2/18/13

LECTURE  14  PETROCHEMICAL  INDUSTRIES  

Chapter 38 in Shreve’s Chemical

Process Industries

OUTLINE  
1.  Introduction  
2.  Physical  Processes  
3.  Thermal  Processes  
4.  Catalytic  Processes  
5.  Conversion  of  Heavy  Residues  
6.  Treatment  of  Refinery  Gas  Streams  

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 HOW  OIL  WAS  FORMED?  

n  Oil  was  formed  from  the  remains  of  animals  and  plants  
that  lived  millions  of  years  ago  in  a  marine  (water)  
environment  before  the  dinosaurs.      Over  the  years,  the  
remains  were  covered  by  layers  of  mud.    Heat  and  
pressure  from  these  layers  helped  the  remains  turn  into  
what  we  today  call  crude  oil  .    The  word  "petroleum"  
means  "rock  oil"  or  "oil  from  the  earth."    

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INTRODUCTION  
 
n  Over  600  refineries  worldwide  have  a  total  annual  
capacity  of  more  than  3500  x  106  tonnes.  
n  Goal  of  oil  refining  is  twofold:  
i.  production  of  fuels  for  transportation,  power  
generation  and  heating;  and  
ii.  production  of  raw  materials.  
n  Oil  refineries  are  complex  plants  but  are  relatively  
mature  and  highly  integrated.  
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CRUDE  OIL  

Crude oil is a non-uniform

material. The composition
depends on its location.

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The majority of crude oil is alkanes, cycloalkanes (naphthenes), aromatics,

polycyclic aromatics, S-containing compounds, etc.
Gasoline: branched alkanes
Diesel: linear alkanes

Heavier crude contains more polycyclic aromatics

Lead to carboneceous deposits called “coke”

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Some crudes contain a lot of sulfur, which leads to processing

considerations.

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OVERVIEW  
n  After  desalting  and  dehydration,  crude  is  separated  into  
fractions  by  distillation.  
n  The  distilled  fractions  can  not  be  used  directly.  
n  The  reason  for  such  a  complex  set  of  processes  is  the  
difference  between  the  crude  oil  properties  and  the  
needs  of  the  market.  
n  Another  reason  for  complexity  is  environmental.  
Legislation  demands  cleaner  products  and  is  the  major  
drive  for  process  improvement  and  development  of  
novel  processes.   12

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REFINING  OPERATIONS  
 Petroleum  refining  processes  and  operations  can  be  separated  into  five  
basic  areas:    
 
n  Fractionation  (distillation)  is  the  separation  of  crude  oil  in  atmospheric  
and  vacuum  distillation  towers  into  groups  of  hydrocarbon  compounds  
of  differing  boiling-­‐point  ranges  called  "fractions"  or  "cuts.”    

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REFINING  OPERATIONS  
 Petroleum  refining  processes  and  operations  can  be  separated  into  five  
basic  areas:    
n  Conversion  Processes  change  the  size  and/or  structure  of  hydrocarbon  
molecules.  These  processes  include:  :  
n  Decomposition  (dividing)  by  thermal  and  catalytic  cracking;    
n  Unification  (combining)  through  alkylation  and  polymerization;  and  
n  Alteration  (rearranging)  with  isomerization  and  catalytic  reforming.    

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REFINING  OPERATIONS  

 Petroleum  refining  processes  and  operations  can  be  separated  into  five  
basic  areas:    
n  Treatment  Processes  to  prepare  hydrocarbon  streams  for  additional  
processing  and  to  prepare  finished  products.    
 Treatment  may  include  removal  or  separation  of  aromatics  and  
 naphthenes,  impurities  and  undesirable  contaminants.      
 Treatment  may  involve  chemical  or  physical  separation  e.g.  
 dissolving,  absorption,  or  precipitation  using  a  variety  and  
 combination  of  processes  including  desalting,  drying,  
 hydrodesulfurizing,  solvent  refining,  sweetening,  solvent  
 extraction,  and  solvent  dewaxing.  
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REFINING  OPERATIONS  

n  Formulating  and  Blending  is  the  process  of  mixing  and  
combining  hydrocarbon  fractions,  additives,  and  other  
components  to  produce  finished  products  with  specific  
performance  properties.    

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REFINING  OPERATIONS  
n  Other  Refining  Operations  include:  
n  light-­‐ends  recovery;  
n  sour-­‐water  stripping;  
n  solid  waste,  process-­‐water  and  wastewater  treatment;  
n  cooling,  storage  and  handling  and  product  movement;  
n  hydrogen  production;  
n  acid  and  tail-­‐gas  treatment;  
n  and  sulfur  recovery.    

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REFINING  OPERATIONS  
n  Auxiliary  Operations  and  Facilities  include:  
n  light  steam  and  power  generation;  
n  process  and  fire  water  systems;  
n  flares  and  relief  systems;  
n  furnaces  and  heaters;  
n  pumps  and  valves;  
n  supply  of  steam,  air,  nitrogen,  and  other  plant  gases;  
n  alarms  and  sensors;  
n  noise  and  pollution  controls;  
n  sampling,  testing,  and  inspecting  and  laboratory;  
n  control  room;  
n  maintenance;  and  
n  administrative  facilities.   18

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FLOW  SCHEME  OF  A  MODERN  REFINERY  

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PHYSICAL  AND  CHEMICAL  PROCESSES  

CHEMICAL  
PHYSICAL  
THERMAL   CATALYTIC  
Distillation   Visbreaking   Hydrotreating  
Solvent  extraction   Delayed  coking   Catalytic  reforming  
Propane  deasphalting   Flexicoking   Catalytic  cracking  
Solvent  dewaxing     Hydrocracking  
Blending   Catalytic  dewaxing  
Alkylation  
Polymerization  
Isomerization  
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PHYSICAL  PROCESSES  
n  Desalting/dehydration  
n  How  does  distillation  work?  
n  Crude  distillation  
n  Propane  deasphalting  
n  Solvent  extraction  and  dewaxing  
n  Blending  
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DESALTING/DEHYDRATION  
n  Crude  oil  often  contains  water,  inorganic  salts,  suspended  solids,  
and  water-­‐soluble  trace  metals.  
n  Step  0  in  the  refining  process  is  to  remove  these  contaminants  
so  as  to  reduce  corrosion,  plugging,  and  fouling  of  equipment  
and  to  prevent  poisoning  catalysts  in  processing  units.  
n  The  two  most  typical  methods  of  crude-­‐oil  desalting  are  
chemical  and  electrostatic  separation,    and  both  use  hot  water  
as  the  extraction  agent.  

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DESALTING/DEHYDRATION  

n  Crude  oil  often  contains  water,  inorganic  salts,  suspended  solids,  
and  water-­‐soluble  trace  metals.  
n  In  chemical  desalting,  water  and  surfactant  (demulsifiers)  are  
added  to  the  crude,  which  is  heated  so  that  salts  and  other  
impurities  dissolve  or  attach  to  the  water,  then  held  in  a  tank  to  
settle  out.  
n  Electrical  desalting  is  the  application  of  high-­‐voltage  electrostatic  
charges  to  concentrate  suspended  water  globules  in  the  bottom  of  
the  settling  tank.    Surfactants  are  added  only  when  the  crude  has  a  
large  amount  of  suspended  solids.  
n  A  third  (and  rare)  process  filters  hot  crude  using  diatomaceous  
earth.   24

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DESALTING/DEHYDRATION  

n  The  crude  oil  feedstock  is  heated  to  

65-­‐180°C  to  reduce  viscosity  and  
surface  tension  for  easier  mixing  
and  separation  of  the  water.  The  
temperature  is  limited  by  the  vapor  
pressure  of  the  crude-­‐oil  feedstock.    

