PRECIPITATION OF ASPHALTENES, QUANTIFICATION OF MALTENES, UV AND FTIR SPECTROSCOPIC STUDIES OF C 7 AND C 5 + C 7 ASPHALTENES FROM 350 O C ATMOSPHERIC RESIDUUM CRUDES. BY ANIGBOGU, IFEOMA VERONICA PG/M.Sc/08/49193 DEPARTMENT OF PURE AND INDUSTRIAL CHEMISTRY, FACULTY OF PHYSICAL SCIENCES UNIVERSITY OF NIGERIA, NSUKKA. NOVEMBER, 2011
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
PRECIPITATION OF ASPHALTENES,
QUANTIFICATION OF MALTENES, UV AND FTIR
SPECTROSCOPIC STUDIES OF C7 AND
C5 + C7 ASPHALTENES FROM 350OC ATMOSPHERIC
RESIDUUM CRUDES.
BY
ANIGBOGU, IFEOMA VERONICA
PG/M.Sc/08/49193
DEPARTMENT OF PURE AND INDUSTRIAL
CHEMISTRY,
FACULTY OF PHYSICAL SCIENCES
UNIVERSITY OF NIGERIA, NSUKKA.
NOVEMBER, 2011
i
PRECIPITATION OF ASPHALTENES, QUANTIFICATION OF
MALTENES, UV AND FTIR SPECTROSCOPIC STUDIES OF C7 AND
C5 + C7 ASPHALTENES FROM 350
OC ATMOSPHERIC RESIDUUM
CRUDES.
BY
ANIGBOGU, IFEOMA VERONICA
PG/M.Sc/08/49193
DEPARTMENT OF PURE AND INDUSTRIAL CHEMISTRY,
FACULTY OF PHYSICAL SCIENCES
UNIVERSITY OF NIGERIA, NSUKKA.
NOVEMBER, 2011.
ii
CERTIFICATION
Anigbogu, Ifeoma V. a postgraduate student of the Department of Pure and
Industrial Chemistry with registration number, PG/M.Sc/08/49193 has
satisfactorily completed the requirements for the course and research work for
the award of the degree of Master of Sciecne (M.Sc) in Fossil Fuel (Petroleum
and Coal) Chemistry. This research project has been approved for the
Department of Pure and Industrial Chemistry, Faculty of Physical Sciences,
University of Nigeria, Nsukka.
By
____________________ ____________________
Prof. C.A. Nwadinigwe Dr. P.A. Obuasi
Project Supervisor Head of Department
iii
DEDICATION
I dedicate this work firstly, to the saviour of my life, Jesus Christ, whom by His
grace, favour and help kept me alive after the terrible sickness that befell me,
and helped me to be able to complete this programme. Even when the going was
tough, he encouraged me and taught me that only the tough gets going.
Secondly, I dedicate this work to my beloved husband Mr. Emmanuel
Anigbogu, who has always been a source of great support and inspiration all
through the cause of this programme.
iv
ACKNOWLEDGEMENTS
I wish to acknowledge the assistance of some individuals who have contributed
to the success of this work. First and foremost, my appreciation goes to my
project supervior Prof. C.A. Nwadinigwe whose advice and helpful suggestion
and support have directed the progress of this programme especially this project
work from its insception to the conclusion. His instructions, criticisms and
contributions greatly improved this work both in scope and in quality. My
appreciation also goes to my Head of Department Dr. P.A. Obuasi.
I will ever remain grateful to my beloved husband, who is God’s gift to me. God
will not disappoint us in Jesus name. I appreaciate my father Mwogeoffery
Ugwu (Rtd), my sliblings, Obinna Ugwu, Mrs. Ngene Chizoba, Mr. Valentime
Ugwu and Ejike for their prayers.
My special thanks go to the senior laboratory technician Mr. Cliford Ezeugwu
(Food Chemistry Department), Mr. Uba and Mr. Menakaya (Laboratory
Attendants), Dr. Parka E. Joshua (Biochemistry Department), who were
instrumental to the success of this work. Also to my special friends. Mrs. Ngozi
Alumona, Obiageli Egbu, Amara Chukwuneke, Mr. Emmanuel Okon, Mr. Alifa
David, Ikenna, Adika, C.C., Madam Gloria, Mr. Oformater, Mrs. Vivian
Okonkwo and others. I say thank you. I have learnt so much from you all
collectively and individually.
I will not forget Jesus Reigns Catholic Charismatic Renewal UNN, a place
where I encountered God as God. I express my thanks to the members of the
singing ministry. I express my gratitude to all my roommates in 330 Odili (PG)
Hall, You all have been like sisters to me.
Lastly my special appreaciation goes to my Darling friend and sister Dr. to be
Miss Phidelia Waziri who with perseverance carefully typed my work.
