Continuous hydrogenation of carbon dioxide to pure formic acid in supercritical CO2

August 6, 2012
Continuous hydrogenation of carbon dioxide to pure formic acid in supercritical CO2

(Phys.org) -- To reduce fossil fuel consumption while simultaneously improving the carbon footprint of fuels and chemical products, the use of carbon dioxide as a carbon source could be an attractive option. In the journal Angewandte Chemie, German researchers have now introduced a method by which carbon dioxide can be catalytically hydrogenated to make formic acid. In this process, carbon dioxide is not only a starting material; it also acts—in a supercritical state—as the solvent for separation of the product. This integrated approach makes it possible to directly obtain free formic acid as the product in a single step for the first time.

The hydrogenation of CO2 to (HCO2H) is a subject of intensive research because it offers direct access to chemical products based on waste products from the use of fossil fuels for energy. Formic acid is an important product in the chemical industry and has many applications, including agriculture, food technology, and the leather industry. It is also being contemplated as a potential hydrogen-storage material: vehicles powered by fuel cells could fill up with formic acid, from which the hydrogen could then be produced catalytically.

Homogeneous catalysts for the production of formic acid from CO2 have been investigated since the mid 1970s. The trouble with this process is that it involves an equilibrium reaction for which the equilibrium heavily favors the reactants. In order to suppress the constantly occurring back-reaction, the formic acid must be removed—in the form of a salt, adduct, or derivative—to take it out of the equilibrium. To obtain the desired free formic acid in the end, additional separation steps are thus required to separate the adducts from the catalyst and finally to release and isolate the formic acid.

A team led by Walter Leitner at the RWTH Aachen University has now developed a new concept that can be used to produce pure formic acid in a continuous process. The reaction and separation steps are integrated in a single processing unit.

Their trick is to use a two-phase reaction system that employs supercritical CO2 as the mobile phase and a liquid salt—an ionic liquid—as the stationary phase. The catalyst and the base used to stabilize the formic acid are both dissolved in the ionic liquid, which holds them both in the reactor. The CO2 flows through the reactor at pressures and temperatures above the critical values (74 bar, 31 °C) and selectively removes the formic acid from the mixture. The dual role played by CO2 as both reactant and extractive phase has significant advantages: The product is continuously extracted and flushed from the reactor, which causes the equilibrium to readjust constantly. Once out of the reactor, the free formic acid can be obtained with high purity by decompression or washing. Ionic liquids do not dissolve in supercritical CO2, nor do the catalyst and base, so these do not contaminate the product. The process can run continuously. In laboratory experiments, stable operation was demonstrated for over 200 hours.

“Our results with formic acid demonstrate that the systematic implementation of modern solvent techniques in continuous reactor equipment makes it possible to perform conversions that cannot be achieved under conventional conditions,” says Leitner. “Naturally we can’t ‘defeat’ thermodynamics in this way—but there are many possibilities for the integration of reactions and materials separation that may open new routes for more efficient and sustainable processes.”

Explore further: Formic acid in the engine (w/ Video)

More information: Walter Leitner, Continuous-Flow Hydrogenation of Carbon Dioxide to Pure Formic Acid using an Integrated scCO2 Process with Immobilized Catalyst and Base, Angewandte Chemie International Edition, dx.doi.org/10.1002/anie.201203185

Related Stories

Formic acid in the engine (w/ Video)

December 1, 2010

(PhysOrg.com) -- Do ants hold the key to the fuel of the future? Formic acid provides more efficient and safer storage of hydrogen. It is an ideal way to store energy from renewable sources or to power 21st century cars.

Putting a fuel cell 'in your pocket'

April 15, 2011

(PhysOrg.com) -- Technology using catalysts which make hydrogen from formic acid could eventually replace lithium batteries and power a host of mobile devices.

Baking powder for environmentally friendly hydrogen storage

June 14, 2011

(PhysOrg.com) -- Hydrogen is under consideration as a promising energy carrier for a future sustainable energy economy. However, practicable solutions for the easy and safe storage of hydrogen are still being sought. Despite ...

New catalyst for safe, reversible hydrogen storage

March 18, 2012

(PhysOrg.com) -- Scientists at the Brookhaven National Laboratory and collaborators have developed a new catalyst that reversibly converts hydrogen gas and carbon dioxide to a liquid under very mild conditions. The work -- ...

Modified microbes turn carbon dioxide to liquid fuel

March 29, 2012

Imagine being able to use electricity to power your car — even if it's not an electric vehicle. Researchers at the UCLA Henry Samueli School of Engineering and Applied Science have for the first time demonstrated a method ...

Recommended for you

Findings illuminate animal evolution in protein function

July 27, 2015

Virginia Commonwealth University and University of Richmond researchers recently teamed up to explore the inner workings of cells and shed light on the 400–600 million years of evolution between humans and early animals ...

New polymer able to store energy at higher temperatures

July 30, 2015

(Phys.org)—A team of researchers at the Pennsylvania State University has created a new polymer that is able to store energy at higher temperatures than conventional polymers without breaking down. In their paper published ...

How to look for a few good catalysts

July 30, 2015

Two key physical phenomena take place at the surfaces of materials: catalysis and wetting. A catalyst enhances the rate of chemical reactions; wetting refers to how liquids spread across a surface.

Yarn from slaughterhouse waste

July 29, 2015

ETH researchers have developed a yarn from ordinary gelatine that has good qualities similar to those of merino wool fibers. Now they are working on making the yarn even more water resistant.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

SteveL
not rated yet Aug 06, 2012
While I didn't completely understand the chemistry, I noticed that the picture of fingerprints at the head of this article had nothing to do with the actual article.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.