PROCESS FOR THE DEHYDRATION OF OXYGENATED COMPOUNDS

Abstract

The present invention relates to a process for the dehydration of at least one oxygenated compound, preferably selected from saturated alcohols, unsaturated alcohols, diols, ethers, in the presence of at least one dehydration catalyst selected from cerium oxide (CeO.sub.2), aluminium oxide (γ-Al.sub.2O.sub.3), aluminium silicate, silica-aluminas (SiO.sub.2-Al.sub.2O.sub.3), aluminas, zeolites, sulfonated resins, ion-exchange resins, metal oxides (for example, lanthanum oxide, zirconium oxide, tungsten oxide, thallium oxide, magnesium oxide, zinc oxide); of at least one basic agent selected from ammonia (NH.sub.3), or from inorganic or organic compounds containing nitrogen capable of developing ammonia (NH.sub.3) during said dehydration process; and, optionally, of silica (SiO.sub.2), or of at least one catalyst for the dissociation of ammonia (NH.sub.3) selected from catalysts comprising silica (SiO.sub.2), preferably of silica (SiO.sub.2).

Claims

1. A process comprising dehydrating at least one oxygenated compound in the presence of (i) at least one dehydration catalyst selected from the group consisting of cerium oxide (CeO.sub.2), aluminum oxide (γ-Al.sub.2O.sub.3), aluminum silicate, silica-alumina (SiO.sub.2Al.sub.2O.sub.3) alumina, a zeolite, a sulfonate resin, an ion exchange resin, and a metal oxide; (ii) at least one basic agent selected from the group consisting of ammonia (NH.sub.3) and an inorganic or organic compound comprising nitrogen capable of developing ammonia (NH.sub.3) during the dehydration; and (iii) optionally silica (SiO.sub.2).

2. A process comprising dehydrating at least one oxygenated compound by feeding to a reactor a mixture comprising the oxygenated compound and at least one basic agent selected from the group consisting of ammonia (NH.sub.3) and an inorganic or organic compound comprising nitrogen capable of developing ammonia (NH.sub.3) during the dehydration, wherein the mixture is fed to the reactor so as to pass first through a first catalytic bed and subsequently through a second catalytic bed in the reaction, wherein the first catalytic bed comprises silica (SiO.sub.2), and the second catalytic bed comprises at least one dehydration catalyst selected from the group consisting of cerium oxide (CeO.sub.2), aluminum oxide (γ-Al.sub.2O.sub.3), aluminum silicate, silica-alumina (SiO.sub.2-Al.sub.2O.sub.3), alumina, a zeolite, a sulfonate resin, an ion exchange resin, and a metal oxide.

3. A process comprising dehydrating at least one oxygenated compound by feeding to a reactor a mixture comprising the oxygenated compound and at least one basic agent selected from the group consisting of ammonia (NH.sub.3) and an inorganic or organic compound comprising nitrogen capable of developing ammonia (NH.sub.3) during the dehydration, wherein the mixture is fed to the reactor so as to pass first through a first catalytic bed and subsequently through a second catalytic bed, in the reactor, wherein the first catalytic bed comprises silica (SiO.sub.2), and the second catalytic bed comprises at least one dehydration catalyst selected from the group consisting of ammonium phosphate and a metal phosphate.

4. The process of claim 1, wherein the oxygenated compound comprises a saturated alcohol having from 1 to 25 carbon atoms.

5. The process of claim 1, wherein the oxygenated compound comprises an unsaturated alcohol having from 2 to 20 carbon atoms.

6. The process of claim 1, wherein the oxygenated compound comprises a diol having from 2 to 20 carbon atoms.

7. The process of claim 1, wherein the oxygenated compound comprises a cyclic or linear ether having from 4 to 12 carbon atoms.

8. The process of claim 1, wherein the oxygenated compound comprises at least one selected from the group consisting of a saturated alcohol, an unsaturated alcohol, a diol and an ether, in either (i) anhydrous form, or (ii) in mixture with water wherein the water is present in an amount higher than or equal to 0.005% by weight, based on a total weight of the mixture.

9. The process of claim 1, wherein the oxygenated compound is derived from a fermentation of one or more sugars obtained from biomass.

