Decarbonisation Technology - February 2024 Issue

from electrolysis into their existing plants, and it is likely that more will follow. As a result, Haber- Bosch is expected to remain the dominant technology for green ammonia synthesis in the coming decades, especially at large scale. Renewable methanol production : Emerging new categories of ‘renewable methanol’, produced via a process that emits a minimal amount of greenhouse gases (GHG), are ‘biomethanol’ from sustainable biomass and ‘e-methanol’ from CO 2 and renewable hydrogen. In essence, these methanol synthesis routes significantly reduce carbon intensity and contribute to energy transition markets. The simplest and most mature method is to produce renewable hydrogen and use it for the catalytic reaction of captured CO 2 to form methanol. Several e-methanol production plants are in the pilot and demonstration scale around the world (Raman, 2023). Renewable and synthetic fuels  Biodiesel : Biodiesel is a renewable fuel that, as it is not entirely fungible with fossil diesel, is blended with fossil diesel and sold as B5, B10, and B20 grades. Most engines cannot run on pure biodiesel without modification, largely due to the higher viscosity of biodiesel, which can lead to issues in fuel injection and atomisation, potentially causing engine deposits and maintenance problems. Additionally, biodiesel has different solvent properties, which can affect engine seals and gaskets. The typical elemental composition of biodiesel includes a higher proportion of oxygen compared to traditional hydrocarbons, with biodiesel containing about 11% oxygen by weight.  Renewable diesel and SAF : Renewable diesel is fully fungible with fossil diesel, so it can be used as a drop-in fuel, which allows the use of existing transportation and distribution infrastructure. “ Most engines cannot run on pure biodiesel without modification, largely due to the higher viscosity of biodiesel, which can lead to issues in fuel injection and atomisation ” 11

One of the routes to SAF uses the same process as renewable diesel but produces kerosene-range hydrocarbons. As these fuels are from renewable sources, the carbon can be part of the carbon cycle. Although renewable jet fuel is fully fungible with fossil jet, blending is limited to less than 50% renewable content, as specified by ASTM D7566. Renewable jet from seed oil or animal fats is low in aromatics, so requires blending with fossil fuel in accordance with ASTM D1655. However, renewable jet can be produced via other feeds and contains aromatics. Several production routes are ASTM-approved, while others are progressing through the certification process.  Biogas : Biogas and biomethane are considered renewable or green fuel since it is produced via anaerobic digestion (AD) from organic matter such as food and agricultural waste, as shown in Figure 1. Biogas can be burned on-site to heat buildings and power boilers with little clean-up process. It can also be used for combined heat and power (CHP) operations or turned into electricity using a combustion engine, fuel cell or gas turbine, with the resulting electricity used on- site or sold onto the electric grid. Biogas can be upgraded to biomethane or RNG and then injected into the existing natural gas grid as well as pipelines, interchangeably with conventional natural gas. RNG can also be used as a vehicle fuel after it is converted to compressed natural gas (CNG) or liquefied natural gas (LNG). In essence, biogas can be upgraded to replace natural gas for use as a fuel for electricity production, ground transportation, and heating commercial and residential buildings. RNG can also be used as feedstock for hydrogen production via CH 4 pyrolysis, representing one of the lowest carbon intensity routes for hydrogen production (USDA, 2023).  Hydrogen : Hydrogen has a much lower GHG potential than CO 2 . Hydrogen can be directly used in fuel cell electric vehicles (FCEV) for application in transport and is twice as efficient as e-fuels-powered combustion engines (Skone, et al., 2015). It can be burned in turbines or combustion engines or transformed into