Abstract:

Organic peroxide is widely used for initiating free radical polymerization in unsaturated polyester copolymerization reaction, and is thermally unstable in the presence of a single oxygen-oxygen bond, which easily leads to thermal runaway accident, i.e. explosion, when exposed to an external heat source. If any contaminant, such as H⁺ or OH^－, is introduced during production, storage or transport, it may accelerate decomposition under an abnormal situation and result in deterioration. A liquid OP-tert-butyl peroxy benzoate (TBPB) was chosen to mix with NaOH and H₂SO₄ to examine H⁺ or OH^－ effects on its thermal hazard using an adiabatic accelerating rate calorimeter. The progresses in thermal decomposition of pure TBPB and mixtures with small amount of NaOH and H₂SO₄ are tracked using single “heat-wait-seek” operation mode and “isothermal age” plus “heat-wait-seek” mode, respectively. In order to characterize the effect of H⁺ and OH^－ on TBPB thermal hazard, the parameters of reaction kinetics and their corrected values with thermal inertia factor are determined from their characteristic parameters of thermal decomposition with pseudo inverse matrix method by least square method under the worst condition, and they are the characteristics of intrinsic thermal hazard of TBPB. The time to maximum heating rate (TMR) is predicted by Townsend equation involving reaction mechanism and reactant concentration. Based on the kinetic parameters and Semenov thermal explosion theory, the thermal hazard parameters, such as self accelerating decomposition temperature (SADT), CT, and ET, can be calculated, which are crucial for application in industry. A comparison of the mixtures to pure TBPB shows two exothermic peaks for mixture of TBPB and OH^－. The first is at 60—70℃ and is characterized by very low heating rate and temperature rise, so that reaction heat is not sufficient to sustain the thermal runaway reaction, resulting in higher initial exothermic temperature and reaction kinetic parameters in the second exothermic stage, i.e. main exothermic stage. In contrast, without two peaks for the mixture of TBPB and H⁺, this mixture has lower reaction kinetic parameters, increasing reactivity and thermal hazard. The TMR and SADT data obtained by calculation indicate that the addition of H⁺ contaminant causes appropriately lower warning temperature. When 30 L high density polyethylene barrel packaging is adopted, the SADT of TBPB contaminated by H⁺falls from 65.9 to 62.6℃, indicating that strict temperature control measures are necessary.

Key words: accelerating rate calorimeter, reaction kinetics, tert-butyl peroxy benzoate, safety, explosion, thermal runaway reaction

摘要：

过氧化苯甲酸叔丁酯(TBPB)对热不稳定,一旦在生产、储运过程中被H⁺或OH^－污染,可能会对其热危险性产生较大影响。采用绝热加速量热仪在“加热-等待-搜索”和“等温”模式下研究了H₂SO₄、NaOH存在下TBPB的热分解反应行为,从热分解特性参数、反应动力学参数、最大反应速率达到时间TMR、自加速分解温度SADT四个方面定量表征了H⁺、OH^－对TBPB热危险性的影响。采用“伪逆矩阵法”确定反应动力学参数,得到最不利条件下的热分解特征参数。采用Townsend算式,得到了考虑反应机理和反应物浓度的TMR推算式。基于Semenov理论,推算了0.5 L Dewar瓶和常用商业包装的SADT。结果表明:OH^-污染物使TBPB发生两次放热,第一次放热释放能量不足以维持热失控反应,但加速TBPB老化变质,从而导致第二次放热反应动力学参数升高,热危险性减弱;H⁺污染物降低TBPB反应动力学参数,加剧热危险性;TMR和SADT推算结果表明H⁺污染物降低了TMR对应的报警温度,降低了包装容器的SADT。

关键词: 绝热加速量热仪, 反应动力学, 过氧化苯甲酸叔丁酯, 安全, 爆炸, 热失控反应