The Uhde STAR process®

Oxydehydrogenation oflight paraffins to olefins

Thys

senK

rupp

A companyof ThyssenKrupp

TechnologiesUhde

Table of contents2

1. Company profile 3

2. Introduction 42.1 Steam reforming and olefin production plants by Uhde 7

3. Oxydehydrogenation – basic principles 8

4. STAR process® technology 94.1 STAR catalyst® 94.2 Process pressure 94.3 Operation cycle 94.4 Oxidant 104.5 Space-Time-Yield 104.6 STAR process® reaction section 104.7 Heat recovery 104.8 Gas separation and fractionation 11

5. Proprietary equipment 135.1 STAR process® reformer 135.2 STAR process® oxyreactor 145.3 Steam generation 15

6. Comparison of dehydrogenation technologies 166.1 General remarks 166.2 Adiabatic reactors connected in series 166.3 Parallel adiabatic reactors 176.4 STAR process® with oxydehydrogenation step 17

7. Application of the STAR process® 187.1 Oxydehydrogenation of propane to propylene 187.2 Oxydehydrogenation of butanes 197.2.1 Oxydehydrogenation for the production of alkylate 197.2.2 Oxydehydrogenation for the production of dimers 21

8. Services for our customers 23

Page

STAR process® – an advanced dehydrogenation technology

Propylene and butylenes are important intermediates for the petrochemical and refining

industry. Their increasing demand can only bemet by highly efficient on-purpose production

technologies like dehydrogenation of light paraffins.By applying the principle of oxydehydrogenation

to its STAR process®, based on fully proven,dependable equipment and the commercially

established STAR catalyst®, Uhde has broughtdehydrogenation economics to a new level.

31. Company profile

Uhde’s head office in Dortmund, Germany

With its highly specialised workforce of more than 4,900 employees and its international network of subsidiaries and branch offices, Uhde, a Dortmund-basedengineering contractor, has, to date, successfully completed over 2,000 projectsthroughout the world.

Uhde’s international reputation has been built on the successful application of its motto Engineering with ideas to yield cost-effective high-tech solutions for itscustomers. The ever-increasing demands placed upon process and application technology in the fields of chemical processing, energy and environmental protectionare met through a combination of specialist know-how, comprehensive service packages, topquality engineering and impeccable punctuality.

The extensive international experience in the design and construction of chemicalplants makes Uhde the ideal engineering contractor for dehydrogenation plants usingthe advanced STAR process®.

2. Introduction4

Medium and long-term forecasts expect to see agrowing demand for on-purpose technologies forolefin production (e.g. propylene, butylenes)such as dehydrogenation of light paraffins.

Today most propylene is produced as co-productin steam crackers (approx. 57%) and as by-product in FCC units (approx. 35%). Only approx.6 - 8% is produced by on-purpose technologieslike propane dehydrogenation (PDH) or metathesis.

However, higher annual growth rates forpropylene than for ethylene are expected. Additionally, steam cracking increasingly shiftsto ethane feedstocks due to more favourableeconomics compared to naphtha or LPG feed-stocks. Because ethane cracking yields con-siderably less propylene than LPG or naphthacracking this will result in a gap for supply ofpropylene. This gap can very economically beclosed by propane dehydrogenation applyingthe STAR process®.

Rapid further growth is expected for on-purposepropylene and butylene production to yield thefollowing derivatives:

Coastal Chemical Inc. in Cheyenne, Wy, USA, Capacity: 100,000 t/y isobutene

Flare

Liquid storageTankfarm

5

C3 splitter for EPP

STAR, which is the acronym for STeam ActiveReforming, is a commercially established dehydrogenation technology that was initiallydeveloped by Phillips Petroleum Company,Bartlesville, OK, USA.

Uhde acquired the technology including processknow-how and all patents related to process andcatalyst from Phillips in December 1999.

Two commercial units applying the STAR process®

technology have been commissioned for thedehydrogenation of isobutane integrated withthe production of MTBE:

• Coastal Chemical Inc., Cheyenne, Wy, USAwas commissioned in 1992 and produces100,000 tonnes per annum of isobutene.

• Polybutenos, Argentina, was designed fora capacity of 40,000 tonnes per annumof isobutene and was commissioned in 1994.

The successful operation of those plants demon-strated the high stability of the STAR catalyst®.

