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Experimental analysis of the evaporation process for gasoline
Journal of Loss Prevention in the Process Industries 25 (2012) 916e922
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Journal of Loss Prevention in the Process Industries journal homepage: www.elsevier.com/locate/jlp
Experimental analysis of the evaporation process for gasoline Ling Zhu a, *, Jiaqing Chen a, Yan Liu a, Rongmei Geng a, Junjie Yu b a b
Department of Environmental Engineering, Beijing Institute of Petrochemical Technology, 19 QingYuan North Road, Beijing 102617, PR China Policy Research Center for Environment and Economy, Ministry of Environmental Protection, Beijing 100029, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 January 2012 Received in revised form 5 May 2012 Accepted 5 May 2012
This paper presents the findings from a study on the evaporation process of 93 RON (research octane number) unleaded gasoline. The parameters measured in the experiment included the weight, the RVP (Reid vapor pressure) and the viscosity of gasoline, the concentration of NMHC (non-methane total hydrocarbon) in the oil vapor and the concentration of the main vapor constituent. Results showed that the parameters changed significantly as evaporation processed. The weight loss reached 86.36% after 300 days and presented a logarithmic curve with time. The RVP decreased from 38 kPa to 9.6 kPa. The viscosity of gasoline increased from 8.6 104 Pa s to 1.51 103 Pa s. All the concentrations of NMHC and the main constituent of vapor decreased in varying amounts. Most of the changes might be attributed to the evaporation of volatile hydrocarbons. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Gasoline evaporation process Gasoline weight loss Viscosity RVP NMHC Gasoline volatility
1. Introduction Gasoline is a complex mixture containing hundreds of different hydrocarbons derived from the distillation of petroleum. Due to the strong volatile properties of most hydrocarbons, volatile organic compounds (VOCs) and hazardous air pollutants (HAP) are emitted during major gasoline transfer operations. In general, gasoline needs to be loaded and unloaded at least 5 times from refinery to vehicle gas tanks, including production process in refinery, transportation to the fuel depot, loading and unloading at fuel depot and oil station, and refueling of the vehicles. Due to its powerful volatility and wide applications, gasoline vapor emissions can cause serious gaseous pollution, especially, photochemical smog in summer, and VOCs that serve as ozone precursors and contribute to ground-level ozone. The primary harmful effects of gasoline vapor emissions are the waste of energy resources and the relevant economic losses. According to the national statistic bulletin of China, the annual oil consumption of China in 2010 was approximately 2.46 billion tons and gasoline consumption was approximately 0.712 billion tons (NBSC, 2011). In a research report from Beijing municipal research institute of environmental protection, the emission factor of gasoline in an oil station could reach 2.30 kg/t if there was no control technology. Of course, the actual loss was far less than that because approximately 90% of gasoline evaporation losses come from storage, loading and unloading operations of
* Corresponding author. Tel.: þ86 10 81294271; fax: þ86 10 81292291. E-mail addresses: [email protected], [email protected] (L. Zhu). 0950-4230/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jlp.2012.05.002
tanks, which have been reduced by replacing fixed-roof tanks with internal floating-roof tanks since the late 1970s. Meanwhile, from the late 1980s onwards, some oil vapor recovery systems have also been applied in refineries, gasoline depots and service stations. Therefore, it was estimated that the relevant annual economic loss from gasoline evaporation in oil stations would exceed 20 billion (RMB) in 2009 (Weiqiu, Juan, Shuhua, & Aihua, 2011). Since the 1970s, many effective oil vapor recovery systems have been widely used in refineries, gasoline depots and service stations to reduce vapor emissions, such as Stage I systems, Stage II systems, EVR systems and ORVR systems, and others. Some of these disposal systems were certified by CARB and EVR (USA), TUV (Germany) and others (http: //www.arb.ca.gov/homepage.htm). Many papers have investigated the operation processes and industrial designs of these systems (Ravanchi, Kaghazchi, & Kargari, 2009). However, papers published on the gasoline evaporation process are comparatively rare. Fingas M. studied the relationship between the evaporation rate of petroleum products and related influencing factors, including sample weight, water concentration, held time and wind velocity (Fingas, 2004). Fingas clarified empirically that oil products evaporated at a logarithmic rate with respect to time and presented a simple model for predicting the weight loss fraction considering different temperatures. However, oil evaporation was not strictly regulated by boundary layer because oil evaporation rates were found to be largely governed by temperature, time, distillation data and the number of components (Fingas, 1997). Katsuhiro O. examined changes of vapor properties for motor gasoline during evaporation (Okamoto, Watanabe, Hagimoto, Miwa, & Ohtani, 2009). The changes in vapor pressure and the
L. Zhu et al. / Journal of Loss Prevention in the Process Industries 25 (2012) 916e922
evaporation rate of gasoline could be expressed as the exponential of weight loss fraction. The prediction model for the amount of gasoline vapor was independent of the evaporative area and the amount of gasoline. An oil spill is another important means of oil loss and oil evaporation. Fingas M. developed a series of models to calculate the evaporation rate under different evaporation conditions, such as the thickness of spill, the spill area, and the amount of spill; however, this model cannot be applied to predict the amount of gasoline vapor under different evaporation conditions because it is an empirical model under the limited conditions (Fingas, 1998). Shiyou Y. used the DCMC (discrete/continuous multicomponent) model to investigate the properties and composition of realistic multicomponent gasoline fuels, and gasoline is assumed to consist of five families of hydrocarbons (Shiyou, Youngchul, & Rolf, 2010). Temerdashev Z. A. detected the trace of gasoline after evaporation and burning, especially the composition of aromatic compounds (Temerdashev & Kolychev, 2009). Cagliari J. monitored the concentration of monoaromatic compounds from gasolineethanol-blend fuels in laboratory sand columns during 77 days. They found that although the content of benzene, toluene and xylenes did not show regular change, but ethanol content had different influence on the concentration change of the three compounds (Cagliari, Fedrizzi, Finotti, Teixeira, & Filho, 2010). The above studies did not conduct a comprehensive test on the changes in the physical properties of gasoline and vapor during the evaporation process, which includes not only weight and pressure of gasoline but also the NMHC value and the main vapor content concentration of gasoline vapor. These physical properties are very important to select a suitable purification system, to adjust the operational parameters, and to ensure satisfactory efficiencies of recover oil vapor. Therefore, in this study, the major parameters of liquid gasoline and gaseous vapor were measured in a continuous evaporation process. 2. Experimental 2.1. Preparation of measured samples Oil used in this study was 93 Research Octane Number (RON) unleaded gasoline, purchased from China Petroleum Chemical Corporation (CPCC) service station. Gasoline was placed in the glass container and left open to the atmosphere under room temperature to simulate the big breathing loss during the gasoline transfer operations. The evaporation process was investigated by testing the parameters of liquid gasoline and gaseous vapor in the container. About 43 g liquid gasoline was transferred to a weighing bottle. The total weight of bottle and gasoline was continually tested during 300 days to investigate the weight change during the course of evaporation. Approximate 200 mL gasoline was poured into a 500 mL conical flask. An air-tight seal syringe with a Luer lockout valve (10 mL, Agilent) was selected as the sampler to extract oil vapor above gasoline in the conical flask. The NMHC concentration of gasoline vapor was measured by gas chromatogram. This test lasted 30 days. Thirty conical flasks (250 mL) with about 100 mL gasoline were prepared in this experiment. Gasoline used to detect the Reid vapor pressure (RVP) and the viscosity was obtained from one of the conical flasks, and this test lasted 30 days. 2.2. Gasoline weight measurement The evaporation rate was measured by the weight loss using an electronic balance (AL 104 Mettler) with an accuracy of 0.001 g. The weight loss fraction a is given by Equation (1).
