My 2 cents

Reactivating Hydroforming Catalysts (1968)

U.S. Patent No. 3,407,135, granted on October 22, 1968, to Henry T. Brown, describes a chemical regeneration and rejuvenation process for platinum-on-alumina reforming catalysts used in petroleum refining. Henry T. Brown, a chemical researcher based in Elizabeth, New Jersey, assigned the patent to the Esso Research and Engineering Company, the technological research arm of Standard Oil of New Jersey (later Exxon).

This specific invention solved a persistent operational bottleneck in catalytic hydroforming: how to consistently restore stripped chlorine on platinum catalysts to an optimum intermediate concentration (0.7 to 1.0 weight percent) uniformly across the reactor bed without causing severe equipment corrosion from hydrochloric acid fumes or triggering rapid coke fouling from over-chlorination.

The Innovation: The Water Presaturation Technique

During the high-temperature conversion of virgin naphthas into high-octane gasoline, platinum-on-alumina catalysts lose activity due to carbon buildup (coking), platinum crystal agglomeration, and the steady loss of essential chloride promoters. While burning off the coke cleans the catalyst, restoring the active chloride previously posed an extreme dilemma.

Dry chlorination at elevated temperatures resulted in severe over-chlorination (1.6 to 1.7 weight percent chloride), causing accelerated coking and rapid catalyst deactivation. Conversely, adding large volumes of steam or stripping with moist air created substantial hydrochloric acid (HCl), causing intense equipment corrosion and non-uniform, graded chloride levels from bed inlet to outlet.

Brown discovered that the key was establishing an equilibrium water vapor pressure on the catalyst prior to introducing chlorine. By presaturating the catalyst with an oxidizing gas containing a very low, strictly controlled moisture level (such as 500 v.p.p.m. water, yielding a partial pressure of 0.11 p.s.i.a.), the catalyst’s uptake capacity during subsequent chlorination is capped at the exact target range.

Why Controlled Water Presaturation?

• Self-Limiting Halogen Uptake: The pre-equilibrated moisture layer prevents excessive chlorine binding, automatically plateauing the halogen content between 0.7 and 1.0 weight percent at breakthrough.
• Bed-Wide Uniformity: It eliminates uneven concentration gradients across fixed beds, yielding a chloride variation within any reactor bed of less than 0.2 weight percent.
• Corrosion Prevention: Operating at low water partial pressure prevents condensation and suppresses acidic HCl effluent gas formation prior to breakthrough.
• History Independence: It functions reproducibly regardless of the catalyst’s age, number of prior regeneration cycles (tested up to 44 cycles), or initial chloride level.

Key Process Parameters

The rejuvenation protocol uses carefully regulated temperatures, pressures, and gas compositions:

Component / Parameter	Specification Range	Process Function
Supported Platinum Catalyst	0.1 to 1.0 wt. % Pt on gamma or eta alumina	Provides dehydrogenation and isomerization active sites for converting low-octane naphthas.
Presaturation Gas	Air or nitrogen with oxygen; 500 to 5,000 v.p.p.m. H2O	Pre-conditions catalyst pores to an equilibrium water partial pressure (ideally 0.11 p.s.i.a.).
Halogen Rejuvenation Stream	0.02 to 1.0 mol % Cl2 (or CCl4) with 200 to 10,000 v.p.p.m. H2O	Redisperses platinum agglomerates and replenishes lattice chloride promoter sites.
Operating Temperature	500 to 800°F (ideally 600°F)	Ensures stable chemical adsorption; prevents loosely held surface physisorption seen at lower temperatures.
Operating Pressure	100 to 400 p.s.i.g. (ideally 200 p.s.i.g.)	Matches commercial unit pressures, maintaining a flow rate of 3 to 30 s.c.f./hr./lb. of catalyst.
Breakthrough Indicator	Starch-iodine solution or optical test	Serves as the precise operational endpoint for terminating chlorine feed to avoid over-chlorination.

Performance: Pilot and Commercial Hydroforming Results

Brown evaluated the rejuvenated catalysts in pilot units running Arabian and Zelten virgin naphthas (boiling range 160 to 350°F) at 500 p.s.i.g. and 915 to 975°F.

