How plasticizers are made

Flexible vinyl can be up to 65% plasticizer by weight. Without it, PVC is hard and brittle.

stations: 5
things upstream: 7
raw sources: 4
steps from the ground: 4

The short version

Most are esters, oily liquids that wedge between plastic chains so they can slide. The commonest route starts with ortho-xylene, oxidized to phthalic anhydride, which then reacts with a branched alcohol such as 2-ethylhexanol. Excess alcohol is recovered and the finished liquid is shipped, and nearly all of it ends up softening PVC.

Separate the ortho-xylene

Reforming naphtha gives a mix of aromatics, and this one isomer is split out. It has slowly displaced naphthalene as the feedstock, partly because it is easier to transport.

Goes in
Naphtha
Oxidize to phthalic anhydride

Vapor and air pass over a vanadium oxide catalyst. The product is a white solid, and its main use is exactly this one. About 3 million tonnes are made each year.

Goes in
Air
Bring in a branched alcohol

Plants make 2-ethylhexanol on a large scale from propylene. The branch in its chain carries over to the finished ester, helping to reduce viscosity and volatility.

Goes in
Propylene
Join acid and alcohol

Excess alcohol reacts with the anhydride under an acid catalyst such as sulfuric acid, giving a diester. The most important one is known as DEHP. Others use adipates, terephthalates and trimellitates in place of the phthalate.
Recover and drum

Leftover alcohol is taken off for reuse, and the oily liquid is sent to compounders in bulk. They mix it into PVC, where it stays unbound to the chains. That is why it can slowly migrate out over the years.

End of the linePlasticizer Next it goes into nail polish, pvc, polyvinyl butyral and 4 more.

Worth repeating

Flexible PVC holds 5% to 65% plasticizer by weight.
Almost 90% of polymer plasticizers are used in PVC.
The new car smell is often blamed on plasticizers, but studies do not find phthalates in it in appreciable amounts.