Method for dehydrating a feedstock comprising an alcohol for the production of alkenes

Abstract

The present invention relates to a method for the isomerization dehydration of a feedstock comprising at least one primary monoalcohol, of formula R-CH2-OH, in which R is a nonlinear alkyl radical of general formula CnH2n+1 where n is an integer between 3 and 20, the method comprising an isomerization dehydration step carried out in the gas phase, at a weighted mean temperature of between 200 and 300°C, at a pressure of between 0.1 and 1 MPa, at a weight hourly space velocity (PPH) of between 1 and 25 h-1, in the presence of a catalyst comprising at least one zeolite, wherein the zeolite has at least one series of channels, the pore opening of which is defined by a ring of eight oxygen atoms (8MR) and has a mesopore volume of 0.10 ml / g or greater.

Description

[0001]Process for dehydrating a feedstock comprising an alcohol for the production of alkenes TECHNICAL FIELD OF THE INVENTION The present invention relates to an improved process for producing alkenes from a feedstock comprising at least one primary monoalcohol, of formula R-CH2-OH, in which R is a non-linear alkyl radical of general formula CnH2n+1 where n is an integer between 3 and 20 (such as isobutanol). This feedstock can be obtained by chemical processes or by fermentation processes. This process implements a dehydration reaction in the presence of a catalyst based on a zeolite having particular textural and morphological characteristics. The alkenes obtained, for example butenes and in particular isobutene, butene-1 and butenes-2, are of significant interest in the field of the petrochemical industry and organic synthesis.PRIOR ART 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 processes (ABE). However, recent developments have significantly improved fermentation yields of isobutanol, making this feedstock accessible and available at an attractive cost. The conversion of branched alcohols to alkenes, such as the conversion of isobutanol to butenes, is of significant interest in the petrochemical field. 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 generated alkenes can undergo oligomerization reactions, particularly on the acid sites of the dehydration catalysts, leading to deactivation of said catalysts (coke formation, pore clogging and poisoning of the acid sites). This well-known phenomenon in the presence of zeolite catalysts and in the absence of hydrogen must be absolutely limited to improve the lifetime of the catalysts and consequently the profitability of the alcohol dehydration process. Furthermore, alcohols produced by fermentation of biomass or syngas contain impurities in the form of oxygenated and nitrogenous compounds produced during the processes of metabolization of feedstocks into alcohols by yeasts.These compounds can have a deleterious effect on catalytic processes using bio-sourced alcohols or products derived from these alcohols, in particular by forming unwanted species responsible for the deactivation of dehydration or oligomerization catalysts, or by poisoning the active sites in the case where these compounds are basic, they can neutralize the acid sites of catalysts commonly used for dehydration, oligomerization or polymerization reactions for example. Oxygenated compounds such as aldehydes, esters, ethers in particular can be partially eliminated by different pretreatments during the separation of the alcohol from the fermentation medium. An additional step can be carried out to eliminate the oxygenated compounds not separated during distillation.Basic nitrogen compounds (amines, pyrazines), due to their basic Brønsted or Lewis function, will poison the acid sites of the 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 of moderate acidity risk greater deactivation in the presence of strong basic molecules. Document WO2016046296 describes the modification of powdered FER structural type zeolites by treatment in the presence of organic acid or by ion exchange, which makes it possible to lower 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 allows to slightly limit the formation of coke on the catalysts, and especially to modify its nature (C / H) while maintaining a good activity and a good selectivity in butenes, without however improving them. Chadwick et al. (Chadwick et al., Chem. Commun., 2010, 46, 4088-4090) tested different zeolites: Theta-1, ZSM-23, ferrierite (Si / Al=10 or 22.5) and ZSM-5 (10MR), at 400°C to carry out the dehydration and simultaneous isomerization of n-butanol to obtain isobutene. They highlight a loss of isomerizing activity of ferrierite for the formation of isobutene over time and attribute it to a negative effect of the water formed by the dehydration reaction leading to its dealumination. This is not observed with the other zeolites tested, ferrierite being the least stable zeolite among the zeolites tested.WO18087031 describes the shaping of a ferrierite zeolite with an alumina binder and its use in the dehydration reaction of alcohols at low temperature. WO18087031 shows that the performance