Process for preparing acrylic acid using an alkali metal-free and alkaline earth metal-free zeolitic material

Abstract

A process for preparing acrylic acid, comprising (i) providing a stream S4 comprising a formaldehyde source and acetic acid; (ii) contacting stream S4 with an aldol condensation catalyst comprising a zeolitic material comprising aluminum in the framework structure to obtain a stream S6 comprising acrylic acid, the framework structure of the zeolitic material in (ii) comprising YO.sub.2 and Al.sub.2O.sub.3, and Y being a tetravalent element; where the total content of alkali metal and alkaline earth metal in the zeolitic material in (ii), calculated as alkali metal oxide and alkaline earth metal oxide, is from 0% to 0.1% by weight, based in each case on the total weight of the zeolitic material, and where the aldol condensation catalyst in (ii) comprises, outside the framework structure of the zeolitic material present therein, from 0% to 1% by weight of vanadium, based on vanadium as vanadium(V) oxide.

Claims

1. A process for preparing acrylic acid, the process comprising contacting a stream comprising a formaldehyde source and acetic acid with an aldol condensation catalyst comprising a zeolitic material having a framework structure comprising aluminum to obtain a stream comprising acrylic acid, wherein the framework structure of the zeolitic material comprises YO.sub.2, X.sub.2O.sub.3 and Al.sub.2O.sub.3, wherein Y is a tetravalent element; and X is a trivalent element other than aluminum, a total content of alkali metal and alkaline earth metal in the zeolitic material calculated as alkali metal oxide (M.sub.2O) and alkaline earth metal oxide (MO), is from 0% to 0.1% by weight, based on a total weight of the zeolitic material, and the aldol condensation catalyst further comprises from 0% to 1% by weight of vanadium, calculated as vanadium(V) oxide and based on a total weight of the aldol condensation catalyst.

2. The process according to claim 1, wherein the zeolitic material is a silicoaluminophosphate (SAPO) material or an aluminophosphate (APO) material.

3. The process according to claim 1, wherein Y is at least one tetravalent element selected from the group consisting of Si, Sn, Ti, Zr, Ge, and V.

4. The process according to claim 1, wherein X is at least one trivalent element selected from the group consisting of B, In, Ga, a transition metal of groups 3 to 12.

5. The process according to claim 1, wherein the zeolitic material is at least partly in an H form.

6. The process according to claim 5, wherein a molar NH.sub.4.sup.+:(Al+X) ratio of the zeolitic material, when the zeolitic material is saturated with NH.sub.3, is from 0.01:1 to 1:1.

7. The process according to claim 1, wherein the zeolitic material comprises at least one non-framework element Z selected from the group consisting of Ti, Zr, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Zn, Ga, Ge, In, Sn, Pb, P, N, and S and any combination thereof.

8. The process according to claim 7, wherein the at least one non-framework element Z is selected from the group consisting of N, P and S, wherein the at least one non-framework element is present at least partly in an oxidic form.

9. The process according to claim 1, wherein the zeolitic material has a structure selected from the group consisting of BEA, MFI, MWW, FAU, MEL, MTN, RRO, CDO LTL, MOR, AFI, FER, LEV and any combination thereof.

10. The process according to claim 1, wherein the aldol condensation catalyst further comprises a binder material.

11. The process according to claim 1, wherein the aldol condensation catalyst is in a form of shaped bodies, is in a star shape, is in a tablet form, is in a form of spheres, or is in a form of hollow cylinders.

12. The process according to claim 1, wherein the contacting is effected at a temperature of from 200 to 400 C.

13. The process according to claim 1, wherein a space-time yield in the contacting is from 0.01 to 2.5 kg/kg/h, and the space-time yield is defined as kg(acrylic acid)/kg(aldol condensation catalyst)/h.

14. The process according to claim 1, wherein the formaldehyde source is an anhydrous formaldehyde source.

15. The process according to claim 1, wherein a temperature-programmed desorption with NH.sub.3 (NH.sub.3-TPD) of the zeolitic material has a desorption spectrum with a desorption maximum within at least one of temperature ranges of from 0 to 250 C., from 251 to 500 C., or from 501 to 700 C., and following deconvolution of the desorption spectrum, the desorption maximum in the temperature range of 0 to 250 C. has a concentration of desorbed NH.sub.3 in a range of from 0.05 to 2.0 mmol/g, the desorption maximum in the temperature range of 251 to 500 C. has a concentration of desorbed NH.sub.3 in a range of from 0.05 to 1.5 mmol/g, and the desorption maximum in the temperature range of 501 to 700 C. has a concentration of desorbed NH.sub.3 in a range of from 0.001 to 0.5 mmol/g, wherein the concentration of desorbed NH.sub.3 is defined as mmol(desorbed NH.sub.3)/g(zeolitic material).

