Investigation Methods for the Characterization of Normal Operating Conditions

33 Investigation Methods for the Characterization of Normal Operating Conditions 

A good experimental characterization is the prerequisite to any application of the safety technical assessment criteria for normal operation. If the opportunity is lacking, the safety assessment must remain superficial. The only information which under cer- 

The probability that the desired reaction is accompanied by a number of undesired processes is very high. Synthesis optimization activities may improve the selectivity, but a value of 1 with respect to the desired reaction is seldom achieved. A calculated heat of reaction can account for these side reactions only if they are definitely known. Otherwise the calculated value has to be regarded as a net value which corresponds to the desired reaction only and which may significantly be wrong with respect to the process in total. 

In most cases the heat flow signal approaches the base line almost asymptotically. If the upper integration limit is fixed at a time value which does not coincide with the moment at which the reaction has reached completion, because the signal cannot clearly be distinguished fi om base line noise anymore, the value determined for the gross enthalpy of reaction will be too small. Some reactions will never achieve complete conversion under the conditions proposed for the process. Possible reasons for such a situation may be, for example, chemical equilibria, pH-value dependent inhibitions, or solubility limits. 

This initial error in the determination of the heat of reaction may propagate if it is attempted in a subsequent step to determine thermokinetic data firom these experimental results. This will be explained with the help of an example in Section 4.3.3.S. 

---