(217a) Carbon-Negative Soda Ash (CODA)

Sodium carbonate or soda ash is an important base chemical (e.g. for glass and detergent industry) that is produced in the chemical industry or mined from natural mineral deposits. The Ammonia-Soda (Solvay) process is used to produce worldwide nearly half of the total 56 million metric tons of soda ash per year¹. Sodium chloride and calcium carbonate are reacted in the Solvay process to form soda ash and calcium chloride. The process involves ammonia as a mediator because the net reaction is thermodynamically supressed and cannot be performed directly. Additionally, the process relies on huge energy inputs from natural gas and coal. Consequently, the Solvay process emits significant amounts of fossil carbon dioxide and potentially environmental harmful waste streams.

The need for avoiding the mentioned emissions is the motivation for the development of a new carbon-negative soda ash process in order to protect our environment and climate. Carbon dioxide from air serves as renewable and climate-positive carbon source for the CODA process. It can be absorbed from air by contacting it with sodium hydroxide solution to react to sodium carbonate. Sodium hydroxide can be produced by electrolysis (ED) or bipolar electrodialysis (BPED) from sodium chloride brine using renewable energy from e.g. wind and solar power plants. In this way, the whole process can be considered as carbon-negative because more CO₂ is removed from air than released. The emissions of the conventional Ammonia-Soda process can be avoided (around 500 kg/t by CDA) and CO₂ from air is utilized (around 400 kg/t by CCU) by CODA. The by-products of the brine electrolysis are hydrogen and chlorine or hydrochloric acid in case of bipolar electrodialysis, which are valuable products and add to the economic viability of the concept.

Additional benefits of the CODA process are the avoidance of limestone mining (keeping the fossil carbon in the ground), ammonia processing and excessive waste handling (calcium chloride brine).

State of the art

Patents^{2, 3} describe processes that are similar to the suggested CODA process. They utilize fossil point sources of higher concentrated carbon dioxide that can lead to a carbon-neutral production.

Carbon dioxide from air was not yet considered as potential carbon source for soda ash production. However, it is well known that sodium hydroxide solution is alkaline enough to react with the very dilute CO₂ from air to form sodium carbonate and corresponding reactor concepts have been reported in literature^{4, 5}.

The ED consumes most of the power required for the process (about 2100 kWh/t NaOH or about 50% less for BPED) and should therefore mainly produce during low-cost energy periods (during peak loads from wind and solar power plants). On-demand flexibility of ED/BPED has been reported ⁶.

The main goals of the CODA project are a) the development of a combined CO₂ air capture and anhydrous soda ash crystallization process that is economic viable and meets the product specifications (e.g crystal size distribution, bulk density and purity), and b) the engineering, realization and testing of a dedicated CODA pilot plant on the industrial site of the project partner CIECH S.A. (Stassfurt/Germany). Especially challenging is the identification of suitable specific operation conditions for both sub-processes. Hereby the capture process will be strongly influenced by the weather conditions (air temperature and humidity).

We will present results of our studies on the gas–liquid and solid–liquid phase equilibria, mass transfer kinetics and reaction kinetics in the NaOH-Na₂CO₃-CO₂-H₂O system, which form the basis for a robust process engineering. Concepts for the combination of the sub-processes and regarding control of the overall process will be also presented.

References

(1) Czaplicka, N.; Konopacka-Łyskawa, D., Studies on the Utilization of Post-Distillation Liquid from Solvay Process to Carbon Dioxide Capture and Storage. SN Applied Sciences 2019, 1, (5).

(2) Coustry, F., Hanse M., Process for jointly obtaining a chlorine derivative and crystals of sodium carbonate. Patent WO2006094968A1, 2006.

(3) Peterson, R., Ice, L., Sheikh, O., B., Hussein, O., A., Method of making sodium carbonate and/or sodium bicarbonate. Patent US2014286850A1, 2014.

(4) Stolaroff, J. K.; Keith, D. W.; Lowry, G. V., Carbon Dioxide Capture from Atmospheric Air Using Sodium Hydroxide Spray. Environ. Sci. Technol. 2008, 42, (8), 2728-2735.

(5) Mahmoudkhani, M.; Keith, D. W., Low-Energy Sodium Hydroxide Recovery for CO2 Capture from Atmospheric Air—Thermodynamic Analysis. International Journal of Greenhouse Gas Control 2009, 3, (4), 376-384.

(6) Otashu, J. I.; Baldea, M., Demand Response-Oriented Dynamic Modeling and Operational Optimization of Membrane-Based Chlor-Alkali Plants. Comput. Chem. Eng. 2019, 121, 396-408.