1.1 Background of Study
Crude oil is one of the components in petroleum that is very important to be commercially sold over the world and they are known as non-renewable energy. Crude oil is an unrefined product that is obtained from the refining process and they vary from light to heavy crude oils based on molecular weight (Aldahik et_al., 2017).They are highly composed of hydrogen and carbons. Crude oil obtained from drilling process and formation of different layers of constituents will subsequently occur after drilling process where natural gas was found above crude oil as they are lighter while saline water is the most bottom layer as they are denser than crude oil. Thus, further refining of the crude oil can turn into many new products such as kerosene, diesel and others which can be sold commercially in the market. Crude oil is one of the major petroleum constituents that can be used almost for all types of manufacturing industries such as fuel for transporting, rubber industries, leather industries and so many more.
Crude oil is classified as fossil fuels that obtained from the decomposition of some organic materials back few hundred years although current studies mentioned that their preliminary sources are hydrogen and carbon. The formation of crude oil is from hydrogen and carbon reacted with some organic materials such as blue-algae and planktonic that been submerged under the Earth. The usage of
crude oil begins at the 19th in the industrial field even they had been discovered during Industrial Revolution itself to replace coal usage that had been used for many years before by many countries. The demand for the usage of the crude oil increases drastically at the 20th century as the usage of internal combustion engines developed rapidly in many countries especially United States of America(USA). USA is one of the most top exporters of the crude oil until the 1960s’. Today, as the usage of crude oil plays a vital role in most industries, thus there are many other countries that act as exporters for the crude oil such as Malaysia, India, Iran and many more other countries.
1.2 Problem Statement of Study
There are many problems arise during the drilling process to produce the crude oil and the main concern or issue that is severely attacking the world of petroleum industries is that the solid deposition in the pipelines during transportation process of crude oil (Energy et al., 2005). Solid deposition here is known as waxes and asphaltenes deposition. Due to this phenomenon, the production lines can be choked and the production of oil had been disrupted unofficially. This reduction of oil production can cause the economy of Malaysia being disrupted indirectly. The highest molecular weight of n paraffin or known as n alkane with hydrocarbon bonding is one of the main component in wax formation in oils especially in crude oil (Energy et al., 2005). Asphaltene is one of the components that found in the crude oil and they are known as high molecular polyaromates or called as resin too sometimes.
Although wax and asphaltenes act structural stabiliser during formation of crude oil, at certain temperature along the transportation can cause them to turn into large clumps which lead to the deposition process. Due to this high coagulation of wax, blockage will occur in the pipeline due to reducing of space or diameter because of high deposition of precipitations. As a result, cost of maintenance of the industries will increase gradually as the cost to improve the pipeline is too high and need to be maintenance frequently by the management of industries. As prevention is always better than cure, an effective method is devised to prevent any issues formed from the deposition along the pipelines by improving the flow properties of crude oil.
Figure 1.1: The deposition of wax in the pipelines
Source: The Role of Temperature in Heavy Organics Deposition
from Petroleum Fluids.
Retrieved from http://www.mansoori.people.uic.edu
Thus, the main focus of this paper is to reduce the viscosity of the crude oil through using chemical inhibitors using ethylene-vinyl acetate (EVA), MCH and toluene and butanol as the inhibitors.
1.3 Aim of the Research
Past researches had been done to find the best method to inhibit the wax precipitation along with asphaltene deposition too along the pipelines. The researches are still going for a few years as they still finding the best formulation of chemical inhibitors that can give the most efficient reduction of viscosity and higher solubility of wax and asphaltenes. They also still searching the best optimum conditions to inhibit the wax and asphaltene in a higher percentage of reduction of viscosity in terms of temperature, concentration and shear rate of the inhibitors.
Eventually, each new study that is proposed for this issue always has been guidelines theoretically for a new treatment to be proposed by new researchers. As an example, the past researches helps to determine the basic knowledge on wax and asphaltene molecular structures, inhibitor structures and the relationship between bonding of the asphaltene or wax with the inhibitors and the treatments that had been used before by the past researchers. This knowledge is very important for a better modified new treatment.
Actually, these past researches had strong guidelines or foundation to identify the essential compounds or functional groups that can act as inhibitors for the wax and asphaltene inhibition. Indirectly, they help to save time for analysing the types of compounds that should be used and modification of the treatment can be done more efficiently without clashing with the theoretical knowledge of engineering.
Thus, the main aim of the research is to maximise the reduction of viscosity by using the different formulation of the chemical inhibitors and the novelty of this research is by using the combination of different formulation of inhibitors by using different structures of solvent which are aromatic and non-aromatic compounds such as toluene and butanol with, ethylene-vinyl acetate copolymer (EVA) dissolved in methylcyclohexane (MCH).
1.4 Objectives of the Research
At the end of this research, these objectives should be achieved:
i) To differentiate the effect of the aromatic and non-aromatic compounds towards wax and asphaltene solubility.
ii) To determine the percentage composition of each chemical, namely, EVA, MCH, butanol and toluene to contribute to the overall inhibitor efficiency.
iii)To optimize the percentage composition of inhibitor and optimum temperature of inhibitor using Response Surface Methodology (RSM).
1.5 Scope of the Work
The research study is subjected to several limitations. The following describes the scope of study in details:
i. The study is done by using only one type of ethylene-vinyl acetate (EVA) which is EVA40.
ii. The method that been used here to analyse the results is by measuring viscosity by using viscometer.
iii. The shear rate and concentration effect on the viscosity are being neglected throughout the research.
iv. The data that taken for each sample is at temperature ranges around 5°C to 20°C only.
v. The analysis of these data done based on two different scenarios such as blank crude oil and crude oil with the different formulation of inhibitors.
1.6 Significance of the Study
There are three main contributions of this study. This study will provide a clear insight into how chemical treatment being conducted to inhibit the deposition in the pipelines. This study will describe the temperature range that will be very suitable for the reduction of viscosity of the crude oil along transportation process. The analysis will be used to find the proper and accurate inhibitors formulations .This study also will explain how different functional groups compounds that can affect the solubility and viscosity of wax and asphaltene in crude oil. Lastly, this study will be beneficial for knowledge to enhance chemical treatment method in future.
1.7 Research Outlines
This study is divided into five chapters. In Chapter 1, the introduction is given about definition of crude oil, history of crude oil and the importance of crude oil for various types of industries. The problem statement of the current research was stated provide a clear picture of the main concern from the deposition of wax and asphaltene to the flow of crude oil in pipelines. Definite objectives of the planned study are provided which to be achieved at the end of the study and the scope of the study covers the research limitation and works to meet these objectives.
