Experimental Investigation on the Absorption Enhancement of CO2 by

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Experimental investigation on the absorption enhancement of CO2 by various nanofluids in hollow fiber membrane contactors Arman Peyravi, Peyman Keshavarz, and Dariush Mowla Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.5b01956 • Publication Date (Web): 29 Oct 2015 Downloaded from http://pubs.acs.org on October 31, 2015

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Experimental investigation on the absorption enhancement of CO2 by various nanofluids in hollow fiber membrane contactors Arman Peyravi a, Peyman Keshavarz a*, Darioush Mowla a a

Department of Chemical Engineering, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz, Iran

ABSTRACT In this work, suspensions of Fe3O4, CNT, SiO2, and Al2O3 nanoparticles in distilled water are produced and tested as new absorbents in a gas-liquid hollow fiber membrane contactor to investigate the effect of nanoparticles on the rate of mass transfer during CO 2 absorption. For this purpose a pilot-scaled hollow fiber membrane contactor was constructed. A gas mixture was passed through the shell-side and the nanofluid flowed co-currently through the lumen side of the fibers. The effects of different operating conditions including gas flow rate, liquid flow rate, inlet CO2 concentration, and nanoparticle concentration on the CO 2 absorption have been studied. The results showed that among operating parameters, liquid flow rate and nano-particle concentration had the greatest effects on the CO2 absorption. Moreover, UV-Vis spectroscopy and DLS method were employed to explore the dispersion stability and hydrodynamic diameter of nanoparticles in the base fluid. The results revealed that nanofluid stability and hydrodynamic diameter of nanoparticles in the base fluid are the key factors in nanoparticle selection for CO 2 absorption in membrane contactor. The obtained results showed that the highest absorption rate enhancements for nanofluids are 43.8% at 0.15wt% Fe3O4, 38.0% at 0.1wt% CNT, 25.9% at 0.05wt% SiO 2, and 3.0% at 0.05wt% Al2O 3 compared with the absorption rate by base fluid.

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1. INTRODUCTION The issue of global warming caused by increased concentrations of greenhouse gases such as CO2 has become a global environmental problem. Each year billions tons of carbon dioxide have been released into the atmosphere as an inevitable byproduct of fossil-fuel combustion. Therefore, the capture and storage of CO2 are of vital importance. Conventional CO2 separation methods including packed towers, spray towers, venture scrubbers and bubble columns, pressure swing adsorption and cryogenic processes separate CO2 by direct contact of two phases. The phase dispersion which occurs during the process frequently causes difficulties such as flooding, weeping, excessive loading, foaming and entrainment. In addition, traditional CO2 absorption methods usually involve complex equipment and high energy consumption. As an alternative, membrane technology with suitable features such as its energy efficiency, straightforward scaleup, simple process design and compact equipment has attracted the attention of scientists in CO2 separation 1, 2. One of the most popular subsets of membrane separation technology is the use of hollow fiber membrane contactors (HFMC) as a gas–liquid contactor. In HFMC, interfacial area between the two phases is constant and well defined. Liquid fluid flow through the fiber is usually laminar, thus the liquid side hydrodynamics are well known. Therefore, calculation of the fiber side mass transfer coefficient from basic principles is easily possible 3. In HFMC, gas–liquid contact time can be changed independently and easily without any change in the interfacial area. Therefore, the HFMC with these features is a very suitable device for CO 2 separation from gas mixtures. Qi and Cussler

4

were the first to use HFMC for CO2 removal. Following their investigation,

the application of HFMC for CO2 separation has been studied widely5-10 . Mansourizadeh and Ismail

11

did a comprehensive review about acid gas capture by HFMC. In the membrane


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contactors, the membrane works only as a barrier between the liquid and the gas phases, and it is usually a non-selective layer. The selectivity is applied only by the absorbents which absorb selected components from gas phase based on solubility or chemical reaction. Gas diffuses through the membrane pores to the gas-liquid interface and it is absorbed by liquid absorbents on the other side. Therefore, the selection of suitable absorbents in the membrane gas separation process is very important. Some criteria in selection of liquid absorbent should be considered including absorption capability and regeneration performance towards CO 2 and the physicochemical parameters containing the surface tension, viscosity and good chemical compatibility with membrane materials. In selecting the absorbent in the membrane separation process, the chemical compatibility with membrane materials is a key factor

12

. One of the

absorbent solutions that has these criteria and has recently been developed for enhancing gas absorption is nanofluid. Nanofluids, prepared by dispersing nanoparticles in a base fluid such as water, have been found to improve heat and mass transfer performance of solutions. Kars et al.

