Preparation of amine functionalized UiO-66, mixing with aqueous N-Methyldiethanolamine and application on CO2 solubility

Accepted Manuscript Preparation of Amine Functionalized UiO-66, Mixing with Aqueous NMethyldiethanolamine and Application on CO2 Solubility Mehdi Vahidi, Ahmad Tavasoli, Ali Morad Rashidi PII:

S1875-5100(15)30290-0

DOI:

10.1016/j.jngse.2015.11.050

Reference:

JNGSE 1146

To appear in:

Journal of Natural Gas Science and Engineering

Received Date: 28 October 2015 Revised Date:

25 November 2015

Accepted Date: 26 November 2015

Please cite this article as: Vahidi, M., Tavasoli, A., Rashidi, A.M., Preparation of Amine Functionalized UiO-66, Mixing with Aqueous N- Methyldiethanolamine and Application on CO2 Solubility, Journal of Natural Gas Science & Engineering (2015), doi: 10.1016/j.jngse.2015.11.050. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Graphical Abstract

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Preparation of Amine Functionalized UiO-66, Mixing with Aqueous N- Methyldiethanolamine and Application on CO2 Solubility

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Mehdi Vahidia,b, Ahmad Tavasolia, Ali Morad Rashidib School of Chemistry, University College of Science, University of Tehran, Tehran 111554563, Iran

b

Nanotechnology Research Center, Research Institute of Petroleum Industry (R.I.P.I.), Tehran 14665-137, Iran

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a

ABSTRACT

In this research, UiO-66-NH2 was synthesized with solvothermal method and analyzed

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by XRD, SEM, BET, TGA and IR spectroscopy to understand its crystalline structure, morphology, thermal stability, and porous structure. Mass fraction of 0.1 % of UiO-66-NH2 added to aqueous solution of mass fraction of 40 % N-Methyldiethanolamine (MDEA). Measurement of zeta potential showed that UiO-66-NH2 particles are stable in aqueous mass fraction of 40 % MDEA. The solubility of carbon dioxide investigated in aqueous solution of mass fraction of 40 % MDEA and the prepared mixture of mass fraction of 0.1 % of UiO-66-

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NH2 nanofluid in aqueous solution of mass fraction of 40 % MDEA at temperatures of 303.15, 313.15, 323.15, and 333.15 K, and carbon dioxide pressures up to 2300 kPa. Results showed that addition of UiO-66-NH2 nanoparticles to the MDEA solution, increased capacity of CO2 absorption of solution up to 10 %. The solubility of CO2 increased with increasing

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partial pressure and decreased with increasing temperature for both systems.

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Keywords: Carbon Dioxide, MDEA, UiO-66-NH2, Nanofluid, Solubility

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1. Introduction Natural gas contains a variety of many undesirable components (such as acidic gases) and must be purified before use. Natural gas has to be purified from acidic gases such as Carbon dioxide because of reducing the heating value of gas, and it increases pumping costs.

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CO2 is also held responsible for the recent climate changes. Therefore, CO2 has to separate from gas streams. There are many ways to separation of CO2 from flue gases and natural gases. One technology used in the removal of carbon dioxide is the absorption-desorption process, in which solutions of alkanolamines are frequently used as solvents (Kohl and

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Nielsen, 1997). Depending on the process requirements, different types and combinations of alkanolamine-based solvents can be used. Nowadays, aqueous solutions of alkanolamines are commonly used for the removal of acidic gases, such as carbon dioxide and hydrogen sulfide,

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from industrial flue gases and natural gases. Some of the common alkanolamines used in the CO2 stripping process include monoethanolamine (MEA), diethanolamine (DEA), diglycolamine (DGA), and methyldiethanolamine (MDEA), Triethanolamine (TEA), another alkanolamine, is no longer used for this purpose. MDEA has an advantage over other amines. Besides, the aqueous MDEA solution has improved properties against degradation (carbamate formation) and corrosion than other alkanolamines such as DEA and MEA. In

