FSU refiners to build more isom capacity

Feb. 12, 2007
The isomerization process is playing a significant role for refiners in the FSU as they try to maintain gasoline pool octane and comply with more stringent gasoline pool requirements.

The isomerization process is playing a significant role for refiners in the FSU as they try to maintain gasoline pool octane and comply with more stringent gasoline pool requirements. This article discusses current isomerization capacity in the FSU and refiners’ plans to build new capacity.

In the FSU, as well as globally, the requirements for motor gasoline are becoming more and more stringent. New standards exclude the use of lead; reduce levels of benzene, sulfur, unsaturated hydrocarbons, and total aromatics; include limitations on oxygenate content; reduce saturated vapor pressure; and control fraction composition.

Such trends significantly affect the methods refiners use to produce motor fuels.

Isomerization

In recent years the isomerization process has become the strategic gasoline process that ensures octane characteristics of the overall gasoline pool. Current total worldwide capacity of isomerization units amounts to about 50 million tonnes/year. During the last 20 years in Europe, isomerization capacity has increased fourfold, and now the region constitutes one-third of worldwide capacity.

Isomerization significantly improves octane number of light gasoline cuts. In combination with other processes it also allows refiners to produce a gasoline with low benzene and sulfur content. Uncertainty about future regulations on the use of methyl tertiary butyl ether necessitates use of isomerization for producing gasoline.

Pentane and hexane isomerization is widely implemented in FSU refineries because it has the advantage of minimizing investment by using idle reactors within catalytic reforming or hydrotreating units.

Main advantages of isomerization also include the availability of considerable feedstock resources, unlike alkylation and dimerization processes.

Feed to an isomerization unit is a pentane-hexane mixture that boils up to 70º C. Its content in crude is 3-5% and even higher in gas condensates. Isomerization reactions are reversible; lower temperatures in the reactor enable the formation of high-octane isomers with branched structures.

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Fig. 1 shows how MON of (equilibrium) isomerate depends on process temperature. It shows that octane numbers of paraffin C5 hydrocarbons are higher than those of C6 hydrocarbons. Conversely, isomerizing paraffin C6 hydrocarbons provides some isomers with midlevel octane numbers (2- and 3-methylphentanes).

Because commercial-scale isomerization units use pentane-hexane cuts (IBP-70º C.) as a feedstock, the equilibrium curve for C5-C6 hydrocarbons shows the best ratio for the feedstock. In practice, octane numbers of reaction products are always lower than equilibrium numbers.

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Table 1 shows that there are currently 16 commercial plants using high, middle, and low-temperature processes either operating, being designed, or under construction at refineries in the FSU.

Process catalysts

Major manufacturers of isomerization catalysts are UOP LLC, Axens, Shell Chemicals LP, Akzo Nobel NV, and Süd-Chemie AG. FSU-produced catalysts are licensed and manufactured by NPP Neftekhim, VNIINeftekhim, Olcat, Promcatalysts, and Katakhim Corp.

Zeolitic catalysts

Zeolitic isomerization catalysts are a platinum-carrying zeolite (mordenite). This catalyst does not require use of any halogen as an activator or promoter. The catalyst works at 250-270º C. and an operating pressure of 1.8-3.5 MPa.

Zeolite-based isomerization catalysts provide products with lower octane numbers than chlorinated catalysts based on alumina. Like all zeolitic catalysts, however, they feature greater resistance to the effects of sulfur, water, and nitrogen, and easily regain their activity after regeneration. The catalysts’ interregeneration service cycle is 2-3 years.

The Novokuibyshevsk refinery, the Khabarovsk refinery, and the Naftan refinery in Novopolotsk, Belarus, all use a Zeolitic catalyst, Hysopar, produced by Süd-Chemie. Its use is also planned at an isomerization unit at the Angarsk Petrochemical Plant (under design).

The only Russian zeolitic catalyst used is IPM-02 produced by VNIINeftekhim. This catalyst is used in the revamped catalytic reforming unit at the Ufa refinery.

UOP’s zeolitic catalyst type HS-10 is not used at FSU refineries and Axens’ catalyst, IP-632, is used in the isomerization section of a catalytic reforming unit at the Novoil refinery.

Chlorinated catalysts

These catalysts have the highest isomerization activity for C5 and C6 hydrocarbons, controlled by a continuous supply of organic chlorine. They also feature extremely high stability and do not need regeneration. Chlorinated catalysts are used in the UOP-designed Penex units. Typical service times are 5 years/reactor and Penex units have two reactors.

Low-temperature isomerization using alumina-based chlorinated catalysts occurs at the Komsomolsk refinery (Axens IS-614A) and the Odessa refinery (UOP Penex-DIG I-8, I-82). These types of processes will be used at units under construction at the Achinsk refinery and Volgograd refinery.

