Licensed Reforming Processes

This classification is based on the frequency and mode of regeneration. The semiregenerative requires unit shutdown for catalyst regeneration, whereas the cyclic process utilizes a swing reactor for regeneration in addition to regular inprocess reactors. The continuous process permits catalyst replacement during normal operation. Worldwide, the semiregenerative scheme dominates reforming capacity at about 57% of total capacity followed by continuous regenerative at 27% and cyclic at 11%. Table 2 presents a regional distribution of catalytic reforming capacity by process design [1]. Most grassroots reformers are currently designed with continuous catalyst regeneration. In addition, many units that were originally built as semiregenerative units have been revamped to continuous regeneration units. A list of commercial reforming processes with a summary of key process features is presented in Table 3.

Table 2 Regional Distribution of Catalytic Reforming Capacity by Process Type [1]

2.1.Semiregenerative Process

The semiregenerative process is characterized by continuous operation over long periods, with decreasing catalyst activity as a result of coke deposition. Eventually, as the reactor temperatures reach end-of-cycle levels, the reformers are shut down to regenerate the catalyst in situ. Regeneration is carried out at low pressure (approximately 8 bar) with air as the source of oxygen. The development of bimetallic and multimetallic reforming catalysts with the ability to tolerate high coke levels has allowed the semiregenerative units to operate at 14–17 bar with similar cycle lengths obtained at higher pressures. It is believed that all reforming licensors have semiregenerative process design options.

The semiregenerative process is a conventional reforming process that operates continuously over a period of typically up to one year. As the catalytic activity decreases, the yield of aromatics and the purity of the byproduct hydrogen drop because of increased hydrocracking. Semiregenerative reformers are generally built with three to four catalyst beds in series. The fourth reactor is usually added to some units to allow an increase in either severity or throughput while maintaining the same cycle length. The longer the required cycle length, the greater the required amount of catalyst. Conversion is maintained more or less constant by raising the reactor temperatures as catalyst activity declines. Sometimes, when the capacity of a semiregenerative reformer is expanded, two existing reactors are placed in parallel, and a new, usually smaller, reactor is

added. Frequently, the parallel reactors are placed in the terminal position. When evaluating unit performance, these reactors are treated as though they are a single reactor of equivalent volume.

Research octane number (RON) that can be achieved in this process is usually in the range of 85–100, depending on an optimization between feedstock quality, gasoline qualities, and quantities required as well as the operating conditions required to achieve a certain planned cycle length (6 months to 1 year). The catalyst can be regenerated in situ at the end of an operating cycle. It is not unheard of that the catalyst inventory can be regenerated 5–10 times before its activity falls below the economic minimum, whereupon it is removed and replaced. Equally likely is the intent to replace the catalyst with a newer market introduction that will offer economic advantage to the refiner.

2.2.Cyclic (Full Regeneration) Process

The cyclic process typically uses five or six fixed catalyst reactor beds, similar to the semiregenerative process, with one additional swing reactor, which is a spare reactor. It can substitute any of the regular reactors in a train while the regular reactor is being regenerated. In this way, only one reactor at a time has to be taken out of operation for regeneration, while the reforming process continues in operation. Usually, all of the reactors are the same size. In this case, the catalyst in the early stages (or front-end reactors) is less utilized; therefore, it will be regenerated at much longer intervals than the later stages. The cyclic process may be operated at low pressures, may utilize a wide boiling range feed, and may operate with a low hydrogen-to-feed ratio. Coke lay-down rates at these low pressures and high octane severity (RON of 100–104) are so high that the catalyst in individual reactors becomes exhausted in time intervals of from less than a week to a month.

The process design of the cyclic process takes advantage of low unit pressures to gain a higher C5þ reformate yield and hydrogen production. The overall catalyst activity, conversion, and hydrogen purity vary much less with time than in the semiregenerative process. However, a drawback of this process is that all reactors alternate frequently between a reducing atmosphere during normal operation and an oxidizing atmosphere during regeneration. This switching policy needs a complex process layout with high safety precautions and requires that all the reactors be of the same maximal size to make switches between them possible.

