Abstract
Instance of countries introducing restrictions on the amount of harmful gases released to the atmosphere is on the rise. Countries like the United States have introduced policies which govern motor vehicle pollution. Gasoline is the main component of debate. As a result several studies have been done to determine the components of gasoline. In this experiment, components of gasoline are determine by an analysis process called gas chromatogram.
Samples of gasoline used in the experiment are collected from four stations BP, Marathon, Moto-Mart and Sunoco from Ashland. The samples are then analyzed using a gas chromatogram. 10 ml was used in each sample. Calculation of the concentrations is then carried out. Afterwards an analysis is presented using tabulations and chromatograms.
Introduction
Several States, for example, United States are legislating policies that puts a benchmark on the amount of gases released to the atmosphere. Gasoline has been regularly put on the limelight because it is made up of aromatic compounds that if ignited and released to the atmosphere will pollute the environment increasing the chances of global warming occurring. As a result of global warming and issues of climate change, environmental conservation policies are now a common topic in most nations, for example, China and the United States. Most of these policies necessitate that dealers of gasoline take certain measures so as to reduce pollution of the atmosphere by gases released from vehicles. An example of these is the use of reformulated gasoline in places that has high ozone (Palmer, Rabah & Kostecka, 1995). Currently there are limits put for aromatic compounds. These limits operate in most States. Studies reveal that aromatic compounds have a “high percentage of Octane and a lower vapor pressure” (Palmer, Rabah & Kostecka, 1995, 853).
Gasoline is petroleum oil that is also known as petrol. It is transparent and is used as fuel for motor vehicles. It is derived from petroleum through a process known as fractional distillation. Gasoline is made up of organic compounds that is been added some additives. Gasoline comes from crude oil that has been separated through fractional distillation. When it passes through this process the end product is called straight-run. Straight run is usually not good for fuels because of the high octane in the product. Gasoline is also made up of stream namely, straight run gasoline, reformate, cat cracked, hydrocrackate, alkylate and isomerate (Palmer, Rabah & Kostecka, 1995).
Gasoline is comprised of components like alkenes, cycloalkenes and olefins. The ration of alkenes, naphthalene and olefins is dependent on the crude oil, company processing and octane rating. According to a study done by Palmer, Rabah and Kostecka (1995), gasoline is made up of several molecules. Mobil gasoline is made up “benzene, toluene, ethylbenzene, m- and p-xylene, o-xylene, 1, 3, 5-trimethylmbenzene, naphthalene and 1- and 2-methylnaphthalene” (Palmer, Rabah & Kostecka, 1995, 854).
Since this experiment is associated with benzene and xylene, a clear illustration of the two components is vital. Benzene is a constituent of crude oil. It is made up of 6 carbons and hydrogen. It catches fires easily and it is colorless. It has a sweet smell. Due to the carbons between the carbon and hydrogen atoms, the molecule has a high melting point. Xylene, on the other hand, is made up of 8 carbons and ten hydrogens’. Like benzene it is colorless and has a good smell. It is highly flammable. Because of the high number of carbons and hydrogens’, the molecule has a high melting point. It is much higher than that of benzene. Therefore, its retention time is much higher than that of a benzene compound. Its concentration in gasoline is low (Palmer, Rabah & Kostecka, 1995).
While dealing with gasoline, the octane number usually comes on regular basis. The octane number determines the longevity of burning by fuels; the capacity of a fuel to oppose ignition. Octane rating is dependent on isooctane and heptanes. Isooctane is rated at 100 while heptanes at 0. Therefore, a gasoline that has been rated 87% means that it comprises of 87% isooctane and 13% heptanes. So, if the octane number is high, the fuel is said to be of good performance. Moreover, the price is much higher than those of low octane rating. It can therefore, be stated that the fuel in this experiment has 87% isooctane and 13% heptanes (Palmer, Rabah & Kostecka, 1995).
This experiment endeavors to do an analysis on gasoline. In order to analyze the composition of gasoline a process known as gas chromatography is used. Gas chromatography is a process that is commonly used in analytical chemistry to determine the composition of a particular compound. This process uses vaporizations and decomposition as the separation process. Gas chromatography is made up of two phase’s namely mobile and stationary phase. The mobile phase uses an inert gas such as helium. Stationary phase, on the other hand, is a liquid that has an inert gas. The liquid is usually inside a glass or tube. The instrument that has the two phases is called gas chromatograph (Palmer, Rabah & Kostecka, 1995).
