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

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The µRC Micro Reaction Calorimeter

The RSD Rapid Screening Device

Carbon capture or carbon sequestration are general termsused to describe the process of removing carbon dioxidefrom the atmosphere and storing it in a different form and/orlocation. Carbon capture can be used to offset high volumesof CO2 production from various industrial processes involvingfossil fuel combustion. There are many different methods ofcarbon capture involving different capture processes andcapturing materials. Liquid amines are one such materialdeemed appropriate for this task.

The details of the process are that exhaust material from theindustrial process is passed through the amine solution. CO2

present in the exhaust material will be absorbed by the aminesolution until it becomes loaded i.e. it cannot absorb anyfurther CO2 at the current atmospheric conditions. Thedegree of loading is generally dependent on temperature andpressure as well as the type and quantity of amine used.

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

Thermal Hazard technology offer two complementarycalorimetric techniques ideally suited to the screening ofamines for carbon capture.

(1) The µRC Micro Reaction Calorimeter can determinethe heat of absorption (which also determines the heat ofdesorption) and the heat capacity of the amine solution.These two measurements establish the energy requirementto release the CO2 from the loaded amine.

(2) The RSD Rapid Screening Device can be used tocalculate the temperature at which the amine will releaseCO2. This information can then be used to screen aminesand see which solvent unloads CO2 at the lowesttemperature.

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

2. Specific Heat Capacity Testing using the µRC MicroReaction Calorimeter

The specific heat capacity of any material involved in aprocess is a crucial thermo-chemical property needed tomodel heat distribution throughout a system which can in turnbe used to calculate utility heating or cooling requirements forvarious reaction and separation vessels.

study to determine the isobaric specific heat capacity of avariety of solvents.

2.1. Experimental Procedure

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

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

the start temperature. Once equilibrated, it will increase thesample temperature by a defined temperature step (°C)measuring the amount of heat required to do so. Thetemperature will then be lowered back to the temperature ofCp measurement by the defined temperature step (°C). Thetest finishes when the temperature returns to the initialtemperature, and the power signal returns to the baselinelevel.

The amount of energy required to heat the defined mass ofsample by the defined temperature step (°C) can then be

automatically integrate under the peak of the powermeasurement found when increasing/ decreasing thetemperature. Integrating the power in watts gives a heat injoules. The average of the two heat values is then calculated.This is the total heat absorbed by the sample to increase itstemperature by the defined temperature step (°C). A ‘blank’experiment is run using an empty vial in sample andreference over the same temperature step. The ‘blank’ heatmeasurement is subtracted from the experimental data. Thecorrected heat value is then divided by the temperature stepand the mass of sample to give a Cp value (J/g K). Thisprocess is automated in the µRC Analysis software.

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

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

Figure 1a.Cp measurement of water at 25°C. Calculated Cp 4.26 J/gK

Figure 1b.Cp measurement of pure MEA at 25°C. Calculated Cp 2.76

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Specific Heat Capacity Testing using the µRC

Figure 2.The µRC MicroReaction Calorimeter

Samples were loaded in a sample size of 20g. The MEAsolution was loaded using a flow rate of approximately10 ml/min (CO2). A stirrer bar was used to allow for morerapid CO2 absorption. A thermocouple was used tomeasure the temperature of the sample as the loadingprocess took place. CO2 was passed through thesample until the temperature recorded on thethermocouple returned to room temperature. Thisindicated no further absorption. The gas was flowedthrough for 5 additional minutes over which time nofurther significant temperature changes were recordedin the sample.

2.2. Results

3. Gas flow testing using the µRC Micro ReactionCalorimeter

An important property of a solvent for use in carbon capturetechnology is the heat of CO2 absorption, and the enthalpyof 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 aBronkhorst Flow Controller. The CO2 used wasapproximately 100% purity. The system configuration isshown below:

Figure 3.THT µRC 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)

Main Headingmain header

Sample Mass(g)

Cp(J/g k)

LiteratureCp Value

Loaded MEA 1.07 3.501.07 3.521.08 3.281.08 3.240.99 3.310.99 3.29

Average 3.360.3 wt MEA 1.06 3.68

1.06 3.751.06 3.741.01 3.83

Average 3.75Pure MEA 0.98 2.76

1.09 2.731.04 2.76

Average 2.75 2.67DEA 1.09 2.41

1.03 2.501.04 2.221.03 2.50

Average 2.41 2.39DMCA:DPA (3M) 1.178 3.151

Loaded DMCA:DPA (3M) 1.181 2.990

Piperazine (0.2 wt) solutions 1.00 1.941.05 2.071.01 1.99

Average 2.00Loaded Piperazine solution 1.07 1.64

1.14 1.711.14 1.49

Average 1.61

Enthalpy calculated by;

Enthalpy of Absorption = HeatNumber of moles of CO2 absorbed

Habs = 222 J0.1244.01( mol

(= 81.6 kJmol-1

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

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

Gas Flow Testing using the µRC Micro ReactionCalorimeter

ConclusionsThe new Gas Flow option accurately controls CO2 dosing andallows direct calculation of CO2 loading in the solvent.

The ability of the µRC Micro Reaction Calorimeter to quicklycarry out heat of absorption and heat capacity measurementsusing micro litre volumes of reagents makes it ideal for routinecarbon capture studies. As expected the heat of absorbtion forthe blended lipophilic amine DMCA:DPA is much lower thanthe typical secondary alkanolamine DEA.

