US2113589A - Wood preservative - Google Patents

Description

Patented Apr. 12, 1938.

UNITED STATES PATENT OFFICE woon PRESERVATIVE No Drawing. Application October 29, 1936, Serial No. 108,307

5 Claims.

The invention relates to wood preservatives and has as an object the provision of a wood preservative produced by the hydrogenation of pitch, particularly coal tar pitch, or coal tar residuum boiling above substantially 350 C.

The most commonly used wood preservative is that known in the art as creosote and is usually derived by distillation of tar resulting in the manufacture of coke from soft coal. The said creosote is distilled from the tars, under present practice at temperatures from substantially 200 C. to 400 C.

It is well understood that a distillate taken off at temperatures starting above 350 C. have substantially no toxic value and is therefore substantially useless as a wood preservative, at least insofar as destroying rot-producing fungi or fungoids.

I have discovered that if coal tar pitch, including thereby any residuum boiling above substantially 350 C'.,'having no, or extremely small, toxic value be subjected to a process of hydrogenation to induce lower boiling fractions, and these fractions be distilled off within the range 0 for wood preservative, as above stated for natural creosote, the wood preservative thus produced will have toxic value equal or superior to the natural creosote removed from the same initial coal tar from which the pitch thus treated was secured at the same distillation range. Tests down to date prove such an advantage to the extent of substantially two-fold.

The tests referred to show that a concentration of one-half of one per cent of natural creosote distilling 22 per cent below 270 C. was re quired for total inhibition of growth of fungi or fungoids, while a concentration of one-quarter of one per cent was, required in the case of the material of the present invention having the same boiling range. In the case of material distilling 37 /2 per cent below 270 C. the required concentrations were one quarter of one per cent and one eighth of one per cent respectively, for natural creosote and that of the present invention.

The product of the invention is a wood preservative falling within the specifications of the creosote of trade when produced by hydrogenation of a residuum of coal tar for this purpose. At present these specifications call for a material evaporating not more than 5% at 210 C. and having a high boiling point of 400 C. The residue left when distilled at 355 C. does not usually exceed 50%.

Since the material of the present invention is a product of the process described and claimed in my copending 'application'Serial No. 14,378, filed April 2, 1935, now Patent No. 2,082,885, issued June 8, 1937, for Method of producing a wood preservative or the like, by which process the resulting material may be varied in accordance with the requirements of the trade, it is within the present invention to depart to some extent from the specific boiling points and distillation ranges given above as shall from time to time be required by commercial change of requirements even to the extent of including fractions boiling as high as 500 C. as set forth in said patent.

Briefly stated the product of the present invention is a hydrogenation product of a coal tar residuum boiling substantially above 350 C., said hydrogenation product consisting of fractions boiling between substantially 200 and 500 C., having a specific gravity between 1.003 and 1.10 and having suitable toxic properties for use as a wood preservative. The residue, when the product is distilled at 350, can be made as low as desired by the process of my Patent 2,082,885, but should not exceed 50%.

An important discovery of the present invention is that hydrogenation of pitch to produce wood preservative falling within the boiling point ranges of creosote induces new toxic properties therein. I am unable to define the chemi cal differences between the synthetic creosote of a the invention and the natural creosote distilled from the initial coal tar. Therefore it seems at present impossible to formulate adequate claims to the product embodying the invention except by referring to the process by which it is produced.

The product of the present invention may be produced by hydrogenation of coal tar pitch as known to the trade. It may equally well be produced by similar treatment of a residuum from distillation of creosote derived by distillation of coal tar, in cases where the creosote was taken under conditions to include too high a residuum boiling at or above 350 C. The refining of such unacceptable creosote leaves a residuum which may or may not be denominated pitch by the trade but is a material which may be hydrogenated to produce the product of the present invention having the necessary toxic properties and other characteristics required for a wood preservative impregnant.

Minor changes may be made in the physical embodiment of the invention within the scope of the appended claims without departing from the spirit thereof.

I claim:

1. A wood preservative consisting of a liquid hydrogenation product of coal tar residuum boiling above substantially 350 C., said product consisting of fractions having boiling points falling between 200 C. and 500 C., and having suitable toxic properties for the purpose indicated.

2. A wood preservative consisting of a liquid hydrogenation product of coal tar residuum boiling above substantially 350 C., said product consisting of fractions having boiling points falling between 200 C. and 500 C., the specific gravity of the fluid being between 1.003 and 1.10, and having suitable toxic properties for the purpose intended.

3. A wood preservative consisting of a liquid produced as a result of hydrogenating coal tar residuum boiling above substantially 350 C., having substantially no toxic properties, said liquid consisting of fractions having boiling points falling between 200 C. and 500 C., and. having suitable toxic properties for the purpose indicated.

4. As a Wood preservative, a toxic liquid hydrogenation product of coal tar residuum boiling substantially above 350 C., said product consisting of fractions boiling between 200 and 400 C., evaporating not more than 5% at 210 C., and having a residue resulting from distillation at 355 C. of not more than 50%.

5. As a wood preservative, a toxic liquid obtained by hydrogenating the residuum of coal tar after removal of commercial creosote therefrom, said product having a toxic value of substantially twice that of the creosote removed from said residuum, and consisting of fractions boiling between 200 C. and 400 0., evaporating not more than 5% at 210 C. and having a residue resulting from distillation at 355 C. of not more than 50%.

JACQUELIN E. HARVEY, JR.