PROCESS FOR THE PRODUCTION OF DIENES

Abstract

Process for the production of a diene, preferably a conjugated diene, more preferably 1,3-butadiene, comprising the dehydration of at least one alkenol in the presence of at least one catalytic material comprising at least one acid catalyst based on silica (SiO.sub.2) and alumina (AI.sub.2O.sub.3), preferably a silica-alumina (SiO.sub.2-AI.sub.2O.sub.3), said catalyst having a content of alumina (AI.sub.2O.sub.3) lower than or equal to 12% by weight, preferably ranging from 0.1% by weight to 10% by weight, with respect to the total weight of the catalyst. Preferably, said alkenol can be obtained directly from biosynthesis processes, or through the catalytic dehydration of at least one diol, preferably a butanediol, more preferably 1,3-butanediol, even more preferably bio-1,3-butanediol, deriving from biosynthesis processes. Preferably, said 1,3-butadiene is bio-1,3-butadiene.

Claims

1. A process for manufacturing a diene, the process comprising dehydrating at least one alkenol in the presence of at least one catalytic material comprising at least one silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) based acid catalyst, said catalyst having a content of alumina lower than or equal to 12% by weight, relative to a total weight of the catalyst.

2. The process according to claim 1, wherein the alkenol is selected from the group consisting of 3-buten-2-ol (methyl vinyl carbinol), 3-buten-1-ol (allyl carbinol), 2-buten-1-ol (crotyl alcohol), and mixtures thereof.

3. The process Process according to claim 1, wherein the alkenol is directly obtained from a biosynthetic process, or by a catalytic dehydration processes of at least one diol, deriving from a biosynthetic process.

4. The process according to claim 1, wherein the alkenol derives from catalytic dehydration of at least one diol deriving from the fermentation of sugars.

5. The process according to claim 4, wherein the diol is a bio-1,3-butanediol deriving from fermentation of sugars obtained from guayule or thistle, including scraps, residues, waste products deriving from said guayule and/or thistle or from their processing.

6. The process according to claim 1, wherein the acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) is obtained by incipient wetness impregnation wherein a volume of a solution of a metal is equal to or lower than that of a pore volume of a solid support.

7. The process according to claim 1, wherein the acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) is obtained by a process comprising: preparing a solution or a suspension of allumina (Al.sub.2O.sub.3), or its precursors, that are selected from the group consisting of aluminium alkoxides, soluble aluminium salts, and aluminates; adding to said solution or suspension of alumina (Al.sub.2O.sub.3), or its precursors, a solution or a suspension of silica (SiO.sub.2), or its precursors; recovering the solid obtained by precipitation or gelation, and subjecting it optionally to a ion-exchange in the presence of at least a compound capable of exchanging ions with the surface of the solid obtained selected from aqueous solutions of salts containing ammonium ions; and/or to a binding step in the presence of at least one precursor of silica (SiO.sub.2) selected from colloidal silicas; or of at least one precursor of alumina (Al.sub.2O.sub.3) selected from boehmite or pseudo-boehmite; and/or to a forming step; and subjecting it to optional thermal and/or optional calcination treatment, said optional thermal and/or optional calcination treatment being carried out before or after one of the above said steps.

8. The process according to claim 1, wherein the acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) has a specific surface area ranging from 50 m.sup.2/g to 800 m.sup.2/g.

9. The process according to claim 1, wherein the catalytic material comprises at least one acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) and at least one binder selected from the group consisting of alumina (Al.sub.2O.sub.3), silica (SiO.sub.2), zirconium oxide, and titanium oxide.

10. The process according to claim 1, wherein the catalytic material comprises at least one acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), and at least one binder selected from alumina (Al.sub.2O.sub.3) or silica (SiO.sub.2), and/or subjected to forming, have a specific surface area ranging from 25 m.sup.2/g to 700 m.sup.2/g.

11. The process according to claim 1, wherein said process is carried out in the presence of a diluent selected from the group consisting of inert gases and compounds having a boiling temperature higher than or equal to 50° C. and a melting temperature lower than or equal to 40° C.

