The Gram-negative oral pathogen, Porphyromonas gingivalis, uses the Type IX Secretion System (T9SS) to secrete major virulence factors (cargo proteins) and anchor them to the cell surface via a novel linking sugar, 2-N-seryl, 3-N-acetylglucuronamide (SAGA), which is a component of a specific type of lipopolysaccharide, A-LPS. The reported structure of the polysaccharide component (A-PS) was a repeating phosphorylated mannan whereas the PS of conventional O-LPS (O-PS) is a repeating Gal-Glu-Rha-GalNAc unit. Here, we have performed extensive mass spectrometric analyses of cargo protein-linked LPS with and without proteinase K treatment to determine the structure of A-LPS. Limited acid hydrolysis of the PS backbone with trifluoromethanesulfonic acid enabled long PS fragments linked to cargo-derived peptides to be identified for the first time. Unexpectedly, rather than finding A-PS units, up to eleven O-PS repeating units were found linked to cargo via a novel pentasaccharide linker designated A-LS, composed of SAGA-Hex-dHex(C4H4O3)(Pent)-Hex. In addition, samples from a wzzP/porT double mutant that produced free truncated O-PS were specifically hydrolyzed to cleave lipid A prior to MS analysis. In these samples A-LS was found attached to a limited number of O-PS repeating units that in turn were associated with a putative core oligosaccharide that included the LPS-specific sugar, 3-deoxy-d-manno-octulosonic acid (Kdo). The proposed structure of A-LPS explains all 11 genes specific to A-LPS biosynthesis, and provides the first structural evidence that cargo proteins such as the gingipains are anchored to the cell surface via a complete LPS molecule.

Data-driven approaches are currently renovating the field of heterogenous catalysis and open the door to advance catalyst design. Their success depends heavily on the synergy among machine learning (ML), experimental data, and quantum mechanical (QM) calculations. In this brief survey of recent progress, we examine catalysis informatics in the context of (1) from experimental data, (3) predictions of catalytic properties and constructions of reaction networks, and (4) ML-enabled large-scale QM simulations. An outlook on the current challenges of this rapidly evolving field is also provided.

The gas-solid flow through a moving bed packed with coarse particles is investigated experimentally and theoretically in this study. By employing a bench-scale moving-bed column, different sizes of fine and coarse particles, gas flowrates, and moving-bed velocities are examined to ascertain the transport characteristics of fines. We propose models to predict the transport characteristics by performing a dimensional analysis and a regularized regression by machine learning. We observe that the transport phenomena of fines are dominated by the hydrodynamic properties of fines rather than the moving-bed velocity, and the size of coarse particles also has an impact on the transport characteristics, especially the fines holdup. Additionally, the split ratio and exiting velocity of fines are found to be a function of the gas flowrate and the size of coarse particles. Results of this study can guide the design of packed moving-bed reactors that utilize fine particles as the feedstock.

Three kinetic models are developed and calibrated for the complete multi-step reduction of an Fe-based oxygen carrier (OC) particle with CH4, CO, and H2, using data from thermogravimetric analysis. The complete reduction rate profiles exhibit complex dynamics whose trajectory is significantly different depending on the reducing gas. A Bayesian model building and parameter estimation framework is applied for simultaneous parameter and model structure uncertainty quantification. The final models show excellent agreement between model predictions and calibration data, as well as new data not used for calibration (for the reduction of the OC with HC4). Parameter uncertainty is quantified by determining their joint posterior distribution, and model structure uncertainty is addressed by incorporating Gaussian process stochastic functions (represented by Bayesian smoothing splines) into the kinetic models. The final kinetic models with discrepancy functions are readily employable in equation-oriented simulation and optimization platforms.

Accurate, predictive reaction models are critical for the design and optimization of chemical looping combustion (CLC) reactors. The formulation and estimation of kinetic parameters for these reaction models using a first-principles equation-oriented (EO) approach is particularly beneficial as large amounts of experimental data spanning process-relevant conditions can be used to estimate parameters in a computationally tractable way. This work demonstrates the application of a novel EO framework to develop reduction reaction kinetic models of an iron-based CLC oxygen carrier (OC). An optimization problem is formulated to estimate kinetic parameters that provide the best fit to the experimental data. The model predicts the state of the OC with mean square error values of 2.5%-4.4% across the full range of validation data, including multiple reduction cycles.