In both methods other chemicals may be added. Ammonia is often

used to reduce corrosion. Caustic or acid may be added to adjust
the pH of the water wash.
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DESALTING/DEHYDRATION  

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HOW  DOES  DISTILLATION  WORK?  

n  Distillation  is  defined  as:  
n  a  process  in  which  a  liquid  or  vapor  mixture  of  two  or  more  
substances  is  separated  into  its  component  fractions  of  
desired  purity,  by  the  application  and  removal  of  heat.  
 

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How  does  distillation  work?  

n  Distillation  is  based  on  the  fact  that  the  vapor  of  a  
boiling  mixture  will  be  richer  in  the  components  that  
have  lower  boiling  points.  
n  Thus,  when  this  vapor  is  cooled  and  condensed,  the  
condensate  will  contain  the  more  volatile  components.    
At  the  same  time,  the  original  mixture  will  contain  more  
of  the  less  volatile  components.  

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How  does  distillation  work?  

n  Distillation  is  the  most  common  separation  technique  
and  it  consumes  enormous  amounts  of  energy,  both  in  
terms  of  cooling  and  heating  requirements.  
n   Distillation  can  contribute  to  more  than  50%  of  plant  
operating  costs.  

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How  does  distillation  work?  

Distillation  columns  are  classified  by  the  manner  in  which  

they  are  operated:  
 
Batch,  in  which  the  feed  to  the  column  is  introduced  batch-­‐
wise.  That  is,  the  column  is  charged  with  a  'batch'  and  then  
the  distillation  process  is  carried  out.  When  the  desired  
task  is  achieved,  a  next  batch  of  feed  is  introduced.  

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How  does  distillation  work?  

Distillation  columns  are  classified  by  the  manner  in  which  

they  are  operated:  
Continuous  columns  process  a  continuous  feed  stream.  No  
interruptions  occur  unless  there  is  a  problem  with  the  
column  or  surrounding  process  units.  They  are  capable  of  
handling  high  throughputs  and  are  the  most  common  of  
the  two  types.  

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CONTINUOUS  DISTILLATION  COLUMNS  

Classified  according  to:    
 
Nature  of  the  feed  that  they  are  processing:  
n  binary  column  -­‐  feed  contains  only  two  components;  
n  multi-­‐component  column  -­‐  feed  contains  more  than  two  components.  

Number  of  product  streams  they  have:  

n  multi-­‐product  column  -­‐  column  has  more  than  two  product  streams.  

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CONTINUOUS  DISTILLATION  COLUMNS  

Classified  according  to:    

Where  extra  feed  exits  when  used  to  help  with  the  separation:  
n  extractive  distillation  -­‐  where  the  extra  feed  appears  in  the  bottom  
product  stream;  
n  azeotropic  distillation  -­‐  where  the  extra  feed  appears  at  the  top  
product  stream.  
Type  of  column  internals:  
n  tray  column  -­‐  trays  of  various  designs  used  to  hold  up  the  liquid  to  
provide  better  contact  between  vapour  and  liquid;  
n  packed  column  -­‐  packings  are  used  to  enhance  vapour-­‐liquid  contact.  
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MAIN  COMPONENTS  OF  DISTILLATION  COLUMNS  

A  vertical  shell  where  separation  

of  liquid  components  is  done.  
Column  internals  e.g.trays/plates  
and/or  packings  which  are  used  
to  enhance  component  
separations.  
A  reboiler  to  provide  the  
necessary  vaporization  for  the  
distillation  process.  

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MAIN  COMPONENTS  OF  DISTILLATION  COLUMNS  

A  condenser  to  cool  and  condense  

the  vapour  leaving  the  top  of  the  
column.  
A  reflux  drum  to  hold  the  
condensed  vapour  from  the  top  of  
the  column  so  that  liquid  (reflux)  
can  be  recycled  back  to  the  
column.  

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TRAYS  AND  PLATES  

Bubble  cap  trays  

 A  riser  or  chimney  is  fitted  
over  each  hole,  and  a  cap  
covers  the  riser.    The  cap  is  
mounted  with  a  space  to  
allow  vapor  to  rise  through  
the  chimney  and  be  directed  
downward  by  the  cap,  finally  
discharging  through  slots  in  
the  cap,  and  bubbling  through  
the  liquid  on  the  tray.  
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TRAYS  AND  PLATES  

Valve  trays  
Perforations  are  covered  by  caps  lifted  by  
vapour,  which  creates  a  flow  area  and  
directs  the  vapour  horizontally  into  the  
liquid  
Sieve  trays  
Sieve  trays  are  simply  metal  plates  with  
holes  in  them.  Vapour  passes  straight  
upward  through  the  liquid  on  the  plate.  
The  arrangement,  number  and  size  of  the  
holes  are  design  parameters.  
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LIQUID  AND  VAPOUR  FLOWS  IN  A  TRAY  

COLUMN  

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LIQUID  AND  VAPOR  FLOWS  IN  A  TRAY  COLUMN  

n  Each  tray  has  2  conduits  called  

downcomers:  one  on  each  
side.    Liquid  falls  by  gravity  
through  the  downcomers  from  
one  tray  to  the  tray  below.  
n  A  weir  ensures  there  is  always  
some  liquid  (holdup)  on  the  
tray  and  is  designed  such  that  
the  the  holdup  is  at  a  suitable  
height,  e.g.  such  that  the  
bubble  caps  are  covered  by  
liquid.  
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LIQUID  AND  VAPOR  FLOWS  IN  A  TRAY  COLUMN  

n  Vapour  flows  up  the  column  

and  is  forced  to  pass  through  
the  liquid  via  the  openings  on  
each  tray.  The  area  allowed  for  
the  passage  of  vapour  on  each  
tray  is  called  the  active  tray  
area.  

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Packings  

n  Packings  are  passive  devices  designed  to  increase  the  interfacial  
area  for  vapour-­‐liquid  contact.  
n  They  do  not  cause  excessive  pressure-­‐drop  across  a  packed  section,  
which  is  important  because  a  high  pressure  drop  would  mean  that  
more  energy  is  required  to  drive  the  vapour  up  the  distillation  
column.  
n  Packed  columns  are  called  continuous-­‐contact  columns  while  trayed  
columns  are  called  staged-­‐contact  columns  because  of  the  manner  
in  which  vapour  and  liquid  are  contacted.  

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BASIC  OPERATION  

n  The  feed  is  introduced  somewhere  

near  the  middle  of  the  column  to  a  
tray  known  as  the  feed  tray.  
n  The  feed  tray  divides  the  column  
into  a  top  (enriching  or  rectification)  
and  a  bottom  (stripping)  section.  
n  The  feed  flows  down  the  column  
where  it  is  collected  in  the  reboiler.  

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BASIC  OPERATION  

n  Heat  (usually  as  steam)  is  supplied  

to  the  reboiler  to  generate  vapour.  
n  The  vapour  from  the  reboiler  is  re-­‐
introduced  into  the  unit  at  the  
bottom  of  the  column.  
n  The  liquid  removed  from  the  
reboiler  is  known  as  the  bottoms  
product  or  simply,  bottoms.

