Microflow high-temperature processing

The application of high pressure in liquid-phase reactions is less common in microflow when compared to high-temperature processing. However, also pressure can have a pronounced effect on the reaction outcome [23], Reactions that are accompanied by a decrease in volume (activation volume) are typically accelerated by pressure. In addition, equilibrium reactions can be shifted toward the side that has a decrease in volume. As such, the use of pressure can lead to an improvement in chemo-, regio-, and stereoselectivity. Such equipment and procedures are far from the common laboratory setups and practices since these require strict safety precautions. However, miniaturization of the reactor setup allows to alleviate many risks associated with high-pressure chemistry [24]. 

In this section, we discuss the cases where the use of microflow reactors allows us to conduct reactions under unconventional conditions, such as high temperatures, which significantly accelerate the rates of the reactions. In the macrobatch processes, however, the use of such reaction conditions may cause undesirable side reactions, such as the decomposition or subsequent reactions of products. Precise temperature control and short residence time, which minimize the consecutive side reactions, are responsible for successful reactions in microflow systems. 

Realization of a flow sensor depends on its specific application. Overall, the spatial and transient resolution and the compatibility of the sensor within the desired device are of major concern [6]. In addition, the protection of the fluids and components demands a reduction in the thermal crossover from the flow sensor. The microflow sensors are usually automatically integrated with the microchannel during the fabrication process. The sensing element should be a resistor that has a resistance with high temperature sensitivity [2, 4, 9]. The heater of the sensor is often fabricated from a platinum or polysilicon resistor and acts as a microheater while the upstream and downstream temperature sensors are made from either polysilicon resistors or thermopiles. Such materials have excellent chemical resistance, hiocompatihUity, and high TCR [9]. 

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