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					CHEMISTRY AND
TECHNOLOGY OF
PETROLEUM




 By Dr. Dang Saebea
REFINING CHEMISTRY
              INTRODUCTION
 Petroleum refining plays an important role in our
  lives.
 Most transportation vehicles are powered by
  refined products such as gasoline, diesel, aviation
  turbine kerosene (ATK) and fuel oil.
    THE REFINING INDUSTRY IN THREE
                 WAYS
Ø   An increased search for fuel products from non-fossil
    sources such as biodiesel and alcohols from vegetable
    sources.
Ø   The development of better methods to process tar
    sand, coal gasification and synthesis of fuels by new
    technology.
       Ø The initiation of long-term plans to look for
                  renewable energy sources.
REFINING MEANS. . .
1.To a pure state, to remove impurities

2.To improve product
REFINING IS CARRIED OUT IN THREE MAIN
                STEPS



            Step 1 – Separation

            Step 2 – Conversion

            Step3 - Purification
         REFINING IS CARRIED OUT
Step 1 - Separation
 The oil is separated into its constituents by
  distillation, and some of these components (such as
  the refinery gas) are further separated with chemical
  reactions and by using solvents.
        REFINING IS CARRIED OUT

Step 2 - Conversion
o The various hydrocarbons produced are then
  chemically altered to make them more suitable for
  their intended purpose.
o For example, naphthas are "reformed" from paraffins
  and naphthenes into aromatics.
         REFINING IS CARRIED OUT

Step3 - Purification
o The hydrogen sulfide gas which was extracted from
  the refinery gas in Step 1 is converted to sulfur,
  which is solid in liquid form to fertiliser
  manufacturers.
INTEGRATION
1. Physical Separation Processes
2. Chemical Catalytic Conversion Processes
 INTEGRATION
3. Thermal Chemical Conversion Processes
1. Physical Separation Processes
 INTEGRATION
  Crude Distillation
Crude Distillation
q Crude oils are first desalted and then introduced
  with steam to an atmospheric distillation column.

q   The atmospheric residue is then introduced to a
    vacuum distillation tower operating at about 50
    mmHg, where heavier products are obtained.
 Atmospheric distillation         Vacuum distillation
1. Physical Separation Processes
 INTEGRATION
Solvent Deasphalting
Ø This is the only physical process where carbon is rejected from
  heavy petroleum fraction such as vacuum residue.
Ø Propane in liquid form (at moderate pressure) is usually to
  dissolve the whole oil, leaving asphaltene to precipitate.
Ø The deasphalted oil (DAO) has low sulphur and metal
  contents since these are removed with asphaltene. This oil is
  also called ‘‘Bright Stock’’ and is used as feedstock for lube oil
  plant.
Ø The DAO can also be sent to cracking units to increase light
  oil production.




                                                  Solvent
                                                deasphalting
                                                  process
1. Physical Separation Processes
 INTEGRATION
Solvent Extraction
q In this process, lube oil stock is treated by a solvent,
  such as phenol and furfural, which can dissolve the
  aromatic components in one phase (extract) and the
  rest of the oil in another phase (raffinate).

q   The solvent is removed from both phases and the
    raffinate is dewaxed.


                                                Solvent
                                               Extraction
1. Physical Separation Processes
 INTEGRATION
Solvent Dewaxing
q The raffinate is dissolved in a solvent (methyl ethyl
  ketone, MEK) and the solution is gradually chilled,
  during which high molecular weight paraffin (wax) is
  crystallized, and the remaining solution is filtered.

q   The extracted and dewaxed resulting oil is called
    ‘‘lube oil’’.

q   In some modern refineries removal of aromatics and
    waxes is carried out by catalytic processes in all ‘‘
    hydrogenation process”
2. Chemical Catalytic Conversion Processes
 INTEGRATION
Catalytic Reforming
q In this process a special catalyst (platinum metal
  supported on silica or silica base alumina) is used to
  restructure naphtha fraction (C6–C10) into
  aromatics and isoparaffins.

