Keng Yinn Wong

Polyvinyl chloride (PVC) pyrolysis is constrained by chlorine release and undesirable product formation, limiting product quality and downstream utilisation. This study investigates the co-pyrolysis of PVC with eggshell (ES), a calcium carbonate-rich waste, to investigate its effects on chlorine chemistry, product distribution, and reaction kinetics. Thermogravimetric analysis confirms that the blends retain the characteristic two-stage degradation behaviour of PVC, while deviations in peak position and intensity indicate interactions between PVC and the calcium-rich phase. TGA–FTIR shows attenuation of C–Cl signals, indicating altered chlorine-containing species during co-pyrolysis. Py-GCMS shows increased mono-aromatic hydrocarbons from 58.1% in PVC to 71.9–78.6% in the blends, while bicyclic aromatics decrease from 11.1% to 5.1% and aldehydes from 13.3% to 1.5–2.3%. Synergism analysis indicates positive synergism for mono-aromatic formation and negative synergism for HCl, chlorinated hydrocarbons, and aldehydes relative to their theoretical contributions. The blends exhibit increased carbon content of 82.8–84.6 wt% and higher heating values of 36.5–37.1 MJ/kg. Kinetic analysis reveals conversion-dependent behaviour, with lower activation energies at early conversion followed by diffusion limitations at higher conversion. Overall, ES alters PVC pyrolysis through coupled chlorine and gas–solid interactions, favouring mono-aromatic formation while suppressing higher-aromatic and oxygenated pathway.

Practical Byzantine Fault Tolerance (PBFT) serves as a cornerstone consensus protocol for distributed systems. However, its inherent limitations, including quadratic communication complexity, scalability bottlenecks, and insufficient privacy protection, hinder its applicability in large-scale and privacy-sensitive environments. This study presents a systematic and comprehensive review of cryptographic advancements aimed at addressing these challenges. By analyzing peer-reviewed literature from 2015 to 2025, we demonstrate that the integration of Verifiable Random Function (VRF) and Boneh–Lynn–Shacham (BLS) aggregate signatures effectively reduces PBFT's communication complexity from O(N²) to O(N) or even O(logN), significantly enhancing scalability and reducing consensus latency. Moreover, advanced cryptographic schemes such as zero-knowledge proofs, homomorphic encryption, group signatures, ring signatures, hash ring, threshold signatures, attribute-based Encryption and lattice-based cryptography are shown to substantially strengthen consensus efficiency, privacy preservation and node security. Despite these improvements, trade-offs arise in terms of computational overhead and system complexity. The findings provide critical insights into the synergetic application of cryptography within PBFT-based systems and offer future directions for constructing scalable, secure, and privacy-preserving distributed architectures, particularly in Internet of Things and other resource-constrained scenarios.

Hybrid battery energy storage systems (HBESS) offer a promising solution for off-grid renewable energy systems by combining batteries with complementary power and energy characteristics. This study develops a multi-period mixed-integer nonlinear programming (MINLP) model in GAMS to optimize the sizing and operation of a hybrid lead–carbon (PbC) and lithium-ion (Li-ion) battery system for an off-grid industrial load supplied by solar photovoltaic (PV) generation. The proposed framework minimizes the total net present cost (NPC) over a 25-year project lifetime while accounting for battery operational constraints and degradation-related limits. Simulation results demonstrate a synergistic operational strategy in which the PbC battery supplies baseload energy, whereas the Li-ion battery is selectively deployed to handle short-duration high-power demand peaks. Comparative analyses with single-battery systems show that a standalone Li-ion system is the most expensive option despite requiring the smallest storage capacity, while a standalone PbC system appears economically attractive but is vulnerable to accelerated degradation under high-rate cycling. The HBESS provides a balanced compromise, achieving lower total system cost than the Li-ion system while improving technical robustness relative to the PbC-only configuration. Sensitivity analyses reveal that the economic feasibility of the HBESS strongly depends on the price differential between battery technologies and the intensity of load peaks. A hybrid configuration is optimal when the high-power battery remains significantly more expensive than the energy-oriented battery and when peak demand events are pronounced. The results confirm that coordinated hybrid storage can enhance system resilience and cost-effectiveness for off-grid renewable energy applications with highly variable load profiles.

The power sector is key to achieving net-zero as electricity demand grows with the economy and population. Cross-border electricity trading can provide cost and environmental benefits while meeting electricity needs. Taking ASEAN as a case study, this study develops an integrated qualitative and quantitative framework to identify practical, feasible strategies for regional energy transition within the context of cross-border electricity trading. The Carbon Emission Pinch Analysis – Automated Targeting Model (CEPA–ATM), complemented by a SWOT analysis, is used to identify the minimum renewable energy capacity required across different trading setups. Four scenarios of electricity source mixes are analysed: high-carbon fossil fuels, natural gas, a hybrid of renewables and natural gas, and an increasing share of renewables. Among these scenarios, trading natural gas proves most effective in the short term, preventing the need for an extra 54.25 TWh of renewable energy annually and substituting 8.38 TWh of coal each year. However, overreliance on natural gas might lead to carbon lock-in, emphasising the need to promote renewable energy alongside it. Policy recommendations focus on building political trust, improving connections to the ASEAN Power Grid, reforming fossil fuel subsidies, and directing revenue from natural gas trading to renewable energy projects. The integrated framework can be adapted to other regions to identify viable trading pathways and support SDG 17 through enhanced transboundary partnerships.