ABSTRACTGaseous diffusion coefficient or diffusivity, D is one of chemical property of gas. This experiment was performed to determine the diffusivity, D of the vapor of an acetone C3H6O liquid based on the established Winkelmann's method. Rate of mass transfer equation was used to calculate the diffusivity, D of acetone liquid. At first, clean water is filled into the water bath, then it was kept constant at 45 oC. Next, capillary tube was filled with acetone liquid to a depth of about 40mm. Capillary tube was inserted vertically through the fitting at the top of water bath. Initial level of acetone liquid was taken. Flexible tube from the air pump was connected to the capillary tube. The pump is turned on, then acetone liquid is allowed to evaporate inside the capillary tube. Every 10 minutes (or 600 second) interval ,level of acetone was observed by using telescope until 4 readings was taken. The initial and the final level of acetone obtained is 40.0 mm and 41.90 mm which satisfied our general hypothesis, level of acetone decrease as time increase proved that acetone had been diffused into the air throughout the time. The acetone level actually decrease although the final value stated was higher, since the scale increase fron top to down. Based on the obtained slope from t/(L-Lo) against (L-Lo) graph plotted and rate of mass transfer equation, the diffusivity, D of acetone liquid was found to be -2.19102 m2/s . Rate of diffusion,NA calculated was 1.5009 x 102 kmol/m2.s

TABLE OF CONTENTS

1.0 INTRODUCTIONThe knowledge of physical and chemical properties of certain materials is important because very often process engineering deal with the transformation and distribution these materials in bulk. One such property is diffusivity. Mass transfer by diffusion takes place when there is a concentration gradient of the diffusing components.The SOLTEQ Gaseous Diffusion Coefficient Apparatus (model: BP 10) has been designed for students experiment on the technique of determining diffusivity of the vapour of a volatile liquid based on the Winkelmanns method. In this method, the volatile liquid is allowed to evaporate in a vertical glass tube to the top of tube in which the vapour-free gas is through. The volatile liquid is diffuse to vapour-free stream due to the concentration. The vapour-free gas is allowed into the test tube, but does not diffuse into the volatile liquid. A water bath is provided for maintaining a steady temperature so that there is no eddy current in the vertical tube and mass transfer executed from the surface by molecular diffusion alone. The rate of evaporation can also be referred as the rate of fall of the liquid surface. With the knowledge of the concentration gradient, the diffusivity of the vapour of the volatile liquid can be calculated.

2.0 OBJECTIVES To determine the gas diffusion coefficient of acetone using the established Winkelmanns method. To determine the diffusion coefficient of acetone vapor at different temperatures.

3.0 THEORYWhen a concentration gradient exists within a fluid consisting of two or more components, there is a tendency for each constituent to flow in such a direction as to reduce the concentration gradient. This is called mass transfer. Mass transfer takes place in either a gas phase or a liquid phase or in both simultaneously. When a liquid is allowed to evaporate in a narrow vertical tube and a steady temperature is maintained, mass transfer takes place from the surface by molecular diffusion alone. This is the technique developed by Winkelmann to determine the diffusivity of the vapor of a volatile liquid. By monitoring the evaporation rate, which is the rate of fall of liquid surface, and with the knowledge of concentration gradient, one may then calculate the diffusivity.The rate of mass transfer is given by:

= D( )() (1) Where,d =diffusivity (m2/s)CA=saturation concentration at interface (kmol/m3)L=efective distance of mass transfer (m)CT=total molar concentration (kmol/m3)CBM=logarithmic mean value of CB (kmol/m3)

where,=density of liquid (kg/m3)M=molecular weight (kg/kmol)

Combining equations 1 and 2 we get:() = D( )() (3) Integrating and putting L = at t = 0 - = ()( )t (4) and L cannot be measured accurately but L - can be measured accurately using the vernier on the microscope:(L - )(L - + 2) = ()( )tor = ()() (L - ) + ( ) (5)If s is the slope of a graph of against (L - ) then: s = ()() (6)Diffusivity D can be calculated from equation 6:D = Where: = ()() = = () = = ()

4.0 DIAGRAM AND DESCRIPTION OF APPARATUS

Figure 1: Gaseous diffusion coefficient apparatusDESCRIPTION OF APPARATUSThe apparatus consists of capillary tube placed on top of the water bath cover. The capillary tube is designed in T-shape vertical tube whereby air is pass through this tube by the air pump. This arrangement allows the maintenance of a partial pressure different in capillary tube between the evaporating liquid surface and the flowing air stream. A travelling telescope with sliding vernier scale is mounted and stand along the side of water bath tank so that it could measure the rate of fall of liquid surface. A water bath is provided for maintaining a steady temperature so that there is n eddy current in the vertical tube and mass transfer can take place from the surface by molecular diffusion alone.

