Evaluation of Crude Oil, Petroleum Products and Petrochemicals Chemical Engineering Notes | EduRev

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Chemical Engineering : Evaluation of Crude Oil, Petroleum Products and Petrochemicals Chemical Engineering Notes | EduRev

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Evaluation of Crude Oil, Petroleum Products and Petrochemicals 

Indigenous and imported crude oils are being process in India for production of gasoline, diesel, kerosene and lube oil, wax and feed stock for petrochemical industry like naphtha, kerosene etc.

Various sources of indigenous crude are:

  • Assam crude
  • Bombay high and satellite fields, North Gujarat & Ankhleshwar
  • KG basin-Rava crude · Cauvery basin crude
  • Rajasthan crude

Various sources of imported crude are

  • Arab mix,
  • Lavan blend
  • Upper Zakum
  • Iran mix
  • Dubai
  • Kuwait crude
  • Suez mix
  • Zeit bay
  • Quaiboe
  • Miri light
  • Bonny light

Types of Evaluation 

Depending on the objective of evaluation, following are the types of evaluation generally carried out.

  • Preliminary Assay: Which is generally comprised of
    •  Key basic properties of crude oil 
    • Distillation data generated through a semi fractionating or fractionating distillation
  • Short Evaluation: 
    • Physico-chemical properties of crude oil fractionating TBP distillation data
    • Yield and some key characteristics of major straight run products (Naphtha, Kerosene, Gas oil cuts and Atmospheric residue)
  • Detailed Evaluation: 
  • Physico-chemical properties of crude oil TBP distillation Assay (Atmospheric and vacuum range)
  • Detailed studies on studies on several straight run cut in fuel oil, lube oil and secondary processing feedstocks and bitumen.   

Rude Oil Evaluation 

Quality of crude being processed affect

  • Plant capacity
  • Feed stock availability and quality for downstream units
  • Product pattern
  • Overall economics

Significant effect on processing scheme and product pattern

Effect of change in crude quality

  • Change of product pattern
  • Change of processing scheme
  • Throughput
  • Economics
  • Effluent quality

Various parameters for prediction of crude oil storage and handling behavior are viscosity, pour point, H2S, base of the crude (characterization factors, BMCI index, viscosity index), mercaptans, acidity, salt and BS & W, distillation, RVP, characteristics of crude, light end analysis, rheology, corrosiveness, impurities, volatility, LPG potential, sulphur wax, CR, Trace metals, naphthenic acid, asphaltenes etc. Details description of parameters are given in Table MVI 2.1.

Table M-VI 2.1: Various Parameters used for Storage & Handling of Crude Oil  

Parameters

Significance

Description

Density and API gravity.

Weight to volume and vice versa

calculation, checking consistency of crude oil, control of refinery operation and give a rough estimation of crude oil. API gravity of lighter crude oil may be of the order of 45 whereas in heavier asphaltenes API is 10-12.

Density = Mass/volume

API gravity =

Evaluation of Crude Oil, Petroleum Products and Petrochemicals Chemical Engineering Notes | EduRev

 

Reid vapor pressure and light end analysis

Indicates the relative percentage of gaseous and lighter hydrocarbons.

 

Cloud point and Pour

Point

For estimating the relative amount of

wax present in the crude oil. Cloud point gives a rough idea above which the oil can be safely handled.

 

Viscosity

Viscosity indicates the relative mobility of various crude oils. Temperature has a marked effect on viscosity.

Kinematic viscosity = absolute

viscosity/ density

Redwood Viscometer, Saybolt Viscometer are used

Aniline point

Aniline point indicates the lowest temperature at which the oil is completely mixed with an equal volume of aniline. High aniline point indicates that the fuel is Paraffinic and hence has a high diesel index and very good ignition quality.

 

Asphaltenes,

carbon

residue and

asphalt

content

Carbon residue and asphaltenes indicate the presence of heavier hydrocarbons in the crude. Carbon residue is the measure of thermal coke forming property.

It is determined by Conradson carbon residue and Ramsbottom

carbon residue method.

Flash and

Flash point is the lowest temperature at

Penskys Martens open/closed cup

fire point

which application of the test flame causes the vapour and air mixture above the sample to ignite.

Fire point is the lowest temperature at which the oil ignites and continues to burn.

is used.

Smoke point

It is an indication of the smoking tendency of fuel. It is used for evaluating the ability of kerosene to burn without producing smoke. It is the maximum flame height in mm at which the fuel will burn without smoking.

Smoke volatility Index( SKI)

= Smoke point + 0.42 x recovery at 204 oC

Acidity

It is an indication of the corrosive properties of products.

