PROCESS

Abstract

The invention provides a process for preparing olefins from a mixed gaseous feed stream, wherein said mixed gaseous feed stream comprises three or more components selected from the group consisting of carbon dioxide, carbon monoxide, hydrogen, methanol and dimethyl ether, said process comprising contacting the mixed gaseous feed stream with a catalyst of formula (I): M(II).sub.Al1.sub.1-PO4 (I), wherein M(II) is a divalent metal ion; and x=0.002 to 0.5

Claims

1. A process for preparing olefins from a mixed gaseous feed stream, wherein said mixed gaseous feed stream comprises three or more components selected from the group consisting of carbon dioxide, carbon monoxide, hydrogen, methanol and dimethyl ether, said process comprising contacting the mixed gaseous feed stream with a catalyst of formula (I):
M(II).sub.xAl.sub.1-xPO.sub.4(I) wherein M(II) is a divalent metal ion; and x=0.002 to 0.5.

2. A process as claimed in claim 1, wherein M(II) is selected from the group consisting of Be, Mg, Ca, Zn, Mn, Fe, Co, Ni, Cu, Cd and Sr, preferably Mg, Co, Zn, Fe, Ni, Cu and Mn, more preferably Mg, Co and Zn, even more preferably Mg.

3. A process as claimed in claim 1 or 2, wherein the catalyst has a pore structure with an eight member ring pore opening.

4. A process as claimed in any of claims 1 to 3, wherein the catalyst has AEI, CHA, AFN or SAV topology

5. A process as claimed in any of claims 1 to 4, wherein said olefins are C2 to C5 olefins, preferably C3 to C4 olefins.

6. A process as claimed in any of claims 1 to 5, wherein said mixed gaseous feed stream is contacted with the catalyst in a single reaction zone.

7. A process as claimed in any of claims 1 to 6, wherein said mixed gaseous feed stream comprises methanol and/or dimethyl ether.

8. A process as claimed in any of claims 1 to 7, wherein said mixed gaseous feed stream comprises carbon dioxide and hydrogen, and optionally carbon monoxide.

9. A process as claimed in any of claims 1 to 7, wherein said mixed gaseous feed stream comprises hydrogen and carbon monoxide.

10. A process as claimed in any of claims 1 to 9, wherein said mixed gaseous feed stream is contacted with the catalyst at a temperature of less than 400 C., preferably less than 375 C.

11. A process as claimed in any of claims 1 to 10, wherein said mixed gaseous feed stream is contacted with the catalyst at a pressure of at least 5 bar, preferably at least 10 bar.

12. A process as claimed in any of claims 1 to 11, wherein said mixed gaseous feed stream is contacted with the catalyst of formula (I) and one or more additional catalysts simultaneously.

13. A process as claimed in claim 12, wherein the one or more additional catalysts is a bi-metallic mixed oxide comprising Zn and Zr.

14. A process for preparing olefins from a mixed gaseous feed stream, wherein said mixed gaseous feed stream comprises two or more components selected from the group consisting of carbon dioxide, carbon monoxide, hydrogen, methanol and dimethyl ether, said process comprising contacting the mixed gaseous feed stream with a catalyst of formula (I):
M(II)xAl1-xPO4(I) wherein M(II) is a divalent metal ion; and x=0.002 to 0.5. and one or more additional catalysts simultaneously, wherein said one or more additional catalysts is a bi-metallic mixed oxide comprising Zn and Zr

15. A process as claimed in claim 14, wherein said process is as defined in any of claims 2 to 11.

16. The use of a compound of Formula (I) as defined in any of claims 1 to 4 as a catalyst in a process for preparing olefins from a mixed gaseous feed stream as defined in any of claims 1 or 5 to 13.

Description

[0069] The invention will now be described with reference to the following non-limiting examples and figures.

[0070] FIG. 1. Powder X-Ray Diffractograms of (a) SAPO-18 and (b) MgAPO-18 catalysts before and after calcination.

[0071] FIG. 2. Catalytic performance of MAPO-18s in MTO reaction conditions. Reaction conditions: 350 C., 1 bar, 0.13 bar MeOH (WHSV=4 g.sub.MeOH/g.sub.cat/h). (a) Activity in terms % sum of MeOH and DME conversion over time-on-stream. b-h: Product selectivity over conversion. Conversion variation was due to catalyst deactivation during runtime.

[0072] FIG. 3. Catalytic performance of MAPO-18s and commercial SAPO-34 (from ACS Materials). (a) Comparison at 350 C., 1 bar, 0.13 bar MeOH and (b) Comparison at 350 C., 20 bar, 1 bar MeOH.

