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Lignocellulosic biomass is a valuable renewable resource that has the potential to be refined into multiple fractions of valuable biomaterials. Extracting and purifying lignin without compromising cellulose quality is a challenging goal. Deep Eutectic Solvents (DESs) have been reported as suitable delignification solvents, and for process development for cellulose extraction, lignin removal is essential. This work describes an investigation on continuous ultrafiltration (UF)-based diafiltration (DF) for recovering and purifying lignin dissolved in a DES-pulping stream comprising lactic acid and choline chloride following lignocellulose delignification. Experiments have been carried out in a stirred dead-end setup. The results indicate that lignin with a molecular weight of 200 g/mol or higher can be rejected by a polyethersulfone UF membrane with a molecular weight cutoff of 5000, reaching rejection values close to 0.85 for the feed solution with lignin concentration ranging from 4.5 to 30 g/L. It was discovered that membrane fouling and flux decline are DES concentration-dependent. A modeling approach was developed to predict the system size and operating conditions necessary to conduct the diafiltration process on a large scale, for which experimental data on lignin fouling at various feed concentrations and hydrodynamic flow characteristics were used. Based on the modeling results, lignin dissolved in DES-dark liquor (lignin-loaded DES) may well be separated and purified by a continuous UF-DF system.

This work investigates the recovery of a deep eutectic solvent (DES) used for pulping wood, by removing remnant hemicellulosic derivatives using reverse osmosis (RO). Xylose and its dehydration product furfural are considered representative hemicellulosic derivatives, and a lactic acid-choline chloride DES was used. Various diluting solvents were considered for the RO feed, namely pure water and binary water-organic solvent (ethanol, acetone, and methanol) mixtures. The results in this work show that the xylose rejection is high in water as well as in the presence of organic solvents such as acetone (with 97% rejection in aqueous acetone solvent and 95% in pure water using the RO membrane). On the other hand, furfural is rejected poorly by the RO membrane in all media (below 60% in all solvents). Finally, based on these results, a separation scheme was proposed to attain a complete mass recovery of each component of this mixture.

The preferential removal of sodium sulfate over sodium chloride (fractionation) by nanofiltration (NF) is studied. A fractionation metric, M, is defined, and a simple set of equations are derived to describe its variation due to operating parameters, such as temperature and pressure. The use of these equations to explain known behavior of NF systems and suggest improvements in system or membrane design is demonstrated. Furthermore, the derived framework is applicable to all membranes used in pressure-driven technologies, without detailed characterization of specific membrane properties, such as structural parameters (pore radius, active layer thickness, tortuosity, porosity) or charge-based parameters. Given that the principal applications of NF involve the selective removal of multivalent ions over monovalent ions, the introduced metric provides a direct measure of its efficacy in such applications, and is shown to be more accurate in some cases than comparing salt rejection ratios, as usually done. Finally, the concept of ‘breakthrough’, commonly observed as the point at which rejection ratio begins to decrease with increase in pressure, is mathematically described, and its implication on selectivity discussed.

The present work demonstrates that experimental salt passage data for reverse osmosis (RO) shows better agreement with models capturing solute-solvent transport coupling (convective coupling), especially as the applied pressure is increased. This conclusion is drawn based on five RO data sets using cellulose acetate and polyamide membranes that were modeled using the classical solution diffusion (SD) model, which does not include convection, as well as the convection-inclusive SD model introduced by Paul in 2004 and the pore-based model, which also includes convective coupling. The improved model-to-experimental data agreement with solute-solvent coupling is more easily noticed from salt passage variation with pressure than from the most commonly studied RO metric, salt rejection ratio. The importance of solute-solvent coupling in RO indicates that free volume in the membrane influences the description of membrane transport, and that these voids *open up as applied pressure is increased. The derivation of the pore-based and SD models from the Maxwell-Stefan equations is shown, and major differences in assumptions used in their derivation are discussed. A study of these differences should aid membrane researchers in selecting the most appropriate modeling approach for a given solute-solvent-membrane system.

