Process for producing olefins from alcohols

Abstract

The invention relates to a process for producing olefins from alcohols by means of catalytic dehydration. More in particular, the present invention relates to a process for producing at least one olefin by dehydrating at least one alcohol having a number of carbon atoms comprised between 2 and 6, preferably comprised between 2 and 4, more preferably at least one alcohol having a number of carbon atoms of 3, even more preferably 2-propanol, in the presence of a catalytic material comprising at least one large pore zeolite in acid form, or predominantly acid form, preferably selected from the group consisting of zeolites having BEA structure, MTW structure and mixtures thereof, and preferably at least one inorganic binder, more preferably alumina. Preferably, the olefin has the same number of carbon atoms as the starting alcohol. Furthermore, preferably the olefin does not contain conjugated double bonds and more preferably the olefin is a mono-olefin. Subject matter of the present invention is also the use of the aforementioned olefin in an alkylation process of aromatic hydrocarbons, in particular the use of propylene for alkylating benzene to provide cumene. The aforementioned cumene can be used in an integrated process for preparing phenol and acetone, in accordance with the Hock method, wherein acetone can be reduced to 2-propanol, to be recycled to the process of the invention to obtain propylene again.

Claims

1. Process for producing at least one olefin by dehydrating at least one alcohol having a number of carbon atoms comprised between 2 and 6, in the presence of a catalytic material comprising at least one large pore zeolite in acid form or predominantly in acid form selected from a zeolite having BEA structure, a zeolite having MTW structure and a mixture thereof, wherein said catalytic material includes at least one inorganic binder, which is carried out in the substantial absence of aromatic compounds, and separating said olefin from a product.

2. Process according to claim 1, wherein said alcohol is 2-propanol.

3. Process according to claim 1, wherein said zeolite has BEA structure.

4. Process according to claim 3, wherein said zeolite having BEA structure has a SAR in a range between 15 and 60.

5. Process according to claim 3, wherein said zeolite having BEA structure is a beta zeolite.

6. Process according to claim 1, wherein said zeolite has MTW structure.

7. Process according to claim 6, wherein said zeolite having MTW structure has a SAR in a range between 40 and 200.

8. Process according to claim 6, wherein said zeolite having MTW structure is a zeolite ZSM-12.

9. Process according to claim 1, wherein the olefin does not contain conjugated double bonds.

10. Process according to claim 1, wherein said olefin has the same number of carbon atoms as the starting alcohol.

11. Process according to claim 1, wherein said inorganic binder comprises at least one of silica, alumina, silico-alumina and mixtures thereof.

12. Process according to claim 1, wherein said inorganic binder is present in an amount that produces said catalytic material in which the ratio between zeolite and binder is in a range between 95:5 and 5:95.

13. Process according to claim 1, carried out at a temperature in a range between 100° C. and 300° C.

14. Process according to claim 1, carried out at a pressure in a range between 0.01 MPa and 2 MPa.

15. Process according to claim 1, conducted in a gaseous or liquid/gaseous phase.

16. Process according to claim 1, wherein the WHSV space velocity is in a range between 0.5 h.sup.−1 and 10 h.sup.−1.

17. Integrated phenol production process comprising the steps: (a) converting 2-propanol as said alcohol to propylene as said separated olefin, by using the process according to claim 1; (b) alkylating benzene with said propylene obtained in step (a) to obtain cumene, in the presence of a catalytic material comprising at least one large pore zeolite in acid form; (c) oxidizing the cumene obtained in step (b) with the formation of cumyl hydroperoxide; (d) treating the cumyl hydroperoxide obtained in step (c) with acid to obtain a mixture of phenol and acetone; (e) separating said phenol from said acetone; (f) hydrogenating said acetone separated in step (e) to obtain 2-propanol, which is at least partially recycled to step (a).

18. Process for producing at least one olefin by dehydrating at least one alcohol having a number of carbon atoms comprised between 2 and 6, in the presence of a catalytic material comprising at least one large pore zeolite in acid form or predominantly in acid form selected from a zeolite having BEA structure, a zeolite having MTW structure and a mixture thereof, said catalytic material including an extrusion of said large pore zeolite that is not calcined, an inorganic binder and a peptizing agent, and separating said olefin from a product.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention relates to a process for preparing at least one olefin by dehydrating at least one alcohol having a number of carbon atoms comprised between 2 and 6, preferably between 2 and 4, even more preferably having a number of carbon atoms of 3, in the presence of a catalytic material comprising at least one large pore zeolite in acid form or predominantly acid form.

