METHOD FOR SYNTHESIZING AN ALKENOIC ACID

Abstract

There is provided a method for synthesizing an alkenoic acid, in particular acrylic acid comprising the step of oxidizing an alkenyl alcohol in the presence of a metal oxide catalyst to form the alkenoic acid. The invention further provides a step of deoxydehydrating a polyol, including glycerol to obtain said alkenyl alcohol including an allyl alcohol.

Claims

1. A method for synthesizing an alkenoic acid comprising the step of oxidizing an alkenyl alcohol in the presence of a metal oxide catalyst to form said alkenoic acid, wherein said metal oxide catalyst has the formula Mo.sub.xV.sub.yW.sub.mO.sub.d where x is a number between 1 to 10; y is a number between 0.05 to 10; m is a number between 1 to 10; and d is calculated based on the formula 3x+2y+3m.

2. The method of claim 1, further comprising, before said oxidizing step, the step of deoxydehydrating a polyol to obtain said alkenyl alcohol.

3. The method of claim 2, wherein said polyol is a triol, tetraol, pentanol or hexanol.

4. The method of claim 3, wherein said polyol is selected from the group consisting of glycerol, 2-methyl-1,2,3-propanetriol, 1,2,3-butanetriol, 2-methyl-1,2,3-butanetriol, 2-methyl-1,2,3,4-butanetetraol, 1,2,3-pentanetriol, 1,2,3-hexanetriol, xylitol, sorbitol, arabinitol, ribitol, mannitol, galactitol, iditol, erythritol, threitol and mixtures thereof.

5. The method of claim 1, wherein said alkenyl alcohol is 2-alkenyl alcohol.

6. The method of claim 5, wherein said 2-alkenyl alcohol is selected from the group consisting of allyl alcohol, 2-buten-1-ol, 2-hexen-1-ol, 2-penten-1,4,5-triol, 2,4-hexadien-1,6-diol, 2-hexene-1,4,5,6-tetraol, 2-methyl-2-butenol, 2-butene-1,4-diol, 2-methyl-2-butene-1,4-diol, methallyl alcohol, and 2-chloroallyl alcohol.

7. The method of claim 1, wherein said alkenoic acid is a linear or branched monocarboxylic or dicarboxylic acid having three to six carbon atoms.

8. The method of claim 7, wherein said alkenoic acid is selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, fumaric acid, 4-hydroxy-2-butenoic acid, 2-hydroxy-3-pentendioic acid, 4,5-dihydroxy-2-pentenoic acid, 2,5-dihydroxy-3-pentenoic acid, crotonic acid, citraconic acid, mesaconic acid, angelic acid, tiglic acid, 4,5,6-trihydroxy-2-hexenoic acid, 2,3,5-trihydroxy-4-hexenoic acid and 4,5-dihydroxy-2-hexenedionic acid.

9.-11. (canceled)

12. The method of claim 1, wherein the metal oxide catalyst is provided on a support.

13. The method of claim 1, wherein the amount of metal oxide catalyst used in the oxidizing step is in the range of 10 mg to 500 mg.

14. The method of claim 1, wherein the oxidizing step is undertaken at a temperature above 300° C.

15. The method of claim 1, wherein the oxidizing step is undertaken at an oxygen content of about 5% to about 20%.

16. The method of claim 2, wherein the deoxydehydrating step is undertaken in the presence of a carboxylic acid.

17. The method of claim 2, wherein the deoxydehydrating step is undertaken at a temperature in the range of about 200° C. to about 280° C., about 235° C.

18. The method of claim 2, wherein the deoxydehydrating step is undertaken in an inert gas atmosphere or in air.

19. The method of claim 16, wherein the carboxylic acid is present at a molar ratio in the range of about 1:1 to about 3.0:1 (carboxylic acid:polyol)

20. A method for synthesizing an alkenoic acid from a polyol comprising the steps of: (a) deoxydehydrating the polyol in the presence of a carboxylic acid to form an alkenyl alcohol; and (b) oxidizing the alkenyl alcohol in the presence of a metal oxide catalyst to form the alkenoic acid, wherein said metal oxide catalyst has the formula Mo.sub.xV.sub.yW.sub.mO.sub.d where x is a number between 1 to 10; y is a number between 0.05 to 10; m is a number between 1 to 10; and d is calculated based on the formula 3x+2y+3m.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0036] FIG. 1 is a scheme showing a conventional process of forming acrylic acid from glycerol (prior art).