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BASIC  OPERATION  
n  Vapor  moves  up  the  column,  exits  the  top,  and  is  cooled  in  a  
condenser.    The  condensed  liquid  is  stored  in  a  holding  vessel  
known  as  the  reflux  drum.  Some  of  this  liquid  is  recycled  back  to  
the  top  of  the  column  and  this  is  called  the  reflux.    The  condensed  
liquid  that  is  removed  from  the  system  is  known  as  the  distillate  or  
top  product.    
n  Thus,  there  are  internal  flows  of  vapour  and  liquid  within  the  
column  as  well  as  external  flows  of  feeds  and  product  streams,  into  
and  out  of  the  column.  

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CRUDE  DISTILLATION  

n  Step  1  in  the  refining  process  is  the  separation  of  crude  oil  into  
various  fractions  or  straight-­‐run  cuts  by  distillation  in  atmospheric  
and  vacuum  towers.    The  main  fractions  or  "cuts"  obtained  have  
specific  boiling-­‐point  ranges  and  can  be  classified  in  order  of  
decreasing  volatility  into  gases,  light  distillates,  middle  distillates,  
gas  oils,  and  residuum.  
   

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CRUDE  DISTILLATION  

 Atmospheric  distillation  
n  The  desalted  crude  feedstock  is  preheated  using  recovered  process  
heat.    The  feedstock  then  flows  to  a  direct-­‐fired  crude  charge  heater  
then  into  the  vertical  distillation  column  just  above  the  bottom,  at  
pressures  slightly  above  atmospheric  and  at  temperatures  ranging  
from  340-­‐370°C  (above  these  temperatures  undesirable  thermal  
cracking  may  occur).  All  but  the  heaviest  fractions  flash  into  vapor.  

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CRUDE  DISTILLATION  

 As  the  hot  vapor  rises  in  the  tower,  its  temperature  is  reduced.    
Heavy  fuel  oil  or  asphalt  residue  is  taken  from  the  bottom.  At  
successively  higher  points  on  the  tower,  the  various  major  products  
including  lubricating  oil,  heating  oil,  kerosene,  gasoline,  and  
uncondensed  gases  (which  condense  at  lower  temperatures)  are  
drawn  off.  

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ATMOSPHERIC  DISTILLATION  

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SIMPLE  CRUDE  DISTILLATION  

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TYPICAL YEILDS

VACUUM  DISTILLATION  
n  To  further  distill  the  residuum  or  topped  crude  from  the  
atmospheric  tower  without  thermal  cracking,  reduced  pressure  is  
required.  
n  The  process  takes  place  in  one  or  more  vacuum  distillation  towers.  
n  The  principles  of  vacuum  distillation  resemble  those  of  fractional  
distillation  except  that  larger  diameter  columns  are  used  to  
maintain  comparable  vapor  velocities  at  the  reduced  pressures.  The  
internal  designs  of  some  vacuum  towers  are  different  from  
atmospheric  towers  in  that  random  packing  and  demister  pads  are  
used  instead  of  trays.  

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VACUUM  DISTILLATION  

n  A  typical  first-­‐phase  vacuum  tower  may  produce  gas  oils,  

lubricating-­‐oil  base  stocks,  and  heavy  residual  for  propane  
deasphalting.  
n  A  second-­‐phase  tower  operating  at  lower  vacuum  may  distill  
surplus  residuum  from  the  atmospheric  tower,  which  is  not  used  
for  lube-­‐stock  processing,  and  surplus  residuum  from  the  first  
vacuum  tower  not  used  for  deasphalting.  
n  Vacuum  towers  are  typically  used  to  separate  catalytic  cracking  
feedstock  from  surplus  residuum.  

53

TYPICAL YEILDS

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PROPANE  DEASPHALTING  

n  Coke-­‐forming  tendencies  of  heavier  distillation  products  

are  reduced  by  removal  of  asphaltenic  materials  by  
solvent  extraction.  
n  Liquid  propane  is  a  good  solvent  (butane  and  pentane  
are  also  commonly  used).  
n  Deasphalting  is  based  on  solubility  of  hydrocarbons  in  
propane,  i.e.  the  type  of  molecule  rather  than  RMM  as  in  
distillation.  
55

PROPANE  DEASPHALTING  

n  Vacuum  residue  is  fed  to  a  countercurrent  deasphalting  

tower.    Alkanes  dissolve  in  propane  whereas  asphaltenic  
materials  (aromatic  compounds),  ʻ‘coke-­‐precursorsʼ’  do  
not.  
n  Asphalt  is  sent  for  thermal  processing.  

56

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VACUUM  DISTILLATION  

57

MODERN  CRUDE  DISTILLATION  

58

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PROPANE  DEASPHALTING  

59

SOLVENT  EXTRACTION  AND  DEWAXING  

n  Solvent  treating  is  a  widely  used  method  of  refining  lubricating  oils  
as  well  as  a  host  of  other  refinery  stocks.  
n  Since  distillation  (fractionation)  separates  petroleum  products  into  
groups  only  by  their  boiling-­‐point  ranges,  impurities  may  remain.  
These  include  organic  compounds  containing  sulfur,  nitrogen,  and  
oxygen;  inorganic  salts  and  dissolved  metals;  and  soluble  salts  that  
were  present  in  the  crude  feedstock.  

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SOLVENT  EXTRACTION  AND  DEWAXING  

n  In  addition,  kerosene  and  distillates  may  have  trace  amounts  of  
aromatics  and  naphthenes,  and  lubricating  oil  base-­‐stocks  may  
contain  wax.  
n  Solvent  refining  processes  including  solvent  extraction  and  solvent  
dewaxing  usually  remove  these  undesirables  at  intermediate  
refining  stages  or  just  before  sending  the  product  to  storage.  

61

SOLVENT  EXTRACTION  

n  The  purpose  of  solvent  extraction  is  to  prevent  corrosion,  protect  
catalyst  in  subsequent  processes,  and  improve  finished  products  by  
removing  unsaturated,  aromatic  hydrocarbons  from  lubricant  and  
grease  stocks.  
n  The  solvent  extraction  process  separates  aromatics,  naphthenes,  and  
impurities  from  the  product  stream  by  dissolving  or  precipitation.  The  
feedstock  is  first  dried  and  then  treated  using  a  continuous  
countercurrent  solvent  treatment  operation.  

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SOLVENT  EXTRACTION  

n  In  one  type  of  process,  the  feedstock  is  washed  with  a  liquid  in  which  
the  substances  to  be  removed  are  more  soluble  than  in  the  desired  
resultant  product.    In  another  process,  selected  solvents  are  added  to  
cause  impurities  to  precipitate  out  of  the  product.    In  the  adsorption  
process,  highly  porous  solid  materials  collect  liquid  molecules  on  their  
surfaces.    
n  The  solvent  is  separated  from  the  product  stream  by  heating,  
evaporation,  or  fractionation,  and  residual  trace  amounts  are  
subsequently  removed  from  the  raffinate  by  steam  stripping  or  
vacuum  flashing.  
63

SOLVENT  EXTRACTION  
n  Electric  precipitation  may  be  used  for  separation  of  inorganic  
compounds.  
n  The  solvent  is  regenerated  for  reused  in  the  process.  
n  The  most  widely  used  extraction  solvents  are  phenol,  furfural,  and  
cresylic  acid.  
n  Other  solvents  less  frequently  used  are  liquid  sulfur  dioxide,  
nitrobenzene,  and  2,2'  dichloroethyl  ether.  
n  The  selection  of  specific  processes  and  chemical  agents  depends  
on  the  nature  of  the  feedstock  being  treated,  the  contaminants  
present,  and  the  finished  product  requirements.  
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AROMATIC  SOLVENT  EXTRACTION  UNIT  

65

SOLVENT  DEWAXING  

n  Solvent  dewaxing  is  used  to  remove  wax  from  either  distillate  or  
residual  basestock  at  any  stage  in  the  refining  process.  
n  There  are  several  processes  in  use  for  solvent  dewaxing,  but  all  
have  the  same  general  steps,  which  are::  
n  mixing  the  feedstock  with  a  solvent;  
n  precipitating  the  wax  from  the  mixture  by  chilling;  and  
n  recovering  the  solvent  from  the  wax  and  dewaxed  oil  for  recycling  by  
distillation  and  steam  stripping.  

