co2 absorbing capacity of mea

Research ArticleCO2 Absorbing Capacity of MEA

Joseacute I Huertas Martin D Gomez Nicolas Giraldo and Jessica Garzoacuten

Tecnologico de Monterrey Eduardo Monroy Cardenas No 2000 50110 Toluca MEX Mexico

Correspondence should be addressed to Jose I Huertas jhuertasitesmmx

Received 6 April 2015 Revised 29 July 2015 Accepted 9 August 2015

Academic Editor Christophe Coquelet

Copyright copy 2015 Jose I Huertas et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

We describe the use of a gas bubbler apparatus in which the gas phase is bubbled into a fixed amount of absorbent under standardconditions as a uniform procedure for determining the absorption capacity of solvents The method was systematically applied todetermine the CO

2absorbing capacity ofMEA (119860

119888) at several aqueousMEA (120573) and gas-phase CO

2concentrations119860

119888approached

the nominal CO2absorbing capacity of MEA (720 gCO

2kgMEA) at very low 120573 levels increasing from 4479 plusmn 181 to 5813 plusmn

323 gCO2kgMEA as 120573 was reduced from 30 to 25 (ww) 119860

119888did not depend on the CO

2concentration in the inlet gas stream

as long as the gas stream did not include other amine sensitive components During the bubbling tests the outlet CO2concentration

profiles exhibited a sigmoidal shape that could be described by an exponential equation characterized by an efficiency factor (119886) anda form factor (119899) Statistical analysis based on correlation analysis indicated that in all cases the experimental data fit the equationwell when a was 61plusmn 035 and 119899was 25plusmn 012 The results of these experiments may be used to optimize scrubber designs for CO

2

sequestration from fossil fuel derived flue gases

1 Introduction

There are several industrial applications in which a liquidphase substance (solvent) is used to selectively absorb one orseveral components (pollutants) from a gas stream passingthrough an absorbing column (scrubber) One applicationof increasing interest is CO

2absorption from fossil fuel

derived flue gases in thermal power plants CO2is the most

widely produced greenhouse gas (GHG) as a result of fossilfuel combustion to satisfy the world energy demand [1 2]Efforts tomitigate global warming include CO

2sequestration

from flue gases for either storage in the sea or empty oilwells or reconversion into CO and O

2through artificial

photosynthesis [3ndash5] Although these technologies are still inan early stage of development amine scrubbing has emergedas the preferredmethod forCO

2sequestration [6]While acid

gas removal from process streams using amines is a maturetechnology [7 8] flue gas scrubbing presents many newchallenges still not adequately met on the scale necessary forGHGabatement [9]Wet scrubbing techniquesmust improveto process large volumes of flue gas at acceptable thermalefficiencies and minimal costs [10 11]

Extensive work has been undertaken to identify the opti-mum packing material geometry to improve hydrodynamic

mixing and maximize mass transfer in order to minimizethe size and pressure drop across the scrubber [12] Theabsorption or removal efficiency (120578 defined in (1) where119910119894and 119910

119900are the pollutant concentration expressed as

molar fraction at the inlet and outlet resp) is a means ofexpressing the performance of the scrubber Several authorshave erroneously referred to 120578 as a solvent property eventhough two scrubbers using the same solvent could havedifferent absorption efficiencies Consider

120578 =119910119894minus 119910119900

119910119894

(1)

Amine Absorbing Capacity Amines are ammonia deriva-tives in which one or more hydrogen atoms are replacedby an organic radical [12] Monoethanolamine (MEA)diethanolamine (DEA) and methyldiethanolamine (MDEA)are the most commonly used amines in scrubbing appli-cations The CO

2absorbing capacity of amines is easily

degraded by the presence of SO2 NO2 HCl HF or O

2in the

gas stream These components form irreversible byproductsthat reduce the reaction rate during the absorption processand increase the complexity of the solvent recovery process

The absorbing capacity is a solvent property defined asthe maximummolar amount of pollutant absorbed per mole

Hindawi Publishing CorporationJournal of ChemistryVolume 2015 Article ID 965015 7 pageshttpdxdoiorg1011552015965015

2 Journal of Chemistry

of solvent This property is used to define the appropri-ate loading (pollutantsolvent molar ratio 120572) in scrubberdesigns Low loadings result in columns with low absorbingefficiencies while high loadings lead to excessive solventrequirements and high operational costs The CO

2absorbing

capacity of amines is dependent on the solvent concentrationthe composition of the gas stream and the operating temper-ature [13]

Amines are capable of chemical and physical CO2absorp-

tion Physical absorption is controlled by the thermodynamicequilibrium between CO

2molecules in the gas and aqueous

phases and is described by Henryrsquos law [8 14]

119875119860= 119910119860119875 = 119867

119860119909119860 (2)

where 119875119860is the equilibrium partial pressure of component

119860 in gas phase 119875 the total pressure 119867119860the Henryrsquos law

constant of component 119860 119910119860the equilibrium concentration

of component 119860 in gas phase (expressed as molar fraction)and 119909

119860the equilibrium concentration of component 119860 in

liquid phase (expressed also as molar fraction)The Henryrsquos law constant is determined in a temperature

and pressure controlled sealed chamber by measuring theequilibrium concentration of the component in the gas andliquid phases using spectrophotometric or chromatographicanalysis [15] This method is appropriate for systems under-going pure physical absorption for example CO

