Use of Lignin
Biomass pretreatment processes break down lignocellulosic feedstocks into:
- hemicellulose, which is then hydrolysed by enzymes/acid to produce fermentable sugars for ethanol production
- lignin, the 'woody component'
Lignin has a number of potential uses, including:
- as a solid fuel
- as biofuel additives (e.g. conversion to oxygenated aromatics or esters)
- to add strength to concrete
- as an antioxidant
- to provide thermal protection to rubber
- for production of carbon fibre, asphalt mixes, plastics and polymers
- use as a paper sizing agent or board binder
- as a soil binder, as a dispersent for pesticide/herbicide applications, and similar agricultural uses
To improve the economics of cellulosic ethanol production in biorefineries, researchers are looking for ways to add value to lignin by conversion to other products (e.g. bio-oils contatining aromatic compunds). Coversion technologies include use of solvents, hydrothermal depolymerisation, and super critical depolymerisation.
In 2015, The US National Renewable Energy Laboratory published a study in the journal Energy and Environmental Science on the conversion of lignin-derived compounds to adipic acid, which is used to to produce nylon, plasticizers, lubricants, polyesters, etc.
In 2014, researchers at University of Wisconsin-Madison (funded by the Great Lakes Bioenergy Research Center), showed that high yields of the aromatics may be obtained by exposure of lignin to oxygen followed by treatment with a weak acid under mild conditions.
Reseachers at University of Tokyo have developed a technology using hydroxycyclopentadienyl iridium complexes as catalysts under hydrogen (dihydrogen) at atmospheric pressure to convert componens of lignin to aromatic chemicals [February 2015].
The University of Bath, UK has investigated ozonolysis in the presence of ethanol to depolymerise lignin, resulting in production of oxygenated aromatics. "Guaiacol, a potential antioxidant, was formed over short reaction times and was found to be completely miscible with low-sulphur petrol (ULSP), diesel, aviation kerosene and rapeseed methyl ester. The mainly aliphatic proportion of the bio-oil produced over 24h could be blended with the fuels replacing a maximum of 12-17wt.% of the hydrocarbon fuel." [Source: Renewable biofuel additives from the ozonolysis of lignin].