C5 C6 fractions isomerization isomalk 2

Pentane-hexane fractions isomerization technology Isomalk-2 is a unique Russian development in the sphere of light naphtha isomerization. The technology efficiency is proved on 10 commercial units. The process was first implemented in 2003 on a converted reforming unit at JSC Ufaneftekhim. Designing and construction of Isomalk-2 units in Russia and other countries are in progress.

Isomalk-2 technology reference list

Specific feature of the technology is application of SI-2 catalyst, which ensures process behavior in low temperature area of 120-180°C, which is thermodynamically favorable for isomerization of paraffin hydrocarbons, and possesses increased tolerance to catalytic poisons  — water, sulfur, nitrogen.

SI-2 catalyst restores its activity in short-term water skip-ups up to 100 ppm and sulfur up to 5 ppm.

Isomerization technology-1

Concerning the basic specifications of SI-2 catalyst, Isomalk-2 technology involves pre-treatment of feed, but unlike chlorinated catalysts, it does not require special adsorptive treatment of hydrogenate to remove sulfur, nitrogen, and water impurities. Necessary requirements of impurities content are met by simple hydrotreatment and stripping of unstable hydrogenate. Reactor section of Isomalk-2 involves one or two reactors with cooling the reactor effluent in a heat exchanger. If one reactor is used, cool hydrogen gas quench is necessary at the second catalyst bed inlet.

Necessity of cooling the reactor effluent is not so much due to exothermic nature of isomerization reactions, but rather because of significant exothermicity of benzene saturation in feed.  Therefore, unit process flow diagram depends on feed composition. Isomalk-2 technology allows processing pentane-hexane fractions, containing considerable amounts of benzene (up to 5-8%) and C7 hydrocarbons – up to 10%. However, specific process solutions are to be applied in such cases.

Specific features of isomerization catalyst SI-2 are the following:

  • Isomerization activity of SI-2 catalyst is much higher than that of zeolite catalysts and is as good as that of chlorinated ones;
  • SI-2 catalyst is tolerant to catalytic poisons, the catalyst restores its activity even after short-time water skip-ups up to 100 ppm and sulfur skip-ups up to 5 ppm;
  • Supply of acid reactants is not required and thus there is no off gas alkalization block;
  • High yield of commercial isomerate – 97-99%;
  • SI-2 catalyst service life is 10-12 years.


Octane number of Isomalk-2 isocomponent product is mainly defined by selection of process scheme.

Isomalk-2 isomerization process flow diagrams (PFD) for all process options are represented below.

1. Isomalk-2 PFD – ONCE-THROUGH is notable for the least capital and operating costs. This scheme makes it possible to produce isocomponent with RON 81 – 85, depending on feed composition, and yield of at least 98 wt. %.

Isomerization technology

Isomalk-2 “once-through” process was implemented on 3 commercial units: JSC Ufaneftekhim (from 2003 till 2008), JSC Ryazan Oil Refining Company and KINEF Ltd. (from 2005 till present time).

2. Isomalk-2 PFD – N-PENTANE RECYCLE (DIP+DP) is used for feed containing 50-70% of pentanes. Due to n-pentane recycle, the octane number of the isocomponent can be raised up to 86-88 RON, the isocomponent yield is not less than 98 wt. %.The scheme makes it possible to separate isopentane cut in the amount, which corresponds to pentanes content in isomerization unit feed.

Isomalk-2 process with n-pentane recycle was implemented in PJSC LINIK (Ukraine) and operated at gasoline isocomponent production mode since 2005 till 2011, when the unit was further equipped with deisohexanization column.

3. Isomalk-2 PFD – RECYCLE OF LOW-BRANCHED HEXANES (DIH) allows increasing octane number of the produced isocomponent due to recycle of low-branched hexanes back to reactor section feed. In comparison with "once-through-run" scheme, this scheme includes additional deisohexanization column (DIH) and provides isocomponent with 87-88 RON. Installation of Deisohexanizer is optimum technical solution for processing of feed, containing 50-70% of hexanes and with high content С7+ hydrocarbons and benzene.

Isomerization technology-3

Isomalk-2 technology with recycle hexanes scheme has been applied in JSC Ufaneftekhim (2008-2012), JSC Ufa Refinery (since 2008 till present time), JSC NOVOIL (since 2009 till present time). This scheme was also selected for implementation on former reforming unit of LUKOIL-Volgogradneftepererabotka, Ltd. (designing is in progress) and small scale refineries JSC Rosneft-Purneftepererabotka and TPP Kogalymneftegaz JSC LUKOIL-West Siberia.

4. Isomalk-2 PFD - FEED DEISOPENTANIZATION AND LOW-BRANCHED HEXANES RECYCLE (DIP+DIH). Further equipping of isomerization unit scheme with feed deisopentanization (DIP) column allows decreasing load on reactor section and increasing pentane isomerization depth. This option is considered to be one of the most optimal technical solutions.

This scheme is applied at PJSC LINIK (since 2011), S.C. Petrotel-Lukoil S.A. (since 2006), JSC Slavneft-YANOS (since 2011), large scale unit construction is coming to an end in JSC Ryazan Oil Refining Company.

