Market and product

Compiled by Bao Hien

A German research team has modeled a process for producing soda ash (sodium carbonate, Na₂CO₃) from brine and CO₂ captured directly from the air, using a hypothetical plant with a capacity of 1,000 tonnes per day. The process uses brine electrolysis to produce caustic soda, which is then used to absorb CO₂. The most promising configuration has an estimated operating cost of around USD 150 per tonne of soda ash and a net CO₂ uptake of approximately 0.15 tonnes per tonne of product. However, this remains a preliminary feasibility study based on computer simulations. The integrated process has not been experimentally validated, and a full life-cycle assessment has yet to be conducted.

The study was conducted by Maria Gutierrez, Heike Lorenz, and Peter Schulze of the Max Planck Institute for Dynamics of Complex Technical Systems in Magdeburg, Germany, and published in Industrial & Engineering Chemistry Research on May 30, 2025.

How It Differs from the Solvay Process

The Solvay process currently accounts for approximately 75% of global soda ash production, equivalent to around 56 million tonnes annually. According to the paper, the process generates direct emissions of approximately 200–300 kg of CO₂ per tonne of soda ash, in addition to indirect energy-related emissions of around 790–1,160 kg of CO₂ per tonne of product. It also produces approximately one tonne of calcium chloride for every tonne of soda ash, most of which is discharged in wastewater.

The new process, which the researchers call CODA, takes a different approach. Instead of relying on the characteristic chemical reactions of the Solvay process, it combines brine electrolysis with direct air capture of CO₂.

First, purified brine containing approximately 26 wt% NaCl is electrolyzed to produce 32 wt% caustic soda, hydrogen, and chlorine. The caustic soda is then diluted to 5–7 wt% before being brought into contact with humidified air, allowing it to absorb CO₂ and form a sodium carbonate solution.

The solution is subsequently crystallized using one of two approaches. The first produces sodium carbonate decahydrate at approximately 10°C, which is then converted into the monohydrate at 45–100°C. The second produces the monohydrate directly in a single crystallization step. Finally, the product is dried at temperatures of up to 150°C to obtain anhydrous soda ash.

According to the simulated design, the process eliminates the need for limestone calcination and uses electricity throughout the system, including for mechanical vapor recompression during crystallization.
Four Configurations for a Simulated 1,000-Tonne-per-Day Plant

The researchers used Aspen Plus to model four process configurations:

• P1: Cross-flow CO₂ absorption with two-step crystallization.
• P2: Droplet-type CO₂ absorption with two-step crystallization.
• P3: Cross-flow CO₂ absorption with single-step crystallization.
• P4: The same configuration as P1, with the additional production of hydrochloric acid from hydrogen and chlorine.

The simulation estimated capital investment at approximately USD 195–209 per tonne of soda ash capacity for configurations using a cross-flow absorber, compared with approximately USD 337 for the droplet-type absorber.

Operating costs were estimated at USD 150 per tonne of soda ash for two-step crystallization and USD 175 per tonne for single-step crystallization. Among the configurations evaluated, P1 was considered the most promising. It achieved an estimated net CO₂ uptake of around 0.15 tonnes per tonne of soda ash. The paper describes this configuration as generating “nearly USD 200 in revenue per tonne of soda ash,” although it does not clearly specify whether this figure represents gross revenue or profit after costs.

The main economic assumptions included a soda ash price of USD 310 per tonne, hydrogen at USD 5,000 per tonne, chlorine at USD 200 per tonne, 33 wt% hydrochloric acid at USD 56.5 per tonne, CO₂ certificates at USD 75 per tonne, electricity at USD 65/MWh, and brine at USD 2 per tonne. The model assumed a capital charge factor of 10% and 7,225 operating hours per year.

Notably, electrolysis accounted for approximately 85% of total electricity consumption in configuration P1. The researchers emphasized that revenue from by-products is crucial to the process's economic viability.

