Process for the production of ethylenically unsaturated carboxylic acids or esters and a catalyst therefor

Abstract

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.sub.4.sup.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.

Claims

1. A catalyst system for the reaction of formaldehyde or a suitable source thereof with a carboxylic acid or ester comprising a crystalline metal phosphate catalyst and a catalyst support wherein the metal phosphate has rod/needle like morphology.

2. The catalyst system according to claim 1, wherein the phosphate is selected from the group consisting of pyrophosphate, hydroxyphosphate, PO.sub.4.sup.3− phosphate and mixtures thereof.

3. The catalyst system according to claim 2, wherein the phosphate is selected from the group consisting of pyrophosphate, hydroxyapatite, and mixtures thereof.

4. The catalyst system according to claim 1, wherein the phosphate is selected from the group consisting of Ca, Sr or Ba or mixtures thereof.

5. The catalyst system according to claim 1, wherein the catalysts are selected from the group consisting of strontium hydroxyapatite and calcium hydroxyapatite.

6. The catalyst system according to claim 1, wherein the catalyst is at least 50% w/w metal phosphate.

7. The catalyst system according to claim 1, wherein the catalyst has a surface layer of crystals depleted below a metal:phosphorus (M:P) mole ratio of 1.67.

8. The catalyst system according to claim 7, wherein the crystal surface metal:phosphorus (M:P) mole ratio is between 1.30 and 1.55.

9. The catalyst system according to claim 1, wherein doping elements are present in the catalyst at a level of up to 20 mol % of the metal M.

10. The catalyst system according to claim 9, wherein the doping elements are metal cations selected from the group consisting of Cs, K, Rb, Na, Li, Zn, Ti, Si, La, 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.

11. The catalyst system according to claim 1, wherein doping anions are present in the catalyst at a level of up to 20 mol % phosphate.

12. The catalyst system according to claim 11, wherein the doping anions are selected from the group consisting of carbonate, chloride and fluoride.

13. The catalyst system 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.

14. The catalyst system according to claim 1, wherein the metal:phosphorus (M:P) mole ratio is between 0.8-1.8.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described with reference to the following non-limiting examples and figures and by way of illustration only in which:—

(2) FIG. 1 shows the surface and bulk M:P ratios for a selection of samples;

(3) FIG. 2 shows the TEM Image of Example 1 crystals;

(4) FIG. 3 shows the TEM Image of Comparative Example 4;

(5) FIG. 4 shows the TEM image of example 3 crystals;

(6) FIG. 5 shows the TEM image of example 6 crystals;

(7) FIG. 6 shows the TEM image of example 8 crystals;

(8) FIG. 7 compares crystallite morphology by XRD for several examples and comparative examples; and

(9) FIG. 8 shows a TEM Image of Example 11 at 100 nm scale showing the presence of nano-rods.

DETAILED DESCRIPTION OF THE INVENTION

EXPERIMENTAL

(10) Analytical Methods

(11) XRD Experimental

(12) The samples were prepared as dry compressed powder thin layer specimens mounted on single silicon crystal discs. The following instrument and settings were used.

(13) TABLE-US-00001 Instrument Siemens Bruker D5000 Diffractometer D6 X-ray Tube Cu LFF Radiation Ca Kα Generator Voltage 40 kV Generator Current 40 mA Diffraction Geometry Reflection Bragg Brentano Variable Divergence Slit- 12 mm irradiated length Variable Antiscatter Slit- 12 mm irradiated length Receiving Slit 0.2 mm Primary soller slit 2.3° Detector Si/Li Energy dispersive (monochromating) Monochromator Detector (Kα) Step Size 0.02° Time per step 3 seconds (“Sr.sub.2P.sub.2O.sub.7 pH 7_1.67 ” = 6 seconds) Scan start angle 1.5 Scan finish angle 90 Specimen format Bulk Specimen loading Compressed powder on silicon discs Specimen spinning Yes Temperature Ambient

(14) Data output is in the form of a diffractogram, showing reflection intensity (counts per second) vs. angle 2θ°. Crystalline phase identification is carried out by comparison to reference ICDD (formerly JCPDS) diffractograms. Peak intensity or peak broadening analysis is performed to quantify morphological parameters for a crystalline phase.

