International Journal of Scientific Research in Chemical Engineering, 1(1), pp. 1-8, 2014

Available online at http://www.ijsrpub.com/ijsrce

ISSN: 2345-6787; ©2014 IJSRPUB

http://dx.doi.org/10.12983/ijsrce-2014-p0001-0008

1

Full Length Research Paper

Comparative Study of Packed Bed Reactor and Fluidized Bed Reactor for the

Production of Propylene Oxide

Abhishek Sao1*

, Omprakash Sahu2*

1Department of Chemical Engineering, IT Guru Ghashi University, Bilaspur (CG), India.

2Department of Chemical Engineering, KIOT, Wollo University, Kombolcha (SW), Ethiopia

*Correspondence Author: ops0121@gmail.com; Tel: +251933520653

Received 02 April 2014; Accepted 02 May 2014

Abstract. Propylene oxide has major uses in different chemical product, with production of more than 6 million tons per year

worldwide. The main goal of study is to compare the efficiency of the packed bed reactor and fluidized bed reactor for the

production of propylene oxide. Currently two are applied for the production of propylene oxide first chlorohydrin process and

second hydroperoxide process. For this study hydroperoxide process was used. It found that the conversion factor with respect

catalysis loading and length of the tube found to be 100 % shown by packed bed reactor. By design and experiment it was

found that packed bed reactor is more suitable as compared to fluidized bed reactor for production of propylene oxide.

Keyword: Acid; Boiling point; Catalysis; Process; Time

1. INTRODUCTION

Propylene oxide (PO) is a major industrial product

with production of more than 6 million tons per year

worldwide. Propylene oxide is a volatile, clear,

colorless, and extremely flammable liquid with an

ether-like odor (Creaser et al., 2000). Its molecular

weight is 58.1, its melting point is -112.13°C, and its

boiling point is 34.23°C. Propylene oxide has a

specific gravity of 0.8304 at 20°C/20°C and an

octanol-water partition coefficient of 0.03 (Sinha et

al., 2003). It is soluble in water and miscible with

acetone, benzene, carbon tetrachloride, diethyl ether,

and ethanol. Propylene oxide is very reactive,

particularly with chlorine, ammonia, strong oxidants,

and acids. It may polymerize explosively when heated

or involved in a fire (Buyevskaya et al., 2000).

Propylene oxide is used primarily as a chemical

intermediate in the production of polyurethane polyols

(60% to 65%), propylene glycols (20% to 25%),

glycol ethers (3% to 5%), and specialty chemicals

(Greben et al., 2005). Polyurethane polyols are used to

make polyurethane foams; whereas, propylene glycols

are primarily used to make unsaturated polyester

resins for the textile and construction industries

(CEFIC, 2005). Propylene glycols are also used in

drugs, cosmetics, solvents and emollients in food,

plasticizers, heat transfer and hydraulic fluids, and

antifreezes (Rihko-Struckmann et al., 2004). In

addition, propylene oxide may be used in fumigation

chambers for the sterilization of packaged foods and

as a pesticide. Approximately 70% of it is used as

polypropylene glycol in the raw materials for

urethane, and the remainder is used as propylene

glycol in the raw materials for unsaturated polyesters,

food product additives and cosmetics (Valbert et al.,

1993). The major application of PO is shown in Fig.

1.

PO production methods that have been

industrialized up to this point can be roughly divided

into two methodologies first chlorohydrins process

and the second is hydroperoxide process. In 1999, the

production capacity was distributed evenly between

these two processes; however, because of the

environmental impacts of the chlorohydrins process,

the most recently built plants are all using

hydroperoxide process technologies (Wang et al.,

2004). However, a disadvantage of the hydroperoxide

processes is the production, in a fixed ratio, of a

coproduct (either styrene or tert-butyl alcohol,

depending on which variant of the hydroperoxide

process is applied) (Bartolome et al., 1975). Because

these co-products are produced in a volume that is 3

times larger than that of propene oxide, the economy

of the process is primarily dominated by the market of

the co-product. A major research effort has been made

in the development of alternative direct epoxidation

Sao and Sahu

Comparative Study of Packed Bed Reactor and Fluidized Bed Reactor for the Production of Propylene Oxide

2

processes for the production of propene oxide (Tullo,

2005).

