DESIGN OF CONTINUOUS STIRRED-TANK REACTOR FOR LARGE-SCALE PHENOL PRODUCTION FROM CUMENE HYDROPEROXIDE

__________________________________________________________

A written report

Presented to the

Chemical Engineering Department

Faculty of Engineering

University of Santo Tomas

__________________________________________________________

In Partial

Fulfillment of the

Requirements of the Degree of

Bachelor of Science in Chemical Engineering

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By Hannah Mae R. Valensoy

5ChE-C

DECEMBER 2014

I. Introduction

Phenol is an aromatic organic compound which consists of a phenyl group bonded to a hydroxyl group. It is considered to be one of the most important starting material for various production of chemical products, such as phenol resin, bis-phenol A, aniline and some agricultural chemicals. Currently, there are four known processes being used commercially to produce phenol. But among the four stated processes, the major process used is the cumene hydroperoxide route, which accounts for about 90% of world capacity.

The basic reaction involved in the phenol production is the cleavage of cumene hydroperoxide to give the desired product, phenol and a useful by-product, acetone.

To give a brief explanation on how the process works, the cumene is oxidized into cumene hydroperoxide (CHP) which then decomposes to form phenol and acetone by using an acid catalyst. This process is very cost effective due to its mild reaction conditions and high percentage yield of phenol.

The reaction is first order kinetics and the most commonly used catalyst is a strong mineral acid such as sulfuric acid.

Phenol has been in the production since the early times of 1860s. Its early use was as an antiseptic. Towards the end of the 19th century, industrial scientists had found new uses for phenol in the synthesis of dyes, aspirin, and one of the first high explosives, picric acid.

For this particular report, a continuous stirred tank reactor was designed to produce 40,000 tons of phenol annually from the cumene hydroperoxide decomposition.

II. Feedstock and Operating Conditions

The cumene hydroperoxide which serves as the sole reactant for this process comes from the

oxidation of cumene into cumene hydroperoxide using a plug-flow reactor (PFR). The cumene

hydroperoxide (CHP) is now fed to a continuous stirred-tank reactor with H2SO4 as the catalyst. Heating

coil is used as the heating medium. The conversion of feed into product will occur isothermally at 65˚C

with a pressure of 2 atm. The order of the reaction is 0.5 (Kao, Chen-Shan & Duh, Yih-Shing., 1998) and

the overall conversion is 85%.

III. Material of Construction

The reactor will be made of a Grade 904L stainless steel cylindrical and ellipsoidal head as

material of construction. This type of stainless steel is a non-stabilized austenitic steel with low

carbon content. The high alloy stainless steel is added with copper to improve its resistance to

strong reducing acids, especially sulfuric acid. Grade 904L stainless steel is also resistant to stress

corrosion cracking and crevice corrosion. It is also non-magnetic, and offers excellent formability,

toughness and weldability.

Composition of Grade 904L stainless steel

Weight %

C 0.02

Mn 2

Si 1

P 0.045

S 0.035

Cr 23

Mo 5

Ni 28

Cu 2

Mechanical Properties

IV. Rationale for Equipment Selection

The stirred tank reactor can be considered as the basic chemical reactor. They are usually used

for homogeneous and heterogeneous liquid-liquid and liquid-gas reactions which suits it best for the

phenol production from cumene hydroperoxide decomposition. The presence of agitator in the

continuous stirred tank reactor is also significant because it increases the product yield of the

decomposition process. To sum up, continuous stirred tank reactors are suitable for reactions and/or

processes where good mass transfer or heat transfer is needed.