is improved when the tested ferrierite with a Si / Al ratio of 20 is shaped with alumina compared to shaping with silica: conversions achieved with ferrierite and alumina catalysts at 250°C, PPH 7h. -1 are greater than 90% and the linear butenes / total butenes ratio is about 87%, while with a ferrierite-based catalyst and a silica binder and a PPH of 7h -1is 72.5% and the ratio of linear butenes to total butenes is about 82%. No mention is made of the stability of the catalysts. Van Daele et al. (Applied Catalysis B: Environmental 284 (2021) 119699) sought to elucidate the mechanism of the isobutanol dehydration reaction on different zeolites and in particular on ferrierite-type zeolites of different Si / Al. His objective was to understand the exceptional selectivity for linear butenes obtained from the branched C4 alcohol, isobutanol. For this, the ratio (surface acidity / total acidity) and nature of acidity (Lewis acidity / Brønsted acidity) were modified by treatment of different ferrierites. Ferrierites with different morphologies to adjust the amount of pores, surface area and external acidity of the crystals were synthesized.An effect of the external acidity of the zeolites on the activity was highlighted, but no clear correlation could be established with the selectivity to n-butenes, nor the stability of the catalysts. A loss of activity of 15% was observed in 4h with ferrierite in the form of nano-needles with an external surface area of ​​240 m² / g, while it is 33% with ferrierite nano-sheets with an external surface area of ​​42 m² / g. The studies were carried out under very low partial pressure of alcohol (45 mbar), at 250°C and a PPH of 100h. -1; the conversion levels are less than 60%. The present invention aims to overcome the drawbacks of the prior art of processes for dehydrating branched alcohols using zeolites to obtain alkenes by providing an improved process, in particular from the point of view of: - the stability of the dehydration catalyst and its lifetime, by limiting its deactivation; - the profitability of the dehydration process in terms of catalyst activity, selectivity and yield of targeted products: linear alkenes.SUMMARY OF THE INVENTION The present invention relates to a process for the isomerizing dehydration of a feedstock comprising at least one primary monoalcohol, of formula R-CH2-OH, in which R is a non-linear alkyl radical of general formula CnH2n+1 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 hourly space velocity (WPH) between 1 and 25 h. -1, in the presence of a catalyst comprising at least one zeolite, in which said zeolite has at least one series of channels whose pore opening is defined by a ring with 8 oxygen atoms (8MR) and has a mesoporous volume greater than or equal to 0.10 ml / g. 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, particularly in terms of stability but also selectivity for linear alkenes and conversion of the charge. The catalyst is active at lower temperatures than those normally used and remains stable. The possibility of working at temperatures below 300°C while maintaining total conversion of the alcohol is also an advantage of the invention.The linear alkenes obtained are of significant interest in the petrochemical industry and organic synthesis. The controlled oligomerization of these alkenes can also make it possible to produce aviation fuels and thus obtain BioJet. The applicant has surprisingly demonstrated that the use of a catalyst comprising a zeolite according to the invention and having particular textural properties in a process for the isomerizing dehydration of a feedstock 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 processes of the prior art, together with a low deactivation of the zeolite catalyst.The applicant has also surprisingly demonstrated that the use of a catalyst comprising a zeolite according to the invention, and in particular having particular textural properties (in particular a particular mesoporous volume), in the isomerizing dehydration reaction makes it possible to capture the basic nitrogenous impurities present in the alcoholic feedstock and to produce an alkene effluent with a low nitrogenous compound content, in particular upstream of an oligomerization step, thus making it possible to protect the catalyst downstream of the isomerizing dehydration, in particular the oligomerization catalyst, from deactivation. The advantage of using a catalyst according to the invention which is very active is that it makes it possible to simultaneously carry out the capture of basic nitrogenous molecules and the isomerizing dehydration of the alcohol at the temperature of the dehydration reaction.This makes it possible to avoid an intermediate step of purification of the effluent comprising the alkenes obtained upstream of the oligomerization step. DESCRIPTION OF THE EMBODIMENTS According to the present invention, the expression "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 ​​are not included in the range described, such precision will be provided by the present invention. For the purposes 