LAB Plug Flow

(1)

T

TA

ABL

BL

E

O

OF

F

CO

CON

NTE

TE

N

NT

T

T TIITTLLEE PPAAGGEESS Abstract / Summary 2 Introduction 3 Objectives 5 Theory 6 Apparatus 8 Procedures 9 Results 11 Sample calculation 14 Discussion 17 Conclusion 19 Recommendation 20 Reference 21 Appendix 22

ABSTRACT

Reactors are used in the chemical industry for the millions of processes. One of many different types of reactors is plug flow reactor (PFR). A plug flow reactor is a pi

(2)

shaped tank where a chemical reaction takes place with walls coated with a catalyst and an inlet flow of pure reactant. The plug flow reactor (PFR) is used in this experiment. There are a few of objectives that are needed to achieved in this experiment such as to find out the calibration curve of conversion of sodium hydroxide, NaOH versus conductivity, to carry out a saponification reaction between NaOH and Et(Ac) in a PFR, and to determine the rate of reaction, rate law, and the reaction rate constant. Besides that, this experiment also wants to determine the conversion of NaOH in the reactor and the effect of residence time on the conversion in a PFR. There are few of graph being plotted with the results that are got from the experiment. One of them is the graph conductivity versus conversion for experiment 1. This graph that had being plotted is inversely proportional. Next graph is plotted between conversions of NaOH in reactor versus residence time distribution. This shows that the residence time is increased as the conversion of NaOH increased. The rate of reaction and rate constant can be calculated after know the values of conversions. However, the value of conversion in this experiment is exceed 100% and this affect the value of rate of reaction.

I

NTRO

N

TRO

D

DU

UCTI

CTI

O

ON

N

Reactors are used in the chemical industry for the millions of processes. There are

(3)

many different types of reactors due to many different factors that can control the formation of product during the reaction. One of many different types of reactors is plug flow reactor (PFR).

A plug flow reactor is a pipe-shaped tank where a chemical reaction takes place with walls coated with a catalyst and an inlet flow of pur1. The pe reactlug flantow reactor

has an inlet flow composed of the reactants. The reactant flow into the reactor and is the converted into the product by certain chemical reaction. The product flows out of the reactor through the outlet flow. In many scenarios, a catalyst is involved in the reaction. Figure below shows that how the enzyme coats the interior of the wall.

Furthermore, plug ﬂow reactors are an idealized scenario where is no mixing

involved in the reactor. Since PFR is an idealized reactor, it does not truly exist in the real world. It is impossible to have no mixing at all during a reaction, but the amount of mixing in the reactor can minimize.

Plug flow reactors are frequently used in the chemical industry due to the non -mixing property of the reactors. Plug flow reactors are frequently used in biological reactions when the substrate flows into the reactor and is converted to product with the use of an enzyme. Besides that, plug flow reactor are useful for continuous production because they have an inlet and outlet stream. In a conclusion, plug flow reactors are most

useful for continuous production, large-scale reactions, or fast reactions.

1‘Plug Flow Reactor’, Product Description by Matthew Grisewood (http!!www"scribd"co#!doc!2$1$%&'!Plug)Flow)Reactor *

(4)

O

OBJ

BJ

EC

TI

V

VE

E

(5)

E

Experxperiimment ent 1:1:

1.To ﬁnd the calibration curve of conversion versus conductivity.

E

Experxperiimment ent 2 and 2 and 3:3:

1

1. .

To carry out a saponiﬁcation reaction between NaOH and Et(Ac) in a plug ﬂow reactor (PFR).

2

2. .

To determine the rate of reaction, rate law, and raction rate constant.

3

3. .

To determine the conversion of NaOH in the reactor.

4

4. .

To determine the eﬀect of residence time on the conversion in a plug ﬂow reactor (PFR).

THEORY

(6)

C

Cononververssiionon

The conversion, AX is the number of moles of reactant that have reacted per mole of reactant fed to the system.

XA=

moles of reactant reacted moles of reactant fed

R

Resiesiddenence tce tiimme, e, τ

The residence time distribution (RTD) of a reactor is a characteristic of the mixing that occurs in the chemical reactor.

