Production of unsaturated carboxylic acids or acid esters with a haloapatite-based catalyst
The present invention relates to the use of haloapatites as catalysts of the dehydration reaction of α-hydroxylated carboxylic acids or acid esters, in particular of lactic acid or of methyl lactate, and also to a process for producing unsaturated carboxylic acids or acid esters, in particular acrylic acid or methyl acrylate, in the gas phase in a stainless steel reactor, in the presence of such a catalyst.
1. Process for producing an unsaturated carboxylic acid or an unsaturated carboxylic acid ester in the presence of a catalyst, said process comprising the steps of:
dehydrating an α-hydroxylated carboxylic acid or an α-hydroxylated carboxylic acid ester, respectively, said step being carried out in the gas phase, in the presence of a solid catalyst containing at least one halogenated apatite of formula (I) below:
Ca 10-x [(PO 4 ) 6−(x+y+z) (HPO 4 ) x+z (CO 3 ) 3 ][Y 2−(x+y+z) (CO 3 ) y+z ] (I)
in which:
Y represents at least one anion selected from the F − , Cl − anions, and the combinations of at least one F − or Cl − anion with an OH − anion;
0≤x≤1;
0≤y≤1;
0≤z≤1;
0≤x+y+z≤1,
said process being carried out in a stainless steel reactor.
2. The process according to claim 1 , wherein the dehydration step is carried out on an α-hydroxylated carboxylic acid or acid ester of formula (II) below:
in which:
R 1 is an alkyl radical having from 1 to 6 carbon atoms,
R 2 represents a hydrogen atom or an alkyl radical having from 1 to 6 carbon atoms;
and results in an unsaturated carboxylic acid or acid ester of formula (III) below being obtained:
in which R 1 and R 2 have the same meaning as in formula (II).
3. The process according to claim 2 , wherein the dehydration step is carried out on an α-hydroxylated carboxylic acid or acid ester of formula (II) in which R1 is an alkyl radical having 1 carbon atom and R2 represents a hydrogen atom, a methyl radical or an ethyl radical.
4. The process according to claim 1 , wherein the dehydration step is carried out using lactic acid and rests in acrylic acid being obtained.
5. The process according to claim 1 , wherein the catalyst contains at least one halogenated apatite of formula (I) in which Y=F − ; x=0; y=0; z=0 and of Ca/P molar ratio=1.67.
6. The process according to claim 1 , wherein the dehydration reaction is carried out at a temperature greater than or equal to 300° C.
7. The process according to claim 1 , wherein the dehydration reaction is carried out at atmospheric pressure.
8. The process according to claim 1 , wherein the gas phase comprises a carrier gas and/or diluent gas.
9. The process according to claim 8 , wherein the carrier gas and/or diluent gas of the gas phase is an inert gas selected from helium and nitrogen.
10. The process according to claim 1 , wherein the halogenated apatite of formula (I) is supported by a solid support.