Pyrolysis Kinetics of Liquid Crystal Wastes

Abstract

This paper reports the results of a one-stage pyrolysis of liquid crystal wastes using thermal gravimetric analysis to characterize their treatment potentials. Liquid crystal can be decomposed at 413–596 K. The kinetic parameters for the liquid crystal pyrolysis were obtained from the TGA experiments which were based on weight loss data at different heating rates from 298 to 673 K at heating rates of 5, 8, and 10 K min⁻¹, respectively. The calculation was based on the classical law of kinetics. The activation energy, preexponential constant and reaction order of the pyrolysis of liquid crystal sample are 17.0 kcal mol⁻¹, 10^8.71 min⁻¹, and 1.15, respectively. The global rate equation for pyrolysis of the liquid crystal can be expressed as dX/dt = 10^8.71 [exp(–17.0/(8.314 × 10⁻³ T))](1 – X)^1.15 (X denotes the reaction conversion). Characteristics of liquid crystal molecules and gases produced from the liquid crystal pyrolysis were also analyzed by using Fourier transform infrared (FTIR) (wave number at 4,000−800 cm⁻¹) spectroscopic methods. The on-line FTIR spectra show that the gaseous products are mainly aliphatic hydrocarbons. The FTIR spectra also indicate that the dissociation of C—NO₂ bonds are not involved in the pyrolysis process.