Enthalpy change during hydrothermal carbonization of biomass: a critical review

Thermal Analysis Technologies for Biomass Feedstocks: A State-of-the-Art Review

“…The decreased activity of lignin at 250 °C accounts for the lower enthalpy of wood in comparison to cellulose. The process is predominantly exothermal, according to the literature on HTC, with an enthalpy change of the order of 1 MJ per 1 kg of dry biomass material [135]. Since the typical water/biomass ratio for biomass HTC ranges from 5 to 20, the separation of the thermal effect associated with the heating of water from that associated with the process is the main problem when dealing with the DSC measurements for the assessment of the enthalpy change of the HTC process.…”

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

“…It typically involves temperatures ranging from 180 °C to 250 °C and autogenous pressures of approximately 2-3 MPa with residence times of 3-6 hours. On the other hand HTL is generally used to produce bio-crude oil [1] and it involves shorter treatment (few minutes to 1-2 hours), higher temperatures (280 °C to 370 °C) and pressures (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) taking advantage of the water subcritical properties (which becomes a solvent and a reaction media).…”

“…According to a recent review article on enthalpy change during HTC [11], it can be evaluated by three different techniques : i) using the Hess law to make a balance between the energetic content of the initial biomass and the hydrothermal reaction products ii) performing DSC measurements mimicking HTC in high pressure capsules containing water and a few milligrams of biomass [12,13] iii) making energy balance on an ad hoc thermally insulated and instrumented HTC reactor [14].…”

“…Each method has advantages and drawbacks: while not needing thermal measurements, the application of the Hess Law requires a detailed characterization of the products (gases, liquid and solid, which are highly complex in HTC/HTL) and often leads to an overestimation of the enthalpy [11]. DSC measurements are particularly efficient for biomasses that are homogeneous such has pure cellulose [13] but lead to high standard deviation for more complex biomasses (35% for wood [13] though recently proposed experimental procedures seem to allow reducing this measurement uncertainty [12]).…”

“…DSC measurements are particularly efficient for biomasses that are homogeneous such has pure cellulose [13] but lead to high standard deviation for more complex biomasses (35% for wood [13] though recently proposed experimental procedures seem to allow reducing this measurement uncertainty [12]). For complex and non-homogeneous biomasses, the authors of the review article [11] suggest that measurements on an ad hoc HTC/HTL reactor is a better solution but that heat loss and thermal inertia issues have to be considered cautiously.…”