Heat Loss in Accelerating Rate Calorimetry Analysis and Thermal Lag for High Self-Heat Rates,Organic Process Research & Development

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Heat Loss in Accelerating Rate Calorimetry Analysis and Thermal Lag for High Self-Heat Rates
Organic Process Research & Development ( IF 3.1 ) Pub Date : 2020-12-18 , DOI: 10.1021/acs.oprd.0c00459
Min Sheng ₁ , Daniel Valco ₁ , Craig Tucker ₁

Affiliation

Accelerating rate calorimetry (ARC) is a common tool used in thermal stability evaluation of hazardous materials to provide self-heat rate and pressure data that are used to model the kinetics of a reaction and even calculate relief vent sizing. The ARC accomplishes a conservative approach by maintaining adiabatic conditions. However, an issue with ARC instrument heating occurs when a reaction with a high self-heat rate is analyzed that results in nonadiabatic conditions and a “thermal lag”. Testing was conducted to determine the self-heat rate threshold for the ARC instrument and to better understand telltale features that occur during analysis of samples with high self-heat rates. The results indicate that while the oven cannot maintain adiabatic conditions, the convective heat loss from the sample container to the ARC oven does not have a significant effect on either the measured self-heat rate or the calculated overall heat of reaction. However, the conductive heat loss from the sample container to the connection fitting does, causing the total heat measured in ARC analysis to be lower by 16% for an adiabatic ARC test, 33% for a nonadiabatic ARC test, and ∼20% for a typical ARC test in comparison with DSC measurements. A corrected phi estimation is proposed with a correction factor to take into consideration the conductive heat loss to address this issue. In addition, the thermal lag caused by the ARC temperature measurement does create a significant difference between the measured peak pressure rate and peak self-heat rate occurrences. Analysis of the results showed that a simple linear correction can be applied to high self-heat rate results for liquid samples, while the pressure rate is still increasing, to correct for these peak rate differences. The pressure rate after correction matches the self-heat rate and better agrees with the prediction from kinetic modeling. Such corrections can be applied to solid samples, where there is an additional thermal lag due to resistance to heat transfer in the solid sample itself. Accounting for the thermal lag in reactions with high self-heat rates is important when modeling of the data is used for kinetic parameters and especially for relief vent sizing.

中文翻译：

高自热率的加速量热分析中的热损失和热滞后

加速量热法（ARC）是用于危险材料热稳定性评估的常用工具，可提供自热率和压力数据，用于对反应动力学进行建模，甚至计算卸压口的尺寸。ARC通过维持绝热条件来实现保守的方法。但是，当分析具有高自热率的反应导致非绝热条件和“热滞后”时，会出现ARC仪器加热的问题。进行测试以确定ARC仪器的自热率阈值，并更好地了解在分析具有高自热率的样品期间发生的信号特征。结果表明，尽管烤箱无法保持绝热条件，从样品容器到ARC炉的对流热损失对测得的自热速率或计算出的反应总热量均无显着影响。但是，从样品容器到连接配件的传导性热损失确实增加了，这使得在ARC分析中测得的总热量对于绝热ARC测试而言降低了16％，对于非绝热ARC测试而言降低了33％，对于绝热ARC测试降低了约20％。典型的ARC测试与DSC测量的比较。提出了具有校正因子的校正phi估计，以考虑传导热损失以解决此问题。此外，由ARC温度测量引起的热滞后确实会在所测量的峰值压力速率和峰值自热速率出现之间产生显着差异。结果分析表明，可以对液体样品的高自热速率结果进行简单的线性校正，而压力速率仍在增加，以校正这些峰值速率差异。校正后的压力率与自热率匹配，并且与动力学模型的预测更好地吻合。这样的校正可以应用于固体样品，其中由于固体样品本身对传热的阻力而存在额外的热滞后。当将数据建模用于动力学参数，尤其是用于泄压口尺寸时，考虑到具有高自热率的反应中的热滞后很重要。校正后的压力率与自热率匹配，并且与动力学模型的预测更好地吻合。这样的校正可以应用于固体样品，其中由于固体样品本身对传热的阻力而存在额外的热滞后。当将数据建模用于动力学参数，尤其是用于泄压口尺寸时，考虑到具有高自热率的反应中的热滞后很重要。校正后的压力率与自热率匹配，并且与动力学模型的预测更好地吻合。这样的校正可以应用于固体样品，其中由于固体样品本身对传热的阻力而存在额外的热滞后。当将数据建模用于动力学参数，尤其是用于泄压口尺寸时，考虑到具有高自热率的反应中的热滞后很重要。

更新日期：2021-01-16

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