Kureha Kagaku Kogyo Kabushiki Kaisha

Kureha Chemical Industry Company, Limited

Yoshihiko Kudo

Kohki Nomoto

Kiyoshi Tagaya

Hiroshi Hagiwara

Yukio Suzuki

Jyuniti Kosugi

Haruo Aoki

Mituru Otomo

Eiji Yoshida

Disclosed herein is a method for producing .alpha.-form gypsum hemihydrate, comprising heating an aqueous slurry containing gypsum dihydrate and a salt of sulfosuccinic acid as the catalyst for crystallization, thereby converting gypsum dihydrate into .alpha.-form gypsum hemihydrate.

Process for producing .alpha.-form gypsum hemihydrate

Disclosed herein is a method for treating a liquid used for absorbing gaseous sulfur dioxide in the wet process for desulfurization of a combustion exhaust gas of the gypsum-by-producing type, which method comprises the steps of, after subjecting a liquid, which has been saturated with gypsum, has dissolved at least magnesium sulfate and magnesium chloride and is used as the above-mentioned liquid for absorbing gaseous sulfur dioxide, to clarifying treatment, passing the liquid saturated with gypsum through an electrodialyzer having three dialyzing chambers comprising one sheet of cation-exchange membrane and two sheets of membrane selectively permeable to monovalent anions as one unit, thereby selectively separating and removing the chloride ion in the above-mentioned liquid as an aqueous solution of magnesium chloride of a high concentration.

Method for treating liquid used for absorbing gaseous sulfur dioxide in

Disclosed is an improvement in a process for desulfurization of off-gas, which process comprises contacting an off-gas which contains sulfur dioxide with an absorbing solution containing at least a sulfosuccinate, a sulfate and a crystalline gypsum to absorb the sulfur dioxide for removal therefrom, and oxidizing the resulting absorbed solution with an oxygen-containing gas while neutralizing the solution with limestone in order to fix the sulfur dioxide in the form of gypsum for separation. The improvement comprises adding maleic anhydride and limestone to the absorbed solution during the residence time of the absorbed solution, the resulting absorbed solution being oxidized with an oxygen-containing gas to reproduce an absorbing solution therefrom so as to be effectively reused for the absorption of sulfur dioxide in the off-gas for separation.

Process for removing sulfur dioxide from off-gas

In the conversion of sulfur dioxide in an off-gas to gypsum for removal by oxidizing with an oxygen-containing gas while neutralizing with limestone an absorbed solution formed by contacting an off-gas containing sulfur dioxide with an absorbing solution containing an organic carboxylate, the addition of a thiocyanate to the absorbing solution makes it possible to inhibit the decomposition of the organic carboxylic acid in the absorbing solution.

Off-gas desulfurization process

The present invention concerns a process for removing sulfur dioxide from a combustion exhaust gas, wherein sulfur dioxide contained in the combustion exhaust gas is absorbed into an aqueous absorbent containing carboxylate salts and after oxidizing the thus formed sulfite and hydrogen sulfite into sulfate, the sulfate is converted into gypsum and separated, the invention particularly concerning a method for suppressing the decomposition of the carboxylate salts at the same time oxidizing the sulfite and hydrogen sulfite.

Process for removing sulfur dioxide from combustion exhaust gas

A process of treating an exhaust gas containing NO.sub.x and SO.sub.2 comprising bringing the gas into contact with an absorbing solution containing iron chelate salt and potassium sulfite, cooling the solution to crystallize and separate absorption products of potassium imidodisulfonate, potassium dithionate and potassium sulfate, heating the separated products at 250.degree. to 400.degree. C. to decompose the potassium dithionate into potassium sulfate and sulfur dioxide, then decomposing the potassium imidodisulfonate into ammonia and simultaneously reducing the potassium sulfate into potassium polysulfide and potassium carbonate, and converting the potassium polysulfide into hydrogen sulfide, gaseous sulfur and potassium carbonate.

Process of treating exhaust gas containing nitrogen oxides and sulfur

A method of treating an exhaust gas at a high temperature containing nitrogen oxides and sulfur oxides by bringing the exhaust gas into contact with an absorbing solution containing at least an iron chelate salt and potassium sulfite to thereby convert said nitrogen oxides and sulfur oxides into a mixture of potassium imidodisulfonate, potassium dithionate and potassium sulfate, characterized in that (1) the exhaust gas at a high temperature is cooled to a temperature below 80.degree. C. before bringing it into contact with the absorbing solution, (2) the concentration of potassium sulfite as the sulfite component in the absorbing solution is kept at least at 0.8 mol/kg, and (3) the mixture of salts produced in the absorbing solution is crystallized by cooling and separated by filtering the absorbing solution.

Treatment of exhaust gas containing sulfur oxides and nitrogen oxides

A process is described for treating an exhaust gas containing NO.sub.x and SO.sub.x in which NO.sub.x and SO.sub.x are effectively converted into industrially useful products of NH.sub.3, or sulfur by use of an aqueous absorbing solution containing at least iron chelate salt and potassium sulfite.

Process for treating an exhaust gas containing nitrogen oxides and

Alpha type calcium sulfate hemihydrate gypsum is obtained by suspending gypsum in an aqueous solution containing a specific monocarboxylate in a specific concentration and heating the resultant suspension in a specific temperature range under atmospheric pressure. The production of this alpha type calcium sulfate hemihydrate is accomplished at an increased rate by adding a specific monocarboxylic acid to the aqueous solution, suspending gypsum in the resultant solution and heating the resultant suspension in a specific temperature range under atmospheric pressure.

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Iwaki, Japan

Yoshihiko Kudo