Colorimetric detection of alcohols in gasoline

A colorimetric method for detecting the presence of alcohol in hydrocarbons, such as gasoline, is disclosed. The method comprises contacting the hydrocarbon with a mixture comprising: PA1 i. an alcohol soluble, hydrocarbon insoluble dye; and PA1 ii. a solid insoluble in hydrocarbon and alcohol whereby the mixture undergoes a color change in the presence of alcohol. The hydrocarbon sample preferably is contacted with a drying agent to remove dissolved water prior to contacting the mixture.

BACKGROUND OF THE INVENTION 
This invention is directed at a method for detecting the presence of 
alcohols in hydrocarbon samples. More specifically, the present invention 
is directed at a colorimetric method for detecting the presence of alcohol 
in gasoline. 
Frequently, it is necessary to determine if alcohol is present in 
hydrocarbons, such as gasoline. Alcohols, such as methanol, ethanol, and 
tertiary butanol, often are added to the gasoline pool to improve octane. 
However, the presence of alcohol, particularly in excess of about 1 volume 
percent, may cause several adverse effects. Since the alcohols are 
oxygenated compounds, their presence in gasoline may affect the oxygen to 
fuel ratio of the fuel being combusted leading to potential operational 
and emission problems. As a result, the United States Environmental 
Protection Administration currently limits the oxygen content of gasoline 
to less than 2 weight percent, (or up to 0.3 volume percent methanol) 
unless specific waivers have been granted. 
In addition, the presence of excessive quantities of alcohol in gasoline 
may cause increased engine corrosion and adversely affect elastomeric 
engine seals. 
In other instances, as for example in performing vapor pressure tests to 
determine the volatility of gasoline, the validity of test results may be 
dependent on the absence of alcohols. Tests which tolerate the presence of 
alcohols tend to be more elaborate and more expensive to perform. Hence, 
these alcohol-tolerant tests normally are conducted only when alcohols are 
known to be present in the sample tested. 
Present methods for detecting the presence of alcohol in gasoline tend to 
be rather expensive, and usually require the use of elaborate analytical 
equipment operated by highly trained technicians. These methods are not 
readily adaptable for use by non-technically trained individuals in the 
field. 
U.S. Pat. No. 4,070,154 discloses a method for measuring the alcohol 
content in jet fuel by mixing a known quantity of jet fuel with a known 
amount of an emulsion comprising a gel of finely grained particles 
saturated with a solution of sodium vanadiate, 8 hydroxyquinoline, water, 
acetic acid and an organic solvent which is free of OH-group chemicals and 
insoluble in water to form an emulsion matrix. The patent discloses that 
this mixture can be stored in a tube prior to use. A series of standards 
are prepared by preparing fuel samples with various known alcohol 
concentrations and passing these samples through tubes containing the 
mixture. The extent to which the emulsion matrix changes color in each 
standard tube is noted. The alcohol content of the fuel then is determined 
by adding a predetermined quantity of fuel to the mixture and noting the 
amount of the mixture that is discolored. This procecdure is not generally 
used because of the rather elaborate preparation required. 
U.S. Pat. No. 2,968,940 discloses a method for detecting dispersed water in 
jet fuel and similar hydrocarbon oils, by contacting the fuel with a small 
amount of a mixture of finely divided, water-soluble, solid anhydrous dye 
and a finely-divided solid capable of taking up or adsorbing any water 
present in the sample. The dye required is the sodium salt of 
o-cresolsulfonphthalein and the finely divided solids were required to be 
anhydrous barium carbonate. Samples of the dye and finely divided solid 
are added to a sample of the fuel and agitated. The intensity of the color 
of the sample is compared with that of samples of known dispersed water 
content to determine the approximate dispersed water content of the 
sample. U.S. Pat. No. 3,505,020 discloses the use of a minor portion of 
fuchsia dye and a major proportion of a finely-divided, substantially 
anhydrous solid, i.e., calcium carbonate, barium carbonate, barium 
sulfate, magnesium carbonate and combinations thereof, to determine the 
approximate dispersed water content in jet fuels and similar hydrocarbon 
oils. A sample of the hydrocarbon is contacted with the dye-anhydrous 
solid mixture and agitated. The color change may be observed and compared 
to samples having known dispersed water contents to determine the 
approximate dispersed water content of the sample. The test procedures of 
these two U.S. patents may not be directly applicable to determining the 
alcohol content of gasoline, which often has a higher dissolved water 
content than the middle distillate fuels, such as jet fuel, since free 
water present would interfere with the test procedure for determining the 
alcohol content. 
Accordingly, it would be desirable to provide a process which is a 
reliable, and inexpensive test for determining the presence of alcohol in 
hydrocarbon samples, such as gasoline. 
It also would be desirable to provide a process which is easily used by 
non-technically trained individuals. 
It also would be advantageous to provide a process which could be utilized 
in the field for qualitative screening of hydrocarbons, such as gasoline, 
for alcohol presence without the necessity of sending all samples for 
detailed analysis. 
