chapter 9 che 126

8/18/2019 Chapter 9 ChE 126

1/94

I N S T R U C T O R :

E N G R . C A R E S S A M A R I E F R I A L - D E J E S U S

Chapter 9:Temperature and Pressure Effects

8/18/2019 Chapter 9 ChE 126

2/94

Reactor design vs. T

8/18/2019 Chapter 9 ChE 126

3/94

Reactor design vs. P

Constant volume batch reactor and ideal gas

8/18/2019 Chapter 9 ChE 126

4/94

Finding the best reactor design based on T&P

3step procedure:

!st:Effects on the e"uilibrium composition# rate ofreaction and product distribution due to changes in

operating T and P .o Reactions sensitive to specific range of T and P $%rrhenius e"n

'nd:Effect of heat effects of chemical reactions on thetemperature of the reacting mi(ture

o

$e.g. Emulsification# e(othermic reaction ma) cause a runa*a)reaction if this e(ceeds a specific range of operating temperature

3rd:Economic considerationso Efficienc) $+ptimum reaction design vs. Cost

8/18/2019 Chapter 9 ChE 126

5/94

,ingle Reactions

Concerned solel) on: Conversion level Reactor stabilit)

-ote: Product distribution is irrelevant.

From thermod)namics:

!. eat liberated or absorbed for a given e(tent ofreaction and#

'. /a(imum possible conversion

8/18/2019 Chapter 9 ChE 126

6/94

eats of Reaction from Thermod)namics

eat of reaction# 0r -ature of the reacting s)stem %mount of material reacting and# Temperature and pressure of the reacting s)stem

or

1ata from tabulated heats of formation# 0f or heats of

combustion# 0c of the reacting materials

8/18/2019 Chapter 9 ChE 126

7/94

eats of Reaction from Thermod)namics

2T! $usuall) 'oC

Reaction:

0r :heat transferred to the reacting s)stem *hen a

moles of % disappear to produce r moles of and s

moles of , *ith the s)stem at the sametemperature and pressure e!"re and a!terthe #han$e.

8/18/2019 Chapter 9 ChE 126

8/94

eats of Reaction and Temperature

4) the of conservation of energ)

5n terms of enthalpies

5n terms of specific heats

*here

8/18/2019 Chapter 9 ChE 126

9/94

eats of Reaction and Temperature

6hen

*e obtain

*here

8/18/2019 Chapter 9 ChE 126

10/94

0r at various temperatures

E(ample 9.!

7asphase reaction at 'oC

6hat is the 0r at !8'oC 5s the reaction e(othermic

at that temperature

%verage Cp values bet*een 'oC and !8'oC are

8/18/2019 Chapter 9 ChE 126

11/94

0r at various temperatures

8/18/2019 Chapter 9 ChE 126

12/94

E"uilibrium constants from Thermod)namics

Real systems do not necessarily achieve the conversion by calculationsbased on thermodynamics. These are only suggested attainablevalues.

Revie* on 7ibbs free energ)

*here: f : fugacit) of the component at e"uilibrium conditions

f o: fugacit) of the component at the selected standard state temp T

∆G o: standard free energ) of a reacting compound $usuall) tabulated

: thermod)namic e"uilibrium constant

8/18/2019 Chapter 9 ChE 126

13/94


,uggested standard states in choosing the follo*ingcomponents

7ases ; pure component at ! atm# at *hich pressure

ideal gas behavior is closel) appro(imated,olid ; pure solid component at unit pressure

8/18/2019 Chapter 9 ChE 126

14/94


Revie*# the e"uilibrium constant

*here

%lso#

8/18/2019 Chapter 9 ChE 126

15/94


7as reactions: 2! atm f o=po=1atm

For an) component 5 of an ideal gas

8/18/2019 Chapter 9 ChE 126

16/94


For a solid component ta>ing part in a reaction ?ariation in fugacit) and pressure are small. Therefore#

8/18/2019 Chapter 9 ChE 126

17/94

E"uilibrium Conversion

E"uilibrium composition E"uilibrium constant Changes in temperature

From thermod)namics# rate of change:

5ntegrating# 0r is constant

8/18/2019 Chapter 9 ChE 126

18/94


6hen variation in 0r needs to be considered#

integrating

8/18/2019 Chapter 9 ChE 126

19/94

E"uilibrium Conversion at 1ifferent Temperatures

E(ample 9.'

