Effect Of Asphaltene And Heteroatom Constituents
Some examples of problems due to sedimentation of asphaltene
constituents
1. Oil Recovery: wellbore plugging and pipeline deposition.
2. Visbreaking and Cracking Processes: degraded asphaltene
constituents resulting more aromatic because loss of aliphatic
chains which is less soluble leading to form coke.
3. Emulsion Formation: if there is a high degree of water
contamination emulsions may be formed; asphaltene constituents
are responsible for the undesired stabilization of emulsions,
since asphaltene constituents are highly polar and surface
active.
4. Storage problems of fuel oils and visbroken residua
sedimentation and plugging can occur due to oxidation of the
asphaltene constituents; increased polarity may cause asphaltene
aggregation and sludge/ sediment formation.
57
CRUDE OIL CLASSIFICATION
Refinery deals with crudes of different origins, many methods
established to group crude oils with similar characteristics.
Crude oils can be classified into three or four groups
depending on the relative ratio of the hydrocarbon
classes that predominates in the mixture. The following
describes three types of crudes:
1. Paraffinic: the ratio of paraffinic hydrocarbons is high
compared
to aromatics
and naphthenes. Like
Pennsylvanian
2. Naphthenic: the ratios of naphthenic and aromatic
hydrocarbons are relatively higher than in paraffinic
crudes.
3. Asphaltic: contain relatively a large amount of polynuclear
aromatics, a high asphaltene content, and relatively less
paraffins than paraffinic crudes.
58
PROPERTIES OF CRUDE OILS
 Crude oils differ in their properties according to origin and the
ratio of the different components in the mixture. Lighter
crudes generally yield more valuable light and middle
distillates and are sold at higher prices.
 Crudes containing a high percent of impurities, such as sulfur
compounds, are less desirable than low-sulfur crudes because
of their corrosively and the extra treating cost.
 Corrosivity of crude oils is a function of many parameters among
which are the type of sulfur compounds and their
decomposition temperatures, the total acid number, the type of
carboxylic and naphthenic acids in the crude and their
decomposition temperatures.
 The following are some of the important tests used to determine
the properties of crude oils
Dr.Firas Salim Mohammed Al-Ghulami
59
Density, Specific Gravity and API Gravity
Density is defined as the mass of unit volume of a material at
a specific temperature. A more useful unit used by the
petroleum industry is Specific Gravity, which is the ratio of
the weight of a given volume of a material to the weight of the
same volume of water measured at the same temperature.
The API (American Petroleum Institute) gravity is another
way to express the relative masses of crude oils. The API
gravity could be calculated mathematically using the following
equation:
A low API gravity indicates a heavier crude oil or a
petroleum product, while a higher API gravity means a
lighter crude or product. Specific gravities of crude oils
roughly range from 0.82 for lighter crudes to over 1.0 for
heavier crudes (41 - 10 °API scale).
60
Salt Content
 The salt content expressed ppm NaCl (or in pounds/barrel)
indicates the amount of salt dissolved in water.
 Water in crudes is mainly present in an emulsified form.
 A high salt content in a crude oil presents serious
corrosion problems during the refining process.
 High salt content is a major cause of plugging heat
exchangers and heater pipes.
 A salt content higher than 10 lb/1,000 barrels (expressed
as NaCl) requires desalting.
Dr.Firas Salim Mohammed Al-Ghulami
61
Sulfur Content
 Determining the sulfur content in crudes is important
because the amount of sulfur indicates the type of
treatment required for the distillates.
 To determine sulfur content. Convert all sulfur compounds in
crude oil to SO2 by burning crude oil in enough amount of
air, which is then further oxidized to SO3 and finally titrated
with a standard alkali.
 Sulfur compounds can easily be hydro-desulfurized to
hydrogen sulfide and the corresponding hydrocarbon.
Dr.Firas Salim Mohammed Al-Ghulami
62
Pour Point
 The pour point of a crude oil or product is the lowest
temperature at which an oil is observed to flow under
the conditions of the test.
 Pour point data indicates the amount of long-chain
paraffins (petroleum wax) found in a crude oil.
 Paraffinic crudes usually have higher wax content than
other crude types.
 Handling and transporting crude oils and heavy fuels is
difficult at temperatures below their pour points.
 Long-chain n-paraffins ranging from C16 – C60, are
responsible for near-ambient temperature precipitation.
