1. Introduction to Linear Alkylbenzene
Linear alkylbenzene (LAB) is a key petrochemical intermediate that serves primarily as the precursor to linear alkylbenzene sulfonates (LAS), which are the most widely used biodegradable anionic surfactants in modern detergents. Since its introduction in the 1960s, LAB has largely replaced branched-chain alkylbenzene (BAB) due to its superior biodegradability and lower environmental persistence. The development of LAB technology represents a significant achievement in both chemical engineering and green chemistry, integrating principles of catalysis, molecular design, and process optimization.
LAB is typically a mixture of homologous compounds, each consisting of a linear alkyl chain (usually C₁₀–C₁₄) attached to a benzene ring through a single aromatic substitution. The exact composition depends on the raw materials and process parameters used in production. The physical and chemical characteristics of LAB, particularly its chain length distribution and degree of linearity, are key to determining its detergent performance and downstream sulfonation behavior.
2. Chemical Identity and Structure
2.1 General Formula
Linear alkylbenzene can be represented by the general chemical formula:
C₆H₅–CₙH₂ₙ₊₁, where n typically ranges from 10 to 14.
This formula describes a benzene ring substituted by a single linear alkyl chain. The carbon chain is saturated, and the alkyl group is generally attached at internal positions (mainly the 2-phenyl and 3-phenyl isomers dominate).
2.2 CAS Number and Composition
LAB is registered under CAS No. 67774-74-7, denoting a mixture of homologues and positional isomers. Typical commercial LAB products contain approximately:
- C₁₀ homologues: 5–15%
- C₁₁ homologues: 20–30%
- C₁₂ homologues: 35–45%
- C₁₃ homologues: 10–20%
- C₁₄ homologues: <10%
The aromatic content typically ranges between 10.5–13.5% (wt%), with a linearity index exceeding 95%, depending on process control.
3. Physical and Chemical Properties
3.1 Physical Characteristics
| Property | Typical Value | Remarks |
| Appearance | Clear, colorless to pale yellow liquid | Low viscosity |
| Molecular weight | ~239–254 g/mol | Depends on chain length |
| Density (20°C) | 0.860–0.870 g/cm³ | |
| Boiling point | 280–320°C | Broad range due to mixture |
| Flash point (closed cup) | 130–150°C | |
| Pour point | –40 to –30°C | Good low-temperature flow |
| Solubility | Insoluble in water; miscible with hydrocarbons | Non-polar |
3.2 Chemical Behavior
LAB is relatively stable under normal storage and handling conditions. It resists oxidation and hydrolysis due to the saturated alkyl chain and the absence of functional groups susceptible to nucleophilic or electrophilic attack. However, under high-temperature or catalytic conditions, LAB can undergo:
- Sulfonation with sulfur trioxide or oleum to produce LAS.
- Oxidation to yield benzoic acid derivatives or CO₂ and water under severe conditions.
- Cracking or dealkylation at elevated temperatures, forming benzene and lighter olefins.
LAB’s low polarity and high hydrophobicity make it an ideal intermediate for surfactant synthesis, as the sulfonation of the aromatic ring provides the desired hydrophilic-lipophilic balance (HLB) for detergent molecules.
4. Raw Materials for LAB Production
The industrial manufacture of LAB relies on benzene and linear mono-olefins as the principal feedstocks. The olefins are derived from paraffin hydrocarbons through various dehydrogenation or cracking routes. Major raw materials include:
- Benzene (C₆H₆): Obtained from reformate or pyrolysis gasoline streams; purified to >99.9% for alkylation.
- Linear paraffins (C₁₀–C₁₄): Sourced from kerosene or naphtha fractions of petroleum distillation.
- Linear mono-olefins (C₁₀–C₁₄): Produced by dehydrogenation of paraffins or olefin oligomerization technologies.
The selection of paraffin cut and dehydrogenation catalyst determines the final carbon number distribution and linearity of LAB.
5. Major Industrial Production Processes
Over the decades, several technologies have been developed for the industrial synthesis of LAB. The two major process routes are:
- Hydrofluoric acid (HF) alkylation process
- Detergent alkylate process using solid acid catalysts (modern processes)
A third route, chlorination–alkylation, was used historically but has been largely phased out due to environmental and safety concerns.
5.1 HF Alkylation Process
5.1.1 Process Overview
The hydrofluoric acid alkylation process, pioneered in the 1960s by UOP and others, involves the alkylation of benzene with linear mono-olefins in the presence of anhydrous HF as the catalyst.
Main reaction:
C6H6+RCH=CH2→C6H5CHRCH3
The HF catalyst promotes carbocation formation from the olefin, enabling electrophilic substitution onto benzene.
5.1.2 Process Description
The process consists of the following key steps:
- Olefin and benzene feed preparation:
The olefin feed is dried and mixed with excess benzene (benzene-to-olefin ratio of 8:1 to 12:1) to minimize polyalkylation. - Alkylation reactor:
The mixture enters a stirred-tank reactor with liquid HF. Reaction temperatures are maintained at 20–40°C under mild pressure (1–3 bar) to keep HF in liquid phase. - Phase separation:
The reactor effluent separates into an organic phase (LAB + unreacted benzene) and an HF-rich phase, which is recycled. - HF recovery and benzene recycle:
The organic phase is neutralized and stripped to recover benzene, which is recycled to the reactor. - LAB purification:
The alkylate product is fractionated to remove light and heavy impurities, yielding high-purity LAB.
