Power-to-X

Over recent years, there has been significant progress in paving the pathway for the green transition in various energy sectors, including power generation as well as heat and cold supply using renewable sources, light transportation using electric vehicles which could be charged by green electricity, process heat and cold which could be supplied by biomass/biogas driven and electrical machines, etc. Despite all this, bringing sustainability to one sector has still remained a challenge for us, and that is the heavy transportation sector, which includes providing sustainable fuel for airplanes, ships, and heavy trucks, for which electrification via battery is practically unattainable. The solution for this challenge is the newly introduced concept called Power-to-X (referred to as PtX in this chapter). PtX in a nutshell means converting surplus green electricity from wind turbines, solar farms, etc. to other energy car­riers (the X here refers to a variety of valuable products) to be used for sustainable purposes. PtX can conventionally refer to a very wide range of terms including power-to-ammonia, -chemicals, -fuels such as gas, hydrogen, or methane, -food, -syngas, -heat, or even -power. However, in this chapter, the more recent yet certain definition, which means "green power to valuable chemical products, especially fuels suitable for the heavy transportation sector," is of focus. In the previous chap­ter, we presented a very thorough discussion about green hydrogen (i.e., water split­ting for hydrogen generation using renewable and sustainable power sources) and various methods for generating that (i.e., various electrolysis methods). That was indeed not only because hydrogen itself is an important topic of the day in the con­text of energy, but also because green hydrogen is the basis of the PtX technologies. Indeed, for making a PtX product, green hydrogen molecules react with either car­bon or nitrogen molecules to have a hydrocarbon or ammonia with four main treat­ments, namely methanation, methanol synthesis, Fischer-Tropsch synthesis, and ammonia synthesis. The chapter presents the fundamentals of the PtX technologies, various methods and products in this framework, the state of the art and practice of the field, and the formulations required to model such systems from energy and exergy points of view. Finally, a discussion of the possible future perspective of this concept from research and applied aspects is presented.