CA2209334A1

CA2209334A1 - Method for reducing odorant depletion

Info

Publication number: CA2209334A1
Application number: CA002209334A
Authority: CA
Inventors: Ali Naraghi
Original assignee: Champion Technologies Inc
Current assignee: Champion Technologies Inc
Priority date: 1996-07-10
Filing date: 1997-06-30
Publication date: 1998-01-10
Also published as: EP0818651A2; MX9705232A; US5746973A; EP0818651A3

Abstract

Odorant depletion is reduced by passivating the internal surface of LP-gas transportation and storage vessels by the addition of passivating agents comprising mixtures of corrosion inhibitors such as phosphate esters, fatty amines, poly amides, imidazolines, poly imidazolines quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, ethoxylated fatty amines, ethoxylated polyamides, ethoxylated alcohols and mixtures thereof in one or more solvents. In a preferred embodiment, the passivating agents contain one or more phosphate esters defined by the equation:

[R-X-[CmH2mO)n]k-PO(OH)(3-k) where;
R is an alkyl group containing 4 to 18 carbon atoms or an alkylaryl group comprising an aryl group selected from the group consisting of phenol, diphenol, and mixtures thereof, and an alkyl group containing 4 to 18 carbon atoms;
X is selected from the group consisting of a carboxyl group (-COO-), oxygen (-O-), a secondary amine group (-NH-) and mixtures thereof;
m is an integer having a value from about 2 to about 4;
n is an integer having a value from about 4 to about 20; and k is an integer having a value from 1 to 2 and one or more fatty amines, poly amides, imidazolines, poly imidazolines, quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, ethoxylated fatty amines, ethoxylated polyamides, ethoxylated alcohols or mixtures thereof and one or more solvents.

Description

METHOD FOR REDUCING ODORANT DEPLETION
EIELD OF THE INVEN~ION
This invention relates to a method for reducing odorant depletion during transfcr and storage of liquefied petroleum gas.

BACKGROUND
Liquefied petroleum gas (LP-gas), which consists primarily of propane with small amounts of lighter and heavier hydrocarbons, is customarily odorized with ethyl mercaptan or other mercaptan-based compounds so that escaping gas can be detected.
The distribution of propane from tlle producer where the odorant is injected to the ultimate consumer may require the propane to be transrerred several timcs in and out of different transportation and storage vessels that are typically made of steel.
Since approximately 1986, it has been recognized that mercaptan-based odorants may be depleted during transportation and/or storage, a phenomenon sometimes refen-ed to as "odor fading." This depletion may occur through oxidation of the odorant compound to a sulfide, or possibly through chemical adsorption at the metal surface inside LP-gas transportation or storage vessels.
Attempts have been made to counteract odorant depletion. For example, U.S. Patent No.
3,669,638 is directed to a method for delivery of a constant dose of odorant wherein odorants are added from an enclosed container through a permeable membrane over selected time periods.
U.S. Patent 3,826,631 is directed to an odorant composition that includes an azeotropic mixture of an organic sulfur odorant and at least one re!atively non-odorous, chemically inert material capable of forming a minimum boiling point azeotrope with the organic sulfur odorant.

SUMMARY OF TI-IE INYEN~ION
According to the present invention, odorant depletion is reduced by passivating the internal surface of LP-gas transportation and storage vessels by the addition of passivating agents designed to create a protective film on the surface of the vessel. The term "passivation," as used herein, means the temporary rendering of the internal surface of a vessel less reactive to the odorant than an unpassivated vessel.
Passivation of the internal surface of the vessels can be accomplished by a "fill-up treatment" method wherein the vessel is completely filled with the selected passivating agent and/or by an "additive treatment" method wherein a passivaling agent that is dispersible, or more preferably soluble, in propane is added directly to thc LP-gas along with the odorant in amounts sufficient to provide a concentration of the selected passivating agent in the range of up to about 2S0 ppm (v/v).
The passivating agents, which may be water soluble or may be dispersible or soluble in LP-gas, comprise blends of corrosion inhibitors such as phosphate esters, fatty arnines, poly amides, imidazolines, poly imidazolines, quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, ethoxylated fatty amines, ethoxylated polyamides, ethoxylated alcohols and the like or mixtures thereof in one or more solvents. Suitable solvents include, but are not limited to, water, glycol ether, heavy alcohols such as butanol, hexanol and the like, and aromatic solvents such as xylene, toluene and the like. In a preferred embodiment, the passivating agents contain one or more phosphate esters, and, in a more preferred embodiment, contain one or more phosphate esters defined by the equation:

[R~~~[CmH2m~)n]l;~Po(oH)(3 k) where;
R is an alkyl group containing 4 to 18 carbon atoms or an alkylaryl gro;lp comprising an aryl group selected from the group consisting of phenol, diphcnol, and mixtures thereof, and an alkyl group containing 4 to 18 carbon atoms;
X is selected from the group consisting of a carbo~cyl group (-COO-), oxygen (-O-), a secondary amine group (-NH-) and mi~tures thereof;
m is an integer having a value from about 2 to about 4;
n is an integer having a value from about 4 to about 20; and k is an integer having a value from I to 2 and one or more fatty amines, poly amides, imidazolines, poly imidazolines, quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, ethoxylated fatty amines, etho~ylated polyamides, etho~cylated alcohols or mixtures thereof and one or more solvents.
Treatment of LP-gas transportation and/or storage vessels in the manner described herein reduces odorant depletion. Moreover, the passivating agents are not carried o-lt of the tank by the release of the propane gas.
These and other features and advantages of the present invention will become apparent from the following detailed description, which is given by way of illustration only.

BRIEFDESCRIPTION_OF THEDRAWINGS
F1GURE 1 represents the ethyl mercaptan (EM) concentrations of passivating agents AN-1-76B, AN-1-76C, AN-1-76D, AN-1-761~ and the blank in the vapor phase in a 250 gallon tank , CA 02209334 1997-06-30 over a 26 week period.
FIGURE 2 represents the ethyl mercaptan (EM) concentrations of passivating agents AN-1-76B, AN-1-76C, AN-1-76D, AN-1-76I; and the blank in thc vapor phase in a 120 gallon tank over a 26 week period.
FIGURE 3 represents the ethyl mercaptan (EM) concentrations of passivating agcnts AN-1-76B, AN-1-76C, AN-1-76D, AN-1-76F and the blank in the vapor phase in a 25 gallon tank over a 26 week pcriod.
FIGURE 4 represents the ethyl mercaptan (EM) concentrations of passivating agents AN-1-76B, AN-1-76C, AN-1-76D, AN-1-76F and the blank in the vapor phase in a S gallon tank over a 26 week period.
FIGURE S represents the ethyl mercaptan (EM) concentrations of passivating agent A~i-1-76C in the liquid phase in a 250 gallon tank over a 26 week period.
FIGURE 6 represents the ethyl mercaptan (EM) concentrations of passivating agent AN-1-76C in the liquid phase in a 120 gallon tank over a 26 week period.
FIGURE 7 represents the ethyl mercaptan (EM) concentrations of passivating agent A~l-1-76E in the liquid phase in a 250 gallon tank over a 26 week period.
FIGURE 8 represents the ethyl mercaptan (EM) concentrations of passivating agent AN-I -76E in the liquid phase in a 120 gallon tank over a 26 week period.

DETAILED DESCRIPTION
According to thc present invention, odorant depletion is reduced by passivating the internal surface of LP-gas transportation and storage vessels by the addition of passi~ating agents designed to create a protectivc film on thc surface of the vessel. Passivation of the internal surface of the vessels can be accomplished by a "fill-up treatment" method wherein the vessel is completely filled with the selected passivating agent and/or by an "additive treatment" method wherein a passivating agent that is dispersible, or more preferably soluble, in propane is added directly to the LP-gas along with the odorant in amounts sufficient to provide a concentration of the selected passivating agent in the range of up to about 250 ppm (v/v).
The purpose of the film provided by the fill-up treatment method is to prevent odorant from coming into contact with the tank surface where it can be depleted through absorption or adsorption processes or through oxidation by the metal o~cides present at thc surface. The purpose of the additive treatment is to maintain the film coating the surface of the vessel. The small amount of passivating agent added by this treatment method replenishes any part of the film that has either been washed off by the LP-gas or been damaged for any other reason.
The passivating agents~ which may be water soluble or may be dispersible or solublc i!l LP-gas, comprise blcnds of corrosion inhibitors such as phosphate esters, fatty amines, pol,v amides, imidazolines, poly imidazolines, quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, ethoxylated fatty amines, ethoxylated polyamides, ethoxylated alcohols and the like or mixtures thereof in one or more solvents. Suitable solvcnts include, but are not limited to water, glycol ether, heavy alcohols such as butanol, hexanol and the like, and aromatic solvents such as xylene, toluene and the like. In a preferred embodiment, the passivating agents contain one or more phosphate esters, and, in a more preferred embodimellt, contaitl one or morc phosphate esters defined by the equatioll:

[R~X~[CmH~m~)n]k~PO(0l~)(3-k) In accordance with the foregoing formula, R is either an alkyl group or an alkylaryl group. The alkyl group may be linear or branched and contain fi-om 4 to 1 carbon atoms. ~,Vhere R is an alkylaryl group, it has the same alkyl group as just mentioned with the addition of an aryl group such as phenol, diphenol, other llydro:~y containing aryl radicals, alkylated hydroxyaryl group, or mixtures thereof.
The component X is selected from the group consisting of a carboxyl group (-COO-), oxygen (-O-), a secondary amine group (-NH-) and mixtures thereof.
The variable m is an integer having a value from about 2 to about 4.
The variable n is an integer having a value from about 4 to about 20.
The variable k is an integer having a value from 1 to 2.
In the preferred embodiment, the passivating agents rurther contain onc or more fatty amines, poly amides, imidazolines, poly imidazolines, quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, etho:cylated fatty amines, ethoxylated polyamidcs, ethoxylated alcohols or mixtures thereof and one~or-more solvents. Suitable solvents include, but are not limited to water, glycol ether, heavy alcohols such as butanol, hexanol and the like, and aromatic solvents such as xylene, toluene and the like.
Such compositions and their preparation are described in co-pending U.S. Patent Applic.~ion 08/599,430 filed January 17, 1996, which is incorporated herein by refcrence.
As demonstrated by the following tests, treatment of LP-gas transportation and storage vessels in the manner described herein reduces odorant depletion. Moreover, the passivating agents are not carried out of the LP-gas transportation or storage vessel by the release of the propane gas.
Passivating agents designated AN-1-76B, AN-1-76C, AN-1-76D, AN-1-76E and AN-I-76I; and having the compositions set forth in TABLE I below were evaluated.

Water Soluble Constituent Actual Weight%Suggested Concentrations By Weight %

Water 20 Approx 10-30 Glycol Ether 20 Approx 10-30 Morpholine/ 5 Approx 5-15 Cyclohexylamine Quaternary Amines 8 Approx 10-19 Imidazoline 15 Approx 10-25 Polymeric Acids 10 Approx 5-15 PhosphateEsters 14 Approx 10-15 Ethoxylated Polyamides 8 Approx 5-17 , CA 02209334 1997-06-30 TABLl~ 1 continucd Water Soluble ConstituentActual Weight %Suggested Concentrations By Weight %
Water 30 Approx 20-,5 Quaternary Amines 10 Approx 8-15 Phosphate Esters 40 Approx 20-40 Imidazoline 10 Approx 6-26 Isopropanol 10 Approx 5-15 Dispersible in LP-gas Constituent Actual Weight% Suggested Concentrations By U'eight %
Aromatic Solvent 40 Approx 25-40 Imidazoline 40 Appro:~ 25-40 PhosphateEster 10 Appro~ 7-16 Polymeric Acids 10 Approx 16-30 TABLE: 1 continucd Soluble in LP-gas ConstituentActual Weight %Suggested Concentrations By Weight %
Glycol Ether 26 Approx 15-35 Imidazoline 66 Approx 3g-77 Fatty Acids 4 Approx ,-11 Phosphate Esters 4 Approx 2-15 AN- 1 -76~
Dispersible in LP-gas Constituent Actual Weight% Suggested Concentrations By Wei~ht %
Amide/Imida701ine 6.2 Approx 4-12 PolymericAcids 11.8 Approx 8-24 Heavy Alcohol 65 Approx 40-70 Ethoxylated Alcohol 4 Approx2-6 Isopropyl Alcohol 13 Appro:; 6-20 The vessels or tanks were prepared as follows. ~orty-rlve (45) tanks ranging in volume from S to 250 gallons were selected.
All tanks arrived sealed and under a positive air pressure. Long term weatllering of 41 tanks was achieved by initially purging the tanks with 30 psig of compressed air for 10 minutes, ¦ CA 02209334 1997-06-30 followed by outdoor storage of the tanks with their valves left open for 90 days. I~or purposes of comparison, tanks # 1, I l, 30 and 40 were not subjected to this weathcring process. Instead those tanks remained sealed as delivered. The purpose of the weatherillg was to simulate field conditions and generate or produce some iron oxide inside the tank, which was assumed to be the worst case scenario in terrns of odorant depletion. However, with the limited sample it was not possible to demonstrate a difference in odorant depletion between weathered and unweathered tanks.
The tarlks were organized in five identical sets of nine. One set was left untreated to serve as a blank, and four sets were treated witll passivating agents desclibed in TABLE ! .
Tank assignment is set forth in TABLE 2.