Nanofiltration performance as a function of feed temperature is relevant to several industrial settings including pretreatment for scale control in thermal desalination. Understanding of solute transport as a function of temperature is critical for effective membrane and system design. In this study, nanofiltration is modeled at 22, 40 and 50 °C using the Donnan Steric Pore Model with dielectric exclusion (DSPM-DE). This modeling includes the temperature dependence of the three modes of solute transport, namely the convective, electromigrative, and diffusive modes, and the three mechanisms of solute exclusion, namely Donnan, steric, and dielectric exclusion. The effect of temperature is captured through the variation of membrane parameters and solvent and ionic mobilities with temperature. We compare the most abundant ionic compound in natural water, sodium-chloride with magnesium-chloride to portray how the salt passage and rejection change for a 1:1 salt compared to a 2:1 salt, and we analyze Arabian Gulf seawater to understand how rejection of scale-forming ions, such as Mg2 + and Ca2 +, is affected by feed temperature. In all cases, solute transport increases with temperature, attributed predominantly to the cumulative effect of membrane parameters and only to a small extent (up to 5%) to the solvent viscosity and ion diffusivity together.

A mathematical model of a Once-Through Multi-Stage-Flash (OT-MSF) desalination system is developed. This study shows the impact of top brine temperature (TBT) of up to 160 °C on both the design and performance characteristics of MSF systems. Such a high TBT can be achieved by nanofiltration pretreatment to remove scale-forming compounds. System performance is evaluated by the thermal performance ratio (PR) and the required specific area (sA). For a fixed brine reject temperature (Tend) and inter-stage temperature drop (ΔT), adding stages results in the TBT increasing by ΔT for each stage added and the PR increases monotonically with the TBT. On the other hand, the required sA decreases and then increases again beyond a certain TBT. The Sirte desalination plant in Libya is taken as a case study. It is found that by increasing the TBT to 161 °C from a typical value of 118 °C keeping Tend and ΔT fixed; the PR can be increased by 41.5%, reaching a value of 14.6 while the required sA increases by 0.9%. Although there is a penalty in terms of the increased number of stages required to achieve this arrangement, there is a clear advantage in terms of PR, with a relatively small compromise in sA., King Fahd University of Petroleum and Minerals, Massachusetts Institute of Technology. Center of Excellence for Research Collaboration

The Donnan Steric Pore Model with dielectric exclusion (DSPM-DE) is implemented over flat-sheet and spiral-wound leaves to develop a comprehensive model for nanofiltration modules. This model allows the user to gain insight into the physics of the nanofiltration process by allowing one to adjust and investigate effects of membrane charge, pore radius, and other membrane characteristics. The study shows how operating conditions such as feed flow rate and pressure affect the recovery ratio and solute rejection across the membrane. A comparison is made between the results for the flat-sheet and spiral-wound configurations. The comparison showed that for the spiral-wound leaf, the maximum values of transmembrane pressure, flux and velocity occur at the feed entrance (near the permeate exit), and the lowest value of these quantities are at the diametrically opposite corner. This is in contrast to the flat-sheet leaf, where all the quantities vary only in the feed flow direction. However it is found that the extent of variation of these quantities along the permeate flow direction in the spiral-wound membrane is negligibly small in most cases. Also, for identical geometries and operating conditions, the flat-sheet and spiral-wound configurations give similar results. Thus the computationally expensive and complex spiral-wound model can be replaced by the flat-sheet model for a variety of purposes. In addition, the model was utilized to predict the performance of a seawater nanofiltration system which has been validated with the data obtained from a large-scale seawater desalination plant, thereby establishing a reliable model for desalination using nanofiltration., Center for Clean Water and Clean Energy at MIT and KFUPM

Cilia are hair-like organelles projecting from a eukaryotic cell, used either for locomotion or as sensors. Cilia commonly occur in patches. To take this into consideration, we represent cilia in multiple patches, instead of the conventional 'dense mat' representation. We focus on the combined action and interplay of these patches. The effects of varying the frequency, spacing and phase lag of the beating of one cilia bunch with respect to the beating of adjacent patches are studied. We model the Airway Surface Liquid (ASL) as a three-layer structure. The possibility of an optimum frequency of beating is noted and the change of mucous flow under different spacing and phase differences are observed. � 2013 Elsevier Ltd.