62 was prepared by dissolving 1.5 grams of CaOH
2
into 1 liter of distilled water and kept overnight for allowing the solid particle to settle down and the resulted clear
solution from the mixture was used to absorb the liberated CO
2
into the solution.
3.1.2.4 Sodium Hydroxide NaOH Solution
Sodium hydroxide 1 M NaOH solution was prepared by dissolving 40 gram of NaOH into 1 liter of distilled water. Since the sample was a strong solution, a
concentrated NaOH solution was used for initial pH adjustment.
3.1.2.5 Sulphuric Acid H
2
SO
4
Solution
Two different concentrations of H
2
SO
4
solutions were used for the present experiments. A concentrated H
2
SO
4
solution i.e. 98 H
2
SO
4
was used during the UVH
2
O
2
process for the adjustment of the pH. In the mean time, determination of un- reacted H
2
O
2
was conducted using 2 N H
2
SO
4
solutions. The 2 N H
2
SO
4
solutions were prepared by dissolving 50 ml of 98 of H
2
SO
4
into 1 liter of distilled water.
3.2 Experimental Set Up
3.2.1 UVH
2
O
2
Oxidation Process
The experiments on UVH
2
O
2
oxidation process was conducted in 700 ml jacketed glass reactor. The reaction zone is a cylindrical borosilicate glass tube, 14 inch long
with 2 inch internal diameter. The photo reactor equipped with 8 Watt low pressure Hg vapor lamp GPH295T5L, S. No. EC90277, USA which produces UV light at
254 nm was used along with a current-voltage control unit, and a small opening at the top for collecting the samples.
63 The experimental set up is shown in Figure 3.4 and the schematic diagram of the
reactor is shown in Figure 3.5.
Figure 3. 4 UVH
2
O
2
oxidation experimental set up.
Figure 3. 5 The schematic diagram of the UVH
2
O
2
photoreactor. 1. Current-voltage control unit; 2. Thermometer; 3. UV lamp; 4. Quartz tube; 5. Jacket; 6. Reaction
zone; 7. Water inlet; 8. Water outlet; 9. Sample port; and 10. Stirrer bar.
64 MDEA solution with a desired concentration was taken in the glass reactor. A
required amount of H
2
O
2
was then added into the solution. The total operating volume of the reactor was maintained at 400 ml. The pH adjustment was made using 1 M
NaOH or 98 H
2
SO
4
. The temperature was maintained by circulating cooling water through the jacket at a required temperature. During the process, 3 ml of liquid
sample was withdrawn from time to time and then diluted for the determination of total organic carbon TOC and also for the estimation of un-reacted H
2
O
2
. The H
2
O
2
concentration was estimated by titration method using KMnO
4
solution [124]. For other analysis, such as, by-product identification and biodegradability test, new
samples were prepared before conducting the analysis. The CO
2
liberation during UVH
2
O
2
oxidation process of MDEA was identified by conducting the UVH
2
O
2
oxidation process using sealed reactor. The seal was made using parafilm paper. Sampling port was connected to a vial filled with
CaOH
2
solution lime water. The experimental set up is shown in Figure 3.6.
Figure 3. 6
Experimental set up for the identification of CO
2
liberation during UVH
2
O
2
oxidation process.
Before After
65 Before running the oxidation experiments, the reactor was flushed by nitrogen gas for
about 30 minutes. This step was conducted to eliminate any possible presence of CO
2
. The CO
2
gas that was liberated from the oxidation process reacted with lime water and then converted into CaCO
3
a white solid, according to the following reaction Equation 3.2:
Ol H
s CaCO
g CO
aq CaOH
2 3
2 2
3.2
The excess of CO
2
during the test would result in colorless solution of CaHCO
3 2
, as shown in Equation 3.3.
2 3
2 2
3
CaHCO g
CO Ol
H s
CaCO
3.3
3.2.2 Biodegradability Test of Partially Degraded MDEA Solution