13

studied the

absorption process of propane in slurries with activated carbon in water and explained the mechanism of the improvement of the absorption rate. Alper et al.

14

studied the oxygen

absorption in a slurry of activated carbon in water and found that the oxygen absorption rate was increased three times. Krishnamurthy et al.

15

studied the mass diffusion of fluorescein dye in a

water-based nanofluid containing 20 nm Al2 O3 nanoparticles and reported that the diffusion coefficient in the nanofluid is about 13 times higher than that in water without nanoparticles. Olle et al.

16

used functional magnetic nanoparticles to enhance oxygen mass transfer and found

that oxygen mass transfer increased up to 6-fold by the water based Fe3O 4 nanofluid. Sumin et al.

17

experimentally investigated the effects of spherical nano-Al2O3 and CNT(Carbon Nano

Tube) on CO2 absorption by applying a stirred thermostatic reactor and compared the 3 ACS Paragon Plus Environment

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experimental results with that of micron-size Al 2O3 and activated carbon (AC) particles. They found no enhancement by micron size Al2O3 and weak enhancement by nano-Al2O3 for the CO2 absorption, while AC and CNT particles increased the gas-liquid mass transfer effectively. Lee and Kang

18

studied CO2 absorption process in Al2O3/NaCl aqueous solution of nanofluid by a

bubble type absorber system. They found that the CO2 absorption is enhanced to 11.0%, 12.5% and 8.7% at 30oC, 20oC and 10oC, respectively. They attributed these enhancements to the positive effects of nanoparticles on the hydrodynamic parameters, especially smaller bubble formation in their bubble absorber. Pang et al. 19 did a comprehensive review about mass transfer characteristics in nanofluids. Two prominent mechanisms have been proposed in the literature for mass transfer enhancement in nanofluids: (1) Brownian motion of nanoparticles 15, 20. Nanometer particles can cause micro-convection in the nanofluid that promotes the mass diffusion in the nanofluid. (2) Grazing effect of nanoparticles13, 14, 21, 22. The particles in the nanofluid adsorb the absorbing gas in the gas-liquid interface, and then rapidly transfer the adsorbates into the liquid bulk. In recent years, a number of investigations on nanofluid properties have shown a significant mass transfer enhancement of nanofluids23-27. However, inconsistency in the results of these studies and the lack of reliable mechanisms to explain these conflicting results show that more research is required to clarify the effect of nanoparticles on mass transfer in each application. The objectives of this paper were to further experimentally investigate the enhancement of CO2 absorption with the use of aqueous Fe3O4, CNT, SiO2, and Al2O3 nanofluids in a hollow fiber membrane contactor. For this purpose a pilot-scaled hollow fiber membrane contactor was constructed. Different operating conditions were tested including gas flow rate, liquid flow rate, inlet CO2 concentration and nanoparticle concentration, and the effects of these conditions on the mass transfer enhancement were analyzed. Moreover, dispersion stability and the hydrodynamic 4 ACS Paragon Plus Environment

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diameter of nanoparticles were studied using UV-Vis spectroscopy and DLS (Dynamic Light Scattering) method as the key parameters that influence the CO 2 absorption in HFMC. The enhancement ratio was defined and calculated to examine the effectiveness of the nanofluids.

2. EXPERIMENTAL SECTION 2.1. Materials The employed nanoparticles of alumina, silica and carbon nanotube were supplied by Neutrino Nanotechnology Co. Also, a magnetite nanoparticle was used in this work, that was prepared in our laboratory using a modified co-precipitation method by sodium dodecyl benzene sulfonate (SDBS) as surfactant

28

. The characterization of these nanoparticles can be seen in Table 1. To

study the CO 2 absorption performance of nanofluids, a cylindrical polypropylene hollow fiber membrane module (from Parsian Poya Polymer Co) was used. The specifications of membrane module are shown in Table 2. 2.2. Preparation of Nanofluids Nanofluids were prepared by dispersing the specified amounts of nanoparticles with weight percentage of 0.05%, 0.1%, 0.15%, and 0.2% in distilled water as base fluid. The nanoparticles were stabilized into the base fluid by using an ultrasonic agitator. Suspension was sonicated for 1h in probe type sonicator (Tomy, ModelNo. UD-201, Japan). It is worth mentioning that in stabilization of nanoparticles, no surfactant was used to prevent their effects on CO2 absorption. Moreover, surfactants decrease the surface tension of the base fluid which may cause wetting phenomena in the membrane 29 .