10. A process comprising: (a) dehydrating 1,3-butanediol, optionally in a mixture with water, in the presence of (i) at least one dehydration catalyst selected from the group consisting of cerium oxide (CeO.sub.2), aluminum oxide (γ-Al.sub.2O.sub.3), aluminum silicate, silica-alumina (SiO.sub.2-Al.sub.2O.sub.3), alumina, a zeolite, a sulfonate resin, an ion exchange resin, and a metal oxide; (ii) an inorganic or organic compound comprising nitrogen capable of developing ammonia (NH.sub.3) during the dehydration; and (iii) optionally, silica (SiO.sub.2), to obtain an unsaturated alcohol; and (b) distilling and further dehydrating the unsaturated alcohol, in the presence of (i′) at least one dehydration catalyst selected from the group consisting of aluminum oxide (γ-Al.sub.2O.sub.3), aluminum silicate, silica-alumina (SiO.sub.2-Al.sub.2O.sub.3), alumina, a zeolite, a sulfonate resin, an ion exchange resin, and an acid earth; (ii′) an inorganic or organic compound comprising nitrogen capable of developing ammonia (NH.sub.3) during the dehydration; and (iii′) optionally silica (SiO.sub.2), to obtain 1 3-butadiene.

11. The process of claim 1, wherein the oxygenated compound is derived from a fermentation of one or more sugars obtained from guayule or from thistle.

12. The process of claim 1, wherein the basic agent is at least one selected from the group consisting of: ammonia (NH.sub.3) in the gaseous form; ammonium hydroxide (NH.sub.4OH); urea; ammonium carbonate or bicarbonate; a primary, secondary or tertiary amine, aliphatic or aromatic, having a boiling point ranging from −8° C. to 250° C.; and a heterocyclic compound comprising a nitrogen atom.

13. The process of claim 1, wherein the basic agent is present in such a quantity such that a concentration of ammonia (NH.sub.3), or an equivalent concentration of ammonia (NH.sub.3), based on a total weight of the oxygenated compound and of optional other organic compounds present, ranges from 0.005% by weight to 4% by weight.

14. The process of claim 1, wherein the silica (SiO.sub.2) is present as a binder or as a carrier of the dehydration catalyst.

15. The process of claim 1, wherein the silica (SiO.sub.2) is present in a quantity ranging from 1% by volume to 100% by volume, with respect to the total volume of the dehydration catalyst.

16. The process of claim 1, wherein the silica (SiO.sub.2) is present in a form of a catalyst comprising, in addition to the silica (SiO.sub.2), iron oxide, aluminum oxide, calcium oxide, or potassium oxide.

17. The process of claim 1, wherein the process is performed in a continuous reactor, either a fixed-bed or a fluid-bed reactor, adiabatically, isothermally or a combination of both.

18. The process of claim 17, wherein the reactor operates at: a temperature ranging from 190° C. to 500° C.; and/or a pressure ranging from 0.3 bara (bar absolute) to 3.5 bara (bar absolute).

19. The process of claim 16, wherein the oxygenated compound is fed to the reactor operating at a Weight Hourly Space Velocity (WHSV) that is a ratio between a total weight of the oxygenated compound, and optionally water, fed in an hour, and a weight of the dehydration catalyst, ranging from 0.5 h.sup.−1 to 30 h.sup.−1.

Description

EXAMPLE 1

[0066] Preparation of 1,3-butadiene (1,3-BDE) by means of two dehydration reactions carried out in series starting from a mixture of 1,3-butanediol (1,3-BDO) [0067] Part I—First Dehydration Reaction of 1,3-BDO to Unsaturated Alcohols

[0068] A mixture of 1,3-BDO, ammonium hydroxide (NH.sub.4OH) and water, having a weight concentration respectively equal to 82.0% of 1,3-BDO, 1.2% of ammonium hydroxide (NH.sub.4OH) and 16.8% of water (mixture 1), was prepared for this purpose and then used for the first dehydration reaction. The equivalent concentration of ammonia (NH.sub.3) in said mixture 1 is equal to 0.5% by weight with respect to the total weight of 1,3-BDO.

