Vinyl aromatic compound distillation unit cleaning process and process comprising such a cleaning process

Abstract

The present disclosure relates to a purging process for a vinyl aromatic compound distillation unit, wherein the vinyl aromatic compound distillation unit comprises one or more distillation columns, the process comprising a purging step of the one or more distillation columns followed by a passivation step of the at least one distillation column, wherein a stream comprising a passivation mixture comprises a component A as one or more polymerization inhibitors; and a component B selected from steam and / or one or more hydrocarbons not containing vinyl groups, is passed through the at least one distillation column under passivation conditions comprising a temperature of at least 90° C. The present disclosure also relates to a purification and production process for one or more vinyl aromatic compounds comprising the purging process.

Description

Technical Field

[0001] The present disclosure relates to a process for treating a distillation column suitable for distilling vinyl aromatic compounds, a process for purifying at least one vinyl aromatic compound, and a process for producing vinyl aromatic compounds from corresponding saturated aromatic compounds, in particular for producing styrene from ethylbenzene. Background Art

[0002] When the components to be distilled contain polymerizable groups, such as vinyl groups, the distillation unit is susceptible to polymer contamination. For example, in the case of purified styrene, the presence of divinylbenzene can clog the distillation column during polymerization. After cleaning and maintenance, living chain polymer residues, which act as polymer seeds, often remain. When the distillation unit is restarted, these polymer seeds are reactivated and contaminate the restart process, resulting in reduced distillation efficiency.

[0003] US Pat. No. 3,476,656 discloses that, because styrene tends to polymerize upon application of heat, it is possible to use various styrene polymerization inhibitors, such as molten sulfur and tert-butylcatechol (TBC). Other styrene polymerization inhibitors, such as diethylhydroxylamine (DEHA), phenyl-p-phenylenediamine, and phenothiazine, can be used. However, the use of polymerization inhibitors during distillation carries costs, and solutions to reduce these costs remain to be found.

[0004] WO 00 / 14039 discloses a composition suitable for inhibiting the polymerization of vinyl aromatic compounds. Such a composition comprises a dihydroxyaromatic hydrocarbon, a hydrogen transfer agent and a stable nitrogen oxide.

[0005] These components are used during the purification of styrene by distillation techniques so that polymerization levels are kept low. However, once the styrene distillation unit is stopped, the styrene distillation column still contains polymer seeds.

[0006] In this regard, KR101299781 discloses a method for cleaning the internal components of a fractionation or distillation column, suitable for fractionation, refining, and distillation of petrochemical substances. This method uses ultrasound to contact the substance to be cleaned with a cleaning solution containing isopropyl alcohol. However, due to the ultrasonic vibrations, this physical cleaning method cannot thoroughly clean the distillation column.

[0007] Regarding heat exchangers, thermal cleaning has been developed as an alternative to traditional high-pressure cleaning. High-pressure cleaning has the disadvantage that the water jets cannot reach every nook and cranny around the heat exchanger, leaving dirt and dust behind. In contrast, thermal cleaning allows the heat exchanger to be restored to its original performance.

[0008] It is therefore an object of the present disclosure to provide a method for efficiently cleaning a distillation unit of vinyl aromatic compounds, in particular a distillation unit of styrene. Summary of the Invention

[0009] According to a first aspect, the present disclosure provides a process for purging a vinyl aromatic distillation unit, wherein the vinyl aromatic distillation unit comprises one or more distillation columns, the process comprising a step of purging the one or more distillation columns, and being notable in that the step of purging the one or more distillation columns is followed by a passivation step of at least one distillation column, wherein a flow (flux) comprising a passivation mixture is passed through the at least one distillation column under passivation conditions comprising a temperature of at least 90° C. and a pressure of up to 300 kPa, wherein the passivation mixture comprises component A as one or more polymerization inhibitors and component B selected from steam and / or one or more hydrocarbons not containing vinyl groups, the one or more hydrocarbons not containing vinyl groups being or comprising one or more aliphatic saturated hydrocarbons and / or one or more aromatic compounds.

[0010] Advantageously, the passivating mixture comprises 0.01 to 2.0% by weight of component A, or 0.01 to 1.0% by weight of component A, or 0.01 to 0.80% by weight of component A, or 0.01 to 0.50% by weight of component A, or 0.01 to 0.10% by weight of component A, preferably 0.02 to 0.08% by weight of component A, more preferably 0.03 to 0.07% by weight of component A, based on the total weight of the passivating mixture, the remainder being made up of component B.

[0011] Surprisingly, it has been found that it is possible to reduce or at least keep low the amount of polymer inhibitors used during a purification process of one or more vinyl aromatic compounds by chemical passivation performed during the cleaning process. Without being bound by theory, the process of the present disclosure allows the inactivation of polymer seeds that remain in the column after cleaning using a passivation step. Thus, the process provides for the deactivation of the inner surface of a distillation column during its lifetime, the deactivation being performed in the presence of polymer seeds during the cleaning process of the column when the distillation is stopped for maintenance. This finding is significant in that the passivation step is not only a pretreatment of the inner surface of the column, but also a regeneration of the original passive behavior of the surface. The passivation step according to the present disclosure chemically inactivates the polymer seeds present in the column, making it possible to reduce or at least keep low the amount of polymer inhibitors used in the next distillation.