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the other words, MDEA has a stable structure and does not degraded easily, so it would not cause problems of corrosion of carbon steel. Because of these, MDEA is becoming more popular in the natural gas industry. However, alkanolamines present several disadvantages such as volatility, toxicity, transfer of water into the gas flues in desorption step, high energy

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consumption and degradation under temperature and pressure conditions. Recently, metal organic frameworks (MOFs) have become high potential materials for

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storage and separation of gases due to their high specific surface area, large pore volume, molecular cell, homogeneous structure and adjustable chemical functionality (Chen et al., 2007; Ma and Mulfort, 2005; Nouar et al., 2008; Mulfort et al., 2009; Long and Yaghi, 2009). Although the adsorption ability of CO2 and CH4 on MOFs is confirmed, the important feature of MOFs is their thermal and water stability. Previous investigations showed that although adsorption capacity of UiO-66 is not high compared to other MOFs, the advantage of UiO-66 is its structural stability in water and high thermal stability (Schoenecker et al., 2012). The mixture of methanol and zeolitic imidazolate framework (ZIF-8) was proposed for CO2 capture by adsorptive absorption at low temperatures (Dai et al., 2015). Zirconium oxide 2

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(ZrO2) has stable properties and the nature of zirconium atom connection with oxygen makes it attractive in the synthesis of MOFs. Adding functional groups is one of the methods to increase the adsorption capacity of MOFs. In recent years, many organic linkers with various substitutions were studied and applied to produce the new MOFs with new characterization

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and application. The objective of the present work is increasing of solubility of carbon dioxide in MDEA solutions at different temperatures by addition of UiO-66-NH2 nanofluids to the Nmethyldiethanolamin solutions (as a routine alkanolamine which is used in many gas refineries). So, UiO-66-NH2 was synthesized and its effect on solubility of carbon dioxide in

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MDEA solutions was studied. UiO-66-NH2 consists of a MOF containing highly Lewis-

2. Materials and methods 2.1.

Materials

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acidic ZrIV ions, in the form of ZrIV6O4(OH)412+ cluster (Fig. 1) (Katz et al., 2015).

All of the materials were reagent grade and used without further purification. Deionized water was degassed in an ultrasonic bath (FUNGILAB, model UA10MFD) at a temperature of 353.15 K and wave frequency of 40 kHz about half an hour before use. The specifications

2.2.

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and sources of the chemicals used in this work are summarized in Table 1.

UiO-66-NH2 synthesis procedure

UiO-66-NH2 was prepared using solvothermal method according to the procedure

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described by Katz et al. (Katz et al., 2013). In detail, a 500 cm3 autoclave was loaded with 1.25 g (5.4 mmol) ZrCl4, 50 ml of the DMF, and 10 ml concentrated HCl before being

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sonicated for 20 minutes until fully dissolved. 1.34 g (7.5 mmol) 2-aminoterephtalic acid and 100 ml of the DMF were then added and the mixture was sonicated for additional 20 minutes before being heated at 120 °C for 24 hour. The resulting solid was then filtered and washed first with DMF (2 x 30 mL) and then with EtOH (2 x 30 mL). The sample was filtered for several hours to remove all residual solvent. The light yellow sediment was then dried at 120 °C for 24 hour under reduced pressure to remove excess solvent.

2.3.

Solution preparation 3

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Similar to the concentrations of MDEA solutions in the gas refining industries, a solution of mass fraction of 40 % MDEA and mass fraction of 60 % water was selected for CO2 capture tests. Then, using analytical balance with accuracy of 0.1 mg (Mettler model AE 200), mass fraction of 0.1 % UiO-66-NH2 is added to the solution. Next, mixed solution was

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put in ultrasonic bath for about 30 min for degassing. The zeta potential is a useful key showing the stability of colloidal dispersions. Generally, electrostatic repulsive and attractive forces exist in a solution contain particles. If electrostatic repulsion force overcomes the attractive force, the dispersion the dispersion may break and coagulate. In this system, Zeta potential becomes small and particles tend to

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flocculate to each other and became unstable. On the other hand, if particles small enough, a high Zeta potential will appear and system can be stable. Therefore, high Zeta potential

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(positive or negative more than 25) leads us to have a stable dispersion. The measured zeta potential for the solution of mass fraction of 0.1 % UiO-66-NH2 in aqueous MDEA (mass fraction of 40 % MDEA and mass fraction of 60 % water) is 26.6, so, the solution has good stability of colloidal dispersions. Fig. 2 shows the zeta potential diagram for the solution of mass fraction of 0.1 % UiO-66-NH2 in aqueous MDEA.

