Traditionally, methanol is produced in large amounts from synthesis gas with heterogeneous Cu/ZnO/Al₂O₃ catalysts under steady state conditions. In this paper, the potential of alternative forced periodic operation modes is studied using numerical optimization. The focus is a well-mixed isothermal reactor with two periodic inputs, namely, CO concentration in the feed and total feed flow rate. Exploiting a detailed kinetic model which also describes the dynamics of the catalyst, a sequential NLP optimization approach is applied to compare optimal steady state solutions with optimal periodic regimes. Periodic solutions are calculated using dynamic optimization with a periodicity constraint. The NLP optimization is embedded in a multi-objective optimization framework to optimize the process with respect to two objective functions and generate the corresponding Pareto fronts. The first objective is the methanol outlet flow rate. The second objective is the methanol yield based on the total carbon in the feed. Additional constraints arising from the complex methanol reaction and the practical limitations are introduced step by step. The results show that significant improvements for both objective functions are possible through periodic forcing of the two inputs considered here.

Focus of this paper is the experimental demonstration of forced periodic operation applied to the synthesis of methanol. A theoretical analysis using the nonlinear frequency response (NFR) method and rigorous mathematical optimization provide a general guideline for analyzing simultaneously carried modulations of inlet composition and total volumetric flow rate. Influences of the forcing parameters (amplitudes, frequencies, phase differences, and shapes of forcing functions) were studied for well‐mixed reactors (CSTR) and theoretically for tubular reactors. Predictions of promising operating conditions were made exploiting a kinetic model developed and validated for an industrial Cu/ZnO/Al ₂ O ₃ catalyst. Confirming the trends of the theoretical results, in an experimental study using a laboratory CSTR, higher time‐averaged product amounts and improved yields were achieved compared to conventional steady state operation applying the optimized phase‐shift. Hereby, square wave modulations of the inputs outperformed sinusoidal modulations. A severe and unsolved problem concerns the deactivation of the catalyst observed in the course of the three months experimental campaign, which caused performance reductions for both steady state and periodic operation.