[0069] The reactor in which said first dehydration reaction was carried out was composed of an AISI 304 stainless steel tubular element having a height (h) equal to 260 mm and an internal diameter (Φ) equal to 10 mm, preceded by and connected to an evaporator, both equipped with electrical heating. The outlet of the reactor, on the other hand, was connected to a first condenser connected to a collection flask, and operating at 15° C., in order to allow the recovery of the products obtained from the first dehydration reaction in liquid form at room temperature (25° C.) in said collection flask. Said collection flask was, in turn, connected to a sampling system consisting of a steel cylinder having a volume (V) equal to 300 ml and equipped, at the two ends, with interception valves. The vapours/gases deriving from the first dehydration reaction and optionally not condensed in the system previously described, could also flow through the above-mentioned steel cylinder, in turn connected to a flow meter which measured their quantity.

[0070] The products obtained, both in liquid form and in the form of vapour/gas, were characterized through gas-chromatography, using: [0071] for products in liquid form, a Thermo Trace gas-chromatograph equipped with a FID detector and AQUAWAX column (Grace 30 m length×0.53 mm internal diameter×1.0 μm film thickness); [0072] for products in the form of vapour/gas, a 490 micro GC Varian/Agilent gas-chromatograph equipped with 4 channels and with the following columns: Pora Plot Q 10 m long, MolSieve 5 Å 4 m long, Al.sub.2O.sub.3 10 m long with “backflush” functionality, CPSil-19 CB 7.5 m long.

[0073] The catalyst used in said first dehydration reaction was a material based on Cerium Oxide (CeO.sub.2) in granules having dimensions ranging from 0.5 mm to 1 mm and was charged into said reactor in a quantity equal to 10 g (3.5 ml). Said catalyst was specifically prepared following the laboratory procedure described hereunder.

[0074] For this purpose, 500 g of a commercial aqueous solution of about 30% of ammonium hydroxide (NH.sub.4OH), (28%-30% NH.sub.3 Basis ACS reagent Aldrich) were added with 500 g of water in a first 3-litre beaker, equipped with a stirring rod having a half-moon Teflon blade, and an electrode was introduced for the measurement of the pH [Metrohm glass electrode for pH (6.0248.030), connected to the pH-meter Metrohom 780]. A solution of 100 g of cerium nitrate hexahydrate (99% Aldrich) was prepared in 1,000 g of water in a second 2-litre beaker, equipped with a magnetic stirrer: the cerium nitrate hexahydrate was then solubilized by vigorous stirring at room (25° C.) temperature.

[0075] The solution obtained was introduced into a dripper and fed dropwise, over a period of 2 hours, to the ammonium hydroxide solution contained in the 3-litre beaker indicated above, under constant vigorous stirring. The pH of the suspension obtained was equal to 10.2. The solid in suspension was filtered, washed with 2 litres of water and then dried in an oven at 120° C., for 2 hours. The synthesis was repeated until 2,000 g of solid had been obtained.

[0076] 1,270 g of the solid thus obtained were introduced, after sieving at 0.125 mm, into an extruder to which 175.9 g of a solution at 25% of ammonium hydroxide (NH.sub.4OH) (obtained by diluting the NH.sub.3 solution at 28%-30% Basis ACS reagent Aldrich) were also fed by means of a Watson Marlow peristaltic pump set to 5 rpm. At the end of this feeding, 158 g of demineralized water were also fed: in this way the correct consistency for the extrusion was obtained. The pellets obtained at the outlet of the extruder were dried in the air and a portion equal to 100 g was subsequently calcined at 800° C. with a temperature ramp of 1° C./minute up to 800° C. followed by an isotherm at that temperature for 6 hours. The calcined solid was granulated and sieved and the fraction of granules having dimensions ranging from 0.5 mm to 1 mm was used as catalyst.

[0077] Said first dehydration reaction was then carried out by feeding the mixture 1, first to the above-mentioned evaporator previously heated to a temperature equal to 250° C., and from this to the above-mentioned tubular reactor previously heated so as to have an internal temperature, during the dehydration reaction, equal to 400° C. Both the evaporator and the reactor were maintained at atmosphere pressure (1 bara).

