1630
I n d . Eng. Chem. Res. 1990, 29, 1630-1635
Sastry, G. S. R.; Murthy, B. G. K.; Aggarwal, J. S. Isomerized safflower oil. Paint Manuf. 1970, 40, 32-35. Snyder, J. M.; Scholfield, C. R. Cis-trans Isomerization of unsaturated fatty acids with p-Toluenesulfinic acid. J . Am. Oil Chem. SOC.1982, 59, 469-470. Sonntag, N. 0. V. Reactions of fats and fatty acids. In Bailey's Industrial Oil and Fat Products, 4th ed.; Swern, D., Ed.; WileyInterscience: New York, 1979; Vol. 1.
Subrahmanyan, V. V. R.; Quackenbush, F. W. Effect of oxygen and other factors in selenium catalyzed isomerization of unsaturated fatty acid esters. J. Am. Oil Chem. SOC.1964, 41, 275-279. Totani, N.; Totani, Y.; Matsuo, N. Heat of cyclization of eleostearate with sulfur. Yukagaku 1978, 27, 83-87. Receioed for reuiew October 11, 1988 Accepted March 8, 1990
MATERIALS AND INTERFACES Water Tolerance of Gasoline-Methanol Blends Gary J. Green* and Tsoung Y. Yan Mobil Research a n d Development Corporation, Central Research Laboratory, P.O. Box 1025, Princeton, New Jersey 08543-1025
A new method based on laser attenuation was devised to accurately measure the phase separation and, in turn, the water tolerance of gasoline-methanol blends with and without cosolvents. Water tolerances were quantified for a variety of blends in model and actual gasolines, as well as in major refinery streams-alkylate, FCC gasoline, and reformate-that make up commercial gasoline pools. Regression analysis of the data shows that the water tolerance behavior of blends with each cosolvent is well-described by a correlation that includes cosolvent concentration, temperature, and base fuel hydrocarbon type.
Introduction Oxygenate Use in Gasoline Is Growing. Oxygenates are gaining importance as gasoline blending components. They conserve crude oil, supply antiknock quality, and offer potential for pollution reduction. Refiners and marketers have been turning to oxygenates to meet increasing demands for gasoline pool octanes in light of more stringent volatility and fuel composition controls. Several states in the Southwest-Colorado, New Mexico, Arizona, and Nevada-have recently mandated the use of oxygenates in gasoline to reduce CO emissions in urban areas during the winter months. Additional regulatory pressures are likely to increase oxygenate use in gasoline. Methanol Use in Gasoline Is Limited by Water Tolerance. Oxygenates, which are important as gasoline blending components, include methanol (MeOH), ethanol (EtOH), isopropyl alcohol (IPA), tert-butyl alcohol (TBA), and methyl tert-butyl ether (MTBE). Because of its low cost and ready availability, MeOH is the most attractive oxygenate from a strictly economic point of view. However, direct use of MeOH as a gasoline blending component in current fuel systems could cause technical problems (Unzelman, 1984). The most serious problem is the separation of blends into hydrocarbon and methanol phases when their water content exceeds a critical level, i.e., water tolerance. This problem is exacerbated at low ambient temperatures. Cosolvents Can Improve Water Tolerance. Water tolerance is defiied as the volume percent of water a blend can retain in solution-"tolerate"-at a given temperature without phase separation. To avoid phase separation, storage tanks and pipe lines must be maintained in essentially dry conditions, a very difficult practical problem. Another approach is addition of cosolvents to increase the water tolerance of the blend. All lower alcohols, up to 0888-5885 / 90/ 2629-1630$02.50/ 0
hexanol, could be useful as cosolvents; however, TBA has been identified as the most attractive for most commercial gasoline applications. Mixtures of MeOH and TBA have been marketed successfully as an oxygenate blending component for gasoline (American Petroleum Institute, 1988),although such mixtures are currently in very limited use in the U.S. Current Study Extends Previous Work. Previous studies on the water tolerance of gasoline-Me0H blends have been both qualitative (Rawat et al., 1984; Khinkova et al., 1985) and quantitative (Osten and Sell, 1983; American Petroleum Institute, 1988) in nature. One quantitative study has investigated the water tolerance of gasoline-Me0H blends to compare the relative effectiveness of IPA vs TBA as cosolvents in a regular-grade leaded gasoline (Osten and Sell, 1983). Other quantitative work (American Petroleum Institute, 1988) has examined the relative effectiveness of other alcohols in gasoline, as well as the effect of changing the level of aromatics and cosolvent on phase separation temperatures. One study has reported the findings of the effect of boiling point and hydrocarbon type in gasoline-MeOH mixtures with no cosolvent (Eccleston and Cox, 1977). However, the effect of base gasoline composition over a wide range on the water tolerance of gasoline-MeOH-cosolvent blends has remained largely unexplored. In the current study, the water tolerance behavior of various gasoline-MeOH blends using several cosolvents was investigated to determine and compare the efficacy of the cosolvents and the effect of fuel composition over a wide range. As part of this work, a useful, new technique based on laser attenuation was devised to rapidly and reliably measure phase separations.
