Module 6 - Catalyst Deactivation

Module from the Hydroprocessing Operations Curriculum curriculum.

CATALYST DEACTIVATION & CYCLE LIFE MANAGEMENT · Learning Objectives · 1. Identify the four primary deactivation mechanisms (coke, metals, sintering, poisoning) 2. Calculate catalyst deactivation rate from WABT trend data 3. Estimate remaining catalyst cycle life 4. Implement operating strategies to extend catalyst life 5. Determine when to schedule catalyst changeout · Catalyst Deactivation Mechanisms

Mechanism	Cause	Rate	Indicator	Mitigation	Reversibility
Coking (carbonaceous deposition)	High temperature, heavy feed, insufficient H2, low H2/oil	1-3°F/month WABT increase	Rising WABT for constant product quality, increasing ΔP	Maintain H2 partial pressure, avoid temperature excursions >750°F	Partially reversible by regeneration (burn off coke at 800-900°F in controlled O2)
Metals Poisoning (Ni, V, Fe, As, Si)	Metals in feed deposit on catalyst surface, block active sites	Progressive, accelerates with metal loading	Feed metals analysis trending up, decreasing HDS activity per °F WABT	Feed pretreatment (guard bed, demetallization reactor), feed selection	Irreversible — metals permanently deposited
Sintering (thermal deactivation)	Prolonged exposure to T >750°F, especially with steam present	Accelerates exponentially above 750°F	Loss of surface area (BET analysis of spent catalyst)	Avoid temperature excursions, maintain proper quench	Irreversible — crystal growth is permanent
Poisoning (specific poisons)	Arsenic, lead, phosphorus, silicon in feed	Can be rapid if slug of poison enters	Sudden loss of activity not explained by temperature or metals	Feed quality monitoring, guard beds, reject contaminated feeds	Generally irreversible — poison chemically binds to active sites
Pore plugging / fouling	Coke, metals, scale accumulation blocking pore mouths	Gradual loss of effective catalyst volume	Rising ΔP, declining activity at constant WABT	Proper grading catalyst, maintain good distribution	Not reversible in-situ (requires catalyst replacement)
Inhibition (temporary)	High H2S or NH3 concentration suppressing reaction rate	Immediate but reversible	Activity drops when contaminant concentration rises	Adjust operating conditions, improve upstream operations	Fully reversible — activity returns when inhibitor removed
Cycle Life Estimation
Parameter	Calculation	Example	Data Source	Assumptions	Notes
Deactivation Rate	ΔT/Δtime (°F/month) from normalized WABT trend	(700-665°F) / 12 months = 2.9°F/month	WABT_Calculator + DCS data	Linear deactivation (approximate for mid-cycle)	Calculate rolling 3-month average for stability
WABT at EOR	Maximum metallurgical limit or vendor-specified max	780°F (typical for Cr-Mo steel reactor)	Reactor design data, metallurgical assessment	No change in feed or product specs	EOR = End of Run
Remaining Life	(WABT_EOR - WABT_current) / Deactivation_Rate	(780 - 700) / 2.9 = 27.6 months	Calculated	Constant deactivation rate, constant feed quality	Update monthly, plan changeout when <6 months remain
Catalyst Age Factor	Activity loss vs time (vendor curves)	After 2 years: ~85% of fresh activity	Catalyst vendor performance guarantee data	Clean feed, proper sulfiding, no upsets	Vendor provides normalized curves
Source: FOS Chief Files — Hydroprocessing Design Manual, Catalyst_Deactivation_Tracker_v1.xlsx, HCU_Cycle_Data_Review_v1.xlsx

Source: Hydroprocessing_Operations_Curriculum_v1.xlsx · Sheet: Module 6 - Catalyst Deactivation

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