Description

DESCRIPTION OF THE FIGURE

(1) FIG. 1 shows the temperature-programmed desorption (NH.sub.3-TPD) which was obtained for the zeolitic material according to example 3. Plotted on the abscissa is the temperature in C., with explicitly stated values, from left to right, of 100; 150; 200; 250; 300; 350; 400; 450; 500; 550 and 600, and on the ordinate the concentration of the desorbed NH.sub.3, measured by means of a thermal conductivity detector, with explicitly stated values, from the bottom upward, of 0.8; 0.9; 1.0; 1.1; 1.2; 1.3 and 1.4. On the curve itself, from left to right, the temperature values, in C., of 212.5 (maximum); 326.1 (shoulder) and 601.4 (last value).

(2) The present invention will now be illustrated further by the examples and comparative examples which follow.

EXAMPLES

I. Analytical Methods

(3) I.1 NH.sub.3-TPD

(4) The temperature-programmed desorption of ammonia (NH.sub.3-TPD) was conducted in an automated chemisorption analysis unit (Micromeritics AutoChem II 2920) having a thermal conductivity detector. Continuous analysis of the desorbed species was accomplished using an online mass spectrometer (OmniStar QMG200 from Pfeiffer Vacuum). The sample (0.1 g) was introduced into a quartz tube and analyzed using the program described below. The temperature was measured by means of an Ni/Cr/Ni thermocouple immediately above the sample in the quartz tube. For the analyses, He of purity 5.0 was used. Before any measurement, a blank sample was analyzed for calibration.

(5) 1. Preparation

(6) Commencement of recording; one measurement per second. Wait for 10 minutes at 25 C. and a He flow rate of 30 cm.sup.3/min (room temperature (about 25 C.) and 1 atm); heat up to 600 C. at a heating rate of 20 K/min; hold for 10 minutes. Cool down under a He flow (30 cm.sup.3/min) to 100 C. at a cooling rate of 20 K/min (furnace ramp temperature); Cool down under a He flow (30 cm.sup.3/min) to 100 C. at a cooling rate of 3 K/min (sample ramp temperature).
2. Saturation with NH.sub.3 Commencement of recording; one measurement per second. Change the gas flow to a mixture of 10% NH.sub.3 in He (75 cm.sup.3/min; 100 C. and 1 atm) at 100 C.; hold for 30 minutes.
3. Removal of the excess Commencement of recording; one measurement per second. Change the gas flow to a He flow of 75 cm.sup.3/min (100 C. and 1 atm) at 100 C.; hold for 60 minutes.
4. NH.sub.3-TPD Commencement of recording; one measurement per second. Heat up under a He flow (flow rate: 30 cm.sup.3/min) to 600 C. at a heating rate of 10 K/min; hold for 30 minutes.
5. End of measurement

(7) Desorbed ammonia was measured by means of the online mass spectrometer, which demonstrates that the signal from the thermal conductivity detector was caused by desorbed ammonia. This involved utilizing the m/z=16 signal from ammonia in order to monitor the desorption of the ammonia. The amount of ammonia adsorbed (mmol/g of sample) was ascertained by means of the Micromeritics software through integration of the TPD signal with a horizontal baseline.

(8) I.2 Gas Chromatography

(9) The analysis of the gaseous product stream was conducted by means of an online GC-MS system from Agilent. The instrument was equipped with a 10-way valve having two sample loops (500 microliters/1000 microliters) which were operated at 220 C. The detection was effected with the aid of a flame ionization detector (FID) and two thermal conductivity detectors. For the FID flow rate supplied through the front inlet, the following parameters were chosen: injector temperature: 275 C.; split: 1:5. An FFAP column having length 30 m, internal diameter 0.32 mm and film thickness 0.5 micrometer (column flow rate: 5 mL/min) was used. The thermal conductivity detectors were supplied with the sample through the rear inlet in parallel by means of a Y adapter (JAS). Here, the following parameters were chosen: injector temperature: 275 C.; split: 1:2. For the first thermal conductivity detector, a column of the Volamine type having a length of 60 m, an internal diameter of 0.32 mm and a film thickness of 0.45 micrometer (column flow rate: 2 mL/min) was used. The second thermal conductivity detector had a column system with two columns. First column: RTX5 having a length of 30 m, an internal diameter of 0.32 mm, a film thickness of 1 micrometer (column flow rate: 5 mL/min). Second column: select permanent gases/CO.sub.2 HR having a length of 50 m, an internal diameter of 0.32 mm, a film thickness of 10 micrometers (column flow rate: 2 mL/min). All columns were operated with helium as carrier gas. The GC oven temperature program was as follows: 40 C. (hold time 2.5 min) heating to 105 C. at a heating rate of 20 K/min (hold time 0 min) heating to 225 C. at a heating rate of 40 K/min (hold time 2.75 min)
I.3 FTIR Spectroscopy

