Naphthalene solubility measurements

Figure 5.6 Illustration of the effect of a completely water-miscible solvent (CMOS, i.e., methanol) on the activity coefficient of organic compounds in water-organic solvent mixtures decadic logarithm of the activity coefficient as a function of the volume fraction of methanol. Note that the data for naphthalene (Dickhut et al., 1989 Fan and Jafvert, 1997) and for the two PCBs (Li and Andren, 1994) have been derived from solubility measurements whereas for the anilins (Jayasinghe etal., 1992), air-water partition constants determined under dilute conditions have been used to calculate y,f.

The potential unreliability of equation 3.18 in predicting solubility can be demonstrated by comparing the above calculated ideal solubility (x = 0.269) of naphthalene with measured solubilities in a few eommon solvents ... 

Detailed measurements of the solubility between the lower and upper critical end points have been made only for the solutions in ethylene of naphthalene,14 hexachlorethane,30 and />-iodochloro-benzene.21 Atack and Schneider2 have used dilute solutions of the last-named substance to study the formation of clusters near the gas-liquid critical point of ethane. 

Conversion of coal to benzene or hexane soluble form has been shown to consist of a series of very fast reactions followed by slower reactions (2 3). The fast initial reactions have been proposed to involve only the thermal disruption of the coal structure to produce free radical fragments. Solvents which are present interact with these fragments to stabilize them through hydrogen donation. In fact, Wiser showed that there exists a strong similarity between coal pyrolysis and liquefaction (5). Recent studies by Petrakis have shown that suspensions of coals in various solvents when heated to 450°C produce large quantities of free radicals (. 1 molar solutions ) even when subsequently measured at room temperature. The radical concentration was significantly lower in H-donor solvents (Tetralin) then in non-donor solvents (naphthalene) (6). 

Saturation properties such as solubility in water and vapor pressure can be measured directly for solids and liquids. For certain purposes it is useful to estimate the solubility that a solid substance would have if it were liquid at a temperature below the melting point. For example, naphthalene melts at 80°C and at 25°C the solid has a solubility in water of 33 g/m3 and a vapor pressure of 10.9 Pa. If naphthalene was a liquid at 25°C it is estimated that its solubility would be 115 g/m3 and its vapor pressure 38.1 Pa, both a factor of 3.5 greater. This ratio of solid to liquid solubilities or vapor pressures is referred to as the fugacity ratio. It is 1.0 at the melting point and falls, in this case at lower temperatures to 0.286 at 25°C. 

Low molecular weight hydrocarbons are moderately to well soluble. Naphthalene is widely used as standard compoimd for solubihty measurements in SCCO2. Some general trends for the solubihty of organic compounds are as follows ... 

Table 6.2 presents data showing the effect of various CMOS on the activity coefficient or mole fraction solubility of naphthalene, for two different solvent/water ratios. To examine the cosolvent effect, Schwarzenbach et al. (2003) compare the Hildebrand solubility parameter (defined as the square root of the ratio of the enthalpy of vaporization and the molar volume of the liquid), which is a measure of the cohesive forces of the molecule in pure solvent. 

Micellar partition coefficient (Kmic) values for phenanthrene and naphthalene below their aqueous solubility limits were determined from experimental fluorescence measurements using nonlinear regression analysis of the following equation ... 

The use of NMR spectroscopy as an analytical technique is well established ( 1 8). In order to quantitate our spin-echo height to the number of protons present, we performed an independent calibration using standard solutions of naphthalene in carbon tetrachloride. Concentrations for the standards were chosen to correspond to the anticipated supercritical C02 solubilities, and all calibration measurements were performed using a sample cell of the same dimensions as the solubility sample cell previously described. The response of our spectrometer to the standard solutions was linear over the concentration range. The reproducibility for independent measurements of the calibration curve was 3 . Throughout the experiment, all spectrometer conditions (pulse lengths, phases, receiver amplifier gain, etc.) were closely monitored, and frequent checks on the calibration of the spectrometer were performed. In this way we were able to obtain the molar solubility of solid naphthalene in supercritical carbon dioxide to an estimated experimental accuracy of 6%. 

