Linear alylbenzene sulphonates (la ss)

PHYSICO-CHEMICAL CHARACTERISTICS AND DISTRIBUTION OF LINEAR ALKYLBENZENE

SULPHONATES (LASs) SURFACTANTS IN EL-MEX BAY, ALEXANDRIA-EGYPT

THESISPresented to graduate school

Faculty of Science, Alexandria UniversityIn Partial Fulfillment of the Requirements for the Degree

Of

Master ScienceIn

Physical Chemistry

Introduced By

Mohamed Nazeih Mohamed Gamal

Supervised By

Prof. Dr. Abd El-Monum M. AhmedProfessor of Physical Chemistry

Faculty of Science, Alexandria University

Prof. Dr. Mohamed Abd El-Aziz OkbahProfessor of Marine Chemistry

National Institute of Oceanography and Fisheries (NIOF)

Chemistry of LAS

LAS are the most popularly used anionic surfactants.

Lab Synthesis

Positional isomerism (26 isomer).

LAS unimers in solution tend to form aggregates (micelles), which gives its excellent detergency and solubilisation properties.

Chemistry of LAS

Micelle in aqueous solution

Concentration at which micelles start to form is called the critical

micelle concentration (CMC).

Synthesis of LAS

LAS was first commercialized in the early 1960s as a replacement for the poorly biodegradable branched alkylbenzene sulphonates (ABS), which caused persistent foam in WWTP, streams and rivers.

SO3- SO3

-

(a)-LAS (b)-ABS

LAB are synthetic compounds used as precursors for the manufacture of LAS, is derived exclusively from petroleum derivatives: benzene and linear paraffins

Synthesis of LAS

Pe

tro

che

mic

al p

lan

ts

De

terg

ent

pla

nts

Processes Steps in LAB – LAS Production

LAS Usage & Production

• LAS currently represents one-third of active ingredients in detergent and cleaning preparations worldwide.

• Virtually all LAB transformed into LAS.

• In 2003, global LAB capacity was 3 million tons/year.

LAS Usage & Production

Production and Consumption scenario in Europe 2000

SurveyTotalHousehold

ECOSOL400 kton330 kton

>80%

Production and Consumption scenario in Egypt

Egypt has obtained complete funding and started detailed feasibility studies for three projects that form part of its petrochemicals master plan for 15 M tone/y petrochemicals by 2021.

Tenders for detailed study will be sent out in 2003 for an 80,000 tones/y LAB plant and it is expected to increase in 2007 after the start up of ELAB project in Alexandria City which is the greatest LAB production project in Middle East region.

Monitoring Studies

Several monitoring studies on LAS in the environment are available

Surface Water

Ground Water

Seawaters

Sludge (WWTP)

Soils

Sediments

Fate of LAS in Environment

Biodegradation

Bioaccumulation

Precipitation

Adsorption

Biodegradation

Biodegradation is a most important mechanism for the total removal of chemicals from the environment

RDS

Dieaway Test

Analysis

QSAR

Biodegradation

Factors affect on LAS Biodegradation

Origin of bacterial culture Temperature

Structure of LAS

DO

Anaerobic Biodegradation

Few studies

Anaerobic proceeded after a period of aerobic exposure

Long t1/2 and no significant difference as a function of alkyl chain length

Bioaccumulation

Bioaccumulation The net result of the uptake, distribution, and elimination of a substance in an organism due to water-borne exposure

BCF Fish TypeReferences

108-280Bluegill sunfishMaki et al 1980

173-245Fathead minnowKimerle et al

1975

231Zebra fishCoenen 1988

Some Fish BCF Values For C12- LAS

Some Fish BCF Values For C12- LAS Hydrophobicity has been

identified as the driving force for bioconcentration.

The longer the alkyl chain the higher are the hydrophobicity and the bioconcentration factor (BCF).

