CA1165142A

CA1165142A - Measuring the aromatic activity of a hydrocarbon composition

Info

Publication number: CA1165142A
Application number: CA000355270A
Authority: CA
Inventors: Carlon C. Chambers
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-07-05
Filing date: 1980-07-03
Publication date: 1984-04-10
Also published as: GB2064767A; FR2461251B1; FR2461251A1; AU544642B2; GB2064767B; JPS56501022A; WO1981000153A1; AU6127080A

Abstract

MEASURING THE AROMATIC
ACTIVITY OF A
HYDROCARBON COMPOSITION
Abstract The relative aromatic activity of hydrocarbon com-positions is determined by measuring and comparing the ability fo the hydrocarbon compostions to be sorbed by a polymeric rubber matrix. The aromatic activity is useful in determining chemical, physical and/or biological activity of a hydrocarbon composition.

Description

5~2 Technical Field:
This invention relates to the field of determining the aromatic activity of a hydrocarbon composition. From this determination it is possible to predict the physical, biological and/or chemical interaction or action of the hydrocarbon composition in different types of environments.
Background Art:
There are several known test methods for determining various types of characteristics of hydrocarbon compounds, many of which are published by the American Society for Testing and Materials CASTM). Many tests are directed toward determining the aromatic content of a liquid hydro-carbon, for example AST~ D2267-68 and ASTM D936-55 both test for aromatics in gasolines and ASTM ~1017-51 tests for the presence of toluene and benzene. ASTM D875-64 (1~68) and ASTM D1019-6~ additionally test for the presence of olefins in petroleum distillates and ASTM D1319-70 tests for the presence of saturates, nonaromatic olefins and aromatics in petroleum fractions by fluorescent indicator absorption.
~0 Most of these tests are very long and involved, as an example, the D1319-70 test takes more than three hours to test one sàmple. Moreover, there is no direct correlation between the relative amounts of aromatics, olefins and saturates in a compound which allows one to predict the activity of the compound~
In the last few years, the environmental impact, e.g., potential toxicity and pollution problems, of known and new compounds has become of great interest and concern.
In fact, the Federal Government and several state ~overnments have promulgated regulations relating to the potential toxicity of compounds which are based on threshold limit values, e.g., the threshold amount of compound in terms of milligrams per cubic meter of air which will cause pc/~

~ ~651~2 toxicity, and acceptable amounts of products which can be airborne based on the compound's photochemical activity. These values are generated for each specific chemical compound and chemical mixture and involve very time consuming techniques. Absent the specific testing of each hydrocarbon compound and hydrocarbon mixture, there is no way of predicting the toxicity or air pollution potential of any given hydrocarbon mixture.
It i5 known that hydrocarbons have the ability to be absorbed by rubber. For example, the ASTM D471-72 test for chanye in properties of elastomeric vulcanizates resulting ~rom immersion in liquids does measure the change in weight or volume of the test elastomer specimen caused by immersion in a liquid. The purpose of the test, however, is to measure the effect of a particular liquid on a particular elastomer, not to measure the activity of the liguid. There has been no recognition that the phenomenon of absorption of a hydrocarbon by a rubber matrix may he used as a ~uantitative assay of a hydrocarbon compound which will enable one to predict the activity of the compound in a number of different circumstances. The present invention relies on this absorption phenomenon to determi,ne the aromatic activity of hydrocarbon which is predictive of a wide variety of chemical and/or physical acti,vi,ties, of the hydrocar~on. Additionally, the test is fairly i,nexpensi,ve, is applicable to liquid, vapor, solid and semisolid hydrocarbons and several samples can be run simultaneously in, for example, a three hour time period.
Disclosure of the Invention:
The relative aromatic actiyity of hydrocarbon compositions is determined by measuring and comparing the ability of the hydrocarbon compositions to be sorbed by a polymeric rubber matrix. One embodiment of the invention pC/ c,b eomprises measuring the ability of the hydrocarbon composition under standardiæed conditions to cause a short term weight gain of a polymeric rubber matrix when in physieal eontact with the rubber matrix and comparing this value to a predetermined aromatic activity of a standard mixture of hydrocarbons to obtain the aromatic equivalent (AE~ value of the hydrocarbon composition.
Another embodiment eomprises measuring the short term weight gains in a polymeric rubber matrix under standardized eonditions eaused by two or more hydroearbon eompositions and eomparing the values to determine the relative activity of the eompositions to each other. In this embodiment at least one of th.e compositions can be a known aromatie eompound, sueh as benzene. The resulting value from comparing the values of the other eompositions to the value of benzene, in any embodiment~ is generally termed herein as the benzene aromatie equivalent, as. deseribed more fully hereinafter.
Any means used to determine lhe aromatic aeti.vity of a hydroearbon composi~ion, by eomparison, may be used whether it be electronlc, such as a computer, mechanical~
such as a cam, a eurve, an equation, ete. For example, the we;ght gain of a test coupon caused by a h.ydroearbon composition may be used in eonjunetion with.the following formula to obtain the aromatic equivalent (AE) value:

y=x~+~lnx wherein: Y = fraetional volume percent AE
X = fractional percent of a corrected and normalized weight gain of a test eoupon = coeffieient = coefficient . 3 _ pc/ ~

