The decomposition process and kinetic analysis of benzene-based liquid crystal in hydrothermal system

- Hydrothermal method can effectively decompose EMOPE into innocuous products.
- Reaction kinetic of EMOPE under optimized conditions is studied.
- Two possible decomposition processes of EMOPE are proposed.
- The mixture of EMOPE and OCBPh can be hydrothermally treated together sufficiently.

Liquid crystal, while being a core component in liquid crystal displays, also has potential harmful effects on ecosystems and human health, especially when it is not treated properly. In this study, a hydrothermal process is proposed to dispose liquid crystal of 1-ethyl-4-[(4-methoxyphenyl)ethynyl]benzene (EMOPE) and mixed liquid crystal of EMOPE and 4-octoxy-4′-cyanobiphenyl (OCBPh). The effect of reaction time, reaction temperature, oxidant addition and solid-to-liquid ratio on decomposition ratio is evaluated. Products from hydrothermal decomposition of EMOPE are characterized, and two possible hydrothermal decomposition pathways are proposed. To get complete decomposition of 4 mg of EMOPE, the conditions required are: 0.3 mL of H2O2 addition, 3.5 mL of water supply, 275 °C and 5 min. The decomposition kinetic analysis of EMOPE indicates that its decomposition process fits the apparent first-order reaction model. For the mixture's decomposition, given conditions of 275 °C, reaction time of 6 min, 3.5 mL of water supply, and 1.5 time of oxidant addition, the decomposition ratio of OCBPh reaches to 99.75%, and EMOPE can be completely decomposed.