[0073] FIG. 4. Catalytic performance of MAPO-18s in various reaction feeds. Reaction conditions: 350 C., 20 bar, 1 bar MeOH (WHSV=2.5 g.sub.MeOH/g.sub.cat/h), 0.6 bar Ar internal standard, 18.4 bar N.sub.2 or H.sub.2 or H.sub.2/X=3 (in which X=N.sub.2, CO.sub.2 or CO), GHSV16 000 mL.sub.total flow/mL.sub.cat./h. a-d|Activity in terms % sum of MeOH and DME conversion over time-on-stream for (a) SAPO-18, (b) MgAPO-18, (c) CoAPO-18 and (d) ZnAPO-18. e-h|Product selectivity at 10 h time-on-stream for (e) SiAPO-18, (f) MgAPO-18, (g) CoAPO-18 and (h) ZnAPO-18.

[0074] FIG. 5. Catalytic performance of MAPO-18s in MeOH carbonylation reaction. Reaction conditions: 350 C., 20 bar, 1 bar MeOH (WHSV=2.5 g.sub.MeOH g.sub.cat.sup.1 h.sup.1), 0.6 bar Ar internal standard, 18.4 bar N.sub.2 or CO, GHSV16 000 mL.sub.total flow mL.sub.cat.sup.1 h.sup.1. a-c|Activity in terms % sum of MeOH and DME conversion over time-on-stream for (a) SAPO-18, (b) MgAPO-18, (c) CoAPO-18. (d) Product selectivity at 10 h time-on-stream.

[0075] FIG. 6. Effect of CO partial pressure on the catalytic performance of SAPO-18s. Reaction conditions: 350 C., 20 bar, 0.5 bar MeOH (WHSV=2.5 g.sub.MeOH g.sub.cat.sup.1 h.sup.1), 0.7 bar Ar internal standard, 18.8 bar H.sub.2/CO.sub.x=3, GHSV16 000 mL.sub.total flow mL.sub.cat.sup.1 h.sup.1. (a and b) Activity in terms % sum of MeOH and DME conversion over time-on-stream, and (c and d) Product selectivity at TOS=10 h.

[0076] FIG. 7. Paraffin selectivity vs. conversion of MAPO-18s in various reaction feeds. Reaction conditions: 350 C., 20 bar, 1 bar MeOH (WHSV=2.5 g.sub.MeOH g.sub.cat.sup.1 h.sup.1), 0.6 bar Ar internal standard, 18.4 bar N.sub.2 or H.sub.2 or H.sub.2/X=3 (in which X=N.sub.2, CO.sub.2 or CO), GHSV16 000 mL.sub.total flow mL.sub.cat.sup.1 h.sup.1. Conversion variation was due to catalyst deactivation during runtime.

[0077] FIG. 8. Olefin selectivity vs. conversion of MAPO-18s in various reaction feeds. Reaction conditions: 350 C., 20 bar, 1 bar MeOH (WHSV=2.5 g.sub.MeOH g.sub.cat.sup.1 h.sup.1), 0.6 bar Ar internal standard, 18.4 bar N.sub.2 or H.sub.2 or H.sub.2/X=3 (in which X=N.sub.2, CO.sub.2 or CO), GHSV16 000 mL.sub.total flow mL.sub.cat.sup.1 h.sup.1. Conversion variation was due to catalyst deactivation during runtime.

[0078] FIG. 9. Catalytic performance of MgAPO-18 and SiAPO-18 in mixed gas feeds at lower temperature of 325 C. Reaction conditions: 325 C., 20 bar, 1 bar MeOH (WHSV=1.7 g.sub.MeOH/g.sub.cat./h), 0.6 bar Ar internal standard, 18.4 bar H.sub.2/CO=3, GHSV 10 000 mL.sub.total flow/mL.sub.cat./h. (a) Activity over cumulative methanol conversion capacity, (b) sum of propylene and butenes selectivity over time-on-stream, (c) Product selectivity and (d) olefin/paraffin ratio distribution at TOS=10 h.

[0079] FIG. 10. Catalytic performance of SAPO-18 and MgAPO-18 with varying BAS density. Reaction conditions: 350 C., 20 bar, 1 bar MeOH (WHSV=2.5 g.sub.MeOH g.sub.cat.sup.1 h.sup.1), 0.6 bar Ar internal standard, 18.4 bar H.sub.2/CO=3, GHSV16 000 mL.sub.total flow mL.sub.cat.sup.1 h.sup.1. (a) Activity in terms % sum of MeOH and DME conversion, (b-d) C.sub.2-C.sub.4 olefins selectivity as a function of BAS density. Symbol size correlates to heteroatom loading (from M/T=0.02 to 0.05) and lines are added to guide the eye.

