In this paper, the power-to-methanol chain is reviewed from a process system engineering perspective with detailed assessments of major technologies. The evaluation encompasses electrolysis technologies and catalyst developments, kinetics, reactor technology options for methanol synthesis, as well as their design principles, modelling techniques, and research and optimisation gaps. The review extends to discuss process synthesis considering water-based and co-electrolysis-based power-to-methanol routes with reference to process integration, optimisation, modelling techniques, industrial applications and the associated techno-economics. Key gaps and opportunities for improvements are identified. The novelty of the paper lies in the holistic evaluation of technology design, performance and modelling. Foremost among the findings, advanced and detailed models of the electrolysis units, methanol reaction kinetics (e.g. considering identifiability and sensitivity) and methanol reactor with improved predictive capabilities under varying conditions are required. Additionally, the overall design, flexibility and reliability requirements concerning variable power-to-methanol deserve further detailed investigation. On the other hand, studies on the model-based process synthesis of power-to-methanol are limited, especially those considering dynamic modelling, multi-objective, process configuration and scheduling optimisations, and techno-economic and environmental analyses under uncertainty conditions. The few model-based studies available are mostly based on deterministic approaches and sequential pinch-analysis. Furthermore, limited studies evaluate power-to-methanol in the context of CO₂/energy/H₂ utilisation industrial hubs and repurposing/retrofitting of existing infrastructures (with part of the capital cost already offset) taking advantages of synergies and application-specific analysis of methanol, which may give additional attractive business cases. Lastly, incentives and dynamics in renewable electricity, electrolysis, CO₂ utilisation and the methanol market hold a strong position to make power-to-methanol feasible and must be investigated further to support policy decisions.

This paper compares different power-to-methanol process configurations encompassing the electrolyser, adiabatic reactor(s) and methanol purification configurations. Twelve different power-to-methanol configurations based on direct CO₂ hydrogenation with H₂ derived from H₂O-electrolysis were modelled, compared, and analysed. A high temperature solid oxide electrolyser is used for hydrogen production. A fixed bed reactor is used for methanol synthesis. The aim of the paper is to give detailed comparison of the process layouts under similar conditions and select the best performing process configuration considering the overall methanol production, carbon conversion, flexibility, and energy efficiency. ASPEN PLUS® V11 is used for flowsheet modelling and the system architectures considered are the open loop systems where methanol is produced at 100 kton per annum and sold to commercial wholesale market as the final purified commodity. Further optimization requirements are established as targets for future work. Three options of power-to-methanol configuration with methanol synthesis from CO₂ hydrogenation are proposed and further evaluated considering process flexibility. From the evaluation, the series–series based configuration with three adiabatic reactors in series performed better in most parameters including the flexible load dependent energy efficiency.

The kinetics of methanol synthesis remains debatable for various reasons, such as the lack of scientifically conclusive agreement about reaction mechanisms. The focus of this paper is on the evaluation of the intrinsic kinetics of the methanol synthesis reaction based on CO₂ hydrogenation and the associated reverse water–gas shift as overall reactions. The industrial methanol synthesis catalyst, Cu/ZnO/Al₂O₃/MgO, was used for performing the kinetic studies. An optimal kinetic model was assessed for its ability to predict the experimental data from differential to integral conditions, contrary to the typical fitting of only the integral conditions’ data (common practice, as reported in the literature). The catalyst testing and kinetic evaluations were performed at various temperatures (210–260 °C) and pressures (40–77 bar), and for different stoichiometric numbers (0.9–1.9), H₂/CO₂ ratios (3.0–4.4) and carbon oxide ratios (0.9–1.0), in an isothermal fixed bed reactor, operated in a plug-flow mode. Experiments with CO in the feed were also generated and fitted. Different literature kinetic models with different assumptions on active sites, rate-determining steps, and hence, model formulations were fitted and compared. The original Seidel model appeared to fit the kinetic data very well, but it has twelve parameters. The modified model (MOD) we propose is derived from this Seidel model, but it has fewer (nine) parameters—it excludes CO hydrogenation, but it takes into consideration the morphological changes of active sites and CO adsorption. This MOD model, with three active sites, gave the best fit to all the data sets.

Dibenzyltoluene/perhydro-dibenzyltoluene (H₀DBT/H₁₈DBT) is considered a promising liquid organic hydrogen carrier (LOHC) pair for the storage and transportation of green hydrogen (H₂). However, at the point of use, the catalytic dehydrogenation of H₁₈DBT is still limited by mass transport limitations. To address this issue, the dehydrogenation of H₁₈DBT was successfully conducted on Pt/Al₂O₃-coated foams in both an unstirred tank reactor and a fixed-bed reactor (FBR). A performance comparison between coated foams and pellets in the tank reactor revealed that H₂ productivities were 12–59% higher in the foam-based reactor than in the pellet-based reactor. Since the textural properties of the foam-supported and pellet-based catalysts were similar, the higher degree of dehydrogenation (DoD) and H₂ productivity achieved by the former were attributed to the geometric properties of the foam structure. Long-term tests performed in the FBR demonstrated the ability of the coated foams to maintain steady activity for >16 h on stream. However, the single-pass DoDs achieved were 34–38%. By recycling the partially dehydrogenated products three times into the FBR, the DoD improved to 63%. The results of this study demonstrated the capabilities of the coated foams in the process intensification of LOHC dehydrogenation reactors.