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3. Apparatus and procedure

Fig. 3 shows the schematic diagram of system. The details of the experimental method for the measurement of gas solubility have previously been presented (Hosseini Jenab et al., 2005) and only a short description will be provided here. The temperature of the double-wall

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equilibrium cell (with total cell volume of 283 ml), which was connected to a water recirculation bath (Lauda model Proline P12), with temperature stability within ± 0.01 K. The

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temperature was measured using TM-917 Lutron digital thermometer with 0.01 K resolution equipped with a Pt-100 sensor inserted into the cell via thermowell. The equilibrium cell pressure was measured using a Druck model PTX 1400 pressure transmitter sensor in the range of 0 to 4000 kPa, which was accurate within 0.1 % of full scale and that of the gas container was measured using a Druck model PTX 1400 pressure transmitter sensor in the range of 0 to 10000 kPa, which was accurate to within 0.1 % of full scale. Both pressure sensors were calibrated with a dead-weight-gauge instrument. First, a vacuum applied to the equilibrium cell using Vacuum Pump BS 5000-11 Type: BS2208 A21042003 (up to 0.1 kPa). Then, certain amount of prepared solution was charged to the equilibrium cell. In the next 4

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step, the temperature was adjusted to the desired value and after reaching the equilibrium state, the pressure sensor of equilibrium cell shows the vapor pressure of solution. The amount of CO2 was introduced to the equilibrium cell from the gas container with well known volume. The amount of CO2 injected into the equilibrium cell were calculated with

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procedure reported by Hosseini Jenab et al. (Hosseini Jenab et al., 2005) and Park and Sandall (Park and Sandall, 2001) and accurate PVT data were obtained from the National Institute

of

Standards

and

Technology

(http://webbook.nist.gov/chemistry/fluid/, 2015). VC P1 P2 ( − ) RTa Z 1 Z 2

for

pure

CO2

(1)

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nCO2 =

(NIST)

Where VC shows the volume of the CO2 container, Z1 and Z 2 are the compressibility factors

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of the initial and final state in the CO2 container before and after injection of CO2 to the equilibrium cell, Ta is the ambient temperature, and P1 and P2 are partial pressures of CO2 in gas container before and after CO2 injection into the equilibrium cell, respectively. The equilibrium state inside the equilibrium cell was normally attained within about 3 hour using mechanical stirrer. The equilibrium partial pressure of CO2 in the gas phase of the

PCO2 = PT − PV

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equilibrium cell, PCO2 , was calculated by

(2)

Where PT denotes the total pressure and PV is vapor pressure of solution. Because of the low vapor pressure of pure MDEA in the temperature range considered here, the partial pressure

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of MDEA in the vapor phase were neglected (Xu et al., 1991; Nguyen et al., 2011). Therefore, PV is the vapor pressure of pure water. Antoine equation was used for calculation of vapor pressure of water at different temperature as A−

B ( C +T )

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(3)

Where A = 8.07131 , B = 1730.63 and C = 233.426 and T is the temperature of water when water temperature is in the range of 273.15-373.15 K. The moles of remaining CO2 in the gas g phase, nCO , was determined from 2 g nCO = 2

Vg PCO2

(4)

Z CO2 RT

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Where Vg is the gas-phase volume in the equilibrium cell, and T is the equilibrium temperature of the equilibrium cell, and Z CO2 is the compressibility factor for carbon dioxide l at PCO2 and T . The moles of CO2 in the liquid phase, nCO , was then calculated with 2 l g nCO = nCO2 − nCO 2 2

