Hexafluoroisopropanol (HFIP) is an important intermediate of sevoflurane, an inhalation anesthetic for pediatric anesthesia, and it is produced industrially mainly by the catalytic hydrogenation reduction of hexafluoroacetone (HFA). In previous studies, the hydrogenation of HFA was usually performed in batch reactors with the disadvantages of harsh reaction conditions and low conversion rates. On the other hand, continuous flow technology is increasingly being used for intrinsically safe hydrogenation processes to avoid safety issues caused by the accumulation of hydrogen gas in high-pressure reactors. In this study, a continuous flow system was developed in a micropackedbed reactor, and the intrinsic kinetics of the reaction were studied. This continuous flow process minimized mass and heat transfer problems and achieved higher productivity in terms of time and space yield than traditional process methods. Under kinetically controlled conditions, the operating conditions were varied with temperature between 363 and 393 K, hydrogen pressure of 10 bar, and catalyst loading between 0.1 and 0.5 g. In the end, we achieved conversion and selectivity of up to 99% and a space−time yield of about 9 times that of the batch reactor. To further investigate the long-term stability of the reaction system, the flow system was successfully operated for 90 h at a liquid flow rate of 0.5 mL/min. In addition, residence time distribution curves at different flow rates were determined, and possible mechanistic pathways of the reaction were explored based on the Langmuir−Hinshelwood method. The reaction was found to be an adsorption−desorption type with a mechanism of competitive adsorption by H 2 dissociation, and the thermodynamic properties associated with the rate constants were estimated.
The applications of flow chemistry (continuous flow reactions) in the synthesis of pharmaceuticals and fine chemicals require more advanced optimization algorithms to guide laboratory-scale and industry-scale optimization. Although several Bayesian Optimization (BO) frameworks have been developed, they are rarely equipped with state-of-the-art noise-handling acquisition functions and have not been benchmarked by multiple real-world continuous flow kinetic models. In this study, we developed FlowBO for flow chemistry, equipped with the recently-developed MOO algorithm qNEHVI that can better handle experimental noise and make parallel recommendations. Also, five kinetic models built from experimental results, including four series reactions, were used as benchmarks for FlowBO and two other recognized BO frameworks. The results show that FlowBO outperforms in all four series reaction cases with optimization results >99.9% for conversion and selectivity. At the same time, FlowBO offers a range of optimum advantages with a wide choice of temperature, residence time, and reactant concentration, facilitating process optimization for subsequent steps (i.e. separation).
The hydrogenation of nitroaromatics to prepare aromatic amines plays a crucial role in the chemical industry. Traditional hydrogenation has the risk of hydrogen leakage from the equipment, and its catalyst has the disadvantage of being easily deactivated and difficult to recover. In this study, we designed an efficient and stable mesoporous catalyst, Pd@SBA-15, which was constructed by impregnating the nanopores of the mesoporous material SBA-15 with palladium nanoparticles. The catalyst was then filled in a micro-packed-bed reactor (MPBR) for continuous flow hydrogenation. The designed continuous flow hydrogenation system has two distinctive features. First, we used mesoporous Pd@SBA-15 instead of the traditional bulk Pd/C as the hydrogenation catalyst, which is more suitable for exposing the active sites of metal Pd and reducing the agglomeration of nanometals. The highly ordered porous structure enhances hydrogen adsorption and thus hydrogenation efficiency. Secondly, the continuous flow system allows for precise detection and control of the reaction process. The highly efficient catalysts do not require complex post-treatment recovery, which continues to operate for 24 h with barely any reduction in activity. Due to the high catalytic activity, the designed mesoporous Pd@SBA-15 showed excellent catalytic performance as a hydrogenation catalyst in a continuous flow system with 99% conversion of nitroaromatics in 1 min. This work provides insights into the rational design of hydrogenation systems in the chemical industry.
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