Recent Submissions

  • Recent Progress on Polymers of Intrinsic Microporosity and Thermally Modified Analogue Materials for Membrane-Based Fluid Separations

    Wang, Yingge; Ghanem, Bader; Ali, Zain; Hazazi, Khalid; Han, Yu; Pinnau, Ingo (Small Structures, Wiley, 2021-09-14) [Article]
    Solution-processable amorphous glassy polymers of intrinsic microporosity (PIMs) are promising microporous organic materials for membrane-based gas and liquid separations due to their high surface area and internal free volume, thermal and chemical stability, and excellent separation performance. This review provides an overview of the most recent developments in the design and transport properties of novel ladder PIM materials, polyimides of intrinsic microporosity (PIM–PIs), functionalized PIMs and PIM–PIs, PIM-derived thermally rearranged (TR), and carbon molecular sieve (CMS) membrane materials as well as PIM-based thin film composite membranes for a wide range of energy-intensive gas and liquid separations. In less than two decades, PIMs have significantly lifted the performance upper bounds in H2/N2, H2/CH4, O2/N2, CO2/N2, and CO2/CH4 separations. However, PIMs are still limited by their insufficient gas-pair selectivity to be considered as promising materials for challenging industrial separations such as olefin/paraffin separations. An optimum pore size distribution is required to further improve the selectivity of a PIM for a given application. Specific attention is given to the potential use of PIM-based CMS membranes for energy-intensive CO2/CH4, N2/CH4, C2H4/C2H6, and C3H6/C3H8 separations, and thin film composite membranes containing PIM motifs for liquid separations.
  • Illuminating the Intrinsic Effect of Water Co-feeding on Methane Dehydroaromatization: A Comprehensive Study

    Caglayan, Mustafa; Paioni, Alessandra Lucini; Dereli, Busra; Shterk, Genrikh; Hita, Idoia; Abou-Hamad, Edy; Pustovarenko, Alexey; Emwas, Abdul-Hamid M.; Dikhtiarenko, Alla; Castaño, Pedro; Cavallo, Luigi; Baldus, Marc; Chowdhury, Abhishek Dutta; Gascon, Jorge (ACS Catalysis, American Chemical Society (ACS), 2021-09-07) [Article]
    Among all catalytic natural gas valorization processes, methane dehydroaromatization (MDA) still has a great potential to be utilized at an industrial level. Although the use of Mo/H-ZSM-5 as an MDA catalyst was first reported almost three decades ago, the process is yet to be industrialized, because of its inherent challenges. In order to improve the overall catalytic performance and lifetime, the co-feeding of water constitutes a promising option, because of its abundance and nontoxicity. Although water’s (limited) positive influence on catalyst lifetime has earlier been exhibited, the exact course of action (like mechanism or the water effect on active sites) is yet to be established. To bridge this knowledge gap, in this work, we have performed an in-depth investigation to elucidate the effects of water co-feeding over a well-dispersed Mo/H-ZSM-5 catalyst by using an array of advanced characterization techniques (nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetry–temperature-programmed oxidation/mass spectroscopy (TG-TPO/MS), scanning transmission electron microscopy (STEM), N2 physisorption, Raman spectroscopy, inductively coupled plasma–optical emission spectroscopy (ICP-OES)). Our results demonstrate that the addition of water results in the occurrence of steam reforming (of both coke and methane) in parallel to MDA. Moreover, the presence of water affects the reducibility of Mo sites, as corroborated with computational analysis to examine the state and locality of Mo sites under various water levels and transformation of the catalyst structure during deactivation. We anticipate that our comprehensive study of the structure–function relationship on Mo/H-ZSM-5 under humid MDA conditions will be beneficial for the development of future methane valorization technologies.
  • Probing the gas-phase oxidation of ammonia: Addressing uncertainties with theoretical calculations