In the period from 2000 to 2004 Uhde significant-ly increased the performance of the STAR pro-cess® by adding an oxydehydrogenation step.

Uhde has a long and broad experience indesign and commissioning of equipment usedin STAR process® technology as well as plantsfor production of olefins and olefin derivatives.

In 2006 Uhde was awarded a lump sum turnkeycontract to build a 350,000 tonne-per-annumPDH/PP complex by Egyptian Propylene & Poly-propylene Company (EPPC) in Port Said, Egypt.

PP storage

PDH plant

PP plant

Utilities

3-D model of PDH/PP complex for Egyptian Propylene and

Polypropylene Company (EPP)

6

SINCOR C.A. in Jose, Venezuela, Capacity: 2 x 97,770 Nm3/h of hydrogen

2.1 Steam reforming and olefin production plants by Uhde

7

Uhde and steam reforming

The references on steam reforming attachedherewith reflect Uhde’s experience in connectionwith the reaction section and steam generationequipment applied in STAR process® technology.Today the total count is as follows:

• Steam reformer: more than 60 installations (basis for STAR process® reformer)

• Secondary reformer: more than 40 installations(basis for STAR process® oxyreactor)

• Fire-tube boiler (process gas cooler): more than 65 installations

Uhde and olefins

Uhde has also designed and successfully commis-sioned plants for a wide range of applicationsfor production of olefins and olefin derivativesusing the technologies described in Table 1. Incombination with the STAR process® Uhde is inthe position to offer complete process routes:

• Production of polypropylene (PP) or propyleneoxide (PO) from propane.

• Production of MTBE or other high octane blendstocks (e.g. alkylate or dimers) from butane.

Another advantage of the STAR process® conceptis the dual function of Uhde, being the technologyowner and licensor on the one hand and theoverall turnkey contractor on the other hand –both functions being synergetically combinedwithin one organisation. Based on this fundament, Uhde is able to fully commit to thenecessary process performance guarantees ofthe STAR process® within a single-point responsibility, turnkey contract.

Product Process Licensor

Ethylene dichloride Vinnolit

Ethylene oxide Shell Chemicals

Ethylene glycol Shell Chemicals

Propylene oxide Evonik-Uhde

High density polyethylene LyondellBasell

Low density polyethylene LyondellBasell

Polypropylene LyondellBasell

Alkylate UOP, ConocoPhillips, Stratco

MTBE/ETBE Uhde

Dimers Axens, UOP

Olefins Uhde

Table 1: Uhde’s portfoliofor the productionof olefins and ole-finderivatives

3. Oxydehydrogenation – basic principles8

Lower hydrocarbons (i.e. lower in carbon numberthan that of the feedstock) are also formed. Minorreactions that occur are cracking, which is primarily thermal and results in the formation ofsmall amounts of coke.

Obviously conversion is limited by the thermodynamic equilibrium for a given pressureand temperature. As conversion approachesequilibrium, reaction velocity decreases andcatalyst activity is not efficiently utilised.However, if oxygen is admitted to the systemthis will form H2O with part of the hydrogen,which in turn will shift the equilibrium of thedehydrogenation reaction to increased conversion. Figure 1 shows the influence of oxygen addition as it shifts the equilibriumtowards increased conversion of propane to propylene. Formation of H2O is exothermic andhence provides the heat of reaction for furtherendothermic conversion of paraffin to olefin.

Major requirements to achieve this objective areas follows:

• The catalyst continues to maintain its activityfor dehydrogenation and does not convert thehydrocarbons to carbon oxides and hydrogen(’Steam reforming’).

• The catalyst is stable in the presence ofsteam and oxygen.

• The STAR catalyst® fully satisfies those requirements.

Above mentioned advantages are utilised in theSTAR process® which connects conventional de-hydrogenation (i.e. the STAR reformer) in serieswith an oxydehydrogenation step (i.e. oxyreactor).

In principle, the concept of oxydehydrogenationhas already been commercially proven for theconversion of butene-1 to butadiene (’Oxo-D’process developed by Petro-Tex Corp.). Sevenunits were installed (five of them in the USA)between the years 1965 to 1983, with plantcapacities ranging from 65,000 to 350,000 tonnesper annum of butadiene. The total installedcapacity was over a million tonnes per annum.Oxidant was air.