Experimental Section Materials. 1. Base Fuels. Gasolines. Three un0 1990 American Chemical Society
Ind. Eng. Chem. Res., Vol. 29, No. 8, 1990 1631 Table 1. Base Fuel Properties gasoline aravitv. "API ;esearch octane number motor octane number Reid vapor pressure, psi distillation, OF 10% 50 70 90 % composition (FIA)," vol % aromatics olefins saturates a
light alkylate 72.7 92.8 91.2 6.3
reformate 46.5 98.9 89.1 7.7
FCC gasoline 56.1 93.4 80.7 9.5
165 215 232
141 247 330
116 223 382
1 1 98
62 2 36
33 36 31
A
B
C
31 3 66
36 15 49
97.6 87.3 13.7
54 1 45
FIA = fluorescent indicator adsorption, ASTM Method D1319.
leaded gasolines, representing both regular and premium grades, were included for study. They are designated as gasolines A, B, and C. Refinery Streams. Three gasoline blending stocks taken directly from refinery streams were also included, individually and as cross-blends: light alkylate, FCC gasoline, and reformate. The properties of the base fuels are summarized in Table I. Model Compounds. Three extreme classes of gasoline hydrocarbon types were simulated as follows: saturates, 85 vol ?& isooctane/ 15 vol 90n-heptane; olefins, 50 vol 9O 1-hexenel25 vol % l-heptene125 vol 9O 1-octene; aromatics, 33 vol ?& benzene134 vol ?& toluene133 vol 70 xylenes. 2. Oxygenates. The following reagent-grade oxygenates were dried over 3A molecular sieves before use in the blends: methanol, ethanol, isopropyl alcohol, tert-butyl alcohol, and methyl tert-butyl ether. Procedures and Apparatus. 1. Sample Preparation. Blends were prepared by mixing the base fuel with 5 vol ?& MeOH and 0,2.5, or 5 vol ?& cosolvent-EtOH, IPA, TBA, or MTBE. 2. Water Determination. The water content of each MeOH-gasoline-cosolvent blend was adjusted by using a precise gravimetric method and was measured directly by using a Brinkmann Model 652 Karl Fischer coulometer. 3. Measurement of Water Tolerance. Apparatus: Principle of Operation. The method of determining the water tolerance of a blend was based on measuring the optical attenuation of a laser beam as it passes through a fuel sample that is undergoing cooling (Green, 1989). A photodiode equipped with a laser line filter is used to measure the intensity of the transmitted laser beam, while a thermocouple is used to simultaneously measure the temperature of the sample. The output voltages from the photodiode and thermocouple are continuously monitored and recorded via a calibrated dual-pen strip chart recorder. When the sample undergoes a phase separation, the transmitted laser beam intensity is attenuated due to scattering caused by small droplets of a second immiscible phase. The temperature that corresponds to the initial rapid loss of photodiode signal is recorded as the phase separation temperature. This is the temperature of phase separation for the given water level in a base fuel-MeOH blend. Accordingly, the water tolerance at this temperature is equal to the measured water content of this sample. Apparatus: Detailed Description. Figure 1 shows the basic features of the apparatus. The laser was a 0.5mW helium-neon laser with an output wavelength of 633 nm. The photodiode probe was equipped with a heliumneon laser line filter and an appropriate neutral density filter to give the desired photodiode signal level. The
I
L
Sample Cell
Purge Shroud Photodiode
TC
Fuel
Stirrln
Line Filter Power Source
I
I
Magnetic Stirrer
Power Source
Figure 1. Experimental apparatus for determining phase separation temperatures.
