(763e) Optimal Process Design for E-Fuel Production: Increasing the Efficiency of OME1 Synthesis Using a New Reaction Pathway

OME₁ is a chemical with many applications. It offers promising properties as a solvent and can be used to produce resins. Its combustion properties in compression ignition engines are particularly interesting: The alternating oxygen carbon bonds in the molecular structure of OME₁ avoid the formation of soot and increase engine efficiency while keeping NO_x emissions at a low level [1]. Consequently, OME₁ is receiving much attention as a clean alternative to fossil diesel.

Conventionally, OME₁ production takes place in multiple (typically separate) process steps comprising of methanol, formaldehyde, and OME₁ production. These multiple process steps lead to high process complexity and accumulation of inefficiencies. Additionally, conventional OME₁ production is based on fossil methanol and thus causes significant greenhouse gas (GHG) emissions. Finally, its synthesis route includes the partial oxidation of methanol to produce formaldehyde. This reaction is redox-inefficient and results in an unfavorable overall stoichiometry adding further inefficiencies to the conventional process concept. Such inefficiencies have recently been addressed by several studies. Process optimization and intensification (e.g., reactive side-stream distillation within the OME₁ process step [2]) have enabled significant energy savings for individual process steps. Heat integration within the entire process chain has reduced the overall heat demand further. For instance, the overall heat demand of a process chain starting from regenerative hydrogen (H₂) and carbon dioxide (CO₂) could be reduced considerably [3]. However, these savings increase the overall process efficiency only by 1% to 74%, which is significantly lower than other e-fuels like methane or dimethyl ether. Since the process efficiency and cost of e-fuel production is mainly dictated by the required amount of feedstock H₂, novel process concepts need to consume less H₂ in order to make OME₁ an efficient and economically viable alternative to fossil diesel.

A previous study [4] has identified a remarkable efficiency improvement by making use of a thermodynamically more favorable reaction pathway: the reduction of methanol (MeOH) to OME₁ [5] according to

2 MeOH + CO₂ + 2 H₂ → OME₁ + 2 H₂O.

This reaction pathway does not involve the formation of formaldehyde such that one process step of conventional OME₁ production is avoided. Moreover, it requires less H₂, thus making the reductive reaction pathway a highly attractive one for economic and sustainable OME₁ production. Whereas the existing analyses for this pathway are limited to potential estimations, the primary objective of this study is to translate the novel synthesis route into an optimized process maintaining a high overall efficiency.

For optimal OME₁ process design, we systematically apply a synthesis framework [6] following three steps: First, we generate all relevant flowsheet candidates considering suitable reaction and separation units. Second, we identify the optimal flowsheet structure by minimizing the energy demand of all candidates using intermediate-fidelity models [7]. Finally, we optimize the operation of the most promising flowsheet candidates using rigorous models. The optimization considers the economic potential of the novel production concept while respecting purity requirements for OME₁. We compare the economic and performance benefits of the novel production concept with the conventional one as well as with other e-fuels in order to guide the way towards a sustainable and economic future mobility.

Acknowledgement:

The authors gratefully acknowledge funding by the German Federal Ministry of Education and Research (BMFB) within the Kopernikus Project P2X: Flexible use of renewable resources – exploration, validation, and implementation of ‘Power-to-X’ concepts.

References:

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