Hot solution

时间:2019-03-07 14:16:00166网络整理admin

By Jeff Hecht USING hot, high-pressure water as a solvent could make the chemicals industry cleaner and greener. Charles Eckert of the Georgia Institute of Technology in Atlanta says that water at temperatures of 250 °C to 350 °C and pressures of 50 to 100 atmospheres can dissolve many hydrocarbons and other compounds that normally require organic solvents. Under these “near-critical” conditions, about a thousand times as many water molecules split into hydroxide ions and hydrogen ions as at room temperature. These ions ensure that organic compounds dissolve more readily. They can also catalyse some chemical reactions. When the water cools, the ions recombine and the products drop out of solution. As well as avoiding the use of potentially polluting organic solvents, this can eliminate the need to separate the final products—the most costly phase of many chemical processes. At last week’s meeting of the American Chemical Society in New Orleans, Eckert’s group described how near-critical water acts as a solvent in the widely used Friedel-Crafts reaction. This type of reaction forms a common step in many chemical syntheses, and usually requires large amounts of aluminium chloride catalyst, which eventually has to be neutralised and disposed of. Near-critical water eliminates all that waste,