vegitable as a sorbent material

7/24/2019 Vegitable as a Sorbent Material

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Experimental investigation of various vegetable fibers assorbent materials for oil spills

T.R. Annunciado, T.H.D. Sydenstricker, S.C. Amico *

Department of Mechanical Engineering, Federal University of Parana(UFPR), P.O. Box 19.011, 81.531-990 Curitiba-PR, Brazil

Abstract

Oil spills are a global concern due to their environmental and economical impact. Various commercial systems have been devel-

oped to control these spills, including the use of fibers as sorbents. This research investigates the use of various vegetable fibers,

namely mixed leaves residues, mixed sawdust, sisal (Agave sisalana), coir fiber (Cocos nucifera), sponge-gourd (Luffa cylindrica)

and silk-floss as sorbent materials of crude oil. Sorption tests with crude oil were conducted in deionized and marine water media,

with and without agitation. Water uptake by the fibers was investigated by tests in dry conditions and distillation of the impregnated

sorbent. The silk-floss fiber showed a very high degree of hydrophobicity and oil sorption capacity of approximately 85 g oil/g sor-

bent (in 24 hours). Specific gravity measurements and buoyancy tests were also used to evaluate the suitability of these fibers for the

intended application.

2005 Elsevier Ltd. All rights reserved.

Keywords: Oil spill; Sorbents; Vegetable fibers; Sorption experiments; Silk floss

1. Introduction

Oil is one of the most important energy and raw mate-

rial source for synthetic polymers and chemicals world-

wide. Whenever oil is explored, transported and stored

and its derivatives are used there is risk of spillage with

the potential to cause significant environmental impact.

Pollution by petroleum oils affects sea life, economy,

tourism and leisure activities because of the coating

properties of these materials. Oil spills harm the beauty

of polluted sites, the strong odor can be felt miles awayand the excessive growth of green algae alters sea color

and the landscape.

When oil is spilled into a marine environment, it is

subject to several processes including spreading, drift-

ing, evaporation, dissolution, photolysis, biodegrada-

tion and formation of wateroil emulsions. Oil

spreading is likely to occur, especially if the sea surface

is still. In the peculiar environment of rivers, pollutants

are driven along the stream. In open seas or in harbors,

the consequences of pollutants are often severe because

of the action of local or tidal currents (Bucas and Saliot,

2002). Viscous oils spread more slowly than less viscous

ones and therefore, water temperature, along with wind

speed and sea conditions have an intense effect on the

extent of oil spreading. Spreading is important in deter-

mining the fate of spilled oil through evaporation, emul-sification and natural dispersion. Loss of volatile

fractions changes oil composition and alters its density,

pour point and flash point. Emulsification and evapora-

tion lead to a decrease in the oilwater density differ-

ence, and an increase in the oil pour-point (Reed

et al., 1999; Wei et al., 2003).

All these processes influence the choice of oil-spill

countermeasures. Nevertheless, it is essential to quickly

collect the oil after a spillage and mechanical recovery

0025-326X/$ - see front matter 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.marpolbul.2005.04.043

* Corresponding author. Fax: +55 361 3131.

E-mail address: [email protected] (S.C. Amico).

www.elsevier.com/locate/marpolbul

Marine Pollution Bulletin 50 (2005) 13401346
mailto:[email protected]:[email protected]


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by sorbents is one of the most important countermea-

sures in marine oil-spill response (Wei et al., 2003).

Two broad categories of sorption phenomena,

adsorption and absorption, can be differentiated by

the degree to which the sorbate molecule interacts with

the sorbent phase and its freedom to migrate within the

sorbent. In adsorption, solute accumulation is in generalrestrict to the surface or interface between the solution

and adsorbent. In contrast, absorption is a process in

which solute, transferred from one phase to the other,

interpenetrates the sorbent phase by at least several

nanometers. Sorption results from a variety of different

types of attractive forces between solute, solvent and

sorbent molecules. Chemical (covalent or hydrogen

bonds), electrostatic (ionion, iondipole) and physical

(Coulombic, Kiesom energy, Debye energy, London

dispersion energy) forces act together, but usually one

type prevails in a particular situation (Weber et al.,

1991).

Despite the fact that synthetic polymers as polypro-

pylene are said to represent ideal materials for marine

oil-spill recovery due to their low density, low water up-

take and excellent physical and chemical resistance,

these sorbents are not renewable and biodegradable.