Residence time, τ =

V _PFR V 0

where: V PFR ₌_r_eac_t_{or vol}_ume

V 0 ₌_t_ot_al_f_eed_ﬂow_r_at_es

R

Ratate Oe Of f RReaeaccttiion on AAnnd d RRatate Lawe Law

The reaction rate (rate of reaction) or speed of reactreactantion for aorproductin a

particularreaction is intuitively deﬁned as how fast or slow a reaction t2_.ak_Foes p_r lace simple deﬁnition, the rate of reactiAon, , is t-rhe number of moles of reactant reacting (disappearance) per unit time per unit volume (mol3_._s₎3/dm_.

The reaction rate equation (or the rate law) is essentially an algebraic equation involving concentration. The common general forms of the rate law equation is shown,

-rA= kACAαC βA

where CAand CBare the individual reactants’ concentrations, each raised to the powers α

and β, while kAis the reaction rate constant.

The order of the reaction refers to the powers to which concentrations are raised in the

2http!!en"wiipedia"org!wii!Plug-.low-reactor-#odel

&/" 0cott Fogler, le#ents o. 3he#ical Reaction ngineering, +

th

dition4, Pearson 5nternational dition (266*

(7)

reaction rate law. From equation above, the overall order of the reaction, n is, n = α + β

For this experiment, this reaction is a second order equimolar with the same initial reactant concentration Ao(C= CBo), the rate law shown to be:

where: X = extent of conversion

CA = exit concentration of reactant NaOH [M]

VO = total inlet ﬂowrate of solutions (mL/min)

CAo = inlet concentration of reactant NaOH in the reactor [M]

The reaction rate constant can be determined by: k = V _o V PFRC Ao

(

X 1−_X

)

7

(8)

A

AP

PP

PA

ARATU

RATU

S

A

AN

ND

D

M

MATE

ATE

RI

A

AL

LS

S

APPARATUS:

• Beaker

• Conical ﬂask

• Burette

• Plug ﬂow reactor (Model: BP 101)

• Conductivity meter

•

Measuring cylinder

MATERIAL:

• Sodium hydroxide solution, NaOH (0.1M)

• Sodium acetate solution, Na (Ac) (0.1M)

• Deionised water, 2HO

•

Hydrochloric acid solution, HCl (0.25M)

(9)

P

PRO

ROCE

CE

D

DU

URE

RE

S

E

EXPEXPERIRIMMEENNT 1T 1

P

Prrepeparataratiioon n oof f calcaliibbrratatiioon n cucurve frve for or conconvversersiion on vversersus cus coonndduuctctiivviittyy

1.The following solutions were prepared:

• 1 liter of sodium hydroxide, NaOH (0.1M)

• 1 liter of sodium acetate, Na(Ac) (0.1M)

• 1 liter of deionised water2O, H

2.The conductivity and NaOH concentration for each conversion values was determined by mixing the following solutions into 100 ml of deionised water:

• 0% conversion : 100 ml NaOH

• _25%_c_onve_r_s_i_on _:₇₅_ml_NaOH_{+ 2}₅_ml_Na(_Ac₎

• 50% conversion : 50 ml NaOH + 50 ml Na(Ac)

• 75% conversion : 25 ml NaOH + 75 ml Na(Ac)

• 100% conversion : 100 ml Na(Ac)

3.All data were recorded.

(10)

4.The calibration curve of conductivity versus conversion was plotted. The slope and y-axis intercept was determined.

E

Eﬀﬀect ect of rof resiesiddenence tce tiimme oe on n tthhe re reacteactiion on iin n a Ta TFRFR

1.The general start-up procedures were performed. 2.Valves V9 and V11 were opened.

3.Both the NaOH and Et(Ac) solutions were allowed to enter the plug reactor R1 and empty into the waste tank B3.

4.P1 and P2 were adjusted to give a constant flow rate of about 300 ml/min at flow meters FI-01 and FI-02. Make sure that both flow rates are the same. The flow rates were recorded.

5.The inlet (QI-01) and outlet (QI-02) conductivity values were started monitored until they do not change over time. This is to ensure that the reactor has reached steady state.

6.Both inlet and outlet steady state conductivity values were recorded. The concentration of NaOH exiting the reactor and extent of conversion from the calibration curve were found.

