25/08/2026
π§ͺThe Heart of Lubricants: A Full Technical Breakdown of Base Oil Production
Opening Introduction
Lubricants are composed of base oil and additives, with base oil being the absolute majority, accounting for 85% to 99% of the formulation. It is no exaggeration to say that the quality of the base oil directly determines the performance ceiling of the finished lubricant product.
The base oil family includes mineral base oils, synthetic base oils, and other types, serving a wide range of applications such as engine oils, gear oils, compressor oils, turbine oils, hydraulic fluids, electrical insulating oils, and more. Additionally, the production processes for white oil and rubber extender oils are highly similar to those for base oils, differing only in product specifications and end-use requirements.
π Chapter 1: The "International ID" of Base Oils β The API Classification System
While individual oil companies often classify base oils by viscosity index, the globally recognized hard standard comes from the American Petroleum Institute (API). In the API 1509 system, base oils are divided into five categories based on saturates content, sulfur content, and viscosity index:
- API Group I: Saturates < 90%, and/or sulfur > 0.03%, viscosity index 80 to aromatics > naphthenes > paraffins. The more aromatic rings, the more readily adsorbed.
The residual impurities in dewaxed oil (resins, naphthenic acids, sulfur/nitrogen compounds, solvents, water, mechanical impurities) are mostly polar and are preferentially adsorbed by clay, while the desirable hydrocarbon components are barely adsorbed, achieving purification.
Process flow (three main steps):
Feedstock β surge tank β mixing tank (clay added with agitation) β heat exchange β furnace β vacuum flash tower.
Overhead vapors/water are condensed into a vacuum receiver, then to a water separator (with baffles); water is drained from the bottom, and distillate oil is sent out.
Bottom oil is cooled to ~130Β°C β coarse and fine filtration β spent clay removed β finished oil cooled to 40β50Β°C and sent out.
π‘ Unique value of clay finishing:
It preferentially adsorbs nitrogen compounds (especially basic nitrogen) over sulfur compounds, resulting in a "high sulfur, low nitrogen" product. It also outperforms hydrofinishing in improving demulsibility and air release properties. Therefore, many Chinese Group I plants still retain clay finishing units.
π 1996 technology upgrade β Denitrogenation + Clay Combination Process:
Solvent-refined oil is treated with an acidic denitrogenation agent for complexation before clay treatment.
- For distillate oils: improves oxidation stability, reduces clay consumption, and increases yield.
- For bright stocks: while oxidation stability improves, clay consumption cannot be significantly reduced (otherwise color fails to meet specs).
π¨ IV. Hydrofinishing (for Group I)
As crude slates become heavier and more sour, and environmental regulations tighten, hydrofinishing has rapidly gained adoption in Group I production.
It is typically used as the final finishing step in conventional flows, replacing clay finishing.
Core function: with minimal change to the hydrocarbon distribution, it removes residual solvents, easily removable oxygenates, part of sulfur compounds, small amounts of nitrogen compounds, and other polar species, significantly improving color, odor, transparency, demulsibility, and additive response.
Mild operating conditions:
- Hydrogen partial pressure: 2.0β8.0 MPa
- Temperature: 200β340Β°C
- LHSV: 0.5β3.0 hβ»ΒΉ
- Hβ/oil ratio: < 500
- Higher pressure favors nitrogen removal and color/color stability improvement
Main reactions: hydrodeoxygenation (HDO), hydrodesulfurization (HDS), and hydrodenitrogenation (HDN) of heteroatomic compounds, producing HβO, HβS, and NHβ, with the hydrocarbon moieties remaining in the oil or separated via stripping/distillation.
β
Advantages: no pollutant emissions, low operating cost, simple operation, suitable for sour crudes.
β οΈ Limitations: mild severity; for high-nitrogen paraffinic feeds, issues like pour point reversion and poor oxidation/light stability may occur.
π Chapter 3: Lubricant Hydroprocessing Technologies (Core Engine for Groups II/III)
L**e hydroprocessing encompasses three major process modules: hydrotreating (hydrocracking), catalytic dewaxing, and hydrofinishing, with catalysts playing the central role.
π₯ I. Hydrotreating
Feedstocks cover paraffinic, intermediate, and naphthenic base oils, including various vacuum gas oils (VGO) and light deasphalted oils, for producing different viscosity grades and performance levels.
Main functions: boost viscosity index, improve stability and color.
