No abstract

CO2 valorization is a key measure to reach climate neutrality. Thermodynamics suggest direct conversion of CO2 into dimethyl ether (DME) to have greater potential than the indirect route via methanol synthesis, followed by purification of methanol and then a separate dehydration into DME. In this work, we introduce heteropoly acids as a capable class of dehydration catalysts for direct DME synthesis from CO2 and H2. To clarify if direct DME synthesis is in fact superior to sole MeOH synthesis, accurate thermodynamic equilibrium calculations are performed and pose as the base of our argumentation. An efficient Cu/ZnO/ZrO2 (CZZ) methanol catalyst is used to compare the methanol synthesis using a feedstock with stoichiometric CO2/3H2 mixture against bifunctional catalysts, containing CZZ and a dehydration component. The dehydration components include a commercial ferrierite (FER) and heteropoly acid (HPA) coated alumina and zirconia. For direct DME synthesis, the CO2 feed gas at gas hourly space velocities (GHSVs) between 1,250 and 158,400 NL kgcat –1 h–1, at temperatures of 210–270 °C and 40 bar pressure, was investigated. Based on the wide parameter window investigated, the following can be concluded at 250 °C: under a thermodynamic regime, CO2 conversion is close to the theoretical limit (30%exp/32%theo) and the direct DME synthesis is superior to sole methanol synthesis (+20%exp/+33%theo). The amount of valuable products (methanol, DME) profits significantly more (+70%exp/+88%theo) from the direct DME synthesis than CO2 conversion indicates. Under a kinetic regime, HPA-coated catalysts show superior apparent activation energies for DME production than the widely used ferrierite (HPA: 45 kJ mol–1/FER: 80 kJ mol–1), making HPA coatings a great option for highly capable dehydration catalysts under CO2- and water-rich conditions.

No abstract

Sector coupling remains a crucial measure to achieve climate change mitigation targets. Hydrogen and Power-to-X (PtX) products are recognized as major levers to allow the boosting of renewable energy capacities and the consequent use of green electrons in different sectors. In this work, the challenges presented by the PtX processes are addressed and different process intensification (PI) strategies and their potential to overcome these challenges are reviewed for ammonia (NH3), dimethyl ether (DME) and oxymethylene dimethyl ethers (OME) as three exemplary, major PtX products. PI approaches in this context offer on the one hand the maximum utilization of valuable renewable feedstock and on the other hand simpler production processes. For the three discussed processes a compelling strategy for efficient and ultimately maintenance-free chemical synthesis is presented by integrating unit operations to overcome thermodynamic limitations, and in best cases eliminate the recycle loops. The proposed intensification processes offer a significant reduction of energy consumption and provide an interesting perspective for the future development of PtX technologies.

Large amounts of renewable energy will have to be stored and transported in the future. For this task, chemical hydrogen storage technologies are particularly suitable. In this paper, we show...