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3. Introduction
❖Butadiene-1,3 is the main monomer in
the production of rubbers for general
and special purposes.
❖Based on it, polybutadiene, butadiene-
styrene rubbers are obtained, it is a
part of butadiene-nitrile rubbers.
4. Production of butadiene-1,3
❖Dehydrogenation of n-butane and n-
butenes is a sequential reversible
reaction:
❖ The equilibrium conditions of the dehydrogenation
reaction are unfavorable, since high temperatures are
required to obtain an acceptable conversion depth,
which in turn leads to the occurrence of side reactions.
Therefore, the process is carried out at reduced
temperatures, but in the presence of a catalyst.
❖ Since the dehydrogenation reaction proceeds with heat
absorption and volume increase, high temperature and low
pressure are favorable for it.
5. Dehydrogenation of n-butane
Dehydrogenation of n-butane can be carried out in
one or two stages with the return of unreacted raw
material to the reactor.
The main factors determining the design of the
dehydrogenation process of n-butane and n-butenes
are:
❖ the need to supply a large amount of heat to the
reaction zone;
❖ providing high temperature and short contact time;
❖ the need to burn coke from the surface of the
catalyst;
❖ the need for rapid cooling of reaction products.
6. One-stage dehydrogenation of n-butane
❖ In the one-stage dehydrogenation of n-butane requires
one dehydrogenation process. The yield of butadiene in
a one-stage dehydrogenation is 50% per n-butane.
❖ The one-stage dehydrogenation process is based on the
fact that at elevated temperatures and pressure the
equilibrium of the n-butane dehydrogenation reaction is
shifted towards the formation of butadiene-1,3:
❖С4Н14 → С4Н8 + Н2 → С4Н6 + 2Н2
7. Catalyst
❖ The one-stage dehydrogenation process proceeds
on an aluminum chromium catalyst.
❖ In addition to butadiene-1,3, a significant number
of butenes are formed, which again return to the
process.
❖ Since a mixture of n-butane with n-butenes is fed
to dehydrogenation, it is essential for the process
that the amount of n-butenes in the contact gas
after the reactor is not less than their content in
the feed gas, otherwise only n-butenes will
dehydrate, and not a one-stage process will be
ensured.
9. ❖ The process is carried out in reactors of a
regenerative type. Due to the fact that an
alumina chromium catalyst is used, dilution of
raw materials with steam is eliminated and
vacuum is created by vacuum-compressors.
The regenerative type of reactors
means that cycles of dehydrogenation
and regeneration of the catalyst
alternate in the same reactor. The heat
released during regeneration is
accumulated by the catalyst and used
for dehydrogenation. However, this heat
is not enough, and to compensate for it,
heat is supplied to the reactor by
burning fuel and feeding a hot oxygen-
containing gas to the regeneration.
10. ❖ To improve the heat exchange between the gas
and the catalyst, the latter is mixed with an inert
coolant, which is a fused Al2O3, at a mass ratio
of 1:3.
❖ The catalyst for single-stage dehydrogenation
should have high activity and increased strength,
stability and high regeneration characteristics.
This is due to the fact that during the alternating
cycles of dehydrogenation and regeneration of
the catalyst, the conditions change significantly,
and the regeneration cycles are very short.
11. ❖Let's consider the basic technological
scheme of one-stage dehydrogenation of
n-butane
12. Principal scheme of one-stage dehydrogenation of
n-butane
1-tubular furnace, 2-reactors, 3-pressurized furnace, 4-gas turbine, 5-compressor,
6-heat-exchanger, 7-waste heat boiler
600-
620 C
590-630 C
0.6 MPa
450 C
520-
540 C
630 C
13. Scheme explanation
❖ The dehydrogenation process takes place in several reactor groups
(3-8 reactors in each group). According to the scheme, the feedstock-
butane-butene fraction containing 25-35% n-butenes - is overheated
in furnace 1 to 600-620 ° C and enters part of the reactors 2 where it
contacts the catalyst. The process temperature fluctuates between
590-630 ° C at the end and the beginning of the dehydrogenation
cycle. Discharging is created by means of two vacuum.
❖ The contact gas from the reactor 2 is supplied for cooling and then
goes to separation. After the end of the dehydrogenation cycle, the
feed stream is switched to the next group of reactors, and the
reactors that were in operation are blown to remove hydrocarbon
fumes. After purging, the reactors are switched to regeneration by
flue gases containing a small amount of oxygen. Then the evacuation
of the combustion products is carried out with a steam jet ejector,
after which the flow of raw materials again begins to flow into the
reactors.
14. Scheme explanation
❖ The air for regeneration is fed to the compressor 5
(pressure 0.6 MPa), heated in the heat exchanger 6 to a
temperature of 520-540 ° C, in the furnace 3 to a
temperature of 630 ° C, and then directed to the
reactor 2.
❖ The regeneration gases leaving the reactor 2 are further
heated in the furnace to a temperature corresponding to
the rational operating mode of the gas turbine 4 from
which the cooled gases enter the top 3 due to work at a
temperature of 450 ° C, they heat up and then give off
some of the heat to the air in heat exchanger 6. After
additional heating of the regeneration gases in the next
furnace 3, they are used to generate water vapor in the
waste heat boiler 7.
15. ❖ This scheme allows you to operate without the
consumption of steam and electricity from the side, but
requires increased pressure in the reactor during the
regeneration process.
❖ There are circuits with five, six, seven and eight
reactors in the group. Switching reactors from mode to
mode is automatic.
❖ Reactors are horizontal hollow units made of steel, lined
inside with ceramic tiles. The mixture of catalyst and
coolant (alundum) is poured onto the lattice by a non-
low layer. The lattice is also made of ceramics to avoid
corrosion caused by the reducing oxidative environment
at high temperatures.
16. Advantages
❖a simple scheme;
❖reduction of
consumption
coefficients for
raw materials;
❖reduction of
energy costs.
Disadvantages
❖short periods of
contact, which
requires complex
automatics;
❖low yield of
butadiene-1,3 per
pass.
