The characterisation of lignin-rich residues and their valorisation as biosolvents and adsorbents

Since the industrial revolution, economies throughout the world have pursued greater capital at the cost of greater environmental pollution, energy consumption and waste accumulation.

To combat this, numerous countries’ governments have set net zero greenhouse gas emission targets. As of 2016, notable emitters of greenhouse gas emissions were chemical and petrochemical manufacturing (3.6%), the burning of agricultural residues (3.5%), and agricultural soils due to synthetic nitrogen fertiliser applications (4.1%).
Therefore, in this thesis, a selection of biomass residues have been investigated for their potential applications as lignin-rich feedstocks to replace synthetic nitrogen fertilisers and petroleum-derived chemicals.

The lignin-rich nature of the biomass residues were explored through a variety of characterisation methods: proximate analysis, ultimate analysis, fibre analysis, atomic absorption spectroscopy and pyrolysis-gas chromatography/mass spectrometry (py-GC/MS). Here, the feedstock that performed best was a tree bark of an unknown species. This work necessitated the characterisation of a selection of identifiable tree barks.
From the characterisation of eleven different species of tree barks, the noble fir sample was found to have the greatest potential as a lignin-rich residue due to its high lignin content, low ash, and low alkaline earth metal content.

The properties of the lignin-rich residues after pyrolysis were investigated for their potential as bio-based solvents. The data from the py-GC/MS was used for the theoretical upgrading (by methylation and hydrogenation) of the key pyrolysis oil-derived components. The hazardousness and solubility of the three types of components were then assessed, with potential applications of lignin-rich residue-derived bio-based solvents being discussed.

The biomass residues were also explored for their application as ammonia adsorbents. The tree barks were tested both untreated and treated, as slow pyrolysis biochars and solvent-extracted samples. The untreated barks performed best and were found to be comparable in performance to costly gamma-alumina sorbents from the literature, but not as well as the most expensive zeolite catalysts. The untreated tree barks, as low-cost residues, may therefore be a good prospective ammonia adsorbent.