Hybrid solvent formulations for total organic sulfur removal and total acidic gas removal

Abstract

A method of treating oil and gas streams to remove total organic sulfur or total acid gas including the step of treating the gas stream with a solution of an amine, physical solvent, and water wherein the amine solution may optionally also contain an activator.

Claims

1. A method of treating oil and gas streams to remove total organic sulfur and total acidic gases, said method comprising: treating said oil and gas streams with an aqueous solution, said aqueous solution comprising: an amine selected from the group consisting of 3-dimethylamino-1, 2-propanediol, 3-diethylaminopropane-1,2-diol, 2-hydroxymethyl-2-dimethylaminopropane-1,3-diol, 2-hydroxymethyl-2-diethylaminopropane-1,3-diol, dimethylethanolamine, 2-hydroxymethyl-2-methylaminopropane-1,3-diol, 2-hydroxymethyl-2-ethylaminopropane-1,3-diol; and mixtures thereof; a physical solvent, wherein said physical solvent is a monohydric glycol ether having the formula: ##STR00001## wherein R is a Methyl group, Ethyl group, Propyl group, or Butyl group, and n=1-5; and an activator.

2. The method of claim 1, wherein said activator is selected from the group consisting of piperazine, hydroxyethylpiperazine, diethanolamine, N-methylaminoethanol, 2-methylpiperazine, N-methylpiperazine, 2-methyl-2-aminopropanol, or monoethanolamine.

3. The method of claim 1, wherein said physical solvent is present at a concentration from about 5 wt % to 60 wt %.

4. The method of claim 1, wherein said aqueous solution additionally comprises an acid, wherein said acid is selected from the group consisting of phosphoric acid, boric acid, sulfuric acid, and mixtures thereof.

5. The method of claim 1, wherein an equal mass ratio mixture of the amine and physical solvent displays a dielectric constant of less than 20 at 25 C.; and wherein the pKa of said amine is at least 9.0 at 25 C.

6. The method of claim 1, wherein said amine has a pKa of 9.0 to 11 at 25 C. and a normal boiling point of at least 200 C.

7. The method of claim 1, wherein the dielectric constant of said aqueous solution ranges from 5 to 20 at 25 C.

8. The method of claim 1, wherein said physical solvent is selected from the group consisting of methoxytriglycol, methoxydiglycol, ethoxytriglycol, butoxytriglycol, methyl capped poly-ethylene glycol ethers, methyl capped poly-propylene glycol, and mixtures thereof.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a schematic depiction of an exemplary gas treating apparatus and process.

(2) FIG. 2 is a graph depicting CO.sub.2 acid gas carrying capacity by Headspace Analysis of Glycol-Amine Mixtures.

(3) FIG. 3 is a graph depicting H2S acid gas carrying capacity by Headspace Analysis of Glycol-Amine Mixtures.

(4) FIG. 4 is a graph depicting MeSH acid gas carrying capacity by Headspace Analysis of Glycol-Amine Mixtures.

(5) FIG. 5 is a graph depicting VLE acquired by Headspace Analysis of Glycol-Amine Mixtures.

DETAILED DESCRIPTION OF THE INVENTION

(6) The invention is a method for treating oil and gas streams to selectively remove total organic sulfur contaminants. The method comprises the steps of treating the oil and gas streams with an amine solution comprising an effective amount of amine constituent, a physical solvent, and a balance of water. Optionally, the solution of the invention also comprises an acid or acid source.

(7) This invention is applicable for the total removal of acidic gases. The invention is also applicable to any number of alkanolamine solutions which are selective to the removal of acidic gaseous species which are total organic sulfur compounds including mercaptans, COS, CS.sub.2, and organic sulfide derivatives, over or in the presence of CO.sub.2. In one preferred mode, the process of the invention will remove those species over CO.sub.2. The composition and method of the invention is also effective in removing total acidic gas species including HCN, SO.sub.2, H.sub.2S, CO and CO.sub.2.

