Dan Cascaval

Selective separation of amino acids by reactive extraction

Abstract The method of reactive extraction with di-(2-ethylhexyl)phosphoric acid (D2EHPA) for the separation of a range of amino acids is studied. The results obtained on the individual reactive extraction indicated the possibility of the amino acids selective separation as a function of the pH value of aqueous solution and the acidic or basic character of each amino acid. Thus, using multistage extraction, the total separation of the following amino acids groups has been performed: neutral amino acids ( l -glycine, l -alanine, l -tryptophan) at pH 5–5.5 (nine extraction stages), basic amino acids ( l -lysine, l -arginine) and l -cysteine at pH 4–4.5 (ten extraction stages), l -histidine at pH 3–3.5 (five extraction stages), and acidic amino acids ( l -aspartic acid, l -glutamic acid) at pH 2–2.5 (three extraction stages).

Modeling of mixing in stirred bioreactors: 2. Mixing time for non-aerated broths

Abstract The mixing time is one of the most useful criterion for mixing intensity of fermentation broths and for scale-up of biosynthesis processes. This parameter value depends mainly on the rheological properties of the broths, biomass concentration and morphology, mixing system characteristics and fermentation conditions. For quantifying the influence of these factors on mixing efficiency for stirred bioreactors, these studies were carried out for non-aerated suspensions of bacteria (Propionibacterium shermanii), yeasts (Saccharomyces cerevisiae) and fungus (Penicillium chrysogenum, free mycelia and mycelial aggregates) of different concentrations, using a laboratory bioreactor with double turbine impeller. By means of the experimental data and using a multiregression analysis method, some mathematical correlations for mixing time having the general expression of: tm=α(CxβLδ/Nγ) were established. The proposed equations are adequate for the flow regime of Re

Selective Pertraction of Carboxylic Acids Obtained by Citric Fermentation

Abstract Pertraction through liquid membranes is one of the most recent liquid–liquid extraction techniques that could be applied for separation of biosynthetic products. This article describes facilitated pertraction has been used for selective separation of citric, malic, and succinic acids from a mixture. The separation equipment included a U‐shaped cell containing 1,2‐dichloroethane as a liquid membrane and Amberlite LA‐2 as a carrier. The experimental data indicated that malic and succinic acids can be initially selectively separated from citric acid at an equimolecular ratio between the carrier and these acids. Then, for a selective separation of malic acid from succinic acid, a carrier molar concentration inside the liquid membrane equal to that of malic acid in the feed phase was required. The favorable effect of carrier concentration on separation selectivity was enhanced by the modification of aqueous phases pH and mixing intensification.

Optimization methodology based on neural networks and self-adaptive differential evolution algorithm applied to an aerobic fermentation process

The determination of the optimal neural network topology is an important aspect when using neural models. Due to the lack of consistent rules, this is a difficult problem, which is solved in this paper using an evolutionary algorithm namely Differential Evolution. An improved, simple, and flexible self-adaptive variant of Differential Evolution algorithm is proposed and tested. The algorithm included two initialization strategies (normal distribution and normal distribution combined with the opposition based principle) and a modified mutation principle. Because the methodology contains new elements, a specific name has been assigned, SADE-NN-1. In order to determine the most influential inputs of the models, a sensitivity analysis was applied. The case study considered in this work refer to the oxygen mass transfer coefficient in stirred bioreactors in the presence of n-dodecane as oxygen vector. The oxygen transfer in the fermentation broths has a significant influence on the growth of cultivated microorganism, the accurate modeling of this process being an important problem that has to be solved in order to optimize the aerobic fermentation process. The neural networks predicted the mass transfer coefficients with high accuracy, which indicates that the proposed methodology had a good performance. The same methodology, with a few modifications, and with the best neural network models, was used for determining the optimal conditions for which the mass transfer coefficient is maximized. A short review of the differential evolution methodology is realized in the first part of this article, presenting the main characteristics and variants, with advantages and disadvantages, and fitting in the modifications proposed within the existing directions of research.

Modeling of oxygen mass transfer in the presence of oxygen-vectors using neural networks developed by differential evolution algorithm

The search capabilities of the Differential Evolution (DE) algorithm - a global optimization technique - make it suitable for finding both the architecture and the best internal parameters of a neural network, usually determined by the training phase. In this paper, two variants of the DE algorithm (classical DE and self-adaptive mechanism) were used to obtain the best neural networks in two distinct cases: for prediction and classification problems. Oxygen mass transfer in stirred bioreactors is modeled with neural networks developed with the DE algorithm, based on the consideration that the oxygen constitutes one of the decisive factors of cultivated microorganism growth and can play an important role in the scale-up and economy of aerobic biosynthesis systems. The coefficient of mass transfer oxygen is related to the viscosity, superficial speed of air, specific power, and oxygen-vector volumetric fraction (being predicted as function of these parameters) using stacked neural networks. On the other hand, simple neural networks are designed with DE in order to classify the values of the mass transfer coefficient oxygen into different classes. Satisfactory results are obtained in both cases, proving that the neural network based modeling is an appropriate technique and the DE algorithm is able to lead to the near-optimal neural network topology.

