Recent Submissions

  • Laminar Burning Velocities of Formic Acid and Formic Acid/Hydrogen Flames: An Experimental and Modeling Study

    Osipova, K.N.; Sarathy, Mani; Korobeinichev, Oleg P.; Shmakov, A.G. (Energy & Fuels, American Chemical Society (ACS), 2021-01-05) [Article]
    Laminar flame speed of formic acid and formic acid/hydrogen (4/1) flames was studied both experimentally and numerically. Experiments with flames of pure formic acid were performed at temperatures of 373 and 423 K, while for formic acid/hydrogen flames the temperature value was 368 K. All of the experiments were performed under atmospheric pressure and at an equivalence ratio ranging from 0.5 to 1.5. To measure the laminar flame speed, the heat flux balance technique was applied. Three detailed chemical-kinetic mechanisms were tested on experimental data. Experiments showed that addition of 20% of hydrogen increases the laminar burning velocity of formic acid, for example, at around 1.5 for stoichiometric flames. The comparison of experimental and numerical data showed that all models tend to overestimate laminar burning velocities of studied flames, especially in the case of rich flames. The obtained results indicate that further improvement of existing chemical-kinetic models of formic acid oxidation is highly required.
  • Hole-Type Spacers for More Stable Shale Gas-Produced Water Treatment by Forward Osmosis

    Alqattan, Jawad; Kim, Youngjin; Kerdi, Sarah; Qamar, Adnan; Ghaffour, NorEddine (Membranes, MDPI AG, 2021-01-03) [Article]
    An appropriate spacer design helps in minimizing membrane fouling which remains the major obstacle in forward osmosis (FO) systems. In the present study, the performance of a hole-type spacer (having holes at the filament intersections) was evaluated in a FO system and compared to a standard spacer design (without holes). The hole-type spacer exhibited slightly higher water flux and reverse solute flux (RSF) when Milli-Q water was used as feed solution and varied sodium chloride concentrations as draw solution. During shale gas produced water treatment, a severe flux decline was observed for both spacer designs due to the formation of barium sulfate scaling. SEM imaging revealed that the high shear force induced by the creation of holes led to the formation of scales on the entire membrane surface, causing a slightly higher flux decline than the standard spacer. Simultaneously, the presence of holes aided to mitigate the accumulation of foulants on spacer surface, resulting in no increase in pressure drop. Furthermore, a full cleaning efficiency was achieved by hole-type spacer attributed to the micro-jets effect induced by the holes, which aided to destroy the foulants and then sweep them away from the membrane surface.
  • On the distillation of waste tire pyrolysis oil: A structural characterization of the derived fractions

    Campuzano, Felipe; Abdul Jameel, Abdul Gani; Zhang, Wen; Emwas, Abdul-Hamid M.; Agudelo, Andrés F.; Martínez, Juan Daniel; Sarathy, Mani (Fuel, Elsevier BV, 2020-12-31) [Article]
    Tire pyrolysis oil (TPO) is a complex mixture of hydrocarbons spanning a wide boiling point range. Due to its complexity, direct implementation of TPO to combustion applications has been challenging. Distillation is a simple method for grouping similar compounds, based on their volatility, thereby facilitating further upgrading and use. In this work, TPO was distilled at atmospheric pressure into different fractions (light, low-middle, high-middle, and heavy), and the structural characteristics of each fraction were explored. Therefore, advanced analytical techniques such as GC–MS, APPI FT-ICR MS and 1H and 13C NMR were utilized. For the light fraction, the GC–MS revealed a significant presence of benzene, toluene, and xylene, as well as limonene. From the APPI FT-ICR MS results, the low-middle, high-middle, and heavy fractions were classified into a number of molecular classes. Among these, pure hydrocarbons (HC), hydrocarbons containing one sulfur atom (S1), hydrocarbons containing two oxygen atoms (O2), etc. Here, HC and S1 were found to be the most abundant molecular classes in all fractions. Finally, a structural analysis of the functional groups present in each TPO fraction was conducted by 1H and 13C NMR. Average molecular parameters (AMPs), such as the number of aromatic, naphthenic, and olefinic carbons/hydrogens, were determined. In addition, derived AMPs, such as the aromaticity factor (fa), C/H paraffinic, C/H aromatic, etc., were calculated. Fractionation by distillation resulted in concentration of both the sulfur and aromatic compounds in the heaviest fraction. In this manner, effective application and upgrading strategies could be individually designed for each fraction.
  • Arabidopsis Plant Natriuretic Peptide Is a Novel Interactor of Rubisco Activase