While carrying out the analysis, the sample is introduced into the tube. In this case 10 ml of gasoline sample is introduced into tube. The sample is swept by the inert gases into the column. However, the movement may be hindered by the adsorption of the samples into the columns. Therefore, the rate of movement of the molecules is directly dependant on the strength of the adsorption. The strength of adsorption is in turn directly related to the type of sample and resources of stationary phase. The components in the sample are then separated as they move along the column. The difference in adsorption rate assists to separate since the components progress at different rates and times. A longer column increases the rate of separation (Palmer, Rabah & Kostecka, 1995).
The column has an oven that is set to heat it. The optimum temperature applied is dependent in the boiling point of the sample. If a temperature higher than the sample is set, then there will be a time elution of 30 minutes. As the sample continues to move in the column there is an increase of temperature that allows it to separate. From the column the sample moves to a mass spectrometer where it is analyzed. The analysis is preceded by the gas molecules being bombarded by electron beams. The impact by electrons leads to the formation of unpaired electrons. The charged and uncharged molecules and ion move to ion analyzer which separates them. The analyzer facilitates the removal of uncharged molecules. This then moves to the detector which usually produces an electronic signal when it comes into contact with an ion. The detector records the m/z of each ion. The data is then recorded in a chromatogram. The chromatogram graphs the findings in terms of peaks and patterns. The graphs have retention time on the x-axis and signal intensity on y-axis (Palmer, Rabah & Kostecka, 1995).
The purpose of this experiment is to analyze Ethylbenzene and p-Xylene in samples of gasoline sampled from three different stations namely BP, Marathon, Moto-Mart and Sunoco from Ashland. Therefore, the experiment seeks to test the difference of four samples of gasoline retrieved from the stations named above. So, the objective of this experiment is to analyze gasoline gas and know its constituents. Main emphasize of the study will be the concentrations of Ethylbenzene and p-xylene in gasoline. The analysis is done using a gas chromatogram which creates the differences of components using retention time and percentage area. The gas chromatogram uses the concept of vaporizations and decomposition.
Experimental Data
The gasoline retrieved from the four stations, were taken individually and passed through the gas chromatograph machine. The samples used in the experiment were collected from BP, Marathon, Moto-Mart, Sunoco from Ashland and OH 87 unleaded. The instrument used had the following features “5890 series II GC; a 5971A MSD; 59822B ionization gauge controller; vacuum pump ana a vectra QS/20 Chemstation” (Palmer, Rabah & Kostecka, 1995, 853). The gas chromatography run parameters were as follows “the injection port, and detector temperature are 250oC and 280o C respectively” (Palmer, Rabah & Kostecka, 1995, 853).
Sample Preparation
The samples are collected from four gas stations BP, Marathon, Moto-Mart and Sunoco from Ashland. The samples are measured in quantities of 10ml which will be injected into the syringe and thus instrument. In order to introduce a sample into a gas chromatrography instrument the analytes must be volatile. Therefore, the sample passes through a head space analysis which is made in a partially filled vial. The volatile components are separated from the non-volatile at this stage. Evaporation is reduced by the use of a seal crucial. The samples are then labeled as follows labels: mm=Moto-mart, B=BP, A=Marathon, S=Sunoco
Sample Dilution
After the sample is prepared, they are diluted. The gas samples are diluted by two successive 1:1000 dilutions by tabing 10 uL of sample into 10 ml volumetric flask, use 10 ml syringe. Mole: decided to add dichloromethane (dilutant) approximately 5 ml before to lessen evaporation of 10uL of gasoline. Secondly, wash 10uL syringe with new sample several times before use for dilution. Thirdly, run samples to determine concentration range desired for external calibration curve. Samples were too dilute or first dilution used instead.
Preparation of Standards
After dilution has taken place, standards are prepared. The standards are as follows Ethylbenyene 1, 3, 5, 7% and p-Xylene 5, 7, 9, 1% for the four standards. Stock solutions are 99.8% and 99% tabe %. 10-1 ml and dilute to 1000 fold by tabing, 10uL and diluting to 10 ml in 10 ml volumetric flask
Sample and Standard Analysis
The samples and standards were analyzed using gas chromatography. The analysis is depicted using chromatographs in graphs. The graphs had peaks showing the different types of components in the different samples of gasoline. The samples were passed through the gas chromatography which separates the different components of gasoline using the concept of boiling point. The components in the samples have different adsorption rate. The higher the adsorption, the longer the time a component will take in the tube. The difference in adsorption separates the components. The analysis of the samples and standards tries to find out the components of gasoline and the concentration of Ethylbenzene and p-xylene.
