Jones D.S.J., Pujado P.R. Handbook of Petroleum Processing
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Chapter 12
The non-energy refineries
D.S.J. Jones
Introduction
Non-energy refineries refer to those plants that produce non-energy products from
crude oil. These fall into two categories, which are:
The Lube Oil Refinery
The Petrochemical Refinery
Both of these types of refineries have already been mentioned in Chapter 1 of this
Handbook. This chapter then provides some further details on these two important
refining aspects of crude oil.
The lube oil refinery
The lube oil refinery is usually included as part of a conventional energy refinery. That
being the case this lube oil section of the process will take its feed from the atmospheric
distillation tower in the form of an atmospheric residue stream. Conventional lube
refining utilizes solvent extraction processes to separate undesirable materials from
the natural desirable ones present in the crude oil. However many of the world’s crude
oils do not have enough of these desirable molecules in them to justify the cost of
elaborate extraction processes, and therefore lube oil refining leans towards processing
the ‘desirable’lube oil crude oils. An example of desirable lube oils are those from
Venezuela (i.e., Tia Juana, and the heavy Bachequero crude). This restriction on
lube oil production often leads to large refineries dedicating a separate atmospheric
distillation unit to provide the necessary lube oil feed.
This problem of lube oil selective crude oils has diminished somewhat with the
development of heavy hydrotreating and hydrocracking for lube oil treating. These
processes virtually eliminate the need for solvent extraction and de-waxing of the
lube oil stock. Hydrotreating of light vacuum distillates to make lube oil specification
483
484 CHAPTER 12
has been in commercial use since the mid-1960s, but with the advancement of this
technology the heavier lube oil stock can also be treated now in a similar manner.
Lube base oil production by severe hydrotreating, hydrocracking, and hydro dewaxing,
also improves color and stability but each crude source of the lube oil stock requires
different processing conditions in these hydro processes. This in turn leads to different
yields of the various cuts to meet their specified viscosity.
Definitions and specifications
Lube oil refining has developed its own series of definitions quite separate to those
of the conventional energy refineries. Some of the major definitions are as follows:
r
Lube base stock
This refers to a lube product that meets all lube specifications and is suitable for
blending to meet performance specifications.
r
Lube slate
A lube slate is the set of lube base stocks produced by the refinery. This is usually
a set of 4–6 base stocks.
r
Neutral lubes
These are obtained from straight run cuts of the vacuum tower.
r
Bright stock lubes
These are processed from the raffinate of the vacuum residue de-asphalting unit.
r
Virgin base lube oils
Are those base stocks obtained by processing straight run distillates from crude.
r
Re-refined base stocks
Are those processed from used or recycled lube oils.
r
Finished lube oil
This is a lube oil that has been blended to meet a final specification.
r
Paraffinic lube oils
These are all grades of lube oils, from both neutral and bright stocks, that have a
finished viscosity index (VI) greater than 75.
r
Naphthenic lube oils
These are lubricants with a VI less than 75.
There are two important specification definitions for lube oils. These are:
r
The Quality Specification
r
The Performance Specification
The quality specification
Quality specification includes those for kinematic viscosity, viscosity index, pour
point, color, flash point. These specifications are determined by standard tests from
THE NON-ENERGY REFINERIES 485
−30 −20 −10
0 10 20 30 40 50 60 70 80 90 100 120 140 160 180 200 220 240
TEMPERATURE, DEGREES FAHBENHEIT
KINEMATIC VISCOSITY, CENTISTOKES
100,000
50,000
20,000
10,000
5,000
3,000
2,000
1,000
500
400
300
200
150
100
75
50
40
30
20
15
10
9
8
7
6
5
4
500,000
100,000
50,000
20,000
10,000
5,000
4,000
3,000
2,000
1,000
800
600
500
400
300
200
100
80
60
50
40
0 10 20 30 40 50 60 70 80 90 100 110
−30 −20 −10
TEMPERATURE CELSIUS °C
VISCOSITY SSU
20W-40
10W-30
SAE 40
SAE 50
SAE 30
SAE 20-20W
SAE 10W
SAE 5W-20
Figure 12.1. Viscosity versus temperature of crankase oil.
