Salting Effect in the Hydrothermal Carbonisation of Bioresources

The salting effect on the hydrothermal carbonisation (HTC) of two natural carbon precursors, sucrose and fish eggs, was investigated. Self-condensation of sucrose produced hydrochar microbeads whose size decreased with the salting-out effect according to Hofmeister's series. More interestingly, the condensation of sucrose on fish eggs allowed obtaining hollow hydrochar spheres whose thickness followed the same trend whereas their diameter only slightly decreased in the presence of a chaotropic salt. This finding was explained by the influence of the anions on the solubility of the hydrophobic polymers formed during HTC of sucrose combined with the denaturation of proteins from fish eggs. We thus showed for the first time that salting-in and salting-out effects may significantly influence the hydrothermal processes, which in turn is an easy and straightforward approach for tuning the structure of hydrothermal carbon materials.