Process for the production of carboxylic acids
A process for the production of a carboxylic acid or its ester by catalytic liquid phase oxidation of a corresponding precursor in acetic acid as solvent, said process comprising: (i) forming a reaction medium comprising acetic acid, oxidation catalyst, precursor and oxidant; (ii) optionally recycling methyl acetate produced from the acetic acid as a by-product back to the reaction medium; (iii) introducing additional methyl acetate and/or methanol into the reaction medium, said additional methyl acetate and/or methanol being additional to any recovered methyl acetate recycled back to the reaction medium.
1 . A process for the production of a carboxylic acid or its ester by catalytic liquid phase oxidation of a corresponding precursor in acetic acid as solvent, said process comprising:
(i) forming a reaction medium comprising acetic acid, oxidation catalyst, precursor and oxidant;
(ii) optionally recycling methyl acetate produced from the acetic acid as a by-product back to the reaction medium;
(iii) introducing additional methyl acetate and/or methanol into the reaction medium, said additional methyl acetate and/or methanol being additional to any recovered methyl acetate recycled back to the reaction medium.
2 . A process according to claim 1 wherein the carboxylic acid is terephthalic acid and said precursor is p-xylene.
3 . A process according to claim 1 wherein the methyl acetate produced from the acetic acid as a by-product is recycled back to the reaction medium.
4 . A process according to claim 1 wherein said recycling of methyl acetate produced as a by-product back to the reaction medium comprises passing the vapour effluent containing the methyl acetate by-product from the reaction medium through a condenser.
5 . A process according to claim 4 wherein at least a portion of said methyl acetate in said vapour is recovered as a condensate from the condenser.
6 . A process according to claim 4 wherein at least a portion of the methyl acetate in the off-gas of the condenser is recovered by scrubbing the off-gas with acetic acid and/or water.
7 . A process according to claim 5 wherein at least a portion of the methyl acetate in the off-gas of the condenser is recovered by scrubbing the off-gas with acetic acid and/or water.
8 . A process according to claim 6 wherein at least a portion of said methyl acetate and acetic acid resulting from scrubbing the off-gas of the condenser is recycled directly back to the reaction medium.
9 . A process according to claim 7 wherein at least a portion of said methyl acetate and acetic acid resulting from scrubbing the off-gas of the condenser is recycled directly back to the reaction medium.
10 . A process according to claim 6 wherein at least a portion of said methyl acetate and acetic acid resulting from scrubbing the off-gas of the condenser is passed to distillation for recovery of acetic acid and methyl acetate and recycle to the reaction medium.
11 . A process according to claim 7 wherein at least a portion of said methyl acetate and acetic acid resulting from scrubbing the off-gas of the condenser is passed to distillation for recovery of acetic acid and methyl acetate and recycle to the reaction medium.
12 . A process according to claim 8 wherein at least a portion of said methyl acetate and acetic acid resulting from scrubbing the off-gas of the condenser is passed to distillation for recovery of acetic acid and methyl acetate and recycle to the reaction medium.
13 . A process according to claim 9 wherein at least a portion of said methyl acetate and acetic acid resulting from scrubbing the off-gas of the condenser is passed to distillation for recovery of acetic acid and methyl acetate and recycle to the reaction medium.
14 . A process according to claim 1 wherein said process for the production of carboxylic acid comprises crystallising the reaction product in one or more crystallisation vessel(s) and wherein said recycling of methyl acetate comprises scrubbing the off-gas of the crystallisation vessel(s) with acetic acid and/or water.
15 . A process according to claim 1 wherein said process for the production of carboxylic acid comprises crystallising the reaction product and recovering the carboxylic acid crystals by filtration and wherein said recycling of methyl acetate comprises passing at least a portion of the filtrate to distillation for recovery of acetic acid and methyl acetate and recycle to the reaction medium.
16 . A process according to claim 15 wherein at least a portion of the filtrate is recycled directly to the reaction medium.
17 . A process according to claim 1 wherein said additional methyl acetate and/or methanol is no more than 4 mole % of the solvent feed.
18 . A process according to claim 1 wherein said additional methyl acetate and/or methanol is no more than 3 mole % of the solvent feed.
19 . A process according to claim 1 wherein said additional methyl acetate and/or methanol is no more than 2 mole % of the solvent feed.