Vegetable fibers are environmentally friendly materials,

with densities close to that of synthetic polymers or even

lower, and may show high oil sorption capacity at a usu-

ally low cost (Wei et al., 2003).

The aim of this work is therefore to investigate

various vegetable fibers, namely mixed leaves residues,

mixed sawdust, sisal, coir, sponge-gourd and silk-floss

fibers as potential sorbent materials for the oil sector.

2. Materials and methods

2.1. Sorbents and oil

Crude heavy-oil from offshore wells of the Campos/

Rio de JaneiroBrazil basin was supplied by Repar/

Petrobras and used in all sorption experiments. The oil

density was 25.8 API (0.90 g/cm3) and its viscosity

was 34 cp at 20 C.

Different vegetable fibrous materials were used as sor-

bents, namely, mixed leaves residues, mixed sawdust,

sisal (Agave sisalana), coir (Cocos nucifera), sponge-

gourd (Luffa cylindrica) and silk-floss (Chorisia speciosa)

fibers. The leaves residues comprised a mix of leaves

from different trees supplied by a local vegetable waste

company and were investigated as a cheap and practical

alternative when commercial sorbents are not available.

Sawdust from various wood-trees was obtained from

a local carpentry workshop. Sisal was supplied by

Cisaf-Nutrinuts/RN, coir fiber by Embrapa/CE and

sponge-gourd by Driana Cosmetic company. Silk-floss

fibers were collected from local trees.

The fibers were separately grounded for 30 min in a

knife mill (Rome) and classified in a set of ASTM sieves

(3.35 mm, 1.70 mm, 850lm, 600 lm, 425 lm, 300 lm

and 212 lm) with the aid of a mechanical sieve-shaking

device (Viatest) before sampling. The silk-floss was not

grounded due to its cotton-like nature, which impairs

this milling procedure.Specific gravity of the fibers, except silk floss, was

measured with the aid of a picnometer and hexane was

chosen as the test fluid since it did not show apparent

indication of reaction with the vegetable fibers used

and also because it was lighter than all fibers being

tested. Due to the large volume occupied by the silk-floss

fibers, their specific gravity was estimated by buoyancy

in pentane (0.62 g/cm3).

Buoyancy tests were carried out following the work

ofRibeiro et al. (2000) in order to suggest fiber suitabil-

ity as a sorbent for water spills. Degree of hydrophobic-

ity of the fibers was estimated according toRibeiro et al.

(2003), who used a heterogeneous mixture of water and

hexane, steering, drying and weighing, and correlated

the ratio of material (i.e., fiber) transferred to the organ-

ic phase as an estimation of the degree of hydrophobic-

ity (or oleophilicity) of the materials.

2.2. Sorption experiments

For the sorption experiments, crude oil was poured

into a 100-ml beaker containing 80 ml of deionized

water (pH = 7.0). After that, 0.5 g of the fibrous mate-

rial was gently and evenly placed onto the oil surface

(Fig. 1a). For the silk-floss, only 0.1 g of fiber was useddue to its bulky nature.

The amount of oil in the beaker was chosen so that

there was still plenty of oil remaining in the beaker after

completion of the sorption test. Thus, the volume of oil

used was 5 ml for all fibers except sisal and silk-floss, for

which 10 and 20 ml of oil were used, respectively, due to

their higher oil sorption.

After a certain period of time, namely, 5, 20, 40, 60

and 1440 min (24 h), the material was removed with

the aid of a nylon collector, which was then placed on

the top of a filter paper, being allowed drainage under

vacuum for 5 min before weighing. All tests were carried

out at 20 1 C and all weighing used an analytical bal-

ance (0.001 g).

The sorption was calculated as the ratio of sorbed

material to dry sorbent mass (S0), sorption = (St S0)/

S0, where St is the total mass of sorbed samples. Thus,

sorption is given in unities of g/g of dry sorbent, being

the sorbent the various vegetable fibers used.

For each type of fiber, between 3 and 5 independent

sorption experiments were carried out. This tech-

nique, although of a simple nature, is expected to give

reliable results, with low standard deviation on the

measurements.

T.R. Annunciado et al. / Marine Pollution Bulletin 50 (2005) 13401346 1341


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Other sorption conditions were experimentally simu-

lated: (i) dynamic system (Fig. 1b): some tests were car-

ried out under constant steering (approximately

500 rpm) in an isothermal magnetic stirrer (Sciencetool)

and (ii) marine conditions: these tests followed the same

methodology above mentioned except for the fact that a

substitute ocean water, produced according to ASTM

D1141-90, was used instead of the deionized water.

