Image for What are green solvents and how do they add value to plantation forests?

*Pic: of Warwick Raverty at an anti-pulp mill rally. Pic by Dave Groves

One of the scientists (and fierce Gunns Pulp Mill opponent) behind Investment in bio-solvent plant heralds new opportunities for forestry explains this astonishing breakthrough ...

Solvents are used in a wide variety of applications ranging from spray painting cars and trucks to making life-saving pharmaceutical drugs.

Water for example is a solvent – a polar solvent, which means that its molecules have an uneven distribution of electrons and this feature enables it to dissolve many salts, proteins and sugars. Other polar solvents include alcohol (chemically known as ethanol), ethyl acetate used to dissolve nail polish and other lacquers and methyl iso-butyl ketone (MIBK) commonly used in car body shops to repaint after panel beating. The last three examples are called organic solvents because they contain carbon, hydrogen and oxygen. They are just a few of many hundreds of organic solvents that are used in industry to dissolve polymers (like those used in paints, varnishes and other coatings) and other materials that are not soluble in water.

When you make apricot brandy, or tarragon vinegar, you are using the ethanol in the brandy and the acetic acid (another organic solvent) in the vinegar to dissolve natural flavour chemicals out of the fruit or herb that would not dissolve in water alone. This is a common feature of solvents – all solvents dissolve some materials, but not others and which materials a solvent dissolves depends largely on this property called polarity.

Polar solvents, like water and ethanol will dissolve polar substances like most sugars, many salts and proteins, but they will not dissolve non-polar materials such as fats, grease and waxes. For these you need so-called non-polar solvents in which the electrons within the molecules are relatively uniformly distributed. Examples of non-polar solvents include petrol, kerosene, toluene and tetrachloroethylene (used by dry cleaners to remove grease and odours from soiled clothes).

Within the pharmaceutical industry a number of very specialised solvents are used in order to bond small molecules together in very specific ways in order to make the larger molecules that have very specific shapes and polarities that enable them to bond to membranes and enzymes in bacteria, fungi and viruses and kill them so that our immune systems have a chance to overcome the diseases they cause.  The solvents are completely removed from the drug before it is sold to consumers. Unfortunately the majority of the special solvents used by the pharmaceutical industry, called ‘polar aprotic solvents’ are quite toxic. Some cause mutations in human and animal cells, while others cause growth malfunctions in foetuses, like the infamous drug Thalidomide. For this reason the European Chemical Authority has recently legislated to progressively ban the use of solvents that pose unacceptably high toxicity and environmental risks when suitable non-toxic alternative solvents come onto the market. Similar legislation is already under consideration in North America, China and Korea.

Currently there are few non-toxic solvents suitable for use by the pharmaceutical industry available in commercial quantities. The joint development by Norske Skog and Circa of the new green solvent Cyrene, made from plantation radiata pine is a world first in this respect. It relies on the fact that the polysaccharide part of wood is mainly cellulose.  Cellulose in turn is made by plants by joining together hundreds of thousands of glucose molecules into long polymer chains that, when combined together, give wood much of its strength. What the new process being examined at the Boyer Mill will be doing is using a special recyclable catalyst to convert the cellulose in the pine wood into a precursor of the new solvent Cyrene, called levoglucosenone, some water and a carbonaceous char. The process itself has been developed over the past 6 years by Circa Group in Melbourne and patents have been granted or pending in all key markets. The char can be used as a solid fuel, or as a fertiliser.

In order for the solvent to be called ‘green’, it must be made from renewable resources (plantation grown wood in this case), it must be biodegradable and non-toxic and capable of being burnt at the end of its life without adding polluting nitrogen oxides and sulfur oxides to the atmosphere. Circa has worked with a major European pharmaceutical manufacturer to demonstrate that all of these criteria are met.

This move towards replacement of toxic solvents used in industry with sustainable non-toxic alternatives is part of a global trend towards what is being termed ‘the circular economy’. What this term implies is that as much as possible of the consumer goods made in the world will be made from renewable resources, like plantation timber, crop residues and food processing wastes. Any waste products from manufacture will be treated to extract materials of value and to remove any toxic by-products. At the end of life, these products will be ‘mined’ to extract materials that are in short supply with remaining metals and plastic being recycled, leaving nothing going to landfill.

This extraction of value from wastes has the potential to create new industries and jobs and Tasmania, with its wealth of plantation forests and food processing is in a prime position to be a key participant in this new emerging circular economy. The Cyrene solvent to be made in the Commercial Demonstration Prototype at Boyer has potential to grow into a future export market of many hundreds of thousands of tonnes, and the proponents and State Government are to be congratulated for seizing the opportunity to become an early participant in a major move towards much more widespread sustainable manufacturing of value added products.

(Dr) Warwick Raverty
Clayton South, Victoria