Reaction Chemistry & Engineering最新文献

The crystal phase of Zr-based solid acid catalysts was modulated by a two-step precipitation method for strongly bonding with sulfate groups. The catalytic performance of these catalysts was subsequently evaluated for condensation of 9-fluorenone with phenol. The results revealed that the catalytic activity of the catalysts was positively correlated with the acidity of the catalysts. Specifically, the SZr@Zr-2 catalyst exhibited the best catalytic performance with a 9-fluorenone conversion of 99.92% and 9,9-bis(4-hydroxyphenyl)fluorene (BHPF) selectivity of 99.86% under the optimized reaction conditions of 110 °C, 3 h and phenol to 9-fluorenone mole ratio of 6. It was demonstrated that the Zr(OH)₄@Zr(OH)₄-2 substrate prepared by two-step precipitation inherited rich Zr(OH)₄ species, which could be easily bonded with more sulfate groups. After calcination, these species were subsequently transformed into tetragonal ZrO₂ species induced by sufficient interaction with sulfate groups. The coordination between sulfate groups and tetragonal ZrO₂ enhanced the acidity of the SZr@Zr-2 catalyst and then boosted the condensation of 9-fluorenone with phenol for BHPF synthesis.

A major barrier for the upscaling of electrosynthetic methods is the transfer of the usually potential-controlled batch experiments to an operation in industry-typical cell designs (i.e. two-electrode flow reactors). To cross this bridge, we here present the implementation of our recently published method for the non-alkaline oxidation of 5-(hydroxymethyl)-furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in a flow channel reactor, powered by a standard laboratory power supply under cell-voltage/current control. For this purpose, the coating method for the used CoOOH catalyst was adapted to enable an electrochemical deposition in the flow channels devoid of a standard three-electrode setup. HMF oxidations were carried out in an acetate buffer (pH 5) at a current density of 1.0 mA cm⁻² and a temperature range between room temperature and 80 °C to provide a direct comparison with the previous batch experiments. The higher electrode surface area of the flow cell thereby allowed a significant reduction of the reaction time while operating under similar (albeit lower) Coulomb efficiencies. Under optimized conditions, the reactor operated at a cell voltage of ca. 2.4 V and yielded 77.1% FDCA at a Coulomb efficiency of 21.0%. Maleic acid was obtained as a side product at a yield of 9.2%.

High-throughput reaction discovery is necessary to understand complex reaction spaces for inorganic nanocrystal synthesis. Here, we implemented a high-throughput continuous flow millifluidic reactor to perform reaction discovery for Cs–Pb–Br nanocrystal synthesis using a ligand assisted reprecipitation (LARP)-type approach. 3D-printed flow resistors enable the screening of up to 16 different mixing ratios within a single 90 s run, allowing for >270 different precursor concentration ratios to be quickly tested to explore the phase space that results in CsPbBr₃, Cs₄PbBr₆, a biphasic mixture, or no product. To construct a full phase map from these high-throughput experiments, a neural network was trained and validated to predict the product composition (∼500 000 points in precursor concentration space). The phase map predicts product composition/phase as a function of Cs–Pb–Br feed ratio. This approach demonstrates how high-throughput flow chemistry can be used in tandem with machine learning to rapidly explore nanocrystal reaction spaces in flow.

E-waste contains a variety of non-renewable precious metal resources, and the amount is significantly higher than the abundance of precious metals in the corresponding ores. Therefore, it is of great significance to recover and reuse precious metals in e-waste. In this study, we successively used a simple one-step oxidation method and physical cross-linking to prepare a poly-m-phenylenediamine composite membrane material (CMC–PmPD composite membrane) containing a large number of recycling groups. The prepared CMC–PmPD composite membrane has high adsorption capacity and adsorption efficiency for Au(III), and the maximum adsorption capacity for Au(III) reaches 421.1 mg g⁻¹. The adsorption follows a second-order kinetic process and a Langmuir isotherm model, indicating that the adsorption mechanism is a monolayer chemisorption. The regeneration of the composite membrane material can be realized after a simple thiourea solution immersion, and 89.5% adsorption efficiency is maintained after five regeneration cycles. In addition, when the CMC–PmPD composite membrane was applied to the treatment of mixed heavy metal ion solutions with different concentrations and compositions, the CMC–PmPD composite membrane was always able to selectively adsorb more than 95% of Au(III) from the simulated solution or e-waste leachate, which was highly selective and applicable. The CMC–PmPD composite membrane has a broad application prospect in metallurgy and fine chemical industry.

Composite flat-sheet membranes functionalized with imidazolium-based ionic liquids (ILs) grafted to poly(vinyl alcohol)/glutaraldehyde as a catalytic layer were developed to enhance the esterification between n-butanol and acetic acid. The functionalized membranes were produced via dip-coating commercial pervaporation membranes, and two distinct Brønsted-acidic ILs with an imidazolium-based cation and different (hydrogen sulfate [HSO₄]⁻ or bromide [Br]⁻) anions were compared. Compact, 12 μm-thick, defect-free catalytic layers were observed on top of the pervaporation membrane supports, and the determined penetration depth of the ILs confirmed their presence in the upper part of the coating. While both ILs could significantly promote the esterification of n-butanol and acetic acid, the [HSO₄]⁻ anion catalyzed the formation of butyl acetate more effectively than [Br]⁻-based species, resulting in yields of up to 50% over 15 h. Furthermore, the coated membranes exhibited enhanced water separation factors compared to the unfunctionalized one owing to the reduced swelling of the coated membranes accompanied with their diminished wettability.

