Retrogradation ratio

Seiko DSC 580 with DSC 10 module heating rate 1 C min" in both the first and second runs sample mass ca 45 mg. The ratio of the heat required for regelatinization (AH2) after storage for 14 days at 5 °C to the heat required for the gelatinization (AH,) is defined as retrogradation ratio. 

Figure 8.9 Retrogradation ratio (AHj/AH,) for mass fraction 33% sweet potato starch suspension as a function of sugar concentration [5. A, sucrose , glucose O, fructose...

DSC revealed that the XG and starch did not interact synergistically and hence did not promote the formation of three-dimensional network structures. However, the hydrocolloid significantly decreased the retrogradation and syneresis of the starch paste, particularly in blends with a starch/XG ratio of 8.5/1.5. Mixing 1% or 2% tamarind XG with 9% cornstarch resulted in an increase in the paste viscosity from 385 to 460 and 560 BU (Brabender units), respectively [298]. The XG is associated with starch, as was evident from the lowering of the pasting temperature and the synergistic increase in pseudoplasticity and yield value of the blend pastes. However, carboxymethylated and hydroxypropylated XGs showed a diminished interaction. 

The culprit is the phenomenon of retrograde condensation, which wa6 previously discussed In connection with hydrocarbon dewpoints. This can best be understood by looking at a graph of equilibrium ratios, commonly called K-values, as shown in Figure 2. We have cross-plotted a limited number of curves, to avoid confusion while Illustrating our point. 

As a practical matter, when producing gas-oil ratio is above 50,000 scf/STB, the quantity of retrograde liquid in the reservoir is very small and the reservoir fluid can be treated as if it were a wet gas (defined later). 

Producing gas-oil ratios for a retrograde gas will increase after production begins when reservoir pressure falls below the dew-point pressure of the gas. 

An initial producing gas-oil ratio of 3300 to 5000 scf/STB indicates a very rich retrograde gas, one which will condense sufficient liquid to fill 35 percent or more of the reservoir volume. Even this quantity of liquid seldom will flow and normally cannot be produced. 

A reservoir containing retrograde gas has a reservoir pressure higher than the dew-point pressure of the gas as evidenced by constant producing gas-oil ratio. The gas is produced through... 

Producing gas-oil ratio from a retrograde gas reservoir is also constant during early production and then increases. When reservoir pressure is above the dew point, the gas carries a constant quantity of components which will liquefy at surface conditions. However, at reservoir pressures below the dew point some of these components condense in the reservoir. This liquid does not flow to any appreciable degree. Thus, the produced gas carries fewer condensable components to the surface and producing gas-oil ratio increases. Dew point pressure cannot be determined from a plot of pressure versus cumulative production the change in slope at the dew point is rarely apparent. 

Volatile oils and retrograde gases are produced routinely through at least three stages of separation. Thus, the calculation procedure requires three gas-liquid equilibria calculations. The equations for producing gasoil ratios are... 

Fig. 14-1. Equilibrium ratios for a retrograde gas at various temperatures and pressures. (Roland, Smith, Kaveler, Oil and Gas Journal 39, No. 46, 128, with permission.)...

Fig. 14-7. Effects of errors in equilibrium ratios on the calculated quantity of liquid of a retrograde gas at reservoir conditions. (Standing, Volumetric and Phase Behavior of Oil Field Hydrocarbon Systems, SPE, Dallas, 1951. Copyright 1951 SPE-AIME.

Figure 14-7 shows the results of calculations for a retrograde gas at reservoir conditions. Inaccuracies in the equilibrium ratios for both the lightest component, methane, and the heaviest components, represented by heptanes plus, result in drastic error in the calculated liquid volume. In fact, an error of only 8% in the equilibrium ratio for methane results in the calculation of a dew point rather than the correct liquid volume. This indicates that calculations near the dew point of a mixture are highly dependent on the accuracy with which equilibrium ratios are known. 

Fig. 14-8. Experimentally determined equilibrium ratios for a black oil (gas-oil) and a retrograde gas (gas-condensate) at 201 °F. (Hoffman, Crump, Hocott, Trans., AiME, 198, 1. Copyright 1953 SPE-AIME.)...

Figure 8.13 Effect of added sugars on retrogradation kinetics (G, AH) ofwaxy maize starch gels at a weight ratio of starch sugar water of 1.0 O.S 1.5 w/w.162...

The feed point should give the most equal slopes on both sides of the feed stage in a key ratio plot (Fig. 2,20). Too high a feed causes excessive retrograde distillation below the feed, and too low a feed causes excessive retrograde distillation above it. In order to reach the optimum feed point, the feed stage should be moved from the sharp maximum (or minimum) toward the flat one (Fig. 2.20). 

Maltodextrins (DE below 20) have compositions that reflect the nature of the starch used. This depends on the amylose/amy-lopectin ratio of the starch. A maltodextrin with DE 12 shows retrogradation in solution, producing cloudiness. A maltodextrin from waxy com at the same DE does not show retrogradation because of the higher level of a-1, 6 branches. As the DE decreases, the differences become more pronounced. A variety of maltodextrins with different functional properties, such as gel formation, can be... 

Figure 3.40 Calculated phase velocity of flexural plate waves vs ratio of plate thickness, d, to wavelength. A, for silicon nitride. Material is assumed to have the elastic properties of Si3N4 and no residual tension. The mode shapes ate illustrated at the right with a greatly enlarged vertical scale for clarity. Ellipses at left show the retrograde elliptical particle motions of the lowest S3rmmetric and antisymmetric modes for d/A = 0.03. (Reprinted with pemtission. See Ref. (621.)...

Relative permeability ratio, 168 Reservoir saturation equation, 160 ff. Retrograde phenomena, 60 ff., 75... 

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