Dr Fatma Ashour

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14 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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Dr
Fatma

Ashour



Lubricating

oils

(or

“Lube

Oils

are

heavy

petroleum

fractions

used

to

lubricate

metallic

surfaces

which

are

in

relative

motion

with

respect

to

one

another
.



The

essential

aim

of

these

oils

is

to

minimize

the

friction

between

the

moving

surfaces

and

hence,

prevent

mechanical

wear

in

the

metals,

and

to

absorb

the

heat

of

friction
.



General

steps

followed

in

producing

finished

lubricating

oils

are
:



A
-
The

crude

oil

is

initially

fractionated

under

atmospheric

pressure

to

produce

the

conventional

top

products

(gases

and

gasoline)

side

products

(kerosene,

gas

oil,

and

perhaps

diesel

oil)

and

a

bottom

product,

usually

known

as

the

“Long

Residue”

(known

as

Mazot
)
.




B
-
The

long

residue

is

then

fractionated

under

vacuum

to

produce

a

top

product

used

for

diesel

oil,

and

side

products

which

could

be

used

for

producing

finished

lube

oils
.

These

side

products

of

the

vacuum

tower

are

known

as

“Wax

Distillates”

The

bottom

product

of

the

vacuum

tower,

known

as

the

“short

Residue”,

may

be

asphalt

on

heavy

oil
.




In

either

case,

this

bottom

product

could

be

used

for

producing

heavy

lubricating

oils,

which

are

then

called

“Residual

Oils”
.



The

products

obtained

from

the

vacuum

distillation

tower

(cannot

be

marketed

as

such
.

They

should

be

refined

to

produce

the

required

grade

of

finished

lube

oils
.





Deasphalted

to

remove

any

asphalt

they

may

contain



Solvent

refined

to

decrease

the

effect

of

temperature

on

its

viscosity

(i
.
e
.

improve

its

Kinematic

Viscosity

Index
-
KVI)



Dewaxed


and

possibly

“percolated

through

clay”

to

remove

any

solid

particles

or

coloring

material



Neutralized”,

especially

if

they

have

been

previously

subjected

to

acid

treatment
.



In

general,

there

are

FOUR

basic

“Lube

Oil

Stocks”

-

three

of

which

are

distillate

oils

and

one

is

a

residual

oil
.




As

a

matter

of

fact,

more

“basic

stocks”

could

be

produced

by

the

vacuum

distillation

of

one

or

more

of

the

previously

obtained

oils
.




Basic

stocks

are

then

“blended”

with

one

another,

in

various

proportions,

to

produce

the

optimum

viscosity

range

necessary

for

the

market
.



The

lube

oil

is

finally

“compounded”

by

the

addition

of

various

additives

to

improve

the

quality

of

the

oil
.

After

compounding,

the

finished

lube

oil

is

ready

for

selling

on

the

market
.




Viscosity
:




Lube

oils

should

have

a

“suitable

viscosity”
.

As

a

matter

of

fact,

for

a

certain

lubricating

job,

the

lube

oil

must

have

a

definite

optimum

viscosity
.




Below

this

optimum

viscosity,

the

lube

oil

cannot

properly

prevent

the

friction

between

the

moving

metallic

parts
;

while

above

this

optimum

viscosity,

the

lube

oil

itself

requires

a

greater

power

to

overcome

its

high

resistance

to

motion,

and

consequently

this

is

a

waste

of

power
.



To

determine

the

optimum

viscosity

required

of

a

certain

lubrication

job,

use

is

made

of

the

fact

that

the

“Coefficient

of

Friction”

between

any

moving

surfaces

depends

upon

the

following

“dimensionless

group”[


N/P]


Where,





=

viscosity

of

the

lube

oil
.



N

=

relative

speed

of

the

moving

surfaces
.



P

=

stress

between

the

moving

surfaces
.


Since

the

values

of

N

and

P

are

fixed

by

the

operating

conditions,

then

for

minimum

friction,

the

value

of



is

also

fixed
.




