Process for purifying a CO2 stream in order to avoid corrosion by hydrochloric acid

Abstract

A process for purifying a by-product stream comprising primarily CO2 that emanates from a an ethylene glycol plant, where the by-product stream may contain organic chlorides and water. The process employs an adsorbent to remove one or more organic chlorides from the by-product stream to produce pure or substantially pure CO2. To improve the efficiency of the organic chloride adsorbent, prior to the organic chloride adsorption process, a moisture adsorbent may be employed to remove at least some of the water from the by-product stream.

Claims

1. A process for purifying a carbon dioxide (CO.sub.2) feed stream comprising primarily CO.sub.2, an organic chloride, and water, the process comprising: cooling the CO.sub.2 feed stream to condense and remove at least a portion of the water from the CO.sub.2 feed stream to produce a cooled CO.sub.2 feed stream comprising less than 0.3 wt. % water; and contacting the cooled CO.sub.2 feed stream with a zeolite adsorbent material to remove at least a portion of the organic chloride from the cooled CO.sub.2 feed stream to produce a purified CO.sub.2 feed stream.

2. The process of claim 1 further comprising: prior to contacting the cooled CO.sub.2 feed stream with a zeolite adsorbent material, contacting the cooled CO.sub.2 feed stream with a silica adsorbent material to remove additional water from the cooled CO.sub.2 feed stream.

3. The process of claim 1, wherein the CO.sub.2 feed stream comprises 5 to 600 ppm of an organic chloride.

4. The process of claim 1, wherein the cooling of the CO.sub.2 feed stream comprises cooling the CO.sub.2 feed stream to a temperature of 35 C. to 55 C.

5. The process of claim 4 further comprising: cooling the cooled CO.sub.2 feed stream to a temperature of 10 C. to 30 C. to condense and remove additional water, if present, from the cooled CO.sub.2 feed stream such that it comprises less than 0.06 wt. % water.

6. The process of claim 1, wherein the zeolite adsorbent material comprises zeolite-13X having a Si/Al ratio of 2 or less.

7. The process of claim 1, wherein the zeolite adsorbent material comprises zeolite-13X adsorbent material having Si:Al ratio in the range of 1.5:1 to 2.5:1.

8. The process of claim 1, wherein the CO.sub.2 feed stream is from an ethylene glycol plant.

9. The process of claim 1, wherein the purified CO.sub.2 feed stream is used as a reactant for an oxidation reaction.

10. The process of claim 9, wherein the amount of hydrochloric acid (HCl) produced in the oxidation reaction is 0 to <0.02 ppmv.

11. The process of claim 1, wherein the organic chloride comprises ethylene di-chloride.

12. The process of claim 1 wherein the CO.sub.2 feed stream comprises 99 to 99.5 vol. % CO.sub.2.

13. The process of claim 1, wherein the CO.sub.2 feed stream comprises 5 to 100 ppmv organic chloride.

14. The process of claim 1, wherein the adsorption conditions comprise a temperature of 15 to 50 C.

15. The process of claim 1, wherein the adsorption conditions comprise a pressure of 15 to 25 barg.

16. The process of claim 1, wherein the adsorption conditions comprise a space velocity of 1 to 5 h.sup.1.

17. The process of claim 1 wherein the cooling of the CO.sub.2 feed stream comprises cooling by a cooling water heat exchanger.

18. The process of claim 1 wherein the cooling of the CO.sub.2 feed stream comprises cooling by a chiller unit.

19. The process of claim 1, wherein the CO.sub.2 feed stream, prior to purification, further comprises saturated and unsaturated hydrocarbons.

20. The process of claim 1, wherein an HCl absorber is not used.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 shows a prior art system for purifying a CO.sub.2 stream from an ethylene glycol plant;

(3) FIG. 2 shows a system for purifying a CO.sub.2 stream from an ethylene glycol plant, according to embodiments of the invention;

(4) FIG. 3 shows a system for purifying a CO.sub.2 stream from an ethylene glycol plant, according to embodiments of the invention;

(5) FIG. 4 shows results of an experiment that tested the adsorption properties of zeolite-13X with respect to an organic chloride; and

(6) FIG. 5 shows results of experiments that tested the adsorption properties of zeolite-13X with respect to an organic chloride in the presence of water.

DETAILED DESCRIPTION OF THE DISCLOSURE

(7) A discovery has been made for purifying a by-product stream comprising primarily CO.sub.2 from an ethylene glycol producing plant. The by-product stream may also contain organic chlorides and water. According to embodiments of the invention, an adsorbent is employed to remove one or more organic chlorides from the CO.sub.2 by-product stream prior to catalytic oxidation to produce pure or substantially pure CO.sub.2. In embodiments of the invention, a moisture adsorbent is used to remove at least some of the water from the CO.sub.2 stream, prior to the organic chloride adsorption process, in order to improve the efficiency of the organic chloride adsorbent process.