    Turek, Ilona; Gehring, Christoph A; Irving, H R (Life, MDPI AG, 2020-12-31) [Article]
    Plant natriuretic peptides (PNPs) are a group of systemically acting peptidic hormones affecting solute and solvent homeostasis and responses to biotrophic pathogens. Although an increasing body of evidence suggests PNPs modulate plant responses to biotic and abiotic stress, which could lead to their potential biotechnological application by conferring increased stress tolerance to plants, the exact mode of PNPs action is still elusive. In order to gain insight into PNP-dependent signalling, we set out to identify interactors of PNP present in the model plant Arabidopsis thaliana, termed AtPNP-A. Here, we report identification of rubisco activase (RCA), a central regulator of photosynthesis converting Rubisco catalytic sites from a closed to an open conformation, as an interactor of AtPNP-A through affinity isolation followed by mass spectrometric identification. Surface plasmon resonance (SPR) analyses reveals that the full-length recombinant AtPNP-A and the biologically active fragment of AtPNP-A bind specifically to RCA, whereas a biologically inactive scrambled peptide fails to bind. These results are considered in the light of known functions of PNPs, PNP-like proteins, and RCA in biotic and abiotic stress responses.
  • Surface engineering of intrinsically microporous poly(ether-ether-ketone) membranes: From flat to honeycomb structures

    Abdulhamid, Mahmoud; Park, Sang-Hee; Zhou, Zuo; Ladner, David A.; Szekely, Gyorgy (Journal of Membrane Science, Elsevier BV, 2020-12-25) [Article]
    Surface engineering of polymeric membranes can induce subtle changes in membrane properties and enhance their performance. Numerous membrane surface modification methods have been developed to improve the material performance. However, these methods can be complex, thus limiting their practical applications. Herein, we present a simple method for fabricating membranes with honeycomb surfaces by controlling the polymer molecular weight (Mw). Spirobisindane-based intrinsically microporous poly(ether-ether-ketone) (iPEEK-SBI) homopolymers with low and high Mws were synthesized and used to prepare organic solvent nanofiltration (OSN) membranes. The significant effects of polymer Mw on its physical properties, membrane morphology, and OSN performance were systematically investigated. iPEEK showed excellent solution processability, high Brunauer–Emmett–Teller surface area, and remarkable thermal stability. Three mechanically flexible OSN membranes exhibiting honeycomb surfaces with different honeycomb cell sizes were prepared using iPEEK-SBI homopolymers with low Mws at concentrations of 27–39 wt% in N-methyl-2-pyrrolidone. By contrast, the use of iPEEK-SBI homopolymers with high Mws yielded membranes with flat surfaces. The Mw cutoffs of the membranes were fine-tuned in the range of 408–772 g mol−1 by adjusting the dope solution concentration. Although the Mw cutoffs were unaffected by polymer Mw, the membranes derived from the polymer with low Mw exhibited substantially higher solvent permeance (18%–26%) than that of the high Mw membrane prepared at the same dope solution concentration. Stable performance was demonstrated over seven days of continuous cross-flow filtration and a six-month aging of the membranes. This work shows the importance of surface engineering for OSN membranes by adjusting polymer Mw. These findings open a new avenue for fine-tuning the properties of OSN membranes.
  • Fundamentals and applications of photo-thermal catalysis

    Mateo, Diego; Cerrillo, Jose Luis; Durini, Sara; Gascon, Jorge (Chemical Society Reviews, Royal Society of Chemistry (RSC), 2020-12-18) [Article]
    Photo-thermal catalysis has recently emerged as an alternative route to drive chemical reactions using light as an energy source. Through the synergistic combination of photo- and thermo-chemical contributions of sunlight, photo-thermal catalysis has the potential to enhance reaction rates and to change selectivity patterns, even under moderate operation conditions. This review provides the fundamentals of localized surface plasmon resonance (LSPR) that explain the photo-thermal effect in plasmonic structures, describes the different mechanistic pathways underlying photo-thermal catalysis, suggests methodologies to disentangle the reaction mechanisms and proposes material design strategies to improve photo-thermal performance. Ultimately, the goal is to pave the way for the wide implementation of this promising technology in the production of synthetic fuels and chemicals
  • Calcium Looping: On the Positive Influence of SO2 and the Negative Influence of H2O on CO2 Capture by Metamorphosed Limestone-Derived Sorbents