2.3.Continuous Catalyst Regeneration Process

The continuous reforming process is characterized by high catalyst activity with reduced catalyst requirements, more uniform reformate of higher aromatic

content, and high hydrogen purity. The process can achieve and surpass reforming severities as applied in the cyclic process but avoids the drawbacks of the cyclic process. The continuous process represents a step change in reforming technology compared to semiregenerative and cyclic processes. Since its introduction in the early 1970s, it has gained wide acceptance by the refining and petrochemical industries worldwide.

In this process, small quantities of catalyst are continuously withdrawn from an operating reactor, transported to a regeneration unit, regenerated, and returned to the reactor system. In the most common moving-bed design, all the reactors are stacked on top of one other. The fourth (last) reactor may be set beside the other stacked reactors. The reactor system has a common catalyst bed that moves as a column of particles from top to bottom of the reactor section. Coked catalyst is withdrawn from the last reactor and sent to the regeneration reactor, where the catalyst is regenerated on a continuous basis. However, the final step of the regeneration, i.e., reduction of the oxidized platinum multimetallic catalyst, takes place in the top of the first reactor or at the bottom of the regeneration train.

Fresh or regenerated catalyst is added to the top of the first reactor to maintain a constant quantity of catalyst in the reactor train. Catalyst transport through the reactors and the regenerator is by gravity flow, whereas the transport of catalyst from the last reactor to the top of the regenerator and back to the first reactor is by the gas lift method. Catalyst circulation rate is controlled to prevent any decline in reformate yield or hydrogen production over time onstream.

In another design, the individual reactors are placed separately, as in the semiregenerative process, with modifications for moving the catalyst from the bottom of one reactor to the top of the next reactor in line. The regenerated catalyst is added to the first reactor and the spent catalyst is withdrawn from the last reactor and transported back to the regenerator.

The continuous reforming process is capable of operation at low pressures and high severity by managing the rapid coke deposition on the catalyst at an acceptable level. Additional benefits include elimination of downtime for catalyst regeneration and steady production of hydrogen of constant purity. Operating pressures are in the 3.5- to 17-bar range and design reformate octane number is in the 95–108 range.

3MAJOR REFORMING PROCESSES

UOP and Axens are the two major licensors and catalyst suppliers for catalytic naphtha reforming. The processes differ in the type of operation (semiregenerative or continuous), catalyst type, and process engineering design. Both licensors agree on the necessity of hydrotreating the feed to remove permanent

reforming catalyst poisons and to reduce the temporary catalyst poisons to low levels. Numerous process design modifications and catalyst improvements have been made in recent years.

3.1.UOP Platforming

Platforming was the first process to use platinum-on-alumina catalysts. The first UOP semiregenerative Platforming unit went onstream in 1949. UOP technology is used in more than 50% of all reforming installations with more than 750 units in service worldwide [2]. The individual capacities of these units range from 150 to 63,000 b/d facilities.

The Platforming process has been adapted to bimetallic catalyst and to both semiregenerative and continuous operation. UOP offers semiregenerative units that use catalyst-staged loading for increased production. In particular, UOP’s R- 72 staged loading system generates the highest C5þ yields. Recently, advanced reforming catalysts were introduced, such as R-86 for semiregenerative units and R-270 for CCR applications. New catalysts are continuously aimed at maximizing hydrogen yield, increase operating flexibility and maximizing C5þ product yield.

As of September 2001, more than 170 stacked-reactor Platforming units were operating with continuous regeneration compared to 550 semiregenerative units. The total capacity of the semiregenerative units exceeded 5.0 million b/d whereas CCRTM units reached 3.8 million b/d. Table 4 presents a regional distribution of UOP Platforming units according to process design and capacity. The simultaneous use of CCR technology and bimetallic catalysts has given UOP a unique position in the field of catalytic reformer process licensing. Recent multimetallic catalyst formulations have improved both aromatic and reformate yields.

