Reaction Chemistry & Engineering最新文献

In this study, we investigate the valorization of 5-(hydroxymethyl)furfural (5-HMF), a versatile and pivotal renewable C6 platform chemical, into a C12 heteroaromatic triol, 5,5′-bis(hydroxymethyl)furoin (DHMF), and a C12 heteroaromatic diol, 5,5′-bis(hydroxymethyl)furil (BHMF). The carboligation of 5-HMF to DHMF is catalyzed by an N-heterocyclic carbene, 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene (TPT), generated in situ from its stable methoxy adduct, 5-methoxy-1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazoline (TPA-OMe). This reaction achieves quantitative yield in dimethyl carbonate, a more environmentally friendly solvent. The resulting DHMF precipitate was readily purified via simple filtration and washing. Moreover, an enhanced selective oxidation was conducted at the secondary hydroxyl group of DHMF to generate the ketone group of BHMF in quantitative yield by using organo-catalysts, anionic exchanger, and NaOH. We proposed and subsequently validated a cyclic catalysis mechanism for the oxidation through the colorimetric detection of the by-product, H₂O₂, in the reaction. All synthetic processes to produce these C12 triol-furoin and diol-furil compounds were successfully demonstrated on a scale ranging from 20 to 400 grams. The feasibility of these processes was established with high yields achieved under moderate reaction conditions and ambient pressure, making them suitable for large-scale production. Consequently, these C12 multi-functional chemicals can find applications in the production of bio-based aromatic polymers such as polyesters, polyurethanes, and polycarbonates.

With the ever-increasing demand for plastics, sustainable recycling methods are key necessities. The current plastics industry can manage to recycle only 10% of the 400 million metric tons of plastic produced globally. Waste plastics, in the current infrastructure, land up mostly in landfills. Although a lot of research efforts have been spent on processing and recycling co-mingled mixed plastics, energy-efficient sustainable and scalable routes for plastic upcycling are still lacking. Catalytic valorization of waste plastic feedstock is one of the potential scalable routes for plastic upcycling. Silica-alumina based materials, and zeolites have shown a lot of promise. A major interest lies in restricting catalyst deactivation, and refining product selectivity and yield for such catalytic processes. This article highlights ChemPren technology as a clean energy solution to waste plastic recycling. Co-mingled, mixed plastic feedstock along with spray dried, attrition resistant, ZSM-5 containing catalysts is preprocessed with an extruder to form optimally sized particles and fed into a fluidized bed reactor for short contact times to produce selectively and in high yields ethylenes, propylenes and butylenes. This techno-economic perspective indicates that the ChemPren technology can produce propylene at $0.16 per lb, whereas the current selling price of virgin propylene is $0.54 per lb. This technology can serve as a platform for mixed plastic upcycling, with more advancements necessary in the form of robust and resilient catalysts and reactor operation strategies for tuning product selectivity.

L-5-Methyltetrahydrofolate (L-5-MTHF) is an active form of folate and widely used as a nutraceutical due to its high bioavailability. Herein, we report an efficient one-pot three-enzyme cascade reaction for the production of L-5-MTHF starting from synthetic folic acid (FA). The newly-designed synthesis route was validated by enzyme screening and process optimization. The highly-active dihydrofolate reductase from Lactobacillus bulgaricus (LbuDHFR) was identified for asymmetric hydrogenation towards unnatural substrate FA, which could remarkably increase the synthetic efficiency. Dimethylsulfoniopropionate-dependent demethylase (DmdA) was successfully employed for directly converting tetrahydrofolate into L-5-MTHF using a cheap methyl donor. RcoDmdA from marine bacteria Ruegeria conchae was selected due to its high tolerance against the inhibition of the demethylated by-product. The optimal one-pot enzymatic synthesis could completely convert 34 mM of FA into 32.5 mM of L-5-MTHF with a molar conversion rate of 95.6%. No FA, dihydrofolate or tetrahydrofolate were detected in the final reaction mixture. Therefore, the new one-pot enzymatic method, circumventing the need for a transition metal catalyst, an unstable strong reductant and crystallization resolution, is proved to be simple, cost-effective, and easy to scale up for the green synthesis of L-5-MTHF.

