Safety methodology for the operation of a continuous intensified reactor

Abstract : Today the chemical industry has to deal with new challenges. In addition to producing more and faster we must produce safer and cleaner. Thusly, new perspectives have emerged to improve production processes. Green chemistry is certainly one of the most relevant examples but not the only: process intensification and safety also focus on finding creative ways to reduce the use of toxic chemicals and minimize the human and environmental impact. Indeed significant progress has been reached in the development of new reactor technologies: today, miniaturised and continuous processes are being developed to attain better heat transfer and safer conditions compared to traditional batch or semi-batch operations. This makes it possible to attain a better chemistry by employing higher concentrations using less solvent and reaction volumes. In this field, new prototypes of "heat-exchanger/reactors" are a good illustration: built like a plate heat exchanger, additive plates are inserted in order to carry out chemical synthesis. But these new concepts of reactor design are less familiar than traditional ones, and research is necessary not only to assess their feasibility and potential but also to develop specific operating protocols. The present paper deals with the establishment of a new methodology in order to transpose an exothermic reaction from a batch process to a continuous intensified one in terms of safety. The propionic anhydride esterification has been chosen to illustrate the different steps which have to be completed: the methodology first starts with a risk assessment using bibliographic sources and calorimetric tools. The bibliography study provides information about the chemical hazards and the synthesis while the thermodynamic and kinetic behaviours of the reaction are characterised by experimental data obtained in a reaction calorimeter. The hazard and operability study (HAZOP) is then applied to the intensified process in order to identify potential hazards and to provide a number of runaway scenarios. Afterwards a dedicated software model has been used to assess the feasibility of the reaction in the "heat-exchanger/reactor" but also to estimate the temperature and concentration profiles during synthesis and to determine optimal operating conditions for safe control. Using these conditions the reaction has been carried out in the reactor. The good agreement between experimental results and the simulation validates the model to describe the behaviour of the process during standard run. In the last part of the method the behaviour of the process is simulated following probable malfunctions: the adiabatic temperature rise is calculated along the spatial coordinates of the reactor as well as the time to maximum rate after reactor shut down. Finally, the dynamic evolution of the temperature profiles is obtained by simulation for the different runaway scenarios extracted from the HAZOP study.