For

minimum

friction,

higher

viscosity

oils

are

required

for

low

speeds

of

rotation

and

for

high

stresses

between

the

moving

surfaces
.

Conversely,

lower

viscosity

oils

are

required

for

high

speeds

of

rotation

and

low

stresses

between

the

moving

surfaces
.



Examples

of

the

choice

of

the

optimum

viscosity

of

lube

oils

are

given

below
:




In

the

case

of

lubricating,

textile

spindles,

the

pressure

load

is

very

low

and

the

speed

of

rotation

is

very

high

consequently,

the

proper

lube

oil

to

be

used

should

have

a

very

low

viscosity
.

For

this

reason,

lube

oils

with

the

lowest

viscosity

are

known

as

“spindle

oils”
.




In

the

case

of

lubricating

cylinders

of

big

engines,

the

speed

is

relatively

low

and

the

pressure

is

high,

thus

the

proper

lube

oil

to

be

used

should

have

a

relatively

high

viscosity
.

Such

lube

oils

are

known

as

“Cylinder

oils”
.




In

case

of

lubricating

gears,

the

stresses

on

the

gears

are

very

high,

while

the

relative

motion

is

significantly

low
;

accordingly,

lube

oils

of

very

high

viscosities

are

therefore

needed,

and

these

are

called

“Gear

Oils”
.




N
.
B
:

Gear

oils

and

cylinder

stocks

are

usually

manufactured

from

residual

oils
.





The

K
.
V
.
I

is

a

measure

of

the

variation

of

viscosity

with

temperature
.




As

a

rule,

the

viscosity

of

a

lube

oil

decreases

with

increase

in

temperature
.

The

variation

of

viscosity

with

temperature

depends

upon
:


-

The

type

of

crude


-

The

extent

of

refining


As

a

matter

of

fact,

paraffinic

hydrocarbons

change

their

viscosities

to

a

smaller

extent

than

naphthenic

ones
.




This

scale

has

been

developed

on

the

basis

of

Two

“Reference

Crudes”

namely
:



i
.

Pennsylvanian

Crude

(PC)

-

highly

paraffinic

crude
.


ii
.

Gulf

Coast

Crude

(GCC)

-

highly

Naphthenic

crude
.



Any

lube

oil

derived

from

the

first

reference

crude

would

have

a

relatively

small

variation

of

viscosity

with

temperature,

and

is

arbitrarily

given

a

K
.
V
.
I

value

of

100
.



On

the

other

hand,

any

lube

oil

derived

from

the

second

reference

crude

would

show

large

variations

of

viscosity

with

temperatures,

and

is

therefore

given

a

K
.
V
.
I

value

of

zero
.


To

find

the

K
.
V
.
I

of

any

lube

oil,

its

kinematic

viscosity

at

two

standard

temperature

levels

of

210
˚and

100
˚F

is

measured
.




Generally

lube

oils

are

broadly

classified

into

the

following

TWO

grades

according

to

their

K
.
V
.
I

values
:



Premium

grade

oil

having

a

K
.
V
.
I

of

85

or

higher
.


Regular

grade

oils

having

a

K
.
V
.
I

of

80

or

less
.



N
.
B
.

Lube

oils

having

K
.
V
.
I

values

between

those

2

grades

are

sometimes

called

“Intermediate

grade

oils”
.

Furthermore,

lube

oils

are

not

marketed

unless

their

K
.
V
.
I
.

value

is

at

least

70

(not

less)
.



Some

lubes

have

a

K
.
V
.
I

value

higher

than

100
;

this

means

that

the

change

of

their

viscosities

with

temperature

is

less

than

the

change

in

viscosity

of

the

corresponding

lube

oil

from

the

first

reference

crude
.



Such

a

lube

could

only

be

obtained

by
:



Starting

from

crude

which

is

more

paraffinic

than

the

Pennsylvanian

crude

(PC)



Subjecting

the

lube

to

intensive

solvent

refining


Adding,

certain

additives

known

to

increase

the

K
.
V
.
I

such

additives

are

known

as

“VI
-
improvers”
.


N
.
B
.

