Graphene Oxide Membrane Reactor for Electrochemical Deuteration Reactions.

The deuteration of organic molecules is considerably important in organic and medicinal chemistry. An electrochemical membrane reactor using proton-conducting graphene oxide (GO) nanosheets was developed to synthesize valuable deuterium-labeled products via an efficient hydrogen-to-deuterium (H/D) exchange under mild conditions at ambient temperature and atmospheric pressure. Deuterons (D+) formed by the anodic oxidation of heavy water (D2O) at the Pt/C anode permeate through the GO membrane to the Pt/C cathode, where organic molecules with functional groups (C≡C and C═O) are deuterated with adsorbed atomic D species. Deuteration occurs in outstanding yields with high levels of D incorporation. We also achieved the electrodeuteration of a drug molecule, ibuprofen, demonstrating the promising feasibility of the GO membrane reactor in the pharmaceutical industry.

A High-Efficiency Bioorthogonal Tumor-Membrane Reactor for In Situ Selective and Sustained Prodrug Activation.

The site-specific activation of bioorthogonal prodrugs has provided great opportunities for reducing the severe side effects of chemotherapy. However, the precise control of activation location, sustained drug production at the target site, and high bioorthogonal reaction efficiency in vivo remain great challenges. Here, we propose the construction of tumor cell membrane reactors in vivo to solve the above problems. Specifically, tumor-targeted liposomes with efficient membrane fusion capabilities are generated to install the bioorthogonal trigger, the amphiphilic tetrazine derivative, on the surface of tumor cells. These predecorated tumor cells act as many living reactors, transforming the tumor into a "drug factory" that in situ activates an externally delivered bioorthogonal prodrug, for example intratumorally injected transcyclooctene-caged doxorubicin. In contrast to the rapid elimination of cargo that is encapsulated and delivered by liposomes, these reactors permit stable retention of bioorthogonal triggers in tumor for 96 h after a single dose of liposomes via intravenous injection, allowing sustained generation of doxorubicin. Interestingly, an additional supplement of liposomes will compensate for the trigger consumed by the reaction and significantly improve the efficiency of the local reaction. This strategy provides a solution to the efficacy versus safety dilemma of tumor chemotherapy.

Different reactor configurations for enhancement of CO2 methanation.

Greenhouse gas emissions are a massive concern for scientists to minimize the effect of global warming in the environment. In this study, packed bed, coated wall, and membrane reactors were investigated using three novel nickel catalysts for the methanation of CO2. CFD modelling methodologies were implemented to develop 2D models. The validity of the model was investigated in a previous study where experimental and simulated results in a packed bed reactor were in a good agreement. It was observed that the coated wall reactor had poorer performance compared to the packed bed, approximately 30% difference between the results, as the residence time of the former was lower. In addition, two membrane configurations were proposed, including a membrane packed bed and membrane coated wall reactor. Additional studies were performed in the coated wall reactor revealing that lower flow rates lead to higher conversion values. As for the bed thickness the optimum layer was found to be 1 mm. In both membrane reactor configurations, the effect of the thickness of M1 membrane, which indicates the membrane for the removal of H2O, didn't show difference while the reduction of the thickness of M2 membrane, which indicates the membrane for the removal of CO2, H2 and H2O, showed better results in terms of conversion.

Production of Modified Nucleosides in a Continuous Enzyme Membrane Reactor.

Nucleoside analogues are important compounds for the treatment of viral infections or cancers. While (chemo-)enzymatic synthesis is a valuable alternative to traditional chemical methods, the feasibility of such processes is lowered by the high production cost of the biocatalyst. As continuous enzyme membrane reactors (EMR) allow the use of biocatalysts until their full inactivation, they offer a valuable alternative to batch enzymatic reactions with freely dissolved enzymes. In EMRs, the enzymes are retained in the reactor by a suitable membrane. Immobilization on carrier materials, and the associated losses in enzyme activity, can thus be avoided. Therefore, we validated the applicability of EMRs for the synthesis of natural and dihalogenated nucleosides, using one-pot transglycosylation reactions. Over a period of 55 days, 2'-deoxyadenosine was produced continuously, with a product yield >90%. The dihalogenated nucleoside analogues 2,6-dichloropurine-2'-deoxyribonucleoside and 6-chloro-2-fluoro-2'-deoxyribonucleoside were also produced, with high conversion, but for shorter operation times, of 14 and 5.5 days, respectively. The EMR performed with specific productivities comparable to batch reactions. However, in the EMR, 220, 40, and 9 times more product per enzymatic unit was produced, for 2'-deoxyadenosine, 2,6-dichloropurine-2'-deoxyribonucleoside, and 6-chloro-2-fluoro-2'-deoxyribonucleoside, respectively. The application of the EMR using freely dissolved enzymes, facilitates a continuous process with integrated biocatalyst separation, which reduces the overall cost of the biocatalyst and enhances the downstream processing of nucleoside production.