~ CA 02209334 1997-06-30 TABLI~ 2 Tank # Tank Si%e Passivating Agent 250 gal. Blank 2 250gal. Blank 3 250 gal. AN-1-76F

4 250 gal. AN-1-76F
250 gal. AN-1-76B
6 250 gal. AN-1-7GB
7 250 gal. AN-1-76C
8 250 gal. AN-1-76C
9 250 gal. AN-1-76D
250 gal. AN-1-76D
I l 120 gal. Blank 12 120 gal. Blank 13 120 gal. AN-1-76F
14 120 gal. AN-1-76F
120 gal. AN-1-76B
16 120 gal. AN-1-76B
17 120 gal. AN-1-76C
1~ 120 gal. AN-1-76C
19 120 gal. AN-1-76D
120 gal. AN-1-76D
21 25 gal. AN-1-76F
22 25 gal-. AN-1-76F
23 25 gal. AN-1-76B
24 25 gal. AN-1-76B

TABLE 2 continued Tank #Tank Size PassivatingAgent 25 gal. AN-1-76C
26 25 gal. AN-1-76C
27 25 gal. AN-1-76D
28 25 gal. AN-1-76D
29 25 gal. Blank 25 gal. Blank 31 5 gal. AN-1-76F
32 5 gal. AN-1-76F
33 5 gal. AN-1-76F
34 S gal. AN-1-76B
S gal. AN-1-76B-36 5 gal. AN-1-76B
37 S gal. AN-1-76C
38 S gal. AN-1-76C
39 5 gal. AN-1-76C

5 gal. Blank 41 5 gal. Blank 42 5 gal. Blank 43 5 gal. AN-1-76D
44 5 gal. AN-1-76D
5 gal. AN-1-76D