(15) XRF Experimental

(16) Powder samples were ground and sieved to achieve particle size <100 μm (mesh). Approximately 1 gram of powder was lightly compacted into a primary sample cup with a thin film transmission base. The primary cup was held within the instrument by a secondary safety cup also with a thin film transmission base. The following instrument and conditions were used.

(17) TABLE-US-00002 Instrument Oxford Instruments (EDXRF) X-Supreme 8000 X-ray source Tungsten Source Energy 6 keV Tube Current 10 μA Chamber purge gas Helium Detector Silicon Drift (SDD) proportional detector Primary cup base Poly4 film (4 μm thick) Secondary cup base Poly4 film (4 μm thick) Specimen spinning Yes Temperature Ambient Repeat scans 3

(18) Ca Kα and P Kα fluorescence intensities (counts per second) were recorded. The ratio of peak intensities was converted to give a Ca:P ratio for the material, using a calibration scale obtained from the Ca Kα and P Kα signals for stoichiometric reference materials.

(19) XPS Experimental

(20) A microspatula of the powder sample was placed onto a piece of silicone-free tape attached to the instrument sample holder, and the loose powder gently flattened with the microspatula tip. The following instrument and settings were used.

(21) TABLE-US-00003 Instrument Kratos “Axis Ultra” X-ray Photoelectron Spectrometer X-ray source Al Kα Monochromator Yes Pass Energy- 160 eV (survey scan), 40 eV&10 eV(high-res scan) Spot size Ellipitic area, ~300 μm × ~700 μm. Repeat scans 2

(22) Established Electron Spectroscopy for Chemical Analysis (ESCA) methods were utilised for qualification of the surface composition by elemental atomic percentage. Signal depth for oxide materials was ca. 3-5 nm, and the detection limit was about 1 atom in 1000 (i.e. 0.1 atom %, or 1000 ppm). Ca:P ratios were initially calculated from the experimental atomic percentages, and subsequently corrected for the presence of surface carbonaceous species.

(23) TEM Experimental

(24) Powder samples of the materials were suspended in water and drops were applied to copper grids bearing Lacey carbon support films. After drying, these were examined in a Philips CM12 TEM at an accelerating voltage of 120 kV.

(25) Micrographs and electron diffraction patterns were collected at matching magnifications/tube-lengths. Selected regions were analysed using the associated NORAN Vantage EDX system. The variety of morphologies, compositions and crystalline species observed were recorded as images. The following instrument and settings were used.

(26) Instrument-Philips CM12 Transmission Electron Microscope Accelerating Voltage 120 kV

(27) Two sets of experiments were run against various prepared examples of the invention and comparative examples. The first series of experiments were run using formaldehyde as a feed stream and the second series were run using dimethoxymethane as a feed stream. Analysis was carried out by gas chromatography, formaldehyde titration and with Karl Fischer apparatus. The analytical data were used to calculate the yield and selectivity of MMA+MAA. The selectivities in mole % relative to mole % MMA+MAA of diethylketone (DEK), dimethyl ether (DME) and toluene by-products are also tabulated in the catalyst test results below.

(28) A Formaldehyde Feed

(29) TABLE-US-00004 TABLE 1 Contact MMA + MAA MAA MMA + MAA Catalyst time yield selectivity selectivity DME DEK Toluene composition [s] [%] [mole %] [mole %] [mole %] [mole %] [mole %] Ex 1 Ca-HAp 10.3 4.1 1.3 93.5 0.5 0.0036 0.00014 pH7_1.67 Ex 2 Ca-HAp pH9- 5.0 4.3 0.6 84.6 0.6 0.0040 0.00009 10_1.67 Ex 3 Ca-PO pH9- 11.4 3.3 0.8 92.1 0.6 0.0026 0.00009 10_1.67_120 Ex 4 Ca-HAp 7.1 2.8 3.7 93.7 3.1 0.0014 0.00018 pH7_1.67_EtOH Ex 5 Ca-HAp 6.9 4.1 0.3 93.6 0.2 0.0014 0.00007 pH7_1.67_1% Cs Comp AlPO_TiO.sub.2_B_urea 3.1 4.7 12.6 69.2 14.4 0.0609 0.00528 Ex 1 Comp AlPO 1.5 4.8 12.9 78.0 10.6 0.0457 0.00446 Ex 2 Comp Comm Ca-HAp 7.0 0.2 0.1 72.3 0.2 0.0004 0.00005 Ex 3 289396 Comp Comm Ca-HAp 10.1 0.1 1.4 11.4 0.0021 0.0025 0.00000 ex 4 677418

