MechChem Africa

The South African government has launched a R37.5-million biorefinery facility in Durban to enable extraction of maximum value from biomass resources. The facility, which is a first for South Africa, will support innovation in forestry, agro-processing and other biomass-based industries. MechChem Africa talks to the CSIR’s Bruce Sithole, the chief scientist and manager of the facility.

Opened by the Minister of Science and Technology, Mmamoloko Kubayi-Ngubane, at the CSIR’s Durban campus in March, the new Biorefinery Industry Development Facility (BIDF) is initially focused on the forestry sector, which is globally still experiencing financial difficulties. The CSIR’s new BIDF aims to use biorefinery technology innovations to develop or extract high value chemicals and products from waste biomass and thus help prevent job losses in the sector and encourage sustainable growth.

CSIR Biorefinery process equipment “Refining waste biomaterials in South Africa’s pulp and paper industry is practised on a very limited scale. Waste in the form of woodchips or sawdust from the wood, pulp and paper processing industries tends to end up in landfill sites, or is burnt, stockpiled or even disposed of by pumping it out to sea,” says Sithole. “The potential to extract value from it is not realised, which means lost opportunities for the country’s economy.

“When trees in South Africa’s plantations are cut down to produce timber boards, paper or dissolving cellulose pulp, only about 47% of the value of the tree is utilised. The majority, therefore, is lost as waste. This includes the leaves, branches, bark, saw dust, process liquors, which are all useful resources for the chemical industry,” he explains.

Sithole cites the three key ingredients and their approximate percentages that make waste wood and forestry products valuable: cellulose (38 to 50%); hemicellulose (23 to 32%); and lignin (15 to 25%). “The pulp and paper industries tend to be only interested in the cellulose and they only use the easily processed parts of the tree. Our mindset is to take everything that is classified as waste from the main stream forestry industries and to further process this waste into high-value chemicals and materials – this is what is called biorefinery processing,” he tells MechChem Africa.

“We begin downstream in the forests and saw mills where the waste is being generated. We recover the branches and bark along with any wood chips and sawdust. Then, using specialised chemical fractionation equipment and advanced analytical facilities, we use the different waste streams to extract a range of useful products,” he continues.

Hemicellulose, for example, is present in the cell walls of all plant material. But unlike cellulose, it is a short chain and branched polymer. It consists of many natural sugar monomers known as polysaccharides. “So we are able to use solvent extraction processes to selectively extract specific sugars, such as Xylose, for example, that can be converted into Xylitol, a low calorific value ‘artificial’ sweetener widely used by diabetics and weight-watchers.

“Eucalyptus trees have a particularly high hemicellulose content, which creates good opportunities for the waste beneficiation process,” Sithole says, adding that Xylitol is currently being imported into South Africa, which further enhances the localisation opportunity presented here.

Lignin, the third most abundant substance in natural wood, is another key area of research for the new BIDF. Lignin is the substance that makes newspaper go yellow over time, says Sithole. Lignin, particularly in its pure form, is a sustainable and renewable alternative ingredient for making thermoplastic materials, as well as phenolic and epoxy resins and isocyanates. Globally only 2.0 % is recovered for use to make products, one of the most notable being Arboform, a natural bioplastic developed in Europe.

 “After extracting the hemicellulose and lignin, the fibrous cellulose material is almost all that remains. But there is also no need for this to go to landfill. We have developed proprietary procedures to convert this fibre into cellulose nano crystals,” says Sithole. “With a tensile strength that exceeds that of stainless steel, this is a fantastic material that is now being used to produce super-high-performance and very lightweight composites – and the market price for crystalline nano fibre is now at about R12 000/kg.

“It is currently manufactured by reprocessing dissolving wood pulp, but the yield from wood to dissolving pulp is already only 35%, and from dissolving pulp to nano fibre, the yield is only 15%. So the current process yield is down to a little over 5.25 %,” Sithole estimates, adding: “Our technology can produce crystalline nano fibre directly from sawdust without the need to first produce dissolving pump – with yields as high as 40%.”

All in all, after having beneficiated each of the three major constituents of wood, very little waste remains, he notes. The facility can also extract pine oils from waste collected from pinewood forests and timber mills. “This can be used to make cleaning products, paint, plastics and even chewing gum.

“If you think about it, since all of our oil originally comes from biomass, most of which was once wood, almost every product currently derived from non-renewable oil-based resources can be produced directly from renewable plantations,” argues Sithole.

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