Chlorinated catalysts require specific feedstock conditions: There are limits on the amounts of water, aromatics, C7+ hydrocarbons, olefins, sulfur, and nitrogen. Chlorinated catalysts also have complex and difficult catalyst loading and unloading operations and feature considerable corrosion of equipment if abnormal operating conditions occur.

Sulfated zircon catalyst

In 1996, a new catalyst grade, LPI-100, based on sulfated zircon was introduced by UOP and sold in the US. Its activity is considerably higher than zeolite catalyst activity, which allows operating the process at 80º C. or lower and obtaining a product with two to three points higher octane number. The catalyst activity is fully recoverable with an oxidizing regeneration step similar to that used for zeolitic catalysts.

Zircon-based catalysts are suitable in operating isomerization units designed for zeolitic catalysts. The service life between regenerations is 2-3 years.

Catalyst SI-2 created by NPP Neftekhim is a Russian equivalent of zirconium-based catalysts. NPP Neftekhim started building the Isomalk-2 process in 1998-99. Manufacturing of the SI-2 catalyst based on an NPP Neftekhim license is by Promcatalysts (Ryazan) and Angarsk Catalysts and Organic Synthesis Plant. In its first commercial application, the new technology proved to be more efficient than zeolite catalysts and close to the chlorinated alumina process.

The Isomalk-2 process has been installed at these FSU refineries:

  • 2003. Revamp of a reforming unit at the Ufa refinery.
  • July 2005. Start-up of a new isomerization unit with a capacity of 250,000 tonnes/year at the Linos refinery.
  • August 2005. Conversion of an isomerization unit that used zeolitic catalyst to catalyst SI-2 at Ryazan refinery.
  • October 2005. Conversion of an isoselectoforming unit at Kirishi refinery in the St. Petersburg region.

Commercial units

Table 2 shows performance data for pentane-hexane isomerization units operated in FSU refineries. It shows that FSU refiners during 2000-05 preferred isomerization technologies based on the zeolitic catalysts Hysopar, IPM-2, and domestic zirconium based catalyst SI-2.

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Isomerization units were built in revamped catalytic reforming units in some refineries, in a hydrodealkylation unit at the Ryazan refinery, and in an ethylene production plant at the Linos refinery.

The Naftan refinery in Belarus, since the end of 2001, has operated a combined unit converted from a catalytic reformer. The unit contains these sections: hydrotreating the feed fraction (IBP-70º C.); fractionation of the hydrotreated fraction with extraction of isopentane; once-through isomerization of the de-isopentanized cut (Fig. 2).

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In 2004, a 120,000 tonne/year pentane-hexane isomerization unit was put into service at the Khabarovsk refinery. This unit is based on a technology similar to the one used at the CEPSA Algeciras refinery in Spain. This unit features isopentane withdrawal and return of a nonreacted pentane cut to the process.

A medium-temperature isomerization unit LSI-200 has been operating at the Novokuibyshevsk refinery since 2004. The process licenser is NPP Neftekhim, Krasnodar, and the engineering company is Lengiproneftekhim, St. Petersburg. The design is based on once-through process that uses a zeolitic catalyst SI-2. While developing detailed documentation, the plant management decided to shift to a proven catalyst: Hysopar T-4500 produced by Süd-Chemie.

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The Isomalk-2 process (Fig. 3) designed by NPP Neftekhim and using a sulfated zircon catalyst SI-2 has been successfully implemented at four refineries. The start-up of an isomerization unit at the Linos refinery considerably improves the ratio of high-octane and low-octane gasolines produced there. The share of AI-95 gasoline increased to 40% from 24%, and AI-92 gasoline to 45% from 35%, due to the reduced output of motor gasoline AI-80 to 14% from 40%.

In addition, analysis of isomerate composition shows that the catalyst SI-2 is considerably superior to zeolitic catalysts (octane number is five points higher) and is as efficient as chlorinated catalysts. The isomerization level of pentanes and hexanes is not reduced, while the resistance to catalyst poisons is much higher.

This low-temperature isomerization process features technological advantages. The level of pentane isomerization (Table 2) is quite high and within the range of 69.1-73.7%; hexane isomerization is within 18.9-31.4%. A maximum RON increase of up to 14 points was achieved.

An isoreforming unit has been operating at the Ufa refinery since 2003. VNIINeftekhim developed the catalyst, IMP-02. Main catalyst specifications are: platinum content of 0.38 wt %; bulk density about 0.7 g/cu cm; and an extrudate diameter of 0.3-2.1 mm. Unit capacity is 25 cu m/hr and isomerate output is 98 wt %.

Process conditions have been optimized during operations by reducting the of total hydrogen circulating gas-feedstock circulation ratio to 730-760 cu m/cu m and increasing temperature upstream of the reactor to 260-270º C.

