Gasoline Composition and Solvent Oil Additive (1960)
U.S. Patent No. 2,955,928, granted on October 11, 1960, to Warren Maxwell Smith and Richard F. Neblett, describes an improved motor fuel designed to combat the internal “gum” and sludge problems common in 1950s engines. Assigned to the Esso Research and Engineering Company, this invention focuses on a specialized “solvent oil” that keeps engine parts clean while providing essential lubrication to the upper cylinders.
As gasoline engines evolved to use higher-octane, catalytically cracked fuels, they became more prone to leaving behind sticky deposits (varnish and resins) on valve stems and piston rings. Smith and Neblett discovered that a specific byproduct of the chemical industry—Oxo bottoms—was the “missing ingredient” to keep these engines running smoothly.
The Problem: Engine “Gumming”
In the mid-20th century, internal combustion engines suffered from “manifold deposits” and “piston ring sticking.”
- The Cause: Unstable components in gasoline react with oxygen to form heavy, sticky gums.
- The Result: Valves get stuck in the open or closed position, leading to power loss, poor fuel economy, and eventually engine failure.
- The Failure of Old Methods: Standard mineral oils could dissolve some hydrocarbons but were powerless against “oxygenated” gums and resins.
The Solution: Fortified “Oxo Bottoms”
The inventors found that by “fortifying” standard mineral solvent oils with Oxo bottoms, they created a cleaner with “high specificity” for tough engine varnishes.
What are Oxo Bottoms?
Oxo bottoms are the heavy “leftovers” from the Oxo Process (carbonylation). In this process, olefins are reacted with carbon monoxide and hydrogen to create alcohols. After the useful alcohols are distilled away, a thick, complex liquid remains at the bottom of the still.
Chemical Makeup of Oxo Bottoms:
- C16 Alcohols: Heavy, branched-chain alcohols.
- C16 Acetals & Ethers: Highly stable oxygenated compounds.
- Esters & Aldols: Minor components that aid in solvency.
Performance Data: The “Sligh Test”
To prove their invention worked, the Esso researchers used the Sligh Test, which measures how much sludge an oil forms when exposed to heat and oxygen. A lower “Sligh Number” means the oil is more resistant to oxidation and better at preventing deposits.
| Solvent Oil Composition | Sligh Number (Lower is Better) |
| Pure Mineral Solvent Oil A | 47.3 |
| Pure Oxo Bottoms | 1.0 |
| 75% Mineral Oil + 25% Oxo Bottoms | 1.6 (Unexpectedly low!) |
| 75% Mineral Oil + 25% Amyl Stearate | 42.6 (Poor performance) |
The “Synergy” Discovery: The inventors noted that the Sligh Number of the mixture (1.6) was much lower than the mathematical average of its parts (24.2). This proved that Oxo bottoms don’t just act as a solvent; they actually chemically stabilize the mineral oil, preventing it from breaking down into sludge.
Key Technical Features
- Upper Cylinder Lubrication: The mixture provides a thin film of lubricant on the cylinder walls and valve stems, areas where regular crankcase oil often fails to reach effectively.
- Aniline Point Reduction: The addition of Oxo bottoms lowers the “aniline point” of the fuel, a technical measurement indicating that the oil has become a much more powerful solvent for dissolving resins.
- Low Concentration: The additive is highly potent; only 0.05% to 1.0% of the total gasoline volume is required to keep the engine clean.
Summary of Claims
The patent explicitly protects a motor fuel comprising:
- A major proportion of light petroleum hydrocarbons (gasoline).
- 0.05% to 1.0% solvent oil acting as both a lubricant and a deposit remover.
- The solvent oil itself must contain 1% to 50% Oxo reaction still bottoms.