a ¼
w0 w w0 wb
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(1)
Here, w0 is the initial weight of gasoline and bottle; w is the weight of the gasoline at the time of detection, wb is the weight of bottle. 2.3. Reid vapor pressure measurement The Reid vapor pressure (RVP), as determined by the ASTM test method D323 (Ministry of Petroleum Industry Research Institute, 1982), is widely used in petroleum industry to measure the volatility of petroleum crude oil, gasoline and other petroleum products. It is a quick and simple method of determining the vapor pressure at 37.8 C (100 F) for crude oil and petroleum products which have an initial boiling point above 0 C (32 F). The RVP of the gasoline samples was measured at 37.8 C using an automated vapor pressure tester (ABH-1, Xufeng Scientific Ltd). The test was performed based on China standard method GB 25764 (Ministry of Petroleum Industry Research Institute, 1982). A sample cylinder bath with 30 mL of gasoline was submerged in a water bath and was maintained at a predetermined temperature (37.8 0.1 C). The cylinder was shaken in the water bath until the gasoline inside the cylinder reached a constant and balanced state, and then, the pressure in the cylinder was measured as the vapor pressure of gasoline. 2.4. Vapor measurement of NMHC The non-methane total hydrocarbon (NMHC) of vapor was tested and calculated using GC 6890 (Agilent) with two FID detectors. The test was performed based on China standard method HJ/T38-1999 (State Environmental Protection Administration, 1999). A stainless steel packed column (1 m 3 mm inner diameter), filled with silylanization micro glass beads, was connected to the front FID detector to measure the concentration of total hydrocarbon. Another stainless steel packed column (3 m 3 mm inner diameter), filled with GDX-104 (porous polymer beads) with a 60e80 mesh particle size, was connected to the back FID detector to measure the concentration of CH4. The concentration of NMHC was calculated from the two different columns. Splitless injection of a 0.1 mL sample was conducted with an auto-sampler, and the injector temperature was 120 C. The GC oven and detector temperature were 80 C and 300 C, respectively. The flow rate of N2, the carrier gas, was 30 mL/min, and those of H2 and air were 25 mL/min and 300 mL/min, respectively. A standard gas containing CH4/N2 (0.149% V/V) was used to measure the concentration of NMHC. Quantization was performed using the five-point calibration curve for individual components. 2.5. Concentration measurements of the main vapor content Samples were analyzed using 7890A gas chromatograph (Agilent) with two FID detectors. An HP-5 silica-fused capillary column (30 m 0.32 mm inner diameter 0.25 mm film thickness) and an Al2O3 silica-fused capillary column (30 m 0.53 mm inner diameter 0.25 mm film thickness) were used to separate the hydrocarbon components and the aromatic hydrocarbon components, respectively. Splitless injection of a 1 mL sample was conducted with an autosampler, and nitrogen was used as the carrier gas at a constant flow rate of 25 mL/min. The GC oven temperature was programmed at 45 C held for 2 min, followed by an increase to 160 C at a rate of
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2.6. Gasoline viscosity measurement
45
Viscosity is used to indicate the friction resistance between molecules in fluid flow and also reflects the fluidity of the oil. Therefore, it is a common parameter for oil quality standards. The kinematic viscosity of gasoline was tested by a rotational viscometer (RV1, HAAKE, Ltd.) in the range of 100 r/mine600 r/min at 20 C.
40
Weight (g)
35 30 25 20
3. Results and discussion
15
3.1. Gasoline weight loss 10 5 0
30
60
90
120
150
180
210
240
270
300
Time (day) Fig. 1. Weight of gasoline vs. time.
Fig. 2. Photos for the samples: (a) origin, (b) 300 days after.
Evaporated Fraction (%)
5 C/min and then to 250 C at 20 C/min (held for 5 min). The injector and detector temperatures were 250 C and 230 C, respectively. Compounds were identified by their retention times. Quantization was performed using the five-point calibration curve for the individual components. The standard gas containing 24 organic compounds was used for quantification. Calibration curves including five different concentrations were constructed using the internal standard method (Zhendi & Fingas, 1997; Zhendi, Fingas, & Page, 1999).
Fig. 1 shows the weight change for gasoline evaporation over 300 testing days. The weight of gasoline in the bottles gradually decreased from 42.7155 g to 5.8265 g, and the cumulative fraction of weight loss was 86.36%. In this study, gasoline and the surrounding atmosphere formed a larger space for volatile diffusion. The light hydrocarbons of gasoline were easy to evaporate, while the heavy hydrocarbon components, which have higher boiling points, were not as easy to volatilize at room temperature. Therefore, the light hydrocarbons evaporated into the air continually, while their content in gasoline declined. As a result, the rate of weight loss became slowly, and it can be predicted that the gasoline weight in the bottle would tend to stabilize at the end of the process. Fig. 2 shows photos for the initial gasoline and the sample after 300 days, and several obvious changes can be seen. First, the change in gasoline volume was significant. Initially, 70% of the space in the weighing bottle was occupied in Fig. 2(a), but only the bottom of the bottle was covered by gasoline after 300 days in Fig. 2(b). The reduction in volume can be attributed to the volatilization of the hydrocarbons. Second, the color of the gasoline changed from faintyellow to dark-brown, which is similar to the typical color of heavy fuel oil (HFO), and the fluidity was also modified. Furthermore, proof of gasoline evaporation could be found at the bottleneck of the bottle in Fig. 2(b), where the residue of the gasoline vapor aggregated and a brown membrane was produced on the surface of the bottleneck. The above changes all resulted from a decrease in the concentration of the volatile hydrocarbons in the gasoline, which is in accordance with the results of the weight experiment. Fig. 3 shows the evaporation rate of gasoline calculated from Fig. 1. Curve fitting is also shown to describe the relationships between a set of data in terms of the best-fit equations. In Fig. 3, a logarithmic equation fit the data best for the evaporation rate, with a regression coefficient R2 of 0.9786. The result is also in accordance with Fingas’ reports (Fingas, 1996). The rate of gasoline evaporation, which consists of several volatile organic compounds, follows in a logarithmic manner, and therefore, the
100 80 60
y = 16.773ln(x) - 10.436 R² = 0.9786
40 20 0 0
50
100
150
200
Time (d) Fig. 3. Logarithmic curve fit to oil evaporation date.
