Net Reaction Research Articles

Quantum Dot Photocatalysts for Organic Transformations.

Quantum dots (QDs) with tunable photo-optical properties and colloidal nature are ideal for a wide range of photocatalytic reactions. In particular, QD photocatalysts for organic transformations can provide new and effective synthetic routes to high value-added molecules under mild conditions. In this Perspective, we discuss the advances of employing QDs for visible-light-driven organic transformations categorized into net reductive reactions, net oxidative reactions, and redox neutral reactions. We then provide our outlook for potential future directions in the field: nanostructure engineering to improve charge separation efficiencies, ligand shell engineering to optimize overall catalyst performance, in situ comprehensive studies to delineate underlying reaction mechanisms, and laboratory automation with the assistance of modern computing techniques to revolutionize the reaction optimization process.

The Importance of Benthic Nutrient Fluxes in Supporting Primary Production in the Laptev and East Siberian Shelf Seas

AbstractThis study presents an assessment of benthic nutrient regeneration and its role for the nutrient budget of the outer Laptev and East Siberian shelf sea. Porewater profiles of the major nutrients dissolved silica (DSi), dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphate (DIP) as well as total dissolved iron (DFe) were evaluated with a one‐dimensional reaction transport model to derive net reaction rates and benthic nutrient fluxes from shelf and slope 16 stations. Integrated over the shelf area the benthic fluxes of DSi, DIN, and DIP were found to be 7.1, 1.2, and 0.5 Gmol/year in the Laptev Sea and 29.8, 9.5, and 2.8 Gmol/year in East Siberian Sea, respectively. A comparison of the ratios of the benthic nutrient fluxes with marine and riverine inputs and Arctic plankton stoichiometry indicate substantial benthic nitrogen loss likely due to denitrification relative to DIP and DSi. Our benthic flux estimation is likely a low estimate of benthic nutrient fluxes considering potentially higher regeneration rates of nutrients from more productive, bioturbated near‐shore sediments. The estimate emphasizes the role of benthic nutrient fluxes by returning nutrients with a fundamentally different stoichiometry to bottom waters from that of Arctic marine phytoplankton, riverine sources, and open water inflow. With a simple box model, we provide a snapshot of today's nutrient budget in the two seas and estimate that about 10%–20% of nutrients required by primary production are derived from sediments. This proportion is expected to increase for a future warmer Arctic continental shelf in response to increasing primary production.

Method for boosting dispersive spectrograph stability 1000× using interferometry with crossfaded pairs of delays

We demonstrate a key step along a technical route to achieving cm/s scale accuracy for astronomical spectrographs over long (multi-year) time scales, which is critical for the Doppler characterization of Earth sized exoplanets, and measurement of small cosmic redshift drift over many years. This same technique also enables searching exoplanet atmospheres for biosignificant molecules in direct planet imaging using, otherwise, insufficiently low resolution and drift prone dispersive (grating or prism) spectrographs. Using a method called crossfading for externally dispersed interferometers (EDIs) to get highly robust spectra, we recently demonstrated a factor of 1000 × reduction in the net shift of an EDI measured ThAr line to a deliberate simulated wavelength translation of the detector. This 1000 × gain in disperser stability can be combined with conventional stability gains afforded by fiber scramblers, vacuum tanks, and thermal control, to provide an additional 1 to 3 orders of magnitude reduction in the net point spread function shift drift. Crossfading combines high- and low-delay fringing signals that react oppositely in phase to cancel their net reaction to a detector wavelength drift. This can be implemented by an interferometer addition to a facility spectrograph.