2absorption

inH2OHowever it is inappropriatewhen the solvent exhibits

chemical absorption since the method does not ensurethat the solvent becomes fully saturated Investigators haveemployed this method for several years expressing theirresults in terms of the equilibrium partial pressure of thegas phase component and referring to these values as thesolubility of the pollutant in the solvent Tong et al [16]combined experimental work with an extensive literaturereview to describe the solubility ofCO

2in 30 (ww) aqueous

solutions of MEA as a function of temperature and loading[17ndash19] For the readerrsquos convenience Figure 1 reproduces theresults published These results cannot be used to describethe absorption capacity of the solvent since the equilibriumconditions under which the data was collected do not ensuresaturation of the solvent Furthermore these results cannotbe used to determineHenryrsquos law constant for theMEA-H

2O-

CO2system since they do not quantify the CO

2remaining

in molecular form within the liquid phase and because asmentioned earlier the system exhibits chemical absorption

Chemical absorption is based on reactions between CO2

and the amine It has been reported that chemical absorptiondoes not increase significantly with pressure [20] There aretwo fundamental mechanisms for the reaction of amines (R-NH2) with CO

2[9]

2R-NH2+ CO2larrrarr R-NH

3

++ R-NH-COOminus (3)

R-NH2+ CO2+H2O larrrarr R-NH

3

++HCO

3

minus (4)

For common primary and secondary amines such as MEAand DEA reaction (3) prevails to form a stable car-bamate (R-NH-COOminus) requiring 2 moles of amine permole of CO

2and thus limiting the absorbing capacity of

01

0001

001

1

10

100

1000

Shen and Li 1992

Lee et al 1976

Tong et al 2012

Jou et al 1995

PCO

2(k

Pa)

00 02 04 06 08

313K

120572CO2

Figure 1 Solubility of CO2in 30 (ww) aqueousMEA solutions at

313 K as a function of loading (moles of CO2per mole of MEA 120572)

from Tong et al [16]

the amine to 05 moles of CO2per mole of amine that

is 360 gCO2KgMEA However unstable carbamates can

hydrolyze to form bicarbonate (HCO3

minus) as described byreaction (4) Under this condition the nominal MEA CO

2

absorbing capacity is one mole of CO2per mole of MEA [9]

that is 720 gCO2KgMEA Tertiary amines such as MDEA

only follow reaction (4) [21]The physical and chemical MEA absorption capacities

are affected by temperature pressure presence of additionalgases and the aqueous MEA concentration

Yeh and Bai [22] measured the CO2absorption capacity

of MEA in a semicontinuous reactor consisting of a 60mmglass bottle containing 200mL of solvent The absorptioncapacities ranged from 360 to 380 gCO

2kgMEA usingMEA

concentrations of 7ndash35 (ww) and gas flow rates of 2ndash10SLPM of 8ndash16 of CO

2diluted in clean air The reaction

temperature varied from 10 to 40∘C Recently Rinprasert-meechai et al [23] used a stirred 100 mL reactor containing50mL of 30 (ww) aqueous MEA concentration at 25∘Cand atmospheric pressure to obtain an absorption capacityof 045 CO

2molesmole amine (324 gCO

2kgMEA) for a

simulated flue gas containing 15 CO2 5 O

2 and 80 N

2

and flowing at 005 SLPMThese two papers neither reportedthe outlet gas flownor removed theO

2in the gas stream lead-

ing to an underestimation of the CO2absorbing capacity of

MEA Recently Kim et al [24] reported an absorbing capacityof 0565CO


2kgMEA) using

30 vol CO2diluted in N

2and a fixed flow rate of 1 SLPM

monitored by amass flow controller and gas chromatographyto determine CO

2concentration at the outlet of the reactor

The disagreements present in previous results are dueto variations in testing methods amine dilution solventtemperature and pressure and inlet gas composition andhighlight the need for a standard method to determine theabsorbing capacity of solvents The resulting experimentaldata are required to optimize scrubber designs for CO

2

sequestration from fossil fuel derived flue gases We propose

Journal of Chemistry 3

Table 1 Recommended values for variables to be monitored during bubbling tests

Variable Resolution Range Uncertainty FS

119860119888

sensibility Observations This work for CO2

119860119888of MEA

Gascomposition

lt05 ofpollutant inletconcentration

0ndash100 ofpollutant inletconcentration

05 for CO2

34

(i) Use well accepted methods fordetermining pollutantconcentration in the gas stream(ii) Avoid using gases with thirdcomponents that could also beabsorbed by the solvent

(i) 13 CO2 87 N

2

(ii) 21 CO2 15

CH4 64 N

2

(iii) 100 CO2

Gas flow 01 SLPM 0ndash2 SLPM 02 52 (i) Use mass flow meter(ii) Ensure gas residence time gt60 s 01ndash10 SLPM

Temperature 05∘C ND 05 3Ensure constant temperature withinplusmn2∘C in the bubbler using a properwater bath

25 plusmn 2∘C

Pressure 1 kPa ND 05 10 ND 1013 kPaTime 1 s ND 05 lt1 ND 0ndash7200 sPore size ND ND ND ND 1 120583m 1 120583m

Bubbler size ND ND ND ND (i) 1 L(ii) Ensure no leaks 1 L

Amount ofsolvent inthe bubbler

ND ND ND ND 05 L 05 L

SolventDilution 05 0ndash50 ND Figure 3

(i) Use analytical grade solvent(ii) Express dilution as weight toweight percentage

0ndash30 (ww)

ND not defined FS full scale

a standardmethod for the determination of absorbing capac-ities consisting of a gas bubbler apparatus in which the gasphase substance is bubbled into a fixed amount of absorbentunder standard conditions We systematically applied thismethod to determine the CO