Example 1

Preparative Example 1

(30) 23.6 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and pH was adjusted to 7 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 dissolved in 50 ml of demineralised water at pH 7 was added dropwise to the solution of calcium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 7 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water. Then it was dried at 110° C. overnight and calcined in air at 400° C. for 1 hr. BET surface area of the material was 44 m.sup.2/g. The sample was identified as a crystalline hydroxyapatite type by XRD analysis. Some amorphous material was found. TEM confirmed the presence of rod like crystal form.

(31) Catalyst testing: 3 g of catalyst as prepared in preparative example 1 was placed in a stainless steel tubular reactor connected to a vaporiser. The reactor was heated to 350° C. and vaporiser to 300° C. The mixture of 56.2 mole % of methyl propionate, 33.7 mole % of methanol, 9.6 mole % of formaldehyde and 0.5 mole % of water was passed through with the contact time indicated. The condensed reaction mixture was analysed by gas chromatography using a Shimadzu GC, equipped with a DB1701 column & a Flame Ionization Detector. For each analysis, the resultant chromatograph is processed using Shimadzu's GCsolution software to obtain peak areas for individual components. FID response factors for the individual components are applied to convert peak areas, first into wt %, and then into mol %, of detectable material in the sample.

(32) Selectivity with respect to MAA or MAA+MMA is calculated from the molar amount of the component produced (exit molar content, less feed molar content), as percentage of the molar amount of propionate converted to products.

Example 2

Preparative Example 2

(33) 23.6 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and pH was adjusted to 9-10 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 9-10 was added dropwise to the solution of calcium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 9-10 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water. Then it was dried at 110° C. overnight and calcined in air at 400° C. for 1 hr.

(34) The preparative example 2 catalyst was tested as described in example 1.

Example 3

Preparative Example 3

(35) 23.6 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and pH was adjusted to 9-10 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 9-10 was added dropwise to a boiling solution of the calcium nitrate while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete, then filtered and washed with demineralised water. After that it was dried at 110° C. overnight and then calcined in air at 400° C. for 1 hr. BET surface area of the material was 9 m.sup.2/g. The sample was identified as monetite and pyrophosphate by XRD analysis. TEM confirmed the presence of plate, rod, leaf and sphere like crystal forms.

(36) The catalyst was tested as described in example 1.

Example 4

Preparative Example 4

(37) 23.6 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and 100 ml of ethanol mixture. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 100 ml of demineralised water was added dropwise to the solution of calcium nitrate at the temperature of 25° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred overnight after the dropwise addition and pH was maintained at 7 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water. Then it was dried at 110° C. overnight and calcined in air at 400° C. for 1 hr. BET surface area of the material was 73 m.sup.2/g. The sample was identified as a crystalline hydroxyapatite type by XRD analysis. Some amorphous material was found. TEM confirmed the presence of rod like crystal form. The catalyst was tested as described in example 1.

Example 5

Preparative Example 5

(38) 3 g of the catalyst prepared as in preparative example 1 was impregnated with 1 wt % of caesium using caesium acetate in methanol and tested as described in example 1.

Comparative Example 1

Preparative Comparative Example 1

(39) The catalyst was synthesised following the preparation method disclosed in U.S. Pat. No. 4,118,588 patent in Example 4.

(40) 3 g of titanium dioxide TiO.sub.2 (Aldrich catalogue number 634662), 2.3 g of aluminium phosphate (prepared as in comparative example 2) and 0.75 g of boric acid H.sub.3BO.sub.3 were mixed together. A paste was produced by addition of 0.25 g of urea in 5 ml of demineralised water. The paste was dried for 2 hrs at 120° C. and then heated for 4 hrs at 600° C.

