Use of aminals to remove acid gases from fluid gas streams

Abstract

An aminal compound is injected into a fluid gas stream including at least one acid gas to reduce the amount of acid gas in the fluid gas stream. Having two reactive sites present in the aminal compound enables a much higher efficiency of acid gas capture than a simple alkanolamine, which isn't effective, for example, under dilute circumstances.

Claims

1. A method for reducing a concentration of at least one acid gas from a fluid gas stream comprises a step of injecting a solution including at least one aminal compound into said fluid gas stream, wherein said at least one aminal compound is an organic compound having two amine groups attached to the same carbon atom and said at least one aminal compound is not a triazine or piperazine, and wherein carbon dioxide is at least one acid gas that the concentration is reduced by said aminal compound.

2. The method of claim 1, wherein said at least one aminal compound is ##STR00006## wherein X.sub.1 and X.sub.2 are the same or different alcohol or alkyl functional group.

3. The method of claim 2, wherein X.sub.1 and X.sub.2 are selected from the group consisting of ethyl alcohol, methyl alcohol, methyl, and ethyl functional group.

4. The method of claim 1 wherein said at least one acid gas further comprises at least one gas selected from the group consisting of hydrogen sulfide, mercaptans, and mixtures thereof.

5. The method of claim 1, wherein said at least one aminal compound is diethanol-amineaminal.

6. The method of claim 1, wherein said at least one aminal compound is dimethyl aminal.

7. The method of claim 1, wherein said solution is an aqueous solution including 90 to 50 wt % water.

8. The method of claim 1, wherein said fluid gas stream includes less than 10 wt. % of said at least one acid gas prior to injecting said solution including at least one aminal compound.

9. The method of claim 1, wherein said fluid gas stream includes less than 5 wt. % of said at least one acid gas prior to injecting said solution including at least one aminal compound.

10. A method for reducing the concentration of at least one acid gas from a fluid gas stream comprises the step of: injecting an aqueous solution including at least one aminal compound into a fluid gas stream including less than 10 wt. % of said at least one acid gas to reduce the concentration of said at least one acid gas by at least 20 wt. %, and wherein said at least one aminal compound is an organic compound having two amine groups attached to the same carbon atom and said at least one aminal compound is not a triazine or piperazine, and wherein carbon dioxide is at least one acid gas that the concentration is reduced by said aminal compound.

11. The method of claim 10, wherein said at least one aminal compound is ##STR00007## wherein X.sub.1 and X.sub.2 are the same or different alcohol or alkyl functional group.

12. The method of claim 11, wherein X.sub.1 and X.sub.2 are selected from the group consisting of ethyl alcohol, methyl alcohol, methyl, and ethyl functional group.

13. The method of claim 10, wherein said fluid gas stream includes less than 5 wt. % of said at least one acid gas.

14. The method of claim 10, wherein said fluid gas stream includes less than 3 wt. % of said at least one acid gas.

15. The method of claim 10 wherein said aqueous solution includes 40-90 wt. % water.

16. The method of claim 10 wherein said aqueous solution includes 40-60 wt. % of said at least one aminal compound.

17. The method of claim 10 wherein said at least one aminal compound is diethanol-amineaminal.

18. The method of claim 10 wherein said at least one aminal compound is dimethyl aminal.

19. The method of claim 10 wherein said fluid gas stream is a natural gas stream.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention, according to certain embodiments, generally relates to compositions, systems, and methods for the removal of at least one acid gas from a fluid gas stream. In particular, the present invention relates to compositions, systems, and methods for the removal of at least one acid gas from a fluid gas stream using a solution including an aminal compound (e.g. diethanolamine aminal).

(2) An “acid gas” is a gas that can form acidic solutions when mixed with water. The most common acid gases are hydrogen sulfide (H.sub.2S) and carbon dioxide (CO.sub.2) gases. Additionally, as applied herein, “acid gas” includes mercaptans. Generally, the overall formula of mercaptans is R—SH, wherein R is a hydrocarbon chain. Example of mercaptans include, but are not limited to, methanethiol—CH.sub.3SH [methyl mercaptan], ethanethiol—C.sub.2H.sub.5SH [ethyl mercaptan], 1-propanethiol—C.sub.3H.sub.7SH [n-propyl mercaptan], 2-propanethiol—CH.sub.3CH(SH)CH.sub.3 [2C3 mercaptan], allyl mercaptan—CH.sub.2═CHCH.sub.2SH [2-propenethiol], butanethiol—C.sub.4H.sub.9SH [n-butyl mercaptan], tert-butyl mercaptan—(CH.sub.3).sub.3CSH [t-butyl mercaptan], pentanethiols—C.sub.5H.sub.11SH [pentyl mercaptan], etc.

