US3404971A

US3404971A - Odorization of combustible hydrocarbon gases

Info

Publication number: US3404971A
Application number: US446740A
Authority: US
Inventors: Sven A Olund
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1965-04-08
Filing date: 1965-04-08
Publication date: 1968-10-08
Anticipated expiration: 1985-10-08

Description

United States Patent ABSTRACT or THE DISCLOSURE A warning agentfor odorization of gaseous hydrocarbon fuels, based on mixtures of ethane dimercaptan with a monomercaptan or a sulfide.

This application is a continuation-in-part of application S.N. 173,832, filed Feb. 16, 1962, now abandoned.

The present invention relates to mixtures of Organic sulfur compounds suitable for the odorization of combustible hydrocarbon gases, such as natural gas, vapors and gases recoverable in the refining of petroleum, and other gases suitable as fuels for heating, illuminating and cooking purposes.

More particularly, the invention is directed to combustible gases suitable as fuels for heating, illuminating and cooking uses, and ordinarily having no marked inherent odor, which contain vaporized therein a small quantity of a mixture of organic sulfur compounds possessing a specific and persistent odor serving to warn of the escape of the combustible gas from containers, trans mission lines or fixtures and, consequently, serving to warn of the danger of explosion and asphyxiation.

A number of organic sulfur compounds are known to be elfective malodorants for combustible gases. These includ monomercaptans, and acyclic and cyclic sulfides. Specific examples of these compounds, in which percentages are by weight, are the following:

( 1) Thiophane,

herein referred to as Odorant A.Sometimes a small amount of some additive, such as to prevent freezing, is included. In some instances thiophane is admixed with a diluent, such as V.M. & P. naphtha, in an amount, for example, of about 50%, and used diluted.

(2) Refinery by-product mercaptans, herein referred to as Odorant B.These are characterized by a boiling point range of about IOU-215 F. and comprise C C mercaptans. Traces of C mercaptans are sometimes present. Typically, this odorant contains 25% ethyl mercaptan, 35% isopropyl mercaptan, 1 5% n-propyl mercaptan, 20% sec.-'butyl mercaptan, 3% isobutyl mercaptan, and 2% n-butyl mercaptan, although they can be present, respectively, within ranges of about 1 to 30; 15 to 50; 5 to 25; to 30; 1 to 6; and 1 to 4.

(3) Mixed aliphatic sulfides of low molecular weight.- One alkyl group may be ethyl and the other group, ethyl, propyl, or butyl. These compounds often contain a small amount, e.g., about 5%, of refinery by-product mercaptans Odorant B, herein referred to as Odorant C, although an amount as high as 10% hy-product mercaptans can be present. A further specific example of mixed sulfides is a mixture of diethyl sulfide and ethyl propyl sulfide. See US. Patent No. 2,823,104.

A mixture of aliphatic acyclic, straight; and branchedchain hydrocarbons with an ASTM distillation of 245 F, to 300 F.

3,404,971 Patented Oct. 8, 1968 (4) t-Butyl mercaptan.Often contains refinery byproduct mercaptans (Odorant B) in an amount of 15 to 50%, 'based on the two. A mixture of the two, herein referred to as Odorant D, in which the refinery mercaptans are present in amount of about 20%, the mixture having a boiling point range of about 132-185 F. is given as a preferred example.

(5) A mixture of dimethyl sulfide and the refinery byproduct mercaptans (Odorant B), in proportions, for example, of 90% dimethyl sulfide and 10% mercaptans, herein referred to as Odorant E.--As little as 5% to as high as 60% mercaptans may be present.

It has now been found that the odor intensity of the above conventional malodorants can be increased by the incorporation in them of a small amount of ethane dimercaptan having the formula HSCH CH SH, ranging from about 1, preferably around 5%, to 20%, preferably about 15%, by weight, based on ethane dimercaptan and malodorant, referred to as base odorant. For example, a mixture of 15% ethane dimercaptan and thiophane used in a dosage of 0.3 pound per million cubic feet (m.c.f.) of hydrocarbon gas has the same odor intensity as thiophane alone used at a dosage level of 1 pound per million cubic feet of the same hydrocarbon gas, indicating a threefold improvement.

