PROCESS FOR PRODUCING DIENES

Abstract

A process for producing a diene, preferably a conjugated diene, more preferably 1,3-butadiene, includes the steps of dehydrating at least one alkenol in the presence of at least one catalytic material having at least one acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), preferably a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), the catalyst having an alumina content (Al.sub.2O.sub.3) lower than or equal to 12% by weight, preferably between 0.1% by weight and 10% by weight, with respect to the catalyst total weight. The alumina content is referred to the catalyst total weight without binder, and a pore modal diameter between 9 nm and 170 nm, preferably between 10 nm and 150 nm, still more preferably between 12 nm and 120 nm. Preferably, the alkenol is obtainable directly from biosynthetic processes, or catalytic dehydration processes of at least one diol, preferably a butanediol, more preferably 1,3-butanediol, still more preferably bio-1,3-butanediol, deriving from biosynthetic processes.

Claims

1. A process for producing a diene, comprising dehydrating 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 (Al.sub.2O.sub.3), said catalyst having an alumina content (Al.sub.2O.sub.3) lower than or equal to 12% by weight, with respect to the catalyst total weight, said alumina content being referred to the catalyst total weight without binder, and a pore modal diameter between 9 nm and 170 nm.

2. The process according to claim 1, wherein said alkenol is selected from:3-buten-2-ol (methyl vinyl carbinol), 3-buten-1-ol (allyl carbinol), 2-buten-1-ol (crotyl alcohol), or mixtures thereof, preferably 2-buten-1-ol (crotyl alcohol), 3-buten-2-ol (methyl vinyl carbinol), or mixtures thereof.

3. The process according to claim 1, wherein said alkenol is directly obtained from biosynthetic processes, or by catalytic dehydration processes of at least one diol, preferably a butanediol, more preferably 1,3-butanediol, still more preferably bio-1,3-butanediol, deriving from biosynthetic processes.

4. The process according to claim 1, wherein said alkenol derives from the catalytic dehydration of at least one diol, preferably a butanediol, more preferably 1,3-butanediol, still more preferably bio-1,3-butanediol, deriving from sugar fermentation, preferably from the fermentation of sugars deriving from biomass.

5. The process according to claim 4, wherein said diol is bio-1,3-butanediol deriving from the fermentation of sugars deriving from biomass, including scraps, residues, waste deriving from said biomass or from the processing thereof preferably it is bio-1,3-butanediol deriving from the fermentation of sugars deriving from guayule, including scraps, residues, waste deriving from said guayule or from the processing thereof.

6. The process according to claim 1, wherein said acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) is obtained by incipient wetness impregnation wherein the volume of a solution comprising at least one alumina precursor selected from aluminium alkoxides (such as tri-sec-aluminium butoxide), soluble aluminium salts (such as aluminium sulphate), aluminates (such as sodium aluminate), in a suitable concentration, is equal to or slightly lower than the pore volume of a solid support (for example, silica).

7. The process according to claim 1, wherein said catalytic material comprising at least one acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), is obtained by a process comprising: preparing an aqueous solution or an aqueous suspension of alumina (Al.sub.2O.sub.3) or of at least one precursor thereof selected from aluminium alkoxides (such as tri-sec-aluminium butoxide), soluble aluminium salts (such as aluminium sulphate), aluminates (such as sodium aluminate); adding to said aqueous solution or aqueous suspension of alumina (Al.sub.2O.sub.3) or of at least one precursor thereof, an aqueous solution or an aqueous suspension of silica (SiO.sub.2) or of at least one precursor thereof selected from silicic acids (such as orthosilicic acid), alkali metal silicates (such as sodium silicate); recovering the solid obtained by precipitation, or gelation, and optionally subjecting it: to an ion exchange step with at least one compound capable of exchanging ions with the surface of the obtained solid that is selected from aqueous solutions of salts containing ammonium ions (such as ammonium acetate, ammonium nitrate, ammonium sulphate); and/or to a binding step with at least one silica precursor (SiO.sub.2) selected from colloidal silicas (such as Ludox® TMA″—Sigma-Aldrich), silica alkoxides (such as tetraethyl-orthosilicate); or of at least one alumina precursor (Al.sub.2O.sub.3) selected from boehmite or pseudoboehmite (such as Versal™ V-250—UOP); and/or to a forming step such as extrusion, spherulization, tableting, granulation; subjecting it to optional thermal treatment and/or optional calcination, said optional thermal treatment and or optional calcination being carried out before or after one of the aforesaid steps, that is ion exchange, and/or binding, and/or forming.

8. The process according to claim 7, wherein said catalytic material comprising at least one acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), obtained after binding and/or forming, has a pore modal diameter between 9 nm and 170 nm.

9. The process according to claim 1, wherein said acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) has a specific surface area between 40 m.sup.2/g and 800 m.sup.2/g.

10. The process according to claim 1, wherein said 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), silica (SiO.sub.2), zirconium oxide, titanium oxide.

11. The process according to claim 10, wherein said catalytic material comprising 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, has a specific surface area between 25 m.sup.2/g and 700 m.sup.2/g.

12. The process according to claim 1, wherein said process for producing a diene is carried out with a diluent selected from: inert gases such as nitrogen (N.sub.2), argon (Ar); or from compounds having a boiling temperature higher than or equal to 50° C. and a melting temperature lower than or equal to 40° C., that are, preferably, in the liquid state at ambient temperature (25° C.) and at ambient pressure (1 atm), such as water, tetrahydrofuran, cyclohexane, benzene; preferably nitrogen (N.sub.2), water, more preferably water.

13. The process according to claim 1, wherein said process for producing a diene is carried out: in case the diluent is selected from inert gases, at a molar ratio of diluent to alkenol/s greater than 0.3: in case 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., that are preferably, in the liquid state at ambient temperature (25° C.) and at ambient pressure (1 atm), at a molar ratio of diluent to alkenol/s between 0.01 and 100.

14. The process according to claim 1, wherein said process for producing a diene is carried out: at a temperature between 150° C. and 500° C.; and/or at a pressure between 0.05 bara and 50 bar (bara=absolute bars); and/or operating at a contact time (i), calculated as the ratio of the catalytic material loaded to feeding volumetric rate, between 0.01 seconds and 10 second.

15. The process according to claim 1, wherein said catalytic material comprising at least one acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), is pre-treated at the temperature to which said process for producing a diene is carried out, that is at a temperature between 150° C. and 500° C., in the presence of at least one diluent.

Description

DETAILED DESCRIPTION OF THE DISCLOSURE

[0053] In accordance with a preferred embodiment of the present disclosure, said alkenol can be selected, for example from: 3-buten-2-ol (methyl vinyl carbinol—CAS Number 598-32-3), 3-buten-1-ol carbinol—CAS Number 627-27-0), 2-buten-1-ol (crotyl alcohol), or mixtures thereof, preferably between 2-buten-1-ol (crotyl alcohol), 3-buten-2-ol (methyl vinyl carbinol—CAS Number 598-32-3), or mixtures thereof.

