What is Direct Air Capture? Part 3: Technology Comparison

This is the third part of a #WhatIsDAC series. Part 1 is about naming and cost estimates. Part 2 is about the world’s first commercial plant opening.

I first learned about direct air capture when I stumbled into a lab in Mudd, an engineering building at Columbia University in 2013. At the time, I was finishing a master’s degree in Environmental Science and Policy and had just begun a communications internship at the Lenfest Center for Sustainable Energy. I was tasked with writing the annual report and it was my job to put the advancements of the center for the year in simple terms. One of the experiments that I got to learn about has dramatically altered the course of my career over the last four years.

Moisture swing glovebox experiment at Columbia University

The experiment demonstrated how a material (an anionic exchange resin with a quarternary ammonium base embedded into Tyvek) could capture CO2 when dry and release it when moist. The material would collect CO2 from ambient air, and then when placed into an enclosed glovebox would release the CO2 and feed it to a plant. It was an invention that came from a now defunct start-up “Global Research Technologies” that was started by former Lenfest Center director Klaus Lackner and Allen Wright. Nonetheless, through presenting on progress that had begun in 2003, Lackner was able to inspire a handful of other direct air capture innovators who went on to start their own companies. I had the pleasure to move with Lackner and Wright to Phoenix in 2014 (until June 2016) when we started the Center for Negative Carbon Emissions at Arizona State University as part of an initiative to publicly demonstrate that direct air capture is affordable, socially useful, and can integrate into the broader sustainability framework.

As part of this work, I got to meet and learn from other start-ups doing similar extracting-CO2-from-the-atmosphere-work. The more I dug into the field while engaging with other parts of the sustainability ecosystem both from conventional carbon capture and storage as well as from renewable energies, the more I realized that DAC is generally poorly understood, often misconstrued, and certainly underfunded even as a potential solution to help reverse the effects of anthropogenic climate change. Each approach is a bit different, but the similarity is that all have an industrial process that is trying to do three things:

  1. Contact the air

  2. Get the CO2 off the contactor

  3. Regenerate the contactor to collect CO2 again

Contactors can be liquid sorbents or solid adsorbents. Those processes can be driven by heat, moisture, and pressure and amongst the companies pursuing the processes there is divergence of the most optimal way to doing that using the least amount of energy and resources. Once you have the CO2 there is a question of what you do with it, why you would need it, how this can serve an existing or create a new market. It remains to be seen what approach will take off and capture the imagination of early adopters who are willing to pay more or policy makers who are willing to put incentives to drive it – I have written ideas last November in “A Secret Master Plan for Direct Air Capture.” All the efforts that are trying to capture CO2 from the atmosphere are motivated however, but the vision of a future that needs negative carbon; one which has weaned itself off fossil fuels but still requires carbon. While it may be more difficult (and expensive) to extract CO2 from the atmosphere versus from a direct emission, DAC has a few unique advantages to become a potentially disruptive force for carbon management.

  1. Commercial demonstration costs are in the millions, not billions. In a world that is cost constrained to pay for expensive first of a kind commercial plants
  2. Modular approaches allow them to scale in numbers and mass manufacture allowing for more rapid cost declines
  3. We have a choice to not burn fossil fuels, but we don’t have choice to not balance the total amount of CO2 in the atmosphere
  4. Since CO2 exists in the air everywhere, theoretically DAC units can go anywhere

Below is a review of the companies and research efforts which either have or are on the pathway to constructing commercial scale plants.

Start-up Companies

Carbon Engineering

Carbon Engineering Pilot Plant in Squamish, BC (air contactor on the right). Credit: Pembina Institute

How the process works: They pull air through a sodium hydroxide liquid solution and absorb CO2 on small pellets. These pellets then double in size and are heated up in a calciner with natural gas using a calciner to drive the CO2 off, resulting in 99% purity CO2.

The special sauce: Of all the direct air capture companies, Carbon Engineering uses the most off-the-shelf-technologies and methods which allow for easier techno-economic-assessment estimates. Their process is quite like what is used in a paper mill.

Progress/First Markets: Carbon Engineering opened their 1 ton a day unit in Squamish, British Columbia in 2015. They have recently partnered with Greyrock Energy to produce liquid hydrocarbons via electrolysis. Pure CO2 + water + electricity = ultra-low carbon fuels. Since they use natural gas to heat up their process, they are not completely carbon neutral and removing/recycling one ton of CO2 from the air will release around 1.5 tons when the fuel is burned.


