Process for the production of ethylenically unsaturated carboxylic acids or esters and a catalyst therefor
A method of producing an ethylenically unsaturated carboxylic acid or ester such as (meth) acrylic acid or alkyl esters thereof, for example, methyl methacrylate is described. The process comprises the steps of contacting formaldehyde or a suitable source thereof with a carboxylic acid or ester, for example, propionic acid or alkyl esters thereof in the presence of a catalyst and optionally an alcohol. The catalyst comprises group II metal phosphate crystals having rod or needle like morphology or a suitable source thereof. The phosphate may be a hydroxyapatite, pyrophosphate, hydroxyphosphate, PO 4 2− phosphate or mixtures thereof. The group II metal may be selected from Ca, Sr, Ba or mixtures thereof, for example, strontium hydroxyapatite and calcium hydroxyapatite. A catalyst system comprising a crystalline metal phosphate catalyst and a catalyst support is also described. The metal phosphate has rod/needle like morphology.
1. A method of producing an α, β ethylenically unsaturated carboxylic acid or ester, comprising the steps of contacting formaldehyde or a suitable source thereof with a carboxylic acid or ester in the presence of a catalyst and optionally an alcohol, wherein the catalyst comprises group II metal phosphate crystals having rod or needle like morphology;
wherein the catalyst has a surface layer of crystals depleted below a hydroxyapatite metal:phosphorus (M:P) ratio of 1.67.
2. The method according to claim 1 , wherein the phosphate is selected from the group consisting of pyrophosphate, hydroxyphosphate, PO 4 3− and mixtures thereof.
3. The method according to claim 1 , wherein the group II metal of the phosphate is selected from the group consisting of Ca, Sr or Ba or mixtures thereof.
4. The method according to claim 1 , wherein the catalysts are selected from the group consisting of strontium hydroxyapatite and calcium hydroxyapatite.
5. The method according to claim 1 , wherein the catalyst is at least 50% w/w metal phosphate.
6. The method according to claim 1 , wherein reaction selectivity to the α, β ethylenically unsaturated carboxylic acid or ester product is at least 40 mole %.
7. The method according to claim 1 , wherein the crystal surface hydroxyapatite metal:phosphorus (M:P) mole ratio is between 1.30 and 1.55.
8. The method according to claim 1 , wherein the carboxylic acid or ester reactant of the present invention is of formula R 3 —CH 2 —COOR 4 , wherein R 4 is either hydrogen or an alkyl group and R 3 is either hydrogen, an alkyl or aryl group.
9. The method according to claim 1 , wherein the α, β ethylenically unsaturated acid or ester produced is selected from the group consisting of acrylic, alkacrylic, 2-butenoic, cyclohexenoic, maleic, itaconic and fumaric acids and their alkyl esters, and also methylene substituted lactones.
10. The method according to claim 1 , wherein doping elements are present in the catalyst at a level up to 20 mol % of the metal M.
11. The method according to claim 10 , wherein the doping elements are metal cations selected from the group consisting of Cs, K, Rb, Na, Li, Zn, Ti, Si, Ln, Ce, Eu, Mg (if not used as a group II metal), Ba (if not used as a group II metal), Pb, Cd, Ag, Co, Cu, Ni and Zr.
12. The method according to claim 1 , wherein doping anions are present in the catalyst at a level of up to 20 mol % phosphate.
13. The method according to claim 12 , wherein the doping anions are selected from the group consisting of carbonate, chloride and fluoride.
14. The method according to claim 1 , wherein the catalyst is on a support selected from the group consisting of alumina, silica, silicon nitride, silicon carbide, colloidal silica, titania or aluminium phosphate.
15. The method according to claim 1 , wherein an overall metal:phosphorus (M:P) mole ratio of the catalyst is between 0.8-1.8.
16. The method according to claim 6 , wherein the ethylenically unsaturated carboxylic acid or ester is an (alk)acrylic acid or alkyl (alk)acrylate.
17. The method according to claim 2 , wherein the phosphate is selected from the group consisting of pyrophosphate, hydroxyapatite, and mixtures thereof.