A kinetic model of the tech. 2,4,5-trichlorophenol synthesis was formulated consisting of 3 consecutive and 3 parallel reactions of the reaction network. Modeling was performed for a lab.- and an industrial-scale semibatch reactor (SBR). The equation system was numerically solved using the backward differential formula method for stable integration. In addn. to the normally operating lab. and industrial SBR, the disturbed operation (failure of cooling) of the industrial reactor was also simulated. The process was optimized by simulating variations of process parameters.