Dehydration process for a feedstock comprising an alcohol for the production of alkenes

Abstract

The present invention relates to an isomerizing dehydration process for a feed comprising at least one primary monoalcohol of formula R-CH2-OH, wherein R is a nonlinear alkyl radical of general formula CnH2n+1, where n is an integer between 3 and 20. The process comprises an isomerizing dehydration step carried out in the gas phase at a weighted average temperature between 200 and 300°C, a pressure between 0.1 and 1 MPa, and a weight-hourly spatial velocity (WHV) between 1 and 25 h⁻¹, in the presence of a catalyst comprising at least one zeolite. The zeolite has at least one series of channels whose pore opening is defined by an 8-oxygen ring (8MR) and a mesoporous volume greater than or equal to 0.10 mL / g. Figure 2 to be published

Description

Title of the invention: Process for dehydrating a feed comprising an alcohol for the production of alkenes. TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to an improved process for producing alkenes from a feed comprising at least one primary monoalcohol, of formula R-CH2-OH, wherein R is a nonlinear alkyl radical of general formula CnH2n+i where n is an integer between 3 and 20 (such as isobutanol). This feed can be obtained by chemical or fermentation processes. This process involves a dehydration reaction in the presence of a catalyst based on a zeolite having particular textural and morphological characteristics.

[0002] The alkenes obtained, for example butenes and in particular isobutene, buten-1 and buten-2, are of important interest in the field of the petrochemical industry and organic synthesis. Previous technique

[0003] Butenes are key molecules in petrochemistry, particularly for the synthesis of gasoline additives such as ETBE and MTBE. The vast majority of scientific publications focus on the production of isobutene from linear butanols, which are more easily produced than isobutanol by conventional fermentation methods (ABE). However, recent developments have significantly improved isobutanol fermentation yields, making this feedstock accessible and available at an attractive cost.

[0004] The conversion of branched alcohols to alkenes, such as the conversion of isobutanol to butenes, is of significant interest in the petrochemical industry. The selectivity of the dehydration reaction in the presence of a solid catalyst and the stability of the catalyst in the presence of water generated by the reaction remain parameters that those skilled in the art are constantly seeking to improve. Furthermore, during alcohol dehydration, the alkenes generated can undergo oligomerization reactions, particularly at the acidic sites of the dehydration catalysts, leading to the deactivation of said catalysts (coke formation, pore clogging, and poisoning of the acidic sites). This phenomenon, well known in the presence of zeolite catalysts and in the absence of hydrogen, must be strictly limited to improve the lifetime of the catalysts and, consequently, the profitability of the alcohol dehydration process.

[0005] Furthermore, alcohols produced by fermentation of biomass or syngas contain impurities in the form of oxygenated and nitrogenous compounds produced during The processes involved in yeast metabolizing alcohols can have a detrimental effect on catalytic processes using bio-based alcohols or products derived from these alcohols. This can include forming unwanted species that deactivate dehydration or oligomerization catalysts, or poisoning active sites. If these compounds are basic, they can neutralize the acidic sites of catalysts commonly used in dehydration, oligomerization, or polymerization reactions, for example. Oxygenated compounds such as aldehydes, esters, and ethers can be partially removed by various pretreatments during the separation of alcohol from the fermentation medium. An additional step can be performed to remove any oxygenated compounds not separated during distillation.Basic nitrogen compounds (amines, pyrazines), due to their Brønsted or Lewis basic function, will poison the acidic sites of catalysts, leading to their deactivation. It is therefore preferable to eliminate them in order to increase the catalyst cycle time and maintain process selectivity. Catalysts with moderate acidity are more susceptible to deactivation in the presence of strong basic molecules.

[0006] Document WO2016046296 describes the modification of powdered FER structural zeolites by treatment in the presence of organic acid or by ion exchange, which reduces the ratio of strong acid sites to weak acid sites below 1. The catalysts are used in the simultaneous dehydration and skeletal isomerization reactions of isobutanol. This treatment slightly limits coke formation on the catalysts and, more importantly, modifies their nature (C / H) while maintaining good activity and selectivity for butenes, without, however, improving them.

