Freezing Point Depression Measurements Research Articles

Dewatering of POME digestate using lignosulfonate driven forward osmosis

High demand for palm oil results in the production of huge quantities of palm oil mill effluent (POME) wastewater containing a high amount of organics. Currently, this is often processed by anaerobic digestion, but the waste water still requires further processing. Dewatering of POME digestate could simultaneously recover nutrients for use as organic fertiliser and treat water sufficiently to allow other uses. This work investigates the feasibility of using a forward osmosis (FO) process driven by lignosulfonate draw solutions. It was found that water fluxes for pure water and simulated POME digestate feeds were lower for lignosulfonates than NaCl as draw solutes, but had much lower reverse solute fluxes. Reverse solute flux is of great importance for dewatering of POME digestate, as concentration of salts in the dewatered feed will preclude their use as organic fertilisers. Na lignosulfonate showed both higher water fluxes and lower reverse solute flux than the Ca lignosulfonate. Water fluxes when using the simulated POME digestate were lower than predicted from the directly measured osmotic pressures of the solutions, suggesting increased membrane resistance due to fouling or concentration polarisation effects. In addition, osmotic pressures of organic solutions were measured directly from dead-end filtration measurements. This showed that the relationship between osmolality measured from freezing point depression measurements and osmotic pressure of solutions varies for different solutes, suggesting that osmolality measurements do not give a reliable measure of osmotic pressure when comparing different organic solutions.

Experimental effervescence and freezing point depression measurements of nitrogen in liquid methane-ethane mixtures

NASA is designing an unmanned submarine to explore the depths of the hydrocarbon-rich seas on Saturn's moon Titan. Data from Cassini indicates that the Titan north polar environment sustains stable seas of variable concentrations of ethane, methane, and nitrogen, with a surface temperature near 93 K. The submarine must operate autonomously, study atmosphere/sea exchange, interact with the seabed, hover at the surface or any depth within the sea, and be capable of tolerating variable hydrocarbon compositions. Currently, the main thermal design concern is the effect of effervescence on submarine operation, which affects the ballast system, science instruments, and propellers. Twelve effervescence measurements on various liquid methane-ethane compositions with dissolved gaseous nitrogen are thus presented from 1.5 bar to 4.5 bar at temperatures from 92 K to 96 K to simulate the conditions of the seas. After conducting effervescence measurements, two freezing point depression measurements were conducted. The freezing liquid line was depressed more than 15 K below the triple point temperatures of pure ethane (90.4 K) and pure methane (90.7 K). Experimental effervescence measurements will be used to compare directly with effervescence modeling to determine if changes are required in the design of the thermal management system as well as the propellers.

Calcium l-tartrate complex formation in neutral and in hyperalkaline aqueous solutions.

The complex formation reaction between the l-tartrate (Tar2-) and calcium ions taking place in neutral and in hyperalkaline (pH > 13) aqueous solutions has been investigated. It was demonstrated that upon NaOH addition the solubility of the CaTar(s) precipitate significantly increases. Conductometric and freezing point depression measurements further confirmed that in this process water soluble species are formed as a result of a reaction between the CaTar(s) and the hydroxide ion (or, conversely, between Ca(OH)2(s) and the Tar2- ion). 13C NMR spectroscopic measurements yielded the value of pK3 = 15.4 ± 0.2 for the proton dissociation of one of the alcoholic OH groups of Tar2- (at 25.0 °C and 4 M Na(Cl) ionic strength). Upon addition of calcium ions to an alkaline Tar2- solution, the 1H NMR signal gradually broadened and the 13C-satellite peaks split to two components, which also indicate complexation. From H2/Pt potentiometric titrations performed with solutions in the 13.6 ≤ pH ≤ 14.4 range, it was observed, that this complex formation is accompanied by a hydroxide ion consuming process. The titration curves can be best described via assuming the formation of the CaTarH-1-(aq) (lg β11-1 = -11.2 ± 0.1) and CaTarH-22-(aq) (lg β11-2 = -25.3 ± 0.1) complexes. In hyperalkaline solutions, these two species account for more than 90-99% of the calcium ions present and the contribution of the other reasonable and well-established calcium-containing solution species is rather small. The possible structures of the above complexes have been modeled via ab initio calculations. The stoichiometries are consistent both with species containing coordinated alcoholate group(s) and with mixed Ca(ii)-hydroxo-tartrato complexes. From the data available at present, both types of structures can be considered as chemically reasonable.

