Ind. Eng. Chem. Prod. Res. D ~ v1983, . 22, 500-505
500
t
60 70 B i n d e r in M i x t u r e , %
50
80
Figure 9. Effect of binder content of paving mixture on Marshall stability. All binders contain 30% weight % lignin.
/*
2. A binder with 30% lignin in AC-10 asphalt had similar rheological behavior to unmodified AC-20 asphalt, both before and after aging. 3. Ductility decreased with increasing lignin content of the binder. 4. At 6% total binder content, stability increased with increasing lignin content but flow declined above 30% lignin content in the binder. 5. For 30% lignin in asphalt binders, the maximum stability occurred at 6% total binder content. 6. Stability and flow were nearly the same at 6% total binder content for unmodified AC-20 asphalt and for 30% lignin in AC-10 asphalt. 7. Field testing of pavement produced with lignin modified binder is recommended when sufficient lignin is available. Acknowledgment We wish to thank the State of Connecticut Department of Transportation for partial support of this research, and Dr. Jack E. Stephens for helpful suggestions during the experimental phase. Registry No. Lignin, 9005-53-2.
Literature Cited
I
50
1
60
I
I
70
I
I 8 0
B i n d e r in Mixture,%
Figure 10. Effect of binder content of paving mixture on Marshall flow. All binders contain 30 wt % lignin.
observed with these binders. With the exception of ductility, then, 30% lignin in AC-10 binder had properties comparable to AC-20 asphalt. Since the pavement mixtures with 30% lignin binder contained 4.2% AC-10 asphalt rather than 6.0% AC-20 asphalt, a savings in asphalt might be achieved by use of lignin-modified binders. Conclusions 1. The viscosity of lignin-modified asphalt binders increased with increasing lignin content.
Allen, B. R. Pretreatment Methods for the Degradation of Lignin, Battelle Report, 1980. Barth, E. J. “Asphail Science and Technology”;Gordon 8 Breach, New York, 1962. Flechter, A. A&. Bbchem. Eng. Vol. 20, Springer-Veriag: New York, 1981. Heitaus, J. J.: Izatt, J. 0. Pfoc. Assoc. Asphalr Pavlng Technol. 1961, 3 0 , 223. Lefebvre. J. R o c . Assoc. Asphalr Paving Technol. 1957, 26, 321. Marchessauk, R. H.; Coulombe, S.;Morlkawa, H.; Robert, D. Can. J. Chem. 1982, 60,2372. Monismith, C. L. “Asphalt Paving Mixtures: Properties Design and Performance”; Short Course Notes, Unlverslty of California, Berkeley, 1962. O’Nelll,~D.J. Ann. Bbmss Energy Systems Conf. 1970. 3 , 515. Sarkanen, K. V.; Ludwig, C. H. “Lignins: Occurrence, Structure, Formation and Reactlons”; Wiley-Intersclence: New York, 1971. Slsko. A. W.; Brunstrom, L. R o c . Assoc. AsphalrPavlng Technol. 1968, 3 7 , 448. Sundstrm, D. W.; Kiei, H. E. BlotechnicaiBioengineering Symposium No. 12, Scott, C. D., Ed.; Wiley-Interscience: New York, 1982. Terrei, R. L.: Rlmsrkong, S.Roc. Assoc. Asphan Paving Technol. 1979, 4 8 , 111. Van Wazer, J. R,; Kim, K. Y.; Coiweii, R. E. “Viscosity and Flow Measurement”: herscience: New York, 1963.
Receiued for reuiew February 24, 1983 Accepted March 28, 1983
Exploslblllty of High Methanol Fuel Blends Sebastian I. Amadi and E. Earl Graham’ Department of Chemical Engineering. The Pennsylvanie State University, Unlverslty Park, Pennsylvania 16802
Experlments were performed to determine the explosibility concentration and temperature limits for methanol, gasoline, and blends of methanol and light hydrocarbon additives under conditions made to simulate a gasoline storage tank. Whereas pure methand woutd be in its exploelve range for temperatures above 11 OC,it was shown that the addition of llght hydrocarbons to methanol could produce a fuel which like gasoline would be sufficiently volatile at subzero temperatures (-30 O C ) to be outslde its explosive limits during normal operation. The systems studled were found to be sufficiently close to equilibrium that the temperature and vapor compositions of the blended fuels could be predicted wlth sknple ideel solution laws. A new correlation was developed which allows the prediction of the explosive limits of mixtures from the explosive limlts and heats of vaporization of the pure components and the vapor composition.
