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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/ j lp
Experimental analysis of the evaporation process for gasoline
Ling Zhu a,*, Jiaqing Chen a, Yan Liu a, Rongmei Geng a, Junjie Yu b
aDepartment of Environmental Engineering, Beijing Institute of Petrochemical Technology, 19 QingYuan North Road, Beijing 102617, PR Chinab 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
Article history:Received 13 January 2012Received in revised form5 May 2012Accepted 5 May 2012
Keywords:Gasoline evaporation processGasoline weight lossViscosityRVPNMHCGasoline volatility
* Corresponding author. Tel.: þ86 10 81294271; faxE-mail addresses: [email protected], zhuling7
0950-4230/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.jlp.2012.05.002
a b s t r a c t
This paper presents the findings from a study on the evaporation process of 93 RON (research octanenumber) 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 totalhydrocarbon) in the oil vapor and the concentration of the main vapor constituent. Results showed thatthe parameters changed significantly as evaporation processed. The weight loss reached 86.36% after 300days and presented a logarithmic curve with time. The RVP decreased from 38 kPa to 9.6 kPa. Theviscosity of gasoline increased from 8.6 � 10�4 Pa s to 1.51 � 10�3 Pa s. All the concentrations of NMHCand the main constituent of vapor decreased in varying amounts. Most of the changes might beattributed to the evaporation of volatile hydrocarbons.
� 2012 Elsevier Ltd. All rights reserved.
1. Introduction tanks, which have been reduced by replacing fixed-roof tanks with
Gasoline is a complex mixture containing hundreds of differenthydrocarbons derived from the distillation of petroleum. Due to thestrong volatile properties of most hydrocarbons, volatile organiccompounds (VOCs) and hazardous air pollutants (HAP) are emittedduring major gasoline transfer operations. In general, gasolineneeds to be loaded and unloaded at least 5 times from refinery tovehicle gas tanks, including production process in refinery, trans-portation to the fuel depot, loading and unloading at fuel depot andoil station, and refueling of the vehicles. Due to its powerful vola-tility and wide applications, gasoline vapor emissions can causeserious gaseous pollution, especially, photochemical smog insummer, and VOCs that serve as ozone precursors and contribute toground-level ozone. The primary harmful effects of gasoline vaporemissions are the waste of energy resources and the relevanteconomic losses. According to the national statistic bulletin ofChina, the annual oil consumption of China in 2010 was approxi-mately 2.46 billion tons and gasoline consumption was approxi-mately 0.712 billion tons (NBSC, 2011). In a research report fromBeijing municipal research institute of environmental protection,the emission factor of gasoline in an oil station could reach 2.30 kg/tif therewas no control technology. Of course, the actual loss was farless than that because approximately 90% of gasoline evaporationlosses come from storage, loading and unloading operations of
: þ86 10 [email protected] (L. Zhu).
All rights reserved.
internal floating-roof tanks since the late 1970s. Meanwhile, fromthe late 1980s onwards, some oil vapor recovery systems have alsobeen applied in refineries, gasoline depots and service stations.Therefore, it was estimated that the relevant annual economic lossfrom 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 havebeenwidely used in refineries, gasoline depots and service stationsto reduce vapor emissions, such as Stage I systems, Stage II systems,EVR systems and ORVR systems, and others. Some of these disposalsystems were certified by CARB and EVR (USA), TUV (Germany) andothers (http: //www.arb.ca.gov/homepage.htm). Many papers haveinvestigated the operation processes and industrial designs of thesesystems (Ravanchi, Kaghazchi, & Kargari, 2009).
