US2869994A - Fuel gas composition containing odorant - Google Patents

Description

1959 A. D. NEVERS ETAL 2,869,994-

FUEL GAS COMPOSITION CONTAINING ODORANT Filed Aug. 21, 1956 FIGURE l THRESHOLD ODOR RANK RATIO DIMET HYLTHIOXANE/SPOTLEAK I008 i DIMETHYL THIOX g X I b4 ODOR RANK RATIO I SPO'ILEAK I008 ODORANT GONG. ROTAMETER READING) FIGURE 2 THRESHOLD ODOR RANK RATIO DIMETHYLTHIOIXANE/ SPOTLEAK I008 ODORANT CONC. (ROTAMETER READING) INVENTORS ASHLEY D.NEVERS EDWARD M. FETTES [Re-60116. 0 m ATTORNEY United States Patent Application August 21, 1956, Serial No. 605,415

Claims. (Cl. 48-195) This invention is directed to odorized gas mixtures. More particularly, this invention is directed to commercial fuel gas compositions containing small amounts of dialkyl p-thioxanes as gas warning agents. The gas warning agents are added to gases having insuflicient odors of their own, the purpose being to make the gases detectable in the atmosphere at lower than toxic or explosive concentrations.

The advantages and objects of the present invention will be seen from the following description taken in conjunction with the drawings in which Figures 1 and 2 are a graphical representation of the threshold odor rank ratio of dimethyl thioxane compared to a commercial fuel gas odorant Spotleak 1008 under two test conditions.

Gases which require odorization for their commercial use include natural gas, manufactured gas, mixtures of natural gas with manufactured gas, coke oven gas and liquefied petroleum'gas. An odorant is not norin most instances a characteristic odor. some cases it is desirable to increase or modify the odor .of manufactured gas for special purposes or when it is admixed with another gas of low odor content.

There are many chemicals possessing sharp, pungent or foul odors which one might expect would make excellent gas odorants. Usually, this is not the case. A

gas odorant should have many special properties in addition to being merely odoriferous.

.mally employed with manufactured gas since this gas has However, in

2,869,994 Patented Jan. 20, 1959 A good gas odorant should have a high threshold rank ratio, a high impact rating and a persistent warning character when diluted with air. Other related proper ties which a good gas odorant should have are low toxicity, a sufficiently high vapor pressure to permit easy volatilization into a gas stream and inertness to the surroundings. In regard to the latter the odorant must be substantially unreactive with the components of the gas with which it is carried under use conditions. -Also, the water solubility should be quite low in order that the odorant is not washed out of the odorized gas by water in gas mains and gas holders.

We have now discovered that dialkyl p-thioxane when incorporated in commercial fuel gases provide compositions having valuable warningor alarm properties. Generally, the dialkyl substituents of p-thioxane useful in our invention are the methyl, ethyl, n-propyl and isopropyl substituents. The alkyl substituents may be identical as they are in dimethyl p-thioxane or they may be of mixed dialkyl groups such as methyl ethyl p-thioxane. Moreover, the term dialkyl thioxane is intended to refer to anyone or a mixture of the 2-5, 3-5 and 2-6 isomers of dialkyl p-thioxane. It is to be understood that the term dialkyl p-thioxane as used throughout this specification and the claims refers to alkyl substituted p-thioxanes as defined in this paragraph.

While the various alkyl substituents of p-thioxane of 1 to 3 carbon length are useful gas odorants for making the new compositions of our invention, we prefer to use the dimethyl p-thioxane because of its distinctive and intense odor.

Small quantities of dimethyl p-thioxane when incorporated into natural gas, mixtures of natural gas and manufactured gas, blast furnace gas and liquefiedpetroleurn gas provide new compositions which are useful to gas producers and distributors.

The proportion of dimethyl p-thioxane required to im-' part a noticeable odor to a substantially odorless gas or gas-air mixture is extremely minute. As. indicated; in

Tables 1 and 2 below, 0.037 pound per 100,000,000 cubic Table 1 Lbs. Percent A B C D E Average .Rotomeodorant] odorized Odor Rank Sequence ter 10 0 gas in Reading gas-air air Odor rank ratio (computed from Figure 1): 1.4. (1) Refers to Spotleak 1008. (2) Refers to dimethyl thioxane. A, B, 0, D, E refer to observers.

