Textural and Surface Characterization of Cork-Based Sorbents for the Removal of Oil from Water

Abstract

This study evaluates the possibility of adding value to cork granulates, byproducts of cork processing, by using them as biosorbents and precursors of activated carbons. Activation was carried out by impregnation with phosphoric acid followed by pyrolysis under N2 flow. Furthermore, biosorbents were treated with a cationic surfactant and activated carbons were subject to a second pyrolysis under propene with the objective of improving hydrophobicity. Physico-chemical, textural, and surface characterization of the materials was carried out employing, among others, N2 adsorption isotherms, Fourier transform infrared (FTIR) spectroscopy, potentiometric titration, temperature programmed desorption (TPD), and immersion calorimetry. Selected samples were tested in the removal of sunflower oil emulsified in water. Activated carbons with higher surface area and lower amount of acidic surface groups showed higher uptake capacity for sunflower oil.

The role of emulsion properties and stability in vegetable oil uptake by regranulated cork sorbents

“…However, this is probably not the case in cork granules, since the hydrogen ion concentration consumed in the control and sorption assays is similar over the whole range of pH, indicating that the positive charges are used in oil droplet charge neutralization. Potentiometric titration results, shown elsewhere, reveal that uptake of hydrogen ions by regranulated cork sorbent in acidic conditions amounts to around 0.2 mmol g −1 at pH 3. Such a difference is not found between control and sorption assays in the current study, so it is assumed that the effect of sorbent protonation in O&G uptake by cork granules is negligible.…”

“…In the cork granules used for sorption, it can be assumed that all carbon is organic, since the ash content is only 1.2%. Thus the f oc corresponds to the total carbon in the solid, which has been determined to be 70.2% . Using the following relationship between the partition coefficients: …”

“…Regranulated cork is a byproduct of cork agglomerate produced inside a closed heating chamber at approximately 380 °C with injection of steam. A detailed characterization of regranulated cork granules can be found elsewhere . Refined sunflower oil was selected as representative of a refined vegetable oil and collected from a vegetable oil refinery in Portugal.…”

“…One of these projects resulted in the new line of absorbents CORKSORB, consisting of granule‐filled pillows, socks and booms for oil spill management . The success of CORKSORB elicits a deeper study on whether cork is a suitable material for oil sorption in wastewaters, following exploratory research on this matter …”

“…In this work, the application of regranulated cork sorbents, which have been considered in a previous study the most advantageous for oil removal from water from a group of eight types of cork‐derived sorbents, is studied further. In order to design successful treatment, it is necessary to understand the interactions occurring between oil droplets and sorbent particles to select operating conditions that promote sorbate–sorbent bonding.…”