PROCESS FOR THE TREATMENT OF POLYALKYLAROMATIC HYDROCARBONS

Abstract

The present invention relates to a process for treating mixtures containing polyalkylaromatic hydrocarbons, intended for transalkylation processes, comprising a mild reduction with hydrogen in the presence of a suitable hydrogenation catalyst. The invention also relates to a transalkylation process of polyalkylaromatic hydrocarbons comprising said treatment.

Description

PROCESS FOR THE TREATMENT OF POLYALKYLAROMATIC HYDROCARBONS FIELD OF INVENTION The present invention relates to an improved process for the treatment of polyalkylaromatic hydrocarbons. In particular, the present invention relates to a process for treating mixtures containing polyalkylaromatic hydrocarbons derived from the alkylation of benzene or other aromatic compounds with alcohols or olefins, more particularly with alcohols, in the presence of acid catalysts, preferably comprising zeolites. BACKGROUND OF THE INVENTION The methods for synthesizing alkylaromatic hydrocarbons by alkylation of aromatic compounds in the presence of acid catalysts are well known and widely used industrially for the production of basic organic intermediates, such as ethylbenzene and eumene, starting materials for obtaining styrene and phenol, and subsequently, among other compounds, polymers such as polystyrene and polycarbonates, as well as alkyl derivatives of naphthalene, etc. These processes use olefins, alcohols, or mixtures thereof as alkylating agents. It is also well known that, although the selectivity of the alkylation reaction has been optimized, at least some of the aromatic reagent undergoes more than one alkylation step, producing undesirable polyalkylated aromatic compounds. These undesirable products are subsequently separated, usually by distillation, from the monoalkylated product and heavy byproducts, and reacted with more non-alkylated aromatic reagent in the presence of acid catalysts to form more monoalkylated product via the known transalkylation reaction. The state of the art of the transalkylation reaction is substantial with respect to polyalkylates from alkylation with olefins, whereas for polyalkylates from alkylation with alcohols nothing specific has been established: the state of the art tends not to differentiate the origin of the polyalkylates. The published European patent application EP 1069100 (filed by the applicant) describes a process for the alkylation of benzene with propylene and isopropanol (IPA), in which the water content of the liquid-phase reaction mixture must be less than 8000 ppm. It is noted that rapid catalyst deactivation occurs when using a beta zeolite-based catalyst at high water concentrations in the liquid phase, above 8000 ppm. This drawback can be mitigated by increasing the benzene / IPA ratio, or, with the same ratio, by increasing the olefin / alcohol ratio in the alkylating mixture and consequently decreasing the water content in the liquid phase, as well as the IPA reuse capacity. Finally, some of the benzene effluent from the reaction can be recycled, or the process can be operated in a mixed phase with water, at least partially in the vapor phase. In this case, however, there is a restricted operating window. coi? Lnn / zznz / E / Yi The published patent application US 2011 / 218366 (filed by the Applicant) claims the use of a ZSM-12 zeolite-based catalyst in a gas-phase alkylation process for the production of eumene, which allows operation with a benzene / IPA ratio of up to 2 without showing signs of catalyst deactivation. However, a drawback of the gas-phase reaction is the significant production of diisopropylbenzenes and triisopropylbenzenes, requiring costly transalkylation with benzene to recover eumene. In fact, the patent claims a selectivity for eumene of 82% and a selectivity for recoverable products (eumene, diisopropylbenzenes, triisopropylbenzenes) of 98.8%