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SOLVENT  DEWAXING  

n  Solvent  dewaxing  is  used  to  remove  wax  from  either  distillate  or  
residual  basestock  at  any  stage  in  the  refining  process.  
n  There  are  several  processes  in  use  for  solvent  dewaxing,  but  all  
have  the  same  general  steps,  which  are::  
n  mixing  the  feedstock  with  a  solvent;  
n  precipitating  the  wax  from  the  mixture  by  chilling;  and  
n  recovering  the  solvent  from  the  wax  and  dewaxed  oil  for  recycling  by  
distillation  and  steam  stripping.  
 

67

SOLVENT  DEWAXING  UNIT  

CHEE 2404: Industrial Chemistry 68

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Solvent  dewaxing  unit  

69

BLENDING  

n  Blending  is  the  physical  mixture  of  a  number  of  different  liquid  
hydrocarbons  to  produce  a  finished  product  with  certain  desired  
characteristics.  
n  Products  can  be  blended  in-­‐line  through  a  manifold  system,  or  
batch  blended  in  tanks  and  vessels.  

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BLENDING  

n  In-­‐line  blending  of  gasoline,  distillates,  jet  fuel,  and  kerosene  is  
accomplished  by  injecting  proportionate  amounts  of  each  
component  into  the  main  stream  where  turbulence  promotes  
thorough  mixing.  
n  Additives  including  octane  enhancers,  anti-­‐oxidants,  anti-­‐knock  
agents,  gum  and  rust  inhibitors,  detergents,  etc.  are  added  during  
and/or  after  blending  to  provide  specific  properties  not  inherent  
in  hydrocarbons.  

71

THERMAL  PROCESSES  
 When  a  hydrocarbon  is  heated  to  a  sufficiently  high  
temperature  thermal  cracking  occurs.  This  is  
sometimes  referred  to  as  pyrolysis  (especially  when  
coal  is  the  feedstock).    When  steam  is  used  it  is  called  
steam  cracking.    We  will  examine  two  thermal  
processes  used  in  refineries.  
n  Visbreaking  
n  Delayed  coking  
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VISBREAKING  

n  Visbreaking is a mild form of thermal cracking that lowers the

viscosity of heavy crude-oil residues without affecting the
boiling point range.
n  Residuum from the atmospheric distillation tower is heated
(425-510ºC) at atmospheric pressure and mildly cracked in a
heater.
n  It is then quenched with cool gas oil to control over-cracking,
and flashed in a distillation tower.

73

VISBREAKING  

n  Visbreaking is used to reduce the pour point of waxy residues

and reduce the viscosity of residues used for blending with
lighter fuel oils. Middle distillates may also be produced,
depending on product demand.
n  The thermally cracked residue tar, which accumulates in the
bottom of the fractionation tower, is vacuum-flashed in a
stripper and the distillate recycled.

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VISBREAKING  

75

VISBREAKING  
n  Alternatively,  vacuum  residue  can  be  cracked.    The  severity  of  the  
visbreaking  depends  upon  temperature  and  reaction  time  (1-­‐8  min).  
n  Usually  <  10  wt%  of  gasoline  and  lighter  products  are  produced.  
 

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VISBREAKING  

77

DELAYED  COKING  

n  Coking  is  a  severe  method  of  thermal  cracking  used  to  upgrade  
heavy  residuals  into  lighter  products  or  distillates.  
n  Coking  produces  straight-­‐run  gasoline  (Coker  naphtha)  and  
various  middle-­‐distillate  fractions  used  as  catalytic  cracking  
feedstock.  
n  The  process  completely  reduces  hydrogen  so  that  the  residue  is  
a  form  of  carbon  called  "coke.”    

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DELAYED  COKING  

n  Three  typical  types  of  coke  are  obtained  (sponge  coke,  
honeycomb  coke,  and  needle  coke)  depending  upon  the  reaction  
mechanism,  time,  temperature,  and  the  crude  feedstock.  
n  In  delayed  coking  the  heated  charge  (typically  residuum  from  
atmospheric  distillation  towers)  is  transferred  to  large  coke  
drums  which  provide  the  long  residence  time  needed  to  allow  
the  cracking  reactions  to  proceed  to  completion.  

79

Sponge  coke  derived  from  a  petroleum  feedstock  that  shows  abundant  pore  
structure.  Note  the  flow  texture  in  the  coke  cell  walls.  
http://mccoy.lib.siu.edu/projects/crelling2/atlas/PetroleumCoke/pettut.html  

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Typical  needle  coke  derived  from  a  petroleum  feedstock.    The  parallel  layers  
and  linear  fractures  are  distinctive  and  provide  slip  planes  to  relieve  stress  in  
the  coke  .  
http://mccoy.lib.siu.edu/projects/crelling2/atlas/PetroleumCoke/pettut.html  

CHEE 2404: Industrial Chemistry 81

DELAYED  COKING  

n  Heavy  feedstock  is  fed  to  a  fractionator.  

n  The  bottoms  of  the  fractionator  are  fed  to  coker  drums  via  a  
furnace  where  the  hot  material  (440°-­‐500°C  )  is  held  
approximately  24  hours  (delayed)  at  pressures  of  2-­‐5  bar,  until  it  
cracks  into  lighter  products.  
n  Vapors  from  the  drums  are  returned  to  a  fractionator  where  gas,  
naphtha,  and  gas  oils  are  separated  out.  The  heavier  
hydrocarbons  produced  in  the  fractionator  are  recycled  through  
the  furnace.  
n  After  the  coke  reaches  a  predetermined  level  in  one  drum,  the  
flow  is  diverted  to  another  drum  to  maintain  continuous  
operation.   82

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DELAYED  COKING  

n  The  full  drum  is  steamed  to  strip  out  uncracked  hydrocarbons,  
cooled  by  water  injection,  and  de-­‐coked  by  mechanical  or  
hydraulic  methods.  
n   The  coke  is  mechanically  removed  by  an  auger  rising  from  the  
bottom  of  the  drum.    Hydraulic  decoking  consists  of  fracturing  
the  coke  bed  with  high-­‐pressure  water  ejected  from  a  rotating  
cutter.  

