Fluidodinamica e secagem do acido adipico em leito vibrofluidizado

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

The objective of this work is the development and building of a vibrofluidized bed and sampling system for the fluid-dynamic study and drying of adipic acid. The adipic acid investigated in this work presents partic1e diameter in the range of 75 - 600 ?m and density of 1340 kg/m3. Adpic acid is the main intermediate product in the synthesis of Nylon. It is the most important of all aliphatic dicarboxylic acid. The moisture content of commercial product is 0.25% w.b. The wet or moistened adipic acid has a tendency to agglomerate. In such case, fluidization does not occur and the partic1e can not be treated in conventional fluidized bed. The effect of vibration helps to maintain the agglomerate in mobile state, when wet, and it improves the circulation ofpartic1es by breaking of the bubbles, when dry. The fluid-dynamic study of the vibrofluidized bed has been done through the fluidization curves for both systems, conventional and vibrated, to verify the pressure drop variation versus air velocity as function of the vibration parameters, frequency and amplitude. The minimum fluidization pressure drop in vibrofluidized bed was found to be lower than in a conventional fluidized bed. With vibration imposition, it has been obtained a decrease on the minimum fluidization pressure drop in the range of 4 - 30%. The effect of vibration had a considerable attenuation on the minimum fluidization pressure drop with increase in the load of partic1es. The reproduction of distinct fluidization curves was obtained in this work as in the literature for a vibrofluidized bed (Strumillo, 1980). The influence of the partic1e size distribution was investigated through the fluidization curves for different vibration parameters. The curves obtained of vibration factor versus vibration frequency showed that for a fixed load, the smaller partic1es are more affected by the vibration than the larger ones. The statistical analysis showed that the minimum fluidization pressure drop and air velocity were influenced strongly by the load of particles, the displacement of the fitted surface was observed varying the load of particles. The fluid-dynamic study with the wet material showed that the interparticle forces in the artificially moistened material act in a different way compared to the existent forces in the industrial wet material, coming from the crystallization process. The drying process of adipic acid is an important stage, because it determines the quality of final product: moisture content and specification of the size and form of the crystals. The sampling system developed in this work presented good results and, practically, did not cause variation of the mass in the bed of particles in the drying experiments. The drying curves analysis showed two steps, constant and decreasing drying rates. The smallest final moisture content obtained was of 0.55 % w.b., while for the commercial product is of 0.25 % w.b. This final moisture content can be reduced by changing the operational conditions, like increasing the air temperature. The variation of the moisture content was observed for different sizes of crystals, due to a wide distribution of size, 75 - 600 ?m. Sorption isotherms were determined at 40 and 60°C. The analysis of sorption isotherms curves showed that the moisture content is not related to water activity. The results of repose angle and Hausner lndex obtained in the equipment "Powder Characteristics" showed that the dry adipic acid in the industry and in the vibrofluidized bed developed in this work presented good flowtability

ASSUNTO(S)

acidos organicos secagem planejamento experimental fluidização

ACESSO AO ARTIGO

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