Industrial Symbiosis: CO2 Utilization by Producing Disodium Octaborate Tetrahydrate and Baking Soda from Borax

Abstract

This paper proposes a novel method for CO2 capture, utilization, and sequestration (CCUS) with borax producing disodium octaborate tetrahydrate (Na2O·4(B2O3)·4H2O ≡ Na2B8O13·4H2O, DSOBTH) equivalent boron compounds and sodium bicarbonate (NaHCO3). We tested the performance of this method experimentally using aqueous ammonium (NH4+) solutions in a pressurized reactor (1 L) continuously purged with pure (99.9%) CO2. Experimental parameters were changed as temperature (T), 45-65 °C; solid-to-liquid ratio (SLR), 0.69-0.92 g/mL; reaction time (t), 30-60 min; pressure (P), 5-30 bar; NH3 concentration (AC) 2.82-5.65 M; and steering speed (SS), 500 rpm. The results showed that P and T were highly influential on the performance. The best conditions for CO2 utilization were found as P = 20 bar; T = 60 °C; SLR = 0.77 g/ml; t = 50 min; and AC = 4.76 M. Per ton of tincal, under these conditions, produced were 0.274 ton of DSOBTH (∼67% B2O3), 0.216 ton of NaHCO3 (∼95% purity), 0.386 ton of avoided boric acid, and 0.417 ton of avoided CO2. The total potential added value can be about $1100/ton of tincal.