Time To Maximum Rate Under Adiabatic Conditions Research Articles

New Kinetic Approach for Evaluation of Hazard Indicators Based on Merging Dsc and Arc Or Large Scale Tests

The present study describes two methods of evaluation of hazard indicators such as Self Accelerating Decomposition Temperature (SADT) or Time to Maximum Rate under adiabatic conditions (TMRad) from the results of the experiments performed in mg scale by Differential Scanning Calorimetry (DSC). We discuss here: (i) the kinetic workflow in which the kinetic parameters of the investigated reaction evaluated from the DSC are used with the heat balance of the system and (ii) a novel merging approach in which DSC data are simultaneously considered with the results of other, temperature recorded experiments as e.g. Accelerating Rate Calorimetry (ARC), large scale experiments as e.g. cookoff, Dewar or SADT determination according to STANAG 4383 and UN regulations (Tests H.4 and H.1), respectively. The commonly kinetic-based approach is discussed and its results confirmed by those obtained in common project with Federal Institute for Materials Research and Testing, Berlin, Germany (BAM) in which the SADT for AIBN was investigated. The novel merging approach is illustrated by the results of the linked DSC-UN test H.1 data and DSC-ARC results applied for SADT determination and for evaluation of TMRad for any starting temperature for AIBN.

A green approach towards adoption of chemical reaction model on 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane decomposition by differential isoconversional kinetic analysis

This study investigated the thermal degradation products of 2,5-dimethyl-2,5-di-(tert-butylperoxy) hexane (DBPH), by TG/GC/MS to identify runaway reaction and thermal safety parameters. It also included the determination of time to maximum rate under adiabatic conditions (TMRad) and self-accelerating decomposition temperature obtained through Advanced Kinetics and Technology Solutions. The apparent activation energy (Ea) was calculated from differential isoconversional kinetic analysis method using differential scanning calorimetry experiments. The Ea value obtained by Friedman analysis is in the range of 118.0–149.0kJmol−1. The TMRad was 24.0h with an apparent onset temperature of 82.4°C. This study has also established an efficient benchmark for a thermal hazard assessment of DBPH that can be applied to assure safer storage conditions.

Thermal risk assessment of vegetable oil epoxidation

This article describes thermal risk assessment of vegetable oil epoxidation by peroxycarboxylic acid. It is a liquid–liquid system where several exothermic reactions occur. Acetic acid was used as the carboxylic acid, and oleic acid was chosen as a model molecule because it is a common fatty acid in the triglyceride molecule. Differential scanning calorimetry (DSC) and accelerating rate calorimetry (ARC) were used to determine safety criteria such as the final temperature (T Final), T D24, and time to maximum rate under adiabatic condition (TMRad). We found that the calculation of TMRad based on DSC data could be incorrect when assuming a zero-order kinetic reaction. By using a process temperature of 70 °C, the extrapolated final temperature was found to be 544 °C from DSC experiments, T D24 was estimated to 20 °C based on ARC experiment, and TMRad was calculated to 164 min from ARC experiments. These criteria indicate the process can lead to a thermal runaway. Therefore, we recommend that vegetable oil epoxidation by peroxycarboxylic acid should not be performed in batch reactor, but in semi-batch mode.

Thermal hazard analysis of cyclohexanone peroxide and its solutions

Cyclohexanone peroxide (CYHPO) is widely used in the chemical industry, but unfortunately, as an organic peroxide, it has been involved in many serious fires and explosions in daily manufacturing, storage, and transportation. We present an advanced methodology of application of thermal analysis for thermal hazard investigation of complex chemical reactions. The applied method is based on a differential isoconversional approach and involves the combination of non-isothermal differential scanning calorimetry (DSC) and adiabatic measurements by accelerating rate calorimeter (ARC) for kinetic analysis and prediction. The kinetic parameters and heat balance were analyzed and used for a simulation of the adiabatic behavior: time to maximum rate under adiabatic conditions (TMRad) and self-accelerating decomposition temperature (SADT). Applications of finite element analysis (FEA) for heat balance and accurate kinetic description allowed us to determine the effect of scale, geometry, heat transfer, thermal conductivity, and ambient temperature on the heat accumulation process. The presented explosion simulations of the thermal behavior of 100kg storage tank at different temperatures, related to the possible storage scenarios, may help in the elucidation of a real accident which occurred in Beijing during CYHPO storage.