Dehydrogenation is an endothermic equilibriumreaction. The conversion of paraffins increaseswith decreasing pressure and increasing tem-perature. In general process temperature willincrease with decreasing carbon number tomaintain conversion at a given pressure. As shownbelow for propane and butane, respectively, themajor reaction is the conversion of paraffin toolefin.

Propane dehydrogenation (PDH):C3H8 C3H6 + H2

Butane dehydrogenation (BDH):

C4H10 C4H8 + H2

60

55

50

45

40

25

30

35

540

20

550 560 570 580 590 600

Temperature [°C]

Con

vers

ion

Prop

ane

[%]

without OxygenO2 / HC Ratio = 0.05O2 / HC Ratio = 0.1

Figure 1: Thermodynamic equilibrium data (Partial pressure 1 bar, molar oxygen to propane ratios)

Process steam

Process condensate

Olefinproduct

Fuel gas

Boiler feed water

Hydrocarbon feed

O2/air

Oxyreactor

STARreformer

Fuel gas

Air

HP steam

Heatrecovery

Feedpreheater

Raw gascompression

Gasseparation Fractionation

Hydrocarbon recycle

4. STAR process® technology 9

4.1 STAR catalyst®

The STAR catalyst® is based on a zinc and calcium aluminate support that, impregnated withvarious metals, demonstrates excellent dehydro-genation properties with very high selectivitiesat near equilibrium conversion. Due to its basicnature it is also extremely stable in the presenceof steam and oxygen at high temperatures. This commercially proven noble metal promotedcatalyst in solid particulate form is utilised in theSTAR process®.

4.2 Process pressure

The reaction takes place in the presence ofsteam, which reduces the partial pressure of thereactants. This is favourable, as the endothermicconversion of paraffin to olefin increases withdecreasing partial pressures of hydrocarbons.Competing dehydrogenation technologies operate at reactor pressures slightly aboveatmospheric pressure or even under vacuum. In the STAR process®, however, reactor exit pressure is approximately 5 bar. This allows sufficient pressure drop to utilise the heat available in the reactor effluent efficiently andalso allows to design the raw gas compressorwith a suction pressure of min. 3.0 bar thussaving investment and operating costs.

4.3 Operation cycle

During normal operation a minor amount ofcoke is deposited on the catalyst which requiresfrequent regeneration of the catalyst. Steampresent in the system converts most of thedeposited coke to carbon dioxide. This leavesvery little coke to be burnt off during the oxidative regeneration, thus allowing longeroperation cycles and making the regenerationquick and simple. Also no additional treatmentfor coke suppression or catalyst reactivation (e.g.sulfiding or chlorinating) is required. The cyclelength is seven hours of normal operation followedby a regeneration period of one hour. Thereforeonly 14.7% additional reactor capacity is neededto account for regeneration requirements, whichis the lowest of all commercial technologies.

Figure 2: The overall block flow scheme of the STAR process® for propane oxydehydrogenation

10

4.4 Oxidant

Oxidant is either air or oxygen enriched air. Useof 90% oxygen is the more economic option asit reduces the amount of nitrogen in the reactoreffluent. This minimises gas volume flow to rawgas compression and gas separation which resultsin an appreciable reduction in operating costs.

4.5 Space-Time-Yield

STAR process® oxydehydrogenation operates ata high Liquid Hourly Space Velocity (LHSV) of 6 compared to 4 in conventional STAR process®

dehydrogenation. LHSV represents the ratio oftotal hydrocarbon feed liquid volume flow at15.6°C (60°F) per volume of catalyst.

In spite of increased space velocity oxydehydro-genation substantially increases the olefin yield in the reaction section. The result is a high space-time-yield, the impact of which (in comparisonwith conventional dehydrogenation) is summar-ised below:

• Reformer tubes are shorter in oxydehydro-genation due to increased space velocity.

• The required amount of catalyst for oxyde-hydrogenation is reduced by more than 35%.

• The externally heated reactor (i.e. top-firedSTAR process® reformer) contains only 80%of the catalyst required. The oxyreactors arefilled with the other 20% of the catalyst. Inother words, the size of the STAR process®

reformer in oxydehydrogenation is considerablysmaller. The amount of catalyst in the refor-mer tubes is reduced by more than 50% andnumber of tubes is reduced by approx. 33%.

