135702609 labreport gas diffusion docx

8/18/2019 135702609 LabReport Gas Diffusion Docx

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1.0 ABSTRACT

Regarding to the experiment objectives which is to determine the diffusivity of the vapour of

acetone and to study the effect of temperature on the diffusivity, this experiment is based on

the mass transfer theory. The instrument used is the Gas Dispersion Apparatus that consists of

an acrylic assembly which is sub divided into two compartments. !ne compartment is

constructed from clear acrylic and is used as a constant temperature water bath. The other

compartment is incorporates an air pump and the necessary electrical controls for the

e"uipment. The experiment is run by using two difference temperatures in order to study the

effect of temperature on the diffusivity of the vapour of acetone. At temperature of #$%&, the

diffusivity of acetone that obtained is '.() x 10− 6

m *+s. eanwhile, at temperature of

-$%&, the diffusivity of acetone that obtained is *.*-* x 10− 6

m *+s. This experiment

showed that gas diffusivity decreased with increasing temperature. owever, supposedly the

temperature increase with the diffusivity of the vapour of acetone increases as well.

1


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2.0 INTRODUCTION

Figure 1: Gaseous Difusion Apparatus

Gaseous difusivity or gas dispersion apparatus which involves difusionwith bulk ow is one o the items o laboratory e uipment that have been

designed to allow measurement o molecular difusivities and also to

make the students become more amiliar with the basic notions o mass

trans er theory! "his apparatus is a bench mounted apparatus or the

determination o difusion coe#cients o a vapour in air$ which uses the

method o measuring the rate o evaporation o a li uid through a

stagnant layer into a owing air stream$ comprising a precision borecapillary tube$ which may be %lled rom a syringe and

the top o which means are provided to pass air &or an inert gas' stream to

remove vapour! "he apparatus also comprise an air pump$ a travelling

microscope with accurate ocus ad(ustment and mounted or vertical a)is

movement against a *ernier scale and a thermostatically controlled water

bath$ in which to place the capillary tube$ capable o accurate

temperature control!

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"he e)perimental capabilities o this apparatus are direct measurement o

mass trans er rates in the absence convective efects$ use o a gas laws to

calculate concentrations diferences in terms o partial pressures$ use o

Fick,s -aw to measure difusion coe#cients in the presence o a stationary

gas$ measurement o the efect o temperature on difusion coe#cients

and gaining amiliarity with the use o laboratory instruments to achieve

accurate measurements o data re uired or industrial process design!

"he difusivity o the vapour o a volatile li uid in air can be conveniently

determined by .inklemann,s method in which li uid is contained in a

narrow diameter vertical tube$ maintained at a constant temperature$ and

an air stream is passed over the top o the tube to ensure the partial

pressure o the vapour is trans erred rom the sur ace o the li uid to the

air stream by molecular difusion! "he molecular difusivity$ D$ is a kinetic

parameter associated with static and dynamic conditions o a process! All

the comple)ity and unwieldiness o many calculations is$ indeed$

connected with the determination o this uantity!

/


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3.0 OBJECTIVES

"he ob(ective o this e)periment is:

/!1 "o determine the difusivity o the vapour o acetone!

/!+ "o study the efect o temperature on the difusivity!

0


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4.0 THEORY

"he difusion o vapour A rom a volatile li uid into another gas can be

conveniently studied by con%ning a small sample o the li uid in a narrow

vertical tube and observing its rate o evaporation into a stream o gas

passed across the top o the tube! 2ormally$ or simple instructional

purposes$ gas is air and vapour A is an organic solvent such as acetone

or methyl alcohol!

"he apparatus consist essentially o a glass capillary tube placed in a

transparent3sided temperature controlled water bath! A hori4ontal glass

tube is %)ed to the upper end o the capillary tube and air is blown

through this by a small air pump included within the unit! "his

arrangement allows the maintenance o a partial pressure diference

within the capillary tube between the evaporating li uid sur aces and the

owing air stream! A travelling microscope$ with sliding vernier scale$ is

mounted on a rigid stand alongside the thermostatic bath and is used to

measure the rate o all o the solvent or air meniscus within the capillary!

"he relation between the measured molar mass trans er rate &2 ,A per unit

area'$ the partial pressure gradient and the difusion coe#cient$ D is

deduced based on the ollowing5

666666666!666!! 7 uation 8192 ,A ; D -?


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6.0 APPARATUS AND MATERIALS

'.( Apparatus

6igure *7 Gaseous Diffusion Apparatus

( TR (# embrane Test 8nit apparatus.