q   The produced naphtha reformate has a much higher
    octane number than the feed. This reformate is used
    in gasoline formulation and as a feedstock for
    aromatic production (benzene–toluene–xylene, BTX).
2. Chemical Catalytic Conversion Processes
 INTEGRATION
Hydrotreating
q This is one of the major processes for the cleaning of
  petroleum fractions from impurities such as sulphur,
  nitrogen, oxy-compounds, chloro-compounds,
  aromatics, waxes and metals using hydrogen.

q   The catalyst is selected to suit the degree of
    hydrotreating and type of impurity. Catalysts, such
    as cobalt and molybdenum oxides on alumina matrix,
    are commonly used.
2. Chemical Catalytic Conversion Processes
 INTEGRATION
Catalytic Hydrocracking
q For higher molecular weight fractions such as
  atmospheric residues (AR) and vacuum gas oils
  (VGOs), cracking in the presence of hydrogen is
  required to get light products.

q   In this case a dual function catalyst is used. It is
    composed of a zeolite catalyst for the cracking
    function and rare earth metals supported on
    alumina for the hydrogenation function.

q   The main products are kerosene, jet fuel, diesel
    and fuel oil.
2. Chemical Catalytic Conversion Processes
 INTEGRATION
Catalytic Cracking
q Fluid catalytic cracking (FCC) is the main player
  for the production of gasoline. The catalyst in this
  case is a zeolite base for the cracking function.

q   The main feed to FCC is VGO and the product is
    gasoline, but some gas oil and refinery gases are
    also produced.
2. Chemical Catalytic Conversion Processes
 INTEGRATION
Alkylation
q Alkylation is the process in which isobutane reacts
  with olefins such as butylene (C4 ) to produce a
  gasoline range alkylate.

q   The catalyst in this case is either sulphuric acid or
    hydrofluoric acid. The hydrocarbons and acid react
    in liquid phase.

q   Isobutane and olefins are collected mainly from
    FCC and delayed coker
2. Chemical Catalytic Conversion Processes
 INTEGRATION
Isomerization
q Isomerization of light naphtha is the process in
  which low octane number hydrocarbons (C4, C5,
  C6) are transformed to a branched product with
  the same carbon number. This process produces
  high octane number products.

q   One main advantage of this process is to separate
    hexane (C6) before it enters the reformer, thus
    preventing the formation of benzene which
    produces carcinogenic products on combustion
    with gasoline.

q   The main catalyst in this case is a Pt-zeolite base.
3. Thermal Chemical Conversion Processes
Delayed Coking
q This process is based on the thermal cracking of
  vacuum residue by carbon rejection forming coke
  and lighter products such as gases, gasoline and
  gas oils.

q   The vacuum residue is heated in a furnace and
    flashed into large drums where coke is deposited
    on the walls of these drums, and the rest of the
    products are separated by distillation.
Flexicoking
q In this thermal process, most of the coke is
  gasified into fuel gas using steam and air.

q   The burning of coke by air will provide the heat
    required for thermal cracking.

q   The products are gases, gasoline and gas oils
    with very little coke.
3. Thermal Chemical Conversion Processes
Visbreaking
q This is a mild thermal cracking process used to
  break the high viscosity and pour points of
  vacuum residue to the level which can be used in
  further downstream processes.

q   In this case, the residue is either broken in the
    furnace coil (coil visbreaking) or soaked in a
    reactor for a few minutes (soaker visbreaker).

q   The products are gases, gasoline, gas oil and the
    unconverted residue.
The End
CRUDE DISTILLATION
          CRUDE DISTILLATION
 Crude distillation unit (CDU) is at the front-end
  of the refinery, also known as topping unit, or
  atmospheric distillation unit.
 It receives high flow rates hence its size and
  operating cost are the largest in the refinery.
 This involves the removal of undesirable
  components like sulphur, nitrogen and metal
  compounds, and limiting the aromatic contents.
TYPICAL PRODUCTS FROM THE
         UNIT ARE:
CRUDE OIL DESALTING
o    The crude oil contains salt in the form of
    dissolved salt in the tiny droplet of water
    which forms a water-in oil emulsion.
o   This water cannot be separated by gravity
    or through mechanical means.
o   It is separated through electrostatic water
    separation. This process is called
    desalting.
CRUDE OIL DESALTING
     In the electrostatic desalter, the salty
 water droplets are caused to coalesce and
 migrate to the aqueous phase by gravity. It
 involves mixing the crude with dilution water
 (5–6 vol%) through a mixing valve.
POOR DESALTING HAS THE
FOLLOWING EFFECTS:

