Potassium acetate solution as a promising option to osmotic distillation for sour cherry (Prunus cerasus L.) juice concentration

Different osmotic agents (OA), such as potassium acetate (CH3COOK), potassium carbonate (K2CO3) and ammonium nitrate (NH4NO3), have been examined as alternatives to the traditionally used calcium chloride (CaCl2) for osmotic distillation concentrating of clarified and pre-concentrated sour cherry (Prunus cerasus L.) juice. Comparison of the process performances based on the permeate fluxes has been carried out. Regarding the permeate flux results, simplified estimation of the overall mass transfer coefficient of the most effective osmotic agent and the reference (CaCl2) solution has been also performed. Furthermore, analytical methods such as total antioxidant activity (TAA) and total polyphenolic content (TPC) using spectrophotometric assays have been also carried out to evaluate the effect of the osmotic distillation on the valuable compounds content of concentrated sour cherry juice. CH3COOK was found to be the most effective, resulted more than 25% higher permeate flux during the sour cherry juice concentration. K2CO3 and NH4NO3 were less effective. The simplified mass transfer estimation showed that the CH3COOK is more effective only at near saturated concentrations compared to the CaCl2. Regarding the TAA and TPC contents, a significant loss was found in case of all OAs during the concentration procedures

Osmotic distillation with propylene glycol, glycerol and glycerol-salt mixtures

Aqueous solutions of propylene glycol, glycerol and glycerol-salt mixtures are investigated as alternative to Calcium Chloride, normally employed to concentrate aqueous mixtures by osmotic distillation. These extractants can overcome the problems of corrosion and scaling associated with the use of brines. The proposed extractants are compared in terms of driving force available for mass transfer, flux achievable, viscosity, penetration pressure through the membrane pores, solvent entrainment. The water activities of the relevant solutions are calculated by predictive methods and, in the case of glycerol-salt mixtures, measured by an isopiestic technique. Propylene glycol and Glycerol solutions exhibit similar extractive power; the concentration has to be limited to 70-75 wt% in order to limit the viscosity, as a consequence these compounds are a bit less effective than highly concentrated CaCl2 solutions. Notwithstanding the good flux achievable, propylene glycol cannot be recommended as extractant for juice concentration, indeed, owing to the not negligible volatility, it diffuses toward the juice in considerable amount, in addition the penetration pressure through the membrane pores is quite small. The ternary mixture glycerol-salt-water allows to obtain the same flux achievable with glycerol alone, but with a substantially lower viscosity

Heat and mass transfer in osmotic distillation with brines, glycerol and glycerol-salt mixtures

Osmotic distillation (O.D.) is not a purely mass transfer operation, in that the flux is limited not only by the concentration polarisation, but also by the cooling of the feed and warming up of the extractant due to the phase change at the membrane interfaces (thermal effect). This study presents O.D. experiments with various extractants in a plate and frame module expressly designed to investigate separately the simultaneous effects of the heat and mass transfer. In co-current operation the temperature difference between the two streams approaches an asymptotic value for large residence time within the module, i.e. for long modules or low flow rates. In asymptotic conditions, which correspond to no heat flux through the system, the problem looks like a pseudo isothermal case, this allows to obtain the relevant membrane transport properties and to evaluate the role played by the concentration polarisation. The temperature difference created by the thermal effect, even of few degrees, greatly reduces the driving force for mass transfer through the membrane, the resulting loss of flux is relevant and increases with the temperature. The concentration polarisation plays a comparable role in the O.D. with calcium chloride or glycerol at room temperature, while is less important in O.D. with glycerol-NaCl mixtures, and negligible in the case of sodium chloride. Among the extractant used, CaCl2 is the most effective, however the advantage over the Glycerol-NaCl mixture is not so high as would appear comparing the respective theoretical driving forces for mass transfer. The length of module needed to approach asymptotic conditions (thermal entry length) can be estimated lower than the typical length of industrial apparatuses. The flux achievable in O.D. applications is thus not much higher than the asymptotic value, larger fluxes can only be obtained in lab devices

Produção científica na EESC/USP: relato de experiência sobre uma reestruturação para o acesso facilitado. (Pôster)

O conjunto de mudanças relativas à reestruturação do Memorial EESC teve como objetivo principal eliminar os obstáculos presentes na organização, armazenamento e recuperação de documentos, acentuados na década de 90, com o surgimento da internet e dos catálogos online. Esse acervo localiza-se na Biblioteca da Escola de Engenharia de São Carlos (EESC/USP) e reflete a produção científica, técnica e artística gerada na Unidade pelos professores, pesquisadores e técnicos especializados de nível superior. A reestruturação baseou-se em dois pontos: a) recuperação e acesso ao documento físico no acervo; b) a sua preservação. As estratégias implementadas apontaram resultados significativos, facilmente notados pelo aumento do número de consulta, facilidade para o usuário na localização do documento no acervo; otimização no seu processamento técnico e preparação do acervo da produção científica da EESC para o projeto de digitalização do SIBi/USP