Effect of Activation Parameters on Conversion in Clay- Catalyzed Esterification of Acetic Acid

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Abstract

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conversion of 78.29% at 200oC activation closely followed by

0.5M with its highest conversion of 74.29% also at 200oC. This makes 0.5M the better option from economic point of view. Longer activation time gave higher conversion during the medium temperature activation but at high activation temperature, conversion decreased with longer activation duration. From the statistical analysis using ANOVA, the strength of the activating acid had the highest significance while the effects activation temperature and duration were less significant.

Index Term

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Esters are important class of chemicals which have their applications in a variety of areas such as solvent, plasticizers, pharmaceuticals and intermediates. They have characteristic pleasant, fruity odour that leads to their use in fragrance and flavour industries [1, 2]. Clays are assemblies of tetrahedral layers of silicate units and octahedral layers of aluminates’ units which result in planar sheets. Thus, adsorbents are constrained to diffuse in two-dimensional space in contrast to three-dimensional reaction volume. This gives rise to increased encounter frequencies between reactants thereby boosting the reaction rate [3]. Clay minerals are acidic in the nature and exhibit ion exchange ability. The acidity of clay

it is relatively easy to convert them into useful catalyst by activating them with acid or cation- exchange using

polyvalent ions Al+3

and Cr3+3. The cations can polarize their coordinated water molecules to yield protons in the interlamellar zone [6]. Smectite clays are known for their activity in promoting acid-catalysed reactions like dimerization and polymerization of

unsaturated hydrocarbons. They are also used in synthesizing ethers from alkenes [7]. In their research on

the activation saponite clay at room temperature and 90oC using different acid/clay ratios, [8] found that the leaching of magnesium from the octahedral sheets is enhanced by increase in the acid/clay ratio and by increase in the temperature of activation. The type of reagents used in activation, the strength/molarity of the reagents, the temperature of the

activation and the activation duration are all believed to have effects on the effectiveness of the clay catalysts. The aim of this research is to elucidate the effects of these activation parameters on a montmorillonite clay catalyst used in esterification reaction.

II. MATERIALS AND METHOD

CLAY ACTIVATION

Three small samples of the clay obtained from Udi stream in Enugu state, Nigeria, were first activated using thermal,

Effect of Activation Parameters on Conversion

in Clay- Catalyzed Esterification of Acetic

Acid

Igbokwe, P.K

a*

Olebunne, F.L.

b,

; Nwakaudu, M.S.

b

.

a

Department of Chemical Engineering, Nnamdi Azikiwe University, Awka, Nigeria. b

Department of Chemical Engineering, Federal University of Technology, Owerrr, Nigeria. *Corresponding Author

International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 05 2

activated clays were pulverized and stored in air-tight containers.

THE REACTION

Each of three activated clay samples was used in esterification reaction to assess their effectiveness. 2.5ml of acetic acid was pipetted into a 10ml stoppered bottle; 0.25g of the clay catalyst was added to it first before 2.5ml of

ethanol was pipetted into it to ensure that the active sites of the catalyst were not blocked by the alcohol. The container was tightly closed, the contents shaken vigorously and immersed in a water bath maintained at 323K for 6hours after which the content was titrated with 1MNaOH. The summary of the reaction equation is

CH3COOH + _{C2H5OH CH3COOC2H5} + _H2O

The result is shown in Figure 1.

SPECIFICATION OF ACTIVATION PARAMETERS

Having confirmed from Figure 1 that acid activation gave much higher conversion than the thermal and alkaline methods, other activation parameters were checked which include: activation temperature, activation duration and

the strength of the activating acid (molarity).