[0080] FIG. 11. Catalytic performance of SAPO-18 and MgAPO-18 with varying M/T ratio. Reaction conditions: 350 C., 20 bar, 1 bar MeOH (WHSV=2.5 g.sub.MeOH g.sub.cat.sup.1 h.sup.1), 0.6 bar Ar internal standard, 18.4 bar H.sub.2/CO=3, GHSV16 000 mL.sub.total flow mL.sub.cat.sup.1 h.sup.1. a-b|Activity in terms % sum of MeOH and DME conversion over time-on-stream for (a) SAPO-18, (b) MgAPO-18. c-d|Product selectivity at TOS=10 h for (c) SAPO-18, (d) MgAPO-18.

[0081] FIG. 12. Hydrocarbon distribution of ZnO:ZrO.sub.2/SAPO-18 catalyst. Reaction conditions: 350 C., 30 bar, H.sub.2/CO.sub.2=3. (a) Varied GHSV with fixed mass loading and mixing of ZnO:ZrO.sub.2/SAPO-18 and (b) Varied mixing of ZnO:ZrO.sub.2/SAPO-18.

[0082] FIG. 13. Hydrocarbon distribution of ZnO:ZrO.sub.2/MgAPO-18 catalyst. Reaction conditions: 350 C., 30 bar, H.sub.2/CO.sub.2=3. (a) Varied GHSV with fixed mass loading and mixing of ZnO:ZrO.sub.2/SAPO-18 and (b) Varied mixing of ZnO:ZrO.sub.2/MgAPO-18.

EXAMPLES

Measurement Methods

[0083] SEM: The size and morphology of the calcined zeotype particles were analyzed by scanning electron microscopy (SEM), recorded with a Hitachi SU 8230 FE-SEM. The elemental composition was determined utilizing energy-dispersive X-ray spectroscopy (EDS) attached to the same instrument.

[0084] N.sub.2-physisorption using BET method: N.sub.2 physisorption was carried out at 77K by using a Belsorp-mini II equipment to determine the BET surface areas and pore volumes. Calcined catalysts were outgassed under vacuum for 4 h, 1 h at 80 C., followed by a period of 3 h at 300 C. The BET surface areas were determined on the basis of a linear fit of the data in the relative pressure (p/po) range of 0.01 to 0.1.

[0085] Temperature-programmed desorption of n-propylamine: Temperature-programmed desorption of n-propylamine was performed at atmospheric pressure in a fixed-bed glass reactor (inner diameter 11 mm). Calcined catalysts (250-420 m) were pretreated at 550 C. under flowing air condition. The catalyst was then cooled to 150 C., after which 80 mL/min N.sub.2 bubbled through a saturator containing n-propylamine at room temperature was then fed to the catalyst for 20 min. The excess amount of n-propylamine was removed by flowing 80 mL/min N.sub.2 for 4 h at 150 C. The temperature was then increased to 550 C. (20 C./min) and the amount of propene desorbed was quantified by using an on-line Pfeiffer Omnistar quadrupole mass spectrometer.

[0086] Powder X-ray diffraction: Powder X-ray diffraction patterns of the as-synthesised and calcined MAPOs were measured using a Siemens Bruker D8 Discover instrument with Bragg-Brentano geometry by using Cu K.sub. radiation (X, =1.5406 ). Samples were mounted on flat sample holders and measured in reflectance mode, Bragg-Brentano geometry. All patterns were fitted using TOPAS6.

Synthesis of MAPO-18 Catalysts

[0087] All catalysts were prepared via hydrothermal synthesis using the same organic structural directing agent, N,N-Diisopropylethylamine (DIPEA, 99%, Sigma-Aldrich). The other chemicals were alumina hydrate (A1O(OH), Pural, Sasol), orthophosphoric acid (85% wt. H.sub.3PO.sub.4 in H.sub.2O, Sigma Aldrich), colloidal silica (40% wt. SiO.sub.2 suspension in H.sub.2O, Ludox AS-40, Sigma-Aldrich), magnesium acetate tetrahydrate ((CH.sub.3COO).sub.2Mg.Math.4H.sub.2O, >98%, Sigma-Aldrich), cobalt(II) acetate tetrahydrate ((CH.sub.3COO).sub.2Co.Math.4H.sub.2O, >98%, Sigma-Aldrich), zinc acetate dihydrate ((CH.sub.3COO).sub.2Zn.Math.2H.sub.2O, >98%, Sigma-Aldrich) and deionized water.

[0088] SAPO-18 was synthesized with a gel composition of AlO(OH)/SiO.sub.2/H.sub.3PO.sub.4/DIPEA/H.sub.2O=1/0.1/0.9/0.95/9.5. The P source, H.sub.2O and DIPEA were first mixed together. Pural was subsequently added slowly with stirring for 5 minutes, and Ludox was finally added. The synthesis gel was left to stir for 20 minutes to ensure homogeneity. The gel was transferred to a Teflon-lined stainless steel autoclave, and heated at 190 C. under rotation for 12 hours.

