Thermodynamic analysis and life cycle assessment of a new method for the preparation of ultrafine copper powders by supercritical hydrothermal synthesis integrating biomass supercritical water gasification

Supercritical hydrothermal synthesis (SCHS) technology is expected to produce small particle size, high-quality ultrafine copper powders on a continuous, large scale. However, current SCHS methods rely heavily on high-value chemical reductant agents for the reduction process. This paper proposed a new method for the preparation of ultrafine copper powders by SCHS integrating biomass supercritical water gasification (SCWG). The use of hydrogen from SCWG of biomass not only avoids the use of chemical reductant agents but also accelerates the reduction rate of the SCHS process. Here, the process model developed for the preparation of ultrafine copper powders was investigated by thermodynamic analysis and life cycle assessment (LCA). The exergy flow analysis showed that the modules with the highest exergy destruction in the original system were the cooler 2 (36.25 %) and the oxidation reactor (23.37 %). Waste heat recovery using the organic Rankine cycle (ORC) and biomass slurry preheating can increase the exergy efficiency of the system by 20.52 % and reduce the energy used to produce 1 kg of Cu by 38.41 MJ. Sensitivity analysis showed that decreasing the ratio of preheated water to slurry and increasing the SCHS temperature favored the system efficiency due to the reduced consumption of combustible gas in the oxidation reactor. LCA quantified the global warming potential (GWP) and acidification potential (AP) of the system during typical operation to be 15.81 kg CO₂-eq/kg Cu and 0.41 kg SO₂-eq/kg Cu, respectively. The use of carbon capture and storage (CCS) technology can avoid CO₂ emissions reducing the GWP to 2.93 kg CO₂-eq/kg Cu, which is 10.91 kg CO₂-eq/kg less than the cyclic solid-phase reduction method. This work may provide new conceptual designs for the preparation of ultrafine copper powders by SCHS.