Life Cycle Assessment for Full Chain CCU Demonstration in the Align-CCUS Project –Dimethyl Ether and Polyoxymethylen Dimethyl Ethers Production from CO2 and its Usages in the Mobility and Electricity Sectors

As part of three years of research and development in the European ALIGN-CCUS project, a CCU demonstration plant was erected at the lignite-fired block K of the RWE power plant at Niederaussem, Germany. It was the aim to demonstrate the full chain of CCU - beginning with the capture of CO2 from the power plant flue gas stream, via the one-step synthesis of dimethyl ether (DME) through to its usage for electricity generation in a peak power diesel engine generator. A secondary target was the synthesis of polyoxymethylen dimethyl ethers (OMEs) and their use in the mobility sector. A thorough Life Cycle Inventory was collected based on real process data for the first time, supported by process modelling with AspenPlus. This includes the inventory for construction and operation of all elements of the demonstrator chain: the power plant with its monoethanolamine (MEA)-based post-combustion capture facility, the newly developed synthesis unit based on a one-step reactor using a bifunctional catalyst (up to 50 kg DME per day) and the reconversion of the produced DME into electricity by an adapted diesel power generator (60-80 litre per hour DME consumption, output 240 kWel). Additionally to the DME-route, the synthesis and usage of OME3-5 as a fuel in an adapted 2 l diesel motor for mobility application were part of the investigation. The extensive inventory enabled a Life Cycle Assessment (LCA) according to ISO standards showing results for both applications. Benchmarking technologies like diesel- and e-mobility and gas turbines for peak power supply enable a comparative analysis identifying advantages and disadvantages of the CCU route. A sensitivity analysis is used to identify weak points along the routes together with future development targets and potentials. To investigate a broad array of results, several varying scenarios, especially regarding energy supply were considered. The use of renewable electricity sources for electrolytic hydrogen production, but also for other processes of the CCU chain was investigated. A range of different impact categories were considered: Global Warming Potential (GWP), Particulate Matter Formation Potential (PM), Fossil Depletion Potential (FDP), Photochemical Ozone Creation Potential (POCP) and Terrestrial Acidification Potential (AP). The results show that the investigated CCU technology routes are highly emission-intensive when using the current German electricity mix: the reuse of CO2 and the reduction of fossil fuel consumption that goes along with it, is outweighed by the energy-intensive nature of the synthesis processes. Using renewable energy sources can drastically reduce GHG emissions, especially to a point where the implementation of a mostly renewable energy supply for the process chain offers a viable mitigation option compared to the investigated benchmark technologies. Findings regarding sensitive LCI data, development targets and technological potentials are discussed in the results.