WO2011138357A1

WO2011138357A1 - Method for producing at least one low-molecular-weight aromatic valuable material from a lignin-containing starting material

Info

Publication number: WO2011138357A1
Application number: PCT/EP2011/057101
Authority: WO
Inventors: Roman Prochazka; Stefan Bitterlich; Otto Machhammer; Stephan Deuerlein; Dirk Klingler; Emmanouil Pantouflas; Alois Kindler; Bernd Zoels; Joachim Werther; Ernst-Ulrich Hartge; Peng Wang; Bernhard Schult; Frank Rimoschat; Heiko Rohde
Original assignee: Basf Se
Priority date: 2010-05-07
Filing date: 2011-05-04
Publication date: 2011-11-10

Abstract

The present invention relates to a method for producing low-molecular-weight aromatic valuable materials from a lignin-containing starting material generated from biomass.

Description

Process for the preparation of at least one low molecular weight aromatic valuable substance from a lignin-containing starting material

description

The present invention relates to a process for the preparation of low molecular weight aromatic recyclables from a lignin-containing starting material produced from biomass. Low molecular weight aromatic compounds and especially phenolic compounds have found wide use as intermediate and value products. They serve z. As a precursor for various resins, surface-active compounds, specialty chemicals, etc. It is known to prepare such compounds from lignin-containing starting materials. However, there remains a need for a simple, low cost process that enables the provision of a variety of different aromatic products for a variety of applications.

It is known to subject streams of various digestion processes of lignin or lignocellulosic materials to aftertreatment for the production of valuable substances.

US 2,057,117 discloses a process for producing vanillin which comprises heating a starting material selected from lignocellulose, a crude lignin extract and lignosulfonic acid with an aqueous alkali metal hydroxide solution under elevated pressure and adding sulfuric acid to the resulting reaction mixture to form organic To precipitate components and convert the vanillin into a soluble form.

WO 99/10450 describes a process for converting lignin into a hydrocarbon fuel. Lignin undergoes base-catalyzed depolymerization and subsequent hydroprocessing. This hydroprocessing involves hydrodeoxygenation and mild hydrocracking. The latter is carried out under conditions in which a partial hydrogenation of the aromatic rings takes place.

WO 2008/027699 A2 describes a process in which lignin originating from a pyrolysis of biomass is decarboxylated and hydrodeoxygenated after separation of water-soluble constituents and the organic products from this process step are subsequently subjected to hydrocracking. WO 2010/026244 describes an integrated process for the production of pulp and of at least one low molecular weight valuable material in which

a) providing a lignocellulose-containing starting material and subjecting it to digestion with a treatment medium,

b) isolating from the digested material a cellulose-enriched fraction and at least one cellulose-depleted fraction, the cellulose-depleted fraction comprising at least part of the treatment medium from step a),

c) subjecting the cellulose-depleted fraction to a treatment to obtain at least one low molecular weight valuable substance, and

d) isolated from the treatment product obtained in step c) the valuable material (s).

In one embodiment of the process, a cellulose-enriched fraction and a fraction enriched in lignin are isolated from the digested material, the lignin-enriched fraction is subjected to depolymerization, and an aromatic compound is isolated from the polymerization product.

WO 2009/108601 describes a process for producing a starting material for biorefinery processes for producing a biofuel from a lignin-containing starting material. Lignin from a black liquor of the pulping process or else the black liquor itself is subjected to hydroprocessing in the presence of a hydrogen-containing gas and a catalyst on an amorphous or crystalline oxidic support. Specifically, a heterogeneous molybdenum sulfide catalyst is used. When using black liquor, the hydroprocessing can also be carried out in two stages. The process can be carried out either at a refinery site to which lignin or black liquor is being transported, or directly at the site of a paper mill. The subsequent to the hydroprocessing biorefinery process is not described in detail.

WO 2009/108599 has a disclosure content comparable to WO 2009/108601 with a focus on papermaking.

M. Stoecker describes in the Angew. Chem. 2008, 120, 9340 - 9351, the catalytic conversion of lignocellulose-rich biomass for the recovery of BTL (biomass-to-liquid) fuels in biorefineries. In this case, the use of a lignin material obtained from the biomass in a pyrolysis to bio-oil and a further work-up to phenolic resins, synthesis gas, etc. are also shown schematically. US 2009/0227823 describes a process for preparing at least one liquid hydrocarbon product from a solid hydrocarbon feedstock (eg, a lignocellulosic material) by subjecting the feedstock to catalytic pyrolysis and subjecting the pyrolysis products to a catalysed sequential reaction to give liquid products ,

G.W. Huber et al. describe in Chem. Rev. 2006, 106, 4044-4098, the synthesis of fuels from biomass. After that, lignocellulosic materials can in principle be converted to three routes into liquid fuels which differ in their primary step: gasification to syngas, pyrolysis to bio-oil, hydrolysis to give sugars and lignin. The bio-oils obtained in the pyrolysis can then be subjected to hydrodeoxygenation in the presence of hydrogen or steam reforming. However, this document does not teach to subject a lignin-containing starting material initially to a pyrolysis and then essentially without separation of a substance component and in particular without condensation directly to a dealkylation process, with the primary purpose of obtaining low molecular weight aromatic recyclables.

Surprisingly, it has been found that the pyrolysis products obtained during the pyrolysis of lignin-containing materials can advantageously be subjected to a dealkylation process (or comparable processes for further molecular weight reduction) without separation of a substance component and in particular without preceding condensation under at least partial gas / aromatic separation , A first object of the invention is therefore a process for the preparation of a

Aromatic composition having a high content of mononuclear, low or unalkylated aromatics from a lignin-containing starting material comprising a) providing a lignin-containing starting material, b) pyrolysis of the lignin-containing starting material to obtain a pyrolysis gas stream, c) substantially the pyrolysis gas stream without separation of a material component in a Dealkylierungszone feeds and reacts in the presence of hydrogen and / or water vapor, d) the Dealkylierungszone takes a discharge and subjected to a separation to obtain the Aromatenzusammensetzung. An aromatics composition with a high content of mononuclear, low or non-alkylated aromatics is understood to mean a composition which, based on its total weight, contains at least 50% by weight of mononuclear aromatic compounds. The content of non-alkylated, non-alkoxylated, at most simply hydroxylated and monoalkylated aromatics is, based on the total weight of the aroma composition, at least 50% by weight in total.

