Porous polymer material

Abstract

The present disclosure relates to a polymer material comprising mesopores extending between melamine-formaldehyde co-polymer nano-particles and wherein micropores extend within the co-polymer nano-particles, methods of producing the same and uses thereof.

Claims

1. A method of making a polymer material comprising a melamine-formaldehyde co-polymer, the method comprising the step of reacting melamine with formaldehyde in the presence of a non-aqueous polar solvent to form a polymer material comprising melamine-formaldehyde co-polymer comprising melamine-formaldehyde co-polymer nano-particles, wherein: the polymer material comprising melamine-formaldehyde co-polymer is composed of repeating units of a monomer having a ring structure, each monomer ring structure comprising at least three melamine groups; and the polymer material comprising the melamine-formaldehyde co-polymer comprises mesopores disposed between the melamine-formaldehyde co-polymer nano-particles, the mesopores extending within the co-polymer nano-particles.

2. The method as claimed in claim 1, wherein the non-aqueous polar solvent is an aprotic solvent.

3. The method as claimed in claim 1, wherein the reaction step is undertaken at a temperature of between 120 C. to 180 C.

4. The method as claimed in claim 1, wherein the molar ratio of formaldehyde to melamine is in a range from 1 to 5.

5. The method as claimed in claim 4, wherein the molar ratio of formaldehyde to melamine is in a range from 1.5 to 2.5.

6. The method as claimed in claim 1, wherein said reacting step is undertaken for a period of from 48 hours to 120 hours.

7. The method as claimed in claim 1, wherein the reaction step is undertaken in a closed pressure reactor.

8. The method as claimed in claim 1, wherein the reaction step is undertaken in a partially heated reactor.

9. The method as claimed in claim 2, wherein the aprotic solvent is selected from sulfoxides and sulfones.

10. The method as claimed in claim 2, wherein the aprotic solvent is an aliphatic sulfoxide.

11. The method as claimed in claim 10, wherein the aliphatic sulfoxide has 2 to 10 carbon atoms.

12. The method as claimed in claim 10, wherein the aliphatic sulfoxide has 2 to 6 carbon atoms.

13. The method as claimed in claim 1, wherein the aliphatic sulfoxide is dimethyl sulfoxide.

14. The method as claimed in claim 3, wherein the non-aqueous polar solvent is provided in admixture with an aqueous medium.

15. The method as claimed in claim 14, wherein the aqueous medium comprises water.

16. The method as claimed in claim 15, wherein the aqueous medium has a volume ratio of polar solvent to water and the volume ratio of polar solvent to water is from 1:1 to 3:1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

(2) FIGS. 1(a) and 1(b) show Transmission Electron Microscope (TEM) images of melamine-formaldehyde co-polymer intermediates after undergoing one hour of reaction.

(3) FIGS. 1(c) and 1(d) show TEM images of the melamine-formaldehyde co-polymer intermediates after undergoing five hours reaction.

(4) FIG. 1(e) shows a TEM image of the melamine-formaldehyde co-polymer intermediate after undergoing ten hours reaction.

(5) FIG. 1(f) shows a TEM image of the mesoporous structure of the synthesized melamine-formaldehyde co-polymer.

(6) FIG. 1(g) shows a Scanning Electron Microscope (SEM) image of the synthesized melamine-formaldehyde co-polymer.

(7) FIG. 2(a) shows a binding model of a carbon dioxide gas molecule with a melamine molecule.

(8) FIG. 2(b) shows a binding model (type-I) of a carbon dioxide gas molecule with a melamine-formaldehyde co-polymer.

(9) FIG. 2(c) shows a binding model (type-II) of a carbon dioxide gas molecule with a melamine-formaldehyde co-polymer.

(10) FIG. 3(a) shows carbon dioxide gas adsorption/desorption isotherms at 273 K using the melamine-formaldehyde co-polymer of Example 2k.

