Preparation of Acid Activated Carbon From Dog Teeth Sample Using Two Moles of Citric Acid (0.5m and 1m) at High Temperature

Preparation of Acid Activated Carbon From Dog Teeth Sample Using Two Moles of Citric Acid (0.5m and 1m) at High Temperature

CHAPTER ONE

AIMS AND OBJECTIVES OF STUDY

The objectives of this study are for the following reasons:

1. To prepare acid activated carbon from dog teeth sample.
2. To identify the unknown crystalline materials present in the sample using the X−ray powder diffraction instrument (XRD).
3. To reveal information about the sample including external morphology (texture), chemical composition, porosity, homogeneity and crystalline structure and orientation of materials making up the acid activated bone (dog teeth) sample.

CHAPTER TWO

LITERATURE REVIEW

Types of Carbon Materials 

All the carbon materials composed of the carbon element has unique bonding with other elements and with itself. Depending on type of hybridization of the carbon atoms, the main allotropic forms of carbon (Delhaes, 1998) are classified as diamond, graphite and fullerenes.

Diamond forms a cubic 3D structure (sp³ – based structure) in which each carbon atom bonds with four other carbon atoms through sp³ σ bonds. The C-C bond length is 154 pm. Diamond has the highest atomic density of any solid and is the hardest material with the highest thermal conductivity and melting point. Graphite has a hexagonal layered structure (sp² – based structure) in which carbon atoms are bonded to neighboring carbon atoms by sp² σ and delocalized π bonds. Graphite has an even higher thermal conductivity than diamond and exhibits a good electrical conductivity. Fullerenes are three dimensional carbon structures where the bonds between the carbon atoms are bent to form an empty cage of sixty (C₆₀) or more carbon atoms. This is due to the re-hybridization, resulting in a sp^2+ε form, which is intermediate between sp² and sp³ (Ebbesen and Takada, 1995).

The majority of carbons exhibit the allotropic forms, i.e. a sp² – based structure. Based on the degree of crystallographic order in third direction (c-direction), the allotropic form of graphite can be classified into graphitic carbons and non-graphitic carbons (Franklin, 1951).

Non-graphitic carbons in turn divided into graphitizable and non-graphitizable carbons. A graphitizable carbon is “a non-graphitic carbon which upon graphitization (heat treatment) is converted into graphitic carbon”, while a non-graphitizable carbon is “a non-graphitic carbon which cannot be transformed into graphitic carbon” by high-temperature treatment.

Carbons exhibit different structures depending on the size and such a wide variety of possible structures gives rise to a large amount of different types of carbons. Figure 2.1 shows a schematic representation of some of these carbon structures (Bandosz, 2006).

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Chapter Three

Research methodology

Characterization of Precursor 

Composition of the raw material is an important factor that dictates the selection of precursor for activated carbon production. The chemical composition of the precursor material, mainly the percentages of the cellulose and lignin present in Dog teeth sample were found by means of standard methods (Thimmaiah, 1999). Materials with high lignin content develops AC with high macropores (> 50 nm), whereas, materials with high cellulose yields AC with predominantly microporous structure (Daud and Ali, 2004; Gani and Naruse, 2007).

Estimation of Cellulose

About 3 ml of acetic : nitric reagent (150 ml of 80 % acetic acid + 15 ml of concentrated nitric acid) was mixed with the 0.5 – 1.0 g of sample in a vortex mixer and placed in water bath at 100 ^oC for 30 min.

After centrifugation the collected residue was washed with water and added 1 ml of 67 % H₂SO₄ and left for1 h. Then 1 ml of the solution was diluted to 100 ml and 10 ml of anthrone reagent was added to 1 ml of this solution and mixed well. The tubes were heated in water bath for 10 min and measured the absorbance at 630 nm after cooling (TAPPI, T 264). The amount of cellulose was determined from the standard graph (40 – 200 µg/L of cellulose).

Chapter four

Results

Selection of Precursor

 

Activated carbons (ACs) can be produced from any carbonaceous materials, both naturally occurring and synthetic. Process economics however dictates the selection of readily available and cheaper feed stocks. Most commonly used precursors for the production of commercial ACs are coconut shell, wood, etc. Biomass precursors offer most economical service because they are renewable with low mineral content and appreciable hardness.

Literature pertaining to use of lignocellulosic materials such as nutshells, coconut shells, apricot stones, plum stones is very extensive. On the contrary, Dog teeth (Aegle Marmelos) shell received much less attention as a precursor for the preparation of AC. The chemical composition and various physical properties of Dog teeth sample were presented in Table 4.1. Proximate and ultimate analyses were performed for the raw material. The proximate analysis was conducted following the procedure described elsewhere (UNE 32001-81, 1981; UNE 32019-84, 1984). The ultimate analysis was performed using a CHNS analyzer. The results reported in Table 4.1 indicate that the Dog teeth sample has a high cellulose content (24.35 %) and low lignin content (19.9 %) than that of coconut shell, which is an important factor for preparation of AC. However, ultimate analysis highlights that the precursor has negligible sulfur and low nitrogen content with high carbon and oxygen contents.

CHAPTER FIVE

CONCLUSIONS

Based on the detail experimental investigation the conclusions derived are as follows.

• Dogteeth(Aegle Marmelos) shell containing high cellulose (24.35%) and volatile content (72% ) proved to be a promising precursor for Activated carbon
• Chemicalactivation of precursor by phosphoric acid, zinc chloride and potassium hydroxide produced ACs of various surface
• Developmentof AC was influenced by various factors such as type of chemical reagent used for impregnation, impregnation ratio, carbonization temperature and holding time
• Maximumyields 47 %, 69.33 %, and 85.33 % were obtained at optimum process conditions for AC-PA, AC-ZC, and AC-PH respectively.
• Phosphoric acid treated activated carbon exhibited maximum values for surface area (1657m²/g) pore volume (0.58 cc/g), micropore surface area (1625 m²/g) and micropore volume (0.56 cc/g) at optimum process conditions (30 % H₃PO₄ impregnation, 400 ^oC carbonization temperature and 1 h holding time).
• AC-PA could remove 98.7 % Cr(VI) at optimum process conditions ( pH – 2.0, Cr(VI)concentration – 10 mg/L, adsorbent dose – 0 g/L, temperature – 30 ^oC and contact time –3.0 h).Adsorption of Cr(VI) on prepared ACs increased with reducing pH from 11.0 to 2.0. AC-PA could remove 76 % Cr(VI) even at nuetral
• AC-PAshowed adsorption capacities of 3 mg/g and 98.6 mg/g at initial Cr(VI) concentrations of 10 mg/L and 100 mg/L, respectively.
• Freundlich model showed best fit to the adsorption data (R²= 0.996) of AC-PA and the kinetic data followed pseudo-second order model signifying both film and pore diffusion mechanisms during adsorption
• SpentAC was regenerated simply by using hot water (80 ^oC) and mild acid (0.1 M H₂SO₄).
• Modeling of Cr(VI) adsorption on AC-PA by using 2⁴Full Factorial Design (FFD) revealed that including all the main factors some interactions such as AB [pH * concentration of Cr(VI)], BC [concentration of Cr(VI) * adsorbent dose] and ABCD [pH * concentration of Cr(VI) * adsorbent dose * temperature] significantly influenced the removal of Cr(VI) from aqueous

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