Ultrapure water, also known as UP water, is an extremely pure water with a resistivity of up to 18 m*cm (25). In addition to water molecules, this kind of water almost does not contain any impurities, and there are no bacteria, viruses, chlorine-containing dioxins and other organic substances, and even lack of minerals and trace elements required by the human body. It can be said that ultrapure water removes almost all atoms except hydrogen and oxygen. This water can be used in the preparation of ultra-pure materials such as semiconductor materials, nanofine ceramic materials, which rely on distillation, deionization, reverse osmosis technology or other appropriate supercritical fine techniques.
In the process of preparing ultrapure water, there are several key indicators that require special attention. Among them, total organic carbon (TOC) and boron and silica are important parameters to measure the quality of ultrapure water. The line width of semiconductors is different, and the smaller the line width, the higher the water quality requirements. Dissolved oxygen control is critical in many preparation processes, with vacuum degassing towers achieving less than 50 ppb of dissolved oxygen, while 10 ppb requires the use of degassing membranes.
In terms of particulate removal, commonly used technologies are RO reverse osmosis, terminal ultrafiltration, and nanofiltration. The water purified by RO reverse osmosis technology is basically pure water, but it produces a large amount of wastewater and the water discharge rate is slowUltrafiltration technology has the advantage of low cost, fast water output and no power supply, but it cannot completely filter heavy metal ionsNanofiltration, on the other hand, retains beneficial trace elements while filtering harmful substances, but it needs to be energized to run and produce wastewater.
In addition, the design of ultrapure water systems requires a variety of factors to be taken into account. For example, if the ultrapure water system has particularly high TOC requirements, the use of reclaimed produced water should be avoided to add to the system;Activated carbon has the function of removing organic matter and residual chlorine, but it is necessary to pay attention to its saturated adsorption capacity and the problem that it may become a source of nutrients or a breeding ground for bacteria to multiplyThe TOC analyzer converts organic matter into carbon dioxide for detection, which has the characteristics of convenience and accuracy.
In the application of ultrapure water, the polishing bed plays a crucial role. It is usually only 1% of its capacity and requires the final water quality to be met before it is fed into the ultrapure water tank. In addition, the pH of the polished mixed bed is close to neutral, and the ability to remove boron is weak. In the process of use, it is necessary to pay attention to maintaining the constant pressure difference of the circulating pipeline, and add a heat exchanger to cope with the problem of rising temperature of the circulating pipeline.
Reverse osmosis technology is also an important means of preparing ultrapure water. The basic principle is to separate a concentrated solution by applying pressure to pass the dilute solution through the reverse osmosis membrane. In the phenomenon of osmosis, when two solutions are separated by a semipermeable membrane, the dilute solution is moved to the concentrated side so that it has the same concentration. In order to obtain a purer dilute solution, the pressure must be greater than the osmolality.
When selecting and using an ultrapure water system, it is important to fully understand and consider its key indicators, preparation technology, application requirements, and maintenance management. Only in this way can the quality of ultrapure water and the reliability of the application be ensured.