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| Author(s): |
Marcus Bruno Soares Forte
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia de Alimentos |
| Defense date: | 2013-02-27 |
| Examining board members: |
Francisco Maugeri Filho;
Eliana Setsuko Kamimura;
Marcio Antonio Mazutti;
Rubens Maciel Filho;
Telma Teixeira Franco
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| Advisor: | Maria Isabel Rodrigues; Francisco Maugeri Filho |
| Abstract | |
The main focus of this thesis was to study the adsorption of clavulanic acid (CA) in layered double hydroxides (LDH) and to use these adsorbents in fixed bed columns for separation of CA from amino acids. The thesis was developed in three steps: first, it was used LDH-type hydrotalcites. Adsorption studies were performed in stirred batch glass reactors. It was shown that distilled water and a solid/liquid ratio of 15.0 mg/L generated the most favourable conditions for adsorption. A calcined hydrotalcite containing 70 % of MgO was selected for further study since it presented the best adsorption performance. Adsorption equilibrium was evaluated from adsorption isotherms determined at different temperatures. The experimental isotherm data were well fitted by a linear equilibrium model with the corresponding adsorption constants being klin = 0.404, 0.602, 0.849 and 1.083 L/g at 16.5, 19.0, 21.5 and 24.0°C, respectively, showing an increased adsorption capacity at higher temperatures. Thermodynamic evaluation of the process allowed the Gibbs¿ free energy (?G°), the standard enthalpy change (?H°) and the standard entropy change (?S°) to be estimated as follows: ?G° = 2.100, 1.301, 0.503 and ¿0.295 kJ/mol at 16.5, 19.0, 21.5 and 24.0°C, respectively; ?H° = 94.602 kJ/mol; and ?S° = 0.319 kJ/(mol.K), respectively. The second step was developed at the Laboratory of Inorganic Materials of the Blaise Pascal University France during a doctoral internship in France. Different LDH compositions have been investigated: Zn2Cr-Cl, Zn2Cr-NO3, Zn2Al-NO3 and Mg2Al-NO3. Zn2Cr-CA hybrid LDH assemblies were prepared through coprecipitation method to evaluate the affinity between the CA molecule and the interlayer sites. Experiments were carried out using two different sources of CA, i.e. the pharmaceutical product Clavulin® and Clavulanate: Avicel (1:1). The resulting inorganic-organic "sandwich" structure was characterized by a combination of techniques showing an expansion of the layered structure from 0.78 nm to values between 2.30 and 2.60 nm upon CA intercalation; a molecular sieve role of LDH host is also pointed out. Isotherms studies were carried out to evaluate the adsorption capacity of LDH towards CA in presence of contaminants such as amino acids. The Freundlich adsorption model was found to fit the data well and indicating relatively large adsorption capacity, as high as 73.63, 128.76 and 229.62 mg1-nFLnFg-1 at 20, 30 and 35°C, respectively. Besides, the adsorption of CA is classified as an endothermic and spontaneous process with the following calculated thermodynamic parameters: ?H° = 20.516 kJ/mol, ?S° = 0.081 kJ/mol.K and ?G° = -3.271, -4.082, -4.488 kJ/mol for 20, 30 and 35°C, respectively. Particularly, the adsorption of CA onto Zn2Cr-NO3 is a favorable process thus allowing us to envisage the use of LDH in CA biomolecule separation. In the third step, microparticles containing crystals of Zn2Cr-NO3 microencapsulated in alginate (LDHME) were obtained by ionic gelation in order to allow the use of these adsorbents in chromatography columns. A column was packed with particles of LDHME to evaluate the separation of CA from mixtures with amino acids such as tyrosine (TYR) and proline (PRO) using the chromatographic pulse methodology. The use of these LDHME microparticles in the CA separation was satisfactory leading to purification factors of 2.32 times the original and a purity of 93% of the solutions. A mathematical model has been developed for adsorption of CA in a fixed bed column packed with LDHME particles. Breakthrough curves were obtained and the system was experimentally assessed in relation to the time of operation as well as efficiencies and yields due to simultaneous variations of experimental conditions, flow rate (Q) and bed height (L) using a central composite rotatable design (CCRD), considering as responses the breakthrough time (tb), the exhaustion time (te), the recovery efficience (frec), the column utilization efficience (fcol) and the process productivity (P). The flow rate was assessed in the range from 0.19 to 0.82 mL/min and the bed height from 3.0 to 5.0 cm. The particle swarm optimization algorithm (PSO) was shown to be effective in the estimation of the parameters of the proposed model. Once validated experimentally under different conditions from those used in the estimation, the model has been used as a tool in optimizing the adsorption of CA by a CCRD, whose results were obtained using simulations with higher levels for the input variables (0.80 < Q < 1.50 mL/min and 7.0 < L < 10.0 cm). This procedure was considered satisfactory since there were significant reductions in operating times and increases in their productivity and efficiencies. The best operating condition of the system studied for CA adsorption were: Q = 1.15 mL/min and L = 10.0 cm, the answers were: tb = 24 min, trec = 96 %, frec = 110 min, frec = 37% and P = 117 kg/h (AU) | |