Applications of Nanoporous Materials in Gas Separation and Storage

Past decades in the field of gas separation and storage utilized the concepts of both cryogenic distillation and non-cryogenic methods such as high-pressure cylinders but few concerns – efficiency, energy intensiveness, cost associated, risk of failure always existed. Recent advances in the field focuses on using porous materials especially nanoporous materials. Nanoporous materials, due to their well-defined structure, range of pore diameters, and striking surface chemistry hold over traditional porous materials for gas separation and storage. With pore diameter less than 2 nm and abundance of energetically favorable sites (such as unsaturated metal sites, channels, cages, cavities etc.), these materials can also undergo various surface decorations to enhance the adsorbate-adsorbent interactions making them suitable for the applications using the principles of pressure swing adsorption. The objective of this study is to show the potential these materials hold in gas separation and storage studies and we provide four different nanoporous materials dedicated to deal with certain gas mixtures. Out of the wide class of nanoporous materials, in first part of this work we show screening of 229 zeolitic frameworks in separation of radiochemically relevant noble gases mixture of Kr/Xe by Grand Canonical Monte Carlo simulations by benchmarking the model by measuring adsorption isotherms at various temperatures. Zeolites with narrow pore system and zig-zag or elliptical cross sections were found to be more selective for Xe. To separate one of the lightest gas mixture of D2/H2 we examine the adsorption into a nanoporous nickel phosphate, VSB-5, which on the basis of gas sorption analysis gives one of the highest heats of adsorption (HOA) for hydrogen (16 kJ/mol). A much higher HOA for D2 with calculated selectivities above 4 for D2 at 140 K suggests that VSB-5 is a promising adsorbent for separations of hydrogen isotopes. iv To understand the storage aspect of nanoporous materials, we utilize the principles of Inelastic Neutron Scattering (INS) to examine the lightest gas (H2) on one of the simplest yet exciting surface of graphene where the H2 gas corresponds to a 2D rotor with a rotational barrier of around 4 meV. This also helps in checking the validity of the model of H2 in an anisotropic potential and thereby provides more insight on the concept of hydrogen storage. A hand-in-hand comparison with a much stronger interaction potential provided by Ni2+ sites in VSB-5 is also studied. A huge shift in the rotational line of hydrogen in VSB-5 represents itself as a case of Kubas complex indicating the strong affinity of the unsaturated metal sites towards H2. To capture a different system of toxic gas of ammonia (NH3), we functionalize a well-studied metal organic framework, HKUST-1 (copper trimesate) containing bound sulfuric acid tethered to the framework through terminal oxygen coordination to the accessible Cu(II) sites. Presence of sulfuric acid in the framework and the NH3 sorption is examined by INS. Here acid modified HKUST-1 shows three times more uptake of NH3 compared with pristine HKUST-1. A series of DFT simulation reveals adsorption of ammonia at the acid -OH site leading to a partial transfer of H + and giving an elongated O-H-N bond rather than a full transfer of H+ and explaining the observed reversibility of adsorption without the destruction of framework

Nucleation and coagulation of particulate matter inside a turbulent exhaust plume of a diesel vehicle