The tanks were passivated by the fill-~lp treatment method. That is, the valve was removed from each tank and the tank completely filled with the selected passivating agent. The , CA 02209334 1997-06-30 tank was then closed and the passivating agent was left in the tank for 10 minutes. Duling that 10 minute period, the tank was lifted and rolled so that all interior surfaces came in contact with the passivating agent. At the end of ten minutes, the tank was drained, and the excess passivating agent was transferred to the next untreated tank and the procedure repeated. When the passivation of all 9 tanks in the selected set was completed, the excess passivating agent was returned to the original drums. After four days, all tanks, both treated and blanks, were evaeuated to 20 inehes vacuum with a commercial pump to remove air and solvent vapors.
All evacuated tanks, both treated and blanks, were filled Wit}l freshly odorized LP-gas.
Odorization followed industry practice of 1.5 Ib. of ethyl mercaptan per 10,000 gallons of LP-gas.
Odorant (ethyl mercaptan) concentration was then measured in the gas output of each tank. Ethyl mercaptan concentrations were measured in ppm (v/v) using Sensidyne stah~ tubes #72 according to the Gas Processors Association Test Method. The stated accuracy of the stain tubes is ~ 25%. In order to increase the accuracy, eaeh tank was sampled using two to four f~lll strokes of the sampling syringe and the ethyl mereaptan eoneentration read direetly from the tube was divided by the number of strokes. Four strokes were used exeept hl cases where the ethyl mereaptan eoneentration was fairly high, e.g. 30 ppm or higher, when only two strokes were used. The blank used for comparison was the weathered tank of similar size, since all the passivated tanks had been weathered.
The concentration of ethyl mercaptan in the vapor phase was expeeted to vary with temperature beeause of the changes in relative volatility of ethyl mercaptan and propane. i.e. the k values. A concentration of 8 ppm (v/v) was chosen as the original ethyl mercaptan concentration for all tanks. This number, which was appropriate for comparison purposes, did not represent the probable concentration at the start of the six month test, since the temperat~lre at that time was low; instcad it corresponded to the probable concentration at the end of the test when the temperatures were expected to reach over 80~F, based on the known amount of ethyl mercaptan injected in the bulk LP-gas at the start of the test.
In the early part of the test some of the readings obtained with thc stain tubes were adjusted according to ambient temperature. A correction factor provided by the manufacturer of the tubes was be used for outside temperatures below 6~~F.
FIGUI~ES 1-4 represent the ethyl mercaptan for all passivating agents and the blank grouped by tank size. As shown in these FIGURES, for the four tank sizes:
250 gallons: The blank lost the odorant by week 10. Two passivating agents, AN- I -76C and AN- I -76D preserved significant amounts of odorant. These two passi~ating agents are clearly superior to the other two agents which had lost the odorant by the end of the test.
120 gallons: The blank lost the odorant by week 6. The two ~vater soluble passivating agents, AN-I -76B and AN-I -76D preserved significant amounts of odorant, with AN-I -76D
being thc best. The propane dispersible AN-1-76C preservcd a low concentration of odorant, while AN- I -76F had lost the odorant before the end of the test.
25 gallons: The blank lost the odorant after 6 months. Two passivating agents, AN-I-76C and AN-1-76D preserved about 50% of the original concentration of odorant.
5 gallons: The blank lost tlle odorant by week 6. All passivating agents work very well for this tank size. The ethyl mercaptan concentration at the end of the test was greater than ; CA 02209334 1997-06-30 the original concentration. This can be explained by the fact that every sampling act in a 5 gallon tank significantly affccts the volume of LP-gas left in the tank, whereas for the larger size tallks the same volume of gas sampled over the duration of ~he test has a much smaller effect on thc volume of unvaporized liquid.
Another smaller scale test was conducted utilizing the additive treatment mcthod of passivation. For this test, tanks # 1, 2, 1 1, and 12, which had previously been used as blanks, were emptied and left outdoors for 30 days with their valves opened. To each tank was added 250 ppm (v/v) of the passivating agent, based on an 80% fill-up of the tank. The same day, after having been purged twice, the tanks were filled with LP-gas. The passivating agents selccted ~or this test were AN-1-76C, which is dispersible in LP-gas, and AN-1-76E, which is formulated to be completely soluble in LP-gas. Tank assignment for this test is set forth in TABLE 3.

Tank # Tank Size Passivating Agent 250 gal. AN-1-76C
2 250 gal. AN-1-76E
I 1 120 gal. AN- I -76C
12 120 gal. AN-1-76E

A Hewlett-Packard 5890 plus gas chromatograph (GC) with a flame ionization detector (FID) and a sulfur chemiluminescence detector (SCLD, Antek Instruments, Inc.) was used to collect the data. The GC column was supplied by Supelco, Inc. ASTM method D5504-94 was used to establish the performance of the GC-SCLD system.