Bicyclo[3.2.0]carbocyclic Molecules and Redox Biotransformations: The Evolution of Closed-Loop Artificial Linear Biocatalytic Cascades and Related Redox-Neutral Systems.

The role of cofactor recycling in determining the efficiency of artificial biocatalytic cascades has become paramount in recent years. Closed-loop cofactor recycling, which initially emerged in the 1990s, has made a valuable contribution to the development of this aspect of biotechnology. However, the evolution of redox-neutral closed-loop cofactor recycling has a longer history that has been integrally linked to the enzymology of oxy-functionalised bicyclo[3.2.0]carbocyclic molecule metabolism throughout. This review traces that relevant history from the mid-1960s to current times.

Toward Continuous-Flow Hyperpolarisation of Metabolites via Heterogenous Catalysis, Side-Arm-Hydrogenation, and Membrane Dissolution of Parahydrogen.

Side-arm hydrogenation (SAH) by homogeneous catalysis has extended the reach of the parahydrogen enhanced NMR technique to key metabolites such as pyruvate. However, homogeneous hydrogenation requires rapid separation of the dissolved catalyst and purification of the hyperpolarised species with a purity sufficient for safe in-vivo use. An alternate approach is to employ heterogeneous hydrogenation in a continuous-flow reactor, where separation from the solid catalysts is straightforward. Using a TiO2 -nanorod supported Rh catalyst, we demonstrate continuous-flow parahydrogen enhanced NMR by heterogeneous hydrogenation of a model SAH precursor, propargyl acetate, at a flow rate of 1.5 mL/min. Parahydrogen gas was introduced into the flowing solution phase using a novel tube-in-tube membrane dissolution device. Without much optimization, proton NMR signal enhancements of up to 297 (relative to the thermal equilibrium signals) at 9.4 Tesla were shown to be feasible on allyl-acetate at a continuous total yield of 33 %. The results are compared to those obtained with the standard batch-mode technique of parahydrogen bubbling through a suspension of the same catalyst.

Membrane-Confined Iron Oxychloride Nanocatalysts for Highly Efficient Heterogeneous Fenton Water Treatment.

Heterogeneous advanced oxidation processes (AOPs) allow for the destruction of aqueous organic pollutants via oxidation by hydroxyl radicals (•OH). However, practical treatment scenarios suffer from the low availability of short-lived •OH in aqueous bulk, due to both mass transfer limitations and quenching by water constituents, such as natural organic matter (NOM). Herein, we overcome these challenges by loading iron oxychloride catalysts within the pores of a ceramic ultrafiltration membrane, resulting in an internal heterogeneous Fenton reaction that can degrade organics in complex water matrices with pH up to 6.2. With •OH confined inside the nanopores (∼ 20 nm), this membrane reactor completely removed various organic pollutants with water fluxes of up to 100 L m-2 h-1 (equivalent to a retention time of 10 s). This membrane, with a pore size that excludes NOM (>300 kDa), selectively exposed smaller organics to •OH within the pores under confinement and showed excellent resiliency to representative water matrices (simulated surface water and sand filtration effluent samples). Moreover, the membrane exhibited sustained AOPs (>24 h) and could be regenerated for multiple cycles. Our results suggest the feasibility of exploiting ultrafiltration membrane-based AOP platforms for organic pollutant degradation in complex water scenarios.

Theoretical Thermodynamic Efficiency Limit of Isothermal Solar Fuel Generation from H2O/CO2 Splitting in Membrane Reactors.

