Characterization of Physicochemical Properties and Process Design for Oil Removal using Ceiba pentandra (L.) Gaertn. as a Natural Sorbent

Ceiba pentandra (L.) Gaertn (Kapok) is a natural sorbent that exhibits
excellent hydrophobic-oleophilic characteristics. The physicochemical properties of
kapok fibre as oil sorbent were characterized. The effect of packing density and the
experimental oil types on the oil sorption characteristics of kapok were studied in a
batch system. Oil sorption capacity, percentage of dynamic oil retention, oil
entrapment stability, packing height reduction, saturation time and kapok reusability
were evaluated. Continuous packed-bed column was developed to examine the
optimum conditions, in terms of flow rates and packing density for the diesel-water
filtration. Chloroform and alkali treatment were employed to investigate the stability
of hollow structure and waxy layer on the kapok surface and their roles in oil sorption.
Based on SEM, OM and FTIR analyses, kapok fibre was shown to be a
lignocellulosic material with hydrophobic waxy coating that covered the hollow
structures. The waxy coatings enhance the oil penetration inside the kapok structure
and the presence of the hollow structure provide ample interstitial network for oil
entrapment. Higher packing density showed lower sorption capacity, but higher
percentage of dynamic oil retention, with 1% of oil drained out from the test cell at
0.08 g/cm3. The percentage of dynamic oil retention was in the decreasing order of:
used engine oil, new engine oil and Diesel. At higher packing density and higher oil
viscosities, kapok exhibited higher saturation but lower bed height reduction. Using
diesel oil as the experimental liquid, only 30% of oil sorption capacity reduction was
observed even after fifteen cycles of reuse at 0.04 g/cm3 packing density. Oil
entrapment inside the packing was stable even after 30 min of shaking inside a
horizontal shaker, with more than 90% of diesel and used-engine oil retained inside
the assembly of 0.08 g/cm3 kapok.
A packed-bed column was constructed to study the performance of kapok
filter for oily water filtration. Statistical analyses suggest that none of the factors
significantly affected the percentage of COD reduction, but the interaction between
packing density and flow rate significantly affected the percentage of turbidity
reduction. However, about 99% COD reductions were observed for all kapok filters at
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different packing densities and flow rate. About 97% turbidity reduction was observed
for kapok at 0.08 g/cm3 and 0.5 L/h flow rate. The excellent turbidity reduction could
be due to the stronger interaction of kapok with oil which can break down oil-water
emulsion.
After 8 hours of chloroform and alkali treatment, kapok fibres had lower oil
sorption capacity, with 2.1 % and 26.3 % reduction, as compared to the raw kapok.
SEM image analyses, in comparison to untreated kapok, showed no major structural
difference after chloroform treatment, but major structural disruption to flattened-like
structure was observed with alkali treatment. These results imply that kapok fibre had
stable hollow structure and wax layer attachment on the kapok surface, and it takes
extreme conditions as that employed with alkali treatment to make any significant
changes. Based on these, the Malaysian kapok indeed has shown great potential as oil
sorbent, in terms of high sorption and retention capacity, structural stability, high
reusability and high COD and turbidity reduction capability.