[0007] Chadwick et al. (Chadwick et al., Chem. Commun., 2010, 46, 4088-4090) tested various zeolites: Theta-1, ZSM-23, ferrierite (Si / Al=10 or 22.5), and ZSM-5 (10MR), at 400°C to achieve the simultaneous dehydration and isomerization of n-butanol to obtain isobutene. They observed a loss of isomerizing activity of ferrierite for the formation of isobutene over time and attributed it to a negative effect of the water formed by the dehydration reaction, leading to its desalination. This was not observed with the other zeolites tested, with ferrierite being the least stable zeolite among those tested.

[0008] Document WO18087031 describes the shaping of a ferrierite zeolite with an alumina binder and its use in the low-temperature dehydration reaction of alcohols. WO18087031 shows that performance is improved when the tested Si / Al 20 ferrierite is shaped with alumina compared to shaping with silica: the conversions achieved with silica-based catalysts With ferrierite and alumina at 250°C, the PPH 7h 1 is greater than 90% and the linear butene / total butene ratio is approximately 87%, whereas with a ferrierite-based catalyst and a silica binder, the PPH 7h 1 is 72.5% and the linear butene / total butene ratio is approximately 82%. No mention is made of the stability of the catalysts.

[0009] Van Daele et al. (Applied Catalysis B: Environmental 284 (2021) 119699) sought to elucidate the mechanism of the isobutanol dehydration reaction on various zeolites, particularly ferrierite-type zeolites of different Si / Al compositions. Their objective was to understand the exceptional selectivity for linear butenes obtained from the branched C4 alcohol, isobutanol. To this end, the ratios (surface acidity / total acidity) and nature of the acidity (Lewis acidity / Brönsted acidity) were modified by treating different ferrierites. Ferrierites with different morphologies were synthesized to adjust the pore size, surface area, and external acidity of the crystals. An effect of external acidity of zeolites on activity was demonstrated, but no clear correlation could be established with n-butene selectivity or catalyst stability.A 15% loss of activity was observed within 4 hours with ferrierite in the form of nano-needles with an external surface area of ​​240 m² / g, while it was 33% with ferrierite nano-sheets with an external surface area of ​​42 m² / g. The studies were conducted under very low partial pressure of alcohol (45 mbar), at 250°C and a partial pressure of 100 h⁻¹; the conversion levels were less than 60%.

[0010] The present invention aims to overcome the drawbacks of the prior art of dehydration processes for branched alcohols using zeolites to obtain alkenes by providing an improved process, particularly with regard to:

[0011] - the stability of the dehydration catalyst and its lifespan, by limiting its dehydration tivation;

[0012] - the profitability of the dehydration process in terms of catalyst activity, se activity and yield in targeted products: linear alkenes. Summary of the invention

[0013] The present invention relates to an isomerizing dehydration process for a feed comprising at least one primary monoalcohol, of formula R-CH2-OH, wherein R is a nonlinear alkyl radical of general formula CnH2n+i where n is an integer between 3 and 20, said process comprising an isomerizing dehydration step carried out in the gas phase, at a weighted average temperature between 200 and 300°C, at a pressure between 0.1 and 1 MPa, at a weight-hour space velocity (PPH) between 1 and 25 h1, in the presence of a catalyst comprising at least one zeolite, wherein said zeolite has at least one series of channels whose pore opening is defined by an 8-atom ring of oxygen (8MR) and has a mesoporous volume greater than or equal to 0.10 ml / g.

[0014] The advantage of the process according to the invention lies in the fact that the use of a catalyst comprising a zeolite according to the invention and having particular textural properties makes it possible to obtain improved performance, in particular in terms of stability but also selectivity in linear alkenes and charge conversion.

[0015] The catalyst is active at lower temperatures than those usually used and remains stable. The ability to operate at temperatures below 300°C while maintaining complete alcohol conversion is also an advantage of the invention.

[0016] The linear alkenes obtained are of significant interest in the petrochemical industry and organic synthesis. Controlled oligomerization of these alkenes can also be used to produce aviation fuels and thus obtain BioJet.

[0017] The applicant has surprisingly demonstrated that the use of a catalyst comprising a zeolite according to the invention and having particular textural properties in an isomerizing dehydration process of a feed comprising a primary monoalcohol makes it possible to obtain a conversion rate of said alcohol much higher than that obtained with the zeolites used in the prior art processes, together with a low deactivation of the zeolite catalyst.

