WO2014012966A1

WO2014012966A1 - Device for temperature swing process

Info

Publication number: WO2014012966A1
Application number: PCT/EP2013/065074
Authority: WO
Inventors: Timo ROESTENBERG; Gerrit Brem
Original assignee: Antecy B.V.
Priority date: 2012-07-17
Filing date: 2013-07-17
Publication date: 2014-01-23
Also published as: NO2905335T3; EP2874727A1; US9550142B2; AU2013292078A1; US20150182904A1; ES2662006T3; EP2874727B1; CA2883058A1; US20150139887A1; AU2013292078B2

Abstract

A device is disclosed for conducting an adsorption/desorption swing reaction. The desorption step of the reaction is conducted at least in part at a temperature below 100 °C. Dry steam is used for purging the reactor and the adsorbent bed in the reactor. For this purpose the device has a water reservoir, and a vacuum source in fluid connection with the water reservoir and the reactor. During the desorption step the vacuum source causes water to evaporate, and the water vapor to flow through the reactor.

Description

DEVICE FOR TEMPERATURE SWING PROCESS

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates generally to a device for conducting an a d so r p t i o n/d e so rp t i o n temperature swing process, and more particularly to such a device that uses dry steam for purging a reactor during the desorption step.

2. Description of the Related Art

[0002] Temperature swing reactors are known in the art. During a temperature swing process a first part of the process is conducted at a first temperature, Ti, and a second part of the process is conducted at a second temperature, T₂. After completion of the second part of the process the temperature is swung back to Ti, and the cycle recommences.

[0003] Temperature swing reactors can be used, for example, for adsorption/desorption processes, wherein the desorption temperature T₂ generally is higher than the adsorption temperature, Ti. It may be desirable to aid the desorption process by purging the reactor with an inert gas. Dry steam is often the preferred inert gas for this purging operation, because it can readily be produced on site, and is generally far less expensive than alternative inert gases, such as nitrogen or hel ium. In addition, water vapor can be easily separated from the desorbing gas by selective condensation.

[0004] Our co-pending patent application, filed on the same day as the instant application, entitled "Materials and Process for Reversible Adsorption of Carbon Dioxide", which is hereby incorporated by reference in its entirety, discloses adsorbent materials from which carbon dioxide can be desorbed at least in part at temperatures below 100 "C. It would be desirable to use an inert purging gas during the carbon dioxide desorption step of the process. However, conventional steam generation processes do not produce dry steam at temperatures below 1 00 T.

[0005] Thus, there is a particular need for a temperature swing reactor in which at least part of the desorption step is conducted at a temperature below 100 "C, and in which dry steam can be used as a purging gas even at temperatures below 100 "C. BRIEF SUMMARY OF THE INVENTION

[0006] The present invention addresses these problems by providing a device for conducting an ad so rp t i o n/d eso rpt ion temperature swing process having a desorption step conducted at least in part at a desorption temperature below 100 °C, said device comprising (i) a reservoir containing water; (ii) a reactor containing an adsorbent; and (iii) a vacuum source; the reservoir, the reactor and the vacuum source being in fluid connection with each other during the desorption step so that the vacuum source causes water in the reservoir to evaporate, and water vapor to flow through the reactor for purging the adsorbent.

[0007] The reservoir can be a vessel containing liquid water; or it can be a water adsorbent material hav ing water adsorbed thereto.

BRI EF DESCRIPTION OF TH E DRAWING

[0008] The features and advantages of the invention will be appreciated upon reference to the following drawings, in which :

[0009] FIG. 1 is a schematic representation of a device according to the invention, in adsorption mode.

[0010] FIG 2 shows the dev ice of FIG 1 in desorpt ion mode.

[0011] FIG 3 show s a device similar to that of FIG s 1 and 2, with a self-drying vacuum pump.

[0012] FIG 4 shows a device according to the invention w ith an adsorption column as the water reservoir.

[0013] FIG 5 shows the production of high-purity C0₂ with the device of Figure 3.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The following is a detailed descript ion of the invention.

[0015] Definitions [0016] The term "dry steam" as used herein means water vapor having a temperature T_w and a partial pressure P_w, wherein the partial pressure P_w is less than the saturated steam pressure at temperature T_w.

[0017] The term "temperature swing process" as used herein means a process comprising at least two steps, wherein a first step is conducted at a first temperature and the second step is conducted at a second temperature, the second temperature being different from the first temperature. During the process the temperature is cycled from the first temperature to the second temperature, and back to the first temperature.