[0081] . This means that 16.8% of the products are sent for transalkylation. In particular, a specific formation of 147 g of diisopropylbenzene per kg of eumene in gas phase is obtained (190°C, 8 bar, Benzene / IPA 3.25 mol / mol). US patent 9,096,488 describes a process for the alkylation of benzene with IPA under trickle-flow conditions. These conditions ensure that the catalyst (always based on ZSM-12 zeolite) is not deactivated even with benzene / IPA ratios of 2.4. These conditions also favor a low molar ratio of diisopropylbenzenes to cumene in the products leaving the reactor. At 190°C, 13 bar, and a benzene / PAH ratio of 3.25, a selectivity to eumene of 92% is obtained, yielding 51.7 g of diisopropylbenzenes per kg of eumene produced. The n-propylbenzene content is 570 ppm compared to the eumene formed. In any case, it should be noted that trickle-flow or slow-flow conditions are achieved with significant recyclability, resulting in higher energy costs, compared to the first two options, which do not require recyclability. As is well known, one of the advantages of using IPA to totally or partially replace propylene in the alkylation reaction of benzene to yield eumene is the possibility of reusing the acetone thus produced in the phenol production process by reducing it to IPA and then recycling it back into the alkylation reaction. However, the three alkylation options described above, despite each having some technical advantages, are usually accompanied by the typical disadvantages of the approach used. In particular, they all produce, to some extent, a quantity of polyalkylated aromatics, which constitute a necessary transalkylation step downstream of the alkylation step. This is to recover as much monoalkyl aromatics as possible from the polyalkyl aromatics obtained in the alkylation step. The transalkylation process has fundamental industrial importance for optimizing aromatic alkylation processes aimed at the production of monoalkylamates. The state of the art regarding the optimization of transalkylation reactions, particularly of polyethylenes to obtain ethylbenzene and of polyisopropylbenzenes to obtain eumene, is extensive and primarily encompasses the optimization of catalysts, operating conditions, and the use of absorbents to purify the feedstocks. The objectives are maximizing the yield and stability of the catalytic system. The state of the art of transalkylation reactions is significant with respect to polyalkylates derived from olefin alkylation, while little or nothing specific exists regarding polyalkylates derived from alcohol alkylation. The current state of the art, especially recent developments, tends not to differentiate the origin of the polyalkylates, including both olefin-based and alcohol-based alkylating agents. The main alkylation and transalkylation processes are described in the publication by C. Perego et al. “Combination of alkylation and transalkylation for the production of alkylaromatics”, Green Chem., 2004 (6), 274-279. In addition, it is noted that the use of acetone in the alkylation of benzene, after reduction of acetone to isopropanol, constitutes a possible approach for obtaining eumene. WO 2006107452 claims a transalkylation process for aromatics, specifically polyisopropylbenzene (PIPB) and polyethylbenzene (PEB), without any distinction regarding the origin of the polyalkylates. In fact, it states that the alkylating agents can be olefins, alcohols, aldehydes, and alkylaldehydes. The catalysts are selected from various families of zeolites suitable for the purpose. No data are available on the catalyst's lifespan or its potential deactivation over time. Published U.S. patent application 2011 / 201858 describes a process for producing eumene from acetone and benzene, wherein the acetone is pre-reduced with hydrogen in the presence of a reducing catalyst. While a selectivity for eumene of no more than 71% is reported, the transalkylation processes are not described, much less the preliminary transalkylation treatments. European patent EP 1257517 describes a process for preparing eumene by alkylation of benzene with isopropanol or isopropanol / propylene mixtures. The patent shows that transalkylation, appropriately applicable to polyalkylates obtained by alkylation of aromatic compounds with alcohols, is a reaction well known to those skilled in the art. The international patent application WO 2017 / 065771 describes an alkylation process useful for the production of alkylaromatic compounds, in particular ethylbenzene and eumene. In the case of eumene, the alkylating agent comprises propylene and / or isopropanol. The patent shows how transalkylation is conveniently applicable to polyalkylates obtained in the described alkylation reaction, without mentioning problems related to the transalkylation reaction itself. Pretreatments for the absorption of impurities in feeds to catalyzed processes are known in the art, but the materials used often have limited absorption capacities, so it is crucial to carry out multiple in situ regenerations to at least partially restore the absorption capacities before the discharge / replacement / disposal operations of the materials themselves, which can make the approach economically unattractive. The international patent application WO 2003 / 074452 describes methods for removing impurities, particularly nitrogen compounds, from the feeds of processes catalyzed by acid zeolites, including alkylation and transalkylation processes of aromatic compounds. Distillation, extraction, and adsorption pretreatments are mentioned. However, mixtures of polyalkylaromatic compounds from alkylation processes are not specifically addressed. coi? Lnn / zznz / E / Yi WO 2016 / 099715 describes a material for use as a protective bed, which has an improved poison absorption capacity, for feeds such as those used in the alkylation and transalkylation processes of aromatic compounds. However, the typical problems of protective beds, such as limited absorption capacity and the need for frequent regeneration / replacement of the bed itself, remain. US patent application 2007 / 112240 describes a pretreatment of feed streams composed of aromatic mixtures from refinery processes, for the purpose of reducing oxygenated compound impurities to below 5 ppm. This pretreatment is based on absorbent materials such as alumina or molecular sieves. Alkylation or transalkylation processes are not mentioned. Therefore, the drawbacks related to the stability and durability of the catalytic system in a transalkylation process of polyalkylaromatic compounds, particularly from alkylation reactions of aromatics with alcohols and / or olefins, more particularly with alcohols, such as, for example, the alkylation of benzene with alkylating mixtures comprising isopropyl alcohol (IPA), do not appear to be clearly identified, or even satisfactorily resolved. BRIEF DESCRIPTION OF THE INVENTION The applicant has now surprisingly found that it is possible to significantly improve the catalyst lifetime, expressed, for example, as time in operation (TOS, i.e., the period in which the catalyst is able to operate with a predetermined minimum performance), in a transalkylation process of aromatic compounds, by a simple hydrogenation treatment on the mixture