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International Journal of Science and Technology Volume 3 No. 8, August, 2014

IJST © 2014– IJST Publications UK. All rights reserved. 435

Reactive Distillation for Phenol Production Using Different Types of Zeolite

Prepared from Rice Husk

Wadood T. Mohammed, Mohammed N. Abbas Chemical Eng. Dept. – College of Engineering – University of Baghdad

ABSTRACT

Production of phenol from exothermic cleavage reaction of cumene hydroperoxide (CHP) was investigated by using reactive distillation

technique in the presence of prepared zeolite catalysts from rice husk. Three types of catalysts have been prepared from Iraqi rice husk

(IRH) as a source of silica, faujasite type Y – zeolite, β – zeolite and ZSM – 5 zeolite. They have been tested as catalyst in the reactive

distillation for phenol production at different variables. These are, feed temperature (55 – 95 oC), liquid hourly space velocity (LHSV) (1

-5 h-1) and bed height (20 and 30 cm), keeping the reaction at atmospheric pressure. The results analysis shows that cumene hydroperoxide

conversion was 100% while percent yield of phenol were 60.39, 57.02 and 46.42 for ZSM – 5, β – zeolite and Y – zeolite catalysts

respectively.

In the theoretical part, rate based or non-equilibrium (NEQ) mathematical model was developed taking into account the effect of mass and

heat transfer in material and energy balances using MATLAB and FORTRUN simultaneously to solve Material Balance (M), Phase

Equilibrium (E), Summation Equations (S), Energy Balance (H), and Reaction Rate Equation (R), i.e, MESHR. The results showed that

this model gave fair agreement with the experimental study.

Keywords: phenol production, cumene hydroperoxide cleavage, zeolite, rice husk, RD simulation.

1. INTRODUCTION

Phenol is one of the most important starting materials for various

chemical products, such as phenol resin, bis-phenol A, aniline

and some agricultural chemicals. There currently are four process

routes being used commercially to produce synthetic phenol.

There are based on benzene and one on toluene. The major

process, which account for about 90% of world capacity, is the

cumene hydroperoxide route. The basic reaction involved in this

process is the cleavage of cumene hydroperoxide to give phenol

and acetone [1].

Although a number of methods for phenol syntheses have been

proposed, the cumene process is now used as the main route for

commercial production of phenol. In the process, cumene is first

synthesized from benzene and propylene, and then oxidized to

CHP, followed by the decomposition to phenol and acetone by

acid catalyst. The process is estimated to be very cost effective

because of its mild reaction conditions and high yield of phenol.

In addition, acetone, which is also a commercially important

chemical, is coproduced with phenol in the process [2].

Reactive distillation, a new technique by which we can reduce

the number of operating equipment, is suitable only for chemical

reactions where the distillation of reaction components occurs in

the same temperature range as the reaction. Inasmuch as

distillation columns are typically operated at higher liquid and

vapor flow rates than conventional reactors, the reduced

residence time in the reactive section of the column will

minimize the formation of byproducts, this is especially

advantageous in the case of CHP decomposition as the

dehydration of 2-phenyl-2-propanol leads to the formation of α-

methyl styrene (AMS), a reactive intermediate that could

undergo further reactions such as dimerization, oligomerization,

and coke formation. Minimizing the formation of heavy

compounds will extend catalyst life if a heterogeneous catalyst is

employed for the reactive section of the column [3].

Models for reactive distillation may be split into two categories;

the equilibrium (EQ) stage model and the rate-based or non-

equilibrium (NEQ) stage model, where the stage may be a tray

or a segment of packing[4]. The equilibrium model includes the

assumption that the streams leaving the stages are at typical

equilibrium. Component material balance, phase equilibrium

equations, summation equations and energy balance for each

stage (MESHR equations) are solved to give composition,

temperature and flow profiles. On the other hand, the non-

equilibrium models are commonly based on the two film theory.

The aim of the present work was to prepare zeolite catalysts from

Iraqi rice husk as a silica source. It was an aim also to design and

construct of packed reactive distillation column, to produce

phenol from cumene hydroperoxide (CHP) at different operating

International Journal of Science and Technology (IJST) – Volume 3 No. 8, August, 2014


conditions. A rate-based model was also developed to describe

the process.

2. MATERIALS AND METHODS

2.1 Materials

Cumene Hydroperoxide (CHP) supplied from Sigma Aldrich Co.

was used as raw material. Iraqi rice husk (IRH) collected from

southern Iraqi farms was used as raw materials for preparation of

the three zeolite catalysts, Y-zeolite, β-zeolite, and ZSM-5.

