Selective hydrogenation of alkynes over ppm-level Pd/boehmite/Al2O3beads in a continuous-flow reactor

A ppm-level Pd/boemite catalyst has been prepared over 3 mm alumina beads and used for the selective hydrogenation of alkynes in a continuous-flow reactor with two modes: closed-loop and flow-through. The flow rates of the alkyne solution and hydrogen gas are critical factors in the control of conversion and selectivity. In closed-loop mode, over 90% selectivity to alkene was achieved at over 90% conversion of phenylacetylene (PA) and 2-butyne-1,4-diol (ByD) in closed-loop mode, whereas diphenylacetylene (DPA) gave only 83% selectivity to (Z)-stilbene. The maximum outputs obtained for the hydrogenations of 22 mM PA, DPA and ByD at 60 °C, with 10 vol% H2 gas bubble at atmospheric pressure in the concurrent flow, were 37.8, 37.5 and 47.0 mmol min−1 g−1 Pd, respectively. In flow-through mode, the optimal H2 flow percentage in the concurrent flow was 44–45 vol%, while the optimal H2/ByD molar ratio was 1.6–1.7 for both concurrent flow rates of 0.4 and 0.7 mL min−1. 90% selectivity to 2-butene-1,4-diol was achieved at over 90% ByD conversion. The maximum output was 25.2 mmol min−1 g−1 Pd. Palladium leaching from the catalyst was evaluated in n-hexane and ethanol under the flow conditions over 100 hours of hydrogenation

Microwave transparent catalytic falling-film microreactor for automated operation

Falling‐film microreactors at different scales were developed to study heterogeneously catalyzed gas‐liquid reactions under microwave irradiation, as part of the EU FP7 project MAPSYN. At pilot scale, this device formed the core part of a fully automated demonstration plant which was used for semi‐hydrogenation reactions at an industrial site. The microchannels of the reaction plate were coated with novel selective catalysts. A special fiber‐optical sensor applicable under microwave irradiation and needed for controlling the liquid level in the sump via the flow rate of the discharge pump was developed and electrically connected with the automation system

Cost analyses of chemical micro processing for highly intensified and high-value raw material processes: real business and virtual cases

As a result of its rapid development within the last years an increasing commercial interest on micro process engineering is given. Process intensification effects of this novel technology were clearly demonstrated. In this context, a generic cost view needs to be developed. As a first investigation, two generic cost analyses investigate here the profitability for two edge cases. One refers to dominance by raw materials, the other by the operator's salary. Both shares dominate the operational costs of a micro-chemical process, but in a varying extent. The write-downs of the investment costs, mainly consistent of the micro-reaction plant itself and the plant engineering, are of minor relevance. The first case study considered here focused on the synthesis of a high-value fine-chemical intermediate where raw-material costs outpaced even the high operator costs. The process under investigation is an economically conducted fine chemical process of the customized chemical producer AzurChem GmbH, the formation of the 4-cyanophenylboronic acid, using the benefits of micro process technology supplied by IMM GmbH [5] among others. This process was chosen since it is representative for several of this company's manufacturing processes of fine and specialty chemicals. The other study refers to a highly intensified process, the aqueous Kolbe-Schmitt synthesis with reaction times being reduced by three orders of magnitude, from some hours to some tens of seconds [24]. Correspondingly, space-time yield and productivity were increased using this so-called high pressure and high temperature (high-p,T) micro processing concept. For a given productivity, the operator costs are notably reduced for the micro-chemical process as compared to a batch process. A detailed view on the different cost portions will be given and demonstrate how the variable and the total costs change. For both case studies, the impact of process intensification (e.g. by scale-out) and parallel operation (e.g. by numbering-up) are pointed out

Agile Green Process Design for the Intensified Kolbe–Schmitt Synthesis by Accompanying (Simplified) Life Cycle Assessment

In order to investigate the potential for process intensification, various reaction conditions were applied to the Kolbe–Schmitt synthesis starting from resorcinol. Different CO₂ precursors such as aqueous potassium hydrogencarbonate, hydrogencarbonate-based ionic liquids, DIMCARB, or sc-CO₂, the application of microwave irradiation for fast volumetric heating of the reaction mixture, and the effect of harsh reaction conditions were investigated. The experiments, carried out in conventional batch-wise as well as in continuously operated microstructured reactors, aimed at the development of an environmentally benign process for the preparation of 2,4-dihydroxybenzoic acid. To provide decision support toward a green process design, a research-accompanying simplified life cycle assessment (SLCA) was performed throughout the whole investigation. Following this approach, it was found that convective heating methods such as oil bath or electrical heating were more beneficial than the application of microwave irradiation. Furthermore, the consideration of workup procedures was crucial for a holistic view on the environmental burdens

Long range strain and electrical potential induced by single edge dislocations in GaN

A dipole like strain state is induced by threading edge dislocations emerging at the surface of gallium nitride (GaN) bulk substrates. This local strain is calculated by means of a three-dimensional elastic deformation potential model, taking into account the free surface of the sample. The calculations are in excellent quantitative agreement with the strain state derived from line shifts of the near band edge excitonic spectrum, measured by micro-photoluminescence (μPL). Scanning surface potential microscope (SSPM) measurements show that the dipole structure is not reflected in the local electrical potential distortions around the dislocations and the potential profile decreases laterally faster than the strain distortion, which is detectable even in several micrometer distance from the dislocation core

Local strain and potential distribution induced by single dislocations in GaN

The presence of a threading edge dislocation terminated at the surface of GaN bulk substrates causes a dipole-like strain state ranging over a several micrometer square area. The local strain state is derived from microphotoluminescence mappings of the near-band-edge spectrum and is quantitatively reproduced by a three-dimensional elastic deformation model approach. These results are compared with the local electrical potential distortion due to the core charge and attracted defects as analyzed by scanning surface-potential microscopy. In contrast to the local strain, the potential profile does not show a dipole-like behavior and decreases laterally faster