    Chavarrio Cañas, Javier Eduardo; Monge Palacios, Manuel; Zhang, Xiaoyuan; Sarathy, Mani (Combustion and Flame, Elsevier BV, 2021-09-05) [Article]
    The kinetics of the reactions H2NO + O2(3Σg−) → HNO(X˜1A′) + HO2 and NH2 + HO2 → NH3 + O2(3Σg−), which are, respectively, very sensitive chain-propagation and chain-termination reactions in ammonia kinetic models, have been revisited by means of high-level electronic structure and variational transition state theory calculations with the goal of improving former predictions and the performance of ammonia kinetic models. In addition, the rate constants of the reactions H2NO + O2(3Σg−) → HNO(a˜3A″) + HO2, NH2 + HO2 → H2NO + OH, and NH2 + HO2 → NH3 + O2(1Δg), which take place on excited-state potential energy surfaces and/or yield the electronically excited species HNO(a˜3A″) and O2(1Δg), have been also calculated for the first time in order to assess their importance in ammonia oxidation. We observed that spin contamination and multi-reference character are pronounced in many of the investigated reactions, and these features were handled by performing post-CCSD(T) electronic structure calculations with the W3X-L composite method as well as restricted open shell coupled cluster calculations. Branching ratios were also analyzed, and indicate that the contribution of the electronically excited species HNO(a˜3A″) and O2(1Δg) are of little importance even at very high temperatures; however, we do not preclude an effect of those species at certain conditions that contribute to their yield. The calculated rate constants were implemented in two recent kinetic models to perform jet stirred reactor, rapid compression machine, and flow reactor simulations, concluding that the model predictions are very sensitive to the reactions H2NO + O2(3Σg−) → HNO(X˜1A′) + HO2 and NH2 + HO2 → NH3 + O2(3Σg−).
  • Bridging the interfacial gap in mixed-matrix membranes by nature-inspired design: Precise molecular sieving with polymer-grafted metal–organic frameworks

    Cseri, Levente; Hardian, Rifan; Anan, Shizuka; Vovusha, Hakkim; Schwingenschlögl, Udo; Budd, Peter Martin; Sada, Kazuki; Kokado, Kenta; Szekely, Gyorgy (Journal of Materials Chemistry A, Royal Society of Chemistry, 2021-09-02) [Article]
    Membrane technology is a dynamically developing field of separation science that is poised to result in new and efficient processes, energy and cost savings, and sustainability benefits. A key challenge in this field is the development of highly selective membranes, which can be addressed by the development of mixed-matrix membranes (MMMs) containing fillers such as metal–organic frameworks (MOFs). However, the lack of interfacial adhesion causes nanosized gaps between the filler and the polymer matrix. In this study, we aim to elucidate the intrinsic properties of MMMs and bridge the gap between their material constituents. A series of novel membranes comprising MOF nanoparticles with similar chemical and morphological properties but increasing pore size (UiO-66–68-NH2) were prepared. The nanoparticles’ surface was covalently grafted with poly(N-isopropylacrylamide) (PNIPAM) chains, which could then become entangled with the membranes’ polymer matrix. Morphological characterization and organic solvent nanofiltration tests revealed that membranes with PNIPAM-grafted fillers do not suffer from the formation of pinholes at the filler–matrix interface that are detrimental to the filtration performance. For the first time, the experimental results showed an excellent match with a predictive model of nanofiltration built around the premise of liquid transport through the highly ordered pores of the MOF filler.
  • Multifunctional Catalyst Combination for the Direct Conversion of CO2 to Propane

    Ramirez, Adrian; Ticali, Pierfrancesco; Salusso, Davide; Cordero-Lanzac, Tomas; Ould-Chikh, Samy; Ahoba-Sam, Christian; Bugaev, Aram L.; Borfecchia, Elisa; Morandi, Sara; Signorile, Matteo; Bordiga, Silvia; Gascon, Jorge; Olsbye, Unni (JACS Au, American Chemical Society (ACS), 2021-09-02) [Article]
    The production of carbon-rich hydrocarbons via CO2 valorization is essential for the transition to renewable, non-fossil-fuel-based energy sources. However, most of the recent works in the state of the art are devoted to the formation of olefins and aromatics, ignoring the rest of the hydrocarbon commodities that, like propane, are essential to our economy. Hence, in this work, we have developed a highly active and selective PdZn/ZrO2+SAPO-34 multifunctional catalyst for the direct conversion of CO2 to propane. Our multifunctional system displays a total selectivity to propane higher than 50% (with 20% CO, 6% C1, 13% C2, 10% C4, and 1% C5) and a CO2 conversion close to 40% at 350 °C, 50 bar, and 1500 mL g–1 h–1. We attribute these results to the synergy between the intimately mixed PdZn/ZrO2 and SAPO-34 components that shifts the overall reaction equilibrium, boosting CO2 conversion and minimizing CO selectivity. Comparison to a PdZn/ZrO2+ZSM-5 system showed that propane selectivity is further boosted by the topology of SAPO-34. The presence of Pd in the catalyst drives paraffin production via hydrogenation, with more than 99.9% of the products being saturated hydrocarbons, offering very important advantages for the purification of the products.
  • CO2/CH4 mixed-gas separation in PIM-1 at high pressures: Bridging atomistic simulations with process modeling