[0054] For the purpose of the present description and of the following claims, the term 2-buten-1-ol (crotyl alcohol) means: both the mixture of the cis and trans isomers, and the cis isomer as such (CAS Number 4088-60-2), as well as the trans isomer as such (CAS Number 504-61-0).

[0055] In accordance with a preferred embodiment of the present disclosure, said alkenol can be obtained directly from biosynthetic processes, or by catalytic dehydration processes of at least one diol, preferably a butanediol, more preferably 1,3-butanediol, still more preferably bio-1,3-butanediol, deriving from biosynthetic processes.

[0056] Biosynthetic processes capable of directly making alkenols are described, for example, in the International patent application WO 2013/130481, or in the American patent application US 2013/109064, reported above.

[0057] For the purpose of the present disclosure, said alkenol can be obtained by catalytic dehydration of at least one diol, preferably of at least one butanediol, more preferably 1,3-butanediol, still more preferably bio-1,3-butanediol deriving from biosynthetic processes, in the presence of at least one catalyst based on cerium oxide, in which said catalyst based on cerium oxide is obtained by precipitation, in the presence of at least one base, of at least one compound containing cerium. Further details relating to said process can be found in the International patent application WO 2015/173780 in the name of the Applicant and incorporated herein by reference.

[0058] In accordance with a particularly preferred embodiment of the present disclosure, said alkenol derives from the catalytic dehydration of at least one diol, preferably a butanediol, more preferably 1,3-butanediol, still more preferably bio-1,3-butanediol, deriving from sugar fermentation, preferably from the fermentation of sugars deriving from biomass.

[0059] For the purpose of the present description and of the following claims, the term “biomass” indicates any organic material of vegetable origin including: products deriving from agriculture such as, for example, guayule, thistle, corn, soy, cotton, flax, rapeseed, sugar cane, palm, including scraps, residues and waste deriving from said products or from the processing thereof; products deriving from crops specifically cultivated for energy use such as, for example, miscanthus, panic, common reed, including scraps, residues and waste deriving from said products or from the processing thereof; products deriving from afforestation or forestry including scraps, residues and waste deriving from said products or from the processing thereof; scraps from agro-food products intended for human consumption or zootechnics; residues from the paper industry; waste coming from the separate collection of municipal solid waste such as, for example, urban waste of vegetable origin, paper.

[0060] Preferably, said diol is bio-1,3-butanediol deriving from the fermentation of sugars deriving from biomass, including scraps, residues, waste deriving from said biomass or from the processing thereof.

[0061] Still more preferably, said diol is bio-1,3-butanediol deriving from the fermentation of sugars deriving from guayule, including scraps, residues, waste deriving from said guayule or from the processing thereof.

[0062] In the case of use of a ligninocellulosic biomass of vegetable origin, in order to produce sugars, said biomass is subjected to physical treatments (such as, extrusion, “steam explosion”, and the like), and/or to chemical hydrolysis and/or to enzymatic hydrolysis, obtaining mixtures of carbohydrates, aromatic compounds and of other products deriving from the cellulose, hemicellulose and lignin present in the biomass. In particular, the obtained carbohydrates are mixtures of sugars with 5 and 6 carbon atoms which include, for example, sucrose, glucose, xylose, arabinose, galactose, mannose and fructose, which will be used in the fermentation. Processes relating to the production of sugars from biomass are described in the art such as for example, in the International patent application WO 2015/087254, in the name of the Applicant. Said fermentation is generally implemented by microorganisms, in particular by genetically modified microorganisms, capable of producing the alcohols of interest. More details relating to processes for the synthesis of 1,3-butanediol, in particular bio-1,3-butanediol, starting from renewable sources can be found, for example, in the American patent applications US 2010/330635, US 2012/0329113 and US 2013/0109064.

[0063] If the diol derives from biosynthetic processes, for example, from the fermentation of sugars, the aqueous mixture of alkenols obtained can be subjected to separation processes known in the art such as, for example, total or partial distillation. Alternatively, said aqueous mixture of alkenols can be used as such, effectively using water as a diluent, with no need to subject said aqueous mixture to expensive water elimination processes or, in any case, limiting said elimination.

[0064] It should be noted that, in the case in which said alkenol derives from the catalytic dehydration of at least one diol, the dehydration of said at least one diol to give at least one alkenol and the subsequent dehydration of said at least one alkenol to give a diene, can be implemented: [0065] in the same reactor or in different reactors, preferably in different reactors; [0066] continuously or discontinuously, preferably discontinuously.

[0067] For the purpose of the present disclosure, said acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), can be obtained by processes known in the art and can be used in various forms as described, for example, in the International patent application WO 2016/135069 reported above in the name of the Applicant and incorporated therein by reference. Further details relating to the processes for preparing said catalyst can also be found in the following examples.

[0068] For the purpose of the present disclosure, said acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), can be used as such, or it can be bound and/or formed by operating according to any process known in the art. Further details relating to said processes can be found, for example, in the American patents U.S. Pat. Nos. 3,974,099, 4,226,743, 6,451,200, 4,499,197, 4,175,118, 5,045,519, 6,642,172; or in: Campanati M. and others, “Fundamentals in the preparation of heterogeneous catalysts”, “Catalysis Today” (2003), Vol. 77, pages 299-314; Haber J. and others, “Manual of methods and procedures for catalyst characterization”, “Pure & Applied Chemistry” (1995), Vol. 67. No. 8-9, pages 1257-1306.

[0069] In accordance with a preferred embodiment of the present disclosure, said acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) can be obtained by “incipient wetness impregnation” wherein the volume of a solution of at least one alumina precursor that can be selected, for example, from aluminum alkoxides (for example, tri-sec-aluminium butoxide), soluble aluminum salts (for example, aluminum sulphate), aluminates (for example, sodium aluminate), in a suitable concentration, is equal to or slightly lower than the pore volume of a solid support (for example, silica).

