it is about reactors which are used in heterogeneous oxidation , oxidation of ethylene oxide with oxygen and about sulfur oxidation

1. 1
Reactors used in
Heterogeneous catalytic
oxidation
Oxidation of Ethylene by
oxygen
About sulfur alkylation
Presentation
on
Presented by
Group 6
Presented to
Mithun Rani Nath
Lecturer, Dept. of ACCE
NSTU

2. 1. Reactors used for Heterogeneous
Catalytic Oxidation Processes:
Reactors which are used for heterogeneous catalytic
oxidation processes are given below:
 Tubular fixed-bed reactor
 Fluidized bed reactor
 Reactor with a sectioned fluidized bed
 Reactor with an ascending catalyst flow
2

3. Steam
Water
Feed Stock
Products
The reaction takes place in the form of a
heterogeneously catalyzed reaction on the
surface of catalysts that are arranged as a bed is
called fixed bed in the reactor.
 Heat is cooled through the inter tube space
by coolant.
 Diameter of the tube is 10 to 25 mm
 Preheated reagents are used.
 Adsorption, chemical reaction, and
desorption of products occurred catalyst
surface.
3 Tubular fixed bed reactor
Fig: Tubular Fixed Bed Reactor

4. Advantage:
1. High conversion per unit mass of catalyst.
2. Low operating cost.
3. Continuous operation.
Disadvantage:
1. Undesired thermal gradients may exist.
2. Poor temperature control.
3. Unit may be difficult to service and clean.
4 Fixed bed reactor

5. Product
Steam
Water
Feed Stock
 The only difference is the absence of
regeneration units.
 A vertical cylindrical vessel containing
fine solid catalyst particles. The feed
is introduced through the bottom.
 Regenerate the catalyst continuously
without shutting down the reactor.
 The ideal solution for heat removal
and maintenance of uniform
temperature.
5 Fluidized bed reactor:
Cyclone
Fig: Fluidized bed Reactor

6. 6
Mechanism of fluidized bed reactor:
Fluidized bad reactor:

7. 7 Fluidized bed reactor:
Advantage:
1. Flexible- large variation in operation and contact time is possible.
2. Efficient for long residence time.
3. Generally low cost.
Disadvantage:
1. Difficulty in regeneration.
2. Difficulty in replacing catalyst.

8. Products
Feed Stock
Steam
Water
 Several distribution grids
which divide the reaction
volume into sections
 Cooling pipes to remove
or maintain heat.
 Cyclones for trapping the
particles entrained by the
gas.
8 - Reactor with a sectioned fluidized bed
Reactor with a
sectioned fluidized bed
Fig: Reactor with a sectioned fluidized bed
Cyclone

9. 9 – Advantages- disadvantages
 Advantages
 Decrease of back-mixing
 Ideal solution to heat
removal
 Maintenance of uniform
temperature
 Disadvantages
 Expensive to construct and
maintain
 Regeneration of catalyst is
expensive
 Attrition, break-up of
catalyst pellets due to
impact against reactor wall

10. Reactor with an
ascending catalyst flow
 A decrease in back-mixing
can also be attained in this
reactor with an ascending
catalyst flow
 The reaction tube is cooled
by a jacket with the boiling
water condensate.
 The catalyst is separated in
the separator or cyclone and
returned through the pipe
into the lower part of the
reactor which is called
proportionating section
10 - Reactor with an ascending catalyst flow
Products
Water
Steam
Feed
Stock
Fig: Reactor with an ascending catalyst flow
Cyclone

11. 11 – Advantage and disadvantage
 Advantages:
 Decrease in back
mixing
 Reactor can be
constructed as a multi
tubular unit
 Equipment cost is
comparatively less
than others
 Disadvantages:
 External cooling is less
effective
 Fail to maintain
uniform temperature

12. 12 - Oxidation of Ethylene by Oxygen
Chemical Reactions:
 H2C=CH2
2. Oxidation of Ethylene by Oxygen:
½ O2
3 O2
O
CH2
H2C
2 CO2 + 2 H2O
Ag

13. C2H4 O2
1
2
3
4
7
5
10
11 EO
Steam
Residue
C2H4
O
12 13
14
6
9
8
15
16
17
Steam
CO2
CO2
EO
CO2 /H2 O
1- Tubular Catalytic reactor,
2,8,10 - Heat exchanger,
3 - Steam generator,
4,15,16,17,18 - Cooler,
5,6,13- Absorber,
7 - Circulation absorber,
9 - Desorber,
11 - Stripping Column,
12,14 – Fractionating Column
13 - Flow Diagram
Flow Diagram :
Oxidation of
Ethylene by
Oxygen:

14.  The recycled gas is compressed to the operating pressure ( 2 Mpa ),
heated in heat exchanger (2) by the hot reaction gas and mixed with fresh
ethylene and oxygen.
 The resultant mixture introduced into the reactor (1) containing 20-30%
of ethylene, 7-8% O2 and 4-5% of CO2 ; it also contains inert
properties (i.e. N2 , Ar etc.) from the gas feed. The oxidation is effected
in tubular catalytic reactor (1), cooled by the intermediate heat transfer
agent; “steam” of 2 M Pa pressure is produced in steam generator
(3).
 The hot reaction gases containing 1.8-2% (by vol %) of ethylene oxide
are cooled in heat exchanger (2) , cooler (4) and transferred to absorber
(5), where all of the ethylene oxide and part of CO2 are absorbed by
water.
Process Description :
14 – Process Description

