(600b) Implementation of Ion Exchange Processes for CO2 Mineralization Using Produced Water Streams
AIChE Annual Meeting
2020 Virtual AIChE Annual Meeting
Sustainable Engineering Forum
Novel Approaches to CO2 Utilization I
Tuesday, November 17, 2020 - 8:15am to 8:30am
The pH shift in our process is effected by the exchange of protons for Na+ ions. Thus, the Na+-H+ exchange isotherms and adsorption rates of 13X and 4A zeolites and TP-207 and TP-260 resins in CO2-saturated water (pCO2 = 1 atm, pH 4) were studied via batch equilibrium experiments. Adsorption isotherms obey the Langmuir model, with the resins achieving higher capacities than zeolites: 2.4 mmol H+/g for TP-207, 2.2 mmol H+/g for TP-260, 1.8 mmol H+/g for 4A and 1.6 mmol H+/g for 13X. Consequently, ion exchange resins were capable of producing aqueous solutions with of pH = 11.3 and 10.9 for TP-207 and TP-260 respectively, compared to a pH = 10.2 and 9.8 for solutions contacted with 4A and 13X respectively. Multi-component mixtures of Ca2+ and Mg2+ cations in CO2-saturated water were used to probe competitive ion exchange. The presence of divalent cations in solution significantly inhibited H+ uptake because of their larger field strength, reducing capacities to as low as 1.2 mmol H+/g for resins and 0.8 mmol H+/g for zeolites. These results indicate the alkalinity inducing reaction for this process must occur in the absence of divalent cations to achieve the desired pH for CO2 mineralization.
The extent of calcite precipitation was evaluated experimentally by mixing the alkaline CO32--rich water solution that is obtained from the ion-exchange column, with a simulated liquid waste stream solution (1.4 M NaCl, 0.1 M CaCl2, 0.056 M MgCl2, 0.01 M CaSO4, 0.0001 M KCl, 0.00044 FeCl2). Experimental calcite yields were 26 mmol/L for cation exchange resins and 8 mmol/L for zeolitic materials, with the formation of goethite (an iron-hydroxide phase, FeOOH) as the primary contaminant phase (99% calcite, 1% goethite). Yields calculated via Gibbs Energy minimization were 26.5 mmol/L and 8.8 mmol/L for the resin and zeolite systems, respectively, indicating that the experimental process was able to achieve thermodynamic maximum production of calcite.
The results from these studies indicate that ion exchange processes can be used as an alternative to the addition of stoichiometric bases to induce alkalinity for the precipitation of CaCO3. The high calcium carbonate yields (1 ton CO2/day utilizing a produced water flow rate = 6.2 L/min and a total bed volume = 0.02 m3) obtained for the materials examined and the successful operation at standard temperature and pressure conditions support their potential for industrial implementation.