Scholarly article on topic 'Heat of Absorption and Specific Heat of Carbon Dioxide in Aqueous Solutions of Monoethanolamine,3-piperidinemethanol and Their Blends'

Heat of Absorption and Specific Heat of Carbon Dioxide in Aqueous Solutions of Monoethanolamine,3-piperidinemethanol and Their Blends Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — Abdurahim Abdulkadir, Aravind V. Rayer, Dang Viet Quang, Nabil El Hadri, Abdallah Dindi, et al.

Abstract In this work the thermodynamic properties of monoethanlonamine (MEA), 3-piperidinemethanol (3PM) and their blends were measured and evaluated. The heat of absorption of the solution of CO2 in the aqueous solution of single amines (5M MEA,3M MEA, 2M MEA, 2M 3PM and 3M 3PM) and aqueous amine blends (2M MEA+ 3M 3PM, 3M MEA+2M 3PM, 3M MEA+3M 3PM) were measured isothermally using a commercially available micro-reaction calorimeter (μRC) at three different temperatures (313.15, 333.15 and 353.15) K and at different CO2 loading capacity. The vapour liquid equilibrium apparatus was also used to obtain different samples of loaded CO2 molCO2/molamine and their corresponding heat of absorption was measured using the micro-reaction calorimeter. In addition, the heat capacities of the above amines were also measured from 303.15K to 353.15K at an interval of 5K. The calorimetric measurements of the heat of absorption at temperature (313.15 oK) indicated that the (3M MEA+2M 3PM) blend has the lowest absorption enthalpy with 75.58kJ/mol CO2 at 0.56 molCO2/molamine (max loading capacity) than (5M-MEA) with a reported value of 87.827kJ/molCO2 at 0.51 molCO2/molamine which corresponds the maximum loading capacity of (5M-MEA). The (3M MEA+3M 3PM) exhibited the lowest heat capacities among the measured blends of MEA and 3PM. 5M MEA was used as a base case for all the experimental measurements for the heat of absorption.

Academic research paper on topic "Heat of Absorption and Specific Heat of Carbon Dioxide in Aqueous Solutions of Monoethanolamine,3-piperidinemethanol and Their Blends"

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Energy Procedía 63 (2014) 2070 - 2081

GHGT-12

Heat of absorption and specific heat of carbon dioxide in aqueous solutions of monoethanolamine,3-piperidinemethanol and their

blends

Abdurahim Abdulkadira, Aravind V Rayera , Dang Viet Quanga , Nabil El Hadria, Abdallah Dindia, Paul H. M. Feronb, Mohammad R. M. Abu-Zahraa*

aMasdar Institute of Science and Technology, P. O.Box 54224, Masdar City, Abu Dhabi, United Arab Emirates. bCSIRO Energy Technology Centre, 10 Murry Dwyer Circuit, Steel River Estate, Mayfield West 2304, NSW, Australia

Abstract

In this work the thermodynamic properties of monoethanlonamine (MEA), 3-piperidinemethanol (3PM) and their blends were measured and evaluated. The heat of absorption of the solution of CO2 in the aqueous solution of single amines (5M MEA,3M MEA, 2M MEA, 2M 3PM and 3M 3PM) and aqueous amine blends (2M MEA+ 3M 3PM, 3M MEA + 2M 3PM, 3M MEA + 3M 3PM) were measured isothermally using a commercially available micro-reaction calorimeter (|uRC) at three different temperatures (313.15, 333.15 and 353.15) oK and at different CO2 loading capacity. The vapour liquid equilibrium apparatus was also used to obtain different samples of loaded CO2 molCo2/molamine and their corresponding heat of absorption was measured using the micro-reaction calorimeter. In addition, the heat capacities of the above amines were also measured from 303.15 K to 353.15 K at an interval of 5 K. The calorimetric measurements of the heat of absorption at temperature (313.15 oK) indicated that the (3M MEA+2M 3PM) blend has the lowest absorption enthalpy with 75.58 kJ/mol CO2 at 0.56 molCO2/molamine (max loading capacity) than (5M-MEA) with a reported value of 87.827 kJ/molCO2 at 0.51 molCO2/molamine which corresponds the maximum loading capacity of (5M-MEA). The (3M MEA + 3M 3PM) exhibited the lowest heat capacities among the measured blends of MEA and 3PM. 5M MEA was used as a base case for all the experimental measurements for the heat of absorption.