Commercially viable H-2 production from H2S demands a well-designed and efficient technology concept with superior H-2 yield. We propose a novel sulfur looping scheme that involves carrier sulfidation and CO2 enabled carrier regeneration to simultaneously utilize H2S and CO2, the two common industrial waste gases, for valuable H-2 production. Using Ni3S2 as the active component, a high-performance sulfur carrier design is developed, where the selection of support is key. ZrO2 and MgAl2O4 supports were tested and both substantially improve the recyclability over cycles by imparting structural stability to Ni3S2. ZrO2 dramatically enhances the carrier performance, exhibiting a maximum increase of similar to 100% in sulfur uptake during the redox cycles compared to MgAl2O4. Furthermore, in fixed bed experiments at a high GHSV of 5000 hr(-1), ZrO2 supported carrier maintained its superior performance over MgAl2O4 with a similar to 9.5% higher total H2S consumption. Density functional theory calculations were performed to unveil the role of supports. ZrO2 is identified as a support with bifunctional characteristics that not only improves textural properties of the carrier, but also catalytically decomposes H2S and induces a synergistic dynamic with Ni3S2. On the other hand, MgAl2O4 acts only as a conventional inert support for morphology modifications with negligible interaction with H2S. This work demonstrates a novel strategy for H2S and CO2 utilization and provides new insights into effective support selection aiding the design of a robust and efficient sulfur carrier.

•Recent developments in reactive H2S separation and removal using oxidative and non-oxidative approaches.•Perspectives on the advances and challenges of existing H2S decomposition schemes.•Combination of experimental and mechanistic studies guides optimal material design.

Decomposition of H2S into sulfur and clean fuel H2 is an attractive process and requires a design concept with a maximum H2S conversion and a minimal energy consumption. Herein, we demonstrate a sulfur looping scheme in a one-reactor system using a low-cost and environmentally safe iron-based sulfur carrier. H2S decomposition is split into cyclic sulfidation and regeneration of sulfur carriers, which overcomes the inherent thermodynamic constraint, allowing in situ H2 generation. We experimentally obtained 24% higher sulfur uptake in 2% Mo-doped iron-based sulfur carriers compared with undoped sulfur carriers. The reaction mechanisms unveiled by the density functional theory indicate that surface hydrogen diffusion is the rate-determining step for sulfidation of the sulfur carrier. Compared with the undoped sulfur carrier, Mo dopant facilitates the surface hydrogen diffusion, thus promoting the overall H2S conversion. This work demonstrates a novel strategy for high-yielding H2S removal through low-percentage dopant modification sulfur carrier and provides new insights for an effective dopant screening strategy aiding the future carrier design.

In this study, a family of second-order process based modified Patankar Runge-Kutta schemes is proposed. The proposed schemes preserve both the mass and mole balance in a stiff reaction network while maintaining the positivity of density and pressure. The accuracy analysis is conducted to derive the sufficient and necessary conditions for the Runge-Kutta and Patankar coefficients. Coupling with the finite volume method, the proposed schemes are extended to Euler equations with non-equilibrium reacting source terms. Benchmark tests are given to prove the prior order of accuracy and validate the positive-preserving property for both density and pressure. (c) 2021 Elsevier Inc. All rights reserved.

Owing to its high fuel conversion efficiency and in-situ CO2 capture capability, chemical looping is a promising and versatile platform for fossil fuel utilization. Through the circulation of oxygen carriers (OCs), which are usually metal oxides, the carbonaceous fuels are oxidized into power/heat and/or value-added chemicals by lattice oxygen of OC in the fuel reactor. The reactivity of OC towards the carbonaceous fuels is crucial to the success of chemical looping processes. Incorporating low-percentage dopants into OC is a promising strategy to improve their reactivity while maintaining the recyclability. Consequently, a systematic screening strategy in dopant selection with a solid physical foundation is highly desired. Using hematite (alpha-Fe2O3) as the model OC material, density functional theory calculations were conducted herein to exemplify the impact of transition metal dopants on the surface reactivity with CO and CH4, the two most common C1 reducing agents in fossil fuels. We found that the amount of electrons accumulated on the lattice oxygen that bound with dopants is a key descriptor to evaluating the surface reactivity in the Mars-van Krevelen type reactions, which can be tailored by dopants with different electronegativities. Cu and Ni were predicted to be the most effective dopants, and such theoretical predictions were validated in temperature-programmed reduction and cyclic redox experiments, where a significant reactivity enhancement was observed using only 1% atomic ratio of effective dopants. The proposed screening strategy is expected to facilitate new OC designs and modifications in an energy and cost effective manner, thus significantly expedites the development of chemical looping technologies.