Results and Analysis
The table 1 above shows the retention time and area of standards low to high. The retention time in all the samples is regular with minimal insignificant difference. The rate of concentration is also tabulated.
Graph 1: Low Conc Standard
Graph 1 shows retention time of gasoline components. It demonstrates it in terms of peak. The peaks are much lower due to the low concentration. The abundance is much lower than that of the high concentration data.
Graph 2:
Graph two above show the retention rate of gasoline components in the high standard concentration. The peak is much higher than the low concentration standard therefore showing the difference in the concentration levels. When the two graphs are compared, the high concentration standard and low concentration standard, it is evident that the area of the peak is similar and equal.
Graph 3: Marathon
Graph 3 is showing the different retention rates of gasoline components in gasoline sample obtained from Marathon. The percentage area of all the components is regular. However, the abundance varies. The peak is high illustrating a higher concentration of Ethylbenyene and p-Xylene
Graph 4: Sunoco
Graph 4 illustrates retention rates gasoline components in a sample collected from Sunoco. The different level of peaks shows the different components of gasoline. The percentage areas vary with the component. The peaks are high depicting that there is higher concentration of Ethylbenyene and p-Xylene.
Graph 5: BP
Graph 5 shows retention time of components in gasoline collected from BP. Percentage area occupied by each peak is similar. The peak low that a lower concentration of Ethylbenyene and p-Xylene in gasoline collected from BP
Graph 6: MotoMart
Graph 6 illustrates retention time of components in gasoline obtained from MotoMart. The area covered by the peaks is regular. The peaks are lower as compared to the high concentration standards. This illustrates that the gasoline has low concentration of Ethylbenyene and p-Xylene.
Discussion
In this analysis the retention rate of the two components in each sample has been tabulated and graphed. With the availability of data from gas chromatography of each sample, our efforts are now directed to identifying and quantifying the components of gasoline. In this case the focus is put on of Ethylbenyene and p-Xylene. Consistent data was noted from the readings retrieved from the gas chromatography readings. The area in each of the samples is the same. This is clear seen from the tabulated data. Therefore, the area percentage of Ethylbenyene and p-Xylene are similar from all the samples. This fact is supported by reading of gasoline with a percentage of 87% isooctane and 13% heptane. The values and conclusion obtained in this study is consistent with that carried out by Hoekman. The figures presented are quite similar to that tabulated by the researcher.
However, the concentration of Ethylbenyene and p-Xylene are not consistent will all the samples collected. Samples from Sunoco and Marathon have high and medium concentrations of the two components of gasoline respectively. This is clearly illustrated by the rise of peaks in each sample. Gasoline collected from MotoMart, on the other hand, has a lower concentration of Ethylbenyene and p-Xylene. Therefore, the concentration of Ethylbenyene and p-Xylene varies with the samples collected from different gas stations. Gasoline may have the same components but the difference come in the percentage of concentration.
Conclusion
Gas chromatogram is a process to be relied on when doing an analysis of gasoline. It values are usually consistent and with insignificant areas. Therefore, it can be used to analyze the components of other materials. The analysis in this experiment is done from four different samples obtained from different has stations. The samples are passed through gas chromatogram to give percentage are and retention time. The tabulated data shows that the retention time of all the samples irrespective of the concentration are almost similar. The difference is not much. Moreover, the percentage area of each sample is regular for the two components. What varies is the concentration rate. Sample from BP has a low-high concentration of Ethylbenyene and p-Xylene. Samples from Sunoco and Marathon have a medium and high concentration of Ethylbenyene and p-Xylene respectively. MotoMart, on the other, hand has a low concentration. Therefore, gasoline may have the same components but they vary in concentration or level.
Reference:
Kostecka, K.S., Rabah, A., & Palmer, C.F. (1995). “GC/MS Analysis of the Aromatic Composition of Gasoline." Journal of Chemical Education, 72(9), 853-854