(8) Generally, amine solutions useful in the invention are those which do not directly react with carbon dioxide to form carbamates. These are generally tertiary amines and sterically hindered amines. Further, it is desired for the amine to have a boiling point of at least about 160 C. and a pKa of at least 9.0. 3-dimethylamino-1, 2-propanediol (DMAPD), 3-diethylaminopropane-1,2-diol, 2-hydroxymethyl-2-dimethylaminopropane-1,3-diol or 2-hydroxymethyl-2-diethylaminopropane-1,3-diol are examples of a tertiary alkanlamine meeting these criteria. In addition, 2-hydroxymethyl-2-methylaminopropane-1,3-diol and 2-methyl-2-hydroxyethylaminopropanol are sterically hindered amine of useful for this invention.

(9) A physical solvent needs to be present in the solution used in the process of the invention. Preferred physical solvents include mono-functional and di-functional alcohols having a dielectric constant of lower than about 20 at 25 C. Useful alcohols include methoxytriglycol (MTG), methoxydiglycol (MDG), ethoxytriglycol, butoxytriglycol and mixtures thereof. Also useful as a physical solvent are glycol ethers such as methyl capped poly-ethylene glycol ethers and methyl capped poly-propylene glycol.

(10) Generally, amine solutions useful in the invention are those which do not directly react with carbon dioxide to form carbamates. These are generally tertiary amines and sterically hindered amines. Further, it is desired for the amine to have a boiling point of at least about 160 C. and a pKa of at least 9.0. 3-dimethylamino-1, 2-propanediol (DMAPD), 3-diethylaminopropane-1,2-diol (DEAPD), 2-hydroxymethyl-2-dimethylaminopropane-1,3-diol (DMTA) or 2-hydroxymethyl-2-diethylaminopropane-1,3-diol (DETA) are examples of a tertiary alkanolamine meeting these criteria. In addition, 2-hydroxymethyl-2-methylaminopropane-1,3-diol (MTA) and 2-hydroxymethyl-2-ethylaminopropane-1,3-diol (ETA) are sterically hindered amines useful for this invention.

(11) Further it has been found that using one or more constituents which decrease the dielectric properties of the composition is also preferable. Decreasing the dielectic properties of the composition is also preferable. Decreasing the dielectric properties of the composition has been found to increase the solubility of organic sulfur compounds in the solution.

(12) If it desired to remove total acidic gas constituents including carbonaceous acidic gases from the oil and gas stream, an activator may be used in the composition of the invention. Useful activators include piperazine compounds such as hydroxyl ethyl piperazine, methyl piperazine, N-methyl piperazine, and piperazine as well as mixtures thereof. Also useful alone or in mixture with piperazines are amine compounds such as diethanolamine, N-methyl amine ethanol, 2-methyl-2-amino propanol, amino ethanolamine, 2-hydroxy methyl-2-methyl amino propane-1,3-diol, and mixtures thereof. The useful concentrations of activators range from about 0.1 wt-% to 20 wt-% of the amine solution depending upon the activator to be used.

(13) Representative concentrations are:

Concentration Guidelines (Mass %)

(14) TABLE-US-00001 Useful Preferable More Preferable Alkanolamine 15-60 20-50 30-50 Physical solvent 5-60 10-50 20-40 Water 5-60 5-50 10-50

(15) TABLE-US-00002 PHYSICAL PROPERTIES General Preferred More Preferred Amine pKa 9.0-15.0 9.0-13.0 9.0-11.0 Dielectric constant.sup.1 5-25 10-25 10-20 .sup.1The dielectric constant specified is for the equal mass ratio mixture of amine and physical solvent.

(16) The ranges of dielectric constant values were selected based on estimated values for a mixture of equal mass ratios of the amine and a physical solvent. The method used for estimation is discussed in Harvey and Prausnitz (1987). Examples for mixtures meeting and not meeting our dielectric constant criteria are shown in the table below for equal mass ratio mixtures of representative amines and physical solvents.

