CATALYST COMPRISING COKE AND PROCESS FOR THE PRODUCTION OF DIENES

Abstract

A catalyst having coke wherein the coke, upon analysis by infrared spectroscopy in diffuse reflection, has at least two peaks at a wavelength between 1450 cm.sup.−1 and 1700 cm.sup.−1.

The aforesaid catalyst having coke can be advantageously used in a process for the production of a diene, preferably a conjugated diene, more preferably 1,3-butadiene, said process having the dehydration of at least one alkenol having a number of carbon atoms greater than or equal to 4.

Preferably, the alkenol having a number of carbon atoms greater than or equal to 4 can be obtained directly from biosynthetic processes, or through catalytic dehydration processes of at least one diol.

When the alkenol is a butenol, the diol is preferably a butanediol, more preferably 1,3-butanediol, even more preferably bio-1,3-butanediol, i.e. 1,3-butanediol deriving from biosynthetic processes.

When the diol is 1,3-butanediol, or bio-1,3-butanediol, the diene obtained with the process is, respectively, 1,3-butadiene, or bio-1,3-butadiene.

Claims

1. A catalyst comprising coke wherein said coke, upon analysis by infrared spectroscopy in diffuse reflection, has at least two peaks at a wavelength comprised between 1450 cm.sup.−1 and 1700 cm.sup.−1.

2. The catalyst comprising coke according to claim 1, wherein said catalyst comprises at least one compound selected from the group consisting of: aluminum oxide (γ-Al.sub.2O.sub.3), aluminum silicate, silicas-aluminas (SiO.sub.2—Al.sub.2O.sub.3), aluminas, zeolites, and metal oxides (such as lanthanum oxide, zirconium oxide, tungsten oxide, thallium oxide, magnesium oxide, zinc oxide, silver oxide).

3. The catalyst comprising coke according to claim 1, wherein said catalyst comprises: (a) from 2% by weight to 30% by weight, with respect to the total weight of said catalyst, of coke; (b) from 70% by weight to 98% by weight, with respect to the total weight of said catalyst, of at least one compound selected from the group consisting of: aluminum oxide (γ-Al.sub.2O.sub.3), aluminum silicate, silicas-aluminas (SiO.sub.2—Al.sub.2O.sub.3), aluminas, zeolites, and metal oxides (such as lanthanum oxide, zirconium oxide, tungsten oxide, thallium oxide, magnesium oxide, zinc oxide, silver oxide); the sum of (a)+(b) being equal to 100.

4. A process for the production of a diene, comprising the dehydration of at least one alkenol having a number of carbon atoms equal to or greater than 4, in the presence of at least one catalyst comprising coke, wherein said coke, upon analysis by infrared spectroscopy in diffuse reflection (“Diffuse Reflectance Infrared Fourier Transform Spectroscopy”—DRIFT), has at least two peaks at a wavelength comprised between 1450 cm.sup.−1 and 1700 cm.sup.−1.

5. The process for the production of a diene, according to claim 4, wherein said linear or branched alkenol has the general formula C.sub.nH.sub.2nO, n being an integer greater than or equal to 4 and less than or equal to 8.

6. The process for the production of a diene, according to claim 4, wherein said alkenol has a number of carbon atoms equal to 4 and is therefore a butenol; said alkenol is selected from the group consisting of 2-buten-1-ol (crotyl alcohol) (2-Bu-1-OH), 3-buten-2-ol (methyl-vinyl-carbinol) (3-Bu-2-OH), 3-buten-1-ol (allylcarbinol) (3-Bu-1-OH), or mixtures thereof.

7. The process for the production of a diene, according to claim 4, wherein said alkenol having a number of carbon atoms equal to or greater than 4, is obtained directly from biosynthetic processes, or through catalytic dehydration processes of at least one diol.

8. The process for the production of a diene, according to claim 4, wherein when said alkenol has a number of carbon atoms equal to 4, and is therefore a butenol, said butenol is obtained by catalytic dehydration of a butanediol, in the presence of a cerium oxide catalyst, wherein said cerium oxide catalyst is obtained by precipitation, in the presence of at least one base, of at least one cerium-containing compound.

9. The process for the production of a diene, according to claim 7, wherein said diol, derives from the fermentation of sugars; said diol derives from the fermentation of sugars deriving from guayule and/or thistle biomass, including scraps, residues, wastes deriving from guayule and/or thistle, or from their processing.

