(503b) Multicomponent Adsorption of Organic Acids in Stratified Beds with Separation Using pH Swing Adsorption

Heterofermentative bacteria such as Lactobacillus sp and Propionibacterium sp produce more than one organic acid as fermentation products of carbohydrate substrates. The cost of recovery and purification of bioproducts is about 60% of the overall process costs [1]. Hence, it is important to find cost-effective routes to recover these products so as to enable the sustainable production of biobased platform chemicals. Single component adsorption of carboxylic acids on polymeric resins and adsorbents has been studied extensively in the literature. However, there is very limited information on multicomponent adsorption and separation of organic acid mixtures. In this study equilibrium and kinetic aspects of multicomponent adsorption of acetic and lactic acids are explored both experimentally and using mathematical models. A conceptual model of a cyclic pH swing adsorption (pHSA) process using fixed-beds is proposed to recover acetic and lactic acids from fermentation broths.

One of the main objectives of this study is to develop suitable multicomponent adsorption models to examine sorption as an effective technology for the recovery of acetic and lactic acids from dilute aqueous solutions. Adsorption equilibrium studies for single and multicomponent adsorption of acetic and lactic acids on a weak base macroporous resin were conducted. Fixed-bed studies were conducted in stratified fixed-beds so as to ascertain the effects solute front sharpening on the roll-up of the weakly sorbed solute. A multicomponent adsorption model was developed to predict the breakthrough profiles and to evaluate the impacts of bed stratification on solute front shape and bed capacity utilization.

Multicomponent sorption experimental data were developed for acetic and lactic acids at pH values of 2.8 and 4.8. The percentage dissociation of these acids depends on the pH and the pK_a of the acids. At pH 2.8 acetic acid is the weakly adsorbed component, whereas at pH 4.8, lactic acid is the weakly adsorbed component. Thus, by swinging the pH between 2.8 and 4.8 it is feasible to separate the two acids using multiple bed configurations similar to PSA systems. Experimental data indicate that reverse stratified bed configurations provide more effective bed capacity utilization than conventional adsorption systems with single or stratified particle layers [2]. Computer model simulation studies indicate that roll-up effect can be exacerbated in reverse stratified beds by increasing the number of layers of adsorbent particles or by increasing the length of the bed. A general rate model will be used to analyze solute behavior in fixed-beds with conventional and reverse stratified tapered bed configurations. The effects of key variables such as bed length, particle stratification, bed geometry, and flow rate will be presented using model simulations and experimental data. A concept of a two-bed pH swing sorption system will be presented for the recovery and separation of acetic and lactic acids.

References

[1] Straathof, A.J.J, The Proportion of Downstream Costs in Fermentative Production Processes, in Comprehensive Biotechnology, Moo-Young (ed.), Elsevier Publ., 2011.

[2] Eppink, A, M. Kuhn, and H. Briesen, Model-based design of stratified packings for enhanced mass transfer using optimal control theory, AIChE J., 2023. https://doi.org/10.1002/aic.18285.