Charcterising Thermal Properties of CO2/Solvent Interactions by Calorimetery

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Use of Reaction Calorimetry in the Screening of Solvents for use in Post Combustion Carbon Capture Technology

The µRC Micro Reaction Calorimeter The RSD Rapid Screening Device

Carbon capture or carbon sequestration are general terms used to describe the process of removing carbon dioxide from the atmosphere and storing it in a different form and/or location. Carbon capture can be used to offset high volumes of CO2 production from various industrial processes involving fossil fuel combustion. There are many different methods of carbon capture involving different capture processes and capturing materials. Liquid amines are one such material deemed appropriate for this task.

Thermal Hazard technology offer two complementary calorimetric techniques ideally suited to the screening of amines for carbon capture.

The details of the process are that exhaust material from the industrial process is passed through the amine solution. CO2 present in the exhaust material will be absorbed by the amine solution until it becomes loaded i.e. it cannot absorb any further CO2 at the current atmospheric conditions. The degree of loading is generally dependent on temperature and pressure as well as the type and quantity of amine used.

(2) The RSD Rapid Screening Device can be used to calculate the temperature at which the amine will release CO2. This information can then be used to screen amines and see which solvent unloads CO2 at the lowest temperature.

The amine may then be stripped of CO2 by heating the loaded solution until the CO2 is released. This pure CO2 can then be collected stored, preventing its escape to the atmosphere.

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(1) The µRC Micro Reaction Calorimeter can determine the heat of absorption (which also determines the heat of desorption) and the heat capacity of the amine solution.

These two measurements establish the energy requirement to release the CO2 from the loaded amine.

In this report, µRC and RSD data is presented for a several common amines as well as ammonia.

Specific Heat Capacity Testing using the µRC

2. Specific Heat Capacity Testing using the µRC Micro Reaction Calorimeter The specific heat capacity of any material involved in a process is a crucial thermo-chemical property needed to model heat distribution throughout a system which can in turn be used to calculate utility heating or cooling requirements for various reaction and separation vessels.

study to determine the isobaric specific heat capacity of a variety of solvents.

The Cp of the following samples were tested; Pure MEA 20 wt% piperazine solution 30 wt% MEA solution Loaded 30 wt % MEA solution Pure DEA Loaded 20% wt Piperazine solution 30 wt% MEA solution DMCA+DPA (3M) solution Loaded DMCA+DPA (3M) solution

2.1. Experimental Procedure A measured mass of a sample is charged into a 2 ml glass vial. An identical (but empty) vial is placed in the reference

are the sample mass, temperature of Cp measurement, size of temperature step and stirring.

the start temperature. Once equilibrated, it will increase the sample temperature by a defined temperature step (°C) measuring the amount of heat required to do so. The temperature will then be lowered back to the temperature of Cp measurement by the defined temperature step (°C). The test finishes when the temperature returns to the initial temperature, and the power signal returns to the baseline level.

Figure 1a.

Cp measurement of water at 25°C. Calculated Cp 4.26 J/gK

The amount of energy required to heat the defined mass of sample by the defined temperature step (°C) can then be automatically integrate under the peak of the power measurement found when increasing/ decreasing the temperature. Integrating the power in watts gives a heat in joules. The average of the two heat values is then calculated.

This is the total heat absorbed by the sample to increase its temperature by the defined temperature step (°C). A ‘blank’ experiment is run using an empty vial in sample and reference over the same temperature step. The ‘blank’ heat measurement is subtracted from the experimental data. The corrected heat value is then divided by the temperature step and the mass of sample to give a Cp value (J/g K). This process is automated in the µRC Analysis software.

Figure 1b.

Cp measurement of pure MEA at 25°C. Calculated Cp 2.76

measured. The Cp for MEA was measured for Lean and Rich (loaded with CO2 till assumed saturation at standard conditions) (30 wt %) MEA solutions.

Figure 2.