organizations such as ASTM, SAE, or API. The specifications generally detail the
characteristics considered important to the application of the specific lube oil. For
example one very well known motor oil specification is SAE viscosity, established by
the Society of Automotive Engineers, an organization that also carries out research,
and publishes specification on a wide range of automotive topics. Figure 12.1 gives a
range of Viscosities versus Temperature for a family of motor crankcase oils.
Although the kinematic viscosity is measured in centistokes, specifications are labeled
in Saybolt seconds (SSU).
Performance specifications
Finished lube oil products are usually certified or qualified against performance
specification requirements established by equipment and vehicle manufacturers,
government bodies, and industrial organizations such as SAE. These qualifications
usually require extensive performance testing using specialized apparatus and engines
486 CHAPTER 12
(including road tests). These tests refer only to those base oils produced in a specific
manner and from specific crudes. Significantly altering the process scheme or the
crude source could violate the intent and validity of the performance qualification
certificate.
The performance of the lube base oils in service cannot be measured until after the
production sequences are long completed. Manufacturing lube base oils therefore
requires good correlations between measured properties at each stage of production
and the final product performance quality. Developing these operating guidelines and
correlations for plant units requires pilot plant and full plant test runs for each crude
oil feedstock and finished products.
Lube oil properties
The important properties that are recognized in lube oil production are:
r
Viscosity
r
Viscosity Index
r
Pour Point
r
Oxidation Stability
r
Flash Point
r
Thermal Stability
r
Volatility
r
Color.
These are discussed in the following paragraphs.
Viscosity. This is the single most important characteristic of any lube oil. At its service
temperature it is the balance to prevent wear and to enhance fuel economy. Most
bearings operate with a hydrodynamic wedge shaped film of lubricant between the
bearing surfaces. This mechanism minimizes wear of the surfaces under the operating
conditions of the machinery. To accomplish this the lube oil must have adequate
viscosity for the operating load, bearing speed, and the bearing surface smoothness
to allow the hydrodynamic head to form and remain between the surfaces. Too high
a viscosity will cause extra friction and heat, while too low a viscosity will allow the
surfaces to touch. A bearing may operate over a wide temperature range, as in an
engine or automatic transmission, and the lube oil has to have adequate viscosity over
the entire temperature range to be effective.
Viscosity index. This is a measure of the amount the viscosity of a lube oil will
change with temperature. A high viscosity index denotes less change of viscosity
with temperature. High viscosity index is necessary for lube oils that are to be used
for services with large temperature operating range.
THE NON-ENERGY REFINERIES 487
Pour point. This property is important for any application in cold climates. Too high a
pour point will result in the oil being gelatinous or even solid at ambient temperatures.
Oxidation stability. This is also an important requirement for a lube oil that is to
operate under severe high-temperature conditions. If the oil has a tendency to oxidize
the product of oxidation is often hard granules (similar to coke) which will damage
bearing surfaces and block up the lube oil system filters and ports.
Flash point. The flash point of a lube oil must be high enough to be safe under any
of the temperature condition that the lube oil will be required to operate.
Thermal stability. This property requirement is similar to that for oxidation stability.
In the case of thermal stability the lube oil must be able to operate within its specified
temperature range without the danger of the oil cracking or breaking down and giving
rise to harmful polymers, acids, or other compounds.
Volatility. This property is important for ensuring minimizing any vaporization of the
oil and thus maintaining the lowest oil consumption.
Color. Unusually dark coloring in a lube oil is indicative of the presence of olefins.
These are undesirable in lube oils as they are thermally unstable. Lube oils are often
filtered through a clay bed (usually bauxite) to improve color. Hydroprocessing always
results in lube stocks with good color.