However, papers published on the gasoline evaporation processare comparatively rare. Fingas M. studied the relationship betweenthe evaporation rate of petroleum products and related influencingfactors, including sample weight, water concentration, held timeand wind velocity (Fingas, 2004). Fingas clarified empirically thatoil products evaporated at a logarithmic rate with respect to timeand presented a simple model for predicting the weight loss frac-tion considering different temperatures. However, oil evaporationwas not strictly regulated by boundary layer because oil evapora-tion 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 motorgasoline 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 917
evaporation rate of gasoline could be expressed as the exponentialof weight loss fraction. The prediction model for the amount ofgasoline vapor was independent of the evaporative area and theamount of gasoline. An oil spill is another important means of oilloss and oil evaporation. Fingas M. developed a series of models tocalculate the evaporation rate under different evaporation condi-tions, such as the thickness of spill, the spill area, and the amount ofspill; however, this model cannot be applied to predict the amountof gasoline vapor under different evaporation conditions because itis 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 realisticmulticomponent gasoline fuels, and gasoline is assumed to consistof five families of hydrocarbons (Shiyou, Youngchul, & Rolf, 2010).Temerdashev Z. A. detected the trace of gasoline after evaporationand burning, especially the composition of aromatic compounds(Temerdashev & Kolychev, 2009). Cagliari J. monitored theconcentration of monoaromatic compounds from gasoline-ethanol-blend fuels in laboratory sand columns during 77 days.They found that although the content of benzene, toluene andxylenes did not show regular change, but ethanol content haddifferent influence on the concentration change of the threecompounds (Cagliari, Fedrizzi, Finotti, Teixeira, & Filho, 2010).
The above studies did not conduct a comprehensive test on thechanges in the physical properties of gasoline and vapor during theevaporation process, which includes not only weight and pressureof gasoline but also the NMHC value and the main vapor contentconcentration of gasoline vapor. These physical properties are veryimportant to select a suitable purification system, to adjust theoperational parameters, and to ensure satisfactory efficiencies ofrecover oil vapor. Therefore, in this study, the major parameters ofliquid gasoline and gaseous vapor were measured in a continuousevaporation 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 ChemicalCorporation (CPCC) service station. Gasoline was placed in the glasscontainer and left open to the atmosphere under room temperatureto simulate the big breathing loss during the gasoline transferoperations. The evaporation process was investigated by testing theparameters 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 testedduring 300 days to investigate the weight change during the courseof evaporation.
Approximate 200 mL gasoline was poured into a 500 mL conicalflask. An air-tight seal syringe with a Luer lockout valve (10 mL,Agilent) was selected as the sampler to extract oil vapor abovegasoline in the conical flask. The NMHC concentration of gasolinevapor was measured by gas chromatogram. This test lasted 30 days.
Thirty conical flasks (250 mL) with about 100 mL gasoline wereprepared in this experiment. Gasoline used to detect the Reid vaporpressure (RVP) and the viscosity was obtained from one of theconical flasks, and this test lasted 30 days.
2.2. Gasoline weight measurement
The evaporation rate was measured by the weight loss using anelectronic balance (AL 104Mettler) with an accuracy of 0.001 g. Theweight loss fraction a is given by Equation (1).
a ¼ w0 �ww0 �wb
(1)
Here, w0 is the initial weight of gasoline and bottle; w is theweight of the gasoline at the time of detection, wb is the weight ofbottle.
2.3. Reid vapor pressure measurement
The Reid vapor pressure (RVP), as determined by the ASTM testmethod D323 (Ministry of Petroleum Industry Research Institute,1982), is widely used in petroleum industry to measure the vola-tility of petroleum crude oil, gasoline and other petroleum prod-ucts. It is a quick and simple method of determining the vaporpressure at 37.8 �C (100 �F) for crude oil and petroleum productswhich have an initial boiling point above 0 �C (32 �F).
The RVP of the gasoline samples was measured at 37.8 �C usingan automated vapor pressure tester (ABH-1, Xufeng Scientific Ltd).The test was performed based on China standard method GB 257-64 (Ministry of Petroleum Industry Research Institute, 1982). Asample cylinder bath with 30 mL of gasoline was submerged ina water bath and was maintained at a predetermined temperature(37.8 � 0.1 �C). The cylinder was shaken in the water bath until thegasoline inside the cylinder reached a constant and balanced state,and then, the pressure in the cylinder was measured as the vaporpressure of gasoline.
2.4. Vapor measurement of NMHC
The non-methane total hydrocarbon (NMHC) of vapor wastested and calculated using GC 6890 (Agilent) with two FIDdetectors. The test was performed based on China standardmethodHJ/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 thefront FID detector to measure the concentration of total hydro-carbon. Another stainless steel packed column (3 m � 3 mm innerdiameter), filled with GDX-104 (porous polymer beads) witha 60e80 mesh particle size, was connected to the back FID detectorto measure the concentration of CH4. The concentration of NMHCwas calculated from the two different columns.