This work aims to study the heat transfer performance of a sophisticated industrial suspension polymerization reactor, which is distinguished by its complex blade structure and capability in efficient heat removal as well as its precise control over temperature distribution through adjusting the flow ratio of cooling water in the agitator and jacket. To achieve this goal, the impact of flow ratio and agitator speed on the heat removal rate and fluid temperature gradient is systematically investigated by CFD simulation. Several indicators are developed to quantitatively assess the reactor's heat transfer capability and fluid temperature uniformity. In addition, a thorough investigation is undertaken to analyze the possible mechanisms by which these factors exert their influence on the heat transfer performance of the reactor. Finally, some strategies for optimal performance through adjusting operational parameters of this type of reactors are proposed.

Solvent selection is crucial for optimizing reaction outcomes of various reactions. Herein, we conducted nitrobenzene hydrogenation in a tubular-flow reactor coated with a Pd/TiO₂ catalyst using 17 different solvents and exhaustively studied the solvent effect through statistical analysis. Results show that protic solvents provide higher conversion and aniline production than aprotic ones, but solvent study could not be interpreted using simple regression alone. Rigorous analyses revealed that the hydrogen donor and acceptor abilities of a solvent are the most important factors assisting nitrobenzene reduction. Importantly, solvent solubility in H₂O and dipole moment are key sub-factors influencing nitrobenzene conversion and aniline yields, which were validated using the statistical analysis of 57 solvent parameters. Our regression model predicts that 2,2,2-trifluoroethanol is a suitable solvent for hydrogenation reactions.

An examination of the temporal dynamics of the moisture curing process of polyurethane (PUR) hot melt adhesives under varied humidity (65–85% RH) and temperature (20–40 °C) was performed via in situ Fourier transform infrared (FTIR) spectroscopy. The commencement of the moisture curing for PUR was substantiated by a reduction in peak intensity at 2271 cm⁻¹. The data revealed that the nascent phase of the moisture curing reaction aligns with the first-order reaction kinetics. Further, there was a noticeable acceleration in the rate of the PUR's moisture curing reaction with an increment in environmental humidity and temperature. Density functional theory (DFT) was harnessed to delve into the effects of additional water clusters on the PUR's moisture curing progression. The theoretical model proposed that these additional water molecules catalyzed the hydrogen transfer, thus bolstering the moisture curing reaction, a finding that corroborated with our empirical observations.

Hydrogen is widely used in industrial chemistry and acts as a promising clean energy carrier that can be produced from different hydrocarbons and water. Currently, the main sources of hydrogen are fossil fuels; however, they are associated with large CO₂ emissions. Alternatively, green hydrogen produced from water electrolysis using renewable energy is still far from large-scale industrial application owing to the poor reliability of renewable energy and water electrolysis. Therefore, the production of blue hydrogen, coupled with the CO₂ capture process, will play a dominant role in the near future in commercial hydrogen production. In this review, membrane reactor technologies based on ceramic-based dense membranes are comprehensively introduced. Membrane reactors are classified into three types according to the properties of the conductive carrier of membrane materials: (1) mixed protonic and electronic conductor (MPEC) membrane reactors, (2) mixed oxide-ionic and electronic conductor (MOEC) membrane reactors, and (3) mixed oxide-ionic and carbonate-ionic conductor (MOCC) membrane reactors. Their working principle, membrane materials, hydrogen sources, operating conditions, and performance are summarized. Finally, the challenges and prospectives of these membrane reactors are discussed for their future development.