Due to lack of technical problem the production

may be affected. In this study compared the efficiency

of packed bed reactor with fluidized bed reactor for

the production of propylene oxide. The effect of

catalysis and length of tube was studied for packed

bed reactor as well as cost estimation was also

calculated.

Fig. 1: Major application of propylene oxide

2. MATERIALS AND METHODS

2.1. Material

Propylene oxide is an organic compound with the

molecular formula CH3CHCH2O. Propylene oxide is a

colourless, low-boiling, highly volatile liquid with a

sweet, ether-like odour and moderately toxic. It is

flammable and reactive, so storage and unloading

areas must be specifically designed and monitored.

This compound is sometimes called 1,2-propylene

oxide to distinguish it from its isomer 1,3-propylene

oxide, better known as oxetane. Its other common

names are 1,2–Epoxypropane, Propene epoxide,

Propene oxide. This colourless volatile liquid is

produced on a large scale industrially, its major

application being its use for the production of

polyether polyols for use in making polyurethane

plastics. It is chiral epoxide, although it commonly

used as a racemic mixture (Trent, 2001).

2.2. Methodology (Hydrogen peroxide)

Propene oxide is currently produced using two

different types of commercial processes: the

chlorohydrin process and the hydroperoxide process

Hydroperoxide processes are based on the

peroxidation of an alkane to an alkyl-hydroperoxide.

These alkyl-hydroperoxides then react with propene,

producing propene oxide and an alcohol. A

characteristic of these processes is that, besides

propene oxide, a coproduct is produced in a fixed

ratio, usually 2-4 times the amount of propene oxide

produced. Currently, two variants of this process are

applied commercially. The first is the propene oxide-

styrene monomer (PO-SM, also commonly

abbreviated as SMPO) process (60% of the

hydroperoxide plants use this version) (Pell and

Korchak, 1969; Dubner and Cochran, 1993; Van and

Sluis, 2003). In this process, ethylbenzene is oxidized

to ethylbenzene hydroperoxide, which reacts with

propene to produce propene oxide and R-phenyl

ethanol. The R-phenyl ethanol is then dehydrated to

produce styrene. The second process in use is the

propene oxide-tert-butyl alcohol (PO-TBA) process.

In this process, isobutane is oxidized to tert-butyl

hydroperoxide (TBHP), which reacts with propene to

produce propene oxide and tert-butyl alcohol. This

can be dehydrated to isobutene or converted directly

with methanol to methyl-tert-butyl ether (MTBE).

International Journal of Scientific Research in Chemical Engineering, 1(1), pp. 1-8, 2014

3

Although other combination processes are possible,

no others have been applied so far (Richey, 1994).

Other possibilities include, for example, acetaldehyde

to acetic acid, 2-propanol to acetone, isopentane (via

tert-pentyl alcohol) to isoprene, cumene (via

dimethylphenyl methanol) to R-methylstyrene, and

cyclohexene (via cyclohexanol) to cyclohexanone

(Kalich et al., 1993). Characteristics of the

hydroperoxide processes are that they are selective

and produce far less waste than the chlorohydrin

process. However, the major disadvantage of the

hydroperoxide processes is that a fixed amount of

coproduct is always produced. Because the markets

for propene oxide and the coproducts are not linked, a

problem could arise, should the demand for one of the

products collapse. Since the use of MTBE as a fuel

additive is becoming less favorable, the latest plants

that have been built using a hydroperoxide process are

all of the PO-SM type (Hayashi et al., 1998). Figure 2

schematically demonstrates the PO-SM process. The

basic principle of the PO-TBA process is similar to

that of the PO-SM process, so both processes are

discussed simultaneously (Cisneros et al., 1995). The

first reactor converts the ethylbenzene or isobutene

noncatalytically to its corresponding hydroperoxide

by direct liquid-phase oxidation, using oxygen or air.

The oxidation is usually performed in a bubble

column at 400 K and 30 bar when isobutane is used,

or 423 K and 2 bars in the case of ethylbenzene.