(41) The catalyst was tested as described in example 1. Modest selectivity was observed but a high level of DME was found.

Comparative Example 2

Preparative Comparative Example 2

(42) 37.5 g of aluminium nitrate nonahydrate Al(NO.sub.3).sub.3.9H.sub.2O and 13.2 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 were dissolved together in 160 ml of demineralised water acidified with nitric acid HNO.sub.3. Solution of ammonium hydroxide was added until pH 7 was reached. Formed hydrogel was mixed for further 1 hr, after that it was filtered and washed with water. It was dried at 80° C. overnight and then calcined in air at 600° C. for 1 hr. BET surface area of the material was 181 m.sup.2/g.

(43) The catalyst was tested as described in example 1. Modest selectivity was observed but a high level of DME was found.

Comparative Example 3

(44) Commercial Ca-hydroxyapatite was used from Aldrich with catalogue number of 289396. The sample was confirmed as a crystalline hydroxyapatite type by XRD analysis. Some amorphous material was found. TEM showed the presence of agglomerated irregular sphere like particles.

(45) The catalyst was tested as described in example 1. The results are shown in table 1. Although selectivity was modest and DME was low the yield was very low indicating a high level of inactivity.

Comparative Example 4

(46) Commercial Ca-hydroxyapatite was used from Aldrich with catalogue number of 677418.

(47) The samples were confirmed as crystalline hydroxyapatite type by XRD analysis. TEM showed evenly-shaped nano-spheres, typically 50-100 nm diameter (although with some individual spheres of 300-800 nm diameter), with no evidence of any non-spherical morphology.

(48) The catalyst was tested as described in example 1. The results are shown in table 1. The yield and selectivity were both very low.

(49) TABLE-US-00005 TABLE 2 Contact MMA + MAA MAA MMA + MAA Catalyst time yield selectivity selectivity DME DEK Toluene Ex. composition [s] [%] [%] [%] [mole %] [mole %] [mole %] Ex 6 Ca-HAp 1.2 1.6 0.2 80.0 0.1 0.0020 0.00015 pH11_1.67

Example 6

Preparative Example 6

(50) 23.6 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and pH was adjusted to 11 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 11 was added dropwise to the solution of calcium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 11 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water. Then it was dried at 110° C. overnight and calcined in air at 400° C for 1 hr. BET surface area of the material was 96 m.sup.2/g.

(51) The sample was identified as a crystalline hydroxyapatite type by XRD analysis, although the presence of some amorphous material was indicated. TEM showed highly crystalline nano-rod structures grouped in bundles of similar orientation.

(52) The catalyst was tested as described in example 1. The results are shown in table 2.

(53) TABLE-US-00006 TABLE 3 Contact MMA + MAA MAA MMA + MAA Catalyst time yield selectivity selectivity DME DEK Toluene Ex. composition [s] [%] [%] [%] [mole %] [mole %] [mole %] Ex 7 Ca-HAp 10.27 4.4 1.7 92.0 2.6 0.0020 0.00014 pH7_1.5 Ex 8 Ca-HAp 3.0 1.6 1.6 92.3 1.2 0.0007 0.00015 pH7_1

Example 7

Preparative Example 7

(54) 14.2 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and pH was adjusted to 7 with ammonium hydroxide. 5.3 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 100 ml of demineralised water at pH 7 was added dropwise to the solution of calcium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 7 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water. Then it was dried at 110° C. overnight followed by calcination in air at 400° C. for 1 hr. BET surface area of the material was 64 m.sup.2/g. The sample was identified as a crystalline hydroxyapatite type by XRD analysis. Some amorphous material was found.

(55) The catalyst was tested as described in example 1.

Example 8

Preparative Example 8

(56) 14.2 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and pH was adjusted to 7 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 100 ml of demineralised water at pH 7 was added dropwise to the solution of calcium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 7 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water. Then it was dried at 110° C. overnight followed by calcination in air at 400° C. for 1 hr. BET surface area of the material was 58 m.sup.2/g. The major phase was identified as a crystalline hydroxyapatite type by XRD analysis. A trace phase similar to calcium hydrogen phosphate CaHPO.sub.4 was present. Some amorphous material was found. TEM showed the presence of rod and sheet like crystal forms.

