Method for removing SOx from gas with modified polyethylene glycol

Abstract

A method for removing SO.sub.x from a gas by using a modified polyethylene glycol solution to absorb the SO.sub.x in the gas. The modified polyethylene glycol solution is contacted with the gas containing SO.sub.x to absorb the SO.sub.x in the gas, wherein x=2 and/or 3, the modified polyethylene glycol is a product derived from etherifying hydroxyl groups in the molecules of ethylene glycol and/or polyethylene glycol and has a general formula: R.sub.1—(O—C.sub.2H.sub.4).sub.n—O—R.sub.2, where n is a positive integer, R.sub.1 and R.sub.2 are the same or different and are each independently alkyl, alkenyl, alkynyl, acyl or aryl.

Claims

1. A method for removing SO.sub.x from a gas, comprising: contacting a modified polyethylene glycol solution with the gas containing SO.sub.x to absorb the SO.sub.x in the gas, wherein x=2 and/or 3, wherein the modified polyethylene glycol is a product derived from etherifying hydroxyl groups in the molecules of ethylene glycol and/or polyethylene glycol and has a general formula:
R.sub.1—(O—C.sub.2H.sub.4).sub.n—O—R.sub.2, wherein n is a positive integer, R.sub.1 and R.sub.2 are the same or different and are each independently alkyl, alkenyl, alkynyl, acyl, or aryl, wherein the modified polyethylene glycol solution is an aqueous solution of modified polyethylene glycol, and the modified polyethylene glycol has a mass percent content of ≧80%.

2. The method for removing SO.sub.x from a gas according to claim 1, wherein the alkyl is C1-C18 linear or branched alkyl; the alkenyl is C2-C18 linear or branched alkenyl; the alkynyl is C2-C18 linear or branched alkynyl; the acyl is ##STR00007## wherein R represents C1-C16 linear or branched alkyl, C2-C16 linear or branched alkenyl, or C2-C16 linear or branched alkynyl; and the aryl is phenyl or substituted phenyl.

3. The method for removing SO.sub.x from a gas according to claim 1, wherein the modified polyethylene glycol solution is a solution of modified polyethylene glycol having a single molecular weight, or a mixed solution of a plurality of modified polyethylene glycols having different molecular weights.

4. The method for removing SO.sub.x from a gas according to claim 1, wherein the modified polyethylene glycol solution further comprises ethylene glycol, or polyethylene glycol, or a mixture of ethylene glycol and polyethylene glycol, in a mass percent content of less than 20% of a total mass of the modified polyethylene glycol solution.

5. The method for removing SO.sub.x from a gas according to claim 1, wherein the modified polyethylene glycol solution comprising a plurality of additives selected from the group consisting of organic amines, alcohol amines, amides, sulfones, sulfoxides, sodium alkoxides, potassium alkoxides, metal carboxylates, and metallorganic compounds, and the plurality of additives are in a mass percent content of less than 20% of a total mass of the modified polyethylene glycol solution.

6. The method for removing SO.sub.x from a gas according to claim 1, wherein the modified polyethylene glycol solution absorbs the SO.sub.x in the gas under atmospheric or increased pressure at an absorption temperature of −20 to 80° C.

7. The method for removing SO.sub.x from a gas according to claim 1, further comprising regenerating the modified polyethylene glycol solution containing the absorbed SO.sub.x by one or more method selected from heating, vacuum, gas stripping, ultrasonic treatment, microwave treatment, and radiation at a regeneration temperature of 0 to 300° C. to release sulfur dioxide and/or sulfur trioxide; and recycling the regenerated modified polyethylene glycol solution.

8. The method for removing SO.sub.x from a gas according to claim 7, further comprising, when the regenerated modified polyethylene glycol solution has a mass percent content of water of more than 20%, removing water from the modified polyethylene glycol solution.

9. The method for removing SO.sub.x from a gas according to claim 1, wherein the gas is a flue gas, a waste gas containing SO.sub.x, or an industrial raw material gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of desulfurization and absorption process.

(2) FIG. 2 is a schematic diagram of desulfurization solution regeneration by heating method.

(3) FIG. 3 is a schematic diagram of desulfurization solution regeneration by vacuum method.

(4) FIG. 4 is a schematic diagram of desulfurization solution regeneration by gas stripping method.

(5) FIG. 5 is a schematic diagram of desulfurization solution regeneration by ultrasonic method, and/or microwave method, and/or radiation method.