Introduction Methanol is one of the most promising alternatives to gasoline as a transport fuel. It could be produced eco0196-4321/83/1222-0500$01.50/0
nomically from coal, oil shale, or biomass such as wood on a scale which could give this countray a significant degree of independence from petroleum-based fuels (Haggin, 1982; 0 1983 American
Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22,
(c) cooling coil I
(d) liquid reservoir
I
(f)
heating coll
(M
variable gap spark plug
Figure 1. Schematic diagram of apparatus used for experiments.
Parkinson, 1982; Wantworth and Othmer, 1982; McCallum, 1982). It could be marketed as a low blend with gasoline, but due to severe water tolerance problems associated with the low blends (10-20% methanol in gasoline), it is likely that methanol would be introduced either as a pure fuel or as a high blend of methanol with light hydrocarbon additives (McCallum, 1982; Fadelis and Shaw, 1980; Parkinson, 1982). High-performance engines could then be used to take advantage of the high octane number of methanol (McCallum, 1982; P a r k o n , 1982). However, pure methanol would be in its explosive range within the fuel storage system under normal temperatures and would require an alternative system for starting. The addition of light hydrocarbons such as butane or pentane not only would make the fuel safer by raising the vapor pressure out of the explosive range during storage but also provide a single self-starting fuel. There are no published data on the explosibility of these alternative fuels. Also the methods of predicting the explosive limits of mixed fuels are at present uncertain and highly empirical. It was the purpose of this study to investigate the explosibility of these alternative fuels under conditions similar to those existing in a gasoline storage system and develop improved methods of predicting explosibility limits of blended fuels.
Experimental Section Apparatus. The schematic diagram of the equipment used is shown in Figure 1. The liquid fuel to be tested was held in a triple-neck 500-mL Pyrex flask immersed in a temperature bath containing a mixture of 50% ethylene glycol and 50% water. The temperature of the bath was controlled by heating coils in the bath walls and cooling coils from an external refrigeration unit. This unit allowed the temperature to be controlled down to -20 f 0.5 "C. For lower temperatures (down to -40 "C)it was necessary to add dry ice to the coolant. The air in the closed loop system was saturated with vapor by bubbling it through the liquid using a glass sparger. The vapor was continually circulated through the explosion cell by means of a peristaltic pump with a flow rate rating of 3.80 mL/min. The vapor was precooled in heat-exchange coils before the liquid reservoir. Thermocouples were used to measure the temperatures of the fuel blend in the reservoir and the vapor phase above it, the temperatures at the inlet and outlet of the explosion cell, and the temperature of the bath. A manometer was connected to the system just before the liquid reservoir and maintained at a pressure of 2 in. of mercury. The pressure of the whole system was close to atmospheric. The explosion cell was a 2.78-L (height = diameter = 6 in.) mild steel cylinder with a clear Perspex cover with a slightly greased groove to fit. An automotive spark plug with an adjustable gap width was mounted halfway up the wall. Inlet and outlet ports were mounted a third of the
No. 3, 1983 501
way from the bottom and top of the cell, respectively. The explosion cell was isolated during ignition by 3-way taps a t the inlet and outlet. Combustion products after an explosion were flushed with air from an external air line. An ignition transformer of about 5.0 kV (drawing its energy from a 6-V battery and standard automobile ignition coil) was used as the source of energy to the spark plug. The gap width was maintained at 5 mm for all the experiments. While the purpose of this arrangement was to stimulate conditions in a gasoline storage tank, this can only be at best a good approximation. The work of Zabetakis and Richmond (1953) and Linnett and Simpson (1957) clearly shows that the explosibility limits are to some extent a function of system pressure, temperature, and geometry (size and shape of explosion chamber, position of ignition source, etc.) and a strong function of the energy of the ignition source below a critical limit. The energy of the ignition source in these studies was very high (above the critical limit) and it is felt that the results presented here will represent a good relative comparison of fuel explosibility in a storage tank under the worse conditions of an intense spark as an ignition