SYNTHESIS OF A NOVEL ORGANOKAOLINITE WITH IMPROVED SORPTION CHARACTERISTICS USING KAOLINITE AND CETYL TRIMETHYL AMMONIUM BROMIDE

  • : Ms Word Format
  • : 75 Pages
  • : ₦3000
  • : 1-5 Chapters
  •  
  • Click to DOWNLOAD Materials

SYNTHESIS OF A NOVEL ORGANOKAOLINITE WITH IMPROVED SORPTION CHARACTERISTICS USING KAOLINITE AND CETYL TRIMETHYL AMMONIUM BROMIDE

ORGANOKAOLINITE

TABLE OF CONTENT

CHAPTER ONE

INTRODUCTION AND LITERATURE REVIEW

1.0 General Introduction

1.1 Clay Minerals
1.1.1 Structureof Clay Minerals

1.1.2 Cation Exchange Capacity (CEC)

1.2 Organoclays
1.2.1 Preparation of organoclay

1.3 Quaternary ammonium cations

1.4 Adsorption

1.4.1 Types of adsorption:

1.4.3 Adsorption equilibria

1.4.4 Isotherm models

1.4.4.1 Langmuir isotherm

1.4.4.2 Freundlich isotherm

1.4.4.3 BET (Brunauer, Emmett and Teller) isotherm:

1.4.5 Determination of appropriate model

1.5 Organic contaminants in the Petroleum Industry

1.5.1 Benzene
1.5.2 Toluene
1.5.3 Ethylbenzene
1.5.4 Xylene
1.6 Aimand objectives
1.6.1 Aim

1.6.2 Objectives

CHAPTER TWO

MATERIALS AND METHODS

2.1 Materials

2.2 Methods
2.2.1 Purification of clay

2.2.2 Determination of cation exchange capacity (CEC)
2.2.3 Preparation of organokaolinite
2.2.4 Characterization of Organoclay
2.3 Preparation of stock solution for adsorption studies
2.4 Adsorption Experiments

CHAPTER THREE
3.0 RESULTS AND DISCUSSIONS
3.1 Measurement of exchangeable cations in kaolinite
3.2 Characterization of organokaolinite
3.2.1 EDX analysis
3.2.2 Elemental Analysis

3.2.3 Morphology of organoclay samples

3.2.4 XRD pattern analysis

3.2.5 FTIR spectral analysis

3.2.6 Thermal analysis on organoclay samples

3.3 Adsorption studies

3.3 .1 Effect of contact time

3.3.2 Adsorption Experiment
REFERENCES

CHAPTER ONE

INTRODUCTION AND LITERATURE REVIEW

1.0 General Introduction

Clay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried or fired. Clay deposits are mostly composed of clay minerals (phyllosilicate minerals) and variable amounts of water trapped in the mineral structure by polar attraction. Organic materials which do not impart plasticity may also be a part of clay deposits. Clay is a widely distributed, abundant mineral resource of major industrial importance for an enormous variety of uses (Ampian, 1985). In both value and amount of annual production, it is one of the leading minerals worldwide. In common with many geological terms, the term “clay” is ambiguous and has multiple meanings: a group of fine-grained minerals which show plasticity through a variable range of water content, and which can be hardened when dried or fired i.e., the clay minerals; a particle size (smaller than silt); and a type of rock i.e., a sedimentary deposit of fine-grained material usually composed largely of clay minerals (Patterson & Murray, 1983; Bates & Jackson, 1987). Clays find wide range of applications, in various areas of science, due to their natural abundance and the propensity with which they can be chemically and physically modified to suit practical technological needs (Xi et al., 2005).
Clays are distinguished from other fine-grained soils by various differences in composition. Silts, which are fine grained soils which do not include clay minerals tend to have large particle sizes than clays but there is some overlap in both particle size and other physical properties, and there are many naturally occurring deposits which include both silts and clays. The distinction between silts and clay varies by discipline.Geologists and soil scientists usually consider the separation to occur at a particle size of 2µm (clays being finer than silts), sedimentologists often use 4-5µm, and colloid chemists use 1um. Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, ISO 14688 grades; clay particles as being smaller than 0.063mm and silts one larger.
There are three or four main groups of clays; kaolinite, montmorillonite-smecite, illite and chlorite. Chlorites are not always considered clay, sometimes being classified as a separate group within the phyllosilicates. There are approximately thirty different types of “pure” clays in these categories but most “natural” clays are mixtures of these different types along with other weathered minerals (Lagaly, 1984).

