ANAGHA YATHEENDRAN (IN)
RAMESH KUMAR (IN)
S ARUN KARTHIK (IN)
| CN103702740B | 2016-11-09 | |||
| TWI568491B | 2017-02-01 |
| We Claim: 1. A nanofiber membrane fabricated by electrospinning an aminoethyl-aminopropyl trimethoxy silane/polyacrylonitrile (AEAPTMS/PAN) composite, with large surface area, having a 100% recyclable CCA adsorption capacity of > 0.77 mmol/g functioning at 24 °C, with complete regeneration at near room temperatureof 45 °C, with an adsorption cycle of 120 minutes and desorption cycle of 30 minutes. 2. The membrane as claimed in claim 1 , wherein the nanofiber is fabricated bymelt spinning, or melt electrospinning, or electrospinning. 3. The membrane as claimed in claim 1, wherein the diameter of the nanofiber is in the range of lpm to 0.1 pm. 4. The membrane as claimed in claim 1 , wherein the CO 2 is adsorbed and desorbed in ambient air with adsorption cycle time not greater than 120 minutes and desorption cycle time not greater than 30 minutes. 5. The membrane as claimed in claim 1, wherein the CCA is adsorbed on homogenous uniformly distributed amine sites. 6. The membrane as claimed in claim 1, wherein CCA is adsorbed by forming ammonium bicarbonate and ammonium carbamate at room temperature, both in the presence and absence of humidity. 7. The membrane as claimed in claim 1, wherein CCA is desorbed by decomposing the formed ammonium bicarbonate and ammonium carbamate at 55 °C, preferably at 50 °C, more preferably at 45 °C or lower. 8. The membrane as claimed in claim 1, wherein the CCA adsorption leads to homogenous uniformly distributed bicarbonate and carbamate sites. 9. The membrane as claimed in claim 1, wherein re-adsorption and re-desorption occurs for multiple cycles with 100% regeneration capacity. 10. The membrane as claimed in claim 1, wherein the nanofiber is integrated within a device comprising air purifier, air conditioner and heater, with adsorption and desorption cycles. 11. The membrane as claimed in claim 10, wherein the CCA is adsorbed after particulate removal from ambient air. 12. The membrane as claimed in claim 10, wherein the nanofiber works in a cycle with 40 minutes of adsorption and 20 minute of desorption or preferably 20 minutes of adsorption and 10 minutes of desorption. |
TITLE OF THE INVENTION
AN ENHANCED CARBON DIOXIDE SORBENT NANOFIBER MEMBRANE AND A DEVICE THEREOF
FIELD OF THE INVENTION
The present invention relates to the field of air purification or air filtration, more specifically relates to a material that adsorbs C0 2 at ambient room condition and desorbs it at near ambient temperature.
BACKGROUND OF THE INVENTION
Rapid increase in the CO 2 concentration in the air in the recent past and its alarming consequences such as global warming, are some of the most important environmental issues facing the planet. This significant increase in C0 2C oncentration is caused due to industrial actions, largely from combustion. Increased C0 2 levels have undesirable consequences on metabolism and neuronal activities. Due to the need to have protection from insects, dust, and such other local disturbances, enclosed environments are desired for living. However, the CO 2 levels in such closed enclosures increase due to biological activities of the inhabitants. Therefore, it is necessary to control the concentration of C0 2 in such environments for healthy living.
It is well known from the literature that, there are many C0 2 scavenging materials including calcium oxide, hyper branched amino silica, as well as amines (primary, secondary, and tertiary). In order to maintain the C0 2 concentration below 450 ppm, compatible to global average concentration of 300 - 500 ppm (ANSEASHRAE Standard 62.1-2010) in a closed room of 20 cubic meters volume with one occupant for a period of two hours, it is necessary to remove approximately 75 g or 1.704 mol of C0 2 . In the ambient condition of 25°C and 90 % relative humidity, removal of such amount of C0 2 is possible by using 0.1910 kg of the best available C0 2 removal media such as amino silica monolith (Harshul Thakkar et. ah, ACS Appl. Mater. Interfaces 2017, 9, 7489-7498). Other available media, metal organic frameworks (MOF) -177 (Hussein RasoolAbid et. ah, Journal of Colloid and Interface Science 2012, 120-124), requires 0.051 kg of material to maintain C0 2 concentration in the above-mentioned case. However, for commercial feasibility, regeneration of silica monolith requires an optimum ambient temperature of 115 °C and, adsorption process of MOF-177 requires an optimum pressure of 4500 kPa. Since, regeneration of the media with best sorption capacity is not possible near ambient conditions, developing a device with a minimum quantity of working sorbent material with efficient cycling capacity near ambient conditions with regeneration is necessary. This will reduces the physical size of the device as well as cost and power requirements.
