Binary Diffusion Coefficients of Biomass-Based Carbochemicals In Subcritical Water Using Chromatographic Peak Broadening Technique
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Carbochemicals such as furfural and HMF are very useful as intermediates in the production of various chemicals and polymers that have numerous food, fuel and medical applications. These carbochemicals can be obtained from sugar degradation upon hydrothermal treatment of biomass substrates such as switch grass and corn stover. However, knowledge of their thermodynamic and mass transfer properties in water as a function of temperature is essential in optimizing reaction conditions for the maximum yield of the carbochemicals from biomass substrates. There is insufficient literature on the diffusion coefficient of such carbochemicals in water at higher temperatures above the boiling point of water, also known as ‘subcritical water’. In this study, Taylor dispersion technique or chromatographic peak broadening technique was used to measure the binary diffusion coefficients at infinite dilution of certain carbochemicals such as furfural, HMF, vanillin, syringaldehyde, 2-furoic acid, ferulic acid, salicylic acid, levulinic acid and laevoglucosan in water at temperatures between 298.15 K and 473.15 K. It was found that the diffusion coefficients of the carbochemicals increased linearly with temperature. For example, the binary diffusion coefficient of HMF increased from 4.56*10-10 m2/sec at 298.15 K to 14.5*10-10 m2/sec at 473.15 K. However, it was also found that the diffusion coefficients of certain carbochemicals such as furfural and 2-furoic acid in water did not increase above 433.15 K which can possibly be related to their thermal degradation in water above that temperature. The diffusion coefficients of the carbochemicals in water were correlated as a function of temperature and solvent viscosity. The experimentally-measured binary diffusion coefficients of the carbochemicals in water as a function of temperature were also compared with those predicted using equations based on the Stokes-Einstein model.