(57) The catalyst was tested as described in example 1. The results are shown in table 3.

(58) TABLE-US-00007 TABLE 4 Contact MMA + MAA MAA MMA + MAA Catalyst time yield selectivity selectivity DME DEK Toluene Ex. composition [s] [%] [%] [%] [mole %] [mole %] [mole %] Ex 9 Ca-HAp 10.4 4.1 2.8 89.8 3.1 0.0017 0.00008 pH7_1.67_25 Ex Ca-HAp 9.8 4.8 4.0 91.4 4.7 0.0033 0.00011 10 pH11_1.00 Ex Ca-PO 15.6 4.4 1.4 94.6 0.42 0.002 0.00024 11 pH5_1.67 ex Ca-PO 6.9 3.1 1.4 90.1 1.8 0.0023 0.00008 12 pH5_1.00

Example 9

Preparative Example 9

(59) 23.6 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and pH was adjusted to 7 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 7 was added dropwise to the solution of calcium nitrate at the temperature of 25° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 7 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water. Then it was dried at 110° C. overnight and calcined in air at 400° C. for 1 hr. TEM showed short crystalline nano-rods <100 nm in length, and some amorphous material. The catalyst was tested as described in Example 1. The results are shown in Table 4.

Example 10

Preparative Example 10

(60) 14.2 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and pH was adjusted to 11 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 11 was added dropwise to the solution of calcium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 11 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water. Then it was dried at 110° C. overnight and calcined in air at 400° C for 1 hr. The sample was identified as a crystalline hydroxyapatite type by XRD analysis. Some amorphous material was found. TEM showed densely-packed short crystalline nano-rods <100 nm in length, and about 10 nm in diameter. The catalyst was tested as described in Example 1. The results are shown in Table 4.

Example 11

Preparative Example 11

(61) 23.6 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and pH was adjusted to 5 with dilute aqueous nitric acid. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 5 was added dropwise to the solution of calcium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 5 with dilute aqueous nitric acid throughout. After that the suspension was filtered and washed with demineralised water. Then it was dried at 110° C. overnight and calcined in air at 400° C. for 1 hr. TEM showed large flat structures, blade or sheet-like, greater than 1 micron in 2 of their dimensions. The edges of the flat structures were fractured into parallel nano-rods of high aspect ratio:greater than 100 nm long, but less than 20 nm diameter. It was identified by XRD that the sample is a combination of monetite CaHPO.sub.4 and pyrophosphate Ca.sub.2P.sub.2O.sub.7 phases probably masking an underlying HAP phase. The catalyst was tested as described in Example 1. The results are shown in Table 4.

Example 12

Preparative Example 12

(62) 14.2 g of calcium nitrate tetrahydrate Ca(NO.sub.3).sub.2.4H.sub.2O was dissolved in 100 ml of demineralised water and pH was adjusted to 5 with dilute aqueous nitric acid. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 5 was added dropwise to the solution of calcium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 5 with dilute aqueous nitric acid throughout. After that the suspension was filtered and washed with demineralised water. Then it was dried at 110° C. overnight and calcined in air at 400° C. for 1 hr. TEM showed non-uniform particles, predominantly as sheets, but also as rods enmeshed in amorphous material. XRD identified the presence of pyrophosphate Ca.sub.2P.sub.2O.sub.7. Amorphous material was also found.

(63) The catalyst was tested as described in Example 1. The results are shown in Table 4.

(64) TABLE-US-00008 TABLE 5 Contact MMA + MAA MAA MMA + MAA Catalyst time yield selectivity selectivity DME DEK Toluene Ex. composition [s] [%] [%] [%] [mole %] [mole %] [mole %] New Ex 13 Sr-HAp pH11_1.67 5.2 7.0 0.7 85.9 0.04 0.0045 0.00005 New Ex 14 Sr-HAp pH11_1.50 5.2 6.8 0.8 92.0 0.17 0.0024 0.00010 New Ex 15 Sr-HAp pH11_1.00 5.0 5.6 1.2 94.1 0.21 0.0012 0.00006

Example 13

Preparative Example 13

(65) 21.2 g of strontium nitrate Sr(NO.sub.3).sub.2 was dissolved in 100 ml of demineralised water and pH was adjusted to 11 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 11 was added dropwise to the solution of strontium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 11 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water.