• The higher yield reduces the dry gas flow tothe raw gas compressor and to the down-stream units handling the product work up.

• As a consequence of these advantages, theinvestment as well as the utility consumptionare less.

Feed Propane Isobutane

Inlet temperature - STAR process® reformer (°C) 510 510

Exit temperature - STAR process® reformer (°C) 580 550

Exit temperature - Oxyreactor (°C) 580 575

Exit pressure - Oxyreactor (bar) 5.3 5.2

Steam-to-hydrocarbon ratio (St/HC) - Overall 4.2 4.2

Steam-to-hydrocarbon ratio (St/HC) - 3.5 3.7STAR process® reformer

Oxygen/Hydrocarbon ratio (molar) 0.08 0.08 to 0.16

Table 2:Process Parameters

4.6 STAR process® reaction section

The reaction section comprises an externallyheated reactor (STAR process® reformer) connected in series with an adiabatic reactor(oxyreactor). This configuration, as shown infigure 3, represents the scheme for all applica-tions described in Section 7.

Table 2 summarises process parameters for the STAR process® reaction section.

Main features of the reaction section are:

• The tubes of the reformer and the oxyreactorsare filled with the STAR catalyst®, where theconversion of paraffin takes place.

• Oxidant is air or 90% oxygen.

• Feed to the oxyreactor is cooled by condensate and steam injection, which alsoadjusts the steam-to-hydrocarbon (St/HC)ratio required in the oxyreactor. Cooling offeed to the oxyreactors is adjusted to set theamount of oxygen that matches the require-ment for conversion and that required to provide the heat of reaction for further dehydrogenation of paraffin.

4.7 Heat recovery

Heat from the process gas is efficiently recoveredand utilised for:

• Production of 45 bar steam (refer to Section 5.3, page 15)

• BFW preheating

• Feed preheating

• Feed vaporisation and superheating

• Direct heating of fractionation column reboilers

11

4.8 Gas separation and fractionation

A steady continuous feed to the fractionation ata constant composition is important to ensure theproduct quality. The gas separation is designedto meet these requirements.

The major features of this design are as follows:

• The cold box virtually removes all the hydrogen and nitrogen from the reactor product. About 70% of methane and minoramounts of ethane are also removed.

• Olefin losses are very low. Olefin recovery inthe product is 99.5% of the olefin producedin the reactor.

• No gas phase is admitted to the fractionation.The entire fractionation feed is liquid, which iscollected in an intermediate storage vessel,from where it is continuously fed to the distil-lation columns. Hence operation of this section is not influenced by the load variations(between the normal and regeneration mode)in the front end.

• Light ends are removed as tail gas in thefractionation. The removal of hydrogen, nitrogen and a substantial amount of methane in the cold box reduces the amountof these components in the light ends. Thisincreases the dew point of the tail gas for agiven pressure. As a result, the required temperature level of the refrigerant is alsorelatively higher, which in turn reduces compression costs.

Figure 3:STAR process® reformer connected in series with the oxyreactor

12

Refractory

Catalyst grid

Furnace bottom

Bellow

Gas conducting tube

Shop weld

Field weld

Carbon steel

Outlet manifold

Figure 4: Reformer tube-to-manifold connection

Figure 5: Furnace box of top-fired

Uhde STAR process® reformer

Inlet manifold

Burners

Reformer

tubes

Cold outlet

manifold system

5. Proprietary equipment 13

5.1 STAR process® reformer

STAR process® reformer is an industrially well known and commercially established top fired „Steam Reformer”, which is atubular fixed bed type and hence will not suffer catalyst lossesdue to attrition. The arrangement of this equipment is shown infigure 5.

Main features of the reformer are:

• Top firing for optimum uniformity of tube skin temperature profile.

• Small number of burners required.

• Internally insulated cold outlet manifold system (Figure 4)made from carbon steel and located externally under the reformer bottom.

• Internally insulated reformer tube to manifold connection operating at moderate temperatures.

• Each tube row connected to separate cold outlet manifold.

Uhde has installed more than 60 reformers of this type since1966 in various parts of the world, to generate synthesis gas for the production of ammonia, methanol, oxo alcohols and hydrogen. The largest unit designed by Uhde has 960 tubes.

As shown in table 3 the operating conditions for the above mentioned applications are far more stringent than those required for the dehydrogenation.