In the context of the invention, pyrolysis is understood as meaning a thermal treatment of the lignin-containing starting material, molecular oxygen being not or only to a small amount being supplied. A small amount is to be understood as an amount which is significantly less than the amount necessary for a complete oxidation of the carbon contained in the lignin-containing starting material to CO2. The amount of molecular oxygen fed in the pyrolysis is preferably at least 50 mol%, more preferably at least 75 mol%, in particular at least 90 mol%, below the amount necessary for complete oxidation of the material contained in the biomass starting material Carbon to CO2 is necessary. Pyrolysis is generally endothermic.

In the context of the invention, "dealkylation" refers to a reaction of the substituted and / or polynuclear aromatic compounds present in an aromatic composition in the presence of hydrogen and / or water vapor, which are at least partially converted so that substituents are replaced by hydrogen and / or several aromatic Cores containing nuclei are cleaved to compounds with fewer nuclei. The hydrogen-substituted substituents are selected from alkyl groups, hydroxyl groups, alkoxy groups, aryloxy, etc. In the context of the invention, the term "dealkylation" also encompasses various reactions associated with a reduction in molecular weight, such as dehydroxylation, dealkoxylation, Aromatenspalte. Aromatea cleavage refers to a reaction in which essentially the number of aromatic nuclei per molecule is reduced without the aromatic nuclei themselves being destroyed.

It has been found that the separate carrying out of pyrolysis and dealkylation according to the invention is particularly advantageous, even if in some cases the same reactions take place in both steps.

Provision of a lignin-containing starting material (step a)

According to the invention, a lignin-containing starting material is provided in step a). Suitable lignin-containing starting materials are pure lignin and lignin-containing compositions. In this case, the lignin content of the compositions is not critical over a wide range, only if the lignin contents are too low can the process no longer be operated economically.

Preferably, in step a), a lignin-containing starting material is provided which contains at least 10% by weight, preferably at least 15% by weight, based on the dry matter of the material, of lignin. Preferably suitable are lignin-containing compositions which contain 10 to 100% by weight, particularly preferably 15 to 95% by weight, based on the dry mass of the material, of lignin. In the context of this invention, the term dry matter is understood in the sense of the standard ISO 1 1465.

Lignocellulose-containing materials are also suitable for providing a lignin-containing starting material for use in the process according to the invention. Lignocellulose forms the structural framework of the plant cell wall and contains lignin, hemicelluloses and cellulose as main components. Other components of the plant cell wall and thus obtained lignocellulose-containing materials are, for. As silicates, extractable low molecular weight organic compounds (so-called extract substances, such as terpenes, resins, fats), polymers, such as proteins, nucleic acids and gum (so-called exudate), etc.

Lignin is a biopolymer whose basic unit is essentially phenylpropane, which, depending on the natural source, may be substituted with one or more methoxy groups on the phenyl rings and with a hydroxy group on the propylene units. Therefore, typical structural units of lignin are p-hydroxyphenylpropane, guaiacylpropane and syringylpropane, which are linked by ether bonds and carbon-carbon bonds. Suitable starting materials for the process according to the invention are both lignocellulose-containing materials which are used without further chemical treatment in natural composition, such as. As wood or straw, as well as lignocellulosic streams from the processing of lignocellulose, z. B. from processes for cellulose production (pulp process).

The lignocellulosic materials which can be used according to the invention are e.g. B. from wood and vegetable fibers available as starting material. Preferred lignocellulosic materials are those of wood and residues of the woodworking industry. These include z. B. the different types of wood, ie hardwoods, such as maple, birch, pear, oak, Er- leek, eucalyptus, hornbeam, cherry tree, linden, walnut, poplar, willow, etc. and conifers such as Douglas fir, spruce, yew, hemlock, pine, larch fir, cedar, etc. Wood can be found not only in deciduous and Softwoods differ, but also in so-called "hardwoods" and "softwoods", which is not synonymous with the terms deciduous or coniferous wood. Soft wood, in contrast to hardwood, means lighter wood (ie wood with a density of less than 0.55 g / cm ³ , such as willows, poplars, lime trees and almost all softwoods). In principle, all hardwoods and all softwoods are suitable for use in the process according to the invention. The wood used in the process according to the invention can also be used in ready-made form, for. In the form of pellets. Suitable residues in the woodworking industry are in addition to wood waste and sawdust, parquet sanding dust, etc. Suitable lignocellulosic materials are still natural fibers such as flax, hemp, sisal, jute, straw, coconut fibers, switchgrass (Panicum virgatum) and other natural fibers. Suitable lignocellulosic materials also fall as a residue in agriculture, z. B. in the harvest of grain (wheat straw, corn straw, etc.), corn, sugar cane (bagasse), etc. Suitable lignocellulosic materials are also available as a residue in forestry, z. In the form of branches, barks, woodchips, etc. A good source of lignocellulosic materials are also short rotation crops, which enable high biomass production in a relatively small area.

Preferably, to provide the lignin-containing starting material, a lignin-containing stream from the digestion of a lignocellulosic material is used to produce cellulose (pulp). The digestion permits at least partial separation of the lignocellulose-containing starting material into cellulose and cellulose accompanying substances, the lignin also being among the latter.

In a preferred embodiment, a lignocellulose-containing material is provided in step a) of the process according to the invention, subjected to digestion and isolated from the digested material, a cellulose-enriched fraction and a lignin-enriched (and simultaneously depleted in cellulose) fraction.

Processes for the digestion of lignocellulose-containing materials for the production of cellulose are known in principle. In principle, lignin-containing streams are suitable for use in the process according to the invention from all the digestion processes known to those skilled in the art. In principle, these processes can be classified with regard to the treatment medium used in aqueous-alkaline processes, aqueous-acidic processes and organic processes. An overview of these methods and the digestion conditions can be found z. In WO 2010/026244. The treatment medium used to digest the lignocellulosic materials is capable of solubilizing at least a portion of the lignin. By contrast, the cellulose contained in the lignocellulose-containing material is generally not or only partially solubilized in the treatment medium. Preferably, the separation of a cellulose-enriched fraction is then carried out by filtration or centrifugation.

Preferably, a lignin-containing (cellulose-depleted) fraction is isolated from the digested material, which contains, in addition to lignin, at least one further component selected from hemicellulose, cellulose, degradation products of the aforementioned components, pulping chemicals and mixtures thereof.

In many cases, it is not critical for the pyrolysis in step b) if a lignin-containing starting material is used which contains at least one further component in addition to lignin.

If a lignin-containing fraction which contains at least one further component in addition to lignin is used to provide the lignin-containing starting material, at least some of the compounds other than lignin can be removed before the pyrolysis in step b). The components removed from the lignin-containing fraction (organic components and / or inorganic process chemicals) are preferably fed to a further work-up and / or thermal utilization, preferably in the course of the cellulose production process from which the lignin-containing fraction was obtained.

