Catalyst Pre-Sulfiding Analysis

Measuring Hydrogen Sulfide in Catalyst Pre-Sulfiding

Catalyst 'presulfiding'is a practice which reduces the extent of early catalyst deactivation by preventing coking (carbon deposits). The procedure involves passing a gas stream containing e.g. H₂S over the catalyst or into the reaction feedstock.

In order to generate the H₂S which will interact with the catalyst, a sulfur carrying agent (e.g. dimethyl sulfide) is injected into the stream. Under high temperature and catalytic reaction, the agent decomposes and releases its sulfur component, forming H₂S. The H₂S reacts with the catalyst's metallic surface to substitute sulfur atoms for oxygen atoms.

The importance of presulfiding is clear, yet the procedure needs to be actively regulated in order to reduce costs and downtime. For example, the presulfiding procedure normally takes 10-36 hours, but can be reduced if presulfiding is terminated as soon as the catalyst is properly sulfided; this can be easily verified by measuring H₂S concentration in the stream after the reactor (if H₂S concentration does not drop when injection is ceased, presulfiding is complete).

The OMA-300 Process Analyzer monitors H₂S and additional analytes at specific sampling points which are critical to the optimization of presulfiding. Measuring real-time H₂S levels downstream from the reactor validates the completion of presulfiding; additional measurements include low level H₂S after the dryer system and continuous measurement of sulfiding agent concentration in order to detect fluctuations due to outages.