: ~ CA 02209334 1997-06-30 The GC sampling system consisted of a needle valve, a gas sample valve, and a liquid sample valve. These three valves were connected in series to each other and to the GC inlet port using a 1!16" Silicosteel tubing. For accurate reproducible results it was necessary to passivate the inncr surfaces of the sampling systcm by sulfiding it and by minimizing the contamination with air (oxygen). The passivation procedure consisted of repeated injection of hexane and gas solutions of ethyl mercaptan and diethyl disulflde through the sampling system into the GC
column, until the peak areas for the two compounds were reproducible. To protect passivated surfaces, diffusion of air into the sampling system was reduced by closing the needle valve during changeover of the sample containers. Additionally, the sample lines ~ere kept filled with a calibration gas when the system was not in use.
Liquid propane from the test tanks was sampled using a 150 ml pressurized sample container known as a Welker unit Stainless steel Quick connect fittings or hoses with Quick connect fittings were used to attach the Welker unit to the propane tanks or the GC sampling system. Before each use, the Welker unit was flushed with oxygen-free nitrogen for about a minute to purge off any residual propane in the sampler and to protect the unit from air contamination. ~,Vhile collecting the LP-gas sample, liquid propane was allowed to flow through the samplers for at least 30 seconds thus protecting the sample from air contamination An external standard method was used to convert observed GC peak areas in LP-gas samples to concentrations. The concentration of tlie odorant, ethyl mercaptan (EM), was measured in each tank and samples taken from the trucks used to charge the tanks with LP-gas.
Diethyl disulfide (DEDS) and an unknown, tentatively identified as diethyl trisulfide (ETS) were detected by the GC analyses and measured along with EM. System performance was monitored ~ CA 02209334 1997-06-30 using a set of gas calibration standards (helium or gas standards) to calibrate the unit.
Calibration gases were delivered to the GC sample valve (I ml) at 44 psig. All LP-gas samples were delivered to the GC gas sample valve (I ml) at 150 psig. For ideal gases, the weight of a gas in a fixed loop filled at 44 psig inlet pressure would be approximatcly one third of thc pressure at 150 psig. Therefore, the estimation of concentration based on the GC peak areas and extemal standards required corrections due to pressure differences.
Concentration was calculated according to the following formula:
Concentration (ng/mg) = {[Peak Area (lo6 counts)/ml propane] x AF x WR~ } in liquid propane where, Weighted Response Factor, WR~ = [Rr(ng/106 counts)] x the Pressure Factor/[Density, propane (1.8 mg/ml)]}
Area Factor, AF = 36/[(peak area for EM x WR, for EM) + (Sum of peak areas for DEDS
and ETS x WR, for DEDS)] .
Using the gas calibration data, and from plots of GC areas versus weight, ng, (ethyl mercaptan or other sulfur compounds), a response ractor, R" was found by expressing thc slope as ng/l o6 counts. Multiplication of the GC peak area in propane with the Rr value gave ng/ml of ethyl mercaptan present in propane. Dividing ng/ml of ethyl mercaptan with density of propane (1.8 mg/ml) expressed results as ng/mg or ppm (w/w). The corrected concentrations were obtained by multiplying the product (ng/ml) with the pressure correction equal to a ratio of psig propane to psig helium.
FIGURES 5-8 represent the ethyl mercaptan concentrations for the two passivating , CA 02209334 1997-06-30 agents lltilized in this test. As is shown in FIGURES S-g, all four tanks contained significant amounts of odorant after three months.
Based on the foregoing tests, it is believed that the most effective method of reducing odorant depletion is a two stage treatment. That is, the tank should be initially treated with a passivating agent by the fill-up treatment method and thereafter treated with a propane soluble passivating agent by the additive treatment method.
A simple test was conducted in order to determine if the passivating agents would be carried out of the tank in the vapor phase. A commercial outdoor gas grill was connected to a tank previously passivated with AN-1-76C. The gas was burned for about g hours a day for several weeks. At the end of that period the grill was examined and no deposits were found on the gas burners. This test provides evidence that no burner fouling ~vill take place when the vaporized LP-gas is used.
The foregoing description has been directed to particular embodiments of the invention for the purposes of illustration and explanation. It will be apparent, however, to those skilled in this art that many modifications and changes in the compositions and methods set forth will be possible without departing from the scope and spirit of the invention. It is intended that the following claims be interpreted to embrace all such modifcations and changes.

Claims

1. A method for reducing odorant depletion during transfer and storage of liquefied petroleum gas comprising the steps of (a) completely filling a liquefied petroleum gas transfer or storage vessel with a passivating agent so that all interior surfaces of said vessel come in contact with said passivating agent, said passivating agent comprising one or more phosphate esters defined by the equation:

[R-X-[CmH2mO)n]k-PO(OH)(3-k) where;
R is an alkyl group containing 4 to 18 carbon atoms or an alkylaryl group comprising an aryl group selected from the group consisting of phenol, diphenol, and mixtures thereof, and an alkyl group containing 4 to 18 carbon atoms;
X is selected from the group consisting of a carboxyl group (-COO-), oxygen (-O-), a secondary amine group(-NH-) and mixtures thereof;
m is an integer having a value from about 2 to about 4;
n is an integer having a value from about 4 to about 20; and k is an integer having a value from 1 to 2 and one or more fatty amines, poly amides, imidazolines, poly imidazolines, quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, ethoxylated fatty amines, ethoxylated polyamides, ethoxylated alcohols or mixtures thereof, and one or more solvents;

(b) draining said passivating agent from said vessel; and (c) evacuating said vessel prior to the introduction of said liquefied petroleum gas into said vessel.