ANIGBOGU IFEOMA VERONICA
v
TABLE OF CONTENTS
Approval page - - - - - - - - - - i
Certification - - - - - - - - - - ii
Dedication - - - - - - - - - - iii
Acknowledgements - - - - - - - - - iv
Abstract - - - - - - - - - - v
Table of contents - - - - - - - - - vi
List of figures - - - - - - - - - - x
List of tables - - - - - - - - - - xi
Chapter one
1.0 Introduction - - - - - - - - - 1
1.1 Background of the study - - - - - - - 1
1.1.1 Types of crude oil - - - - - - - - 1
1.1.2 Fractions of crude oil - - - - - - - - 2
1.2 Origin of asphaltene from petroleum/crude oil - - - - 5
1.3 Statement of the Asphaltenes/Resins problem - - - - - 8
1.4 Aims and objectives - - - - - - - - 10
1.5 Scope of the study - - - - - - - - 12
CHAPTER TWO
2.0 Literature review - - - - - - - - 13
2.1 Occurrence and nature of asphaltenes and resins - - - - 15
vi
2.2 Composition of asphaltenes and resins - - - - - 17
2.3 Structure and chemistry of asphaltenes and other heavy organic deposits - 22
2.4 Asphaltene chemical structure under pyrolysis condition - - - 26
Crude oil is a naturally occurring substance consisting of organic compounds in the form
of gas, liquid, or semisolid. The simplest of these compounds is methane.
Figure 1.2(a) Examples of some organic compounds in petroleum
Figure 1.2(a) shows some examples of organic compounds in petroleum, from the
simplest (methane) to the most complex (asphaltene). Asphaltenes are the most complex and
most polar fractions found in crude oil, with more than 36 carbon atoms bound to more than 167
hydrogen atoms, three nitrogen atoms, two oxygen atoms, and two sulphur atoms. [26][27]
Semisolid petroleum is tar, which is dominated by larger complex hydrocarbons and
asphaltenes (Figure 1.2a).[25] Petroleum formation takes place in sedimentary basins, which are
6
areas where the earth crust subsides and sediments accumulate within the resulting depression.
Throughout geologic time, the world oceans have expanded and receded over the earth’s land
surfaces and contributed sediment layers to subsiding sedimentary basins. [26] Development of
stagnant water conditions in some of the expanded oceans caused the bottom waters to be
depleted in oxygen (anoxic), which allowed portion of the decaying plankton to be preserved as
a sediment layer enriched in organic matter. Methane producing microorganisms referred to as
methanogens may thrive under certain favorable condition within the organic rich sediment layer
during its early burial. There microorganisms consume portions of the organic matter as food
source and generate methane as a byproduct. This methane, which is typically the main
hydrocarbon in natural gas, has a distinct neutron deficiency in its carbon nuclei which allows
microbial natural gas to be readily distinguished from methane generated by thermal processes
later in the basin’s subsidence history. The microbial methane may bubble up into the overlying
sediment layers and escape into the ocean waters or atmosphere. If impermeable sediment layers,
called seals, hinder the upward migration of microbial gas, the gas may collect in underlying
porous sediments, called reservoirs.
Burial of the organic-rich rock layer may continue in some subsiding basins to depths of
6,000 to 18,000 feet, exposing the rocks to temperatures of 150 to 350°F (66 to 177°C) for a few
million to tens of billions of years. The organic matter within the organic rich rock layer begins
to cook during this period of heating and portions of it thermally decompose into crude oil and
natural gas. If the original source of the organic matter is plankton (i.e. algae, bacteria e.t.c)
crude oil will be the dorminant petroleum generated with lesser amounts of natural gas
generation.
7
Petroleum has a lower density, than the water that occupies pores, voids and cracks in the
source rock and the overlying rock and sediment layers. This density difference forces the
generated petroleum to migrate upwards by buoyancy until sealed reservoirs in the proper
configurations serve as traps that concentrate and collect the petroleum Figure 1.2(b).
Figure 1.2(b): Continued buried of sediment and rock layers in subsiding basin.
In some basins, petroleum may not encounter a trap and continue migrating upwards into
overlying water or atmosphere as petroleum seeps. Crude oil that migrates to or near the surface
of a basin will lose a considerable amount of its hydrocarbons to evaporation, water washing,
and microbial degradation leaving a residual tar enriched in large complex hydrocarbons and
asphaltenes.[25]
Asphaltene is an important constituents in crude oils. While it is also a major factor that
causes difficulties in oil recovery.[28][29] During the evolution and migration of oil reservoirs, the
8
asphaltenes may be flocculated or precipitated out from crude oils due to the changes of pressure,
temperature and/or the composition of reservoir fluid. [30]
Owing to the alteration of ambient conditions, asphaltenes are liable to be precipitated out
during oil recovery, transportation and post-processing. It can make oil production more arduous
and costly because of the partially plugging in oil well- and pipeline by asphaltenes. It may
further decrease recovery efficiency or even stop oil production due to the shutoff of oil pore
throat or even of the whole oil well. [30]
1.3 STATEMENT OF THE ASPHALTENES/RESINS PROBLEMS
Asphaltenes are best known for the problems they cause as solid deposit that obstruct
flow in the production system.[31] In asphaltene self associate and/or precipitate, the self
association and precipitation is mediated by other solubility fractions particularly the resins.[32]
Hence asphaltenes and their related compounds resins have often been lumped together as
residue in crude oil [8] causing reduction in crude oil production as they can block the pores of
reservoir rocks and can also plug the wellbore tubing, flowlines, separators, pumps, tanks and
other equipment and as a result, causing barrier to the flow of oil as shown schematically below:
[33][34]
9
Figure 1.3(a): Asphaltene precipitation and deposition in subsea flowlines, near wellbore region,
Seperators. e.t.c. [8]
Not only do asphaltenes increase fluid viscosity and density, they also have the potentials
to derail upstream activities, and can also cause downstream disruptions, such as adhering to hot
surfaces in refineries. [8] As mentioned earlier asphaltene precipitation can make oil production
more arduous and costly because of the partially plugging in oil well and pipeline by asphaltene.