source. Procedure. Before each experiment any combustion products were flushed from the system with air from an external air line. The fuel was then added to the liquid reservoir and the fuel-air mixture circulated for at least 1 h. The vapor composition was determined by a gas chromatograph using a thermal conductivity detector. A column cm in diameter and 1.0 m long packed with Poropak Q (50/80 mesh) was used. The column temperature was maintained at 100 "C and the helium carrier gas at a pressure of 20 psig. Samples of exactly 1mL were periodically taken after 1 h by an automatic sampling value. Steady state was established by obtaining identical chromatograms. The initial compositions of the liquid blends were analyzed using the above gas chromatograph with a heated liquid injection part and sample size of 0.5 mL. When the system was at steady state, the explosion cell was isolated from the rest of the system by valves as shown in Figure 1. This prevented any danger of a flame working itself back to the liquid reservoir. The explosive cell was also located in a well-vented safety hood with a safety glass door. This arrangement allowed for complete safety and in addition allowed visual observation of the ignition source or spark and any resulting flame or explosion.
Results and Discussion Partial Pressure and Equilibrium. A list of the systems studied is given in Table J. For all systems studied the partial pressure of the hydrocarbon vapor in air could be represented by an Antoine-type equation of the form In Pi = Ai - ( B J T )
(1)
where Pi= partial pressure of hydrocarbon, Ai, Bi= constants, and T = absolute temperature, K. The correlation conetants for the experimental studies are presented in Table I1 along with the correlation coefficient. Equation 1is a form of the Clausius-Clapeyronequation in which the constant Bi would be replaced by (AHi/R) In Pi = A, - (AHi)/RT (2) where AH, is the heat of vaporization of a given pure hydrocarbon and R is the universal gas constant. For pure methanol and pure n-pentane the values of (AHi/R)at 20 "C are 4238 and 3093 K, which compare reasonably well with the experimental values given in Table I1 of 4717 and
502
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 3, 1983 100
Table I. Systems Studied temp range, "C
liquid compn methanol-air gasoline-air n-pentane-air pentane-methanol-air
gasoline-methanol-air
butane-me thanol-air
a
.~
100% methanol 100% 82-octane gasolinea 100%n-pentane 5 vol % pentane-95 vol % methanol 1 0 vol % pentane-90 vol % methanol 1 5 vol % pentane-85 vol % methanol 5 vol % gasoline-95 vol % methanol 1 0 vol % gasoline-90 vol % methanol 1 5 vol % gasoline-85 vol % methanol 3.2 mol %butane, 96.8 mol % methanol 4.1 mol % butane, 95.9 mol % methanol
-23 t o 25 -27 to 25 -23 to 1 5 -30 to 25 -32 t o 1 5
-40 t o 3 30
-23 t o 25
20 I-
-22 to 8
IO
I
-36 t o 25
~
100%methanol 100% n-pentane 100% 82sctane gasoline 100%n-butane
I
0
10
20
30 Y
Table 11. Antione-Type Constants for Pure Fuels (Experimental) fuel
I
-34 t o 25
Octane number refers to research octane number.
~~~
1
-21 to 25
temp range,"C
A,
B,
correl coeff
-20 t o 1 5 -22 t o 1 5 -27 t o 1 5
20.5 15.8 11.05
4717 3015 1712
-0.994 -0.948 -0.888
3015 K. This is taken as an indication that the systems studied may be treated as at equilibrium. For the mixtures of methanol and various hydrocarbons, the partial pressure of each component also could be represented by a Antoine-type equation which over the range of compositions studied agreed to within f10% of the values for the pure hydrocarbons. This suggests that the solutions of hydrocarbon additives and methanol are behaving as ideal solutions. To test this, the vapor-liquid equilibrium (y, vs. x,) for methanol was calculated using Raoult's law P, = y,P = x,P," (3) where x, and y , are the mole fraction of methanol in the liquid and vapor phase, P, is the partial pressure of methanol (mmHg), P is the total pressure = 760 mmHg, and P," is the vapor pressure of methanol at a given temperature For the system 95 vol % methanol and 5 vol % n-pentane, a plot of y,P vs. x,P," is shown in Figure 2. Although there is considerable scatter in the data, the plot shows that the vapor-liquid equilibrium for methanol is adequately represented by Raoult's law. Similar plots for the other systems studied (Amadi, 1982) showed that methanol could be represented by Raoult's law for methanol concentrations down to 95 mol % methanol (with an average error of *20%). Similarly, for each of the hydrocarbon additives the vapor-liquid equilibrium could be represented by Henry's law. P, = Hn, (4) where H is an experimentally determined constant in mmHg which depends on the system components and temperature.
