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Production of unleaded Gasoline in Riyadh Oil Refinery

Conference Paper · September 2001

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 Production of unleaded Gasoline in Riyadh Oil Refinery

Prof. Ibrahim S. Al-Mutaz and Riyadh N. Furiji

Chemical Eng. Department, College of Engineering, King Saud University
P.O. Box 800, Riyadh 11421, Saudi Arabia
e-mail : almutaz@ksu.edu.sa
presented at 6th World Congress of Chemical Engineering, Melbourne,
Australia, September 23-27, 2001.

ABSTRACT:

Due to the health consequences of lead exposure and the wide use of catalytic
converters many countries were forced to reduce the lead content in the gasoline
toward the complete elimination of lead additives in motor gasoline. Leaded gasoline
is a major source of human lead exposure. By reducing gasoline lead content,
airborne lead emissions and blood lead levels can be reduced. Evidently, lead is
considered as a harmful pollutant.

A growing number of countries have seen a successful transition to unleaded

gasoline. In the United States, lead was completely eliminated from all US motor
gasoline since 1990.Almost all Western European countries had reduced the lead
contents in gasoline to 0.4 gm/liter since 1986. A further reduction to 0.15 gm/liter
was planned. In Japan about 96% of the gasoline pool is already lead-free.

There are some operational changes that can be done for immediate reduction of lead
concentration of gasoline. These changes require no capital investment. For further
reduction of lead, installations of new refinery units and/or modifications of the
existing ones are required. In this paper, the production of lead-free gasoline from
Riyadh oil refinery will be discussed. Operational changes, installation of new
processes as well as the blend of octane enhance compounds will be considered.

1. INTRODUCTION
Gasoline is a complex mixture of light hydrocarbons containing 5 to 11 carbon atoms
o o o
and having a boiling range of 15 C to 190 C (60 to 375 F). In the atmospheric
distillation, the fraction identified as light naphtha, medium naphtha and heavy
naphtha are the potential components of gasoline. The clear research octane number,
RON, of these components varies from 60 to 70 for light naphtha and 40 to 60 for
medium and heavy naphtha. So they are not used directly as gasoline, since the RON
requirements of gasoline are 90 to 98. To meet the gasoline octane requirements,
portion of the recovered naphtha should be upgraded. Usually a catalytic reformer is
used for this purpose, where a higher octane components such as isoparaffines and
aromatics are formed. Lead compounds, mainly tetra ethyl lead, TEL, are then added
to enhance the octane number of the gasoline. As high as 0.84 gm/liter of TEL is
added to the gasoline. About 47% of the atmospheric lead is caused by the gasoline
additives and gasoline combustion accounts for about 95% as the source of lead
emissions.
Most countries have taken serious actions to reduce the lead content of gasoline or to
switch completely to unleaded gasoline. By reducing gasoline lead content, airborne
lead emissions can be reduced. Evidently, lead is considered as a harmful pollutant.
Its concentration in the populated cities at high traffic locations reached the threshold
level which can cause bad health effects. The reduction of lead in the gasoline is
desirable not only because of its toxicity but also it hindered the reduction of the other
automotive pollutants, mainly hydrocarbons, carbon monoxide and nitrogen oxides
[1]. All of the automotive pollution control devices currently in use are intolerant of
lead and require lead-free gasoline.

2. RIYADH REFINERY PROCESSING FACILITIES

Riyadh refinery produces about 30% of the total domestic premium gasoline. The
average lead level of manufactured premium gasoline is nearly 0.30 grams/liter. The
major units of the refinery are platformer, vacuum distillation, hydrocracker,
hydrogen manufacture units and asphalt oxidizer as well as the light fraction
processing units.

The refinery consists of a large crude oil stabilization unit of 140,000 barrels per day
capacity and 100,000 barrels per day refining capacity. The capacity of the vacuum
distillation is 40,000 barrels per day to fractionate the atmospheric distillation residue.
The capacity of platformer is 26,000 barrels per day. The products of platformer are
demetalized and are used in gasoline blending. The major objective of demetalization
unit is to produce demetallized oil for further processing in the hydrocracker.
Platforming is the most common refinery process used to upgrade medium and heavy
naphtha.