LAS

Uptake/depurationperiod

BCF

C10-2 168-192 h/96 h6.0

C11-2 168-192 h/96 h31.9

C12-2168-192 h/96 h99.1 – 211.5

C13-2168-192 h/96 h987.2

C11-5168-192 h/96 h6.1 – 9.8

C12-5168-192 h/96 h10.0

C13-5168-192 h/96 h34

C12-6168-192 h/96 h31.9

Whole body BCF values in fathead minnow ( Pimephales promelas )

Bioaccumulation

LAS Precipitation

LAS + Ca2+ Ca (LAS)2

LAS biodegradation, precipitation and adsorption enhance its elimination from water column and consequently decrease of the bioavailability for aquatic organisms, and consequently a toxicity reduction.

Considering the solubility product of the calcium-LAS salts, this effect can be neglect for the lower LAS homologues but can contribute to the removal from the aqueous medium of the longer LAS homologues (C12-C14 LAS) at high water hardness

LAS sorption on sludge and sediment particles can be facilitated in hard water

Area of Study

El-Mex Bay

El-Mex District is an industrial zone west of Alexandria City. As a consequence of growing heavy industries (petrochemicals, pulp metal planting, industrial dyes, textiles) and the uncontrolled disposal of the resulting waste, costal water of El-Mex Bay receives huge amounts of untreated industrial wastes (Fe, Mn, Cu, Zn, Cd, Pb and Ni) as revealed by sediment analysis and water analysis 0

West of Alexandria (29º 50´ E & 31º 10´ N).

Elliptical in shape.

El-Mex Bay

Extends for about 15 km from El-Agmy headland to WH and from the shoreline seaward to a depth 20 m

Surface area about 19.4 km2 and its volume 190*106 m3

Area of Study (El-Mex Bay)

El-Mex Bay represents a good model for the environmental exposure for different types of pollutants

El-Mex Bay receives a heavy load of waste water (2.4 x 109 m3/year).

Directly to the sea from industrial outfalls

Indirectly from Lake Maryout via El-Mex Pumping Station

The industrial area in the southern part of the Alexandria city disposes of its waste water directly into Lake Maryout (2 x 105 m3/d).

Lake Maryout itself is connected to the sea from the west at El-Mex Bay

The eastern part of the bay receives brackish water (90.000 m3/day) from the Nubaria Canal loaded with tanneries wastes through WH outlets

Cement factory & Shipping activities


Water sampling


Sediment Sampling

LAS Analysis using RP-HPLC

Sorption Experiments

1/2

1/2

Material and Methods

Hydrographic & Hydrochemical Parameters

Temperature

Hydrogen ion concentration

Dissolved oxygen

Oxidizable organic matter

Salinity

Physical Parameters

Total hardness

Calcium hardness

Alkalinity

Total dissolved solids

Chemical Parameters of sediments

Calcium carbonates

Organic carbon content

Redox potential

Determination of LAS in sea water

The method based on the reaction between linear alkylbenzene sulphonates (LAS), as anionic surfactants, and methylene blue (MB), as cationic dye, to form associated ion-pair (LAS-MB ion pair) in water with 1:1 molar ratio which can be easily extracted to the organic phase (chloroform, CHCl3).

R SO3-

S

N

N(CH3)2(CH3)2N

+

R SO3

S

N

N(CH3)2(CH3)2N

LAS MB

LAS-MB ion pair

CHCl3


Determination of LAS in sea water

Aqueous Phase (H2O)

LAS (H2O) + MB (H2O) LAS-MB (H2O)

Equilibrium scheme of LAS and MB in water and chloroform (organic) phases.

LAS (CHCl3) + MB (CHCl3) LAS-MB (CHCl3)

Organic Phase (CHCl3)


Determination of LAS in Sediment Samples

Both HPLC and GC techniques have been used to measure alkylbenzene sulphonates in environmental samples. Both HPLC and GC techniques have been used to measure alkylbenzene sulphonates in environmental samples.


