In this article a description about different processes which are commercialized to produce propylene via Propane dehydrogenation were presented. To receive more reports about cost estimation analysis and other reports (about the propylene and PDH ) contact the author.

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Propylene Production by
Propane Dehydrogenation (PDH)
(Process Review)
Amir Razmi
May 2019

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Contents
About Propane ................................................................................................................ 3
Applications ................................................................................................................. 3
About Propylene.............................................................................................................. 5
Applications ................................................................................................................. 5
PG Propylene Production ............................................................................................ 6
Propane Dehydrogenation (PDH) ................................................................................... 8
UOP Olefex Technology.............................................................................................. 9
Uhde STAR Technology............................................................................................ 10
CB&I Lummus CATOFIN Technology ....................................................................... 12

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About Propane
Propane with the molecular formula C3H8 is a gas at standard temperature and pressure,
but compressible to a transportable liquid. A by-product of natural gas processing and
petroleum refining, it is commonly used as a fuel. Propane is one of a group of liquefied
petroleum gases (LP gases). The others include butane, propylene, butadiene, butylene,
isobutylene, and mixtures thereof.
The density of liquid propane at 25 °C (77 °F) is 0.493 g/cm3, which is equivalent to 4.11
pounds per U.S. liquid gallon or 493 g/L. Propane expands at 1.5% per 10 °F. Thus, liquid
propane has a density of approximately 4.2 pounds per gallon (504 g/L) at 60 °F
(15.6 °C).
The processing of natural gas involves removal of butane, propane, and large amounts
of ethane from the raw gas, in order to prevent condensation of these volatiles in natural
gas pipelines. Additionally, oil refineries produce some propane as a by-product of
cracking petroleum into gasoline or heating oil.
Applications
Propane is used as a popular choice for barbecues and portable stoves because the low
boiling point of −42 °C (−44 °F) makes it vaporize as soon as it is released from its
pressurized container. Therefore, no carburetor or other vaporizing device is required; a
simple metering nozzle suffices. Propane powers buses, forklifts, taxis, outboard boat
motors, and ice resurfacing machines and is used for heat and cooking in recreational
vehicles and campers. Propane is also used in some locomotive diesel engines as a fuel
added into the turbocharger yielding much better combustion.

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Propane is also instrumental in providing off-the-grid refrigeration, as the energy source
for a gas absorption refrigerator and is commonly used for camping and recreational
vehicles.
Properties[2]
Chemical
formula
C3H8
Molar mass 44.097 g·mol−1
Appearance Colorless gas
Odor Odorless
Density 2.0098 kg/m3
(at 0 °C, 101.3
kPa)
Melting point −187.7 °C; −305.8 °F; 85.5 K
Boiling point −42.25 to −42.04 °C; −44.05 to
−43.67 °F; 230.90 to 231.11 K
Solubility in water 47mgL−1
(at 0 °C)
log P 2.236
Vapor pressure 853.16 kPa (at 21.1 °C
(70.0 °F))
Henry's law
constant (kH)
15 nmol Pa−1
kg−1
Conjugate acid Propanium
Magnetic
susceptibility (χ)
-40.5·10−6
cm3
/mol

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About Propylene
Propylene is the other name of Propene, also known as methyl ethylene, is an
unsaturated organic compound having the chemical formula C 3 H 6 . It has one double
bond, and is the second simplest member of the alkene class of hydrocarbons. It is a
colorless gas with a faint petroleum-like odor.
Propylene is a byproduct of oil refining and natural gas processing. During oil refining,
ethylene, Propylene, and other compounds are produced as a result of cracking larger
hydrocarbons. A major source of propylene is naphtha cracking intended to produce
ethylene, but it also results from refinery cracking producing other products. Propylene
can be separated by fractional distillation from hydrocarbon mixtures obtained from
cracking and other refining processes; refinery-grade propylene is about 50 to 70%.
Propylene also produced in natual gas processing. IN fact, the production of Propylene
from such a plant is so important that the name of olefins plant is offen applied to this kind
of manufacturing facilities. In an olefin plant, Propylene is generated by the pyrolysis of
the incoming feed, followed by purification. Except where ethane is used as the feedstock,
propylene is typically produced at levels ranging from 40 to 60percent of the ethylene
produced. The excat yield of propylene produced in a pyrolysis furnace is a function of
the feedstock and operating severity of the pyrolysis. Propylene can also be produced in
an on-purpose reaction (for example, in propane dehydrogenation, metathesis or syngas-
to-olefins plants).
Commercialy, Proplylene is traded in three grades:
*Polymer grade (PG): min. 99.5% of purity
* Chemical Grade: (CG) 90-96% of purity
*Refinery Grade (RG): 50-70% of purity
Since propylene is volatile and flammable, precautions must be taken to avoid fire
hazards in the handling of the gas. If propylene is loaded to any equipment capable of
causing ignition, such equipment should be shut down while loading, unloading,
connecting or disconnecting. Propylene is usually stored as liquid under pressure,
although it is also possible to store it safely as gas at ambient temperature in approved
containers.
Applications
Propylene is the second most important starting product in the petrochemical industry
after ethylene. In the year 2013 about 85 million tons of propylene were processed
worldwide. It is the raw material for a wide variety of products. The Propylene market is
dominated by the PG propylene, which is mainly used in polypropylene production and
account for nearly two thirds of all demand. Polypropylene end uses include films, fibers,
containers, packaging, and caps and closures. PG is also used for the production of

