of light olefins from their corresponding paraffin. An Oleflex unit can dehydrogenate
propane, isobutane, normal butane, or isopentane feedstocks separately or as mixtures
spanning two consecutive carbon numbers. This process was commercialized in 1990,
and by 2002 more than 1,250,000 metric tons per year (MTA) of propylene and more
than 2,800,000 MTA of isobutylene were produced from Oleflex units located throughout
● Reactor section
● Product recovery section
● Catalyst regeneration section
Hydrocarbon feed is mixed with hydrogen-rich recycle gas (Fig. 5.1.1). This combined
feed is heated to the desired reactor inlet temperature and converted at high monoolefin
selectivity in the reactors.
The reactor section consists of several radial-flow reactors, charge and interstage
heaters, and a reactor feed-effluent heat exchanger. The diagram shows a unit with four
reactors, which would be typical for a unit processing propane feed. Three reactors are
used for butane or isopentane dehydrogenation. Three reactors are also used for blends of
C3-C4 or C4-C5 feeds.
Because the reaction is endothermic, conversion is maintained by supplying heat
through interstage heaters. The effluent leaves the last reactor, exchanges heat with the
combined feed, and is sent to the product recovery section.
is cooled, compressed, dried, and sent to a cryogenic separation system. The dryers
serve two functions: (1) to remove trace amounts of water formed from the catalyst
regeneration and (2) to remove hydrogen sulfide. The treated effluent is partially condensed
in the cold separation system and directed to a separator.
Two products come from the Oleflex product recovery section: separator gas and separator
liquid. The gas from the cold high-pressure separator is expanded and divided into
two streams: recycle gas and net gas. The net gas is recovered at 90 to 93 mol % hydrogen
purity. The impurities in the hydrogen product consist primarily of methane and ethane.
The separator liquid, which consists primarily of the olefin product and unconverted paraffin,
is sent downstream for processing.
UOP Platforming* process. The CCR unit performs four functions:
● Burns the coke off the catalyst
● Redistributes the platinum
● Removes the excess moisture
● Reduces the catalyst prior to returning to the reactors
The slowly moving bed of catalyst circulates in a loop through the reactors and the
regenerator. The cycle time around the loop can be adjusted within broad limits but is typically
anywhere from 5 to 10 days, depending on the severity of the Oleflex operation and
the need for regeneration. The regeneration section can be stored for a time without interrupting
the catalytic dehydrogenation process in the reactor and recovery sections.
Oleflex process units typically operate in conjunction with fractionators and other
process units within a production plant. In a propylene plant (Figure 5.1.3), a propanerich
liquefied petroleum gas (LPG) feedstock is sent to a depropanizer to reject butanes
and heavier hydrocarbons. The depropanizer overhead is then directed to the Oleflex
unit. The once-through conversion of propane is approximately 40 percent, which
closely approaches the equilibrium value defined by the Oleflex process conditions.
Approximately 90 percent of the propane conversion reactions are selective to propylene
and hydrogen; the result is a propylene mass selectivity in excess of 85 wt %. Two
product streams are created within the C3 Oleflex unit: a hydrogen-rich vapor product
and a liquid product rich in propane and propylene.
Trace levels of methyl acetylene and propadiene are removed from the Oleflex liquid
product by selective hydrogenation. The selective diolefin and acetylene hydrogenation
step is accomplished with the Hüls SHP process, which is available for license through
UOP. The SHP process selectively saturates diolefins and acetylenes to monoolefins
without saturating propylene. The process consists of a single liquid-phase reactor. The
diolefins plus acetylene content of the propylene product is less than 5 wt ppm.
Ethane and lighter material enter the propylene plant in the fresh feed and are also created
by nonselective reactions within the Oleflex unit. These light ends are rejected from
the complex by a deethanizer column. The deethanizer bottoms are then directed to a
propane-propylene (P-P) splitter. The splitter produces high-purity propylene as the overhead
product. Typical propylene purity ranges between 99.5 and 99.8 wt %. Unconverted
propane from the Oleflex unit concentrates in the splitter bottoms and is returned to the
depropanizer for recycle to the Oleflex unit.
of methyl tertiary butyl ether (MTBE) from butanes and methanol. Ethanol can be substituted
for methanol to make ethyl tertiary butyl ether (ETBE) with the same process
configuration. Furthermore, isopentane may be used in addition to or instead of field
butanes to make tertiary amyl methyl ether (TAME) or tertiary amyl ethyl ether
(TAEE). The complex configuration for a C5 dehydrogenation complex varies according
to the feedstock composition and processing objectives.