Flow chart of HPLC determination of LAS

Sediment sample

20% NaOH (w/w)

CH3OH extraction

Evaporation

DilutionCH3OH / H2O (30:70)HCl (pH 4-7)

C18 column1. CH3OH / H2O (30:70)2. CH3OH elution

one discard

Two eluate

RP-HPLC Recorder Integrator


Distribution of LAS in El-Mex Bay Waters

Results

0.000

0.050

0.100

0.150

0.200

0.250

1 2 3 4 5 6 7 8

station

LA

S (

ppm

)

surface (S)

bottom (B)

Regional variation of LAS (ppm) average values at surface (S) and bottom (B) layers of El-Mex Bay during investigation period of study.

0.24 mg LAS/l(4.17‰)

(1.87 mgO2/l)

0.15 mg LAS/l(4.36‰)

(1.31 mgO2/l)

0.14 mg LAS/l

0.05 mg LAS/l

S=0.07 mg LAS/l

B=0.06 mg LAS/l

Results

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

Apr-

05

May-0

5

Jun-0

5

Jul-

05

Aug

-05

Sep-0

5

Oct-

05

Nov

-05

Dec-0

5

Jan-0

6

Feb-0

6

Mar-

06

season

LA

S (

ppm

)

surface (S)

bottom (B)

Spring season

Summer seasonAutumn season

Winter season

Seasonal variation of LAS (ppm) average values at surface and bottom (B) layers of El-Mex Bay during investigation period of study.

Vertical profile in water column LAS concentration in surface water was higher than the bottom water at all stations and seasons


Discussion

Station 1 was selected to check for El-Umum Drain contribution, as water enters the bay

The high LAS content at stations 1 & 2 & 5 is attributed to the presence of these stations located at El-Umum Drain (station 1) and in the vicinity of the drain which discharge its waste water into the coastal area.

Station 3 had the lowest LAS concentration at both surface and bottom water due to

station 3 was situated away from El-Umum Drain at the entrances of the bay.

Situated away from land sources (off-shore)

affected by the open sea water reflecting the lower values


The spread of the wastewater in the bay was investigated by studying the distribution of LAS at surface and bottom layers during investigation period of survey as a function of distance from El-Umum Drain point of discharge, considered as zero characteristics of the brackish compartment (depth; 0.5 m, salinities > 10‰) and marine compartment (depth; 15 m, salinities < 30‰) of the bay.

Discussion

The concentration of surfactants dropped rapidly with distance from the point of discharge. conclusion

The distribution of LAS residues in El-Mex Bay water column is characterized by pronounced maxima at the brackish water-sea water interface.


Discussion

The discharge affects not only the near shore stations but also reached the off-shore stations and stations away from the point of sewage discharge with low concentrations and that detergents are not degraded so fast during transportation as it affects the water off-shore stations.

Conclusion It may point to the possible use of detergents as tracers for pollution in the Mediterranean Sea

It may also performed to gain insight into the question of whether these compounds are present in marine ecosystem.

This stresses the need to introduce better waste water treatment facilities in Alexandria City.


Discussion

The decrease in LAS concentration with the distance from the source of contamination was faster than that predicted based on dilution only. It is anticipated that removal mechanisms from the seawater column include biodegradation, sorption to suspended solids and sediments, and precipitation with divalent cations

It is observed that the summer had the highest concentrations at both surface (0.13 mg LAS/l) and bottom (0.06 mg LAS/l) layers which are predicted of adverse effect due to increasing in water temperature of summer season which lead to more efficient degradation during the summer because, temperature was found to have a decisive effect on the degradation rate.


Discussion

Vertical

Profile

Generally most of the surface water samples, LAS concentrations was higher than in the bottom water at all stations and seasons

That surfactants nature of LAS results in the tendency for it to accumulate first on the surface of the aqueous medium (air-seawater interface) into which it is discharged and accompany the lighter water which floats at the surface

The degradation improves when it occurs at salinity value closest to the initial value of the water sediment (high salinity) where in 38.50-40.50‰ range.


