Jisong Zhang

Design and Scaling Up of Microchemical Systems: A Review

The past two decades have witnessed a rapid development of microreactors. A substantial number of reactions have been tested in microchemical systems, revealing the advantages of controlled residence time, enhanced transport efficiency, high product yield, and inherent safety. This review defines the microchemical system and describes its components and applications as well as the basic structures of micromixers. We focus on mixing, flow dynamics, and mass and heat transfer in microreactors along with three strategies for scaling up microreactors: parallel numbering-up, consecutive numbering-up, and scale-out. We also propose a possible methodology to design microchemical systems. Finally, we provide a summary and future prospects.

Preparation of poly(p-phenylene terephthalamide) in a microstructured chemical system

A microstructured chemical system, mainly including a micro-sieve mixer, a delay loop and a stirring tank, was designed to implement the polycondensation of p-phenylenediamine (PPD) and terephthaloyl chloride (TPC) for the preparation of poly(p-phenylene terephthalamide) (PPTA). A two-step method was exhibited, which consisted of fast conversion of more than 90% of the reactive groups in the delay loop and further chain growth in the stirring tank. This new polycondensation method had several advantages, such as continuous operation at higher temperature and out of pyridine, which made the process more controllable and environmentally friendly. PPTA particles with a weight-average molecular weight (MW) from 4000 to 16 000 were obtained at different synthesis conditions, and their structures were characterized by XRD, POM, IR, EA and SEM. The apparent reaction kinetics in the delay loop was also studied, which showed that the apparent activation energy was 12 kJ mol−1 with a pre-exponential factor of 5.4 × 103 L (mol−1 s−1).

Non-aqueous suspension polycondensation in NMP-CaCl2/paraffin system — A new approach for the preparation of poly(p-phenylene terephthalamide)

A non-aqueous suspension polycondensation method was proposed to proceed the reaction of p-phenylenediamine and terephthaloyl chloride for the preparation of poly(p-phenylene terephthalamide) (PPTA). The system was operated with NMP-CaCl2 solution as the dispersed phase and inert liquid paraffin as the continuous phase. Each of NMP-CaCl2 solution microdroplet suspended in paraffin served as a microreactor where the polycondensation took place. According to the results of TGA, XRD, IR, SEM and EA, PPTA with good quality was obtained through this novel method, and a number of main factors influencing this process were investigated to determine the optimum condition for the preparation of PPTA. Besides, this two-phase polycondensation system brings many unique advantages compared to the conventional solution polycondensation method, including a sealed reaction environment keeping the reactants away from oxygen and water, easy removal of HCl to promote the reaction, well-controlled temperature and low viscosity which means less energy cost.

Highly efficient synthesis of polyvinyl butyral (PVB) using a membrane dispersion microreactor system and recycling reaction technology

We herein propose a highly efficient method for the synthesis of polyvinyl butyral (PVB), an important resin material used for laminated glass in vehicles. The condensation reaction between polyvinyl alcohol (PVA) and n-butanal was successfully implemented in a reaction system containing a membrane dispersion microreactor and an aging vessel reactor, allowing the energy costs associated with cooling and mixing of the reactant solutions to be reduced. Upon changing the original reactant from a PVA–butanal emulsion to a PVA–HCl solution, the microreactor system allowed the development of a new recycling technology for the reuse of HCl, water, and excess n-butanal present in the product solution. In addition, with the aid of a two-step n-butanal feeding method, the developed recycling technology resulted in a 98.7% n-butanal utilization ratio, while the consumption of HCl and water during the reaction process was reduced by 85.6%. These results indicate that our novel process represents a more environmentally friendly approach to the PVB synthesis.

Kinetic Study and Intensification of Acetyl Guaiacol Nitration with Nitric Acid-Acetic Acid System in a Microreactor

Nitration of acetyl guaiacol, one typical aromatic nitration, is highly exothermic and extremely fast. Better control and high efficiency can be achieved in the microreactor due to its enhanced mixing and heat transfer rates. In this study, nitration of acetyl guaiacol was carried out in a microreactor using nitric acid-acetic acid as nitrating agent. The nitration kinetics was first investigated, and a kinetic model was established and revealed good prediction of experimental results at higher temperatures. Effects of molar ratio of nitric acid-acetyl guaiacol, residence time, temperature, and nitric acid concentration on the reaction were studied in detail. Under optimized condition, 90.7% yield of desired product, 5-nitroguaiacol, was achieved with 40% of nitric acid concentration, nitric acid-acetyl guaiacol molar ratio of 2.6, reaction temperature of 120 °C, and residence time of 2 min. Compared to traditional batch reactor, microreactor showed the advantages of higher yield and selectivity, much shorter reaction time, and less use of nitric acid.

Gas/liquid/liquid three-phase flow at micrometer scale

Gas-liquid-liquid three-phase flow at micrometer scale is an important issue in the research of microfluidics, microstructured chemical system, μ-TAS, and some other fields. The research topics on the gas-liquid- liquid three-phase microflow are mainly focused on new devices and techniques of microdispersion, scaling laws of dispersed particles, flow and transport properties in microchannels, and the application of gas-liquid-liquid three-phase microflows in reaction, separation and material preparation processes. The results show the gas-liquid- liquid three-phase microflows have more complicated dispersed rules and unique flow, transport and reaction performances, compared with the gas-liquid and liquid-liquid two-phase processes. The research progress of gas- liquid-liquid three-phase microflows are summarized and the future development directions are suggested.