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• Layer melt crystallization of monoethylene glycol was investigated. • Impurity under study was 1,2-pentanediol and solvent additive acetone. • Thermodynamic driving forces with and without solvent additive were determined. • Crystallization kinetics affects purity of final product. Separation of glycols with close boiling points and relatively high viscosity at their melting point is a challenge in the production of high purity products downstream of biorefinery processes. In this work, the efficiency of the layer melt crystallization process with acetone as the assisting solvent was evaluated for a mixture of monoethylene glycol and 1,2-pentanediol. Solid-liquid equilibrium was measured and modelled with the NRTL and modified UNIFAC group-contribution models to evaluate the thermodynamic driving force of crystallization. Layer melt crystallization was conducted to determine the effect of solvent composition on purity, distribution coefficient of impurity, crystal growth rate, and yield at different operating conditions. Addition of the solvent altered the thermodynamics and kinetics of crystallization, thereby altering the purity level of the final product. An effective distribution coefficient of impurity between 0.1 and 0.6 in one-step crystallization was obtained, depending on the solvent composition and the applied operating conditions. [ABSTRACT FROM AUTHOR]

Ni 2+ in excess of maximum recommended limits must be removed from wastewater prior to discharge because of its persistent bio-accumulative and detrimental nature. Natural freezing is suggested as a purification technique to treat huge volumes of wastewater containing Ni 2+ in a sustainable and energy efficient manner. In order to evaluate the feasibility of such a technique for purification of wastewater, natural freezing was simulated experimentally for ice crystallization from different NiSO 4 (aq) solutions. The impact of solution concentration at different freezing conditions such as different ambient air temperature, freezing time and freezing rate on the efficiency of the purification process was investigated. Experimental results demonstrated that at the growth rate ( G ) of 3.5 × 10 −8 m/s, the ice layer formed from 1 wt.% (≈10,000 ppm) NiSO 4 (aq) solution incorporated only 0.0038 wt.% (≈38 ppm) NiSO 4 as impurity, i.e., the ice is more than 250 times pure than the original salt solution. In the case of freezing of very dilute solutions, e.g., 0.1 wt.% NiSO 4 (aq) solution, which is the dilution level of practical interest, the same growth condition is likely to produce an ice layer of even higher purity. For example, at G of 7.4 × 10 −8 m/s, the ice layer impurity that had formed from 0.1 wt.% NiSO 4 (aq) solution was only 0.001 wt.% (≈10 ppm). For this reason, this purification technique has potential for implementation on the surface of wastewater ponds in cold climate regions where the temperature drops below 0 °C. In addition, inclusion formation within the ice matrix during freezing was investigated for various solution concentrations both macroscopically and microscopically. [ABSTRACT FROM AUTHOR]

Natural freezing has the possible use to be used as a purification technique to treat wastewater. Natural freezing was simulated experimentally for ice crystallization from unsaturated Na 2 SO 4 (aq) solutions to assess the feasibility of such a technique for being used to purify wastewater. The influence of solution concentration and different growth conditions, such as ambient temperature, freezing time and freezing rate, on the efficiency of the purification process was investigated by analysis of the effective distribution coefficient ( K ) of the solute between the ice and the solution. A calculation method is introduced to estimate the concentration of solution at the advancing ice–solution interface in terms of the limiting distribution coefficient ( K ⁎ ) from experimental K values at different growth conditions. The heat transfer controlled growth rate of the ice limited by the free convective heat transfer coefficient of air ( h air ) rather than the thermal conductivity of the ice ( k ice ) and the heat transfer coefficient of the solution ( h sol ) found to prevail over the mass transfer of rejected solute molecules from the ice–solution interface to the bulk solution. Advancement of the thermal ( δ T ) and concentration boundary layer ( δ C ) at the ice–solution interface was proportional to the square root of freezing time. A simplified model is developed to estimate the thickness of the ice layer formed from solutions at different freezing conditions and the model is validated with experimental results. [ABSTRACT FROM AUTHOR]

