US2313596A - Asphalt composition - Google Patents

Description

Patented Mar. 9, 1943 2,313,596 ASPHALT COMPOSITION Stanley S. Sorem and Alvin P. Anderson, Berkeley, Calif'., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application June 10, 1940, Serial No. 339,762

11 Claims.

This invention deals with compounded asphalt compositions containing added ingredients to neutralize the asphalt. This invention is particularly adapted for use with blown asphalts and for use when asphalts are applied to zinc or other surfaces subject to corrosive attack by acids contained in asphalts. When asphalt is used as a coating or sealing medium for galvanized iron considerable difiiculty is often encountered in that the asphalt forms a very poor bond with the galvanized metal. In many instances, particularly when water is present, the asphalt will be completely removed from the galvanized sur face within a few weeks time.

It is therefore the object of this invention to provide an asphaltic composition which will maintain a firm bond with galvanized surfaces indefinitely even in the presence of water. It is a further object to provide a method for the neutralization of asphalts.

It has been found that the reason forvthe disbonding of normal asphalts from the galvanized surfaces lies in the presence of free acids such as naphthenic and/or asphaltogenic acids in the asphalt. Almost all asphalts including both natural asphalts such as Trinidad asphalt and manufactured asphalt, i. e., those produced by the distillation of petroleum oils, contain some acid. Blown asphalts produced by air blowing asphalts at elevated temperatures (or by equivalent chemical treatment such as with chlorine or sulfur) contain particularly large amounts of acid. Asphalts ordinarily have acid numbers ranging from about .1 to about mg. of KOH per gm. of asphalt (A. S. T. M. test D188-27T). These acids react with the zinc of the galvanized surface to form zinc salts thereby destroying the bond which links the asphalt and the galvanized surface and causing the asphalt to become separated from the surface. It has been attempted to neutralize these acids as potassium, sodium and calcium hydroxides but this neutralization has been found to be ineffective since the salts so formed attack the zinc almost as rapidly, possibly because of differences in solubilities of the second salts involved. Therefore, the net result is about the same as though the free acid were present.

It has now been found that finely divided zinc metal dispersed in the asphalt particularly at high temperatures in the presence of air or steam effectively neutralizes the free acid and that the salts formed thereby do not disrupt the bond between the asphalt and galvanized surfaces. The temperature is preferably about 200 to 600 with caustic alkalis such F. The amount of zinc should be at least equal to, and preferably twice or more than the chemical equivalent of the acids present. In other words, since most asphalts have acid numbers of from about .1 to 5 the amount of the zinc which needs be added should be at least from about .12 to 6 lbs. per ton of asphalt.

The following example illustrates our invention;

A galvanized sheet of iron was covered with a .05 inch layer of an asphalt having an acid number of 4.3 The sheet so covered was immersed in water. Peeling of the asphalt began within 3 days. The same asphalt was then mixed with an amount of zinc equivalent to twice the amount of acid which it contained. Another galvanized sheet of iron was coated with a layer of the resulting mixture and was immersed in water. No sign of disbonding was noted after 11 weeks. I

It is possible to substitute aluminum hydroxide, metallic lead, its oxide or hydroxide, or zinc oxide for all or part of the zinc metal to give practically as good results. In each case an amount is used which is at least equivalent to and preferably at least twice the equivalent of the acids present in the asphalt. The material used should be in the form of a powder or a gel.

Some few asphalts are found to be practically free from acids. However, on exposure to air the asphalt sometimes oxidizes so that acids are formed. Thus adding zinc or other agents as listed above has been found to be beneficial even in asphalts which are practically free from acids. The acid number of the asphalt should be reduced to a maximum of 1.5 to give satisfactory results. Some asphalts normally contain less than this amount of acid but the use of zinc or other neutralizing agent has been found useful even in these asphalts of low acidity since even small amounts of acid exert some harmful effect.

