From one barrel of crude oil comes a full spectrum of petroleum products, such as gasoline, engine oil, and alcohol.
By Kevin O’Shaughnessy
Motor oil, gasoline and diesel come from the same barrel of crude. Methyl, ethyl, isopropyl and synthetic oils can also be derived from that same barrel. The difference between fossil-derived and synthetic oils lies in the process of distillation and chemical reactions.
Crude is a complex mixture of many different hydrocarbon molecules, ranging from light butane gas to heavy asphalt. The first step of any refining is a distilling process, where molecules are separated by density. Crude is heated to about 750 F, then introduced into a multilevel cooling chamber or condenser.
Hydrocarbons separate by density, with lighter on top of heavier. This process is repeated to refine densities even further. Each level of the chamber is designed to capture and siphon a specific density of hydrocarbons, with butane at the top gasoline at the upper-midsection, diesel/oil at the lower-mid-section and asphalt/bitumen at the bottom.
The next step is to take these raw materials and treat impurities or change their chemical structure. This is where the process has significant flexibility to reform or crack molecules. Simple hydrotreating is used to separate impurities such as salt and sulfur or to separate lighter gasses from target materials. This method involves pumping steam into the material.
Hydrocracking is used to break large and heavy molecules, such as fuel oil, into lighter molecules such as diesel oil. Catalysts are materials that cause or accelerate a reaction, sometimes to reform or add other atoms to a molecule. Various products are made through these processes, such as jet fuel, LPG, kerosene, base oils and diesel oil. The primary purpose of refining is to create fuels. A barrel of crude will produce about 16 gallons of fuel and less than a half-gallon of engine oil. Although the various reactions used in refining could produce more engine oil, demand does not require it.
Base Oils: Refined lubrication oils are separated into Groups I-V. Many of these materials are made after the refining process through additional cracking and catalyzation. Lower numbers generally indicate less refinement. With more refinement comes more consistent chemical structure, stability at higher temperatures and pressures, and longevity.
Group I oils have the least refinement, typically only using hydrotreating. This makes them less stable and best suited for heavy machinery.
Group II oils are hydrotreated and partially hydrocracked, which permits use in conventional engine and gear oils. These oils have reasonable consistency and stability.
Group III oils are fully hydrocracked and hydrotreated which creates a very consistent and stable base. These oils are considered premium conventional oils, with some considered synthetic. They have a high level of consistency and stability.
Group IV oils are considered fully synthetic poly-alpha-olefins (PAO). This category has the highest level of refinement, consistency and stability, but are expensive to produce and typically used as viscosity modifiers rather than the primary base oil, for cost considerations.
Group V oils are the ones that don’t fall within any of these categories and have various ranges of refinement. These oils include silicones, oil and fuel additives, esters used for brake fluid, and polyglycols used for antifreeze.
Oil Blends: Blending is the process of mixing base oils and additives to support specific demands and manage price points. Not all are created equal. Engine lubricants are primarily comprised of base oils. A conventional motor oil would likely be made of Group II and possibly lower grade Group III. A semi-synthetic would likely be primarily Group II with some Group III synthetics, allowing a marketable low cost “synthetic.”
While there is no regulation on how much of each is used, the oil will have to pass tests required by API and JASO. The fluid will perform to standard, but not all will perform for the same timeframe or with the same level of protection. This is where quality full synthetics may pay for themselves.
Full synthetic oils may combine Group III oils with Group IV to provide consistency and reduce cost. The base oil blend provides a certain viscosity, which is relative to the protective barrier. Changes in temperatures affect viscosity, barrier and flow. Higher temperatures thin the oil and lower temperatures thicken it. Viscosity modifiers reduce this change. These could be compared to a mass of spider-like molecules that expand and slow fluid movement when hot, but contract and allow more flow when cold. The result is less flow change at different operating temperatures and consistent protection.
Unfortunately, low quality modifiers are susceptible to shearing loads, which crack the molecule and reduce oil viscosity quickly. High quality PAOs are more resistant to shear, therefore last longer, but cost more. Once the viscosity and modifiers are determined, the additives are packaged to create resistance to specific contaminants, antioxidation, antiwear, sacrificial elements, antifoaming, emulsification and seal protection.