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Ultraviolet–Visible (UV–Vis) spectroscopy was used in the current study to explore the dispersion and stability of nanoparticles in an aqueous solution. UV–Vis spectrometry was applied to recognize the effect of nanoparticle concentrations on stability of nanofluid. 2.3. Apparatus Figure 1 shows a schematic diagram of the employed experimental apparatus for CO 2 absorption process. A gas mixture containing CO2 and air with various volume ratios was selected as the feed gas. The feed gas was fed into the system from compressed gas cylinders and the flow rate was adjusted by a flow controller which can precisely control the gas flow rate. Then the gas was interred into the static mixer where the mixtures can be mixed homogeneously. The feed gas flowed through the shell side of the hollow fibers, and its pressure was set at a constant value of 0.3 bar by a backpressure controller. Two pressure gauges measured the gas pressures at the inlet and outlet of the membrane module. The inlet and outlet gas compositions were analyzed by CO 2 analyzer (Testo 535). Distilled water with a specified amount of nanoparticle was chosen as liquid absorbent. Liquid was pumped using a stainless steel centrifugal pump through the lumen side of the hollow fibers. The flow rate of liquid was controlled by a flow controller. The gas phase and liquid phase flowed co-currently through the module. Experimental conditions are listed in Table 3. 2.4. Data reduction Equations (1) and (2) have been used to calculate the values of CO2 mass transfer rate ( removal efficiency

) and

of nanofluids with obtained experimental data.

(1)


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( where

)

(

)

(2)

represents the CO2 removal efficiency of nanofluids, (in percent);

transfer rate, mol/(m2.h); m3/h;

and

respectively;

and

is the CO2 mass

denote the inlet and outlet gas flow rates, respectively,

are the inlet and outlet CO 2 volumetric flow rates in the gas phase, is the gas temperature, K and

denotes the gas-liquid mass transfer area, m2 .

In order to quantify the effect of nanoparticles on the absorption rate of CO 2 in the nanofluids, the enhancement factor (

) is defined as the ratio of the absorption rate of the nanofluids to that

of the base fluid, which is obtained by Eq. (3). (3)

where,

and

are the CO2 absorption rates for the nanofluids and the base fluid,

respectively. 2.5. Experimental error analysis In this work, all experiments repeated for at least 3 times to ensure the validity of data. The experimental errors in the measurement of gas flow rate, CO 2 concentration, and temperature are estimated as 2.6%, 0.55%, and 4.4% respectively. Uncertainty of CO 2 mass transfer rate (

)

can be calculated by the following equation, recommended by Holman 30:

{( (

) [(

)

(

) ]

(

) [(

)

(

) ]

) }


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where

and

respectively, respectively, and

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are errors in measurements of CO2 concentration of inlet and outlet gas and

are errors in measurements of inlet and outlet gas flow rates is the error in measurements of temperature. Maximum calculated

uncertainty in mass transfer rate is 4.71% using the above equation.

3. RESULTS AND DISCUSSION 3.1. Effect of inlet gas flow for different nanofluids Inlet gas flow rate is one of the most important process parameters in gas separation operations. Figures 2 and 3 show the effect of gas flow rate on the CO 2 mass transfer rate and CO2 removal efficiency for distilled water and aqueous based Fe3O 4, CNT, SiO 2 and Al2 O3 nanofluids. The results show that increasing the gas flow rate without considering the type of nanofluid causes increasing in the mass transfer rate and decreasing the CO 2 removal. The increasing in mass transfer rate is due to the increase in CO2 concentration at the gas-liquid interface when the gas retention time decreases. Also, the decrease in CO2 removal efficiency is a result of reduction in the retention time of gas in HFMC. The results also show that Fe3O4 , CNT, and SiO2 nanofluids cause an increase in the absorption rate better than the distilled water up to 41%, 39%, and 22%, respectively. On the other hand, separation of CO2 by Al2O3 nanofluid is about 4% lower than the separation by distilled water. These observations can be seen in Figure 4 based on enhancement factor, which will be analyzed in the next sections. 3.2. Effect of nanofluids flow rate on CO 2 removal efficiency Figures 5 and 6 demonstrate the variation of mass transfer rate and CO 2 removal efficiency with liquid flow rate using distilled water and nanofluids of Fe3O4, CNT, SiO2 , and Al2O3 as 8 ACS Paragon Plus Environment