Probing the application of kinetic theory to Mg-phyllosilicate growth with Si isotope doping

The Principle of Detailed Balance (PDB) played a defining role in the derivation of the widely-used Transition State Theory rate law equation and serves as an important link between geochemical kinetics and thermodynamics. Although significant improvements have been made in applying the PDB to comparatively simple systems (e.g., SiO2-water), experimental verification of the PDB is lacking for more complex minerals such as the phyllosilicates. Providing kinetic constraints on the rates of phyllosilicate growth from supersaturated solutions is particularly important for constructing facies models, constraining element cycling in the lacustrine and marine environments, and interpreting paleo-biogeochemistry. Here, we use 29Si isotopic doping techniques to quantify the rates of reaction between Mg-phyllosilicate substrates (amorphous Mg-silicate (a talc-like phase) and crystalline talc) and supersaturated solutions at 21 and 60 °C. The results show that the ratio of the forward and backward rates of amorphous Mg-silicate-water reaction approaches unity as the saturation state of the solution approaches the apparent solubility of amorphous Mg-silicate. The precipitation rates coupled with equivalent dissolution rates obtained from experiments with amorphous Mg-silicate substrates appear to obey the same rate function as the precipitation rates coupled with negligible dissolution rates obtained from experiments with crystalline Mg-silicate substrates over the degrees of supersaturation we explore, suggesting that the elementary step limiting the rate of precipitation remains the same. Accordingly, our results demonstrate that the PDB is applicable to amorphous Mg-phyllosilicate-water reactions, thereby reinforcing the use of TST rate equations to describe Mg-phyllosilicate growth. The experimental data can also be taken as evidence that the apparent solubility of amorphous Mg-silicate, a concept previously explained using the kinetic theory of nucleation and growth, also has a thermodynamic meaning, in that it represents a metastable equilibrium with the poorly crystalline phase. The measured, non-negligible forward and backward rates suggest that, even in this metastable state where little if any net reaction is occurring, isotopic signatures can be reset. Moreover, the significant discrepancy between the heterogeneous net growth rates on the amorphous Mg-silicate substrate versus those measured on crystalline talc and sepiolite substrates indicates that mineral crystallinity likely plays a key role in mineral growth during diagenesis.

Analysis of Undergraduate Mathematic Students’ Understanding on Microscopic Representation of General Chemistry Lecture based on their Scientific Reasoning Ability

Undergraduate mathematic students (UMS)’ scientific reasoning can affect their ability to do abstraction of microscopic phenomenon. Based on Piaget’s theory of cognitive development of UMS are in operational formal category, but this research was found that only 2 students of UMS whose have scientific reasoning as formal category. The aim of this research was analysing UMS’ achievement on understanding microscopic representation based on their scientific reasoning (concrete, transition, or formal category). Mixed method was used in this research which integrated quantitative data (test score) and qualitative data (analysing of understanding and scientific reasoning ability). The research funding that mean score test of UMS as formal reasoned (F) were the highest. UMS as transition reasoner and concrete reasoner were difficult to solve stoichiometry calculation which contains microscopic representation. Question about limiting reactant based on molecule representation, that 10,7% of UMS as concrete reasoner (C) answered there was no limiting reactant. The characteristic of concrete reasoner (C) is understanding based on observable object. They difficult to transform it as microscopic representation (number of molecules as reactant and product) which was written on net reaction as symbolic representation. They did not consider stoichiometric chemical equation by using representation of X as a variable in mathematical calculations. Another response that 14,3% of UMS as transition reasoner (T) determined limiting reactant by using logical mathematic equation of (mole=mass/molar mass) without considered coefficient in net reaction. In general chemistry learning, requires innovation to visualize microscopic aspects, so that UMS at concrete reasoning and transitions reasoning have the ability to interpret microscopic phenomena which is not observed by naked eyes.

Photocatalyzed Dual-Oxidative Trifluoromethylthio-Trifluoromethylation of Alkenes with CF 3 SO 2 Na

A novel photocatalyzed trifluoromethylthio-trifluoromethylation of alkenes has been developed, using CF3SO2Na as both CF3 and SCF3 source. This photocatalyzed dual-oxidative strategy, which combine...