Further tests were conducted to evaluate water up-

take by the fibers. These were divided into: (i) dry system

(Fig. 1c), following the same methodology above except

for the fact that oil was poured into a beaker with no

water in it and (ii) evaluation of water by distillation

of the sorbent after sorption, according to ASTM

D95-83.

3. Results and discussion

The mean specific gravity of the fibers is shown in

Table 1. It can be seen that sisal, the leaves residues,

sawdust and coir fiber are heavier than water, whereas

sponge gourd and silk-floss are lighter. Sisal and the

leaves residues are particularly heavy and this may influ-

ence their performance on the sorption test, which de-

pends on their buoyancy in water, especially for the

static system.

Fig. 2shows a histogram with the results of the clas-

sification of the grounded fibers where it can be seen that

different fibers showed variable length dispersion. The

granulometry range 1.700.850 mm obtained the largest

percentage of grounded fibers for leaves residues, sponge

gourd and sawdust, and also obtained enough of the

other two fibers (sisal and coir fiber) for the experiments.

Therefore, this was the granulometry range chosen as

the standard one, being used in the sorption tests. Nev-

ertheless, preliminary sorption tests were carried out to

investigate the effect of granulometry on sorption.

Table 2 shows the findings of such tests conducted for

60 min, where one can notice that a reduction of fiber

Fig. 1. Different sorption systems used in tests carried out at room temperature just after fiber placement on the oil surface: (a) static system,

(b) dynamic system and (c) dry system.

Fig. 2. Histogram of the granulometry distribution of the differentgrounded fibers.

Table 2

Oil sorption of the various fibers at different granulometry ranges

Fiber >3.35 mm

(g/g sorbent)

0.851.70 mm

(g/g sorbent)

Sorption

increase (%)

Sisal 3.0 6.4 113

Leaves residues 1.4 2.7 93

Sawdust 4.1 6.4 56

Coir fiber 1.8 5.4 200

Sponge gourd 1.9 4.6 142

Table 1

Specific gravity of the different fibers

Fiber Specific gravity (g/cm3) Standard deviation

Sisala 1.26

Leaves residues 1.16 0.04

Sawdust 1.07 0.03

Coir fiber 1.01 0.02

Sponge gourdb 0.92 0.05

Silk-floss


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granulometry, from greater than 3.35 mm to 0.85

1.70 mm, is responsible for an increase in sorption that

may reach 205%. Thus, these tests have confirmed the

importance of controlling granulometry when compar-

ing the results for different fibers and also that sorption

is indeed very dependent on the availability of surface

area per gram of sorbent, as reported by Shukla et al.(2002).

Fig. 3 shows the results of the sorption tests for the

static system and, as expected, sorption increases with

the sorption period, from 5 to 1440 min. Sorption capac-

ity followed the general trend: silk-floss > sisal > saw-

dust > coir fiber > sponge gourd > leaves residues.

Fig. 4 shows the results of the sorption tests for the

dynamic system, where the same features mentioned

above are seen, namely, (a) a continuously higher sorp-

tion for all fibers as the sorption time increases, (b) the

sorption capacity of the fibers followed the general

trend: silk-floss > sisal > sawdust > coir fiber > sponge

gourd > leaves residues and (c) a much larger sorption

for the silk-floss. The very low sorption capacity of the

leaves residues suggests that they may only be indicated

as a cheap low-performance alternative, in case a more

efficient sorbent is not available.

Not all weight gain shown inFigs. 3 and 4refers to oil

sorption, since water is also incorporated into the fibersto an extent dependent on the particular fiber. Table 3

shows the evaluation of water uptake for the silk-floss

fiber. Comparison of sorption results for the static

(water + oil) system (column B) and the dry (oil only)

system (column A) suggests that water uptake varied be-

tween 2.5% and 6.3% of the total sorbed mass (column

C). However, this method will give accurate results only

if the kinetics of oil sorption of these two systems is com-

parable and any other influencing factor is constant and

due to these drawbacks, a distillation technique was also

used to check these findings. In fact, a narrower range of

results was obtained with distillation (column D), with

water uptake in the range of 3.14.1%. Besides, due to

the small differences found in column D ofTable 3,with-

in the experimental error, no particular trend regarding

the variation of water uptake with time was identified.