(8) By removing one or more organic chlorides from the CO.sub.2 by-product stream, one or more compounds that react to form HCl is removed from the feed to a catalytic oxidation reactor employed in the purification of the CO.sub.2 by-product stream, thereby preventing, or at least reducing, the formation of HCl in the catalytic oxidation reactor. In this way, the issue of HCl corrosion of equipment downstream from the catalytic oxidation reactor is addressed by preventing, or reducing, the formation of HCl, instead of attempting to mitigate HCl's effect once it is formed.

(9) Embodiments of the invention includes a process that uses zeolite-13X (Si:Al ratio of 1.5:1 to 2.5:1, preferably 2:1 or thereabout) to remove the organic chlorides, in particular ethylene dichloride (EDC), from the impure CO.sub.2 by-product gas of the ethylene glycol plant. However, it is contemplated that other zeolites can be used to remove organic chlorides from the CO.sub.2 stream. Non-limiting examples of other zeolites that can be used in the context of the present invention include zeolite-Y, zeolite-X, ZSM-5, etc.

(10) Referring to FIG. 2, system 20 for purifying a CO.sub.2 stream from an ethylene glycol plant is shown. CO.sub.2 feed stream S200 may include 99.5 Vol % CO.sub.2, approximately 5-100 ppmv organic chloride (e.g., ethylene dichloride (C.sub.2H.sub.4Cl.sub.2)), approximately 1 ppmv unsaturated hydrocarbons, and approximately 1 ppmv saturated hydrocarbons. CO.sub.2 feed stream S200 is fed to multi-stage compressor 200. Multi-stage compressor 200 performs multi-stage compression of CO.sub.2 feed stream S200 to form compressed CO.sub.2 feed stream S201. This multistage compression of CO.sub.2 feed stream S200 removes at least some of the water from CO.sub.2 feed stream S200 such that compressed CO.sub.2 feed stream S201 has a lower water content than CO.sub.2 feed stream S200. The multistage compression of CO.sub.2 feed stream S200 also causes compressed CO.sub.2 feed stream S201 to have a higher pressure and temperature than CO.sub.2 feed stream S200. Compressed CO.sub.2 feed stream S201 is flowed to heat exchanger 201, which cools compressed CO.sub.2 feed stream S201 to form cooled CO.sub.2 stream S202 at a temperature in the range of 35 to 55 C., and all ranges and values there between including ranges 35 C. to 40 C., 40 C. to 45 C., 45 C. to 50 C., 50 C. to 55 C. and values 35 C., 36 C., 37 C., 38 C., 39 C., 40 C., 41 C., 42 C., 43 C., 44 C., 45 C., 46 C., 47 C., 48 C., 49 C., 50 C., 51 C., 52 C., 53 C., 54 C., and 55 C., preferably a temperature 45 C. or thereabout. At this temperature, H.sub.2O vapor from compressed feed stream S201 condenses to liquid H.sub.2O in cooled stream S202. Heat exchanger 201 may use water as the cooling fluid. However, in embodiments of the invention, other cooling fluids may be used.

(11) Cooled stream S202 may be routed to gas/liquid separator 202 to have the liquid H.sub.2O removed from cooled CO.sub.2 stream S202. Specifically, gas/liquid separator 202 separates cooled CO.sub.2 stream S202 into liquid stream S203 and CO.sub.2 vapor stream S204. CO.sub.2 vapor stream S204, emerging from gas/liquid separator 202, may have water content in the range of 0.1 to 0.6 wt. %, and all ranges and values there between including ranges 0.1 to 0.2 wt. %, 0.2 to 0.3 wt. %, 0.3 to 0.4 wt. %, 0.4 to 0.5 wt. %, 0.5 to 0.6 wt. % and values 0.1 wt. %, 0.2 wt. %, 0.3 wt. %, 0.4 wt. %, 0.5 wt. %, and 0.6 wt. %, preferably 0.2 wt. % or thereabout or less than 0.3 wt. %. From gas/liquid separator 202, CO.sub.2 vapor stream S204 may be split into two CO.sub.2 vapor streams S205, where each vapor stream S205 may be flowed to one of water adsorbent beds 203. Water adsorbent beds 203 may include silica/molecular sieve adsorbent material, non-limiting examples of which include silica gel, activated carbon, and its composite materials, faujasite zeolite, zeolite type 3A etc. In FIG. 2, two adsorbent beds are shown but any number of adsorbent beds may be used in the context of the present invention (e.g., 3, 4, 5, 6, 7, or more adsorbent beds). Water adsorbent beds 203 are adapted to remove water present in CO.sub.2 vapor streams S205 to form dry CO.sub.2 vapor streams S206, which have no water or a small amount of water in them (e.g., 0 wt. % to 0.2 wt. % of water).

