TECHNICAL FIELD

Hie present disclosure relates to a method and system for studying adsorption kinetics of an adsorbent and adsorbate pair. More specifically, but not exclusively, the present disclosure relates to a method and system employing laser for studying the adsorption kinetics of an adsorbent and adsorbate pair.

BACKGROUND

Adsorption is the adhesion of atoms, ions or molecules from a gas, a liquid or a dissolved solid to a surface. The atoms, ions or molecules from the gas, the liquid or the dissolved solid are termed as adsorbate. The surface over which the adsorbate is adsorbed is termed as an adsorbent. Adsorption creates a film of the adsorbate on the surface of the adsorbent. The key aspects of adsorption kinetics are determining adsorbate concentration around adsorbent, determining adsorption rate at different pressure, temperature and concentration of adsorbate, determining different adsorption environments employing low speed, high speed flow of adsorbate, different configurations of adsorbent, and different geometric shapes of adsorbent (power, particle, liquid).

The existing solutions present for studying adsorption kinetics include techniques like thermogravimetry, Differential Scanning Calorimetry (DSC), and Large Temperature Jump (LTJ) method. The existing techniques are highly specific to adsorbent and adsorbate pair. Thermogravimetry includes measurement of mass of adsorbent sample and is highly dependent on a mass measuring instrument. DSC is used for studying desorption from solid adsorbent and is based on temperature measurement. Hence, the application of DSC for use of liquid adsorbent and adsorption is limited. Further, flow of adsorbate over adsorbent cannot be studied using thermogravimetry or DSC. LTJ method is mostly used to study adsorption kinetics of bed of adsorbent particle and hence studying adsorption kinetics of single particle/finite mass is not possible with this method. Further, LTJ method is also based on measurement of temperature difference between an inlet and an outlet of a system implementing the LTJ method, for studying tire adsorption kinetics. None of the above methods can measure adsorbate concentration during adsorption process and these methods are not suitable for chemisorption measurement. Tire above-mentioned techniques involve measurement of indefinite parameters like mass, temperature and pressure and correlate the measurement with the adsorption kinetics and hence are inaccurate.

Most of the available measurement methodologies do not work under the conditions involving calculation of spatial and temporal variation of adsorbate concentration around adsorbent during adsorption process with or without flow'. Further, the available measurement methodologies do not measure adsorption kinetics for different configurations of the adsorbent like bunch/array/s ingle adsorbent particle/adsorbent powder/adsorbent liquid drop. Also, the existing measurement methodologies do not measure time history of adsorption. The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any fonn of suggestion that this information forms the prior art already known to a person skilled in the art.

Hence, there is a need for a method and system that pro vides an improved measurement of adsorption kinetics of adsorbent and adsorbate pair to overcome one or more limitation in the existing art.

SUMMARY

The features and advantages realized through the techniques of the present disclosure are brought out. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

The one or more shortcomings of the prior art are overcome, and additional advantages are provided through the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

In an embodiment, the present disclosure discloses a method for determining concentration of an adsorbate around an adsorbent. The method comprising generating a laser beam and passing the generated laser beam tangentially to a surface of the adsorbent, wherein the adsorbent is included in a medium . The method further comprises detecting laser beam projected out of the medium, processing the detected laser beam to produce an output signal, and determining concentration of the adsorbate around the adsorbent based on the output signal.

In another embodiment, the present disclosure discloses a system to determine concentration of an adsorbate around an adsorbent. The system comprises a laser configured to generate a laser beam, a medium configured to receive the generated laser beam tangential to the adsorbent, wherein the medium includes the adsorbate and the adsorbent, a photodetector configured to detect laser beam projected out of the medium, and process the detected laser beam to produce an output signal; and a controlling device coupled to the laser, wherein the controlling device is configured to determine concentration of the adsorbate around the adsorbent based on tire output signal.