1. Salts deposit inside the tubes of furnaces and on
  the tube bundles of heat exchangers creating
  fouling, thus reducing the heat transfer
  efficiency;
2. Corrosion of overhead equipment.
3. The salts carried with the products act as
  catalyst poisons in catalytic cracking units.
TYPES OF SALTS IN CRUDE OIL
 Salts in the crude oil are mostly in the form of
  dissolved salts in fine water droplets emulsified
  in the crude oil. The salts can also be present in
  the form of salts crystals suspended in the crude
  oil.
 These are mostly magnesium, calcium and
  sodium chlorides with sodium chloride being the
  abundant type.
TYPES OF SALTS IN CRUDE OIL
Ø   These chlorides, except for NaCl, hydrolyze at
    high temperatures to hydrogen chloride:




   Hydrogen chloride dissolves in the overhead
    system water, producing hydrochloric acid, an
    extremely corrosive acid
DESALTING PROCESS
The process is accomplished through the
following steps:
1. Water washing:
- Water is mixed with the incoming crude oil through
a mixing valve.
- The water dissolves salt crystals and the mixing
distributes the salts into the water, uniformly
producing very tiny droplets.
- Demulsifying agents are added at this stage to aide
in breaking the emulsion by removing the
asphaltenes from the surface of the droplets.
DESALTING PROCESS
  2. Heating:
 - The crude oil temperature should be in the range of
 49-54 ˚C (120–130 F) since the water–oil separation
 is affected by the viscosity and density of the oil.
DESALTING PROCESS
3. Coalescence:
- The water droplets are so fine in diameter in the
range of 1–10 mm that they do not settle by gravity.
Coalescence produces larger drops that can be
settled by gravity.
- This is accomplished through an electrostatic
electric field between two electrodes.
- The electric field ionizes the water droplets and
orients them so that they are attracted to each other.
 - Agitation is also produced and aides in coalescence.
DESALTING PROCESS
4. Settling: According to Stock’s law the settling
  rate of the water droplets after coalescence is
  given by




 where      is the density
             is the viscosity,
         d is the droplet diameter
         k is a constant.
DESCRIPTION OF DESALTER


                                           Two electrodes




Simplified flow diagram of an electrostatic desalter
DESCRIPTION OF DESALTER


                                       A primary field of
                                       about 600 V/cm

                                       This field helps
                                       the water droplets
                                       settle faster.




Simplified flow diagram of an electrostatic desalter
DESCRIPTION OF DESALTER


                                       A secondary field of
                                       about 1000 V/cm

                                       The ionization of
                                       the water droplets
                                       and coalescence
                                       takes place here




Simplified flow diagram of an electrostatic desalter
 TWO-STAGE DESALTING




- The desalter of this design achieves 90% salt removal.
However 99% salt removal is possible with two-stage
desalters.
-A second stage is also essential since desalter maintenance
requires a lengthy amount of time to remove the dirt and
sediment which settle at the bottom.
-The crude unit can be operated with a one stage desalter
while the other is cleaned.
DESALTER OPERATING VARIABLES
For an efficient desalter operation, the following
variables are controlled:
Ø Desalting temperature: The settling rate depends on
the density and viscosity of the crude
  T     density & viscosity   settling rate

Desalting temperature can vary between 50 and 150 ˚C

ØWashing water ratio: Adding water to the crude oil
helps in salt removal.

 Wash water rate         Coalescence rate
DESALTER OPERATING VARIABLES
ØWater level:
- Raising the water level reduces the settling time for the
water droplets in the crude oil

-However, if the water level gets too high and reaches the
lower electrode, it shorts out the desalter.