© 2014TheAuthors. Publishedby Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of the Organizing Committee of GHGT-12

Keywords: Heat of absorption; Heat capacities; Calorimeter; Post-Combustion Capture; MEA; 3PM

* Corresponding author. Tel.: +97128109181. E-mail address: mabuzahra@masdar.ac.ae

1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of the Organizing Committee of GHGT-12

doi: 10.1016/j.egypro.2014.11.223

1. Introduction

One of the most viable processes for the removal of CO2 from power plant flue gases is post-combustion by using alkanolamine aqueous solutions which are used in the capture process to absorb the gas in the absorber unit and then be regenerated in the stripper unit. However, in the stripper unit high energy is required for solvent regeneration [1, 2]. The regeneration energy is the contribution of desorption enthalpy, the sensible heat and the water evaporation. The magnitude of heat of absorption has a direct effect on the regeneration energy and also an indirect effect on the temperature sensitivity of the equilibrium curves [3] . For instant, aqueous solution of 5M MEA has been widely used in the CO2 post combustion capture but it has drawbacks due to its high energy requirement for regenerating the amine and this causes a high energy penalty and increase the cost of electricity up to about 80% by the application of this technology to power plant [4-7]. The steam which is required for the amine regeneration costs over half the running cost of the plant. Therefore, it is worthy that the enthalpy of absorption to be low and the measured data to be as accurate as possible.

One of the strategies for reducing the cost of amine based CO2 capture is the development of novel performing solvents which can be achieved by the synthesis or by blending two or more conventional solvents. Blends of alkanolamine, such as the mixtures of {primary (or secondary) + tertiary (or stertically-hindered)} have an advantage in the absorption operation due to the combined effects of the fast reaction and low cost of solvent regeneration respectively.

There are only a few experimental studies for the heat of absorption of (MEA+ CO2+ HO2) available in literature: flow calorimeter was used to determine the enthalpies of absorption of aqueous MEA solutions [8]; amine blends of [MEA+AEEA] [9]; [MEA+MDEA+H2O] [10] are also reported, while the enthalpy of CO2 in aqueous solutions of MEA at temperature of 322.5 K and 372.9 K was measured at an elevated pressure up to 5 MPa [11].

The Heat capacity of MEA with some binary and ternary aqueous alkanolamine solutions like MDEA,AMP, 2-PE have been reported in literature : (MEA+H2O) [12, 13]; (MEA + MDEA) [12]; (MEA + MDEA + H2O) [14, 15]; (MEA + AMP + H2O) [14, 16]; (5M-MEA+CO2+H2O)[17] (MEA + 2-PE + H2O) [18].

In this paper, since direct calorimetric measurements provide an accurate means of obtaining the enthalpy of absorption and the specific heat for acid gases in a solution. The thermodynamic properties of two different amines, monoethanolamine (MEA) and 3-piperidinemethanol (3-PM) were measured using a micro-reaction calorimeter. functionalized piperidine derivatives which are heterocyclic monoamines with substituents such as hydroxyl-, alkyl-and hydroxyalkyl-groups have high CO2 absorption capacities and rates[19]. Therefore, this work focused on 3-piperidinemethanol (3PM), functionalized piperidine derivative, in blends with MEA, with a view to evaluate the Heat of absorption and specific heat of carbon dioxide in aqueous solutions of these blends.

The enthalpy of absorption and the heat capacity of the stand-alone 3PM and their aqueous blends of MEA + 3PM have not yet appeared in the literature. It is the purpose of this study to experimentally determine the heat of absorption of the stand-alone and blends of MEA and 3PM at three different temperatures (313.15, 333.15 and 353.15) oK and also their heat capacities from (303.15 to 353.15) oK respectively using a micro-reaction calorimeter (mRC).