πΉ 1. Stability-Improving Reactions
- Removal of oxygen, sulfur, and nitrogen heteroatoms is the first prerequisite. API Group II requires sulfur β€ 300 ΞΌg/g.
- Basic nitrogen is one of the key heteroatoms affecting stability.
- Involved reactions: hydrodeoxygenation (HDO), hydrodesulfurization (HDS), and hydrodenitrogenation (HDN).
πΉ 2. Viscosity Index-Improving Reactions
- Hydrodearomatization (HDA): Multi-ring aromatics have low VI, high pour points, and poor photo-oxidation stability. Hydrogenation saturation significantly improves performance.
- Saturated ring opening (SRO) of polycyclic naphthenes: cracking and ring opening produce mono- or bi-ring naphthenes with long side chains, markedly increasing VI while reducing viscosity β beneficial for low-viscosity, high-VI automotive base oils.
β οΈ For high-viscosity Group II oils, SRO must be controlled to avoid excessive viscosity loss and yield reduction.
β Undesired side reactions:
- Hydrocracking of normal and iso-paraffins
- Hydrodealkylation of long-side-chain naphthenes
β These reactions lower VI, reduce yield, and increase hydrogen consumption.
βοΈ II. Catalytic Dewaxing
Hydrotreated oils still contain high-pour-point wax components (normal paraffins, short-branched long-chain paraffins, long-side-chain aromatics/naphthenes), impairing low-temperature fluidity.
Since the 1970s, two technical routes have been developed:
πΉ 1. Selective Catalytic Cracking Dewaxing (often referred to as catalytic dewaxing or pour-point reduction in hydrogen)
Principle: Using a shape-selective zeolite catalyst (typically ZSM-5) in hydrogen, high-pour-point hydrocarbons are selectively cracked into smaller gas molecules or lower-pour-point components.
- The reaction proceeds via a carbenium ion mechanism on acid sites.
- Due to pore-size restrictions, only normal paraffins or slightly methyl-branched paraffins can enter the channels for reaction. Products are low-pour-point paraffins, olefins, and small hydrocarbons (Cβ, Cβ).
Features:
- Pore restrictions prevent secondary reactions such as cyclization and condensation, reducing coke formation and ensuring good stability.
- Sulfur/nitrogen compounds and aromatics cannot enter the channels, thus do not participate in reactions or affect internal acid sites.
- Metal centers provide hydrogenation/dehydrogenation functions, promoting olefin formation, which readily forms carbenium ions, lowering the required reaction temperature and further suppressing coke.
π° Compared to solvent dewaxing: lower capital investment, lower operating costs, and better product quality.
π― Suitable for: low-wax-content feedstocks, such as naphthenic base oil production. Even after the advent of isomerization dewaxing, selective cracking retains a niche due to its simplicity and low cost.
πΉ 2. Isomerization Dewaxing
Selective cracking removes wax by "cracking it away," inevitably sacrificing yield. Isomerization dewaxing, by contrast, isomerizes normal paraffins (and slightly branched paraffins) into iso-paraffins, retaining them in the base oil product and significantly improving yield.
Since the 1990s, it has become the mainstream hydroprocessing route.
Core chemistry:
- Main reaction: hydroisomerization
- Side reactions: aromatic hydrogenation and hydrocarbon hydrocracking (the latter must be minimized to avoid yield loss)
The key challenge: maintain high isomer selectivity while achieving good pour-point reduction.
Reaction mechanism (carbenium ion + metal-acid bifunctional):
Paraffin β dehydrogenation on metal sites β olefin β carbenium ion on acid sites β isomerization/cracking β olefin β hydrogenation on metal sites β isoparaffin desorption.
Catalyst design essentials:
- Bifunctional (acid + hydrogenation)
- Acidic component must preferentially adsorb and convert normal paraffins (specific zeolites)
- Hydrogenation function usually provided by noble metals
- Precise preparation control is needed to match metal activity with acid functionality
π III. Hydrofinishing
After catalytic dewaxing or isomerization dewaxing, the oil still contains unstable species such as olefins, partially saturated polycyclic aromatics, and alkenyl aromatics, which are prone to oxidation and polymerization, affecting photo- and oxidation stability.
Hydrofinishing saturates these unsaturated compounds via hydrogenation with minimal change to average molecular weight and structure.
π Thermodynamics: hydrogenation saturation is exothermic and reversible; high pressure and low temperature favor deep removal of unsaturates.
