1,720,986 research outputs found
AN INTEGRATED APPROACH FOR THE EARLY DETECTION OF RUNAWAY REACTIONS BY USING UV-VISIBLE AND TEMPERATURE SENSORS
No full textWe report here on a novel approach for the early runaway detection in chemical reactors, based on the integration of two kinds of sensors: i) a set of three Pt thermo-resistances for measuring the temperatures both within the reactor and in the cooling jacket and ii) an UV-visible probe for the indirect evaluation of the conversion through measurements of light absorbance. The measured variables (temperature and conversion) were used as input to our model based on the divergence calculation. The early warning detection system (EWDS) was tested for the sulphuric acid catalyzed esterification of acetic anhydride and methanol, a very simple reaction but releasing ~70 kJ per mole of anhydride consumed. The responses given by EWDS were examined during the simulation of runaway reactions in a lab-scale reactor working under batch isoperibolic conditions. Different chemical heat flows were generated by varying the concentration of the sulphuric acid and adding at once the acetic anhydride into the reactor. The behaviour of the detection criterion was evaluated comparing the EWDS signals using both temperature and conversion as input variables, with the responses obtained from only temperature measurements. A detailed kinetic model was also developed to solve the differential energy and mass balance equations and define the runaway boundaries. Results showed the importance of an input variable indirectly related to conversion in such kinds of processes where other enthalpy variations (i.e. due to an endothermic mixing of the reagents) may hide a runaway reaction occurring
Fitting isoperibolic calorimeter data for reactions with pseudo-first order chemical kinetics
Full text linkThe non-linear least squares fitting of the chemical heat flow and the reactor temperature are compared for reactions with
pseudo-first order chemical kinetics carried out in an isoperibolic calorimeter operating quasi-isothermally. Both methods give very
similar results for the reaction rate constant and enthalpy of reaction but fitting the reactor temperature appears to have some advantages
especially when there is an enthalpy of mixing of the reagents
La calorimetria di processo: uno strumento per il monitoraggio e controllo di reattori industriali
No full text
Applicazione della Calorimetria a Temperatura Oscillante allo studio di processi di polimerizzazione
No full textTemperature Oscillation Calorimetry (TOC) is a technique for the on line determination
of heat transfer coefficient UA, and is therefore suitable for studying processes where there
is a large increase in the viscosity and a consequent decrease in UA as the reaction
proceeds.
The free radical polymerization of methyl methacrylate in ethyl acetate has been studied
in a stirred, jacketed calorimeter with a volume of two litres. Sinusoidal temperature oscillation
of amplitude 1-2°C and period 5-6 minutes are imposed on the fluid circulating in
the jacket. The heat transfer coefficient is obtained from an analysis of the oscillating
parts of the jacket and reactor temperatures, while the chemical heat flow is obtained from
the non-oscillating parts of these temperatures.
The results obtained show the utility of TOC in studying polymerization processes. A limitation
has been encountered with concentrated solution where both the temperature
oscillation and the value of UA may become irregular. Under these conditions a correlation
between UA and the stirred torque may be used to correct the values of UA
Analisi di sicurezza di processi altamente reattivi mediante l'uso di tecniche calorimetriche integrate
No full text
On line determination of the heat transfer coefficient in polymerization reactors
No full textPolymerization processes are characterized by strong exothermicity and a large increase of the viscosity, that influence the kinetics of the reaction and the heat and mass transfer phenomena.
Technique developed in the T.U. of Berlin by the research group of Prof. Reichert that permits to solve some problems of commercial calorimeters
The principle of this method is based on an oscillatory response that is evaluated during the reaction in order to determine on-line the variation of the global heat transfer coefficient (UA
Studio dell'idrolisi dell'anidride acetica utilizzando un sistema calorimetrico semplice e a basso costo
No full textA simple, flexible, low cost, computer controlled laboratory scale reaction calorimeter
has been assembled using commercially available components. The calorimeter may be
used for research, routine analysis and teaching. It has been used, operating in the isoperibolic
mode, to study the hydrolysis of acetic anhydride in relatively dilute solution (~0,5
M with respect to acetic anhydride) in the temperature range 5 – 40°C. A small enthalpy
of mixing has been observed. This is exothermic at the lower temperatures and becomes
endothermic at higher temperatures. The second order reaction rate constant has been derived
from the heat flow measuraments assuming pseudofirst order kinetics and it is in
good agreement with values reported in the literature
The integration of an ultraviolet-visible spectrometer and a reaction calorimeter
No full textA small ultraviolet-visible absorption spectrometer which uses fibre optic coupled immersion
probes has been incorporated into a laboratory scale reaction calorimeter. The combined instrument
has been tried out using the hydrolysis of acetic anhydride as a test reaction. With the calorimeter operating
in the isoperibolic mode good agreement is found for the pseudo-first order reaction rate constant
as determined from spectroscopic and calorimetric measurements. Experiments have been
made in order to follow the reaction indirectly using optical pH measurements with acid-base indicators.
The possibility of determining the temperature dependence of the rate constant in a single experiment
has also been investigated
- …