[0018] The applicant has also demonstrated, surprisingly, that the use of a catalyst comprising a zeolite according to the invention, and in particular possessing specific textural properties (notably a specific mesoporous volume), in the isomerizing dehydration reaction makes it possible to capture the basic nitrogenous impurities present in the alcohol feedstock and to produce an alkene effluent with a low nitrogen content, particularly upstream of an oligomerization step, thus protecting the catalyst downstream of the isomerizing dehydration, especially the oligomerization catalyst, from deactivation. The advantage of using a catalyst according to the invention, which is highly active, is that it allows for the simultaneous capture of basic nitrogenous molecules and the isomerizing dehydration of the alcohol at the temperature of the dehydration reaction.This avoids an intermediate step of purifying the effluent, which includes the alkenes obtained upstream of the oligomerization step. Description of the implementation methods

[0019] According to the present invention, the expressions "between ... and ..." and "between ... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this is not the case and the limit values ​​do not are not included in the range described, such precision will be provided by the present invention.

[0020] In the sense of the present invention, the different parameter ranges for a given step, such as pressure ranges and temperature ranges, can be used alone or in combination. For example, in the sense of the present invention, a preferred range of pressure values ​​can be combined with a more preferred range of temperature values.

[0021] In the following, particular embodiments of the invention may be described. They may be implemented separately or in combination with each other, without limitation of combinations where technically feasible. Charge

[0022] According to the invention, the feed treated in the process according to the invention is a feed comprising, preferably consisting of, at least one primary monoalcohol, of formula R-CH2-OH, in which R is a non-linear alkyl radical of general formula CnH2n+i where n is an integer between 3 and 20 (such as isobutanol), alone or in mixture.

[0023] In the remainder of this exposition, the term alkyl refers to a hydrocarbon compound of general formula CnH2n+i where n is an integer between 3 and 20, preferably between 3 and 10, preferably between 3 and 5, or even equal to 4.

[0024] In one embodiment, the charge comprises at least 40% by weight of primary monoalcohol relative to the total weight of said charge.

[0025] In one embodiment, the charge comprises at least 70% by weight of primary monoalcohol relative to the total weight of said charge.

[0026] In an embodiment, wherein the charge comprises at least 90% by weight of primary monoalcohol relative to the total weight of said charge.

[0027] Examples of primary monoalcohols according to the invention include isobutanol; 2-methylbutan-l-ol; 2,2-dimethylpropan-l-ol; 2-methylpentan-l-ol; 2,2-Dimethylbutan-l-ol; 2-Ethylbutan-l-ol. They can be used alone or in mixtures.

[0028] Said primary monoalcohol is preferably isobutanol or 2-methyl-1-butanol, alone or in a mixture. Most preferably, said primary monoalcohol is isobutanol. Preferably, the charge comprises between 40 and 100% by weight, preferably between 70 and 100% by weight, preferably between 90 and 100% by weight of isobutanol.

[0029] Said feedstock may originate from chemical or biochemical processes, for example fermentation processes. In particular, this feedstock may originate from at least one biomass fermentation process, in particular lignocellulosic biomass.

[0030] Said charge may contain water, in particular up to 60% water by weight, preferably up to 30% water, preferably up to 10% water by weight. It may also include mineral-type impurities (such as Na, Ca, P, Al, Si, K, SO4) and organic-type impurities (such as methanol, ethanol, n-butanol, aldehydes, ketones, and corresponding acids, e.g. furanic, acetic, isobutyric acid).

[0031] Said charge may contain nitrogenous impurities, in particular between 5 and 100 ppm of total nitrogen. Process

[0032] According to the invention, the process comprises an iso-merizing dehydration step of the feed comprising at least one primary monoalcohol of formula R-CH 2-OH, preferably carried out in the gas phase, at a weighted average temperature of between 200 and 300°C, preferably between 210 and 280°C, most preferably between 230 and 270°C, at a pressure of between 0.1 and 1.0 MPa, preferably between 0.3 and 1.0 MPa, most preferably between 0.5 and 1.0 MPa, at a weight-hourly spatial velocity (PPH) of between 1 and 25 h', preferably between 1 and 20 h1, most preferably between 1 and 18 h1, in the presence of a dehydration catalyst.

[0033] Advantageously, the dehydration is carried out in a reactor or series of reactors, comprising at least one catalytic bed.

