A CHEMICAL FORMALDEHYDE FILTER

Abstract

Presented is a chemical formaldehyde filter comprising a filter substrate having a porous structure; the filter substrate comprising a mixture of a formaldehyde absorbent and a porous framework material. Further, a method for fabricating such a filter is described.

Claims

1. A chemical formaldehyde filter comprising a filter substrate having a porous structure; the filter substrate comprising a mixture of a formaldehyde absorbent and a porous framework material, wherein the formaldehyde absorbent is an amine-containing formaldehyde absorbent chemical compound, and the porous framework material is plaster, plaster gypsum, or lime.

2. The chemical formaldehyde filter according to claim 1, wherein the filter substrate is made from the mixture.

3. The chemical formaldehyde filter according to claim 1, wherein the filter substrate comprises a substrate coated with the mixture.

4. The chemical formaldehyde filter according to claim 1, wherein the formaldehyde absorbent is tris(hydroxymethyl)aminomethane.

5. The chemical formaldehyde filter according to claim 1, wherein the mixture further comprises an alkaline buffering agent.

6. The chemical formaldehyde filter according to claim 5, wherein the buffering agent comprises one or more of a hydrogen carbonate salt and a formate salt.

7. The chemical formaldehyde filter according to claim 5, wherein the buffering agent comprises at least one of KHCOO and KHCO.sub.3.

8. The chemical formaldehyde filter according to claim 1, wherein the filter substrate has a honeycomb structure.

9. The chemical formaldehyde filter according to wherein the porous framework material is -CaSO.sub.4.2H.sub.2O or -CaSO.sub.4.H.sub.2O.

10. A method of fabricating a chemical formaldehyde filter, comprising: mixing a solution containing a formaldehyde absorbent with a porous framework material; casting the resulting mixture into a monolith structure and drying the cast mixture, or coating the resulting mixture on a substrate and drying said coated substrate, wherein the formaldehyde absorbent is an amine-containing formaldehyde absorbent chemical compound, and the porous framework material is plaster, plaster gypsum, or lime.

11. The method according to claim 10, wherein the drying step is carried out at a temperature of from about 25 C. to about 150 C.

12. The method according to claim 10, wherein the solution containing a formaldehyde absorbent is an aqueous solution.

13. The method according to claim 12, wherein the aqueous solution further comprises a buffering agent.

14. The method according to claim 13, wherein the buffering agent comprises one or more of a hydrogen carbonate salt and a formate salt.

15. The method according to claim 13, wherein the buffering agent comprises at least one of KHCOO and KHCO.sub.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0040] FIG. 1A shows a microscopic image of the ceramic substrate coated with functional framework material (formaldehyde absorbent and framework material) prepared in Example 2.

[0041] FIG. 1B shows an SEM image of the functional framework material on the surface of the ceramic substrate prepared in Example 2.

[0042] FIG. 2 is a graph showing relative humidity change in the test chamber of Example 2.

[0043] FIG. 3A is a graph showing the results of Clean Air Delivery Rate tests carried out at RH 90% in Example 2.

[0044] FIG. 3B is a graph showing relative humidity change during the test carried out at RH 90% in Example 2.

[0045] FIG. 3C is a graph showing the results of Clean Air Delivery Rate tests carried out at RH 30% in Example 2.

[0046] FIG. 3D is a graph showing relative humidity change during the test carried out at RH 30% in Example 2.

[0047] FIG. 4A shows the filter structure of Example 3.

[0048] FIG. 4B is a graph showing the results of Clean Air Delivery Rate tests carried out at RH 70% in Example 3.

[0049] FIG. 5A shows the filter structure of Example 4.

[0050] FIG. 5B is a graph showing the CADR test results carried out at RH 50% in Example 4.

EXAMPLES

Example 1

[0051] A chemical formaldehyde filter is made by moulding a mixture of a framework material and an active agent (i.e. formaldehyde absorbent). The framework material is -CaSO.sub.4.H.sub.2O. The active agent is TRIS. The active agent is mixed with the framework material as part of an aqueous solution containing 20% TRIS, 15% KHCOO, and 15% KHCO.sub.3. The framework material is mixed with the aqueous solution at 1:1 weight ratio to form a functional framework material (i.e. a mixture of a formaldehyde absorbent and a framework material). The functional framework material is cast on a mould to form a filter having a honeycomb structure and then put in the oven to dry the material. The filter is baked at 100 C. overnight. The filter is obtained by detaching the material from the mould.

Example 2

[0052] A chemical formaldehyde filter is made by coating a mixture of a framework material and an active agent (i.e. formaldehyde absorbent) on a ceramic substrate. The framework material is -CaSO.sub.4.H.sub.2O. The active agent is TRIS. The active agent is mixed with the framework material as part of an aqueous solution containing 20% TRIS. The framework material is mixed with the aqueous solution at 1:0.8 weight ratio to form a functional framework material. A ceramic substrate is immersed in solution containing 20% TRIS, 15% KHCOO, and 15% KHCO.sub.3. The ceramic substrate is then coated with the functional framework material slurry, and shaken to let the slurry go through the holes in the ceramic substrate. Then, air is blown at and through the ceramic substrate to provide an even coating on the surface of the ceramic substrate and to avoid blocks in the honeycomb structure. The ceramic coated with functional frame material is then dried in the oven at 100 C. for 1 hour to form microsphere on the filter surface. FIG. 1A shows a microscopy image of the ceramic substrate coated with formaldehyde absorbent and framework material. FIG. 1B shows an SEM image of the functional framework material on the surface of the ceramic substrate. In FIG. 1B, it can be seen that microspheres have been formed.