Comparative Study on Reactive Extraction of Nicotinic Acid with Amberlite LA‐2 and D2EHPA

Abstract The comparative study of reactive extraction of nicotinic acid with Amberlite LA‐2 and D2EHPA in three solvents with different polarity indicated that the extractant type and solvent polarity control the extraction mechanism. Thus, the reactive extraction with Amberlite LA‐2 in low‐polar solvents occurs by means of the interfacial formation of an aminic adduct with 3 or 2 extractant molecules. If solvents with higher polarity are used, each reactant participates with one molecule to the interfacial reaction. The mechanism of reactive extraction with D2EHPA involves in all cases the formation of a salt as the product of the interfacial reaction between one molecule of each reactant.

Succinic acid fermentation in a stationary-basket bioreactor with a packed bed of immobilized Actinobacillus succinogenes: 1. Influence of internal diffusion on substrate mass transfer and consumption rate

This paper is dedicated to the study on external and internal mass transfers of glucose for succinic fermentation under substrate and product inhibitions using a bioreactor with a stationary basket bed of immobilized Actinobacillus succinogenes cells. By means of the substrate mass balance for a single particle of biocatalysts, considering the Jerusalimsky kinetic model including both inhibitory effects, specific mathematical expressions have been developed for describing the profiles of the substrate concentrations and mass flows in the outer and inner regions of biocatalyst particles, as well as for estimating the influence of internal diffusion on glucose consumption rate. The results indicated that very low values of internal mass flow could be reached in the particles center. The corresponding region was considered biologically inactive, with its extent varying from 0.24% to 44% from the overall volume of each biocatalyst. By immobilization of bacterial cells and use of a basket bed, the rate of glucose consumption is reduced up to 200 times compared with the succinic fermentation system containing free cells.

New extraction techniques on bioseparations: 1. Reactive extraction

The complexity of downstream processes for biosynthetic products constitutes a particularity of industrial biotechnologies, especially because of the biosynthetic product high dilution in fermentation broth, their chemical and thermal liability and the presence of secondary products. For these reasons, new separation techniques have been developed and applied to bioseparations. Among them, reactive extraction, pertraction (extraction and transport through liquid membranes) and direct extraction from broths have considerable potential and are required for the further development of many biotechnologies. This review is structured on two parts and presents our original results of the studies on the separation of some biosynthetic products (antibiotics, carboxylic acids, amino acids, alcohols) by reactive extraction in the first part, and by pertraction and direct extraction from broths without biomass filtration in the second. For all the analyzed cases, these extraction techniques simplify the technologies by reducing material and energy consumption, by avoiding product inhibition, by increasing the separation selectivity, therefore decreasing the overall cost of the product.

INFLUENCE OF SOLVENT POLARITY ON INTERFACIAL MECHANISM AND EFFICIENCY OF SUCCINIC ACID REACTIVE EXTRACTION WITH TRI-n-OCTYLAMINE

This article presents the results of a comparative study of reactive extraction of succinic acid with tri-n-octylamine (TOA) dissolved in solvents with different dielectric constants (dichloromethane, n-butyl acetate, and n-heptane), with and without octan-1-ol addition as phase modifier. The positive effect of octan-1-ol on extraction efficiency was quantified by means of amplification factors. For all studied systems, the addition of octan-1-ol into the solvent phase led to an increase of extraction efficiency, the most important effect being recorded for the solvent with the lowest polarity, namely n-heptane. The maximum value of amplification factor was reached for pH = 6 and indicated an increase of reactive extraction yield of about 1.26 times for dichloromethane, 1.55 times for n-butyl acetate, and 2.88 times for n-heptane.

Glucose Mass Transfer Under Substrate Inhibition Conditions in a Stationary Basket Bioreactor with Immobilized Yeast Cells

The work is dedicated to the study on the external and internal mass transfers of glucose for alcoholic fermentation under glucose inhibition limitation using a bioreactor with stationary basket beds of immobilized Saccharomyces cerevisiae cells. By means of the substrate mass balance for a single particle of biocatalysts, considering the kinetic model adapted for the inhibitory effect of glucose, specific mathematical models have been developed for describing the profiles of the substrate concentration in the outer and inner regions of biocatalysts and, implicitly, for estimating its mass flows in the liquid boundary layer surrounding the particle and inside the particle. The values of the mass flows are significantly influenced by the internal diffusion velocity of substrate and rate of the biochemical reaction of substrate consumption, but also by the position inside the basket bed. These influences cumulated led to the appearance of biological inactive region near the particle centre, its magnitude varying from 0.34 to 31% from the overall volume of particles. The presented results are the first unitary approach of the aspects of substrate mass transfer in a basket bed of immobilized biocatalysts, the proposed models being original and complex.