[0070] In accordance with a further preferred embodiment of the present disclosure, said catalytic material comprising at least one acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), can be obtained by a process comprising: [0071] preparing an aqueous solution or an aqueous suspension of alumina (Al.sub.2O.sub.3) or of at least one precursor thereof that can be selected, for example, from aluminum alkoxides (for example, tri-sec-aluminium butoxide), soluble aluminum salts (for example, aluminum sulphate), aluminates (for example, sodium aluminate); [0072] adding to said aqueous solution or aqueous suspension of alumina (Al.sub.2O.sub.3) or of at least one precursor thereof, an aqueous solution or an aqueous suspension of silica (SiO.sub.2) or of at least one precursor thereof that can be selected from silicic acids (for example, orthosilicic acid), alkali metal silicates (for example, sodium silicate); [0073] recovering the solid obtained by precipitation, or gelation, and optionally subjecting it: [0074] to an ion exchange step with at least one compound capable of exchanging ions with the surface of the obtained solid that can be selected, for example, from aqueous solutions of salts containing ammonium ions (for example, ammonium acetate, ammonium nitrate, ammonium sulphate); and/or [0075] to a binding step with at least one silica precursor (SiO.sub.2) that can be selected, for example, from colloidal silicas (for example, Ludox® TMA″—Sigma-Aldrich), silica alkoxides (for example, tetraethylorthosilicate); or of at least one alumina precursor (Al.sub.2O.sub.3) that can be selected, for example, from bohemite or pseudo-bohemite (for example, Versal™ V-250—UOP); and/or [0076] to a forming step such as, for example, extrusion, spherulization, tableting, granulation; [0077] subjecting it to optional thermal treatment and/or optional calcination, said optional thermal treatment and/or optional calcination being carried out before or after one of the aforesaid steps, that is ion exchange, and/or binding, and/or forming.

[0078] It should be noted that, for the purpose of the present disclosure, said aqueous solution or aqueous suspension of alumina (Al.sub.2O.sub.3) or of at least one precursor thereof, can be added in one or more steps to said aqueous solution or aqueous suspension of silica (SiO.sub.2) or of at least one of the precursors thereof.

[0079] It should be noted that, for the purpose of the present disclosure, said aqueous solution or aqueous suspension of alumina (SiO.sub.2) or of at least one precursor thereof, can be added in one or more steps to said aqueous solution or aqueous suspension of silica (Al.sub.2O.sub.3) or at least one of the precursors thereof.

[0080] The additions described above can be carried out using methods known in the art, as well as referring to normal laboratory practices (by way of example, but not limiting to the scope of the present disclosure, by weighing, by volumetric dosages, etc.). The addition steps can however be greater than two without however constituting a criticality and, therefore, a limitation of the present disclosure.

[0081] For the purpose of the present disclosure, said aqueous solution or aqueous suspension of alumina (Al.sub.2O.sub.3) or of at least one precursor thereof, can comprise from 0.1% by weight to 70% by weight, preferably from 0.3% by weight to 60% by weight, still more preferably from 0.5% by weight to 50% by weight, with respect to the total weight of said aqueous solution or aqueous suspension of alumina (Al.sub.2O.sub.3) or of at least one precursor thereof.

[0082] Alternatively, instead of said aqueous solution or aqueous suspension of alumina (Al.sub.2O.sub.3) or of at least one precursor thereof, a hydroalcoholic solution comprising from 0.1% by weight to 95% by weight, preferably from 0.3% by weight to 60% by weight, still more preferably from 0.5%, by weight to 30% by weight, with respect to the total weight of said hydroalcoholic solution, of at least one alcohol selected, for example, from ethanol, 2-methoxyethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, tert-butanol, or mixtures thereof can be used.

[0083] For the purpose of the present disclosure, said aqueous solution or aqueous suspension of silica (SiO.sub.2) or of at least one precursor thereof, can comprise from 5% by weight to 70% by weight, preferably from 10% by weight to 60% by weight, still more preferably from 15% by weight to 50% by weight, with respect to total weight of said aqueous solution or aqueous suspension, of silica (SiO.sub.2) or at least one precursors thereof.

[0084] Alternatively, instead of said aqueous solution or aqueous suspension of silica (SiO.sub.2) or of at least one precursor thereof, a hydroalcoholic solution comprising from 5% by weight to 95% by weight, preferably from 15% by weight to 60% by weight, still more preferably from 20% by weight to 30% by weight, with respect to the total weight of said hydroalcoholic solution, of at least one alcohol selected, for example, from ethanol, 2-methoxyethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, tert-butanol, or mixtures thereof can be used.

[0085] The solid obtained by the aforesaid process can be recovered through processes known in the art such as, for example, filtration, decantation, and the like.

[0086] The aforesaid possible heat treatment can be carried out at a temperature between 100° C. and 200° C., preferably between 105° C. and 150° C., for a time between 2 hours and 72 hours, preferably between 3 hours and 18 hours.

[0087] The aforesaid optional calcination can be carried out at a temperature between 150° C. and 1500° C., preferably between 200° C. and 1400° C., still more preferably between 300° C. and 1200° C., for a time between 1 hour and 24 hours, preferably between 2 hours and 10 hours, still more preferably between 4 hours and 8 hours. Generally, said calcination can be carried out in the air, or with an inert gas [such as nitrogen (N.sub.2)], or in a controlled atmosphere (oxidizing or reducing), preferably in air.

[0088] As stated above, the acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), when not obtained by incipient wetness impregnation, can be used in various forms. For example, said catalyst can be used as such, or it can be formed by operating according to any forming process known in the art such as, for example, extrusion, spherulation, tableting, granulation, and the like. The optional heat treatment and the optional calcination reported above can be carried out before or after one of said forming processes.

[0089] Preferably, said acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), when not obtained by incipient wetness impregnation, can be used in extruded form, optionally containing traditional binders such as, for example, alumina (Al.sub.2O.sub.3), silica (SiO.sub.2), zirconium oxide, titanium oxide, preferably silica (SiO.sub.2) or alumina (Al.sub.2O.sub.3), still more preferably alumina (Al.sub.2O.sub.3).

[0090] If said traditional binders are present, the extrusion generally also provides for the use of a peptizing agent such as, for example, aqueous solutions of acetic acid, nitric acid, or ammonium hydroxide, which can be mixed with the catalyst and the binder before extrusion, until a homogeneous mixture is obtained. At the end of said extrusion, the pellets obtained are generally subjected to calcination by operating as described above.

[0091] The solid obtained after binding and/or forming can contain from 5% by weight to 90% by weight, preferably from 10% by weight to 75% by weight, more preferably from 20% by weight to 55% by weight, of binder, with respect to the total weight of said acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3).

[0092] It should be noted that after binding and/or forming said catalytic material comprising at least one acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) has a pore modal diameter in the range reported above, i.e. a pore modal diameter between 9 nm and 170 nm, preferably between 10 nm and 150 nm, still more preferably between 12 nm and 120 nm.

[0093] In accordance with a preferred embodiment of the present disclosure, said catalytic material comprising at least one acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), obtained after binding and/or forming, has a pore modal diameter between 9 nm and 170 nm, preferably between 10 nm and 150 nm, still more preferably between 12 nm and 120 nm.

[0094] In accordance with a preferred embodiment of the present disclosure, said acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3) can have a specific surface area between 40 m.sup.2/g and 800 m.sup.2/g, preferably between 45 m.sup.2/g and 700 m.sup.2/g, still more preferably between 50 m.sup.2/g and 600 m.sup.2/g.