To remove at least a portion of the compounds other than lignin, the pH of the lignin-containing fraction may first be adjusted to a suitable value. Lignin-containing fractions from aqueous-alkaline processes (such as the Kraft process) can be treated with an acid to adjust the pH. Suitable acids are, for. As CO2, mineral acids such as hydrochloric acid, sulfuric acid and phosphoric acid. Particularly preferred acid is CO2 (or the resulting carbon dioxide with water). Preferably, CO2 is used from an exhaust gas stream of the process according to the invention or a pulp process coupled to the process according to the invention. Suitable is z. As the exhaust from a black liquor combustion (recovery boiler) or a lime kiln. In this case, the exhaust gas can be introduced into the lignin-containing fraction either directly or after separation from the other components (for example by means of a washing process such as Benfield scrubbing). The carbonates and / or hydrogencarbonates resulting from addition of CU2 can generally be easily incorporated into the coupled pulp process bring back, z. B. in a previously taken to Ligningewinnung black liquor. The use of CO2 to adjust the pH of the lignin-containing fraction is therefore associated with lower costs than with the use of other acids and also generally allows a good integration into a pulp process.

Lignin-containing fractions from aqueous-acidic processes can be mixed with a base to adjust the pH. Suitable bases are, for. As alkali metal bases, such as sodium hydroxide or potassium hydroxide, alkali metal carbonates, such as soda or potassium carbonate, alkali metal bicarbonates, such as sodium bicarbonate or potassium bicarbonate and alkaline earth metal bases, such as calcium hydroxide, calcium oxide, magnesium hydroxide or magnesium carbonate, and ammonia or amines.

Preferably, in step a) the removal of at least a portion of the lignin-different compounds from the lignin-containing fraction) by filtration, centrifuging, extraction, precipitation, distillation, stripping or a combination thereof. The person skilled in the art can control the composition of the lignin-containing fraction and thus of the lignin-containing starting material for the pyrolysis in step b) via the separation process. The at least partial separation of the components other than lignin can be carried out in one or more stages. Usual filtration methods are z. Cake and depth filtration (eg, described in A. Rushton, AS Ward, RG Holdich: Solid-Liquid Filtration and Separation Technology, VCH Verlagsgesellschaft, Weinheim 1996, pages 177ff., KJ Ives, in A. Rushton (A. Hg.): Mathematical Models and Design Methods in Solid-Liquid Separation, NATO ASI Series E No. 88, Martinus Nijhoff, Dordrecht 1985, pages 90ff.) And crossflow filtrations (eg described in J. Med. Altmann, S. Ripperger, J. Membrane Sci. 124 (1997), pages 1 19-128). Usual centrifugation are z. See, for example, G. Hultsch, H. Wilkesmann, "Filtering Centrifuges," DB Purchas, Solid-Liquid Separation, Upland Press, Croydon 1977, pp. 493-559; and in H. Trawinski, The Equivalent Clarifying Surface of Centrifuges, Chem. Ztg. 83 (1959), pages 606-612. For extraction z. As a non-miscible with the treatment medium from the pulp production solvent or at least one miscibility-exhibiting solvent can be used in the lignin and optionally other desired components in a sufficient amount is soluble. The separation of components which can be decomposed without decomposition from the lignin-containing fraction can be carried out by customary distillation processes known to the person skilled in the art. Suitable apparatus for working up by distillation include distillation columns, such as tray columns, which may be equipped with bells, sieve plates, sieve trays, packings, random packings, valves, side draws, etc., evaporators, such as thin film evaporators, falling film evaporators, forced circulation evaporators, Sambay evaporators, etc., and combinations from that. In a special embodiment, a lignin-containing stream from the digestion of a lignocellulose material which comprises at least part of the liquid treatment medium from the digestion is used to provide the lignin-containing starting material in step a). Preferably, the lignin-containing stream is then subjected to a lignin-containing fraction precipitation followed by partial or complete removal of the liquid components to provide the lignin-containing starting material for the pyrolysis in step b). Preferably, the lignin-containing starting material is provided in the context of a process for the production of cellulose (pulp) into which the production according to the invention of low molecular weight aromatic recyclables is integrated.

In a specific embodiment, the removal of at least a portion of the liquid compounds is then carried out in the context of the process for the production of pulp. Thus, to provide the lignin-containing starting material z. B. a black liquor are used, which is taken before or during the individual evaporation steps of the underlying pulp process. Preferably, a lignin-containing stream from the digestion of a lignocellulosic material with an alkaline treatment medium is used to provide the lignin-containing starting material in step a). Particularly preferably, a black liquor is used, in particular a black liquor from the sulfate digestion (power digestion). To provide a lignin-containing material, a black liquor from the Kraft digestion can first be acidified to precipitate at least a portion of the lignin contained and then the precipitated lignin can be isolated. For acidification, the aforementioned acids are suitable. In particular, CO2 is used. Preferably, the pH of the black liquor is lowered to a value of at most 10.5. The isolation of the precipitated lignin is preferably carried out by a filtration process. Suitable filtration methods are those mentioned above. If desired, the isolated lignin may be subjected to at least one further work-up step. This includes z. B. a further cleaning, preferably a wash with a suitable washing medium. Suitable washing media are for. For example, mineral acids such as sulfuric acid, preferably in aqueous solution. In a special embodiment, to supply a lignin-containing material, a black liquor from the kraft digestion is first acidified with CO 2 to precipitate at least part of the lignin contained, then the precipitated lignin is isolated by filtration and the filtrate or filter cake? subjected to a wash with sulfuric acid. A process for isolating lignin from a black liquor by precipitation with CO2 is described in WO 2008/079072, to which reference is made here. Also particularly suitable is the so-called lignoboost process, which is described in WO

2006/038863 (EP 1797236 A1) and WO 2006/031 175 (EP 1794363 A1), to which reference is also made.

Pyrolysis (step b)

In step b) of the process according to the invention, the lignin-containing starting material is subjected to pyrolysis, a pyrolysis gas stream being obtained.

The pyrolysis can be carried out batchwise or continuously. Continuous pyrolysis is preferred.

The pyrolysis takes place in at least one pyrolysis zone. For pyrolysis, the ligninhal- term starting material z. B. as a moist or predried solid by means of suitable transport facilities, such. B. screw conveyor or pneumatic conveying, are registered in a pyrolysis zone.