Three primary catalytic processes are used in an MTBE complex:
● Paraffin isomerization to convert normal butane into isobutane
● Dehydrogenation to convert isobutane into isobutylene
● Etherification to react isobutylene with methanol to make MTBE
Field butanes, a mixture of normal butane and isobutane obtained from natural gas condensate,
are fed to a deisobutanizer (DIB) column. The DIB column prepares an isobutane
overhead product, rejects any pentane or heavier material in the DIB bottoms, and makes
a normal butane sidecut for feed to the paraffin isomerization unit.
The DIB overhead is directed to the Oleflex unit. The once-through conversion of
isobutane is approximately 50 percent. About 91 percent of the isobutane conversion reactions
are selective to isobutylene and hydrogen. On a mass basis, the isobutylene selectivity
is 88 wt %. Two product streams are created within the C4 Oleflex unit: a hydrogen-rich
vapor product and a liquid product rich in isobutane and isobutylene.
The C4 Oleflex liquid product is sent to an etherification unit, where methanol reacts
with isobutylene to make MTBE. Isobutylene conversion is greater than 99 percent, and
the MTBE selectivity is greater than 99.5 percent. Raffinate from the etherification unit is
depropanized to remove propane and lighter material. The depropanizer bottoms are then
dried, saturated, and returned to the DIB column.
Given the more favorable C4 and C5 olefin equilibrium, butylene and amylene production
costs are lower per unit of olefin when adjusted for any differential in feedstock
value. The basis used for economic calculations is shown in Table 5.1.1. This basis is
typical for U.S. Gulf Coast prices prevailing in mid-2002 and can be used to show that
the pretax return on investment for such a plant is approximately 24 percent.
The LPG feedstock is the largest cost component of propylene production. The quantity of
propane consumed per unit of propylene product is primarily determined by the selectivity
of the Oleflex unit because fractionation losses throughout the propylene plant are small.
The Oleflex selectivity to propylene is 90 mol % (85 wt %), and the production of 1.0 metric
ton (MT) of propylene requires approximately 1.2 MT of propane.
An overall mass balance for the production of polymer-grade propylene from C3 LPG
is shown in Table 5.1.2 for a polymer-grade propylene plant producing 350,000 MTA,
based on 8000 operating hours per year. The fresh LPG feedstock is assumed to be 94 LV %
propane with 3 LV % ethane and 3 LV % butane. The native ethane in the feed is rejected in
the deethanizer along with light ends produced in the Oleflex unit and used as process fuel.
The butanes are rejected from the depropanizer bottoms. This small butane-rich
stream could be used as either a by-product or as fuel. In this example, the depropanizer
bottoms were used as fuel within the plant.
The Oleflex process coproduces high-quality hydrogen. Project economics benefit
when a hydrogen consumer is available in the vicinity of the propylene plant. If chemical
hydrogen cannot be exported, then hydrogen is used as process fuel. This evaluation
assumes that hydrogen is used as fuel within the plant.
in Table 5.1.3. These estimates are based on the use of an extracting steam turbine to
drive the Oleflex reactor effluent compressor. A water-cooled surface condenser is used
on the steam turbine exhaust. A condensing steam driver was chosen in this example for
the propane-propylene splitter heat-pump compressor.
Oleflex process are shown in Table 5.1.4. These costs are based on feed and product
values defined in Table 5.1.1. The fixed expenses in Table 5.1.4 consist of estimated
labor costs and maintenance costs and include an allowance for local taxes, insurance,
and interest on working capital.
propylene is approximately $145 million (U.S. Gulf Coast, mid-2002 erected cost).
This figure includes the reactor and product recovery sections, a modular CCR unit, a
Hüls SHP unit, and a fractionation section consisting of a depropanizer, deethanizer,
and heat-pumped P-P splitter. The costs are based on an extracting steam turbine driver
for the reactor effluent compressor and a steam-driven heat pump. Capital costs are
highly dependent on many factors, such as location, cost of labor, and the relative workload
of equipment suppliers.
Total project costs include ISBL and OSBL erected costs and all owner’s costs. This
example assumes an inclusive mid-2002 total project cost of $215 million including:
● ISBL erected costs for all process units
● OSBL erected costs (off-site utilities, tankage, laboratory, warehouse, for example)
● Initial catalyst and absorbant loadings
● Technology fees
● Project development including site procurement and preparation
economics for the Oleflex process are largely dependent on the price differential
between propane and propylene. Assuming the values of $180/MT for propane and
$420/MT for propylene, or a differential price of $240/MT, the pretax return on investment
is approximately 24 percent for a plant producing 350,000 MTA of propylene.