12. The process according to claim 1, wherein said process is carried out: if the diluent is selected from inert gases, at a molar ratio between diluent and alkenol higher than 0.3; if the diluent is selected from compounds having a boiling temperature higher than or equal to 50° C. and a melting temperature lower than or equal to 40° C., at a molar ratio between diluent and alkenol ranging from 0.01 to 100.

13. The process according to claim 1, wherein said process is carried out: at a temperature ranging from 150° C. to 500° C.; and/or at a pressure ranging from 0.05 bara (absolute bar) to 50 bara (absolute bar); and/or by working at a contact time (τ), calculated as ratio of the volume of catalytic material charged with respect to the volumetric feeding flow-rate, ranging from 0.01 seconds to 10 seconds.

14. The process according to claim 1, wherein the catalytic material is pre-treated at the temperature at which said process is carried out.

Description

EXAMPLE 1

[0107] Preparation of a Silica-Alumina (SiO.sub.2—Al.sub.2O.sub.3) Having a Content of Alumina (Al.sub.2O.sub.3) Equal to 0%, with an Alumina (Al.sub.2O.sub.3) Binder

[0108] 7.6 g of tri-sec-butanol (Aldrich) were introduced into a first 500 ml flask. 50 g of orthosilicic acid (Aldrich, <20 mesh), as silica precursor (SiO.sub.2), and 250 g of demineralized water were introduced into a second 500 ml flask: the suspension of orthosilicic acid obtained was slowly added (10 minutes) to said first flask and the whole mixture was maintained at room temperature (25° C.), under vigorous stirring (500 rpm), for about 2 hours. The suspension obtained was then heated to 90° C., and kept at this temperature, under vigorous stirring (500 rpm), for about 1 hour. After cooling to room temperature (25° C.), the suspension obtained was filtered, 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 silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) in the form of a colourless powder (46 g), having a BET specific surface area, determined as described above, equal to 479 m.sup.2/g.

[0109] A part of said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), 20.5 g, was mixed with 11.4 g of pseudo-bohemite Versal™ V-250 (UOP), as alumina precursor (Al.sub.2O.sub.3) of the binder, and 300 ml of a solution at 4% of acetic acid (Aldrich) in a 800 ml beaker. The mixture obtained was kept under vigorous stirring (500 rpm), at 60° C., for about 2 hours. The beaker was then transferred to a heating plate and the mixture was kept, under vigorous stirring (500 rpm), for a night, at 150° C., until it was dry. The solid obtained was calcined at 550° C., for 5 hours, obtaining a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with an alumina binder (Al.sub.2O.sub.3), in the form of a colourless solid (24 g) which was subsequently granulated mechanically and the fraction of granules having dimensions ranging from 0.5 mm to 1 mm was used as catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with an alumina binder (Al.sub.2O.sub.3) had a BET specific surface area, determined as described above, equal to 389 m.sup.2/g.

EXAMPLE 2

[0110] Preparation of a Silica-Alumina (SiO.sub.2—Al.sub.2O.sub.3) Having a Content of Alumina (Al.sub.2O.sub.3) Equal to 3.8%, with an Alumina (Al.sub.2O.sub.3) Binder

[0111] 7.6 g of aluminium tri-sec-butoxide (Aldrich), as alumina precursor (Al.sub.2O.sub.3), were introduced into a first 500 ml flask. 50 g of orthosilicic acid (Aldrich, <20 mesh), as silica precursor (SiO.sub.2), and 250 g of demineralized water were introduced into a second 500 ml flask: the suspension of orthosilicic acid obtained was slowly added (10 minutes) to said first flask and the whole mixture was maintained at room temperature (25° C.), under vigorous stirring (500 rpm), for about 2 hours. The suspension obtained was then heated to 90° C., and kept at this temperature, under vigorous stirring (500 rpm), for about 1 hour. After cooling to room temperature (25° C.), the suspension obtained was filtered, 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 silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) in the form of a colourless powder (48 g), whose elemental analysis, carried out as described above, showed a content of alumina (Al.sub.2O.sub.3) equal to 3.8%. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) had a BET specific surface area, determined as described above, equal to 490 m.sup.2/g.