[0012] The polymer seed was found to be stable at ambient temperatures (e.g., temperatures used when cleaning a column). The process of the present disclosure uses Component B to raise the temperature to at least 90°C to activate the polymer seed, which then reacts with a polymerization inhibitor to prevent further polymerization during distillation. The use of a polymerization inhibitor in the passivation mixture further allows the distillation column to be passivated at a temperature equal to or higher than the temperature at which distillation is conducted, without requiring the supply of excess heat necessary to combust the polymer seed. The process of the present disclosure is particularly effective for treating distillation columns that have undergone a polymerization event (i.e., where polymerization has occurred). It allows the distillation unit to be restarted with the original behavior.

[0013] For example, the vinyl aromatic compound is selected from styrene, α-methylstyrene, divinylbenzene, polyethylenebenzene, and any mixture thereof; preferably, the vinyl aromatic compound is or contains styrene.

[0014] For example, the stream comprising the passivation mixture that passes through at least one distillation column during the passivation step is free of vinyl aromatic compounds.

[0015] For example, the vinyl aromatic compound is or comprises styrene, and the stream comprising the passivation mixture which passes through at least one distillation column during the passivation step comprises ethylbenzene and / or is free of styrene.

[0016] For example, the step of cleaning one or more distillation columns is or includes mechanical cleaning; preferably, the mechanical cleaning of one or more distillation columns includes high-pressure cleaning of one or more distillation columns.

[0017] Advantageously, the passivation conditions comprise a temperature in the range of 10°C above the boiling point of the vinyl aromatic compound under pressure conditions to a temperature of at most 20°C above the boiling point of the vinyl aromatic compound under pressure conditions, or in the range of 15°C above the boiling point of the vinyl aromatic compound under pressure conditions to a temperature of at most 20°C above the boiling point of the vinyl aromatic compound under pressure conditions.

[0018] For example, the passivation conditions include a temperature of at least 95°C; for example, at least 100°C; for example, at least 105°C; for example, at least 110°C; for example, at least 115°C; for example, at least 120°C.

[0019] For example, the passivation conditions include a temperature of at most 250°C; for example, at most 220°C; for example, at most 200°C; for example, at most 180°C; for example, at most 160°C; for example, at most 150°C or at most 145°C.

[0020] For example, the passivation conditions include a temperature ranging from 90°C to 250°C; for example, 95°C to 220°C; for example, 100°C to 200°C; for example, 105°C to 180°C; for example, 110°C to 160°C; for example, 115°C to 150°C; for example, 120°C to 145°C.

[0021] For example, the passivation conditions include pressure conditions of up to 300 kPa, preferably in the range of 90 kPa to 200 kPa; more preferably in the range of 98 kPa to 120 kPa, such as 100 kPa to 115 kPa.

[0022] For example, the passivation conditions include a passivation time ranging from 1 to 24 hours; for example, 2 to 20 hours; for example, 3 to 18 hours; for example, 5 to 15 hours.

[0023] For example, the passivation step is performed under an atmosphere provided by one or more inert gases, such as nitrogen and / or argon.

[0024] For example, component A contains at least one polymerization inhibitor selected from the group consisting of molten sulfur, phenyl-p-phenylenediamine, phenothiazine, tert-butylcatechol, diethylhydroxylamine, butylated hydroxytoluene, butylated hydroxyanisole, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, quinone methide, 2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-diene-1-ylidene)acetonitrile, 2,6-di-tert-butyl-4-(methoxymethylene)cyclohexa-2,5-dienone, 4-benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone, and any mixture thereof; preferably selected from the group consisting of tert-butylcatechol, diethylhydroxylamine, and any mixture thereof, and more preferably, component A is diethylhydroxylamine.

[0025] In one embodiment, component B is steam.

[0026] In a second embodiment, component B is one or more hydrocarbons that do not contain vinyl groups, wherein the one or more hydrocarbons that do not contain vinyl groups are or comprise one or more selected from saturated hydrocarbons and / or aromatic compounds; preferably, at least one aromatic compound that does not contain vinyl groups is selected from benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, aliphatic mixtures of benzene / ethylbenzene, and any mixtures thereof. For example, the one or more aliphatic saturated hydrocarbons are one or more selected from heptane, octane, nonane, decane, and any mixtures thereof. For example, when a benzene / ethylbenzene mixture is selected, the mixture comprises 10% to 30% by weight of benzene and 70% to 90% by weight of ethylbenzene, based on the total weight of the benzene / ethylbenzene mixture.

[0027] In a third embodiment, component B is a mixture of steam and one or more hydrocarbons not containing vinyl groups, wherein the one or more hydrocarbons not containing vinyl groups are or comprise one or more aliphatic saturated hydrocarbons and / or one or more aromatic compounds; preferably, at least one aromatic compound not containing vinyl groups is selected from benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, a mixture benzene / ethylbenzene, and any mixture thereof.

[0028] According to a second aspect, the present disclosure provides a process for purifying one or more vinyl aromatic compounds, the process comprising distilling the one or more vinyl aromatic compounds using a vinyl aromatic distillation unit, wherein the vinyl aromatic distillation unit comprises one or more distillation columns, the process comprising interrupting the distillation of the one or more vinyl aromatic compounds at least once to perform a cleaning process of the vinyl aromatic distillation unit, notably, the cleaning process of the vinyl aromatic distillation unit is according to the first aspect; preferably, the one or more vinyl aromatic compounds are or contain styrene.

[0029] For example, the cleaning process includes a passivation step performed at a higher temperature than the temperature at which the distillation is performed.