\

ln = natural logarithm Prior to obtaining the AE value of the hydrocarbon, the weights of the rubber coupons should be corrected to a -standard weight, e.g., 1.0000 grams and, if necessary, the exposure time of the rubber coupon to the hydrocarbon should be corrected to a standard time and then the weight gains caused by-the hydrocarbons should be normalized.
The significance of a benzene aromatic equivalent value is related to the fact that benzene is recognlzed as 10. being the most active of the aromatic hydrocarbon series.
Because of this, it also has the highest solvency power and the highest human toxicity rating of the same series of hydrocarbons. This series of hydrocarbons is aefined as the benzenoid series of aromatic hydrocarbons ~hich.is based on the unsaturated, six carbon benzene ring molecular structure. Thus, the BAE value, as well as the AE value to another aromatic compound, is useful in predicting various physical., biolo~ical and/or chemical activities of hydro-carbons. For e~ample, it is useful in the determination of;
the relative or average toxicity of pure hydrocarbons and mixtures of hydrocarbons; the presence of like boiling range aromatic impurities in high purity aliphatic hydrocarbon process streams; the presence of like boiling range aliphatic hydrocarbon impurities in high purity aromati.c hydrocarbon streams; dissolved aromatic hydrocarbon contamination of water r an aqueous stream containing inorganic compounds and/or an aliphatic hydrocarbon stream; probable compatibility or stability of a substance within a mixture;

compliance with product or process stream specifications defined with respect to AE values; and compliance for a given product with air pollution regulations.
Description of the Figure:

. . .
The Figure is a graph of two di`.fferent curves ~- - 4 -pc/~

~ 5 .1 ~ ~

showing weight gain caused by mixtures of calibration liquids. Curve 1 utiliæes Tiechert 350 (a low vapor pressure, non-aromatic hydrocarbon solvent mixture manufactured by the Tiechert Techtonics Company) as the zero calibration point liquid, benzene is the lOQ
calibration point liquid and the intermediate points are representative of weight gains caused by mixtures of these calibration liquids. N-decane is the zero calibration point and benzene is the 100 calibration point of Curve 2.
Best Mode for Carrying Out the Invention:
For the purposes of this inventipn, the aromatic activity of a hydrocarbon composltion is defined as the ability of the hydrocarbon composition to cause a short term weight gain and/or swelling of a polymeric rubber matrix, when in physical contact with the rubber matrix. The relative aromatic activity is determined by comparing the weight gains and/or swellings caused by more than one hydrocarbon composition. The aromatic equivalent (AE~ value of a hydrocarbon composition is defined as the ability of the hydrocarbon composition to cause a short term weight gain and/or swelling of a polymeric rubber matrix, when in physcial contact with the rubber matrix, that is equivalent in action to a known volume percent of an aromatic calibration compound, such as benzene, w~en mixed with a diluent calibration compound having low-aromatic activity, e.g., a non-aromatic hydrocarbon, preferably an aliphatic hydrocarbon, such as n-decane or isooctane. Within the defined limits of the test, a 1~0 volume precent concentration of the aromatic calibration compound gives an AE value oF 100 and a 100 volume percent concentration of the diluent calibration compound gives an AE value of zero.

pc/ Gk~

:~ :16~ 14~

It is preferred that each of the calibration compounds be pure compounds, not mixtures~ and that the diluent calibration compound have a vapor pressure no greater than that of the aromatic calibration compound.
Although calibration compounds which are mixtures or diluent cali~ration compounds having vapor pressures greater than the aromatic calibration compound may ~e used, the sensitivity of the test will not be as great.
Any of a number of aromatic compounds can be used as the 1~ aroma~ic calibration compound, for example, benzene, toluene, chlorinated aromatic compounds and naphthene.
The particular aromatic calibration compound selected will ~e dependent upon the purpose for determining the AE value of a hydrocarbon composition. Since benzene is readily available, many of its phys;ical and chemical properties are known and it has a high aromatic activity, it is a convenient aromatic calibration compound to use.
Generally, the lower the aromatic activity of a diluent calibration compound, the more pre~erred it is. For

2~ example, isooctance is preferred over n-decane because it causes a smaller weight gain in a polymeric rubber matrix.
The AE value is determined by comparing the corrected and normalized short term weight gain of a polymeric matrix caused by a hydrocarbon composition to a predetermined aromatic activity of a standard mixture of known hydrocarbon calibration compounds. Predetermined aromatic activity values and predetermined aromatic activity of a standard mix-ture refer to any data which establish corrected and/or normalized weight gains of a polymeric matrix by ~nown hydrocarbon compositions. The predetermined aromatic activity of a standard mixture may be utilized in the form of a curve, an equation, a mechanical form, such as a cam, an electronic form, such as a computer, etc.

