Precipitation vessel

Prazipitier-fass, n. precipitating cask or vat. -gefass, n. precipitating vessel, -mittel, n. precipitant, -zylinder, m. precipitating jar. Prazipitin, n. precipitin, prazis, a. precise. 

An electric precipitator contains sets of electric plates. A high-voltage (20,000-V) electric current is applied across these plates, or electrodes. The droplets of water are electrically attracted to these plates, or grids. The water droplets coalesce into larger heavier droplets on the plates. They fall rapidly to the bottom of the electric precipitator vessel. 

If you see the amps on your precipitator creeping up, or spiking up, something is beginning to short-circuit the electric grids, or insulators. Most commonly, corrosion products are falling off the walls of the precipitator vessel. In my experience, this is the most common cause of precipitator failure. 

Twenty grams of silver nitrate are dissolved in 100ml of distilled water and treated with a solution of 5g of pure sodium hydroxide in an equal volume of water. The brown precipitate is washed three times by decantation with 100ml of water and drained well in the precipitating vessel Forty-five milliliters of water are added to the moist silver oxide, followed by 5g of ehloropentammineehromium (III)... 

The methanol level in the precipitation vessel (25%) was optimized in studies of process conditions for the precipitation When methanol levels below 25% were used, gumming of the product was observed. The product of the above precipitation process filtered and washed well, did not agglomerate during drying, and, physically, appeared and behaved the same as micronized material. Such a continuous process was operationally attractive despite the dilution, since it shortened the time cycle (a large crystallizer was available) and avoided the labor intensive and dusty micronization process. However, the micronization process using wet API was adopted since it was deemed useable on all production sites. 

There are several ways to carry out the precipitation process (Fig. 3) [14]. The simplest implementation of the precipitation reaction is the batch operation where the solution from which the salt is to be precipitated is usually present in the precipitation vessel and the precipitating agent is added. The advantage of this mode of operation is the simple way in which the product can be obtained the most severe disadvantage is the variation of batch composition during the precipitation process. This can lead to differences between the product formed during the initial stages of the precipitation and the precipitate formed at the end of the process. If a coprecipitation is carried out this way, it is important to decide which compounds are present in the vessel and which compounds are to be added. If the pre-... 

These problems are avoided if a continuous process is employed for the precipitation however, this makes higher demands on the process control. In a continuous process all parameters as temperature, concentrations, pH, and residence times of the precipitate can be kept constant or altered at will. Continuous operation is, for instance, used for the precipitation of aluminum hydroxide in the Bayer process. Bayer aluminum hydroxide is the main source for the production of cata-lytically active aluminas. The precipitation step of the Bayer process is carried out continuously. An aluminum solution supersaturated with respect to Al(OH)3, but not supersaturated enough for homogeneous nu-cleation, enters the precipitation vessel which already contains precipitate so that heterogeneous precipitation is possible. The nucleation rate has to be controlled very carefully to maintain constant conditions. This is usually done by controlling the temperature of the system to within 2-3 degrees [7]. 

The continuous process usually allows precipitation at low supersaturation conditions, since seeds are already present in the precipitation vessel. Thus, no homogeneous precipitation, which needs high levels of supersaturation, is necessary, and nucleation occurs heterogenously with the associated lower supersaturation levels. 

Figure 1 Schematic of the experimental apparatus. Legend C02 reservoir (A) CO2 bomb (B) expansion vessel (E) flow indicator (F) precipitation vessel (PR) HPLC pump (PS) C02 pump (PV) flow meter (R) heat exchanger (S ) valve (V ) regulating valve (VMM).

The absence of commercial equipment for US-assisted sample preparation clearly reflects that the analytical chemists give little importance to this way of accelerating the operations. For this reason, most applications in this area have been developed by using standard laboratory materials such as round-bottomed flasks or even beaker or precipitation vessels. Some authors have implemented US-assisted sample preparation in commercially available cells specially designed for organic synthesis or have designed and constructed their own custom devices. 

When performing single-stage extraction on the laboratory scale, the chemist employs a separating funnel as mixing and precipitating vessel [23, 31 ]. 

The analgesic paracetamol has been processed in a pilot plant from dimethylformamide (DMF), ethanol, and acetone. The plant used had the capacity of 30kg/hr of CO2 and 0.6m /hr solution and included an 8 L precipitation vessel. The operating temperature was fixed at 45° C while the pressure was varied between 100 and 200 bar. Particle size and morphology varied mostly with the nature of the solvent. Spherical particles were obtained from DMF and acetone, while needle-shaped particles could be produced from ethanol and acetone. Rhombic particles were produced only from ethanol. Particle size varied between 1 and 10 pm depending on the operating pressure. ... 

Earlier work (9) has shown that the size of the precipitate, but not the protein recovery, depends on the method of addition of the polymer to the protein solution. Mixing conditions in the precipitation vessel also affect the precipitate size (lOh The solubility of the protein-polyelectrolyte complex depends strongly on the solution conditions—pH, ionic strength, polymer dosage level, and the nature of the protein and polyelectrolyte. These factors are discussed below ... 

Figure 5 (a) Flow pattern in the precipitation vessel from a two-component mixing nozzle, (b) Distribution of fluid density in this system at 20 MPa and 323.1 K in the vessel. 

Figure 7 Effects of mixing ethanol and CO2 in the nozzle for inlet temperature Tf = 323.1 K and pressure in the precipitation vessel P = 20 MPa (a) distribution of the average mixture fraction f, (b) distribution of the mixture fraction concentration variance, and (c) distribution of temperatures in the system.

The scheme of the SAS apparatus is shown in Figure 1. The apparatus comprises of two HPLC pumps (Jasco, PU-980 for solution and PU-I58O-CO2 for CO2), a back pressure regulator (Jasco, BP-1580-81), a precipitation vessel and a GC oven. 

Most precipitation systems exhibit a metastable supersaturation zone where supersaturation is too low for nucleation to take place. As the supersaturation is increased, the point at which nucleation just begins to occur corresponds to the maximum metastable (critical) supersaturation allowable without nucleation. If crystals are present at this moment in the precipitation vessel, they grow at a maximum (critical) growth rate. 

The population balance technique was also successfully applied to the run-seed, triple-jet precipitation of silver halide crystals (Wey 1990). In addition to silver nitrate and halide salt solutions, a third solution containing stable silver halide seed crystals was simultaneously introduced into the precipitation vessel. For a seed-crystal solution that contains monodisperse seed... 

Figure 2.3-7 Diagram of a GASP process P = precipitation vessel E = expansion vessel PRV = valve for pressure reduction SOL = liquid solution feed ...

Figure 2.3-8 Apparatus for GASP batch A = SCF tank HI, H2 = heat exchangers PV = high pressure volumetric pump P = precipitation vessel E = expansion vessel V = on/off valves V3 = three-way valves PRV = valve for pressure reduction F = flow meter G = rotameter PI = pressure indicator TI = thermometer.

A stainless steel precipitation vessel P, possibly with a glass window, designed to work up to 120 bar. It has to be thermostatted by either a jacket, or a heating tape. It must be equipped with a safety system (rupture disk, check valve) and possibly a magnetic stirrer. 

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