Current and Foreseeable Applications of Supercritical Water for Energy and the Environment

Abstract

It is crucial to develop economical and energy-efficient processes for the sustainable transformation of biomass into fuels and chemicals. In this context, supercritical water biomass valorization (SCBV) processes are an alternative way to produce biogas, biofuels, and valuable chemicals. Supercritical water technology has seen much progress over the last fifteen years and an industrial application has merged: the supercritical water oxidation of wastes. The evolution from lab-scale to pilot-scale facilities has provided data on reaction mechanisms, kinetics, modeling, and reactor technology as well as an important know-how, which can now be exploited to use the reactivity in supercritical water to transform biomass into gases (CO, H(2), CO(2), CH(4), and N(2)) or into liquids (liquid fuel and valuable chemicals) with the supercritical water biomass gasification and liquefaction processes, respectively. This Review highlights the potential of SCBV processes to transform biomass into gas and liquid energy sources and highlights the developments that are still necessary to push this technology onto the market.

The BioSCWG Project: Understanding the Trade-Offs in the Process and Thermal Design of Hydrogen and Synthetic Natural Gas Production

“…% hydrogen cases was almost 4 times that recorded for the BioSNG cases. Similarly in block A2, the net reactor demand (hydrolysis + gasification) and the internal stepwise heating demand (salt separator heat jacket + SCWG reformer preheater) are significantly higher in the hydrogen cases compared to the BioSNG base case, all of which have a similar SCWG operating temperature of 600 • C. However, it is worth noting that the lower net reactor demand is also partially attributed to the endothermic nature of hydrogen formation pathways at 600 • C compared to the exothermic nature experienced with CH4 formation [7,9]. If the two BioSNG cases are compared, the influence of the SCWG reactor temperature at 450 • C for the 2nd case plays an additional role in the lower demand.…”

“…It is worth noting that the organic structure, solid-to-water ratio, residence time, pressure, catalysis and process units' mechanical configurations also influence the specific yields of each product as has been reported [4][5][6]9,11,[13][14][15][16]. However, such information available in literature is diverse and fragmented, and temperature levels remain the governing processing parameter that identify the product phase distribution.…”

“…The solubility of de-polymerized intermediates, some of which are char and tar precursors that account for conversion inefficiencies in more traditional processes, lead to higher recovery and utilization of the chemical energy initially stored within the solid feedstock. This feature was attributed by Loppinet-Serani [9] as the main motivation behind the current interest in SCWG and its already commercially available and energetically self-sufficient sister application of supercritical water oxidation (SCWO). The latter which is utilized for the degradation and destruction of organic and toxic sludge in water or agro-industrial waste treatment facilities.…”

“…At such acute conditions, above the vapor pressure of water, the organic constituents of biomass are decomposed and valorized into a wider range of value added products. Extensive reviews on technology progress, the advantageous nature of supercritical water's chemical and physical properties and the up-to-date research findings can be found in the publications of Yakaboylo et al [4], Akiya et al [5], Kruse et al [6,7], Brunner [8], Loppinet-Serani et al [9], Knez et al [10], Peterson et al [11] and many others.…”

Correspondence Between Structure and Reactivity During Hydrothermal Conversion of Lignocellulosic Macromolecules

“…Due to the complex chemical composition of lignocellulosic biomass, its hydrothermal conversion produces a complex mixture of products. The high polydispersity of these products in terms of oxygenated chemical functions and molecular weights makes their characterization awkward [7][8][9][10][11][12][13][14]. The approach that can be carried out to simplify the reaction pathway investigation consists in studying transformation of compounds representative of lignocellulosic constituents (i.e.…”