[0089] MAPO-18 (where M refers to Mg, Co or Zn) were synthesized with identical gel compositions of AlO(OH)/(CH.sub.3COO).sub.2M/H.sub.3PO.sub.4/DIPEA/H.sub.2O=1/0.1/0.9/0.95/19. The metal acetate precursor was first dissolved in minimal amount of H.sub.2O. The P source, H.sub.2O and DIPEA were then mixed together. Pural was subsequently added slowly with stirring for 5 minutes, and M acetate precursor solution was finally added. The synthesis gel was left to stir for 20 minutes to ensure homogeneity. The gel was transferred to a Teflon-lined stainless steel autoclave (50% filled), and heated at 160 C. under rotation for 8 days. All products were washed and centrifuged three times with deionized water and dried at 100 C. for 18 hours. Calcination was performed at 550 C. (3 C./min) under static air condition for 4 h.

[0090] Properties of the materials are reported in Table 1 and in FIG. 1.

TABLE-US-00001 TABLE 1 Textural and acidic properties of the MAPO-18s. Elemental Density Brnsted Composition .sup.c of M Acidity Crystal Crystal size S.sub.BET M/ (mmol/ (mmol/ shape .sup.a (m) .sup.a (m.sup.2/g) .sup.b P/Al M/Al (Al + P) g.sub.cat) .sup.c g.sub.cat) .sup.d SAPO-18 rods ~0.5 750 1.0 0.12 0.06 0.61 0.29 MgAPO-18 cubes ~0.5 730 1.1 0.12 0.05 0.55 0.17 CoAPO-18 cubes 0.5 639 1.0 0.16 0.08 0.78 0.27 ZnAPO-18 irregular ~1.0 96 1.1 0.14 0.07 0.66 0.04 Properties determined using .sup.a SEM, .sup.b N2-physisorption using BET method, .sup.c SEM-EDS, .sup.d propylamine-TPD.

Catalytic Performance at MTO Reaction Conditions

[0091] The influence of acid strength created by various heteroatom substitution was first evaluated under conditions relevant for the MTO process using an ambient pressure test rig. The reaction conditions were selected to illustrate the true deactivation profile of these catalysts, meaning 100% conversion was not sustained over time-on-stream (TOS).

[0092] The quantity of calcined catalyst loaded (250-420 m) was varied depending on the reaction temperature. 100 mg of MAPO-18 was loaded in a fixed-bed U-shaped quartz reactor and heated to 550 C. (5 C./min) in synthetic air feed (N.sub.2/O.sub.2=80/20% v., 25 mL/min). At 550 C., the synthetic air feed was switched to 100% v. 02 feed for 1 h, after which the temperature was decreased to the reaction temperature of 350 C. (2 C./min) in 100% v. N.sub.2 feed. During reaction, methanol was fed to the reactor by passing He through a saturator at 20 C., resulting in a methanol partial pressure of 0.13 bar and WHSV of 4 g.sub.MeOH/g.sub.cat/h. The total feed flow was 40 mL/min. The effluent from the reactor was analyzed by an online GC-MS instrument (Agilent 7890 with flame ionization detector and 5975C MS detector) equipped with two Restek Rtx-DHA-150 columns. Hydrogen (Praxair, purity 6.0) was used as the carrier gas. Both methanol and dimethyl ether were considered to be reactants when calculating the conversion for activity. Product selectivity was determined based on carbon atoms measured by the FID detector.

[0093] From FIG. 2a, SAPO-18 deactivated the slowest in the first 5 h TOS, followed by MgAPO-18, ZnAPO-18 and CoAPO-18. After 5 h TOS, the activity of the MAPO-18s appeared to stabilize at 10-25% conversion.

[0094] Referring to FIG. 2b, the DME/MeOH ratio was the highest for SAPO-18, irrespective of conversion level. DME is a product of MeOH dehydration and MeOH and DME are often considered as reactant feed. FIG. 2c to h gives an overview of product selectivity over a range of conversion for all MAPO-18s. All MAPO-18s were selective towards propylene, attaining 49% propylene selectivity. On the other hand, ethylene selectivity varied depending on the heteroatom and was 5% higher for SAPO-18 than MgAPO-18. Correspondingly, methane, butenes and pentenes selectivities were lower for SAPO-18.

[0095] FIG. 3a shows the comparison of MAPO-18s with a SAPO-34 purchased from supplier ACS Materials, at MTO reaction conditions of 350 C., 1 bar and MeOH in inert H.sub.2 feed. The M(II)APO-18s performed better than the commercial SAPO-34, but not as efficient as SAPO-18.