to be transalkylated. Criticality, or criticality capability, was not clearly identified in the industry literature. The scientific literature on transalkylation with zeolite-based catalysts has not yet demonstrated that catalyst decomposition can be slowed or even inhibited by hydrogenation pretreatment of the mixture to be transalkylated. Therefore, it has been surprisingly found that a hydrogen reduction treatment of the mixture containing the polyalkylated aromatic compounds from an alkylation step of aromatic compounds, with alcohols or olefins, preferably with alcohols, even more preferably with isopropyl alcohol, allows for a considerable improvement in the stability and duration (e.g., in terms of productivity and / or time-on-stream, TOS) of the transalkylation catalyst, while also avoiding the handling and optimization of absorbent beds, overcoming the aforementioned problems. Productivity here refers to the monoalkylated product and is expressed in kg of monoalkylated product per kg of catalyst used in the reaction. A first object of the present invention is therefore a process comprising a reduction step, preferably with hydrogen, in the presence of a suitable hydrogenation catalyst, of a polyalkylated product comprising at least one polyalkylaromatic compound, said polyalkylated product being obtained in at least one step of an alkylation process of at least one aromatic compound, preferably benzene, by means of an alkylating agent selected from an alcohol, a primary olefin or a mixture thereof, preferably an alcohol or a mixture of an alcohol with a primary olefin. DETAILED DESCRIPTION OF THE INVENTION Other purposes and objects of the invention may be evident from what follows in the present description and in the claims. For the purposes of this description and the following claims, the definitions of the numerical ranges always include the extreme values ​​unless otherwise specified. For the purposes of this description and the following claims, percentages are always by weight, except where otherwise specified. In describing the embodiments of the present invention, the use of the terms “comprising” and “containing” indicates that the options described, for example, in relation to the steps or stages of a method or process, or the components of a product or device, are not necessarily exhaustive. However, it is important to note that terms used herein, such as “consisting of” or “consisting essentially of,” or analogues thereof, even if not explicitly stated, are included within the meaning and scope of the terms “comprising” and “containing.” For the purposes of this description and the following claims, with respect to the chemical elements and the groups to which they belong, reference is made to the Periodic Table of the Elements published by the IUPAC in 2016, and the CAS (Chemical Abstract Service) numbering is used. For the purposes of the present invention, a reference to a group in the Periodic Table includes any element in that group, excluding the transuranic elements. For the purposes of this description and the following claims, the meaning of terms such as at least one, at least an and at least a also includes the meaning of indefinite articles such as one, an, a. For the purposes of this description and the following claims, a polyalkylaromatic compound is understood to be any aromatic compound substituted on the same ring or on more rings fused together, with at least two alkyl groups, optionally substituted with halogen atoms, particularly fluorine. Preferred polyalkylaromatic compounds are those having from 8 to 20 carbon atoms. Preferably, the aromatic and polyalkylaromatic compounds according to the present invention are those that do not contain heteroatoms on the aromatic rings. Typical non-limiting examples of polyalkylaromatic compounds according to the present invention are xylenes, 1,3,5-trimethylbenzene, 1,2-diethylbenzene, 1,3-diethylbenzene, 1,4-diethylbenzene, 4-ethyltoluene, 1,3-diisopropylbenzene, 1,4-diisopropylbenzene, 1,3,5-triisopropylbenzene, 1,4-dimethylnaphthalene, 1,7-dimethylnaphthalene and mixtures thereof.The preferred polyalkylaromatic compounds are mixtures of polyethylenebenzenes and polyisopropylbenzene isomers obtained from the alkylation processes of benzene with ethyl alcohol and / or ethylene, and isopropyl alcohol and / or propylene, respectively. The polyalkylated product subjected to reduction in the process according to the present invention normally consists of a mixture of compounds. It may consist of one or more polyalkylaromatic compounds, or it may comprise, in addition to at least one polyalkylaromatic compound, other components, such as, for example, solvents or diluents, non-alkyl-substituted aromatic compounds such as benzene or naphthalene, monoalkyl-substituted aromatic compounds such as toluene, ethylbenzene, isopropylbenzene, n-propylbenzene, and any other impurities or by-products from the alkylation process, such as water and oxygenated organic compounds such as, for example, alcohols, acetone, benzophenone.Preferably, the polyalkylated product fed to the present process comprises from 1 to 50% by weight, preferably from 2 to 25% by weight, more preferably from 5 to 25% by weight, of polyalkylaromatic compounds and up to a maximum of 2%, preferably from 0.0010 to 0.50% by weight, of oxygenated organic compounds. In one embodiment of the present invention, said polyalkylated product can be further mixed with solvents, diluents, non-alkylated aromatic compounds, and with any recycling product from the corresponding alkylation process before being subjected to said hydrogen reduction step. Suitable solvents and diluents that can be included or added to the polyalkylated product according to the present invention are typically liquids that are essentially inert to the reduction reaction, such as saturated and unsaturated hydrocarbons, preferably aromatic, having from 6 to 20 carbon atoms. According to a preferred embodiment, the polyalkylated product comprises or is added to an aromatic compound that can function as both a solvent and / or diluent and as a reagent in a subsequent transalkylation step, for example, benzene. Preferably, the polyalkylated product subjected to reduction is obtained by an alkylation process of benzene, preferably with an alcohol or an alcohol / olefin mixture, and is mixed with benzene such that the resulting mixture, when subjected to reduction, contains from 40 to 90%, more preferably from 60 to 85% by mass of benzene relative to the total mass of the mixture. Said polyalkylated product is preferably a mixture (also definable as a stream if the process is carried out continuously) of polyalkylaromatic compounds and other compounds, obtained as a by-product of an alkylation process of aromatic compounds, preferably benzene, with at least one alcohol, at least one olefin or a mixture thereof, preferably an alcohol or a mixture of an alcohol with a primary olefin, in the presence of an acid catalyst, preferably a zeolitic-based acid catalyst.As is known in the industry literature and mentioned above, acid-catalyzed alkylation processes of aromatic compounds involve the formation of unwanted polyalkylated aromatic compounds that are separated from the desired monoalkylated product