Ratio, solid/water

Waste nylon-6,6 was washed in a diluted commercial detergent solution at 100°C for 0.5 h and then rinsed twice with water to remove any finishes present. The washed nylon-6,6 was then reacted with molten adipic acid for 1.5 h or more at a temperature of 175°C with a weight ratio of nylon-to-adipic acid of 0.15 1. The molten product was then exposed to steam at a temperature of 230-233°C to remove any stabilizers present. The acidolysis product was then hydrolyzed with water at a temperature of 204°C under autogenous pressure for 0.5 h or longer with a ratio of water to acidolysis product of 0.50 1 (w/w). The hot solution was then filtered at 100°C to remove any titanium dioxide present. The filtered product was then mixed with HMDA to neutralize any excess acid present. The solution was then filtered to remove any solids. A 50% by weight aqueous solution of HMDA was added to the filtrate, and under standard polymerization conditions, polyhexamethylene adipamide (nylon-6,6) was produced. 

The reaction mass consists of two liquid phases and one solid phase no solvent is required. The major liquid phase is the crude amine product itself. The solid phase is promoted sponge nickel catalyst. Surrounding the catalyst is a second liquid phase consisting of concentrated caustic and water. Water and caustic are added continuously to make up for losses leaving in the crude product. The ratios of water, caustic, and catalyst in the reaction mass are controlled to produce high yields of product amine and very low catalyst usages. High catalyst concentrations are employed in the reaction mass to keep the concentration of unreacted nitriles very low the upper limit on the catalyst concentration is the point where the circulation rate is inhibited. 

The partitioning of As in the aquifer solid-water interface can best be explained with the distribution coefficient, Kd (a ratio of solute adsorbed in sediment to that of dissolved in groundwater). Due to being simplistic in nature, Kd has long been well appreciated as well as applied by geochemical modelers. 

Figure 7.7 Influence of the increasing molar ratio of water and carbon monoxide, and of the addition of 50% H2 to the feed gas mixture on the CO conversion in WGS reaction over Cu0 2Ce08O2 y, catalyst at different feed compositions with SV = 5000 hr1. The solid lines are model fits assuming first-order reversible kinetics. The dotted lines represent the equilibrium conversions for the specific feed compositions. (Reprinted from [51 ]. With permission from Elsevier.)...

Although dairy interests continue to advertise milk as the perfect1 or bear perfect food, the fact remains that cows milk is not a very good source of B vitamins in terms of percent composition by weight. After all, milk solids constitute only 12-13% of fluid milk and that means a rather large intake ratio of water to solids (about 7/1)> not exactly ideal for obtaining trace nutrients such as the B vitamins. 

This figure shows that the equilibrium values Xf, yf depend upon the solid/water ratio. There is no thermodynamic inconsistency in this because, in terms of Fig. 1 all that Fig. 2 implies is that X-f for two solid/water ratios will yield two values of Xj, each with its thermodynamically corresponding Yf (see Figure... 

Thus, larger solid/water ratios such as are encountered in pore waters of sediments lead to smaller MgC(>3 contents in the equilibrium magnesian calcites although in either case the magnesium content of the solid increases. Wollast and Reinhard-Derie presented data to support the theory from the standpoint of dissolution and some of our results for the precipitation case... 

Figure 2. Equilibrium Curve A and conservation of mass Curve B. The equilibrium point D corresponds to a very large solid/water ratio and the reverse is...

The equilibrium pH in the multistate equilibrium as a function of the solid/water ratio (Cole and Pytkowicz, in preparation) for artificial seawaters with modified (Mg +). The last two columns for calcite refer to... 

Solid/water ratio, and water throughput. Different elements within any given residue will tend to exhibit different concentration profiles as a function of teaching time or of the number of pore-volumes that have passed through the waste (Stollenwerk 1980). 

Our own data for the chemical composition of Estonian combustion ashes (Table 7) based on 4-acid extracts and aqueous leachates of these (ratio of solid/water = 1/10) show that Hg... 

Of course, in a two-phase system,/ + f2 must be equal to 1 (which can be easily checked). Note that Eqs. 3-62 and 3-63 are also valid if one of the phases is a solid (e.g., solid-water partitioning in a lake or in an aquifer, or solid-air partitioning in the atmosphere). In such cases, Kn2 is often expressed by the ratio of mole of i per mass of solid concentration and mole of i per volume concentration, and therefore, rl2 is then given by the ratio of the mass of solid and the volume of the bulk liquid or gas phase present in the system considered. 

To assess the extent to which a compound is associated with solid phases in a given system at equilibrium (see below), we need to know the ratio of the compound s total equilibrium concentrations in the solids and in the aqueous solution. We denote this solid-water distribution coefficient as Kid (e.g., in L kg 1 solid) ... 

A common way to determine Kid values is to measure sorption isotherms in batch experiments. To this end, the equilibrium concentrations of a given compound in the solid phase (Cis) and in the aqueous phase (CIW) are determined at various compound concentrations and/or solid-water ratios. Consider now the sorption of 1,4-dinitrobenzene (1,4-DNB) to the homoionic clay mineral, K+-illite, at pH 7.0 and 20°C. 1,4-DNB forms electron donor-acceptor (EDA) complexes with clay minerals (see Chapter 11). In a series of batch experiments, Haderlein et al. (1996) measured the data at 20°C given in the margin. 

