Preparation Of Nano-materials Via Precipitation In Microchannel Reactors

Microchannel reactors can optimize the chemical engineering process, especially in the fields of highly exothermic and fast reactions. Recently, nano-particles have drawn great attention due to their excellent characteristics. A microchannel is very attractive to produce nano-particles, as reaction conditions can be precisely controlled quite easily during continuous production. From this viewpoint, a number of studies on forming nano-particles have been conducted. However, most of the studies were taken under low-velocity and low- concentration conditions. The output was limited. Our studies were focused on preparing nano-materials with high throughput.T-type, Y-type and multi-channel reactors were designed in this thesis. The efficiencies of micromixing in different kinds of micro reactors were compared. The Villermaux-Dushman parallel competing reaction system was used to quantify the micromixing quality in an explicit way. The mixing of two water flows with different colors was observed using a digital video camera providing snapshots. The efficiency of micromixing is increased with the increasing of Re number. It is also affected by the structure of the micro reactor. The multi-channel reactors have high efficiency of micromixing just as the single ones. When Re number is high enough, Xs is close to 5.0×10^-4, suggesting almost perfect micromixing.High throughput methodology is suitable for fast precipitation reactions. Barium sulfate nano-particles prepared in microchannel reactors are much smaller and more even-distributed than those prepared in conventional ways. Monodispersed BaSO₄ nanocrystals of 18 nm were prepared when the flow rates were 20 ml/min and concentrations of the reactants were 0.5 mol/l. An 8-channel micro reactor has the ability of producing nano barium sulfate of nearly 1 kg/h.The combination of micro reactors and conventional process offer a flexible way to prepare various kinds of nano-materials. We successfully prepared crystallized boehmite and zinc sulfide by combining the micro reactors and conventional process. When the pH values were between 7 and 9, pure and well crystallized boehmite was obtained after aging for a certain time. Well crystallized zinc sulfide with the diameters of 2.5⁴.5 nm were successfully synthesized.