Though there are many adsorption media for C0 2 removal in recent years, still there is a need for a better and efficient sorbent material for removing C0 2 in ambient conditions. Thus the present invention provides a new material of composite fiber that adsorbs C0 2 at room temperature and desorbs C0 2 at near ambient temperature.
SUMMARY OF THE INVENTION
This invention relates to the field of air purification or air filtration, more specifically relates to a material that adsorbs C0 2 at room temperature and desorbs it at near ambient temperature.
In one embodiment the invention relates to the fabrication of nanofiber membrane by electrospinning an aminoethyl-aminopropyl trimethoxy silane/polyacrylonitrile (AEAPTMS/PAN) composite, with large surface area, having a 100% recyclable C0 2 adsorption capacity of > 0.77 mmol/g functioning at 24 °C, with complete regeneration at near room temperature of 45 °C, with an adsorption cycle of 120 minutes and desorption cycle of 30 minutes. C0 2 is adsorbed by forming ammonium bicarbonate and ammonium carbamate at room temperature, in the presence and absence of humidity, respectively and desorbed by decomposing the formed ammonium bicarbonate and ammonium carbamate at 55 °C, preferably at 50 °C,more preferably at 45 °C or lower.
In other embodiment, the invention illustrates the use of the fabricated nanofiber membrane in air purification by integrating it within a device comprising air purifier, air conditioner and heater, with adsorption and desorption cycles.Wherein, the nanofiber works in a cycle with 40 minutes of adsorption and 20 minute of desorption or preferably 20 minutes of adsorption and 10 minutes of desorption. BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 SEM image of AEAPTMS/PAN composite electrospun material.
Figure 2 depicts C0 2 sorption capacity of electrospun AEAPTMS/PAN (composite- 1).
Figure 3 depicts cyclic C0 2 sorption capacity of electrospun AEAPTMS/PAN (composite- 1). Figure 4 depicts ambient temperature and relative humidity during C0 2 sorption by electrospunAEAPTMS/PAN (composite- 1 ).
Figure 5 depicts % relative humidity dependence of C0 2 adsorption capacity of electrospunAEAPTMS/PAN (composite- 1 ).
Figure 6 depicts temperature dependence of C0 2 adsorption capacity of electrospun AEAPTMS/PAN (composite- 1).
Figure 7 depicts the rate of desorption at different ambient temperature for AEAPTMS/PAN (composite- 1).
Figure 8 depicts the FTIR spectrum of electrospun AEAPTMS/PAN (composite- 1) before adsorption, after C0 2 adsorption and after C0 2 desorption.
Figure 9 depicts the Raman spectrum of electrospun AEAPTMS/PAN (composite- 1 ) before adsorption, after C0 2 adsorption and after C0 2 desorption.
Figure 10 depicts the schematic diagram of proposed device for C0 2 adsorption and desorption process using electrospun APAETES/PAN membrane.
Referring to the drawings, the embodiments of the present invention are further described. The figures are not necessarily drawn to scale, and in some instances the drawings have been exaggerated or simplified for illustrative purposes only. One of ordinary skill in the art may appreciate the many possible applications and variations of the present invention based on the following examples of possible embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
As required, detailed embodiments of the present invention are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various forms. The figures are not necessary to scale exemplary of the invention that may be embodied in various forms. The figures are not necessary to scale; some features may be exaggerated to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention.
The present invention shows the possibility of using the well-known carbamate and bicarbonate chemistry of amines in scavenging C0 2 by a suitable combination of amines and polyacrylonitrile polymer. The nanofiber membranes of large surface area are produced by electrospinning the composite and this composite material can also be processed into fibrous membrane using melt-spinning process. Due to the inherent curvature and exposed functionalities, large C0 2 uptake is possible resulting in a C0 2 scavenger functioning at room temperature and ambient pressure.Homogeneous distribution of C0 2 scavenging sites leads to the uniformly ordered formation of carbamate and bicarbonates. This electrospinning induced homogeneity in carbamate and bicarbonate formation on AEAPTMS/PAN structure leads to sharp desorption of C0 2 . The saturated material desorbs C0 2 in the temperature window of 47- 50°C enabling complete regeneration. This process can be repeated several times. Even with the comparatively poor adsorption capacity of AEAPTMS/PAN material, room temperature adsorption and near complete desorption close to ambient conditions, make it possible to design a system for C0 2 sequestration with a reduced quantity of the material. A device incorporating such materials with reduced energy input requires 1.64 kg of AEAPTMS/PAN composite material for maintaining C0 2 concentration below 450 ppm in a room of 20-meter cube volume with one active adult occupant. The adsorption happens at 25 °C, preferably at 22 °C with 60% relative humidity and desorption occurs at 50°C, preferably at 47 °C.