83

DELAYED  COKING  

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CATALYTIC  PROCESSES  
n  Fluid  Catalytic  Cracking  (FCC)  
n  Hydrotreating  
n  Hydrocracking  
n  Catalytic  Reforming  
n  Alkylation  

85

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87

CATALYTIC  CRACKING  
n  Main  incentive  for  catalytic  cracking  is  the  need  to  
increase  gasoline  production.  
n  Feedstocks  are  typically  vacuum  gas  oil.  
n  Cracking  is  catalyzed  by  solid  acids  which  promote  the  
rupture  of  C-­‐C  bonds.    The  crucial  intermediates  are  
carbocations  (+ve  charged  HC  ions)  formed  by  the  action  
of  the  acid  sites  on  the  catalyst.  
n  Besides  C-­‐C  cleavage  many  other  reactions  occur:  
   -­‐  isomerization  
   -­‐  protonation  and  deprotonation  
   -­‐  alkylation   CHEE 2404: Industrial Chemistry 88
   -­‐  polymerization  
   -­‐  cyclization  and  condensation  
 

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CATALYTIC  CRACKING  

n  Main  incentive  for  catalytic  cracking  is  the  need  to  
increase  gasoline  production.  
n  Feedstocks  are  typically  vacuum  gas  oil.  
n  Cracking  is  catalyzed  by  solid  acids  which  promote  
the  rupture  of  C-­‐C  bonds.    The  crucial  intermediates  
are  carbocations  (+ve  charged  HC  ions)  formed  by  the  
action  of  the  acid  sites  on  the  catalyst.  
 

89

CATALYTIC  CRACKING  

n  Besides  C-­‐C  cleavage  many  other  reactions  occur:  

   -­‐  isomerization  
   -­‐  protonation  and  deprotonation  
   -­‐  alkylation  
   -­‐  polymerization  
   -­‐  cyclization  and  condensation  
 

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CATALYTIC  CRACKING  

n  Catalytic  cracking  comprises  a  complex  network  of  

reactions,  both  intra-­‐molecular  and  inter-­‐molecular.  
n  The  formation  of  coke  is  an  essential  feature  of  the  
cracking  process  and  this  coke  deactivates  the  catalyst.  
n  Catalytic  cracking  is  one  of  the  largest  applications  of  
catalysts:    worldwide  cracking  capacity  exceeds  500  
million  t/a.  

91

CATALYTIC  CRACKING  

n  Catalytic  cracking  was  the  first  large-­‐scale  application  

of  fluidized  beds  which  explains  the  name  fluid  
catalytic  cracking  (FCC).    
n  Nowadays  entrained-­‐flow  reactors  are  used  instead  of  
fluidized  beds  but  the  name  FCC  is  still  retained.  

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FLUID  CATALYTIC  CRACKING  

n  Oil  is  cracked  in  the  presence  of  a  finely  divided  catalyst,  which  is  
maintained  in  an  aerated  or  fluidized  state  by  the  oil  vapours.  
n  The  fluid  cracker  consists  of  a  catalyst  section  and  a  fractionating  
section  that  operate  together  as  an  integrated  processing  unit.  
n  The  catalyst  section  contains  the  reactor  and  regenerator,  which,  
with  the  standpipe  and  riser,  form  the  catalyst  circulation  unit.  The  
fluid  catalyst  is  continuously  circulated  between  the  reactor  and  
the  regenerator  using  air,  oil  vapors,  and  steam  as  the  conveying  
media.  

93

FLUID  CATALYTIC  CRACKING  

n  Preheated  feed  is  mixed  with  hot,  regenerated  catalyst  in  the  riser  
and  combined  with  a  recycle  stream,  vapourized,  and  raised  to  
reactor  temperature  (485-­‐540°C)  by  the  hot  catalyst.  
n  As  the  mixture  travels  up  the  riser,  the  charge  is  cracked  at  0.7-­‐2  
bar.  
n  In  modern  FCC  units,  all  cracking  takes  place  in  the  riser  and  the  
"reactor"  merely  serves  as  a  holding  vessel  for  the  cyclones.  
Cracked  product  is  then  charged  to  a  fractionating  column  where  
it  is  separated  into  fractions,  and  some  of  the  heavy  oil  is  recycled  
to  the  riser.  

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FLUID  CATALYTIC  CRACKING  

n  Spent  catalyst  is  regenerated  to  get  rid  of  coke  that  collects  on  
the  catalyst  during  the  process.  
n  Spent  catalyst  flows  through  the  catalyst  stripper  to  the  
regenerator,  where  most  of  the  coke  deposits  burn  off  at  the  
bottom  where  preheated  air  and  spent  catalyst  are  mixed.  
n  Fresh  catalyst  is  added  and  worn-­‐out  catalyst  removed  to  
optimize  the  cracking  process.    
 

95

FLUID  CATALYTIC  CRACKING  

96

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FLUID  CATALYTIC  CRACKING  

97

FLUID  CATALYTIC  CRACKING  

98

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HYDROTREATING  

n  Catalytic  hydrotreating  is  a  hydrogenation  process  used  to  

remove  about  90%  of  contaminants  such  as  nitrogen,  sulfur,  
oxygen,  and  metals  from  liquid  petroleum  fractions.  
n  If  these  contaminants  are  not  removed  from  the  petroleum  
fractions  they  can  have  detrimental  effects  on  equipment,  
catalysts,  and  the  quality  of  the  finished  product.  

99

HYDROTREATING  

n  Catalytic  hydrotreating  is  a  hydrogenation  process  used  to  

remove  about  90%  of  contaminants  such  as  nitrogen,  sulfur,  
oxygen,  and  metals  from  liquid  petroleum  fractions.  
n  If  these  contaminants  are  not  removed  from  the  petroleum  
fractions  they  can  have  detrimental  effects  on  equipment,  
catalysts,  and  the  quality  of  the  finished  product.  

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HYDROTREATING  
n  Typically,  hydrotreating  is  done  prior  to  processes  such  as  catalytic  
reforming  so  that  the  catalyst  is  not  contaminated  by  untreated  
feedstock.    Hydrotreating  is  also  used  prior  to  catalytic  cracking  to  
reduce  sulfur  and  improve  product  yields,  and  to  upgrade  middle-­‐
distillate  petroleum  fractions  into  finished  kerosene,  diesel  fuel,  
and  heating  fuel  oils.  
n  In  addition,  hydrotreating  converts  olefins  and  aromatics  to  
saturated  compounds.  

101

CATALYTIC  HYDRODESULFURIZATION  PROCESS  

n  Hydrotreating  for  sulfur  removal  is  called  hydrodesulfurization.  

n  In   a   typical   catalytic   hydrodesulfurization   unit,   the   feedstock   is  
deaerated   and   mixed   with   hydrogen,   preheated   in   a   fired   heater  
(315°-­‐425°   C)   and   then   charged   under   pressure   (up   to   70   bar)   through  
a  trickle-­‐bed  catalytic  reactor.  

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CATALYTIC  HYDRODESULFURIZATION  PROCESS  

n  In   the   reactor,   the   sulfur   and   nitrogen   compounds   in   the   feedstock  
are  converted  into  H2S  and  NH3.  
n  The  reaction  products  leave  the  reactor  and  after  cooling  to  a  low  
temperature   enter   a   liquid/gas   separator.   The   hydrogen-­‐rich   gas  
from  the  high-­‐pressure  separation  is  recycled  to  combine  with  the  
feedstock,  and  the  low-­‐pressure  gas  stream  rich  in  H2S  is  sent  to  a  
gas  treating  unit  where  H2S  is  removed.  

103

CATALYTIC  HYDRODESULFURIZATION  PROCESS  

n  The  clean  gas  is  then  suitable  as  fuel  for  the  refinery  furnaces.  The  
liquid  stream  is  the  product  from  hydrotreating  and  is  normally  sent  
to  a  stripping  column  for  removal  of  H2S  and  other  undesirable  
components.  
n  In  cases  where  steam  is  used  for  stripping,  the  product  is  sent  to  a  
vacuum  drier  for  removal  of  water.  
n  Hydrodesulfurized  products  are  blended  or  used  as  catalytic  
reforming  feedstock.  