    Homsy, Sally Louis; Moreno, Joseba; Dikhtiarenko, Alla; Gascon, Jorge; Dibble, Robert W. (ACS Omega, American Chemical Society (ACS), 2020-12-07) [Article]
    The CO2 capture performance of sorbents derived from three distinct limestones, including a metamorphosed limestone, is studied under conditions relevant for calcium looping CO2 capture from power plant flue gas. The combined and individual influence of flue gas H2O and SO2 content, the influence of textural changes caused by sequential calcination/carbonation cycles, and the impact of CaSO4 accumulation on the sorbents’ capture performance were examined using bubbling fluidized bed reactor systems. The metamorphosed limestone-derived sorbents exhibit atypical capture behavior: flue gas H2O negatively influences CO2 capture performance, while limited sulfation can positively influence CO2 capture, with space time significantly impacting CO2 and SO2 co-capture performance. The morphological characteristics influencing sorbents’ capture behavior were examined using imaging and material characterization tools, and a detailed discussion is presented. This insight into the morphology responsible for metamorphosed limestone-derived sorbent’s anomalous capture behavior can guide future sorbent selection and design efforts.
  • Efficient Visible-Light Driven Photothermal Conversion of CO 2 to Methane by Nickel Nanoparticles Supported on Barium Titanate

    Mateo, Diego; Morlanes, Natalia Sanchez; Maity, Partha; Shterk, Genrikh; Mohammed, Omar F.; Gascon, Jorge (Advanced Functional Materials, Wiley, 2020-12-04) [Article]
    Solar-driven methanation represents a potentially cost-efficient and environmentally friendly route for the direct hydrogenation of CO2. Recently, photothermal catalysis, which involves the combination of both photochemical and thermochemical pathways, has emerged as a promising strategy for the production of solar fuels. For a photothermal catalyst to efficiently convert CO2 under illumination, in the absence of external heating, effective light harvesting, an excellent photothermal conversion and efficient active sites are required. Here, a new composite catalyst consisting of Ni nanoparticles supported on barium titanate that, under optimal reaction conditions, is able to hydrogenate CO2 to CH4 at nearly 100% selectivity with production rates as high as 103.7 mmol g–1 h–1 under both UV–visible and visible irradiation (production rate: 40.3 mmol g−1 h–1) is reported. Mechanistic studies suggest that reaction mostly proceeds through a nonthermal hot-electron-driven pathway, with a smaller thermal contribution.
  • A theoretical study of the Ḣ- and HOȮ-assisted propen-2-ol tautomerizations: Reactive systems to evaluate collision efficiency definitions on chemically activated reactions using SS-QRRK theory