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important chemicals such as propylene oxide, acrylonitrile, butyraldehyde, and acrylic
acid.
RG is used in LPG and motor gasoline in addition to produce cumene and isopropanol
(propan-2-ol). However, the most significant application of RG is production of CG or PG.
CG is used to production of acrylonitrile, propylene oxide, and epichlorohydrin. The
industrial production of acrylic acid involves the catalytic partial oxidation of propylene.
PG Propylene Production
As mentioned before, the largest volume of PG is produced from NGL or naphtha in steam
cracking process. In both of these processes, PG is the byproduct of other products,
normally ethylene. However, it can also be manufactured through on purpose processes
which their main product is PG. The main processes for on-purpose PG are propane
propane dehydrogenation (PDH), metathesis, methanol-to-olefins (MTO) and catalytic
Olefins (OCT) processes. Picture below presents a review to these processes:
Toady, below reasons are driving the PG production from a by product methods to on-
purposes methods:
 Tight supply-demand brings price volatility
 Strength of derivatives demand and inventory management

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 Operational outages and seasonal turn around
 Alternative RG propylene value and on purpose production economics
 Arbitrage opportunity for import
Below picture presents the strength of prices for ethylene, propylene and butadiene from
2000 to 2012.
Table below compares the on-purpose processes for PG production and shows the
advantage and disadvantage of each process.

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Propane Dehydrogenation (PDH)
Propane dehydrogenation (PDH) converts propane into propylene and by-product
hydrogen. The propylene from propane yield is about 85 m%. Reaction by-products
(mainly hydrogen) are usually used as fuel for the propane dehydrogenation reaction.
Propane Propylene + Hydrogen
The table above compared this process with the other commercial processes.
The difference between Propane/Propylene pricing (mentioned in below diagram), drives
project economics. After increasing the shale gas production in US that leads to decrease
in the propane global price reduction, many chemical companies planned to establish
PDH plants to take advantage of low price raw material.
This reaction runs in fixed bed, fluid bed, and moving bed reactors and all of them are
commercialized by different companies. The main differences between each of them
concerns the catalyst employed, design of the reactor and strategies to achieve higher
conversion rates.
Already there are 3 main PDH processes which are established all around of the world:
 UOP Olefex Technology
 CB&I Lummus CATOFIN Technology
 Uhde STAR Technology
Picture below presents the quantity and capacity of existing plants for each of these
processes until 2015.

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In continue, each of these processes are described simply:
UOP Olefex Technology
PDH is an endothermic equilibrium reaction. The PDH process depicted below is similar
to the Oleflex process developed by UOP LLC (Des Plaines, Ill.; www.uop.com), and is
suited to produce polymer-grade (PG) propylene from propane. The maximum unit
capacity is around 650,000 ton/yr. This process is carried out in the presence of a
platinum catalyst and achieves overall propylene yields of about 90 wt.%.
The industrial plant can be divided into two main sections: reaction and product recovery.
In the reaction section, after heavy impurities removal in the de-oiler column, propane is
sent to the dehydrogenation reactors. The propylene yield in such reactors is favored by
higher temperatures and lower pressures. However, temperatures that are too elevated
will promote thermal cracking reactions that generate undesirable byproducts. Therefore,
the PDH reaction usually occurs at temperatures of about 650°C and near atmospheric
pressures.
In order to purge the coke accumulated on the catalyst surface during the reaction, a
continuous catalyst regenerator (CCR) unit is required. The catalyst circulates in moving
beds through the reactors, before being fed to the CCR unit, which operates
independently of the reaction, burning off the coke and returning the catalyst to its reduced
state.

