Scaling-Up Of SFEE, Identification Of Process Parameters On Product Characteristics And Economic Impact

A scaled-up SFEE equipment (Fig 1) was designed and used for producing sufficient amount of aqueous suspensions for PGSS-drying treatment. Using PGSS-drying water content of aqueous suspensions was extracted, and hence long-term stability of product was increased, without irreversible change on its morphology. The scaled-up SFEE equipment consists of an electrically tempered extractor vessel with a micrometric valve on its outlet position, to maintain a controlled continuous scCO2 flow, bubbling through the initially against pressure injected emulsion, throughout the whole treatment time. Emulsion was also stirred, using a magnetic stirrer with a mixing rate of 300 rpm. Due to the usegae of a continuous CO2 flow, the methodology of the process was changed from to batch to semi-continuous, and upon applying a significantly shorter treatment time – comparing to batch process –, a higher amount of suspension is obtained.

Fig 1: Scaled-up SFEE semi-continuous process

Dimensions of extractor vessel – compared to batch extractor vessel – was increased according to detail, presented on Fig 2. The Scaling-up factor was the ratio of the height- and the diameter of the o/w emulsion filled into the extractor vessel. This ratio was chose keeping considered, that the contact speed of scCO2 – o/w emulsion as a key factor of SFEE process, and the speed of the evaporation of EtAc contained scCO2, mainly depends on the available free surface area of the emulsion. This means, height of the emulsion column is limited by its diameter, as free surface area. Contact area of scCO2 – emulsion was increased by the perforation of the CO2 inlet tube in several axial positions, along the whole emulsion column. Value of scaling-up ratio was kept at approximate at 0.8, and theoretically treatable volume of o/w emulsion increased from 25 to 196 mL.

Fig 2: Dimensions of extractor vessel in batch and scaled-up device

Regarding economic impact and product characteristics the consumption of CO2, the density of CO2 and process duration are identified as main process parameters. All these factors are characterizing the demand of CO2, which is the most important factor on product characteristics and process economy regarding thermo-economic indicators. To obtain high value product on lowest possible cost: maximum consumed CO2 / L of emulsion is 5.5; applied slightly above its supercritical point, and with a maximum treatment time of 90 min.

Gyorgy Levai

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