US3199211A - Method of preseasoning green or partially seasoned wood - Google Patents

Description

United States Patent METHOD-F PRESEASONING GREEN 0R PARTIALLY SEASONED WOOD Ralph H. Bescher, Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation of Delaware No Drawing. Filed Feb. 16, 1962, Ser. No. 173,774

6Claims. (Cl. 34-95) This application is a continuation-in-part of my copending application Serial No. 821,661, filed June 22, 1959, and now abandoned. v

This invention relates generally to the preservation of wood in a manner to preseason the Wood in a fire-proof hazardless process by means of liquefied petroleum gas.

A common practice in the wood preserving industry is to season Wood prior to, during or after impregnating the wood with a preservative. A conventional method of seasoning wood has been to air dry the wood, that is, the wood is placed or stored in a lumber yard to await the natural evaporation and evacuation of the water from the wood.

It is well known that green lumber containswater in two different conditions, that is, a portion of the water is free in the wood, whereas the remainder is actually bound in the cellulosic material of the wood and is considered to have saturated the fibers of the Wood. This air drying method of seasoning is primarily used to remove the free Water contained in green Wood. The green or unseasoned Wood that is exposed to the open air but protected from rain will gradually dry out until the greatest portion of the free water has been removed. The normal procedure in the .WOOCl preserving industry,

after air seasoning is completed, is to place this pre seasoned Wood into a kiln and'under high temperatures force as much of the remaining water as possible to evaporate from the wood. 1

The commonly used method of air seasoning wood has not proven entirely satisfactory because of the excessive costs necessitated by'the length of time required to remove the water in this manner, and because of the high inventory of wood which must be kept on hand during the time the seasoning is taking place in the air. Additionally, sapwood material and the heartwood of nondurable species may become infected with decay (storage rot) in the seasoningv pile especially during warm, humid weather.

In addition to seasoning lumber, it has been common practice to treat wood chemically, either before the lumber has been dried or after'drying has occurredto increase the service life when the wood is'to be used under conditions that favor the early deterioration of the wood as by decay, insects and other destructive agencies. This treatment of Wood is generally carried out by forcing preservative chemicals into the wood by pressure. Conventionally, this treatment involves subjecting the wood to a predetermined air pressure (super atmosphericor subatrnospheric) and without releasing this pressure, introducing a bath of a preservative onto the wood, then increasing the pressure and usually elevating the temperature of the preservative nearly to the boiling point of water and maintaining this elevated pressure for an interval of time to obtain the desired injection of the preservativein the wood. Thereafter, the bath of preserva tive is removed from the wood and the wood is sub- 7 3,199,211 Patented Aug. 1o, lass jected to sub-atmospheric pressure whereby excess preservative solution is removed from the Wood.

The pressure treatment of wood is conventionally dewood. These two processes difier mainly in the initial treating steps. The wood is subjected to sub-atmospheric pressure in the full-cell process so as to empty the cells of air-before the wood is subjected to the bath of preservative, and the wood is placed under super-atmosphe'ric air pressure in the empty-cell process to force a considerable amount of air into the cells of the Wood before subjecting the wood to a bath of preservative so that When the pressure is released, the air in the cells will eject some of the preservative from the cells.

Conventionally, an aqueous or an oil solution of a preservative is used as the bath. The aqueous or oil solvent places the preservative in a form that will penetrate the cells of the wood; If the wood to be impregnated is green, that is, it has not been air seasoned, a great amount of water will be present. If the cells of the wood contain this great amount of water, it follows that in attempting to impregnate a preservative solution into the wood, the water already contained therein will resist to some extent the penetration of the preservative. As a result, the efiiciency of the impregnation process is reduced. Additionally, the presence of the water is undesirable after the preservative is in the wood. The use'of Water as a carrier for the preservative will increase the amount of water left in the wood and thus requires that the wood be dried subsequent to the impregnation with the preservative. The subsequent drying, of course, requires extra heat and time and is somewhat dif ficult as the wood cell normally includes water. The moisture content of thoroughly seasoned wood is, forexample, within the'range of 6 to 15 percent of the dryv weight of. the wood. Also, the wetting during impregnation and the subsequent drying tends to cause checking of the wood and an undesirable raising of the grain.