It may further decrease recovery efficiency or even stop oil production due to the shut off of oil
pore throat or even of the whole oil well. [30]
At reservoir conditions, the adsorption of asphaltene to mineral surfaces causes a reversal
in wettability of the reservoir from water wet to oil wet and also results in insitu permeability
reductions. Both factors also reduce oil production. Apart from the production loss, the cost of
removing precipitated asphaltene from equipment and flowlines can be very expensive and
significantly alter the economics of a project. Examples of this cases have been reported in the
prinos field, Greece, Hansimessaoud field, Algeria, Ventura Avenue field, California, and other
places throughout the world.[35][33]
10
Furthermore, flocculation of asphaltene was found to reduce the effectiveness of wax
inhibitors, due to the formation of complex asphaltene paraffin solid aggregate. [36] Asphaltene
precipitation can cause major problems during the transportation of bitumen and heavy oil. The
flow of paraffin diluted bitumen through transportation pipelines and processing equipment can
result in deposition of precipitated asphaltenes. This deposition causes higher pumping rates and
can lead to a build up of internal pipeline pressure.[37] as shown in figure 1.3b below.
Figure 1.3b: Deposition and plugging of petroleum flow conduits due to streaming potentail generated and sticking of asphaltene particles to the walls.[34]
Some other examples of problems that arise due to asphaltene flocculation and/or
sedimentation are: Destabilization of asphaltene constituent as a result of the change in medium
during fuel oil-heavy crude oil blending. Ignition delay and poor combustion (often caused by
high content of asphaltene constituent (≥6%) in crude oil) leading to boiler fouling, diminished
heat transfer, stack (particulate) emissions, and corrosion.[9] e.t.c. Thus, with all these and other
problems – that arise as a result of asphaltene precipitation, it can be seen that there is need for
predicting the conditions for asphaltene precipitation.
1.4 AIMS AND OBJECTIVES
The definition of the non-volatile constituents of petroleum (i.e., the asphaltene
constituents, the resin constituents and to some extent, part of the oils fraction, insofar as
11
nonvolatile oils occur in residue and other heavy feed stocks) is an operational aid. It is difficult
to base such separations on chemical or structural features. This is particularly true for the
asphaltene constituents and the resin constituents, for which the separation procedure not only
dictates the yield but can also dictate the quality of the fraction. The technique employed also
dictates whether or not the asphaltene contains coprecipitated resins. This is based on the general
definition that asphaltene constituents are insoluble in n-pentane (or in n-heptane) but resins are
soluble in n-pentane (or n-heptane). To date, little or no effort has been made to study asphaltene
precipitation from crude oil using mixed n-pentane/n-heptane solvent system. Since the use of
different hydrocarbon liquids influences the yield of asphaltenes as well as resins fraction,
The objectives of this present work are as follows:
� To investigate the effect of the pure solvent i.e., n-heptane and also the mixed n-
pentane/n-heptane solvent systems, on asphaltene precipitation.
� To investigate the effect of stirring time on asphaltene precipitate.
� To fractionate the resulting maltenes obtained – after precipitation of asphaltenes and
compare their ratios (i.e. of aromatics to saturates and resins to asphaltenes) with the
extent of precipitation of asphaltene.
� Determine the melting point of the asphaltene precipitate obtained.
� To ascertain the functional group properties (i.e., using IR and UV) of each asphaltene
precipitate, in other to elucidate if the compound is truly asphaltene.
� To determine the role resins play, if any, in asphaltene stability which may help chemists
develop better methods for preventing and remediating asphaltene problems.
12
1.5 Scope of the Study
� Three different crude oil samples will be used for this work.
� The samples will be collected and distilled at 350°C to strip off lighter fractions.
� For each oil sample (3500C atmospheric residuum), asphaltene precipitation reaction will
be carried out, keeping crude oil/solvent constant, varying stirring time and also weighing
asphaltene yield in each case.
� Functional group properties of each asphaltene precipitation will be ascertained (IR and
UV). Also melting point analysis will be carried out on the asphaltenes precipitated.
� To fractionate the resulting maltenes obtained after precipitation of asphaltenes and
compare their ratios (i.e. aromatics to saturates and resins to asphaltenes ) with the extent
of asphaltenes obtained.