The range of the parameters is:

Activation temperature, (x1) 100oC - 300oC

Activation duration, (x2) 3hours - 6hours

Molarity of acid, (x3) 0.1M - 1M

The three-way Analysis of Variance (ANOVA) arrangement is as shown,

X1

X2

3hrs

4.5hrs

6hrs

100

C

1M

0.5M

0.1M

200

C

0.5M

0.1M

1M

300

C

0.1M

1M

0.5M

III. RESULTS AND DISCUSSION

A total of 18 clay samples were variously activated and used the esterification reaction. The results are shown in Figures (2) – (7) and the ANOVA Table I.

a. Effect of activation method

From Figure 1, it can be seen that the acid-activated clay gave high conversion while the thermal and alkaline activation only improved the conversion a little above the uncatalysed reaction. This is an indication that the

b. Effect of the strength of the activating acid

Figures (2) – (4) show the conversions recorded after six hours from the three clay samples activated with different molarity of sulphuric acid. In the graphs, the clay activated with very dilute acid (0.1M) has very low conversion about 30%. Conversion improved remarkably for the clay activated with medium strength acid (0.5M) up to

74%. However, doubling the acid strength to 1M only added about 5% to the conversion with

International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 05 4

c

Figures (2) – (7) indicate that activating the clay between

100oC – 200oC has favourable conversion while decline in

conversion was noted above 200oC. Clay catalysts are known to exhibit both Bronsted and Lewis acid sites depending on type of heating chemical treatment. The good conversion

obtained at activation temperature 100 ≤ T ≥ 200oC confirms that when clays are heated at moderate temperature to remove most of the interlamellar water, the Bronsted acidity is increased while heating at high

International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 11 No: 05 6

Effect of activation duration

From Figures (5) –(7),it can be seen that when the clay

was activated in temperature range 100 – 200oC, longer

heating time improves conversion but above

200oC,longer heating time becomes unfavourable. This shows that as more interstitial water is driven out during the moderate temperature heating, the Bronsted acidity

increases gradually while the resultant collapse of the clay’s interlayer structure during high temperature

heating brings corresponding decrease in the clay acidity as the heating lasts longer. Thus, if the clay should be activated at high temperature, it should be for a short time, just long enough to drive out the interlamellar water content of the clay.

TABLE I

Analysis of Variance Result using MATLAB Software

Source Sum Sq. d.f. Mean Sq. F Prob. (F)

X1 148.776 2 74.388 3.5085 0.2218

X2 30.8706 2 15.4353 0.72799 0.57871

X3 4266.7153 2 2133.3576 100.6183 0.00984

Error 42.405 2 21.2025

Total 4488.7668 8

IV. CONCLUSION

The various activation parameters that could affect the effectivness of a clay catalyst for esterification were examined. Acid activation was found to be the best compared with thermal and alkaline activation. The best

activation temperature was found to be 200oC.

Longer activation time has good effect below 200oC but at higher temperature, longer activation time has adverse effect. The strength of the activating acid was found to have the highest impact on the effectiveness of the activated clays. The little difference between the conversion obtained with

1M and 0.5M acid makes 0.5M more favourable from economic standpoint.

REFERENCES

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Solids’, Journal of Pure and

[4] Applied Chemistry, Vol.62, No.10, pp 2027-2030.

[5] Dintzner, M.R; Wucka, P; Lyons, T.W. (Retrieved 2008) ‘Microwave-assisted Synthesis of Natural Insecticide on Basic Montmorillonite Clay’ Dept. of Chemistry, DePaul University Chicago.

[6] Correa, K.S.; Bernin, R.B.; Mattos, M.C.; Aguiar, M.R.; and Guarino, A.W.; (2007) ‘A New Environmental-Friendly Clay

Catalyst for One-pot Coiodination and Epoxidation of Alkenes’ Brazilian Journal of Chemistry Society. Vol.18, No.8, Page 1509-1514.

[7] http:// www.

designer-drug.com/pte12.162.180.114/ded/chemistry/mw.clays.txt [8] Adams, J.M; Clement, D.E. and Graham, S.H. (1982) ‘Synthesis

of Methyl-t-Butyl Ether from

[9] Methanol and Isobutene usinga Clay Catalyst’ Clays and Clay Minerials, Vol.30, No.2, pp 129-

[10] 134.

[11] Kooli, F. and Jones,W.(1997) ‘Characterization and Catalyst Properties of a Saponite Clay