(17) TABLE-US-00003 Estimated Exam- Permit- ple Mixture Composition tivity 1 MDEA Ethylene glycol 30.7 2 MDEA Diethylene glycol 26.8 3 MDEA Triethylene glycol 23.0 4 MDEA Methoxytriglycol 17.5 5 MDEA Ethyoxytriglycol 16.9 6 MDEA Butoxytriglycol 15.7 5 MDEA Glycerol 30.6 6 MDEA Sulfolane 31.5 7 MDEA Propylene Carbonate (PC) 41.5 8 MDEA Ethylene carbonate (EC) 52.8 8 MDEA Ethylene carbonate (EC) 52.8 9 MDEA N-methyl-2-pyrrolidone 27.0 (NMP) 10 Dimethylethanolamine Ethylene glycol 27.2 11 Dimethylethanolamine Diethylene glycol 23.6 12 Dimethylethanolamine Triethylene glycol 20.1 13 Dimethylethanolamine Methoxytriglycol 15.2 14 Dimethylethanolamine Ethyoxytriglycol 14.6 15 Dimethylethanolamine Butoxytriglycol 13.5 16 Dimethylethanolamine Glycerol 26.9 17 Dimethylethanolamine Sulfolane 27.8 18 Dimethylethanolamine Propylene Carbonate (PC) 37.0 19 Dimethylethanolamine Ethylene carbonate (EC) 47.2 20 Dimethylethanolamine N-methyl-2-pyrrolidone 24.0 (NMP) 21 Triethanolamine Ethylene glycol 34.1 22 Triethanolamine Diethylene glycol 30.0 23 Triethanolamine Triethylene glycol 26.0 24 Triethanolamine Methoxytriglycol 20.2 25 Triethanolamine Ethyoxytriglycol 19.5 26 Triethanolamine Butoxytriglycol 18.2 27 Triethanolamine Glycerol 34.1 28 Triethanolamine Sulfolane 35.1 29 Triethanolamine Propylene Carbonate (PC) 45.4 30 Triethanolamine Ethylene carbonate (EC) 57.5 31 Triethanolamine N-methyl-2-pyrrolidone 30.1 (NMP)

(18) From the table it can be seen that the amine as well as the physical solvent dielectric constant are important for meeting the criteria. For example, mixture 4 has a dielectric constant in the more preferred range, whereas mixture 24, which has the same physical solvent, but a more polar amine, does not. Compositions used in the invention may also comprise corrosion inhibitors, antifoaming agents and stripping aids, and mixtures thereof. Any number of corrosion inhibitors may be used in the methods and compositions of the invention which are consistent with the environment of use.

(19) Here again, the composition of the invention may comprise antifoaming agents consistent with the environment of use. Exemplary antifoaming agents used in the oil and gas industry include silicone based defoamers and EO/PO based defoamers such as polysiloxane, and polypropylene glycol copolymers among others at a concentration of about 10 ppm to 200 ppm.

(20) The composition of the invention may also comprise stripping aids such as mineral acids including phosphoric acid, sulfuric acid, boric acid and mixtures thereof at a concentration of about 0.1 wt % to 10 wt %.

PROCESSING

(21) The invention set forth herein has great application in the petrochemical and energy industries. For example, the invention can be used for the treatment of fluid streams, gas, liquid, or mixtures, in an oil refinery, the treatment of sour gas, the treatment of coal steam gas, the treatment of hazardous stack emissions, the treatment of land field gases, and a new series of devices dealing with hazardous emissions for human safety.

(22) The fluid streams to be treated by the process of the present invention contain an acid gas mixture which may include gases such as CO.sub.2, N.sub.2, CH.sub.4, C.sub.2H.sub.6, C.sub.3H.sub.8, H.sub.2, CO, H.sub.2O, COS, CS.sub.2, HCN, NH.sub.3, O.sub.2 as well as other organic sulfur compounds such as mercaptans, and the like. Often such gas mixtures are found in combustion gases, refinery gases, town gas, natural gas, syn gas, tail gas, water gas, propane, propylene, heavy hydrocarbon gases, etc. The aqueous amine solution herein is particularly effective when the fluid stream is a gaseous mixture, obtained, for example, from shale oil retort gas, coal or gasification of heavy oil with air/steam or oxygen/steam thermal conversion of heavy residual oil to lower molecular weight liquids and gases, or in sulfur plant tail gas clean-up operations.

