A SORBENT AND A FILTER

Abstract

A sorbent for capture of ethylene gas includes an amorphous precipitated silica material having a BET surface area of at least 200 m.sup.2/g and an organic compound in the form of an amine, an imine or an amide bound to a surface of the amorphous precipitated silica material. The organic compound is configured for chemisorption of ethylene. An ethylene gas filtration system for a refrigerator includes an ethylene gas filter including the sorbent and a fan. The ethylene gas filter is mounted in conjunction with the fan such that gas is actively circulated through the ethylene gas filter by means of the fan. The organic compound may be triisopropanolamine, polyethylenimine or polyamide.

Claims

1. A sorbent for capture of ethylene gas, comprising: an amorphous precipitated silica material having a BET surface area of at least 200 m.sup.2/g; and an organic compound in the form of an amine, an imine or an amide bound to a surface of the amorphous precipitated silica material, wherein the organic compound is configured for chemisorption of ethylene.

2. The sorbent according to claim 1, wherein the amorphous precipitated silica material has a BET surface area of at least 300 m.sup.2/g.

3. The sorbent according to claim 1, wherein the amorphous precipitated silica material is a mesoporous material comprising agglomerates of porous particles according to the formula Me.sub.yOm SiO.sub.2, wherein Me denotes any two or more metals selected among Ca, Mg, Cu, Zn, Mn, Cd, Pb, Ni, Fe, Cr, Al, Ti, V, Co, Mo, Sn, Sb, Sr, Ba and W, y denotes the molar ratio of metallic constituents to oxygen, and m denotes the molar ratio of SiO.sub.2/Me.sub.yO.

4. The sorbent according to claim 3, wherein Me denotes Ca and Mg.

5. The sorbent according to claim 1, wherein the organic compound is present within the sorbent in an amount of 1-20 wt. %.

6. The sorbent according to claim 1, wherein the organic compound is a polyamide.

7. The sorbent according to claim 1, wherein the organic compound is triisopropanolamine.

8. The sorbent according to claim 1, wherein the organic compound is polyethylenimine.

9. An ethylene gas filter for a refrigerator comprising the sorbent according to claim 1.

10. An ethylene gas filtration system for a refrigerator, comprising the ethylene gas filter according to claim 9 and a fan, wherein the ethylene gas filter is mounted in conjunction with the fan such that gas is actively circulated through the ethylene gas filter by means of the fan.

11. A method comprising using the sorbent according to claim 1 for capture of ethylene gas.

12. The sorbent according to claim 1, wherein the amorphous precipitated silica material has a BET surface area of at least 400 m.sup.2/g.

13. The sorbent according to claim 1, wherein the organic compound is present within the sorbent in an amount of 2-12 wt. %.

14. The sorbent according to claim 1, wherein the organic compound is present within the sorbent in an amount of 5-10 wt. %.

15. The sorbent according to claim 2, wherein the amorphous precipitated silica material is a mesoporous material comprising agglomerates of porous particles according to the formula Me.sub.yOm SiO.sub.2, wherein Me denotes any two or more metals selected among Ca, Mg, Cu, Zn, Mn, Cd, Pb, Ni, Fe, Cr, Al, Ti, V, Co, Mo, Sn, Sb, Sr, Ba and W, y denotes the molar ratio of metallic constituents to oxygen, and m denotes the molar ratio of SiO.sub.2/Me.sub.yO.

16. The sorbent according to claim 2, wherein the organic compound is present within the sorbent in an amount of 1-20 wt. %.

17. The sorbent according to claim 3, wherein the organic compound is present within the sorbent in an amount of 1-20 wt. %.

18. The sorbent according to claim 4, wherein the organic compound is present within the sorbent in an amount of 1-20 wt. %.