[0018] In its broadest aspect the present invention relates to an adsorpt ion /desorpt ion temperature swing process. The process comprises an adsorption step, conducted at a first temperature Tj, and a desorption step conducted at least in part at a second temperature T₂, with T₂ > Ti. The second temperature T₂ is less than 100 °C, which means that at least part of the desorption step is conducted at a temperature below 100 °C. Examples of such a process are disclosed in detail in our co-pending patent application of the same date, entitled

"Materials and Process for Reversible Adsorption of Carbon Dioxide," the disclosures of which are incorporated herein by reference.

[0019] The device of the present invention addresses the need for dry steam to be used as a purging gas during the desorption step, including the portion or portions of the desorption step conducted at temperatures below 100 "C.

[0020] The device of the invention comprises (i) a reservoir containing water; (ii) a reactor containing an adsorbent; and (iii) a vacuum source. The reservoir may be a vessel containing liquid water, or it can be a water adsorbent material hav ing water adsorbed thereto.

[0021] During the desorption step the reservoir, the reactor and the vacuum source are in fluid connection with each other. The vacuum source causes water in the reservoir to evaporate (in case of a vessel with liquid water) or to desorb (in case of an adsorbent having water adsorbed thereto), and water vapor to flow through the reactor for purging the adsorbent.

[0022] In case of a vessel containing liquid water, the reservoir has a temperature T_w, w hich is lower than the temperature T_d of the reactor during the any portion of the desorption step. For example, the reservoir may be kept at ambient temperature, e.g., 25 "C. The vacuum source reduces the pressure in the reservoir, which causes water in the reservoir to evaporate. However, the partial pressure of the water vapor will be equal to, or less than, P₂5 the saturated steam pressure at 25 °C. The desorption temperature Tj in the reactor is more than 25 "C. As a result, the water vapor passing through the reactor having a partial pressure P25, has a lower pressure than the saturated steam pressure of T_d. In other words, the water vapor purging the reactor meets the definition of dry steam. No condensation of water vapor takes place in the reactor during the desorption step.

[0023] As the purpose of the desorption step is to collect gases adsorbed to the adsorbent during the adsorpt ion step, the device conveniently comprises a reservoir for collecting gas desorbed from the adsorbent during the desorption step.

[0024] It is desirable to remove water vapor from the desorbing gas prior to collecting the desorbing gas in a reservoir. To this end, the device may contain one or more heat exchangers for cool ing down the desorbed gas, whereby an important portion of the water vapor present in the desorbing gas is removed by condensation. The heat exchanger or exchangers allow heat from gases leaving the reactor to be recovered.

[0025] In an embodiment, heat recovered from gases leaving the reactor is transferred to water in the reservoir.

[0026] Conveniently, the vacuum source can be a vacuum pump. Since condensation of water vapor may occur in or near the vacuum pump, the vacuum pump preferably is a self- drying vacuum pump.

[0027] One of the tasks of the vacuum pump is to provide an operating pressure that is low enough to cause significant evaporation of water in the reservoir. Preferably the operating pressure is low enough to cause the water in the reservoir to boil. In practice the operating pressure can be, for example, 30 mbar or less, preferably 25 mbar or less. For perspective, 25 mbar is the saturated steam pressure at 21 °C; 30 mbar is the saturated steam pressure at 24 "C. It will be understood that different reservoir temperatures dictate different operating pressures. If, for example, the reservoir temperature is 1 5 "C the operating pressure may be kept at 1 7 mbar; if the reservoir temperature is 35 °C the operating pressure may be as high as 56 mbar. [0028] The dev ice conveniently comprises a water source for replenishing water in the reservoir. In addition, the dev ice may contain a reservoir for collecting demineralized water from the v acuum source and/or the one or more heat exchangers.

[0029] The use of water as purging gas has a disadvantage in that the presence of water during the desorption step shifts the ad so rp t i o n/d eso rp t i o n equilibrium to the adsorption side. This is because the adsorption of carbon dioxide (under formation of a bicarbonate) consumes water, and the desorption generates water. The equilibrium -shifting effect of the water present in the purge gas is greatly diminished, however, due to the fact that the desorption step is carried out under reduced pressure. For this reason the use of a vacuum source offers advantages even at desorption temperatures in excess of 100 "C, because it permits the use of water as a purge gas without incurring a serious equilibrium-shifting penalty.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS/EXAMPLES

[0030] The following is a description of certain embodiments of the invention, given by way of example only and with reference to the drawings. Referring to FIG. 1 , a dev ice is shown during the adsorpt ion step. The device of figure 1 is set up for adsorbing carbon dioxide and water from atmospheric air. It will be understood that the dev ice can be modified for adsorbing carbon dioxide from a gas mixture other than air, such as flue gas, or for selectively adsorbing a gas other than carbon dioxide from any type of gas mixture.