1.2 Clay Minerals
Clay minerals likely are the most utilized minerals not just as the soils that grow plants for foods and garment, but a great range of applications, including oil absorbants, iron casting, animal feeds, pottery, china, pharmaceuticals, drilling fluids, waste water treatment, food preparation, paint e.t.c.
Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays form flat hexagonal sheets similar to the micas. Clay minerals are common weathering products (including weathering of feldspar) and low temperature hydrothermal alteration products. Clay minerals are very common in fine grained sedimentary rocks such as shale, mudstone, and siltstone and in fine grained metamorphic slate and phyllite. Clay minerals are usually (but not necessarily) ultrafine-grained (normally considered to be less than 2µm in size on standard particle size classifications) and so may require special analytical techniques for their identification/study. These include x-ray diffraction, electron diffraction methods, various spectroscopic methods such as Mössbauer spectroscopy, infrared spectroscopy, and SEM-EDX or automated mineralogy solutions. These methods can be enlarged by polarized light microscopy, a traditional technique establishing fundamental occurrences or petrologic relationships.
Clay minerals can be classified as 1:1 or 2:1clays; this originates from the fact that they are fundamentally built of tetrahedral silicate sheets and octahedral hydroxide sheets, as described in Figure 1 below. A 1:1 clay would consist of one tetrahedral sheet and one octahedral sheet, for example, kaolinite and serpentine. A2:1 clay consists of an octahedral sheet sandwiched between two tetrahedral sheets, for example, talc, vermiculite and montmorillonite.
Clay minerals include the following groups:
· Kaolin group which includes the minerals kaolinite, dickite, halloysite, and nacrite (polymorphs of Al2Si2O5(OH)4). Some sources include the kaolinite-serpentine group due to structural similarities (Bailey 1980).

· Smectite group which includes dioctahedral smectites such as montmorillonite and nontronite and trioctahedral smectites, for example,saponite.

· Illite group which includes the clay-micas. Illite is the only common mineral.

· Chlorite group includes a wide variety of similar minerals with considerable chemical variation.

Other 2:1 clay types exist such as sepiolite or attapulgite, which areclays with long water channels internal to their structure.

Typically, the structural formula for kaolinite is Al4Si4O10(OH)8 and the theoretical chemical composition given in Table 1.

Table 1: Theoretical Chemical Composition of Kaolinite (J.Fafardet al; 2012)

Chemical Compound
Percentage Composition (%)
SiO2
46.54
Al2O3
39.50
H2O
13.96
Mixed layer clay variations exist for most of the above groups. Ordering is described as random or regular ordering, and is further described by the term reichweite, which is German for range or reach.

1.1.1 Structureof Clay Minerals

Like all phyllosilicates, clay minerals are characterized by two-dimensional sheets of corner sharing SiO4 tetrahedral and/or AlO4 octahedral. The sheet units have the chemical composition (Al,Si)3O4. Each silica tetrahedron shares 3 of its vertex oxygen atoms with other tetrahedral forming a hexagonal array in two-dimensions. The fourth vertex is not shared with another tetrahedron and all of the tetrahedral “point” in the same direction; that is, all of the unshared vertices are on the same side of the sheet. In clays, the tetrahedral sheets are always bonded to octahedral sheets formed from small cations, such as aluminum or magnesium, and coordinated by six oxygen atoms. The unshared vertex from the tetrahedral sheet also forms part of one side of the octahedral sheet, but an additional oxygen atom is located above the gap in the tetrahedral sheet at the center of the six tetrahedral. This oxygen atom is bonded to a hydrogen atom forming an OH group in the clay structure. Clays can be categorized depending on the way that tetrahedral and octahedral sheets are packaged into layers.

Fig 1. Structure of kaolinite( Papke,Keith1970)

1.1.2 Cation Exchange Capacity (CEC)

The ion-exchange capability of clay minerals, in particular, kaolinites, influences their unique physical properties, such as the cation retention and diffusion processes of charged and uncharged molecules. These processes influence cation and molecule migration through clay-rich barriers in nature. The numerical value of this property is described by the cation exchange capacity (CEC). Methods for determining CEC involve the complete exchange of the naturally occurring cations by a cationic species, such as ammonium, K, Na, methylene blue, Co(III) hexamine complex (RadmyandOrsini, 1976), Ba, Ag thiourea complex, and Cu(II) ethylenediamine complex. Exchange with organic cations, such as alkylammonium, provides an indirect method for the determination of CEC.

