12 research outputs found
Porous solids for low temperature CO2 adsorption
Carbon dioxide (CO2) is seen as one of the major global contributors to global warming.
CO2 is produced naturally in the environment, however, with the advent of climate change,
CO2 emissions from manmade sources has come under scrutiny as a driver of manmade
climate change. Combustion of fossil fuels and related practices is seen as the primary
source of such emissions. Current CO2 capture technologies tend to be limited by cost and effectiveness.
The basis of this project was to design a novel adsorbent material capable of removing
significant levels of CO2 from gaseous streams. As a fundamental requirement, the
developed adsorbent material was synthesised using economically viable materials, such as
amine modified microporous zeolites which have not been extensively studied to date
compared to amine modified mesoporous solids such as SBA-15. This study looks primarily
at CO2 adsorption from low temperature exhaust streams with two primary factors of
interest; CO2 adsorption capacity and regeneration energy requirements.
Various microporous solids, including zeolite-Y and zeolite- , were chosen with the view of
examining their potential as supports for liquid amine. A number of techniques were
employed for surface modification and subsequently tested using a gas adsorption rig with
online mass spectrometry. The most successful technique for synthesising amine modified
adsorption, which showed preferable properties in terms of CO2 adsorption and
regeneration, was chosen for further testing. The solid which performed best during CO2
adsorption/desorption testing was aminopropyltriethoxysilane (APTES) modified zeolite -
25, prepared using a amine solution impregnation technique whereby APTES was dissolved
in toluene, zeolite- was then added to the mixture and subsequently heat treated. This solid
was found to have a CO2 adsorption capacity of 216 mg CO2 g-1 solid adsorbent.
Other factors investigated included the effects of silica-alumina ratios on amine
functionalisation, the effects of surface pre-treatments, such as acid treatment, in boosting
surface modification and finally, the use of alternative amines to modify microporous solids.
These tests showed that with decreasing silica/alumina ratio the adsorption capacity of each
solid similarly decreased. Dilute acid pre-treatment was found to boost surface hydroxyl
groups for subsequent amine bonding in some samples. The weight percentage amine
loading of solid supports was also found to be an important factor as too much amine was
found to be detrimental to the CO2 adsorption properties.
A number of amine modified mesoporous materials were also prepared for comparative
purposes. APTES, polyethyleneimine (PEI) and tetraethylenepentamine (TEPA) were used
to modify a number of MCM-type mesoporous silicas. MCM-41 and porous silica spheres
were synthesised for this investigation. The TEPA modified MCM-41 samples produced an
adsorbent with the most favourable CO2 adsorption/desorption properties. The adsorption
capacities obtained were up to 196 mg CO2 g-1 for modified MCM-41 with desorption
occurring at temperatures as low as 75°C.
Co-condensed silicas were prepared by incorporating aminosilanes into the synthesis
mixtures in order to synthesise MCM-type materials with a homogeneous distribution of
functional amines on the solids surface. CO2 TPD studies showed that the adsorption
capacity of the 15% TRI amino silane co-condensed spheres was found to be 65 mg CO2 g-1.
This sample was subsequently exposed to secondary post synthesis modification. This
sample achieved a CO2 adsorption capacity of 211.3 mg CO2 g-1 sorbent. The amine cocondensed
solids showed promising results as both supports and adsorbents for CO2 capture.
Solid characterisation was carried out using N2 adsorption isotherm analysis to establish the
surface area and pore sizes. The morphologies of the silica supports were examined using
scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The
organic contents of solid adsorbents were examined using Fourier transform infrared
spectroscopy (FTIR), thermogravimetric analysis (TGA) and C.H.N. elemental analysis.
The two most adsorbent samples were examined using CO2 adsorption isotherms and
kinetics studies. These were used to show the effects of flue gas parameters on the CO2
adsorption properties of APTES and TEPA modified solid supports. CO2 partial pressure,
exhaust temperature and exhaust constituents such as moisture and other flue gases can
impact on the CO2 adsorption characteristics of the amine modified adsorbent. The
adsorption isotherms for each sample follow the assumptions of the Langmuir model which
suggests that there are a fixed amount of adsorption sites which CO2 can interact with during
the adsorption process. Qst values of 131 kJ mol-1 and 161 kJ mol-1 were obtained for 40%
TEPA/MCM41(R)EtOH and APTES/N -25(WI) Tol, respectively.
