Biobased bitumen analogue formation during hydrothermal treatment of microalgae residues, part 1: Influence of reaction enthalpy on the process

The hydrothermal conversion process of industrial Spirulina sp. residues into bitumen analogue is studied with an instrumented reactor heated at 260 degrees C under autogenous pressure. During hydrothermal conversion experiments, an exothermic reaction starts during the heating ramp above 200 degrees C and perturbs the thermal regulation of the process. The end of the reaction is detected from recorded pressure and temperature signals. Thermal insulation of the reactor and monitoring of the electrical energy input for thermal regulation allows estimating a total reaction enthalpy Delta H-r approximate to - 1.7 MJ/kg of dry biomass by performing two successive heating-isotherm experiments: First with biomass until complete reaction and again with reaction products after cooling. This second run is used as a reference for energy balance calculations.