Primary conversion of lignocellulosic biomass for the production of furfural and levulinic acid

The production of energy and chemicals from renewable resources has gained significant attention as a means to support the transition from fossil fuels towards\nclean and sustainable technologies. Due to its availability and rich carbohydrate\ncomposition, lignocellulosic biomass represents a valuable starting material\nand requires primary processes to unlock its components. The main focus\nof this research was to study and develop further knowledge on the primary\nsteps of conversion of lignocellulosic materials, i.e. biomass fractionation, cellulose/\nhemicellulose hydrolysis, and the production of furanic compounds (furfural,\n5-hydroxymethylfurfural) and levulinic acid.\nIn an initial stage, the fractionation of Miscanthus giganteus and sugarcane\nbagasse was investigated using hydrogen peroxide in formic acid solutions. This\ntreatment removed more than 70% of the lignin in the feedstocks after 13 h at\nroom temperature and after 15 min at temperatures over 150 oC. The use of\nhydrogen peroxide in formic acid under transient temperature facilitated the separation\nof >90% of the lignin and 80-98% of hemicellulose sugars, resulting in\nnearly pure cellulosic pulps. Likewise, lignin was recovered from the liquor and\npresented aromaticity properties proper of Organosolv lignins.\nThe conversion of lignocellulosic biomass to levulinic acid and furfural via acid\nhydrolysis was undertaken using sulphuric acid as catalyst. Biomass feedstocks,\nincluding agricultural, municipal wastes (paper) and rotational crops from Brazil\nand Ireland, led to levulinic acid yields between 150 and 400 kg/ton dry biomass.\nAdditionally, the kinetics of acid hydrolysis of Miscanthus to produce levulinic\nacid and furfural were studied at mild temperatures (150-200 oC) and high acid\nconcentrations (0.10-0.53 M H2SO4). A two-stage process was found to maximise\nfurfural (27.3 mol%) in a first reactor operated at 185 oC with 0.5 M H2SO4. A\nsecond stage leads to levulinic acid yields between 58-72 mol% at temperatures\nof 160-200 oC.\nA kinetic modelling study of the dehydration reactions of xylose, arabinose and\nglucose was carried out using formic acid as catalyst. Experimental data was obtained\nfrom the conversion of xylose, arabinose, glucose and furfural at 130-170\noC and high formic acid concentrations (10-64 wt%). High temperatures (>160\noC) favoured the formation of furfural (62-68 mol%) from xylose and arabinose;\nhowever, fundamental di erences in the reaction mechanisms followed by the pentoses\nwere found. Formic acid was not an effective catalyst of the conversion of\nglucose at temperatures under 150 oC. Temperatures above 200 oC favoured the\nformation of 5-hydroxymethylfurfural (20 mol%), while levulinic acid was maximised\n(40 mol%) at milder temperatures (170-200 oC). Experimental evidence\nwas obtained in relation to the side reactions affecting the conversion of xylose\nin liquors from the fractionation of Miscanthus. The conversion of xylose, arabinose,\nand glucose and the formation of 5-hydroxymethylfurfural and levulinic\nacid in the liquors were described satisfactorily by the kinetic models. However,\nwhen lignin was not separated prior to the reaction, the furfural concentrations\nobserved were significantly 40% lower than those predicted by the models. By\ninducing the lignin separation from the liquor, no losses in the selectivity of furfural\nwere observed. The effect of lignin model compounds and polymeric soluble\nlignin on the selectivities of the dehydration of xylose and glucose was investigated\nat 150 and 170 oC and acid concentrations of 60-62 wt% HCOOH. The\nresults con rmed that the oligomeric soluble lignin led to detrimental effects on\nthe selectivity of the furfural formation from xylose.