    Grajales Gonzalez, Edwing; Monge Palacios, Manuel; Sarathy, Mani (Combustion and Flame, Elsevier BV, 2020-12-01) [Article]
    In combustion, enols can undergo keto-enol tautomerizations, which are intermediate steps in the formation of pollutant species. In this work, we performed a theoretical kinetic study of the step-wise propen-2-ol tautomerization catalyzed by hydrogen and hydroperoxyl radicals. Ab initio calculations at the CCSD(T)/aug-cc-pVTZ//M06-2X/cc-pVTZ level were run, and rate constants were calculated using the multistructural torsional variational transition state theory with small-curvature tunneling corrections. Hydrogen and hydroperoxyl radicals can induce a step-wise mechanism toward keto formation with a lower barrier than that of unimolecular tautomerization. The potential energy surface comprising these reactions is complex, involving different intermediates that are connected by different types of pathways. The hydrogen-assisted tautomerization consists of two steps where the formation of an intermediate radical takes place as a result of the addition of the hydrogen atom to the double bond of propen-2-ol. The high-pressure limit rate constants of the reactions of this intermediate radical toward propen-2-ol and acetone exhibit an Arrhenius behavior, in agreement with previous works. In the hydroperoxyl-assisted tautomerization, the acetone formation has two routes involving an overall of four steps. The route with the highest energy barrier becomes prominent above 800 K due to multistructural anharmonicity effects, which must be included for an accurate kinetic description of the titled reactions. Calculations of pressure-dependent rate constants showed that the original system-specific quantum Rice-Ramsperger-Kassel theory, together with the modified strong collision model (SS-QRRK/MSC), significantly underpredict the bimolecular stabilization rate constants for the hydrogen-assisted tautomerization above 1200 K by factors of up to three orders of magnitude when compared with the benchmark Rice-Ramsperger-Kassel-Markus/master equation method. To solve this problem, we tested two alternative definitions of the collision efficiency parameter by using an improved implementation of the SS-QRRK/MSC approach developed by us for chemically activated reactions. One of these definitions, provided by Gilbert et al. (1983), corrected the bimolecular stabilization rate constant behavior and yielded a maximum deviation factor of only 4.5 at 2000 K and 100 atm. For the hydroperoxyl-assisted tautomerization, pressure effects are negligible because the stabilization of the energized adduct cannot compete with the reaction leading to the final product for most of the physical conditions studied. Our calculated rate constants can be used to perform more accurate kinetic modeling of alcohols. Besides, the implementation of the SS-QRRK theory with the collision efficiency of Gilbert et al. (1983) proposed in this work is useful for computing pressure-dependent rate constants of chemically activated reactions, including all possible refinements (multi-dimensional tunneling, multistructural anharmonicity, etc.) considered in high-pressure limit calculations.
  • Advances in the Design of Heterogeneous Catalysts and Thermocatalytic Processes for CO2 Utilization

    De, Sudipta; Dokania, Abhay; Galilea, Adrian; Gascon, Jorge (ACS Catalysis, American Chemical Society (ACS), 2020-11-20) [Article]
    Utilization of CO2 as feedstock to produce fine chemicals and renewable fuels is a highly promising field, which presents unique challenges in its implementation at scale. Heterogeneous catalysis with its simple operation and industrial compatibility can be an effective means of achieving this challenging task. This review summarizes the current developments in heterogeneous thermal catalysis for the production of carbon monoxide, alcohols, and hydrocarbons from CO2. A detailed discussion is provided regarding structure−activity correlations between the catalyst surface and intermediate species which can aid in the rational design of future generation catalysts. Effects of active metal components, catalyst supports, and promoters are discussed in each section, which will guide researchers to synthesize new catalysts with improved selectivity and stability. Additionally, a brief overview regarding process design considerations has been provided. Future research directions are proposed with special emphasis on the application scope of new catalytic materials and possible approaches to increase catalyst performance.
  • Elucidating the Promotional Effect of Cerium in the Dry Reforming of Methane

    Rodriguez Gomez, Alberto; Lopez-Martin, Angeles; Ramirez, Adrian; Gascon, Jorge; Caballero, Alfonso (ChemCatChem, Wiley, 2020-11-19) [Article]
    A series of Ni-Ce catalysts supported on SBA-15 has been prepared by co-impregnation, extensively characterized and evaluated in the carbon dioxide reforming of methane (DRM). The characterization by TEM, XRD and TPR has allowed us to determine the effect of metal loading on metal dispersion. Cerium was found to improve nickel location inside the mesopores of SBA-15 and to suppress coke formation during the DRM reaction. The analysis by XPS allowed us to associate the high cerium dispersion with the presence of low-coordinated Ce 3+ sites, being main responsible for its promotional effect. A combination of XAS and XPS has permitted us to determine the physicochemical properties of metals under reduction conditions. The low nickel coordination number determined by XAS in Ni-Ce doped systems after reduction suggests the generation of very small nickel particles which showed greater catalytic activity and stability in the reaction, and a remarkable resistance to coke formation.
  • Molecularly-porous ultrathin membranes for highly selective organic solvent nanofiltration