$a4et*een 8oC and !88oC determine the e"uilibrium conversionfor the elementar) a"ueous reaction

Present the results in the form of a plot of temperature versusconversion.

$b6hat restrictions should be placed on the reactor operatingisothermall) if *e are to obtain a conversion of @A or higher

8/18/2019 Chapter 9 ChE 126

20/94


,olution: 6ith

8/18/2019 Chapter 9 ChE 126

21/94


8/18/2019 Chapter 9 ChE 126

22/94


8/18/2019 Chapter 9 ChE 126

23/94


8/18/2019 Chapter 9 ChE 126

24/94


8/18/2019 Chapter 9 ChE 126

25/94

7eneral 7raphical 1esign Procedure

For an) single homogeneous reaction

8/18/2019 Chapter 9 ChE 126

26/94


8/18/2019 Chapter 9 ChE 126

27/94


8/18/2019 Chapter 9 ChE 126

28/94


Reactor siBe for a given dut) and temperatureprogression:

!. 1ra* the reaction path on the % vs T plot.

'. Find the rates at various % along this path.3. Plot the lD$r % versus % curve for this path.

. Find the area under this curve $?DF %+.

8/18/2019 Chapter 9 ChE 126

29/94


8/18/2019 Chapter 9 ChE 126

30/94


8/18/2019 Chapter 9 ChE 126

31/94

Construction of the $;riiT

E(ample 9.3 $p.'!@# inetics# find the rate e(pression for thisreaction and prepare the conversiontemperature

chart *ith reaction rate as parameter.

8/18/2019 Chapter 9 ChE 126

32/94

Construction of the $;riiT Chart

8/18/2019 Chapter 9 ChE 126

33/94


8/18/2019 Chapter 9 ChE 126

34/94


%t tH! min# THGoC# % H8.!# %eH8.9

%t tH!8 min# TH'oC# % H8.G8# %eH8.99

8/18/2019 Chapter 9 ChE 126

35/94


8/18/2019 Chapter 9 ChE 126

36/94


6hat if e(ample 9.3 used a C,TR rather than a 4R

8/18/2019 Chapter 9 ChE 126

37/94


%t tH! min# THGoC# % H8.!# %eH8.9

%t tH!8 min# TH'oC# % H8.G8# %eH8.99

8/18/2019 Chapter 9 ChE 126

38/94

+ptimum Temperature Progression

Progression *hich minimiBes %&F AO for a given

conversion of reactant

5sothermal or nonisothermal

4R# PFR or series of C,TR 5deal for estimation of the real s)stem

5n an) t)pe of reactor: At any composition, it illalays be at the temperature here the rate isma!imum.

8/18/2019 Chapter 9 ChE 126

39/94

+ptimum Temperature Progression

8/18/2019 Chapter 9 ChE 126

40/94

eat Effects

8/18/2019 Chapter 9 ChE 126

41/94

eat Effects

8/18/2019 Chapter 9 ChE 126

42/94

%diabatic +perations

8/18/2019 Chapter 9 ChE 126

43/94


Enthalp) of entering feed:

8/18/2019 Chapter 9 ChE 126

44/94


Enthalp) of leaving feed:

8/18/2019 Chapter 9 ChE 126

45/94


Energ) absorbedDreleased b) the reaction:

8/18/2019 Chapter 9 ChE 126

46/94


8/18/2019 Chapter 9 ChE 126

47/94


8/18/2019 Chapter 9 ChE 126

48/94


For complete conversion:

8/18/2019 Chapter 9 ChE 126

49/94


8/18/2019 Chapter 9 ChE 126

50/94


6hen$

8/18/2019 Chapter 9 ChE 126

51/94

,iBe of Reactor for %diabatic +perations

Plug flo* Tabulate the rate vs. % along the %+< Prepare the !D$r% vs % plot and integrate.

C,TR Jse the rate at the conditions *ithin the reactor

8/18/2019 Chapter 9 ChE 126

52/94


PFR

8/18/2019 Chapter 9 ChE 126

53/94


C,TR

8/18/2019 Chapter 9 ChE 126

54/94


Finding the best adiabatic operations ,hifting the operating line $changing the inlet temp to rates of

highest mean value.