[0112] A part of said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), 40.4 g, was mixed with 24.4 g of pseudo-bohemite 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 (Aldrich) in a 800 ml beaker. The mixture obtained was kept under vigorous stirring (500 rpm), at 60° C., for about 2 hours. The beaker was then transferred to a heating plate and the mixture was kept, under vigorous stirring (500 rpm), for a night, at 150° C., until it was dry. The solid obtained was calcined at 550° C., for 5 hours, obtaining a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with an alumina (Al.sub.2O.sub.3) binder, in the form of a colourless solid (53 g) which was subsequently granulated mechanically and the fraction of granules having dimensions ranging from 0.5 mm to 1 mm was used as catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with an alumina binder (Al.sub.2O.sub.3) had a BET specific surface area, determined as described above, equal to 355 m.sup.2/g.

EXAMPLE 3

[0113] Preparation of a Silica-Alumina (SiO.sub.2—Al.sub.2O.sub.3) Having a Content of Alumina (Al.sub.2O.sub.3) Equal to 8.7%, with an Alumina (Al.sub.2O.sub.3) Binder

[0114] 130 g of aluminium sulfate (Aldrich), as alumina precursor (Al.sub.2O.sub.3), and 200 g of demineralized water were introduced into a 500 ml flask: the mixture obtained was maintained at room temperature (25° C.), under vigorous stirring (500 rpm), for about 1 hour, obtaining a limpid solution. Subsequently, 250 g of an aqueous solution of sodium silicate having a silica (SiO.sub.2) content equal to 26.5% (Aldrich), as silica precursor (SiO.sub.2), were slowly added (15 minutes) to said limpid solution, obtaining a colourless gel. The gel obtained was transferred to a 1 litre beaker and treated 4 times with 500 ml of an aqueous solution of ammonium sulfate at 10% (Aldrich), obtaining a solid. Said solid was filtered, dried at 120° C. for a night, and subsequently calcined at 500° C. for 5 hours, obtaining a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) in the form of a colourless powder (64 g), whose elemental analysis, carried out as described above, showed a content of alumina (Al.sub.2O.sub.3) equal to 8.7%. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) had a BET specific surface area, determined as described above, equal to 300 m.sup.2/g.

[0115] A part of said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), 60 g, was mixed with 36 g of pseudo-bohemite Versal™ V-250 (UOP), as alumina precursor (Al.sub.2O.sub.3) of the binder, and 200 ml of a solution at 4% of acetic acid (Aldrich) in a 500 ml beaker. The mixture obtained was kept under vigorous stirring (500 rpm), at 60° C., for about 2 hours. The beaker was then transferred to a heating plate and the mixture was kept, under vigorous stirring (500 rpm), for a night, at 150° C., until it was dry. The solid obtained was calcined at 550° C., for 5 hours, obtaining a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with an alumina binder (Al.sub.2O.sub.3), in the form of a colourless solid (84 g) which was subsequently granulated mechanically and the fraction of granules having dimensions ranging from 0.5 mm to 1 mm was used as catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with an alumina binder (Al.sub.2O.sub.3) had a BET specific surface area, determined as described above, equal to 253 m.sup.2/g.

EXAMPLE 4

[0116] Preparation of a Silica-Alumina (SiO.sub.2—Al.sub.2O.sub.3) Having a Content of Alumina (Al.sub.2O.sub.3) Equal to 12.8%, with an Alumina (Al.sub.2O.sub.3) Binder

[0117] 171.6 g of an aqueous solution of sodium silicate having a silica (SiO.sub.2) content equal to 26.5% (Aldrich), as silica precursor (SiO.sub.2), and 40.1 of demineralized water were introduced into a first 500 ml flask, obtaining a first solution. 30.3 g of sodium aluminate (Aldrich), as alumina precursor (Al.sub.2O.sub.3), and 271 g of demineralized water were introduced into a second 300 ml flask, obtaining a second solution. Said first and said second solution were poured into a 250 ml flask and kept under vigorous stirring (500 rpm), at room temperature (25° C.), for 1 hour, obtaining a suspension which was subsequently heated to 80° C., and kept under vigour stirring (500 rpm), at said temperature, for 1 hour. After cooling to room temperature (25° C.), the pH of the suspension obtained was brought from pH 13 to pH 12 by adding a solution of sulfuric acid at 96% (Aldrich), obtaining a colourless gel. The gel obtained was transferred to a 1 litre beaker and treated 4 times with 500 ml of an aqueous solution of ammonium sulfate at 10% (Aldrich), obtaining a solid. Said solid was filtered, dried at 120° C. for a night, and subsequently calcined at 500° C. for 5 hours, obtaining a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) in the form of a colourless powder (42 g), whose elemental analysis, carried out as described above, showed a content of alumina (Al.sub.2O.sub.3) equal to 12.8%. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) had a BET specific surface area, determined as described above, equal to 163 m.sup.2/g