[0078] The flow-rate of mixture 1 fed to the evaporator was equal to 100 g/h, whereas the flow-rate fed to the reactor, expressed as WHSV, was equal to 10 h.sup.−1.

[0079] The test was carried out for a time sufficient for collecting an adequate amount of products, collected in both liquid form and in the form of vapour/gas which, when subjected to gas-chromatographic analysis, showed the composition indicated in Table 1 for the liquid fraction (mixture 2), with particular reference to the presence of undesired by-products containing a carbonyl group. These carbonyl compounds, expressed in relation to the unsaturated alcohols which, on the other hand, represent the desired products in the first dehydration reaction, are grouped into two categories: [0080] methylvinylketone+acetaldehyde [0081] other carbonyl compounds (acetone, butanone, butanal, etc.)
and were calculated according to the following formula:

[00001]$r_{C/A}=\frac{\underset{i}{.Math.}.Math..Math.{\mathrm{carb}}_i}{\underset{i}{.Math.}.Math..Math.{\mathrm{alc}}_i}\times 100;$

wherein: [0082] r.sub.C/A=grams of carbonyl compounds per 100 g of unsaturated alcohols produced; [0083] carb.sub.i=grams of i-th carbonyl compound produced [referring to methylvinylketone, acetaldehyde, other carbonyl compounds]; [0084] alc.sub.i=grams of i-th unsaturated alcohol produced

[0085] [referring to 3-buten-2-ol (methylvinylcarbinol) and to 2-buten-1-ol (crotyl alcohol)]

TABLE-US-00001 TABLE 1 Acetaldehyde + Other carbonyl NH.sub.3 methylvinylketone compounds equivalents (g/100 g of (g/100 g of (%) unsaturated alcohols) unsaturated alcohols) 0.5 0.57 0.80 [0086] Part II Second Dehydration Reaction of Unsaturated Alcohols to 1,3-BDE

[0087] Mixture 2 previously obtained as described above, was subjected to purification, by means of distillation, in order to remove the non-reacted 1,3-butandiol. Said distillation was carried out at atmospheric pressure, adding 3,5-di-tert-4-butylhydroxytoluene (BHT) to mixture 2 present in the boiler of the distillation column, so as to have a concentration of the same in said mixture 2 equal to about 200 ppm. Said distillation was carried out using an Oldershaw column having 40 plates (2 segments of 20 plates), charging said mixture 2 into the boiler in a single tranche and condensing and collecting the cut at the head, included within the temperature range of 103.1° C. to 210.0° C., and progressively concentrating the heaviest components in the boiler. Said head cut (mixture 3) was characterized by the following final composition by weight: [0088] unsaturated alcohols (3-buten-2-ol and 2-buten-1-01) equal to 60%; [0089] water equal to 38%; [0090] other compounds (C.sub.2-C.sub.4 alcohols, carbonyl compounds, etc.) equal to 2%.

[0091] Two catalytic beds were parallelly charged in series, in a reactor analogous to the previous reactor. A first catalytic bed was therefore charged in a quantity equal to 4 g (5.2 ml) of silica (SiO.sub.2) obtained starting from colloidal silica (Ludox® TMA—Sigma-Aldrich) according to the laboratory procedure described hereunder.

[0092] For this purpose, 400.0 g of colloidal silica (Ludox® TMA—Sigma-Aldrich) were charged into a 800 ml beaker and the whole mixture was kept under vigorous stirring (500 rpm), on a heating plate at 150° C., until it was dry. The solid obtained was dried in an oven at 120° C., for 12 hours, and subsequently calcined at 600° C., for 5 hours, obtaining 136.5 g of a colourless product. The product obtained was granulated mechanically and the fraction of granules having dimensions ranging from 0.5 mm to 1.0 mm was used as in said first catalytic bed.

[0093] A second catalytic bed was subsequently charged, in a quantity equal to 4 g (10 ml), with a catalyst based on a material specifically prepared according to the laboratory procedure described hereunder.