(2) The process according to the present invention may be realized by placing in contact at least one alcohol having a number of carbon atoms comprised between 2 and 6, preferably between 2 and 4, even more preferably having a number of carbon atoms of 3, with a catalytic material comprising at least one large pore zeolite in acid form or predominantly acid form, to obtain at least one olefin.

(3) The catalytic material is preferably formed, most preferably formed, in the presence of at least one inorganic binder.

(4) The aforementioned large pore zeolite in acid form, or predominantly acid form, constitutes the active phase of said catalytic material.

(5) In a preferred aspect, said zeolite is selected from the group consisting of zeolites having BEA structure, MTW structure, and mixtures thereof.

(6) In a further preferred aspect, said large pore zeolite in acid form, or predominantly acid form, is selected from the group comprising zeolites having BEA structure.

(7) Furthermore, the zeolite having BEA structure is characterized by a SAR comprised between 15 and 60 and more preferably comprised between 20 and 30.

(8) Preferably the zeolite having BEA structure may be a zeolite Beta described, for example, in U.S. Pat. No. 3,308,069.

(9) In accordance with U.S. Pat. No. 3,308,069, the composition of the zeolite Beta can be represented, in terms of molar ratio of oxides, as follows:
[(x/n)M(1±0.1−x)TEA]AlO.sub.2.ySiO.sub.2.wH.sub.2O

(10) where x may have a value from 0 to 1, y is comprised between 5 and 100, w is less than or equal to 4, M is a metal ion such as sodium, n is the valency of the metal ion M, TEA is the tetraethylammonium ion.

(11) In a second preferred aspect, said large pore zeolite in acid form, or predominantly acid form, is selected from the group comprising zeolites having MTW structure.

(12) Furthermore, said zeolite having MTW structure is characterized by a SAR comprised between 40 and 200 and more preferably comprised between 70 and 150.

(13) Preferably the aforementioned zeolite having MTW structure may be a ZSM-12 zeolite described, for example, in U.S. Pat. No. 4,552,739.

(14) In accordance with U.S. Pat. No. 4,552,739, the composition of the zeolite ZSM-12 can be represented, in terms of molar ratio of oxides, as follows:
(1.0±0.4)M.sub.2/n/O.Al.sub.2O.sub.3.XSiO.sub.2.zH.sub.2O

(15) where M is at least one cation having valency n, X can vary from 20 to infinity and z can vary from 0 to 60.

(16) Zeolite ZSM-12, and the different synthesis methodologies thereof are described in the prior art, for example in U.S. Pat. No. 3,832,449 and in EP 0 018 089.

(17) Preferably, the olefin obtained with the process according to the present invention does not contain conjugated double bonds and more preferably said olefin is a mono-olefin, i.e. an olefin containing only one double bond.

(18) Furthermore, the olefin preferably has the same number of carbon atoms as the starting alcohol.

(19) Specific examples of alcohols that are particularly useful for the purpose of the present invention are: ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, iso-butanol, tert-butanol, 1-pentanol, 2-pentanol, 3-pentanol, isoamyl alcohol, 2-methyl-1-butanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-1-butanol, 3-methyl-1-pentanol.

(20) In a further preferred aspect, the starting alcohol is a propanol, even more preferably 2-propanol.

(21) Preferably, said 2-propanol derives from the hydrogenation of acetone.

(22) As mentioned, the large pore zeolite, in acid form, or predominantly acid form, used in the process according to the invention, can be formed in the presence of at least one inorganic binder.

(23) The aforementioned inorganic binder can comprise a material conventionally used as a binder for catalysts. Non-limiting examples of inorganic binders can comprise, for example, silica, alumina, silica-alumina, zirconium oxide, titanium oxide, anionic and cationic clays, saponite, gibbsite, bentonite, kaolin, sepiolite, hydrotalcite, or mixtures thereof. In a preferred aspect, the inorganic binder is selected from the group comprising silica, alumina, silica-alumina and mixtures thereof and more preferably is alumina. Also preferred is an alumina-precursor binder, even more preferably γ-alumina. As is known to a person skilled in the art, γ-alumina can derive from calcination of pseudoboehmite or boehmite (as described, for example, by the already mentioned T. K. Phung, et al., in “A study of commercial transition aluminas and of their catalytic activity in the dehydration of ethanol” (2014), J. Catal., vol. 311, pag. 102-113), which is also available commercially with the name Versal™.