 

Copper

corrosion

test

This test serves as a measure of

possible difficulties with copper, brass, bronze part of the fuel system.

 

Water, salt

and

sediments

These causes irregular behavior in the

distillation and cause blocking and fouling of heat exchanger and result in corrosion

Water content is determined by

Dean & Starck. Sediment and water is determined by centrifuging a mixture of crude oil and toluene. Salt content is determined by titrating the water extract with KCNS/AgNO3.

Parameters

Significance

Description

Base of the

crude oil

For characterisation of the crude oil base- paraffinic / intermediate /Naphthenic and for measurement of the aromaticity. Various parameters used are characterisation factor, BMCI, VGC

Characterization factor

K=VTB / Sp. Gr at 15.6/15.6.

Tb =Mean av. Boiling point in Rankin

paraffinic base k= >12.1; Intermediate base k= 11.5-12.1; naphthenic k = 11.5; aromatics k = 9.8-12.0

BMCI (Bureau of Mines Correlation Index)

BMCI= 48640/ oK + 473.7 g- 456.8

K= avg. boiling point in oK, g specific gravity 15.6/15.6 oC

BMCI value:

Paraffinic = <15;

Intermediate =15-50; Naphthenic = >50

Viscosity Gravity correlation (VGC)

VGC= 10 G - 1 0752 log( V - 38 )

10 - log( V - 38 )

G is sp gravity and V is Saybolt universal viscosity

Paraffinic base: 0.80-0.83; Intermediate base: 0.83-0.88, Naphthenic base: 0.88-0.95

TBP Assay

It is done for generating distillation data and for study of variations of some key properties throughout the distillation range.

 

Gum

It is indication of gum at the time of test and amount of deposition during service time.

 

Colour

Indication of the thoroughness of the refining process.

 

Antiknock

quality

(octane

number)

Octane number is the percentage of iso-octane in the reference fuel which match the knocking tendency of the fuel under test

Research octane number (RON)

and Motor octane number (MON) are two methods used.

Anti knock index (AKI)=

(RON + MON)/2

Cetane

number

Cetane number is the percentage of

cetane which must be mixed with hepta methylnonane to give the same ignition performance as the fuel in question.

 

Stability test

It is used for the evaluation of storage stability and resistance to oxidation.

 

Carbon

Hydrogen

ratio

 

CH ratio=(7 4+15 d)/(26-15 d), where d is sp. Gr. at 15 oC/15oC

Diesel index

It is an indication of ignition quality of a diesel.

Diesel index =

(Aniline point in oF x API)

/100

Diesel Index = cetane number-

10/0.72

Weathering test for LPG

This test shows the volatility of the LPG

 

Frass breaking pointThis is the temperature below which the bitumen tends to break rather than flow. 
 
Product Evaluation: 
Major parameters for gasoline and diesel specification are given below

Major Parameters of Gasoline Specifications

Major parameters for gasoline included in Bharat or Euro norms are

  • Lead phase out
  • Lower RVP
  • Lower benzene & aromatics
  • Lower olefin content
  • Limited Oxygen content
  • Lower Sulfur content

Other parameters of importance are RON, MON, Lead, gum, oxidation stability, density, VLI index, FBP. In case of reformulated gasoline aromatics, olefins oxygen, Antiknock index, vapor lock index

Major Parameters of Diesel Specifications

Major parameters for diesel included in Bharat or Euro norms are

  • Low sulfur
  • Low aromatics
  • High cetane number
  • Lower density
  • Lower distillation end point Other parameters for diesel are density, viscosity, cetane number distillation range, sulphur, carbon residues, oxidation stability, Flash point, acid value, ash and water contents  

Evaluation of Feed Stocks for Petrochemicals (Olefin, Aromatics, and Linear Alkyl Benzen (Lab) Plants) 

Olefin , aromatic and LAB production are three major Petrochemical building blocks.  Various feed stocks olefins, aromatics and surfactants are given in Table M-VI 2.2.

Input cost of feed constituents is a major portion of the variable cost of production in petrochemical plants. Major feed input olefin, aromatics and surfactants are  Ethane propane from natural gas, naphtha, kerosene from the refinery and LPG from refinery, pyrolysis gasoline  from steam crackers, Benzene from aromatic plant. Feed quality monitoring and improvement efforts are therefore very important aspects having significant impact on the economics of the operation cost. The precursors and undesirable constituents in feed including catalyst and adsorbents poisons should be known, analyzed and monitored continuously.  