(6) FIG. 6 is a gas-liquid equilibrium diagram for absorption of ethylene glycol dimethyl ether (EGDME) solution and a mixed gas of sulfur dioxide and nitrogen at the temperature of 303.15 K, 308.15 K and 313.15 K under the pressure of 122.66 kPa.

(7) FIG. 7 is a gas-liquid equilibrium diagram for absorption of diethylene glycol dimethyl ether (DEGDME) solution and a mixed gas of sulfur dioxide and nitrogen at the temperature of 303.15 K, 308.15 K and 313.15 K under the pressure of 122.66 kPa.

(8) FIG. 8 is a gas-liquid equilibrium diagram for absorption of triethylene glycol dimethyl ether (TriEGDME) solution and a mixed gas of sulfur dioxide and nitrogen at the temperature of 303.15 K, 308.15 K and 313.15 K under the pressure of 122.66 kPa.

(9) FIG. 9 is a gas-liquid equilibrium diagram for absorption of tetraethylene glycol dimethyl ether (TetraEGDME) solution and a mixed gas of sulfur dioxide and nitrogen at the temperature of 303.15 K, 308.15 K and 313.15 K under the pressure of 122.66 kPa.

(10) FIG. 10 is a gas-liquid equilibrium diagram for absorption of dioxane (1,4-Dioxane) solution and a mixed gas of sulfur dioxide and nitrogen at the temperature of 303.15 K, 308.15 K and 313.15 K under the pressure of 122.66 kPa.

(11) FIG. 11 is a gas-liquid equilibrium diagram for absorption of ethylene glycol methyl ether (EGME) solution and a mixed gas of sulfur dioxide and nitrogen at the temperature of 303.15 K, 308.15 K and 313.15 K under the pressure of 122.66 kPa.

(12) FIG. 12 is a gas-liquid equilibrium diagram for absorption of diethylene glycol methyl ether (DEGME) solution and a mixed gas of sulfur dioxide and nitrogen at the temperature of 303.15 K, 308.15 K and 313.15 K under the pressure of 122.66 kPa.

DETAILED DESCRIPTION

(13) The desulfurization method by modified polyethylene glycol according to the invention is described below with reference to some specific embodiments. The embodiments described hereinafter are only for better illustrating the present invention rather than limiting the claims of the present invention.

(14) The first process is a desulfurization and absorption process as shown in FIG. 1. The gas containing SO.sub.x (2) is fed from the bottom of the desulfurization tower (1) and contacted with the desulfurization lean liquor (4) counter-currently. The SO.sub.x in the gas containing SO.sub.x (2) is absorbed by the lean liquor (4). The gas containing SO.sub.x (2) is converted into purified gas (3) which is discharged out from the top of the desulfurization tower (1). The desulfurization lean liquor (4) with absorbed SO.sub.x is converted into desulfurization rich liquor (5) at the bottom of the desulfurization tower (1). The desulfurization rich liquor(5) is discharged out from the bottom of the desulfurization tower (1) and transferred to the regenerator to be regenerated by one or more of heating method, vacuum method, gas stripping method, ultrasonic method, microwave method, and radiation method.

(15) According to FIG. 1, the content of sulfur dioxide in the gas is measured by gas chromatography, and the content of sulfur dioxide in liquid phase is measured by iodometry. The absorption equilibrium is studied when some modified polyethylene glycol (also referred to as “ethylene glycol derivatives”) solutions, such as ethylene glycol dimethyl ether (EGDME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TriEGDME), tetraethylene glycol dimethyl ether (TetraEGDME), dioxane (1,4-Dioxane), ethylene glycol methyl ether (EGME), and diethylene glycol methyl ether (DEGME), are contacted with a mixed gas of sulfur dioxide and nitrogen under the pressure of 122.66 kPa at different temperatures (303.15 K, 308.15 K and 313.15 K). The absorption equilibrium data is shown in table 1.

