Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Maintaining environment nondestructive to metal
Reexamination Certificate
1998-10-14
2001-10-09
Warden, Jill (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Maintaining environment nondestructive to metal
C422S016000, C252S188280, C252S390000, C252S393000, C252S394000, C507S939000
Reexamination Certificate
active
06299836
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable
REFERENCE TO A “MICROFICHE APPENDIX”
Not applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to inhibiting corrosion in gas treating solutions comprised of alkanolamine solutions or other solvents used in the removal of hydrogen sulfide, carbon dioxide, mercaptans or other acid gases from natural gas or other hydrocarbon gases or liquids. Specifically, the present invention relates to passivating the metals in contact with the corrosive solutions by reducing the metal's oxidation state to a lower number. The reduced oxidation state results in a less corrosive, harder, impervious, and insoluble layer in contact with the treating solution. Additionally, the corrosion inhibitor may contain a metal oxide that will help to catalyze or increase the activity of the corrosion inhibitor and to also add passivation to pre-existing pits, crevices, or imperfections in the metal in contact with the gas treating solution.
2. General Background of the Invention
Contaminants in crude hydrocarbons subjected to refining or purification operations include acids or acid-forming materials such as CO
2
, H
2
S, mercaptans, and sulfides. These acid-forming materials must be removed from the natural and cracked hydrocarbon or refined streams (which contain such hydrocarbons as methane, ethane, propane, etc. and olefins such as ethylene, propylene, butylene, etc). One typically used method of removing the acids and acid-forming materials from hydrocarbon gases or liquids is by absorption in an amine regenerative solution absorbent unit. Regenerative amine solution units include columns with trays or other packing which are used to contact the aqueous alkanolamine solution with the hydrocarbon gases or liquids which contain the acids or acid-forming compounds. The amine solution can be regenerated by thermal stripping with steam to remove the acids or acid-forming compounds such as H
2
S, CO
2
, mercaptans and sulfides. This is accomplished in a regeneration section of the unit comprised of a column with trays or other packing in which the amine is contacted with steam, a reboiler in which the steam is formed, a reflux condenser and return system in which the steam is conserved, and other associated heat exchange equipment used for energy conservation or subsequent cooling of the amine prior to its return to the absorption section of the unit. Due to the presence of these acids and acid-forming compounds, corrosion is often observed in the equipment containing the solutions.
The metallurgy of the equipment contacting the treating solution is usually carbon steel or stainless steel. The iron in these steels are typically hydrolyzed or oxidized to any of the following iron hydroxides or iron oxides: Fe(OH)2, Fe(OH)3, FeO(OH), Fe2O3, or Fe3O4. The latter of these, Fe3O4 or magnetite, is the hardest, most impervious, and most insoluble of the iron oxides or iron hydroxides. Due to the much lower corrosion potential, it is highly desirable to maximize the conversion of iron in contact with the treating solution to the magnetite form.
Corrosion rates in the equipment sustaining the treating solution increase with increased amine concentration and acid gas concentration in solution. This usually limits the overall capacity of the treating solution for removal of more acid gas components from the gas or liquid stream it contacts. Corrosion results because the stability of the hydrolyzed or oxidized form of the steel that generally provides some passive resistance to corrosion is reduced when amine or treating solution concentration increases and when the concentration of the acid component in solution with the treating solution increases. By strengthening the passive film, the system capacity for handling more acid gas removal per unit volume of treating solution can be increased.
BRIEF SUMMARY OF THE INVENTION
The apparatus of the present invention solves the problems confronted in the art in a simple and straightforward manner.
The present invention relates to the addition of oxygen scavengers to alkanolamine solutions, blends of different alkanolamines, mixtures of alkanolamines with physical absorbents such as sulfolane or tetraglyme, and with physical solvent such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, sulfolane, or dimethylethers of polyethylene glycol. The oxygen scavengers serve as corrosion inhibitors by reducing the iron oxides and hydroxides to the more corrosion resistant magnetite form. Additionally solutions of metal oxides may also be added to provide supplemental corrosion protection through additional passivation. By improving the passivation of the metal, corrosion is reduced. By lowering corrosion rates treating solution capacity can be increased without the normal limitations normally imposed by corrosion.
The oxygen scavengers can comprise quinone and an oxime, quinone and a hydroxylamine, or quinone and an oxime and a hydroxylamine. The oxygen scavengers can advantageously be mixed in deionized water. The resulting aqueous solution is preferably added to treating solution in a concentration of 0.0001-50,000 ppm, and more preferably 100-500 ppm (aqueous solution to treating solution).
The present invention includes a method of inhibiting corrosion in gas or light hydrocarbon treating systems utilizing as a treating solution alkanolamine aqueous solutions or physical solvents or combinations thereof by adding to the treating solution a mixture of oxygen scavengers in a concentration of from 0.001 to 50,000 ppm comprised of mixtures of a quinone and oximes of the formula
in which R
1
and R
2
are the same or different and are selected from hydrogen or lower alkyl groups of one to six carbon atoms. The oxime is preferably selected from a group consisting of methylethylketoxime, acetaldoxime, butyraldoxime, and propionaldoxime. The quinone is preferably hydroquinone. The alkanolamine is preferably selected from a group consisting of monoethanolamine, diethanolamine, methyldiethanolamine, triethanolamine, methylmonoethanolamine, 2-(2-aminoethoxy)ethanol, and diisopropanolamine. The treating solution preferably comprises mixtures of two or more amines or an amine and a physical absorbent from a group consisting of piperzine and sulfolane. The physical solvent is preferably a dimethylether of a polyethyleneglycol, tetraethyleneglycol, or sulfolane. Sodium molybdate is sometimes preferably added with the oxygen scavengers in a concentration of from 0.001 to 50,000 ppm to the treating solution.
The present invention also comprises a method of inhibiting corrosion in gas or light hydrocarbon treating systems utilizing as a treating solution alkanolamine aqueous solutions or physical solvents or combinations thereof by adding to the treating solution a mixture of oxygen scavengers from 0.001 to 50,000 ppm comprised of mixtures of a quinone and hydroxylamines of the formula
in which R
1
and R
2
are the same or different and are selected from hydrogen or lower alkyl groups of one to six carbons. The hydroxylamine is preferably selected from a group consisting of diethylhydroxylamine, isopropylhydroxylamine, dimethylhydroxylamine, hydroxylethylhydroxylamine, or hydroxylmethylhydroxylamine. The quinone is preferably hydroquinone. The alkanolamine is preferably selected from a group consisting of monoethanolamine, diethanolamine, methyldiethanolamine, triethanolamine, methylmonoethanolamine, 2-(2-aminoethoxy)ethanol, and diisopropanolamine. The treating solution preferably comprises mixtures of two or more amines or an amine and a physical absorbent from a group consisting of piperzine and sulfolane. The physical solvent is preferably a dimethylether of a polyethyleneglycol, tetraethyleneglycol, or sulfolane. Sodium molybdate is sometimes preferably added with the oxygen scavengers in a concentration of from 0.001 to 50,000 ppm to the treating solution.
The present invention also comprises a method of inhibiting corrosion in gas or l
Trahan David O.
Veldman Ray R.
Coastal Chemical Co., L.L.C. (A Louisiana limited liability comp
Cross LaToya I.
Garvey, Smith, Nehrbass & Doody, L.L.C.
Warden Jill
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