PVT properties of N,N,N′,N′-Tetraoctyl-3-oxapentanediamide (TODGA)

Abstract

N,N,N′,N′-Tetraoctyl-3-oxapentanediamide (TODGA) is a versatile extractant for partitioning of fission products from highly active raffinate wastes. Its PVT properties are not available in literature. In this work, PVT properties of TODGA, estimated using group contribution method, are reported. A corresponding-states based equation as well as Wagner constants were also reported in the range of 273.15 K to critical temperature.

Introduction

N,N,N′,N′-Tetraoctyl-3-oxapentanediamide (TODGA) is used as the extractant for partitioning of fission products. VLE calculations are required for many design steps as well as for predicting air-borne concentration of TODGA in the event of an exposure. Therefore, knowledge of PVT properties of TODGA for accurate prediction of vapour pressure and other parameters is quite important.

The PVT properties of TODGA have not been listed in literature. Based on Marrero and Gani [1] group contribution method, recently Kumar and co-workers [2–5] proposed PVT properties of tri-n-butyl phosphate (TBP), di-2-ethylhexyl phosphoric acid (DEHPA), phenyltrifluoromethyl sulfone (FS-13) and tri-iso-amyl phosphate (TiAP). On similar lines, PVT properties of TODGA are estimated and reported in this paper.

Results and discussion

Estimation of T_b, T_c, V_c and P_c

For the sake of group contribution method, the basic molecule TODGA may be written as (C₈H₁₇)₂-N-CO-CH₂-O-CH₂-CO-N-(C₈H₁₇)₂. The molecular structure is shown in Fig. 1. Therefore, it is observed that the target molecule TODGA consists of only first order groups and it does not have any higher order interactions. The CON(CH₂)₂ group contribution value is not available for critical pressure, critical temperature and critical volume. Thus, this groups contribution is assumed to be the same as CON(CH₃)₂. In this case, group contribution method of Marrero and Gani [1] can be simplified as follows in Eq. 1.

$$ f\left( x \right) = \sum\limits_{i} {n_{i} C_{i} } $$

(1)

where f(x) is a particular function for the thermodynamic property, n is the number of occurrence and C _i is the contribution for the individual groups. These functions are listed in Table 1. The list of first order groups, its occurrences and its contributions are given in Table 2. Normal boiling point T _b was estimated to be 767.42 K. T _c , V _c and P _c were estimated to be 969.1 K, 2,193.93 dm³/mol and 8.5 bar, respectively. These values are listed in Table 3.

Fig. 1

Molecular structure of TODGA

Table 1 Functions used in group contribution method of Marrero and Gani [1]

Table 2 Contribution of various groups to boiling point and critical properties

Table 3 Estimated PVT properties of TODGA

Estimation of acentric factor ω

As per Poling et al. [6], acentric factor is calculated as

$$ \omega = - \frac{{\ln (P_{c} /1.01325) + f^{(0)} (T_{br} )}}{{f^{(1)} (T_{br} )}} $$

(2)

Where P _c is in bar and T _br  = T _b /T _c . The functions f ⁽⁰⁾ and f ⁽¹⁾ were proposed by Ambrose and Walton [7] as follows—

$$ f^{(0)} = \frac{{ - 5.97616\tau + 1.29874\tau^{1.5} - 0.60394\tau^{2.5} - 1.06841\tau^{5} }}{{T_{br} }} $$

(3a)

and

$$ f^{(1)} = \frac{{ - 5.03365\tau + 1.11505\tau^{1.5} - 5.41217\tau^{2.5} - 7.46628\tau^{5} }}{{T_{br} }} $$

(3b)

where τ = (1–T _br ). In this case, T _br is equal to 0.791. With help of Eq. 2 and Eqs. 3a and 3b, ω was estimated as 0.5244.

Estimation of vapour pressure of TODGA by Ambrose–Walton corresponding states method

Vapour pressure of TODGA can be estimated by the Pitzer expression listed as—

$$ \ln \left( {\frac{P}{{P_{c} }}} \right) = f^{(0)} + \omega f^{(1)} + \omega^{2} f^{(2)} $$

(4)

where corresponding functions were proposed by Ambrose and Walton [7] as

$$ f^{(0)} = \frac{{ - 5.97616\tau + 1.29874\tau^{1.5} - 0.60394\tau^{2.5} - 1.06841\tau^{5} }}{{T_{r} }} $$

(5)

and

$$ f^{(1)} = \frac{{ - 5.03365\tau + 1.11505\tau^{1.5} - 5.41217\tau^{2.5} - 7.46628\tau^{5} }}{{T_{r} }} $$

(6)

and

$$ f^{(2)} = \frac{{ - 0.64771\tau + 2.41539\tau^{1.5} - 4.26979\tau^{2.5} + 3.25259\tau^{5} }}{{T_{r} }} $$

(7)

It may be noted that while estimating vapour pressure of TODGA only T _b is required. No experimental vapour pressure values were used in the related computations. Thus this method provides an independent means to verify experimental data and derived Wagner constants.

Estimation of Wagner constants for vapour pressure of TODGA

Many forms of Wagner equations are being used in the literature. Authors have used the following form, reported by Ambrose [8]

$$ \ln \left( {\frac{P}{{P_{c} }}} \right) = \frac{{a\tau + b\tau^{1.5} + c\tau^{2.5} + d\tau^{5} }}{{T_{r} }} $$

(8)

where τ = 1–T _r . Constant of Eq. 8 were estimated by linear regression from the predicted vapour pressure by the Ambrose–Walton corresponding states method and were listed in Table 4. Figure 2 shows the estimated vapour pressure of TODGA in a temperature range of 273.15 K–T _c.

Table 4 Regressed Wagner constants for TODGA

Fig. 2

The predicted vapour pressure of TODGA using Ambrose–Walton corresponding states method

Conclusions

PVT properties of TODGA, extractant used in the partitioning of fission products from the highly active radwaste, have been estimated using group contribution method and its vapour pressure was predicted using Wagner equation.