7.Sampling valve V15 was opened and a 50ml sample was collected. A back titration procedure was carried out to manually determine the concentration of NaOH in the reactor and extent of conversion.

8.Step 4 to 7 were repeated for different residence times by reducing the feed flow rates of NaOH and Et(Ac) to about 250, 200, 150, 100 and 50 ml/min. make sure that both flow rates are the same.

(11)

E

B

Back ack ttiittrratatiion on pprroocedceduurres fes foor r mmananuual al conconversversiioon n detdeterermmiinnatatiioonn

1.A burette was ﬁlled up with 0.1M NaOH solution. 2.10 ml of 0.25M HCl was measured in a ﬂask.

3.50 ml sample was obtained from the experiment and the sample was added to the HCl immediately in the ﬂask to quench the saponiﬁcation reaction.

4.A few drops of pH indicator were added into the mixture.

5.The mixture was titrated with NaOH solution from the burette until the mixture is neutralized. The amount of NaOH titrated was recorded.

R

RE

ESU

SU

L

LTS

TS

Experiment 1:

S

SOLOLUUTTIION ON MMIIXXTTUURREESS CCONVONVEERRSSIIONON (

(%%))

CO

CONNDDUUCTICTIVVIITYTY ( (mmS)S) 0 0..1 1 MM N NaaOOHH 0 0..1 1 MM N Naa((AcAc)) H H22OO 100 mL - 100 mL 0 12.46 75 mL 25 mL 100 mL 25 10.46 50 mL 50 mL 100 mL 50 8.72 25 mL 75 mL 100 mL 75 6.50 - 100 mL 100 mL 100 4.66 11

(12)

0 20 40 60 80 100 120 0 2 4 6 8 10 12 14 f(x) = - 0.08x + 12.47 f(x) = - 0.08x + 12.47

CONDUCTIVITY versus C

CONDUCTIVITY versus CONVERS

ONVERSION

ION

CONVERSION (%) CONVERSION (%) CONDUCTIVI

CONDUCTIVITY (TY (mS)mS)

(13)

Experiment 2:

Reactor volume = 0.4 L Concentration of NaOH in the feed tank = 0.1 M Concentration of Et(Ac) in the feed tank = 0.1 M

N NOO F FLOLOWW RATE RATE OOFF N NaaOOHH ( (mmL/L/mmiin)n) F FLOLOWW RATE RATE OOFF E Ett((AAc)c) ( (mL/mL/mmiin)n) TO

TOTAL FTAL FLOWLOW RATE RATE OOFF SO SOLUTILUTIOONN V V00((mmL/L/mmiin)n) RESI RESIDDENCENCEE

TI

TIMME (E (mmiin)n) O OUTLEUTLETT CO

CONNDDUUCTICTIVVIITYTY (

(mmS/S/ccmm)) CO

CONNVERSVERSIIOONN,, X X ( (%%)) REAC REACTITIOONN RATE RATE CONSTANT CONSTANT ( (LL//mmolol..mmiinn)) RATE RATE OOFF REAC REACTITIOONN ( (mmolol//LL..mmiinn)) 1 1sstt i innlletet 2 2nndd o ouuttlletet 1 313 331 644 0.621 7.2 6.6 101.8 -910.54 -2.95 x 10-3 2 256 253 509 0.786 7.1 5.8 103.0 -436.89 -3.93 x 10-3 3 206 204 410 0.976 6.9 5.6 102.6 -404.48 -2.73 x 10-3 4 152 154 306 1.307 6.5 5.1 103.2 -246.71 -2.53 x 10-3 5 101 103 204 1.961 6.1 4.8 106.2 -87.36 -3.36 x 10-3 6 53 51 104 3.846 5.3 4.2 108.2 -0.20 -1.34 x 10 -5 1&

(14)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 98 100 102 104 106 108 110 f(x) = 1.97x + 101.05

CONVERSION vs RESIDENCE TIME

Residence time, Residence time, τ (min) (min) Conversion,  (%)

Conversion,  (%)

Experiment 3:

(15)

TI

TITRATRATITIOON N SSAAMMPLPLEE (

(mL)mL)