2.2 Preparation of Rice Husk Ash (RHA)

Rice husk was treated with 10% sulfuric acid (H2SO4) for 24

hours for preliminary removing all impurities. Washed with

distilled water, filtered, dried in air, and calcined at 750 oC for 6

h. 12 g of calcined IRH were then subjected for dissolution in

Sodium hydroxide NaOH (4 M) followed by refluxing at 90 oC

for 12 h. Concentrated Hydrochloric acid (HCl (37%)) was then

added to the aforementioned base dissolved (IRH) for complete

precipitation. Rice husks were filtered, washed with excess

distilled water to be freeing from chloride ions and finally dried

in an oven at 120 oC for 6 h [5,6].

2.3 Synthesis of Zeolite Catalyst

2.3.1 Synthesis of Y- Zeolite Catalyst

Sodium hydroxide of 1.67 g was added slowly to deionized water

and stir until clear and homogenous solution appeared. Seed gel

was prepared according to the following molar chemical

composition: 10.67 Na2O: 1 Al2O3: 10 SiO2: 180 H2O

2 milliliter aqueous solution of sodium hydroxide was added to

0.75 g sodium aluminate oxide until a homogenous mixture was

formed; Rice husk (1.53 g) was added separately to 5.5 ml

sodium hydroxide aqueous until homogenously mixed. Both of

the preparations were heated under vigorous stirring to obtain a

homogenous mixture. The sample was aged for 24 hours at room

temperature in the Teflon bottle. The aluminate and silicate

solutions were mixed together until completely homogenized.

This combined solution was used as the feed stock gel [5].

2.3.2 Synthesis of β Zeolite Catalyst

Firstly, the gel was prepared according to the following molar

chemical composition: 19.6 Na2O: 27 SiO2: Al2O3: 5 TEA2O:

240 H2O. Tetraethylammonium hydroxide solution (23.71) g

was dissolved in 4.60 g of distilled water, followed by the

addition of 1.21 g of sodium aluminate. The mixture was stirred

until a clear and viscous solution was formed. Sodium hydroxide

(0.36 g) dissolved in 9.00 g of distilled water were added

followed by 11.10 g of rice husk. The whole mixture was stirred

vigorously for about two hours. The gel formed was then

transferred into a stainless steel autoclave and kept in an air oven

for crystallization at 150°C for 6 days. The solid product

recovered by filtration and washed repeatedly with

demineralized hot water until the pH of the filtrate was ~ 7.0.

Finally, the product was dried at 100°C in an air oven overnight

and calcined at 550°C for 16 hours to remove the organic

material occluded in the zeolite pores and to obtain the sodium

form of the β- Zeolite(7).

2.3.3 Synthesis of ZSM-5 Zeolite Catalyst

Sodium aluminate, NaAlO2, was prepared by adding 0.30 g

Aluminum oxide Al2O3 and 0.20 g of NaOH to 25 ml deionized

water and stirred until dissolved. A 1.7 ml of 96% H2SO4 and 4

g of tetrapropylammonium bromide was added to 50 ml water in

other flask. 56 g of rice husk was mixed with 100 g of distilled

water with 1.04 g of sodium hydroxide added to this solution. All

solutions were mixed simultaneously to form the gel. The pH was

controlled to be in the range of 11-12. The product was filtered

and rinsed with water until the pH is about 8. The product was

then dried at 100°C in an air oven overnight and calcined at

550°C for 16 hours to remove the organic material occluded in

the zeolite pores and to obtain the sodium form of the zeolite

ZSM-5 (8). The prepared zeolites (Y, β and ZSM-5) which were

in powder form, mixed with montmorillonite clay (15 %) as a

binder. Zeolites then mixed with water to form a paste. A

spherical shape (0.5 cm) formed, dried overnight at 110 oC.

2.3.4 Preparation of H-Zeolite Catalyst

The hydrogen zeolite form was prepared by exchanging Na+ ions

in 30 g of sodium form zeolites (Y-Zeolite, β-Zeolite and ZSM-

5-Zeolite) with 2N ammonium chloride solution (NH4Cl) in

order to obtain ideal degree of ion exchange. The exchanged

ammonia zeolite was filtered off, washed with deionized water

to be free of chloride ions, dried overnight at 120oC and then

calcined at 550oC for 5 h (9).

2.4 Characterization of Prepared Zeolites

Characterization techniques were done in order to investigate the

structure and properties of the zeolite catalysts. The catalysts

were characterized using X-ray Diffraction (XRD), BET surface

area measurement, scanning electron Microscopy (SEM), bulk

crushing strength, and loss on attrition, besides to conventional

properties, particle density, packed bed density, pore volume and

pore size.