For endothermic Hstarting at the highest allo*able tempFor e(othermic locating the locus of ma(imum rates *ith minimum ?DF %+

8/18/2019 Chapter 9 ChE 126

55/94


Finding the best reactor t)pe /inimiBes the ?DF %+ from % vs T

Plug flo* ; if rate progressivel) decreases *ith conversion$endothermic reaction and close to isothermal e(othermic reaction behavior

8/18/2019 Chapter 9 ChE 126

56/94


Finding the best reactor t)pe /inimiBes the ?DF %+ from % vs T

E(othermic reactions *ith large temp rise during reaction:

/i(ed flo* ; for small $pure gaseous reactantsPlug flo* ; for large $gas much inerts# or li"uid s)stems

8/18/2019 Chapter 9 ChE 126

57/94

-onadiabatic +perations

8/18/2019 Chapter 9 ChE 126

58/94


6ith relativel) negligible difference of heat capacities

8/18/2019 Chapter 9 ChE 126

59/94


8/18/2019 Chapter 9 ChE 126

60/94

E(othermic in C,TR

C,TR

%t lo* temp# rate is lo*# is lo*.

%t high temp# rises and approaches e"uilibrium.4e)ond e"iulibrium temp# decreases.

8/18/2019 Chapter 9 ChE 126

61/94

E(othermic in C,TR

C,TR

%t lo* temp# rate is lo*# is lo*.

%t high temp# rises and approaches e"uilibrium.

4e)ond e"uilibrium temp# decreases.

8/18/2019 Chapter 9 ChE 126

62/94

E(othermic in C,TR

5rreversible Reactions

insufficient heat liberated. -ot selfsustaining. Conversion is negligible.

more than enough heat liberated.

8/18/2019 Chapter 9 ChE 126

63/94

E(othermic in C,TR

Reversible e(othermic reactions

,pecific range of temperature to maintain conversion

8/18/2019 Chapter 9 ChE 126

64/94

Performance for the +ptimal Temperature Progression

Jsing the optimal temperature progression in a plug flo*reactor for the reaction of E(amples 9.' and 9.3#

$a calculate the space time and volume needed for 8Aconversion of a feed of " A, = 1### mol$min here % Ao = &

mol$liter.$b plot the temperature and conversion profile along the

length of the reactor.

8/18/2019 Chapter 9 ChE 126

65/94


4asis: molD<

8/18/2019 Chapter 9 ChE 126

66/94


1ra* the locus of ma(imum rates.

Ta>e note of the 9oC ma(imumallo*able temperature and 8Afeed conversion needed.

Ra(graph)

ra Xa 1/ra A

0.10 0.40 0.80 2.50 0.19

0.20 0.80 0.70 1.25 0.05

0.29 1.18 0.65 0.85 0.07

0.45 1.82 0.55 0.55 0.06

0.83 3.33 0.40 0.30 0.03

2.25 9.00 0.27 0.11

0.40

8/18/2019 Chapter 9 ChE 126

67/94


9.88 8.'@ 8.!! 8.8Ra(grap

h) ra Xa 1/ra A

0.10 0.40 0.80 2.50 0.19

0.20 0.80 0.70 1.25 0.05

0.29 1.18 0.65 0.85 0.07

0.45 1.82 0.55 0.55 0.06

0.83 3.33 0.40 0.30 0.03

2.25 9.00 0.27 0.11

0.40

8/18/2019 Chapter 9 ChE 126

68/94


9.88 8.'@ 8.!! 8.8Ra(grap

h) ra Xa 1/ra A

0.10 0.40 0.80 2.50 0.19

0.20 0.80 0.70 1.25 0.05

0.29 1.18 0.65 0.85 0.07

0.45 1.82 0.55 0.55 0.06

0.83 3.33 0.40 0.30 0.03

2.25 9.00 0.27 0.11

0.40

8/18/2019 Chapter 9 ChE 126

69/94


8/18/2019 Chapter 9 ChE 126

70/94


9.88 8.'@ 8.!! 8.8Ra(grap

h) ra Xa 1/ra A

0.10 0.40 0.80 2.50 0.19

0.20 0.80 0.70 1.25 0.05

0.29 1.18 0.65 0.85 0.07

0.45 1.82 0.55 0.55 0.06

0.83 3.33 0.40 0.30 0.03

2.25 9.00 0.27 0.11

0.40

!8A increments# %reaH8.8 %rea at % from 8.'@ to 8. is 8.83.

