Sustainable methane synthesis enhancement in power-to-gas systems using adsorption technologies

Making industrial activities sustainable is necessary in order to curb current climate alterations. In this regard, the energy sector is among the most critical ones, hence its defossilization is crucial. One possibility for enabling the energy transition in the immediate term is the production of sustainable alternatives to fossil fuels to be used as their replacement. This would allow machines and infrastructures currently in use to remain unaltered. Synthetic methane, in particular, could be extremely attractive as a natural gas substitute. Natural gas is widely used in multiple sectors and has an extremely widespread network that can be easily used for the transmission and distribution of a sustainable energy carrier such as synthetic methane. By exploiting renewable electricity to produce hydrogen from water and by using captured carbon dioxide, power-to-gas systems combine the two species through catalytic methanation processes, enabling the production of synthetic methane in a sustainable manner. In particular, the efficient implementation of the carbon dioxide capture process and the methanation process is crucial. In fact, on the one hand, efficient carbon dioxide capture allows minimizing climate-altering emissions while, on the other hand, efficient methane synthesis allows obtaining a gas of adequate purity to be distributed in the natural gas network. Since both processes deal with gas mixtures of various types, both carbon dioxide capture and catalytic methane synthesis could benefit from the use of adsorbent materials. Such materials, in fact, are capable of selectively trapping a specific gas by adsorbing it onto the surface pores and then separating it from the rest of the mixture that does not interact with the solid. The trapped gas can, subsequently, be released by desorption. However, for the effective application of adsorption technologies in power-to-gas plants, there is the need to analyze in detail the behavior of the system in its entirety and the interaction between the various components, in dynamic conditions. This is necessary because the alternation between adsorption and desorption phases sets the system in a permanent transient state. Accordingly, the purpose of this thesis is to investigate aspects related to the dynamics of power-to-gas systems that include adsorption technologies. In particular, this research will deal with aspects related to adsorptive carbon dioxide capture and sorption-enhanced catalytic methanation, in each case the process is considered in the perspective of power-to-gas systems. The methodologies adopted for investigation include both the development of dynamic mathematical models for simulation and experimental tests. Specifically, with reference to carbon dioxide capture, the behavior of an adsorption bed with different sources of carbon dioxide from post-combustion will be evaluated. In addition, the use of hydrogen as a purge agent to assist desorption will be examined. The conversion of the captured carbon dioxide and purge hydrogen into methane will be analyzed by additionally including a catalytic methanation reactor in the system. Reference will be made to the cyclic behavior of the system once the regime condition is reached. With reference to sorption-enhnaced methanation, the response of the system will be examined in response to transient partial load conditions. In addition, by analyzing the operation two sorption-enhanced methanation reactors alternating between the methane production and the bed regeneration phases, the importance of proper drying of the catalytic bed to ensure adequate purity of the synthesized gas will be evaluated.