The present invention is directed at a method for determining the presence 
of alcohols, such as methanol, ethanol, the propanols and the butanols, in 
a hydrocarbon, such as gasoline, and comprises contacting the hydrocarbon 
with a mixture comprising: 
A. an alcohol soluble, hydrocarbon insoluble dye; and, 
B. an alcohol insoluble, hydrocarbon insoluble solid, and noting whether 
the mixtrue changes color. A color change indicates the presence of 
alcohol. 
SUMMARY OF THE INVENTION 
The present invention is directed to a method for detecting the presence of 
alcohol in hydrocarbon which comprises contacting the hydrocarbon with a 
mixture comprising: 
i. an alcohol soluble, hydrocarbon insoluble dye; and 
ii. an alcohol insoluble, hydrocarbon insoluble solid, whereby the mixture 
undergoes a color change in the presence of alcohol. 
The hydrocarbon preferably is treated with a drying agent, such as 
magnesium sulfate, sodium sulfate, calcium chloride or mixtures thereof, 
to remove water present in the hydrocarbon prior to the hydrocarbon 
contacting the dye mixture. 
The dye comprises between about 0.1 and about 5 weight percent of the 
mixture, preferably between about 0.5 and about 1 weight percent of the 
mixture. 
Among the preferred dyes are the following: hexamethyl p-rosaniline 
chloride, bromophenol blue, bromocresol green. 
The hydrocarbon and alcohol insoluble solid preferably is finely divided 
and preferably is selected from the group consisting of salts of Group IIA 
metals, i.e., calcium, magnesium, barium, strontium. A preferred solid is 
calcium carbonate. 
The alcohol detected typically will be methanol, ethanol, propanol, i.e., 
n-propanol and i-propanol, and/or butanol, i.e., n-butanol, sec. butyl 
alcohol, isobutanol and tertiary butyl alcohol, while the hydrocarbon 
frequently will be gasoline, although the test also may be applicable to 
middle distillate fuels, such as diesel fuel. 
The concentration of the mixture in the hydrocarbon typically may range 
between about 0.1 grams and about 10 grams per 100 ml. of fuel, preferably 
between about 0.5 grams and about 1 gram per 100 ml of fuel. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention is directed at a colorimetric method for detecting 
the presence of the lower alcohols, such as methanol, ethanol, propanol 
and butanol in hydrocarbon samples, such as gasoline. 
The present invention is not dependent upon the use of a particular dye. 
This invention may be practiced using any dye which is alcohol soluble and 
hydrocarbon insoluble. As used herein, the term "alcohol soluble dye" is 
defined to mean that the dye is sufficiently soluble to produce a color 
change in the presence of the alcohol. The term "hydrocarbon insoluble 
dye" is defined to mean that the dye does not produce a detectable color 
change in the presence of the hydrocarbon alone. Among the dyes which are 
alcohol soluble and hydrocarbon insoluble are the following: hexamethyl 
p-rosaniline chloride, bromphenol blue, bromcresol green, methylene blue, 
brilliant green, and orange one. 
While the addition of alcohol soluble hydrocarbon insoluble dye directly to 
the hydrocarbon sample often may prove satisfactory, this method is not 
preferred because, while the quantity of dye required normally is very 
small, the dye may be relatively expensive. The addition of very small 
quantities of the dyes may lead to variations in the results obtained. In 
addition, the presence of color containing compounds in the sample tested 
may lead to erroneous test results. 
To overcome these problems, the present invention is directed at pre-mixing 
the dye with a solid, preferably a relatively inexpensive finely divided 
solid which is insoluble in both the alcohol and the hydrocarbon. The 
alcohol insoluble solid preferably is of a color different from that of 
the dye when alcohol is present. 
The present invention eliminates the problems of adding only small 
quantities of dye to the sample, since a relatively large quantity of the 
mixture is added. In addition, detection of a color change is facilitated 
if the alcohol and hydrocarbon insoluble solid is of a different color 
than the dye in the presence of an alcohol. 
Preferred finely divided alcohol and hydrocarbon insoluble solids include 
the salts of Group IIA metals of the Periodic Table, i.e., calcium, 
magnesium, barium and strontium, such as calcium carbonate, calcium 
sulfate, calcium chloride, barium carbonate, barium sulfate, magnesium 
carbonate and mixtures thereof, with calcium carbonate being particularly 
preferred, since it is finely divided, insoluble in the test system, 
relatively inexpensive, non-toxic and presents a good background for 
detecting any color change in the system, since it is white. 
The accuracy of the present invention is not affected adversely by the 
presence of gasoline dyes, corrosion inhibitors, detergents and 
antioxidants, or by other additives commonly present in gasoline. 
The dye may comprise between about 0.01 and about 5 weight percent of the 
mixture, preferably between about 0.5 and about 1 weight percent. The 
concentration of the mixture in the hydrocarbon may range between about 
0.1 and 10 grams per 100 ml. of fuel, preferably between about 0.5 and 1.0 
grams per 100 ml. of fuel. The concentration of the dye in the mixture and 
the amount of the mixture added to the fuel will be dependent, in part, on 
the particular dye utilized. 
