COMPARATIVE ANALYSIS OF ACID ACTIVATED NTEJE CLAY AND TWO COMMERCIALLY AVAILABLE ADSORBENTS (FULLER’S EARTH AND ACTIVATED CARBON)

ABSTRACT

The composition and bleaching properties of Nteje clay in comparison with two commercially available  adsorbents  (activated  carbon  and  fuller’s  earth)     were  investigated  to  study  its competence for use as an alternative to high cost imported adsorbents. The modification of the raw clay sample was carried out by acid activation to enhance the surface area of the clay by exchange of octahedral cations e.g Al3+, Fe3+ and Mg2+   with H+  ions which led to the modification of the clay crystalline structure. The raw clay sample was characterized using X-ray Diffraction (XRD) analysis and Fourier Transfer Infrared Spectroscopy. The acid activated sample was used along the two  commercially  available  adsorbents  (activated  carbon  and  fuller’s  earth)  in  adsorptive

bleaching of palm  oil  to  study its  adsorptive capacity.  The  bleaching  was  done  at  constant temperatures of 60 oC, 80 oC, 100 oC, 120 oC and 140 oC varying time at 10, 20 30, 40 and 50 minutes at each constant temperature. The kinetics and thermodynamics of the adsorption reaction was investigated at 333 k, 353 k, 373 k, 393 k and 413 k. To further understand the kinetics, the

adsorption data were analyzed by pseudo-second order, elovich and power function equations. Adsorptive bleaching of palm oil was carried out using optimum operating   conditions of temperature, clay dosage and reaction time. The results revealed that the adsorption followed power function equation for both activated carbon (A.C) and  fuller’s earth (F.E) with linear regression coefficient (R2) values of 0.987 and 0.990 respectively and followed elovich equation for activated Nteje clay (A.N.C) with (R2) value of 0.985. Analysis of the equilibrium data using Langmuir and Freundlich isotherms showed that Langmuir isotherm provided the best fit for the three adsorbents understudy. Furthermore, the evaluation of the adsorption thermodynamic parameters revealed that the adsorption process was spontaneous and exothermic because of the free energy change, negative change in enthalpy and positive change in entropy. A maximum colour reduction of 79 % was obtained for both A.N.C and F.E and 78 % for A.C all at 140 oC. The  results  from  this  study  reveals  that  modification  of  this  alumino-silicate  increased  its adsorptive capacity and produced equal results and responses like their commercially available counterparts. Application of the low cost modification technique Nteje Clay therefore should not be doubted, as this  study have  establish that  it  competes and  compares favourably with the imported, commercially available adsorbents.

CHAPTER ONE

INTRODUCTION

1.1      Research Background

Natural clay minerals are well known and familiar to mankind from the earliest days of civilization1. Because of their low cost, abundance in most continents of the world, high sorption properties, high dissolubility in acidic solutions and potential for ion exchange, clay materials are suitable  substances as  source of  metals  and  adsorbents.  Clay  is  composed  mainly of  silica, alumina,  water  and frequently with appreciable quantities of iron, alkalis as well as alkali earth metals. Two structural units are involved in the atomic lattices of most clay minerals. One unit consists of closely packed oxygen atoms and hydroxyls in which aluminum, iron and magnesium atoms are embedded in an octahedral combination so that they are at equal distant from six oxygen or hydroxyls. The second unit is built of silica tetrahedrons. The silica tetrahedrons (Si4O6(OH)4) are arranged to form a sheet of composition2.

Clay deposits are widespread over the regions of Nigeria and are under utilized in the process industries largely because we do not have the technology. These clay deposits can be mined, purified and processed into useful raw materials for the process industries. Naturally occurring clays are alumino-silicate minerals containing sodium, potassium, and calcium, with traces of magnesium and iron which may be substituted for aluminum. The structure of these clays can be altered by heating or reaction with strong acids or alkalis to improve their adsorptive properties and colour. The majority of these clays do not possess such properties, but, may be activated by some forms of treatment and their efficiency in the bleaching of vegetable oils can be improved.

Activation of clays can be accomplished by calcinations, reaction with mineral acids/alkalis, or combination of both techniques.

1.2      Research Objective and Scope

The aim of this research was to make comparative analysis of the bleaching efficiency of a locally substituted adsorbent, Nteje clay  to the imported, commercially available activated carbon and fuller’s earth. Because little or no work has been done in comparing the bleaching efficiency of Nteje clay to its commercial standards, hence the need for the study. This study if found efficient to the imported bleaching efficiencies of activated carbon and fuller’s earth, should be able to operate at various quality of crude palm oil (C.P.O) fed and produce equal results and responses as its commercial standards. By doing so, the purity of the final product including its commercial and health values will be enhanced.

Therefore, the specific objectives of the research were:-

1.        Preparation,  characterization  of  activated  and  unactivated  Nteje  clay  as  well  as  its activation.

2.       To carry out adsorption of colour pigment from palm oil

3.       To study the chemical kinetics, thermodynamics and equilibria of the adsorption process.

1.3      Problem Statement

1.         Despite positive results by researchers of the bleaching capacity of Nteje clay, it is still facing heavy industrial discrimination leading to little or no patronage

2.        This study was also motivated by the easy contamination of vegetable and seed oils due to the presence of both physical and chemical impurities.

3.       The importation of large quantities of adsorbents and at a very high cost.

4.         There is the problem of few locally substituted earth sources for research compared to activated carbon with several substituted local sources.

5.         Research have revealed  that there are more than enough earth (clays) available that can be used as adsorbent to meet our local demand.

1.4      Significance of Study

Nteje clay has been reported by several authors to have been successful in the adsorptive bleaching of palm oil and its potency of being an alternative to costly, imported adsorbents.

Despite these successful results, it is more valuable when the adsorptive power of these local clays are strong enough to permit it to compete actively with adsorbents already accepted as the standard quality for refining oils. Hence, the main objective of this research which was to compare the widely reported bleaching efficiency of this  locally substituted adsorbent (Nteje clay)  to  the imported, commercially available standards (fuller’s earth and activated carbon). The study will properly validate its use as a local substituent for industrial and scientific applications, if found competent.

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