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Membrane-based technology is a low-cost alternative for gas purification processes due to its easy implementation and low energy consumption. However, the participation of membrane systems in the CO2 separation technologies market for natural gas sweetening is only 10% due to the trade-off between permeability and selectivity and poor stability of the polymeric materials available. Therefore, to expand current operating conditions or meet adverse requirement in new applications, such as low pressure and high flue gas temperatures, new membrane materials need to be developed. Mixed matrix membranes (MMMs) formed by the incorporation of inorganic fillers in polymeric matrices can overcome the high cost of inorganic membranes and reduce polymeric membrane limitations. The main challenge is the development of MMMs with a defect-free interfacial morphology. In this sense, the type of load is one of the most important factors. Among the inorganic fillers, carbon nanotubes (CNTs) have great potential for chemical adaptation, as well as high mechanical and thermal properties, which can result in high performance MMMs. This review was prepared to summarize the advances achieved with polymeric matrices incorporated with CNTs (CNTs-MMMs) and contribute to their development by showing the possibilities of combining CNTs with different polymers and their respective properties. It has been observed that CNTs can increase the mechanical, thermal and transport properties of polymeric membranes. Furthermore, Robeson's upper bound revealed that some CNTs-MMMs were suitable for industrial use because of their excellent performances and with greatest application potential for CO2/N2 separation.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior Membranas de matriz mista (MMMs) simétricas e assimétricas foram preparadas utilizando polissulfona (PSF) e nanotubos de carbono de paredes múltiplas funcionalizados com grupos oxigenados (MWNT-O). As membranas simétricas foram preparadas pelo método de evaporação de solvente (dry), enquanto as membranas assimétricas foram obtidas por precipitação por imersão (wet) e pela combinação dos dois métodos (dry/wet). Foram utilizados MWNT-O com teor de funcionalização de 6 %m/m e 9%m/m, incorporados na PSF com teores entre 0,1 e 5 %m/m. As membranas foram caracterizadas usando microscopia eletrônica de varredura (MEV), análise termogravimétrica (TGA), calorimetria exploratória diferencial (DSC), espectroscopia no infravermelho com transformada de Fourier (FTIR) e testes de permeação com CO2 e N2 puros. A taxa de precipitação do polímero foi afetada pela incorporação dos MWNT-O, de tal forma que ocorreram mudanças significativas na morfologia das MMMs. A estabilidade térmica das MMMs foi discretamente reduzida e mostrou ser dependente das respectivas morfologias. Os resultados de FTIR indicaram a presença dos MWNT-O nas MMMs e a formação de interações dos grupos funcionais presentes na superfície dos MWNT-O com a PSF. Considerando as propriedades de transporte, as MMMs simétricas e assimétricas preparadas com 1 %m/m de MWNT-O apresentaram o melhor desempenho. Para membranas simétricas, houve indícios de que a incorporação de MWNT-O aumentou a tortuosidade do caminho de difusão dos gases, reduzindo a permeabilidade e aumentando a seletividade da membrana de PSF pura. Para membranas assimétricas, em termos de permeância, o método wet se mostrou mais efetivo, originando a MMM que teve a permeação do CO2 aumentada de 11 para 80 GPU em relação à membrana de PSF pura. Por outro lado, em termos de seletividade, o método dry/wet mostrou o melhor desempenho, originando uma MMM com seletividade para CO2/N2 de 14,3, enquanto a membrana de PSF pura apresentou uma seletividade de 9,5. Os resultados indicam que a PSF e os MWNT-O podem ser combinados com sucesso para preparação de membranas assimétricas com potencial para aplicação na separação do CO2. Symmetric and asymmetric mixed matrix membranes (MMMs) were developed using polysulfone (PSF) and multi-walled carbon nanotubes functionalized with oxygenated groups (MWNT-O). The preparation of the symmetric membranes was performed by solvent evaporation technique (dry phase inversion), while the asymmetric membranes were obtained by immersion precipitation (wet phase inversion) and by combining the two methods (dry/wet phase inversion). MWNT-O with functionalization contents of 6 wt.% and 9 wt.% were used, incorporated into PSF with contents between 0.1 and 5 wt.