INTRODUCTION:The aim of this study was to evaluate white spot lesion (WSL) remineralization and fluoride uptake by the application of fluoride varnishes directly onto artificial WSLs in vitro.METHODS:MI varnish containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and 2.26% fluoride and Duraphat varnish containing 2.26% fluoride (no added calcium) were compared with a placebo varnish (no added calcium or fluoride). Two WSLs were prepared in enamel slabs and varnish applied to cover one of the two lesions. Each slab was immersed in artificial saliva for 14 days at 37°C. Mineral content was determined using transverse microradiography and fluoride uptake using electron probe microanalysis. The data were statistically analysed using a linear mixed model.RESULTS:Both MI and Duraphat varnishes significantly remineralized the covered and uncovered WSLs when compared with the placebo varnish (P < 0.001). The WSLs covered with varnish showed greater remineralization than those uncovered. MI varnish produced the highest level of remineralization and significantly greater fluoride uptake (0.44 ± 0.08 wt%) compared with Duraphat (0.24 ± 0.03 wt%) and the placebo varnish (0.06 ± 0.05 wt%).CONCLUSION:Varnish containing fluoride and CPP-ACP was superior to varnish containing fluoride alone in promoting WSL remineralization and fluoride uptake.

To meet the globally growing energy demands, it is essential to develop schemes with higher fuel conversion efficiency at temperatures <1000 degrees C while suppressing emissions of CO2. Iron oxide nanoparticles supported by mesoporous silica SBA-16 (Fe2O3@SBA-16) is conceived and developed in this study for chemical looping partial oxidation, yielding syngas selectivity above 95% with operating temperatures as low as around 400 degrees C is achieved, a temperature that is 600 degrees C lower than the conventional operating temperature. The methane conversion rate for Fe2O3 @SBA-16 is 52 and 660% higher than those for established nanoparticle oxygen carriers and bulk oxygen carriers, respectively. Dynamic Monte Carlo simulations are conducted that demonstrate the distinct effects of nanoparticle loading and particle size distribution on 3-D interconnected Fe2O3@SBA-16, affirming its accelerated reaction kinetics. This finding has significant implications in mesoporous materials and broadens research domains in other cyclic redox energy systems.

The methane-to-syngas (MTS) chemical looping process is an advanced methane reforming technology for the production of high purity syngas. The developed MTS process utilizes metal oxide oxygen carriers in a cocurrent moving bed reactor to partially oxidize the methane such that the resulting syngas stream is undiluted by nitrogen in air or H-2 from overconversion and directly suitable for downstream processing. The oxygen carriers are regenerated with air in a separate fluidized bed reactor producing a spent air stream separate from the product syngas, circumventing the need for cryogenic air separation units. In this work, a 15 kW(th) subpilot unit is designed and operated in a continuous manner to experimentally confirm the viability of the MTS process. Reactor design considerations and methodology are discussed in detail. An iron-titanium composite oxygen carrier is used as the oxygen carrier for its ability to achieve high methane conversion while regulating the product syngas to the partial oxidation products, CO and H-2. Syngas is produced with an H-2/CO ratio of similar to 2, and a purity of similar to 97% is produced with methane conversion exceeding 99%. The coinjection of methane with H-2 and/or H2O is explored for the purpose of H-2 utilization and flexible H-2/CO ratios, allowing the MTS process to produce syngas for a variety of downstream processes without reactor modification. The results indicate that syngas with H-2/CO ratios ranging from 1.19 to 2.50 with high methane conversion and syngas purity can be produced with coinjection. No evidence of carbon deposition on the oxygen carrier is revealed, and the oxygen carrier retained structural integrity after subjection to reaction and circulation in the subpilot unit.

Carbon deposition can be promoted by catalyst-assisted C-H bond dissociation, which is one of the most concerning issues in reaction engineering. Treatment of carbon contamination inevitably generates CO2 which has a detrimental effect on the environment. Consequently, the development of efficient oxygen carriers is important to commercial viability of chemical looping processes. In this work, density functional theory (DFT) calculations were conducted and reveal that carbon deposition is a cascade reaction of accumulative C-C bond forming that deactivates LFO surface due to gradual accumulation of lattice oxygen vacancies. Guided by DFT mechanistic predictions, we tailor catalytic reactive perovskite LaFeO3 (LFO) with high oxygen carrying hematite Fe2O3 (FO) into a hybrid oxygen carrier LFO-FO. The LFO-FO oxygen carrier exhibits excellent carbon inhibition capability and high reactivity with syngas selectivity above 98 %. This work proposes a promising strategy toward oxygen carrier development with low cost, high reactivity, and selectivity for chemical looping technology.