Effect of CO2 Dilution on Methane/Air Flames at Elevated Pressures: An Experimental and Modeling Study

This study reports experimental and kinetic modeling results on the effects of CO2 dilution on laminar premixed methane/air flames, based on spherically propagating flames and one-dimensional adiabatic planar flame simulations, at elevated pressure. The laminar burning velocities of air mixtures with CH4 and CO2 at different dilution ratios were measured. In order to have a comprehensive understanding of the effects of CO2 dilution both chemically and physically, sensitivity analysis, chemical reaction rate analysis, and mole fraction analysis of active radicals were carried out using the Aramco 1.3 kinetic mechanism. The chemical impact of the addition of CO2 was segregated from its physical effects using fictitious species, FCO2 with the same thermochemical and transport characteristics as CO2, but does not participate in any chemical reactions. The CO2 dilution percentage varied was from 0 to 70% (by volume) to measure SLo at 300 K, 1 and 5 bar, and equivalence ratios (Φ) of 0.6 to 1.4. Results show that increasing CO2 dilution ratio decreases the SLo of these CH4/CO2/air mixtures. The results simulated using Aramco 1.3 illustrate that the chemical effect is less important at elevated pressure than at ambient pressure. The H and OH radical reduction rates are remarkably reduced at elevated pressure, where H radicals are primarily controlling the combustion. Elementary reactions with a negative sensitivity coefficient exhibit higher sensitivity toward pressure compared to the dilution effect, while elementary reactions with a positive sensitivity coefficient were equally sensitive to both pressure and dilution effects. The increase in initial pressure suppresses the peak net reaction rates for all the elementary reactions, with increasing CO2 concentration.

Propene oligomerization on Beta zeolites: Development of a microkinetic model and experimental validation

The microkinetic modelling methodology that we developed previously to describe Brønsted acid-catalyzed propene oligomerization on medium-pore MFI zeolites has been extended successfully to large-pore Beta zeolites. The extension of the model was supported by the identification of the key descriptors that account for the different topologies and acid strengths of the zeolite frameworks (physisorption enthalpies, stabilization enthalpies, frequency factors). The model is validated with experimental conversion and selectivity data measured in a plug-flow reactor on a commercial Beta zeolite over a range of operating conditions. Analysis of net reaction rates allowed identifying the preferred pathways that increase oligomerization selectivity toward C9 species with increasing propene pressure. The model was additionally used to investigate how the stabilization enthalpies of chemisorbed intermediates, an important catalyst descriptor, influenced the selectivity and surface coverage at iso-conversion. This analysis provides mechanistic insights into the propene oligomerization reaction network and its dependence on zeolite topology, and demonstrates how microkinetic models can describe catalyst behaviour and aid in catalyst and process optimization.

Dynamics of arsenic and its interaction with Fe and S at the sediment-water interface of the seasonal hypoxic Changjiang Estuary

The dynamics of As at the sediment-water interface (SWI) is an important link in driving As release into the upper water column to affect biological activities. At present, it is unclear about the As cycling at the SWI, especially under the influence of seasonal hypoxia in the Changjiang Estuary. In this study, the profile variations of As in porewater and solid phases from the Changjiang Estuary were studied. Results suggested that As profiles presented the “removal-release-removal” pattern with depth. Arsenic profiles were typically characterized by subsurface maxima in porewater and surficial enrichment in solid phase, which were closely related to Fe and S cycling. The occurrence of porewater As peaks and its obvious speciation transition at subsurface layers, companied by the conversion of dominant phases of solid As from reductive to oxidative fractions at the same layers indicated the reductive release of As at redoxcline. Arsenic species, saturation indexes (SI) and net reaction rates (RnetAs) suggested that the removal of As at surface and deep layers were attributed to the adsorption of As(V) by Fe oxides and the formation of orpiment and/or adsorption by Fe sulfides, respectively. The benthic hypoxic environment in late-summer was more favorable for upward migration and diffusion of As. This process was considered as an important contribution to the elevated aquatic As in the Changjiang Estuary.

