RSS 1.0Chemical Engineering Program
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Recent Submissions
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NMR Chemical Shifts of Emerging Green Solvents, Acids, and Bases for Facile Trace Impurity Analysis(ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2023-03-27) [Article]The straightforward identification of impurity signals in nuclear magnetic resonance (NMR) spectra is imperative for the structure elucidation and signal assignment of synthetic products and intermediates. To keep pace with the emergence of novel green solvents and auxiliary compounds (e.g., acids and bases), NMR impurity tables and databases must be regularly updated. This study reports the residual 1H and 13C NMR chemical shifts of 42 green solvents, acids, and bases in eight NMR solvents, namely, dimethylsulfoxide-d6, chloroform-d, D2O, CD3OD, CD3CN, acetone-d6, tetrahydrofuran-d8, and toluene-d8. The multiplicities and coupling constants of 1H signals are also determined herein. The analysis of the recorded NMR spectra provides important information regarding the reactivity or multicomponent nature of the green solvents, acids, and bases. Herein, the results of this study are combined with earlier reports on residual NMR impurities to form a comprehensive database. This database forms the basis of an online interface (http://www.nmrimpurities.com) through which users can browse solvent spectra and search for signals of unknown origins to easily identify residual impurities in NMR spectra.
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Hydrocracking Mechanisms of Oxygenated Plastics and Vacuum Gasoil Blends(Elsevier BV, 2023-03-27) [Preprint]We explore the holistic composition of products obtained from hydrocracking oxygen-containing waste plastics, such as polymethylmethacrylate or polyethylene terephthalate, blended with vacuum gasoil (VGO). Reactions are performed in a semi-batch reactor at 400 ºC or 420 °C using a platinum-palladium supported on a faujasite zeolite catalyst. The gas, liquid, and solid product compositions are resolved using bidimensional chromatography (GC×GC), nuclear magnetic resonance (NMR), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Then, the data are fused to resolve the composition and gain insights into the reaction mechanisms. The results reveal a synergistic transformation of heavy species from the VGO and the polymers, with a remarkable fuel selectivity (> 60%). The molecular-level description of the samples can be used to analyze and propose the reaction mechanisms of these complex blends.
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A wide range experimental and kinetic modeling study of the oxidation of 2,3-dimethyl-2-butene: Part 1(Combustion and Flame, Elsevier BV, 2023-03-26) [Article]2,3-Dimethyl-2-butene (TME) is a potential fuel additive with high research octane number (RON) and octane sensitivity (S), which can improve internal combustion engine performance and efficiency. However, the combustion characteristics of TME have not been comprehensively investigated. Thus, it is essential to study the combustion characteristics of TME and construct a detailed chemical kinetic model to describe its combustion. In this paper, two high-pressure shock tubes and a constant-volume reactor are used to measure ignition delay times and laminar flame speeds of TME oxidation. The ignition delay times were measured at equivalence ratios of 0.5, 1.0, and 2.0 in “air”, at pressures of 5 and 10 bar, in the temperature range of 950 – 1500 K. Flame speeds of the TME/ “air” mixtures were measured at atmospheric pressure, at a temperature of 325 K, for equivalence ratios ranging from 0.78 to 1.31. Two detailed kinetic mechanisms were constructed independently using different methodologies; the KAUST TME mechanism was constructed based on NUIGMech1.1, and the MIT TME mechanism was built using the Reaction Mechanism Generator (RMG). Both mechanisms were used to simulate the experimental results using Chemkin Pro. In the present work, reaction flux and sensitivity analyses were performed using the KAUST mechanism to determine the critical reactions controlling TME oxidation at the conditions studied.