2absorbing capacity of MEA

as a function of MEA concentration and CO2concentration

in the gas stream The saturation curves obtained during theabsorption tests exhibited a sigmoidal shape that could bedescribed by an exponential function characterized by twoparameters the shape and efficiency factors The proper useof these factors could lead to more compact and efficientscrubber designs

2 Materials and Methods

Figure 2 illustrates the methodology proposed to determinethe chemical and physical absorbing capacity of solventsThe apparatus consists of a gas bubbler setup in which thegas stream is bubbled through a fixed amount of absorbentunder standard conditions Prior to testing the system istested for leaks and purged using an inert gas Experimentsare conducted under standard conditions of pressure andtemperature (101 kPa 25∘C) To ensure constant temperaturein the presence of exothermic or endothermic reactionsthe system is placed inside a thermostated water bath Thereactor is continuously stirred to prevent stratification orinhomogeneities within the reactor The inlet and outletgas composition and flow are measured using well acceptedmethods It is important to use a water vapor trap before

PT

Yi Qi Qo Yo

Water vaporcondenser

Temperature

MEA solutionBubbler

Magnetic stirrer

controlled water bath

Figure 2 Proposed apparatus to determine the absorbing capacityof gas phase components by liquid phase absorbers

measuring the outlet gas flow to preventmeasurement distor-tions due to the presence of water in the gas stream after thebubbling processThe total gas flow across the bubbler shouldbe as low as possible (lt1 SLPM) to ensure a full interactionof the gas with the solvent The temperature pressure andconcentration of the absorbing substance are also monitoredThe volume of solution in the bubbler is maintained at 05 L

Table 1 describes the variables to be measured and therecommended values for the independent variables as well asthe requirements for the sensors in terms of resolution rangeandmeasurementmethod Several trials should be conductedto verify the reproducibility of the results


0

5

10

15

20

25

30

35

0 5000 10000 15000 20000 25000Time (s)

5

10

25

50

75 100

Outflow

Inflow

CO2

conc

entr

atio

n (

)

Figure 3 Evolution of CO2molar concentration at inlet and outlet

of bubbler as function of aqueous MEA concentration

The method was applied to the determination of theCO2absorbing capacity of MEA at several aqueous MEA

concentrations and gaseous CO2concentrations

3 Results

Figure 3 depicts theCO2molar concentration of the gas phase

stream at the inlet and outlet of the bubbler It shows thatat an inlet concentration of 30 CO

2 MEA concentrations

lower than 50 (ww) were not able to absorb 100 of theCO2present in the gas streamThis low absorbing efficiency is

not a property of the MEA solvent but rather a characteristicof the test apparatus and indicates that the residence time ofthe gas stream within the bubbler for low MEA concentra-tions is too low to obtain accurate measurements

31 CO2Absorbing Capacity of MEA Using the values of

119910119894 119910119900 119876119894 and 119876

119900obtained as function of time during the

bubbling test (shown in Figure 3) the absorbing capacity ofthe solvent is determined by

119860119888=

119875119872

1198770119879119898int

119905119890

119905119904

(119910119900119876119900minus 119910119894119876119894) 119889119905 (5)

where 119872 is the molecular weight of component beingabsorbed 1198770 is the universal gas constant 119879 is the standardabsolute temperature119875 is the standard pressure 119905 is the time119904 and 119890 are indices to indicate the start and end of saturationprocess 119898 is the mass of solvent within bubbler 119876 is the gasvolumetric flow expressed at standard conditions and 119894 and119900 are theindices indicating inlet or outlet values

Figure 4 is a comparison of the values obtained the datareported in previous works and the nominal CO

2absorbing

capacity of MEAMore than 100 complete sets of experiments were carried

out by several collaborators It was found that the CO2

absorbing capacity of MEA is concentration dependentincreasing from 4479 plusmn 181 to 5813 plusmn 323 gCO

2kgMEA

Table 2 CO2absorbing capacity of MEA at 25∘C and 1013 kPa

120573 119860119888

Uncertaintylowast

ww gCO2KgMEA gCO

2KgMEA

25 5813 32350 4999 37175 4803 122100 5256 142150 5046 160200 4641 111250 4490 157300 4530 163lowastwith 95 of confidence

200

400

600

800

0 10 20 30

Yeh and Bai 1999

Rinprasertmeechai et al 2012 Kim et al 2013

219 CO2

131 CO2

416 CO2

Nominal Ac

= minus4665 ln(120573) + 60558

R2 = 04793

Ac(g

CO2k

gMEA

)

120573 (ww)

Ac

Figure 4 CO2absorbing capacity of MEA for several levels of

aqueous MEA concentration (120573) obtained using the bubblingmethod Yeh and Bai [22] used a reactor with 200mL of solvent anda gas flow rates of 2ndash10 SLPM of 8ndash16 of CO

2diluted in clean air

Temperature varied from 10 to 40∘C Rinprasertmeechai et al [23]used a stirred reactor containing 50mL of 30 (ww) aqueousMEAconcentration at 25∘C and with a simulated flue gas containing 15CO2 5 O

2 and 80 N

2and flowing at 005 SLPM Kim et al [24]

used a stirred reactor with 1 L of 30 (ww) aqueous MEA at 25∘Cwith 30 vol CO

2diluted in N

2and a flow rate of 1 SLPM All works

were conducted at atmospheric pressure

when 120573 was reduced from 30 to 25 (ww) and loga-rithmically approaching the nominal absorbing capacity of720 gCO