Evolution of fluid–rock interaction in the Reykjanes geothermal system, Iceland: Evidence from Iceland Deep Drilling Project core RN-17B

We describe the lithology and present spatially resolved geochemical analyses of samples from the hydrothermally altered Iceland Deep Drilling Project (IDDP) drill core RN-17B. The 9.3m long RN-17B core was collected from the seawater-dominated Reykjanes geothermal system, located on the Reykjanes Peninsula, Iceland. The nature of fluids and the location of the Reykjanes geothermal system make it a useful analog for seafloor hydrothermal processes, although there are important differences. The recovery of drill core from the Reykjanes geothermal system, as opposed to drill cuttings, has provided the opportunity to investigate evolving geothermal conditions by utilizing in-situ geochemical techniques in the context of observed paragenetic and spatial relationships of alteration minerals. The RN-17B core was returned from a vertical depth of ~2560m and an in-situ temperature of ~345°C. The primary lithologies are basaltic in composition and include hyaloclastite breccia, fine-grained volcanic sandstone, lithic breccia, and crystalline basalt. Primary igneous phases have been entirely pseudomorphed by calcic plagioclase+magnesium hornblende+chlorite+titanite+albitized plagioclase+vein epidote and sulfides. Despite the extensive hydrothermal metasomatism, original textures including hyaloclastite glass shards, lithic clasts, chilled margins, and shell-fragment molds are superbly preserved. Multi-collector LA-ICP-MS strontium isotope ratio (87Sr/86Sr) measurements of vein epidote from the core are consistent with seawater as the dominant recharge fluid. Epidote-hosted fluid inclusion homogenization temperature and freezing point depression measurements suggest that the RN-17B core records cooling through the two-phase boundary for seawater over time to current in-situ measured temperatures. Electron microprobe analyses of hydrothermal hornblende and hydrothermal plagioclase confirm that while alteration is of amphibolite-grade, it is in disequilibrium and the extent of alteration is dependent upon protolith type and water/rock ratio. Alteration in the RN-17B core bares many similarities to that of Type II basalts observed in Mid-Atlantic Ridge samples.

Interfacial behavior and water solubility of various asphaltenes at high temperature

Asphaltenes from six different crude oils were isolated and tested with respect to their water solubility and interfacial behavior at temperatures up to 190°C and 125°C, respectively, in (1) water with 18MΩcm resistance, (2) a 8wt.% NaCl–2wt.% CaCl2 salt solution, and (3) artificial seawater. None of the asphaltenes had any water solubility except for possibly very slight solubility in two cases. A higher interfacial activity was found to be loosely correlated with asphaltene molecular weight as measured by freezing point depression measurements; a lower molecular weight asphaltene had a higher interfacial activity. Chemical measurements of the asphaltenes were performed and only hydrogen content appeared to possibly correlate with interfacial activity; the interfacial activity decreased as the hydrogen content increased. Overall, the interfacial activity was highest for artificial seawater, and lowest for pure water and brine. Interfacial tensions (IFTs) were also measured from room temperature to 125°C at a fixed concentration of 5g/l in toluene for the artificial seawater and pure water. With a couple of exceptions, decreases of IFT with temperature were very similar for all asphaltenes and smaller than that of the pure water/toluene system. Higher temperature did lead to a slightly larger decrease of IFT at long times where rearrangement of the interfacial layer has been postulated to occur.

Binary and ternary VLE of the 2-(diethylamino)-ethanol (DEEA)/3-(methylamino)-propylamine (MAPA)/water system

A mixed 2-(diethylamino)-ethanol (DEEA) and 3-(methylamino)-propylamine (MAPA) system could be an attractive alternative solvent to improve the performance of CO2 capture for low partial pressure cases. This solvent has the advantages of forming two liquid phases upon CO2 loading, one rich in CO2 and the other very low in CO2. Having a highly concentrated rich solvent improvements could be reached by reducing the sensible heat and improving the equilibrium sensitivity hence reducing the need for stripping steam. Also it is possible that the heat of absorption may change to the better.To better understand this system in designing the separation unit requires substantial work on characterization of the solvent. One important aspect is to provide equilibrium data. In this work new ebulliometric VLE data for the binary DEEA/H2O and DEEA/MAPA systems and the ternary DEEA/MAPA/H2O system are reported at different temperatures and concentrations. Results show that pure MAPA is more volatile than DEEA, but in aqueous solution MAPA was found to be less volatile. A mix of DEEA and MAPA in aqueous solution tends to lower the volatility thus makes the system more advantageous by reducing volatility. The activity coefficients for the species in the ternary aqueous system are found to be lower than the activity coefficients obtained from the corresponding binary aqueous mixtures.The UNIQUAC framework was implemented to represent the experimental data. The six UNIQUAC parameters were determined and were able to predict P-T-x-y, activity coefficient, excess enthalpy and freezing point depression for both the binary and ternary systems. However, a small inconsistency was observed between water activity coefficients determined from ebulliometer and freezing point depression measurements.

