Abstract

Methanol is commonly used as a hydrate inhibitor in gathering and transportation systems for natural gas streams containing H2S. While efforts are made to prevent carryover, some residual methanol can end up reaching downstream facilities. If residual methanol is still present in an acid gas stream after amine separation from sales gas, it normally undergoes quantitative conversion to CO and H2 in the front-end thermal reactor of the Claus sulfur recovery unit. However, if the Claus sulfur recovery unit is operating in a split-flow configuration in such a scenario, some acid gas, and the corresponding methanol, bypasses the thermal reactor and gets introduced directly to the first catalytic converter. While the fate of methanol in the thermal reactor of a Claus sulfur recovery unit has been established, an understanding of methanol reactivity and influence within the first catalytic converter is lacking. To shed light on this issue, we have performed a series of laboratory experiments, simulating field conditions, that elucidate the effect of methanol in the first catalytic converter of a Claus sulfur recovery unit, which can contain titania (TiO2) and/or alumina (Al2O3) catalysts. The results obtained identify that methanol is converted to CS2, via a CH3SH intermediate, which is then hydrolyzed to form H2S and CO2. Strategically designed experiments support this methanol conversion mechanism over both Al2O3 and TiO2. Although catalyst discoloration was observed in some experiments with methanol, no significant catalyst deactivation was observed, where CS2 conversion was monitored as a method for assessing activity once steady-state had been reached. Results from catalyst surface area analyses agreed with these observations. Finally, it was also found that there was no change in the carbon content of the sulfur formed during experiments where methanol was present when compared to control experiments without methanol addition to the feed.