The purpose of the project is to address the optimization and startup operation of a modular coal direct chemical looping (CDCL) combustion system integrated with a steam cycle for power generation to reduce the risks involved in further scale-up of the technology. The modular reactor design of the CDCL process provides flexibility in the fabrication of the reactor and in its operating capacity (i.e. turndown ratio) at the cost of a more complex heat exchange network (HEN) design and integration. To address the technology gaps and advance the efficiency and economic feasibility of the CDCL technology, the project will perform a detailed and comprehensive analysis of the integration of a modular CDCL reactor system and a steam cycle system under both static and transient conditions via HEN process performance simulations and system dynamic modeling, respectively. The scope of work consists of 1) Experimental and computational studies of the CDCL combustor reactor 2) Comprehensive static (i.e. steady-state) system HEN design analysis in CDCL 550 MWe commercial unit for power generation and 3) Dynamic modeling of site specific design of 10MWe CDCL large pilot plant. The project team has successfully developed and validated a kinetic model for the oxidation of oxygen carriers in the combustor using the unreacted shrinking core model (UCSM). The model is capable of capturing the oxidation kinetics of fully or partially reduced oxygen carrier particles. A computational fluid dynamics (CFD) model is developed to simulate the hydrodynamics, heat transfer, and chemical reaction occurring in the CDCL combustor. The model is developed in MFIX and ANSYS Fluent. Key aspects of CDCL combustor operation, including heat transfer, oxygen carrier oxidation, and the transport of oxygen carrier particles, are simulated using this CFD model. The HEN for a commercial scale 550 MWe CDCL power plant is simulated and optimized using ASPEN Plus. Practical design considerations are incorporated based on industrial experiences. The performance and cost for the commercial CDCL plant is updated based on these analyses. A dynamic model for the 10 MWe CDCL pilot plant is developed in ProTRAX simulation software. The model is based on the pilot plant design developed in project DE-FE0027654 “10 MWe CDCL Large Pilot Plang – Pre-FEED Study” and the steam cycle data obtained from Dover Light & Power plant. The transient behaviors during pilot plant load variation are simulated using the dynamic model.

Chemical looping is a promising technology for fossil fuel utilization due to its high fuel conversion efficiency with in-situ CO2 capture capability. Metal oxide are used as oxygen carriers (OCs) and circulate between a fuel reactor and an air reactor to perform reduction and oxidation reactions, respectively. In general, OC exiting the fuel reactor is not reduced fully to its metallic state due to many factors including carbon deposition and OC deactivation. Therefore, the effect of the initial reduction state on the OC oxidation in the air reactor is a significant parameter for consideration in developing the oxidation kinetic model. The objective of this work is to develop a physically significant kinetic model that applies to the oxidation of both initially fully and partially reduced OC with air. For this study, 1.5 mm Fe-based OC particle supported with TiO2 was used as the model OC particle due to its complex multistep reaction nature. The oxidation kinetics were experimentally investigated in a thermogravimetric analyzer (TGA). Results indicate a significant difference in the oxidation rate profile for the OCs when oxidized from an initially fully reduced compared to an initially partially reduced state. Elemental mapping via energy-dispersive X-ray spectroscopy (EDS) reveals a shrinking-core type topochemical pattern across the OC particle, which was identified to be the cause of the dependency of kinetics on the initial reduction state. A generalized kinetic model was developed based on the observed shrinking-core behavior without presuming any rate-determining steps and experimentally validated over a broad range of temperatures (800-1000 degrees C) and oxygen concentrations (5, 7, 10, and 15 mol%). Impacts of particle porosity, size, and core-shell structure on the OC oxidation kinetics were analyzed in the developed oxidation kinetic model to suggest methods of improving the oxidation rate of the OC without modifying the chemical composition.

Chronic periodontitis has a polymicrobial biofilm etiology and interactions between key oral bacterial species, such as Porphyromonas gingivalis and Treponema denticola contribute to disease progression. P. gingivalis and T. denticola are co-localized in subgingival plaque and have been previously shown to exhibit strong synergy in growth, biofilm formation and virulence in an animal model of disease. The motility of T. denticola, although not considered as a classic virulence factor, may be involved in synergistic biofilm development between P. gingivalis and T. denticola. We determined the role of T. denticola motility in polymicrobial biofilm development using an optimized transformation protocol to produce two T. denticola mutants targeting the motility machinery. These deletion mutants were non-motile and lacked the gene encoding the flagellar hook protein of the periplasmic flagella (ΔflgE) or a component of the stator motor that drives the flagella (ΔmotB). The specificity of these gene deletions was determined by whole genome sequencing. Quantitative proteomic analyses of mutant strains revealed that the specific inactivation of the motility-associated gene, motB, had effects beyond motility. There were 64 and 326 proteins that changed in abundance in the ΔflgE and ΔmotB mutants, respectively. In the ΔflgE mutant, motility-associated proteins showed the most significant change in abundance confirming the phenotype change for the mutant was related to motility. However, the inactivation of motB as well as stopping motility also upregulated cellular stress responses in the mutant indicating pleiotropic effects of the mutation. T. denticola wild-type and P. gingivalis displayed synergistic biofilm development with a 2-fold higher biomass of the dual-species biofilms than the sum of the monospecies biofilms. Inactivation of T. denticola flgE and motB reduced this synergy. A 5-fold reduction in dual-species biofilm biomass was found with the motility-specific ΔflgE mutant suggesting that T. denticola periplasmic flagella are essential in synergistic biofilm formation with P. gingivalis.

