Abstract Crystallization in a Direct Contact Membrane Distillation (DCMD) process was studied both theoretically and experimentally. A mathematical model was proposed in order to predict the transmembrane flux in DCMD. The model fitted well experimental data for the system NaCl-H2O from undersaturated to supersaturated conditions in a specially designed crystallization setup at a bench scale. It was found that higher transmembrane fluxes induce higher temperature and concentration polarizations, as well as higher supersaturation in the vicinity of the solution-vapor interface. In this region, the supersaturation ratio largely exceeded the metastable limit for NaCl crystallization for the whole range of transmembrane fluxes of 0.37 to 1.54 kg/ (m2 h), implying that heterogeneous primary nucleation occurred close to such interface either in solution or on the membrane surface. Solids formed in solution accounted for 14 to 36% of the total solids, whereas solid formed on the membrane surface (fouling) was responsible for 6 to 19%. The remaining solids deposited on other surfaces such as in pumps and pipe fittings. It was also discovered that, by increasing the supersaturation ratio, heterogeneous nucleation in solution increased and on the membrane surface decreased. Heterogeneous nuclei in solution grew in size both by a molecular mechanism and by agglomeration. Single crystals were cubic shaped with well-formed edges and dominant size of about 40 µm whereas agglomerates were about 240 µm in size. The approach developed here may be applied to understanding crystallization phenomena in Membrane Distillation Crystallization (MDC) processes of any scale.

Derivados claros de petróleo consistem de hidrocarbonetos não polares os quais são agressivos ao aço-carbono devido à presença de água. Neste trabalho, será mostrado experimentalmente e teoricamente que o pH da fase aquosa durante a corrosão é controlado pela interação da fase aquosa com o CO2 atmosférico e com os produtos de corrosão de ferro tanto em solução, quanto no precipitado. Durante o processo de corrosão, o pH da solução varia, independentemente do seu valor inicial, no sentido de um valor neutro. Este comportamento explica a razão da corrosividade de uma emulsão de derivado de petróleo não ser influenciada pelo pH inicial da fase aquosa.

Light petroleum derivatives consist of nonpolar hydrocarbons, which are aggressive to carbon steel due to the presence of water. In this study, we show both experimentally and theoretically that the water-phase pH during corrosion is controlled by the interaction of the aqueous phase with the atmospheric CO2 and with iron corrosion products in both solution and precipitates. During the corrosion process, the pH of the solution changes, regardless of its initial value, towards a neutral value. This behaviour explains why the corrosiveness of a petroleum derivative emulsion is not influenced by the initial water-phase pH.

An organic-mineral fertilizer based on humic substances (HSs) and potassium was developed based on the alkaline extraction of HSs from peat. The HSs have interesting properties for use as a fertilizer since they improve the physical and chemical structure of the soil and provide a source of organic carbon which is readily absorbable by the plants, whereas potassium is a primary nutrient for plants. It was found that highly decomposed peats containing a small inorganic fraction are more favorable for the extraction of HSs. Using these peats, organic-mineral fertilizers that meet the Brazilian legislation have been obtained for a peat-extractant mixture containing 2.57 wt% total organic content (TOC), a K2O/TOC ratio of 1 wt% and an extraction time of 12 hours.

Fluid dynamics simulations were applied for evaluating the suspension of particles in stirred vessels. The spatial distribution of particles throughout the vessel was characterized by a single parameter, here called the suspension quality (s). Based on simulation results, a semi-empirical correlation was developed that correlated the suspension quality with the vessel geometry and solid and fluid properties, including a large variety of conditions, such as vessel and impeller diameters, impeller clearances, rotational speeds, particle densities and sizes. Comparison of the model with experimental data from the literature (Bohnet and Niesmak, 1980) suggests that the model can be extended to systems with different impeller geometries by adjustment of one single empirical parameter. The model can be used in the design of stirred vessels for the identification of the rotation speeds necessary to promote a specified suspension quality.