    Balçık, Marcel; Tantekin-Ersolmaz, S. Birgül; Pinnau, Ingo; Ahunbay, M. Göktuğ (Journal of Membrane Science, Elsevier BV, 2021-09) [Article]
    Polymeric membranes with intrinsic microporosity have been at the center of attention for gas separation applications since the introduction of PIM-1. This study utilizes atomistic simulations to model and to understand the pure- and mixed-gas transport properties of PIM-1 for the CO2/CH4 gas pair. Monte Carlo and molecular dynamics methods were combined in the estimation of sorption and diffusion of CO2 and CH4 in PIM-1. Simulated sorption and permeability data compared very well with experimental reports. Mixed-gas adsorption simulations proved the existence of competitive adsorption, favoring CO2, hence resulting in an increase in solubility selectivities. However, in mixed-gas environment CH4 permeabilities increased significantly compared to pure gas conditions, overall decreasing perm-selectivities of the polymer. Plasticization of the polymer around 25 bar CO2 partial fugacity was apparent both in pure- and mixed-gas conditions. Simulations at different gas feed compositions proved the dependence of competitive sorption and CO2-induced swelling in partial feed gas fugacities. Simulation results were combined to obtain a macroscopic permeability model that relates the multicomponent permeability to the permeate pressure and composition. Accurate estimations of permeabilities by the model were achieved allowing future implementation of the model in process simulation tools.
  • Single-Step Conversion of Crude Oil to Petrochemicals using a Multi Zone Reactor: Reactor Design and Catalysts Assessment

    Alabdullah, Mohammed A. (2021-09) [Dissertation]
    Advisor: Gascon, Jorge
    Committee members: Rueping, Magnus; Castaño, Pedro; Yuriy, Roman
    One hundred million barrels of oil are produced every day. Economic and population growth stirred a significant increase in the demand of oil over the last century. Today circa 75% of the crude oil barrel is dedicated to the manufacture of transportation fuels, while less than a 15 % is used for the production of chemicals. However, the demand for oil derived fuels is expected to first peak and then decrease. This is mostly due to environmental concerns related to CO2 emissions, the rapid development of green energy technology and improvements in efficiency. On the other hand, the demand for petrochemicals is still forecasted to continue growing in the foreseeable future. By 2040, the barrel split is indeed expected to reach a 34% for the production of petrochemicals. To fill the chemical demand gap, we need to maximize the production of light olefins and aromatics, preferably by developing direct conversion routes leading to chemicals yields in the order of 60-65 %. By converting crude oil directly to chemicals, several energy intensive refinery processes may be optimized and/or avoided, positively impacting the environment by reducing emissions. Equally important, this technology will be highly efficient for the production of highly valued chemicals, which will lead to cost-saving and, at the same time, double the profitability. This PhD Thesis describes a catalytic reactor concept consisting of a multi-zone fluidized bed (MZFB) able to perform several refining steps in one single reactor vessel along with a new catalyst formulation. The new configuration allows for in situ catalyst stripping and regeneration, while the incorporation of silicon carbide in the formulated catalyst confers it with improved physical, mechanical, and heat transport properties. As a result, this reactor has shown stable conversion of untreated Arabian Light crude to light olefins with yields per pass over 35 wt.% with a minimum production of dry gas on spray-dried catalysts containing 1:1 mixtures of ZSM-5 and FAU zeolites (alongside binder, clay, and Silicon carbide). Coke deposition and catalyst deactivation can be correlated to the nature and content of each zeolite component.
  • Hydrogen Evolution from Hydrocarbon Pyrolysis in a Simulated Liquid Metal Bubble Reactor

    Angikath Shamsudheen, Fabiyan; Abdulrahman, Faseeh; Khandavilli, Muralikrishna; Zhang, Xiaoyuan; Sarathy, Mani (Energy & Fuels, American Chemical Society (ACS), 2021-08-27) [Article]
    The evolution of hydrogen from methane decomposition in a liquid metal bubble reactor (LMBR) has become a recent subject of interest; this study examines a novel approach to hydrogen production from pyrolysis of complex hydrocarbon fuels. Modeling hydrocarbon fuel decomposition in an LMBR is executed in two stages of pyrolysis: First, primary pyrolysis intermediates are simulated using a functional-group-based kinetic model (FGMech). Then, a detailed high temperature mechanism (AramcoMech 1.3 + KAUST PAH + 5 solid carbon chemistry) is applied to simulate secondary pyrolysis of intermediates. The quantities of major products of the secondary pyrolysis simulation (CH4, H2, Cs, C6H6) are approximated by simplified regression equations. Further decomposition of smaller hydrocarbons (until exiting the reactor) is simulated using a coupled kinetic and hydrodynamics model that has been reported in the literature. The mixing effects of bubble coalescence and breakup are investigated in a comparative study on homogeneous and non-homogeneous reactors. Finally, a qualitative relationship between H2 yield per mass of fuel, functional group, and other factors such as temperature, pressure, and residence time is analyzed. In general, the H/C ratio and cyclic/aromatic content are the main features influencing total conversion to H2.
  • Ionic Functionalization of Multivariate Covalent Organic Frameworks to Achieve Exceptionally High Iodine Capture Capacity.