19. The sorbent according to claim 2, wherein the organic compound is a polyamide.

20. The sorbent according to claim 3, wherein the organic compound is a polyamide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Embodiments of the invention will in the following be described with reference to the appended drawings, in which:

[0025] FIG. 1 shows removal efficiency of sorbents according to embodiments of the invention as a function of time for an ethylene gas concentration of 200 ppm, and

[0026] FIG. 2 shows removal efficiency of sorbents according to an embodiment of the invention for an ethylene gas concentration of 10 ppm as a function of time.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0027] A sorbent for capture of ethylene gas according to an embodiment of the invention comprises an amorphous precipitated silica material having the general formula Me.sub.yOm SiO.sub.2, wherein Me denotes any two or more metals selected among Ca, Mg, Cu, Zn, Mn, Cd, Pb, Ni, Fe, Cr, Al, Ti, V, Co, Mo, Sn, Sb, Sr, Ba and W, y denotes the molar ratio of metallic constituents to oxygen, and m denotes the molar ratio of SiO.sub.2/Me.sub.yO. The amorphous precipitated silica material may be in the form of a Quartzene material of CMS type, which can be written as (Ca.sub.0.35, Mg.sub.0.65)O3.35 SiO.sub.2, i.e. Me=(Ca.sub.0.35, Mg.sub.0.65), y=1 and m=3.35.

[0028] A method of manufacturing this material by mixing alkali silicate with a salt solution is disclosed in WO 2006/071183. The material is formed as a precipitate by mixing alkali silicate with a salt solution. The precipitate is thereafter processed in various ways to obtain an end product having desired properties in terms of pore size, particle size, surface area, density, etc. The amorphous precipitated silica material used for the sorbent according to embodiments of the invention has a mesoporous structure with a BET surface area of at least 200 m.sup.2/g, preferably of at least 300 m.sup.2/g or more preferably of at least 400 m.sup.2/g.

[0029] The amorphous precipitated silica material is doped with an organic compound in the form of an amine, an imine or an amide bound to a surface of the amorphous precipitated silica material, wherein the organic compound is configured for chemisorption of ethylene. The organic compound may preferably be in the form of triisopropanolamine (TIPA), but also polyamide (PA) and polyethylenimine (PEI) have been found to be beneficial for the capture of ethylene gas. The organic compound is preferably present within the sorbent in an amount of 1-20 wt. %, more preferably in an amount of 2-12 wt. %, and even more preferably in an amount of 5-10 wt. %. However, this depends on e.g. which organic compound is used, the method of doping, the available BET surface area of the amorphous precipitated silica material as well as the pore size of this material.

[0030] The sorbent according to the invention may advantageously be included in an ethylene gas filter placed in a refrigerator, intended to remove ethylene gas from the internal environment of the refrigerator. The sorbent may for this purpose be supported on a gas permeable carrier, such as in a filter cassette. The ethylene gas filter may preferably form part of an ethylene gas filtration system for a refrigerator, which apart from the ethylene gas filter comprises a fan, such as an evaporator fan of the refrigerator. The ethylene gas filter is in this case located either upstream or downstream of the fan such that air containing ethylene gas is actively circulated through the ethylene gas filter by means of the fan. When air containing ethylene gas at low concentrations, such as at 1-10 ppm, passes through the ethylene gas filter, the ethylene gas becomes chemisorbed by the sorbent and is thereby removed from the internal environment of the refrigerator.

EXAMPLES

[0031] A number of exemplary ethylene sorbents according to embodiments of the invention, S1-S4, were manufactured and tested together with reference prior art sorbents, Ref1-Ref3. The tested sorbents are listed in Table I.

TABLE-US-00001 TABLE I Density Ethylene uptake Sample Description (g/cm.sup.3) (mg/g sorbent) S1 10 wt. % TIPA on 0.57 4.34 precipitated silica S2 5 wt. % PA on 0.57 0.85 precipitated silica S3 20 wt. % PEI on 0.40 1.28 precipitated silica S4 40 wt. % PEI on 0.40 2.25 precipitated silica Ref1 Commercial carbon 0.11 1.22 filter (Electrolux) Ref2 Activated carbon 0.43 1.43 (Jacobi) Ref3 Activated carbon 0.43 1.32 (Silcarbon Aktivkohle)

[0032] The amorphous precipitated silica material of S1-S4 was a CMS type Quartzene material. The sorbents S1, S3 and S4 were prepared in accordance with the method described in WO 2006/071183, wherein calcium and magnesium sources were added to a dilute active aqueous sodium silicate solution. A salt solution comprising MgCl.sub.2 and CaCl.sub.2 was prepared at a ratio of 68 mol % Mg and 32 mol % Ca. The salt solution was poured onto the 1.5 M (with respect to SiO.sub.2) sodium silicate solution, and the resulting mixture was agitated at room temperature. Subsequent coagulation occurred and the slurry formed was thereafter washed and dewatered on a filter cloth by means of vacuum suction to become a cake or gel. A dilute solution comprising one of TIPA and PEI, was added to the obtained gel. After thorough mixing, the doped gel was dried to obtain the sorbent in powder or granular form.

