Supercritical fluids are good alternative for environmentally unsafe organic solvents, because of their tunable physicochemical properties with temperature and pressure. Also they possess a wide range of gas-like to liquid-like properties and can be employed as unique media to overcome poor solubility strength of gases and hindered mass traortation in conventional liquids. Among supercritical fluids, ethanol, offer novel media for both chemical reactions and separations, because it has an accessible critical properties ( T c = 240.85 ? C, P c = 61 bar) and it is less corrosive and more reactive. Several industrially important reactions such as catalytic etherification have been successfully done in hot alcohols. Diethyl ether because of its high volatility, low autoignition temperature, and good combustion characteristics is a valuable chemical and an attractive fuel additive. Diethyl ether has been synthesized in sub- and supercritical ethanol for the first time in Iran in this project. A continuous flow reactor and homogeneous catalysts namely para toluene sulfonic acid and sulfuric acid was used and the effect of temperature, flow rate, pressure and catalyst concentration was investigated. In the best condition (temperature = 200 o C, flow rate = 0.1 mL.min -1 and 4 (% w/v ) concentration of para toluene sulfonic acid) at pressure of 80 bar, the percent yield and selectivity was 60 and 94, respectively. In the same condition but with 2 (% w/v ) concentration of sulfuric acid 75 and 99 percent yield and selectivity was achieved respectively .