V. Material Balance

Component Mass Balance:

V CAO−V C A−¿V CAO−V C A−[V∗(k CA ) ]=0

Where:-rA = k*CA

0.5

-rA=1.007 mol/m3 min

Cumene Hydroperoxide (CHP)

CSTR

T=65˚C

30, 000 tons/year Phenol

13, 000 tons/year Acetone

Tensile strength(MPa)

490

Yield Strength(MPa)

220

Elongation(% in 50 mm)

36

Hardness 70-90

Energy Balance

VI. Equipment Design Theoretical Calculations

1. Design pressure and temperature

Based on working temperature + 30°C

T = 65°C + 30°C

T = 95°𝐶Based on working pressure + [10% of working pressure or 25 psi, depends on which is greater]

P = 202.65𝑘𝑃𝑎 + [25𝑝𝑠𝑖 𝑥 (101.325 𝑘𝑃𝑎)/(14.7 𝑝𝑠𝑖)]

P = 374.971 𝑘𝑃𝑎2. Calculation for reactor volume

mrb=30,000 ton/year

mrc=13,000 ton/year

MWb=94.111 kg/mol

MWc=58.079 kg/mol

Fb=mrb∗1000∗( 1MWb )∗( 1365 )∗( 1

24)

Fb=36.39 mol/hr

83.801 mol/hr CHP

T=25˚C

CSTR

T=65˚C

 

85% Products (Phenol + Acetone)

15% unreacted CHP

T=65˚C

Q generated (from agitation and heating coil)

Fc=mrc∗1000∗( 1MWc )∗( 1365 )∗( 1

24)

Fc=25.552 mol/hr

Let x=nao

0.85(x)=61.94

nao=72.87 mol/hr

0.15(nao)=10.931 mol/hr

Unreacted CHP=10.931 mol/hr

Total Fao=unreacted CHP + nao=72.87+10.931

Total Fao=83.801 mol/hr

Fao=83.801 mol/hr

ρa=1020 kg/m3

MWa=152 kg/mol

Xa=0.85

Cao= ρaMWa

Cao=6.711 mol/m3

vao= FaoCao

vao=12.487 m3/hr =0.25/hrƮ

V=vao* =(12.487)(0.25)Ʈ

V=3.122 m3

3. Dimensions of the reactor vessel

The reactor vessel will be in vertical orientation and with hemispherical head.

V=( π4 )∗¿

h=1.683 m

h=D=1.683 m

r=D/2=1.683/2=0.842

r=0.842 m

a=h/2=0.842 m

H/D=0.8

H=1.346 m

Vhemisphere=

4 π r3

32

Vhemisphere=1.248 m3

Vcylinder=( π4 )∗D2∗h

Vcylinder=2.994 m3

Vtank=Vcylinder + Vhemisphere= 1.248 + 2.994=4.242 m3

Vtank=4.242 m3

4. Shell thickness

Welded Joint Efficiency

Double-welded butt joints, fully radiographed (seamless shells and heads)

E = 1.0

Corrosion Allowance

Vessels in contact with corrosive fluids

CC = 9mm

t shell=Pr

SE−0.6 P+CC

t shell=(374.971 )( 1.6832 )

¿¿

t shell=0.01115m

t head=112 [ P Da

SE−0.1 P ] [2+( Da

2h )2]+C c

t head=112 [ 374.971 (1.683+2 (0.01115 ) )

(146.667 x103 x1.0 )−0.1 (374.971 ) ][2+(1.683+2 (0.01115 )2 (1.346 ) )

2]+ 91000

t head=0.411m

5. Power requirements and agitation

P=922.512 W

*Rule of Thumb Summary by Ludwig

*Unit Operations of Chemical Engineering

By McCabe, Smith, Harriot

*Values of KL and KT (Peters & Timmerhaus, 1991)

Agitator type: Pitched 4-blade turbine

m

kg/m3

rps

ω = 14.703 m/s

VII. Heuristics

Heuristics are experience-based techniques for equipment design that find a

solution which is not guaranteed to be optimal, but good enough for a set given set of

objectives. It is commonly called as rules of thumb. It simplifies equipment design calculations

regarding suitable sizes or performance of equipment; and it is already established and

standardized by experienced engineers (Walas, 1987).

The heuristics for reactor design and its mixing and agitation are the following:

1. Mild agitation is obtained by circulating the liquid with an impeller at superficial velocities of

30.48–60.9mm/s (0.1–0.2ft/s), and intense agitation at 213.4–304.8mm/s (0.7– 1.0ft/s).

