Feed phase

During the feed period - following the completion of the injection and holding pressure phases - material for a new shot must be prepared and provided in the proper quantity. The material is fed or metered.  

To this end, the material in the hopper above the plasticating unit is drawn in by the rotating screw and conveyed along the serew flights in the direction of the nozzle. As it moves toward the nozzle, the material is exposed to many different stresses. 

Heat is transmitted to the material from the eylinder wall of the plasticating unit. This transfer of heat is called thermal conduction. 

The material is sheared by the rotation of the serew and further warmed by the resulting fiictional heat. This effect is intensified by the fact that the height of the screw flights decreases in the direction of the nozzle. The material is thus being compressed increasingly. It is simultaneously mixed (homogenized) in a thorough manner. The pressure conditions in the space between the screw and the cylinder wall cause trapped air to be conveyed in the direction of the feed zone. 

The intense compression and mixing of the material is desirable for ensuring that its properties are as uniform as possible. By the time it reaches the tip of the screw, the material has become molten. It accmmflates in firont of the screw in the ante-chamber. As the screw can be moved in an axial direction, it yields to the pressure of the accumulating material and moves backward. In order to improve homogenization, this movement is restricted by adjustable resistance, known as back-pressure. 

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In the classical set-up of bulk liquid membranes, the membrane phase is a well-mixed bulk phase instead of an immobilized phase within a pore or film. The principle comprises enantioselective extraction from the feed phase to the carrier phase, and subsequently the carrier releases the enantiomer into the receiving phase. As formation and dissociation of the chiral complex occur at different locations, suitable conditions for absorption and desorption can be established. In order to allow for effective mass transport between the different liquid phases involved, hollow fiber... 

The actual volume of each phase in element AV is that of the total volume of the element, multiplied by the respective fractional phase holdup. Hence considering the direction of solute transfer to occur from the aqueous or feed phase into the organic or solvent phase, the mass balance equations become ... 

Here the nomenclature is the same as in Sec. 4.4.2 and in addition, Dq is the effective eddy dispersion coefficient for the organic or extract phase (m / s) and Dl is the effective eddy dispersion coefficient for the aqueous or feed phase (m / s). The above equations are difficult to solve analytically (Lo et al., 1983) but are solved with ease, using digital simulation. 

Consider a batch two-phase extraction system, with a single solute transferring from the feed phase into an immiscible solvent phase. The background to the problem is discussed in Section 3.3.1.1... 

Fig. 2 Time-dependent concentrations for the feed phase in stages 1 to 5 [ctL = 0.15 and ac = 0.15].

Fig. 2 Concentration variations in the feed phase for stages 1 to 5 and for start up from initially zero concentration conditions with full control implementation (Kc = 5).

The second method of constructing an extraction isotherm initially requires the choice of a suitable phase ratio, and the organic and aqueous (feed) phases are contacted at this ratio until equilibrium is obtained. The phases are allowed to separate, and the aqueous phase is removed and analyzed. A small measured portion of the organic phase is also taken for analysis. Fresh aqueous feed is then added to the remainder of the organic phase, in an amount to give the same phase ratio as that originally used. The... 

In the emulsion liquid membrane configuration, the liquid membrane is formed by dispersing into the feed (phase 1) an emulsion of the stripping... 

F-Feed phase, M-Membrane phase R-Receiving phase F/M, M/R Interfaces... 

Diffusion of cephalosporin anion (P ) from the bulk feed phase (III) to feed-membrane (III-II) interface of the emulsion globule... 

The CPC present in the aqueous phase is distributed between the aqueous and organic phases at the SLM-liquid interface. By maintaining low Cl ion concentration in the feed phase and high Cl ion concentration in the stripping phase, the distribution ratio of CPC (P ion form) at the aqueous feed-SLM interface can be made much higher than that at the aqueous strip-SLM interface. Under this condition, the steady-sate overall CPC flux across the membrane can be obtained from Pick s distribution law applied to aqueous diffusion film as well as the membrane itself and from interfacial reaction kinetics which describe the interfacial flux. 

In case of very low solute concentration, the complex concentration in the hquid membrane is almost equal to zero. Thus, the transport process is mainly controlled by aqueous film resistance, and Kp is equal to kf, which is independent of time. By integrating Eq. (35), the concentration variation of solute in feed phase... 

The permeation or the mass transfer rate in aqueous film can be obtained from the slope of time course of solute concentration in the feed phase. 

In this case, the solute concentration in feed phase is so high that all of the carrier in the liquid membrane are in a complex form and the complex concentration is equal to the overall carrier concentration. So, mf and m become... 

Figure 33. Principle of proton-driven uphill transport for dopamine under a countertransport mode. The concentration of the carrier lasalocid A in o-dichlorobenzene was 0.1 M. The feed phase (100 ml) was 10 mM Tris-HCI buffer solution (pH 7.4) containing 1 mM ascorbic acid. The receiving phase (0.5-2.0 ml) was a hydrochloric acid solution (pH 0.5-3.0). The initial dopamine concentration in the feed solution was in the range from 1.00 x 10 to 1.00 x 10 M (reprinted with permission from Anal. Sci. 1996, 12, 333. Copyright 1996 The Japan Society for Analytical Chemistry).

Another class of solvents that appears to have significant appeal for green processing of metal waste solutions relies on solvent-coated magnetic particles dispersed within the feed phase to be treated (Nunez et al., 1996). Once the desired solutes have been removed by extraction, these particles can be recovered conveniently using magnetic filtration. 

Fig. 19.3 The solution-diffusion transport model in pervaporation. a Solution of compounds from the feed phase into the membrane surface, b Diffusion across the membrane barrier, c Desorption from the membrane permeate (downstream) side into the permeate phase...

Fig. 23.4 Organophilic pervaporation (PV) for in situ recovery of volatile flavour compounds from bioreactors. The principle of PV can be viewed as a vacuum distillation across a polymeric barrier (membrane) dividing the liquid feed phase from the gaseous permeate phase. A highly aroma enriched permeate is recovered by freezing the target compounds out of the gas stream. As a typical silicone membrane, an asymmetric poly(octylsiloxane) (POMS) membrane is exemplarily depicted. Here, the selective barrier is a thin POMS layer on a polypropylene (PP)/poly(ether imide) (PEI) support material. Several investigations of PV for the recovery of different microbially produced flavours, e.g. 2-phenylethanol [119], benzaldehyde [264], 6-pentyl-a-pyrone [239], acetone/buta-nol/ethanol [265] and citronellol/geraniol/short-chain esters [266], have been published...

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