The air drying methodfor seasoning wood hereinabove discussed has included a slow evaporation of the water while the wood is standing in the air for long periods of time. This drying period may extend for from 3 months to three years depending on the particular species of wood being dried. The principal object of this invention is to obtain an improved process for preseasoning green or partially seasoned lumber to obtain a product which (a) does not require an air seasoning period, (b) need not be kept in inventory for any length of time prior to kiln drying or impregnation with a preservative, (c) has had the free water removed within a 24 hour period, (d).is not subected to excessive heat, (e) is not damaged by treat ment, and (f) has not been changed in size.

It hasnow been found, in accordance with this invention, that wood may be readily preseasoned (free Water removed) by subjecting the Wood to treatment with an aliphatic hydrocarbon which (a) boils below the boiling point of water at ambient atmospheric pressure, but (b) readily liquefies' at ambient atmospheric temperature when placed under elevated pressure. p

In the process of this invention, the wood is subjected to a predetermined pressure and then without change in pressure is subjected to .an aliphatic hydrocarbon so that the pressure is increased to inject the hydrocarbon into the wood and thereafter the hydrocarbon evaporates from the wood.

Using the process hereinabove described, it is possible to remove the free water contained in green or in partially seasoned wood by the mechanical action of the hydrocarbon when it leaves the wood.

The novel process of this invention is applicable to all commercial species of wood. In fact, it has been found that the process of this invention is applicable to preseasoning refractory species (those species of wood which resist penetration more than the conventional species).

The above defined method of preseasoning lumber is economically and conveniently effective in apparatus commonly used for pressure treatment of lumber. In this respect, it is a novel method of removing the free water from green lumber in that while other processes of impregnation will normally leave water in the green lumber during pressure impregnation or will attempt to evaporate the water with excessive temperatures, the novel process of this invention is a mechanical process wherein the water is literally kicked out of the wood by the expanding aliphatic hydrocarbon gas. As a result of the novel mechanical removal of water, there is no checking of the wood nor undesirable time consuming, waiting period prior to kiln drying or impregnating the wood with a preservative.

The novel process of this invention will remove at least 50% of the free water contained in green or partially seasoned wood. The amount of water removed during the processing will, of course, depend upon the species of wood being treated. For any species, however, at least 50% of the free water is removed. The removal of this amount of water from wood in the very short period of time (less than 24 hours) is a totally unexpected, unusual and novel result. Since it has heretofore been common to air season for up to three years certain species of lumber, the removal of at least 50% of the free water from wood according to the process of this invention makes this invention an extremely practical and time saving method for preseasoning green or partially seasoned wood.

Suitable hydrocarbons for use in accordance with this invention include, for example: liquefied petroleum gas, butane, isobutane, propane, etc. The boiling point and heat of vaporization of these hydrocarbons is such that the temperature and heat of the wood itself is sufhcient so that, when the wood is removed from contact with the bath and the pressure lowered, this heat stored in the wood will vaporize the solvent remaining on and in the wood.

Accordingly, the process is desirably carried out at temperatures and pressures at which the solvent will be self-evaporating from the wood when the bath is removed from the wood. These hydrocarbons have vapor pressures such that the wood can be heated from 150 to 200 F. without developing excessive pressure. The application of high pressure to the wood has a tendency to damage the wood by crushing the cells of the wood. In addition, temperatures higher than 200 F. tend to weaken the cell structure of the wood so that the wood becomes more susceptible to crushing under pressure.

The processing of wood in accordance with this invention, wherein wood is preseasoned in a low boiling hydrocarbon has manifold advantages. The treated wood is clean; there is a decrease in weight of the wood; since the hydrocarbon has no aflinity for wood, as does water, and since the vapor pressure of the hydrocarbon is greater than the final pressure in the treating chamber, the hydrocarbon readily escapes from the wood. Thus, air storage is not required. The hydrocarbon itself serves as :an instrument for removing the residual free water from the wood, i.e., at the conclusion of the pressure phase, the rapidly expanding solvent gases expel the free water from the wood. The wood treated in accordance with this invention leaves the bath substantially dimensionally unchanged. Wood treated in accordance with this invention is odorless and has a non-oily surface, an advantage, of course, if the wood is to be painted.

