No abstract

No abstract

This paper reports on an evaluation of the intrinsic kinetic parameters of the specific sorption of clavulanic acid (CA) by ion-exchange chromatography. The first step of this work was to determine the diffusivity of CA in the pores of a resin, using a model based on diffusion with instantaneous adsorption. However, the adsorption rate step was found to affect the adsorption process. A mathematical kinetic model for the adsorption and desorption of CA was, therefore, proposed considering both kinetics and diffusion. Intrinsic kinetic parameters were obtained using the same experimental data utilized in determining diffusivity. In this case, the adsorption rate was considered to be the process-limiting factor. Tests were carried out in a 200 mL stirring tank, with the initial solution at pH ) 7.0 and the temperature maintained at 10 °C. The results showed that both the reaction rate and mass-transfer limitation have to be taken into account in the analysis of CA adsorption by ion-exchange resins.

This work presents kinetic models of cellulose and hemicellulose extraction during hydrothermal pretreatment of sugarcane straw. Biomass was treated under conditions of 180, 195, and 210°C, using a solid/liquid ratio of 1:10 (w/v). In this study, cellobiose, glucose, formic acid and hydroxymethylfurfural (from cellulosic fraction) and xylose, arabinose, acetic acid, glucuronic acid and furfural (from hemicellulosic fraction) were taken into account in the kinetic parameters determination. The global search algorithm Simulated Annealing was used to fit the models. At 195°C/15min, 85% of hemicellulose and 21% of cellulose removal was reached. For the confidence regions, it was observed that it can be broad, which is coherent with the fact that the parameters are highly correlated. Kinetic models proposed for both cellulosic and hemicellulosic fractions degradation fitted well to the experimental data.

No abstract

Population growth and the increasing search for healthy foods have led to a major consumption of coconut water and, hence, to an environmental impact caused by the inappropriate

ABSTRACT. Second generation ethanol from lignocellulose materials has been used in applications for food processing wastes. Since Brazil has a leading position in orange juice exports, the influence of acid and alkali pretreatments on liquor saccharification, solubilization of solid fraction and mass yield was evaluated. Time and C acid or C alkaline at different concentrations of solids (low to moderate, 1 to 9%) and high catalyst concentrations were analyzed. A hydrothermal pretreatment was conducted under the same conditions of acid and alkaline treatments to investigate the relative selectivity increase in using the catalysts. The chemical analyses of wastes indicated a 70% total carbohydrate level denoting a promising raw material for bioethanol production. Pretreatment caused acid saccharifications between 25 and 65% in total reducing sugars (TRS) and mass yields (MY) between 30 and 40%. In alkaline pretreatment, these rates ranged between 2 and 22.5% and between 30 and 80, respectively. In hydrothermal pretreatment, solubilized TRS varied between 3 and 37%, whereas MY remained between 45 and 60%, respectively. C biomass strongly influenced the three variables; in the same way, time affected MY.Keywords: pretreatment, biomass, experimental design, orange.Sacarificação de resíduo cítrico sob diferentes tratamentos químicos RESUMO. Etanol de segunda geração a partir de materiais lignocelulósicos tem sido abordado como uma das aplicações de resíduos de processamento de alimentos. Sendo o Brasil líder na exportação de suco de laranja, avaliou-se a influência de pré-tratamentos ácidos e alcalinos na sacarificação do licor, na solubilização da fração sólida e no rendimento mássico. Para isso, estudou-se tempo e C ácido ou C álcali em diferentes concentrações de sólidos (baixo a moderado, 1-9%) e altas concentrações de catalisador. Um pré-tratamento hidrotérmico foi realizado, tendo as mesmas condições dos tratamentos ácido e alcalino, a fim de investigar o aumento da seletividade em relação ao uso desses catalisadores. Análises químicas de resíduos indicaram um nível total de carboidratos de 70%, denotando uma matéria-prima promissora para a produção de bioetanol. O pré-tratamento conduziu a sacarificações ácidas de 25 a 65% em açúcares redutores totais (ART) e rendimentos mássicos (RM) entre 30 e 40%. Para o pré-tratamento alcalino, esses valores foram de 2 a 22,5%, e de 30 a 80%, respectivamente. No pré-tratamento hidrotérmico, o ART solubilizado variou entre 3 e 37%, enquanto que o RM manteve-se entre 45 e 60%. A C biomassa influenciou fortemente as três variáveis, bem como o tempo utilizado com o RM.Palavras-chave: pré-tratamento, biomassa, planejamento experimental, laranja.

Clavulanic acid (CA) is a beta-lactamase inhibitor produced by strains of Streptomyces clavuligerus. Nowadays, the combination of CA with amoxycillin is the most successful example of the use of a beta-lactam antibiotic sensitive to beta-lactamases together with an inhibitor of these enzymes. Clavulanic acid is purified from fermentation broth by a series of steps consisting mainly of two-phase separation processes such as liquid-liquid extraction, adsorption or ion-exchange chromatography, among others. Amberlite IRA 400, a strong anion-exchange resin, has a very high adsorption capacity for CA (Mayer et al. 1997). This resin can be pre-treated with NaCl (chloride cycle), to remove selectively only those anions, which are able to displace chloride from the resin or with NaOH (hydroxyl cycle), to remove all species of anions. In order to decide the best operating conditions for CA recovery by ion-exchange resins and then to construct a model of this separation process, batch experiments were conducted using Amberlite IRA 400 in the chloride cycle. These runs were carried out in a 200 ml stirred tank, at two different initial solution pH, 6.2 and 4.0; the temperature was maintained at 10 degrees C and 20 degrees C during adsorption and 30 degrees C during the desorption step. It was possible, on the basis of these batch results, to model the separation process, including the adsorption kinetics, equilibrium data and mass transfer limitations.