By-product Volumes Could Determine Economic Viability

Brine electrolysis produces not only caustic soda but also hydrogen and chlorine. Based on stoichiometric calculations in this analysis, each tonne of soda ash corresponds to approximately 0.67 tonnes of chlorine and 19 kg of hydrogen.

For a plant producing 1,000 tonnes of soda ash per day, the estimated by-product output would reach approximately 670 tonnes of chlorine and 19 tonnes of hydrogen daily.

Applying the prices assumed in the study, hydrogen could generate revenue of around USD 95 per tonne of soda ash, while chlorine could contribute approximately USD 134 per tonne of soda ash. These amounts represent substantial potential revenue relative to the estimated operating costs.

However, producing large quantities of by-products does not necessarily mean that all of them can be sold. The paper identifies hydrogen and chlorine as potentially marketable products, but the material reviewed does not provide a full assessment of whether the market could absorb such a large volume of chlorine. The sensitivity of the process economics to changes in hydrogen prices also requires further examination.

Consequently, market demand for by-products, storage and transportation requirements, and the costs of handling any unsold output are important factors in evaluating the process's practical feasibility.

Negative Carbon Emissions Depend on the Electricity Source

Based on the chemical stoichiometry, the reaction can absorb approximately 0.415 tonnes of CO₂ per tonne of soda ash. The paper's introduction gives a similar figure of around 400 kg. However, the net uptake reported in the abstract is only approximately 0.15 tonnes of CO₂ per tonne of soda ash, substantially lower than the stoichiometric amount.

One possible explanation is that the figure of 0.15 tonnes accounts for emissions associated with electricity consumption. However, this is an inference from the reported figures rather than an explanation explicitly confirmed in the paper.

In its emissions calculations, the research team considered only electricity consumption and applied an emissions factor of 0.127 kg CO₂-equivalent/kWh, corresponding to the value used for onshore wind power. Emissions associated with the production and treatment of raw brine, as well as the handling of hydrogen and chlorine, were excluded. The authors stated that a full life-cycle assessment would be needed in future research.

Based on a reverse calculation in this analysis, if the electricity emissions factor exceeds approximately 0.2 kg CO₂/kWh, the process may no longer achieve net-negative emissions. The potential for negative carbon emissions therefore depends significantly on the electricity source and the system boundaries used in the assessment.

In other words, capturing CO₂ from the air does not automatically make the entire process carbon-negative. Establishing its actual climate benefit requires accounting for emissions throughout the supply chain, including raw material production, operation, by-product handling, and other associated stages.

The Model Remains at the Preliminary Feasibility Stage

The study provides some validation for individual process models. The thermodynamic model was compared with data from the literature and experiments conducted by the research team, as presented in the supplementary information. The absorption-column model had also been validated in an earlier publication.

However, the integrated process as a whole has not been experimentally validated. The electrolyzer was not simulated directly; instead, a model from the literature was used to represent it. The dimensions of the absorption column and humidification equipment were estimated using correlations reported in previous studies. The cost of the vacuum compressor was estimated based on conventional compressors, although actual cost estimates would require additional data from equipment manufacturers.

Heat integration between process stages was also assessed only at a preliminary level. The simulation results therefore provide an initial basis for evaluating the process configuration and its economic drivers, but they are not sufficient to establish the operating performance or costs of a real industrial plant. The authors themselves characterize the work as a preliminary feasibility study and recommend further development and scale-up of the technology.

Overall, CODA presents an approach to soda ash production that combines brine electrolysis with direct air capture of CO₂. Its feasibility, however, depends not only on the ability to capture CO₂ but also on electricity costs, access to low-carbon power, the marketability of hydrogen and chlorine, and the reliability of the assumptions used in the economic model. Experimental validation at a larger scale and a more comprehensive assessment of life-cycle emissions will be necessary before its commercial potential can be established.

Reference
Gutierrez, M. F., Lorenz, H., & Schulze, P. (2025). “Carbon-negative production of soda ash: Process development and feasibility evaluation.” Industrial & Engineering Chemistry Research, 64(23), 11474–11496. https://doi.org/10.1021/acs.iecr.5c00483