10. The process for the production of a diene, according to claim 4, wherein said alkenol having a number of carbon atoms equal to or greater than 4 is mixed with a diluent that is selected from the group consisting of: an inert gas, such as nitrogen (N.sub.2), and argon (Ar); or said alkenol is mixed with a compound having a boiling temperature comprised between 25° C. and 150° C. under normal conditions, and a melting temperature less than or equal to 20° C. under normal conditions, selected from the group consisting of water, tetrahydrofuran, cyclohexane, benzene, and mixtures thereof, said diluent is selected from nitrogen (N.sub.2) and water.

11. The process for the production of a diene, according to claim 10, wherein: if the diluent is selected from inert gases, said process is carried out with a molar ratio of diluent to alkenol (or alkenols) greater than 0.3; and if the diluent is selected from compounds having a boiling temperature comprised between 25° C. and 150° C. under normal conditions, and a melting temperature less than or equal to 20° C. under normal conditions, said process is carried out with a molar ratio of diluent to alkenol (or alkenols) comprised between 0.01 and 100.

12. The process for the production of a diene, according to claim 4, wherein said process is carried out: at a temperature comprised between 250° C. and 500° C.; and/or at a pressure comprised between 5 kPa and 5000 kPa; and/or in the gas phase or mixed liquid/gas phase; and/or in a fixed-bed reactor, in a moving-bed reactor, or in a fluidised-bed reactor; and if it is carried out in a mixed liquid/gas phase, using a continuous stirring reactor (“Continuous flow Stirred-Tank Reactor”, CSTR) containing the catalyst comprising coke in dispersion; and/or continuously or in batches; and/or if carried out continuously, the space velocity WHSV (“Weight Hourly Space Velocity”), that is, the ratio of the amount by weight of reactant fed to the reactor to the quantity of catalyst weight in the reactor, is comprised between 0.5 h.sup.−1 and 10 h.sup.−1; and/or the contact time (τ), calculated as the ratio of the volume of catalyst comprising coke loaded into the dehydration reactor over the volumetric supply flow rate in the reaction conditions, is comprised between 0.01 seconds and 10 seconds.

13. A process for the production of a catalyst comprising coke, wherein said coke, upon analysis by infrared spectroscopy in diffuse reflection has at least two peaks at a wavelength comprised between 1450 cm.sup.−1 and 1700 cm.sup.−1, said process comprising the dehydration of a mixture of alkenols comprising 3-buten-2-ol (3-Bu-2-OH) and 2-buten-1-ol (2-Bu-1-OH), in the presence of at least one compound selected from the group consisting of: aluminium oxide (γ-Al.sub.2O.sub.3), aluminum silicate, silicas-aluminas (SiO.sub.2—Al.sub.2O.sub.3), aluminas, zeolites, and metal oxides (such as lanthanum oxide, zirconium oxide, tungsten oxide, thallium oxide, magnesium oxide, zinc oxide, silver oxide), said process being carried out at a temperature comprised between 250° C. and 500° C., for a time comprised between 2 hours and 10 hours.

Description

EXAMPLE 1

(i) Preparation of a Mixture of Raw Butenols

[0082] For the purpose, a mixture of 1,3-butanediol (1,3-BDO) was carried out, having a concentration by weight equal to 83% of 1,3-butanediol (1,3-BDO), 17% of water (mixture 1), respectively, which was then used for the dehydration reaction.

[0083] The reactor in which said dehydration reaction was carried out was comprised of an AISI 304 stainless steel tubular element of height (h) equal to 260 mm and internal diameter (Φ) equal to 10 mm, preceded and connected to an evaporator, both provided with electric heating. The outlet of the reactor was instead connected to a first condenser connected to a receiving flask, and operating at 15° C., for the purpose of enabling the recovery of the products obtained from the first dehydration reaction in the form of liquid at room temperature (25° C.) in said receiving flask. Said receiving flask was in turn connected to a sampling system comprising a steel cylinder of volume (V) equal to 300 ml and provided at both ends with interception valves. The vapours/gases deriving from the first dehydration reaction and optionally not condensed in the system previously described could further flow through the aforesaid steel cylinder connected in turn to a volumetric meter that therefore measured the quantity thereof.