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(5)

finally, the molality of the loaded CO2 in the liquid phase, mCO2 , is defined as

mCO2 =

l nCO 2

(6)

wsol

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l Where wsol is mass of solvent in kilogram. The uncertainty of nCO explicitly depends on 2

the uncertainties of measuring equipments (thermometer, pressure sensors and balance)

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which all determine by suppliers. The volume of gas phase in equilibrium cell, V g , is obtained from the difference between the cell volume and the volume of uncharged solvent. It has experimentally found that, if the one third of the cell charged with solution, the effect of change of solution density on gas phase volume will be about uncertainty of solubility data. (Shokouhi et al., 2015; Shokouhi et al., 2015).

The volumes of the gas container and equilibrium cell were obtained by performing

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pressure swing experiments (PSE). The PSE consisted of measuring the pressure drop when valve between unknown and well known reference volume get opened. First, the reference volume was pressurized and the unknown volume was evacuated. Then, the valve between unknown and well known reference volume opens and by applying Charles-Gay-lussac law

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and using the several measurements by this method, both gas container and equilibrium cell volumes and their uncertainty were obtained equal to 600.87 ± 1.3 cm3 and 283.58 ± 1.5 cm3,

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respectively.

4. Results and discussion

4.1.

UiO-66-NH2 characterization

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The physico-chemical properties of UiO-66-NH2 is studied by different techniques including XRD, TGA, SEM, BET and FTIR to understand its crystalline structure, morphology, thermal stability, and porous structure.

XRD analysis

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4.2.

The XRD pattern is given in Fig. 4(A). This Fig. shows that synthesis of UiO-66-NH2 is complete and successful. Characteristic peaks of at 2θ values of 7.34° and 8.48° showed good

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agreement between crystallinity of synthesized samples with that reported in the literature (Nik et al., 2012; Loc et al., 2013; Kandiah et al., 2010; Silva et al., 2010). Besides, this figure consists of narrow lines and shows high crystallinity of the sample. In addition, the

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powder X-ray diffraction pattern of sample after mixing with water for10 days is shown on Fig. 4(B). As this figure shows, UiO-66-NH2 showed no changes on its crystalinity after treating with water during 10 days. The highly stable UiO-66 was reported in 2008 (Cavka et al., 2008). Steric factor near the metal center of UiO-66-NH2 provides the significant activation energy for reaction kinetics of water molecules for reaction with metal center of MOF. Since the number of coordination of Zr ion in UiO-66-NH2 is high and pKa of

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carboxylate ligands is relatively low, the structure of UiO-66-NH2 is highly stable at presence of large amounts of water (DeCoste et al., 2013; Jeremias et al., 2013; Low et al., 2009; Zhang et al., 2013). Also, UiO-66-NH2 is stable in water because of thermodynamically and kinetically aspects (Burtch et al., 2014). Using XRD pattern the crystal size is determined as

SEM morphology

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about 85 nm.

The SEM picture of the UiO-66-NH2 is shown in Fig. 5. As shown in this figure, the

crystals of UiO-66-NH2 formed spherical shape and the average particle size is about 100 nm (according to BET calculations). Elemental composition of UiO-66-NH2 was measured by EDS analysis and results reveal that sample contain Zr, O, C, and N. Fig. 6 represents the EDS analysis.

4.4.

Thermogravimetric analysis(TGA) 7

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Thermogravimetric analysis (TGA) was investigated for thermal stability of UiO-66NH2. There are three weight loss steps. First, is between 303-433 K and is related to vaporization of water. Second, occurs between 423-723 K due to dehydroxylation of OH− at

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530 K and 617 K (Cavka et al., 2008). Third step, which is above 618 K, is related to breakdown of materials. So, UiO-66-NH2 seems to be stable up to 618 K. These results of Thermogravimetric analysis (TGA) is shown in Fig. 7.

Solid state FTIR spectroscopy

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4.5.

The IR spectrum of UiO-66-NH2 is presented in Fig. 8. This spectrum shows good

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agreement with that reported in the literature (Abid et al., 2013; Luu et al., 2015). There are four absorption bands in FTIR spectrum of UiO-66-NH2. First, absorption band at 1575.66 cm-1, which reveals possibility of reaction of –COOH with Zr4+. Second, absorption band at 1497.59 cm-1, which is related to C=C from aromatic. Third, absorption band at 1656.08cm-1 which indicates carboxyl group from free aromatic carboxylic acid (Abid et al., 2013; Bauer et al., 2008). Fourth, absorption band at 3430.08 cm-1 is due to symmetric and asymmetric

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vibrations of NH2 groups on the organic linker. Low intensities of these peaks may be due to the strong bonding of the amino groups in the coordinated acid with C=O groups of free NH2 on the organic linker inside the pores and bridging OH groups in the metal center. By the other word, bridging OH groups can interact with amino groups on the organic linker by

BET surface area analysis

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4.6.

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hydrogen bonding.

It has been found that addition of NH2 group to the UiO-66 decreases the surface area,

pore volume and pore diameter (Luu et al., 2015). Nevertheless, High surface area up to 842 m2 g−1 observed in Synthesized UiO-66-NH2. Micro pore volume of UiO-66-NH2 was 0.340 cm3 g−1, pore diameter was 19.0871 Å, average particle size of 71.249 Å and thermal stability up to 618 K. Fig. 9 shows the pore size distribution of synthesized UiO-66-NH2. This figure represents that 62.5 % of pore width is in the range of 0-5 nm.

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4.7.

Solubility measurement tests

Before starting the test and data acquisition, we must calibrate and validate the experimental set up. For this purpose, the solubility data of CO2 in aqueous 2.00 kmol/m3

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MDEA at 25, 40, and 70 °C was measured and compared with the results presented by Jou et al. (Jou et al., 1982). Results are given in Fig. 10. Fig. 11 shows our CO2 solubility data in aqueous mass fraction of 40 % MDEA and compares our results with the results reported by Shojaeian and Haghtalab (Shojaeian and Haghtalab, 2013). Each experiment was carried out three times and results reveal good agreement between the experimental data obtained in this

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work and available literature data.

In Table 2 and Table 3 numerical values of the experimental data of CO2 solubility in

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MDEA solution and MDEA solution + UiO-66-NH2 nanofluid are reported. The results show that absorption of CO2 increases with adding of UiO-66-NH2 to MDEA solutions and this proves that UiO-66-NH2 is an effective component in absorbing CO2 into MDEA solutions. The data on this table shows that, temperature has a negative effect on CO2 absorption. Fig. 12 and Fig. 13 show the solubility data of CO2 at different conditions. This figures show that solubility of CO2 increases with increasing of partial pressure and it decreases with increasing

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of temperature. Due to high surface area of UiO-66-NH2 nanofluid and addition of this nanoparticle component into MDEA solutions, increase of capacity of CO2 sorption occurs up to 10 %.

The error propagation theory (EPT) was used to estimate the uncertainties of final results

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(Shoemaker et al., 1981). According to EPT theory, the uncertainty δq of the interest variable

q(r … u) is given by

2

2

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 ∂q    ∂q   δq = ±  .dr  + ... +  .du   ∂r    ∂u  

(7)

The measured quantity q is dependent upon the variables r… u which fluctuates randomly and independent manner. The uncertainties of all of the instruments used in the measurements were considered for estimating the uncertainty of the solubility data of CO2 in the liquid phase. The main contributions to the uncertainty of the solubility data are related to errors in the pressure sensor for equilibrium cell and gas container (both are equal to ±0.003 MPa),

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temperature sensors (±0.01 K), and scale for the amount of solvent in equilibrium cell (±0.0001 g). According to Equation (6) and Equation (7), the CO2 solubility is related to the quantity

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l , and mass of solvent. Using the error propagation of absorbed gas in the liquid phase, nCO 2

theory (EPT), the uncertainties of mCO2 were calculated and are given in tables 2 and 3.

