INHIBITING CORROSION CAUSED BY AQUEOUS ALDEHYDE SOLUTIONS

Abstract

Aldehydes useful as H2S sulfide scavengers may be corrosive to some metals such as steel, iron and aluminum, but the corrosive effect of the aldehydes may be mitigated by employing a corrosion inhibitor selected from the group consisting of a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof.

Description

BACKGROUND

1. Field of the Disclosure

The invention relates to the prevention or mitigation of corrosion. The invention particularly relates to the prevention or mitigation of corrosion caused by aldehydes.

2. Background Of The Disclosure

H₂S Sulfide (H₂S) and/or mercaptans are often encountered in the exploration for and production of oil and natural gas. The presence of H₂S and mercaptans is usually objectionable because they may react with other hydrocarbons or fuel system components. Another reason that the H₂S and mercaptans are objectionable is that they are often highly corrosive. Still another reason that H₂S and mercaptans are undesirable is that they have highly noxious odors. The odors resulting from H₂S and mercaptans are detectable by the human nose at comparatively low concentrations and are well known. For example, mercaptans are used to odorize natural gas and used as a repellant by skunks and other animals.

One solution to these problems is to “scavenge” H₂S and/or mercaptans. Certain aldehydes are known to be useful for these purposes. For example, glyoxal (OHCCHO) has been used at pH neutral as a successful scavenger. Glyoxal and other aldehydes such as acrolein and formaldehyde are known to be useful in a variety of other applications such as biocides, disinfectants, and the like.

But the use of such aldehydes can of themselves sometimes be a problem. Aldehydes may be corrosive to metals such as aluminum, iron, and steel. It would be desirable to be able to employ such aldehydes at high concentration while minimizing the corrosion caused to metals in contact with the aldehydes.

SUMMARY

In one aspect, the invention is a method for employing an aldehyde in an aqueous solution while mitigating corrosion to metal in contact with the aldehyde solution. The method includes employing a corrosion inhibitor prepared using a member selected from the group consisting of a mono-basic soluble phosphate salt, di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof.

In another aspect, the invention is, in a process for the exploration for or the production of crude oil and/or natural gas, employing an aldehyde as a H₂S sulfide scavenger and employing a corrosion inhibitor prepared using a member selected from the group consisting of a mono-basic soluble phosphate salt, di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof.

DESCRIPTION

In one embodiment, the disclosure is directed to a method for employing an aldehyde in an aqueous solution while mitigating corrosion to metal in contact with the aldehyde solution, the method including employing a corrosion inhibitor prepared using a formulation including a mono-, di- or tri-basic soluble phosphate salt. In practicing the various embodiments of the method of the disclosure, an aldehyde aqueous solution is employed. The aldehydes which may be employed in the practice of the method of the disclosure include, but are not limited to glyoxal, acrolein, glutaraldehyde, formaldehyde, and combinations thereof. Any aldehyde that may be employed in an aqueous solution and is effective at scavenging H2S may be employed.

The aldehydes may be particularly a problem when in a comparatively concentrated form. For example, in some embodiments, the method of the disclosure is often employed where the aldehydes are present at a concentration of from about 20 to about 95% by weight. When the aldehydes are more dilute or concentrated, they often are not sufficiently corrosive to warrant a corrosion inhibitor; however they may be employed anytime that the aldehydes are present at a concentration such that a significant amount of corrosion may occur. This will vary according to the type of metal the aldehydes are contacting and the level of resilience of the system to which they are applied. For example, in some embodiments, the aldehyde will be present at a concentration of from about 25 to about 80 wt. %. In other embodiments, the concentration may be from about 30 to about 75 wt. %.

In the practice of the application, a mono-, di- or tri-basic soluble phosphate salt is used to mitigate corrosion by the aldehydes as discussed about. While any soluble salt may be used, in many embodiments, the phosphate salts employed will be selected from the group consisting of LiH₂PO₄ NaH₂PO₄, Na₂HPO₄, Na₃HPO₄, KH₂PO₄, K₂HPO₄; K₃HPO₄; and combinations thereof.

