The MixAlco process, a proprietary technology owned by Texas A&M University, converts biomass (e.g., municipal solid waste, sewage sludge, paper, agricultural residues, and energy crops) into usable chemicals (e.g., acetic acid) and fuels (e.g., ethanol). Historically, calcium carbonate has been used as the buffer. Recently, it was found that using ammonium bicarbonate as the buffering agent enhances the fermentation conversion. In this case, fermentation broth contains ammonium salts (e.g., ammonium acetate, propionate, butyrate, pentanoate). Therefore, the downstream processing steps (including extraction, purification, esterification, and product separation) must be compatible with the ammonium carboxylate salts formed in the fermentation. This research focuses on converting fermentation broth carboxylate salts into their corresponding acids via "acid springing." Reactive extraction and thermal conversion (distillation) are crucial parts of the acid springing process. Because the components of the fermentation broth are over 80% ammonium acetate and 20% other ammonium carboxylate salts (ammonium propionate, butyrate, pentanoate, etc.), all the initial experiments in this study were performed using reagentgrade ammonium acetate to simplify the reaction. Later, actual fermentation broth was employed. The primary objective of this study was to provide the optimal operating conditions to make the downstream processing steps of the MixAlco process compatible with ammonium carboxylate salts formed in the fermentation. The optimal initial concentration for reactive extraction should be 150-200 g/L and the volume ratio of aqueous phase and extractant should be 1:1. The distribution coefficient reaches the maximum value when the concentration of TOA is 20% (vol %) in n-octanol. The batch distillation study shows that there are two reaction stages: (1) water leaves the system at 100-106 °C and (2) the acid-amine complex decomposes at 160-180 °C.

Lactic acid recovery from dilute fermentation broths is a growing requirement due to the increasing demand for pure lactic acid. Reactive extraction is proposed as an alternative to conventional methods of recovery, since the selectivity of separation is remarkably enhanced in reactive extraction. The aim of this study is to perform the equilibrium studies for the recovery of lactic acid from its synthetic aqueous solutions (not from real fermentation broths) by reactive extraction and investigate the effects of various parameters such as initial lactic acid concentration in the aqueous phase (0.25 - 1.3 M), initial pH of the aqueous phase (2 &ndash / 6), organic phase extractant concentration (0.1 &ndash / 0.5 M), type of the extractant (chloride, hydrogensulphate and hydroxide salts of tri-n-octylmethylammonium) and the type of diluent (oleyl alcohol or octanol). The results of the experiments showed that the degrees of extraction decreased with increasing use of diluent with the extractant and increasing initial lactic acid concentration of the aqueous phase. Highest degrees of extraction were achieved for undiluted extractants. The performance of the diluents were investigated by performing extraction experiments with solutions of TOMAC in oleyl alcohol or octanol at different pH values and it was observed that octanol had a higher solvating power than oleyl alcohol especially at lower aqueous phase pH values. Higher extraction efficiencies were obtained for TOMAC dissolved in octanol rather than oleyl alcohol. Initial aqueous pH of 6 was identified as the optimum pH for the extraction, also due to its being equal the average fermentation pH for the extractions with Lactobacillus species. Among the different salts of tri-n-octylmethylammonium, hydroxide salt exhibited the highest degrees of extraction (83% with undiluted TOMA(OH) and 78% with 0.5 M TOMA(OH) in octanol for the extraction of 0.316 M lactic acid solutions). The present work is the first step in the design of an industrial reactive extraction process that is going to attempt forward and backward extraction of lactic acid simultaneously in a hollow fiber membrane module that is going to be attached to the lactic acid fermentor to achieve continuous product recovery. The equilibrium data obtained from this study can be combined with the kinetic studies as the next step of designing a separation module.

Lactic acid is a fermentation-derived organic acid used in a wide range of industries, such as food processing and pharmaceuticals. Its market is expected to expand due to the worldwide concern for the environment, as it is an essential feedstock for biodegradable polymers. However, fermentation product is a very dilute, multicomponent aqueous solution. Subsequent separation, purification and concentration of organic acids is difficult because of high affinity of the acids for water. Reactive extraction is a viable alternative to classical separation techniques. Amine extractants dissolved in organic diluents are suitable agents with reasonable ranges of viscosity and density of the solvent phase. The product is obtained in an organic phase after reactive extraction. The aim of this study is to obtain equilibrium data of back extraction of lactic acid into appropriate aqueous solutions from the organic phase. Aqueous solutions of NaCl, NaOH, Na2SO4, NaNO3 and Na2CO3 were examined as back extractant in various initial concentrations (0.005 &ndash / 3 M). The organic phase consists of tri-n-octylmethylammonium lactate (TOMA(La)) dissolved in either oleyl alcohol or octanol with initial concentrations between 0.1 and 0.3 M. According to results of the experiments, the level of back extraction generally increased with increasing initial salt concentration in aqueous phase and decreased with increasing initial TOMA(La) concentration in organic phase. For all salts investigated, considerable levels of back extraction were obtained. NaOH was considered as the most suitable back extractant among the salts investigated since it exhibits higher distribution coefficients, regenerates tri-n-octylmethylammonium hydroxide (TOMAOH) in the organic phase and has no adverse effect on fermentation medium when forward and backward extraction steps are coupled with the fermentation. The effect of diluent type of TOMA(La) was also investigated during the experiments and it was concluded that octanol is a better diluent since it gives higher equilibrium distribution coefficients in addition to its higher solvating power and lower viscosity. The present work is a part of a comprehensive research program aiming to collect data and develop knowledge for the design of an industrial reactive extraction process coupling forward and backward extraction of lactic acid in a single unit and integrating fermentation and product separation. The kinetic parameters should be obtained as the next step for the design of such a process.