%. The membranes were characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential exploratory calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and permeation tests with pure CO2 and N2. The polymer precipitation rate was affected by the incorporation of MWNT-O, such that significant changes occurred in the morphology of the MMMs. The thermal stability of the MMMs was slightly reduced and was shown to be dependent on their respective morphologies. The FTIR results indicated the presence of the MWNT-O in the MMMs and the formation of interactions of the functional groups present on the surface of the MWNT-O with the PSF. Considering the transport properties, the symmetric and asymmetric MMMs prepared with 1 wt.% of MWNT-O showed the best performance. For symmetric membranes, there were evidence that the incorporation of MWNT-O increased the tortuosity of the gas diffusion path, reducing the permeability and increasing the selectivity of the pure PSF membrane. For asymmetric membranes, in terms of productivity, the instantaneous precipitation method proved to be more effective, giving rise to the MMM that had the CO2 permeation increased from 11 to 80 GPU compared to the pure PSF membrane. On the other hand, in terms of selectivity, the delayed-immersion precipitation method proved to be more effective, originating a MMM with selectivity for CO2/N2 of 14.3, while the pure PSF membrane showed a selectivity of 9.5. The results indicate that PSF and MWNT-O can be successfully combined to prepare asymmetric membranes with potential application in CO2 separation.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais Este trabalho apresenta a investigação experimental do desempenho termo-hidráulico do nanofluido composto por nanopartículas de grafeno dispersas em uma mistura de água e etilenoglicol numa proporção de 70:30% em volume. Os testes foram realizados sob convecção forçada no interior de um tubo circular com fluxo de calor uniforme na parede para o regime de transição laminar-turbulento. A vazão mássica variou de 40 a 70 g/s correspondendo aos números de Reynolds entre 3000 e 7500. O fluxo de calor foi mantido constante nos valores de 11, 16 e 21 kW/m², assim como, a temperatura de entrada em 15, 20 e 25°C. Foram produzidas três amostras de nanofluido com concentração em volume de 0,05%, 0,10% e 0,15%. Foram determinadas as propriedades termofísicas de todas as amostras que foram criticamente comparadas e discutidas com modelos teóricos mais comumente utilizadas na literatura. Inicialmente, experimentos com água destilada confirmaram a validade do equipamento experimental para os testes termo-hidráulicos. Logo após, as amostras de nanofluido que apresentaram maior condutividade térmica, correspondendo às concentrações em volume de 0,15% e 0,10% foram submetidas aos testes. O desempenho termo-hidráulico para ambas as amostras foi insatisfatório. Os coeficientes de transferência de calor por convecção dos nanofluidos reduziram, em média, para a amostra com =0,15% em 21% e para a amostra com =0,10% em 26%. A perda de carga das amostras foi superior ao fluido base. Por fim, a perda de carga e o coeficiente de transferência de calor por convecção das duas amostras também foram comparadas com modelos teóricos. Os modelos utilizados para a perda de carga apresentaram excelente concordância com os resultados experimentais, o que é notável considerando o regime de transição. This work presents an experimental investigation of thermal hydraulic performance of the nanofluid composed by graphene nanoparticles dispersed in a mixture of water and ethylene glycol at a ratio of 70:30% by volume. The tests were carried out under forced convection inside a circular tube with uniform heat flux on the wall for the laminar-turbulent transition regime. The mass flow rate ranged from 40 to 70 g/s corresponding to Reynolds numbers between 3000 and 7500. The heat flux was maintained constant at values of 11, 16 and 21 kW/m², as well as the inlet temperature of 15, 20 and 25°C. Three samples were produced with the nanofluid volumetric concentration of 0.05%, 0.10% and 0.15%. Thermophysical properties were experimentaly measured for all samples that were critically compared and discussed with theoretical models most commonly used in the literature. Initially, experiments with distilled water confirmed the validity of the experimental equipment for the thermo-hydraulic tests. Therefore, nanofluid samples that showed the highest thermal conductivity, corresponding to the volumetric concentrations of 0.15% and 0.10%, were subjected to the tests. The thermal-hydraulic performance for both samples was unsatisfactory. The heat transfer coefficients for convection of nanofluids reduced 21% in average, for the sample with = 0.15% and 26% and for =0.10%. The pressure drop of the samples was higher than the base fluid. Finally, the pressure drop and heat transfer coefficient by convection of both samples were also compared to theoretical models. The models used for pressure drop showed an excellent agreement with experimental results, which is remarkable considering the transitional flow. Dissertação (Mestrado)