Electrochemical methods are environmentally friendly and have unique advantages in the synthesis of organic chemicals. However, their implementation is limited due to the complex transport problems posed by traditional electrochemical reactors. Recently, the application of microreaction technology in electrosynthesis studies has reduced the transport distance of ions and increased the specific surface area of electrodes, leading to efficient, successive, and easily scaled-up electrosynthesis technologies. In this review article, engineering advantages of using microchannels in electrosynthesis are discussed from process enhancement perspective. Flow patterns and mass transfer behaviors in recently reported electrochemical microreactors are analyzed, and prototypes for the reactor scale-up are reviewed. As a relatively new research area, many scientific rules and engineering features of electrosynthesis in microreactors require elucidation. Potential research foci, considered crucial for the development of novel electrosynthesis technology, are therefore proposed.
One-dimensional (1D) Pt-based electrocatalysts demonstrate outstanding catalytic activities and stability toward the oxygen reduction reaction (ORR). Advances in three-dimensional (3D) ordered electrodes based on 1D Pt-based nanostructure arrays have revealed great potential for developing highperformance proton exchange membrane fuel cells (PEMFCs), in particular for addressing the mass transfer and durability challenges of Pt/C nanoparticle electrodes. This paper reviews recent progress in the field, with a focus on the 3D ordered electrodes based on self-standing Pt nanowire arrays. Nanostructured thin-film (NSTF) catalysts are discussed along with electrodes made from Pt-based nanoparticles deposited on arrays of polymer nanowires, and carbon and TiO2 nanotubes. Achievements on electrodes from Pt-based nanotube arrays are also reviewed. The importance of size, surface properties, and the distribution control of 1D catalyst nanostructures is indicated. Finally, challenges and future development opportunities are addressed regarding increasing electrochemical surface area (ECSA) and quantifying oxygen mass transport resistance for 1D nanostructure array electrodes.
Crystallization is a fundamental separation technology used for the production of particulate solids. Accurate nucleation and growth process control are vitally important but difficult. A novel controlling technology that can simultaneously intensify the overall crystallization process remains a significant challenge. Membrane crystallization (MCr), which has progressed significantly in recent years, is a hybrid technology platform with great potential to address this goal. This review illustrates the basic concepts of MCr and its promising applications for crystallization control and process intensification, including a state-of-the-art review of key MCr-utilized membrane materials, process control mechanisms, and optimization strategies based on diverse hybrid membranes and crystallization processes. Finally, efforts to promote MCr technology to industrial use, unexplored issues, and open questions to be addressed are outlined.
Interactions involving chemical reagents, solid particles, gas bubbles, liquid droplets, and solid surfaces in complex fluids play a vital role in many engineering processes, such as froth flotation, emulsion and foam formation, adsorption, and fouling and anti-fouling phenomena. These interactions at the molecular, nano-, and micro scale significantly influence and determine the macroscopic performance and efficiency of related engineering processes. Understanding the intermolecular and surface interactions in engineering processes is of both fundamental and practical importance, which not only improves production technologies, but also provides valuable insights into the development of new materials. In this review, the typical intermolecular and surface interactions involved in various engineering processes, including Derjaguin–Landau–Verwey–Overbeek (DLVO) interactions (i.e., van der Waals and electrical doublelayer interactions) and non-DLVO interactions, such as steric and hydrophobic interactions, are first introduced. Nanomechanical techniques such as atomic force microscopy and surface forces apparatus for quantifying the interaction forces of molecules and surfaces in complex fluids are briefly introduced. Our recent progress on characterizing the intermolecular and surface interactions in several engineering systems are reviewed, including mineral flotation, petroleum engineering, wastewater treatment, and energy storage materials. The correlation of these fundamental interaction mechanisms with practical applications in resolving engineering challenges and the perspectives of the research field have also been discussed.
The need for the separation of azeotropic mixtures for the production of high-end chemicals and resource recovery has spurred significant research into the development of new separation methods in the chemical industry. In this paper, a green and sustainable method for azeotrope separation is proposed based on a chemical-looping concept with the help of reversible-reaction-assisted distillation. The central concept in the chemical-looping separation (CLS) method is the selection of a reactant that can react with the azeotrope components and can also be recycled by the reverse reaction to close the loop and achieve cyclic azeotrope separation. This paper aims to provide an informative perspective on the fundamental theory and applications of the CLS method based on the separation principle, reactant selection, and case analysis, for example, the separation of alkenes, alkane, aromatics, and polyol products. In summary, we provide guidance and references for chemical separation process intensification in product refining and separation from azeotropic systems for the development of a more sustainable chemical industry.