and other reaction byproducts by distillation or other methods known in the art. These byproducts form a polyalkylated product (or stream) that is typically subjected to a transalkylation reaction in the presence of an excess of a non-alkylated aromatic compound to further produce a monoalkylated aromatic product. This polyalkylated product constitutes the polyalkylated product fed to the process according to the present invention. The process according to the present invention is preferably a transalkylation process comprising, in addition to said hydrogen reduction step, a subsequent reaction step of the polyalkylated product subjected to reduction, wherein at least one polyalkylated aromatic compound, wherein the alkyl groups are preferably ethyl or propyl, preferably at least one dialkylated aromatic compound, is reacted with a different aromatic compound, preferably non-alkylated, preferably benzene, in the presence of an acid catalyst, wherein at least a portion of the alkyl substituents of said polyalkylated aromatic compound is transferred onto said different aromatic compound, preferably non-alkylated. In a different embodiment, the present invention relates to an alkylation process of at least one aromatic compound, comprising an alkylation step of an aromatic compound by reaction with an alkylating agent selected from an olefin, an alcohol, or a mixture thereof, preferably an alcohol, in the presence of a suitable acid catalyst, and at least one reduction step of the polyalkylated product obtained as a by-product, preferably with hydrogen, of the type specified above, followed by a transalkylation step. Alkylation processes for aromatic compounds are well-known and can be carried out under different conditions and with different acid catalysts. They are described, for example, in the following patent publications or patent applications, the content of which is incorporated herein by reference: EP 1069100, US 2011 / 0218366, US 9096488, US 9259722, US 7371910. An alkylation process for aromatic compounds can be carried out industrially in continuous, semi-continuous, or batch modes, and in gas, liquid, or mixed phases. To maintain the temperature within an optimal range and reduce the byproducts of polyalkylated aromatic compounds, the catalyst can be arranged in the reactor in several layers. For example, as reported in US patent 6,512,153, rapid cooling (using the most common terminology) can be performed between layers with inert solvents and / or some of the aromatics and / or some of the alkylating agent, alcohol, or olefin. With proper operation, high aromatic / alkylating agent ratios can be achieved in a single layer without increasing the overall ratio, offering a clear advantage in the subsequent separation and recycling of the aromatic compounds. Temperature control can be achieved not only by quenching with reagents and / or inert agents, but also through intercooling between layers, for example, by inserting refrigerants. The alkylation reaction can be effectively carried out in two or more reactors in series, intercooled to control the temperature.The feed of olefin, alcohol and / or aromatic compounds can be appropriately divided between different reactors and different reactor layers, i.e., the alkylating agent and / or aromatic compounds are added in more than one step; optionally the alkylating agent can be diluted with the aromatic compounds or with an inert agent to aid temperature control. The alkylating agent is fed in an amount such that an overall molar ratio [Aromatic compounds] / [Alkylating agent] is obtained preferably between 1 and 20, more preferably between 2 and 8. coi? Lnn / zznz / E / Yi The reaction temperature is between 100°C and 300°C, preferably between 120°C and 230°C; the pressure is between 0.5 and 5 MPa, preferably between 1 and 4 MPa; the space velocity WHSV is between 0.1 and 200 h-1, preferably between 1 and 10 h-1. However, it should be noted that the combination of temperature and pressure conditions actually adopted must be such that it ensures that the alkylation reaction takes place at least partly in the liquid phase, and preferably occurs substantially in the liquid phase. Typical acid catalysts for the alkylation of aromatic compounds are heterogeneous zeolite-based catalysts, which have now largely replaced catalysts such as AlCh-HCl, hydrofluoric acid, and homogeneous-phase catalysts in general, especially in newly designed plants. Depending on the type of alkylation, zeolitic catalysts with different pore sizes can be used to make the reaction more selective toward the desired product. For example, 10MR structures such as ZSM-5 (MFI) have been patented and are used in the vapor phase. Liquid-phase processes with 12MR zeolites allow for a considerable increase in catalyst lifetime. Zeolites Y (FAU) and Beta (BEA) are also claimed and / or used industrially. A fixed-bed process with a mordenite-based catalyst (MOR) is described and patented for the production of eumene.MCM-22 (MWW) zeolites are mentioned as catalysts that produce a low concentration of dialkylated products. A consistent list of aromatic compound alkylation technologies and related catalysts can be found in the publications Catalysis Today 73 (2002) 3-22 (Recent advances in the industrial alkylation of aromatic compounds: new catalyst and new processes), in Thomas F. Degnan et al., Applied Catalysis A: General Volume 221, Issues 1-2, 30 November 2001, Pages 283-294 (Alkylation of aromatics with ethylene and propylene: recent developments in commercial processes), and in the aforementioned C. Perego et al., Green Chem., 2004, 6, 274-279, (Combining alkylation and transalkylation for the production of alkylaromatics). The alkylation step is preferably carried out with an alcohol or an alcohol / olefin mixture as the alkylating agent. Typically, ethanol and / or ethylene are used to alkylate benzene to ethylbenzene, and isopropanol and / or propylene to alkylate benzene to eumene. The appropriate alcohols and / or olefins corresponding to the alkyl group to be introduced into the aromatic compound are used to prepare other alkylated aromatic compounds, according to established principles of organic chemistry. The product of the alkylation stage is subsequently fed to one or more separation stages according to the state of the art, to recover the desired alkylated product and separate the polyalkylated aromatic compounds that are inevitably produced at least in small quantities, for further use as such, or for feeding into a transalkylation process. As an example, distillation of the reaction residue from the alkylation step of benzene with isopropanol allows the separation of the monoalkylate and yields a mixture consisting mainly of diisopropylbenzenes (e.g., 93.2%), with traces of acetophenone, as well as several heavy polyalkylates. This fraction, mixed with benzene, preferably water-free (H₂O < 100 ppm), in suitable weight proportions (e.g., 20–80), generates a mixture containing the polyalkylate, which can be conveniently hydrogenated, for example, in copper chromite-based catalysts, prior to transalkylation. Comparison with the transalkylation of similar, but non-hydrogenated, mixtures highlights the advantages of the invention. According to the present