CEC may be defined as the quality of exchangeable cations expressed in milliequivalents per 100g of ignited weight of clay (Newman 1987).The cation exchange capacity (CEC) of a clay is a measure of the quantity of negatively charged sites on clay surfaces that can retain positively charged ions (cations) such as calcium (Ca2+), magnesium (Mg2+), and potassium (K+), by electrostatic forces. Cations retained electrostatically are easily exchangeable with cations in the clay solution, so clay with a higher CEC has a greater capacity to maintain adequate quantities of Ca2+, Mg2+ and K+ than clay with a low CEC. It is also a very important tool in the preparation of organoclay. CEC is a good indicator of clay quality and productivity. It is normally expressed in one of two numerically equivalent sets of units: meq/100 g (milliequivalents of charge per 100 g of dry clay) or cmolc/kg (centimoles of charge per kilogram of dry clay).Because of the differing methods to estimate CEC, it is important to know the intended use of the data. For clay classification purposes, clay’s CEC is often measured at a standard pH value. Examples are the ammonium acetate method of Schollenberger and Dreibelbis (1930) which is buffered at pH 7, and the barium chloride-triethanolamine method of Mehlich (1938) which is buffered at pH 8.2 (Rhoades,1982.) . This procedure involves determination of the expansion of the layers and calculations involve charge density (Oliset et al., 1990; Lagaly, 1981). Depending on the method utilized, the excess of the exchanged cations is removed in a subsequent step and the amount retained on the clay is determined. However, the determined CEC values are dependent on the method used. Although time consuming, the exchange with ammonium acetate is the standard method for CEC determination (Mackenzie, 1951).

To obtain complete ion exchange and to obtain reliable values of CEC, either a high surplus of an exchanging cation or a cation with a high affinity for the clay mineral must be employed.