13
CHAPTER TWO
2.0 Literature Review
Crude oils can be fractionated and classified in a number of ways. Standard laboratory
methods have been defined for the fractionation of petroleum. The older ASTM D – 2006
method and ASTM D-2007 method are no longer in official use but may still find use in private
laboratories. Indeed, these methods found such wide use that many modifications have been
proposed that are still in use.[32] The overall product of these fractionation methods, which with
the ensuing sub-fractionation, provides the representation of petroleum a composite of the four
fractions (saturates, aromatics, resins and asphaltenes).[9][2] Fig 2.0(a) below:
3.6.4 MELTING POINT ANALYSIS: This analysis was carried out in Pharma-chem
laboratory (U.N.N). It was done by putting a pinch of the asphaltene precipitate in a capillary
tube and dropped in one of the three compartments in the melting point analyser (electrothermal
melting point analyser, which heats up to the range of 350-450°C) as shown in picture 3.10
below
58
Picture 3.10: Melting point analyser (Electrothermal melting point analyser) Cat no.: 1A6304,
For all these analysis, the samples decomposed between the range of 350-410OC to a darker
material (carbonaceous material).
EXPERIMENTAL PROCEDURE TO DETERMINE THE ROLE OF RESINS IN
STABILISING (SOLUBILISING) ASPHALTENES IN CRUDE OIL USING n-HEPTANE
SINGLE SOLVENT ONLY.
To 1ml of each of Bonny Export, Bodo and Mogho crudes (atmospheric residium) 40mls
of n- heptane was added and to this mixture, the same quantity of resins extracted from the
fractionation of n-heptane maltenes (that was obtained from 80mins asphaltenes
precipitation)from Bonny Export, Bodo, and Mogho crudes respectively were added to the same
crude from which they were extracted and stirred with a magnetic stirrer for 80minutes and the
mixtures (resins+1ml of crudes + 40mls of n-heptane) were allowed to age (ie equilibrate) for 2
days (48hours).
After 48hours equilibration (aging) the mixture was Centrifuged for 30minutes at
2000rpm using a Centrifuging apparatus (model no: 80 – 2B). after this procedure the
Supernatant (maltenes) was decanted and kept seperately while the solid residue composed
59
mainly of asphaltenes was kept rinsing with the liquid precipitant (about 40mls) until a clear
solvent was observed. The precipitated asphaltenes were slowly dried in a vacuum
oven/incubator (model; mini/50) at about 80°C until no change in weight was observed .Details
of this result is as shown in chapter 4.
PURIFICATION OF PRECIPITATED C7 – ASPHALTENES WHEN RESINS
WAS ADDED TO THE CRUDE OIL: The dried C7 – asphaltenes were purified to remove any
non asphaltic materia that co-precipitated along with the asphaltenes. To remove this solids the
asphaltenes were dissolved in 10ml of toluene and filtered to remove any solid particles, the
fraction of the C7 – asphaltenes that did not desolve in toluene (non aspaltenic) was discarded.
To the soluble part (composed of asphaltenes) 20ml of n-heptane was added, and then dried in a
vacuum oven at 80°C until no change in weight was observed. Detailed result of this experiment
is shown in chapter 4.
60
CHAPTER FOUR
4.0: RESULTS AND DISCUSSIONS
Asphaltenes has been precipitated from Bonny, Bodo and Mogho (Porth Harcourt) crudes
using n-heptane and n-pentane+n-heptane mixed solvent at various reaction time (20mins,
40mins, 60mins and 80mins). The results of the distillation and composition of the asphaltenes
and maltenes in each of the three different crudes and the role resins play in solubilising
asphaltenes in crude oils are shown in table 4.1, 4.2a, 4.2b.
4.1 RESULTS OF THE PHYSICAL PROPERTIES OF BONNY EXPORT, BODO
AND MOGHO CRUDE OILS BEFORE AND AFTER DISTILLATION AT 350O
C
Table 4.1: PHYSICAL PROPERTIES OF BONNY EXPORT, BODO AND MOGHO
CRUDE OILS BEFORE AND AFTER DISTILLATION
Source of the crude oils Bonny Export Bodo Mogho
Weight of crude used (g) 528.5 632.7 415.8
Weight of atmospheric residuum (g)
182.02 211.7 126.17
Volume of crude (ml) 675 750 500
Volume of atmospheric residuum (ml)
224 250 140
Density of crude (g/ml) 0.78 0.84 0.83
Density of atmospheric residuum (g/ml)
0.81 0.85 0.90
API gravity of crude 49.91 o 36.95 o 38.89 o
API gravity of atmospheric residuum
45.3 o 34.97 o 25.72 o
61
COMMENTS
As accepted generally, there are various types of crudes, the extra heavy crude oil, the heavy
crude oil, the medium crude oil, the light crude oil and the very light crude oil.
� Extra heavy crude oil is any liquid petroleum with an API gravity less than 10°API.
� Heavy crude oil is defined as any liquid petroleum with an API gravity less than 20°API.
� Medium crude oil is any liquid petroleum with an API gravity between 22 - 33° API.
� Light crude oil is any liquid petroleum with an API gravity between 34 - 39°API.
� Very light crude oil is defined as any liquid petroleum with an API gravity above
40°API.