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, for the purposes of the present invention, a preferred pressure range of values ​​can be combined with a more preferred temperature range of values.In the following, particular embodiments of the invention may be described. They may be implemented separately or combined with each other, without limitation of combinations when this is technically feasible. Charge In accordance with the invention, the charge treated in the process according to the invention is a charge 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 C. n H 2n+1where n is an integer between 3 and 20 (such as isobutanol), alone or as a mixture. In the remainder of the description, the term alkyl designates a hydrocarbon compound of general formula CnH2n+1 where n is an integer between 3 and 20, preferably between 3 and 10, more preferably between 3 and 5, or even equal to 4. In one embodiment, the feed comprises at least 40% by weight of primary monoalcohol relative to the total weight of said feed. In one embodiment, the feed comprises at least 70% by weight of primary monoalcohol relative to the total weight of said feed. In one embodiment, in which the feed comprises at least 90% by weight of primary monoalcohol relative to the total weight of said feed. As primary monoalcohol according to the invention, mention may be made of isobutanol; 2-methylbutan-1-ol; 2,2-dimethylpropan-1-ol; 2-methylpentan-1-ol; 2,2-dimethylbutan-1-ol; 2-ethylbutan-1-ol. They can be alone or in mixture.Said primary monoalcohol is preferably isobutanol or 2-methyl-1-butanol, taken alone or in a mixture. Very preferably, said primary monoalcohol is isobutanol. Preferably, the feedstock comprises between 40 and 100% by weight, preferably between 70 and 100% by weight, preferably between 90 and 100% by weight of isobutanol. 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. Said feedstock may contain water, in particular up to 60% by weight of water, preferably up to 30% of water, preferably up to 10% by weight of water.It may also comprise impurities of mineral type (such as Na, Ca, P, Al, Si, K, SO4) and of organic type (such as methanol, ethanol, n-butanol, aldehydes, ketones, and the corresponding acids, for example furanic, acetic, isobutyric acid). Said feed may contain nitrogenous impurities, in particular between 5 and 100 ppm of total nitrogen. Process According to the invention, the process comprises a step of isomerizing dehydration of the feedstock comprising at least one primary monoalcohol of formula R-CH2-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, very 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, very preferably between 0.5 and 1.0 MPa, at a weight hourly space velocity (WPH) of between 1 and 25 h. - 1 , preferably between 1 and 8 p.m. -1, most preferably between 1 and 6 p.m. -1, in the presence of a dehydration catalyst. Advantageously, the dehydration is carried out in a reactor or series of reactors, comprising at least one catalytic bed. PPH means "Weight per Weight per Hour" which corresponds to the weight hourly space velocity. Weight hourly space velocity (PPH) means the mass flow rate of primary monoalcohol of the feedstock (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". Weighted average temperature (TMP) means the average temperature in the catalytic bed, the bed being all the beds present in the reactor, beds in which the catalytic reaction takes place, calculated along the axis of the flow in said bed.Given a bed of length L and surface area S, the reactive mixture flowing along the longitudinal axis x of this bed, the inlet into the catalytic bed forming the origin of the axis (x=0), the weighted average temperature, noted TMP, is expressed according to the following formula: The reaction being endothermic and the reactor operating either in isothermal mode or in adiabatic mode, the weighted average temperature will be representative of the reaction temperature. The reaction advantageously takes place in one or more reactors, for example isothermal or adiabatic, arranged in particular in series or parallel, preferably in series, and each reactor is operated under specific or identical conditions. A person skilled in the art will be able to adjust the choice of operating conditions (pressure, TMP temperature, residence time) of each reactor according to the feedstock to obtain optimal conversion and the desired selectivity for linear olefins.Preferably, the dehydration catalyst is arranged in one or more fixed beds, which can be operated in ascending, descending or radial flow. The dehydration reaction being endothermic, the dehydration step advantageously comprises a supply of calories, the supply of calories being carried out by any heating means known to those skilled in the art. Preferably, before contacting with the feedstock to be treated, the dehydration catalyst is activated by any means known to those skilled in the art, for example by heat treatment in air. The process according to the invention makes it possible to work at low temperature, in particular at a temperature less than or