A multiphase fixed-bed reactor (FBR) model for Fischer−Tropsch Synthesis has been developed. A high level of details is considered for description of the phenomena on the reactor and particle scale. Detailed kinetics is used, with parameters estimated from experiments with a cobalt-based catalyst. Model robustness has been validated using literature data. Performance analysis was made for a conventional scale FBR with egg-shell distribution of catalyst and a millimeter-scale FBR with small particles and uniform distribution. In both cases, diffusion limitations are almost eliminated due to use of small diffusion lengths. For similar qualitative results, a milli-scaled design would result in a significantly lower reactor volume, but the capital costs could be high due to large wall area and a vast number of tubes. Heat removal is efficient in both cases, and pressure drop in the milliscale reactor is low due to the use of a shorter bed and lower velocity.

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Our previously developed mathematical model is used for parametric sensitivity and optimization study of conventional and milliscale fixed-bed reactors (FBRs) for Fischer−Tropsch synthesis (FTS). Five indicators are chosen to analyze the influence of eight parameters on the FBRs' performance. The results show the scale of the effects caused by changing single parameter values and highlight the most important ones.Subsequently, the model is used to perform a rigorous multivariable optimization of the FBRs' performance in the steady state. Three optimization functions are used, depicting different reactor costs. Four design parameters (tube length and diameter, particle diameter, and catalyst layer thickness) and five operating parameters (inlet and wall temperature, inlet pressure, H 2 /CO ratio, velocity) are optimized simultaneously. The results indicate that optimal results, in terms of reactor design and operating parameters and FBR performance, highly depend on the selected objective function and values of constrained parameters (especially methane selectivity and the partial pressure of water).

The transition towards a CO2 neutral industry is currently spurring many new developments regarding processes for the conversion of CO2, or CO2-rich streams, into platform molecules such as methanol and dimethyl ether (DME). New processes give rise to new separation challenges, as well as novel opportunities for joint optimization of reaction and separation. In this context, the separation of CO2 and DME can be performed very efficiently using the newly developed concept of stripping enhanced distillation (SED). SED is a distillation process that utilizes an additional stripping component (clearing gas) to promote the separation in the column. SED benefits from the utilization of the feedstock components as a clearing gas that can afterwards be recycled back to the conversion unit with the vapor distillate. Strongly improving the separation performance in the column, this approach also removes the need for external stripping mediums and, in addition, this recycling approach may significantly reduce the demand on the conversion unit upstream of SED. The benefits of using SED are demonstrated for two different processes for DME synthesis: (i) CO2–DME separation after the sorption enhanced DME synthesis (SEDMES) process, using hydrogen as clearing gas, and (ii) CO2–DME separation after direct DME synthesis via dry reforming (DIDR), using methane as a clearing gas. For the different cases, it is shown that, with minimal adaptations, the energy consumption for distillation is reduced by 20–30%, while product losses are minimized at the same time.