[0037] FIG. 2 is a graph showing the conversion of glycerol as a function of molar ratio of formic acid to glycerol. Glycerol 18.2 g (0.2 mol), reaction temperature 235° C., reaction time 2 hours and conversions were determined by High Performance Liquid Chromatography (HPLC).

[0038] FIG. 3 is a schematic diagram showing a continuous reaction setup for the formic acid mediated deoxydehydration of glycerol to allyl alcohol.

[0039] FIG. 4 is a graph showing the temperature dependence of allyl alcohol oxidation over an experimental catalyst (identified in the examples as catalyst 2#). Reactions conditions were 200 mg, 35 to 60 mesh (catalyst), 20 wt % of allyl alcohol in water at 0.5 ml/h (feed) and 10% O.sub.2/He, 20 ml/minute (carrier gas). The weight hourly space velocity (WHSV) was 0.5 g/(g h).

[0040] FIG. 5 is a series of graphs showing the time on stream tests for allyl alcohol oxidation over (A) a first experimental catalyst (identified in the examples as catalyst 2#) and (B) a second experimental catalyst (identified in the examples as catalyst 8#). Reactions conditions were 200 mg, 35 to 60 mesh (catalyst), 20 wt % of allyl alcohol in water at 0.5 ml/h (feed) and 10% O.sub.2/He, 20 ml/minute (carrier gas). The weight hourly space velocity (WHSV) was 0.5 g/(g h).

EXAMPLES

[0041] Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1—Production of Allyl Alcohol

[0042] All starting materials were commercially available and were used as received, unless otherwise indicated. Formic acid (99%), glycerol (99%), ammonium monovanadate (99%), and ammonium heptamolybdate (99%) were purchased from Merck Millipore of Massachusetts of the United States of America Ammonium metatungstate (99%) was purchased from Fluka (under Sigma-Aldrich of Missouri of the United States of America).

[0043] The process of Scheme 1 was used to form acrylic acid. In a typical condition for the first step of Scheme 1, glycerol was heated with formic acid at 235° C. under ambient atmosphere, and allyl alcohol was collected by condensation. The reaction was very fast and the product was observed immediately when the reaction temperature reached 235° C. The reaction was clean and there was no other side products collected besides water. The conversion of glycerol depended on the amount of formic acid added to the reaction (FIG. 2). At a formic acid to glycerol molar ratio of 1.8:1, 90% glycerol was converted (allyl alcohol yield 89%) in 2 hours. Around 20 to 40% of unreacted formic acid was also collected together with the product. As the formic acid was added in 3 portions, the reaction was almost complete in about 6 hours (including 2 hours interim cooling down and heating up), and allyl alcohol was collected at 97% yield (Entries 1 and 2, Table 1). A gas flow can facilitate the distillation, and there was no difference for nitrogen or air. Moisture and methanol were the main potential impurities in crude glycerol; however, they did not affect the current deoxydehydration reaction even at 20 wt % content (Entries 3 and 4, Table 1). More formic acid was recovered when 20 wt % water was presented (Entry 3, Table 1).

TABLE-US-00001 TABLE 1 Formic acid Conv..sub.gly Yield recovered Entry Glycerol Atmosphere (%).sup.[c] (%) (%) 1.sup.[a] 100% N.sub.2 98 97 23 2.sup.[a] 100% Air 99 98 27 3.sup.[a] 80 wt % in H.sub.2O N.sub.2 98 97 33 4.sup.[a] 80 wt % in MeOH N.sub.2 99 98 27 5.sup.[b] 100% N.sub.2 99 99 34 Deoxydehydration of glycerol by formic acid. Reaction conditions: glycerol 18.4 g (0.2 mol), formic acid 16.5 g (0.36 mol), 235° C. .sup.[a]Formic acid was added in 3 portions (11.9, 2.3, and 2.3 g). Reaction time: 6 hours. .sup.[b]Continuous reaction. A mixture of glycerol (18.4 g, 0.2 mol) and formic acid (16.5 g, 0.36 mol) was added continuously to the reactor. Reaction time: 2 hours. .sup.[c]Yield and conversion were determined by HPLC.