pc/ C~

5 ~ ~ ~

The invention is applicable to a wide variety of hydrocarbon compositions which are defined as hydro-carbons and hydrocarbon mixtures including hydrocarbons which have been nitrated, sulfonated, oxygenated and/or halo~enated. It is especially applicable to unsaturated hydrocarbons~ preferably unsaturated hydrocarbon ring structures, for example, those of the benzenoid series, naphthalene and anthracene. Totally saturated paraffinic hydrocarbons having a vapor pressure less than that of an 1~ aromatic compound will glve an AE value of zero or close to zero. For the purposes of this invention, it is not necessary to know the analytical structure or composition of the hydrocarbon being tested. The hydrocarbon may be a solid, semisolid, liquid or a vapor. If it is a solid or a semisolid, it is first dissolved in a solvent prior to measuring its sorption by a rubber coupon. The AE
values of solid, semisolid and liquid hydrocarbons are determined from a predetermined aromat;c activity of a standard mixture of liquids; whereas, the AE values of hydrocarbon gases are determined from a predetermined aromatic activity of a standard mixture of vapors.
The polymeric rubber coupons: useful in this analytical technique consist of synthetic rub~ers which are not readily dissolved by either the calibration compounds of the standard mixture used in establishing the predetermined aromatic activity or by the hydxocarbon compositions being tested. The synthetic rubbers must have the ability to exhibit a preferential sorption between aliphatic and aromatic hydrocarbons. Generally, they will exhibit a preference for aromatic hydrocarbons.
However, if a synthetic rubber exhibits a preference for the sorption of aliphatic hydrocarbons, then the technique is used to show the al;`phatic activity equival~nce of the pc/~

hydrocarbon composition and the AE value will be an inverse measure of the aliphatic activity equivalence.
Viton~ (trademark of the duPont Company), a copolymer of vinylidene fluoride and hexafluoropropylene, and H-1262, a blend of hycar rubber (polyacrylic rubber) and styrene butadiene rubber manufactured by the Mercer Rubber Company of Trenton, N.J., are examples of suitable rubbers for the test coupons. JH-21 (manufactured by the Mercer Rubber Co.), a 100 percent polyacrylic elastomer, is a preferred synthetic rubber. Neoprene and Hypalon~, a chlorosulfonated polyethylene elastomer, are not-suitable rubbers for determining BAE values inasmuch as ; they are partially dissolved by benzene.
To determine the weight gains of the rubber test coupons caused by the hydrocarbons, one rubber coupon of a standard weight range is placed in an enclosed container in physical contact for a specific time period with a specific amount of the hydrocarbon composition being tested.
Immediately, thereafter, the coupon is separated from the hydrocarbon composition, blotted dry, if necessary, and weighed at a specified time, preerably within thirty seconds of its exposure to the atmosphere. When the hydro-carbon composition is a liquid or a solid or semisolid dissolved in a liquid solvent, the container may ~e a flask.
~hen the hydrocarbon composition is a gas, a flo~ cell may be used as the container and a specific amount of the hydrocarbon may be injected or aspirated through the cell for the specified time period.
The standardized rubber coupons are prepared from sheets of specially compounded rubber as described above. These sheets should be of uniform thickness of from about 0.0625 (0.16 cm.~ to about 0.125 (0.32 cm.) inches thick and cut into strips that are about 0.5 ~;
~; - 8 -pc/ c b .. .
~ 165 1~2 inches (1.3 cm.) wide. These strips a.re then cut into lengths which will give a coupon weight of l.Q + 0.25 grams. To obtain standardized results, all of the AE
test results are standardized, for example, to a 1.0000 gram rubber coupon. The percentage correction required for tests in which the coupon weight is other than l.O.QOQ
grams is defined by the following curve fitting equation:

X=al~ + a wherein: X = the percentage difference of results from results that would have heen obtained h.ad the coupon weight been 1.0000 grams.
= actual coupon wei.ght in grams.
al = a constant aO = a constant When H-1262 is used as the rubber coupon, al i.s -18.2550 and aO is 19.1350. The corrected wei.ght of the coupon for each test (Xl~ is obtained by adding or su~tracting the indicated correction to obtain the wei.ght corrected X
which is Xlw~
The test is generally standardized using a two hour exposure time. Diferent exposure times may be used;
however, the results will differ from those obtained from a standard two hour tes.t. Thus, the results from a test of a different time period must be corrected to th.e Xl of a two hour test by applying the equation shown below.
This will allow the determination of the percentage difference of the test time from the two hour standard based on the standardi~ed coupon weight. This correction is determined by the same curve fitting equation:

X=alY + aO

pc/ ~

1 1~5 1~
wherein: X = the percentage difference oE the results from the results that would have been obtained with a two hour test.
Y = the percentage difference of the . test time from the two hour standard.
al = a constant -~: aO = a constant When H-1262 is used as the rubber coupon, al i5 Q.5620 and lQ aO is -0.0800. The indicated correction is applied in the same manner as the weight correction to the Xl or Xlw of the applicable test to obtain a corrected Xl`(Xl corrected for time is XlT, or corrected for time and coupon weight is XlTW) ' The corrected weight gain and/or swelling of a polymeric rubber matrix caused by the standard mixture may cause the AE value of the aromatic calibration compound to deviate from a value of 100. Therefore, so that comparative values may be obtained, the weight gain percentages of all :~ 20 samples~after being corrected should be normalized with respect to the predetermined aromatic activity of a sta~dard mixture ln accordance with the following formula:

n 3 ~ ) wherein: Xn = normalized weight gain percentage X3 = the corrected weight gain percentage (~time and/or ~eight~
X2 = X3 of the lQQ percent calibration test b = X3 of the 0 percent calibration test It is the normalized weight gain percentage (Xn) which is used in determining the final AE value of a hydrocarbon composition.
The AE value of each hydrocarbon composition is pc/~ .