    Huang, Tiefan; Moosa, Basem; HOANG, PHUONG; Liu, Jiangtao; Chisca, Stefan; Zhang, Gengwu; Alyami, Mram Z.; Khashab, Niveen M.; Nunes, Suzana Pereira (Nature Communications, Springer Science and Business Media LLC, 2020-11-18) [Article]
    AbstractEngineering membranes for molecular separation in organic solvents is still a big challenge. When the selectivity increases, the permeability tends to drastically decrease, increasing the energy demands for the separation process. Ideally, organic solvent nanofiltration membranes should be thin to enhance the permeant transport, have a well-tailored nanoporosity and high stability in harsh solvents. Here, we introduce a trianglamine macrocycle as a molecular building block for cross-linked membranes, prepared by facile interfacial polymerization, for high-performance selective separations. The membranes were prepared via a two-in-one strategy, enabled by the amine macrocycle, by simultaneously reducing the thickness of the thin-film layers (<10 nm) and introducing permanent intrinsic porosity within the membrane (6.3 Å). This translates into a superior separation performance for nanofiltration operation, both in polar and apolar solvents. The hyper-cross-linked network significantly improved the stability in various organic solvents, while the amine host macrocycle provided specific size and charge molecular recognition for selective guest molecules separation. By employing easily customized molecular hosts in ultrathin membranes, we can significantly tailor the selectivity on-demand without compromising the overall permeability of the system.
  • Architecting Neonicotinoid-Scavenging Nanocomposite Hydrogels for Environmental Remediation

    Alammar, Abdulaziz; Park, Sang-Hee; Ibrahim, Izwaharyanie; Arun, Deepak; Holtzl, Tibor; Dumée, Ludovic F.; Lim, Hong Ngee; Szekely, Gyorgy (Applied Materials Today, Elsevier, 2020-11-13) [Article]
    The ubiquitous presence of neonicotinoid insecticides in the environment poses potential health concerns across all biomes, aquatic systems, and food chains. This global environmental challenge requires robust, advanced materials to efficiently scavenge and remove these harmful neonicotinoids. In this work, we engineered nanocomposite hydrogels based on sustainable cellulose acetate for water treatment. The nanocomposite hydrogels were incorporated with small quantities of polymers of intrinsic microporosity (PIM-1) and graphene oxide (GO). We prepared the hydrogels using green solvents such as Cyrene and MeTHF via simple dropwise phase inversion. High adsorption capacity and fast kinetic behavior toward acetamiprid, clothianidin, dinotefuran, imidacloprid, and thiamethoxam were observed. We also developed a rapid and sustainable ultrasound-assisted regeneration method for the hydrogels. Molecular dynamics of the complex quaternary system revealed the synergistic effects of the components, and the presence of PIM-1 was found to increase the GO surface area available for neonicotinoid scavenging. We demonstrated the robustness and practicality of the nanocomposites in continuous environmental remediation by using the hydrogels to treat contaminated groundwater from the Adyar river in India. The presented methodology is adaptable to other contaminants in both aqueous environments and organic media.
  • A natriuretic peptide from Arabidopsis thaliana (AtPNP-A) can modulate catalase 2 activity.

    Turek, Ilona; Wheeler, Janet; Bartels, Sebastian; Szczurek, Jolanta; Wang, Yu Hua; Taylor, Phil; Gehring, Christoph A; Irving, Helen (Scientific reports, Springer Science and Business Media LLC, 2020-11-12) [Article]
    Analogues of vertebrate natriuretic peptides (NPs) present in plants, termed plant natriuretic peptides (PNPs), comprise a novel class of hormones that systemically affect salt and water balance and responses to plant pathogens. Several lines of evidence indicate that Arabidopsis thaliana PNP (AtPNP-A) affects cellular redox homeostasis, which is also typical for the signaling of its vertebrate analogues, but the molecular mechanism(s) of this effect remains elusive. Here we report identification of catalase 2 (CAT2), an antioxidant enzyme, as an interactor of AtPNP-A. The full-length AtPNP-A recombinant protein and the biologically active fragment of AtPNP-A bind specifically to CAT2 in surface plasmon resonance (SPR) analyses, while a biologically inactive scrambled peptide does not. In vivo bimolecular fluorescence complementation (BiFC) showed that CAT2 interacts with AtPNP-A in chloroplasts. Furthermore, CAT2 activity is lower in homozygous atpnp-a knockdown compared with wild type plants, and atpnp-a knockdown plants phenocopy CAT2-deficient plants in their sensitivity to elevated H2O2, which is consistent with a direct modulatory effect of the PNP on the activity of CAT2 and hence H2O2 homeostasis. Our work underlines the critical role of AtPNP-A in modulating the activity of CAT2 and highlights a mechanism of fine-tuning plant responses to adverse conditions by PNPs.
  • Using deep neural networks to diagnose engine pre-ignition

