Production Of Furfural From Pentose By Reaction-Extraction Coupled Process With Acetic Acid As Catalyst

The dehydration of pentose gives furfural, however, furfural is rapidly decomposed and polymerized under the condition necessary for its formation. High yields of furfural can only be achieved by the rapid and continuous removal of furfural from the aqueous solution. Reaction-extraction coupled process is a process in which dehydration reactions of pentose are carried out in the presence of an immiscible organic solvent so that most of the furfural can be extracted from the aqueous reacting phase almost as soon as it is formed to prevent furfural loss reactions. It is considered to be the most promising new furfural production technology because of more energy-saving, higher furfural yield and more green enviroment protected compared to traditional steam stripping process. In this study, the production of furfural by reaction-extraction coupled process with acetic acid as catalyst was studied intensively.Firstly, an accurate analytical method of pentosan was established by correcting the errors of GB/T 745-2003. The results of this experiments proved that furfural yield could reach 100% if the furfural formed could be removed from the aqueous phase quickly enough. The reaction kinetics of the dehydration of pentose to furfural was studied, and the kinetics equation with its parameters were obtained. The experiment results proved that acetic acid had strong catalytic activity to the dehydration of pentose to furfural.A series of high boiling aromatic compounds were evaluated as solvents for the proposed extraction coupled reaction system, o-nitrotoluene was selected for further study. The effect of temperature on the mutual solubilities for the water-o-nitrotoluene system and the distribution coefficients for furfural and acetic acid in the water-o-nitrotoluene system were studied. The results indicated that o-nitrotoluene had a high selectivity for frufrual, a low selectivity for acetic acid, and high thermal stability under the condition necessary for furfural production. Therefore, o-nitrotoluene was considered as a suitable solvent for furfural production in reaction-extraction coupled process.The experiment results proved that the mass transfer model based on two-film theory could predict furfural mass transfer between water and o-nitrotoluene perfectly even under high temperature (473.15 K) necessary for furfural production. The furfural degradation rates decreased remarkably in water and o-nitrotoluene system under the condition necessary for furfural formation.Continuous multistage counter-current furfural production process was first carried out in a scheibel column, and several factors such as reaction temperature, initial xylose concentration, solvent ratio, agitation speed and so on, were investigated. The experiment results indicated that the furfural selectivity could reach 75% under the condition that reaction temeprature 483.15 K, initial xylose concentration 120 g/L, acetic acid concentration 0.5 mol/L when xylose convension was 76%, this indicated that continuous multistage counter-current process could improve furfural selectivity remarkably.