The pyrolysis zone may be designed in various embodiments, for. B. as a rotary kiln or fluidized bed. Both stationary and circulating fluidized beds are suitable. In the execution of the pyrolysis zone as a fluidized bed, a fluidizing gas (preferably water vapor or a gas mixture from one of the subsequent process steps) and as a fluidized material under the given conditions inert granular additive is supplied. Particularly suitable as an additive is quartz sand. Such a fluidized bed process is z. For example, in US 4,409,416 A described. In an alternative embodiment, the pyrolysis zone comprises at least one fixed bed. The fixed beds may comprise at least one inert fixed bed and / or at least one catalytically active fixed bed. If the process according to the invention is operated with at least one fixed bed as the pyrolysis zone, then an interval operation may be advantageous in which a pyrolysis phase is followed by a combustion phase in order to remove low-volatility components from the fixed bed.

For pyrolysis, a fluidizing gas can be fed into the pyrolysis zone. Preferred fluidizing gases are water vapor, carbon dioxide, nitrogen, etc., or mixtures of these gases. Preference is given to using a diluent gas which, under the conditions of pyrolysis, undergoes essentially no reaction with the lignin-containing starting material or the pyrolysis products resulting therefrom. In a first preferred embodiment, the pyrolysis is not accompanied by the addition of hydrogen and / or hydrogen-containing gases and / or hydrogen-transferring compounds carried out. In this embodiment, the hydrogenating reaction takes place essentially exclusively in the dealkylation step c). In a second suitable embodiment, the pyrolysis is carried out with the addition of hydrogen and / or hydrogen-containing gases and / or hydrogen-transferring compounds. This embodiment of the pyrolysis can also be referred to as hydrocracking.

If desired, the pyrolysis can be carried out in the presence of at least one pyrolysis catalyst. As pyrolysis z. For example, silica, alumina, aluminosilicates, aluminosilicates with layered structures and zeolites, such as mordenite, faujasite, zeolite-X, zeolite-Y and ZSM-5, zirconium oxide or titanium dioxide.

The temperature in the pyrolysis is preferably in a range of 200 to 1500 ° C, more preferably 250 to 1000 ° C, especially 300 to 800 ° C. The pressure in the pyrolysis is preferably in a range of 0.5 to 250 bar (absolute), preferably 1, 0 to 40 bar (absolute).

The residence time at the pyrolysis temperature can be a few seconds to several days. In a specific embodiment, the residence time at the pyrolysis temperature is 0.5 second to 5 minutes, more specifically 2 seconds to 3 minutes. The

Dwell time especially in a fluidized bed reactor results from the quotient of total volume of the reactor to the volume flow of the fluidizing gas under the pyrolysis. Suitable processes for the catalyzed or uncatalyzed pyrolysis of lignin are e.g. Also described in WO 96/09350 (Midwest Research Institute, 1996) or US 4,409,416 (Hydrocarbon Research Institute, 1983), which is incorporated herein by reference. In the pyrolysis zone, the lignin is converted into a mixture of components which under the conditions of pyrolysis are partly gaseous ("pyrolysis gas") and partly solid and / or liquid (eg tarry or "coke") ,

From the pyrolysis zone, a discharge is taken, which can still contain fractions of solid and / or liquid components in addition to the pyrolysis gases. These are z. B. to low-volatility components formed during pyrolysis (coke). If at least one solid aggregate is used for the pyrolysis in step b), the discharge from the pyrolysis zone may also contain fractions of the aggregate. These solid and / or liquid components can be prepared by means of a suitable method. direction, z. As a cyclone, are separated from the pyrolysis gas. Separate solid additives are preferably recycled to the pyrolysis zone. From aggregates different separated components are supplied to another utilization, eg. Example, a combustion for heat recovery, which is preferably used again in the inventive method or an integrated method. The fuel gas thus obtained, which contains mainly CO2 and water and optionally O2, can also be recycled. It is also possible to bring a discharge from the pyrolysis zone, which contains at least one additive and components which have low volatility under the pyrolysis conditions, into contact with an oxygen-containing gas, preferably air, in a combustion zone which is spatially separate from the pyrolysis zone, which causes it to burn off of low-volatility components ("coke") produced during pyrolysis. By a suitable separator, the aggregate is then separated from the resulting fuel gas and passed back through a suitable conveyor in the pyrolysis zone.

The immediately separated from the discharge from the pyrolysis zone, d. H. Under the pyrolysis not vaporizable (= gaseous) solid and / or liquid fractions, are not attributed to the pyrolysis gas according to the invention and are not considered as separated from the pyrolysis material component in the context of the invention.

The pyrolysis gas stream obtained in step b) contains substituted aromatics and / or polynuclear aromatics. The pyrolysis gas stream may contain, in addition to aromatics, other components selected from water vapor, inert gas (e.g.

Nitrogen), non-aromatic hydrocarbons, H2, CO, CO2, sulfur-containing compounds, such as. As H2S, etc. and mixtures thereof. The non-aromatic hydrocarbons are preferably degradation products, such as methane.

Dealkylation (step c)

In the dealkylation, the aromatic lignin decomposition products formed during the pyrolysis in step b) are at least partially converted by the action of hydrogen and / or water vapor so that substituents are replaced by hydrogen and / or several compounds containing aromatic nuclei are converted into compounds with less Number of cores are split. As previously stated, "dealkylation" thus also denotes reactions in which no alkyl substituent is exchanged for hydrogen, such as dehydroxylation, dealkoxylation, aromatic cleavage, etc. The substituents replaced by hydrogen are preferably selected from alkyl groups, hydroxy groups, alkoxy groups and aryl oxy groups.

Dealkylation processes suitable for use in step c) include hydrodekylation, vapor dealkylation or mixtures thereof. In the case of pure hydrodealkylation according to the invention, in addition to the pyrolysis gas stream, molecular hydrogen is fed into the dealkylation zone (in pure form or mixed with other components, such as CO), but no water. In the case of a pure steam dealkylation according to the invention, water is fed into the dealkylation zone in addition to the pyrolysis gas stream (in pure form or in a mixture with other components), but no molecular hydrogen. The dealkylation process in step c) can also be used as a mixed form of hydrodealkylation and

Dampfdealkylierung be configured. Then, in addition to the pyrolysis gas stream, both water and molecular hydrogen are fed into the dealkylation zone. In the following, suitable and preferred process parameters are given in part specifically for the hydrodealkylation or the steam dealkylation. With this information, the person skilled in the art is able to determine suitable and preferred process parameters for a mixed form of hydrodealkylation and steam dealkylation. Preferably, the reaction gas used for dealkylation then has a mixing ratio of H2 to H2O in the range from about 0.1: 99.9 to 99.9: 0.1. A particularly suitable mixing ratio of H2 to H2O is in the range of about 40:60 to 60:40.

