Decarbonisation Technology - February 2024 Issue

potassium hydroxide, to form biodiesel, aka fatty acid methyl ester (FAME) and glycerine. Its composition varies as the feedstocks for biodiesel production are diverse, ranging from soybean oil to waste cooking oil, and even emerging sources like algae, expected to produce high yields from a smaller land or sea area. The production process yields approximately 100 pounds of biodiesel and 10 pounds of glycerine from 100 pounds of oil or fat. Glycerine, a valuable co-product, is used to produce pharmaceuticals (US DoE, 2022), (Pruszko, 2020), (Ahmed, et al., 2021). The methanol required to produce the biodiesel (FAME) is currently from non- renewable sources. In the future, FAME based on renewable methanol will make the blendstock totally renewable.  Hydrogen production : The two major pathways for renewable hydrogen production are shown in Figure 3 . The splitting of water molecules is done by electrolysis using renewable electricity, like wind and solar. The different systems that can be used for water electrolysis are the Anion exchange membrane (AEM), alkaline water electrolysis (AWE), solid oxide water (SOE), and proton exchange membrane (PEM) (US DoE, 2023). They operate using the same principles but under different conditions using different metal electrodes and electrolytes. There is a need to massively scale up the production of hydrogen from water as currently this represents less than 1% of hydrogen production (Bettenhausen, 2023) Biological and thermochemical mechanisms are the two approaches that can be used to produce hydrogen from biomass due to its large reserves and supply, easy oxidation, and high annual output. The thermochemical method is mainly made up of gasification and pyrolysis, in which the biomass is converted into hydrogen-rich gases and hydrogen. Both conversion methods produce CH 4 and carbon monoxide (CO), along with other gaseous products, which can be further treated using the water gas shift (WGS) and steam reforming processes to increase the yield of hydrogen. Of the two thermochemical methods, biomass gasification is an economical and efficient way

Renewable resources

Water feedstock

Biomass (hydrocarbon feedstock)

Electrolysis: Others could include Thermolysis and Photolysis

Biological treatment: Fermentation and Photolysis

Thermochemical treatment: Gasication, Pyrolysis, Combustion or Liquefaction

Figure 3 Hydrogen production pathways

contaminants, such as inorganic compounds. Although no change in chemical composition or conversion occurs, this is a key process in the upgrading of seed and animal fats to renewable feeds as it prevents problems in downstream processes such as hydrotreatment.  FCC unit : FCC upgrades feeds to more valuable liquid products but is currently limited to liquid feeds. The cracking of renewable triglycerides removes some of the oxygen from the liquids, but some oxygen remains. Also, the triglyceride side chains are already in the naphtha or diesel boiling range, so cracking of these reduces the selectivity to liquids compared to hydroprocessing. Repurposing the existing installed capacity of FCC unit processes is an attractive process for upgrading renewable feeds.  Hydroprocessing : The addition of hydrogen removes oxygen and sulphur from the feed and saturates any olefins to increase the levels of paraffinic hydrocarbons in the product. This has been the processing choice for upgrading seed and animal fats. Both co-processing and 100% processing schemes are employed or planned. Both renewable diesel and SAF are produced, and the pathways are approved.  Esterification : Biodiesel is produced in a chemical process where fats and oils react with alcohol, usually methanol, in the presence of a catalyst, along with sodium hydroxide or