Since dyes which are alcohol soluble normally also are at least partially 
soluble in water, it may be preferred to remove water present in the 
hydrocarbon sample. Failure to remove minor amounts of water present from 
the sample may result in the dye dissolving in the water even when 
alcohols are not present, thereby erroneously indicating the presence of 
alcohol. Minor amounts of water can be removed from the sample by the 
addition of a drying agent or desiccant, such as magnesium sulfate, sodium 
sulfate, calcium chloride or mixtures thereof. Addition of about 1 to 
about 10 grams of desiccant per 100 ml. of fuel sample, followed by brief 
shaking normally will remove water from the fuel sample subsequently drawn 
off. 
The detectable limit of an alcohol depends on the particular dye used in 
the test. The presence of alcohol at concentrations above the detectable 
limit in the test sample will be evidenced by a color change of the 
alcohol insoluble solid within a relatively short period of time, i.e., 
about four minutes after the addition of the mixture to the fuel sample. 
If fuel samples containing the mixture are left for extended periods of 
time before the samples are checked for a color change, the erroneous 
presence of alcohols may be indicated by the dye dissolving in very small 
amounts of residual water present in the fuel. 
For ease of handling and in order to facilitate the carrying out of the 
method of the invention, it will generally be found convenient to package 
the mixed dye and alcohol insoluble solid in capsules or ampules of 
polyethylene or a similar material. Each capsule may contain sufficient 
mixed dye and alcohol insoluble solid for one test. For relatively short 
periods of time it is sufficient to store the capsules in a tightly closed 
glass jar. Where the capsules are to be stored for extended periods of 
time or under severe weather conditions, it may be preferred to maintain 
them in a sealed vessel in the presence of a desiccant. 
The exact nature and objects of the invention are further illustrated by 
the following examples. 
As shown in the following Examples and tables, the present invention has 
been able to repeatedly detect alcohol concentrations as low as 0.05 
volume percent methanol; 0.2 volume percent ethanol; and 0.3 volume 
percent tertiary butanol.

EXAMPLE 1 
A mixture of 0.3 weight percent hexamethyl p-rosaniline chloride was 
admixed with about 99.7 weight percent calcium carbonate. Two hundred 
milligrams of this mixture was admixed with about 20 cc of gasoline 
containing varying amounts of methanol, ethanol and tertiary butanol. The 
presence of alcohol was determined by observing whether the calcium 
carbonate changed in color from white to pink. From the summary of test 
results shown as Table I, it can be seen that this method was able to 
detect methanol concentrations as low as 0.5 volume percent methanol and 1 
volume percent ethanol. 
TABLE 1 
______________________________________ 
Detection of Alcohols Using Mixture Comprising 
0.3 Weight Percent Hexamethyl P-Rosaniline Chloride 
and 99.7 Weight Percent Calcium Carbonate 
Alcohol Color Change of 
Alcohol Concentration 
Calcium Carbonate 
Present Volume % Detected 
______________________________________ 
methanol 0.5 pink 
1:1 methalol:tert. butanol } 
0.5 no change 
1:1 methanol:tert. butanol } 
1.0 pink 
ethanol 0.5 no change 
ethanol 1.0 pink 
______________________________________ 
EXAMPLE 2 
A mixture of 0.7 weight percent bromophenol blue and 99.3 weight percent 
calcium carbonate was prepared. To avoid any interference by dissolved 
water present in the gasoline, 1 gram of a drying agent, magnesium 
sulfate, was added to 20 ml. of gasoline and the sample was capped. The 
gasoline and drying agent were shaken for about 10 seconds and allowed to 
settle for at least two minutes. The supernatent gasoline layer was 
evacuated into a sealed tube containing about 200 milligrams of the 
dye-calcium carbonate mixture under vacuum. The gasoline, dye and calcium 
carbonate were intermixed by shaking for about 10 seconds and allowed to 
settle. The calcium carbonate changed from white to blue within less than 
four minutes if the alcohol contents of the gasoline were greater than the 
following: methanol 0.05 volume percent; ethanol 0.2 volume percent; 
tertiary butanol 0.3 volume percent. 
A summary of the test data is set forth in Table II. 
TABLE II 
______________________________________ 
Detection of Alcohols Using Mixture Comprising 
0.7 Weight Percent Bromophenol Blue 
and 99.3 Weight Percent Calcium Carbonate 
Alcohol Color Change of 
Alcohol Concentration 
Calcium Carbonate 
Present Volume % Detected 
______________________________________ 
methanol 0.05 blue 
1:1 methanol:tert. butanol } 
0.1 blue 
ethanol 0.1 no change 
ethanol 0.2 blue 
tertiary butanol 
0.2 no change 
tertiary butanol 
0.3 blue 
______________________________________ 
While the present method will not provide an accurate measurement of the 
alcohol content of the sample, the intensity and speed of the color change 
will be a function of the alcohol concentration and thereby a rough 
indicator of the quantity of alcohol present. 
Although the present invention does not provide detailed analytical-type 
information on the sample tested, it does provide a simple, quick, and 
reliable screening method for determining the presence of alcohol. If 
necessary, more detailed analytical test procedures then could be 
conducted to determine the specific alcohol or alcohols present and their 
concentration in the sample.