1.2 Organoclays
Surface modifications of clay minerals have received attention because it allows the creation of new materials and new applications. The main focus of surface modification of clays is materials science, because organoclays are essential to develop polymer nanocomposites. Nanocomposites constitute one of the most developed areas of nanotechnology. It is reportedTheng (1974), that the adsorption capacity of organoclays is improved over and above untreated clays for the removal of various organic contaminants. Besides, organoclays are more cost effective compared with other adsorbents, such as activated carbon and have been shown to be potentially effective for the uptake of water contaminants in aqueous solution.
Clay minerals have been found to be ineffective adsorbents in removing organic compounds because the hydration of inorganic cations on the surface of the clay makes them hydrophilic (Y. Xi et al; 2011). However, with the use of quaternary ammonium compounds (QACs), the surface properties of clay minerals have been greatly improved by replacing the natural inorganic interlayer cations with the organic cations present in the QACs (A.R. McLauchlin and N.L. Thomas;2008) to produce organoclays that are highly effective as adsorbents used in organic contaminant attenuation. The intercalation of a cationic surfactant between the clay layers renders the clay mineral hydrophobic at the surface while also increasing its wettability and thermodynamically favorable interactions with organic molecules (Y. Xi et al; 2011).
The studies on the interaction between clay minerals and organic compounds have been conducted from the beginning of the 20th century increasing in number and in topics. The research of intercalation of organic molecules into the interlayer space of clay minerals started in the 1920s, after the introduction of X-ray diffraction in 1913 (Merinska et al., 2002). One of the earliest papers was from Smith in 1934 on interactions, Gieseking (1939) found methylene blue to be very effective in replacing interlayer cations. These results suggested the possibility of using ammonium ions of the NHR3+, NH2R2 +, NHR3+, and NR4+ types to throw more light on the mechanism of cation exchange in clay minerals. Kaolinites, beidellite and nontronite types of clay minerals were treated with solutions of the hydrochlorides or hydroiodides of the various amines. The clay minerals adsorbed the organic ions, giving rise to basal spacing greater than those of the same clay minerals saturated with smaller cations such as calcium or hydrogen.
McEwan (1944) reported that the identification of montmorillonite was notoriously difficult. For this reason, he developed an unambiguous method based on the intercalation of glycerol into the interlayer space of the clay mineral. He observed that when montmorillonite was treated with glycerol, a very sharp and intense first-order basal reflexion was obtained at 1.77 nm, and the method is very suitable for identification.
Bradley (1945) studied the molecular association between montmorillonite and organic liquids aliphatic di- and polyamines and glycols, polyglycols and polyglycol ethers. Analysis of the complexes established that the amines are active in base exchange, while glycerol and glycol enter into the interlayer space without displacing cations.
Studies of interactions between clay minerals and organic compounds have been presented, among others, by Theng (1974), Lagaly (1984), and Yariv and Cross (2002). The countless clay–organic complexes of great industrial importance are the organoclays prepared from smectites and quaternary ammonium salts.
Hauser (1950) in his patent (US 2,531,427) described procedures for obtaining organoclays that swell and disperse forming gels in organic liquids in the same way as sodium smectites usually swell in water. Jordan first developed a research group on those organophilic clays (Beneke and Lagaly, 2002) and published important papers on their properties (Jordan, 1949; Jordan et al., 1950; Jordan, 1954). Jordan (1949) investigated some of the factors involved with the swelling of organoclays and the extent of the conversion of the clay from hydrophilic to hydrophobic.
Organophilic kaolinites were prepared by the reaction of kaolinite with various aliphatic ammonium salts. The swelling of the organoclays was studied in several organic liquids and liquid mixtures. Jordan concluded that the degree of solvation depends on at least three factors:
i. The extent of the surface coating of the clay particles by organic matter;
ii. The degree of saturation of the exchange capacity of the clay mineral by organic cations; and
iii. The nature of the organic liquid.
In 1950 Jordan et al. investigated the formation of gels of organoclays in several organic liquids and liquid mixtures and an optimum gelation occurred. Intercalation of organic guest species into kaolinite is a way of constructing ordered inorganic–organic assemblies with unique microstructures controlled by host–guest and guest–guest interactions (Kakegawa and Ogawa, 2002). Currently, an important application of the organoclays is in the polymer nanocomposites.
Organoclays are the most dominant commercial nanomaterial to prepare polymer nanocomposites, accounting for nearly 70% of the volume used (Markarian, 2005). Proper organophilization procedure is a key step for successful exfoliation of clay minerals particles in the polymeric matrix. The organophilic feature reduces the energy of the clay mineral and makes it more compatible with the organic polymers. The addition of organoclays into polymeric matrices improves mechanical, physical (thermal and barrier) and chemical properties of the matrices and reduces cost in some cases. Typically, organoclays replace talc or glass fillers at a 3:1 ratio. For example, 5% of an organoclay can replace 15–50% of a filler like calcium carbonate reducing cost and improving mechanical properties (Markarian, 2005). Organoclays also have been used in other applications. These applications include adsorbents, rheological control agents, paints, grease, cosmetics, personal care products, oil well drilling fluids, etc. (Santos,1989; Beall and Goss, 2004; Xi et al., 2005; Araújoet al., 2005). These clay minerals swell in water into a manner similar to smectites, and have interlayer charge densities higher than that of smectites. Unlike natural clay minerals, they have high crystallinity, controllable composition and fewer impurities. For this reasons, the use of such micas as host materials is expected to be more advantageous than the use of natural clay minerals. However, there are few studies about the chemical intercalation of hectorite, sepiolite and synthetic fluoro-micas.

1.2.1 Preparation of organoclay

The synthesis of organoclays is based on the mechanisms of the reactions that the clay minerals can have with the organic compounds. Displacement reactions occur when water molecules in the interlayer space of kaolinites and vermiculites are displaced by polar molecules. Neutral organic compounds can form complexes with the interlayer cations. In the case of kaolinite the adsorption of neutral molecule is driven by various chemical interactions: hydrogen bonds, ion–dipole interaction, co-ordination bonds, acid base reactions, charge transfer, and van der Waals forces. The interlayer cations can be exchange by various types of organics cations. Grafting reactions, i.e. forming covalent bonds between reactive surface groups and organic species are important steps to hydrophobise the surface of many clay mineral particles (Lagaly, 1984).