5.0 EXPERIMENTAL PROCEDURESGENERAL OPERATING PROCEDUREA) General Start-up Procedure The water bath with clean (preferably filtered) water was filled approximately to 20 mm from the top. The main cable to the eletrical supply was plugged. The voltage of the supply was ensured correct to suit the equipment. The main power on the control panel was switched on. The set point value on the temperature controller was adjusted to 45 C The heater was switched on. The water temperature heats up to 45 C was observed and remained constant. The equipment was ready for the student experiment.B) Priming Procedure for Capillary Tube A weak solution of detergent was prepared. To fill the tube with the solution, a Hirschmann pipette was used. It is needed to tap the outside of the tube if the solution is trapped and does not flow down. The tube was turned upside-down and shaked. The tube was emptied. Steps 2 to 3 with acetone was repeated. The tube was ready for student experiment.C) General shut-down Procedure The heater and air pump was switched off. The set point value of the temperature controller was adjusted approximately to 5 C below the room temperature. The water was allowed to cool down until it is safe to touch. The drain valve was opened and the water tank was emptied. The flexible tubing was detached and the capillary tube was cleaned for next use. The main power was swicthed off. The main cable was unplugged if the equipment will not be used for a long period.D) Operating Procedure The start-up procedure as outlined in section (A) was performed. The capillary tube with the acetone to a depth of about 40mm from bottom of was partially filled. The capillary tube was carefully inserted through the fitting on top of the water bath cover. The fitting should not be over-tight. The initial level of acetone was observed through telescope. If the acetone level cannot be observed by using telescope, increased the tank water level. The flexible tubing from the air pump line to one end of the capillary tube was connected. The air pump was switched on. The air pump was switched off to perform a reading on telescope. The flexible tubing was disconnected and the two capillary tube ends with the cap provided was closed. The level of acetone was observed and recorded. Steps 4 to 6 at 10 minutes intervals were repeated.

6.0 RESULTSTemperature = 45 = 40 mmTime, t

Reading of vernier, L (mm)Liquid level () (mm)(min/mm)(ks/mm)

Mins

0040.000.000.000.00

1060040.100.10100.006000.00

20120040.200.20100.006000.00

30180040.300.30100.006000.00

40240040.400.40100.006000.00

50300040.550.5590.915454.55

60360040.650.6592.315538.46

70420040.750.7593.335600.00

80480040.800.80100.006000.00

90540041.900.90100.006000.00

DISCUSSION The objective of this experiment is to determine the diffusivity of the vapour of acetone and to study the effect of temperature on the diffusivity which based on the mass transfer theory of the molecular diffusion in gases. To achieve the objectives of this experiment, the gas dispersion apparatus is used. This apparatus is combined with Vernier scale and microscope which is used to measure and read the level pf meniscus in the capillary tube which contains acetone. From the calculation, it shows that, the value of diffusivity is affected by the temperature. The higher the temperature, the diffusivity of the vapor or the diffusion coefficient of acetone would increases. The experiment is conducted with a constant temperature which is at 45. Based on the result obtained, the level of acetone decrease as the time is increases. This is happen by a diffusion process of the acetone to the air. Molecular diffusion is the transfer of molecule through a fluid by random molecular movements. The molecule is flow from high concentration to the low concentration. Molecular diffusion can occur in both directions in the system. For this experiment, the acetone is diffuses through the non diffusing air which is pass through the top of the tube that containing the acetone. The air is not diffuse into the acetone but allowed flow into the tube. The diffusion is occurred over the time and the level of acetone is taken for every 10 minute. The diffusion of acetone through air and the evaporating liquid surface level decreases down by time. The level of acetone inside the tube is decrease because of the heat transfer from the process of boiling water that generates heat to the acetone. The level of acetone inside the tube is decreases and stop until reach at the time of 90 minutes. This because the acetone has been diffuses to the air. Due to the driving force and existing of concentration gradient, the molecule move from the tube to the surrounding air which is has a less concentration. The theory is accepted because of the level of acetone inside the tube is decreases as the time is increases. In this experiment, the temperature used for conducted the experiment is must not be exceeded the boiling point of the acetone which is 56.5. This because the higher temperature will lead the acetone to reached it boiling point. This will cause the diffusivity occurred immediately. In addition, the characteristic of the acetone solution is volatile. The higher temperature that exceeded to the acetone boiling point will cause the acetone volatile rapidly. The higher pressure has a significant effect on the relative volatility of the component in the liquid mixture. If the temperature conducted exceeded to the boiling point of the acetone the rate of volatility of the acetone will increase. Therefore, there is difficult to read the scale of the vernier since the solution is volatile rapidly. Based on the graph plotted, the trend of the graph is increase proportional. The slope of the graph is 0.3024. The slope of the graph is positive. The value of the s is same as the value of the slope from the graph. From the value the diffusivity can be calculated and the diffusivity of this experiment is -2.19 x 102 . It shows that, the correlation coefficient, R2 value is 0.2423. There is some error during the experiment conducted. The value of the acetone level must take at least for 3 times and get the average to make sure it will reduce the mistake. Hence, the experiment is successful based on the procedures and the theory is accepted. 7.0 SAMPLE CALCULATIONCalculation on determining the gas diffusion coefficient of acetone by using Winkelmanns method. The rate of mass transfer, (equation 7.1):