It is to be understood that the aspects and embodiments of the invention described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the invention. The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS

The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

Figure 1 shows an exemplar _)? block diagram of an absorption spectroscopy system for studying absorption kinetics, in accordance with embodiments of the present disclosure;

Figure 2 shows an exemplary' experimental setup of a Tunable Diode Laser Absorption Spectroscopy (TDLAS) system for studying the adsorption kinetics adsorbent and adsorbent pair, in accordance with some embodiments of the present disclosure;

Figure 3 show's flowchart illustrating a method of determining concentration of adsorbate over adsorbent, in accordance with an embodiment of the present disclosure; Figure 4 shows a diagram indicating different locations of concentrating a laser beam for studying adsorption kinetics, in accordance with some embodiments of the present disclosure;

Figure 5 illustrates a calibration curve for measuring concentration of adsorbate around an adsorbent, in accordance with some embodiments of the present disclosure;

Figure 6a illustrates uptake (amount of water vapour adsorbed against time) for Re=0 and single silica gel particle, in accordance with some embodiments of the present disclosure;

Figure 6b illustrates uptake (amount of water vapour adsorbed against time) for Re=0 and array of silica gel particles, in accordance with some embodiments of the present disclosure;

Figure 7 illustrates uptake (amount of water vapour adsorbed against time) for Re=l and single silica gel particle, in accordance with some embodiments of the present disclosure;

Figure 8a illustrates radial water vapour pressure variation against time for Re=0 and array of silica gel particles, in accordance with some embodiments of the present disclosure;

Figure 8b illustrates azimuthal water vapour pressure variation against time for Re=0 and array of silica gel particles, in accordance with some embodiments of the present disclosure;

Figure 9a illustrates radial water vapour pressure variation against time for Re=! and array of silica gel particles, in accordance with some embodiments of the present disclosure; and

Figure 9b illustrates azimuthal water vapour pressure variation against time for Re=l and array of silica gel particles, in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION In the present document, the word "exemplary _' " is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary'" is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below'. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure.

The terms“comprises”,“comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps hut may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a device or system or apparatus proceeded by“comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the device or system or apparatus.

In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that fonn a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.

Figure 1 shows a block diagram of an absorption spectroscopy system 100 for studying the absorption kinetics in accordance with embodiments of the present disclosure. The absorption spectroscopy system 100 comprises of a controlling device 101, a laser 102, a medium 103, and a photo detector 106. The medium 103 further comprises an adsorbate 104 and an adsorbent 105. o The controlling device 101 is connected to the laser 102 via a connector (not shown). The controlling device 101 may be used to control the laser 102, and issue commands to the laser 102 for emitting laser beam . The laser beam is projected through the medium 103 comprising the adsorbate 104 and the adsorbent 105, resulting in partial absorption of the laser beam by the medium 103, wherein the laser beam is projected tangential to a surface of the adsorbent 105. The resulting laser beam projecting out of the medium 103 is detected by the photo detector 106. Further, the photo detector 106 determines an intensity of the resulting laser beam. The photo detector 106 produces an output signal corresponding to the intensity of the resulting laser beam. Further, the controlling device 101 receives the output signal of the photo detector 106, records and processes the output signal. The controlling device 101 specifically determines a change in intensity by comparing the intensity of the resulting laser beam with an intensity of the emitting laser beam. Further, based on the change in the intensity the controlling device 101 determines an absorption coefficient of the laser beam. Further, the controlling device 101 may determine concentration of the adsorbate 104 around the adsorbent 105 using the determined absorption coefficient. In an embodiment, the controlling device 101 may include, but are not limited to, computing systems, such as a microprocessor, an application specific integrated circuit, a computer and the like. The system 100 is capable of fast measurements to determine concentration of the adsorbate 104 around the adsorbent 105 at 100 KHz. It therefore can measure rapid variations in concentration close to the adsorbent 105.

The laser beam emitted by the laser 102 may be tunable i.e., emission wavelength intensity and other parameters of the laser 102 may be tuned as required. Tire laser beam is passed through the medium 103 comprising the adsorbate 104 and the adsorbent 105. A part of the laser beam gets absorbed when passed through the medium 103 and hence results in a reduction of intensity of the laser beam . The laser 102, may be, but not limited to a semiconductor laser, solid-state laser, a gas laser and a liquid laser.

Hie medium 103 comprises the adsorbate 104 and tire adsorbent 105. Hie medium 103 may be a gaseous medium or a liquid medium. The adsorbate 104 may be any substance that is capable of being adsorbed or accumulated on a surface of the adsorbent 105. The adsorbate 104 may be one of, but not limited to water (liquid form), water (gaseous form), methanol, COi, Hi, and tire like. The adsorbent 105 may be any substance on winch the adsorption occurs. The adsorbent 105 may be a solid or a liquid. The adsorbent 105 may be, but not limited to a silica gel, zeolites, carbon sieves, a bone char, or any solid adsorbent. In an embodiment, the adsorbent 105 may be silica gel and the adsorbate 104 may be water. The adsorbent 105 may comprise of a single adsorbent particle or an array of adsorbent particles. The adsorbent 105 and the adsorbate 104 may be collectively represented as adsorbent and adsorbate pair hereafter in the present disclosure.