distance from the sample cell to the laser was 5 cm, as was the distance from the cell to the photodiode. The thermocouple used was a Chromel-Alumel (type K)with dual junctions, referenced to 0 "C. One junction was monitored via a digital temperature indicator for convenience (not shown in the figure), while the output voltage from the other was fed to one channel of a dual-pen strip chart recorder. The photodiode output signal was amplified via a controller and fed to the other channel of the recorder. The sample cell is a double-walled Pyrex tube (1%" i.d. X 235 mm in length), with 1atm of dry N2 in the space between the walls. The sample cell holds 25 mL of fuel and is stoppered at the top, with a provision for a thermocouple feedthrough. The sample cell is inserted into a cylindrical Pyrex purge shroud, through which dry N2 flow at a low rate. The purge shroud is needed to prevent any moisture condensation on the walls of the sample cell that might be encountered at subambient temperature. The tip of the thermocouple is positioned along the central axis of the cell at a point 1cm above the laser beam path. The temperature of the sample is kept uniform throughout its entire volume via a special magnetic stirring bar. Procedure. The sample handling procedure is as follows: 25 mL of the desired fuel sample is introduced into the sample cell (which is withdrawn from the purge shroud for filling). The sample cell is then stoppered and immersed in a controlled temperature bath, typically ice water, dry ice-alcohol, or liquid Nz,until the temperature
-
1632 Ind. Eng. Chem. Res., Vol. 29, No. 8, 1990 2
-\
I
Base Fuel
Gasoline A 5 V IoMeOH
L. I
Tolerance. YO1 4,
05
c
Water Tolerance.
05
EtOH Cosolvent. 5 V
O1 0 25
I
-
Cosolvent None
005 4
6
5
3 25
r
TBA, VOI %
5
4
Figure 4. Effect of aromatics content on water tolerance of refinery stream-MeOH blends (aromatics contents shown in parentheses).
F u e l-
5
B
FCC Gasolli
\
4 25
1OOOll. 1/K
Figure 2. Effect of temperature on water tolerance of a gasolineMeOH-EtOH blend.
:
3 15
35
tMWT 1 K
E
I
Reformate
Water Tolerance. voi %
"' "L
-
01
1
3
Cosolvent. 5 VoI %
.05
%
+ TBA IPA EtOH MTBE No Cosolvenl
\
35
1
1
4
45
I
.02
5
.o 1
A
I
3
iOWTT, irK
Figure 3. Effect of TBA concentration on water tolerance of FCC gasoline-MeOH-TBA blends.
of the sample begins to fall, as monitored on the digital temperature indicator. The sample cell is immediately withdrawn and inserted into the path of the laser beam within the N2 purge shroud. Due to the double-walled construction of the sample cell, cooling continues for several minutes after withdrawal. When the sample passes through a phase transition upon cooling, a distinct drop in the photodiode signal on the chart recorder is observed, indicating the phase transition temperature. Measurements are typically complete within 2 min, with a repeatability of better than 0.5 "C. For samples with phase transition temperatures above ambient, the sample cell is immersed in a hot water bath prior to insertion into the purge shroud. The magnetic stirrer is kept on continuously for all runs. Cooling rates were 1-5 OC/min, depending on the particular temperature range under consideration. Measurements were made over a temperature range of -116 to 44 "C, depending on the fuel blend under consideration. No systematic influences on the experimental data were observed due to Schlieren effects of subcooling effects over the range of conditions employed in this work.