The objective of this study is to develop a physical model to accurately predict the nucleation, coagulation, and dynamics of particulate matter emission from diesel-fueled engines. The uniqueness of this research is that measured particulate matter (PM) size distribution data is not required a priori to solve the nucleation/coagulation equations; instead the PM concentration is predicted based on the fuel sulfur content, fuel to air ratio, exhaust flow rate, and the ambient conditions. This study presents the CFD modeling of an exhaust plume dispersed from a stack pipe of a tractor truck powered by a 330 HP diesel engine. This effort uses the k-epsilon eddy dissipation model to predict the CO2 variation concentration coming out of the stack pipe into the ambient. The effect of the recirculation region near the truck walls on dispersion of CO2 is presented. The predicted results showed an excellent agreement with the experimentally measured values of CO2 concentration, dilution ratio, and the temperature in the wind tunnel. It was predicted that the relative concentration of CO2 from the stack dropped rapidly from 1 to 0.01 within a distance of 2.54 m downstream of the exhaust outlet.;Additionally, the simultaneous effects of nucleation, condensation and coagulation are incorporated in predicting the PM emissions from on-road heavy-duty diesel vehicles. It was predicted that the critical nucleus diameter decreased by approximately 30% and the number concentration increased by a factor of 6 with the increase in relative humidity from 10% to 90% for a fuel with 50 ppm sulfur content. Numerical simulations suggested that the condensation effects are very important near the stack. Ignoring the contribution from condensation term decreased PM count median diameter (CND) from 52 nm to 10 nm. The root mean square error in the numerically predicted particle number concentration was within 14.3% of the experimentally measured values. An increase in CMD from 52 nm to 62 nm was predicted for a distance of 0.51 m from the stack exit to 8.56 m from the stack exit, and the number concentration for the same distance decreased from 8.77 E+6 to 2.1 E+5 No./cm 3

Electrowetting: from basics to applications

Electrowetting has become one of the most widely used tools for manipulating tiny amounts of liquids on surfaces. Applications range from 'lab-on-a-chip' devices to adjustable lenses and new kinds of electronic displays. In the present article, we review the recent progress in this rapidly growing field including both fundamental and applied aspects. We compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high. We discuss in detail the origin of the electrostatic forces that induce both contact angle reduction and the motion of entire droplets. We examine the limitations of the electrowetting equation and present a variety of recent extensions to the theory that account for distortions of the liquid surface due to local electric fields, for the finite penetration depth of electric fields into the liquid, as well as for finite conductivity effects in the presence of AC voltage. The most prominent failure of the electrowetting equation, namely the saturation of the contact angle at high voltage, is discussed in a separate section. Recent work in this direction indicates that a variety of distinct physical effects¿rather than a unique one¿are responsible for the saturation phenomenon, depending on experimental details. In the presence of suitable electrode patterns or topographic structures on the substrate surface, variations of the contact angle can give rise not only to continuous changes of the droplet shape, but also to discontinuous morphological transitions between distinct liquid morphologies. The dynamics of electrowetting are discussed briefly. Finally, we give an overview of recent work aimed at commercial applications, in particular in the fields of adjustable lenses, display technology, fibre optics, and biotechnology-related microfluidic devices

Plantwide Control and Simulation of Sulfur-Iodine Thermochemical Cycle Process for Hydrogen Production

A PWC structure has developed for an industrial scale SITC plant. Based on the performance evaluation, it has been shown that the SITC plant developed via the proposed modified SOC structure can produce satisfactory performance – smooth and reliable operation. The SITC plant is capable of achieving a thermal efficiency of 69%, which is the highest attainable value so far. It is worth noting that the proposed SITC design is viable on the grounds of economic and controllability

Calculated Combustion: An Investigation of Electronic Equipment Tenability in Data Center Fires

Fire presents a clear and present danger to computer equipment and generally results in tremendous expense or irreplaceable loss. This study serves as a proof of concept for using computer-based fire modeling to investigate the resilience of typical data center equipment to fire. In this analysis, the National Institute of Standards and Technology’s Fire Dynamics Simulator computer-based fire modeling tool is utilized to simulate fire scenarios within a rack-mount-style computer enclosure containing six circuit boards. Outcomes including effects of combustion (heat, mixture fraction, and species generation) and water-based sprinkler suppression are explored. Although the presence of standard water-based sprinkler suppression proves advantageous, it is not consistently effective in terminating this class of combustion. Results indicate that fire’s thermal effects constitute the largest impact and ultimately determine component survivability. The use of computer-based simulation proves to be a valuable tool in the ultimate enhancement of electronic equipment tenability

Quantum Chemical Studies on Tropospheric Nucleation Mechanisms Involving Sulfuric Acid