2. Experimental Section

2.1. Materials

The Monoethanolamine (MEA, >99%) and 3-piperidinemethanol (3PM, >96%) were purchased from Sigma -Aldrich. Both amines were used without any further purification. The single and blended solution of MEA and 3PM were prepared from distilled water.

2.2. Working Procedure

Micro-reaction calorimeter provided by Thermal Hazard Technology (THT) from UK can perform isothermal enthalpy measurements based on the exothermic reactions between CO2 gas and aqueous amine solution. The versatility of the instrument allows measurement of the heat of reaction at different temperatures, flow rates, volumes of solution and gas pressures.The schematic diagram of the experimental setup of the micro-reaction calorimeter is shown in Fig. 1.The setup consists of a cell which contains the amine solution sample and an empty cell which is considered as the reference cell. A flow rate of CO2 at a fixed pressure is introduced into the cell with amine solution for reaction.

The heat of absorption enthalpy of (5M MEA,3M MEA, 2M MEA, 2M 3PM and 3M 3PM) and their blends (2M MEA+ 3M 3PM, 3M MEA + 2M 3PM, 3M MEA + 3M 3PM) were measured at an isothermal temperature of (313.15, 333.15 and 353.15) oK and a pressure of 100 kPa. The heat of absorption determined by the micro-reaction calorimeter operating under a gas flow mode. The sample cell containing approximately 0.6 g of the amine solution was placed in the sample cell of the calorimeter as shown in Fig 1. The volume fraction of the CO2 injected to the sample cell from the cylinders was regulated by mass flow controllers. Before the CO2 enters to the sample cell, a desiccant column was used to remove the water and also the flow rate is adjusted. The pressure regulator was used to control the total gas pressure of the system. The test is performed under an isothermal mode using the micro-reaction calorimeter control software. When the power signal becomes constant, CO2 gas was injected to the sample cell at the rate of 1 mL/min for all the experiments using gas flow controller Bronkhurst HighTech El-Flow.An exothermic reaction occurred once the CO2 was injected to the amine solution in the sample cell and the power signal increased immediately. Test was over once the power signal became constant again. The obtained calorimetric data can be used to calculate the absorption heat enthalpy. The integral heat (Q) was computed using ^RC analysis software and the heat of absorption AH (kJ/mole of CO2) was calculated by dividing the integral heat by the mole of CO2 absorbed.

The heat capacity was measured using the micro-reaction calorimeter. Heat capacity was measured at temperature ranging from (303.1 to 353.15) oK. The measurement of the heat capacity was achieved by making "step-change" in the temperature of the cell in comparison to an empty vial. At each temperature, the heat was repeatedly measured 3 times with a step of + 0.5 K. First, blank test was conducted with an empty vial. Then, approximate (0.5 to 1) g of absorbent was placed in the sample analysis vial and conducted test with the same condition used for the blank. The results of the heat of capacities were displayed as the variation of power (mW) with time (s) as illustrated in Fig 2.

The different concentration of the amine systems studied in this work for measuring the heat of absorption with experimental parameters of temperature and pressure are listed in table 1. Since, there is a continous flow of CO2 to the sample cell of the micro-reaction calirometer the heat of absorption is only measured when the amine is fully saturated. Hence, to get a pre-loaded amine samples with CO2 the vapour liquid equilibrium appratus was used.

The solubility experiment set-up is shown in Fig 3, which includes a reactor vessel with volume capacity of 160 cm3 covered with a glass jacket. The set-up model has a maximum operating gas pressure of 10 bar in the reactor with a ±0. 5% accuracy pressure controller. A sample of loaded MEA and 3PM with CO2 was taken from the VLE reactor at different time interval and further analyzed using 85% phosphoric acid titration method before it was put in the micro-reaction calorimeter for measuring the heat of absorption vs mol Co2/mol amine at an isothermal temprature.

Fig. 1 : Experimental setup of the micro-reaction calorimeter for measuring the heat of absorption.

Fig 2: An example of the heat flow and three step change in the reactor's temperature for measuring the heat capacities recorded as a function of

time from start to the end of one experiment.

Table 1: List of amine systems studied in this work.