Thermal stability of lauroyl peroxide by isoconversional kinetics evaluation and finite element analysis

Lauroyl peroxide (LPO) is a commonly used organic peroxide that has caused many thermal runaway reactions and explosions worldwide. Differential scanning calorimetry (DSC) was used to investigate the thermal decomposition of LPO and its exothermic onset temperature, reaction heat, and other safety parameters for prevention of runaway reactions and thermal explosions. Pre-exponential factor and apparent activation energy were determined by Friedman isoconversional method, which demonstrates that the decomposition of LPO shows a multi-step nature. The kinetic parameters and heat balance were analyzed and used for simulation of the adiabatic behavior time to maximum rate under adiabatic conditions (TMRad) and self-accelerating decomposition temperature (SADT). When the initial temperature is 32.7°C, TMRad equals 24h and calculated SADT of LPO is 45°C. Application of finite element analysis (FEA) and accurate kinetic description allows determining the effect of scale, geometry, heat transfer, thermal conductivity, and ambient temperature on the heat accumulation. The reaction progress (α) and temperature distribution can be determined quantitatively at every point in time and space. This information is essential for the design of containers of LPO, cooling systems, and the measures to be taken in the event of a cooling failure.

From Kinetic Study to Thermal Safety Assessment: Application to Peroxyformic Acid Synthesis

This article proposes a kinetic and thermal study of the formic acid perhydrolysis in a semibatch process at various hydrogen peroxide concentrations (5.32–8.21 mol/L), formic acid molar inlet flow rates (0.04–0.22 mol/min), reaction temperatures (30–60 °C), and catalyst amount (0.0–10.6 g). A cation-exchange resin, i.e., Amberlite IR-120, was used as a catalyst. Synthesis and decomposition of peroxyformic acid were modeled by coupling the energy and mass balances, and a pseudohomogeneous model for the reaction kinetics. A nonlinear regression method was used to estimate the kinetic parameters, such as rate constant, and thermal parameters, such as reaction enthalpy. The knowledge of these parameters allows the determination of maximum temperature of the synthesis reaction (MTSR), the time to maximum rate under adiabatic condition (TMRad), and the criticality classification. These safety parameters are important to properly design the industrial reactor.

Thermal reactive hazards of 1,1-bis(tert-butylperoxy)cyclohexane with nitric acid contaminants by DSC

Abstract With two active O–O peroxide groups, 1,1-bis(tert-butylperoxy)cyclohexane (BTBPC) has a certain degree of thermal instability. It is usually used as an initiator in chemical processes, and therefore reckless operation may result in serious thermal accidents. This study focused on the runaway reactions of BTBPC alone and mixed with various concentrations of nitric acid (1, 2, 4, and 8 N). The essential thermokinetic parameters, such as exothermic onset temperature (To), activation energy (Ea), frequency factor (A), time to maximum rate under adiabatic condition (TMRad) and time to conversion limit (TCL), were evaluated by differential scanning calorimetry at the heating rate of 4 °C min−1, and a kinetics-based curve fitting method was used to assess the thermokinetic parameters. All the results indicated that BTBPC mixed with one more than 4 N nitric acid dramatically increased the degree of thermal hazard in the exothermic peak and became more dangerous. However, it was relatively safe for BTBPC ...

Advanced kinetic tools for the evaluation of decomposition reactions

An advanced kinetic study on the thermal behaviour of pyrotechnic ignition mixtures has been carried out by differential scanning calorimetry using different B/KNO3 mixtures (50:50, 30:70, 20:80) as a model reaction. The experimental conditions applied (isochoric conditions/closed crucibles and isobaric conditions/open crucibles) as well as the composition of the mixtures noticeably influences the relative thermal stabilities of the energetic materials. The kinetic study focused on the prediction of the thermal stability of the different mixtures both in extended temperature ranges and under temperature conditions at which ordinary investigation would be very difficult. Using advanced numerical tools [1], thermal ageing and influence of the complex thermal environment on the heat accumulation conditions were computed. This can be done for any surrounding temperature profile such as isothermal, non-isothermal, stepwise, modulated, shock, adiabatic conditions and additionally for temperature profiles reflecting real atmospheric temperature changes (yearly temperature profiles of different climates with daily minimal and maximal fluctuations). Applications of accurate decomposition kinetics enabled the determination of the time to maximum rate under adiabatic conditions (TMRad) with a precision given by the confidence interval of the predictions. This analysis can then be applied for the examination of the effects of the surrounding temperature for safe storage or transportation conditions (e.g. determination of the safe transport or storage temperatures).