This shows that from the results obtained for API gravity in table 4.1 above Bonny Export is
a very light crude i.e. with an API gravity of 49.91°, Bodo crude is a light crude because its API
gravity is 36.95°API also Mogho crude is a light crude because its API gravity is 38.98° API.
However, after distillation when all the lighter fractions of the various crudes has been
removed, Bonny Export (atmospheric residuum) still behaved like a very light crude but its
density became slightly higher than normal. Bodo (atmospheric residuum) behaved like a light
crude with a slightly raised density compared to its original density but in the case of Mogho
crude though a light crude but after distillation it behaved more like a medium crude and its
density increased greatly compared to its original density. This shows that the heavy organics in
Mogho crude oil will be more compared to that in Bonny Export and Bodo crudes, indicating the
presence of a very high paraffinic material which light crude oils are known for meaning that
Mogho crude may probably have the highest asphaltene content compared to Bodo and Bonny
Export crude, because asphaltene have very limited solubility in paraffinic materials
62
It is a well known fact that density measurement is the simplest way to estimate the
cohesive forces and, therefore, the interaction energies of a particular material. The density is
also a measurement of the molecular parking of the solid, and in the case of aromatic
compounds, this parking strongly depends on the structural molecular topology of the molecules.
This indicates that Mogho crude and Bodo crude with higher densities are likely to have higher
aromaticity, therefore higher asphaltene precipitates and more complex structures than Bonny
Export crude.[80]
4.2: RESULTS FROM ASPHALTENE PRECIPITATION
Detailed result of the compositions of asphaltene and the physical properties of the
maltenes from each of the three crude oils are as shown in the tables below.
Table 4.2a: Composition of Asphaltenes in Bonny Export crude for both n-heptane single
solvent and n-pentane + n-heptane mixed solvent.
Stirring Time
(solvent+ crude)
Solvent Weight of
asphaltenes after
drying (g)
% weight of
asphaltenes (%)
20mins n-heptane 0.001 0.69
40mins n-heptane 0.006 1.33
60mins n-heptane 0.007 1.67
80mins n-heptane 0.009 2.14
20mins n-pentane + n-heptane 0.003 0.88
40mins n-pentane + n-heptane 0.007 1.60
60mins n-pentane + n-heptane 0.008 2.05
80mins n-pentane + n-heptane 0.010 2.90
Table 4.2(a): Shows clearly that the weight / weight 0/0 of asphaltenes increased with increase in stirring time for both single n-heptane solvent and the mixed n-pentane + n-heptane solvents. This is also shown in figure 4.2a and b.
63
FILTRATE (MALTENES) FROM BONNY EXPORT CRUDE AS SHOWN BELOW:
Table 4.2b: Physical Properties of maltenes (filtrate) from Bonny Export crude
Stirring Time
(solvent+ crude)
Solvent Weight of
maltenes
Volume of
maltenes
Density of
maltenes (g/ml)
20mins n-heptane 5.962 9.00 0.662
40mins n-heptane 6.559 9.40 0.698
60mins n-heptane 6.706 9.60 0.699
80mins n-heptane 7.248 10.2 0.711
20mins n-pentane + n-heptane 4.564 7.60 0.6005
40mins n-pentane + n-heptane 4.907 7.20 0.6815
60mins n-pentane + n-heptane 5.066 7.20 0.7036
80mins n-pentane + n-heptane 3.917 5.40 0.7254
Table 4.2 (b): Shows that the densities of the maltenes from Bonny Export crude increased with
increase in asphaltene yield.
Fig. 4.2a(i): % weight of asphaltens for bonny Export Crude (n
Fig. 4.2a(ii): % weight of asphaltenes from Bonny Export Crude (n
solvent system) versus time
0
0.69
0
0.5
1
1.5
2
2.5
3
3.5
0 20mins 40mins
0
0.88
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 20mins 40mins
weight of asphaltens for bonny Export Crude (n-heptane solvent) with time
% weight of asphaltenes from Bonny Export Crude (n-pentane + n
1.33
2.08
3.2
40mins 60mins 80mins
% weight of asphaltene vs
time
1.71
2.9
3.85
40mins 60mins 80mins
% weight of asphaltenes vs
time
64
heptane solvent) with time
pentane + n-heptane
% weight of asphaltene vs
% weight of asphaltenes vs
65
Table 4.3a: Composition of the asphaltenes from Bodo Crude for both n-heptane single
solvent and n-pentane + n-heptane mixed solvent.
Stirring Time
(solvent+ crude)
Solvent weight of
asphaltene
after drying (g)
% weight of
asphaltene
(0/0)
20mins n-heptane 0.012 5.850
40mins n-heptane 0.013 6.191
60mins n-heptane 0.040 7.390
80mins n-heptane 0.039 6.500
20mins n-pentane + n-heptane 0.014 6.830
40mins n-pentane + n-heptane 0.030 7.850
60mins n-pentane + n-heptane 0.043 8.600
80mins n-pentane + n-heptane 0.041 7.523
Table 4.3 (a) : shows that the weight / weight 0/0 of the asphaltenes increased from 20mins to 60
mins but decreased slightly at 80mins stirring time for both the single n-heptane solvent and
mixed n-pentane + n-heptane solvent system. This is also shown in Figure 4.3 a and b.
