Experimental evidence for excess entropy discontinuities in glass-forming solutions

Glass transition temperatures T_g are investigated in aqueous binary and multi-component solutions consisting of citric acid, calcium nitrate (Ca(NO_3)_2), malonic acid, raffinose, and ammonium bisulfate (NH_4HSO_4) using a differential scanning calorimeter. Based on measured glass transition temperatures of binary aqueous mixtures and fitted binary coefficients, the T_g of multi-component systems can be predicted using mixing rules. However, the experimentally observed T_g in multi-component solutions show considerable deviations from two theoretical approaches considered. The deviations from these predictions are explained in terms of the molar excess mixing entropy difference between the supercooled liquid and glassy state at T_g. The multi-component mixtures involve contributions to these excess mixing entropies that the mixing rules do not take into account

Observing the space- and time-dependent growth of correlations in dynamically tuned synthetic Ising antiferromagnets

We explore the dynamics of artificial one- and two-dimensional Ising-like quantum antiferromagnets with different lattice geometries by using a Rydberg quantum simulator of up to 36 spins in which we dynamically tune the parameters of the Hamiltonian. We observe a region in parameter space with antiferromagnetic (AF) ordering, albeit with only finite-range correlations. We study systematically the influence of the ramp speeds on the correlations and their growth in time. We observe a delay in their build-up associated to the finite speed of propagation of correlations in a system with short-range interactions. We obtain a good agreement between experimental data and numerical simulations taking into account experimental imperfections measured at the single particle level. Finally, we develop an analytical model, based on a short-time expansion of the evolution operator, which captures the observed spatial structure of the correlations, and their build-up in time

The cost effectiveness of electrodialysis for diverse salinity applications

We provide a thermoeconomic assessment of electrodialysis indicating that the technology is most productive and efficient for the partial desalination of feed streams at the higher end of the brackish range of salinities. After optimising the current density to minimise the sum of energy and equipment costs, we demonstrate that at low feed salinities the productivity, and hence equipment costs, of electrodialysis are hampered by the limiting current density. By contrast, at higher feed salinities both productivity and efficiency are hampered by the reduced chemical potential difference of salt in the diluate (low salinity) and concentrate (high salinity) streams. This analysis indicates the promise of further developing electrodialysis for the treatment of waters from oil, gas and coal-bed methane as well as flue-gas de-sulphurisation, where the partial desalination of streams at the high-end of the brackish range can be beneficial.Center for Clean Water and Clean Energy at MIT and KFUPM (Project R15-CW-11)United States. Dept. of State (International Fulbright Science & Technology Award)International Desalination Association (Channabasappa Memorial Scholarship)MIT Martin Family Society of Fellows for SustainabilityHugh Hampton Young Memorial Fellowshi

The benefits of hybridising electrodialysis with reverse osmosis

A cost analysis reveals that hybridisation of electrodialysis with reverse osmosis is only justified if the cost of water from the reverse osmosis unit is less than 40% of that from a stand-alone electrodialysis system. In such cases the additional reverse osmosis costs justify the electrodialysis cost savings brought about by shifting salt removal to higher salinity, where current densities are higher and equipment costs lower. Furthermore, the analysis suggests that a simple hybrid configuration is more cost effective than a recirculated hybrid, a simple hybrid being one where the reverse osmosis concentrate is fed to the electrodialysis stack and the products from both units are blended, and a recirculated being one hybrid involving recirculation of the electrodialysis product back to the reverse osmosis unit. The underlying rationale is that simple hybridisation shifts salt removal away from the lowest salinity zone of operation, where salt removal is most expensive. Further shifts in the salinity at which salt is removed, brought about by recirculation, do not justify the associated increased costs of reverse osmosis.Hugh Hampton Young Memorial FellowshipCenter for Clean Water and Clean Energy at MIT and KFUPM (Project R15-CW-11

Hybrid electrodialysis reverse osmosis system design and its optimization for treatment of highly saline brines

The demand is rising for desalination technologies to treat highly saline brines arising from hydraulic fracturing processes and inland desalination. Interest is growing in the use of electrical desalination technologies for this application. The hybridization of electrodialysis (ED) with reverse osmosis (RO) allows high salinities (beyond the range of RO alone) to be reached while avoiding the operation of ED with a low conductivity diluate stream. Such hybrid systems have been experimentally investigated for concentrates from brackish and seawater desalination. However, progress is required in the modelling and optimization of hybrid systems at higher concentrations. A novel hybrid arrangement of counterflow ED systems with reverse osmosis is presented to concentrate a saline feed at 120 ppt. The system is considered from the perspective of efficiency, membrane productivity and the levelised cost of water, with emphasis on the optimisation of current density. In contrast to brackish ED systems, membrane resistances are found to dominate diluate and concentrate resistances at high salinity. The current density found to minimise LCW (levelised cost of water) is significantly greater than the current density found to maximise efficiency, indicating the high current capital cost of ED per unit membrane area and poor membrane transport properties relative to RO. Finally, performance at high recoveries is found to be limited by high stream-to-stream concentration differences, increasing water transport via osmosis, decreasing efficiency and increasing the LCW.Fulbright ProgramMartin Family Society of Fellows for SustainabilityInternational Desalination Association (Channabasappa Memorial Scholarship

An Analysis of Likely Scalants in the Treatment of Produced Water from Nova Scotia