2.5 Experimental Setup

A laboratory scale continuous flow RD reactor system was used

in this study (Fig.1). The column which had a height of 1.5 m and

diameter of 0.05 m, was divided into three sub-sections of

approximately 0.5m each. The upper, middle and lower sections

were the rectifying, the reaction and the stripping sections

respectively. The rectifying and the stripping sections were

packed with Raschig rings while the reaction sections was filled

with the catalyst. The reboiler was spherical in shape and had a



volume of 2 liters. The condenser was of diameter and height of

5 cm and 22.5 cm respectively placed at the top of the setup.

The column was fed with CHP at a liquid hourly space velocity

varied from 1 to 5 h-1, and temperature ranges from 55 to 95 oC,

keeping the pressure and reflux flow rate constant at 1 bar and 1

h-1 respectively. During the process, the top and the bottom

products are collected and analyzed by gas chromatography

(GC).

Fig. 1 Schematic of Experimental Setup

2.6 Gas Chromatography Analysis

CHP cleavage reaction products samples were analyzed by gas

chromatography (GC) device (Dani, model GC 1000 DPC). The

GC was fitted with FID. Propylene glycol capillary column of 15

m long and 0.1 mm inside diameter. The oven and injector

temperatures were 453 and 433 K respectively; nitrogen was

used as the carrier gas.

3. MODELING OF REACTIVE

DISTILLATION

For the design of reactive distillation process, two types of

modeling approaches were adopted; the equilibrium and the non-

equilibrium stage models. The most difference between these

models is that the mass and heat transfer rates should be

considered in every stage in the non-equilibrium stage model. In

the present study, only the non-equilibrium stage model was

considered (10).

3.1 Non Equilibrium Stage Model (NEQ)

The NEQ stage model for reactive distillation should follow the

philosophy of rate-based models for conventional distillation.

The schematic diagrams are shown in Fig. 2 and 3. In general,

the assumptions adapted are as follows:

1. Operation reaches steady state.

2. System reaches mechanical equilibrium in every stage.

3. The vapor and liquid bulks are mixed perfectly and assumed

to be at non – equilibrium thermodynamic state.

4. Heat of mixing can be neglected.

5. There is no accumulation of mass and heat at the interface.

6. The condenser is considered as an equilibrium stage.

7. Reactions take place in the liquid bulk within the interface.

8. The heat generated due to chemical reaction is neglected.

Fig. 2 Schematic representation of a NEQ stage.

Fig. 3 Two film model of the NEQ stage.

Component material balance equations:

j,iV

j,iV

j,iV

j,ijj,ij

V

j,iNFzyVyV

dt

dM 11 (1)

Ljk,j

r

k

k,i

L

j,iLj,i

Lj,ij,ijj,ij

L

j,iRvNFzxLxL

dt

dM

1

11 (2)



The overall molar balances

c

k

Vj,k

Vj,ijj

Vj

NFVVdt

dM

1

1 (3)

c

i

Ljj,k

r

k

k,i

c

k

Lj,k

Lj,ijj

Lj

RvNFLLdt

dM

1 11

1 (4)

The mole fractions of the vapor and liquid phases are calculated

from respective phase molar holdups:

Lj

Lj,i

j,iVj

Vj,i

j,iM

Mx,

M

My (5)

The summation equations at the bulk

1111

c

i

j,i

c

i

j,i y,x (6)

The energy balance for the vapor and liquid phases

Vj

Vj

Vj

Vj

Vjj

Vjj

Vj

QEHFHVHVdt

dE 11 (7)

Lj

Lj

Lj

Lj

Ljj

Ljj

Lj

QEHFHLHLdt

dE 11 (8)

The molar transfer rate NiL in the liquid phase is related to the

chemical potential gradients by Maxwell-Stefan equation:

c

kLk,i

Li

Li

Lk

Lk

Li

Li

L

Li

AC

NxNx

RT

x

1

(9)

Where L

ki, represents the mass transfer coefficient of i,k pair

in the liquid phase; it was estimated from information on the

corresponding Maxwell-Stefan diffusivity L

kiD , .

The summation equations at the interface are:

1111

c

i

j,iVf

c

i

j,iLf y,x (10)

The interface energy transfer rates ELf have conductive and

convective contributions:

Lf

i

c

i

LfLf

LfLf HNT

AhE

1

(11)

At the vapor-liquid interface, we assume phase equilibrium:

Ij,ij,i

Ij,i xKy (12)

Interface continuity of mass and energy:

ILf

IVf

I

Lf

iI

Vf

i EE,NN (13)

3.2 Vapor – Liquid Equilibrium System (VLE)

The prediction of multi-component vapor-liquid equilibrium

behavior is very important for the design of chemical process

plants and particularly for separation processes. It is used to

calculate the composition and coexisting phases of systems

occurring in many of industrial interest.

There are many ways to express that the most widely used

i

ii

x

yK (14)

Antoine equation is mainly used in the calculation of equilibrium

coefficient by calculating saturated vapor pressure of a

component at a given temperature.