Chapter 2 or literature review covers the fundamental of crude oil, characteristics of crude oil, wax and asphaltene characteristics, wax treatment and asphaltene treatment, wax and asphaltene inhibitors .
Chapter 3 or experimental methodology describes the steps that were conducted to prepare the chemical inhibitors treatment to study the viscosity of the crude oil.
Chapter 4 comprises of results that obtained from the experiment that had been conducted to treat this deposition of wax and asphaltene in crude oil. Finally, Chapter 5 covers the conclusion and recommendation for future work and development.
2.1 Crude Oil
In this world that is developing day by day, crude oil has become one of the important natural resources in terms of fossil fuels. Crude oil is actually one of most necessary resources especially for the industrial field nowadays( Alkhalili et.al, 2017). Due to the development of petroleum industries in the global world, the demands on crude oil production and exploitation increasing gradually every day.
The formation of crude oil is about 500 million years and to form crude oil is actually a very slow process as it occurs naturally. The production of oil occurs from thedeposition of sediments naturally especially in bottoms of seas and lakes for approximately thousand and formed a layer of microorganisms, plants and animal (Abdel-Raouf, 2012).
The definition of crude oil is based on its chemical composition as they are a mixture that is very complicated where consists of main elements such as carbon and hydrocarbons where hydrocarbons are made of 90% from its overall composition while the derived organics in crude oil are sulphur, nitrogen, oxygen and organometallic. Crude oil can be divided into two types of classes such as hydrocarbons and non-hydrocarbons as shown in figure below
Figure 2.1: The flow chart of formation of crude oil
Source: retrieved from http://www.scranton.edu
There are three types of crude oils which are light, medium and heavy. They have divided into these three different types due to the compositions of fractions that will derive from refining process(Ezugwu, ; Nwadinigwe, 2016).The higher petroleum demands caused the heavy oils to be used in higher percentage rather than light crude oil.
Figure 2.2: The percentage of reserved crude oil
Source: retrieved from http://www.bravenewclimate.com
There are four different main classes of hydrocarbon which are saturated as in alkanes and cycloparaffins, aromatics, resins and asphaltenes. Resins are actually fractions that formed by heteroatoms such a nitrogen, oxygen and sulphur while asphaltene is molecules that are heavier than the resins. (Abdel-Raouf, 2012).
Figure 2.3: The Percentage of Elements in Hydrocarbons
Source: retrieved from http://www.scranton.edu
2.2 Characterization of Crude Oil
These heavy crude oils cause many issues along their transportation in the pipelines as heavy crude oil are more viscous and less fluidised type than the light crude oil. The special character of heavy crude oils which makes them has higher viscosity rather than light crude oil is that they have higher oil compositions such as resins, sulphur, and asphaltene. The main purpose to do SARA composition analysis should be done is to identify and reduce the effect of asphaltene composition to the clogging process in pipelines(Ezugwu, ; Nwadinigwe, 2016).Furthermore when there is the presence of natural surfactants, they play a vital part in reducing the emulsion and stabilised them by lowering the tension that occurs on the interfacial surface of the crude oil(Wen, Zhang, Wang, ; Zhang, 2016).Moreover, heavy crude oils have complicated interactions among different types of oil species which makes them be less fluidised compared than light crude oil (Khan et al.,2017).
Another classification of crude oil is based on derived elements which are sulphur and this class is known as non-hydrocarbons crude oil. Crude oil has many types of inorganic sulphur which appears either in form of suspended sulphur or dissolving sulphur itself. Crude oil can be classified as sweet and sour crude oil other than heavy or light crude oil. This character can be determined from the percentage of sulphur content in the crude oil. The crude oil considered as sweet crude oil if the sulphur is less than 0.5 wt% and if the sulphur is more than 0.5 wt% is known as sour crude oil. Sweet crude oil is more profitable than the sour crude oil and this is because crude oil that contains more sulphur is not environmental friendly. The organic sulphur in the crude oil comes in two forms which are heterocyclics and non-heterocyclics. There are few types of sulphur in crude oil such as mercaptans, sulphides, disulphides and thiophenes. Mercaptan is known as acidic sulphur as they contain thiol group while non-acidic sulphur is sulphide and thiophenes (Alkhalili et.al, 2017).The aromatic sulphur in described in the diagram below:
Figure 2.4: The aromatic compound of sulphur in crude oil
Source: Alkhalili et al. (2017)
Crude oil contains mechanical impurities too such as particles of solid. Those particles of solid undergo adsorption process into the oil-water interface which stabilises emulsion of particles. Thus formation of these emulsions will affect the characteristics of flow of crude oil in the pipelines and might cause blockage in the pipelines which currently affecting petroleum industries worldwide especially in Malaysia( Zhang et.al, 2016)
Crude oil is actually a mixture of liquid that comes in a very complicated form. They are absolutely made of hydrocarbons such as waxes and asphaltenes (Ghanbari et.al, 2015).Crude oil has been categorised into three main different categories which are the light, medium and heavy( Nwadinigwe et.al, 2016). They are divided based on the fractions composition from the refining process of the crude oil(Nwadinigwe et al., 2016).
Wax is defined as the ester that is formed from the combination of a long chain of alcohol and fatty acids. This eventually makes them hydrophobic to water where they are resistant to the presence of water.
Figure 2.5: The structure of long chain of wax ester
Source: Retrieved from http://www.lipidhome.co.uk
They are actually a fraction of the crude oil that has the biggest molecular weight of paraffin and they were affected when the temperature of the oil is below than the pour point of the oil itself. The long ester compounds are being formed after great Paraffin is approximately 20 wt% of the total mixture of hydrocarbon(Patel, Chitte, ; Bharambe, 2016).A complex morphology with in form of the 3-dimensional shape of a compound derived as wax crystals(Energy et al., 2005). Wax can be divided into many types of different categories based on the chemical structure such as bees wax, carnauba wax from carnauba leaves and many others. The common wax constituents are being shown in the diagram below:
Figure 2.6: The structures for some common wax constituents Source: Retrieved from http://www.lipidhome.co.uk
Based on the previous research, the lower the oil temperature than the pour point, the easier the wax can be separated from the crude oil. The contents of the paraffin are that they are a mixture of hydrocarbons where comes in many chains around more than 20 carbon attached together in form of alkanes. Wax crystallisation caused precipitation occurs along with phase separation. Based on Behbahani(2015), the limitation of value to build a stable wax crystals compound is such as 2% w/w and that what called as the wax-oil gel (Behbahani et al., 2015). Wax is being formed from the aggregation process where this process helps to produce bigger wax crystals.