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absorbents, respectively. The results show that CO 2 mass transfer rate and CO2 removal efficiency are increased when liquid flow rate for all absorbents are increased . The liquid phase boundary layer decreases by increasing the liquid flow rate, which results in growing of CO2 diffusion into the absorbents. Therefore, the gas-liquid interface could be maintained at a fresh absorbent, which enhances the CO 2 removal efficiency. Figures 5 and 6 also show that Fe3 O4, CNT and SiO2 nanofluids give higher fluxes and higher removal efficiencies compared to distilled water, while Al2O3 nanofluid decreases CO2 mole flux and removal efficiency about 6% compared to distilled water. As shown in Figure 7, the CO2 absorption enhancement factor decreases with increasing the flow rates of Fe3O 4, CNT, and SiO2 nanofluids. The reason behind this effect might be attributed to higher Reynolds in the liquid phase at higher liquid velocities that can decrease the mass transfer resistance and it can overlap the micro convection and adsorption effects of nanoparticles. Therefore, the positive influence of nanoparticles in enhancing the CO 2 absorption could be covered by decreasing the mass transfer resistance of liquid phase. On the other hand, Figure 7 shows that Al2O3 nanofluid has a relatively fixed negative effect on the CO 2 absorption rate in all flow rates. 3.3. Effect of inlet CO2 concentration on CO2 removal efficiency In general, the CO2 concentration in flue gas is a key factor for process selection. Changes in the CO2 content of feed gas directly affect the absorption performance. Power plants and other industrial processes that produce flue gases are usually at atmospheric pressure with low CO 2 partial pressure, and it contains oxygen, nitrogen and other impurities. Therefore solvents have to be carefully selected to have a low desorption energy requirement and a high capacity to absorb CO2. Therefore, in this study, different gas mixtures with low CO2 concentration were applied.


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Figures 8 and 9 demonstrate the variation of CO 2 mass transfer rate and removal efficiency against inlet concentration of CO2. As the inlet concentration of CO 2 rises, the CO2 concentration gradient at the liquid-gas boundary layer increases. Therefore, the CO 2 driving force of mass transfer in the gas is enhanced, which leads to an increase in the CO 2 mass transfer rate. However, CO2 removal efficiency is approximately constant, since inlet concentration of CO 2 (Cin) appears in both numerator and denominator of equation (1). Figure 10 shows the enhancement factor for each nanofluid verses CO 2 inlet concentration. It is found that the enhancement factor is approximately constant with increasing the CO 2 inlet concentration. It means that in this range of CO2 inlet concentrations, each nanofluid has a fixed effect on the absorption rate. 3.4. Effect of nanoparticle concentration on CO 2 removal efficiency The effects of nanoparticle concentrations of Fe3O4 , CNT, SiO2 , and Al2O3 have been investigated in this section. As shown in Figures 11 and 12, mass transfer rate and enhancement factor of Fe3O4 and CNT nanofluids have been increased with increasing the nanoparticle concentration to a maximum value and then decreased. Therefore, there was an optimum nanoparticle concentration for CO2 absorption by these nanofluids. On the other hand, both absorption rate and enhancement factor of Al2O 3 and SiO2 nanoparticles will decrease continuously by increasing the concentration. The highest absorption rate enhancements for different nanofluids are observed to be 43.8% at 0.15wt% Fe3O4 , 38.0% at 0.1wt% CNT, 25.9% at 0.05wt% SiO2 and 3.0% at 0.05wt%Al2O3. As mentioned earlier, Shuttle effect and Brownian motion of nanoparticles are two prominent mechanisms that explain the mass transfer enhancement in the nanofluids. An increase in the nanoparticle concentration is expected to increase both shuttle effect and micro convections that lead to enhanced mass transfer rate.


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However, nanoparticle concentration can also affect the nanofluid stability and size of nanoparticles in the base fluid

31

. In addition, stability and nanoparticle diameter have direct

influences on the shuttle effect and Brownian motion according to Stokes-Einstein equation. Nanoparticle diameter can have a significant rule in HFMC, since nanoparticles can block the membrane pores if nanoparticle diameter is greater than membrane pore. This effect can dramatically reduce the absorption efficiency of HFMC. Therefore, in this study, UV–vis spectrophotometric measurements have been used to quantitatively characterize colloidal stability of the dispersions, and dynamic light scattering (DLS) method has been used to determine the nanoparticle diameters in nanofluid. These results have been reported in the next sections. While these results generally show positive effects of these particles on absorption performance, it is still difficult to judge about the large scale applications, and more studies are required in this field. For example, the effects of nanoparticles in the presence of a chemical absorbent is still questionable. 3.5. Dispersion stabilization To determine the stability of nanofluids, the proper amounts of nanoparticle were added to 100 ml distilled water to obtain 0.1 wt % and 0.2 wt % nanofluids. The suspensions were stirred for 20 min using a magnetic stirrer and subjected to the following treatment in an ultrasonic agitator for 60 min. Sample preparation process was the same for all nanofluids used in this study. The dispersion stability of nanofluids was evaluated by the absorbance of suspension using a model Genesys 10UV UV-Visible spectrometer. Suspensions were scanned in UV regions between 190 to 790 nm, and then the maximum absorption was measured at the specific wave length. The amount of absorbance is proportional to the amount of the particles per unit volume; therefore calibration curve was plotted by using the absorbance and concentrations. To determine the