Splitless injection of a 0.1 mL sample was conducted with anauto-sampler, and the injector temperature was 120 �C. The GCoven and detector temperaturewere 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 performedusing the five-point calibration curve for individual components.
2.5. Concentration measurements of the main vapor content
Samples were analyzed using 7890A gas chromatograph (Agi-lent) with two FID detectors. An HP-5 silica-fused capillary column(30 m � 0.32 mm inner diameter � 0.25 mm film thickness) and anAl2O3 silica-fused capillary column (30 m � 0.53 mm innerdiameter � 0.25 mm film thickness) were used to separate thehydrocarbon components and the aromatic hydrocarbon compo-nents, respectively.
Splitless injection of a 1 mL sample was conducted with an auto-sampler, and nitrogenwas used as the carrier gas at a constant flowrate of 25 mL/min. The GC oven temperature was programmed at45 �C held for 2 min, followed by an increase to 160 �C at a rate of
0 30 60 90 120 150 180 210 240 270 300
5
10
15
20
25
30
35
40
45
Wei
ght
(g)
Time (day)
Fig. 1. Weight of gasoline vs. time.
Fig. 2. Photos for the samples: (a) origin, (b) 300 days after.
L. Zhu et al. / Journal of Loss Prevention in the Process Industries 25 (2012) 916e922918
5 �C/min and then to 250 �C at 20 �C/min (held for 5 min). Theinjector 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 curvefor the individual components.
The standard gas containing 24 organic compounds was usedfor quantification. Calibration curves including five differentconcentrations were constructed using the internal standardmethod (Zhendi & Fingas, 1997; Zhendi, Fingas, & Page, 1999).
0
20
40
60
80
100
0 50 100
Eva
pora
ted
Fra
ctio
n(%
)
T
Fig. 3. Logarithmic curve fit
2.6. Gasoline viscosity measurement
Viscosity is used to indicate the friction resistance betweenmolecules 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 rotationalviscometer (RV1, HAAKE, Ltd.) in the range of 100 r/mine600 r/minat 20 �C.
3. Results and discussion
3.1. Gasoline weight loss
Fig. 1 shows the weight change for gasoline evaporation over300 testing days. The weight of gasoline in the bottles graduallydecreased from 42.7155 g to 5.8265 g, and the cumulative fractionof weight loss was 86.36%.
In this study, gasoline and the surrounding atmosphere formeda larger space for volatile diffusion. The light hydrocarbons ofgasoline were easy to evaporate, while the heavy hydrocarboncomponents, which have higher boiling points, were not as easy tovolatilize at room temperature. Therefore, the light hydrocarbonsevaporated into the air continually, while their content in gasolinedeclined. As a result, the rate of weight loss became slowly, and itcan be predicted that the gasoline weight in the bottle would tendto stabilize at the end of the process.
Fig. 2 shows photos for the initial gasoline and the sample after300 days, and several obvious changes can be seen. First, the changein gasoline volume was significant. Initially, 70% of the space in theweighing bottle was occupied in Fig. 2(a), but only the bottom ofthe bottle was covered by gasoline after 300 days in Fig. 2(b). Thereduction in volume can be attributed to the volatilization of thehydrocarbons. Second, the color of the gasoline changed from faint-yellow to dark-brown, which is similar to the typical color of heavyfuel oil (HFO), and the fluidity was also modified. Furthermore,proof of gasoline evaporation could be found at the bottleneck ofthe bottle in Fig. 2(b), where the residue of the gasoline vaporaggregated and a brownmembrane was produced on the surface ofthe bottleneck. The above changes all resulted from a decrease inthe 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 fromFig. 1. Curve fitting is also shown to describe the relationshipsbetween a set of data in terms of the best-fit equations.
In Fig. 3, a logarithmic equation fit the data best for the evapo-ration rate, with a regression coefficient R2 of 0.9786. The result isalso in accordance with Fingas’ reports (Fingas, 1996). The rate ofgasoline evaporation, which consists of several volatile organiccompounds, follows in a logarithmic manner, and therefore, the
y = 16.773ln(x) - 10.436R² = 0.9786
150 200 250 300
ime (d)
to oil evaporation date.