= diffusivity [m2/s] = saturation concentration at interface [kmol/m3] = effective distance of mass transfer [m] = total molar concentration ([kmol/m3] = logarithmic mean value of CB [kmol/m3]= molecular volume [m3/kmol]= temperature of acetone (K) = 45 oC =273.15 + 45 = 318.15 K= pressure total (kPa)= pressure of acetone at specified temperature (kPa) = = = () = = = = = C = = = = = 0.0383 = = Antoines Equation:= A [ ]Value of A,B and C for Acetone range from 247.15 K to 350.15K, A = 14.3145 B = 2756.22 C = -45.090 = 14.3145 [ ] = = 14.3145 [ ] = = = = 1.256 = = = -0.0873 = = 0.3154 = = = = () = () = - 0.1643

= + = 0.1256 + 0.3154 = 0.441

The evaporation of the liquid, (equation 7.2)

= density of liquid acetone () = 791.0 = molecular weight of acetone () = 58.08

Combine equation 7.1 & 7.2, yield equation 7.3: =

is the value slope of a graph of t/ (L Lo) against (L Lo). equation 7.4:Slope, (Obtain from graph) = 0.3024

From the arrangement of the equation 7.4, the diffusivity, can be obtained, D = = = -2.19 102

Ficks Law with bulk flow, the rate of diffusion is

= -2.19 102 = 1.5009 x 102

8.0 CONCLUSIONS AND RECOMMENDATIONS CONCLUSIONSLevel of acetone decrease as the time increase. Acetone keep evaporating and more accetone being diffused into the air throughout the time until experiments stop.Based on Winkelmann's method, the gas diffusion coefficient of acetone is found to be 2.78102 m2/s.The diffusivity,D value is determined from the calculation using rate of mass transfer equation. Last but not least, results obtained did follow the theory where the level of acetone inside the tube is decreases as the time is increases.

RECOMMENDATIONSFrom the data collected an analyzed, it has been determined that the experimental procedure used here can determine the diffusivity coefficient with some level of accuracy. For future experiments, some form of air flow regulation should be investigated. Since this experiment only use air pump as air source, Something as simple as a room fan could be placed next to the scale to ensure a more constant air flow. Another increase in accuracy could be achieved by regulating the temperature with more consistency. If the experiment could be performed in a large insulated room, the temperature may not vary as much. It is also suggested to do comparative experiment between using air pump, fan, and room air either these would effect on value of diffusivity coefficient. Another recommendation to improve the results accuracy are: -Its is necessary for each students to have a knowledge on how to read the scale of vernier calliper. -There is no need to disconnect the flexible tubing from the capillary tube when the reading of acetone level is taken during 10 minutes time interval because its such a waste of time to connect it back.- The Telescope should be place at fixed position so it is not be movable and level of acetone can be observed accurately - To get an accurate value of reading, it is recommended for only one person who takes all the value reading to avoid multiple reading from every person.

9.0 REFERENCES[1]Munson, B., Young, D., Okiishi, T., & Huebsch, W.(2010). Fundamental of Fluid Mechanics ( 6th ed.) .111 River Street, Hoboken, NJ : John Wiley & Sons. Page 420[2]Yunus A. Cengel & Afshin J.Ghajar.(2011). Heat and mass transfer (4th ed.). New York : McGrawHill . Page 796-797[3]Robert H.Perry, Don W.Green, Perrys Chemical Engineers Handbook, McGraw Hill,1998.[4]Antoine equation (2013) Retrieved April,11th 2015. from http://en.wikipedia.org/wiki/Antoine_equation[5]Chemical engineering design (2013) Retrieved April,11th 2015, from http://books.google.com.my/books

10.0 APPENDICES

15