The prediction of thermal stability of self-reactive chemicals

An advanced study on the thermal behaviour of double base (boost and sustain propellant) rocket motor used in a ground to air missile has been carried out by differential scanning calorimetry (DSC). The presence of two propellants as well as the different experimental conditions (open vs. closed crucibles) influence the relative thermal stability of the energetic materials. Several methods have been presented for predictions of the reaction progress of exothermic reactions under adiabatic conditions. However, because decomposition reactions usually have a multi-step nature, the accurate determination of the kinetic characteristics strongly influences the ability to correctly describe the progress of the reaction. For self-heating reactions, incorrect kinetic description of the process is usually the main source of serious errors for the determination of the time to maximum rate under adiabatic conditions (TMRad). It is hazardous to develop safety predictive models that are based on simplified kinetics determined by thermoanalytical methods. Applications of finite element analysis (FEA) and accurate kinetic description allow determination of the effect of scale, geometry, heat transfer, thermal conductivity and ambient temperature on the heat accumulation conditions. Due to limited thermal conductivity, a progressive temperature increase in the sample can easily take place resulting in a thermal explosion. Use of both, kinetics and FEA [1], enables the determination of the reaction progress and temperature profiles in storage containers. The reaction progress and temperature can be determined quantitatively at every point in time and in space. This information is essential for the design of containers of self-reactive chemicals, cooling systems and the measures to be taken in the event of a cooling failure.

Comparison of different methods for estimating TMRad from dynamic DSC measurements with ADT 24 values obtained from adiabatic Dewar experiments

Recently, a method for estimating the time to maximum rate under adiabatic conditions (TMRad) from non-isothermal DSC measurements was presented by Keller, A., Stark, D., Fierz, H., Heinzle, E., & Hungerbühler, K. (1997). J. Loss. Prev. Process. Ind., 10, 31–41. The method was tested on the basis of isoperibolic data only, because data from adiabatic experiments were not available. In this study we used results from 180 Dewar vessel experiments with an adiabatic shield and the corresponding dynamic DSC measurements provided by Aventis Research and Technologies (former Hoechst AG) to test the estimation method suggested. The data were obtained for reaction mixtures, bottom residuals, reaction residuals, and products. We found that in all cases the predicted TMRad at a given temperature was shorter than the experimental value determined from adiabatic measurements. This result shows that the TMRad estimation method is useful as a screening tool for the assessment of thermal risk. Furthermore, the estimation method introduced by Keller et al., is more on the safe side than other common and often applied estimation methods like the so-called 100 degree rule or the 50 degree rule. We also describe how to derive adiabatic induction times for different temperatures by using a minimum number of adiabatic experiments.

Kinetic system identification by using short-cut techniques in early safety assessment of chemical processes

Abstract The chemical industry uses complicated reacting systems under a wide range of physical conditions. Besides production maximisation, stable and safe operation are important goals. This objective has to be considered in all the engineering calculations from the process design phase until the plant operation. Modelling and simulation of the processes accelerates and improves design. It may include qualitative information and/or heuristic rules. Process modelling, optimisation and control allow safe plant design and operation if enough information about the process is available. An experimental and a numerical technique will be combined in this paper. The `Differential Scanning Calorimetry' (DSC; Hohne, Hemminger & Flammersheim, 1996, Differential scanning calorimetry) is an experimental technique that can be used to investigate the mechanism and kinetics of a chemical process by measuring the thermal effect of the reaction following a very elaborated strategy. At early stages in process design, DSC is used as a screening tool to assess the thermal safety. Under the assumption of zero order Arrhenius kinetics, the activation energy and therefore the time to maximum rate under adiabatic conditions (TMRad) may be estimated (ANSI/ASTM, E 698-79; Keller, Stark, Fierz, Heinzle & Hungerbuhler, 1997, J. Loss Prev. Process Ind., 10, 31–41). A similar way can be applied to determine the kinetic constants and TMRad for an nth order reaction. Attempts to fit more complex kinetic models to DSC thermograms encounter many difficulties; one of them is model discrimination, a question not yet answered. The `Modified Integral Transformation Procedure' (MIP; Maria & Rippin, 1997 , Comp. & Chem. Eng., 21, 1169–1190) was proposed for quick process identification by considering previous information stored in data-banks and incomplete information about the process. The estimation technique is effective even if few but distributed process data are available and it can be easily coupled with other statistical data analysis and estimation techniques. The MIP is integrated in an expert system for process identification ( Maria & Rippin, 1996 , Comp. & Chem. Eng., S20, S587–S592) which facilitates computer-based plant analysis. It is the scope of this paper to investigate the effectiveness of using these coupled experimental and numerical short-cut techniques and an interactive data-bank in quick identification of complex chemical kinetics. If model discrimination is not possible, an experimental procedure to close existing data gaps most efficiently can be developed. The identified model can be further used in predicting optimum operating conditions for a chemical process by considering the desired product maximisation, waste and by-product minimisation, safety and operability as goals. The developed quick experimental and PC-coupled numerical identification and process analysis are exemplified in some simple complex kinetic cases. The effectiveness of the elaborated calculation methodology is discussed together with possibilities of further improvements.