Solar fuel generation from thermochemical H2O or CO2 splitting is a promising and attractive approach for harvesting fuel without CO2 emissions. Yet, low conversion and high reaction temperature restrict its application. One method of increasing conversion at a lower temperature is to implement oxygen permeable membranes (OPM) into a membrane reactor configuration. This allows for the selective separation of generated oxygen and causes a forward shift in the equilibrium of H2O or CO2 splitting reactions. In this research, solar-driven fuel production via H2O or CO2 splitting with an OPM reactor is modeled in isothermal operation, with an emphasis on the calculation of the theoretical thermodynamic efficiency of the system. In addition to the energy required for the high temperature of the reaction, the energy required for maintaining low oxygen permeate pressure for oxygen removal has a large influence on the overall thermodynamic efficiency. The theoretical first-law thermodynamic efficiency is calculated using separation exergy, an electrochemical O2 pump, and a vacuum pump, which shows a maximum efficiency of 63.8%, 61.7%, and 8.00% for H2O splitting, respectively, and 63.6%, 61.5%, and 16.7% for CO2 splitting, respectively, in a temperature range of 800 °C to 2000 °C. The theoretical second-law thermodynamic efficiency is 55.7% and 65.7% for both H2O splitting and CO2 splitting at 2000 °C. An efficient O2 separation method is extremely crucial to achieve high thermodynamic efficiency, especially in the separation efficiency range of 0-20% and in relatively low reaction temperatures. This research is also applicable in other isothermal H2O or CO2 splitting systems (e.g., chemical cycling) due to similar thermodynamics.

Increased γ-Aminobutyric Acid Content of Germinated Brown Rice Produced in Membrane Reactor.

RESEARCH BACKGROUND: Rice germination is a natural approach to enhance the physical and functional properties of brown rice. Thus, the aim of this study is to investigate the influence of different germination methods on functional properties of germinated brown rice and evaluate the process feasibility. EXPERIMENTAL APPROACH: Brown rice of IPB 3S variety was germinated with three different methods: (i) complete soaking without water replacement, (ii) complete soaking with water replacement every six hours, and (iii) complete soaking with continuous washing in the developed membrane-facilitated soaking reactor. RESULTS AND CONCLUSIONS: The application of the membrane reactor for producing germinated brown rice maintained the pH of the soaking solution relatively constant (i.e. 6.8-7.0). This indicated the circumvention of natural fermentation during brown rice germination. Moreover, the mass fraction of γ-aminobutyric acid in germinated brown rice produced in the membrane reactor was about 4.5-fold higher (169.2 mg/100 mg) than in ungerminated brown rice (36.82 mg/100 mg), and also higher than that of the other two soaking methods. The γ-oryzanol mass fractions and the antioxidant capacity expressed as ascorbic acid equivalents of germinated brown rice obtained with the three soaking methods varied from 32 to 38 mg/100 mg and 18 to 28 mg/100 g, respectively. Within this study, germination could also slightly reduce the transition temperatures of germinated brown rice starch gelatinization (t o=73-74 °C, t p=76-77 °C and t c=~80 °C, where t o, t p and t c are onset, peak and conclusion (final) temperatures). In conclusion, the production of germinated brown rice in the membrane reactor could enhance its γ-aminobutyric acid mass fraction and reduce wastewater production and is therefore considered more feasible. NOVELTY AND SCIENTIFIC CONTRIBUTION: This study demonstrates the feasibility of germinated brown rice production using a membrane-facilitated soaking reactor with enhancement of bioactive compound content, especially γ-aminobutyric acid, and minimised wastewater production.

Highly Selective CO2 Conversion to Methanol in a Bifunctional Zeolite Catalytic Membrane Reactor.

The hydrogenation of sequestrated CO2 to methanol can reduce CO2 emission and establish a sustainable carbon circuit. However, the transformation of CO2 into methanol is challenging because of the thermodynamic equilibrium limitation and the deactivation of catalysts by water. In the present work, different reactor types have been evaluated for CO2 catalytic hydrogenation to methanol. Best results have been obtained in a bifunctional catalytic membrane reactor (CMR) based on a zeolite LTA membrane and a catalytic Cu-ZnO-Al2 O3 -ZrO2 layer on top. Due to the in situ and rapid removal of the produced water from the catalytic layer through the hydrophilic zeolite LTA membrane, it is effective to break the thermodynamic equilibrium limitation, thus significantly increasing the CO2 conversion (36.1 %) and methanol selectivity (100 %). Further, the catalyst deactivation by the produced water can be effectively inhibited, thus maintaining a high long-term activity of the CMR.