The NMR method we have developed gives a direct, in situ determination of the solubility and also allows us to obtain phase data on the system. In this study we have measured the solubilities of solid naphthalene in supercritical carbon dioxide along three isotherms (50.0, 55.0, and 58.5°C) near the UCEP temperature over a pressure range of 120-500 bar. We have also determined the pressure-temperature trace of the S-L-G phase line that terminates with the UCEP for the binary mixture. Finally, we have performed an analysis of our data using a quantitative theory of solubility in supercritical fluids to help establish the location of the UCEP. 

In a batch slurry reactor, the liquid-solid mass-transfer coefficient can be measured by dissolving a sparingly soluble solid in liquid. The concentration of dissolved solid in liquid (Bt) can be measured as a function of time, preferably by a continuous analytical device. Systems such as the dissolution of benzoic acid, jS-naphthol, naphthalene, or KMn04 in water can be used. A plot of B( as a function of time and the slope of such plot at time t = 0 can give ks as... 

Erkey and Akgerman [8] reported an adsorption equilibrium constant for naphthalene in alumina pores filled with supercritical CO2. Analysis shows that this desorption equilibrium constant is simply proportional to the solubility of naphthalene in CO2 as measured by Tsekhanskaya et al. [9]. Hence, the desorption rate constant was estimated from the following type of correlation reported for the naphthalene-ethylene system by Tsekhanskaya et al. [9] ... 

The influence of the parameters concentration, pre- and post-expansion pressure and pre- and post-expansion temperature and geometry of the nozzle on the particle size distribution wasn t studied at all. Merely Mohamed [4] examined the influence of concentration, pre- and post-expansion pressure and temperature of the system carbon dioxide - naphthalene. No particle size distribution was measured, only the size of the smallest and biggest particles were measured. For these investigations, anthracene was used as a model substance, while the solubility of anthracene in carbon dioxide [5] is approximately more then 100 times smaler than for naphthalene. 

In Figure 3 the equilibrium solubility of naphthalene in toluene expanded with carbon dioxide at 25°C is shown. There is a considerable deviation to the data of Dixon et al [2]. In both works, it was made sure that excess solids were present. Proper filtration of the naphthalene particles in situ prior to sampling is the crucial step of the experiment. Therefore, small amounts of particles leaking through the filter can cause an error in concentration determination. The samples in this work were analysed for naphthalene content by density measurement and additionally by refractive index measurement. The reproducability was better than 0.8 mole percent. 

Then a and By were optimized to minimize the percent absolute average relative deviation (% AARD) between the calculated solubility and the experimental solubilty measured here, and the experimental solubilities at 35 C reported by Tsekhanskaya et al. (11) and by McHugh and Paulaitis (12), The equilibrium solubilities of naphthalene in CO2 used to calculate the mass transfer coefficients are given in Table IL The optimized values of ay, By, and %AARD are 0.0402, 6.5384 and 9.23 respectively. Prediction of the solubility with these two optimized parameters is given in Figure 2 with data of Tsekhanskaya et al. (Ij, McHugh and Paulaitis (12) and our experimental solubility data (below the critical pressure). 

It follows from Tables 17 and 18 that tetrakis(dimethylamino)naphthalenes 35 and especially 65 possess higher basicity in comparison with parent compound 1. It was hoped that a further increase in the number of NMe2 groups would increase the basicity even higher. Unfortunately, the first representatives of such compounds, namely hexa- and heptakis(dialkylamino)naphthalenes (Section II.B.2), turned out to be scarcely soluble in MeCN, DMSO, EtOH and H2O. Yet, their pK, values were measured in 80% aqueous dioxane by a potentiometric titration technique166. The acid ionization constants are summarized in Table 19 together with the pXa values of tetrakis(dimethylamino)naphthalenes 35 and 65 determined under the same conditions. 

In the dye procedure, the globulin fraction is isolated by ammonium sulfate precipitation, and allowed to react with naphthalene black in a citric acid buffer. The stained globulins are then separated by centrifugation, and the amount of dye in the supernatant fluid is measured in a colorimeter (Pll). The resulting loss of soluble dye is related to the globulin concentration, and the procedure is standardized with pure 7-globulin. 

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