The Uhde STAR process Oxydehydrogenation of light paraffins to olefins

Transcription

1 The Uhde STAR process Oxydehydrogenation of light paraffins to olefins A company of ThyssenKrupp Technologies Uhde ThyssenKrupp

2 2 Table of contents 1. Company profile 3 2. Introduction Steam reforming and olefin production plants by Uhde 7 3. Oxydehydrogenation basic principles 8 4. STAR process technology STAR catalyst Process pressure Operation cycle Oxidant Space-Time-Yield STAR process reaction section Heat recovery Gas separation and fractionation Proprietary equipment STAR process reformer STAR process oxyreactor Steam generation Comparison of dehydrogenation technologies General remarks Adiabatic reactors connected in series Parallel adiabatic reactors STAR process with oxydehydrogenation step Application of the STAR process Oxydehydrogenation of propane to propylene Oxydehydrogenation of butanes Oxydehydrogenation for the production of alkylate Oxydehydrogenation for the production of dimers 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 be met 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 brought dehydrogenation economics to a new level.

3 1. Company profile 3 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-based engineering contractor, has, to date, successfully completed over 2,000 projects throughout 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 its customers. The ever-increasing demands placed upon process and application technology in the fields of chemical processing, energy and environmental protection are 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 chemical plants makes Uhde the ideal engineering contractor for dehydrogenation plants using the advanced STAR process.

4 4 2. Introduction Medium and long-term forecasts expect to see a growing demand for on-purpose technologies for olefin production (e.g. propylene, butylenes) such as dehydrogenation of light paraffins. Today most propylene is produced as co-product in steam crackers (approx. 57%) and as byproduct in FCC units (approx. 35%). Only approx. 6-8% is produced by on-purpose technologies like propane dehydrogenation (PDH) or metathesis. However, higher annual growth rates for propylene than for ethylene are expected. Additionally, steam cracking increasingly shifts to ethane feedstocks due to more favourable economics compared to naphtha or LPG feedstocks. Because ethane cracking yields considerably less propylene than LPG or naphtha cracking this will result in a gap for supply of propylene. This gap can very economically be closed by propane dehydrogenation applying the STAR process. Flare Liquid storage Tankfarm Rapid further growth is expected for on-purpose propylene and butylene production to yield the following derivatives: Coastal Chemical Inc. in Cheyenne, Wy, USA, Capacity: 100,000 t/y isobutene

5 5 P storage Utilities PP plant PDH plant 3-D model of PDH/PP complex for Egyptian Propylene and Polypropylene Company (EPP) C3 splitter for EPP STAR, which is the acronym for STeam Active Reforming, is a commercially established dehydrogenation technology that was initially developed by Phillips Petroleum Company, Bartlesville, OK, USA. Uhde acquired the technology including process know-how and all patents related to process and catalyst from Phillips in December Two commercial units applying the STAR process technology have been commissioned for the dehydrogenation of isobutane integrated with the production of MTBE: Coastal Chemical Inc., Cheyenne, Wy, USA was commissioned in 1992 and produces 100,000 tonnes per annum of isobutene. Polybutenos, Argentina, was designed for a capacity of 40,000 tonnes per annum of isobutene and was commissioned in The successful operation of those plants demonstrated the high stability of the STAR catalyst. In the period from 2000 to 2004 Uhde significantly increased the performance of the STAR process by adding an oxydehydrogenation step. Uhde has a long and broad experience in design and commissioning of equipment used in STAR process technology as well as plants for production of olefins and olefin derivatives. In 2006 Uhde was awarded a lump sum turnkey contract to build a 350,000 tonne-per-annum PDH/PP complex by Egyptian Propylene & Polypropylene Company (EPPC) in Port Said, Egypt.