The hydrogen required for the reaction is formed in situ in the case of steam dealkylation by reaction of water with (mainly organic) components which are either present in the educt mixture of the steam dealkylation or are formed during steam dealkylation. As an example, the formation of hydrogen from methane and water can be named according to the equation CH ₄ + H2O - CO + 3 H2.

It is an essential feature of the process according to the invention that the pyrolysis gas stream from step b) is fed into the dealkylation zone essentially without removal of a material component. In this case, components which are difficult to volatilize under the conditions of pyrolysis in step b) and which are not gaseous in the discharge from the pyrolysis zone but solid or liquid are not added to the pyrolysis gas stream.

"Substantially without separation of a material component" in the context of this invention means that of the pyrolysis gas stream obtained in step b). 10 vol .-% are separated before the pyrolysis gas is fed into the Dealkylierungszone. Preferably, at most 1% by volume, more preferably at most 0.5% by volume, of the pyrolysis gas stream obtained in step b) are separated off before the pyrolysis gas stream is fed into the dealkylation zone.

In particular, substantially no components contained therein are condensed out of the pyrolysis gas stream obtained in step b) before it enters the dealkylation zone. Specifically, from the pyrolysis gas stream obtained in step b) at most 10 wt .-%, particularly preferably at most 5 wt .-%, in particular at most 0.5 wt .-%, especially at most 0.1 wt .-%, of the condensable contained therein Components condensed out before the pyrolysis gas stream is fed into the Dealkylierungszone. The pyrolysis gas stream is maintained under suitable conditions which substantially preclude condensation of components contained therein.

Preferably, the temperature of the pyrolysis gas stream before entering the Dealkylierungszone always at most 200 ° C, more preferably always at most 100 ° C, below the outlet temperature from the pyrolysis zone. Preferably, the temperature in the dealkylation zone is in a range from 400 to 900 ° C, more preferably from 500 to 800 ° C.

The absolute pressure in the dealkylation zone is preferably in the range from 1 to 100 bar, particularly preferably from 1 to 20 bar, in particular from 1 to 10 bar.

In a first preferred embodiment, the pyrolysis gas stream is subjected to a hydrodealkylation in step c). For this, the reaction in step c) takes place in the presence of hydrogen. The temperature in the dealkylation zone for the hydrodealkylation is preferably in the range from 500 to 900 ° C., particularly preferably from 600 to 800 ° C.

The absolute pressure in the dealkylation zone for the hydrodealkylation is preferably in a range from 1 to 100 bar, particularly preferably from 1 to 20 bar, in particular from 1 to 10 bar.

For the hydrodealkylation, the feed ratio of H 2 to H 2 (stoichiometric) is preferably in a range from 0.02 to 50, particularly preferably from 0.2 to 10. H 2 (stoichiometric) stands for the amount H 2, which is theoretically straightforward full conversion of the aromatics supplied to the dealkylation zone to benzene is required, assuming that 1 mole H is reacted per nuclear substituent.

For the hydrodealkylation, the residence time in the dealkylation zone is preferably in the range from 0.1 to 500 s, more preferably from 0.5 to 200 s.

In a second preferred embodiment, the pyrolysis gas stream is subjected to a steam dealkylation in step c). For this purpose, the reaction in step c) takes place in the presence of water vapor.

The temperature in the dealkylation zone for the vapor dealkylation is preferably in the range from 400 to 800 ° C., particularly preferably from 475 to 600 ° C., in particular from 525 to 600 ° C. The absolute pressure in the dealkylation zone for the vapor dealkylation is preferably in a range from 1 to 100 bar, particularly preferably from 1 to 20 bar, in particular from 1 to 10 bar.

For the steam dealkylation, the amount ratio of H 2 O to C ^{* is} preferably in a range from 0.1 to 20 mol / mol, particularly preferably from 0.5 to

2 mol / mol. C ^* stands for the molar amount of carbon, determined by carbon-based balancing of the pyrolysis or by determining the amounts of the product exhausts from the steam dealkylation by methods known to the person skilled in the art. For steam dealkylation, the molar ratio of H2 to CH4 in the dealkylation zone is preferably in a range of <50: 1, particularly preferably <25: 1.

Preferably, for a steam dealkylation in the absence of Dealkylierungskata- lysators the molar ratio of OR (where R = H, alkyl) to C _ge including in the Dealkylierungszo- ne in a range of> 0.05: 1, more preferably from 0.1: 1 to 0.2: 1.

Preferably, for steam dealkylation in the absence of a dealkylation catalyst, the ratio of OR (with R = H, alkyl) to Cabs in the dealkylation zone is in the range of> 0.5: 1, more preferably from 1: 1 to 10: 1 , in particular from 1: 1 to 2: 1.

For the steam dealkylation, WHSV is preferably in a range from 0.05 to 10 kg / (L ^* h), particularly preferably from 0.1 to 2 kg / (L ^* h). The steam dealkylation can be carried out in the presence or absence of a catalyst. In a specific embodiment, steam dealkylation is carried out in the absence of a catalyst. A catalyzed process for steam dealkylation is in

WO 2008/148807 A1. Reference is made in its entirety to this document and the references cited therein to suitable catalysts. Further information on catalyst types and process steps of steam dealkylation can be found in WO 2007/051852 A1, WO 2007/051851 A1, WO 2007/051855 A2, WO 2007/051856 A1, WO 2008/135581 A1 and WO 2008/135582 A1

(EP 2008055585), without thereby limiting. US Pat. No. 3,775,504 describes that steam dealkylation actually consists of a combination of steam dealkylation and hydrodealkylation, since at least part of the hydrogen generated is inherently reacted again at the same time.

In the dealkylation step c), at least one low molecular weight aromatic substance is formed as the target product of the process according to the invention. The low molecular weight aromatic valuable substances are preferably selected from benzene and phenolic compounds, such as phenol and / or dihydroxybenzenes.

In particular, they have lower proportions of the following components than the pyrolysis effluent before being fed into the dealkylation step c): mono-, di- and polyalkylated phenols; Alkoxyphenols, such as methoxyphenols; polyalkylated benzenes; Compounds containing two or more aromatic rings. These components are referred to below as "low or non dealkylated aromatics". Separation of the discharge from the dealkylation zone (step d))

The dealkylation zone is sampled and subjected to separation to yield the target aromatics composition having a high content of mononuclear, low or unalkylated aromatics.