[0033] The sorbent S2 containing PA was prepared according to a somewhat different scheme. In this case, PA was initially dissolved in a methanol/CaCl.sub.2 solution according to a method previously described in B. Sun, Study on the mechanism of nylon 6, 6 dissolving process using CaCl.sub.2/MeOH as the solvent, Chinese Journal of Polymer Science, vol. 12 p. 57, 1994. The methanol/CaCl.sub.2 solution comprising PA was thereafter, as a first step, mixed with the sodium silicate solution, resulting in precipitation of amorphous silica doped with PA. Subsequently, the MgCl.sub.2 solution was added to the mixed solution to make the reaction complete. The gel could thereafter be washed, filtered and dried to obtain sorbent in powder or granular form.

[0034] The sorbents listed in Table I were divided into samples of 3 g each. The samples S1-S3 and Ref1-Ref3 were thereafter tested in a first test run by passing air containing 200 ppm ethylene gas through the samples at a temperature of 7 C. and a relative humidity of 70% RH. The temperature and relative humidity resemble the conditions in a refrigerator, but the ethylene concentration can normally be expected to be much lower in a refrigerator, such as of the order of 1 ppm. The volume flow of air was 0.9 l/min. The removal efficiency in percent as a function of time is shown in FIG. 1. As can be seen from the graph in FIG. 1, the sorbent 51 comprising 10 wt. % of TIPA has under these conditions a removal efficiency that is significantly higher than the other samples over time. After one hour, the removal efficiency is approximately 25%, after two hours approximately 20% and after six hours approximately 10%. Thus, after six hours, this sorbent still has capacity left. The other sorbents all show similar removal efficiencies.

[0035] The total uptake in mg ethylene during the first test run at 200 ppm ethylene for the different sorbents is shown in Table I. The total uptake is highest for the sample 51 containing 10 wt. % of TIPA, and is also relatively high for the sample S4 containing 40 wt. % of PEI.

[0036] Some of the samples were further tested by passing air containing 10 ppm of ethylene gas through the samples at a temperature of 7 C. and at varying relative humidity concentrations of 70% RH, 50% RH and 18% RH. The results are shown in table II, listing uptake in mg ethylene per gram sorbent. For the sorbent 51 comprising 10 wt. % of TIPA, the total ethylene uptake is 0.30 mg ethylene per gram sorbent for 70% RH, 0.34 mg per gram sorbent for 50% RH and 0.04 mg per gram sorbent for 18% RH. In other words, the sorbent S1 comprising TIPA needs a certain amount of relative humidity to function optimally. A comparison between the sorbents S1, S2 comprising PA and Ref3 at an ethylene concentration of 10 ppm and a relative humidity of 50% RH shows that the total uptake is highest for the sorbent 51 containing TIPA (0.034 mg per gram sorbent), followed by the sorbent S2 containing PA (0.05 mg per gram sorbent), while the total uptake of the reference sorbent Ref3 is much lower (0.004 mg per gram sorbent) at this concentration, in spite of a slightly higher ethylene uptake than sample S2 at 200 ppm ethylene.

TABLE-US-00002 TABLE II 10 ppm at 10 ppm at 10 ppm at Sample 70% RH 50% RH 18% RH S1 0.30 0.34 0.04 S2 0.05 S4 0.04 Ref3 0.004

[0037] It was also tested whether the sorbent 51 comprising 10% of TIPA can be reused by letting the sorbent rest between two test runs with 10 ppm ethylene gas at 50% RH and at 7 C. The first test run resulted in a 22% weight loss, which was attributed to water loss. Following a resting period of 17 days, a corresponding amount of water was added to the sorbent to compensate for the weight loss and the sorbent was thereafter subjected to a second test run under the same conditions. The results are shown in FIG. 2, showing removal efficiency as a function of time for the two test runs. It was found that the sorbent worked nearly as good in the second test run as in the first test run.

[0038] To summarize, the experimental results show that all sorbents S1-S4 can function for capture of ethylene gas at conditions similar to those in a refrigerator.

[0039] The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.