    Kuzhagaliyeva, Nursulu; Thabet, Ali; Singh, Eshan; Ghanem, Bernard; Sarathy, Mani (Proceedings of the Combustion Institute, Elsevier BV, 2020-11-12) [Article]
    Engine downsizing and boosting have been recognized as effective strategies for improving engine efficiency. However, operating the engines at high load promotes abnormal combustion events, such as pre-ignition and potential superknock. Currently the most effective method for detecting pre-ignition is by using in-cylinder pressure sensors that have high precision and sensitivity, but also high cost. Due to rapid advances in automotive technology such as autonomous driving, computer-aided designs and future connectivity, we propose to use a complimentary data-driven strategy for diagnosing abnormal combustion events. To this end, a data-driven diagnostics approach for pre-ignition detection with deep neural networks is proposed. The success of convolutional neural networks (CNNs) in object detection and recurrent neural networks (RNNs) in sequence forecasting inspired us to develop these models for pre-ignition detection. For a cost-effective strategy, we use data from less expensive sensors, such as lambda and low-resolution exhaust back pressure (EBP), instead of high resolution in-cylinder pressure measurements. The first deep learning model is combined with a commonly used dimensionality reduction tool–Principal Component Analysis (PCA). The second model eliminates this step and directly processes time-series data. Results indicate that the first model with reduced input dimensions, and correspondingly smaller size of the network, shows better performance in detecting pre-ignition cycles with an F1 score of 79%. Overall, the proposed deep learning approach is a promising alternative for abnormal combustion diagnostics using data from low resolution sensors.
  • Electropolymerized Conjugated Microporous Nanoskin Regulating Polysulfide and Electrolyte for High-Energy Li–S Batteries

    Guo, Dong; Li, Xiang; Wahyudi, Wandi; Li, Chunyang; Emwas, Abdul-Hamid M.; Hedhili, Mohamed N.; Li, Yangxing; Lai, Zhiping (ACS Nano, American Chemical Society (ACS), 2020-11-09) [Article]
    A popular practice in Li–S battery research is to utilize highly nanostructured hosts and excessive electrolytes to enhance sulfur-specific capacities. However, from the perspective of commercialization, this is a less meaningful approach in the pursuit of high-energy Li–S batteries. Herein, we report the fabrication of a nanoskin composed of a conjugated microporous polymer by electropolymerization to create a closed system for a sulfur cathode. The nanoskin is ultrathin, conductive, continuous, and contains uniform micropores of approximately 0.8 nm. The nanoskin sealing prevents the shuttling of polysulfide species without using the absorption effect, enhances the utilization of electrolytes, and allows a fast transport of lithium ions. As a result, the Li–S batteries comprising the cathode with nanoskin exhibit superior stability (∼86% capacity retention) under lean electrolyte conditions and a prolonged lifetime (1000 cycles). At a low electrolyte/sulfur ratio of 4 μL mg–1, the designed cathode delivered a practical energy density of over 300 Wh kg–1 without using any sophisticated hosts.
  • A functional-group-based approach to modeling real-fuel combustion chemistry – II: Kinetic model construction and validation