0 5 10 15 20 25 308
12
16
20
24
28
32
36
40
Rei
d va
por
pres
sure
(kP
a)
Time (d)
Fig. 4. Reid vapor pressure (RVP) of gasoline vs. time.
0 5 10 15 20 25 300
5
10
15
20
25
30
35
CM
NH
C%
(V
/V)
Time (d)
Fig. 6. Concentration of non-methane total hydrocarbon (NMHC) of gasoline vapor vs.time.
L. Zhu et al. / Journal of Loss Prevention in the Process Industries 25 (2012) 916e922 919
loss of mass is also approximately logarithmic with time. This kindof behavior is due to the number of components evaporating atonce, each of which has linear evaporation behavior. The envelopeof these linear rates results in a logarithmic curve, especially whenapproximately 7 or more components evaporate simultaneously.
3.2. Gasoline Reid vapor pressure
The Reid vapor pressure of the gasoline sample varied with timeas shown in Fig. 4.
At any given temperature, the liquid gasoline is in equilibrium inthe fuel vapor. The pressure generated by the gasoline vapor iscalled the saturated vapor pressure, which is one of the mainquality parameters and can be used to evaluate the weight lossduring the course of storage and transportation. In this study, thePVR was adopted to characterize the saturated vapor pressure. InFig. 4, the values of PVR show a downward trend, decreasing from38 kPa to 9.6 kPa over time.
Gasoline is a complex mixture of various hydrocarbons; there-fore, the total vapor pressure cannot be calculated using theDaltoneRaoult equation. However, according to theClapeyroneClausius equation, the vapor pressure can be describedas a function of temperature and composition. Normally, thecomposition of gasoline changes with the penetration rates, and
0 5 10 15 20 25 30
0.0009
0.0010
0.0011
0.0012
0.0013
0.0014
0.0015
Ver
cosi
ty (
Pa
s)
Time (d)
Fig. 5. Viscosity of gasoline vs. time.
the hydrocarbon components with low boiling points are easy tovolatilize and gasify, resulting in an increase in the content of heavyhydrocarbons and a decrease in the vapor pressure.
Gasoline with a higher RVP indicates that it gasifies more easilyand contains a larger amount of light hydrocarbons. As a result,gasoline can be mixed with air more evenly, and the mixture mayachieve a more complete combustion in the cylinder. Therefore, thehigher RVP can ensure a normal combustion of gasoline, and thecombustion has the advantages of a low ignition temperature, fastcombustion speed, high combustion efficiency and low fuelconsumption. But from the perspective of value, this kind ofgasoline is not suitable for storage over longer periods.
3.3. Gasoline viscosity measurement
Fig. 5 presents the change in viscosity for gasoline over 30experimental days. Throughout the testing process, the curve didnot follow a clear trend, but it did display upward trends with thechanging slopes. The viscosity of the gasoline increased from8.6 � 10�4 Pa s to 1.51 � 10�3 Pa s.
The main factors affecting gasoline viscosity include chemicalcomposition, molecular weight, temperature and pressure. More-over, viscosity is one of the physical parameters describing thefriction between liquid molecules, and therefore, it is closelyrelated to the chemical composition of the gasoline. Normally,when hydrocarbons have the same number of carbon atoms, theirviscosities are arranged in the following order:alkanes < isoparaffin < aromatic hydrocarbons < cycloalkanes. Inother words, when the molecular weights are similar, the viscosityof hydrocarbons with ring structures is greater than that of thosewith a chain structure, and a greater number of rings meana greater viscosity. When the hydrocarbons have the same ringnumber, the longer the side-chain is, the larger is the viscosity. Forthese reasons, after evaporation for a few days, the concentration ofheavy hydrocarbons with larger molecular weights in gasolineincreased. For the same series of hydrocarbons, with an increasinghydrocarbon molecular weight, the attraction between moleculesstrengthened; therefore, the viscosity increased approximately 1.75times under the open evaporation test.