The quantity of the wax will be categorized by the high pour point, high viscosity, strength of the gel and finally the deposition of the wax(Al-sabagh et.al, 2013). If the wax is below the required temperature then they can easily remove out from the crude oil. The crude oil is called as gelated oil or wax when they crystallized themselves by interlocking to each other so indirectly they are increasing the flow resistance(Al-sabagh et al., 2013). Thus an inhibitor is required to prevent the wax crystallisation.
The wax crystallisation took shorter time at the wall of the pipeline while longer time at the centre of the pipe. This is because of the temperature difference between two different points of the pipe. Indirectly, the reduction in temperature causes the pipe to have some blockage or gelation in transporting the wax(Patel et al., 2016). The maximum temperature for a wax to melt is about 62°C based on DSC analysis (Motawie et al., 2015). There are many possible solutions that can be done to transport the wax maybe such as heating the crude oil earlier before releasing them into the pipeline, having a special system to modify the wax, controlling the thermal condition to reduce the effect for the pour point. However based on previous researches, each solution have their own limitations(Patel et al., 2016). The most economical or best way to overcome the wax precipitation and crystallisation is by using the additives of polymeric chemicals and oil-soluble surfactants(Patel et al., 2016).
Wax build-up is the most difficult issues that to be handled in petroleum industries. Wax crystallisation from crude oils can be affected by many parameters such as composition, temperature and pressure of the system(Hosseinipour et.al,2016). The purification of the natural gas from the petroleum industries need a better separation process that caused carbon dioxide content reached 70%(Hosseinipour et al., 2016). Wax produced because from the transportation of the crude oils, seabed and the temperature of the surface of the pipe.
The main purpose to remove n-paraffin from the crude oils is to obtain less fraction of wax in crude oil. The wax crystal will attach together to create the crystal in solid and affect the characteristics of the crude oil. Gel emulsion properties can be affected by n-paraffin content and that n-paraffin content can cause waxy crude oils. These highly molecular weights of the paraffin caused the petroleum industries to face a very major problem in their transporting away the crude oil through the pipelines. The transportation of these waxy crude oils should be done above the wax appearance temperature(WAT) to prevent any clogging occurred in the transportation line(Gonza, 2001).When there is disruption on the wax crystal agglomeration, then the formation of the wax will become softer which caused the flow of the crude oil become easier and smoother(Theyab, Diaz, Theyab, ; Diaz, 2017).
2.4 Paraffin Wax Characteristics
Wax in crude oil also known as paraffin waxes. They were categorised based on their melting point and the limit of degree of refining if they are in macrocystalline waxes. If they are soft paraffin waxes, then the degree of melting temperature should be less than 45°C while hard paraffin will have higher than 45°C but not more than 60°C. The classification for the refining of paraffin waxes is in three main categories which are refined waxes, technical and finally semi-refined. The content of oil is less than six weight percent (wt %) in technical grade paraffin waxes and they are the products of the slacks through dewaxing process. If the semi refined paraffin waxes, the content of oil will be more than three weight percent (wt%) which shows that they are heavier than the technical paraffin waxes. Usually, the paraffin appearance of semi-refined paraffin waxes will be yellow or in white in colour. Last but not least, the refined waxes will be colourless and they are less toxic to health and odourless too but they contain the least amount of oil or wax. Classification of paraffin waxes can be divided into two main groups which are the macrocrystalline waxes and microcrystalline waxes.
Paraffin waxes are made of more than 25 atoms of saturated hydrocarbons. If they do not have any effect on the properties of wax, then they are macrocrystalline paraffin waxes where they have a number of aromatic ring compounds with less molecular weight. Usually, the most common compound that builds the aromatic rings in paraffin waxes is alkylbenzene.
Figure 2.7: The structure of paraffin waxes
Source: Anne (2012)
2.5 Wax Adsorption
Nowadays in petroleum oil industry, the deposition of wax in the oil-water multiphase transportation line had been a great issue that being attacking the flow of oil in the industries. This is due to the formation of wax-oil in emulsion due to higher adsorption between the surfaces of the wax. Based on Zheng and Fogler (2015), they mentioned that blocking of the diffusion path occurred due to the wax droplets that formed in the pipelines.
There is a study is being conducted currently where the adsorption of natural oil can be classified into two major elements where they focus more on the asphaltene and the wax crystals. From the previous research, the emulsion can be stabilised by adding some fine particles such as crystals of the wax and silica where they are known as picking emulsion. The adsorption of the wax can occur very fast at the interface of the oil-water if the wax had formed co-crystals with the addition of ester or acid molecules together and without the presence of a surfactant. Surfactant sometimes can act as inhibitors to prevent wax deposition in the crude oil too and reduce the wax adsorption on the interface of crude oil. Wax adsorption become more stable if they are in the continuous phase of the emulsion in state oil-wax.(Qianli Ma et al., 2017). Moreover, the temperature will also affect the gelation and adsorption of wax where the increase in temperature can cause the adsorption of wax on the interface of crude oil decreases and eventually increase the solubility of wax.
Figure 2.8: Adsorption with the presence of surfactant
Source: Ma et al. (2017)
2.6 Wax Treatment
Next interesting part about wax removal from crude oil is that there is exposure to the traditional experimental method (Aiyejina et.al, 2011). The methods that they had been explaining here is the direct method such as “take out” and pigging method. When there is a removal of pipe to measure the deposition of the wax, it is called as ‘Take out’ method. There is another new method to calculate the volume of wax by inventing the strain gauge even to detect the smallest change in the wax percentage and the result from this invention was really predictable as expected. The disability to expand the design is that the experiment can only be conducted in laboratory scale to represent the actual system.
Another traditional method that had been practised in the new research is by using acrylate polymer, acts as pour point depressant (PPD)which comes in room temperature and it is in solid form polymer(Admiral et al., 2016).There are some findings of PPD where PPD were improvised to enhance the ability of a crude oil to flow in the pipeline. The viscosity of traditional acrylate polymer is lower where it comes in solid form than the emulsified acrylate polymer (Admiral et al., 2016).They come to a conclusion that the emulsified pour point dispersant is better compared than traditional pour dispersants. Emulsified PD90 can be created when emulsion technique is used to form droplets of PPD (Admiral et al., 2016).Emulsified PD90 shows good result in the reduction of pour point depressant other than the solvent based on PD90. This is because that the content of kinetic energy of emulsified PD90 or inhibitors is higher than the pure PD90 and this caused the molecules of wax move freely around the atoms of crude oil and it eventually inhibits the crystallization of wax (Admiral et al., 2016)
The deposition of crude oil can be treated with several methods such as developing pressure in the pipeline, applying heating principles and finally coating the pipelines with any materials. The main purpose to increase the pressure is that to have higher shear rate so that the deposition of wax becomes slower than usual. By heating method and coating method, the adhering of wax can be prevented and caused the flow of the crude oil to be smoother.