Figure 6 shows, that the top fired reformer ensures a uniformtemperature profile with a steady increase of temperature in thecatalyst bed, thus efficiently utilising the activity of the catalyst.

Uhde reformers demonstrate a very high availability of five yearsof operation between maintenance shut downs.

Application Pressure [bar abs] Temperature [°C]

Ammonia 40 780 - 820

Methanol 20 - 25 850 - 880

Hydrogen 20 - 25 880

Oxogas 9 - 12 900

Olefins (STAR process®) 5 - 6 550 - 590

450 500 550 600 650 700 7500

20

40

60

80

100

Catalyst bedtemperature

Tube walltemperature

Temperature [°C]

Hea

ted

Leng

th [

%]

Table 3: Industrial applications of steam reformers

Figure 6: Temperature profile of the reformer tubes

Service Ammonia Olefins(STAR process®)

Operating pressure (bar abs.) 38 max. 6

Operating temperature (°C) 970 max. 600

14

5.2 STAR process® oxyreactor

The adiabatic oxyreactor is a refractory linedvessel, which means that no metallic surfacesare exposed to the reaction zone. The design ofthis equipment, as shown in figure 7, is virtuallythe same as the Uhde secondary reformer, whichis used in ammonia plants. The only differenceis the kind of distribution of the oxidant. Air oroxygen-enriched air diluted with steam is dis-tributed so as to allow the oxygen to come intocontact with the process medium at the top ofthe catalyst bed.

Compared to ammonia plants, the operatingconditions in oxydehydrogenation are a lot milder (refer to table 4).

Uhde’s answer to a safe and reliable design ishighlighted by the following features:

• Reactor effluent from STAR process® reformerenters the STAR process® oxyreactor at thebottom and passes into one centrally arrangedtube, which conducts the gas to the top. Thiseliminates troublesome external hot piping tothe head of the reactor.

• Process gas is discharged from the central tubeinto the dome for reversal of the flow direction.

• Air or oxygen is admitted to the system anduniformly distributed directly over the catalystsurface via a proprietary oxygen distributionsystem. In other words, process gas andoxygen are rapidly mixed and directly contacted with the catalyst bed to achievehigh selectivities for the conversion of hydrogen with oxygen.

Table 4: Comparison of operating conditions of the secondary reformer for production of synthesis gas for ammonia and of theSTAR process® oxyreactor for dehydrogenation

Figure 7: STAR process® oxyreactor design

15

5.3 Steam generation

The process gas cooler (see figure 8) for pro-duction of 45 bar steam is a horizontal fire-tubeboiler, which is a commercially proven equipmentin Uhde’s ammonia and hydrogen plants.

The major features and advantages are as follows:

• Simple fixed-tubesheet design. Tubesheetsare thin with tubes joined to tubesheets bymeans of full penetration welds.

• No crevice corrosion.

• Operation on a reliable free convection flow.There are no heated dead ends on waterside where debris can settle.

• Hot inlet chambers and tubesheets arerefractory lined. Hence metal temperaturesare low in this area.

• Low-alloy steel is used.

• Steam drum is mounted on top of the processgas cooler and is supported by downcomersand risers. Erection costs are low due to shopassembly.

• Access for maintenance and inspection is easy.

Figure 8: Process gas cooler and steam drum design

Figure 9: Temperature and conversion profile foradiabatic reactors

4000 20 806040 100

500

600

700

Tem

pera

ture

[°C

]

Catalyst bed volume [%]

0

70

Con

vers

ion

[%]

Temperatureprofile

Equilibriumconversion

Actualconversion

Intermediate Heaters

6. Comparison of dehydrogenation technologiesThe reaction section of the STAR process® with oxydehydrogenation step offers significant advantages compared to competing technologies, which will be explained in the following.

16

6.1 General remarks

Dehydrogenation is an endothermic equilibrium reaction. As more and more product is formed, the residence time requiredfor production of a certain amount of product will continuouslyincrease due to the fact that the driving force decreases. This means, as the dehydrogenation reaction progresses, theyield per time and catalyst volume (space-time-yield) will decrease.

The following chapters describe the technologies available on themarket.

The two most expensive units within a dehydrogenation plant arethe reaction section and the raw gas compression. Defining thereaction pressure will also define the required compression ratiofor the raw gas compressor, which directly influences compressoroperating and investment costs.