5 ~ ~ ~
obtained by comparing the corrected and normalized weight gain caused by the hydrocarbon composition to a predetermined aromatic activity of a standard mixture.
The predetermined aromatic activity of a standard ~ixture is established by performing the above described technique in a zero percent standard, i.e., a diluent calibration compound, on a 100 percent standard, i.e., an aromatic calibration compound, and various combinations of the two. The predetermined aromatic actîvity values lQ are readily utilized in the form of a curve whIch may be established by plotting the corrected and normalized results of these tests on three cycle semilog graph paper - with corrected and normalized percentage weight increase on the X ax;s ~log scale~ and the volume percent aromatic equivalent (~E~ on the Y axis (linear scale~.
The predetermined aromatic act~vity values are standarized not only with respect to the form of the compound being tested, i.e., liquid or vapor~ but also with respect to batches of reagents, volume of compound tested, time of contact between the compound and the rubber coupon, etc. Thus, when any parameter of th~e test~ng technique is altered, it is best to generate new predetermined aromatic activity values or at least run comparative samples reflecting this change in parameter so that if this change affects the AE value, its effect will be known. Even when predetermined aromatic activity values of standardized conditions are already established, if samples are tested infrequently, it is a good practice to include a zero percent, a 100 percent and an intermediate percentage calibration tests with each test series. This will give confidence as to the results by ensuring that no-thing has changed the effectiveness of the coupons or calibration reagents.

pc/ ~

:~ ~6~ ~2 When the predetermined aromatic activity of a standard mixture is used in the form of a curve, the curve is defined by an equation of the following form:

y=~+~lnx wherein: Y = fractional volume percent AE
- X - fractional percent of a corrected and normalized weight gain of a test coupon a = coefficient ~ = coefficient ln = natural logari.thm When this equation is used, percentages.-mus.t he expressed as their decimal equivalents of a fraction.
The coefficients are defined by a s.tandard linear least squaxes regression curve fit of:

~ lnX) vs. lnX
in the form of y = ~x ~ ~, wherein:

lnY
Y lnX
x = lnX

2~ ~xy - ~x ~y ~ 2 - n ~X - (~x) Y n X = ~X
n = number of inputs and wherein X and Y are values taken from the predetermined aromatic activity of a standard mixture or from a plotted curve of those aromatic activity values. The above equa-pc/~

~ ;L65 ~41~
tion, y = ~x ~ ~, ls the form used to derive the constants for the weight and time corrections, X = alY -~ a , referred to previously, after X and Y are interchanged and al =
d aO
When the curve is that of n-decane and benzene using a polymeric coupon of H-1262 rubber, i.e., curve 2 of the Figure, ~ is 0.567828078 and ~ is -0.04098875Q.
Although this equation does not represent an exact fit of a curve of predetermined aromatic activity of a standard mixture, it is sufficient to define an AE. For example, with respect to Curve 2 of the Figure, the deviations are small with the greatest variance being 3.1 BAE units and the largest percentage errors are associated with Y being less than or e~ual to 0.5. If more accurate results are required, then the predetermined aromatic values should be used directly, e.g., in the form of a curve, to determine the AE value or a better equation which more accurately fits the curve should be derived. Similar equations can be readily derived, including ones which may more accurately fit the curve.
The tests should always be run ~ith a standardized volume of either a liquid sample or a vapor sample inasmuch a~ different volumes have a significant e~fect which is non-linear. Therefore, all sample volumes should be the same.
Temperature does not appear to ~e critical and may vary over a fairly wide range. It is preferred that the temperature be in a range from about 65-8QF.
The sensitivity of the AE test can be varied by many parameters. Examples include, changing the weight of the rubber coupon and/or its thickness, changing the surface to volume ratio of the rubber coupon or changing the test time interval. For example, a coupon o~ greater weight will result in a smaller percentage weight increase.

pc/ ~

.
~ 1~5 l~
~onversely, as the wei.ght of the coupon is decreased, a greater weight percentage increase wi.ll be reflected.
A decrease in the thickness of a coupon allows the hydrocarbon composition to go through the coupon faster so the weight gain and/or swelling occurs quic~er.
Similarly, as the test time interval is increased, the potential weight gain caused by the compound being tested increases. The sensitivity of the test will generally increase as the surface area of the rubber coupon lQ increases for a given volume of coupon.
When the hydrocarbon composition being tested is a solid or a semisolid which necessitates its dissolution in a solvent, the AE (Y~ that is obtained wi.ll be of the blend ~Yb~. To calculate the AE of the hydrocarbon or hydrocarbon mixture (Yx) the follo~ing equation is used:

( VbYb~ - (Vs.
V

wherein: Vb = volume percent of the blend, assumed to be lOa percent Vs = vol~ne ~ercent of th.e solvent in the blend Vx = volume percent of the unknown in the - blend Yb = volume percent AE of the blend Ys = volume percent AE of the solvent Y = volume percent AE of the hydrocarbon or hydrocarbon mixture, and wherein Yb > VS' In the case of a solid or s.emi.solid hydrocarbon, when the solvent used is other than one used in the calibration composition of the predetermined aromatic activity, a sample of the pure organic solvent used to pc/~

