CPB30503- Petr ochemicals Experiment
2:
&
Petroleum
Determination of API
Refining
Technology
gravity
Page |1
1.0 OBJECTIVES
The main purposes of this experiment are therefore: i. ii.
To determine the specific gravity of oil using hydrometer and density meter. To compare the specific gravity and API gravity of different oils.
2.0 SUMMARY
The experiment was carried out under few objectives. First, it was in order to determine specific gravity of oil using hydrometer and density meter. The types of oil used were lubricant oil, diesel, kerosene and petrol. The average readings for density of each oil was studied using hydrometer and density meter which then to be proceed with the calculation for specific gravity. The density values for oils then were compared with the standard value to determine the accuracy of the equipment respectively and it had been stated that density meter gave more accurate readings. Final objective was to compare specific gravity and API gravity of the oils, where API gravity was calculated by using the given formula and it occurred that the relationship between API gravity and specific gravity is an inverse.
3.0 INTRODUCTION AND THEORY
API gravity is defined as American Petroleum Institute (API) gravity is an arbitrary scale expressing the gravity or density of liquid petroleum products. The API gravity value is in range 10 to 50 ºAPI. API gravity is the most commonly used property to classify crude oil and refined petroleum products in petroleum industry. It has also been used to predict many other characteristics of petroleum oils such as sulphur content (Yasin et al., 2013). API is related to specific gravity in a way that it introduces scale for oils that are lighter than water which is measure of how heavy or light a petroleum liquid is compared to water (Santos et al., 2014) where it is calculated using the specific gravity of oil. The higher API gravity of oil than water, oil will floats when mix with water. API gravity is found as follows: ºAPI gravity (ºAPI) =
4.
− 131.5
Specific density, y (at 60 ºF =
; where p water = 1 g/cm3 or 1000 kg/m 3
(1)
(2)
CPB30503- Petr ochemicals Experiment
2:
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Petroleum
Determination of API
Refining
Technology
gravity
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Specific gravity, y, for API calculation is always determined at 60 degree Fahrenheit is a relative value where it dimensionless, is a ratio of the density of one substance to the density of a reference substance, usually water at the same temperature. Temperature and pressure play a major part when measuring specific specifi c gravity (Yasin et al., 2013). In industries, temperature may vary depending on its own standards and needs. The API gravity is the standard specific gravity used by the oil industry, which compares the density of oil to that of water through a calculation designed to ensure consistency in measurement. Less dense oil or “light oil” is preferable to more dense oil as it contains greater quantities of hydrocarbons that can be converted to gasoline. Specific gravity of liquid in the oil industry is often measured by sense form of hydrometer that has its special scale. API gravity value has been used to determine the specification of the oil and to categorize the type of oil itself where lower specific gravity value will increase the API gravity value. Next, sulphur content in crude oil is indicated based on the API gravity in the crude oil where the higher the API gravity value, the lower the sulphur content in the crude oil. From API gravity value, the higher the API gravity, more paraffinic crude oil, the higher yields of gasoline and the lighter the compound. In contrast, the lower the API gravity, more aromatic crude oil, the lower yields of gasoline, the heavier the compound. Basically, API gravity is used to determine classification of oil into 4 types which is light, medium, heavy and extra heavy which are: i.
Light crude oil is defined as having API gravity higher than 31.1 ºAPI.
ii.
Medium crude oil is defined as having API gravity between 22.3 ºAPI and 31.1 ºAPI.
iii.
Heavy crude oil is defined as having API gravity less than 22.3 ºAPI.
iv.
Extra heavy crude oil is defined as having API gravity less than 10 ºAPI. (Petroleum.co.uk., 2017) Hydrometer and density meter methods are commonly used in order to determine the
specific gravity of oil and to compare specific gravity and API gravity of crude petroleum and liquids petroleum products (Rand, 2003). Hydrometer and density meter differs on the way the reading is recorded, manually and digitally. Apart from determining density, hydrometer is also used to determined oil gravity in the oil field. When a hydrometer is placed in oil, it will float with its axis vertical after it has displaced a mass of oil equal to the mass of hydrometer where the reading will be read
CPB30503- Petr ochemicals Experiment
2:
&
Petroleum
Determination of API
Refining
Technology
gravity
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manually, it benefits in a way that it is portable, fast-giving-result and cheap. The hydrometer can be used at atmospheric pressure or at any other pressure in a pressure cylinder (Yasin et al., 2013). The only problem is the accuracy and chances of parallax errors to occur are high. The portable density meter is an accurate tool to determine the density of the sample. Density is measured by a hollow, oscillating U-tube. The frequency of vibration of the U-tube is directly related to the density of the liquid sample. Temperature is measured at the same time, and the instrument automatically performs the temperature correction. The DMA 35N handheld digital density meter defines the state of the art of portable density measurement. It had been designed for use in the most demanding industrial environments. The DMA 35N will give the density, specific density or % concentration of the sample by simply press the lever on the built-in-pimp and within seconds the results are shown on the large, bright display. The DMA 35N consists of three main parts which are an RS 232 interface with infrared data port, a rubber shock protector and elongated filling tube. These two methods covers the laboratory determination, using a glass hydrometer, of the density, relative density, or API gravity of crude petroleum, petroleum products, or mixtures of petroleum and non-petroleum products normally handled as liquids and having a Reid vapour pressure of 1.8 bar (179 kPa) or less (Rand, 2003). The values are me asured on a hydrometer at convenient temperatures, readings of density being reduced to 15 ºC, and that of specific gravity and API gravity to 15.6 ºC, by means of international standard tables (Rand, 2003). Generally, density meter is more accurate compare to hydrometer because it is auto reading by digital measurement and make it less error e rror occur when conducting the experiment. In contrast, hydrometer is less accurate accurat e due to affect by b y many factors such as hydrometer keep on bouncing up and down and will easily cause parallax error.
