Oil-Soluble Ashless Dispersant-Detergent-Inhibitors (1970)
U.S. Patent No. 3,511,780, granted on May 12, 1970, to Richard F. Neblett and Norman Tunkel, describes an advanced multi-functional chemical additive for hydrocarbon compositions, including motor lubricants, gasolines, and fuel oils. Richard F. Neblett, an accomplished research chemist at Esso Research and Engineering Company (later ExxonMobil), was a pioneer in petroleum additive chemistry and industrial lubrication science.
This specific invention solved a persistent dilemma in internal combustion engine maintenance: conventional heavy-duty detergents and dispersants relied on organometallic compounds (such as barium or calcium sulfonates) that formed inorganic “ash” deposits during combustion. These ash residues fouled spark plugs, burned exhaust valves, and triggered destructive engine pre-ignition. Neblett and Tunkel developed a completely metal-free, ashless chemical architecture that provided high-efficiency sludge dispersancy while simultaneously delivering built-in antioxidant and antiwear protection.
The Innovation: The “Balanced Phosphorus-Sulfur Neutralization”
Polyisobutenyl succinic anhydride (PIBSA) reacted with polyamines yields succinimide dispersants that solubilize crankcase sludge. However, early succinimide dispersants lacked wear resistance and oxidative stability, requiring heavy doses of external metallic additives.
Neblett and Tunkel discovered that reacting the residual, unreacted basic amine sites of a succinimide intermediate with organic thio-acids of phosphorus—specifically phosphosulfurized hydrocarbons (such as P2S5-treated polyisobutylene) and dialkyl dithiophosphoric acids—transformed the basic dispersant into a single multi-functional, ashless additive package.
Why Organic Thio-Acids of Phosphorus?
- Balanced Neutralization: Leaving at least one free amino nitrogen atom per molecule preserves basic dispersancy and detergent capacity, while partially neutralizing the amine chain with thio-acids builds in wear and oxidation resistance.
- Total Ash Elimination: Provides antiwear and antioxidant functionality directly on the organic polymeric backbone without introducing metallic salts that create combustion-chamber ash.
- Synergy in Base Stocks: The resulting condensation polymer dissolves completely in paraffinic, naphthenic, and synthetic mineral oils without falling out of solution or destabilizing during high-temperature engine cycling.
Key Chemical Components
The additive is synthesized through a multi-stage condensation where each component serves a distinct mechanical and chemical role:
| Component | Function |
| Alkenylsuccinic Anhydride (PIBSA) | Reaction product of maleic anhydride and an olefin polymer (typically 800–1200 molecular weight polyisobutylene); provides oil solubility and a polymeric backbone. |
| Aliphatic Polyamine | Alkylene polyamines (e.g., tetraethylene pentamine) providing basic amine sites to disperse acidic sludge precursors. |
| Carboxylic Acid (e.g., Acetic Acid) | Optional co-condensing agent (1 to 30 carbon chain) used to moderate amine reactivity and optimize intermediate solubility. |
| Phosphosulfurized Hydrocarbon | Prepared by reacting P2S5 with polyisobutylene; reacts with residual amino groups to impart antioxidant potency and deposit control. |
| Dialkyl Dithiophosphoric Acid | Reaction product of P2S5 and mixed aliphatic alcohols (e.g., isobutyl and primary amyl alcohols); supplies active antiwear sulfur-phosphorus complexes. |
| Mineral Oil Diluent | Solvent neutral carrier oil used to stabilize concentrates (typically 20% to 80% active ingredient) for bulk handling. |
Performance: Sludge Control and Wear Reduction
Neblett and Tunkel benchmarked their formulations against standard commercial organometallic lubricants using rigorous automotive industry dynamometer sequences:
Ford ER4-90 Engine Sludge Dynamometer Test:
- Merit Rating Scale: 10 represents a completely clean engine part; 0 indicates maximum sludge accumulation.
- Commercial Barium Detergent (Composition 2): Rated 9.9 at 100 hours, dropping steeply to 7.4 at 200 hours and 6.7 at 286 hours (with 10% oil screen clogging).
- Neblett-Tunkel Additive A (Composition 1): Maintained 9.95 at 100 hours, 9.7 at 200 hours, and 9.1 at 286 hours (zero screen clogging).
- Neblett-Tunkel Additive B (Composition 3): Achieved a near-perfect 9.99 at 100 hours, 9.9 at 200 hours, and 9.7 at 286 hours (zero screen clogging).
Valve Lifter (Tappet) Antiwear Test:
- Failure Threshold: Engine oil fails if mechanical wear exceeds 10 x 10^-4 inches on any individual tappet.
- Standard Multigrade 10W-30 Motor Oil: Exhibited high wear averaging 8 x 10^-4 inches.
- Neblett-Tunkel Formulated Lubricant: Passed with an average wear of less than 1 x 10^-4 inches, with no individual tappet exceeding 1 x 10^-4 inches.
The Manufacturing Process
The patent outlines a sequential condensation procedure to produce the finished additive concentrate:
- PIBSA Synthesis: Heat 800 MW polyisobutylene and maleic anhydride at 450°F for 24 hours under a dry nitrogen blanket.
- Imidization & Dilution: Dilute with light mineral oil (75% solids), introduce an antifoam agent, add tetraethylene pentamine and acetic acid, and heat at 300°F for 10.5 hours with nitrogen stripping until water evolution stops.
- Thio-Acid Preparation: React polyisobutylene with P2S5 at 425–450°F to synthesize the phosphosulfurized hydrocarbon; separately react mixed amyl and isobutyl alcohols with P2S5 at 170°F to prepare mixed dialkyldithiophosphoric acids.
- Final Condensation: Blend the amine-containing succinimide intermediate with the phosphosulfurized hydrocarbon and dialkyldithiophosphoric acid; agitate at 212–225°F for 1 to 2 hours under nitrogen bubbling.
- Product Standardization: Filter and blend with solvent neutral mineral oil to yield a shelf-stable, 50% active liquid additive concentrate.
About the Inventor: Richard F. Neblett
Dr. Richard F. Neblett was a prominent African American research chemist and corporate executive whose career spanned basic petroleum chemistry, industrial research management, and scientific advocacy:
- Academic Background: Born in Richmond, Virginia, Neblett earned his B.S. in chemistry from Virginia Union University and his Ph.D. in organic chemistry from the University of Cincinnati.
- Industrial Research: Joining Esso Research and Engineering in the 1950s, he authored numerous patents and scientific publications covering petroleum refining, synthetic lubricants, high-performance crankcase additives, and fuel deposit control agents.
- Executive Leadership and Philanthropy: Neblett later served as Director of External Relations at Exxon Corporation, president of the National Technical Association (NTA), and a national board leader dedicated to advancing STEM education and career pipelines for underrepresented minorities in science and engineering.
Summary of Claims
The patent explicitly claims:
- A method of preparing an oil-soluble mineral oil additive by reacting a PIBSA-polyamine or PIBSA-polyamine-carboxylic acid condensation product with at least 0.01 molar proportion of a phosphosulfurized hydrocarbon and at least 0.01 molar proportion of a dialkyl dithiophosphoric acid at 100°F to 400°F.
- The composition derived from alkenylsuccinic anhydrides having alkenyl chains of 40 to 250 carbon atoms paired with alkylene polyamines such as tetraethylene pentamine.
- The specific incorporation of mixed dialkyl dithiophosphoric acids synthesized from isobutyl and amyl alcohols.
- Concentrated mineral oil additive packages comprising 20% to 80% by weight of the reaction product, formulated optionally with conventional metal sulfonates or zinc dialkyldithiophosphates.
