(10600030)cr_removal_2.pdf - ethesis

Susmita Mishra (Project Guide) who suggested the topic and provided guidance, motivation and constructive criticism throughout the course of the project. The electrochemical method is applied as one of the surface modification methods of activated carbon available in the market. Our project work includes the fabrication of an experimental setup, surface modification (anode oxidation) in 0.5 M KCl solution with different current intensities, and recent comparisons of BET surface area, porosity, FTIR analysis (for identification of changes in bonds after electrochemical oxidation) and adsorption in the spectrophotometer.

As the intensity of oxidation is increased by increasing the intensity of source current, the amount of adsorption also increases. It is also observed that if the intensity of current is increased from 0.1 Amp to 2.1 Amp, the amount of adsorption increases. Pollution load of the environment is increasing every day due to the global increase in pollution and our pursuit to lead comfortable life, leading to explosive growth of industries, mining operations and increased use of natural resources. Chromium (a metal) compounds are widely used in industries such as electroplating, flour finishing, tanning, pigments, etc.

Activation of carbon involves pyrolysis of the precursor in an inert environment followed by activation. The disadvantage of the chemical activation process is lower purity of activated carbon is produced and this method also causes environmental pollution.

LITERATURE REVIEW

• Activated carbon
• Production
• Physical activation: By the help of gas the precursor is developed into activated carbon. One or combination of the following process can be used
• Chemical activation: First of all the raw material is impregnated with chemicals like solution of strong acid (phosphoric acid, sulphuric acid ), strong base (potassium
• Classifications
• Powdered activated carbon (PAC)
• Extruded activated carbon(EAC)
• Impregnated carbons
• Polymers coated carbon
• Characterization of activated carbon .1 Gas adsorption
• Physical and chemical adsorption
• Physical adsorption force
• Physical adsorption on macropores (assumed as a planar molecule)
• Physical adsorption on mesopores
• Physical adsorption on micropores
• Isotherms
• Classification of adsorption isotherm

It is one of the experimental methods (SAXS, SANS. Mercury porosimetry, SEM, STM thermoporometry, NMR methods and others) available for surface area and pore size distribution [Lowell et al., Kluwer Academic Publn, (2004)]. Depending on the strength of the interaction, all adsorption processes can be divided into two categories: chemical (irreversible) and physical adsorption. The adsorption isotherm is the amount of adsorbate adsorbed to the adsorbent as a function of its pressure (gas) or concentration (liquid) at constant temperature.

Where, x is the amount of adsorbate adsorbed, P is the pressure of the adsorbate, m is the mass of the adsorbent, and k and n are empirical constants for each adsorbate-adsorbent pair at a given temperature. If θo is the fraction of unoccupied surface, then the number of collisions with bare surface per unit surface area per second is. Ndes=Nmθ1v1e-E/RT (2.9) Where, Nm is the number of molecules in a complete layer per unit area.

Where P and P0 are the equilibrium and saturation pressures of adsorbate at the given adsorption temperature, v is the adsorbed gas, vm is the amount of the adsorbed gas in the monolayer and c is the BET constant, which is expressed by E1 is the heat of adsorption for the first layer; EL is the heat of adsorption for the second and higher layers and is equal to the heat of liquefaction.

RS shows the progressive sensing of mesopores inferring that the largest mesopore is in position S. As the nitrogen pressure decreases in the device, the equilibrium positions (desorption isotherm) do not follow the SR line but the SUR line to create hysteresis. meeting the loop at point R.

It shows pore condensation and hysteresis. Initial part shows weak attractive interactions between the adsorbent and the adsorbate

Quantachrome BET surface area analyzer

The BET surface analyzer is based on the BET theory of adsorption of gas molecules on the surface of the adsorbent.

FTIR analyzer

• Spectra of transmittance with different wave numbers The spectra of different functional groups are as follows

Carbon fibers were subjected to electrochemical oxidation (25 oC, 0-450 mAmp, NaOH as electrolytic solution) and then dried (110 C for 6 hours). Nitrogen adsorption isotherms for BET surface area and pore volumes were measured at 77K [Park et al., Carbon (1999)]. Result [Park et al., Carbon (1999)] shows specific surface area, average pore diameter, micropore volume does not change much.

The result also shows that the amount of adsorption and the adsorption rate of chromium from the aqueous solution increases with increased electrochemical oxidation of ACF. Surface area, acid sites, batch and continuous sorption experiment and kinetics were analyzed [Rengel-Mendez et al., Trans IchemE, (2000)]. Result [Rengel-Mendez et al., Trans IchemE, (2000)] shows a decrease in the BET surface area and the total oxygen-containing functional groups increased by 3.36 times.

Kinetic experiment shows that the adsorption rate of cadmium was fast and 96% of fractional approach to equilibrium was achieved in 12 min using both unoxidized electrochemically oxidized carbon. Result [Park et al., Mat Sc and Engg. 2005)] shows total pore volume and micropore volume decrease. This is due to increase in oxygenated functional groups and blocking of the pores.

