ESTIMATION OF REACTION RATES AND KINETIC PARAMETERS FROM NON- ISOTHERMAL TRANSIENT TEMPERATURE DATA OF A BATCH REACTOR
Prof. Damaraju Phaneswararao (Retired), Department of Chemical Engineering IIT Delhi.
9th November, 2017, Thursday at 4.00 pm in Seminar Hall, Dept of Chemical Engineering.
The homogeneous exothermic hydrolysis reaction of acetic anhydride in acetic acid solvent catalysed by sulphuric acid was used to demonstrate the utility of transient temperature data obtained by employing a 1 litre stirred uninsulated thin walled stainless steel batch reactor. A mathematical model was used for characterizing the radiation, natural convection and evaporation mechanisms of heat loss from the batch reactor and the model parameters were estimated by using experimental data obtained by conducting specially designed heat loss experiments. The heat loss model was also validated by verifying with additional experimental data. Different reaction experiments with varying initial reactant and catalyst. compositions and initial reactor temperatures were performed to obtain transient temperature data. Due care was taken to obtain maximum accuracy of temperature recording by using bare chromel constantan thermocouples and an accurate constant temperature bath to serve as a reference temperature junction for the thermocouple. A rigorous mathematical model for the reactor was developed which took reactor wall dynamics besides the different mechanisms of heat loss. A Chebyshev polynomial was fitted to the temperature data based on least squares fitting procedure which was then analytically differentiated to obtain temperature derivative as a function of time. Knowing the temperature derivative, and solving the mathermatical model by Gear’s method, reaction rates were estimated as a function of reaction mixture composition and temperature. A rigorous reaction mechanism was proposed based on literature data pertaining to acid catalysed hydrolysis. The Arrhenius parameters of rate constants for the acid catalysed hydrolysis reaction mechanisms besides the direct molecular reaction mechanism of sulphuric acid reaction with acetic anhydride were determined. The sulphuric acid catalysed hydrolysis reaction system was used to demonstrate thermal runaway of a batch reactor, and high parametric sensitivity of a countercurrent cooled tubular fixed bed reactor besides steady state multiplicity and limit cycle behaviour in a continuous flow stirred tank reactor. Fallacies in the recent published literature on the experimental and theoretical approaches used to study reaction kinetics from nonisothermal reactor temperature data, and interpret runaway behavior of the above reaction system were pointed out. The utility of the above reaction system to study the performance of conventional PID and advanced control schemes for control of a batch reactor under runaway conditions was successfully demonstrated experimentally and theoretically. Further work to investigate the influence of thermal and mass micromixing effects on the reactor performance as well as chaotic behavior besides accurate kinetics study involving exact Hammett acidity function are suggested.
References:-
1. PHANESWARARAO, D., AND PAREY, S.K.B., IND. CHEM. ENGR., 30, T87 (1988) 2. Wilson H. Hirota , Rodolfo B. Rodrigues , Cla ́udia Sayer , Reinald Giudici "Hydrolysis of acetic anhydride:Non-adiabatic calorimetric determination of kinetics and heat exchange”, Cmical Engineering Science, 65 (2010) 3849-3858.
3. Phaneswararao damarju “Comments on the paper titled “Hydrolysis of acetic anhydride: N, on- adiabatic calorimetric determination of kinetics and heat exchange” by Wilson H. Hirota, Rodolfo B. Rodrigues, Cláudia Sayer, Reinaldo Giudici Chemical Engineering Science, 65 (2010),3849–3858” CHEMICAL ENGINEERING SCIENCE, VOL 144, 444-445 (2016)