[0030] According to a third aspect, the present disclosure provides a process for producing vinyl aromatic compounds from corresponding saturated aromatic compounds, said process being notable in that it comprises the following steps:

[0031] a) providing a catalytic component comprising one or more zeolites;

[0032] b) providing a stream comprising saturated aromatic compounds;

[0033] d) contacting the stream comprising saturated aromatic compounds with the catalytic component under dehydrogenation reaction conditions comprising a temperature of at least 550° C. to obtain a stream enriched in vinyl aromatic compounds;

[0034] e) subjecting said stream rich in vinyl aromatic compounds to said purification process of at least one vinyl aromatic compound according to the second aspect;

[0035] f) optionally, recovering the vinyl aromatic compound from the vinyl aromatic compound-rich stream.

[0036] For example, the vinyl aromatic compound produced is styrene and the corresponding saturated aromatic compound is ethylbenzene; preferably, the stream provided in step (b) further comprises diethylbenzene, and the process further comprises a step (c) of removing the diethylbenzene from the stream provided in step (b) before contacting the stream with the catalyst component.

[0037] Preferably, the one or more zeolites are selected from the group consisting of MWW, FAU, MFI, MOR, or zeolite beta, or any mixture thereof, more preferably from the group consisting of MWW, FAU, MFI, or zeolite beta, or any mixture thereof.

[0038] For example, the catalytic component further comprises at least one transition metal; preferably, the at least one transition metal is selected from Cr, Mn, Fe, Co, Ni, Cu, Zn, and any mixture thereof; more preferably, the transition metal is Fe.

[0039] Advantageously, the catalytic component further comprises, in addition to the at least one transition metal, at least one alkali metal; preferably, the alkali metal is selected from the group consisting of Li, Na, K, and Cs, more preferably, the alkali metal is K.

[0040] For example, the catalytic component is or comprises a ferrite such as potassium ferrite, K2Fe 22 O 34 .

[0041] For example, the catalytic component is or comprises a ferrite, preferably a ferrite having an active surface comprising potassium iron oxide with a K / Fe atomic ratio in the range of 1 / 1 to 1 / 11, and preferably wherein the iron is only in its trivalent state. Further information on examples of ferrites can be found in the study of Muhler M., et al. (J. of Cata., 1992, 138, 413-44). BRIEF DESCRIPTION OF THE DRAWINGS

[0042] - Figure 1 : An apparatus comprising a vinyl aromatic compound distillation unit according to the present disclosure.

[0043] - Figure 2 : Gamma scan of a contaminated distillation column.

[0044] - Figure 3 : Gamma scan of the distillation column after performing the cleaning process of the vinyl aromatic compound distillation unit according to the present disclosure. DETAILED DESCRIPTION

[0045] For the purposes of this disclosure, the following definitions are given:

[0046] Zeolite codes (eg, CHA...) are defined according to "Atlas of Zeolite Framework Types", 6th revised edition, 2007, Elsevier, which is also incorporated herein by reference.

[0047] As used herein, the terms "comprising," "comprises," and "consisting of" are synonymous with "including," "includes," or "containing," and are inclusive or open-ended and do not exclude additional, unrecited members, elements, or method steps. The terms "comprising" and "consisting of" also include the term "composed of."

[0048] The recitation of numerical ranges by endpoints includes all integers and, where appropriate, subsumes fractions within the range (e.g., 1 to 5 when referring to, for example, the number of elements, includes 1, 2, 3, 4, 5, and when referring to, for example, measurements, includes 1.5, 2, 2.75, and 3.80). The recitation of endpoints also includes the recited endpoint values themselves (e.g., 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all subranges subsumed therein.

[0049] The term "transition metal" refers to an element whose atoms have partially filled d subshells or can produce cations with incomplete d subshells (IUPAC definition). According to this definition, the transition metals are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, and Cn.

[0050] The metals Ga, In, Sn, Tl, Pb, and Bi are considered "late transition" metals.

[0051] The metals Au, Ag, Ru, Rh, Pd, Os, Ir, and Pt exhibit excellent oxidation resistance and are considered "noble" metals. Other metals may be considered "non-noble" metals.

[0052] The term "alkali metal" refers to an element classified as being from Group 1 (or Group IA) of the Periodic Table of the Elements, excluding hydrogen. According to this definition, the alkali metals are Li, Na, K, Rb, Cs, and Fr.

[0053] The term "alkaline earth metals" refers to elements classified as being from Group 2 (or Group IIA) of the Periodic Table of the Elements. According to this definition, the alkaline earth metals are Be, Mg, Ca, Sr, Ba, and Ra.

[0054] The terms "bottom" and "top" are to be understood relative to the overall orientation of the distillation unit, in particular the vinyl aromatic distillation unit. Thus, "bottom" will imply a greater proximity to the ground along the vertical axis than "top." In the various figures, the same reference numerals designate the same or similar elements.

[0055] As will be apparent to one skilled in the art from this disclosure, the particular features, structures, characteristics or embodiments may be combined in any suitable manner in one or more embodiments.

[0056] Cleaning process for vinyl aromatic distillation units

[0057] The present disclosure provides a process for purging a vinyl aromatic distillation unit, wherein the vinyl aromatic distillation unit comprises one or more distillation columns, the process comprising a step of purging the one or more distillation columns 1, and being notable in that the step of purging the one or more distillation columns is followed by a step of passivating the at least one distillation column 1, wherein a stream comprising a passivation mixture is passed through the at least one distillation column 1 under passivating conditions comprising a temperature of at least 90° C. and a pressure of up to 300 kPa, wherein the passivation mixture comprises a component A which is one or more polymerization inhibitors, and a component B selected from the group consisting of steam and / or one or more hydrocarbons not containing vinyl groups, the one or more hydrocarbons not containing vinyl groups being or comprising one or more aliphatic saturated hydrocarbons and / or one or more aromatic compounds.

