MM2 - Abstract The objective of this experiment is to study...

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Abstract The objective of this experiment is to study the unit operation of gas absorption in a randomly packed column and to determine the volumetric mass transfer coefficient of carbon dioxide (CO 2 ) in water. The experiment consists of 11 runs. In each run the gas -(CO 2 )- outlet flow rate was determined while the gas inlet flow rate was kept constant at 680 (cm 3 / min)and the liquid (water) flow rate changed from 1000 to 0 (cm 3 /min) with 100 (cm 3 /min) decrease in each run . For the first run the gas outlet flow rate was 260(cm 3 /min). So the total CO 2 absorption rate (q) =(680-260)=420 cm 3 /min and it equals to 2.82x10 -7 kmol/s, liquid flow rate (Q L )=1000 cm 3 /min and equals 1.67x10 -2 (m 3 /s). Thus the experimental value of volumetric liquid side mass transfer coefficient (k L a) is (1.64x10 -2 ) s -1 while the theoretical value is (1.59x10 -2 ) s -1 and the percentage error is 3.77% and the experimental value of height of liquid phase transfer unit(H L ) is(0.319m) while the theoretical value is(0.331m) with percentage error equals to 3.63%. Introduction Absorption of gases into liquids is an important unit operation and requires intense mixing of both phases as well as gas-liquid interfacial area. The gas may be absorbed into solution physically where the values of volumetric mass transfer coefficient, k L a and k G a and the solubility data are only required for its design procedures. In order to enhance the gas absorption rate a reactant may be involve and in case the reaction rate is required but in this experiment the equilibrium constant of carbonic acid is very small so the entire dissolved CO 2 is essentially in the molecular form and the process is an example of physical gas absorption. Theoretical Background In packed column, both gas and liquid are essentially in “plug-flow” and a small but statistically representative volume element may be modeled using Whitman two-film model. Here it is assumed that both phases are well 1
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mixed in bulk and molecular diffusion occurs through two stagnant films adjacent to the gas-liquid interface. It is also assumed that equilibrium exist at interface so that Pi and Ci are equilibrium concentrations and if Henry’s law is valid, P i =HeC i. Hence there are only two resistance (gas-side and liquid side) against the interphase mass transfer but in this experiment, the gas consists of pure carbon dioxide, therefore there is only liquid-side resistance and P=HeC * . In this case, the gas absorption rate per unit interfacial area, R is given by: R = K L (C * -C) (1) The mass balance around a differential slice of packing yields:
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This note was uploaded on 12/30/2010 for the course CHEMICAL E CHE 309 taught by Professor M.elgaily during the Fall '09 term at King Fahd University of Petroleum & Minerals.

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MM2 - Abstract The objective of this experiment is to study...

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