The effect of turbulence on mass transfer in solid fuel combustion: RANS model

In this paper, a kinetic-diffusion surface combustion model is examined. The model is modified such that two effects of turbulence are included: 1) enhancement of the mass transfer due to relative velocity between particles and fluid and 2) reduction of the mass transfer due to turbulence-induced particle clustering. Details of the implementation are discussed and the influence of parameters such as air-fuel ratio, particle number density, particle diameter, turbulence intensity and characteristic length scales are studied theoretically. A simplified numerical model of a combustion chamber is created to explore the effects of the combustion model predictions. Finally, the model is incorporated into simulations of an industrial-scale boiler to investigate the effect of turbulence on the net surface reaction rate in a real system. The study shows that although on average this effect is rather minor, there exist regions in which the carbon conversion rate is either decreased or increased by turbulence.

Enhanced conversion of CO2 into O2-free fuel gas via the Boudouard reaction with biochar in an atmospheric plasmatron

In this work, CO2 reaction with biochar via the Boudouard reaction (CO2 + C → 2CO) has been investigated in an atmospheric non-thermal plasmatron for the first time, aiming for enhanced conversion of CO2 into O2-free fuel gas (mainly CO). The motion behavior and electrical characteristics of the plasmatron in CO2 was studied to understand its physical characteristics. Both the CO2 decomposition reaction and CO2 reaction with biochar were evaluated in the plasmatron under different flow rates and applied voltages. The results showed that the discharge experiences a consecutive circle of breakdown – elongation – extinguishment - re-breakdown outside of the electrode region. For the CO2 decomposition process without biochar, a high voltage of 10 kV shifts the optimal flow rate to a remarkably higher value, yielding a CO2 conversion of 6.9 % and an energy efficiency of up to 36.4 % at flow rate = 13 L/min. In the presence of coconut shell biochar, the net Boudouard reaction becomes the dominant contributor to CO2 conversion with contributions of up to >96.0 % (applied voltage =10 kV). As a result, a significantly enhanced CO2 conversion of up to 21.3 % can be achieved in comparison to the CO2 decomposition process, simultaneously with a dramatically higher CO (e.g., increases from 2.31% to 34.08%) but remarkably lower O2 concentration (e.g., decreases from 1.0 % to 0.06 %) in the products. The immediate study reveals that the plasmatron assisted CO2 reaction with biochar via the Boudouard reaction is a promising route for energy efficient CO2 conversion into O2-free fuel gas.

Structure and Combustion Characteristics of Methane/Air Premixed Flame under the Action of Wall

In order to obtain the combustion characteristics of the CH4/Air premixed flame under the action of the wall interaction, a study on the impact of the jet flame on the wall at different separation distances was carried out. The separation distance from the burner outlet to the lower surface of the wall is changed and the flame structure is obtained through experiments. The temperature, velocity and reaction rate are obtained through numerical simulation, and the law of flame characteristics change is obtained through analysis. The results show that as the separation distance increases, the premixing cone inside the flame gradually changes from a horn shape to a complete cone shape and the length of the premixing cone profile increases. Also, the peak temperature and velocity of the mixture in the axial direction gradually increase, and the temperature and velocity in the radial direction first increase and then decrease. The temperature gradient and velocity reach the maximum when the separation distance is 11 mm. The peaks of reactants (CH4) net reaction rate intermediate products (CO) and products (CO2, H2O) on the axis and the axial distance corresponding to the peaks increase accordingly. The chemical reaction rate near the wall also gradually decreases with the increase of the separation distance.

