1 CHAPTER 3.2 CHEMICAL AND MECHANICAL DESIGN (DESIGN BY: MOHAMAD HAKIM KAMARUDDIN) (2011924237) OXIDATIVE-DEHYDROGENATION REACTOR (CRV-100) (SINGLE REACTOR UNIT) 3.2.1 Process overview 1,3-Butadiene is a major product with wide range of application in the petrochemical industry. 1,3-Butadiene is mainly produced by steam cracking of naphtha and direct dehydrogenation of 1-butene which characterized as an endothermic reaction (Naoki Ikenaga, 2012). The steam cracking process is a very early stage of separating the constituent of the crude oil drilled from the sea. Therefore, the process not only produces 1,3-Butadiene but also many other petrochemical raw material such as ethylene, propylene and isobutene simultaneously. The temperature required for both steam cracking and dehydrogenation of n-butene are 900 o C and 600 o C which is considered higher than oxidative dehydrogenation of 1-butene which will usually ranging from 400-550 o C depending on the type of catalyst used for the reaction. Oxidative dehydrogenation of n-butenes has replaced many older processes for commercial production of butadiene. Several processes and many catalyst systems have been developed for the oxidative dehydrogenation of either n-butane or of n- butene feed stocks. 1-butenes are much more reactive, however, it require less severe operating conditions than that of n-butane to produce an equivalent amount of product. Recently, oxidative dehydrogenation of 1-butene has taken the spotlight in 1,3- Butadiene production at a view point of energy saving. Since oxidative dehydrogenation
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CHAPTER 3.2
CHEMICAL AND MECHANICAL DESIGN
(DESIGN BY: MOHAMAD HAKIM KAMARUDDIN) (2011924237)
OXIDATIVE-DEHYDROGENATION REACTOR (CRV-100)
(SINGLE REACTOR UNIT)
3.2.1 Process overview
1,3-Butadiene is a major product with wide range of application in the petrochemical
industry. 1,3-Butadiene is mainly produced by steam cracking of naphtha and direct
dehydrogenation of 1-butene which characterized as an endothermic reaction (Naoki
Ikenaga, 2012). The steam cracking process is a very early stage of separating the
constituent of the crude oil drilled from the sea. Therefore, the process not only
produces 1,3-Butadiene but also many other petrochemical raw material such as
ethylene, propylene and isobutene simultaneously. The temperature required for both
steam cracking and dehydrogenation of n-butene are 900oC and 600oC which is
considered higher than oxidative dehydrogenation of 1-butene which will usually
ranging from 400-550oC depending on the type of catalyst used for the reaction.
Oxidative dehydrogenation of n-butenes has replaced many older processes for
commercial production of butadiene. Several processes and many catalyst systems
have been developed for the oxidative dehydrogenation of either n-butane or of n-
butene feed stocks. 1-butenes are much more reactive, however, it require less severe
operating conditions than that of n-butane to produce an equivalent amount of product.
Recently, oxidative dehydrogenation of 1-butene has taken the spotlight in 1,3-
Butadiene production at a view point of energy saving. Since oxidative dehydrogenation
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of 1-butene is an exothermic reaction, it allows the system to operate at lower
temperature rather than other processes such as steam cracking and hydrogenation of
n-butane. Therefore, the oxidative dehydrogenation of 1-butene has been recognized
as a process that can produce 1,3-Butadiene environmentally non jeopardizing.
The less severe operating condition for the oxidative dehydrogenation process is
contributed by its lower temperature requirement for the reaction and its pressure. The
increment of both parameters contributes significantly with increment of cost in
designing the vessels. The increase of temperature will decrease the stress design of
the vessels at which if insufficient will affect the selection of the design material. The
increment of pressure will also increase the thickness of the design whether in vessel
thickness or dome head design.
The design that is performed in this part is selectively iterate to ensure that it will serve
the design objective for good efficiency parallel with the cost of fabricating the oxidative
dehydrogenation of 1-butene to 1,3-Butadiene reactor (CRV-100).
3.2.2 Objectives
In designing a reactor that can deliver high performance in specific processes, the most
important element is to determine the characteristic of all reactor type or at least the
most common used in the industry. The knowledge on the process characteristics, type
of catalyst used, the optimum orientation of the reactor are hugely significant in
ensuring that there is no miss calculation that is causes by lack of understanding
towards the concept of the design. Therefore a preliminary comparison between
reactors characteristic is made to highlight the pros and cons of each type of reactor.
There are few characteristic that are normally used to classify reactor design:
1. Mode of operation
- Batch or continuous
2. Phases present
- Homogeneous or heterogeneous
3. Reactor geometry
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- Flow pattern and manner of contacting the phases
i) Stirred tank reactor
ii) Tubular reactor
iii) Packed bed and fixed
iv) Fluidized bed
Table 3.1: The comparison between packed bed reactor and CSTR
Type of reactor Packed/Fixed Bed Reactor CSTR
Advantages High ratio of catalyst to reactant.
High conversion.
Longer residence time
Very suitable for exothermic reaction.
Involve fluid solid heterogeneous reaction
Well mix condition
Continuous operation
Easy to clean
Simple in design and
operation.
Disadvantages Poor heat transfer
The catalyst difficult to replace and need to shut down.
Lowest conversion per unit volume.