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Engineering grain boundaries in monolayer molybdenum disulfide for an efficient water/ion separation(Research Square Platform LLC, 2023-03-20) [Preprint]Atomically thin two-dimensional (2D) materials have long been considered as ideal platforms for developing separation membranes. However, it is difficult to generate uniform subnanometer pores over large areas on 2D materials. Herein, we report that the well-defined defect structure of monolayer MoS2, namely, eight-membered ring (8-MR) pores typically formed at the boundaries of two antiparallel grains, can serve as molecular sieves for efficient water/ion separation. The 8-MR pores (4.2 × 2.4 Å) in monolayer MoS2 allow rapid single-file water transport while rejecting various hydrated ions. Further, the density of grain boundaries and, consequently, the density of pores can be tuned by regulating the nucleation density and size of MoS2 grains during the chemical vapor deposition process. The optimized MoS2 membrane exhibited an ultrahigh water/NaCl selectivity of ~6.5 × 104 at a water permeance of 232 mol m−2 h−1 bar−1, outperforming the state-of-the-art desalination membranes. When used for direct hydrogen production from seawater by combining the forward osmosis and electrochemical water splitting processes, the membrane achieved ~40 times the energy conversion efficiency of commercial polymeric membranes. It also exhibited a rapid and selective proton transport behavior desirable for fuel cells and electrolysis. The bottom-up approach of creating precise pore structures on atomically thin films via grain boundary engineering presents a promising route for producing large-area membranes suitable for various applications.
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Is photocatalytic hydrogen production closer to application?(Chem Catalysis, Elsevier BV, 2023-03-16) [Article]Although state-of-the-art photocatalysts display a solar-to-hydrogen (STH) efficiency lower than 3%, Zhou et al. report in Nature an indium-gallium-nitride-based photocatalyst that can achieve an STH efficiency of ∼9%. These unprecedented results could get us closer to the industrial implementation of this technology.
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On the Products from the Pyrolysis of Heavy Fuel and Vacuum Residue Oil(Elsevier BV, 2023-03-12) [Preprint]Incorporating unconventional fuel sources into the global energy mix is necessary to meet increasing energy demand. One attractive option is the gasification of residual fuels, such as heavy fuels, which produce clean combustible gases. Pyrolysis is the first step in the gasification process, so its understanding can help in the development of the gasification process. The information on the pyrolysis products can serve the development of chemical kinetics mechanisms for gasification of heavy fuels for their efficient utilization. In this study, pyrolysis of heavy fuel oil (HFO) and vacuum residue oil (VRO) is reported. Prior to the pyrolysis experiments, these fuels were characterized for proximate analysis, elemental and trace metal composition. The pyrolysis experiments were conducted in a wide temperature range of 400–1000 °C in a customized tubular furnace-based reactor. A two-stage condensation system was used to collect the condensable fraction evolved from the pyrolysis of HFO and VRO and non-condensable gases were collected in Tedlar® bags. Both liquid and gaseous products were characterized using a gas chromatography (GC)-mass spectrometry (MS)-flame ionization detector (FID) and Fourier transform–ion cyclotron resonance–mass spectrometer (FT-ICR-MS) to understand the presence of different types of compounds. The identified compounds were classified as benzene derivatives, naphthalene derivatives, polycyclic aromatic hydrocarbons, saturated and unsaturated hydrocarbons and sulfur-containing compounds. In order to better understand the liquid fraction, the heavy fraction (with high molecular weight) which could not be analyzed and identified in GC/MS-FID was analyzed in FT-ICR-MS. This shed significant insights on the deconstruction of HFO and VRO. Twenty lighter hydrocarbons ranging from C1-C5 were identified and quantified in the pyrolysis vapors of both fuels.
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Elucidating the photodissociation fingerprint and quantifying the determination of organic hydroperoxides in gas-phase autoxidation(Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, 2023-02-27) [Article]Hydroperoxides are formed in the atmospheric oxidation of volatile organic compounds, in the combustion autoxidation of fuel, in the cold environment of the interstellar medium, and also in some catalytic reactions. They play crucial roles in the formation and aging of secondary organic aerosols and in fuel autoignition. However, the concentration of organic hydroperoxides is seldom measured, and typical estimates have large uncertainties. In this work, we developed a mild and environmental-friendly method for the synthesis of alkyl hydroperoxides (ROOH) with various structures, and we systematically measured the absolute photoionization cross-sections (PICSs) of the ROOHs using synchrotron vacuum ultraviolet-photoionization mass spectrometry (SVUV-PIMS). A chemical titration method was combined with an SVUV-PIMS measurement to obtain the PICS of 4-hydroperoxy-2-pentanone, a typical molecule for combustion and atmospheric autoxidation ketohydroperoxides (KHPs). We found that organic hydroperoxide cations are largely dissociated by loss of OOH. This fingerprint was used for the identification and accurate quantification of the organic peroxides, and it can therefore be used to improve models for autoxidation chemistry. The synthesis method and photoionization dataset for organic hydroperoxides are useful for studying the chemistry of hydroperoxides and the reaction kinetics of the hydroperoxy radicals and for developing and evaluating kinetic models for the atmospheric autoxidation and combustion autoxidation of the organic compounds.
