Abstract:
The corrosion inhibiting activity of quaternary ammonium compounds is enhanced by the addition of a carbamide, specifically urea. In particular, the arylquinolinium halide corrosion inhibitor&#39;s activity with respect to a galvanized surface is significantly enhanced by the addition of the urea.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Corrosion inhibitors are used for a variety of different applications. Certain corrosion inhibitors are particularly suited for preventing corrosion of different metals, such as steel, copper and galvanized coatings.  
         [0002]     In many process water systems such as boilers and cooling towers, scale deposits present a significant concern. These scale deposits can inhibit heat exchange and/or water flow. Acids can be used to dissolve the scale. However, the acids generally promote corrosion. To deal with this, corrosion inhibitors have been added to the water in the process water systems. Quaternary ammonium compounds have been used as corrosion inhibitors and, in particular, to reduce corrosion of galvanized metal surfaces.  
       SUMMARY OF THE INVENTION  
       [0003]     The present invention is premised on the realization that corrosion inhibition provided by quaternary ammonium compounds can be enhanced by the addition of a water soluble carbamide and, in particular, urea. Urea in combination with, for example, an aryl quaternary ammonium compound, such as a quinolium halide, provides significantly greater corrosion inhibitor than the quaternary ammonium compound itself.  
         [0004]     The objects and advantages of the present invention will be further appreciated in light of the following detailed description. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0005]     A corrosion-inhibiting composition includes a quaternary ammonium corrosion inhibitor in combination with a carbamide. When used as a scale remover, an acid is included.  
         [0006]     The corrosion inhibitor comprises a composition including a quaternary ammonium compound of the general formula (R) 4  N + X −  wherein the R&#39;s represent the same or different long chain alkyl, cycloalkyl, aryl or heterocyclic groups, and X represents an anion such as, for example, a halide. Examples of such compounds include N-alkyl, N-cycloalkyl and N-alkylaryl pyridinium halides such as N-cyclohexylpyridinium bromide, N-octylpyridinium bromide, N-dodecylpyridinium bromide, N,N-didodecyldipyridinium dibromide, N-tetradecylpyridinium bromide, N-laurylpyridinium chloride, N-dodecylbenzylpyridinium chloride, N-dodecylquinolinium bromide. N-(1-methylnapthyl)quinolinium chloride, N-benzyl)quinolinium chloride and the like. Other quaternary ammonium compounds include monochloromethylated and bischloromethylated pyridinium halides, ethoxylated and propoxylated quaternary ammonium compounds, didodecyldimethylammonium chloride, hexadecylethyldimethylammonium chloride, 2-hydroxy-3-(2-undecylamidoethylamino)-propane-1-triethylammonium hydroxide, 2-hydroxy-3-(2-heptadecylamidoethylamino)-propane-1-triethylammonium hydroxide, 2-hydroxy-3-(2-heptadecylamidoethylamino)-propane-1-triethylammonium hydroxide, and the like.  
         [0007]     The preferred corrosion inhibitor of the present invention is an aryl quaternary ammonium compound and, in particular, an aryl quinolinium halide, and, in particular 1-benzylquinolinium halide. Generally, this is the chloride. This particular product is commercially available under the trade name Dodicor 2565.  
         [0008]     The corrosion inhibitor is combined with a carbamide. Any water soluble carbamide will be useful in the present invention. The primary and least expensive water soluble carbamide available for use is urea.  
         [0009]     The ratio of the quaternary ammonium compound to urea compound will be about 3:1 to 1:3 by weight. Generally, there will be slight excess of the urea.  
         [0010]     When the present formulation is used to remove scale, the composition will include an acid. Generally, any organic or inorganic acid can be used. Suitable acids include lactic acid, sulfamic acid, glycolic acid, citric acid, hydrochloric acid, phosphoric acid and methane sulfonic acid. These are all suitable for use in boilers and cooling towers. The concentrated scale remover will typically include 2-20% by weight acid,0.1-25% quaternary ammonium compound, and 1-20% by weight of the carbamide or urea.  
         [0011]     The corrosion inhibitor without the acid is formed by mixing the individual components in water. The order of addition is not significant. Heating is not required. The scale remover is formulated by adding the corrosion inhibitor to the acid with stirring. The urea is then added with additional stirring.  
         [0012]     The preferred scale remover is methane sulfonic acid 75% (70% active), Dodecor 2565 15% (about 30% active), and urea 10%. These are added to the water in a process water system at a concentration effective for the acid to remove scale. Generally, the concentration in a water system will be about 2-20% of system volume. This solution is circulated with the water and can be added as needed.  
         [0013]     The present invention can also be used to provide a cleaning gel wherein an acid is combined with a thickener, the urea and the quaternary ammonium compound. In this embodiment, the thickening agent, preferably a cationic surfactant thickening agent, is added to enable the product to adhere to a vertical surface, generally 200 to 6000 cps. The acid dissolves the white rust while the urea and quaternary ammonium compound reduce zinc corrosion.  
         [0014]     An exemplary composition is shown below. This product would be used as a white rust removal agent for cooling towers at 100%. The cooling tower is drained first. The gel is then applied as a spray onto the galvanized surface to remove the white rust, which is zinc carbonate or zinc hydroxide. This is rinsed off after the white rust has been substantially dissolved, generally about an hour. This permits the use of about 1/20th of the amount of chemical required in a typical white rust removal process.  
                                                       Hydrochloric Acid   19.0000           Water   64.9975           Acid Thickener   3.0000           Urea   9.0000           Dodicor   4.0000           Alphazurine FGND (conc.)   0.0025                      
 
         [0015]     This invention will be further appreciated in light of the following detailed example.  
       EXAMPLE  
       [0016]     To demonstrate the efficacy of the present invention, five different 10% lactic acid solutions were prepared. The first contained 5% DodicorV2565 and 8.5% urea; the second 10% Dodicor and 8.4% urea; the third 14.8% Dodicor and 8.4% urea; the fourth 23% Dodicor with no urea, and the fifth no Dodicor and 10% urea. These solutions were then tested to determine corrosion of galvanized metal with the results provided in terms of mils per test (mpt). In this test, 8 gallons of water per minute at 120° F. was circulated aver a galvanized coupon for 8 hours. The mils per year (mpy) represents an extrapolation of the mpt data.  
         [0017]     As shown in the Table, the mpt for the urea by itself was 15, which, effectively, provided no corrosion inhibition. The Dodicor by itself had an mpt of 0.22. The combinations of urea and Dodicor had mpts of0.11, .11 and0.35, respectively.  
         [0018]     This test demonstrated that the addition of urea enabled one to effectively cut the concentration of Dodicor in half and double the corrosion inhibition. Even with only 5% Dodicor and 8.4% urea, the mpt was comparable to 23% Dodicor by itself. Thus, the present invention allows one to reduce the amount of corrosion inhibitor and improve corrosion inhibition by the addition of the carbamide. This significantly reduces cost and improves efficacy.  
                                                         TABLE                                   mpy   mpt   % Dodicor   % Urea                                        383.25   0.35   5   8.4           120.45   0.11   10   8.4           120.45   0.11   14.8   8.4           240.9   0.22   23   0           16,425   15   0   10                      
 
         [0019]     This has been a description of the present invention along with the preferred method of practicing the present invention. However, the invention itself should only be defined by the appended claims, WHEREIN