DE4204941A1 - Fixation of chromium-free wood preservatives - by evacuation and then pressurisation with acid gas - Google Patents

Abstract

Fixation of Cr-free wood preservatives contg. Cu or Zn salts or complexes and/or polymeric betaines is effected by subjecting wood pretreated with the preservatives to a subatmospheric pressure in a pressure vessel, and then subjecting it to a superatmospheric pressure of acid gas. Pref. the pretreated wood is subjected to a subatmospheric pressure of 80 in bar (sic) for 15-30 min, followed by a CO2 pressure of 2-3 bar for 0.5-2.5 hr. The excess CO2 is recovered by pressure-swing adsorption and recompressed for re-use. ADVANTAGE - The process is simple, provides deep penetration of the preservative in short treatment times, and fixes the preservative so that it resists leaching and provides long-term protection. In an example, Wood samples were impregnated with a soln. of 11.57g ethanolamine, 6.16g basic Cu carbonate and 2.4g boric acid in 980 ml H2O. The samples were placed in an autoclave and pressurised with CO2 at 3 bar for 6 hr. The Cu uptake was 0.6g, of which 0.057g (9.5%) was removed in a leaching test (DIN 52172). Without CO2 pressure treatment, the corresp. values were 0.58g and 0.1102g (19%). (N.B., no examples involving subatmospheric treatment are disclosed).

Description

The invention relates to a method for fixation Chromium-free, copper salt-containing wood preservative.

Even today, wood is growing despite increasing Environmental awareness still predominantly with conservation Impregnated chrome-containing wood preservatives, as for No long-term fixation of the active ingredients fully satisfactory substitutes have been found.

Since the corresponding chromates are in the form of dusts or aerosols have been shown to cause cancer and are considered to be hazardous to water is in more detail Future a total ban on the use of these salts expected by lawmakers.

As chrome-free wood preservatives such. B. Formulations known based on inorganic Copper compounds with alkanolamines as complexing agents (EP 89 958 B1). The copper fixation takes place in the Wood through slow, dragging over weeks Reactions.

Basic compounds are formed, e.g. B. Copper hydroxide, which has a pH of up to approx. 5.0  are insoluble, but by dilute acids as in acidic soils or in acid rain be solved so that under these conditions the Salts are washed out to an increased extent.

The use of other complexing agents for the copper, such as B. polyamines has the disadvantage that the Cu washout can be 40% and more. The same applies to the use of hydroxycarboxylic acids in pH range above 6, e.g. B. tartaric acid. The washout this increases in part to over 50%.

It is therefore an object of the invention to quickly to provide a practicable procedure, thus chrome-free wood preservation salts, which may be amines or quaternary ammonium compounds or other salts included, placed as deep as possible in the wood and through a simple process step within Minutes or hours can be fixed in the wood that they are resistant to washing out and one provide long-term protection.

The task is solved by using Wood preservative pretreated wood in one pressure-resistant system is exposed to a negative pressure and then one created by an acid gas Overpressure is exposed. Preferably that is pretreated wood under vacuum for 15 to 30 minutes exposed to 80 m bar and then at 2 to 3 bar pressure treated with carbon dioxide. Not for Fixation of used, excess carbon dioxide can by pressure swing adsorption on activated carbon recovered and again after recompression be used in the process.  

It is known mechanically or through Weather influences of heavily used woods impregnated to a so-called To achieve "full impregnation" and the Introduce wood preservative deep into the wood. Here the wood to be treated with increased air pressure flooded with the impregnating agent.

The pressure is slowly built up in a known manner and about a certain, depending on the type of wood Duration kept constant.

The impregnation solution is then removed and the boiler filled with wood evacuated so that Escape any excess waterproofing agent from the wood can and thus a later bleeding is prevented. Depending on the type and quality of wood, this can Treatment to be repeated.

It is common to use railway sleepers, telegraph poles or woods for soundproof walls in this way impregnate. Even beechwoods, due to their Condition impregnating agent very difficult can penetrate through a varied Boiler pressure process (e.g. DBP-12 62 558) in one Impregnate the step. Aqueous, copper-containing, Chrome-free wood preservatives can be used according to this Process to a depth of more than 3 mm into the Bring in wood, but this is the lack Fixation not resolved.

It has now been found that zinc or copper-containing wood protection salts in a simple manner in Let wood fix if the impregnated wood with an acid gas is pressurized. Acid gases  are those that form upon contact with water react from protons. This reaction takes place e.g. B. with carbon dioxide, sulfur dioxide and HCl.

In this way, by pressure swing impregnation water-soluble salts that are introduced deep into the wood fungicidal and insecticidal properties on Effect of gas penetration, in particular Carbon dioxide to be fixed immediately.

