Citric acid is one of the organic acids of which world market is growing every year. This paper proposes reactive extraction of citric acid with trioctylamine as an alternative to the classical method [1]. An experimental setup with solvent recycling is presented. As organic solvents were used: octanol, cyclohexanol, iso-butyl alcohol and paraf®n oil. The removal ef®ciency is enhanced when the reactive extraction is accompanied by back-extraction using sodium carbonate as stripping agent.
The extraction-back extraction column of low concentration species by means of an organic closed loop flow, considered as liquid membrane, was modelled then simulated, using some simplifying assumptions. The main hypotheses are: the aqueous phase is perfectly mixed, the drops of the organic phase are lumped into a plug-flow inner cylinder co-axial with the aqueous phase, and the organic phases under the sieve and on the top of the column are perfectly mixed also. The dynamic model of the extraction-back extraction column is, then, applied to the recovery of the hydrocarboxylic acids. The mathematical model, reduced through orthogonal collocation to a system of ordinary differential equations, was solved using a self-adaptive (RK)-type method. Its validation was done based on batch experimental data; the optimal model parameters (the specific mass transfer coefficients for both extraction and back-extraction zones), ensuring the agreement with the experiment, were found by means of a modified genetic algorithm technique. Then, a sensitivity analysis was done, to grasp the behaviour of the system with respect to the main operating parameters - the organic flow in the closed loop, the partition coefficient and the buffer volume.
New green and sustainable sources were chosen to obtain chitosan, an important material, with many applications in different fields. The present study is focused on egg capsules of Rapana venosa waste as raw material for chitosan oligomers. As previous studies revealed that chitosan extraction from this material takes place with a low yield, the present research aimed to optimize this step. A 22 experimental plan, with three replicates in the center, was proposed to investigate the influence of NaOH concentration and temperature on the yield extraction. After a primary analysis of the experimental data, a favorable temperature value was selected (90 °C) at which the total dissolution of the egg capsules was obtained. Then, at this temperature, the experimental plan was extended exploring the influence of the NaOH concentration on three levels (5, 6, and 7%) and the extraction duration on two levels (60 and 85 min). Based on all experimental data, a neural model was obtained and validated. The neural model was used to maximize the yield, applying Genetic Algorithm (GA) implemented in Matlab®. The resulting optimal solution is: NaOH concentration 6.47%, temperature 90 °C, duration 120 min, with a yield value of 7.05%.
Chitin extraction from crab shells was studied experimentally and optimized aiming to obtain chitosan with predefined deacetylation degree and molecular mass. To find out the optimum operating conditions that ensure the obtaining of a chitosan with highest deacetylation degree and specific molecular mass four parameters were varied: the concentration of NaOH and the temperature for deproteinization step, respectively HCl concentration and the number of acidic treatments for the demineralization stage. The experiment was carried on following Taguchi orthogonal array L9, and the best combination of factors was found using the desirability function approach. The optimization results showed that 5% NaOH concentration and low temperatures lead to a chitosan with high deacetylation degree. High molecular mass chitosan is obtained when a single step acidic treatment is used, while a chitosan with low molar mass is obtained for multiple acid contacts and higher HCl concentration.
A reactive extraction/back-extraction process was studied experimentally in a two-stage column. The mathematical model of the reactive extraction using a closed loop moving organic liquid membrane, based upon first principle equations, was derived as a set of Partial/Ordinary Differential Algebraic Equations (P/ODAE). The mathematical model, reduced through orthogonal collocation to a system of ODAE, was solved using a self-adaptive Runge-Kutta (RK)-type method. The mathematical model was calibrated using own batch experimental data and a modified genetic algorithm as optimizer.
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