    Zhang, Xiaoyuan; Sarathy, Mani (Combustion and Flame, Elsevier BV, 2020-11-07) [Article]
    Construction of kinetic models to predict real-fuel combustion properties requires significant human and computational resources. In the first of this two-part study, a functional group correlation approach called FGMech was proposed for predicting the stoichiometric parameters in lumped pyrolysis reactions. The stoichiometric parameters were implemented in a recent real-fuel kinetic model, HyChem (Xu et al., 2018), and the validity of this approach was demonstrated for simulating real-fuel combustion. The present work extends the FGMech approach for developing surrogate and real-fuel kinetic models. Our approach is fundamentally different from the HyChem development approach in that no parameters are tuned to match actual real-fuel pyrolysis/oxidation data, and all model parameters are derived only from functional group data. Along with the stoichiometric parameters obtained in the first part of this study, the thermodynamic data, lumped reaction rate parameters and transport data were predicted in this work based on the functional group characterization of real fuels. The Benson group additivity method was adopted to estimate the thermodynamic data of real fuels, while rate rules developed for pure fuels were used to estimate the rate constants of lumped reactions in real-fuel models. For transport data, normal boiling point, critical temperature and pressure (estimated using the Joback group contribution method) were used to obtain Lennard-Jones parameters. The format of lumped reactions in FGMech followed the HyChem approach, and the base mechanism was adopted from the AramcoMech 2.0 and USC Mech II, respectively, to compare the model performance with different base mechanisms. Fourteen surrogate and twelve real-fuel models were developed based on this approach; they were validated against the experimental data in the literature. FGMech's performance was also compared with detailed and reduced models available in the literature. FGMech reasonably captures the experimental data in the literature, indicating that the present modeling approach is promising for modeling the combustion behavior of fuel, including surrogate mixtures and real fuels.
  • A functional-group-based approach to modeling real-fuel combustion chemistry – I: Prediction of stoichiometric parameters for lumped pyrolysis reactions

    Zhang, Xiaoyuan; Yalamanchi, Kiran K.; Sarathy, Mani (Combustion and Flame, Elsevier BV, 2020-11-07) [Article]
    Real fuels are complex mixtures of hundreds of molecules, which makes it challenging to unravel their combustion chemistry. Several approaches in the literature have helped to clarify fuel combustion, including multi-component surrogates, lumped fuel chemistry modeling, and functional-group based methods. This work presents an innovative advancement to the lumped fuel chemistry modeling approach, using functional groups for mechanism development (FGMech). Stoichiometric parameters of lumped fuel decomposition reactions dictate the population of the key pyrolysis products, previously obtained by fitting experimental data of real-fuel pyrolysis. In this work, a functional group-based approach is proposed, which can account for real-fuel variability and predict stoichiometric parameters without experimentation. A database of the stoichiometric parameters and/or yields of key pyrolysis products was first constructed for approximately 50 neat fuels, based on previous pyrolysis data and a lumped kinetic model we developed. The effects of functional groups on the stoichiometric parameters and/or yields of key pyrolysis products were then identified and quantified. A quantitative structure-stoichiometry relationship was developed by multiple linear regression (MLR) model, which was used to predict the stoichiometric parameters and/or yields of key pyrolysis products based on ten input features (eight functional groups, molecular weight, and branching index). Products from the pyrolysis of surrogate mixtures and real-fuels were predicted using the MLR model and validated against experimental data in the literature. Comparison with the stoichiometric parameters from the HyChem experiment-based approach (Xu et al., 2018) showed that the predicted values in this work were in reasonable agreement (generally within a factor of two). When the stoichiometric parameters in the jet fuel (POSF 10325) HyChem kinetic model were replaced with this functional-group based prediction, only minor discrepancies were observed in the predictions of key pyrolysis products and global combustion parameters (such as ignition delay times and laminar flame speeds). Sensitivity analysis on stoichiometric parameters revealed their different roles in predicting speciation and global parameters. The functional group approach for predicting stoichiometric parameters in this work was the first step towards developing FGMech for modeling real-fuel combustion chemistry. Further development of the FGMech model's thermodynamic, kinetic, and transport data will be presented in a following study.
  • Theoretical Kinetic Study of Gas Phase Oxidation of Nicotine by Hydroxyl Radical