[0031] Figure 1 shows a device comprising a water reservoir 1 , a reactor 2, and a v acuum source 3. However, water reservoir 1 and vacuum source 3 are not operational during the adsorption step.

[0032] During the adsorption step atmospheric air enters the dev ice at 1 0, and flows via valve 1 1 into reactor 2. The air is propelled by a fan or a pump (not shown). It is also possible to propel the air flow by other means, for example a solar chimney, an atmospheric vortex device, or by making use of day time/night, time temperature differences.

[0033] The air flow passes through adsorbent bed 12, where water vapor and carbon dioxide are adsorbed from the air flow onto the adsorbent. From adsorbent bed 12 the air flows through valv e 1 3 to v ent 14, where it is released into the atmosphere. Instead of a single adsorbent bed, reactor 2 can contain two or more adsorbent beds. The adsorbent beds can be of identical composition or of differing compositions. In the latter case each adsorbent bed can be designed for adsorbing different gas components, or combinations of gas components, from the air flow.

[0034] In the embodiment the adsorpt ion step is conducted at ambient temperature. It will be understood that the adsorption step can be conducted at a higher or a lower temperature.

[0035] Figure 2 shows the device of Figure 1 during the dcsorption step. Valves 1 1 and 13 have been switched, so that air inlet 10 and vent 14 are closed off, and fluid communication is established between vacuum source 3 and water reservoir 1. Vacuum source 3 establishes a pressure low enough to create an operating pressure inside water reservoir 1 of 25 mbar (allowing for any pressure drops over restrictions between the vacuum source 3 and water reservoir 1 , such as adsorbent bed 1 2 and valves 1 1 and 13 ).

[0036] Initially the adsorbent bed 12 is kept at ambient temperature. The operating pressure of 25 mbar in water reservoir 1 causes water to evaporate. Water vapor is caused by vacuum source 3 to flow through the reactor 2 and adsorbent bed 1 2. This flow of water vapor purges air from the reactor.

[0037] While air is being purged valve 1 5 directs the gas flow via arrows 19 and 20 to heat exchanger 21 , and from there to vent 22. The gas flow is cooled in heat exchanger 21 , and any condensed water is collected in demineralized water tank 23. Heat recovered by heat exchanger 2 1 is transferred to the water in reservoir 1.

[0038] Once the air has been purged from reactor 2, the reactor bed is heated to 30 °C to start the actual dcsorption. step. The gas flow is now directed by valve 1 5, via arrows 16 and 17, to heat exchanger 18 and eventually to carbon diox ide tank 24. It may be desirable to remove residual water from gas leaving heat exchanger 18, for example with a zeolite bed (not shown). The gas flow is cooled in heat exchanger 18, and any condensed water is collected in demineralized water tank 23. 1 1 eat recovered by heat exchanger 2 1 is transferred to the water in reservoir 1 . [0039] During the desorption step it is desirable to gradually increase the temperature of adsorbent bed 12, to ensure a more complete desorption. For example, the temperature of the desorption bed may be gradually increased from 30 °C to 180 "C.

[0040] Since water is evaporated from reservoir 1 , and recovered demineralized water is collected in tank 23 and not returned to reservoir 1 , it w ill be necessary to replenish the water in reservoir 1 v ia inlet valve 25. Any source of water can be used, including tap water, well water, industrial water, surface water (such as river water or lake water), and even salt water from a sea or ocean, with the proviso that the water source preferably be substantially free of volatile contaminants. To avoid excessive build-up of minerals and contaminants in reservoir 1 the reservoir can be purged using inlet 25 and outlet 26.

[0041] Optional ly the conduits leading from the reactor 2 to the vacuum source 3 can be heated, for example with heating tape 27, to prevent condensation of water upstream of vacuum source 3. However, if a self-drying vacuum pump is used, such heating is generally not necessary.

[0042] Figure 3 shows a dev ice similar to that of Figures 1 and 2, except that vacuum pump 3 is of the self-drying kind. Liquid water is allowed to col lect in the head of pump 3, from w hich it is purged from time to time by closing a valve inside the pump (not shown ), which temporarily disconnects the pump from the reactor.