Comparative Pilot Plant Results:

Aged 0.3% Platinum Catalyst (Standard vs. Brown Process):

• Standard Dry Reactivation (975°F): Catalyst chloride reached 1.2 wt. %; cycle lasted only 1 month before excessive deactivation shut down the unit; produced 96 Research Octane Number (RON) reformate at 69.5% C5+ liquid yield.
• Brown Water-Presaturated Reactivation: Catalyst chloride locked at 0.80 wt. %; continuous cycle lasted over 3 months; produced 98 RON reformate with 1.13 wt. % hydrogen yield.

Aged 0.6% Platinum Catalyst (Standard vs. Brown Process):

• Standard Dry Reactivation: Catalyst chloride reached 1.1 wt. %; cycle ran 5 months; produced 96 RON reformate with 0.85 wt. % hydrogen yield.
• Brown Water-Presaturated Reactivation: Catalyst chloride maintained uniformly at 0.90 wt. %; run operated smoothly for more than 7 months; delivered 71.7 liquid volume % C5+ yield at 97 RON with 1.16 wt. % hydrogen yield.

The Commercial Reactivation Sequence

The patent outlines an integrated, step-by-step operating cycle for multi-bed semi-regenerative hydroforming units:

1. Purge and Coke Burn: Cut off oil feed and recycle gas; purge residual hydrocarbons with inert nitrogen; burn off carbon deposits with flue gas containing 0.3 to 0.8 mol % oxygen at 800 to 1000°F until oxygen breakthrough occurs.
2. Cooling and Conditioning: Purge combustion gases; raise oxygen concentration to 20%; cool fixed beds to 600°F under 200 p.s.i.g. by circulating air.
3. Moisture Presaturation: Pass air saturated with water vapor (500 v.p.p.m. H2O, equivalent to air saturated at 33°F, yielding 0.11 p.s.i.a. water partial pressure) through the catalyst bed for 2 to 10 hours until inlet and outlet water concentrations equalize.
4. Breakthrough Chlorination: Inject 0.05 mol % chlorine (elemental Cl2 or vaporized carbon tetrachloride, CCl4) into the moist treat gas stream; pass through each reactor bed at 9 s.c.f./hr./lb. of catalyst at 600°F until chlorine breakthrough is detected in the effluent via starch-iodine testing.
5. High-Temperature Soak: Treat the bed with air at 975°F for 2 hours with an in-line drier to lock in catalyst structure.
6. Inert Purge and Hydrogen Reduction: Purge air with nitrogen; treat with hydrogen gas at 800 to 975°F to reduce metallic oxides; cool to 800°F before reintroducing naphtha oil feed.

About the Inventor: Henry T. Brown

Henry T. Brown was a pioneering African American chemical engineer and research scientist whose career helped shape modern petrochemical process engineering.

• Industry Leadership: Working as a research engineer at Esso Research and Engineering Company, Brown focused on heterogeneous catalysis, fluidized systems, and petroleum reforming kinetics during the 1960s expansion of high-octane fuel refining.
• Professional Impact: Brown became deeply involved in professional leadership, later serving as an influential figure within the American Institute of Chemical Engineers (AIChE), where he championed minority participation in chemical engineering and STEM careers.
• Technical Legacy: His work on controlled halogenation and catalyst surface equilibrium addressed real-world mechanical and metallurgical constraints, turning an erratic chemical treatment into a safe, predictable, and commercially scalable refinery standard.

Summary of Claims

The patent explicitly claims:

• A method of reactivating regenerated platinum-group alumina catalysts by first presaturating the catalyst at 500 to 800°F and 0 to 400 p.s.i.g. with a water-containing gas (500 to 5,000 v.p.p.m. water) until vapor pressure equilibrium is established.
• Contacting the water-saturated catalyst with a treating gas comprising 0.02 to 1.0 mol % chlorine, 0.02 to 1.0 mol % water, 0 to 21 mol % oxygen, and nitrogen until chlorine breakthrough occurs in the effluent gas.
• Achieving a final, uniform catalyst chloride content between 0.70 and 1.00 weight percent throughout the bed, substantially eliminating effluent hydrochloric acid formation during treatment.
• The specific use of volatile organic chlorine-releasing agents, including carbon tetrachloride (CCl4), as the active halogen source during the wet treating phase.