Compositions – Preservative agents – Anti-corrosion
Reexamination Certificate
1998-06-02
2001-02-13
Medley, Margaret (Department: 1714)
Compositions
Preservative agents
Anti-corrosion
C252S391000, C252S395000, C208S047000, C208S207000, C208S236000, C422S007000, C422S013000
Reexamination Certificate
active
06187227
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates the inhibition of corrosion in aqueous alkanolamine units. More particularly, the present invention relates to methods of inhibiting corrosion of metals in contact with aqueous alkanolamine solutions in acid gas removal amine units using thiacrown ether compounds.
BACKGROUND OF THE INVENTION
The conditioning of naturally occurring liquid and gas streams by absorbing acid gases such as CO
2
and H
2
S in an absorbent solution is a well known commercial practice. Acid gas removal is commonly practiced in the oil refining, natural gas recovery, ammonia plant and wood pulp industries. For example, when crude oil and natural gas are removed from a formation they frequently contain CO
2
or H
2
S (acid gases). Acid gases are removed from the hydrocarbon in an acid gas removal amine system (amine unit). Amine units are typically constructed of carbon steel and operate at temperatures of from about 110° to about 300° F., at pressures of from about 10 to about 500 psig and with less than about 10 ppm of oxygen present as an undesirable contaminant in the aqueous alkanolamine solution. An amine unit utilizes an alkanolamine such as monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), diisopropylamine (DIPA), and diglycolamine (DGA) in an aqueous solution. The hydrocarbon containing acid gases are contacted with the aqueous amine solution in a tray or packed absorber where the amine reacts with the acid gases thereby removing them from the hydrocarbon and forming an aqueous amine solution containing the absorbed acid gases (rich stream). The amine-acid gas reaction is later reversed in a plate or packed stripper resulting in an acid gas stream and a reusable aqueous amine solution (lean stream).
Amine units present a variety of corrosion control problems. Unreacted carbon dioxide dissolved in the aqueous alkanolamine solution forms acid species which are corrosive to metals. Oxygen can enter an amine unit through storage tanks, sumps, surge vessels, and the like and attack metals causing corrosion. Oxygen also can oxidize the alkanolamine. Oxidation and degradation products of alkanolamines can cause metal corrosion. Efforts to control corrosion in amine units usually focus on the use of metallurgy, minimization of acid gas flashing, filtration, stress relieving, process controls and corrosion inhibitors such as metal passivating agents. However, environmental and safety concerns have limited the practicality of using some materials such as nickel, cobalt, calcium, copper, chromium, zinc, tin, aluminum, magnesium and cyano compounds and the like as corrosion inhibiting agents. Since corrosion, if left untreated, can cause shut-down of an amine unit, corrosion control is a very important consideration. In addition, most corrosion control efforts have focused on treating the rich stream of the amine unit. However, the lean sections of amine units also experience corrosion.
Therefore, a need exists for compositions which when added to an aqueous alkanolamine solution in an acid gas removal amine unit inhibits corrosion of metals in contact with the aqueous alkanolamine solutions and which are effective for inhibiting corrosion in both the rich and lean portions of the amine unit.
Accordingly, it is an object of the present invention to provide compounds for inhibiting corrosion of metals in contact with aqueous alkanolamine solutions.
It is an additional object of the present invention to provide aqueous acid gas removal solutions for use in amine units which are inhibited against acid gas promoted corrosion of metals.
It is yet another object of this invention to provide a method for inhibiting corrosion of metals in contact with aqueous alkanolamine solutions in amine acid gas removal units.
PRIOR ART
J. Buter et. al. Organic Synthesis Vol. 65, pages 150-158 (1987) teaches the synthesis of thiacrown ether 1,4,8,1 1-tetrathiacyclotetradecane. The synthesis is conducted by first reacting 1,3-propanedithiol with 2-chloroethanol to form 3,7-dithianonan-1,9-diol. This diol is reacted with thiourea to give 3,7-dithianonane-1,9-dithiol. The dithiol is then reacted with 1,3-dibromopropane to give 1,4,8,11-tetrathiacyclotetradecane.