equal to 300°C, preferably less than or equal to 270°C.The advantage of working at low temperature in the process according to the invention makes it possible to avoid local overheating of the alcohol (temperature in contact with the metal surface of the reactor or the feedstock transport lines too high) which risks causing degradation of the primary monoalcohol, such as isobutanol, to reduce the consumption of utilities as well as the operating cost. The process according to this embodiment is therefore economically very advantageous. Dehydration catalyst 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 a ring with 8 oxygen atoms (8MR) and which has a mesoporous volume greater than or equal to 0.10 ml / g.According to one embodiment, said zeolite can also advantageously have at least one series of channels whose pore opening is defined by a ring containing 10 oxygen atoms (10 MR). These series of channels are defined in the classification “Atlas of Zeolite Framework Types”, Ch. Baerlocher, LB Mc Cusker, DH Olson, 6th Edition, Elsevier, 2007, Elsevier". Said zeolite is advantageously chosen from zeolites having 8 and 10MR channels such as zeolites of structural type FER and MFS, taken alone or in a mixture. The zeolite is more advantageously chosen in the FER type from the zeolites ferrierite, FU-9, ISI-6, NU-23, ZSM-35 and for the MFS type, it is the zeolite ZSM-57, taken alone or in a mixture. Said zeolite is very advantageously of the FER type and preferably it is ferrierite. Preferably, said zeolite is made of ferrierite.In one embodiment, the zeolite has a mesoporous volume greater than or equal to 0.15 ml / g. In one embodiment, the zeolite has a mesoporous volume greater than or equal to 0.18 ml / g. 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, more preferably greater than or equal to 0.24 ml / g. 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, more preferably less than or equal to 0.35 ml / g, more preferably less than or equal to 0.30 ml / g. In one embodiment, the zeolite has a mesoporous volume of between 0.18 and 0.50 ml / g. In one embodiment, the zeolite has a mesoporous volume of between 0.20 and 0.40 ml / g. In one embodiment, the zeolite has a mesoporous volume of between 0.22 and 0.35 ml / g.In one embodiment, the zeolite has a mesoporous volume of between 0.24 and 0.30 ml / g. In one embodiment, the zeolite has a Si / Al molar ratio of between 5 and 45. In one embodiment, the zeolite has a Si / Al molar ratio of between 5 and 30. In one embodiment, the zeolite has a Si / Al molar ratio of between 8 and 20. In one embodiment, the zeolite has a Si / Al molar ratio of between 9 and 15. In one embodiment, the zeolite has a Si / Al molar ratio of between 11 and 13. In one embodiment, the zeolite has a microporous volume of between 0.100 and 0.150 ml / g. In one embodiment, the zeolite has a micropore volume of between 0.110 and 0.145 ml / g. In one embodiment, the zeolite has a micropore volume of between 0.120 and 0.140 ml / g.In one embodiment, the zeolite has a micropore volume of between 0.130 and 0.140 ml / g. In one embodiment, the zeolite has a micropore volume of between 0.133 and 0.138 ml / g. In one embodiment, the zeolite has an external surface area of ​​between 10 and 70 m² / g. In one embodiment, the zeolite has an external surface area of ​​between 20 and 65 m² / g. In one embodiment, the zeolite has an external surface area of ​​between 30 and 60 m² / g. In one embodiment, the zeolite has an external surface area of ​​between 35 and 55 m² / g. In one embodiment, the zeolite has an external surface area of ​​between 45 and 50 m² / g. In one embodiment, the zeolite has an average crystal size of less than or equal to 100 nm. In one embodiment, the zeolite has an average crystal size of between 10 and 100 nm.In one embodiment, the zeolite has an average crystal size of between 30 and 95 nm. In one embodiment, the zeolite has an average crystal size of between 40 and 90 nm. In one embodiment, the zeolite has an average crystal size of between 50 and 85 nm. In one embodiment, the zeolite has an average crystal size of between 60 and 80 nm. In one embodiment, the zeolite has a BET surface area of ​​greater than or equal to 400 m. 2 / g. In one embodiment, the zeolite has a BET surface area of ​​between 405 and 450 m 2 / g. In one embodiment, the zeolite has a BET surface area of ​​between 410 and 440 m 2 / g. In one embodiment, the zeolite has a BET surface area of ​​between 415 and 430 m 2 / g. The crystals of the zeolites according to the invention have a rounded and elongated shape, in particular an oblong or spheroidal shape. Advantageously, the crystals of the zeolites according to the invention are not in the form of needles or platelets. The crystals of the zeolites according to the invention are arranged in the form of aggregates, preferably in spherical form, unlike the zeolites used in the processes of the prior art. The catalyst may be in powder form or shaped. Advantageously, the dehydration catalyst has a zeolite content of at least 50% by weight, preferably between 55 and 90% by