Nucleation is the first step of the process by which gas molecules in the atmosphere condense to form liquid or solid particles. Despite the importance of atmospheric new-particle formation for both climate and health-related issues, little information exists on its precise molecular-level mechanisms. In this thesis, potential nucleation mechanisms involving sulfuric acid together with either water and ammonia or reactive biogenic molecules are studied using quantum chemical methods. Quantum chemistry calculations are based on the numerical solution of Schrödinger's equation for a system of atoms and electrons subject to various sets of approximations, the precise details of which give rise to a large number of model chemistries. A comparison of several different model chemistries indicates that the computational method must be chosen with care if accurate results for sulfuric acid - water - ammonia clusters are desired. Specifically, binding energies are incorrectly predicted by some popular density functionals, and vibrational anharmonicity must be accounted for if quantitatively reliable formation free energies are desired. The calculations reported in this thesis show that a combination of different high-level energy corrections and advanced thermochemical analysis can quantitatively replicate experimental results concerning the hydration of sulfuric acid. The role of ammonia in sulfuric acid - water nucleation was revealed by a series of calculations on molecular clusters of increasing size with respect to all three co-ordinates; sulfuric acid, water and ammonia. As indicated by experimental measurements, ammonia significantly assists the growth of clusters in the sulfuric acid - co-ordinate. The calculations presented in this thesis predict that in atmospheric conditions, this effect becomes important as the number of acid molecules increases from two to three. On the other hand, small molecular clusters are unlikely to contain more than one ammonia molecule per sulfuric acid. This implies that the average NH3:H2SO4 mole ratio of small molecular clusters in atmospheric conditions is likely to be between 1:3 and 1:1. Calculations on charged clusters confirm the experimental result that the HSO4- ion is much more strongly hydrated than neutral sulfuric acid. Preliminary calculations on HSO4- NH3 clusters indicate that ammonia is likely to play at most a minor role in ion-induced nucleation in the sulfuric acid - water system. Calculations of thermodynamic and kinetic parameters for the reaction of stabilized Criegee Intermediates with sulfuric acid demonstrate that quantum chemistry is a powerful tool for investigating chemically complicated nucleation mechanisms. The calculations indicate that if the biogenic Criegee Intermediates have sufficiently long lifetimes in atmospheric conditions, the studied reaction may be an important source of nucleation precursors.Nukleaatio on ensimmäinen askel prosessissa, jossa ilmakehän kaasumolekyylit tiivistyvät nestepisaroiksi tai kiinteiksi hiukkasiksi. Vaikka ilmakehän hiukkasmuodostus on ensiarvoisen tärkeä tutkimusaihe pienhiukkasten ilmasto- ja terveysvaikutusten takia, hiukkasmuodostuksen molekyylitason mekanismeista on olemassa hyvin vähän tietoa. Väitöskirjassa on tutkittu kvanttikemiallisten menetelmien avulla mahdollisia nukleaatiomekanismeja, jotka liittyvät rikkihappoon, sekä veteen ja ammoniakkiin, tai reaktiivisiin orgaanisiin molekyyleihin. Kvanttikemia tarkoittaa Schrödingerin aaltoyhtälön ratkaisemista systeemille, joka koostuu atomiytimistä ja näitä ympäröivästä elektroniverhosta. Käytännössä yhtälön ratkaiseminen edellyttää lukuisia likimääräisoletuksia. Eri likimääräisoletusten yhdistelmät muodostavat laajan kirjon erilaisia laskentamenetelmiä. Laskentamenetelmien vertailu osoittaa, että mikäli rikkihappo - vesi - ammoniakkiklustereille halutaan laskea tarkkoja tuloksia, tulee menetelmä valita huolella. Väitöskirjan tulokset osoittavat, että rikkihapon hydraatiota eli veteen sitoutumista koskevat kokeelliset tulokset voidaan kvantitatiivisesti toisintaa, mutta vain jos käytetään riittävän korkeatasoisia kvanttikemiallisia menetelmiä. Ammoniakin rooli rikkihappo-vesinukleaatiossa selvitettiin laskemalla muodostumisenergioita klustereille, joiden kokoa kasvatettiin joko rikkihappoa, vettä tai ammoniakkia lisäämällä. Kuten kokeelliset