Method for preparing low-grade unsaturated fatty acid ester

Abstract

Provided is a method for preparing a lower unsaturated fatty acid ester, which comprises carrying out an aldol condensation reaction between dimethoxymethane (DMM) and a lower acid or ester with a molecular formula of R.sub.1CH.sub.2COOR.sub.2 on an acidic molecular sieve catalyst in an inert atmosphere to obtain a lower unsaturated fatty acid or ester(CH.sub.2C(R.sub.1)COOR.sub.2), wherein R.sub.1 and R.sub.2 are groups each independently selected from the group consisting of H and C.sub.1-C.sub.4 saturated alkyl group.

Claims

1. A method for preparing a lower unsaturated fatty acid or ester, comprising carrying out an aldol condensation reaction between dimethoxymethane and an acid or ester with a molecular formula of R.sub.1CH.sub.2COOR.sub.2 in a reactor loaded with an acidic molecular sieve catalyst to obtain the corresponding lower unsaturated fatty acid or ester, wherein R.sub.1 and R.sub.2 are each independently selected from H, CH.sub.3, CH.sub.3CH, CH.sub.3(CH.sub.2).sub.2 and CH.sub.3(CH.sub.2).sub.3; wherein the acidic molecular sieve catalyst is selected from the group consisting of a SAPO-34 molecular sieve, a DNL-6 molecular sieve, a ZSM-35 molecular sieve, a ZSM-5 molecular sieve, a MOR molecular sieve, a Y molecular sieve, a eta molecular sieve, a MCM-22 molecular sieve and a combination thereof; and the aldol condensation reaction takes place in a moving bed reactor.

2. The method according to claim 1, wherein R.sub.1 and R.sub.2 are each selected from H and CH.sub.3.

3. The method according to claim 1, wherein the acidic molecular sieve catalyst is selected from the group consisting of a silica-alumina molecular sieve, an aluminum phosphate molecular sieve and combinations thereof.

4. The method according to claim 3, wherein the silica-alumina molecular sieve in the acidic molecular sieve catalyst has an atomic ratio of silicon to aluminum in a range of 1.sup.50:1.

5. The method according to claim 3, wherein the silica-alumina molecular sieve in the acidic molecular sieve catalyst has an atomic ratio of silicon to aluminum in a range of 2.sup.25:1.

6. The method according to claim 3, wherein the acidic molecular sieve catalyst is further modified by a metal element other than the framework constituent elements of the molecular sieve.

7. The method according to claim 6, wherein the metal element is selected from the group consisting of potassium, cesium, copper and combinations thereof.

8. The method according to claim 7, wherein the metal element is introduced into the acidic molecular sieve catalyst by in-situ synthesis, metal ion exchange or impregnation.

9. The method according to claim 8, wherein the weight percentage of the metal element calculated by metal elementary substance is in a range from 0.01 wt % to 10.0 wt %, based on the total weight of the acidic molecular sieve catalyst.

10. The method according to claim 1, wherein the acidic molecular sieve catalyst comprises a binder selected from the group consisting of alumina, silica, zirconia, magnesia and combinations thereof.

11. The method according to claim 10, wherein the content of the binder is in a range from 0 wt % to 50 wt % excluding 0 wt %, based on the total weight of the acidic molecular sieve catalyst.

12. The method according to claim 1, wherein the molar ratio of dimethoxymethane to the acid or ester is in a range from 1/20 to 5/1; the total mass space velocity of raw materials in the aldol condensation reaction is in a range from 0.05 h.sup.1 to 10.0 h.sup.1; the reaction temperature is in a range from 200 C. to 400 C.; and the reaction pressure is in a range from 0.2 MPa to 15.0 MPa.

13. The method according to claim 12, wherein the molar ratio of dimethoxymethane to the acid or ester is in a range from 1/10 to 2/1; the total mass space velocity of raw materials in the aldol condensation reaction is in a range from 0.3 h.sup.1 to 2.0 h.sup.1; the reaction temperature is in a range from 250 C. to 350 C.; and the reaction pressure is in a range from 0.2 MPa to 5.0 MPa.

14. The method according to claim 1, wherein the aldol condensation reaction is carried out in an atmosphere comprising a gas selected from the group consisting of N.sub.2, He, Ar, CH.sub.4, C.sub.2H.sub.6, H.sub.2, CO, CO.sub.2 and combinations thereof.

15. The method according to claim 3, wherein the acidic molecular sieve catalyst comprises a binder selected from the group consisting of alumina, silica, zirconia, magnesia and combinations thereof.

