Making plastic: Use plants, not petroleum.

Miao, X, R Malacea, C Fischmeister, C Bruneau and PH Dixneuf. 2011. Ruthenium–alkylidene catalysed cross-metathesis of fatty acid derivatives with acrylonitrile and methyl acrylate: a key step toward long-chain bifunctional and amino acid compounds.Green Chemistry http://dx.doi.org/10.1039/c1gc15569e.

Synopsis by Audrey Moores, Dec 02, 2011

 

Researchers greatly improved the use of plant oil – instead of petroleum – as a raw material to produce high-end plastics resins.

Plant oil can be used instead of traditional oil from fossil fuels to produce highly desired specialty plastics called polyamides.

A study in the journal Green Chemistry describes how researchers in France identified the material – a metal called ruthenium – that makes this type of chemical reaction possible. This discovery expands the scope of using plant oil derivatives to make industrially-important molecules, such as those needed as starting materials for producing polyamides. Polyamides are a family of polymers with many useful applications, ranging from fibres – such as nylon – to highly resistant metal coatings. Polymers are large molecules composed of repeating units of a smaller molecule.

The bulk of plastics are made from fossil fuels. As oil supplies dwindle, there is a need to find novel, renewable sources of raw materials that can be used to make everyday products, such as plastics, detergents and drugs. Oil from plants can serve that purpose, and researchers are actively looking to use them.

In the study, researchers from Rennes proposed an improved method to turn plant oil products into high-end polymers, such as resin coatings to protect metal from corrosion. They selected two streams of renewable materials to achieve this discovery. On one end, they selected fatty acids – basically fat molecules – from castor oil gathered from the castor plant seed. On the other, they chose acrylonitrile – a compound easily accessible from glycerol, a waste product of biodiesel production.

The fatty acids and acrylonitrile are combined with an additive containing a metal called ruthenium. The specific reaction fused the acid and the nitrile part of the acrylonitrile together and created the precursors to known and novel types of polyamides. The reaction was highly efficient – much material was made for the amount of energy put in.

This reaction is difficult to perform in the laboratory because acrylonitrile tends to destroy the ruthenium additive. To overcome this obstacle, the chemists screened a large number of additives and reaction conditions – temperature, pressure, time – to find the way that provided high yields.

Researchers also made diester molecules, which are necessary in formulation processes. Formulation is the mixing of ingredients to form stable gels, creams or pastes for the cosmetic or detergent industry. This reaction is a very efficient way to access such molecules from renewable feedstock.

An often discussed problem of using plant oil to make molecules for manufacturing products is the competition between plants for food and plants for chemicals. One way around this dilemma is to reuse frying oil or get it from spent coffee beans. Another idea is to use oil from plants not used for food, such as oil from the castor plant that was used in this study.

This study proved that it is possible to use renewable feedstock to make complex molecules like polyamides. Industrial applications remain to be demonstrated, but the resarchers did optimize their chemical process with this in mind. Read more science at Environmental Health News.