In other embodiments, there may be more than a single cation in the salt, for example, Na₂KPO₄ or NaLiKPO₄, and the like. Stated another way, the mono-, di- or tri-basic soluble phosphate salt may include more than one cation. In some embodiments, when the mono-, di- or tri-basic soluble phosphate salt includes two or more cations, they may be selected from the group consisting of lithium, potassium, and sodium.

The phosphate salts may be employed in any concentration effective to prevent or mitigate corrosion caused by the aldehydes. For example, in some embodiments, the mono-, di- or tri-basic phosphate salts may be present at a concentration of from about 100 ppm to 30% (by wt.). In other embodiments, they may be present at a concentration of from about 1000 ppm to about 20%. In still other embodiments, they are present at a concentration of from about 1 percent to about 10 percent.

The phosphate salts, aldehyde, and water may be admixes in any way known to be useful to those of ordinary skill in the art of preparing additives. For example these components may be combined in a single container batch and admixed using a static or active mixer. In another embodiment, the aldehyde and water may be first admixed and then a solution of the mono-, di- or tri-basic phosphate salt introduced. In still another embodiment, the three streams may be introduced simultaneous through a static mixes into a vessel.

The alkaline phosphate salts useful with the method of the disclosure may be employed at a pH range of from about 4.0 to about 9.0. In some embodiments, the pH range may vary from about 4.5 to about 8.5 while in other embodiments the pH may be from about 5 to about 9.

While not wishing to be bound by any theory, it is nevertheless believed that the mono-, di- and tr-basic salt employed in the method of disclosure work in two ways to prevent corrosion. In a first way, it is believe that the phosphates contact and build an inorganic insoluble metal phosphate film on the metal surface. For example, in the case of iron or steel, an iron phosphate film forms. In the second way, it is believed that the basic nature of the mono-, di- and tri-basic phosphate salts either partially or perhaps fully removes the acidic H₂S(s) from the aldehydes. Interfering with the acid H₂S could affect the ability of the aldehydes to chelate metal thus removing or at least moderating this corrosion mechanism.

In another embodiment, the disclosure includes a process for the exploration for or the production of crude oil and/or natural gas, the process including employing an aldehyde as a H₂S sulfide scavenger and employing a corrosion inhibitor prepared from a formulation including a mono-, di- or tri-basic soluble phosphate salt. The process of the disclosure includes both exploration and production. Exploration includes drilling an oil and gas well, and then completing the well to start production of hydrocarbons. Production includes producing production fluid from the oil and gas well.

In some applications, the drilling fluids, formation brines, or the crude oil and/or natural gas encountered in either exploration or production may include undesirable levels of H2S and/or other mercaptans. Employment of an aldehyde scavenger as well as a corrosion may be required in these circumstances.

The aldehyde scavengers maybe employed in the process of the disclosure in any way known to be useful to those of ordinary skill in the art of producing oil and gas. For example, it may be atomized and introduced into a gas stream or directly admixed, liquid phase to liquid phase, with a crude oil stream. It may be employed as in, for example, the U.S. Provisional Patent Application having the Ser. No. 61/467116, which application is fully incorporated herein by reference.

EXAMPLES

The following examples are provided to illustrate the invention. The examples are not intended to limit the scope of the invention and they should not be so interpreted. Amounts are in weight parts or weight percentages unless otherwise indicated.

Examples 1 & 2 and Comparative Examples A-D.

Corrosion tests were performed by holding mild steel corrosion coupons at 60° C. for the times shown in the Table. Corrosion was determined as mils per year loss of metal. The concentration of each compound tested was 1% except as noted below. The blank (control) and each sample was 40% by weight aqueous glyoxal. Results are shown below in the table.