Amine Molar Concentration Temperature / 0K Pressure/kPa

Aqueous Stand-alone Amines

MEA 5M 313.15, 333.15,353.15 100

MEA 3M 313.15, 333.15,353.15 100

MEA 2M 313.15, 333.15,353.15 100

3-PM 2M 313.15, 333.15,353.15 100

3-PM 3M 313.15, 333.15,353.15 100 Aqueous Amine blends

MEA+3-PM 2M+3M 313.15, 333.15,353.15 100

MEA+3-PM 3M+2M 313.15, 333.15,353.15 100

MEA+3-PM 3M+3M 313.15, 333.15,353.15 100

Fig 3: Schematic diagram of vapour-liquid equilibrium set-up.

3. Results and Discussion

3.1. Heat of absorption (kJ/mol CO2) for stand-alone MEA and 3PM at 313.15, 333.15 and 353.15 K

The heat of absorption of CO2 with (5M MEA, 3M MEA, 2M MEA, 2M 3PM and 3M 3PM) were measured isothermally using micro-reaction calorimeter (^RC) at three different temperatures (313.15, 333.15 and 353.15) oK and their results are presented in Table 2. The measured heat of absorption is obtained at the maximum loading capacity (mol CO2/mol amine) as there is continuous flow of CO2 to the reactor sample cell until it gets fully saturated. There is a direct relationship between the heat of absorption and the temperature, as temperature increases the heat of absorption increases. However, as temperature increases the CO2 loading capacity decreases significantly and this indicates as there is an inverse relationship between the heat of absorption and the CO2 loading capacity. For instant, the CO2 loading capacity at 353.15 oK is lower than the values at 313.15 oK for both MEA and 3PM at the given experimental conditions . It can also be noticed that as the molar concentration of both MEA and 3PM increases their corresponding heat of absorption decreases e.g. at 313.15 oK, 5M MEA shows the lowest heat of absorption than 2M and 3M MEA of about 87.82 kJ/mol CO2 while for 3M 3PM it is only 36.72 kJ/mol CO2.This can make 3M 3PM as a potential candidate for energy efficient CO2 absorbent. At higher temperature of 353.15 oK, the 2M MEA which has CO2 loading maximum of 0.56 molCO2/molamine exhibits the highest heat of absorption of 123.31 kJ/mol CO2 among the tested stand-alone amines.

Table 2: Heat of Absorption (kJ/mol CO2) of MEA and 3-PM at 313.15, 333.15 and 353.15 oK

m Maximum Loading Capacity Heat of Absorption

Amine Temperature (K) (mol CO2/mol amine) (kJ/mol CO2)

MEA (5M) MEA (3M) MEA (2M) 3-PM (2M) 3-PM (3M)

313.15 313.15 313.15 313.15 313.15

MEA (5M) MEA (3M) MEA (2M) 3-PM (2M) 3-PM (3M)

333.15 333.15 333.15 333.15 333.15

MEA (5M) MEA (3M) MEA (2M) 3-PM (2M) 3-PM (3M)

353.15 353.15 353.15 353.15 353.15

0.51 0.63 0.74 0.68 0.85

87.82 92.62 104.31 57.41 36.72

0.42 0.57 0.67 0.61 0.74

91.82 97.62 114.31 67.47 43.12

0.41 0.51 0.56 0.54 0.65

96.52 102.13 123.31 77.81 56.72

3.2. Heat capacities (J.g~10K~1) of stand-alone MEA and 3-PM.

The heat capacities of the aqueous solutions of (5M MEA, 3M MEA, 2M MEA, 2M 3PM and 3M 3PM) were measured using the micro-reaction calorimeter from 303.15 to 353.150K. The results for these stand-alone amines are presented in Table 3 and Fig 4. The values of the heat capacities increases as temperatures increase. Only the

heat capacities of 5M MEA present in literature and there is good agreement between literature results and the present study of the Cp measurement for these alkanolamine aqueous solutions [12]. The 5M MEA showed the lowest heat capacities from the different molar concentration studied in this work (2M MEA and 3M MEA) at all temperatures and the lowest heat capacity for the 3PM was noticed with 3M 3PM when compared with the 2M 3PM.