5.1.3 Advantages and Disadvantages
Advantages:
- High conversion (>99%) and selectivity for LAB.
- Relatively simple and mature technology.
Disadvantages:
- Corrosive and toxic HF catalyst poses severe environmental and safety hazards.
- High maintenance costs for corrosion-resistant materials.
- Complex HF recovery systems required.
Due to these drawbacks, the HF process is being phased out in favor of solid catalyst technologies.
5.2 Detergent Alkylate Process (Solid Catalyst Process)
5.2.1 Introduction
Modern LAB plants increasingly use solid acid catalysts such as zeolites, heteropolyacids, or modified silica–alumina systems for benzene alkylation. This shift aligns with “green process engineering” principles, eliminating hazardous HF and improving product linearity.
5.2.2 Process Chemistry
The fundamental reaction remains the same — alkylation of benzene with linear mono-olefins — but the reaction mechanism involves surface acid sites on the solid catalyst rather than HF-mediated carbocations. Zeolite catalysts such as zeolite Beta, MCM-22, or ZSM-5 (modified) exhibit high selectivity toward linear monoalkylbenzenes.
5.2.3 Process Description
- Feed preparation:
Olefins and benzene are purified to remove sulfur, water, and unsaturated impurities. - Reactor system:
Fixed-bed tubular reactors operate at 120–200°C and 10–20 bar, with a benzene-to-olefin molar ratio of 10–20 to ensure monoalkylation. - Product separation:
The reactor effluent is cooled, and unreacted benzene is recovered and recycled. The bottom product is LAB, which is purified by distillation. - Catalyst regeneration:
Catalysts are periodically regenerated by oxidative burn-off of carbonaceous deposits.
5.2.4 Advantages
- No corrosive or toxic catalyst.
- Higher linearity (up to 98% 2-phenyl isomer content).
- Simplified handling and lower environmental footprint.
- Long catalyst life and easy regeneration.
This process is commercialized by several licensors, including UOP’s Detal Process and others developed by CTC, Petresa, and Reliance.
5.3 Paraffin Dehydrogenation (Feedstock Preparation)
Before alkylation, linear paraffins (n-paraffins) must be converted to linear mono-olefins. This is typically achieved using the dehydrogenation process (e.g., UOP’s Pacol process).
5.3.1 Reaction
CnH2n+2→CnH2n+H2
This endothermic reaction is catalyzed by platinum-based catalysts supported on alumina at 500–550°C.
5.3.2 Process Steps
- Feed purification: Paraffins are hydrogenated and dried.
- Dehydrogenation reactor: Tubular fixed-bed reactor with hydrogen recycle.
- Separation: Hydrogen is separated and recycled; the olefin–paraffin mixture proceeds to alkylation.
The overall selectivity to mono-olefins is typically 85–90%, with minor byproducts such as diolefins and cracked hydrocarbons.
6. Process Integration: The Complete LAB Complex
A modern LAB production facility typically integrates three main sections:
- Pacol unit (paraffin dehydrogenation)
- Detal unit (benzene alkylation over solid catalyst)
- Finishing and sulfonation feed preparation
The hydrogen generated in the Pacol unit can be used internally for catalyst regeneration or other refinery processes, improving overall plant economics and sustainability.
7. Quality Parameters and Specifications
Commercial LAB must meet stringent specifications to ensure high-quality LAS production. Typical specifications include:
| Property | Specification |
| Linearity | ≥95% |
| Bromine Index | <50 mg Br₂/100 g |
| Color (APHA) | <20 |
| Density (20°C) | 0.86–0.87 g/cm³ |
| Flash Point | ≥130°C |
| Sulfonation Reactivity | ≥98% conversion |
| Acid Value | <0.05 mg KOH/g |
High linearity and low bromine index are crucial for producing high-purity LAS with minimal unsulfonated organic matter (USOM).
8. Industrial Applications
8.1 Surfactant Manufacture (Primary Use)
Over 95% of LAB produced globally is converted to linear alkylbenzene sulfonate (LAS) through sulfonation:
C6H5CnH2n+1+SO3→C6H4(SO3H)CnH2n+1
LAS is the backbone surfactant for:
- Household detergents (powders, liquids, bars)
- Industrial and institutional cleaners
- Personal care products (shampoos, soaps)
LAS offers excellent foaming, detergency, and emulsification, while maintaining high biodegradability — a key environmental advantage over branched alkylbenzene sulfonates (ABS).
8.2 Intermediate in Specialty Chemicals
LAB is also used as a hydrophobic base in:
- Lubricant additives
- Emulsifiers
- Plasticizers
- Oilfield chemicals (e.g., drilling mud dispersants)
The alkylbenzene structure provides both aromatic stability and nonpolar solubility, making LAB derivatives useful in diverse chemical formulations.
