Towards industrial carbon recycling: Assessing the environmental and economic performance of CO2-based production of methane and methanol and derived polymers

Recycling CO2 within the technosphere by means of renewable energy may be regarded as key element of a future sustainable industrial metabolism. While renewable power becomes increasingly available in countries like Germany,... [ view full abstract ]

Recycling CO₂ within the technosphere by means of renewable energy may be regarded as key element of a future sustainable industrial metabolism. While renewable power becomes increasingly available in countries like Germany, the energy requirements for transforming CO₂ into hydrocarbons are significant and additional infrastructure like wind turbines is needed. Therefore, we compared CO₂- and renewable energy based production routes with conventional ones, in order to determine trade-offs between greenhouse gas savings and additional material resource requirements. We also analyzed the factors determining their economic performance and the conditions under which they could become commercial.

We analyzed the production of methane, methanol, and synthesis gas as basic chemicals and derived polyoxymethylene (POM), polyethylene and polypropylene as polymers by calculating the output-oriented indicator global warming impact (GWI) and the resource-based indicators raw material input (RMI) and total material requirement (TMR) on a cradle-to-gate basis. As carbon source, we analyzed the capturing of CO₂ from air, raw biogas, cement plants, lignite-fired power and municipal waste incineration plants. Our data were derived from both industrial processes and process simulations.

Life-cycle costing was employed on a cradle-to-gate basis in order to determine production costs of CO₂-based methane, methanol, PtL diesel, and POM in comparison with conventional routes. Possible scenarios were considered until 2030 and 2050, including both BAU and changes of regulatory factors.

The results demonstrate that the analyzed CO₂-based process chains reduce the amount of greenhouse gas emissions in comparison to the conventional ones. At the same time, the CO₂-based process chains require an increased amount of (abiotic) resources. This trade-off between decreased greenhouse gas emissions and increased resource use is assessed. The environmental preference depends largely on the source and amount of energy used to produce hydrogen.

Based on current prices, renewables-based CO₂ recycling to hydrocarbons is not commercial. It could become competitive in mid-term, when prices of natural gas and petroleum increase, and mandatory quotas like for PtL diesel would become effective and/or certain requirements of the Renewable Energy Act in Germany would be adapted, while CO₂ emission pricing would remain ineffective for that purpose.

Areas of surplus wind power, like in the Northwest of Germany, may be predestined to implement industrial symbiosis with CO₂ emitting plants to produce base chemicals.

Key words: Carbon capture and utilization (CCU), power-to-X, resource efficiency, global warming potential, life-cycle assessment (LCA), life-cycle-costing (LCC), regulatory analysis