Discussion

Effect of salinity Effect of TH Effect of DO

Extent of mixing of seawater in the bay with

sewage discharge

Extent of mixing of seawater in the bay with

sewage discharge

r = -0.78

Sewage discharge containing LAS

Strong sedimentation & biodegradation

r = -0.67

Strong precipitation of LAS as Ca(LAS)2 when

Ca2+ concentration increases & seems to promote cooperative

sorption at high LAS and Ca2+ concentrations

r = -0.50

High amount of DO lead to increase in

biodegradation rate of LAS that introduced to

a natural system and LAS concentration will

be diminished.


Conclusion

Detergents are not degraded so fast during transportation

Sites where high levels of surfactants were found seem to correlate well with locations where fecal contamination existed

The concentration of LAS dropped rapidly with distance from the point of discharge.

Decrease in LAS concentration with the distance from the source of contamination was faster than that predicted based on dilution only

Vertical profile show that concentration of LAS in surface layers higher than the bottom layers.


StationpHEHH2O

Content%CaCO3 %TOC w/w

SS17.31184.9079.2988.270.90

SS27.56207.9077.4991.661.07

SS37.72197.0072.2795.540.95

SS47.78209.2075.1295.601.16

El-Mex Bay sediment quality parametersEl-Mex Bay sediment quality parameters

Distribution of LAS in Bay Sediments

StationLAS homologues (μg/g)0

C10C11C12C13Total

SS1ND0.4500.0470.0430.540

SS20.0200.3120.0410.0400.413

SS3ND0.3150.0340.0320.381

SS40.0150.3090.0350.0340.393

Spatial distribution of LAS homologues in sediment from El-Mex Bay Spatial distribution of LAS homologues in sediment from El-Mex Bay

LAS homologues usually detected were those of between 10 and 13 carbon atoms, with C11 and C12 being the most abundant.

No major differences in homologue distribution in any station of sediment samples collection.


0

10

20

30

40

50

60

70

80

90

C10 C11 C12 C13

Alkyl chain length

% of

total

LAS

StationLAS homologues(%)

C10C11C12C13

SS10.0083.308.707.90

SS24.8079.4010.4010.10

SS30.0082.708.908.30

SS43.8081.709.309.00

Alkyl homologues (%) distribution of LAS in the bay sedimentsAlkyl homologues (%) distribution of LAS in the bay sediments

Key intermediates

Most adsorbed

Persist biodegradation


Total LAS Distribution

The maximum LAS concentrations were detected close to El-Umum Drain discharge outlets decrease with the distance from the drain discharge outlets.

0.000

0.100

0.200

0.300

0.400

0.500

0.600

SS1 SS2 SS3 SS4

Distance from point of dischargeLA

S (m

icro

g/g

)

The high LAS concentration at station SS1 coincide with very low amount of DO (0.5-1.9 mg O2/l) so that LAS persists at these regions due to oxygen limitation

DO limitation indicates anaerobic biodegradation conditions, this evidence can be supported by low Eh-values at stations near to El-Umum Drain outlet (<100) refers to slight increase in anaerobic conditions at which LAS decomposition rate will be decreased.


Physical mixture of the water column and the existence of wastewater discharged either onto the surface or at depth due to changeable wind velocities in the bay during the different seasons leads to LAS not accumulate at surface water according to its surfactant character and increased its tendency to accumulate at the interfaces of the sediments.

In both samplings (seawater and sediments), it can be observed that the evolution of total LAS concentrations in solids is similar to found in water. An increase is seen in the process of adsorption onto sediments, in line with an increase of LAS in seawater.

y = 504.9x - 118.27

R2 = 0.981

0

20

40

60

80

100

120

140

160

180

0 0.1 0.2 0.3 0.4 0.5 0.6

LAS (micro g/g)

LAS

(micr

o g/

l)

Generally, the degradation rate of LAS is very high in the presence of sediment which means that the period of acclimatization of the bacterial flora was substantially shortened


LAS homologues Distribution

The results show a great affinity of LAS for the solid phase, as well as an increase in adsorption in line with increased chain length, this being evidence of a hydrophobic-type interaction.