TABLE
	Corrosion Rate	Corrosion Rate
	(mpy)	(mpy)
Sample ID/Inhibitor	2 day test	14 day test
Ex. 1: Na2HPO4	15	110
Ex. 2: K2HPO4*	—	8
A: Blank	120	750
B: Cinnamaldehyde	80	—
C: NaOH	100	—
D: Bytyl-2yne-1,4 diol	40	—
*2% concentration

Discussion of the Examples

The Examples clearly show that di-basic phosphate salts are effective at mitigation of corrosion by glyoxal.

Claims

1. A method for employing an aldehyde in an aqueous solution while mitigating corrosion of metal in contact with the aldehyde solution, the method comprising employing a corrosion inhibitor with the aldehyde wherein the corrosion inhibitor comprises a member selected from the group consisting of a mono-basic soluble phosphate salt, a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof.

2. The method of claim 1 wherein the aldehyde is selected from the group consisting of glyoxal, acrolein, glutaraldehyde, formaldehyde, and combinations thereof.

3. The method of claim 1 wherein the member selected from the group consisting of a mono-basic soluble phosphate salt, a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof is selected from the group consisting of LiH2PO4, NaH2PO4, Na2HPO4, Na3HPO4, KH2PO4, K2HPO4, K3HPO4 and combinations thereof.

4. The method of claim 1 wherein the member selected from the group consisting of a mono-basic soluble phosphate salt, a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof includes more than one cation.

5. The method of claim 4 wherein the member selected from the group consisting of a mono-basic soluble phosphate salt, di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof includes two or more cations selected from the group consisting of lithium, potassium, sodium and combinations thereof.

6. The method of claim 1 wherein the aqueous aldehyde solution has an aldehyde concentration of from about 20 to about 90 weight percent.

7. The method of claim 1 wherein the member selected from the group consisting of a mono-basic soluble phosphate salt, a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof is present in the aqueous aldehyde solution at a concentration of from about 100 ppm to 30% (by wt.).

8. The method of claim 1 wherein the aldehyde and corrosion inhibitor solution is employed at a pH range of from about 4.0 to about 9.0.

9. The method of claim 8, wherein the pH range may vary from about 4.5 to about 9.

10. A process for exploring for or producing crude oil and/or natural gas comprising employing a H2S sulfide scavenger solution comprising an aldehyde and employing a corrosion inhibitor in the solution comprising a member selected from the group consisting of a mono-basic soluble phosphate salt, a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof.

11. The process of claim 10 wherein the aldehyde is selected from the group consisting of glyoxal, acrolein, glutaraldehyde, formaldehyde, and combinations thereof.

12. The process of claim 10 wherein the member selected from the group consisting of a mono-basic soluble phosphate salt, a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof is selected from the group consisting of LiH2PO4; NaH2PO4, Na2HPO4; Na3HPO4; KH2PO4, K2HPO4; K3HPO4; and combinations thereof.

13. The process of claim 10 wherein the member selected from the group consisting of a mono-basic soluble phosphate salt, a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof includes more than one cation.

14. The process of claim 13 wherein the member selected from the group consisting of a mono-basic soluble phosphate salt, a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof includes two or more cations selected from the group consisting of lithium, potassium, sodium, and combinations thereof.

15. The process of claim 10 wherein the H2S sulfide scavenger solution has an aldehyde concentration of from about 20 to about 90 weight percent.

16. The process of claim 10 wherein the member selected from the group consisting of a mono-basic soluble phosphate salt, a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof is present in the H2S sulfide scavenger solution at a concentration of from about 100 ppm to 30% (by wt.).

17. The process of claim 10 wherein the H2S sulfide scavenger solution comprising aldehyde and member selected from the group consisting of a mono-basic soluble phosphate salt, a di-basic soluble phosphate salt, a tri-basic soluble phosphate salt, and combinations thereof, has a pH range of from about 4.0 to about 9.0.

18. The process of claim 17, wherein the pH range may vary from about 4.5 to about 9.

19. The process of claim 10 wherein the H2S sulfide scavenger and corrosion inhibitor is atomized and injected into a gas stream.

20. The process of claim 10 wherein the H2S sulfide scavenger and corrosion inhibitor is admixed with crude oil.