* -$$ m9 bea2ers.

/ :lectronic balance.

# Gloves

L


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- Ruler

'.* aterials

( Acetone* ;odium &hloride/ 3ater

7.0 RESULTS

(.$ $.>$(.* (./ $.>*(.- (.4 $.4/(.4 *.( $.4'*.( *.# $.44*.# *.) $.4>*.) /.$ $.>$/.$ /.# $.44

Table (

(.' $.-'(.* $.4 (.-$(.- (./ (.(-(.4 *.4 $.'#*.( *.4 $.)-*.# /./ $.)/*.) /.4 $.)(/.$ #./ $.'>

Table *

1E


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%.0 CALCULATIONS

%.& S'm le c'lc)l'tio s

4.(.( Time from commencement of experiment7

5 min x

3600 s1 min

÷($$$ = $./2s

9i"uid level ?9 @ 9o 7 = $./

t L− Lo =

0.3

0.3 = (.$ 2s+mm

4.(.* &alculation on diffusivity, D ?T = #$ M&

6igure /7 Graph of

t

Lo− L against 9 o @ 9

11

• Density of acetone, B = )>$ 2g+ m3

• Gas constant, R =8.314

J

mol . K

• olecular weight of acetone =58.08 kg

mol

• Capor pressure, v = -' 2E+m /

• ;lo e s = $.$/' ks / mm2

= /.' x 107


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• Assume standard conditions ? = ($(./* 2E+ m2

, C=**.# m3

, T = *)/ F• Tempereature, T a = #$ M& = /(/ F

&T = ?(+C ?T + Ta .. :"uation H4I

= ?(+**.# ?*)/+/(/

= $.$/4> 2mol+m /

&J( = &T = $.$/4> 2mol+m /

To find & J* 7

&J* = ? a @ v + a &T . .. :"uation H>I

= ?($(./* -'+ ($(./* $.$/4>

= $.$()# 2mol+m/

To find & J 7

&J = ?&J( &J* +ln ?&J( +&J* .. .. :"uation H($I

= ?$.$/4> @ $.$()# +ln ?$.$/4>+$.$()#

= $.$*')

To find & a 7

&a = ? v+ a &T .. :"uation H((I

= ?-'+($(./* $.$/4>

= $.$*(- 2mol+m /

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To find diffusivity,D 7

....... . . :"uation H)I

D = ?)>$ ?$.$*')+/.' x 107

?*x-4.$4x$.$*(-x$.$/4>

D * 6.&7 + 10− 6

m $s

&alculation steps is repeated to find diffusivity, D at T = -$ %&

1/

D ; & C- H = m '>


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4.(./ &alculation on diffusivity, D ?T = - $ M&

6igure #7 Graph oft

Lo− L against 9 o @ 9

• Assume standard conditions ? = ($(./* 2E+ m2

, C=**.# m3

, T = *)/ F• Tempereature, T a = -$ M& = /*/ F

&T = ?(+C ?T + Ta .. :"uation H(I

10

• Density of acetone, B = )>$ 2g+ m3

• Gas constant, R =8.314 J

mol . K

• olecular weight of acetone = 58.08 kgmol

• Capor pressure, v = -' 2E+m /

• ;lo e s = $.( ks / mm2

= (.$ x 108

s / m2


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= ?(+**.# ?*)/+/*/

= $.$/)) 2mol+m /

&J( = &T = $.$/)) 2mol+m / .. :"uation H*I

To find & J* 7

&J* = ? a @ v + a &T .. :"uation H/I

= ?($(./* -'+ ($(./* $.$/))

= $.$('> 2mol+m /

To find & J 7

&J = ?&J( &J* +ln ?&J( +&J* :"uation H#I

= ?$.$/)) $.$('> +ln ?$.$/))+$.$('>

= $.$*->)

To find & a 7

&a = ? v+ a &T . . :"uation H-I

= ?-'+($(./* $.$/))

= $.$*$4 2mol+m /

To find diffusivity,D 7

D = B & J +s?* & a &T . .. :"uation H'I

D = ?)>$ ?$.$*->)+(.$ x 108

?*x-4.$4x$.$*$4x$.$/))

D * . 5 + 10− 6

m $s

1


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-.0 DISCUSSIONS


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The calculations were proceeds with the aim to find the diffusivity of vapour acetone at

different temperature.


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&0.0 CONCLUSION

As a conclusion, the result for diffusivity coefficient at #$ 5& is *-$#.-/ m *+s and the

diffusivity coefficient at #- 5& is /'-$.-- m *+s. There are some errors when the experiment

was done. ;ome of recommendations step should be ta2en otherwise the result for diffusivity

would not be accurate. To sum up, the experiment had been done with "uite accurate results

although some error happened.