It can be suggested that due to high ionic radius of copper (II) 0.70 Ao and Nickel (II) 0.69 Ao compared to that of Chromium (VI) 0.52 Ao, causes a rapid saturation of adsorption sites due to steric crowding.

Chemicals used

Sample used

Glassware and Apparatus used

Fabrication

• Fabrication of perplex column
• Fabrication of stand (support to the perplex columns)
• Fabrication of clamps (to hold the columns)
• Preparation of electrolytic solution
• Oxidation of activated carbon
• Drying of oxidized (surface modified sample) The sample was dried in oven at 85 o C for 24 hours

To cut the anode side of the copper plate, which is 50 mm thick, a power-operated hex saw is needed. With a glass marking pen, the plate was marked so that it only fits into the baffled column. This mesh is then attached to one side (the ends) of the column with the help of epoxy glue.

Three plastic holders of equal size (3 mm x 20 mm x 55 mm) were cut from a large cuboidal plastic fiber in the fluid flow laboratory by hand with the help of a hex saw. The edges were also bent at 90o so that it does not slide off the column. Inside it there is a cathode plate, mixer, thermometer and an arrangement for the oxidation of active carbon.

This arrangement consists of a 2 cm high (2.75'' diameter) three-legged baffle column with a mesh covering the entire area within it. To restrict the flow of electrolytic solution from the side, another baffled column (2 cm height x 2.75'' diameter) with a gasket insulator is supported on it. To have a tight fit between these two turbulent columns three clamps (GI sheet made) are used.

A circular copper plate of 5 mm thickness, which just fits into the perplex column, serves as anode. Thick copper plate is taken to limit electrolytic solution to get on top of it and inhibit oxidation there. Before starting oxidation, the sample was allowed to wet with the solution for 20 minutes.

After oxidation, the sample was taken in a beaker and washed continuously in distilled water for 20 minutes.

Fig 3.1: photograph of plastic net, perplex column, 5 mm copper plate, plastic stand used

Method for surface area and porosity analyses

Method of absorbance analyses in spectrophotometer .1 Preparation of potassium dichromate solution

• Preparation of standard indicator
• Method for spectrophotometeric analysis

Method for FTIR analysis

In order to determine the optimal current to be supplied for the oxidation of commercially available activated carbon, we analyzed the absorbance of the adsorbed chromium solution for five different concentrations (2 mg/L, 4 mg/L, 6 mg/L, 8 mg/L and 10 mg). /L). A graph of this absorbance is plotted with the X axis as the concentration of the adsorbed sample of various initial concentrations with the Y axis showing the current. From the graph, we conclude that by increasing the current strength from 0.1 A to 2.1 A, the amount of adsorption increases.

If it is considered that, 2.1 Amp as the optimal final oxidation current, then we can study the adsorption characteristics and FTIR analysis of the sample oxidized at 2.1 Amp.

Table 4.1: concentration of chromium at different intensity of oxidation Current(amps)→

FTIR analysis

The FTIR spectra show that a decrease in transmittance was observed in the range 3700-3400 cm-1. The adsorption bands in the region of 1640-1500 cm-1 are due to the overlap of aromatic ring bands and double band (C=C) vibrations with the bands of C=O units.

Fig 4.2: FTIR spectra of ACF of 2.1 Amp oxidized carbon Table 4.3: FTIR report of raw sample with 22 chosen points

Surface area and porosity

0 amp

1 amp

9 amp

Analysis of pore volume with current

The pore volume of various oxidized samples, including that of the raw sample, is given below. The result shows that as the intensity of oxidation increases, the pore volume decreases.

Analysis of pore diameter with current

The pore diameter measured by the analyzer is mainly due to the contribution of mesopores and macropores. Severe reduction in pore size can be attributed to the presence of a certain amount of humic substances in micro- and mesopores. These are some salts of metals like copper and potassium that are used during the experiment.

The fabrication was carried out in such a way that a large surface area was available for carbon to undergo oxidation. The parameters on which the adsorption study was carried out included the effect of flow on the surface area, pore volume and pore size. The oxidation process also causes the destruction of the pores, resulting in an eventual decrease in surface area.

A significant loss in porosity was observed and is due to blocking of pores by the formation of functional groups (carboxylic acid groups, hydroxyl groups, lactonic groups, phenolic groups) and aggregation of humic substances. Strict decrease in pore size can be attributed due to the presence of a certain amount of humic substances in micro and mesopore. These are some salts of copper and potassium that are formed during the experiment.

This concludes that the rate of formation of functional groups (which are responsible for adsorption) increases with increasing current. It is also found that as the current strength increases from 0.1 A to 2.1 A, the amount of adsorption increases. In the FTIR spectra, it can be seen that a drop in permeability was observed in the range 3600-3200 cm-1.

The adsorption bands in the region of 1640-1500 cm-1 suggest the overlap of aromatic ring bands and double band (C=C) vibrations with the bands of C=O units. Berenguer R., Marco-Lozar JP, Quijada C., Cazorla-Amoro's D., Morallo'n E., Effect of electrochemical treatments on the surface chemistry of activated carbon. Reporting physisorption data for gas/solid systems, with particular attention to the determination of surface area and porosity.