STUDY OF ADSORPTION ON DIFFERENT TYPES OF CHARCOALS

 ABSTRACT

The present investigation has been so designed as to provide some insight on various aspects of adsorption power of carbon materials.Inthis investigation we use various types of charcoal of approaximately same particle  size, namely activated charcoal ,wood charcoal, coconut shell charcoal, paddy shell charcoal and studied  their power using oxalic acid as adsorbate.

INTRODUCTION

      In recent years research in the field of adsorbents and adsorption has gained considerable importance because of its wide applications. Activated charcoal is used as adsorbent in gas masks in which al toxic gases and vapors are adsorbed by the charcoal and pure air is passed through it. Silica and alumina gel are used as adsorbents for removing moisture and for controlling humidity in closed bottles ,bottles, boxes and rooms. Adsorption also plays an important role in heterogeneous catalysis. For example the role of finely divided iron in the manufacture of ammonia by Haber process .Animal charcoal is used as a decolorize in the manufacture of cane sugar .

Various aspects of the phenomenon of Adsorption

Adhesion of atoms , ions, biomolecules or molecules of gas, liquid or dissolved solids to a surface is called adsorption. Adsorption is different from absorption. In adsorption process two substances are involved.

Adsorbent : The substance on whose surface the adsorption occurs is known as adsorbent. 

Adsorbate : The substance whose molecules get adsorbed on the surface of the adsorbent ( i.e. solid or liquid ) is known as adsorbate.

 

Types of adsorption: 

Depending upon the nature of forces existing between adsorbate molecules and adsorbent, the adsorption can be classified into two types:

 1.Physical adsorption (physisorption): If the force of attraction existing between adsorbate and adsorbent are Vander Waal’s forces, the adsorption is called physical adsorption. It is also known as Vander Waal’s adsorption. In physical adsorption the force of attraction between the adsorbate and adsorbent are very weak, therefore this type of adsorption can be easily reversed by heating or by decreasing the pressure.

2. Chemical adsorption (chemisorption): If the force of attraction existing between adsorbate and adsorbent are almost same strength as chemical bonds, the adsorption is called chemical adsorption. It is also known as Langmuir adsorption. In chemisorption the force of attraction is very strong, therefore adsorption cannot be easily reversed.

 

Adsorption process is usually studied through graphs known as adsorption isotherm. That is the amount of adsorbate on the adsorbent as a function if its pressure or concentration at constant temperature .The quantity adsorbed is nearly always normalized by the mass of the adsorbent to allow comparison of different materials. 

Adsorbents

The material upon whose surface the adsorption takes place is called an adsorbent .Activated carbon is used as an adsorbent. Adsorbents are used usually in the form of spherical pellets, rods, moldings, or monoliths with hydrodynamic diameters between 0.5 and 10 mm. They must have high abrasion resistance, high thermal stability and small pore diameters, which results in higher exposed surface area and hence high surface capacity for adsorption. The adsorbents must also have a distinct pore structure which enables fast transport of the gaseous vapours. Most industrial adsorbents fall into one of three classes:

Oxygen-containing compounds - Are typically hydrophilic and polar, including materials such as silica gel and zeolites.

Carbon-based compounds - Are typically hydrophobic and non-polar, including materials such as activated carbon and graphite.

Polymer-based compounds - Are polar or non-polar functional groups in a porous polymer matrix.

Activated carbon is used for adsorption of organic substances and non-polar adsorbates and it is also usually used for waste gas (and waste water) treatment. It is the most widely used adsorbent since most of its chemical (eg. surface groups) and physical properties (eg. pore size distribution and surface area) can be tuned according to what is needed. Its usefulness also derives from its largemicropore (and sometimes mesopore) volume and the resulting high surface area.

Mechanism of Adsorption Using Adsorbent

Applications of  adsorption:

 The  principle of adsorption is employed:

o   in heterogeneous catalysis.

o   in gas masks where activated charcoal adsorbs poisonous gases.

o   in the refining of petroleum and decolouring cane juice.

o   in creating vacuum by adsorbing gases on activated charcoal.

o   in chromatography to separate the constituents' of a mixture.

o   to control humidity by the adsorption of moisture on silica gel.