The findings of this thesis clearly demonstrate that amine modified zeolites show significant
potential as an alternative adsorbent in the removal of CO2 from flue gas streams when
compared with more expensive mesoporous materials
Monolithic metalâorganic frameworks for carbon dioxide separationâ
Carbon dioxide (CO2) is both a primary contributor to global warming and a major
industrial impurity. Traditional approaches to carbon capture involve corrosive and
energy-intensive processes such as liquid amine absorption. Although adsorptive
separation has long been a promising alternative to traditional processes, up to this
point there has been a lack of appropriate adsorbents capable of capturing CO2 whilst
maintaining low regeneration energies. In the context of CO2 capture, metalâorganic
frameworks (MOFs) have gained much attention in the past two decades as potential
materials. Their tuneable nature allows for precise control over the pore size and
chemistry, which allows for the tailoring of their properties for the selective adsorption
of CO2. While many candidate materials exist, the amount of research into material
shaping for use in industrial processes has been limited. Traditional shaping strategies
such as pelletisation involve the use of binders and/or mechanical processes, which can
have a detrimental impact on the adsorption properties of the resulting materials or can
result in low-density structures with low volumetric adsorption capacities. Herein, we
demonstrate the use of a series of monolithic MOFs (monoUiO-66, monoUiO-66-NH2 &
monoHKUST-1) for use in gas separation processes
Highly selective trace ammonium removal from dairy wastewater streams by aluminosilicate materials
Water is a key solvent, fundamental to supporting life on earth. It is equally important in many industrial processes, particularly within agricultural and pharmaceutical industries, which are major drivers of the global economy. The results of water contamination by common activity in these industries is well known and EU Water Quality Directives and Associated Regulations mandate that NH4+ concentrations in effluent streams should not exceed 0.3âmgâLâ1, this has put immense pressure on organisations and individuals operating in these industries. As the environmental and financial costs associated with water purification begin to mount, there is a great need for novel processes and materials (particularly renewable) to transform the industry. Current solutions have evolved from combating toxic sludge to the use of membrane technology, but it is well known that the production of these membrane technologies creates a large environmental footprint. Zeolites could provide an answer; their pore size and chemistry enable efficient removal of aqueous based cations via simple ion exchange processes. Herein, we demonstrate efficient removal of NH4+ via both static and dynamic methodology for industrial application. Molecular modelling was used to determine the cationâframework interactions which will enable customisation and design of superior sorbents for NH4+ capture in wastewater
Enhanced Stability toward Humidity in a Family of Hybrid Ultramicroporous Materials Incorporating Cr<sub>2</sub>O<sub>7</sub><sup>2â</sup> Pillars
Dichromate (Cr<sub>2</sub>O<sub>7</sub><sup>2â</sup>) pillared <b>pcu</b> hybrid ultramicroporous materials, while previously shown
to exhibit benchmark selectivity for small polarizable gases, sometimes
suffer from poor stability when exposed to moisture, which could limit
their potential application in gas separation systems. In attempting
to improve their stability toward humidity, we have crystal engineered
two new families of <b>DICRO-L-M-i</b> materials of formula
[MÂ(L)<sub>2</sub>(Cr<sub>2</sub>O<sub>7</sub>)]<sub><i>n</i></sub> (M = Ni<sup>2+</sup>, Co<sup>2+</sup>; L = <b>5</b>:
1,4-bisÂ(4-pyridyl)Âxylene; <b>6</b>: 1,4-bisÂ(4-pyridyl)Âdurene).
Evaluating these materials in combination with a previously reported
analogue, <b>DICRO-4-Ni-i</b>, in terms of their stability toward
humidity has revealed a relationship between increasing the number
of methyl groups on the dipyridyl organic linkers and a greater stability
toward humidity
Immobilization of a polar sulfone moiety onto the pore surface of a humid stable MOF for highly efficient CO2 separation under dry and wet environment through direct CO2-sulfone interaction
The stability of microporous metalâorganic frameworks (MOFs) in moist environments must be taken into consideration for their practical implementations, which has been largely ignored thus far. Herein, we synthesized a new moisture-stable Zn-MOF, {[Zn2(SDB)2(L)2]·2DMA}n, IITKGP-12, by utilizing a bent organic linker 4,4âČ-sulfonyldibenzoic acid (H2SDB) containing a polar sulfone group (âSO2) and a N, N-donor spacer (L) with a BrunauerâEmmettâTeller surface area of 216 m2 gâ1. This material displays greater CO2 adsorption capacity over N2 and CH4 with high IAST selectivity, which is also validated by breakthrough experiments with longer breakthrough times for CO2. Most importantly, the separation performance is largely unaffected in the presence of moisture of simulated flue gas stream. Temperature-programmed desorption (TPD) analysis shows the ease of the regeneration process, and the performance was verified for multiple cycles. In order to understand the structureâfunction relationship at the atomistic level, grand canonical Monte Carlo (GCMC) calculation was performed, indicating that the primary binding site for CO2 is between the sulfone moieties in IITKGP-12. CO2 is attracted to the bonded structure (V-shape) of the sulfone moieties in a perpendicular fashion, where CCO2 is aligned with S, and the CO2 axis bisects the SO2 axis. Thus, the strategic approach to immobilize the polar sulfone moiety with a high number of inherent stronger MâN coordination and the absence of coordination unsaturation made this MOF potential toward practical CO2 separation applications