(24) The aforementioned inorganic binder is present in quantities such as to produce a catalytic material in which the weight ratio between zeolite and binder, in terms of relative quantity ranges is comprised between 95:5 and 5:95, preferably between 20:80 and 80:20, even more preferably between 35:65 and 65:35.

(25) In order to facilitate the forming operations of the catalytic material, it is possible to add to said large pore zeolite in acid form, or predominantly acid form, and to said at least one inorganic binder, at least one peptizing agent preferably selected from aqueous solutions of: acetic acid, nitric acid, ammonium hydroxide. Said peptizing agent can be mixed with said zeolite and with the inorganic binder prior to forming, until a uniform paste is obtained, in accordance with methodologies known to a person skilled in the art.

(26) To improve the rheological characteristics of the catalytic material, during the forming step it is possible to add one or more additives. These additives may preferably comprise: starches, cellulose or derivatives thereof, stearates, glycols, surfactants, or a mixture thereof.

(27) For applications in fixed bed or fluidized bed reactors, the forming of the catalytic material in the presence of at least one inorganic binder is fundamentally important in order for the catalyst to maintain its physical integrity during use.

(28) The large pore zeolite in acid form, or predominantly acid form, used in the process of the present invention can be subjected to forming according to any one of the methods known to a person skilled in the art, for example extrusion, spherudizing, tableting, granulation, and the like, in the presence of an inorganic binder, operating as described, for example, in EP 0 847 802 or in WO 2015/056167 A1, all by the Applicant and the contents of which are included here for reference purposes.

(29) At the end of the forming step, the catalytic material may be in different forms, for example such as spheres, microspheres, granules, pellets, extruded cylindrical, three-lobe, four-lobe forms, etc. and may possibly be subjected to calcination. In a particularly preferred aspect, said catalytic material is in pellet form having a diameter that ranges from 1 to 6 mm, preferably from 1.5 to 5 mm and a length that ranges from 1 to 50 mm.

(30) The aforementioned calcination can be performed in a muffle furnace, at a temperature comprised between 250° C. and 1200° C., preferably comprised between 450° C. and 800° C., for a time comprised between 1 hour and 36 hours, preferably comprised between 2 hours and 24 hours, even more preferably comprised between 4 hours and 18 hours. Said possible calcination can be performed in air, or in the presence of an inert gas (e.g. nitrogen), and is preferably performed in air.

(31) The process for preparing an olefin by dehydrating an alcohol in accordance with the present invention can be performed at a temperature comprised between 100° C. and 300° C., preferably comprised between 150° C. and 250° C. and more preferably comprised between 175° C. and 220° C.

(32) In a particularly preferred aspect of the invention, the aforementioned process is performed at a temperature comprised between 180° C. and 210° C.

(33) Furthermore, said process can be conducted at a pressure comprised between 0.01 and 2 kPa, more preferably comprised between 0.05 and 1.5 kPa, even more preferably comprised between 0.08 and 0.5 kPa. In a particularly preferred aspect of the invention, said process is realized at a pressure comprised between 0.09 and 0.2 MPa.

(34) Therefore, in a particularly preferred aspect of the invention, said process can be realized at a temperature comprised between 180° C. and 210° C., at a pressure comprised between 0.09 MPa and 0.2 MPa.

(35) In a further preferred aspect said process can be performed in gaseous phase or in mixed liquid/gaseous phase, and more preferably is performed in gaseous phase.

(36) The process of the present invention can be preferably carried out in the substantial absence of any solvent or inert diluent. In particular, it is preferably carried out in the substantial absence of an aromatic compound.

(37) The process of the present invention can be realized continuously (e.g. in one or more catalytic reactors in series) or discontinuously (e.g. in a heated and agitated autoclave) and is preferably realized continuously.

(38) Said process may be conducted in any type of reactor, preferably in a fixed bed reactor, a moving bed reactor or in a fluidized bed reactor.