Table 2 Lbs. Percent A B C D E Average Rotomeodorant] odorized Odor Rank Sequence ter 10' OF gas in Reading gas-air air 1 mix I l .01 0. 037 0.031 1, 1 1 l. 2 1-, 1 2, 1 1, 1 2, 2 0. 50 1. 25 02 0.074 0. 060 1--,l 1,1 2, 2 1 1, ,2 1, 2 1, 1 2, 2 0. 85 1. 2G .04 0.148 0.12 2, 1 2, 2, 2 2, 2 2, 1 1, 1 1, 2,1 2, 2 2, 2 1. l. .05 0. 100 0. 16 2, 2, 2 2, 2 2, 2 2, 2 2, 2 1, 2 2, 2 1, 1 2, 2 1. '70 2.00 .07 0.259 0. 22 2-, 1, 2, 2 2, 2 1 1, 1 2,1 1, 1 2, 2 2, 2 1. 35 1. 30 10 0.40 0.33 2,2 2,2 2, 2 2, 2 1,2 2,2 2, 1 2, 2 1,2 2,2 1. 2.00 15 O. 60 0. 50 2, 2 2,- 2, 2 2, 2 2, 1 2, 2 2, 2 2, 2 2, 2 2, 2 1. 1.80

Odor rank ratio (computed from Figure 2): 1.6. (1) Refers to Spotleak 1008.

(2) Refers to dimethyl thloxano.

A, B, O, D, E refer to observers.

and gas holders.

feet of the gaseous mixture was at least perceptible to guard against, explosions it is'important to maintain sufficient odorant in .the gas to be definitely detectable in gas-air compositions which. are below the lower explosive unit. in this connection it is generally considered satrs- "factory if a warning odor exists at a dilution of one volume of odorized gas with about 100 volumes. of air. A fuel gas, such as natural gas, when mixed with as little as 0. 04 pound of dimethyl p-thioxaneper million cubic feet has a distinctive odor which is strongly ap parent to people of good olfactory perception even when the gas is diluted to 1% in air and is noticeable to most people at this safe dilution. Thus, a fuel gas so odorized is far less hazardous for distribution and use than the unodorized gas.

'In general, however, it is desirable from the stand point of safety from explosions to use higher concentrations of dimcthyl p-thioxane and a concentration of at least 0.2 poundpenmillion cubic feet of fuel gas is preferred. All gas volumes mentioned herein are at standard temperature and pressure unless otherwisespecified.

Thedirnethyl p-thioxane is compatible with other gas odorants normally encountered, and itisentirely'feasiblc to use it in conjunction with one or more other odorants.

Such odorant mixtures may be blended prior to introduction into the'fuel gas, or may be introduced separately into the gas whereby .vapor phase mixing takes place due to the turbulence and convection currents of the gas stream. Thus, dimethyl p-thioxane may be introduced into preodorized gas from a transmission line in order to suitably adjust the odor level and quality for local distribution. In such event and in other situations involving supplementary odorization, the concentration of dime'thyl p-thioxane required in the gas will naturally be less than when it constitutes the sole odorant.

Dimethyl 'p-thioxane'may be used if desired at unusually high concentrations in fuel gas, for example, at 5 pounds per million cubi feet, without causing difficulties of physical or chemical nature, such as corrosion or condensation. For ordinary purposes of leak etec tion andwa'rning of explosion hazard in fuel gas transmission and distribution systems, however, it is almost never necessary to exceed two pounds per million cubic insoluble in .vater and is not scrubbed out of the gas by' liquid water with which it comesin contactin pipelines Thus, it is resistant to fadingfa serious defect of many existing gas odorants under certain conditions of gas composition and flow. It is thereforepossible by use of dimethyl p-thioxane to maintain -p-thioxane is also useful in toxic fuel gases wherein its concentration may be maintained at a suificient level to provide warning of the presence of a detrimental concentration of toxicant in the atmosphere. For example, dinrethyl p-thioxane may be incorporated into a coke oven gas containing carbon monoxide. The concentration in the toxic gas of dimethyl p'thioxane required for adehave an extremely low threshold concentration.

1i quate warning will of course depend upon the degree of'toxicity of the gas which in turn depends upon the kind and amount of toxicant present. Blast furnace gas as ordinarily produced in steel mills may contain about 30% carbon monoxide, and about 2 pounds of dimethyl p-thioxane per million cubic feet of such gas will sufiice for adequate warning. However, much higher concentrations ofdirnethyl pithioxane may be incorporated into a toxic fuel gas, such ,asfive pounds or more per million cubic feet without detriment to the usefulness of the gas or harm to the equipment. The use of such high proportions of our odorant may be desirable in particular circumstances.

When dimethyl p-thixane is added to gaseous fuels in a an amount of at least 0.2 pound per million cubic feet,

the maingas streamwhereby contact with gasstream causes it to vaporize and mix uniformly with the'gas stream. A second method known as by-pass odorization involves passing .a predetermined minor fraction of the gas stream to be odorized over a pool of liquid odorant ventional expedients in the art and any type of odorizing equipment can be used. In the case of liquified petroleum gas (LPG) the odor-ant in liquid form is normally dissolved in the liquid hydrocarbon.

