Process for treating wood

A process for treating wood with a heat-fixable preservative which comprises the steps of:

• (A) placing the wood to be treated in a treatment vessel;
• (B) applying a vacuum to the treatment vessel to thereby reduce the pressure in a treatment vessel below atmospheric pressure;
• (C) introducing a treatment solution comprising an aqueous medium and the preservative into the treatment vessel while maintaining the pressure in the vessel below atmospheric pressure;
• (D) raising the pressure in the treatment vessel to a level above atmospheric pressure and impregnating the wood with the preservative;
• (E) reducing the pressure in the treatment vessel to a level of about atmospheric pressure, recovering any excess preservative in the treatment vessel and removing the treated wood from the treatment vessel;
• (F) placing the treated wood resulting from step (e) in a fixation vessel;
• (G) fixing the preservative in the treated wood by contacting the treated wood with an aqueous heat transfer fluid which has been pre-heated to a temperature of about 55.degree. to 95.degree. C. for a period of time of about thirty minutes to two hours, said fluid containing an oxidant comprising an inorganic chlorate salt which will oxidize any wood extractives resulting from such contact without any significant reaction occurring between the oxidant and the preservative;
• (H) removing from the fixation vessel the heat transfer fluid together with rinse water heated to a temperature of up to about 95.degree. C. which has been introduced into the fixation vessel as recited in step (K);
• (I) reducing the level of any contamination of the aqueous heat transfer fluid resulting from any wood extractives, any unfixed preservative and/or any particulate matter present in the fluid by one or more of the following procedures, in any combination thereof:
• (a) cooling the heat transfer fluid and the rinse water removed from the fixation vessel by heat exchange with clean water, thereby producing (i) cooled heat transfer fluid and rinse water which are used for preparing the treatment solution and (ii) heated clean water which is reserved for step (K);
• (b) filtering the heat transfer fluid and rinse water removed from the fixation vessel to remove any particulate matter contained therein;
• (c) adding to the heat transfer fluid and the rinse water removed from the fixation vessel a pH adjustment agent;
• and
• (d) establishing a pressure in the fixation vessel which will oppose movement of any wood extractives and any unfixed preservative into the heat transfer fluid and rinse water;
• (J) reducing the pressure in the fixation vessel to a level of about 0.3 to 0.9 atmosphere and maintaining such reduced pressure in the fixation vessel for a period of time of about 5 to 30 minutes;
• (K) introducing rinse water heated to a temperature of up to about 95.degree. C. into the fixation vessel and rinsing the treated and fixed wood in the vessel;
• and
• (L) raising the pressure in the fixation vessel to about atmospheric pressure and removing the treated and fixed wood and the rinse water from the vessel.