[0094] For this purpose, 7.55 g of aluminium tri-sec-butoxide (Aldrich) were introduced into a first 500 ml flask, as alumina precursor (Al.sub.2O.sub.3), and 50.02 g of orthosilicic acid (Aldrich, <20 mesh), were introduced, as silica precursor (SiO.sub.2), into a second 500 ml flask with 250.02 g of demineralized water. The suspension of orthosilicic acid obtained was slowly added (10 minutes) to said first flask containing aluminium tri-sec-butoxide, and the mixture obtained was maintained at 90° C., for about 1 hour, under vigorous stirring (500 rpm). After cooling to room temperature (25° C.), the suspension obtained was filtered and the solid obtained was washed with 5 litres of demineralized water, dried at 120° C. for a night and subsequently calcined at 500° C. for 5 hours obtaining a colourless powder (47.95 g) (called “active phase”).

[0095] Part of the above-mentioned active phase (40.42 g) was mixed with 24.43 g of pseudoboehmite Versal™ V-250 (UOP), as alumina precursor (Al.sub.2O.sub.3) of the binder, and 302 ml of a solution at 4% of acetic acid, in a 800 ml beaker. The mixture obtained was kept under stirring at 60° C., for about 2 hours. The beaker was subsequently transferred to a heating plate and the mixture was heated, under vigorous stirring, for a night, at 150° C., until it was dry. The solid obtained was subsequently calcined at 550° C., for 5 hours, obtaining 60.45 g of a colourless product which was granulated mechanically, the fraction of granules having dimensions ranging from 0.1 mm to 1.0 mm was used as dehydration catalyst in said second catalytic bed.

[0096] Parallelly, a quantity of ammonium hydroxide (NH.sub.4OH) was added to mixture 3 prevalently containing unsaturated alcohols, operating according to the same procedure described above, so as to have an equivalent concentration of ammonia (NH.sub.3) equal to 1.0% by weight with respect to the total weight of the compounds present in said mixture 3 [i.e. unsaturated alcohols (3-buten-2-ol and 2-buten-1-ol) and other compounds (C.sub.2-C.sub.4 alcohols, carbonyl compounds, etc.)]. The new mixture thus obtained was fed, in the form of vapour and at a flow-rate expressed as WHSV (referring to the dehydration catalyst) equal to 3.3 h.sup.−1, to the reactor, previously charged with said first catalytic bed and with said second catalytic bed as indicated above, operating at atmospheric pressure (1 bara) and at a temperature equal to 300° C., so that said mixture passed first through said first catalytic bed and subsequently through said second catalytic bed.

[0097] The second dehydration reaction was then carried out for a time sufficient for collecting an adequate quantity of products collected in both liquid form and in the form of vapour/gas which, when subjected to gas-chromatographic analysis allowed the parameters indicated in Table 2, to be calculated in terms of conversion of the unsaturated alcohols (C.sub.ALCH.) and selectivity to 1,3-BDE (S.sub.1,3-BDE) determined according to the formulae indicated hereunder.

[00002]$C_{\mathrm{ALCH}.}=\frac{{\left({\mathrm{moles}}_{\mathrm{ALCH}.}\right)}_{\mathrm{in}}-{\left({\mathrm{moles}}_{\mathrm{ALCH}.}\right)}_{\mathrm{out}}}{{\left({\mathrm{moles}}_{\mathrm{ALCH}.}\right)}_{\mathrm{in}}}\times 100;$$S_{1,3-\mathrm{BDE}}=\frac{{\mathrm{moles}}_{1,3-\mathrm{BDE}}}{{\left({\mathrm{moles}}_{\mathrm{ALCH}.}\right)}_{\mathrm{in}}-{\left({\mathrm{moles}}_{\mathrm{ALCH}.}\right)}_{\mathrm{out}}}\times 100;$

wherein: [0098] (moles.sub.ALCH.).sub.in=moles of unsaturated alcohols at the inlet; [0099] (moles.sub.ALCH.).sub.out=moles of unsaturated alcohols at the outlet; [0100] moles.sub.1,3-BDE=total moles of 1,3-butadiene.