[0044] As the reaction was fast, the continuous reaction model was also tried (FIG. 3, Entry 5, Table 1). Under steady state, a mixture of glycerol (18.4 g, 0.2 mol) and formic acid (16.5 g, 0.36 mol) at a glycerol:formic acid ratio of 1:1.8 (2) was added continuously to a 50 ml flask (heated at 235° C., containing glycerol and formic acid at the same molar ratio) (6) in around 2 hours, and 11.5 g of allyl alcohol (99% yield) (4) was collected together with 5.6 g of unreacted formic acid. This example demonstrates that the continuous production of allyl alcohol from glycerol is feasible and that the productivity is excellent.

[0045] The allyl alcohol obtained was then oxidized to acrylic acid in a series of examples below.

Example 2—Effect of Catalyst on Production of Acrylic Acid

[0046] Mo and V based multiple metal oxide catalysts with formula Mo.sub.xN.sub.yA.sub.mB.sub.nO.sub.δ were used for the further oxidation of allyl alcohol to acrylic acid in fixed-bed gas-phase system. Table 2 lists the samples and their surface area (S.sub.BET). Catalysts 1# to 6# were unsupported catalysts while catalysts 7# to 9# were supported catalysts, in which the support material is SBA-15 (a mesoporous silica material). The unsupported Mo—V—W—O catalysts were prepared by decomposing the ammonium salts of the metal precursors. Stoichiometric amounts of ammonium monovanadate, ammonium heptamolybdate, and ammonium metatungstate were dissolved in deionised water and then evaporated to dryness. The combination was calcined at 275° C. for 4 hours in air and then at 325° C. for 4 hours in a helium environment. The powder sample was pressed into pellets, crushed and sieved using a 35 to 60 mesh before activity evaluation. For the preparation of the supported catalyst, an aqueous solution containing calculated amounts of vanadium, molybdenum, and tungsten precursors was impregnated onto SBA-15 (purchased from Sigma-Aldrich) under stirring at room temperature. The material was dried at 100° C. overnight to remove solvent before calcination at 275° C. for 4 hours in air and then at 325° C. for 4 hours in a helium environment.

TABLE-US-00002 TABLE 2 S.sub.BET Catalyst Type of catalyst (m.sup.2 g.sup.−1) 1# Mo.sub.8V.sub.2O.sub.δ 8.9 2# Mo.sub.8V.sub.2WO.sub.δ 12.4 3# Mo.sub.8V.sub.2W.sub.2O.sub.δ 9.9 4# Mo.sub.9V.sub.3O.sub.δ 8.2 5# Mo.sub.9V.sub.3WO.sub.δ 10.1 6# Mo.sub.9V.sub.3W.sub.2O.sub.δ 10.5 7# 60% Mo.sub.8V.sub.2WO.sub.δ/SBA-15 187.3 8# 40% Mo.sub.8V.sub.2WO.sub.δ/SBA-15 272.9 9# 20% Mo.sub.8V.sub.2WO.sub.δ/SBA-15 329.7

[0047] Table 3 shows the results of allyl alcohol oxidation over the catalysts. Over 1# and 4# catalysts, acrolein was dominant in the products when the reaction temperature was below 320° C. Other products are acrylic acid, acetaldehyde, acetic acid, and carbon oxides. When the reaction temperature was increased, acrolein was consecutively oxidized to acrylic acid, however the selectivity to acetic acid and the total oxidized products (CO, CO.sub.2) was also increased. Over the 2# and 5# catalysts, full allyl alcohol conversion and selectivity to acrylic acid of about 87% and 86% respectively was achieved at a reaction temperature of 340° C.

TABLE-US-00003 TABLE 3 T Conv. Selectivity [%] Cat. [° C.] [%] Acr AcOH AA CO CO.sub.2 1# 300 80.5 75.2 0.8 1.4 1.7 4.0 340 100.0 57.2 7.4 16.9 7.6 8.6 2# 300 87.7 20.0 5.8 61.9 0.5 1.7 340 100.0 0.1 7.3 87.2 0.3 0.6 3# 300 75.3 62.8 2.6 13.4 1.4 3.9 340 100.0 17.8 8.2 61.1 3.7 6.2 4# 300 88.1 81.1 0.4 1.5 2.0 4.6 340 100.0 26.0 6.4 47.1 7.8 8.9 5# 300 90.4 37.5 2.8 42.1 1.1 2.9 340 100.0 0.5 6.0 86.2 1.2 2.2 6# 300 100.0 56.8 2.1 18.8 3.7 7.4 340 100.0 0.2 10.1 62.4 10.3 14.2 Reaction conditions: catalyst, 200 mg, 35~60 mesh; feed, 20 wt % allyl alcohol in H.sub.2O, 0.5 ml h.sup.−1; carrier gas, 10% O.sub.2/He, 20 ml min.sup.−1. Acr: acrolein. AA: acrylic acid. AcOH: acetic acid. WHSV = 0.5 g/(gh).