Fig. 2: Flow diagram for production of propylene oxide by hydrogen peroxide method (Nijhuis et al., 2006)

3. RESULTS AND DISCUSSIONS

3.1. Packed bed reactor

3.1.1. Design of packed bed reactor

It can be calculated by

Where, W = Weight of catalyst, FA0 = Molar Flow

Rate, XA = Conversion, -rA = Rate of Reaction

W/ FAo = 2.3965x 10

6

W= weight of Catalyst = 2.395×106×19.14 = 4.5×104

Kg

Weight of catalyst can be given by formula

W= ρc ×V × (1-ф)

Where, ρc = Density of catalyst =3.35×103 Kg/m3, V

= Volume of Reactor, ф = Porosity of Catalyst Bed =

0.3, ∴ W = ρc ×V × (1- ф), 4.5×104= 3.35×103×V ×

(1-0.3), ∴ V = 19.18 m3 =677 ft3

Sao and Sahu

Comparative Study of Packed Bed Reactor and Fluidized Bed Reactor for the Production of Propylene Oxide

4

It was decided to use a bank of 2 inch schedule 80

pipes in a parallel that are 60 ft in length. For pipe

schedule 80, the cross sectional area is 0.0205 ft2 the

number of pipe necessary is

n = Volume of the Reactor Cross sectional Area x Length

Number of tubes in the reactor is 550

3.1.2. Pressure Drop in the Reactor

Most gas phase reaction is takes place in packed bed

reactor. Equation most used to calculate pressure drop

in packed bed reactor is Ergun equation

Where, P = Pressure, P0 = Inlet Pressure = 10 atm,

ф = Porosity = (Volume of Void / Total Bed Volume)

= 0.3, ∴ 1- ф = (Volume of Solid / Total Bed Volume)

= 0.7, gc = Conversion Factor = 1 (in the metric

system), dp = Diameter of Particle in the bed = 0.005

m, μ = Viscosity of gas passing through bed =

0.0942x10-3

, z = Length of Reactor =60 ft = 18.3 m,

ρc = Density of catalyst =3.35×103, G = ρ x u =

Superficial Mass Velocity = 2931 Kg / (m2 s),

Therefore,

β = 0.0815

(P/Po)=0.15

P=1.5atm

Hence the pressure drop (∆P) = 8.5 atm

3.1.3. Effect of catalysis weight:

The effect of catalysis weight on conversion is shown

in Fig. 3. It was found that the conversion was

increase with increase in increase in weight of

catalysis. When the catalysis loading was 1, 2, 3, 4,

the conversion was 12, 23, 30 and 45% was observed.

Almost 98 percentage of conversion was found to at

5.5kg of catalysis. Then it maintained constant for the

conversion of long time (Diakov et al., 2002).

Fig. 3: Effect of catalysis loading on conversion

3.1.4. Effect of length on conversion

The effect of length of tube on the conversion of

propylene is shown in Fig. 4. It was found that

conversion was increase with increase in length of

tube (Ramos et al., 2000). The maximum conversion

was 90% found at 18 ft of tube length in reactor. The

total number of tube in the reactor is 550.

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International Journal of Scientific Research in Chemical Engineering, 1(1), pp. 1-8, 2014

5

Fig. 4: Effect of tube length on conversion

3.2. Design of Fluidized Bed Reactor

3.2.1. The design equation for Fluidized Bed

Reactor is same as for CSTR

By solving above equation analytically, we can find

the concentration profile with respect to time constant.

That concentration profile shown in figure below.

Conversion in the packed bed reactor is,

Weight of catalyst in the reactor calculated by formula

W= ρc ×V × (1-ф )

Assume Porosity = 0.6

W = 3350 ×19.18× (1-0.65) = 2.25×104 Kg

3.2.2. Effect of concentration on time

The effect of concentration on the reaction time is

shown in Fig. 5. It was found that the concentration of

component C was 7.2 mole/liters maximum at 250min

of reaction time. The concentration of component A

was 3.5mole/liters at zero time and the concentration

of component was 1.5 mole/liters at 250 min (Leveles,

2002).