From Fig 4, it can clearly be noticed as the 3M 3PM has the lowest heat capacities from all the stand-alone amines studied in this work. This can make the 3PM as the best solvent as it showed lowest heat capacities and lowest heat of absorption as explained in section 3.1.

Table 3: Heat capacities (J.g-1.0k-1) of MEA and 3-PM from T = (303.15 to 353.15) 0K..

Temperature(0K) MEA (5M)

303.15 3.92

308.15 3.93

313.15 3.94

318.15 3.94

323.15 3.95

328.15 3.96

333.15 3.97

338.15 3.99

343.15 4.01

348.15 4.02

353.15 4.04

MEA (2M) MEA (3M)

4.21 4.1

4.22 4.1

4.22 4.11

4.23 4.13

4.24 4.14

4.25 4.14

4.25 4.16

4.27 4.17

4.27 4.19

4.28 4.21

4.29 4.21

3-PM (2M) 3-PM (3M)

3.97 3.74

3.98 3.75

3.99 3.77

3.99 3.78

4.01 3.78

4.02 3.79

4.05 3.81

4.07 3.81

4.09 3.83

4.11 3.83

4.13 3.84

Q. 3.8

—•— MEA (5M)

3.6 —A— MEA (2M)

—♦— MEA (3M)

—•— 3PM (2M)

3.4 —■— 3PM (3M)

T (oC)

Fig 4: Heat capacities (J.g"1.°C"1) of stand-alone MEA and 3PM from T = (30 to 80) 0C.

3.3. Heat of absorption (kJ/mol CO2) of MEA and 3PM blends at 313.15, 333.15 and 353.15 0K

The heat of absorption results for CO2 with (2M MEA+ 3M 3PM, 3M MEA + 2M 3PM, 3M MEA + 3M 3PM) were measured isothermally using a commercially available micro-reaction calorimeter (^RC) at three different temperatures (313.15, 333.15 and 353.15) oK as shown in Table 4.

The heat of absorption of MEA blended with 3PM was measured at different molar concentration and different CO2 loading capacity. For the blends of MEA and 3PM the same trends has happened like the standalone amine, the heat of absorption increases with temperature and decreases with the CO2 loading capacity. For instance, MEA (3M) + 3-PM (3M) at 353.15 oK showed an increase of almost 20 kJ/mol CO2 when compared with heat of absorption at 313.15 0K. It can be noticed that the blends of MEA and 3PM have relatively lower heat of absorption than the stand-alone a mines which shows the advantage of blending amines. It can also be noticed that the blends MEA and 3PM studied in this work has shown relatively lower CO2 loading capacity when it is compared to their corresponding stand-alone amines. The blend MEA (3M) + 3PM (2M) showed the lowest heat of absorption of about 75.58 kJ/mol CO2 at an absorber temperature ( 313.150K) from all the measured blends that is why further measurements of heat of absorption at different CO2 loading capacities was carried out as shown in table 5.

Table 5 shows the heat of absorption of 3M MEA + 2M 3PM blend which is considered as most promising solvent from the other blends because of its low heat of absorption. The Vapour liquid equilibrium (VLE) was used to get different samples of loaded CO2 at different time intervals and then their corresponding heat absorption was measured using the micro-reaction calorimeter. For this blend, its heat of absorption was measured at only two temperatures (313.15 and 353.15) 0K and the CO2 loading capacity in the range of (0.1 to 0.6) mol CO2/mol amine and their corresponding heat of absorption is given in table 5. The heat of absorption achieved for the 3M MEA + 2M 3PM is much lower than the base case 5M MEA which makes this blend as a promising solvent for CO2 capture.