The µRC Micro Reaction Calorimeter

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Use of Reaction Calorimetry in the Screening of Solvents for Main Heading main header use in Post Combustion Carbon Capture Technology

2.2. Results Sample

Mass (g) 1.07 1.07 1.08 1.08 0.99 0.99

Average DMCA:DPA (3M)

1.178

Cp Literature (J/g k) Cp Value 3.50 3.52 3.28 3.24 3.31 3.29 3.36 3.68 3.75 3.74 3.83 3.75 2.76 2.73 2.76 2.75 2.67 2.41 2.50 2.22 2.50 2.41 2.39 3.151

Loaded DMCA:DPA (3M)

1.181

2.990

Loaded MEA

Average 0.3 wt MEA

1.06 1.06 1.06 1.01 Average

Pure MEA

0.98 1.09 1.04 Average

DEA

1.09 1.03 1.04 1.03

Piperazine (0.2 wt) solutions 1.00 1.05 1.01 Average Loaded Piperazine solution 1.07 1.14 1.14 Average

1.94 2.07 1.99 2.00 1.64 1.71 1.49 1.61

3. Gas flow testing using the ÂľRC Micro Reaction Calorimeter An important property of a solvent for use in carbon capture technology is the heat of CO2 absorption, and the enthalpy of CO2 absorption which can be derived from this value.

3.1 Experimental Procedure CO2 gas flow tests were performed on the following solvents.

The gas flow was controlled to a specific flow rate using a Bronkhorst Flow Controller. The CO2 used was approximately 100% purity. The system configuration is shown below:

Figure 3.

THT ÂľRC Flow Option Set Up

Piperazine 20 wt% solution Ammonia 30 wt% MEA 30 wt% solution Ammonia 8 wt % (giving a similar number of N atoms in solution) MDEA:MEA (3:1 wt ratio 3M) MEA 30 wt% solution Pure DPA DEA in H2O (30 wt%) DMCA:DPA (3:1 wt ratio 3M) Enthalpy calculated by;

Enthalpy of Absorption =

Source of literature values: Heat Capacity of Alkanolamines by Differential Scanning Calorimetry, rsity, Li-Feng Chiu et al. J. Chem. Eng. Data, 1999, 44 (3), pp 631-636

Habs = 4

(

Heat Number of moles of CO2 absorbed

222 J = 81.6 kJmol-1 0.12 mol 44.01

(

Samples were loaded in a sample size of 20g. The MEA solution was loaded using a flow rate of approximately 10 ml/min (CO2). A stirrer bar was used to allow for more rapid CO2 absorption. A thermocouple was used to measure the temperature of the sample as the loading process took place. CO2 was passed through the sample until the temperature recorded on the thermocouple returned to room temperature. This indicated no further absorption. The gas was flowed through for 5 additional minutes over which time no further significant temperature changes were recorded in the sample.

Gas Flow Testing using the µRC Micro Reaction Calorimeter

3.2. Results Sample

MEA 0.3 (wt)

Flow rate CO2 CO2 of CO2 feed Absorbed Absorbed (ml/min) (g) (mmol)

Energy released (J)

Enthalpy (kJ/mol)

0.98

0.12

2.7

222.4

81.55

1.11

0.12

2.7

226.0

82.87

0.56

0.11

2.5

209.0

83.60

0.26

0.12

2.7

224.0

82.13

Average

0.73

0.12

2.7

220.4

82.54

MDEA:MEA, 3:1. 3M

0.96

0.11

2.5

148.0

59.20

Ammonia 0.08 (wt)

0.56

0.13

3.0

208.0

70.40 65.56

0.56

0.10

2.3

149.0

Average

0.56

0.12

2.6

178.5

67.98

Piperazine 0.2 (wt)

0.98

0.10

2.4

153.8

65.07

0.98

0.11

2.5

162.5

65.00

0.98

0.10

2.3

149.9

65.95 65.03

Average

0.98

0.10

2.4

155.4

Pure DPA

0.56

0.16

3.6

256.0

72.52

DEA 0.3 (wt)

0.84

0.12

2.7

171.1

62.31

DMCA:DPA, 3:1. 3M

0.56

0.021

0.48

19.63

41.70

DMCA:DPA, 3:1. 3M

0.56

0.020

0.45

19.55

39.02

Average

0.73

0.12

2.7

220.4

82.54

Figure 4a . µRC sample cell for ambient pressure flow up to 20ml/min with stirring

Figure 4b.

Pressure cell (stainless steel) rated to 10 bar over pressure with flow

Conclusions The new Gas Flow option accurately controls CO2 dosing and allows direct calculation of CO2 loading in the solvent.