(23) The process of the present invention is preferably used to selectively remove H2S from a gas stream comprising other acid gas impurities, for example N.sub.2, CO.sub.2, CH.sub.4, C.sub.2H.sub.6, C.sub.3H.sub.8, H.sub.2, CO, H.sub.2O, COS, HCN, NH.sub.3, O.sub.2, and/or mercaptans.

(24) The absorption step of this invention generally involves contacting the fluid stream, preferably gaseous mixture, with the aqueous alkanolamine solution in any suitable contacting vessel, for examples of representative absorption processes see U.S. Pat. Nos. 5,736,115 and 6,337,059, both of which are incorporated herein by reference in their entirety. In such processes, the fluid stream containing H.sub.2S and/or other impurities from which the acid gases are to be removed may be brought into intimate contact with the aqueous alkanolamine solution using conventional means, such as a tower or vessel packed with, for example, rings or with sieve plates, or a bubble reactor.

(25) In a typical mode of practicing the invention, the absorption step is conducted by feeding the fluid stream into the lower portion of the absorption tower while fresh aqueous alkanolamine solution is fed into the upper region of the tower. The fluid stream, freed largely from the H.sub.2S and CO.sub.2 if present emerges from the upper portion (sometimes referred to as treated or cleaned gas) of the tower, and the loaded aqueous alkanolamine solution, which contains the absorbed H.sub.2S and CO.sub.2, leaves the tower near or at its bottom. Preferably, the inlet temperature of the absorbent composition during the absorption step is in the range of from 60 F. to 300 F., and more preferably from 80 F. to 250 F. Pressures may vary widely; acceptable pressures are between 1 and 5,000 pounds per square inch (psi), preferably 2 to 2,500 psi, and most preferably 5 to 2,000 psi in the absorber. The contacting takes place under conditions such that the H.sub.2S is preferably absorbed by the solution. The absorption conditions and apparatus are designed so as to minimize the residence time of the aqueous alkanolamine solution in the absorber to reduce CO.sub.2 pickup while at the same time maintaining sufficient residence time of the fluid stream with the aqueous absorbent composition to absorb a maximum amount of the H.sub.2S gas. Fluid streams with low partial pressures, such as those encountered in thermal conversion processes, will require less of the aqueous alkanolamine solution under the same absorption conditions than fluid streams with higher partial pressures such as shale oil retort gases.

(26) A typical procedure for the H.sub.2S removal phase of the process comprises absorbing H.sub.2S via countercurrent contact of a gaseous mixture containing H.sub.2S and CO.sub.2 with the aqueous alkanolamine solution of the amino compound in a column containing a plurality of trays at a temperature, of at least 60 F., and at a gas velocity of at least 0.3 feet per second (ft/sec, based on active or aerated tray surface), depending on the operating pressure of the gas, said tray column having fewer than 20 contacting trays, with, e.g., 4 to 16 trays being typically employed.

(27) After contacting the fluid stream with the aqueous alkanolamine solution, which becomes saturated or partially saturated with H.sub.2S, the solution may be at least partially regenerated so that it may be recycled back to the absorber. As with absorption, the regeneration may take place in a single liquid phase. Regeneration or desorption of the acid gases from the aqueous alkanolamine solution may be accomplished by conventional means of heating, expansion, stripping with an inert fluid, or combinations thereof, for example pressure reduction of the solution or increase of temperature to a point at which the absorbed H.sub.2S flashes off, or by passing the solution into a vessel of similar construction to that used in the absorption step, at the upper portion of the vessel, and passing an inert gas such as air or nitrogen or preferably steam upwardly through the vessel. The temperature of the solution during the regeneration step should be in the range from 120 F. to 400 F. and preferably from 140 F. to 300 F., and the pressure of the solution on regeneration should range from 0.5 psi to 100 psi, preferably 1 psi to 50 psi. The aqueous alkanolamine solution, after being cleansed of at least a portion of the H.sub.2S gas, may be recycled back to the absorbing vessel. Makeup absorbent may be added as needed.

