Chemical Engineering Science最新文献

In this work, a penalty-free hybrid stochastic-deterministic algorithm framework is proposed for large-scale heat exchanger networks (HENs) synthesis (HENS), formulated as a computationally-hard mixed-integer nonlinear programming (MINLP) problem. In the outer level, an improved genetic algorithm (GA) is developed to optimize process stream matches represented by integer variables whose values are generated by a unique heat exchanger vector. Unlike previous researches, the improved GA does not rely on any penalty terms, because we propose a feasible stream matching principle to exclude all infeasible process stream matches and only feasible matches are considered in optimization process. In the inner level, a reduced-size MINLP model is solved using deterministic methods to minimize total annualized costs (TACs), which are then used to evaluate the fitness of candidate HENs. Through this way, the proposed framework combines deterministic and stochastic methods to enhance optimization efficiency and global search capability. Illustrative tests on six benchmark cases demonstrate that the framework can efficiently achieve lower-cost solutions compared to deterministic, stochastic, or hybrid methods. The results show a decrease in TAC for all six cases and a reduction in solution time ranging from 11.1% to 97.2%. Importantly, the proposed framework can be extended to solve MINLP problems in other process networks.

In order to achieve ultra-low sulfur fuel production, it is essential to design highly efficient catalysts for deep desulfurization. In this work, trivacant Keggin-type tungstophosphate PW₉ (Na₉[A-PW₉O₃₄]•7H₂O) was innovatively utilized to synthesize polyoxometalate-based supported silica C₁₆-PW₉/SiO₂. The intact presence of polyoxometalates (POMs) was evidenced by several techniques of describing the structure and composition of the obtained hybrid samples. Compared with the saturated tungstophosphate ([PW₁₂O₄₀]³⁻), the [A-PW₉O₃₄]⁹⁻ showed better coordination, which can coordinate with five ILs (C₁₆MIM). More ILs make it easier for the catalyst to attract DBT to the vicinity of PW₉, and the abundance of metal oxide W = O on PW₉ endows the catalyst’s excellent catalytic activity. Specifically, C₁₆-PW₉/SiO₂ exhibited excellent oxidative desulfurization performance, achieving 100 % dibenzothiophene (DBT) conversion efficiency at 50 °C for 10 min, and the turnover frequency (TOF) number reached 723.4 h⁻¹, which is higher than the catalysts of the POMs type that have been published. The strategy of combining lacunary polyoxometalates with ionic liquids offers a fresh viewpoint on the creation of POM-based catalysts.

An improved manifold-projection trajectory based dimension reduction algorithm (MTDR) to automatically generate skeletal chemical kinetic mechanisms was proposed and validated in this study. This algorithm is implemented by constructing an approximate manifold-based trajectory of the combustion system using Euclidean distances between two adjacent points and cosine similarities between two adjacent vectors in the manifold space, and then evaluating the importance of species by calculating the error of manifold-based trajectories before and after the projection of the manifold. In this method, the nature of the combustion system is well reflected since the combustion process information can be captured by the location of the state point in the manifold space. The calculation during the reduction process is simplified by using the manifold-based trajectory instead of the complex differential equations. Compared to our previous work, this study improves the prediction accuracy of the reduced mechanisms through a more comprehensive error evaluation in the mechanism reduction process. The detailed mechanisms of fuels including iso-cetane, iso-octane and gasoline surrogate mixtures of toluene, iso-octane and n-heptane were reduced to portray the prowess of the algorithm. It’s demonstrated that the number of species of the fuels is reduced from 492, 254 and 1389 to 95, 87 and 427 within an acceptable error, respectively. Meanwhile, the case of iso-octane mechanism reduction was chosen to compare the performance of MTDR with traditional methods including path flux analysis (PFA) and directed relation graph with error propagation and sensitivity analysis (DRGEPSA), and it is shown that the MDTR can generate more compact mechanism under a broad range of error limits.