~issolve the solid or semisolid must be included in the test series so that its AE can ~e determined. This will allow for the AE of the solid or semisolid hydrocarbon composition to be determined.
Similarly, the relative aromatic activity of two or more hydrocarbon compositions can be determined.
Each hydrocarbon composition is exposed to the same kind of rubber coupon under standardized conditions. The time of exposure and weight of each of the rubber coupons should be corxected, if necessary, and normalized, and the weight gains of the hydrocarbon compositions corrected accordingly. The hydrocarbon composition which causes the greatest weight gain will exhibit the greatest aromatic activity. Conversely, the hydrocarbon which causes the smallest weight gain will exhibit the least aromatic activity.
Becaus.e not all aromatic type molecules have.
the same activity as pertains to physcial, chemical or biological actions, the significance of the measurement of 2~ the aromatic equivalent value of a hydrocar~on composition lies in the fact that it is a very good measure of aromatic activity. The higher the AE value, th.e more aromatic activity the composition exh.ibits.. Thi~
measurement of aromatic activity is of signifi.cance in many different types. of applications. For example, it is of value in determining or predicting the compati.hility of organic materials, detecting aromatic hydrocarbon impurities, setting and determining specifications for product process streams, determining the presence of aromatic impurities in wateL, aqueous s.olutions and aliphatic streams, predicting the relative biological activity and toxicity of aromatic hydrocarbons in human beings or animals and predicting the photochemical ~ 15 -pc/~

1 4 ~
act:ivity of an aromatic hydrocarbon as an air pollutant.
AE values can be very useful in the research and development oE new and useful products made from blended or reacted organic materials. One of the pro~lems in developing such products is that not all organic materials are compatible with one another. AE values are useful in determining the stability and compatibility of hydrocarbon compositions with each other~ The AE values of known hydrocarbon compositions with known desired characteristics are determined empirically. The AE values of these ~ydro-carbon compositions are then used to establish AE ran~es indicative of stable and compatible ~ixtures of the type of product sought, thereby allowing one to predict the stability of other known and unknown hydrocarbon compositions when blended. The compatible AE value ranges will vary depending upon the type of product being manufactured, its desired properties and the type starting materials used.
The use of AE values is especially useful when blending one or more hydrocarbons having unknown compositions.
2~ For example, if a paraffinic hydrocarhon is blended with another hyd~oc~rbon which has a high asphaltene content, the asphaltenes will precipitate and the resulting liquid phase is viscosity unstable. Since the paraffinic and/or asphaltene content o~ the blended hydrocarbons may not be known, these effects may not be reco~ni~ed immediately and may result in the inadvertant manufacture of a product that will have a very short shelf life, i.e., a product which will precipitate solids and thicken. Stability in such blends depends on selecting compounds that will be compatible.
When selecting a hydrocarbon composition to be mixed with a hydrocarbon mixture known to contain asphaltenes, e.g., asphalt, pitch and gilsonite, the AE value of the pC/ ck~

-`` 1165~2 nydrocarbon composition should be at least equal to or greater than the AE value of the hydrocarbon asphaltene mixture~ The greater the percentage of asphaltenes in the mixture, the greater the AE value of the hydrocarbon composition should be over that of the asphaltene mixture.
For example, if the mixture contains 5 percent or 10 percent asphaltenes, the BAE value of the hydrocarbon mixture being added should be about 100-llQ percent and about 100-120 percent, respectively, of the BAE value of the`asphaltene-mixture. The technique is useful in th.e formulation of a number of products contai.ning asphaltenes, including, pavement sealers, ground sealers., rubberized asphalt membranes, pond liners and water stop coatings.
BAE values can also be of use in predicting the compatibility of elastomeric and rigid polymers with other hydrocarbon materials. As an example, solvents used to dissolve elastomeric polymers and some ri.gid polymers should have a BAE value.of from about 37 to about 115.
Outside of these ranges there is no si.gniEicant dissolution of the polymers. The optimum BAE value of a solvent for polystyrene is about 95; polybutadiene is about 66;
polyisoprene is about 52; polyethylene~butylene is about ~6; and polysulfide is about 9~. There is also a certain range of.aromatic activity that asphalt hydrocar~ons must have to be able to achieve ma~imum levels of performance from styrene butadiene type elastomers i.n asphalt based hot melts. The desired aromatic activity is a BAE value of from about 28 to about 42. This value is dependent upon the asphaltene content of the asphalt. When the asphaltene content is lower, a BAE value of about 28 is. preferred;-whereas, when the asphalt contains 20 percènt asphaltenes, a BAE value of about ~2 is preferred~ Below this ran~e of compatibility there will be a phase separation; and above pc/ ~ .

5 1 ~ ~
lt, there will be no beneficial difference in blend properties due to polymer addition. It is possible to empirically predict the AE value range for solvents of other elastomers and of hydrocarbon compositions to he blended to form a hot melt of another type.
The determination of AE values is also helpful in checkin~ product purity or contamination of pure chemicals or mixtures~ For example, AE determinations can detect like boiling range aromatic impurities in high purity aliphatic hydrocarbon process streams or they can indicate like boiling range aliphatic hydrocarbon impuritles in high purity aromatic hydrocarbon streams. A stream containing an aromatic impurity will have a higher AE
value than the pure aliphatic hydrocarbon stream.
Similarly, an aliphatic hydrocarbon, an aqueous and/or inorganic impurity is indicated by a lower AE value than the AE value of the high purity aromatic hydrocarbon stream alone.
Additionally, dissolved aromatic hydrocarbon contaminants can be detected in water throu~h the use of AE values. Water will have a AE value of-Q and the presence of an aromatic hydrocar~on contaminant will cause the AE
value to be greater than Q. A somewhat related use of AE
values is their use to define the specifications of a product or process stream. A deviation from an established AE
value for a process stream would be indicative of a substandard product or process stream.
Air pollution has become a major concern of both the Federal Government and the state governments. Very often, a compoun~'s propensity to cause air pollution is determined by its photochemical reactivity. Limited data indicates that the BAE values of aromatic hydrocarbons have an inverse relationship to the photochemical pc/ (~

