Anion-free water

This paper discusses the use of specific ion electrodes for determining the anion-free water. This method is simpler and more accurate at low electrolyte concentration than ordinary chemical methods. It is potentially useful for oilfield application and laboratory automation. The mobility of this water is also examined under forced conditions with pressure gradients. It is expected that by using the methods developed in this paper, one may obtain a better understanding of the clay properties. 

The amount of anion-free water was calculated by a material balance of chloride and water in the system. The calculation can be simplified by using volume concentrations. Details of the calculation are illustrated in Appendix I. 

Figure 1. Anion-free Water As A Function of NaCl Concentration.

Mobility of The Anion-Free Water. It is well known that water in the electrical double layer is under a field strength of 10 -10 V/cm and that the water has low dielectric constants (36). Since anion-free water is thought to be the water in the electrical double layer between the clay and the bulk solution, at high electrolyte concentrations, the double layer is compressed therefore, the water inside is likely quite immobile. At low electrolyte concentrations, the electrical double layer is more diffuse, the anion-free water is expected to be less immobile. Since the evaluation of the shaly formation properties requires the knowledge of the immobile water, experiments were conducted to find out the conditions for the anion-free water to become mobile. 

By definition, the anion-free water is free of salt. When pressure is applied to a clay-brine slurry to force out water (as that described in the experimental section), the solution that flows out of the cell should maintain the same chloride concentration as the brine s if the anion-free water is immobile. Otherwise, the concentration of the chloride decreases. Pressure forces water to flow through the pores with a certain velocity meanwhile, the pore size... 

Table II shows the result of compaction experiments with Glen Rose Shale. Column 2 gives the equilibrium NaCl concentration of the solution before the compaction experiment. Column 3 gives the anion-free water calculated as shown in Appendix I. Column 4 gives the amount of the bulk solution which has the NaCl concentration given in Column 2. Column 5 gives the total amount of fluid flowing out of...

Experiments No. 1,2 and 3 were performed at gas pressure beginning at 15 psi and stepping up to 77 psi. The total fluid collected was less than the bulk solution in the system. The concentration of chloride in the fluid collected in these three runs was about the same as the values given in Column 2. It was concluded that under these conditions, the anion-free water was immobile. It was observed that under the same applied pressure, the higher the NaCl concentration, the faster the flow rate — consistent with observations reported by Engelhardt and Gaida (38). 

In order to increase the flow rate without too much pressure, Experiment 4 was performed with a Fann filter press which has a wider cross sectional area. A constant air pressure of 100 psi was applied, the flow rate was 26 times that of Experiment 1 while the NaCl concentration was only slightly higher than that of Experiment 1. Although the flow rate was much increased in Experiment 4, the result was similar to Experiment 1. The water retained in the clay (Column 8) determined by drying was found to be close to the amount of anion-free water. The porosity of the sediment was 0.4 and the average pore diameter was 4466 X. It was concluded from this experiment, that the anion-free water was immobile even at 100 psi and 7.4 ft/day. The pore size distributionQof the sample showed 90% of the pores to have a diameter above 350 A and less than 3% of the pores to have a diameter below 100 X (Figure 4). 

It was decided to increase the pressure in subsequent experiments to push the anion-free water out. Experiments 5 and 6 were performed at 400 psi at a NaCl concentration around 0.01 M. Experiments 5-10 were performed in the compaction cell as described in the experimental section. This apparatus was rated for 10,000 psi. The pressure regulation at 400 psi region was about 100 psi. Some evaporation occurred that made the total fluid collection less than expected from total material balance. NaCl concentration of the collected fluid could not be measured accurately. However, the amount of fluid collected and the amount of water retained in the sediments in Experiments 5 and 6 clearly indicated some anion-free water was mobilized. 

Anion-free water determined by using a chloride ion electrode agrees well with data given in the literature. (2) A new equation has been proposed for the bound water calculation. (3) The mobility of the anion-free water was found to be affected by pressure, porosity and electrolyte concentration. (4) Compaction experiments indicated that the anion-free water will not move until all the bulk water has been removed. (5) It is possible to increase the ratio of bound water to bulk water in a sample through compaction experiment. 

