The Separation of Hexamethylenediamine from Aqueous Solution by Solvent Extraction with Butanol
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Authors
Sargent, Michael J
Slater, Nigel KH
Dennis, John S
Smith, Gary J
Pearlman, Paul S
Publication Date
2022Journal Title
Separation and Purification Technology
ISSN
1383-5866
Publisher
Elsevier
Type
Article
This Version
AM
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Sargent, M. J., Slater, N. K., Dennis, J. S., Smith, G. J., & Pearlman, P. S. (2022). The Separation of Hexamethylenediamine from Aqueous Solution by Solvent Extraction with Butanol. Separation and Purification Technology https://doi.org/10.1016/j.seppur.2022.120655
Abstract
This paper details an investigation into the separation of hexamethylenediamine (HMD) from dilute aqueous
solutions by solvent extraction. This separation is potentially useful in (i) reclaiming HMD from waste
generated in the production of nylon, (ii) for extracting HMD produced by fermentation, or (iii) reclaiming it
from waste emanating from the depolymerization of nylon during recycling. Butanol was identified as a
suitable solvent for the preferential dissolution of HMD from an aqueous solution, and it was found that the
addition of sodium hydroxide resulted in improved separation. It was deduced that HMD has a bridging
effect on the partial miscibility of water and butanol, and approximately 10 wt% of HMD was sufficient to
allow for complete miscibility and the avoidance of phase separation. However, the addition of NaOH to the
system reversed this bridging effect and reduced the solubility of butanol in the aqueous phase whilst also
increasing the partitioning of HMD between the organic and aqueous phase.
A model for an equilibrium mixer-settler unit was developed with three important findings emerging. Firstly,
the amount of water which could be dissolved in the organic phase was found to increase with the amount
of HMD present, although this effect was neutralised by the presence of sufficient NaOH. Secondly, the
amount of butanol which could be dissolved in the aqueous phase was found to decrease as the amount of
NaOH present increased but was largely independent of the amount of HMD. Lastly, the partitioning
coefficient of HMD was found to decrease as the amount of HMD increased but increased as the molar ratio
of NaOH to HMD was raised. Fitted equations for these three findings allowed closure to be achieved. This
model predicted a set of operating conditions giving 99.95% extraction of a very dilute aqueous HMD
solution (1 wt%), including a doubling of the HMD concentration in the organic product.
Embargo Lift Date
2023-02-28
Identifiers
External DOI: https://doi.org/10.1016/j.seppur.2022.120655
This record's URL: https://www.repository.cam.ac.uk/handle/1810/334123
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