Richard E. DeSimon et. al. proposes in J. Am. Chem. Soc. 97, 942 (1975) an “inside out” crystal structure involving the distortion of C-4 and C-5 carbon atoms in 1,4,8,11-tetrathiacyclotetradecane (abbreviated as 14-S-4) when it is forming a complex with NbCl
5
in benzene.
Masao Tomoi et. al. describes in Japan Kokai 55-19221 and Makromol. Chem. 184, pp. 2431-2436 (1983) a macrocyclic bound to a crosslinked polystyrene resin support. The polythiaethers are disclosed to be highly efficient adsorbents of Ag (I) and moderately effective adsorbants for Cu(II). The thiacrown ethers/macroporous polystyrene resins are disclosed as being in solid form and as being reuseable.
Keiji Yamashita et. al. describe in Reactive and Functional Polymers 31, 47-53 (1996) the polymerization and copolymerization of 6-(4′-vinylbenzyloxy)-1,4,8,11-tetrathiacyclotetradecane and 9-(4′-vinylbenzyloxy)-1,4,7,14,17-hexathiacycloeicosane with styrene or N-vinylpyrrolidone. Polymers were studied for their ability to bind Ag(I) and Hg(II).
U.S. Pat. No. 5,071,581 to R. Cipriano discloses monomeric crown ethers (i.e., having only one crown ether in a molecule of the ether) and polymeric crown ethers (i.e., having at least one but possibly more crown ethers in a polymeric chain) wherein sulfur atoms replace oxygen atoms. The polymeric crown ethers are disclosed as being useful as a component of electrorheological fluid. The structure and configuration of the thiacrown compounds of the present invention are not disclosed.
WO 96/38493 discloses water-soluble polymers having particular formulas, functionalized by various groups. Thiocrown ethers are listed among the polymer substituents. The structure and configuration of the thiacrown compounds of the present invention are not disclosed.
U.S. Pat. No. 3,133,028 to Kenhere discloses that corrosion of metals in contact with water can be inhibited by the use of water-soluble hexavalent chromium compounds in conjunction with water-soluble thiocyanates, and/or water soluble thiourea compounds of the type represented by the formula:
where R, R
1
, R
2
and R
3
are selected from the group consisting of hydrogen, alkali metal, and alkyl radicals containing from 1 to 4 carbon atoms. Zinc compounds are also disclosed as corrosion inhibiting compounds when used in conjunction with water-soluble hexavalent chromium.
U.S. Pat. No. 4,100,100 to Clouse et al. discloses the corrosion of iron and steel by an aqueous sour gas conditioning solution to remove CO
2
from a gas stream is inhibited by a combination of a quaternary pyridinium salt and an organic thioamide or water-soluble thiocyanate and a water-soluble cobalt salt. The patent discloses that the cobalt compound, the thio compound or the pyridinium salt alone will provide no inhibition or only partial inhibition.
U.S. Pat. No. 4,102,804 to Clouse et al. discloses the corrosion of iron and steel in an aqueous sour gas conditioning system is inhibited by a combination of a quaternary pyridinium salt and an organic thioamide, a water-soluble sulfide or a water-soluble thiocyanate. The patent also discloses that either the thio compound or the pyridinium salt alone will provide no inhibition or only partial inhibition.
U.S. Pat. No. 4,446,119 to DuPont et al. discloses a corrosion inhibited composition containing a gas conditioning solution such as an alkanolamine with water or with organic solvents and with soluble thiocyanate compounds, soluble trivalent bismuth compounds with or without soluble divalent nickel or cobalt compounds.
U.S. Pat. No. 4,431,563 to Krawcyzk et al. discloses that corrosion of ferrous metals in gas conditioning apparatus is inhibited by using a gas conditioning solution such as aqueous alkanolamines which contain thionitrogen compounds such as metal thiocyanates or thioamides. The patent discloses th
Gaboury Janet A.
Minevski Ljiljana V.
Betzdearborn
Greenblum & Bernstein P.L.C.
Medley Margaret
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