[0034] PPH stands for "Weight per Weight per Hour," which corresponds to the hourly space velocity in weight. Hourly space velocity in weight (PPH) is defined as the mass flow rate of primary monoalcohol in the feed (considered dry) at the reactor inlet divided by the mass of catalyst in said reactor. This concept is also sometimes referred to by its English acronym WHSV, or "Weight Hourly Space Velocity."

[0035] By weighted average temperature (denoted TMP), we mean the average temperature in the catalytic bed, the bed being the set of beds present in the reactor, beds in which the catalytic reaction takes place, calculated along the flow axis in said bed. Given a bed of length L and surface area S, with the reactive mixture flowing along the longitudinal axis x of this bed, the inlet to the catalytic bed forming the origin of the axis (%=0), the weighted average temperature, denoted TMP, is expressed according to the following formula: TMP

[0036] Since the reaction is endothermic and the reactor operates either in isothermal mode or in adiabatic mode, the weighted average temperature will be representative of the reaction temperature.

[0037] The reaction advantageously takes place in one or more reactors, for example Isothermal or adiabatic reactors, arranged in series or parallel, preferably in series, operate each reactor under specific or identical conditions. Those skilled in the art will know how to adjust the operating conditions (pressure, temperature, residence time) of each reactor according to the load to achieve optimal conversion and the desired linear olefin selectivity.

[0038] Preferably, the dehydration catalyst is arranged in one or more fixed beds, which can be operated in upward, downward or radial flow.

[0039] Since the dehydration reaction is endothermic, the dehydration step advantageously includes a supply of calories, the supply of calories being achieved by any means of heating known to a person skilled in the art.

[0040] Preferably, before contact with the charge to be treated, the dehydration catalyst is activated by any means known to those skilled in the art, for example by heat treatment under air.

[0041] The process according to the invention allows operation at low temperatures, in particular at temperatures less than or equal to 300°C, preferably less than or equal to 270°C. The advantage of operating at low temperatures in the process according to the invention is that it avoids local overheating of the alcohol (temperature at the point of contact with the metallic surface of the reactor or the feed transport lines being too high), which could lead to degradation of the primary monoalcohol, such as isobutanol, and reduces utility consumption as well as operating costs. The process according to this embodiment is therefore very economically advantageous. Dehydration catalyst

[0042] According to the invention, the dehydration catalyst used comprises at least one zeolite which has at least one series of channels whose pore opening is defined by an 8-atom oxygen ring (8MR) and which has a mesoporous volume greater than or equal to 0.10 ml / g.

[0043] According to one embodiment, said zeolite may also advantageously have at least one series of channels whose pore opening is defined by a ring containing 10 oxygen atoms (10 MR). These channel series are defined in the classification “Atlas of Zeolite Framework Types”, Ch. Baerlocher, LB McCusker, DH Oison, 6th Edition, Elsevier, 2007, Elsevier.

[0044] Said zeolite is advantageously selected from zeolites having 8 and 10MR channels, such as structural FER and MFS zeolites, taken alone or in mixtures. The zeolite is most advantageously selected from among the FER type zeolites ferrierite, FU-9, ISL6, NU-23, and ZSM-35, and for the MFS type, it is the ZSM-57 zeolite, taken alone or in mixtures. Said zeolite is most advantageously of the FER type and preferably ferrierite. Preferably, said zeolite is composed of ferrierite.

[0045] In one embodiment, the zeolite has a mesoporous volume greater than or equal to 0.15 ml / g.

[0046] In one embodiment, the zeolite has a mesoporous volume greater than or equal to 0.18 ml / g.

[0047] In one embodiment, the zeolite has a mesoporous volume greater than or equal to 0.20 ml / g, preferably greater than or equal to 0.22 ml / g, preferably greater than or equal to 0.24 ml / g.

[0048] Preferably, the zeolite has a mesoporous volume less than or equal to 0.50 ml / g, preferably less than or equal to 0.40 ml / g, preferably less than or equal to 0.35 ml / g, preferably less than or equal to 0.30 ml / g.

[0049] In one embodiment, the zeolite has a mesoporous volume of between 0.18 and 0.50 ml / g.

[0050] In one embodiment, the zeolite has a mesoporous volume of between 0.20 and 0.40 ml / g.

[0051] In one embodiment, the zeolite has a mesoporous volume of between 0.22 and 0.35 ml / g.