Table 3also suggests that direct comparison of exper-

imental results obtained in different systems may incur

in misleading findings. Column E (sorption in the dy-

namic system) has given lower values than column A

(oil sorption in the dry system) for up to 60 min sorp-

tion time. This may have happened because the fre-

quent waterfiber contact, a consequence of agitation,

decreases sorption rate in such a way that even the

combined sorption of oil and water is not sufficient toequal the absorption of oil in the dry system, being this

an indication of the hydrophobicity of the silk-floss. The

dynamic system, therefore, has ratified the need to use

the distillation technique, which has given water uptake

values (column F) in the range of 2.73.5%, in the same

range as that for the static system.

Lee et al. (1999)reported a considerable reduction in

oil sorption when water and severe agitation (with an

orbital shaker) is present during sorption; a reduction

from 30.62 to 8.07 g diesel oil/g sorbent (74% reduction)

was obtained for natural cotton. In this work, the mea-

sured oil sorption reduction was less important, around

7%, possibly due to the significantly less severe agitation,

higher hyrophobicity of the silk-floss, and also because

in the work of Lee, the relationship between water and

oil was 250/20 whereas in this work this relationship

was 80/20.

Another interesting finding of Figs. 3 and 4 regards

the kinetics of sorption. Fibers such as sisal and silk-

floss in both systems, static and dynamic, sorb more

than 80% of their 24-h (1440 min) capacity in just

5 min. Besides, except for sisal that is of more difficult

packing into the beaker, the dynamic system was in gen-

eral responsible for retarding sorption.Fig. 4. Sorption of the different fibers at various sorption times

dynamic system.

Fig. 3. Sorption of the different fibers at various sorption timesstatic

system.



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A straightforward, quantitative comparison between

oil sorption in the static and dynamic systems, however,

needs to consider a combination of factors, such as

waterfiber and oilfiber contact, buoyancy, hydropho-

bicity, accessibility of dry fibers to oil once the first

layers of fibers become wet, kinetics of water and oil

sorption, sorption capacity and time necessary to

achieve equilibrium. The net result of these factors

is dependent on a particular fiber and therefore of diffi-

cult general prediction. A more detailed analysis into

these aspects will be given below for the silk-floss.

Considering that the water uptake for the silk-floss is

minimum and independent on sorption time and agita-

tion, all systems should approach a similar oil sorption

value upon equilibrium. Fig. 5 shows the sorption

evolution with time for the three systems. The static sys-

tem shows higher sorption than the dry system due to

the combined oil and water uptake. If the mean water

uptake of 3.5% (average of column D inTable 3) is sub-tracted from each point, a new curve is built (Static sys-

tem minus water curve inFig. 5) which is very similar to

the dry system especially for longer sorption period. For

the dynamic system a different scenario is seen. The dy-

namic system curve is below the dry system one for most

of the time, meaning that the sorption kinetics is dis-

turbed by the agitation, that favors waterfiber contact

and consequently delays oil sorption, and only on the

long-run oil sorption is able to approach the expected

value. One could expect that since there is more

waterfiber contact, more water would be driven to

the sorbent, but this is not verified, suggesting that the

fiber has a hydrophobic nature. Nonetheless, once the

water-share of the sorption (3.0%average of column

F inTable 3) is subtracted from the total sorption, the

data (dynamic system minus water curve in Fig. 5)

approach that of the dry system in the long-term.

In all, irrespective of the sorption conditions, the 24-h

oil sorption of the silk-floss reached approximately

85 g oil/g sorbent. This sorption capacity is much higher

than those reported in the literature for other vegetable

fibers.Witka-Jezewska et al. (2003)showed sorption val-

ues from different authors and a maximum of 40 g oil/g

sorbent for unscoured cotton. Saito et al. (2003) re-

ported a maximum of 16.5 g oil/g sorbent for Sugi Bark.

Lee et al. (1999) reported around 78 g diesel oil/g of

ground, refined or extracted Kenaf core and bast,

whereas natural cotton showed a much higher sorption,reaching 30 g diesel oil/g sorbent. Ribeiro et al. (2003)

has found 11.6 g oil/g sorbent for salvinia sp. (mostly

leaves) with a 237 cp oil (Marlin). This author has also

reported 2.7 g oil/g peat sorb (


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Preliminary evaluation of water uptake as shown in

column C ofTable 3 for silk-floss, has been also used

for the other fibers and the results are shown in Table

4.It can be seen that water uptake vary in a wide range

for the various fibers. Sponge gourd and coir fibers have

shown the highest water uptake (4251%), whereas sisal,

leaves residues and sawdust have shown intermediatevalues (2133%). These values are in the same range as

those reported by Pasila (2004) for the separation of

oil from a mixture of deionized water and lubricating

or fuel oil, around 3056% water content and 2353%

water content for filters composed of flax and hemp

fibers, respectively.

