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2,291,336 Patented July 28, 1942 UNHTED STATES 2,291,336 METHOD OF PREPARING WOOD IIVIPREGNANT Jacquelin E. Harvey, Jr., Atlanta, Ga., assignor of one-half to Southern Wood Preserving Com pany, East Point, Ga., a corporation of Georgia No Drawing. Application February 10, 1941, Serial No. 378,307 (Cl. 196-63) 1 Claim. clude the elimination of the apparent toxicity The present process relates to the elimination, blanketing effect in the entire residue above at least partial, of the toxicity blanketing e?ect 270° C. or any fractional part thereof, for it has in wood preserving impregnants. been shown that bene?cial toxic results are ac In the preparation of wood preserving im complished by eliminating or lowering the toxic pregnants from oils of aromatic content, it has U1 ity blanketing effect in only a portion of the long been a desideratum in the art to provide a residue above 270° C., as for instance the residue above 355° C. There are, perhaps, many reasons attaching to the decrease of toxicity as the residue above 270° C. increases, which, however, is of no con cern to the development of the data at hand. It is now discovered that, perhaps among other things, the character of the residue above 270° C. preserving impregnant of maximum toxic prop erties without sacri?cing permanency. How ever, research has disclosed that maximum toxic properties and good permanency of Wood pre serving impregnant are not always compatible. To secure a high toxic e?iciency of a wood pre serving impregnant, the permanency of the im pregnant must, to a certain degree, be sacri?ced. The converse is true. 15 influences the reduction of toxicity. In wood preserving impregnants of the oil type, as for instance impregnants of the tar-derived type, the As an‘ example of a wood preserving impreg nant of high toxic properties, but of relatively fractions above 270° C. contain in varying per low permanency, may be mentioned a coal tar creosote, identi?cation No. 7838, having 47.7% distilling above 270° C. and a killing concentra centages oxygen-containing compounds, tion of 0.075%. By killing concentration is meant the percentage of the wood preserving im pregnant required to kill wood destroying fungi and is fully described on page 2 under the cap tion “Method of conducting the test,” in Techni cal Bulletin No. 346, March, 1933, U. S. Depart ment of Agriculture. In the tabular data shown below are listed sev eral woo-d preserving impregnants and the indi cated relationship between their residue above 270° C. and their respective killing concentra tions. I _ Impregnant identi?cation No. 7838 _________________________________________ _ _ Killing Residue concentration above 270° 0 Per cent Per cent 0. 075 0.150 0.350 2. 500 47. 7 56. 7 73. 0 85. 0 of the impregnant in question. Research has disclosed that the toxicity blanketing effect of the residue above 270° C. may be eliminated, at least to a degree, by the decomposition or partial decomposition of the oxygenated compounds contained in said residue. The following examples will serve to illustrate modes of practicing the process, but are not to be construed as limitations inasmuch as those skilled in the art will readily recognize that the present process is possible of many variations. Example 1.-—A coal tar creosote having an oxygen containing residue of 47.7% above 270° C. and a killing concentration of 0.075% is stripped to remove the residue above 270° C. The residue is treated with hydrogen at 400° C. and 275 at mospheres pressure for one hour, the while in cluding the presence of a catalyst selected from the group consisting of halogens, halids and de 40 rivatives thereof. By the inclusion of said cata lyst oxygenated compounds are decomposed. As indicated by the tabular data shown above, the impregnant having the highest residue above 270° C. is the least toxic and those having the “a. 5 lowest residue above 270° C. are the most toxic. However, those having the least residue above 270° C. are the least permanent in the Wood treated therewith. Many and divergent theories have been advance-d for the decrease in toxicity as the residue in the impregnant above 270° C. increases. The present process is concerned with a novel manner of eliminating, at least to a degree, the apparent toxicity blanketing e?ect of the residue above 270° C., which statement is meant to in the 20 presence of which tends to blanket the toxicity The treated residue of lowered oxygen content is blended with the originally stripped low boil ing material to provide an overall toxic material having a killing concentration of less than 0.075%. EmampZe 2.-—A coal tar having an oxygen con taining residue of 85% above 270° C. and a kill ing concentration of 2.5% is stripped to remove the residue above 270° C. The residue is treated with hydrogen at 410° C. and 300 atmospheres pressure for one and one-half hours, with the inclusion of three tenths percent iodine based on the weight of the residue. By the aid of the 55 inclusion of said iodine, oxygenated compounds 2 2,291,336 are decomposed at least partially. The treated residue of lowered oxygen content is then com mingled with the originally stripped 10w boil ing material to provide an overall toxic material having a killing concentration of less than 2.5%. Example 3.—~A coal tar is distilled to substan toxic material having a killing concentration of less than 0.31%. Viewed broadly, the present invention provides a process for decomposing at least a portion of the oxygen containing compounds contained in said residue above 270° C‘. of toxic materials whose toxic efficiency is blanketed by the presence of'said oxygenated compounds. tial dryness to provide a creosote having an oxy gen containing residue of 73% above 270° ‘C'. and a killing concentration of 0.35%. As the creo Pressures and temperatures of in excess of 100 sote is being recovered from the coal tar it is cut 10 atmospheres and 300° C., respectively, are pre into two portions, the out being made at substan ferred. However lower pressures and tempera tially 345° C. The residue above 345° C‘. is sub tures may be used but the time element will be jected to the action of hydrogen at 415° C‘. and extended. a pressure of 200 atmospheres for a period of Minor changes may be made within the scope one hour, the while including a catalyst adapted 15 of the appended claim without departing from to in?uence the decomposition of oxygen con the spirit of the invention. taining compounds, said catalyst being selected I claim: from the group consisting of halogens, halids In the diminution of toxicity-blanketing effect and derivatives thereof. The treated residue of lowered oxygen content is then commingled with 20 in a high temperature coal tar creosote due to oxygenated compounds contained in the residual the low boiling portion of the creosote previously material boiling above 270° 0., the process which cut to provide an overall toxic material having comprises: stripping said creosote at a tempera a killing concentration of less than 0.035%. ture not below 270° 0. to provide a distillate and Example 4.-A high residue creosote having a residual having oxygen-containing fractions; substantially 75% residue above 270° C. and a said residual to a single action of hy killing concentration of substantially 0.3% is 25 subjecting drogen catalyzed by a catalyst selected from the stripped up to: 355° C. to provide a residue char group consisting of halogens, halids and deriva acterized by oxygen containing compounds that tives thereof, said catalyst adapted to in?uence blanket toxicity in the parent material. The oxy gen containing residue is treated with hydrogen 30 the elimination of oxygen from said oxygen-con in the presence of a catalyst selected from the taining residual; continuing the treatment for such a length of time and with pressure and tem perature so chosen as to provide at least partial elimination of oxygen from said residual; distill ing the treated residual to provide a newly formed group consisting of halogens, halids and deriva tives thereof; time of treatment, two and one quarter hours and pressure 300 atmospheres. The treated residue of lowered oxygen content is 35 residual having an initial boiling point similar to distilled to an upper limit to provide a residue the high boiling point of the distillate ?rst having an initial boiling point similar to the high "named; and commingling the residue last named boiling point of the distillate previously recovered with the distillate ?rst named whereby to provide from the high residue creosote starting material. a toxic material having a smaller killing con The distillate ?rst recovered and the residue last 40 centration than the parent material. named are commingled to provide an overall JACQUELIN El. HARVEY, JR.