This invention describes a method for C0 2 control in closed environments to enhance the quality of human life.
Properties of all the best-known materials for C0 2 sorption as of today and their performances are listed in Table 1.
Table 1 Adsorption capacity of various adsorbents and theiroperational parameters
The present invention relates to the development of electrospun AEAPTMS/PAN fibrous membranewith a high surface area for C0 2 adsorption. The electrospun fiber’s surface contains numerous uniform amine sites for C0 2 capture. Figure 1 shows the SEM images of the surface. According to the invention, the composite- 1 comprises of the electrospun material, N-[3- (Trimethoxysilyl) propyl]ethylenediamine (AEAPTMS) functionalized polyacrylonitrile (PAN/AEAPTMS) as the adsorbent surface which has a higher surface area with a nanofiber diameter of I p , preferably 0.5pm, more preferably 0.1 pm. Figure 1 shows that the fibers are 0.359±0.065pm in diameter. The electrospun polymeric material does effective adsorption of CO 2 at room temperature and desorption at 50 °C enabling complete regeneration of the adsorbent material.
Further, this invention demonstrates the CO 2 sorption capacity of the AEAPTMS/PAN and solvent composition. The adsorbent surface was prepared by the electrospinning technique. Amine loaded nano-fibrous material, composite- 1 was prepared by dissolving l2wt% PAN in dimethylformamide (DMF) with 1 ml AEAPTMS in use. In another aspect, amine loaded nano- fibrous material, composite-2 was prepared by dissolving 14 wt% PAN in DMF with 2.0 ml of AEAPTMS. Figure 2 shows an adsorption capacity of 0.77mmol/g CO 2 for composite- 1, nanofiber material in an ambience having 70 % relative humidity, 24 °C temperature and 3400 ppm C0 2 concentration.
The adsorption-desorption experiments were performed in an air-tight desiccator having pre-determined humidity and concentration of CO 2 andAEAPTMS/PAN fibrous material sheet and C0 2 measuring meter kept in it. Relative humidity, temperature and C0 2C oncentration in the desiccator were monitored and logged each minute. Adsorption experiments were done at an average temperature of 25°C and desorption tests were performed at 50°C. Desiccator was kept in a hot air oven for high temperature studies and air-conditioned roomfor low temperature studies. Three adsorption - desorption cycles in Figure 3 shows 100% cycling capacity of 0.8 g of composite- 1 material with an initial CO2 concentration of 2304 ppm. The graph shows the uptake of CO2 by the fibers when the composite- 1 fibers were exposed to the gas in an enclosure. The adsorption experiment was repeated after desorption of the adsorbed CO2 at 50 °C. Figure 4 shows the corresponding changes occurred in temperature and % relative humidity during three adsorption-desorption cycles. Electrospuncomposite- 1 shows an average of 0.347mmol/g C0 2 adsorption capacity for initial 30 minutes of adsorption cycle and 100% desorption capacity when the material was heated up to 50 °C. The rate of CO2 desorption increases as the temperature of the material increases. The C0 2 sorption capacity of the developed composite material is dependent on ambient humidity and temperature. The higher value of humidity and lower value of temperature will favor enhanced rate of adsorption. Table 2 shows the amount of C0 2 adsorption for each cycle with a maximum of 0.55mmol/g at 70 % relative humidity and 25 °C.
Table 2 C0 2 concentration in the chamber after each sorption cycle for electrospun AEAPTMS/PAN (composite- 1)
Bicarbonate and carbamate chemistry based CO 2 adsorption capacity is dependent on initial C0 2 concentration, ambient temperature and % relative humidity. CO 2 adsorption capacity increases with increase in initial C0 2 concentration, decrease in ambient temperature and increase in % relative humidity. Presence of water vapor enhances bicarbonate formation and increases the C0 2 adsorption capacity. C0 2 desorption rate increases at higher temperature.