Similarly

oil

with

a

(
-
ve

)

K
.
V
.
I

indicates

that

the

variation

in

viscosity

(kinematic

viscosity)

with

temperature

is

greater

than

the

variation

of

the

kinematic

viscosity

of

the

Gulf

Coast

reference

crude

(GCC)
.



Stricter

environmental

requirements

and

mileage

standards

for

new

cars

have

created

a

growing

demand

for

high
-
quality

multigrade

motor

oils

which

have

lower

volatility

and

oil

consumption

characteristics

and

reduced

thickening

of

the

oil

by

oxidation

during

service

which

increases

fuel

consumption
.




Solvent

refined

oils

have

difficulty

in

meeting

the

new

standards

and

are

increasingly

being

replaced

with

hydrocracked

and

poly
-
alpha
-
olefin

based

oils,

especially

in

the

lower

viscosity

grades

such

as

5
W
-
30

and

10
W
-
30

multigrades
.



The

low
-
viscosity

multigrade

oils

are

typically

blended

from

low
-
viscosity

mineral
-
based

oils

which

have

volatilities

and

tendency

to

high

oil
-
consumption

and

rapid

thickening

by

oxidation

during

service
.




Hydrocracking

of

base

stocks,

followed

by

solvent

extraction

to

remove

partially

hydrocracked

aromatic

compounds,

offers

a

more

cost
-
effective

route

than

production

of

poly
-
alphaolefins



Wax

particles

in

lube

oils

are

undesirable

for

the

following

reasons
:





A

high

wax

content

results

in

a

high

pour

point,

hence

the

lube

will

tend

to

solidify

in

cold

weather

conditions

(causing

friction)
.



Wax

is

susceptible

to

cracking

at

high

T

&

P
.

Hard

solid

particles

deposited

on

the

lubricated

surfaces

will

increase

the

friction
.




Wax

is

easily

oxidized

and

will

result

in

the

breaking

of

the

chain

into

shorter

molecules,

and

hence

the

viscosity

is

lowered
.



N
.
B
.

Wax

was

formerly

removed

from

lube

oils

by

“Chilling”

operations,

wherein

the

wax

solidifies

and

could

then

be

filtered

off,

or

left

to

SWEAT
.


More

modern

dewaxing

methods

are

now

adopted

using


Solvent

Refining


methods,

(
e
.
g
.

using

propane

or

ketones

especially

methyl

ethyl

ketone



MEK)
.

As

a

matter

of

fact,

the

oil

is

soluble

in

these

liquid

solvents,

and

thus

the

wax

could

be

filtered

off
.



Asphaltic

particles

are

undesirable

because

they

would

tend

to

stick

to

the

lubricated

surface

and

increase

the

friction

between

them
.




Deasphalting

is

therefore

one

of

the

main

processes

adopted

in

lube

oil

refining
.




Sulphuric

acid

treatment

or

“percolation

through

active

clay”

to

adsorb

the

asphaltic

particles
.





Solvent

extraction

processes
.




Typical

solvent

used

is

propane
-

ie

the

“propane

deasphalting


methods
.

In

this

process,

the

propane

dissolves

the

oil

and

leaves

the

asphaltenes

(hard

asphaltic

particles)

to

deposit

and

could

be

separated

by

filtration
.


The

most

important

refining

operations

to

which

these

raw

fractions

are

subjected

to

are

outlined

in

the

following

steps
:



1
-

Deasphalting
:

to

remove

any

solid

or

asphaltic

particles

which

deposit

on

the

lubricating

surfaces

causing

friction
.

Deasphalting

is

accomplished

by

the

following

methods
:



A
-

H
2
SO
4

treatment

(
98
%
)
:

carried

out

in

a

series

of

agitation

and

settling

tanks

at

temperatures

ranging

from

35
-
65


C

and

not

higher

because

of

possible

cracking
.



B
-

Clay

treatment
:

the

raw

fractions

are

basically

percolated

through

active

clay
.



C
-

Solvent

extraction
:

the

raw

fractions

are

essentially

dissolved

in

a

suitable

solvent



(e
.
g
.

propane)

whereby

asphaltic

particles

are

deposited

and

can

thus

be

removed
.