2. The method of claim 1 wherein said passivating agent comprises water, glycol ether, morpholine or cyclohexylamine or mixtures of morpholine and cyclohexylamine, quaternary amines, imidazoline, polymeric acids, phosphate ester and ethoxylated polyamides.

3. The method of claim 2 wherein said passivating agent comprises from about 10 to about 30 weight % water;
from about 10 to about 30 weight % glycol ether;
from about 5 to about 15 weight % morpholine or cyclohexylamine or a mixture of morpholine and cyclohexylamine;
from about 10 to about 19 weight % quaternary amines;
from about 10 to about 25 weight % imidazoline;

from about 5 to about 15 weight % polymeric acids;
from about 10 to about 15 weight % phosphate ester; and from about 5 to about 17 weight % ethoxylated polyamides.

4. The method of claim 3 wherein said passivating agent comprises about 20 weight % water;
about 20 weight % glycol ether;
about 5 weight % morpholine or cyclohexylamine or a mixture of morpholine and cyclohexylamine;
about 8 weight % quaternary amines;
about 15 weight % imidazoline;
about 10 weight % polymeric acids;
about 14 weight % phosphate ester; and about 8 weight % ethoxylated polyamides.

5. The method of claim 1 wherein said passivating agent comprises water, quaternary amines, phosphate esters, imidazoline, and isopropanol.

6. The method of claim 5 wherein said passivating agent comprises from about 20 to about 35 weight % water;
from about 8 to about 15 weight % quaternary amines;
from about 20 to about 40 weight % phosphate esters;

from about 6 to about 26 weight % imidazoline; and from about 5 to about 15 weight % isopropanol.

7. The method of claim 6 wherein said passivating agent comprises about 30 weight % water;
about 10 weight % quaternary amines;
about 40 weight % phosphate esters;
about 10 weight % imidazoline; and about 10 weight % isopropanol.

8. The method of claim 1 wherein said passivating agent comprises aromatic solvent, imidazoline, phosphate ester, and polymeric acids.

9. The method of claim 8 wherein said passivating agent comprises from about 25 to about 40 weight % aromatic solvent;
from about 25 to about 40 weight % imidazoline;
from about 7 to about 16 weight % phosphate esters; and from about 16 to about 30 weight % polymeric acids.

10. The method of claim 9 wherein said passivating agent comprises about 40 weight % aromatic solvent;
about 40 weight % imidazoline;

about 10 weight % phosphate ester; and about 10 weight % polymeric acids.

11. The method of claim 1 wherein said passivating agent comprises glycol ether, imidazoline, fatty acids, and phosphate esters.

12. The method of claim 11 wherein said passivating agent comprises from about 15 to about 35 weight % glycol ether;
from about 38 to about 77 weight % imidazoline;
from about 3 to about 11 weight % fatty acids; and from about 2 to about 15 weight % phosphate esters.

13. The method of claim 12 wherein said passivating agent comprises about 26 weight % glycol ether;
about 66 weight % imidazoline;
about 4 weight % fatty acids; and about 4 weight % phosphate esters.

14. A method for reducing odorant depletion during transfer and storage of liquefied petroleum gas comprising the step of (a) adding a passivating agent that is dispersible or soluble in propane directly to said liquefied petroleum gas in a transportation or storage vessel along with said odorant in an amount sufficient to provide a concentration of said passivating agent in the range of up to about 250 ppm (v/v), said passivating agent comprising one or more phosphate esters defined by the equation:

[R-X-[CmH2mO)n]k-PO(OH)(3-k) where;
R is an alkyl group containing 4 to 18 carbon atoms or an alkylaryl group comprising an aryl group selected from the group consisting of phenol, diphenol, and mixtures thereof, and an alkyl group containing 4 to 18 carbon atoms;
X is selected from the group consisting of a carboxyl group (-COO-), oxygen (-O-), a secondary amine group (-NH-) and mixtures thereof;
m is an integer having a value from about 2 to about 4;
n is an integer having a value from about 4 to about 20; and k is an integer having a value from 1 to 2 and one or more fatty amines, poly amides, imidazolines, poly imidazolines, quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, ethoxylated fatty amines, ethoxylated polyamides, ethoxylated alcohols or mixtures thereof, and one or more solvents.

15. The method of claim 14 wherein said passivating agent comprises aromatic solvent, imidazoline, phosphate ester, and polymeric acids.

