The Accelerating Rate Calorimeter (ARC) is used to assess the thermal stability of a substance or mixture under adiabatic conditions. This test is commonly conducted to identify the temperature at which an exothermic decomposition begins, as well as to determine the kinetics and magnitude of the resulting runaway reaction.
Applicable Standard: ASTM E1981 Standard Guide for Assessing Thermal Stability of Materials by Methods of Accelerating Rate Calorimetry
PRINCIPLE OF OPERATION
The ARC instrument can be operated in two modes: the heat-wait-search (HWS) mode and the isothermal age mode. The main principle of this instrument is to maintain the sample under adiabatic conditions once exothermic reaction or self-heating of the sample is detected. This accelerates the reaction rate due to the generated heat. ARC experiments are generally time-consuming but effective for reactions with low self-heat rates.
Test Method
The test is conducted using a small, metallic sample bomb with a volume of 10 ml. The bomb is filled with 1 to 6 g of the substance being tested. Spherical bombs made from different metals can be used to prevent corrosion or any potential catalytic issues.
The bomb is equipped with a pressure transducer and temperature sensor and placed in the center of an adiabatic enclosure. The HWS method, more commonly used, involves heating the sample step-by-step using a radiant heater. After each heating step, the system waits for thermal equilibration and then searches for any signs of exothermic heat release above the detection threshold (typically set at 0.02 K·min-1). This process is repeated until an exothermic activity is detected, at which point the reaction is actively monitored until completion under adiabatic conditions. The test cell is usually not agitated but possesses a high thermal inertia (phi factor), while having excellent pressure capacity (up to several hundred bar) and high sensitivity.
DATA INTERPRETATION
The onset temperature of an exotherm is identified as the lowest temperature when the detection threshold of the calorimeter is surpassed. By analyzing the raw temperature/pressure/time data, the rates and magnitudes of the reaction can be determined. If the thermal inertia of the cell and the heat capacity of the sample are known, the temperature rise can be converted into the heat of reaction. Additionally, important kinetic parameters like activation energy can be calculated. Despite the high thermal inertia, the calorimetric study allows the temperature data to be corrected using the phi factor, which provides insights into parameters like time to maximum rate. This information, along with supporting data, can be used to estimate the self-accelerating decomposition temperature (SADT) of a sample. It’s worth noting that the onset temperature of activity, if left uncorrected, requires a safety margin of 20°C to 40°C, depending on the specific application.
ARC test typically has a phi factor that falls within the range of 1.5 to 3. This means that mathematical correction of the data is necessary for direct application, or a suitable safety margin should be considered when determining maximum plant exposure temperatures. Since the test vessel is typically not agitated, it may affect the ability to study biphasic systems. Additionally, initiating a reaction through remote additions can be extremely challenging due to the small size of the test cell.
In summary, you may obtain:
- Adiabatic temperature rise and reaction heat.
- Temperature rise rate and pressure rise rate.
- Vapor-liquid phase equilibrium data – Antoine plot,
- Identify gas generation.
- Identify autocatalytic feature of testing sample.
- Lumpsum reaction kinetic parameters such as activation energy, reaction order, and preexponential factor.
- Onset T of the exothermic reaction, but with an appropriate safety factor.
- Time to maximum rate (TMR) and TD24, i.e., the temperature at which the TMR is 24 hours.
- Temperature of no return (TNR)
- Self-accelerating decomposition temperature (SADT)
- Induction time of autocatalytic reaction but need expert guidance for testing procedure and data interpretation.
Why perform ARC test?
Performing Accelerating Rate Calorimetry (ARC) tests in process safety is essential due to its ability to provide crucial information about the thermal behavior and potential hazards associated with chemical reactions. ARC tests measure the rate of heat release of a material as a function of temperature or time, allowing for the identification of exothermic reactions that may lead to runaway reactions. By conducting ARC tests, process safety professionals can assess the thermal stability and behavior of substances, evaluate the impact of process conditions, and design appropriate control measures to prevent accidents. ARC testing plays a vital role in understanding and managing the risks associated with chemical reactions, improving safety outcomes, and protecting personnel, facilities, and the environment.
Why use us?
- We have a team of highly trained and experienced professionals who are skilled in conducting accelerating rate calorimetry tests, ensuring accurate and reliable results.
- Our state-of-the-art equipment and advanced technologies enable us to efficiently and effectively perform accelerating rate calorimetry tests, providing you with precise data on the thermal hazards and reactivity of your materials.
- Our team provides thorough analysis and interpretation of the results, helping you understand the behavior and potential risks associated with your materials.
- By choosing us, you can save time and resources by outsourcing the complex accelerating rate calorimetry testing to our experienced professionals.
FAQS
1. What is an Accelerating Rate Calorimeter (ARC)?
An Accelerating Rate Calorimeter (ARC) is a specialized instrument used to evaluate the thermal hazards and determine the temperature and pressure rise rate of reactions, mixtures, and materials. It is extensively used in process safety assessments to identify hazards related to exothermic reactions and reactive materials.
2. How does an ARC work?
An ARC typically consists of a small 10 ml sample bomb that holds the reaction or mixture being analyzed. The instrument monitors the temperature of the sample while a controlled heat source is applied, allowing for the measurement and assessment of the heat release rate. The ARC provides valuable data on the potential dangers of a reaction, including onset temperature, self-heating rates, heat of reaction, and time to maximum rate of heat release.
3. Why is an ARC important in process safety?
ARC plays a critical role in process safety by providing insights into the thermal behavior and hazards of reactions. It helps identify potential runaway reactions and thermal explosions, aids in designing safe reaction conditions, and assists in evaluating and selecting appropriate preventive measures for process safety.
4. What are the advantages of using an ARC?
Using an ARC offers several advantages, such as:
- Early identification of potential thermal hazards during a reaction or with reactive materials.
- Quantitative measurement of heat release rates, allowing for the accurate assessment of reaction hazards.
- Generating valuable data for process safety assessments and enabling the development of effective safety protocols.
- Assisting in the selection and evaluation of preventative measures, such as temperature control, venting systems, or the use of specialized equipment and materials.
5. Can an ARC be used for scale-up considerations?
While an ARC primarily focuses on evaluating small-scale thermal hazards, the data obtained from its measurements can be informative for scale-up considerations. By providing insights into the heat release rate and potential thermal hazards, an ARC can help guide the design and safety considerations when scaling up a process. However, additional measurements and analyses would usually be required to ensure safety at larger production scales.