| 摘要 |
Fibre-grade terephthalic acid is produced from an impure terephthalic acid containing 4-carboxy-benzaldehyde by catalytically hydrogenating said impure terephthalic acid in an aqueous solution at elevated temperature and pressure for a time sufficient to effect substantial reduction of said 4-carboxy-benzaldehyde, and recovering a terephthalic acid of fibre-grade quality. The hydrogenation may be effected within the range of 200 DEG to 400 DEG C. for 0.005 to 10 hours, particularly with a Group VIII metal catalyst, several catalysts being specified. The hydrogenation may be carried out as a batch process under static conditions, as in a sealed autocalve, or by bubbling hydrogen into the aqueous solution, or the aqueous solution of impure terephthalic acid may be percolated through a bed of hydrogenation catalyst while maintaining either a static hydrogen atmosphere or a flow concurrent or counter-current of hydrogen through the catalyst chamber. The product is obtained by cooling the aqueous solution and separating terephthalic acid crystals. The impure terephthalic acid may be made by liquid phase air oxidation of p-xylene, using a heavy metal and bromine as catalyst as in Specification 807,901, or using heavy metal catalysts promoted with acetaldehyde or methyl ethyl ketone, or the impure acid from the nitric acid oxidation of p-xylene, or from the isomerization of dipotassium phthalate or the disproportionation of potassium-benzoate may be similarly treated if carboxybenzaldehyde or reducible impurities are present. |
