Oxidation characteristic and thermal runaway of isoprene

Abstract

In this study, the oxidation characteristics of isoprene were investigated using a custom-designed mini closed pressure vessel test (MCPVT). The results show that isoprene is unstable and polymerization occurs under a nitrogen atmosphere. Under an oxygen atmosphere, the oxidation process of isoprene was divided into three stages: (1) isoprene reacts with oxygen to produce peroxide; (2) Peroxides produce free radicals through thermal decomposition; (3) Free radicals cause complex oxidation and thermal runaway reactions. The oxidation of isoprene conforms to the second-order reaction kinetics, and the activation energy was 86.88 kJ·mol^-1. The thermal decomposition characteristics of the total oxidation product and purified peroxide mixture were determined by differential scanning calorimetry (DSC). The initial exothermic temperatures T_on were 371.17 K and 365.84 K, respectively. And the decomposition heat Q_DSC were 816.66 J·g^-1 and 991.08 J·g^-1, respectively. It indicates that high concentration of isoprene peroxide has a high risk of thermal runaway. The results of thermal runaway experiment showed that the temperature and pressure of isoprene oxidation were prone to rise rapidly, which indicates that the oxidation reaction was dangerous. The reaction products of isoprene were analyzed by gas chromatography-mass spectrometry (GC-MS). The main oxidation products were methyl vinyl ketone, methacrolein, 3-methylfuran, etc. The main thermal runaway products were dimethoxymethane, 2,3-pentanedione, naphthalene, etc. Based on the reaction products, the possible reaction pathway of isoprene was proposed.

Keywords: Hazard; Isoprene; Oxidation kinetic; Peroxide; Thermal runaway.

Fig. 1

The experimental device of isoprene

Fig. 2

The temperature and pressure behavior of isoprene under a nitrogen atmosphere, a T-t; b P–t

Fig. 3

Plots of n-t of isoprene under a nitrogen atmosphere

Fig. 4

Plots of P and T vs. reaction time t of isoprene oxidation

Fig. 5

The curve of n-t of isoprene oxidation

Fig. 6

Plots of ln n vs. 1000/T of isoprene oxidation

Fig. 7

The plot of molar number versus time for the two models

Fig. 8

Plots of ln k vs 1000/T

Fig. 9

The TLC analysis of isoprene peroxides under different temperatures

Fig. 10

The effect of reaction conditions on peroxide value, a Reaction time; b temperature

Fig. 11

Heat flow vs. temperature of isoprene oxidation products

Fig. 12

First derivative of heat flow as a function of temperature

Fig. 13

Thermal runaway for different molar ratios of isoprene, a T-t; b The expansion of near-ignition region of 1:2.0; c P–t

Fig. 14

Thermal runaway with the isoprene amount of 0.42 g

Fig. 15

The first derivative of pressure and temperature as a function of time, 1–0.21 g isoprene; 2–0.42 g isoprene; a dT/dt-t; b dP/dt-t

Fig. 16

The residues after explosion of isoprene

Scheme 1

Probable reaction pathways of isoprene with oxygen