CENG0027 - Molecular Thermodynamics: CO2/N2 Adsorption Study

This project investigates the adsorption behavior of carbon dioxide (CO2) and nitrogen (N2) on Silicalite (MFI) and Faujasite (FAU) zeolites using molecular simulations. The study aims to determine the suitability of these materials for gas separation via pressure swing adsorption (PSA). The research begins by characterizing the adsorbent materials, computing their surface area, void fraction, and pore size distribution. Single-component adsorption isotherms for CO2 and N2 are computed and compared for both MFI and FAU. Furthermore, the enthalpy of adsorption is calculated for both gases. Multicomponent Grand Canonical Monte Carlo (GCMC) simulations are performed to simulate the adsorption of CO2/N2 mixtures, generating multicomponent adsorption isotherms and reporting the selectivity of the adsorbents across a range of pressures. The results are discussed in relation to the single-component adsorption behavior and the potential for PSA applications. The study highlights the high selectivity of CO2 adsorption over N2 in these zeolites, which varies with the crystal type and mixture composition.

CENG0027 - Molecular Thermodynamics
Study of Carbon Dioxide and Nitrogen
Equilibrium Adsorption on Silicalite(MFI) or
Faujasite (FAU) as Adsorbent
Abstract: The adsorption homes of CO2 and N2 in silica zeolite and Faujasite had been
studied the use of molecular simulations. Adsorption isotherms for single components in MFI
had been each measured and computed showing good agreement. In addition, simulations in
different all silica systems have been carried out for a huge range of pressures and
temperatures and for unmarried components in addition to binary and ternary combinations
with varying bulk compositions. The adsorption selectivity becomes analysed for mixtures with
the bulk composition of fifty:50 CO2/N2, 10:90 CO2/N2 and five: ninety: five CO2/N2/ in MFI
and FAU showing high selectivity of adsorption of CO2 over N2 that varies with the sort of
crystal and with the mixture bulk composition.
Keywords: Adsorption. Carbon dioxide. Nitrogen. Silicalite. Faujasite
Table of Contents
Introduction……………………………………………………………………………………………………………………………...2
Materials and Methods………………………………………………………………………………………………………….….3
Results and Discussion……………………………………………………………………………………………………………….5
Conclusion………………………………………………………………………………………………………………………………...8
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CENG0027 - Molecular Thermodynamics
1.Introduction
In recent times, selective removal of carbon dioxide from methane is one of the crucial issues of
environmental engineering (Rodrigues, 2012). Global warming is one of the maximum vital
environmental worrying conditions, and carbon dioxide (CO2) has classified as a dangerous fuel
to the surroundings and public fitness. In addition, CO2 is one of the critical natural gas
contaminants, which need to be eliminated to growth the natural fuel strength content
material and reduce its corrosive homes in herbal gasoline storage and transportation. The
traditional technique for putting off CO2 from nitrogen (N2) in business applications is amine
absorption, that could be a poisonous and noneconomic technique. Currently, adsorptive
strategies using nanoporous substances, which might be known as green strategies, have
appealed loads research (Winston Ho, 2012).
Molecular sieves together with zeolites and zeotypes are nanoporous substances that are
locating splendid software as a catalyst and adsorbent in company techniques. The small pore
period, excessive thermal and chemical balance of zeotype, and zeolite molecular sieves
purpose them to a fantastic material for use in adsorption techniques. The pore diameter and
ground place of the absorbents are the vital thing parameters in its adsorption.
The development of new advanced adsorbents for gas separation in masses of industrials
packages thru adsorption procedures is receiving growing hobby. those materials want to be
characterised for a large kind of gases (Peter Schreier, 2011). Zeolites as adsorbents are
unexpectedly turning into the generation of choice for the petroleum and chemical enterprise
for minimizing their emissions to the environment, specifically risky herbal compounds. except
their importance in many (LeVan, 2012) commercial catalytic techniques, zeolites are presently
locating big packages in agency, in particular in environmentally touchy business tactics.
Separation of methane, nitrogen, and carbon dioxide combinations is a tough research
challenge remember for each environmental and financial reasons. From the environmental
factor of view, it is crucial to develop powerful separation generation to reduce the carbon
dioxide emissions which might be pretty prolonged because of using fossil fuels. From the much
less pricey issue of view, the removal of carbon dioxide from natural fuel and the recovery of
methane from landfill gasoline (containing methane, carbon dioxide and small quantities of
nitrogen) are examples of thrilling separations. a number of the functionality routes explored
for fuel separations, adsorption strategies associated with zeolites have demonstrated a
developing significance due to the fact the ones materials have an excessive thermal,
mechanical, and chemical stability. Besides, the zeolite pores have a period similar to the
molecular dimensions of many substances and therefore they facts extremely good
mechanisms of diffusion in which the framework performs the most vital role.
