An Exploratory Study of Hydrochar as a Matrix for Biotechnological Applications.

This paper explores the potentialities of hydrochar in protein separation and enzyme immobilization for non-energy biorefinery applications of hydrothermal carbonization. An innovative experimental procedure monitors soluble protein-hydrochar interactions and enzymatic reactions in a continuously stirred tank reactor. The hydrochar comes from hydrothermal carbonization of silver fir (200 °C, 30 min, 1/7 solid/water ratio) and standard activation (KOH, oven, 600 °C). Bovine serum albumin, a non-active, globular protein, was adsorbed at ≤3300 mg/g. Sip's isotherms fitted data well (R2 = 0.99999). The immobilization used a commercial ß-glucosidase, which catalyzes the hydrolysis of cellobiose to glucose, a bottleneck of the cellulose to fermentable sugar bioconversion network due to the fast enzyme deactivation. The hydrochar adsorbed ≤26 w/w% of enzyme. The heterogeneous biocatalyst operational stability was 24 times that of the soluble one. The results encourage further investigations and foreshadow process schemes coupling hydrothermal carbonization and industrial bioconversions.

Hydrothermal carbonization of waste biomass: An experimental comparison between process layouts.

This paper contributes to the knowledge on waste biomass conversion processes occurring in the presence of hot compressed water. The experimental procedure detailed herein assesses different process schemes based on the low-temperature reaction known as hydrothermal carbonization. The performances of two lab-scale reactor configurations, with and without a downstream flash expansion step, were evaluated and compared. Each setup was tested with six different types of waste biomass. Fir, beech, and olive prunings are representative of lignocellulosic raw materials, while potato, pea, and carrot are representative of non-lignocellulosic wastes from processing in the local agro-food industry. The batch reactions (200 °C, water/solid = 7/1) were carried out for up to 120 min. The hydrochars were characterized by elemental composition, humidity, heating value, and mass and energy yields. The extent of difference between the results obtained for the two procedures varied significantly with the material treated. At a residence time of 30 min, the solid yields increased due to expansion, ranging from 10 to 36% for lignocellulosic material and 50 to 220% for agro-food industry scraps. The downstream flash expansion step causes an increase of the solid yields, especially for hydrochars from lignocellulosic materials, leading to higher energy recovered compared to the configuration without expansion. Lignocellulosic and agro-food wastes behaved dissimilarly, likely because of different hydrothermal reaction pathways. The additional expansion step can considerably increase the efficiency of energy recovery in full-scale plants, the extent of which depends on the biomass waste substrate used.

Hydrothermal conversions of waste biomass: Assessment of kinetic models using liquid-phase electrical conductivity measurements.

This experimental study proposes the systematic monitoring of liquid phase electrical conductivity as a new technique for evaluating kinetic models for hydrothermal conversion of biomass. The application to the hydrothermal carbonization of three different wooden materials is validated by batch experiments at 200 °C, up to 120 min of reaction time, and at a 7:1 water to solid ratio. Whatever the biomass, the time course of electrical conductivity follows a unique law, unquestionably corresponding to the evolution of solid-phase carbon content. The model tested comes from literature, and is a simple first-order pattern. The network of elementary steps satisfactorily explains the experimental data. The evidence reported demonstrates that the electrical conductivity should become a standard measurement. In fact, this lumped parameter is for the first time used for predicting the time variation of furfural, an important compound ubiquitously found in the HTC liquid phases. Ordered trends also appear from experiments at higher temperatures, up to 440 °C, but the method highlights a different behavior. The observed discrepancies give useful feedback for steering the upgrading of kinetic equations toward a more structured model, which necessarily should account for the bio-crude. Additional runs with potato peels, an entirely different kind of biomass were used here as a stress test for the method, and as expected gave different results. This new response correctly signals that another model is required for describing the process applied to starchy materials, and confirms the power of the proposed technique as a tool for build-up suitable kinetic models.

Hydrothermal carbonization of Biomass: New experimental procedures for improving the industrial Processes.

This study aims to introduce new experimental methods, not yet described in the literature, to be adopted in hydrothermal carbonization processes. Silver fir was selected as model biomass in batch experiments in the range 200-300°C, up to 120min of reaction time, and at a 7:1 water to solid ratio. Simple equations were proposed for modeling the evolution of the process variables during the reaction, particularly the electrical conductivity of the liquid phase, correctly described by a simple two-step first order mechanism, regardless of the reaction temperature. At 200°C, a perfect correspondence (R2=0.9992) exists between liquid phase electrical conductivity and solid phase carbon content. The authors propose to monitor the industrial process withdrawing from the reactor the liquid and sampling its conductivity. The benefits of a flash expansion step between the reactor and the hydrochar drying units were discussed, and experiments demonstrated the usefulness of this process innovation.