Carboxylation of Acetylene without Salt Waste: Green Synthesis of C₄ Chemicals Enabled by a CO₂‐Pressure Induced Acidity Switch

Abstract

The inherent formation of salt waste in C−H carboxylations is a key obstacle precluding the utilization of CO2 as C1 building block in the industrial synthesis of base chemicals. This challenge is addressed in a circular process for the production of the C4 base chemical dimethyl succinate from CO2 and acetylene. At moderate CO2 pressures, acetylene is doubly carboxylated in the presence of cesium carbonate. Hydrogenation of the C−C triple bond stabilizes the product against decarboxylation. By increasing the CO2 pressure to 70 bar, the medium is reversibly acidified, allowing an esterification of the succinate salt with methanol. The cesium base and the hydrogenation catalyst are regenerated and can be reused. This provides the proof of concept for a salt‐free route to C4 chemicals from biogas (CH4/CO2). The origin of this reversible acidity switch and the critical roles of the cesium base and the NMP/MeOH solvents were elucidated by thermodynamic modeling.

Influence of Solvents and Salts on CO2 Solubility and the Impact on an Esterification Reaction

“…Thus, electrolyte PC-SAFT (ePC-SAFT) advanced was developed, which contains a modified Born term to account for the concentration-dependent dielectric-induced solvation of the ions . This model shows predictive capabilities concerning CO 2 solubility. − Moreover, ePC-SAFT advanced was also successfully applied in previous works to model solid–liquid equilibria (SLE) of electrolytes in organic solvents, cf., Pabsch et al , In the literature, several works experimentally investigated the CO 2 solubility in organic solvents, such as alcohols, acids, and esters. − However, the CO 2 solubility in solvent mixtures containing electrolytes is scarcely reported in the literature.…”