WO1991010869A1

WO1991010869A1 - Scrubbing solution formulation for reducing solvent losses in amine scrubbing systems

Info

Publication number: WO1991010869A1
Application number: PCT/US1991/000135
Authority: WO
Inventors: John H. Dibble
Original assignee: Dibble John H
Priority date: 1990-01-08
Filing date: 1991-01-07
Publication date: 1991-07-25

Abstract

Normal losses of amine solvents used in amine scrubbing systems are reduced by the addition of 50 to 10,000 ppm of certain polyoxypropylene compounds.

Description

SCRϋBBING SOLUTION FORMULATION FOR REDUCING SOLVENT LOSSES IN AMINE SCRUBBING SYSTEMS

BACKGROUND OF THE INVENTION

Amine scrubbing systems employing amine solvents are used for a wide variety of gas or liquid hydrocarbon treating applications where hydrogen sulfide (H2S) and/or carbon dioxide (CO2) are present in a gas or in a liquid hydrocarbon feed stream. The applications involve the intimate contact of the feed stream with a second (liquid) phase called the amine scrubbing solution. The feed stream and amine scrubbing solution necessarily have limited solubility in each other, except that H₂S and CO2 do have good solubility in the amine scrubbing solution. Several amine solvents are commercially used in amine scrubbing solutions including monoethano±am±ne (MEA), diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine (DIPA) , diglycolamine (DGA), methyldiethanolamine (MDEA), n-methylethanolamine (NMEA), and mixtures thereof. A simple amine scrubbing solution consists of one or more of these amine solvents diluted with water. The amine solvent concentration ranges from 5 to 80%, typically 10-60%. In addition, other non-amine compounds are sometimes present in the amine scrubbing solution. For example, sulfolane is sometimes added to aid in the absorption of other sulfur compounds such as mercaptans which are not readily absorbed into the simple amine scrubbing solution. Another example is the addition of small amounts of corrosion inhibitors to reduce corrosion in the amine scrubbing system.

Contact of the feed stream with the amine scrubbing solution is typically accomplished using trayed or packed towers called contactors. The feed stream (gas or liquid hydrocarbon) enters at the bottom of the contactor and rises to the top via gravity difference with, and flowing countercurrently to, the amine scrubbing solution. Once at the top, the contact having been completed, the product stream (gas or liquid hydrocarbon) separates or disengages from the amine scrubbing solution and exits the contactor. To minimize equipment cost, the equipment is designed as small as possible which results in high contact velocities and highly agitated contact between the two phases. Consequently, disengagement of the gas or hydrocarbon liquid from the amine scrubbing solution is generally not complete. This results in loss of some of the amine scrubbing solution which is entrained as a fine mist in the product stream (gas or liquid hydrocarbon) .

A similar situation exists in the regeneration tower where the hydrogen sulfide and carbon dioxide in the rich amine scrubbing solution from the contactor are removed via steam stripping at elevated temperatures. The stripping process is carried out in a trayed or packed vessel called a regeneration tower. A gas stream commonly referred to as "acid gas" and consisting of primarily H2S, CO2, and water exits at the top of the regeneration tower. Typically, some of the amine scrubbing solution is entrained in and lost with the acid gas.

The aforementioned amine scrubbing solution losses are undesirable due to the expense of replacing the solvent(s) that are lost.

SUMMARY OF THE INVENTION

In the current invention, it has been unexpectedly discovered, that dramatic and permanent reductions in solvent losses via entrainment are possible by adding certain polyoxypropylene compounds to the amine scrubbing solution. In this invention, the compounds can be added to an existing amine scrubbing solution or premixed in a concentrated solvent mixture which is subsequently diluted with water before use. The compounds suitable for this invention are limited to a specific group of compounds selected from a group of polyoxypropylene compounds having the general formula:

R'O-(CH₂-CH-0)_ή- " CH₃

where R' and R" represent alkyl groups having a total of 1-5 carbon atoms. Olin Chemicals sells a series of products with this general structure under the trade name Poly-G^R WI Fluids. The Dow Chemical Company sells products with this general structure referred to as polypropylene glycols, L- Series. Union Carbide Chemical Company sells products having the above general structure under the UC0N^R LB Fluids tradename. The products in these series differ in molecular weight (viscosity) .

DETAILED DESCRIPTION OF THE INVENTION

The selected polyoxypropylene products in the aforementioned series for the current invention are those having a viscosity between 50 and 2000 SUS at 100°F, preferably between 100 and 700 SUS. These selected and preferred products are used in the amine solution at a concentration of 50 to 10,000 parts per million (ppm) by weight, and more preferably at a concentration of from 50 to 2000 ppm. The amine solution can contain from 5 to 80 weight percent of any combination of the aforementioned amine solvents with water comprising the balance. The current invention is practiced by either adding the polyoxypropylene compounds to an amine solution that is currently operating in an amine scrubbing system, or by adding the polyoxypropylene compounds to a concentrated amine solution containing 0 to 20 weight percent water followed by a dilution of^" the concentrated amine solution such that the water content becomes 20 to 95 weight percent.