- it is always better to keep the level constant for stable
operation.
DESALTER OPERATING VARIABLES
ØWashing water injection point:
-Usually the washing water is injected at the mixing
valve.

- However, if it is feared that salt deposition may
occur in the preheat exchangers, part or all of the
washing water is injected right after the crude feed
pump.
DESALTER OPERATING VARIABLES
ØType of washing water:
-Process water in addition of fresh water is used for
desalting. The water should be relatively soft in order to
prevent scaling.

- It should be slightly acidic with a pH in the range of 6.
It should be free from hydrogen sulphide and ammonia
so as to not create more corrosion problems.
ATMOSPHERIC DISTILLATION



 330 ˚C




Process flow diagram of an atmospheric
distillation unit
COMPONENT OF ATMOSPHERIC
DISTILLATION

                Rectifying section



                 Flash zone




                 Stripping section
Description OF ATMOSPHERIC
DISTILLATION
                ØThe vapor from pipestill furnace
                discharge as a foaming stream
                into distillation tower.

                ØThe partially vaporized crude is
                transferred to the flash zone.

                ØThe vapour goes up the tower to
                be fractionated into gas oil that is
                called the overhead product .

                Øliquid portion of feed go down to
                bottom of tower
Description OF STRIPPING SECTION
                Ø Steam reboilers may take the form of
                a steam coil in the bottom of the tower
                or a separate vessel.

                ØThe bottom product from the tower
                enters the rebolier where part is
                vaporized by heat from steam coil.

                ØThe hot vapor is directed back to the
                bottom of the tower and the nonvolatile
                leaves the rebolier and passes through a
                heat exchanger, where its heat is
                transferred to the feed to the tower.
Description OF STRIPPING SECTION

 Ø Steam is also injected into the column
 -To strip the atmospheric residue of any light
 hydrocarbon.
 - To lower the partial pressure of the hydrocarbon
 vapours in the flash zone. This has the effect of
 lowering the boiling point of the hydrocarbons and
 causing more hydrocarbons to boil and go up the
 column to be eventually condensed and withdrawn as
 side streams.
Description OF RECTIFYING SECTION
                ØAs the hot vapours from the
                flash zone rise through the
                trays up the column, they are
                contacted by the colder reflux
                down the column.

                ØIn the overhead condenser,
                the vapours are condensed and
                part of the light naphtha is
                returned to the column as
                reflux.

                Ø Reflux is provided by several
                pumparound streams along the
                column.
IMPROVEMENT OF DISTILLATION
EFFICIENCY WITH PUMPAROUND


Ø   Vapours       Cold liquid condenses     Reflux
     To compensate for the withdrawal of products from
    the column.

Ø   The addition to the heat removal from the condenser.
    The thermal efficiency of the column is improved and
    the required furnace duty is reduced.
Description OF RECTIFYING SECTION
      Liquid collects on each tray to a depth,
  and the depth controlled by a dam or weir.
  As the liquid spills over the weir into a
  channel, which carries the liquid to the tray
  below.
IMPORTANT OF STRIPPING AND
RECTIFYING SECTION
v   Stripping section
         The more volatile component are stripped
         from the descending liquid

v   Rectifying section
         The concentration of the less volatile
        component in the vapor is reduced
                         Straight-Run Naphtha and Gases


            125 ˚C          Heavy Naphtha


            160 ˚C           Kerosene

            250 ˚C           Gas Oil
Crude Oil
            300 ˚C      The Temperature of tray is
                         progressively cooler from bottom
                         to top



                         Residuum
THE EFFICIENT OPERATION OF THE
DISTILLATION

                 ØTower requires the rising
                 vapors to mix with liquid on
                 each tray.
                 ØThis is usually achieved by
                 installing a bubble caps.
                 ØThe cap forces the vapor to go
                 below the surface of the liquid
                 and to bubble up through it.
LIMITING TEMPERATURE OF
ATMOSPHERERIC DISTILLATION
   It is important not to subject the crude oil to temperatures
    above 350 °C because the high molecular weight components
    in the crude oil will undergo thermal cracking and
    form petroleum coke .

