Recovery of Organic Solvents from Wood Pressure Impregnated with Solutions of Copper Naphthenate or Pentachlorophenol

Treatment of wood with solutions of copper naphthenate or pentachlorophenol imparts good decay resistance. The chemicals are not leachable, and the wood remains paintable. The problem of excessive concentration of chemical at the surface of the wood is usually overcome by using an “anti-blooming” agent along with steaming following treatment. A new procedure is now described. A charge of kiln-dried southern pine lumber (e.g., 2 inches) is placed in a cylinder. The air pressure is raised to 50 psi, following which the cylinder is filled with about 10 percent solution of copper naphthenate or pentachlorophenol in xylol, and the pressure raised to 100 psi. After 1 hour, the pressure is released, and the cylinder drained and subjected to a vacuum of 24 inches mercury for 1 hour. The wood now contains about 7-1/2 lb./ft.3 of solution or 0.75 lb./ft.3 of preservative. The vapor drying process is now used to reduce the concentration of preservative at the surface. Fresh solvent is introduced into the bottom of the cylinder, and the temperature is raised to 260?F. The xylol vapors condense on the cooler wood, dissolve some chemical at the surface, and drop back into the bottom. After 1 hour, heat is cut off and a vacuum applied again for 1 hour. The cycle of heating and evacuation is repeated and the solution drained from to cylinder. At this point, the wood has about 0.35 lb./ft. solvent and 0.57 lb./ft.3 copper naphthenate or 0.26 lb./ft.3 penta; the higher retention of the former is due to its fixation by lignocellulose. Douglas-fir and red oak require longer treating times and longer solvent removal times. Following removal of solvent, distribution of chemical is improved and a clean surface is presented. The total cost using penta is $4 per thousand board feet less than that when steaming is used along with an anti-blooming agent.

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