40
50
60
70
Pk"
Figure 2. Partial pressure of methanol in n-pentanelmethanol blends at 1 atm (Raoult's law). Table 111. Henry's Constants (H) for n-Butane in n-Butane/Methanol Blenda equilib ratio, K 2.50 4.51 5.44 10.50 20.5
temp, "C -34.5 -20.5 -7.2 7.4 22.5 a H = 8205.312 ficient = 0.9357.
+
H, mmHg (exptl) 1900.0 3427.6 4134.4 7980.0 15580.0
H, mmHg @red) 1212 4050 6746 9705 12361
202.708T("C). Correlation coef-
Table IV. Henry's Constants (H) for n-Butane in Gasoline/Methanol Blend temp, "C
equilib ratio, K
11.33 -8.33
77 26
H, mmHg 58520 19760
Table V. Henry's Constants ( H ) for n-Pentane in n-PentanelMethanol Blend temp. "C
equilib ratio, K
-30 0 15 25
0.419 2.130 4:720 8.100
H = 2815 0.9525.
+
H, mmHg (exptl) 318 1687 3874 5650
H, mmHg (pred) -365 281 5 4405 5465
106T("C). Correlation coefficient =
Tables 111-V give the Henry's law constants for each system as a function of temperature, and Figure 3 shows a typical vapor-liquid equilibrium plot for n-pentane for the n-pentane-methanol system. The vapor-liquid equilibrium could be represented by Henry's law for all systems for hydrocarbon composition up to about 5 mol %. It should be noted that for the gasoline-methanol system the Henry's law constant is given only for the nbutane component of the gasoline additive. In general, the vapor pressure of gasoline will result from contributions of many components of which n-butane is usually the major one. Since the Henry's law constant is an empirical constant its value will show a strong dependence on the exact chemical species present. The Henry's law constants given here for n-butane therefore would vary with the type of gasoline and definitely do not imply that a component
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 3, 1983
503
Table VI. Explosibility Limits of Methanol Blend Fuels exptl values fuel 100% methanol 100% n-pentane 100%gasoline 100% n-butanec 5% n-pentane/95% methanol 10% n-pentane/90% methanol 15% n-pentane/85% methanol 5% gasoline/95% methanol 10% gasoline/90% methanol 15%gasoline/85% methanol n-butane/methanola n-butanelmethanol
lower limit
T, "C
6.5
11.39
5.2
-17.22
3.2 mol % butane initially in liquid phase. octane.
upper limit
T, "C
5.6 7.69
-22.5 -27.22
5.72 6.62 6.52 11.42 9.80 12.02 7.14 7.13
-0.28 -14.44 -19.72 25.5 6.89 2.56 -30.55 -35.28
4.1 mol % butane initially in liquid phase. 1
05,
lit. values
04:
C1 3 1
7
\
251
3-3O'C
36 4.5-8.0 7.1 -7.6d 5.7-8.5
Literature value.
\
4
3
n-Pentane/Methonol
A
Gasoline/Mefhonol
i
i-I
I
1
II
I
I /
i
I---
-25'
-
-
- -
-
--___ - - -- -
-351
1
~
o
w
'
1
0.1
0.2
0.3
'2
87
-I
3
I I4 021
-1
1i
O'C
6.0-7.33 1.5 1.4 1.9
I1
351
A 15°C
upper limit
45
s 25'C
0
lower limit
-45
-55
I
'
4 1 I I
5
IO 15 20 25 Volume percent additive
30
35
Figure 3. Vapor-liquid equilibria for n-pentanelmethanol blends at 1 atm.