TC

BApln i

(15)

The vapor phase assumed ideal and the deviation from ideality is

in liquid phase only.

3.2.1 UNIFAC Equations

Liquid activity coefficients have been estimated

using UNIFAC method.

UNIFAC method depends on the concept that a liquid mixture

may be considered as a solution of structural units from which

the molecules are formed. These structural units are called

subgroups. This model also called group contribution method;



which is based theoretically on UNIQUAC equation. The

activity coefficient consists of two parts, combinatorial

contribution and residual contribution that are shown in

equations:

r

ic

i lnlnln (16)

Combinational part c

i takes into account effects arising from

difference in molecular size and shape while residual part r

i

taking into account energetic interactions between the functional

group in the mixture,

)L

Jln

L

J(qJlnJln

i

i

i

i

iii

c

i 151 (17)

)]S

lneS

([qlnk

ikki

k k

ikki

ri

1 (18)

where

j

jj

ii

xr

rJ (19)

j

jj

i

ixq

qL (20)

j

mimiS (21)

In addition the following definitions were applied:

k

k

)i(

ki Rr (22)

k

k

)i(

ki Qq (23)

mk

m

miik e (24)

j

jj

i

kiii

kqx

eqx

(25)

T

aexp mk

mk (26)

Subscript i identify species, and j is a dummy index running

overall species. Subscript k identifies subgroups, and m is a

dummy index running overall subgroups. The quantity of )(i

k is

the number of subgroups of type k in a molecule of species i.

3.2.2 Bubble Point Calculation

Bubble point (BP) is calculated, because a new stage temperature

is computed during each time step from bubble point equations.

Discrete element concept is used instead of Height Equivalent of

Theoretical Plates (HETP) concept to accomplish dynamic

modeling of the CD. In discrete element method, the inert and

reactive packed sections is divided into segments of ∆z height

(∆z = Height of packed section /NT). For each ∆z element energy

and mass transfer, equations are considered.

3.2.3 Pressure Drop Calculation

The correlation derived by Stichlmair et al.[10] is used for the

calculation of the pressure drop.

p

gg

d

u

.

dryf

z

P

2

654

1

4

3

(27)

where:

350

21 CRe

C

Re

Cf

.

gg

(28)

f

Re

C

Re

C

C

.

gg50

21

2

(29)

where : C1, C2 and C3 are constants related to the packing

material.

3.2.4 Holdup Calculation

Liquid holdup can be predicted from several correlations. Kister (11) fitted experimental holdup data to within ± 20 to 25% for

random packing. The holdup correlation is given by:

506

1

12

1 .

pL

L

L auM

(30)

3.3 Solution Procedure of the Non-Equilibrium Model

In order to solve the non-equilibrium or rate based model

equations, a computer program using MATLAB (R2009b) has



been developed to show the liquid and vapor mole fractions,

interface, vapor and liquid temperatures, reaction rate profile,

liquid and vapor enthalpies, liquid and vapor flow rates along

stages, mass and energy transport rates for both phases and total

mass flux. The rate based model program begins by specifying

the model specifications and introduces the packing size and

dimensions in order to be used later in calculation of interfacial

area and the mass and heat transfer coefficients. The model

results of all components are converted to percent volume

fraction for comparison with the results obtained from GC

analysis of samples in experimental work. Figure 4 shows the

flow diagram of the program.

4. RESULTS AND DISCUSSION

4.1 Catalysts Characterizations

4.1.1 X-Ray Diffraction:

Powder XRD studies were performed on the calcined samples in

order to identify or detect different crystalline phases present in

the catalyst. Figures 5-7 illustrate XRD patterns of HY-Zeolite,

Hβ-Zeolite and H-ZSM-5 Zeolite prepared from rice husk

respectively. XRD shows that there is small decrease in the

intensity of the peaks located around differences regions, this is

due to the similarity nature of silica source, which were used in

the preparation method.

4.1.2 SEM Analysis

Figures 8-10 show the SEM images of the three prepared

catalysts; HY-Zeolite, Hβ-Zeolite and H-ZSM-5 Zeolite

respectively.

4.1.3 Chemical Analysis

The chemical analysis composition of the prepared zeolites (HY,

Hβ and HZSM-5) are shown in Table 1. The SiO2/Al2O3 molar

ratio are 9.17, 25.2 and 31.88 for the prepared Y-Zeolite, β-

Zeolite and ZSM-5 Zeolite respectively which are slightly

smaller than that in commercial Y-Zeolite (10), β-Zeolite (27)

and ZSM-5 Zeolite (35). However, these ratios are typical for

such type of zeolite.