[0084] The products obtained, both in the form of liquid, and in the form of vapour/gas, were characterized by gas chromatography, using: [0085] for the products in liquid form, a Thermo Trace gas chromatograph, equipped with an FID detector and AQUAWAX column (Grace 30 m length×0.53 mm internal diameter×1.0 μm film thickness); [0086] for the products in gas form, a 490 micro GC Varian/Agilent gas chromatograph with four channels equipped with the following columns: Pora Plot Q length 10 m, MolSieve 5 Å length 4 m, Al.sub.2O.sub.3 length 10 m with “backflush” functionality, CPSil-19 CB length 7.5 m.

[0087] The catalyst used in said dehydration reaction was a Cerium oxide (CeO.sub.2) based material in granules of a size comprised between 0.5 mm and 1 mm and it was loaded into the aforesaid reactor in a quantity equal to 10 g (3.5 ml). Said catalyst was prepared according to the laboratory procedure described below.

[0088] For that purpose, 500 g of a commercial aqueous solution of about 30% ammonium hydroxide (NH.sub.4OH), (28%-30% NH.sub.3 Basis ACS reagent Aldrich) were added to a first 3 litre beaker provided with a half-moon stirrer blade made of teflon, with 500 g of water, and an electrode was introduced for measuring the pH [Metrohm glass electrode for measuring the pH (6.0248.030), connected to the Metrohm 780 pH meter]. In a second 2 litre beaker provided with a magnetic anchor stirrer, a 100 g cerium nitrate hexahydrate solution (99% Aldrich) was prepared in 1000 g of water: the cerium nitrate hexahydrate was then dissolved through vigorous stirring at room temperature (25° C.). The solution obtained was inserted into a dropping funnel and fed drop by drop, in 2 hours, to the ammonium hydroxide solution described above, contained in the 3 litre beaker, with constant vigorous stirring. The pH of the suspension obtained was equal to 10.2. The solid in suspension was filtered, washed with 2 litre of water, and then dried in a stove, at 120° C., for 2 hours. The synthesis was repeated until 2000 g of solid were obtained.

[0089] 1270 g of the solid thus obtained, subject to screening at 0.125 mm, were inserted into an extruder to which 175.9 g of 25% ammonium hydroxide (NH.sub.4OH) solution were also added (obtained by diluting the solution at 28%-30% NH.sub.3 Basis ACS reagent Aldrich) using a Watson Marlow peristaltic pump set to 5 rpm. After said addition, 158 g of demineralized water were also added, thus providing the right consistency for extrusion. The “pellets” obtained at the outlet of the extruder were dried in air and, subsequently, a 100 g portion was calcined at 800° C. with a 1° C./minute ramp to 800° C., followed by isotherm in temperature for 6 hours. The calcined solid was granulated and screened and the fraction of granules of size comprised between 0.5 mm and 1 mm was used as a catalyst.

[0090] Said dehydration reaction was then carried out by supplying the mixture 1, first to the aforesaid evaporator previously heated to a temperature of 250° C., and from this to the aforesaid tubular reactor previously heated so as to have an internal temperature during the dehydration reaction equal to 400° C. Both the evaporator and the reactor were kept at atmospheric pressure (1 bar).

[0091] The flow rate of the mixture 1 supplied to the evaporator was equal to 100 g/h, whereas the flow rate to the reactor, expressed as WHSV, was equal to 10 h.sup.−1.

[0092] The test was carried out for a sufficient time for collecting a suitable quantity of raw product.

(ii) Purification of Raw Butenols

[0093] The mixture of raw butenols obtained as described above was subjected to a first purification, through distillation, for the purpose of removing the unreacted 1,3-butanediol (1,3-BDO). It is to be noted that the butenols present in said mixture form, with water, azeotropic mixtures for which it is not possible through simple distillation to separate them from the water in order to obtain them pure.

[0094] The distillation was carried out at atmospheric pressure, adding to said mixture contained in the boiler, 3,5-di-tert-4-butylhydroxytoluene (BHT) so as to have a concentration thereof in said mixture equal to about 200 ppm. Said distillation was carried out using a 40-plate Oldershaw column (2 sections with 20 plates), loading said mixture into the boiler in a single batch and taking various head samples on the basis of the temperatures recorded, gradually concentrating the boiler of the heavier components. The distillation conditions (reflux ratio, boiler heating power, quantity of distillate taken) were varied as a function of the boiling temperatures of the species to be separated and the head temperatures recorded.

