E-fuels make CO₂-neutral car journeys a possibility

For many, CO₂ is the epitome of climate change. But CO₂ is more than just a greenhouse gas: it’s also a chemical building block that can be used in many ways: for example, to produce synthetic diesel, which generates far less emissions than fuels made with petroleum.

Thanks to lower fine particulate and NO₂ emissions, this would be directly beneficial for the environment. At the same time, the use of such fuels would assist in protecting the climate, as no carbon dioxide would be emitted from fuel additionally burnt.

The concept of producing synthetic diesel fuel from power plant flue gases may soon become reality at the Niederaussem Coal Innovation Centre. Over the next two years, a pilot facility will be built at this RWE site with the goal of harnessing carbon dioxide in the interests of climate protection.

Capturing and utilising CO₂

At the end of 2017, in cooperation with BASF and Linde, CO₂ scrubbing, a method for CO₂ separation and storage – known as CCS, or carbon capture and storage – was successfully tested and perfected for market use at RWE’s Niederaussem plant. Scrubbing the flue gases at the lignite-fired power plant with optimised plant engineering (BoA) yields pure CO₂, which can be utilised as a valuable raw material in other chemical processes.

With this carbon dioxide, the new pilot facility at the Niederaussem plant will produce a fuel that can be used in any diesel engine. Only a few changes need to be made to the fuel tank and injection system, as this synthetic fuel has a slightly lower calorific value and must be stored under pressure. No additional catalyst processes or additives are necessary for the new fuel to burn with lower emissions of particulate matter and nitrous oxides compared to traditional diesel fuel.

CO₂ is used to produce dimethyl ether

This new fuel is actually a substance which is quite well known from daily life: dimethyl ether, or DME for short. This chemical is currently primarily used as a propellant in spray cans. But the easily flammable, non-toxic gas has characteristics that make it ideal for use as a fuel. In addition to carbon dioxide, you only need water and electricity to produce DME. By electrolysis, water is broken down into its components: hydrogen and oxygen. The resulting hydrogen then reacts with CO₂ in a synthesis unit, yielding the desired dimethyl ether with the chemical formula C₂H₆O.

The ability to store renewable electricity

The CO₂ used to produce this fuel at the pilot facility in Niederaussem is obtained directly from the flue gases resulting from burning coal to generate electricity. In the future, the electricity for the electrolysis will mainly come from surplus electricity generated by renewables. This means, for instance, that wind power could also be used at night when production from wind farms would otherwise overwhelm the public supply infrastructure. With the production of dimethyl ether, it is thus possible to store surplus green electricity over the long term, helping to solve one of the core problems of the energy transition.

From CCS to CCU

The pilot facility in Niederaussem is an excellent example of how carbon capture and storage (CCS) technology can be used for carbon capture and usage (CCU) technology, allowing the sequestered carbon dioxide to be utilised for economic purposes.

This project, entitled ALIGN-CCUS, received funding of around 1.7 million euros from European Union (EU) and the German government. Two other projects involving the use of captured CO₂ are OCEAN, which focuses on the production of oxalic acid as a base material for high-quality chemical products, and LOTER.CO2M, which aims to make the production of methanol more efficient. This allows the greenhouse gas CO₂ to be transformed into a new raw material.