Another characteristic of dimcthyl p-thioxane useful in gas odorant application is its low order of toxicity. Moreover, the combustion products of dimethyl p-thioxaneand a gaseous fuel are non-toxic and non-irritating at the concentrations normally encountered in fuel odorization.

Probably, the .most important requirement of a gas odorant is that it beperceptible in gas-air mixtures at extremely low concentrations; that is, that the odorant The threshold concentration is that concentration of the odorant in a gas which is-barely perceptible to a human observer.

Since human observers are widely different in then perception of odors,.and moreover, since the same individual will varysfrom day to day, the practical method in measuring threshold concentrations requires a statistical analysis of many human observations.

Odorants of relatively high threshold concentration sufierthe disadvantage of high cost per unit volume of gas odorized and excessive bulk of odorant material to be handled, and in the case of sulfur containing odorants, excessive contribution of sulfur to the gas itself. A high sulfur concentration leads to corrosion of equipment and sulfur dioxide odor upon combustion.

odor intensity. 'Our experimental procedure is described below.

An odorized gas-air mixture of known and controlled odorant concentration is prepared in an apparatus which permits adjustment, both of the odorant concentration in the gas and of the concentration of odorized gas inair. The odorous mixture thus prepared is presented to an observer through a funnel-shaped opening. The observer sniffs the mixture and, upon request, may also sniff unodorized air for reference purposes. The observer then reports his olfactory reaction by one of three designations:

(-) No perceptible difierence from purified air;

(1) Barely perceptible difference from purified air; and

(2) Definite perception e. g. sufiicient to permit characterization of odor type. 1

Similarly, tests are run at other selected concentrations, suitably spaced, over the entire gamut of concentrations under consideration. The lowest concentration submitted to the panel is always zero, the highest is normally the concentration at which substantially all observers report 'a definite odor perception (value of 2 as defined above). For improved precision a duplicate set of observations are made after the first set has been completed. Following the collection of the above data, the arithmetical average values of the observations for each concentration are calculated.

In computing the arithmetical averages the No perceptible difference observation is given a numerical value of zero while the 1 and 2 observations are given the value of 1 and 2. respectively. These average odor ranks for dimethyl p-thioxane and for Spotleak 1008, a high intensity commercial odorant, are presented in the last two columns of Tables 1 and 2 above representing two different series of tests spaced several weeks apart. In the tables Sequence represents the order in which the concentrations are presented to the observers. The capital letters represent the different observers.

These average odor rank values are then plotted against the log of the concentrations to which they pertain, and the best fitting straight line is drawn through the points. Any convenient units of concentration may be used in making this plot, providing only that the same units are used for each of the two odorants being compared. In Figures 1 and 2 the concentrations plotted are the rotometer readings which in this case are directly proportional to the concentration of the odorant in the gas-air mixture as presented to the observers.

The resulting curve is used to compute the threshold odor rank ratio relative to a selected control or comparison odorant. This is accomplished by repeating the entire procedure as given above except that a control odorant is substituted for the test odorant. By this procedure the straight line showing the odor rank versus log of the concentrations for the said control odor ant is determined. The threshold odor rank ratio of the test odorant, in this instance, dimethyl p-thioxane, in comparison with the control odorant, in this instance, Spotleak 1008, is determined readily from the respective odor rank curves discussed above. For this purpose these curves are plotted on the same graph as in Figures 1 and 2, and the desired ratio is the numerical value of the average odor rank of dimethyl p-thioxane at the concentration for which Spotleak 1008 has an average odor rank of 1. Thus, in Figure 1 said ratio is about 1.4, in Figure 2 about 1.6.

The threshold odor rank ratio thus compares the odor intensity of the test odorant as compared to a comparative odorant at the concentration when the comparative odorant is barely distinguishable from purified air. As seen in Figures 1 and 2 the odor of dimethyl p-thioxane was found to be 40 and 60% more intense 6 thantho'se'of Spotleak '1 008at the threshold concentration for Spotleak 1008.

All observations ofthe test odorant and the control odorant in one series are made on the same day in order that various extraneous factors such as humidity of the reference air are minimized.

Another comparison using the procedure described above was made with four observers making duplicate observations at each of seven concentrations employed. Dimethyl p-thioxane was compared with tetrahydrothio phene and Spotleak 1008both of them being'high intensity commercial gas odorants. The average odor ranks of this test series are presented in Table 3.

Table 3 Average Odor Rank Concentration (arbitrary units) THIP (tetrahy- Spotleak Dimethyl drothio- 1008 p-thioxane phene) Again, the superiority of dimethyl p-thioxane over the two reference odorants was outstanding at the lower concentrations. The concentration and odor rank figures are the same as described in Tables 1 and 2.