SIGNIFICANCE OF WORK

This study is based on important topic adsorption which has application in various fields of industries. Different varieties of charcoal considered in this investigation have showed considerable adsorption power. It is found that ordinary varieties of charcoal are highly active and they can be used for removing impurities of metal ions even from drinking water.

OBJECTIVES 

·        To understand the adsorption power of ordinary varieties of charcoal. 

·      To make sure that ordinary charcoals are highly active in removing impurities 

    METHODOLOGY

 

One litre of 1 N Oxalic acid solution was prepared by weighing from which 500 ml of .5N,0.25N,0.125N oxalic acid  solutions  were prepared. Charcoals were labelled as Sample I (Activated charcoal ),Sample II (Wood charcoal), Sample III (Paddy shell charcoal) ,Sample IV (Coconut shell charcoal) . 32 well cleaned  and dried bottles were taken  and labeled .For each sample of charcoals 4 different concentrations of oxalic acid were allowed to adsorb. Duplicates were also prepared .1 gram of charcoal was accurately weighed and completely transferred into each bottle 50 ml of oxalic acid of particular concentration as per label was also pipette into each bottle. The bottles were tightly stoppered and shaken for 1.30 hour.

Then the bottles were placed in a water bath for about half an hour in order to attain equilibrium temperature .Then the supernatant liquid was filtered through a dry filter paper .The initial 5 to 10ml solution was  rejected  and the remaining solution was  collected . The first fraction was rejected since adsorption of the solution to the filter paper  may occur which decrease the concentration of the solution .The same procedure was followed for all the 18 bottles . Then 10ml of the solution was pipette out and titrated against standard KMnO4 solution.

         A graph was plotted for each type of charcoal by taking ce /(x/m) values along Y axis  and Ce along  X axis. Here  Ce is the equilibrium concentration of oxalic acid after adsorption .A straight line wil indicate the verification of Langmuir adsorption .The different graphs will also indicate highest adsorbing charcoal. 

RESULTS & DISCUSSION

All the charcoal samples we are made uniform size by using serves. The charcoal samples we are uniformly activated by heating.

According to Langmuir Adsorption theorem

Verification of Langmuir Adsorption theory ; x/m=abCe/1+aCe

Where ‘Ce’ is the equilibrium concentration of the adsorbate . ’x’ is the amount of oxalic acid adsorbed .It is calculated from the titre values .Here ‘a’ and ‘b’ constants .

A plot of  Ce/(x/m)  values   against  Ce must give a straight line with slope 1/b and intercept 1/ab. Here samples are labeled according to the charcoal sample used and concentration of oxalic acid after adsorption the equilibrium concentration of oxalic acid was determined by titrating 10 ml of solution with KMnO4 of known concentration

 

Then x/m is calculated, where m is the mass of charcoal added in each case Ce/(x/m) is calculated .A graph was ploted by taking  Ce/(x/m)  values  Y axis and Ce along x axis .A straight line was obtained which verifies Langmuir Theorem.

CALCULATION OF EQUILIBRIUM ON CONCENTRATION OF OXALIC ACID

Charcoal Used	Bottle No	C0 Concentration of oxalic acid before adsorption	VKMnO4 [10 ml filtrate against KMnO4]	C0=(N KMnO4 * VKMnO4)/10 Concentration of oxalic acid after adsorption
Sample 1 Activated charcoal	1 a1	1	89	.89
	1a2		89	.89
	1b1	.5	45.7	.457
	1b2		45.7	.457
	1c1	.25	20.8	.208
	1c2		20.8	.208
	1d1	.125	10.3	.103
	1d2		10.3	.103
Sample 2 Wood charcoal	IIa1	1	49.6	.992
	IIa2		49.6	.992
	IIb1	.5	46.5	.465
	IIb2		46.5	.465
	IIc1	.25	22.1	.221
	IIc2		22.1	.221
	IId1	.125	19.6	.098
	IId2		19.6	.098
Sample 3 Paddy shell charcoal	IIIa1	1	49	.98
	IIIa2		49	.98
	IIIb1	.5	47.3	.473
	IIIb2		47.3	.473
	IIIc1	.25	23.1	.231
	IIIc2		23.1	.231
	IIId1	.125	21.5	.1075
	IIId2		21.5	.1075
Sample IV Coconut shell charcoal	Iv a1	1	49	.98
	Iva2		49	.98
	IVb1	.5	40.6	.466
	IVb2		40.6	.466
	IVc1	.25	22	.22
	IVc2		22	.22
	IVd1	.125	21.1	.211
	IVd2		21.1	.211

