Viscosity Variation of Model Compounds during Hydrothermal Liquefaction under Subcritical Conditions of Water

Abstract

Recent assessments in waste-to-energy technologies highlight hydrothermal liquefaction (HTL) as a suitable process for converting organic-rich waste with high moisture content into a useful resource. Organic waste materials, including sewage sludge, food, and agricultural waste residues, typically contain lipids, carbohydrates, proteins, and lignin with varying compositions depending on their origin. Fluid properties of reacting HTL slurries under subcritical water conditions, particularly viscosity and density, affect material flow and heat transfer in both batch and continuous HTL process systems. Real-time viscosity variations of 20 wt % water slurries of model compounds, sunflower oil, sucrose, and soy protein were determined in a stirred tank batch reactor using the Metzner−Otto method. Measured torque on the impeller shaft at a fixed impeller speed was used to determine the changes in the viscosity of the reacting slurry at different reaction temperatures. Changes in the viscosity of the sunflower oil mixture were insignificant as compared to viscosity variations with sugar-and soy protein-derived feedstock. The viscosity of the soy protein solution decreased rapidly with the temperature during hydrolysis of polypeptides into amino acids between 25 and 100 °C. Further increase in the temperature led to minimal changes in viscosity as more soluble compounds were produced above 100 °C. The viscosity of the sucrose solution changed significantly above 250 °C when carbon compounds precipitated from the solution. Viscosity variations of mixtures of model compounds were determined to predict viscosity changes in biomass.

Mixing Due to Natural Convection in a Hydrothermal Reactor: A CFD Study

“…Hydrothermal treatments are known for decreasing the viscosity of sludges, making their handling easier. , However, this effect is measured after the treated sludge is cooled down. Although recently Edifor et al described the viscosity variation of some model compounds under subcritical hydrothermal conditions, no study has ever provided a description of a sludge’s rheological behavior during the hydrothermal process itself. We have thus decided to employ a simplified approach to draw some first considerations.…”

Role of agitation in the freezing process of liquid foods using sucrose aqueous solution as a model liquid

“…This method was proposed by Metzner and Otto (1957), and its concept has been approved by many researchers, such as Anne-Archard et al ( 2006) and Kaminoyama et al (2011). The Metzner-Otto concept is mainly utilized for not only liquid mixing but also slurry agitation (Herman et al, 2012;Edifor et al, 2021). The definition of viscosity of frozen material is quite complicated.…”