Fluidized beds are characterized by heterogeneous structures, which significantly influence the interphase drag and heat transfer. To account for the effects of sub-grid structures on heat transfer in coarse-grid simulations, this study proposes a multiscale heat transfer model based on the steady-state energy-minimization multi-scale (EMMS) approach. This model introduces four structure-dependent internal energy balance equations into the steady-state EMMS model. The heat source and sink terms are included in the internal energy balance equation to maintain a steady-state condition for heat transfer. Solving the model yields the functions of both multiscale drag and heat transfer coefficients. These functions are integrated into coarse-grid simulations under the two-fluid model framework. The simulation results are fairly consistent with the experimental data in terms of both flow and temperature fields, with flow regimes covering bubbling fluidization, fast fluidization and dilute transport.

Airborne droplets containing viruses from infected persons can present long range disease transmission risks. In this study, we examine the trajectory of an airborne droplet based on a point force model. The interplay between gravity, drag, inertia and deformation are factored in, for drop sizes ranging from micrometer to millimeter size. In particular, we propose an expression for the drag force which enables analytical solutions for cases of practical interest, such as the transient velocity behavior and spreading distances. This allows us to obtain physical insights which are not obvious from direct numerical simulations. Effects such as droplet deformation, breakup and evaporation are also considered. Our analytical solutions compare favorably with numerical and experimental data. The evaporation rate was determined experimentally with a levitating device and some experimental drop velocity versus time data were obtained with falling millimeter sized droplets.

For molten halide salt mixtures already being utilized or under consideration for carbon-free energy production systems, it is crucial that their viscosity is well understood so that system thermal hydraulics can be reliably assessed. Because of the difficulty in accurately measuring molten halide viscosity and the sheer size of the matrix of possible higher order salt mixtures that may be of interest to the energy industry, there are several gaps in the quantified understanding of molten halide viscosity across this matrix. As such, both first-principles and semi-empirical modeling techniques may be crucial for rapidly assessing this broad, complex compositional domain. Herein, the Redlich-Kister framework is applied to assess the feasibility of broadly interpolating and estimating the viscosity of several pseudobinary and pseudoternary molten halide salt systems that may be of key interest to the energy industry. The framework is based on the assumption that an ideal component and a nonideal component collectively describe the viscosity as a function of composition and temperature for a given molten halide system. Three different ideal models were considered for the ideal component, including Grunburg-Nissan, Katti-Chaudhri, and Gambill methods. Regarding the pseudobinary interpolations, the Redlich-Kister models with either the Grunburg-Nissan or Katti-Chaudhri models as the ideal component resulted in either highly (average error less than 5%) or reasonably (average error less than 15%) accurate interpolations of pseudobinary halide viscosity; BeF₂- or UF₄-bearing salts tended to result in reasonably accurate interpolations, whereas other pseudobinary mixtures tended to show high accuracy. Regarding the pseudoternary extrapolations, the Redlich-Kister framework shows reasonable success at estimating the extent to which a pseudoternary system may indicate deviations from ideal Grunburg-Nissan mixing, where discrepancies with comparative experimental data generally stay within 30%. The primary reasons identified for such discrepancies are (1) inaccuracy in the underlying experimental data, (2) different complexation behavior in the higher order systems compared to the pseudobinary subsystems, and (3) extrapolation into temperatures too far out of the domain, which is valid for the underlying experimental data feeding the Redlich-Kister model.

This paper focused on the mass transfer of Taylor bubbles composed of pure carbon dioxide in organic solvent in microchannels. Combined with the Henry’s law, the carbon dioxide concentration at the two-phase interface was dynamically updated by using a compressible fluid model and considering the variation of gas density in the bubble. The critical bubble shape factor could help to judge the dominant mechanism of bubble deformation. The entire mass transfer process was divided into three stages: the rapid dissolution stage, the two-end dissolution stage, and the diffusion-like dissolution stage. The gas–liquid mass transfer capacity and influencing factors of each stage were analyzed, and the dominant mass transfer mechanism of each stage was summarized. It was found that the non-uniform degree of gas density in the bubble was related to the bubble Reynolds number and bubble volume by analyzing the distribution variation of solute density.