[0118] A part of said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), 40.4 g, was mixed with 24.4 g of pseudo-bohemite Versal™ V-250 (UOP), as alumina precursor (Al.sub.2O.sub.3) of the binder, and 300 ml of a solution at 4% of acetic acid (Aldrich) in a 500 ml beaker. The mixture obtained was kept under vigorous stirring (500 rpm), at 60° C., for about 2 hours. The beaker was then transferred to a heating plate and the mixture was kept, under vigorous stirring (500 rpm), for a night, at 150° C., until it was dry. The solid obtained was calcined at 550° C., for 5 hours, obtaining a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with an alumina binder (Al.sub.2O.sub.3), in the form of a colourless solid (56 g) which was subsequently granulated mechanically and the fraction of granules having dimensions ranging from 0.5 mm to 1 mm was used as catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with an alumina binder (Al.sub.2O.sub.3) had a BET specific surface area, determined as described above, equal to 154 m.sup.2/g.

EXAMPLE 5

[0119] Preparation of a Silica-Alumina (SiO.sub.2—Al.sub.2O.sub.3) Having a Content of Alumina (Al.sub.2O.sub.3) Equal to 1.8%, with a Silica (SiO.sub.2) Binder

[0120] 3.8 g of aluminium tri-sec-butoxide (Aldrich), as alumina precursor (Al.sub.2O.sub.3), were introduced into a first 500 ml flask. 50 g of orthosilicic acid (Aldrich, <20 mesh), as silica precursor (SiO.sub.2), and 250 g of demineralized water were introduced into a second 500 ml flask: the suspension of orthosilicic acid obtained was slowly added (10 minutes) to said first flask and the whole mixture was maintained at room temperature (25° C.), under vigorous stirring (500 rpm), for about 2 hours. The suspension obtained was then heated to 90° C., and kept at this temperature, under vigorous stirring (500 rpm), for about 1 hour. After cooling to room temperature (25° C.), the suspension obtained was filtered, 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 silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) in the form of a colourless powder (53.4 g), whose elemental analysis, carried out as described above, showed a content of alumina (Al.sub.2O.sub.3) equal to 1.8%. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) had a BET specific surface area, determined as described above, equal to 501 m.sup.2/g.

[0121] A part of said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), 41.1 g, was mixed with 57.7 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 800 ml beaker: the mixture obtained was kept under stirring, at 60° C., for about 2 hours. The beaker was then transferred to a heating plate and the mixture was kept, under vigorous stirring (500 rpm), for a night, at 150° C., until it was dry. The solid obtained was calcined at 550° C., for 5 hours, obtaining a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with a silica binder (SiO.sub.2), in the form of a colourless solid (56.3 g) which was subsequently granulated mechanically and the fraction of granules having dimensions ranging from 0.5 mm to 1 mm was used as catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with a silica binder (SiO.sub.2) had a BET specific surface area, determined as described above, equal to 357 m.sup.2/g.

EXAMPLE 6

[0122] Preparation of a Silica-Alumina (SiO.sub.2—Al.sub.2O.sub.3) Having a Content of Alumina (Al.sub.2O.sub.3) Equal to 3.8%, with a Silica (SiO.sub.2) Binder

[0123] 7.6 g of aluminium tri-sec-butoxide (Aldrich), as alumina precursor (Al.sub.2O.sub.3), were introduced into a first 500 ml flask. 50 g of orthosilicic acid (Aldrich, <20 mesh), as silica precursor (SiO.sub.2), and 250 g of demineralized water were introduced into a second 500 ml flask: the suspension of orthosilicic acid obtained was slowly added (10 minutes) to said first flask and the whole mixture was maintained at room temperature (25° C.), under vigorous stirring (500 rpm), for about 2 hours. The suspension obtained was then heated to 90° C., and kept at this temperature, under vigorous stirring (500 rpm), for about 1 hour. After cooling to room temperature (25° C.), the suspension obtained was filtered, 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 silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) in the form of a colourless powder (48 g), whose elemental analysis, carried out as described above, showed a content of alumina (Al.sub.2O.sub.3) equal to 3.8%. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) had a BET specific surface area, determined as described above, equal to 490 m.sup.2/g.

