Batch reaction process safety chemistry

Process chemistry issues and their effects on batch reaction systems safety are presented in Table 2, beginning on page 11. This table is meant to be illustrative but not comprehensive. 

Understanding the behavior of all the chemicals involved in the process—raw materials, intermediates, products and by-products, is a key aspect to identifying and understanding the process safety issues relevant to a given process. The nature of the batch processes makes it more likely for the system to enter a state (pressure, temperature, and composition) where undesired reactions can take place. The opportunities for undesired chemical reactions also are far greater in batch reaction systems due to greater potential for contamination or errors in sequence of addition. This chapter presents issues, concerns, and provides potential solutions related to chemistry in batch reaction systems. 

The fine chemicals business is characterized by a small volume of products manufactured. Therefore, batch production predominates and small-scale reactors are used. The need to implement fine chemistry processes into existing multiproduct plants often forces the choice of batch reactors. However, safety considerations may lead to the choice of continuous processing in spite of the small scale of operation. The inventory of hazardous materials must be kept low and this is achieved only in smaller continuous reactors. Thermal mnaways are less probable in continuous equipment as proven by statistics of accidents in the chemical industries. For short reaction times, continuous or semicontinuous operation is preferred. 

All process development starts with chemistry. The selection criteria for the most suitable chemistry for a continuous process do not suffer from the same constraints as those for a large-scale batch process. For example, highly exothermic reactions are not only possible in a flow reactor, but are in fact preferred [47]. As operator exposure will be low and so will stock levels, different safety considerations come into play that may allow utilisation of otherwise intolerably toxic reagents. Process telescoping is a necessity to minimise the number of intermediate isolations. Examination of all these factors is facilitated by online analysis because of its speed and maintenance of experimental integrity (i.e. no requirement for sampling). 

One of the main aspects of modem chemistry is the safety of the chemical processes. It is easy to see that the volume of a batch reactor must be some orders of magnitude higher than that of the continuous-flow microreactor to reach the identical quantity of final products (using equal amounts of reactants). The small quantity of reactants in the reactor minimizes the potential of thermal explosion by dangerous reactions. Indeed, explosion or depressurization of reaction systems with hazardous substances in the continuous microreactors leads only to insignificant technical problems or to a minimum leakage of chemicals, as opposed to the scales of explosions or leaks in standard reactor volumes. Microreactors, with their narrow channel dimensions, hold such a small quantity of reaction fluid that a mechanical failure in one reactor requires merely a temporary shutdown and subsequent replacement. 

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