Table 4 List of Commissioned UOP Reforming Units [2]

Table 5 Relative Severities for the Semiregenerative and CCR Platforming Units [3]

One recent development in CCR technology is second-generation CCR Platforming with several modifications in the reactor and regenerator sections. The high-efficiency regenerator design resulted in an increased coke burning capacity with reduced regeneration severity and complexity. CycleMax regenerator provided easier operation and enhanced performance over other regenerator designs. The operation at ultralow pressure (3.4 bar) and the use of low-platinum R-34 catalyst ensured the highest yield of the reformate and aromatic product with more cost-effective process operation. The net gas recovery schemes maximized the yields of reformate and hydrogen. Moreover, the new regenerator allowed higher regeneration rates to support the coke generation of the low-pressure operation and high conversion levels.

RZ Platforming

The RZ Platforming process and the RZ-100 catalyst offer constant aromatics selectivity, in the range of 80% or higher. RZ-100 catalyst differs greatly from

Table 6 Typical Yields of UOP Semiregenerative and CCR Units for a Middle East Naphtha Feed [4]

cycle. The operating pressure of this process is in the range of 12–25 bar (170– 350 psig) with low-pressure drop in the hydrogen loop. The product RON-clear is in the range 90–100. Multimetallic catalyst formulations for semiregenerative applications offer higher selectivity and stability.

The decrease in the reformate yield during the run cycle of the semiregenerative version (in spite of improvement in catalyst stability) has led Axens to also develop a catalyst moving-bed system that allows continuous regeneration of the catalyst. This version, the Octanizing process, is an advanced design that reflects the results of several decades of research and development efforts. Aromizing is Axens continuous reforming process for the selective production of aromatics. It is the petrochemical complement to the Octanizing process. The technology employs an advanced catalyst formulation to achieve high BTX aromatics yield. The technology offers high aromatics yields, low investment and operating costs, and high onstream factor. Table 8 presents a summary of key features of the continuous reforming processes. The heart of the Octanizing technology differentiates itself in its catalyst circulation and continuous catalyst regeneration systems. A schematic flow diagram of the Octanizing process is presented in Figure 2 [7]. The overall process comprises the following:

A conventional reaction system consisting of a series of four radial flow reactors that use a stable and selective catalyst suitable for continuous regeneration.

A catalyst transfer system using gas lift to carry the catalyst from one

reactor to the next and finally to the regenerator.

A catalyst regeneration section, which includes a purge to remove combustible gases, followed by catalyst regeneration.

In the Octanizing or Aromizing processes, treated naphtha is mixed with recycle hydrogen, preheated, and passed through a series of adiabatic reactors

Table 8 Key Features of Octanizing and Aromizing Processes [7]

Figure 2 Schematic of Axens Octanizing and Aromizing processes.

and heaters where it is converted to rich-aromatics stream and hydrogen. The effluent is cooled by heat exchange and liquid product is separated from recycle and hydrogen gases. Axens regenerative technology has been improved to allow faster circulation of the catalyst and, as a consequence, increased regeneration frequency as required by the more severe operating conditions (low pressure, low H2-to-hydrocarbon ratio). The Octanizing process features high on-stream efficiency, flexibility, and reliability. Major improvements, compared with previous designs, are the development of catalysts of increased activity, selectivity, and hydrothermal stability along with substantial increases in the yields of C5 þ reformate and hydrogen. Table 9 presents typical yields of the Axens conventional and regenerative process. The total number of installations using the Axens technology is 90 licensed units; of these, 30 units are designed for continuous regenerative technology.

Table 9 Typical Yields of Axens Semiregenerative and Octanizing Processes for a 90–1708C Cut Light Arabian Feedstock [4]

4OTHER REFORMING PROCESSES

Several other commercial reforming processes are available for license worldwide. As with the major reforming processes, these processes differ in the type of operation (semiregenerative, continuous, or cyclic), catalyst type, and process engineering design [8]. All licensors agree on the necessity of feed hydrotreating. Licensors include Houdry Division, Chevron, Engelhard, ExxonMobil, Amoco. The following is a brief description of the processes that are listed in alphabetical order.