[0058] Typically, the vinyl aromatic distillation unit may be configured as follows: Figure 1 The unit comprises at least one distillation column 1, the bottom of which is fluidically connected to a reboiler loop comprising, for example, two reboilers (9, 19). Figure 1 As shown, the reboilers (9, 19) are in parallel. The top of the distillation column 1 is fluidly connected to a reflux loop comprising a condenser 11 upstream of a reflux drum 13 upstream of the distillation column 1 .

[0059] The component A, which can be stored in a container 15, is injected into the reflux loop at the level of the reflux drum 13. When the component A comes from the container 15, the line between the container 15 and the reflux drum 13 may, for example, comprise a pump 17. From the reflux drum 13, the stream comprising the component A passes through the distillation column 1.

[0060] It is also possible to inject the component A directly into the distillation column 1 and / or into the reboiler loop.

[0061] However, the component A can be injected into the reflux loop at the level of the reflux drum 13 and also directly into the distillation column 1 and / or into the reboiler loop.

[0062] Furthermore, component B is passed through the distillation column 1. This can be done by injecting component B directly at the level of the distillation column 1 and / or in the reboiler loop. Thanks to the reflux loop, component B will be introduced into the reflux loop and will thus mix with the component A circulating in the reflux loop, subsequently forming a passivated mixture that will be introduced into the distillation column 1 in the form of a stream.

[0063] Thus, regardless of where component A is injected, the passivation mixture always contains component A and component B. In particular, the passivation mixture contains 0.01 to 2.0 wt.-% of component A, or 0.01 to 1.0 wt.-% of component A, or 0.01 to 0.80 wt.-% of component A, or 0.01 to 0.50 wt.-% of component A, or 0.01 to 0.10 wt.-% of component A, preferably 0.02 to 0.08 wt.-% of component A, more preferably 0.03 to 0.07 wt.-% of component A, based on the total weight of the passivation mixture, the remainder being made up of component B.

[0064] For example, the vinyl aromatic compound is selected from styrene, α-methylstyrene, divinylbenzene, polyethylenebenzene, and any mixture thereof; preferably, the vinyl aromatic compound is or contains styrene.

[0065] For example, the stream containing the passivation mixture passed through at least one distillation column during the passivation step is free of vinyl aromatic compounds. In the treatment of a distillation column suitable for the distillation of vinyl aromatic compounds (e.g. styrene), the use of a mixture of one or more hydrocarbons free of vinyl groups allows the distillation column to be washed free of the components and simultaneously provides suitable heat to activate the polymer seeds present. Component B is selected to have no chemical moieties susceptible to polymerization.

[0066] For example, the vinyl aromatic compound is or comprises styrene, and the stream comprising the passivation mixture which passes through at least one distillation column during the passivation step comprises ethylbenzene and / or is free of styrene.

[0067] For example, the step of cleaning one or more distillation columns is or includes mechanical cleaning; preferably, the mechanical cleaning of one or more distillation columns includes high-pressure cleaning of one or more distillation columns.

[0068] Selection of passivation conditions

[0069] For example, the deactivation conditions include a temperature in the range of 10° C. above the boiling point of the vinyl aromatic compound under pressure conditions to a temperature of at most 20° C. above the boiling point of the vinyl aromatic compound under pressure conditions, or in the range of 15° C. above the boiling point of the vinyl aromatic compound under pressure conditions to a temperature of at most 20° C. above the boiling point of the vinyl aromatic compound under pressure conditions. The deactivation conditions always include a temperature that is higher than (above) the temperature at which the distillation of the vinyl aromatic compound is carried out.

[0070] For example, the passivation conditions include a temperature of at least 95°C; for example, at least 100°C; for example, at least 105°C; for example, at least 110°C; for example, at least 115°C; for example, at least 120°C.

[0071] For example, the passivation conditions include a temperature of at most 250°C; for example, at most 220°C; for example, at most 200°C; for example, at most 180°C; for example, at most 160°C; for example, at most 150°C or at most 145°C.

[0072] For example, the passivation conditions include a temperature in the range of 90°C to 250°C; for example, 95°C to 220°C; for example, 100°C to 200°C; for example, 105°C to 180°C; for example, 110°C to 160°C; for example, 115°C to 150°C; for example, 120°C to 145°C.

[0073] The choice of temperature for the passivation step is related to the choice of component B. For example, when component B is or comprises ethylbenzene, a person skilled in the art will have the advantage of selecting a temperature in the range of 115°C to 150°C; for example, 120°C to 145°C.

[0074] Those skilled in the art can also adjust the temperature according to the pressure selected for the passivation conditions. For example, when working at reduced pressure (i.e., below atmospheric pressure), the passivation temperature corresponds to a temperature below that which would be selected if the working pressure were atmospheric pressure. Thus, the passivation temperature is advantageously in the range of 90°C to 110°C, preferably 95°C to 105°C.

