Exothermic reactions safety issues

At this point it is important to consider safety. Safety issues are obviously of paramount importance and have to be dealt with adequately, especially in exothermic reactions. Specifically, laboratory and pilot reactors are usually made of small-diameter tubes and therefore effective heat removal can be achieved. On the other hand, commercial reactors have large diameters, approaching adiabatic conditions, and heat build-up may appear (Dutta and Gualy, 2000). 

However, several exothermic reactions are characterized by moderate or low values of the B number here, the transition stages from safe to runaway conditions may cover a quite wide range of the parameter values, and the choice of the boundaries for the safe region is very discretional. Hence, not surprisingly, the main discrepancies among the different criteria are found at low B numbers [14, 15]. Moreover, in this case, runaway is a less dramatic phenomenon posing the problem to decide whether a bland explosion still represents a safety issue. In this case, an effective runaway criterion should be more properly determined on the basis of the actual ability of the system to comply with certain levels of temperature and pressure. 

Safety. When transferring processes from the laboratory to the pilot plant, it is important to identify and address potential safety issues as early as possible in the transfer process. Typically, calorimetry studies and process hazard reviews are carried out to meet this requirement. Calorimetry experiments can assist in the identification and quantification of reaction exotherms associated with the process. This information can then be used to determine the capability of the pilot equipment to control the reaction. 

Reaction safety- hsnasii test data, hazardous bond groups, and exothermic reactions. Powder handling/milling-diist explosion issues. 

Of the many potential safety issues, two are singled out for coverage here because they must be confronted often in the design of chemical, petroleum, and petrochemical plants and in other plants in which exothermic reactions and operations occur at elevated pressures. 

Free-radical polymerization is a highly exothermic process and reactor temperature control is an important issue for both polymer quality and operation safety. At the temperatures used in commercial practice, most radical polymerizations are irreversible. However, because it is an exothermic reaction, at sufficiently high temperatures the reaction becomes reversible and complete conversion cannot be achieved. Methyl methacrylate is a major monomer that suffers from this problem, with an equilibrium concentration of 0.139 mol at 110°C [12[. 

Process safety is an important issue for chemical industry in general and for exothermic reactions and reactions involving hazardous chemicals in particular. High hold-up of reactants in conventional batch reactors leads to very high impact in the case of accidents. A common approach to handle fast exothermic... 

When handling strong exothermic processes or hazardous substances, safety issues also became a major driver for the use of microreactors. Finally, several academic studies can be found in the literature focusing on the analysis of mass transport and flow characteristics within microfluidic charmels by using electrophilic aromatic substitutions as model reactions. 

A crude yield of 90% was obtained in ether at —25 °C. When performed in a batch mode on 70 mg scale, no safety issues were taken and an 81% yield was obtained [42]. Reaction calorimetry reveals a very exothermic reaction after feeding and subsequent mixing with an initiation period that is, the response of the heat flow curve is delayed by about 1 min as compared to the feed curve (see Figure 11.6). Therefore, the heat release rate with this mode of addition is not feed controlled. The reaction is very sluggish, since the reaction occurs at a single blow as soon as 60% of the material has been added. Calculating the worsttemperature rise shows that the reaction would rapidly increase in temperature and can approach the solvent reflux temperature, possibly throwing out the reaction mixture in case of... 

The thermal effect of any reactions is mild and does not induce a phase change or a significant change in the temperature of the process units. Hence, the specific enthalpies of the feed and effluent streams, h and h2, of the process units are of comparable magnitude 2 = 2,s/ i,s = 0(1). (Note that this assumption is by no means restrictive rather, it reflects current industrial practice. For example, the use of adiabatic units in highly exothermic processes is avoided for safety reasons, and external cooling systems are preferred. This issue is addressed in detail in Chapter 7.)... 

---