16. The method according to claim 9, wherein the acidic molecular sieve catalyst comprises a binder selected from the group consisting of alumina, silica, zirconia, magnesia and combinations thereof.

Description

DETAILED DESCRIPTION OF THE EMBODIMENT

(1) The present invention provides carrying out an aldol condensation reaction between an acid or ester with a molecular formula of R.sub.1CH.sub.2COOR.sub.2 and dimethoxymethane (DMM) in a reactor loaded with an acidic molecular sieve to prepare a lower unsaturated fatty acid or ester (CH.sub.2C(R.sub.1)COOR.sub.2), wherein R.sub.1 and R.sub.2 are groups each independently selected from the group consisting of H, CH.sub.3, CH.sub.3CH.sub.2, CH.sub.3(CH.sub.2).sub.2 and CH.sub.3(CH.sub.2).sub.3, etc.

(2) In a specific embodiment, the present invention provides a method for preparing acrylic acid and its esters by an aldol condensation of methyl acetate and dimethoxymethane on an acidic molecular sieve catalyst.

(3) Preferably, the silica-alumina molecular sieve in the acidic molecular sieve catalyst used in the present invention has an atomic ratio of silicon to aluminum in a range from 1 to 50, more preferably from 2.5 to 25.

(4) Preferably, the acidic molecular sieve catalyst further comprises one or more metal elements selected from the group consisting of potassium, cesium and copper; the metal element is introduced into the acidic molecular sieve catalyst by in-situ synthesis, metal ion exchange or impregnation; preferably, the weight percent of the metal element calculated by metal elementary substance is 0.01 wt % to 10.0 wt %, based on the total weight of the acidic molecular sieve catalyst.

(5) Preferably, the acidic molecular sieve catalyst used in the present invention comprises any one selected from the group consisting of alumina, silica, zirconia and magnesia or a combination thereof as a binder; preferably, the content of the binder is in a range from 0 wt % to 50 wt %, based on the total weight of the acidic molecular sieve catalyst.

(6) Preferably, the lower fatty acid ester used in the present invention is methyl acetate, and acrylic acid and methyl acrylate are obtained after the aldol condensation reaction.

(7) Preferably, the aldol condensation reaction used in the present invention is carried out under the following conditions: a temperature in a range from 200 C. to 400 C.; a reaction pressure in a range from 0.2 MPa to 5.0 MPa; a total mass space velocity of raw materials in a range from 0.3 h.sup.1 to 2.0 h.sup.1.

(8) Preferably, the aldol condensation reactor used in the present invention is a fixed bed reactor, a fluidized bed reactor or a tank reactor.

(9) Preferably, the aldol condensation reaction is carried out in an atmosphere comprising any one of N.sub.2, He, Ar, CH.sub.4, C.sub.2H.sub.6, H.sub.2, CO and CO.sub.2 or a combination thereof.

(10) Furthermore, although it is not particularly limited, in a preferred aldol condensation reaction, the molar ratio of dimethoxymethane to methyl acetate is in a range from 1/10 to 2/1.

EXAMPLES

(11) The present invention is described in detail below by means of examples, but the present invention is not limited to these examples.

(12) The aluminum phosphate molecular sieves DNL-6 and SAPO-34 were produced and supplied by the Dalian Institute of Chemical Physics according to the methods reported in Microporous and Mesoporous Materials 144 (2011) 113-119 and Microporous and Mesoporous Materials 111 (2008) 143-149, respectively; the remaining molecular sieves and the related raw materials were purchased commercially.

(13) The analytical methods and conditions in the examples of the present application are as follows:

(14) The raw materials and products were tested online by Agilent's Aligent 7890A gas chromatograph using Agilent's FFAP capillary column.

(15) According to an embodiment of the present application, a fixed bed reactor was used, the total mass space velocity of the raw materials was in a range from 0.3 h.sup.1 to 2.0 h.sup.1, the reaction temperature was in a range from 200 C. to 400 C., and the reaction pressure was in a range from 0.2 MPa to 5.0 MPa. The raw materials entered the reactor in the following way:

(16) The raw materials of methyl acetate and dimethoxymethane were thermostated in a water bath (20 C.) and bubbled through nitrogen N.sub.2, the saturated steam carrying the raw materials entered the fixed bed reactor, and the amount of substance of the raw materials entering the reactor might be adjusted according to the flow rate of nitrogen. The saturated vapor pressure of the raw materials under different temperature conditions can be calculated by the following formula:
lgP*=AB/(t+C)

