bsc-assignment-dion.docx

Bachelor thesis: Colloid formation in carboxylic acid extraction

A promising method to remove organic acids from dilute aqueous streams is reactive extraction with an organic base, like tri-n-octylamine (TOA). Typical applications are the removal of acetic acid from waste streams or removal of lactic acid from fermentation broths. Over the years many experiments were executed to gain insights in the mechanisms and equilibria of acid extractions with organic bases [1][2].

https://upload.wikimedia.org/wikipedia/commons/thumb/1/1a/Micelle_scheme2-en.svg/562px-Micelle_scheme2-en.svg.pngA typical extraction equilibrium is the distribution of lactic acid between an aqueous phase and an organic phase containing TOA dissolved in 1-octanol. At high acid concentrations in the organic phase, it becomes cloudy. This implies the formation of colloids in the organic phase. These colloids are small “drops” of liquid evenly dispersed into the organic phase. These can be formed when long, non-polar molecules have one polar site. These polar sites may cluster together with the non-polar sites pointing at the outside of the colloid, as schematically shown in figure 1. It is assumed that at low concentrations the acid molecule forms a hydrogen bond with the nitrogen site of the organic base. There are however equilibria described in literature where the number of acid molecule significantly outnumbers the number of base molecules. At high acid concentrations it is unknown whether the acid molecules are dissolved in the organic phase or form a colloid. Formation of colloids is a fundamental part in understanding acid extractions, but has never been investigated yet.

It is your task to determine when colloids are formed and how stable they are. The size distribution of colloids can be determined by Dynamic Light Scattering (DLS). This is a technique which uses light scattering to determine the distribution profile of small particles in a suspension. Using this technique you will answer the following research questions:

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When do colloids form in reactive extraction of organic acids?

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What is the influence of the acid loading?

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What is the influence of the diluent?

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What is the influence of water co-extraction?

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How stable are the colloids?

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Does the size distribution change over time?

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Wat is the influence of temperature?

[1] Tamada, Janet A., Kertes, A. Steven, King, C. Judson, Extraction of carboxylic acids with amine extractants. 1. Equilibria and law of mass action modeling, 1990, Industrial and Engineering Chemistry Research, 29 (7), pp. 1319-1326.

[2] Qin, W., Li, Z., Dai, Y., Extraction of Monocarboxylic Acids with Trioctylamine: Equilibria and Correlation of Apparent Reactive Equilibrium Constant, 2003, Industrial and Engineering Chemistry Research, 42 (24), pp. 6196-6204.