    Xie, Yaqiang; Pan, Tingting; Lei, Qiong; Chen, Cailing; Dong, Xinglong; Yuan, Youyou; Shen, Jie; Cai, Yichen; Zhou, Chunhui; Pinnau, Ingo; Han, Yu (Angewandte Chemie (International ed. in English), Wiley, 2021-08-25) [Article]
    Adsorption-based iodine (I 2 ) capture is of great potential for the treatment of radioactive nuclear waste. Here we employ a "multivariate" synthetic strategy to construct ionic covalent organic frameworks (iCOFs) with large surface area, high pore volume, and abundant binding sites for I 2 capture. The optimized material iCOF-AB-50 exhibits static I 2 uptake capacity of 10.21 g·g -1 at 75 °C, and dynamic uptake capacity of 2.79 g·g -1 at ~400 ppm of I 2 and 25 °C, far exceeding the performances of previously reported adsorbents under similar conditions. It also shows fast adsorption kinetics, good moisture tolerance, and full reusability. The promoting effect of ionic groups on I 2 adsorption has been elucidated by experimentally identifying the iodine species adsorbed at different sites and calculating their binding energies. This work demonstrates the essential role of balancing the textural properties and binding sites of the adsorbent in achieving high I 2 capture performance.
  • Waltzing around the stereochemistry of membrane crosslinkers for precise molecular sieving in organic solvents

    Abdulhamid, Mahmoud; Hardian, Rifan; Szekely, Gyorgy (Journal of Membrane Science, Elsevier BV, 2021-08-14) [Article]
    Crosslinking of polymeric membranes induces changes in both membrane stability and separation performance. Numerous membrane-crosslinking methods have been developed with the objective of obtaining improved membranes. However, none of these methods systemically investigated the stereochemical effects of the crosslinker in the pursuit of better stability and performance. Herein, we address this knowledge gap by presenting a systematic investigation of the stereochemistry of crosslinkers. The intrinsically microporous poly(ether-ether-ketone)-containing Tröger's base (iPEEK-TB) was synthesized and employed in the fabrication of organic solvent nanofiltration (OSN) membranes. Crosslinkers were carefully selected based on the stereochemical position of the two benzyl bromide functional groups, separated by distances of 4.3, 8.2, 8.5, and 12.4 Å and significant effects arising from crosslinking on membrane physical properties, morphology, and OSN performance were investigated. Crosslinked membranes showed excellent solvent resistance, mechanical flexibility, and thermal stability. As a function of crosslinking distance, the molecular weight cutoff (MWCO) values of the membranes varied in the range of 575–750 g mol−1. The para isomer of the crosslinkers resulted in higher permeance relative to membranes crosslinked with their counterpart ortho isomers, and vice versa, the ortho substitution resulted in higher solute rejection values compared with para isomers. An increase of 50% and 12% in acetonitrile permeance relative to the annealed benchmark membrane was observed upon the treatment using iPEEK-TB with 4,4′-bis(bromomethyl)biphenyl (p-BBMBP) and 2,2′-bis(bromomethyl)-1,1′-biphenyl (o-BBMBP), respectively, whereas a permeance decrease of approximately 23% and 32% was noted upon treatment with α,α′-Dibromo-p-xylene (p-DBX) and α,α′-Dibromo-o-xylene (o-DBX), respectively. The corresponding MWCO changes were found to decrease for all crosslinked membranes within the range of 12%–40%. The crosslinked membranes demonstrated stable performance in polar aprotic solvents such as N,N-dimethylformamide and N-methyl-2-pyrrolidone. The Molecular dynamic (MD) simulations supported the obtained performance results through the variations in the fractional free volume (FFV). This work demonstrates the importance of crosslinker selection for OSN membrane performance and solvent resistivity and opens new avenues for fine-tuning membrane stability and OSN performance.
  • Combustion chemistry of ammonia/hydrogen mixtures: Jet-stirred reactor measurements and comprehensive kinetic modeling