Prevention is always better than cure and prevention is the best decision to solve this current issue in petroleum industries. Reduction of cost for the maintenance of the blocked pipeline together with the replacement of new equipment can be done through prevention or treatment methods. Thus, there are many types of researches still being conducted by some researchers so that they can find the best inhibitors to obtain 100% efficiency in preventing the deposition of wax.
2.7 Wax Inhibitors
Although there are many traditional methods to remove wax precipitation, the most frequent method that is used is the wax inhibitor. An inhibitor is being categorised as the modifier of the crystals, depressants of the pour point and inhibitors of paraffin followed by the flow improvers(Energy et al., 2005). A wax inhibitor can ensure that the growth of the wax stopped and able to prevent any wax blockage occur in the pipeline (Theyab et al, 2017). They are actually one of the methods to protect the pipelines of crude oil from wax deposition.
Figure 2.9: The pipelines in presence and absence of
Source: Retrieved from http://www.drdakin.tripod.com
Wax inhibitors are being influenced by many external factors such temperature, concentration and shear rate of the inhibitors themselves. In the past reviews papers, they had to use the high-pressure micro differential scanning calorimeter to measure the curve of the solubility of wax under the Wax Appearance Temperature (WAT). Some researchers had been conducting further research to identify the new parameter that can control the first formation of wax crystals such as carbon dioxide being studied in one of past researches (Hosseinipour et al., 2016). From one of the results, the Wax Appearance Temperature (WAT) of all crudes oils from Malaysia is above 25°C. This proves that Malaysian crude oils should use the wax inhibitors and Malaysian petroleum industry is not recommended to use single line pipeline due to the value of WAT is too high and the average temperature of the seabed is approximately or more than 25°C.
Based on Hoffmann and Amundsen (2013), both of them came in a conclusion that the thickness of the wax can be reduced approximately 60% to 90% when the wax inhibitor being applied in different concentrations when they did their experimental work. In one of the research, the inhibitors that had been used is related to the polymers that classified as pour points depressants to solubilized the wax crystals in the pipelines (Theyab et al., 2017). Wax is known as a compound that looks like a cage which inhibits the flow of the crude oil(Admiral, Abdullah, ; Ariffin, 2016). Wax can be classified in term of stability based on the particle size of the wax crystals. In the opinion of previous researches, there is still lacking on the studies of the wax deposition in the crude oil. The justification from all the researches, wax becomes the most important part of the crude oil that need to be removed to ensure a proper flow in the pipelines and reduce the blockage or clogging critical issues. Wax inhibitors should be used for the deposition of wax that occurs in a long run pipelines such below:
Figure 2.10: The deposition of wax in the inner surface of pipeline walls.
Source: Nanochemistry drives new method for removal and control of wax (Journal of Petroleum Technology)
Figure 2.11: The deposit appearance without inhibitors (left), with inhibitor (right)
Source: Hoffmann ; Amundsen (2013)
In order to maintain the productivity of the crude oil and ensure the flow properties of the crude oil, inhibitors should be introduced for the paraffin or wax deposition in the pipeline (Al-sabagh et al., 2013). In the research done by Amel A Nimer (2009), there are actually two types of methods to ensure the wax to be removed from the surface of the crude oil. The methods are solvent removal and catalytic removal where solvent removal is the most effective way compared than the catalytic removal (Rabah, 2017).This is because based on the review from the article, solvent removal method can remove the hydrocarbons that come in the heavy form or lighter form while catalytic removal only light hydrocarbons or the carbons that are above the boiling range (Rabah,2017). The researchers of this article had been using toluene and methyl ethyl ketone (MEK) as their inhibitors for solvent removal method. They used toluene in their research experiment because they are the one of the purest solvents which acts as the best removal for any oil surfaces even the wax crystals followed by the usage of methyl ethyl ketone(MEK) as they can precipitates the wax better. There are many frequently used polymers before and they had given some efficient results in inhibiting the wax deposition in crude oil. The common polymers used are such as below:
Figure 2.12: Structure of Ethylene/vinyl acetate (left),
Source: Kelland (2009)
There are many types of inhibitors that can be used for the removal of wax in the natural oil not only crude oil and the structure for each inhibitors being described as shown in the figure below:
Figure 2.13: The structure of common inhibitors used
Source: Madhi et al. (2017)
The dewaxing method in terms of solvent requires more energy to be consumed rather than the catalytic waxing especially for the regeneration of the solvent and pumping. Moreover in this study, they proposed that the ratio of the crude oil should be lower than the solvent ratio because increased solvent quantity can solubilised the crystallised form of the wax and the earlier literature shows that the ratio should be in 16:1 or 32:1 in term of mass(Rabah, 2017). In this research, they managed to find the operational conditions for the wax production. The results are such as to produce wax in a higher amount and it requires 75% MEK, ratio of 20:1 solvent to oil with -17°C in 30 minutes with retention time about approximately 20 minutes. The wax that had been formed from these operational conditions consists of a smaller amount of the 6% of lighter n-paraffins. The justifications form this literature review of this article is that toluene could be replaced with another solvent like butanol or benzene along with the MEK being substituted with Methylcyclohexane (MCH) to obtain different observations for the operational temperature to have a smoother flow of crude oil in pipelines.
Based on another article by Muhammad Ali Theyab and Pedro Diaz(2017), chemical addition become one of the methods that can be used to inhibit the deposition of wax (Theyab et al., 2017). They come with an idea to know the results for different inhibitors with the aid of the programmable Rheometer rig. The wax appearance temperature can be reduced drastically when they add these types wax of inhibitors in their experiments. The inhibitors that used in this experiment actually prevent the formation of wax by merging and absorbing with the wax crystals. They also mentioned that the polymers that contain wax structure can act as an inhibitor to reduce the crystal growth by covering the wax site to form smaller wax. The temperature where the wax in semi-solid called pour point reducing from 27.6°C to 13.2°C and the viscosity reducing to 52.5% if the temperature is higher than 5°C( Theyab et al., 2017).
One of the past research study mentioned that the flow improvers act as pour point depressants actually makes the crude oil transportation along the pipelines can be done easily(Patel et al., 2016). In this research, the polymers that had been taking part are such as maleic anhydride and n-alkyl oleate which they were tested by the free radical polymerisation. They were tabulated based on the results from the Fourier Transform Infrared Spectroscopy (FITR) and the Gel Permeation Chromatography. The results were based on the apparent viscosity, plastic viscosity and finally the yield value. As a conclusion, the results of the apparent viscosity, the yield value and the viscosity of the plastic reduce to the most appropriate values for the crude oil that is virgin(Patel et al., 2016).