The metabolic importance of the glutaminase II pathway in normal and cancerous cells

In rapidly dividing cells, including many cancer cells, l-glutamine is a major energy source. Utilization of glutamine is usually depicted as: l-glutamine → l-glutamate (catalyzed by glutaminase isozymes; GLS1 and GLS2), followed by l-glutamate → α-ketoglutarate [catalyzed by glutamate-linked aminotransferases or by glutamate dehydrogenase (GDH)]. α-Ketoglutarate is a major anaplerotic component of the tricarboxylic acid (TCA) cycle. However, the glutaminase II pathway also converts l-glutamine to α-ketoglutarate. This pathway consists of a glutamine transaminase coupled to ω-amidase [Net reaction: l-Glutamine + α-keto acid + H2O → α-ketoglutarate + l-amino acid + NH4+]. This review focuses on the biological importance of the glutaminase II pathway, especially in relation to metabolism of cancer cells. Our studies suggest a component enzyme of the glutaminase II pathway, ω-amidase, is utilized by tumor cells to provide anaplerotic carbon. Inhibitors of GLS1 are currently in clinical trials as anti-cancer agents. However, this treatment will not prevent the glutaminase II pathway from providing anaplerotic carbon derived from glutamine. Specific inhibitors of ω-amidase, perhaps in combination with a GLS1 inhibitor, may provide greater therapeutic efficacy.

The metabolic importance of the overlooked asparaginase II pathway

The asparaginase II pathway consists of an asparagine transaminase [l-asparagine + α-keto acid ⇆ α-ketosuccinamate + l-amino acid] coupled to ω-amidase [α-ketosuccinamate + H2O → oxaloacetate + NH4+]. The net reaction is: l-asparagine + α-keto acid + H2O → oxaloacetate + l-amino acid + NH4+. Thus, in the presence of a suitable α-keto acid substrate, the asparaginase II pathway generates anaplerotic oxaloacetate at the expense of readily dispensable asparagine. Several studies have shown that the asparaginase II pathway is important in photorespiration in plants. However, since its discovery in rat tissues in the 1950s, this pathway has been almost completely ignored as a conduit for asparagine metabolism in mammals. Several mammalian transaminases can catalyze transamination of asparagine, one of which – alanine-glyoxylate aminotransferase type 1 (AGT1) – is important in glyoxylate metabolism. Glyoxylate is a precursor of oxalate which, in the form of its calcium salt, is a major contributor to the formation of kidney stones. Thus, transamination of glyoxylate with asparagine may be physiologically important for the removal of potentially toxic glyoxylate. Asparaginase has been the mainstay treatment for certain childhood leukemias. We suggest that an inhibitor of ω-amidase may potentiate the therapeutic benefits of asparaginase treatment.

Experimental and Numerical Investigation of Laminar Flame Characteristics of Isooctane/air Mixtures at High Preheating Temperatures and H2O Dilution Ratios

ABSTRACT Liquid water injection technology is an effective method to improve the fuel economy and reduce the emissions of an internal-combustion engine. In this study, the laminar burning velocity and Markstein length of isooctane/air mixtures at a fixed pressure of 101.3 kPa, H2O dilution ratios of 0–10%, and preheating temperatures of 400–500 K was investigated using a combustion bomb and high-speed schlieren photography. The different effects of water vapor and preheating temperatures on the laminar burning velocity of isooctane/air mixtures were analyzed using the CHEMKIN software. The physical (dilution and thermal) and chemical effects of water vapor on the laminar burning velocity were identified. The results demonstrate that the laminar burning velocity decreases linearly with an increasing H2O dilution ratio and increases exponentially as the preheating temperature increases. The Markstein length increases gradually with the increase of H2O dilution ratio. The laminar burning velocity decreases by 0.13 m/s-0.17 m/s with 1% H2O dilution ratio at a preheating temperature of 400 K. The addition of water vapor decreases the concentration of free radicals. The physical and chemical effects increase linearly as the H2O dilution ratio increases. The physical effects are the main reason for the decrease in the laminar burning velocity. The chemical effects reduce the mole fraction of free radicals (H and O) and increase that of OH, which increases the net reaction rate of the reaction O + H2O = 2OH.