[0075] However, those skilled in the art may have the advantage of working at least at atmospheric pressure (i.e. 101325 Pa) or higher, so that the passivation conditions include pressure conditions of up to 300 kPa; preferably, the passivation conditions include pressure conditions in the range of preferably 90 kPa to 200 kPa; more preferably 98 to 120 kPa, for example, 100 to 115 kPa.

[0076] For example, the passivation conditions include a passivation time in the range of: 1 to 24 hours; for example, 2 to 20 hours; for example, 3 to 18 hours; for example, 5 to 15 hours.

[0077] For example, the passivation step is performed under an atmosphere provided by one or more inert gases, such as nitrogen and / or argon.

[0078] For example, one or more distillation columns of the vinyl aromatic distillation unit comprise a reboiler. The flow of the passivation mixture has a flow at the reboiler level in the range of 1 to 250 l / h, preferably 50 to 100 l / h, more preferably 60 to 90 l / h, even more preferably 65 to 85 l / h.

[0079] Selection of Component A

[0080] For example, component A comprises at least one polymerization inhibitor selected from the group consisting of molten sulfur, phenyl-p-phenylenediamine, phenothiazine, tert-butylcatechol (TBC), diethylhydroxylamine (DEHA), quinone methide (QM), 2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-diene-1-ylidene)acetonitrile (QM-CN), 2,6-di-tert-butyl-4-(methoxymethylene)cyclohexa-2,5-dienone (QM-OMe), 4 -benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone (QM-Ph), butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-OH-TEMPO), and any mixture thereof; preferably tert-butylcatechol (TBC), diethylhydroxylamine (DEHA), and any mixture thereof; more preferably component A is diethylhydroxylamine (DEHA).

[0081] Selection of component B

[0082] For example, component B is steam.

[0083] For example, component B is one or more hydrocarbons not containing vinyl groups, wherein the one or more hydrocarbons not containing vinyl groups are or contain one or more aliphatic saturated hydrocarbons and / or one or more aromatic compounds; preferably, at least one aromatic compound not containing vinyl groups is selected from benzene, toluene, o-xylene, m / xylene, p-xylene, ethylbenzene, a mixture benzene / ethylbenzene, and any mixture thereof.

[0084] Component B may be or comprise BTX; ie, benzene, toluene, o-xylene, m-xylene, p-xylene, and any mixture thereof.

[0085] Component B may be or comprise BTEX; ie, benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, and any mixture thereof.

[0086] For example, the aliphatic saturated hydrocarbon is one or more selected from heptane, octane, nonane, decane, and any mixture thereof. For example, when a benzene / ethylbenzene mixture is selected, based on the total weight of the benzene / ethylbenzene mixture, the mixture comprises 10 to 30 wt % of benzene and 70 to 90 wt % of ethylbenzene, preferably, the mixture comprises 15 to 25 wt % of benzene and 75 to 85 wt % of ethylbenzene.

[0087] For example, component B is a mixture of steam and one or more hydrocarbons not containing vinyl groups, wherein the one or more hydrocarbons not containing vinyl groups are or contain one or more aliphatic saturated hydrocarbons and / or one or more aromatic compounds; preferably, at least one aromatic compound not containing vinyl groups is selected from benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, a mixture of benzene / ethylbenzene, and any mixture thereof. For example, the aliphatic saturated hydrocarbon is one or more selected from heptane, octane, nonane, decane, and any mixture thereof. For example, when a mixture of benzene / ethylbenzene is selected, the mixture comprises 10% to 30% by weight of benzene and 70% to 90% by weight of ethylbenzene, based on the total weight of the mixture of benzene / ethylbenzene. Preferably, the mixture comprises 15% to 25% by weight of benzene and 75% to 85% by weight of ethylbenzene.

[0088] For example, when component B is a mixture of steam and one or more hydrocarbons not containing vinyl groups, the ratio of steam to one or more hydrocarbons ranges from 0.25 to 4, preferably from 1 to 3.

[0089] Preferably, component B is one or more selected from the group consisting of a mixture of steam and benzene, a mixture of steam and ethylbenzene, a mixture of steam, benzene and ethylbenzene, and any mixture thereof.

[0090] The one or more hydrocarbons not containing vinyl groups present in the mixture used to treat the distillation column are aromatic compounds not containing vinyl groups, which can be selected from the list consisting of benzene, ethylbenzene, toluene, o-xylene, m-xylene, and p-xylene. More preferably, the one or more hydrocarbons not containing vinyl groups are selected from benzene and / or ethylbenzene, and even more preferably, ethylbenzene. In practice, since the process of the present disclosure is useful for passivating distillation columns suitable for vinyl aromatic compounds, it is more efficient to use a mixture of one or more hydrocarbons belonging to the same chemical class as the vinyl aromatic compounds. Thus, in one example, when styrene is the vinyl aromatic compound to be distilled, ethylbenzene can be the hydrocarbon of choice.

[0091] Process for the purification of one or more vinyl aromatic compounds

[0092] The present disclosure also provides a purification process for at least one vinyl aromatic compound comprising the above-described cleaning process.

[0093] Thus, the present disclosure provides a process for purifying one or more vinyl aromatic compounds, the process comprising distilling the one or more vinyl aromatic compounds using a vinyl aromatic distillation unit, wherein the vinyl aromatic distillation unit comprises one or more distillation columns, the process comprising interrupting the distillation of the one or more vinyl aromatic compounds at least once to perform a cleaning process of the vinyl aromatic distillation unit, notably, the cleaning process of the vinyl aromatic distillation unit is according to the first aspect; preferably, the one or more vinyl aromatic compounds are or contain styrene.