(12) Dry CO.sub.2 vapor streams S206 are flowed to organic chloride adsorbent beds 204. Organic chloride adsorbent beds 204 may include zeolite-13X adsorbent material (Si:Al ratio of 1.5:1 to 2.5:1, preferably 2:1 or thereabout or less than 2:1). Organic chloride adsorbent beds 204 are adapted to remove organic chlorides from dry CO.sub.2 vapor streams S206 to form purified CO.sub.2 vapor streams S207. In embodiments of the invention, organic chloride adsorbent beds 204 cause the adsorption of organic chloride at a pressure of 15 to 25 barg, temperature of 15 to 50 C., and space velocity of 1 to 5 hr.sup.1. Purified CO.sub.2 vapor streams S207 may be combined to form purified CO.sub.2 vapor stream S208. Purified CO.sub.2 vapor stream S208 may be heated in heat exchanger 205 and heat exchanger 206 to form hot purified CO.sub.2 vapor stream S209. The heating fluid in heat exchanger 205 may be product stream S210 from catalytic oxidation reactor 207. In embodiments of the invention, other fluids may be used as heating fluid.

(13) After heating in heat exchanger 205 and heat exchanger 206, hot purified CO.sub.2 vapor stream S209 is sent to catalytic oxidation reactor 207. Because there is no organic chloride (or reduced amounts of organic chloride, e.g., a maximum of 0.01 ppmv in CO.sub.2 vapor stream 209 (as compared to CO.sub.2 feed stream S200), formation of HCl is prevented (or substantially reduced) during the catalytic oxidation process that takes place in catalytic oxidation reactor 207. In embodiments of the invention, during the catalytic oxidation process, no HCl is produced or, if any HCl is produced, the quantity is so small that it is non-detectable. In embodiments of the invention, the maximum amount of HCl produced in and flows from catalytic oxidation reactor 207 is <0.02 ppmv. In this way, HCl, the main cause for corrosion in the downstream heat exchanger is avoided.

(14) Another non-limiting embodiment of the present invention is provided in FIG. 3. Referring to FIG. 3, system 30 for purifying a CO.sub.2 stream from an ethylene glycol plant is shown. CO.sub.2 feed stream S300 may include 99.5 vol. % CO.sub.2, approximately 5-100 ppmv organic chloride (e.g., ethylene dichloride (C.sub.2H.sub.4Cl.sub.2)), approximately 1 ppmv unsaturated hydrocarbons, and approximately 1 ppmv saturated hydrocarbons. CO.sub.2 feed stream S300 is fed to multi-stage compressor 300. Multi-stage compressor 300 performs multi-stage compression of CO.sub.2 feed stream S300 to form compressed CO.sub.2 feed stream S301. This multistage compression of CO.sub.2 feed stream S300 removes at least some of the water from CO.sub.2 feed stream S300 such that compressed CO.sub.2 feed stream S301 has a lower water content than CO.sub.2 feed stream S300. The multistage compression of CO.sub.2 feed stream S300 also causes compressed CO.sub.2 feed stream S301 to have a higher pressure and temperature than CO.sub.2 feed stream S300. Compressed CO.sub.2 feed stream S301 is flowed to heat exchanger 301, which cools compressed CO.sub.2 feed stream S301 to form cooled CO.sub.2 stream S302 at a temperature in the range of 35 to 55 C., and all ranges and values there between including ranges 35 C. to 40 C., 40 C. to 45 C., 45 C. to 50 C., 50 C. to 55 C. and values 35 C., 36 C., 37 C., 38 C., 39 C., 40 C., 41 C., 42 C., 43 C., 44 C., 45 C., 46 C., 47 C., 48 C., 49 C., 50 C., 51 C., 52 C., 53 C., 54 C., and 55 C., preferably a temperature of 45 C. or thereabout. At this temperature, H.sub.2O vapor from compressed feed stream S301 condenses to liquid H.sub.2O in cooled stream S302. Heat exchanger 301 may use water as the cooling fluid. However, in embodiments of the invention, other cooling fluids may be used.