6 6 SINCOR C.A. in Jose, Venezuela, Capacity: 2 x 97,770 Nm 3 /h of hydrogen

7 2.1 Steam reforming and olefin production plants by Uhde 7 Uhde and steam reforming The references on steam reforming attached herewith reflect Uhde s experience in connection with the reaction section and steam generation equipment 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 commissioned plants for a wide range of applications for production of olefins and olefin derivatives using the technologies described in Table 1. In combination with the STAR process Uhde is in the position to offer complete process routes: Production of polypropylene (PP) or propylene oxide (PO) from propane. Production of MTBE or other high octane blendstocks (e.g. alkylate or dimers) from butane. Another advantage of the STAR process concept is the dual function of Uhde, being the technology owner and licensor on the one hand and the overall turnkey contractor on the other hand both functions being synergetically combined within one organisation. Based on this fundament, Uhde is able to fully commit to the necessary process performance guarantees of the STAR process within a single-point responsibility, turnkey contract. Table 1: Uhde s portfolio for the production of olefins and olefin derivatives Product Ethylene dichloride Ethylene oxide Ethylene glycol Propylene oxide High density polyethylene Low density polyethylene Polypropylene Alkylate MTBE/ETBE Dimers Olefins Process Licensor Vinnolit Shell Chemicals Shell Chemicals Evonik-Uhde LyondellBasell LyondellBasell LyondellBasell UOP, ConocoPhillips, Stratco Uhde Axens, UOP Uhde

8 8 3. Oxydehydrogenation basic principles Figure 1: Thermodynamic equilibrium data (Partial pressure 1 bar, molar oxygen to propane ratios) Conversion Propane [%] Dehydrogenation is an endothermic equilibrium reaction. The conversion of paraffins increases with decreasing pressure and increasing temperature. In general process temperature will increase with decreasing carbon number to maintain conversion at a given pressure. As shown below for propane and butane, respectively, the major reaction is the conversion of paraffin to olefin. Propane dehydrogenation (PDH): C 3 H 8 C 3 H 6 + H 2 Butane dehydrogenation (BDH): C 4 H 10 C 4 H 8 + H 2 without Oxygen O 2 / HC Ratio = 0.05 O 2 / HC Ratio = Temperature [ C] Lower hydrocarbons (i.e. lower in carbon number than that of the feedstock) are also formed. Minor reactions that occur are cracking, which is primarily thermal and results in the formation of small amounts of coke. Obviously conversion is limited by the thermodynamic equilibrium for a given pressure and temperature. As conversion approaches equilibrium, reaction velocity decreases and catalyst activity is not efficiently utilised. However, if oxygen is admitted to the system this will form H 2 O with part of the hydrogen, which in turn will shift the equilibrium of the dehydrogenation reaction to increased conversion. Figure 1 shows the influence of oxygen addition as it shifts the equilibrium towards increased conversion of propane to propylene. Formation of H 2 O is exothermic and hence provides the heat of reaction for further endothermic conversion of paraffin to olefin. Major requirements to achieve this objective are as follows: The catalyst continues to maintain its activity for dehydrogenation and does not convert the hydrocarbons to carbon oxides and hydrogen ( Steam reforming ). The catalyst is stable in the presence of steam and oxygen. The STAR catalyst fully satisfies those requirements. Above mentioned advantages are utilised in the STAR process which connects conventional dehydrogenation (i.e. the STAR reformer) in series with an oxydehydrogenation step (i.e. oxyreactor). In principle, the concept of oxydehydrogenation has already been commercially proven for the conversion of butene-1 to butadiene ( Oxo-D process developed by Petro-Tex Corp.). Seven units were installed (five of them in the USA) between the years 1965 to 1983, with plant capacities ranging from 65,000 to 350,000 tonnes per annum of butadiene. The total installed capacity was over a million tonnes per annum. Oxidant was air.

9 4. STAR process technology 9 Figure 2: The overall block flow scheme of the STAR process for propane oxydehydrogenation HP steam Air Fuel gas 4.1 STAR catalyst The STAR catalyst is based on a zinc and calcium aluminate support that, impregnated with various metals, demonstrates excellent dehydrogenation properties with very high selectivities at near equilibrium conversion. Due to its basic nature it is also extremely stable in the presence of steam and oxygen at high temperatures. This commercially proven noble metal promoted catalyst in solid particulate form is utilised in the STAR process. 4.2 Process pressure The reaction takes place in the presence of steam, which reduces the partial pressure of the reactants. This is favourable, as the endothermic conversion of paraffin to olefin increases with decreasing partial pressures of hydrocarbons. Competing dehydrogenation technologies operate at reactor pressures slightly above atmospheric 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 and also allows to design the raw gas compressor with a suction pressure of min. 3.0 bar thus saving investment and operating costs. STAR reformer Feed preheater Raw gas compression Fuel gas O 2 /air Oxy reactor Heat recovery Gas separation Fractionation Olefin product Hydrocarbon feed Boiler feed water Hydrocarbon recycle Process condensate Process steam 4.3 Operation cycle During normal operation a minor amount of coke is deposited on the catalyst which requires frequent regeneration of the catalyst. Steam present in the system converts most of the deposited coke to carbon dioxide. This leaves very little coke to be burnt off during the oxidative regeneration, thus allowing longer operation cycles and making the regeneration quick and simple. Also no additional treatment for coke suppression or catalyst reactivation (e.g. sulfiding or chlorinating) is required. The cycle length is seven hours of normal operation followed by a regeneration period of one hour. Therefore only 14.7% additional reactor capacity is needed to account for regeneration requirements, which is the lowest of all commercial technologies.