What to Buy
Buy quality, tested brands and choose the short or long-term investment that works best for you. Inexpensive conventional oils that meet API, ISO or JASO requirements for your vehicle are fine, if you change them often. Quality full synthetic oils last longer than conventional, which can also cost less per mile. Some engines, particularly those with accelerator pumps, worn rings or those using hard throttle or constant starts and stops, will cause enough combustion blow by to contaminate engine oil prematurely. In this case, it’s not worth spending money on an expensive oil. You’re better off buying a cheaper oil and changing it more often. Also, go cheap on vehicles that will sit unused. Oil should be changed after a year, regardless of use.
While not a lubrication, the refining process is centered on fuel production.
Because of the high demand for gasoline, several processes involve hydrocracking and reforming to change the chemical properties of overly heavy or light hydrocarbons to a range that can be blended with gasoline. Widening this range is necessary to maximize barrel output for gasoline and includes reactions that improve octane ratings.
Alcohols are hydroxyls or hydrocarbons bonded with oxygen. They are typically created through secondary processes using crude or biomass, though some, such as phenol, are naturally occurring in crude, coal and plants. Isopropyl, methyl and ethyl alcohol are the most common used as fuel additives.
Many bathroom cabinets house a container of isopropyl alcohol. This chemical is made by taking propene from crude refining and combining it with steam. It’s used primarily in transportation as a “gas dryer” or hygroscopic fuel additive, which bonds to moisture and consumes it through the combustion cycle. This reduces pooling and corrosion. Methyl alcohol, aka methanol or “wood alcohol,” was originally made by distilling wood chips. Most methanol is currently made by catalyzing carbon monoxide and hydrogen, which are both byproducts of crude refining. Methanol is used in transportation as a fuel additive cleaner and octane booster.
Ethyl alcohol, aka ethanol or “grain alcohol,” is one of the oldest chemicals produced by man through fermentation and distillation. Varieties consumed by humans are still produced through fermentation. Until the 1980s, industrial ethanol was made primarily by using phosphoric acid to catalyze water and ethylene (from crude). After the 1973 oil crisis, legislation pushed for a reduction of imported fuels, in which ethanol production turned predominantly to corn fermentation and distillation. Ethanol is used to mitigate petroleum use, acts as a fuel system cleaner, emissions reducer and octane booster.
Crude vs Bio
Any hydrocarbon, including wood or corn, can be reformed or cracked into lubrication oils, fuels or alcohols, though the complexity of refinement changes with the state of the material. Converting a raw tree into gasoline would require major refining and additional resources. A living plant has a limited range of hydrocarbons available and would require external energy for heat and catalysts, which are not self-sustained.
Alcohol can be distilled and/or fermented efficiently, but only a small portion of the plant is consumed and significant waste is created. Fermented waste product is currently used as feed for animals, though recent testing shows high concentrations of elements not fit for animal consumption. These same animals are being used for human consumption.
Alcohol is also not as efficient as gasoline, requiring approximately 1.5 times more fuel to produce the same energy output. Crude, which is primarily created by algae trapped underground, has been pressurized, mechanically and thermally altered and consumed by bacteria for millions of years. The waste and byproduct of each reaction creates new chemical sources for further reactions. It’s the ultimate biological, thermal, mechanical and chemical decomposition system.
A barrel of crude is nearly self-sufficient, providing a massive range of hydrocarbons, including the heating fuel used for distillation and many of the chemicals to hydrotreat, catalyze and hydrocrack. Water is one of the few outsourced elements needed for crude refinement. Every part of a barrel of crude can be used for something, other than salts, which are separated and disposed of. Gasoline is the primary product. Bitumen is used as road asphalt or for waterproofing roofs. Remaining products are used for industrial solvents, lubricants, heating and plastics. The primary environmental impact of both biomass and crude is carbon dioxide, though significant efforts are being made to capture and resource these emissions.