PROCESS FOR FORMALDEHYDE MANUFACTURE

Abstract

A process for the production of formaldehyde from methanol comprising the steps of: feeding to a reactor a feed stream comprising the methanol and an oxygen-containing gas; reacting the methanol in the gas phase with the oxygen-containing gas in the reactor in the presence of a catalyst comprising oxides of iron and molybdenum; and recovering a formaldehyde reactor outlet stream from the reactor, the formaldehyde reactor outlet stream comprising formaldehyde and carbon monoxide. The catalyst comprises copper in an amount of at least 0.025 wt %, or at least 0.05 wt %, of the catalyst and in that the molar ratio of carbon monoxide to formaldehyde in the formaldehyde reactor outlet stream is at least 5% less than the molar ratio of carbon monoxide to formaldehyde in the formaldehyde reactor outlet stream in the same process using a catalyst containing essentially no copper.

Claims

1. A process for the production of formaldehyde from methanol comprising the steps of: feeding to a reactor a feed stream comprising the methanol and an oxygen-containing gas; reacting the methanol in the gas phase with the oxygen-containing gas in the reactor in the presence of a catalyst comprising oxides of iron and molybdenum; and recovering a formaldehyde reactor outlet stream comprising formaldehyde and carbon monoxide from the reactor; wherein the catalyst comprises copper in an amount of at least 0.025 wt % of the catalyst.

2. The process according to claim 1, wherein the catalyst comprises copper in an amount of at least 0.05 wt % of the catalyst.

3. The process according to claim 1, wherein the reactor is operated at an inlet pressure of at least 0 barg.

4. The process according to claim 3, wherein the reactor is operated at an inlet pressure of at least 1 barg.

5. The process according to claim 1, wherein said oxygen-containing gas is air.

6. The process according to claim 1, wherein a portion of said feed stream comprises a recycled portion of the formaldehyde reactor outlet stream.

7. The process according to claim 1, wherein said feed stream comprises methanol at a concentration of from 1% to 20% by volume of said feed stream.

8. The process according to claim 1, wherein the molar ratio of carbon monoxide to formaldehyde in the formaldehyde reactor outlet stream is less than 6%.

9. The process according to claim 1, wherein the process produces at least 7.4 MTPD of formaldehyde.

10. The process according to claim 9, wherein the at least 7.4 MPTD of formaldehyde is produced as at least 20 MPTD 37 wt % formaldehyde solution in water.

11. The process according to claim 1, wherein the catalyst has been calcined at a temperature of not more than 525° C., not more than 500° C., or not more than 475° C.

12. The process according to claim 11, wherein the catalyst has been calcined at a temperature of at least 425° C.

13. A use of a catalyst comprising oxides of iron and molybdenum and copper in an amount of at least 0.025 wt % of the catalyst to reduce CO loss in a process for the production of formaldehyde from methanol.

14. The use according to claim 13, wherein the process comprises the steps of: feeding to a reactor a feed stream comprising the methanol and an oxygen-containing gas; reacting the methanol in the gas phase with the oxygen-containing gas in the reactor in the presence of the catalyst; and recovering a formaldehyde reactor outlet stream from the reactor, the formaldehyde reactor outlet stream comprising formaldehyde and carbon monoxide; wherein the CO loss is reduced such that the molar ratio of carbon monoxide to formaldehyde in the formaldehyde reactor outlet stream is at least 0.25% less than the molar ratio of carbon monoxide to formaldehyde in the formaldehyde reactor outlet stream in the same process using a catalyst containing essentially no copper.

15. The use according to claim 13, wherein the process is for the production of formaldehyde from methanol comprising the steps of: feeding to a reactor a feed stream comprising the methanol and an oxygen-containing gas: reacting the methanol in the gas phase with the oxygen-containing gas in the reactor in the presence of a catalyst comprising oxides of iron and molybdenum; and recovering a formaldehyde reactor outlet stream comprising formaldehyde and carbon monoxide from the reactor; wherein the catalyst comprises copper in an amount of at least 0.025 wt % of the catalyst, wherein the catalyst comprises copper in an amount of at least 0.05 wt % of the catalyst.

16. A use of a catalyst comprising oxides of iron and molybdenum and copper in an amount of at least 0.025 wt % of the catalyst to reduce methyl formate loss in a process for the production of formaldehyde from methanol.

