RU2311949C1 - Boron isotopes separation method - Google Patents

Abstract

FIELD: isotopes separation methods.

SUBSTANCE: invention relates to chemical engineering and to isotopes separation methods, in particular to a method of separating boron isotopes. Separation is accomplished through flow-inversion chemical exchange in biphasic system, the latter consisting of aqueous phase in the form of boric acid solution and organic phase in the form of complex of boron with nitrogen-containing phenol-formaldehyde resol oligomer having average molecular mass 450-500 is a diluent. Flows are reversed by re-extraction of boric acid with water followed by evaporation of re-extract. Above-mentioned oligomer is prepared via tert-butylphenol/formaldehyde polycondensation in presence of ammonia. In the cascade with required number of separation steps, more than 90% separation can be achieved to produce 10B.

EFFECT: enhanced separation efficiency.

3 cl, 2 tbl, 3 ex

Description

The invention relates to chemical technology, to methods for the separation of isotopes, and in particular to methods for the separation of isotopes of boron.

Known methods for the separation of boron isotopes by distillation of boron-containing compounds. The possibility of using such substances as BF ₃ , BCl ₃ , H ₃ BO ₃ , B (CH ₃ O) ₃ , B (C ₂ H ₅ O) ₃ , B (C ₄ H ₉ O) was investigated as working substances for distillation ₃ , (C ₂ H ₅ O) ₃ B · 2BF ₃ and elementary boron (Results of science and technology. Series "Radiochemistry. Nuclear Technology". Volume 2. Separation and use of stable boron isotopes. M .: VINITI, 1990, p. 22-45). Studies have shown that the distillation of elemental boron and boric acid is not of any practical interest for the production of boron isotopes due to the extremely small values of the separation coefficient α (ibid., P.22). Studies of the isotopic equilibrium of boron between liquid and vapor in the distillation processes of compounds of the trialkoxibore type and the BF ₃ complex with triethylboron revealed the unpromising use of them for the industrial production of boron isotopes (ibid., P. 27). One of the main ways of producing a light boron isotope - ¹⁰ V, as well as the production of highly concentrated ¹¹ V is the distillation of BF ₃ (ibid., P.29).

The hardware design of the BF ₃ rectification process for producing highly concentrated boron isotopes is described in (Results of science and technology. Series “Radiochemistry. Nuclear Technology.” Volume 2. Separation and use of stable boron isotopes. M .: VINITI, 1990, pp. 41-45) . The process uses relatively short columns (12–16 m long), which are characterized by a small volume at a high level of productivity. The latter is a consequence not only of a relatively large value of α, but also of a low value of VETS (the height of the equivalent theoretical stage characterizing the rate of interfacial isotope exchange), which weakly depends on the load of columns L and their diameter. The absence of a sharp dependence of VETS on the diameter of the columns is especially important for scaling production plants. Mass transfer columns are filled with highly efficient nozzles, which make it possible not only to provide a large contact surface between the liquid and vapor flows involved in the mass transfer, but also to achieve a small pressure drop along the columns, as well as uniform distribution of liquid and vapor flows over their cross section.

The main disadvantage of the BF ₃ rectification process is the necessity of carrying it out at low temperatures, which, however, substantially exceed the normal boiling point of the refrigerant, is liquid nitrogen. This circumstance leads to the need to develop special measures to ensure thermal insulation of the columns, as well as the required temperature regime in them. Another problem associated with the implementation of the rectification process in industry is due to the need to utilize waste (depleted in the target isotope) boron trifluoride streams (ibid., Pp. 44-45).

Known methods for the separation of boron isotopes by chemical isotope exchange and chemical exchange rectification. They are characterized by a significantly higher separation coefficient compared, for example, with distillation processes and are realized at significantly higher temperatures, often close to room temperature.

The methods are based on the use of thermally unstable complexes of boron-containing gas - boron trifluoride - with organic complexing agents and are implemented in gas - liquid or gas (steam) - liquid systems in columns with thermal phase reversal.