The gas oil is produced from vacuum distillation is fed to the hydrocracker while the
vacuum residue is used in the asphalt unit. In the hydrocracker unit, an Isomax unit,
vacuum gas oil is converted to high octane C5 and C6 isomaxate which is blended
into the gasoline. The capacity of the hydrocracker unit is 27,500 barrels per day. The
hydrocracking unit produces two types of gasoline components, light and heavy
hydrocrackates. Light product is blended directly with gasoline. While heavy
hydrocrackate is upgraded in the catalytic reforming unit. There are additional
kerosene hydrotreater unit.

Table 1 shows products of the atmospheric distillation in Riyadh refinery. Fuel oil
from atmospheric distillation is sent to the vacuum tower which is operated with a
capacity of 40,000 barrels per day. Products of the vacuum unit in the refinery are
vacuum gas oil and vacuum residue. The vacuum residue is thermally cracked in
delayed coker to produce wet gases used in asphalt unit. The vacuum gas oil product
is fed to the hydrocracker unit. Table 2 shows the volume and mass flow rate of each
stream in the refinery.
Table 1 : Atmospheric Distillation of Arabian Light Crude Oil in Riyadh Refinery
_____________________________________________________________________
Products Percent Yield Flow Rate
(barrels/day)
_____________________________________________________________________
Gases (ethane, propane, butane) 1.0 1150
Light naphtha (C5-80oC) 4.5 5170
Medium naphtha (80-95oC) 1.3 1495
o
Heavy naphtha (95-175 C) 17.2 19780
o
Kerosine (175-270 C) 9.5 10925
o
Diesel/gas oil (230-370 C) 26.5 30475
Fuel oil (+370oC) 40.0 46000
Total 100.0 115000
_____________________________________________________________________

Table 2 : Volume flow rate and mass flow rate for gasoline pool in Riyadh refinery
_____________________________________________________________________
Component Volume API Sp.gr. Density of Volume Mass flow
3
component (m /hr) rate
( bbl/day) 3
(Kg/m ) (Kg/hr)
_____________________________________________________________________

H. naphtha 16,500 57.0 0.750 750 109.0 81953.70

L. naphtha 6,000 71.0 0.697 697 40.0 27695.36
Reformate 23,000 39.7 0.790 790 152.3 120331.00
H. hydrocrackate 13,500 29.1 0.762 762 89.4 68125.80
C5/C6 Isomaxate 5,000 57.0 0.697 697 33.0 23079.00
Atm.residue 46,000 44.0 0.806 806 304.0 245536.40
_____________________________________________________________________

3. GASOLINE POOL
The current gasoline pool in Riyadh refinery consists of light straight run naphtha,
light isomaxate from hydrocracking and platformate. Platforming is the most common
refinery process used to upgrade medium and heavy naphtha. Table 3 shows the yield
of platforming of medium and heavy naphtha based on 95 RON severity and Arabian
light feedstock at low pressure. However, the yield of the high octane reformate
depends on the following factors.

- Operating pressure: Low pressure improves reformate yield. Typical pressure range
are 125 to 450 psig.

- The type of catalyst used : Replacement of reformer catalyst with catalyst of greater
capacity such as R62 will cause substantial reduction in the lead level.
- The quality of naphtha : Reformate yield increases at high aromatic and naphthene
content.

- The severity of operation : Higher severity leads to higher RON of reformate but
reduces the yield.

Table 3: Products of Catalytic Reforming of Medium or Heavy Naphtha (80 - 175oC)

______________________________________________________

Products Percent yield

vol.% wt.%
______________________________________________________

Hydrogen 10.0 13.3

Refinery gas 8.0 2.9
Propane 3.0 0.6
Butanes 3.0 0.6
High octane reformate 76.0 82.6
______________________________________________________

Premium gasoline is manufactured by blending the high octane reformate together

with all the light hydrocrackate (C5/C6 Isomaxate) and the light straight run
naphtha. About 0.3 g/liter of lead is then added to increase RON to the premium
specification. Butane is also added to regulate the vapor pressure. Table 4 show the
blending stream capacity.

