Abstract
Formic acid assisted conversion of lignin to liquids (LtL-process), where lignin is hydrodeoxygenated in a one-step conversion, produces bio-oils with a molecular weight range of 300–600 Da that comprise a complex mixture of monomeric phenols, e.g., phenol, cresol, guaiacol, catechol, etc., and more hydrogenated products. This paper addresses depolymerisation of lignin at small and large lab scales and includes characterisation of the products. Lignin conversion is performed using a 5 L stirred reactor and a 0.025 L unstirred reactor to evaluate the effect of increased volume and stirring on the oil yield and oil quality. The amount of oil yields is investigated for different types of lignin/lignin-rich residues, reaction temperatures (320–380 °C), reaction times (0.75–3 h) and reaction solvents (aqueous or ethanolic), and have been shown to be highest for the 0.025 L reactor. Furthermore, the relationship between the yields and reaction conditions are systematically explored using principal component analysis (PCA). For the Eucalyptus lignin-rich residue, ethanol tends to give higher oil yields (36–52 wt%) at most of the operating temperatures compared to water as reaction solvent (20–50 wt%). At both reaction scales and both solvent-systems, oil yields tends to decrease at reaction temperatures above 350 °C due to increased char formation. Reaction time does not seem to have any significant effect on oil yield at either scale. More than 40 wt% of the input lignin can be recovered as oil at 320 °C at both scales and solvent systems.
Highlights
1.1 Background: from current fossil carbon based energy system to future biomass based energy systemThe increasing industrialization and motorization of the world has led to a steep rise in the demand for fossil fuels
The physical state of the reaction system at the selected temperatures was not explicitly known, but torque readings during the heating period indicated that lignin melted into a viscous liquid, which dissolved at higher temperatures
Results obtained from GC-mass spectrometry (MS) analysis indicated that the reaction temperature influenced the composition of the gas chromatography mass spectroscopy (GC-MS) detectable part of the bio-oils, while the abundance of peaks depended on the other reaction conditions used, i.e. stirring rate, level of loading in the reactor and catalyst use
Summary
1.1 Background: from current fossil carbon based energy system to future biomass based energy systemThe increasing industrialization and motorization of the world has led to a steep rise in the demand for fossil fuels. Recent economic developments in many countries all around the world have heightened the need for alternative energy resources, based mainly on renewable sources due to the depletion of fossil fuel, increasing energy demand, greenhouse gasses emission and global warming. The incoming raw material is completely converted to a range of products such as fuels and value-added chemicals [6,7,8] In this context, research on second-generation biofuel is focused on the more abundant and often relatively cheap plant-derived lignocellulosic biomass. Lignin can be obtained as a cheap byproduct either from the pulp and paper industry or from bio-ethanol production At present, it is mostly burned as low value fuel for process energy purposes and only approximately 2% is used commercially [1,5,9,10,11,12]
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