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stability of nanofluids, the absorption of suspension was recorded in each hour and the concentration was determined by calibration curve. Decrease in the concentration of nanoparticle in suspension shows that sedimentation occurs in the sample, so the stability of the particles in the suspension can be denoted. Figures 13 and 14 show the colloidal stability of nanofluids. These graphs display the particle concentration in the base fluid against time. It is shown that Fe3O4 , CNT and SiO2 nanofluids are very stable. After 12 h, their relative concentration is maintained over 80% compared with the initial concentration. However, Al2O3 nanofluid has poor stability and it sediments a few hours after dispersion. Figures 13 and 14 demonstrate that an increase in the concentration of Fe3O4 , CNT and SiO2 has no effect on their stability in the base fluid. However, in case of Al 2O3, increase in the nanoparticle concentration has a considerable influence on dispersion stability. 3.6. Hydrodynamic diameter Dynamic light spectroscopy is a measurement that delivers information of nanoparticles size distribution. Although DLS method is suitable to determine the diameter of sphere shape particles, it can still provide hydrodynamic diameter for nanotubes

32

; therefore, in this study

DLS method is used to determine the hydrodynamic diameter of Fe 3O 4, CNT, SiO2 , and Al2O3 nanoparticle in nanofluid. Figure 15 illustrates the particle concentration effects on the hydrodynamic diameter of nanoparticles in the base fluid. All nanoparticles show concentration dependency as their hydrodynamic diameter increases with the concentration increment. The results show that Fe3O4 and CNT have smaller hydrodynamic diameter and lower concentration dependency, while SiO2 and Al2O3 have larger particle sizes in most concentrations. It reveals that the hydrodynamic diameters of Al2O 3 and SiO2 have strong dependency on particle concentration.


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The results of Figures 13-15 can be used to explain the trends of Figures 11 and 12. Al2O3 has the highest particle size in its nanofluid, and it also has very low stability. Its hydrodynamic diameter in nanofluid is so high that it can block the membrane pores. Therefore, its flux is lower than other nanofluids and even lower than pure water. SiO2 has a relatively good stability with time (Figures 13 and 14), however, its hydrodynamic diameter increases relatively sharply with increasing the concentration based on Figure 15. A higher hydrodynamic diameter means lower micro-convection and shuttle effects. The best stability is shown for Fe3 O4 and CNT and they also have the smallest hydrodynamic diameters. These nanofluids have an optimum concentration, since higher concentration gives higher adsorption (or shuttle effect), while it also causes higher hydrodynamic diameter, which decreases micro-convections and pore blocking. 3.7. Effects of Adsorption capacity of particles Table 4 demonstrates the adsorption capacity of Al 2O3 , CNT, Fe3O4 and SiO2 in dry condition. It should be noted that these data are typical and other data might be found in other references33-36. The reported results show that the adsorption performances of these adsorbents in dry basis are different and the order of their adsorption performance is as follows: CNT > Fe3O4

SiO2

Al2 O3. These data reveals that one reason for higher absorption performance of CNT can be its higher adsorption capacity. However, this table also shows that the adsorption capacity of these solids might not be the most important factor for absorption performance of nanofluids, for example compared to hydrodynamic effects.


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4. CONCLUSIONS Experimental study has been carried out to investigate the effect of nanoparticles on the mass transfer during the absorption of CO2 by the aqueous based nanofluid in a HFMC. The effect of gas/liquid flow rates, CO2 inlet concentration and nanoparticle concentration in the base fluid were studied. Moreover, the rule of stability and hydrodynamic diameter of nanoparticles in CO 2 absorption of nanofluid in the hollow fiber membrane were examined. The following results are drawn from this study. 1) It is concluded that the gas flow rate has no significant effect on the enhancement factor of nanofluids in the membrane contactor. However, increase in the liquid flow rate causes decrease in the enhancement factor of nanofluids as a result of reducing the mass transfer resistance at high liquid rates. 2) The results showed that the increase in CO 2 inlet concentration causes an increase in the mass transfer rate. However, it has no important effect on recovery and enhancement factor in our HFMC. 3) It is found that the nanoparticle concentration has an important role on the enhancement factor of nanofluids in hollow fiber membrane contactor. An increase in the nanoparticle concentration causes increasing the micro convection and shuttle effect of nanoparticles in the base fluid. On the other hand, it increases nanoparticle hydrodynamic diameter and decreases the nanofluid stability that affects the CO2 absorption performance of nanofluids and, in extreme conditions, can block the membrane pores. Therefore, there is an optimum concentration for each nanoparticle in the CO 2 absorption process by hollow fiber membrane contactor.