TABLE-US-00002 TABLE 2 NH.sub.3 Duration of equivalents dehydration Conversion Selectivity (%) (hours) (%) (%) 1.0 8 100.sup.(2) 86.sup.(1) 128  83.sup.(2) 92.sup.(1) .sup.(1)values referring to 1,3-BDE; .sup.(2)values referring to unsaturated alcohols.

[0101] The test was interrupted after 128 hours of continuous running, when the conversion and selectivity values reported in Table 2 had become stabilized.

EXAMPLE 2 (comparative)

[0102] Preparation of 1,3-butadiene (1,3-BDE) by means of two dehydration reactions carried out in series starting from a mixture of 1,3-butanediol (1,3-BDO)

[0103] Example 2 was carried out under the same operating conditions described above for Example 1, with the exception that: [0104] in Part I ammonium hydroxide (NH.sub.4OH) was not used; [0105] in Part II ammonium hydroxide (NH.sub.4OH) was not used; [0106] in Part II the first catalytic bed comprising silica (SiO.sub.2) was not used.

[0107] The results obtained are indicated in Table 3 for Part I and in Table 4 for Part II.

TABLE-US-00003 TABLE 3 Acetaldehyde + Other carbonyl NH.sub.3 methylvinylketone compounds equivalents (g/100 g of (g/100 g of (%) unsaturated alcohols) unsaturated alcohols) 0.0 3.01 1.81

[0108] The values indicated in Table 3 show a formation of carbonyl compounds as by-products in the first dehydration reaction (Part I) which is much higher than those obtained in Example 1 and indicated in Table 1.

TABLE-US-00004 TABLE 4 NH.sub.3 Duration of equivalents dehydration Conversion Selectivity (%) (hours) (%) (%) 0.0 8 100.sup.(2) 85.sup.(1) 54  74.sup.(2) 76.sup.(1) .sup.(1)values referring to 1,3-BDE; .sup.(2)values referring to unsaturated alcohols.

[0109] The test was interrupted after only 54 hours of continuous running, when the conversion and selectivity values indicated in Table 4 had dropped well below those obtained in Example 1 and indicated in Table 2, due to a high deactivation of the catalyst used in the second dehydration reaction (Part II).

EXAMPLE 3 (comparative)

[0110] Preparation of 1,3-butadiene (1,3-BDE) by means of two dehydration reactions carried out in series starting from a mixture of 1,3-butanediol (1,3-BDO)

[0111] Example 3 was carried out under the same operating conditions described above for Example 1, with the exception that: [0112] in Part II, a quantity of ammonium hydroxide (NH.sub.4OH) was added so as to have an equivalent concentration of ammonia (NH.sub.3) equal to 0.1% with respect to the total weight of the compounds present in said mixture 3 [i.e. unsaturated alcohols (3-buten-2-ol and 2-buten-1-ol) and other compounds (C.sub.2-C.sub.4 alcohols, carbonyl compounds, etc.)], instead of being equal to 1.0% by weight as indicated in Example 1; [0113] in Part II, the first catalytic bed comprising silica (SiO.sub.2) was not used.

[0114] The results obtained, only for the Part II, are indicated in Table 5.

TABLE-US-00005 TABLE 5 NH.sub.3 Duration of equivalents dehydration Conversion Selectivity (%) (hours) (%) (%) 0.1 8 99.sup.(2) 87.sup.(1) 24 69.sup.(2) 69.sup.(1) .sup.(1)values referring to 1,3-BDE; .sup.(2)values referring to unsaturated alcohols.

[0115] The test was interrupted after only 24 hours of continuous running, when the conversion and selectivity values indicated in Table 5 had dropped well below those obtained in Example 1 and indicated in Table 2, due to a high deactivation of the catalyst used in the second dehydration reaction (Part II).

