The study addresses the formation of secondary hydrochar and the morphology of secondary microparticles from black liquor. The black liquor solution was hydrothermally converted at 350 °C and 16.5 MPa in batch reactors running from 15 min to 24 h at different heating and cooling rates. Spherical carbon microparticles were obtained at a short reaction time (< 90 min) and then coalesced to form aggregates. At a very long reaction time (24 h), spherical carbon microparticles were obtained once again. The carbonaceous solid was enriched in carbon during the first 4 h of reaction. In parallel, the concentrations of total organic carbon and total phenols in the solution decreased drastically. The formation of solids was mainly due to chemical reactions occurring during the first 4 h. Subsequent changes in the solids were mainly due to physical reorganization since the chemical compositions of solutions were almost stable.

该研究解决了黑液中次级水焦的形成和次级微粒的形态。黑液溶液在分批反应器中以350℃和16.5 MPa水热转化，反应器运行15分钟至24小时，加热和冷却速率不同。在较短的反应时间（<90分钟）内获得球形碳微粒，然后聚结形成聚集体。在很长的反应时间（24小时）下，再次获得了球形碳微粒。在反应的最初4小时内，碳质固体富含碳。同时，溶液中总有机碳和总酚的浓度急剧下降。固体的形成主要是由于在最初的4小时内发生了化学反应。