[0124] A part of said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), 40.3 g, was mixed with 57.2 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 800 ml beaker: the mixture obtained was kept under stirring, at 60° C., for about 2 hours. The beaker was then transferred to a heating plate and the mixture was kept, under vigorous stirring (500 rpm), for a night, at 150° C., until it was dry. The solid obtained was calcined at 550° C., for 5 hours, obtaining a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with a silica binder (SiO.sub.2), in the form of a colourless solid (55.9 g) which was subsequently granulated mechanically and the fraction of granules having dimensions ranging from 0.5 mm to 1 mm was used as catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with a silica binder (SiO.sub.2) had a BET specific surface area, determined as described above, equal to 302 m.sup.2/g.

EXAMPLE 7 (COMPARATIVE)

[0125] Preparation of a Catalyst Based on Alumina (Al.sub.2O.sub.3) with an Alumina (Al.sub.2O.sub.3) Binder

[0126] 50 g of pseudo-bohemite Versal™ V-250 (UOP), as alumina precursor (Al.sub.2O.sub.3), were calcined at 500° C., for 5 hours. After cooling to room temperature (25° C.), the solid obtained was mixed with 200 ml of an aqueous solution of acetic acid at 4% (Aldrich) and a further 16.5 g of pseudo-bohemite Versal™ V-250 (UOP), as alumina precursor (Al.sub.2O.sub.3) of the binder, in a 500 ml beaker. The beaker was then transferred to a heating plate and the mixture was kept, under vigorous stirring (500 rpm), for a night, at 150° C., until it was dry. The solid obtained was calcined at 550° C., for 5 hours, obtaining a catalyst based on alumina (Al.sub.2O.sub.3) with an alumina binder (Al.sub.2O.sub.3), in the form of a colourless solid (32.3 g) which was subsequently granulated mechanically and the fraction of granules having dimensions ranging from 0.5 mm to 1 mm was used as catalytic material. Said catalyst based on alumina (Al.sub.2O.sub.3) with an alumina binder (Al.sub.2O.sub.3) had a BET specific surface area, determined as described above, equal to 229 m.sup.2/g.

[0127] Table 1 indicates the various types of catalysts obtained in Examples 1-7.

TABLE-US-00001 TABLE 1 Exam- Alumina ple Type Precursor (Al.sub.2O.sub.3) (%) Binder 1 silica (SiO.sub.2) orthosilicic 0 alumina acid (Al.sub.2O.sub.3) 2 silica- aluminium tri- 3.8 alumina alumina sec-butoxide (Al.sub.2O.sub.3) (SiO.sub.2—Al.sub.2O.sub.3) and orthosilicic acid 3 silica- aluminium 8.7 alumina alumina sulfate and (Al.sub.2O.sub.3) (SiO.sub.2—Al.sub.2O.sub.3) sodium silicate 4 silica- sodium 12.8 alumina alumina aluminate and (Al.sub.2O.sub.3) (SiO.sub.2—Al.sub.2O.sub.3) sodium silicate 5 silica- aluminium tri- 1.8 silica (SiO.sub.2) alumina sec-butoxide (SiO.sub.2—Al.sub.2O.sub.3) and orthosilicic acid 6 silica- aluminium tri- 3.8 silica (SiO.sub.2) alumina sec-butoxide (SiO.sub.2—Al.sub.2O.sub.3) and orthosilicic acid 7 alumina Versal ™ 100 alumina (compar- (Al.sub.2O.sub.3) V-250 (Al.sub.2O.sub.3) ative)

EXAMPLES 8-15

Catalytic Tests

[0128] The catalytic materials obtained in Examples 1-7, were used in catalytic dehydration tests of a mixture of alkenols obtained by the catalytic dehydration of 1,3-butanediol operating as described hereunder.

