Simulation-based environmental-impact assessment of glycerol-to-hydrogen conversion technologies

Abstract

Abstract This simulation-based comparative assessment aims to quantify the environmental and human-health impacts of greener hydrogen (H2) production via three glycerol-based technologies, including: supercritical water reforming (SCWR), aqueous-phase reforming (APR) and autothermal reforming (ATR). The GaBi (2018 edition) life-cycle assessment (LCA) platform is used to develop cradle-to-gate product system models for these technologies and the TRACI 2.1 methodology is used to quantify their midpoint impact categories. Aspen HYSYS (v11) process-simulation software is used to generate the life-cycle inventory (LCI) primary data required to produce 1 kg of H2 via each of the indicated glycerol-reforming technologies. Per ISO 14040:2006 reporting requirements for the LCA results interpretation step, three base case (BC) scenarios and four sensitivity scenarios (SS) are developed and quantified to compare the effects of different process electricity sources (US grid mix versus wind power) and thermal energy sources (natural gas versus biogas) on the LCA results. The high operating pressure (viz. 240 bar) of SCWR enabled assessment of the impact of in situ electricity generation to offset some of electricity required for this technology. The major insights from this research are as follows: (i) per 1 kg of produced H2, APR reduces CO2 emissions by ≈95% compared to ATR and by ≈92% compared to SCWR, (ii) for BC scenarios, the primary energy consumption (in MJ/kg of produced H2) is in the following order from highest to lowest: ATR > SCWR > APR and (iii) H2 production via glycerol APR is more environmentally sustainable than SCWR and ATR, and thus offers a promising path for greener H2 production. Future environmental sustainability studies should focus on expanding the scope of this study to include H2 production via water electrolysis using renewable electricity sources and via solar and nuclear-driven thermochemical water splitting.