TBPS 454 & TNPS 537 General Presulfiding Conditions

The following discussion is not intended to supercede recommendations given by individual catalyst suppliers concerning procedures for in-situ presulfiding specific catalysts. It is provided for discussion purposes to point out how the polysulfides TBPS 454 and TNPS 537 can simplify and decrease the time of your sulfiding turnaround.

Time-Temperature Presulfiding Profile

Region A -- After drying the catalyst for several hours at 150 °C, the temperature is raised to 200-220 °C with feed present; polysulfide spiking starts around 175 °C.

Region B -- The catalyst bed is held for several hours at the low temperature sulfiding condition until H2S breakthrough occurs. About half the polysulfide amount is added by the end of the hold period.

Region C -- Catalyst bed temperature is raised near to start of run condition, which will vary depending on the feed stream, but will be somewhere around 300 °C. Sulfiding continues until the calculated amount of sulfur has been taken up for metal sulfide conversion.

Region D -- Product is monitored for residual sulfur until target specification is met. Unit is then on stream.

General Comments

In Region A above, the liquid feed is spiked with polysulfide TBPS 454 or TNPS 537 so that the total sulfur content is about 1%. Some reactive sulfur material should be present by the time the catalyst bed reaches 175-200 °C to prevent reduction of metal oxides by the hydrogen treat gas. A general profile is shown for a given catalyst reactor bed position.

In Region B, the polysulfide spike can be increased to achieve a total feed content of 2% sulfur. The temperatures of the reactor inlet, intermediate, and outlet should be closely monitored; differential temperatures can be controlled to less than 10-15 °C by controlling the injection rate of the polysulfide spike. Lower the rate of polysulfide addition to lower the exotherm if necessary. Polysulfides decompose at 150-200 °C, considerably lower than the 200-250 °C for sulfiding agents like dimethyl disulfide (DMDS) or dimethyl sulfide (DMS). The initial low temperature sulfiding can take place at 200-220 °C and provide more room to prevent excessive sulfiding reaction exotherms if sulfiding at 230-260 °C as for DMDS or DMS.

Region C can begin when the off gas shows a strong increase in H2S content (0.3 vol%). The polysulfide spike of 1-2% continues until at least the calculated stoichiometric amount of sulfur has been added. Region C ends and Region D begins when start of run conditions are reached. Region D ends when the unit reaches product sulfur specification target or less.

For more information on catalyst sulfidation, call our sulfiding support group at 832-813-4862.