3Nylon: Issues

Production methods summary

The formation of a polyamide polymer is based on the condensation reaction between an organic acid and an amine. The choice of acid and amine determines the polyamide produced.

PA 6 is made from just one monomer, whereas PA 6,6 requires two. Their manufacturing processes are therefore different, although the starting point is normally benzene for both. Methylbenzene or dimethylbenzene may also be used. Find out how benzene is made.

The first stage is the production of a mixture of cyclohexanone (a ketone) and cyclohexanol (an alcohol) from benzene. The KA (ketone/alcohol) mixture is then used in the production of both PA 6and PA 6,6. Click to find more about making KA from benzene.

Polyamide 6
This can be made by a condensation reaction using one monomer with an amine group at one end and an acid group at the other.

chemical formula: polyamide 6 monomer
In practice the starting material is caprolactam, a cyclic compound made from benzene via cyclohexanone. Click here for more on the manufacture of PA 6.

It is also possible to make caprolactam from recycled carpets, reducing dependence on petrochemical feedstock (for benzene) and removing significant bulk from landfill disposal. Click to find out more about polyamide recycling

Polyamide 6,6

Two monomers are required, hexanedioic acid (adipic acid) providing the acid groups, and 1,6 diaminohexane providing the amine groups. In excess of 2 million tonnes of hexanedioic acid are manufactured worldwide each year, with the vast majority being used to make PA 6,6.

chemical formula: polyamide 6.6 monomers

These monomers are both made from benzene, "Producing … (KA) from Benzene" via cyclohexane and "KA", a mixture of the ketone cyclohexanone and the alcohol cyclohexanol. Click here for more on the manufacture of PA 6,6.

Recycling

Polyamides are thermoplastic, and so can be re-melted and pelleted for re-use. This is done with PA 6,6 (from carpet re-cycling) and the pellets are used for injection moulding of vehicle components. Chemical recycling, producing fresh feedstock, is also possible with both PA 6 and PA 6,6.

This is an increasingly important process as many countries seek to reduce the amount of waste material being placed in landfill sites. Click here to find out more about polyamide recycling

New Routes to Hexanedioic acid

The commonly used production method for PA 6,6 suffers from two disadvantages, from a "green" perspective:

It uses non-renewable petrochemical feedstock (the source for benzene)
The reaction used to produce hexanedioic acid (commonly called adipic acid) generates large quantities of dinitrogen monoxide, a pollutant gas that is difficult to treat.

Considerable research has gone into finding paths to hexanedioic acid that address these two issues. Find out more by clicking this link.