Acid cleaning and corrosion inhibiting compositions comprising gluconic acid

Abstract

A biodegradable acid cleaning composition for cleaning stainless steel, and other surfaces is disclosed. The composition comprises urea sulfate in combination with gluconic acid which serves as a corrosion inhibitor. The composition retains the cleaning and corrosion prevention properties of similar phosphoric acid solutions but is safe for the environment and is less expensive to produce. Applicants have surprisingly found that the traditionally alkaline corrosion inhibitor, gluconic acid, can work effectively in an acidic cleaning composition.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This is a Divisional Application of U.S. Ser. No. 12 / 751,674, filed Mar. 31, 2010, herein incorporated by reference in its entirety.FIELD OF THE INVENTION[0002]The present invention relates to aqueous, acid cleaners for cleaning metal and other surfaces, particularly stainless steel and for inhibiting corrosion. Methods of use and manufacturing of the same are also disclosed.BACKGROUND OF THE INVENTION[0003]Steel is the generic name for a group of ferrous metals, composed principally of iron, which have considerable durability and versatility. By the proper choice of carbon content, addition of alloying elements, and by suitable heat treatment, different kinds of steel can be made for various purposes and the use in industry of all kinds of steel is now quite expansive.[0004]Stainless steel is defined as a steel alloy, with a minimum of 11% chromium content by mass. Stainless steel does not stain, corrode, or rust as easily as traditional...

AI Technical Summary

Benefits of technology

[0015]The present invention employs the use of gluconic acid as a corrosion inhibitor for use in acid cleaning compositions. Applicants have found, surprisingly that the combination of gluconic acid as a corrosion inhibitor in an acidic cleaning solution works well and almost prohibits all corrosion. The invention employs an aqueous solution of a pH of less than 7, which uses an acid as the cleaning component. Any acid used in an acid cleaning composition may be combined with gluconic acid according to the invention, such as acetic acid, citric acid, oxalic acid, and sulfuric acid, all of which are traditionally used in acid cleaning compositions. In a preferred embodiment, the acid is sulfuric acid, which is more preferably combined with urea to form a urea sulfate acid cleaning composition. The acid cleaning compositions of the invention retain the anti-corrosive properties of phosphoric acid as well as the cleaning capabilities and are biodegradable and less expensive to produce.

[0018]Applicants have found that the level of gluconic acid to urea sulfate must be at least greater than about 0.15% to 25% or a ratio of percent by weight of 0.012 to 1 of gluconic acid to urea sulfate. Levels less than this critical ratio, were found to not significantly inhibit corrosion. There is really no upper limit on the amount of gluconic acid that can be added to the solution, so long as the desired corrosion inhibition is achieved with the acid cleaner. The solution could even have a greater gluconic acid content than urea sulfate. Not only does the gluconic acid protect the surface of the metal from the sulfuric acid, it makes the composition less expensive and retains the low corrosivity and cleaning properties of phosphoric acid based cleaners. Applicants have found that addition of the corrosion inhibitor gluconic acid which was thought to only work in alkaline cleaning compositions, surprisingly, also works in an acidic cleaning composition.

Problems solved by technology

One of the problems which arises in the use of steel is its corrosion, either by the atmosphere or by the environment in which it is used.

Other metals, for example copper, and aluminum, also increase corrosion resistance but they are limited in their usefulness.

Although stainless steel has appreciable resistance to corrosion, it will still corrode in certain circumstances and attempts have been made to prevent or reduce this corrosion.

However this and other proposed inhibitors are not entirely satisfactory since, like copper sulphate, they may be expensive, introduce an effluent disposal problem and, moreover, are not entirely effective.

Thioureas are not appropriate for food and beverage situations as any remnant thiol compounds are considered contamination for such surfaces.

The type of acid used has also presented problems in development of acid cleaners.

Phosphoric acid has recently fallen out of favor due to environmental concerns.

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