Another literature review that had been proposed for this topic is that investigation on the behaviour of the crude oil in term of rheological with or without the inhibitors or known as pour point depressants (PPD). The polymer that had been used in this experiment is that ethylene vinyl acetate (EVA) polymer. They used Iranian waxy crude oil as the sample for this experimental purpose. The polymers used based on different characterisation based on the content of nitrogen, the content of carbon and hydrogen followed by various molecular weight of the polymer to enable getting various results at the end of the experiment (Behbahani et al., 2015). At the end of the experiment, the result of the viscosity is dependent on two parameters which are shear rate and the temperature of the inhibitors. The formation of the gel network actually boosted up the viscosity of the crude oil and those gels had been formed in the experiment when the temperature of the wax reduced in between 5°C and 30°C.
These inhibitors for wax functions as a modifier of the structure of the wax chemically where the reduction in the growth of wax crystals occurred in the pipelines of crude oil. Although there were many types of researches that had been done before for these inhibitors method, the only drawback that had been suggested by them from this method is that the inhibitors only can reduce the growth of the paraffin waxes but still do not fully stopped the deposition process of wax in crude oil which may lead to a continuous deposition process along the flow of crude oil in the pipelines (Anisuzzaman et al., 2017).
2.8 Asphaltene in Crude Oil
One of the constituents in the crude oil other than wax is asphaltene which can cause deposition and leads to blockage of pipelines in petroleum industries. Asphaltenes are known as impure compounds as they consist thousands of different species with different molecular weights but similar behaviours chemically(Wei et_al, 2016). Their nature is actually very complicated and complex which makes the study of their characteristics becomes harder(Rocha et_al,2006).
Asphaltenes have higher solubility in the non-polar solvent such as toluene and they are not soluble in the polar solvents such as glycerine, water, n-heptane and n-pentane compounds(Adebiyi ; Thoss, 2014). Moreover, asphaltenes always exist in suspended solid form or known as colloidal particles and the structures of the asphalthenes being interconnected by bridges that are formed from some aromatic compounds as sulphur or alkyl(Zhang et al., 2014). The existence of aliphatic or aromatic chains caused them to be one of the heaviest elements in the crude oil.
Figure 2.14: The illustration of asphaltenes structures by Speight
Source: Petroleum Science and Technology 25(1-2):67-80(2007)
Table 2.1: The composition of asphaltenes that derived from four different countries
Source: The Chemistry and Technology of Petroleum (Speight, 1999).
2.9 Asphaltene Treatment
Before analysing the asphaltene treatments, the needs to differentiate between three common terms that will be frequently used which are precipitation, flocculation and finally deposition is very important. Precipitation is a process that forms particles in semi-solid through aggregation process and usually, they are in one-micrometre size particles. After a big cluster of precipitate is formed, then they are known as flocculate and this is so called as flocculation process. Finally, deposition is the last stage process that forms the blockage in pipelines due to heavy or large adsorbed particles on the surface of the pipelines(Shadman et_al, 2017).
Deposition of asphaltene occurs due to its stability and the deposition always occurs at many target places along the pipelines such as inside the pumps, valves, and flow lines of the pipes(Adebiyi ; Thoss, 2014).Based on Kokal and Sayegh(1995), they mentioned that the deposition or precipitation of the asphaltene occurred due to many reasons such as temperature changes, the composition of the chemicals themselves, chemical properties due to the mixture of oil and other substances. These depositions caused a severe problem in terms of transport and process facilities in petroleum industries almost all over the world.
Thus, there are many types of treatments that can be done to overcome the precipitation of asphaltene in crude oil. The treatments or methods that had been used by many types of previous researches are such as mechanical removal, ultrasonic removal, removing the deposition by using any high temperature or hot fluids such as water steam, and finally adding the inhibitors or other types of dispersants that can breaks the structure of the asphaltene and prevent them from growing bigger to form a precipitate (Rocha et al., 2006). Based on Shadman (2017), he introduced a treatment that can inhibit the deposition of asphaltene by using the viscometer by using various types of amphiphiles. The result of the treatment is that the stability of asphaltene is affected by the concentration of amphiphiles and when the concentration increases, eventually the stability increases too. Although there are many treatments or method applied to inhibit the asphaltene deposition, the most efficient treatment is by using chemical inhibitors.
2.10 Asphaltene Inhibitors
As mentioned before, the best treatment is by using chemical inhibitors to reduce the blockage in the pipelines due to the asphaltene deposition. Thus, solvent treatment becomes the best treatment to treat this issue and the most common solvents that can be used as inhibitors are such as toluene, benzene and xylene which they are aromatic compounds. Treatment by using these chemical solvent can saves the cost as well as acts a preventive method for this critical issue. Usually, the inhibitors used to reduce the effect of this problem should be used on a large quantity of crude oil as then the inhibitors can dissolve in a solution that is highly concentrated. Based on Muhammad Ali Karambeigi (2016), he mentioned that the most effective inhibitor that he had used for the Iranian crude oil is IR95 inhibitor with 34% asphaltene reduction in precipitation compared to others tested inhibitors(Karambeigi et_al,2016). This is because IR95 has higher polarity and they are in aromatic form compounds which make the asphaltene to dissolve easily and improved the flow of crude oil.
The purpose of chemical inhibitors which have different functional groups and structures is to delay the formation of asphaltene deposition by increasing adsorption to the surface of the asphaltene. Based on the Cenergy(2001), the treatment that had frequently used is by direct injection process into the asphaltene deposition and they are known as a physical-chemical process. The relationship between Van der Waals and electrostatic force between inhibitor increases the adsorption process to the surface of the crude oil.
Based on Chang and Fogler (1994), the concentration of amphiphiles as inhibitor will affect the stabilisation of asphaltenes. When increasing the amphiphiles’ heads, then bonding between the asphaltene and amphiphiles becomes stronger due to higher polarity. This proves that chemical inhibitor such as alkanes improvised the flow of the crude oil in the pipelines by modifying the bonding between the molecules in asphaltene so that they become more stable. Rogel(2010) mentioned that the reduction in asphatene sizes does not change when the inhibitor had reached the maximum or optimum concentration value and this shows that the concentration of inhibitor plays a role in inhibiting the deposition other than the temperature of the inhibitors with crude oil. The end result of this inhibition process will be more efficient if using cationic inhibitors. Cationic inhibitors can speed up neutralisation of asphaltenes’ polarity and caused them to be easily reacted with non-polar substances eventually fasten up the reduction of the deposition process in the crude oil. Most of the chemical inhibitors can react well at the temperature around 10°C and if their concentration range is about from 500ppm to 5000 ppm. Thus, it is very important in choosing the proper chemical inhibitors with accurate structural functional groups to treat asphaltene issues in petroleum pipelines so that this issue can be solved easily with less costing (Ridzuan et_al, 2016).
