Optimization in support layer production pilot scale system for reverse osmoz membranes

Water is the most important substance necessary for the survival of nature and of all the beings that it contains. Although 2/3 of the earth is covered with waters, 97.5 % of these resources are saline and brackish water and 2.5 % is fresh water. This limited freshwater resources shrinks by irregular urbanization, excessive population growth and increasing industrialization. Countries are classified in three groups as water-poor, water-deprived and water-rich countries in terms of the amount of water per capita per year. In Turkey which is defined as a country suffering from water stress, the amount of water is 1520 m3 per capita. It is predicted that in 15 years the amount of water per capita will fall down to 1100 m3 and we will be considered water-poor country. In order to cope this problem and tackle the freshwater shortage at the future, seawater as an alternative water resource has been considered to produce potable water. So the seawater desalination has become popular and increase day by day over the world as an efficient way to produce water from global water resources. Membrane process is the most way to practice the desalination. In the reverse osmosis process, dynamic pressure is exerted on the osmotic pressure of the salt solution. This ensures that the membrane is permeated by the salt solution containing water to the side containing clean water. Salts are trapped with reverse osmosis membrane and differentiation is carried out. Reverse osmosis membranes are composed of three parts including polyester layer as nonwoven and support layer overlying the polyester layer and the third part is the active layer overlying the support layer. Even though the separation happens on the active layer but the support layer has major effect on the membranes' performance. The chemistry, pore size, pore size distribution, cross-sectional morphology directly affect the performance of membrane. The aim of this study is to investigate the effect of the rolling speed of the membrane by machine on the pore diameter and the optimization of the support layer by setting the rolling speed and evaporation time while fixing the solution concentration, water under ambient temperature. In the study, flat sheet reverse osmosis membranes were fabricated. Support layer production was done on pilot scale flat sheet device and thin film composite (TFC) membrane was made by thin film coating method on the support layer. For phase inversion process water bath temperature was set at 15 °C and 25 °C and the evaporation was occurred under constant room temperature of 25 °C. The rolling speed of the membrane which directly affect the evaporation time was tried at five different speeds, 4 m / min, 5 m / min, 6 m / min, 7 m / min and 7.4 m / min. Thus a total of 10 support layers were casted, 5 membrane at 15 °C and 5 membrane at 25 °C. Polysulfones (PSf), polyvinylprolidone (PVP) and dimethylformamide (DMF) were used as the polymer in the support layer solution. Afterwards, contact angles, permeability, optical profilometry and SEM analysis were performed on these support layers to characterize the porosity distribution. In the second phase of the work, fabricated support layers were coated with polyamide (PA) thin film to obtain reverse osmosis membranes. As a result of the study, rejection, flux and SEM images of the obtained reverse osmosis membranes were investigated. As a result, for this study, it is shown that the most suitable support layer can be produced at a draw speed of 4 m / min and water with temperature of 15 °C as the increase in temperature and the increase in the draw rate usually change the structure of the support layer in a opposite direction to the target parameters.