Closely linking a NDA process with a pen process

In a process for producing polyethylene naphthalate from 2,6-naphthalene dicarboxylic acid, an improvement which avoids the need for handling dry solid 2,6-naphthalene dicarboxylic acid and derivatives thereof which comprises:

• a) Reacting a hydrocarbon stream containing predominantly methylnaphthalene with an oxygen-containing gas in the presence of a suitable solvent and catalyst to form a crude mixture of naphthoic acid (crude product NA), wherein said crude product NA remains dissolved in the solvent;
• b) Recovering said crude product NA by evaporation of solvent and washing said crude product NA with water;
• c) Debrominating said crude product NA by passing over a supported catalyst in the presence of hydrogen, and water-washing said crude debrominated product NA;
• d) Contacting said crude, debrominated product NA with an aqueous base of potassium to extract pure NA as the aqueous potassium salt of NA;
• e) Separating said aqueous potassium salt of NA from the remaining organic liquid (containing methylnaphthalene and partially oxidized reaction intermediates), and recycling said organic liquid to step a);
• f) Contacting said aqueous potassium salt of NA with naphthalene vapor, adding a solid catalyst, and removing water by evaporation to form a slurry of solid potassium salt of NA and catalyst suspended in liquid naphthalene;
• g) Reacting said slurry in the presence of carbon dioxide to convert solid potassium salt of NA to liquid naphthalene and solid dipotassium salt of 2,6-NDA(2,6-K2NDA);
• h) Reducing the pressure to vaporize the naphthalene, and separating the solids from the naphthalene vapor by a novel separation using cyclones, recycling a portion of the naphthalene to step (f), and recovering the remainder as a product, or methylating the naphthalene via direct alkylation or transalkylation to provide additional methylnaphthalene feed for step (a);
• i) Contacting the solids with water to create a mixture of aqueous potassium salts (comprising the potassium salt of NA, KNA, and the dipotassium salt of 2,6-NDA, 2,6-K2NDA, and its isomers) and solid catalyst;
• j) Separating the solid catalyst from the mixture of aqueous potassium salts and recycling it to step (f);
• k) Adding aqueous potassium bicarbonate to the mixture of aqueous potassium salts and evaporating a portion of the water to selectively crystallize the dipotassium salt of 2,6-NDA as a solid, separating said solid, and recycling the remaining liquid to step (d);
• l) Dissolving the solid dipotassium salt of 2,6-NDA in water;
• m) Optionally passing said aqueous dipotassium salt of 2,6-NDA through an activated carbon bed to remove impurities;
• n) Contacting said aqueous dipotassium salt of 2,6-NDA with carbon dioxide to create a mixture of solid monopotassium salt of 2,6-NDA and aqueous potassium bicarbonate, separating said solids, and recycling the aqueous potassium bicarbonate to step (k);
• o) Contacting solid monopotassium salt of 2,6-NDA with water, optionally in the presence of carbon dioxide, to form solid 2,6-NDA, aqueous dipotassium salt of 2,6-NDA, and potassium bicarbonate;
• p) Separating the solid 2,6-NDA and recycling the liquid containing aqueous dipotassium salt of 2,6-NDA and potassium bicarbonate to step (n);
• q) Contacting solid 2,6-NDA with water in a pipe reactor to remove traces of potassium ion impurity;
• r) Separating solid 2,6-NDA and recycling water to step o)
• s) Washing the solid 2,6 NDA with additional water
• t) Performing a crude separation of the water from the solid, producing wet polymer grade 2,6 NDA, and recycling most of the water to step q)
• u) Adding water to the wet polymer grade 2,6-NDA to form a pumpable slurry,
• v) Pumping the aqueous slurry directly into a process for making PEN,
• w) Removing the slurry water during the first esterification reaction at the same time the water of reaction is removed.