Table 2.2: The degree of inhibition in percentage for various types of inhibitors at 5°C
Type of inhibitor Percentage inhibition efficiency (%)
Blank crude oil NA
Source: Evaluation of the inhibitor selection on wax deposition for Malaysian crude oil (2016)
In a summary for all types of researches that had been studied, the most common used treatment is inhibitors method which is very high-cost saving and the latest technology for this method is that by using the different formulation of inhibitors where it can help to reduce the precipitation of both major components in crude oil which is wax and asphaltenes.
Most of the studies, they had been using the ethylene vinyl acetate (EVA) as the major inhibitor with some aromatic compounds such as toluene and xylene which speed up the reaction faster. These combinations of two different compounds such as EVA and xylene really gives the best results and EVA 30 gives better end result rather than other EVA. The presences of Methyl Ethyl Ketone (MEK) at 75% fasten up the inhibition process if MEK is added together with another solvent as EVA and any other aromatic compounds.
Moreover, from the previous studies, there are many parameters that had been analysed for the solubility of wax and asphaltenes. The parameters are such as temperature, carbon dioxide concentration, the concentration of the inhibitors and shear rate of the concentration. Based on the previous researches, the optimum temperature or the wax appearance temperature (WAT) is between 11 to 25°C and to reduce the viscosity, the temperature of inhibitors should be increased. The shear rate that been used for the most of the studies is around 800ppm to 1000 ppm but it is influenced by the concentration of the asphaltene in the crude oil. The summary of the articles that been studies had been done in a form of a table as below:
Technology Results/Description References
1 Thin layer chromatography flame-ionization(TLC-FID) which is high-liquid performance chromotography If pour point is below the environment temperature, there will be higher formation of gel in the form of matrix. The WAT is 41?C based on the TLC-FID. The viscosity and pour points differs for each crude oils and wax represents the n paraffin content. The viscous of the crude oil depends on the n paraffin. The fluid will achieve equilibrium with proper temperature whenever there are long shutdowns.
“Flow Assurance Study for Waxy Crude Oil”, Marcia et al. (2011)
2 Chemical addition by adding chemical polymers The WAT temperature is based on 27.6?C to 11?C and WAT can be reduced together with pour-point as there are growing of polyacrylate and acrylated monomer at the edge of crystals due to the addition of phenol aromatic naphtha. The inhibitors will affect the viscosity of the crude oil by increasing monomers
by preventing wax crystals to be formed.
“Experimental Study on the Effect of Inhibitors on Wax Deposition”, Muhamad Ali Theyab and Pedro Diaz (2016)
3 Solvent extraction The line of isotherm reaches the asymptote at the time of 20 minutes which gives the maximum yield of wax. The temperature increases with wax yield because there is a decrease in viscosity due to the heating process and caused the rate of distribution of solvent in the mixture. As crystal growth being prevented by presence of solvent so the more solvent used to oil ratio can reduce the growth. Indirectly the viscosity of the mixture will reduce but still there are no changes if the ratio of solvent to oil is is 20:1.Moreover, in this literature done by the researcher, the pure Methyl Ethyl Ketone (MEK) can cause the formation of the third phase where there is a new phase to be formed and there are some molecules formed to clogs the filter and reduce the rate of filtration which directs to blockage of waxy crude oils in pipelines. “Wax Separation using MEK Toluene Mixtures”, Amel A Nimer et al. (2009)
4 Differential Scanning Calorimetry Technique (DSC) which is thermoanalytical
Technique based on temperature and heat The rate of wax formation is affected by the one of the parameters which is temperature. They have tendency to crystallise the wax if the temperature is below the solid liquid equilibrium temperature. They have stronger effect to the Wax Appearance Temperature (WAT) where they have the shorter hydrocarbon chains. If the temperature is lower than WAT, then they are able to form waxy crude oils. This is because nucleation process occurs here to make nuclei to be more stable. Moreover the increasement in carbon dioxide causes the WAT to be decreased. In this research they had used the light ends of crude oil where they have huge capabilities to act as a flow improver for the waxy crude oils transportation. WAT in crude oils really helps us to ensure awareness on safe inhibition for the formation of wax and enable smoother flow in the pipelines. “The Effect of CO2 on WAT Crude Oils”, Arya et al. (2016)
5 SPSS technology software for analytical purposes The wax deposition is being affected by the crude oil temperature and they increases until the maximum range of temperature which is 38°C. Insulation layer thickness also affects the deposition of wax and it decreases with increasement of temperature. The suitable temperature during 3°C in winter and 15°C in summer and if there is no insulation layer then the thickness of wax is large. The deposition of wax outside the insulated is thicker and obvious rather than wax deposition inside the insulated pipeline. “Prediction of Wax Deposition in An Insulation Pipeline”, Z. Hu et al. (2015)
6 Acid-catalysed esterification where reaction of alcohol and acid In this research, the best flow improver occurs at higher concentrations where they act as the most effective pour point depressant. The viscosity and the yield value of virgin crude oil will be reduce by flow improver from oleic acid. Wax growth inhibited by oleic acid to improve the flow due to increase in alkyl chain length. This is because of polar part helps to block wax growth. “Oleic Acid Based Polymeric Flow Improves in Laghnaj”, Mayur et al. (2015)
7 Chemical Addition and Artificial Neural Network (ANN) where analysed based
computational model Shear rate decreases the wax formation by affecting the viscosity of the wax crude oil and it had been reduced to 780 cp from 2250 cp. If it is below the pour point, solid crude oil will be formed where the viscosity will increase. Viscosity is being affected by temperature and shear rate where if temperature and shear rate increases can cause the viscosity to decrease. At 30°C there is no effect from the improvers to reduce the wax deposition. The factors that affect the flow improvers are the concentrations and the types of
of flow improvers themselves. If the temperature is below the pour point depressant, the viscosity reduces because there is formation of paraffin crystals. Moreover, in this study they found that higher molecular weight of flow improvers has higher efficiency for wax inhibition by affecting pour point and the rheological behaviour. The Artificial Neural Network (ANN) model gives better results than Solid Solution (SS) model as they do not involve wax critical properties. Artificial Neural Network (ANN) method gives better results than Solid Solution (SS) model. “Investigation on Wax Precipitation in Crude Oil”, Tarareh et al. (2015)
8 Commercially available wax inhibitor chemical addition The precipitation of wax will occur at 25 °C and the purpose of wax inhibitor is to change the rheological behaviour of the wax itself. When the experiments done at 23°C, at 125 ppm the thickness of the wax had been observed to have a very obvious reduction until 70% for uninsulated layer while to 90% for insulated layer. At 250 ppm, there is no significant decrease in wax deposition at this temperature. It just had been decrease about 10% from the deposition of wax 125ppm. At 20°C the wax deposition is pretty higher than the wax deposition at
23°C. If the temperature is below than 23°C, 250 ppm of inhibitor does not affect the wax inhibitor as there are no changes with the wax deposition but only 500 ppm is eligible at this lower temperature. If the temperature below than 23?C for 250 ppm of an inhibitor has no effect on wax depositor but for 125 ppm, it reduces to 70%. “Influence of Wax Inhibitor on Fluid and Deposit Properties”, Hoffman et al. (2013)
9 Magnetic treatment by using sintered magnets such as MQII and LDC magnet Sedimentation and wax formation lower at temperature 2?C to 3?C compared to other temperature at 0.1 kg/m2 per hour. “Influence of Processing Conditions on Sedimentation Kinetics of Highly Waxy Crude Oil”, Y.V. Loskutova et al. (2015)
10 Polarized Light Microscopy (PLM) by using
optical microscopy tecnhiques A higher driving force or light intensity required to build higher asphaltene molecules. “Effect of Asphaltenes on Crude Oil Wax”, Pavel Kriz and Simon I. Andesen (2004)
11 Asphaltene Stabiliser and Solid Detection System(SDS) where it is a PVT cell with a piston floats and attached to an impeller works magnetically The samples characterised by their stability through SARA test and the results shows that the higher aromatic compounds has the best inhibition efficiency to asphaltenes.
