Economic and environmental analyses for achieving net-zero CO2 emissions of a green diesel production process

Background

In this study, palm oil hydrotreating for producing green diesel has been thoroughly explored, emphasizing high yields, reduced environmental impact, and lower energy consumption, particularly with solar collectors.

Methods

This study addresses these gaps by evaluating impacts on multiple fronts, including carbon revenue, GHG emissions, and overall environmental effects. The Life Cycle Assessment (LCA) technique, utilizing the CML method developed by Centrum voor Milieukunde Leiden (the Center for Environmental Science at Leiden University, The Netherlands) in SimaPro®, is employed to assess the environmental impact of green diesel production processes. The CML method evaluates environmental impacts through three phases: characterization, which quantifies environmental loads; midpoint, which assesses intermediate impact stages such as global warming potential; and damage, which evaluates potential harm to human health, ecosystems, and resource availability. The scope of work includes simulating the production process and incorporating a CO₂ capture unit with Aspen Plus®. Additionally, kinetic parameters for the palm oil hydrotreating reaction were validated, and energy consumption was optimized using the Aspen Energy Analyzer.

Significant findings

The net-zero emissions of the green diesel (GD) production from crude palm oil (CPO) is achieved by using an integration of an evacuated tube solar collector (ETSC), heat exchanger network, and a post-separation CO₂ capture process. Through the life cycle assessment (LCA), the terrestrial ecotoxicity potential (TEIP) is identified as a significant environmental factor due to chemical pesticides used in the oil palm cultivation. The carbon neutrality is validated by producing 1 kg of GD from CPO down to 0.0617 kg total CO₂ emissions since the net CO₂ sequestration for palm oil from oil palm plantation is taken into account. Referring to the Guthrie method, the economic indicators including the net present value (NPV) and the payback period are estimated at around 0.9 M$ in the 15th year and 9 years, respectively, if the CPO purchase price and the GD selling price are assumed to be $0.47/kg CPO and $1.98/kg GD, respectively, and the increased annual carbon credit is taken into account.