Multinuclear complex formation in aqueous solutions of Ca(ii) and heptagluconate ions

The equilibria and structure of complexes formed between the Ca(2+) ion and the heptagluconate (Hglu(-)) ion in both neutral and alkaline solutions have been studied. In alkaline solutions an uncharged, multinuclear complex is formed with the composition of Ca3Hglu2(OH)4 (or [Ca3Hglu2H(-4)](0)) with an unexpectedly high stability constant (lg β(32-4) = 14.09). The formation of the trinuclear complex was deduced from potentiometry and confirmed by freezing-point depression measurements and conductometry as well. The binding sites of Hglu(-) were determined from NMR measurements. Besides the carboxylate group, the O atoms on the second and third carbon atoms proved to be the most probable sites for Ca(2+) binding.

Coordination Chemistry of α‐ω‐Bis(pyridylimine) Ligands Containing Flexible Linkers with Copper(I)

AbstractCopper(I) complexes of a series of six potentially tetradentate bis(pyridylimine) ligands were prepared, where the pyridylimine groups were separated by different linking units [in L1, CH2CH2CH2(SiMe2O)20SiMe2CH2CH2CH2; in L2, CH2CH2CH2SiMe2OSiMe2CH2CH2CH2; in L3, CH2CH2; in L4, CH2(CH2)4CH2; in L5, CH2(CH2)7CH2; in L6, CH2CH2CH2OCH2CH2OCH2CH2OCH2CH2CH2]. The solubilities of L1, L2 and [Cu(L2)](PF6) in supercritical carbon dioxide were determined. The coordination chemistry of L1–L2 with CuI was studied by UV/Vis, multinuclear NMR and IR spectroscopy, MALDI‐TOF and ESI mass spectrometries and elemental analysis. These data suggested that [1+1] complexes had formed. Dicopper complexes of L3–L6 were prepared for comparison, and [Cu2(L5)2](PF6)2 characterized by single‐crystal X‐ray diffraction analysis. Close methylene C–H···π interactions are observed within the structure. PGSE NMR spectroscopy was used to determine the hydrodynamic radii of the species in solution and comparison of these data with computational models for the complexes was made. Freezing point depression measurements afforded molecular weights for solution‐state species in agreement with the formulations proposed via NMR and mass spectrometric data. There is no evidence to support linear metallopolymer formation but data suggest that [2+2] and [1+1] metallomacrocyles were formed, with siloxane linking groups encouraging the formation of [1+1] species. Solid‐state NMR spectroscopic data on [Cu(L1)](PF6) indicate the presence of two different environments for the PF6– anions.

Solubilization of the novel anionic amphiphilic photosensitizer TPCS 2a by nonionic Pluronic block copolymers

The influence of four nonionic Pluronic block copolymers (L44, F68, P123 and F127) on the solubilization and aggregation of the novel anionic amphiphilic photosensitizer TPCS 2a, intended for use in the technology of photochemical internalization (PCI), was evaluated in aqueous media as part of pharmaceutical preformulation studies. The evaluation was performed by use of UV–Vis spectroscopy for diluted samples of TPCS 2a (3 × 10 −6 M), and capillary viscosimetry, freezing point depression measurements and atomic force microscopy (AFM) at pharmaceutical relevant concentrations (2; 10 or 30 mg/ml TPCS 2a). The critical micelle concentration (CMC) of the Pluronics in presence of TPCS 2a was determined spectrophotometrically. The Pluronic block copolymers solubilized the photosensitizer above CMC at ambient temperature by formation of vehicle–drug complexes apparently organized in networks of varying viscosity and morphology, which were sensitive towards the addition of neutral and charged excipients.

Oligo(FcDC-co-CholDEA) with Ferrocene in the Main Chain and Cholesterol as a Pendant Group—Preparation and Unusual Properties

With ever-increasing need for thin, flexible, and functional materials in electrochemical systems, various techniques have been explored for creating materials used in fuel cells, batteries, electrochromic devices, solar cells, and sensors. In the present study, a novel ferrocene (Fc) and cholesterol (Chol)-containing oligomer, oligo(FcDC-co-CholDEA), was specially designed and prepared by putting Fc in the main chain and Chol as a side group. MALDI-TOF MS and freezing point depression measurements revealed that in average each oligomer contains three Fc units and three Chol units. Cyclic voltammetric measurements revealed that the oligomer displays superior electrochemical stability if compared with other Fc derivatives containing only one Fc unit and one or two Chol unit and with poly(ferrocenylsilane) with Fc in the main chain. In particular, the Fc-containing oligomer possesses an unusual oxidation center, of which the oxidation potential could be as high as 1.81 V. The oligomer is also superior in self-assembly, as demonstrated by forming an LB film of layered structures. Furthermore, supramolecular films with high mechanical strength in the wet state can be prepared by employing a simple solution casting method. This finding demonstrates that self-assembly is a simple but effective way to create films of potential uses in real-life applications provided proper building blocks are designed and employed.