-
Results and Discussion Laser Attenuation Technique Improves Data Acquisition. Water tolerance data were obtained on over 50 gasoline-MeOH-cosolvent blends (- 200 data points) in this study using the laser attenuation technique. The collective results demonstrated the utility of this electrooptic approach for routine and reliable laboratory measurement of phase transition temperatures in fuel blends. Previous techniques for such measurements, including ASTM methods, have generally relied on visual observation by an operator and manual recording of the temperature as read from a thermometer. These techniques are often time consuming and subject to inconsistent visual observation by one or more operators, and their accuracy can be influenced by ambient lighting conditions. The current technique significantly alleviated these problems.
I
I
I
I
I
I
I
3.5
4
4.5
5
5.5
6
6.5
7
iooO,T,1IK
Figure 5. Effect of cosolvent type on water tolerance of reformate-Me0H blends.
L
I
'11 .\\,
'-
\
-0 Alkylate 5 Vol % MeOH Cosolvent, 4TBA 5 Vol %
A
Water Tolerance. VOl x ~5
, EIOH PA MTBE
No Cosolvent
.02 .01
,005
I
+
-/
I
\
\
I
3
3.25
3.5
3.75
4
4.25
4.5
IWoTT, IIK
Figure 6. Effect of cosolvent type on water tolerance of alkylateMeOH blends.
Water Tolerance Improves with Increasing Temperature. The water tolerance of gasoline-Me0H blends increases with temperature. To illustrate this, water tolerances are plotted vs 1/T for gasoline A-MeOH-EtOH blends (Figure 2), for FCC gasoline-Me0H blends with and without TBA as the cosolvent (Figure 3), for refinery streams containing MeOH alone (Figure 4), for reformate-MeOH blends with various cosolvents (Figure 5), and for alkylate-MeOH blends with various cosolvents (Figure 6). The relationship between the water tolerance of a fuel blend and temperature is adequately described by In WT = m ( l / T )
+k
(1)
where WT is the water tolerance, vol %; m and k are constants depending on the nature of the base fuel and the nature and concentration of the cosolvent; and T is the temperature, K. This linear relationship between log WT and the reciprocal of temperature was found to be valid for all fuels, cosolvents, and concentration levels investigated in this study, as illustrated in Figures 2-6. Equation 1 is useful
Ind. Eng. Chem. Res., Vol. 29, No. 8, 1990 1633 Table 11. Effect of Temperature on Water Tolerance: Constants for Equation 1 and Calculated Water Tolerance at 0 and 20 "C WT a t WT at m k ooc 2O0C fuel blend" 0.0019 0.0109 alkylate-MeOH -7.082 19.64 + MTBE -4.729 12.99 0.0133 0.0432 9.205 0.0411 0.0958 + EtOH -3.386 4.670 0.0955 0.1542 + IPA -1.917 + TBA -1.726 4.176 0.1173 0.1805 FCC gasoline-Me0H -2.143 4.369 0.0309 0.0528 2.484 0.0881 0.1232 + MTBE -1.342 + EtOH -1.716 4.480 0.1649 0.2532 3.734 0.2270 0.3240 + IPA -1.425 2.321 0.2287 0.2963 + TBA -1.037 3.822 0.0724 0.1125 reformate-Me0H -1.761 0.997 0.1275 0.1570 + MTBE -0.835 1.444 0.2152 0.2638 + EtOH -0.814 0.169 0.2462 0.2741 + IPA -0.429 + TBA -0.451 0.313 0.2623 0.2936 100% saturates-Me0H -4.739 11.789 0.0038 0.0126 + MTBE -4.234 11.279 0.0147 0.0423 + EtOH -5.899 18.067 0.0293 0.1280 4.998 0.1193 0.1939 + TBA -1.946 100% olefins-MeOH -2.061 4.401 0.0431 0.0721 + MTBE -2.000 4.675 0.0709 0.1168 4.133 0.1651 0.2474 + EtOH -1.621 + TBA -1.142 2.671 0.2209 0.2939 4.932 0.1575 0.2502 100% aromatics-Me0H -1.852 1.116 0.2055 0.2471 + MTBE -0.737 1.920 0.4300 0.5192 + EtOH -0.755 + TBA -0.627 1.382 0.4011 0.4691 a Fuel blends contain 5 vol % MeOH and, for those containing a cosolvent, 5 vol % cosolvent.