BENTONITE

BENTONITE SUSPENSION IN WATER

CENTRIFUGATION

CATION EXCHANGE REACTION

FILTRATION/WASHING

DRYING

MILLING

ORGANOCLAY

 

Fig.2Diagrammatic Representationof Organoclay Preparation

1.3 Quaternary ammonium cations

Quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR4+, R being an alkyl group or an aryl group. Unlike the ammonium ion (NH4+) and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged, independent of the pH of their solution. Quaternary ammonium salts or quaternary ammonium compounds (called quaternary amines in oilfield parlance) are salts of quaternary ammonium cations with an anion.(Sheng et al., 1996; Shen, 2004).

Quaternary ammonium compounds are prepared by alkylation of tertiary amines, in a process called quaternization. Typically one of the alkyl groups on the amine is larger than the others. A typical synthesis is for benzalkonium chloride from a long-chain alkyldimethylamine and benzyl chloride:

CH3(CH2)nN(CH3)2 + ClCH2C6H5 → [CH3(CH2)nN(CH3)2CH2C6H5] +Cl-…………………… (1)

Quaternary ammonium salts are used as disinfectants, surfactants, fabric softeners, and as antistatic agents (e.g. in shampoos). In liquid fabric softeners, the chloride salts are often used. In dryer anticling strips, the sulfate salts are often used. Spermicidal jellies also contain quaternary ammonium salts (Huang et al., 2007; Zhu and Zhu, 2007; Lin and Juang, 2009).

1.4 Adsorption

Adsorption is the process in which matter is extracted from one phase and concentrated at the surface of a second phase. (Interface accumulation). This is a surface phenomenon as opposed to absorption where matter changes solution phase, e.g. gas transfer. This is demonstrated in the following schematic diagram.

Fig3Schematic demonstration of difference between adsorption and absorption (Ahmedna,2000)

If we have to remove soluble material from the solution phase, but the material is neither volatile nor biodegradable, we often employ adsorption processes.

1.4.1 Types of adsorption:

There are two main types of adsorption which includes;

• Physical adsorption: Van der Waals attraction between adsorbate and adsorbent. The attraction is not fixed to a specific site and the adsorbate is relatively free to move on the

• Chemical adsorption: Some degree of chemical bonding between adsorbate and adsorbent characterized by strong attractiveness. Adsorbed molecules are not free to move on the surface. There is a high degree of specificity and typically a monolayer is formed. The process is seldom reversible.

Generally some combination of physical and chemical adsorption is responsible for activated carbon adsorption in water and wastewater surface. This is relatively weak, reversible, adsorption capable of multilayer adsorption.

1.4.3 Adsorption equilibria

If the adsorbent and adsorbate are contacted long enough equilibrium will be established between the amount of adsorbate adsorbed and the amount of adsorbate in solution. The equilibrium relationship is described by isotherms.

qe = mass of material adsorbed (at equilibrium) per mass of adsorbent.

Ce = equilibrium concentration in solution when amount adsorbed equals qe.

qe/Cerelationships depend on the type of adsorption that occurs, multi-layer, chemical, physical adsorption, etc. A general isotherm is shown in the figure below
Fig 4. General Adsorption isotherm (Archana 2007)

1.4.4 Isotherm models

There are threecommon isotherm models used to investigate sorption mechanism of organic compounds.

1.4.4.1 Langmuir isotherm

The theory of Langmuir isotherm was proposed by Langmuir (V.K Gupta et al; 2006) and it described the relationship between the adsorption of adsorbate and the surface of the adsorbent. The adsorbate is strongly attracted to the surface and it is assumed that a monolayer adsorption is involved. The surface has specific homogenous sites and all the vacant sites are equally sized and shaped. Once adsorption takes place at specific sites within the adsorbent and no further adsorption occurs at the specific sites. Hence, the adsorption to the surface is strongly related to the driving force and surface area. The Langmuir model can be expressed in the form

……….………………………. (4)

qe represents the maximum adsorption capacity (monolayer coverage) (g solute/g adsorbent).

