Residual water estimation

The extent of reaction (yield). The yield obtained in the polymerisations depended on the water concentration in the manner illustrated in Figure 13, and from the intercepts of plots such as these the amount of residual water could be estimated as equivalent to... 

Such behaviour has been attributed to co-catalysis by residual water (which is not consumed) and the concentration of this can be estimated from a plot of rate against added water concentration. The reasoning behind this interpretation was that no reaction between stannic chloride, styrene, and nitrobenzene and/or carbon tetrachloride was known, or indeed seemed plausible, which would give an ionic or ester-like product. (See, however, p.115.)... 

Wear gloves and eye protection. The crystals can be swept up and discarded as for waste disposal. For spills of Diquat solutions, cover with a 1 1 1 mixture of sodium carbonate or calcium carbonate, clay cat litter (bentonite), and sand. Scoop into a container and add to a pail of water. Estimate the weight of Diquat in the spilled solution, and for each 0.1 g, add 2 g of potassium permanganate. Stir until dissolved and allow to stand at room temperature overnight. Reduce the excess permanganate with solid sodium bisulfite, and then decant the liquid to the drain with water. The residue can be treated as normal refuse.5... 

Finally, although compounds with a high Kqw (i e. a high solubility in octanol relative to the solubility in water) may remain in the lipid layer of the skin (stratum comeum) and not become absorbed systemically, insufficient documentation exists to support exclusion of skin-bound residues from estimates of dermal absorption, based on the X ow of the test material alone. 

Errors. Errors were estimated from duplicate measurements. The calorimetric measurements are accurate to about 4%, the saturation water contents to 1%, and the residual water contents are reproducible to about 3%, except at the lowest coverages, where the error is greater. 

The experiments of Johnson and Leroy were conducted with a static system with product water remaining in the system, the water presumably being absorbed by the alumina in the catalyst. Johnson and Leroy estimated that the residual water pressure in their system was about 0.1 torr. It was implied (65) that the water level in the experiments of Johnson and Leroy was typical of that encountered in actual catalytic reforming reactors. 

The greatest uncertainty is in the value of the residual water content i//w as determined by DSC. It is obtained by determining the area under the DSC curve between Te and Tm and above the (uncertain) base line (cf. Figure 16.2). It has been shown that this method tends to involve a number of errors, which altogether lead to considerable overestimation of the value of i// w. For instance, most values published for sucrose are around 0.36, whereas 0.17 is now considered to be the best estimate. It must be assumed that most of the published values for pure substances are too high by a substantial amount. The best way to obtain the value of j/ w is to find Tg, e.g., by DSC, and then separately determine Tg versus i//s for mixtures of low... 

At 400°C methanol replaced about 30% of the hydroxyl groups to form methoxyl groups. Failure to displace all of the hydroxyl groups may have been due to small traces of residual water in the reagents. From quantitative analysis of the methoxyl groups by oxidation to COa, McDonald estimated absorption coefficients as 3 x 104 cm2/mole for CH at 2857 and 2959 cm-1, 2 x 10 cm2/mole for CH at 2995 cm-1, and about 106 cm2/mole for OH at 3750 cm-1. However, these absorption coefficients may be subject to large error. 

The data for Ni-faujasite are complicated by incomplete ion-exchange (27 Ni and 4 Ca indicated by chemical analysis) and possible presence of residual water resulting from dehydration at 400°C. Olson (46) observed double peaks at I and II ascribed to residual water molecules adjacent to the Ni ions. The situation is unclear but Olson suggested bonding between Ni ions and water molecules. The apparent deficiency of Ni ions (estimated total, 22.1) may result from neglect of other ions including Ca, or entrance of protons. 

The reliable estimation of residual water in dried solids is of importance but is beset by several problems, mainly related to the shape and interpretation of DSC heating traces, as illustrated in Figure 11 for a typical aqueous mixture, maximally frozen, from which any relaxation enthalpy contribution has been removed by annealing." The drawn-out DSC heating trace represents the superposition of several distinct processes Tg of the mixture, the heat of dilution, produced by ice... 

A weakness, common to all Karl Fischer-type methods, lies in the limitation that they measure the total water content of the sample, irrespective of the water distribution within the sample. In solids that are partially crystalline and partially amorphous, the residual water will be concentrated in the amorphous phase, thus depressing its Tg. This can accelerate or even promote the crystallisation of small molecule substances within the amorphous matrix. Take as an example crystalline sucrose that contains 0.5% of amorphous material and 0.17% of residual water. Since all the water is concentrated in the amorphous phase, the real water content will be 20% with a Tg of 9°C. It is also instructive to calculate the number of water molecule layers for differently sized sucrose particles. This is shown in Table 1. If the measured water content were to rise to 0.5%, corresponding to 50% in the amorphous phase, then Tg of the amorphous phase would be depressed to —70°C. It is therefore useful, if not essential, to have a reasonable estimate of the amorphous content of a preparation. Several more or less laborious methods for its determination hnd application, and they are... 

Kohlrausch and Heydweiller did not use their experimental value for the specific conductance of water, but the smaller value 3.8 X IQf cm . This was obtained by appl3ung a correction for residual impurities, estimated by comparing the observed temperature coefficient of conductance with that calculated from the known temperature coefficient of mobility of the ions and the calorimetric value of the heat of ionization of water. This corrected value in conjunction with a more recent value of. djj+- -ylQg = 489 Q mole cm at 18 °C gives iCw=0.61 x 10 mole 1 , which is in astonishingly good agreement with modem values. 

An initial tracer test was performed at 100% water saturation to estimate the pore volume and determine the homogeneity of the soil pack in columns. Then 1.1 to 1.5 pore volumes of DNAPL were injected from the bottom at an interstitial velocity of 6 to 7 m/d. The flow direction was then reversed and about 5 pore volumes of water were injected from the top of the column at an interstitial velocity of 6 to 7 m/d until residual DNAPL saturation was reached. In order to reach residual jet fuel saturations, jet fuel was injected from the top followed by a waterflood from the bottom of the soil column. In each case, the flow direction corresponds to the gravity stable direction. Residual NAPL saturations were calculated based on the difference in weight of the uncontaminated soil column and the contaminated soil column. The residual saturation estimate based on weighing the soil column will be referred to as the mass balance estimate of residual NAPL saturation. Residual saturations were also estimated from partitioning tracer tests [40]. The surfactant solutions were injected into the column from the top for the DNAPLs and from the bottom in case of the LNAPLs since these are the favorable directions with respect to gravity. A list of the column experiments discussed in this chapter is given in Table 1. 

Fissore et al. (2008b, 2011b) proposed an innovative approach to determine the residual water content of the dried product vs. time and to give a reliable estimation ofthe time that is necessary to complete secondary drying, that is, to fulfill the requirement on the final water content ofthe product. The method uses the values of water (or solvent) desorption rate that can be calculated from the PRT (Eq. 4.26) and a mathematical model that describes the change with time ofthe residual water content in the dried product. To this purpose it is required to model the dependence of the desorption rate of water (or solvent) from the residual water content in the product. Various models have been proposed in the literature the desorption rate can be assumed to be proportional to the residual water content, or to the difference between the residual water content and the equilibrium value. It is possible to use the exact mechanism, if it is known. Otherwise the first-mentioned model, that is much simpler and that has been demonstrated to describe adequately the process (Liapis and Bruttini, 1995) can be applied ... 

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