8/18/2019 Chapter 9 ChE 126

71/94


+ ti C,TR Fl R t P f

8/18/2019 Chapter 9 ChE 126

72/94

+ptimum C,TR Flo* Reactor Performance

% concentrated a"ueous %solution of the previous e(amples $C %+ H molDliter# "A, = 1### mol$min' is to be (#) converted in a mi!ed floreactor.

$a 6hat siBe of reactor is needed

$b 6hat is the heat dut) if feed enters at 'LC and product is to be

*ithdra*n at this temperature-ote that


8/18/2019 Chapter 9 ChE 126

73/94


4asis: molD<


8/18/2019 Chapter 9 ChE 126

74/94


C,TR operating point atpoint C.


8/18/2019 Chapter 9 ChE 126

75/94


%di b ti PFR P f

8/18/2019 Chapter 9 ChE 126

76/94

%diabatic PFR Performance

Find the siBe of adiabatic plug flo* reactor to react thefeed of E(ample 9. $F %oH !888 molDmin and % Ao = &

mol$liter' to (#) conversion.

%di b ti PFR P f

8/18/2019 Chapter 9 ChE 126

77/94


4asis: molD<

%di b ti PFR P f

8/18/2019 Chapter 9 ChE 126

78/94



8/18/2019 Chapter 9 ChE 126

79/94



8/18/2019 Chapter 9 ChE 126

80/94


CSTR 'FR Opt(mum

!@'8 < '888 < 8' <

E( 9. E( 9.G E( 9.

%diabatic PFR *ith Rec)cle

8/18/2019 Chapter 9 ChE 126

81/94


Ta>e the problem E(ample 9.G but no* allo* rec)cleto product stream.

$E(. 9.G:Find the siBe of adiabatic plug flo* reactor toreact the feed of E(ample 9. $F %oH !888 molDmin

and % Ao = & mol$liter' to (#) conversion.


8/18/2019 Chapter 9 ChE 126

82/94



8/18/2019 Chapter 9 ChE 126

83/94


/ultiple Reactions

8/18/2019 Chapter 9 ChE 126

84/94

/ultiple Reactions

Reactor siBeProduct distribution

/anipulate temp:

+btain desirable product distribution

/a(imum desired product in a reactor *ith given

space time.

Product 1istribution and Temperature

8/18/2019 Chapter 9 ChE 126

85/94



8/18/2019 Chapter 9 ChE 126

86/94


A high temperature favors the reaction of higher *,a lo temperature favors the reaction of loer *.


8/18/2019 Chapter 9 ChE 126

87/94


For parallel reactions

5f E! M E' : high T

5f E! N E' : lo* T


8/18/2019 Chapter 9 ChE 126

88/94


For series reactions

5f E! M E' : high T

5f E! N E' : lo* T


8/18/2019 Chapter 9 ChE 126

89/94


For seriesparallel reactions


8/18/2019 Chapter 9 ChE 126

90/94

Construction of the $ ri i T Chart

Jsing E(cel for

8/18/2019 Chapter 9 ChE 126

91/94


/a>e sure to install ,olver in )our E(cel,et up e"uations

,et range $e.g. T

Jse ,olver

/a>e chart $tip: onl) use the data needed

Jsing E(cel for7raphing the +ptimum Path

8/18/2019 Chapter 9 ChE 126

92/94

7raphing the +ptimum Path

Jsing the generate chart# find the ma(imum pointsfor each rates

/a>e another set of table for these data

7enerate curve from these data $ %

vs T

Compute for the !D$ri vs % data

7enerate curve from these data $!D$ri vs %

Jsing E(cel for7raphing the %diabatic +perating

8/18/2019 Chapter 9 ChE 126

93/94

7raphing the %diabatic +perating e other lines in thegraph $trial and error to find the desired %+<

depending on the reactor scheme.

Jsing E(cel for7raphing the %diabatic +perating

8/18/2019 Chapter 9 ChE 126

94/94

7raphing the %diabatic +perating

chapter 9 che 126

Documents