[0052] In one embodiment, the zeolite has a mesoporous volume of between 0.24 and 0.30 ml / g.

[0053] In one embodiment, the zeolite has a Si / Al molar ratio between 5 and 45.

[0054] In one embodiment, the zeolite has a Si / Al molar ratio between 5 and 30.

[0055] In one embodiment, the zeolite has a Si / Al molar ratio between 8 and 20.

[0056] In one embodiment, the zeolite has a Si / Al molar ratio between 9 and 15.

[0057] In one embodiment, the zeolite has a Si / Al molar ratio between 11 and 13.

[0058] In one embodiment, the zeolite has a microporous volume of between 0.100 and 0.150 ml / g.

[0059] In one embodiment, the zeolite has a microporous volume between 0.110 and 0.145 ml / g.

[0060] In one embodiment, the zeolite has a microporous volume of between 0.120 and 0.140ml / g.

[0061] In one embodiment, the zeolite has a microporous volume of between 0.130 and 0.140 ml / g.

[0062] In one embodiment, the zeolite has a microporous volume between 0.133 and 0.138 ml / g.

[0063] In one embodiment, the zeolite has an external surface area of ​​between 10 and 70 m2 / g.

[0064] In one embodiment, the zeolite has an external surface area of ​​between 20 and 65 m2 / g.

[0065] In one embodiment, the zeolite has an external surface area of ​​between 30 and 60 m2 / g.

[0066] In one embodiment, the zeolite has an external surface area of ​​between 35 and 55 m2 / g.

[0067] In one embodiment, the zeolite has an external surface area of ​​between 45 and 50 m2 / g.

[0068] In one embodiment, the zeolite has an average crystal size of less than or equal to 100 nm.

[0069] In one embodiment, the zeolite has an average crystal size of between 10 and 100 nm.

[0070] In one embodiment, the zeolite has an average crystal size of between 30 and 95 nm.

[0071] In one embodiment, the zeolite has an average crystal size of between 40 and 90 nm.

[0072] In one embodiment, the zeolite has an average crystal size of between 50 and 85 nm.

[0073] In one embodiment, the zeolite has an average crystal size of between 60 and 80 nm.

[0074] In one embodiment, the zeolite has a BET surface area greater than or equal to 400 m2 / g.

[0075] In one embodiment, the zeolite has a BET surface area of ​​between 405 and 450 m2 / g.

[0076] In one embodiment, the zeolite has a BET surface area of ​​between 410 and 440 m2 / g.

[0077] In one embodiment, the zeolite has a BET surface area of ​​between 415 and 430 m2 / g.

[0078] The zeolite crystals according to the invention have a rounded and elongated shape, in particular an oblong or spheroid shape.

[0079] Advantageously, the zeolite crystals according to the invention are not in the form of needles or platelets.

[0080] The zeolite crystals according to the invention are arranged in the form of aggregates, preferably in spherical form, unlike the zeolites used in prior art processes.

[0081] The catalyst can be in powder form or shaped.

[0082] Advantageously, the dehydration catalyst has a zeolite content of at least 50% by weight, preferably between 55 and 90% by weight, most preferably between 60 and 80% by weight relative to the total weight of said dehydration catalyst.

[0083] In one embodiment, the dehydration catalyst does not include any metals.

[0084] The term "no metals" means that no metals are added during preparation.

[0085] According to a particular embodiment of the invention, the catalyst is formed with a binder, advantageously inert for the intended reaction (isomerizing dehydration of a primary monoalcohol). Forming the catalyst with a binder makes it possible to obtain a macroscopic catalyst whose physical properties (geometry, specific pore volume, etc.) can be adapted by those skilled in the art. Indeed, when the zeolite cannot be used industrially in powder form, the binder provides the final solid with the mechanical strength necessary for industrial use and increased resistance in the presence of water. The binder also allows the catalyst thus formed to be used in a fixed bed in a reactor without causing excessive pressure loss.

[0086] The binder is preferably chosen from a silicic binder such as silica, an aluminic binder such as gamma alumina, AlPO4, clay, zirconia, Ti oxide, SiC, or mixtures thereof.

[0087] Preferably, the binder is a silicic or aluminic binder. Preferably, the binder is a silicic binder, consisting essentially of silica; that is to say, the silicic binder consists of silica except for impurities, which have no catalytic effect. In particular, said silica is amorphous silica.

