Dehydration of alpha-substituted carboxylic acids in the presence of water at high pressures
The present invention describes a process for dehydrating alpha-substituted carboxylic acids in the presence of water at high pressures while avoiding by-products.
1. Process for dehydrating alpha-substituted carboxylic acid of formula (1):
where R 1 is CHR′R″; R 2 and R 3 are each independently H or a carbon radical comprising 1-7 carbon atoms, linear, branched or alicyclic; R 4 is H or a carbon radical comprising 1-3 carbon atoms, linear or branched; R′ and R″ are each independently H or a carbon radical comprising 1-3 carbon atoms,
comprising reacting an alpha-substituted carboxylic acid of formula (1) in the presence of water and at pressures of 40-1000 bar.
2. Process according to claim 1 , wherein said reaction is carried out at 280-400° C.
3. Process according to claim 1 , wherein a residence time in a pressure reactor is 1-300 s.
4. Process according to claim 1 , wherein the process is carried out as a catalyst-free process.
5. Process according to claim 1 , wherein a crude methacrylic acid obtained downstream of a pressure reactor comprises less than 2% of dimeric or oligomeric by-products.
6. Process according to claim 1 , wherein the process is carried out as a continuous process.
7. Process according to claim 1 , wherein said alpha-substituted carboxylic acid is alpha-hydroxyisobutyric acid.
8. Process according to claim 1 , wherein said pressure is 80-500 bar.
9. Process according to claim 1 , wherein said pressure is 100-350 bar.
10. Process according to claim 3 , wherein said residence time is 3-60 s.
11. Process according to claim 3 , wherein said residence time is 5-35 s.
12. Process according to claim 2 , wherein said temperature is 300 to 380° C.
13. Process according to claim 2 , wherein said temperature is 320 to 360° C.
14. Process according to claim 1 , wherein a concentration of water during reaction is 10-90% based on alpha-substituted carboxylic acid.
15. Process according to claim 1 , wherein a concentration of water during reaction is 30-70% based on alpha-substituted carboxylic acid.
16. Process according to claim 1 , wherein a concentration of water during reaction is 40-60% based on alpha-substituted carboxylic acid.