(11) FIG. 3(b) shows the gas cycling experiment using the melamine-formaldehyde co-polymer of Example 2i, under gas flow of carbon dioxide, followed by nitrogen.

(12) FIG. 3(c) shows the dynamic performance of the melamine-formaldehyde co-polymer of Example 2i used for carbon dioxide capture and carbon dioxide removal.

(13) FIG. 3(d) shows the schematic diagram for the through-flow experiment.

(14) FIG. 4 shows the Photo-Acoustic Fourier Transform Infrared Spectroscopy (PA-FTIR) spectrum of the synthesized melamine-formaldehyde co-polymer.

(15) FIG. 5 shows the .sup.13C NMR spectrum of the synthesized melamine-formaldehyde co-polymer showing peaks associated with triazine carbon at 166 ppm, and bridging CH.sub.2 groups at 48-54 ppm. The signal at 29.46 is from DMSO.

(16) FIG. 6 shows the Thermogravimetric Analysis (TGA) profile of the synthesized melamine-formaldehyde co-polymer, showing thermal stability of up to about 400 C.

(17) FIG. 7(a) shows a SEM image of the melamine-formaldehyde co-polymer synthesized by heating in an oven, using reaction conditions of 2.0M concentration and a paraformaldehyde to melamine ratio of 2.25:1.

(18) FIG. 7(b) shows a SEM image of the melamine-formaldehyde co-polymer synthesized by heating in an oven, using reaction conditions of 2.0M concentration and a paraformaldehyde to melamine ratio of 3.75:1.

(19) FIG. 7(c) shows a SEM image of the melamine-formaldehyde co-polymer synthesized by heating on a hotplate, using reaction conditions of 2.0M concentration and a paraformaldehyde to melamine ratio of 2.25:1.

(20) FIG. 7(d) shows a SEM image of the melamine-formaldehyde co-polymer synthesized by heating on a hotplate, using reaction conditions of 2.0M concentration and a paraformaldehyde to melamine ratio of 3.75:1.

(21) FIG. 8 shows the nitrogen gas adsorption/desorption isotherms of Example 2a at 77K.

(22) FIG. 9 shows the breakthrough curve for carbon dioxide gas adsorption by the synthesized melamine-formaldehyde co-polymer of Example 2i.

(23) FIG. 10 shows a reaction scheme for synthesis of a monomer ring comprising a melamine-formaldehyde copolymer.

DETAILED DESCRIPTION OF DRAWINGS

(24) Referring to FIG. 1(a), there are shown, nano-particle flakes in the region of 10-50 nm formed by precipitating melamine-formaldehyde co-polymers. The initial melamine-formaldehyde monomer units are stabilized by the hydrogen bonding between the amine hydrogens with the solvent. Once nano-particle flakes with the size in the region of 10-50 nm are formed, the poor solubility of the melamine-formaldehyde co-polymers in the DMSO solvent induces precipitation. The flakes precipitate from the solvent as melamine-formaldehyde nano-particles comprising micropores within the structure of the nanoparticle flakes. In FIG. 1(b), there are shown, micro sized particles formed by agglomeration of nano-particle flakes. This agglomeration connects the nano-particle flakes, forming mesopores within the network of connecting nano-particles. FIGS. 1(c) to 1(g) show the step by step agglomerating the nanoparticle flakes to form a meso-porous melamine-formaldehyde co-polymer.

(25) FIG. 2 shows carbon dioxide binding models, the density functional theory (DFT) calculations were carried out with the Gaussian 03 software. The exchange-correlation functional employed is known as Becke, three-parameter, Lee-Yang-Parr (B3LYP) which includes a fraction of Hartree-Fock exchange to reduce the self-interaction error. In the analysis, the 6-31/G(d,p) basis sets were used. After the structure of each compound was fully optimized, the total energy was obtained.