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Elucidating the promoting role of Ca on PdZn/CeO2 catalyst for CO2 valorization to methanol(Fuel, Elsevier BV, 2023-02-26) [Article]The viability of catalyzed CO2 conversion routes strongly depends on improving the catalytic performance and understanding of the process. Herein, we investigate the effect of Ca loading on PdZn/CeO2 catalysts prepared using the sol–gel chelatization method for CO2 hydrogenation to methanol. A remarkable improvement in catalyst performance was revealed with the optimum amount of Ca (0.5 wt%) in synergetic cooperation with the PdZn alloy (main active phase for the CO2 hydrogenation to methanol reaction), compared to the Ca-free counterpart. The following key performance indicators are attained at 230 °C, 20 bar, and 2400 h−1 GHSV for the optimized catalyst: 16 % CO2 conversion, > 93 % methanol selectivity, and ∼ 124 g/kgcat/h methanol space–time yield. The overall catalytic performance observed is attributed to the optimum Ce3+/Ce4+ ratio, Ca2+ promotion, surface area, pore volume, and basic sites, as revealed by various characterization techniques. Results shown here indicate that the presence of Ca in the vicinity of the PdZn active enhances basicity, creates oxygen vacancies, and phase may have improved the spill-over ability of H2, consequently favoring CO2 activation and methanol formation.
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Data-driven investigation of process solvent and membrane material on organic solvent nanofiltration(Journal of Membrane Science, Elsevier BV, 2023-02-25) [Article]Organic solvent nanofiltration (OSN) studies are largely limited to small and specialized datasets, hindering the investigation of broader relationships and contexts. Larger datasets have recently emerged but they are limited to a single membrane and few solvents. To improve the understanding of solute rejection in OSN, we introduced a large dataset containing 1938 rejection values derived from three membranes and ten industrially relevant green solvents. We examined two polydimethylsiloxane membranes, namely, GMT-oNF-2 and Solsep 030306, and a custom polybenzimidazole membrane. Structure–property relationship methods were used to identify the connections between the performance of membranes, solvents, and solutes. We observed polarity selectivity, which was explained using the classical solution diffusion model, and demonstrated the translation of the rejection database into the corresponding rejection selectivity dataset to characterize separation performance. The obtained rejection selectivity data enabled the process-oriented analysis of solvent and membrane characteristics. Our selectivity-based investigation highlighted the inadequacy of the solute molecular weight to properly characterize membrane material and separation performance. Consequently, our findings support the need for more comprehensive modeling approaches for rejection and process performance prediction, while providing process-oriented insights into the performance of OSN membranes.
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Atypical stability of exsolved Ni-Fe alloy nanoparticles on double layered perovskite for CO2 dry reforming of methane(Applied Catalysis B: Environmental, Elsevier BV, 2023-02-20) [Article]Dry reforming of methane simultaneously achieves several sustainability goals: valorizing methane-activating carbon dioxide while producing syngas. The catalyst has an enormous influence on the process viability by controlling activity, selectivity, and stability. A catalyst with uniform-sized Ni-Fe alloy nanoparticles anchored into PrBaMn1.6Ni0.3Fe0.1O5+δ double-layered perovskite is assembled via a facile one-step reduction strategy. Our method attains more exsolved Ni nanoparticles (94 %) than the common conditions. The exsolved Ni0.15Fe0.05 catalyst shows exceptional stability in 260 h tests at 800 °C, with one of the slowest coke formation rates compared with the state-of-the-art catalysts. Besides, no deactivation was observed during 40 h operation at more demanding and coking conditions (14 bar) where this process is more likely to operate industrially. Via experimental characterizations and computational calculations, the stability of the robust exsolved Ni-Fe catalyst is demonstrated by its unique balance of adsorbed species, which inhibits coking.