Ce has units of mg/L.K has units of L/mg.
Fig. 5 Langmuir isotherm model (Hassler; 1963)

1.4.4.2 Freundlich isotherm

Freundlich suggested an empirical expression to describe the adsorption theory (Q.H Zeng et al; 2004). The model is based on the assumption that the adsorbent surface is heterogeneous and consists of different classes of adsorption sites. The adsorption takes place at the heterogeneous surfaces or surfaces supporting supporting sites of varied affinities. This model is only capable of predicting the infinite surface coverage which involves the multilayer adsorption of the surface. The Freundlich isotherm is shown below

……………………………………. (5)

Where is the amount of adsorbed solute, is Freundlich constant related to the adsorption capacity (L/mg), n is Freundlich constant related to the adsorption intensity of the adsorbent and is the concentration of solute in the solution at equilibrium (mg/L).
Fig. 6Freundlich isotherm model (Hassler; 1963)

1.4.4.3 BET (Brunauer, Emmett and Teller) isotherm:

This is a more general, multi-layer model. It assumes that a Langmuir isotherm applies to each layer and that no transmigration occurs between layers. It also assumes that there is equal energy of adsorption for each layer except for the first layer

……………………….. (6)

CS =saturation (solubility limit) concentration of the solute. (mg/L)

Kb = a parameter related to the binding intensity for all layers.

Note: when Ce<<CS and KB>> 1 and K = KB/Cs BET isotherm approaches Langmuir isotherm.
Fig. 7 BET isotherm model (Hassler; 1963)

1.4.5 Determination of appropriate model

To determine which model to use to describe the adsorption for a particular adsorbent/adsorbate isotherms experiments are usually run. Data from these isotherm experiments are then analyzed using the following methods that are based on linearization of the models

For the Langmuir model linearization gives:

………………….…………………………………… (7)

A plot of Ce/qe versus Ceshould give a straight line with intercept: and slope: . To predict the favorable or unfavorable adsorption process, a dimension constant, is also calculated using the equation below:

= ………………………………………………………….. (8)

Where K is the Langmuir constant and C0 is the initial liquid phase concentration(mg/L). Te adsorption process is considered as unfavorable (when ), linear (when = 1), favorable (when 0 ˂ ˂ 1), and irreversible (when = 0).

For the Freundlich isotherm use the log-log version:

……………………………………………….. (9)

A log-log plot should yield an intercept of logKfand a slope of 1/n. When the value of n is higher than 1 (n˃ 1), the adsorption process is favorable and multilayer sorption is formed on the surface of the adsorbent. However, the adsorption process is more favorable at high concentration than at low concentrations when the value of n is less than 1 (n˂ 1).

