Valorization of lignin from biorefineries for fuels and chemicals

Joachim Bachmann Nielsen

Research output: Book/ReportPh.D. thesisResearch

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Direct lignin liquefaction is a promising process for lignin valorization in which ligninis treated in a solvent at elevated temperature and pressure. Liquefaction of sulfur freelignin obtained as a waste product from 2nd generation bio-ethanol production canprovide a sulfur free bio-oil which may substitute fossil fuel.In this Ph.D. study the direct liquefaction of a biorefinery lignin (hydrothermallypretreated enzymatic hydrolysis lignin) is explored. The goal is to provide a bio-crude which can substitute marine diesel as the engines found aboard large ships are adapted to more crude fuels. A novel process, which easily integrates with existing biorefinery infrastructure, is presented. The process yields a lignin-diesel oil (LDO) by noncatalyticsolvolysis in ethanol without hydrogen addition. The LDO is superior topyrolysis oil as it is non-acidic, stable and readily blends with fossil diesel without theneed for exhaustive deoxygenation. Batch autoclave experiments on lignin supercritical solvolysis in ethanol revealed the effects of different reaction temperatures, reaction times and degrees of ligninloading on product yields and bio-oil quality. The highest oil yield of 50 wt%d.a.f. was obtained for solvolysis of 10 g lignin for 8 h at 400 °C but 47 wt% of the solvent was also disadvantageously consumed. A lower reaction temperature and short reactiontime (<1 h) yielded an improved tradeoff between oil yield and solvent consumption. In particular a high lignin:solvent ratio of up 1:2 (w:w), which is a previously unexplored domain of lignin solvolysis, provided a deoxygenated bio-oil with a low oxygencontent of 9.7 wt% and an increasingly narrowed molecular size distribution dominated by species <300 g/mol (lignin monomers and dimers). Decarboxylation is the main contributor to deoxygenation as the majority of CO2 comes from the lignin. Solvent reaction routes were investigated in a separate study where different primaryalcohols (methanol, ethanol, 1-propanol and 1-butanol) were used. Primary reactions responsible for solvent loss were direct decomposition to gas through decarbonylation,formation of light condensation products and incorporation of the alcoholinto the bio-oil through covalent bonding. The latter may advantageously inhibit repolymerization and improve oil yield. An economic study complemented the results of the parameter study and highlighted that optimum profitability is obtained with short reaction time, high ligninloading and lower reaction temperature such as 350 °C instead of 400 °C. The key challenges of lignin solvolysis in alcohols are optimizing liquefaction faction yield relative to solvent consumption and continuous processing may provide an improvement.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages167
Publication statusPublished - 2016


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