The feed quality was very low: It contains only 22-26 wt % of n-pentanes and the end boiling point was 81-82º C. The isomerate was obtained with a MON of 76.6 and the increase accounted for 4.0-5.2 points only.

Improving the feed quality (fractional and hydrocarbon composition) as well as process stabilization enabled the operator to reach optimum performance of the zeolitic catalysts. Unit operating parameters were: feedstock fraction 28-70º C.; total content of C5s was 60-65 vol % including n-C5 of 35-39 vol %; hydrogen partial pressure was 2.1-2.2 MPa; circulation ratio was 550-650 cu m/cu m; feed space velocity was 2 hr-1; process temperature was 270º C.; and the hydrogen content in circulating gas was 80 vol % minimum. Isomerate MON is 78-79.

The first low-temperature pentane-hexane isomerization unit in Russia was commissioned in May 2002 at the Komsomolsk refinery in Far East Russia. The detailed design was from Ukrneftekhimproject, Kiev, based on the license from Axens. The unit (Table 2) operates very efficiently: Isomerate octane number is 87.2-87.9. The process efficiency is due to processing a feedstock with low hexane content.

The low-temperature isomerization process has some serious disadvantages that prevent it from wide implementation at FSU refineries. Specifically:

  • Stringent requirements on the content of sulfur, nitrogen, water, benzene, C7+ hydrocarbons, and olefins in the feedstock.
  • Constant injection of chlor-organics to maintain the catalyst activity.
  • A complex and labor-instensive system for catalyst loading and unloading, and mandatory catalyst regeneration at manufacturer’s catalyst plants.
  • Equipment corrosion.

A Penex-DIG unit with a capacity of 120,000 tonnes/year of feedstock, licensed by UOP, was commissioned in September 2004 at the Odessa refinery in Ukraine. The unit consists of two reactors loaded with catalyst I-8 and I-82 in the amount of 14.2 and 15.2 tonnes, respectively. The first year of operation had a high efficiency with a specified octane of 88.0-89.2, an increase of up to 12 points, and a high conversion of n-pentane and hexane.

Construction of UOP low-temperature isomerization units (Penex-DIG) will be commissioned at the Achinsk and Volgograd refineries by 2008.

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The light-naphtha isomerization process ParIsom (Fig. 4) is becoming popular among Russian oil companies; the main feature of the process is the catalyst LPI-100. The process features certain important advantages over isomerization based on zeolitic and chlorinated catalysts, namely:

  • There is no need for organic chemicals to be injected to maintain catalyst activity, which allows the elimination of alkaline washing and avoids problems related to use and disposal of alkali.
  • The higher activity of catalyst LPI-100 (at 80º C.) vs. zeolitic catalysts, which precludes the use of fire heating and reduces required capital investments.
  • Possible process operations using high feed space velocities, which allows a reduction in the volume of catalyst and reactor size, a high isomerate output, and better octane characteristics.
  • Low sensitivity of the catalyst to contaminants such as sulfur and water, which eliminates the need for feed dryers.
  • It is an environment friendly and waste-free process.

Currently the process is implemented at the Nizhny Novgorod refinery and construction of a process unit is planned at the Yaroslavnefteorgsyntez refinery.

The unit configuration is similar to units operating with zeolitic catalysts. This process is cost competitive and in the future it will gain a leading role at Russian refineries.

The authors

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Akop Mirimanyan is the deputy general director for JSC Petrochim Engineering, Moscow. Previously, he worked as a project engineer and chief process engineer for the State Institute for Refinery and Process Engineering (Azgiproneftekhim), Baku, during 1961-89. In 1989-93, he was deputy chief engineer for Nizhniy Novgorod and in 1994-99, he was a refining consultant for Stork Comprimo BV. Mirimanyan holds a MEng (1957) from the Azerbaijan Petroleum Institute, Baku.

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Alexey Vikhman is a general director for JSC Petrochim Engineering, Moscow, a position he has held since 1995. During 1974-95, he held positions as a junior research assistant, senior research assistant, laboratory head, and department head for VNIIneftemash. He holds a PhD in engineering from the I.M. Gubkin Moscow Oil & Gas Institute.

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Mikhail Rudin ([email protected]) is a chief technical advisor with WorleyParsons, New York City. He has worked for WorleyParsons since 2001 as an approvals manager and the Moscow Branch Manager. Before joining WorleyParsons, he worked for Lengipronftekhim, a St. Petersburg engineering company (1960-94) as a process manager and vice-president, Litwin Engineers & Constructors Inc., Raytheon Co., and Mustang Engineering Inc. Rudin has been involved in the design of downstream and upstream projects and is the author of more than 19 textbooks and reference books. He holds an MS in chemical engineering and PhD in organic chemistry from St. Petersburg Technology University.