Replacing oil with wood in chemical making

RESEARCHERS have developed a new process to replace petroleum with wood as precursors for manufacturing pharmaceuticals, plastics or fertilisers.

Two research projects from the Swiss National Science Foundation’s (SNSF’s) National Research Programme “Resource Wood” (NRP 66) have made advances towards replacing oil with biomass derived from plants, particularly from wood. The projects focussed on using the two main constituents of wood, cellulose and lignin.

A team from the École polytechnique fédérale de Lausanne (EPFL) in Lausanne, Switzerland has designed new catalytic processes to efficiently transform cellulose, a long chain carbohydrate found in plant cell walls, into hydroxymethylfurfural (HMF), a precursor for the production of plastics, fertilisers or biofuels. The process used several types of ionic liquids (molten salts) to convert the cellulose into HMF. Activated by microwaves, the reaction begins with the ionic liquids disrupting the hydrogen bonding between the cellulose polysaccharides. The team hydrolysed the polysaccharides to form monosaccharides and dehydration to form HMF, producing a 62% yield.

Sviatlana Siankevich, a doctoral assistant at EPFL, said: “Our procedure operates…without high temperatures or pressure or strong acids. We've also been able to reduce the amount of undesired by-products, an important point if the reaction is to be scaled up for industrial processes. Our process can work with wood, but it's often easier to use cellulose extracted from herbaceous plants.”

A team at the Fachhochschule Nordwestschweiz (FHNW) in Muttenz, Switzerland were responsible for breaking down lignin. They were inspired by the action of fungi degrading rotting wood, by using selected enzymes capable of cutting lignin into aromatic compounds useful for making solvents, pesticides, plastics such as polystyrenes and active pharmaceutical ingredients.

The team tested dozens of enzyme combinations to select the most efficient ones. By adding a further catalytic step involving heating of formic acid with sodium formate with the lignin and enzymes over two days, they managed to transform 40% of the lignin into very small molecules such as vanillin.

The FHNW team also developed a way to reuse the enzymes by attaching them onto iron nanoparticles coated with silica. After the reaction, they used a magnet to attract the particles and recover the enzymes. As this method can be reused up to ten times, the energy and resources needed are significantly reduced.

Philippe Corvini, professor of environmental biotechnology at FHNW, said: “Until now, lignin was…often burned, but it can be cut into aromatic structures. These components represent huge volumes for the chemical industry, and have been so far almost exclusively obtained from petroleum. Lignin is presently the most serious alternative.”

Further aspects must be considered to assess whether wood can serve as an economically viable substitute for oil. A third project of NRP 66 has recently carried out a sustainability assessment of the production of succinic acid, another important chemical, from wood residues. The study concluded that smart process design can lead to energy savings and environmental benefits.

To be economically viable, wood as a replacement for petrochemicals must be used to the greatest extent possible. Siankevich added, “Extracting only one component from wood in small quantities is not enough”.

The next step for all teams involved will be to find complementary processes to use all of the components for chemical manufacturing means.

NRP 66 will now compile an overall list of recommendations for sustaining all the presented alternatives as a replacement for oil in 2017.

ChemSusChem DOI: 10.1002/cssc.201600313

Energy Environmental Science DOI: 10.1039/C6EE00634E