2KgMEA at very low concentrations Table 2 lists

the average values and the experimental error observedChanges in the CO

2absorbing capacity with solvent

dilution were also observed by Yeh and Bai [22] for theNH3H2OCO

2system Changes in the CO

2absorption

capacity of MEA with concentration may be explained byconsidering that excess water favors reaction (4) and thatthis reaction leads to a nominal absorbing capacity twice thatobtained through reaction (3) Therefore low concentrationsof MEA result in maximal CO

2absorption at the expense

of reducing the interaction between the CO2and MEA

molecules and lower probability of reaching full amine sat-uration in a reasonable time Changes in the CO

2absorption

capacity of MEA with solvent dilution could also be due tosolvation effects


2

4

6

8

10

0 10 20 30

a

120573 (ww)

219 CO2

131 CO2

(a)

0

1

2

3

4

5

0 10 20 30

n

120573 (ww)

219 CO2131 CO2

(b)

Figure 5 Results of curve fitting of CO2concentration to (6) The efficiency factor (119886) is plotted on the left and the form factor (119899) is plotted

on the right as function of the aqueous MEA concentration The blue horizontal line indicates the corresponding average value

These results define the technological challenge in estab-lishing optimum scrubber operating conditions High MEAconcentrations ensure 100 removal efficiency but providelow CO

2absorbing capacities and increase the amount

of MEA required in the process On the other side lowconcentrations provide high CO

2absorbing capacity but low

removal efficiency It is possible that a sequential two-stepprocess could be the most cost-effective means of achievingthese opposing objectives

Figure 4 also compares the CO2absorbing capacities of

MEA measured in these experiments with those reported inpreviousworks Although the results are not fully comparablesince they were obtained under different conditions Figure 4shows that the values are similarThemost relevant differencewith Yeh and Bai [22] and Rinprasertmeechai et al [23] wasthe presence of O

2in the gas stream and with Huertas et al

[7] was the presence of H2S in the gas stream Besides CO

2

MEA can absorb H2S SO2 and HCl [22] MEA is degraded

by the presence of O2 NO2 SO2 HCl andHF [25]Therefore

in the determination of the CO2absorbing capacity of MEA

it is important to eliminate the interference of these speciesFigure 4 also shows that the absorbing capacity was

independent of gas phase CO2concentration It was found

that this conclusion is true as long as the gas stream does notinclude MEA sensitive components such as O

2and H

2S

It could be argued that the increase in MEA absorbingcapacity at low concentrations is due to the contributionof the CO

2absorbing capacity of water Therefore a set of

experiments was performed to determine the CO2absorbing

capacity of pure water Using the present methodology itwas found that water absorbed 03 g CO

2kgH2O a negligible

amount compared to the variations in CO2absorption

capacity observed in aqueous MEA solutions Since water isonly capable of physical CO

2absorption this measurement

was compared to the value obtained from Henryrsquos lawconstant For the conditions under which the experimentwas carried out Henryrsquos constant is 144MPa [26] and theCO2absorbing capacity of water at standard conditions is

0375 gCO2kgH2OThis agreement demonstrates the ability

of the proposed method to measure both chemical andphysical absorption

32 Characterization of the Saturation Process Figure 3 indi-cates that the outlet CO

2concentration profiles during the

bubbling tests exhibited a sigmoidal shape and could be fittedto the following equation

119884 minus 119884119904

119884119890minus 119884119904

= 1 minus 119890minus119886((119905minus119905

119904)(119905119890minus119905119904))119899

(6)

where 119886 is the efficiency factor 119899 is the form factor 119905 is thetime and 119904 and 119890 are indices to indicate the start and end ofsaturation process 119886 and 119899 may be obtained by linear curvefitting when (6) is expressed as follows

ln(minus ln(1 minus119884 minus 119884119904

119884119890minus 119884119904

)) = 119899 ln(119905 minus 119905119904

119905119890minus 119905119904

) + ln (119886) (7)

The correlation coefficients obtained from curve fits for allcases were near unity (1198772 gt 097) indicating that theexperimental data fit well with (6)This demonstrates that thesaturation process was well represented by 119886 and 119899 and thesetwo parameters uniquely characterize the solvent absorbingcapacity

Figure 5 contains plots of the results for 119886 and 119899 It canbe observed that the factor form 119899 and the efficiency factorwere not concentration dependent (119886 = 61 plusmn 035 and 119899 =

25 plusmn 012)These factorsmay be used to estimate the CO

2absorption

capacity of MEA at any aqueous concentration to comparedifferent solvents and to determine the saturation time duringthe bubbling test

33 Sensitivity Analysis According to (5) 119860119888is a function

of pressure temperature gas phase CO2concentration volu-

metric flow rate and saturation time Applying the equationof error composition ((8) where 120597119860

119888120597119902119894is the absolute

value of the partial derivative of 119860119888with respect to each


independent variable 119902119894[27]) to (5) and considering the

precision of the instruments specified in Table 1 (Δ119902119894) and the

range of the values typically measured by each variable (alsospecified in Table 1) the uncertainty of the values obtainedfor 119860119888(Δ119860119888) is less than 1 of the reported values The CO

2

concentration and volumetric flow had the greatest effect onthe absorbing capacity determination and special attentionshould be given to the accuracy and precision of instrumentsused to monitor these two variables Table 1 includes theapproximate percent contribution of each variable to the totaluncertainty of the values obtained for 119860