Dental caries, erosion and hypersensitivity are major public health problems. SnF2 is used widely in oral care products to help prevent/treat these conditions. Casein phosphopeptide-stabilised amorphous calcium phosphate nanocomplexes (CPP-ACP) are a biomimetic nanotechnology of salivary phosphopeptide-ACP complexes that deliver bioavailable calcium and phosphate ions to promote dental remineralisation (repair). We show here using in vitro studies and a double-blind, randomised controlled, cross-over design in situ clinical trial that SnF2 and CPP-ACP interact to form a nanofilament coating on the tooth surface and that together they are superior in their ability to promote dental remineralisation. Sn(II) by cross-linking the CPP-ACP helps to stabilise the complexes which improves delivery to the tooth surface and enhances binding and ion incorporation into tooth mineral. The combination of SnF2 and CPP-ACP in oral care products may significantly improve their efficacy in prevention/treatment of dental caries/erosion and hypersensitivity.

•World’s first chemical looping pilot plant utilizing moving bed reactors.•Achieved near-full conversion of coal-derived syngas in the moving bed reducer.•Achieved 99% purity hydrogen production with in-situ carbon capture.•Validated operational results by ASPEN process simulation.

The Syngas Chemical looping (SCL) process provides efficient and economic means to utilize the abundant fossil reserve of coal. The main problem associated with coal utilization is the CO2 emissions resulting from its combustion. Even though CO2 regulation or carbon tax is currently not in place, its enforcement is expected in the near future. Such a greenhouse gas emission control, if adopted in current power plant systems, will drive the efficiency down and increase the cost of electricity, due to the energy and capital-intensive nature of current CO2 separation techniques. This highlights the need to develop technologies that present a solution to the rising cost of electricity in the future. The integrated gasification combined cycle (IGCC) presents an improvement to the above predicament, but it is capital intensive due to the extensive unit operations involved. The efficiency for a CO2 capture incorporated IGCC system is around ~32%, resulting in approximately 45% increase in cost of electricity. This is definitely a better path to traverse than the conventional pulverized coal (PC) power plants as it has improved economics and efficiencies accompanied by product flexibility. The SCL process advances the benefits even further when integrated with the IGCC process. The SCL process removes the expensive WGS system and CO2 separation columns, thereby saving on capital and operational expenses. This integration results in a 12 – 21% increase in efficiency accompanied by a reduction in cost of electricity by 15 – 28%, over conventional IGCC systems. Therefore, SCL process provides the best route to harness the energy from coal. The overall project objective was to construct and operate a syngas chemical looping pilot scale test unit at the NCCC. The project scope of work was divided into 3 phases. In Phase I, cold flow model studies using a 1:1 scale acrylic test unit constructed at Particulate Solids Research, Inc. (PSRI) was successfully completed confirming robust solid flow control is achievable in the non-mechanical system design. In Phase II, the high pressure, high temperature, chemical looping reactor was successfully designed with all necessary equipment and safety instrumentation/controls specified to allow for fabrication, site construction, and assembly to commence in Phase III. In Phase III, the SCL pilot plant was successfully assembled and all necessary functional checks and pre-startup safety reviews completed. During unit commission over the course of 200 hours of testing, operational issues were observed with premix burner used for system startup. With the grants awarded by the National Energy Laboratory (NETL) and the Ohio Development Services Agency (ODSA) under awards DE-FE0023915 and D-14-18, the SCL pilot unit underwent three auxiliary equipment modifications to resolve all of the startup operational issues encountered. The unit was successfully demonstrated with 300+hr continuous operation. Key results obtained include high syngas conversion of 97.95% with 16.03% oxygen carrier conversion in the moving bed reducer and >99% purity H2 produced from the moving bed oxidizer.