Phase-pure M1 MoVNbTeOx/TiO2 nanocomposite catalysts: highly catalytic performance for oxidative dehydrogenation of ethane

The catalytic performance of the phase-pure M1 MoVNbTeOx catalyst is enhanced by introducing TiO2 in oxidative dehydrogenation of ethane (ODHE). The space-time yield (STY) of the M1/TiO2 composite catalyst increases...

Potential and Scale-Up of Pore-Through-Flow Membrane Reactors for the Production of Prebiotic Galacto-Oligosaccharides with Immobilized β-Galactosidase

The production of prebiotics like galacto-oligosaccharides (GOS) on industrial scale is becoming more important due to increased demand. GOS are synthesized in batch reactors from bovine lactose using the cost intensive enzyme β-galactosidase (β-gal). Thus, the development of sustainable and more efficient production strategies, like enzyme immobilization in membrane reactors are a promising option. Activated methacrylatic monoliths were characterized as support for covalent immobilized β-gal to produce GOS. The macroporous monoliths act as immobilized pore-through-flow membrane reactors (PTFR) and reduce the influence of mass-transfer limitations by a dominating convective pore flow. Monolithic designs in the form of disks (0.34 mL) and for scale-up cylindric columns (1, 8 and 80 mL) in three different reactor operation configurations (semi-continuous, continuous and continuous with recirculation) were studied experimentally and compared to the free enzyme system. Kinetic data, immobilization efficiency, space-time-yield and long-term stability were determined for the immobilized enzyme. Furthermore, simulation studies were conducted to identify optimal operation conditions for further scale-up. Thus, the GOS yield could be increased by up to 60% in the immobilized PTFRs in semi-continuous operation compared to the free enzyme system. The enzyme activity and long-time stability was studied for more than nine months of intensive use.

Development of a Continuous System for 2-Phenylethanol Bioproduction by Yeast on Whey Permeate-Based Medium

2-Phenylethanol (2-PE) is an alcohol with a rosy scent and antimicrobial activity, and therefore, it is widely used in the food and cosmetic industries as an aroma and preservative. This work was aimed to draw up a technology for 2-PE bioproduction on whey permeate, which is waste produced by the dairy industry, rich in lactase and proteins. Its composition makes it a harmful waste to dispose of; however, with a properly selected microorganism, it could be converted to a value-added product. Herein, two yeast Kluyveromyces marxianus strains and one Kluyveromyces lactis, isolated from dairy products, were tested for 2-PE production, firstly on standard media and then on whey permeate based media in batch cultures. Thereafter, the 2-PE bioproduction in a continuous system in a 4.8 L bioreactor was developed, and subsequently, the final product was recovered from culture broth. The results showed that the yield of 2-PE production increased by 60% in the continuous culture compared to batch culture. Together with a notable reduction of chemical oxygen demand for whey permeate, the present study reports a complete, effective, and environmentally friendly strategy for 2-PE bioproduction with a space-time yield of 57.5 mg L−1 h−1.

Localized Electroconvection at Ion-Exchange Membranes with Heterogeneous Surface Charge

Operating electrochemical membrane processes beyond the limiting current density bears the potential to decrease the investment cost of desalination plants significantly. However, while there are strategies for successfully reducing energy demand by shortening the plateau region, their influence on the formation of electroconvection is still unknown. This study demonstrates control over the electroconvective vortices' rotational direction and position using a surface patterning method. We compare the development of electroconvection at two membranes modified with patterns of different surface charges. We analyze the electroconvective vortex field's build-up, the vortices' rotational direction, and structural stability in the steady-state. Finally, we showcase the control possibilities by enforcing a specific structure along an asymmetric letter pattern. Such tailor-made patterns have the potential to diminish the plateau region's energy loss completely. Furthermore, the scale-up of these membranes to industrial processes will allow the economic operation in the overlimiting regime, significantly increasing their space-time yield.

Figures of Merit for Photocatalysis: Comparison of NiO/La-NaTaO3 and Synechocystis sp. PCC 6803 as a Semiconductor and a Bio-Photocatalyst for Water Splitting

While photocatalysis is considered a promising sustainable technology in the field of heterogeneous catalysis as well as biocatalysis, figures of merit (FOM) for comparing catalytic performance, especially between disciplines, are not well established. Here, photocatalytic water splitting was conducted using a semiconductor (NiO/La-NaTaO3) and a bio-photocatalyst (Synechocystis sp. PCC 6803) in the same setup under similar reaction conditions, eliminating the often ill-defined influence of the setup on the FOMs obtained. Comparing the results enables the critical evaluation of existing FOMs and a quantitative comparison of both photocatalytic systems. A single FOM is insufficient to compare the photocatalysts, instead a combination of multiple FOMs (reaction rate, photocatalytic space time yield and a redefined apparent quantum yield) is superior for assessing a variety of photocatalytic systems.