3.4. NMHC concentration of the gasoline vapor
Gasoline evaporation can be divided into static evaporation anddynamic evaporation. When gasoline is in a dynamic state, it
Fig. 7. The gas chromatogram of gasoline vapor.
24
28
32
36
(V/V
)
C5
light hydrocarbon hydrocarbon
ΣΣ
L. Zhu et al. / Journal of Loss Prevention in the Process Industries 25 (2012) 916e922920
disperses to fine particles along the flow of air and evaporates to thesurrounding atmosphere. When gasoline in the container remainsin 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 thecontainer are the main cause of evaporation, which is also definedas small breathing losses. This kind of loss is very common duringgasoline storage.
The NMHC concentration of gasoline vapor is an importantindicator to evaluate the air pollution near oil stations and oildepots and is also a major factor to evaluate the quality of gasoline.An experiment was performed to test the concentration changes inNMHC for the gasoline vapor over a month, and the result is shownin Fig. 6. The concentration was reduced from 34.7378% (V/V) to2.8207% (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, suchas thermodynamics and kinetics, and many factors may affect theevaporability of gasoline, but it is still largely determined by thecomposition. 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 downwardtrend overall.
0 3 6 9 12 15 18 21 24 27 300
4
8
12
16
20
Con
cent
ratio
n %
Time (d)
Fig. 8. Concentration of the main vapor constituents (C5, light hydrocarbon and totalhydrocarbon) vs. time.
3.5. Concentration of the main vapor content
Gasoline is a multicomponent compound mixture, and the rateof evaporation of each individual component will differ as a result.Consequently, the component and the content continuously changeduring the course of evaporation, especially the light hydrocarboncomponents. Fig. 7 gives the gas chromatogram of gasoline vaporwhen gasoline was transferred into bottle and opened in the aironly for 10 min Fig. 8 shows the concentration of C5, total lighthydrocarbon component and the total hydrocarbon componentduring the 30 experimental days. Table 1 lists the calculatedconcentration of the main vapor constituent.
In this paper, C5 is the content of pentane in the oil vapor. Theconcentration of light hydrocarbons is determined by addingtogether the values of C1, C2, C3, C4 and C5. Similarly, the concen-tration of hydrocarbon is obtained by adding up the total constit-uents, calculated from the GC result and compared with thestandard gas, including the 24 organic compounds. Therefore, itmust be emphasized that some trace constituents are not distin-guished and are included in the total hydrocarbon component, andthe calculated concentration using the GC method is slightly lessthan the actual value. However, if we compare the results of Figs. 8and 6, we find that the value of the NMHC was slightly more thanthat of the total hydrocarbon component, where the originalconcentrations were 34.7378% (V/V) and 33.406% (V/V), respec-tively. Although the concentration of the NMHC was computedwith the total hydrocarbon concentration byminusing themethane
Table
1Con
centrationof
themainva
por
consisten
tov
er30
day
s(V
/V).
0d
1d
2d
3d
4d
6d
8d
10d
12d
14d
16d
19d
22d
26d
28d
30d
C1(CH4)
0.03
150.02
570.01
930.01
690.01
470.01
20.01
080.01
010.00
950.00
630.00
45e
ee
ee
C2(C
2H6)
0.31
10.27
480.23
310.18
670.14
360.08
020.04
270.01
050.00
760.00
50.00
40.00
3e
ee
e
C2¼(C
2H4)
0.02
20.01
30.01
40.00
80.00
50.00
3e
ee
ee
ee
ee
e
C3(C
3H8)
1.86
251.35
291.05
420.80
750.58
390.50
550.42
820.35
980.31
040.25
390.19
350.15
750.12
580.08
310.04
360.03
29C3¼(C
3H6)
0.00
650.00
340.00
210.00
150.00
050.00
1e
ee
ee
ee
ee
e
C4(C
4H10)
7.47
96.39