The empty cell process is advantageously used to afford a fireproof, hazardless procedure with this process, as the high vapor pressure of the solvent aids in the ejection of the hydrocarbon from the cells at the end of the pressure treating step of the process, thereby reducing the quantity of hydrocarbon which must be evaporated from the wood. The gas used for impregnating the cells prior to their impregnation with the solvent and preservative may be air, but preferably is nitrogen, carbon dioxide, or other inert non-condensable gases since the hydrocarbons are flammable. The empty cell process may be used with complete safety and freedom from fire or other hazardous conditions even though the vapor pressure characteristics of the solvent lends itself to full cell process.

The invention will be illustrated further by comparison of the empty cell process in Example II with the full cell processes in Examples 1 and III in the following examples.

EXAMPLE I Green timbers of southern pine are placed in a closed cylinder and a vacuum of 25 inches of mercury is maintained on the cylinder for one half hour. Then, without admitting air, the cylinder is filled with liquid butane. The cylinder is then heated until the pressure in the cylinder increases to l25200 pounds per square inch guage. During the heating period, additional solution is pumped into the wood and to maintain the pressure at -200 pounds per square inch gauge pressure, and these pressures and temperatures are maintained on the wood for about two hours. Then, the hydrocarbon solution is removed from the cylinder and the cylinder subjected to a vacuum of 25 inches of mercury for an hour. Thereafter, the wood is removed from the cylinder. The wood is substantially dry, clean and odorless.

EXAMPLE II Green timbers of southern pine are placed in a closed container and air in amounts beyond :the explosive limits, or nitrogen or carbon dioxide, is injected into the container until the pressure in the container reaches 50 pounds per square inch gauge. Thereafter, butane is forced into the container and air is withdrawn from the container at a rate to maintain a constant pressure of 50 pounds per square inch gauge in the container. After the solution fills the container, the pressure is increased to 200 pounds per square inch gauge by raising the temperature, this pressure maintained for two hours, and then released. As soon as this pressure is released, the compressed gas in the wood expands and forces the hydrocarbon from the wood to a considerable extent. The hydrocarbon is drained from the cylinder and the wood subpected to a vaccum of 25 inches of mercury for a period of an hour, during which time the heat in the wood evaporates the solvent remaining.

EXAMPLE III Green southern pine is placed in a closed container and subjected to steam at a pressure of 15 pounds per square inch gauge for six hours. The steam is released and the cylinder evacuated for a period of two hours. Thereafter, butane is pumped into the cylinder, and after the butane fills the cylinder, the butane is heated to increase the pressure to about 200 pounds per square inch gauge and this pressure maintained for two hours. The pressure is then released and the wood subjected to a vacuum of 25 inches of mercury for a period of thirty minutes. The wood presents a product that has been partially dried in less than 10 hours.

EXAMPLE IV Hard maple 1" by 3" by 4 is placed in a closed con trainer and subjected to steam at a pressure of 15 pounds. per square inch gauge for 6 hours. The steam is released and the container evacuated for a period of 2 hours. Thereafter, isobutane is pumped into the container and,

after the isobutane fills the container, the isobutanc is heated to increase the pressure to about 200 pounds per square inch gauge and this pressure maintained for 2 hours. The pressure is then released. and then following this release of pressure, another pressure period of approximately 2 hours is again applied to the maple in the I cylinder. Then pressure of the second pressure period is released and the wood is subjected to a vacuum of 25 inches of mercury for a period of 30 minutes. The wood is then removed from the cylinder and the moisture content is measured. For'these particular species of wood the molsture content was reduced from 57% to 36%.

EXAM PLE V Stump green southern yellow pine poles were seasontreated with isobutane. A total of 7 hours pressure was used followed by a 2 hour final vacuum. The poles had average butt diameters of in. and were 36 ft. long. During treatment, the weight per cubic foot of these poles was reduced from 59.6 to 44.0 lbs./cu. ft.