EXAMPLE 4

[0116] Preparation of 1,3-butadiene (1,3-BDE) by means of two dehydration reactions carried out in series starting from a mixture of 1,3-butanediol (1,3-BDO)

[0117] Example 4 was carried out under the same operating conditions described above for Example 1, with the exception that: [0118] in Part II, a quantity of ammonium hydroxide (NH.sub.4OH) was added so as to have an equivalent concentration of ammonia (NH.sub.3) equal to 1.2% with respect to the total weight of the compounds present in said mixture 3 [i.e. unsaturated alcohols (3-buten-2-ol and 2-buten-1-ol) and other compounds (C.sub.2-C.sub.4 alcohols, carbonyl compounds, etc.)], instead of being equal to 1.0% by weight as indicated in Example 1; [0119] in Part II, a different dehydration catalyst was used having silica (SiO.sub.2) as binder prepared as described hereunder, for the second catalytic bed; [0120] in Part II, the second dehydration reaction was carried out maintaining the reactor at a temperature of 350° C.; [0121] in Part II, the first catalytic bed comprising silica (SiO.sub.2) was not used.

[0122] For preparing the dehydration catalyst, 7.6 g of aluminium tri-sec-butoxide (Aldrich), were introduced into a first 500 ml flask, as alumina precursor (Al.sub.2O.sub.3), and 50 g of orthosilicic acid (Aldrich, <20 mesh), were introduced into a second 500 ml flask, as silica precursor (SiO.sub.2), with 250.09 g of demineralized water. The suspension of orthosilicic acid obtained was added slowly (10 minutes) to said first flask containing aluminium tri-sec-butoxide, and the mixture obtained was maintained at 90° C., for about 1 hour, under vigorous stirring (500 rpm). After cooling to room temperature (25° C.), the suspension obtained was filtered, the solid obtained was washed with 5 litres of demineralized water, dried in an oven at 120° C., for a night, and subsequently calcined at 500° C., for 5 hours, obtaining a colourless powder (52.23 g) (called “active phase”).

[0123] Part of the above-mentioned active phase (41.10 g) was mixed with 52.72 g of colloidal silica (SiO.sub.2) (Ludox® TMA—Sigma-Aldrich), as silica precursor (SiO.sub.2) of the binder, and 150 ml of demineralized water in a 500 ml beaker: the mixture obtained was kept under stirring at 60° C., for about 2 hours. The beaker was subsequently transferred to a heating plate and the mixture was heated, under vigorous stirring, for a night, at 150° C., until it was dry. The solid obtained was calcined at 550° C., for 5 hours, obtaining a colourless solid which was granulated mechanically. 4 g (9.3 ml) of the fraction of granules having dimensions ranging from 0.1 mm to 1.0 mm was used as catalyst.

[0124] The results obtained, only for the Part II, are indicated in Table 6.

TABLE-US-00006 TABLE 6 NH.sub.3 Duration of equivalents dehydration Conversion Selectivity (%) (hours) (%) (%) 1.2 8 100.sup.(2) 90.sup.(2) 76  42.sup.(1) 81.sup.(1) .sup.(1)values referring to 1,3-BDE; .sup.(2)values referring to unsaturated alcohols.

[0125] The test was interrupted after 76 hours of continuous running: it should be noted that the presence of the catalyst obtained as described above comprising silica (SiO.sub.2) as binder, allows a greater duration of the second dehydration reaction (Part II) with respect to that of Example 3 in which neither said first catalytic bed comprising silica (SiO.sub.2) was used, nor the catalyst comprising silica (SiO.sub.2) as binder.

EXAMPLE 5

[0126] Preparation of 1,3-butadiene (1,3-BDE) by means of two dehydration reactions carried out in series starting from a mixture of 1,3-butanediol (1,3-BDO)

[0127] Example 5 was carried out under the same operating conditions described above for Example 4, with the exception that: [0128] in Part II, a quantity of ammonium hydroxide (NH.sub.4OH) was added so as to have an equivalent concentration of ammonia (NH.sub.3) equal to 2.4% by weight with respect to the total weight of the compounds present in said mixture 3 [i.e. unsaturated alcohols (3-buten-2-ol and 2-buten-1-ol) and other compounds (C.sub.2-C.sub.4 alcohols, carbonyl compounds, etc.)], instead of being equal to 1.2% as indicated in Example 4.

[0129] The results obtained, only for the Part (II), are indicated in Table 7.