(17) Among them, A, B and C represent respectively the physical property parameters of different raw materials, which can be found in the Lange's Handbook of Chemistry, and t represents temperature. This allows the calculation for the saturated vapor pressure of the raw materials at any temperature. The amount of substance of the raw materials entering the reactor per unit time can be calculated by the saturated vapor pressure.
The conversion rate of dimethoxymethane=[(the molar number of dimethoxymethane in the feed)(the molar number of dimethoxymethane in the discharge)]+(the molar number of dimethoxymethane in the feed)(100%)
The conversion rate of methyl acetate=[(the molar number of methyl acetate in the feed)(the molar number of methyl acetate in the discharge)]+(the molar number of methyl acetate in the feed)(100%)
The selectivity of acrylic acid and methyl acrylate=(the molar number of carbon in acrylic acid and methyl acrylate in the discharge)+(the total molar number of carbon in all productsthe molar number of carbon in dimethyl ether)(100%)

(18) The products in the examples of the present application contain a large amount of dimethyl ether, which might be recycled in industry to replenish raw materials, and therefore, the dimethyl ether product was not considered in calculating the selectivity.

1 Preparation Example of Catalyst

1.1 Aluminum Phosphate Molecular Sieve

(19) SAPO-34 and DNL-6 were prepared by the Dalian Institute of Chemical Physics in accordance with the hydrothermal method. The raw powders were calcined at 550 C. for 4 hours, and extruded to obtain 1 # and 2 # catalysts of 20-40 mesh for use, respectively.

1.2 Silica-Alumina Molecular Sieve

(20) 100 g of NaY, Na-MOR, Beta and Na-ZSM-5 molecular sieves after calcination, with an atomic ratio of silicon to aluminum of 2.5, 6.5, 20 and 21.5 respectively, were exchanged three times with 0.5 mol/L aqueous ammonium nitrate solution respectively (2 hours for each time), washed with deionized water, dried, and calcined at 550 C. for 4 hours to obtain a hydrogen type Y molecular sieve, a hydrogen type MOR molecular sieve, a hydrogen type Beta molecular sieve and a hydrogen type ZSM-5 molecular sieve, which were extruded to obtain 3 #, 4 #, 5 # and 6 # catalysts of 20-40 mesh, respectively.

1.3 Molding of Hydrogen Type MOR Silica-Alumina Molecular Sieve

(21) 80 g Na-MOR molecular sieve with a atomic ratio of silicon to aluminum of 6.5, 28 g pseudo-boehmite and 10% dilute nitric acid were mixed homogeneously and extruded for molding, then calcined at 550 C. for 4 hours, exchanged with 0.5 mol/L ammonium nitrate for three times (2 hours for each time), washed with deionized water, dried, and calcined at 550 C. for 4 hours to obtain 7 # catalyst.

(22) 80 g Na-MOR molecular sieve with a atomic ratio of silicon to aluminum of 6.5, 20 g pseudo-boehmite and 10% dilute nitric acid were mixed homogeneously and extruded for molding, then calcined at 550 C. for 4 hours, exchanged with 0.5 mol/L ammonium nitrate for three times (2 hours for each time), washed with deionized water, dried, and calcined at 550 C. for 4 hours to obtain 8 # catalyst.

(23) 80 g Na-MOR molecular sieve with a atomic ratio of silicon to aluminum of 6.5, 50 g pseudo-boehmite and 10% dilute nitric acid were mixed homogeneously and extruded for molding, then calcined at 550 C. for 4 hours, exchanged with 0.5 mol/L ammonium nitrate for three times (2 hours for each time), washed with deionized water, dried, and calcined at 550 C. for 4 hours to obtain 9 # catalyst.

1.4 Loaded Type M/ZSM-5 Catalyst

(24) The loaded type M/ZSM-5 catalysts were prepared by the equal volume impregnation method. 2.02 g of KNO.sub.3, 3.24 g of Cs.sub.2CO.sub.3 and 1.88 g of Cu(NO.sub.3).sub.2 were each dissolved in 18 ml of deionized water to prepare the corresponding aqueous nitrate solutions. 20 g of 6 # catalyst was added to each of the above salt solutions, stood for 24 hours, then separated, and washed with deionized water. The obtained samples were dried in an oven at 120 C. for 12 hours. The dried samples were placed in a muffle furnace, heated to a treatment temperature of 550 C. with a heating rate of 2 C./min and calcined for 4 h to obtain 10 #, 11 # and 12 # catalysts, respectively.