250
300
40
35
36
30
32
919
25
CMNHC% (V/V)
Reid vapor pressure( kPa)
L. Zhu et al. / Journal of Loss Prevention in the Process Industries 25 (2012) 916e922
28 24 20
20 15 10
16 5
12 0 0
8 0
5
10
15
20
25
30
5
10
15
20
25
30
Time (d)
Time (d) Fig. 6. Concentration of non-methane total hydrocarbon (NMHC) of gasoline vapor vs. time.
Fig. 4. Reid vapor pressure (RVP) of gasoline vs. time.
loss of mass is also approximately logarithmic with time. This kind of behavior is due to the number of components evaporating at once, each of which has linear evaporation behavior. The envelope of these linear rates results in a logarithmic curve, especially when approximately 7 or more components evaporate simultaneously. 3.2. Gasoline Reid vapor pressure The Reid vapor pressure of the gasoline sample varied with time as shown in Fig. 4. At any given temperature, the liquid gasoline is in equilibrium in the fuel vapor. The pressure generated by the gasoline vapor is called the saturated vapor pressure, which is one of the main quality parameters and can be used to evaluate the weight loss during the course of storage and transportation. In this study, the PVR was adopted to characterize the saturated vapor pressure. In Fig. 4, the values of PVR show a downward trend, decreasing from 38 kPa to 9.6 kPa over time. Gasoline is a complex mixture of various hydrocarbons; therefore, the total vapor pressure cannot be calculated using the DaltoneRaoult equation. However, according to the ClapeyroneClausius equation, the vapor pressure can be described as a function of temperature and composition. Normally, the composition of gasoline changes with the penetration rates, and
0.0015
Vercosity (Pa s)
0.0014 0.0013 0.0012 0.0011 0.0010 0.0009 0
5
10
15
20
25
30
the hydrocarbon components with low boiling points are easy to volatilize and gasify, resulting in an increase in the content of heavy hydrocarbons and a decrease in the vapor pressure. Gasoline with a higher RVP indicates that it gasifies more easily and contains a larger amount of light hydrocarbons. As a result, gasoline can be mixed with air more evenly, and the mixture may achieve a more complete combustion in the cylinder. Therefore, the higher RVP can ensure a normal combustion of gasoline, and the combustion has the advantages of a low ignition temperature, fast combustion speed, high combustion efficiency and low fuel consumption. But from the perspective of value, this kind of gasoline is not suitable for storage over longer periods. 3.3. Gasoline viscosity measurement Fig. 5 presents the change in viscosity for gasoline over 30 experimental days. Throughout the testing process, the curve did not follow a clear trend, but it did display upward trends with the changing slopes. The viscosity of the gasoline increased from 8.6 104 Pa s to 1.51 103 Pa s. The main factors affecting gasoline viscosity include chemical composition, molecular weight, temperature and pressure. Moreover, viscosity is one of the physical parameters describing the friction between liquid molecules, and therefore, it is closely related to the chemical composition of the gasoline. Normally, when hydrocarbons have the same number of carbon atoms, their viscosities are arranged in the following order: alkanes < isoparaffin < aromatic hydrocarbons < cycloalkanes. In other words, when the molecular weights are similar, the viscosity of hydrocarbons with ring structures is greater than that of those with a chain structure, and a greater number of rings mean a greater viscosity. When the hydrocarbons have the same ring number, the longer the side-chain is, the larger is the viscosity. For these reasons, after evaporation for a few days, the concentration of heavy hydrocarbons with larger molecular weights in gasoline increased. For the same series of hydrocarbons, with an increasing hydrocarbon molecular weight, the attraction between molecules strengthened; therefore, the viscosity increased approximately 1.75 times under the open evaporation test. 3.4. NMHC concentration of the gasoline vapor
Time (d) Fig. 5. Viscosity of gasoline vs. time.
Gasoline evaporation can be divided into static evaporation and dynamic evaporation. When gasoline is in a dynamic state, it
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Fig. 7. The gas chromatogram of gasoline vapor.
3.5. Concentration of the main vapor content Gasoline is a multicomponent compound mixture, and the rate of evaporation of each individual component will differ as a result. Consequently, the component and the content continuously change during the course of evaporation, especially the light hydrocarbon components. Fig. 7 gives the gas chromatogram of gasoline vapor when gasoline was transferred into bottle and opened in the air only for 10 min Fig. 8 shows the concentration of C5, total light hydrocarbon component and the total hydrocarbon component during the 30 experimental days. Table 1 lists the calculated concentration of the main vapor constituent.
In this paper, C5 is the content of pentane in the oil vapor. The concentration of light hydrocarbons is determined by adding together the values of C1, C2, C3, C4 and C5. Similarly, the concentration of hydrocarbon is obtained by adding up the total constituents, calculated from the GC result and compared with the standard gas, including the 24 organic compounds. Therefore, it must be emphasized that some trace constituents are not distinguished and are included in the total hydrocarbon component, and the calculated concentration using the GC method is slightly less than the actual value. However, if we compare the results of Figs. 8 and 6, we find that the value of the NMHC was slightly more than that of the total hydrocarbon component, where the original concentrations were 34.7378% (V/V) and 33.406% (V/V), respectively. Although the concentration of the NMHC was computed with the total hydrocarbon concentration by minusing the methane
36
C5
32
Concentration %(V/V)
disperses to fine particles along the flow of air and evaporates to the surrounding atmosphere. When gasoline in the container remains in a quiet state and the gas above the liquid surface does not flow, the evaporation would be considered to be static evaporation. Temperature differences between inside and outside of the container are the main cause of evaporation, which is also defined as small breathing losses. This kind of loss is very common during gasoline storage. The NMHC concentration of gasoline vapor is an important indicator to evaluate the air pollution near oil stations and oil depots and is also a major factor to evaluate the quality of gasoline. An experiment was performed to test the concentration changes in NMHC for the gasoline vapor over a month, and the result is shown in Fig. 6. The concentration was reduced from 34.7378% (V/V) to 2.8207% (V/V) after 30 days, especially after the first 16 days, exceeding 83% of the final reduction. The process of gasoline evaporation involves many aspects, such as thermodynamics and kinetics, and many factors may affect the evaporability of gasoline, but it is still largely determined by the composition. With a decrease in the weight of light hydrocarbons, the remaining weight of the heavy hydrocarbons increases; therefore, the concentration of gasoline vapor displays a downward trend overall.
Σ light hydrocarbon Σ hydrocarbon
28 24 20 16 12 8 4 0
0
3
6
9
12
15
18
21
24
27
30
Time (d) Fig. 8. Concentration of the main vapor constituents (C5, light hydrocarbon and total hydrocarbon) vs. time.