invention, the polyalkylated product obtained after the separation stage or stages of the mixture coming out of the alkylation stage, is subjected to a reducing treatment, preferably with hydrogen and a suitable reduction catalyst as claimed. According to the present invention, the hydrogen reduction step of the polyalkylated product is preferably carried out at temperatures between 60 and 220°C, preferably between 100 and 180°C, and at hydrogen pressures between 0.1 and 5.0 MPa, preferably between 1.0 and 3.0 MPa. This step can be carried out continuously or in batches, in a reactor with a solid catalyst that can be in suspension, fixed bed, or fluidized bed form. Preferably, the catalyst is fixed bed for continuous processes and in suspension for batch processes. The reduction reaction, preferably hydrogenation, is preferably carried out under conditions that do not produce hydrogenation of the aromatic ring of the compounds present in the mixture. These conditions are known to those skilled in the art, depending on the catalyst used, or can be easily identified through simple preliminary tests. The reducing agent, preferably hydrogen, is preferably fed pure or substantially pure to the reduction step. However, it is not excluded according to the present invention that the hydrogen may also contain significant quantities of other gases, provided they are inert to the catalyst and the substrate to be hydrogenated, such as nitrogen, noble gases, methane, etc. The hydrogen may optionally be preheated to a temperature above ambient temperature. The molar ratio between the hydrogen and the polyalkylaromatic compounds contained in the polyalkylated product is preferably between 0.01 and 10, more preferably between 0.1 and 5. In the preferred case where the process of the present invention is carried out continuously, the space velocity (WHSV), calculated on the total volume of the feed, including any diluents, is preferably between 0.5 and 10 Ir1, more preferably between 1 and 5 h'1, even more preferably between 1 and 3 h1. The polyalkylated product, optionally supplemented with a suitable solvent, which may also be the same aromatic reagent to be alkylated in a subsequent transalkylation step, is reacted with hydrogen in the presence of a suitable catalyst, under the aforementioned conditions, such that there is no substantial hydrogenation of aromatic groups or rings. Therefore, the process of the present invention is preferably carried out such that, in the hydrogen reduction step, the amount of aromatic rings hydrogenated is less than 1%, preferably less than 0.5%, and even more preferably between 0 and 0.1%, with respect to the total number of aromatic rings fed. The amount of hydrogenated aromatic rings can be determined by the skilled worker using any known technique, such as, for example, infrared spectroscopy, gas chromatography, etc. coi? Lnn / zznz / B / Yi According to the present invention, the hydrogen reduction is carried out in the presence of a suitable catalyst. Suitable catalysts are those typically used for selective hydrogenation reactions of oxygenated organic substrates, such as, for example, catalysts based on Ni, Raney Ni, Pd, Pt, Cu, copper chromite, etc. The term “selective” here means that the hydrogenation reaction does not produce significant ring hydrogenation of any aromatic compounds that may be present. Such hydrogenation catalysts are well known in the art and are commercially available. See, for example, the following articles in the publication “Handbook of Heterogeneous Catalysis” (2008) (eds. G. Ertl, H. Knozinger, F. Schuth, and J. Weitkamp): Blaser H., Schnyder A. et al. “Selective Hydrogenation of Functionalized Hydrocarbons”, and; Smith AJ and Wainwright MS “Skeletal metal catalysts”. Preferably, the catalyst usable in the present hydrogen reduction process is based on copper chromite. Such catalysts are known catalysts for selective hydrogenation reactions and are commercially available, as reported, for example, in the publication “PRASAD and SINGH, Bulletin of Chemical Reaction Engineering & Catalysis, pp. 63–113, Nov. 2011,” which describes applications and methods for preparing copper chromite-based catalysts. Documents EP 563327 and WO2017 / 144337 report, for example, other copper-based catalysts and, in particular, copper chromite catalysts suitable for the hydrogen reduction step of the present invention. The present process is particularly advantageous if the polyalkylated product is derived at least 15%, preferably at least 40%, more preferably at least 60%, and up to 100%, from alkylation processes of aromatic compounds with an alcohol (the remainder from alkylation processes with a specific alcohol), these percentages referring to the mass of the polyalkylated product. For example, from alkylation processes of benzene with isopropyl alcohol, preferably at least 25%, and even more preferably from 40%, with the remainder from alkylation processes with propylene. coi? Lnn / zznz / E / Yi Preferably, the polyalkylated product, after separation from the monoalkylated product and any higher-boiling byproducts, is fed to the hydrogen reduction stage without undergoing further treatments to reduce impurity content, such as molecular sieve purification, filtration through selective membranes, or other reducing treatments, which are not excluded from the scope of the claimed process. In any case, the process according to the present invention is simple to implement, efficient, and economically advantageous, while also contributing to the alkylation of aromatic compounds using alcohols or mixtures of alcohols and olefins, but in a more efficient and competitive manner compared to using olefins alone. The process according to the present invention may comprise other steps and reactions in addition to the aforementioned hydrogen reduction step. In a preferred embodiment, the process of the present invention comprises a transalkylation step of the aromatic compounds contained in the polyalkylated product, following their treatment for impurity reduction with hydrogen. Therefore, the process according to the present invention preferably also comprises a transalkylation step of said at least one polyalkylaromatic compound contained in the polyalkylated product, after the hydrogen reduction step, which can be carried out according to one of the various methods known to the skilled in the art and as described, for example, in document EP 847802 (in the name of the applicant), the content of which is incorporated herein by reference.The transalkylation catalysts suitable for the present invention may be materials known in the art, for example, zeolites in acidic or protonic form, used in a form suitable for fixed-bed applications known to the art, for example, extruded, added with traditional binders such as, for example, alumina (Al₂O₃), silica (SiO₃), zirconium oxide, titanium oxide, preferably silica (SiO₂) or alumina (Al₂O₃), or mixtures thereof. When alumina is used as a binder, a gamma-alumina phase structure is preferred. Typical examples of alumina precursor binders are commercial pseudoboehmite-based materials (sometimes called boehmite), such as those marketed under the brand name VERSAL (for example, Versal V-250 from UOP Company).Gamma-alumina