Reaction Chemistry & Engineering最新文献

Flow biocatalysis has emerged as a promising alternative to conventional batch processes, offering improved energy efficiency, enhanced reaction control, and reduced waste generation. This review presents recent advances in flow biocatalysis, with a focus on system design, enzyme handling strategies, and catalytic performance. Based on enzyme retention, these systems are broadly categorized into flow biocatalysis using free enzymes, where enzymes are co-eluted with the product, and flow biocatalysis using immobilized enzymes, where enzymes are immobilized within the reactor. The latter are further divided into wall-coated and packed systems, including multilayered coatings, grafted surfaces, and monolithic structures. Representative applications in pharmaceutical synthesis, fine chemicals, and environmental remediation are discussed to illustrate the practical impact of these technologies. Finally, future perspectives are outlined, highlighting the potential of carrier material innovation, reactor design optimization, and data-driven process control to further drive the development of flow biocatalysis.

Nitro compounds are widely used as building blocks in many industrial syntheses, and are a key component of therapeutic drugs, pesticides and explosives. Due to the harsh environmental conditions associated with their traditional preparation, the development of biocatalyzed processes is crucial for the pharmaceutical and chemical industries. For this purpose, N-oxygenases appear as a relevant option due to their ability to oxygenate primary amines obtaining partially or fully oxygenated derivatives. Streptomyces, which constitute the main source of these enzymes, are microorganisms involved in the biosynthesis of antibiotics and other relevant secondary metabolites. In this study, agarose-immobilized Streptomyces griseus whole cells were utilized as a biocatalyst with N-oxygenase activity. To enhance enzymatic performance, the system was stimulated with extracellular media derived from microbial cocultures, aiming to induce secondary metabolism. Specifically, the addition of cell-free broths from S. griseus : Bacillus cereus cocultures (70 : 30 w/w) resulted in p-aminobenzoic acid to p-nitrobenzoic acid conversion yields exceeding 60%, demonstrating the efficacy of coculture-derived elicitors in modulating enzymatic performance. Taken together, these characteristics make this biocatalyst a promising candidate for N-oxygenation reactions on a preparative scale.

Theaflavins (TFs) are the principal quality and active compounds present in fermented tea, generated during the fermentation process. Due to the exceedingly low concentration of TFs in black tea, the in vitro synthesis of TFs has emerged as a predominant trend in industrial production. Despite significant advancements in the in vitro research of TFs in recent years, several challenges remain in the preparation of TFs according to established literature methods. These challenges include the high cost of natural enzyme preparation, difficulties in preservation, and poor thermal and chemical stability. Consequently, the development of efficient and stable catalysts has emerged as a critical issue for the industrial preparation of TFs. This study investigated the feasibility of utilizing Cu-BTC (copper(II) benzene-1,3,5-tricarboxylate) metal–organic frameworks (MOFs) as biomimetic catalysts for the synthesis of TFs from catechins. Cu-BTC was synthesized using a solvothermal method and characterized. The synthesized Cu-BTC exhibited an octahedral structure and demonstrated commendable thermal stability. The enzyme-like activity of Cu-BTC was evaluated using catechol as the substrate, yielding kinetic parameters of V_max = 0.0338 mM s⁻¹ and K_m = 14.19 mM, which indicated substantial polyphenol oxidase-like catalytic activity. Cu-BTC was employed to catalyze the oxidation of catechins to synthesize TFs. The results indicated that the total yield of catechins using Cu-BTC as a biomimetic catalyst was 30% higher than that achieved through chemical oxidation methods and 50% higher than that of tyrosinase. The optimal catalytic reaction conditions were determined as follows: a reaction temperature of 80 °C, a reaction time of 60 minutes, a pH of 5.0, and a Cu-BTC dosage of 0.05 g mL⁻¹, resulting in a total yield of TFs of 800 μg mL⁻¹. This study verified that the copper-based MOF Cu-BTC was not only facile to prepare, but also exhibited excellent catalytic activity and thermal stability, which opens promising prospects for the development of new biomimetic catalysts for the synthesis of TFs.

The effective removal of iodine-129 from gaseous emissions during used nuclear fuel processing is critical for minimizing environmental contamination and ensuring environmental regulatory compliance. Recent research has focused on optimizing process air, scrubber conditions, and integrating complementary techniques, such as solid sorbents as a polishing step, to improve iodine capture efficiency. The efficiency of a caustic scrubber is influenced by several factors, such as pH, temperature, gas–liquid contact time, and the presence of oxidants, yet the existing literature tends not to consider how these factors might interact or change in importance with process scaling. This perspective advocates for reconsidering how to mitigate many of these factors, especially in view of the transition from laboratory bench to pilot scale and beyond. This paper reviews the principles, operational parameters, and advancements in caustic aqueous scrubbing for radioiodine mitigation, aims to direct the next scientific pursuit of this technology, and inform environmental decision-making.

In response to the prominent environmental risks associated with traditional smelting processes for bastnaesite–monazite mixed rare earth ores, this study proposes a carbochlorination synergistic metallurgy technology based on alumina-based fluorine fixation, systematically elucidating the phase transformation mechanism of mixed rare earth ores. Thermodynamic calculations confirmed the feasibility of the reactions. Experimental results demonstrated that under the conditions of 10% Al₂O₃ addition, a chlorination temperature of 800 °C, a chlorine flow rate of 10 L min⁻¹, and a reaction time of 60 min, the chlorination rates of rare earths, Ca, Ba, and Fe reached 94%, 99%, 96%, and 99%, respectively, with a fluorine fixation efficiency of 75.72%. Combined XRD and in situ SEM-EDS analysis revealed that Al₂O₃ reacts with fluorine in the mineral lattice to form AlF₃, effectively blocking the generation path of hydrogen fluoride while simultaneously promoting the conversion of rare earth oxides to rare earth chlorides. Based on the shrinking core model, a two-stage interfacial chemical reaction-controlled kinetic equation with activation energies of 27.48 KJ mol⁻¹ and 14.83 KJ mol⁻¹ was established, revealing the stepwise mechanism of the carbochlorination process.

