Mitsubishi Gas Chemical Company, Inc.

Toyo Boseki Kabushiki Kaisha

Mizushima Aroma Company, Ltd.

Takahisa Furuya

Fumio Ohkoshi

The present invention proposes a crystallization process comprising the steps of feeding a slurry solution in which a terephthalic acid solution or a part of the terephthalic acid is precipitated to a crystallization vessel, precipitating the terephthalic acid in the crystallization vessel, generating a slurry containing crystals and solvent, discharging the slurry, and further comprising the steps of introducing the slurry in a tangential the direction of a hydrocyclone, returning the slurry flowing out as a downward swirling flow from a lower part of the hydrocyclone to the vessel, and discharging the slurry overflowing from the upper part of the hydrocyclone. According to the present invention, crystals of large particle size is obtained and a stable driving ranging long term can be achieved because any adhesion or accumulation of the terephthalic acid crystals does not appear at all in the crystallization vessel.

Method of crystallization

A crystallization process comprising introducing a solution or a slurry formed by incomplete crystallization of a solute into a crystallization tank, crystallizing the solute in the crystallization tank, forming a slurry comprising crystals and a solvent and discharging the formed slurry to an outside, the crystallization being conducted, wherein a portion or an entire amount of the formed slurry is taken out of the crystallization tank and introduced into a crystal recycling apparatus, the crystals in the slurry are separated or the slurry is concentrated in the crystal recycling apparatus and the separated crystals or the concentrated slurry is recycled to the crystallization tank. Since the crystal recycling apparatus disposed and the crystallization is conducted while the separated crystals or the concentrated slurry is recycled from the crystal recycling apparatus to the crystallization tank, the residence time of the crystals and the concentration of the slurry in the crystallization tank can be increased. By controlling the flow rate of the recycled crystals, the distribution of the particle diameter can be improved and crystals having a desired average particle diameter can be obtained. Sticking of crystals to the liquid surface portions of the crystallization tank and apparatuses connected to the crystallization tank can be prevented.

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Okayama, Japan

Takahisa Furuya