Due to the COVID-19 pandemic, Jessica Maria Gomez Hernandez could not visit our facility. Instead the laboratory work was performed by Nicole Engelen and Brigit Beelen. The reporting was done by Nicole, Brigit and Koen Meesters.
The work was split in 3 phases: Sample preparation, Extraction experiments, Translation to full scale counter current installation
- Three methods were tested to increase the surface to volume ratio of the collected orange peels. The Thermomix yielded good results and the resulting material was used in the extractions.
- Extractions were performed at room temperature and at 40°C (beaker experiments) as well as at the solvent’s boiling point (Soxhlet). Extracts from the Soxhlet were used to scan light absorbance as a function of wavelength. Two peaks were found at 280 nm and 315 nm. All other samples were measured at these wavelengths as a proxy for target molecule concentration.
Five observations were important:
- Extraction was better with water and ethanol than with ethyl acetate.
- Extraction efficiency with ethanol increases with temperature, while extraction efficiency with water decreases with temperature.
- Water had a shoulder instead of a peak at 315 nm.
- Extraction took around 1-2 hours.
- Water was well absorbed by the peels (4 times dry weight).
- Based on the observations the following conclusions may be drawn for a full-scale counter current extraction situation:
The characteristic mass transfer time is around 1-2 hours. This is sufficient and could be improved by further size reduction of the peels in order to further increase the surface to volume ratio.
Water and ethanol are the preferred solvents. Water shows a high absorption to the peels. This may be a drawback as, for efficient recovery, the extract flow rate needs to be larger than the flow rate of absorbed solvent moving with the solids in opposite direction. Some target molecules will dissolve better in ethanol than in water (especially target molecules with absorption at 315 nm). For those target molecules ethanol will be the preferred solvent.
Considerable extra costs will be involved when using a toxic, flammable and expensive solvent. These costs may be overcome by a better extraction yield and lower recovery costs. Recovery costs with ethanol as a solvent may be reduced by a higher concentration of the target molecule in the extract and the lower heat capacity and heat of evaporation of ethanol compared to water. More detailed information on the target molecule behaviour will needed to decide on the optimum solvent.
The samples prepared by WFBR will be sent to the Universidad de los Andes for more detailed analysis early 2021.
Fig 1.
Extracts after Soxhlet extraction. Water, Ethyl Acetate, Ethanol (from left to right)
Fig 2.
Absorbance at 315 nm * Dilution factor of samples from batch extractions (RT = Room Temperature)
Fig 3.
Top: Pulp from orange fruit, pulp from orange peel, Bottom: juice from orange fruit and slurry from orange peel
Fig 4.
Weight increase of orange peels (due to absorption of solvent)