119888using the bubbling

test Consider

Δ119860119888= sum

10038161003816100381610038161003816100381610038161003816

120597119860119888

120597119902119894

10038161003816100381610038161003816100381610038161003816

Δ119902119894 (8)

4 Conclusions

A standard test is described for the determination of thephysical and chemical absorbing capacity of gas phase com-ponents by liquid phase absorbers It consists of a gas bubblerapparatus in which the gas stream is bubbled into a fixedamount of absorbent under standard conditions Sensitivityanalysis indicated that gas composition and volumetric floware the variables with the greatest effect on the absorbingcapacity determination and special attention should be givento the accuracy and precision of the instruments used tomonitor them

Thismethodwas applied to determine the CO2absorbing

capacity of MEA (119860119888) at several aqueousMEA concentration

levels (120573) and gaseous CO2concentrations It was found

that 119860119888approaches the nominal CO

2absorbing capacity

(720 gCO2kgMEA) at very low 120573 increasing from 4479 plusmn

181 to 5813plusmn323 gCO2kgMEAwhen 120573was reduced from

30 to 25 (ww) These results agree with values reportedfor 119860

119888in previous studies As expected the CO

2absorbing

capacity ofMEAdid not depend on the CO2concentration in

the inlet gas stream as long as the gas stream did not includeother components that could react with the amine such asH2S or O

2

During the bubbling tests the outlet CO2concentration

profiles exhibited a sigmoidal shape that could be describedby an exponential equation containing an efficiency factor (119886)and a form factor (119899) Statistical analyses based on correlationanalysis revealed that in all cases the experimental data fitwellto that equation when 119886 was 61 plusmn 035 and 119899 was 25 plusmn 012

and therefore these two parameters characterize the CO2

absorbing capacity of MEA under standard conditions

Symbols

119886 Efficiency factor119860119888 CO

2absorbing capacity of MEA (gCO

2KgMEA)

119867119860 Henryrsquos constant of component 119860 (kPa)

119898 Mass of MEA within the bubbler (kg)119872 Molecular weight of the component being absorbed

(kgkmol)119899 Form factor

119875 Standard pressure (kPa)119875119860 Equilibrium partial pressure of component 119860 in gas

phase (kPa)119876 Gas volumetric flow expressed at standard

conditions (m3s)1198770 Universal gas constant (kJkmol K)

SLPM Standard liters per minute119905 Time (s)119879 Standard absolute temperature (K)119909119860 Equilibrium concentration of component 119860 in the

liquid phase expressed as molar fraction119910119860 Equilibrium concentration of component 119860 in gas

phase expressed as molar fraction120572 Loading (moles of CO

2mole of amine)

120573 Aqueous MEA concentration (kg of amine per kgof water)

120578 Removal efficiency ()119894 119900 Index for inlet and outlet respectively119904 119890 Index to indicate the start and end of the saturation

process respectively

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This project was partially financed by the National and EstateMexican Council of Science and Technology (CONACYTand COMECYT) the MOPESA Company of Mexico theGlobal Institute of Sustainability of Tecnologico deMonterreyof Mexico and the EANUniversity of ColombiaThe authorsalso express their gratitude for contributions to this workfrom Engineers Maryin Rache and Johana Diez of theNational University of Colombia

References

[1] Intergovernmental Panel on Climate Change (IPCC) Climatechange Synthesis Reportmdash4th Assessment Report 2007

[2] IPCC SRRENmdashFinal Release IPCCmdashWG IIImdashMitigation andClimate Change IPCC 2011

[3] A F Ghoniem ldquoNeeds resources and climate change cleanand efficient conversion technologiesrdquo Progress in Energy andCombustion Science vol 37 no 1 pp 15ndash51 2011

[4] International Energy Agency (IEA) Energy Technology Anal-ysis CO

2Capture and Storage International Energy Agency

(IEA) Paris France 2008[5] M Kanniche R Gros-Bonnivard P Jaud J Valle-Marcos J-M

Amann and C Bouallou ldquoPre-combustion post-combustionand oxy-combustion in thermal power plant for CO

2capturerdquo

Applied Thermal Engineering vol 30 no 1 pp 53ndash62 2010[6] G T Rochelle G S Goff J T Cullinane and S Freguia

ldquoResearch results for CO2capture from flue gas by aqueous

absorption strippingrdquo in Proceedings of the Laurance Reid GasConditioning Conference pp 131ndash151 Norman Okla USAFebruary 2002


[7] J I Huertas N Giraldo and S Izquierdo ldquoRemoval of H2S

and CO2from biogas by amine absorptionrdquo in Mass Transfer

in Chemical Engineering Processes chapter 7 InTech RijekaCroatia 2011

[8] R E Treybal Mass Transfer Operations McGraw-Hill Singa-pore 3rd edition 1996

[9] M Rameshni Carbon Capture Overview Worley ParsonsResources and Energy 2010 httpwwwworleyparsonscomCSGHydrocarbonsSpecialtyCapabilitiesDocumentsCar-bon20Capture20Overview20(3)pdf

[10] H Herzog An Introduction to CO2Separation and Capture

Technologies MIT Energy Laboratory 1999[11] J T Yeh H W Pennline and K P Resnik ldquoStudy of CO

2

absorption and desorption in a packed columnrdquo Energy andFuels vol 15 no 2 pp 274ndash278 2001

[12] A Kolh and R Nielsen Gas Purification Elsevier Science GulfProfessional Publishing Burlington Mass USA 1st edition1997