Figure 4. Temperatures at which upper limit mixtures of n-pentane/methanol and gasoline/methanol fuel blends are formed.
in a blend of hydrocarbons such as pure gasoline behaves thermodynamically as does n-butane in gasoline-methanol blend. This point is clearly shown by the studies reported in the section on Retainability where the escaping tendency of n-butane is much greater in the blends than in pure gasoline. The Henry's law constant reported here is a useful empirical constant limited to the system they are reported for at dilute compositions. Explosibility Limits. The data taken from the experiments give the explosibility limits shown in Table VI. These values have been checked to be within f0.5 ~ 0 1 % . The lower explosibility limit of pure methanol was found to be 6.5 vol % and this compares with the values of 6.0 to 7.3 vol % reported by Coward and Jones (1952). The upper explosibility limits of pure n-pentane and 82-octane gasoline (Research) were found to be 5.6 and 7.69 vol % , respectively. These values compare with the literature values of 4.5 to 8.0 and 7.1 to 7.6 vol % reported for npentane and 87-octane (Research) gasoline, respectively, reported by Coward and Jones (1952). The upper explosibility limit of pure methanol was not determined because it occurs at a temperature well above normal room temperature, and the experimental setup was not appropriate for operation above room temperature. A value of 36 vol % as reported by Zabetakis (1965) was used as the upper explosibility limit of pure methanol when estimating the upper explosibility limits of high methanol blend fuels. Similarly, an average literature value of 7.1
vol % (5.6 to 8.5) was used for the upper explosibility limit of pure n-butane. Table VI also shows the temperature at which the limit vapors of both the pure and blended fuels were formed. These values are within an error margin of f l . O OC. It is shown that the addition of low-boiling components to the methanol reduces the temperature at which the upper limit vapor mixture is formed. Increasing the amount of the low-boiling component gives a greater decrease in temperature until a limiting temperature is reached. This minimum limiting temperature is approximately equal to the temperature at which the upper vapor limit of the pure lower boiling component is formed. These results are shown graphically in Figure 4. A similar trend for the upper explosibility limit is shown in Figure 5. With the addition of small amounts of low boiling materials (e.g., 5%),the upper explosibility limit of methanol is drastically reduced from 36% to a value close to that of the low-boiling additive. Both the lower and upper limits of explosibility of a mixture of gases are usually estimated by the empirical relation given by LeChatelier (1891). In the form given by Coward et al. (1978) the upper limit of mixture of n combustibles (L) is given by L = l / i=l Ly
(5)
where ui = volume percent of fraction of combustible
504
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 3, 1983
Table VII. Upper Explosibility (or Flammability) Limits of Mixtures (Comparison of Le Chatelier's Formula with Present Method) upper limit compn in air fuel blend 5%n-ventanel 95%methanol 10%n-pentane! 90%methanol 15%n-pentane/ 85%methanol 5%gasoline/ 95% methanol 10%gasoline! 90%methanol 15%gasoline/ 85%methanol n-butane/ methanol 1 n-butane 21 methanol 2
upper limit compn without air
upper explosibility limit of mixture
methanol
additive
methanol
additive
%
%
%
%
Le Chatelier's method
2.06
3.66
36.010
63.99
5.72
8.047
5.95
1.33
5.29
20.090
79.91
6.62
6.700
5.78
0.94
5.58
14.420
85.58
6.52
6.380
5.72
10.49
0.93
91.850
8.144
11.42
27.710
14.17
4.20
5.60
42.857
57.143
9.80
11.610
9.25
3.40
9.83
25.70
74.300
12.02
9.650
8.55
0.23
6.91
3.21
96.790
7.14
7.290
7.14
0.23
6.90
3.23
96.770
7.13
7.290
7.14
exptl
present method
Substituting these limits into eq 7 gives a = l1 and 0
- l2 and eq 7 becomes
n-Pentnne/Methmoi
= I,
L = 11 - (11 - 12)U2n (10) Since L is defined in eq 6 (11) n = f(AHi, A H 2 , T , p ) From the experimental data and the physics of the problem
0 Ga?ioline/MOlhanol
(12) Since n must also be dimensionless, this suggests the following form for n. O C n l l
n=
,
0
5
0
,
10 15 20 25 Volume percent additive
I
30
35
species i on an air-free basis and li = upper explosibility limit of combustible gas i in air. Considering the form of the curves in Figures 4 and 5, a more fundamental method for estimating the upper explosibility limits of gaseous mixtures is suggested. In general E
f ( L 12, 0 2 ,
A H 1 9 m2,T , P )
(6)
where L is the upper explosibility (or flammability) limit of a binary gaseous mixture, u2 is the volume fraction of the low-boiling component 2, and AHl and AH2 are the latent heats of vaporization of components 1and 2. T and P are experimental temperature and pressure, respectively. The curves shown in Figure 5 suggest that the mathematical form for the upper explosibility limit could be expressed as
L = a' - pv,n
-
(13)
where R is the universal gas constant. Substituting eq 13 into eq 10 gives the final equation for L.