 In middle distillates, less than 1% wax can be sufficient
to cause solidification of the fuel.
Dr.Firas Salim Mohammed Al-Ghulami
63
Ash Content
 This test indicates the amount of metallic constituents in
a crude oil.
 Defined, the ash left after completely burning an oil sample
usually consists of stable metallic salts, metal oxides, and
silicon oxide.
 The ash could be further analyzed for individual elements
using Atomic Absorption Spectroscopic techniques (AAB).
Conradson Carbon Residue %
The Conradson Carbon Residue test gives an indication of the
amount of carbonaceous material formed by a gas oil when this is
burned in a limited supply of air.
Specifically, as an indicator to detect the presence of excessive
amounts of higher-boiling materials which might cause excessive
carbon formation in pressure jet burners.
64
Reid Vapor Pressure (RVP)
The Reid Vapor Pressure (RVP) of a product is the vapor pressure
determined in a volume of air four times the liquid volume at
37.8 °C (100°F). This property provide two things:
 Measures the vapor-lock tendency of a motor gasoline in which
excessive vapors are produced in the fuel line causing
interruption of the supply of liquid fuel to the engine.
 Indicates the explosion and evaporation hazards of the fuel.
Dr.Firas Salim Mohammed Al-Ghulami
65
Flash Point
The flash point of a liquid hydrocarbon is the lowest temperature
at which sufficient vapors are produced above the liquid such
that spontaneous ignition will occur if a spark is present.
Flash point indicates the fire and explosion potential of a fuel. A low
flash point fuel is a higher fire hazard.
It is an important specification for gasoline and naphtha related to
safety in storage and transport in high temperature environments.
Bottom Sediment and water (BS & W)
Indicate the concentrations of aqueous contaminants, present in the
crude either originally or picked up by the crude during handling
and storage.
When extracted petroleum from an oil reservoir, the crude oil will
contain some amount of water and suspended solids from the
reservoir formation.
66
Dr.Firas Salim Mohammed Al-Ghulami
The water content can vary greatly from field to field, and may be
present in large quantities for older fields, or if oil extraction is
enhanced using water injection technology.
The residual content of these unwanted impurities is
measured as BS&W. Bottom Sediment and Water up to
0.5% are considered to be acceptable.
The centrifuge methods are still employed, but many
laboratories prefer the Dean and Stark adaptor
A weighed amount, corresponding to approximately 100
mL of oil, is placed in the flask with 25 mL of dry toluene.
The flask is heated gently until the 25 mL of toluene has
distilled into the graduated tube. The water distilled with
the toluene separates to the bottom of the tube where
the volume is recorded as milliliter, or the weight as
milligram, or per cent.
Dr.Firas Salim Mohammed Al-Ghulami
67
To determine the sediment in petroleum or in a petroleum product,
the method involves solvent extraction using a Soxhlet Extractor.
The
higher
the
bottom
sediment and water content,
the higher sludge and deposit
formation rates can be
expected in the stored crude
oil.
68
Dr.Firas Salim Mohammed Al-Ghulami
CRUDE OILS
crude oils are not used directly as fuels or as feedstocks for
the production of chemicals. This is due to the complex
nature of the crude oil mixture and the presence of some
impurities that are corrosive or poisonous to processing
catalysts.
Crude oils are refined to separate the mixture into simpler
fractions that can be used as fuels, lubricants, or as
intermediate feedstock to the petrochemical industries.
A general knowledge of this composite mixture is essential for
establishing a processing strategy.
Dr.Firas Salim Mohammed Al-Ghulami
69
Crude Oil Types Versus Demand
Gasoline
Gasoline
5 - 15 %
20 - 30 %
Distillate
20 - 25%
Distillate
25 - 35%
Heavy Fuel
Oil
60 - 75%
Heavy Fuel
Oil
35 - 55%
Light Crude
Product
Composition
Heavy Crude
Product
Composition
Dr.Firas Salim Mohammed Al-Ghulami
Naturally occuring
hydrocarbon molecules do
not meet customer needs.
The refining processes must
adjust the molecules, reshape
them and remove contaminants
to ensure they meet
requirements for:
- end use performance
- environmental performance
Gasoline
40 - 45%
Distillate
30 - 35%
Heavy Fuel
Oil
~10%
Asphalt ~5%
Other ~5 -10%
Example
Product
Demand
70