(26) In FIG. 2(a) there is shown a carbon dioxide molecule binding to a melamine molecule. The melamine is shown to display electrostatic interactions between the carbon of carbon dioxide molecule and the triazine nitrogen atom (CN: 2.86 ). In addition, there are hydrogen bond interactions between the carbon dioxide molecule and hydrogen atoms of the amine functional groups (HO: 2.27 and 2.28 ). The calculated total energy difference for this binding is 25.7 kJ/mol. The possible electrostatic interactions and slightly exothermic hydrogen bond interactions indicate a favorable physisorption model for binding of a carbon dioxide molecule to a melamine molecule. The low exothermic bond energy of the hydrogen bonds, further indicate that the binding model would be easily reversed.

(27) In FIG. 2(b) there is shown a type-I binding of carbon dioxide molecule to melamine-formaldehyde co-polymer. The calculated energy difference for this binding model is around 25.3 to 26.5 kJ/mol. This is similar to FIG. 2(a). Hence, melamine-formaldehyde co-polymer should also bind reversibly to carbon dioxide.

(28) In FIG. 2(c) there is shown a type-II binding of carbon dioxide molecule to melamine-formaldehyde co-polymer. This binding model displays only strong hydrogen interaction between carbon dioxide molecule and the melamine-formaldehyde co-polymer. The energy difference of type-II binding is about 15.2 kJ/mol, which is still favorable.

(29) This physisorptive model is in agreement with the BET carbon dioxide adsorption/desorption behavior. Further, this also displays the importance of the role of micropores and mesopores in carbon dioxide gas absorption. The greater the microporosity of the melamine-formaldehyde co-polymer, the larger the capacity of the melamine-formaldehyde co-polymer is for gas adsorption. Of course, the example uses carbon dioxide gas as a model, however this would be applicable for other gases with similar molecular properties and interactions.

(30) FIG. 4 shows the Photo-Acoustic Fourier Transform Infrared Spectroscopy (PA-FTIR) spectrum of the synthesized melamine-formaldehyde co-polymer showing peaks associated with NH.sub.2 or NH stretching at 3400 cm.sup.1, CH2 stretching at 2950 cm.sup.1, imine stretching at 1600 cm.sup.1, and triazine stretching at 1550 cm.sup.1 and 1480 cm.sup.1. The first can be assigned to the carbon atoms present in the triazine ring and the double resonances at 48 and 54 ppm can be correlated to CH.sub.2 groups that link two melamine molecules or a terminal NHCH.sub.2OH group.

(31) There is shown in FIG. 10, a reaction scheme for the formation of a two dimensional melamine-formaldehyde ring monomer unit. In a well controlled reaction, the synthesis of the melamine-formaldehyde will result in tessellation of the ring monomer unit. However, in a practical situation, perfect control of reaction conditions would not be possible. Hence, formation of the tessellated ring monomer unit will be interposed with periods of amorphous irregular geometry in the formation of melamine-formaldehyde nano-particles.

EXAMPLES

(32) Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

(33) The solvents used in the following examples, DMSO, tetrahydrofuran (THF), Dichloromethane (CH.sub.2Cl.sub.2) and acetone were purchased from Tee Hai Chemicals, Singapore. Melamine and paraformaldehyde were purchased from Sigma-Aldrich, United States of America.

Example 1

(34) Mesoporous Melamine-Formaldehyde Co-Polymers Synthesized on a Hot Plate

(35) Melamine and paraformaldehyde were added to a 20-ml glass vial, followed by the addition of anhydrous DMSO. The reaction mixture was heated gradually to give a colorless solution. Further heating at 180 C. for 72 hrs resulted in the formation of a white solid. The solid was filtered, and washed with water (3) and acetone (2). The resulting solid was dried under vacuum at 80 C. for 24 h.

(36) Using the above protocol, 8 samples of mesoporous PMF (Examples 1a to 1h) were prepared. The molar ratios of reactants, amount of solvent, reaction time and temperature for Examples 1a to 1h are provided in Table 1 below. The resulting samples were analyzed by nitrogen sorption at 77 K; surface area and pore diameter were obtained by the Brunauer-Emmet-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, respectively. Carbon dioxide sorption isotherm was analyzed at 273 K, and the results are also shown in Table 1 below.

