Kinetic Assessment For Selective Production of FURFURAL from C5 sugars contained in Biomass

Furfural is nowadays one of the most important biomass derived chemicals having a market of roughly 300 ktonn/year. It finds application in many chemicals sectors, being used as a solvent itself, or as starting material for almost all the furanic compounds. In a biobased economy furfural could replace or substitute many oil derivatives as platform chemical and be a starting material for liquid fuels production: furanic biofuels have lately been addressed to represent a very interesting option to current biofuels showing advantageous qualities. Moreover, being furfural derived from the C5 sugars contained in biomass, its integration in a modern biorefinery concept might represent a profitable way of valorizing the hemicellulose. Currently furfural is produced mainly through batch processes where biomass is cooked in acidic condition and furfural is stripped out by steam. Low total yields achievable in this kind of processes and high energy use drive up furfural price. A modern production process is to be developed at Delft University of Technology where furfural is produced continuously with high yields and with lower operational costs. To this aim kinetics of reaction from C5 sugars to furfural and furfural destruction in acidic water environment at temperature between 150 and 200 °C must be deeply investigated being the knowledge of C5 sugar chemistry available in literature incomplete or missing. An experimental setup has been designed and built to this scope which enables liquid phase reactions in broad range of conditions. It mainly consists of a titanium tube reactor immersed in a thermostatic oil bath where the reactants are fed by means of a HPLC pump. Mean residence time can be varied from 90 to 4500 seconds, titanium not alloyed ensures high corrosion resistance and no catalytic effects, an electrical heater at the inlet of the reactor and a pipe-in-pipe cooler at the outlet ensure steep temperature profiles. Due to these features reaction conditions and mean residence time can be accurately controlled. Experiments have being carried out using pure D-Xylose as model compound; H2SO4 is used to set H+ concentration at the desired level. Analysis is done using an HPLC apparatus equipped with UV and RI detectors. From the first experimental results a model has been proposed in which D-Xylose undergoes two parallel second order reactions in D-Xylose and H+ concentration, leading the former to furfural and the last to non identified fractionation products. The model shows a good agreement with experimental results at different temperatures and pH. Furfural degradation reaction has also been investigated at the same conditions of temperature and pH. Estimation of H+ concentration at reaction conditions is crucial and second dissociation constant of sulfuric acid dependence on temperature needs to be taken into account