2. Intensities of agitation with impellers in baffled tanks are measured by power input,

hp/1000gal., and impeller tip speeds:

3. Proportions of a stirred tank relative to the diameter D: liquid level= D; turbine impeller

diameter= D/3; impeller level above bottom= D/3; impeller blade width= D/15; four vertical

baffles with width= D/10.

4. The rate of reaction in every instance must be established in the laboratory, and the

residence time or space velocity and product distribution eventually must be found from a

pilot plant.

5. The optimum proportions of stirred tank reactors are with liquid level equal to the tank

diameter, but at high pressures slimmer proportions are economical.

6. Power input to a homogeneous reaction stirred tank is 0.1–03kw/m3 (0.5–1.5hp/1000gal.)

but three times this amount when heat is to be transferred.

7. Ideal CSTR (continuous stirred tank reactor) behavior is approached when the mean

residence time is 5–10 times the length needed to achieve homogeneity, which is

accomplished with 500–2000 revolutions of a properly designed stirrer.

VIII. Equipment Specifications

Specification of reactor vessel Design dimensions

Diameter of the reactor 1.683 m

Height of the reactor 1.346 m

Aspect ratio 0.8

Head depth 0.842 m

Shell thickness (vessel) 0.01115 m

Shell thickness (head) 0.411 m

Diameter of the baffle (width) 0.1683 m

Type of impeller Four-pitched blade turbine

Number of blades 4

Agitator diameter 0.561 m

Height of agitator from tank bottom 0.561 m

Agitator blade width 0.1122 m

Input power 922.512 W

Agitator speed 14.703 m/s

IX. Rendered 3D-Model

REFERENCES

1. Green, Don W., Perry, Robert H. Perry’s Chemical Engineer’s Handbook, 8th edition. New York: McGraw-Hill, 2008

2. Sinnott, Rey., Towler, Gavin. Chemical Engineering Design, 5th edition. San Francisco: Elsevier, 2009

3. Levenspiel, Octave. Chemical Reaction Engineering 3rd edition.

4. Rules of thumb summary by Walas

5. Harriott, Peter. Chemical Reactor Design. New York: Marcel Dekker, Inc., 2002

6. Rengaraj, K., Selvin, Rosilda. Catalytic decomposition of cumene hydroperoxide into phenol and acetone. Applied Catalysis A:General 219 (2001) 125-129

7. Design of Ideal Continuous Stirred Tank Reactors http://www.rshanthini.com/tmp/CP303/set5.pdf

8. Rase, Howard F. Chemical Reactor Design for Process Plants, Volume two: Case studies and Design Data. New York: John Wiley & Sons.

9. Kao, Chen-Shan., Duh, Yih-Shing. Thermal decomposition kinetics of cumene hydroperoxide. Trans IChemE, Vol 76, Part B (1998)

Appendices for Calculations

Calculation for Q gained:

TO=25˚C

Tf=65 ˚C

FAO=83.801 mol/hr

Q=ΔHout-ΔHin+ΔHrxn

ΔHout= ΔHin=0

Q= ΔHrxn

ΔHrxn=ΔHR+ ΔHP+ ΔHF

At 25˚C:

ΔHFA=-475463.9

Residence time, =0.25 1/hrƮ*(M.Sittig, 1969)

ΔHFB=-165000

ΔHFC=-248000

ΔHF=[( ΔHFB+ ΔHFC)- ΔHFA] x Fao∗103

60

ΔHF=872.423x105 W

At Tave=65+252

=45˚ C :

CpA=2179.64

CpB=2154.558

Cpc=2241.623

ΔHR=[( CpA x MWA x Fao)]*(25-65)*160

ΔHR=-185.32x105 W

ΔHP=[(CpB x MWB X FB) + (Cpc x MWc x Fc)]*(65-25)*160

ΔHP=71.369x105 W

ΔHRXN= ΔHF + ΔHR + ΔHP

ΔHRXN=7.585x107 W

Q= ΔHRXN=7.585x107 W