Christian Jens

CO from CO2 and fluctuating renewable energy via formic-acid derivatives

Integrating fluctuating renewable energy into continuously operating industries requires energy storage. Energy storage can be achieved by using hydrogen from fluctuating, renewable energy for hydrogenation of CO2. The resulting molecule serves as storage. The simplest molecule that can be stored in liquid form is formic acid. Stored formic acid can then be reformed continuously to carbon monoxide, a common feedstock for the chemical industry. Since formic-acid synthesis is thermodynamically challenging, we investigate alternative storage molecules such as formamides or formates. Currently, it is unknown which storage molecule leads to the most efficient storage process. Thus, we systematically identify the most efficient storage molecule, together with an optimal combination of solvent and process flowsheet. We identify this combination with a novel hierarchical model-based approach, which starts by screening with the predictive thermodynamic model COSMO-RS and ends by using experimental property data. In the novel approach, we evaluate more than 100 000 combinations of storage molecules, solvents and process flowsheets. The most efficient combination identified uses the storage molecule N,N-dimethylformamide, and reduces the exergy loss by more than a factor of 15 compared to storage of formic acid, and still 65% compared to a literature benchmark. The largely reduced exergy loss indicates an environmentally promising route for linking fluctuating, renewable energy with continuously operating chemical industries. Our findings therefore highlight the importance of catalyst development for N,N-dimethylformamide in the optimal solvents.

Life cycle assessment of CO2-based C1-chemicals

Carbon dioxide (CO2) and hydrogen are promising feedstocks for a sustainable chemical industry. Currently, the conversions of CO2 and hydrogen are most advanced for chemicals with 1 carbon atom, the so-called C1-chemicals, with the first pilot plants in operation. For formic acid, carbon monoxide, methanol, and methane, CO2-based C1-chemicals can reduce the impacts of fossil depletion and global warming through the substitution of fossil-based processes. Existing life cycle assessment (LCA) studies for carbon monoxide, methanol, and methane show that a reduction in environmental impacts is achieved if hydrogen is supplied by water electrolysis with renewable electricity. However, in the foreseeable future, renewable electricity will be limited. Thus, from an environmental point of view, renewable electricity should be employed for chemical processes in the order of highest environmental impact reductions. Environmental impact reductions are the difference in environmental impacts of fossil-based processes and CO2-based processes. In this study, we compared the CO2-based production of formic acid, carbon monoxide, methanol, and methane. We determined the reduction of global warming and fossil depletion impacts using 1 kg of hydrogen. Our results show that the CO2-based production of formic acid achieves the highest environmental impact reductions, followed by carbon monoxide and methanol. The lowest environmental impact reductions are achieved for CO2-based methane production. Our analysis reveals that the CO2-based production of formic acid can reduce environmental impacts, compared to the fossil-based process, even if hydrogen is supplied by fossil-based steam-methane-reforming.

Integrated Design of Solvents in Hybrid Reaction-Separation Processes Using COSMO-RS

Solvents have a large impact on process performance due to their influence on e.g., selectivity in absorption, equilibrium conversion in reactions or exergy demand in distillation. Optimization of process performance therefore needs to integrate solvents as degree of freedom. In this work, an integrated design approach is presented to select solvent molecules as part of flowsheet-wide process optimization. The design approach is based on COSMO-RS for the prediction of thermodynamic properties and uses advanced pinch-based process models for absorption and distillation. Pinch-based process models allow for rapid and accurate process optimization. Thus, a large design space of solvents can be evaluated efficiently. The design approach is demonstrated for a novel concept for integrated CO2 capture and utilization (ICCU) to carbon monoxide. The complete flowsheet containing absorption, multiphase reaction and distillation is optimized successfully for more than 4000 solvents to minimize the overall process exergy demand. The approach is shown to discover process inherent trade-offs in molecular properties of the solvents allowing for optimal solvent and process design.

Integrated process and solvent design using COSMO-RS for the production of CO from CO2 and H2

Abstract Fluctuating H 2 from renewable energy can be integrated into the chemical value chain by conversion of CO 2 to CO via chemical storage. An efficient process combines the right chemical storage molecule in an optimized flowsheet with tailored solvents. For the resulting integrated process and solvent design problem, we present a hybrid stochastic-deterministic optimization approach combining computer-aided molecular design based on COSMO-RS and pinch-based process models for reactions and separations. Thereby, we are able to explore a large molecular design space and find optimal solvents for CO production based on a sound process-level design target. The optimization approach is shown to be both efficient and effective by designing novel solvents which improve process performance by more than 12% compared to a massive database screening of over 80,000 combinations of solvents and structural process variants.