2
-

Solvent

Extraction
:

to

improve

the

KVI

of

the

lube

oil

through

the

removal

of

ring

compounds,

namely

naphthenes

and

aromatics

whose

viscosities

change

substantially

with

tempt
.



This

is

achieved

by

a

solvent

extraction

process

using

special

“selective

solvents”

such

as

phenol,

chlorex
,

and

above

all

furfural

which

is

presently

the

most

widely

used

solvent
.



Solvent

refining

process

is

carried

out

to

remove

naphthenes

&

aromatics

(in

addition

to

acids)

thus

resulting

in

the

improvement

of

the

KVI

of

the

finished

lube

oil
.



The

most

widely

used

solvent

is

Furfural

(a

liquid

aldehyde

of

B
.
P

=

180

C,

heavier

than

water

but

miscible

with

it,

obtained

as

a

byproduct

in

the

starch

industry
-
especially

when

starch

is

produced

from

maize)
.





N
.
B
.

Such

a

solvent,

called

a

“Selective

solvent”,

only

dissolve

the

ring

structures

which

DO

NOT

have

a

LONG

side

chain

(i
.
e
.

:

those

which

lower

the

KVI),

this

is

because

such

ring

structures

with

a

long

side

chain

could

break

to

n
-
paraffins

that

have

a

high

KVI
.



Flash

Point
:

Normally,

the

flash

point

of

lube

oil

is

not

of

particular

importance
.

It

is

sometimes

essential

however,

to

have

lube

oils

with

high

flash

points
.

Such

oils

could

be

obtained

by

“steam

refining”

(
ie
.

by

flashing

the

lighter

constituents

in

the

oil

using

superheated

steam)
.

These

oils

having

high

flash

points

are

referred

to

as

“steam

refined

oils”
.



For

example,

lubricating

oil

given

the

grade

(
600

SR)

indicates

oil

which

has

been

steam

refined

and

whose

flash

point

is

600
˚F
.




N
.
B
.

The

flash

point

of

lube

oil

is

used

to

detect

contamination

with

lighter

volatile

hydrocarbons
.


Ex
:

Crank
-
case

oil

when

it

is

contaminated

with

gasoline
.

Flash

point

determination

is

the

easiest

method

to

detect

such

a

contamination

(or

cheating)
.



Acidity
:

Acidity

in

the

lube

oil

resulting

from

mineral

or

organic

acids,

leads

to

corrosion

of

the

lubricated

surfaces
.

Hence,

any

acidity

in

the

lube

oil

must

be

neutralized

before

marketing
.

Solid

lime

is

usually

used

for

that

purpose
.



Emulsification
:

When

the

lube

oil

is

to

be

used

in

high

speed

steam

turbines,

it

usually

has

the

tendency

to

form

emulsions

with

the

water
.

Such

emulsions

destroy

the

lubricating

properties

of

the

oil
.

For

this

reason,

certain

additives

are

used

to

reduce

such

a

tendency
.







Furfural

is

a

liquid

aldehyde
,

which

is

susceptible

to

oxidation,

hence

the

lube

oil

charge

(feed)

must

be

deaerated

before

mixing

it

with

the

solvent,

by

passing

it

through

a


Deaerator


which

is

subjected

to

a

vacuum

system
.




The

deaerated

lube

is

then

introduced

into

an

Extraction

tower

where

it

meats

a

counter

current

flow

of

the

furfural

solvent
.

The

raffinate

will

be

obtained

through

the

top

of

the

extractor

while

the

extract

will

be

obtained

through

the

bottom
.




N
.
B
.

Both

the

raffinate

and

the

extract

contain

some

solvent

which

must

be

recovered
.

Accordingly,

both

streams

are

subjected

to

a

series

of

fractionation

Process

followed

by

steam

stripping

to

recover

the

furfural

solvent
.