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The reactor effluent is compressed, dried and sent to the product recovery section. In this
section, a hydrogen-rich stream is recovered and light hydrocarbons and hydrogen traces
are removed in a de-ethanizer. The PG propylene product is further purified in a propane-
propylene (P–P) splitter and leaves as the top product.
Uhde STAR Technology
The PDH process is similar to the STAR (steam active reforming) process (Uhde GmbH;
Dortmand, Germany; uhde.co.za), which applies the oxydehydrogenation principle.
The STAR process was the first to apply the oxydehydrogenation principle for propylene
production, significantly enhancing its performance. In this technology, oxygen is added
to the system to react with hydrogen, forming water. This reaction lowers the hydrogen
partial pressure, shifting the equilibrium to higher conversion of propane into propylene
while providing the required heat of reaction. The chart shows the effect of oxygen
addition on propane conversion, according to different oxygen-to-propane molar ratios.
Reaction
Propane is fed into a depropanizer column for heavy impurities removal. The
depropanizer distillate is vaporized, mixed with steam, and pre-heated before entering
the reformer reactor, which is an externally fired tubular reactor where most of the
propane conversion occurs. Next, the reformer effluent is fed to the oxyreactor, where
hydrogen is selectively combusted by oxygen. The process gas is cooled in a series of
heat exchangers to recover process heat. Then, it is compressed and sent to the next
area.

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Product Recovery Section
In this area, there is a low-temperature separation unit, the objective of which is to
separate hydrogen and light byproducts generated in the reaction step from the main
product. The hydrogen-rich stream is then sent to a pressure-swing adsorption (PSA)
unit. The liquid stream generated in the low-temperature separation is fed to distillation
facilities for product recovery. The distillation facilities consist of a de-ethanizer and a
propylene-propane splitter, the latter producing the recycled propane stream that is used
in the reaction step.
CO2 Separation
The compressed gas is fed to an absorption column, where CO2 is removed in the
bottoms by washing with an aqueous piperazine-activated methyldiethanolamine (MDEA)
solution. The bottoms stream is depressurized, liberating gases that are recycled to the
absorption column. The CO2-rich liquid solution from the flash vessel is fed to the solvent
regeneration column, which separates CO2 in the overheads from the MDEA solution in
the bottoms, which is recycled to the absorption column.
Gas Separation
The overhead stream of the absorption column is dried in a molecular sieve and fed to a
low-temperature separation system (cold box) for the removal of lights. In this system, a
hydrogen-rich stream is also obtained, which is purified in a pressure swing adsorber
(PSA) unit to obtain high-purity hydrogen byproduct.
Fractionation
The liquid fraction from the cold box is sent to the fractionation area, which consists of a
de-ethanizer column for removal of lights and a P-P splitter, where polymer-grade (PG)
propylene is obtained. Unreacted propane from the P-P splitter bottoms is recycled to the
reaction area.

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CB&I Lummus CATOFIN Technology
PDH reaction is an endothermic catalytic process that converts propane into propylene
and hydrogen. The figure below illustrates a technology similar to the Catofin process, by
Lummus Technology, which uses fixed-bed reactors and a chromium-based catalyst. It is
carried out in two main areas: reaction and regeneration; and product recovery. The yield
of propylene is about 85 wt.%. The reaction byproduct (mainly hydrogen) are usually used
as fuel for the reaction. As a result, propylene tends to be the only product, unless local
demand exists for the hydrogen byproduct.
Reaction and Regeneration Section
Fresh propane feed is mixed with recycled propane from a propylene-propane splitter.
This stream goes to a de-oiler for impurities removal and then is carried to the reaction
step, which is continuous and operates in cycles. In this step, multiple reactors undergo
a controlled sequence of reaction, catalyst reduction and catalyst regeneration.
Product Recovery Section
In this area, there is a low-temperature separation unit, the objective of which is to
separate hydrogen and light byproducts generated in the reaction step from the main
product. The hydrogen-rich stream is then sent to a pressure-swing adsorption (PSA)
unit. The liquid stream generated in the low-temperature separation is fed to distillation
facilities for product recovery. The distillation facilities consist of a de-ethanizer and a
propylene-propane splitter, the latter producing the recycled propane stream that is used
in the reaction step.
Table below summarize the processes:

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