NetRed, an algorithm to reduce genome-scale metabolic networks and facilitate the analysis of flux predictions

Flux balance analysis (FBA) of large, genome-scale stoichiometric models (GSMs) is a powerful and popular method to predict cell-wide metabolic activity. FBA typically generates a flux vector containing O(1,000) fluxes. The interpretation of such a flux vector is difficult, even for expert users, because of the large size and complex topology of the underlying metabolic network. This interpretation could be simplified by condensing the network to a reduced, yet fully representative version. Toward this goal we report NetRed, an algorithm that systematically reduces a stoichiometric matrix and a corresponding flux vector to a more easily interpretable form. The reduction offered by NetRed is transparent because it relies purely on matrix algebra and not on optimization. Uniquely, it involves zero information loss; therefore, the original unreduced network can be easily recovered from the reduced network. The inputs to NetRed are (i) a stoichiometric matrix, (ii) a flux vector with numerical flux values, and (iii) a list of “protected” metabolites recommended by the user to remain in the reduced network. NetRed outputs a reduced metabolic network containing a reduced number of metabolites, of which the protected metabolites are a subset. The algorithm also generates a corresponding reduced flux vector. Due to its simplified presentation and easier interpretability, the reduced network allows the user to quickly find fluxes through metabolites and reaction modes or pathways of interest. In this manuscript, we first demonstrate NetRed on a simple network consisting of glycolysis and the pentose phosphate pathway (PPP), wherein NetRed reduced the PPP to a single net reaction. We followed this with applications of NetRed to E. coli and yeast GSMs. NetRed reduced the size of an E. coli GSM by 20- to 30-fold and enabled a comprehensive comparison of aerobic and anaerobic metabolism. The application of NetRed to a yeast GSM allowed for easy mechanistic interpretation of a double-gene knockout that rerouted flux toward dihydroartemisinic acid. When applied to an E. coli strain engineered for enhanced valine production, NetRed allowed for a holistic interpretation of the metabolic rerouting resulting from multiple genetic interventions.

Defluorinative Functionalization of Pd(II) Fluoroalkyl Complexes.

When subjected to arylboranes, anionic trifluoromethyl and difluorobenzyl palladium(II) complexes undergo fluoride abstraction followed by 1,1-migratory insertion. The resulting intermediate fluoroalkyl species can be induced to undergo a subsequent transmetalation and reductive elimination from either an in situ formed fluoroboronate (FB(Ar3)-) or an exogenous boronic acid/ester (ArB(OR)2) and nucleophilic activator, representing a net defluorinative arylation reaction. The latter method enabled a structurally diverse substrate scope to be prepared from either an isolated palladium-CF3 complex, or from Pd(PPh3)4 and other commercially available reagents.

Dual Hydrogen- and Oxygen-Transport Membrane Reactor for Solar-Driven Syngas Production

A novel thermochemical dual-membrane reactor is considered with the goal of efficiently converting CO2 to fuels using concentrated solar energy as the process heat source. In contrast to the temperature-swing redox cycle, in this isothermal system the thermolysis of H2O at above 1800 K is assisted by removal of O2 across an oxygen-permeable membrane and of H2 across a hydrogen-permeable membrane. The latter is consumed by a stream of CO2 via the reverse water-gas shift reaction to re-form H2O and continuously generate CO. The net reaction is the splitting of CO2 to CO and ½O2. Because reactions at such high temperature are expected to be thermodynamically controlled, thermodynamic models are developed to calculate the equilibrium limits of the proposed dual-membrane configuration. For comparison, two reference configurations comprising either a single oxygen-permeable membrane or a single hydrogen-permeable membrane are analyzed. At 1800 K, 1 bar total pressure, and (not applicable for the hydrogen-membrane reactor) 10 Pa O2, the equilibrium mole fraction of fuel is 2% with a single oxygen membrane, 4% with a single hydrogen membrane, and 15% in the dual-membrane system. In all cases, total selectivity of CO2 to CO and O2 is obtained. Assuming thermodynamic equilibrium, the solar-to-fuel energy efficiency realistically attainable is 4% with a single oxygen membrane, 8% with a single hydrogen membrane, and 17% in the dual-membrane configuration at the aforementioned conditions. By increasing the pressure of the feed of steam to 100 bar, the dual-membrane model system could theoretically approach full mass conversion of CO2 and reach up to 26% solar-to-fuel energy efficiency. However, developing appropriate and stable ceramic materials for such a system poses a significant challenge.