825.04
383.98
143.50
173.35
92.65
052.14
851.54
851.27
820.95
50.70
770.49
140.32
330.28
740.26
95C4¼(C
4H8)
5.74
154.39
623.30
22.54
391.83
641.14
950.68
40.24
450.11
650.05
620.04
390.02
820.01
930.01
030.00
320.00
21C5(C
5H12)
8.86
57.89
577.25
576.68
346.37
955.88
325.27
414.40
722.85
652.09
341.86
051.42
251.26
971.06
370.73
910.61
23C6(C
6H14)
6.71
455.88
284.94
754.03
613.68
73.21
812.57
332.08
451.65
721.15
551.01
040.92
470.79
260.69
810.54
180.42
09C7(C
7H16)
1.07
050.97
750.82
050.70
10.56
550.44
680.39
050.31
040.24
590.18
710.10
420.07
410.03
920.02
090.01
360.00
87C8(C
2H6)
0.01
650.01
480.01
150.01
050.00
660.00
550.00
250.00
10.00
07e
ee
ee
ee
C9(C
8H18)
0.00
350.00
310.00
310.00
210.00
180.00
07e
ee
ee
ee
ee
e
Ben
zene(C6H6)
1.14
751.11
831.10
550.93
80.87
690.80
70.63
810.54
720.49
70.42
730.34
180.31
790.28
360.26
970.25
340.20
83toluen
e(C7H8)
0.07
40.04
450.04
050.03
60.02
850.02
760.02
650.01
730.01
750.01
360.01
240.01
070.00
80.00
830.00
510.00
43ethylbe
nze
ne(C
8H10)
0.05
70.05
450.04
850.04
30.03
720.02
250.02
060.01
820.02
010.01
420.01
150.00
80.00
630.00
550.00
3e
Dim
ethylbe
nze
ne(C
8H8)
0.00
350.00
280.00
250.00
210.00
190.00
170.00
180.00
150.00
120.00
07e
ee
ee
e
ligh
thyd
roca
rbon(�
C 5)
24.319
20.359
916
.924
214
.229
312
.465
310
.993
49.09
037.18
064.84
93.69
33.06
142.31
891.90
621.48
041.07
330.91
68totalhyd
roca
rbon(S
HC)
33.406
28.458
223
.903
819
.998
117
.670
715
.523
312
.743
610
.160
77.28
865.49
144.54
173.65
433.03
592.48
291.89
021.55
9
L. Zhu et al. / Journal of Loss Prevention in the Process Industries 25 (2012) 916e922 921
concentration, the maximum methane concentration was only0.0315% (V/V), which might be ignored compared to the value of34.7378% (V/V), whichwas the NMHC content. Thismay account forthe difference in the two results.
In Fig. 8, the three profiles exhibit the same downtrend. Thelight 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) inthe last 18 days. The loss ratios were 83.19% and 16.81%, respec-tively. That is to say, most of the volatile compounds evaporated atthe beginning of experiment, which is consistent with the weightresults and the NMHC measurements. We also found that duringthe first 12 days, the total hydrocarbon concentration decreasedfrom 33.406% (V/V) to 7.2886% (V/V), and 19.479% (V/V) can beattributed to the evaporation of the light hydrocarbons. In otherwords, a major portion of the reduction in total hydrocarbonconcentration resulted from the evaporation of the lighthydrocarbons.
4. Conclusion
This study examined changes in the properties of liquid gasolineand gaseous vapor during the evaporation process. The weightdecreased from 42.7155 g to 5.8265 g, and the weight decrease canbe expressed by a logarithmic equation. The viscosity of gasolineincreased from 8.6 � 10�4 Pa s to 1.51 � 10�3 Pa s, and RVP alsodecreased from 38 kPa to 9.6 kPa. All the NMHC concentrations andthe main constituents of the vapor decreased with differentdegrees. Most of the changesmight be attributed to the evaporationof light hydrocarbons. The concentration of light hydrocarbonsdecreased from 24.319% (V/V) to 0.916% (V/V) and that of the totalhydrocarbon declined from 33.406% (V/V) to 1.559% (V/V). All ofthese results indicate that the changes can be attributed to theevaporation of volatile organic compounds, and for all the param-eters analyzed in this study, the major changes occurred at thebeginning of the experiments.
Acknowledgment
This work was supported by grants from the Funding Project forAcademic Human Resources Development in Institutions of HigherLearning under the Jurisdiction of Beijing Municipality (PHR201107147, PHR 201107213, and PHR 201108365).
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