Residence times solid solution

These are similar to stabilization ponds except that oxygen is added by mechanical surface aerators. This cuts the residence time of the water by 80%. It also means that the depth of the lagoons can be increased to 18 ft (5.5 m) and aerobic conditions can be maintained. The surface aerator power level is usually between 0.008 and 0.06 hp/1,000 gal (0.0002-0.016 hp/m3). This is not enough power to keep all the solids in solution. To do that would require 0.05-0.1 hp/1,000 gal (0.013-0.026 hp/m3).33... 

Adsorption Isotherms. The adsorption isotherms were determined using the serum-replacement adsorption or desorption methods (7). For the adsorption method, the latex samples (50 or 100 cm 2% solids) containing varying amounts of PVA were equilibrated for 36 hours at 25°C, placed in the serum replacement cell equipped with a Nuclepore membrane of the appropriate pore size, and pressurized to separate a small sample of the serum from the latex. For the desorption method, the latex samples (250 cm 2.5% solids) were equilibrated for 36 hours at 25°C and subjected to serum replacement with DDI water at a constant 9-10 cm /hour. The exit stream was monitored using a differential refractometer. The mean residence time of the feed stream was ca. 25 hours. It was assumed that equilibrium between the adsorbed and solute PVA was maintained throughout the serum replacement. For both methods, the PVA concentration was determined using a An-C calibration curve. 

The results are shown in Figure 2-3, in which the solid line is the exact solution. This numerical approach shows no sign of instability even for a time step of 40 years, nearly five times larger than the residence time of atmospheric carbon dioxide (distime). In fact, the reverse Euler method is nearly always stable, and so I shall use it from now on. 

Metal-catalyzed cross-couplings are key transformations for carbon-carbon bond formation. The applicability of continuous-flow systems to this important reaction type has been shown by a Heck reaction carried out in a stainless steel microreactor system (Snyder et al. 2005). A solution of phenyliodide 5 and ethyl acrylate 6 was passed through a solid-phase cartridge reactor loaded with 10% palladium on charcoal (Scheme 2). The process was conducted with a residence time of 30 min at 130°C, giving the desired ethyl cinnamate 7 in 95% isolated yield. The batch process resulted in 100% conversion after 30 min at 140°C using a preconditioned catalyst. 

The geochemical fate of most reactive substances (trace metals, pollutants) is controlled by the reaction of solutes with solid surfaces. Simple chemical models for the residence time of reactive elements in oceans, lakes, sediment, and soil systems are based on the partitioning of chemical species between the aqueous solution and the particle surface. The rates of processes involved in precipitation (heterogeneous nucleation, crystal growth) and dissolution of mineral phases, of importance in the weathering of rocks, in the formation of soils, and sediment diagenesis, are critically dependent on surface species and their structural identity. 

The level of impurity uptake can be considered to depend on the thermodynamics of the system as well as on the kinetics of crystal growth and incorporation of units in the growing crystal. The kinetics are mainly affected by the residence time which determines the supersaturation, by the stoichiometry (calcium over sulfate concentration ratio) and by growth retarding impurities. The thermodynamics are related to activity coefficients in the solution and the solid phase, complexation constants, solubility products and dimensions of the foreign ions compared to those of the ions of the host lattice [2,3,4]. 

Chemically pure reagents were used. Cadmium was added as its sulfate salt in concentrations of about 50 ppm. Lanthanides were added as nitrates. For the experiments with other metal ions so-called "black acid from a Nissan-H process was used. In this acid a large number of metal ions were present. To achieve calcium sulfate precipitation two solutions, one consisting of calcium phosphate in phosphoric acid and the other of a phosphoric acid/sulfuric acid mixture, were fed simultaneously in the 1 liter MSMPR crystallizer. The power input by the turbine stirrer was 1 kW/m. The solid content was about 10%. Each experiment was conducted for at least 8 residence times to obtain a steady state. During the experiments lic iid and solid samples were taken for analysis by ICP (Inductively Coupled Plasma spectrometry, based on atomic emission) and/or INAA (Instrumental Neutron Activation Analysis). The solid samples were washed with saturated gypsum solution (3x) and with acetone (3x), and subsequently dried at 30 C. The details of the continuous crystallization experiments are given in ref. [5]. 

One of the major consideration in polymerization reactors is that the viscosity of the solution changes with degree of polymerization, going from very low viscosity initially to a solid at complete polymerization. This means that tubular reactor must be used very cautiously for polymerization because the viscosity will increase, especially near the wall where the residence time is longest. Many of these fluids also have viscosities that are dependent on the shear rate. 