6.2 Adiabatic reactors connected in series

The endothermic reaction will cause a temperature drop across the catalyst bed. Reactor feed needs to be preheated soas to contain the heat of reaction. Across the catalyst bed, the temperature profile and conversion are counter current.

Hence conversion is limited by the reactor exit temperature whichis lower than the inlet temperature.

This system, besides a charge heater, will also require preheatingof partially reacted gases prior to admittance of the next reactor(Figure 9), which results in cracking of already formed olefin.Hence measures are needed to suppress coke formation in theintermediate heaters. Otherwise coke deposit on catalyst willincrease thereby causing temporary deactivation of the catalyst.Furthermore the space time yield is low.

One of the measures to suppress coke formation is to recycle hydrogen. This is bound to decrease the driving force of the reaction as hydrogen is also a dehydrogenation product.

17

6.4 STAR process® with oxydehydrogenation step

This configuration of an externally heated tubular reactor (STAR process® reformer) followed by an air or oxygen operatedadiabatic reactor (oxyreactor) combines the advantages of bothreactor systems:

• STAR process® reformer, as known from the steam reforming process for the production of synthesis gas, monitors the temperature profile to efficiently utilise the activity of the catalyst.

• External heating in the reformer monitors a steady increase of temperature in the catalyst bed (see figure 11). This is in accordance to the thermodynamic requirements in terms of increasing conversion.

• Admission of oxygen to the oxyreactor shifts the thermodynamic equilibrium and provides the heat of reaction for further dehydrogenation (Figure 11).

• The overall effect is a high space-time-yield at increased conversion and selectivity.

• Due to higher operating pressure lower compression costs.

4000 20 806040 100

500

600

700

Tem

pera

ture

[°C

]

Catalyst bed volume [%

Reformer Oxyreactor

]

0

70

Con

vers

ion

[%]

Addition ofoxygen

Temperatureprofile

Equilibriumconversion Actual

conversion

Figure 11: Temperature and conversion profile for an externally heated tubular reactor followed by an adiabatic oxyreactor (STAR process® with oxydehydrogenation step)

5000 20 40 60 80 100

550

600

650

Catalyst bed volume [%]

Tem

pera

ture

[°C

]

t0

t1

t2

t3

t4

Figure 10: Temperatures in the catalyst bed for different times (t0-t4)

6.3 Parallel adiabatic reactors

Such systems require multiple parallel beds, particularly for largecapacities. Ensuring efficient distribution of feed is bound to limitthe diameter of the reactor. Allowable pressure drop will limit thebed height as well. Extent of conversion is carried out in one bedwhich will also limit the space velocity.

Typically, feed preheated does not supply sufficient heat for high conversion. This means that during the regeneration phase heathas to be introduced into the system which is utilised during thefollowing reaction phase. Catalyst is used as a heat source forendothermic reaction. During reaction phase catalyst bed tem-perature decreases, which in turn leads to short cycle length ofonly 6 - 10 minutes. Hence several parallel beds at large capaci-ties cannot be avoided. Space-time-yield is even lower comparedto adiabatic systems connected in series.

For world scale plants a large number of reactors in parallel isrequired. Only few of them are used at the same time for de-hydrogenation.

Typical space time yield (kg product/kg catalyst hour) 0.8 - 1.0

Typical compression ratio 6 - 10

Required number of reactor systems for world-scale plants for propylene production(450,000 tonnes per annum) 2

7. Application of the STAR process®18

Table 5: Typical consumption figures for propane oxydehydrogenation

Designation Unit for specific Relative consumptionconsumption per tonne of product

Propane feed t/ t product 1.188

HP Steam t/ t product 2.2

Cooling water m3/ t product 165

Fuel gas GJ/t product 2.01

Electrical energy kWh/t product 85

7.1 Oxydehydrogenation of propane to propylene

Propylene is a base petrochemical used for theproduction of polypropylene (PP), oxo-alcohols,acrylonitrile, acrylic acid (AA), propylene oxide(PO), cumene and others.

About 60% of the propylene produced today is used as feedstocks for the production of PP.

With the STAR process® technology Uhde cansupply complete process routes to propylenederivatives, e.g. PP or PO, based on on-purposepropylene production from propane within a single-point repsonsibility. Process economicsfor a production complex, e.g. of PP from propaneby PDH (STAR process®) and subsequent poly-merisation are very favourable.