16. The method of claim 15 wherein said passivating agent comprises from about 25 to about 40 weight % aromatic solvent;
from about 25 to about 40 weight % imidazoline;
from about 7 to about 16 weight % phosphate esters; and from about 16 to about 30 weight % polymeric acids.

17. The method of claim 16 wherein said passivating agent comprises about 40 weight % aromatic solvent;
about 40 weight % imidazoline;
about 10 weight % phosphate ester; and about 10 weight % polymeric acids.

18. The method of claim 14 wherein said passivating agent comprises glycol ether.
imidazoline, fatty acids, and phosphate esters.

19. The method of claim 18 wherein said passivating agent comprises from about 15 to about 35 weight % glycol ether;
from about 38 to about 77 weight % imidazoline;

from about 3 to about 11 weight % fatty acids; and from about 2 to about 15 weight % phosphate esters.

20. The method of claim 19 wherein said passivating agent comprises about 26 weight % glycol ether;
about 66 weight % imidazoline;
about 4 weight % fatty acids; and about 4 weight % phosphate esters.

21. A method for reducing odorant depletion during transfer and storage of liquefied petroleum gas comprising the steps of (a) completely filling a liquefied petroleum gas transfer or storage vessel with a first passivating agent so that all interior surfaces of the vessel come in contact with said first passivating agent, (b) draining said first passivating agent from said vessel;

(c) evacuating said vessel;

(d) filling said vessel with liquefied petroleum gas;

(e) adding an odorant compound to said liquefied petroleum gas in said vessel; and (f) adding a second passivating agent that is dispersible or soluble in propane directly to said liquefied petroleum gas along with said odorant in an amount sufficient to provide a concentration of said second passivating agent in the range of up to about 250 ppm (v/v);

said first and second passivating agents each comprising one or more phosphate esters defined by the equation:

[R-X-[CmH2m))n]k-PO(OH)(3-k) where;
R is an alkyl group containing 4 to 18 carbon atoms or an alkylaryl group comprising an aryl group selected from the group consisting of phenol, diphenol, and mixtures thereof, and an alkyl group containing 4 to 18 carbon atoms;
X is selected from the group consisting of a carboxyl group (-COO-), oxygen (-O-), a secondary amine group (-NH-) and mixtures thereof;
m is an integer having a value from about 2 to about 4;
n is an integer having a value from about 4 to about 20; and k is an integer having a value from 1 to 2 and one or more fatty amines, poly amides, imidazolines, poly imidazolines, quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, ethoxylated fatty amines, ethoxylated polyamides, ethoxylated alcohols or mixtures thereof, and one or more solvents.

22. A method for reducing odorant depletion during transfer and storage of liquefied petroleum gas comprising the steps of (a) completely filling a liquefied petroleum gas transfer or storage vessel with a passivating agent so that all interior surfaces of said vessel come in contact with said passivating agent, said passivating agent comprising corrosion inhibitors selected from the group consisting of phosphate esters, fatty amines, poly amides, imidazolines, poly imidazolines, quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, ethoxylated fatty amines, ethoxylated polyamides, ethoxylated alcohols or mixtures thereof, and one or more solvents;

(b) draining said passivating agent from said vessel; and (c) evacuating said vessel prior to the introduction of said liquefied petroleum gas into said vessel.

23. A method for reducing odorant depletion during transfer and storage of liquefied petroleum gas comprising the steps of (a) completely filling a liquefied petroleum gas transfer or storage vessel with a first passivating agent so that all interior surfaces of the vessel come in contact with said first passivating agent, (b) draining said first passivating agent from said vessel;

(c) evacuating said vessel;

(d) filling said vessel with liquefied petroleum gas;

(e) adding an odorant compound to said liquefied petroleum gas in said vessel; and (f) adding a second passivating agent that is dispersible or soluble in propane directly to said liquefied petroleum gas along with said odorant in an amount sufficient to provide a concentration of said second passivating agent in the range of up to about 250 ppm (v/v);

said first and second passivating agents each comprising corrosion inhibitors selected from the group consisting of phosphate esters, fatty amines, poly amides, imidazolines, poly imidazolines, quaternary amines, poly quats, dimer acids, trimer acids, polymeric acids, ethoxylated fatty amines, ethoxylated polyamides, ethoxylated alcohols or mixtures thereof, and one or more solvents.