Ammonia-free water may be prepared in a conductivity-water still, or by means of a column charged with a mixed cation and anion exchange resin (e.g. Permutit Bio-Deminrolit or Amberiite MB-1), or as follows. Redistil 500 mL of distilled water in a Pyrex apparatus from a solution containing 1 g potassium permanganate and lg anhydrous sodium carbonate reject the first 100 mL portion of the distillate and then collect about 300 mL. 

CASRN 56-40-6 molecular formula C2H5NO2 FW 75.07 Chemical/Physical Products identified from the oxidation of glycine and OH radicals (generated from H2O2/UV) in oxygenated water were oxalic acid, formic acid, and ammonium ions. In oxygen-free water, oxalic and formic acids were not produced, i.e., glycine oxidized directly to ammonium ions. The rate constant for the reaction of OH radicals with the zwitterion ion is 1.7 X 10 /M-sec and with the anionic form is 1.9 x 10 /M-sec (Vel Leitner et al., 2002). 

Nitrogen-bearing cyclophanes like 351 [16] and 352 [17] bind larger organic anions in water due to superposition of the hydrophobic effect and electrostatic attraction. The phenanthridinium hosts like 351 have been found to form the most stable nucleotide complexes known so far. On the other hand, free tetrapyrrolic porphyrins do not bind anions since their cavity is too small to take advantage of the convergent N-H dipoles for the complex stabilization [18]. However, expanded diprotonated porphyrins like sapphyrin 353 were shown to form stable complexes with phosphate [19a] and halide [19b] anions. 

This bimodal dynamics of hydration water is intriguing. A model based on dynamic equilibrium between quasi-bound and free water molecules on the surface of biomolecules (or self-assembly) predicts that the orientational relaxation at a macromolecular surface should indeed be biexponential, with a fast time component (few ps) nearly equal to that of the free water while the long time component is equal to the inverse of the rate of bound to free transition [4], In order to gain an in depth understanding of hydration dynamics, we have carried out detailed atomistic molecular dynamics (MD) simulation studies of water dynamics at the surface of an anionic micelle of cesium perfluorooctanoate (CsPFO), a cationic micelle of cetyl trimethy-lainmonium bromide (CTAB), and also at the surface of a small protein (enterotoxin) using classical, non-polarizable force fields. In particular we have studied the hydrogen bond lifetime dynamics, rotational and dielectric relaxation, translational diffusion and vibrational dynamics of the surface water molecules. In this article we discuss the water dynamics at the surface of CsPFO and of enterotoxin. 

The subsurface maximum in pore-water HgT (Figure 3) suggested that diffusion from the profundal sediments to the overlying water column could be important. Fickian diffusive flux calculations (eq 2) were used to estimate Hg loading from pore waters. Diffusion coefficients for mercury in pore waters were not available. However, free-water diffusion coefficients for monovalent anions (see Table I) averaged about 5 X 10"6 cm2/s (53, 55) and... 

Ionic Strength While most experimental solubility data have been determined in distilled, salt-free water, natural water usually contains various anionic and cationic species of mineral salts which change the electrolytic property of water and, hence, its capacity to dissolve organic compounds. Distilled water solubility and the solubility at different salt concentrations can be estimated knowing the ionic strength, I, of the solution. I is defined as follows ... 

A CE determination of fluoride in rain water was compared with IC and ISE potentiometry the IC response was related to the total concentration, whereas CE and ISE responded to free fluoride [50]. The fluoride concentrations obtained by CE and ISE were systematically lower than those obtained by IC due to the fluoride complexation with aluminium. The detection limits for IC and ISE were similar (0.2 and 0.3 pmol/l) and somewhat lower than those for CE (0.6 xmol/l). CE was evaluated as an alternative method to the EPA ion chromatographic method for the determination of anions in water and a better resolution and a shorter analysis time were found for CE [51]. 

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