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HYDROTREATING:  FLOW  SCHEME  

105

HYDROTREATING:  TRICKLE-­‐BED  REACTOR  

106

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OTHER  HYDROTREATING  PROCESSES  

n  Hydrotreating  also  can  be  used  to  improve  the  quality  of  pyrolysis  
gasoline  (pygas),  a  by-­‐product  from  the  manufacture  of  ethylene.  
n  Traditionally,  the  outlet  for  pygas  has  been  motor  gasoline  
blending,  because  of  its  high  octane  number.  However,  only  small  
portions  can  be  blended  untreated  owing  to  the  unacceptable  
odor,  color,  and  gum-­‐forming  tendencies  of  this  material.  
n  The  quality  of  pygas,  which  is  high  in  diolefin  content,  can  be  
satisfactorily  improved  by  hydrotreating,  whereby  conversion  of  
diolefins  into  mono-­‐olefins  provides  an  acceptable  product  for  
motor  gas  blending.  
107

OTHER  HYDROTREATING  PROCESSES  

n  Hydrotreating   processes   differ   depending   upon   the   feedstock  
available  and  catalysts  used.  
n  Hydrotreating  can  be  used  to  improve  the  burning  characteristics  
of   distillates   such   as   kerosene.   by   converting   aromatics   into  
naphthenes,  which  are  cleaner-­‐burning  compounds.    

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OTHER  HYDROTREATING  PROCESSES  

n  Lube-­‐oil  hydrotreating  uses  hydrogen  to  improve  product  quality.  
With   mild   lube   hydrotreating   saturation   of   olefins   and  
improvements   in   color,   odor,   and   acid   nature   of   the   oil   are  
achieved.      
n  Operating   temperatures   and   pressures   are   usually   below   315°   C  
and   60   bar.   Severe   lube   hydrotreating   (T   ~   315   -­‐   400°C   and  
hydrogen   pressures   up   to   205   bar)   is   capable   of   saturating  
aromatic   rings,   along   with   sulfur   and   nitrogen   removal,   to   impart  
specific  properties  not  achieved  at  mild  conditions.  
109

HYDROCRACKING  

n  Hydrocracking   is   a   two-­‐stage   process   combining   catalytic   cracking  

and   hydrogenation,   wherein   heavier   feedstock   is   cracked   in   the  
presence  of  hydrogen  to  produce  more  desirable  products.  
n  The   process   employs   high   pressure,   high   temperature,   a   catalyst,  
and  hydrogen.  Hydrocracking  is  used  for  feedstock  that  are  difficult  
to   process   by   either   catalytic   cracking   or   reforming,   since   these  
feedstock   are   characterized   usually   by   a   high   polycyclic   aromatic  
content   and/or   high   concentrations   of   the   two   principal   catalyst  
poisons,  sulfur  and  nitrogen  compounds.  
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HYDROCRACKING  

n  The  process  largely  depends  on  the  nature  of  the  feedstock  and  the  
relative   rates   of   the   two   competing   reactions,   hydrogenation   and  
cracking.   Heavy   aromatic   feedstock   is   converted   into   lighter  
products   under   a   wide   range   of   very   high   pressures   (70-­‐140   bar)  
and   fairly   high   temperatures   (400°-­‐800°C),   in   the   presence   of  
hydrogen  and  special  catalysts.    

111

HYDROCRACKING  
n  When  the  feedstock  has  a  high  paraffinic  content,  the  primary  
function  of  hydrogen  is  to  prevent  the  formation  of  polycyclic  
aromatic  compounds.  
n  Another  important  role  of  hydrogen  in  the  hydrocracking  process  is  
to  reduce  tar  formation  and  prevent  buildup  of  coke  on  the  
catalyst.  

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HYDROCRACKING  
n  Hydrogenation  also  serves  to  convert  sulfur  and  nitrogen  
compounds  present  in  the  feedstock  to  hydrogen  sulfide  and  
ammonia.    
n  Hydrocracking  produces  relatively  large  amounts  of  isobutane  for  
alkylation  feedstock  and  also  performs  isomerization  for  pour-­‐point  
control  and  smoke-­‐point  control,  both  of  which  are  important  in  
high-­‐quality  jet  fuel.  

113

HYDROCRACKING  
n  Preheated   feedstock   is   mixed   with   recycled   hydrogen   and   sent   to  
the  first-­‐stage  reactor,  where  catalysts  convert  sulfur  and  nitrogen  
compounds  to  H2S  and  NH3.    Limited  hydrocracking  also  occurs.    
n  After   the   hydrocarbon   leaves   the   first   stage,   it   is   cooled   and  
liquefied  and  run  through  a  separator.  The  hydrogen  is  recycled  to  
the  feedstock.  

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HYDROCRACKING  
n  The  liquid  is  charged  to  a  fractionator.  
n  The  fractionator  bottoms  are  again  mixed  with  a  hydrogen  stream  
and   charged   to   the   second   stage.   Since   this   material   has   already  
been  subjected  to  some  hydrogenation,  cracking,  and  reforming  in  
the   first   stage,   the   operations   of   the   second   stage   are   more   severe  
(higher   temperatures   and   pressures).   Again,   the   second   stage  
product   is   separated   from   the   hydrogen   and   charged   to   the  
fractionator.  

115

HYDROCRACKING  PROCESS  

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HYDROCRACKING  FLOW  SCHEME  

117

CATALYTIC  REFORMING  

n  Catalytic  reforming  is  an  important  process  used  to  convert  low-­‐
octane  naphthas  into  high-­‐octane  gasoline  blending  components  
called  reformates.  
n  Reforming  represents  the  total  effect  of  numerous  reactions  such  
as  cracking,  polymerization,  dehydrogenation,  and  isomerization  
taking  place  simultaneously.  

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CATALYTIC  REFORMING  
n  Depending  on  the  properties  of  the  naphtha  feedstock  (as  
measured  by  the  paraffin,  olefin,  naphthene,  and  aromatic  content)  
and  catalysts  used,  reformates  can  be  produced  with  very  high  
concentrations  of  benzene,  toluene,  xylene,  (BTX)  and  other  
aromatics  useful  in  gasoline  blending  and  petrochemical  processing.  
n  Hydrogen,  a  significant  by-­‐product,  is  separated  from  the  reformate  
for  recycling  and  use  in  other  processes.  

119

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CHEE 2404: Industrial Chemistry 121

CATALYTIC  REFORMING  

n  A  catalytic  reformer  comprises  a  reactor  and  product-­‐recovery  

section.  
n  There  is  a  feed  preparation  section  comprising  a  combination  of  
hydrotreatment  and  distillation.  
n  Most  processes  use  Pt  as  the  active  catalyst.  Sometimes  Pt  is  
combined  with  a  second  catalyst  (bimetallic  catalyst)  such  as  
rhenium  or  another  noble  metal.  

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CATALYTIC  REFORMING  

n  There  are  many  different  commercial  processes  including  

platforming,  powerforming,  ultraforming,  and  Thermofor  catalytic  
reforming.  
n  Some  reformers  operate  at  low  pressure  (3-­‐13  bar),  others  at  high  
pressures  (up  to  70  bar).  Some  systems  continuously  regenerate  
the   catalyst   in   other   systems.   One   reactor   at   a   time   is   taken   off-­‐
stream  for  catalyst  regeneration,  and  some  facilities  regenerate  all  
of  the  reactors  during  turnarounds.  