(37) TABLE-US-00001 TABLE 1 N.sub.2 Adsorption at 77 K Reaction Conditions using BET and BJH methods Total PMF to Reaction Surface Pore Micropore CO.sub.2 Conc of Melamine T. Time Area Diameter TPV Volume Adsorption Sample reactants. (M) (Molar Ratio) ( C.) (h) (m.sup.2/g) (nm) (cm.sup.3/g) (cm.sup.3/g) Capacity (wt %) 1-a 2.0 3.75 180 72 743 10.4 1.06 0.14 14.0 1-b 2.0 4.50 180 72 713 8.9 1.00 0.10 11.4 1-c 1.5 3.75 180 72 898 11.1 1.48 0.14 14.3 1-d 2.5 3.75 180 72 739 10.0 0.89 0.16 14.1 1-e 2.0 3.75 180 48 852 10.7 1.30 0.16 14.9 1-f 2.0 3.75 180 120 684 9.2 0.66 0.17 14.1 1-g 2.0 3.75 160 72 636 13.3 1.41 0.09 12.0 1-h 2.0 2.25 180 72 72.9 19.2 0.06 0.02 7.8

Example 2

(38) Mesoporous Melamine-Formaldehyde Co-Polymers Synthesized in an Oven

(39) Melamine and paraformaldehyde were added to a 10 ml Teflon container with a magnetic stirrer, followed by addition of anhydrous DMSO. The Teflon container was capped and secured within a steel bomb reactor, which was heated to 120 C. in an oven (Memmert Universal UNE 400) for 1 hr. The bomb reactor was removed from the oven for stirring on a magnetic plate for 30 minutes to obtain a homogeneous solution. The bomb reactor was then heated again in the oven at 170 C. for 72 hours. The reactor was allowed to cool to room temperature, and the solid product obtained was crushed, filtered, and washed with DMSO, acetone (3), THF (3) and CH.sub.2Cl.sub.2. The resulting white solid was dried under vacuum at 80 C. for 24 hr.

(40) 12 different samples (Examples 2a to 21) were produced based on the above described protocol. The molar ratios of reactants, solvent volume are provided in Table below. The samples were analyzed according to the analytical methods mentioned in Example 1, and the results are also shown in Table 2 below.

(41) TABLE-US-00002 TABLE 2 Reaction Conditions N.sub.2 Adsorption at 77 K Conc PMF to Melamine BET Surface BJH Pore Total Pore Micropore CO.sub.2 Adsorption Sample (M) (Molar Ratio) Area (m.sup.2/g) Diameter (nm) Volume (cm.sup.3/g) Volume (cm.sup.3/g) Capacity (wt %) 2-a 1.5 2.25 1099 10.3 2.09 0.13 15.3 2-b 1.5 3.00 1004 8.3 1.78 0.06 11.4 2-c 2.0 2.25 1017 12.4 2.21 0.13 14.5 2-d 2.0 3.00 971 10.2 2.08 0.06 11.0 2-e 2.0 3.75 915 5.9 1.14 0.06 11.2 2-f 2.5 2.25 1074 17.5 3.29 0.14 15.7 2-g 2.5 3.00 1046 16.5 3.46 0.08 12.6 2-h 2.0 1.80 791 11.7 1.35 0.15 13.9 2-i 2.5 1.80 930 15.7 1.90 0.21 18.7 2-j 2.75 1.80 903 23.0 2.79 0.20 17.7 2-k 2.5 1.65 785 13.8 1.21 0.20 17.7 2-l 2.5 1.95 905 15.9 2.22 0.16 15.5

Example 3

(42) Mesoporous Melamine-Formaldehyde Co-Polymers Synthesized Using a Solvent Admixture of DMSO and H.sub.2O

