Under Elevated Pressure

Efficiency of starch dispersion can be further improved when an excess quantity of steam is used97 or when the starch is held under pressure in a retention device (tank or coil) before discharge to the atmosphere. Both processes require a flash chamber (cyclone) to remove excess steam and steam relieved by the pressure drop. Excess steam refers to a multiple of the quantity required to reach target temperature and pressure. The quantity of saturated steam to reach a target temperature can be calculated from its heat content, the slurry temperature, the specific heats of starch and water, and the enthalpy of starch gelatinization. The action of excess steam in the dispersion zone between the jet and back-pressure valve causes a shear effect that enhances disintegration of the starch granules. In many applications, a three-fold excess of steam is used. 

The products of starch cooking with retention are similar to those obtained by dispersion with excess steam. Retention of starch paste for several minutes under pressure requires that all steam is condensed otherwise false body of uncondensed steam will shorten the retention. Jet cooking with retention is practiced for on-site chemical starch modification. 

Pigment and heat-stable coating adjuncts may be added to the starch slurry for processing through the cooker jet or added to the dilution water. It is thus possible to obtain complete size-press formulations or low solids pigmented coatings in a continuous and on-demand fashion. The specific heat of the additives needs to be considered in the thermal balance for the system. 

The colloidal dispersion resulting from thermal/chemical oxidative conversion can rapidly retrograde, which makes immediate neutralization of the acid product to a pH 8.0 to 8.5 mandatory. Discoloration of the paste is lessened when sodium bisulfite is added to the starch slurry and/or sodium sulfite added to the paste. Multivalent ions in the paste can induce colloidal destabilization, and may require the addition of a sequestrant.  

All steam that is injected into the starch slurry has to be condensed in order to achieve the desired retention time under pressure for the reaction. Air released from the starch slurry will affect retention. Steam used for the reaction is superheated. 

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Fiber dimensions have been studied for hemodialysis. When blood is circulated through the fiber lumen (m vivo), a significant reduction in apparent blood viscosity may occur if the flow-path diameter is below 100 p.m (11). Therefore, current dialy2ers use fibers with internal diameters of 180—250 p.m to obtain the maximum surface area within a safe range (see Dialysis). The relationship between the fiber cross section and the blood cells is shown in Figure 5. In many industrial appUcations, where the bore fluid is dialy2ed under elevated pressure (>200 kPa or 2 atm), fibers may burst at points of imperfection. Failure of this nature is especially likely for asymmetric fibers that display a large number of macro voids within the walls. 

A thin layer of a mix of natural rubber, sulfur, precipitated silica, water, and some additives, such as carbon black and vulcanizing agents, is extruded on a paper support belt, calendered, and vulcanized as a roll in an autoclave under elevated pressure and temperature ( 180 °C). A modi-... 

Although liquid chromatography (l.c.) under elevated pressure is now used essentially for determining the molecular weight of heparin,74,75 as an alternative to methods using soft gels,76 it can undoubtedly be used as well for rapid analysis of mixtures of glycosaminoglycans. 

Figure 5. Design of a cell for photoassisted electrolysis of C02 under elevated pressures.97 (1) Photoelectrode (2) reference electrode (3) counter electrode (4) sampling port with septum (5) pressure regulator (6) pressure gauge (7) O-rings (8) reaction cell (9) separator (10) quartz window (11) insulated connection (12) bolts (13) connections to potentiostat.

Scheme 7.45 Acidic cleavage under elevated pressure.

Since the zero-point energy is positive, that is of repulsive type and quite large, it is capable of practically balancing the effect of the attractive forces. Hence, solidification is possible only under elevated pressures. 

Different types of equipment are available for the investigation of deflagration properties of substances under physical confinement or under elevated pressures. 

The synthesis of radioactive ketones with C in carbonyl was achieved by carbonylative cross-coupling of aryl iodides or triflates with methyl-, phenyl-, or 2-thienylboronic acids under elevated pressure of CO. To ensure fast reaction, harsh conditions were used. Interestingly, under such conditions the addition of a base is not necessary (Equation (18))." ... 

The components within the F1PLC system are interconnected by short segments of transfer tubing with a very small internal diameter (0.1mm). Traditionally constructed from stainless steel, transfer tubes can also be made of PEEK a (polyetheretherketone), a coloured, flexible polymer that is less expensive to fabricate than stainless steel and is resistant to common solvents under elevated pressures (up to 350 bar). 

Dilatometric studies have demonstrated the negative thermal expansivity for many oriented crystalline polymers 64,170 176). The results of these experimental studies may be summarized as follows. Cold-drawing of PE below Tm 172) and solid-state extrusion under elevated pressure 170 1711 lead to a monotonous decrease of the positive thermal expansion coefficient with increasing draw ratio. At a certain degree of orientation, dependent on temperature, PM becomes negative with Pi < Pell (Fig. 16). This is the second way of reaching negative expansivity applied, e.g. to POM (w = 63 % Tdr = 423 K) 173>. 

Figure 5.2-38. Comparison between the experimental results under elevated pressures and the correlations (5.2-31) (after Lara-Marquez et al. [57]).

C. Mozenski and E. Kucharski, Hydraulics of packed columns under elevated pressure, Inzyniera Chemiczna I Procesowa, 3 (1986) 373-384. 

F, Larachi, A. Laurent, N. Midoux and G. Wild, Liquid saturation data in trickle beds operating under elevated pressure, AIChE Journal, 37 (1991) 1109-1112. 

F. Larachi, A. Laurent, G. Wild and N. Midoux, Some experimental liquid saturation results in fixed-bed reactors operated under elevated pressure in cocurrent upflow and downflow of the gas and the liquid, Ind. Engng. Chem. Res., 30 (1991) 2404-2410. 

For the design of plants which are to operate under elevated pressures the following items are relevant ... 

Liquid chromatography (l.c.) under elevated pressure has now been introduced into glycosphingolipid separation. Glycolipids are analyzed as perbenzoylated,112-116 N-acetylated O-benzoylated,"7 "8 and N-(p-nitro-benzoyl)ated O-acetylated119-122 derivatives, as well as in their native... 

Telomenzation reactions are as a rule earned out at an elevated temperature up to 250 degrees. When volatile reactants are used, the reaction is carried out under elevated pressures, e.g., between 20 and 1000 atmospheres. 

Wunderlich, B. and Arakawa, T. Polyethylene crystallized from the melt under elevated pressure, J. Polymer Sci., Part A, 2, 3697 (1964)... 

Gogolewski, S. and Pennings, A. J. Crystallization of polyamides under elevated pressure 5 Pressure-induced crystallization from the melt and annealing of folded chain crystals of nylon-11, poly(aminoundecaneamide) under pressure, Polymer 18, 660 (1977) Stamhuis, J. E. and Pennings, A. J. Crystallization of polyamides under elevated pressure 6. Pressure-induced crystallization from the melt and annealing of folded chain crystals of nylon-12, polylaurolactam under pressure. Polymer 18, 667 (1977)... 

For dense-phase fluidization at high gas velocities and/or under elevated pressures, the bubble size may not always increase with the gas velocity. With 0.1 MPa < p <1.1 MPa (in either the bubbling or the turbulent regime), the bubble size can be empirically correlated... 

The variation of the TDH with respect to the bed diameter as well as the gas velocity is illustrated by Fig. 9.20. It shows that a higher TDH results from an increase in the gas velocity at a given D. In addition, the TDH may also increase under elevated pressures [Chan and Knowlton, 1984]. 

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