5. Conclusions

In this work, UiO-66-NH2 was synthesized by solvothermal method and analyzed with

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XRD, SEM, BET, TGA and solid state IR spectroscopy. Results show that because of presence of NH2 group in UiO-66-NH2 particles and interaction with water and MDEA

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molecules, the UiO-66-NH2 nanoparticle are stable in solution of MDEA according to Zeta potential of mixture. The effects of presence of UiO-66-NH2 nanofluid on solubility of CO2 in aqueous MDEA solutions were studied. UiO-66-NH2 nanofluid increases the solubility of CO2 in MDEA solution. Results showed that addition of UiO-66-NH2 nanoparticles to the MDEA solutions, increased capacity of CO2 absorption of solution up to 10 % because of high surface area of UiO-66-NH2. Besides, results show that solubility of CO2 increases with

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Zhang, W., Huang, H., Liu, D., Yang, Q., Xiao, Y., Ma, Q., Zhong, C. 2013. A new metal–organic framework with high stability based on zirconium for sensing small molecules. Microporous Mesoporous Mater., 171, 118-124.

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Table 1 Specifications and sources of chemicals used in our work. Molecular formula

CAS registry number

Purity

Source

Carbon dioxide

CO2

[124-38-9]

99. 5 %

Roham Gas Company

Zirconium chloride

ZrCl4

[10026-11-6]

99%

MERCK

Dimethylformamide

C3H7NO

[68-12-2]

99%

ALDRICH

Hydrochloric acid

HCl

[7647-01-0]

37 %

MERCK

Ethanol

C2H6O

[64-17-5]

99.5%

MERCK

2-aminoterephtalic acid

C8H7NO4

[10312-55-7]

99%

ALDRICH

Methyldiethanolamine

C5H13NO2

[105-59-9]

99%

ALDRICH

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Chemical name

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Table 2 Solubility data of CO2 in mass fraction of 40 % MDEA solution.

PCO2 (kPa) ± 0.7

mCO2 (moleCO2 / kg solvent ) ± δmCO2

303.15

183.33

2.830±0.15

303.15

352.37

3.104±0.15

303.15

629.42

3.382±0.15

303.15

854.35

3.553±0.16

303.15

1072.74

3.636±0.20

303.15

1251.60

303.15

1486.42

303.15

1798.65

3.826±0.20

303.15

2155.89

3.877±0.20

313.15

291.90

2.823±0.17

313.15

452.48

3.052±0.18

313.15

724.88

3.283±0.18

904.26

3.387±0.18

1177.17

3.443±0.19

1510.54

3.552±0.18

313.15

1878.35

3.654±0.18

313.15

2264.46

3.715±0.19

323.15

138.71

2.156±0.19

323.15

298.70

2.521±0.19

323.15

492.41

2.812±0.19

323.15

700.13

2.973±0.20

323.15

919.87

3.098±0.20

323.15

1148.89

3.202±0.20

313.15

SC 3.724±0.20 3.768±0.20

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EP

313.15

TE D

313.15

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T ( K ) ± 0.01

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1341.83

3.284±0.19

323.15

1704.37

3.401±0.19

323.15

2158.84

3.479±0.19

333.15

208.37

1.852±0.19

333.15

328.68

2.201±0.18

333.15

468.99

2.453±0.19

333.15

700.21

2.712±0.19

333.15

928.86

2.856±0.17

333.15

1149.33

333.15

1376.32

333.15

1698.32

3.153±0.17

333.15

2200.24

3.226±0.17

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323.15

3.026±0.17

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EP

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3.074±0.17

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Table 3 Solubility data of CO2 in mass fraction of 40 % MDEA + mass fraction of 0.1 % UiO-66NH2 mixtures.