Interest in recovery of carboxylic acids from their aqueous solutions and production media has been growing with the improvements in the production techniques. Reactive extraction is proposed as a promising method to achieve high distribution coefficients with good selectivity. In the present study, equilibrium and kinetic studies, needed for the design of a recovery unit were carried out. Reactive extraction of pyruvic, acetic and lactic acids from their single and mixed acid solutions were carried out with tertiary amines, Alamine 336 and trioctylamine, dissolved in diluents, 1-octanol and oleyl alcohol. The kinetic parameters such as reaction order and rate constant were calculated by using the aqueous solution of pyruvic acid with 1-octanol solution of trioctylamine. The distribution coefficient of pyruvic acid was obtained as 0.30 and 0.07 with 1-octanol and oleyl alcohol respectively. The trend did not change after the addition of the extractants to the diluents. As expected, the more polar diluent extracted more acid than the less polar one. The extractant was observed to be the limiting reagent of the reversible complexation reaction in the organic phase. It was seen that loading ratio was not affected by the concentration of the extractant in the organic phase but increased with the equilibrium concentration of the acid in the aqueous phase. The results showed that mainly (1-1) acid-amine reaction occurred in the organic phase. Because tertiary amines can react with only undissociated acids, the increase in the initial pH of the aqueous phase caused a decrease in the distribution coefficients of the carboxylic acids studied. The effect of the concentration of the organic phase disappeared when the initial pH of the aqueous phase was 4.0 and a distribution coefficient value of 0.1 was achieved for all concentration levels of organic phase. Similar results were obtained for acetic and lactic acids and this behavior was used to propose a selective recovery of the acids from their mixed acid solutions. The presence of acetic acid prevented the extraction of pyruvic acid. The increase in the concentration of the extractant in the organic phase caused an increase in the distribution coefficient of pyruvic acid. During the extraction process, lactic acid could not be recovered from ternary acid solutions because of its high hydrophilicity. The results of reactive extraction of lactic and pyruvic acids from their binary acid solutions showed that at higher concentration of lactic acid, the distribution of pyruvic acid was negatively affected. On the other hand, the presence of lactic acid at a low concentration level did not affect the distribution of pyruvic acid. It was found that the reaction between pyruvic acid and trioctylamine in 1-octanol was first order with respect to the reactants with a second order rate constant of 0.94 L mol-1 s-1. The enhancement factor of the system was obtained as 25.

L’acide 3-hydroxypropionique (3-HP) est une molécule plate-forme, particulièrement visée pour ses dérivés acrylés et les polyesters. Sa production par voie biotechnologique fait l’objet de nombreuses études, afin de les obtenir de manière biosourcée. Cependant, dans ces procédés, le 3-HP est dilué dans des milieux de fermentation contenant de nombreuses impuretés. De plus, l’accumulation de l’acide dans les milieux crée une forte inhibition sur les microorganismes producteurs. Nous proposons alors un procédé visant à extraire sélectivement le 3-HP du milieu de fermentation en même temps qu’il est produit afin de limiter son accumulation et de le purifier en continu. Les propriétés du 3-HP ainsi que les meilleures conditions de fermentation actuelles ont permis d’identifier l’extraction liquide-liquide réactive en contacteur membranaire comme une technique de choix. Nous avons tout d’abord élucidé le mécanisme réactionnel impliqué dans le système puis modélisé les équilibres associés afin de pouvoir prédire les rendements d’extraction en fonction de paramètres opératoires. Plusieurs méthodes de désextraction ont été testées, ce qui a permis de coupler les étapes d’extraction et de désextraction dans un procédé semi-continu mimant une production fermentaire. La modélisation dynamique de ce mode de fonctionnement a permis de prédire précisément les résultats expérimentaux. Les milieux ont alors été complexifiés afin de mieux représenter la réalité d’un milieu biologique en identifiant l’impact de chaque constituant. / 3-hydroxypropionic acid (3-HP) is a platform molecule targeted for its acrylated derivatives and polyesters. Its production through biological pathways is widely studied in order to make them bio-based. However, in such processes, 3-HP is diluted in fermentation broths containing many impurities. Moreover, the accumulation of the acid in the broths generates a strong inhibition towards the producing microorganisms. We suggest here a process aiming at extracting 3-HP selectively as soon as it is produced in order to reduce its accumulation and have it purified continuously. 3-HP properties as well as the current best fermentation conditions made us identify reactive liquid-liquide extraction in membrane contactors as promising technique. First, we elucidated the reaction mechanism of extraction in our system and then modeled the associated thermodynamic equilibria as a function of operating paramaters. Several back-extraction methods were tested and it allowed the coupling of the extraction and back-extraction steps in a semi-continuous process mimicking a biological production. The dynamic modeling of this operating mode made possible the accurate prediction of experimental results. The aqueous phase were then made more and more complex in order to better describe an actual fermentation broth and identify the influence of each component on the process efficiency in terms of yield, kynetics and selectivty.