C11-LAS constitute more than 75% of total LAS in all the samples, reaching 84% at station SS1 (the area

with relatively high %OC).

Organic carbon content is one of the most important parameter which effect on the rate of LAS adsorption

onto marine sediment as described earlier by experimental work in this research.


Concentration of LAS at El-Mex Bay sediments

Ad

sorp

tion

Bio

deg

rad

atio

n

Chain length

%OCPhysical mixture

DO conc.

Heavy metal conc.

Chain length

Concentration of LAS in water column

Distance from wastewater point of discharge

Sediment


Adsorption Experiments

Sorption

Process of transfer of surfactants molecules from bulk solution phase to the surface/interface.

Influence fate and effect of surfactants when release into aquatic or terrestrial environment.

Is important mechanism for LAS removal from the marine water column which may affected by several factors such as chain length, salinity and TH.

Plays a role in determining the resistance time of a chemical in soils and sediments. In addition may affect the expression of effects of surfactants towards benthic and soil dwelling organisms and plants.

Involves single ions (unimers) rather than micelles


surfactant onto sediments or soil depends on many factors including:

physicochemical properties of surfactants

sediment or soil nature

environmental parameters

data can be used to estimate the

distribution of the surfactant in environment.

bioavailability of the surfactant,

Few studies

Sorption

Generally Equilibrium and kinetics of ionic surfactants adsorption

The nature of solid surface (hydrophobic or hydrophilic) and the electrical interactions play an important role in the kinetics of adsorption of surfactant at the solid-liquid interface.

ΔGads = ΔGelec + ΔGspec

ΔGelec accounts for the electrical interactions

ΔGspec is a specific adsorption term, which contains all other contributions to the adsorption free energy that are dependent on the 'specific' (non-electrical) nature of the system



Kinetic Experiments (Rate experiments)1

The rate of LAS sorption onto El-Mex bay marine sediment was determined by agitation of the LAS seawater-sediment mixture sediment sample, for respectively 0.5, 1, 2, 3, 4, 5, 6 and 7 hours.

kinetic I

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

0 0.5 1 2 3 4 5 6 7

Time (h)

Sorp

tion

perc

ent

Initial concentration (Ci) was 10 ppmAmount of sediments was 0.6 g/l

The sorption of LAS is a fast phenomena and all systems achieved equilibrium within 4 hr of contact time


These results are in agreement with literature for adsorption of LAS on marine sediments and soils and adsorption of organic substances on activated sludge.

0.0010.0020.0030.0040.0050.0060.00

0 0.5 1 2 3 4 5 6 7 20 24

Time (h)

Degr

adati

on pe

rcent

The amount of LAS degraded during this time of experiments is negligible as indicated by blank experiments of LAS in standard seawater without addition of sediment.

The sorption on the wall of the receptacle is negligible owing to its small value

The equilibrium time determined from rate experiments was applied in isotherm experiments


2 Isotherm Experiments (Sorption Experiments)

50 ml of LAS solution in seawater ranging in concentration from 1 to 100 ppm were added to 3.0 g (d.w) of sediment in a Teflon-stoppered Pyrex bottles. The suspensions were adjusted to appropriate pH values (3, 8 and 12) with dilute NaOH or HCl solution and subsequently placed on shaker for 5 hours at 25 ºC. Filtration was carried out to obtain a clear solution for the determination of LAS. The amount of sorption was expressed as mg LAS per g of dry sediment.

Salinity of seawater was 36 ‰Temperature 25ºCpH adjusted 3, 8 or 12The sediment was coarse and medium sand as proved by GSA


0

200

400

600

800

1000

1200

1400

1600

1800

0 10 20 30 40 50 60 70

LAS in solutionA

mou

nt o

f ads

orbe

d LA

S Sample I

Sample II

Sample III

Sample IV

The adsorption of anionics such as LAS appears to be in influenced mainly by hydrophobic mechanisms.

