Process for production of purified terephthalic acid
A technology of terephthalic acid and p-toluic acid, which is used in the preparation of carboxylate, the preparation of organic compounds, and the preparation of carboxylic acid by oxidation, to achieve the effect of reducing the number of crystallizers, simplifying the crystallization process, and reducing the size
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Embodiment 1
[0070] This example illustrates the ability to refine crude terephthalic acid having a p-toluic acid concentration of 429 ppmw below the acceptable purity limit (150 ppm) for purified terephthalic acid. It is also illustrated that this requirement can be met by isolating terephthalic acid at temperatures below the boiling point of the solvent.
[0071] The autoclave was charged with water (solvent) and crude terephthalic acid in the amounts listed in Table I, Experiments 1, 2 and 3. These amounts represent an approximate 30% aqueous solution of terephthalic acid. On a solid basis, the content of p-toluic acid in the crude terephthalic acid was 429.37 ppmw. The autoclave charge was heated to 280°C and held at this temperature for one hour to ensure that all solids dissolved. To simulate multiple crystallizers in series, the autoclave feed was cooled to room temperature at a rate of 30 °C per hour. The autoclave charge was then reheated to 60°C and the charge was maintained a...
Embodiment 2
[0075] In this example, which illustrates the effect of separation temperature on the purity of the final product, a portion of the room temperature autoclave feed from Experiments 1, 2 and 3 of Example 1, respectively, was placed into a well mixing vessel. Instead of reheating to 60°C as done in Example 1, in Example 2 the portions were reheated to 95°C and held at this temperature for 1 hour. Solid-liquid separation was performed at 95°C to obtain a solid sample, and the sample was analyzed for p-toluic acid concentration. The results are also listed in Table I. As we can see, the separation at the higher 95°C resulted in a product with a lower p-toluic acid concentration than the material isolated at the lower 60°C. Raising the separation temperature from 60°C while still keeping the solid-liquid separation temperature below the boiling point of the solvent can improve product purity.
Embodiment 3
[0077] The autoclave was charged with water and crude terephthalic acid in the amounts listed in Experiments 4 and 5 of Table II. These samples represent an approximate 20% aqueous solution of crude terephthalic acid. The concentration of p-toluic acid in the crude terephthalic acid was 429.37 ppmw. The sample was heated to 280°C and held at this temperature for one hour to ensure that all solids were dissolved. The sample was cooled to room temperature at a rate of 30°C per hour. Then, following the procedure of Examples 1 and 2, a portion of each sample was heated to 60°C and separated at this temperature, and a portion of each sample was heated to 95°C and separated at this temperature. The p-toluic acid concentrations of the resulting solids are listed in Table II.
[0078] substance
Experiment 4
Experiment 5
Crude terephthalic acid (parts)
25.0104
25.0017
water (parts)
99.9537
100.2292
p-toluic acid ...
PUM
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