Comparison of mass transfer performance of pulsed columns with Tenova kinetics internals and standard disc and doughnut internals
Introduction
Solvent extraction is one of the most effective separation processes to be applied widely in industries such as hydrometallurgy, pharmaceuticals and waste treatment (Rydberg, 2004). In the extraction process, two immiscible liquid phases, typically an aqueous solution and an organic solvent, are contacted to extract a desirable solute. One of the most common types of contactors are pulsed solvent extraction columns due to their low maintenance, easy operation, smaller footprint and lower loss of organic. Different types of pulsed solvent extraction columns are available, including pulsed packed columns, pulsed perforated plate columns and pulsed disc and doughnut columns. The design of pulsed column internals can significantly affect column performance.
Pulsed disc and doughnut columns have been successfully applied to kinetically fast systems, such as the extraction of Uranium by Alamine 336 and Nickel by Cyanex 301. Trials with slower kinetic systems, such as copper with a range of oximes, has not been as successful due to the high height required to achieve sufficient recoveries.
Recently, Tenova Kinetics Internals (TKI) have been developed to improve column performance, particularly in kinetically slower systems. TKI have “teeth” on the edges of disc and doughnut sheets which are designed to enhance breakage of the dispersed phase droplets, and therefore achieve less backmixing and improved mass transfer for the same flux. Our previous studies of the hydrodynamic (Li et al., 2017; Li et al., 2018a) and axial dispersion performance (Li et al., 2018b) of TKI showed that the kinetic internals have higher potential throughput and similar axial dispersion coefficients compared with the standard disc and doughnut internals.
This study investigates the potential of using columns for a kinetically slow system, particularly with the newer design internals. The mass transfer performance of the TKI and DDI are compared. The height of mass transfer unit (Hoc) was measured and analysed over a wide range of column working conditions, including pulsation intensities, dispersed and continuous phase velocities, in a 2 m high and 76 mm diameter pilot scale pulsed column. To provide the overall mass transfer performance of pulsed columns for two liquid – liquid systems, sulphuric acid (aq) – 3 v/v % Alamine 336, 1 v/v % isodecanol in ShellSol 2046 (org) and copper sulphate (aq) – 6.4 v/v % LIX 84 in ShellSol 2046 (org) systems are used. The sulphuric – Alamine system is representative of a fast kinetics system (first order kinetic reaction rate of 1.4 s−1 (Wasewar et al., 2002) and the copper sulfate – LIX 84 system is representative of a slow kinetics system with (first order kinetic reaction rate of 2.1 × 10−2 s−1 (Younas et al., 2015).
Section snippets
Background
The mass transfer performance of pulsed solvent extraction columns is influenced by the interfacial area (a), the concentration driving force (∆cc or ∆cd) and the overall mass transfer coefficient (koc or kod). The mass transfer rate can be expressed as Eq. (1) where c⁎c and c⁎d are concentration of solute at interface of continuous and dispersed phases, respectively (Lewis and Whitman, 1924).
The overall mass transfer coefficients, koc and kod, based on the
Liquid-liquid systems
Two liquid-liquid systems were selected for investigation in this study, one slow and one fast kinetics systems. The fast system selected was ~ 0.04 M sulphuric acid solution (aqueous phase). The solution was prepared via dilution of 98% sulphuric acid (Sigma Aldrich) with Milli-Q water. The organic phase was a mixture of 3 v/v % Alamine 336 (tri-n-octylamine) (BASF) and 1 v/v % isodecanol (ExxonMobil) in ShellSol 2046 (Shell). The isodecanol was added to eliminate the formation of third phase
Results and discussion
The effect of pulsation intensity, the continuous and dispersed phase velocities on the height of mass transfer unit and overall mass transfer coefficient based on the continuous phase with DDI and TKI using H2SO4-Alamine 336 system and CuSO4-LIX 84 system have been studied under a wide range of operating conditions. The pulsation intensity was varied from 0.005 m/s to 0.03 m/s, and the continuous and dispersed phase velocities were varied from 6.62 × 10−4 m/s to 1.43 × 10−3 m/s and 7.35 × 10−4
Conclusions
The conclusions from this work can be summarised as follows:
- 1.
For CuSO4 – LIX 84 system, the height of mass transfer unit (Hoc) decreases with increasing pulsation intensity (Af) and increases with either increasing continuous or dispersed phase velocities for both DDI and TKI using the CuSO4 – LIX 84 system. In comparison with DDI, the TKI reduced the Hoc at the same operating conditions and also reduced the impact of phase velocity on the Hoc making them more efficient.
- 2.
For H2SO4-Alamine 336
Nomenclature
- a
Interfacial area, m2
- A
pulsation amplitude, m
- c
solute concentration in liquid phase, M
- d
drop equivalent sphere diameter, m
- d32
Sauter-mean drop diameter, m
- D
molecular diffusivity, m2/s
- E
actual axial mixing coefficient, m2/s
- f
pulsation frequency, Hz
- g
gravity acceleration, m/s2
- Hoc
height of mass transfer unit based on continuous phase, m
- kd/kc
individual mass transfer coefficient of dispersed phase/continuous phase, m/s
- kod/koc
overall mass transfer coefficient of dispersed phase/continuous phase, m/s
- K
Acknowledgement
The authors would like to acknowledge the funding provide by the Australian Research Council through Linkage grant LP130100305 and BHP Billiton, Olympic Dam, for this project, and would also like to thank the Particulate Fluids Processing Centre – a Special Research Centre of the Australian Research Council for the resources provided for this project.
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