MICMAT4070

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Amine loaded zeolites for carbon dioxide capture: Amine loading andadsorption studies

Ravikrishna Chatti, Amit K. Bansiwal, Jayashri A. Thote, Vivek Kumar, Pravin Jadhav,Satish K. Lokhande, Rajesh B. Biniwale, Nitin K. Labhsetwar, Sadhana S. Rayalu *

National Environmental Engineering Research Institute, Nagpur, India

a r t i c l e i n f o

Article history:Received 3 June 2007Received in revised form 17 December 2008Accepted 8 January 2009Available online 18 January 2009

Keywords:ZeoliteCO2 CaptureAmine immobilizationQuantitative estimations

a b s t r a c t

Novel functionalised adsorbents have been synthesized by immobilization of various amines on syntheticzeolite 13X. Various primary and secondary amines namely monoethanolamine (MEA), ethylenediamine(ED) and isopropanol amine (IPA) have been immobilized on zeolite 13X. Quantitative estimations of theamine loadings were undertaken using different analytical techniques namely titrimetric, total organiccarbon and gas chromatography analysis. Fairly good correlation was obtained for amine loadings esti-mated using the three techniques. Effect of various parameters like effect of solvent, shaking time, syn-thesis temperature, and wetting of pellets prior to amine loadings was also studied. The results revealedthat maximum loading was achieved for methanol-mediated synthesis conducted using previously wet-ted pellets at room temperature and with 15 min of shaking time. Preliminary attempts have also beenmade to determine the CO2 adsorption capacities of these newly developed materials. The adsorptioncapacities obtained were 16.01 mg/g for unmodified zeolite 13X and 19.98, and 22.78 mg/g for zeolitemodified with monoethanol amine, and isopropanol amine.

� 2009 Published by Elsevier Inc.

1. Introduction

With the advent of the industrial revolution, man has improvedthe utilization of his resources and this has increased industrialactivity to new heights. However, this has also become the startingpoint for serious problems in the environment like the greenhouseeffect leading to the global warming. The major greenhouse gasesare carbon dioxide, chlorofluorocarbons (CFCs), N2O methane, etc.

However, the major culprit is carbon dioxide. CO2 acts as a blan-ket to trap the infrared radiations coming from the earth’s atmo-sphere, thus resulting in warming of the earth’s surface and risein surface temperature. The ambient concentration of CO2 has in-creased from about 280 ppm from the pre-industrial revolutionperiod (early 1900) to the current levels of 380 ppm [1]. The devel-opment of suitable carbon capture and sequestration technologiesis the solution to tackle this global phenomenon. Research is goingon to develop feasible options for CO2 sequestration. Post combus-tion CO2 capture has emerged as one of the significant options to-wards reducing the anthropogenic CO2 emissions. CO2 capture hasbecome a key issue to be addressed by the scientific community.Research in this key area is going on at a global scale and the exist-ing CO2 capture methods are amine based absorption, membranebased separation, adsorption and cryogenic separation [2]. There

is an increasing need to capture the CO2 emitted from coal-firedpower plants, operating at temperatures around 120 �C–150 �C. Awide range of adsorbent materials have been investigated like zeo-lites, activated carbons, pillared clays and metal oxides [3–15].

However, in these conventional adsorbents, physical adsorptionplays an important role in the adsorption of CO2. It has been re-ported by Siriwardene et al. that CO2 adsorption capacity of zeo-lites 13X, 4A and activated carbon was about 160, 135 and110 mg/g adsorbent, respectively, at 25 �C and 1 atm CO2 partialpressure. The adsorption capacity decreases rapidly with increas-ing temperature. Thus, these adsorbents need to be modified soas to facilitate chemical adsorption in these adsorbents. Thus, thereis an increasing demand to design highly selective adsorbents,which can operate at such high temperatures [16].

