Greenhouse gas emission evaluation of the GTL pathway
Environmental Science and Technology
Sasol Synfuels International, Sasol North America, 900 Threadneedle, Houston, TX 77079-2990, United States; Sasol Synfuels International, 33 Baker Street, Rosebank 2196, Johannesburg, South Africa; Baker and o'Brien, Inc., 12221 Merit Drive, Dallas, TX 75251, United States
Gas to liquids (GTL) products have the potential to replace petroleum-derived products, but the efficacy with which any sustainability goals can be achieved is dependent on the lifecycle impacts of the GTL pathway. Life cycle assessment (LCA) is an internationally established tool (with GHG emissions as a subset) to estimate these impacts. Although the International Standard Organization's ISO 14040 standard advocates the system boundary expansion method (also known as the "displacement method" or the "substitution method") for life-cycle analyses, application of this method for the GTL pathway has been limited until now because of the difficulty in quantifying potential products to be displaced by GTL coproducts. In this paper, we use LCA methodology to establish the most comprehensive GHG emissions evaluation to date of the GTL pathway. The influence of coproduct credit methods on the GTL GHG emissions results using substitution methodology is estimated to afford the Well-to-Wheels (WTW) greenhouse gas (GHG) intensity of GTL Diesel. These results are compared to results using energy-based allocation methods of reference GTL diesel and petroleum-diesel pathways. When substitution methodology is used, the resulting WTW GHG emissions of the GTL pathway are lower than petroleum diesel references. In terms of net GHGs, an interesting way to further reduce GHG emissions is to blend GTL diesel in refineries with heavy crudes that require severe hydrotreating, such as Venezuelan heavy crude oil or bitumen derived from Canadian oil sands and in jurisdictions with tight aromatic specifications for diesel, such as California. These results highlight the limitation of using the energy allocation approach for situations where coproduct GHG emissions reductions are downstream from the production phase. © 2011 American Chemical Society.
Allocation methods; California; Co-products; Coproduct; Displacement method; Energy allocations; Gas to liquids; GHG emission; Heavy crude oil; Heavy crudes; Hydrotreating; International standard organizations; Life cycle analysis; Life-cycle assessments; Petroleum diesel; Production phase; Substitution method; System boundary expansion; Crude oil; Gas emissions; Global warming; Life cycle; Oil sands; Greenhouse gases; diesel fuel; bitumen; carbon emission; crude oil; diesel; energy resource; greenhouse gas; heavy oil; life cycle analysis; oil sand; sustainability; article; carbon footprint; diesel engine; greenhouse gas; life cycle assessment; methodology; Air Pollution; Conservation of Energy Resources; Environmental Monitoring; Gasoline; Greenhouse Effect; California; United States