2021 Articles

Thermomorphic Hydrophilicity Base-Induced Precipitation for Effective Descaling of Hypersaline Brines

Boo, Chanhee; Qi, Heyang; BIllinge, Ian Henry; Shah, Kinnari Malav; Fan, Hanqing; Yip, Ngai Yin

This study presents a novel technology, termed thermomorphic hydrophilicity base-induced precipitation (THBIP), for the effective removal of hardness ions from hypersaline brines with high-scaling propensity. THBIP utilizes thermoresponsive amine bases for the controlled precipitation of scaling constituents in alkaline conditions and subsequently uses low-temperature heat to trigger the phase separation of amine from aqueous solution, thus enabling reuse of the base. Three amines exhibiting distinct water solubility and basicity, specifically, diisopropylamine (DIPA), N-ethylcyclohexylamine (ECHA), and N,N-dimethylisopropylamine (DMIPA), were examined to identify the key parameters affecting THBIP performance. The amine bases were added to solutions containing hardness ions, Mg2+ or Ca2+, to induce the precipitation of hydroxide minerals (i.e., Mg(OH)2(s) and Ca(OH)2(s)). All three amines are effective in increasing solution pH, leading to high Mg2+ removals of over 90%. But because Ca(OH)2(s) is relatively more soluble, only DIPA, which is both highly miscible in water and also the strongest base, obtained significant removal of Ca2+ ions (>33%). The observed precipitation and hardness removal are quantitatively consistent with the principles of aqueous chemistry. Using a simulated hypersaline feedwater (240 g/L total dissolved solids) of high-scaling propensity, THBIP with DIPA achieved ∼80% hardness removal. Subsequent elevation of the temperature from 15 to 70 °C triggered demixing of the thermoresponsive base from the aqueous solution, to enable liquid–liquid separation for amine reuse. The study demonstrates the proof-of-concept of using thermomorphic hydrophilicity bases as an alternative strategy to effectively reduce the scaling potential of hypersaline brines.