Reaction Chemistry & Engineering最新文献

In this work, a facile and efficient ultrasound-assisted fast synthesis of quinazolinones from o-aminobenzamides and aldehydes is reported. The reaction proceeds smoothly under ambient temperature and pressure conditions without the need for a metal catalyst in just 15 minutes. In addition, this approach exhibits broad substrate tolerance and provides a series of quinazolinones with moderate to excellent yields. The results reported here reveal an important new application of ultrasound-assisted synthesis in the fast synthesis of valuable organic products.

In an umbrella-shaped microchannel reactor, the continuous selective aerobic oxidation of toluene derivatives to aromatic aldehydes over a Co/Mn/Br catalytic system using acetic acid/water as the solvent was studied. Taking the oxidation of p-nitrotoluene (PNT) to p-nitrobenzaldehyde (PNBD) as a model, the effects of the Co²⁺(Mn²⁺) amount, ratio of Co²⁺, Mn²⁺ and Br⁻, reaction temperature, reaction pressure, oxygen flow rate, residence time and water content on the reaction were systematically investigated. Under the optimized reaction conditions, an 11.8% conversion could be achieved with a good selectivity of 67.1% to PNBD, significantly superior to the results obtained in a kettle reactor. In addition, various toluene derivatives could be tolerated by the present reaction process. This aerobic oxidation over the microchannel reaction technology has the features of an easy-to-operate process and easily controlled reaction parameters, providing an economical and environmentally friendly protocol for the synthesis of aromatic aldehydes.

Covalent linkages between lignin and cellulose/hemicellulose, referred to as lignin carbohydrate complexes (LCCs), have been identified to significantly contribute to the refractory nature of lignocellulosic biomass. However, experimental resolution of LCCs is limited, leading to a very limited knowledge of the chemical and structural details of LCCs. As a result, the present work uses first-principles based computational methods to quantify the reaction mechanisms, kinetics and thermodynamics associated with the formation and deconstruction of the prominent phenyl glycoside (PG) LCC linkage in biomass. The two previously proposed formation mechanisms, hemi-acetal and transglycosylation, are associated with significant activation barriers, suggesting these pathways are kinetically limited. A new mechanism is proposed, the electrophilic addition of hemicellulose to a lignin quinone methide (QM) intermediate, that possesses facile kinetics and is exergonic, suggesting it could be the pathway responsible for the significant fraction of PG linkages observed in the native biomass. Moreover, PG formation showed a composition dependence, suggesting that xylans will have higher fractions of PG linkages compared to mannans, explaining why softwoods and hardwoods have different reported types of LCCs. Additionally, the reaction mechanisms, kinetics and thermodynamics associated with the deconstruction of the PG LCC linkages in biomass under acidic conditions are investigated. The chemical degradation of the hemicellulose moieties is the primary competing reaction; however, the deconstruction energetics demonstrate that breaking PG linkages is kinetically and thermodynamically favored in acid catalyzed deconstruction. This indicates that PG linkages may not significantly contribute to the biomass recalcitrance.

Metallic sealants are widely used with high-temperature membranes. Here we show that their use in supported molten-salt membranes results in order-of-magnitude differences in CO₂ flux and introduces O₂ co-permeation. The ‘short-circuiting’ effect they introduce has important implications for the design of future experiments, and the interpretation of past work.

Decarbonization of clean energy carriers such as H₂ by coherent integration of multiphase chemical pathways with inherent carbon mineralization is a thermodynamically downhill pathway designed for a sustainable climate, energy, and environmental future. In this effort, a low-temperature water–gas shift reaction (WGSR) with Pt/Al₂O₃ catalysts is integrated with in situ carbon mineralization in a multiphase reaction environment. The hypothesis that Pt-based catalysts favor selective formation of H₂ over CH₄ has been investigated. H₂ yields increased by 30.8%, 9.5%, 8.3%, and 1.7% in the presence of Ca(OH)₂, Mg(OH)₂, Mg₂SiO₄, and CaSiO₃ relative to the blank experiment without the sorbent at constant experimental conditions of 250 °C and reaction time of 12 hours in the presence of Pt/Al₂O₃ catalyst with initial CO and N₂ pressures of 8 bar and 12 bar, respectively. These studies unlock the feasibility of advancing single-step multiphase pathways for enhancing H₂ yields with inherent CO₂ capture and mineralization for a low carbon and sustainable energy and resource future.

Removing carbon contaminants from the surfaces of pulse-compressed gratings is a critical aspect of maintaining the functionality and efficiency of a chirped pulse amplification system. In this study, a method of in situ cleaning pulse-compressed gratings by low-pressure plasma is proposed and delves into the microscopic chemical reaction mechanism involved in eliminating carbon contaminants. Firstly, the surface contamination state and formation mechanism of the grating were analyzed, and the influence of the contaminants on the morphology and diffraction efficiency was discussed. The diffraction efficiency of the grating post-contamination can decrease by one-third. After a 5.5 hour low-pressure air plasma cleaning, carbon contaminants on the grating surface were completely removed, restoring both the diffraction efficiency and the surface morphology of the grating. Reactive molecular dynamics simulations were executed to model the intricate reaction mechanisms of eliminating carbon contaminants using low-pressure plasma. The cleaning efficiency, particularly on pulse-compressed gratings, was studied under low-pressure plasma conditions to elucidate the underlying mechanisms responsible for carbon contaminant removal. The research revealed a detailed pathway of chemical reactions initiated by the interaction of carbon contaminants with the plasma cleaning. Notably, the study identified key stages in the process, including the breakdown of carbon chains, the formation of new chemical bonds, and the evolution of molecular structures on the grating surface. Insights gained from this study provide valuable information for optimizing plasma cleaning processes tailored to pulse-compressed gratings, paving the way for improved maintenance strategies in optical applications.

Most conventional zeolite synthesis takes place in closed batch autoclaves that cannot be monitored or controlled during the process. Moreover, the study of time-dependent parameters of the synthesis with the conventional “cooling-opening” procedure not only reduces accuracy as a series of reactors (never 100% identical) needs to be started in parallel (and stopped at different times), it is also labor intense. Furthermore, the classic batch concept does not permit the intermediate addition of species without disrupting synthesis and the cooling-reheating effects. In this study, we developed a technique for zeolite synthesis monitoring in one-pot experiments using the sampling feature of fed-batch (FB) reactors. These one-pot syntheses can save time and ingredients instead of performing plenty of classic batch experiments. In addition, we could control and manipulate the zeolite synthesis by using the feeding function of the FB reactor and the intermediate addition of precursors at operational temperatures and pressures. Stannosilicate and zincosilicate syntheses were carried out via the FB reactor to investigate the intermediate timed-addition and the possibility of optimizing feeding rates of heteroatoms opposed to a classic synthesis, which faces challenges when a high amount of heteroatom precursor presents at the start. Finally, a modified FB platform was further developed to be able to monitor essential kinetic and synthetic parameters on-line (T, P, and also pH) on-line without intervention. For instance, pH profiles can allow one to estimate key events in zeolite synthesis, but in the art, these profiles are always measured ex situ (including cooling effects etc.).

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.