CO₂ hydrogenation to formic acid using tertiary amine and diol solvents

Carbon dioxide (CO₂) hydrogenation to higher added-value products has been reported as a promising alternative to adapt the current industry to produce high-valuable chemicals via lower CO₂ emission processes. The CO₂ hydrogenation to formic acid via the tertiary amine & diol route was investigated in the present study. This process requires two reactors, and the tertiary amines’ size strongly influences both reactors’ performances. The present study investigated the thermodynamic influence of tertiary amines in each reactor and presented the most suitable amines’ size on each reactor’s performance. Suitable predictive thermodynamic models were assessed, and the most accurate ones were applied to estimate all species missing properties and systems equilibrium. This set of models is suggested to be used on further developments of similar processes. Eight tertiary amines, ranging from trimethylamine (C₁) to tri-octylamine (C₈), were studied. The thermochemical evaluation indicated that the amines’ size influences the two reactions inversely: small-sized tertiary amines were more efficient in the first reaction, whereas higher chain ones increased the second reaction’s conversion. Tertiary amines with radicals sized from ethyl (C₂) to hexyl (C₆) presented the most equilibrated performances in both reactions. Thermodynamic analysis revealed that high pressures and low temperatures favor the first reaction, and low pressures and high temperatures favor the second. Notably, triethylamine (C₂) demonstrated high conversions in both reactors, exceeding 90% conversion in both reactions.