Another Method for Determining the Pressure inside an Intact Carbonated Beverage Can (or Bottle)

Previous letters and articles in this Journal have described methods for finding the pressure of CO2 inside carbonated beverages. One communication in particular describes a method for estimating this pressure without even opening the container. This communication describes yet another method, using a combination of Henry’s law and freezing point depression measurements, for quantitative determination of CO2 inside carbonated beverages without opening the container.

The Nature of Aqueous Solutions: Insights into Multiple Facets of Chemistry and Biochemistry from Freezing‐Point Depressions

Contrary to current widely held beliefs, many concentrated aqueous solutions of electrolytes and nonelectrolytes behave ideally. For both, the same simple equation yields mole fractions of water that are equal to the theoretical activities of water. No empirical activity coefficients or ad hoc parameters are needed. Thermodynamic hydration numbers and the number of particles produced per mole of solute are found by searching freezing-point depression measurements, as if asking the water, "How much available water solvent is left and how many solute particles are there?" The results answer questions currently under debate: Do solutes alter the nature of water outside their immediate surroundings? What is the number of ion pairs formed by various electrolytes and what affects extents of their formation? What are some factors that cause precipitation of proteins, latexes, and so forth from aqueous solutions upon addition of other solutes (Hofmeister series)? Which nonelectrolytes form aggregates in water and what are the implications? Why do different solutes affect viscosity differently? How do ion-selective channels in cell membranes function at the molecular level?

Investigation of the H2O-NaCl-LiCl System: A Synthetic Fluid Inclusion Study and Thermodynamic Modeling from -50 to +100 C and up to 12 mol/kg

Lithium can reach high concentrations in some geological environments, such as rare element pegmatites, continental brines, and hydrothermal systems. The H 2 O-NaCl-LiCl system was investigated as a model for fluid inclusion studies in lithium-rich fluids. We first compiled experimental data (freezing point depression measurements and halite solubility data). Synthetic fluid inclusions were then prepared in quartz crystals, in order to obtain new solubility data and to observe phase transitions in a system characterized by the presence of numerous hydrates. The combination of Raman microspectrometry and microthermometry leads to identify undoubtedly the phase transition succession. Raman revealed partial crystallization and metastable phase transitions. A new spectrum for LiCl pentahydrate, the stable phase melting at the eutectic, is presented. The Pitzer model was used to calculate phase solubility using published expressions of activity coefficients for the H 2 O-NaCl and H 2 O-LiCl systems. We finally propose a representation of the H 2 O-NaCl-LiCl phase diagram for the interpretation of phase transitions in Li-rich chloride-dominated fluid inclusions in the range −50° to +100°C.

Aqueous Solutions of Calcium Ions: Hydration Numbers and the Effect of Temperature

Hydration numbers of calcium ions are determined from extensive measurements of colligative properties of water solutions of calcium salts. The hydration numbers reported refer to the average number of water molecules that are bound sufficiently strongly to calcium ions so as to be removed from the solvent and become part of the solute. Contrary to common descriptions of deviations from ideal behavior for concentrated solutions, ideal behavior is demonstrated when mole fractions are calculated by taking account of such bound water. Measurements over wide concentration and temperature ranges are used to obtain the effect of temperature on the average hydration number of Ca(2+). Freezing point depression measurements yield a hydration number of 12.0 +/- 0.8. Boiling point elevations yield 6.7 +/- 0.6. Consistent with this, vapor pressure measurements from 0 to 200 degrees C show a gradual decrease in hydration number with increasing temperature, with a value of 5.0 at 200 degrees C.

Osmotic properties of sulfobutylether and hydroxypropyl cyclodextrins.

