EXPERIMENT 2 : Absorption of Carbon Dioxide in Water

1. OBJECTIVE

a. Study the basic principles of the absorption of a gas into liquid using packed-columnb. Study the absorption of carbon dioxide into water.c. Study the effect of water flow rate on absorption of carbon dioxide into water.

2. INTRODUCTION

Gas absorption is a widely used unit operation in chemical engineering. The gas absorption unit is pilot plant scale unit designed to demonstrate the principles of gas absorption and for students to investigate the principles of packed tower absorption processes and hydrodynamics as well as provide practical training in the operation of gas absorption plant. This absorption column is designed to absorb carbon dioxide, CO2 from an air/ CO2 mixture into water flowing down the column.

3. EQUIPMENT

Legend

A. Control PanelB. CO2 RegulatorC. CO2 CylinderD. Reservoir with Pressure GaugeE. Air CompressorF. Collecting TankG. Water PumpH. Water TankI. Boris SaddleJ. Tower ColumnK. Manometer (Bottom-Middle)L. Manometer (Bottom-Top)M. Air Flow Meter N. Water Flow Meter

O. CO2 Flow meterP. CO2 Cylinder ValveQ. Main ON/OFF & Water Pump

ON/OFFR. CO2 Control ValveS. Water Control ValveT. Air Control ValveU. CO2 sensor (final)V. CO2 sensor (initial)W. Gas Stream Incoming ValveX. Gas Stream Drain ValveY. Water Pump By-pass ValveZ. Water Stream Drain ValveAA. Collecting Tank Inlet Valve

4. RESULTS

(refer next page)

5.0 DISCUSSION

The objective of the experiment was to examine the basic principles of absorption of a gas into liquid using packed-column, as well as the absorption of carbon dioxide in water and the effect of water flow rate on the absorption of the same chemical in water.

The experiment was conducted for ten minutes, with the intervals of 2 minutes. The experiment was ran twice, resulting a total of 20 minutes of experiment. The flowrate for carbon dioxide was maintained at 6.00 SCFH and at fixed value of 2.832 LPM. In the first experiment, the recorded amounts of air flowrate were both in 1.00 SCFH and 28.316 LPM. During t0 = 0 minute, the number flowrate was recorded. The initial reading of CO2 was at 0.62 and the final reading was at 0.48. During the initial stage, only 0.14 of carbon dioxide was absorbed.

The similar occurs in the following 2 minutes where the readings continue to increase marginally, with only slight difference per increment. The L/V ratio values increased continually as the experiment progressed. This is also can be seen in other readings. The experiment was continuously recorded in the following 2 minutes up to the last (4 minutes, 6 minutes, 8 minutes, 10 minutes). In the final 4 minutes involving the reading for initial and final CO2 as well as for the CO2 absorbed, however was the only difference that was displayed. The number of final CO2 did not change as it remained at 0.55, and the value of initial CO2 also decreased from t6 = 13.14 to t8 = 12.77 the n t10 = 12.47. This also resulted in the reduction in number of CO2 absorbed. This is because the absorption limit had already reached for the device, hence the reduction in reading.

For the second experiment, similar parameters were also maintained. Air flowrate, CO2 flowrate as well as Mix Air/CO2 flowrate was also let at constant throughout the 10-minute experiment. However, the reading for initial CO2 here differs at t0 = 10.81 while the rest were maintained at the range of 6.00 to 7.00. The number of final CO2 also fluctuates between 0.40 – 0.55. The number of CO2 absorbed also differs. The first reading shows the CO2 is absorbed almost entirely, leaving only a small portion behind. However as for the next 2 minutes up to the end, the reading fluctuates but still ranges between 6.00 to 6.40. This is most likely due to the nature of the gas.

6.0 CONCLUSION

It can be concluded from the experiment that the rate of absorption differs from system to another system. During the first experiment, it is easier to describe the flow since the values are ascending until it reaches a constant stage. This displays the nature of the chemical (carbon dioxide) and the device that it will reach a saturated point. As for the second experiment, it differs slightly for the amount of carbon dioxide absorbed. As a conclusion, both methods can be used.

7.0 REFERENCES

http://pubs.acs.org/doi/abs/10.1021/ie50270a011 - Rate of Absorption of Carbon Dioxide in Water and in Alkaline Media

www.iupac.org/publications/pac/10/4/0625/pdf/ - THE ABSORPTION OF GASES IN LIQUIDS - IUPAC