[0129] In this respect, the catalyst based on cerium oxide was first prepared, which was used in the dehydration of 1,3-butanediol in order to obtain a mixture of alkenols, operating as described hereunder.

[0130] 500 g of a commercial aqueous solution at 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 Teflon moon-shaped stirrer shaft, 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 1000 g of water in a second 2-litre beaker, equipped with a magnetic anchor stirrer: the cerium nitrate hexahydrate was then solubilized by vigorous stirring (500 rpm), at room (25° C.) temperature. The solution obtained was introduced into a dripper and fed dropwise, over a period of 2 hours, to the solution of ammonium hydroxide (NH.sub.4OH) contained in the 3-litre beaker indicated above, under constant vigorous stirring (500 rpm). The pH of the suspension obtained was equal to 10.2. The suspension obtained was filtered and the solid obtained was washed with 2 litres of water and then dried in an oven, at 120° C., for 2 hours. The above synthesis was repeated until 2000 g of solid had been obtained.

[0131] 1270 g of the solid thus obtained were charged, after sieving at 0.125 mm, into an Erweka planetary mixer with a motor model AMD. The powder was dry mixed for 1 hour and 180 g of an aqueous solution at 25% of ammonium hydroxide (NH.sub.4OH), previously prepared by diluting the commercial aqueous solution at 28%-30% (28%-30% NH.sub.3 Basis ACS reagent Aldrich), were subsequently added dropwise, in sequence, over a period of 50 minutes, followed by 160 ml of demineralized water, also over a period of 50 minutes, obtaining a paste which was extruded with a Hutt extruder on which rolls with 2 mm holes were assembled. The pellets obtained from the extrusion were left to dry in the air for two days, a batch equal to 100 g was then calcined at 800° C., with a temperature rise of 1° C. per minute up to 800° C., followed by an isotherm at that temperature for 6 hours, obtaining a solid (87.7 g), which was subsequently granulated mechanically and the fraction of granules having dimensions ranging from 0.5 mm to 1 mm was used as catalyst. The catalyst thus obtained, based on cerium oxide, had a BET specific surface area, determined as described above, equal to 5 m.sup.2/g.

[0132] The fraction of granules having dimensions ranging from 0.5 mm to 1 mm of the catalyst based on cerium oxide obtained as described above, was charged into a reactor, in order to carry out the dehydration reaction of 1,3-butanediol and obtain a mixture of alkenols.

[0133] Said dehydration reaction of 1,3-butanediol was carried out in an AISI 316L steel fixed-bed tubular reactor, 400 mm long and with an internal diameter equal to 9.65 mm. A well was present inside the reactor, along its axis, having an external diameter equal to 3 mm which housed the thermocouple for the temperature regulation. The reactor was placed in an oven with electric heating which allowed the temperature selected for the above reaction, to be reached.

[0134] The catalyst charge, equal to 3 g, was inserted in the above reactor between two layers of inert material (corundum), the catalytic bed was held in place by means of a sintered steel septum positioned on the bottom of the reactor which had a down-flow configuration.

[0135] The feeding was carried out from the top of the reactor, above the area filled with inert material which acted as evaporator and allowed the reagents to reach the reaction temperature before entering into contact with the catalyst.

[0136] The liquid reagents were fed by means of a dosing pump of the type used in High Performance Liquid Chromatography (HPLC). The gases were fed by means of a Thermal Mass Flow-meter (TMF). The products obtained were cooled in a heat exchanger, downstream of the reactor, and the condensed liquid was collected in glass bottles using a series of motorized valves. The uncondensed gases, on the other hand, were sent to a wet-gas flow meter, in order to measure the volume of the gases produced. A small part of the gases were sampled in a gas-chromatograph (GC) on-line for analysis. The on-line analysis of the gases was carried out using an Agilent HP7890 gas-chromatograph with a HP-Al/S column having a length of 50 m, a diameter of 0.53 mm, 15 micron film, the carrier used was helium with a flow-rate equal to 30 cm/s, the detector was a flame detector. The analysis of the gases was carried out using an external standard with calibration curves for the single known components.