Regular problems faced due to oil spills and soluble contaminants have increasingly caused serious water pollution. Therefore, there is an urgent need to develop efficient strategies to purify wastewater. This study aims to formulate a synergistic treatment technology of sorption and ultraviolet light catalysis for oil–water separation and degradation of dyes in wastewater. In this study, TiO₂ doped PVF sponge (DTMS-TiO₂@PVF) was prepared with a water contact angle of 151.5° and a removal rate of 98.86 % of MB in 120 min. Meanwhile, DTMS-TiO₂@PVF sponge could easily realize the selective separation of oil–water mixtures. Its saturated sorption capacity for oil and organic solvent was 4.13–10.05 g/g. In addition, DTMS-TiO₂@PVF sponge had better environmental stability, which could withstand chemical corrosion (acid, alkaline, and salt solutions). Therefore, DTMS-TiO₂@PVF sponge showed great potential for application as an efficient oil–water separation and photocatalytic material, especially in the field of treating oil wastewater and water purification.

Porous structure with larger specific surface area is more conducive to ion diffusion for the anode materials of metal-ion batteries. In this work, some 3D porous structures with larger and more pores in three directions were designed based on 2D penta-graphene (PG) nanoribbons. By systematically calculations, it was found two of them (h-PG40 and o-PG36) are both thermally and mechanically stable, even at such high temperatures of 1000 K. The alkali metal-ions of Li, Na, and K can be absorbed and diffuse in the pores of h-PG40/o-PG36, and all the porous structures remain metallic regardless of adsorbed ions. Using ab initio molecular dynamics (AIMD) simulation, the diffusion coefficients of Li, Na, and K at different temperatures were calculated. It is found that Li ions can rapidly diffuse in h-PG40 along three directions, but alkali metal-ions of Na and K with larger radii can rapidly diffuse along larger pores in both structures, and have good rate performance. Based on the diffusion coefficients, the obtained diffusion barriers of Li, Na, and K in the h-PG40/o-PG36 structures were 0.19/0.27, 0.26/0.17, 0.41/0.27 eV, which are considerably smaller compared to the minimum diffusion barrier observed in graphite. As the anode of LIB/SIB/PIB, the theoretical specific capacities of h-PG40 and o-PG36 are above 1451.67/781.67/781.67 and 1116.67/868.52/496.30 mAh·g⁻¹, respectively, and the calculated OCV of both structures are smaller than 1.5 V. This reflects their good specific capacity and cycling performance. This theoretical exploration may open a new frontier in searching more practical 3D porous structures as anode materials for alkali metal-ion batteries.

It is significant to gain insights into the electronic interfacial interactions on non-reducible oxides as they can effectively improve the catalytic performance. Herein, we reported the fabrication of Au⁰Pd^δ+ alloy (average size: 1.9 nm) co-modified with Na₁₂[α-P₂W₁₅O₅₆] (P₂W₁₅) nanoclusters on aluminum oxide (denoted as AuPd/P₂W₁₅-Al₂O₃) by deposition–precipitation and covalent immobilization strategy. The as-prepared AuPd/P₂W₁₅-Al₂O₃ exhibited 92 % conversion, 96 % selectivity of benzaldehyde with the reaction rate of 4.9 × 10⁴h⁻¹ when applied for the selective oxidation of benzyl alcohol, which was superior to AuPd/Al₂O₃, Au/P₂W₁₅-Al₂O₃ and Pd/P₂W₁₅-Al₂O₃ catalysts. Such excellent catalytic performance can be ascribed to the fact that: the electrons transfer from P₂W₁₅ to Au⁰Pd^δ+ alloy resulted in the electron-rich Au⁰Pd^δ+ alloy species, and the enhanced interfacial interactions between Au⁰Pd^δ+ alloy and P₂W₁₅ nanoclusters facilitated activation of O₂ to generate superoxide radicals •O₂^–. Moreover, density-functional theory (DFT) calculation confirmed that the P₂W₁₅ clusters modulated the d-band center of Au⁰Pd^δ+ alloy and accelerated the adsorption of benzyl alcohol, O₂ activation and desorption of benzaldehyde.