30 d 28 d
e e e 0.0436 e 0.2874 0.0032 0.7391 0.5418 0.0136 e e 0.2534 0.0051 0.003 e 1.0733 1.8902 e e e 0.0831 e 0.3233 0.0103 1.0637 0.6981 0.0209 e e 0.2697 0.0083 0.0055 e 1.4804 2.4829
22 d
e e e 0.1258 e 0.4914 0.0193 1.2697 0.7926 0.0392 e e 0.2836 0.008 0.0063 e 1.9062 3.0359
19 d
e 0.003 e 0.1575 e 0.7077 0.0282 1.4225 0.9247 0.0741 e e 0.3179 0.0107 0.008 e 2.3189 3.6543
16 d
0.0045 0.004 e 0.1935 e 0.955 0.0439 1.8605 1.0104 0.1042 e e 0.3418 0.0124 0.0115 e 3.0614 4.5417
14 d 12 d
0.0108 0.0427 e 0.4282 e 2.6505 0.684 5.2741 2.5733 0.3905 0.0025 e 0.6381 0.0265 0.0206 0.0018 9.0903 12.7436 0.012 0.0802 0.003 0.5055 0.001 3.359 1.1495 5.8832 3.2181 0.4468 0.0055 0.0007 0.807 0.0276 0.0225 0.0017 10.9934 15.5233
0.0101 0.0105 e 0.3598 e 2.1485 0.2445 4.4072 2.0845 0.3104 0.001 e 0.5472 0.0173 0.0182 0.0015 7.1806 10.1607
8d 6d
10 d
0.0095 0.0076 e 0.3104 e 1.5485 0.1165 2.8565 1.6572 0.2459 0.0007 e 0.497 0.0175 0.0201 0.0012 4.849 7.2886
0.0063 0.005 e 0.2539 e 1.2782 0.0562 2.0934 1.1555 0.1871 e e 0.4273 0.0136 0.0142 0.0007 3.693 5.4914
26 d
e e e 0.0329 e 0.2695 0.0021 0.6123 0.4209 0.0087 e e 0.2083 0.0043 e e 0.9168 1.559
L. Zhu et al. / Journal of Loss Prevention in the Process Industries 25 (2012) 916e922
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concentration, the maximum methane concentration was only 0.0315% (V/V), which might be ignored compared to the value of 34.7378% (V/V), which was the NMHC content. This may account for the difference in the two results. In Fig. 8, the three profiles exhibit the same downtrend. The light hydrocarbons value decreased from 24.319% (V/V) to 4.849% (V/V) in the first 12 days and from 4.849% (V/V) to 0.916% (V/V) in the last 18 days. The loss ratios were 83.19% and 16.81%, respectively. That is to say, most of the volatile compounds evaporated at the beginning of experiment, which is consistent with the weight results and the NMHC measurements. We also found that during the first 12 days, the total hydrocarbon concentration decreased from 33.406% (V/V) to 7.2886% (V/V), and 19.479% (V/V) can be attributed to the evaporation of the light hydrocarbons. In other words, a major portion of the reduction in total hydrocarbon concentration resulted from the evaporation of the light hydrocarbons. 4. Conclusion This study examined changes in the properties of liquid gasoline and gaseous vapor during the evaporation process. The weight decreased from 42.7155 g to 5.8265 g, and the weight decrease can be expressed by a logarithmic equation. The viscosity of gasoline increased from 8.6 104 Pa s to 1.51 103 Pa s, and RVP also decreased from 38 kPa to 9.6 kPa. All the NMHC concentrations and the main constituents of the vapor decreased with different degrees. Most of the changes might be attributed to the evaporation of light hydrocarbons. The concentration of light hydrocarbons decreased from 24.319% (V/V) to 0.916% (V/V) and that of the total hydrocarbon declined from 33.406% (V/V) to 1.559% (V/V). All of these results indicate that the changes can be attributed to the evaporation of volatile organic compounds, and for all the parameters analyzed in this study, the major changes occurred at the beginning of the experiments.
4d
0.0147 0.1436 0.005 0.5839 0.0005 3.5017 1.8364 6.3795 3.687 0.5655 0.0066 0.0018 0.8769 0.0285 0.0372 0.0019 12.4653 17.6707
3d
0.0169 0.1867 0.008 0.8075 0.0015 3.9814 2.5439 6.6834 4.0361 0.701 0.0105 0.0021 0.938 0.036 0.043 0.0021 14.2293 19.9981
Acknowledgment This work was supported by grants from the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality (PHR 201107147, PHR 201107213, and PHR 201108365).
2d
0.0193 0.2331 0.014 1.0542 0.0021 5.0438 3.302 7.2557 4.9475 0.8205 0.0115 0.0031 1.1055 0.0405 0.0485 0.0025 16.9242 23.9038 0.0257 0.2748 0.013 1.3529 0.0034 6.3982 4.3962 7.8957 5.8828 0.9775 0.0148 0.0031 1.1183 0.0445 0.0545 0.0028 20.3599 28.4582
1d 0d
0.0315 0.311 0.022 1.8625 0.0065 7.479 5.7415 8.865 6.7145 1.0705 0.0165 0.0035 1.1475 0.074 0.057 0.0035 24.319 33.406 C1 (CH4) C2 (C2H6) C2¼ (C2H4) C3 (C3H8) C3¼ (C3H6) C4 (C4H10) C4¼ (C4H8) C5 (C5H12) C6 (C6H14) C7 (C7H16) C8 (C2H6) C9 (C8H18) Benzene(C6H6) toluene(C7H8) ethylbenzene (C8H10) Dimethylbenzene (C8H8) light hydrocarbon (C5) total hydrocarbon (SHC)
Table 1 Concentration of the main vapor consistent over 30 days (V/V).
References Cagliari, J., Fedrizzi, F., Finotti, A. R., Teixeira, C. E., & Filho, I. N. (2010). Volatilization of monoaromatic compounds (benzene, toluene, and xylenes; BTX) from gasolines: effect of the ethanol. Environmental Toxicology and Chemistry, 29(4), 808e812. Fingas, M. (1996). The evaporation of oil spills: prediction of equations using distillation data. Oil Spill Science and Technology, 3(4), 191e192. Fingas, M. (1997). Studies on the evaporation of crude oil and petroleum products:I. The relationship between evaporation rate and time. Journal of Hazardous Materials, 56, 227e236. Fingas, M. (1998). Studies on the evaporation of crude oil and petroleum products II. Boundary layer regulation. Journal of Hazardous Materials, 57, 41e58. Fingas, M. (2004). Modeling evaporation using models that are not boundary-layer regulated. Journal of Hazardous Materials, 107, 27e36. http://www.arb.ca.gov/homepage.htm. Ministry of Petroleum Industry Research Institute. (1982). GB 257e64, engine fuelsdetermination of vapour pressure-Reid method. (in Chinese). NBSC (National Bureau of Statistics of China). (2011). Statistical bulletin of national economy and social development of 2010. Available at http://www.stats.gov.cn/ tjsj/ndsj/2010/indexeh.htm. Okamoto, K., Watanabe, N., Hagimoto, Y., Miwa, K., & Ohtani, H. (2009). Changes in evaporation rate and vapor pressure of gasoline with progress of evaporation. Fire Safety Journal, 44, 756e763. Ravanchi, M. T., Kaghazchi, T., & Kargari, A. (2009). Application of membrane separation processes in petrochemical industry: a review. Desalination, 235, 199e244.