(43) Paraformaldehyde and melamine were mixed in a molar ratio of 3:1 and reacted in the presence of a solvent admixture comprising DMSO and H.sub.2O. The total concentration of the reactants was 2.0 M and the overall reaction was performed in a bomb reactor that was heated in an oven for 72 hrs. 7 samples (Examples 3a-3g) of mesoporous PMF were produced using the above described protocol. The volume ratio of DMSO to H.sub.2O, oven temperatures were varied according to Table 3. The product samples were analyzed according to the analytical methods mentioned in example 1, with the results also shown in Table 3 below.

(44) TABLE-US-00003 TABLE 3 Reaction Conditions N.sub.2 Adsorption at 77 K DMSO/H.sub.2O Temp. BET Surface BJH Pore Total Pore Micropore CO.sub.2 Adsorption Sample Volume Ratio ( C.) Area (m.sup.2/g) Diameter (nm) Volume (cm.sup.3/g) Volume (cm.sup.3/g) Capacity.sup.c (wt %) 3-a 1:3 140 11.9 67.9 0.14 0.002 7.3 3-b 1:1 140 581 10.0 0.46 0.18 15.9 3-c 3:1 140 996 7.1 1.36 0.12 14.9 3-d 1:1 140 581 10.0 0.46 0.18 15.9 3-e 3:1 140 996 7.1 1.36 0.12 14.9 3-f 1:1 100 168.1 12.1 0.46 0.007 4.3 3-g 1:1 120 235.7 13.1 0.55 0.03 8.6

Comparative Example 4

(45) Mesoporous PMF Synthesized with N-Methylpyrrolidone (NMP) as Solvent

(46) Paraformaldehyde and melamine were mixed in a molar ratio of 3.75 to 1 and reacted in the presence of NMP. The overall concentration of reactants was 2.0 M and the reaction mixture was heated at a temperature of 180 C. for 72 hrs. The resulting sample was analyzed according to the analytical methods in example 1, and the results are provided below.

(47) Surface Area (m.sup.2/g)=4.6

(48) Pore size (nm)=57.5

(49) Total Pore Volume (cm.sup.3/g)=0.005

(50) Micropore Volume (cm.sup.3/g)=0.003

(51) CO.sub.2 adsorption (wt %)=4.7

(52) This comparative Example demonstrates that DMSO is likely to play an important role in the formation of micropores, which strong correlates with the carbon dioxide gas adsorption capacity of the resulting mesoporous PMF. In this Example, it can be seen that both the micropore volume and surface area obtained are significantly inferior to the PMFs obtained in Examples 1-3, which accordingly translated to an adsorption capacity of less than 5 wt %.

Example 5

(53) TGA Gas Cycling Experiments

(54) Melamine-formaldehyde co-polymer from Example 2i was subjected to the following gas cyclic treatment at 25 C. carbon dioxide (99.8%) gas flow (20 ml/min) for 30 min, followed by nitrogen (99.9995%) gas flow (20 ml/min) for 45 min.

(55) Changes in weight of the PMF sample were recorded by the TGA instrument. Prior to the cyclic treatment, the sample was first purged at 120 C. for 60 minutes under nitrogen gas flow, followed by cooling to room temperature. Change in buoyancy effects arising from the switching of gases was recorded using an empty sample pan, and the buoyancy effects were corrected for in the TGA curve.

(56) The results may be described with reference to FIG. 3(b). There was an evident sudden sharp increase in weight % of the synthesized melamine-formaldehyde co-polymer which continued until a maximum adsorption at 9.3 weight % was achieved. Once the gas feed was switched to nitrogen gas, a similarly rapid weight % loss was observed, due to the desorption of the carbon dioxide from the PMF. The adsorption and desorption cycle was continued for 6 successive cycles and, no loss in either the speed or capacity of adsorption/desorption was observed. This Example clearly demonstrates the suitability of the PMF for use in large scale industrial gas scrubbing applications, due to its efficient gas uptake and discharge during regeneration, and its durability for multiple-use without exhibiting any loss in adsorption capacity.

Example 6

(57) Through-Flow Column Adsorption

(58) A schematic diagram for the experimental set-up is provided in FIG. 3(d). A steel column of 10 cm in length and 10 mm internal diameter was packed with 1.036 g of melamine-formaldehyde co-polymer powder from Example 2i. The packed column was subsequently connected to a cylinder of 15% carbon dioxide gas in nitrogen gas. Gas flow was controlled with a cylinder regulator and a gas flow meter at a flow rate of 2.5 ml/min. The output gas from the packed column was connected directly to a Gas Chromatograph for analysis. The Gas Chromatograph instrument was conditioned for 1 h at 200 C. prior to the analysis. An optimized Gas Chromatograph method of isothermal analysis at 75 C. for 1.8 min was employed. Retention time for nitrogen gas peak and carbon dioxide gas peak were at 0.68 min and 1.48 min respectively. The time interval between consecutive Gas Chromatograph analyses was 2.15 min. The peak areas were calculated to obtain % carbon dioxide, with 15% carbon dioxide gas in Nitrogen gas as a reference gas mixture. Vacuum was applied to the experimental setup before analysis and the gas lines were purged with inert helium gas prior to carbon dioxide gas adsorption by synthesized melamine-formaldehyde co-polymer. For recycling of the synthesized melamine-formaldehyde co-polymer, vacuum (pressure of about 1 mbar) was applied to the column for 1 h and the adsorption analysis repeated as stated above.

(59) The use of an analyte gas at 15% carbon dioxide gas in nitrogen gas simulates the actual composition of flue gas discharged by power plants. FIG. 9 shows that almost all the carbon dioxide gas in the gas feed was adsorbed by the synthesized melamine-formaldehyde co-polymer in the first 40 minutes until the synthesized melamine-formaldehyde co-polymer was approaching saturation. With reference to FIG. 3(c), the carbon dioxide adsorption capacity of the synthesized melamine-formaldehyde co-polymer reached 3.8, 4.2 and 4.7 wt % for 99%, 95% and 90% removal of CO.sub.2 from the analyte gas respectively. This performance is comparable to an optimized dynamic capacity of a 30% MEA solution.

(60) Vacuum was used to regenerate the packed column and full carbon dioxide adsorption capacity was recovered. This again exemplifies the ease of regeneration and indicates the suitability of the presently disclosed melamine-formaldehyde co-polymer as a more cost-effective and energy efficient alternative to current liquid and/or solid gas sorbents used in the industry.

(61) It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Applications

(62) The disclosed mesoporous PMF can be envisioned as a cost-effective and viable alternative to current liquid carbon dioxide gas scrubbers, such as MEA. In particular, the disclosed solid PMF sorbent is inexpensive to produce and in contrast to MEA, the disclosed PMF sorbent can be easily regenerated due to the weakly binding intermolecular forces between PMF and CO.sub.2, thereby negating or at least minimizes the energy penalties so commonly associated with MEA. Further in contrast to MEA, the disclosed PMF sorbent does not require periodic replenishment and therefore entails additional cost savings.

(63) The disclosed mesoporous PMF is also superior to currently known solid gas sorbents, not least due to its high BET surface area and micropore volume, which allows the disclosed mesoporous PMF to exhibit up a CO.sub.2 adsorption capacity of up to about 20 wt %. Even more advantageously, the disclosed mesoporous PMF does not require complex synthesis procedures. In particular, the disclosed PMF may be produced in a one-step solvothermal reaction process, without requiring the use of basic catalysts and/or other pH modifying processing steps. In contrast to existing methods of producing PMF for gas sorption, which may be cumbersome and potentially expensive, the straightforward synthesis method disclosed in the present invention lends itself industrial scale-up potential and ease of implementation.

(64) It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.