TABLE-US-00007 TABLE 7 NH.sub.3 Duration of equivalents dehydration Conversion Selectivity (%) (hours) (%) (%) 2.4 8 100.sup.(2) 90.sup.(2) 76  36.sup.(1) 73.sup.(1) .sup.(1)values referring to 1,3-BDE; .sup.(2)values referring to unsaturated alcohols.

[0130] The test was interrupted after 76 hours of continuous running; it should be noted that the presence of the catalyst obtained as described in Example 4 comprising silica (SiO.sub.2) as binder, allows a greater duration of the second dehydration reaction (Part II), in spite of the greater quantity of equivalents of ammonia (NH.sub.3) used, with respect to that of Example 3 in which neither said first catalytic bed comprising silica (SiO.sub.2) was used, nor the catalyst comprising silica (SiO.sub.2) as binder.

EXAMPLE 6 (comparative)

[0131] Preparation of 1,3-butadiene (1,3-BDE) by means of two dehydration reactions carried out in series starting from a mixture of 1,3-butanediol (1,3-BDO)

[0132] Example 6 was carried out under the same operating conditions described above for Example 4, with the exception that: [0133] in Part II ammonium hydroxide (NH.sub.4OH) was not used.

[0134] The results obtained, only for the Part II, are indicated in Table 8.

TABLE-US-00008 TABLE 8 NH.sub.3 Duration of equivalents dehydration Conversion Selectivity (%) (hours) (%) (%) 0.0 8 100.sup.(2) 94.sup.(2) 32  35.sup.(1) 70.sup.(1) .sup.(1)values referring to 1,3-BDE; .sup.(2)values referring to unsaturated alcohols.

[0135] The test was interrupted after only 32 hours of continuous running, when the conversion and selectivity values indicated in Table 8 had dropped well below those obtained in Example 1 and indicated in Table 2, and those obtained in Example 4 and indicated in Table 6, due to a high deactivation of the catalyst used in the second dehydration reaction (Part II).

EXAMPLE 7 (comparative)

[0136] Preparation of 1,3-butadiene (1,3-BDE) by means of two dehydration reactions carried out in series starting from a mixture of 1,3-butanediol (1,3-BDO)

[0137] Example 7 was carried out under the same operating conditions described above for Example 4, with the exception that: [0138] in Part II, a quantity of pyridine [instead of ammonium hydroxide (NH.sub.4OH)] was added so as to have an equivalent concentration of ammonia (NH.sub.3) equal to 1.2% by weight with respect to the total weight of the compounds present in said mixture 3 [i.e. unsaturated alcohols (3-buten-2-ol and 2-buten-1-ol) and other compounds (C.sub.2-C.sub.4 alcohols, carbonyl compounds, etc.)].

[0139] After a few hours of continuous running, the total deactivation of the catalyst used for the second dehydration reaction (Part II), was registered.

EXAMPLE 8

[0140] Preparation of 1,3-butadiene (1,3-BDE) by means of two dehydration reactions carried out in series starting from a mixture of 1,3-butanediol (1,3-BDO)

[0141] Example 8 was carried out under the same operating conditions described above for Example 2, with the exception that: [0142] in Part II, a quantity of pyrrole was added so as to have an equivalent concentration of ammonia equal to 0.01% by weight with respect to the total weight of the compounds present in said mixture 3 [i.e. unsaturated alcohols (3-buten-2-ol and 2-buten-1-ol) and other compounds (C.sub.2-C.sub.4 alcohols, carbonyl compounds, etc.)].

[0143] The results obtained, only for the Part (II), are indicated in Table 9.

TABLE-US-00009 TABLE 9 NH.sub.3 Duration of equivalents dehydration Conversion Selectivity (%) (hours) (%) (%) 0.01 8 100.sup.(2) 92.sup.(1) 78  99.sup.(2) 95.sup.(1) .sup.(1)values referring to 1,3-BDE; .sup.(2)values referring to unsaturated alcohols.

[0144] The test was interrupted after 78 hours of continuous running; it should be noted that the addition of pyrrole allows an increasing, in term of both duration and selectivity, of the second dehydration reaction (Part II), with respect to that of Example 2 in which pyrrole was not used. After 78 hours, in fact, the conversion is equal to 99% and the selectivity is much higher with respect to that of Example 2.