SELECTIVE ACID-CATALYZED FURFURAL GENERATION FROM C5-SUGARS CONTAINED IN BIOMASS: A REACTION KINETICS OPTIMIZATION ASSESSMENT

摘要

Furfural has gained renewed interest in the last years due to its potential for competing with oil derivatives as platform chemical and also as starting material for fuels or fuels additives production. Current uses in many chemicals sectors are as a solvent itself, or as starting material for the production of almost all the furanic compounds. Nowadays furfural is still produced mainly through batch processes where biomass is cooked under acidic conditions and furfural is separated by steam stripping. Low total yields, the lack of process integration and high energy use due to the large steam consumption, make furfural more costly to produce than oil derived commodities. Until now, the knowledge of C_5-sugar chemistry available in literature is yet incomplete or showing inconsistencies between different works, often rather old kinetic studies. This is why the kinetics of reaction from C_5- sugars into furfural and furfural destruction in acidic water environment at temperature between 150 and 200 °C are being deeply investigated. An experimental lab-scale tube reactor has been designed and built for this purpose, which enables liquid phase reactions under various conditions of acidity and temperature. Model components, mainly DXylose, are used for the reaction and the analysis is carried out by means of a HPLC apparatus equipped with a UV and refractive index detector. Results of reaction rate determination experiments leading to useful rate expressions are shown, indicating that Xylose parallel reactions represent a major loss in furfural production in an aqueous acidic environment. In addition to pH, the nature of the acid and anion type also seems to play a role in the reaction catalysis. Chloride ions led to significant improvements with respect to the H_2SO_4 base case. The addition of NaCl to a 50mM HCl aqueous solution (0.18%wt) allowed to attain even up to 90% selectivity to furfural. Among the salts tested FeCl_3 showed very interesting preliminary results, producing exceptionally high xylose reaction rates. Reaction conditions like temperature and reactant dilution, as well as the methods for furfural separation from the reaction mixture, might play a role in terms of selectivity and efficiency of the process.