Pd/Fe nanoparticle integrated PMAA-PVDF membranes for chloro-organic remediation from synthetic and site groundwater.

The poly(methacrylic acid) (PMAA) was synthesized in the pores of commercial microfiltration PVDF membranes to allow incorporation of catalytic palladium/iron (Pd/Fe) nanoparticles for groundwater remediation. Particles of 17.1 ± 4.9 nm size were observed throughout the pores of membranes using a focused ion beam. To understand the role of Pd fractions and particle compositions, 2-chlorobiphenyl was used as a model compound in solution phase studies. Results show H2 production (Fe0 corrosion in water) is a function of Pd coverage on the Fe. Insufficient H2 production caused by higher coverage (> 10.4% for 5.5 wt%) hindered dechlorination rate. With 0.5 wt% Pd, palladized-Fe reaction rate (surface area normalized reaction rate, ksa = 0.12 L/(m2-h) was considerably higher than isolated Pd and Fe particles. For groundwater, in a single pass of Pd/Fe-PMAA-PVDF membranes (0.5 wt% Pd), chlorinated organics, such as trichloroethylene (177 ppb) and carbon tetrachloride (35 ppb), were degraded to 16 and 0.3 ppb, respectively, at 2.2 seconds of residence time. The degradation rate (observed ksa) followed the order of carbon tetrachloride > trichloroethylene > tetrachloroethylene > chloroform. A 36 h continuous flow study with organic mixture and the regeneration process show the potential for on-site remediation.

Comparison between an electrochemical reactor with and without membrane for the nor oxidation using novel ceramic electrodes.

The electrochemical oxidation of the antibiotic Norfloxacin (NOR) in chloride media on different anodic materials was studied at two different electrochemical reactors. The results were compared with those obtained in sulphate media. The anodes under study were a commercial boron-doped diamond (BBD) and two different ceramic electrodes based on tin oxide doped with antimony oxide in the presence (CuO) and absence (BCE) of copper oxide as sintering aid. The reactors employed were a one-compartment reactor (OCR) and a two-compartment one with a membrane separating both electrodes (EMR). The use of the membrane clearly enhanced both NOR degradation and TOC mineralization for all the anodic materials studied since some parallel reactions were avoided. Additionally, two different pathways for NOR oxidation were observed as a function of the reactor employed. The EMR also favoured the ionic by-products generation and the electrolyte dechlorination. NO3- increased with the oxidation power of the anode employed and it was also enhanced by the EMR use. Chloride media favours ceramic electrodes performance independently of the reactor employed as they did not generate an excess of oxidants as BDD did. The BCE electrode is an interesting alternative to BDD since although its oxidative power was lower, it presented similar current efficiency with lower energy consumption.

Treatment of aqueous wastes by means of Thermophilic Aerobic Membrane Reactor (TAMR) and nanofiltration (NF): process auditing of a full-scale plant.

This work focuses on the Thermophilic Aerobic Membrane Reactor (TAMR) process. The research was carried out on a full-scale facility where, all along a 12-year period, daily monitoring and process audit tests were conducted for the process analysis and optimization. The plant treated -light and high-strength aqueous wastes and two different configurations were adopted: (1) thermophilic biological reactor + ultrafiltration (TAMR) and (2) TAMR + nanofiltration (TAMR + NF). In the latter case, the average chemical oxygen demand removal yield was equal to 89% and an effective denitrification (nitrogen oxides removal equal to 96%) was achieved by reducing the dissolved oxygen concentration in the bioreactor. Low specific sludge production was observed. Poor sludge settling properties were measured by a lab-scale settling test; respirometric tests (nitrogen uptake rate and ammonia uptake rate) showed the presence of denitrification and the inhibition of nitrification. Hydrodynamic tests revealed the presence of a significant dead space, thus showing room for improving the overall process performance. Finally, the rheological properties of the sludge were measured as a function of the biomass concentration, pH, temperature, and aeration scheme.

Laccase grafted membranes for advanced water filtration systems: a green approach to water purification technology.

PURPOSE: Conventional wastewater treatment technologies are not good enough to completely remove all endocrine disrupting compounds (EDCs) from the water. Membrane separation systems have emerged as an attractive alternative to conventional clarification processes for waste and drinking water. Coupling of a membrane separation process with an enzymatic reaction has opened up new avenues to further enhance the quality of water. This review article deliberates the feasibility of implementing enzymatic membrane reactors has been deliberated. MATERIALS AND METHODS: A comprehensive study of conventional water treatment technologies was carried out and their shortcomings were pointed out. Research findings from the leading groups working on enzyme grafted membrane based water purification were summarized. This review also comprehends the patent documents pertinent to the technology of enzyme grafted membranes for water purification. RESULTS: Immobilization of an enzyme on a membrane improves the performance of membrane filtration, and processes for the treatment of polluted water. Research has started exploring the potential for laccase enzymes because it can catalyze the oxidation of a wide range of substrates, structurally comparable to EDCs, by a radical-catalyzed reaction mechanism, with corresponding reduction of oxygen to water in an electron transfer process. Further, in the presence of certain mediators, the substrate range of laccases can be further enhanced to non-aromatic substrates. CONCLUSIONS: Removal of EDCs by laccase cross-linked enzyme aggregates in fixed-bed reactors or fluidized-bed reactors and laccase immobilized ultrafiltration (LIUF) membranes are proving their worth in water purification technology. The major operational issues with the use of LIUF membranes are enzyme instability in real wastewater and membrane fouling. In view of the above-stated characteristics, laccases are considered as the most promising enzyme for a greener and less expensive water purification technology.

Continuous production of pectic oligosaccharides from sugar beet pulp in a cross flow continuous enzyme membrane reactor.

Sugar beet pulp pectin is an attractive source for the production of pectic oligosaccharides, an emerging class of potential prebiotics. The main aim of the present work was to investigate a new process allowing to produce pectic oligosaccharides in a continuous way by means of a cross flow enzyme membrane reactor while using a low-cost crude enzyme mixture (viscozyme). Preliminary experiments in batch and semi-continuous setups allowed to identify suitable enzyme concentrations and assessing filtration suitability. Then, in continuous experiments in the enzyme membrane reactor, residence time and substrate loading were further optimized. The composition of the obtained oligosaccharide mixtures was assessed at the molecular level for the most promising conditions and was shown to be dominated by condition-specific arabinans, rhamnogalacturonans, and galacturonans. A continuous and stable production was performed for 28.5 h at the optimized conditions, obtaining an average pectic oligosaccharide yield of 82.9 ± 9.9% (w/w), a volumetric productivity of 17.5 ± 2.1 g/L/h, and a specific productivity of 8.0 ± 1.0 g/g E/h. This work demonstrated for the first time the continuous and stable production of oligosaccharide mixtures from sugar beet pulp using enzyme membrane reactor technology in a setup suitable for upscaling.

Production of egg white protein hydrolysates with improved antioxidant capacity in a continuous enzymatic membrane reactor: optimization of operating parameters by statistical design.

This study focuses on the influence of operating conditions on Alcalase-catalyzed egg white protein hydrolysis performed in a continuously stirred tank reactor coupled with ultrafiltration module (10 kDa). The permeate flow rate did not significantly affect the degree of hydrolysis (DH), but a significant increase in process productivity was apparent above flow rate of 1.9 cm3 min-1. By contrast, an increase in enzyme/substrate (E/S) ratio provided an increase in DH, but a negative correlation was observed between E/S ratio and productivity. The relationship between operating conditions and antioxidant properties of the hydrolysates, measured by three methods, was studied using Box-Behnken experimental design and response surface methodology. The statistical analysis showed that each variable (impeller speed, E/S ratio, and permeate flow rate) had a significant effect on the antioxidant capacity of all tested systems. Nevertheless, obtained response functions revealed that antioxidative activity measured by DPPH, ABTS and FRAP methods were affected differently by the same operating conditions. High impeller speeds and low permeate flow rates favor ABTS while high impeller speeds and high permeate flow rates had a positive effect on the DPPH scavenging activity. On the other hand, the best results obtained with FRAP method were achieved under moderate operating conditions. The integration of the reaction and ultrafiltration membrane separation in a continuous manner appears to be a right approach to improve and intensify the enzymatic process, enabling the production of peptides with desired antioxidant activity.