EXAMPLE VII Stump green southern yellow pine poles were treated and seasoned with isobutane. A total of 7 hours pressure was used followed by a 2 hour final vacuum. These poles had an average butt diameter of i0" and were 36' long. The average moisture content of the outer l in. of these poles was 65% beforetreatment and 33% after treatment. Approximately 11.7 lbs. of water was removed per cubic foot of wood. 1 As further verification of the ability of this. process'to remove the free water contained in green or partially seasoned lumber, several other' specimens of southern yellow pine and redwood lumber were subjected to treatment with liquefied petroleum gases and tested for moisture content before and after treatment. The results of the treatment of the southern yellow pinespoles are shown below. in Table I.

Table I SEASONXNO DATA ON sou'rnsaN YaLnow rma POLES Moisture Content (Percent) Dimensions Polo Outer t" r" to m" Wt.

Dim, Length, Cubic Before After Bolero After ei.

in. Ft. Feet irest- Treat- Treat- Treatmeat snout assent meat 1 10.: as? one rss 42 a: at 2 m2 sas at: 92 or we 0.1 80.0 is. M 89 M 47 n.4- Mil one we so or as ms am no no or us so 0 IOJ 36.6 NJ ill 60 H0 48 use can car 124 as or an ass 11.0 or as ms to ma ass no or as n so months and then kiln dry it toa final moisture content of about l0%. Using theprocess ofthis invention, the

moisture level of heavy or medium segregation can be immediately reduced to about in less than 24 hours, obviating the use orthe need of any prolonged air seasoning. Table it shows the resultsof'2l specirnens of redwood lumber which were preseasoncd' according to 1 this invention and then measured for moisture content after seasoning.

Table II BEASONXNG DATA ON REDWOOD LUMBER [Dimensions 2 x 6 X 81 Moisture Content (Percent) Moisture Board No. Wt. Loss, Content tin/c1. Reduction Before After (Percent) Treatment Treatment 46 29.0 105'. 46 29.4 106 lit 00 --l0.0 M 1H 63 l3.2 61 181 61 l9.0 70 I llil 61 -18. 5 70 m as -a1.o tea m 10 -26. 0a 17'] 64 --26. 7 ms for the removal of hydrocarbon. The solvent, in addition to self-evaporation from the wood,'creat'cs a me.-

chanical force which removes the free water contained in v green or partially seasoned lumber and thus exerts apreseasoning effect upon the Wood.

What is claimed is: 1. A method of rapidly preseasoning green and partially seasoned wood which comprisesthe steps of f subjecting said wood to a predetermined pressure with' inert noneondensable gas so as to impregnate the wood with said gas, and thereafter without changing the pressure,

subjecting said wood to an aliphatic hydrocarbon which boils below the boiling point of water but which can be liquefied at ambient temperature conditions at pressurev above atmospheric pressure and which is a liquefied petroleumgas selected from the group consisting of butane, isobutane, propane and isopropane,

subjecting said 'wood and hydrocarbon to increased pressure whereby the hydrocarbonpenetrates said wood as a liquid, and

thereafter releasing the pressure, thereby expanding the non-condensable gas and evaporating the hydrocar bon and thus expelling the free water and removing the hydrocarbon from the wood.

2. A method of quickly prcseasoning green and partially seasoned woodby removing the free water therefrom. which comprises the steps of: V

subjecting said woodto a predetermined pressure with inert non-condensable gas so asto impregnate the wood with said gas, thereafter, without changing thepressure, subjecting said wood to an aliphatic hydrocarbon which boilsbelow the boiling point of water but which can be liquefied at ambient temperature conditions at pressures above atmospheric pressure and which is a. liquefied petroleum gas selected from the group consisting of butane, isobutane, propane and isopropane, subjecting said 'wood and hydrocarbon to increased: pressure whereby the hydrocarbon penetrates said" wood as a: liquid, andthereafter-evaporating the hydrocarbon from the wood 7 from the'wood, and whereby said preseasoning occurs in less thana 24-hour period.

