Reaction Chemistry & Engineering最新文献

In order to improve the performance of carbonylation reactions in flow, we compared the tube-in-tube system to a gas–liquid two-phase setup. We found that the two-phase slug flow reactor significantly improved the yield and throughput of the reactions tested. First, we performed a reference reaction, methoxycarbonylation of 4-chlorobenzonitrile, using conditions described in the literature and obtained 57% calculated yield in the biphasic setup and 16% in the tube-in-tube setup, with side product formation of 1% and 8% respectively. The reaction was further optimized in both apparatuses, improving the yield in the biphasic setup to 86%, while the tube-in-tube method was limited to about 34%. Finally, a 1.5 g scale-up of a project-relevant building block yielded 73% of the product in the tube-in-tube setup vs. 92% when two-phase flow was used, with more than a ten-fold increase in throughput in the biphasic method. Using gas–liquid flow enabled higher yield and throughput due to direct contact of gas and liquid, better control of CO equivalents and intensification of process conditions: higher temperature, pressure and concentration in the system and significant reduction of residence time.

Glycolysis is the most promising chemical recycling method to depolymerize poly(ethylene terephthalate) (PET) with ethylene glycol (EG) into the monomer bis(2-hydroxyethyl) terephthalate (BHET). Boosting the depolymerization kinetics while staying under comparatively mild and green reaction conditions is required to bring glycolysis to industrial scale utilization. This work suggests achieving this goal by a combined pressure, temperature and co-solvent addition approach. By using the environmentally friendly γ-valerolactone (GVL) as a suitable co-solvent in the traditional PET glycolysis system, and slight temperature and pressure elevation, the kinetics was boosted by almost two orders of magnitude compared to the standard literature process. A kinetic model was employed to describe the kinetics as a function of temperature and GVL concentration. The optimized condition allowed nearly full conversion after 2 minutes only.

The oxidation of glyoxal by nitric acid to glyoxylic acid is a complex process with parallel and consecutive side reactions. The complete reaction kinetics has not been thoroughly reported before. In this work, a continuous flow microreactor system, consisting of micromixers, preheating capillary loops, a capillary microreactor and quenching device, is designed to achieve oxidation under homogeneous conditions. A complete kinetic model is established and all kinetic parameters are obtained. The effects of the molar ratio of nitric acid to glyoxal, reaction temperature and concentration of nitric acid on the reaction are investigated systematically. Based on the process reengineering of existing devices, two schemes of segmented feeding (nitric acid in several segments) and recirculating feeding (incompletely reacted material is returned to the reactor for reaction) are proposed. Finally, the optimal reaction conditions are determined. At 68 °C (the initial molar ratio of nitric acid to glyoxal was 1.26, with a final molar ratio of 1.4 after segmented feeding at once, the molar ratio of sodium nitrite to glyoxal is 0.15, and the mass concentration of nitric acid is 35%), the yield of glyoxal acid is 89.2% and the selectivity is 95.9%. This work refines the kinetic data for the oxidation reaction of glyoxal nitrate. It is of theoretical importance for optimising reaction performance (temperature and residence time regulation strategies) and reactor design.

Dual-phase membranes have been successfully developed using x wt% Ce_0.9La_0.1O_2−δ and 100 − x wt% La₂CuO_4+δ (xCLO-(100 − x)LCO) with no alkaline earth metals contained in the system. The 60CLO-40LCO dual-phase membrane exhibits the highest oxygen permeation rate of 0.25 mL min⁻¹ cm⁻² under He sweep gas conditions at 950 °C. Additionally, excellent CO₂ tolerance was obtained using this sample. Its stable oxygen permeability and outstanding CO₂ tolerance performance make the 60CLO-40LCO dual-phase membrane highly promising in the oxyfuel technologies for the CO₂ capture and sequestration application.

Glycolic acid finds extensive applications in the production of biodegradable polymers, pharmaceuticals, and fine chemicals. In this study, a Pt catalyst supported on the Sn-Beta zeolite (Pt/Sn-Beta) was developed to achieve the efficient and highly selective catalytic oxidation of ethylene glycol with molecular oxygen to prepare glycolic acid at near-room temperature (30 °C). Characterization results, including XRD, TEM, XPS, FT-IR, and O₂-TPD, revealed that the relatively uniform dispersion of Pt particles, the optimal density of Lewis and Brønsted acid sites in the catalyst, and the synergistic interaction between Sn and Pt sites might be key factors contributing to the excellent catalytic performance of the Pt/Sn-Beta catalyst. By optimizing the reaction conditions, a 90% conversion of ethylene glycol and an 81% selectivity of glycolic acid were obtained. Furthermore, Pt/Sn-Beta exhibited excellent stability, with no significant decrease in catalytic performance after six repeated uses.