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Shiyou, Y., Youngchul, R., Rolf, D. R., Brad VanDer, W., & Jianwen, Y. (2010). Development of a realistic multicomponent fuel evaporation model. Atomization and Sprays, 20(11), 965e981. State Environmental Protection Administration. (1999). HJ/T38e1999, stationary source emission-determination of nonmethane hydrocarbons-gas chromatography. (in Chinese). Temerdashev, Z. A., & Kolychev, I. A. (2009). Study and analysis of gasolines modified during evaporation and burning. Inorganic Materials, 45(14), 1593e1597.
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Contents lists available at SciVerse ScienceDirect
Journal of Loss Prevention in the Process Industries journal homepage: www.elsevier.com/locate/jlp
Experimental analysis of the evaporation process for gasoline Ling Zhu a, *, Jiaqing Chen a, Yan Liu a, Rongmei Geng a, Junjie Yu b a b
Department of Environmental Engineering, Beijing Institute of Petrochemical Technology, 19 QingYuan North Road, Beijing 102617, PR China Policy Research Center for Environment and Economy, Ministry of Environmental Protection, Beijing 100029, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 January 2012 Received in revised form 5 May 2012 Accepted 5 May 2012
This paper presents the findings from a study on the evaporation process of 93 RON (research octane number) unleaded gasoline. The parameters measured in the experiment included the weight, the RVP (Reid vapor pressure) and the viscosity of gasoline, the concentration of NMHC (non-methane total hydrocarbon) in the oil vapor and the concentration of the main vapor constituent. Results showed that the parameters changed significantly as evaporation processed. The weight loss reached 86.36% after 300 days and presented a logarithmic curve with time. The RVP decreased from 38 kPa to 9.6 kPa. The viscosity of gasoline increased from 8.6 104 Pa s to 1.51 103 Pa s. All the concentrations of NMHC and the main constituent of vapor decreased in varying amounts. Most of the changes might be attributed to the evaporation of volatile hydrocarbons. Ó 2012 Elsevier Ltd. All rights reserved.
Keywords: Gasoline evaporation process Gasoline weight loss Viscosity RVP NMHC Gasoline volatility
1. Introduction Gasoline is a complex mixture containing hundreds of different hydrocarbons derived from the distillation of petroleum. Due to the strong volatile properties of most hydrocarbons, volatile organic compounds (VOCs) and hazardous air pollutants (HAP) are emitted during major gasoline transfer operations. In general, gasoline needs to be loaded and unloaded at least 5 times from refinery to vehicle gas tanks, including production process in refinery, transportation to the fuel depot, loading and unloading at fuel depot and oil station, and refueling of the vehicles. Due to its powerful volatility and wide applications, gasoline vapor emissions can cause serious gaseous pollution, especially, photochemical smog in summer, and VOCs that serve as ozone precursors and contribute to ground-level ozone. The primary harmful effects of gasoline vapor emissions are the waste of energy resources and the relevant economic losses. According to the national statistic bulletin of China, the annual oil consumption of China in 2010 was approximately 2.46 billion tons and gasoline consumption was approximately 0.712 billion tons (NBSC, 2011). In a research report from Beijing municipal research institute of environmental protection, the emission factor of gasoline in an oil station could reach 2.30 kg/t if there was no control technology. Of course, the actual loss was far less than that because approximately 90% of gasoline evaporation losses come from storage, loading and unloading operations of
* Corresponding author. Tel.: þ86 10 81294271; fax: þ86 10 81292291. E-mail addresses: [email protected], [email protected] (L. Zhu). 0950-4230/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jlp.2012.05.002
tanks, which have been reduced by replacing fixed-roof tanks with internal floating-roof tanks since the late 1970s. Meanwhile, from the late 1980s onwards, some oil vapor recovery systems have also been applied in refineries, gasoline depots and service stations. Therefore, it was estimated that the relevant annual economic loss from gasoline evaporation in oil stations would exceed 20 billion (RMB) in 2009 (Weiqiu, Juan, Shuhua, & Aihua, 2011). Since the 1970s, many effective oil vapor recovery systems have been widely used in refineries, gasoline depots and service stations to reduce vapor emissions, such as Stage I systems, Stage II systems, EVR systems and ORVR systems, and others. Some of these disposal systems were certified by CARB and EVR (USA), TUV (Germany) and others (http: //www.arb.ca.gov/homepage.htm). Many papers have investigated the operation processes and industrial designs of these systems (Ravanchi, Kaghazchi, & Kargari, 2009). However, papers published on the gasoline evaporation process are comparatively rare. Fingas M. studied the relationship between the evaporation rate of petroleum products and related influencing factors, including sample weight, water concentration, held time and wind velocity (Fingas, 2004). Fingas clarified empirically that oil products evaporated at a logarithmic rate with respect to time and presented a simple model for predicting the weight loss fraction considering different temperatures. However, oil evaporation was not strictly regulated by boundary layer because oil evaporation rates were found to be largely governed by temperature, time, distillation data and the number of components (Fingas, 1997). Katsuhiro O. examined changes of vapor properties for motor gasoline during evaporation (Okamoto, Watanabe, Hagimoto, Miwa, & Ohtani, 2009). The changes in vapor pressure and the
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evaporation rate of gasoline could be expressed as the exponential of weight loss fraction. The prediction model for the amount of gasoline vapor was independent of the evaporative area and the amount of gasoline. An oil spill is another important means of oil loss and oil evaporation. Fingas M. developed a series of models to calculate the evaporation rate under different evaporation conditions, such as the thickness of spill, the spill area, and the amount of spill; however, this model cannot be applied to predict the amount of gasoline vapor under different evaporation conditions because it is an empirical model under the limited conditions (Fingas, 1998). Shiyou Y. used the DCMC (discrete/continuous multicomponent) model to investigate the properties and composition of realistic multicomponent gasoline fuels, and gasoline is assumed to consist of five families of hydrocarbons (Shiyou, Youngchul, & Rolf, 2010). Temerdashev Z. A. detected the trace of gasoline after evaporation and burning, especially the composition