The development of alternative processes for the production of chemicals was often caused by scarcities of particular resources, e.g., the oil embargo in Germany during the Second World War, leading to the development of the Fischer-Tropsch-synthesis of hydrocarbons ( Henrici-Olivé and Olivé, 1976), or the abundance of resources like coal leading to a majority of coal-based chemicals in China ( Xu et al., 2017). This would allow the chemical industry to use established process chains without major transformation challenges in the near future. By substituting the feedstock of these bulk chemicals-replacing fossil resources by renewables-the production processes and amounts of downstream products like plastics or pharmaceuticals could remain unchanged. A discussion about the effect of substituting bulk chemicals such as methanol or ethylene through CCU products was started by Kätelhön et al. While most of the latest publications focus on the production of power-to-gas or power-to-liquid fuels ( Merano and Ciferno, 2001 Jaramillo et al., 2008 Zhang et al., 2015 Sternberg and Bardow, 2016 UBA, 2016 Schmidt et al., 2018 Alhyari et al., 2019 Koj et al., 2019), only few consider the application of CCU for the production of chemicals ( Kaiser et al., 2013 Kim et al., 2014 Otto et al., 2015).
In order to reduce greenhouse gas (GHG) emissions and to access alternative carbon sources in the chemical industry, new approaches through carbon capture and utilization (CCU) are discussed in science and industry ( Mikkelsen et al., 2010 Kuckshinrichs and Hake, 2015 Otto et al., 2015 Sanz-Pérez et al., 2016 DECHEMA, 2017 Artz et al., 2018 Kätelhön et al., 2019). The intense use of fossil resources leads to growing carbon dioxide (CO 2) concentrations in the atmosphere and significant global warming, caused by the anthropogenic greenhouse effect ( IPCC, 2018). We therefore identify the reduction of emissions through improved base material production processes and recycling of aluminum, copper, steel and concrete as main objectives to reduce negative impacts for the production of basic chemicals from CCU technologies. The future scenario using improved background technologies leads to a further small reduction of GHG emissions and largely reduces other environmental impacts. At the same time, an overall reduction of the German GHG emissions by 6% is achieved, when using offshore wind power for these processes only. Replacement of all plants for the production of the investigated products in Germany with CCU processes would lead to a 2–7% higher total primary energy demand for the whole country. The main contributors to the environmental impacts are the energy supply for water electrolysis and direct air capture. At the same time, other environmental impacts like eutrophication and ozone depletion will increase. LCA results show that the synthesis of the investigated chemicals from CCU processes will reduce greenhouse gas (GHG) emissions by 88–97%, compared to fossil-based production routes, when electricity from offshore wind turbines is used. A scenario was set up by exchanging the background processes for the production of important infrastructure materials like aluminum, copper, steel, and concrete with future processes that are less resource intensive, less carbon intensive and include higher recycling rates (e.g., electric arc furnaces for steel production).
The system boundary includes all relevant processes from cradle to gate. Electricity is supplied by offshore wind turbines. Investigated process chains comprise the following technologies: CO 2 capture from an industrial point-source or from the atmosphere through direct air capture (DAC) alkaline water electrolysis for hydrogen production methanol synthesis methanol-to-olefins and methanol-to-aromatics synthesis including aromatics separation. Here, we present a life cycle assessment (LCA) on a cradle-to-gate basis for the production of the following large volume organic chemicals: methanol, ethylene, propylene, benzene, toluene, and mixed xylenes. The combination of carbon capture and utilization (CCU) and water electrolysis technologies can be used for the production of basic chemicals from carbon dioxide (CO 2) and hydrogen. Institute for Energy- and Environmental Research, Heidelberg, Germany.
Marian Rosental *, Thomas Fröhlich and Axel Liebich
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