Activated Coconut Shell Charcoal Carbon Using Chemical-Physical Activation

07 Apr.,2022

The use of activated carbon from natural material such as coconut shell charcoal as metal absorbance of the wastewater is a new trend. The activation of coconut shell charcoal carbon by using chemical-physical activation has been investigated.

 

The use of activated carbon from natural material such as coconut shell charcoal as metal absorbance of the wastewater is a new trend. The activation of coconut shell charcoal carbon by using chemical-physical activation has been investigated. the parking brake was pyrolized in kiln at temperature about 75 - 150 °C for about 6 hours in producing charcoal. The charcoal as the sample was shieved into milimeter sized granule particle and chemically activated by immersing in various concentration of HCl, H3PO4, KOH and NaOH solutions. The samples then was physically activated using horizontal furnace at 400 °C for 1 hours in argon gas environment with flow rate of 200 kg/m3 . The surface morphology and carbon content of activated carbon were characterized by using SEM/EDS. The result shows that the pores of activated carbon are openned wider as the chemical activator concentration is increased due to an excessive chemical attack. However, the pores tend to be closed as further increasing in chemical activator concentration due to carbon collapsing.

 

INTRODUCTION

Heavy metals such as iron, copper etc may be commonly present in wastewater and ground water system. The heavy metal is toxic since it can not be degraded biologically into environment freindly product. Thus the heavy metals removal from wastewater and ground water is an important treatment to avoid them absorbed by the living organism, enter the food chain and at the end accumulate into human body.

 

Removing heavy metals can utilize a natural absorbent such as coconut shell charcoal since it has high carbon density and porosity. The charcoal can be activated physically by using by varying argon gas pressure, activation time and temperature. It showed that the pores of charcoal were distributed uniformly and the pores size reduced as the physical activation parameters were increased. The chemical activation was performed by emmersing the charcoal into chemical solution so that the solution penetrate deep into the carbon charcoal structure to develop the pores. The results showed that the nanopores were developed on the charcoal. The investigation result showed that the narrowed pores size distribution were developed accurately by using physical activation while the high density carbon that impact to the high volumetric adsorption was developed by using chemical activation. In this study, the coconut shell charcoal was activated by using chemical-physical activation comination to achieve optimum activated carbon performance.

 

EXPERIMENT

The coconut shell charcoal was produced by pyrolysis process in kiln at temperature about 75-150 °C for about 6 hours. Before activation process, the charcoal samples were washed by using aquades and dried by using furnace at temperature of 120 °C for about 12 hours. Next, the charcoal was sieved into milimeter size granule then cleaned by using aquades and subsequently cleaned by using ultrasonic cleaner in 96% alcohol at room temperature for 30 minutes and dried by using hot plate for 60 minutes. Four various chemical solutions as the activator used were KOH solution with various concentration of 30, 40, 50% and 60%. NaOH solution with various concentration of 1%, 2%, 4%, 7% and 11%. HCl and H3PO4 solutions with both various concentration of 2%, 4% and 6%. All the charcoal samples were emmersed into the activator solution for about 24 hours and then washed by using aquades and dried by using hot plate for 3 hours. After the chemical activation process was accomplished, the physical activation was performed by using horizontal furnace at temperature of 400 °C in argon gas environment with its pressure of 200 kg/m3 for an hour. The experimental equipment was shown in Figure 1.

 

Activated Coconut Shell Charcoal Carbon Using Chemical-Physical Activation

FIGURE 1. Horizontal furnace for physical activation with argon gas supply.

 

The composition, surface morphology and pore structure of activated carbon was characterized by using SEM/EDS (Scanning Electron Microscopy /Energy Dispersive Spectroscopy) analysis.

 

RESULTS AND DISCUSSION

The SEM analysis result of surface morphology of activated carbon with KOH activator were showed in Fig. 1. It shows that the pore size tend to increase as the KOH concentration is increased. EDS analysis of activated carbon is summarized in Table 1. It shows that in general, the carbon content of activated carbon decreases.