(39) In a preferred aspect of the present invention, said process can be performed in a fixed bed reactor. In this case, the catalytic material may be maintained in a single bed or split into various beds.

(40) The reactor layout may comprise the recycling of part of the reaction effluents or of the catalytic material, in a “recirculation” reactor configuration.

(41) In a further preferred aspect, when the process of the present invention is performed in mixed liquid/gaseous phase, and therefore there is a liquid phase present one or more Continuous flow Stirred Tank Reactors (CSTRs) can be used, containing the catalytic material in dispersion.

(42) The process according to the present invention can also be performed continuously in a reactor configuration envisaging at least two reactors in parallel, preferably two fixed bed reactors in parallel, in which, when one reactor is operating, the catalytic material can be regenerated in the other reactor.

(43) When the process is conducted continuously, in the temperature and pressure conditions specified above, the WHSV (Weight hourly space velocity), i.e. the ratio between the quantity by weight of reagent fed to the reactor and the quantity by weight of catalyst in the reactor itself, may be comprised between 0.5 h.sup.−1 and 10 h.sup.−1, is preferably comprised between 0.7 h.sup.−1 and 7 h.sup.−1 and even more preferably is comprised between 0.7 h.sup.−1 and 4 h.sup.−1. In a particularly preferred aspect, the WHSV is comprised between 0.8 and 3 h.sup.−1.

(44) The olefins produced with the process of the present invention are mainly used as intermediates in the synthesis processes of different compounds of industrial interest, and for obtaining polymers.

(45) In particular, the olefins obtained through the aforementioned process can be used for alkylating aromatic hydrocarbons.

(46) When the olefin obtained through the aforementioned process is propylene, said propylene may be used for alkylating benzene and obtaining cumene. The cumene thus produced can in turn be used for producing phenol through the Hock process, known to a person skilled in the art, and acetone as a co-product. Said acetone, after being separated from phenol, can be in turn advantageously subjected to hydrogenation to produce 2-propanol, which can be fed again to the process of the present invention.

(47) Therefore, the subject matter of the invention is a process for producing propylene by dehydrating 2-propanol, performed in the presence of a catalytic material that comprises at least one large pore zeolite in acid form, or predominantly acid form, selected from the group comprising zeolites with BEA structure, MTW structure and mixtures thereof, preferably formed in the presence of at least one inorganic binder, where said 2-propanol derives from the hydrogenation of acetone obtained as a co-product of the synthesis of phenol through the Hock process.

(48) The present invention finally relates to an integrated process for producing phenol which comprises the following steps: (a) converting 2-propanol to propylene, by using the process for preparing at least one olefin by dehydrating at least one alcohol according to the present invention, as described above; (b) alkylating benzene with the propylene obtained in step (a) to obtain cumene, in the presence of a catalytic material comprising at least one large pore zeolite in acid form, preferably with BEA structure; (c) oxidizing the cumene obtained in step (b) with the formation of cumyl hydroperoxide; (d) treating the cumyl hydroperoxide with acids to obtain a mixture of phenol and acetone; (e) separating phenol from acetone; (f) hydrogenating the acetone separated in step (e) to obtain 2-propanol, which is at least partially recycled to step (a).

(49) For the purpose of the invention “at least partially recycled” means an amount comprised between 50% and 100% of the total amount of 2-propanol fed to step (a) of the process described above, the complement to 100% being comprised of fresh 2-propanol.

EXAMPLES

(50) For the purpose of putting the present invention into practice and illustrating it more clearly, below are some non-limiting examples.

Example 1 in Accordance with the Invention (Preparation of Catalytic Material Comprising Zeolite ZSM-12)

(51) 2.4 g of sodium aluminate (56% Al.sub.2O.sub.3) were dissolved in 84 g of an aqueous solution of 35% by weight tetraethylammonium hydroxide. The clear solution thus obtained was mixed with 200 g of Ludox® HS 40 colloidal silica in a 40% by weight suspension. After mixing, a uniform and clear gel was obtained, which was inserted into an AISI 316 steel autoclave equipped with an anchor stirrer. The gel was left to crystallize in hydrothermal conditions at 160° C. for about 70 hours. At the end, after cooling, the solid phase was separated from the mother liquor from the suspension obtained by filtration. The aforementioned solid phase was subjected to washing with demineralized water until washing water was obtained having a pH less than 9.

