CA1058143A - Activation of water soluble amines by halogens for trapping radioiodine from air streams - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Gas adsorbent charcoals impregnated with an aqueous solution of the reaction product of a tertiary amine and elemental iodine or bromine are better than 99 percent efficient in trapping methyl iodine 131. The chemical addition of iodine or bromine to the tertiary amine molecule increases the efficiency of the impregnated charcoal as a trapping agent, and in conjunction with the high flash point of the tertiary amine raises the ignition temperature of the impregnated charcoal.

Description

10~ 43 BACKGROUND OF THE INVENTION
All nuclear reactor system~ mu~t interface with the environment through an adsorbent system, normally charcoal, and a high efficiency particulate filter Iodinel31 is one of the lmportant fission-product gases that must be trapped fro~ reactor air streams; some of this nuclide is in the form of methyl iodide In efforts to remove this fission-product certain i pr gnated charcoal protucts have been used Of particular int-re-t has been triethylene di~ne (TDDA) becau~e of the rapld rat- of reactlon of this impregnant with air borne m thyl iodide However, cvon higher reaction rates are d-~ir d In addition to adsorption characteristics, a very isportant property of impregnated charcoals is the m~gnitude of the spontaneous ignition temperature In general, i~pr-gnated charcoals ignite at tenperatures considerably b-lo~ that of the base charcoal, usually in the neighborhood of the fla~h point of the impregnant DESCRIPTION OF THE INVENTION
It has been discover~d that ele~entary iodine crystals, liquid bromine, or iodine chloride can be completely reacted at u~bient temperatures in aqueous solutions with tertiary a d ne~, and that charcoal impregnated with the~e solution~
1- an eff~ctive adsorbent for iodine fission products ~uch a~ iodinel31 and methyl iodinel31 These amine-iodlne 1058~43 reaction products not only increase ~he ad~orption effic~ency of the amine impregn~ted charco~l but al~o r~ise its ignition t-mperature.
In carrring out this lnvention the iodine i8 added a8 flnely divlded c~ystals and the bromine or iodine chloride are addod as liquids to a solution of the tertiary amine; the concontration of the tertiary amine in the solution may range b-tween 8 g/100 ml and 25 g/100 ml. The concentrations depend on th- so~ubility of the amine in water and the quantity of ~ater is controlled by the desired final moisture content aftor imprognation. Tho resulting impregnated charcoal will contain 2 to 7 por cent of tertiary amine and 0.4 to 1.6 p-r cent of a halogen based on the dry weight of th- charcoal.
In proparing tbe ad~orbent material any charcoal suitable for ga- ad-orptlon ma~ be usod. E~amples of water soluble tertiary a d nes which Qay be usod are he~amethylenetetramine, triothanola~ino, triethylenediamine, N-methylmorpholine, N, N, ~, N' - tetram~ethylethrlenediamine, l-dimethyla~ino-2-propanol, N-mothrlpiperazino, and N, N, N', N'-tetramethyl-l, 4-butanediamine. The concentrations of tertiary amine and of halogen in the aqueous olution that is best suited for the imprognation of a charcoal will vary with the amine and tho halogon. There is an optimun raDge below and above which the trapping efficiency falls off. Also, the impregnation is bost accomplished with a quantity of wat~r that loaves the product of a dry appearanco.
This invention _ y be best illustrated by the infor~ation 1()5~43 generated by uslng hexamethylenetetramine (HMIA) a8 an e~ample of a tertiary amlne and crystalline lodine a~ an examplo of the halogen. A number of samples of charcoal impregnated with varying amounts of NMIA alone and NMIA with iodine were prepared and, after dryi~g, the~e were exposed to a gas stream contalning methyl iodidel31. The results of these tests are summarized in Table I. As can be noted in the first part of Table I, the penetration of methyl iodide through a one-inch or two-inch thick bed of the HMrA
impregnated charcoal is seen to be considerable when impregnated ~ith the amine alone. A remarkab}e increase in adsorption is ob~erved when the formulation includes iodine added to HMIA
a~ ho~n in the 8econd part of Table I.
In th~se tests the charcoal bed In all cases was two inche~ in dia eter and the air flow for pre-equilibration with air at the humid$ty 95 + 2 relative humidity was 5.5 liters/min.
and the flow was increased to 11 liters/min. for the subsequent test period of four hours. The dose of methyl iodide labeled ; with 1131 in this four hour period was 25 g/g. of impregnated charcoal of activity which permitted total counts up to 300,000 in 2 minutes. Each ~ample bed was divided into 8 equal parts, each of 1/4 inch depth, separated by stalnless ~teel wire screens. However, the percentage of penetration is depicted in Table I in terms of four parts taken together.

iO S~ ~ 4 3 TABLE I

Tr~pping Efficiencles of Charcoals ~mpregnated w~ HMTA-Iodine Solutlons as % Pen~tration of Methyl I