structured materials are generally obtained by calcination of pseudoboehmite, as experts in the art know and as reported, for example, in the booklet “UOP 5502, April 2012”. In many industrial applications, such as fixed-bed catalyst reactors, catalyst formation is necessary, and often a binder must be added to facilitate this process. In applications requiring a formed catalyst, it is crucial that the catalyst maintains its physical integrity during use; without sufficient strength, the catalyst can be damaged or degraded, negatively impacting the reaction and / or the equipment. Catalysts for fixed-bed applications are typically formed into spheres or granules. Following this formation process, the resulting granules are generally calcined. The solid obtained after bonding and forming can contain from 5% to 90% by weight, preferably from 10% to 75% by weight, and more preferably from 20% to 55% by weight, of binder, relative to the total weight of the zeolite-based catalyst. Particularly useful in the transalkylation process are beta-zeolite-based catalysts as described in EP 847802 or Y-zeolite-based catalysts as described in US 8,658,553. Preferably, said subsequent step for the transalkylation of aromatic compounds by reaction with one or more polyalkylated aromatic compounds is catalyzed by a catalytic composition comprising a zeolite of crystalline structure with holes formed by 12 tetrahedra (wide-pore zeolites) and, as an inorganic binder, γ-alumina, said composition being preferably characterized by a pore volume, obtained by addition of the mesoporosity and macroporosity fractions present in the catalytic composition itself, greater than or equal to 0.7 cc / g, where at least 30% of said volume is made up of pores of a diameter greater than 100 nanometers. Catalytic compositions containing zeolite Y or beta in acid form are preferably used. The aromatic hydrocarbon is preferably benzene. The polyalkylated aromatic hydrocarbon is preferably selected from diethylbenzene, and optionally triethylbenzene and diisopropylbenzene, and optionally triisopropylbenzene. Transalkylation of benzene with diisopropylbenzene and optionally triisopropylbenzene to provide eumene is particularly preferred. The transalkylation reaction must be carried out under conditions such that it takes place at least partially in the liquid phase and preferably substantially in the liquid phase. It is preferably carried out at a temperature between 150 and 300°C, a pressure between 2 MPa and 5 MPa, and a space velocity (WHSV) between 0.5 and 10 h1. The molar ratio between the aromatic hydrocarbon to be transalkylated and the sum of the polyalkylated aromatic hydrocarbons in the feed mixture for the transalkylation reaction can vary between 1 and 40, preferably between 3 and 30. The catalyst is normally arranged in a fixed bed and is used particularly in chamber reactors equipped with one or more fixed catalyst beds. An additional aspect of the present invention is a process for preparing monoalkylated aromatic hydrocarbons comprising: a) contacting and reacting under alkylation conditions, in the presence of an alkylation acid catalyst, an aromatic hydrocarbon and at least one alcohol and / or at least one primary olefin, preferably an alcohol or a mixture of alcohol and primary olefin, more preferably an alcohol, said alcohol and olefin having 2 to 4, preferably 3 carbon atoms; b) separating the reaction product obtained in step a) into a fraction containing the aromatic hydrocarbon that has not reacted in step a), a fraction containing a monoalkylated aromatic hydrocarbon, a fraction comprising a polyalkylated product comprising at least one polyalkylaromatic compound, preferably containing at least 60% by weight of dialkylated aromatic hydrocarbons; c) subjecting said fraction comprising a polyalkylated product, obtained in step b) to a reduction step with hydrogen in the presence of a suitable hydrogenation catalyst to obtain a reduced polyalkylated product; d) reacting said reduced polyalkylated product, obtained in step c), with an aromatic hydrocarbon, preferably the same one that was reacted in step (a), under transalkylation conditions, in the presence of a suitable acid catalyst, which is preferably selected from a beta zeolite or a Y zeolite. In the alkylation step (a), a solid acid catalyst containing a medium- or large-pore zeolite is preferably used. The zeolites preferably used in the catalytic composition for the alkylation step are MWW (MCM-22) zeolite among medium-pore structures, and BEA (beta), FAU (zeolite Y), and MTW (ZSM-12) structures among large-pore structures, as described, for example, in WO2015056167 and WO2012175614. Beta zeolite or ZSM-12 is preferably used, and even more preferably ZSM-12, as described, for example, in WO2015 / 056167. The alcohol preferably used in the alkylation step is selected from ethanol and isopropanol. The aromatic hydrocarbon used in the alkylation step is preferably benzene. It is particularly preferred that in the alkylation step (a) benzene and isopropanol are contacted in the presence of beta zeolite or Y zeolite or ZSM-12. Step (a), as previously described, can be carried out in a substantially gaseous, substantially liquid or mixed phase, preferably in a parallel stream or in a trickling bed. The separation of the fractions in step (b) is normally carried out by distillation according to known methods. In particular, for example, when the alkylation product is obtained by the alkylation reaction of benzene with ethanol or isopropanol, respectively, or with a mixture of ethanol or isopropanol and the corresponding olefin, in step (b) the first fraction will contain benzene, the second will contain ethylbenzene or eumene, respectively, the third will consist mainly of diethylbenzenes or diisopropylbenzenes, and the last fraction will consist of a mixture of heavy hydrocarbons with a boiling point greater than or equal to 260°C–300°C. The third fraction, which substantially forms the polyalkylated product comprising at least one polyalkylaromatic compound, (for example a mixture consisting mainly of dialkylbenzenes, with less than 10% trialkylbenzenes), optionally supplemented with a suitable volume of the same aromatic hydrocarbon from step (a), in step (c), is contacted with a selective hydrogenation catalyst, preferably selected from catalysts based on Ni, Ni Raney, Pd, Pt, Cu and copper chromite. Preferably, the hydrogen reduction step (c) is carried out at temperatures between 60 and 220°C, preferably between 100 and 180°C, and hydrogen pressures between 0.1 and 5.0 MPa, preferably between 1.0 and 3.0 MPa. The transalkylation step d) is carried out in the presence of an acid catalyst, preferably containing beta or Y zeolite, under transalkylation conditions as previously described, preferably in at least partially liquid phase. Preferably, said steps (c), or (c) and (d), of the process mentioned above, are carried out in accordance with or coincide with the process according to claim 1 or claim 8, respectively. To better understand the present invention and put it into practice, some illustrative and non-limiting examples of it are described below. EXAMPLES Reagents and Catalysts Hydrogenation catalyst: The commercial catalyst called BASF 1230 based