1.5 Organic contaminants in the Petroleum Industry

Organic contaminants are compounds that contain hydrocarbons, used in many solvents which are exposed to the environment through gasoline leakage from storage tanks, pipeline and petrochemical waste water e.t.c. They contaminate air, water and soil. (E. Jindrova et al; 2002), these compounds includes phenols, BTEX (benzene, toluene, ethyl benzene and xylene), VOCs (volatile organic compounds), PAHs (polycyclic aromatic hydrocarbons) e.t.c.
BTEX are the most dangerous of these organic compounds because the cause adverse effects like cancer, Irritation of mucosal membranes, respiratory problems and pulmonary damages. According to the World health organization (WHO), the maximum permissible concentration of benzene, toluene , ethyl benzene and xylene in drinking water are 0.01mg/l, 0.7mg/l, 0.3mg/l and 0.5mg/l respectively ( WHO guidelines; 2005). Hence removal of BTEX from water is essential.
BTEX are contaminants that are of particular concern due to their toxicity and are introduced into the environment in many ways e.g. incomplete oxidation of fossil fuels, disposal of effluents, oil spills e.t.c. They have the tendency to accumulate in ground water but can contaminate the soil and air as well (Forte et al; 2007: Finotti et al; 2001). Such compounds are extremely harmful to human health because they cause chronic toxicity even in small concentrations and may permanently damage the central nervous system. Benzene is the most toxic member and is carcinogenic. Acute exposure by inhalation or ingestion can be lethal (Forte et al; 2007: Moura et al; 2011).
Various conventional and advanced technologies have been used to treat and remediate areas that are contaminated with BTEX. To reduce the cost of current treatments, the technologies generally applied during the removal of organic compounds usually include biological treatments, membrane filtration and adsorption with activated carbons or organoclays. (Vidal et al; 2011).
1.5.1 Benzene
Benzene is a clear, colorless-to-yellow liquid and highly flammable aromatic hydrocarbon. It is present in petroleum products such as motor fuels and solvents, and motor vehicle emissions constitute the main source of benzene in the environment. Benzene occurs naturally in crude oil and is an additive and a by-product of oil-refining processes. It constitutes approximately 1-2% of unleaded gasoline by volume (US DHHS, 2011). Tobacco smoke is another significant source of exposure (WHO, 2010).
Human exposure to benzene occurs primarily through inhalation (WHO, 2010). When released to surface waters, benzene rapidly volatilises to the air (WHO, 2010). Benzene is not persistent in surface water or soil and either volatilises to air or is degraded by bacteria under aerobic conditions (WHO, 2010). For water contamination, benzene is therefore of most concern in groundwater. Unlike other petroleum hydrocarbons such as ethylbenzene, toluene and xylene the odour threshold for benzene is relatively high at 10mg/L (WHO, 2003).
Acute exposure to high concentrations affects the central nervous system causing dizziness, nausea, vomiting, headache and drowsiness. Inhalation of very high concentrations can cause death. Chronic and subchronic exposure to lower concentrations leads to a range of adverse effects on the blood system including pancytopenia, aplastic anaemia, thrombocytopenia, granulocytopenia and lymphocytopenia with white blood cells being the most sensitive (WHO 2003; Health Canada, 2009)
1.5.2 Toluene
Toluene is a colorless liquid, which occurs naturally as a component of crude oil and is present in petrol. It can enter water sources through atmospheric deposition, by leaching from synthetic coatings used to protect storage tanks, and by point-source pollution. Toluene, also known as methylbenzene is produced in large quantities during petroleum refining and is a byproduct in the manufacture of styrene and coke-oven preparations. It also occurs in natural gas and emissions from volcanoes, forest fires, and cigarettes. Toluene has a taste and odour threshold at 0.025mg/L.
The predominant effects of acute exposure were impairment of the central nervous system and irritation of the mucous membranes, with fatigue and drowsiness being the most obvious symptoms.Based on health considerations the concentration of toluene should not exceed 0.8 mg/L.

1.5.3 Ethylbenzene
Ethylbenzene is a clear colourless liquid, which occurs naturally as a component of crude oil and is present in petrol, but in small quantities. Ethylbenzene is produced commercially by the alkylation of benzene with ethylene, and by fractionation of petroleum. It is a major component of commercial xylene and is used commercially in paints, insecticides, blends of petrol, and in the production of styrene. It can also be found as a constituent of asphalt and naphtha. Ethylbenzene has a taste and odour threshold of 0.003mg/L.
Ethylbenzene is readily absorbed from the human gastrointestinal tract. It can be stored in fat and is metabolised to mandelic and phenylglyoxalic acids and excreted in the urine. It can cross the placenta.Based on health considerations the concentration of ethylbenzene in drinking water should not exceed 0.3 mg/L.

1.5.4 Xylene
The term ‘xylene’ encompasses three isomers of dimethylbenzene. The isomers are distinguished by the designations ortho- (o-), meta- (m-), and para- (p-), which specify to which carbon atoms (of the benzene ring) the two methyl groups are attached. o-xylene is also known as 1,2-dimethylbenzene, m-xylene is also known as 1,3-dimethylbenzene, and p-xylene is also known as 1,4-dimethylbenzene. The mixture is a slightly greasy, colourless liquid commonly encountered as a solvent. It represents about 0.5–1% of crude oil, depending on the source (hence xylene is found in small amounts in petrol and aviation fuels). It is mainly produced from reformate. Xylene have a taste and odour threshold of 0.02 mg/L.Xylene is readily absorbed after inhalation and metabolised almost completely to methyl benzoic acid. It can cross the placenta. Based on health considerations the concentration of xylenes should not exceed 0.6 mg/L.
1.6 Aimand objectives
1.6.1 Aim

The preparation and characterization of organoclays from kaolinitic clay deposits in Nigeria aimed at developing materials with enhanced industrial applications in various industrial processes.

1.6.2 Objectives

• To prepare organoclay materials from kaolinitic clay samples using cetyltrimethyl ammonium bromide.

• To characterize the organoclay samples using state of the art techniques to investigate what structural changes accompany the treatment of kaolinitic clay with organic molecules.

• To assess BTEX adsorption efficiency by organokaolinite.

Sharing is caring!

Leave a Reply

shares