Factors affecting membrane separation technology

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1 Operating pressure: The operating pressure has a significant impact on the membrane separation process. In the process of treating oily wastewater using membrane separation technology, there is a critical operating pressure. Before reaching this critical pressure, the membrane flux increases as the operating pressure rises; once the operating pressure exceeds this critical value, the membrane flux begins to decrease as the operating pressure continues to increase. This is due to the compressibility of the oil droplets; when the operating pressure is too high, the oil droplets are squeezed and deformed, causing blockage of the membrane pores and concentration polarization, which in turn leads to a decrease in membrane flux. 2 Operation time: The impact of operation time on membrane separation efficiency is also very significant. During the membrane separation process, the membrane flux decreases over time. This is due to contamination of the membrane surface or the formation of a concentrated solution or colloidal layer on it. 3 Temperature: The effect of temperature on the membrane separation process is mainly due to its influence on viscosity. As the temperature rises, the viscosity of the oil decreases and its diffusion coefficient increases, reducing the effect of concentration polarization and thus aiding in increasing membrane flux. Furthermore, changes in temperature also affect the interaction between the membrane surface and membrane pores with the contaminating components in the feed solution, all of which can lead to a decrease in membrane flux. 4 Feed solution concentration: The feed solution concentration also has a significant impact on the separation efficiency. The membrane separation process is a concentration process for a liquid feed, and there is a limit to the degree of concentration possible. When the concentration of the feed solution is low, it is difficult for a coating layer to form on the membrane surface; as the concentration increases, the resistance at the membrane surface rises, resulting in a significant decrease in membrane flux ； When the concentration of the liquid feed is high, the oil droplet sizes increase, forming a thin layer on the membrane surface that prevents small particles from entering the membrane pores, thereby reducing membrane clogging and keeping the membrane flux essentially unchanged. The pore size of the membrane is one of its basic characteristics; it is generally believed that an increase in pore size leads to a significant increase in membrane flux ； The higher the porosity, the greater the membrane flux ； The smaller the curvature of the membrane pores, the greater the membrane flux. 6 Membrane thickness The effect of membrane thickness on separation efficiency has a dual nature. An increase in membrane thickness reduces membrane flux, but it improves separation efficiency. Therefore, it is necessary to select the membrane thickness through experiments in order to improve the separation efficiency of the membrane without reducing the flux. 7 Membrane surface flow rate: The membrane flux increases as the flow rate at the membrane surface rises, reaching a maximum value; once the flow rate increases further, the membrane flux decreases instead. One reason is that excessive flow rates increase the back pressure, thereby reducing the membrane permeation pressure ； Another reason is that the high flow rate causes the oil in the mixture to leave the membrane at a much faster rate than it enters the membrane, resulting in a decrease in membrane flux. Therefore, when selecting the flow rate across the membrane surface, it is not the case that a higher flow rate is always better; once the flow rate exceeds a critical value, it no longer leads to any significant improvement in the membrane separation performance. Furthermore, studies have shown that the membrane fabrication process, the types and amounts of additives used in membrane production, electrolytes, and surfactants all have an impact on the membrane separation process.