for interpolating the experimental data and predicting the effect of water tolerance of fuel blends at various temperatures. In general, the higher the water tolerance of a given blend set, the less sensitive that fuel-MeOH-cosolvent combination tends to be with respect to temperature (Figures 3-6). Table I1 gives the constants m and k derived from linear least-squares fits of the data from representative blend sets, as well as the corresponding water tolerances at 0 and 20 "C calculated for these blends. The slope, m, represents the sensitivity of the water tolerance of the blend with respect to temperature. For any given MeOH-cosolvent combination, the temperature sensitivities (slopes) tend to decrease in the order of alkylate, FCC gasoline, and reformate and similarly decrease in the order of saturate, olefin, and aromatics. This decrease in temperature sensitivity correlates with increasing water tolerance as illustrated by the calculated water tolerances at 0 and 20 "C for each blend set shown in Table 11. "his sensitivity decreases as cosolvent is added (Figure 3) and as the efficacy of the cosolvent improves (Figures 5 and 6). Water Tolerance Improves as Aromatics in Base Fuel Increase. The composition of the base gasoline has a significant effect on the water tolerance of blends containing MeOH. As indicated in Figure 4 and Table 11, water tolerance increases in the following order for the refinery streams: reformate > FCC gasoline >> alkylate. For example, at 0 "C the water tolerances are 0.0724, 0.0309, 0.0019 vol % for 5 vol % MeOH blends of reformate, FCC gasoline, and alkylate, respectively, based on the data shown in Table 11. Here, reformate is 2.3 times more water tolerant than FCC gasoline, which, in turn, is 16.2 times more water tolerant than alkylate. This relative ordering of water tolerance among base fuel types is generally maintained even upon addition of cosolvents, as indicated by the data in Table 11. For example, at 0 "C
Tolerance, Water VOl
1
.05 "
x
I
\
I
\
\LA
Model A Aromalics Fuel 8
.02
I
Olefins Saturates
MXH 5 VOI
3
x
I
I
I
1
I
3.5
4
4.5
5
IOWTT. 1IK
Figure 7. Effect of hydrocarbon type on water tolerance of model fuel-MeOH blends.
the water tolerances are 0.2152,0.1649,and 0.0411 vol % for 5 vol 70 MeOH-5 vol % EtOH blends of reformate, FCC gasoline, and alkylate. The relative water tolerance behavior observed for the refinery streams is coupled to the specific hydrocarbon types present in the stream, improving in the order of increasing concentrations of aromatics >> olefins >> saturates. This finding is confirmed by the model compound data shown in Figure 7 for MeOH blends with no cosolvent. Here, on the basis of linear least-squares fits, the water tolerance at 0 OC is 0.1575, 0.0431, and 0.0038 vol % for 100% aromatics, 100% olefins, and 100% saturates, respectively. As before, this relative ordering persists in the presence of cosolvents as well and is consistent with the relative contributions of both polar and hydrogen-bonding effects of each hydrocarbon type. An examination of solubility parameters (Hoy, 1975) for these chemical types shows that, in addition to strong nonpolar effects, aromatics carry a significant amount of polar and hydrogenbonding affinity, while olefins carry somewhat lower polar and hydrogen-bonding contributions, and saturates carry no polar or hydrogen-bonding character needed to effectively interact with water and alcohols. Use of an aromatics-rich gasoline not only improves the water tolerance for a given MeOH blend but also minimizes the cosolvent volume required to attain a given water tolerance. For example, when TBA was used as the cosolvent to maintain a water tolerance of 0.1 vol % at 0 "C, the TBA concentration required was 1.0, 2.2, and 4.8 vol % for 5 vol % MeOH blends of reformate, FCC gasoline and alkylate, respectively. A knowledge of the base fuel composition can become key to selecting an optimal cosolvent dosage. Effectiveness of Cosokent