   Formation of coke would result in plugging the tubes in
    the furnace and the piping from the furnace to the
    distillation column as well as in the column itself.

   The constraint imposed by limiting the column inlet crude
    oil to a temperature of less than 350 °C yields a residual oil
    from the bottom of the atmospheric distillation column.
VACUUM DISTILLATION

              To further distill the residual oil from the
               atmospheric distillation column, the
               distillation must be performed
               at absolute pressures as low as 10 to
               50 mmHg  so as to limit the operating
               temperature to less than 350°C.


              Vacuum distillation is the reduced
               temperature requirement at lower
               pressures.


              Vacuum distillation increases
               the relative volatility of the key
               components.
    Vacuum distillation can improve a
    separation by:
 Prevention of product degradation or polymer
  formation because of reduced pressure leading to
  lower tower bottoms temperatures.
 Reduction of product degradation or polymer
  formation because of reduced mean residence
  time especially in columns using packing rather
  than trays.
 Reduction of capital cost because of reduced the
  height and diameter.
FRACTIONS OBTAINED BY VACUUM
DISTILLATION
                       used as catalytic cracking stock
             Gas Oil   or, after suitable treatment, light
                       lubricating oil


               Light
               Medium        Lube oil

               Heavy




                              used directly as asphalt or
              Residuum,       converted to asphalt
              Nonvolatile
OPERATION OF CRUDE DISTILLATION
UNITS
  The factors affect the design and operation of the unit
  are explored
1. Fractionation
       The degree of fractionation in a crude unit is
  determined by the gap or overlap between two adjacent
  side stream products.

Example: The gap or overlap in the boiling point range
  between kerosene and LGO.
Lighter product: kerosene      end boiling point

Heavier product: LGO             initial boiling point

  In the ideal case there would be no overlap
     However, if we compare the ASTM distillation
boiling points, and since ASTM distillation does not
give perfect fractionation. Since determining the
initial and end point on the laboratory test is not
always possible or accurate.

      The fractionation gap is defined as the
difference between the ASTM 5% boiling point of
the heavier product and the 95% point of the lighter
product.
a gap indicating good
fractionation




some of the light
product is still in the
heavier product
2. Overflash
   The partially vaporized crude is transferred to the
    flash zone. The furnace outlet temperature should be
    enough to vaporize all products withdrawn above the
    flash zone plus about 3–5 vol% of the bottom product.

   This overflash has the function of providing liquid
    wash to the vapours going up the column from the
    flash zone.

   The overflash improve fractionation on the trays
    above the flash zone, thereby improving the quality of
    the HGO and reducing the overlap with the bottom
    products below the flash zone.
3. Column Pressure

 The pressure inside the CDU column is
  controlled by the back pressure of the overhead
  reflux drum at about 0.2–0.34 bar gauge (3–5
  psig).
 The top tray pressure is 0.4–0.7 bar gauge (6–10
  psig) higher than the reflux drum.
 The flash zone pressure is usually 0.34–0.54 bar
  (5–8 psi) higher than the top tray.



         Pflash zone > PTop tray > Preflux
         drum
4. Overhead Temperature

      The overhead temperature must be controlled to
 be 14–17 ˚C higher than the dew point temperature
 for the water at the column overhead pressure so that
 no liquid water is condensed in the column.

      This is to prevent corrosion due to the hydrogen
 chloride dissolved in liquid water (hydrochloric acid).
EXAMPLE
If the overhead stream contains 8.5 mol% water
at a pressure of 34.7 psia (2.36 bars), calculate
the overhead temperature for safe operation.
EXAMPLE
 If the overhead stream contains 8.5 mol% water
 at a pressure of 34.7 psia (2.36 bars), calculate
 the overhead temperature for safe operation.

Solution:
The saturation temperature of water at the partial
pressure of water in the overhead vapour.
Water partial pressure = 0.085 x 2.36 =0.2 bars
From the steam tables:
Saturated steam temperature at 0.2 bars = 61 ˚C
Safe overhead operating temperature = 61+17 ˚C
The End

				
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