Catalyst selection:
- Both sulfided and reduced metal catalysts can be used.
- Currently, noble metal catalysts are mainstream (high hydrogenation activity, lower reaction temperatures, slower coke buildup, longer cycles).
- Support and pore structure design are critical, especially for bulky multi-ring aromatics with many branched chains (steric hindrance), requiring optimized pore architecture to facilitate saturation.
π Hydrofinishing catalysts are typically used in combination with catalytic dewaxing or isomerization dewaxing catalysts to ensure final product quality.
ποΈ Chapter 4: API Group II/III Base Oil Production Processes (Five Industrial Routes)
The ideal base oil components are isoparaffins and single-ring naphthenes with long alkyl side chains; the non-ideal components are polycyclic aromatics and polycyclic naphthenes.
Based on feedstock characteristics and target products, the following five routes have been commercialized in China:
πΉ Route 1: High-Pressure Hydrotreating β Solvent Dewaxing β Hydrofinishing
- Hydrotreating directly processes VGO and DAO (high non-ideal components and impurities)
- Severe conditions, pressure β₯ 18.0 MPa
- Advantages: simple flow, good naphtha/diesel quality, strong feedstock flexibility
- Disadvantages: high pressure, significant viscosity loss, moderate main product yield; MEK dewaxing negatively affects low-viscosity oil VI and color
πΉ Route 2: Solvent Refining β Medium/High-Pressure Hydrotreating β Solvent Dewaxing β Hydrofinishing
- Moderate solvent refining upstream removes resins, asphaltenes, polycyclic aromatics, and polar heteroatomic compounds, improving hydrotreating feed quality
- Hydrotreating can operate at medium (12.0 MPa) or high (>16.0 MPa) pressure
- Advantages: flexible operation, lower reaction temperatures, less viscosity loss, higher base oil yield; can co-produce high-quality wax; particularly suitable for bright stock production from intermediate-base crudes
- Disadvantages: longer flow scheme, higher energy consumption
πΉ Route 3: Mild Solvent Refining β High-Pressure Hydrotreating (Cracking) β Isomerization Dewaxing β Hydrofinishing
- Mild solvent refining upstream removes resins, asphaltenes, polycyclic aromatics, and polar heteroatoms to improve reactivity
- High-pressure hydrotreating significantly boosts VI while maintaining viscosity grade
- Strong feedstock adaptability; can produce Group II/III oils from intermediate-base feeds; light byproduct quality also improved
- Disadvantage: longer flow scheme
πΉ Route 4: High-Pressure Hydrotreating (Cracking) β Catalytic Dewaxing/Isodewaxing β Hydrofinishing (All-Hydrogen Route)
- Catalytic dewaxing replaces solvent dewaxing, achieving a "fully hydrogenated" flow
- For low-wax naphthenic feeds β selective cracking dewaxing; for high-wax intermediate/paraffinic feeds β isomerization dewaxing (less gas, higher liquid yield)
- Isomerization dewaxing has stricter feed quality requirements, forcing the pre-treatment section to operate at more severe conditions, potentially causing viscosity loss
- Focuses on low-to-medium viscosity, high-VI products; not suitable for high-viscosity bright stocks
πΉ Route 5: Isodewaxing β Hydrofinishing (Using Hydrocracker Tail Oil as Feed)
- Hydrocracker tail oil is an excellent feedstock: mainly isoparaffins and low-ring naphthenes, aromatics β€ 5%
- Very simple flow, excellent product quality, high yield (overall β₯ 80%), can produce extremely low pour point and ultra-high VI (>130) products
- Limitation: relatively narrow distillation range; generally does not produce products with kinematic viscosity > 10 mmΒ²/s at 100Β°C, focusing on 4β6 mmΒ²/s low-viscosity grades
𧴠Chapter 5: White Oil and Rubber Extender Oil Production Technologies (Specialty Products)
These two product families share the same origins as regular base oils but differ significantly in performance and safety requirements.
π§Ό I. White Oil and Its Production Technology
White oil is a specialty product made from l**e base oil fractions via ultra-deep refining. It is colorless, odorless, chemically inert, and has excellent photo- and thermal stability, widely used in daily chemicals, food processing, polymer processing, textiles, pharmaceuticals, toys, agriculture, etc.
Beyond performance, safety is a hard requirement β especially strict regulatory limits on aromatics (particularly polycyclic aromatics) to meet non-toxicity standards.
