Synthesis and structural characterization of CO2-soluble oxidizers [Bu4N]BrO3 and [Bu4N]ClO3 and their dissolution in cosolvent-modified CO2 for reservoir applications

CO₂ utilization in upsteam oil and gas applications requires CO₂-soluble additives such as polymers, surfactants, and other components. Here we report the facile synthesis of CO₂-soluble oxidizers composed of judiciously selected organic cations paired with oxidizing anions. [Bu₄N]BrO₃ and [Bu₄N]ClO₃ are prepared using a double displacement synthetic strategy, whereby the crystalline product is readily obtained in high yield and structurally characterized using single-crystal X-ray diffraction. The facility of the approach is demonstrated through the preparation of several additional alkylammonium bromate compounds. Static solubility studies using a high-pressure cell with viewing windows showed that tetrabutylammonium compounds could be solubilized using cosolvent-modified CO₂. Using 4 mol% ethanol as cosolvent, >3 mM [Bu₄N]BrO₃ could be dissolved in CO₂, while ∼0.75 mM [Bu₄N]ClO₃ could be dissolved in the same solvent system. The solubility properties of [Bu₄N]BrO₃ along with its thermal stability up to ∼200 °C suggest that it is a promising oilfield oxidizer that can be utilized in subterranean CO₂ applications.

Bromate and chlorate salts were hydrophobically modified with tetrabutylammonium to yield oxidizers that are soluble in CO₂-cosolvent mixtures.