Increases with Concentration. The water tolerance of gasoline-Me0H blends improves significantly by the addition of a cosolvent in increasing concentrations. For example, by adding 2.5 and 5 vol70 TBA to FCC gasoline-5 vol % MeOH blends, the water tolerances at 0 "C were increased from 0.032 to 0.11 and 0.24 vol % , respectively (Figure 3). These correspond to 3.4- and 7.6-fold increases in water tolerance, respectively. Similar effects are realized in the other base fuel blends. The effect of base fuel composition on water tolerance persists but diminishes as the concentrations of cosolvent are increased. For example, the relative water tolerances at 0 "C-with and without TBA-are as follows for 5 vol % MeOH blends in the refinery streams: 0
alkylate FCC gasoline reformate
1
16 38
TBA, vol 5% 2.5
5.0
15 61 85
62 118 138
1634 Ind. Eng. Chem. Res., Vol. 29, No. 8, 1990
Table 111. Results of Rearession Analysis of Collective Water Tolerance Data (Eauation 2) coeff cosolventD C tl t7 S 0 a none 0.001 74 -0.00001 -0.00024 0.00042 0.001 40 MTBE 0.01089 0.001 89 0.00001 -0.00040 0.00023 0.001 40 -0.001 04 0.000 13 0.002 00 EtOH 0.031 36 0.00304 0.00001 IPA 0.033 76 0.002 26 0.000 01 -0.000 55 0.000 30 0.001 50 TBA 0.039 75 0.002 63 0.00001 -0.00077 0.000 20 0.001 66
no. of data points 19 68 73 46 62
correlation coeff, r 2 0.8492 0.9289 0.9060 0.9182 0.9604
In fuels blends containing 5 vol % MeOH.
25
2
Water Tolerance, VOl
' 0
15
-
F u e lFCC Gasoline + 5 v So MeOH
tg-
collective effects of temperature, base fuel hydrocarbon type, and cosolvent concentration as follows: 2
Temperature 0 'C
1
5
Figure 8. Effect of cosolvent type and concentration on water tolerance of FCC gasoline-Me0H blends.
Effectiveness of Cosolvent Depends on Its S t r u c ture. The collective results confirm that higher alcohols are effective cosolvents for improving the water tolerance of MeOH/gasoline blends. The cosolvent behavior of MTBE, although poorer than that for the alcohols, indicates that ethers also can improve the water tolerance of gasoline-Me0H blends. To illustrate this finding, the water tolerances of FCC gasoline-Me0H blends at 0 " C are plotted against cosolvent concentration in Figure 8. Between the dosages of 2.5 and 5 vol %, the cosolvent efficacies are 0.056,0.056, 0.030, and 0.012 vol 70/vol (70 for TBA, IPA, EtOH, and MTBE, respectively. Consistent with this finding, and as illustrated in Figures 5 and 6, cosolvent performance for other fuel blends also generally follows the order TBA IPA > EtOH > MTBE. Alcohols are more effective cosolvents than is MTBE because of their hydrophilic OH groups, which can effectively hydrogen bond with the OH group on both water and MeOH. EtOH is not as effective as TBA and IPA since it does not have as large a hydrocarbon component in its structure to efficiently interact with the hydrocarbon phase. However, once the alkyl portion of the alcohol reaches three carbons in size, adding a fourth carbon does little to increase the effectiveness; TBA and IPA are nearly equally effective cosolvents. More specific influences of alkyl chain length vs alkyl chain branching in cosolvent effectiveness were not investigated for the C3and C4 alcohols in this study. The relative cosolvent effectiveness shown above is consistent, however, with trends in solubility parameters (Hoy, 1975),which show the balancing between contributions to nonpolar, polar, and hydrogen bonding for each of these oxygenate cosolvents. As the temperature increases, the relative differences in efficacy of each cosolvent begin to diminish (Table 11). A t 20 "C, EtOH begins to approach the effectiveness of TBA and IPA in many blends. However, because wintertime transport, storage, and use of gasoline-MeOH blends is where phase separation problems are likely to occur, higher alcohols such as IPA or TBA would be preferred cosolvents. Regression Analysis Provides Good Correlation for Water Tolerance Prediction. The water tolerance of a MeOH-cosolvent blend can be expressed in terms of the