White oil grades (China): Industrial, Cosmetic, and Pharmaceutical/Food grades.
Traditional production methods:
- Sulfonation (fuming sulfuric acid or SOβ), adsorption, extraction
- The common objective: remove aromatics and sulfur/nitrogen/oxygen components, improving color, odor, stability, and safety
- Polycyclic aromatics and other heteroatomic polycyclic compounds are carcinogenic; for pharmaceutical/food grades, carbonizable substances and UV absorbance are key quality control indicators
β οΈ Drawbacks of sulfonation: low yield, high consumption, difficult acid sludge disposal, severe pollution, batch operation with inconsistent quality β now phased out.
Hydroprocessing (absolute mainstream):
Uses hydrogenation to remove heteroatoms and deeply saturate aromatics, converting non-ideal components into white oil components.
- Advantages: high yield (>99%), stable quality, no waste sludge/solvent pollution, especially advantageous for high-viscosity white oils
- In China, hydroprocessing units with isomerization dewaxing as the core can already produce industrial white oil or food-grade white oil feedstocks, providing ample raw material for high-grade white oil production
White oil hydroprocessing routes (by feedstock type):
- Feedstock from hydroprocessed base oils (sulfur < 10 ΞΌg/g, nitrogen < 5 ΞΌg/g, aromatics < 5%): Single-stage process using non-noble or noble metal catalysts for deep dearomatization.
- Feedstock from traditional "classic three" base oils: Two-stage process.
- Stage 1 (pretreatment): NiW or NiMo sulfided catalysts for HDS, HDN, and partial HDA; product is stripped or topped before entering Stage 2.
- Stage 2 (deep dearomatization): Group VIII non-noble or noble metal reduced catalysts for deep saturation of residual aromatics to meet carbonizable substances and UV absorbance specs.
π Stage 2 conditions: higher hydrogen partial pressure + lower temperature to favor aromatic saturation, with essentially no cracking.
β οΈ For both single-stage and two-stage processes, the deep dearomatization catalysts are reduced-state (non-noble or noble) with special preparation; they are typically replaced directly at end-of-life rather than regenerated.
π II. Rubber Extender Oil and Its Production Technology
ASTM D2226 classifies oils for SBR and BR rubbers into four categories:
- 101 (high-aromatic)
- 102 (aromatic)
- 103 (naphthenic)
- 104 (paraffinic)
- Aromatic oils: excellent compatibility, high loading capacity, used for black or stain-tolerant rubber goods
- Paraffinic oils: high VI, high flash point, good color stability, but poor compatibility β lower usage
- Naphthenic oils: intermediate properties, good color and light stability β widely used
β οΈ Environmental challenge: Polycyclic aromatics are associated with carcinogenicity, mutagenicity, and reproductive toxicity. For tire-grade aromatic rubber oils, the technical difficulty is to remove three-ring-and-above aromatics while retaining mono- and di-ring aromatics to maintain high compatibility.
Process differences by rubber oil type:
- Paraffinic rubber oils: Essentially the same as conventional base oil processes; if extremely strict photo/thermal stability is required, deep aromatic hydrogenation is added.
- Naphthenic rubber oils: Naphthenic crude fractions undergo hydrotreating β hydrodewaxing β hydrogenation saturation; premium non-yellowing grades use noble metal hydrofinishing catalysts to reduce aromatics to very low levels.
- Aromatic rubber oils: Traditionally produced via solvent extraction (known as TDAE abroad), using selective solvents to remove three-ring+ aromatics while retaining mono/di-ring aromatics. Hydrogenation alone faces a dilemma: deep saturation meets PAH specs but lowers total aromatics β poor compatibility; mild saturation maintains compatibility but fails PAH specs.
β
The optimal compromise: moderate-depth hydrogenation + solvent extraction combination process, converting PAHs into desirable mono/di-ring components while meeting both yield and environmental targets.
π Closing Summary
From the "classic three" to all-hydroprocessing, from Group I to Group III, from regular base oils to white oils and eco-friendly rubber oils β the entire industry has always been doing one thing: selecting and tailoring hydrocarbon structures at the molecular level.
There is no "one-size-fits-all" process; only the "best combination for the feedstock and target."
Understanding base oil production logic is understanding half the technical history of lubricants.
π Let's Connect and Discuss
If you work in refining, lubricants, additives, OEM, or end-use applications, I'd love to hear your thoughts on base oil process routes. Technology never ends; it only iterates.