Catalytic Performance at Mixed Feed Reaction Conditions: Effect of Various Reactive Feeds

[0096] The influence of various heteroatom substitution was next evaluated under conditions relevant for the mixed feed. Specifically, the reaction pressure was increased from 1 bar to 20 bar and relevant reactants N.sub.2, H.sub.2, CO and CO.sub.2 were co-fed with MeOH.

[0097] Methanol conversion over the MAPO-18s at 20 bar in various reactive feeds was investigated using a commercial Microactivity-Effi test rig from PID Eng & Tech. Blank reactor tests were also performed and they showed no reactivity of methanol or CO/CO2. 400 mg of calcined MAPO-18 (250-420 m) was loaded in a silicon-coated (Silcolloy coating from SilcoTek) stainless steel reactor with an inner diameter of 6 mm. The catalyst bed (isothermal zone of 5 cm) was supported by glass wool placed above 5 mm glass beads, and a thermocouple (Type K) was inserted in the catalyst bed. The catalyst was heated to the reaction temperature of 350 C. (5 C./min) at 1 bar in 100% v. inert feed (N2 and Ar) for 1 h. The feed flow was then switched to bypass the reactor for 4 h so as to obtain a stable methanol feed flow. N.sub.2 was used to pressurize the methanol liquid feed tank and line, and methanol liquid feed flow was controlled with a Cori Flow controller (Bronkhorst). Methanol was evaporated in the hot box at 140 C. and swept by the flowing gas stream.

[0098] Methanol feed flow was 1 g/h, and internal standard Ar feed flow was 7 mLn/min. Individual gas mass flow controllers (Bronkhorst) were used to set the flow rate for each gas, namely CO.sub.2, CO, H.sub.2, N.sub.2, Ar, and the gases were mixed before the methanol feed line. Total feed flow was 220 to 230 mLn/min, resulting in a GHSV of 16 000 h.sup.1. The reaction pressure of 20 bar was controlled by a back pressure regulator after the reactor and this is a PID Eng & Tech patented system based on a high-speed precision servo-controlled valve (VMM01) with eight turns of rotational movement. The product stream was connected to the vent and the online-GC (Scion 456-GC). The GC was equipped with 1 TCD and 2 FID detectors, and 6 columns (MolSieve 13X, HayeSep Q, HayeSep N, Rt-Stabilwax, Rt-Alumina/MAPD and Rtx-1). Helium was used as carrier gas in the TCD channel but N.sub.2 was used as carrier gas in both FID channels.

Results are presented in FIG. 4 and Table 2.

TABLE-US-00002 TABLE 2 MeOH conversion capacity and Olefins-to-Paraffins ratios at 350 C., 20 bar, 1 bar MeOH (WHSV = 2.5 g.sub.MeOH/g.sub.cat./h), 0.6 bar Ar internal standard, 18.4 bar N.sub.2 or H.sub.2 or H.sub.2/X = 3 (in which X = N.sub.2, CO.sub.2 or CO). (MeOH + DME) conv. capacity Olefins/Paraffins after 16 h (g.sub.MeOH/g.sub.cat) (C.sub.2-4=/) at 10 h TOS H2/N.sub.2 = H.sub.2/CO.sub.2 = H.sub.2/CO = H.sub.2/N.sub.2 = H.sub.2/CO.sub.2 = H.sub.2/CO = N.sub.2 H.sub.2 3 3 3 N.sub.2 H.sub.2 3 3 3 SAPO-18 5.1 13.1 10.6 9.6 9.1 40.2 0.3 0.8 1.4 9.6 MgAPO-18 7.6 30.2 30.2 30.3 29.1 101.0 0.2 1.1 1.1 22.8 CoAPO-18 8.4 34.1 28.5 32.4 28.7 81.5 0.3 1.5 1.2 22.7 ZnAPO-18 4.6 22.0 13.7 17.0 16.4 95.8 0.5 0.8 1.3 91.2

[0099] The increase in pressure from 1 bar to 20 bar (0.13 vs. 1 bar MeOH in inert N.sub.2 feed) had negligible influence on the deactivation profiles. All MAPO-18s deactivated strongly in the first 5 h TOS and their activities subsequently stabilized at 10-20% conversion. Propylene selectivity over MgAPO-18 was the highest at 49%, followed by CoAPO-18 and ZnAPO-18 at 47%, and SAPO-18 at 44%. In comparison to the other M(II)APO-18s, SAPO-18 showed higher ethylene and C.sub.6+ selectivities.

