One-pot synthesis of ethyl levulinate from wastes and its potential applications

The depletion of fossil chemicals and fuels expected in the next future makes urgent their substitution with the renewable ones. In this regard, alkyl levulinates represent outstanding platform chemicals and bio-fuels, in this case maintaing the fuel properties within the recommended limits and reducing the CO and soot emissions when mixed with gasoline or Diesel. They can be obtained through the acid catalysed esterification of pure levulinic acid or, more advantageously under the economic perspective, through the one-pot alcoholysis of carbohydrates and real biomasses. In particular, ethyl levulinate (EL) is one of the most investigated because it can be a fully bio-derived compound when bioethanol is adopted as alcohol. However, together with the desired EL, also the formation of both a solid by-product (humins) originating from the condensation of furanic intermediates/carbohydrates and ethyl ether took place. This latter derives from the etherification of ethanol, thus it represents an obstacle to the scale-up of the process causing loss of solvent. In the present work, the one-pot synthesis of EL has been carried out starting from monosaccharides (fructose and glucose), disaccharide (sucrose), polysaccharide (inulin) and waste biomass (defatted and steam exploded cardoon), employing H2SO4 as homogeneous catalyst. In particular, high substrate loadings, up to 14 wt%, have been adopted in agreement with the high-gravity approach aiming at the production of concentrated EL streams, which make easier the product separation and allow the increase of productivity. Under the same reaction conditions, fructose led to higher EL yield than that reached starting from glucose due to the absence of the Lewis acidity necessary in the conversion of glucose. On the other hand, when sucrose has been adopted as feedstock, an intermediate EL yield was achieved thank to the presence of the more reactive fructose moiety. Due to the pronounced reactivity of fructose, also the one-pot ethanolysis of inulin has been studied by the support of a statistical model that confirmed the synergistic role of the process parameters and allowed the identification of the optimal reaction conditions when the EL yield or EL concentration is to be maximized. Finally, a lignocellulosic biomass as the defatted and steam exploded cardoon, composed mainly by cellulose (60 wt%) and lignin (35 wt%), was employed as substrate leading to very promising EL yield, thus highlighting the feasibility of the one-pot ethanolysis starting from a waste. The obtained EL can find several potential applications and in the present work it has been proposed as bio-blendstock, thus preliminary engine tests have been performed leading to the reduction of soot and CO emissions, without any significant change in the engine performances.