###### Abstract  
The methanation process is discussed as one way to chemically store renewable energy in a future energy system. An important criterion for its application is the availability of compact, low-cost reactor concepts with high conversion rates for decentralized use where the renewable energy is produced. Current research focuses on the maximization of the methane yield through improved temperature control of the exothermic reaction, which attempts to avoid both kinetic and thermodynamic limitations. In this context, traditional manufacturing methods limit the design options of the reactor and thus the temperature control possibilities. The use of additive manufacturing methods removes this restriction and creates new freedom in the design process. This paper formulates the requirements for a novel methanation reactor and presents their implementation to a highly innovative reactor concept called 'ADDmeth'. By using a conical reaction channel expanding from \(\mathcal{O}\) 8 to 32 mm, three twisted, expanding heat pipes (\(\mathcal{O}\) 8 mm in evaporation zone, \(\mathcal{O}\) 12 mm in condenser zone) and a lattice structure for feed gas preheating and mechanical stabilization of the reactor, the design explicitly exploits the advantages of additive manufacturing. The reactor is very compact with a specific mass of 0.36 kg/kW and has a high share of functional volume of 52%. The reactor development was accompanied by tensile tests of additively manufactured samples with the used material 1.4404 (316 L), strength calculations for stability verification and feasibility studies on the printability of fine structures. Ultimate tensile strengths of up to 750 N/mm\({}^{2}\) (at room temperature) and sufficiently high safety factors of the pressure-loaded structures against yielding were determined. Finally, the paper presents the manufactured bench-scale reactor ADDmeth1 and its implementation. reactor design; additive manufacturing; catalytic methanation; conic reaction channel; heat pipes +
Footnote †: journal:
\[\text{CO}+3\;\text{H}_{2}\;\rightleftharpoons\;\text{CH}_{4}+\text{H}_{2}\text{O}_{ (\text{g})}\;\Delta H_{R}^{0}=-206\frac{\text{kJ}}{\text{mol}} \tag{2}\]  
The decentralized deployment of PtG concepts requires both simple, compact reactors and low process complexity to keep investment costs low [5]. For the methanation process, this means that the highest possible conversion of the reactants to the desired product methane must be achieved in the fewest possible methanation stages, which should be designed as simply as possible. Commercially available, highly complex methanation technologies such as Lurgi Methanation or [PERSON]'s TREMP [6] are therefore unsuitable for this application. Hence, many research groups are working on the process intensification of the methanation, often via the development of new reactor concepts [7; 8; 9; 10]. [PERSON] et al. [11] developed a heat pipe cooled structured fixed-bed reactor for use in PtG applications. Its design aims for an improved temperature control of the exothermic methanation and thus an increased methane yield in only one reactor stage. By limiting the diameter of the single fixed-bed reaction channels to 8 mm, the reactor meets the two main objectives of active temperature control for methanation illustrated in Figure 1. On the one hand, the maximum temperature occurring in the reactor is limited to the permissible maximum temperature of the catalyst to prevent its deactivation due to sintering processes. On the other hand, low temperatures are achieved at the reactor outlet, which influences the equilibrium position in favor of CH\({}_{4}\). However, the experimental results display a kinetic limitation in the second half of the reactor, which is why the thermodynamic equilibrium cannot be reached at low outlet temperatures. This in turn results in a loss of methane yield. This problem of kinetic limitation is addressed by the development of a novel reactor concept presented in this work. Based on the reactor described by [PERSON] et al.