Abstract
Levulinic acid (LA) can be produced from lignocellulosic materials via hydroxylation followed by an acid-catalyzed conversion of hexoses. Inorganic homogeneous catalysts are mostly used, in particular sulphuric acid, yielding a mixture of LA with sulphuric acid, formic acid (FA) and furfural. Significant attention has been paid to optimization of the yield, but purification of the LA is a challenge too. This work focuses on the separation of LA from the complex aqueous mixtures by liquid-liquid extraction. Two aqueous product feeds were considered, reflecting two different processes. One aqueous product stream contains sulphuric acid and LA, while the second product stream also contains formic FA and furfural. Furfural could be removed selectively via liquid-liquid extraction with toluene. For selective extraction of LA and FA without co-extracting sulphuric acid, 30 wt.% of trioctylphosphine oxide (TOPO) in methylisobutylketone (MIBK) was found most suitable, showing a high selectivity over sulphuric acid, and a high equilibrium partitioning of LA. When instead of MIBK, 1-octanol was applied as diluent, the co-extraction of FA was enhanced, while hexanoic acid suppressed the acid extraction. To obtain the LA pure, eventually a distillation is required, and the potential of temperature swing back extraction (TSBE) at 90 °C to pre-concentrate the acid solutions was evaluated for 30 wt.% TOPO in MIBK. This pre-concentration step increased the concentrations of LA and FA by a factor of 2.45 and 2.45 respectively, reducing the distillation reboiler duty from roughly 31.5 to 11.3 GJ per ton LA, at a cost of roughly 4.5 GJ heating duty per ton produced LA.
Highlights
Levulinic acid (LA) is widely described as one of the high potential platform chemicals which can be derived from lignocellulosic materials [1]
It is important to find a solvent that shows a high selectivity for LA over sulphuric acid, and here, we report a solvent screening study focusing on the acid fractionation, which is a key step in the process allowing product isolation without loss of catalyst
High Pressure Liquid Chromatography (HPLC) The aqueous phase concentrations of LA, Formic acid (FA), furfural and sulphuric acid were determined with HPLC using an Agilent 1200 series apparatus, equipped with a Hi-Plex-H column (300 Â 7.7 mm) and a refractive index detector (RID). 5 mM aqueous sulphuric acid solution was applied as eluent at a flow rate of 0.6 mL/min
Summary
Levulinic acid (LA) is widely described as one of the high potential platform chemicals which can be derived from lignocellulosic materials [1]. The high reaction temperature and diluted catalyst option is most often applied [6,7,12,16,20,22,29,32] This prevents the use of expensive equipment which can withstand the high acid concentration, which is considered beneficial over the advantage of high acid concentrations that according to Mullen et al [6] Reunanen et al [12] and Cuzens et al [24] result in less char formation, a higher LA yield and fewer by-products at lower temperatures. It is important to find a solvent that shows a high selectivity for LA over sulphuric acid, and here, we report a solvent screening study focusing on the acid fractionation, which is a key step in the process allowing product isolation without loss of catalyst. 1-octanol (!99%), formic acid (!95%), heptane (99%), 4-tertbutylcatechol (!98.0%), 4-methyl-2-pentanone (!98.5%), dodecane (!99%), sulphuric acid (95.0–98.0%), toluene (!99.9%), diisopropyl ether (!98.5%), furfural (99%), 1-pentanol (!99%), 1-butanol (!99.7%), 1-hexanol (!99%), hexanoic acid (!98.0%), trioctylamine (99.6%) and trioctylphosphine oxide (99%)
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