[0088] Preferably, the dehydration catalyst has a binder content of between 10 and 45% by weight, preferably between 20 and 40% by weight relative to the total weight of said catalyst.

[0089] The dehydration catalyst can be shaped into extrudates, according to a geometry for example cylindrical or multilobe, in particular trilobed or a quadrilobe.

[0090] The process according to the invention, which uses a dehydration catalyst comprising a zeolite having such morphological and textural characteristics, makes it possible to obtain optimized isomerizing dehydration performance of a primary alcohol, particularly in terms of alcohol conversion and selectivity towards linear alkenes. Furthermore, such a dehydration catalyst also exhibits improved deactivation stability, and therefore an increased lifespan, which allows for an attractive profitability of the isomerizing dehydration process. Description of analytical methods

[0091] To determine the microporous volume, the t-method (of Lippens and De Boer) described in the Journal of Catalysis (Studies on pore systems in catalysts V. The t-method, J. Catal., 1965, 4(3), p. 319) is used. It is based on the comparison between the experimental isotherm of the microporous solid and the reference isotherm (non-porous solid) of the same chemical nature. From the Lippens-De Boer equation, the thickness t of the multilayer can be calculated with the following equation (called the t-plot): J. 01399 ï ' ( 0.034 - Lg(AA) J

[0092] Or P / P0 is the relative nitrogen pressure.

[0093] The microporous volume is calculated using the following equation:

[0094] where Y is the y-intercept of the t-plot curve (and D is the density conversion factor (D = 15.468 x 10⁻⁴, a coefficient to ensure the conversion of the gaseous volume to the liquid volume). The chosen range of t corresponds to a plateau on the nitrogen adsorbed volume versus thickness t curve and is between 0.4 and 0.8 nm.

[0095] The mesoporous surface, also called the external surface here, is calculated using the t-plot curve with the following equation: Smeso / ext{m3f,q}=IhS

[0096] Where S is the slope of the t-plot line and D is the density conversion factor (D = 15.468 x 10-4, coefficient for converting gaseous volume into liquid volume).

[0097] The mesoporous volume is here considered equal to the total volume of nitrogen adsorbed at P / PO max less the microporous mass volume.

[0098] The specific surface area or BET surface area is determined by the BET (Brunauer, Emmet, and Teller) method described in the journal "The Journal of the American Society", 1938, 60, 309. It is based on the specificity of physical adsorption: multimolecular adsorption on sites of the same energy. The set of assumptions (equivalent sites, no lateral interaction between adsorbed molecules, each adsorbed molecule can serve as an adsorption site) put forward in this theory made it possible to deduce the specific surface area from the volume of nitrogen adsorbed on the monolayer Vm, using the following equation: SB ET(m2 / g)=4.37 * Vm,

[0099] The average size of the zeolite crystals is measured by transmission electron microscopy (TEM), bright-field. Crystal size histograms Measurements were taken from photographs taken using transmission microscopy in bright-field mode. The average size was determined from the measurement of 200 crystals. The crystals observed for the zeolite according to the invention are preferably oblong or spheroid in shape. The crystal is represented in the photograph as its projection along the beam axis. The dimension used is an estimate of the size of a crystal along the beam axis shown in [Fig. 1], with an average then calculated from a sample of 200 crystals.

[0100] The following examples and figures illustrate the invention, in particular particular embodiments of the invention, without limiting its scope. List of figures

[0101] [Fig.1]

[0102] Fig. 1 schematically represents a crystal and the axis along which the electron microscopy beam travels through said crystal to calculate its size.

[0103] [Fig.2]

[0104] Figure [Fig. 2] represents a scanning electron microscope (SEM) view of solid B according to the invention.

[0105] [Fig.3]

[0106] Fig. 3 represents a scanning electron microscope (SEM) view of the comparative solid C. EXAMPLES

[0107] Example 1: Testing of different catalyst samples in a process for dehydrating isobutanol to n-butene

[0108] The dehydration step is carried out on a multi-reactor EHD catalytic test unit comprising fixed-bed reactors operating in "downflow" mode. The dehydration catalysts tested each comprise 100% by weight of a zeolite. Several zeolites were tested (see Table 2).

[0109] The catalysts are loaded separately into the reactors in powder form, having been previously pelletized, ground, and then sieved to retain the 300-500 µm fraction. The catalysts are loaded into the 4 mm internal diameter quartz reactors between two SiC beds. The catalysts are then activated at 450°C under air purging for 6 hours after a temperature ramp of 5°C / min. The temperature is then lowered to the test temperature under nitrogen to remove any air present in the system before injection of the isobutanol feedstock. The test is performed at atmospheric pressure (approximately 0.1 MPa).

[0110] Different PPHs are evaluated: 9, 6 and 3h 1 at two temperatures 240 and 250°C, a return point is made at the end of the test at 240°C PPH 9h*. Each condition is The temperature was maintained for 9 hours, allowing for the acquisition of 5 chromatograms and the evaluation of zeolite deactivation. The test lasted 72 hours. The sequence of conditions is presented below; these were applied identically to all catalysts. [YES] [Table 1] Condition No. PPH isobutanol (h1) Temperature (°C) 1 9 240 2 6 240 3 3 240 4 9 250 5 6 250 6 3 250 7 9 240

[0112] The charge is an isobutanol / water mixture in a mass ratio of 99 / 1. It is vaporized in the SiC bed at the top of the reactor before coming into contact with the catalytic bed.

[0113] The analysis of the total effluent is carried out at the reactor outlet on an online gas chromatograph equipped with two capillary columns, which makes it possible to determine the conversion of isobutanol, the selectivities in different products and in particular the selectivity in butenes and the fraction of linear butenes in the butenes cut, a fraction which we seek to maximize.

[0114] The zeolites tested are presented in the following table:

[0115] [Tables2] Solid Zeolite Type A (According to the invention) Ferrierite B (According to the invention) Ferrierite C (Comparative) Ferrierite CP914C D (Comparative) Ferrierite CP914 E (Comparative) ZSM-5 CBV5020 F (Comparative) ZSM-5 CBV2314

[0116] The textural properties of the evaluated zeolites are presented in the following table:

[0117] [Tables3] Solid Average crystal size measured by TEM (nm) Observed crystal morphology BET surface area (m² / g) Total volume (ml / g) Microporous volume (Vp) per plot (ml / g) Mesoporous volume = Vtotal-Vp (ml / g) Molar Si / Al (FX) External surface area (m² / g) A 100 Spheroid 400 0.297 0.132 0.165 10.0 29.0 B 72 Spheroid 425 0.401 0.136 0.265 12.5 47.0 C 170 Faceted polyhedral 337 0.206 0.130 0.076 10.0 8.6 D 3000 Platelets 398 0.222 0.146 0.076 25.0 15.0 E 40 Pebbles = needle aggregates and small crystals 408 0.399 0.115 0.284 25.0 42.0 F 500 Faceted polyhedral 431 0.225 0.135 0.090 12.0 31.0

[0118] The catalytic results obtained at reaction times between 8-9 h of testing and after 70-72 h of testing, for the different zeolites tested, are presented in Table 4 below. The catalytic results presented are the conversion of isobutanol, the proportion of N-butenes in total butenes (N-butenes / total butenes) at the beginning of the test and after at least 70 h under load, the loss of activity (or deactivation) as a percentage per unit of time between the conversion at the initial point (at approximately 8-9 hours) and the conversion at the final point (i.e., around 70-72 hours) under the same conditions (240°C, PPH 9h*).

[0119] [Tables4] Solid Time Under Load (h) Isobutanol Conversion (%) Total N-butene / butene Deactivation or Conversion Loss (% / h) A 9.3 99.5 67.9 1.189 72.4 24.4 58.9 B 8.8 100.0 69.5 0.000 72.0 100.0 68.2 C 8.1 22.7 56.2 0.243 71.3 7.4 46.9 D 7.9 15.0 57.6 0.157 71.0 5.0 45.0 E 7.6 90.6 32.3 0.800 70.8 40.0 34.9 F 8.3 99.3 38.3 1.004 71.5 35.9 39.0

[0120] It is observed that among the four ferrierites tested (A, B, C, and D), those according to the invention, which have a mesoporous volume greater than 0.10 ml / g (i.e., zeolites A and B), exhibit a much higher activity after 8 to 10 hours under load than those with a mesoporous volume less than 0.10 ml / g (C and D). For example, at a similar molar ratio (Si / Al of 10), ferrierite A exhibits a higher initial activity than ferrierite C (99.5% conversion at approximately 9 hours for zeolite A versus 22.7% conversion at approximately 8 hours for zeolite C).