[0095] In accordance with a preferred embodiment of the present disclosure, said 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 that can be selected, for example, from alumina (Al.sub.2O.sub.3), silica (SiO.sub.2), zirconium oxide, titanium oxide, preferably silica (SiO.sub.2) or alumina (Al.sub.2O.sub.3), still more preferably alumina (Al.sub.2O.sub.3).

[0096] In accordance with a further preferred embodiment of the present disclosure, said catalytic material comprising 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, can have a specific surface area between 25 m.sup.2/g and 700 m.sup.2/g, preferably between 100 m.sup.2/g and 600 m.sup.2/g, still more preferably between 110 m.sup.2/g and 500 m.sup.2/g.

[0097] For the purpose of the present description and of the following claims, the term “specific surface area” indicates the BET specific surface area determined by static absorption of nitrogen (N.sub.2), at the temperature of the liquid nitrogen equal to −196.15° C. (77 K), with ASAP 2010 instrument from Micromeritics, in accordance with the ASTM D3663-03 (2008) standard.

[0098] The elementary analysis of said acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), was carried out via WD-XRF (“Wavelength dispersion X Ray fluorescence”), with a PANalytical Axios Advanced spectrometer equipped with a 4 KW X-ray tube with rhodium (Rh) anode.

[0099] In accordance with a preferred embodiment of the present disclosure, said process for producing a diene can be carried out with at least one diluent that can be selected, for example, from: inert gases such as, for example, nitrogen (N.sub.2), argon (Ar), preferably nitrogen (N.sub.2); or from compounds having a boiling temperature higher than or equal to 50° C. and a melting temperature lower than or equal to 40° C., that are, preferably, in the liquid state at ambient temperature (25° C.) and at ambient pressure (1 atm), such as, for example, water, tetrahydrofuran, cyclohexane, benzene. Nitrogen (N.sub.2), water, are preferred, water is particularly preferred.

[0100] In accordance with a preferred embodiment of the present disclosure, said process for producing a diene can be carried out, in case the diluent is selected from inert gases, at a molar ratio of diluent to alkenol/s greater than 0.3, preferably between 0.5 and 2.

[0101] In accordance with a preferred embodiment of the present disclosure, said process for producing a diene can be carried out, in case 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., that are preferably, in the liquid state at ambient temperature (25° C.) and at ambient pressure (1 atm), at a molar ratio of diluent to alkenol/s between 0.01 and 100, preferably between 0.1 and 50, more preferably between 1 and 10.

[0102] In accordance with a preferred embodiment of the present disclosure, said process for producing a diene can be carried out at a temperature between 150° C. and 500° C., preferably between 200° C. and 450° C., more preferably between 250° C. and 400° C.

[0103] In accordance with a preferred embodiment of the present disclosure, said process for producing a diene can be carried out at a pressure between 0.05 bara and 50 bara, preferably between 0.3 bara and 3,5 bara, more preferably between 0.8 bara and 2.5 bara (bara=absolute bars).

[0104] In accordance with a preferred embodiment of the present disclosure, said process for producing a diene can be carried out by operating at a contact time (τ), calculated as the ratio of the catalytic material loaded to feeding volumetric rate, between 0.01 seconds and 10 seconds, preferably between 0.05 seconds and 8 seconds, more preferably between 0.1 seconds and 4 seconds.

[0105] In accordance with a preferred embodiment of the present disclosure, said catalytic material comprising at least one acid catalyst based on silica (SiO.sub.2) and alumina (Al.sub.2O.sub.3), preferably a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), can be pre-treated at the temperature to which said process for producing a diene is carried out, that is at a temperature between 150° C. and 500° C., preferably between 200° C. and 450° C., more preferably between 250° C. and 400° C., preferably in the presence of at least one diluent selected from those reported above, more preferably in the presence of water.

[0106] For the purpose of the present disclosure, said process for producing a diene can be carried out in the gas phase or in the mixed liquid/gas phase, preferably in the gas phase, discontinuously (for example, in a stirred and heated autoclave), or continuously (for example, in one or more catalytic reactors in series), preferably continuously. Said reactors can be with fixed bed, or with fluidized bed, preferably with fixed bed. If they are with fixed bed, the catalytic material can be divided into several beds. Said reactors can contemplate a recycling of part of the reaction effluents or of the catalytic material by configuring a recirculated reactor. If a liquid phase is present, the process for producing dienes can be carried out in continuous stirring reactors, containing the dispersed catalytic material.

[0107] In order to better understand the present disclosure and to put it into practice, some illustrative and non-limiting examples thereof are reported below.

Example 1 (Comparative)

Preparation of a Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8% and Pore Modal Diameter Equal to 7 nm

[0108] 3360.3 g of an aqueous solution of sodium silicate having a silica content (SiO.sub.2) equal to 26.5% (Aldrich), as a silica precursor (SiO.sub.2) were introduced into a first 5 l flask. In a second 21 flask, 26.6 g of sodium aluminate (Aldrich), as an alumina precursor (Al.sub.2O.sub.3), and 650.9 g of demineralized water, were introduced obtaining a second aqueous solution. Said second aqueous solution was poured into the 5 l flask and the resulting solution was kept under vigorous stirring (500 rpm), at ambient temperature (25° C.), for 1 hour, obtaining a suspension which was subsequently heated to 80° C., and kept under vigorous stirring (500 rpm), at said temperature, for 1 hour. After cooling to ambient temperature (25° C.), the pH of the suspension obtained was brought from pH 13 to pH 12 by adding a 96% sulfuric acid solution (Aldrich), obtaining a colourless gel. The gel obtained was granulated, transferred to a 12 l plastic container and treated 4 times with 500 ml of an aqueous solution of 10% ammonium sulphate (Aldrich). The material was filtered, washed with 10 l of demineralized water, dried at 120° C. for one 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 colourless powder (936 g), the elemental analysis of which, carried out as described above, showed an alumina content (Al.sub.2O.sub.3) equal to 1.8%. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 259 m.sup.2/g, and pore modal diameter, determined as reported above, equal to 7 nm.

Example 2 (Comparative)

Preparation of a Catalyst Based on Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8%, with Alumina Binder (Al.SUB.2.O.SUB.3.) and Pore Modal Diameter Equal to 3 nm

[0109] A part of the silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) obtained in Example 1, 63.8 g, was mixed with 30.8 g of pseudoboemite Versal™ V-250 (UOP), as an alumina precursor (Al.sub.2O.sub.3) of the binder, and 300 ml of a 4% solution of acetic acid (Aldrich) in a 500 ml beaker. The obtained mixture was kept, under vigorous stirring (500 rpm), at 60° C., for about 2 hours. Subsequently, the beaker was transferred onto a heating plate and the mixture was kept, under vigorous stirring (500 rpm), at 150° C., for one night, until 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 alumina binder (Al.sub.2O.sub.3) in the form of a colourless solid (84 g) which was subsequently mechanically granulated and the fraction of granules having dimensions from 0.5 mm to 1.0 mm was used as the catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with alumina binder (Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 254 m.sup.2/g and pore modal diameter, determined as reported above, equal to 3 nm.

