Liquefied synthetic methane from ambient CO2 and renewable H2 - A technoeconomic study

Abstract Methane has enormous potential as a carrier for renewable H2. The required infrastructure for a methane gas economy is readily available, and it can compete with its energy-intensive liquefied hydrogen (LH2) counterpart. In this work, we conducted a technoeconomic analysis of the production of liquefied synthetic methane (LSM) from ambient CO2 and renewable H2. The process entails (1) capture of CO2 directly from ambient air, referred to as Direct Air Capture (DAC) using an amine-based system; (2) generation of H2 from renewable sources, (3) conversion of CO2 and H2 to synthetic methane; and (4) liquefaction of synthetic methane. The technoeconomic model used in this study is based on mass/material energy flow analysis and includes the economics of all processes involved. Building on our previous work, we reduced the overall capture cost for the studied scale of 0.291 t/h CO2 production from US$557 to ~$365/tCO2. At a scale equivalent to 1 MtCO2/year capture, which is the basis for production of LSM in this work, we estimated the cost of DAC to be ~$114/tCO2. Per GJ of methane produced, the overall cost of LSM was ~$31.5/GJ, comprising around $21.7/GJ ($2.4/kg H2) for hydrogen production, $5.6/GJ for DAC, $1.4/GJ for methanation and $2.8/GJ for methane liquefaction. The energy conversion efficiency of LSM was lower than for LH2, mainly due to the large amount of heat required for DAC. The levelised cost per unit of energy for LSM was lower at small scales, while the costs were the same (~$32/GJ) at a larger scale of 180 kt/year hydrogen production. Our detailed analysis provides insights into the suitability of LSM as a carbon-neutral fuel that can compete economically with LH2.