Separate H2 and CO production from CH4-CO2 cycling of Fe-Ni

Fe-Ni materials with varying Ni loading are developed for separate H2 and CO production by CH4-CO2 chemical looping. The product streams are obtained by first feeding CH4, which decomposes to H2 and carbon. The latter acts as reductant for the subsequent CO2 feed, which together with Fe re-oxidation yields CO. After 25 CH4-CO2 cycles, 10Fe5Ni@Zr has a higher H2 space-time-yield than 10Fe0Ni@Zr (〖20mmol∙s〗^(-1)∙kg_(Fe+Ni)^(-1) vs. 〖15mmol∙s〗^(-1)∙kg_(Fe+Ni)^(-1)), a 2.6 times higher CO (〖57mmol∙s〗^(-1)∙kg_(Fe+Ni)^(-1)) and lower deactivation. This improvement has two reasons: (i) CH4 activation over Ni leading to cracking, (ii) product hydrogen causing deeper FeO reduction. Deactivation follows from accumulated carbon, non-reactive for CO2. On Ni and Fe sites, carbon can be removed by lattice oxygen or CO2, yielding more CO compared to the theoretical value for Fe oxidation. However, carbon that migrates away from the metals requires oxygen for removal, which restores the activity of the Ni-containing samples.

Hydrogel-Based Enzyme and Cofactor Co-Immobilization for Efficient Continuous Transamination in a Microbioreactor

A microbioreactor was developed in which selected amine transaminase was immobilized together with the cofactor pyridoxal phosphate (PLP) to allow efficient continuous transamination. The enzyme and cofactor were retained in a porous copolymeric hydrogel matrix formed in a two-plate microreactor with an immobilization efficiency of over 97%. After 10 days of continuous operation, 92% of the initial productivity was retained and no leaching of PLP or enzyme from the hydrogel was observed. The microbioreactor with co-immobilized cofactor showed similar performance with and without the addition of exogenous PLP, suggesting that the addition of PLP is not required during the process. The space-time yield of the microbioreactor was 19.91 g L−1 h−1, while the highest achieved biocatalyst productivity was 5.4 mg mgenzyme−1 h−1. The immobilized enzyme also showed better stability over a wider pH and temperature range than the free enzyme. Considering the time and cost efficiency of the immobilization process and the possibility of capacity expansion, such a system is of great potential for industrial application.

Slug flow as tool for selectivity control in the homogeneously catalysed solvent-free epoxidation of methyl oleate

Catalytic oxidation of sustainable raw materials like unsaturated fats and oils, or fatty acids and their esters, lead to biobased, high-value products. Starting from technical grade methyl oleate, hydrogen peroxide as a green oxidant produces only water as by-product. A commercially available, cheap water-soluble tungsten catalyst is combined with Aliquat® 336 as a phase-transfer agent in solvent-free reaction conditions. In this study, we first report the transfer of this well-known batch system into continuous mode. The space–time yield is improved from 0.08 kg/L.h in batch to 1.29 kg/L.h in flow mode. The improved mass transfer and reduced back mixing of the biphasic liquid–liquid slug flow allows for selectivity control depending on physical parameters of slug flow namely volumetric phase ratio, volumetric flow rate, and slug length. Even though the product, methyl 9,10-epoxystearate is obtained at a maximum selectivity of only 58% in flow mode, higher space time yield combined with possible reactant recycling in flow mode offers a promising avenue of research. This work analyses the use of slug flow parameters as tools for controlling selectivity towards oxidation products of methyl oleate.

Enhanced Thermostability of Pseudomonas nitroreducens Isoeugenol Monooxygenase by the Combinatorial Strategy of Surface Residue Replacement and Consensus Mutagenesis

Vanillin has many applications in industries. Isoeugenol monooxygenase (IEM) can catalyze the oxidation of isoeugenol to vanillin in the presence of oxygen under mild conditions. However, the low thermal stability of IEM limits its practical application in the biosynthesis of natural vanillin. Herein, two rational strategies were combined to improve the thermostability of IEM from Pseudomonas nitroreducens Jin1. Two variants (K83R and K95R) with better thermostability and one mutant (G398A) with higher activity were identified from twenty candidates based on the Surface Residue Replacement method. According to the Consensus Mutagenesis method, one mutant (I352R) with better thermostability and another mutant (L273F) with higher activity were also identified from nine candidates. After combinatorial mutation, a triple mutant K83R/K95R/L273F with the best thermostability and catalytic efficiency was generated. Compared with the wild-type IEM, the thermal inactivation half-lives (t1/2) of K83R/K95R/L273F at 25 °C, 30 °C, and 35 °C increased 2.9-fold, 11.9-fold, and 24.7-fold, respectively. Simultaneously, it also exhibited a 4.8-fold increase in kcat, leading to a 1.2-fold increase in catalytic efficiency (kcat/Km). When the whole cell of K83R/K95R/L273F was applied to the biotransformation of isoeugenol on preparative scale, the vanillin concentration reached 240.1 mM with space-time yield of 109.6 g/L/d, and vanillin was achieved in 77.6% isolated yield and >99% purity.