4.1.4 Surface Area

The surface areas of the zeolites (H-Y, H-β and H-ZSM-5) were

determined by nitrogen physisorption method (BET). The results

show that the H-ZSM-5 catalyst has higher surface area as

compared with the other types of zeolites catalysts as shown

in Table 2.

Figure 4: Simulation Code for Modeling Reactive Distillation

Phase equilibrium parameters

Pressure at the

bottom

Liquid and vapor

compositions

Temperature

profile

Holdup

Profiles of liquid

and vapor flow

rates

Guess values of

variables at start

Properties of

catalyst material

Holdup of

condenser

Initial composition

and feed rate

Enthalpy

calculation

Phase equilibrium

composition

Iterative solution of

the model equations

Calculation of

mass and energy

fluxes

Profile of vapor

and liquid flow rates

Computation of

holdup



Table 1 Chemical Analysis of Different Prepared Zeolites and its References

Chemical Composition

(mol. %)

HY-Zeolite Hβ-Zeolite HZSM-5 Zeolite

Prepared Commercial Prepared Commercial Prepared Commercial

SiO2 9.72 10 26.73 27 33.47 35

Al2O3 1.06 1 1.06 1 1.05 1

Na2O 10.24 10.67 18.87 19.6 14.38 13.8

SiO2/Al2O3 (mol) 9.17 10 25.2 27 31.88 35

Figure 5: XRD of HY- Zeolite

Figure 6: XRD of Type Hβ- Zeolite



Figure 7: XRD of HZSM-5- Zeolite

Fig. 8 SEM Image for HY-Zeolite

Fig. 9 SEM Image for Hβ-Zeolite



Fig. 10 SEM Image for ZSM-5-Zeolite

Table 2 Surface Area of Prepared Catalysts

/g)2Area (mSurface

H-Y Zeolite H-β Zeolite H-ZSM-5 Zeolite

362 388 415

These values lie in the acceptable range of commercial Y zeolite

(312 –453) m2/g, β zeolite (354 – 489) m2/g and ZSM-5 zeolite

(372 - 511) m2/g [12].

4.2 Phenol Production

4.2.1 Effect of Feed Temperature

The effect of feed temperature on the phenol production using

three types of prepared zeolite catalysts is illustrated in Figs 11-

13. These figures show that the phenol production increases with

increasing the feed temperature for the three types. This may be

due to the considerable enhancing effect of acid sites at the

surface of zeolite catalyst, also may be due to the highly

exothermic reaction of CHP decomposition into phenol and

acetone, that led to an increase in the reaction rate of all of the

reactions. In general when the temperature of CHP feed enters to

the reactor zone near its boiling point which is 101.5°C, CHP

needs shorter time to decompose to the products and this cause

increasing the amount of light product especially acetone that is

recycled to the reactive distillation unit to increase the activity of

the catalyst packed the reactor. These results are in agreement

with Levin [3].

Figure 11 Effect of Feed Temp. on the Phenol Production

(HY-Zeolite Prepared from Iraqi RiceHusk, Feed flow rate 5 h-1, and Catalyst Bed Height of 30 cm)

55°C

65°C

75°C

85°C

95°C

Time, min

Yie

ld o

f P

hen

ol

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25 30 35 40 45 50 55 60 65



Figure 12 Effect of Feed Temperature on the Phenol Production

(Hβ-Zeolite Prepared from Iraqi Rice Husk, Feed flow rate 5 h-1, and Catalyst Bed Height of 30 cm)

Figure 13 Effect of Feed Temperature on the Phenol Production

(H-ZSM-5-Zeolite Prepared from Iraqi Rice Husk, Feed flow rate 5 h-1, and Catalyst Bed Height of 30 cm)

4.2.2. Effect of Feed Flow Rate

The effect of feed flow rate on the phenol production is illustrated

in Figs. 14-16 for different catalysts. These figures show that the

phenol production increases with increasing the feed flow rate

within the range used (1 – 5 h-1) keeping other variables constants

(i.e. feed temperature (95°C) and height of catalyst bed (30 cm)).

Industrially, the liquid hourly space velocity (LHSV) based on

cumene hydroperoxide is within the range of 0.1 to 100 h-1. The

cumene hydroperoxide is preferably diluted with an organic

solvent inert and most preferably with acetone. Control of the

dilution level can be achieved by setting the reflux rate through

the tower, or directly adding the recycled overhead containing

the solvent to the cumene hydroperoxide feed. The flow of

diluted cumene hydroperoxide through the reactor is maintained

at a rate sufficient to keep the catalyst temperature at or near the

boiling point of the feed.