Example 3—Effect of Contact Time and Space Velocity of Catalyst

[0048] The contact time and space velocity of the catalysts were studied by varying the amount of catalyst loading for the best performed 2# catalyst (Table 4). At lower reaction temperature (e.g. 280° C.), the conversion of allyl alcohol increased with increasing amount of catalyst loaded. When 100 mg of catalyst was loaded, only 33% allyl alcohol conversion but more than 90% acrolein selectivity were observed at 280° C. Both conversion and the selectivity to acrylic acid were improved when the amount of catalyst was increased to 200 mg, and 87% acrylic acid yield was obtained at 340° C. Further increase in the amount of catalyst to 300 mg led to more acetic acid and carbon oxides being produced due to over oxidization. Thus, it is possible to selectively synthesize acrolein or acrylic acid by controlling the reaction temperature and the amount of catalyst or space velocity.

TABLE-US-00004 TABLE 4 Contact Cat. time WHSV T Conv. Selectivity [%] [mg] [s] [g/(gh)] [° C.] [%] Acr AcOH AA CO CO.sub.2 100 0.27 1.00 280 33.4 91.0 0.0 0.0 0.7 2.0 400 100 19.4 4.7 70.7 1.0 2.5 200 0.54 0.50 280 62.7 51.4 3.6 23.9 0.7 2.7 340 100.0 0.1 7.3 87.2 0.3 0.6 300 0.81 0.33 280 93.3 70.6 0.6 3.1 1.9 3.7 340 100 3.3 8.4 74.3 4.4 7.0 Reaction conditions: feed, 20 wt % allyl alcohol in H.sub.2O, 0.5 ml h.sup.−1; carrier gas, 10% O.sub.2/He 20 ml min.sup.−1. Acr: acrolein. AA: acrylic acid. AcOH: acetic acid.

Example 4—Effect of Oxygen Content

[0049] The oxygen content in the carrier gas was further investigated for the 2# catalyst (Table 5). The conversion of allyl alcohol generally increased with increasing oxygen content. When 5% oxygen was used as the carrier gas, about 81% selectivity to acrylic acid was achieved at 340° C. while the selectivity to the total oxidized products (CO and CO.sub.2) was less than 1%. Increasing the oxygen content to 10% gave about 87% yield of acrylic acid at 340° C. Further increasing the oxygen content to 20% led to lower selectivity to acrylic acid. Thus, the oxygen content from 5% to 10% is preferable for the current oxidation reaction.

TABLE-US-00005 TABLE 5 O.sub.2 T Conv. Selectivity [%] [%] [° C.] [%] Acr AcOH AA CO CO.sub.2  5% 300 58.7 20.2 6.5 58.6 0.3 1.1 340 99.3 6.0 5.4 81.5 0.2 0.5 10% 300 87.7 20.0 5.8 61.9 0.5 1.7 340 100.0 0.1 7.3 87.2 0.3 0.6 20% 300 99.0 1.2 5.7 75.3 1.5 4.4 340 100.0 0.4 8.7 78.3 4.6 6.4 Reaction conditions: 2# catalyst, 200 mg, 35~60 mesh; feed, 20 wt % allyl alcohol in H.sub.2O, 0.5 ml h.sup.−1; carrier gas x % O.sub.2/He 20 ml min.sup.−1. Acr: acrolein. AA: acrylic acid. AcOH: acetic acid. WHSV = 0.5 g/(g h).

Example 5—Effect of Temperature

[0050] The temperature dependence of the reaction performance of 2# is shown in FIG. 4. The allyl alcohol conversion increased monotonously at elevated temperatures in the 240 to 320° C. region, and full conversion was achieved at a temperature above 320° C. Acrolein is the key intermediate to acrylic acid. The selectivity to acrolein decreased rapidly with the temperature rise, indicating that acrolein was quickly oxidized at higher temperature. In contrast, the selectivity to acrylic acid increased rapidly with the temperature rise, reaching a maximum value of 86.3% at 340° C. Further increase in the temperature led to decreased selectivity to acrylic acid due to over oxidization, as reflected by the increasing amount of acetic acid, CO, and CO.sub.2. The selectivity to acetic acid, CO, and CO.sub.2 were lower than 10% in the whole temperature range. Acetaldehyde was observed as the main side product at temperature below 320° C., while the formation of acetaldehyde was notably reduced as the temperature increased.

Example 6—Effect of Supported Catalysts

[0051] The supported catalysts were evaluated under optimized reaction conditions and the results are listed in Table 6. In contrast to the 87.7% allyl alcohol conversion over the unsupported 2# catalyst at 300° C., full conversion was achieved over all the supported catalysts at the same reaction temperature, indicating much higher activity of the supported catalysts. Over the catalysts 7# and 8# catalysts, greater than 82% acrylic acid yields were observed at reaction temperatures above 340° C. It was also noted that higher reaction temperature did not affect the selectivity to acrylic acid over the supported catalysts. When the reaction temperature was raised from 340° C. to 380° C., the selectivity to acrylic acid for 7# and 8# catalysts was kept above 82%, while it dropped from 86% to 72% for unsupported 2# (data not shown).

TABLE-US-00006 TABLE 6 T Conv. Selectivity Cat. [° C.] [%] Acr AcOH AA CO CO.sub.2 2# 300 87.7 20.0 5.8 61.9 0.5 1.7 340 100.0 0.1 7.3 87.2 0.3 0.6 7# 300 100.0 29.7 22.2 25.5 2.9 4.3 340 100.0 0.4 9.9 85.2 1.7 2.1 8# 300 100.0 6.3 22.3 50.3 2.9 5.0 340 100.0 1.0 10.9 82.8 1.1 1.9 9# 300 100.0 9.6 15.2 51.6 2.7 4.9 340 100.0 4.9 11.2 61.8 2.0 4.8 Reaction conditions: catalyst 200 mg, 35~60 mesh; feed, 20 wt % allyl alcohol in H.sub.2O, 0.5 ml h.sup.−1; carrier gas, 10% O.sub.2/He, 20 ml min.sup.−1. Acr: acrolein. AA: acrylic acid. AcOH: acetic acid. WHSV = 0.5 g/(g h).

Example 7—Catalytic Performance of Catalysts

[0052] The catalytic performance of catalysts under the optimal reaction conditions were further studied as a function of time on stream (FIG. 5). The complete conversion of allyl alcohol was kept for more than 90 hours over both 2# and 8#. For the 2# catalyst, the selectivity to acrylic acid decreased from 80% to 70% in the initial 30 hours, and then stabilized at around 70% till 90 hours on stream; meanwhile, the selectivity to acetic acid increased from 8% to 20%. The 8# catalyst showed excellent stability. At 100 hours on stream, the selectivities to acrylic acid and acetic acid were well maintained at 80% and 11%, respectively. Considering the fast deactivation of the catalysts in direct glycerol oxidehydration to acrylic acid of the prior art, the performance of the current catalytic system is outstanding in terms of the high activity, selectivity, and stability.

[0053] In conclusion, the inventors have demonstrated a highly efficient protocol for the production of acrylic acid from glycerol. The process involved glycerol deoxydehydration to allyl alcohol in liquid phase and allyl alcohol oxidation to acrylic acid in gas phase. About 84% overall yield of acrylic acid was achieved from glycerol by the two-step reaction. Formic acid (a cheap and green chemical) was used as key reagent in the first step and metal oxides were used as catalyst in the second step. It is noteworthy that both steps can be carried out in the continuous manner, and this is very favorable for the practical application of the process. Compared with the fast catalyst deactivation in the process of glycerol oxidehydration to acrylic acid (of the prior art), the current catalytic system is highly stable and 80% yield to acrylic acid was maintained for 100 hours. Hence, the current application provides a new and prominent method for the production of acrylic acid from bio-renewable glycerol.

INDUSTRIAL APPLICABILITY

[0054] The disclosed method may enable the production of arylic acid from glycerol at high yields, high selectivities to acrylic acid and may be highly stable. The disclosed method made up of the two steps of deoxydehydration and oxidation may be carried out in a continuous manner. The metal oxide catalysts used in the disclosed method may not suffer from catalyst deactivation.

[0055] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.