15.  The gas leaving the absorber is separated into two steams one steam is
recycled and the other is sent to absorber (6) , where it is purified from CO2.
the purified gas is returned to the operating pressure by compressor (7)
 The solution absorbed in the absorber (6) is heated in heat exchanger (8) by
counter current absorbent stream, throttled and run to desorber (9), where
CO2 is removed on heating. The regenerated absorbent is pumped through
heat exchanger (8) to absorber 6.
 The aqueous solution of ethylene oxide and CO2 from the still to absorber
(5) is throttled up to 0.5 Mpa and is led through heat exchanger(10) to
stripping column (11), where ethylene oxide, CO2 and part of H2O are
distilled off.
15

16.  The major amount of H2O is left in the still and then returned to
absorber (5) after being cooled in heat exchanger (10).
 The vapor leaving stripping column (11) are sent to fractionator
(12), where CO2 and part of ethylene oxide is absorbed from the
gas by H2O in absorber (13) , the aqueous solution being returned
to column (11).
 The still liquid of column (12) passes to fractionator (14), where
pure ethylene oxide is obtained.
16

17.  Thiols are readily alkylated to give thioethers The
reaction is typically conducted in the presence of a
base or using the conjugate base of the thiol.
Thioethers undergo alkylation to give sulfonium
ions .
 A thiol is a organosulfur compound of the form R−SH,
where R represents an alkyl or other organic substituent.
Thiols are the sulfur analogue of alcohols (that is, sulfur
takes the place of oxygen in the hydroxyl group of an
alcohol)
17
3. Sulfur Alkylation
Formulation of a covalent bond between a sulfur atom in a substrate
and an alkyl group

18.  In industry, methanethiol is prepared by the reaction of
hydrogen sulfide with methanol . This method is employed
for the industrial synthesis of methanethiol :
CH3OH + H2S → CH3SH + H2O
 Such reactions are conducted in the presence of acidic
catalysts. The other principal route to thiols involves the
addition of hydrogen sulfide to alkenes. Such reactions are
usually conducted in the presence of an acid catalyst or UV
light. Halide displacement, using the suitable organic halide
and sodium hydrogen sulfide has also been utilized.
18
Preparation

19. Another method entails the alkylation of sodium
hydrosulfide is
RX + NaSH → RSH + NaX (X = Cl, Br, I)
This method is used for the production of thioglycolic acid
from chloroacetic acid
 Reaction:
Thiols, or more specific their conjugate bases, are readily
alkylated to give thioethers:
RSH + R′Br + B → RSR′ + [HB]Br (B = base)
19

20. Examples of thiols
 Methanethiol – CH3SH [methyl
mercaptan]
 Ethanethiol – C2H5SH [ethyl
mercaptan]
 1-Propanethiol – C3H7SH [ n -propyl
mercaptan]
 2-Propanethiol – C3CH (SH) CH3
 Allyl mercaptan – CH2=CHCH2 SH
[2-propenethiol]
20
 Butanethiol – C4H9SH [ n -
butyl mercaptan]
 tert -Butyl mercaptan –
(CH3)3 CSH [ t -butyl
mercaptan]
 Pentanethiols – C5 H11SH
[pentyl mercaptan]
 Thiophenol – C6H5SH

21. Thioether
 A thioether is a functional group in organosulfur
chemistry with the connectivity C–S–C as shown on
right. Like many other sulfur-containing compounds,
volatile thioethers have foul odors.
21
Ethers can be alkylated at oxygen only with difficulty, but
thioethers are readily alkylated to give stable
sulfonium salts, such as trimethylsulfonium iodide :
S(CH3)2 + CH3 I → [S(CH3)3] + I-

22. A sulfonium ion , also known as sulphonium ion or
sulfanium ion , is a positively charged ion (a " cation
") featuring three organic substituents attached to
sulfur. These organosulfur compounds have the
formula [SR 3 ] +. Together with a negatively
charged counterion, they give sulfonium salts . They
are typically colorless solids that are soluble in
organic solvent.
22

23. Synthesis
 Sulfonium compounds are usually synthesized by the reaction of
thioethers with alkyl halides. For example, the reaction of dimethyl
sulfide with iodomethane yields trimethylsulfonium iodide :
CH3 –S- CH3 + CH3 I → (CH3)3–S + I-
 Before the above reaction, the sulfur atom has two lone electron
pairs. One of these lone pairs links to the methyl group. At the
same time, as part of a concerted nucleophilic substitution
mechanism (SN2), the iodide leaving group departs. This leaves a
positively charged trimethylsulfonium ion, whose charge is
balanced by the iodide. The rate of reaction is even faster with
stronger methylating agents, such as methyl
trifluoromethanesulfonate .
23

24. References:
 Chemistry & Technology of Basic Organic
Petrochemical Synthesis – N. N. Lebedev
24 - Reference