VO

VOLLUMUME E oof f NaNaOOH H ((mLmL)) AAVEVERAGE RAGE VOVOLLUMUME E ooff N NaaOOH H ((mmLL)) 1 1sstt_T_{T R}_RI_I_A_AL_L nnd₂₂d_TR_TR_I_I_A_AL_L 300 25.00 25.90 25.45 250 25.50 26.00 25.75 200 25.90 25.40 25.65 150 25.90 26.00 25.80 100 26.10 27.00 26.55 50 25.70 26.60 27.05

S

SA

AM

MP

PL

LE

E

CA

CAL

LCU

CU

L

LATI

ATI

O

ON

N

EXPERIMENT 2 and 3:

NaOH + HCl NaCl + 2OH

U

Unknknownown qun quantantiittyy

Concentration of NaOH in the reactNaNaorOOHH, C = 0.1 M

K

Knnowown n ququantantiittiieses

Volume of sample, sV = 50 mL

Concentration of NaOH in the feed vessNaOH,elf, C = 0.1 M Volume of HCI for quenching, HCI,sV = 10 mL Concentration of HCI in standard solutiHCIon, ,s C = 0.25 M Volume of titrated NaOH, 1 V = 25.45 mL Concentration of NaOH used for titratiNaOH,on, sC = 0.1 M

(16)

S

Samampplle Ce Calalccululatatiion on ((ffor sor samampplle ﬂe ﬂow ow rratate of 3e of 300m00mll//mmiinn))

Concentration of NaOH entering the reactNaOH,or, oC = (CNaOH,f)/ 2

= 0.1

2

= 0.05 mol/L

Volume of unreacted quenching HCI2, V = C NaOH ,s C HCI , s x V1 = 0.1 0.25 x 25.45 = 10.18 mL Volume of HCI reacted with NaOH in sam3 ple, V = VHCI,s- V2 = 10 – 10.18 = - 0.18 mL Moles of HCI reacted with NaOH in sampl1 e, n = CHCI,sx V3 = 0.25 x −0.18 1000 = -4.5 x -510_mol Moles of unreacted NaOH in sampl2= e, n1n = -4.5 x -510mol 1

(17)

Concentration of unreacted NaOH in the recNaOHator, C = n2/ ( Vs/1000 ) = −4.5 x10−5 50 1000 = -9.0 x -4_mol10_/L

Conversion of NaOH in the reactor, X = (1 -C NaOH C NaOH ,o ) x 100% = (1 – −9.0_×10−4 0.05 ) x 100 % = 101.8 %

Residence time, τ = V ₍ PFR₎ Vo = 0.4 L 644mL/min x 1000_mL 1_L = 0.621 min Rate constant, k = Vo V ( PFR)CA 0 ₍ X 1−_X )

where X is taking from the calculation in experiment 2 = 644/1000 0.4_x0.1 ( 1.018 1−1.018 ) = -910.54 L/mol.min 17

(18)

Rate of reaction, -r = kC A 0 2 (1-X)2 = (-910.54)(0.1)2_(1-1.018)2 = -2.95 x -310moL/L.min

D

DI

I

SCU

SS

I

O

ON

N

There are three experiments for plug ﬂow reactor (PFR). These experiments are conducted to achieve a few objectives, which are to carry out a saponiﬁcation reaction between NaOH and Et(Ac) in a PFR, to determine the rate of reaction, the conversion of

NaOH in the reactor and to find the effect of residence time on the conversion in a plug flow reactor (PFR).

(19)

In experiment one, the conductivity meter is used to measure the conductivity in the two solutions which are sodium hydroxide, NaOH and sodium acetate, Na(Ac). Using the same concentration but diﬀerent volume of each solution is conducted to achieve desire conversion. Then, the conductivity for each new solution that has being mixed is tested by conductivity meter. The calibration curve of conductivity versus conversion is plotted. The slope of this graph is -0.0782 and y-axis intercept is 12.472. The conductivity lower when the conversion is increased.