The method of mixing the conventional or base odorant and the odor-boosting ethane dimercaptan is not critical. Since these materials are low-boiling liquids, one or the other can be added to the other in the indicated proportions, i.e., in a manner applicable to the mixing of any compatible liquids.

To show the odor-boosting effectiveness of the odorant mixture of the present invention, determinations were made according to the so-called Walk-in Room Test, the test utilized in the following tabulated examples.

According to this test, odor intensity is determined by a panel of at least five persons, preferably ten or more, according to the scale hereinbelow Set forth.

A room with a volume of approximately 1500 cubic feet is used. The room has facilities for ventilation between tests and is free from any significant air movement during the tests. No odor other than that of the warning agent being tested is present during the test.

A 3.2 ml. of ethanol solution of the odorant is then vaporized into the room, the vaporization taking not more than 5 minutes to occur. The odorant concentration in the 3.2 ml. solution is such as to give a concentration equivalent to that obtained from odorized gas (methane) diluted to 1% gas in air. Thus, at a concentration corresponding to one pound odorant per 1,000,000 cubic feet gas and one volume percent gas concentration in the room, the ethanol solution will contain 2.13 g. odorant per liter of solution.

The person vaporizing the odorant does not participate in rating the samples to be tested, and at least 15 minutes is allowed between each test to allow the olfactory nerve to recover. After vaporization into the room, a five-membered or larger odor panel rates odor intensity of the compositions according to the following scale:

Odor intensity: Rating No odor 0 Barely noticeable 1 Easily noticeable 2 Strong 3 various odorants alone and of odorant compositions containing the indicated proportions of ethane dimercaptan are given. The odor intensity determinations were made using the indicated amounts of ethane dimercaptan and base odorant, the letters corresponding to those already given in identifying the base odorant.

TABLE I.EFFECT OF ETHANE DIMERCAPTAN ON ODOR INTENSITY OF NATURAL GAS ODORANTS Odorant composition Example Average No. Base Odorant Ethane Rating Dimercaptan I Type GmsJliter (gm/liter) A 2. 13 1. 9 A 2.02 0. 11 2. A 1. 81 0.32 2. 7 B 2. 13 0 2. 3 B 2.02 0. 11 2. 7 B 1. 81 0.32 2. 8 C 2. 13 0 1.8 C 2. 02 O. 11 2. 1 C 1. 81 0. 32 2. 3 D 2. 13 0 2. 2 D 2.02 0. 11 2. 4 D 1. 81 0.32 2. 6 E 2. 13 0 1. 9 E 2. 02 0. 11 2. 2 E 1. 81 0.32 2. 7

On the basis of the work of Katz et al., ethane dimercaptan at a concentration equivalent to one pound in one million cubic feet of gas (methane) diluted to one percent in air gives a rating on the same basis as Table I, of 1.1; and a rating of 0, at concentrations of 0.11 and 0.32. However, the odor-boosting effect of ethane dimercaptan is clearly evident. To illustrate: when a small amount (about 5%) of ethane dimercaptan is added to thiophane (Example la), odor intensity is markedly increased. Increasing the amount of ethane dimercaptan to about 15%, further enhances odor intensity (Example lb); yet these amounts of ethane dimercaptan used alone are reportedly ineffective. Similar results as shown in the table are obtained with the other base odorants.

The tabulated experiments below further show the effectiveness of the malodorant compositions of the present invention as compared with base odorant without the odorant booster.

