Suitability of hydrothermal carbonization to convert water hyacinth to added-value products

Abstract

Water hyacinth hydrothermal carbonization was studied under different temperature (160–250 C), time (30–120 min) and biomass/water ratio (10–50%) conditions. The research was designed following response surface methodology, which was very useful to infer interactions between variables and to develop models predicting the system behaviour with good accuracy. Output functions were solid yield, hydrochar C and N content, as well as their captures, and heating value. It was found that while temperature was the most influential variable promoting HTC reactions, time and even biomass load were decisive to provide particular C and N captures; based on these results, reaction mechanisms were discussed. On the other hand, 2D graphs allowed to build different scenarios in which target properties might be achieved under a wide range of dissimilar conditions, leading to process optimization. The study was complemented by exploring hydrochar surface properties by N2 adsorption at 77 K, SEM micrography and XPS analyses.