A description of major processes in lube oil refining
It is not proposed to describe or discuss the hydro units now used extensively in modern
lube oil refining. These units have a similar process configuration as those described
elsewhere in this book, only the conditions applicable to their specific application will
be different. The major processes described here are:
r
The propane deasphalting process
r
An aromatic extraction—Furfural
r
A de-waxing process—MEK
The deasphalting process
Deasphalting the heavy end of crude, that is the vacuum residue, is not entirely reserved
for the production of lube oils. In energy refineries it is used to remove the asphaltene
portion of the residue to prepare a suitable feedstock for catalytic conversion units. In
most of these conversion units the performance of the catalyst is greatly impaired by
the presence of heavy metals and the high Conradson carbon content of the residue
488 CHAPTER 12
feed. Most of the metals are entrained in the asphaltene compounds which makes
up most of the asphalt portion of the residue. These asphaltenes are also high in
Conradson carbon content, so the removal of these serves to eliminate both the heavy
metal content and the high Conradson carbon.
In the case of lube oil production the light liquid phase resulting from the extraction of
the asphalt makes excellent lube base oil. This deasphalted oil is termed ‘Bright Stock’
and can now be further refined in the same way as neutral base stock which are vacuum
distillates to meet the specifications for blend stocks. The process configuration is
shown as Figure 12.2.
The configuration shown here is that for a propane deasphalting unit. Vacuum residue
feed enters the unit directly from the vacuum distillation tower and is heated to an inlet
temperature of around 140
◦
F before entering the top section of a trayed extraction
tower at a pressure of 485 psig. Liquid propane is introduced into the bottom of the
tower below the bottom tray.
The propane solvent moves up the tower counter current to the precipitated asphalt.
The extracted asphalt is removed from the bottom of the tower and is routed through
a fired heater to enter the top tray of a baffle-trayed separator. Some of the propane
entrained in the asphalt phase is removed from the overhead of the flash tower. The
asphalt phase leaves the bottom of the flash tower, and is reduced in pressure before en-
tering the asphalt stripper tower above the top row of baffles. Steam is introduced to the
bottom of the tower, and the remaining entrained propane is stripped out of the asphalt.
The stripped asphalt leaves the bottom of the tower, is cooled to battery conditions and
routed to storage or the asphalt blending plant. The propane stripout enters the suction
side of a propane compressor and on discharge routed to the propane accumulator.
The deasphalted oil phase from the extraction tower overhead enters a high-pressure
oil vaporizer which removes most of the entrained propane. The propane stream leaves
the vaporizer to be cooled and enter the propane accumulator. On leaving the vaporizer,
the oil phase enters the top row of baffles in a low-pressure stripper tower. Steam is
introduced to the bottom trays of the tower and moves up the tower counter current
to the oil phase. The residual propane is stripped out of the oil phase and leaves the
top of the stripper tower with the steam. This overhead vapor stream joins the stream
from the low-pressure asphalt stripper at the suction of the propane compressor.
The compressed propane is cooled and drained free of the water from the stripping
steam in the accumulator. The dry propane is then recycled to enter the extraction
tower.
Typical data on deasphalting Aramco crude residuum for lube oil with a propane treat
of 600% volume on feed are as follows (Table 12.1).
HP Oil Vaporizer
LP Oil Stripper
LP Asphalt Stripper
DE Asphalted Oil
Extraction Tower
Steam
Steam
Vacuum Residue Feed
Water
Propane Accumulator
HP Asphalt Flash Tower
Propane Compressor
Steam
C W
Asphalt
Asphalt Heater
CW
Figure 12.2. Propane de-asphalting process.