weight, very preferably between 60 and 80% by weight relative to the total weight of said dehydration catalyst. In one embodiment, the dehydration catalyst does not comprise metals. The term "no metals" means that no metals are added during the preparation.According to a particular embodiment of the invention, the catalyst is shaped with a binder, advantageously inert for the targeted reaction (isomerizing dehydration of a primary monoalcohol). The shaping of the catalyst with a binder makes it possible to obtain a macroscopically sized catalyst for which the skilled person can adapt the physical properties (geometry, pore mass volume, etc.). Indeed, when the zeolite cannot be used industrially in powder form, the binder makes it possible to give the final solid 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 giving too great a pressure loss.The binder is preferably chosen from a silicic binder such as silica, an alumina binder such as gamma alumina, an AlPO4, a clay, a zirconia, a Ti oxide, SiC, or mixtures thereof. Preferably, the binder is a silicic or alumina binder. Preferably, the binder is a silicic binder, consisting essentially of silica, that is to say that the silicic binder consists of silica apart from impurities, these having no catalytic effect. In particular, said silica is an amorphous silica. 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. The dehydration catalyst can be shaped into extrudates, for example according to a cylindrical or multi-lobe geometry, in particular trilobe or quadrilobe.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 performances of a primary alcohol, in particular in terms of alcohol conversion and selectivity towards linear alkenes. In addition, such a dehydration catalyst also has improved deactivation stability, therefore an increased lifetime, which makes it possible to achieve an interesting profitability of the isomerizing dehydration process. Description of the analytical methods To determine the micropore volume, the t method (of Lippens and De Boer) described in the periodical 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 t-plot):. Where P / P0 is the relative nitrogen pressure. The micropore volume is calculated with the following equation: where Y is the y-intercept of the t-plot curve (and D is the density conversion factor (D = 15.468 x 10-4, coefficient to ensure the conversion of the gas volume into liquid volume). The chosen range of t corresponds to a plateau on the curve of adsorbed nitrogen volume as a function of the thickness t and is between 0.4 and 0.8 nm. The mesoporous surface area, also called external surface area here, is calculated using the t-plot curve with the following equation: Where S is the slope of the t-plot line and D is the density conversion factor (D = 15.468 x 10-4, coefficient to transform the gas volume into liquid volume). The mesoporous volume is here considered equal to the total volume of nitrogen adsorbed at P / P0 max minus the micropore mass volume.The specific surface area or BET surface area is determined by the BET method (Brunauer, Emmet and Teller) described in the periodical "The Journal of American Society", 1938, 60, 309. It is based on the specificity of physical adsorption: multimolecular adsorption on sites of the same energy. All the hypotheses (equivalent sites, no lateral interaction between the adsorbed molecules, each adsorbed molecule can serve as adsorption sites) 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: The average size of the zeolite crystals is measured by transmission electron microscopy or TEM, bright field. Crystal size histograms were made from photos taken by 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 spheroidal in shape. The representation of the crystal in the photo is its projection along the axis of the beam. The dimension used is an estimate of the size of a crystal along the axis traveled by the beam shown in Figure 1, an average then being calculated on a sample of 200 crystals. The examples and figures which follow illustrate the invention, in particular particular embodiments of the invention, without limiting its scope. List of figures Figure 1 schematically represents a crystal as well as the axis along which the electron microscopy beam travels through said crystal to calculate its size. Figure 2 represents a scanning electron microscope (SEM) view of solid B according to the invention. Figure 3 represents a scanning electron microscope (SEM) view of comparative solid C.EXAMPLES Example 1: Testing different catalyst samples in a process for dehydrating isobutanol to n-butenes The dehydration step is carried out on an EHD multireactor 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). The catalysts are loaded separately into the reactors in powder form, previously pelletized, ground and then sieved to retain the 300-500 µm fraction. The catalysts are loaded into quartz reactors with an internal diameter of 4 mm, between two SiC beds. The catalysts are then activated at 450°C under air flushing for 6 hours after a temperature rise ramp of 5°C / min.The