10 Oxidant Oxidant is either air or oxygen enriched air. Use of 90% oxygen is the more economic option as it reduces the amount of nitrogen in the reactor effluent. This minimises gas volume flow to raw gas compression and gas separation which results in an appreciable reduction in operating costs. 4.6 STAR process reaction section The reaction section comprises an externally heated reactor (STAR process reformer) connected in series with an adiabatic reactor (oxyreactor). This configuration, as shown in figure 3, represents the scheme for all applications described in Section 7. Table 2: Process Parameters Feed Propane Isobutane Inlet temperature - STAR process reformer ( C) Exit temperature - STAR process reformer ( C) Exit temperature - Oxyreactor ( C) Exit pressure - Oxyreactor (bar) Steam-to-hydrocarbon ratio (St/HC) - Overall Steam-to-hydrocarbon ratio (St/HC) STAR process reformer Oxygen/Hydrocarbon ratio (molar) to Space-Time-Yield STAR process oxydehydrogenation operates at a high Liquid Hourly Space Velocity (LHSV) of 6 compared to 4 in conventional STAR process dehydrogenation. LHSV represents the ratio of total hydrocarbon feed liquid volume flow at 15.6 C (60 F) per volume of catalyst. In spite of increased space velocity oxydehydrogenation substantially increases the olefin yield in the reaction section. The result is a high spacetime-yield, the impact of which (in comparison with conventional dehydrogenation) is summarised below: Reformer tubes are shorter in oxydehydrogenation due to increased space velocity. The required amount of catalyst for oxydehydrogenation is reduced by more than 35%. The externally heated reactor (i.e. top-fired STAR process reformer) contains only 80% of the catalyst required. The oxyreactors are filled with the other 20% of the catalyst. In other words, the size of the STAR process reformer in oxydehydrogenation is considerably smaller. The amount of catalyst in the reformer tubes is reduced by more than 50% and number of tubes is reduced by approx. 33%. The higher yield reduces the dry gas flow to the raw gas compressor and to the downstream units handling the product work up. As a consequence of these advantages, the investment as well as the utility consumption are less. 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 oxyreactors are filled with the STAR catalyst, where the conversion of paraffin takes place. Oxidant is air or 90% oxygen. Feed to the oxyreactor is cooled by condensate and steam injection, which also adjusts the steam-to-hydrocarbon (St/HC) ratio required in the oxyreactor. Cooling of feed to the oxyreactors is adjusted to set the amount of oxygen that matches the requirement 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 recovered and 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 11 Figure 3: STAR process reformer connected in series with the oxyreactor 4.8 Gas separation and fractionation A steady continuous feed to the fractionation at a constant composition is important to ensure the product quality. The gas separation is designed to 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 minor amounts of ethane are also removed. Olefin losses are very low. Olefin recovery in the product is 99.5% of the olefin produced in the reactor. No gas phase is admitted to the fractionation. The entire fractionation feed is liquid, which is collected in an intermediate storage vessel, from where it is continuously fed to the distillation 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 the fractionation. The removal of hydrogen, nitrogen and a substantial amount of methane in the cold box reduces the amount of these components in the light ends. This increases the dew point of the tail gas for a given pressure. As a result, the required temperature level of the refrigerant is also relatively higher, which in turn reduces compression costs.

12 12 Inlet manifold Furnace bottom Catalyst grid Bellow Burners Gas conducting tube Reformer tubes Shop weld Field weld Carbon steel Refractory Outlet manifold Figure 4: Reformer tube-to-manifold connection Figure 5: Furnace box of top-fired Uhde STAR process reformer Cold outlet manifold system