Hydrogen produced by dehydrogenation can bepurified and used as feedstock for subsequentplants (e.g. for H2O2 production in connectionwith the Evonik-Uhde HPPO process) minimisingraw material costs.

Contaminants regarding the feed to a subse-quent plant (CO, CO2 and sulphur components)are efficiently removed in the STAR process®.Thus, a Selective Hydrogenation Unit (SHU) orguard beds for removal of trace components arein most of the cases not required. Additionally,recycle streams from the PP plant can be purifiedwith the existing equipment of the PDH plant.Integration of utilities and offsites units (steam,cooling water, refrigerant, oxygen/nitrogen, etc.)will further increase project economics.

The process configuration for a stand-alone propane oxydehydrogenation plant is outlined infigure 2, page 9.

Typical consumption figures summarised beloware based per tonne of polymer-grade propyleneproduced.

Since 2008 the world’s first commercial scale plant for the production of propylene oxide based on the innovative HPPO process has been in successful operation.

19

7.2 Oxydehydrogenation of butanes

Dehydrogenation of isobutane to isobutene forthe production of MTBE is a commercially wellestablished process route. MTBE is phased outin the USA. However, it is not clear, whether thiswill apply to other regions as well.

Other options for octane boosting are alkylateand dimers. Dehydrogenation of butanes tobutenes can also be utilised for the productionof alkylate or dimers, which are used as blendingstock to enhance the quality of unleaded gasolineto premium grade.

7.2.1 Oxydehydrogenation for the production of alkylate

Both HF and H2SO4 alkylation are mature andefficient technologies for the production of C7 and C8 alkylate from propene and butenes. C8 alkylate has higher octane numbers than C7 alkylate.

Table 6: RON of alkylatedepending onalkylation technology andolefin

Figure 12: Alkylate frommixed butanes

The Research Octane Number (RON) of thealkylate produced will depend on the type ofolefin as well as the process applied (refer totable 6). It is worthwhile to limit isobutene whenthe alkylation process is based on H2SO4, whereas preferable feed components for HF alkylation are butene-2 and isobutene.Plant configuration will depend on the alkylationscheme selected. For alkylation based on H2SO4the preferred plant feed is mixed butanes.

The process steps are as follows:

• STAR process® oxydehydrogenation

• Butenex®

• Selective hydrogenation

• H2SO4 alkylation

Butenex®, a technology licensed by Uhde, is anextractive distillation process. C4 fraction fromSTAR is separated into butenes and butanes.Solvent is a mixture of N-formylmorpholine (NFM)and morpholine. NFM is a commercially wellestablished solvent known from its application inUhde’s Morphylane® process for the extractivedistillation of aromatics. To date two commercialButenex® units have been successfully designedand commissioned by Uhde.

Alkylate RON

Alkylate from HF alkylation H2SO4 alkylation

Butene-1 91 98

Butene-2 97 98

Isobutene 95 91

STAR process® Butenex® Selectivehydrogenation

H2SO4

alkylation

N-butane recycle

Mixedbutanes

Hydrogen

Fuel gas

Isobutane

C8alkylate

STAR process® HFalkylation

Isobutane

Fuel gas

C8alkylate

20

Depending on the content of isobutane in mixedbutanes feed, the STAR process® unit could beconceived to include a deisobutaniser column soas to separate isobutane from n-butane in themixed butanes feed. N-butane is recycled fromthe Butenex® unit to the STAR process® unit.Butadiene in the unsaturated C4 stream (extract)from Butenex® is selectively hydrogenated tobutene-1. The selectively hydrogenated streamis the olefin feed to alkylation.

It seems to be advantageous to process isobutane(instead of mixed butanes), if the selected schemeis HF alkylation.

The reasons are:

• RON of C8 alkylate derived from isobutene ishigh (95).

• For a given conversion the selectivity of isobutene (from isobutane) is higher thanthat of n-butenes (from n-butane). In otherwords plant feed is less by 6%.

• Selective hydrogenation of butadiene will notbe required.

• STAR process® unit can be designed to provide an isobutane/isobutene mixture in thedesired stochiometric ratio for the alkylation.In other words recycle of unconverted paraffinto the STAR process® unit will not be required.This in turn will eliminate the requirement of aButenex® unit.