Example 3 (Disclosure)

Preparation of a Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8% and Pore Modal Diameter Equal to 14 nm

[0110] 1056.8 g of an aqueous solution of sodium silicate having a silica content (SiO.sub.2) equal to 26.5% (Aldrich), as a silica precursor (SiO.sub.2) and 786.6 g of demineralized water were introduced into a first 5 l flask. In a second 2 l flask, 8.5 g of sodium aluminate (Aldrich), as an alumina precursor (Al.sub.2O.sub.3), and 1199.1 g of demineralized water, were introduced obtaining a second aqueous solution. Said second aqueous solution was poured into the 5 l flask and the resulting solution was kept under vigorous stirring (500 rpm), at ambient temperature (25° C.), for 1 hour, obtaining a suspension which was subsequently heated to 80° C., and kept under vigorous stirring (500 rpm), at said temperature, for 1 hour. After cooling to ambient temperature (25° C.), the pH of the suspension obtained was brought from pH 13 to pH 8.5 by adding a 96% sulfuric acid solution (Aldrich), obtaining a colourless gel. The gel obtained was transferred to a 12 l plastic container and treated 4 times with 5 kg of an aqueous solution of 10% ammonium sulphate (Aldrich), obtaining a solid. Said solid was filtered, washed with 10 kg of demineralized water, dried at 120° C. for one 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 colourless powder (236 g), the elemental analysis of which, carried out as described above, showed an alumina content (Al.sub.2O.sub.3) equal to 1.8%. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 262 m.sup.2/g, and pore modal diameter, determined as reported above, equal to 14 nm.

Example 4 (Disclosure)

Preparation of a Catalyst Based on Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8%, with Alumina Binder (Al.SUB.2.O.SUB.3.) and Pore Modal Diameter Equal to 14 nm

[0111] A part of the silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) obtained in Example 3, 26.6 g, was mixed with 14.7 g of pseudoboemite Versal™ V-250 (UOP), as an alumina precursor (Al.sub.2O.sub.3) of the binder, and 300 ml of a 4% solution of acetic acid (Aldrich) in a 500 ml beaker. The obtained mixture was kept, under vigorous stirring (500 rpm), at 60° C., for about 2 hours. Subsequently, the beaker was transferred onto a heating plate and the mixture was kept, under vigorous stirring (500 rpm), at 150° C., for one night, until 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 alumina binder (Al.sub.2O.sub.3) in the form of a colourless solid (34 g) which was subsequently mechanically granulated and the fraction of granules having dimensions from 0.5 mm to 1.0 mm was used as the catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with alumina binder (Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 255 m.sup.2/g and pore modal diameter, determined as reported above, equal to 14 nm.

Example 5 (Disclosure)

Preparation of a Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8% and Pore Modal Diameter Equal to 40 nm

[0112] 1057.3 g of an aqueous solution of sodium silicate having a silica content (SiO.sub.2) equal to 26.5% (Aldrich), as a silica precursor (SiO.sub.2) and 787.0 g of demineralized water were introduced into a first 5 l flask. In a second 2 l flask, 9.0 g of sodium aluminate (Aldrich), as an alumina precursor (Al.sub.2O.sub.3), and 1219.8 g of demineralized water, were introduced obtaining a second aqueous solution. Said second aqueous solution was poured into the 5 l flask and the resulting solution was kept under vigorous stirring (500 rpm), at ambient temperature (25° C.), for 1 hour, obtaining a suspension which was subsequently heated to 80° C., and kept under vigorous stirring (500 rpm), at said temperature, for 1 hour. After cooling to ambient temperature (25° C.), the pH of the suspension obtained was brought from pH 13 to pH 8.5 by adding a 96% sulfuric acid solution (Aldrich), and the whole was kept under stirring, at ambient temperature (25° C.), for 72 hours, obtaining a colourless gel. The colourless gel obtained was transferred to a 12 l plastic container and treated 4 times with 5 kg of an aqueous solution of 10% ammonium sulphate (Aldrich), obtaining a solid. Said solid was filtered, washed with 10 kg of demineralized water, dried at 120° C. for one 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 colourless powder (252.8 g), the elemental analysis of which, carried out as described above, showed an alumina content (Al.sub.2O.sub.3) equal to 1.8%. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 221 m.sup.2/g, and pore modal diameter, determined as reported above, equal to 40 nm.

Example 6 (Disclosure)

Preparation of a Catalyst Based on Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8% and Pore Modal Diameter Equal to 37 nm, with Alumina Binder (Al.SUB.2.O.SUB.3.)

[0113] A part of the silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) obtained in Example 5, 100.1 g, was mixed with 55.2 g of pseudoboemite Versal™ V-250 (UOP), as an alumina precursor (Al.sub.2O.sub.3) of the binder, and 300 ml of a 4% solution of acetic acid (Aldrich) in a 500 ml beaker. The obtained mixture was kept, under vigorous stirring (500 rpm), at 60° C., for about 2 hours. Subsequently, the beaker was transferred onto a heating plate and the mixture was kept, under vigorous stirring (500 rpm), at 150° C., for one night, until 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 alumina binder (Al.sub.2O.sub.3) in the form of a colourless solid (138 g) which was subsequently mechanically granulated and the fraction of granules having dimensions from 0.5 mm to 1.0 mm was used as the catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with alumina binder (Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 212 m.sup.2/g and pore modal diameter, determined as reported above, equal to 37 nm.

Example 7 (Disclosure)

Preparation of a Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8% and Pore Modal Diameter Equal to 37 nm

[0114] 1056.9 g of an aqueous solution of sodium silicate having a silica content (SiO.sub.2) equal to 26.5% (Aldrich), as a silica precursor (SiO.sub.2) and 787.9 g of demineralized water were introduced into a first 5 l flask. In a second 2 l flask, 9.0 g of sodium aluminate (Aldrich), as an alumina precursor (Al.sub.2O.sub.3), and 1219.2 g of demineralized water, were introduced obtaining a second aqueous solution. Said second aqueous solution was poured into the 5 l flask and the resulting solution was kept under vigorous stirring (500 rpm), at ambient temperature (25° C.), for 1 hour, obtaining a suspension which was subsequently heated to 80° C., and kept under vigorous stirring (500 rpm), at said temperature, for 1 hour. After cooling to ambient temperature (25° C.), the pH of the suspension obtained was brought from pH 13 to pH 8.5 by adding a 70% nitric acid solution (Aldrich), and the whole was kept under stirring, at ambient temperature (25° C.), for 72 hours, obtaining a colourless gel. The colourless gel obtained was transferred to a 12 l plastic container and treated 4 times with 5 kg of an aqueous solution of 10% ammonium sulphate (Aldrich), obtaining a solid. Said solid was filtered, washed with 10 kg of demineralized water, dried at 120° C. for one 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 colourless powder (254.5 g), the elemental analysis of which, carried out as described above, showed an alumina content (Al.sub.2O.sub.3) equal to 1.8%. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 252 m.sup.2/g, and pore modal diameter, determined as reported above, equal to 37 nm.