17. The use according to claim 16, wherein the process comprises the steps of: feeding to a reactor a feed stream comprising the methanol and an oxygen-containing gas; reacting the methanol in the gas phase with the oxygen-containing gas in the reactor in the presence of the catalyst; and recovering a formaldehyde reactor outlet stream from the reactor, the formaldehyde reactor outlet stream comprising formaldehyde and carbon monoxide; wherein the methyl formate loss is reduced such that the molar ratio of methyl formate to formaldehyde in the formaldehyde reactor outlet stream is at least 0.01% less than the molar ratio of methyl formate to formaldehyde in the formaldehyde reactor outlet stream in the same process using a catalyst containing essentially no copper.

18. The use according to claim 16, wherein the process is for the production of formaldehyde from methanol comprising the steps of: feeding to a reactor a feed stream comprising the methanol and an oxygen-containing gas: reacting the methanol in the gas phase with the oxygen-containing gas in the reactor in the presence of a catalyst comprising oxides of iron and molybdenum; and recovering a formaldehyde reactor outlet stream comprising formaldehyde and carbon monoxide from the reactor; wherein the catalyst comprises copper in an amount of at least 0.025 wt % of the catalyst, wherein the catalyst comprises copper in an amount of at least 0.05 wt % of the catalyst.

Description

DESCRIPTION OF THE DRAWINGS

[0027] Embodiments of the present invention will now be described, by way of example, and not in any limitative sense, with reference to the accompanying drawings, of which:

[0028] FIG. 1 is a schematic of a process for the production of formaldehyde;

[0029] FIG. 2 is a graph of CO loss against conversion for various catalyst samples; and

[0030] FIG. 3 is a graph of CO loss against conversion for various catalyst samples.

[0031] FIG. 4 is a graph of methyl formate loss against conversion for various catalyst samples.

[0032] FIG. 5 is a graph of CO loss against conversion for samples S and T.

DETAILED DESCRIPTION

[0033] Formaldehyde can be produced by the catalytic oxidative dehydrogenation of methanol. Processes for carrying out such production are known, for example from WO9632189 or U.S. Pat. No. 2,504,402. A well-known process for the production of formaldehyde is the Formox process offered by Johnson Matthey. The Formox process is illustrated schematically in FIG. 1. In the illustrated Formox process 1a fresh air stream 5 is passed through a pressurisation blower 4 and then mixed with a recirculation stream 22 to form a mixed stream 23 before being fed via a recirculation blower 3 to a vaporiser 10. In the vaporiser 10, the mixed stream 23 is mixed with a methanol stream 2 and vaporised using heat from a formaldehyde reactor outlet stream 24 leaving a reactor 9. The resulting feed stream 25 is fed to the reactor 9 which, in this embodiment, is an isothermal reactor cooled by vaporisation of a heat transfer fluid 32. The heat transfer fluid 32 passes to a condenser 8, where it is condensed and steam 6 generated from boiler feed water 7, before returning to the reactor 9. In the reactor 9, the methanol in the feed stream 25 reacts on catalyst beds to produce formaldehyde, which exits the reactor 9 in a formaldehyde reactor outlet stream 24 comprising the formaldehyde, carbon monoxide produced as a by-product, water, other by-products (such as dimethyl ether, methyl formate, carbon dioxide, and/or dimethoxymethane), and unreacted parts of the feed stream 25. In processes according to the present invention, the catalyst beds comprises catalyst comprising at least 0.025 wt % copper, or at least 0.05 wt % copper, and the molar ratio of carbon monoxide to formaldehyde in the formaldehyde reactor outlet stream 24 is preferably less than 6%, less than 5%, less than 4%, or less than 3%. The formaldehyde reactor outlet stream 24 passes through the vaporiser 10, where heat in the formaldehyde reactor outlet stream 24 is used to vaporise the feed stream 25, and is fed to an absorber 11. In the absorber 11, process water 12 and optionally urea 13 flows down and strips the formaldehyde from the process stream 24 flowing up the absorber 11. The water 12, and optionally urea 13, together with the formaldehyde exits the bottom of the absorber as a product stream 21. That product stream 21 is typically 55% formalin, if just process water 12 is used, or UFC if urea 13 is used. The remainder of the formaldehyde reactor outlet stream 24 exits the top of the absorber as a waste gas stream 26. That waste gas stream 26 is partially recycled as the recirculation stream 22 and the remainder is sent to an emissions control system 16. In the emissions control system 16, the waste gas stream 26 is first heated in a pre-heater 14 using energy from the combusted waste gas stream 27 leaving the emissions control system 16 and then combusted in a catalyst bed 15 having a catalyst comprising structured or supported Pd on Al.sub.2O.sub.3 and/or Pt on Al.sub.2O.sub.3 to form the combusted waste gas stream 27. The combusted waste gas stream 27 leaving the catalyst bed 15 has a temperature of around 500° C. to 540° C. and is fed to a steam generator 20, where the combusted waste gas stream 27 is cooled and boiler feed water 19 is turned into steam 18, and then fed back to the pre-heater 14 of the emissions control system 16 to heat the incoming waste gas stream 26. The combusted waste gas stream 27 leaving the pre-heater 16 is sent to a stack 17.

