Production of MgAl/layered double hydroxide microspheres and investigation of the volumetric heat transfer coefficient in spray drying.

Layered Double Hydroxides (LDH) are synthetic materials nanostructured in two dimensions that present positively charged layers with interspersed anions for charge and structure balancing. Being recognized as a promising material for various applications, a complete exploration of its possible attractive properties and its synthesis process is essential. However, drying, a necessary step in the process, is still little studied. This work aimed to produce MgAl-CO3/LDH microspheres and calculate the volumetric heat coefficient in spray drying, evaluating the drying air inlet temperature and the concentration of the feed paste in the dryer. LDH synthesis was carried out using the coprecipitation method, maintaining a 2:1 Mg/Al ratio. The infrared spectra presented the bands characteristic of the hydrotalcite-type material. Through XRD, it was possible to observe that the variation in drying air temperature and feed paste concentration produced LDHs with structural differences. The results obtained for the basal spacing ranged from 7.685 to 7.705 Å. Scanning electron microscopy images confirm the production of LDH microspheres, showing variation in the size of the agglomerates with changes in the feed paste concentration. The volumetric heat transfer coefficient values ranged from 4.31 to 5.36 W m-3 K-1, with only the air inlet temperature significantly influencing the process under the conditions studied.

Effect of Drying on the Fabrication of MgAl Layered Double Hydroxides.

This study aimed to evaluate the synthesis of MgAl/LDH from the drying process perspective, evaluating the influence of temperature (75-90 °C) and time (16-20 h) in the drying process. The synthesis was performed, maintaining a ratio of 2:1 of Mg/Al, and the drying was conducted according to a 22 experimental design: four axial points and three repetitions at the central point. The surface area and pore diameter ranged from 4.09 to 18.55 m2/g and 12.50 to 24.46 nm. Fourier transform infrared (FTIR) analysis indicated the drying-caused variation of the LDH typical bands intensities. Scanning electron microscopy (SEM) images showed the tendency of the increase of agglomeration with the temperature elevation. The drying parameters' influence was evident for X-ray diffraction (XRD) analysis observing the crystallite size increment, from 13.10 to 38.94 nm, and basal spacing variation, from 7.52 to 7.64 Å. The statistical models for growing crystal and reduction of the basal spacing were physically consistent but with low values of R 2. The drying time and temperature had a considerable influence on the chemical, physical, structural, and morphological properties of LDH.