Preferably, the effluent from the dealkylation zone is subjected to separation to give the following three streams:

D1) an enriched in mononuclear, low or non-alkylated aromatics stream,

D2) an enriched in low or non dealkylated aromatics stream, D3) an enriched lighter than D1) and D2) by-products stream.

Optionally, the effluent from the dealkylation zone may be subjected to separation to yield additional streams, such as e.g. B. a hydrous stream.

Stream D1) is the aromatic compound prepared in the process according to the invention with a high content of mononuclear, low or non-alkylated aromatics. In addition, stream D1) can be subjected to a further work-up to obtain the aroma composition prepared according to the invention.

The stream D1) contains, based on the total amount of D1), preferably at least 70 wt .-%, more preferably at least 80 wt .-%, in particular at least 90 wt .-%, of mononuclear aromatic.

The stream D1), based on the total amount of D1), preferably at most 30 wt .-%, more preferably at most 20 wt .-%, in particular at most 10 wt .-%, of low or non-dealkylated aromatics. As mentioned above, in the context of the invention "dealkylation" also refers to the replacement of substituents other than alkyl groups (such as alkoxy groups, aryloxy groups, hydroxy groups, etc.) by hydrogen. Depending on the composition of the lignin-containing starting material provided in step a) or of the pyrolysis gas stream obtained in step c), stream D1) then also has a high content of aromatics in which one substituent other than alkyl groups has been replaced by hydrogen. Specifically, stream D1) has a high content of low-alkoxylated or non-alkoxylated aromatics.

The stream D2), based on the total amount of D2), preferably at least 70 wt .-%, more preferably at least 80 wt .-%, in particular at least 90 wt .-%, of low or non-dealkylated aromatics.

The stream D3) contains components that z. B. are selected from non-aromatic hydrocarbons, especially methane, hydrogen, carbon monoxide, carbon dioxide and mixtures thereof. Depending on the lignin-containing starting material provided in step a), the stream D3) may contain further components. When using a lignin-containing starting material from the Kraft process include sulfur-containing by-products, especially h S. Preferably, a gaseous effluent is removed from the dealkylation zone and subjected to separation in step d).

As a method for separation, the well-known thermal Trennver- can be used.

The separation of the discharge from the dealkylation zone in step d) preferably comprises an absorption. In the absorption, the gaseous effluent from the dealkylation zone is contacted with a solvent (absorbent), whereby a part of the components contained in the gas stream is absorbed and thus separated.

The absorption is carried out in a suitable apparatus, e.g. B. a countercurrent column, bubble column, etc. Preferably, the absorption is carried out in a countercurrent column.

The absorption can be configured in one or more stages.

For absorption, a solvent (unloaded: absorbent, loaded: absorbate) is preferably used in which the aromatics obtained in the dealkylation are soluble in a sufficient amount and the volatile by-products which differ from them are substantially insoluble. In this case, together with the mononuclear, low or non-alkylated aromatics (= target product) and the low or non-dealkylated at least partially absorbed.

During absorption, therefore, an aromatics-laden absorbent is obtained on the one hand. The aromatic components contained in the absorbate correspond in composition to the sum of the aromatics in the streams D1) and D2) plus any aromatics optionally present in the absorbent. The components contained in the remaining gas stream correspond in their composition to stream D3). If desired, the gas stream may be subjected to an additional aromatic aromatics removal step. These can then be combined again with the aromatics contained in the separated solvent for joint workup. In general, however, such isolation of aromatics from the separated gas stream is not required.

In a preferred embodiment, the separation of the discharge from the dealkylation zone in step d) comprises the following substeps: Contacting the discharge from the dealkylation zone obtained in step c) with an absorbent to obtain an aromatics-enriched absorbent and a gas stream D3 enriched in aromatics (or a by-product which is lighter than D1) and D2),

Separation of the absorbate into a stream containing the absorbent, a stream D 1 enriched in mononuclear, low or non-alkylated aromatics and stream D 2 enriched in slightly or non-dealkylated aromatics,

Recycling the absorbent-containing stream to step d1), optionally recycling at least a portion of stream D2) to the dealkylation zone of step c).

Preferably, the absorbent has a boiling point which is above the components of stream D1). Further preferably, the absorbent has a high dissolving power for the aromatics formed in the dealkylation step. Suitable solvents are, for. As aliphatic, cycloaliphatic and aromatic hydrocarbons, aliphatic, cycloaliphatic and aromatic alcohols, amides, such as N-methylpyrrolidone or dimethylformamide. Aliphatic, cycloaliphatic and aromatic hydrocarbons preferably have a carbon atom number of at least 6. Aliphatic, cycloaliphatic and aromatic alcohols preferably have a carbon atom number of at least 4.

In a particularly preferred variant, the solvent used is an aromatic compound which can be obtained by the process according to the invention. This is specifically a mixture of aromatics that are not or not fully converted in the dealkylation. In a particularly preferred variant, the solvent used is a partial stream of stream D2) or a mixture of D1) and D2). In this variant, the solvent can be obtained by partial condensation of the stream from the dealkylation or a gas stream from a downstream of the dealkylation high boiler pre-separation. Here, it may be advantageous to switch between the said partial condensation and the absorption of a further partial condensation in which in particular water is condensed out.

In this variant as well, together with the absorption of desired product, at least partial absorption of the aromatics which are not reacted or not fully converted takes place. Ie. In this variant too, the aro- matic components of their composition of the sum of the aromatics of the streams D1) and D2).

In step d2), the aromatics-enriched absorbate is preferably separated by distillation. The thereby recovered solvent is, optionally after removal of absorbed water, in the absorption (step d1)) recycled. The aromatics are processed further as described above and below.

In step d2), the aromatics-enriched absorbate is preferably separated by distillation in at least one column ("regeneration column"). The distillation conditions are preferably selected so that substantially low or non-alkylated aromatics and, if present, water and, as the bottom product, substantially low or non-dealkylated aromatics are obtained as top product. It is understood that in the distillative separation in step d2), the bottom temperature is chosen so low that undesirable side reactions of the bottom product are substantially avoided. This can be achieved in particular by setting a suitable column pressure and / or by the low-boiling content in the bottoms (the low-content content can be further reduced by a downstream stripping).

The top product obtained in the distillation in step d2) contains the target product of the process according to the invention. It can either be withdrawn directly as stream D1) or subjected to further work-up. Water contained in the overhead product can be separated off by known processes. For this purpose, the overhead product, after condensation of the vapors from the distillation, can be fed to a phase separator for the removal of water. The resulting water is discharged as another stream from the process. The organic phase from the phase separator can either be at least partially withdrawn as stream D1) or subjected to further work-up. The organic phase from the phase separator can be partly recycled as reflux to the column and / or subjected to a further distillative work-up. This is preferably used for the removal of water still contained and / or undesirable organic components.

