Fate of Nitrogen during Hydrothermal Carbonization

Abstract

Carrot green, the algae Chlorella pyrenoidosa, and straw as representatives for different types of biomass are converted by hydrothermal conversion. The amount of nitrogen remaining in the hydrochar as well as in the aqueous phase is determined, and the amount of nitrate, nitrite, and ammonia in the process water is analyzed. The nitrogen content of hydrochar has an significant impact on the properties of hydrochar; therefore, a control of the nitrogen content would be useful to design hydrochar for different applications. With regard to the fate of nitrogen, the different biomass feedstocks show significant differences as a result of the different chemical nature of nitrogen compounds in the feedstock. A complete removal of nitrogen from the hydrochar could not be achieved. In contrast, wood incorporates nitrogen when impregnated with the amino acid cysteine during hydrothermal carbonization.

Towards Biochar and Hydrochar Engineering—Influence of Process Conditions on Surface Physical and Chemical Properties, Thermal Stability, Nutrient Availability, Toxicity and Wettability

“…For the case of CD, this decrease with reaction severity is only observed for NO − 3 and PO 3− 4 (p < 0.05). These results are in contrast to observations from other HTC experiments, which reported an increase of NH + 4 in the liquid phase with reaction temperature or no significant change at all [69,72]. These contradicting results can be possibly explained with the varying nutrient concentrations used in the different experiments.…”

“…HTC of nutrient rich CD leads to different observations: the same amount of available nutrients of the feedstock are recovered in the process water for the case of NH + 4 and K + , but there is a significant reduction of NO − 3 and PO 3− 4 . This is likely due to the precipitation of salts, leading to a recovery of these nutrients with the solids [72]. Indeed, the observed high amount of extractable PO 3− 4 on the hydrochar (data not shown) cannot be explained by solved PO 3− 4 in the hydrochars moisture content, i.e., that a significant amount of solid PO 3− 4 precipitates during the reaction.…”

Feedstock-Dependent Phosphate Recovery in a Pilot-Scale Hydrothermal Liquefaction Bio-Crude Production

“…The nitrogen that was recovered in the HTL liquid phase, which resulted from the degradation of proteins under hydrothermal conditions [15,26], was clearly higher for HTL-SPR-LP than for HTL-PSS-LP. The different levels of nitrogen (as ammonium) in the HTL liquid phase between PSS and SPR resulted in different pH levels [68]. The pH of the HTL liquid phase from the processing of SPR became basic (pH 8.5), and that of PSS became neutral (pH 7.0), which in turn induced alteration of the mineral solubility.…”

Hydrothermal Carbonization Brewer’s Spent Grains with the Focus on Improving the Degradation of the Feedstock

“…With a higher water content, more N-compounds are solved and not incorporated in the hydrochar. In addition, at higher temperatures, N-containing functional groups are hydrolyzed [16].…”

“…As most of them also occur simultaneously, the study of the process is quite complex. According to Kruse et al [16], the reactions are divided on two major pathways. Firstly, the solid-to-solid conversion of original biomass takes place (here, the structure of the hydrochar has the morphology and structural elements of the initial feedstock).…”