[0100] Next, H.sub.2 was co-fed with MeOH at high pressures. Remarkably, a comparison between the four materials showed that less H.sub.2 is needed to acquire high, semi-stable activity over MgAPO-18 than over the other three materials (FIG. 4a-d). Furthermore, for SAPO-18, the only M(IV) heteroatom among the four, a steep initial deactivation is observed (FIG. 4a). This suggests that less hydrogen addition may be needed to balance the steady-state HC pool composition in a favourable direction for the non-transition metal catalyst with stronger acid sites, MgAPO-18, followed by Co- and Zn-APO-18.

[0101] H.sub.2 does not only hydrogenate coke-precursors, but it also hydrogenates the olefinic products hence decreasing the olefins-to-paraffins ratio (Table 2). Applicable to all MAPO-18 catalysts, the olefins-to-paraffins ratio was lowest for C.sub.2, followed by C.sub.3 and then C.sub.4 (FIG. 4e-h, Table 3).

[0102] The simultaneous hydrogenation of olefinic products due to H.sub.2 co-feeding calls for an improvement to this strategy for enlarging lifetime, so we proposed to co-feed CO with H.sub.2 and methanol. Although this approach resulted in a negative effect on the semi-stable conversion level for most materials (FIG. 4a-d), it also led to a dramatic, positive effect on the olefins-to-paraffins ratios for all MAPO-18 catalysts (FIG. 4e-h, Table 3). Strikingly, MgAlPO-18, the non-transition metal material with highest acid strength, showed similar, enhanced conversion level as with H.sub.2 co-feed, yet with olefins-to-paraffins ratios higher than 22 for the C.sub.2-C.sub.4 products (Table 2). From Table 3, the higher DME/MeOH ratios from M(II)APO-18s shows another positive effect of the M(II)APO-18s, which is their ability to catalyse MeOH dehydration under such mixed feed conditions.

[0103] Complimentary tests in which CO was co-fed with methanol over the Si-, Mg- and CoAPO-18 catalysts, without H.sub.2 co-feed, showed negligible impact on the activity and product distribution (FIG. 5). The reaction conditions used in these tests mimic the reaction conditions for MeOH carbonylation.

[0104] Wider range of reaction conditions, including different CO/CO.sub.x feed ratios and lower methanol partial pressure, were then explored with SAPO-18 (FIG. 6). At those conditions, the ratio between H.sub.2 and hydrocarbon products was higher and almost 100% paraffins selectivity was obtained in the presence of exclusively CO.sub.2 (CO/CO.sub.x=0 in FIG. 6). A clear decrease in paraffins selectivity was observed when CO/CO.sub.x ratio was increased. With lower MeOH partial pressure, i.e. higher H.sub.2/MeOH ratio, paraffin selectivity was also close to 100% in presence of CO.sub.2, yet less than 20% in presence of CO. This affirmed the inhibition of olefin hydrogenation due to the presence of CO, in a wider range of reaction conditions.

[0105] FIGS. 7 and 8 are provided to affirm the validity of the above discussion for all conversion levels.

TABLE-US-00003 TABLE 3 Catalytic performance of MAPO-18s in various reaction feeds. Reaction conditions: 350 C., 20 bar, 1 bar MeOH (WHSV = 2.5 g.sub.MeOH g.sub.cat.sup.1 h.sup.1), 0.6 bar Ar internal standard, 18.4 bar N.sub.2 or H.sub.2 or H.sub.2/X = 3 (in which X = N.sub.2, CO.sub.2 or CO), GHSV 16 000 mL.sub.total flow mL.sub.cat.sup.1 h.sup.1. Olefin-to- Ethylene/ DME/ Reaction paraffin ratio Propylene MeOH Catalyst Conditions C2=/ C3=/ C4=/ ratio ratio N.sub.2 39.2 53.6 27.2 0.38 5.4 H.sub.2 0.0 0.2 0.6 0.00 4.5 SAPO-18 H.sub.2/N.sub.2 = 3 0.3 1.0 0.9 0.09 5.0 H.sub.2/CO.sub.2 = 0.4 1.8 1.9 0.12 5.0 3 H.sub.2/CO = 3 5.2 13.6 8.1 0.27 4.8 N.sub.2 58.2 110.5 122.6 0.25 4.1 H.sub.2 0.0 0.1 0.6 0.00 21.6 MgAPO-18 H.sub.2/N.sub.2 = 3 0.1 1.0 1.8 0.04 20.1 H.sub.2/CO.sub.2 = 0.1 1.0 2.2 0.03 21.3 3 H.sub.2/CO = 3 16.4 19.4 38.0 0.20 19.0 N.sub.2 58.1 97.3 78.6 0.36 5.1 H.sub.22 0.0 0.2 0.9 0.00 CoAPO-18 H.sub.2/N.sub.2 = 3 0.3 1.7 2.7 0.09 21.6 H.sub.2/CO.sub.2 = 0.1 1.2 2.3 0.05 18.5 3 H.sub.2/CO = 3 22.8 19.9 30.6 0.28 23.9 N.sub.2 57.3 115.1 101.2 0.29 0.5 H.sub.2 0.0 0.4 1.2 0.02 0.7 ZnAPO-18 H.sub.2/N.sub.2 = 3 0.5 0.9 1.0 0.20 0.7 H.sub.2/CO.sub.2 = 0.4 1.5 2.0 0.15 0.8 3 H.sub.2/CO = 3 60.8 105.8 93.6 0.30 0.8

