Gluconic Acid Synthesis in an Electroenzymatic Reactor

AbstractGlucose was selectively oxidized to gluconic acid in a membraneless, flow-through electroenzymatic reactor operated in the mode of co-generating chemicals and electrical energy. At the anode the enzyme glucose oxidase (GOx) in combination with the redox mediator tetrathiafulvalene (TTF) was used as catalyst, while the cathode was equipped with an enzyme cascade consisting of GOx and horseradish peroxidase (HRP). The influence of the electrode preparation procedure, the structural and the operating parameters on the reactor performance was investigated in detail. Under optimized conditions, an open circuit potential of 0.75V, a current density of 0.6mAcm−2 and a power density of 100μAcm−2 were measured. The space time yield of gluconic acid achieved at a glucose conversion of 47% was 18.2gh−1cm−2

Protective effects of vapour phase corrosion inhibitors tested in laboratory conditions

This research investigates protective effects of vapour phase corrosion inhibitors (VpCI) tested in laboratory conditions. Such tests are required to control the production quality and to provide for high-quality protection of products during exploitation. There are three different tests run to obtain results on effectiveness of protective effect of VpCIs (Razor Blade Test, Water Drop Test and VIA Test). Each test differs in its defined performance procedure, as well as in evaluation of the obtained results, yet all three tests confirmed that vapour phase corrosion inhibitors provide adequate protection of the material exposed to an aggressive atmosphere. Therefore, it is justified to use vapour corrosion inhibitors as a protection mechanism when designing surface protection technology

Pore Network Simulation of Gas-Liquid Distribution in Porous Transport Layers

Pore network models are powerful tools to simulate invasion and transport processes in porous media. They are widely applied in the field of geology and the drying of porous media, and have recently also received attention in fuel cell applications. Here we want to describe and discuss how pore network models can be used as a prescriptive tool for future water electrolysis technologies. In detail, we suggest in a first approach a pore network model of drainage for the prediction of the oxygen and water invasion process inside the anodic porous transport layer at high current densities. We neglect wetting liquid films and show that, in this situation, numerous isolated liquid clusters develop when oxygen invades the pore network. In the simulation with narrow pore size distribution, the volumetric ratio of the liquid transporting clusters connected between the catalyst layer and the water supply channel is only around 3% of the total liquid volume contained inside the pore network at the moment when the water supply route through the pore network is interrupted; whereas around 40% of the volume is occupied by the continuous gas phase. The majority of liquid clusters are disconnected from the water supply routes through the pore network if liquid films along the walls of the porous transport layer are disregarded. Moreover, these clusters hinder the countercurrent oxygen transport. A higher ratio of liquid transporting clusters was obtained for greater pore size distribution. Based on the results of pore network drainage simulations, we sketch a new route for the extraction of transport parameters from Monte Carlo simulations, incorporating pore scale flow computations and Darcy flow

Model-Based Analysis of the Limiting Mechanisms in the Gas-Phase Oxidation of HCl Employing an Oxygen Depolarized Cathode

The electrochemical oxidation of HCl to Cl2 plays an important role in the production of polycarbonates and polyurethanes. Recently, the gas-phase oxidation of HCl proved to be significantly more efficient than the current state-of-the-art process based on the oxidation of hydrochloric acid. In experimental investigations of this gas-phase reactor, a limiting current can be observed that is so far not understood but impedes the overall reactor performance. In the present work, a nonisothermal multiphase agglomerate model is developed to investigate the underlying reasons for this limiting behavior in more detail. It is shown that the thermal management of the cell plays a significant role and that minor changes to its thermal resistance lead to the limiting behavior being caused by either flooding of the cathode or dehydration of the membrane and anode. An optimization of operational and structural parameters of the cell based on these insights leads to an increase in the limiting current by more than 90%. Interestingly, under these conditions a third phenomenon, the rate determining Tafel step in the microkinetic reaction mechanism of the HCl oxidation, limits the overall reactor performance. These insights harbor the potential for enormous energetic savings in this industrially highly relevant process

Selectivity and Sustainability of Electroenzymatic Process for Glucose Conversion to Gluconic Acid

Electroenzymatic processes are interesting solutions for the development of new processes based on renewable feedstocks, renewable energies, and green catalysts. High-selectivity and sustainability of these processes are usually assumed. In this contribution, these two aspects were studied in more detail. In a membrane-less electroenzymatic reactor, 97% product selectivity at 80% glucose conversion to gluconic acid was determined. With the help of nuclear magnetic resonance spectroscopy, two main side products were identified. The yields of D-arabinose and formic acid can be controlled by the flow rate and the electroenzymatic reactor mode of operation (fuel cell or ion-pumping). The possible pathways for the side product formation have been discussed. The electroenzymatic cathode was found to be responsible for a decrease in selectivity. The choice of the enzymatic catalyst on the cathode side led to 100% selectivity of gluconic acid at somewhat reduced conversion. Furthermore, sustainability of the electroenzymatic process is estimated based on several sustainability indicators. Although some indicators (like Space Time Yield) are favorable for electroenzymatic process, the E-factor of electroenzymatic process has to improve significantly in order to compete with the fermentation process. This can be achieved by an increase of a cycle time and/or enzyme utilization which is currently low