‘Effect on Inhibitors on asphaltene precipitation for Marrat Kuwaiti Reservoirs’
( Ghloum et.al, 2010)
12 Physical MCR 301,apparatus attached with rheometer that rotate together with attached cone and plate
The results is if the solvent used has parameter of solubility less than 16.5 Mpa, then the solvent considered as the best inhibitor for the asphaltene precipitation in the crude oil. ‘Asphaltene in Heavy Crude Oil’
( Sergey et al., 2017)
13 SARA test to separate the crude oil based on its solubility From this research, they obtained that the salicylic acids is the best inhibitors and they also come to a conclusion that the higher polar and aromatic compounds reduce the precipitation of asphaltene better than other compounds. ‘ Experimental Evaluation of Asphaltene Inhibitors Selection for the Standard and Reservoirs’
(Karambeigi et al.,2016)
14 IR spectrometer to analyse the compounds structure in crude oil The result showed that the asphaltene formation in crude oil is due to the higher content of porphyrins and heterogeneous compounds. ‘Organic Elemental Elucidation of Asphaltene Fraction Nigerial’
(Adebiyi ; Thoss, 2014)
15 Varian 400 NMR spectrum to determine structure of molecule The research proved that the phenolic aromatic compounds seems removed higher amount of asphaltene compared to other compounds which they only contain 1.22 intensity of asphaltene in the final product. ‘Characterisation of Asphaltene Extracted from the Indonesian Oil Sand Using NMR,DEPT and MACDI’
(Zheng et al., 2015)
16 UV Visible Spectrometry Shidmanzu Class Vp Version 6.13 SP2 software to analyse the solubility Dodecyl benzene sulfonic acid (DBSA) and BisACII act as asphaltene inhibitor. The final result is determined by the wavelength of the inhibitors and the software which shows that BisACII in mixture of xylene or toluene can reduce the asphaltene inhibition better than DBSA. An ITC Study of Interaction and Complexation of Asphaltene Model Compounds in a polar solvent II’
(Wei et al., 2016)
17 Chemical Inhibitors such as toluene,n-heptane and n-hexane The efficiency of asphaltene increases with chemical inhibitors with addition of some organic acids. Moreover, it is proven that the aromatic compound toluene has better inhibitor characteristics rather than aliphatic compounds. ‘Inhibition of Asphlatene Precipitation in Brazilian Crude Oil using New Oil Soluble Amphiphiles'(Junior et al.,2005)
18 Transmission of Electron Microscope to view the morphology structure of asphaltene to determine the end deposit. The result concluded that the larger polarity of C7 in toluene and n-hexane solution decreases the solubility of apshaltene and found that the deposition of asphatene is less than other carbon through microscope. ‘Study on the Polarity, Solubility and Stacking Characteristics of Asphaltene
(Zhang et al.,2014)
19 Brookfield DV-II and programmable viscometer, FTIR and H-NMR spectrocopy The result is the copolymer which has average molecular weight, higher index of polydispersity and higher amount of nitrogen affect the pour point efficiently which eventually decreases the concentration of inhibitors. The viscosity decreases as temperature increases as 7.29 mPa at 39°C, 190.95 mPa at 27°C and 358mPa at 15°C. ‘Synthesis of Phthalimide and Succimide copolymers and their Evaluation as Flow Improvers for an Egyptian Waxy Crude Oil’
(Al-Sabagh et al.,2013)
20 SPSS software to determine the equation for wax deposition rate The wax deposition rate increases when the insulated layer of the pipelines becomes thicker and temperature decreases. ‘Prediction of wax Deposition in an Insulation Crude Oil Pipelines’
Hu et al.(2015)
2.12 Limitations of Literature Review
After many researches that had been studied, the limitations that had been found from the review of all previous articles that there had no justifications done on viscosity of crude oil based on effect of aromatic and non-aromatic compounds on various temperature and form different inhibitors which are EVA,MEK and toluene or butanol. They only managed to come with a result for the aromatic compound formulations but not yet with the non-aromatic compounds. So eventually,this proves that there had been a small space between all these previous researches where the researchers had been neglected the effect of combination of inhibitors with aromatic compounds and non-aromatic compounds in different temperature ranges. Thus, using the different combination of inhibitors can help to do better comparison on solubility of the wax and asphaltene and together with the viscosity of the crude oil.
In this chapter, there are some aspects being described such as experimental setup, the procedures to conduct the experiment and analysis method. In this experiment, the main sample that being used is crude oil which is about 20g of crude oil and the crude oil is being tested for the viscosity and the wax appearance temperature (WAT) at vary temperature from 5°C to 20°C where the interval between each temperature is about 5°C. The result of the tested samples been analyzed by comparing with the properties of WAT of crude oil and the viscosity of crude oil. The data is being tabulated in manually form by plotting graph and Research Surface Methodology (RSM).