Catalytic Performance at Lower Temperature

[0106] Following the identification of the key descriptors of the catalyst and reaction conditions, we attempted to further close the gap between the optimal conditions of the MTO and methanol synthesis reactions by decreasing the reaction temperature to 325 C. Referring to FIG. 9a, the lower reaction temperature expectedly led to faster deactivation and lower semi-stable conversion levels because the dealkylation of aromatics was unfavourable. Nonetheless, the superior activity and stability of MgAPO-18 over SAPO-18 remained. Importantly, the superior product selectivity of MgAPO-18 over SAPO-18 was convincingly exhibited and maintained at lower temperatures (FIG. 9b-d). From FIG. 9b, selectivity towards propylene and butenes increased during the first 5 h TOS and subsequently stabilized at 72% for MgAPO-18. The selectivity towards propylene and butenes was stable at 50% for SAPO-18, and the 20% difference was due to paraffins (FIG. 9c). This finding was further illustrated in FIG. 9d which shows the olefin-to-paraffin ratio of each hydrocarbon product. Comparing the influence of reaction temperature on the olefin-to-paraffin ratio (FIG. 9d), the olefin-to-paraffin ratios of MgAPO-18 were consistently higher than SAPO-18 at both 350 C. and 325 C. The olefin-to-paraffin ratios of MgAPO-18 appears to be independent of reaction temperature, but those of SAPO-18 clearly decreased at 325 C.

Synthesis Procedure of Additional Catalyst Samples (SAPO-18 and MgAPO-18 with Different Amounts of Si or Mg)

[0107] SAPO-18a-d was synthesised by varying Si/T atomic composition in the synthesis gels. The P source, H.sub.2O and DIPEA were first mixed together. Pural was subsequently added slowly with stirring for 5 minutes, and Ludox was finally added. The synthesis gel was left to stir for 20 minutes to ensure homogeneity. The gel was transferred to a Teflon-lined stainless steel autoclave, and heated at 190 C. under rotation for 12 hours.

[0108] MgAPO-18a-c were prepared with the same M/T atomic composition in the synthesis gels as SAPO-18a-c. The metal acetate precursor was first dissolved in minimal amount of H.sub.2O. The P source, H.sub.2O and DIPEA were then mixed together. Pural was subsequently added slowly with stirring for 5 minutes, and M acetate precursor solution was finally added. The synthesis gel was left to stir for 20 minutes to ensure homogeneity. The gel was transferred to a Teflon-lined stainless steel autoclave (50% filled), and heated at 160 C. under rotation for 8 days. All products were washed and centrifuged three times with deionised water and dried at 100 C. for 18 hours. Calcination was performed at 550 C. (3 C./min) under static air condition for 4 h.

Characterisation

[0109]

TABLE-US-00004 TABLE 4 Textural and acidic properties of the SAPO-18 and MgAPO-18 catalysts with varied M/T atomic ratios. SAPO-18 and MgAPO-18 were catalysts presented in Table 1 as part of the series of MAPO-18 (M = Si, Mg, Co and Zn). SAPO-18_a to d and MgAPO-18_a to c were prepared by varying M/T ratios in the synthesis gel recipes. Elemental Density Brnsted Crystal S.sub.BET Composition .sup.c of M Acidity size (m.sup.2/ P/ M/ M/T (mmol/ (mmol/ (m) .sup.a g) .sup.b Al Al Atoms g.sub.cat) .sup.c g.sub.cat) .sup.d SAPO-18 ~0.5 749 1.0 0.12 0.06 0.61 0.29 SAPO-18 a ~0.5 729 1.0 0.06 0.03 0.51 0.33 SAPO-18_b ~0.5 772 1.0 0.09 0.04 0.71 0.41 SAPO-18_c ~0.5 685 0.9 0.12 0.06 0.94 0.45 SAPO-18_d ~0.5 749 0.9 0.12 0.06 1.01 0.25 MgAPO-18 ~0.5 730 1.1 0.12 0.05 0.55 0.17 MgAPO-18_a ~0.5 748 1.0 0.06 0.03 0.49 0.23 MgAPO-18_b ~0.5 755 1.0 0.08 0.04 0.65 0.30 MgAPO-18_c ~0.5 741 1.0 0.11 0.05 0.81 0.39 Properties determined using .sup.a SEM, .sup.b N.sub.2-physisorption using BET method, .sup.c SEM-EDS, .sup.d propylamine-TPD.

