Pascal Schäfer

Highly Active N,O Zinc Guanidine Catalysts for the Ring-Opening Polymerization of Lactide

New zinc guanidine complexes with N,O donor functionalities were prepared, characterized by X-Ray crystallography, and examined for their catalytic activity in the solvent-free ring-opening polymerization (ROP) of technical-grade rac-lactide at 150 °C. All complexes showed a high activity. The fastest complex [ZnCl2 (DMEGasme)] (C1) produced colorless poly(lactide) (PLA) after 90 min with a conversion of 52 % and high molar masses (Mw =69 100, polydispersity=1.4). The complexes were tested with different monomer-to-initiator ratios to determine the rate constant kp . Furthermore, a polymerization with the most active complex C1 was monitored by in situ Raman spectroscopy. Overall, conversion of up to 90 % can be obtained. End-group analysis was performed to clarify the mechanism. All four complexes combine robustness against impurities in the lactide with high polymerization rates, and they represent the fastest robust lactide ROP catalysts to date, opening new avenues to a sustainable ROP catalyst family for industrial use.

Challenges in process optimization for new feedstocks and energy sources

Abstract Current and future challenges of optimization in the process industry are discussed. The gap between academic research and industrial workflow is analyzed. Moreover, issues arising from the shift from conventional fossil fuels as both feedstock and energy source to nonconventional feedstocks (shale gas, tar sands, CO2 and biomass) and penetration of intermittent renewable energy are discussed. This manuscript focuses mainly on offline model-based optimization of design and operation, including the generation and selection of promising process alternatives for new feedstocks in conceptual design, multi-objective optimization, the estimation of thermodynamic parameters of new intermediates and the optimization of process operation under the volatile availability of the new feedstocks and energy sources. Moreover, a number of opportunities and needs for research and development are identified, including the simultaneous optimization of feedstocks, processes and products and a production able to process a variety of feedstocks and to utilize energy when it is cheap.

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.