MechanicalTree at ASU Could Slow Carbon Emissions and Climate Change


A stainless steel drum sits under a blue gantry at Arizona State University in Tempe on March 15, 2022. The drum is filled with 150 sorbent-filled discs, which are pulled apart like an accordion to expose them to more air, says Travis Johnson, associate director of ASU’s Center for Negative Carbon Emissions. (Photo by Emma VandenEinde/Cronkite News)

TEMPE – As carbon emissions rise steadily, engineers at Arizona State University are working to slow its damaging effects by creating tree-like metal structures that attract carbon dioxide like a magnet and trap it like a sponge.

A prototype of what is trademarked as MechanicalTree sits in a small lot next to ASU’s Biodesign Institute. A dark blue arch – known as the portico – towers over what appears to be a 10ft tall beer keg. But you won’t find any foam inside.

“Inside that drum right now is 150 discs,” said Travis Johnson, associate director of ASU’s Center for Negative Carbon Emissions. “On these discs is the sorbent that captures the CO2. So that’s where the magic happens.

(Audio by Emma VandenEinde/Cronkite News)

The magic his team is trying to create involves removing carbon dioxide from the atmosphere without requiring expensive materials or the assistance of power-hungry machinery to blow wind through it.

The project was researched by Klaus Lackner, director of ASU’s Center for Negative Carbon Emissions, and marketed by Carbon Collect Inc., a renewable energy manufacturer in Dublin. The tree is one of six projects funded by the US Department of Energy to slow the effects of carbon dioxide in the environment.

The ASU team received $2.5 million to build the device. The objective is to build three “tree farms” in the coming years to capture 1,000 tonnes of CO2 per day.

Climate change is accelerating

Carbon emissions, which are a major contributor to climate change, are increasing. The U.S. Energy Information Administration found that oil-related carbon emissions increased 8% in 2021 and are expected to increase 5% this year. This increase in carbon dioxide accounts for two-thirds of the temperature increase in our climate, according to the National Oceanic and Atmospheric Administration.

Scientists fear that the world is not adapting fast enough to cope with this change. This point emerges from the latest report of the United Nations Intergovernmental Panel on Climate Change, which also indicates that heat caused by carbon emissions is killing crops, trees and fish – all of which contribute to the survival of the planet.

“The problem of carbon in the atmosphere is turning out to be a much tougher problem than I think people expected it to be,” said Gary Dirks, president of Carbon Collect. “We are literally not progressing at the pace we need to.”

Dirks said ASU’s trees are a step to help reduce emissions.

“We need to stop broadcasting as quickly as possible,” he said, “but if we go over, we’ll need something that can bring it back again.”

Part of the disc structure sits inside the Biodesign Institute at Arizona State University in Tempe on March 15, 2022. Each triangular corner is filled with a sorbent that attracts and captures carbon dioxide from the air . (Photo by Emma VandenEinde/Cronkite News)

How does the “tree” work?

Johnson said the MechanicalTree is the next tool in the climate researchers’ toolbox.

To capture the carbon, the blue gantry extends the device like an accordion to expose its “leaves” so the wind can blow on the CO2, grabbing the sorbent, a porous material that looks a lot like moonsand.

“You can see the stainless steel drum over there with the lid on top, which is being hoisted up there in the air,” Johnson said. “The lid comes off and the discs are attached to it. So it comes back a bit like an accordion.

When activated, the MechanicalTree stays open for 20-30 minutes to catch a breeze.

“Each of these cut corners is filled with these bags of sorbent,” Johnson said. “You can see these very small beads here, and there will be about 14,000 of these bags filling this tree.”

The sorbent works like a magnet, retaining the carbon dioxide like a sponge until the discs are lowered back into the steel drum. Then the carbon is stored underground or reused for products such as soft drinks.

“The goal is to make sure every little piece of sorbent is exposed to the air every time. That way we maximize system efficiency and capacity,” Johnson said.

Will it make a dent?

A MechanicalTree should collect approximately 187 pounds of carbon per day. A normal tree catches only 48 pounds per year.

However, Dirks said one tree would not solve the planet’s carbon problem.

Travis Johnson, associate director of ASU’s Center for Negative Carbon Emissions, holds a bag of sorbent in a lab at the Biodesign Institute in Tempe on March 15, 2022. The material looks a lot like moonsand, but it actually attracts carbon like a magnet and absorbs it like a sponge. Each MechanicalTree will use 14,000 bags of sorbent. (Photo by Emma VandenEinde/Cronkite News)

“It will take millions of trees to make a difference,” he said. “Twelve trees will capture about a ton a day. The need for intervention is quantified in gigatonnes, that is to say in billions of tonnes.

Thirty-five million mechanical trees would be needed to begin reducing gigatons of carbon. A gigatonne is the same mass as 200 million elephants – a large number that would take years to reach.

But ASU’s fast manufacturing might make that time frame more achievable.

“Think about making cars,” Johnson said. “We can learn quickly because we make them so quickly, so we can inject that new learning into production and learn faster and lower the cost curve.”

And unlike other projects, this one doesn’t depend on anyone being there for the tree to work.

“We rely on the wind to blow our sorbent, unlike other companies that do, all of which have big giant fans or blow air,” Johnson said. “So we try to avoid that cost.”

The effects of the MechanicalTrees won’t really be seen for five to seven years – construction takes time, and the future of the project depends on more federal investment and grants.

But for Johnson, creating these trees is personal.

“I have four little kids and I want to be able to tell them that I tried to stop some of the bad consequences that you have to deal with,” he said.

For now, the MechanicalTree team is collecting data on their model in Tempe. He plans to load the shaft with sorbent and start collecting CO2 within the next two months.

If successful, there could be more of these mechanical trees across the country in the next few years.


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