In recent years, self-optimization strategies have been gradually utilized for the determination of optimal reaction conditions owing to their high convenience and independence from researchers' experience. However, most self-optimization algorithms still focus on homogeneous reactions or simple heterogeneous reactions. Investigations on complex heterogeneous gas–liquid–solid reactions are rare. Based on the Nelder–Mead simplex method and Bayesian optimization, this work proposes a reaction optimization framework for optimizing complex gas–liquid–solid reactions. Three gas–liquid–solid reactions including the hydrogenations of nitrobenzene, 3,4-dichloronitrobenzene, and 5-nitroisoquinoline are investigated, respectively. Reaction parameters (temperature, hydrogen pressure, liquid flow rate, and gas flow rate) are optimized. Compared with the traditional OVAT method, the proposed Bayesian based optimization algorithm exhibits remarkable performance with higher yields (0.998, 0.991 and 0.995, respectively) and computational efficiency.

Bayesian based reaction optimization for complex continuous gas–liquid–solid reactions

Abstract For di-nitroaromatics hydrogenation, it is a challenge to achieve the multi-step hydrogenation with high activity and selectivity due to the complexity of the process involving two nitro groups. Consequently, many precious metal catalysts suffer from low activity for this multi-step hydrogenation reaction. Herein, we employ a fully exposed Pt clusters catalyst consisting of an average of four Pt atoms on nanodiamond@graphene (Pt n /ND@G), demonstrating excellent catalytic performance for the multi-step hydrogenation of 2,4-dinitrotoluene. The TOF (40647 h −1 ) of Pt n /ND@G is significantly superior to that of single Pt atoms catalyst, Pt nanoparticles catalyst, and even all the known catalysts. Density functional theory calculations and absorption experiments reveal that the synergetic interaction between the multiple active sites of Pt n /ND@G facilitate the co-adsorption/activation of reactants and H 2 , as well as the desorption of intermediates/products, which is the key for the higher catalytic activity than single Pt atoms catalyst and Pt nanoparticles catalyst. 

pdf/fully-exposed-pt-clusters-for-efficient-catalysis-of-multi-32sy9sg0bo.pdf

Fully exposed Pt clusters for efficient catalysis of multi-step hydrogenation reactions

Continuous hydrogenation of nitriles to primary amines with high selectivity in flow

Aromatic nitration with mixed acid is an important step in the industrial synthesis of basic industrial chemicals, while the highly exothermic and heterogeneous nature of the reaction renders difficulties in achieving high safety and efficiency. In this work, a continuous flow microreactor system was developed for the nitration of nitrobenzene. Under the premise of high conversion and selectivity, the reaction time and temperature were reduced from more than 2 h and 80 ℃ in industrial operation to 10 min and 65 ℃ in microreactors, respectively. The reaction mechanism was verified that the reaction took place not only in the bulk aqueous phase but also at the phase interface. The kinetic parameters were then determined based on the assumption of pseudo-homogeneous reaction mixture. These findings may shed important insights into the high degree of controllability of nitration for a better process design and reactor optimization. 

Heterogeneous nitration of nitrobenzene in microreactors: Process optimization and modelling

Abstract In this work, the liquid–liquid two‐phase pressure drop and mass transfer characteristics in micro‐packed beds with different shaped packing are investigated. The experimental results show that the liquid–liquid mass transfer performance of micro‐packed bed is significantly affected by both apparent flow rates and phase ratio. By changing the characteristic size of the micro‐packed bed, the experimental results show that the average volume mass transfer coefficient has no obvious correlation with the length of the bed, which indicates that the flow and dispersion behavior along the length of the micro‐packed bed is basically stable. By considering dispersion strengthening, vortex strengthening and size effect, a semi‐empirical model for predicting liquid–liquid mass transfer performance in a micro‐packed bed is established for the first time. The model is in good agreement with the experimental results and has strong applicability to various shaped packings. In addition, by considering the contribution of inertia force, viscous force and interfacial tension to energy dissipation, a semi‐empirical model of liquid–liquid two‐phase pressure drop in a micro‐packed bed is established. The pressure drop prediction model can also be applied to different shaped packings. 

Liquid–liquid mass transfer and pressure drop behavior in micro‐packed beds with different shaped packings

Hydrogenation kinetics of m-dinitrobenzene in a continuous micro-packed bed reactor

The selective hydrogenation of halogenated nitroaromatic compounds is of great importance in the fine chemical industry. However, the hydrogenation reactions in commonly utilized batch reactors suffer from the undesired dehalogenation, resulting in higher requirement for subsequent separation processes and severe corrosion to industrial fatalities. In this work, a H-flow system with the micropacked bed reactor was developed for the selective hydrogenation of halogenated nitroaromatic compounds and the reduction of 3,4-dichloronitrobenzene was selected as the model reaction. With the optimal hydrogenation conditions, the yield of 3,4-dichloroaniline was obtained as high as 99.8% under mild conditions. With this strategy this flow system was successfully employed to the reduction of other chlorinated nitroaromatics also demonstrating low dehalogenation. The H-flow system enables negligible dehalogenation and remarkable yield of target product with higher efficiency and lower energy cost compared with the batch reactor.

Continuous hydrogenation of halogenated nitroaromatic compounds in a micropacked bed reactor

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Hydrogenation kinetics of m-dinitrobenzene in a continuous micro-packed bed reactor

Continuous hydrogenation of halogenated nitroaromatic compounds in a micropacked bed reactor