CPB30503- Petr ochemicals Experiment
2:
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Petroleum
Determination of API
Refining
Technology
gravity
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4.0 RESULTS AND DISCUSSIONS/ TUTORIAL RESULTS
Experiment 2A: Determination of special gravity using hydrometer procedure Density (g/cm3)
Petroleum Product
1
2
3
Average
Specific
API
gravity
gravity
Diesel
0.836
0.837
0.837
0.8367
0.8367
37.62
Petrol
0.778
0.780
0.779
0.779
0.7790
50.14
Kerosene
0.795
0.795
0.795
0.795
0.7950
46.49
0.845
0.845
0.844
0.845
0.8447
36.02
Lubricating oil
Experiment 2B: Determination of specific gravity using density meter Density (g/cm3)
Petroleum Product
API
gravity
gravity
1
2
3
Diesel
0.8364
0.8363
0.8363
0.8363
0.8363
37.70 37.70
Petrol
0.7794
0.7796
0.7797
0.7796
0.7796
50.00
Kerosene
0.7952
0.7957
0.7959
0.7956
0.7956
46.35
0.8474
0.8472
0.8453
0.8466
0.8466
35.64
Lubricating oil
Average
Specific
DISCUSSIONS
This experiment has been conducted in order for student to fulfil the objectives which are to determine the specific gravity of oil using hydrometer and density meter and also to compare the specific gravity and API gravity of different oils. oil s. This experiment involves four different type of oil that were used as the indicator for each parameters which are diesel, petrol, kerosene and also the lubricating oil. The specific gravity and also the API gravity were set to be the major finding in this experiment by using using different apparatus which are the hydrometer and also the density meter.
CPB30503- Petr ochemicals Experiment
2:
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Petroleum
Determination of API
Refining
gravity
Technology Page |5
Furthermore this experiment have been separated into two parts which A and B. For the part A, it is to determine the specific gravity using the hydrometer procedure. The result from this part shows that lubricating oil has the highest specific gravity which is 0.8447 compared to diesel (0.8367), kerosene (0.7950), and diesel (0.8367). The specific gravity can be define as the ratio between the density of an object to a reference liquid which usually used is the water. For API gravity result, petrol s hows the highest value of API gravity which is 50.14 compared to the others oil which 46.49 for kerosene, 37.62 for diesel, and lastly 36.02 for the lubricating oil. The API gravity is a measure of how heav y or light a petroleum liquid is compared to water. By referring to the the ory, it was said that API gravity which is greater than 10 , the oil is lighter and will floats on the water and if it is less than 10 the oil is heavier and it will sinks into the water. The experiment was continue to be carried out for part B which was the determination of specific gravity using the density meter. For this part the result for the specific specifi c gravity and also the API gravity for each oil shows slightly s lightly different from the result produce by the hydrometer. The specific gravity for this part shows that lubricating oil still is the highest which 0.8466 compare to the other oil which 0.8363 for diesel, 0.7956 for kerosene and 0.7796 for petrol. For the API gravity, the value obtained are 50.00 for petrol, 46.35 for kerosene, 37.70 for diesel and 35.64 for lubricating oil. Basically the result from this two parts of experiment even the value are slightly different which lubricating oil have the highest highest specific gravity and petrol are with the highest hi ghest API gravity. The theory behind the result can be explained by the properties of the oil itself. From the result it can be said that t hat oil with the higher API gravity contains more paraffinic crude which will produce greater yield of the gasoline. API gravity also shows the weight of the oil where high number of API gravity is said to be more lighter compare to lo w API gravity. For this case, petrol is said to be the oil which have high number of paraffinic crude compared to the other oil. For the oil which have low API gravity value, it shows that the oil contain high number of aromatic crude which then affecting the density of the liquid. Higher number in the aromatic crude will resulting in heavier the oil it will be and force to produce lower yields of gasoline. In addition, for the specific gravity both for hydrometer and also the density meter lubricating oil have recorded the highest specific gravit y compared to the other oil. The specific gravity itself can be defined as the ratio between the density densit y of the object to the
CPB30503- Petr ochemicals Experiment
2:
&
Petroleum
Determination of API
Refining
Technology
gravity
Page |6
density of water. Based on the theory, those with specific gravity greater than 1 are denser than water and will affecting the surface surf ace tension thus sink into the water. From the patter n of the results, it can be said that the higher the density the lower the API gravity it will be. This can be explained by paraffinic and the aromatic crude which contain inside the oil that will be affecting the weight of the oil.
