US3130314A - Method of using radioactive tracers - Google Patents

Description

United States Patent O M 3,130,314 METHQD OF USING RADIOACTIVE TRACERS Alan Beer-bower and John L. Murray, Westfield, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware N Drawing. Filed Nev. 23, 1959, Ser. No. 854,530 11 Claims. (Cl. 2501tl6) The present invention relates to an improved method of using radioactive tracers for the purpose of studying mixing, fluid flow, leakage and similar problems, particularly in respect to the processing of petroleum hydro carbons in oil refineries and similar installations. More particularly, the improved tracer technique herein devised relates to the development of a practical, cheap, and improved method of using tracers that have a relatively short half life.

The use of radioactive tracer elements in the determination of rates of flow, mixing, inventory, leakage, and, in general, as an inspection tool in the chemical and petroleum refining industry is well-known. This highly useful technique has, as in the past, been attendant with several shortcomings; for example, some of the radioactive isotopes possess extremely long half lives and, particnlarly in instances where the tracer isotopes are to be directly injected into the process streams, reaction vessels and the like, the use of isotopes having a long half life, for example, strontium 90 or cobalt 60 presents contamination problems because in most instances, at least small amounts of the radioactive materials finally appear in the products of reaction. This necessitates safety precautions in the storage and handling of such products or it requires the decontamination of the products prior to their sale on the open market or prior to their usage in other processes, particularly in installations where safety precautions have not or cannot be instituted and main tained.

Where a direct injection of the isotope tracer elements is to be followed, in most cases it becomes a general necessity to employ isotopes having relatively short half lives; i.e., of the order of 36 hours or less. It is recognized, moreover, that from one standpoint, namely that of safety, the shorter the half life of the isotope employed, the less expensive storage or decontamination facilities that are required. On the other hand, while isotope having a half life of the order of a few minutes can be desirably employed in some instances, oftentimes the purely physical requirements of manipulation, injection, size of equipment, and the process through which the progress of the tracer is to be followed, necessitate the use of tracers having half lives of at least several hours. Almost invariably when using such tracers, recycle streams, exit product lines, storage tanks, surge tanks, and other various pieces of equipment connected with the processing become contaminated, and it is not possible to select a particular radioactive isotope so that the contamination problem and attendant radiation hazard is eliminated or obviated at the exact point and time at which the isotope finally emerges with the product from the process. In general and for practical purposes, most radioactive tracers employed can be considered as radioactively dangerous for a period of roughly ten times their half life. It is therefore desirable in employing a radioactive isotope of a particular element, for tracer studies, to select one which will have a sufficiently long total radioactive life that a thorough and complete inspection of the system can be accomplished while, at the same time, avoiding radiation hazards due to the contamination of the final product for any great period of time after that product is finally withdrawn from the system under study.

The present invention seeks to accomplish these ends by shortening the time for preparing the isotope tracer 3,139,314 Patented Apr. 21, 1964 sample for injection and, thus, making possible the use of a tracer with a correspondingly shorter half life than Would otherwise be the case. For example, British Patent 795,028 attempted to solve this problem by dispersing isotope in an aqueous solution. This aqueous solution was then admixed with oil and alcohol and another solvent in order to produce either a true solution or at least a homogeneous mixture suitable for injection into a system that was primarily water immiscible and that would not ordinarily distribute an aqueous solution in a uniform manner. Prior to the introduction of the tracer, the alcohol and the solvent were removed by either distillation or evaporation before injection of the solution into the system. Both of these procedures require additional time, thus cutting down on the remaining time that the isotope will be useful in the subsequent tracer studies. This is a real problem, particularly in cases where sodium 24, aluminum 28, and iodine 132 are employed, because their half lives are respectively 15 hours, 2.3 hours, and 2.33 hours. Similarly, Te 99 has a half life of approximately six hours.

The present invention has obviated the necessity for employing such cumbersome and time-consuming techniques in preparing an isotope sample for injection into a system for tracer studies. The invention is particularly useful for a system whose predominant components are water-immiscible such as hydrocarbon streams, crude oil processing, alkylation processes, fluid coking operation or, in fact, any system employing petroleum oils in the liquid phase.

The novel process eliminates distillation and evaporation steps and is able to accomplish the solubilizing or the preparation of homogeneous mixtures for injection in tracer studies in a minimum of time and is thus able to employ isotope tracers of shorter half lives than has heretofore been thought possible to accomplish the same ends. For most refinery inspection purposes, the ideal half life of a tracer is about 36 hours or less, preferably about one 8-hour shift. In this way the disposal or safety precaution problem is practically non-existent. The solution of the problem involved lies in the use of solubilizing or surface active solubilizing agents. The extremely powerful emulsifying or surface active agents which are useful in conditioning the aqueous solutions of water soluble salts of the radioactive isotopes employed may be any of those commonly available to the trade today; The following are examples of these agents and are of the type of surface active solubilizing agents that are particularly useful in practicing the herein described novel process: Sodium mahogany sulfonates, sodium keryl-benzene sulfonates, fatty alcohol sodium sulfates, amine salts of these acids, sorbitol oleates, alkyl-phenol ethylene oxide condensation products, metallic naphthenates, fatty alcohol-ethylene oxide condensation products, alkali or amine salts of alkyl phosphoric acid, partial esters, acetylenic alcohols. Additional specific solubilizing agents are: An emulsifier concentrate of sodium mahogany sulfonate concentrate admixed with sodium naphthenate, diethylene glycol and water, and the potassium soap of tall oil admixed with isopropyl alcohol and water and containing sodium sulfonate.

One source of radioactive tracer materials which have relative short half lives and are suitable for the practice of the present invention, is described in the article entitled Development of Methods for the Production of Certain Short-Lived Radioistotopes, by L. G. Stang, Jr., et al., UNESCO/NS/RIC/ 190, and appearing in Radioisotopes in Scientific Research, vol. 1, Pergamon Press, London, N.Y., and Paris, 1958, pp. 50-70. A system of mother-daughter pairs takes care of the problem of transportation. In short, a generator or milker is i supplied from which a solution of the daughter isotope Mother Daughter Stable Product To 132 I 132 Xe 132 Ba 140 La 140 Ce 140 Us 137 Ba 137 La 137 lVIg 28 Al 28 Si 28 Mo 99 Te 99 Ru 99 On the other hand, many elements do not lend themselves to this type of transportation and must be either shipped as rapidly as possible from the nearest nuclear reactor or prepared on the spot by bombardment with neutrons, deuterons, etc. from an electrical accelerator. Such isotopes useful in the present process are Na 24, Mn 56, Br 82, As 76, Ga 72, Cu 64, and K 42. These are seldom carrier free and often contain over 99.9% of inactive isotopes. The chloride, carbonate, nitrate or any other water soluble salt of the radioisotope is prepared in an aqueous solution depending upon the chemical nature of the particular element. Relatively small amounts of radioactive metal salt in water may be employed.

In one specific example about 0.07 microgram of the salt Na 24 nitrate plus 25 grams of carrier Na 23 nitrate in about 10 grams of water was mixed with about 500 grams of an emulsifier concentrate and stirred for about one minute. The activity was 200 millicuries. A light naphtha in the amount of about 500 cc. was then added and stirred for an additional minute. The final mixture was clear and homogeneous and placed in a pressure bomb and forced by nitrogen pressure into the hot pitch feed line leading to a fluid coker operation. The usual instruments for detecting gamma radiation through metal were employed for recording the path of the hot pitch feed and a flow pattern, residence time and the like was determined based upon the gamma radiations recorded by the instruments. The emulsifier concentrate employed contained the following ingredients in the approximate percentages shown:

52% Na mahogany white oil sulfonate 21% naphthenic lubricating oil of 300 SSU 100 F. 15% Na naphthenate 5% diethylene glycol 7% water In place of the light naphtha or Varsol, a small amount of the feedstock itself (if suitable) may be mixed with the solubilized aqueous tracer solution by stirring or violent agitation, and this concentrate may then be injected into the system for the conducting of tracer studies. Sodium 24 nitrate having a half life of about hours was employed in the particular study undertaken so that at the end of about one weeks time the naphtha products of the reaction were so low in radioactive contamination as to be of no potential hazard to human beings.