[0095] The distillation conditions are shown in Table 1.

TABLE-US-00001 TABLE 1 Distillation conditions of alkenols at atmospheric pressure ΔT boiler ΔT head (° C.) (° C.) RR.sup.(1) Load — — — Fraction 1 101.3-103.0 56.0-84.5 100  Fraction 2 103.1-104.3 85.0-86.8 100-30  Fraction 3 104.9-133.6 86.4-87.1 30 Fraction 4 114.6-152.3 87.1-94.4 30-40 Fraction 5 154.3-167.9  93.6-119.4 40-60 Fraction 6 169.2-208.6 120.1-121.2 60-70 Fraction 7 208.6-210.8 121.2-130.1 70 Boiler — — — .sup.(1)reflux ratio.

[0096] In particular: [0097] Fraction 1 (up to about 84° C.) corresponds to the lightest part to be removed; [0098] Fraction 2 and Fraction 3 correspond to an azeotrope at T=86.5° C.-87° C. between the lowest boiling point alkenol, i.e. 3-buten-2-ol (methylvinylcarbinol) (3-Bu-2-OH) and water (said azeotrope having composition: 73% by weight of 3-buten-2-ol (3-Bu-2-OH) and 27% by weight of water); [0099] in Fraction 4, 2-buten-1-ol (crotyl alcohol in the cis and trans forms) (2-Bu-1-OH) and the small portion of 3-buten-1-ol (allyl carbinol) (3-Bu-1-OH) together with 35% by weight of water, also start to distillate; [0100] in Fraction 5 the water runs out and therefore the temperature rises to about 120° C.; [0101] Fraction 6 and Fraction 7 correspond to 2-buten-1-ol (crotyl alcohol) (2-Bu-1-OH) at 95%-97%.

[0102] The fractions containing butenols were joined in a single fraction that represents the mixture used for producing the catalyst comprising coke according to the present disclosure. The composition is described in Table 2.

TABLE-US-00002 TABLE 2 Water 37.0% Light.sup.(1) 0.1% 2-Bu-1-OH + 3-Bu-2-OH 60.3% 3-Bu-1-OH 0.2% Medium boiling point.sup.(2) 2.2% Heavy.sup.(3) 0.2% .sup.(1)lightest compounds of low boiling point butenol, i.e. 3-buten-2-ol (3-Bu-2-OH) (T.sub.BOILING = 97° C.); .sup.(2)lightest compounds of high boiling point butenol, i.e. 2-buten-1-ol (2-Bu-1-OH) (T.sub.BOILING = 121.5° C.); heavier than low boiling point alkenol, i.e. 3-buten-2-ol (3-Bu-2-OH) (T.sub.BOILING = 97° C.), excluding 1,3-butadiene (1,3-BDE) [includes the medium boiling point 3-buten-1-ol (3-Bu-1-OH) (T.sub.BOILING = 113.5)]; .sup.(3)heavier compounds of the high boiling point butenol, i.e. 2-buten-1-ol (2-Bu-1-OH) (T.sub.BOILING = 121.5° C.).

EXAMPLE 2

Formation of the Catalyst Comprising Coke and Production of 1,3-butadiene (1,3-BDE)

[0103] A first test was carried out by supplying the mixture of butenols obtained as described in Example 1 and reported in Table 2, in a fixed-bed tubular reactor—PFR (“Plug Flow Reactor”) made of AISI 316L stainless steel, with a length equal to 400 mm and diameter equal to 9.65 mm, loaded with 0.6 g of silica-alumina, containing 3.8% of Al and obtained as described below.

[0104] 7.55 g of aluminium tri-sec-butoxide (Aldrich) as an alumina precursor (Al.sub.2O.sub.3) were inserted into a first 500 ml round-bottom flask, and 50.02 g of orthosilicic acid (Aldrich, <20 mesh), as a silica precursor (SiO.sub.2), were inserted into a second 500 ml round-bottom flask, with 250.02 g of demineralized water. The suspension of orthosilic acid obtained was added slowly (10 min) to said first round-bottom flask containing aluminium tri-sec-butoxide, and the mixture obtained was kept at 90° C., for about 1 hour, with vigorous stirring (500 rpm). After cooling to room temperature (25° C.), the suspension obtained was filtered and the solid obtained was washed with 5 litres of demineralized water, dried at 120° C. for one night and subsequently calcined at 500° C. for 5 hours, obtaining a colourless powder (47.95 g) (defined as the “active phase”).

[0105] Part of the aforesaid “active phase, 40.42 g, was mixed with 24.43 g of pseudoboehmite Versal™ V-250 (UOP), as an alumina precursor (Al.sub.2O.sub.3) of the binder, and 302 ml of a 4% acetic acid solution, in a 800 ml beaker. The mixture obtained was kept, under agitation, at 60° C., for 2 hours. Then, the beaker was transferred to a heating plate and, with vigorous stirring, the mixture was heated for a night to 150° C. until dry. The solid obtained was then calcined at 550° C. for 5 hours, obtaining 60.45 g of a colourless product which was mechanically granulated and the fraction of granules of dimensions comprised between 0.1 mm and 1.0 mm was used as a dehydration catalyst in said tubular reactor.

[0106] The catalyst prepared as described above (0.6 g) was inserted into the reactor using quartz wool as a support for the granules so that they were arranged in the isotherm area of the reactor. The reactor was set with a down flow arrangement.

[0107] The catalyst was pre-treated in situ at 300° C. under nitrogen (N.sub.2) flow.

[0108] The supply of the aforesaid mixture of butenols was carried out from the top of the reactor, at atmospheric pressure (0.1 MPa), through vaporization, so as to allow the reactants to reach the reaction temperature before entering into contact with the catalyst, through the use of an infusion pump and a 5 mL Hamilton pump connected to a heated steel line and subsequently sent to the reactor, under nitrogen (N.sub.2) flow: the total volumetric flow rate was equal to 28 mL/min of which 2% by volume of said mixture of butenols. Said reactor was heated to a temperature of 300° C. using an electric oven and the temperature was controlled by an integrated thermocouple connected to the temperature controller of the electric oven and a second axial thermocouple, placed inside said tubular reactor, which indicates the real temperature of the catalytic bed and was selected as the reference temperature.

[0109] The temperature of the tubular reactor was maintained at 300° C. as described above and the contact time (τ) was equal to 0.67 seconds.

[0110] Downstream of the reactor, the products obtained were sampled in a gas chromatograph (GC) online for analysis. The online analysis of the gases was carried out through an Agilent HP6890 gas chromatograph (GC) equipped with two capillary columns: an HP-5 column (“crosslinked” 5% phenyl methyl siloxane) 50 m in length, 0.2 mm diameter, 0.33 micron of film, connected to a flame ionization detector (FID) and a HP-Plot-Q column (“bonded” polistyrene divinyl benzene) 30 m in length, 0.32 mm diameter, 20 micron of film, connected to a thermal conductivity detector (TCD). The carrier used in both columns was helium with a flow equal to 0.8 mL/min (HP-5 column) and equal to 3.5 mL/min (HP-Plot-Q column).

DETAILED DESCRIPTION OF THE DRAWINGS

[0111] The results are shown in FIG. 1 [in the ordinate the conversion and the yield as a percent (%) were reported; in the abscissa the reaction time in hours (h) was reported].

[0112] The catalytic performance levels shown in FIG. 1 are expressed by calculating the conversion of the alkenols (C.sub.ALCH.), the selectivity to 1,3-butadiene (S.sub.1,3-BDE) and the yield to 1,3-butadiene (R.sub.1,3-BDE) according to the formulae reported below:

[00001]$C_{\mathrm{ALCH}}=\frac{{\left({\mathrm{moli}}_{\mathrm{ALCH}}\right)}_{\mathrm{in}}-{\left({\mathrm{moli}}_{\mathrm{ALCH}}\right)}_{\mathrm{out}}}{{\left({\mathrm{moli}}_{\mathrm{ALCH}}\right)}_{\mathrm{in}}}\times 100$$S_{1,3-\mathrm{BDE}}=\frac{{\mathrm{moli}}_{1,3-\mathrm{BDE}}}{{\left({\mathrm{moli}}_{\mathrm{ALCH}.}\right)}_{\mathrm{in}}-{\left({\mathrm{moli}}_{\mathrm{ALCH}.}\right)}_{\mathrm{out}}}\times 100$$R_{1,3-\mathrm{BDE}}=\frac{C_{\mathrm{ALCH}.}\times S_{1,3-\mathrm{BDE}}}{100}$

wherein: [0113] moli.sub.ALCH=moles of alkenols [referring to 3-buten-2-ol (3-Bu-2-OH) and to 2-buten-1-ol (2-Bu-1-OH)]; [0114] (moli.sub.ALCH.).sub.in=moles of alkenols at the inlet; [0115] (moli.sub.ALCH.).sub.out=moles of alkenols at the outlet; [0116] mol.sub.1,3-BDE=moles of 1,3-butadiene (1,3-BDE) produced.