(10) The IR measurements were effected on a Nicolet 6700 spectrometer. The zeolitic material was compressed to a pellet without the addition of additives. The pellet was introduced into the high-vacuum cell of the IR spectrometer. Before the measurement, the sample was pretreated under high vacuum (10.sup.5 mbar) at 300 C. for 3 h. The spectra were recorded after the cell had been cooled down to 50 C. The spectra were recorded within a range from 4000 cm.sup.1 to 800 cm.sup.1 at a resolution of 2 cm.sup.1. The spectra obtained were shown by a plot with the wavelength on the abscissa and the absorption (in arbitrary units) on the ordinate. For quantitative evaluation of the signal intensities and the ratio of the signals, a baseline correction was undertaken.

(11) I.4 Water absorption

(12) The isotherms with respect to the water adsorption/desorption were measured on a VTI SA instrument from TA Instruments. The experiment consisted of one pass or a series of passes of a sample which was introduced into the weighing pan of the microbalance within the instrument. Prior to the measurement, the residual moisture was removed from the sample by heating to 100 C. (heating rate 5 K/min) and holding it at this temperature in a nitrogen stream for 6 h. After drying, the temperature in the cell was lowered to 25 C. and kept isothermal during the measurements. The microbalance was calibrated, and the weight of the dried sample served as reference value (maximum deviation in mass: 0.01% by weight). The water absorption of the sample was determined from its increase in weight compared to the dry sample. First of all, an adsorption curve was recorded with increasing relative humidity (RH; in % by weight of water in the atmosphere within the measurement cell) to which the sample was exposed, and the water absorption of the sample was measured at equilibrium. The relative humidity was increased in steps of 10 percentage points by weight from 5% to 85%. In each step, the system checked the relative humidity, recorded the weight of the sample until attainment of equilibrium conditions, and also recorded the water absorption. The total amount of water that the sample absorbed was determined by exposing the sample to a relative humidity of 85% by weight. During the desorption measurement, the relative humidity was reduced in steps of 10 percentage points from 85% by weight to 5% by weight. The change in weight of the sample (water absorption) was monitored and recorded.

II. Production of the Zeolitic Materials

II.1 Example 1

(13) 30.01 g of zeolitic material (CP814E, from Zeolyst; NH.sub.4.sup.+ form; Na.sub.2O: 0.05% by weight) were mixed with 0.928 g of graphite and tableted (Korsch XP1, 13 mm die, upper setting wheel: 6.5 mm, lower setting wheel: 7.0 mm, 15 kN; resulting tablet height: 1 mm). Then the tableted mixture was comminuted, so as to obtain a powder having a particle diameter in the range from 0.315 mm to 0.500 mm. The material obtained was brought to 500 C. (heating rate 1 K/min) and converted to the H form at 500 C. in a nitrogen stream (0.4 L/min) for 2 h.

II.2 Example 2

(14) 29.15 g of zeolitic material (CP814C, from Zeolyst, NH.sub.4.sup.+ form; Na.sub.2O: 0.05% by weight) were mixed with 0.901 g of graphite and tableted (Korsch XP1, 13 mm die, upper setting wheel: 6.5 mm, lower setting wheel: 7.0 mm, 15 kN; resulting tablet height: 1 mm). Then the tableted mixture was comminuted, so as to obtain a powder having a particle diameter in the range from 0.315 mm to 0.500 mm. The material obtained was brought to 500 C. (heating rate 1 K/min) and converted to the H form at 500 C. in a nitrogen stream (0.4 L/min) for 2 h.

II.3 Example 3

(15) The material obtained from example II.2 was mixed with 3% by weight of graphite and tableted (Korsch XP1, 13 mm die, 35 kN). Then the tableted mixture was comminuted, so as to obtain a powder having a particle diameter in the range from 0.315 mm to 0.500 mm.

(16) Subsequently, water absorption of the material thus obtained was determined by stepwise addition of small portions of water until attainment of the maximum amount of water absorbable by the material.