The purpose of this study was to determine the osmolality of sulfobutylether (SBE) and hydroxypropyl (HP) derivatives of cyclodextrins (CDs) via vapor pressure osmometry (VPO) and freezing point depression (FPD). (SBE) and HP-CDs are efficient excipients capable of solubilizing and stabilizing poorly water-soluble drugs in parenteral formulations. (SBE)-CDs have also been used as solubility enhancers and osmotic agents for the sustained release of poorly water-soluble drugs from osmotic pump tablets. The knowledge of the CD's osmolality in solution or inside such tablets would allow one to further characterize the release mechanisms. Experiments were conducted at 37 degrees C with eight types of HP and (SBE)-CDs. The aqueous solutions ranged from 0.005-0.350 mol(-1). Methods were developed to allow the measurement of high osmolalities using a vapor pressure osmometer or a differential scanning calorimeter. The osmolality calculations from the VPO and FPD measurements correlated well. The osmolality of (SBE)-CDs was significantly higher than the osmolality of HP-CDs and increased with the total degree of substitution (TDS). All CDs showed deviations from ideality at high concentrations. Empirical correlations of osmolality with concentration and TDS allowed the prediction of osmolality over a wide concentration range. This study also gave some useful insights into the behavior of CD derivatives in solution.

A simple method to determine the water activity of ethanol-containing samples

The water activity (aw) of microbial substrates, biological samples, and foods and drinks is usually determined by direct measurement of the equilibrium relative humidity above a sample. However, these materials can contain ethanol, which disrupts the operation of humidity sensors. Previously, an indirect and problematic technique based on freezing-point depression measurements was needed to calculate the aw when ethanol was present. We now describe a rapid and accurate method to determine the aw of ethanol-containing samples at ambient temperatures. Disruption of sensor measurements was minimized by using a newly developed, alcohol-resistant humidity sensor fitted with an alcohol filter. Linear equations were derived from aw measurements of standard ethanol-water mixtures, and from Norrish's equation, to correct sensor measurements. To our knowledge, this is the first time that electronic sensors have been used to determine the aw of ethanol-containing samples. Copyright 1999 John Wiley & Sons, Inc.

Effects of Precursor Composition on Pore Morphology for Thermally Polymerized Acrylic Acid/Methyl Methacrylate-Based Microemulsions

Thermal polymerization has not been extensively studied as a technique for the polymerization of bicontinuous microemulsions. Other more rapid techniques have been employed such as visible- and UV-initiated polymerization. However, the industrial preparation of porous solids would be facilitated by the use of the cheaper and simpler thermal polymerization. The effects of changing composition of the precursor on the resulting matrix morphology for thermally polymerized microemulsions were studied. The factors examined were the surfactant loading of the aqueous phase, the aqueous to organic phase ratio, the monomer ratio of the organic phase, and the cross-linker content of the organic phase. SEM, drying rate studies, and freezing point depression measurements were used to determine matrix morphology. The surfactant loading of the aqueous phase and the cross-linker content of the organic phase were found to have no significant effect on the morphology while the phase ratio and monomer ratio were found to have significant effects on the resulting polymer matrix morphology.

Tris(2-6-dimethoxephenyl) borane and its adducts

Tris(2,6-dimethoxpphenyl)borane, φ3B(φ = 2,6,-(MeO)2C6H3), an air-stable crystalline compound, formed isolable 1:1 adducts with ammonia and some primary amines but not with tertiary amines, secondary amines, or sec-alkylamines. Some tetraalkylammonium tris(2,6-dimethoxypyenyl)cyanoborates [R4N][φ3BCN] are soluble both in water and in benzene, and the stearyltrimethylammonium salt is soluble even in n-hexane. The freezing point depression measurements for some tetraalkylammonium salts suggested that they are associated in benzene by several molecules.

The sign of the nuclear overhauser effect as a function of temperature in contact ion pairs

The signs and magnitudes of nuclear overhauser effects observed in closed-shell ion pairs in C2HCl3 show an unusual temperature dependence; freezing point depression measurements support the proposal that the observed dependence is due at least in part to the formation of ion aggregates.

Evidence for a countercurrent exchanger in the intestinal villi of suckling swine.

The possible existence of a countercurrent exchanger (multiplier) in the intestinal villi of suckling swine was investigated with three different methods: (1) Comparing venous appearance of oxygen and red cells in the mesenteric vein after close i.a. injection of a blood sample equilibrated with pure oxygen and containing methaemoglobinaemic red cells. (2) Determining sodium (micrograms) over protein (mg) ratios along villi. (3) Estimating tissue osmolality in the villus tissue from measurements of freezing-point depression. It was observed that oxygen appeared earlier than red cells in the mesenteric vein after i.a. injection. Furthermore, both the chemical measurements of sodium/protein ratios in the villi and the estimations of tissue osmolality indicate that there exists a gradient of osmolalities along the villus length, the villus tip being hyperosmolar as compared to the villus base. We conclude that a countercurrent exchanger (multiplier) exists in the villi of suckling swine. Its possible pathophysiological significance is discussed.