Example 8 (Disclosure)

Preparation of a Catalyst Based on Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8% and Pore Modal Diameter Equal to 36 nm, with Alumina Binder (Al.SUB.2.O.SUB.3.) (Extruded)

[0115] A part of the silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), obtained in Example 7, was subjected to an extrusion process. For this purpose, 100.1 g of said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) and 86.6 g of pseudoboemite Versal™ V-250 (UOP), as an alumina precursor (Al.sub.2O.sub.3), of the binder were introduced into an Erweka AR 402 mixer: the powders were mixed at a rotation speed of 80 rpm, for 2 hours. Subsequently, 253.0 g of a 5% solution of acetic acid were supplied: the mixture obtained was kept at a rotation speed of 80 rpm, for a further 2 hours. Subsequently, the mixture was transferred to a Hosokawa-Bepex Pharmapaktor L 200/50 G laboratory extruder, operating under the following conditions: [0116] temperature: 25° C.; [0117] rotation speed of the screws:15 rpm; [0118] applied force:150 kN.

[0119] Pellets were obtained at the exit from the extruder which were dried in the air, then calcined at 550° C. for 5 hours. 133.7 silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with alumina binder (Al.sub.2O.sub.3) in the form of a colourless solid was obtained which was subsequently mechanically granulated and the fraction of granules having dimensions from 0.5 mm to 1.0 mm was used as the catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with alumina binder (Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 260 m.sup.2/g and pore modal diameter, determined as reported above, equal to 36 nm.

Example 9 (Disclosure)

Preparation of a Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8% and Pore Modal Diameter Equal to 100 nm

[0120] 251.4 g of an aqueous solution of sodium silicate having a silica content (SiO.sub.2) equal to 26.5% (Aldrich), as a silica precursor (SiO.sub.2) and 105.0 g of demineralized water are introduced into a first 1 l flask. In a second 1 l flask, 1.8 g of sodium aluminate (Aldrich), as an alumina precursor (Al.sub.2O.sub.3), 11.1 g of sodium dihydrogen phosphate (NaH.sub.2PO.sub.4.H.sub.2O) (Aldrich) and 255.0 g of demineralized water were introduced obtaining a second aqueous solution. Said second aqueous solution was poured into the 1 l flask and the resulting solution was kept under vigorous stirring (500 rpm), at ambient temperature (25° C.), for 1 hour, obtaining a suspension which was subsequently heated to 80° C., and kept under vigorous stirring (500 rpm), at said temperature, for 1 hour. After cooling to ambient temperature (25° C.), the pH of the suspension obtained was brought from pH 13 to pH 8.5 by adding a 96% sulfuric acid solution (Aldrich), obtaining a colourless gel. The gel obtained was transferred to a 5 l plastic container and treated 4 times with 2 kg of an aqueous solution of 10% ammonium acetate (Aldrich), obtaining a solid. Said solid was filtered, washed with 500 g of demineralized water, dried at 120° C. for one 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 colourless powder (54 g), the elemental analysis of which, carried out as described above, showed an alumina content (Al.sub.2O.sub.3) equal to 1.8%. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 57 m.sup.2/g, and pore modal diameter, determined as reported above, equal to 100 nm.

Example 10 (Disclosure)

Preparation of a Catalyst Based on Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8% and Pore Modal Diameter Equal to 100 nm, with Alumina Binder (Al.SUB.2.O.SUB.3.)

[0121] A part of the silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) obtained in Example 9, 20.0 g, was mixed with 12.0 g of pseudoboemite Versal™ V-250 (UOP), as an alumina precursor (Al.sub.2O.sub.3) of the binder, and 300 ml of a 4% solution of acetic acid (Aldrich) in a 500 ml beaker. The obtained mixture was kept, under vigorous stirring (500 rpm), at 60° C., for about 2 hours. Subsequently, the beaker was transferred onto a heating plate and the mixture was kept, under vigorous stirring (500 rpm), at 150° C., for one night, until 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 alumina binder (Al.sub.2O.sub.3) in the form of a colourless solid (28 g) which was subsequently mechanically granulated and the fraction of granules having dimensions from 0.5 mm to 1.0 mm was used as the catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with alumina binder (Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 118 m.sup.2/g and pore modal diameter, determined as reported above, equal to 100 nm.

Example 11 (Comparative)

Preparation of a Catalyst Based on Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8% and Pore Modal Diameter Equal to 3 nm (Extruded)

[0122] A part of the silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), prepared in Example 1, was subjected to an extrusion process.

[0123] For this purpose, 450.1 g of said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) and 217.0 g of pseudoboemite Versal™ V-250 (UOP), as an alumina precursor (Al.sub.2O.sub.3), of the binder were introduced into an Erweka AR 402 planetary mixer. The powders were mixed at a rotation speed equal to 80 rpm, for 2 hours. Subsequently, keeping the rotation speed equal to 80 rpm in the mixer, 766.1 g of a 4% solution of acetic acid (Aldrich) were supplied. Subsequently, the mixture was transferred to a Hosokawa-Bepex Pharmapaktor L 200/50 G laboratory extruder, operating under the following conditions: [0124] temperature: 25° C.; [0125] rotation speed of the screws: 15 rpm; [0126] applied force: 150 kN.

[0127] Pellets were obtained at the exit from the extruder which were dried in the air, then calcined at 550° C. for 5 hours. 300.6 g of silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with alumina binder (Al.sub.2O.sub.3) in the form of a colourless solid was obtained which was subsequently mechanically granulated and the fraction of granules having dimensions from 0.5 mm to 1.0 mm was used as the catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with alumina binder (Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 252 m.sup.2/g and pore modal diameter, determined as reported above, equal to 3 nm.

Example 12 (Disclosure)

Preparation of a Catalyst Based on Silica-Alumina (SiO.SUB.2.—Al.SUB.2.O.SUB.3.) Having an Alumina Content (Al.SUB.2.O.SUB.3.) Equal to 1.8% and Pore Modal Diameter Equal to 36 nm, with Alumina Binder (Al.SUB.2.O.SUB.3.) (Extruded)

[0128] A part of the silica-alumina (SiO.sub.2—Al.sub.2O.sub.3), prepared in Example 5, was subjected to an extrusion process.