of aromatic compounds (Temerdashev & Kolychev, 2009). Cagliari J. monitored the concentration of monoaromatic compounds from gasolineethanol-blend fuels in laboratory sand columns during 77 days. They found that although the content of benzene, toluene and xylenes did not show regular change, but ethanol content had different influence on the concentration change of the three compounds (Cagliari, Fedrizzi, Finotti, Teixeira, & Filho, 2010). The above studies did not conduct a comprehensive test on the changes in the physical properties of gasoline and vapor during the evaporation process, which includes not only weight and pressure of gasoline but also the NMHC value and the main vapor content concentration of gasoline vapor. These physical properties are very important to select a suitable purification system, to adjust the operational parameters, and to ensure satisfactory efficiencies of recover oil vapor. Therefore, in this study, the major parameters of liquid gasoline and gaseous vapor were measured in a continuous evaporation process. 2. Experimental 2.1. Preparation of measured samples Oil used in this study was 93 Research Octane Number (RON) unleaded gasoline, purchased from China Petroleum Chemical Corporation (CPCC) service station. Gasoline was placed in the glass container and left open to the atmosphere under room temperature to simulate the big breathing loss during the gasoline transfer operations. The evaporation process was investigated by testing the parameters of liquid gasoline and gaseous vapor in the container. About 43 g liquid gasoline was transferred to a weighing bottle. The total weight of bottle and gasoline was continually tested during 300 days to investigate the weight change during the course of evaporation. Approximate 200 mL gasoline was poured into a 500 mL conical flask. An air-tight seal syringe with a Luer lockout valve (10 mL, Agilent) was selected as the sampler to extract oil vapor above gasoline in the conical flask. The NMHC concentration of gasoline vapor was measured by gas chromatogram. This test lasted 30 days. Thirty conical flasks (250 mL) with about 100 mL gasoline were prepared in this experiment. Gasoline used to detect the Reid vapor pressure (RVP) and the viscosity was obtained from one of the conical flasks, and this test lasted 30 days. 2.2. Gasoline weight measurement The evaporation rate was measured by the weight loss using an electronic balance (AL 104 Mettler) with an accuracy of 0.001 g. The weight loss fraction a is given by Equation (1).
a ¼
w0 w w0 wb
917
(1)
Here, w0 is the initial weight of gasoline and bottle; w is the weight of the gasoline at the time of detection, wb is the weight of bottle. 2.3. Reid vapor pressure measurement The Reid vapor pressure (RVP), as determined by the ASTM test method D323 (Ministry of Petroleum Industry Research Institute, 1982), is widely used in petroleum industry to measure the volatility of petroleum crude oil, gasoline and other petroleum products. It is a quick and simple method of determining the vapor pressure at 37.8 C (100 F) for crude oil and petroleum products which have an initial boiling point above 0 C (32 F). The RVP of the gasoline samples was measured at 37.8 C using an automated vapor pressure tester (ABH-1, Xufeng Scientific Ltd). The test was performed based on China standard method GB 25764 (Ministry of Petroleum Industry Research Institute, 1982). A sample cylinder bath with 30 mL of gasoline was submerged in a water bath and was maintained at a predetermined temperature (37.8 0.1 C). The cylinder was shaken in the water bath until the gasoline inside the cylinder reached a constant and balanced state, and then, the pressure in the cylinder was measured as the vapor pressure of gasoline. 2.4. Vapor measurement of NMHC The non-methane total hydrocarbon (NMHC) of vapor was tested and calculated using GC 6890 (Agilent) with two FID detectors. The test was performed based on China standard method HJ/T38-1999 (State Environmental Protection Administration, 1999). A stainless steel packed column (1 m 3 mm inner diameter), filled with silylanization micro glass beads, was connected to the front FID detector to measure the concentration of total hydrocarbon. Another stainless steel packed column (3 m 3 mm inner diameter), filled with GDX-104 (porous polymer beads) with a 60e80 mesh particle size, was connected to the back FID detector to measure the concentration of CH4. The concentration of NMHC was calculated from the two different columns. Splitless injection of a 0.1 mL sample was conducted with an auto-sampler, and the injector temperature was 120 C. The GC oven and detector temperature were 80 C and 300 C, respectively. The flow rate of N2, the carrier gas, was 30 mL/min, and those of H2 and air were 25 mL/min and 300 mL/min, respectively. A standard gas containing CH4/N2 (0.149% V/V) was used to measure the concentration of NMHC. Quantization was performed using the five-point calibration curve for individual components. 2.5. Concentration measurements of the main vapor content Samples were analyzed using 7890A gas chromatograph (Agilent) with two FID detectors. An HP-5 silica-fused capillary column (30 m 0.32 mm inner diameter 0.25 mm film thickness) and an Al2O3 silica-fused capillary column (30 m 0.53 mm inner diameter 0.25 mm film thickness) were used to separate the hydrocarbon components and the aromatic hydrocarbon components, respectively. Splitless injection of a 1 mL sample was conducted with an autosampler, and nitrogen was used as the carrier gas at a constant flow rate of 25 mL/min. The GC oven temperature was programmed at 45 C held for 2 min, followed by an increase to 160 C at a rate of
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2.6. Gasoline viscosity measurement
45
Viscosity is used to indicate the friction resistance between molecules in fluid flow and also reflects the fluidity of the oil. Therefore, it is a common parameter for oil quality standards. The kinematic viscosity of gasoline was tested by a rotational viscometer (RV1, HAAKE, Ltd.) in the range of 100 r/mine600 r/min at 20 C.
40
Weight (g)
35 30 25 20
3. Results and discussion
15
3.1. Gasoline weight loss 10 5 0
30
60
90
120
150
180
210
240
270
300
Time (day) Fig. 1. Weight of gasoline vs. time.
Fig. 2. Photos for the samples: (a) origin, (b) 300 days after.
Evaporated Fraction (%)
5 C/min and then to 250 C at 20 C/min (held for 5 min). The injector and detector temperatures were 250 C and 230 C, respectively. Compounds were identified by their retention times. Quantization was performed using the five-point calibration curve for the individual components. The standard gas containing 24 organic compounds was used for quantification. Calibration curves including five different concentrations were constructed using the internal standard method (Zhendi & Fingas, 1997; Zhendi, Fingas, & Page, 1999).