In a second example, the liquid from an I 132 milker was used. This consisted of about 5 10 micrograms of NaI 132, about 2.5 grams of sodium acetate and about 0.5 gram of acetic acid in about 40 cc. of water. This was solubilized in about 17 lbs. of lead naphthenate and about 17 lbs. of lubricating oil to form a concentrate, which in turn was added to an unmixed 17,000 gal. batch of gear lubricant. Mixing was then stated, and a Geiger counter used to measure the activity of the batch at various levels. It was possible to detect differences until at about 20 minutes the 'batch proved to be uniform. The

4 I 132, with its short half life of 2.33 hours, was decayed to undetectability in about 24 hours.

The use of surface active agents involved a very short period of time in preparing the radioactive concentrate for injection into the hydrocarbon system so that it was possible to employ a relatively short half life isotope and, at the same time, avoid any major amount of decay of the activity before the test was under way and completed. The shortening of the time required in the preparation operation and the obtaining of a uniform distribution of the isotope in the system under inspection were two major advantages in the use of the novel technique employed.

In general, the radioisotope is but a minor constituent of the mixture. The inert carrier may be present in substantial amounts or totally absent, depending on the method of preparation of the isotope. It will range from 0 to 5% of the final mixture. Reagents used in milking or dissolving the isotope may amount to from 0 to 2%. The water must be adequate to dissolve the carrier and/ or reagents, and is usually from 2 to 15% of the final mixture. to 50 times the amount of water plus salts; 10% to of the final preparation injected may be this material. Diluent may not be required but, if used, the amount will vary from 0% to 75%, the exact quantity being a function of solubilizing agent Viscosity and the viscosity of the stream into which the injection is to be made.

Having now thus fully described and illustrated the nature of the invention, what is desired to be secured by Letters Patent is:

1. An improved method of employing radioactive tracers which comprises, admixing a surface active solubilizing agent with an aqueous solution of a water soluble salt of a radioactive element having a relatively short half life, injecting said mixture into a water-immiscible hydrocarbon and determining by use of radiation sensitive instruments the location of the radioactive material in said hydrocarbon.

2. A process as in claim 1 wherein the aqueous mixture containing the surface active agent is mixed with a portion of the hydrocarbons into which it is to be introduced prior to introducing the admixture into said hydrocarbon.

3. A process as in claim 1 wherein the radioactive element has a half life of less than about 36 hours.

4. A process as in claim 1 wherein the radioactive element is Na 24.

5. A process as in claim 1 wherein the radioactive element is I 132.

6. A process as in claim 1 wherein the surface active agent is an organic sulfonate.

7. A process as in claim 1 wherein the surface active agent is a mixture of sodium mahogany white oil sulfonate, sodium naphthenate, light lubricating oil, diethylene glycol and water.

8. A process as in claim 1 wherein the surface active agent is a mixture of sodium sulfonate, salts of long chain fatty acids, potassium soap of tall oil, isopropyl alcohol and water.

9. A process as in claim 4 wherein the radioactive element is sodium 24 in the form of its nitrate.

10. A process as in claim 5 wherein the radioactive element is I 132 in the form of its sodium salt.

11. An improved method of employing short life radioactive tracers, which method comprises admixing a surface active solubilizing agent with an aqueous solution of a water soluble salt of a radioactive element having a half life of less than about 36 hours, the amount of the surface active agent being from 5 to 50 times the amount of the aqueous solution, and injecting said mixture into a liquid petroleum hydrocarbon stream whereby the location of said radioactive element may be determined with radiation instruments.

(References on following page) The solubilizing agent is at least five times and up References Cited in the file of this patent UNITED STATES PATENTS Ferris Apr. 6, 1943 Herzog June 22, 1948 De Forrest June 7, 1949 Stokeley et a1. Aug. 16, 1949 Linderman June 15, 1954 Juterbock et al May 1, 1956 Fries May 20, 1958 OTHER REFERENCES Gore et al.: Radioactive Tracer Techniques, Journal of Petroleum Technology, September 1956, pp. 1216.

Claims (1)

1. AN IMPROVED METHOD OF EMPLOYING RADIOACTIVE TRACERS WHICH COMPRISES, ADMIXING A SURFACE ACTIVE SOLUBILIZING AGENT WITH AN AQUEOUS SOLUTION OF A WATER SOLUBLE SALT OF A RADIOACTIVE ELEMENT HAVING A RELATIVELY SHORT HALF LIFE, INJECTING SAID MIXTURE INTO A WATER-IMMISCIBLE HYDROCARBON AND DETERMINING BY USE OF RADIATION SENSITIVE INSTRUMENTS THE LOCATION OF THE RADIOACTIVE MATERIAL IN SAID HYDROCARBON.