(52) The solid was then subjected to calcination at 550° C. in air atmosphere, for 5 hours. The solid obtained was dispersed in an aqueous solution of ammonium acetate. The concentration of ammonium acetate in the solution was selected so that the molar ratio between ammonium ions and aluminum present in the dispersed solid was greater than or equal to 5. The solid was recovered through filtration and washed with demineralized water. The ion exchange process with the ammonium acetate solution and washing with demineralized water was repeated a second time. At the end, the solid was separated from the aqueous phase and placed to dry in an oven at 100° C. for 3 hours, in air atmosphere. A zeolite in ammonium form is obtained, containing residual sodium less than 50 ppm. The X-Ray Diffraction (XRD), performed by applying methodologies known to a person skilled in the art, confirmed the presence of a single crystalline zeolite phase characteristic of the MTW structure, while the chemical analysis of the material allowed the SAR of zeolite to be determined, which was equal to 99. Different preparations of zeolite performed according to the process described were mixed together so as to obtain a sample having uniform structural, morphological and compositional characteristics. 545 g of zeolite in ammonium form prepared in accordance with the protocol indicated above, were mixed with 600 g of Versal™ 150 pseudoboehmite in a planetary mixer for 30 minutes for the purpose of obtaining uniform distribution of the powders.

(53) At the end, 300 mL of a 2% by weight acetic acid solution was added over 30 minutes to the mixture of powders, while mixing constantly. After the addition, the pasty mixture was unloaded from the mixer and transferred into a roller extruder equipped with a draw-plate with holes having a 2 mm diameter. The catalytic material was extruded in the form of pellets having a diameter of about 2 mm and a length of about 10 mm. The material was subsequently calcinated in air atmosphere for 2 hours at 350° C. and subsequently for another 3 hours at 550° C. After calcination, an extrusion of zeolite and alumina (gamma) is obtained with a mutual weight ratio of 55:45, determined based on the weight loss at 550° C. of the starting components, in which the zeolite is in acid form.

(54) The final catalytic material thus obtained has a surface area of 246 m.sup.2/g and a radial compression resistance of 7 kg, determined by means of a TBH 30 (Erweka) hardness tester.

Example 2 in Accordance with the Invention (Preparation of Catalytic Material Comprising Zeolite Beta)

(55) The extruded catalytic material based on zeolite beta in acid form and bound with alumina is prepared as reported in Example 4 of EP 0 847 802.

(56) 1.9 g of sodium aluminate (56% Al.sub.2O.sub.3) were dissolved in 58.8 g of an aqueous solution of 40% by weight tetraethylammonium hydroxide. 58.4 g of demineralized water were added to the solution. The mixture was heated to 80% and stirring was continued until the complete dissolution of the powders. The clear solution thus obtained was mixed with 37.5 g of Ludox® HS 40 colloidal silica in a 40% by weight suspension. After mixing, a uniform gel having pH=14 was obtained, which was inserted into an AISI 316 steel autoclave equipped with an anchor stirrer. The gel was left to crystallize in hydrothermal conditions at 150° C. for about 10 days under static conditions and at autogenous pressure. At the end, after cooling, the solid phase was separated from the mother liquor from the suspension obtained by filtration. The aforementioned solid phase was subjected to washing with demineralized water.

(57) The wet panel was dispersed again in an aqueous solution of ammonium acetate (200 g water and 16 g ammonium acetate) for ion exchange. The suspension was heated for an hour to 80° C. The suspension was then filtered and the solid obtained re-dispersed in demineralized water (150 mL) for washing. The suspension was re-filtered obtaining a wet panel of zeolite beta in ammonium/alkyl ammonium form. The aluminum content is 3.38%. The XRD analysis confirmed the presence of a single crystalline zeolite phase characteristic of the BEA structure, while the chemical analysis of the material allowed the SAR of the zeolite to be determined, which was 19 and the residual sodium content, which was 112 ppm. The material thus prepared, without being preliminarily calcinated, was extruded with pseudoboehmite as an alumina precursor and solutions of acetic acid as peptizing agents, as described in Example 4 of EP 0 847 802 obtaining a 50% zeolite material and a surface area of 482 m.sup.2/g.