3.2 Experimental Setup
3.2.1 Materials and Chemicals
The main material that was used in this experiment is the crude oil that is obtained from Sabah, Malaysia. Thus, the type of crude oil is known as Malaysian crude oil where they contain higher fractions of asphaltene compared to the wax fraction.
The wax inhibitor that had been using is ethylene vinyl acetate (EVA). EVA is a type of polymer that can increase adhesion process to the surface of wax molecules. Thus, the size of the wax particles can be prevented from growing and forming a big structure of crystals that can cause heavy deposition. EVA that been used in this experiment is EVA with 40% wt vinyl acetate. This is because past researchers commonly used EVA 32%wt and 40wt% and the availability of EVA 40wt% is higher than the others EVA.
Figure 3.1: The type of EVA that used for this experiment
The used solvent for the EVA for this experiment is Methylcyclohexane (MCH).The melting point of EVA40 is at around 46-47.5?. Thus to ensure EVA fully dissolved in the organic solvent as the reaction occurs at very high temperature, the boiling point of the organic solvent should be more than the melting point of the EVA. So, MCH is the one of suitable organic material as they have a higher boiling point which is at 84°C.
Figure 3.2: The Methylcyclohexane
(MCH) used in this experiment
The most appropriate inhibitor forasphaltene is toluene but in this experiment, butanol is actually used together so that the comparison of the aromatic and non-aromatic compounds can be studied on the effect on viscosity and the WAT temperature. These types of solvents were used to decrease the formation of crystals of asphaltene and increase the adhesion process to the surface of the asphaltene so that flocculation was prevented on the surface of the crude oil.
The main equipment is viscometer and they play a vital role in this experiment results. The viscometer is used to obtain the results for the viscosity of the crude oil samples that are being mixed with the different formulation of inhibitors. The viscometer used is the Brookfield Programmable Viscometer DV-II + PRO. The standard settings of the equipment are as below.
Table 1.1: Standard settings of viscometer
Spindle Size 63
Rotational Speed 100 rpm
The proper method to obtain accurate reading ensures that the viscometer is auto-zeroed before testing the new samples and at different temperature intervals. The viscometer should be left around 10 minutes before using them as a pre-warm up for the device so accurate readings can be obtained at the end of the experiment. The spindle for the viscometer should be handled carefully because it is very sensitive and can break if being handled carelessly beside ensure the calibration of the crude oil is not affected.
Figure 3.3: The DVII + Pro viscometer
used to measure viscosity.
The next equipment used is Binder Oven. This oven is used to heat the crude oil pre-night until they reach 90°C before mixing with the inhibitors the next day.
Figure 3.4: Diagram of Binder Oven for
heating the crude oil
The function of hot plate stirrer in this experiment is to provide a temperature of 70 -90? during the mixing of EVA, MCH and toluene and butanol, and also during the mixing process of crude oil and the different formulation of inhibitors.
Figure 3.5: The cimarec hot
The important equipment that was used in this experiment is water bath. The role of the water bath is to decrease the temperature of the samples gradually as intervals around 5°C between the two temperatures and the temperature range is between 5°C and 20°C during the experiments. The type of thermometer used to measure the temperature of the samples is digital temperature.
Figure 3.6: Water bath used to control
A mass balance is used to measure the weight of EVA which is around 20 g so that a more accurate weight of EVA is obtained. The digital micropipette is used to obtain the accurate readings for the solvents that come in liquid form.
Figure 3.7: The micropipette used for
3.3 Pre-experimental Preparation of Chemicals and Crude Oil
The pre-step for the experiment is that the crude oil is heated in the Binder oven at the temperature about 90? for an overnight. This step is to melt any deposition of wax crystals that had been formed earlier and the structure of asphaltene that being agglomerates in the crude oil. The preliminary step before this experiment being conducted is the apparatus that will be using such as the spindle of viscometer, measuring cylinder and pipette were heated to 60? so that the precipitation of wax and asphaltene at the point of contact between the hot crude oil and cold apparatus can be avoided and to obtain accurate results. Before mixing of the inhibitor together EVA, MCH and toluene or butanol are heated in a water bath to increase the temperature to 60?.
3.4 Preparation of inhibitor
The inhibitors were prepared by conducting them on a hot plate at a temperature of about 90?. Instead of using the oven, using hot plate can help to save time and space for the experiment to be conducted as the limitation of lab equipments in preparing the chemicals. The individual chemicals, EVA, MCH and Toluene are measured separately of its respective volume and weight in accordance with the manipulated percentage composition. The unit for the EVA is grams of mass while MCH is in mL and toluene and butanol in mL. The total volume of inhibitor used is 0.4g. Thus, for example, if the percentage composition of the samples prepared are 50% EVA, 10% MCH and 40% Toluene, then 0.2 g EVA is measured using a mass balance, 0.04 mL of MCH is measured using a micropipette and 0.16 mL of Toluene is measured using a micropipette.
The precaution step here is to replace the tube for the micropipette for each new sample that was taken so that contamination can be avoided and accuracy of the results obtained can be improvised .Care is taken to replace the micropipette tube for both chemicals to avoid contamination. The purpose of the reaction to be in high temperature which is 90 °C is to ensure that the EVA pellets is completely melted in the inhibitors. After complete melting of EVA occurred, then the crude oil that were placed in the oven overnight should be mixed with the EVA and the inhibitor solutions. If the crude oil is placed overnight, then complete dissolved wax crystal will obtained at the next day. Later, the samples obtained should be shaken around 30 seconds or around a minute. This is to ensure the crude oil and the inhibitors completely mixed. Then, the samples are placed again in the oven for 15 minutes to allow the reaction to take place.
Figure 3.8: The prepared samples with labels
Figure 3.9: The samples heated in the
3.5 Experimental Procedure
The samples prepared were tested for viscosity by using viscometer. Moreover, in this experiment, the samples were tested for the optimum temperature for the efficient reduction of wax and asphaltene appearance on the surface of the crude oil. The viscosity of the samples was taken from the temperature range from 5° C and 20° C with each every 5? intervals. The control sample in this experiment is blank crude oil that is free from inhibitors. The viscosity of the blank crude oil is measured after taken from the oven at room temperature. The temperature of the sample is observed by using the digital thermometer and the decrease in temperature gradually is observed carefully. The step is repeated at every 5? interval until the sample temperature drops exactly to 5?.The sample is immersed in an iced water bath so that the temperature can reduce to the expected temperature. The precaution step here is during handling the spindle of the viscometer and the temperature reading should be taken in eye meniscus level to avoid parallax error in readings. The procedure is repeated for each of the other samples that contain the different formulation of inhibitors with various percent of the composition of solvents and polymers. Before starting a new sample each time, the spindle and temperature probe is lightly cleaned to avoid contamination of the samples.