2 Synthesis Example

2.1 Aldol Condensation Reaction on Different Molecular Sieves

(25) 1 # to 12 # acidic molecular sieves with different topologies were pressed under a pressure of 40 MPa, and particles of 20-40 mesh were screened for testing. The molecular sieve catalyst was packed in a fixed bed reactor, and the catalyst was preactivated under the following conditions: the N.sub.2 flow rate was 30 ml/min, and the temperature was raised to 500 C. at a heating rate of 2 C./min and kept at 500 C. for 1 hour. Then the temperature was lowered to the desired reaction temperature of 350 C. at a nitrogen atmosphere, the pressure of the reaction system was raised to 3 MPa with nitrogen, the molar ratio of dimethoxymethane to methyl acetate was 2/1, and the total mass space velocity of raw materials was 0.3 h.sup.1. The results of the aldol condensation reaction under these conditions are shown in Table 1.

(26) TABLE-US-00001 TABLE 1 Evaluation results of catalysts for aldol condensation reaction of methyl acetate and dimethoxymethane The conversion The conversion The selectivity of rate of rate of acrylic acid and methyl acetate dimethoxymethane its esters Catalyst (%) (%) (%) 1# 19.8 99.4 0.6 2# 26.4 100.0 0.3 3# 51.8 100.0 1.0 4# 17.7 65.4 4.0 5# 53.6 100.0 3.7 6# 28.0 95.1 43.5 7# 16.6 72.3 6.2 8# 25.4 67.2 8.6 9# 13.2 58.7 6.7 10# 38.8 100.0 20.1 11# 57.6 100.0 30.8 12# 40.6 95.7 12.4

2.2 Aldol Condensation Reaction Results at Different Reaction Temperatures

(27) 0.5 g of 6 # catalyst was added into a fixed-bed reactor with an inner diameter of 8 mm, and the temperature was raised to 500 C. at a heating rate of 2 C./min under nitrogen atmosphere and was kept at 500 C. for 1 hour. Then the temperature was lowered to the desired reaction temperature under nitrogen atmosphere, and the pressure of the reaction system was raised to 3 MPa with nitrogen. The reaction raw materials were introduced into the reactor from top to bottom. The molar ratio of dimethoxymethane to methyl acetate was 2/1, and the total mass space velocity of raw materials was 0.3h.sup.1. The results of aldol condensation reaction at different reaction temperatures are shown in Table 2.

(28) TABLE-US-00002 TABLE 2 Evaluation results of aldol condensation reaction at different reaction temperatures The conversion The conversion The selectivity of Reaction rate of rate of acrylic acid and temperature/ methyl acetate dimethoxymethane its esters C. (%) (%) (%) 230 23.4 100.0 0.0 260 11.7 96.3 0.0 290 12.8 96.3 9.7 320 16.4 96.0 29.4 350 28.0 95.1 43.5 380 34.9 94.0 54.7 410 40.2 92.7 51.3

2.3 Aldol Condensation Reaction Results Under Different Reaction Pressures

(29) 0.5 g of 6 # catalyst was added into a fixed-bed reactor with an inner diameter of 8 mm, and the temperature was raised to 500 C. at a heating rate of 2 C./min under nitrogen atmosphere and was kept at 500 C. for 1 hour. Then the temperature was lowered to 350 C. under nitrogen atmosphere, and the pressure of the reaction system was raised to the pressure required for the reaction with nitrogen. The reaction raw materials were introduced into the reactor from top to bottom. The molar ratio of dimethoxymethane to methyl acetate was 2/1, and the total mass space velocity of raw materials was 0.3 h.sup.1. The results of aldol condensation reaction at different reaction pressures are shown in Table 3.

(30) TABLE-US-00003 TABLE 3 Results of aldol condensation reaction on acidic molecular sieves at different reaction pressures Reaction pressure (MPa) 0.2 3 5 The conversion rate of 100.0 95.1 90.2 dimethoxymethane (%) The conversion rate of methyl 12.5 28.0 31.2 acetate (%) The selectivity of acrylic acid and 9.4 43.5 47.5 methyl acrylate (%)

2.4 Aldol Condensation Reaction Results at Different Molar Ratios of Dimethoxymethane to Methyl Acetate

(31) 0.5 g of 6 # catalyst was added into a fixed-bed reactor with an inner diameter of 8 mm, and the temperature was raised to 500 C. at a heating rate of 2 C./min under nitrogen atmosphere and was kept at 500 C. for 1 hour. Then the temperature was lowered to 350 C. under nitrogen atmosphere, and the pressure of the reaction system was raised to the pressure of 3 MPa required for the reaction with nitrogen. The reaction raw materials were introduced into the reactor from top to bottom. The total mass space velocity of raw materials was 0.3 h.sup.1. The molar ratios of dimethoxymethane to methyl acetate were 2/1, 1/1 and 1/10, and the results of the aldol condensation reaction are shown in Table 4.

