High throughput preparation of magnesium hydroxide flame retardant via microreaction technology

Abstract

Magnesium hydroxide (MH) has attracted much attention as an environmentally friendly flame retardant. In this paper, high throughput preparation of high-grade MH flame retardant was successfully achieved via microreaction technology and hydrothermal treatment. The results indicated that the reactant molar ratio and reactant concentration had a significant effect on the properties of MH including the morphology, average particle size and BET specific surface area, while the flow velocity and reaction temperature had little effect. To obtain MH with desirable properties, a highly concentrated NaOH solution was added into the hydrothermal slurry. The properties of MH were remarkably influenced by hydrothermal parameters such as NaOH concentration, time, temperature and solid content. High-grade MH flame retardant can be obtained with a NaOH concentration ≥2.4 M, hydrothermal time ≥3 h, hydrothermal temperature ≥170 °C and solid content ≤6.0 wt%. On the basis of laboratory work, a microreaction system based on a stacked plate microchannel reactor with an external volume of 7 L was developed for the pilot scale preparation of MH. The production capacity of MH slurry was up to 12.6 m³ h⁻¹, and the pressure drop of the microreaction system was kept at 1.1 bar. The average particle size and BET specific surface area of as-prepared MH were 1.0 μm and 3.4 m² g⁻¹, respectively, which met the requirement of high-grade flame retardant.