Development of Nanocomposite Membranes Based on PVA (Polyvinyl Alcohol) and Functionalized Nano Cellulose for Biogas Upgrading

Abstract

Globally, the consumption of energy has increased compared to the average rate of growth. To fulfill the world energy requirement, the demand for fuels has also increased. From initial decade fossil fuel was used as a major source of energy production. These sources of fossil fuels are depleting very rapidly. So, the world is now moving toward renewable energy resources. Biogas is one of the most suitable options to use as a renewable energy source. It is required to upgrade the raw biogas to fulfill high quality energy and demands. It can be upgraded by removing CO2 from CH4. After upgradation of biogas, CH4 contents in biogas has increased up to 95%. This upgraded biogas can be used in various applications such as fuel of vehicles, in power grid stations and for domestic use. For upgrading biogas, it is essential to follow such process of upgrading which has high efficiency and low energy-consumption. Membrane technology is one of the green and emerging technology. As compared to commercially available technology, it has many advantages over other state of the art technologies. Permeability and selectivity are the major parameters to determine the performance of membranes. In order to compete with other technologies available in the market, it required to have high CO2 permeance and high selectivity of membranes. Different type of materials is used for membrane fabrication like organic (polymeric), inorganic, ceramics, and ionic liquid. Polymeric membranes are most suitable option to be used as commercial membranes because of its easy fabrication, low cost and high separation performance. Facilitated transport membranes (FTMs) are one of the innovative approaches for CO2 separation with high CO2 permeance and high selectivity. In these membranes, additives are embedded in polymeric matrixes to facilitate the CO2 transport through solution diffusion mechanism. In most FTMs water/moisture act as carrier that enhances the CO2 transportation through membrane. Therefore, the performance of FTMs can be improved by increasing its moisture uptake ability. In this research work, novel FTM (nanocomposite membrane) was developed based on polyvinyl alcohol (PVA) as a basic polymer with aminated cellulose nanocrystal (Am-CNC) as a filler. CNC were first functionalized and then added to PVA matrix. The casted membranes were characterized by using X-ray Diffraction (XRD), Fourier Transform Infra-red (FTIR) and Scanning Electron Microscopy (SEM) as supporting techniques. XRD technique was used to investigate the crystalline nature of nanocomposite membranes and crystallinity of CNC and Am-CNC while FTIR technique was used to investigate the amine functional group attachment to the CNC and in nanocomposite membrane while SEM was used to observed the surface morphology and cross sectional of nanocomposite membrane. Permeance testing was used to observed the permeability and selectivity performance of nanocomposite membranes for CO2/CH4. It was observed that by increasing the concentration of Am-CNC, the thickness of selective dense layer also increased that result in decrease in permeability. However, the moisture uptake ability was also investigated that shows maximum value up to addition of 1 wt.% of Am-CNC. The permeance and selectivity of CO2 and CH4 across membranes against high feed pressures i.e. 5, 10, 15 bar was investigated. It was noticed that by increasing feed pressure both the permeance and selectivity of CO2 and CH4 was decreased. However, the values for CO2 permeance are comparably high as compared to that for CH4. The best result for CO2 permeance and selectivity was observed for 1 wt.% Am-CNC/PVA based nanocomposite membrane. This research work consists of single gas testing however, the results support that membranes has high affinity towards CO2 as compared to CH4.The resultant membranes can be used for upgrading the biogas system as a potential technology in future