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Dimethyl Terephthalate: Terephthalic Acid and Methanol Sprayed through a Hot Tube
Dimethyl terephthalate (DMT) is the methyl ester of terephthalic acid, a raw material for polyesters. Terephthalic acid does not melt, so Lotz and Gerlach (US 2,876,252, 1959) spray it as a suspension in methanol, with a little phosphoric acid, into a tube heated to 280–300 °C. The ester condenses as long needles that melt at 141 °C; the patent's yield was 97 %.
The picture: our diagram.
Advanced
Continuous
Instructions
1
1
Make the suspension
Make the suspension
Stir 1000 g of finely powdered terephthalic acid and 60 cc of 85 % phosphoric acid into 1000 cc of methanol.
Materials for this step:
Terephthalic Acid1000 g
Methanol1000 mlTools needed:
Phosphoric Acid (85%)
Balance Scale
Graduated Cylinder
Chemical Splash Goggles
Rubber Gloves2
2
Heat the reaction tube
Heat the reaction tube
Heat a long cylindrical reaction tube electrically to 280–300 °C (the patent's was 300 cm long and 40 cm wide). A cooled condenser follows it.
Tools needed:
Heated Reaction Tube
Thermocouple with Readout
Condenser Coil3
3
Spray it in with nitrogen
Spray it in with nitrogen
Spray the suspension with nitrogen through a nozzle into the tube, so the fine spray travels in a spiral along the tube wall. The acid and methanol react on the way.
Tools needed:
Atomising Spray Nozzle
Nitrogen Gas CylinderHeated Reaction Tube
Heat-Resistant Gloves4
4
Collect the needles
Collect the needles
The dimethyl terephthalate collects in the cooled condenser as long prismatic needles, melting point 141 °C. The patent's yield was 97 %.
Tools needed:
Condenser CoilRubber Gloves5
5
Recycle nitrogen and methanol
Recycle nitrogen and methanol
Draw the nitrogen and the excess methanol out with a membrane (diaphragm) pump and send them round again.
Tools needed:
Diaphragm PumpNitrogen Gas CylinderTools Required
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