The following examples are presented as illustrative embodiments only and are not intended to limit the scope of this invention. EXAMPLES

A concentrated amine solution product having the following composition was prepared and evaluated in commercial amine scrubbing systems:

MDEA 99.9%

Olin Poly-G WI 285 0.1%

This mixture was used in several amine scrubbing systems in aqueous solutions at concentrations ranging from 20 to 60%. Initial commercial tests produced striking results in reducing solvent losses.

In case I a refinery was using 25% generic MDEA to treat a fuel gas and a liquid hydrocarbon stream. MDEA solvent losses were about 35,000 lb/month. Shortly after the MDEA product whose composition is described above was introduced into this system, losses decreased to about 900 lb/month. No additives or carbon filtration had been used in this amine system either before or after the introduction of.the MDEA product of the current invention. Immediately, prior to the introduction of the MDEA product of the current invention, this system was being operated on generic MDEA. However, earlier, 35,000 pounds of a formulated MDEA solvent called UCARSOL HS 101 was added to this system as makeup with no noticeable reduction in losses. In case II of 31% UCARS0L^R HS 101 MDEA solution was used to treat a fuel gas and a liquid hydrocarbon stream. SAG^R 10 Antifoam was routinely added to the MDEA solution and the solution was continuously filtered with a carbon bed to help control foaming in the contactor. The system was losing 22,000 pounds per month of the MDEA solvent. Soon after the formulated MDEA product of this invention was added to the system, MDEA losses decreased to 13,000 pounds per month.

Practice with the invention will allow users to acquire the proper mix for their particular needs, working within the parameters of the invention, and consistent with the hereinafter appended claims.

Claims

What is claimed is:

1. A method for reducing solvent losses in amine scrubbing processes comprising adding to a water-amine scrubbing solution a predetermined amount of at least one polyoxypropylene compound characterized as

R'O-CCH - OJ_TΓR"

where R'and R" represent alkyl groups having a total of 1-5 carbon atoms, the viscosity of any such compounds ranging between 50 and 2000 S.U.S. at 100°F, which limits n, and said predetermined amount is from about 50 ppm to about 10,000 ppm of total such compounds in said solution.

2. The method of Claim 1 wherein the adding step is performed on an aqueous amine solution containing from about 5 to about 80 weight percent amine.

3. A composition for reducing solvent losses in an amine scrubbing process characterized as an aqueous amine solution containing at least one of several polyoxypropylene compounds of the form

where R'and R" are alkyl groups of from 1 to 5 carbon atoms and n ranges in accord with polyoxyproplyene compounds having an individual viscosity limit ranging from about 50 to about 2000 S.U.S. at 100°F.

4. Employing polyoxypropylene compounds of the general formula

R'O-<CH₂-CH-0)JJ—R" CH₃ where R' and R" represent alkyl groups having a total of 1-5 carbon atoms and where the individual viscosities of the pure polyoxypropylene compounds are between 50 and 2000 S.U.S at 100°F, in aqueous amine scrubbing solutions at concentrations of from 50 to 10,000 ppm total of any or any combination of the said propylene glycol compounds; such that said solution provides for reduced amine solution losses as compared to the losses for the corresponding amine solution free of said polyoxypropylene compounds.

5. Composition as claimed in Claim 4 wherein the aqueous amine scrubbing solution contains 5-80 weight percent amine.

6. Composition as claimed in Claim 4 wherein the amine scrubbing solution is concentrated, containing 0-20 weight percent water and said concentrated amine scrubbing solution is diluted to contain 20-95 weight percent water prior to actual use as a scrubbing solution.

7. Composition as claimed in Claim 4 wherein said polyoxypropylene compounds are present at total concentrations of 50 to 2000 ppm.

8. Composition as claimed in Claim 4 wherein the individual viscosities of said polyoxypropylene compounds are between 100 and 700 S.U.S. at 100°F.

9. Composition as claimed in Claim 4 wherein the amine in said amine scrubbing solution is monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine (DIPA), diglycolamine (DGA), methyldiethanolamine (MDEA), n-methylethanolamine (NMEA), or mixtures thereof.

10. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Olin Poly-G I 285 or the equivalent.

11. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Olin Poly-G WI 625 or the equivalent.

12. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Dow Polypropylene Glycol L-1150 or the equivalent.

13. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Dow Polypropylene Glycol L-910 or the equivalent.

14. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Union Carbide UC0N^R Lubricant LB-285 or the equivalent.

15. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Union Carbide UC0N^R Lubricant LB-65 or the equivalent.

16. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Union Carbide UC0N^R Lubricant LB-135 or the equivalent.

17. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Union Carbide UC0N^R Lubricant LB-165 or the equivalent.

18. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Union Carbide UC0N^R Lubricant LB-385 or the equivalent.

19. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Union Carbide UCON^R Lubricant LB-525 or the equivalent.

20. Composition as claimed in Claim 4 wherein said polyoxypropylene compound is Union Carbide UC0N^R Lubricant LB-625 or the equivalent.