    Chavarrio Cañas, Javier Eduardo (2020-11) [Thesis]
    Advisor: Sarathy, Mani
    Committee members: Mishra, Himanshu; Castaño, Pedro
    Cigarette smoke is suspected to cause diverse illnesses in smokers and people breathing second- and third-hand smoke. Although different studies have been done to elucidate the impact on health due to smoking, there is a lack of kinetic information regarding the degradation of nicotine under different environmental conditions. As a consequence, currently it is not possible to determine thoroughly the risk due to exposure to nicotine and the compounds derived from its decomposition. With the aim of contributing to clarify the different degradation paths followed by nicotine during and after the consumption of cigarettes, this work presents a theoretical study of the hydrogen atom abstraction reaction by hydroxyl radical at four sites in the nicotine molecule in a broad range of temperature, specifically be-tween 200-3000 K. The site-specific kinetic rate constants were computed by means of the multi-structural torsional variational transition state theory with small curvature tunneling contribution, performing ab initio calculations at the level M06-2X/aug-cc-pVQZ//M06-2X/cc-pVTZ. According to our computations, the dependence on temperature of the studied rate constants exhibited a non-Arrhenius fashion, with a minimum at 873 K. A negative temperature dependence was observed at temperatures lower than 873 K, indicating more prolonged exposure to nicotine in warmer environments. On the other hand, the opposite behavior was observed at higher temperatures; this non-Arrhenius be-havior results of interest in tobacco cigarette combustion, inducing different reaction mechanisms depending on the burning conditions of the different smoking devices. The results indicate that multi-structural and torsional anharmonicity is an im-portant factor in the computation of accurate rate constants, especially at high tem-peratures where the higher-energy conformers of the different species exert a larger influence. The anharmonicity factors suggest that disregarding the anharmonic de-viations leads to overestimation of the rate constant coefficients, by a factor between four and six. Our computed overall kinetic rate constant at 298 K exhibited very good agreement with the only experimental value meausred by Borduas et al. [1], af-fording certainty about our calculated site-specific rate constants, which are currently inaccessible to experiments. However, further experimental studies are necessary to validate our kinetic studies at other temperatures.
  • Arsenic Removal via Defect-Free Interfacially-Polymerized Thin-Film Composite Membranes

    Aljubran, Murtadha A. (2020-11) [Thesis]
    Advisor: Pinnau, Ingo
    Committee members: Han, Yu; Lai, Zhiping
    Billions of people rely solely on groundwater for drinking and daily use. In the last few decades, groundwater was shown to be contaminated with arsenic in high concentrations, especially in Asian countries such as Bangladesh. Arsenic (As) is ranked the first among 20 toxic substances by the Agency for Toxic Substances and Disease Registry (ATSDR) and United States Environmental Protection Agency (USEPA). Because many diseases and deaths were linked to consumption of arsenic-contaminated groundwater, the world health organization (WHO) reduced the arsenic standard level for drinking water from 50 to 10 µg L-1. Urgent demands for safe drinking water lead to developing potential technologies for removal of arsenic from groundwater. Arsenic is mainly present as uncharged As(III) in groundwater, which makes it difficult to be efficiently removed by conventional treatment methods. Therefore, membrane technology could be a promising potential solution. Because membrane technology has not been widely tested for arsenic removal, a novel in-house defect-free interfacially-polymerized (IP) cross-linked polyamide thin-film composite (TFC) nanofiltration membrane, namely, PIP-KRO1, was tested in this research. Two commercial TFC membranes, namely Dow NF270 and Sepro RO4, were also tested and compared to PIP-KRO1. The membranes were tested at four different pH conditions (4, 6, 8, and 10) in a cross-flow flat sheet membrane unit. The experiments were divided into two parts: (i) the membranes were tested for water permeance and salt (NaCl) removal and (ii) tested for As(III) removal in the presence of 250 ppm NaCl. The results in this study showed strong size sieving rejection for RO4 and a combination of size sieving and charge exclusion mechanisms for PIP-KRO1 and NF270. In general, the rejection trend was RO4 > PIP-KRO1 > NF270 for both NaCl and As(III). In contrast, the trend for water permeance was NF270 > PIP-KRO1 > RO4. The minimum and maximum salt rejection at pH 4 and pH 10, respectively, were 85 and 98.8% for RO4, 57 and 89% for PIP-KRO1, and 34 and 76.8% for NF270. In addition, the TFC membranes demonstrated a maximum As(III) rejection of 98.7, 69.5, and 46.3% for RO4, PIP-KRO1, and NF270, respectively. Based on the characterizations of the membranes, PIP-KRO1 had the highest cross-linking (N/O ratio) followed by RO4 and NF270, respectively. The same trend was observed for the thickness of the polyamide selective layer (PIP-KRO1 > RO4 > NF270). The zeta potential for NF270 was slightly higher than that for PIP-KRO1; RO4 had much lower membrane surface charge. In terms of surface roughness, the following trend was observed: RO4 > PIP-KRO1 > NF270.

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