temperature is then lowered to the test temperature under nitrogen to eliminate the air present in the system before injection of the isobutanol charge. The test is carried out at atmospheric pressure (approximately 0.1 MPa). Different PPHs are evaluated: 9, 6 and 3h. -1 at two temperatures 240 and 250°C, a return point is carried out at the end of the test at 240°C PPH 9h -1 Each condition was maintained for 9 hours, which allowed 5 chromatograms to be acquired and the deactivation of the zeolites to be evaluated. The test lasted 72 hours. The sequence of conditions is presented below; these were applied to all catalysts in a strictly identical manner. Table 1 The feedstock is an isobutanol / water mixture in a mass ratio of 99 / 1. It is vaporized into the SiC bed at the top of the reactor before coming into contact with the catalytic bed. 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 into different products and in particular the selectivity into butenes and the fraction of linear butenes in the butene cut, a fraction that we seek to maximize. The zeolites tested are presented in the following table: Table 2 The textural properties of the evaluated zeolites are presented in the following table: Table 3 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 the 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) in percentage per unit of time between the conversion at the initial point (at about 8-9 hours) and the conversion at the final point (i.e. around 70-72 hours) at iso conditions (240°C, PPH 9h -1 ). Table 4 It is noted 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 an activity after 8 to 10 h under load that is much higher than those having 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 h for zeolite A compared to 22.7% conversion at approximately 8 h for zeolite C).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 having 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 the temperature and the PPH. This zeolite combines high initial and final conversions, improved selectivity for linear butenes and is almost stable over the test time compared to the 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.Example 2: Testing the ability of catalysts to capture nitrogen compounds In this example, the feedstock is an isobutanol / water mixture in a 95 / 5 mass ratio including 6 ppm of acetonitrile. The same apparatus is used. The feedstock is vaporized into the SiC bed at the top of the reactor before coming into contact with the catalytic bed. Different catalysts were tested: zeolites A, B, C, D, E and F described in Example 1 and a gamma alumina (see Table 6). Gamma alumina has a low total NH3 acidity (300 µmol / g). The catalysts are prepared as described in Example 1. The catalysts were tested under strictly identical conditions (except for the presence of nitrogen compound) to those of Example 1. The following table shows the nitrogen, carbon and hydrogen contents of the different catalysts, analyzed after 72 h of reaction for the different catalysts tested: Table 5. It is noted that zeolites A to F have a nitrogen content significantly higher than that measured for gamma alumina, which allows us to deduce that the zeolites capture at least in part the nitrogen impurities of the isobutanol feedstock. In addition, it appears that ferrierites A and B have a nitrogen content (respectively 0.115% and 0.212%) higher than that of ferrierites C and D whose nitrogen content is less than 0.10%. This indicates that the catalysts according to the invention, ferrierite B very significantly, have a capacity to capture nitrogen compounds superior to the ferrierite zeolites used in the processes of the prior art.

Claims

Claims 1. Process for the isomerizing dehydration of a feedstock comprising at least one primary monoalcohol, of formula R-CH2-OH, in which R is a non-linear alkyl radical of general formula C n H 2n+1where 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 hourly space velocity (WPH) between 1 and 25 h-1, in the presence of a catalyst comprising at least one zeolite, in which said zeolite has at least one series of channels whose pore opening is defined by a ring with 8 oxygen atoms (8MR) and has a mesoporous volume greater than or equal to 0.10 ml / g.

2. Process according to claim 1 in which the zeolite has a Si / Al molar ratio of between 5 and 45.

3. Process according to any one of the preceding claims in which the zeolite has an external surface area of ​​between 10 and 70 m² / g, preferably between 20 and 65 m² / g, very 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 process 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. A process according to claim 5 wherein the zeolite is of the FER or MFS structural type.

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

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

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

10. Method according to any one of the preceding claims in which the feedstock comes from at least one lignocellulosic biomass fermentation process.

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