(28) In a preferred regeneration technique, the total organic sulfur compounds-rich aqueous amine solution is sent to the regenerator wherein the absorbed components are stripped by the steam which is generated by boiling the solution. Pressure in the flash drum and stripper is usually 1 psi to 50 psi, preferably 5 psi to 30 psi, and the temperature is typically in the range from 120 F. to 340 F., preferably 170 F. to 300 F. Stripper and flash temperatures will, of course, depend on stripper pressure; thus at 15 psi to 30 psi stripper pressures, the temperature will be 170 F. to 250 F. during desorption. Heating of the solution to be regenerated may very suitably be affected by means of indirect heating with low-pressure steam. It is also possible, however, to use direct injection of steam. The resulting hydrogen sulfide-lean aqueous alkanolamine solution may be used to contact a gaseous mixture containing total organic sulfur compounds.

(29) FIG. 1 represents an example of a gas treating process. An aqueous amine absorbent solution is introduced via feed line 5 into the upper portion of a gas-liquid countercurrent packed-bed absorption column 2. The gas stream is introduced through feed line 1 into the lower portion of column 2 at a gas flow rate of 10 liter per minute. The absorber pressure is adjusted to 238 psia. The clean gas (i.e., reduced amounts of total organic sulfur compounds and CO.sub.2) is discharged at the top of the absorber 2 through line 3 levels of acid gases are determined by gas chromatography (GC) analysis. The aqueous amine solution loaded with total organic sulfur compounds and CO.sub.2 flows toward the lower portion of the absorber, and leaves via line 4. The aqueous amine in line 4 is reduced in pressure by the level control valve 8 and flows through line 7 to heat exchanger 9, which heats the loaded aqueous solution. The hot rich solution enters the upper portion of the regenerator 12 via line 10. The regenerator 12 is equipped with random packing which effects desorption of the total organic sulfur compounds and CO.sub.2 gases. The pressure of the regenerator is set at 17 psia. The gases are passed through line 13 into condenser 14 wherein cooling and condensation of any residual water and amine occurs. The gases enter a separator 15 wherein the condensed liquid is separated from the vapor phase. The condensed aqueous solution is pumped via pump 22 through line 16 to the upper portion of the regenerator 12. The gases remaining from the condensation are removed through line 17 for final collection and/or disposal. The regenerated aqueous solution flows down through the regenerator 12 and the close-coupled reboiler 18. The reboiler 18, equipped with an electrical heating device, vaporizes a portion of the aqueous solution to drive off any residual gases. The vapors rise from the reboiler and are returned to the regenerator 12 which comingle with falling liquid and then exit through line 13 for entry into the condensation stage of the process. The regenerated aqueous solution from the reboiler 18 leaves through line 19 and is cooled in heat exchanger 20, and then is pumped via pump 21 back into absorber 2 through feed line 5.

(30) Preferably, solutions of the invention are introduced into a gas treating process via line 4, 5, 10, 13, 16 and/or 19.

(31) Preferably the clean gas contains equal to or less than 20 ppm of total organic sulfur compounds meeting some environmental regulations, more preferably equal to or less than 10 ppm total organic sulfur compounds.

(32) A preferred embodiment of the invention involves performing the method of the invention continuously, or as a continuous process. However, the method may be performed batch wise or semi-continuously. Selection of the type of process used should be determined by the conditions, equipment used, type and amount of gaseous stream, and other factors apparent to one of ordinary skill in the art based on the disclosure herein.

WORKING EXAMPLES

(33) The following examples provide a non-limiting illustration of certain embodiments of the invention.

(34) CO.sub.2 Acid Gas Carrying Capacity by Headspace Analysis of Glycol-Amine Mixtures.