Table 4: Manufacture of Unleaded Gasoline in Riyadh Refinery

______________________________________________________

Stream Volume RON

(bbl/d)
______________________________________________________

Reformate 23000 97
C5/C6 Isomaxate 5000 81
LSR 6000 65
Butane 750 95

It was found by Linear programming that 26,290 barrels per day platformate (91
RON) can be blended with 4,090 barrels per day of C5/C6 isomaxate (80 RON) to
produce 30,380 barrels per day of premium gasoline (95 RON). About 13,020 barrels
per day (83.5 RON) of regular gasoline can be produced by blending 7800 barrels per
day of LSR gasoline (65 RON) and 5,220 barrels per day of platformate (91 RON).
For the production of only premium gasoline, 7,800 barrels per day of LSR gasoline
(65 RON), 31,510 barrels per day of platformate (91 RON) and 4,090 barrels per day
of C5/C6 isomaxate (80 RON) can be blended to produce 43,400 barrels per day (95
RON) of premium gasoline[2].

4. LEAD PHASE-OUT OPTIONS

Petromin announced the following Saudi plan for the lead phase-down in the domestic
refineries [3]:

-In 1987 : All domestic refineries will produce a single grade gasoline only premium
with a research octane number, RON, of 95 and with a maximum lead content of 0.60
g/liter.

-After 1995 : One grade of unleaded gasoline with 95 RON will be produced.

Due to many technical and economical reasons, these plans were not met.

4.1 Options That Involve Operational Changes

The reduction of lead content in gasoline increases octane requirements to maintain
the current production rate and quality of gasoline. The following options can be used
to deal with the octane shortage resulting from the reduction in the lead content of
gasoline[4]:
1- increase reforming severity
2- increase aromatic blending
3- increase oxygenate blending such as methyl tertiary butyl ether (MTBE).

Oxygenates (hydrocarbons containing oxygen) provide an alternative route for

increasing the octane quality of gasoline. Methanol (RON 130), ethanol (RON 129)
and methyl tertiary butyl ether (RON 117), MTBE, are examples of useable
oxygenates[5]. Methanol in gasoline blends causes some problems such as phase
separation, vapor lock and wear on engine parts. It is also a carcinogenic compound.
Ethanol has lesser problems than methanol but still has derivability, handling and
phase separation problems. Two of the Saudi Basic Industries Corporation, SABIC,
companies (Al-Razi and Ibn Sina) produce methanol with a total production of
1,280,000 and 770,000 tons/year, respectively. Ethanol is produced from one of
SABIC companies, the Saudi petrochemical company (SADAF), at a rate of 300,000
ton/year. All of the Saudi ethanol production is committed to an overseas sales
contract. MTBE due to its good properties is considered the best oxygenate for
gasoline blending [5,6]. SABIC is producing MTBE from three companies, Ibn Sina,
Ibn Zahr and SADAF, with a total production rate of 700,000, 1,200,000 and 700,000
tons/year, respectively. The blending of MTBE in Riyadh refinery coupled with
certain operational changes will be one of the possible routes toward the production of
lead-free gasoline.

The selection among these does not involve any extra capital investment. These
process options are suitable at the lead elimination stage.

The average lead level can be reduced to 0.20 g/liter by increasing the reformer
severity to maximum while producing the two grades of gasoline, regular and
premium, at the previous grade split. Further reduction in the average lead level to
0.09 g/liter can be achieved by replacement of the reformer catalyst. These
operational changes involve no investment[6,7].

4.2 Options That Involve Installation of New Processes

Isomerization, alkylation and polymerization are refinery processes that produce high
octane gasoline components. Isomerization is used to increase the octane of the light
naphtha either by a once-through operation or by recycling. For high olefinic LPG,
polymerization and alkylation can be used to produce gasoline volume and octane.
The major source of olefins in a refinery is the fluid catalytic cracking (FCC) Less
amount of olefins are produced from thermal cracking and visbreaker units. Riyadh
refinery has no FCC unit. The main purpose of the FCC is to increase the yield of
light products from vacuum gas oil. It can produce large quantities of cracker gasoline
with RON of 88 - 93.

The following are some options for immediate lead phase down in the refinery[6,7]:

1- Installation of new once-through isomerization of light naphtha and/or light

hydrocrackate.

2- Installation of new recycle isomerization of light naphtha and/or light

hydrocrackate.

3- Reformer catalyst change to a catalyst of greater stability. Replacement of catalyst

in the refinery required:

a- new naphtha hydrotreater to treat both heavy naphtha and heavy hydrocrackate.

b- Reformer modifications to lower pressure operation.

4- Extra reforming reactor to increase severity for a given cycle of time.

