Method for preparing electronic grade sulfuric acid from waste sulfuric acid solution

A method for preparing an electronic grade sulfuric acid, comprising the steps of:

• (A) subjecting a waste sulfuric acid solution to a concentration treatment so as to obtain a concentrated waste sulfuric acid solution including sulfuric acid that is present in an amount ranging from 80 wt % to 90 wt % based on a total weight of the concentrated waste sulfuric acid solution, the concentrated waste sulfuric acid solution is then subjected to a cracking treatment performed at a temperature ranging from 1000° C. to 1200° C. for 1.5 seconds to 3.5 seconds so as to obtain a gas mixture containing sulfur dioxide gas, oxygen gas, and water vapor, followed by subjecting the gas mixture to a purification treatment in which the gas mixture was cooled from the temperature ranging from 1000° C. to 1200° C. to a lower temperature ranging from 300° C. to 400° C., and then purified and further cooled to an even lower temperature of not greater than 40° C. so as to obtain a pure sulfur dioxide gas;
• (B) subjecting the pure sulfur dioxide gas to a first oxidation treatment in the presence of vanadium pentoxide so as to obtain a gas substance containing sulfur trioxide gas and residual sulfur dioxide gas;
• (C) performing a first absorption treatment in which a first oleum is used to absorb the sulfur trioxide gas and the residual sulfur dioxide gas of the gas substance so as to obtain a second oleum, and then performing a second oxidization treatment in which the residual sulfur dioxide gas in the second oleum is oxidized to sulfur trioxide using an oxidizing agent selected from at least one of hydrogen peroxide, sodium persulfate, and ozone so as to obtain a third oleum, a concentration of sulfur trioxide in each of the second oleum and the third oleum being greater than that of the first oleum,
• wherein the second oleum includes sulfur trioxide that is present in an amount ranging from 25 wt % to 40 wt % based on a total weight of the second oleum, and sulfur dioxide having a concentration ranging from 5 ppm to 50 ppm, the third oleum includes sulfur trioxide that is present in an amount ranging from 25 wt % to 40 wt % based on a total weight of the third oleum, and sulfur dioxide having a concentration ranging from 0 ppm to 0.5 ppm;
• (D) subjecting the third oleum to an evaporation treatment at a temperature ranging from 130° C. to 150° C. for extracting sulfur trioxide gas therefrom, so as to obtain a first purified sulfur trioxide gas;
• (E) performing, in a demisting apparatus, a first removal treatment in which an acid mist containing metal ions and anion impurities entrained by the first purified sulfur trioxide gas was removed so as to obtain a second purified sulfur trioxide gas having a purity higher than that of the first purified sulfur trioxide gas, the demisting apparatus including at least two demister units connected in sequence, each of the demister units including a filler unit which has a support frame and a filler material filled in the support frame, the support frame being made of at least one material selected from the group consisting of perfluoroalkoxy vinyl ether copolymer and modified polytetrafluoroethylene, the filler material being made of a material selected from the group consisting of perfluoroalkoxy vinyl ether copolymer and modified polytetrafluoroethylene;
• (F) performing a second absorption treatment in which a first electronic grade sulfuric acid is used to absorb the second purified sulfur trioxide gas so as to obtain a second electronic grade sulfuric acid having a concentration higher than that of the first electronic grade sulfuric acid;
• and
• (G) performing a second removal treatment in which residual sulfur dioxide in the second electronic grade sulfuric acid is removed so as to obtain a third electronic grade sulfuric acid having a concentration higher than that of the second electronic grade sulfuric acid.