(3) An aminal compound is a type of organic compound that has two amine groups attached to the same carbon atom. In a preferred embodiment, the present invention provides an aminal compound including diamine capable of scavenging the acid gases carbon dioxide, hydrogen sulfide, and/or mercaptan. This invention uses an aminal compound as provided in Formula 1 that is not sterically bound.

(4) ##STR00002##

(5) Wherein X.sub.1 and X.sub.2 may be the same or different alcohol or alkyl. Preferred alcohol groups include, but are not limited to, ethanol and methanol. Preferred alkyl groups include, but are not limited to methylene and ethylene. In a preferred embodiment, alkanol amines are used due to their high affinity for CO.sub.2.

(6) The aminal compound of Figure 1 is ideally suited for removing at least one acid gas, such as carbon dioxide, hydrogen sulfide, and/or at least one mercaptan, under both concentrated and dilute conditions. In one embodiment, the dilute conditions includes fluid gas streams having <10 wt. % acid gas, such as carbon dioxide. In one embodiment, the dilute conditions includes fluid gas streams having <5 wt. % acid gas, such as carbon dioxide. In another embodiment, the dilute conditions include fluid gas streams having <2 wt. % acid gas, such as carbon dioxide. The intramolecular interactions of the aminal compound with carbon dioxide are more efficient under varied conditions. In a preferred embodiment, the aminal compound is not a triazine or piperazine

(7) In a preferred embodiment, diethanolamineaminal is used as the aminal compound for scavenging at least one acid gas, such as carbon dioxide, hydrogen sulfide, and/or at least one mercaptan.

(8) ##STR00003##

(9) In another preferred embodiment, dimethyl aminal is used as the aminal compound for scavenging at least one acid gas, such as carbon dioxide, hydrogen sulfide, and/or at least one mercaptan.

(10) ##STR00004##

(11) The aminal compound may be provided as a solvent system to the fluid gas stream. The solvent system may include, but is not limited to, monoethanolamine (MEA) and water. As such, the aminal compound may be provided as an aqueous aminal solution. As used herein, “an aqueous aminal solution” is intended to refer to a solution that includes an aminal compound in accordance with the present invention and water. The definition is not intended to exclude the inclusion of other solvents (for example alcohols) or other additives. Typically, the solution may contain from 90 to 40% (w/w) water, or 60 to 40% (w/w) water.

(12) The aminal compound exhibits greater than predicted acid gas absorption capacity than found in standard alkanolamine solutions. In one embodiment of the present invention, at least one aminal compound reduces the concentration of at least one acid gas in a fluid gas stream by at least 20 wt. %, preferably by at least 25 wt. %, more preferably by at least 28 wt. %. In yet another embodiment of the present invention, at least one aminal compound reduces the concentration of at least one acid gas in a fluid gas stream by at least 20 wt. %, preferably by at least 25 wt. %, more preferably by at least 28 wt. % when the fluid gas stream includes<10 wt. %, or <5 wt. %, or <3 wt. % of the acid gas prior to contact with at least one aminal compound.

Example 1—Aminal Dialkanolamines Production

(13) TABLE-US-00001 MW % lbs moles MEA 61.08 99.60 135080 999118.8007 HCHO 30.03 52.25 38314 302380.8105

(14) Mole ratio HCHO:MEA=0.302648

(15) 135,850 lbs of MEA was loaded into a reactor, and then 38314 lbs of 52.25 wt. % formaldehyde was added. This produced an MEA aminal solution.

Example 2

(16) A solution of 49.27 wt. % MEA aminal (the remainder water and MEA) was injected at a rate of 15 gallons per day into a 600 psi natural gas stream (216F). The natural gas stream, i.e. the fluid gas stream, contained 2.75 wt. % carbon dioxide and flowed at a rate of 119 MCF. Downstream of the MEA aminal addition, the carbon dioxide levels dropped to 2.05 to 2.15 wt. % percent carbon dioxide.

(17) Under similar conditions the following compounds did not lower the concentration of carbon dioxide. As such, the following compounds are not included within the definition of aminal compound as provided herein:

(18) ##STR00005##

Example 3

(19) A solution of 49 wt. % MEA aminal (the remainder water and MEA) was injected at a rate of 90 gallons per day into a 1000 psi natural gas stream. The gas stream contained 3.9 wt. % carbon dioxide and flowed at a rate of 365 MCF. Downstream of the MEA aminal addition, the carbon dioxide levels dropped to 2.8% carbon dioxide.

(20) Although the present invention has been disclosed in terms of a preferred embodiment, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention as defined by the following claims: