Takahiro Nomura

For the sake of the recycle of waste PVC in the process of ferronickel production, reaction behaviors of mixtures of Fe2O3 and PVC, and NiO and PVC were investigated at elevated temperatures from 623K(350oC) to 1273K(1000oC) under Ar atmosphere. The obtained reaction products were examined using XRD and thermodynamic considerations were carried out. The explanations of reaction mechanism through thermodynamic consideration were excellent agreement with experimental results.HCl evolution occurred from 523K(250oC) to 650K(377oC) which was almost the same as the literature value. Reaction products of mixtures of Fe2O3 and PVC, and NiO and PVC at 623K(350 oC) showed an existence of FeCl2 and NiCl2 respectively. When temperature increased, Fe2O3 reduced to Fe3O4 from 723K(450oC) to 873K(600 oC) and completely reduced to Fe at 1073K(800oC) and 1273K(1000oC). The mixture of NiO and PVC showed a mixture of NiO-NiCl2-Ni at 723K(450oC), and reduced to Ni completely at 923K(650oC). These reduction behaviors occurred very low temperature in comparison with ordinary reduction system such as CO or H2 reduction. It was considered that a chlorination reaction in low temperature at 623K(350oC) will affect to the later reduction behavior in higher temperature.

Long-term thermal storage can decarbonize heat utilization by resolving mismatches between heat supply and demand. However, common heat storage materials cannot store energy for long periods. Here, we report an ultralong-term latent heat storage “glass” based on a ternary eutectic sugar alcohol mixture. The as-prepared material exhibits a solid–liquid phase change and glass transition at 423 and 289 K, respectively, with heat release via cold crystallization at 346 K. Remarkably, the glass transition temperature increases to 313 K after aging at ambient temperature for 12 hours due to structural relaxation. This phase change material (PCM) conserves the latent heat of fusion at 423 K for at least 180 days in the glass state at ambient temperature. These results establish a third-generation latent heat storage mode, retaining the charged state as a kinetically arrested amorphous solid and thereby fundamentally shifting the stability criterion from supercooled-liquid nucleation suppression to glass-transition and structural-relaxation kinetics.

This study investigates a passive type of thermal regulation for CO2 methanation using catalyst pellets, comprising Ni catalysts supported on pellets composed of an Al-Cu-Si based microencapsulated phase change material (MEPCM, heat storage temp.: 519 °C), with latent heat storage functions. The effects of catalyst bed configurations; a uniform type and multi-stage types on temperature profiles in the catalyst beds and CO2 conversion were mainly investigated. Here, uniform type is only Ni/Al-Cu-Si MEPCM pellets were packed. The multi-stage types are with different mass fractions of Ni/MEPCM pellets and MEPCM pellets (no catalyst) in each stage. Compared to the uniform configuration, the multi-stage gradient configuration demonstrated an extended duration of temperature stagnation at around the heat storage temperature of the MEPCM and a reduction in the steady-state temperature at the inlet-side location. This effect can be attributed to the dilution of the catalyst bed with Al-Cu-Si MEPCM pellets, which suppressed the heat generated by the reaction and prevented excessive temperature increases. On the other hand, at the downstream temperature, the two-stage gradient and three-stage gradient configurations exhibited shorter durations of temperature stagnation and higher steady-state temperatures. In addition, the CO2 conversion observed for the multi-stage gradient configurations were lower than that of the uniform configuration.

The need for thermal energy storage as a middle-long duration energy storage technology has increased in tandem with the widespread adoption of variable renewable energy sources. Latent heat storage using metallic phase change materials (PCMs) presents a promising solution by combining high thermal conductivity with high heat storage density. Recent advances in microencapsulated PCMs (MEPCMs) have addressed corrosion and leakage issues commonly associated with metallic PCMs. This study develops an MEPCM composite, with suitable structure, performance, and strength for adapting GWh-scale thermal energy storage systems, using an Al–Cu–Si-based MEPCM as the primary component. The MEPCM composite is fabricated by microencapsulating Al–Cu–Si eutectic alloy powder, which has a eutectic temperature of 520 °C, with an Al oxide shell formed via chemical conversion and heat-oxidation treatments, followed by mixing with an alumina sintering aid, forming, and sintering. The composite exhibits a heat storage density of approximately 1.0 GJ m–3 under a temperature difference (ΔT) of 200 °C, which is 2–3 times higher than that of conventional sensible heat storage materials. It retains both its heat storage performance and structural integrity after 1000 thermal cycles. The thermal conductivity ranges from 4.1 to 6.6 W m–1 K–1 between 300 and 600 °C. This study is the first to evaluate the compressive strength of composite PCMs in the liquid state, where the composite retains a compressive strength of 32 MPa at 600 °C—a value comparable to that of ordinary concrete. In the solid state, the composite exhibits 83 MPa at room temperature and 49 MPa at 500 °C. Thus, MEPCM composites are expected to possess substantial compressive strength for applications in medium-to-high-temperature heat storage and thermal management systems, even beyond the eutectic temperature of the PCM.