 Table M-VI 2.2: Feed stocks for Olefin, Aromatics ans LAB  

Plant

Feed stock

OLEFINS

Ethane, Propane, Naphtha, Gas oil

AROMATICS

Naphtha, Pyrolysis gasoline, LPG

LAB

Kerosene for paraffins, benzene

Olefin Plants 
 
Olefins playing important role in petrochemical industry by providing raw materials for chemical intermediates like ethylene oxide ethylene glycol, acetaldehyde, vinyl chloride etc and poly olefins. Olefin production requires more paraffinic naphtha. Desired components in feed for olefins productions.
 
  • Naphthenes: Naphthene yield olefins of higher carbon number. Butane yield increases appreciable with naphthenic feed. Naphthenes also enhance production of aromatics.
  • Aromatics: The aromatics is feed are highly refractory and they pass through the furnace unreacted.
  • Sulphur: The sulphur in feed suppress stream reforming reaction catalyzed by nickel present in radiant coil. Optimum level of sulphur is 1 ppm.
  • Physical Properties: Density, distillation range are useful and give a rough assessment of feed quality.
  • Ethylene: The following components in feed give ethylene in decreasing order:  
    • Ethane, Butane to Decane, 3 and 2 Methyl hexane, 2 methyl Pentane/ 2,2 Dimethyl Butane, Isopentane
  • Propylene: The following components in feed give propylene in decreasing order:
    • Isobutane, n-nutane, n-propane, 3 methyl pentane, 2,3 dimethyl butane, 2 methyl hexane, n-pentane, 3 methyl hexane, iso pentane.
  • Butadiene: The following components of feed give butadiene is decreasing order:
    • Cyclo hexane, methyl cyclo pentane. 
Some of the key properties for evaluation of naphtha for olefin production  are density, ASTM distillation, TBP, FBP, Saybolt colour, sulphur, RVP and paraffin, naphthanes and aromatics content 
 
Aromatic Plant 
 
Aromatics  especially benzene toluene, xylenes (p- and o-xylenes) are important petrochemical feed stocks for manufacture of synthetic fibre, pesticides, explosive, surfactants, synthetic rubber. Aromatics are either  processed  in Refinery in Catalytic reforming   are processed separately separately in petrochemical complex for manufacture of p-xylene required for DMT/PTA plant. Quality of naphtha and impurities present in naphtha are very crucial in quality of aromatics as well as long life of catalyst..    
 
Naphtha cut C6 to C9 
 
Paraffin, Napthenes, Aromatics 110 to 140 o
 
Dehydrogenation of C8Napthene yield C8 aromatics. Most desirable component 
 
90% of C8napthalene in feed get converted to C8 aromatics 
  • C8 Paraffin's: Dehydro cyclisation of C8 paraffin's yield aromatics difficult to 20% Cparaffins gets converted to C8 aromatics.
  • CAromatics: Pass as refractory and directly contribute to Caromatic production.
  • C8 Aromatic Precursors: It is useful to monitor aromatic precursors= 0.2* C8 P + 0.9 * C8 N + 1.0 C8 A  
Some of thre key properties of naphtha aromatic pro duction are density, ASTM distillation, IBP,FBP sulphur, nitrogen, chloride, metallic poisons, component analysis  for paraffins, naphtthanes and aromatics (PNA).

Surfactants:  

Linear alkyl benzene is one of important feed stock for production of surfactant whose demands is increasing with increasing population all over the world. LAB requires paraffins for production of olefins of carbon range C10-12 to have more biodegradable detergent.  Benzene is required for alkylation of olefin to produce LAB. Feed stock for praffins are Kerosene feed 150-265 oC cut from refinery containing mainly nC7 to NC18 components which is fractionated to remove lighter and heavier fractions. The fractionated cut is hydrotreated for removal of sulphur and nitrogen catalyst which are poisonous to molex adsorbent molecular sieve.

Desirable:

 LAB requires olefin and benzene. At present trend is for manufacture of biodegradable low molecular weight LAB, Paraffins containing  nC10 to nC13 carbon atoms are required in LAB  manufacture which is obtained by fractionation of kerosene. Nc12 improve the flammability of LAB product.

Some of the undesirable components in the feed which are sensitive to molex molecular sieves are contaminants like water, sulphur, nitrogen, oxygen, chlorides, metallic poisons.Kkey properties of LAB feed stocks are density, ASTM distillation, IBP,FBP, sulphur, bromine index  ,aromatics, saybolt colour, smoke point, flash point, nitrogen component analysis for n-C10 to nC13, total normal paraffins.

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