Mapping Greenhouse Gas Emissions of the U.S. Chemical Manufacturing Industry: The Effect of Feedstock Sourcing and Upstream Emissions Allocation

Greenhouse gas emissions from 135 commodity chemical manufacturing processes in the United States were estimated based on benchmark process data from U.S. petrochemical manufacturing models. Total greenhouse gas emissions of the 135 processes evaluated are dominated by a small number of process types that have high emission intensities (emissions per mass of product produced) and high production volumes. These processes include facilities for manufacturing ethylene, ammonia, and chlorine. If upstream emissions associated with feedstock sources are included, well-To-gate emission estimates of the chemical manufacturing processes are affected by emission allocation and quantification methods in upstream production, with allocation methods becoming important when the feedstocks are sourced from oil and gas regions that produce multiple products. Well-To-gate emission estimates of ethylene (produced from ethane via steam cracking) and ammonia (produced from natural gas via steam methane reforming) ranged from 2.5 to 4.2 and 1.6-2.9 kg CO2e/kg production, respectively, depending on how upstream emissions are assigned to natural gas and natural gas liquids feedstocks and how methane emissions are quantified. Accurately characterizing emissions from upstream production of feedstock sources with consistent and transparent metrics is important in identifying potential emission reduction opportunities for chemical manufacturing and for evaluating greenhouse gas benefits arising from recycling of chemical products (e.g., plastics).