Run HMTA I2 % Penetration No. (wt% of the charcoal) l" bed 2" bed S 0 41% ---50 __ 4 5 o 20%

s 5 0.5 16.3 2.3 6 7 1.0 7.0 0.54 7 10 1.0 7.5 0.36 8 7 2 3u9 0.00 9 5 1 0~00 0.00 1 0.00 0.00 11 4 1 6 . 7 o . 53 12 7 1 10.2 0.65 The iodine crystals and the amine were reacted at ambient tesperature ln the designated proportions (~eight percent of the charcoal) given in the lower part of Table I. Each solution was clear and almost colorless and proved stable over long storage periods. After spray impregnatlon and dryin~
the observed trapping efficiencies were dramatically increased over the amine alone as shown in Table I.
Since each sample bed was divided into 8 equal parts, it was pos~ible to report the dependence of penetration on 1058~43 charcoal depth. A linear plot is in general valid forlogarithm activity as a function of bed depth; it is possible from this behavior to estimate the depth of charcoal required for the effluent to reach the background count. A typical plot is shown in the Figure. For example, the efluent air ~trea~s from Run~ 9 and 10 in Table I attained background activity with a charcoal depth of three-fourths inch. In the-e tests the amount of methyl iodidel31 removed is sub~eantially the same as the amount of methyl iodidel31 removed in the air stream from an intermediate size nuclear reactor which has been operating for about 2 year~.
In a separate series of tests, elementary bromine was reacted at room temperature with an aqueous solution of HMIA.
Table II show~ the amine to br~ine proportions and the ob~-rved penetrations of I131 in the fonm of methyl iodide after impregnation in charcoal.
T~BLE II

Trapping Efficiencies of Charcoals Impregnated with ~ -Bromlne Solutions Determined by % Penetration of Methyl I

E~periment HMTA Br % Penetration No. (wt%) (wt~) 1" bed 2" bed ' 13 9 0.8 19 4.8 14 5 3.2 24.5 5.8 9 0.9 19.9 5.1 16 7 1.6 26.4 7.8 17 0 1.6 40.6 18 18 2.5 0.9 ---- 10 lVS13143 Here again the depth of charcoal that is required for the effluent air stream to reach background can be e~timated.
From the tests summarized in Tables I and II it is evident that the iodine complex has been found to be slgnificsntly more efficient than bromine using charcoal in bed depths of one or ~wo inches.
The introduction of the halogen (bromine, iodine chloride, and iodine) into the amine impregnation formNlation also raised the ignition temperature observed for the charcoal.
This feature is of the greatest importance inasmuch a~ the adsorption of methyl iodidel31 from the reactor effluent may take plAce at elevated temperatures.

ExamPle 1 Hexamethyleneeetramine (62.1 g.~ was dlssolved at room temperature in 200 m. distilled water. Crystalline iodine ~12.42 g.) was added with vigorous stirring. The first indication o~ reaction was the immediate development of a yellow coating on the iodine crystals, followed by an amber yellow coloration of the solution. With continuous stirring, the mixture then attained a yellow murky appearance which soon become muddy brown. The stirring wa8 continued overnight, and the mixture gradually became less murky and finally clear and al~ost colorless. The solution was diluted to 800 ml. and was impregnated on 3000 ml. of gas adsorbent charcoal (coal-base). The charcoal was rotated at 31 r.p,m. and the solution was sprayed under pressure into the charcoal through a flat spray nozzle tip. The product was free-flowing and ~ 58 ~ 4 3 was air dried in a forced-convection oven at lOO-C overnight.
The penetration of methyl iodide (I131) was observet to be zero through a bed depth of two inches (2-inch diameter) and 5% through a bed depth of 1 inch.
Example 2 N, N, N , N -Tetramethyi 1,4-butanediamine (Sg.) was dlssolved in 2S ml. water. Crystalline iodine (1.0 g.) wa~
added and the mixture ~tirred vigorously. The appearance of th- mixture changed from a turbid bright yellow to a muddy brown, and with prolonged stirring, all at room temperature, the solution became clear and colorless. The solution was ;~ impregnated on 100 g. of a coal-base adsorbent charcoal. A
rotary mixer (31 r.p.m.) with four llfting vanes was used and a laboratory atnm~zer, operated with pulsed filtered air supply, was u~ed to introduce the solution. The impregnated charcoal wa~ free-flowing and was air-dried by drawing warm air through a heat-d column of charcoal. The volume of resultant condensate was 20 ml. and had a pH of 7. The penetration of methyl iodide (1131) was ob~erved to be zero through a sample bed of 2-inch diameter and 2-inch depth and 0.0% through a bed 2-inch diameter and l-inch depth.

Claims (2)

What is claimed is:

1. The method of removing methyl iodine 131 gas from the effluent of a reactor comprising passing said effluent gas through charcoal impregnated with an aqueous solution of an elemental halogen selected from the group consisting of iodine, iodine chloride, and bromine and reacted with a tertiary amine compound selected from the group consisting of hexamethylenetetramine, triethyanolamine, triethylenediamine, N-methylmorpholine, N, N, N', N'-tetramethylethylenediamine, 1, dimethylamino-2-propanol, N-methylpiperazine, and N, N, N', N'-tetramethyl-1, 4-butanediamine, wherein the concentration of halogen in the charcoal ranges between 0.4 and 1.6%, and the concentration of tertiary amine in the charcoal between 2 and 7%, based on the weight of the charcoal to adsorb said methyl iodine 131 on said charcoal and thereby remove said methyl iodine 131 from the reactor effluent.

2. A composition of matter comprising charcoal which is impregnated with an aqueous mixture of an halogen selected from the group consisting of iodine and bromine, and reacted with a tertiary amine selected from the group consisting of hexamethylenetetramine, triethyanolamine, triethylenediamine, N-methylmorpholine, N, N, N', N'-tetramethylethylenediamine, 1, dimethylamino-2-propanol, N-methylpiperazine, and N, N, N', N'-tetramethyl-1, 4-butanediamine, wherein the concentration of halogen in the charcoal ranges from 0.4 to 1.6%, and the concentration of tertiary amine in the charcoal between 2 and 7%, based on the weight of the charcoal.