!
Figure 5. Upper explosibility limits of n-pentanelmethanol and gasoline/methanol fuel blends.
L
I( g )(s)'l
(7)
where a , P , and n are constants for a given system. At the two limits the following conditions would need to hold at u, = 0, L = I ,
(8)
at u2 = 1, L = 1,
(9)
L = 1, - (il - 12)U21(Afh/RT)-1- ( A f W W ' l
(14)
A similar formula can be written to estimate the temperature at which the upper exposibility (or flammability) limit mixture of combustible gases in equilibrium with the liquid mixture is formed. where TL is the upper explosibility (or flammability) limit temperature of the mixture, TL1and TL2are the upper explosibility (or flammability) limit temperatures of components 1 and 2, respectively, x 2 is the mole fraction of component 2 in the liquid mixture, AH1and AH2 are the latent heats of vaporization of components 1 and 2, respectively, and R is the universal gas constant. The values calculated using eq 14 and 15 are compared with the experimental values and the values calculated with LeChatelier's law in Tables VI1 and VIII, respectively. It can be seen that the present formula predicts more reasonable values for the upper explosibility (or flammability) limits than LeChatelier's law. When the mole percent of the low boiling hydrocarbon is more than 3.0'70, eq 15 predicts reasonable values for the temperature at which the upper explosibility (or flammability) limit mixtures are formed. The agreement between the equations and experimental values is worse when gasoline is used as the additive as would be expected since gasoline is a mixture of many different hydrocarbons. More data
Ind. Eng. Chem. Prod. Res+Dev., Vol. 22, No. 3, 1983 505
Table VIII. Temperatures at Which Upper Limit Mixtures are Formed (Experimentaland Estimated Values) liquid mole upper limit fractions of temp, "C fuel blend present fuel blend methanol additive method 5%n-pentane/ 0.982 0.018 -0.28 -14.36 95% methanol 10%n-pentane/ 0.9622 0.0378 -14.44 -15.78 90% methanol 15% n-pentane/ 0.9413 0.05869 -19.72 -16.65 85% methanol 5% gasoline/ 0.9852 0.01472 25.5 3.68 95% methanol 10%gasoline/ 0.96942 0.03058 6.89 -0.76 90% methanol 15%gasoline/ 0.95228 0.04772 2.56 -3.62 85%methanol n-butane-l/ 0.96775 0.03225 -30.55 -39.16 methanol 1 n-butane-2/ 0.95922 0.04078 -35.28 -40.17 methanol 2
~~
are needed to check the accuracy of these formulas. Retainability. In these studies it is clear that n-butane was the best additive in terms of lowering the explosive limits of methanol as would be expected since it is a gas at normal pressures and temperatures. This raises the serious question of how well n-butane would be retained in the methanol. Studies with open beakers of different diameters and then thus different area for surface evaporation, showed that the n-butane would be quickly lost if the mixture was exposed to the atmosphere (Amadi, 1982). The same problem exists for gasoline, but similar tests showed that under the same conditions gasoline would retain the n-butane much longer than would methanol. In a mixture of similar hydrocarbons (as in gasoline) n-butane clearly has a much lower escaping tendency (is more ideal) than in a mixture consisting mainly of a relatively polar compound such as methanol. To more exactly qualify the seriousness of this problem and to test the possibility of using further additives to act as retaining agents for the butane are clearly important areas for further work. Conclusions I t