Fig. 5: Effect of concentration time

Sao and Sahu

Comparative Study of Packed Bed Reactor and Fluidized Bed Reactor for the Production of Propylene Oxide

6

3.3. Cost estimation

3.3.1. Packed Bed Reactor

Weight of Material Required Tube

= 2 π r L× Thickness × Density × Number

= 427185 lb

Weight of Material Required Shell

= 2 π r L × Thickness × Density

= 10010.8 lb

Weight of Material Required Head

= 4090 lb

Total weight of Material required

= 427185 10010.8 + 4090

= 441288 lb

= 200164 Kg

Actual weight of Material required

= 200164+ 20% Extra weight

= 240169 Kg

Cost of Material required

= 240.169 tone× 887 $/tones

= 213054.56 $

= Rs. 1.0226×107

Cost of Catalyst Required

= W e i g h t of Catalyst × Cost per kg of Catalyst

= 4 . 5 × 104 ×40(Assume)

= R s . 1.8 ×106

Miscellaneous Cost = 100000 Rs/yr

1) Total Equipment Cost =

1.0226×107 + 1.8 ×106

+100000

= Rs. 12.12 ×106

2) Insulation Cost = 15 %

Equipment Cost

= Rs. 1.818 ×106

3) Piping and Instrumentation

= 10% Equipment Cost

= Rs. 12.12 ×105

Total Reactor Cost = 12.12 ×106 +1.818 ×10

6 +12.12

×105 + 60000 = Rs. 1.521 ×10

7

3.3.2. Fluidized Bed Reactor

Weight of Material Required Shell

= 2 π r L× Thickness × Density

= 3823.95 lb

Weight of Material Required Head

= 8112.2 lb

Total weight of Material required

= 3823.2 + 8112.2

= 11935.4 lb

= 5 4 1 3 . 8 Kg

Actual weight of Material required

= 5413.8+ 20% Extra weight

= 6 4 9 6 . 5 6 Kg Cost of Material required

= 6.49656 tone× 887 $/tone

= $ 57.62.45

= Rs. 2.765×105Cost of Catalyst Required

= Weight of Catalyst × Cost per kg of Catalyst

= 2.25×104 Kg× 40 (assumed)

= Rs. 9 ×105

Miscellaneous Cost = 100000 Rs/yr

1) Total Equipment Cost = 2.765×105 + 9 ×105 Rs

+100000 = Rs. 1.27 ×106

2) Insulation Cost = 15 % Equipment Cost

= Rs. 1.914 ×105

3) Piping and Instrumentation = 10% Equipment Cost

= Rs. 1.27 ×105

4) Land

= Rs. 60000

Total Reactor Cost = 1.27 ×106 +1.914 ×105+1.27

×105 + 60000 = Rs. 1.6484 ×106

4. CONCLUSION

This study demonstrated that packed bed reactor is

more suitable as compared to fluidized bed reactor.

The conversion factor with respect catalysis loading

and length of the tube found to be approximately 100

percentages. Packed bed reactor shows good

efficiency at 550 numbers of tubes, 8.5 Atm pressure

drops, 98% of conversion at 5.5 Kg catalysis and 90%

conversion 18feet. The fixed bed reactor shows upto

80% conversion. The hydroperoxide processed will

maintain a very important position as long as there is a

high demand for their coproducts. Considering the

huge market for styrene, especially, the PO-SM

process will be in use for a long time. The new

processes developed fulfilled the requirement.

Improvements are being made continuously and new

processes to replace the two existing processes are

beginning to be applied.

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Sao and Sahu

Comparative Study of Packed Bed Reactor and Fluidized Bed Reactor for the Production of Propylene Oxide

8

Mr. Abhishek Sao was finial year Chemical Engineering student in department of chemical

engineering, IT, Guru Ghasi Das University, Bilaspur (CG), India in 2011. His specialization is

process engineering.

Mr Omprakash Sahu was graduated from department of Chemical Engineering, ITGGV Bilaspur

(CG) India in the year of 2003.His specialization in Chemical, Energy and Environment