~ 5 3 ~ ~
reactivity of aromatic hydrocarbons. In other words, the higher the BAE value of an aromatic compound is, the lower its photochemical reactivity is.
Moreover, a direct relationship has been found between the recited toxicity of hydrocarbons and the hydrocarbons' sAE values. Compounds having higher BAE
values are more toxic than compounds with lower BAE values, at least with respect to toxicity caused by absorption of the compound through the skin or by inhalation. By correlating the BAE values and toxicity values, e.g., threshold limit values, of hydrocarbon compositions whose toxicity is known, it is possi~le to determine the toxicity of a hydrocarbon composition, whose toxic-ty is not known, by applying the correlation factor to the BAE value of the hydrocarbon composition. The BAE values are especially useful in the formulat;on of liquid products which in liquid or vapor form will comply with various health and air pollution regulations.

-Rubber coupons were prepared from samples of H-1262 synthetic rubber which were of a uniform thickness of between 0.625 and a .125 inches and cut into strip~ of 0.5 inches ~ide and a length such that each~coupon had a weight of from between 0.7 and 1.0 grams. To prevent contamination, the rubber coupons were handled with gloves and they were stored in airtight containers until used. Exactly 25 milliliters of each liquid to be tested were placed in separate, numbered 250 milliliter Erlenmeyer flasks. The numbers on the flasks correspond to numbers ~iven to the coupons. To each flask was added the corresponding rubber coupon, a cork stopper was ti~htly installed and the flask was lightly swirled, and set aside for a period of two hours at a temperature of 6S-75 F. At exactly two hours pc/ C~

5~2 ~or each sample and within 30 seconds time, the stoppex was removed, the liquid was dumped, the coupon was shaken out onto a paper towel, blotted dry and the weight of the coupon was obtained to the nearest 0.1 milligram. The weight increase of each coupon was calculated as a percentage increase from the original weight. The liquids tested were 100 percent n-decane, 100 percent benzene and varying mixtures of these two liquids. The obtained values were corrected for the weight differences of the rubber coupons and the weight gain percentage was normalized pursuant to the equations previously described. The results are given in the Figure as curve 2.
Example 2 The same test techniques of Example 1 were utilized with the exception that the liquids tested were Tichert 350, benæene and mixtures of these two liqu~ds.
Tichert 350 (a low vapor pressure nonaromatic mixture of hydrocarbons) was used for the zero point and its true value was subtracted as a blank from all the other calibration points. Benzene was used at the 100 percent point and the ratio required to bring its true value to lQ0 percent was applied to all the other calibration points after subtracting the blank. The rubber COUpOIlS were not corrected for their differences in weight; however, the weight increase experienced by each rubber coupon was normalized. The data is given below in Ta~le 1 and it is plotted in the Figure as curve 1.

Normalized BAE Value Weight increase O
1.0 .19 2.0 ,34 4.a ,53 8.0 1.2~
16.0 3 33 25.0 6.96 pc/ ~

~ 165 ~

32.0 10.32 40.0 15.85 50.0 22 49 64.0 38 82 75.0 52.66 85.0 80.. 84 100 . O 100 . O

Example 3 sased on curve 1 of F;gure 1, the benzene aromatic equivalent content of the following compos;tions were determined using the techniques of Example 2, The compositions and B~E are given below in Table 2.
TABLE_2 Tested Normalized Composition~eight Gain_~ RAE, V

Toluene 89.24 ~5Ø
LaBarge cutter 1.32 8.1 I.aBarge (southwest) 1.94 ll.Q
Dalton cutter .45 2.~
20 Western cutter 1.81 lQ.5 T-350 cutter .08 ~.1 Plateau cutter 1.38 8.2 RC-O cutter 1.5~ 9.Q
Pasco cutter 1.58 9.3 Shale oil 64 4 0 Tire oil 4 28 18 9 Hunt oil cutter .61 4.Q

Example 4 Using th.e technique of Example 1, th.e BAE volume percentages of six different hydrocarbon compositions were detexmined. These are shown in Table 3 along with the threshold limit valuesi for the same compounds.. The thres-hold limit values are published by th.e Ameri.can Conference of Governmental Industrial Hygenists (May 21, 1~73) and often.form the basis for threshold limit values of a compound which are allowable under state laws. For example, regulatory agencies of the State of Colorado have used these values to define acceptable limi.ts of compounds to which people can be exposed. There is an inverse relationship between the BAE values. and the TLV values, whi.ch leads to a direct relationship between the BAE values and relative pc/ ~,~

~ 1~5 1~
.oxicities.
TAsLE 3 TLV
Substance BAE, V%mg/cubic meter air Benzene 100 80 Toluene 95 375 Xylene ~mixed~ 83 435 Methyl ethyl ketone 83.7 59Q
Methyl isobutyl keton 62O9 410 Ethyl alcohol 0 1900 PC/o~-~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for determining the relative aromatic activity of hydrocarbon compositions comprising measuring and comparing the ability of the compositions to be sorbed by a polymeric rubber matrix.

