Introduction

With growth and development of car industries, refining industries have been steadily under pressure of demands for better fuels.

In addition, major historic air pollution problems have typically been high levels of impurities arising from the combustion of fossil fuels.

New legislations and standards caused the refiners to look for economical solutions meeting new specifications for producing environmentally clean fuels, containing more limited harmful components such as benzene in gasoline and lower contaminants like sulfur in oil derivatives.

To improve gasoline octane number several methods, like bellows have been utilized:

• Addition of TEL
• Thermal / Catalytic reforming of naphtha
• Thermal polymerization of olefin light ends to hexenes , heptens & octenes.
• Alkylation of olefins.

With  TEL  phase out , interest  in  isomerization  of  straight  run  gasoline  heightened .Gasoline pool in a refinery may contains different constituents such as FCC naphtha , reformate, cokenaphtha, polygasoline , oxygenates, butane, light naphtha, alkylate and isomerate.

Light naphtha comprises typically 10% of the gasoline pool. This fuel cut contains mostly pentanes and hexanes.

Research octane number (RON) of light naphtha is around 70. Isomerization of this constituent can improve its octane number to about 90, so isomerate could be named as a RON booster.

C₅/C₆ Paraffin Isomerization Reactions

In the presence of proper catalyst and appropriate conditions, skeletal isomerization of normal paraffins of light naphtha take place:

C₅/C₆ Isomerization Reactions

During isomerization of normal paraffins in the reactor, some other reactions such as hydrocracking, ring opening and benzene saturation in the presence of hydrogen will take place.

1)      Hydrocracking :

2)      Ring Opening ( Hydrodecyclization ) :

3)      Benzene Saturation :

       
Most of reactions yield to higher octane number components.
 

C₅/ C₆ Isomerization Units in Iran Refineries 

Annual consumption growth rate of gasoline in Iran in recent eight years has been around 12%.

Year	1997	2005	2010
Gasoline production    (MM Liters/Day)	28	40	122
Gasoline consumption (MM Liters/Day)	33	64.5	?

Gasoline Production and Consumption in Iran (1997-2010)

The main reasons for this unprecedented growth rate are the followings:

- High population growth rate (currently near 30% of 70 million population in Iran is under 14 years  old; median age: 25)
- High economy growth rate (average 6 percent since 2000)
- Addition of new cars to the market (near 700,000 annually)
- Failure to discard old cars consuming 10-16 liters gasoline per l00 kilometers
- Non-adequately developed public transportation system
- Low gasoline price (9 cents per liter)

To meet domestic needs several options such as substitution of gasoline with compressed natural gas (CNG), more development of public transportation system, obsolete of old cars, decline of population growth rate, construction of gas condensate refineries in south pars gas field, energy price reform and also expansion and upgrading of present refineries have been under consideration.

Nine refineries are in operation in Iran. Expansion & upgrading of these refineries will raise one million barrel a day their refining capacity. Other objectives of this project are:

         1- Process improvement
         2- Capacity optimization
         3- Products upgrading
         4- Increase of lights and middle distillates and decrease of heavy derivatives
         5- Observation of new environmental requirements

National Iranian Oil Refining & Distribution Company (NIORDC) plans to raise the quality of fuels from present level to Euro 2005 standard level. This project requires twelve billion dollars investment. In the following table nominal and future refining capacities of refineries in Iran are indicated:

No.	Refinery name	Year of completion	Nominal /Current capacity (BPSD)	Total capacity  after expansion (BPSD)
1	Bandar Abbas	1996	232,000	640,000
2	Tehran	1968&1975	225,000	250,000
3	Esfahan	1980	200,000	376,000
4	Arak	1993	150,000	250,000
5	Abadan	1912	320,000	500,000
6	Tabriz	1975	100,000	165,000
7	Shiraz	1973	40,000	70,000
8	Lavan	1975	20,000	45,000
9	Kermanshah	1922	15,000	35,000
Total			1,302,000	2,331,000

Nominal and Future Capacities of Refineries in Iran

Total gasoline production is currently 40 million liters daily but 64.5 million liters a day is needed this year (2005).