66
FILTRATE (MALTENES) FROM BODO CRUDE AS SHOWN BELOW:
Table 4.3b: Physical Properties of maltenes (Filtrate) from Bodo Crude for both n-heptane
single solvent and n-pentane + n-heptane mixed solvent.
Stirring Time
(solvent+ crude)
Solvent Weight of
maltenes
Volume of
maltenes
Density of
maltenes (g/ml)
20mins n-heptane 0.838 6.800 0.120
40mins n-heptane 0.837 5.800 0.144
60mins n-heptane 0.811 4.840 0.169
80mins n-heptane 0.820 7.900 0.104
20mins n-pentane + n-heptane 0.836 8.400 0.100
40mins n-pentane + n-heptane 0.818 7.200 0.114
60mins n-pentane + n-heptane 0.820 3.600 0.228
80mins n-pentane + n-hepta ne 0.817 5.000 0.163
Table 4.3(b), shows clearly that the densities of the maltenes from Bodo crude increased
with its resulting asphaltenes (Table 4.3a).
Fig. 4.3a(i) % weight of asphaltenes from Bodo Crudes (n
Fig. 4.3a(ii) % weight of asphaltenes from Bodo Crudes (n
solvent)
0
5.8546.191
0
1
2
3
4
5
6
7
8
0mins 20mins 40mins
0
6.829
7.850
0
1
2
3
4
5
6
7
8
9
10
0mins 20mins 40mins
% weight of asphaltenes from Bodo Crudes (n-heptane single solvent)
% weight of asphaltenes from Bodo Crudes (n-pentane + n
6.191
7.390
6.500
60mins 80mins
% weight of
asphaltene vs time
7.850
8.600
7.520
60mins 80mins
% weight of
asphaltene vs time
67
heptane single solvent)
pentane + n-heptane mixed
68
Table 4.4a: Composition of the asphaltenes in Mogho crude for both n-heptane single
solvent and n-pentane + n-heptane mixed solvent.
Stirring Time Solvent Weight of
asphaltene after
drying (g)
% weight of
asphaltene
20mins n-heptane 0.029 10.623
40mins n-heptane 0.027 10.189
60mins n-heptane 0.018 6.590
80mins n-heptane 0.024 9.877
20mins n-pentane + n-heptane 0.036 11.688
40mins n-pentane + n-heptane 0.029 10.546
60mins n-pentane + n-heptane 0.024 6.838
80mins n-pentane + n-heptane 0.025 10.081
Table 4.4(a), shows clearly that the weight / weight 0/0 of the asphaltenes decreased from
20mins to 60mins but increased slightly with 80mins stirring time giving a precipitate slightly
higher than the precipitate obtained from 60mins stirring time for the n-heptane single solvent
and the n-pentane + n-heptane mixed solvent. This is also shown in Figure 4.4 a and b.
69
FILTRATE (MALTENES) FROM MOGHO CRUDE AS SHOWN BELOW:
Table 4.4b: physical properties of maltenes from Mogho crude for both n-heptane single
solvent and n-pentane + n-heptane mixed solvent.
Stirring Time Solvent Weight of
maltenes
Volume of
maltenes
Density of
maltenes (g/ml)
20mins n-heptane 0.871 10.20 0.085
40mins n-heptane 0.873 10.60 0.082
60mins n-heptane 0.876 12.00 0.073
80mins n-heptane 0.882 11.20 0.0788
20mins n-pentane + n-heptane 0.864 4.80 0.180
40mins n-pentane + n-heptane 0.876 5.00 0.175
60mins n-pentane + n-heptane 0.871 6.00 0.145
80mins n-pentane + n-heptane 0.875 6.20 0.14
Table 4.4b, shows clearly that the densities of the maltenes increased along side with
their corresponding asphaltenes, but decreased at 60mins stirring time for n-heptane single
solvent and also decreased at 80mins stirring time for n-pentane + n-heptane mixed solvent.
Fig. 4.4a(i) % weight of asphaltenes from Mogho Crude (n
Fig. 4.4(ii) % weight of asphaltenes from Mogho Crude
vs time
00
2
4
6
8
10
12
0mins 20mins
00
2
4
6
8
10
12
14
0mins 20mins
% weight of asphaltenes from Mogho Crude (n-heptane single solvent) vs time
% weight of asphaltenes from Mogho Crude (n-heptane + n-pentane mixed solvent)
10.62310.189
6.59
9.877
20mins 40mins 60mins 80mins
% weight of
asphaltenes vs time
11.688
10.546
6.838
10.081
20mins 40mins 60mins 80mins
% weight of
asphaltenes vs time
70
heptane single solvent) vs time
pentane mixed solvent)
asphaltenes vs time
asphaltenes vs time
71
4.3 COMPARISM OF THE WEIGHT OF THE PRECIPITATED ASPHALTENE
WITH STIRRING TIME USING N-HEPTANE SINGLE SOLVENT AND N-
PENTANE + N-HEPTANE MIXED SOLVENT.
