GB1377061A - Method of treating wood - Google Patents

Abstract

1377061 Impregnating wood RENTOKIL Ltd 23 Nov 1971 [23 Nov 1970] 55694/70 Heading DIP A process for the chemical treatment of wood e.g. in the form of timber, plywood or chipboard, comprises a first stage in which the wood is impregnated in a treatment vessel with a solution of a treatment agent in at least one halogenated hydrocarbon solvent which is inert to the agent, the solution being forced into the wood by a pressure differential, and a second stage in which, after removal of excess solution, the solvent remaining in the wood is removed therefrom by passing heated air through the vessel so as to cause evaporation of the solvent, the solvent being recovered. The solvent may be dichloromethane, trichloroethylene, perchloroethylene or fluorotrichloromethane. The impregnant may be phosphorus oxychloride, a boric or phosphoric acid ester, a wax or a film forming resin or a mixture of these. Solvent evaporation may be assisted by reducing the pressure in the vessel. The bulk of the evaporated solvent may be recovered by cooling or pressurising and cooling. The remainder may be removed by absorption on carbon followed by steam stripping and condensation. The process may be a full or empty cell process e.g. a Bethell, Rueping or Lowry process, or a double vacuum process. In Fig. 1 a piece of wood &c in a treatment vessel 2 is impregnated with solution previously run in from a tank 3 through a valve V4, under pressure provided a pump 4 connected through a valve V6 to a calibrated tank 5 which registers the gross uptake of solution. After removal of excess solution by a pump 6 back to the tank 3, air is circulated by a pump 7 through a heater 8 and the vessel 2 and evaporates solvent from the wood. The solvent vapour is collected in a condenser 9 and the condensed liquid run through a valve V9 into a tank 10 where it is admixed with further treatment agent prior to being returned to the tank 3. The level in the calibrated tank is returned to a desired point by regulating valve V7. In Fig. 2 wood &c 1 in a vessel 2 is impregnated with treatment solution by applying a pressure to the solution in a tank 3 which forces the solution into the vessel through a valve V11, air being vented through a valve V12. After impregnation, the compression is released and the solution is allowed to run back into the tank. Heated air is circulated through the vessel by a pump 7 and solvent is condensed at 9. Further solvent is removed by passing fresh air through the vessel via valve 14 and into a carbon recovery plant 11. The pressures applied during impregnation may be 10 or 20 p.s.i.g. The air may be at about 60‹C and 22‹C on leaving the heater and condenser respectively.