A direct liquefaction technique, the SRC process involves mixing dried and finely pulverized coal with a hydrogen donor solvent, such as tetralin, to form a coal-solvent slurry. The slurry is pumped together with hydrogen into a pressurized, vertical flow reactor. The reactor temperature is about 825°F (440°C) and pressures range from 1,450 to 2,000 psi. A residence time in the reactor of about 30 minutes is required for the carbonaceous material to dissolve into solution. From the reactor, the product passes through a vapor/liquid separation system. The slurry solids remaining in the reactor are then removed and filtered. Various filtration techniques have been developed to remove solids from recoverable oil. 

Analytical solutions for x and y as functions of the bed-length, z, and time, t, are available [45,52], The expressions are a useful extension of two-phase model applied to plug-flow. These two models are appropriate in describing the extraction of crushed or broken seeds to recover the seed oil, either in shallow beds or in plug flow. As shown by Sovova [52], applying the plug-flow model requires corrections for non-ideal residence-time distribution (non-plug flow) of the fluid in contact with the solid. 

For the separation of benzene and thiophene that form a solid solution, a tray efficiency of more than 40% could be realized. Flow rates of 100-1000 kg/m2 hr have been tested. The residence time of crystals was about 30 min per stage. Eutectic systems also have been handled satisfactorily. A column 500 mm dia and 3 m long with 19 trays has been built it is expected to have a capacity of 300 tons/yr. 

As mentioned earlier, sea water seems to be in equilibrium with CuO. An apparent undersaturation is seen for Zn and Cd. Nevertheless, assuming that CuO, ZnO, and CdC03 are minor constituents of solid solutions—such as occur in manganese nodules—it is possible that the ocean is slightly oversaturated with respect to these three elements. A small oversaturation would indeed agree with the residence times given here. 

Calcite will therefore precipitate in the upper layers of the sea, but it will redissolve when sedimented to depths of about 1000 or 2000 meters. There seems to be a dynamic equilibrium, which is consistent with the long residence time. The same is true for Sr where we observe equilibrium if we assume a solid solution of SrCC>3 in calcite as the controlling solid phase. 

In an alternate version of the process ( 7), designated SRC-II, a portion of the coal solution is recycled as solvent in place of the distillate solvent of the SRC-I process. The filtration step is eliminated and, typically, the process operates at a higher pressure, higher temperature, and longer residence time than the SRC-I process. Hydrogen consumption and the conversion of dissolved coal is increased, and the primary product is a liquid rather than the solid product of the SRC-I process. The liquid product of the SRC-II process is the feedstock that is the subject of the work described in this chapter. 

One of the critical units in the production of paper is a reactor called a digester. In the kraft process this reactor is a two-phase tubular reactor in which the lignin that binds the wood chips together is broken down through a combination of chemical and thermal effects. The white liquor (aqueous solution of sodium hydroxide and hydrosulfide) and solid wood chips flow countercurrently in some zones and co-currently in others. The residence time of the pulp is about 10 h. 

The dissolution process can be interpreted stochastically since the profile of the accumulated fraction of amount dissolved from a solid dosage form gives the probability of the residence times of drug molecules in the dissolution medium. In fact, the accumulated fraction of the drug in solution, q (t) /goo, has a statistical sense since it represents the cumulative distribution function of the random variable dissolution time T, which is the time up to dissolution for an individual drug fraction from the dosage form. Hence, q (t) /q can be defined statistically as the probability that a molecule will leave the formulation prior to t, i.e., that the particular dissolution time T is smaller than t ... 

It is noteworthy that this process does not create any additional solid waste, as all constituents of the waste solution can either be recovered by destination, or chemically decomposed at relatively moderate temperatures. Corrosion attack is small because no halogen compounds are involved, and the only potentially hazardous material is the ion exchange resin. When operated at room temperature, there are no detectable signs of decomposition within one to two month s residence time. The spent resin can be stored safely in alkaline media before incorporation into concrete. 

Fig. 22 Schematic comparison between the residence times tR of waters in the hydrosphere (ocean to rainfall), the dissolution of various minerals in unsaturated solutions at pH 5 (quartz to gypsum) and the half-life tm of chemical processes (recristallization to solid-solid reactions) (data after Langmuir 1997, Drever 1997)...

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