Dimethyl p-thioxane may be prepared by the method of Harman and Vaughn described in U. S. 2,562,145, granted July 24, 1951, or it may be prepared by the reaction of dichloroisopropyl ether with alcoholic sodium sulfide as described in J. A. C. 8., vol. 57, p. 1696. The pure compound has a sulfur content of 24.28% and boils at 162 C.

Commercial dimethyl p-thiox'ane contains minor amounts of impurities such as unreacted dichloroisopropyl ether and a seven membered saturated heterocyclic compound containing one oxygen, four carbon and two sulfur atoms, the latter being at the 4,5 ring positions. Since this latter compound possesses useful gas odorant characteristics, its presence in dimethyl p-thioxane is not at all detrimental. The sulfur content of commercial dimethyl p-thioxane ranges from 25 to 33% while the chlorine content will range from 0 to 3%.

While the above discussion and examples have been specific to dimethyl p-thioxane, it is to be understood that the discussion and examples are equally applicable to the dialkyl-p-thiox-anes in which the alkyl substituents are of 1 to 3 carbon content.

Examples of other dialkyl-p-thioxanes useful in practicing our invention were presented earlier in this specification.

We claim:

1. The composition comprising a member of the group consisting of natural gas, mixtures of natural gas and manufactured gas, coke oven gas and liquefied petroleum gas and at least 0.04 pounds dialkyl p-thioxane per million cubic feet of the said gas, the alkyl substituents of the said dialkyl p-thioxane being limited from 1 to 3 carbon atoms.

2. The composition of claim 1 in which the alkyl substituents are identical- 1 3. The composition of claim 2 in which the alkyl substituents are methyl.

4. The composition comprising natural gas and at least 0.04 pounds of dialkyl p-thioxane per million cubic feet of natural gas in which the alkyl substituents are limited from, 1 to 3 carbon atoms.

5. The composition of claim 4 in which the dialkyl p-thioxane is present at a concentration of from 0.04

pound :to :510 ppounds :perQmillion :eubic :ieet :of the said natural gas.

16. The composition -;of :claim 5 .in which the :alkyl substituents are .methyl.

7. The composition -of vclaim .5 in which the valkyl substituents are methyl.

8. The process of odorizing a, member of the group consisting of natural gas, mixtures of natural and manufactured gas, coke oven: gas and liquefied ;petroleum:gas comprising introducing an odor perceptible quantity, of clialkyl p-thioxane ,into thesaid gas, the -,-alky1 ,zsubstitucuts of the said dialkyl .p-thioxane being limited from 1 to 3 carbon :atoms.

9. The process of odorizing natural gas comprising introducing an odor perceptible amount of dialkyl p-thioxane into the said gas, the alkyl substituents of the dialkyl p-thioxane being limited from 1 to 3 carbon atoms.

1.0. Ihepmcess .of-claim -,9,:ina-whieh;the'concentration of the dialkyl p-thioxane is at least 0.04 pound per-million cubic feet of natural 7 gas.

11. The :process ofrclaim 8;in whiehthedialkyl-p-thi- Duane is dimethyl p-thioxane.

,12. The process of claim 9 in which the dialkyl p-thiexane is dimethyl p-thioxane.

113. The comp.osition of claim .1111 which :thediallfyl p-thioxaneisipresent in the 17ange..of' fr.om'0.04 to 5.0 pounds per vmillion cu bic;;feet,of the-gsaid, gas.

14. The. process ,of claim -8 in -which the :quantity "of dialkyl p-thioxane introduced into the .said gas;.ranges from 0.04 to 5.0 pounds per million cubic feet of gas.

15. The process of claim 14 .in which the dialkyl pthioxane is ;dimethyl p-thioxane.

No references cited.

Claims (2)

1. THE COMPOSITION COMPRISING A MEMBER OF THE GROUP CONSISTING OF NATURAL GAS, MIXTURES OF NATURAL GAS AND MANUFACTURED GAS, COKE OVEN GAS AND LIQUEFIED PETROLEUM GAS AND AT LEAST 0.04 POUNDS DIALKYL P-THIOXANE PER MILLION CUBIC FEET OF THE SAID GAS, THE ALKYL SUBSTITUENTS OF THE SAID DIALKYL P-THIOXANE BEING LIMITED FROM 1 TO 3 CARBON ATOMS.

8. THE PROCESS OF ODORIZING A MEMBER OF THE GROUP CONSISTING OF NATURAL GAS, MIXTURES OF NATURAL AND MANUFACTURED GAS, COKE OVEN GAS AND LIQUEFIED PETROLEUM GAS COMPRISING INTRODUCING AN ODOR PERCEPTIBLE QUANTITY OF DIALKYL P-THIOXANE INTO THE SAID GAS, THE ALKYL SUBSTITUENTS OF THE SAID DIALKYL P-THIOXANE BEING LIMITED FROM 1 TO 3 CARBON ATOMS.

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