**6. The effect of cross linking to the nitrogen isotope separation**

Separation and concentration of a stable isotope from an isotopic mixture with natural occurrence is a very complex problem and usually, the isotopic separation coefficients of natural abundance are very low. In general, cation exchange process is a promising technique to produce highly enriched isotope due to the nature of small HETP value. Among the operating parameters in cation exchange process, cross linking is known as a decisive factor on the process of nitrogen isotope separation. It is interesting to evaluation the chromatographic performance of 15N isotope separation by ion exchange resin with different percentage of cross linking.

The cation exchange resins with different cross linking were synthesized from the law material of styrene and the synthetic method was given in Figure 7. When different cross

**Figure 7.** Synthetic method of the cation exchange resin with different cross linking percentage

linking was synthesized, high cross linking means high divynybenzene (DVB) materials contained in the resin structure and this means the percentage of ion exchange functional group was decreased in the same amount resin. The relationship between 15N enrichment percentage and cross linking with 2.0 m migration was given in Figure 8. Enriched 15N isotopes were decreased from 0.93 to 0.68 when compared with the cross linking of twenty and forty percentage. Since high cross linking means low exchange capacity, it is reasonable that the 15N enrichment percentage is reduced with the increase of cross linking at the same given migration distances. SQS-6 resin has 8% cross linking and 15N enrichment percentage was 1.56% when SQS-6 resin was performed under the same condition, and low cross linking resin has much higher enrichment ability than high cross linking resin.

356 Ion Exchange Technologies

ion exchange enrichment.

different percentage of cross linking.

CH=CH2

CH=CH2

CH CH2 CH CH2

SO2Cl

cat.

Styrene Divynylbenzene(DVB) Styrene/DVB resin

CH CH2 CH CH2 CH CH2

SO2Cl SO2Cl

CH=CH2

ClSO3H

+

The results of Run 1-4 clearly indicate that the practical limit of 14N enrichment by the ion exchange packed column is 99.99%. The reason for this limit has not yet been elucidated, but it is estimated that this limit of 99.99% may be applicable for the enrichment of 15N as well. So far, the target of 15N enrichment for nitride fuels is 99.9%. The present work realized the enrichment of 99.678% 15N in Run 5. The results suggest that the 99.9% 15N is attainable by

Separation and concentration of a stable isotope from an isotopic mixture with natural occurrence is a very complex problem and usually, the isotopic separation coefficients of natural abundance are very low. In general, cation exchange process is a promising technique to produce highly enriched isotope due to the nature of small HETP value. Among the operating parameters in cation exchange process, cross linking is known as a decisive factor on the process of nitrogen isotope separation. It is interesting to evaluation the chromatographic performance of 15N isotope separation by ion exchange resin with

The cation exchange resins with different cross linking were synthesized from the law material of styrene and the synthetic method was given in Figure 7. When different cross

CH CH2 CH CH2

NaOH

Chlorosulfonated resin Ion-exchange resin

CH CH2 CH CH2 CH CH2

CH CH2 CH CH2

SO3Na

CH CH2 CH CH2 CH CH2

SO3Na SO3Na

**Figure 7.** Synthetic method of the cation exchange resin with different cross linking percentage

**6. The effect of cross linking to the nitrogen isotope separation** 

The observed HETP values of different cross linking were plotted in Figure 9. It is seen in the figure that cross linking can affect the HETP value obviously. HETP value proportionally increase with the cross linking at the present work and low cross linking has much advantage for HETP. HETP value of 0.036 cm was obtained at the present system by using 20% cross linking and the present resin can be used for the large scale of nitrogen isotope industrial production.

**Figure 8.** Relationship between enriched 15N and cross linking

(Square dot was the result of SQS-6 resin)

**Figure 9.** Observed HETP values and cross linking