490 CHAPTER 12
Table 12.1. Product yield and properties—propane deasphalting
Feed Deasphalted oil Extract
Yield vol% 100 52 48
Gravity
◦
API 11 21 1.5
Viscosity, SSU @ 210
◦
F 1,150 175 –
Viscosity, SSU @ 275
◦
F – – 250
Con carb wt% 10 2.7 –
Color TR dilute – 9 –
Softening pt, R&B,
◦
F – – 135
The salient operating conditions for this unit are as follows:
Treater tower:
Top temperature, 140
◦
F
Bottom temperature, 105
◦
F
Tower pressure, 485 psig
Deasphalted oil vaporizer, 315
◦
F
Deasphalted oil stripper, 310
◦
F
Vaporizer pressure, 220 psig
Stripper pressure, 5 psig
Asphalt flash tower, 525
◦
F
Asphalt stripper, 515
◦
F
Flash tower pressure, 220 psig
Stripper pressure, 5 psig
The lube oil extraction process—furfural extraction
The furfural extraction process described here is designed to produce lube oil base oils
(before dewaxing) having high viscosity indices and other desirable lube oil qualities,
such as color and stability. The furfural process is one of a few means of removing
aromatic and naphthenic compounds from both neutral feed stocks and the bright oil
feed stocks (de asphalted oils) by extracting them using furfural as solvent. The other
most common processes to attain this is extraction using liquid SO
2
as solvent and a
process using phenol as solvent. The furfural process configuration is shown below
as Figure 12.3.
Either straight run distillate feed or Bright Stock oils (or a blend of both) enter an
trayed extraction tower below the bottom tray. A dry furfural stream enters above
the top tray to move counter current to the oil feed. The undesirable compounds are
Extraction Tower
Extract Stripper
Extract to Slop
Inert Gas
Inert Gas
Feed
Furfural
Raffinate to De-wax Process
Inert Gas to Recycle
Furfural Accumulator
Raffinate Stripper
Figure 12.3. A furfural lube oil extraction process.
492 CHAPTER 12
Table 12.2. Product yields and properties—furfural
extraction
Untreated oil Feed A Feed B
Viscosity index 70 89
Gravity
◦
API 25 28
Viscosity, SSU @ 210
◦
F5544
Treated oil
Yield vol % 69 55
Viscosity index (de-waxed) 102 113
removed from the lube oil feed to leave the bottom of the tower as a rich furfural
stream. This stream is heated in a fired heater before entering an extract stripper. The
furfural is stripped off and leaves the top of the stripper to be cooled and enter the
furfural accumulator vessel. Stripping of the furfural is achieved using an inert gas
stripping stream introduced below the bottom row of trays in the stripper. Inert gas is
used as the stripping medium because furfural is highly susceptible to polymerizing
on exposure to steam or air. The extract leaves the bottom of the tower to be cooled
and routed to refinery fuel or the fuel oil pool.
The raffinate oil essentially free of aromatic and naphthene compounds leaves the
top of the extraction tower to be heated in a fired heater before entering the raffinate
stripper. The entrained furfural is again stripped out using an inert gas as the stripping
medium leaving the raffinate to be routed from the bottom of the stripper to a de-
waxing plant. The stripped furfural stream leaves the top of the stripper to be cooled
and collected in the furfural accumulator.
The entrained inert gas from the stripping is flashed off the furfural collected in the
accumulator to be either vented to the atmosphere or returned to the refinery’s inert
gas system.
Some data on this process is given in Table 12.2. These data are based on two typical
feedstocks A and B which cover the usual range of feedstock parameters.
The Extraction Tower operates at between 150 and 200 psig and at a temperature
Top/Bottom of between 190/140
◦
F and 195/135
◦
F.
The dewaxing process—MEK dewaxing
There are several dewaxing processes in use today. Among them are the propane de-
waxer, Edeleanu’sSO
2
/benzol combination of extraction and dewaxing, the MIBK
(methyl iso butyl ketone), and the more common MEK (metyl ethyl ketone) process.
These processes, except the Edeleanu process, have a similar process configuration.
The one based on MEK is shown in Figure 12.4.