[0137] The characterization of the liquids collected was carried out by means of gas-chromatographic analysis using an Agilent HP6890 gas-chromatograph (GC) equipped with a Split/Splitless injector on a Quadrex 007 FFAP column having a height of 25 mm, a diameter of 0.32 mm, 1 micron film, the carrier used was helium with a rate equal to 50 cm/s, the detector was a flame detector. The determination was carried out using an internal standard with calibration curves for the single known components.

[0138] The catalytic performances indicated in Table 2 are expressed calculating the conversion of 1,3-butanediol [1,3-BDO] (C.sub.1,3-BDO) and the selectivity (S.sub.i) to the various alkenols according to the formulae indicated hereunder:

[00001]$C_{1,3-\mathrm{BDO}}=\frac{{\left({\mathrm{moli}}_{1,3-\mathrm{BDO}}\right)}_{\mathrm{in}}-{\left({\mathrm{moli}}_{1,3-\mathrm{BDO}}\right)}_{\mathrm{out}}}{{\left({\mathrm{moli}}_{1,3-\mathrm{BDO}}\right)}_{\mathrm{in}}}\times 100$$S_i=\frac{{\mathrm{moli}}_i}{{\left({\mathrm{moli}}_{1,3-\mathrm{BDO}}\right)}_{\mathrm{in}}-{\left({\mathrm{moli}}_{1,3-\mathrm{BDO}}\right)}_{\mathrm{out}}}\times 100$

wherein: [0139] moles.sub.i=moles of alkenols produced (moles of each single i-th alkenol); [0140] (moles.sub.1,3-BDO).sub.in=moles of 1,3-butanediol at the inlet; [0141] (moles.sub.1,3-BDO).sub.out=moles of 1,3-butanediol at the outlet.

[0142] The above catalyst based on cerium oxide, ground and sieved in the fraction ranging from 0.5 mm to 1 mm, charged into the reactor as described above, was pre-treated in situ, at 300° C., in a flow of nitrogen (N.sub.2).

[0143] 30 g/h of 1,3-butanediol (Fluka, purity ≧99%), were then fed to the above reactor, together with water in a molar ratio 1,3-butanediol:water equal to 1.2, at atmospheric pressure (1 bara—absolute bar), at the reaction temperatures and times indicated in Table 2.

[0144] Table 2 indicates the catalytic results obtained in terms of conversion of 1,3-butanediol [1,3-BDO] (C.sub.1,3-BDO) and selectivity (S), said selectivity (S) corresponding to the sum of the selectivity (S.sub.i) indicated above, i.e. S=ΣS.sub.i, calculated as described above, the temperature (° C.) and the reaction time (Time on Stream—T.o.S.) (hours), i.e. the time for which the catalyst was in contact with the feeding stream under the process conditions.

TABLE-US-00002 TABLE 2 Reaction time Temperature C.sub.1,3-BDO S (T.o.S.) (hours) (° C.) (%) (%) 99 380 83 97 216 380 84 98 412 385 85 96 608 385 88 96 846 385 86 98 854 388 88 93

[0145] The mixtures of alkenols leaving the reactor thus obtained were distilled, obtaining an aqueous solution of alkenol isomers having the composition indicated in Table 3.

TABLE-US-00003 TABLE 3 Composition (%) 2-buten-1-ol 24 3-buten-2-ol 40 3-buten-1-ol 0.4 water 35

[0146] The mixture of alkenols thus obtained was subjected to catalytic dehydration operating as follows.

[0147] The reactor in which said catalytic dehydration reaction was carried out consisted 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 electric 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 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 its quantity.

[0148] The products obtained, both in liquid form and in the form of vapour/gas, were characterized via gas-chromatography, using: [0149] 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 μm film thickness); [0150] 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 functionality “backflush”, CPSil-19 CB 7.5 m long.

[0151] The catalytic material used in the form of granules having dimensions ranging from 0.5 mm to 1 mm and in a quantity equal to 3 g, was prepared as described above in Examples 1-7.

