Desenvolvimento de membranas de destilação de polifluoreto de vinilideno (PVDF) para tratamento de efluente têxtil

Abstract

The textile industry is of vital importance in the Brazilian economy, being the second sector with most employees in Brazil in 2017. This industry segment is characterized by the intensive use of water in various stages of production, generating large amount of aqueous effluent. The effluent has a complex composition, making it difficult to treat because it has a wide range of dyes, toxic and carcinogenic compounds, making the treatment process vitally important. Membrane separation technology proves to be a viable technology for the treatment of liquid effluents, being a good alternative to classic methods. Within membrane separation processes, membrane distillation has gained importance in the 21st century due to its efficiency in purifying aqueous solutions and simplicity of operation. Studies of this process are more recent than other membrane separation processes such as nanofiltration and reverse osmosis. Due to the fact that it is a technology that only in recent years has been gaining ground in the scientific scenario, there are few studies on the process and manufacture of specific membranes for it, so much has yet to be developed to scale the process from laboratory level to the industrial one. Thus, this work aims the development of polyvinylidene fluoride (PVDF) membranes by the non-solvent phase inversion process (NIPS) for the membrane distillation process. Distilled water and ethanol (in different proportions) were tested as non-solvent and N'N'-dimethylformamide (DMF) as solvent. Characterization tests of physical, chemical, morphological and thermal properties of the membrane were performed and salt retention tests to determine the membranes ability to perform the proposed process. Contact angle analysis ruled out the use of pure distilled water as a non-solvent due to the hydrophilic character of the sample. The pressure of liquid invasion showed that the samples produced with pure ethanol became excessively fragile, making their use impossible. Membrane samples obtained with mixtures of water and ethanol as non-solvent were used for the characterization and distillation testing sequence. SEM analysis indicated that increasing the ethanol concentration there was a decrease in macropore occurrence and increased void formation inside the sample. The XRD and FTIR analyzes indicated that with the proposed methodology, the membranes present amorphous, α and β phases. Thermal analysis indicated that about 7% of the polymer mass used is actually plasticizer, and that the samples presented crystallinity above 62%. The membranes are effective for retention of the pollutants tested, with the sample synthesized with a 50% v/v ethanol coagulation bath with better salt retention and the 25% v/v ethanol membrane with dye retention. This work achieved its goal of preparing polymeric membranes for the membrane distillation process, showing the great future potential of the technique.