4.1.Houdriforming Process

The Houdriforming process is licensed by the Houdry Division of Air Products and Chemicals, Inc. The process is used to upgrade various naphthas to aviation blending stocks, aromatics, and high-octane gasoline in the range of 80–100 RON clear. The process operates in a conventional semiregenerative mode with four reactors in series for BTX production, compared with three reactors for gasoline. The catalyst used is usually Pt/Al2O3 or may be bimetallic. A small “guard case” hydrogenation pretreater can be used to prevent catalyst poisons in the naphtha feedstock from reaching the catalyst in the reforming reactors. The guard case reactor is filled with the usual reforming catalyst but operated at a lower temperature. It is constructed as an integral stage of the Houdriforming operation when required for the feedstock.

At moderate severity, the process may be operated continuously for either high-octane gasoline or aromatics, without provision for catalyst regeneration. However, operation at high severity requires frequent in situ catalyst regeneration. Typical operating conditions are temperature 755–810 K, pressure 10–27 bar, LHSV 1–4 h21, and H2/HC ratio 3–6. The total capacity of Houdriforming units is about 250,000 b/d.

4.2.Magnaforming Process

The Magnaforming process, which is licensed by Engelhard Corporation, is used to upgrade low-octane naphtha to high-octane reformate. The product is a premium blending component or aromatic hydrocarbon source. The feature that most distinguishes the Magnaforming process from other reforming processes is its use of a split hydrogen recycle stream to increase liquid yields and improve operating performance. About half of the recycled gas is compressed and recycled to the first two reactors, which are operated at mild conditions. The greater portion of the recycle gas is returned to the terminal reactors, which operate under severe conditions. It is believed that substantial compressor power saving can be achieved by splitting the recycle.

Engelhard does not offer a continuous design, but it does offer a semiregenerative design and a combination of semiregenerative and cyclic regeneration. The combination design is made by supplementing the terminal reactors with a swing reactor that can alternate with the terminal reactors. It can also operate in parallel with the terminal reactors, permitting these reactors to be regenerated without unit shutdown. Smaller Magnaforming units use a conventional three-reactor system, compared with four reactors in large units.

The process was initially designed to operate with established monometallic platinum catalysts but was adapted to include the newer platinum-rhenium-based catalyst of the E600 and E800 series. The catalysts provide greater activity and stability, enabling use in units where high-severity operation and long cycle lengths are required. A wide range of catalysts has been used in the Magnaforming process in order to optimize operating performance and to produce desired product specifications. Many units incorporate Sulfur Guard technology to reduce sulfur in reformer feed to ultralow levels. There are approximately 150 units totaling 1.8 million b/d using the Engelhard reforming technology.

4.3.Powerforming Process

Powerforming is offered by ExxonMobil to produce gasoline blending stocks from low-octane naphthas. Alternatively, the process may be operated to give high yields of benzene or other aromatics or to produce aviation blending stocks. The process also produces large quantities of hydrogen, which can be used to hydrotreat or improve other products. Powerforming features a semiregenerative or cyclic configuration and proprietary catalyst system tailored to the client’s specific needs. Advantages of Powerforming include cost-competitive installations for units less than 12,000 b/d, 98 RON products, mild severity operations, and long cycle lengths.

The staged catalyst system is represented to have a high stability, good selectivity, and adequate selectivity maintenance. It uses the high-activity KX130 catalyst with very high stability and high benzene/toluene yields. KX-130 is an appropriate debottlenecking catalyst or BTX-producing catalyst. The dualcatalyst system offers high activity catalyst, high benzene/toluene yields, and a C5þ yield advantage relative to the KX-130 catalyst system. ExxonMobil’s catalyst management techniques for hot flue gas regeneration in cyclic units, onstream chlorination, and analytical tools for monitoring catalyst help enhance the unit’s performance. Cyclic Powerformers are designed to operate at low pressure, with a wide range of feed boiling point and low hydrogen-to-feed ratio. The unit has four reactors in series plus a swing reactor. The use of the swing reactor allows any of the on-stream reactors to be taken out of service for regeneration while maintaining continuous operation of the unit. The frequency of

regeneration can be varied to meet changing process objectives as well as operating under high-severity, low-pressure conditions, since coke deposition is maintained at low levels. Regeneration is generally performed on a predetermined schedule to avoid having two or more reactors regenerated at the same time. Usually the terminal reactors are scheduled for more frequent regenerations than the early-stage reactors. Run lengths of up to 6 years between shutdowns could be achieved. Powerforming has a wide range of potential refining applications and has been commercially applied in nearly 50 semiregenerative units and more than 30 cyclic units ranging from 1000 b/d to 65,000 b/d.