(32) TABLE-US-00004 TABLE 4 Results of aldol condensation reaction at different molar ratios of dimethoxymethane to methyl acetate The molar ratio of dimethoxymethane to methyl acetate 2/1 1/1 1/10 The conversion rate of 95.1 98.4 100.0 dimethoxymethane (%) The conversion rate of 28.0 20.3 18.7 methyl acetate (%) The selectivity of acrylic 43.5 50.9 38.6 acid and methyl acrylate (%)

2.5 Aldol Condensation Reaction Results Under Dimethoxymethane with Different Fatty Acid Esters on Acidic Molecular Sieves

(33) 0.5 g of 6 # catalyst was added into a fixed-bed reactor with an inner diameter of 8 mm, and the temperature was raised to 500 C. at a heating rate of 2 C./min under nitrogen atmosphere and was kept at 500 C. for 1 hour. Then the temperature was lowered to 350 C. under nitrogen atmosphere, and the pressure of the reaction system was raised to the pressure of 3 MPa required for the reaction with nitrogen. The reaction raw materials were introduced into the reactor from top to bottom. The total mass space velocity of raw materials was 0.3 h.sup.1, and the molar ratio of dimethoxymethane to different fatty acid esters was 2/1. The results of aldol condensation reaction are shown in Table 5.

(34) TABLE-US-00005 TABLE 5 Results of aldol condensation reaction under dimethoxymethane with different fatty acid esters on acidic molecular sieves The conversion The conversion The selectivity rate of rate of of unsaturated fatty acid ester dimethoxymethane fatty acid ester R.sub.1 R.sub.2 (%) (%) (%) H CH.sub.3 28.0 95.1 43.5 H H 35.7 99.5 51.3 CH.sub.3 H 15.6 90.1 31.2

2.6 Aldol Condensation Reaction Results Under Different Mass Space Velocities of Raw Materials

(35) 6 # catalyst was used, the reaction temperature was 350 C., the total mass space velocities of raw materials were 0.3 h.sup.1, 1.0 h.sup.1 and 2.0 h.sup.1, and the other conditions were the same as those in Example 2.1. The reaction results are shown in Table 6.

(36) TABLE-US-00006 TABLE 6 Results of aldol condensation reaction under different mass space velocities of raw materials The total mass space velocity of raw materials (h.sup.1) 0.3 1.0 2.0 The conversion rate of 95.1 98.4 100.0 dimethoxymethane (%) The conversion rate of 28.0 40.1 56.3 methyl acetate (%) The selectivity of acrylic 43.5 50.9 38.6 acid and methyl acrylate (%)

2.7 Reaction Results Under Different Reactor Types

(37) 7 # catalyst was used, the reaction temperature was 350 C., the reactors were a fluidized bed reactor and a moving bed reactor respectively, and the other conditions were the same as those in Example 2.1. The reaction results are shown in Table 7.

(38) TABLE-US-00007 TABLE 7 Results of aldol condensation reaction on acidic molecular sieves under different reactor types Reactor type Fixed bed Moving bed The conversion rate of 72.3 80.1 dimethoxymethane (%) The conversion rate of methyl 16.6 11.2 acetate (%) The selectivity of acrylic acid and 6.2 8.9 methyl acrylate (%)

2.8 Reaction Results Under Different Reaction Atmospheres

(39) 10 # catalyst was used, the reaction temperature was 350 C., the reaction atmospheres were N.sub.2, H.sub.2, He and CO, respectively, and the other conditions were the same as those in Example 2.1. The reaction results are shown in Table 8.

(40) TABLE-US-00008 TABLE 8 Results of aldol condensation reaction on acidic molecular sieves under different reaction atmospheres Reaction atmosphere N.sub.2 H.sub.2 He CO The conversion rate of 100.0 100.0 100.0 100.0 dimethoxymethane (%) The conversion rate of 38.8 58.6 35.6 12.5 methyl acetate (%) The selectivity of acrylic 30.8 10.9 29.7 6.8 acid and methyl acrylate (%)

(41) The present invention has been described in detail as above. However, the present invention is not limited to the specific embodiments as mentioned herein. It will be understood that any other variations and modifications may be made by those skilled in the art without departing from the scope of the present invention. The scopes of the present invention are limited by the claims as appended.