Zeolites are aluminosilicates with crystalline structures crafted from TO4 tetrahedral (T = Si, Al).
the ones crystals are characterised through manner of a uniform three-dimensional pore
machine, with pores that adjust in shape and of precisely described diameters inner molecular
dimensions. maximum of the zeolitic materials investigated to this point for separations of
mixtures associated with carbon dioxide, nitrogen, and methane belong to the MFI-type have
moreover been studied. The mechanism for separation in zeolites can be pretty complicated
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considering the fact that versions in the length and geometry of the cavities and pores will
make contributions to the general regular typical overall performance of the zeolites (Enrico
Drioli, 2011).
Molecular simulations are presently playing a vital characteristic in growing the information of
the relation between microscopic and macroscopic houses of confined molecular fluids in
zeolites.
A great paintings of the adsorption homes of these materials can be beneficial to offer an
explanation for the underlying mechanisms of adsorption and diffusion strategies, in addition to
pick out in addition applications of zeolites as catalysts and adsorbents.
2.Materials and Methods
The adsorption isotherms have been computed the use of Monte Carlo (MC) simulations inside
the grand canonical (GC) ensemble (Jiri Cejka, 2007). The zeolite lattices are inflexible all
through simulations, with static atomic costs which might be assigned by means of manner of
selecting qSi = +2.05 and qO = -1. zero.5, following the artwork of Jaramillo and Auerbach. The
crystallographic facts are to be had some other place. The interactions among guest molecules
adsorbed (CO2, N2, and CH4) with amazing adsorbates and with the zeolite are modelled
through the usage of using Lennard-Jones and Coulombic potentials (Fahmina Zafar, 2016). The
Coulombic interactions inside the machine are calculated with the beneficial aid of Ewald
summation for periodic structures. The interactions dominated amongst adsorbed molecules
and the zeolite are dispersive forces among the pseudo-atoms and the oxygen atoms of the
zeolite and the interactions of silicon and aluminium are considered via a powerful capability
with best the oxygen atoms.
The internal shape of the adsorbate and the adsorbate-adsorbate interactions are as critical
due to the homes ruled by the sturdy interactions with the pressure difficulty produced thru
using the zeolite (Council of clinical & commercial studies (India), Indian national generation
Academy, 2009). We are the usage of pressure situation parameters that effectively reproduce
the homes of pure fuel adsorption of CO2, N2, and CH4, as well as their combos in one in every
of a type kinds of all-silica zeolites. Maximum of these pressure place parameters have been
first of all ready to reproduce the adsorption isotherms in Silicalite and secondly examined in
extraordinary pure silica systems. CH4 molecules are defined with a united atom version,
wherein every molecule is dealt with as an unmarried interplay centre. CO2 molecules are
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taken linear and rigid with bond period C–O of one sixteenth.
Figure: selective adsorption of CO2
N2 molecules are modelled as a dumbbell with a rigid interatomic bond of 1.098Å. The partial
prices of N2 and CO2 are allotted around each molecule to breed experimental quadrupole
moment. The interaction among adsorbed molecules is described with Coulombic and Lennard-
Jones phrases. On this work we're the use of the version proposed with the useful resource of
Harris et al. (Harris and Yung, 1995) for CO2 and the model proposed with the useful resource
of Murthy et al for N2. The ones fashions were additionally utilized by Watanabe et al. And
Makrodimitris et al. (Makrodimitris et al., 2001). The partial Prices and Lennard-Jones
parameters utilized in our simulations are listed in desk 1. The Lennard-Jones potentials are
shifted and cut at 12 Å. The extensive sort of unit cells within the simulation box modified into
selected such that the minimum length in each of the coordinate instructions end up massive
than 24 Å. Periodic boundary conditions have been employed. In addition, GCMC information
are to be had in previous guides. Experimental adsorption isotherms had been finished for
nitrogen and carbon dioxide in MFI at several temperatures. The zeolite used on this
investigation became kindly provided via ITQ and corresponds to an absolutely natural porous
crystalline silicon dioxide; the extraordinarily siliceous shape of silicalite-1 with the MFI crystal
structure. The porous network of the zeolite come to be characterised by using way of helium
density (2.36 g cm-3) and N2 adsorption isotherm at seventy-seven ok. In accurate settlement
with literature, the experimental N2 isotherm at seventy-seven k Silicalite well-known suggests
tow adsorption sub-steps.