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PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion: Further insights by spectroscopic characterization(Applied Catalysis A: General, Elsevier BV, 2023-02-20) [Article]The present work aims at further investigating a previously studied PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion. High activity and selectivity for propane was proved and the results obtained by NAP-XPS measurements and CO adsorption at liquid-nitrogen temperature (LNT) followed by FT-IR spectroscopy are shown. After reduction, we confirmed the formation of PdZn alloy. At LNT, Pd carbonyl IR band shows a peculiar behavior linked to an intimate interaction between PdZn particles, ZnO and ZrO2. The combined system was characterized as fresh, used and regenerated. On the fresh PdZn/ZrO2+SAPO-34 the characteristic features of the two components do not appear perturbed by the mixing. As for the used system, the absence of Pd carbonyls and the decrease of CO on SAPO-34 Brønsted acid sites are correlated to organic species revealed by ssNMR. Regeneration in oxygen restores catalytic sites, although new Pd2+/Zn2+ carbonyls appear due to ion exchange into SAPO-34 framework.
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Elevating carbonium ion chemistry in zeolite catalysis(Chem Catalysis, Elsevier BV, 2023-02-16) [Article]In this issue of Chem Catalysis, Chen et al. explore—through the combination of ab initio molecular dynamics, 13C solid-state nuclear magnetic resonance (NMR), and in situ Fourier transform infrared spectroscopy—the catalytic relevance of “three-center-two-electron (3c-2e)” carbocations in the industrially relevant C4 isomerization process over zeolite ZSM-5.
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Post-Synthetic Surface Modification of Metal-Organic Frameworks and Their Potential Applications.(Small methods, 2023-02-15) [Article]Metal-organic frameworks (MOFs) are porous hybrid materials with countless potential applications. Most of these rely on their porous structure, tunable composition, and the possibility of incorporating and expanding their functions. Although functionalization of the inner surface of MOF crystals has received considerable attention in recent years, methods to functionalize selectively the outer crystal surface of MOFs are developed to a lesser extent, despite their importance. This article summarizes different types of post-synthetic modifications and possible applications of modified materials such as: catalysis, adsorption, drug delivery, mixed matrix membranes, and stabilization of porous liquids.
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Maximizing Active Fe Species in ZSM-5 Zeolite Using Organic-Template-Free Synthesis for Efficient Selective Methane Oxidation(Journal of the American Chemical Society, American Chemical Society (ACS), 2023-02-14) [Article]The selective oxidation of CH4 in the aqueous phase to produce valuable chemicals has attracted considerable attention due to its mild reaction conditions and simple process. As the most widely studied catalyst for this reaction, Fe-ZSM-5 demonstrates high intrinsic activity and selectivity; however, Fe-ZSM-5 prepared using conventional methods has a limited number of active Fe sites, resulting in low CH4 conversion per unit mass of the catalyst. This study reports a facile organic-template-free synthesis strategy that enables the incorporation of more Fe into the zeolite framework with a higher dispersion degree compared to conventional synthesis methods. Because framework Fe incorporated in this way is more readily transformed into isolated extra-framework Fe species under thermal treatment, the overall effect is that Fe-ZSM-5 prepared using this method (Fe-HZ5-TF) has 3 times as many catalytically active sites as conventional Fe-ZSM-5. When used for the selective oxidation of CH4 with 0.5 M H2O2 at 75 °C, Fe-HZ5-TF produced a record-high C1 oxygenate yield of 109.4 mmol gcat-1 h-1 (a HCOOH selectivity of 91.1%), surpassing other catalysts reported to date. Spectroscopic characterization and density functional theory calculations revealed that the active sites in Fe-HZ5-TF are mononuclear Fe species in the form of [(H2O)3Fe(IV)═O]2+ bound to Al pairs in the zeolite framework. This differs from conventional Fe-ZSM-5, where binuclear Fe acts as the active site. Analysis of the catalyst and product evolution during the reaction suggests a radical-driven pathway to explain CH4 activation at the mononuclear Fe site and subsequent conversion to C1 oxygenates.