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Figure 4a .µRC sample cell for ambientpressure flow up to 20ml/minwith stirring

Figure 4b.Pressure cell (stainless steel)rated to 10 bar over pressurewith flow

3.2. Results

Sample Flow rateof CO2 feed(ml/min)

CO2Absorbed(g)

CO2Absorbed(mmol)

Energyreleased(J)

Enthalpy(kJ/mol)

MEA 0.3 (wt) 0.98 0.12 2.7 222.4 81.551.11 0.12 2.7 226.0 82.870.56 0.11 2.5 209.0 83.600.26 0.12 2.7 224.0 82.13

Average 0.73 0.12 2.7 220.4 82.54MDEA:MEA,3:1. 3M

0.96 0.11 2.5 148.0 59.20

Ammonia0.08 (wt)

0.56 0.13 3.0 208.0 70.40

0.56 0.10 2.3 149.0 65.56Average 0.56 0.12 2.6 178.5 67.98Piperazine0.2 (wt)

0.98 0.10 2.4 153.8 65.07

0.98 0.11 2.5 162.5 65.000.98 0.10 2.3 149.9 65.95

Average 0.98 0.10 2.4 155.4 65.03Pure DPA 0.56 0.16 3.6 256.0 72.52DEA 0.3 (wt) 0.84 0.12 2.7 171.1 62.31DMCA: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

4. CO2 Desorption Studies using the RSD

Using the RSD it is possible to trace the pressure profileof both loaded and unloaded solvent samples with timeand temperature. By performing a test with a positivetemperature differential over time, the difference inpressure values between the loaded and unloadedsample should be equal to the value of pressure exertedby the release of CO2 in the system. This can then beanalysed to give the percentage of CO2 release from theloaded solution at specific temperatures.

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CO2 Desorption Studies using the RSD

Figure 5.The RSD RapidScreening Device

From the pressure versustemperature data (below) it canbe seen that as the temperatureof the system decreases, as doesthe pressure in the bomb. Whilstsome of this pressure drop will bedue to the increase in density ofgas upon cooling (based on idealthe gas law), the graph showsthat the pressure returns to itsoriginal value, indicating that themajority of CO2 released wasreabsorbed into the solution.

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Pressure(bar)

Temperature °C

Graph 1. showing Pressure vs Temperature for 3 samples run in the RSD in one test.Sample mass of 7g

Loaded 0.3 wtMEA

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120

Pressure(bar)

Time (minutes)

Graph 2. showing pressure vs time

Loaded 0.3 wtMEA

Unloaded 0.3 MEA

Pure MEA

Pres

sure

(bar

)Pr

essu

re (b

ar)

loading process took place. CO2 was passed throughthe sample until the temperature recorded on the ther-mocouple returned to room temperature. The gas wasflowed through for 5 additional minutes.

4.2 Results

Results for MEA are shown below.

CO2 release from loaded solvent

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

Conclusions

The RSD makes it possible to screen a range ofsolvents to see which solvent unloads CO2 at the lowesttemperature.

0

5

10

15

20

25

30

35

40

45

0 50 100 150 200 250

?Pressure(bar)

Temperature (°C)

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

temperature

MEA 0.3 wt

MDEA:MEA(3:1 wt 3M)

4.1. Experimental Procedure

Loading of solvents was performed on a sample size of20g. The MEA solution was loaded using a flow rate ofapproximately 10 ml/min (CO2). A stirrer bar was usedto allow for greater CO2 absorption. A thermocouple wasused to measure the temperature of the sample as the

Specifications of the µRC and RSD

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µRC Specification RSD Specification

Temperature Range -10 to 150°C

Modes of Operation Isothermal, Scanning, Titration

Scan Rate Up to 2°C/min

Sensitivity +/- 5µW

Dynamic Range 5µW to 300µW

Injection Volume 1 to 250µl

Cell Volume 2.0ml

Cell Types Removable glassRemoval Stainless Stell

Stirring 0 to 400rpm

Software Dedicated Windows basedcontrol and data analysissoftware

PC Requirements(Included with system)

USB PortMonitor Resolution 1200 x 768

Measurement Principle Power Compensation

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

Gas Flow Option

Temperature Range -140 to 400°C

Modes of Operation Isothermal or scanning

Scan Rate 0 - 10°C / min

Detection Sensitivity Less than 10 J/g

Pressure Range Up to 160 bar (alternative rangesavailable)

Pressure Resolution 0.2 bar

Sample Size up to 100g or ml

Sample Quantity 1 - 6 samples

Stirring Up to 2000rpm

Software Dedicated Windows basedcontrol and data analysissoftware through serial link to PC

PC Requirements USB PortSerial PortMonitor Resolution: 1280 x 1024

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

Power Supply Single phase

(Note: customer to supply CO2 and N2 cylinders with cylinder heads/regulators)

Maximum Flow Rate(gas dependant)

20ml per minute

Maximum System Pressure 10 bar

Calibrated Gases CO2, N2, AirMore available upon request

Comprising a metal housing with all necessarycomponents for pressure, static and flow tests

4 way valve for immediate CO2 / N2 switching3 way valve for CO2 / N2 gas selectionPressure on/off valve x 2Back Pressure RegulatorMass flow controllerConnectors for CO2 and N2 cylindersStainless steel pressure vials x 2Fail-safe connectors for flow and pressure option connection

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