THE PRODUCTION OF FURFURAL IN AN EXTRACTION COUPLED REACTION SYSTEM
Abstract
The dehydration of xylose gives furfural; however, furfural is rapidly decomposed and polymerized under the conditions necessary for its formation. By using a suitable solvent most of the furfural can be extracted from the aqueous reacting phase as soon as it is formed, minimizing the loss of product due to undesirable side reactions. In addition to giving high furfural yields, such an extraction coupled reaction system is much more energy efficient, and hence, potentially more economical, than the conventional method of steam stripping. Aqueous phase kinetic studies indicate that the presence of furfural may affect the rate of reaction of xylose. This observation, which contradicts results reported by previous researchers, has led to a modification of the well-known Dunlop model for the acid catalyzed aqueous phase conversion of xylose to furfural. After considering several solvents for the proposed extraction coupled reaction system, three (toluene, 1,2,4-trichlorobenzene and o-nitrotoluene) were selected for further study. Effects of the direction of mass transfer, furfural concentration, temperature and solvent ratio have been examined. The interphase mass transfer of furfural between water and an immiscible solvent has been modeled by Whitman's two-film theory. Both the furfural mass transfer and distribution coefficients have been modeled as functions of temperature. Kinetic models have been developed for two-phase batch and continuous reaction systems by combining the aqueous phase kinetics and the two-film theory of interphase mass transfer. Predictions from these comprehensive two-phase models are compared to experimental data. The limiting case of instantaneous mass transfer is also considered. Simulated studies in a continuous stirred tank reactor show the sensitivity of process variables such as: distribution coefficient, solvent ratio, temperature and initial xylose concentration. Also, the two-phase CSTR model has been expanded to incorporate series of continuous stirred tank reactors. Furfural yields have been predicted for systems with the solvent flow co-current, cross-current and counter-current with respect to the aqueous phase. Finally, process flow diagrams are presented for the production of furfural from hemicellulose hydrolzate in a two-phase CSTR with product recovery by distillation and subsequent recycle of the solvent. The cost of producing furfural by the proposed process has been estimated and compared to the current market value of furfural.
Degree
Ph.D.
Subject Area
Chemical engineering
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