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Photoelectrochemical Lithium Extraction(Elsevier BV, 2023-02-11) [Preprint]The direct conversion of solar energy to valuable chemicals by mimicking the photosynthesis of natural leaves, known as artificial leaves, is promising for utilizing renewable energy. Herein, we demonstrate the successful extraction of lithium (Li) from natural brine using a photoelectrochemical (PEC) system, combined with a Li-selective membrane process. A Si photoelectrode, with three p–n junctions connected in series (3S-Si), was seamlessly embedded into an H-cell with two compartments separated by a Li1+xAlxGe2−x(PO4)3 membrane. The unassisted PEC Li extraction was performed under AM 1.5G illumination without other external energy input. The Li concentration in the enriched solution reached 2924.96 ppm with 99.4% atomic selectivity after two PEC stages, and the solar-to-Li extraction efficiency reached 0.355%. Finally, we obtained the valuable product Li2CO3 with 99.93% purity. Economic analysis revealed that this solar-driven Li extraction system was more profitable than the PEC systems for H2 generation, N2 and CO2 reduction. Our study offers a promising approach for Li mining using sustainable energy and improves the economic viability of Li extraction from natural brine.
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Combustion chemistry of ammonia/C1 fuels: A comprehensive kinetic modeling study(Fuel, Elsevier BV, 2023-02-10) [Article]The application of ammonia (NH3) as a fuel could contribute to mitigating global warming and achieving carbon neutrality by mid-century. To enhance the reactivity of NH3 combustion, cofiring NH3 with hydrogen or C1 fuels like syngas, methanol and methane is proposed. In previous work, we studied the combustion chemistry of NH3/H2 mixtures using a comprehensive kinetic model. In this work, we expanded our comprehensive kinetic model to cover NH3/syngas, NH3/methanol and NH3/methane mixtures. Rate constants of critical cross reactions between C- and N-containing species were evaluated based on previous experimental and theoretical studies for selection and incorporation in the present model. Experimental data for both NOx/C1 and NH3/C1 fuels were selected from literature to test the present model, including speciation data measured in shock tubes, flow reactors, jet-stirred reactors, burner-stabilized flames, and the global parameters like ignition delay times and laminar flame speeds. The kinetic model validation conditions cover temperatures of 473–2000 K, pressures of 0.04–100 atm, and equivalence ratios of 0.04–116. In general, the present model adequately captures the selected experimental data. The present model can not only be used to predict the combustion of NH3/C1 fuel mixtures, but is also capable to predict the mutual interaction of NOx/C1 fuels. It is found that the rate constants between C-containing species and H2-related radicals are generally faster than (or close to) those between C- and N-containing species. At high temperatures, H2-related radicals (i.e. H, O, OH) have higher concentrations than reactive N-related radicals (NH, NH2, NO2). Therefore, under these conditions, C-containing species are more likely to react with H2-related radicals rather than N-related ones, making the C/N cross reactions less prominent. However, under low- and intermediate-temperature conditions, the concentrations of H and O radicals become lower, while those of NH2 and NO2 become higher, making the cross reactions between C- and N-containing species possible to compete with C/H cross reactions. The present model can be used as the base chemistry model for NH3/larger hydrocarbon fuels.
