Input Obstacles to Scaling DAC: Research Notes

The cost of energy and chemical resources makes DAC impractical for industrial scaling. Scaling up DAC means "a major refocusing of the manufacturing and chemical industries for sorbent production, and a large need for electricity and heat."

Background: There are 2 types of DAC: liquid and solid.

• Liquid solutions, commonly hydroxide solutions, remove CO2 from air passed through it, returning air to environment.

• Solid sorbent filters, commonly amine-modified sorbents like monoethanolamine (MEA), chemically bind to CO2 when air is passed through. CO2 can be recovered when sorbents are heated up.

Generally, lower temperature solid sorbent DAC is preferred to higher temperature aqueous solutions DAC due to lower heat supply costs and the potential to use waste heat.

This 2018 paper estimated the cost to remove 1 ton of CO2, taking advantage of waste heat, at $161 in 2020 and as low as $39 by 2050. However, it is important to note that these estimates were done in the context of a DAC system based in Morocco (a prime location for potentially sequestering carbon) and powered by a hybrid solar, wind, and battery system. So while these competitive removal costs show promise, we should understand that low carbon energy is a must for making DAC competitive with source capture or other carbon mitigation methods.



Replacement rates of solvents for liquid DAC and sorbents for solid DAC were used to calculate material and energy costs in this 2019 paper. These numbers are based on 30 Gt/year removal of CO2:

• 0.17-0.29 ton/ton of CO2 for solvent NaOH and sorbent MEA

• This translates to 5.1-8.7 Gt/year of NaOH and 2.15-3.67 TW-years of electricity for electrolysis.

  • Industrial electrolysis also produces huge amounts of Cl2 gas at 4.6-7.8 Gt/year, which is well over Cl2 utilization capacity of 76.8 Mt/year.

• While solid sorbents do not require as much energy as hydroxide solutions need for electrolysis, sorbents do require higher temperatures >800 degrees Celsius to regenerate.

  • This translates to 6.57-9.9 GJ/ton of CO2. This isn't as much energy as required by liquid capture, but taking into account the energy required to produce the inputs for MEA in sorbents (16.3–27.8 Gt of NH3 and 3.3–5.6 Gt ethylene oxide EO), would still amount to somewhere between 2-35 TW-years, depending on if the NH3 and EO are produced by natural gas or electrolysis.

• It is mainly the enormous costs of NH3 and EO inputs for MEA production that make solid sorbent DAC unviable.

For future innovations, more of these comprehensive techno-economic analyses are needed to assess process, but this study underscores the importance of assessing material and energy needs at gigaton scale as well.