-
WT = cConc,,,,lvent + t,T f t,T2 sSat
+
+ oOlef + aArom
(2)
where Conccosolvent is in vol % , T is temperature in "C, and Sat, Olef, and Arom are in vol % and are derived from FIA analysis (ASTM 1319D). Equation 2 closely approximates the observed water tolerance behavior of all base fuel-MeOH-cosolvent blends examined in this study and is the result of a multiple linear regression analysis of the collective data. The results of the analysis are summarized in Table 111, which gives the coefficients (at the 95% significance level) for each term in eq 2 for each cosolvent. The correlation coefficient for each fit, r2, is also given, as is the number of data points considered. The correlation coefficients indicate that eq 2 fits the observed data well, despite the fact that the temperature dependence was linearized in terms of a quadratic relationship instead of a log c vs 1 / T relationship for convenience. Nonlinearities evident in the cosolvent concentration dependence data (Figure 8) were not statistically strong enough over the whole range to warrant a nonlinear concentration term. The results shown in Table I11 tie together the main quantitative findings discussed above in the separate analyses. For example, the relative ordering of cosolvent efficacy is reflected in the values of the relative coefficients c across a wide range of temperatures and compositions (TBA > IPA > EtOH >> MTBE). Similarly, the relative ordering of chemical type effects on water tolerance is reflected in the relative coefficients s, 0,and a across a wide range of temperatures and compositions (aromatics >> olefins >> saturates). Although this regression-based correlation may not be expected to accurately predict water tolerances a t the very extremes of concentration, temperature, and composition (for example, 100% saturates a t 0 "C and no cosolvent), it is useful for predicting behaviors of MeOH-cosolvent blends across a wide range of practical gasoline compositions. Acknowledgment B.A. Jones is gratefully acknowledged for her significant contributions to the experimental portion of this work. Registry No. MTBE, 1634-04-4;IPA, 67-63-0; TBA, 75-65-0; MeOH, 67-56-1; EtOH, 64-17-5; water, 7732-18-5.
Literature Cited American Petroleum Institute. Alcohols and Ethers: A Technical Assessment of Their Application as Fuels and Fuel Components. API Publication 4261, 2nd ed.; American Petroleum Institute: Washington, DC, July 1988 and references therein. Eccleston, B. H.; Cox, F. W. Physical Properties of Gasoline/Methanol Mixtures. Report BERC/RI-76/12; Energy Research and Development Administration: Bartlesville, OK, Jan 1977. Green, G. J. U.S. Patent 4,804,274, Feb 14, 1989.
Ind. Eng. Chem. Res. 1990,29, 1635-1640 Hoy, K. Table of Solubility Parameters; Chemicals and Plastics Research Development Department, Union Carbide Corporation: Tarrytown, NY, May 16, 1975. Khinkova, M.; Ivanov, S.; Georgiev, P.; Boneva, M.; Sopov, D. Properties of Stable Gasoline-Alcohol Blends. Ropa Uhlie 1985, 27 (41, 202-210. Osten, D. W.; Sell, N. J. Methanol-gasoline Blends: Blending Agents to Prevent Phase Separation. Fuel 1983,62 (3),268-270.
1635
Rawat, B. S.; Khanna, M. K.; Nagpal, J. M.; Gulati, I. B. Water Tolerability of Gasoline-Methanol Blends. Res. Znd. 1984,29 (2), 114-122. Unzelman, G. H. Problems Hinder Full Use of Oxygenates in Fuel. Oil Gas J. 1984,82, 59-65. Received for review January 25, 1990 Accepted May 4, 1990
Viscosity of n -Hydrocarbons and Their Mixtures Edvard Aasen,+Erling Rytter, and Harald A. 0ye* Institute of Inorganic Chemistry, The Norwegian Institute of Technology, Trondheim, Norway
The viscosity of the following n-hydrocarbons, either as pure liquids or in a mixture, has been studied: C6H14,C10H22,C22H46, CS2HM, CMHw,and C60H122.An oscillational viscometer is utilized. The data are described by eq 8 with a standard deviation of 1.0% for pure compounds and 1.9-3.8% for mixtures including pure compounds.