TABLE II.QUANTITY OF MIXED ODORANT REQUIRED TO GIVE THE SAME ODOR INTENSITY AS ONE POUND OF BASE ODORANT IN ONE MILLION CUBIC FEET OF NATURAL GAS Pounds of mixed odorant per million cubic feet of gas Base odorant 95% base odorant, 5% 85% base odorant, 15% ethane dimercaptan ethane dimercaptan The data in the table indicate that compositions prepared in accordance with the invention are equally efiective, although used in smaller quantities, as untreated base odorant used in larger quantities. For example Odorant E (dimethyl sulfide-mercaptans) when containing 5% and 15% ethane dimercaptan is just as effective in quantities of 0.5 pound and 0.2 pound, respectively, as 1 pound of untreated Odorant E.

The malodorant mixture herein described is eminently suitable for use in combustible gases, such as natural gas used in the home or in industry for cooking or illumination. It possesses a distinctive odor, thereby providing a 2 Bureau of Mines Technical Paper 480, Intensities of Odors and Irritating efiects of Warning Agents for Infiammaole and Poisonous Gases (1930).

timely warning of escaping gas, even th oughpresen't in sm all concentration. Although effective, the rnalodorant of the present invention is not so offensive that users of the combustible gas object to its presence. Further, it is odorless when burned. The malodorant mixture herein described in the amounts used does not cause any objectionable skin irritation, lachrymation, or other harmful physiological effects. Finally, with the .present malodorant composition, a gradual cumulationof odor intensity does not cause olfactory fatigue to the extent some other odorants do. I T

Iclaim:

1. A warning agent suitable for the odorization of gaseous hydrocarbon fuels, said agent consisting essentially of a mixture of ethane dimercaptan. and a gas odorant selected from the group consisting of monomercaptans, acyclic and cyclic sulfides, said ethane dimercaptan being present in said mixture in an amount, by weight, based on said mixture, ranging from about 120%.

2. A warning agent as defined in claim 1, wherein the gas odorant is thiophane.

3. A warning agent as 'defin'ed in claim 1, wherein the gas odorant is a mixture of C -C aliphatic monomercaptans having a boiling range of about IOU-215 F.

4. A warning agent as defined in claim 1, wherein the gas odorant is a mixture of low molecular weight sulfides.

5. A warning agent as defined in claim 1, wherein the gas odorant is dimethyl sulfide. 1

6. A warning agent as defined in claim 5, wherein there is present in addition a minor amount of.C C monomercaptans having a boiling range of about 2l5 F.

7. Process for the odorization of a hydrocarbon fuel gas which comprises incorporating in said gas from about 0.3 to 1 pound. per one million cubic feet of said gas of a warning mixture consisting essentially of ethane dimercaptan and a gas odorant selected from the'group consisting of monomercaptans, acyclic and cyclic sulfides, said ethane dimercaptan being present in said warning mixture in an amount, by weight, based on it and gas odorant, ranging from about 120%.

8. Process according to claim 7, wherein the ethane dimercaptan is present in amount of 515%.

9. Process according to claim 8, wherein the gas odorant is thiophane.

10. Process according to claim 8, wherein the gas odorant is a mixture of C -C aliphatic monomercaptans having a boiling range of about 100-215 F.

11. Process according to claim 8, wherein the gas odorant is a mixture of low molecular weight sulfides and a minor amount of C -C monomercaptans having a boiling range of about 100-2l5 F. I

12. Process according to claim 8, wherein the gas odorant is a mixture comprising dimethyl sulfide and a minor amount of C -C monomercaptans having a boiling point range of about 100215 F.

References Cited UNITED STATES PATENTS 2,402,456 6/1946 Signaigo 260609 X 2,823,104 2/1958 McClure 48195 2,935,391 5/1960 Evans et al. 48l95 OTHER REFERENCES Katz et al.: Bureau of Mines Technical Paper 480', Intensities of Odors and Irritating Effects of Warning Agents for Inflammable and Poisonous Gases, pages 7-9, 12-27, 33, 34 1930).

JOSEPH SCOVRONEK, Primary Examiner.