The effect of centred versus offset interpenetration on C2H2 sorption in hybrid ultramicroporous materials
Fine-tuning of hybrid ultramicroporous materials (HUMs) can significantly impact their gas sorption performance. This study reveals that offset interpenetration can be antagonistic with respect to C2H2 separation from C2H2/C2H4 gas mixtures
Metalâorganic material polymer coatings for enhanced gas sorption performance and hydrolytic stability under humid conditions
Physisorbent metalâorganic materials (MOMs) have shown benchmark performance for highly selective CO2 capture from bulk and trace gas mixtures. However, gas stream moisture can be detrimental to both adsorbent performance and hydrolytic stability. One of the most effective methods to solve this issue is to transform the adsorbent surface from hydrophilic to hydrophobic. Herein, we present a facile approach for coating MOMs with organic polymers to afford improved hydrophobicity and hydrolytic stability under humid conditions. The impact of gas stream moisture on CO2 capture for the composite materials was found to be negligible under both bulk and trace CO2 capture conditions with significant improvements in regeneration times and energy requirements
supporting information from Flue-gas and direct-air capture of CO<sub>2</sub> by porous metal-organic materials
Sequestration of CO<sub>2</sub>, either from gas mixtures or directly from air (direct air capture), is a technological goal important to large-scale industrial processes such as gas purification and the mitigation of carbon emissions. Previously, we investigated five porous materials, three porous metal-organic materials (MOMs), a benchmark inorganic material, <b>Zeolite 13X</b> and a chemisorbent, <b>TEPA-SBA-15</b>, for their ability to adsorb CO<sub>2</sub> directly from air and from simulated flue gas. In this contribution, a further 10 physisorbent materials that exhibit strong interactions with CO<sub>2</sub> have been evaluated by temperature-programmed desorption for their potential utility in carbon capture applications: four hybrid ultramicroporous materials, <b>SIFSIX-3-Cu</b>, <b>DICRO-3-Ni-i</b>, <b>SIFSIX-2-Cu-i</b> and <b>MOOFOUR-1-Ni</b>; five microporous MOMs, <b>DMOF-1</b>, <b>ZIF-8</b>, <b>MIL-101</b>, <b>UiO-66</b> and <b>UiO-66-NH<sub>2</sub></b>; an ultramicroporous MOM, <b>Ni-4-PyC</b>. The performance of these MOMs was found to be negatively impacted by moisture. Overall, we demonstrate that the incorporation of strong electrostatics from inorganic moieties combined with ultramicropores offers improved CO<sub>2</sub> capture performance from even moist gas mixtures but not enough to compete with chemisorbents
Efficient CO2 removal for ultra-pure CO production by two hybrid ultramicroporous materials
Removal of CO2 from CO gas mixtures is a necessary but challenging step during production of ultraâpure CO as processed from either steam reforming of hydrocarbons or CO2 reduction. Herein, two hybrid ultramicroporous materials (HUMs), SIFSIXâ3âNi and TIFSIXâ2âCuâi, which are known to exhibit strong affinity for CO2, were examined with respect to their performance for this separation. The singleâgas CO sorption isotherms of these HUMs were measured for the first time and are indicative of weak affinity for CO and benchmark CO2/CO selectivity (>4000 for SIFSIXâ3âNi). This prompted us to conduct dynamic breakthrough experiments and compare performance with other porous materials. Ultraâpure CO (99.99â%) was thereby obtained from CO gas mixtures containing both trace (1â%) and bulk (50â%) levels of CO2 in a oneâstep physisorptionâbased separation process
Amino functionalised hybrid ultramicroporous materials that enable single-step ethylene purification from a ternary mixture
Pyrazine-linked hybrid ultramicroporous (pore size <7 Ă
)
materials (HUMs) offer benchmark performance for trace carbon
capture thanks to strong selectivity for CO2 over small gas molecules,
including light hydrocarbons. That the prototypal pyrazine-linked
HUMs are amenable to crystal engineering has enabled second
generation HUMs to supersede the performance of the parent HUM,
SIFSIX-3-Zn, mainly through substitution of the metal and/or the
inorganic pillar. Herein, we report that two isostructural
aminopyrazine-linked HUMs, MFSIX-17-Ni (17 = aminopyrazine; M =
Si, Ti), which we had anticipated would offer even stronger affinity for
CO2 than their pyrazine analogs, unexpectedly exhibit reduced CO2
affinity but enhanced C2H2 affinity. MFSIX-17-Ni are consequently the
first physisorbents that enable single-step production of polymer grade (>99.95% for SIFSIX-17-Ni) ethylene from a ternary equimolar
mixture of ethylene, acetylene and CO2 thanks to coadsorption of the
latter two gases. We attribute this performance to the very different
binding sites in MFSIX-17-Ni versus SIFSIX-3-Zn