2. A method for determining the aromatic activity of a hydrocarbon composition comprising determining the aromatic equivalent (AE) value of the composition by measuring the ability of the composition, when in physical contact with a polymeric rubber matrix under standardized conditions, to cause a short term weight gain and/or swelling of the rubber matrix and comparing this value to a predetermined aromatic activity of a standard mixture to obtain the volume percent AE value.

3. A method for determining the aromatic activity of a hydrocarbon composition comprising determining the aromatic equivalent (AE) value of the composition by measuring the ability of the composition, when in physical contact with a polymeric rubber matrix under standardized conditions, to cause a short term weight gain and/or swelling of the rubber matrix, correcting the weight of the rubber matrix to a standard weight, correcting the time of exposure of the rubber matrix to the hydrocarbon composition to a standard time, then normalizing the weight gain and/or swelling measured and comparing the corrected and normalized weight gain and/or swelling to a predetermined aromatic activity of a standard mixture to obtain the volume percent AE value.

4. The method of Claim 3 wherein the standard mixture comprises mixtures of an aromatic calibration compound and a diluent calibration compound which exhibits low aromatic activity.

5. The method of Claim 4 wherein the aromatic calibration compound is benzene and the AE value is the benzene aromatic equivalent (BAE).

6. The method of Claim 5 wherein the weight gain and/or swelling is used in accordance with the following equation:
y = x.alpha.+.beta.lnx wherein: X = fractional volume percent BAE
Y = fractional percent of the weight gain, or the corrected and/or normalized weight gain,of the rubber matrix .alpha. = coefficient .beta. = coefficient ln = natural logarithm to obtain the fractional volume percent BAE value.

7. The method of Claim 2 or Claim 3 wherein the weight gain and/or swelling is used in accordance with the following equation:
y =x.alpha.+.beta.lnx wherein: X = fractional volume percent AE
Y = fractional percent of the weight gain, or the corrected and/or normalized weight gain, of the rubber matrix .alpha. = coefficient .beta. = coefficient ln = natural logarithm to obtain the fractional volume percent AE value.

8. The method of Claim 2 or Claim 3 wherein the standardized conditions consist of a specific contact time of the rubber matrix with the hydrocarbon composition, a specific amount of the hydrocarbon composition and a temperature within a range of from about 65-80°F wherein the temperature and amount of hydrocarbon composition are the same as those used in obtaining the predetermined aromatic activity of the standard mixture.

9. The method of Claim 1 wherein the rubber matrix consists of a synthetic rubber capable of sorbing aromatic hydrocarbons and which is not readily dissolved by the hydrocarbon compositions.

10. The method of Claim 2 or Claim 3 wherein the rubber matrix consists of a synthetic rubber capable of sorbing aromatic hydrocarbons and which is not readily dissolved by compositions used to establish the predetermined aromatic reactivity of the standard mixture or by the hydrocarbon compositions being tested.

11. The method of Claim 1 wherein the relative aromatic activity is used to determine compliance with process stream specifications defined with respect to aromatic activity.

12. The method of Claim 2 or Claim 3 wherein the AE value is used to determine compliance with process stream specifications defined with respect to AE values.

13. The method of Claim 1 wherein the relative aromatic activity is used to determine the presence of an aromatic impurity in a high purity process stream selected from the group consisting of an aqueous process stream, an aqueous process stream containing dissolved inorganic compounds, an aliphatic hydrocarbon stream and mixtures thereof.

14. The method of Claim 3 wherein the AE value is used to determine the presence of an aromatic impurity in a high purity process stream selected from the group consisting of an aqueous process stream, an aqueous process stream containing dissolved inorganic compounds, an aliphatic hydrocarbon process stream and mixtures thereof.

15. The method of Claim 13 wherein the process stream is an aqueous stream comprised of water.

16. The process of Claim is wherein the relative aromatic activity is used to determine the presence of a dissolved aromatic hydrocarbon contaminant in water comprising:
determining the aromatic activity of the water alone;
determining the aromatic activity of the water being evaluated; and comparing the two aromatic activities to determine the presence of the dissolved aromatic hydro-carbon indicated by the aromatic activity of the water being evaluated being greater than the aromatic activity of the water alone.

17. The method of Claim 13 wherein the process stream is an aliphatic hydrocarbon process stream.

18. The process of Claim 17 wherein the relative aromatic activity is used to determine the presence of an aromatic impurity in a high purity aliphatic hydrocarbon process stream comprising:
determining the aromatic activity of the high purity aliphatic hydrocarbon stream alone;
determining the aromatic activity of the high.
purity aliphatic hydrocarbon process stream being evaluated; and comparing the two aromatic activities to determine the presence of an aromatic impurity indicated by an aromatic activity of the process stream being evaluated which is greater than the aromatic activity of the high purity aliphatic stream alone.

19. The method of Claim 14 wherein the process stream is an aqueous process stream.

20. The process of Claim 19 wherein AE values are used to determine the presence of a dissolved aromatic hydrocarbon contaminant in water comprising:
determining the AE value of the water alone;
determining the AE value of the water being evaluated; and comparing the two AE values to determine the presence of the dissolved aromatic hydrocarbon indicated by the AE value of the water being evaluated being greater than the AE value of the water alone.

