CA1042791A - Composition and method for maintaining a constant concentration of agents and amount of solvent in a wood treating process - Google Patents

Abstract

ABSTRACT
A wood treating composition and method for impregnating wood. The composition comprises a) from 5 to 40 weight percent of a wood preservative such as penta-chlorophenol, b) from 2 to 60 weight percent of a glycol, polyglycol, or glycol ether dissolved or dispersed in a halogenated hydrocarbon solvent of 1-2 carbon atoms. The composition is useful for restoring depleted wood treating solution to its original composition.

Description

~042791 This invention concerns a wood treating compo-sition and a method for impregnating wood.
The utilization of halogenated hydrocarbon solvents as carriers for the impregnation of wood with preservatives, dyes, antiblooming agents, fire-retardants and the like has provided the art with a process superior to creosote oil, petroleum oil or liquefied petroleum gas techniques. The halogenated hydrocarbon solvent process is less expensive and more versatile, providing treated wood which is lighter, and therefore generally less expensive to ship. Also, wood treated in this manner has good retention of the additives and may be painted which was more difficult or impossible with older techniques.
Such halogenated solvent processes generally comprise soaking wood in a solution of a wood preservative in a relatively low boiling solvent such as methylene chloride or trichloroethylene. Pentachlorophenol is a commonly used preservative. The solution may also contain an antiblooming additive such as a glycol or glycol derivative. The soaking step may be carried out at ambient or somewhat elevated temperature and pressure. When the wood has been sufficiently impregnated by the treating solution~ the excess solution is drawn off and the wood is heated to vaporize the solvent in the wood. Solvent removal is completed by air drying. A final treatment of the wood by application of reduced pressure may also be used for this purpose.
The wood treating technique using a halogenated hydrocarbon solvent results in a loss of from 0.5 to 1.5 pounds (8-24 kg.) of solvent per cubic foot (meter) of ,, ~

16,147-F -1-104279~L
wood treated in addition to the additives retained by the wood. Thus, it has been necessary for the operator to "test and add" to his treating tank in order to maintain the desired concentration of treating agents and to make up solvent lost. In the "test and add" technique, since many of the preservatives are not readily soluble in the halohydrocarbon solvent and preservatives such as penta-chlorophenol are soluble only to about 10 percent by weight in the solvent, the operator must recirculate large quan-tities of solvent through a solid bed of the preservativeto his storage tank. The present invention provides a composition and method for replenishing the depleted treating solution by the continuous or intermittent addition of the liquid concentrate, thereby maintaining the concentration of the treating agents and replacing lost solvent at the same time.
The present invention provides a wood treating composition comprising A) from 5 to 40 weight percent of a wood preservative; B) from 2 to 60 weight percent of at least one of ethylene glycol, propylene glycol, a corres-ponding liquid polyglycol having a molecular weight up to 4000, or a mono aLkyl ether of ethylene or propylene glycol or polyglycol dissolved or dispersed in a halogenated aliphatic hydrocarbon solvent of 1-2 carbon atoms, said solvent boiling between ambient temperature and 140C.
Other wood treating additives such as dyes may also be present in the concentrate in minor amounts, but those listed are the essential components.
This invention further provides a process for impregnating wood which comprisss the steps: (l) contacting 1()4Z791 wood with a solution in a halogenated hydrocarbon solvent of 1-2 carbon atoms containing 2-6 weight percent of a wood preservative and 0.5-4 weight percent of a glycol component which is at least one of ethylene glycol, pro-pylene glycol, a corresponding liquid polyglycol ofmolecular weight up to 4000, or a lower aIkyl monoether thereof at from ambient temperature to 140C. and at a pressure to maintain the solvent in a liquid state, (2) removing excess solution from contact with the wood and returning it to storage, (3) heating the wood at least to the boiling point of the solvent, condensing the thereby vaporized solvent, and combining the condensed solvent with the excess solution, characterized by adding a composition as defined above to the depleted combined excess solution ànd condensed solvent to restore it to about the compo-sition of the starting solution.
The use of the polyglycol or the glycol ether allows a larger amount of preservative to be held in the concentrate as well as providing beneficial characteristics to the treated wood. Thus, it acts as a co-solvent in the three-component system and it also aids the retention of the preservative in the wood. Only about 9/O by weight of pentachlorophenol is soluble in methylene chloride alone, whereas if the concentrate solution contains 20-25% by weight of glycol, polyglycol or glycol ether, as much as 40/O by weight of the preservative can be present in solution, the remainder being the methylene chloride.
Similarly, chloroform, ethylene dichloride, methyl chloro-form, trichloroethylena, dichloroethylene, and perchloro-ethylene have relatively low solvency for most wood 16,147-F -3-104;~791 preservative agents, especially the chlorinated phenols.
With these solvents; the use of a glycol, polyglycol or glycol ether as a co-solvent also makes it possible to dissolve a substantially larger amount of preservative in the concentrate solution.
A typical solvent wood treating process is here-after described.
Wood impregnation with a preservative is achieved by soaking wood under pressure in a solution of the desired preservative in a halogenated hydrocarbon solvent with glycol additive and subsequently steaming or otherwise heating the treated wood to recover the solvent employed to carry the preservative into the wood. A finishing application of reduced pressure to the heated wood may be -`~ 15 employed to remove more residual solvent and water. Wood treated in this manner contains little or no residual solvent, and is therefore essentially free of surface bleeding. The process likewise provides the additional advantage of producing a treated wood product which retains the light color and natural appearance of untreated wood and which does not darken with age.
The present invention is preferably used as an added step in a wood treating process comprising the following operations:
(1) Wood in the desired form such as poles, lumber, or timbers is contacted in a suitable treating chamber with a solution or dispersion in a halogenated hydrocarbon solvent, preferably methylene chloride, con- - -taining 2-6 percent by weight of a wood preservative such as pentachlorophenol and 0.5-4 percent of a glycol or glycol 16,147-F -4-ether antiblooming agent at ambient temperature to 140C.
and at a pressure sufficient to maintain the ~olvent in the liquid state at the operating temperature. The time of contact may be from 1 to 12 hourcl, depending upon the type 5~ and specie of wood employed.

