Life Cycle Greenhouse Gas Emissions Analysis of the Chlor-Alkali Process and By-Product Hydrogen in the United States

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Hydrogen is considered a key energy carrier for which interest has grown over recent years. Chlor-alkali plants in the United States (U.S.) can potentially recover and supply the by-product hydrogen at scale. However, there is a scarcity of standard analysis for energy use and emissions associated with products from chlor-alkali plants owing to lack of data and variations in chlor-alkali plant technology and operation. A rigorous life cycle analysis (LCA) is needed to quantify the emissions of by-product hydrogen and other products from chlor-alkali plants. In this study, we performed well-to-gate (WTG) emissions analysis of chlor-alkali products based on U.S. plant operating data gathered from the U.S. Environmental Protection Agency’s (EPA’s) Chemical Data Reporting database, the U.S. Energy Information Administration survey EIA-923 form, and the EPA’s Greenhouse Gas Reporting Program. We performed process-level mass allocation to allocate energy use and emissions to the chlor-alkali products. This study shows that the by-product hydrogen has WTG CO2 emissions of 1.3–1.9 kgCO2/kg H2 for plants without combined heat and power (non-CHP) and 1.5–2.4 kgCO2/kg H2 for plants with combined heat and power (CHP). Furthermore, we identified that electricity upstream emissions are the key driver affecting the emissions of by-product hydrogen from non-CHP plants, while CHP emissions can be reduced by electricity export to grids with higher carbon intensity (CI). Finally, the study shows that chlor-alkali plants in the U.S. can potentially meet up to 320 kilotons of hydrogen demand (approximately 3% of total demand) annually.