(16) TABLE-US-00002 TABLE 1 Gas-liquid equilibrium data for some ethylene glycol derivatives GLE for EG Derivatives at 122.66 kPa and Different Temperatures T = 303.15 K T = 308.15 K T = 313.15 K C.sub.SO2 (mol .Math. m.sup.−3) p.sub.SO2 (Pa) C.sub.SO2 (mol .Math. m.sup.−3) p.sub.SO2 (Pa) C.sub.SO2 (mol .Math. m.sup.−3) p.sub.SO2 (Pa) EGDME 3.98 17.5 3.21 21.3 2.07 19.6 ethylene glycol 8.12 31.8 5.69 31.2 3.47 27.4 dimethyl ether 10.87 43.4 8.28 41.9 8.90 50.6 15.11 60.1 12.26 58.6 11.59 62.6 19.61 75.3 16.82 76.2 14.33 77.5 24.84 94.3 21.94 101.4 17.08 93.7 6.31 40.5 DEGDME 1.91 10.7 1.81 11.3 1.81 16.0 diethylene glycol 2.62 14.1 2.59 14.0 3.36 30.0 dimethyl ether 8.30 39.9 8.85 45.9 5.54 49.6 14.59 69.4 10.92 54.9 5.95 53.4 21.68 101.6 13.25 69.4 7.76 66.6 20.87 95.4 15.84 83.5 10.09 89.6 10.66 51.9 18.94 101.5 TriEGDME 2.59 13.6 2.74 13.1 1.45 10.9 triethylene glycol 3.83 18.5 5.07 25.8 4.50 33.1 dimethyl ether 6.57 31.2 7.14 36.2 10.82 71.3 10.35 48.4 10.25 50.8 13.87 92.6 15.78 75.8 13.87 70.6 8.38 58.2 21.48 105.1 21.37 106.2 7.14 49.4 TetraEGDME 4.14 23.1 1.14 13.2 1.60 15.3 tetrathylene glycol 6.31 33.4 2.17 19.5 6.78 50.2 dimethyl ether 7.87 43.7 6.16 39.8 4.71 39.8 10.97 57.2 10.35 63.3 8.49 64.5 14.33 70.7 12.94 76.3 12.63 92.9 19.87 93.1 17.44 95.2 3.67 31.0 0.88 11.5 8.02 50.0 11.18 82.3 1,4-Dioxane 7.88 28.1 4.91 18.8 0.62 10.4 dioxane 13.91 49.6 7.98 34.0 1.91 15.0 16.56 60.5 10.94 46.6 4.14 25.5 20.74 72.1 11.10 48.8 6.83 38.6 23.89 80.7 14.14 61.7 11.90 65.4 27.01 89.1 16.71 70.4 14.49 79.8 29.84 96.9 19.96 79.5 18.22 97.3 34.57 104.9 26.67 98.0 31.40 118.2 EGME 2.85 19.4 2.07 20.6 1.29 19.9 ethylene glycol 5.69 33.2 4.55 38.6 2.74 30.8 methyl ether 8.95 51.1 8.18 63.0 4.92 49.6 13.04 74.1 9.68 71.3 7.87 72.4 15.53 88.4 14.39 101.1 9.47 86.9 19.51 106.3 6.62 52.9 6.57 62.2 10.97 62.5 12.21 89.7 12.68 107.7 DEGME 2.07 20.7 0.26 7.3 0.52 8.4 diethylene glycol 4.81 34.9 4.40 36.0 1.71 20.6 methyl ether 8.12 51.0 6.37 53.1 3.62 36.4 10.51 68.4 8.64 70.5 6.88 69.4 12.68 81.5 11.90 90.0 9.83 89.6 17.08 100.9 1.76 18.1 5.43 56.1 6.57 42.4 10.61 83.1 12.94 114.4

(17) The data shown in table 1 are plotted to the gas-liquid equilibrium diagrams shown in FIG. 6-12.

(18) From the experiment results described above, it can be seen that the modified polyethylene glycol solution has a strong capability to absorb sulfur dioxide, and is a relatively desirable desulfurization solvent. The capability of the modified polyethylene glycol solution to absorb sulfur dioxide will increase as the absorption pressure increases, and will decrease as the absorption temperature decreases. Therefore, regeneration can be easily carried out by decreasing pressure and increasing temperature so as to recycle the solution.

(19) The second process is the regeneration process of desulfurization solution. The regeneration methods for it include heating method, vacuum method, gas stripping method, ultrasonic method, microwave method, and radiation method.