This quick fix procedure is applicable for Wood preservatives in which, as from the literature known, copper or zinc ionogenic or in complex Form may be mixed with other components available. The metals can be complexed with water soluble primary, secondary, tertiary Alkanolamines or polyamines, such as. B. mono-, di- or Triethanolamine, propylenediamine, 3-amino-1-methylaminopropane, dipropylenediamine or N-nitroso-cyclohexylhydroxylamine or others. For Quaternary protection can also increase Ammonium salts such as e.g. B. Didecyldimethylammonium chloride, Octyldecyldimethylammonium chloride or others but also borates, fluoroboric acid, polyborates or polymers quaternary ammonium borates, so-called polymeric betaines, be included. The latter can also be used alone Wood preservatives are used and the subjected to quick fixation according to the invention.

The advantage of this method is that it can be carried out directly after the impregnation process without additional heat and moisture. The carbon dioxide gas can penetrate deeply into the wood through the pores and become effective, while with hot steam fixing according to DE-OS 36 09 317 water can deposit on and in the cold wood, which prevents uniform heating and makes fixing more difficult. Even after the CO ₂ treatment, the washability of the copper salts is reduced by more than 33% compared to other known fixing methods, in which the wood preservative can only be considered fixed after it has been stored for several days.

Compared to wood preservatives, in which the fixation takes place through the formation of water-insoluble carboxylic acid salts (DE-OS 36 09 317), this process offers the possibility of considerable savings in raw materials, since the salt formers, such as. As oxalic acid or sorbic acid, superfluous and less complexing agent is required. To carry out the fixation, the wood impregnated in the spray, impregnation or pressure swing process is exposed to a negative pressure of 80 in bar for 15 to 30 minutes. The pressure vessel is then gassed with an acidic gas, in particular CO ₂ , and the wood is exposed to the gas for 0.5 to 2.5 hours under an excess pressure of 2 to 3 bar.

After relaxing and drying, the impregnated is ready Wood to use directly without further treatment or available for further processing.

In a special embodiment of the method, excess CO ₂ can be recovered by pressure swing adsorption and reused. For this purpose, the carbon dioxide, which was not used for fixation, is passed onto activated coke or activated carbon and adsorbed there. It can be released again by vacuum, compressed again and used again in the process.

To illustrate the invention, standard blocks according to E 113 were treated by the method according to the invention and the washability of the copper and zinc salts was determined in accordance with EN 84 .

EXAMPLE 1 Fixation of chrome-free salts with CO ₂

10 test sticks are made according to DIN EN 113 with a Impregnated solution, 11.57 g for its preparation Ethanolamine, 6.16 g basic copper carbonate, 2.4 g Boric acid have been dissolved in 980 ml of water.

Five samples are then gassed with CO ₂ in a laboratory autoclave (pressure approx. 3 bar, duration 6 hours). The other sample blocks are stored in a desiccator during this time. The five test specimens from a washout are then washed out in accordance with DIN 52 172 and the amount of copper eluted is determined using AAS:

The average solution uptake of the samples fumigated with CO ₂ is: 172.16 g = 0.6 g Cu; washed-out amount of Cu: 0.057 g = 9.5%.

The average solution intake of not treated samples is: 167.25 g = 0.58 Cu; washed-out amount of Cu: 0.1102 g = 19%.  

Table 1

Penetration depths of chrome-free impregnation salts

Composition of the impregnation solutions used

VP 105 S (1000 g solution):

38.55 g ethanolamine
20.53 g basic copper carbonate
8.00 g boric acid
10.00 g polymeric quaternary ammonium borate
922.92 g water

KD 2000 CEB (1000 g solution):

38.55 g ethanolamine
20.53 g basic copper carbonate
8.00 g boric acid
932.92 g water

Claims (4)

1. A method for fixing chromium-free wood preservatives containing copper or zinc salts, their complexes and / or polymeric betaines, characterized in that wood pretreated with wood preservative is exposed to a vacuum in a pressure-resistant system and then exposed to an excess pressure generated by acidic gas becomes. 2. The method according to claim 1, characterized in that that wood pretreated with wood preservative in a pressure-resistant system for 15 to 30 minutes exposed to a negative pressure of about 80 in bar is then gassed with an acid gas and for 0.5 to 2.5 hours under 2 to 3 bar Overpressure is exposed to this gas. 3. The method according to claims 1 and 2, characterized characterized in that as an acid gas carbon dioxide is initiated.   4. The method according to claims 1 to 3, characterized characterized in that the excess gas means Pressure swing adsorption on activated carbon recovered and after recompression is used again in the process.