For the next experiment, the plug flow reactor (Model:BP 101) is used. The feed of sodium hydroxide, NaOH and ethyl acetate, Et(Ac) is varied to get different of residence time, τ. The theory of residence time distributions generally begins with three assumptions which are the reactor is at steady-state, transport at the inlet and the outlet takes place only by advection, and the fluid is incom4. prFoessr each ible different residence

time, the 50 mL of sample is collected and being back titrate with hydrochloric acid to determine the concentration of sodium hydroxide, NaOH in that sample. Then, the conversion of NaOH in the reactor is calculated. The graph of conversion of NaOH and residence time is plotted. This graph shows that the conversion is increase as the residence time increase. For the real case, the conversion must increase as the residence time increase5_._How_ever_,_t_he_con_ve_r_si_on_t_{hat i}_{s cal}_cu_l_at_ed_i_{s ‘}_wei_r_d’_becau_{se t}_he_con_ve_r_si_on_i_s

higher than 100%. From the conversion value, the rate constant and rate of reaction can be calculated too. All the rates of reaction that are get from the calculation are negative values. These happened because the conversion values are more than 100%.

Therefore, it can say that there are errors occurs during conducted this experiment. One of the errors that can happened in this experiment is there are impurities in the conical ﬂask during the titration process. This can aﬀect the amount of sodium hydroxide solution used. Next, maybe there was some leakage at any valve that did not noticed during conduct the experiment. Other than that, the colour obtained during titration does not

4Levenspiel, O., ‘Chemical Reaction Engineering’ (3r_{ei!i"n). #"$n %ile& ' "ns, * (1999).}

%Research 0aponi.ication o. thyl 8cetate by 0odiu# /ydro9ide in a Plug Flow Reactor4 by :indsey ;ato, 0hawna <ogioa, :ue 0ugie (February 2, 266%*

(20)

exactly in light pink. So, it might affect the value of NaOH use and affect the calculations. Plug flow reactors are frequently used in the chemical due to the non-mixing property of the reactors. Plug flow reactors are used for some of the following applications such as large-scale reactions, fast reactions, homogenous or heterogeneous reactions, continuous production, and high-temperature react6i.ons

CO

CON

NCL

CL

U

US

SI

I

O

ON

N

This experiment is not perfectly success; however, the objectives of this experiment were achieved. From this experiment, the collected data are suﬃcient but there are some errors that are happened during run the experiment. For experiment 1, the graph of conductivity versus conversion of sodium hydroxide using conductivity meter is inversely proportional. Then, for next experiment, it can be concluded that the conversion of sodium hydroxide is increase as the residence time increase. The graph shows that the conversion versus

http!!en"wiipedia"org!wii!Plug-.low-reactor-#odel=8pplications

(21)

residence time is directly proportional. The experiment is said to not be perfectly successful because the value of conversion of sodium hydroxide is exceed 100%.

RE

COM

COMM

ME

EN

NDAT

DAT

I

O

ON

N

There are a few suggestions to get more precise result for this experiment:

• Run more trial on the experiment to get precise value especially in back titration • Ensure there are no leakage at the valve on the equipment

• Make sure all the colour of titration should be in same colour which is light pink. • Make sure all valve correctly set up and are in right position.

(22)

R

REF

EF

EREN

C

CES

ES

Books:

1.H. Scott Fogler, “Elements of Chemical Reaction Engineerth_Eing, _di_t_i_on”,4 _Pearson International Edition (2006).

2.Levenspiel, O., Chem‘ ical Reaction Engineering’(3rd_ed_i_t_i_on₎_._J_oh_n_Wi_l_ey_{& So}_ns_,_USA

(1999).

3.Smith J.M., “Chemical Engineering Kinetics”, Mc Graw Hill (Singapore), 1981. 4.Astarita G., “Mass Transfer with Chemical Reaction”, Elsevier, 1967.

(23)

I

nt

n

t

ern

et

:

1.http://www.scribd.com/doc/29195386/Plug-Flow-Reactor

2.http://en.wikipedia.org/wiki/Plug_ﬂow_reactor_model

3.http://en.wikipedia.org/wiki/Plug_ﬂow_reactor_model#Applications

O

Ot

t

h

her

er

s

:

1.‘Plug Flow Reactor’, Product Description by Matthew Grisewood

2.Research “Saponiﬁcation of Ethyl Acetate by Sodium Hydroxide in a Plug Flow Reactor” by Lindsey Kato, Shawna Togioka, Luke Sugie (February 2, 2005)