The objective of the present work was to synthesize novel adsor-bents by immobilization of different primary and secondary amineson zeolite 13X matrix. This immobilization is expected to imparthigh adsorption capacity for CO2 as compared to the bare zeolite13X matrix. The adsorbent support chosen was zeolite 13X as ithas a pore size of 10 Å. This pore size can accommodate both theimmobilized amines in the zeolite pore and the adsorbed CO2.

2. Experimental

The amines used in the synthesis of the adsorbents were analyt-ical grade monoethanolamine, ethylene diamine and isopropanol

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* Corresponding author. Tel./fax: +91 712 2247828.E-mail address: [email protected] (S.S. Rayalu).

Microporous and Mesoporous Materials 121 (2009) 84–89

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amine, respectively. These amines were procured from E-Merck,India and were used as such without any further purification.The solvent used was HPLC grade methanol and was procured fromQualigens, India. Zeolite 13X in the form of pellets of approxi-mately 1.5 mm was procured from E-Merck, India. GC grade nitro-gen (99.995%) and ultra pure helium (99.999%) were obtained fromChemito Technologies, Nashik, India for conducting the adsorptionstudies. Carbon dioxide (99.99%) was procured from M/s. SirinGases, Nagpur, India.

2.1. Synthesis of the adsorbents

The synthesis of amine-immobilized adsorbents was carried outusing three different routes. These routes differ in the manner theamine was immobilized on the zeolite. Scheme 1 represents aschematic description of the different routes of synthesis under-taken during the experiments. Details of the synthesis of the differ-ent adsorbents are given below.

2.1.1. Amine immobilization in aqueous mediaAqueous solutions of monoethanolamine, ethylene diamine and

isopropanol amine were added to appropriate amount of zeolite13X in a solid–liquid ratio of 1:2 and the mixture was agitatedon a rotary shaker for different periods of time (15 min, 2 h and4 h). Three different amine concentrations were studied with ini-tial concentration as 25, 50 and 80 wt%. Amine solution was sepa-rated from the zeolite after shaking by decantation and thesamples were air dried overnight.

2.1.2. Amine immobilization in organic solventThe immobilization of amines was also carried out through

alcoholic solutions of amine. The amine solutions with differentconcentrations corresponding to 25, 50 and 80 wt% loadings wereprepared in methanol. The zeolite was wetted with methanol priorto agitation with amine solution by agitating zeolite 13X beads andmethanol in solid liquid ratio of 1:2 for a period of 10 min in twostages. The wetted beads were then air-dried and then agitatedwith alcoholic amine solution for a period of 15 min and 4 h on arotary shaker at ambient temperature, keeping the solid liquidratio at 1:2. The amine solution was decanted and stored foranalysis whereas the zeolite beads were allowed to dry in airovernight.

2.1.3. Immobilization of amines through reflux methodThe synthesis of amine loaded zeolite 13X was also carried out

by refluxing the zeolite beads with respective amine solution at70 �C to study the effect of temperature on amine loadings. In atypical synthesis, 15 g of zeolite 13X beads were refluxed with30 ml of alcoholic amine solution in a round bottom flask equippedwith a water condenser. After 2 h reflux, the amine solution wasdecanted and the beads were allowed to dry in air overnight.

2.2. Characterization of the synthesized adsorbents

The synthesized adsorbents were characterized to obtain a use-ful comparison with the unmodified zeolite 13X, using differentcharacterization techniques. Powder X-ray diffraction studies werecarried out using a Phillips Analytical Xpert diffractometer withmonochromatic Cu Ka radiation (k = 1.54 Å). To assess the struc-tural integrity of the adsorbents after the incorporation of thedifferent amines, the adsorbents were analyzed in a 2h range of5�–60�.

A Micromeritics BET surface area analyzer (Model No. ASAP2020) equipped with TriStar 3000 V6.03-A software was utilizedto determine the N2 BET surface area and pore volume of the syn-thesized adsorbents. To avoid the possibility of degradation of theincorporated amine, evacuation of the adsorbents was carried outat 90 �C and then subjected to N2 adsorption at liquid nitrogentemperature (�196 �C). The BET surface area and pore volumewas determined by using the single point adsorption method.

Thermogravimetric analysis was performed using a Rigaku-TAS-200 apparatus to study the thermal stability and dehydrationcharacteristics of the synthesized adsorbents. About 20 mg of thesample was kept in TG pan and was heated at a heating rate5 �C/min in an atmosphere of air. The samples were heated fromroom temperature to 500 �C. The weight loss and the rate of weightloss (dTG = dW/dT) was recorded.

The IR spectra of the synthesized materials were recorded usinga Perkin–Elmer spectrometer using the KBr pellet technique. Thesamples were analyzed in the wavelength region 4000–400 cm�1.

2.3. Determination of amine loadings

The weight percent loadings of the different amines on the13X zeolite beads were calculated from the difference in amine con-

• Immobilization in aqueous

media.

• Different intervals of stirring

maintained.

• Study was conducted using

three different amine

concentrations.

• Immobilization in organic

solvent, methanol.

• Wetting of zeolite was done prior to immobilization.

• Pre-treatment improved amine immobilization.

• Study was conducted using

three different amine

concentrations.

• Immobilization was

done by the reflux

method.

• Refluxed at a

temperature of 700C.

• Method does not yield

higher amine loading

as compared to the

solvent immobilization

method.

Different routes for immobilization of amines in the zeolite matrix

Scheme 1. Different routes for immobilization of amines in the zeolite matrix.

R. Chatti et al. / Microporous and Mesoporous Materials 121 (2009) 84–89 85


centrations before and after treating with zeolite. The concentra-tions of amines were determined using titrimetric analysis, gaschromatography (GC) and total organic carbon estimation (TOC).

The amine concentrations in initial and final amine solutionswere determined by titrimetric analysis using the procedure de-scribed by Seaman and Allen [17]. According to this procedure,mixture of amine solution and glacial acetic acid was titratedagainst a 0.1 N solution of perchloric acid in glacial acetic acid.From the difference of amine content in the initial amine solution(i.e., before loading) and residual amine solution (obtained afterloading) the amount of amine loaded on zeolite 13X was calculatedin terms of weight percent of amine incorporated in the zeolitematrix.

Gas chromatographic determinations of amines were carriedout with GC with Flame Ionization Detector (FID) (Perkin–Elmer,Model Autosystem). A chromosorb stainless steel column, 80–100 mesh provided by PCI services was used in the analysis. GCgrade nitrogen was used as the carrier gas for the analysis. A cali-bration plot for each amine was plotted by injecting a known vol-ume (1 ll) of different molar solutions of amine. After plotting thecalibration plot between the peak area and the molarity of the dif-ferent amine solutions, the experimental solutions of each aminesolution were injected and the estimation of the residual aminecontent was done.

Since amine is a source of organic carbon, TOC technique can beused indirectly to estimate the amine content. The TOC of the ini-tial and residual amine solutions were analyzed using a non-dis-persive infrared (NDIR) TOC analyzer (Thermo ElectronCorporation, Model 1200).

2.4. CO2 adsorption studies

CO2 adsorption was studied using breakthrough adsorptioncurves method. The breakthrough curve (BTC) method was chosenas the evaluation method due to its usefulness in comparing thevarious adsorbents. In addition, this method offers a distinctadvantage to determine the dynamic adsorption capacity and toevaluate in practical way, i.e., packed bed, flow system etc. whichcan be very useful to study a simulated flue gas stream as de-scribed in our previous studies [18,19]. The experimental set uphad mass flow controllers (Aalborg, USA), adsorption column(diameter = 1 cm; height = 30 cm), sample selector valve (Valco,

USA), 1 ml sample loop and gas chromatograph (Chemito Technol-ogies; Model GC 7610). In a typical evaluation protocol, 10 g dryadsorbent was pretreated in He gas flow (20 ml/min) at 140 �Cfor 6 h, cooled to adsorption temperature (75 �C) and contactedwith 15 vol% CO2 gas in He balance at a total flow rate of 52 ml/min. The outlet was continuously monitored using GC–TCD fittedwith Porapak-Q column and the adsorption breakthrough pointwas determined. Commercial zeolite 13X (E-Merck, India) and zeo-lite 13X modified with MEA and IPA at 50 wt% initial amine con-centration were studied for CO2 adsorption.

3. Results and discussion

3.1. Characterization

Characterization of the representative adsorbents namely barezeolite 13X and zeolite 13X contacted with MEA solution of con-centration 50 wt% was studied. The effect of amine loading onthe structural properties of zeolite matrix was investigated byobtaining XRD patterns before and after amine incorporation. Fromthe x-ray diffractogram of monoethanolamine (MEA) incorporatedzeolite presented in Fig. 1 it can be observed that the structuralintegrity of zeolite 13X is maintained even after the incorporationof the amine.

Reduction in the BET surface area and pore volume of the zeo-lite 13X after the incorporation of MEA was observed which indi-cates that the amine molecules have occupied the pore volume(Table 1). These results provide a correlation with the pore filingeffect of MEA and also confirm that MEA was immobilized in thezeolite pores. This trend is reported in literature [20].

It can be observed from the TG profile given in Fig. 2, thatunmodified 13X and MEA modified 13X zeolites show weight losstill 400 �C. It has been reported that, zeolites exhibit dehydrationtill 350 �C [21]. However, this temperature is dependent on the

Fig. 1. XRD pattern of 50% MEA/13X.

Table 1Surface area and pore volume analysis of adsorbents.

S. no. Adsorbents BET surface area (m2/g) Pore volume (cm3/g)

1. 13X zeolite matrix 386.4 0.23352. 50% MEA/13X zeolite 14.9 0.0441

86 R. Chatti et al. / Microporous and Mesoporous Materials 121 (2009) 84–89


heating rate used in the experiment. As a higher heating rate wasused in the present study, complete dehydration was observed atcomparatively higher temperature. Initial desorption of the pre-ad-sorbed moisture and other volatiles (including methanol used forwetting of 13X) was observed in all the adsorbents.

It can be observed that in case of 13X, there is a presence of onlya single continuous weight loss ‘step’ from room temperature to450 �C. This has stabilized with a total weight loss of about18.73%. A major weight loss is observed at 130 �C, which may beattributed to desorption of methanol and the moisture in the wet-ted 13X zeolite beads. In the case of MEA modified 13X, it has beenobserved that there are a total of three distinct weight loss steps at70, 150 and 240 �C. Since MEA has a boiling point of 170.8 �C, wemay attribute the second weight loss between 120 and 200 �C tovolatilization and degradation of MEA. The weight loss is observedto be 5.63% in this region. A total weight loss of 22.56% is observedwhich is about 4% higher than the unmodified adsorbent.

The presence of a peak at a frequency of about 3400 cm�1 is ob-served in the FT–IR spectra of the MEA modified zeolite 13X sam-ple, which was evaluated for CO2 adsorption. This may beattributed to the N–H stretching vibration. A peak at a frequencyof 3300 cm�1 is also observed which may be attributed to the N–H stretch of carbamate species (–NHCOO–), which may be formed

by the interaction of the amine molecule with carbon dioxide. TheFT-IR spectrum is presented in Fig. 3.

3.2. Effect of solvent in immobilization of amine

To understand the significance of solvent used in the synthesis,the synthesis was carried out using water and methanol as sol-vents for the immobilization. For these experiments, the analysistechnique used was the titrimetric method as this method can beeasily set up in the laboratory. Water was selected as a solvent con-sidering the solubility of amines in water and it’s use as a universalsolvent and it’s non-hazardous nature. Methanol was chosen spe-cifically as the solvent because of lower boiling point (64.7 �C) ascompared to water (100 �C), which may facilitate the proper dryingof the sample after immobilization. This would ultimately lead to auniform loading of the amine on the zeolite matrix. Fig. 4 comparesthe estimated MEA loading using methanol and water solvents.

From the above observations, we can conclude that comparableMEA loadings can be achieved by using methanol in lesser timethan water as solvent. It was also observed that the solvent immo-bilized sorbents can be dried in a lesser time period as compared totheir aqueous counterparts which can be attributed to the high vol-atility of methanol. Thus, from these observations, we can infer

0

5

10

15

20

25

0 100 200 300 400 500 600

Temperature (ºC)

Wei

ght (

mg)

-0.0025

-0.002

-0.0015

-0.001

-0.0005

0

dTG

13X-MEA-50, TG

13X, TG

13X, dTG13X-MEA-50, dTG

Fig. 2. Representative TG profile of the adsorbents.

Fig. 3. FTIR spectra of 50% MEA modified 13X zeolite evaluated for CO2 adsorption.

0

5

10

15

20

25

30

nim042nim51Agitation Period

MEA

load

ing

(wt%

)

WaterMethanol

Fig. 4. Effect of solvent on MEA loading.



that methanol is solvent of choice for the immobilization of MEAon the zeolite matrix.

3.3. Effect of contact time on the amine loadings

The contact time of zeolite and amine solution show a significanteffect on amine loadings (Fig. 4). As evident from the results thatthe highest loading achieved in case of aqueous medium with con-tact time of 4 h, whereas comparative loading was achieved with15 min contact time using methanol as solvent. Thus, we can inferthat when methanol is used as the solvent, lesser time is required toimmobilize a comparative content of amine on the zeolite. Sincehigher loadings were obtained using methanol, all further synthe-ses were carried out using methanol as the solvent of choice.

3.4. Effect of wetting of the zeolite matrix by methanol

Further, the effect of wetting of the zeolite 13X beads by thechoice solvent, prior to the immobilization procedure was alsostudied. Two experiments were planned. The first set of experimentwas the immobilization of the amine onto the surface of the zeolitebeads directly without any pretreatment, i.e., without any wettingprocedure. The second set of experiment was performed by the ini-tial wetting procedure of the zeolite beads with the solvent in a so-lid to liquid ratio of 1:2 in two stages. In both of the experiments,the agitation period was optimized at 15 min and they were con-ducted at room temperature. It was observed that without pretreat-ment, there was not any significant loading. Whereas, for the pre-wetted zeolite, the loading was observed to be 18.69%.

A uniform dispersion of the amine molecules in the zeolite ma-trix may be attributed to this pre-treatment of zeolite beads in theprocess of amine immobilization. The silanol and aluminol groupspresent in the zeolite react with methanol to form Si–O–CH3 andwater.

Si—OHþ CH3OH! Si—O—CH3 þH2O ð1Þ

The Si–O–CH3 group formed reacts with amine molecule to form ahighly reactive species as per the reaction (2).

Si—O—CH3 þHO—CH2—CH2—NH2

! Si—O—CH2—CH2—CH2—NH2 ð2Þ

Thus it can be inferred that the pretreatment of the zeolite 13Xbeads has a profound influence on the amine immobilization.

3.5. Effect of temperature in amine immobilization

The effect of temperature was studied for the immobilizationprocess. Two experiments were planned for this study. In boththe experiments the pre-treatment was given to the 13X beadsby wetting the beads with solvent and the solid to liquid ratiowas kept at 1:2. The first experiment was conducted by immobiliz-ing MEA on zeolite 13X beads at room temperature by using meth-anol as the solvent. The second experiment was carried out in around bottom flask and the reaction mixture was refluxed at70 �C. The concentration of the alcoholic amine solutions was50 wt% in both the cases. The MEA loadings observed in the formercase was 18.69% and that in the latter was 13.88%.

Thus it can be inferred that reflux method does not yield higheramine loading than the simple mixing method.

3.6. Comparison of estimation of amine loadings through varioustechniques

After optimizing the different parameters involved in theimmobilization techniques, the amine content estimated by the

different techniques like GLC and TOC and was compared withthe simple titrimetric technique followed in the laboratory. Adsor-bents were synthesized using three different concentrations ofeach amine. The amine content was analyzed by all the techniquesmentioned above. The results have been discussed in the subse-quent tables (Tables 2–4) representing each individual amine.

Thus it can be observed that the agreement between the analyt-ical techniques for estimating loadings of the different amines isfairly good. However, the titrimetric method involves human errorunlike the instrumental methods. Also, the procedure involves theconstant use of glacial acetic acid, which has harmful effects on thehealth of the analyst. Thus estimating the amine content by thetitrimetric method is not a good idea. In a similar manner, the li-quid TOC method of estimation is also quite reliable and can becorrelated with the estimated values obtained by the GLC tech-nique. However, the GLC technique is the best method to analyzethe amine content in all the amines. This is because, apart frombeing an instrumental technique, the calibration plots for the dif-ferent amines show linearity with a R2 factor of about 0.99 whichis fairly accurate.

3.7. CO2 adsorption capacities of the adsorbents

The results of the CO2 adsorption studies using the break-through method are presented in Table 5. We observe that theadsorption capacity of the amine loaded zeolite is increased byapproximately 20–30% in comparison with that of the bare zeolitematrix at 75 �C. This may appear contrary to the expectation, that adecrease in surface area and pore volume of the amine modifiedadsorbent may reduce the adsorption capacity of the adsorbent.However, this can be explained by the classification of the processof adsorption, as physical adsorption or physisorption, and chemi-cal adsorption or chemisorption. At ambient temperature, physi-sorption is dominant over chemisorption. Surface area of theadsorbent thus holds a vital key to the adsorption process at ambi-ent temperature. However, at elevated temperatures, (75 �C in the

Table 2Estimation of MEA on the zeolite matrix.

S.no.

Targeted loading of MEA onZeolite - 13X (wt%)

Techniques to estimate achieved loading

Titrimetry(wt%)

GC-FID(wt%)

TOC (liquid)(wt%)

1. 25 13.53 ± 0.2 14.66 ± 0.2 8.6 ± 0.22. 50 18.69 ± 0.2 24.03 ± 0.2 21.3 ± 0.23. 80 28.75 ± 0.2 36.92 ± 0.2 29.1 ± 0.2

Table 3Estimation of ED on the zeolite matrix.

S.no.

Targeted loading of ED onZeolite - 13X (wt%)


Titrimetry(wt%)

GC-FID(wt%)

TOC (liquid)(wt%)

1. 25 15.89 ± 0.2 9.50 ± 0.2 7.3 ± 0.22. 50 24.53 ± 0.2 19.41 ± 0.2 18.4 ± 0.23. 80 18.09 ± 0.2 15.68 ± 0.2 14.9 ± 0.2

Table 4Estimation of IPA on the zeolite matrix.

S.no.

Targeted loading of IPA onZeolite - 13X (wt%)


Titrimetry(wt%)

GC-FID(wt%)

TOC (liquid)(wt%)

1. 25 4.48 ± 0.2 2.28 ± 0.2 4.8 ± 0.22. 50 11.10 ± 0.2 11.11 ± 0.2 13.4 ± 0.23. 80 16.88 ± 0.2 17.01 ± 0.2 11.9 ± 0.2

88 R. Chatti et al. / Microporous and Mesoporous Materials 121 (2009) 84–89


present study), chemisorption is the dominant process due toincorporation of the amine group in the zeolite. Thus, we observean increase in the adsorption capacity at higher temperature, dueto increase in the chemisorption process. A representative break-through curve of zeolite 13X/MEA and 13X/IPA is shown in Fig. 5.

Thus, it is observed that the modification of zeolite 13X usingamines has enhanced the adsorption capacity as compared to thatof the zeolite 13X matrix. To substantiate the values of adsorptioncapacities obtained by the breakthrough method, we have also car-ried out CO2 adsorption studies for the different adsorbents usingthe volumetric adsorption principle. The experiments have beencarried out at 1 bar gauge pressure at 75 �C in the presence of pureCO2 stream in comparison to 15 vol% CO2 gas in He balance, as per-formed in case of the breakthrough method (Table 6). Further stud-ies using the volumetric method, will be the scope of futureexperimental work.

3.8. Possible reaction mechanism

It is envisaged that the amine exists as a solvent in the confinedpores of the zeolite. The pores are functioning like micro-reactorsfor the capture of carbon dioxide. The loading of the amine in thezeolite 13X matrix overcomes the disadvantages or limitationsassociated with the liquid-amine-based scrubbing systems. Thelimitations identified are the corrosive nature of the amines beingused, higher energy costs in regenerating the scrubbing units andproblems associated with the viscous nature of the amine solutions[22]. The reactions taking place between the solid-amine basedadsorbents are essentially the same, as that between the liquidamine and the gaseous CO2 [23], wherein there is formation ofthe carbamate species as shown in reaction (3):

2RNH2 þ CO2 ! RNHCOO� þ RNHþ3 ð3ÞRNHCOO� þH2O! RNH2 þHCO�3 : ð4Þ

The enhancement in the adsorption capacity of the amine loadedzeolite materials can be attributed to this chemisorptive interactionof CO2 with amine in the pores of the zeolite 13X. Thus, we observea hybrid mechanism of absorption and adsorption taking place inthese amine modified zeolite 13X sorbents. We may also describethis process as a dry CO2 scrubbing system. IR peak correspondingto carbamate species, which is possibly formed by reaction of CO2

with amine functional groups was observed. Further studies are inprogress to elucidate this mechanism.

4. Conclusions

Novel amine immobilized adsorbents have been synthesizedusing 13X zeolite beads as the matrix. They have been analyzedfor estimation of the amine content on the zeolite using differentanalytical approaches. The gas liquid chromatography methodhas been identified as the method of choice owing to its accuracy.The amine immobilized adsorbents have also been evaluated fortheir respective CO2 adsorption capacities and it has been observedthat there is an enhancement in the adsorption capacity of thesematerials over that of the conventional zeolite 13X matrix, whichcan be attributed to a hybrid absorption–adsorption mechanism.

Acknowledgements

This work has been carried out under the National ThermalPower Corporation (NTPC) sponsored project S-3-1392 and CSIRNetwork Project No. CORE-08 (1.1). The authors sincerely acknowl-edge the valuable assistance provided by JNARDDC, Nagpur andM/s. Blue Star India Ltd., Mumbai in various evaluation and charac-terization studies conducted during the course of this work. Oneof the authors Ravikrishna Chatti would also take the opportunityto sincerely acknowledge the Council of Scientific and IndustrialResearch (CSIR) India for granting the Senior Research Fellowship.

References

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Table 5Breakthrough adsorption capacities of zeolite 13X and amine modified zeolites(50 w%) at 75 �C.

S. no. Adsorbent material Breakthrough adsorption capacity (mg/g)

1. 13X matrix 16.012. 13X/MEA 19.983. 13X/IPA 22.78

00.10.20.30.40.50.60.70.80.91

0 10 20 30 40 50 60Time (min)

C/C

0 13X-MEA-5013X-IPA-50

Fig. 5. Breakthrough curves of CO2 on MEA modified zeolite 13X and IPA modifiedzeolite 13X at 75 �C.

Table 6Equilibrium adsorption capacities of zeolite 13X and MEA modified zeolite 13X(50 w%) at 75 �C and 1 bar gauge pressure.

S.no.

Adsorbentmaterial

Equilibrium adsorption capacity (mg/g) using volumetricadsorption principle

1. 13X matrix 37.332. 13X/MEA 48.64


MICMAT4070

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