Dual Hydrogen- and Oxygen-Transport Membrane Reactor for Solar-Driven Syngas Production

A novel thermochemical dual-membrane reactor is considered with the goal of efficiently converting CO2 to fuels using concentrated solar energy as the process heat source. In contrast to the temperature-swing redox cycle, in this isothermal system the thermolysis of H2O at above 1800 K is assisted by removal of O2 across an oxygen-permeable membrane and of H2 across a hydrogen-permeable membrane. The latter is consumed by a stream of CO2 via the reverse water-gas shift reaction to re-form H2O and continuously generate CO. The net reaction is the splitting of CO2 to CO and ½O2. Because reactions at such high temperature are expected to be thermodynamically controlled, thermodynamic models are developed to calculate the equilibrium limits of the proposed dual-membrane configuration. For comparison, two reference configurations comprising either a single oxygen-permeable membrane or a single hydrogen-permeable membrane are analyzed. At 1800 K, 1 bar total pressure, and (not applicable for the hydrogen-membrane reactor) 10 Pa O2, the equilibrium mole fraction of fuel is 2% with a single oxygen membrane, 4% with a single hydrogen membrane, and 15% in the dual-membrane system. In all cases, total selectivity of CO2 to CO and O2 is obtained. Assuming thermodynamic equilibrium, the solar-to-fuel energy efficiency realistically attainable is 4% with a single oxygen membrane, 8% with a single hydrogen membrane, and 17% in the dual-membrane configuration at the aforementioned conditions. By increasing the pressure of the feed of steam to 100 bar, the dual-membrane model system could theoretically approach full mass conversion of CO2 and reach up to 26% solar-to-fuel energy efficiency. However, developing appropriate and stable ceramic materials for such a system poses a significant challenge.

Energy recovery through reverse electrodialysis: Harnessing the salinity gradient from the flushing of human urine

Urine dilution is often performed to avoid clogging or scaling of pipes, which occurs due to urine's Ca2+ and Mg2+ precipitating at the alkaline conditions created by ureolysis. The large salinity gradient between urine and flushing water is, theoretically, a source of potential energy which is currently unexploited. As such, this work explored the use of a compact reverse electrodialysis (RED) system to convert the chemical potential energy of urine dilution into electric energy. Urine’ composition and ureolysis state as well as solution pumping costs were all taken into account. Despite having almost double its electric conductivity, real hydrolysed urine obtained net energy recoveries ENet of 0.053–0.039 kWh/m3, which is similar to energy recovered from real fresh urine. The reduced performances of hydrolysed urine were linked to its higher organic fouling potential and possible volatilisation of NH3 due to its high pH. However, the higher-than-expected performance achieved by fresh urine is possibly due to the fast diffusion of uncharged urea to the freshwater side. Real urine was also tested as a novel electrolyte solution and its performance compared with a conventional K4Fe(CN)6/K3Fe(CN)6 couple. While K4Fe(CN)6/K3Fe(CN)6 outperformed urine in terms of power densities and energy recoveries, net chemical reactions seemed to have occurred in urine when used as an electrolyte solution, leading to TOC, ammonia and urea removal of up to 13%, 6% and 4.4%, respectively. Finally, due to the migration of K+, NH4+ and PO43−, the low concentration solution could be utilised for fertigation. Overall, this process has the potential of providing off-grid urine treatment or energy production at a household or building level. [Display omitted]