Azeotropic Drying of Hardwoods Under Vacuum

Samples of tulip poplar, sugar maple, red oak, white oak, and black walnut measuring 2 by 3 inches in cross section and 10 inches long were azeotropically dried at temperatures ranging from 50 to 90?C., using toluene as the solvent. As expected, those species most easily seasoned by conventional means were also the ones most easily dried azeotropically. Results indicated, however, that even hard-to-dry species such as white oak could be dried fairly rapidly by azeotropic means. In general, all species tested could be dried below 10 percent moisture content in 8 days or less. These laboratory results should not be interpreted, however, to mean that equally good results could necessarily be obtained in commercial practice. Relatively small samples were used in these studies, and drying rates would undoubtedly decrease if longer specimens were used. Furthermore, only one specimen was treated at a time. Significant differences in rates of drying of individual samples within a species were noted, and it would most probably be difficult to dry all of the material in a charge to a uniform moisture content. Solvent recovery could also be a problem. Solvents such as toluene also pose fire and health hazards. Considerable research is obviously needed, therefore, to evaluate these factors. In spite of these shortcomings, this method does show considerable promise should economic conditions justify its use.

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