Finally, noting that we refer to the quotient, A/S/Vw, as the solid-water phase ratio, rsw (e.g., kg-L ) in the environmental compartment of interest, we may describe the fraction of chemical in solution as a function of Kid and this ratio ... 

The fraction of the total volume, Ftot, that is not occupied by solids, the porosity, 0, is often used instead of rsw to characterize the solid-water phase ratio in some environmental systems like sediment beds or aquifers. In the absence of any gas phase, 0 is related to parameters discussed above by ... 

The application of such solution- versus solid-associated speciation information may be illustrated by considering an organic chemical, say 1,4-dimethylbenzene (DMB), in a lake and in flowing groundwater. In lakes, the solid-water ratio is given by the suspended solids concentration (since Vw Ftot), which is typically near lO-6 kg-L-1. From experience we may know that the Kid value for DMB in this case happens to be 1 L kg-1 therefore we can see that virtually all of this compound is in the dissolved form in the lake ... 

Therefore, we may not be too surprised to find that nonionic chemicals show increasing solid-water distribution ratios for soils and sediments with increasing amounts of natural organic matter. This is illustrated for tetrachloromethane (carbon tetrachloride, CT) and 1,2-dichlorobenzene (DCB) when these two sorbates were examined for their solid-water distribution coefficients using a large number of soils and sediments (Fig. 9.7, Kile et al., 1995.)... 

Figure 9.7 Observed increase in solid-water distribution ratios for the apolar compounds, tetrachlo-romethane (0) and 1,2-dichIoro-benzene (A) with increasing organic matter content of the solids (measured as organic carbon, /oc, see Eq. 9-21) for 32 soils and 36 sediments. Data from Kile et al. (1995).

With the empirical measures of AT 1 reported in the growing literature and understandings of the stoichiometries of both the ion exchange and ligand exchange processes, we can now estimate the solid-water distribution ratios of such ionic organic sorbates (see Illustrative Example 11.7). 

Note that for the total (dissolved and particulate) concentration, Ct, the abrupt change of the solid-to-water-phase ratio, rsw (Eq. 9-15), at the sediment surface acts like a phase change. The numerical example given in Table 19.1 demonstrates that the transition from the open water column of a lake or the ocean to the sediments involves an increase of rsw by 5 to 6 orders of magnitude. Typically, in the open water, rs p is of order 10 3 kg m-3 while in the sediment column lies between 102 and 103 kg nr3. Thus, at equilibrium the total (dissolved and sorbed) concentration per unit bulk volume on either side of the interface for compounds with small to moderate solid-water distribution ratios (Ki <10 m3kg ) is approximatively given by (see Box 19.1, Eq. 4) ... 

The sorption equilibrium is expressed by (Kf solid-water distribution ratio Eq. 9-7) ... 

Since the open water column is nearly pure water (op =1, rs p = 0), for compounds with small to moderate solid-water distribution ratios (Kd < 10 m3kg ), the above equilibrium partition coefficient can be simplified to ... 

The radial diffusion model and the linear sorption model are compared in Fig. 18.76. Since according to Eq. 19-76 the total mass of the chemical associated with the particle aggregate, (M(r), and the macroscopic solid-water distribution ratio, Kd(t), are linearly related ... 

In this section the distinction between dissolved and sorbed species is introduced into the box model concept in the simplest possible manner, that is, by assuming a reversible linear equilibrium relationship between the dissolved concentration, C (molm 3), and the species sorbed on solids, Cs(mol kg 1). (The units m3 and kgs refer to water volume and solid mass, respectively.) The sorption/ desorption process shall be fast compared to other processes which affect the chemical (e.g., mixing, chemical transformation). As discussed in Chapter 9 (Eq. 9-7), the (observed) solid-water distribution ratio Kd is defined by. 

Note that if the sediment surface were to consist of freshly sedimented particles with concentration Cssc = C°p, then the pore water in equilibrium with these particles would have the aqueous concentration C c = C p, and thus according to Eq. 23-24 the diffusive exchange flux Fsed difr would be zero. However, in most cases the sediment surface is not in equilibrium with the water column, because diagenetic processes change the physicochemical properties of the sediments and thus its solid-water distribution ratio, Kf, relative to. Furthermore, the sediment surface usually reflects a longer history of exposure to the chemical under consideration than the water column. Therefore, water and sediments would approach equilibrium only if the external loading to the lake has changed very slowly in the past. For manmade chemicals this is usually not the case. 

Ksdc(z)is the solid-water distribution ratio in the SMSL at lake depth z... 

Porous media have much larger solid-to-solution phase ratios (rsw) than surface waters (lakes and rivers). Therefore, even the transport of a chemical with moderate to small solid-water distribution ratios (/Q may be influenced by sorption processes. The basic mathematical tools which are needed to quantify the effect of sorption on transport are described in Section 18.4 and summarized in Box 18.5. 

Since surfactants are designed to be enriched at interfaces, surfactant sorption onto environmental solids should be of major importance particularly when the ratio of water volume to water-solid interface is small. Those conditions exist in wastewater treatment and in soil. 

---