Increase in C0 2 adsorption rate with increase in % relative humidity at 25 °C temperature is shown in Figure 5. At ambient temperature, bicarbonate formation is the dominant mechanism for C0 2 adsorption, than by carbamate formation. As temperature increases, formation rate of bicarbonate decreases and carbamate formation becomes the more dominant mechanism for C0 2 adsorption. As temperature increases, the C0 2 adsorption rate further decreases because of an aggregate decrease in the rate of formation of ammonium bicarbonate and ammonium carbamate, hence saturation uptake is delayed. The same phenomenon is shown in Figure 6.
Desorption tests were performed at a fixed temperature of 50 °C, with different temperature ramp rates. To obtain the different temperature rate of 1.11, 1.25 and 1.85 °C/minute, oven temperature was set to 60, 70 and 80 °C, respectively. Once oven temperature reaches 50 °C, it was maintained the same. At three different ramping rates of 1.11, 1.25 and 1.85 °C/minute, composite- 1, takes 45, 40 and 27 minutes, respectively for full desorption of adsorbed 0.308 mmol of C0 2 . The rate of desorption is high with a high-temperature ramp rate. Rate of desorption at different temperature windows is given in Figure 7.
FTIR analysis shows the formation of ammonium bicarbonate and ammonium carbamate on composite- 1 after C0 2 adsorption in humid ambience with 60 % relative humidity and 24 °C temperature. Figure 8 A), B) and C) shows the ATR - FTIR spectra of composite- 1 before adsorption, after adsorption and after desorption, respectively. The difference spectrum B-A shows the difference between the spectrum after C02 adsorption and before C0 2 adsorption and C-A difference spectrum shows the difference between the spectrum after C0 2 desorption and before C0 2 adsorption, respectively.
Upon C0 2 adsorption, various surface species are readily formed and the spectrum shows IR features in the range of 1600 to 500 cm 1 . The IR bands in the region, 1600-500 cm l are due to carbamate, bicarbonate and carbamic acid species. Adsorption of C0 2 with H 2 0 molecule present in the humid air on the uniformly distributed homogeneous sites leads to the formation of bicarbonate peaks at 816, 1318 and 691 cm 1 . Chemisorption of C0 2 on amine groups present on the surface results in carbamate and carbamic acid peaks at 1478, 1561 and 593 cm l. The peak at 2245 cm 'can be attributed to unreacted polyacrylonitrile. Assignments are summarized in Table 3. The available transmittance peak intensities in the difference spectrum B-A confirms the formation of bicarbonate and carbamate after C0 2 adsorption whereas the absence of corresponding peak intensities in the difference spectrum C-A, suggests reversal of the formed bicarbonate and carbamate and re-availability of homogeneous adsorption sites.
The Raman spectrum of AEAPTMS functionalized fiber before C0 2 adsorption, after C0 2 adsorption and after C0 2 desorption are shown in Figure 9. Similar to FTIR, Raman analysis corroborates the formation of ammonium bicarbonate and ammonium carbamate on composite- 1 after C0 2 adsorption in humid ambience with 60 % relative humidity and 24 °C temperature.
The Raman shift in the region 1000-3000cm ' is due to bicarbonate andcarbamte species. Adsorption of C0 2 from humid air on the uniformly distributed homogeneous sites leads to the formation of bicarbonate peak at 1075 cm 1 . Chemisorption of C0 2 on the amine groups present on the surface results in amide peak at 1465 cm 1 and the peak at 1687 cm 'can be attributed to secondary carbamate (CHN group), carbonyl group of acid and antisymmetric CO stretching of bicarbonate. The peak at 2260cm 1 is due to unreacted nitrile which also gets intensified after adsorption of CO 2 due to overlap of NH + group vibration. The peak at 2900 cm 1 is due to CH stretching vibrations, vibrations of O-CH3 group and shift of alkane stretching to higher wave number due to the protonation of amines through C0 2 adsorption.
Table 3 IR band assignments after C02 adsorption on AEAPTMS/PAN (composite- 1).
A schematic diagram of device with AEAPTMS/PAN membrane and inbuilt heater is shown in Figure 10. During the operation of device, air enters through particulate filter where suspended µ-particles are removed. After the particulate filter, air goes through filaments of heater and then subsequently through electrospun AEAPTMS/PAN membrane, where CO 2 from ambient air is removed. This provides best efficiency when operated in air-conditioned room without causing any energy inefficiency to existing air-conditioning system. Heater is kept on and off for C0 2 adsorption and desorption cycle, respectively. During desorption, temperature of inlet air increases to temperature above 45°C or preferably 55°C.
It may be appreciated by those skilled in the art that the drawings, examples and detailed description herein are to be regarded in an illustrative rather than a restrictive manner.