Lourdes Calvo

Performance of the Biocompatible Surfactant Tween 80, for the Formation of Microemulsions Suitable for New Pharmaceutical Processing

The aim of this work was to investigate the phase behaviour and the structure of the n-hexane/water emulsions based on a nonionic, nontoxic and biocompatible surfactant, Tween 80. This system is of interest for new pharmaceutical techniques based on supercritical fluids to form nano- and encapsulated particles. However, it showed a lack of stability denoted by large areas of macroemulsion. For this reason, the effect of additives (alcohols and brine) and external variables (temperature) were explored. The replacement of water by brine caused negligible impact due to the nonionic character of Tween 80. On the contrary, the presence of an alcohol (ethanol or 1-butanol) enhanced the solubility of the surfactant in the oil phase and decreased the mixture viscosity, resulting in improved surface activity. Similar results were obtained by raising the temperature until the cloud point was reached (60°C). With these modifications, microemulsions at relatively low concentrations of surfactant (around 30%) and within a broad interval of compositions could be obtained, widening their possible use in pharmaceuticals manufacturing (such as controlled drug delivery, enzymatic reactions, or excipient processing). The understanding of the surfactant performance could be further used to substitute the n-hexane by a greener solvent, such as supercritical CO2.

Inactivation of Alicyclobacillus acidoterrestris spores by high pressure CO2 in apple cream

Alicyclobacillus acidoterrestris (A. acidoterrestris) is a bacillus-type spore former that causes significant alterations in fruit products. It is highly resistant to typical pasteurization regimes; thus, this work explored the use of high-pressure CO₂ (HPCD) for its deactivation in apple cream. The assays were conducted in a high-pressure apparatus where the cream was placed in an agitated vessel and the CO₂ passed over under different operating conditions for distinct periods of time. The HPCD was able to deactivate the A. acidoterrestris spores in the apple cream by four orders of magnitude at 30 °C and 10 MPa. On the other hand, the lethal effect of HPCD was independent of the thermal effect since the application of dry heat without CO₂ at the same temperature did not cause any A. acidoterrestris deactivation. The important variables in terms of improving the method were the flow regime and the way to put in contact the HPCD and the cream. Finally, the HPCD treatment did not affect the most important sensorial and rheological properties of the cream; although there was a slight reduction in the vitamin C content due to thermal degradation.

Continuous esterification or dehydration in supercritical carbon dioxide

This paper describes a study conducted on the catalytic esterification of 2-ethylhexanoic acid with 2-ethyl-1-hexanol in supercritical carbon dioxide (SC-CO2). The effect of pressure (150–250 bar), temperature (75–140 °C), flow rate of CO2 (0.36–0.72 g min−1), mole ratio of the alcohol to the acid (0.5–2), and the type of catalyst (Amberlyst® 15 as a strong solid-acid catalyst, zirconium oxide as a Lewis acid catalyst, and Novozym 435 as an enzymatic catalyst) has been evaluated. The ester, 2-ethylhexyl 2-ethylhexanoate, was continuously synthesized with 100% selectivity and 40% conversion using zirconium oxide, while the enzymatic catalysis gave no significant conversion (3%) due to acid inactivation. Amberlyst® 15 preferentially catalyzed the dehydration of 2-ethyl-1-hexanol to produce 2-ethyl-1-hexene. High temperatures favoured this reaction, so at 140 °C and 150 bar, the conversion to alkene was 99%. This catalyst was stable within the explored pressure interval. An excess of acid resulted in higher ester yield, while increasing the flow rate had no significant impact. Supercritical conditions were compared to liquid phase conditions in n-hexane. The results proved that the conversion to substrates was higher in SC-CO2, although the selectivity changed. Results were related to the solvating capacity and mass transport properties of the supercritical solvent.