Introduction
locking arrangement is constructed to prevent damage to the sensitive torsion wire (92% Pt-8% W alloy, 0.7-mm The aim of the present work was to arrive a t a model diameter, 580-mm length) during installation and when for the viscosity of n-hydrocarbons and their mixtures in the pressure is regulated. The wire is annealed at about the high molecular region over as wide a range as possible, 1100 "C and permanently elongated 3-4% to make it mainly based on our own measurements. The upper limit linear. The torsion wire is fastened to an electronic balance was C60H122, which was the heaviest n-hydrocarbon we (Sartorius 5407 MP8-1). could obtain commercially with satisfactory purity. The The cup, 2-cm inner diameter and 8-cm inner length, model can be used for interpolation of hydrocarbons, inis made of the nickel-chrome alloy Inconel 625. The inner cluding mixtures, whose viscosity has not been measured diameter of the cup is determined within an accuracy of and for application in software design, e.g., slurry reactor 2 pm. The piston grooves give a dynamic seal that does simulations. not leak when exposed to 400 bar pressure at 200 OC. The A high precision oscillational viscometer described Viton O-rings in the piston and upper lid are renewed after earlier (Torklep and (aye, 1979; Berstad et al., 1988) was each measuring series. utilized for the experimental studies. When this viscomProcedure. When the sample was solid a t room temeter, with a solid body oscillating in the liquid, is used for perature (waxes),the following filling procedure was used. liquids with low vapor pressure, a standard deviation of The upper lid was dismantled, and the sample was filled ;t0.02% and an estimated absolute error of 0.05% on the from the top with the piston in the lowest position. The 68% level can be obtained (Berstad et al., 1988). The total amount of sample and the composition (in the case accuracy is about 0.5% for liquids with high vapor presof the mixture) were determined by weighing on a balance. sures (Knapstad et al., 1989), as the liquid has to be conThen the upper lid and upper valve (c) were connected tained in a completely filled cup. The experimental setup and the space above the sample was evacuated. When a is as indicated on Figure 1. The hollow cup filled with vacuum of about lo4 bar was reached, the upper valve was liquid is oscillated freely and the oscillation is detected by closed and the sample was compressed by injecting Nz gas shining a laser beam on a mirror fastened to the pendulum of about 20 bar through the lower valve (k). In this way, and recording time intervals as the beam passes two the sample was formed into a gas-free solid cylinder. It photodetectors. The filling procedure is a critical point was not necessary to melt the sample before compression, and is different for hydrocarbons that are gaseous at room although this was done at the out-set of the studies. temperature (Knapstad et al., 1991), hydrocarbons that A modified filling procedure was used when the sample are liquid at room temperature (Knapstad et al., 1989),or was liquid a t room temperature. The cup was first evachydrocarbons that are solid at room temperature, as in the uated to about lo-' bar with the piston in the upper present case. position. The upper valve was connected to the sample reservoir through a '/gin.-diameter high-pressure tube that Experimental Section was evacuated. The upper valve was then closed, and the sample entered the tube volume between the reservoir and Apparatus. Here only the torsion wire, the particular cup used, and the filling procedure will be described. the upper valve. Then the upper valve was opened and Figure 2 shows the cup that is used. The liquid is conthe small dead volume (about 0.1 cm3)in the cup was filled tained between the fixed lid (d) and the piston (f). The up. In order to overcome the friction in the piston, the sample is pressurized by nitrogen with a double set of sample reservoir was set under a Nzgas pressure of about Viton O-rings as seals. During oscillations, the two valve 10 bar. The amount of sample to be injected in the cup handles (a) are removed and the whole assembly is screwed was regulated roughly by adjusting the back pressure of onto the torsion wire chucks by the grooves (b). A special N2 gas below the piston. The weight of the sample was then measured by weighing the cup before and after filling with the one-line electronic balance built on top of the Present affiliation: Laboratory of Chemical Engineering, The Norwegian Institute of Technology. viscometer (Berstad and (aye, 1991). The same procedure 0888-5885/90/2629-1635$02.50/0 0 1990 American Chemical Society
