Continuous Photocatalytic Acetylene Conversion to Ethylene in Liquid Under Ambient Conditions

Ethylene is a basic building block for polymer synthesis, but its purification from petroleum-based processes (e.g., thermo-catalytic acetylene hydrogenation) and its production from coal-based processes (e.g., Fischer-Tropsch synthesis) normally require high temperature, high pressure, and gaseous hydrogen. Here, we report a continuous ethylene photosynthesis approach as a new platform technology that enables highly efficient and selective conversion of acetylene to ethylene in liquid under mild conditions. This platform technology is compatible with a wide range of solvents, catalysts, and hydrogen sources. Using Pd/mpg-C₃N₄ as the model photocatalyst, a complete conversion of acetylene was achieved with high ethylene selectivity (>93%) under the continuous flow of either a pure acetylene stream or a crude ethylene stream containing acetylene impurity. The process performance remained stable for at least 72 h. Physical, theoretical, and in situ spectroscopy investigations showed that the photocatalytic acetylene hydrogenation follows the proton-coupled electron transfer (PCET) and atomic hydrogen-mediated indirect electron transfer pathways with proton as the hydrogen source. The technoeconomic analysis (TEA) demonstrated that this photocatalytic approach has large profitable margins for both ethylene purification and ethylene production processes. This study provides a green and sustainable technology for both petrochemical (ethylene purification) and coal-chemical (ethylene production) industries.