(17) Based on the water absorption of the material thus determined, an aqueous (NH.sub.4)H.sub.2(PO.sub.4) impregnating solution was prepared; the concentration and amount of the impregnating solution were chosen such that, in the subsequent contacting with the tableted and comminuted material, assuming complete absorption of the impregnating solution by the material, a P content of 4.2% by weight, based on the resulting material, was obtained.

(18) The tableted and comminuted material and the impregnating solution described were contacted with one another, so as to obtain, for the material, a P content of 4.2% by weight, based on the resulting material.

(19) The material thus obtained was aged under air at room temperature for 30 min and then blanketed with liquid nitrogen. The material thus shock-frozen was dried at 10 C. and 2.56 mbar for 16 h. Subsequently, the material was brought to 500 C. (heating rate 1 K/min) and calcined at 500 C. under air for 2 h.

II.4 Comparative Examples

(20) In addition, the following commercially available zeolitic materials were used:

(21) TABLE-US-00001 TABLE 1 Materials used in the comparative examples, corresponding manufacturers, product name, molar SiO.sub.2:Al.sub.2O.sub.3 ratio and Na.sub.2O content in % by weight Compar- Molar Na.sub.2O ative ratio content/ % example Manufacturer Product name SiO.sub.2:Al.sub.2O.sub.3 by weight C1 Zeochem ZEOcat PB (Na- 20 0.6 Beta) C2 Zeochem ZEOcat PZ 400 0.7 2/400 (Na-ZSM-5) C3 Zeochem ZEOcat FM-8 12 6.8 (Na-Mor) C4 Zeolyst NH.sub.4-MFI 30 30 0.05 (CBV3024E)

III. Catalytic Studies

(22) A stream consisting of trioxane (6.3% by volume; Sigma-Aldrich, 1,3,5-trioxane, 99%), acetic acid (83.7% by volume; PanReac AppliChem, acetic acid 100% for analysis C, A0820) and argon (10% by volume; 5.0 purity) was heated to 200 C. and hence evaporated (acetic acid:formaldehyde equivalents=4.4:1).

(23) The gaseous mixture was then contacted with a pulverulent aldol condensation catalyst according to examples 1 to 3 and the comparative examples at 260 or 290 C. and 1.1 bar (GHSV: 200 h.sup.1).

(24) The temperature was measured at the start of the experiment by means of a thermocouple in the isothermal zone of the reactor, i.e. of the catalyst bed, and corresponds to the temperature at which the reactions were conducted. The product stream was subsequently diluted with nitrogen (purity: 5.0) (N.sub.2: product stream=22:1), and the composition was determined by gas chromatography.

(25) The data shown below show the averaged result, the process according to the invention having been conducted for 6 h. Tables 2 and 3 show the results of the process according to the invention; tables 4 and 5 show the analogous data, with use here of the commercially available zeolitic materials detailed under 11.2 as aldol condensation catalyst.

(26) The analytical data for the zeolitic materials according to examples 1 to 3 are shown in table 6.

(27) TABLE-US-00002 TABLE 2 Catalytic results of the inventive examples at a temperature of 290 C. Zeolitic material Carbon AA AA STY/ according conversion/ yield/ selectivity/ kg/kg(cat.)/ to ex. %.sup.(2) %.sup.(3) %.sup.(4) h.sup.(5) 1 9.06 7.09 78.39 0.0965 1b.sup.(1) 10.10 8.25 81.60 0.1498 2 9.66 7.59 78.47 0.0794 3 9.27 8.05 86.24 0.0795 .sup.(1)Zeolitic material was produced as described in II and used directly; samples without addition of b were first subjected to an experiment at 260 C. (cf. table 2), regenerated under air at 350 C. for 24 h (10% by volume of argon, 2% by volume of oxygen, 88% by volume of nitrogen; GHSV: 2000 h.sup.1 ) and then used at 290 C. .sup.(2)The carbon conversion (C) is calculated by the following equation: C = 100 * (NC.sup.P.sub.sum/(NC.sup.E.sub.FA + NC.sup.E.sub.ES)) NC.sup.P.sub.sum = (NC.sup.E.sub.FA + NC.sup.E.sub.ES) (NC.sup.P.sub.FA + NC.sup.P.sub.ES); NC.sup.E.sub.FA = number of carbon atoms present in stream S4 in the form of a formaldehyde source; NC.sup.E.sub.ES = number of carbon atoms present in stream S4 in the form of acetic acid; NC.sup.P.sub.FA = number of carbon atoms present in product stream S6 in the form of a formaldehyde source; NC.sup.P.sub.ES = number of carbon atoms present in product stream S6 in the form of acetic acid; .sup.(3)The yield (Y) of acrylic acid is calculated by the following formula: Y = 100 * (NC.sup.P.sub.AS/(NC.sup.E.sub.FA + NC.sup.E.sub.ES)) NC.sup.P.sub.AS = number of carbon atoms present in product stream S6 in the form of acrylic acid. .sup.(4)The acrylic acid selectivity (S) is calculated by the following formula: S = 100 * (NC.sup.P.sub.AS/NC.sup.P.sub.sum). .sup.(5)The STY (space-time yield) represents the ratio of the mass flow rate of acrylic acid in stream S6 in [mass/time] to the mass of the aldol condensation catalyst in (ii) in [mass]; unit: [kg acrylic acid/kg aldol condensation catalyst/h]