Import of 24.5 million liters a day will cost 4.5 billion dollars (approx.)  in the current Iranian year (began in March 2005) while it was 3 billion dollars last year. Therefore expansion & upgrading of refineries is one of the urgent projects nowadays. With implementation of this project percent of gasoline product with respect to total products of refineries will raise from 16.43 at present to 33.3 at 2010. In the following table current and future gasoline production capacities in some refineries are shown.

           
        
Gasoline Production in Iran

To improve quality of gasoline, construction of isomerization units in six refineries has been planned.

Refinery Name	Isomerization Unit Capacity (BPSD)
Bandar Abbas	14800
Tehran	18000 (LNHDT+ISOM)
Esfahan	29500 (LNHDT +ISOM)
Arak	8500
Abadan	4000
Lavan	5000
Shiraz	5700

Anticipated Locations and Capacities of Isomerization Units in the Refineries of Iran

In 2001 Research Institute of Petroleum Industry (RIPI) started to investigate naphtha isomerization technologies in   the   world. We found   that the   catalyst of isomerization  named Hysopar, made by Sud-Chemie Company is one of the best catalysts in this field due to its advantages such as shown in the following table:

Hysopar Catalyst General Advantages

-         Medium operating temperature
-         High activity
-         Low investment & operating costs
-         No corrosion risks
-         Toleration of water (up to 100 ppmw) & sulfur (up to 100ppmw)
-         Feed pretreatment optional
-         Long service life
-         Regenerability
-         No disposal problems

After evaluation of this catalyst and its capabilities  to do isomerization  reactions, kinetic study  were carried out successfully in CATA TEST facility and all process variables in the reactor were studied and investigated completely  .

In 2003 results of this study  was patented by research institute of petroleum industry (RIPI) and national Iranian oil eng. & construction company (NIOEC) in Iran and named

ISOMIR Technology

Isomerization unit in Arak refinery is based on this technology .Basic design of this unit has been done by RIPI and approved by JGC Corporation in 2004 .Some of Arak ISOM unit specifications are presented here.

Arak ISOM Unit Specifications  

Feed Characteristics:

      Name: Hydrotreated Light Naphtha (from NHT unit)
      Flow Rate: 8500 BPSD
      Compositions (Mole%)

n-Pentane	16.74
iso-Pentane	9.82
n-Hexane	17.05
iso-Hexane	19.39
Cyclopentane	6.45
Methylcyclopentane	13.27
Cyclohexane	9.44
Benzene	5.87
C7+	1.97
Total	100.00

Specific gravity               : 0.661
Total sulfur,      ppmw     : <0.5
Total nitrogen,  ppmw     : <0.1
Pressure , barg                : 4
Temperature , ^oC            : 50 
RON                               : 73

Product Specifications: 

       Name: Isomerate
       Specific gravity                  : 0.639
       Pressure, barg                   : 6
       Temperature, ⁰C                : 40
       RON                                 : 87
       Yield, vol.%                       : 97        

In the figure below, schematic diagram of ISOM unit in Arak refinery is shown:   

Schematic diagram of ISOM unit in Arak refinery (Iran)
 

RIPI with well-experienced engineers hopes to cooperate more in expansion and upgrading projects of other refineries in Iran and intends to participate in design of naphtha isomerization units in other countries.

ISOMIR Technology Advantages

1- COMPATIBILITY WITH ENVIRONMENT
2- NO CHEMICAL INJECTION REQUIREMENT TO MAINTAIN CATALYST ACTIVITY
3- LONG CATALYST SERVICE LIFE
4- PROCESS SIMPLICITY
5- NO DISPOSAL PROBLEMS
6- HIGH CATALYST TOLERANCE TO FEED STOCK IMPURITIES
7- FEEDSTOCK PRETREATMENT OPTIONAL