Selective Condensation Reaction of Phenols and Formaldehyde Using a Micromixer

摘要

The method of mixing should significantly affect the efficiency and selectivity of some chemical reactions. Some fast reactions are expected to be conducted in a highly controlled manner through extremely fast mixing and efficient heat transfer using microdevices. We studied the condensation reaction of hydroxybenzylalcohol (HBA) with phenol, to control the selectivity of bis-phenols (desired product) over tris-phenols (by-product) using various micromixers in a flow system. We attempted to terminate the main condensation reaction rapidly without raising the mole ratio of phenol to formaldehyde, in order to avoid the consecutive side reaction, by utilizing a micromixing method. We also compared the selectivity for bis-phenols under various phenol/HBA mole ratios with a batch system using a flask. The selectivity for bis-phenols using a multilamination type micromixer (channel width 40 μm) was high at low mole ratios of phenol/HBA, and mole ratios only half of that used in the batch system were necessary to obtain the same selectivity. The flow rate, however, could not be increased to more than 6 mL/min, because of the high pressure loss. Furthermore, clogging of the microchannels occurred within 2 min. To overcome these problems, a new micromixer was tested, which has several channels converging on one point (8 channels of 200 μm width), developed by MCPT. The reaction was conducted steadily at a flow rate of more than 18 mL/min with low pressure loss and without clogging. The selectivity for bis-phenols was successfully increased to a level comparable to that achieved with a multilamination-type micromixer.