Recent Advances in Pd-Based Membranes for Membrane Reactors.

Palladium-based membranes for hydrogen separation have been studied by several research groups during the last 40 years. Much effort has been dedicated to improving the hydrogen flux of these membranes employing different alloys, supports, deposition/production techniques, etc. High flux and cheap membranes, yet stable at different operating conditions are required for their exploitation at industrial scale. The integration of membranes in multifunctional reactors (membrane reactors) poses additional demands on the membranes as interactions at different levels between the catalyst and the membrane surface can occur. Particularly, when employing the membranes in fluidized bed reactors, the selective layer should be resistant to or protected against erosion. In this review we will also describe a novel kind of membranes, the pore-filled type membranes prepared by Pacheco Tanaka and coworkers that represent a possible solution to integrate thin selective membranes into membrane reactors while protecting the selective layer. This work is focused on recent advances on metallic supports, materials used as an intermetallic diffusion layer when metallic supports are used and the most recent advances on Pd-based composite membranes. Particular attention is paid to improvements on sulfur resistance of Pd based membranes, resistance to hydrogen embrittlement and stability at high temperature.

Immobilized biocatalytic process development and potential application in membrane separation: a review.

Biocatalytic membrane reactors have been widely used in different industries including food, fine chemicals, biological, biomedical, pharmaceuticals, environmental treatment and so on. This article gives an overview of the different immobilized enzymatic processes and their advantages over the conventional chemical catalysts. The application of a membrane bioreactor (MBR) reduces the energy consumption, and system size, in line with process intensification. The performances of MBR are considerably influenced by substrate concentration, immobilized matrix material, types of immobilization and the type of reactor. Advantages of a membrane associated bioreactor over a free-enzyme biochemical reaction, and a packed bed reactor are, large surface area of immobilization matrix, reuse of enzymes, better product recovery along with heterogeneous reactions, and continuous operation of the reactor. The present research work highlights immobilization techniques, reactor setup, enzyme stability under immobilized conditions, the hydrodynamics of MBR, and its application, particularly, in the field of sugar, starch, drinks, milk, pharmaceutical industries and energy generation.

Highly efficient production of rare sugars D-psicose and L-tagatose by two engineered D-tagatose epimerases.

Rare sugars are monosaccharides that do not occur in nature in large amounts. However, many of them demonstrate high potential as low-calorie sweetener, chiral building blocks or active pharmaceutical ingredients. Their production by enzymatic means from broadly abundant epimers is an attractive alternative to synthesis by traditional organic chemical means, but often suffers from low space-time yields and high enzyme costs due to rapid enzyme degradation. Here we describe the detailed characterization of two variants of d-tagatose epimerase under operational conditions that were engineered for high stability and high catalytic activity towards the epimerization of d-fructose to d-psicose and l-sorbose to l-tagatose, respectively. A variant optimized for the production of d-psicose showed a very high total turnover number (TTN) of up to 10(8) catalytic events over a catalyst's lifetime, determined under operational conditions at high temperatures in an enzyme-membrane reactor (EMR). Maximum space-time yields as high as 10.6 kg L(-1) d(-1) were obtained with a small laboratory-scale EMR, indicating excellent performance. A variant optimized for the production of l-tagatose performed less stable in the same setting, but still showed a very good TTN of 5.8 × 10(5) and space-time yields of up to 478 g L(-1) d(-1) . Together, these results confirm that large-scale enzymatic access to rare sugars is feasible.

Reverse-Bumpy-Ball-Type-Nanoreactor-Loaded Nylon Membranes as Peroxidase-Mimic Membrane Reactors for a Colorimetric Assay for H2O2.

Herein we report for the first time fabrication of reverse bumpy ball (RBB)-type-nanoreactor-based flexible peroxidase-mimic membrane reactors (MRs). The RBB-type nanoreactors with gold nanoparticles embedded in the inner walls of carbon shells were loaded on nylon membranes through a facile filtration approach. The as-prepared flexible catalytic membrane was studied as a peroxidase-mimic MR. It was found that the obtained peroxidase-mimic MR could exhibit several advantages over natural enzymes, such as facile and good recyclability, long-term stability and easy storage. Moreover, the RBB NS-modified nylon MRs as a peroxidase mimic provide a useful colorimetric assay for H2O2.