[0117] From the data reported in FIG. 1, it can be deduced that the yield to 1,3-butadiene (Y 1,3BDE) starts from an initial value of about 47%, settling after 4 hours to about 70%. After 4 hours, the yield to 1,3-butadiene (Y 1,3BDE) continues to increase slowly until stabilizing at an average value of 80% after 10 hours. FIG. 1 also shows the trend of the carbon loss (C loss) that represents the indicator of the coke that gradually forms on the catalyst. In FIG. 1: [0118] X 2-Bu-1-OH refers to the conversion of 2-buten-1-ol (2-Bu-1-OH); [0119] X 3-Bu-2-OH refers to the conversion of 3-buten-2-ol (3-Bu-2-OH); [0120] X 3-Bu-1-OH refers to the conversion of 3-buten-1-ol (3-Bu-1-OH).

[0121] For the purpose of better highlighting the role of coke on the increased yield, the aforesaid Example 1 was repeated 3 times, interrupting the reaction after 3 h, 8 h and 20 h. The catalysts unloaded from the reactor at said times, were subjected to Thermal Gravimetric Analysis (TGA) in air to calculate the amount of coke adsorbed. Said analysis was carried out using an SDT Q 600 instrument (TA Instruments), loading 15 mg of catalyst, in air flow (100 mL/min) and with a temperature ramp (10° C./min until 900° C. and subsequent isotherm at 900° C. for 5 minutes) so as to quantify the organic residues present. The results are shown in FIG. 2 [in the ordinate the weight loss as a percentage (%) was reported; in the abscissa the temperature in degrees centigrade (° C.) was reported]. From FIG. 2, considering the weight loss connected with the presence of coke (temperatures greater than 380° C.), it can be deduced that there is rapid formation of coke in the first 3 h (5% weight loss): to this time interval corresponds the fastest increase in yield up to pre-settlement values (as shown in FIG. 1). The other two curves of the TGA show that at values greater than 3 h the coke continues to be formed but more slowly: to this condition corresponds the settlement at maximum yield values (as shown in FIG. 1) which takes place slowly up to 10 hours before stabilizing completely.

EXAMPLE 3

[0122] For the purpose of verifying which is the type of catalyst comprising coke active in the catalysis, Example 2 was repeated but instead of using the mixture of butenols it uses the individual isomers supplied separately, i.e. 3-buten-2-ol (3-Bu-2-OH), 2-buten-1-ol (2-Bu-1—OH) and 3-buten-1-ol (3-Bu-1-OH). The conditions used were the same as in Example 2. From these tests it can be deduced that both 3-buten-2-ol (3-Bu-2-OH) [FIG. 3 in which in the ordinate the conversion and yield as a percentage (%) were reported; in the abscissa the time in hours (h) was reported], and 2-butenl-ol (2-Bu-1-OH) [FIG. 4 in which in the ordinate the conversion and yield as a percentage (%) were reported; in the abscissa the time in hours (h) was reported], have an analogous yield profile to that of the mixture of butenols used in Example 2, as shown in FIG. 1 (rapid increase in yield between 0 and 3 hours and then a further increase until settlement at the maximum values after 10 hours).

[0123] The behaviour of 3-buten-1-ol (3-Bu-1-OH) is completely different [FIG. 5 in which in the ordinate the conversion and yield as a percentage (%) were reported; in the abscissa the time in hours (h) was reported], which mainly produces propylene (40%-50% in yield) and abundant coke (C loss).

In FIG. 3:

[0124] X 3-Bu-2-OH refers to the conversion of 3-buten-2-ol (3-Bu-2-OH); [0125] C loss refers to the trend of the “carbon loss”.

In FIG. 4:

[0126] X 2-Bu-1-OH refers to the conversion of 2-buten-1-ol (2-Bu-2-OH); [0127] C loss refers to the trend of the “carbon loss”.