5- Modification of the existing three reformers to continuous operation to improve

yields and increase severity.

However, the production of unleaded gasoline in the refinery would require

installation of new equipment and/or modifications of the existing ones. All changes
are aimed to increase the clear RON of light naphtha, light isomaxate and reformate.
The following is a possible route for producing unleaded gasoline in the refinery:

a- Installation of a new 8,000 barrels per day light naphtha hydrotreater.

b- Installation of a new Penex unit (design capacity 10,000 barrels/day) to process
all of the desulphurized light naphtha plus the recycle from the molex unit.
c- Installation of a new Molex unit to process 10,000 barrels per day of Penex
effluent and to produce about 7,600 barrels per day of isomaxate from hydrocrackers
directly as gasoline blend-stock.
d- Modify the Unifiner of the new refinery to process heavy naphtha and heavy
hydrocrackate from the two refineries. The required capacity would then be 38,000
barrels per day.
e- Increase the new refinery platformer severity to 98 RON. Platforming capacity
would be changed to 20,000 barrels per day and about 14,400 barrels per day
reformate.
f- Installation of a new 18,000 barrels per day of CCR platformer to produce 13,950
barrels per day of plateformate at 102 RON. Table 5 illustrates the products of this
alternative route.

If the addition of MTBE is considered, only 2,500 barrel per day of MTBE are needed
for the production of 97 RON unleaded gasoline as shown in Table 6.

Table 5: Manufacture of Unleaded Gasoline in Riyadh Refinery

______________________________________________________
Volume Clear Octane
Stream (bbl/day) (RON)
______________________________________________________

Isomerate from Penex/Molex 7,600 90

C5/C6 isomaxate 7,410 80
Reformate 14,400 98
Reformate from CCR platformer 13,950 102
______________________________________________________
Total 43,360 95
______________________________________________________

Table 6: Manufacture of Unleaded Gasoline in Riyadh Refinery with MTBE Blending

____________________________________________________________

Stream Volume Clear octane

(bbl/day) (RON)
____________________________________________________________

Isomerate 5,000 83
Reformate 23,000 97
MTBE 2,500 130
____________________________________________________________

Total 40,500 97

5. CONCLUSIONS

Lead emissions are mostly caused by automobiles. Lead emissions have reached
dangerous levels in countries using leaded gasoline. It is required to eliminate the
lead compounds from the gasoline to achieve better control on the automotive
emissions. As a step to reach this goal, a rapid lead phase-down is required.
 Some operational changes can be made in the refinery for immediate reduction in the
lead lvel of gasoline. These changes require no extra capital investment. For further
reduction of lead, installations of new refinery units and/or modifications of the
existing ones are required. The production of unleaded gasoline in Riyadh refinery
would require improvement of the clear RON of light naphtha, light isomaxate and
reformate. However, only a once-through isomerization unit will be needed if MTBE
blending is planned.

REFERENCES
[1] I.S. Al-Mutaz, "Automotive Emission Problem in Saudi Arabia", Environment
International 13, 335, 1987.
[2] Al-Mutaz,I.S., and Al-Fariss,T.F., “Optimum Gasoline Production in Riyadh
Refinery by Linear Programming”, Oil and Gas (European Magazine) 23(2) June
1997.
[3] Petromin Report on Strategy for controlling Automotive Emissions, General
Petroleum and Mineral Organization, Petromin Services, Project Management and
Data Processing, Jeddah, August 1986.
[4] I.S. Al-Mutaz and T.F. Al-Fariss, "Impact of Lead Phasedown on Saudi
Refineries", Hydrocarbon Processing 65, 66B, 1986.
[5] I.S. Al-Mutaz, "Saudi MTBE Plant and Its Role in the Lead Phasedown in the
Country", Energy Progress 7(1), 18, 1987.
[6] Al-Mutaz,I.S., Al-Fariss,T.F., and Abdullah,A.I, “Production of Lead-Free
Gasoline From Riyadh Refinery", Transaction of Egyptian Society of Chemical
Engineers(TESCE), vol. 14,1988. (Presented at the Third Chemical Engineering
Congress, Egyptian Engineering Society, Cairo, March 19-21, 1988.)
[7] Al-Mutaz,I.S, “How to Implement a Gasoline Pool Lead Phase-out”, Hydrocarbon
Processing 75(2), 63, Feb. 1996.

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