Optimization of Dehydrogenation to produce Propylene from Propane
Propylene is a major industrial chemical intermediate that serves as one of the building blocks for an
array of chemical and plastic products. Historically propylene is produced as a by-product of petroleum
refining and of ethylene production by steam cracking of hydrocarbon feedstock. US natural gas supplies
have significantly increased due to the rising exploitation of shale gas. Ethylene producers are shifting to
lighter feedstock’s (more ethane, less naphtha), which is decreasing yields of propylene in cracking
operations.
The increasing demand for propylene and the availability of low-cost feedstock make propane
dehydrogenation an economically attractive chemical route. Propane is recovered from propane-rich
liquefied petroleum gas (LPG) streams from natural gas processing plants. Propane maybe obtained in
smaller amounts as a by-product of petroleum refinery operations, such as hydrocracking and fluidized
catalytic cracking (FCC).
Dehydrogenation of propane involves the breaking of two carbon-hydrogen bonds with the
simultaneous formation of a hydrogen molecule. The double bond is a highly reactive and facilitates the
use of molecules as an intermediate for the production of typical petrochemical products such as
polymers.
C H ↔C H +H
3 8
3 6
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The Propane Dehydrogenation Process (PDH) is used to supply polymer-grade propylene from propane
to meet the growing propylene market needs, independent of a steam cracker or FCC unit. PDH process
provides a dedicated, reliable source of propylene with control over feedstock costs for downstream
chemical operations.
Reaction system for the dehydrogenation of propane must supply a large amount of reaction heat at a
temperature and maintain strict control of the temperature, to minimize the formation of by-products.
The reaction paths lead to the depositing of carbon (coke) on the surface of the catalyst. Even with a
highly selective catalyst, the depositing of coke gradually makes the catalyst less active. The maximum
level of coke accumulation and consequent time needed for each phase in the reaction cycle and
regeneration depend on the nature of the particular catalyst used.
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To purge the coke accumulated on the catalyst surface during the reaction either a continuous catalyst
regenerator (CCR) or a fixed-bed reactor is required. In the CCR unit the catalyst circulates in moving
beds through the reactors, before being fed for regeneration. The CCR operates independently of the
reaction, burning off the coke and returning the catalyst to its reduced state. In the fixed-bed reactor
process at least two (or more) reactors must be used so that the catalyst in one reactor can be
regenerated without stopping the process. The advantage with a moving bed or a fluidized bed is that
the catalyst can be continuously removed from the reactor and be regenerated. The disadvantage is that
a separate regeneration unit is needed.
Steam
Propane
Dehydrogenration
Reaction
Gas Compresion &
Separation
Heat Recovery
Propylene Product
Fractionation
Fuel Gas
Propane Recycle
Fixed Bed Reactor 1
These processing conditions, together with the thermodynamic and kinetic requirements, have pushed
researchers to develop optimal reactor design solutions for the industrial exploitation of
dehydrogenation reactions. The available commercial technologies offer different choices as regards the
reaction system, tending to simultaneously optimize the reaction conditions and the supply of energy to
the reaction.
Real-time measurement of process gases and impurities is critical to optimize product conversion,
product purity and catalyst regeneration cycles. Process Mass Spectrometry is the premier technology
for process gas analysis being able to measure these compounds regardless of the catalyst regeneration
process.
Some of the primary advantages of Mass Spectrometry are;
 Primary Analytical Method
 High Sensitivity and Selectivity
 Analysis time is less than 10 seconds per stream
 Measure of multiple reactor on a single analyzer
 Measure multiple components simultaneously
 Low Life Cycle Cost of Ownership
 Web/Server based operating system to interface with DCS
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Stream Analysis Table:
Estimate
Concentration
Sensitivity
Detected
Mass
RIF
RSD(F)
RSD(M)
STD(F)
%
%
vol. pm
HYDROGEN
28.50%
0.175
2
<0.01
0.13
N-BUTANE
0.04%
2
58
0.73
4.03
ETHYLENE
0.70%
1
26
16.22
1.89
132
ETHANE
0.90%
1
30
3.41
1.30
117
PROPANE
39.90%
1
29
<0.01
0.05
190
PROPYLENE
26.40%
1
41
0.21
0.06
170
ISOBUTANE
0.16%
2
43
32.01
3.05
49
1-BUTENE
0.56%
1
56
<0.01
0.63
36
OXYGEN
0.10%
0.98
32
<0.01
0.96
10
METHANE
1.79%
0.698
16
0.05
0.27
o-Xylene
30ppm
2
106
<0.01
6.14
0.82
TOLUENE
30ppm
2
92
0.11
4.87
0.65
BENZENE
0.04%
2
78
<0.01
1.06
N-PENTANE
0.03%
2
72
0.06
5.63
Name
STD(M)
vol.
ppm
383
0.54
16
2.15
49
0.25
0.19
4
0.75
17
0.23
Definition of terms appearing in the evaluation tables.
RIF:
Relative Interference Factor, (intensity of all interfering ions/intensity of the ion of
interest)
RSD(F):
Relative Standard Deviation (one sigma) as a % of the reported concentration with the
use of Faraday Cup detector
RSD(M):
Relative Standard Deviation (one sigma) as a % of the reported concentration with the
use of Electron Multiplier detector
STD(F):
Standard Deviation (one sigma) in absolute units of concentration with the use of
Faraday Cup detector
STD(M):
Standard Deviation (one sigma) in absolute units of concentration with the use of
Electron Multiplier detector
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