Essentially one thing. More than ninety-five per cent is sulphonated to linear alkylbenzene sulphonic acid and then neutralised to linear alkylbenzene sulphonate, which is the primary anionic surfactant in laundry powder, liquid detergent, dishwash and hard surface cleaners worldwide. Smaller volumes go into agricultural emulsifiers, oilfield surfactants, lubricant sulphonate detergents and speciality surfactants for textile and paper processing.

Because the branched version was an environmental failure. The original synthetic detergent alkylate was made from propylene tetramer and was heavily branched, and bacteria in sewage treatment could not degrade the branched chain. Through the 1950s and 1960s, surfactant passed through treatment plants unchanged and rivers across Europe and North America developed persistent foam — in places metres deep below weirs. The industry response was to switch the feedstock to linear paraffins from kerosene, giving a straight chain that bacteria break down readily by oxidising it from the end. The word linear in the product name records that change, and biodegradability remains the reason linearity is a specification rather than a description.

It changes how the finished surfactant behaves in formulation. The benzene ring attaches somewhere along the alkyl chain rather than at its end, and the 2-phenyl isomer — attached at the second carbon — has the ring near one end, giving a more linear, less bulky surfactant molecule. Higher 2-phenyl content produces LAS with better water solubility, higher viscosity in liquid formulations and better detergency at low wash temperature. Hydrogen fluoride catalysed LAB typically runs 15 to 20 per cent 2-phenyl; solid acid fixed bed processes reach 28 to 30 per cent. A formulator switching between them at the same nominal specification will see the viscosity of their liquid detergent change noticeably, which is why the figure belongs on the enquiry.

All three alkylate benzene with linear olefins, and they differ in catalyst and isomer outcome. Hydrogen fluoride is the long-established route, giving good linearity and moderate 2-phenyl content, but it requires handling anhydrous HF, which brings serious safety and permitting requirements. Aluminium chloride gives higher 2-phenyl content but generates a catalyst sludge that has to be disposed of. Solid acid fixed bed processes, introduced commercially in the 1990s, avoid liquid acid handling entirely, produce high 2-phenyl material and generate no acid waste, and most new capacity is built this way. For a buyer the practical consequence is the isomer distribution, not the catalyst.

Because LAB is a UVCB — a substance of unknown or variable composition — and UVCB identity is defined by the process and the composition rather than by a molecular structure. CAS 67774-74-7 covers benzene C10-13-alkyl derivatives and is the number most commonly quoted, but other registry numbers are in use for material that a buyer would recognise as LAB, depending on the chain distribution and how the producer has characterised and registered it. Since REACH registration, customs classification and downstream regulatory filings all reference that number, it needs to match the supplier's actual registration for the grade being shipped. Carrying a CAS across from a generic reference or another producer's datasheet is a recurring source of documentation problems.

Every shipment includes a Certificate of Analysis covering alkyl chain distribution, average molecular weight, linearity, 2-phenyl isomer content, bromine index, sulphonability, tetralins, non-aromatics, water, Klett colour after sulphonation, Saybolt colour, density and distillation range; a Safety Data Sheet for the specific grade; written confirmation of the CAS number and REACH registration applicable to the material supplied; an origin certificate; and destination-market certificates where required.