Benzaldehyde is a highly desirable chemical due to its extensive application in medicine, chemical synthesis and food sector among others. However, its production generally involves hazardous solvents such as trifluorotoluene or acetonitrile, and its conversion, especially selectivity in the aqueous phase, is still not up to expectations. Hence, developing an environmentally benign, synthetic process for benzaldehyde production is of paramount importance. Herein, we report the preparation of a photocatalyst (PW12-P-UCNS, where PW12 is H3PW12O40·xH2O and P-UCNS is phosphoric acid-modified unstack graphitic carbon nitride) by incorporating phosphotungstic acid on phosphoric acid-functionalised graphitic carbon nitride (g-C3N4) nanosheets. The performance of PW12-P-UCNS was tested using the benzyl alcohol photo-oxidation reaction to produce benzaldehyde in H2O, at room temperature (20 °C). The asprepared PW12-P-UCNS photocatalyst showed excellent photocatalytic performance with 58.3% conversion and 99.5% selectivity within 2 h. Moreover, the catalyst could be reused for at least five times without significant activity loss. Most importantly, a proposed Z-scheme mechanism of the PW12-P-UCNScatalysed model reaction was revealed. We carefully investigated its transient photocurrent and electrochemical impedance, and identified superoxide radicals and photogenerated holes as the main active species through electron spin-resonance spectroscopy and scavenger experiments. Results show that the designed PW12-P-UCNS photocatalyst is a highly promising candidate for benzaldehyde production through the photo-oxidation reaction in aqueous phase, under mild conditions.
In this study, the support effects on the Pd-catalyzed semi-hydrogenation of acetylene have been investigated from the structural and kinetic perspectives. According to the results of kinetic analysis and X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, temperature-programmed hydride decomposition, and in situ X-ray diffraction measurements, using carbon nanotubes as support for Pd nanocatalysts with various sizes instead of a-Al2O3 decreases the Pd0 3d binding energy and suppresses the formation of undesirable palladium hydride species, thus increasing the ethylene yield. Furthermore, X-ray absorption spectroscopy, high-resolution transmission electron microscopy, and C2H4 temperature-programmed desorption studies combined with density-functional theory calculations reveal the existence of a unique Pd local environment, containing subsurface carbon atoms, that produces positive geometric effects on the acetylene conversion reaction. Therefore, tailoring the Pd local environment and electronic properties represents an effective strategy for the fabrication and design of highly active and selective Pd semi-hydrogenation catalysts.
This study provides new insights into the comparison of cable-stayed and extradosed bridges based on the safety assessment of their stay cables. These bridges are often regarded as identical structures owing to the use of inclined cables; however, the international standards for bridge design stipulate different safety factors for stay cables of both types of bridges. To address this misconception, a comparative study was carried out on the safety factors of stay cables under fatigue and ultimate limit states by considering the effects of various untoward and damaging factors, such as overloading, cable loss, and corrosion. The primary goal of this study is to describe the structural disparities between both types of bridges and evaluate their structural redundancies by employing deterministic and nondeterministic methods. To
achieve this goal, three-dimensional finite-element models of both bridges were developed based on the current design guidelines for stay cables in Japan. After the balanced states of the bridge models were achieved, static analyses were performed for different safety factors of stay cables in a parametric manner. Finally, the first-order reliability method and Monte Carlo method were applied to determine the reliability index of stay cables. The analysis results show that cable-stayed and extradosed bridges exhibit different structural redundancies for different safety factors under the same loading conditions. Moreover, a significant increase in structural redundancy occurs with an incremental increase in the safety factors of stay cables.
Carbon dioxide (CO2) capture by gas-separation membranes has become increasingly attractive due to its high energy efficiency, relatively low cost, and environmental impact. Polyvinylamine (PVAm)-based facilitated transport (FT) membranes were developed in the last decade for CO2 capture. This work discusses the challenges of applying PVAm-based FT membranes from materials to processes for postcombustion CO2 capture in power plants and cement factories. Experiences learned from a pilot demonstration system can be used to guide the design of other membranes for CO2 capture. The importance of module and process design is emphasized in the achievement of a high-performance membrane system. Moreover, the results from process simulation and cost estimation indicate that a three-stage membrane system is feasible for achieving a high CO2 purity of 95 vol%. The specific CO2 capture cost was found to significantly depend on the required CO2 capture ratio, and a moderate CO2 capture ratio of 50% presented a cost of 63.7 USD per tonne CO2 captured. Thus, FT membrane systems were found to be more competitive for partial CO2 capture.