The

solvent

furfural,

recovered

from

the

various

parts

of

the

plant,

is

collected

then

mixed

with

the

make
-
up

solvent

and

finally

recycled

to

the

extractor

tower


Dewaxing

process

is

carried

out

by
:



Clay

treatment



Chilling

operation

and

most

widely

by

solvent

extraction
.

In

the

latter

method,

the

solvents

generally

used

are

ketones

of

different

types

(e
.
g
.:

acetone,

methyl



ethyl

ketone

MEK,

propyl



ethyl

ketone

or

diethyl

ketone
)




N
.
B
.

It

has

been

found

that


Ketones


are

excellent

dewaxing

agents

whereby

they

dissolve

the

oil

and

precipitate

the

wax
.

Furthermore,

it

has

also

been

found

that

when

aromatics

are

mixed

with

ketones

(i
.
e
.:

in

the

form

of

a

“Solvent

Mixture”)

then,

the

aromatics

reduce

the

solubility

of

the

wax

in

oil

resulting

in

a

higher

efficiency

of

dewaxing

(greater

than

the

propane

dewaxing

process)
.


The

most

widely

used

dewaxing

process

is

the


MEK

Dewaxing

Process”

where

the

solvent

ketone

is

methyl

ethyl

ketone

(MEK)

and

the

mixed

aromatics

are

essentially

benzene

and

toluene

in

approximately

the

following

proportions
:


MEK

=

65
%


Solvent

Mixture

:

Benzene

=

25
%



Toluene

=

10
%




Propane

deasphalting

is

based

on

the

fact

that

liquid

propane

is

capable

of

dissolving

the

lube

oil

&

precipitating

the

asphaltic

particles
.



N
.
B
.

The

rate

of

precipitation

(i
.
e
.

the

extractive

power)

of

asphaltic

particle

is

increased

by

increasing

the

temperature
.



It

has

been

found

the

optimum

operating

temp

is

about

70

C

(not

higher

otherwise

the

paraffin

would

crack)

using

a

high

press

of

450

psi

(to

maintain

the

propane

in

the

liquid

phase)
.



The

lube

oil

and

liquid

propane

are

contacted

in

vertical

drums

which

are

heated

by

internal

steam

coils
.

These

drums

are

maintained

at

the

required

operating

conditions

(
70

C

&

450

psi)
.

The

asphalt

is

obtained

from

the

bottom

while

the

lube

oil,

containing

the

main

bulk

of

the

propane

solvent,

is

withdrawn

from

the

top
.








N
.
B
.

Both

the


raffinate


(lube

oil)

and

the

“extract”

(asphalt)

contain

propane
.

This

propane

is

recovered

by

heating

and

evaporation

using

a

TSH

for

asphalt

and

a

reboiler

for

the

lube

oil
.

The

reboiler

still

contains

some

propane

which

is

removed

by

a

stripper

(
i
.
e
:

using

S
.
H
.
S)
.



Asphaltic

particles

are

obtained

as

a

bottom

product

from

a

stripper
.



N
.
B
.

The

propane

obtained

from

the

various

parts

of

the

process

units,

is

collected,

compressed

and

mixed

with

make
-
up

propane

then

finally

recycled

with

the

feed
.



Advantages

of

this

Process
:

a)

Propane

could

be

obtained

from

the

refinery

at

a

cheap

price
.

b)

Efficiency

of

separation

is

very

high
.

c)

Only

asphaltenes

are

removed

hence

the

oil,

originally

present

with

the

asphalt,

is

recovered

with

the

lube

oil
.

d)

This

method

could

be

applied

to

any

lube

oil
.


Disadvantages

of

this

Process
:




The

only

disadvantage

is

that

hard

asphaltenes

have

No

use
.

This

was

overcome

by

any

of

the

following

procedures
:


i
)

Adding

them

to

soft

asphalt

to

increase

its

hardness
.


ii)

Adding

them

to

viscous

Fuel

Oil

to

convert

it

to

ordinary

F
.
O
.


iii)


Adding

them

to

soft

asphalt

then

blowing

with

hot

air

to

produce

much

harder

grade

of

asphalt,

known

as

“Air

blown

asphalt”
.