The bottom product obtained during the distillation in step d2) contains the aromatics which are not or not sufficiently converted in the case of dealkylation, ie it is enriched in aromatics which are sparingly or not dealkylated. It can either be withdrawn directly as stream D2) or subjected to further work-up. Prefers is the resulting in the distillation in step d2) bottom product divided into at least two partial streams. Preferably, a first substream in step d) of the absorptive separation of the discharge from the Dealkylierungszone, z. As a solvent, recycled. For this purpose, this partial stream, if necessary, cooled to a suitable temperature. A second partial stream is withdrawn as stream D2). This stream D2) is preferably at least partially recycled to the dealkylation zone of step c). Stream D2) may be subjected to separation of constituents other than stream D2) prior to recycling to the dealkylation zone of step c). This is z. B. advantageous if an absorption solvent is used, which is not obtained as an intermediate of the process according to the invention. It is also advantageous at this point of stream D2) deduct a purge and z. B. in a combustion device to reduce the accumulation of under the conditions of dealkylation not or slowly reacting components.

The stream D2) is preferably subjected to evaporation before it is fed into the dealkylation. A preferred variant is shown in FIG. 2 and explained in the associated description of the figures. The stream D3) obtained in step d), which is depleted of aromatics and enriched in highly volatile by-products, can be put to various uses. This includes on the one hand the combustion. When the process according to the invention is spatially close to a pulp process, it may be advantageous to feed stream D3) into an apparatus of the pulp process. Particularly preferably, the stream D3) is fed into the waste liquor combustion (recovery boiler). These

Embodiment has the advantage that no additional devices for the steam or power generation or the flue gas desulfurization in the combustion of the stream D3) are needed. In another variant, the combustion of the stream D3) is a desulfurization, z. B. upstream in the form of a hydrogen sulfide removing gas, followed by a conversion of the formed H2S in elemental sulfur. The formation of sulfur can by known methods, for. As the Claus process done.

Preferably, the stream D3) obtained in step d) is used at least partly for the production of synthesis gas. If, according to the preferred embodiment of the process according to the invention described above, the separation of the discharge from the dealkylation zone in step d) comprises an absorption, the gas stream leaving the absorption device (stream D3), if appropriate after a cleaning step for the removal of absorbent and / or aromatics, preferably at least partially used for the production of synthesis gas.

The term "synthesis gas" in the context of the invention refers to a carbon monoxide and hydrogen-containing gas mixture. This gas mixture may additionally contain other gases, such as CO2, CH ₄ , etc. Advantageously, the inventive method allows the production of synthesis gas with a high content of carbon monoxide and hydrogen. Optionally, at least one further stream can be used for synthesis gas production, the z. B. water vapor and / or oxygen. It is also possible to use an exhaust gas stream from the pyrolysis in step b) and / or the dealkylation in step c) in the syngas production. It may be z. B. to act as a combustion gas from the combustion of volatile components. By feeding such an exhaust gas stream, the H2 / CO ratio of the synthesis gas can be reduced.

The synthesis gas production preferably comprises the following stages:

a reforming stage,

- A conversion stage (in the still necessary additional water is performed), in which the water gas shift reaction (CO + H ₂ 0 H ₂ + C0 ₂ ) takes place, optionally a stage for the partial separation of acid gases, such as. B. C0 ₂ . The execution of the syngas generation corresponds to the prior art, as he z. In Ullmann's Encyclopedia of Industrial Chemistry, article "Gas Production", DOI: 10.1002 / 14356007.a12_169.pub2.

In a preferred variant, the synthesis gas stream 1 1 produced in the process according to the invention (if necessary after further purification steps known per se for removing water, sulfur-containing components, CO 2, etc.) is used completely or partially for use in at least one process comprising hydrogen, CO or mixtures of both consumed used. These include z. As a hydrogenation, hydroformylation, carbonylation, methanol synthesis, synthesis of hydrocarbons Fischer-Tropsch, etc.

In a preferred embodiment of the method according to the invention, a synthesis gas-containing stream produced in the process or a hydrogen-enriched stream prepared from the synthesis gas is introduced into the pyrolysis in step b). and / or into the dealkylation in step c). An enrichment of the synthesis gas to hydrogen, as described above, carried out by water gas shift reaction. Preferably, a synthesis gas-containing stream produced in the process or a hydrogen-enriched stream prepared from the synthesis gas is fed into the dealkylation in step c). The particular advantage of this variant is that the proportion of phenol (s) in the products of the dealkylation is higher than in the pure steam dealkylation, ie without hydrogen supply. The higher phenol formation represents an economic advantage, since phenol is a higher value material than oxygen-free aromatics, such as benzene. In addition, hydrogen, which is not produced in the process according to the invention, more expensive and in many cases not or only with great effort available, especially if the dealkylation is to be performed away from a chemical Verbundortortsorts.

figure description

A preferred embodiment of the method according to the invention is shown in FIG.

A lignin-containing starting material (1) is subjected to pyrolysis.

The pyrolysis gas (2) is fed together with a hydrogenation gas stream (5) into a dealkylation unit, essentially without any condensation or other separation of the stream being carried out.

The discharge from the dealkylation zone (6) is subjected to separation into the following three streams:

Value product (stream (7)), a substance or substance mixture which has arisen through the above-described deal-deal;

not or incompletely dealkylated product (stream (8)). This contains substances that have not been dealkylated or to a lesser extent than the desired product; Stream (9) containing volatile by-products. These are selected from methane and other hydrocarbons, H2O, CO, CO2 and sulfur-containing by-products (in the case of lignin from the Kraft process, especially H2S).

Optionally, a stream of water is separated and discharged from the discharge from the dealkylation zone (6). Stream (7) is withdrawn, optionally after further work-up, as a product stream.

The enriched in only slightly or non-dealkylated aromatics stream (8) is returned via an evaporation of the dealkylation. A preferred embodiment of the evaporation is shown in FIG. 2 and described below.

The stream (9) from the separation containing the volatile byproducts can be used for various purposes, such as e.g. B. a suitable combustion, are supplied, wherein it is advantageous in spatial proximity to a pulp process to lead current (9) in an apparatus of the same, particularly preferably in the waste liquor combustion (recovery boiler). This design has the advantage that no additional apparatus for steam or electricity generation or flue gas desulfurization are needed. In another variant, the combustion is a deflagration, z. B. in the form of a hydrogen sulfide removing gas scrubber, followed by a conversion of the F S in elemental sulfur (eg Claus process) upstream.