3. A- process for preseasoning green or partially sea soned lumber to obtain a product'which does not require an air seasoning period, need notbe kept in'inventory for a length of time prior to kiln drying or impregnation with a preservative, and lias'at least 50% of 'the free water removed within a 24-hour period, the

process: a.

subjecting said wood to an elevated pressure with an inert non-condensable gas so as to impregnate the wood with said gas,

thereafter without changing the pressure, subjecting said wood to a lower aliphatic hydrocarbon which boils below the boiling point of water but which can be liquefiedat ambient temperature conditions at preswhereby the free water is expelled and hydrocarbon is removed from the wood to provide a preseasoned wood which is dry in that at least 50% of the free water has been removed therefrom and which has a non-oily surface. 4. A process of rapidly presessonlng green and partially seasoned wood which comprises:

impregnating wood with a liquid hydrocarbon which is a liquefied petroleum gas selected from the group consisting of butane, isobutane, propane and isopropane under superatmospheric pressure, and releasing said pressure so that said hydrocarbon autogenously vaporizes and the vapors expel the free water in liquid form from the wood. 5. A process of rapidly preseasoning green and partially seasoned wood which comprises:

injecting a liquid hydrocarbon which is a liquefied of'butane', isobutane, propane and isopropane into wood,-

heating said wood andhydrocarboniunder pressure,

i and 4 releasing said pressure to from the wood. 6. A method of preseasoning green and partially seasoned wood which comprises the steps of subjecting said wood to a liquid aliphatic hydrocarbon which is a liquefied petroleum gas selected from the group consisting of butane, isobuta'ne, propane and isopropane,

subiectingsaid wood and hydrocarbon to increased pressure'whereby the hydrocarbon is injected into said wood as a liquid, and

thereafter releasing the pressure and evaporatingthe hydrocarbon and thus expelling the free water as a hydrocarbon from the wood.

Q RefereheesCitedbytheEsamlner UNITED STATES PATENTS 1,023,745 4/12 Marr 117-59 1,760,444 5/30 Secord 349.5 X 1,967,990 7/34 Edwards 34-95 X 2,152,665 4/39 Rosenthal 34-37 X 2,507,190 5/50 Barksdale 349.5 2,860,070 11/58 McDonald.

6/59 Hutchinson 34-9.5

OTHER REFERENCES Encyclopedia of Chemical Technology, vol. 7, pages 632 and 639, 1951 Ed., The Interscience Encyclopedia lnc., NY. 7

Encyclopedia of Chemical Technology, Vol. '10, 1953, page 138, The lnterscienoe Encyclopedia Inc., New York.

NORMAN YUDKOFF, Primary Examiner.

petroleum gas selected from the group.consisting" vaporize, said hydrocarbon so that the vapors expel the freewater as a liquid UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,199,211 August 10, 19c

Ralph H. Bescher It is hereby certified that error appears in the above numbered petent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 27, after "the", first occurrence, insert cylinder to replace the material forced into the lines 50 and 51 for "subpected to a vaccum" read subjected to a vacuum column 6, line 47, for "pressure",

first occurrence, read pressures Signed and sealed this 29th day of March 1966.

(SEAL) Attest:

ERNEST W. SWIDER \ltesting Officer EDWARD J. BRENNER Commissioner of Patents

Claims (1)

1. A METHOD OF RAPIDLY PRESEASONING GREEN AND PARTIALLY SEASONED WOOD WHICH COMPRISES THE STPES OF: SUBJECTING SAID WOOD TO A PREDETERMINED PRESSURE WITH INERT NON-CONDESABLE GAS SO AS TO IMPREGNATE THE WOOD WITH SAID GAS, AND THEREAFTER WITHOUT CHANGING THE PRESSURE, SUBJECTING SAID WOOD TO AN ALIPHATIC HYDROCARBON WHICH BOILS BELOW THE BOILING POINT OF WATER BUT WHICH CAN BE LIQUEFIED AT AMBIENT TEMPERATURE CONDITIONS AT PRESSURE ABOVE ATMOSPHERIC PRESSURE AND WHICH IS A LIQUEFIED PETROLEUM GAS SELECTED FROM THE GROUP CONSISTING OF BUTANE, ISOBUTANE, PROPANE AND ISOPROPANE, SUBJECTING SAID WOOD AND HYDROCARBON TO INCREASED PRESSURE WHEREBY THE HYDROCARBON PENETRATES SAID WOOD AS A LIQUID, AND