on Copper Chromite, (extruded in three 1 / 16 inch lobes or trilobes with the following composition: barium oxide 7-10%, copper oxide 15-25%, chromium (III) oxide 25-50%), produced by BASF GMbH; Hydrogen: (purity from supplier Sapio 99.95%); Benzene: Sigma Aldrich product, code 319953, purity > 99%. Chromatographic analysis: The gas chromatographic analyses described here were obtained using a Thermo Electron Focus gas chromatograph equipped with a 25 m HP1 column. The conditions applied for the chromatographic analysis are as follows: coi? Lnn / zznz / B / Yi • Carrier gas: helium • Column: HP1 - 25 m capillary - 0.32 mm internal diameter, 0.52 pm film thickness • Oven temperatures: -40°C for 2', 45" - 10°C / min up to 290°C - 290°C for 5' • Detector: FID Determination of water content: using the Metrohm Karl Fischer 701 instrument. EXAMPLE OF PREPARATION A An extruded beta zeolite-based catalyst, suitable for alkylation and transalkylation reactions of aromatic compounds, was prepared as described in Example 4 of published European patent EP 847802, incorporated herein by reference. Specifically, 58.8 g of tetraethylammonium hydroxide (40% wt. aqueous solution) and 1.9 g of sodium aluminate (56% Al₂O₃) are added to 58.4 g of demineralized water. The mixture is heated to approximately 80°C and stirred until completely dissolved. The resulting clear solution is then added to 37.5 g of Ludox HS colloidal silica (40% wt. SiO₂). A homogeneous suspension with a pH of 14 is obtained, which is then placed in a steel autoclave and crystallized under hydrothermal conditions at 150°C for 10 days under static conditions and autogenous pressure. The crystallized product is separated by filtration, redispersed in demineralized water (approximately 150 g), and filtered again: a wet zeolite panel is obtained that still contains significant amounts of an organic heat-sensitive agent, tetraethylammonium sodium. The wet panel is redispersed in an aqueous ammonium acetate solution (200 g of water and 16 g of ammonium acetate) for ion exchange. This suspension is heated with stirring for approximately one hour at 80°C. The suspension is then filtered, and the resulting solid is redispersed in demineralized water (150 mL) for washing. The suspension is then filtered again, yielding a wet beta zeolite panel in ammonium / alkylammonium form. After elemental chemical analysis, the sodium residue in this last sample is indeed equal to 112 ppm. The aluminum content is equal to 3.38% [Al] / [Na] = 257). The resulting solid (wet beta zeolite in ammonia form containing an organic heat-sensitive agent) was premixed with pseudoboehmite as a precursor to the gamma-alumina binder to achieve a binder content of 50% by weight in the solid after calcination, and with an acetic acid solution as a peptizing agent, and then extruded. The resulting solid was calcined in an air atmosphere for 2 hours at 350°C, and subsequently for another 3 hours at 550°C. After calcination, an extruded catalyst of zeolite and alumina (gamma) in a mutual weight ratio of 50:50 was obtained. The catalyst thus obtained is characterized by a pore fraction with a radius > 100 Å greater than 35%, while the total extrazeolitic pore volume of EPV is 0.81 ml / g. EXAMPLE 1 (pre-hydrogenation) coi? Lnn / zznz / E / Yi From a process of alkylation of benzene with isopropyl alcohol (IPA) to produce eumene, a primer mixture containing polyalkylated aromatic compounds was obtained by distillation, which constitutes a polyalkylated product according to the present invention. A liquid mixture (Mixture A), obtained by mixing benzene and the polyalkylated product in an approximately 4:1 weight ratio, was fed upwards into a continuous fixed-bed reactor (25 cm long, 1 cm cross-section) containing 22.9 g of Cu-1230E 1 / 16 hydrogenation catalyst (BASF). The composition of said Mixture A is shown in Table 1 below under gas chromatography. coi? Lnn / zznz / B / Yi Table 1 Compound Mixture A (% by weight) Mixture B (% by weight) Benzene 78.50 78.23 β-Diisopropylbenzene 0.02 0.03 Cumene 0.02 0.02 m-Diisopropylbenzene 4.30 4.42 o-Diisopropylbenzene 0.08 0.10 p-Diisopropylbenzene 16.20 16.40 Acetophenone 0.03 < 0.001 Phenylbenzene + high boiling point 0.85 0.79 H2O < 0.001 0.005 In Table 1, the term “high boiling point” means all compounds that in gas chromatographic analysis elute after the diisopropylbenzenes until the end of the analysis. The reactor was operated in an upflow regime at T = 120°C, P = 20 bar H2, WHSV = 2 Ir1, yielding a hydrogenated mixture (Mixture B) at the outlet with the composition shown in the third column of Table 1. A substantial reduction in the acetophenone content during the reaction can be observed. It should also be noted that, under the reaction conditions adopted, the aromatic compounds do not undergo substantial hydrogenation of the aromatic ring. Example 2 Transalkylation assays of diisopropylbenzenes were performed continuously in an upflow spiral fixed-bed reactor (tube length 5 m, cross-section 2.98 mm²) heated by forced air circulation within a thermostatically controlled chamber. A pneumatic valve at the furnace outlet regulates the pressure within the system. The reagents are stored in a 25-liter steel tank saturated with nitrogen to prevent oxidation of the reagents. The reaction effluents are sampled and analyzed periodically by gas chromatography and water content determination according to previously reported methods. The hydrogenated mixture, (Mixture B in Table 1), obtained according to the previous example 1, was subjected to transalkylation in said reactor, setting the thermostat to 220°C, with hydrogen pressure of 2 MPa and WHSV of 5 h1, using 12.7 g of the beta zeolite-based extruded catalyst, prepared as described in the previous Preparation Example A. The transalkylation reaction was carried out for more than 200 hours of operating time, corresponding to the productivities and conversions reported in Table 2. As can be seen, during this time period the catalyst shows no significant signs of deactivation. Table 2 coi? Lnn / zznz / E / Yi Time (h) Diisopropylbenzene Conversion (%) Cumene Yield (%) 43 86.3 76.9 163 87.6 77.4 235 86.6 77.1 The diisopropylbenzene conversion is the mole percent ratio of diisopropylbenzene converted to diisopropylbenzene fed. The eumene yield is the mole percent ratio of eumene produced to diisopropylbenzene fed. Example 3 (Comparative) In the same reactor, with the same catalytic system and under the same conditions used in Example 2 above, the mixture to be transalkylated fed to the reactor was changed, using the untreated mixture (Mixture A from Table 1). Table 3 shows the trend in the conversion of diisopropylbenzenes and in the yield of eumene, which clearly tend to decrease over time. Table 3 Time (h) Diisopropylbenzene Conversion (%) Cumene Yield (%) 22 82.2 73.1 47 81.7 72.8 95 81.2 72.0 From what has been reported, it is therefore evident that a reducing pre-treatment of the mixture to be transalkylated, preferably from alkylation with IPA, surprisingly with respect to the state of the art, allows improving the stability of the catalytic transalkylation system by eliminating, or in any case making less frequent, the need to apply regeneration processes known to experts in the art.