(66) Then it was dried at 110° C. overnight and calcined in air at 400° C. for 1 hr. The sample was identified as a crystalline strontium-apatite type by XRD analysis. TEM images show nano-rods as the only observed morphology, typically 100 nm length and 20 nm diameter. The catalyst was tested as described in Example 1. The results are shown in Table 5.

Example 14

Preparative Example 14

(67) 19.0 g of strontium nitrate Sr(NO.sub.3).sub.2 was dissolved in 100 ml of demineralised water and pH was adjusted to 11 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 11 was added dropwise to the solution of strontium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 11 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water.

(68) Then it was dried at 110° C. overnight and calcined in air at 400° C. for 1 hr. The sample was identified as a crystalline strontium-apatite type by XRD analysis. TEM images show tightly clustered nano-rods, typically 100 nm length and 20 nm diameter. The catalyst was tested as described in Example 1. The results are shown in Table 5.

Example 15

Preparative Example 15

(69) 12.7 g of strontium nitrate Sr(NO.sub.3).sub.2 was dissolved in 100 ml of demineralised water and pH was adjusted to 11 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 11 was added dropwise to the solution of strontium nitrate at the temperature of 80° C. while stirring. A suspension forms on addition of the phosphate to the nitrate solution. This mother suspension was continuously stirred for 3 hrs after the dropwise addition was complete and pH was maintained at 11 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water.

(70) Then it was dried at 110° C. overnight and calcined in air at 400° C. for 1 hr. The sample was identified as a strontium-apatite type by XRD analysis. TEM images show clusters of long nano-rods, typically 100-500 nm in length, and 10-20 nm in diameter. The catalyst was tested as described in Example 1. The results are shown in Table 5.

(71) B Dimethoxymethane Feed

(72) TABLE-US-00009 TABLE 6 Contact MMA + MAA MAA MMA + MAA Water Catalyst time yield selectivity selectivity DME content DEK Toluene composition [s] [%] [%] [%] [mole %] [wt %] [mole %] [mole %] Ex Ca-HAp pH7_1.67 16.0 4.9 0.03 89.59 1.0 0.06 0.0095 0.00009 16 Ex Ca-HAp pH11_1.67 14.9 6.2 1.7 81.9 0.6 0.09 0.0249 0.00018 17 Comp AlPO_TiO.sub.2_B_urea 14.3 4.9 3.7 57.8 11.4 2.21 0.0263 0.00388 Ex 5 Comp AlPO 9.7 15.0 9.6 81.01 8.3 2.32 0.0107 0.00604 Ex 6 Comp AlPO_MgPO 12.0 3.0 0.2 50.3 6.5 0.15 0.0104 0.00086 Ex 7 Comp TiO.sub.2_Ca.sub.3(PO.sub.4).sub.2_B_urea 9.4 3.2 0.1 58.3 0.8 0.05 0.0149 0.00046 Ex 8 Comp Comm Ca-HAp 289396 11.7 0.23 0.0 64.7 0.4 0.03 0.0033 0.00008 Ex 9 Comp Comm Ca-HAp 677418 10.3 0.008 0.8 1.36 0.006 0.05 0.1477 0.00000 Ex 10 Comp Comm Ca.sub.2P.sub.2O.sub.7 693871_1 10.5 0.095 2.6 29.0 2.5 0.03 0.0009 0.00017 Ex 11

Example 16

(73) The catalyst was prepared as in preparative example 1. Catalyst testing: 3 g of catalyst was placed in a stainless steel tubular reactor connected to a vaporiser. The reactor was heated to 350° C. and vaporiser to 300° C. The mixture of 70 wt % of methyl propionate and 30 wt % of dimethoxymethane was passed through. The condensed reaction mixture was analysed by gas chromatography equipped with CP-Sil 1701.