Catalytic Testing

[0110] The series of SAPO-18 and MgAPO-18 with varying heteroatom loadings were prepared to elucidate the acidity-performance relations. Results are shown in FIGS. 10 and 11. From FIG. 10a, the higher activity and stability of the stronger acidic MgAPO-18 over SAPO-18 catalysts were upheld over a range of BAS density and heteroatom content. This indicates the stronger influence of acidic strength on performance in comparison to density of acidic sites, thus further supporting the advantage of using M(II) heteroatom substitution. Olefin product selectivities appeared to be independent of BAS density and heteroatom loading (FIG. 10b-d), but with clear distinctions between SAPO-18 and MgAPO-18. Notably, MgAPO-18 enhanced the production of butenes while SAPO-18 produced more ethene. Furthermore, all MgAPO-18 samples maintained high activity after 10 hrs on stream, while the SAPO-18 samples deactivated strongly, hence supporting the conclusions made in earlier sections.

Mixed Catalyst System

[0111] MgAPO-18 and SAPO-18 were mixed with ZnZrO in varying ratios and tested at 350 C., 30 bar, H.sub.2/CO.sub.2=3/1, GHSV=6000-24000 ml/g h. Results obtained after reaching steady-state performance are shown in the Table 5 and in FIGS. 12 and 13. When mixed with ZnZrO, MgAPO-18 and SAPO-18 yielded similar CO.sub.2 conversion and hydrocarbon selectivities under each set of conditions. However, the mixture of ZnZrO with MgAPO-18 yielded higher Propene/Propane product ratios under all sets of conditions, thereby further demonstrating the superior catalytic properties of MgAPO-18 compared to SAPO-18 under mixed feed conditions.

TABLE-US-00005 TABLE 5 Results for Mixed catalyst systems. GHSV is calculated based on the amount of (Catalyst 1 + Catalyst 2). Cat1: T P GHSV Conv C3 prod % C3.sup.=/ Catalyst 1 Catalyst 2 Cat2 ( C.) (Bar) (ml/g/h) (% CO.sub.2) (mol/kg/h) S.sub.Hydrocarbons S.sub.C3 C3.sub.tot ZnO:ZrO.sub.2 SAPO-18 1:1 350 30 6000 9.5 0.5 54.9 25.0 71.6 ZnO:ZrO.sub.2 SAPO-18 1:1 350 30 12000 7.0 0.8 57.9 27.4 82.5 ZnO:ZrO.sub.2 SAPO-18 1:1 350 30 24000 4.9 1.3 60.6 31.1 91.6 ZnO:ZrO.sub.2 MgAPO-18 1:1 350 30 6000 10.1 0.5 59.9 25.0 90.1 ZnO:ZrO.sub.2 MgAPO-18 1:1 350 30 12000 7.1 0.8 64.9 28.5 95.9 ZnO:ZrO.sub.2 MgAPO-18 1:1 350 30 24000 5.0 1.2 63.7 28.1 94.9 ZnO:ZrO.sub.2 SAPO-18 3:1 350 30 18000 7.1 1.4 60.8 32.1 92.0 ZnO:ZrO.sub.2 SAPO-18 2:1 350 30 16000 7.5 1.3 64.0 32.0 89.7 ZnO:ZrO.sub.2 SAPO-18 1:1 350 30 12000 7.0 0.8 57.9 27.4 82.5 ZnO:ZrO.sub.2 SAPO-18 1:2 350 30 8000 6.8 0.5 55.7 26.1 61.5 ZnO:ZrO.sub.2 SAPO-18 1:3 350 30 6000 7.2 0.4 52.5 26.8 39.9 ZnO:ZrO.sub.2 MgAPO-18 3:1 350 30 18000 7.8 1.3 53.2 26.7 97.6 ZnO:ZrO.sub.2 MgAPO-18 2:1 350 30 16000 7.6 1.2 61.0 28.9 97.1 ZnO:ZrO.sub.2 MgAPO-18 1:1 350 30 12000 7.1 0.8 64.9 28.5 95.9 ZnO:ZrO.sub.2 MgAPO-18 1:2 350 30 8000 6.9 0.5 61.1 25.6 89 ZnO:ZrO.sub.2 MgAPO-18 1:3 350 30 6000 6.4 0.3 59.9 24.6 93.8