Table 4: Heat of Absorption of MEA and 3-PM blends at 313.15, 333.15 and 353.15 oK

Temperature (oK)

Maximum Loading Capacity (mol CO2/mol amine)

Heat of Absorption (kJ/mol CO2)

MEA (2M) + 3-PM (3M) MEA (3M) + 3-PM (2M) MEA (3M) + 3-PM (3M)

313.15 313.15 313.15

0.53 0.56 0.46

89.2 75.58 82.45

MEA (2M) + 3-PM (3M) MEA (3M) + 3-PM (2M) MEA (3M) + 3-PM (3M)

333.15 333.15 333.15

0.47 0.51 0.41

95.56 79.98 98.67

MEA (2M) + 3-PM (3M) MEA (3M) + 3-PM (2M) MEA (3M) + 3-PM (3M)

353.15 353.15 353.15

0.38 0.48 0.36

99.78 84.73 100.78

Table 5: Heat of Absorption of MEA (3M) + 3PM (2M) at different CO2 loading capacity.

m Loading Capacity Heat of Absorption

Amine Temperature (K) (mol CO2/mol amine) (kJ/mol CO2)

MEA (3M) + 3-PM (2M) 313.15 0.176 49.26

0.234 57.58

0.346 61.45

0.453 69.35

0.561 75.58

0.614 77.98

0.173 75.9

0.221 86.43

353.15 0.361 100.78

0.421 102.53

0.534 109.24

0.671 112.76

3.4. Heat capacities (J.g~10C~1) of MEA and 3PM blends.

Heat capacities of (2M MEA+ 3M 3PM, 3M MEA + 2M 3PM, 3M MEA + 3M 3PM) were measured using the micro-reaction calorimeter from 303.15 to 353.150K. The results for these blends of amines are presented in Table 6 and Fig 5. The values of the heat capacities increases as temperatures increase. The heat capacities of these blends are not presented in literature as of yet. The (3M MEA + 3M 3PM) showed the lowest heat capacities from the different molar concentration studied in this work (2M MEA+ 3M 3PM, 3M MEA + 2M 3PM) at all temperatures.

From Fig 5, it can clearly be noticed as the (3M MEA + 3M 3PM) have the lowest heat capacities from all the stand-alone amines studied in this work. This can make the (3M MEA + 3M 3PM) as the best solvent as it showed lowest heat capacities and with a moderate heat of absorption.

Abdurahim Abdulkadir et al. /Energy Procedia 63 (2014) 2070 - 2081 Table 6: Heat capacities (J.g-1.°k-1) of MEA and 3PM blends from T = (303.15 to 353.15) °K.

Temperature (0K) MEA (3M) + 3PM (3M) MEA (3M) + 3PM (2M) MEA (2M) + 3PM (3M)

303.15 3.51 3.75 3.97

308.15 3.53 3.76 3.98

313.15 3.55 3.76 3.98

318.15 3.55 3.77 3.99

323.15 3.57 3.77 4.01

328.15 3.58 3.78 4.01

333.15 3.59 3.79 4.02

338.15 3.61 3.79 4.03

343.15 3.63 3.81 4.04

348.15 3.65 3.83 4.05

353.15 3.66 3.84 4.07

CL 3.8 O

■4-♦--

MEA (2M) + 3PM (3M) MEA (3M) + 3PM (2M) MEA (3M) + 3PM (3M)

T (oC)

Fig. 5: Heat capacities (J.g-1.0C-1) of MEA and 3-PM blends from T = (30 to 80) 0C.

4. Conclusions

A micro reaction calorimeter was used to measure the enthalpies of absorption of CO2 in (5M MEA,3M MEA, 2M MEA, 2M 3PM and 3M 3PM) aqueous solutions of MEA,3PM and their blends (2M MEA+ 3M 3PM, 3M MEA + 2M 3PM, 3M MEA + 3M 3PM) at three different temperatures 313.15 K, 333.15 K and 353.15 0K.The {2M 3PM+3M MEA} blend showed significantly lower heat of absorption in comparison to [5M MEA]. Moreover, the specific heat of the above amines was also measured from 303.15 K to 353.15 0K at an interval of 5 0K. Blends of {3M MEA + 3M 3PM} showed the lowest specific heat from all the blends and the 3M 3PM for the stand-alone amines. In conclusion, the {3M MEA + 2M 3PM} is the best blend with lower solvent regeneration energy and moderate specific heat capacities. The results from this work may be used for thermodynamic modeling of CO2 capture processes using MEA blended with 3PM.

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