The preferred method of incorporating the zinc or other additive in petroleum asphalt is during the processing of the crude oil from which the asphalt is made. If a blown asphalt is to be prepared it is best to add the zinc metal to the asphalt just before it is blown. In this way the zinc salts are formed immediately on the forma-' tion of the acids in blowing. It should here be noted that the amount of zinc added is not governed by the acidity of the unblown asphalt, but rather by the acidity which the asphalt would have on the completion of the blowing if the zinc had not been added. If a straight run asphalt is to be prepared the zinc metal is preferably added to the topped crude oil during or prior to its distillation. This can best be done by injecting the zinc metal into the flash tower. The zinc may thus be used during the distillation to supplant the lime or other alkali ordinarily used. If a natural asphalt is used or if it is inconvenient to incorporate the zinc during the manufacture of a petroleum asphalt the zinc may be added by melting the asphalt and dispersing the zinc therein.

Although simple mixing of the zinc or other neutralizing agent with the asphalt has been found to be beneficial in reducing acidity, best results are obtained when the zinc and asphalts are heated to elevated temperatures and blown with a gas such as air, steam, chlorine, flue gases, etc. This may be most conveniently done in a blowing still or distillation unit as outlined above, or maybe done in any other suitable refinery equipment.

Besides the zinc metal other additive agents such as fillers and bonding aids may be added to the asphalt.

We claim as our invention:

1. As a new product an unemulsified asphalt composition capable of forming a durable bond with galvanized metal surfaces comprising an asphalt and an amount of a finely divided material chosen from the group consisting of zinc,

zinc oxide, lead, lead oxide, lead hydroxide and aluminum hydroxide in excess of that required to neutralize asphaltic acids formed by oxidation of said asphalt to maintain the product noncorrosive for prolonged periods of time.

2. As a new product a substantially neutral.

unemulsified asphalt composition capable of forming a stable bond with galvanized metal surfaces comprising an asphalt originally containing normal amounts of free asphaltic acids; an amount of a finely divided material chosen from the group consisting of zinc, zinc oxide, lead,

lead oxide, lead hydroxide and aluminum hy-- droxide in excess of that required to neutralize asphaltic acids formed in the product through oxidation to maintain it non-corrosive for prolonged periods; and soap formed by reaction of said free acid with said material.

3. As a new product an unemulsified asphalt originally containing normal amounts of free asphaltic acids and having an acid number above 1.5 which acid number has been reduced below 1.5 by the addition of an amount of a finely divided material chosen from the group consisting of zinc, zinc oxide, lead, lead oxide, lead hydroxide and aluminum hydroxide to form soaps with said acids, in excess of that required to neutralize acids formed by the oxidation of said asphalt to maintain said asphalt non-corrosive for prolonged periods.

4. The composition of claim 1 in which the amount of material added to the asphalt is at least twice the chemical equivalent of the free acid present in the asphalt.

5. The composition of claim 1 in which the material added to the asphalt is incorporated at an elevated temperature while blowing the asphalt with a gaseous material.

6. As a new composition of matter, a substantially neutral unemulsified asphalt composition comprising an asphalt containing an amount of finely divided zinc dispersed in said asphalts in excess of that required to neutralize asphaltic acids formed in said composition through oxidation to maintain it non-corrosive for prolonged periods.

7. As a composition of matter, a substantially neutral unemulsified asphalt composition comprising an asphalt and an amount of finely divided lead dispersed in said asphalt in excess of that required to neutralize asphaltic acids formed in said composition through oxidation to maintain it non-corrosive for prolonged periods.

8. The method of reducing corrosiveness of asphalts comprising adding an amount of a finely divided material chosen from the group consisting of zinc, zinc oxide, lead, lead oxide, lead hydroxide and aluminum hydroxide to the asphalt, and blowing the asphalt with a gas at an elevated temperature, said amount being in excess of that required to neutralize asphaltic acids formed by oxidation to maintain said asphalt non-corrosive for prolonged periods of time.

9. The method of preparing an asphalt of low corrosiveness capable of prolonged adhesion to metals subject to corrosive attack by asphalt acids, comprising incorporating in a topped crude oil during the process of manufacturing asphalt therefrom an amount of a finely divided substance chosen irom the group consisting of zinc, zinc oxide, lead, lead oxide, lead hydroxide and aluminum hydroxide, said amount being in excess of that required to neutralize asphaltic acids formed by oxidation to maintain said asphalt non-corrosive for prolonged periods of time.

10. The method of claim 9 in which the topped crude oil is distilled in the presence of the finely divided material.

11. The method of claim 9 in which the asphalt is blown in the presence of the finely divided material.

STANLEY S. SOREM. ALVIN P. ANDERSON.