13 5. Proprietary equipment STAR process reformer STAR process reformer is an industrially well known and commercially established top fired Steam Reformer, which is a tubular fixed bed type and hence will not suffer catalyst losses due to attrition. The arrangement of this equipment is shown in figure 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 since 1966 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 uniform temperature profile with a steady increase of temperature in the catalyst bed, thus efficiently utilising the activity of the catalyst. Uhde reformers demonstrate a very high availability of five years of operation between maintenance shut downs. Temperature [ C] Application Pressure [bar abs] Temperature [ C] Ammonia Methanol Hydrogen Oxogas Olefins (STAR process ) Heated Length [%] Catalyst bed temperature Tube wall temperature Table 3: Industrial applications of steam reformers Figure 6: Temperature profile of the reformer tubes

14 STAR process oxyreactor The adiabatic oxyreactor is a refractory lined vessel, which means that no metallic surfaces are exposed to the reaction zone. The design of this equipment, as shown in figure 7, is virtually the same as the Uhde secondary reformer, which is used in ammonia plants. The only difference is the kind of distribution of the oxidant. Air or oxygen-enriched air diluted with steam is distributed so as to allow the oxygen to come into contact with the process medium at the top of the catalyst bed. Compared to ammonia plants, the operating conditions in oxydehydrogenation are a lot milder (refer to table 4). Service Ammonia Olefins (STAR process ) Operating pressure (bar abs.) 38 max. 6 Operating temperature ( C) 970 max. 600 Table 4: Comparison of operating conditions of the secondary reformer for production of synthesis gas for ammonia and of the STAR process oxyreactor for dehydrogenation Uhde s answer to a safe and reliable design is highlighted by the following features: Reactor effluent from STAR process reformer enters the STAR process oxyreactor at the bottom and passes into one centrally arranged tube, which conducts the gas to the top. This eliminates troublesome external hot piping to the head of the reactor. Process gas is discharged from the central tube into the dome for reversal of the flow direction. Air or oxygen is admitted to the system and uniformly distributed directly over the catalyst surface via a proprietary oxygen distribution system. In other words, process gas and oxygen are rapidly mixed and directly contacted with the catalyst bed to achieve high selectivities for the conversion of hydrogen with oxygen. Figure 7: STAR process oxyreactor design

15 Steam generation The process gas cooler (see figure 8) for production of 45 bar steam is a horizontal fire-tube boiler, which is a commercially proven equipment in Uhde s ammonia and hydrogen plants. Figure 8: Process gas cooler and steam drum design The major features and advantages are as follows: Simple fixed-tubesheet design. Tubesheets are thin with tubes joined to tubesheets by means of full penetration welds. No crevice corrosion. Operation on a reliable free convection flow. There are no heated dead ends on water side where debris can settle. Hot inlet chambers and tubesheets are refractory lined. Hence metal temperatures are low in this area. Low-alloy steel is used. Steam drum is mounted on top of the process gas cooler and is supported by downcomers and risers. Erection costs are low due to shop assembly. Access for maintenance and inspection is easy.

16 16 6. Comparison of dehydrogenation technologies The reaction section of the STAR process with oxydehydrogenation step offers significant advantages compared to competing technologies, which will be explained in the following. 6.1 General remarks Dehydrogenation is an endothermic equilibrium reaction. As more and more product is formed, the residence time required for production of a certain amount of product will continuously increase due to the fact that the driving force decreases. This means, as the dehydrogenation reaction progresses, the yield per time and catalyst volume (space-time-yield) will decrease. The following chapters describe the technologies available on the market. The two most expensive units within a dehydrogenation plant are the reaction section and the raw gas compression. Defining the reaction pressure will also define the required compression ratio for the raw gas compressor, which directly influences compressor operating 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 so as 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 which is lower than the inlet temperature. This system, besides a charge heater, will also require preheating of 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 the intermediate heaters. Otherwise coke deposit on catalyst will increase 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 Temperature profile Temperature [ C] Equilibrium conversion Intermediate Heaters Actual conversion Conversion [%] Catalyst bed volume [%] Figure 9: Temperature and conversion profile for adiabatic reactors