4.4.Rheniforming Process

The Rheniforming process is used to convert naphthas to high-octane gasoline blendstock or aromatics plant feedstock. The process has gained wide acceptance since Chevron patented the bimetallic Pt/Re catalyst in 1968. Rheniforming is basically a semiregenerative process that comprises a sulfur sorber, three radial flow reactors in series, a separator, and a stabilizer. The process is characterized by the sulfur control step, which reduces sulfur to 0.2 ppm in the reformer feed. A new Rheniforming F/H catalyst system has been used that permits low-pressure operation. The high resistance to fouling of the catalyst system increases the yields of aromatic naphtha product and hydrogen due to the long cycle lengths, which reach 6 months or more. Optimized operating techniques permit maintenance of high catalyst activity throughout each cycle and return to fresh activity after each regeneration. The increased resistance to fouling also provides for expansion of existing plants by using higher space velocities, lower recycle ratios, or increased product octane. Converted units are operating with H2/HC ratios of 2.5–3.5 and long cycles between regeneration. It is believed that a total of 73 Rheniformers are on stream with a total capacity of more than 1 million b/d.

4.5.Ultraforming Process

The Amoco Ultraforming process is used to upgrade low-octane naphthas to high-octane blending stocks and aromatics. The process is a fixed-bed cyclic system with a swing reactor incorporated in the reaction section, which is usually specified for aromatic (BTX) production. The system can be adapted to semiregenerative operation with the conventional three radial flow reactors in series. The process uses rugged, proprietary catalysts permitting frequent regeneration and high-severity operations at low pressures. The catalyst system has relatively low precious metals content, and its estimated life is perhaps 4 years for cyclic operation vs. 8 years for semiregenerative operation. The swing reactor in cyclic operation replaces any reactor while the catalyst bed in this

reactor is being regenerated. Normally, the reactors are all the same size; however, the first reactor is loaded with half the usual amount of catalyst.

Ultraformers may be designed to produce high-purity xylenes and toluene, which can be separated by straight distillation before the extraction step. The benzene fraction can be recovered by extractive distillation. High yields of C5þ reformate and hydrogen have been reported for the Ultraforming process. The total capacity of Ultraforming is more than 530,000 b/d for 39 commercial units worldwide. However, no new Ultraformers have been licensed in recent years.

4.6.Zeoforming Process

Zeoforming process is a new reforming technology for high-octane gasoline production from hydrocarbon raw materials of various origins (straight-run naphtha fractions from both gas condensates and crude oils, condensates of accompanying gases, olefin-containing gases, secondary hydrocarbon fractions of refinery and petrochemical plants), boiling up to 200–2508C. The process has been developed by the SEC Zeosit Center of the Siberian branch of Russian Academy of Sciences. A special stable and selective IC-30 catalyst based on modified pentasil zeolite is used in the process [9].

Due to acid shape–selective mechanism possibilities for the hydrocarbon conversions in the Zeoforming process, the product gasoline has a lower aromatics content than the reformate with the same octane number. Reactions proceeding under Zeoforming process conditions allow operation to reach benzene concentration under 1 vol % and to produce gasoline with low sulfur content without naphtha hydrotreating owing to the tolerance of the catalyst to sulfur compounds in the feedstocks. The process is based on the catalytic conversion of linear paraffins and naphthenes into isoparaffins and aromatics over zeolite-containing catalysts, which allows an increase of the octane number of naphtha from 45–60 MON up to 80–85 MON.