CALCULATION OF Ce/(x/m)VALUES FOR   DIFFERENT SAMPLES

Charcoal used	Bottle No	C0 –C e	X =(C0 – C e) ×50×63/1000			x/m	Ce/(x/m)
Charcoal I	1 a1	.11	.3465			.3465	2.568
	I a2	.11	.3465			.3465	2.568
	I b1	.043	.13545			.13545	3.373
	I b2	.043	.13545			.13545	3.373
	I c1	.042	.1323			.1323	1.572
	I c2	.042	.1323			.1323	1.572
	I d1	.022	.0693			.0693	1.486
	I d2	.022	.0693			.0693	1.486
Charcoal 2	II a1	.008	.0252			.0252	39.3
	IIa2	.008	.0252			.0252	39.3
	IIb1	.035	.1102			.1102	4.219
	II b2	.035	.1102			.1102	4.219
	II c1	.029	.0913			.0913	5.09
	II c2	.029	.0913			.0913	5.09
	II d1	.027	.08505			.0852	1.1522
	II d2	.027	.08505			.0852	1.1522
Charcoal 3	IIIa1	.02	.063			.063	15.55
	IIIa2	.02	.063			.063	15.55
	IIb1	.027	.08505			.08505	5.5614
	IIIb2	.027	.08505			.08505	5.5614
	III c1	.019	.05985			.05985	3.859
	IIIc2	.019	.05985			.05985	3.859
	IIId1	.0175	.055125			.055125	1.950
	IIId2	.0175	.055125			.055125	1.950
Charcoal 4	IV a1	.02	.063			.063	15.55
	IV a2	.02		.063	.063		15.55
	IV b1	.034		.1071	.1071		4.3510
	IV b2	.034		.1071	.1071		4.3510
	IVc1	.03		.0945	.0945		2.328
	IV c2	.03		.0945	.0945		2.328
	Iv d1	.0195		.061425	.061425		1.7175
	IV d2	.0195		.061425	.061425		1.7175

     

Table showing adsorption of oxalic acid per gram of charcoal .  ( with different concentration of oxalic acid)

1 N Oxalic acid			.5 N Oxalic acid				.25 N Oxalic acid			.125 N Oxalic acid
Bottle NO.	x	x/m	Bottle No	x	x/m		Bottle No.	x	x/m	Bottle No.		x	x/m
Ia1	.3465	.465	I b1	.1354	.1354		Ic1	.1323	.1323	Id1		.0693	.0693
Ia2	.3465	.3465	Ib2	.1354	.1354		Ic2	.1323	.1323	Id2		.0693	.0693
IIa1	.0252	.0252	IIb1	.1102	.1102		IIc1	.0913	.0913	IId1		.08505	.08505
IIa2	.0252	.0252	IIB2	.1102	.1102		IIc2	.0913	.0913	IId2		.08505	.08505
IIIa1	.063	.063	IIIb1	.0850	.0850		IIIc1	.05985	.0598	IIId1		.05512	.05512
III a2	.063	.063	IIIb2	.08505	.08505		IIIc2	.05985	.05985	IIId2		.055125	.055125
IVa1	.063	.063	IVb1	.1071		.1071	IVc1	.0945	.0945		IVd1	.061425	.061425
IVa2	.063	.063	IVb2	.1071		.1071	IVc2	.0945	.0945		IVd2	.061425	.061425

CONCLUSION

The different varieties of charcoal considered in this investigation has showed considerable adsorption power. It is found that ordinary varieties of charcoal are highly active and they can be used for removing impurities of metal ions even from drinking water.

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