These results obtained here may be due to the highly exothermic

reaction of CHP decomposition into phenol and acetone, where

an increase in feed flow rate increases the amount of CHP feed

decomposition per unit time, this lead to increase the amount of

heat generated, so the reaction zone reach to the boiling point of

CHP feed (101.5°C) in a short time, therefore the amount of

acetone and other light product increase, and hence the amount

of acetone recycled in the reaction distillation unit will increased,

this means that the activity of the catalyst packed the reactor is

55°C

65°C

75°C

85°C

95°C

Time, min

Yie

ld o

f P

hen

ol

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25 30 35 40 45 50 55

55°C

65°C

75°C

85°C

95°C

Time, min

Yie

ld o

f P

hen

ol

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25 30 35 40 45 50



increased due to of catalyst wetting, this lead to increase the main

product. These results are agreement with Levin [3].

Figure 14 Effect of Feed LHSV on the Phenol Production

(HY-Zeolite Prepared from Iraqi Rice Husk, Feed Temperature 95°C, and Catalyst Bed Height of 30 cm)

Figure 15 Effect of Feed LHSV on the Phenol Production Using

(Hβ-Zeolite Prepared from Iraqi Rice Husk, Feed Temperature 95°C, and Catalyst Bed Height of 30 cm)

Figure 16 Effect of Feed LHSV on the Phenol Production

(H-ZSM-5-Zeolite Prepared from Iraqi Rice Husk, Feed Temperature 95°C, and Catalyst Bed Height of 30 cm)

1 hr-1

2 hr-1

3 hr-1

4 hr-1

5 hr-1

Time, min

Yie

ld o

f P

hen

ol

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25 30 35 40 45 50 55 60 65

1 hr-1

2 hr-1

3 hr-1

4 hr-1

5 hr-1

Time, min

Yie

ld o

f P

hen

ol

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25 30 35 40 45 50 55

1 hr-1

2 hr-1

3 hr-1

4 hr-1

5 hr-1

Time, min

Yie

ld o

f P

hen

ol

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25 30 35 40 45 50



4.2.3 Effect of Catalyst Bed Height

The effect of catalyst bed heights on phenol production was

studied through using two different heights (20 and 30 cm) as

illustrated in Figs. 17-19. These figures show that the phenol

production increases with increasing the height of catalyst bed

for the three types of catalysts used at constant feed temperature

(95°C) and feed flow rate (5 h-1).

This may be due to highly exothermic reaction of CHP

decomposition into phenol and acetone, where an increase of

catalyst bed led to an increase in the surface area of the catalyst

that has active sites led to an increase in the amount of heat

generated in a shorter time, therefore the amount of acetone and

other light product producing from CHP feed decomposition in

the reaction zone is increasing, and hence the amount of acetone

recycled in the reactive distillation unit will increased, that led to

an increase in the activity of the catalyst. These results are in

agreement with Levin [3].

Figure 17 Effect of Catalyst bed Height on the Phenol Production

(HY-Zeolite Prepared from Iraqi Rice Husk, Feed Temperature 95°C, and Feed Flow Rate 5 h-1)


(Hβ-Zeolite Prepared from Iraqi Rice Husk, Feed Temperature 95°C, and Feed Flow Rate 5 h-1)

20 cm

30 cm

Time, min

Yie

ld o

f P

hen

ol

0.24

0.28

0.32

0.36

0.40

0.44

0.48

0.52

0 5 10 15 20 25 30 35 40

20 cm

30 cm

Time, min

Yie

ld o

f P

hen

ol

0.30

0.36

0.42

0.48

0.54

0.60

0 5 10 15 20 25 30 35




(H-ZSM-5-Zeolite Prepared from Iraqi Rice Husk, Feed Temperature 95°C, and Feed Flow Rate 5 h-1)

4.2.4 Effect of Catalysts Types

The effect of using three different types of prepared zeolite

catalysts on phenol production in reactive distillation unit is

illustrated in Fig. 20. These figures show that the catalyst activity

are as follow: HZSM-5 > Hβ-zeolite >HY zeolite. This may be

due to their high ratio of Si/Al. This ratio make the acidity of

HZSM-5 zeolite lower than Hβ-zeolite and HY-zeolite.

The term acidity is related to both acid strength and acid site

density. Both may be important properties concerning catalytic

activity of a solid acid towards CHP decomposition. The

maximum number of protonic sites in (ideal) H-zeolites is equal

to the number of framework aluminum atoms[13].

However, acid strength of these sites is inversely proportional to

Al content, i.e. directly proportional to Si/Al ratio [14].

HZSM-5 zeolite activity may be rather related to diffusion

limitation caused by small pore size in HZSM-5 zeolite, taking

into account that strongest acid sites are located in the inner

surface of its pores. Similar weak acidity of HZSM-5 zeolite was

found previously for superelectrophilic activation of some

organic molecules [15-17].

