Linear olefins are manufactured using two distinct chemistries:
1. oligomerization, either in the Ziegler process to form the so-called Ziegler olefins, or using a newer process with organometallic mixed catalysts.
2. dehydrogenation of n-paraffins by various methods.

Olefin oligomerization supplies mainly α-olefins, while n-paraffin dehydrogenation leads predominantly to α-olefins only in cracking processes.

To 1:

The Ziegler process for the manufacture of α-olefins (Alfen process) consists of a controlled ethylene growth reaction carried out in the presence of triethylaluminum and takes place in two steps:
1. The building of the carbon chain takes place at relatively low temperatures between 90-120 °C and about 100 bar. Ethylene from triethylaluminum is inserted into an alkyl chain bonded to aluminum. A mixture of higher trialkyl-aluminums is formed in accordance with the following simplified scheme:



2. A mixture of ethylene oligomers is released and the catalyst is regenerated in a displacement reaction at more elevated temperatures (200-300 °C) and lower pressure (50 bar):

The alkyl groups are cleaved as straight chain a-olefins with an even number of carbon atoms. These olefins are obtained in high purity as no isomerization can occur. The first part of the Ziegler olefin synthesis is thus analogous to the Alfol synthesis. Both processes have the same unisolated intermediate, the trialkylaluminum compound Al[(CH₂CH₂)_n-C₂H₅]₃. The triethylaluminum, employed in stoichiometrical amounts, must be recovered in an additional process step before being reintroduced.

The industrial manufacture of α-olefins can take place in two steps as already described, i. e., with separate synthesis and subsequent (short period) high-temperature displacement. Furthermore, the synthesis can be coupled with a transalkylation step to produce a higher share of C₁₂-C₁₈ olefins, important in alcohol manufacture.

The α-olefin manufacture can also be conducted as a single-step process. The high-temperature ethylene oligomerization is carried out at 200°C and 250 bar with catalytic amounts of triethylaluminum (ca. 0.5 wt%). The ethylene is restricted in order to obtain a high proportion of unbranched α-olefins. The catalyst is destroyed by alkaline hydrolysis after the reaction and remains in the olefin product. A further characteristic of the single-step process is the broader carbon number distribution (between C₄ and C₃₀) of the resulting olefin mixture compared to the two-step route, as shown in the following table:



The α-olefin mixtures are separated by distillation into the required olefin fractions in both processes.

The two-step process is operated by the Ethyl Corporation in the USA (cap. 470000 tonnes per year, 1994), and the single-step process by Chevron in the USA (cap. 295000 tonnes per year, 1994), by Idemitsu in Japan (cap. 50000 tonnes per year, 1994) and by Mitsubishi Chemical in Japan (cap. 50000 tonnes per year, 1994).

Other manufacturing processes for α-olefins use ethylene as the feedstock, but differ in the catalyst used for the oligomerization. Exxon has developed a process where ethylene is oligomerized to very pure linear α-olefins with a soluble alkylaluminum chloridekitanium tetrachloride catalyst at temperatures between -70 to +70 °C in organic solvents. The molecular weights of the olefins increase with higher reaction temperature and decreasing polarity of the solvent. The a-olefins formed are in the range C₄-C₁₀₀.

Variations of a-olefin manufacture have also been developed by Mitsui Petrochemical (mixed catalyst containing titanium), by Idemitsu (mixed catalyst containing zirconium and organic ligands), and by Shell (nickel phosphine complex catalyst). The Shell SHOP process (Shell Higher Olefin Process) was first used industrially in the USA in 1977, and has since been employed in other plants.

To 2:

n-Paraffins mixed with branched paraffins, present in the petroleum or diesel-oil fractions of crude oils with a paraffin base, are available in sufficient quantities for dehydrogenation. The branched paraffins are usually undesirable components (high pour point) and can be removed from the mixture by freezing. To do this, the oil fraction is diluted and then cooled. Suitable solvents are mixtures of methyl ethyl ketone and benzene (or toluene), or methylene chloride and 1,2-dichloro-ethane, or liquid propane under pressure. A mixture of branched, unbranched and cyclic paraffins crystallizes out and is filtered. The straight chain component can be separated by adsorption processes.