(2) The excess solution is removed from contact with the wood and returned to storage.

(3) The treated wood is heated at least to the boiling point of the solvent, preferably with steam, and the solvent vapors thereby formed are condensed and conlbined in storage with the excess solution removed in step (2), thereby forming a wood treating solution containing lower concentrations of both preservative and antiblooming agent than the original solution.

(4) (Optional) The heated wood is subjected to - reduced pressure to vaporize most of the residual solvent in the wood and the solvent vapors are condensed and com-bined with the recovered solution and solvent from steps (2) and (3).
The concentrate of the present invention is then added as the sole source of makeup to the depleted wood treating solution in a quantity sufficient to restore it to its original concentrations of preservative and antiblooming agent and the restored solution is returned to the process for another wood treating cycle. In the above-described - process, some modifications of procedure or materials may be made without altering the essential nature of the process. For example, in step (3), the wood can be heated with superheated solvent vapors rather than steam, thereby reducing the volume of water which has to be separated from 16,147-F ~5~

11~)4Z791 the condensed vapors before returning the recovered solvent to storage.
A preferred concentrate composition consists essentially of 10-35 percent by weight of pentachlorophenol and 5-55 percent of glycol antiblooming additive in methylene chloride. Although any of the glycols and glycol ethers described below can be used to advantage in the process, particularly preferred antiblooming additives are diethylene glycol and polypropylene glycol of about 750 molecular weight.
The treated wood produced by this process as described above has a clean, natural appearance when removed from the treating chamber and is essentially ready for use at that time.
The amounts of preservative and the depth of penetration necessary to provide the desired protection are well known to those skilled in the art of wood preser-vation. In the case of pentachlorophenol and closely related compounds, a desirable concentration is from about 0.35 to 0.7 lbs. (5.6-11.2 kg.) of preservative per cubic foot (meter) of wood on a dry weight basis, depending upon the species of wood.
Halogenated aliphatic hydrocarbon solvents suit-able for use in the present invention are those which have boiling points of from about room temperature up to 140C., ` preferably up to 100C. Examples of such solvents are the polyhalomethanes, polyhaloethanes and polyhaloethylenes such as methylene chloride, chloroform, carbon tetrachloride, methylene chlorobromide, l,l,l-trichloroethane, dibromo- -difluoroethane (BrFCHCHFBr), ~richlorotrifluoroethane ~' 16,147-F -6-':- . . . . .