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4) The obtained results showed that the absorption performance of nanofluids in the HFMC are different and the order of their absorption performance is as follows: Fe3O4 > CNT > SiO2 >Al2O3

AUTHOR INFORMATION * Corresponding Author Peyman Keshavarz Department of Chemical Engineering, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz, Iran E-mail: [email protected] ; Tel.: +987136133713; Fax: +987136473180


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absorption enhancement by nano-Al2O3 and carbon nanotube particles. Chinese Journal of Chemical Engineering 2013, 21, (9), 983-990. (18)

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characteristics in nanofluids. International Journal of Thermal Sciences 2015, 87, 49-67. 17 ACS Paragon Plus Environment

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Ma, X.; Su, F.; Chen, J.; Bai, T.; Han, Z., Enhancement of bubble absorption process

using a CNTs-ammonia binary nanofluid. International Communications in Heat and Mass Transfer 2009, 36, (7), 657-660. (21)

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stirred reactors: influence of carbon particles and electrolyte. Chemical Engineering Science 2003, 58, (20), 4719-4728. (22)

Golkhar, A.; Keshavarz, P.; Mowla, D., Investigation of CO2 removal by silica and CNT

nanofluids in microporous hollow fiber membrane contactors. Journal of Membrane Science 2013, 433, 17-24. (23)

Kim, J. H.; Jung, C. W.; Kang, Y. T., Mass transfer enhancement during CO2 absorption

process in methanol/Al 2O3 nanofluids. International Journal of Heat and Mass Transfer 2014, 76, 484-491. (24)

Komati, S.; Suresh, A. K., Anomalous enhancement of interphase transport rates by

nanoparticles: Effect of magnetic iron oxide on gas− liquid mass transfer. Industrial & Engineering Chemistry Research 2009, 49, (1), 390-405. (25)

Lee, J. W.; Jung, J.-Y.; Lee, S.-G.; Kang, Y. T., CO2 bubble absorption enhancement in

methanol-based nanofluids. international journal of refrigeration 2011, 34, (8), 1727-1733. (26)

Pineda, I. T.; Choi, C. K.; Kang, Y. T., CO2 gas absorption by CH3OH based nanofluids

in an annular contactor at low rotational speeds. International Journal of Greenhouse Gas Control 2014, 23, 105-112. (27)

Samadi, Z.; Haghshenasfard, M.; Moheb, A., CO2 Absorption Using Nanofluids in a

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characterization of superparamagnetic Fe3O4 nanoparticles. Journal of Alloys and Compounds 2011, 509, (37), 9093-9097. (29)

Keshavarz, P.; Fathikalajahi, J.; Ayatollahi, S., Analysis of CO2 separation and simulation

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large anthropogenic point sources. ChemSusChem 2009, 2, (9), 796-854.


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Energy & Fuels

Table captions: Table 1. Nanoparticles Characterization Table 2. Specification of the membrane module Table 3. Experimental conditions. Table 4. Adsorption capacity of different dry particles

Table 1. Nanoparticles Characterization Name

Magnetite

Carbon nanotube

Alumina

Silica

Chemical formula

Fe3O4

-

γ-Al2O3

SiO2

Color

Black

Black

White

White

Spherical

Tubular

Spherical

Spherical

4

*

20

15

Morphology Average particle size, nm *

Outside diameter: 8 nm, Inside diameter: 2-5 nm, Length: 10 𝜇m

Table 2. Specification of the membrane module Kind

Poly propylene

Configuration

Hollow fiber

Number of fiber

400

Length of fiber, m

0.4

Fiber outer diameter, mm

0.45

Fiber inner diameter, mm

0.32

Average pore size, nm

100~150

Membrane contact area, m2

0.16

Module inner diameter, cm

2


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 31

Table 3. Experimental conditions. Test section pressure (bar)

0.3

o

Temperature ( k)

303

Base fluid

Distilled water

Nano particles

Fe3O4, CNT, SiO2, Al2O3

Inlet CO2 Concentration (ppm)

2000~10000

Nano particle concentration (wt%)

0.05, 0.10, 0.15, 0.20

Liquid flow rates (l/h)

5~24

Gas flow rates (l/h)

6~30

Table 4. Adsorption capacity of different dry particles Particle type Al2O3

Adsorption Capacity (mmol/g) (1bar & 25oC) 0.55

Reference (33)