tulokset osoittavat, ammoniakki edistää klustereiden kasvua nimenomaan rikkihappojen lisäyksen kautta. Tässä väitöskirjassa esitetyt laskut ennustavat, että ilmiön merkitys ilmakehässä tulee merkittäväksi kun rikkihappomolekyylien lukumäärä kasvaa kahdesta kolmeen. Toisaalta, pienet molekyyliklusterit tuskin sisältävät enemmän kuin yhden ammoniakkimolekyylin kutakin rikkihappoa kohden. Tulos on merkittävä, sillä isommissa klustereissa on mitattu ammoniakkimolekyylejä olevan jopa tuplaten rikkihappomolekyyleihin verrattuna. Laskut siis osoittavat että pienten ja isojen aerosolihiukkasten kemiallinen koostumus voi erota merkittävästi. Varatuilla klustereilla suoritetut laskut vahvistavat kokeellisen tuloksen, jonka mukaan HSO4- ioni on huomattavan paljon voimakkaammin sitoutunut veteen kuin neutraali rikkihappo. Alustavat laskut HSO4- NH3 klustereille näyttävät osoittavan että ammoniakilla on korkeintaan vähäinen rooli rikkihappo- vesi - systeemin ioni-indusoidussa nukleaatiossa. Rikkihapon ja stabilisoitujen Criegee - väliaineiden väliselle reaktiolle lasketut termodynaamiset ja kineettiset parametrit osoittavat, että kvanttikemia on voimakas työkalu kemiallisesti monimutkaisten nukleaatiomekanismien tutkimiseen. Mikäli k.o. väliaineiden elinikä ilmakehässä on tarpeeksi pitkä, tutkittu reaktio saattaa laskentatulosten perusteella tuottaa merkittäviä määriä nukleaatioon tehokkaasti osallistuvia tiivistymiskykyisiä yhdisteitä.Nukleation är det första steget i processen där gasmolekyler i atmosfären bildar nya aerosolpartiklar. Fast uppkomsten av aerosolpartiklar i atmosfären är viktigt både ur klimat- och hälsoperspektiv, finns det endast lite information om nukleationsmekanismer på molekylnivå. I denna doktorsavhandling har potentiella nukleationsmekanismer som inbegriper svavelsyra, tillsammans med antingen vatten och ammoniak eller reaktiva biogeniska molekyler, undersökts med hjälp av kvantkemiska metoder. Kvantkemi, även kallad beräkningskemi, baserar sig på det numeriska lösandet av Schrödingerekvationen för ett system av atomer och elektroner med hjälp av vissa approximationer. Detaljerna i dessa approximationer ger upphov till ett stort antal så kallade modellkemier. En jämförelse av olika kvantkemiska metoder visar att modellkemin bör väljas noggrant om pålitliga beräkningsresultat för svavelsyra - vatten - ammoniak - kluster eftersträvas. Resultaten som rapporteras i denna doktorsavhandling visar att experimentella resultat gällande svavelsyramolekylens benägenhet att binda till sig vatten kan kvantitativt reproduceras av beräkningskemin, men endast med hjälp av tillräckligt avancerade metoder. Ammoniakets roll i nukleation av svavelsyra - vattenkluster har klargjorts genom att beräkna formationsenergier för kluster vars storlek ökades genom att tillsätta antingen svavelsyra-, vatten- eller ammoniakmolekyler. I enlighet med experimentella mätningar visar beräkningarna att ammoniak främjar tillväxten av kluster främst genom att binda nya svavelsyramolekyler starkare. Beräkningarna i denna doktorsavhandling visar att ammoniakets roll i atmosfäriska förhållanden blir viktig när mändgen svavelsyramolekyler ökar från två till tre. Å andra sidan visar beräkningarna att de minsta partiklarna i atmosfären antagligen innehåller högst en ammoniakmolekyl per svavelsyra, och antagligen mindre. Detta resultat är synnerligen intressant, eftersom större aerosolpartiklar enligt mätningar ofta innehåller upp till två ammoniakmolekyler per svavelsyra. Beräkningsresultaten visar alltså att den kemiska konsistensen av små och stora aerosolpartiklar kan skilja sig avsevärt från varandra. Beräkningar med laddade kluster bestyrker det experimentella resultatet at HSO4- jonen är mycket starkare bundet till vattenmolekyler än neutral svavelsyra H2SO4. Preliminära beräkningar med HSO4-*NH3 kluster tyder på att ammoniaket endast spelar en mycket liten roll i jon-inducerad svavelsyra - vatten nukleation Termodynamiska och kinetiska parametrar beräknade för reaktionen mellan svavelsyra och stabiliserade Criegee-intermediärer visar att kvantkemin är ett effektivt redskap för att studera kemiskt komplicerade nukleationsmekanismer. Om dessa intermediärers livstid i atmosfären är tillräckligt lång, kan den studerade reaktionsmekanismen producera betydliga mändger organosulfater som effektivt deltar i nukleationsprocesser