Example 17

(74) The catalyst was prepared as in preparative example 6.

(75) The catalyst was tested as described in example 16.

Comparative Example 5

(76) The catalyst was prepared as in comparative preparative example 1.

(77) The catalyst was tested as described in example 16.

Comparative Example 6

(78) The catalyst was prepared as in comparative preparative example 2

(79) The catalyst was tested as described in example 16.

Comparative Example 7

Comparative Preparative Example 7

(80) 3 g of magnesium phosphate hydrate Mg.sub.3(PO.sub.4).sub.2.xH.sub.2O (Aldrich catalogue number 344702) was mixed with 3 g of aluminium phosphate (prepared as in comparative example 2). A paste was produced by addition of 5 ml of demineralised water. The paste was dried for 2 hrs at 120° C. and then heated for 4 hrs at 600° C.

(81) The catalyst was tested as described in example 16.

Comparative Example 8

Comparative Preparative Example 8

(82) The catalyst was synthesised following the preparation method disclosed in U.S. Pat. No. 4,118,588 patent in Example 3.

(83) 3 g of titanium dioxide TiO.sub.2 (Aldrich catalogue number 634662), 2.3 g of calcium phosphate Ca.sub.3(PO.sub.4).sub.2 (Aldrich catalogue number 50552) and 0.75 g of boric acid H.sub.3BO.sub.3 were mixed together. A paste was produced by addition of 0.25 g of urea in 5 ml of demineralised water. The paste was dried for 12 hrs at 120° C. and then heated for 3 hrs at 580° C.

(84) The catalyst was tested as described in example 16.

Comparative Example 9

(85) Commercial Ca-hydroxyapatite was used from Aldrich with catalogue number of 289396.

(86) The sample was confirmed as a crystalline hydroxyapatite type by XRD analysis. TEM showed the presence of agglomerated irregular sphere like particles.

(87) Some amorphous material was found.

(88) The catalyst was tested as described in example 16.

Comparative Example 10

(89) Commercial Ca-hydroxyapatite was used from Aldrich with catalogue number of 677418.

(90) BET surface area disclosed by Aldrich is 9.4 m.sup.2/g.

(91) The sample was confirmed as a crystalline hydroxyapatite type by XRD analysis. TEM analysis revealed sphere like crystals. Some amorphous material was found.

(92) The catalyst was tested as described in example 16.

Comparative Example 11

(93) Commercial Ca.sub.2P.sub.2O.sub.7 was used from Aldrich with catalogue number of 693871.

(94) BET surface area disclosed by Aldrich is 12 m.sup.2/g. TEM showed sphere like non-crystalline particles.

(95) The catalyst was tested as described in example 16. The results are shown in table 6.

(96) TABLE-US-00010 TABLE 7 Contact MMA + MAA MAA MMA + MAA Water Catalyst time yield selectivity selectivity DME content DEK Toluene Ex. composition [s] [%] [%] [%] [mole %] [wt %] [mole %] [mole %] Ex Ca-HAp 10.5 5.9 0.02 89.29 2.5 0.03 0.0048 0.00025 18 pH7_1.5 Ex Ca-HAp 3.3 1.2 0.1 84.1 0.7 0.02 0.0050 0.00015 19 pH7_1

Example 18

(97) The catalyst was prepared as in preparative Example 7.

(98) The catalyst was tested as described in example 16 and the results are shown in table 7.

Example 19

(99) The catalyst was prepared as in preparative Example 8.

(100) The catalyst was tested as described in example 16 and the results are shown in table 7.

Example 20

(101) The catalyst of preparative example 13 was tested as described in example 16. The results are shown in table 8.

Example 21

(102) The catalyst of preparative example 14 was tested as described in example 16. The results are shown in table 8.

Example 22

(103) The catalyst of preparative example 15 was tested as described in example 16. The results are shown in table 8.

