Rather the Rule than the Exception: Non-Convex Pareto Sets and their Navigation in Distillation Processes

Novel algorithms for adaptive approximation and interactive navigation of Pareto sets are applied to various homogeneous distillation processes with recycle streams within an industrial flowsheet simulator. The adaptive approximation scheme shows that the Pareto set consists of both convex and non-convex regions when the product purities are maximised while minimising the total heat duties. It is illustrated how such Pareto sets can be navigated interactively using a ray tracing technique. Our results suggest that the occurrence of non-convex regions in the Pareto sets is due to recycle streams in the flowsheets and is therefore the rule rather than the exception in multi-objective optimisation of flowsheet simulations in chemical engineering.     

Fe-Zeolite as on-Site Regenerable Adsorber for Chlorohydrocarbons in Groundwater – from Laboratory to Pilot Test

This study describes the design and upscaling of an on-site regenerable adsorbent fixed bed of Fe-loaded MFI zeolite for removal of chlorinated hydrocarbons (CHCs) from contaminated groundwater from laboratory studies to pilot scale. The zeolite has an excellent adsorption performance for the hydrophilic CHCs and can be regenerated on-site by flushing with H₂O₂ to degrade adsorbed contaminants by a catalytic Fenton-like reaction. In the pilot test, the Fe-zeolite (30 kg) maintained its performance over treatment of 1470 m³ of groundwater in 12 adsorption/regeneration cycles.     

Potential of Integrated Semi-Continuous Enzymatic Synthesis and Filtration Processes for Efficiency Enhancement

Galacto-oligosaccharides (GOS), increasingly popular prebiotics, are synthesized by enzymatic conversion of lactose. Among others, the total production costs are significantly influenced by the costly enzyme. Therefore, it was investigated if the reuse and full recovery of the enzyme is feasible, followed by the development of a semi-continuous process in order to maintain a consistent high GOS yield. As a preliminary step, the enzyme-catalyzed reaction was recorded within the permissible operating parameters. It was successfully shown that steady high GOS yields can be synthesized semi-continuously within a filtration plant functioning as an enzymatic membrane reactor.     

Cell-Free Protein Synthesis for the Screening of Novel Azoreductases and Their Preferred Electron Donor

Azoreductases are potent biocatalysts for the cleavage of azo bonds. Various gene sequences coding for potential azoreductases are available in databases, but many of their gene products are still uncharacterized. To avoid the laborious heterologous expression in a host organism, we developed a screening approach involving cell-free protein synthesis (CFPS) combined with a colorimetric activity assay, which allows the parallel screening of putative azoreductases in a short time. First, we evaluated different CFPS systems and optimized the synthesis conditions of a model azoreductase. With the findings obtained, 10 azoreductases, half of them undescribed so far, were screened for their ability to degrade the azo dye methyl red. All novel enzymes catalyzed the degradation of methyl red and can therefore be referred to as azoreductases. In addition, all enzymes degraded the more complex and bulkier azo dye Brilliant Black and four of them also showed the ability to reduce p-benzoquinone. NADH was the preferred electron donor for the most enzymes, although the synthetic nicotinamide co-substrate analogue 1-benzyl-1,4-dihydronicotinamide (BNAH) was also accepted by all active azoreductases. This screening approach allows accelerated identification of potential biocatalysts for various applications.     

Debottlenecking of an In Vitro Enzyme Cascade Using a Combined Model- and Experiment-Based Approach

Designing a feasible in vitro enzyme cascade is a challenging task that is often preceded by optimization steps. Computational methods can increase the efficiency of the optimization process by providing a deeper insight into the system. In this study, bottlenecks of a farnesyl pyrophosphate-producing in vitro enzyme cascade were determined by a combination of in silico modeling and wet-lab experiments. ATP and the precursor-isomerizing enzyme isopentenyl diphosphate δ-isomerase were identified as limitations of the in vitro enzyme cascade.     

Spectral Sensitization of Dediazoniation by the 2-electron-transfer system meso-tetraphenylporphinato-dichlorostannate(IV)/10-methyl-9-Phenyl-9.10-dihydro-acridine

The photoreduction of meso-tetraphenylporphinatodichlorostannate(IV) (SnCl₂TPP) by 9-phenyl-10-methyl-9,10-dihydro-acridine (ACH) in 1,2-dichloroethane/acetonitrile 1:1 (v/v) under argon proceeds only with a low quantum yield in spite of the fact that ACH is in other cases an excellent 2-electron donor. The reason may be the formation of a triplet exciplex which opens a new deactivation channel. Evidence for such an exciplex is given by means of the WARE treatment of flash-photolytic experiments and quantum yields of dediazoniation, K_eq ≈ 650 M⁻¹ and τ_exc = 46 μs. The exciplex reacts fast with p-N,N-dimethylamino-benzenediazonium tetrafluoroborate (k_r = 4.1 × 10⁸ M⁻¹ s⁻¹) under electron transfer leading to dediazoniation. At high ACH concentrations (8 × 10⁻³ M) the dediazoniation gives even at very low diazonium salt concentrations (≈ 4 × 10⁻⁵ M) quantum yields as high as 1.95 (0.37 stemming from sensitization by the SnCl₂ complex of tetraphenylchlorine present as an impurity of SnCl₂TPP. SnCl₂TPP) remains unchanged during the sensitization reaction, i.e. the process is fully photocatalytic.     

Numerical and Experimental Investigation on the Self-Healing Potential of Interpenetrating Metal–Ceramic Composites

An interpenetrating metal ceramic composite (IMCC) has been investigated regarding the potential as well as the feasibility of self-healing. Triggered by heating, cracks in the damaged composite located mainly in the Al₂O₃ ceramic or at the interface could be filled and closed by the liquid AlSi10Mg metal alloy. This healing procedure promises to reduce stress concentrations at crack tips and to improve the mechanical properties compared to the predamaged composite. Two different numerical approaches have been introduced to investigate this assumption and the potential of self-healed IMCCs for a best case scenario: 1) A simple 2D model to analyze the reduction of stress concentrations in front of a crack tip within the ceramic due to healing and 2) a 3D model based on CT-scan reconstructed microstructures to study how macroscopic mechanical properties can be restored depending on the amount of predamage. Further, the self-healing approach has been investigated experimentally for the same composite. Despite the fact that experimental self-healing of the investigated IMCC is only moderately feasible so far, the study shows the great potential that can still be exploited in order to extend the service life time of IMCC engineering components.