An example of a process that is characterized by the almost complete dissociation of the complex in the vapor-gas phase into a boron-containing gas and a complexing agent is the anisole process of the separation of boron isotopes. An interphase isotopic exchange of boron between boron trifluoride in a gas and its complex with anisole in a liquid proceeds in a mass transfer countercurrent column. The upper circulation reversal is achieved by removing heat in the countercurrent adsorber by absorbing the anisole stream of boron trifluoride leaving the column in it and then returning the complex to the gas in a countercurrent flow to the gas. The bottom circulation of the flows is carried out when the complex is heated to the boiling point of the complexing agent, and the complex completely dissociates. The resulting boron trifluoride in the form of gas is returned to the column countercurrently to the complex resulting from it, and the anisole freed from boron trifluoride after cooling and purification from the thermal decomposition products is again fed to the adsorber to carry out the overflow (Results of science and technology. Series “Radiochemistry “Nuclear technology.” Volume 2. Separation and use of stable boron isotopes. M.: VINITI, 1990, p. 45-47).

The anisole process of the separation of boron isotopes is selected as the prototype (Results of science and technology. Series "Radiochemistry. Nuclear technology". Volume 2. Separation and use of stable boron isotopes. M .: VINITI, 1990, p. 45-47).

The objective of the invention is to expand the arsenal of methods for the separation of boron isotopes.

The objective of the invention is solved by the fact that in the method for the separation of boron isotopes by chemical exchange in a two-phase system with flow reversal, the aqueous phase in the form of a solution of boric acid and the organic phase in the form of a complex of boron with a nitrogen-containing phenol-formaldehyde resol oligomer having an average molecular weight of 450 500 atomic units in a diluent, and the circulation of the streams is carried out by re-extraction of boric acid with water, followed by evaporation of the stripping.

The method uses an oligomer obtained by polycondensation of p-tert-butylphenol with formaldehyde in the presence of ammonia.

A mixture of octanol and tridecane in a ratio of 1: 1 by volume is used as a diluent.

The method is as follows.

The separation of boron isotopes is carried out in the extraction system "an aqueous solution of boric acid - a solution in an organic diluent of a nitrogen-containing phenol-formaldehyde resole oligomer having an average molecular weight of 450-500 atomic units." The method used phenol-formaldehyde resole oligomer obtained by polycondensation of p-tert-butylphenol with formaldehyde in the presence of ammonia, brand "Yarresin B" (hereinafter - NRS). A mixture of octanol and tridecane, in a volume ratio of 1: 1, is mainly used as a diluent.

In addition to the tridecane-octanol mixture, the oligomer diluent can be aromatic diluents (toluene, xylene, trialkylbenzene), chlorinated hydrocarbons (chloroform, carbon tetrachloride, hexachlorobutadiene), oxygen-containing compounds (alcohols, ketones). In these diluents, the solubility of the nitrogen-containing oligomer is more than 200 g / l. Limit hydrocarbons (hexane, tridecane, kerosene, etc.) can also be oligomer diluents, although the oligomer dissolves somewhat worse without the addition of alcohols. The extraction properties of the oligomer when changing the diluent change little.

The nitrogen content in different batches of NRS was different and ranged from 1 to 2.2 wt.%, Mainly about 1.3 wt.%.

The concentration of boric acid in the aqueous phase ranged from 0.1 mol / L to 0.8 mol / L, the concentration of oligomer in the organic phase ranged from 0.2 mol / L to 0.5 mol / L.

The ratio of the volumes of the organic and aqueous phases at the O: B extraction stage was from 5: 1 to 1: 1. The extraction temperature is in the range from 20 ° C to 70 ° C.

Re-extraction of boric acid was carried out with water using a large amount of water (O: B ratio was approximately 1:10), the re-extract was evaporated to a predetermined volume.

Examples.

Boric acid was extracted with a solution of 0.5 mol / L NRS in a mixture of octanol - tridecane, 1: 1 by volume. The change in the concentration of boron-10 in the raffinates after several consecutive contacts of aqueous solutions of boric acid with portions of the NRS solution is shown in Table 1.

Table 1. Example Number Number of contacts, O: B Boron concentration initial, intermediate, final, mol / l The concentration of boron-10 initial, final,% at. Depletion of the aqueous phase in boron-10,% one 3 pins
30 min each
O: B = 1: 1 0.8189
0.6395, 0.4715
0.3182 19.87
19.74 0.66 2 4 pins
30 min each
O: B = 1: 1 0.7495
0.5593, 0.4268, 0.295
0.1982 19.80
19.60 1,0 3 2 pins
60 min each
O: B = 2: 1 0.8189
0.464
0.1477 19.87
19.60 1.4

In the first example, three extraction contacts were made with a volume ratio of organic and aqueous phases of 1: 1 with a duration of each contact of 30 minutes. The initial concentration of boric acid in the aqueous phase is 0.8189 mol / L, after extraction contacts 0.6395, 0.4715, and 0.3182 mol / L, respectively. The content of boron-10 in the aqueous phase changed by 0.66% (from 19.87 at.% To 19.74 at.%).