Stepanov et al. [9] reported that a small scale plant of 120 b/d of naphtha was operated successfully in the north of Siberia, Russia in 1992. Catalyst life reached more than 1.5 years. A new industrial plant based on the Zeoforming process of 1000 b/d capacity has been operating at Glimar Refinery in Poland since 1997. Commercial products of the plant are Eurosuper-95 gasoline and liquefied gas with total product yields up to 92–95%. The first catalyst load had worked more than 1.7 years. Other units of capacities of 120–1000 b/d are under various stages of design and construction in Russia, Kirghizia, Ukraine, and Georgia.

5COMMERCIAL REFORMING CATALYSTS

Beginning in the 1950s, commercial naphtha-reforming catalysts have been essentially monometallic heterogeneous catalysts composed of a support material

(usually chlorided alumina) on which platinum metal was placed. These catalysts were capable of producing high-octane products; however, because they quickly deactivated as a result of coke formation, they required high-pressure, lower octane operations. In the early 1970s, bimetallic catalysts were introduced to meet increasing severity requirements. Platinum and another metal (often rhenium, tin, germanium, or iridium) account for most commercial bimetallic reforming catalysts. The catalyst is most often presented as 1/16-, 1/8-, or 1/4- in. Al2O3 cylindrical extrudates or spheres into which Pt and any other metal have been deposited. In commercial catalysts, platinum concentration ranges between 0.3% and 0.7% and chloride is added (0.1–1.0%) to the alumina support (h or g) to provide acidity.

At present, there are six international manufacturers of reforming catalysts producing more than 80 different types of catalysts suitable for different applications and for a variety of feedstocks. The current demand for reforming catalysts is mainly a replacement market with about 75–80% of it as bimetallics. Reforming catalyst manufacturers continue to develop new catalyst formulations designed to meet a wide array of challenges. Many of these challenges involve environmental regulations that refiners have been, and will be, required to meet during the coming years. Table 10 presents a compilation of commercial reforming catalysts that are available by sale or license to refiners [10]. The list provides information on catalyst supplier, catalyst type, and other selected catalyst properties. In addition, new catalyst introductions have been discussed in Chapter 8 of this book.

6CONCLUDING REMARKS

The refining industry worldwide has been adapting to the ongoing changes and challenges in recent years. New fuel regulations will significantly affect refinery operations. Catalytic reforming will continue to be an important process unit in refinery operations for gasoline production and to further link refining and petrochemical operations. The longer-term trend for catalytic reforming shows increased interest in the development of more selective and stable catalysts for converting naphtha into BTX aromatics and hydrogen alone.

ACKNOWLEDGMENT

The author acknowledges the support of the Research Institute at King Fahd University of Petroleum & Minerals, Dhahran, in publishing this chapter.

REFERENCES

1.Bell, L. Worldwide refining. Oil Gas J. 2001, Dec. 20, 46.

2.Godwin, G.; Moser, M.; Marr, G.; Gautam, R. In Latest Developments in CCR Platforming Catalyst Technology, 40th International Petroleum Conference, Bratislava, September 2001.

3.Dachos, N.; Kelly, A.; Felch, D.; Reis, E. UOP platforming process. In Handbook of Petroleum Refining Processes; Meyers, R. ed., McGraw-Hill: New York, 2nd ed., 1997; p. 4.3.

4.Refining Handbook 2000; Hydrocarbon Processing; November 2000; 97.

5.Clause, O.; Dupraz, C.; Frank, J. Continuing innovation in catalytic reforming. In NPRA Annual Meeting, San Antonio, Texas, March 1998.

6.Le Goff, P.; Pike, M. Increasing semi-regenerative reformer performance through catalytic solutions. In 3rd European Catalyst Technology Conference, Amsterdam, February 2002.

7.Axens process brochures for octanizing and aromizing processes, Paris, 2002.

8.Aitani, A. Catalytic reforming processes. In Catalytic Naphtha Reforming; Antos G. et al. Eds.; Marcel Dekker: New York, 1995; p. 409.

9.Stepanov, V.G.; Snytnikova, G.P.; Ione, K.G. In A New Effective Process for Motor Gasoline Production over Zeolite Catalysts, 5th European Congress on Catalysis, Limerick, September 2001.

10.Stell, J. Catalyst developments driven by clean fuel strategies. Oil Gas J. 2003, Oct. 6, 42.