A trifunctional catalyst facilitating a series of hydroxylation, oxidative ring opening, and aqueous-phase reforming reactions was developed to convert phenolic wastewater into syngas. The definitive screening design experiment at 250 °C for 5 h with 1.75% H₂O₂ and 2 wt% catalyst loading demonstrated the importance of Fe, Mn, and Ni among the first-row transition metals to be impregnated into hydrotalcite to acquire the trifunctional feature. The surface chemistry characterization revealed that they improved the amount of strong and weak Brønsted (SBrA and WBrA) and Lewis (SLA and WLA) acidic active sites. The mechanistic roles of these sites via semi-continuous kinetic investigation at 200–300 °C for 1–5 h with 1.75% H₂O₂ and 2 wt% catalyst loading were unraveled: (1) SBrA (surface metal oxyhydroxides) facilitated hydroxylation and homolytic cleavage producing hydroxyphenols; (2) WBrA (surface metal hydroxides) promoted ring opening of hydroxyphenols yielding oxo- and di-carboxylic acids; (3) WLA (mineral phase with a tetrahedral coordination) catalyzed reforming of acids into syngas; and (4) SLA (mineral phase with an octahedral coordination) improved the H₂ yield by promoting the water–gas shift reaction. The optimal content of Fe, Mn, and Ni was 49.4, 21.2, and 29.4 wt%, respectively, from 20 wt% of active metals on the support to achieve the maximal organic carbon removal (∼82%) and H₂ yield (∼80%) with a CO-to-H₂ ratio of 0.6, useful for chemical building block synthesis. The optimized catalyst demonstrated high activity and reusability, with a turnover number and frequency of ∼1 × 10⁶ and ∼6 × 10⁴ s⁻¹, respectively, marking a breakthrough in sustainable syngas production.

In this study, a novel method was developed to understand the liquid-state reactions occurring inside the intermediate liquid component (ILC) during biomass fast pyrolysis. A new experimental setup using a heated 300 μm inner diameter capillary microchannel with flow visualization was designed to study isothermal kinetics and reaction mechanisms of liquid-state sugar hydrolysis reactions. Heat- and flow patterns were investigated to confirm the intrinsic character of the kinetic measurements. Following the conventional dimensional analysis, observations with a high-speed camera and computational fluid dynamics modelling (CFD) in COMSOL Multiphysics® were used to confirm the hydrodynamic slug-flow pattern and the scale function of the temperature. The microfluidic reactor can operate within a temperature range of 453–533 K, up to 7 MPa, and a residence time within the hot section of 5 to 80 s, which is controlled by the volumetric flow rate. The novelty of this reactor is that under the specified operating conditions and residence times, it can provide isothermal measurements of intrinsic reaction kinetics, which have never been reported for hydrolysis systems. After hydrolysis in the microfluidic reactor, liquid samples were analysed off-line through HPLC to determine the sugar conversion and product yields. A fitting kinetic approach was developed to treat the kinetic data and extract intrinsic kinetic parameters describing sugar hydrolysis, key reactions occurring in the softening phase of biomass fast pyrolysis that are too often overlooked. It is proposed to integrate this experimental kinetic information into complete biomass fast pyrolysis models to take into consideration the solvent-like reactional environment.

Here we demonstrate that Ga,Al-*BEA zeolites are effective bifunctional catalysts for para-xylene (p-xylene) production from bio-derived 2,5-dimethylfuran (DMF) through tandem Diels–Alder/dehydration reactions. A series of catalysts was synthesized via direct (one-pot) and post-synthesis techniques to introduce Brønsted and Lewis acid sites. The synthesis approach employed in this study avoids cost- and time-intensive processes typically associated with the preparation of metal-substituted *BEA zeolite catalysts for p-xylene production. Our findings reveal that Ga,Al-*BEA catalysts enhance DMF conversion and p-xylene selectivity in comparison to Al-*BEA zeolite. The pairing of Ga and Al in a single catalyst yields fewer byproducts, such as 2,5-hexanedione, 1-methyl-4-propyl-benzene, alkylated products, and oligomers. Comparisons of zeolites prepared with different Ga content reveal a higher turnover frequency for DMF conversion to p-xylene over Ga,Al-*BEA catalysts prepared by a one-pot synthesis compared to Al-*BEA catalysts. We observed a correlation between Ga content and p-xylene selectivity and yield, which is attributed to the Brønsted acidity of Ga framework sites (with reduced acid strength compared to Al sites) and to the Lewis acidity of extra-framework Ga species. The latter contribution was confirmed by analysis of Ga-impregnated Al-*BEA zeolites, which are less active than framework species but have a positive effect on p-xylene selectivity. Our collective findings indicate that tuning zeolite acidity by optimizing the amount of heteroatom incorporation in the crystal framework to tailor the speciation and strength of acid sites is beneficial to maximize p-xylene production from renewable resources.