The ability of the µRC Micro Reaction Calorimeter to quickly carry out heat of absorption and heat capacity measurements using micro litre volumes of reagents makes it ideal for routine carbon capture studies. As expected the heat of absorbtion for the blended lipophilic amine DMCA:DPA is much lower than the typical secondary alkanolamine DEA. 5

CO2 Desorption Studies using the RSD

4. CO2 Desorption Studies using the RSD Using the RSD it is possible to trace the pressure profile of both loaded and unloaded solvent samples with time and temperature. By performing a test with a positive temperature differential over time, the difference in pressure values between the loaded and unloaded sample should be equal to the value of pressure exerted by the release of CO2 in the system. This can then be analysed to give the percentage of CO2 release from the loaded solution at specific temperatures.

From the pressure versus temperature data (below) it can be seen that as the temperature of the system decreases, as does the pressure in the bomb. Whilst some of this pressure drop will be due to the increase in density of gas upon cooling (based on ideal the gas law), the graph shows that the pressure returns to its original value, indicating that the majority of CO2 released was reabsorbed into the solution.

Figure 5.

The RSD Rapid Screening Device

loading process took place. CO2 was passed through the sample until the temperature recorded on the thermocouple returned to room temperature. The gas was flowed through for 5 additional minutes.

4.2 Results Results for MEA are shown below.

CO2 release from loaded solvent

Temperature of desorption (CO2 release) onset Delta pressure of loaded MEA versus unloaded MEA. Clearly shows CO2 release profile against temperature

Graph 1. showing Pressure vs Temperature for 3 samples run in the RSD in one test.

Sample mass of 7g 80 70 60

Pressure (bar)

r) 50 a b ( e r 40 u ss e r P30

Loaded 0.3 wt MEA

20 10 0 0

50

100 150 Temperature 째C

200

250

Graph 2. showing pressure vs time

80 70

Conclusions

60

Loaded 0.3 wt MEA

Pressure (bar)

r) 50 a b ( re 40 u ss e r P 30

Unloaded 0.3 MEA Pure MEA

20

The RSD makes it possible to screen a range of solvents to see which solvent unloads CO2 at the lowest temperature.

Chart showing pressure differentials between loaded and unloaded solvents (pressure exerted by CO2) for two solvents tested in 2 seperate tests , against temperature

10 45

0 0

20

40

60

80

100

120

40

Time (minutes) 35

4.1. Experimental Procedure Loading of solvents was performed on a sample size of 20g. The MEA solution was loaded using a flow rate of approximately 10 ml/min (CO2). A stirrer bar was used to allow for greater CO2 absorption. A thermocouple was used to measure the temperature of the sample as the

30 )r a b (25 re u ss 20 re P ?

MEA 0.3 wt

MDEA:MEA (3:1 wt 3M)

15 10 5 0

6

0

50

100 150 Temperature (째C)

200

250

Specifications of the µRC and RSD

µRC Specification

Temperature Range Modes of Operation Scan Rate Sensitivity Dynamic Range Injection Volume Cell Volume Cell Types

-10 to 150°C Isothermal, Scanning, Titration Up to 2°C/min +/- 5µW 5µW to 300µW 1 to 250µl 2.0ml Removable glass Removal Stainless Stell

Stirring Software

0 to 400rpm Dedicated Windows based control and data analysis software

PC Requirements (Included with system) Measurement Principle

USB Port Monitor Resolution 1200 x 768 Power Compensation

Footprint

70cm x 43cm x 40cm (width x height x depth)

RSD Specification

Temperature Range Modes of Operation Scan Rate Detection Sensitivity Pressure Range Pressure Resolution Sample Size Sample Quantity Stirring Software

-140 to 400°C Isothermal or scanning 0 - 10°C / min Less than 10 J/g Up to 160 bar (alternative ranges available) 0.2 bar up to 100g or ml 1 - 6 samples Up to 2000rpm Dedicated Windows based control and data analysis software through serial link to PC

PC Requirements

USB Port Serial Port Monitor Resolution: 1280 x 1024

Footprint

70cm x 43cm x 40cm (width x height x depth) Single phase

Power Supply

Gas Flow Option Comprising a metal housing with all necessary components for pressure, static and flow tests

4 way valve for immediate CO2 / N2 switching 3 way valve for CO2 / N2 gas selection Pressure on/off valve x 2 Back Pressure Regulator Mass flow controller Connectors for CO2 and N2 cylinders Stainless steel pressure vials x 2 Fail-safe connectors for flow and pressure option connection Maximum Flow Rate

20ml per minute

(gas dependant)

Maximum System Pressure 10 bar Calibrated Gases CO2, N2, Air More available upon request (Note: customer to supply CO2 and N2 cylinders with cylinder heads/regulators)

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