[0034] It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

EXAMPLES

Example 1

[0035] The following catalyst samples were prepared using the method described below. [0036] A—Iron Molybdate sol-gel [0037] B—Iron Molybdate with 0.64 wt % Al (10 mol % Fe content of ‘A’ substituted for Al). [0038] C—Iron Molybdate with 1.5 wt % Cu (10 mol % Fe content of ‘A’ substituted for Cu). [0039] D—Iron Molybdate with 1.54 wt % Zn (10 mol % Fe content of ‘A’ substituted for Zn). [0040] E—Iron Molybdate with 1.3 wt % Mn (10 mol % Fe content of ‘A’ substituted for Mn). [0041] F—Iron Molybdate with 0.32 wt % Al (5 mol % Fe content of ‘A’ substituted for Al). [0042] G—Iron Molybdate with 0.75 wt % Cu (5 mol % Fe content of ‘A’ substituted for Cu). [0043] H—Iron Molybdate sol-gel with 0.38 wt % Cu (2.5 mol % Fe content of ‘A’ substituted for Cu). [0044] I—Iron Molybdate sol-gel repeat of A

[0045] Samples A and I were prepared as follows. 7.5 g iron nitrate nonahydrate was dissolved in 100 mL H.sub.2O and 10 g citric acid was added. A solution of 7.54 g ammonium paramolybdate in 100 mL was then added and the solution dried on a hotplate at 80° C. until a glassy texture was observed. Drying was completed in a vacuum oven overnight at 70° C. The resulting glassy material is broken up with a pestle and mortar and then calcined. The calcination procedure is as follows: 2° C./min to 230° C., hold for 30 minutes, 10° C./min to 350° C., hold for 1 minute, 2° C./min to 450° C., hold for 30 minutes, 10° C./min to 500° C. hold for 2 hours, 20° C./min cool to room temperature.

[0046] Samples B, C, D and E were prepared as above, except that 6.7484 g of iron nitrate nonahydrate was mixed with the following: [0047] B—0.6962 g aluminium nitrate nonahydrate [0048] C—0.4317 g copper nitrate hemi-pentahydrate [0049] D—0.4852 g zinc nitrate tetrahydrate [0050] E—0.4658 g manganese nitrate tetrahydrate Samples F and G were prepared as above for samples A and I, except that 7.125 g of iron nitrate was mixed with: [0051] F—0.3482 g aluminium nitrate nonahydrate [0052] G—0.2159 g copper nitrate hemipentahydrate

[0053] Sample H was prepared as above for samples A and I, except that 7.3515 g iron nitrate was mixed with 0.1079 g copper nitrate hemipentahydrate

[0054] All catalyst samples were granulated to 250-470 microns for testing and blended with silicon carbide (450 mg SiC per 100 mg catalyst) with a 300 mg SiC layer on top of the bed. For several catalysts the catalyst loading was varied in order to achieve different conversions and enable comparison of catalysts at the same conversion (particularly when comparing to the reference iron molybdenum only catalyst).

[0055] Testing was carried out in a 5 mm ID stainless steel reactor, with the reactor set to 310° C. A stream of methanol-water-formaldehyde was passed over the catalyst with the products analysed using a GC. The composition of the gas stream was as follows: [0056] 90 mL/min air [0057] 90 mL/min helium [0058] 40 mL/min nitrogen [0059] 38 μL/min liquid pump rate

[0060] This gave an oxygen content of approximately 7.38%, a methanol concentration of approximately 4.9%, water at approximately 5.7% and formaldehyde at approximately 2.2%. The precise methanol concentration was determined by sampling through the reactor bypass run at the start of each experiment and, after adjusting for reactor conversion, the performance of the catalyst was determined.