Thermal conductivity enhancement of graphene polymer composites through edge functionalization and expansion of graphite

In this work, we report an ultra-high enhancement of 4030% in thermal conductivity of polyetherimide/graphene nanocomposite (k = 9.5 Wm-1K-1) prepared through the use of expanded graphite (EG) with hydrogen peroxide as an intercalating agent at 10 weights% composition (k of pure polyetherimide ~ 0.23 Wm-1K-1). This value represents the highest thermal conductivity ever measured in a polymer composite at this low filler loading and is more than a factor of 2 higher relative to earlier reported results. This ultra-high thermal conductivity value is found to be due to an expanded graphite mediated interconnected graphene network throughout the composite, establishing a percolative environment that enables highly efficient thermal transport in the composite. Comparative studies were also performed using sodium chlorate as an intercalating agent. At 10 wt% composition, sodium chlorate intercalated expanded graphite was found to lead to a smaller enhancement of 2190% in k of composite. These results highlight the distinct advantage of hydrogen peroxide as an intercalating agent in enhancing thermal conductivity. Detailed characterization performed to elucidate this advantage, revealed that hydrogen peroxide led to primarily edge oxidation of graphene sheets within expanded graphite, leaving the basal plane intact, thus preserving the ultra-high in-plane thermal conductivity of ~ 2000 Wm-1K-1. Sodium chlorate, on the other hand, led to a higher degree of oxidation, with a large number of oxygen groups on basal plane of graphene, dramatically lowering its in-plane thermal conductivity. To directly shed light on the effect of intercalating agents on thermal conductivity of graphene itself, we prepared expanded graphite paper by compressing expanded graphite particles together. Thermal diffusivity of hydrogen-peroxide prepared expanded graphite paper was measured to be 9.5 mm2/s while that of sodium chlorate case measured to be 6.7 mm2/s, thus directly confirming the beneficial impact of hydrogen peroxide on k of graphene itself. This study is the first to address the role of intercalating agents on k of expanded graphite/polymer composites and has led to the discovery of hydrogen peroxide as an effective intercalating agent for achieving ultra-high thermal conductivity values. The work is also the first to address the comparison between edge and basal plane functionalization of graphene for enhancement of k of graphene-nanoplatelet /polyetherimide (GnP/PEI) composites. Graphene nanoplatelets (GnPs) comprise of multiple layers of graphene stacked parallel to each other. Edge functionalization enables the advantage of coupling the edges of all sheets of GnP with the embedding polymer, thus enabling the entire nanoplatelet to efficiently conduct heat through the composite. Basal-plane functionalization only couples the outermost layers of GnP with the polymer, thus causing only part of the nanoplatelet to be effective in conducting heat. Another very important advantage of edge-functionalization lies in leaving the basal plane of graphene intact. This preserves the ultra-high in-plane k of graphene (k~ 2000 Wm-1K-1). Basal plane functionalization, on the other hand, introduces a large number of defects in the basal plane of graphene dramatically lowering its intrinsic k value. Molecular dynamics simulations have revealed that even 5% functionalization of the basal plane can lower graphene thermal conductivity by as much as 90%. In this work, we experimentally realized the outlined advantages of edge-functionalization on the enhancement of k. Edge functionalization was achieved by oxidizing graphene with an excess of carboxyl groups through use of sulfuric acid, sodium chlorate and hydrogen peroxide. Carboxyl groups are known to preferentially attach to edges of graphene leading to edge oxidation. Basal plane oxidation was achieved through Hummer’s method by using sulfuric acid and potassium permanganate. Measurements reveal edge-oxidized graphene to enhance composite k by 18%, while basal-plane oxidized graphene reduced composite k by 57% at 10 wt% composition, clearly outlining the advantage of edge-functionalization on enhancement of thermal conductivity. Detailed characterization was performed to confirm edge versus basal plane oxidation. X-ray photoelectron spectroscopy showed greater fraction of carboxyl groups in edge-oxidized graphene, while basal plane oxidized graphene had larger fraction of hydroxyl/epoxy oxygen groups. 2D Raman mapping was used to obtain ID/IG ratios separately on edge and basal plane of GnPs. Edge oxidized graphene demonstrated higher ID/IG ratio on edge, while basal plane oxidized graphene demonstrated higher ID/IG ratio on basal plane. These studies for the first time, comprehensively demonstrate that edge functionalization can lead to superior thermal conductivity enhancement. Unique breakthroughs outlined in this thesis will lead to promising new avenues to achieve next-generation ultra-high thermal conductivity polymer-graphene nanocomposites

