A Systematic Procedure for the Assessment of the Thermal Safety and for the Design of Chemical Processes at the Boiling Point

A systematic procedure is presented for application in designing safe processes or in assessing safety of existing processes that are performed at or could reach the boiling point. The evaporative cooling is very efficient, but the maximal rate of heat dissipation is limited by two factors.One is the flooding of the vapor tube; the second is the swelling of the reaction mass due to ebullition. No reliable method is available for predicting the behaviour of a reactor at boiling point. For both cases, correlations are proposed for calculating the maximum admissible rate of heat release. They are based on the physico-chemical properties of the boiling solvent and on the geometric data of the reactor.These tools are linked together in a general procedure for the design of safe reaction processes where the boiling point plays an important role. They can also be used to assess the safety of existing processes

The Thermal Risk of Autocatalytic Decompositions: A Kinetic Study

A method is presented for the estimation of the 'time to maximum rate under adiabatic conditions' of autocatalytic decompositions and for their safety assessment. This method is based on the kinetics: a first-order reaction in competition with a Prout-Tompkins step was choosen. Isothermal or temperature-programmed Differential Scanning Calorimeter curves were used to obtain the kinetic parameters. The method requires the heat release rates at the start of the reaction and at its maximum. It is in agreement with previously published ones, but is more easy to apply and allows, therefore, to performe a quick assessment of the safety of a process. Results found for the adiabatic case were confirmed by Accelerating Rate Calorimeter experiments

A microreactor-based system for the study of fast exothermic reactions in liquid phase: characterization of the system

A new system combining a microreactor and a microcalorimetric chip was investigated. The small size of the microreactor channel permits maintaining isothermal conditions necessary for the kinetic characterization of highly exothermic reactions. These conditions are not easily obtained in classical calorimetric systems. The degree of mixing in the microchannel, which plays an important role for the characterization of fast reactions, was determined experimentally using an iodate–iodide system and confirmed by calculations. The calorimetric system was calibrated by performing the neutralization reaction of NaOH with H2SO4 in the microchannel. Several optimizations of the microreactor design allowed to raise the sensitivity of the system and to preheat the entering fluids. The results obtained were repeatable and reproducible. The establishment of the heat balance and the evaluation of the various resistances allowed a better global understanding of the system

Reaktionstechnische Vorteile in Konkurrenz zum Gefahrenpotential: Chemical and Theoretical Advantages in Competition with the Hazard Potential

In most industrial syntheses, one or more reactive groups must be introduced in a raw material before any synthesis becomes possible at all. Since natural raw materials are mostly not reactive by themselves, they are forced to reaction by the use of highly reactive materials. This high reactivity may appear to be an advantage in that a high reaction rate, meaning high productivity, is achieved. But the drawback is that the high reaction rate is often coupled to a poor selectivity. Thus, the use of highly reactive materials is submitted to the art of chemists and chemical engineers, in order to obtain the desired result.Additionally, the high reactivity is also the cause of the hazards linked to the handling of these materials. If released, they are able to react in an undesired way with the environment or with living bodies. Thus, most of them are toxic for humans or for the environment. Consequently, they can only be used if specific safety measures are taken, which presents a technical challenge and is also a cost factor. The fact that products whose objective is to improve the quality of life can only be manufactured by using highly reactive materials is either unknown or, if known, not accepted by the public. Some examples stemming from the industrial practice will illustrate the way how highly reactive materials can be used in a safe and economic way despite of the restraining conditions implied by the hazards. The technical development allowed great improvements, but there is also space for even more improvements in the future

On Risk Acceptance in the Industrial Society

The public, and society in general, is concerned by risks arising from technological projects and industrial activities. Responsible handling can only be achieved if the required knowledge about the hazards, and their consequences, is available in the industry and can be communicated to the public. Chemical industries occupy a special position in this context, since accidents, even if seldom, may have a strong impact on the public.One possible way to achieve acceptance is education and information, which facilitate communication between the different parties. Some experiences in the education of professionals and risk communication in the chemical process industry will be presented

ChemInform Abstract: Determination of Heats of Reaction Under Refluxing Conditions

The accuracy of thermal measurements under reflux conditions strongly depends on the experimental conditions. The temperature difference TJ–TR imposed on the system and the temperature of the reactor lid and reflux equipment play an important role. The optimization of these parameters and their use in the evaluation of different chemical model reactions is shown