At low concentration

There are no significant sorbate-sorbate interactions at the low concentrations

As concentration increases

active sorption sites on solid surface become less and less available, and more and more hemimicelles form

At higher concentrations

sorption may entail the formation of more structured arrangements these arrangements may be governed mainly by interactions between hydrophobic moieties of surfactant molecules.


Sorption of LAS on El-Mex Bay marine sediments can be described by using

Freundlich equation

x/m = K Ce1/n

x/m is the amount of LAS adsorbed per unit of adsorbent (µg/g)

Ce is the equilibrium concentration of LAS in solution (mg/l)

K is a Freundlich sorption coefficient (l/kg), related to the bounding energy.

1/n is a power function related to the sorption mechanism & measure the sorption intensity

log x/m = log K + 1/n log Ce


iso 1

y = 0.6882x + 2.4016

R2 = 0.9173

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

-2.000 -1.500 -1.000 -0.500 0.000 0.500 1.000

log Celo

g m

icro

g/g

Freundlich isotherm

Non-linear relationship between the amount of LAS sorbed and the equilibrium solution concentration

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

-2.500 -2.000 -1.500 -1.000 -0.500 0.000 0.500 1.000 1.500 2.000

log Ce

pH 8.5

pH 3.8

pH 12

Linear (pH 12)

Linear (pH 8.5)

Linear (pH 3.8)

Effect of pH on LAS sorption


Sample NoTOC (w/w)pHK1/nR2

I0.90

1238.770.6820.962

8.5252.120.6880.917

3.8351.080.6720.964

II0.95

1245.060.6970.971

8.5331.050.710.985

3.8388.420.670.968

III1.07

1254.0510.6440.988

8.5350.830.6610.972

3.8409.070.6310.963

IV1.16

1252.0710.6620.977

8.5367.110.6630.968

3.8387.610.6350.919

Results



Discussion

Non-linear relationship

There is interaction between adsorbed molecules and the adsorption is localized in multilayer, thus resistance time of LAS on sediment will be increase (adsorption become easy)

The data was fitted to Freundlich isotherm not Langmuir isotherm

The sorption of LAS on sediment increase as the TOC increase

The narrow range of K-values indicates that the %OC of sediment have a moderate effect on adsorption.

The relatively small value of 1/n (less than 1) indicates sorption intensity is relatively small.


Discussion

The relatively small K-values indicates the adsorption of LAS was moderate because

This because the negative charge of the sediment minerals (sand & high carbonate contents) which repels the anionic surfactants (LAS).

Adsorption is still localized in monolayer at low equilibrium concentration

Positive correlation found between K-values and REDOX potential


Discussion

The LAS sorption on sediments was strongly affected by pH and decreased with increasing pH for each sediment sample

Acidic conditions yield a positively charged sites onto which negatively charged LAS homologues can adsorb. Acidic conditions yield a positively charged sites onto which negatively charged LAS homologues can adsorb.

Hydrogen ion enhances adsorption in bilayer, and would confirm the affinity for the anionic surfactant after an initial adsorption in a monolayer.

Hydrogen ion decrease of the electrostatic repulsion ionic head of LAS.

Decrease in pH clearly enhances the sorption of LAS homologues on sludge and seems to promote

cooperative sorption at high surfactant concentrations


Discussion

A difficulty in comparing K coefficients is that often K is determined as the ratio of adsorbed fraction to the dissolved fraction.

the amount of soil or sediment and the test chemical concentration should be mentioned.the soil/solution ratio applied in the adsorption experiment influences the adsorption coefficient K

This simplified K can be compared with the Freundlich K when 1/n equals 1 or in the linear range of sorption (Stern-Graham equation)

x/m = K*Ce


Summary

Due to their chemical features, LAS (anionic surfactant) molecules may sorb directly onto solid surfaces or may interact with sorbed surfactant molecules. The sorption mechanism is dependent on the nature of the sorbent and the surfactant concentration.

Under real marine environment where LAS levels are rather low, the LAS sorption ability of a sediment is very weak

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Mohammed Nazeih M. GamalChemist

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