21. The process of Claim 14 wherein the process stream is an aliphatic hydrocarbon process stream.

22. The method of Claim 21 wherein the AE value is used to determine the presence of an aromatic impurity in a high purity aliphatic hydrocarbon process stream comprising:
determining the AE value of the high purity aliphatic hydrocarbon stream alone;
determining the AE value of the high purity aliphatic hydrocarbon process stream being evaluated; and comparing the two AE values to determine the presence of an aromatic impurity indicated by an AE value of the process stream being evaluated which is greater than the AE value of the high purity aliphatic stream alone.

23. The method of Claim 1 wherein the relative aromatic activity is used to determine the presence of an aliphatic impurity in a high purity aromatic hydrocarbon process stream.

24. The method of Claim 23 wherein the relative aromatic activity is used to determine the presence of an aliphatic impurity comprising:
determining the aromatic activity of the high purity aromatic hydrocarbon stream alone;

determining the aromatic activity of the high purity aromatic hydrocarbon process stream being evaluated; and comparing the two aromatic activities to determine the presence of an aliphatic impurity indicated by the aromatic activity of the process stream being evaluated being less than the aromatic activity of the high purity aromatic stream alone.

25. The method of Claim 3 wherein the AE value is used to determine the presence of an aliphatic impurity in a high purity aromatic hydrocarbon process stream.

26. The method of Claim 25 wherein AE values are used to determine the presence of an aliphatic impurity comprising:
determining the AE value of the high purity aromatic hydrocarbon stream alone;
determining the AE value of the high purity aromatic hydrocarbon process stream being evaluated, and comparing the two AE values to determine the presence of an aliphatic impurity indicated by the AE value of the process stream being evaluated being less than the AE value of the high purity aromatic stream alone.

27. The method of Claim 1 wherein the aromatic activity is used to determine the compatibility of the hydrocarbon composition within a hydrocarbon mixture.

28. The method of Claim 26 where the relative aromatic activity is used to determine the compatibility of a hydrocarbon composition within a hydrocarbon mixture to formulate a stable product comprising:
determining a range of acceptable aromatic activity by empirically determining the aromatic activity of known hydrocarbon compositions having desired characteristics of the product to be formulated;
determining the aromatic activity of the potential hydrocarbon composition to be incorporated into the hydrocarbon mixture;
selecting the hydrocarbon composition having an aromatic activity within the acceptable range of aromatic activity values; and incorporating the hydrocarbon composition into the hydrocarbon mixture to form a stable product.

29. The method of Claim 3 wherein the AE value is used to determine the compatibility of a hydrocarbon composition within a hydrocarbon mixture.

30. The method of Claim 29 wherein the AE value is used to determine the compatibility of a hydrocarbon composition within a hydrocarbon mixture to formulate a stable product comprising:
determining a range of acceptable AE values by empirically determining the AE values of known hydrocarbon compositions having desired characteristics of the product to be formulated;
determining the AE values of the potential hydrocarbon composition to be incorporated into the hydrocarbon mixture;
selecting the hydrocarbon composition having an AE value within the acceptable range of AE values; and incorporating the hydrocarbon composition into the hydrocarbon mixture to form a stable product.

31. The method of Claim 1 wherein the relative aromatic activity is used to determine the relative toxi-cities of the hydrocarbon compositions.

32. The method of Claim 3 wherein the AE value is used to determine the relative toxicity of the hydro-carbon composition.

33. The method of Claim 31 wherein the relative aromatic activity value is used to determine the toxicities of the hydrocarbon composition comprising:
determining the aromatic activity of the hydrocarbon compositions; and applying a correlation factor to the aromatic activities to obtain the toxicity of the hydrocarbon compositions wherein the correlation factor defines the relationship between the aromatic activities and the toxicity values of hydrocarbon compositions whose toxicities are known.

34. The method of Claim 32 wherein the AE value is used to determine the toxicity of the hydrocarbon composition comprising:
determining the AE value of the hydrocarbon composition; and applying a correlation factor to the AE value to obtain the toxicity of the hydrocarbon composition wherein the correlation factor defines the relationship between AE values and toxicity values of hydrocarbon compositions whose toxicities are known.

35. The method of Claim 31 wherein the relative aromatic activity is used to determine the threshold limit values (TLV) of the hydrocarbon compositions comprising:
determining the aromatic activity of the hydro-carbon compositions; and applying a correlation factor to the aromatic activities to obtain the TLV values of the hydrocarbon compositions wherein the correlation factor defines the relationship between aromatic activities and TLV values of hydrocarbon compositions whose TLV values are known.

36. The method of Claim 32 wherein the AE value is used to determine the threshold limit value (TLV) of a hydrocarbon composition comprising:

determining the AE value of the hydrocarbon composition; and applying a correlation factor to the AE value to obtain the TLV value of the hydrocarbon composition wherein the correlation factor defines the relationship between AE values and TLV values of hydrocarbon compositions whose TLV values are known.

37. The method of Claim 14 wherein the AE value is a benzene aromatic equivalent.

38. The method of Claim 29 wherein the AE value is a benzene aromatic equivalent.

39. The method of Claim 34 wherein the AE value is a benzene aromatic equivalent.

40. The method of Claim 36 wherein the AE value is a benzene aromatic equivalent.