One electrolyser, three loops: how Parallel Carbon integrates direct air capture and hydrogen production

Parallel Carbon has been named in C&EN's 10 Start-Ups to Watch for 2026. The publication's profile focuses on the potential for our technology to make synthetic fuels and chemicals more competitive. This post looks at the process behind that story: how we integrate direct air capture (DAC) and hydrogen production in one system.

Why integrate DAC and electrolysis?

Direct air capture removes carbon dioxide (CO2) from the atmosphere. Water electrolysis produces hydrogen. Parallel Carbon's approach brings these processes together, using an electrolyser that produces hydrogen alongside the acids and bases used in the DAC process to produce CO2.

Integration is beneficial for two reasons:

• Two feedstock gases, CO2 and H2, are produced at the same site using the same power source.

• Equipment is shared across the two processes, helping to reduce capital costs.

  
  

By combining these processes, Parallel Carbon aims to produce both feedstocks more affordably than if each were produced independently.

Integrating CO2 capture chemistry with hydrogen production

Our capture process uses calcium hydroxide (Ca(OH)2) as a sorbent which reacts with CO2 in ambient air to form calcium carbonate (CaCO3).

Generating a pure CO2 gas for use or storage requires processing of the reacted CaCO3 sorbent through a water treatment process using an acid and a base. Treating CaCO3 with acid releases a concentrated CO2 stream and subsequent treatment with base regenerates the  Ca(OH)2 sorbent used in capture.

The acids and bases are produced by Parallel Carbon's proprietary membraneless electrolyser, which also produces hydrogen. These chemicals, along with the sorbent, can be stockpiled cost-effectively, allowing the capture process to continue operating when the electrolyser is switched off. The integrated system enables on-demand CO2 production from variable renewable power alongside hydrogen generation.

Parallel Carbon's integrated process connects three sub-processes: direct air capture using calcium hydroxide, water treatment to recover concentrated CO2 and regenerate the sorbent, and electrochemical production of hydrogen, acids and bases. The electrolyser supplies the chemicals needed for capture and regeneration, linking CO2 removal and hydrogen production in one system.

Designed around modular components

The process is designed around modular units, with each sub-process occupying a footprint comparable to a standard 20-foot container. This modular approach is intended to support deployment and replication without requiring the entire system to be built as a bespoke industrial installation.

The process also avoids the high-temperature calcination step used in conventional calcium-based sorbent regeneration, instead using an aqueous water treatment process. The electrochemically-driven process offers much greater tolerance to renewable power variability than thermal processes. Additionally, dedicated high-temperature process equipment is replaced by an electrolyser which produces the hydrogen co-product, reducing the equipment cost dedicated to DAC while increasing project revenues.

From hydrogen and CO2 to a wide range of products

Parallel Carbon is developing an integrated platform designed to supply the building blocks for a wide range of fuels and chemicals. Its outputs, hydrogen and captured CO2, support pathways to e-methanol, e-SAF (synthetic sustainable aviation fuel), e-methane, e-LNG and e-syngas, as well as e-urea, carbon-negative ammonia and carbon-negative hydrogen to name a few.

These products serve different markets, from aviation and shipping fuels to industrial chemicals and hydrogen supply. Using Parallel Carbon’s technology for Power-to-X applications simplifies project development, reduces production costs, and offers more degrees of freedom for finding sites with the most strategic and economic potential. By integrating hydrogen production with direct air capture, Parallel Carbon aims to provide two key inputs for these pathways within a single system.

Read the C&EN profile of Parallel Carbon and explore the wider 10 Start-Ups to Watch for 2026 list.