A novel non-aqueous biphasic solvent of PZ/AMP/NMF for CO2 capture: Solid-liquid phase change controllable

• A novel phase change controllable solvent of PZ/AMP/NMF was proposed for CO 2 capture. • The phase transition loading was 60.6 % of the saturated loading (1.202 mol/mol). • The interaction of AMP and PZ helped to extend the time of phase transition nodes. • The enhanced polarity and hydrogen bonding interaction lead to solid powder products. Solid-liquid biphasic solvents(SLBS) are considering as promising absorption for CO 2 chemical capture because of their potential energy-saving potential and easily separation of solid products. Nevertheless most of the SLB systems still with some defects, such as premature phase transition and viscous solid products. This work proposed a novel non-aqueous biphasic absorbent with controllable solid–liquid phase transition, composed of piperazine (PZ), 2-amino-2-methyl-1-propanol (AMP), and N-methylformamide (NMF). When NMF is 90 % by volume as solvent and the volume ratio of PZ and AMP is 3:1, the absorbent maintained a homogeneous phase with CO 2 loading below 0.729 mol/mol, which was about 60.6 % of the saturated loading (1.202 mol/mol). As the loading further increased, the solid products generated and the solution separated into solid–liquid two phases. And the solid product into the saturated solution was only 14 % of the total volume while contained about 93.29 % of total loading. The phase-transition mechanism was investigated by using 13 C NMR analysis and molecular simulations. Due to the higher reactivity of PZ with CO 2 compared to AMP, CO 2 initially reacted with PZ to form PZCOO − and PZH + . The enhanced polarity of the final products, PZ(COO − ) 2 and PZ(H + ) 2 , together with a marked increase in ESP difference, promotes the formation of small-volume, CO 2 -rich solids in the later stages of absorption. During this process, intermediate products (PZCOO − and PZH + ) interact with AMPCOO − and AMPH + , allowing early-stage dissolution of products in the solvent and ultimately producing easily separable solids with high CO 2 enrichment. The regeneration heat duty of the novel SLBS was estimated about 0.76 GJ/ton CO 2 , representing just 20.0 % of the industry standard for MEA (3.80 GJ/ton CO 2 ), which indicated extremely energy-saving advantage of the novel solvent.