Abstract
Nanofiltration can be used to separate succinic acid (SA) from other organic acids in a fermentation broth. However, commercial nanofiltration membranes can be insufficiently selective since some produced organic acids have similar molecular weights. SA production from biomass fermentation entails separation of succinic acid from the other concomitantly produced organic acids such as acetic acid, formic acid, pyruvic acid etc. In this study, five commercial nanofiltration membranes were tested for SA rejection and selectivity under dead-end and crossflow modes of SA recovery from selected synthetic solutions and a real fermentation broth. SA rejections up to 94.1 ± 1.5% and 95.5 ± 3.5% were observed for the synthetic broth and the fermentation broth, respectively. The SA fractions obtained in the retentate were nearly 70% and 60% for synthetic and fermentation broth, respectively. The highest rejections and SA fraction values were achieved with DK and NF270 membranes, which also showed the highest permeate flux. Model evaluation using the Donnan-steric pore model with dielectric exclusion (DSPM-DE) showed that 99% of the SA rejection occurs at the membrane interface and not inside the membrane. Based on the modelling, the most important mechanism affecting separation was dielectric exclusion at both sides of the membrane surfaces. Moreover, identified sensitive model parameters, i.e. pore dielectric constant (εpore), charge density (Xd) and pore radius (rp), were estimated through model fitting and were found to be highly correlated with significant variations. Finally, for the first time, a calibrated model with synthetic broth was successfully used to predict organic acids rejection for a real fermentation broth (with 12% and 3% prediction error for succinate rejection by NF270 and DK, respectively). Such prediction was achieved only by measuring organic acid concentrations in the fermentation broth and using the three sensitive parameters. Furthermore, the potential contribution of different transport mechanisms of SA was quantified for the first time.
Highlights
Succinic acid (SA) is an organic acid that can replace petroleum to produce several commercial products such as solvents and lubricants, synthetic resins and biodegradable polymers as well as cosmetics, food additives and pharmaceuti cals intermediates [1,2]
Model evaluation using the Donnan-steric pore model with dielectric exclusion (DSPM-DE) showed that 99% of the succinic acid (SA) rejection occurs at the membrane interface and not inside the membrane
The aim of this study was to assess the performance of selected commercial NF membranes in synthetic and real SA fermentation broths
Summary
Succinic acid (SA) is an organic acid that can replace petroleum to produce several commercial products such as solvents and lubricants, synthetic resins and biodegradable polymers (polybutylene succinate and polyamides) as well as cosmetics, food additives and pharmaceuti cals intermediates [1,2]. Though SA is historically a petrochemical refinery product, it has recently been efficiently obtained from the fermentation of many biomasses, including agricultural and industrial wastes [3]. Microfiltration and ultrafiltration have been efficiently used for step I and II [9] and a high degree of isolation of SA from pigments, amino acids (step III) and other organic acids (IV) can be achieved via nanofiltration (NF) [10,11,12]. NF is effi ciently used to separate monovalent inorganic and organic ions from the divalent one and from bigger molecules [13]
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