Reaction Chemistry & Engineering最新文献

Chelating agents can increase the porosity of coal by leaching metal ions from it. Therefore, selecting the most suitable chelating agent based on the characteristics of the coal type is crucial when applying chelating agents. In this study, lignite from southwest China was chosen as the sample. Four chelating agents, namely tetrasodium iminodisuccinate (IDS), diethylenetriaminepentaacetic acid (DTPA), tetrasodium aspartate diacetate (ASDA), and tetrasodium glutamate diacetate (GLDA), were evaluated for their impact on the leaching of constant metal ions (CMIs). The leaching effect of CMIs was characterized and analyzed using inductively coupled plasma, scanning electron microscopy, and Brunauer–Emmett–Teller measurements. The results indicated that the ASDA chelating agent was the most effective in leaching Ca²⁺, Mg²⁺, Fe^2+/3+, and Al³⁺. Under the optimal concentration condition of 2500 mg L⁻¹, the leaching effect of CMIs from different chelating agents could be ranked as: ASDA > DTPA > IDS > GLDA. The contact angle of the ASDA chelating agent with the coal sample decreased from 48.2° at 1 s to 26.5° at 20 s. The metal minerals on the surface of the coal dissolved under the action of the ASDA chelating agent, and the micropores on the coal surface transitioned to mesopores and macropores. The pore volume of coal samples increased from 0.0254 cm³ g⁻¹ to 0.0276 cm³ g⁻¹, and the pore size increased from 3.26 nm to 4.06 nm. As the pore size of the coal increased, the permeability also significantly increased.

We investigate acid-catalyzed upcycling of PPG polymer, emphasizing crucial features on multiple length scales that span reaction engineering on macroscopic length scales down to zeolite catalyst design on the nanoscale. We modified a previously described semi-batch reactor configuration to minimize coking and enhance recovered selectivities by incorporating rapid quenching of reaction products (instead of slower quenching with a condenser, which facilitates sequential coupling reactions), and decreased the initial carrier-gas residence time in the bed consisting of mixed catalyst and PPG polymer, further reducing the deposition of solid residues in the used catalyst. Our results highlight the importance of tight interfacial contact between the catalyst surface and the initial PPG polymer reactant, which is achieved via a pretreatment that removes adsorbed water, for drastically increasing the propionaldehyde selectivity, particularly for the large surface-area mesoporous catalysts. Our best catalyst consisted of mesoporous Y zeolite synthesized at an alkalinity of 0.16 M and exhibited nearly the same high propionaldehyde selectivity of approximately 95% (86% propionaldehyde yield) for a PPG polymer with molecular weights of 425 and 2000 Daltons (Da), suggesting the absence of mass transport restrictions. We also deconvolute the catalyst attribute between extra-framework aluminum (Al_EF) content and mesopore external surface area that most sensitively controlled propionaldehyde selectivity. This was performed by synthetically incorporating Al_EF content into our optimum catalyst, at a high and low alumina dispersion. The high dispersion alumina catalyst consisted of a uniform 10 nm-thick alumina layer covering the interior pores of the mesoporous Y catalyst, whereas the low dispersion alumina catalyst had a completely phase-separated alumina phase, commensurate in size to the zeolite particles. Our results demonstrate that Al_EF content in the catalyst decreases propionaldehyde yield by increasing the amount of solid residues in the catalyst post reaction, and had a minor effect on the propionaldehyde selectivity. These results point to a Brønsted rather than Lewis acid-catalyzed mechanism of catalysis for PPG polymer upcycling to propionaldehyde. In summary, our study demonstrates the most sensitive controlling attribute of the zeolite catalyst for selective propionaldehyde synthesis is its mesoporosity (as reflected in the mesopore volume and surface area) and that the multiscale details of the catalyst and reactor design also have profound consequences in achieving high propionaldehyde selectivity and yield.

Various heterogeneous catalysts have been investigated in the transesterification of glycerol with ethylene carbonate to glycerol carbonate in a batch reactor, and a commercially available 4A molecular sieve exhibited relatively high catalytic performance for its surface strong basic and acidic sites. Further, an integrated vacuum reactive distillation process was developed for the transesterification in the presence of the 4A molecular sieve. The produced ethylene glycol could be efficiently removed from the reaction system to overcome the equilibrium, and excellent glycerol conversion (99%) and glycerol carbonate selectivity (>99%) were obtained under the optimal reaction conditions. The recycling and the scale-up experiments demonstrate the excellent practical potential of the present process, thus providing an efficient reaction process for the preparation of glycerol carbonate.

This study aims to bridge significant knowledge gaps in the understanding of graphene growth mechanisms. We enhance current kinetic models through a detailed investigation of C₂H₂ deposition processes on solid graphene surfaces. These processes represent key elementary reaction steps in the complex heterogeneous network responsible for pyrocarbon formation during chemical vapor deposition and infiltration processes. Unlike previous methodologies that relied on analogies with gas-phase systems, our research meticulously explored the actual system, providing a comprehensive overview of the reactions involved in graphene growth at both armchair and zigzag edges. Utilizing transition state theory, we calculate accurate, temperature-dependent rate constants for all elementary reactions in graphene edge growth. This sheds light on the mechanisms and kinetics of pyrocarbon growth, including the potential for structural defect formation. Findings are compared with analogous gas-phase reactions responsible for soot particle formation, assessing the impact of surface interactions. A lumping technique is applied to reduce the complexity of species and reactions while preserving the accuracy of the chemical description. As such, this approach offers valuable insights into relevant pathways paving the way towards a deep understanding of the chemistry of the pyrolysis of hydrocarbons aiming to produce nanomaterials with targeted properties.

In order to improve the performance and efficiency of a process, understanding the influence of various variables on a desired output or response is a common task in engineering challenges. This paper aims to investigate the effect of three parameters – namely the free H₂SO₄ rate, the solid rate, and the percentage of P₂O₅ in the ranges of 2.4–5.8%, 32–37%, and 28–32%, respectively – on the reactive crystallization phase during the phosphoric acid production. The experiments were carried out using a filterability workbench and a semi-continuous reactor that replicated the operating conditions of the dihydrate process. The investigation conducted using the factorial and Box–Behnken methods enabled the optimization and determination of operational significant conditions affecting the filterability of the phosphoric slurry to be thoroughly evaluated and controlled. Overall, response surface methodology (RSM) has several advantages over classical one-variable-at-a-time optimization, including the ability to assess the interaction effect between variables on the response of interest and the ability to generate large amounts of data from a limited number of experiments. Furthermore, the desirability function approach has been successfully implemented for the identification of the optimal conditions, and phosphogypsum crystals offering high and low filterabilities were characterized and compared. Finally, we anticipate that our paper will serve as a foundation for the explanation of how the natural giant gypsum crystals of Naica and Pulpí were formed.

The adoption of electrochemical reactors has effectively mitigated the environmentally detrimental challenges in industrial manufacturing processes. A novel method for the eco-friendly synthesis of hexanitrostilbene using a difunctional electrochemical reactor is introduced, facilitating effective blending of feedstock and transformation of C–C bonds into CC bonds simultaneously. The effectiveness has been confirmed by significant improvements in yield, increasing from 36% to 58.5% when exposed to 8 mA current for 30 min. Moreover, the purity rose from 86% to 98.2%, accompanied by a notable elevation in the decomposition temperature of hexanitrostilbene.