It is generally accepted that asphaltene precipitation depends mainly on the stability of
the asphaltenes and stability depends not only on the properties of the asphaltene fraction but on
how good a solvent the rest of the oil is for its asphaltenes.
In comparism of the weight of the asphaltene precipitated using n– heptane single solvent
and n–pentane + n-heptane mixed solvent with respect to stirring time for Bonny Export, Bodo
and Mogho crudes:
Table 4.2 (a-b), table 4.3 (a-b), and table 4.4 (a-b) shows the percentage weight of
asphaltenes precipitated from Bonny Export, Bodo and Mogho crudes and their resulting
maltenes using n-heptane single solvent and n-pentane + n-heptane mixed solvent for 20, 40, 60
and 80 minutes stirring time for each of the crudes.
Table 4.2 (a-b) from Bonny Export crude shows that the weight of asphaltenes precipitate
increased with increase in stirring time, for both the C7 – asphaltene and the C5 + C7 –
asphaltenes (Figure 4.2 a - b), also the densities of their maltenes increased with increase in
stirring time.
In the case of Bodo crude (Table 4.3 a-b) and Mogho crude (Table 4.4 a-b), their
asphaltene precipitate do not follow the same trend as in Bonny Export crude (Figure 4.3 a-b and
Figure 4.4 a-b), but the densities of their maltenes increased alonge with their corresponding
asphaltene precipitate. According to these results, it is possible to suppose that asphaltene
precipitation depends on stirring time but due to the presence of other solubility fractions (i.e. the
saturates, aromatics and resins) which may not be present in the right ratios, Bodo and Mogho
crudes did not depend on stirring time. It may also be because the other solubility fractions
as saturates, aromatics and resins)
asphaltenes, therefore making their asphaltenes unstable and so prec
were more and did not depend on stirring time.
It was also noticed that Mogho crude (though a light crude) precipitated more asphaltenes
followed by Bodo crude and then Bonny Export crude for both single and mixed solvent system
(Figure 4.5 and 4.6 below). This indicates that the amount and characteristics of the asphaltene
constituents in crude oil depends to a greater
MIXED GRAPH OF ASPHALTENE PRECIPITATE FROM BONNY
AND MOGHO CRUDES USING N
TO TIME.
Figure 4.5: Effect of n-heptane single solvent with
and Mogho Crudes
0
2
4
6
8
10
12
20mins 40mins
0.691.33
5.856.191
10.62310.189
not depend on stirring time. It may also be because the other solubility fractions
as saturates, aromatics and resins) in Bodo and Mogho crude oils are not good solvents for their
asphaltenes, therefore making their asphaltenes unstable and so precipitation in these crudes
not depend on stirring time.
Mogho crude (though a light crude) precipitated more asphaltenes
followed by Bodo crude and then Bonny Export crude for both single and mixed solvent system
. This indicates that the amount and characteristics of the asphaltene
l depends to a greater extent on the source of the crude.[9]
HALTENE PRECIPITATE FROM BONNY EXPORT, BODO
CRUDES USING N-HEPTANE SINGLE SOLVENT WITH RESPECT
heptane single solvent with stirring time on Bonny
Crudes
40mins 60mins 80mins
2.08
3.2
6.191
7.390
6.5
10.189
6.59
9.877
% weight of asphaltenes
for Bonny Export crude
using single solvent
% weight of asphaltenes
for Bodo crude using
single solvent
% weight of asphaltenes
for Mogho crude using
single solvent
72
not depend on stirring time. It may also be because the other solubility fractions (such
not good solvents for their
ipitation in these crudes
Mogho crude (though a light crude) precipitated more asphaltenes
followed by Bodo crude and then Bonny Export crude for both single and mixed solvent system
. This indicates that the amount and characteristics of the asphaltene
[9]
EXPORT, BODO
SOLVENT WITH RESPECT
Bonny Export, Bodo
% weight of asphaltenes
for Bonny Export crude
% weight of asphaltenes
for Bodo crude using
% weight of asphaltenes
for Mogho crude using
MIXED GRAPH OF ASPHALTENE PRECIPITATE FROM BONNY
AND MOGHO CRUDES USING N
WITH RESPECT TO STIRRING
Figure 4.6: Effect of n-heptane
Bodo and Mogho Crudes
COMMENT
For both Bonny Export, Bodo and Mogho crudes as shown in
mixed solvent precipitant (n-pentane + n
solvent (n-heptane) precipitant. This is due to the addition of n
made up the mixed solvent system as
asphaltene precipitation increases with decrease in the carbon chain
solvent. [75] This increase in asphaltene yield for precipitation using mixed solvent system is also
indicative of the fact that for a given crude oil sample, the yield and properties of the precipitated
20mins
0.88
6.82911.688
% weight of asphaltenes for Bonny Export Crude using mixed solvent
% weight of asphaltenes for Bodo Crude using mixed solvent
% weight of asphaltenes for Mogho Crude using mixed solvent
ALTENE PRECIPITATE FROM BONNY EXPORT, BODO
USING N-PENTANE + N-HEPTANE MIXED SOLVENTS
STIRRING TIME.
