Production of solid hydrochar from waste seaweed by hydrothermal carbonization: effect of process variables

This study provides a comparison of hydrothermal carbonization (HTC) char, starting from two different species of waste seaweed, namely the green algae Ulva pertusa and the brown algae Sargassum horneri . The effect of reaction temperature (180 ~ 250 ℃), biomass residence time (1 ~ 6 h), and water mass ratio (1 ~ 10) on HTC yield (38 ~ 57%) was investigated. Surface area (5 ~ 52 m 2 g −1 ), methylene blue removal efficiency (71 ~ 99%), methylene blue adsorption capacity (11 ~ 88%), and hydrochar composition have been assessed. An increasing residence time and HTC temperature led to an increase in surface area up to a maximum of 51 m 2 g −1 , while the yield in HTC hydrochar decreased around 35% for both HC. The van Krevelen diagram was extended to compare the variation in elemental composition of the waste seaweed derived hydrochars. Results of the methylene blue adsorption experiments are best described by a Langmuir model with maximal adsorption capacity values of 112 ± 7.63 mg g −1 for the Sargassum based char, produced at 180 ℃, with water/biomass ratio of 5 and 4 h residence time. Graphical abstract