123

CATALYTIC  REFORMING  
n  In  the  platforming  process,  the  first  step  is  preparation  of  the  
naphtha  feed  to  remove  impurities  from  the  naphtha  and  reduce  
catalyst  degradation.  
n  The  naphtha  feedstock  is  then  mixed  with  hydrogen,  vaporized,  
and  passed  through  a  series  of  alternating  furnace  and  fixed-­‐bed  
reactors  containing  a  platinum  catalyst.  

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CATALYTIC  REFORMING  

n  The  effluent  from  the  last  reactor  is  cooled  and  sent  to  a  separator  
to  permit  removal  of  the  hydrogen-­‐rich  gas  stream  from  the  top  of  
the  separator  for  recycling.  
n  The  liquid  product  from  the  bottom  of  the  separator  is  sent  to  a  
fractionator  called  a  stabilizer  (butanizer).  It  makes  a  bottom  
product  called  reformate;  butanes  and  lighter  go  overhead  and  are  
sent  to  the  saturated  gas  plant.  

125

CATALYTIC  REFORMING  SCHEME  

126

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SEMI-­‐REGENERATIVE  CATALYTIC  REFORMING  

127

CONTINUOUS  REGENERATIVE  REFORMING  

128

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CATALYTIC  REFORMING  REACTORS  

129

ALKYLATION  
n  Alkylation   combines   low-­‐molecular-­‐weight   olefins   (primarily   a  
mixture   of   propylene   and   butylene)   with   isobutene   in   the  
presence  of  a  catalyst,  either  sulfuric  acid  or  hydrofluoric  acid.  
n  The   product   is   called   alkylate   and   is   composed   of   a   mixture   of  
high-­‐octane,  branched-­‐chain  paraffinic  hydrocarbons.  
n  Alkylate   is   a   premium   blending   stock   because   it   has   exceptional  
antiknock  properties  and  is  clean  burning.  The  octane  number  of  
the   alkylate   depends   mainly   upon   the   kind   of   olefins   used   and  
upon  operating  conditions.  
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SULPHURIC  ACID  ALKYLATION  PROCESS  

n  In   cascade   type   sulfuric   acid   (H2SO4)   alkylation   units,   the  

feedstock   (propylene,   butylene,   amylene,   and   fresh   isobutane)  
enters   the   reactor   and   contacts   the   concentrated   sulfuric   acid  
catalyst  (in  concentrations  of  85%  to  95%  for  good  operation  and  
to  minimize  corrosion).  
n  The   reactor   is   divided   into   zones,   with   olefins   fed   through  
distributors   to   each   zone,   and   the   sulfuric   acid   and   isobutanes  
flowing  over  baffles  from  zone  to  zone.    

131

SULPHURIC  ACID  ALKYLATION  PROCESS  

n  The   reactor   effluent   is   separated   into   hydrocarbon   and   acid  

phases   in   a   settler,   and   the   acid   is   returned   to   the   reactor.   The  
hydrocarbon   phase   is   hot-­‐water   washed   with   caustic   for   pH  
control   before   being   successively   depropanized,   deisobutanized,  
and   debutanized.   The   alkylate   obtained   from   the   deisobutanizer  
can   then   go   directly   to   motor-­‐fuel   blending   or   be   rerun   to   produce  
aviation-­‐grade   blending   stock.   The   isobutane   is   recycled   to   the  
feed.    

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SULPHURIC  ACID  ALKYLATION  PROCESS  

133

SULPHURIC  ACID  ALKYLATION  PROCESS  

134

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ALKYLATION  WITH  H2SO4  IN  STRATCO  

CONTACTOR  WITH  AUTOREFRIGERATION  

CHEE 2404: Industrial Chemistry 135

CONVERSION  OF  HEAVY  RESIDUES  

n  Processing  of  light  crude,  even  in  a  complex  refinery  with  FCC,  
hydrocracking  etc.  does  not  yield  a  satisfactory  product  
distribution.    The  amounts  of  fuel  oil  are  too  high.  

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CONVERSION  OF  HEAVY  RESIDUES  

n  For  heavy  oil  the  situation  is  even  worse  with  ~  50%  fuel  oil  being  
produced  even  in  a  complex  refinery.  
n  Fuel  oil  is  worth  <  original  crude.    The  value  of  the  products  
decreases  in  the  order:  gasoline>  kerosene/gas  oil  >  crude  oil  >  fuel  
oil.  

137

CONVERSION  OF  HEAVY  RESIDUES  

 There  are  several  reasons  for  an  increased  incentive  to  convert  fuel  oil  
into  lighter  products:  
 
1.  The  demand  for  light  products  such  as  gasoline  and  automotive  diesel  
fuels  continues  to  increase  while  market  for  heavy  fuel  oil  is  declining.  
2.  Environmental  restrictions  become  more  important.    Fuel  oil  contains  
high  amounts  of  S,  N,  and  metals,  so  measures  must  be  taken  to  lower  
emissions.  

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CONVERSION  OF  HEAVY  RESIDUES  

 There  are  several  reasons  for  an  increased  incentive  to  
convert  fuel  oil  into  lighter  products:  
 
1.  With  the  exception  of  Western  Europe,  the  quality  of  crude  oil  
shows  a  worsening  trend.    It  becomes  heavier  with  higher  
amounts  of  hetero-­‐atoms,  so  more  extensive  processing  is  
required  to  obtain  the  same  amount  and  quality  of  products.  

139

CONVERSION  OF  HEAVY  RESIDUES  

 In  principle  there  are  two  solutions  for  upgrading  residual  oils  
and  for  obtaining  a  better  product  distribution.    These  are  
carbon  out  and  hydrogen  in  processes.  
 
1.  Examples  of  carbon  rejection  processes  are  the  Flexicoking  
process  (Exxon)  and  the  FCC  process  discussed  earlier.  
2.  Examples  of  hydrogen  addition  processes  are  the  LC-­‐fining  
process  (Lummus)  and  the  HYCON  process  (Shell).  

CHEE 2404: Industrial Chemistry 140

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FLUID  COKING  AND  FLEXICOKING  

n  Both  FLUID  COKINGTM  and  FLEXICOKINGTM  use  fluid  bed  
technology  to  thermally  convert  heavy  oils  such  as  vacuum  
residue,  atmospheric  residue,  tar  sands  bitumen,  heavy  
whole  crudes,  deasphalter  bottoms  or  cat  plant  bottoms.  
n  FLEXICOKING  goes  one  step  further  than  FLUID  COKING:  in  
addition  to  generating  clean  liquids,  FLEXICOKING  also  
produces  a  low-­‐BTU  gas  in  one  integrated  processing  step  
that  can  virtually  eliminate  petroleum  coke  production.  

141

FLUID  COKING  AND  FLEXICOKING  

n  The  advantages  are:  flexibility  to  handle  a  variety  of  feed  
types;  high  reliability  with  the  average  service  factor  between  
90  -­‐95%;  large  single  train  capacity  provides  an  economy  of  
scale  that  lowers  investment  cost;  able  to  process  65  kB/SD  of  
20  wt%  Conradson  Carbon  resid  in  a  single  reactor;  time  
between  turnarounds  routinely  approaches  two  years;  able  to  
process  very  heavy  feed  stocks  such  as  deasphalter  bottoms  
at  high  feed  rates.  
n  Additional  FLEXICOKING  benefit:  Integrated  gasification  of  up  
to  97%  of  gross  coke  production    

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THE  FLUID  COKING  PROCESS  

n  The  fluid  coking  residuum  conversion  process  uses  non-­‐

catalytic,  thermal  chemistry  to  achieve  high  conversion  
levels  with  even  the  heaviest  refinery  feedstocks.  
n  Since  most  of  the  sulfur,  nitrogen,  metals,  and  Conradson  
Carbon  Residue  feed  contaminants  are  rejected  with  the  
coke,  the  full-­‐range  of  lighter  products  can  be  feed  for  an  
FCC  unit.  

