The function, manufacturing and prospect of nitrous oxide (N2O)
(based on Mr.Shi’s article , translated by Tianjin Summit Special Gases)
Nitrous Oxide, with its formula as N2O, is a kind of gas with sweet odor but not color. It can , on some conditions, support the combustion. General is stable and slightly anaesthetic.
N2O is one of the six green-house gases to be controlled stipulated in Kyoto Protocol, and therefore is a long-term subject of study in the field of exploration, exploitation for the reduction of green house gases.
1 Application
Medication: nitrous oxide is one of earliest anaesthetics used by the human beings in the medical realm, and by now still used in the surgical and dental operation based on its anaesthetic
Food: The national health & family planning commission approved the nitrous oxide as a new type of food additive, with its application limited to the “process of diluted cream, thin cream or its likes as the cream will be expandable and operational to the degree of tasting more smoothly.
Manufacturing of Electronic Parts: The nitrous oxide is used more and more in the process of manufacturing the micro-electronic and optical photoelectrons. In the process of production of integrated circuit (IC)and light emitting diode (LED), N2O, as a kind of special gases, silicon dioxide (SiO2) turned out through the chemical reaction is deposited to the silicon substrate to prevent the harmful impurities from entering. The purity of N2O is to affect the membrane purity of SiO2, further more bring the negative effect to the end electronic components. The demand on the nitrous oxide from this industry in on the rise steadily over the past few years. With the upgrading of chip sizes, the demand on the quality of nitrous oxide is more stricter.
In the field of panel display, more than 80% of the market is taken by thin film transistor, and the organic lighting diode is also put into production for the high end uses while the nitrous oxide plays an important role in the above processes. The insulated membrane of the panel displayer, i.e., silicon nitride previous made by reaction of ammonia and silane, now phased out with the replacement of reaction of nitrous and silicon dioxide. In the photovoltaic industry the mainstream process is the crystalline silicon cell, using this special gas in its etching and diffusion.
Rocket propellant and racing car acceleration：composite propellant based on based is of many advantages such as non-toxicity, high specific impulse and simple operation so that is the trend to replace the traditional propellants in various spacecrafts. In the drag racings of automobiles, NOS system makes use of liquid nitric oxide, which is of the high pressure liquid in gas cylinders, mixed with air in the engine, releasing nitrogen and oxygen after burning. The oxygen is the combustion supporting gas while the nitrogen helps the temperature decrease, thus the efficiency of combustion raised to boost the power.
In addition, the nitrous oxide is also used as leakage detection, refrigerant, preservative as well as the supportive agent of combustion in the atomic absorption spectrometer. In the industry, it is used to detect the leakage of underground piping and vacuum. N2O, matched with acetylene, is used in laboratory for the analysis of insoluble elements. In general, the best perspective of its quality use is still in the process of electronic products, i.e., the unique application in the manufacturing of semiconductor chips and liquid panel displayers will face a bright future of quick development.
2 Process of Plant Production
The main methods in China are the heating decomposition of ammonium nitrate, and chemical tail-gas purification.
Heating decomposition of ammonium nitrate: NH4NO3, decomposed into industrial grade N2O by way of heating, if necessary the high purity product can be obtained by further purification
Main Process: ammonium nitrate of granulation, dumped into the feed-tank of the melting vessel, with some quantity of water and diammonium hydrogen phosphate, a catalyst, supporting N2O’s dissolution before its pumping to the reactor by a injecting pump. All products in the reactor pushed to the condenser and pre-scrubber and the latter condenses the steam of all products into water and then discharged with the cooling water together. At the time all impurities of water-soluble and mechanical matters also washed away. The nitrous oxide while the water and steam excluded, is brought to the purification column, through the steps of water scrubbing, acid pickling, alkali wash, to eliminate the remaining nitric oxide, nitrogen dioxide, and ammonia. The product of 99% transmitted to the gas storage, compressed to a pressure up to5~8 megapascal (MPa) to get rid of the over-saturate free water due to the compression by means of high efficiency water separator, then dried in the adsorption and drying unit. The dried gas is liquified to the liquid N2O in the succedent high pressure condenser.
The decomposition of ammonium nitrate is of simple process, and better quality, dominating the high purity market of the gas. But the price of the imported equipment is not inexpensive. Fortunately the technique has already been studied and mastered by some experts in China and domestic equipment can be a good substitution. In addition, the ammonium nitrate is quite sensitive to the heat, a potential source of explosion if not handled carefully in terms of its temperature control. The ammonium nitrate, itself also a chemical material of danger, pose some unforeseen risks in the storage and operation, is finding its way not of wide perspective plus the consideration of purchase cost.
Recovery and Purification from Nylon Monomer: N2O rich gas turned out in the production of nylon such as in the processes of nitric acid and adipic acid. The direct scrubbing satisfied the environmental stipulation but also cause the waste of some potential resource. Therefore the recovery technology of nitrous oxide from the tail gas becomes the highlight of the industry. It is proved by the enterprises which have completed the production, that the quality of nitrous oxide is fully capable of replacing the high purity gas from the ammonium nitrate. Because of the low cost and more environment-friendly process, it is taking the market share drastically.
Other Methods: Some companies in Japan once take the urea treatment, aminosulfonic way, ammonia catalyze-oxidation., which are rarely used today.
3 Outlook
Each step upgraded in the electronic gas purity, will result in the quality leap of electronic components, and the nitrous oxide, as a newcomer in the electronic gases, is looked upon well by the related industries.
By now, the tail-gas recovery of nitrous oxide is in full swing with large amount turned out and the production is the year 2023 meets its new peak. With the account of governmental support in its decicated funds, the nitrous oxide will surely become the wholly china-make electronic gas.