[13] E Ross Carbon Dioxide Absorption Desorption and Diffusionin Aqueous Piperazine and Monoethanilamine University ofTexas Austin Tex USA 2009

[14] J T Hvitved J Vollertsen and H A Nielsen Microbial andChemical Process Engineering of Sewer Networks CRC Press 1stedition 2001

[15] K Wark C F Warner andW T Davis Air Pollution Its Originand Control Addison-Wesley 3rd edition 2007

[16] D Tong J P M Trusler G C Maitland J Gibbins and PS Fennell ldquoSolubility of carbon dioxide in aqueous solutionofmonoethanolamine or 2-amino-2-methyl-1-propanol exper-imental measurements and modellingrdquo International Journal ofGreenhouse Gas Control vol 6 pp 37ndash47 2012

[17] J I Lee F D Otto and A E Mather ldquoEquilibrium betweencarbon dioxide and aqueous monoethanolamine solutionsrdquoJournal of Applied Chemistry and Biotechnology vol 26 no 10pp 541ndash549 1976

[18] K Shen and M Li ldquoSolubility of carbon dioxide in aqueousmixtures of monoethanolamine with methyldiethanolaminerdquoJournal of Chemical amp Engineering Data vol 37 no 1 pp 96ndash100 1992

[19] F-Y Jou A E Mather and F D Otto ldquoSolubility of CO2in a

30 mass percent monoethanolamine solutionrdquo The CanadianJournal of Chemical Engineering vol 73 no 1 pp 140ndash147 1995

[20] Q He M Chen L Meng K Liu and W P Ping Studyon Carbon Dioxide removal from Flue Gas by Absorptionof Aqueous Ammonia Institute for Combustion Science andEnvironmental Technology 2004

[21] H Arcis K Ballerat-Busserolles L Rodier and J-Y CoxamldquoEnthalpy of solution of carbon dioxide in aqueous solutionsof triethanolamine at temperatures of 3225 K and 3729 K andpressures up to 5MPardquo Journal of Chemical amp Engineering Datavol 57 no 12 pp 3587ndash3597 2012

[22] A C Yeh and H Bai ldquoComparison of ammonia andmonoethanolamine solvents to reduce CO

2greenhouse gas

emissionsrdquo The Science of the Total Environment vol 228 no2-3 pp 121ndash133 1999

[23] S Rinprasertmeechai S Chavadej P Rangsunvigit and SKulprathipanja ldquoCarbon dioxide removal from flue gas usingamine-based hybrid solvent absorptionrdquo International Scholarlyand Scientific Research amp Innovation vol 6 no 4 pp 362ndash3662012

[24] Y E Kim J A Lim S K Jeong Y I Yoon S T Bae and SC Nam ldquoComparison of carbon dioxide absorption in aqueousMEA DEA TEA and AMP solutionsrdquo Bulletin of the KoreanChemical Society vol 34 no 3 pp 783ndash787 2013

[25] G S Goff and G T Rochelle ldquoMonoethanolamine degrada-tion O

2mass transfer effects under CO

2capture conditionsrdquo

Industrial and Engineering Chemistry Research vol 43 no 20pp 6400ndash6408 2004

[26] J J Carroll J D Slupsky and A E Mather ldquoThe solubility ofcarbon dioxide in water at low pressurerdquoThe Journal of PhysicalChemistry vol 20 no 6 pp 1201ndash1209 1991

[27] A A CliffordMultivariate Error Analysis A Handbook of ErrorPropagation and Calculation in Many-Parameter Systems JohnWiley amp Sons New York NY USA 1973

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of solvent This property is used to define the appropri-ate loading (pollutantsolvent molar ratio 120572) in scrubberdesigns Low loadings result in columns with low absorbingefficiencies while high loadings lead to excessive solventrequirements and high operational costs The CO

2absorbing

capacity of amines is dependent on the solvent concentrationthe composition of the gas stream and the operating temper-ature [13]

Amines are capable of chemical and physical CO2absorp-

tion Physical absorption is controlled by the thermodynamicequilibrium between CO

2molecules in the gas and aqueous

phases and is described by Henryrsquos law [8 14]

119875119860= 119910119860119875 = 119867

119860119909119860 (2)

where 119875119860is the equilibrium partial pressure of component

119860 in gas phase 119875 the total pressure 119867119860the Henryrsquos law

constant of component 119860 119910119860the equilibrium concentration

of component 119860 in gas phase (expressed as molar fraction)and 119909

119860the equilibrium concentration of component 119860 in

liquid phase (expressed also as molar fraction)The Henryrsquos law constant is determined in a temperature

and pressure controlled sealed chamber by measuring theequilibrium concentration of the component in the gas andliquid phases using spectrophotometric or chromatographicanalysis [15] This method is appropriate for systems under-going pure physical absorption for example CO

2absorption

inH2OHowever it is inappropriatewhen the solvent exhibits

chemical absorption since the method does not ensurethat the solvent becomes fully saturated Investigators haveemployed this method for several years expressing theirresults in terms of the equilibrium partial pressure of thegas phase component and referring to these values as thesolubility of the pollutant in the solvent Tong et al [16]combined experimental work with an extensive literaturereview to describe the solubility ofCO

2in 30 (ww) aqueous

solutions of MEA as a function of temperature and loading[17ndash19] For the readerrsquos convenience Figure 1 reproduces theresults published These results cannot be used to describethe absorption capacity of the solvent since the equilibriumconditions under which the data was collected do not ensuresaturation of the solvent Furthermore these results cannotbe used to determineHenryrsquos law constant for theMEA-H

2O-

CO2system since they do not quantify the CO

2remaining

in molecular form within the liquid phase and because asmentioned earlier the system exhibits chemical absorption

Chemical absorption is based on reactions between CO2

and the amine It has been reported that chemical absorptiondoes not increase significantly with pressure [20] There aretwo fundamental mechanisms for the reaction of amines (R-NH2) with CO

2[9]

2R-NH2+ CO2larrrarr R-NH

3

++ R-NH-COOminus (3)

R-NH2+ CO2+H2O larrrarr R-NH

3

++HCO

3

minus (4)

For common primary and secondary amines such as MEAand DEA reaction (3) prevails to form a stable car-bamate (R-NH-COOminus) requiring 2 moles of amine permole of CO

2and thus limiting the absorbing capacity of

01

0001

001

1

10

100

1000

Shen and Li 1992

Lee et al 1976

Tong et al 2012

Jou et al 1995

PCO

2(k

Pa)

00 02 04 06 08

313K

120572CO2

Figure 1 Solubility of CO2in 30 (ww) aqueousMEA solutions at

313 K as a function of loading (moles of CO2per mole of MEA 120572)

from Tong et al [16]

the amine to 05 moles of CO2per mole of amine that

is 360 gCO2KgMEA However unstable carbamates can

hydrolyze to form bicarbonate (HCO3

minus) as described byreaction (4) Under this condition the nominal MEA CO

2

absorbing capacity is one mole of CO2per mole of MEA [9]

that is 720 gCO2KgMEA Tertiary amines such as MDEA

only follow reaction (4) [21]The physical and chemical MEA absorption capacities

are affected by temperature pressure presence of additionalgases and the aqueous MEA concentration

Yeh and Bai [22] measured the CO2absorption capacity

of MEA in a semicontinuous reactor consisting of a 60mmglass bottle containing 200mL of solvent The absorptioncapacities ranged from 360 to 380 gCO

2kgMEA usingMEA

concentrations of 7ndash35 (ww) and gas flow rates of 2ndash10SLPM of 8ndash16 of CO

2diluted in clean air The reaction

temperature varied from 10 to 40∘C Recently Rinprasert-meechai et al [23] used a stirred 100 mL reactor containing50mL of 30 (ww) aqueous MEA concentration at 25∘Cand atmospheric pressure to obtain an absorption capacityof 045 CO


2kgMEA) for a

simulated flue gas containing 15 CO2 5 O

2 and 80 N

2

and flowing at 005 SLPMThese two papers neither reportedthe outlet gas flownor removed theO

2in the gas stream lead-

ing to an underestimation of the CO2absorbing capacity of

MEA Recently Kim et al [24] reported an absorbing capacityof 0565CO


2kgMEA) using

30 vol CO2diluted in N

2and a fixed flow rate of 1 SLPM

monitored by amass flow controller and gas chromatographyto determine CO

2concentration at the outlet of the reactor

The disagreements present in previous results are dueto variations in testing methods amine dilution solventtemperature and pressure and inlet gas composition andhighlight the need for a standard method to determine theabsorbing capacity of solvents The resulting experimentaldata are required to optimize scrubber designs for CO

2

sequestration from fossil fuel derived flue gases We propose




119860119888


119860119888of MEA

Gascomposition



05 for CO2

34


(i) 13 CO2 87 N

2

(ii) 21 CO2 15

CH4 64 N

2

(iii) 100 CO2



25 plusmn 2∘C







0ndash30 (ww)








PT

Yi Qi Qo Yo


Temperature

MEA solutionBubbler

Magnetic stirrer






0

5

10

15

20

25

30

35

0 5000 10000 15000 20000 25000Time (s)

5

10

25

50

75 100

Outflow

Inflow

CO2

conc

entr

atio

n (

)





3 Results







119910119894 119910119900 119876119894 and 119876



119860119888=

119875119872

1198770119879119898int

119905119890

119905119904

(119910119900119876119900minus 119910119894119876119894) 119889119905 (5)



2absorbing




2kgMEA


120573 119860119888

Uncertaintylowast

ww gCO2KgMEA gCO

2KgMEA


200

400

600

800

0 10 20 30

Yeh and Bai 1999


219 CO2

131 CO2

416 CO2

Nominal Ac

= minus4665 ln(120573) + 60558

R2 = 04793

Ac(g

CO2k

gMEA

)

120573 (ww)

Ac





2 and 80 N



2diluted in N









2absorption





2absorption



2

4

6

8

10

0 10 20 30

a

120573 (ww)

219 CO2

131 CO2

(a)

0

1

2

3

4

5

0 10 20 30

n

120573 (ww)

219 CO2131 CO2

(b)












2







2and H

2S





2kgH2O a negligible










119884 minus 119884119904

119884119890minus 119884119904


119904)(119905119890minus119905119904))119899

(6)



119884119890minus 119884119904

)) = 119899 ln(119905 minus 119905119904

119905119890minus 119905119904

) + ln (119886) (7)




2absorption





119888120597119902119894is the absolute






2



test Consider

Δ119860119888= sum

10038161003816100381610038161003816100381610038161003816

120597119860119888

120597119902119894

10038161003816100381610038161003816100381610038161003816

Δ119902119894 (8)

4 Conclusions






2absorbing capacity





2absorbing



2





Symbols



2KgMEA)










2mole of amine)






Acknowledgments


References








2capturerdquo












2














2greenhouse gas



















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




119860119888


119860119888of MEA

Gascomposition



05 for CO2

34


(i) 13 CO2 87 N

2

(ii) 21 CO2 15

CH4 64 N

2

(iii) 100 CO2



25 plusmn 2∘C







0ndash30 (ww)








PT

Yi Qi Qo Yo


Temperature

MEA solutionBubbler

Magnetic stirrer






0

5

10

15

20

25

30

35

0 5000 10000 15000 20000 25000Time (s)

5

10

25

50

75 100

Outflow

Inflow

CO2

conc

entr

atio

n (

)





3 Results







119910119894 119910119900 119876119894 and 119876



119860119888=

119875119872

1198770119879119898int

119905119890

119905119904

(119910119900119876119900minus 119910119894119876119894) 119889119905 (5)



2absorbing




2kgMEA


120573 119860119888

Uncertaintylowast

ww gCO2KgMEA gCO

2KgMEA


200

400

600

800

0 10 20 30

Yeh and Bai 1999


219 CO2

131 CO2

416 CO2

Nominal Ac

= minus4665 ln(120573) + 60558

R2 = 04793

Ac(g

CO2k

gMEA

)

120573 (ww)

Ac





2 and 80 N



2diluted in N









2absorption





2absorption



2

4

6

8

10

0 10 20 30

a

120573 (ww)

219 CO2

131 CO2

(a)

0

1

2

3

4

5

0 10 20 30

n

120573 (ww)

219 CO2131 CO2

(b)












2







2and H

2S





2kgH2O a negligible










119884 minus 119884119904

119884119890minus 119884119904


119904)(119905119890minus119905119904))119899

(6)



119884119890minus 119884119904

)) = 119899 ln(119905 minus 119905119904

119905119890minus 119905119904

) + ln (119886) (7)




2absorption





119888120597119902119894is the absolute






2



test Consider

Δ119860119888= sum

10038161003816100381610038161003816100381610038161003816

120597119860119888

120597119902119894

10038161003816100381610038161003816100381610038161003816

Δ119902119894 (8)

4 Conclusions






2absorbing capacity





2absorbing



2





Symbols



2KgMEA)










2mole of amine)






Acknowledgments


References








2capturerdquo












2














2greenhouse gas



















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0

5

10

15

20

25

30

35

0 5000 10000 15000 20000 25000Time (s)

5

10

25

50

75 100

Outflow

Inflow

CO2

conc

entr

atio

n (

)





3 Results







119910119894 119910119900 119876119894 and 119876



119860119888=

119875119872

1198770119879119898int

119905119890

119905119904

(119910119900119876119900minus 119910119894119876119894) 119889119905 (5)



2absorbing




2kgMEA


120573 119860119888

Uncertaintylowast

ww gCO2KgMEA gCO

2KgMEA


200

400

600

800

0 10 20 30

Yeh and Bai 1999


219 CO2

131 CO2

416 CO2

Nominal Ac

= minus4665 ln(120573) + 60558

R2 = 04793

Ac(g

CO2k

gMEA

)

120573 (ww)

Ac





2 and 80 N



2diluted in N









2absorption





2absorption



2

4

6

8

10

0 10 20 30

a

120573 (ww)

219 CO2

131 CO2

(a)

0

1

2

3

4

5

0 10 20 30

n

120573 (ww)

219 CO2131 CO2

(b)












2







2and H

2S





2kgH2O a negligible










119884 minus 119884119904

119884119890minus 119884119904


119904)(119905119890minus119905119904))119899

(6)



119884119890minus 119884119904

)) = 119899 ln(119905 minus 119905119904

119905119890minus 119905119904

) + ln (119886) (7)




2absorption





119888120597119902119894is the absolute






2



test Consider

Δ119860119888= sum

10038161003816100381610038161003816100381610038161003816

120597119860119888

120597119902119894

10038161003816100381610038161003816100381610038161003816

Δ119902119894 (8)

4 Conclusions






2absorbing capacity





2absorbing



2





Symbols



2KgMEA)










2mole of amine)






Acknowledgments


References








2capturerdquo












2














2greenhouse gas



















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


2

4

6

8

10

0 10 20 30

a

120573 (ww)

219 CO2

131 CO2

(a)

0

1

2

3

4

5

0 10 20 30

n

120573 (ww)

219 CO2131 CO2

(b)












2







2and H

2S





2kgH2O a negligible










119884 minus 119884119904

119884119890minus 119884119904


119904)(119905119890minus119905119904))119899

(6)



119884119890minus 119884119904

)) = 119899 ln(119905 minus 119905119904

119905119890minus 119905119904

) + ln (119886) (7)




2absorption





119888120597119902119894is the absolute






2



test Consider

Δ119860119888= sum

10038161003816100381610038161003816100381610038161003816

120597119860119888

120597119902119894

10038161003816100381610038161003816100381610038161003816

Δ119902119894 (8)

4 Conclusions






2absorbing capacity





2absorbing



2





Symbols



2KgMEA)










2mole of amine)






Acknowledgments


References








2capturerdquo












2














2greenhouse gas



















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





2



test Consider

Δ119860119888= sum

10038161003816100381610038161003816100381610038161003816

120597119860119888

120597119902119894

10038161003816100381610038161003816100381610038161003816

Δ119902119894 (8)

4 Conclusions






2absorbing capacity





2absorbing



2





Symbols



2KgMEA)










2mole of amine)






Acknowledgments


References








2capturerdquo












2














2greenhouse gas



















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of









2














2greenhouse gas



















Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of