The invention relates to a method for preparing
naphthalene sulphonic acid by sulfonating
sulfur trioxide in a
microreactor, belonging to methods for preparing dye intermediates in the field of
fine chemical engineering. The method comprises the following steps: taking
alkyl halide and
nitromethane as an
organic solvent,
naphthalene and derivative thereof as the
raw material and organic solution of liquid
sulfur trioxide as a sulfonating agent, preparing a solution according to the mol ratio of the
organic solvent, the
raw material and the sulfonating agent of 19-74:1:1-3 in the
microreactor of with channel with the
diameter of 10-50 microns, and sulfonating the reaction solution to prepare the
naphthalene sulphonic acid by controlling the sulfonation
reaction temperature to be between 17DEG C below zero and90 DEG C. The method adopts a
continuous flow reactor, solves the problem of impossible transient mixing in the conventional reactor, prevents secondary reaction caused by local excess, and is especially suitable for strong
exothermic reaction, fast reaction and flammable and explosive reaction. Compared with the preparation technology in the traditional
batch reactor, the invention has the advantages of no generation of waste water and waste acid, clean and environment-friendly technology, consumption of sulphonic acid close to the theoretical quantity, fast
reaction speed, low sulfonation temperature, high product yield, good
repeatability, high labor productivity and low equipment cost.