Fig. 1 shows the weight change for gasoline evaporation over 300 testing days. The weight of gasoline in the bottles gradually decreased from 42.7155 g to 5.8265 g, and the cumulative fraction of weight loss was 86.36%. In this study, gasoline and the surrounding atmosphere formed a larger space for volatile diffusion. The light hydrocarbons of gasoline were easy to evaporate, while the heavy hydrocarbon components, which have higher boiling points, were not as easy to volatilize at room temperature. Therefore, the light hydrocarbons evaporated into the air continually, while their content in gasoline declined. As a result, the rate of weight loss became slowly, and it can be predicted that the gasoline weight in the bottle would tend to stabilize at the end of the process. Fig. 2 shows photos for the initial gasoline and the sample after 300 days, and several obvious changes can be seen. First, the change in gasoline volume was significant. Initially, 70% of the space in the weighing bottle was occupied in Fig. 2(a), but only the bottom of the bottle was covered by gasoline after 300 days in Fig. 2(b). The reduction in volume can be attributed to the volatilization of the hydrocarbons. Second, the color of the gasoline changed from faintyellow to dark-brown, which is similar to the typical color of heavy fuel oil (HFO), and the fluidity was also modified. Furthermore, proof of gasoline evaporation could be found at the bottleneck of the bottle in Fig. 2(b), where the residue of the gasoline vapor aggregated and a brown membrane was produced on the surface of the bottleneck. The above changes all resulted from a decrease in the concentration of the volatile hydrocarbons in the gasoline, which is in accordance with the results of the weight experiment. Fig. 3 shows the evaporation rate of gasoline calculated from Fig. 1. Curve fitting is also shown to describe the relationships between a set of data in terms of the best-fit equations. In Fig. 3, a logarithmic equation fit the data best for the evaporation rate, with a regression coefficient R2 of 0.9786. The result is also in accordance with Fingas’ reports (Fingas, 1996). The rate of gasoline evaporation, which consists of several volatile organic compounds, follows in a logarithmic manner, and therefore, the
100 80 60
y = 16.773ln(x) - 10.436 R² = 0.9786
40 20 0 0
50
100
150
200
Time (d) Fig. 3. Logarithmic curve fit to oil evaporation date.
250
300
40
35
36
30
32
919
25
CMNHC% (V/V)
Reid vapor pressure( kPa)
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28 24 20
20 15 10
16 5
12 0 0
8 0
5
10
15
20
25
30
5
10
15
20
25
30
Time (d)
Time (d) Fig. 6. Concentration of non-methane total hydrocarbon (NMHC) of gasoline vapor vs. time.
Fig. 4. Reid vapor pressure (RVP) of gasoline vs. time.
loss of mass is also approximately logarithmic with time. This kind of behavior is due to the number of components evaporating at once, each of which has linear evaporation behavior. The envelope of these linear rates results in a logarithmic curve, especially when approximately 7 or more components evaporate simultaneously. 3.2. Gasoline Reid vapor pressure The Reid vapor pressure of the gasoline sample varied with time as shown in Fig. 4. At any given temperature, the liquid gasoline is in equilibrium in the fuel vapor. The pressure generated by the gasoline vapor is called the saturated vapor pressure, which is one of the main quality parameters and can be used to evaluate the weight loss during the course of storage and transportation. In this study, the PVR was adopted to characterize the saturated vapor pressure. In Fig. 4, the values of PVR show a downward trend, decreasing from 38 kPa to 9.6 kPa over time. Gasoline is a complex mixture of various hydrocarbons; therefore, the total vapor pressure cannot be calculated using the DaltoneRaoult equation. However, according to the ClapeyroneClausius equation, the vapor pressure can be described as a function of temperature and composition. Normally, the composition of gasoline changes with the penetration rates, and
0.0015
Vercosity (Pa s)
0.0014 0.0013 0.0012 0.0011 0.0010 0.0009 0
5
10
15
20
25
30
the hydrocarbon components with low boiling points are easy to volatilize and gasify, resulting in an increase in the content of heavy hydrocarbons and a decrease in the vapor pressure. Gasoline with a higher RVP indicates that it gasifies more easily and contains a larger amount of light hydrocarbons. As a result, gasoline can be mixed with air more evenly, and the mixture may achieve a more complete combustion in the cylinder. Therefore, the higher RVP can ensure a normal combustion of gasoline, and the combustion has the advantages of a low ignition temperature, fast combustion speed, high combustion efficiency and low fuel consumption. But from the perspective of value, this kind of gasoline is not suitable for storage over longer periods. 3.3. Gasoline viscosity measurement Fig. 5 presents the change in viscosity for gasoline over 30 experimental days. Throughout the testing process, the curve did not follow a clear trend, but it did display upward trends with the changing slopes. The viscosity of the gasoline increased from 8.6 104 Pa s to 1.51 103 Pa s. The main factors affecting gasoline viscosity include chemical composition, molecular weight, temperature and pressure. Moreover, viscosity is one of the physical parameters describing the friction between liquid molecules, and therefore, it is closely related to the chemical composition of the gasoline. Normally, when hydrocarbons have the same number of carbon atoms, their viscosities are arranged in the following order: alkanes < isoparaffin < aromatic hydrocarbons < cycloalkanes. In other words, when the molecular weights are similar, the viscosity of hydrocarbons with ring structures is greater than that of those with a chain structure, and a greater number of rings mean a greater viscosity. When the hydrocarbons have the same ring number, the longer the side-chain is, the larger is the viscosity. For these reasons, after evaporation for a few days, the concentration of heavy hydrocarbons with larger molecular weights in gasoline increased. For the same series of hydrocarbons, with an increasing hydrocarbon molecular weight, the attraction between molecules strengthened; therefore, the viscosity increased approximately 1.75 times under the open evaporation test. 3.4. NMHC concentration of the gasoline vapor
Time (d) Fig. 5. Viscosity of gasoline vs. time.
Gasoline evaporation can be divided into static evaporation and dynamic evaporation. When gasoline is in a dynamic state, it
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Fig. 7. The gas chromatogram of gasoline vapor.
3.5. Concentration of the main vapor content Gasoline is a multicomponent compound mixture, and the rate of evaporation of each individual component will differ as a result. Consequently, the component and the content continuously change during the course of evaporation, especially the light hydrocarbon components. Fig. 7 gives the gas chromatogram of gasoline vapor when gasoline was transferred into bottle and opened in the air only for 10 min Fig. 8 shows the concentration of C5, total light hydrocarbon component and the total hydrocarbon component during the 30 experimental days. Table 1 lists the calculated concentration of the main vapor constituent.
In this paper, C5 is the content of pentane in the oil vapor. The concentration of light hydrocarbons is determined by adding together the values of C1, C2, C3, C4 and C5. Similarly, the concentration of hydrocarbon is obtained by adding up the total constituents, calculated from the GC result and compared with the standard gas, including the 24 organic compounds. Therefore, it must be emphasized that some trace constituents are not distinguished and are included in the total hydrocarbon component, and the calculated concentration using the GC method is slightly less than the actual value. However, if we compare the results of Figs. 8 and 6, we find that the value of the NMHC was slightly more than that of the total hydrocarbon component, where the original concentrations were 34.7378% (V/V) and 33.406% (V/V), respectively. Although the concentration of the NMHC was computed with the total hydrocarbon concentration by minusing the methane
36
C5
32
Concentration %(V/V)
disperses to fine particles along the flow of air and evaporates to the surrounding atmosphere. When gasoline in the container remains in a quiet state and the gas above the liquid surface does not flow, the evaporation would be considered to be static evaporation. Temperature differences between inside and outside of the container are the main cause of evaporation, which is also defined as small breathing losses. This kind of loss is very common during gasoline storage. The NMHC concentration of gasoline vapor is an important indicator to evaluate the air pollution near oil stations and oil depots and is also a major factor to evaluate the quality of gasoline. An experiment was performed to test the concentration changes in NMHC for the gasoline vapor over a month, and the result is shown in Fig. 6. The concentration was reduced from 34.7378% (V/V) to 2.8207% (V/V) after 30 days, especially after the first 16 days, exceeding 83% of the final reduction. The process of gasoline evaporation involves many aspects, such as thermodynamics and kinetics, and many factors may affect the evaporability of gasoline, but it is still largely determined by the composition. With a decrease in the weight of light hydrocarbons, the remaining weight of the heavy hydrocarbons increases; therefore, the concentration of gasoline vapor displays a downward trend overall.