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The initial adsorption steps as a lot as p/po < zero.1 corresponds to microporous pore filling.
The second one sub-step takes place at relative pressures among zero.1-0. Three and the extent
adsorbed of nitrogen increase by way of the usage of 25 cm3 STP g-1. This behaviour has been
interpreted as an adsorbate transition from a lattice fluid-like phase to crystalline-like stable
one (i.E., solidification kind phase transition).
Certain experimental techniques were reported and cited some different region. In quick,
previous to the adsorption measurements the samples were outgassed in situ below vacuum at
673 ok in a single day to do away with any adsorbed impurities. A Micrometrics ASAP 2010 gas
adsorption analyser modified into used to appropriately degree the N2 uptake at seventy-seven
ok in the pressure variety from 10-four kPa to one hundred kPa. The tool became prepared with
a molecular drag vacuum pump and 3 unique strain transducers (0.133 kPa, uncertainty within
0.12 % of reading; 1.33 kPa and 133 kPa, uncertainty inner 0.15 % of analyzing) to beautify the
sensitivity in the low-strain range, this is particularly useful in adsorption research on
microporous substances. The CO2 adsorption isotherms were finished in a TriStar 3000 from
Micrometrics, using a circulating temperature-controlled bath, within the pressure variety from
10-1 kPa as much as 100 and twenty kPa. The gaseous adsorptive, N2 and CO2, in which sold
with an extremely-immoderate purity.
3.Results and Discussion
We had been given executed molecular simulations to reproduce our measured unmarried
detail isotherms in MFI, 2) examine with to be had experiments of, CO2, and N2 single and
binary combos in MFI, DDR, ITE and ISV zeolites are expecting the vicinity of the molecules
within the crystal pores and four) achieve ternary combination adsorption isotherms for a given
bulk composition. To test the ternary combination adsorption behaviour, we have been given
selected three systems with one-of-a-kind sort of porous: MOR (shape with one-dimensional
channels), MFI (form with intersecting channels), and FAU (structures with cages separated
with the beneficial resource of slim home windows).
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Figure: adsorption isotherms of MFI
Our computed and measured adsorption isotherms for CO2 at 253K, 273K, and 310K are
mounted in discern 1. Greater adsorption isotherms for CO2 and N2 in MFI had been received
for numerous temperatures and in contrast with available previous facts. Decide 1 indicates
proper settlement among our computed isotherm for N2 at 308 precise enough and the
handiest of Goj et al. Comparable proper agreement is decided most of the information
acquired in this artwork for CO2 and the experimental measurements. Adsorption isotherms of
CO2, CH4, and N2 in MOR were computed at 3 hundred true sufficient and 210 ok and in
contrast with the isotherms of Delgado et al. And Webster et al. As tested in determine 2a. The
calculated isotherms show extremely good agreement with experiments in all type of
pressures. The small discrepancies amongst our results and the experimental values are due to
the Si/Al ratio of the MOR systems used inside the experimental measurements. Simulations
have been completed for natural silica MOR even as experimental facts for methane and CO2
have been received for H-MOR with Si/Al = 6 and seven protons consistent with unit cellular,
and experimental information of N2 have been received for Na-MOR with Si/Al = 20 and more
than one sodium cations consistent with unit cellular. Figure 2b compares the simulated
isotherms of CO2, CH4, and N2 in CHA with the experimental isotherms of Li et al. For SAPO-34
-an isotype of CHA proving incredible settlement as a whole lot due to the fact the form of
pressures used for the experimental isotherms. The computed values for N2 also are in
incredible agreement with preceding facts of Gray et al.
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Figure: CO2 and N2 adsorption in alkali metal ion exchanged X-Faujasite
Besides computing the adsorption of natural components in numerous zeolites, we have been
given got finished simulation on mixtures of the chosen gases. Decide three suggests the
obtained adsorption isotherms for equimolar combinations of CO2/N2 in MFI at 308 adequate
(figure 3a) and the computed adsorption selectivity for the equimolar and the ten:90 CO2/N2
bulk combination in MFI at the same temperature. Comparable calculations were finished for
ITE (50:50 bulk aggregate) and ISV (50:50 and 10: 90 bulk aggregate) at 498 top sufficient and
308 k, respectively. The following simulation records are validated in discern 4. The selectivity is
defined because of the fact the ratio of adsorbed molar fraction over bulk molar fraction.