It should be noted that the involvement of Lewis acid sites (LAS)

in CHP decomposition is also possible. Significant contribution

of these sites in reactivity of HZSM-5 zeolite is well known. LAS

may initiate CHP cleavage directly or via in situ producing ،،proton sites’’ derived from coordination of hydroxyl groups of

CHP, phenol or residual water with LAS [18]. In addition to the

acid site strength, sorption – desorption properties of zeolites

types can strongly influence the efficiency of CHP cleavage.

Fig. 20 Yields of phenol for the three different types of prepared catalysts

(Operating condition: Feed Temp. 95oC, LHSV 5h-1, and Height of catalyst) bed 30 cm)

20 cm

30 cm

Time, min

Yie

ld o

f P

hen

ol

0.42

0.46

0.50

0.54

0.58

0.62

0 2 4 6 8 10 12 14 16

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30 40 50

Yiel

d o

f P

hen

ol

Time, min

Y-Zeolite

β-Zeolite

ZSM-5 Zeolite



4.2 Comparison of Experimental and Theoretical

Results

Figures 21 to 23 show the comparison of experimental results

with the results predicted from rate based model for the best

results obtained using HY-Zeolite catalyst, Hβ-Zeolite catalyst

and HZSM-5-Zeolite catalyst respectively. From the above

figures, the percent volume of each component produced from

the reaction of CHP cleavage are nearly equal to the

corresponding value obtained from rate based model program i.e.

the deviation is very low.

The error between the results of rate based model program and

experimental data are plotted in Figs. 24-26.

Fig. 21 Comparison of experimental results non-equilibrium model bed

(HY-Zeolite catalyst prepared from Iraqi Rice Husk feed, LHSV 5h-1, and Height of catalyst) bed 30 cm)

Fig. 22 Comparison of experimental results and non-equilibrium model

(Hβ-Zeolite catalyst prepared from Iraqi Rice Husk feed, LHSV 5h-1, and Height of catalyst bed 30 cm)

Experimental

Theoritical

Temperature, o

C

% Y

ield

of

Ph

en

ol

45.8

46.0

46.2

46.4

46.6

46.8

47.0

50 55 60 65 70 75 80 85 90 95 100

Experimental

Theoritical

Temperature, o

C

% Y

ield

of

Ph

en

ol

57.00

57.02

57.04

57.06

57.08

57.10

57.12

57.14

57.16

50 60 70 80 90 100



Fig. 23 Comparison of experimental results and non-equilibrium model

(HZSM-5 Zeolite catalyst prepared from Iraqi Rice Husk feed, LHSV 5h-1, and Height of catalyst bed 30 cm)

Fig. 24 Error between experimental results and non-equilibrium model program results for phenol production using HY-Zeolite catalyst

prepared from Iraqi Rice Husk

Fig. 25 Error between experimental results and non-equilibrium model program results for phenol production using Hβ-Zeolite catalyst

prepared from Iraqi Rice Husk.

Experimental

Theoritical

Temperature, o

C

% Y

ield

of

Ph

en

ol

59.0

59.2

59.4

59.6

59.8

60.0

60.2

60.4

60.6

50 60 70 80 90 100

Theoritical

Ex

perim

en

tal

46.0

46.2

46.4

46.6

46.8

47.0

46.15 46.25 46.35 46.45 46.55 46.65 46.75 46.85

Theoritical

Ex

perim

en

tal

57.01

57.03

57.05

57.07

57.09

57.11

57.13

57.050 57.055 57.060 57.065 57.070 57.075 57.080 57.085 57.090



Fig. 26 Error between experimental results and non-equilibrium model program results for phenol production using HZSM-5-Zeolite catalyst

prepared from Iraqi Rice Husk.

5. CONCLUSIONS

It is possible to get 100% conversion of CHP decomposition over

HZSM-5 zeolite prepared from Iraqi rice husk using RD

technique with phenol yield of 60.38% at the best conditions of

temperature = 95 oC, LSHV = 5 h-1, catalyst bed height = 30 cm,

reflux flow rate = 1 h-1, and atmospheric pressure. The catalysts

can be ranked as follows in terms of activity; HZSM-5 > Hβ-

zeoite > HY-zeolite.

Theoretical study based on non-equilibrium model was found to

be in good agreement with the experimental results.