[0152] The conversion of the alkenols (C.sub.ALCH.) and the selectivity to 1,3-butadiene (S.sub.1,3-BDE) were calculated as follows:

[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: [0153] (moles.sub.ALCH.).sub.in=moles of alkenols at the inlet; [0154] (moles.sub.ALCH.).sub.out=moles of alkenols at the outlet; [0155] moles.sub.1,3-BDE=total moles of 1,3-butadiene.

[0156] Table 4 indicates: the catalyst used, obtained as described above in Examples 1-7 (Catalyst); the temperature at which the catalytic dehydration is carried out [T (° C.)]; the contact time [τ (s)] calculated as a ratio of the volume of catalytic material charged/volumetric feeding flow-rate; the dilution at which it operates, i.e. the molar ratio water:alkenols in the feed, obtained by adding suitable quantities of water to the mixture of Table 2 [Dilution (mol/mol)]; “Time on Stream”, i.e. the time for which the catalyst was in contact with the feeding stream under the process conditions [T.o.S. (hours)]; the selectivity to 1,3-butadiene [S.sub.1,3-BDE (%)]; and the conversion of the alkenols [C.sub.ALCH.(%)].

TABLE-US-00004 TABLE 4 Ex- Dilution am- T τ (mol/ T.o.S. S.sub.1,3-BDE C.sub.ALCH. ple Catalyst (° C.) (s) mol) (hours) (%) (%) 8 Example 2 300 2 2.6:1 31 89 100 300 2 2.6:1 54 76 74 9 Example 7 300 2 2.6:1 29 49 87 (compara- tive) 10 Example 3 300 0.5 .sup. 8:1 30 90 73 11 Example 4 300 0.5 .sup. 8:1 30 81 56 12 Example 2 300 0.5 .sup. 8:1 29 93 99 300 0.5 .sup. 8:1 53 74 62 13 Example 1 300 2 2.6:1 27 88 100 300 2 2.6:1 51 78 90 14 Example 6 300 2 2.6:1 24 93 77 15 Example 5 300 2 2.6:1 30 94 92 16 Example 6 350 2 2.6:1 24 95 100 17 Example 2 270 4 2.6:1 29 88 99 18 Example 3 350 0.5 .sup. 8:1 6 83 100 19 Example 18 350 0.5 .sup. 8:1 6 95 100 (regener- ated)

[0157] From the data indicated in Table 4, the following results can be observed: [0158] on comparing Example 8 and Example 9, it can be seen that the catalytic material based on alumina alone (Al.sub.2O.sub.3) (content of alumina (Al.sub.2O.sub.3) equal to 100%) (Comparative Example 7) has a low selectivity with respect to the catalytic material according to the present invention (Example 8); [0159] on comparing Examples 10, 11 and 12, it can be seen that with a decrease in the aluminium content in the catalytic material according to the present invention, the productivity of the catalyst increases (higher selectivity and conversion); [0160] on comparing Example 13 and Example 8, it can be seen that the catalytic material according to the present invention having an alumina content equal to 0% (Example 13) has a selectivity and conversion similar to those of the catalytic material according to the present invention having an alumina content equal to 3.8% (Example 8); [0161] on comparing Example 14 and Example 15, it can be seen that also in the presence of silica (SiO.sub.2) as binder, with a decrease in the alumina content (Al.sub.2O.sub.3) in the catalytic material according to the present invention, a higher selectivity and conversion are obtained; [0162] on comparing Examples 16, 17, 18 and Example 19, it can be seen that the dehydration reaction of the mixture of alkenols can be carried out within a wide range of operating conditions (dilution, temperature, contact times), maintaining good results in terms of selectivity and conversion; [0163] Example 19 also shows how the catalytic material of Example 18, after regeneration, maintains good results in terms of selectivity and conversion.

[0164] In order to obtain the catalytic material used in Example 19, the catalytic material used in Example 18 was subjected to oxidative regeneration. Said oxidative regeneration was carried out by bringing the temperature inside the reactor to 450° C. and subsequently passing a flow of air and nitrogen according to the following procedure: [0165] Air: 30-60-90-130 ml/min; [0166] Nitrogen: 100-70-40-0 ml/min; [0167] Time: 1-1-1-10 hours

[0168] At the end of the regeneration, the flow of air was interrupted and substituted with nitrogen whereas the reactor was brought to the temperature required for the subsequent test.