Current World Environment

Introduction

SO₂ and its derivatives produce strong irritation on the eyes and nasal passage ways. It causes intense irritation even at 2.5 ppm levels to the eyes and respiratory tract.^1-3 It is absorbed by the nasal system leading to swelling and stimulated mucus secretion and it causes lung cancer.^4-6 The accumulation of transport vehicles such as automobiles at the signal points on the main arteries of the city and the consequent emission of exhaust of considerable quantity is everyday sequence. So the present study deals with controlling technologies of SO₂ by batch adsorption by using MnO₂ as an adsorbent.

Methods and Materials

Selection of the Adsorbent

Manganese dioxide is selected as an adsorbent for the present studies. MnO₂ is amphertic in nature and it is a good oxidizing agent. It can easily to take an atom of oxygen. Due to the oxidizing nature of MnO₂ a reaction takes place between them. Taking that factor into consideration MnO₂ is selected as an adsorbent.
 

Figure - 1: Variation of contact time between MnO2 and SO2 Click kere to view figure

The present studies are conducted by batch adsorption techniques. These methods are selected because SO₂ is present in low concentrations and it is noncombustible. The experiments are conducted with respect to contact time concentration, adsorbent dosage and with respect to temperature.

Experimental Procedure

Effect of Contact Time and Particle Size on Adsorption of SO₂ :

To study the effect of contact time, SO₂ gas diluted with N₂ gas is made to pass through a catalytic tube, which is maintained at a constant temperature. The catalytic tube is filled with a fixed amount of 0.8gms. The flow rate of 60 ml/min. was maintained. The experiments are conducted with 500mic. and 250mic. The results are shown in fig.1.
 

Figure - 2: Variation of initial concentration Click kere to view figure

Effect of Concentration

Different concentrations of SO₂ diluted with N₂ gas are made to pass through a catalytic tube, which consists a constant amount of MnO₂. The concentration of the gas is determined before and after adsorption of SO₂ by using SO₂ analyzer. The experiments are conducted with respect to 250 MIC and 500 MIC particle size. The results are shown in fig.2
 

Figure - 3: Variation of adsorbent dosages Click kere to view figure

Effect of Adsorbent Dosages

To study the effect of MnO₂ dosages, definite concentration of SO₂ is made to pass through a catalytic tube which consists of adsorbent. The adsorbent dosages are varied and initial conc. of SO₂ and final conc. of SO₂ are determined by using SO₂ analyser which is based on west-Gaeke method. The results are shown in fig.3.
 

Figure - 4: Relationship between Log x/m and log Ce Click kere to view figure

Effect of Temperature

To study the effect of temperature, the experiments are conducted at three different temperatures i.e., 45⁰C, 65⁰C and 85⁰C.

Results and Discussion

Fig.1 shows that initially the percentage removal of SO₂ increases with the increase in contact time.^7-8 The optimum time for the removal of SO₂ is 20 min. The percentage removal of SO₂ increases with decrease in particle size.^9-10 The percentage removal of SO₂ increases with increase in contact time and it follows a smooth curve which indicates that the process is of first order.¹¹ Initially the adsorption capacity is practically proportional to contact time initially the MnO₂ surface is free from SO₂ once equilibrium is established adsorption no longer depends on the surface area.
 

Figure - 5: Relationship between 1/T and Ln K Click kere to view figure

Fig.2 represents the percentage removal of SO₂ decreases with the increase in concentration.^11-12 The number of gas molecules will be low at low concentrations and at the higher concentrations the number of gas molecules is more so adsorption is less.

Fig.3 represents that the percentage removal of SO₂ increases with the increase in adsorbent dosage . Greater the number of adsorbent sites, greater is the percentage of adsorption.

Fig.4 represents that adsorption process follows Freundlich adsorption isotherm.¹⁵

It is observed the adsorption capacity increases with increase in temperature i.e., 85⁰C. Thermodynamic parameters are calculated by plotting logk_c verses 1/T.

A straight line is obtained. The negative 43, slope of the straight line indicates that the process of adsorption is exothermic in nature. The free energy of the process is negative which indicate that process is feasible and spontaneous in nature,

References