1l)~279:1 (C12FC-CF2Cl)~ tetrafluorodibromoethane (BrF2C-CF2Br), tetrachlorodifluoroethane (C12Fc-CFC12), cis- and trans-dichloroethylene (ClCH:CHCl), trichloroethylene, perchloro-ethyleneJ l,l-dichloroethaneJ ethylene dichloride, or 1J 1J 2-trichloroethane. Particularly preferred solvents are lower boiling chlorinated compounds such as methylene chloride or ~richloroethylene.
Wood preserving agents which can be employed in this invention include those which are solvent-soluble or solvent-dispersibleJ unreactive with the solvent and are essentially nonvolatile at or below the boiling point of the solvent from which they are being impregnated into the wood. If more than one such agent is utilizedJ it is desirable that they do not react with one another in such a way as to interfere with the property or properties which they are intended to impart to the wood.
It is preferred that the agents be soluble in the solvent selectedJ but the solubility need not be great. For example, as little solubility as about one weight percent of preservative is operableJ but generallyJ preservatives are used which are soluble at least to the extent of 2 to 6 weight percent. Polyglycol and glycol ether antiblooming agents are employed in from 0.5 to 4 weight percent based upon the weight of solvent and these of course increase the amount of polychlorinated phenols and other preser-vatives that can be dissolved in the composition.
Wood preservatives for use in the process des-cribed above and which are employed in preparing the concentrates of this invention include pentachlorophenol, 2,3,4,6-tetrachlorophenol, 2,4,5-trichlorophenol, 2,4,6-16,147-F -7-1~)4;~791 -trichlorophenol, 4-chloro-2-chLoropentylphenol, beta--napththol, copper naphthenate, and phenyl mercury oleate.
Other known wood preservative compounds which are soluble or can be dispersed in halogenated hydrocarbon solvents with the aid of co-solvents or dispersants may also be used. Pentachlorophenol and its mixtures with tetrachloro-phenol are preferred.
Glycols suitable for preparing the concentrate of the present invention and which are also useful in providing antiblooming properties are ethylene glycol, propylene glycol and corresponding liquid polyalkylene - glycols having molecular weights of up to 4000. Glycol ethers which are useful in accordance with the present invention are those liquid Cl 4 alkyl monoethers of these glycols and polyglycols such as the methyl, ethyl or butyl monoethers of the mono-, di- and tri-ethylene and propylene glycols. Representatives of the above class of solvents are propylene glycol, diethylene glycol, dipropylene glycol, tripropylene glycol, ethylene glycol methyl ether, diethylene glycol butyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether, and tripropylene glycol methyl ether. Mixtures of two or more of such compounds can be used.
The following examples illustrate the invention.

A treating solution of pentachlorophenol and di-ethylene glycol in methylene chloride which had been used in the wood treating process, and which had originally ; contained about 5.0~ pentachlorophenol and 2.5% glycol - 30 based on the total weight of ~olution, was found by analysis 16,147-F

' after treatment to contaln 2.5% pentachlorophenol and 1.25% glycol. To 1000 pounds (450 kg.) of this depleted solution was added 110 pounds (50 kg.) of concentrate con-taining 28.6% pentachlorophenol and 14.3% diethylene glycol, the remainder being methylene chloride. The resulting 1110 (500 kg.) pounds of solution contained 5.09% penta-chlorophenol and 2.54% diethylene glycol, which was then at the proper concentration for processing more wood.

In another instance a somewhat stronger concen-trate was used to replenish the depleted wood treating solution. Thus to 1000 pounds (450 kg.) of treating solution was added 70 pounds (31.5kg.) of a concentrate containing 33.3% pentachlorophenol and 22.2% diethylene glycol in methylene chloride based on the total weight of the concentrate. The treating olution was thus brought from a concentration of 3.0% pentachlorophenol and 1.5% glycol to a useable concentration of 4.98% pentachloro-phenol and 2.85% glycol.

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A wood treating composition comprising A) from 5 to 40 weight percent of a wood preservative; B) from 2 to 60 weight percent of at least one of ethylene glycol, propylene glycol, a corresponding liquid polyglycol having a molecular weight up to 4000, or a mono alkyl ether of ethylene or propylene glycol or polyglycol dissolved or dispersed in a halogenated aliphatic hydro-carbon solvent of 1-2 carbon atoms, said solvent boiling between ambient temperature and 140°C.

2. A composition as defined in Claim 1 wherein the wood preservative is pentachlorophenol.

3. A composition as defined in Claim 1 wherein the solvent is methylene chloride.

4. A composition as defined in Claim 1, 2, or 3 wherein the glycol component is diethylene glycol.

5. A process for impregnating wood which comprises the steps: (1) contacting wood with a solution in a halogenated hydrocarbon solvent of 1-2 carbon atoms containing 2-6 weight percent of a wood preservative and 0.5-4 weight percent of a glycol component which is at least one of ethylene glycol, propylene glycol, a corres-ponding liquid polyglycol of molecular weight up to 4000, or a lower alkyl monoether thereof at from ambient temper-ature to 140°C. and at a pressure to maintain the solvent in a liquid state, (2) removing excess solution from contact with the wood and returning it to storage, (3) heating the wood at least to the boiling point of the solvent, conden-sing the thereby vaporized solvent, and combining the condensed solvent with the excess solution, characterized by adding a composition as defined in Claim 1 to the depleted combined excess solution and condensed solvent to restore it to about the composition of the starting solu-tion.