17 Parallel adiabatic reactors Such systems require multiple parallel beds, particularly for large capacities. Ensuring efficient distribution of feed is bound to limit the diameter of the reactor. Allowable pressure drop will limit the bed height as well. Extent of conversion is carried out in one bed which will also limit the space velocity. Typically, feed preheated does not supply sufficient heat for high conversion. This means that during the regeneration phase heat has to be introduced into the system which is utilised during the following reaction phase. Catalyst is used as a heat source for endothermic reaction. During reaction phase catalyst bed temperature decreases, which in turn leads to short cycle length of only 6-10 minutes. Hence several parallel beds at large capacities cannot be avoided. Space-time-yield is even lower compared to adiabatic systems connected in series. For world scale plants a large number of reactors in parallel is required. Only few of them are used at the same time for dehydrogenation. 6.4 STAR process with oxydehydrogenation step This configuration of an externally heated tubular reactor (STAR process reformer) followed by an air or oxygen operated adiabatic reactor (oxyreactor) combines the advantages of both reactor 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. Typical space time yield (kg product/kg catalyst hour) Typical compression ratio 6-10 Required number of reactor systems for world-scale plants for propylene production (450,000 tonnes per annum) 2 Reformer Oxyreactor t0 Addition of oxygen Temperature [ C] t1 t2 t3 t Catalyst bed volume [%] Figure 10: Temperatures in the catalyst bed for different times (t0-t4) Temperature [ C] Equilibrium conversion Temperature profile Actual conversion Catalyst bed volume [%] Figure 11: Temperature and conversion profile for an externally heated tubular reactor followed by an adiabatic oxyreactor (STAR process with oxydehydrogenation step) Conversion [%]

18 18 7. Application of the STAR process 7.1 Oxydehydrogenation of propane to propylene Propylene is a base petrochemical used for the production 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 can supply complete process routes to propylene derivatives, e.g. PP or PO, based on on-purpose propylene production from propane within a single-point repsonsibility. Process economics for a production complex, e.g. of PP from propane by PDH (STAR process ) and subsequent polymerisation are very favourable. Hydrogen produced by dehydrogenation can be purified and used as feedstock for subsequent plants (e.g. for H 2 O 2 production in connection with the Evonik-Uhde HPPO process) minimising raw material costs. 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. Designation Unit for specific Relative consumption consumption per tonne of product Propane feed t/t product HP Steam t/t product 2.2 Cooling water m 3 /t product 165 Fuel gas GJ/t product 2.01 Electrical energy kwh/t product 85 Table 5: Typical consumption figures for propane oxydehydrogenation Contaminants regarding the feed to a subsequent plant (CO, CO 2 and sulphur components) are efficiently removed in the STAR process. Thus, a Selective Hydrogenation Unit (SHU) or guard beds for removal of trace components are in most of the cases not required. Additionally, recycle streams from the PP plant can be purified with 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 in figure 2, page 9. Typical consumption figures summarised below are based per tonne of polymer-grade propylene produced.

19 Oxydehydrogenation of butanes Dehydrogenation of isobutane to isobutene for the production of MTBE is a commercially well established process route. MTBE is phased out in the USA. However, it is not clear, whether this will apply to other regions as well. Other options for octane boosting are alkylate and dimers. Dehydrogenation of butanes to butenes can also be utilised for the production of alkylate or dimers, which are used as blending stock to enhance the quality of unleaded gasoline to premium grade Oxydehydrogenation for the production of alkylate Both HF and H 2 SO 4 alkylation are mature and efficient technologies for the production of C 7 and C 8 alkylate from propene and butenes. C 8 alkylate has higher octane numbers than C 7 alkylate. The Research Octane Number (RON) of the alkylate produced will depend on the type of olefin as well as the process applied (refer to table 6). It is worthwhile to limit isobutene when the alkylation process is based on H 2 SO 4, whereas preferable feed components for HF alkylation are butene-2 and isobutene. Plant configuration will depend on the alkylation scheme selected. For alkylation based on H 2 SO 4 the preferred plant feed is mixed butanes. The process steps are as follows: STAR process oxydehydrogenation Butenex Selective hydrogenation H 2 SO 4 alkylation Butenex, a technology licensed by Uhde, is an extractive distillation process. C 4 fraction from STAR is separated into butenes and butanes. Solvent is a mixture of N-formylmorpholine (NFM) and morpholine. NFM is a commercially well established solvent known from its application in Uhde s Morphylane process for the extractive distillation of aromatics. To date two commercial Butenex units have been successfully designed and commissioned by Uhde. Table 6: RON of alkylate depending on alkylation technology and olefin Alkylate RON Alkylate from HF alkylation H 2 SO 4 alkylation Butene Butene Isobutene Fuel gas Hydrogen Figure 12: Alkylate from mixed butanes Mixed butanes STAR process Butenex Selective hydrogenation H 2 SO 4 alkylation C 8 alkylate N-butane recycle Isobutane

