A fully automated workstation has been developed and applied to the measurement of liquid−liquid
equilibrium. The measurements, starting from solution preparations through equilibrium establishment
and chemical analysis of both phases and ending with the determined solute concentration in both phases,
can be done on a 24 h per day basis with no human intervention at all. To evaluate the accuracy of the
measurements, the equilibrium distribution ratios of acetone between toluene and water at 20 °C and of
caprolactam between toluene and water at 40 °C and between benzene and water at 20 °C are measured
and the results are compared with the values reported in the literature and, for the caprolactam systems,
also with those obtained in a jacketed equilibrium cell. Furthermore, the distribution ratio of caprolactam
between toluene and water has been measured several times for the same initial caprolactam mass fraction
in order to evaluate the repeatability. The obtained results are in very good agreement with the literature
values for the acetone system and with those measured in the glass cell for the caprolactam systems,
while a coefficient of variation of 1.8% for a seven times repeated measurement was found.
Several aqueous salt solutions are evaluated as reactive extraction solvents for the recovery of
aldehydes and ketones, present in few-percent concentrations in apolar hydrocarbons. The
influence of the type (amino, hydrazine, or bisulfite) and structure of the salt on the extraction
performance toward aromatic and linear aliphatic aldehydes, as well as toward cycloaliphatic
and linear aliphatic ketones, was analyzed. The results show that some of the aqueous salt
solutions enable distribution ratios of carbonyl as high as 300, which are much higher than the
values obtained in most conventional solvents. We observed that bisulfite and hydrazine salt
solutions have much higher capacities than solutions of amine salts. Furthermore, the presence
of a carboxylic group instead of a sulfonic group, but also a larger distance of the acidic group
from the reacting amino center, makes an amine a better extractant. Generally, it was noticed
that the extractability using aqueous salt solutions decreases in the order linear aldehyde >
aromatic aldehyde > cyclic ketone > linear ketones. Most of the evaluated salt solutions showed
a decrease in the carbonyl distribution ratio with increasing temperature, indicating that a
temperature shift might be a feasible option for reextraction. The losses of organic solvent in
extract or water in raffinate are not significantly influenced by the presence of salt. Therefore,
aqueous salt solutions show great potential to be used as reactive extraction solvents for the
recovery of carbonyl compounds from apolar organic solvents.
Oxygenates like carboxylic acids, aldehydes/ketons and alcohols are often present in less than 10 wt-% concentrations in apolar organic solvents from which they are industrially recovered by a highly energy-consuming distillation process. Depending on their concentration a reduction in operational costs between 40 and 85% may be achieved by using reactive extraction with aqueous salt solutions whereas water is environmentally friendly, practically immiscible in any apolar organic solvent, and not-contaminating the system. The poor capacity of pure water can be significantly increased by the introduction of an environmentally and toxicologically benign salt if it could selectively react with the oxygenate, modifying it into a charged compound. This interaction should be reversible to assure regeneration.For the recovery of aldehydes and ketons, hydrogen sulphite and hydrazine salt solutions give distribution ratios of carbonyl compounds like benzaldehyde as high as 300. This is orders of magnitude higher than obtained for most conventional solvents. These salt solutions show a significant decrease in the carbonyl distribution ratio with increasing temperature, indicating that a temperature shift might be a feasible option for back-recovery.For the reactive extraction of carboxylic acids a combination of using an aqueous solution of sodium hydrogen carbonate for the forward extraction, and carbon dioxide under pressure for the backrecovery by new phase (liquid or solid) formation or by back-extraction due to a pH-shift was observed to be feasible.For the reactive extraction of alcohols only a few extractants were able to achieve a slight improvement of the distribution ratio of alcohol relative to pure water. A second approach, in which the alcohol is modified prior to the extraction into a monoester which subsequently is reactively extracted with an aqueous solution of sodium hydrogen carbonate, can provide a 100-fold increase in the distribution ratio of benzyl alcohol. It is found that backrecovery of the extracted alcohol can be performed by back-extraction in combination with a spontaneous hydrolysis. The rate of hydrolysis can be efficiently controlled by temperature.The reactive recovery of benzaldehyde is feasible in a pilot plant pulsed disc and doughnut column and was found to be 99.9 % using an aqueous solution of sodium hydrogen sulphite. No extraction was found in the absence of this salt.
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