Example 3 (Comparative): (Preparation of Catalytic Material Comprising Zeolite Y)

(58) The preparation is performed as reported in Example 1 of EP 1 572 357 B1.

(59) 260 g of commercial zeolite Y in ammonium form (CBV 712, Zeolyst Intemational™) were mixed dry with 278 g of Versal™ V250 pseudoboehmite (UOP LLC) in a mixer for about 60 minutes.

(60) At the end, 310 mL of a 0.5% by weight acetic acid solution were added over 36 minutes to the mixture of powders, while mixing constantly. After the addition, the pasty mixture was left to mix further at 400 rpm for 12 minutes, then unloaded from the mixer and transferred into an extruder and extruded in the form of rectangular pellets.

(61) After drying in a ventilated oven at 25° C. for 48 hours the pellets of catalytic material were placed in a muffle furnace and calcinated in air atmosphere at a temperature programmed according to the following gradient: from room temperature to 120° C. in 6 hours; 120° C. constant for 2 hours; from 120° C. to 350° C. in 6 hours; 350° C. constant for 4 hours; from 350° C. to 550° C. in 4 hours; 550° C. constant for 8 hours.

(62) The finished catalyst is in the form of rectangular pellets having an approximate length of 7 mm and approximate diameter of 2.1 mm.

(63) Based on the weight loss at 550° C. measured on the starting components, an extrusion of zeolite and γ-alumina was obtained in a weight ratio of 50:50 in which the zeolite is in acid form. The material thus obtained has a surface area of 499 m.sup.2/g.

Example 4 Comparative (Preparation of the Catalytic Material Based on Alumina)

(64) A commercial bayerite (Versal™ B, UOP) was used, with high purity, high crystalline density and that provides catalytic compositions characterized by a high surface area after calcination and a higher acidity with respect to gamma aluminas. The calcination of the bayerite evolves through alumina phases with a high surface area, such as eta and theta. 1000 g of Versal™ B (UOP) were mixed with 500 mL of a 1% by weight acetic acid solution, over 60 minutes. After the addition, the pasty mixture was aged at ambient temperature for 24 hours, then transferred into a roller extruder equipped with a draw-plate with holes having a 2 mm diameter. The material was extruded in the form of pellets having a diameter of about 2 mm. The material was then calcinated in air atmosphere for 2 hours at 350° C. and subsequently for another 3 hours at 550° C. The material thus obtained has a surface area of 212 m.sup.2/g.

Examples 5, 6, 7, 8, 9 in Accordance with the Invention (Catalytic Dehydration Test of 2-Propanol with Catalytic Material Comprising Zeolite ZSM-12 in Acid Form)

(65) The dehydration tests of 2-propanol were performed using a tubular reactor 3 m long having a section of 2.98 mm.sup.2, with vertical spiral insertion in a thermostated chamber with forced air circulation at controlled temperature and pressure.

(66) About 10 g of catalytic material based on ZSM-12 zeolite in acid form, formed in the presence of an alumina-based binder, prepared in accordance with Example 1, were loaded into the reactor.

(67) The tests were performed by feeding 2-propanol continuously to the reactor from the bottom upwards (upflow), using an HPLC pump.

(68) The tests were performed at temperatures comprised between 200° C. and 205° C. and pressures comprised between 0.1 MPa and 0.2 MPa, in space velocity conditions (WHSV) comprised between 1 h.sup.−1 and 2 h.sup.−1.

(69) The reaction effluent leaving the reactor is cooled in a glass column in whose outer jacket a fluid cooled to 5° C. flows. This column separates a liquid phase (mainly comprising water) and a gaseous phase (substantially comprising propylene), which passes into a glass manifold and then into a measuring instrument with a volumetric flow rate from which it is possible to measure the weight of the product.

(70) The liquid phase collected on the bottom of the cooled glass column was taken for weighing and gas chromatography analysis, in a HP 6890 gas chromatograph equipped with a PONA column (50 m) and a flame ionization detector. For analyzing the liquid phase, 0.5 μl samples were used, in which methyl-ethyl-ketone were added as the internal standard.

(71) For analyzing the gaseous phase, 0.5 ml samples of said gaseous phase, collected by the glass manifold, were subjected to gas chromatography analysis as described above.

(72) The results of the tests are shown in Table 1 below.