A significant barrier to further use of hydraulic fracturing to recover shale oil and/or gas is the treatment and/or disposal of hypersaline produced water. This work is an analysis of produced water from Nova Scotia, with the aim of understanding how scale impacts the choice of desalination system used in its treatment. Four water samples are presented, and for a representative case, the supersaturation of some likely scalants is estimated as a function of temperature, recovery ratio, and pH. This supersaturation map is then compared to conditions representative of common desalination systems, allowing the identification of limitations imposed by the water's composition. In contrast to many natural waters, it is found that sodium chloride is the most likely first solid to form at high recovery ratios, and that the top temperature of thermal desalination systems is unlikely to be scale-limited in the treatment of these waters.Center for Clean Water and Clean Energy at MIT and KFUPM (Project R4-CW-08

Formulation of Seawater Flow Exergy Using Accurate Thermodynamic Data

Seawater is a complex electrolyte solution of water and salts with sodium chloride as the major constituent. However, the thermodynamic properties of seawater are considerably different from those of aqueous sodium chloride solution. In the literature, exergy analyses of seawater desalination systems have sometimes modeled seawater by sodium chloride solutions of equivalent salt content or salinity; however, such matching does not bring all important properties of the two solutions into agreement. Furthermore, some published studies attempt to represent sodium chloride solutions as a specific model for an ideal mixture of liquid water and solid sodium chloride, which is shown to have serious shortcomings. In this paper, the most up-to-date thermodynamic properties of seawater are compared with those of aqueous sodium chloride solution as well as the ideal mixture model. The flow exergy is calculated using various models and the results are compared. In addition, the minimum work required to desalinate a unit mass of fresh water from seawater of varying salinity is calculated using these models. The flow exergy calculated using the ideal mixture model in question is about 50% less than that of seawater. Accordingly, the minimum desalination work is underpredicted by about 50% when calculating it using that ideal mixture model. This consequently shows that exergy analysis and the second law efficiency calculations performed using the ideal mixture model is comparatively far from the actual values.Center for Clean Water and Clean Energy at MIT and KFUP

Effect of entropy generation on the performance of humidification-dehumidification desalination cycles

This paper applies irreversibility analysis to characterize humidification-dehumidification (HD) desalination cycles and to identify how to further improve cycles and components. It is shown that minimizing specific entropy generation of the cycle maximizes the gained output ratio (GOR). It is also shown that each cycle has one limiting component that cannot be substantially improved and a second component that should be the target of efforts to minimize entropy generation. Finally, the failure of exergy analysis to yield conclusive results for on-design HD cycle analysis is discussed briefly.Center for Clean Water and Clean Energy at MIT and KFUP

New and extended parameterization of the thermodynamic model AIOMFAC: calculation of activity coefficients for organic-inorganic mixtures containing carboxyl, hydroxyl, carbonyl, ether, ester, alkenyl, alkyl, and aromatic functional groups

We present a new and considerably extended parameterization of the thermodynamic activity coefficient model AIOMFAC (Aerosol Inorganic-Organic Mixtures Functional groups Activity Coefficients) at room temperature. AIOMFAC combines a Pitzer-like electrolyte solution model with a UNIFAC-based group-contribution approach and explicitly accounts for interactions between organic functional groups and inorganic ions. Such interactions constitute the salt-effect, may cause liquid-liquid phase separation, and affect the gas-particle partitioning of aerosols. The previous AIOMFAC version was parameterized for alkyl and hydroxyl functional groups of alcohols and polyols. With the goal to describe a wide variety of organic compounds found in atmospheric aerosols, we extend here the parameterization of AIOMFAC to include the functional groups carboxyl, hydroxyl, ketone, aldehyde, ether, ester, alkenyl, alkyl, aromatic carbon-alcohol, and aromatic hydrocarbon. Thermodynamic equilibrium data of organic-inorganic systems from the literature are critically assessed and complemented with new measurements to establish a comprehensive database. The database is used to determine simultaneously the AIOMFAC parameters describing interactions of organic functional groups with the ions H^+, Li^+, Na^+, K^+, NH_(4)^+, Mg^(2+), Ca^(2+), Cl^−, Br^−, NO_(3)^−, HSO_(4)^−, and SO_(4)^(2−). Detailed descriptions of different types of thermodynamic data, such as vapor-liquid, solid-liquid, and liquid-liquid equilibria, and their use for the model parameterization are provided. Issues regarding deficiencies of the database, types and uncertainties of experimental data, and limitations of the model, are discussed. The challenging parameter optimization problem is solved with a novel combination of powerful global minimization algorithms. A number of exemplary calculations for systems containing atmospherically relevant aerosol components are shown. Amongst others, we discuss aqueous mixtures of ammonium sulfate with dicarboxylic acids and with levoglucosan. Overall, the new parameterization of AIOMFAC agrees well with a large number of experimental datasets. However, due to various reasons, for certain mixtures important deviations can occur. The new parameterization makes AIOMFAC a versatile thermodynamic tool. It enables the calculation of activity coefficients of thousands of different organic compounds in organic-inorganic mixtures of numerous components. Models based on AIOMFAC can be used to compute deliquescence relative humidities, liquid-liquid phase separations, and gas-particle partitioning of multicomponent mixtures of relevance for atmospheric chemistry or in other scientific fields