[0094] For example, the cleaning process includes a passivation step that is performed at a higher temperature than the temperature at which the distillation is performed. In fact, working at a higher temperature allows for a relatively quick activation of any remaining polymer and / or any polymer seeds. Once activated, they will be oxidized and decomposed during the cleaning process.

[0095] For example, a preferred vinyl aromatic compound that can be purified is styrene. The distillation unit can include multiple distillation columns for processing the resulting vinyl aromatics-rich stream. In the first distillation column, benzene and toluene are separated. Then, in a subsequent column, ethylbenzene is separated from styrene, and in a third column, the styrene is further purified. Advantageously, the ethylbenzene separated in the second column can be recycled to the production process or the cleaning process.

[0096] Process for the production of vinyl aromatic compounds from the corresponding saturated aromatic compounds

[0097] The present disclosure also provides a process for producing a vinyl aromatic compound from a corresponding saturated aromatic compound, which comprises the above-mentioned cleaning process and / or purification process.

[0098] Thus, the present disclosure provides a process for the production of vinyl aromatic compounds from the corresponding saturated aromatic compounds, said process being notable in that it comprises the following steps:

[0099] a) providing a catalytic component comprising one or more zeolites;

[0100] b) providing a stream comprising saturated aromatic compounds;

[0101] d) contacting the stream comprising saturated aromatic compounds with the catalytic component under dehydrogenation reaction conditions comprising a temperature of at least 550° C. to obtain a stream enriched in vinyl aromatic compounds;

[0102] e) subjecting said stream rich in vinyl aromatic compounds to said purification process of at least one vinyl aromatic compound according to the second aspect;

[0103] f) optionally, recovering the vinyl aromatic compound from the vinyl aromatic compound-rich stream.

[0104] For example, the vinyl aromatic compound produced is styrene and the corresponding saturated aromatic compound is ethylbenzene; preferably, the stream provided in step (b) further comprises diethylbenzene, and the process further comprises a step (c) of removing the diethylbenzene from the stream provided in step (b) before contacting the stream with the catalyst component.

[0105] For example, the one or more zeolites are selected from the group consisting of MWW, FAU, MFI, MOR, or zeolite beta, or any mixture thereof. Preferably, the one or more zeolites are selected from the group consisting of MWW, FAU, MFI, or zeolite beta, or any mixture thereof.

[0106] For example, when the zeolite is a zeolite from the MWW class, the zeolite is MCM-22. A particular example of a zeolite from the MWW class is a zeolite used in an ethylbenzene alkylation process such as EBMax SM craftsmanship.

[0107] For example, when the zeolite is from the MFI class of zeolites, the zeolite is ZSM-5.

[0108] For example, when the zeolite is a zeolite selected from the FAU class, the zeolite is zeolite Y and / or USY. For example, the catalytic component further comprises at least one metal derivative; preferably, the metal of the at least one metal derivative is iron. For example, the catalytic component is or comprises a ferrite, preferably a ferrite having an active surface comprising potassium iron oxide with a K / Fe atomic ratio of 1 / 1, wherein the iron is only in its trivalent state. Further information on examples of ferrites can be found in the study of M. Muhler et al. (J. of Cata., 1992, 138, 413-44).

[0109] For example, the dehydrogenation reaction conditions include one or more of the following:

[0110] - a temperature in the range of 500°C to 700°C, preferably 525°C to 675°C, more preferably 550°C to 650°C; and / or

[0111] - a pressure in the range of 0.01 MPa to 100 MPa, preferably in the range of 0.1 MPa to 90 MPa, more preferably 1 MPa to 80 MPa, even more preferably 10 MPa to 75 MPa, most preferably 20 MPa to 70 MPa, even most preferably 30 MPa to 65 MPa, or 35 MPa to 60 MPa; and / or

[0112] - Range 0.3 h -1 to 1.0 h -1 , preferably 0.4 h -1 to 0.9 h -1 or 0.5 h -1 to 0.8 h -1 Liquid hourly space velocity.

[0113] In a preferred embodiment of the present disclosure, the vinyl aromatic compound is styrene and the corresponding saturated aromatic compound is ethylbenzene. Thus, the present disclosure provides a process for producing styrene from ethylbenzene, the process being notable in that it comprises the following steps:

[0114] a) providing a catalytic component comprising one or more zeolites;

[0115] b) providing a stream comprising ethylbenzene;

[0116] d) contacting said stream comprising ethylbenzene with said catalytic component under dehydrogenation reaction conditions to obtain a styrene-rich stream;

[0117] e) subjecting said styrene-rich stream to said purification process of at least one vinyl aromatic compound according to the second aspect; and

[0118] f) optionally, recovering styrene from said styrene-rich stream.

[0119] Examples of commercially available catalytic components for the production of styrene from ethylbenzene are StyroStar® S6-42 or StyroMax® UL3.

[0120] Advantageously, in said preferred embodiment, said stream provided in step (b) further comprises diethylbenzene, and said process further comprises a step (c) of removing diethylbenzene from said stream provided in step (b) before contacting said stream with said catalyst component.

