Toyo Boseki Kabushiki Kaisha

Toyo Boeski Kabushiki Kaisha

Fuyuhiko Kubota

Kiyoshi Hotta

Go Matsuoka

Yoshio Araki

Masakatsu Ohguchi

Makiko Koyama

Masahiko Fukushima

The present invention provides a purification method of phosphoric acid, which includes bringing phosphoric acid containing arsenic into contact with hydrogen halide, thereby to remove the arsenic from the phosphoric acid, and a purification method of phosphoric acid, which includes bringing phosphoric acid containing arsenic into contact with hydrogen halide in the presence of a compound capable of generating hydrogen halide under acidic conditions. According to the method for purifying phosphoric acid of the present invention, a completely new method for removing arsenic in phosphoric acid is provided, which does not require a filtration or deaeration step or shows a great amount of residual sodium, unlike a sulfide coagulation method. This method is applicable to high concentration phosphoric acid, particularly polyphosphoric acid, and can be practiced at a low cost. In addition, a conventionally nonexistent high purity polyphosphoric acid having an arsenic (As) content of not more than 1 ppm and low contents of heavy metal, silica, sodium and the like can be provided.

Method for purification of phosphoric acid high purity polyphosphoric acid

Aromatic diamine/aromatic dicarboxylate and production method thereof

Polybenzazole and fiber thereof

A method for producing polybenzazole in the presence of iron(II) ion. The polybenzazole obtained by this method can be formed into a highly strong fiber having a high elastic modulus and a heat resistant film. The method enables economical production of polybenzazole having fine tone and high polymerization degree.

Method for producing polybenzazole

A method for producing polybenzazole, which comprises reacting a PBZ monomer salt with an AA-PBZ monomer or a BB-PBZ monomer in a non-oxidizing solvent having a dehydrating action to give an oligomer, and adding the AA-PBZ monomer or BB-PBZ monomer, which has not been subjected to the above reaction, to allow reaction with the oligomer, whereby to give a polymer having a desired polymerization degree. According to this method, the polymerization degree of the polymer to be obtained finally and of the polymer during production process can be easily controlled.

Method for production of polybenzazole

A method for stabilizing DAR during storage, comprising storing DAR in the presence of a reducing agent having a standard redox potential of not less than -0.20 volt and not more than 0.34 volt, in a proportion of not less than 100 ppm and not more than 10,000 ppm of DAR. The present invention improves storage stability of DAR. This in turn results in easy handling and long-term preservation of DAR. Thus, a high quality polymer PBO can be easily produced and the invention greatly contributes to the industrial field.

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Shiga, Japan

Fuyuhiko Kubota