    Zhang, Xiaoyuan; Puthukkadan Moosakutty, Shamjad; Rajan, Rajitha P.; Younes, Mourad; Sarathy, Mani (Combustion and Flame, Elsevier BV, 2021-08-12) [Article]
    To investigate the oxidation of ammonia (NH3)/hydrogen (H2) mixtures at intermediate temperatures, this work has implemented jet-stirred reactor (JSR) oxidation experiments of NH3/H2 mixtures at atmospheric pressure and over 800-1280 K. The H2 content in the NH3/H2 mixtures is varied from zero to 70 vol% at equivalence ratios of 0.25 and 1.0. Species identification and quantification are achieved by using Fourier-transform infrared (FTIR) spectroscopy. A kinetic model for pure NH3 and NH3/H2 mixtures is also developed for this research, and validated against the present experimental data for pure NH3 and NH3/H2 mixtures, as well as those for pure NH3, H2/NO, H2/N2O, NH3/NO, NH3/NO2 and NH3/H2 mixtures in literature. The model basically captures the experimental data obtained here, as well as in literature. Both measured and predicted results from this work show that H2 blending enhances the oxidation reactivity of NH3. Based on the model analysis, under the present experimental conditions, NH3 + H = NH2 + H2 proceeds in its reverse direction with increasing H2 content. The H atom produced is able to combine with O2 to produce either O and OH via a chain-branching reaction, or to yield HO2 through a chain-propagation reaction. HO2 is an important radical under the present intermediate-temperature conditions, which can convert NH2 to OH via NH2 + HO2 = H2NO + OH; H2NO is then able to convert H to NH2 and OH. In this reaction sequence, NH2 and H2NO are chain carriers, converting HO2 and H to two OH radicals. Since the OH radical is the dominant radical to consume NH3 under the present conditions, the enhanced OH yield via H + O2 = O + OH, NH2 + HO2 = H2NO + OH and H2NO + H = NH2 +OH, with increasing H2 content, promotes the consumption of NH3. For NOx formation, non-monotonous trends are observed by increasing the content of H2 at the 99% conversion of NH3. These trends are determined by the competition between the dilution effects and the chemical effects of H2 addition. Nitrogen related radicals, such as NH2, NH and N, decrease as H2 increases, and this dilution effect reduces NOx formation. For chemical effects, the yields of oxygenated radicals, such as O, OH and HO2, are enhanced with increasing H2 content, which results in enhancing effects on NO formation. For N2O formation, the enhanced oxygenated radicals (O, OH and HO2) suppress its formation, while the enhanced NO promotes its formation.
  • Is Hydroxide Just Hydroxide? Unidentical CO2 Hydration Conditions during Hydrogen Evolution and Carbon Dioxide Reduction in Zero-Gap Gas Diffusion Electrode Reactors

    Haspel, Henrik; Gascon, Jorge (ACS Applied Energy Materials, American Chemical Society (ACS), 2021-08-12) [Article]
    The implementation of gas diffusion electrodes is a prerequisite to achieving industrially relevant reaction rates in gas-phase electrochemical CO2 reduction (CO2RR). In the state-of-the-art anion exchange membrane flow electrolyzers, however, there is a substantial loss of reactants due to a nonelectrochemical CO2 consumption at the cathode and the transport of its products to the anode. Our detailed analysis of CO2 crossover in a zero-gap CO2-to-CO flow electrolyzer showed a change in the chemical nature of the transported ionic species through the membrane. With the increasing reaction rate, a continuous shift from HCO3– to CO32– conduction was found to be similar to pure carbonate conduction in the high current density region (>100 mA cm–2). As competing hydrogen evolution takes over the cathodic reaction in a CO2-rich environment, hydroxide conduction becomes more pronounced. This reveals an alteration in the chemical CO2 consumption, the so-called CO2 hydration (CO2 + OH– ↔ HCO3– + OH– ↔ CO32–), implying an unidentical environment for the hydroxide ions generated in CO2RR and hydrogen evolution reaction under a CO2 atmosphere. Our work draws attention to the incomplete description of CO2 hydration at the confined cathode/membrane interface in membrane electrode assembly-type zero-gap CO2 electrolyzers.
  • Electrochemical synthesis of continuous metal–organic framework membranes for separation of hydrocarbons