[0121] In the preferred embodiment, the stream containing ethylbenzene provided in step (b) advantageously contains at most 50 ppm, preferably at most 40 ppm, more preferably at most 30 ppm, even more preferably at most 20 ppm, and most preferably at most 10 ppm of diethylbenzene, or is free of diethylbenzene. Indeed, under the dehydrogenation reaction conditions, p-diethylbenzene or m-diethylbenzene can be converted into p-divinylbenzene or m-divinylbenzene, respectively, which are polymerizable compounds due to the vinyl groups they contain. Under the dehydrogenation reaction conditions, o-diethylbenzene can be converted into naphthalene, a heavy component that is difficult to remove from a distillation column. Therefore, when the stream provided in step (b) contains diethylbenzene, it is advantageous for the process to include a step of removing the diethylbenzene from the stream.

[0122] This integrated system, in which styrene is produced from ethylbenzene, followed by purification of a styrene-rich stream according to the process for purification of at least one vinyl aromatic compound described in the present disclosure, i.e., in which a distillation column is first treated with a mixture containing ethylbenzene at a passivation temperature, said passivation temperature being at least the temperature at which the distillation column operates under styrene distillation conditions, i.e., including a passivation temperature of at least 90° C. under passivation conditions, preferably in the range of 120° C. to 145° C. at atmospheric pressure, allows efficient production of styrene from ethylbenzene, since, after the ethylbenzene has passed through the catalytic component, the styrene-rich stream (which also contains unconverted ethylbenzene) can be fed directly to the distillation column. Said unconverted ethylbenzene will be mixed with the ethylbenzene used to treat the distillation column and will be separated at this stage, allowing the styrene to be properly recovered.

[0123] Test and measurement methods

[0124] Gamma scan

[0125] The gamma device used is the Tru-Scan™ gamma device from Tracerco . A small source emitting gamma rays is placed on one side of the device. On the opposite side, an electronic detector sensitive to radiation is used to measure the radiation transmitted through the tower, allowing it to be measured with a chord through the tower. The source and detector are aligned at the same height and lowered simultaneously in small steps along a predetermined part of the tower. At each step, the detector measures the transmitted radiation and records it on a computer. At the end of the scan, the results are represented by graphs (such as those shown on the left side of the figure) emitted by the signal measured against the height. For a restricted window of gamma rays, the intensity of the radiation transmitted through the device is defined by the following formula: I = I0e (-μρx) ; wherein (I) is the radiation transmitted through the device and measured by the detector; (I o ) is the radiation transmitted through the empty device; (x) is the thickness of the material between the source and the detector; (ρ) is the density of the material; and (μ) is a constant called the mass attenuation coefficient.

[0126] Therefore, if the distance (path within the container) is maintained, the transmitted radiation is a function of the density within the device. By taking multiple measurements (typically four), it is possible to detect whether the column is empty (and therefore clean) or not (and therefore contaminated).

[0127] Example

[0128] Styrene is produced from an ethylbenzene stream containing some diethylbenzene. The resulting vinyl aromatic (i.e., styrene)-rich stream undergoes a purification process that includes distilling the styrene using a vinyl aromatic distillation unit including a distillation column 1. However, after approximately 4.5 years of operation, contamination of the styrene with divinylbenzene (DVB) was observed due to a high polymerization event, and distillation column 1 became contaminated.

[0129] Therefore, the vinyl aromatic compound distillation unit was shut down and a mechanical cleaning process including high pressure cleaning of the column and replacement of some structural packing (e.g. column internals) damaged by contamination was performed on the distillation column 1. The vinyl aromatic compound distillation unit was shut down for 1 month.

[0130] The unit was then restarted, but after 2 months of operation without any DVB contaminated crude styrene, separation problems reappeared due to maldistribution and contamination. These problems increased until the distillation was again stopped for a month to perform cleaning of distillation column 1. Figure 2 The control scan (left) shows poor distribution and contamination, where gaps can be seen between the different curves.

[0131] As defined in the present disclosure, the cleaning process performed includes a passivation step after the cleaning step. The cleaning step is mechanical and includes high-pressure cleaning of column 1 and replacement of the packing. The passivation step is performed by injecting 3 kg of DEHA as component A into each of the reboilers (9, 19). The total amount of DEHA is distributed to the distillation column 1 via both the reflux loop and the reboiler loop. A baseline pH check is performed before the injection of DEHA, indicating a pH of 4 to 5. The correct circulation of component A is actually checked by collecting a sample at the bottom of the distillation column and measuring the pH using a wet pH strip test. A pH in the range of 8 to 9 is an indication of correct circulation of DEHA within the distillation column 1. In the event that the pH is below the range of 8 to 9, additional injection of DEHA can be performed. Once the correct circulation of DEHA within the distillation column is confirmed, ethylbenzene is injected into the reboiler loop as component B. The injection of ethylbenzene is continuous and totals up to 4500 kg. The flow rate of the passivation mixture comprising DEHA and ethylbenzene measured at the level of one of the reboilers (9, 19) was 70 l / h. After purging the distillation column 1, the distillation column 1 was restarted and the control scan showed a good condition. The control scan showed that Figure 3 In the figure (left), all density lines are grouped together, showing good distribution within column 1. The large peaks that can be seen correspond to the positions of the horizontal distribution trays (3, 5, 7) shown schematically on the right side of the figure. Since then (16 months later), the distillation unit is still performing well.