5. Isomalk-2 PFD - N-PENTANE AND LOW-BRANCHED HEXANES RECYCLE (DIP+DP+DIH) allows maximum usage of Isomalk-2 technology capabilities in pentane-hexane fractions isomerization. Isocomponent octane number (91-92) is achieved due to n-pentane and hexanes recycle. In spite of high capital and operating costs, implementation of naphtha isomerization technology under this scheme has become an optimal option for refineries in Omsk and Saratov in conditions of necessity of motor gasoline production meeting Euro-3 and Euro-4 standards.


allows decreasing capital and operating costs due to stable isomerate separation in one column instead of two. Isocomponent octane number achieves 90.5-91.5 RON. Besides, this scheme saves space occupied by the unit.




L-35-5/300 reforming unit conversion to Isomalk-2 isomerization process

The unit at JSC Ufaneftekhim is the first commercial unit where Isomalk-2 technology for C5-C6 fractions isomerization process was introduced. The unit was commissioned in October, 2003.

Initially L-35-5 reforming unit was converted for isomerization process under “once-through" scheme with pre-hydrotreatment on the unit L-24/300-1. Due to high space velocity (3.5-4.0 h-1) this unit produced isomerate with 79-80 RON and has 300 KTA capacity.

Conversion included re-piping of isomerization feed furnace; “quench” line installation, inclusion of recycle hydrogen gas drying section with NaA adsorbent (consists of two drying adsorbers and furnace for adsorbent regeneration), SI-2 catalyst loading into 2 reactors.

In June, 2008 the unit was revamped to increase feed capacity and to convert to scheme with unreacted hexanes recycle.

In August, 2011 SI-2 catalyst was regenerated and additional quantity of fresh catalyst (6.5 tons) was loaded to reactor R-3.

In December, 2012 the unit was revamped, including additional equipping with deisopentanization section for separation of isopentane fraction (as an overhead product) and pentane fraction (as a side cut), and construction of new furnace F-1 with one pass heating before reactor R-1.

2012 revamp allowed increasing the unit product octane number up to 90-91 RON at space velocity of 2.4-2.8 h-1 and increasing the capacity up to 500 KTA.



The unit conversion from SI-1 zeolite catalyst to SI-2 oxide catalyst

In 1999 JSC Ryazan Oil Refining Company commissioned the first isomerization unit under Russian technology called Isomalk-1. “Detol” isomerization unit was operated over SI-1 zeolite catalyst.

In August, 2005 the unit was converted to Isomalk-2 technology over SI-2 oxide catalyst. The revamp involved replacement of zeolite catalyst by low-temperature oxide SI-2 catalyst, implementation of scheme with make-up hydrogen gas supply through dryer, “quench” line installation, re-piping of the dryer from compressors discharge to suction, and construction of new hydrotreatment section for feed pre-hydrotreating.

First catalyst regeneration was made in 2009. Current service cycle is 4 years. The unit produces 400 KTA of isomerate.

The conversion of isomerization unit to SI-2 catalyst allowed decreasing the process temperature up to 130-140 °С and achieving isomerate octane number up to 83 RON that is 6 numbers higher than zeolite catalyst performances.



Conversion of L-35-11/300 reforming unit to Isomalk-2 technology under “once-through” scheme

In 2005 L-35 -11/300 reforming unit, operated earlier over isoselectoforming technology, was converted to “once-through” low-temperature isomerization process using SI-2 oxide catalyst. Unit revamp included F-1 furnace and reactors re-piping; additional equipping of operating F-1 furnace sections with pilot burners, having flame alarms; hydrogen gas supply line installation to reactors inlet; additional cooler installation on hydrogen gas supply line to reactors; stripper reflux drum replacement, and re-piping of drying adsorbers.

In 2008 the unit revamp was performed that involved regeneration of KGM-70 hydrotreating catalyst and equipment replacement in hydrotreatment section because of physical depreciation.

In 2012 the unit turnaround was performed without SI-2 catalyst regeneration.

The conversion of isomerization unit to SI-2 catalyst allowed increasing the isomerate octane number by 7-8 numbers that significantly enhanced operating efficiency of KINEF, LTD.

From the time of the unit start-up in October, 2005 until the present time SI-2 catalyst has not been regenerated, and RON of produced isomerate keeps the level of 82-83 (at the start of run RON is 83-84), the capacity is 500 KTA.



Unit conversion from LPI-100 catalyst to SI-2 catalyst

In December, 2006 pentane-hexane fractions isomerization unit, operating before under Parisom technology over LPI-100 catalyst, was reloaded to SI-2 catalyst without revamp. The catalyst was replaced in two reactors; space velocity in reactor section was 2 h-1.

The unit operates under Isomalk-2 technology with feed deisopentanization and low-branched hexanes recycle. The unit capacity is 180 KTA. RON of isopenatane fraction is 93, RON of isomerate is 86-87.

In February, 2013 the unit was shut down for turnaround with isomerization reactors replacement, therefore the catalyst was regenerated. 6 years and 2 months had passed since the time of the start-up until the first regeneration.

