A new technology that transforms water and carbon dioxide into a supercritical fluid and uses this fluid to carry out chemical reactions
is receiving great attention in Japan and is being applied rapidly
In Japan industry.
Substances such as water, carbon dioxide and methanol exhibit some characteristics of gases
and liquids under high temperature and high pressure. They can accelerate chemical reactions like gases and act like liquids. /p>
p>
It is also easy to dissolve other substances, which then become supercritical fluids. Japanese research into the use of supercritical fluids began in 1998. This new technology was first used for environmental protection, such as the treatment of plastic waste, waste sludge and purification, dioxins and other harmful substances, processing of industrial waste
in renewable resources, etc. For example, supercritical water is used to recover toluenediamine (TDA). The processing time only takes 30 minutes, which is only 1/20 of the acid catalyst method, and the recovery efficiency is 80%, the recycled products can be reused as raw materials. materials for manufacturing polyurethane resin.
This new technology can also transform the plastic sheath of the wires into lamp oil and gasoline, with a recovery rate of up to 80%, and the time required is much shorter than the thermal decomposition method.
“The 21st century is a time when water and carbon dioxide play a leading role in the chemical industry. » This is the opinion put forward by a Japanese scientist. Therefore, the use of supercritical fluids to manufacture raw materials for pharmaceuticals, cosmetics, pesticides, plastics and other industrial products becomes an important research and development focus for Japanese government scientific research institutions. The Institute of Materials Science and Technology of the Ministry of International Trade and Industry
conducted experiments on the use of supercritical methanol and carbon dioxide to synthesize resins and raw materials pharmaceuticals and pesticides
Methanol and carbon dioxide here not only play the role of catalysts, but also transform into synthetic materials, which can achieve the effect of "killing two birds with one stone ".
Professor Akiyoshi Sakada of the University of Tokyo develops the use of supercritical fluids to extract oligosaccharides, formic acid, acetic acid and technology for lignin and other pharmaceuticals and plastic raw materials has now produced pilot equipment, and the next step is to develop large-scale production systems.
In high-tech industries such as semiconductors, the use of supercritical carbon dioxide to replace chlorine-containing fluorocarbon detergents has also attracted attention. This method can degrease, separate oil, remove impurities, etc. The advantage is that it is easy to use, has good effects and does not pollute the environment. A scientific research consortium consisting of the government and Japanese companies has begun developing "industrial cleaning devices using supercritical fluids."
If low-grade coal and heavy oil with high sulfur content are oxidized and burned in supercritical water, desulfurization, denitrification and dust removal devices will not be necessary.
p>
, the carbon dioxide produced is equalrelatively easy to recover. Therefore, the Japan Chemical Technology Strategy Promotion Agency plans to research and develop "supercritical hydropower generation technology".
The use of supercritical carbon dioxide to sterilize is also a topic of practical importance. Carbon dioxide can penetrate the cell wall of bacteria in a supercritical state and cause an oxidation reaction inside, thereby killing the bacteria. The technology of using supercritical carbon dioxide to sterilize liquid foods
will be put into practice in 2000.
Is supercritical water corrosive?
< p>Yes, in the field of hazardous waste disposal, ENN Environmental Protection takes supercritical water oxidation technology as a basis according to the categories and characteristics of hazardous waste. , The integration of techCorresponding pretreatment technology can realize the harmless treatment and recycling of various hazardous liquid organic wastes. Compared with traditional disposal methods, hazardous waste disposal solutions with supercritical water oxidation technology as the core have the characteristics of high reaction efficiency, clean and thorough treatment effect , small footprint, etc. At the same time, the disposal cost is also more favorable, and it is used in pharmaceutical, chemical, etc. industries. Various industries have broad application prospects.Principle of supercritical water oxidation technology
Supercritical water has two important characteristics. First, it has extremely strong oxidation capacity, and the substances that need to be treated are put into supercritical water. , when filled with oxygen and peroxyde of hydrogen, this substance will be oxidized and hydrolyzed. Some can even ignite spontaneously and ignite in water. Another feature is that it can be mixed with oil and other substances and has a wider melting capacity. These characteristics allow supercritical water to produce strange functions.
It has strong oxidizing properties and can react with more substances, thus corroding
The self- Saying supercritical, refers to a particular state of fluid matter. When the temperature and pressure of a fluid in vapor-liquid equilibrium increase, thermal expansion causes the density of the liquid to decrease, and the increase in pressure causes the phase interface between the vapor and liquid phases to disappear and becomes a homogeneous system. This is the critical point. When the temperature and pressure of the fluid are respectively higher than the critical temperature and the pressurecritical ion, it is said to be in a supercritical state. Supercritical fluids have good fluidity similar to gases, but their density is much higher than gases, so they have many unique physical and chemical properties.
The critical point of water is a temperature of 374.3°C and a pressure of 22.064 MPa. If the water temperature and pressure are high above the critical point, it is supercritical water. and conductivity Basic properties such as dielectric constant and dielectric constant are very different from those of ordinary water, showing similar properties to non-polar organic compounds. Therefore, supercritical water is completely miscible with nonpolar substances (such as hydrocarbons) and other organic substances, while inorganic substances, especially salts, have very low ionization constants and solubility.bles in supercritical water. At the same time, supercritical water is completely miscible with gases such as air, oxygen, nitrogen and carbon dioxide.
As supercritical water is an excellent solvent for both organic matter and oxygen, the oxidation of organic matter can be carried out in a homogeneous oxygen-rich phase, and the reaction does not has no limitations due to the need for phase transfer.system. At the same time, the high reaction temperature of 400-600°C also accelerates the reaction, and a killing rate of more than 99% can be achieved within a few seconds of reaction time. The oxidation reaction of organic matter in supercritical water can be simply expressed as:
Acid + Na0H-inorganic matter
The oxidation reaction of organic matter in supercritical water is completed: organic carbon is converted to CO2, hydrogen converted to H20, halogen atomsene are converted to halide ions, sulfur and phosphorus are converted to sulfate and phosphate, respectively, and nitrogen is converted to nitrate and nitrite ions or nitrogen gas. In addition, the supercritical water oxidation reaction is to a certain extent similar to a simple combustion process, releasing a large amount of heat during the oxidation process.
In order to further accelerate the reaction speed, reduce the reaction time and lower the reaction temperature, so that supercritical water oxidation technology can take full advantage of its own advantages, research on supercritical catalytic water oxidation technology has been carried out to treat wastewater is increasingly emerging.