Claims

1. A process for cleaning a vinyl aromatic distillation unit, wherein the vinyl aromatic distillation unit comprises one or more distillation columns (1), the process comprising a step of cleaning the one or more distillation columns (1), and characterised in that the step of cleaning the one or more distillation columns (1) is followed by a step of passivating the at least one distillation column (1), wherein a stream comprising a passivation mixture is passed through the at least one distillation column (1) under passivating conditions comprising a temperature of at least 90° C. and a pressure of up to 300 kPa, wherein the passivation mixture comprises component A as one or more polymerization inhibitors and component B selected from steam and / or one or more hydrocarbons not containing vinyl groups, the one or more hydrocarbons not containing vinyl groups being one or more aliphatic saturated hydrocarbons and / or one or more aromatic compounds.

2. The cleaning process according to claim 1, characterized in that The passivating mixture comprises 0.01 wt % to 2.00 wt % of component A, with the remainder made up of component B, based on the total weight of the passivating mixture.

3. The cleaning process according to claim 1 or 2, characterized in that: The passivation conditions comprise a temperature of at least 100°C and / or at most 250°C; and / or the passivation conditions comprise a temperature ranging from 10°C above the boiling point of the vinyl aromatic compound to at most 20°C above the boiling point of the vinyl aromatic compound.

4. The cleaning process according to claim 1 or 2, characterized in that: The passivation conditions include a pressure in the range of 98 to 120 kPa; and / or the passivation step is performed under an atmosphere provided by one or more inert gases.

5. The cleaning process according to claim 1 or 2, characterized in that: At least one aromatic compound not containing a vinyl group is selected from benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, a benzene / ethylbenzene mixture, and any mixture thereof; and / or the one or more aliphatic saturated hydrocarbons are one or more selected from heptane, octane, nonane, decane, and any mixture thereof.

6. The cleaning process according to claim 1 or 2, characterized in that: Component A comprises at least one polymerization inhibitor selected from the group consisting of molten sulfur, phenyl-p-phenylenediamine, phenothiazine, tert-butylcatechol, diethylhydroxylamine, quinone methide, 2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)acetonitrile, 2,6-di-tert-butyl-4-(methoxymethylene)cyclohexa-2,5-dienone, 4-benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone, butylated hydroxytoluene, butylated hydroxyanisole, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, and any mixture thereof.

7. The cleaning process according to claim 6, characterized in that The polymerization inhibitor is selected from the group consisting of tert-butylcatechol, diethylhydroxylamine, and any mixture thereof.

8. The cleaning process according to claim 1 or 2, characterized in that: The stream comprising the passivation mixture which passes through at least one distillation column (1) during the passivation step is free of vinyl aromatic compounds.

9. The cleaning process according to claim 1 or 2, characterized in that: The vinyl aromatic compound is selected from the group consisting of styrene, α-methylstyrene, divinylbenzene, polyvinylbenzene, and any mixture thereof.

10. The cleaning process according to claim 9, characterized in that: The vinyl aromatic compound comprises styrene.

11. The cleaning process according to claim 9, characterized in that: The vinyl aromatic compound is styrene.

12. The cleaning process according to claim 1 or 2, characterized in that: The passivation step is performed during a time range of 1 to 24 hours.

13. The cleaning process according to claim 12, characterized in that: The passivation step is carried out during a time range of 5 to 15 hours.

14. The cleaning process according to claim 1 or 2, characterized in that: The step of cleaning the one or more distillation columns (1) comprises mechanical cleaning.

15. The cleaning process according to claim 14, characterized in that: The step of cleaning one or more distillation columns (1) is mechanical cleaning.

16. The cleaning process according to claim 14, characterized in that Said mechanical cleaning of the one or more distillation columns (1) comprises pressure washing of the one or more distillation columns (1).

17. Process for the purification of one or more vinyl aromatic compounds, comprising distillation of one or more vinyl aromatic compounds using a vinyl aromatic distillation unit, wherein the vinyl aromatic distillation unit comprises one or more distillation columns (1), the process comprising interrupting the distillation of the one or more vinyl aromatic compounds at least once to perform a cleaning process of the vinyl aromatic distillation unit, characterized in that The cleaning process of the vinyl aromatic compound distillation unit is according to any one of claims 1 to 16.

18. The purification process according to claim 17, characterized in that The one or more vinyl aromatic compounds comprises styrene.

19. The purification process according to claim 17, characterized in that The one or more vinyl aromatic compounds is styrene.

20. The purification process according to claim 17, wherein The cleaning process includes a passivation step performed at a higher temperature than the temperature at which the distillation is performed.

21. A process for the production of vinyl aromatic compounds from the corresponding saturated aromatic compounds, said process comprising the following steps: a) providing a catalytic component comprising one or more zeolites; b) providing a stream comprising saturated aromatic compounds; d) contacting the stream comprising saturated aromatic compounds with the catalytic component under dehydrogenation reaction conditions comprising a temperature of at least 550° C. to obtain a stream rich in vinyl aromatic compounds; e) subjecting said stream rich in vinyl aromatic compounds to said purification process of at least one vinyl aromatic compound according to any one of claims 17 to 20; f) optionally, recovering the vinyl aromatic compound from the vinyl aromatic compound-rich stream.

22. The production process according to claim 21, characterized in that The vinyl aromatic compound produced is styrene and the corresponding saturated aromatic compound is ethylbenzene.

23. The production process according to claim 22, characterized in that The stream provided in step (b) further comprises diethylbenzene, and the process further comprises the step (c) of removing the diethylbenzene from the stream provided in step (b) before contacting the stream with the catalyst component.

24. The production process according to any one of claims 21 to 23, characterized in that The one or more zeolites are selected from the FAU, MFI or MOR classes, and / or the catalytic component further comprises at least one transition metal.

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