This study explored the insights into the theory of dry solids classification, in particular the classical dynamics aspects related to the mass loading of particles, deck inclination of the screen, and resulting measures of flowability. Prototype screening equipment was fabricated and experiments were carried out with ideal rounded mono-shaped glass beads. The overall performance of the prototype was assessed in relation to two screen design variables, the tilt angle of inclination and the mass throughput of the feed, which affects particles flow. Mathematical models relating to the classification process were developed, simulated and compared to the results obtained from the experiments. Important parameter ranges within which equipment may be operated with minimal malfunctioning were approximated from the models. Screen loading, bulk flow velocity, and screen inclination angles determine flowability of powders and particles in gravity classification; these parameters were used in this study to assess how well the particles flowed over the screens. A close correlation was found between theory, simulation models and the experimental results, which facilitated development of empirical models that may be used to predict and estimate the classification rates, efficiencies and flowability for such systems. Dense screen loading improved the classification rates, but hampered flowability, and consequently the efficiency. Increase in deck inclinations improved flowability and efficiency, but only to a certain optimum point after which it led to excessive overflow. [ABSTRACT FROM AUTHOR]

Nitrofurantoin can form two monohydrates, which have the same chemical composition and molar ratio of water, but differ in the crystal arrangements. The two monohydrates (hydrates I and II) could be produced independently via evaporative crystallization, where supersaturation and solvent composition were both found to have an effect. Hydrate I showed much slower crystallization than hydrate II. During cooling crystallization, the nucleation and growth of hydrate II was again dominant, consuming all supersaturation and leading to no hydrate I formation. Seeding of hydrate I during cooling crystallization was also applied, but the hydrate I seeds were not able to initiate its nucleation rather than dissolving into crystallizing solution. Although solubility tests revealed that hydrate II is more stable than hydrate I due to its lower solubility (110 ± 4 and 131 ± 12 µg/mL for hydrates II and I, respectively), this difference is rather small. Therefore, the small free energy difference between the two hydrates, together with the slow crystallization of hydrate I, both lead to a hindrance of hydrate I formation. Furthermore, the crystal structure of hydrate II demonstrated a higher H-bonding extent than hydrate I, suggesting its more favorable crystallization. This is in good agreement with experimental results. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:753–763, 2010 [ABSTRACT FROM AUTHOR]

Due to stringent legislation, wastewater needs to be treated before dispersing in the environment. Wastewater can be purified through the formation of less contaminated ice layer by freezing. Freezing of the wastewater leaves the remaining wastewater more concentrated. Attainment of eutectic point (both ice and soluble salt crystallize simultaneously) by freeze crystallization can add extra financial value in terms of salt recovery. Separation of ice from salt becomes very easy because of significant density difference. Na 2 SO 4 is one of the key components present in wastewater emanating from different industrial sources, considered as a model compound in this study. Recovery of Na 2 SO 4 from the aqueous solution by eutectic freeze crystallization air-cooled through the ice layer and solution surface is an energy-efficient and cost effective method. This method was investigated experimentally to recover Na 2 SO 4 from its solution. Furthermore, the influence of different factors and operating conditions was studied on the efficiency of the purification and recovery process. [ABSTRACT FROM AUTHOR]

The black liquor from the kraft pulping process is a potential source of organic acids (e.g. hydroxy acids) which could have applications as a raw material for biodegradable polymers. However, the recovery of the hydroxy acids has rarely been studied and they are not yet utilised. The aim of this paper is to study separation phenomena in the ultrafiltration and nanofiltration stages of the recovery and purification of organic acids from black liquor. Ultrafiltration, acidification, and cooling crystallisation were applied prior to purification by nanofiltration and adsorption. Direct ultrafiltration with a 1 kDa membrane removed 75% of the lignin. Acid molecules permeated the membrane faster than water molecules due to the Donnan exclusion and electroneutrality principles. As a result, the total acid concentration in the accumulated permeate stream was 1.4 fold compared to the original black liquor. However, ultrafiltration prior to precipitation and cooling crystallisation processes had a detrimental effect on the acid purity and the flux in downstream nanofiltration. The separation during nanofiltration in acidic conditions occurred mostly by size exclusion. It was also observed that the changes in the feed composition affected the retention of individual organic acids differently. Nanofiltration removed a significant amount of sulphate ions and residual phenolic compounds, but permeated most of the acid molecules in acidic pH conditions and finally the organic acid purity of the total dissolved solids in the NF permeate was about 80% at the highest. [ABSTRACT FROM AUTHOR]