Investigation of Glassy State Molecular Motions in Thermoset Polymers

This dissertation presents the investigation of the glassy state molecular motions in isomeric thermoset epoxies by means of solid-state deuterium (2H) NMR spectroscopy technique. The network structure of crosslinked epoxies was altered through monomer isomerism; specifically, diglycidyl ether of bisphenol A (DGEBA) was cured with isomeric amine curatives, i.e., the meta-substituted diaminodiphenylsulfone (33DDS) and para-substituted diaminodiphenylsulfone (44DDS). The use of structural isomerism provided a path way for altering macroscopic material properties while maintaining identical chemical composition within the crosslinked networks. The effects of structural isomerism on the glassy state molecular motions were studied using solid-state 2H NMR spectroscopy, which offers unrivaled power to monitor site-specific molecular motions. Three distinctive molecular groups on each isomeric network, i.e., the phenylene rings in the bisphenol A structure (BPA), the phenylene rings in the diaminodiphenylsulfone structure (DDS), and the hydroxypropoyl ether group (HPE) have been selectively deuterated for a comprehensive study of the structure-dynamics-property relationships in thermoset epoxies. Quadrupolar echo experiments and line shape simulations were employed as the main research approach to gain both qualitative and quantitative motional information of the epoxy networks in the glassy state. Quantitative information on the geometry and rate of the molecular motions allows the elucidation of the relationship between molecular motions and macro physical properties and the role of these motions in the mechanical relaxation. Specifically, it is revealed that both the BPA and HPE moieties in the isomeric networks have almost identical behaviors in the deep glassy state, which indicates that the molecular motions in the glassy state are localized, and the correlation length of the motions does not exceed the length of the DGEBA repeat unit. BPA ring motions contribute to the low temperature (around -80 to -50 °C) region, and HPE chain motions to the even lower temperature range (-110 °C) of the mechanical relaxation as detected by DMA. The differences in the physical properties of the isomeric epoxies are mostly attributed to the DDS moieties. The occurrence of 44DDS ring motions decreases the modulus and the swept-out space from its ring axis fluctuation explains the higher hole-size free volume of the para-substituted networks. 33DDS rings do not exhibit large amplitude motions but only undergo fast small-angle fluctuations, which results in a decrease in the magnitude of the high temperature part of the γ relaxation of 33A, a phenomenon often seen in the anti-plasticization process