Abstract
Lignin-rich digested stillage from second-generation bioethanol production is a unique biomass-derived feedstock, not only because it contains high amounts of lignin but also due to its residual amounts of cellulose and hemicellulose. In this study, catalytic hydrotreatment experiments were conducted on pyrolysis liquids obtained from the lignin-rich feedstock using sulphided NiMo/Al2O3 and CoMo/Al2O3 catalysts. The aim was to obtain a high conversion of the initial pyrolysis feed into a hydrotreated oil with a high phenolics and aromatics fractions. Experiments were carried out in a stirred batch reactor at 350 °C and 10 MPa of H2 (initial pressure). Product oils were obtained in about 60–65% w/w, the remainder being an aqueous phase (12–14% w/w), solids (7–8% w/w) and gas phase components (all on initial pyrolysis oil feed basis). The product oils were characterised in detail using various techniques (elemental composition, GCxGC-FID, GPC, and 2D HSQC NMR). The oxygen content was reduced from 23% w/w in the pyrolysis oils to 7.5–11.5% in the hydrotreated oils, indicative of the occurrence of hydrodeoxygenation reactions. This was also evident from the chemical composition, showing an increase in the amounts of low molecular weight aromatics, alkylphenolics, alkanes and cycloalkanes in hydrotreated oils. Performance of the two catalysts was compared, and a higher degree of deoxygenation was observed for the NiMo catalyst. The implications of the findings for the valorisation of second-generation bioethanol residues are also discussed.
Highlights
The use of fossil resources for energy generation, transportation fuels and chemicals is under debate, because of high CO2 emissions
Characterisation of the pyrolysis liquid used for the hydrotreatment experiments
The pyrolysis liquid feed contain up to 20% w/w of low molecular weight compounds belonging to various groups, and a high proportion of higher molecular weight, non-GC detectable compounds, such as sugar oligomers and lignin fragments, as shown by gel permeation chromatography (GPC) analysis
Summary
The use of fossil resources for energy generation, transportation fuels and chemicals is under debate, because of high CO2 emissions. Alternative resources are required, [1,2] and biomass is considered as an attractive alternative for biofuels and biobased chemicals, because it is currently the only viable source of sustainable carbon [3,4]. Liquefaction of lignocellulosic biomass is considered to be of high importance as it facilitates transport and logistics [5]. Inevitably a solid residue is co-produced, known as stillage. This residue contains the original lignin, which is not converted in the process and residual cellulose and hemicellulose fragments [8]. Anaerobic digestion has been applied as a means to convert the stillage to biogas, but significant quantities of a lignin-rich solid residue, known as digested stillage, remains [9,10]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