[0129] For this purpose, 103.0 g of said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) and 57.0 g of pseudoboemite Versal™ V-250 (UOP), as an alumina precursor (Al.sub.2O.sub.3), of the binder were introduced into an Erweka AR 402 planetary mixer. The powders were mixed at a rotation speed equal to 80 rpm for 2 hours. Subsequently, keeping the rotation speed equal to 80 rpm in the mixer, 450.0 g of a 4% solution of acetic acid (Aldrich) were supplied. Subsequently, the mixture was transferred to a Hosokawa-Bepex Pharmapaktor L 200/50 G laboratory extruder, operating under the following conditions: [0130] temperature: 25° C.; [0131] rotation speed of the screws: 15 rpm; [0132] applied force: 150 kN.

[0133] Pellets were obtained at the exit from the extruder which were dried in the air, then calcined at 550° C. for 5 hours. 98.6 g of silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with alumina binder (Al.sub.2O.sub.3) in the form of a colourless solid (138 g) was obtained which was subsequently mechanically granulated and the fraction of granules having dimensions from 0.5 mm to 1.0 mm was used as the catalytic material. Said silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) with alumina binder (Al.sub.2O.sub.3) had a specific BET surface area, determined as reported above, equal to 226 m.sup.2/g and pore modal diameter, determined as reported above, equal to 36 nm.

[0134] Table 1 shows the different types of catalysts obtained in Examples 1-12.

TABLE-US-00001 TABLE 1 Pore modal Ageing diameter Example Type pH (hours) (nm) 1 (comparative) silica-alumina 12   — 7 (SiO.sub.2—Al.sub.2O.sub.3) 2 (comparative) silica-alumina — — 3 (SiO.sub.2—Al.sub.2O.sub.3) from Example 1, with alumina binder 3 (disclosure) silica-alumina 8.5 — 14 (SiO.sub.2—Al.sub.2O.sub.3) 4 (disclosure) silica-alumina — — 14 (SiO.sub.2—Al.sub.2O.sub.3) from Example 3, with alumina binder 5 (disclosure) silica-alumina 8.5 72 40 (SiO.sub.2—Al.sub.2O.sub.3) 6 (disclosure) silica-alumina — — 37 (SiO.sub.2—Al.sub.2O.sub.3) from Example 5, with alumina binder 7 (disclosure) silica-alumina 8.5 72 37 (SiO.sub.2—Al.sub.2O.sub.3) 8 (disclosure) silica-alumina — — 36 (SiO.sub.2—Al.sub.2O.sub.3) from Example 7, with alumina binder 9 (disclosure) silica-alumina 8.5 — 100 (SiO.sub.2—Al.sub.2O.sub.3) 10 (disclosure) silica-alumina 8.5 — 100 (SiO.sub.2—Al.sub.2O.sub.3) from Example 9, with alumina binder 11 (comparative) silica-alumina — — 3 (SiO.sub.2—Al.sub.2O.sub.3) from Example 1, with alumina binder (extruded) 12 (disclosure) silica-alumina — — 36 (SiO.sub.2—Al.sub.2O.sub.3) from Example 5, with alumina binder (extruded)

[0135] From the comparison between Example 1 (comparative), Example 3 (disclosure), Example 5 (disclosure), Example 7 (disclosure) and Example 9 (disclosure), it can be seen that through suitable expedients, such as the pH variation in one phase of the silica-alumina synthesis (SiO.sub.2—Al.sub.2O.sub.3), an increase in ageing in another phase of the synthesis or, finally, by the use of compounds having the function of pore forming or templating such as, for example, compounds containing heteroatoms such as phosphorus (P) (as reported, for example, by Wen Wen and others, “Effect of sol aging time on the anti-reflective properties of silica coatings templated with phosphoric acid”, “Results in Physics” (2016), pages 1012-1014, https://doi.org/10.1016/j.rinp2016.11.028) it is possible to obtain a catalyst having a pore modal diameter in accordance with the present disclosure. It should be noted that, for the purpose of the present disclosure, said expedients are to be intended as examples and not limitations of the same: the pore modal diameter in accordance with the present disclosure could also be obtained by means of other methods.

[0136] From the comparison between Example 3 (disclosure) and Example 4 (disclosure), it can be seen that the pore modal diameter, after binding, is in accordance with the present disclosure.

[0137] From the comparison between Example 7 (disclosure) and Example 8 (disclosure), it can be seen that the pore modal diameter, after binding and extrusion, is in accordance with the present disclosure.

[0138] From the comparison between Example 5 (disclosure), Example 6 (disclosure) and Example 12 (disclosure), it can be seen that the pore modal diameter, after binding (Example 6) and extrusion (Example 12), is in accordance with the present disclosure.

[0139] Finally, from the comparison between Example 1 (comparative), Example 2 (comparative) and Example 11 (comparative), starting from a catalyst having a pore modal diameter outside the range of the present disclosure it can be seen that the pore modal diameter, after binding (Example 2) and extrusion (Example 11), are not in accordance with the present disclosure.

Examples 13-18

Catalytic Tests

[0140] The catalytic materials obtained in Examples 1-12 were used in the catalytic dehydration test of a mixture of butenols obtained by catalytic dehydration of 1,3-butanediol operating as described in Examples 8-15 of the international patent application WO 2016/135609 reported above.

[0141] The mixtures of butenols obtained at the exit of the reactor were distilled obtaining an aqueous solution of isomeric butenols having the composition reported in Table 2.

TABLE-US-00002 TABLE 2 Composition (%) 2-buten-1-ol 24 3-buten-2-ol 40 3-buten-1-ol 0.4 water 35

[0142] The aqueous solution of butenols reported in Table 2, diluted in water as reported in Table 3, was subjected to catalytic dehydration operating as follows.

[0143] The reactor in which said catalytic dehydration reaction was carried out is a tubular reactor with fixed bed made of AISI 316L steel, 350 mm long and with an internal diameter of 9.65 mm. Inside the reactor, along the axis thereof, there was a well with an external diameter equal to 3 mm which housed the thermocouple for temperature regulation. The reactor was placed in an oven with electric heating which allowed to reach the temperature selected for the aforesaid reaction.

[0144] The catalyst charge, equal to 3 g, was inserted in the aforesaid reactor between two layers of inert material (corundum), the catalytic bed was held in place by means of a sintered steel septum placed on the bottom of the down-flow reactor.

[0145] The feeding was carried out from the top of the reactor, above the area filled with inert material which acted as an evaporator and allowed the reactants to reach the reaction temperature before coming into contact with the catalyst.