(20) The regeneration method by heating is shown in FIG. 2. The desulfurization rich liquor (5) is tranferred to the heating-regenerator (6) and is heated to release gaseous sulfur dioxide and/or sulfur trioxide (7). The gaseous sulfur dioxide and/or sulfur trioxide (7) are processed into by-products of liquid sulfur dioxide and/or sulfur trioxide of high purity. Meanwhile, sulfur foams and/or dusts (8) may be produced or accumulated, and are separated from the desulfurization solution. The separated sulfur foams and/or dusts (8) can be further processed into sulfur by-products, and there are also some ash residues discharged. The desulfurization rich liquor (5) is regenerated by heating-regenerator (6) and is then converted into the desulfurization lean liquor (4). The desulfurization lean liquor (4) can be transferred directly to the desulfurization and absorption process for recycle use. Alternatively, it can be transferred to the vacuum-regenerator and/or gas stripping-regenerator, and/or ultrasonic-regenerator, and/or microwave-regenerator, and/or radiation-regenerator to be further regenerated.

(21) The regeneration method by vacuum is shown in FIG. 3. The desulfurization rich liquor (5) is tranferred to the vacuum-regenerator (9), vacuum is created with the aid of vacuumizer (10) to release gaseous sulfur dioxide and/or sulfur trioxide (7). The gaseous sulfur dioxide and/or sulfur trioxide (7) are processed into by-products of liquid sulfur dioxide and/or sulfur trioxide of high purity. Meanwhile, sulfur foams and/or dusts (8) may be produced or accumulated, and are separated from the desulfurization solution. The separated sulfur foams and/or dusts (8) can be further processed into sulfur by-products, and there are also some ash residues discharged. The desulfurization rich liquor (5) is regenerated by vacuum-regenerator (9) and is then converted into the desulfurization lean liquor (4). The desulfurization lean liquor (4) can be transferred directly to the desulfurization and absorption process for recycle use. Alternatively, it can be transferred to the heating-regenerator and/or gas stripping-regenerator, and/or ultrasonic-regenerator, and/or microwave-regenerator, and/or radiation-regenerator to be further regenerated.

(22) The regeneration method by gas stripping is shown in FIG. 4. The desulfurization rich liquor (5) is transferred to the gas stripping-regenerator (11), and contacted counter-currently with the inert gas (12) (including nitrogen, argon and water vapour, etc.) from the bottom of the gas stripping-regenerator (11). The sulfur dioxide and/or sulfur trioxide in the desulfurization rich liquor (5) are released into the inert gas and a mixed gas (13) of sulfur dioxide and/or sulfur trioxide with high concentration is formed and discharged from the top of the gas stripping-regenerator (11). The discharged sulfur dioxide and/or sulfur trioxide in the inert gas are processed into by-products of liquid sulfur dioxide and/or sulfur trioxide of high purity. The desulfurization rich liquor (5) is regenerated by the gas striping-regenerator (11) and is then converted into the desulfurization lean liquor (4). The desulfurization lean liquor (4) can be transferred directly to the desulfurization and absorption process for recycle use. Alternatively, it can be transferred to the heating-regenerator and/or vacuum-regenerator, and/or ultrasonic-regenerator, and/or microwave-regenerator, and/or radiation-regenerator to be further regenerated.

(23) The regeneration by ultrasonic method, and/or microwave method, and/or radiation method is shown in FIG. 5. The desulfurization rich liquor (5) is transferred to the ultrasonic-, and/or microwave-, and/or radiation-regenerator (14) and regenerated under the conditions of ultrasonic, and/or microwave, and/or radiation to release gaseous sulfur dioxide and/or sulfur trioxide (7). The gaseous sulfur dioxide and/or sulfur trioxide (7) are processed into by-products of liquid sulfur dioxide and/or sulfur trioxide of high purity. Meanwhile, sulfur foams and/or dusts (8) may be produced or accumulated, and are separated from the desulfurization solution. The separated sulfur foams and/or dusts (8) can be further processed into sulfur by-products, and there are also some ash residues discharged. The desulfurization rich liquor (5) is regenerated by ultrasonic-, and/or microwave-, and/or radiation-regenerator (14) and is then converted into the desulfurization lean liquor (4). The desulfurization lean liquor (4) can be transferred directly to the desulfurization and absorption process for recycle use. Alternatively, it can be transferred to the heating-regenerator, and/or vacuum-regenerator, and/or gas stripping-regenerator to be further regenerated.

(24) When the regenerated modified polyethylene glycol solution has relatively high water content and the desulfurization effects are influenced, it is needed to remove water from the modified polyethylene glycol solution. The methods for removing water include distillation method by heating, absorption method with water absorbent or combination thereof. The modified polyethylene glycol solution with water removed is recycled for use. The commonly used water absorbents include CaO, anhydrous CaSO.sub.4, silica gel and water absorbent resins.