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W2N-MXene composite anode catalyst for efficient microbial fuel cells using domestic wastewater(Chemical Engineering Journal, Elsevier BV, 2023-02-09) [Article]Microbial fuel cells (MFCs) have enormous potential to treat wastewater and reduce the energy demands of wastewater treatment plants while generating electricity using active microorganisms as biocatalysts. However, the practical application of MFCs is limited by the low power density produced, mainly due to poor anode performance. Herein, a tungsten nitride (W2N)-MXene composite catalyst is introduced to modify the anode surface for use in microbial fuel cells during domestic wastewater treatment. The aim is to improve the wettability, electrical conductivity, electron transfer efficiency, and microorganism attachment capability of the anode and ultimately increase the overall performance of the microbial fuel cell to produce electricity during wastewater treatment. In detail, a hydrofluoric acid etching approach is used to synthesize the Ti3C2Tx MXene, the urea glass technique is used to prepare the W2N particles, and an adequate mixing and heat treatment approach is used to produce the W2N-Ti3C2Tx composite catalyst. The W2N-Ti3C2Tx composite on carbon cloth anode provides one of the best performances recorded for MXene in this type of fuel cells and using real domestic wastewater: with a 523% increase in the power density (548 mW m-2), an 83% decrease in the chemical oxygen demand (COD), and a 161% increase in the electron transfer efficiency compared to those of the plain carbon cloth. We demonstrate that this outstanding performance is due to the improvements in hydrophilicity and microorganism attachment, particularly nanowires (or pili) which promote electron transfer. The present work offers an interesting avenue towards the process scale-up and optimization of single-chamber microbial fuel cells.
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Elucidating the rate-determining step of ammonia decomposition on Ru-based catalysts using ab initio-grounded microkinetic modeling(Catalysis Science and Technology, Royal Society of Chemistry (RSC), 2023-02-08) [Article]Decarbonizing the current energy system requires a shift toward renewable energy sources, among which ammonia is a remarkable hydrogen carrier. However, developing an efficient process for the catalytic decomposition of ammonia is still required. Here, we propose a combined modeling-experimental approach to elucidate the rate-determining step in ammonia decomposition on Ru-based catalysts. We characterize and test two supported Ru and Ru-K catalysts in the reaction. We develop several microkinetic models based on ab initio calculations considering different rate-determining steps and validate them with the results of packed bed experiments. For the method validation, we develop a fitting strategy based on modifying the lowest number of parameters from those initially obtained theoretically. A good agreement between the simulated and measured experimental ammonia conversions is obtained, thus widening our understanding of this critical hydrogen production process. The approach presented here allows distinguishing the rate-determining step accurately, and it could be applied to other catalytic systems used in ammonia decomposition to avoid over-relying on empirical models.
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Nonintrusive parameter adaptation of chemical process models with reinforcement learning(Journal of Process Control, Elsevier BV, 2023-02-07) [Article]Model-based control is one of the most prevalent techniques for designing and controlling engineering systems. However, many of these systems are complex and characterized by changing dynamics. Hence, online system identification is required to achieve optimum adaptive control performance for such complex systems. This work proposes an algorithm for nonintrusive, online, nonlinear parameter estimation of physical models using deep reinforcement learning (RL). The problem of training a neural network for parameter estimation is formulated as a reinforcement learning problem. The RL-based parameter estimation policy is tested on a simulation of the selective hydrogenation of acetylene, which is a highly nonlinear system. The learned model estimation policy is able to correctly predict the states of the system with a prediction error of less than 1% in various conditions, such as in the presence of measurement noise and structural differences in models.
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Modeling-aided coupling of catalysts, conditions, membranes, and reactors for efficient hydrogen production from ammonia(Reaction Chemistry and Engineering, Royal Society of Chemistry (RSC), 2023-02-02) [Article]The production of high-purity, pressurized hydrogen from ammonia decomposition in a membrane catalytic reactor is a feasible technology. However, because of the multiple coupled parameters involved in the design of this technology, there are extensive opportunities for its intensification. We investigated the coupling between the type of catalyst, process conditions, type of membrane, and reactor operation (isothermal and non-isothermal) in the catalytic decomposition of ammonia. First, we developed an agnostic dimensionless model and calculated the kinetic parameters for a set of lab-made Ru- and Co-based catalysts and the permeation parameters of a Pd-Au membrane. The non-isothermal model for the Pd-Au membrane reactor was validated with the experiments using Co-based catalysts. Finally, we analyzed the coupling conditions based on the model predictions, results obtained in the literature and our experimental results, including several case studies. The thorough analysis led us to identify optimized combinations of catalyst-conditions-membrane-reactor that yield similar or improved results compared to the ones of Ru-based catalyst in a non-membrane reactor. Our results indicate that optimizing a single factor, such as the catalyst, may not lead to the desired outcome and a more holistic approach is necessary to produce pressurized and pure hydrogen efficiently.
