Evolution of coal molecular structure during constant current electro-oxidation of coal–water slurry in alkaline media

Abstract

Compared to the oxygen evolution reaction, coal–water slurry electrolysis as an anodic reaction can significantly reduce the cell voltage of the cathodic hydrogen evolution reaction or cathodic carbon dioxide reduction reaction. However, because the polarization curves of cathode and anode are different and vary with time, it is difficult to control the cell voltage and operation time so that the cathode and anode operate effectively under their respective optimum conditions at the same time. We investigated the evolution of coal during constant current electrolysis, where the reactions at the cathode and anode were simultaneously controlled by the circuit current. Constant current electrolysis was performed on coal–water slurries (CWS). The alkali-soluble matter separated from the CWS was subjected to constant current electrolysis and constant potential electrolysis. The results showed that constant current electrolysis was dominated by the oxidation of alkali-soluble matter, followed by the combination of alkali-soluble matter and residual coal, and finally the residual coal. The molar fraction of the aromatic bridgehead carbon in the residual coal increased from 0.132 to 0.214, which is close to that of the bicyclic structure of naphthalene (0.2). The aromatics in the alkali-soluble matter underwent a ring-opening reaction, the degree of condensation decreased from 0.08 to 0.03, and the aliphatic chain length increased from 1.77 to 2.38. The results provide a reference for simultaneously controlling the cathodic and anodic reactions using circuit current and time.