(15) Cooled stream S302 may be routed to gas/liquid separator 302 to have the condensed H.sub.2O removed from cooled CO.sub.2 stream S302. Specifically, gas/liquid separator 302 separates cooled CO.sub.2 stream S302 into liquid stream S303 and CO.sub.2 vapor stream S304. CO.sub.2 vapor stream S304, emerging from gas/liquid separator 302, may have water content in the range of 0.1 to 0.6 wt. %, and all ranges and values there between including ranges 0.1 to 0.2 wt. %, 0.2 to 0.3 wt. %, 0.3 to 0.4 wt. %, 0.4 to 0.5 wt. %, 0.5 to 0.6 wt. % and values 0.1 wt. %, 0.2 wt. %, 0.3 wt. %, 0.4 wt. %, 0.5 wt. %, and 0.6 wt. %, preferably 0.2 wt. % or thereabout or less than 0.3 wt. %.

(16) From gas/liquid separator 302, CO.sub.2 vapor stream S304 may be routed to chiller unit 303. Chiller unit 303 may cool CO.sub.2 vapor stream S304 to form chilled CO.sub.2 vapor stream S305 at a temperature in the range of 10 C. to 30 C., and all ranges and values there between including ranges 10 C. to 15 C., 15 C. to 20 C., 20 C. to 25 C., 25 C. to 30 C. and values 10 C., 11 C., 12 C., 13 C., 14 C., 15 C., 16 C., 17 C., 18 C., 19 C., 20 C., 21 C., 22 C., 23 C., 24 C., 25 C., 26 C., 27 C., 28 C., 29 C., and 30 C., preferably 20 C. or thereabout. Chilled CO.sub.2 vapor stream S305 may be then routed to gas/liquid separator 304, which removes Liquid H.sub.2O from chilled CO.sub.2 vapor stream S305 to form liquid stream S306 and CO.sub.2 vapor stream S307. CO.sub.2 vapor stream S307 may have a temperature in the range of 10 to 30 C., and all ranges and values there between including ranges 10 C. to 15 C., 15 C. to 20 C., 20 C. to 25 C., 25 C. to 30 C. and values 10 C., 11 C., 12 C., 13 C., 14 C., 15 C., 16 C., 17 C., 18 C., 19 C., 20 C., 21 C., 22 C., 23 C., 24 C., 25 C., 26 C., 27 C., 28 C., 29 C., and 30 C., preferably 20 C. or thereabout, and water content in the range of 0.01 to 0.1 wt. %, and all ranges and values there between including 0.01 wt. %, 0.02 wt. %, 0.03 wt. %, 0.04 wt. %, 0.05 wt. %, 0.06 wt. %, 0.07 wt. %, 0.08 wt. %, 0.09 wt. %, and 0.1 wt. %, preferably 0.05 wt. % or thereabout or less than 0.06 wt. %. CO.sub.2 vapor stream S307 may also include organic chloride such as ethylene dichloride.

(17) CO.sub.2 vapor stream S307 may be split into two CO.sub.2 vapor streams S308, where each stream S308 is flowed to one of water adsorbent beds 305. In FIG. 3, two adsorbent beds are shown but any number of adsorbent beds may be used in the context of the present invention (e.g., 3, 4, 5, 6, 7, or more adsorbent beds). Water adsorbent beds 305 may include silica/molecular sieve adsorbent material, non-limiting examples of which include silica gel, activated carbon, and its composite materials, faujasite zeolite, zeolite type 3A etc. Water adsorbent beds 305 are adapted to remove water present in CO.sub.2 vapor streams S307 to form dry CO.sub.2 vapor streams S309, which have no water or a small amount of water in them (e.g., 0 wt. % to 0.001 wt. % of water).

(18) Dry CO.sub.2 vapor streams S309 are flowed to organic chloride adsorbent beds S306. Organic chloride adsorbent beds 306 may include zeolite-13X adsorbent material (Si:Al ratio of 1.5:1 to 2.5:1, preferably 2:1 or thereabout or less than 2:1). However, it is contemplated that other zeolites can be used to remove organic chlorides from the CO.sub.2 stream. Non-limiting examples of other zeolites that can be used in the context of the present invention include Zeolite-Y, Zeolite-X, ZSM-5 etc. Organic chloride adsorbent beds 306 are adapted to remove organic chlorides from dry CO.sub.2 vapor streams S309 to form purified CO.sub.2 vapor streams S310. In embodiments of the invention, organic chloride adsorbent beds 306 results in the adsorption of organic chloride at a pressure of 15 to 25 barg, temperature of 10 to 50 C., and space velocity is 1-5 hr.sup.1. Purified CO.sub.2 vapor streams S310 may be combined to form purified CO.sub.2 vapor stream S311. Purified CO.sub.2 vapor stream S311 may be heated in heat exchanger 307 and heat exchanger 308 to form hot purified CO.sub.2 vapor stream S311. The heating fluid in heat exchanger 307 may be product stream S313 from catalytic oxidation reactor 309. In embodiments of the invention, other fluids may be used as heating fluid.