    Zhou, Sheng; Shekhah, Osama; Jia, Jiangtao; Czaban-Jozwiak, Justyna; Bhatt, Prashant; Galilea, Adrian; Gascon, Jorge; Eddaoudi, Mohamed (Nature Energy, Springer Science and Business Media LLC, 2021-08-09) [Article]
    Membrane-based approaches can offer energy-efficient and cost-effective methods for various separation processes. Practical membranes must have high permselectivity at industrially relevant high pressures and under aggressive conditions, and be manufacturable in a scalable and robust fashion. We report a versatile electrochemical directed-assembly strategy to fabricate polycrystalline metal–organic framework membranes for separation of hydrocarbons. We fabricate a series of face-centred cubic metal–organic framework membranes based on 12-connected rare-earth or zirconium hexanuclear clusters with distinct ligands. In particular, the resultant fumarate-based membranes containing contracted triangular apertures as sole entrances to the pore system enable molecular-sieving separation of propylene/propane and butane/isobutane mixtures. Prominently, increasing the feed pressure to the industrially practical value of 7 atm promoted a desired enhancement in both the total flux and separation selectivity. Process design analysis demonstrates that, for propylene/propane separation, the deployment of such face-centred cubic Zr-fumarate-based metal–organic framework membranes in a hybrid membrane–distillation system offers the potential to decrease the energy input by nearly 90% relative to a conventional single distillation process.
  • Low-temperature oxidation chemistry of 2,4,4-trimethyl-1-pentene (diisobutylene) triggered by dimethyl ether (DME): A jet-stirred reactor oxidation and kinetic modeling investigation

    Zhang, Xiaoyuan; Cao, Chuangchuang; Zou, Jiabiao; Li, Yang; Zhang, Yan; Guo, Junjun; Xu, Qiang; Feng, Beibei; Sarathy, Mani; Yang, Jiuzhong; Wang, Zhandong; Qi, Fei; Li, Yuyang (Combustion and Flame, Elsevier BV, 2021-08-07) [Article]
    This paper explores the low-temperature (low-T) oxidation chemistry of 2,4,4-trimethyl-1-pentene (IC8D4, diisobutylene) by using jet-stirred reactor (JSR) experiments of both IC8D4/dimethyl ether (DME) mixture and pure IC8D4 at near atmospheric pressure and low temperatures. Oxidation species are measured using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), gas chromatography (GC) and GC combined with mass spectrometry (GC/MS). It is found that the oxidation of pure IC8D4 at atmospheric pressure presents negligible low-T reactivity and negative temperature coefficient (NTC) behavior, and that the oxidation reactivity of IC8D4/DME mixture is lower than that of butene/DME mixtures previously studied. A kinetic model for low-T IC8D4/DME oxidation is developed from recent oxidation models of IC8D4 and DME. Thermodynamic data of IC8D4 and key species in its sub-mechanism are obtained from theoretical calculations in this work, while rate constants of critical reactions are updated from recent theoretical calculation studies in literature. Based on the modeling analysis, four main pathways are found to be responsible for the consumption of IC8D4 at low temperatures. Among them, the first three pathways initiated by H addition, OH addition and H abstraction on allylic carbon sites are similar to those in 1-butene/DME and isobutene/DME oxidation. These three pathways are mainly responsible for promoting or retaining OH formation. The fourth pathway initiated by H abstraction on the alkyl carbon site differs from the other three in that it is only important in IC8D4/DME oxidation while not important in butenes/DME oxidation. This fourth pathway incorporates stepwise O2 addition and cycloaddition reaction sequences, which can promote and inhibit OH formation, respectively. The increasing contribution of this fourth pathway in IC8D4/DME oxidation reduces its reactivity compared to that of butenes/DME oxidation.
  • High-performance polymer molecular sieve membranes prepared by direct fluorination for efficient helium enrichment

    Ma, Xiaohua; Li, Kaihua; Zhu, Zhiyang; Dong, Hao; Lv, Jia; Wang, Yingge; Pinnau, Ingo; Li, Jianxin; Chen, Bowen; Han, Yu (JOURNAL OF MATERIALS CHEMISTRY A, Royal Society of Chemistry (RSC), 2021-08-04) [Article]
    One of the biggest challenges facing membrane-based helium (He) recovery from natural gas is the lack of efficient He separation membranes featuring both high He permeability and He/CH4 selectivity (>1000). Here, we report that this goal can be achieved by directly fluorinating membranes made of an intrinsically microporous polymer (PIM-1). All of the resulting membranes exhibit unprecedent He/CH4, He/N2, and He/CO2 separation performances that are placed well above the latest perfluoropolymer upper bounds. Among them, FPIM-5 has the best overall performance, with a high He permeability of 754 Barrer and an unprecedented He/CH4 selectivity of 3770 as well as good permeation and mechanical stability. This membrane also shows excellent aging resistance due to the fluorine substitution effect. The high He permeability is attributed to the intrinsically large fractional free volume of FPIM-1s, while the extremely high selectivity is the combined result of improved solubility selectivity through fluorination and significantly increased size sieving diffusion selectivity due to the pore blocking effect caused by fluorine atom substitution. When used for He/CH4 (0.6/99.4) binary mixed-gas separation, the downstream He concentration of FPIM-5 is greater than 84% even at an upstream pressure of 20 bar. The direct fluorination of microporous membranes provides a convenient method for efficiently enriching small gas molecules, such as helium and hydrogen, from various resources.
  • Hydrodynamics of a Gas-Solid Counter-Current Downer Reactor Using a Time-Resolved Planar Digital Particle Image Velocimetry and Digital Image Analysis Techniques