The unit conversion to Isomalk-2 technology allowed increasing the octane number of isocomponents mixed fraction by 3-4 numbers and proved high activity of SI-2 catalyst in comparison with analogue oxide catalysts.



Light naphtha isomerization2Isomerization unit conversion from zeolite catalyst to SI-2 catalyst

Isomerization unit at Novo-Ufimsky Refinery is represented by section 300 of L-35-11-1000 unit, converted to isomerization process in 1997.

Initially the unit was commissioned under “once-through” scheme, and isomerization process was performed over zeolite catalyst. Hydrotreatment was performed at section 100 (feed treatment section of L-35-11-1000 unit).

At the first stage the revamp came down to re-piping and reloading the reactor section. Subsequently the unit has been equipped with deisohexanization column.

In February, 2009 the isomerization unit was converted to Isomalk-2 with low-branched hexanes recycle (DIH).

The revamp included replacement of zeolite catalyst by low-temperature oxide catalyst SI-2, inclusion H2 gas recycle drying section into the scheme, installation of reactor section emergency blow-down scheme, and replacement of isomerization reactors internals.

In November, 2012 revamp was performed, that involved internals replacement in hydrotreating section stripper and isomerization and reforming feed treatment column, as well as deisopentanization (DIP) section installation at absorbing gas fractionating unit AGFU-1.

The unit conversion to SI-2 catalyst allowed producing the isomerate octane number of 87-88 RON which is 7-8 numbers higher than that of zeolite catalyst.



Light naphtha isomerizationReforming unit revamp

In December, 2011 JSC SIE Neftehim developed Design Basis (Process Design Regulations) for conversion of L-35-11/300/400-95N catalytic reforming unit at Lukoil-Volgogradneftepererabotka Ltd. to light naphtha isomerization process. It is under design now.

The isomerization unit will include feed pre-hydroteatment section, and Isomalk-2 isomerization section with low-branched hexanes recycle.

In the process of unit revamp the maximal using of existing equipment is provided.

The isomerization section feed will be IBP-75°С fraction with C7+ hydrocarbons content up to 3.0 wt. % and benzene up to 1.5 wt. %. This fraction is produced at gasoline re-distillation unit No.7 and Crude Desaulter/CDU-1 (after construction completing).

After revamp guaranteed isocomponent octane number will be 86-88 RON at space velocity of 2.5 h-1 and with yield of not less than 96 wt. %. The unit capacity is 300 KTA.




New isomerization unit under scheme with feed deisopentanization, pentanes and low-branched hexanes recycle has been designed under license of JSC SIE Neftehim. It is the largest isomerization unit under Isomalk-2 technology. It is the first national unit that was designed and constructed according to the Russian technology from start to finish.

JSC SIE Neftehim provided Engineering Design Basis for the unit in 2007.

Designing and engineering documentation was elaborated by JSC Neftechimproekt, Saint-Petersburg, under the supervision of JSC SIE Neftehim.

General design contractor is JSC OMSKNEFTECHIMPROEKT.

The unit engineering and construction were performed in a uniquely short period - 3 years. This became possible because engineering documentation elaboration and procurement of long-lead equipment were carried out as early as during designing stage. Moreover, design engineering was not suspended even under complex economical circumstances in the country.

800 KTA capacity unit start-up took place in November, 2010.

Isomalk-2 unit at Omsk Refinery allows producing isopentane fraction with octane number of 92-93 numbers and light isohexane fraction with octane number up to 92.5 RON.



The new isomerization unit with throughput of 720 KTA besides isomerization section includes feed pretreatment and pentane-hexane fraction prehydrotreatment sections. Naphtha isomerization is performed under feed deisopentanization and low-branched hexanes recycle process scheme.

The unit was designed by JSC Neftechimproekt, Russia, Saint- Petersburg.

Design Basis was provided by JSC SIE Neftehim in 2007.

The fist construction stage had been finished by 2009.

Author supervision was carried out, FEED and Detailed Engineering Documentation for equipment, as well as process regulations were approved. Equipment procurement and the unit construction had been completed by August, 2011.

The long terms of the unit construction were conditioned with construction suspension due to complex economic situation.

Start-up was performed in October, 2011.

The unit produces hexane isocomponent with octane number of 89-89.5 and isopentane fraction with 92-93 RON.



In view of the necessity to bring commercial motor gasolines quality into compliance with Euro-4 the refinery management made a decision to introduce isomerization process. Feed of the isomerization unit hydrotreatment section is straight-run fraction IBP-70°С from gasoline re-destillation section at Crude Desalter-CDU.

Design Basis was developed by JSC SIE Neftehim in March, 2008.

In 2008 JSC NEFTECHIMPROEKT carried out FEED stage.

The whole engineering process was carried out under strict control of the Licensor.

Start-up of the unit was conducted in March, 2013.

Feed unit capacity is 300 KTA. Isomerization process proceeds under the scheme with feed deisopentanization, n-pentane and low-branched hexanes recycle. The unit produces isocomponent with octane number of 91.5-92.5.