CO2 Gas Absorption Experiment, Study notes of Information and Computer Technology

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CO2 Gas Absorption Experiment

By: Stephen LaBonia

Table of Contents

• Abstract
• Introduction
• Objectives
• Experimental Procedure
  • Materials
  • Equipment
  • Experimental Design
  • Experimental Protocol
  • Safety
• Results and Discussion.....................................................................................................................
• Conclusions
• Acknowledgements
• References

Experimental Procedure

Materials

Table 1: Materials used during experiment Materials Usage Properties

Water Wash out absorption column and collect absorption data

• Physical state: Liquid
• Molecular Weight: 18. g/mol
• Density: 0.9970474 g/mL at 25 °C
• Viscosity: 8.9x 10-4 Pa.s

Potassium Carbonate (Anhydrous)

Create a 30 wt/wt % solution to act as solvent

• Physical state: solid
• Molecular Weight: 138. g/mol - Density: 2. 43 g/mL at 19 °C
• Solubility: Soluble in water - pH: 11.6 (10% aq solution)

Carbon Dioxide Chemical that will be absorbed from the gas phase

• Physical state: gas
• Molecular Weight: 44 g/mol - Density: 1.98 kg/m^3 at STP

Equipment

The system uses a combination of sensors, pumps, and tubing to transport both gas and solvent throughout the experiment. Figure 1 below shows the process flow diagram for the experiment as well as labels for all valves and equipment.

Figure 1: Process Flow Diagram for CO2 Gas Absorption System

The experimental system spans all three floors of the unit operations lab and each section below shows what equipment is found on each of these floors:

First Floor:

Figure 2 lays out the connections to the first story solvent storage tank. This is where solvent will be measured and added to the system and pumped up to the third story storage tank. This first story tank will

Figure 3: Control Panel

Third Floor:

Figure 4 displays the third story solvent storage tank. This is where solvent will be mixed through the use of a mixing pump before being sent to the flowmeter located on the control board.

Figure 4: Third floor configuration of CO2 gas absorption system

Experimental Design

The objective of this experiment is to alter the liquid/gas ratio in the absorption column and notice how it plays a role on the absorption of CO2. The flowrate of gas will remain constant while only solvent flowrate is changed. Data will be organized using the following format for each trial ran:

Table 2: Format for data collection Time Co2 % in CO2 % out pH

Before data can be accurately collected, calibrations must also be done for the CO2 and solvent flowmeters as they are not calibrated from the manufacturer for these chemicals. Calibrations for CO flow rate were done using Equation 1 below and gave the following calibration curve shown in Figure

6. 5 1

Experimental Protocol

Vary Liquid/Gas ratio in the column:

 Ensure solvent is thoroughly mixed and configure valves to flow to second story control board  Open compressed air and CO2 lines and configure their respective rotameters to achieve an inlet CO2 concentration of 13.5%  Open valves and solvent flowmeter to flow solvent to column and down to the first story storage tank.  Monitor pH and outlet concentration of CO  Allow system to reach steady state before changing to a different solvent flowrate

Safety

a) Personal Protective Equipment a. Hard hat b. Safety glasses c. Long pants d. Closed-toe shoes e. N-95 Respirator (if handling anhydrous chemical) f. Nitrile gloves (if handling solvent)

b) Safety Hazards and Prevention

Table 3: Safety hazards and prevention Safety Hazard Prevention

Trip/Slip

• Remove trip objects
• Locate tubes and valves near floor

Chemical Spills

• Follow instructions outlined at http://ww2.che.ufl.edu/unit-ops- lab//safety.htm

Potassium Carbonate (Anhydrous) (Harmful lung irritant)

• Sign and review safety procedures for wearing N-95 respirator mask
• Wear mask whenever in direct contact with solid
• Do not wear contact lenses as the solid particles can get into eyes

Potassium Carbonate (30 wt/wt % solution)

• Wear nitrile gloves when handling solvent due to its corrosive properties

CO2 Heater

• Heater should not be touched while in operation but if needed, wear steam rated heat gloves when handling

Results and Discussion

During experimental runs, our team was able to observe CO2 absorption as well as trends for when Liquid/Gas ratio changes. The data collected was all compiled into one graph (Figure 7) that compares time and % CO2 absorbed through the system using both water and K2CO3:

Figure 7: CO2 Absorption data vs time

As can be seen from the graph, CO2 absorption decreases as liquid/gas ratio also deceases. This was an expected trend because if you lower the solvent flowrate, the reaction between the CO2 and solvent will decrease. The graph includes linear trend lines as a way to show this decrease. The reason for the jumps between different flowrates is due to our team changing the flowrates while running the

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% CO2 Absorbed

Time (min)

CO2 Absorbance

L/V = 12.5 [L/m^3]

L/V = 10 [L/m^3]

L/V = 7.5 [L/m^3]

Water @ L/V = 12.62 [L/m^3]

Linear (L/V = 12.5 [L/m^3])

Linear (L/V = 10 [L/m^3])

Linear (L/V = 7.5 [L/m^3])

Linear (Water @ L/V = 12. [L/m^3])

Figure 9: McCabe-Thiele Analysis for L/G ratio of 3

To reach the desired CO2 outlet concentration from what was experienced during the experiment, the McCabe-Thiele analysis suggests a molar flowrate Liquid/gas ratio of 3. The experimental run, however, was ran at a molar flowrate Liquid/Gas ratio of 12 (which corresponds to L/V = 12. [L/m^3]). The difference in the expected vs theoretical ratios may be due to the Henrys constant chosen. In the future, this constant could be found through benchtop experimentation in the Unit Operations lab and could show better predictions.

Regarding the calculations for the overall mass transfer coefficient, its value did not change for each of the three liquid/gas ratios tested. This could be due to how the number of equilibrium stages was found. They were approximated using drawing tools on the graph where they could accurately be calculated through the use of coding. The value for the overall mass coefficient found was 22, mol/(m^3*h).

Conclusions

Overall, the gas absorption system showed expected trends regarding the effect of CO2 absorption with respect to Liquid/Gas ratio. As the Liquid/Gas ratio was decreased, the percent CO2 absorbed decreased as well. At peak absorbance, the system was able to absorb approximately 29%. This absorbance takes into account the background absorption caused by the wet packing material with no solvent flow. Experimental data was then compared to theoretical predictions using the McCabe-

Thiele analysis for low concentration systems. There was a significant difference between the two and this could be caused by an inaccurate Henrys constant for potassium carbonate 30 wt% solution. An overall mass transfer coefficient was also calculated and was the same for all Liquid/Gas ratios tested which should not be the case. This could be caused by how the number of theoretical stages was calculated. If more precise methods could be used to find the number of stages, a more accurate coefficient could be calculated.

Acknowledgements

I would like to acknowledge Dr. Rivera and the rest of my IPPD team for the help in constructing and designing this experiment.

References

1. https://www.sciencedirect.com/science/article/pii/S