Module 3 - Sulfiding

Module from the Hydroprocessing Operations Curriculum curriculum.

CATALYST SULFIDING PROCEDURES · Learning Objectives · 1. Explain why sulfiding is necessary (convert oxide to active sulfide form) 2. Execute in-situ DMDS sulfiding procedure with proper temperature control 3. Monitor H2S breakthrough and exotherm limits during sulfiding 4. Compare in-situ vs ex-situ presulfiding approaches 5. Troubleshoot common sulfiding problems (delayed breakthrough, excessive exotherm) · In-Situ DMDS Sulfiding — Step-by-Step Protocol

Step	Activity	Temperature (°F)	Duration	Critical Parameters	Hold Criteria
1	Establish H2 circulation at >80% design flow	Ambient	4-12 hrs	H2 purity >99.5%, flow stable, no leaks	Stable H2 flow confirmed
2	Heat to Phase 1 sulfiding temp at ≤50°F/hr	Ambient → 450	8-12 hrs	Ramp rate ≤50°F/hr, uniform bed heating	All bed TCs within 450 ±25°F
3	Begin DMDS injection at 0.5-1.0 vol% of H2	450	—	Injection pump calibrated, check for pooling	DMDS flowing, no injection issues
4	Hold Phase 1 — monitor H2S breakthrough Bed 1	450-500	12-48 hrs	H2S at bed 1 exit rising toward 500 ppm target	H2S >500 ppm at first bed exit
5	Confirm H2S breakthrough all beds, hold at 450-500°F	450-500	12-36 hrs	H2S at reactor outlet >500 ppm sustained	All beds showing H2S breakthrough
6	Ramp to Phase 2 temperature at ≤25°F/hr	500 → 600	4-6 hrs	Ramp rate ≤25°F/hr, monitor exotherms closely	Target 600°F at reactor inlet
7	Hold Phase 2 — complete sulfiding at elevated temp	600-650	12-36 hrs	H2S 1000-2000 ppm at outlet, exotherms stable	Total S consumed meets vendor target (1-3 wt% on catalyst)
8	Transition — reduce DMDS, adjust to operating conditions	650 → operating temp	12-24 hrs	Gradual DMDS reduction, start feed intro preparation	Ready for hydrocarbon feed introduction
Sulfiding Troubleshooting
Problem	Possible Cause	Indicator	Corrective Action	Risk if Ignored	Prevention
Delayed H2S breakthrough	DMDS injection rate too low, poor distribution, cold spots	Expected breakthrough at 12-24 hrs not occurring	Increase DMDS rate (within vendor limits), check inlet distribution	Incomplete sulfiding → poor initial catalyst activity	Verify injection rate before starting, ensure uniform temperatures
Excessive exotherm (>100°F/bed)	DMDS rate too high, liquid DMDS pooling on catalyst	Rapid temperature spike in bed, ΔT >100°F	Cut DMDS immediately, increase quench, reduce temperature	Catalyst damage (sintering), sulfide banding, hot spots	Start DMDS at low rate, ramp slowly, monitor continuously
Temperature overshoot >700°F	Exotherm plus high heater output	Reactor TC exceeding 700°F	Cut DMDS, reduce heater firing, activate emergency quench	Permanent catalyst damage above 750°F	Maintain heater on manual, conservative firing rate
DMDS pump failure	Mechanical pump issue, plugged injection point	Loss of DMDS flow, H2S dropping at outlet	Switch to spare pump, if no spare: hold temperature, do not increase temp without DMDS	Sulfiding stalls, catalyst left partially sulfided	Pre-startup pump test, verify spare pump ready
H2S >5000 ppm at outlet	DMDS rate excessive for current bed temperature	High H2S analyzer reading, strong odor at sample points	Reduce DMDS rate by 50%, hold temperature	Downstream equipment corrosion, amine system overload	Follow vendor sulfiding curve exactly
Non-uniform bed temperatures	Poor gas distribution, plugged distributor	Radial ΔT >30°F between thermocouples at same bed level	Check inlet distributor, may need to reduce flow and re-establish	Uneven sulfiding → channeling in operation	Verify distribution during N2 circulation before sulfiding
Source: FOS Chief Files — Hydroprocessing sulfiding procedures, Catalyst & Loading folder, Sulfiding_Balance_Calculator_v1.xlsx

Source: Hydroprocessing_Operations_Curriculum_v1.xlsx · Sheet: Module 3 - Sulfiding

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