We report a structured, multi-stage catalytic system for converting CO₂ into solid carbon via the reverse water–gas shift (RWGS) reaction and carbon monoxide disproportionation. By spatially separating the reaction zones using spiral and hollow-tube catalysts, the system achieves high CO₂ conversion, suppresses methanation, and enables continuous carbon collection. Stable performance is maintained under continuous flow, and additional experiments confirm that RWGS occurs in situ within the carbon capture zone, supplying CO for downstream carbon formation. SEM and Raman analyses reveal that fibrous carbon structures are maintained throughout the reactor axis, with a gradual decrease in fiber diameter toward the downstream positions. Despite this morphological refinement, carbon productivity remains stable, demonstrating the durability and scalability of this CO₂-to-carbon platform for carbon-negative applications.

In three-phase CO₂ methanation dibenzyl toluene is used as the liquid phase in a slurry bubble column reactor. At reactor temperatures (T_R) higher than 260 °C deactivation of the Ni/SiO₂ catalyst was observed. After deactivation for 120 h at T_R = 320 °C, stationary operation is possible with a loss of catalytic activity of ≈50%. Based on experimental results, it can be stated that deactivation is caused by decomposition of dibenzyl toluene at high reactor temperature, resulting in carbon deposition on the catalyst surface.

In this study, a novel covalent organic framework material, g-TPYP-COF, was systematically investigated. By leveraging the time-dependent density functional theory (TDDFT), the first 100 excited states of its monolayer structure were precisely calculated to comprehensively explore the material's optical absorption properties within a specific energy interval. Initially, first-principles calculations were performed to obtain the stable two-dimensional porous planar structure of g-TPYP-COF along with its key structural parameters. Subsequently, an in-depth electron–hole analysis was carried out, and it was conclusively determined that the eight main excited states were all of the local-excitation type. Finally, the ultraviolet-visible (UV-vis) spectrum was simulated. The results clearly revealed a remarkable correlation between the oscillator strength and the UV-vis absorption spectrum. It was found that the material exhibited a strong optical response mainly in the blue-violet light band, with an extremely high maximum absorption intensity of 8 564 470 L mol⁻¹ cm⁻¹. Collectively, these results firmly demonstrate that g-TPYP-COF holds great potential as a high-performance light-absorbing material, which could open up new opportunities for its application in various optoelectronic fields.

The recycling of polyolefins is gaining attention as society transitions toward a more circular economy. Pyrolysis is a promising method; however, its product distribution can be unpredictable. Moreover, the resulting compounds often require additional hydrogenation if they are to be used as feedstock for naphtha crackers. An alternative approach is hydrogenolysis, in which polyolefins are depolymerised into shorter, fully saturated alkanes using a heterogeneous catalyst under a hydrogen atmosphere. Literature indicates that the hydrogenolysis of polyolefins appears to be a slow process, requiring reaction times up to 96 hours to achieve a significant yield of useful products, such as naphtha or fuels. In this work, it is shown that these long reaction times are resolved when physical mass transport limitations are overcome: in 40 minutes, full conversion of low-density polyethylene to gas and liquid products is reached. Introducing a hollow-shaft mechanical stirrer instead of no or limited stirring significantly increases the gas contact area and mass transfer coefficient to the polymer melt, resulting in a decrease in mass transport limitations and thus an increase in overall reactivity. Monitoring the (hydrogen) pressure over time generates more insight into the reaction kinetics, as at a similar hydrogen consumption level, the product distribution changes if the system is stirred instead of kept stagnant. The authors would like to emphasise the importance of these findings regarding the influence of hydrogen mass transfer through the melt, as this could also result in novel catalysts possibly performing even better than currently reported, making hydrogenolysis a more viable option for the chemical recycling of polyolefins.

Cu·ZnO·Al₂O₃ (CZA) catalysts promoted with alkaline earth oxides (MgO, CaO and BaO) were prepared and tested in the CO₂ hydrogenation to methanol. The aging conditions was varied to observe the transformation of the amorphous georgeite into crystalline malachite phase. At the standard aging conditions (60 °C and 100 min), only the traditional CZA catalyst and the MgO-promoted catalysts showed highly crystalline malachite phases. For CaO and BaO promotion, the malachite phase began to be detected only after prolonged aging times. The precursors that formed the malachite phases presented higher surface areas and TPR profiles with lower reduction temperatures. The CO₂ hydrogenation at 30 bar and 10 h⁻¹ showed increased methanol productivity for the catalysts that formed the malachite phase, with the difference being more significant at lower temperatures. The MgO-promoted catalysts showed the highest productivity and selectivity to methanol at all temperatures studied, also producing less CO. These results were interpreted in terms of the incorporation of Mg²⁺ into the lattice to form magnesian-zincian-malachite phase in the precursor, which after calcination and reduction may favour the formation of Cu/MgO interfaces that are highly active for the hydrogenation of the CO molecules formed by RWGS.