An integrated approach for the early detection of runaway reactions by using UV-visible and temperature sensors

Monitoring the dynamical behaviour of chemical reactors is of paramount importance in industrial plants, especially when the process involves exothermic reactions and runaway phenomena may occur. One of the main issues is the lack of reliable sensors suited to detect in time the onset of a runaway reaction. In this context we report here on a novel approach for the early runaway detection based on the integration of two kinds of sensors: i) a set of three Pt-thermoresistances for measuring the temperatures both within the reactor and in the cooling jacket and ii) a UV-visible probe for the indirect evaluation of the conversion through measurements of light absorbance. The measured variables (temperature and absorbance) were used as input to our model based on the divergence calculation [1,2]. The early warning detection system (EWDS) was tested for the hydrolysis of acetic anhydride to acetic acid, a very simple reaction but releasing ~60 kJ per mole of anhydride consumed. The responses given by EWDS were examined during the simulation of runaway reactions in a laboratory batch reactor working under isoperibolic conditions. Different chemical heat flows were generated by varying the concentration of H2SO4, which catalyses the hydrolysis, and adding at once the acetic anhydride into the reactor. The behaviour of the detection criterion was evaluated comparing the EWDS signals using both temperature and absorbance as input variables, with the responses obtained from only temperature measurements. Results showed the importance of an input variable directly related to conversion in such kinds of processes where other enthalpy variations (i.e. due to an endothermic mixing of the reagents) may hide a runaway reaction occurring. References J. M. Zaldívar and F. Strozzi, Phase-space volume based control of semibatch reactors, Chem. Eng. Res. Des., 88 (2010) 320-330. C. Ampelli and G. Maschio, Investigation of Thermal Runaway in Semibatch Chemical Reactors by an Early Warning Detection Device, Chemical Engineering Transactions, 26 (2012) 57-62.