PCO2 (kPa) ± 0.7

mCO2 (moleCO2 / kg solvent ) ± δmCO2

303.15

259.17

3.260±0.16

303.15

456.46

3.507±0.16

303.15

692.16

3.756±0.16

303.15

910.47

3.872±0.16

303.15

1115.49

303.15

1256.48

303.15

1410.58

4.091±0.17

303.15

1714.58

4.156±0.17

303.15

2054.69

4.220±0.17

313.15

178.82

2.811±0.16

313.15

348.97

3.152±0.17

SC 3.976±0.16

4.041±0.16

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TE D

313.15

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T ( K ) ± 0.01

564.23

3.378±0.18

755.37

3.556±0.18

1060.65

3.707±0.19

313.15

1250.30

3.813±0.19

313.15

1521.90

3.913±0.19

313.15

1815.47

3.971±0.19

313.15

2163.79

4.069±0.19

323.15

229.03

2.595±0.19

323.15

351.22

2.850±0.20

323.15

528.26

3.137±0.20

323.15

699.35

3.314±0.20

323.15

931.60

3.467±0.20

313.15

AC C

EP

313.15

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1202.37

3.625±0.20

323.15

1512.81

3.736±0.20

323.15

1783.25

3.824±0.20

323.15

2160.91

3.861±0.19

333.15

193.20

2.058±0.17

333.15

348.65

2.497±0.17

333.15

539.31

2.801±0.17

333.15

753.99

3.056±0.17

333.15

1029.52

333.15

1351.84

333.15

1761.74

3.564±0.18

333.15

1998.48

3.604±0.18

333.15

2259.53

3.670±0.18

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323.15

3.254±0.17

AC C

EP

TE D

M AN U

3.422±0.17

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Fig. 1. molecular structure of UiO-66-NH2 (Katz et al., 2015)

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Figure Captions

Fig. 2. Zeta potential diagram of solution of 0.4 mass fraction of MDEA+0.6 mass fraction of water+0.001 mass fraction of UiO-66-NH2 Fig. 3. Schematic diagram of CO2 absorption system

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Fig. 4. The powder X-ray diffraction pattern of synthesized UiO-66-NH2, A: as synthesized (before mixing with water), B: after 10 days mixing with water

Fig. 6. EDS analysis of UiO-66-NH2 Fig. 7. TG analysis of UiO-66-NH2 Fig. 8. IR spectrom of UiO-66-NH2

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Fig. 5. SEM morphology of UiO-66-NH2

Fig. 9. Pore size distribution of UiO-66-NH2

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Fig. 10. Comparison of solubility data of CO2 for 2.00 kmol/m3 MDEA solution at three given temperatures from this work and Jou et al (Jou et al., 1982) Fig. 11. Comparison of solubility data of CO2 for mass fraction of 40 % MDEA solution at 323.15 K from this work and Shojaeian and Haghtalab (Shojaeian and Haghtalab, 2013)

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Fig. 12. Comparison of solubility data of CO2 for mass fraction of 40 % MDEA solution and mass fraction of 40 % MDEA + mass fraction of 0.1 % UiO-66-NH2 nanofluid at different temperatures: A)303.15 K, B)313.15 K, C)323.15 K, D)333.15 K.

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Fig. 13. Comparison of solubility data of CO2 at different temperatures; left, mass fraction of 40 % MDEA + mass fraction of 0.1 % UiO-66-NH2 nanofluid; right, mass fraction of 40 % MDEA solution

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Fig. 3

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Fig. 4

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Fig. 5

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Fig. 6

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Fig. 7

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EP

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Fig. 8

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Fig. 9

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AC C

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Fig. 10

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AC C

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Fig. 11

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Fig. 12

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Highlights

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UiO-66-NH2 nanofluid was synthesized by solvothermal method.

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Solubility of carbon dioxide in mixture of mass fraction of 0.1 % of UiO-66-NH2

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nanofluid in aqueous solution of mass fraction of 40 % MDEA at temperatures of 303.15, 313.15, 323.15, and 333.15 K, and carbon dioxide pressures up to 2300 kPa is investigated. •

Results showed that addition of UiO-66-NH2 nanoparticles to the MDEA solution,

•

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increased capacity of CO2 absorption of solution up to 10 %.

The solubility of CO2 increased with increasing pressure and decreased with

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increasing temperature.