(19) After heating in heat exchanger 307 and heat exchanger 308, hot purified CO.sub.2 vapor stream S312 is sent to catalytic oxidation reactor 309. Because there is no organic chloride (or reduced amounts of organic chlorides (e.g., a maximum of 0.01 ppmv) in CO.sub.2 stream 312 (as compared to CO.sub.2 feed stream S300), formation of HCl is prevented (or substantially prevented) during the catalytic oxidation process that takes place in catalytic oxidation reactor 309. In embodiments of the invention, during the catalytic oxidation process, no HCl is produced or, if any HCl is produced, the quantity is so small that it is non-detectable. In embodiments of the invention, the maximum amount of HCl produced in and flows from catalytic oxidation reactor 309 is <0.02 ppmv. In this way, HCl, the main cause for corrosion in the downstream heat exchanger is avoided.

(20) By implementing either of system 20 or system 30 in a CO.sub.2 purification plant, any one or all of the following benefits can be achieved: (1) the expense of designing and installing equipment to withstand HCl corrosion can be reduced or avoided; (2) the expense of designing, installing, and maintaining HCl absorbers can be reduced or avoided; and/or (3) the operational difficulties of removing salts amines and water can be reduced or avoided. Alternatively, system 20 or system 30 may be implemented with one or more of the prior art methods to have a more robust system to address the corrosive effect of HCl.

EXAMPLES

Example 1

Adsorption of EDC with Zeolite-13X

(21) A first adsorption experiment was performed with zeolite-13X at 1 bar pressure and ambient temperature. In this first experiment, 10 grams of zeolite-13X having a diameter of 1.5 mm and length approximately 2 mm was packed in an adsorbent bed reactor and allowed to contact with 10 g/hr of CO.sub.2 containing approximately 600 ppm of ethylene dichloride (EDC). The EDC content of the CO.sub.2 gas coming out of the adsorbent bed was constantly monitored by gas chromatography (GC). For up to 100 hours of operation, it was observed that there was no EDC coming out of the adsorbent bed. This indicates that zeolite-13X completely adsorbed the EDC during this period of time. FIG. 4 shows results (a plot showing the breakthrough curve) for the first adsorption experiment.

Example 2

Adsorption of EDC with Zeolite-13X in Presence of Water

(22) A second adsorption experiment was performed. This experiment was performed with zeolite-13X in the presence of water vapor. In this second experiment, 20 grams of zeolite-13X having a diameter of 1.5 mm and length approximately 2 mm was packed in an adsorbent bed reactor and allowed to contact with 10 g/h of CO.sub.2 containing approximately 600 ppm of EDC and approximately 200 ppm of water vapor. An approximately 30% reduction in EDC adsorption capacity of zeolite-13X was observed for this second experiment as compared to the first experiment that did not have water in the inlet feed. FIG. 5 shows results (a plot showing the breakthrough curve) for the second adsorption experiment. The reduction in adsorption capacity of zeolite-13X in the second experiment may be due the competitive adsorption of water at the same sites where EDC gets adsorbed. In the second experiment, the time taken to get the breakthrough is 96 hrs. Based on these experimental results, it is observed that the adsorption capacity of zeolite-13X has been reduced from 6 wt. % to 4 wt. % because of the presence of water.

Example 3

Adsorption of EDC with Regenerated Zeolite-13X in Presence of Water

(23) A third experiment was conducted. This experiment was conducted with regenerated catalyst at the same operating condition mentioned for 600 ppm of EDC and approximately 200 ppm of water vapor). The regeneration was carried out at 250 C. under the N.sub.2 flow of 120 ml/min for 4 hrs. The results of this experiment are shown in FIG. 5. FIG. 5 shows that the adsorption property of regenerated catalyst is very similar to that of fresh adsorbent. From these experimental results, it is clear that zeolite-13X can be used for repeated adsorption experiments.

(24) Based on the results from Examples 1 to 3, it may be concluded that zeolite-13X may be used effectively in the adsorption of organic chloride in CO.sub.2 streams. Further, the results show that regenerated zeolite-13X is also effective, which is a significant factor in designing cost effective removal systems.

(25) Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

(26) Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification.