Patent Application
20090169422
This invention relates generally to industrial brines and more specifically to reducing the corrosion rate of ferrous metals when exposed to industrial brines.
The corrosion problem caused by the exposure to and/or use of industrial brines has been a long standing problem in the industry. One approach has been the addition of various anti-corrosive agents to the brine in order to reduce its corrosive effect. These various additives can be expensive and to a large extent have been ineffective in controlling the corrosivity of industrial brines.
The following U.S. patents are exemplary of the current state of the art with respect to attempts to control or limit corrosion in industrial brines and other corrosive aqueous solutions.
U.S. Pat. No. 4,536,302 is directed to a method of inhibiting corrosion of ferrous metals by aqueous mediums such as exposure to brines. The patent teaches that the corrosiveness of aqueous mediums such as brines on ferrous metals can be reduced by including an effective amount of a mixture of a sulfur compound and a reducing sugar. Reducing sugar includes only glucose and fructose which are found in high concentrations in corn syrups, DCS etc., and in minor concentrations in molasses where the major low molecular weight carbohydrate is sucrose. Sugars include monosaccharides, disaccharides, oligosaccharide or mixtures thereof. It is further stated that while the reducing sugar can be present in a substantially pure form such as glucose, that for economic reasons it maybe desirable to employ other sugar sources such as molasses obtained from sugar cane or sugar beets or other similar syrups that are natural occurring and inexpensive.
U.S. Pat. No. 4,975,219 relates to corrosion inhibitors for protecting metals which are in contact with water and boiler water systems. The corrosion inhibitor includes tannic acid or a salt thereof, a sugar, and an aldonic acid of hexoses or heptoses and/or a salt thereof. The sugars used in this formulation may include D-glucose and fructose.
U.S. Pat. No. 5,073,270 is directed to the treatment of a hot aqueous brine solution in order to reduce scale forming components. Organic reducing agents are taught and include those which would be effective at a pH of between 5 and 7 and include carbon dioxide, sodium formate, formaldehyde, starch, dextrose, sucrose and corn syrup. It is stated that the sucrose and starch decompose to form dextrose thereby making them suitable as reducing agents or reducing agent precursors in the desired pH treatment range.
U.S. Pat. No. 5,330,683 is directed to a method of inhibiting corrosion in brine solutions in which an aqueous brine solution is treated with gluconate or sorbitol.
U.S. Pat. No. 6,447,717 relates to a method for inhibiting metal corrosion and in particular corrosion induced by carbon dioxide on ferrous metals in aqueous systems. Corrosion inhibiting compositions include a combination of an amino thiol or amino disulfide compounds with acidic amino acid polymers. In column 7, beginning line 45 it is stated that examples of co-monomers useful in production of the acidic amino acid polymer of the present invention include, but are not limited to glucose, fructose and sucrose.
For purpose of this invention a brine may be defined as any solution of sodium chloride and water, and usually containing other salts. More specifically a brine is an aqueous solution of chloride salts alone or in combination, usually containing sodium, potassium, calcium and magnesium cations. The brine may be made by dissolving the solid chloride e.g. common salt, NaCl, in water or it can be obtained from natural sources such as subterranean wells in the American Midwest, in desert lakes e.g. Great Salt Lake (Utah), Dead Sea (Jordan/Israel), or from the ocean. Natural brines are also associated with natural gas and oil deposits. Anions are also found with natural brines e.g. sulfate, bromide, borate.
The present invention is based upon the discovery that an industrial brine solution which contains a carbohydrate in a narrow molecular weight range exhibits superior corrosion resistance over conventional brine solutions. The molecular weight which provides superior corrosion resistance is in the range of 180 to 342. The best corrosion resistance was obtained for fructose and sorbose having a molecular weight of 180, which are classified as ketose sugars.
The following table shows the corrosion rate for a 24% magnesium chloride brine and for a 24% calcium chloride brine for a grouping of carbohydrates in the molecular weight range of 150 to 342. Corrosion rates for carbohydrates outside this molecular weight range are significantly higher.
The test protocol employed in Table I (as well as Table IV) was that used by the Pacific Northwest Snowfighters (PNS) Test Method B for corrosion rate determination as conducted from the National Associate of Corrosion Engineers (NACE) Standard TM 0169-95 (1995 Revision) and as modified by PNS.
Pure saccharides were unavailable (at reasonable cost) with a Mol. Wt. range of 504 to 1476. Therefore an industrial mixture of saccharides was used (Star Dri 200 from A.E. Staley Co.). A test solution of 10 wt % (Star Dri 200) with 24 wt % MgCl2 gave a reduction in corrosion of 32.5%. The molecular weight average Mw of Star Dri 200 was 3746 and its composition was as follows:
From Table II it can be seen:
concentration for 180 and 342 Mol. Wt is 10.2%
concentration for 504 to 990 Mol. Wts are 36.6%
concentration for 1152 to 1476 Mol. Wts are 13.7%
concentration for 180 to 990 Mol. Wts are 46.8%
concentration for 180 to 1476 Mol. Wts are 60.5%
The conclusions to be drawn from the use of Star Dri 200 (Table II) are as follows:
Molecular Weights and Ranges
The contribution of Mol. Wt. 180 and 342 saccharides to the reduction in corrosion is quite small due to the low concentrations of 2.1 % and 8.1 %. Note that the concentrations of the saccharides in the 504 to 1476 range is 50.3% and will have a major contribution. The following compares the sucrose result with the Star Dri 200 180 to 1476 fraction (60.5% composition from Table II) i.e. 10%×60.5/100=6.05%.
The slightly better results for Star Dri 200 would be expected due to the 3.7% concentration of Higher Saccharides >DP11 with a molecular weight average of 8,706. This would result in higher viscosity at the corrosion cell and would retard the movement of ferrous ions from the anode.
It should be noted that the ketoses fructose and sorbose are superior corrosion inhibitors to the aldoses.
Ketose and Aldoses
As expected, the ketoses; fructose and sorbose, are superior to the aldoses; glucose, galactose, arabinose and xylose. There are some 14 aldoses but the above are most common. The superiority of the ketose fructose is lost when it is combined with glucose in the disaccharide sucrose. The other dissacharides maltose (two glucose units) and lactose (one glucose and one galactose unit) have the same inhibitory effect as sucrose.
Natural Brines Containing Calcium Chloride
Two naturally occurring brines were tested having the following compositions:
The corrosion rates for these brines with various carbohydrate additives are tabulated below:
3Casco is a corn syrup DE 42
4The high fructose corn syrup is High Sweet 42 from Roquette America Inc. and the low molecular weight carbohydrate distribution in this mixture is: Glucose 8.09% Fructose 6.53% Higher saccharides 0.94%
From the above data it can be seen that the two naturally occurring brines which contain varying ratios of CaCl2 and MgCl2 both exhibit a signification reduction in corrosion rate when varying amounts of carbohydrate are added to the brine.
While the present invention has been particularly shown and described with reference to the preferred mode, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.
This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 61/016,959, filed Dec. 27, 2007, and entitled IMPROVED CORROSION RESISTANCE OF INDUSTRIAL BRINE SOLUTIONS, which application is incorporated herein by this reference.
| Number | Date | Country | |
|---|---|---|---|
| 61016959 | Dec 2007 | US |