Our results are normal with the previous atomistic results of Goj et al proving for all the
systems the preferential adsorption of CO2 over N2. The preferential adsorption of carbon
dioxide is partially due to its quadrupole 2nd that strengths the adsorbate-adsorbent Coulombic
interactions, thereby increasing the adsorption inside the form. A similar behaviour may be
consequently anticipated in the route of the adsorption of CO2/CH4 mixtures and the received
effects in MFI and DDR systems are verified in determine 5. The simulated isotherms are in
concordance with previous experimental effects. The adsorption selectivity is useful for CO2 in
every cases and stays nearly steady with the boom of stress. The adsorption of CO2 is kind of
unaffected through the usage of the presence of nitrogen, however N2 adsorption is distinctly
sensitive to presence of CO2. Decide 5b indicates the isothermal-isobaric (one hundred kPa)
gasoline phase adsorbed diagram for the aggregate nitrogen and carbon dioxide on DDR (298
good enough) and MFI (313 exact enough). Our results propose a quick upward thrust inside
the mole fraction of CO2 in adsorbed degrees at low CO2 fraction in gasoline segment. This
behaviour has moreover been positioned via Himeno et al. (Himeno et al., 2006) and Harlick
and Tezel (2003) in DDR and MFI respectively and is because of the dominant CO2 adsorption in
the binary tool. Our effects are in settlement with the ones acquired via the usage of Himeno
but show a few discrepancies with the experimental data of Harlick and Tezel for MFI that may
be described via using the usage of manner of the versions within the systems. The simulations
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for this artwork were executed in all silica MFI even as Harlick and Tezel used ZSM-5. As we
stated before the Coulombic interactions some of the CO2 and the electric trouble of the
zeolite will choose the preferential adsorption of carbon dioxide over methane in the form. This
selectivity may be more appropriate in protonated aluminosilicates structures as ZSM-five
because of the fact those materials show off more potent nearby electric powered fields than
the all silica zeolites.
The computed adsorption isotherms for 50:50 combos of CO2 and CH4 and five: 90 five combos
of CO2 and N2 in MOR are showed in figure 6a and 6b, respectively. CO2 adsorbs better than
methane and N2 on this shape for all kind of pressures. MOR kind structures includes
fundamental parallel channels associated with small side channels known as thing-pockets.
Those wallets are the favoured adsorption net sites for small molecules (which incorporates
CO2, N2 and CH4) at room temperature. Whilst the ones web sites are filled, the primary
channels emerge as occupied. In an aggregate of CO2 with CH4 or N2 the previous adsorbs
preferentially within the component pockets and the latter fill then the primary channels. This
could be in fact decided in determine 6 from the snapshots taken from our simulations at a
thousand kPa and room temperature. At the decrease pressures CO2 molecules adsorb in the
element wallet and once those are full they adsorb within the critical channels collectively with
the CH4 and N2
Molecules.
The adsorption isotherms for 5:5:90 bulk ternary mixture of CO2, and N2 were computed at
three hundred ok for a diffusion of pressures that spans from zero.01 to 107 kPa. Decide 7
indicates that as for the binary mixtures, CO2 achieves the very excellent adsorption in all
instances.
The lower or higher CO2 adsorption selectivity is determined by the usage of the form and the
dimensions of the crystal pore. CO2 achieves the very first-rate adsorption whilst growing the
confinement because of a combination of entropic (it is than CH4 and N2) and Coulombic
(better quadrupole second than CH4 and N2) consequences. Therefore, CHA with small cages
separated via slender home windows offers better selectivity than MOR -with one-dimensional
channels- and this one higher than MFI that is not unusual through 3 dimensional intersecting
channels.
4.Conclusion
This portray analyses the adsorption behaviour of CO2, N2, and CH4 in all silica zeolites.
Isotherms for pure additives were measured and computed, showing in all instances an
settlement with preceding to be had experiments. The adsorption selectivity for binary and
ternary combinations is constantly in favour of CO2 and strongly relies upon on the form of
form and on the mixture bulk composition. Our simulations offer a device to count on 1) the
adsorption behaviour of multicomponent combinations and a couple of) the area of the
molecules for a given temperature, pressure, and bulk chemical composition.
References
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