3.5.3. Influence of process variables on the HETP
The influence of process design variables such as solvent-toliquid
ratio, liquid load, and reflux ratio are of especial interest
for the scale-up of countercurrent column operating with external
reflux. Fig. 19 illustrates the influence of the solvent-to-liquid
ratio on the HETP values at 373K and pressures between 26 and
29 MPa for the separation palmitic/(oleic + linoleic) acids from palm
fatty acid mixtures. The HETP values increase as the solvent-toliquid
ratio increases. The lower the number of stages, the higher
the HETP values, as the height of the extraction column remains
constant. Higher solvent-to-liquid ratios lead to smaller residence
time and back mixing and this has a negative effect over the mass transfer. Fig. 19 shows the HETP values increase in a linear
fashion with increasing solvent-to-feed ratio. Since the column
internal diameter is proportional to the solvent-to-liquid ratio, it
is, therefore, possible to conclude that the HETP can scaled as a
linear function of the column internal diameter. The HETP values
decreases as the system pressure increases. This is due not only to
an increase in the separation factor of the pseudo-binary mixture
saturated/unsaturated fatty acids but also a decrease in the liquid
phase viscosity with increasing pressure.
3.5.3. Influence of process variables on the HETPThe influence of process design variables such as solvent-toliquidratio, liquid load, and reflux ratio are of especial interestfor the scale-up of countercurrent column operating with externalreflux. Fig. 19 illustrates the influence of the solvent-to-liquidratio on the HETP values at 373K and pressures between 26 and29 MPa for the separation palmitic/(oleic + linoleic) acids from palmfatty acid mixtures. The HETP values increase as the solvent-toliquidratio increases. The lower the number of stages, the higherthe HETP values, as the height of the extraction column remainsconstant. Higher solvent-to-liquid ratios lead to smaller residencetime and back mixing and this has a negative effect over the mass transfer. Fig. 19 shows the HETP values increase in a linearfashion with increasing solvent-to-feed ratio. Since the columninternal diameter is proportional to the solvent-to-liquid ratio, itis, therefore, possible to conclude that the HETP can scaled as alinear function of the column internal diameter. The HETP valuesdecreases as the system pressure increases. This is due not only toan increase in the separation factor of the pseudo-binary mixturesaturated/unsaturated fatty acids but also a decrease in the liquidphase viscosity with increasing pressure.
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