heptane + n-pentane mixed solvent precipitant on
Bodo and Mogho Crudes
, Bodo and Mogho crudes as shown in figures 4.5 and 4.6 above, the
pentane + n-heptane) precipitated more asphaltenes than single
This is due to the addition of n – pentane to n
made up the mixed solvent system as in agreement with the generally accepted fact that
asphaltene precipitation increases with decrease in the carbon chain – length of the precipitating
This increase in asphaltene yield for precipitation using mixed solvent system is also
cative of the fact that for a given crude oil sample, the yield and properties of the precipitated
40mins 60mins 80mins
1.71
2.93.85
7.8508.600
7.52310.546
6.838
10.081
% weight of asphaltenes for Bonny Export Crude using mixed solvent
% weight of asphaltenes for Bodo Crude using mixed solvent
% weight of asphaltenes for Mogho Crude using mixed solvent
73
EXPORT, BODO
MIXED SOLVENTS
on Bonny Export,
figures 4.5 and 4.6 above, the
heptane) precipitated more asphaltenes than single
pentane to n – heptane which
in agreement with the generally accepted fact that
length of the precipitating
This increase in asphaltene yield for precipitation using mixed solvent system is also
cative of the fact that for a given crude oil sample, the yield and properties of the precipitated
74
asphaltenes strongly depend on the specific precipitation method and precipitant used. This
means that a single oil could have two or more results depending on the precipitant used.[8]
4.4 SUMMARY OF THE RESULT OF FTIR SPECTROPHOTOMETRIC
ANALYSIS
Table 4.5a: RESULT OF IR ANALYSIS OF ASPHALTENES OBTAINED USING
SINGLE N-HEPTANE SOLVENT
Samples (A)
Asphaltenes Precipitation
using Single Solvent (n-
heptane)
Approximate
characteristic
frequencies (cm-1
)
Bonds
Bonny Export Crude
733.94
1264.38
3056.31
Substituted aromatic hydrocarbon.
C – H bending.
C – H of aromatics.
Mogho (Port Harcourt) Crude
734.90
1265.35
1441.84
2930.9
3080.
Substituted aromatic hydrocarbon.
C – H bending.
C – H bending.
Cyclic aliphatic hydrocarbon.
C-H of aromatics.
Bodo Crude
734.9
971.19
1271.13
1373.36
1456.30
1601.93
1718.63
2933.83
3060
Substituted aromatics hydrocarbon
C = C – H bending out of plane.
C–H bending.
C-H bending.
C – H bending.
C = C of aromatic
C = O (acid, aldehydes, ketones and esters
Cyclic aliphatic hydrocarbon. C-H of aromatics.
75
TABLE 4.5b: RESULTS OF IR ANALYSIS OF ASPHALTENES OBTAINED USING N-
PENTANE + N-HEPTANE MIXED SOLVENT SYSTEM.
Samples B
Asphaltenes Precipitated
using mixed Solvent (n-
pentane+n-heptane)
characteristic
frequencies (cm-1
)
Bonds
Bonny Export Crude at
733.94
1264.38
2932.86
Substituted aromatic hydrocarbon
C – H bending
Cyclic aliphatic hydrocarbon.
Mogho (Port Harcourt) Crude
736.83
1266.31
1450.52
2931.9
Substituted aromatic hydrocarbon.
C – H bending.
C – H bending.
Cyclic aliphatic hydrocarbon.
Bodo Crude 734.90
1276.92
1459.2
1726.35
2929.97
Substituted aromatic hydrocarbon.
C – H bending.
C – H bending.
C = O (acid, aldehydes, ketones and esters
Cyclic aliphatic hydrocarbon.
IR INTERPRETATION
Data from IR as shown in figure I-VI in the appendice is summarized in table 4.5a and b,
obtained from Bonny Export, Bodo and Mogho crudes shows characteristic frequencies at
3056.31,3060,3080 that are due to C-H stretch for aromatic hydrocarbon. This is supported by
the absorptions at 733.94, 734.90, 736.83 that are due to substituted aromatic hydrocarbon. This
confirms the same class of crude oil composition, this class of crude oil composition consist of
the unsaturated part of asphaltenes, that is that part of asphaltenes that consist of fused benzene
rings. However, absorption frequencies at 2933.83, 2930.93, 2932.86, 2929.97 and 2931.9 are
76
due to cyclic aliphatic hydrocarbon. This is supported by the absorptions at 1264.34, 1271.17,
1265.35, 1276.92, 1266.31 that are due to C-H bending. These suggest the same class of crude
oil composition. These classes of crude oil consist of the saturated part of asphaltenes structure.
The IR reveals that asphaltenes fraction of crude oil is made up of both saturated and unsaturated
part as supported by our UV spectra on the asphaltene precipitates.
4.5 RESULTS OF UV/VISIBLE SPECTROPHOTOMETRIC ANALYSIS.
Table 4.6: UV Spectra of the Asphaltene Fractions of Crude Oil.