Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Maintaining environment nondestructive to metal
Reexamination Certificate
1999-02-16
2002-01-15
McKane, Elizabeth (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Maintaining environment nondestructive to metal
C422S006000, C252S392000
Reexamination Certificate
active
06338819
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to corrosion inhibition, and more particularly to inhibition of corrosion in environmentally sensitive aqueous media.
BACKGROUND OF THE INVENTION
Corrosion of metal surfaces in aqueous media, such as sea water, is a longstanding problem. The problem is especially troublesome in deep sea operations, such as offshore drilling and production, where conditions are particularly rigorous. Corrosion inhibitors for use in offshore operations must be effective under demanding deep sea conditions, and also must be environmentally acceptable. The corrosion inhibitors must meet stringent standard toxicity requirements, and also should be compatible with the sensitive life forms that are indigenous to the area. For example, in North Sea operations, the corrosion inhibitor should be compatible not only with fish, but also with indigenous algae, such as
Skeletonema costatum.
Commonly used inhibitors have proven to be too toxic for compatibility with
Skeletonema costatum
. Even a concentration of less than one part per million by weight (ppm) of conventional inhibitors has been found to retard growth of
Skeletonema costatum
test populations by 50% in 96 hours (EC
50
<1 ppm). Corrosion inhibitors are needed which have an EC
50
>1 ppm for
Skeletonema costatum.
The corrosion inhibitor also should be sufficiently biodegradable that, within 28 days after treatment, the inhibitor degrades at least 60%, most preferably 100% in terms of the theoretical oxygen consumption required for complete degradation (i.e., the biochemical oxygen demand BOD−28≧60%, preferably=100%). The inhibitor also should be sufficiently water soluble to avoid or minimize bio-accumulation in fat in lower life forms. Fat soluble inhibitors tend to become more concentrated as they move up the food chain.
Imidazolines have promise as corrosion inhibitors from an environmental standpoint because imidazolines are effective as corrosion inhibitors even though they do not contain sulfur or phosphorus. However, imidazoline inhibitors are needed which are both effective as corrosion inhibitors and which also meet stringent toxicity standards, such as an EC
50
>1 ppm for
Skeletonema costatum.
SUMMARY OF THE INVENTION
The present invention provides a method of inhibiting corrosion of metal equipment in an aqueous medium comprising components selected from the group consisting of
Skeletonema costatum
, fish, other algae, and a combination thereof, said method comprising incorporating into the aqueous medium an amount of a water soluble corrosion inhibitor effective to inhibit said corrosion. The corrosion inhibitor comprises an N-ethoxy, 2-substituted imidazoline. The N-ethoxy substituent comprises a quantity of ethylene oxide effective to render the imidazoline water soluble. The 2-substituent comprises a fatty acid chain consisting essentially of 18 carbon atoms or less.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides imidazolines with reduced toxicity which are effective to inhibit the corrosion of metal equipment in an aqueous environment. Toxicity is minimized by reducing the chain length of the acid used to make the imidazoline. Imidazolines with shorter chain lengths tend to be less effective as corrosion inhibitors; however, the addition of certain wetting agents has been found to increase the effectiveness of these less toxic imidazolines as corrosion inhibitors.
Preferred corrosion inhibitors do not contain sulfur or phosphorus and are “environmentally compatible.” As used herein, the term environmentally compatible shall mean that a substance has little or no deleterious environmental effects on a medium of concern, and includes, but is not necessarily limited to considerations such as toxicity, water-solubility, biodegradability, and so forth. Although the term “non-toxic” is used herein, nearly every substance is toxic at some concentration. The term “non-toxicity” refers to very low toxicity at the relevant concentration. For example, for offshore drilling and production, the term “non-toxicity” or “non-toxic” refers to compositions having and EC
50
greater than 1 ppm by weight for
Skeletonema costatum.