[0053] This filter was tested in 30 m.sup.3 chamber for water leakage test and clean air delivery rate measurement.

Water Leakage Test

[0054] The new formaldehyde filter was placed in an air purifier (AC4072) and run in 30 m.sup.3 at RH 90% for 4 hour continuously. There was no solution leakage from the filter. FIG. 2 is a graph showing the change of relative humidity over time. Each arrow shows the point of increase in chamber humidity. From FIG. 2, it is seen that the filter can absorb water and reach equilibrium at RH 87.4%. This result means the filter can store some water at high humidity without any solution leakage.

Clean Air Delivery Rate (CADR)

[0055] Air purifier (AC4072) with new formaldehyde filter was run in a test chamber for 3 hours keeping relative humidity around 90% (23 C.). Then, a CADR test was run under high humidity conditions. After that, the relative humidity was reduced to 30% and another CADR value at low humidity was tested. FIGS. 3A-D show the CADR results at two humidity levels and the humidity change during the test. FIG. 3A shows the CADR results (CHOH ppm) at RH 90% (high humidity). FIG. 3B shows the change in relative humidity (RH %) over time during the high humidity test. FIG. 3C shows the CADR results (CHOH ppm) at RH 30% (low humidity). FIG. 3D shows the change in relative humidity (RH %) over time during the low humidity test. The diamond data points represent RH %. The square data points represent temperature. The arrows indicate where air conditioning is first turned on and then turned off. At high humidity, the filter was in equilibrium with chamber RH and no increase of RH was observed during one hour test. The CADR is 145.7 m.sup.3 h from 1 hour data and 160.2 m.sup.3 h from 30 min data. At low humidity, the chamber RH was increased due to the water desorption from frame material. The CADR value is 160.2 m.sup.3 h from 30 min data. From the RH change trend, it is seen that the filter can intake water at high humidity and release water at low humidity, which will make this filter work well over a large range of humidities.

[0056] All results demonstrate that the filter developed in this invention can solve problems of current chemisorption filter. The claimed filter can reach high reactive surface, high CADR value at low humidity, and no solution leakage.

Example 3

[0057] A chemical formaldehyde filter is made of an organic polymer sheet covered with functionalized framework material. The organic polymer sheet is made of polyvinyl alcohol. Functional framework material is a mixture of inorganic cement material and formaldehyde absorbent. Here, the inorganic cement material is -CaSO42H.sub.2O. The formaldehyde absorbent is TRIS and is employed as a formaldehyde absorbent solution containing 20% TRIS, 5% KHCOO, 5% KHCO.sub.3. Inorganic cement material is mixed with the formaldehyde absorbent solution at 1:1 weight ratio. The size of organic polymer sheet covered with functionalized framework material is 36 cm in length, 28 cm in width and 1 cm in thickness. The holes were drilled with 5 mm diameter. The distance between holes is 5 mm. The organic polymer sheet covered in functionalised framework material is shown in FIG. 4A.

[0058] The filter was evaluated in a 30 m.sup.3 chamber of an air purifier (AC 4072) at different humidities. FIG. 4B shows the CADR test results (CHOH ppm) at RH 70%. The clean air delivery rate measured was 25.2 m.sup.3 h at RH 50% and 55.8 m.sup.3h at RH 70% respectively. The results demonstrate that this filter can capture formaldehyde from the air and the filter works better at high humidity. No solution leakage is observed by running this filter at high humidity continuously.

[0059] The structure of filter could be adjusted. By increasing the holes number and reducing the diameter of holes, it is expected to have high clean air delivery rate. The hole could go down to 1 mm with 1 mm space by the way of making the filter.

Example 4

[0060] A chemical formaldehyde filter is made of honeycomb ceramics coated with a functional framework material. A honeycomb ceramic has 1 mm holes and 0.2 walls between each hole. The honeycomb ceramic is immersed in a solution of 10% KHCOO and 10% KHCO.sub.3 before it is coated with functional framework material. The functional framework material is a mixture of plaster and 20% TRIS solution at 0.8: 1 weight ratio. The functional framework material is coated on the ceramic surface and is dried in the oven at 100 C. FIG. 5A shows the filter structure of Example 4.

[0061] Performance of this filter was tested. FIG. 5B is a graph showing the CADR test results (CHOH ppm) carried out at RH 50%the filter is placed in a Philips air purifier AC 4072 and tested in a 30 m.sup.3 chamber. The clean air delivery rate at RH 50% was 90 m.sup.3 h. Furthermore, there is no solution leakages observed by running the filter at RH 90% in a 3 m.sup.3 chamber continuously for 4 hours.

[0062] According to the inherent microstructure of this chemical formaldehyde filter and test results reported herein, the lifetime of this filter is demonstrated to be longer than currently known filters.

[0063] The above embodiments as described are only illustrative, and not intended to limit the technique approaches of the present invention. Although the present invention is described in details referring to the preferable embodiments, those skilled in the art will understand that the technique approaches of the present invention can be modified or equally displaced without departing from the spirit and scope of the technique approaches of the present invention, which will also fall into the protective scope of the claims of the present invention. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope.