Key Engineering Materials Vols.

594-595 (2014) pp 160-167

© (2014) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/KEM.594-595.160

Carbon Dioxide Separation using Amine Modified Zeolite in Pressure

Swing Adsorption System

N. ALIAS1, a, K.S.N. KAMARUDIN2,b , N.A. GHAZALI1,c , T.A.T. Mohd1,d

A. Sauki1,e and M.R. Jaafar2,f
1
Faculty of Chemical Engineering, Universiti Teknologi Mara, 40500 Shah Alam, Selangor, Malaysia
2
Faculty of Petroleum and Renewable Energy Engineering, Universiti Teknologi Malaysia, 81710
Skudai, Johor, Malaysia
a
nurhashimah@salam.uitm.edu.my, bkhairolsozana@gmail.com, cnurulaimi@salam.uitm.edu.my,
d e f
amran865@salam.uitm.edu.my, arina_sauki@salam.uitm.edu.my and mohdredwanj@gmail.com

Keywords: Carbon dioxide, Adsorption, Pressure swing adsorption, Amined zeolite, Advanced
material

Abstract. Carbon dioxide (CO2) removal from natural gas attracts more attention than other
impurities due to its corrosiveness property and it also possess no heating value in the sales natural
gas. Amine based chemical absorption has been used commercially for CO2 separation in gas
processing plant. However, the liquid amine based processes pose operating difficulties due to high
regeneration energy, large equipments size and solvent leakage. This research studies modification of
porous materials, zeolite NaY by grafting amine functional group using monoethanolamine directly to
the surface of the solid sorbents. The structures and physical properties of amine modified adsorbent
were characterized using powder X-Ray Diffraction (XRD), nitrogen adsorption at 77K and
thermogravimetric analysis. Since application of Pressure Swing Adsorption (PSA) has been widely
used in various plants in the world, this research was extended to study carbon dioxide separation
using amine modified adsorbents in PSA experimental system. Effects of adsorption and regeneration
behaviour on CO2 separation were investigated. Amine modified NaY showed better result compared
to unmodified NaY in term of improvement in physical and chemical properties, high CO2 adsorption
capacity and modified adsorbents were ease of regeneration.

Introduction

The production and subsequent release of carbon dioxide into the atmosphere, no matter the
source, is becoming an increasingly serious issue with respect to its affect on global warming [1]. As
one of the more familiar greenhouse gases, carbon dioxide has the ability to warm the planet by
trapping energy radiated from the surface of the earth that would otherwise be released to space. One
of the major sources of carbon dioxide release into the atmosphere is through the burning of fossil
fuels for energy, which unfortunately makes it ubiquitous. Liquid phase absorption in amine solutions
has been widely used to treat gases from medium to high CO2 concentration. However, due to the high
energy requirements and corrosion problems [2], it is highly desirable to develop less energy intensive
technologies like adsorption [3]. Although the adsorption method attracted researchers’ attention to
capture the CO2, conventional adsorbents such as zeolite molecular sieves, activated carbons, silica
gels and carbon molecular sieves were not effective to capture of CO2 from its mixtures. This is
because, even though these adsorbents can reversibly adsorb a large quantity of CO2 at room
temperature, their capacity diminishes quickly at elevated temperature and the selectivity over water
is very poor. Hence, a porous structure material in which the interior has a basic organic compound
that can help in the retention of CO2 molecules and can facilitate both physical and chemical
adsorptions is proposed. Various porous supports impregnated with liquid amines have been reported
[4-6]. Amine functional groups are useful for CO2 removal because of their ability to form

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,
www.ttp.net. (ID: 183.171.163.147-14/11/13,16:52:51)
 Key Engineering Materials Vols. 594-595 161

ammonium carbamates and carbonates reversibly at moderate temperature [7]. In addition, the
incorporation of organic amines into a porous support is a promising approach for CO2 sorbents
combining good capacity and selectivity at ambient temperature.

Pressure swing adsorption (PSA) has earned widespread acceptance and is being used
extensively for gas purification and separation [3]. Since the first introduction of a basic 4-step PSA
cycle by Skarstrom in 1960, modified and new cycles have been proposed to improve a performance
of separation or to separate a binary gas mixture simultaneously. The basic 4-step cycle has been the
most intensively studied theoretically and experimentally for production of light gases components
[8]. The PSA cycles and the operating conditions can be manipulated to meet a variety of demands
such as to provide high purity or high recovery and to minimize power requirements as in demands
situation [9-11]. Like all adsorption separation processes, PSA involve two basic steps. The first step
is adsorption step, where certain components of a gaseous mixture are selectively adsorbed on a
porous solid. This operation, performed at relatively high pressure by contacting the gaseous mixture
with the adsorbent in a packed column, produces a gas stream enriched in the less strongly adsorbed
component of the feed mixture. After a given time of operation, the adsorbing bed approach saturation
and regeneration is needed. Meanwhile, the second step is regeneration or desorption step, where the
adsorbed components are released from the solid by lowering their gas phase partial pressures inside
the column. After this operation, the adsorbent is ready to be employed in a further cycle. The gaseous
mixture obtained from regeneration is enriched in more strongly adsorbed components in the feed
stream. Although PSA technology for removal of trace amounts of CO2 from air is well known, the
cycles used for this purpose are not suitable to recover CO2 from stream which contain >3 % CO2
[12].

Specifically, the purpose of this work is to develop adsorbents presenting a tailored surface
functionality for improved CO2 adsorption. The novel adsorbents were synthesized by impregnating
monoethanolamine (MEA) on NaY zeolite matrix. This aminated NaY zeolite is expected to impart
high adsorption capacity for CO2 as compared to the bare NaY zeolite matrix. The adsorbent support
chosen was NaY zeolite and it has a pore size of 7 Å. This pore size can accommodate both the
impregnated amines in the zeolite pore as well as the adsorbed CO2. The 3D cage shape of NaY
zeolite is particularly a highly versatile member of the faujasite family which plays a great role in the
gas separation industries. In addition, Tabliabue and co-researchers [11] reported that CO2 adsorption
on polar surfaces zeolites are mainly promoted by surface field gradient–molecular quadrupole
interactions. In this present work also, CO2 separations using modified and unmodified NaY zeolite
using PSA system were investigated. As the vital parameters in PSA system that will affect the
separation are the cycle step time and regeneration behaviours, the experimental and theoretical
studies under these conditions were performed.

Methodology

Preparation of Amined NaY Zeolite. NaY zeolite with a SiO2/Al2O3 molar ratio of 2.88 was
purchased from Zeolyst International Corporation. MEA was introduced into Na-Y zeolite using wet
impregnation method. Using this method, amine solutions with 25 wt% loadings was prepared in
methanol. The zeolite was firstly wetted with methanol prior to agitation with amine solution by
agitating NaY zeolite beads and methanol in solid liquid ratio of 1:4 for a period of 10 min in two
stages. The wetted beads were then air-dried and then agitated with alcoholic amine solution for a
period of 15 min and 4 hours at ambient temperature and solid liquid ratio was kept at 1:4. The zeolite
beads were allowed to be air dried for 24 hours.
162 Advanced Materials Engineering and Technology II

Adsorbent Characterizations. The modified NaY-zeolite was characterized to obtain

constructive comparison with the unmodified NaY-zeolite, using different characterization
techniques. Crystalline structures studies were carried out using a Siemens D5000 X-Ray
Diffractometer with CuKα radiation at a wave length 1.5418 Å. To assess the structural integrity of
the adsorbents before and after modification, the adsorbents were analyzed in a 2θ range of 2° - 50°. A
Micromeritics BET surface area analyzer (Model No. ASAP 2000) was utilized to determine the N2
BET surface area and pore volume of the adsorbents. The BET surface area and pore volume was
determined using the single point adsorption method. Thermogravimetric analysis (TGA) was
performed using Perkin Elmer TGA 7 to analyze the thermal stability and dehydration characteristics
of the adsorbents. About 20 mg of the adsorbent sample was kept in small platinum pan and heated at
a heating rate of 10° C/min. The samples were heated from room temperature up to 900° C.

CO2 Adsorption. The adsorption performance of the adsorbents was further examined in the
PSA system. The separation of CO2 from CO2-N2 gas mixtures using PSA was carried out by feeding
16.89 % of CO2 and 83.11 % of N2 into a two-column PSA unit. A schematic diagram of the
two-colunm PSA unit as shown in Fig. 1 was assembled to perform the traditional Skarstrom cycle
and the Skarstrom cycle with co-current equalization is as shown in Fig 2.

Figure 1. Schematic diagram of the two columns PSA experimental system.

Figure 2. Skarstrom cycle in PSA system

The two stainless steel columns are packed with a known amount of adsorbent. The column
dimensions are: 1.5 cm (0.6 in) internal diameter and 15 cm (5.9 in) long. The columns are connected
using 3 mm (1/8 in) copper tubing. The flowrates of the feed were monitored by gas flow controller.
Pressure gauges (PG) were used to monitor the column pressures and other PSA operating conditions
 Key Engineering Materials Vols. 594-595 163

were tabulated in Table 1. The concentrations of product stream were finally analyzed by a gas
chromatography (GC).

Table 1. PSA dual columns operating conditions

Bed length (mm) 40 mm
3
Volume of adsorbent (cm ) 7.10 cm3
Mass of zeolite in each column 7.7459 g
Feed flow rate (cm3/min) 1000
Pressure (Padsorption atm) 1.5 atm

CO2 Desorption or Regeneration. The principle of a PSA process is to adsorb gases at a

higher level of pressure and to regenerate the saturated adsorbent at a lower level of pressure.
Therefore, the adsorption must be reversibled, otherwise the PSA process cannot be continued. CO2
desorption were carried out on the same setup as shown in Fig. 1. The column was first fed with the
mixture of CO2 and N2 at 1.5 bar. The flow rate was kept at 1000 cm3/ min. When the column was
saturated with CO2, the column pressure released to the atmospheric (1 bar), and then the column was
purged with a stream of nitrogen. The flow rate of the purging stream was kept at 800 cm3/ min.

Result and Discussions

Characterization. Characterization of the representative adsorbents namely bare NaY zeolite

and NaY zeolite impregnated with MEA solution of concentration 50 wt% were studied. The effect of
amine loading on the structural properties of zeolite matrix was investigated by obtaining XRD
patterns before and after amine modification. The XRD measurements of the modified materials
showed that the long-range order of the materials were retained after the modification as shown in Fig.
3. The diffraction peaks of the amine grafted materials occur at similar angle in comparison with bare
NaY. Thus indicated that no substantive change in the microporous matrix after amine modification
treatment. The peak intensities of XRD reflections for aminated NaY zeolite were decreased due to
the presence of MEA particles within the framework of the zeolite NaY.

Figure 3. XRD patterns of modified and unmodified NaY zeolite.

Reduction in the BET surface area of the NaY zeolite after the incorporation of MEA was
observed which indicates that the amine molecules have occupied the pore volume as tabulated in
Table 2. These results provide a correlation with the pore filing effect of MEA and also confirm that
MEA was impregnated in the zeolite pores. This trend is also reported by [13].
164 Advanced Materials Engineering and Technology II

Table 2. Surface area analysis of adsorbents.

Adsorbent NaY Zeolite NaY/MEA
2
BET area (m /g) 635 3.12

TGA results for NaY zeolites before and after MEA modification are shown in Fig 4. [14]
reported that, zeolites exhibit dehydration until 350 °C. However, this temperature is dependent on
the heating rate used in the experiment. It can be observed that for unmodified NaY a single
continuous weight loss ‘step’ presence from room temperature to 400 °C and it contributed to a total
weight loss of 22.26 %. A major weight loss was observed at 70 °C, which may be attributed to the
desorption of physically adsorbed water in NaY zeolite beads. In the case of MEA modified NaY a
total of three distinct weight loss steps at temperatures 70 °C, 200 °C and 300 °C were observed.
Since MEA has a boiling point at temperature 170.8 °C, the second weight loss between temperatures
140 °C and 200 °C may attributed to volatilization and degradation of MEA. The weight loss was
observed to be 9.55 % in this region. A total weight loss of 29.79 % was observed for modified NaY
which is about 7.53 % higher than the unmodified adsorbent.

100

95

90
Weight (%)

85

80

75

70

65
0 100 200 300 400 500 600 700 800 900 1000

Temperature (oC)

ZEOLITE/MEA ZEOLITE

Figure 4. Representative TG profile of the adsorbents.

CO2 Adsorption. Result for adsorption studies on unmodifed NaY and modified NaY/MEA
conducted using 16.89 % of CO2 and 83.11 % of N2 in a two-column PSA unit at 298 K are shown in
Fig. 5. The results showed that N2 concentration decreased gradually as the number of cycle
increased. This trend shows that CO2 concentration in the mixture increased as the prolonged cyclic
employed. Tabulated Table 3 compares the N2 concentration at exit stream for both NaY and
NaY/MEA.

CO2 ADSORPTION
N2 Concentration in Exit Stream

120.00
100.00
80.00
60.00
40.00
(%)

20.00
0.00
0 2 4 6 8 10
1/2 Cycle

Adsorption in NaY Adsorption in NaY/MEA

Figure 5. Comparison of N2 concentration at exit stream in NaY and NaY/MEA adsorption at cyclic
state for cycle 1 to 5.
 Key Engineering Materials Vols. 594-595 165

Table 3. Adsorption analysis of adsorbents.

Run Adsorption Adsorption
(1/2 cycle) NaY/MEA (%) NaY (%)
1. 92.86 89.36
2. 95.96 86.30
3. 95.63 97.74
4. 98.15 89.93
5. 86.52 73.57
6. 84.90 70.94
7. 73.04 72.52
8. 85.47 71.82
9. 81.14 82.51
10. 88.59 68.77

It shows that N2 concentration retained at exit stream after 5 cycles adsorption using NaY/MEA
(88.59 %) was higher compared to NaY (68.77 %) and it concluded that, more CO2 was adsorbed
using NaY/MEA adsorbent. This is due to the more CO2 affinity sites were exposed for
chemisorption. Eventhough NaY/MEA adsorbent used in this study provides lower surface area as
compared to unmodified NaY, the adsorbent still produced higher CO2 adsorption capacity. This
indicates that an excellent separation of CO2 from a gas mixture of N2 and CO2 can be improved using
MEA modified NaY adsorbent with higher surface area.

CO2 Desorption or Regeneration. Variations of the N2 concentrations trend with different

cycles are shown in Fig. 6. It compares N2 concentration at exits stream between NaY and modified
NaY/MEA during CO2 desorption. The trend shows N2 concentrations at exit stream using
NaY/MEA adsorbent were more or less same with NaY adsorbent which was in average of 84 % after
5 cycle operations as tabulated in Table 4. It is also shown that the concentrations of N2 in the purging
stream for modified NaY/MEA were maintained after the fifth cycle. Therefore, the adsorption was
reversibled and the adsorbent can be fairly well regenerated at the ambient temperature.

CO2 DESORPTION
N2 Concentration in Exit

150.00
Stream (%)

100.00

50.00

0.00
0 2 4 6 8 10
1/2 Cycle
Desorption in NaY Desorption in NaY/MEA

Figure 6. Comparison of N2 concentration at exit stream in NaY and NaY/MEA desorption at cyclic
state for cycle 1 to 5.
166 Advanced Materials Engineering and Technology II

Table 4. Desorption analysis of adsorbents.

Run Desorption Desorption
(1/2 cycle) NaY/MEA (%) NaY (%)
1. 92.45 96.13
2. 89.90 98.70
3. 91.80 84.58
4. 82.94 85.48
5. 84.18 85.32
6. 83.52 79.73
7. 82.54 74.02
8. 74.71 80.74
9. 88.46 87.31
10. 78.84 70.32

Conclusion

CO2 adsorption and desorption studies were carried out using unmodified NaY and modified
NaY/MEA using a dual PSA system. Based on the study, NaY and NaY/ MEA showed preferential
CO2 adsorption at ambient temperature and pressure up to 1.5 bar. Thus, it can be concluded that
modified NaY/MEA adsorbent with low surface area was able to give higher CO2 adsorption capacity
compared to unmodified NaY even after 5 cycle operations. However CO2 desorption using
NaY/MEA by N2 purging at 1 bar give the more or less similar result to CO2 desorption using NaY.
However, the NaY/MEA adsorbent still ease to be regenerated at ambient temperature. In conclusion,
surface area of adsorbent affects the CO2 adsorption and desorption capacities. In conjunction to these
results, the surface area of modified NaY/MEA could be increase by decrease the MEA concentration
in NaY adsorbent in order to improve the results of CO2 separation using PSA system.

Acknowledgements

The authors would like to thank Minister of Higher Education and Universiti Teknologi Mara for the
financial support given through the Research Dana Pembudayaan Penyelidikan (RAGS)
600-RMI/RAGS 5/3(74/2012).

References
[1] C.M. White, B.R. Strazisar, E.J. Granite, J.S. Hoffman and H.W. Pennline: Separation and
Capture of CO2 from Large Stationary Sources and Sequestration in Geological
Formations—Coalbeds and Deep Saline. J. AirWaste Manage. Assoc., Vol. 53 (2003), p.
645–715.
[2] A. Veawab, P. Tontiwachwuthikul and A. Chakma: Corrosion Behavior of Carbon Steel in the
CO2 Absorption Process Using Aqueous Amine Solutions. Ind. Eng. Chem. Res. Vol. 38
(1999), p. 3917-3924.
[3] D.M. Ruthven, S. Farooq and K.S. Knaebel: Pressure Swing Adsorption. New York: VCH
Publishers (1994).
[4] N. Hiyoshi, K. Yogo and T. Yashima: Adsorption Characteristics of Carbon Dioxide on
Organically Functionalized SBA-15. Micropor. Mesopor. Mater. Vol. 84 (2005), p. 357-365.
[5] C. Knöfel, J. Descarpentries, A. Benzaouia, V. Zeleňák, S. Mornet, P.L. Llewellyn and V.
Hornebecq: Functionalised Micro-Mesoporous Silica for the Adsorption of Carbon Dioxide.
Micropor. Mesopor. Mater. Vol. 99 (2007), p. 79 – 85.
 Key Engineering Materials Vols. 594-595 167

[6] J. Li, W. Lina, Q. Tao, Y. Zhou, C. Liu, J. Chu, and Y. Zhang: Different N-Containing
Functional Groups Modified Mesoporous Adsorbents for Cr(VI) Sequestration: Synthesis,
Characterization and Comparison. Micropor. Mesopor. Mater. Vol. 110 (2008), p. 442 – 450.
[7] M.L. Gray, Y. Soong, K.J. Champagne, H. Pennline, J.P. Baltrus, R.W. Stevens Jr., R. Khatri,
S.S.C. Chuang and T. Filburn: Improved Immobilized Carbon Dioxide Capture Sorbents. Fuel
Proc. Tech. Vol. 86 (2005), p. 1449-1455.
[8] H. Shin: Separation of a Binary Gas Mixture by Pressure Swing Adsorption: Comparison of
Different PSA Cycles. Adsorption Vol 1 (1995), p. 321-333.
[9] V.G. Gomes and K.W.K. Yee: Pressure Swing Adsorption for Carbon Dioxide Sequestration
from Exhaust Gases. Separ. Purif. Tech. Vol. 33 (2002) 163 – 177.
[10] S.P. Reynolds, A.D. Ebner and J.A. Ritter: New Pressure Swing Adsorption Cycles for
Carbon Dioxide Sequestration. Adsorption Vol. 11 (2005), p. 531-536.
[11] M. Tagliabue, D. Farrusseng, S. Valencia, S. Aguado, U. Ravon, C. Rizzo, A. Corma and C.
Mirodatos: Natural Gas Treating by Selective Adsorption: Material Science and Chemical
Engineering Interplay. Chem. Eng. J., Vol. 155 (2009), p. 553–566.
[12] D. Aaron and C. Tsouris: Separation of CO2 from Flue Gas: A Review. Sep. Sci. Tech. Vol. 40
(2005), p. 321–348.
[13] X. Xu, T.C. Song, B.G. Miller and A.W. Scaroni: Adsorption Separation of Carbon Dioxide
from Flue Gas of Natural Gas-Fired Boiler by a Novel Nanoporous “Molecular Basket”
Adsorbent, Fuel Processing Technology, Vol. 86 (2005), p.1457-1472.
[14] R.V. Siriwardane, M.S. Shen and E.P Fisher: Adsorption of CO2 on Zeolites at Moderate
Temperatures. Energy & Fuels Vol. 19 (2005), p. 1153-1159.