(35) A 40 wt % aqueous solution of MDEA is compared with solutions containing 40 wt % of tested amine, 20 wt % of water and 40 wt % of a physical solvent. The solutions are loaded with about 1, 2.5 and 5 wt % of CO.sub.2 and then analyzed by headspace analysis at 40 C. and 40 psig. The results are set forth in FIG. 2.

(36) The results are showing that formulations comprising amines with a pKa of at least 9.0 (DMAPD & DEAPD) display higher capacity for CO.sub.2 compared to formulations comprising amines with a pKa lower than 9.0 (MDEA).

(37) H2S Acid Gas Carrying Capacity by Headspace Analysis of Glycol-Amine Mixtures.

(38) A 40 wt % aqueous solution of MDEA is compared with solutions containing 40 wt % of tested amine, 20 wt % of water and 40 wt % of a physical solvent. The solutions are loaded with about 1, 2.5 and 5 wt % of H.sub.2S and then analyzed by headspace analysis at 40 C. and 40 psig. The results are set forth in FIG. 3.

(39) The results are showing that formulations comprising amines with a pKa of at least 9.0 (DMAPD & DEAPD) display higher capacity for H.sub.2S compared to formulations comprising amines with a pKa lower than 8.7 (MDEA).

(40) MeSH Acid Gas Carrying Capacity by Headspace Analysis of Glycol-Amine Mixtures.

(41) A 40 wt % aqueous solution of MDEA is compared with solutions containing 40 wt % of tested amine, 20 wt % of water and 40 wt % of a physical solvent. Sulfuric acid (0.3 mol of acid per mol of amine) is added in each solution and the vial headspaces are loaded to 8.3, 16.7, 33.3 and 75% of MeSH and then analyzed by headspace analysis at 40 C. and 40 psig. The results are set forth in FIG. 4.

(42) The results are showing that formulations comprising a physical solvent display better performance in the removal of MeSH than aqueous solution. In addition, amines with a pKa of at least 9.0 (DMAPD & DEAPD) display higher capacity for MeSH compared to formulations comprising amines with a pKa lower than 9.0 (MDEA).

(43) Finally the impact of the amount of sulfuric acid on MeSH removal has been studied. In a formulation containing 40 wt % DMAPD, 40 wt % MTG and 20 wt % water, sulfuric acid is added at 0.2, 0.4 and 0.6 mol of acid per mol of amine. Then, the vial headspaces are loaded to 41.7% MeSH and then analyzed by headspace analysis at 40 C. and 40 psig.

(44) TABLE-US-00004 H2SO4 Average MeSH in H2SO4 (mol/mol) (mol/mol) the Headspace the Headspace 1 0.2 1318.2 1.49 2 0.4 1355.7 1.54 3 0.6 1541.4 1.75

(45) The results indicate that the amount of sulfuric acid has little influence on the performance of MeSH removal. Thus, formulations displaying greater capacity for acid gases such as CO.sub.2 and H.sub.2S will still be capable of removing MeSH.

(46) VLE Acquired by Headspace Analysis of Glycol-Amine Mixtures.

(47) Solution containing 50 wt % of amine, 25 wt % of water and 25 wt % of a physical solvent are loaded with about 1, 2.5 and 5 wt % of H.sub.2S and then studied by headspace analysis at 50 C. and 20 psig. The results are set forth in FIG. 5.

(48) The dielectric constant of physical solvents can be used as a value to indicate for their polarity.

(49) TABLE-US-00005 Physical Solvent MTG TEG EG Glycerol Water Dielectric 13 24 40 41 78 Constant

(50) The results are showing that, as the polarity of the molecule replacing water increase (MTG<TEG<EG<Glycerol), the capacity of the formulation for acid gases increases.

(51) Although the present invention has been described by reference to its preferred embodiment as is disclosed in the specification and drawings above, many more embodiments of the present invention are possible without departing from the invention. Thus, the scope of the invention should be limited only by the impended claims.