In a particularly preferred embodiment, stream (9) is fed to a reforming unit in which, optionally with the introduction of an optional stream (10) containing water or oxygen, the organic components contained are converted to a synthesis gas (11) containing CO and H. ,

When the dealkylation is a hydrodealkylation, a hydrogen-containing stream (12) obtained from synthesis gas production can be passed into the dealkylation.

If hydrogen is used for the pyrolysis, a hydrogen-containing stream (13) obtained from synthesis gas production can be conducted into the pyrolysis.

Figure 2 shows the evaporation of an aromatics-containing stream, as z. B. in the absorptive and distillative separation of the discharge from the Dealkylierungszone as stream D2) (in Figure 1 with (8) denotes) is obtained. Stream (8) is preferably subjected to evaporation before being returned to the dealkylation, as shown in FIG.

The Aromatenstrom (8) is preheated in apparatus A to a temperature at which no significant decomposition takes place in the liquid phase. The thus preheated stream (stream 100) is in an apparatus B with a gaseous stream (stream 200) merged, the amount, temperature and composition are chosen so that the stream 100 partially or completely evaporated. Stream 200 contains dealkylation reactants, ie steam in the case of steam dealkylation and hydrogen-containing gas in case of hydrodealkylation (stream 5 in FIG. 1). The amounts of streams 100 and 200 are adjusted so that stream 300 leaving in apparatus B gives a composition favorable for the type of dealkylation chosen.

Apparatus B is designed as a liquid-gas contact apparatus according to the prior art, for. B. as a container with jet nozzle or column, wherein stream 100 is supplied at the top. Liquid and gas are passed in cocurrent or countercurrent, in the lower part, if necessary, a low-volatile residue (stream 250) are deducted. Alternatively, apparatus B can also be designed as a fluidized bed. Via the externally heated fluidized material, additional energy can be efficiently entered into the stream 100.

In a preferred variant, stream 300 is split into streams 400 and 500, with dealkylation stream 400 and stream 500 returned to apparatus B via heat exchanger C. This variant allows limiting the temperatures of the streams 100, 200 and 500 (after heat exchangers) to limit values that result from the availability of the heat sources, the thermal stability of the materials and the stability of the materials. The naturally occurring pressure loss along the streams 300, 400 and 500 is compensated by a suitable means for compression. For this purpose, well-known compressor or fans can be used. But it is also possible to carry out the apparatus B completely or partially as a liquid jet fan, wherein current 100 is used as the driving medium. In this case, if the amount of stream 100 is not sufficient for the required compaction performance, liquid can be circulated via apparatus B in the circuit.

Claims

claims

A process for the preparation of an aromatics composition high in mononuclear, low or unalkylated aromatics from a lignocellulosic starting material comprising: a) providing a lignocellulosic starting material, b) pyrolysis of the lignocellulosic starting material to obtain a pyrolysis gas stream, c) the pyrolysis gas stream essentially without separation of a material component in a Dealkylierungszone feeds and reacts in the presence of hydrogen and / or steam, d) the Dealkylierungszone takes a discharge and subjected to a separation to obtain the Aromatenzusammensetzung.

A method according to claim 1, wherein in step a) a lignin-containing starting material is provided which contains at least 10% by weight, preferably at least 15% by weight, based on the dry matter of the material, of lignin.

Method according to one of the preceding claims, wherein for providing the lignin-containing starting material in step a) a lignocellulosic material of wood and / or vegetable fibers is used.

Method according to one of the preceding claims, wherein for providing the lignin-containing starting material in step a) a lignin-containing stream from the digestion of a lignocellulosic material for the production of cellulose (pulp) is used.

The method of claim 4, wherein for providing the lignin-containing starting material in step a) a lignin-containing stream from the digestion of a lignocellulosic material is used with an alkaline treatment medium, preferably a black liquor, in particular a black liquor from the Kraft pulping (sulfate pulping).

6. The method of claim 5, wherein to provide the lignin-containing starting material in step a) a black liquor is acidified, so that at least at least part of the lignin contained precipitates and the precipitated lignin is isolated by filtration.

7. The method according to any one of the preceding claims, wherein the pyrolysis gas stream obtained in step b) contains substituted aromatics and / or polynuclear aromatics.

8. The method according to any one of the preceding claims, wherein from the pyrolysis gas stream obtained in step b) prior to its entry into the Dealkylierungszone substantially no components contained therein are condensed out.

9. The method according to any one of the preceding claims, wherein the temperature of the pyrolysis gas stream after exiting the pyrolysis zone and before entering the Dealkylierungszone always at most 200 ° C, more preferably always at most 100 ° C, below the outlet temperature from the pyrolysis zone.

A process according to any one of the preceding claims, wherein the reaction in step c) comprises a hydrodealkylation or a vapor dealkylation or a mixed form thereof.

1 1. A process according to any one of the preceding claims, wherein the temperature in the dealkylation zone is in a range of from 400 to 900 ° C, preferably from 500 to 800 ° C.

12. The method according to any one of the preceding claims, wherein the absolute pressure in the dealkylation zone in a range of 1 to 100 bar, more preferably from 1 to 20 bar, in particular from 1 to 10 bar, is located.

13. The method according to any one of the preceding claims, wherein the discharge from the dealkylation zone in step d) is subjected to a separation to obtain the following three streams:

D1) an enriched in mononuclear, low or non-alkylated aromatics stream,

D2) an enriched in low or non dealkylated aromatics stream, D3) an enriched stream of volatile by-products lighter than D1) and D2).

A process according to any one of the preceding claims, wherein the separation of the effluent from the dealkylation zone in step d) comprises absorption.

The process of claim 14, wherein the separation of the discharge from the dealkylation zone in step d) comprises the following substeps: d1) contacting the effluent from the dealkylation zone obtained in step c) with an absorbent to obtain an aromatics-enriched absorbate and an aromatics-depleted Gas stream D3),

Recycling the stream containing the absorbent

Step en), d4) optionally recycling at least part of the stream D2) into the dealkylation zone in step c).

Process according to one of claims 13 to 15, wherein the stream D3) obtained in step d) is used at least partly for the production of synthesis gas.

The process of claim 16, wherein the stream obtained in step d) is at least partially subjected to reforming and / or conversion.

A process according to any one of claims 16 or 17, wherein a synthesis gas-containing stream or a hydrogen-enriched stream prepared from the synthesis gas is fed into the pyrolysis in step b) and / or into the dealkylation in step c).