[0043] During its operation the device effectively converts inexpensive water to far more valuable demineralized water. In addition, the adsorbent bed may adsorb water from ambient air during the adsorption step. Such water is collected as demineralized water during the desorption step. Demineral ized water produced by the device can be used for industrial purposes, such as chemical reactions; for agricultural purposes, such as drinking water for cattle, or water for irrigation, optionally after addition of nutrients; for household use, such as laundry and cleaning; and even as drinking w ater for humans, after addit ion of appropriate minerals.

[0044] Figure 4 shows an alternate embodiment of the device. In this device the water reservoir is replaced w ith column 40 containing a bed 4 1 of a water absorbent material, such as silica gel . During the adsorption step air enters column 40 v ia valve 42. Pre-dried air leaving column 40 is led to adsorbent bed 1 2 via conduit 43. The pre-dried air should contain enough moisture to enable the adsorption of carbon diox ide in bed 12, i.e., the p red tied air should contain water and carbon dioxide in a waterxarbon dioxide molar ratio of at least 1 : 1 . Put differently, since air contains approximately 400 ppm carbon dioxide by weight, the predried air should contain at least about 160 ppm water by weight. Under typical conditions the p re-dried, air contains well in excess of 160 ppm water by weight, which is acceptable.

Carbon dioxide adsorption proceeds as explained with reference to Figure 1 .

[0045] During the desorption mode valve 42 is closed and vacuum pump 3 is switched on. First the temperature of bed 41 is increased, to initiate the release of adsorbed water.

Dcsorbcd water from bed 4 1 is passed through bed 1 2 to purge air from bed 1 2. After bed 12 has been purged, the temperature of bed 1 2 is increased to initiate the desorption of water and carbon dioxide from bed 1 2. Desorbed water and carbon dioxide are collected in water tank 23 and carbon dioxide tank 24, as described with reference to Figure 2.

[0046] It will be understood that no external source of liquid water is required for the operation of the device of Figure 4. Moreover, the dev ice captures water from ambient air, and makes it available in a very pure form. Depending on demand, the device can be used as a source of carbon dioxide, with clean water as a byproduct; as a source of clean water with carbon dioxide as a byproduct; or as a source of both clean water and carbon dioxide.

[0047] The device of Figure 3 was used in the fol low ing experiment. The adsorbent was active carbon impregnated with K₂CO₃.

[0048] Adsorption and desorption were carried out as described above. The desorption temperature was programmed as shown in Figure 4 (dotted line; Setpoint T). The sol id l ine shows the Liner Temperature, which closely follow ed the Setpoint Temperature. The Core Temperature initial ly lagged behind the former two temperatures, but eventual ly stabilized at 140 "C.

[0049] It should be noted that the scale on the left hand side of the graph show s the temperature in °C and the CO_? concentration of the desorbing gas in %. The dashed/dotted line shows the CO_? concentration as a function of time. As can be seen, the desorbing gas is highly enriched in C0₂, around 60% at Core temperatures up to about 70 "C. As the Core Temperature increased further the C0₂ concentration increased to reach about 100%.. [0050] Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

[0051] Many modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not l imiting upon the scope of the invention.

Claims

WHAT IS CLAIMED IS:

1 . A device for conducting an adsorption/desorption temperature swing process having a desorption step conducted at least in part at a desorption temperature below 100 °C, said dev ice comprising (i) a reservoir containing water; (ii) a reactor containing an adsorbent; and (iii) a vacuum source; the reservoir, the reactor and the vacuum source being in fluid connection with each other during the desorption step so that the vacuum source causes water in the reservoir to evaporate, and water vapor to flow through the reactor for purging the adsorbent.

2. The device of claim 1 wherein the reservoir containing water is a reservoir containing l iquid water.

3. The dev ice of claim 1 wherein the reservoir containing water is an absorption column containing a water adsorbent having water adsorbed thereto.

4. The dev ice of any one of claims 1 - 3 further comprising a reservoir for collecting gas desorbed from the adsorbent during the desorption step.

5. The device of any one of the preceding claims further comprising one or more heat exchangers for recovering heat from gases leaving the reactor.

6. The device of claim 5 wherein heat recovered from gases leaving the reactor is

transferred to water in the reservoir.

7. The device of any one of the preceding claims wherein the vacuum source is a vacuum pump.

8. The device of claim 7 wherein the vacuum pump is a self-drying vacuum pump.

9. The device of any one of the preceding claims wherein the vacuum source prov ides an operating pressure of 30 mbar or less, preferably 25 mbar or less.

10. The device of any one of the preceding claims further comprising a water source for replenishing water in the reservoir.

1 1. The device of any one of claims 5 through 1 0 further comprising a reservoir for

collecting demineralized water from the vacuum source and/or the one more heat exchangers.