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Conducting safety studies on exothermic reactions with BatchReactor
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Process simulation is a proven technique which adding value needs not to be demonstrated anymore and which utilization is continuously growing among process industries professionals. Main benefits of simulation are found in risk reduction, improved knowledge of physical phenomena, reduced time to market for new products and, of course, improved process efficiency.
To be efficient in all these domains, the simulation software requires knowledge models built upon the fundamental laws of physics and chemicals: conservation equations (mass, energy, momentum…), thermodynamics (phase equilibrium…) kinetics… These simulators can predict the behaviour of the system, in a range of possible operating conditions that is much larger than that of experimental data. However, when dynamic simulation is handled, advanced, complex numerical methods need to be used.
ProSim’s BatchReactor simulates chemical reactors in batch mode. It results from a long time research partnership with French INPT-ENSIACET and was validated by over ten years of intensive utilization in chemical and pharmaceutical industries. The reactor can be described in details and a wide range of options are available to model the heating or cooling and the condensing devices. This software has a kinetic identification module (from experimental data such as concentration time evolutions, calorimetric data…). From the knowledge of the system chemistry (species, reactions stoechiometry and kinetics), of the reactor geometry and of operating conditions (heating, cooling, feeding, steps durations…) BatchReactor will calculate mass and energy balances and phase equilibria. It will also provide the time evolution of different operating parameters of the system: mass fraction, temperature, pressure…
A typical application of BatchReactor is the analysis of exothermic reaction in order to put in place safety measures. In this example, we study the synthesis of mono alkyl ester from maleic anhydride and 1-hexanol.
The reaction is exothermic and controlled by an Arrhenius law, which kinetic parameters were identified by the software from experimental data. These parameters are summarized in the table below:
| Pre exponential factor | 4.92 1015 l/mol h |
| Activation energy | 105 kJ/mol |
| Reaction enthalpy | 33 500 Cal/mol |
Characteristics of the industrial reactor are presented in the figure below:
| Reactor initial load | 500 kg of maleic anhydride |
| Feed | 100 kg/h of pure 1-hexanol at 95°C |
| Pressure | 1 atm |
| Temperature in the reactor | Regulated at 85°C with the cooling fluid |
The events selected to end the simulation are the duration of reaction (8 hours) or the quantity of maleic anhydride remaining in the reactor below 10 kg.
The graph below represents the evolution of mass concentrations in the reactor:
The reaction lasts a little more than 6 hours and the first event reached (that ends the simulation) is the quantity of maleic anhydride. From this nominal point several scenarios can be simulated. The chosen one is a loss of thermal fluid regulation (fluids flows doubles) after 3 hours of reaction followed by a failure of the mixing device after fifteen minutes. The following graphs depict the consequences of these incidents on the reactor temperature and on mass concentrations.
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| Evolution of temperature in the reactor (click to expand) |
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Evolution of mass concentrations (click to expand) |
As the thermal fluid flow is not controlled anymore the reactor temperature drops which leads to the deterioration the reaction efficiency and the production of mono alkyl ester. Continuing the synthesis in these conditions would have led to a maleic anhydride conversion of only 57,8%.
The failure of the mixing device leads to switch from a forced convection regime to a natural convection regime. Exchange coefficients and therefore seriously reduced and the energy produced by the reaction is not expelled anymore. The temperature inside the reactor rises quickly until all the maleic anhydride is consumed, after about 5 hours of reaction.
Dynamic simulation of batch reaction allows a thorough analysis of possible incidents. In this case, safety procedures should be set up in order to face the failure of the mixing device. However this type of analysis will also allow optimizing processes installations and recipes during both design and exploitation phases. Other frequent applications are the testing of a different mixing device, vessel, of a new recipe on the same installation, scale-up from a pilot plant or VOC emission reduction.
Author and contributors: Olivier BAUDOUIN, Philippe GUITTARD, Gilles HAMEURY (ProSim)
More information: BatchReactor page, Contact
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