Overpressurization of tanks and vessels continues to be a hazardous scenario of concern in industrial plants. Although much has been published in the literature on the design and selection of pressure protective systems, a systematic comparison of the hazard rates for different systems as a function of operating conditions is not easily obtained. This study evaluates five commonly used pressure protective systems using Markov models. Quantified hazard rates are presented as a function of pressure demand rates and maintenance schedules using typical failure rate data. Various alternatives for meeting a given hazard rate goal can be readily compared and subjected to cost analysis for selection purposes.
Catalytic and thermal hydrodealkylation of alkyl-substituted aromatics is reviewed. Data are presented for pilot plant hydrodealkylation of a Cg to C11 aromatic stock to produce an aromatic stream containing greater than 40 vol. 7 0 mixed xylenes. A detailed kinetic analysis of the process provides five grouped isomer rate constants for the five consecutive dealkylation reactions progressing from CI, aromatics to benzene. It was found that the operating range for maximum xylene yield per pass i s also the range of optimum production cost. The extension of the Houdry Detol process i o the controlled hydrodealkylation of C9 to CI1 provides a new commercial technique for producing maior quantities of mixed xylenes.YDRODEALKYLATION is now commercialized as a major starting jvith a pentamethyl benzene (Cll). a sequence such a s
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