Figure 13: Alkylate from isobutane

STAR process®Selective

hydrogenation

Butanes recycle

Fresh feed(mixed butanes orisobutane)

Hydrogen

Fuel gas

Gasoline

DimerisationJet fuel

21

7.2.2 Oxydehydrogenation for the production of dimers

Amount and quality (RON) of gasoline producedwill depend on the process option whether isobutene is selectively dimerised or whether allbutenes present in the feed are dimerised.Furthermore when processing mixed butenes,the concentration of isobutene in mixed buteneswill also influence the quality of gasoline.

Dimerisation of mixed butenes will result in aliquid product of which max. 80% is gasolineand 20% is jet fuel. Liquid product yield will bearound 95 - 98% of butenes present in feed.Octane rating will increase as the concentrationof isobutene in feed increases. Isobutene concentration of about 50% (in total butenes)will be required to obtain unleaded premiumgasoline (RON 95) quality.

Selective dimerisation of isobutene (in the mixedbutenes feed) will result in a liquid product whichwill primarily consist of high octane gasoline(RON 99) and a minor amount (4% of liquidproduct) of jet fuel.

However, liquid product yield is low. Whereasisobutene is virtually completely dimerised theconversion of n-butenes will be only in the orderof 50%. Isobutene will be completely convertedto high octane gasoline (RON 99).

The process configuration (Figure 14) consistsof the following process steps:

• STAR process® oxydehydrogenation

• Selective hydrogenation of butadiene

• Dimerisation unit (incl. product hydrogenation)

Selective hydrogenation of butadiene is onlyrequired if plant feed consists of mixed butanes.

Hydrogen required for selective hydrogenation offeed to dimerisation and for product hydrogenationwill be supplied from the STAR process®. Theutility system of the dimerisation and hydroge-nation units is integrated with the STAR process®

unit to enhance process economy. Unconvertedbutanes are recycled from the dimerisation unitto the STAR process® unit.

Figure 14: Dimers from butane

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Inside view of the furnace box of an Uhde steam reformer

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We promote active communicationby organising and supporting technicalsymposia.

8. Services for our customers

Uhde is dedicated to providing its customerswith a wide range of services and to supportingthem in their efforts to succeed in their line ofbusiness.

With our worldwide network of subsidiaries,associated companies and experienced localrepresentatives, as well as first-class backingfrom our head office, Uhde has the idealqualifications to achieve this goal.

We at Uhde place particular importanceon interacting with our customers at an earlystage to combine their ambition and expertisewith our experience.

Whenever we can, we give potential customersthe opportunity to visit operating plants and topersonally evaluate such matters as processoperability, maintenance and on-stream time.We aim to build our future business on theconfidence our customers place in us.

Uhde provides the entire spectrum of servicesassociated with an EPC contractor, from theinitial feasibility study, through financing conceptsand project management right up to the com-missioning of units and grass-roots plants.

Our impressive portfolio of services includes:

• Feasibility studies/technology selection

• Project management

• Arrangement of financing schemes

• Financial guidance based on an intimateknowledge of local laws, regulations andtax procedures

• Environmental studies

• Licensing incl. basic/detail engineering

• Utilities/offsites/infrastructure

• Procurement/inspection/transportation services

• Civil works and erection

• Commissioning

• Training of operating personnel using operator training simulator

• Plant operation/plant maintenance

The policy of the Uhde group and itssubsidiaries is to ensure utmost quality in theimplementation of our projects. Our head officeand subsidiaries worldwide work to the samequality standard, certified according to:DIN/ISO 9001/EN29001.

We remain in contact with our customers evenafter project completion. Partnering is ourbyword.

By organising and supporting technical sympo-sia, we promote active communication betweencustomers, licensors, partners, operators andour specialists. This enables our customers tobenefit from the development of new technolo-gies and the exchange of experience as well astroubleshooting information.

We like to cultivate our business relationshipsand learn more about the future goals of ourcustomers. Our after-sales services includeregular consultancy visits which keep the ownerinformed about the latest developments orrevamping options.

Uhde stands for tailor-made concepts andinternational competence. For more informationcontact one of the Uhde offices near you or visitour website:

www.uhde.eu

Further information on this subject can be foundin the following brochures:

• Ammonia• Organic chemicals and polymers• Propylene oxide

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