The photo detector 106 senses light intensity of the resulting laser beam. The photo detector 106 may have a p-n junction that converts light photons into current. The photo detector 106 may be one of a photo diode or a photo transistor. The photo detector 106 detects the intensity of the resulting laser beam, once the laser beam has passed through the medium

103. Further, the photo detector 106 produces an output signal corresponding to the intensity of the resulting laser beam. The output signal of the photo detector 106 is provided to the controlling device 101, to compute an output intensity (intensity of laser beam after being transmitted through the medium 103).

Figure 2 shows an exemplary experimental setup of the absorption spectroscopy system 100 used for studying the adsorption kinetics of an adsorbent and adsorbent pair, in accordance with some embodiments of the present disclosure.

The absorption spectroscopy system 100, may be referred to as a Tunable Diode Laser Absorption Spectroscopy (TOLAS) system 100 as it utilizes a tunable laser diode for measuring concentration of the adsorbate 104 around the adsorbent 105, in the medium 103 The TDLAS system 100 comprises the controlling device 101, a connector 201, a laser 102, an optic cable 202, an optic cable 202a, an optic cable 202b, an optic spliter 203, a first Laser Mount (LM1) 204a, a second Laser Mount (LM2) 204b, a reference cell 205, a test cell 206, the adsorbate

104, the adsorbent 105, a first Photo Diode (PD1) 106a, and a second Photo Diode (PD2) 106b. In an embodiment, the PDi 106a and the PD1 106b may be collectively represented as photo detector 106.

The embodiment described below, indicates the general working of the TDLAS system 100. In the TDLAS system 100 the laser 102, emits the laser beam at the transmitted intensity (intensity of the laser beam at the time of em ission from the laser 102). The laser beam passes through the medium 103 comprising the adsorbent and adsorbate pair. The adsorbate 104 absorbs some amount of the laser beam passing through the medium 103. The resulting laser beam from the medium 103 is received by the photo detector 106. The intensity of the resulting laser beam is measured by the photo detector 106 and hence determines a change in the intensity by comparing the intensity of the resulting laser beam with an intensity of the emitted laser beam. Further, based on the change in the intensity the controlling device 101 determines an absorption coefficient of the laser beam. The absorption coefficient of the laser beam m the medium 103 indicates the rate of decrease in the intensity of the laser beam as it passes through a through the medium 103 comprising the adsorbent and adsorbate pair. The absorption coefficient of the laser beam is computed using the equation 1.

-a(v)L

liv) 1, e ( 1) where,

I(v) is the output intensity,

T is the transmitted intensity,

L is length of a cell comprising the medium 103 which the laser beam traverses,

v is frequency, ce(v) is absorption coefficient,

product -<x(v)L is called absorbance.

The absorption coefficient is determined by the controlling device 101 using the equation 1. The adsorbate 104 may be termed as an absorbing species as it absorbs the laser beam. The concentration of the absorbing species can be calculated from the absorbance or the absorption coefficient according to Beer-Lambert's law. The absorption coefficient or absorbance of the light beam passing though the medium 103 is directly proportional to the concentration of the adsorbate 104 present in the medium 103.

The embodiment described below, indicated the working of the experimental setup. The controlling device 101 is connected to the laser 102 using the connector 201. The connector 201 may be a BNC 2110 connector. The BNC 2110 connector is a connector block with signal- labelled BNC connectors. The controlling device 101 issues commands to control the laser 102 via the connector 201. The laser beam emitted by the laser 102 is provided to an optic splitter 203 through an optic cable 202. The optic spliter 203 splits the laser beam into two beams a fi rst laser beam and a second laser beam .

The adsorbent and adsorbate pair considered for the experimental setup is silica gel and water. Water may be in the form of water vapour or water droplets. The experimental setup utilizes two cells, the reference ceil 205 and the test cell 206. The reference cell 205 is first filled with dry air. Silica gel particles are heated using a heater at 15G ^° C for an hour and the heated silica gel particles are filled in the reference cell 205 so that, air inside the reference cell 205 is completely dried. The silica gel may be in the form of a silica gel particle or an array of silica gel particles. The heated silica gel particles are removed from the reference cell 205. Fresh silica gel particle or array of silica gel particles (free of humidity) along with water droplets are introduced into the test cell 206.

The first laser beam is passed through the optic cable 202a. The second laser beam is passed through the optic cable 202b. The LM1 204a and LM2 204b holds tire optic cable 202a and the optic cable 202b in a predefined position such that the first laser beam and the second laser beam are projected into the reference cell 205 and the test cell 206 respectively. The reference ceil 205 is mounted on a stand under the LM1 204a in a direction perpendicular to the fi rst laser beam. The sides of the reference cell 205 are tapered at 21 ^° angle to prevent the reflections from the surface of the reference cell 205 from superposing onto the first laser beam. Likewise, the test cell 206 is mounted on a stand under the LM2 204b in a direction perpendicular to the second laser beam. The sides of the test cell 206 are tapered at 21 ^° angle to prevent the reflections from the surface of the test cell 206 from superposing onto the second laser beam.

Silica gel particle (of measured mass 4.9-5.1 mg size and 2mm diameter) is placed in the test cell 206 at a predefined distance from a dotted line (as illustrated in the test ceil 206 of Figure 2). Water drop of predefined size is introduced into the test cell 206 and placed at a distance equal to three times the diameter (3d) of silica gel. The test cell 206 is now flashed with dry air thus, humidifying the test cell 206. The test ceil 206 now contains water vapour. The water vapour gets adsorbed on the surface of silica gel particle 105.

The first laser beam is passed through the reference cell 205 containing dry air and the output intensity of the first laser beam is measured by the PD1 106a. The output of the PD1 106a is referred to as a reference signal. The second laser beam is passed through the test cell

206 containing water vapour. The output intensity of the second laser beam is measured by the PD2 106b. Tire output of the PD2 106b is referred to as the output signal. The output signal is normalized with the help of the reference signal to obtain a final signal. The final signal is processed by the controlling device 101 to determ ine an absorbance curve and hence a Full Width Half Maximum (FWHM) of the absorbance curve. The FWHM is equivalent to the absorbance of tire final signal. The absorbance indicates the amount of water vapour adsorbed by the silica gel particle . FWHM value is then converted to concentration of water vapour using the calibration curve as illustrated in Figure 5. The absorption spectroscopy system 100 as explained above may be used in one of applications, but not limited to innovative hybrid cooling system for air conditioning, heat pump systems, medical diagnostics, material removing, water purification, C02 capture, Gas dryer, Chemical capture, Hydrogen storage, oral delivery' system of liquid-based nanoparticles, and drag deliver} _' in biomedical applications

Hie calibration curve as illustrated Figure S is a plot of partial pressure of water [kPa] versus average FWHM. The partial pressure of water is equivalent to concentration of water. Calibration curve is a standard curve used for detennining the concentration of water, for a known FWHM. The FWHM values obtained are converted into water vapour concentration using the calibration curve . Thus, obtaining the wate r vapour concentration along a laser path. The system is capable of dynamic measurements at various flow conditions that are relevant to real life systems where flow' of water vapor is always present.

At every instance of using the TOLAS system 100, tire controlling device 101 generates the absorption curve and determines the FWHM of the absorption curve. Further, the controlling device 101 correlates the FWHM with the corresponding partial pressure value using the calibration curve illustrated in the Figure 5.

In an embodiment, dry air may be introduced over the water drop placed in the test cell 206, at different Reynolds number. Reynolds number defines the flow' rate of dry' air in the given instance. Evaporation of the water droplet in the test cell 206 is based on the Reynolds number. For an instance, with a low* Reynolds number the water droplet evaporation may take place at a low rate. Whereas with a high Reynolds number the wnter droplet evaporation may take place at a high rate Reynolds number may be denoted as Re in the present disclosure.

Figure 3 shows flowchart illustrating a method 30Q of determining concentration of adsorbate over adsorbent, in accordance with an embodiment of the present disclosure.

At a‘ ^‘ Generate a laser beam” block 302, the laser beam is generated by a laser. The laser beam emitted by the laser 102 may be tunable i .e., emission wavelength intensity and other parameters of the laser 102 may be tuned as requi red.

At a“Pass the laser beam tangential to a surface of adsorbent” block 3Q4, the generated laser beam is passed through the medium 103 such that the laser beam is tangential to a surface of adsorbent 105. In one embodiment, the medium 103 comprises the adsorbate 104 and the adsorbent 105 The medium 103 may he a gaseous medium or a liquid medium. The adsorbate 104 may be any substance that is capable of being adsorbed or accumulated on the surface of the adsorbent 105.