(104) TABLE-US-00011 TABLE 8 MMA + MMA + MAA MAA MAA DME Water Catalyst Contact yield selectivity selectivity [mole content DEK Toluene Ex. composition time [s] [%] [%] [%] %] [wt %] [mole %] [mole %] Ex Sr-HAp 11.6 4.1 0.03 73.3 0.07 0.04 0.0747 0.00012 20 pH11_1.67 Ex Sr-HAp 10.9 5.9 0.02 91.3 0.45 0.06 0.0030 0.00011 21 pH11_1.50 Ex Sr-HAp 12.4 8.7 0.02 92.4 0.66 0.11 0.0064 0.00008 22 pH11_1.00

Example 23

Preparative Example 23

(105) 21.2 g of strontium nitrate Sr(NO.sub.3).sub.2 was dissolved in 100 ml of demineralised water and pH was adjusted to 7 with ammonium hydroxide. 7.9 g of diammonium hydrogen phosphate (NH.sub.4).sub.2HPO.sub.4 in 50 ml of demineralised water at pH 7 was added dropwise to a solution of strontium nitrate at the temperature of 80° C. while stirring. The mother suspension was mixed for 3 hrs and pH was maintained at 7 with ammonium hydroxide throughout. After that the suspension was filtered and washed with demineralised water.

(106) Then it was dried at 110° C. overnight and calcined in air at 400° C. for 1 hr. The sample was identified as a crystalline strontium pyrophosphate by XRD analysis. TEM images show large flat structures, blade or sheet-like, typically 2-5 micron in length and 0.2-0.5 micron in width. The flat structures were fringed with clusters of nano-rod structures, with individual rods being typically 20 nm in diameter and 200 nm in length.

(107) The catalyst was tested as described in example 1. The results are shown in Table 9.

Example 24

(108) The catalyst of example 23 was tested with dimethoxymethane feed, as described in Example 16. The results are shown in Table 9.

(109) TABLE-US-00012 TABLE 9 Contact MMA + MAA MAA MMA + MAA Water Catalyst time yield selectivity selectivity DME content DEK Toluene Ex. composition [s] [%] [%] [%] [mole %] [wt %] [mole %] [mole %] Ex Sr2P2O7 11.3 4.5 0.6 94.1 0.2 — 0.0011 0.00014 23 pH7_1.67 Ex. Sr2P2O7 11.1 2.5 0.05 88 0.4 0.03 0.0058 0.00009 24 pH7_1.67

(110) Table 10 shows the Ca:P synthesis ratios of various examples and comparative examples as well as the Ca:P ratios in the final crystals (XRF) and on the crystal surfaces (XPS). Comparative example 12 is a commercial pyrophosphate in the form of amorphous spheres purchased from Aldrich under catalogue number 693871. It can be seen that at the ideal hydroxyapatite ratio of 1.67 both the bulk crystal and the crystal surface are depleted in calcium but that the surface is more depleted. However, at low M:P synthesis ratios ideal for pyrophosphates of 1:1, the surface is richer in metal than the bulk of the crystal. This suggests the formation of a preferred surface arrangement on the crystals. The surface and bulk ratios for a series of examples are plotted in FIG. 1. It can be seen that at higher overall ratios the surface ratio is depressed and that at lower overall ratios the surface ratio is increased.

(111) The XRD peak intensity data was collected and the ratios of certain peaks for several samples were compared. The results are shown in FIG. 7. The 002:211 ratio for the samples of the invention could be indicative of a strong nano-rod presence.

(112) TABLE-US-00013 TABLE 10 XRF Peak Ca:P Area Ratio Bulk Ca:P Surface Ca:P Example (stoich) (Ca:P) (XRF m/m) (XPS m/m) Comp Ex 12 1.00 2.505 0.940 0.89 Comp Ex 3 1.67 4.046 1.597 1.42 Comp ex 4 1.67 4.748 1.896 1.78 Ex 3 1.67 2.711 1.028 1.08 Ex 6 1.67 4.086 1.614 1.49 Ex 1 1.67 4.168 1.648 1.46 Ex 8 1.00 3.531 1.377 1.31 Ex 7 1.50 3.846 1.511 1.38 Ex 9 1.67 3.801 1.492 1.36 Ex 11 1.67 2.945 1.128 1.23