    Alzailaie, Abdulrahman (2021-08) [Thesis]
    Advisor: Castaño, Pedro
    Committee members: Gascon, Jorge; Thoroddsen, Sigurdur T; Ruiz-Martinez, Javier
    This work analyzes the solid flow dynamics of gas-solid downer fluidized bed reactor in co-current and, particularly, in counter-current mode. This reactor is potentially interesting for catalytic applications where very short (sub second) and precise contact times are required between the solid catalyst and the gaseous reactants-products. To this aim, a 1.5 m and 36 mm ID downer reactor setup was built to replicate the conditions in a real unit in cold flow and using materials that enable the observation of the solid particle dynamics. Specifically, two state-of-the-art techniques have been used: Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA). Three types of particles have been used: two commercial fluidized catalytic cracking (FCC) particles (ρp = 1300 kg/m3, dp = 75 and 56 μm) and sand (ρp=2600 kg/m3, dp= 370 μm). High-speed cameras were positioned in two axial positions: 70 and 140 cm from the top, to reveal the flow behavior across the reactor. It was found that the solid flow initially was segregated because of the solid feeding design. Thus, 3D printed re-distributer was used to even the solid flow. The solid particles in the counter-current downer was approaching the plug-flow behavior with 23% variation in the velocity gradient across the radial direction, compared with 40% for the co-current counterpart. A method to estimate solid hold-up based on images was developed, yielding values in a good agreement with literature. Keywords: Hydrodynamics, counter-current, downer, PIV, DIA, Solid hold-up
  • Polycrystalline metal-organic framework (MOF) membranes for molecular separations: Engineering prospects and challenges

    Abdul Hamid, Mohamad Rezi; Qian, Yutian; Wei, Ruicong; Li, Zhen; Pan, Yichang; Lai, Zhiping; Jeong, Hae-Kwon (Journal of Membrane Science, Elsevier BV, 2021-08) [Article]
    Metal-organic frameworks (MOFs), owing to their ordered porous structure, ease of synthesis, and versatility of surface functionalization have attracted significant research interests for membrane-based separations. Zeolitic-imidazolate frameworks (ZIFs), a subclass of MOFs, have drawn the most research attention by virtue of their ease of forming high-quality membranes and potential in hydrocarbon mixture separations. Other MOF-based membranes such as IRMOFs, HKUST-1, MILs, UiOs, etc., were also well-studied for hydrogen purification and carbon capture. In this review, we summarize a chronological development of MOF membranes for gas separations, focusing on ZIF-8 membranes for C3H6/C3H8 separation. Other MOF membranes for H2/CO2, CO2/CH4, and CO2/N2 separations are also reviewed. Following this, we provide a thorough assessment and evaluation of the engineering challenges, including cost-effectiveness, module design, and membrane stability and reproducibility for industrial scale-up. Finally, we provide our point of view on future research and development in the area.
  • An investigation into the pyrolysis and oxidation of bio-oil from sugarcane bagasse: Kinetics and evolved gases using TGA-FTIR

    Ordonez-Loza, Javier; Chejne, Farid; Jameel, Abdul Gani Abdul; Telalovic, Selvedin; Arrieta, Andrés Amell; Sarathy, Mani (Journal of Environmental Chemical Engineering, Elsevier BV, 2021-07-31) [Article]
    Bio-oil produced from the pyrolysis of sugarcane bagasse has the potential to be used as a sustainable and renewable energy source. In the present study, a non-isothermal thermo-gravimetric analysis (TGA) of the pyrolysis (in N2 atmosphere) and combustion (in the air) of bio-oil from sugarcane bagasse was investigated at three heating rates: 5, 10, and 20 °C/min. The sample was heated from room temperature up to 900 °C and the evolved gases in the TG furnace were carried to a Fourier transform infrared (FTIR) cell where the composition of the gases and the functional groups present there were analyzed. A global kinetic analysis was performed to obtain the Arrhenius kinetic parameters for the pyrolysis and oxidation of the bio-oil using the distributed activation energy model. Three distinct stages, namely; low-temperature oxidation (LTO), fuel decomposition (FD), and high-temperature oxidation (HTO) were observed during the oxidation of bio-oil. The initial devolatilization of the oxygenated compounds observed during pyrolysis was similar to the LTO stage observed during combustion. The intensity of the CO2 FTIR peaks seen during the bio-oil combustion was 10 times the intensity of the CO2 peaks attained during pyrolysis. The TGA-FTIR analysis of the sugarcane bagasse bio-oil sheds new light on its thermal degradation/oxidation characteristics.
  • The Ionic Liquid–H2O Interface: A New Platform for the Synthesis of Highly Crystalline and Molecular Sieving Covalent Organic Framework Membranes