(73) TABLE-US-00001 TABLE 1 Selectivity Selectivity Selectivity to non- Operating Temper- 2-propanol to to ether recoverable time WHSV ature Pressure conversion propylene (IPE) products Productivity (hours) Example (h.sup.−1) (° C.) (MPa) (%) (%) (%) (%) kg.sub.p/kg.sub.c (h) 5 2 200 0.1 99.3 98.3 0.01 1.65 228 168 6 2 200 0.1 99.2 99.0 0.01 0.97 422 312 7 1 200 0.1 99.6 97.9 0.01 2.10 439 550 8 2 200 0.1 99.1 99.7 0 0.32 758 814 9 2 205 0.1 99.6 99.4 0 0.63 1243 1008

(74) The “non-recoverable” products conventionally comprise products that cannot be exploited to provide propylene, e.g. isobutane, acetone and olefins and C.sub.4, C.sub.5 and C.sub.6 paraffins. Since isopropylether (IPE) is instead a product that can be recovered to provide propylene, it is not included in the “non-recoverable” products and therefore its selectivity is stated. The productivity is determined as the ratio between the weight of the desired product (kg.sub.p) and the weight of the catalyst (kg.sub.c).

(75) The reaction was voluntarily stopped after 1008 hours of operation, in the absence of significant decay processes, in the absence of any yield reductions or flow rate losses. From Example 9 it can be deduced that by using catalytic material comprising zeolite ZSM-12 at a temperature equal to 205° C., pressure of 0.1 MPa and WHSV equal to 2 h.sup.−1 a 99.6% conversion of 2-propanol and a 99.0% yield of propylene are obtained, with a selectivity of 99.4%, even after 1008 hours of operation and a total productivity of 1243 kg propylene for every kg of catalyst.

(76) From the comparison between the data of Examples 5, 6, 8 the absence of significant decay processes is highlighted. Examples 7 and 9 show that even when the space velocity and temperature are varied, within the claimed intervals, the aforementioned catalytic system can still be used with excellent results, even at higher operating times than the exemplified ones, although evidence of deactivation can start to be displayed.

(77) The catalyst and the reaction conditions, according to the invention, are therefore applicable to industrial contexts, as well as being new and surprisingly efficient with respect to the catalysts described in the art.

Examples 10, 11, 12 in Accordance with the Invention (Catalytic Dehydration Test of 2-Propanol with Catalytic Material Comprising Zeolite Beta in Acid Form)

(78) About 10 g of catalytic material based on zeolite beta in acid form, formed in the presence of an alumina-based binder, prepared in accordance with Example 2, were loaded into a reactor like the one used in Example 5 above.

(79) The tests were performed as described above for Examples 5, 6 and 7, but at temperatures comprised between 185° C. and 200° C. and pressures comprised between 0.1 MPa and 1.5 MPa, in space velocity conditions (WHSV) comprised between 1 h.sup.−1 and 2 h.sup.−1.

(80) The results of the tests are shown in Table 2 below.

(81) TABLE-US-00002 TABLE 2 Selectivity Selectivity Selectivity to non- Operating Temper- 2-propanol to to ether recoverable time WHSV ature Pressure conversion propylene (IPE) products Productivity (hours) Example (h.sup.−1) (° C.) (MPa) (%) (%) (%) (%) kg.sub.p/kg.sub.c (h) 10 2 200 1.5 93.8 97.4 0.46 2.18 188 148 11 2 200 0.1 99.5 99.0 0 0.98 552 408 12 1 185 0.1 97.6 99.3 0.04 0.67 814 670

(82) Using catalytic material comprising zeolite beta in acid form at a temperature of 200° C., pressure of 0.1 MPa and WHSV of 2 h a 99.5% conversion of 2-propanol is obtained with 99.0% selectivity, even after 408 hours of operation (Example 11).

(83) Variations to the operating conditions such as space velocity increases, pressure increases (Example 10) and temperature reductions (Example 12) may be managed by using appropriate combinations of the operating conditions themselves, within the claimed ranges, without substantially sacrificing the system performance levels.

(84) The reaction was voluntarily stopped after 670 hours of operation, but in the absence of significant decay processes, in the absence of any yield reductions or flow rate losses.