Nomenclature

[A] Concentration of A in Catalyst

Pores mol/m3

a Interfacial Surface Area m2/m3

C Constant of Mechanical Tests of

Catalysts –

Cp Specific Heat J/mol.K

D diameter of the bed m

D Diffusivity m2/s

dp Particle diameter m

e Rate of Heat Transfer J/s

E Energy J

F Feed flow rate mol/s

fo Correction Factor –

HV Vapor mixture enthalpy J/mol

h Liquid mixture enthalpy

J Diffusion Flux mol/ m2.s

kSL-A Solid liquid Mass Transfer

coefficient for A mol/ m2.s

L Liquid flow rate mol/s

M Molar holdup mol

N Mass Transfer Rate mol/s

P Pressure kPa

Q Heat load J/hr

r Reaction rate mol/s

R Universal gas constant J/mol.K

RA Rate of Decomposition of A, i.e

CHP mol/m3.s

Re Reynolds Number –

Sa Activation entropy J/mol.K

T Temperature K

t Time s

u Velocity m/s

V Vapor flow rate mole/s

x Mole fraction in liquid phase –

y Mole fraction in vapor phase –

z Mole Fraction in Feed Flow Rate –

Activity coefficient -

η Distance along diffusion path m

μ Viscosity kg/m.s

ν Stoichiometric Coefficient –

ρ Density g/cm3

τ Tortuosity –

Theoritical

Ex

perim

en

tal

59.0

59.2

59.4

59.6

59.8

60.0

60.2

60.4

60.6

59.2 59.4 59.6 59.8 60.0 60.2 60.4 60.6



ε Reaction Volume –

REFERENCES

[1]. Stobaugh R.B., “Phenol: How, Where, Who-Future”,

Hydrocarbon Processing, Jan. 1996, P.134.

[2]. Phenol-BP Chemicals Ltd., Hydrocarbon Processing, Nov.

1969, P. 214.

[3]. Levin D. and Santiesteban J.G., “Production of phenol using

reactive distillation”, US Patent 6410804 (2002).

[4]. Gomez, J. M., Reneaume, J. M., Roques, M., Meyer, M.,

and Meyer, X. “ A Mixed Integer Nonlinear Programming

Formulation for Optimal Design of Catalytic Distillation

Column Based on a Generic Non Equilibrium Model ”, Ind.

Eng. Chem. Res., 45, 1373-1388 (2006).

[5]. Rahman, M. M., Hasnida, N., and Wan Nik, W.B.,

“Preparation of Zeolite Y Using Local Raw Material Rice

Husk As a Silica Source”, J. Sci. Res. 1 (2), 285-291 (2009).

[6]. Mohammed M. M., Zidan, F.I., and Thabet, M. “Synthesis

of ZSM-5 Zeolite from Rice Husk Ash: Characterization and

Implication for Photocatalytic Degradation Catalyst”,

Micropores and Mesoporous Materials, 108 (2008) 193-203.

[7]. Prasetyoko, D., Ramli, Z, Endud, S., Hamdan, H, and

Sulikowski, B., “Conversion of Rice Husk to Zeolite Beta”,

Waste Management 26 (2006) 1173-1179.

[8]. G. Lisensky, I. Blitz, Rollman, L. D., Valyocsik, E. W., and

Whittingham, S., “Preparation of Zeolite ZSM5 and

Catalysis of Xylene Isomerization”, Inorganic Syntheses,

22, 61-68 (1983).

[9]. Sherman, J.D., Danner, R.P., Dranoff, J.S., and Sweed,

N.H., “Adsorption and Ion Exchange Separation”, AIChE,

74, 179 (1978).

[10]. Stichlmair, J., Bravo J.L., Fair, J.R., “General Model for

the Prediction of Pressure Drop and Capacity of

Countercurrent Gas / Liquid Packed Columns”, Gas

Separation and Purification, Volume 3 (1), pp. 19 – 28,

(1989).

[11]. Kister, H. Z., “Distillation Design”, McGraw-Hill, Inc.,

New York (1992).

[12]. Vishnol, S., and Rutnasamy, P., “J. of Catal.”, 72, 111

(1981).

[13]. Louis, B., Walspurger, S., and Sommer, J., Catal. Lett. 93

(2004) 435.

[14]. M. Guisnet, J., Gilson, P., Zeolites for Cleaner

Technologies, Imperial College Press, London, (2002).

[15]. Marcilla, A., Beltran, M.I., Hernandez, F., and Navarro, R.,

“HZSM5 and HUSY deactivation during the catalytic

pyrolysis of polyethylene”,Appl.Catal.A: Gen 278, 37

(2004).

[16]. Baerlocher, Ch., Meier, W.M., and Olson, D.H., “Atlas of

Zeolite Structure Types”, Elsevier, London, (2001).

[17]. Koltunov, K. Yu., Walspurger, S., and Sommer, “

Superelectrophilic Activation of Polyfunctional Organic

Compounds”, J., Chem. Commun. 15, 1754 (2004).

[18]. Katada, N., Kageyamaa, Y., Takahara, Kanai, T., Beguma,

H. A., and Niwa, M., “Acidic property of modified ultra

stable Y zeolite: increase in catalytic activity for alkane

cracking by treatment with ethylenediaminetetraacetic acid

salt”, J. Mol. Catal. A: Chem. 211, 119 (2004).

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