In FIG. 5:

[0128] X 3-Bu-1-OH refers to the conversion of 3-buten-1-ol (3-Bu-1-OH).

[0129] The catalysts comprising coke formed by the three isomers were subjected to analysis by infrared spectroscopy in diffuse reflection (“Diffuse Reflectance Infrared Fourier Transform Spectroscopy”—DRIFTS) operating as follows.

[0130] For that purpose, three samples of fresh catalyst were prepared (i.e. 0.6 g of silica-alumina containing 3.8% di Al) operating as described in Example 2. Each sample was diluted in potassium bromide (KBr) in the ratio of 1:10, treated at 450° C. in helium (He) for 20 minutes and then cooled to 50° C.: then a “single pulse” of the reactant was carried out, i.e. of the isomer 3-buten-2-ol (3-Bu-2-OH) (first sample), 2-buten-1-ol (2-Bu-1-OH) (second sample) and 3-buten-1-ol (3-Bu-1-OH) (third sample) on the sample and then, subsequently, the temperature was increased and the spectrum was recorded at 300° C. The aforesaid analysis was carried out using a FT-IR Bruker Vertex 70 spectrophotomer equipped with a Pike DiffusIR cell and with a MCT detector: the spectra were recorded and processed using the processing of data acquired through OPUS software. The analysis parameters were as follows: [0131] scanning interval: 4000 cm.sup.−1-450 cm.sup.−1; [0132] number of scans per sample: 32; [0133] background: spectrum recorded by positioning the starting catalyst (without coke) in the accessory housing; [0134] spectral resolution: 4 cm.sup.−1; [0135] regulation of the mirrors: 3.5 mm (the mirrors of the DRIFTS accessory were aligned so that the instrument detector could detect the maximum absorbance).

[0136] The results obtained are shown in FIG. 6 in which in the ordinate the absorption in absorbance units was reported; in the abscissa the wave number in cm.sup.−1 was reported. From the spectrum reported in FIG. 6 it can be deduced that effectively in the case of the two isomers that are mainly formed 1,3-butadiene (1,3-BDE), i.e. 3-buten-2-ol (3-Bu-2-OH) (first sample—indicated in FIG. 6 as 3But2ol) and 2-buten-1-ol (2-Bu-1-OH) (second sample—indicated in FIG. 6 as 2ButIol), the coke of the catalyst comprising coke obtained has two characteristic bands at 1465 cm.sup.−1 and 1573 cm.sup.−1, whereas the isomer 3-buten-1-ol (3-Bu-1-OH) (third sample—indicated in FIG. 6 as 3But1ol) (which leads to the formation of propylene and coke as reported in FIG. 5) has a band at 1650 cm.sup.−1 confirming the different nature of the two types of coke. Said bands are attributed to the stretching C═C and C—H of aromatic type (“coke bands”) as reported in literature by Ibarra A. et al, in the article “Dual coke deactivation pathways during the catalytic cracking of raw bio-oil and vacuum gasoil in FCC conditions”, “Applied Catalysis B: Environmental” (2016), Vol. 182, pp. 336-346.

EXAMPLE 4

[0137] For comparative purposes, Example 2 was repeated only supplying 3-buten-1-ol (3-Bu-1-OH), for 4 hours.

[0138] After 4 hours, the 3-buten-1-ol (3-Bu-1-OH), was replaced with the same mixture of butenols used in Example 2 (i.e. the mixture of butenols obtained as described in Example 1 and reported in Table 2). The results are shown in FIG. 7 in which in the ordinate the conversion and the yield as a percent (%) were reported; in the abscissa the time in hours (h) was reported. From FIG. 7 it can be deduced that the coke formed by 3-buten-1-ol (3-Bu-1-OH) has no effect on the promotion of the yield of catalyst: in fact, only after the replacement, in the supply, of 3-buten-1-ol (3-Bu-1-OH), with the same mixture of butenols used in Example 2, can an increase in the yield to 1,3-butadiene (Y 1,3BDE) be observed.

In FIG. 7:

[0139] X 2-Bu-1-OH refers to the conversion of 2-buten-1-ol (2-Bu-1-OH); [0140] X 3-Bu-2-OH refers to the conversion of 3-buten-2-ol (3-Bu-2-OH); [0141] X 3-Bu-1-OH refers to the conversion of 3-buten-1-ol (3-Bu-1-OH); [0142] C loss refers to the trend of the “carbon loss”.