143

THE  FLUID  COKING  PROCESS  

n  Use  as  a  single  train  reduces  manpower  requirements  and  

avoids  process  load  swings  and  frequent  thermal  cycles  that  
are  typical  of  batch  processes  such  as  delayed  coking.  
n  The  configurations  available  with  fluid  coking  are:  extinction  
recycle,  once-­‐through,  and  once-­‐through  with  hydroclones.  

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CHEE 2404: Industrial Chemistry 145

THE  FLEXICOKING  PROCESS  

n  Flexicoking  is  a  thermal  technology  for  converting  heavy  
feedstocks  to  higher  margin  liquids  and  producing,  a  low  BTU  
(i.e.  a  low  energy  content)  gas,  instead  of  coke.  
n  The  conversion  of  coke  to  clean  fuel  gas  maximizes  refinery  
yield  of  hydrocarbons.  
n  The  carbon  rejection  process  results  in  lower  hydrogen  
consumption  than  alternative  hydrogen-­‐addition  systems.  
n  The  low  BTU  gas  is  typically  fed  to  a  CO  boiler  for  heat  
recovery  but  can  also  be  used  in  modified  furnaces/boilers;  
atmospheric  or  vacuum  pipestill  furnaces;  reboilers;  waste  
heat  boilers;  power  plants  and  steel  mills;  or  as  hydrogen  
plant  fuel,  which  can  significantly  reduce  or  eliminate  
purchases  of  expensive  natural  gas.  
CHEE 2404: Industrial Chemistry 146
n  The  small  residual  coke   produced  can  be  sold  as  boiler  fuel  for  
generating  electricity  and  steam  or  as  burner  fuel  for  cement  
plants.  

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THE  FLEXICOKING  PROCESS  

n  Flexicoking  is  a  thermal  technology  for  converting  heavy  

feedstocks  to  higher  margin  liquids  and  producing,  a  low  BTU  
(i.e.  a  low  energy  content)  gas,  instead  of  coke.  
n  The  conversion  of  coke  to  clean  fuel  gas  maximizes  refinery  
yield  of  hydrocarbons.  
n  The  carbon  rejection  process  results  in  lower  hydrogen  
consumption  than  alternative  hydrogen-­‐addition  systems.  

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THE  FLEXICOKING  PROCESS  

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CATALYTIC  HYDROGENATION  OF  RESIDUES  

n  This  is  a  “hydrogen-­‐in”  route.  

n  It  serves  two  purposes:  removal  of  Sulphur,  Nitrogen  and  
metal  compounds,  and  the  production  of  light  products.  

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CATALYTIC  HYDROGENATION  OF  RESIDUES  

Reactions  are  similar  to  those  occurring  in  hydrotreating  and  

hydrocracking  of  gas  oils,  but  there  are  two  important  differences.  
n  (1)  Residues  contain  much  higher  amounts  of  sulphur,  
nitrogen  and  polycyclic  aromatic  compounds;  and  
n  (2)  removal  of  metals,  which  are  concentrated  in  the  residual  
fraction  of  the  crude,  means  that  operating  conditions  are  
more  severe  and  hydrogen  consumption  greater  than  for  
hydroprocessing  of  gas  oils.  

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CATALYST  DEACTIVATION  

n  Deposition  of  metals  causes  catalyst  deactivation.  

n  Basically  all  metals  in  the  periodic  table  are  present  in  crude  
oil  with  the  major  ones  being  Ni  and  V.  
n  At  the  reaction  conditions  H2S  is  present,  hence  metal  
sulphides  are  formed.  

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CATALYST  DEACTIVATION  

n  The  reaction  scheme  is  complex  but  may  be  represented  
simply  as:  
 Ni-­‐porphyrin  +  H2  →  NiS  +  hydrocarbons                          and  
   V-­‐porphyrin  +  H2  →  V2S3  +  hydrocarbons  
n  The  catalyst  is  poisoned  by  this  process  because  most  of  the  
deposition  occurs  on  the  outer  shell  of  the  catalyst  particles,  
initially  poisoning  the  active  sites  then  causing  pore  
plugging.    

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REACTORS  USED  FOR  CATALYTIC  HYDROGENATION  

n  Three  types  of  reactor  are  used:  (1)  fixed-­‐bed  reactors;  (2)  fluidized-­‐
bed  reactors  (also  called  ebulliated-­‐bed  reactors);  and  (3)  slurry  
reactors.  

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THE  LC-­‐FINING  PROCESS  

n  Developed  by  Lummus.  
n  Uses  fluidized-­‐bed  reactors.  

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Processes  with  fixed-­‐bed  reactors  

n  Replacement  of  deactivated  catalyst  in  a  conventional  fixed-­‐bed  reactor  is  
not  possible  during  operation.  
n  Depending  on  the  metal  content  of  the  feedstock  various  combinations  
can  be  applied.  

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HYCON  process  

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CATALYST  REJUVENATION  

n  Catalyst  rejuvenation  is  achieved  by  removal  of  metal  sulphides  and  
carbonaceous  deposits  (essentially  by  oxidation),  and  by  extraction  of  the  
metals.  

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PROCESSES  WITH  SLURRY  REACTORS  

n  Slurry  processes  for  residue  processing  are  normally  

designed  with  the  objective  of  maximizing  residue  
conversion.  
n  Downstream  reactors  are  then  used  to  treat  the  liquid  
products  for  S  and  N  removal.  
n  Examples  of  the  slurry  process  are  the  Veba  Combi-­‐Cracking  
and  CANMET  process.  

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PROCESSES  WITH  SLURRY  REACTORS  

n  Conversion  of  residual  feed  takes  place  in  the  liquid  phase  in  
a  slurry  reactor.  
n  After  separation  the  residue  from  the  products  they  are  
further  hydro-­‐treated  in  a  fixed-­‐bed  reactor  containing  an  
HDS  catalyst.  
n  A  cheap,  once-­‐through  catalyst  is  used  which  ends  up  in  the  
residue.  

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VEBA  COMBI-­‐CRACKING  PROCESS  

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TREATMENT  OF  REFINERY  GASES  

n  Removal  of  H2S  from  gases  is  usually  performed  by  absorption  in  
the  liquid  phase.  
n  The  concentrated  H2S  is  frequently  converted  to  elemental  sulphur  
by  the  “Claus”  process  (partial  oxidation  of  H2S)  
n  In  the  Claus  process  95-­‐97%  of  the  H2S  is  converted.  

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TREATMENT  OF  REFINERY  GASES  

n  H2S  is  often  removed  with  solvents  that  can  be  regenerated,  usually  
alkanolamines:  e.g.  CH2(OH)CH2NH2  MEA  (mono-­‐ethanolamine).  
n  These  amines  are  highly  water  soluble  with  low  volatility  and  their  
interaction  with  H2S  is  much  faster  than  with  CO2  so  that  the  
amount  of  absorbed  CO2  can  be  limited  by  selecting  appropriate  
conditions.  

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Flow  scheme  for  H2S  removal  by  amine  

absorption  

164

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Flow  scheme  of  a  typical  Claus  process  

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REFERENCES  
 Some  great  websites  are:  
n  http://lorien.ncl.ac.uk/ming/distil/distil0.htm  
n  http://science.howstuffworks.com/oil-­‐refining.htm  

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