(Source: Sinnot and Towler, 2009 & Fogler.S.H,200
The oxidative dehydrogenation of 1-butene to 1,3-Butadiene reaction occurs in a gas
phase with heterogeneous catalyst at which for a better accuracy and performance, a
catalyst that have activation and deactivation energy at 370oC to 500oC. Therefore,
CSTR type of reactor is utterly incompetent in providing the reaction condition. Based
on the characteristic of the catalyst and the reaction of oxidative dehydrogenation
process, the most proper condition of the reaction is to be held in a vessel with static
solid catalyst. The comparison was continued with a more similar behavior sort of
reactor which is the fluidized bed reactor and the fixed bed reactor. According to
(Umich, 2010) the fluidized bed reactor are most commonly used in a heterogeneous
gas phase reaction with a catalyst and it also has good uniformity of temperature
although it has uncertain scale up. The proposed type of reactor according to (Shell,
1964) is fixed bed reactor, tubular reactor and multi tubular fixed bed reactor.
The multi tubular fixed bed reactor is very efficient in controlling the temperature of the
reactor. It requires 2 inlet feed for shell and tube and 2 outlet feed for the shell and tube.
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The shell inlet and outlet line purpose is to allow cooling water flows into the reactor and
maintain the temperature of the reactor at its designed temperature. The reaction
occurs during the oxidative dehydrogenation process is highly exothermic with heat
release of △H = -132 kJ/mol (Naoki Ikenaga, 2012), therefore the temperature that will
increase due to the release of energy will need to be controlled at which if not, the
increment could lead to deactivation of catalyst that will contribute to decreased of yield.
Taking into account the tube arrangement in the shell of the reactor at which the tube
will be loaded with catalyst pallet and the reactant will have contact with the catalyst;
the reaction will took place inside a tube while having the heat transfer occurs
simultaneously. Therefore, there should be thousands of tube arranged inside the
reactor. The weight of the reactor will be significantly heavy although the volume
predicted is still logical.
The Conclusion drawn from observing the characteristic of each of the reactor and the
characteristic of the process is drawn towards the choosing of multi-tubular fixed bed
reactor as the design concept.
The stream that involve with the reactor is stream 6 & stream 7 from Aspen Hysys
Simulation program version 7.3 at which have been performed in Design Project 1
previously. Figure 3.1 below shows the general flow of the reactor.
Figure 3.1: Multi-tubular Fixed Bed Reactor
T= 350 oC
P= 8 atm
C4H8 =16368 kg/hr
O2 = 2532 kg/hr
H2O = 45009 kg/hr
T= 400 oC
P= 7 atm
C4H8=2847 kg/hr
C4H6=12657 kg/hr
H2O = 49743 kg/hr
Stream 6 Stream 7
R-101
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3.2.2.1 Overall process flow diagram (PFD)
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LC
LT
LC
TT
LC
TC
Cooling water
LC
TT
LC
TC
HE-101
HE-102Refrigerent
TTTC
FC
FT
LT LC
PT PC
FTFC
FTFC
LT
LC
PT PC
To waste
water treatment
Cooling water from water treatment
V-101
TT
LT
LC
PC
PT
Hot water out
LC
PT
PC
TT
TC
FT FC
LT
T-101
F-101
350
8 atm
V-102
CRV-100
7
400
7 atm
8
5
7 atm
9
10
5
7 atm
11
30.85
7 atm
12
14
16
5
5 atm
17
-7.85
1 atm
18
100
1 atm
FTFC
LT
LC
PTPC
TT
PT
V-103
15
PI
FC
FC
FC
FC
Hot water that is reheat
to steam from reactor
Hot water
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TC
FT
TT
FC
FC
FC FT
LT
LIC
FC
R
FT
FI
TI
PI
LFA
FC
FI
TI
LLA
PA
LLAPI
FI
TI
PA
FT
FI TI
PIRC
LC
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3.2.2.2 Process flow diagram for Multi tubular fixed bed reactor (CRV-100)
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The summary off component that involve in the feed and outlet stream are
concluded in table 1.2 below
Table 3.2: Component mass flow and mole flow in inlet and outlet of stream
Component
In Out
MW (kg/kmol)
Mass Flowrate (kg/hr)
Mole Flowrate (kmol/hr)
Mass Flowrate
kg/hr)
Mole Flowrate (kmol/hr)
C4H8 56.11
16368 290.628 2847 50.76
C4H6 54.096
- - 12657 234
O2 15.99
2532 158.4 - -
H2O 18.2
45009 2498.4 49743 2761.2
3.2.3 CHEMICAL DESIGN
Figure 1.2 illustrated the stages of determining the chemical design for the oxidative de
hydrogenation reactor.
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Figure 3.2: Flow chart for chemical design of hydrogenation reactor
The chemical design purpose is to determine the crucial required properties of
designing a reactor such as volume, residence time, catalyst weight and heat balance.
Oxiative-Dehydrogenation of 1-Butene is characterized by exothermic reaction and from
the energy balance; the heat released for this reaction is ΔH = -132 kJ/mol. The
Make assumption for the reactor
Calculate the basis for calculation
Calculate the reaction kinetics
Calculate the volume of reactor
Calculate diameter of reactor
Selected of catalyst
Calculate the volume & weight of catalyst
Heat balance
Tube Design
Calculate pressure drop on the tube side
Calculate pressure drop on the shell side
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reaction consumes stoichiometrically one mole 1-Butene and 1/2 moles of Oxygen to
produce one mole of 1,3- Butadiene and one mole of water as given by equation below:
Reaction in Oxidative-Dehydrogenation of 1-Butene
( )
( )
Where;
A= 1- Butene
B= Oxygen
C= 1,3-Butadiene
D= Water
3.2.3.1 Assumption of chemical design
Packed bed reactor will be design in the production of purification terephthalic acid. In
order to design the reactor, there are several assumptions were made to design this
reactor. Assume that the mass transfer limited between cured terephthalic acid and
hydrogen gas is coefficient therefore the mass transfer between liquid phase and gas
phase is neglected. The other assumption taken in this design as below: