Drying of Methanol and Methyl Acetate from Poly(vinyl alcohol) Flakes

Abstract

Diffusion coefficients and equilibrium solubility of methanol/poly(vinyl alcohol) (PVOH) and methyl acetate/PVOH systems were examined to predict the drying rate of the solutes from PVOH flakes. The diffusion coefficients of the solutes strongly depended on the concentration of the solutes in PVOH, and the concentration dependency was well-represented in the form of D = D(0)exp{alpha C/beta+C} Numerical integration of the diffusion equation was successful using the Tri Diagonal-Matrix Algorithm. Our analyses demonstrated that an increase in the drying temperature shortened the drying time, while a reduction of the dew point of the solute in the drying gas negligibly affected the drying rate due to the formation of dense skin. As the excessive elevation of drying gas temperatures would degrade PVOH product qualities, reduction of the flake thickness and/or addition of methyl acetate to the drying gas were suggested as efficient tools to increase the methanol drying rate.