8.3 Other Emerging Uses
Recent research explores LAB as:
- Scintillator solvent in neutrino detection experiments (e.g., Daya Bay, JUNO).
LAB’s optical transparency, high flash point, and chemical stability make it a superior solvent for organic scintillators. - Carrier fluid in heat transfer systems or specialty lubricants, due to its low volatility and high oxidative stability.
9. Environmental and Safety Considerations
9.1 Environmental Impact
LAB itself is considered to have low aquatic toxicity and good biodegradability once sulfonated. Its replacement of branched alkylbenzene sulfonates has significantly reduced surfactant residues in aquatic environments.
However, environmental management is crucial for production facilities, especially regarding:
- Benzene emissions (a known carcinogen)
- HF waste handling (if applicable)
- Catalyst disposal and regeneration residues
9.2 Safety Measures
LAB is classified as a combustible liquid, but not highly flammable. Key safety guidelines include:
- Storage in closed tanks under nitrogen blanket to avoid oxidation.
- Avoidance of contact with strong oxidizing agents.
- Proper ventilation in sulfonation and alkylation units.
- Use of explosion-proof equipment in LAB handling areas.
Personal protective equipment (PPE) such as gloves, goggles, and flame-resistant clothing are recommended during handling and sampling.
10. Global Production and Market Overview
10.1 Production Scale
Global LAB production exceeds 4 million metric tons per year, with major producers located in:
- Middle East (Saudi Arabia, UAE, Iran)
- Asia-Pacific (India, China, Indonesia)
- Europe (Spain, Italy)
- South America (Brazil, Argentina)
10.2 Major Producers
Some leading companies include:
- CEPSA Química (Spain)
- Farabi Petrochemicals (Saudi Arabia)
- Reliance Industries Ltd. (India)
- Quimica Venoco (Venezuela)
- Jubail Chemical Industries (KSA)
10.3 Market Drivers
- Rising global demand for biodegradable detergents.
- Expanding urbanization and hygiene awareness.
- Shifts toward solid-acid catalyst technology, reducing environmental footprint.
- Integration with refinery operations to utilize kerosene cuts effectively.
11. Technological Developments and Innovations
11.1 Catalyst Improvements
Modern research focuses on tailoring zeolite pore structures to optimize LAB selectivity and reduce heavy alkylate formation. Modified MCM-22 and Beta zeolites with controlled acidity and pore geometry enhance para-selectivity and linearity.
11.2 Process Intensification
Emerging technologies include:
- Reactive distillation for simultaneous alkylation and product separation.
- Membrane-assisted benzene recovery to reduce energy consumption.
- Continuous regeneration systems for dehydrogenation catalysts.
11.3 Sustainability and Circular Chemistry
The concept of a “bio-LAB” is under exploration, using bio-based n-paraffins from renewable feedstocks such as vegetable oils or fatty alcohols. These initiatives aim to decarbonize surfactant supply chains while maintaining performance and quality standards.
12. Engineering Design Considerations
12.1 Reactor Design
- HF process: Requires corrosion-resistant materials (Monel, Inconel) and phase separation vessels.
- Solid acid process: Fixed-bed reactors with temperature control and minimized hot spots.
12.2 Heat Integration
Dehydrogenation and alkylation steps can be thermally coupled to improve energy efficiency. Waste heat from dehydrogenation furnaces can preheat feeds or generate steam for other units.
12.3 Material Selection
LAB process units handle hydrocarbons and aromatic compounds; hence, carbon steel and stainless steel are common. HF units, however, demand exotic alloys.
12.4 Process Control
Advanced DCS (Distributed Control Systems) ensure:
- Accurate temperature and pressure control.
- Real-time monitoring of olefin conversion.
- Automatic catalyst regeneration scheduling.
13. Future Outlook
The future of LAB production is closely tied to sustainability and technological modernization. Key trends include:
- Elimination of HF catalysts in favor of solid acid systems (now the global standard for new plants).
- Increased process efficiency via digitalization and predictive maintenance.
- Expansion of renewable feedstock options, paving the way for partially or fully bio-based LAB.
- Integration into circular economy models, where waste hydrogen and benzene streams are recycled within petrochemical complexes.
As global detergent demand continues to rise, especially in emerging economies, LAB will remain a critical intermediate for decades to come — yet its production must evolve toward lower carbon intensity and safer, greener processes.
14. Conclusion
Linear alkylbenzene (LAB, CAS: 67774-74-7) occupies a central role in the modern chemical and detergent industries. Its unique molecular structure — combining an aromatic ring with a long linear alkyl chain — imparts ideal surfactant properties when converted to LAS. From an engineering perspective, LAB production epitomizes the integration of catalytic science, process design, and environmental stewardship.
The transition from HF-catalyzed processes to solid-acid technologies marks a milestone in sustainable chemical manufacturing, minimizing hazardous waste and improving product quality. With continuous innovation in catalysts, feedstock sourcing, and energy efficiency, LAB will continue to serve as both a vital industrial chemical and a benchmark for environmentally responsible process engineering.