Sonochemical conversion of CO2 into hydrocarbons: The Sabatier reaction at ambient conditions

Md Hujjatul Islam; Odne S Burheim; Jean-Yves Hihn; Bruno G Pollet

doi:10.1016/j.ultsonch.2021.105474

Sonochemical conversion of CO₂ into hydrocarbons: The Sabatier reaction at ambient conditions

Ultrason Sonochem. 2021 May:73:105474. doi: 10.1016/j.ultsonch.2021.105474. Epub 2021 Feb 2.

Authors

Md Hujjatul Islam¹, Odne S Burheim², Jean-Yves Hihn³, Bruno G Pollet²

Affiliations

¹ Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. Electronic address: md.h.islam@ntnu.no.
² Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
³ Hydrogen Energy and Sonochemistry Research Group, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway; UTINAM UMR 6213 CNRS, Université Bourgogne Franche-Comté, Besançon, France.

Abstract

In this study, we investigated an alternative method for the chemical CO₂ reduction reaction in which power ultrasound (488 kHz ultrasonic plate transducer) was applied to CO₂-saturated (up to 3%) pure water, NaCl and synthetic seawater solutions. Under ultrasonic conditions, the converted CO₂ products were found to be mainly CH₄, C₂H₄ and C₂H₆ including large amount of CO which was subsequently converted into CH₄. We have found that introducing molecular H₂ plays a crucial role in the CO₂ conversion process and that increasing hydrogen concentration increased the yields of hydrocarbons. However, it was observed that at higher hydrogen concentrations, the overall conversion decreased since hydrogen, a diatomic gas, is known to decrease cavitational activity in liquids. It was also found that 1.0 M NaCl solutions saturated with 2% CO₂ + 98% H₂ led to maximum hydrocarbon yields (close to 5%) and increasing the salt concentrations further decreased the yield of hydrocarbons due to the combined physical and chemical effects of ultrasound. It was shown that CO₂ present in a synthetic industrial flue gas (86.74% N₂, 13% CO₂, 0.2% O₂ and 600 ppm of CO) could be converted into hydrocarbons through this method by diluting the flue gas with hydrogen. Moreover, it was observed that in addition to pure water, synthetic seawater can also be used as an ultrasonicating media for the sonochemical process where the presence of NaCl improves the yields of hydrocarbons by ca. 40%. We have also shown that by using low frequency high-power ultrasound in the absence of catalysts, it is possible to carry out the conversion process at ambient conditions i.e., at room temperature and pressure. We are postulating that each cavitation bubble formed during ultrasonication act as a "micro-reactor" where the so-called Sabatier reaction -CO₂+4H₂→UltrasonicationCH₄+2H₂O - takes place upon collapse of the bubble. We are naming this novel approach as the "Islam-Pollet-Hihn process".

Keywords: Carbon dioxide; Hydrocarbons; Sabatier reaction; Seawater; Sonochemistry; Ultrasound.