[0061] Results from methanol oxidation testing are summarised in FIG. 2. The data points are labelled with the catalyst sample letter.

[0062] The results show that copper addition, at a range of loadings, leads to a consistently lower CO loss when compared to an equivalent iron-molybdenum oxide only catalyst.

[0063] The CO loss is reduced by approximately 0.75% in absolute terms. The other metals are less effective, aluminium has little effect at 5% substitution and increases CO loss at 10%. Zinc leads to a slight reduction in CO loss, while manganese substantially reduces catalyst activity and could not achieve conversion comparable to the standard catalysts.

[0064] The addition of copper thus shows a surprising reduction in the CO loss both compared to standard catalysts and compared to the addition of other metals.

Example 2

[0065] A further test was carried out in which the catalyst samples were prepared by precipitation rather than the sol-gel method. Precipitation is more commonly used for the commercial production of prior art catalysts. In this example, copper is added to the catalyst washing water post-precipitation and the iron content is not reduced to account for the addition of copper.

[0066] A precipitate (‘FeMo’) was prepared according to Soederhjelm, et al., “On the Synergy Effect in MoO.sub.3—Fe.sub.2(MoO.sub.4).sub.3 Catalysts for Methanol Oxidation to Formaldehyde,” Top Catal (2008) 50:145-155.

[0067] Following addition, the precipitate was aged for 2 hours at 60° C., before being filtered, washed with 250 mL distilled water, and filtered again.

[0068] After the fourth filtration, the solids content of the filter cake was determined, the filter cake was weighed, and the amount of catalyst present was determined based on the total mass, solids content, and accounting for 10% mass loss on calcination. The amount of copper (II) nitrate hemipentahydrate added to the catalyst was for each sample was: [0069] Sample J—FeMo+Cu (0.0052 g Cu-nitrate per g catalyst) [0070] Sample K—FeMo+Cu (0.0260 g Cu-nitrate per g catalyst) [0071] Sample L—FeMo+Cu (0.0520 g Cu-nitrate per g catalyst) [0072] Sample M—FeMo+Cu (0.00904 g Cu-nitrate per g catalyst) [0073] Sample N: FeMo+Cu (0.0025 g Cu-nitrate per g catalyst) [0074] Sample O: FeMo+Cu (0.0013 g Cu-nitrate per g catalyst) [0075] Sample P: FeMo+Cu (0.0071 g Cu-nitrate per g catalyst)

[0076] The Cu was added in the form of a Cu-nitrate solution by dispersing the filter cake in the solution and then filtering.

[0077] The Cu-containing filter cake was recovered, dried at 100° C. overnight and then calcined at 500° C. for 2 hours (10° C./min ramp up and down).

[0078] Reference sample Q was prepared in the same way, except that no copper (II) nitrate was added.

[0079] Catalysts were granulated to 250-470 microns for testing and blended with silicon carbide (450 mg SiC per 100 mg catalyst) with a 300 mg SiC layer on top of the bed. For several catalysts the catalyst loading was varied in order to achieve different conversions and enable comparison of catalysts at the same conversion (particularly when comparing to the reference iron molybdenum only catalyst).

[0080] Testing was carried out in a 5 mm ID stainless steel reactor, with the reactor set to 310° C. A stream of methanol-water-formaldehyde was passed over the catalyst with the products analysed using a GC. The composition of the gas stream was as follows: [0081] 90 mL/min air [0082] 90 mL/min helium [0083] 40 mL/min nitrogen [0084] 38 μL/min liquid pump rate

[0085] This gave an oxygen content of approximately 7.38%, a methanol concentration of approximately. 4.9%, water at approximately 5.7% and formaldehyde at approximately 2.2%. The precise methanol concentration was determined by sampling through the reactor bypass run at the start of each experiment and, after adjusting for reactor conversion, the performance of the catalyst was determined. [0086] ICP results are shown below:

TABLE-US-00001 Sample Mo/wt % Fe/wt % Cu/wt % J 53.1 14 0.11 K 52.9 14.3 0.32 L 52.5 14.3 0.51 M 53.1 14.6 0.21 N 53.4 14.6 0.07 O 52.8 14.7 0.04 P 52.6 14.7 0.18 Q 53.4 13.8 0

[0087] BET surface area measurements were performed on the samples:

TABLE-US-00002 BET Surface Area Sample (m2/g) J 10.21 K 9.9 L 10.08 M 9.61 N 11.04 O 11.06 P 10.49 Q 10.55

[0088] Catalyst testing results for the samples are illustrated in FIGS. 3 and 4 and show a marked reduction in CO loss and methyl formate loss, respectively for the catalysts where copper was added. Results show CO loss is around 1% lower and the methyl formate loss was 0.4% lower, in absolute terms, for the copper containing catalysts, although catalyst activity was diminished at ˜2.14 μmol m.sup.−2s.sup.−1 compared to ˜2.65 μmol m.sup.−2s.sup.−1 for the copper free catalyst. Note the catalysts are tested over the same conversion ranges making the results comparable.