(28) TABLE-US-00003 TABLE 3 Catalytic results of the inventive examples at a temperature of 260 C. Zeolitic material Carbon AA yield/ AA selectivity/ STY/ according to ex. conversion/% % % kg/kg(cat)/h 1 7.16 5.89 82.53 0.080 2 9.08 7.88 86.93 0.082 3 9.97 9.44 94.76 0.093

(29) TABLE-US-00004 TABLE 4 Catalytic results of the comparative examples at a temperature of 290 C. Zeolitic material Carbon AA yield/ AA selectivity/ STY/ according to ex. conversion/% % % kg/kg(cat)/h C1 5.01 3.22 64.24 0.0347 C2 5.10 4.65 91.10 0.0407 C3 3.20 0.77 24.10 0.0063 C4 7.18 5.26 77.39 0.0583

(30) TABLE-US-00005 TABLE 5 Catalytic results of the comparative examples at a temperature of 260 C. Zeolitic material Carbon AA yield/ AA selectivity/ STY/ according to ex. conversion/% % % kg/kg(cat)/h C1 5.74 5.29 92.26 0.057 C2 1.51 1.19 79.28 0.010 C3 6.20 0.45 7.84 0.004 C4 10.28 8.74 86.60 0.072

(31) TABLE-US-00006 TABLE 6 Analysis of examples 1 to 3 with regard to NH.sub.3-TPD, IR spectroscopy and water absorption Zeolitic NH.sub.3-TPD/ FTIR material mmol NH.sub.3/g cat. 3790 3690 3590 Water according 0 to >250 to >500 to to to to absorption/ to ex. 250 C. 500 C. 700 C. 3691 cm.sup.1 3591 cm.sup.1 3490 cm.sup.1 % 1 0.9440 0.3420 0.0180 X X 2 0.415 0.331 0.05 13.20 3 0.488 0.2 0.026 X X 19.40

(32) As can be inferred from the results, inventive examples 1 to 3 show, at a higher carbon conversion, a higher yield of acrylic acid and a higher space-time yield compared to all the comparative examples C1 to C4 at a temperature of 290 C. In addition, inventive examples 1 to 3 exhibit a higher acrylic acid selectivity at a temperature of 290 C. compared to comparative examples C1, C3 and C4.

(33) At a temperature of 260 C., inventive examples 1 to 3 show a higher carbon conversion than comparative examples C1 to C3. In addition, inventive example 3 shows a higher yield of acrylic acid than comparative examples C1 to C4, and inventive examples 1 and 2 show a higher yield of acrylic acid than comparative examples C1 to C3. In addition, inventive example 3 has a higher acrylic acid selectivity than comparative examples C1 to C4, while the value for inventive example 2 is above that for comparative examples C2 to C4 and that of inventive example 1 is above that of comparative examples C2 and C3. Finally, all the inventive examples 1 to 3 show a higher space-time yield at a temperature of 260 C. than the comparative examples C1 to C4.

(34) Therefore, the invention provides a process for preparing acrylic acid using a formaldehyde source and acetic acid as reactants, which, through the use of a zeolitic material which does not comprise any alkali metals and alkaline earth metals, gives better catalytic results, particularly with regard to carbon conversion, yield of acrylic acid and acrylic acid selectivity, and especially with regard to space-time yield.

(35) U.S. Provisional Patent Application No. 62/005,011, filed 30 May 2014, is incorporated into the present application by literature reference. With regard to the abovementioned teachings, numerous changes and deviations from the present invention are possible. It can therefore be assumed that the invention, within the scope of the appended claims, can be performed differently from the way described specifically herein.

LITERATURE CITED

(36) Vitcha and Sims, I & EC Product Research and Development, Vol. 5, No. 1, March 1966, pages 50 to 53 Wierzchowsky and Zatorski, Catalysis Letters 9 (1991), pages 411 to 414 DE 2010 040 921 A1 DE 2010 040 923 A1 US 2013/0085294 A1