The improved treatment of liquid crystals into non-hazardous molecules using a microwave-assisted hydrothermal method

[Display omitted] •Microwave-assisted hydrothermal method can effective decompose liquid crystal.•The decomposition rate of liquid crystal reaches 100 % under the optimized condition.•Reaction kinetic analysis of liquid crystal under optimized conditions is studied.•Two possible decomposition processes of liquid crystal are proposed.•The liquid crystal mixture is treated sufficiently into non-hazardous products. Liquid crystal (LC), as a crucial component of liquid crystal display (LCD), improperly treatment of which will possibly impair ecosystems and human health. In view of the advantages of hydrothermal reaction and microwave irradiation, this paper intensively studied the process of microwave-assisted hydrothermal (MWAH) decomposition of LC wastes. The experimental materials include a kind of refractory fluorinated liquid crystal commonly used in thin-film transistor LCD, and its mixture with the other two typical liquid crystal monomers in the waste low-end display panels. Under the MWAH process, the optimized condition for thorough decomposition of 0.67 g.L−1 fluorinated liquid crystal is 0.653 mol.L−1 H2O2, 1 g.L−1 AC, 300 mL water, 250 °C and 7 min. The superiority of microwave in enhancing hydrothermal treatment efficiency was verified by the first-order kinetic reaction equation fitted for the decomposition process under optimal condition, along with two possible decomposition pathways tentatively proposed after characterizing the intermediate products. Under the same condition, 1 g.L−1 mixture of fluorinated liquid crystal and the other two liquid crystal monomers were entirely decomposed with no harmful byproduct detected, suggesting that microwave irradiation could effectively promote the hydrothermal decomposition of liquid crystal wastes.