Example 3

[0089] A further test was carried out in which the catalyst preparation of example 2 was scaled up (sample S). 1 kg of catalyst was prepared using precipitation, and then washed, and filtered. The filter cake was dispersed solution, and copper was added in the form of a Cu-nitrate solution. The Cu-containing filter cake was recovered, dried at 100° C. overnight.

[0090] The Cu-containing filter cake was blended with tabletting aids, pre-compacted, granulated and pelleted using a single-punch tableting machine. The tablets were formed as Raschig rings with dimensions of 5.0 mm (outer diameter), 2.7 mm (inner diameter) and 2.7 mm (height) post calcination.

[0091] The tablets were calcined at 473° C. for 4 hours.

[0092] The XRF and BET surface area results are shown below:

TABLE-US-00003 Elemental composition (XRF) BET Surface Area Sample Mo/wt % Fe/wt % Cu/wt % (m2/g) Sample S 53.39 13.60 0.07 5.9

[0093] Testing was carried out on a pilot plant in a 21 mm ID stainless steel reactor using a Johnson Matthey standard loading plan, with reactor heated to 267° C. using a HTF system. The pressure at the reactor inlet was set to 1.68 barg. A stream of methanol-water was passed over the catalyst with the products analysed using a GC. The gas consisted of approximately 10.0% methanol, 2.7% water, 9.6% oxygen and 77.7% nitrogen. The total flow was 66.9 NI/min.

[0094] Sample S was compared to a commercial reference catalyst (“standard FeMo”). See also FIG. 5:

TABLE-US-00004 MeOH Yield (%) Sample conversion (%) FA CO DME MF DMM Standard FeMo 97.04 88.19 5.17 3.14 0.19 0.11 Sample S 96.94 88.90 4.32 3.28 0.16 0.03

Example 4

[0095] A pilot scale test was carried out using a copper containing catalyst which was prepared by an incipient wetness impregnation technique (sample T). Here, the preparation follows that in example 3, in that the precipitation, washing and filtration steps are the same. After drying at 110° C. for 24 h, the powder, having <3% moisture content was dispersed in a crystallisation dish. Then, an aqueous copper solution (copper chloride, 0.21 wt % for final dried catalyst) was poured over the top of the dry powder. After air drying at ambient conditions, the powder was then dried at 110° C. for 24 h again.

[0096] The Cu-containing powder was blended with tabletting aids, pre-compacted, granulated and pelleted using a single-punch tableting machine. The tablets were formed as Raschig rings with dimensions of 5.0 mm (outer diameter), 2.7 mm (inner diameter) and 2.7 mm (height) post calcination.

[0097] The tablets were calcined at 460° C. for 4 hours.

[0098] The XRF and BET surface area results are shown below:

TABLE-US-00005 Elemental composition (XRF) BET Surface Area Sample Mo/wt % Fe/wt % Cu/wt % (m2/g) Sample T 53.08 13.71 0.21 6.5

[0099] Testing was carried out on a pilot plant in a 21 mm ID stainless steel reactor using a Johnson Matthey standard loading plan, with reactor heated to 267° C. using a HTF system. The pressure at the reactor inlet was set to 1.68 barg. A stream of methanol-water was passed over the catalyst with the products analysed using a GC. The gas consisted of approximately 10.0% methanol, 2.7% water, 9.6% oxygen and 77.7% nitrogen. The total flow was 66.9 NI/min.

[0100] Sample T was compared to a commercial reference catalyst (“standard FeMo”). See also FIG. 5:

TABLE-US-00006 MeOH Yield (%) Sample conversion (%) FA CO DME MF DMM Standard FeMo 97.04 88.19 5.17 3.14 0.19 0.11 Sample T 94.99 84.66 3.86 3.45 0.29 2.52