[0121] In terms of stability, the ferrierite B according to the invention, having a mesoporous volume of 0.265 ml / g (therefore greater than 200 ml / g, or even greater than 0.22 ml / g), and advantageously exhibiting an external surface area of ​​between 35 and 55 m² / g, or even between 45 and 50 m² / g, and a Si / Al molar ratio of 12.5, converts isobutanol optimally, since it converts 100% of isobutanol for 72 hours regardless of temperature and PPH. This zeolite combines high initial and final conversions, improved and virtually stable linear butene selectivity over the test time compared to other zeolites tested, and low deactivation (or even zero deactivation over 72 hours). Ferrierite C and D deactivate little, but the initial conversion of isobutanol on these solids is less than 50% at 240°C.

[0122] Example 2: Test of the ability of catalysts to capture nitrogen compounds

[0123] In this example, the feedstock is an isobutanol / water mixture with a mass ratio of 95 / 5, containing 6 ppm of acetonitrile. The same apparatus is used. The feedstock is vaporized in the SiC bed at the top of the reactor before contacting the catalytic bed. Various catalysts were tested: zeolites A, B, C, D, E, and F described in Example 1, and gamma alumina (see Table 6). Gamma alumina has a low total NH3 acidity (300 pmol / g). The catalysts are prepared as described in Example 1. The catalysts were tested under conditions that were strictly identical (except for the presence of nitrogen compounds) to those of Example 1.

[0124] The following table presents the nitrogen, carbon and hydrogen contents of the different catalysts, analyzed after 72 h of reaction for the different catalysts tested:

[0125] [Tables5] Solid N content (%) H content (%) C content (%) A 0.115 1.253 8.137 B 0.212 1.383 8.956 C 0.057 1.112 7.642 D 0.084 0.87 5.884 E 0.147 1.113 9.148 F 0.197 1.054 9.691 Gamma alumina <0.004 0.9 3.600

[0126] It is noted that zeolites A to F have a significantly higher nitrogen content than that measured for gamma alumina, which allows us to deduce that the zeolites capture at least in part the nitrogenous impurities of the isobutanol charge.

[0127] Furthermore, it appears that ferrierites A and B have a higher nitrogen content (0.115% and 0.212% respectively) than ferrierites C and D, whose nitrogen content is less than 0.10%. This indicates that the catalysts according to the invention, ferrierite B in particular, possess a greater capacity to capture nitrogen compounds than the ferrierite zeolites used in prior art processes.

Claims

Demands

1. A process for the isomerizing dehydration of a feed comprising at least one primary monoalcohol, of formula R-CH2-OH, wherein R is a nonlinear alkyl radical of general formula CnH2n+i where n is an integer between 3 and 20, said process comprising an isomerizing dehydration step carried out in the gas phase, at a weighted average temperature of between 200 and 300°C, at a pressure of between 0.1 and 1 MPa, at a weight-hour spatial velocity (PPH) of between 1 and 25 h-1, in the presence of a catalyst comprising at least one zeolite, wherein said zeolite has at least one series of channels whose pore opening is defined by an 8-atom oxygen ring (8MR) and has a mesoporous volume greater than or equal to 0.10 ml / g.

2. A method according to claim 1 wherein the zeolite has a Si / Al molar ratio between 5 and 45.

3. A method according to any one of the preceding claims wherein the zeolite has an external surface area of ​​between 10 and 70 m2 / g, preferably between 20 and 65 m2 / g, most preferably between 35 and 55 m2 / g.

4. A process according to any one of the preceding claims wherein the zeolite has a microporous volume of between 0.100 and 0.150 ml / g.

5. A method according to any one of the preceding claims wherein the zeolite also has a series of channels whose opening is at 10 oxygen atoms (10MR).

6. Method according to claim 5 wherein the zeolite is of structural type FER or MFS.

7. A method according to claim 6 wherein the zeolite is a ferrierite.

8. A method according to any one of the preceding claims wherein the charge comprises from 90 to 100% by weight of primary monoalcohol relative to the total weight of said charge.

9. A process according to any one of the preceding claims wherein the primary monoalcohol is isobutanol.

10. A process according to any one of the preceding claims wherein the feedstock is derived from at least one lignocellulosic biomass fermentation process. 18

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