Herein, calcium-based energy-storage materials that directly absorb solar energy were prepared through wet modification of carbide slag (solid waste). It was found that at a carbonization temperature of 700 °C and calcination temperature of 800 °C, the carbonation conversion rate of 50%FA-100 : 10 Mn remains 66.7% after 10 cycles, which is only 6.4% lower than the initial rate. Through ultraviolet spectrophotometry, it was found that after the addition of a small amount of manganese nitrate, the average absorbance of the energy-storage material was 44.14% higher than that of carbide slag. The use of formic acid as a solvent to acidify modified calcium carbide slag for the preparation of energy-storage materials improves the internal structure of the energy-storage materials, which facilitates the entrance of carbon dioxide into the energy-storage material during the diffusion reaction stage to initiate carbonation reaction. The kinetic calculation shows that the activation energy of the modified energy-storage material decreases by 11.3 kJ mol⁻¹ in the carbonation reaction stage and 9.25 kJ mol⁻¹ in the calcination reaction stage. After the activation energy decreases, the carbonation/calcination reaction is easier to carry out; thus, the reaction time is reduced.

Biocatalysis has become an attractive and powerful technology for resource-efficient conversions of starting materials to products because of selectivity, safety, health, environment and sustainability benefits. One of the key success factors for any synthetic method has traditionally been the yield of the product which has been isolated from the reaction mixture after the conversion and purified to the required purity. The conversion economy and the final product recovery, which determine the isolated yield of a product, are therefore also of key importance for biocatalytic processes, from biocatalytic single-step to multi-step reactions and total synthesis. In order to progress towards complete biocatalytic conversions and to aim at completely recovering and isolating the pure product, relevant thermodynamic, kinetic and other constraints leading to incomplete biocatalytic conversions and incomplete product recovery need to be identified and overcome. The methods and tools for overcoming various types of bottlenecks are growing and can provide valuable guidance for selecting the most suitable approaches towards the goal of achieving 100% yield of the isolated pure product for a specific biocatalytic conversion.

In microwave (MW)-assisted flow syntheses, the size, and hence, the volume of the reactor may be a limiting factor. In this paper, we introduce a novel nonlinear accomplishment by applying recirculation within the flow system. In this way, higher conversions were attained even with a 10 mL reactor cell recirculating larger volumes (25–100 mL) of the reactants. The model reaction was the ionic liquid-catalyzed direct esterification of phenyl-H-phosphinic acid with butyl alcohol. The effect of the flow rate, the absence or presence of the catalyst, and the temperature and volume of the reaction mixture on the conversion were studied in detail. Preparative yields of 64–72% for the butyl phenyl-H-phosphinate with a 5.9–8.6 g h⁻¹ productivity were obtained. Comparative thermal experiments confirmed the special role of MW irradiation. The method was then extended to esterification with other alcohols.

To maximize the benefits of a continuous flow reaction, a continuous work-up is also needed. Herein, we present a process design and novel equipment for a continuous amine resolution reaction, integrated with liquid–liquid (L–L) extraction, back-extraction into a different solvent, and crystallisation purification for product isolation. The reaction, in iso-propyl acetate, flows through a heated fixed-bed reactor with solid supported Candida antarctica lipase which catalyses the resolution of (rac)-1-phenylethylamine to give the (R)-amide in 50% conversion and 96% enantiomeric excess (ee). This is separated from the unreacted (S)-amine co-product by mixing with an acidic aqueous stream and separating the phases using our recently reported coalescence filter separator. The aqueous stream is neutralised by mixing with base and back-extracted into methyl-THF solvent before separating the phases using a membrane separator. Finally, a solid amine salt is isolated by filtration, achieved by mixing the free base with an organic acid to cause crystallisation to give the (S)-1-phenylethylamine in 43% yield and >99% ee from racemate. The work illustrates how typical reactions, work-up and purification steps that involve multiple phases can be telescoped together using both new and commercially available laboratory equipment. This continuous system uses mild reaction conditions, green solvents and minimises their use for reduced waste.

Waste polymethyl methacrylate (PMMA) has become a more prominent contributor to global plastic waste in the aftermath of the COVID-19 pandemic. Recycling PMMA relies either on mechanical recycling or thermal depolymerization. Mechanical properties deteriorate after several mechanical recycling cycles. Depolymerization technologies operate in an inert atmosphere and require costly monomer purification downstream. Therefore, neither chemical nor mechanical recycling of PMMA is economically viable. Here, we demonstrate a sustainable recycling method through catalytic hydrolysis to upcycle PMMA while reaching higher product purity. PMMA reacts over zeolites and produces methacrylic acid instead of methyl methacrylate offering technical, economical, and market benefits. Direct hydrolysis of PMMA over an H-type zeolite with an SiO₂/Al₂O₃ ratio of 80 produced methacrylic acid with a yield of 56% and a selectivity of 58%. Coke formed within the framework of large-pore zeolites, causing reversible deactivation of medium–strong acid sites and Brønsted acid sites. The catalytic decarboxylation of methacrylic acid primarily produces acetone and CO, and six-membered glutaric anhydride forms in solid residues.