In the second example, four extraction contacts were made with a volume ratio of the organic and aqueous phases of 1: 1 with a duration of each contact of 30 minutes. The initial concentration of boric acid in the aqueous phase is 0.7495 mol / L, after extraction contacts 0.5593, 0.4268, 0.295 and 0.1982, respectively. The content of boron-10 in the aqueous phase changed by 1.00% (from 19.80 at.% To 19.60 at.%).

In the third example, two extraction contacts were made with a volume ratio of organic and aqueous phases of 2: 1 with a duration of each contact of 60 minutes. The initial concentration of boric acid in the aqueous phase is 0.8189 mol / L, after extraction contacts 0.464 and 0.1477 mol / L, respectively. The content of boron-10 in the aqueous phase changed by 1.40% (from 19.87 at.% To 19.60 at.%).

As can be seen from table 1, in extraction systems with NRS, a pronounced isotope effect is observed, which reaches its maximum value in the last example.

Based on the data obtained, the number of steps required to obtain boron-10 enrichment of 90% and 95% was estimated.

When assessing the average degree of separation per extraction step, the root of the nth degree was calculated from experimentally obtained values of the degree of separation at n extraction steps. If in the natural mixture the ratio of concentrations R _ref = boron-11 / boron-10 = 4.05, then in products of 90% and 95% enrichment along boron-10 the ratio of isotope concentrations is respectively R ₉₀ = 9 and R ₉₅ = 19, which means it is required to enrich the natural isotope mixture 9 / 4.05 = 2.22 and 19 / 4.05 = 4.69 times, respectively. In order to estimate the number of required separation steps, we found the ratio of the logarithms of the required enrichment and the change in R _i per one step:

N ₉₀ = log (9 / 4.05) / log (R _i ) to obtain 90% boron-10,

N ₉₅ = log (19 / 4.05) / log (R _i ) to obtain 95% boron-10,

where N ₉₀ and N ₉₅ - the corresponding required number of elementary steps to obtain the desired product.

The change in the concentration ratio R = boron-11 / boron-10 during extraction and the required number of steps in the extraction cascade are shown in table 2.

Table 2. Experimental definition Modeling Sample Numbers Values R0, R (initial, final) Total change R / R0

Change R one step,

The required number of steps to obtain 90% boron-10 The required number of steps to obtain 95% boron-10 one 2 3 four 5 6 one 4,033
4,066 1,0082 1.00274 292 565 2 4,0505
4,102 1,0127 1,00316 253 490 3 4,033
4,102 1,0172 1,00856 94 181

As can be seen from table 2, in the first example, in which the change in the concentration of boron-10 in the aqueous phase was 0.66% (see example 1 in table 1), to obtain from a natural mixture of isotopes of a product with a concentration of boron-10 of 90 at. %, 292 extraction contacts will be required, and 565 steps will be required to obtain a product with a boron concentration of 10 95 at.%.

In the second example, in which the change in the concentration of boron-10 in the aqueous phase was 1.00% (see example 2 in table 1), 253 extraction contacts would be required to obtain from a natural mixture of isotopes of a product with a concentration of boron-10 90 at.% and to obtain a product with a boron concentration of 10 95 at.% 490 steps are required.

In the third example, in which the change in the concentration of boron-10 in the aqueous phase was 1.40% (see example 3 in table 1), 94 extraction contacts would be required to obtain a product with a natural mixture of isotopes of boron-10 90 at.% and to obtain a product with a boron concentration of 10 95 at.%, 181 steps will be required.

Thus, when using the proposed method in a cascade with the required number of stages of separation can be achieved more than 90% enrichment upon receipt of boron-10.

Claims (3)

1. The method of separation of boron isotopes by chemical exchange in a two-phase reverse-flow system, characterized in that the aqueous phase in the form of a solution of boric acid and the organic phase in the form of a complex of boron with a nitrogen-containing phenol-formaldehyde resol oligomer having an average molecular weight of 450- 500 atomic units, in a diluent, and the circulation of the streams is carried out by re-extraction of boric acid with water, followed by evaporation of the re-extract. 2. The method according to claim 1, characterized in that the oligomer obtained by polycondensation of p-tert-butylphenol with formaldehyde in the presence of ammonia is used. 3. The method according to claim 1, characterized in that as a diluent use a mixture of octanol and tridecane in a ratio of 1: 1 by volume.