Claims

1. A process comprising a hydrogen reduction step in the presence of a suitable hydrogenation catalyst, of a polyalkylated product comprising at least one polyalkylaromatic compound, said polyalkylated product being obtained in at least one step of an alkylation process of at least one aromatic compound, by an alkylating agent selected from an alcohol, a primary olefin or a mixture thereof, preferably an alcohol, or a mixture of an alcohol with an olefin.

2. The process according to claim 1, further characterized in that said polyalkylated product comprises at least one polyethylbenzene or at least one polyisopropylbenzene.

3. The process according to one of the preceding claims 1 or 2, further characterized in that said catalyst is a hydrogenation catalyst of oxygenated organic substrates, preferably selected from catalysts based on Ni, Ni Raney, Pd, Pt, Cu, more preferably catalysts based on copper chromite.

4. The process in accordance with any of the preceding claims, further characterized in that said reduction step is carried out at temperatures between 60 and 220°C, preferably between 100 and 180°C, and hydrogen pressures between 0.1 and 5.0 MPa, preferably between 1.0 and 3.0 MPa.

5. The process in accordance with any of the preceding claims, further characterized in that said polyalkylated product is derived at least 15% by mass and up to 100% by mass, preferably at least 40% by mass, from alkylation processes of aromatic compounds with an alcohol.

6. The process according to any of the preceding claims, further characterized in that in the hydrogen reduction stage, the amount of hydrogenated aromatic rings is less than 1% by mass, preferably less than or equal to 0.1% by mass, with respect to the total number of aromatic rings fed in.

7. The process according to any of the preceding claims, further characterized in that said polyalkylated product is obtained from a benzene alkylation process, and is mixed with benzene prior to the hydrogen reduction step, such that the mixture thus obtained contains from 40 to 90%, preferably from 60 to 85% by mass of benzene with respect to the mass of the mixture itself.

8. The process in accordance with any of the preceding claims, further characterized in that it comprises, downstream of the hydrogen reduction step, a transalkylation step of the aromatic compounds contained in the polyalkylated product subject to reduction.

9. The process according to claim 8 above, further characterized in that said transalkylation step is carried out in the presence of a beta zeolite-based or Y zeolite-based catalyst.

10. The process according to any of the preceding claims 8 or 9, further characterized in that said transalkylation step is carried out at a temperature between 150 and 300°C, at a pressure between 2 MPa and 5 MPa and at a space velocity (WHSV) between 0.5 and 10 h1. coi? Lnn / zznz / E / Yi 11. A process for preparing monoalkylated aromatic hydrocarbons, characterized in that it comprises: a) contacting and reacting under alkylation conditions, in the presence of an acid alkylation catalyst, an aromatic hydrocarbon and at least one alcohol and / or at least one primary olefin, preferably an alcohol or a mixture of an alcohol and a primary olefin, more preferably an alcohol, said alcohol and the olefin having 2 to 4, preferably 3, carbon atoms; b) separating the reaction product obtained in step (a) into a fraction containing the aromatic hydrocarbon that has not reacted in step (a), a fraction containing a monoalkylated aromatic hydrocarbon, and a fraction comprising a polyalkylated product comprising at least one polyalkylaromatic compound, preferably containing at least 60% by weight of dialkylated aromatic hydrocarbons;c) subjecting said fraction comprising a polyalkylated product, obtained in step (b) to a reduction step with hydrogen in the presence of a suitable hydrogenation catalyst to obtain a reduced polyalkylated product; d) reacting said reduced polyalkylated product, obtained in step (c), with an aromatic hydrocarbon, preferably the same as that reacted in step (a), under transalkylation conditions, in the presence of a suitable acid catalyst, preferably selected from a beta zeolite or a Y zeolite; 12. The process according to claim 11, further characterized in that said hydrogenation catalyst in step c) is a hydrogenation catalyst of oxygenated organic substrates, preferably selected from catalysts based on Ni, Ni Raney, Pd, Pt, Cu, more preferably catalysts based on copper chromite.

13. The process in accordance with any of the preceding claims 11 and 12, further characterized in that said reduction step c) is carried out at temperatures between 60 and 220°C, preferably between 100 and 180°C, and hydrogen pressures between 0.1 and 5.0 MPa, preferably between 1.0 and 3.0 MPa.

14. The process in accordance with any of the preceding claims 11 to 13, further characterized in that said alcohol is ethanol or isopropanol, and said aromatic hydrocarbon in step a) is benzene.

15. The process in accordance with any of the preceding claims 11 to 14, further characterized in that said aromatic hydrocarbon in step d) is a non-alkylated aromatic hydrocarbon, preferably benzene.

16. The process according to claim 11, further characterized in that said step c) is carried out in accordance with or coincides with the process according to claim 1.

17. The process according to claim 11, further characterized in that said steps c) and d) are performed in accordance with or coincide with the process according to claim 8.