Photo taken at Climeworks plant opening

How the process works: Climeworks pulls air through a proprietary filter material that saturates with CO2 and then releases it through the application of low grade heat.

The special sauce: They are able to take advantage of waste heat and build in modules they can multiply in numbers which allows them to mass produce and scale more quickly.

Progress/First Markets: Climeworks commissioned the first commercial integration of a unit that feeds 3 tons per day to a greenhouse. They have 7 more integrations that will role out over the next two years which includes CO2 for beverage carbonation, synthetic fuels, sequestration and potentially others.

Infinitree (USA)

How the process works: Infinitree uses the moisture swing technology first invented by Lackner and Wright at Global Research Technologies, subsequently enhanced by Kilimanjaro Energy, and further improved by Infinitree engineers to rotate contactors through dry and wet environments to deliver CO2 directly.

The special sauce: Unlike the other approaches pursuing direct air capture, this process is completely passive by relying on evaporation to regenerate the contactor. This approach has the advantage of using virtually no additional energy to upgrade CO2 from ambient concentrations to desired levels for greenhouses.

Progress/First markets: Infintree intends to supply CO2 enriched air to accelerate plant growth in indoor greenhouses as well as for duckweed applications.

Skytree (The Netherlands)

High concentration CO2 prototype: photo credit Max Beaumont

How the process works: Skytree uses a solid sorbent that captures CO2 on distributed plastic beads. It is regenerated by low-grade heat. They have two prototypes: a gas enrichment prototype and a CO2 supply prototype.

The special sauce: Recognizing that the smallest quantities of CO2 command the highest prices, Skytree is occupying a small demand for CO2. Their technologies have been modified from space technology.

Progress/First markets: Skytree is collaborating with the Gensoric and Innergy teams to build zero carbon methanol synthesis units powered by renewable energy which should be functional by the end of summer.

Global Thermostat (USA)

Demonstration Plant in Menlo Park, Ca. Photo Credit: MIT Technology Review

How the process works:Global Thermostat uses an amine-based chemical sorbent bonded to honeycomb ceramic monoliths. It takes advantage of waste heat and a steam solution to release the CO2 from the contactor.

The special sauce: Global Thermostat uses a contactor with high surface area and lowest pressure drop to move the air. Their method also has fast kinetics and their cost estimations of capturing 1 million tons/year range between $10-35/ton.

Progress/First markets: Global Thermostat is pursuing 6 commercial merchant CO2 integrations in different verticals including beverage carbonation, water desalinzation, among others, with a strategy to roll out 40 plants in 7 years. .

Soletair (Finland)

How the process works: Soletair uses low grade heat to drive a fully integrated direct air capture adsorption/desorption process with an electrolyzer that uses a contactor and low-grade heat and then create liquid fuels.

The special sauce: Soletair is building a mobile unit that will be fully fitted with renewable energy and can go anywhere to make carbon neutral fuels from air and water. Among other aspects, this research effort is paying attention to the effects of capturing CO2 at different temperatures. Since CO2 exists everywhere, optimizing a process to the local environment is a key part of their research.

Progress/First markets: The current demonstration unit is capturing around 3.8 kg of CO2/day and came online in April 2017. This is a project is a collaboration between VTT Technical Research Centre of Finland and Lappeenranta University of Technology LUT with a number of technical partners that runs from 2016-2018.

CNCE technician Jason Kmon holding a cube with the filter material in front of a piece of the sail. Photo Credit: ASU Now

Center for Negative Carbon Emissions (USA)

How the process works: The Center for Negative Carbon Emissions (CNCE) at Arizona State is developing units that operate like a folding sail to capture CO2 when open and dry, and release it when wet. This process has been shown at the lab scale to maintain over a 100 fold upgrade of CO2 from 0.04% (400 parts per million (ppm)) to ~ 5% CO2 (50,000 ppm) using only evaporation.

The special sauce: Because this approach uses the same underlying moisture swing technology as Infinitree, it is optimized for removing the most amount of CO2 using the least amount of energy, but operates best in warm dry climates. Because this research effort is not a commercial endeavor, CNCE has a goal to make result publicly available.

Progress/First Markets: The first integration for this type of technology will be shown as part of a Department of Energy Funded “Targeted Algal Based Biofuels” grant, delivering atmospheric CO2 to algae.


Also published on Medium.

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