    Gao, Shuaiqi; Li, Zhiyong; Yang, Yingying; Wang, Zhenzhen; Wang, Yanlei; Luo, Shuangjiang; Yao, Kaisheng; Qiu, Jikuan; Wang, Huiyong; Cao, Li; Lai, Zhiping; Wang, Jianji (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2021-07-26) [Article]
    Covalent organic frameworks (COFs) are highly porous crystalline polymers with uniform pores and large surface areas. Combined with their modular design principle and excellent properties, COFs are an ideal candidate for separation membranes. Liquid-liquid interfacial polymerization is a well-known approach to synthesize membranes by reacting two monomers at the interface. However, volatile organic solvents are usually used, which may disturb the liquid-liquid interface and affect the COF membrane crystallinity due to solvent evaporation. Simultaneously, the domain size of the organic solvent-water interface, named the reaction zone, can hardly be regulated, and the diffusion control of monomers for favorable crystallinity is only achieved in the water phase. These drawbacks may limit the widespread applications of liquid-liquid interfacial polymerization to synthesize diverse COF membranes with different functionalities. Here, we report a facile strategy to synthesize a series of imine-linked freestanding COF membranes with different thicknesses and morphologies at tunable ionic liquid (IL)-H<sub>2</sub>O interfaces. Due to the H-bonding of the catalysts with amine monomers and the high viscosity of the ILs, the diffusion of the monomers was simultaneously controlled in water and in ILs. This resulted in the exceptionally high crystallinity of freestanding COF membranes with a Brunauer-Emmett-Teller (BET) surface area up to 4.3 times of that synthesized at a dichloromethane-H<sub>2</sub>O interface. By varying the alkyl chain length of cations in the ILs, the interfacial region size and interfacial tension could be regulated to further improve the crystallinity of the COF membranes. As a result, the as-fabricated COF membranes exhibited ultrahigh permeance toward water and organic solvents and excellent selective rejection of dyes.
  • Air-Resistant Lead Halide Perovskite Nanocrystals Embedded into Polyimide of Intrinsic Microporosity

    Yang, Haoze; Gutierrez Arzaluz, Luis; Maity, Partha; Abdulhamid, Mahmoud; Yin, Jun; Zhou, Yang; Chen, Cailing; Han, Yu; Szekely, Gyorgy; Bakr, Osman; Mohammed, Omar F. (Energy Material Advances, American Association for the Advancement of Science (AAAS), 2021-07-15) [Article]
    Although cesium lead halide perovskite (CsPbX3, X = Cl, Br, or I) nanocrystals (PNCs) have been rapidly developed for multiple optoelectronic applications due to their outstanding optical and transport properties, their device fabrication and commercialization have been limited by their low structural stability, especially under environmental conditions. In this work, a new approach has been developed to protect the surface of these nanocrystals, which results in enhanced chemical stability and optical properties. This method is based on the encapsulation of CsPbX3 NCs into a polyimide with intrinsic microporosity (PIM-PI), 4,4′-(hexafluoroisopropylidene)diphthalic anhydride reacted with 2,4,6-trimethyl-m-phenylenediamine (6FDA-TrMPD). The presence of 6FDA-TrMPD as a protective layer can efficiently isolate NCs from an air environment and subsequently enhance their optical and photoluminescence stability. More specifically, comparing NCs treated with a polymer to as-synthesized nanocrystals after 168 h, we observe that the PL intensity decreased by 70% and 20% for the NCs before and after polymer treatment. In addition, the PNC film with a polymer shows a much longer excited-state lifetime than the as-synthesized nanocrystals, indicating that the surface trap states are significantly reduced in the treated PNCs. The enhancement in chemical and air stability, as well as optical behavior, will further improve the performance of CsPbBr3 PNCs yielding promising optical devices and paving the way for their production and implementation at a large scale.

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