Suitable imidazolines for use as corrosion inhibitors include, but are not necessarily limited to N-ethoxy, 2-substituted imidazolines, the N-ethoxy substituent comprising an amount of ethylene oxide effective to render said imidazoline water soluble, preferably from about 3 to about 9 moles of ethylene oxide, and the 2-substituent comprising an unsaturated or polyunsaturated fatty chain comprising less than about 18 carbon atoms, preferably less than about 10 carbon atoms, more preferably less than about 8 carbon atoms. Preferably, the fatty chain has at least 6 carbon atoms, most preferably from about 6 to about 8 carbon atoms.
The foregoing imidazolines are prepared by reacting a starting amine, preferably an N-substituted amine, most preferably 2,2-aminoethylamino ethanol (AEEA) or a diethylene tetramine (DETA), with a fatty acid to form an imidazoline. A most preferred starting amine is an N-substituted ethylene diamine having the formula H
2
NCH
2
CH
2
NHRMH, wherein R is an organic moiety and —MH is a terminal group comprising a hetero atom such as oxygen, nitrogen or sulfur, preferably oxygen or nitrogen, and at least one hydrogen, providing a site for attachment of ethylene oxide. Although R may include nitrogen atoms, it is preferred for R to be an alkylene, an arylene, or an aralkylene. Of these, preferred R groups are ethylene, isopropylene and —(CH
2
CH
2
O)
n
(CH
2
CH
2
)—, wherein n is an integer from about 1 to about 30. Out of these possibilities, preferred R groups are ethylene and the group —(CH
2
CH
2
O)
n
(CH
2
CH
2
)— wherein n is an integer from about 1 to about 17. Most preferably, R is ethylene.
The group MH provides a site for attachment of ethylene oxide for ether or polyether formation. Preferably, MH is selected from the group consisting of —OH, —NH
2
, or —SH, with SH being least preferred and —OH being most preferred. Specific, preferred N-substituted ethylene diamines include, for example, NH
2
CH
2
CH
2
NH—CH
2
CH
2
(CH
3
)OH; NH
2
CH
2
CH
2
NH—CH
2
CH
2
NH
2
; and, most preferably, NH
2
CH
2
CH
2
NH—CH
2
CH
2
OH.
The starting amine and the fatty acid are reacted in about a 1:1 molar ratio under a vacuum with the addition of heat, such as up to about 240° C., until all water is removed. The resulting imidazoline is then ethoxylated to build the N-substituent of the imidazoline to include a total of 3-9 moles of ethylene oxide, as necessary, to render the product water-soluble. As used herein, the term water-soluble means miscible with water at the concentration to be employed for corrosion inhibition. The resulting product has the following structure:
wherein R and R′ (the residue of the fatty acid) are alkyl groups comprising from about 6 to about 28 carbon atoms; M is t he residue from the —MH group after removal of the R, preferably —O—, —NH—, or —S—, most preferably —O—; x (the number of —RM groups) is 0 or 1 and y is an integer from 0 to about 28 selected so that the total number of ethoxy units in the N-substituent is from about 1 to about 28, preferably from about 3 to about 9).
In order to be effective, the corrosion inhibitor preferably inhibits corrosion to about 50 mils per year (mpy) or less, as measured by green kettle testing. Imidazolines having 8 or fewer carbon atoms may be effective when used alone as corrosion inhibitors, but are more effective and preferably are used in combination with a wetting agent. Suitable wetting agents include, but are not necessarily limited to oxyalkylated alcohols having from 6 to about 32 carbon atoms, preferably from about 8 to about 10 carbon atoms. Oxyalkylation, preferably ethoxylation, makes the alcohol more water-soluble. Each carbon atom of the alcohol preferably should have at least one hydrogen to provide superior biodegradability. Alfol 8-10 (a mixture of C8 to C10 alcohols), which is available from a variety of sourc
Alink Bernardus A. Oude
Braga Thomas G.
Martin Richard L.
McMahon Jo Ann
Outlaw Benjie T.
Baker Hughes Incorporated
Madan Mossman & Sriram P.C.
McKane Elizabeth
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