Low temperature production of levulinic acid from cellulose using concentrated phosphoric and sulfuric acid solutions.
Résumé
Environmental and economical issues linked to fossil resources {oil, gas, coal) production have driven research towards the utilization of renewable feedstocks for fuels and chemicals production. Lignocellulosic biomass, such as wood or straw, is particularly interesting because this widespread feedstock does not threaten food supply. This study aims at converting lignocellulosic biomass into levulinic acid, a valuable building block which can lead to various products such as solvents, polymers, herbicides or additives. This platform intermediate can be obtained by acid-catalyzed conversion of cellulose contained in raw biomass. However, the state of the art concerning this acid-catalyzed reaction revealed that the current conditions {diluted acids in harsh temperature conditions) result in numerous by-products formation. The selectivity issue often deals with process control, in particular with reaction time optimization. Ionie liquids have recently been described as suitable media for the transformation of cellulose using smoother reaction conditions. Ionie liquid performances can be related to the strong interactions between cellulose hydrogen bonds and ionie liquid anions. Nevertheless, cellulose is mainly transformed into 5-HMF. However, due to the low a mount of water in the medium, levu li nic acid has never been observed in cellulose transformation involving ionie liquids. Our approach lies in using concentrated phosphoric and sulfuric acids as alternative media to catalyze the conversion of cellulose . lndeed, these strong acidic media are known to interact with hydrogen bonds in cellulose fibrils and favor cellulose decristallization. Their properties should promote the transformation of cellulose into levulinic acid at lower temperature th us limiting the formation of by-products. An extensive study on Avicel cellulose conversion in concentrated acids was performed. Levulinic acid yields were determined by HPLC analysis and a special attention was dedicated to the identification and quantification of soluble or insoluble by-products. A range of different acid concentrations was screened in order to optimize reaction yield. Catalytic results reveal high yields of levulinic acid {>50%) at 105 *c in both concentrated phosphoric and sulfuric aqueous solutions. A correlation between the medium acidity and levulinic acid yield is proposed.