A Study on the GHG Emission Factor of Co-Product Hydrogen in the NCC Process by LCA Allocation Methods

This study aims to quantify the greenhouse gas (GHG) emission factors of by-product hydrogen generated from the Naphtha Cracking Center (NCC) process using Life Cycle Assessment (LCA), and to analyze the differences in emission results based on the selection of allocation criteria. The allocation methods were categorized by referring to international LCA guidelines such as ISO 14044, EU Product Environmental Footprint (PEF), ILCD Handbook, and Hy Guide. Four allocation criteria were applied: mass, lower heating value (LHV), economic value, and mole number. The study examines how the choice of allocation approach significantly influences LCA results and the calculated GHG emission factors. Mass-based allocation offers simplicity and general applicability, but lacks the ability to reflect product characteristics. LHV-based allocation is reasonable when all co-products are used as energy sources, but may not be appropriate when their end-uses vary. Economic allocation reflects market reality but is highly sensitive to price fluctuations. Mole-based allocation is theoretically sound as it reflects chemical stoichiometry, but its practical applicability is limited due to the lack of precedent in industrial or policy applications. The calculated GHG emission factors for each method were as follows 1.25 kgCO2eq./kgH2 for mass based allocation, 3.219 kgCO2eq./kgH2 for LHV based allocation, 13.24 kgCO2eq./ kgH2 for economic value based allocation, and 13.93 kgCO2eq./kgH2 for mole based allocation.