&&.0 RECOMMENDATIONS

;ome recommendations should be implements in this experiment. !ne of them is insulating

the glass container.


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& .0 APPLICATIONS

All gas diffusion methods are based on interfacing the donor stream containing the analytic,

with an acceptor stream containing a reagent. The porous hydrophobic membrane serves as a

barrier that allows only the gaseous species passed through. This ma2es the gas diffusion

methods very selective, since the non volatile species will not reach the detector. The

instrumental setup can be configured in two ways7

&. The continuous programmable flow method where both donor and acceptor stream

are continuously pumped.

. The stopped flow techni"ue where both donor and acceptor stream are controlled by

syringe pumps.

The gas diffusion unit for continuous flow has diffusion path * cm long and * mm wide. The

acceptor stream is monitored by a flow cell with ($ cm long light path. The flow injection

system is operated at a programmable flow rate of $.)-m9+min per channel while the sample

passes through the diffusion unit and at a flow rate of /.$m9+min during flush period. The

injection volume is /$$ microliters of sample and sampling fre"uency is #$ injections per

hour.

The stop flow method uses the sandwich gas sensor, where the injected analytic is in contact

with the gas diffusion membrane during the stopped flow period.


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The ;andwich Gas Diffusion ;ensor uses a pair of optical fibres that monitor the acceptor

solution adjacent to the diffusion membrane. The stop flow 6< techni"ue is robust, since it

uses syringe pumps, and therefore suitable also for continuous monitoring. ;ensitivity of this

method is easily adjusted by selecting the duration of the stopped flow time, while using the

same experimental setup and reagent concentrations. The ;andwich ;ensor provides response

in real time, since it monitors the 2inetics of the diffusion and of the subse"uent chemical

reaction and uses smaller volumes of sample than the continuous flow method.

6igure '

6igure -

+E


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& .0 RE//ERNCES

• Lournal of hysical and &hemical Reference Data. Gaseous Diffusion &oefficients.

Retrieved Eovember (-, *$(* from

http7++jpcrd.aip.org+resource+(+jpcrbu+v(+i(+p/Ms(NisAuthoriKed=no

• Gases7 Graham1s 9aws of Diffusion and :ffusion. Graham1s 9aw. Retrieved

Eovember (-, *$(* from

http7++www.chem.tamu.edu+class+majors+tutorialnotefiles+graham.htm

• Diffusion of Gases. Diffusion and :ffusion. Retrieved Eovember (' *$(* from

http7++chem.salve.edu+chemistry+diffusion.asp

• 8;:&. Gaseous Diffusion. RetrievedEovember (', *$(* from

http7++www.usec.com+gaseous diffusion

• Advancing the &hemical ;ciences. 9earn &hemistry7 Diffusion of gases of ammonia

and hydrogen chloride. Retrieved Eovember (', *$(* from http7++www.rsc.org+learn

chemistry+wi2i+Teacher:xpt7DiffusionMofMgasesM MammoniaMandMhydrogenMchloride

& .0 APPENDI1

Refer attachment on the next page ?page **

+1
http://jpcrd.aip.org/resource/1/jpcrbu/v1/i1/p3_s1?isAuthorized=nohttp://www.chem.tamu.edu/class/majors/tutorialnotefiles/graham.htmhttp://chem.salve.edu/chemistry/diffusion.asphttp://www.usec.com/gaseous-diffusionhttp://www.rsc.org/learn-chemistry/wiki/TeacherExpt:Diffusion_of_gases_-_ammonia_and_hydrogen_chloridehttp://www.rsc.org/learn-chemistry/wiki/TeacherExpt:Diffusion_of_gases_-_ammonia_and_hydrogen_chloridehttp://www.chem.tamu.edu/class/majors/tutorialnotefiles/graham.htmhttp://chem.salve.edu/chemistry/diffusion.asphttp://www.usec.com/gaseous-diffusionhttp://www.rsc.org/learn-chemistry/wiki/TeacherExpt:Diffusion_of_gases_-_ammonia_and_hydrogen_chloridehttp://www.rsc.org/learn-chemistry/wiki/TeacherExpt:Diffusion_of_gases_-_ammonia_and_hydrogen_chloridehttp://jpcrd.aip.org/resource/1/jpcrbu/v1/i1/p3_s1?isAuthorized=no

135702609 labreport gas diffusion docx

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