COMPARATIVE STUDY OF CO2 CAPTURE USING ZEOLITE (ZSM-5) AND ACTIVATED CARBON FROM SUGARCANE BAGASSE

ABSTRACT

The increasing energy demand can be meet globally with the use of non-renewable fossil fuels, however the use of these fossil fuels is associated with tremendous release of CO2, which largely contributed to greenhouse gases effect (GHG‘s). Climate change or globally warning is one of the result of GHG‘s effect, to prevent global warming or climate change, the excess amount of CO2 in the atmosphere must be reduced to its bearable minimum, hence the  need  for  carbon  capture  and  storage  techniques  (CCS).  CCS  uses  different  solid adsorbents to remove excess CO2  from the atmosphere which could be stored in aquifer or buried under the soil. In this work zeolite and activated carbon from sugarcane bagasse were used as an adsorbent for CO2 adsorption from the atmosphere. The adsorption capacity of the adsorbents were determined and the result revealed that the amount of CO2  adsorbed using activated carbon (65 mg/g) was higher than that of the zeolite (50 mg/g), however for both adsorbents, the adsorption capacity were higher than that of the commercial adsorbents when compared. The adsorption isotherm and kinetic models employed in this study revealed that the correlation coefficient, R2 values of 0.9859 and 0.9691 respectively are close to unity, this closeness to unity indicates a favorable adsorption process. Increase in temperature from 25OC to 100OC was observed with a decrease in adsorption capacities of the adsorbents, whereas increasing the adsorbent dosage from 0.5g to 1.5g shows appreciable increase in the adsorption capacities of zeolite and activated carbon. The BET analysis on the adsorbents revealed the surface areas of 224.2m2/g and 388.3m2/g for activated carbon and  zeolite respectively.         The         activation         energy         Ea              of         15.3KJ/mol         and 13.5KJ/mol for activated carbon and zeolite obeys physiosorption.

CHAPTER ONE

1.0  INTRODUCTION

1.1 Background to the Study

The tremendous demand of energy in the world these days has caused the rising of greenhouse gases (GHG) emission, which is becoming the major concern by the public recently. Associated with that, carbon dioxide (CO2) is labeled as the most important GHGs that contribute to the global warming through anthropogenic emission from power plant generation, transportation, and industrial sector (Rashidi et al., 2014). Instead of adapting to the substantial effect of global warming, mitigation of the CO2  emission is preferable. Therefore, immediate and continuous action should be taken to decrease the CO2 concentration in the atmosphere. The CO2 reduction can be done by some options such as an enhancement in combustion and energy efficiency, reduction in the use of fossil fuel, switch to non-carbon-emitting resources i.e. renewable energy, and to capture and sequester CO2 (CCS) permanently. Amongst these options, CCS is considered as a useful technique, since it provides an ample time for the development of low-cost renewable energies and cleaner usage of fossil fuels resources during the transition period (Plaza et al., 2007).

Among the possible technologies for CO2  capture, solid adsorption is preferred due to low energy requirements, low capital and operating cost, together with limited secondary waste generation (Rashidi et al., 2014). Activated carbon is one of the promising solid adsorbents that can be utilized to capture CO2  due to its numerous benefits, such as inexpensive, easy for regeneration, insensitiveness towards the moisture, high CO2  adsorption capacity at ambient condition, high specific surface area, adequate pore size distribution, high mechanical strength, as well as low energy requirement (Lua and Guo, 2001) .

In general, there are two main steps for the preparation of activated carbon (1) the carbonization of raw materials below 800 oC, in the absence of oxygen, and (2) the activation of carbonized product (char), either using physical or chemical activation methods (Sutrisno et al., 2016).

Sugarcane bagasse (SCB) is  suitable for preparing activated carbons  due to  their excellent natural structure and low ash content. SCB is a byproduct of sugarcane industries obtained after the extraction of juice for production of sugar. Conversion of sugarcane bagasse into activated carbons which can be used as adsorbents, ion exchange, carbon molecular sieve, catalyst would add value to these agricultural wastes help reduce the cost of waste disposal, and provide a potentially cheap alternative to existing commercial carbons. Studies on CO2  adsorption using activated carbon from sugarcane bagasse have been reported in literature and hence the present study attempts to compare CO2 capture using zeolite (ZSM-5) and activated carbon from sugarcane bagasse.

Several  technologies  to  separate  and  capture  the  industrial  emissions  of  CO2   have  been developed. Among them, certain technologies are based on the CO2  adsorption/desorption by using natural, synthetic zeolites and activated carbon. The zeolites are a subclass of tectosilicates that possess a framework formed by a three dimensional assemblage of tetrahedra [SiO4] and [(AlO4)-] (Danielle et al., 2008).

The CO2 usually undergoes a physical adsorption (physisorption) at the surface of zeolites. The zeolites are recognized to be the potent CO2 adsorbents that are able to adsorb and desorb CO2. The adsorption capacity of zeolites depends on several factors including the size, polarizing power, distribution and the number of cations in their porous structure, Si/Al ratio, size, the form of their pores, the polarity and size of adsorbed molecules, the presence of water and other gas

and presence of carbonates at their surface. Experimental conditions such as pressure and temperature are also among the factors influencing the adsorption capacity of zeolites. (Danielle et al., 2008)

1.2 Aim of the Study

The   research   project   is   aimed   at   studying   comparatively,   CO2    capture   using   zeolite

(ZSM-5) purchased and activated Carbon produced from Sugarcane Bagasse.

1.3 Objectives of the Study

The aim will be achieved through the following objectives:

1.   Production of activated carbon from sugarcane bagasse

2.   Characterization of activated carbon and zeolite using SEM, FITR, BET and TGA.

3.   Carrying out batch adsorption process to remove CO2 using Zeolites and activated carbon from sugarcane bagasse.

4.   Investigation on adsorption mechanisms, kinetics, and thermodynamic.

5.   Comparison of the results from the two adsorbents

1.4 Statement of the Research Problem

Several authors have reported the use of activated carbon and zeolite as a good adsorbent for  capture, but the information about the comparison between activated carbon from sugarcane bagasse and zeolite (ZSM-5), to inform their choice in  capture is limited, such information is what this research work seeks to address.

1.5 Scope of the Study

The scope of this work is limited to comparative study CO2 capture using activated carbon and zeolites with varying adsorption variables such as initial concentration, contact time, temperature and adsorbent dosage at constant flowrate, as well as investigate the kinetics, isotherm and thermodynamic of the adsorption mechanism.

1.6       Justification of the Study

Comparison between activated carbon from sugarcane bagasse and zeolite in removing CO2 will help to determine the best adsorbent suitable in removing excess CO2 from the atmosphere.

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