From the experiment results, it shows that in general, the use of the chemical agent is to open wider the pore. It was reported that during the chemical activation, the supplemental pores and internal surface were created on the charcoal carbon. The pore number increase as the chemical agent concentration is increased. However at further increasing concentration of chemical agent, the number of pores decrease due to an excessive chemical attack that cause the phenomenon of the incipient carbon collapsing. It was reported that the pores became wider and broader as the chemical agent (ZnCl2) concentration was increased. However, there were two competing mechanism phenomenom during activation process, namely micropore formation and pore widening.

During activation process, the porosity is developed by three steps. First, open the previously inaccessible pores. Second, create the new pores and last, wide the existing pores. The chemical agent penetrate deep into carbon structure causing tiny pores formation thus increase the surface area of activated carbon. As the chemical concentration is increased, the surface area increases and larger pores are developed. A heterogeneous surface was produced due to the reaction between chemical activator with the sample.

 

Activated Coconut Shell Charcoal Carbon Using Chemical-Physical Activation

FIGURE 2. SEM of activated carbon at KOH activator concentration of (a) 30%, (b) 40%, (c) 50% and (d) 60%

 

Activated Coconut Shell Charcoal Carbon Using Chemical-Physical Activation

FIGURE 3. SEM of activated carbon at NaOH activator concentration of (a) 2%, (b) 4%, (c) 7% and (d) 11%.

 

Activated Coconut Shell Charcoal Carbon Using Chemical-Physical Activation

FIGURE 4. SEM of activated carbon at HCl activator concentration of (a) 2%, (b) 4%, (c) 6%.

 

Activated Coconut Shell Charcoal Carbon Using Chemical-Physical Activation

FIGURE 5. SEM of activated carbon at H3PO4 activator concentration of (a) 2%, (b) 4%, (c) 6%.

 

Activated Coconut Shell Charcoal Carbon Using Chemical-Physical Activation

 

The chemical agent such as H3PO4 and ZnCl2 in activation process may dehydrate the residual organic molecules that prevent hydrocarbon deposition on the carbon surface while the physical activation process at high temperature and inert gas environment to remove the absorbed hydrocarbon. Thus the purpose of both process are to improve the surface area. H3PO4 is hehydrating agent that inhibit the release of volatile matter and produce high yield carbon content in charcoal. However the precentage yield strated to decrease as further increasing in H3PO4 concentration. It also inhibit the formation of tar and other liquid that might fill the pores during activation process. The use of phosporic acid as an activating agent promotes depolymerization, dehydartion and redistribution of contituent biopolymer thus increases the yield of activated carbon. The increase of carbon yield is related to the microporosity development. Both procesess is occured simultaneously. KOH is a type of strong base and can react with hidrocarbon and microcrystalline carbon, which can develop some pores in charcoal. In further chemical activating reaction, the pores size become larger. It lead the decrease of micropores number and increase the mesopores and macropores. It was reported that the pore size distribution became narrowest as KOH concentration was increased. However at higher KOH concentration, the pore size distribution was widen. For the increase of hidroxide concentration, the chemical agent of KOH not only produces pores but also wekens and progressively destroys the incipient carbon structure. The use KOH as an activating agent makes not only more microporous of activated carbon but also more lignin transformation into activted carbon during the activation process. It was reported that the use of activator agent NaOH did not produce surface area as high as KOH due to KOH dehydrate and oxidize stronger than NaOH for activating biomass. While the activation with HCl acid increased the porosity of activated carbon thus created more reactive sites for metal ion adsoption. During activation, reaction between C and HCl make the devolatilization process occurs and develop the rudimentary pore structure in the charcoal.

 

CONCLUSION

The activated coconut shell charcoal carbon can be prepared by using chemical-physical activation. The effect of chemical activator is to open the pore of carbon wider as the chemical concentration is increased due to chemical reation with the carbon element in the charcoal. However at higher chemical concentration the pore is closed due to carbon collapsing.

 

Activated Coconut Shell Charcoal Carbon Using Chemical-Physical Activation