TUTORIAL
1. Calculate the API gravities of each oil. oil . Using hydrometer: Diesel ,
SG = 0.8367
ºAPI =
Petrol ,
SG = 0.7790
ºAPI =
Kerosene ,
SG = 0.7950
ºAPI =
Lubricating oil, SG = 0.8447
ºAPI
=
4.
- 131.5 = 37.62
4.
- 131.5 = 50.14
4.
- 131.5 = 46.49
4.
- 131.5 = 36.02
Using density meter: Diesel ,
SG = 0.8363
ºAPI =
Petrol ,
SG = 0.7796
ºAPI =
Kerosene ,
SG = 0.7956
ºAPI =
Lubricating oil, SG = 0.8466
ºAPI
=
4.
- 131.5 = 37.70
4.
- 131.5 = 50.00
4.
- 131.5 = 46.35
4.
- 131.5 = 35.64
CPB30503- Petr ochemicals Experiment
2:
&
Petroleum
Determination of API
Refining
gravity
Technology Page |7
2. What does the specific gravity and API gravity indicate? The American The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if less les s than 10, it is heavier and sinks. API gravity is thus an inverse measure of a petrol eum liquid's density liquid's density relative to that of water (also known as specific as specific gravity). gravity). It is used to compare densities densitie s of petroleum petroleum liquids. Crude oil is classified as light, medium, or heavy according to its measured API gravity.
Light crude oil has an API gravity higher than 31.1 Medium oil has an API gravity between 22.3 and 31.1 Heavy crude oil has an API gravity below 22.3 Extra heavy oil has an API gravity below 10.0
The specific gravity is the ratio between the density of an object, and a reference substance. The specific gravity can tell us, based on its value, if the object will sink or float in our reference substance. Usually our reference substance is water which always has a density of 1 gram per milliliter or 1 gram per cubic centimeter.
CPB30503- Petr ochemicals Experiment
2:
&
Petroleum
Determination of API
Refining
gravity
Technology Page |8
5.0 CONCLUSION AND RECOMMENDATIONS RECOMMENDATIONS CONCLUSION
The objectives of this Experiment 2 : Determination of API Gravity is to determine specific gravity of oil using hydrometer and density meter and to compare s pecific gravity and API gravity of different oils. As you can see f rom the stated objectives above, the experiment is divided into two parts. The first part is to determine specific gravity by using hydrometer and the second part is to determine the specific gravity by using the density meter. There are two different apparatus with the same purpose which is to determine the specific gravity. The differences between these t wo apparatus is their efficienc y to give an accurate result. Hydrometer is a glass body which s dipped into the sample. For the second apparatus, density meter is an automatic apparatus which allow the tube to suck in the sample and the specific gravity of the sample will appear at the screen. Based on the result of using hydrometer, lubricating oil has the highest specific gravity which is 0.8447 compared to diesel (0.8367), kerosene (0.7950), and diesel (0.8367). For API gravity result, petrol shows the highest value of API gravity which is 50.14 compared to the others oil which 46.49 for kerosene, 37.62 for diesel, and lastly 36.02 for the lubricating oil. From using the density meter, lubricating oil still is the highest which 0.8466 compare to the other oil which 0.8363 for diesel, 0.7956 for kerosene and 0.7796 for petrol. For the API gravity, the value obtained are 50.00 for petrol, 46.35 for kerosene, 37.70 for diesel and 35.64 for lubricating oil. The hypothesis of this experiment is the higher the specific gravity, the lower the API gravity. The conclusion from the result above is for the oil ( lubricating oil) with low API gravity contain high number of aromatic crude. Thus, resulting in heavier the oil will be and produce lower yields of gasoline. Meanwhile, petrol have the highest API gravit y, which is said to have high number of paraffinic crude compared to other oil.
CPB30503- Petr ochemicals Experiment
2:
&
Petroleum
Determination of API
Refining
Technology
gravity
Page |9
RECOMMENDATIONS
Hydrometer is a manual apparatus and they only suitable to use only on one sample. In this experiment, the hydrometer was not cleaned well and still may have traces of others sample (oil). Thus, it will affect the value that was obtained. Besides that, there might be a parallax error where the position of the eye is not parallel to the scale during measuring of the specific gravity. Hence, the result that was recorded is not entirely accurate. Other than that, there might be a slight bubble exist in the tube of the density meter during the sucking of the sample. Therefore, the value that occurred on the screen of the density meter is not correct. To overcome the problems above, the hydrometer must be cleaned well. The hydrometer should be rinsed with soap and water to make sure the glass surface is clean and not contaminated with other sample. Next, to make sure that was no parallax error occurred is by placing the right eye positioning that was parallel to the scale. This is to get the accurate value on the scale. Last but not least, to avoid any bubble in the tube of density meter is by immersing the tube fully into the sample and suck the s ample slowly and carefully.
