Corrosion inhibitor

Abstract

A corrosion inhibitor for use with Urea Ammonium Nitrate solutions is disclosed, comprising a blend of molybdate and one or more of the inorganic phosphates (including phosphates, polyphosphates, and pyrophosphates) and organic phosphates or phosphonates. Inorganic phosphates include, but are not limited to, SHMP (Sodium Hexametaphosphate) and TKPP (Tetra-Potassium Pyrophosphate). Phosphoric acid may also be utilized to provide phosphate ions, by itself or in combination with other phosphorous containing compounds as a secondary inhibitor. There are numerous other inorganic phosphates that will also serve as suitable secondary inhibitors. Organic phosphates or phosphonates include, but are not limited to, HEDP (1-Hydroxyethylidine-1,1-diphosphonic acid; also known as ethanol diphosphonate, acetodiphosphonic acid, or etidronic acid), ATMP (aminotri(methylenephosphonic acid)), PBTC (Phosphonobutane tricarboxylic acid), DETPMP (Diethylenetriaminepenta(methylene phosphonic acid)), and HPA (hydroxyphosphono acetic acid). There are numerous other organic phosphates and phosphonates that will also serve as suitable secondary inhibitors. The amount of molybdate can range from 1 ppm to 500 ppm by weight of fertilizer solution, with the preferred range from 10 ppm to 200 ppm. Amounts of inorganic or organic phosphate can also range from levels as low as 1 ppm up to 500 ppm, with the preferred range being from 5 ppm to 50 ppm.

Description

FIELD OF THE INVENTION [0001] This invention relates to corrosion inhibitors to be used with Urea Ammonium Nitrate solutions, commonly used as agricultural fertilizer. Such solutions can be very corrosive to metals, particularly ferrous metals. BACKGROUND OF THE INVENTION [0002] Aqueous solutions of Urea Ammonium Nitrate (“UAN”) are commonly used as agricultural fertilizer. However, these solutions, typically 50%-80% UAN by weight (20% to 50% water), are very corrosive to metals, particularly ferrous containing metals. Manufacturers of UAN solutions have tried a number of methods to resolve the corrosion problem. [0003] The production of UAN solutions can be by batch or continuous process. Urea and Ammonium Nitrate solutions are blended with water and pH adjusted, sometimes using ammonia. During production or post-production, efforts are made to defeat or limit the corrosive effects of the UAN solution. Some manufacturers use filmers, that act to coat the metal coming into contact w...

AI Technical Summary

Benefits of technology

[0005] It has been found that low levels of molybdate in combination with low levels of various phosphorous containing compounds controls corrosion in ferrous metals caused by contact with UAN solutions. In addition, foaming, sludge formation, and / or focused or localized corrosion has not been observed in connection with the use of the molybdate with certain phosphorous containing compounds. Additionally, the use of molybdate in combination with phosphorous containing compounds prevents or reduces the formation of precipitates, including iron and other potential precipitates. It is believed that the phosphorous containing compounds used in the instant invention act to tie up or sequester iron and others materials in a manner which maintains the potential precipitate in solution. Precipitates can cause localized corrosion, by creating a site which the inhibitor cannot reach, sometimes referred to as under-deposit corrosion. The avoidance of precipitates by the use of phosphorous containing compounds prevents the occurrence of under-deposit corrosion.

[0007] The combination of low levels of molybdate with low levels of one or more of these phosphorous containing compounds has resulted in lower corrosion rates than either inhibitor used alone, even at comparable dosage rates, and has resulted in cleaner UAN solutions with little iron or other material precipitates than with either inhibitor used alone.

Problems solved by technology

In addition, foaming, sludge formation, and / or focused or localized corrosion has not been observed in connection with the use of the molybdate with certain phosphorous containing compounds.

Precipitates can cause localized corrosion, by creating a site which the inhibitor cannot reach, sometimes referred to as under-deposit corrosion.

The dosage of molybdate and phosphorous containing compounds can vary within a wide range, limited on the low side by the amount needed to insure adequate corrosion inhibition (taking into account that UAN solution may be further diluted by the consumer prior to use), and on the high side by the cost of the inhibitor and by the solubility of the inhibitors in the UAN solution.

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