Adsorption is a unit operation in which surface active materials in true solution are removed from the solvent by interface transfer to the surfaces of an adsorbent particle.

To investigate the properties of activated carbon as an adsorbent, to define the systemic parameters that are required for design of a continuous flow system, and to describe the operational characteristics of packed-bed adsorbent contactors.

A. CALIBRATION CURVE

Prepare a 10-5 M solution of methylene blue (M.W. = 319.85)
Generate an absorption spectra (absorbance vs. wavelength) for the methylene blue solution using a spectrophotometer.
Determine the wavelength at which maximum absorbance occurs.
Prepare dilutions of the 10-5 M solution of methylene blue prepared under step 1 to produce a calibration curve of at least 5 points. More than 5 points are desirable to compensate for anomalous results. Obtain absorbance readings for each of the dilutions at the wavelength determined in step 3.
Plot absorbance vs. concentration in moles/liter as the standard calibration curve.

B. ADSORPTION KINETICS

Prepare two liters of a 10-5 M solution of methylene blue.
Place the solution into a 2-liter baffled vessel and stir vigorously with a laboratory paddle stirrer.
At time zero add 500 mg of the one of the size fractions of prepared granular activated carbon.
Initial samples of the solution should be taken at 5, 10, 15, 30, 45, 60, 75, 90, 105, 120, 150, and 180 minutes. Sampling should be continued until the system equilibrates, but the samples may be collected at periodic intervals when convenient. If disintegration of the activated carbon should occur, sample may require centrifugation or filtration.
Determine the absorbance of the solution in each of the samples and convert to concentration units by use of the calibration curve.
Plot the normalized solution-phase concentration vs. time.
Calculate the quantity of methylene blue that was transferred to the surface of the activated carbon (moles of MB/gram of carbon) for each sample that was collected. Plot these uptake values vs. time on the graph developed in step 6 above.

C. ADSORPTION EQUILIBRIA

Prepare twenty 4-ounce French square bottles (or equivalent) by placing the following weights of granular activated carbon into the bottles: 0, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90,100, 120, 140, 160, 180, and 200 mg.
Prepare two liters of a 10-3 M solution of methylene blue.
Transfer 100 ml of the 10-3 M solution of methylene blue into each of the twenty bottles.
Agitate the bottles vigorously on a laboratory shaker for 7 days. Then settle or filter the suspension to remove the carbon.
Determine the absorbance of the solution in each bottle and convert to concentration units by use of the calibration curve.
Calculate the quantity of methylene blue that was transferred to the surface of the activated carbon for each bottle in moles of MB/g of carbon.
Plot the data in a standard adsorption isotherm format.
Determine the Freundlich and Langmuir adsorption constants by plotting the fitted curves on the graph developed.

D. CONTINUED FLOW SYSTEM

Place 50 g of prepared granular activated carbon into a 2 cm ID x 20 cm glass or Plexiglas column. The column should be fitted at the base with a flow distributor which also serves to retain the carbon in the column. The carbon should be thoroughly wetted before introduction into the column to ensure against the entrapment of air in the carbon bed. Carbon dioxide might also be used to purge the air from the carbon, subsequently dissolving into the water.
The column may be operated in an upflow (fluidized-bed) or in a downflow (packed-bed) fashion. Difficulties in maintaining flow rates and problems of air binding are lessened when the columns are operated in the upflow mode.
Prepare 250 liters of a 10-4 M solution of methylene blue feed solution with tap water.
Adjust the flow rate through the column at 25 ml/min/cm2 (approximately 5 gpm/sf).
Initiate flow of feed solution through the column at the preadjusted flow rate. record the time as time zero.
Sample and determine the concentration of MB in the column effluent one hour after initiation of flow and at least five times daily thereafter until complete breakthrough of the column is attained.
Plot the breakthrough curve showing both the concentration of MB in the column influent and effluent as a function of time.
Calculate the quantity of MB that was transferred to the surface of the activated carbon as a function of time by graphically integrating the area between the curves of the column influent vs. time and column effluent vs. time. Plot these uptake values vs. time.
From the adsorption isotherm which was experimentally determined in C above, calculate the time required for square-wave breakthrough assuming an infinite rate of adsorption. Plot this curve on the graph developed in step 8 above. How does this theoretical breakthrough correspond to your experimental results?

Volumetric flasks: 2000 ml, 100 ml
Assorted pipettes
Laboratory shaker
20 4 ounce French square bottles
Glass or Plexiglas column, 2-3 cm ID x 20 cm
Laboratory pump, 0-2000 ml/minute
Spectrophotometer
Whatman #2 filter paper

Granular activated carbon; sieved, washed of fines, and dried to constant weight at 105oC
Methylene blue
10-2 M methylene blue stock solution

Discuss results of experiments in the context of design and operation of real-world adsorption systems.

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