[0146] The liquid reagents were fed through a metering pump of the type used in “High Performance Liquid Chromatography” (HPLC). The gases were supplied through the “Thermal Mass Flow-meter” (TMF). Downstream of the reactor, the products obtained were cooled in a heat exchanger and the condensed liquid was collected in glass bottles by means of a series of timed valves. The uncondensed gases were instead sent to a volumetric wet gas meter, in order to measure the volume of gases produced. A small portion of the gases were sampled in an on-line gas chromatograph (GC) for analysis. The on-line gas analysis was carried out using an Agilent HP7890 gas chromatograph (GC) with a 50 m long HP—Al/S column with 0.53 mm diameter, 15 micron of film, the carrier used was helium with a flow equal to 30 cm/s, the detector was with flame. The analysis of the gases was carried out using an external standard with calibration curves for the single known components.

[0147] The characterization of the collected liquids was carried out by gas chromatographic analysis using an Agilent HP6890 gas chromatograph (GC) equipped with a “Split/Splitless” injector on a 25 m high Quadrex 007 FFAP column with 0.32 mm diameter, 1 micron of film, the carrier used was helium with a speed equal to 50 cm/s, the detector was with flame. The determination was carried out by means of an internal standard with calibration curves for the single known components.

[0148] The catalytic material used in the form of granules having dimensions between 0.5 mm and 1 mm and in an amount equal to 3 g, was prepared as described above in Examples 2 (comparative), 4 (disclosure), 6 (disclosure), 8 (disclosure), 10 (disclosure), 11 (comparative) and 12 (disclosure).

[0149] Table 3 shows: the catalyst used (Catalyst); the temperature to which the catalytic dehydration is carried out [T (° C.)]; the contact time [τ (s)] calculated as the ratio of the volume of catalytic material loaded to feeding volumetric rate; the dilution implemented, that is the molar ratio of water:butenols being fed, obtained by adding suitable amounts of water to the butenol mixture [Dilution (mol/mol)]; productivity to 1,3-butadiene (g.sub.1,3-BDE/g.sub.CAT) defined as the amount of 1,3-butadiene produced expressed in grams, compared to the amount of catalytic material used expressed in grams, on a single cycle, reached before the conversion drops below 80%.

TABLE-US-00003 TABLE 3 T τ Dilution (g.sub.1,3-BDE/g.sub.CAT) Example Catalyst (° C.) (s) (mol/mol) (grams) 13 Example 2 300 1.2 1.8:1 100 (comparative) 14 Example 4 300 1.2 1.8:1 130 (disclosure) 15 Example 6 300 1.2 1.8:1 185 (disclosure) 16 Example 10 300 1.2 1.8:1 240 (disclosure) 17 Example 11 300 1.2 1.8:1 70 (comparative) 18 Example 12 300 1.2 1.8:1 125 (disclosure) 19 Example 8 300 1.2 4.3:1 163 (disclosure)

[0150] The data reported in Table 3 show the following: [0151] from the comparison between Example 13 (comparative) and Example 14 (disclosure) it can be seen that a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) having a pore modal diameter higher than 10 nm in accordance with the present disclosure, allows obtaining a higher productivity (g.sub.1,3-BDE/g.sub.CAT); [0152] from the comparison between Example 13 (comparative), Example 14 (disclosure) and Example 15 (disclosure), it can be seen that a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) having a pore modal diameter in accordance with the present disclosure, obtained thanks to the increase of ageing of the gel in the synthesis phase, allows obtaining a high productivity (g.sub.1,3-BDE/g.sub.CAT); [0153] from the comparison between Example 13 (comparative) and Example 16 (disclosure), it can be seen that a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) having a pore modal diameter in accordance with the present disclosure, obtained thanks to the use of NaH.sub.2PO.sub.4.H.sub.2O in the synthesis phase, allows obtaining a high productivity (g.sub.1,3-BDE/g.sub.CAT); [0154] from the comparison between Example 17 (comparative), Example 18 (disclosure) and Example 19 (disclosure), it can be seen that a silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) having a pore modal diameter in accordance with the present disclosure, obtained by extrusion, allows obtaining a high productivity (g.sub.1,3-BDE/g.sub.CAT).

Example 19

Life Tests of the Catalyst of Example 8

[0155] The catalyst obtained as described in Example 8 was subjected to a life tests consisting of a series of reaction cycles and subsequent regeneration if the conversion of the reactants had dropped below 80%.

[0156] The regeneration was carried out in the following modalities: the catalyst was loaded into a tubular reactor with fixed bed AISI 316L, 350 mm long and with an internal diameter of 9.65 mm and was brought to a temperature of 450° C. in nitrogen flow (GHSV=1500 h.sup.−1) for 1 hour in order to remove therefrom all the volatile organic compounds present. Subsequently, air gradually began to be sent to said reactor progressively increasing the concentration thereof until the complete supply of air in the range of 4 hours. The regeneration was carried on for another 24 hours at the end of which the catalyst was cooled to the reaction temperature in nitrogen (N2) and used in the subsequent reaction cycle.

[0157] Table 4 shows, for some of the reaction cycles carried out [No. Cycle (React./Reg.)]; the reaction time (“Time on Stream”—T.o.S.) (hours), that is, the time during which the catalyst has been in contact with the feeding stream under the process conditions before the conversion drops below 80%; the contact time [τ (s)] calculated as the ratio of the catalytic material loaded to feeding volumetric rate; the dilution used, that is the molar ratio water:butenols being supplied, obtained by adding suitable amounts of water to the mixture of butenols [Dilution (mol/mol)]; productivity at 1,3-butadiene (g.sub.1,3-BDE/g.sub.CAT) defined as the amount of 1,3-butadiene produced expressed in grams, compared to the amount of catalytic material used expressed in grams, on a single cycle, reached before the conversion drops below 80%.

TABLE-US-00004 TABLE 4 No. Cycle T.o.S. T τ Dilution (g.sub.1,3-BDE/g.sub.CAT) (React./Reg.) (hours) (° C.) (s) (mol/mol) (grams) 3 240 300 1.2 4.3:1 163 300 9 933 300 1.2 4.3:1 155 14 1536 300 1.2 4.3:1 160 17 1897 300 1.2 4.3:1 144 38 3953 300 1.2 4.3:1 163

[0158] From the data reported in Table 4 it can be seen that silica-alumina (SiO.sub.2—Al.sub.2O.sub.3) of Example 8, having a pore modal diameter in accordance with the present disclosure, allows obtaining a good productivity (g.sub.1,3-BDE/g.sub.CAT) even after several reaction/regeneration cycles. Furthermore, it should be noted that the catalyst had a total duration greater than 4000 hours, it reached 39 reaction cycles undergoing 38 regenerations while maintaining, however, an average productivity, per reaction cycle as described above, higher than 140 grams (g.sub.1,3-BDE/g.sub.CAT) without ever showing signs of decay.