Based on the synthesis of mesoporous zirconium phosphate in the presence of magnetic nanoparticles (NPs) and its functionalization with propyl sulfonic acid groups, a new and effective heterogeneous acidic catalyst (MMZP-Pr-SO₃H) was prepared. It was attempted to alter the catalyst's properties in this study in order to boost reactant conversion yield and remove unselective reaction pathways by offering complementary characterization. MMZP-Pr-SO₃H was used for the eco-friendly and efficient preparation of various tetrazole derivatives through condensation of aryl nitriles and sodium azide in water solvent at 60 °C. This protocol was also practical for benzoazole (benzimidazole, benzoxazole, and benzothiazole) synthesis starting from the in situ oxidation of benzyl alcohol, which demonstrates the dual role of the MMZP-Pr-SO₃H catalyst in oxidation and condensation reactions. For both investigated reactions quantitative conversion of the desired product was obtained and the catalyst was simply separated from the reaction mixture by employing an external magnetic field. The MMZP-Pr-SO₃H catalyst was regenerated and reused for at least 6 runs without a significant decrease in reaction yield. With the aid of lenses on catalyst active sites, the structural characteristics of the recycled catalyst were thoroughly examined. In contrast to our earlier attempts to study the structural features of the MZP and ZP substrates and use them as catalysts for organic reactions, the MMZP-Pr-SO₃H catalyst offers a sustainable and clean synthetic methodology for the large-scale preparation of derivatives of tetrazoles and benzoazoles.

A new experimental technique has been developed for studies of transport diffusion in the Knudsen regime. At atmospheric pressure, the Knudsen regime is prevalent for gas diffusion in mesoporous materials. A unique, specially designed Ultra-High Vacuum Diffusion Setup has been built that allows the generation of high Knudsen numbers at macroscopic scales by employing ultra-high vacuum conditions. The diffusion channel of the setup can, therefore, act as a magnified nanopore model to help study the impact of different pore geometries on Knudsen diffusion. Pore channels with varying pore length, pore cross-sectional shape, and pore diameter were realised and tested with this setup. The results obtained using this experimental technique can be compared with analytical and computational results to gain insight into diffusion in nanoporous materials.

This study aims to prepare titanium dioxide (TiO₂) with a narrower band gap, namely black TiO₂, using sodium tetrahydroborate (NaBH₄) as a reducing material with different mixing ratios and microwave heating, which is a faster, greener, and simpler method than the existing method using furnace heating. Scanning electron microscopy (SEM) inspections indicate that incremental changes of agglomeration are observed upon increasing the NaBH₄ mixing ratio, with a moderate 2-fold increase in the particle size (up to 49.9 ± 3.0 nm). The X-ray diffraction (XRD) patterns and Raman spectroscopy confirm that TiO₂ is fully converted to the anatase phase after microwave-assisted synthesis. The gradual shift in intense E_g phonon vibration mode at 141 cm⁻¹ to a longer Raman wavelength infers simultaneous defect formations on both pristine and reduced TiO₂ surfaces. Furthermore, high-resolution X-ray photoelectron spectroscopy (XPS) measurements confirmed the formation of Ti³⁺ and O_v. The photodegradation results showed that after visible light irradiation for 4 hours, the T-50 sample exhibited R6G degradation of 49.2 ± 2.0%, outperforming the pristine P25. Moreover, bandgap reduction is successfully achieved from 3.20 eV (P25) to 1.50 eV (T-50) from diffuse reflectance UV-vis (DRUV) spectroscopy measurements. Photoluminescence (PL) spectroscopy found that the energy transfer efficiency of the T-50 sample was 30.6 ± 4.6% during the decomposition of R6G. This combined effort promotes the use of potent black TiO₂ through photocatalysis towards fabrication of highly efficient remediation materials in the future.

Liquid hydrogen is a comparatively high volumetric energy density option for storage and transportation. It however typically requires refrigeration to ∼20 K, which incurs a substantial energy penalty. An additional contribution to this energy consumption is the required exothermic conversion between ortho- and para-hydrogen spin isomers. To realise this conversion in a practical timeframe, the use of a spin conversion catalyst is required. To this end, available reaction data in the literature for the ortho–para forward and backward reaction for the range of catalysts considered is summarised and reviewed. Furthermore, the application of a range of reaction kinetic expressions to this assembled data is considered. Available conversion data for ortho-para conversion is sparse, particularly in the temperature–pressure range relevant to hydrogen liquefaction processes. This is less the case for the reverse para–ortho conversion, presumably a consequence of these data being experimentally easier to access. It can also be concluded, based on the available conversion data, that there is currently no compelling reason to adopt anything more complex than first-order kinetics during hydrogen ortho–para conversion reactor design. Finally, a case study is executed which quantifies the sensitivity of this design to current reaction kinetic parameter uncertainty. This review highlights the sparsity of experimental conversion data at relevant cryogenic conditions and the need for a more comprehensive and fundamental understanding of the origins of the spin conversion catalyst effect and how it is impacted by various deactivation mechanisms.

Catalysts for the selective catalytic reduction of nitrogen oxides (NO_x) with NH₃ are currently limited by low activity at low temperatures and deactivation under hydrothermal conditions. Herein, we developed a highly active and hydrothermally stable zeolite-based catalyst, Fe–Cu/SSZ-13, using Bayesian optimization (BO). An initial surrogate BO model was constructed and used to identify the optimal Cu and Fe composition through iterative experiments. At each step, the next candidate which optimized the objective function and maximized the acquisition function was selected. The optimized catalyst comprised 2.0 wt% Cu and 2.0 wt% Fe in SSZ-13 zeolite, which was prepared by an incipient wetness impregnation. This catalyst achieved 95.8% NO_x conversion at 250 °C and excellent hydrothermal stability, which outperformed the commercial catalyst. Structural characterization demonstrated that its excellent hydrothermal stability resulted from the effect of optimized loading of Fe co-cation. This study highlights the effectiveness of employing BO to design multicomponent catalysts.