was found from the experiment that the addition of low-boiling hydrocarbons, e.g., n-butane or n-pentane to methanol reduces its upper explosibility limits, thereby making a high methanol blend fuel less hazardous as an automotive fuel. Addition of gasoline to methanol has the same effect but to a lesser degree. The experimentally determined limits were found to be dependent on both the type and amount of additive. Of all the additives used, n-butane gave an explosibility characteristic most similar to ordinary gasoline, but it is difficult to retain the butane in methanol. It was found that the hydrocarbon vapor composition of the high methanol blends could be predicted from knowledge of the liquid compositions using Henry's law
for the additive and Raoult's law for the methanol. Relations were derived which allowed the prediction of the upper explosibility concentrations and temperatures for binary mixtures of hydrocarbons and methanol. The relationships require knowledge of the heat of vaporization and explosive limits of the pure components and the concentration of each component in the vapor and liquid phase. Experimental data for the systems studied showed good agreement with the new relations and a substantial improvement over the commonly used LeChatelier's formula. More experimental data would be useful to further test the new relations and extend the procedures to methanol mixtures containing two or more additives. Nomenclature Ai = constant, defined by eq 1 and 2 Bi = constant, defined by eq 1 H = Henry's law constant, eq 4 AHi = heat of vaporization of species i K = equilibrium ratio = y i / x i L = upper explosibility limit of mixture of gases in air li = upper explosibility limit of species i in air n = constant, defined by eq 9 Pi = partial pressure of species i Pi" = vapor pressure of species i R = universal gas constant T = temperature TL= upper explosibility limit temperature of mixture of gases in air ui = volume fraction of species i (on an air-free basis) x i = mole fraction of species i in liquid phase yi = mole fraction of species i in vapor phase Greek Letters = constant, defined by eq 9
LY
Subscripts i = 1 = methanol i = 2 = hydrocarbon additive
Registry No. Methanol, 67-56-1; n-butane, 106-97-8;n-pentane, 109-66-0. Literature Cited Amadi, S. I . M.S. Thesis, Department of Chemical Engineering, The Pennsylvania State Unhrerslty, University Park, PA, 1982. Boubiik, T. "The Vapor Pressure of Pure Substances", 1st ed.;Elsevier: Amsterdam, 1973. Coward, H. F.; Carpenter, C. W.; Payman, W. J. Chem. SOC. 1918, 115, 27. Coward, H. F.; Jones, G. W. U S . Bur. Mines Bull. No. 503, 1952. Fadeiis, C. D.; Shaw, H. "Encyclopedia of Chemical Technology"; Voi. 3 Kirt, R. E.; Othmer, D. F., Ed.; Wiiey: New York, 1980. Haggin, J. Chem. €178. News 1982, 60(29). 24. LeChateiier, H. Ann. Mlnes 1981, 19(8), 388. Linnett, J. W.; Simpson, C. J. "Limits of Inflammability"; Sixth Combustion Symposium; Reinhokl: New York, 1957; p 20. McCaiium, P. W.; Tlmbarlo, T. J.; Bechtold, R. L.; Ecklund, E. E. Chem. Eng. Pmg. 1982, 78(8), 52. Parkinson, 0.; Stole, R.; McQueen, S.; Payne, A. Chem. Eng. 1982, 89(2), 30. Wentworth, T. 0.; Othmer, D. F. Chem. Eng. Prcg. 1982, 78(8), 29. Zabetakis, M. G. U S . Bur. Mines Bull. No. 627, 1965. Zabetakis, M. G.; Richmond, J. K. "Fourth Symposium (International) on Combustion"; Williams and Wiikins, 1953; p 121.
Received for review February 14, 1983 Accepted June 2, 1983