20 20 Depending on the content of isobutane in mixed butanes feed, the STAR process unit could be conceived to include a deisobutaniser column so as to separate isobutane from n-butane in the mixed butanes feed. N-butane is recycled from the Butenex unit to the STAR process unit. Butadiene in the unsaturated C 4 stream (extract) from Butenex is selectively hydrogenated to butene-1. The selectively hydrogenated stream is the olefin feed to alkylation. Figure 13: Alkylate from isobutane Fuel gas Isobutane STAR process HF alkylation C 8 alkylate It seems to be advantageous to process isobutane (instead of mixed butanes), if the selected scheme is HF alkylation. The reasons are: RON of C 8 alkylate derived from isobutene is high (95). For a given conversion the selectivity of isobutene (from isobutane) is higher than that of n-butenes (from n-butane). In other words plant feed is less by 6%. Selective hydrogenation of butadiene will not be required. STAR process unit can be designed to provide an isobutane/isobutene mixture in the desired stochiometric ratio for the alkylation. In other words recycle of unconverted paraffin to the STAR process unit will not be required. This in turn will eliminate the requirement of a Butenex unit.

21 Oxydehydrogenation for the production of dimers Amount and quality (RON) of gasoline produced will depend on the process option whether isobutene is selectively dimerised or whether all butenes present in the feed are dimerised. Furthermore when processing mixed butenes, the concentration of isobutene in mixed butenes will also influence the quality of gasoline. Dimerisation of mixed butenes will result in a liquid product of which max. 80% is gasoline and 20% is jet fuel. Liquid product yield will be around 95-98% of butenes present in feed. Octane rating will increase as the concentration of isobutene in feed increases. Isobutene concentration of about 50% (in total butenes) will be required to obtain unleaded premium gasoline (RON 95) quality. Selective dimerisation of isobutene (in the mixed butenes feed) will result in a liquid product which will primarily consist of high octane gasoline (RON 99) and a minor amount (4% of liquid product) of jet fuel. However, liquid product yield is low. Whereas isobutene is virtually completely dimerised the conversion of n-butenes will be only in the order of 50%. Isobutene will be completely converted to high octane gasoline (RON 99). The process configuration (Figure 14) consists of the following process steps: STAR process oxydehydrogenation Selective hydrogenation of butadiene Dimerisation unit (incl. product hydrogenation) Selective hydrogenation of butadiene is only required if plant feed consists of mixed butanes. Hydrogen required for selective hydrogenation of feed to dimerisation and for product hydrogenation will be supplied from the STAR process. The utility system of the dimerisation and hydrogenation units is integrated with the STAR process unit to enhance process economy. Unconverted butanes are recycled from the dimerisation unit to the STAR process unit. Figure 14: Dimers from butane Fresh feed (mixed butanes or isobutane) STAR process Hydrogen Selective hydrogenation Dimerisation Fuel gas Gasoline Jet fuel Butanes recycle

22 22 Inside view of the furnace box of an Uhde steam reformer

23 8. Services for our customers 23 We promote active communication by organising and supporting technical symposia. Uhde is dedicated to providing its customers with a wide range of services and to supporting them in their efforts to succeed in their line of business. With our worldwide network of subsidiaries, associated companies and experienced local representatives, as well as first-class backing from our head office, Uhde has the ideal qualifications to achieve this goal. We at Uhde place particular importance on interacting with our customers at an early stage to combine their ambition and expertise with our experience. Whenever we can, we give potential customers the opportunity to visit operating plants and to personally evaluate such matters as process operability, maintenance and on-stream time. We aim to build our future business on the confidence our customers place in us. Uhde provides the entire spectrum of services associated with an EPC contractor, from the initial feasibility study, through financing concepts and project management right up to the commissioning 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 intimate knowledge of local laws, regulations and tax 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 its subsidiaries is to ensure utmost quality in the implementation of our projects. Our head office and subsidiaries worldwide work to the same quality standard, certified according to: DIN/ISO 9001/EN We remain in contact with our customers even after project completion. Partnering is our byword. By organising and supporting technical symposia, we promote active communication between customers, licensors, partners, operators and our specialists. This enables our customers to benefit from the development of new technologies and the exchange of experience as well as troubleshooting information. We like to cultivate our business relationships and learn more about the future goals of our customers. Our after-sales services include regular consultancy visits which keep the owner informed about the latest developments or revamping options. Uhde stands for tailor-made concepts and international competence. For more information contact one of the Uhde offices near you or visit our website: Further information on this subject can be found in the following brochures: Ammonia Organic chemicals and polymers Propylene oxide

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