(85) It is important to note that it is possible to reduce the temperature to 185° C., maintaining the pressure equal to 0.1 MPa, and to obtain a satisfactory conversion value of 2-propanol (97.6%) at space velocity of 1 h, compatible values with industrial applications.

Comparative Examples 13, 14, 15 (Catalytic Dehydration Test of 2-Propanol with Catalytic Material Comprising Zeolite Y in Acid Form)

(86) About 10 g of catalytic material based on zeolite Y in acid form, formed in the presence of an alumina-based binder, prepared in accordance with comparative Example 3, were loaded into a reactor like the one used in Example 5 above.

(87) The tests were performed as described above for Examples 5, 6 and 7, but at a temperature of 200° C. and pressures comprised between 0.1 MPa and 1.5 MPa, in space velocity conditions (WHSV) equal to 2 h.

(88) The results of the tests are shown in Table 3 below.

(89) TABLE-US-00003 TABLE 3 Selectivity Selectivity Selectivity to non- Operating Temper- 2-propanol to to ether recoverable time WHSV ature Pressure conversion propylene (IPE) products Productivity (hours) Example (h.sup.−1) (° C.) (MPa) (%) (%) (%) (%) kg.sub.p/kg.sub.c (h) 13 2 200 1.5 93.3 98.2 0.54 1.29 146 118 14 2 200 0.1 98.1 99.2 0.04 0.72 338 262 15 2 200 0.1 97.1 99.4 0.11 0.54 593 454

(90) Using catalytic material comprising zeolite Y lower conversions of 2-propanol are obtained with respect to those obtained with catalytic materials comprising zeolite ZSM-12 or zeolite beta. Even if in some cases a satisfactory selectivity is obtained, especially at high pressure, these results are however not constant in the long term, highlighting lower stability as a function of the operating time. From the comparison between examples 6 and 8 no decay of the yield to 2-propanol is highlighted after a productivity of the ZSM-12 based catalyst of 336 kg/g, (−0.1% Conversion); from the comparison between examples 14 and 15 a decay of the yield to 2-propanol in the proximity of a percentage point is highlighted already after a productivity of the zeolite Y based catalyst of 255 kg.sub.p/kg.sub.c (−1.0% conversion)

Comparative Examples 16 and 17 (Catalytic Dehydration Test of 2-Propanol with Catalytic Material Comprising Alumina)

(91) About 10 g of alumina based catalytic material, prepared in accordance with the comparative Example 4, were loaded into the reactor.

(92) The tests were performed as described for Examples 5, 6 and 7 in the operating conditions stated in Table 4.

(93) TABLE-US-00004 TABLE 4 Selectivity Selectivity Selectivity to non- Operating Temper- 2-propanol to to ether recoverable time WHSV ature Pressure conversion propylene (IPE) products Productivity (hours) Example (h.sup.−1) (° C.) (MPa) (%) (%) (%) (%) kg.sub.p/kg.sub.c (h) 16 0.7 242 0.1 61.6 70.0 29.9 0.10 21 96 17 2 290 0.1 99.8 99.8 0 0.17 525 774

(94) From the comparative tests, the following is highlighted:

(95) The state of the art is confirmed in the sense of the importance of operating at temperatures in the proximity of 300° C. with alumina based catalytic materials in order to obtain good conversions. At temperatures less than 240° C. good conversion values cannot be obtained, even at low space velocity (WHSV) values. Alumina starts to become significantly active at temperatures that are at least 50° C. higher than the reaction temperatures of catalysts containing zeolites. The catalytic contribution of the binding aluminas used in the examples according to the invention, under the stated operating conditions, can therefore be considered null or secondary.

(96) Surprisingly, it has been demonstrated that the use of catalytic materials comprising MTW structure and BEA structure zeolites, such as zeolite ZSM-12 and zeolite beta, maintain high yields for suitable durations for industrial use, better than large pore zeolite Y, known in the art as one of the best catalysts for dehydrating ethanol (as described by T. K. Phung, L. Proietti Hernández, A. Lagazzo and G. Busca in “Dehydration of ethanol over zeolites, silica alumina and alumina: Lewis acidity, Brønsted acidity and confinement effects” (2015), Appl. Catal. To: General, vol. 493, pag. 77-89).

(97) Finally, it is however to be understood that further changes and variations may be made to the process described and illustrated herein which do not depart from the scope of protection defined by the appended claims.