However, differently from the other fibers, silk-floss

showed extremely low water uptake. This low water up-

take and the lower oil sorption in the dynamic system

may be partially explained by a high hydrophobicity.

Table 4 shows the hydrophobicity of all fibers and in

fact silk-floss showed values around 98%, along with

the leaves residues. An opposite behavior was shown

by sisal and sponge gourd with 0.0% hydrophobicity

according to the methodology used, whereas sawdust

and coir fibers showed intermediate values.

Fig. 6 shows the results for the static and dynamic

systems when artificial marine water was used. In gen-

eral, the simulation of a marine environment did not

compromise sorption capacity and since the values were

within the estimated experimental error, no particular

trend was identified. The silk-floss showed the best sorp-

tion capacity in all situations compared to the other

fibers and also a similar sorption capacity in any simu-

lated environment, suggesting that it may be used in

any case of spill control with similar oil removal

efficiency.

The results of the buoyancy tests are shown inTable

5. Silk-floss, with 100% buoyancy for all simulated

experimental conditions, showed the opposite behavior

of sisal, with 0% buoyancy. The results of the dynamic

system were higher than the respective ones for the static

system and, as expected, all fibers showed higher buoy-

ancy under marine condition in comparison to the

deionized water. Coir fiber, with a specific gravity of

1.01 g/cm3, largely benefits from the small increase in

density of the marine water (1.024 g/cm3

) in comparisonto the deionized one (0.998 g/cm3), showing an increase

from 20.6% to 90.0% and 49.9% to 98.0% for the static

and dynamic systems, respectively.Table 5clearly indi-

cates the inability of sisal, sponge gourd and sawdust to

be used in any water oil-spill conditions due to their low

buoyancy, whereas the leaves residues and the coir fiber

may be used in marine environments.

4. Conclusions

The use of different vegetable fibers as sorbents of

crude oil was investigated in various simulated condi-

tions, deionized and marine water, with and without

agitation.

The sorption capacity of the fibers followed the

general trend: silk-floss > sisal and sawdust > coir

fiber > sponge gourd > leaves residues and the sorption

capacity may be further increased by reducing

granulometry.

The silk-floss showed a rapid oil sorption and a very

high sorption capacity of approximately 85 g oil/g

sorbent (in 24 h), high degree of hydrophobicity and

low water uptake. The sorption capacity was aroundFig. 6. Sorption of the different fibers for a 60-min sorption period:

static and dynamic system and deionized and salty water environment.

Table 4

Water uptake of the various fibers and their degree of hydrophobicity

in different water conditions

Fiber Water uptake (%) Hydrophobicity

Deionizedwater (%)

Marinewater (%)

Sisal 2731 0.0 0.0

Leaves residues 2333 86.9 99.3

Sawdust 2127 56.5 87.9

Coir fiber 4245 38.6 77.7

Sponge gourd 5051 0.0 0.0

Silk-floss 2.55.0 97.6 98.2

Table 5

Buoyancy of the various fibers under different conditions

Fiber Static system Dynamic system

Deionized

(%)

Marine

(%)

Deionized

(%)

Marine

(%)

Sisal 0.0 0.0 0.0 0.0

Leaves residues 65.5 75.3 85.6 95.0Sawdust 12.4 16.0 17.7 22.9

Coir fiber 20.6 90.0 49.9 98.0

Sponge gourd 3.4 3.9 3.4 8.1

Silk-floss 100.0 100.0 100.0 100.0



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8.512 times that of two commercial products composed

of peat sorb.

Several of the low-cost vegetable fibers investigated

may be used in dry environments, with variable sorption

capacity. On the other hand, buoyancy tests indicated

the inability of sisal, sponge gourd and sawdust to be

used in any water oil-spill conditions, whereas the leavesresidues and the coir fiber may be adequate for marine

environments.

Acknowledgement

The authors would like to thank PRH-24/ANP/

MCT, Repar/Petrobras, Driana buchas, Embrapa and

Cisaf-Nutrinuts for their support.

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vegitable as a sorbent material

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