At a‘ ^‘ Detect and Process laser beam projected out of medium ^’ ’ block 306, the laser beam projected out of the medium 103 is detected by the photo detector 106 and the detected laser beam is processed to produce an output signal. The photo detector 106 senses light intensity of the resulting laser beam. The photo detector 106 may have a p -n junction that converts light photons into current. The photo detector 106 may be one of a photo diode or a photo transistor. The photo detector 106 detects intensity of the resulting laser beam, once the laser beam has passed through the medium 103. Further, the photo detector 106 produces an output signal corresponding to the intensity of the resulting laser beam.

At a“Determine concentration of adsorbate around adsorbent” block 308, the concentration of adsorbate around the adsorbent is detemiined based on output signal.

Figure 4 shows a diagram indicating the different locations of concentrating the laser beam for studying the adsorption kinetics of the adsorbent and adsorbate pair. The Figure 4 illustrates 5 locations around the adsorbent 105, at which the laser beam can be directed in order to determine the water vapour concentration at the respective location. A first location 401 may be present at a distance of 4mm from the adsorbent 105, a second location 402 may be at a distance of 2mm from the adsorbent 105, a third location 403, a fourth location 404 and a fifth location 405 are present on different locations on the surface of the adsorbent 105 which is tangential to the adsorbent 105. For example, the third, location 403, the fourth location 404, and the fifth location 405 may be as shown in the Figure 4. The above-mentioned experiment may be carried out at each of the locations illustrated in the Figure 4 to determine the concentration of water vapour and thickness of the concentration at the respective location. In one em bodiment, the system is capable to m onitor the concentration at various spatial locations using a single laser.

In one embodiment the distant from the adsorbent were the laser beam is pointed varies based on adsorbent and adsorbate . The distance indicated in the Figure 4 for point 401 and 402 is an example and should not be consider as lim itation. Further, number of points observed away from the adsorbent is not limited. It can be varied as per the requirement and understanding by a person skilled in the art.

In an embodiment, water vapor adsorption kinetics by silica gel may be described by use of Langmuir equation. Tire Langmuir equation provides flux of water vapor at the surface silica gel based on partial pressure, temperature of water vapor around silica gel and initial uptake of silica gel.

The results of the above experiment have been illustrated in Figure 6a, Figure 6b, Figure 7, Figure 8a, Figure 8b, Figure 9a and Figure 9b.

Figure 6a illustrates uptake (amount of water vapour adsorbed against time) for Re=0 and single silica gel particle.

Figure 6b illustrates uptake (am ount of water vapour adsorbed against time) for Re=0 and array of silica gel particles.

Figure 7 illustrates uptake (amount of water vapour adsorbed against time) for Re=T and single silica gel particle.

Figure 8a illustrates radial water vapour pressure variation against time for Re ^: =0 and array of silica gel particles.

Figure 8b illustrates azimuthal water vapour pressure variation against time for Rc 0 and array of silica gel particles.

Figure 9a illustrates radial water vapour pressure variation against time for Re=l and array of silica gel particles.

Figure 9b illustrates azimuthal water vapour pressure variation against time for Re=l and array of silica gel particles. The TOLAS system 100 allows studying of key aspects of adsorption kinetics such as adsorbate concentration around the adsorbent 105, adsorption rate at different pressure, temperature and concentration of the adsorbate 104.

The TOLAS system 100 allows studying of adsorption kinetics of the adsorbent and adsorbate pair in a known flow-field and tire measurements carried out are non-invasive, fast and accurate as it involves laser to measure the adsorption kinetics unlike the prior arts which utilize bulk measurement.

The TOLAS system 100 can he easily modified to create different adsorption environment such as low speed, high speed flow of adsorbate 104, different configurations of adsorbent 105, different geometric shape of adsorbent 104 (powder, particle, liquid).

The TOLAS system 100 allows measurement of adsorption kinetics at different locations around the adsorbent.

A description of an embodiment with several components in comm unication with each other does not imply that all such components are required. On the contrary, a variety of optional components are described to illustrate the wide variety of possible embodiments of tire invention.

When a single device or article is described herein, it will be readily apparent that more than one device/article (whether or not they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be readily apparent that a single device/article may be used in place of the more than one device or article or a different number of devices/articles may be used instead of the shown number of devices or programs. The functionality and/or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality/features. Thus, other embodiments of the invention need not include the device itself

Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this description.

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