Σ light hydrocarbon Σ hydrocarbon
28 24 20 16 12 8 4 0
0
3
6
9
12
15
18
21
24
27
30
Time (d) Fig. 8. Concentration of the main vapor constituents (C5, light hydrocarbon and total hydrocarbon) vs. time.
30 d 28 d
e e e 0.0436 e 0.2874 0.0032 0.7391 0.5418 0.0136 e e 0.2534 0.0051 0.003 e 1.0733 1.8902 e e e 0.0831 e 0.3233 0.0103 1.0637 0.6981 0.0209 e e 0.2697 0.0083 0.0055 e 1.4804 2.4829
22 d
e e e 0.1258 e 0.4914 0.0193 1.2697 0.7926 0.0392 e e 0.2836 0.008 0.0063 e 1.9062 3.0359
19 d
e 0.003 e 0.1575 e 0.7077 0.0282 1.4225 0.9247 0.0741 e e 0.3179 0.0107 0.008 e 2.3189 3.6543
16 d
0.0045 0.004 e 0.1935 e 0.955 0.0439 1.8605 1.0104 0.1042 e e 0.3418 0.0124 0.0115 e 3.0614 4.5417
14 d 12 d
0.0108 0.0427 e 0.4282 e 2.6505 0.684 5.2741 2.5733 0.3905 0.0025 e 0.6381 0.0265 0.0206 0.0018 9.0903 12.7436 0.012 0.0802 0.003 0.5055 0.001 3.359 1.1495 5.8832 3.2181 0.4468 0.0055 0.0007 0.807 0.0276 0.0225 0.0017 10.9934 15.5233
0.0101 0.0105 e 0.3598 e 2.1485 0.2445 4.4072 2.0845 0.3104 0.001 e 0.5472 0.0173 0.0182 0.0015 7.1806 10.1607
8d 6d
10 d
0.0095 0.0076 e 0.3104 e 1.5485 0.1165 2.8565 1.6572 0.2459 0.0007 e 0.497 0.0175 0.0201 0.0012 4.849 7.2886
0.0063 0.005 e 0.2539 e 1.2782 0.0562 2.0934 1.1555 0.1871 e e 0.4273 0.0136 0.0142 0.0007 3.693 5.4914
26 d
e e e 0.0329 e 0.2695 0.0021 0.6123 0.4209 0.0087 e e 0.2083 0.0043 e e 0.9168 1.559
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concentration, the maximum methane concentration was only 0.0315% (V/V), which might be ignored compared to the value of 34.7378% (V/V), which was the NMHC content. This may account for the difference in the two results. In Fig. 8, the three profiles exhibit the same downtrend. The light hydrocarbons value decreased from 24.319% (V/V) to 4.849% (V/V) in the first 12 days and from 4.849% (V/V) to 0.916% (V/V) in the last 18 days. The loss ratios were 83.19% and 16.81%, respectively. That is to say, most of the volatile compounds evaporated at the beginning of experiment, which is consistent with the weight results and the NMHC measurements. We also found that during the first 12 days, the total hydrocarbon concentration decreased from 33.406% (V/V) to 7.2886% (V/V), and 19.479% (V/V) can be attributed to the evaporation of the light hydrocarbons. In other words, a major portion of the reduction in total hydrocarbon concentration resulted from the evaporation of the light hydrocarbons. 4. Conclusion This study examined changes in the properties of liquid gasoline and gaseous vapor during the evaporation process. The weight decreased from 42.7155 g to 5.8265 g, and the weight decrease can be expressed by a logarithmic equation. The viscosity of gasoline increased from 8.6 104 Pa s to 1.51 103 Pa s, and RVP also decreased from 38 kPa to 9.6 kPa. All the NMHC concentrations and the main constituents of the vapor decreased with different degrees. Most of the changes might be attributed to the evaporation of light hydrocarbons. The concentration of light hydrocarbons decreased from 24.319% (V/V) to 0.916% (V/V) and that of the total hydrocarbon declined from 33.406% (V/V) to 1.559% (V/V). All of these results indicate that the changes can be attributed to the evaporation of volatile organic compounds, and for all the parameters analyzed in this study, the major changes occurred at the beginning of the experiments.
4d
0.0147 0.1436 0.005 0.5839 0.0005 3.5017 1.8364 6.3795 3.687 0.5655 0.0066 0.0018 0.8769 0.0285 0.0372 0.0019 12.4653 17.6707
3d
0.0169 0.1867 0.008 0.8075 0.0015 3.9814 2.5439 6.6834 4.0361 0.701 0.0105 0.0021 0.938 0.036 0.043 0.0021 14.2293 19.9981
Acknowledgment This work was supported by grants from the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality (PHR 201107147, PHR 201107213, and PHR 201108365).
2d
0.0193 0.2331 0.014 1.0542 0.0021 5.0438 3.302 7.2557 4.9475 0.8205 0.0115 0.0031 1.1055 0.0405 0.0485 0.0025 16.9242 23.9038 0.0257 0.2748 0.013 1.3529 0.0034 6.3982 4.3962 7.8957 5.8828 0.9775 0.0148 0.0031 1.1183 0.0445 0.0545 0.0028 20.3599 28.4582
1d 0d
0.0315 0.311 0.022 1.8625 0.0065 7.479 5.7415 8.865 6.7145 1.0705 0.0165 0.0035 1.1475 0.074 0.057 0.0035 24.319 33.406 C1 (CH4) C2 (C2H6) C2¼ (C2H4) C3 (C3H8) C3¼ (C3H6) C4 (C4H10) C4¼ (C4H8) C5 (C5H12) C6 (C6H14) C7 (C7H16) C8 (C2H6) C9 (C8H18) Benzene(C6H6) toluene(C7H8) ethylbenzene (C8H10) Dimethylbenzene (C8H8) light hydrocarbon (C5) total hydrocarbon (SHC)
Table 1 Concentration of the main vapor consistent over 30 days (V/V).
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