Fe3O4

0.65

(34)

CNT

1.57

(35)

SiO2

0.56

(36)


Page 23 of 31

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Energy & Fuels

Figure captions: Figure 1 The schematic diagram of the experimental apparatus. Figure 2. Mole Flux Variation with Gas Flow Rate (Qliquid: 7 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar) Figure 3. CO2 Removal Variation with Gas Flow Rate (Qliquid: 7 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar) Figure 4. Enhancement Factor Variation with Gas Flow Rate (Qliquid: 7 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar) Figure 5. Mole Flux Variation with Gas Flow Rate (QGas: 16 l/h, C iCO2: 9900 ppm, T: 303 K, P: 0.3 Bar ) Figure 6. CO2 Removal Variation with Liquid Flow Rate (QGas: 16 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar) Figure 7. Enhancement Factor Variation with Liquid Flow Rate (QGas: 16 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar) Figure 8. Mole Flux Variation with inlet CO 2 concentration (QGas: 16 l/h, Q Liquid: 7 l/h, T: 303 K, P: 0.3 Bar) Figure 9. CO 2 Removal Variation with inlet CO2 concentration (QGas: 16 l/h, Q Liquid: 7 l/h, T: 303 K, P: 0.3 Bar) Figure 10. Enhancement Factor Variation with inlet CO 2 concentration (QGas: 16 l/h, Q Liquid: 7 l/h, T: 303 K, P: 0.3 Bar) Figure 11. Influence of nanoparticle concentration on the CO 2 absorption rate (Q Liquid : 7 l/h, QGas: 16 l/h, CiCO2: 9000 ppm, T: 303 K, P: 0.3 Bar) Figure 12. Enhancement factor Variation with Nano particle Concentration (Q Liquid: 7 l/h, QGas: 16 l/h, CiCO2: 9000 ppm, T: 303 K, P: 0.3 Bar) Figure 13. Nano Particle Concentration Variation with Time (Initial Nano Particle Concentration: 0.1 wt%, Ultra-Sonic duration: 1 hour, T: 303 K) Figure 14. Nano Particle Concentration Variation with Time (Initial Nano Particle Concentration: 0.2 wt %, Ultra-Sonic duration: 1 hour, T: 303 K) Figure 15. Nano Particle Diameter Variation with Nano particle Concentration (Ultra-Sonic duration: 1 hour, T: 303 K)


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Page 24 of 31

6

5

14 4

11

9

3

8 1

13

2 7 12

15

10 Figure 1 The schematic diagram of the experimental apparatus. 1. CO2 cylinder; 2. Air cylinder; 3. Regulator; 4. Flow controller; 5. Static mixer; 6. Globe valve; 7. Needle valve; 8. Liquid flow meter; 9. Rotameter; 10. Pump; 11. Pressure gage; 12. Liquid tank; 13. Membrane contactor; 14. Gas analyzer; 15. Waste solvent tank


Page 25 of 31

0.014

JCO2 (mol/m2.h)

0.012 0.01 0.008

0.006

Distilled water 0.1% wt SiO2

0.004

0.1 %wt Fe3O4 0.1 %wt CNT

0.002

0.1 %wt Al2O3 0 0

5

10

15 20 Gas flow rate (l/h)

25

30

35

Figure 2. Mole Flux Variation with Gas Flow Rate (Qliquid: 7 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar)

60 Distilled water 50 CO2 Removal (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.1%wt SiO2 0.1%wt Fe3O4

40

0.1 %wt CNT

0.1 %wt Al2O3

30 20

10 0 0

5

10

15 20 Gas flow rate (l/h)

25

30

35

Figure 3. CO2 Removal Variation with Gas Flow Rate (Qliquid: 7 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar)


Energy & Fuels

1.6

Enhancment Factor

1.4 1.2 1 0.8 0.1 %wt SiO2

0.6

0.1 %wt Fe3O4 0.4

0.1 %wt CNT

0.2

0.1 %wt Al2O3

0 0

5

10

15 20 Gas Flow rate (l/h)

25

30

35

Figure 4. Enhancement Factor Variation with Gas Flow Rate (Qliquid: 7 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar)

0.016 0.014 0.012 JCO2 (mol/m2.h)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 31

0.01 0.008

Distilled water 0.006

0.1%wt SiO2 0.1%wt Fe3O4

0.004

0.1%wt CNT

0.002

0.1 %wt Al2O3

0

0

5

10 15 20 Liquid flow rate (l/h)

25

30

Figure 5. Mole Flux Variation with Liquid Flow Rate (QGas: 16 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar )


Page 27 of 31

40 35

CO2 Removal (%)

30 25 20

Distilled water

15

0.1 %wt SiO2 0.1 %wt Fe3O4

10

0.1 %wt CNT

0.1 %wt Al2O3

5 0 0

5


25

30

Figure 6. CO2 Removal Variation with Liquid Flow Rate (QGas: 16 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar)

1.6

1.4 Enhancment factor

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.2 1 0.8 0.1 %wt SiO2 0.6 0.1 %wt Fe3O4

0.4

0.1 %wt CNT

0.2

0.1 %wt Al2O3

0 0

5


25

30

Figure 7. Enhancement Factor Variation with Liquid Flow Rate ( QGas: 16 l/h, CiCO2: 9900 ppm, T: 303 K, P: 0.3 Bar )


Energy & Fuels

0.012

Distilled water 0.1 %wt SiO2

J CO2 (mol/m2.h)

0.01

0.1 %wt Fe3O4 0.1 %wt CNT

0.008

0.1 %wt Al2O3 0.006 0.004 0.002

0 0

2000

4000 6000 8000 CO2 Inlet concentration (ppm)

10000

Figure 8. Mole Flux Variation with inlet CO2 concentration ( QGas: 16 l/h, QLiquid: 7 l/h, T: 303 K, P: 0.3 Bar )

40

35 30 CO2 Removal (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 31

25 20 Distilled water 0.1%wt SiO2 0.1%wt Fe3O4 0.1%wt CNT 0.1 %wt Al2O3

15 10 5

0 0

2000


10000

Figure 9. CO2 Removal Variation with inlet CO2 concentration ( QGas: 16 l/h, QLiquid: 7 l/h, T: 303 K, P: 0.3 Bar)


Page 29 of 31

1.6 1.4 Enhancment Factor

1.2 1 0.8 0.1 %wt SiO2

0.6

0.1 %wt Fe3O4

0.4

0.1 %wt CNT 0.2

0.1 %wt Al2O3

0 0

2000


10000

12000

Figure 10. Enhancement Factor Variation with inlet CO2 concentration (QGas: 16 l/h, QLiquid: 7 l/h, T: 303 K, P: 0.3 Bar)

0.014

0.012 JCO2 (mol/m2.h)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.01 0.008 0.006

SiO2

0.004

Fe3O4

CNT

0.002

Al2O3 0 0

0.05 0.1 0.15 0.2 Nano Particle Concentration (wt%)

0.25

Figure 11. Influence of nanoparticle concentration on the CO2 absorption rate (QLiquid: 7 l/h, QGas: 16 l/h, CiCO2: 9000 ppm, T: 303 K, P: 0.3 Bar)


Energy & Fuels

1.6

Enhancment factor

1.4 1.2

1 0.8 SiO2

0.6

Fe3O4

0.4

CNT 0.2

Al2O3

0 0

0.05

0.1 0.15 0.2 Nano particle Concentration (wt%)

0.25

Figure 12. Enhancement factor Variation with Nano particle Concentration (QLiquid: 7 l/h, QGas: 16 l/h, CiCO2: 9000 ppm, T: 303 K, P: 0.3 Bar)

1.2 1 0.8 C/Ci

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 31

0.6 0.1 %wt Fe3O4 0.4

0.1 %wt CNT 0.1 %wt SiO2

0.2

0.1 %wt Al2O3

0 0

2

4

6 8 10 12 Time (h) Figure 13. Nano Particle Concentration Variation with Time (Initial Nano Particle Concentration: 0.1 wt %, Ultra-Sonic duration: 1 hour, T: 303 K)


Page 31 of 31

1.2

1

C/Ci

0.8 0.6 0.2 %wt Fe3O4 0.4

0.2 %wt CNT 0.2 %wt SiO2

0.2

0.2 %wt Al2O3

0 0

2

4

6 Time (h)

8

10

12

Figure 14. Nano Particle Concentration Variation with Time (Initial Nano Particle Concentration: 0.2 wt %, Ultra-Sonic duration: 1 hour, T: 303 K)

400

180

SiO2

160

Fe3O4

140

CNT

120

Al2O3

350 300

250

100

200

80

150

60

100

40

Al2O3 Diameter (nm)

200 Fe3O4, CNT, and SiO2 Diameter (nm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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50

20 0 0

0.05 0.1 0.15 0.2 Nano particle Concentration (wt%)

0 0.25

Figure 15. Nano Particle Diameter Variation with Nano particle Concentration (Ultra-Sonic duration: 1 hour, T: 303 K)


Experimental Investigation on the Absorption Enhancement of CO2 by

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