WO2024125974A1

WO2024125974A1 - Process for manufacturing an aqueous hydrogen peroxide solution by using alkyl-cyclohexane carbonitrile solvents

Info

Publication number: WO2024125974A1
Application number: PCT/EP2023/082510
Authority: WO
Inventors: Pierre THILMANY; Frédéric GILLIN; Karol Lorent; François Dabeux
Original assignee: Solvay Sa
Priority date: 2022-12-12
Filing date: 2023-11-21
Publication date: 2024-06-20

Abstract

The present invention relates to the use of alkyl-cyclohexane carbonitrile solvents as polar solvents in a hydrogen peroxide production process using alkyl-anthraquinones and/or their tetrahydro form.

Description

Process for Manufacturing an Aqueous Hydrogen Peroxide Solution by using Alkyl-Cyclohexane Carbonitrile Solvents

This application claims priority filed on December 12, 2022 in Europe with Nr 22212867.0.

TECHNICAL FIELD

The present invention relates to the use of alkyl-cyclohexane carbonitrile solvents as polar solvents in a hydrogen peroxide production process using alkylanthraquinones and/or their tetrahydro form.

TECHNICAL BACKGROUND

Hydrogen peroxide is one of the most important inorganic chemicals to be produced worldwide. Its industrial applications include textile, pulp and paper bleaching, organic synthesis (propylene oxide), the manufacture of inorganic chemicals and detergents, environmental and other applications.

Synthesis of hydrogen peroxide is predominantly achieved by using the Riedl-Pfleiderer process (originally disclosed in U.S. Pat. Nos. 2,158,525 and 2,215,883), also called anthraquinone loop process or AO (auto-oxidation) process.

This well-known cyclic process makes use typically of the auto-oxidation of at least one alkylanthrahydroquinone and/or of at least one tetrahydroalkylanthrahydroquinone, most often 2-alkylanthrahydroquinone, to the corresponding alkylanthraquinone and/or tetrahydroalkylanthraquinone, which results in the production of hydrogen peroxide.

The first step of the AO process is the reduction in an organic solvent (generally a mixture of solvents) of the chosen quinone (alkylanthraquinone or tetrahydroalkylanthraquinone) into the corresponding hydroquinone (alkylanthrahydroquinone or tetrahydroalkylanthrahydroquinone) using hydrogen gas from any source and a catalyst. The mixture of organic solvents, hydroquinone and quinone species (working solution, WS) is then separated from the catalyst and the hydroquinone is oxidized using oxygen, air or a mixture of oxygen and other gases thus regenerating the quinone with simultaneous formation of hydrogen peroxide. The organic solvent of choice is typically a mixture of two types of solvents, one being a good solvent of the quinone derivative (generally a non-polar solvent for instance a mixture of aromatic compounds) and the other being a good solvent of the hydroquinone derivative (generally a polar solvent for instance a long chain alcohol or an ester or a tetraalkylurea or a trialkylphosphate). Hydrogen peroxide is then typically extracted with water and recovered in the form of a crude aqueous hydrogen peroxide solution, and the working solution with quinone species is returned to the hydrogenator to complete the loop.

The use of for example di-isobutylcarbinol (DBC) as polar solvent is namely described in Patent applications EP 529723, EP 965562 and EP 3052439 in the name of the Applicant. The use of a commercial mixture of aromatics sold under the brand Solvesso®-150 (CAS no. 64742-94-5) as non-polar solvent is also described in said patent applications. This mixture of aromatics is also known as Caromax, Shellsol, A150, Hydrosol, Indusol, Solvantar, Solvarex and others, depending on the supplier. It can advantageously be used in combination with sextate (methyl cyclohexyl acetate) as polar solvent (see namely US Patent 3617219).

Most of the AO processes use either 2-amylanthraquinone (AQ), 2- butylanthraquinone (BQ) or 2-ethylanthraquinone (EQ). Especially in the case of EQ, the productivity of the working solution is limited by the lack of solubility of the reduced form of ETQ (ETQH). It is namely so that EQ is largely and relatively quickly transformed in ETQ (the corresponding tetrahydroalkylanthraquinone) in the process. Practically, that ETQ is hydrogenated in ETQH to provide H2O2 after oxidation. The quantity of EQH produced is marginal in regards of ETQH. It means that the productivity of the process is directly proportional to the amount of ETQH produced. The reasoning is the same for a process working with AQ or BQ instead of EQ.

The hydrogenated quinone solubility issue is known from prior art and some attempts were made to solve it. In EP 3543208 or in WO 2021/048364 the Applicant of the present invention discloses the use of non-aromatic cyclic nitrile type solvents as polar solvents in an AO process, more specifically the use of cyclohexane carbonitriles substituted with 3 or 4 methyl groups for example 2,2,6-trimethyl-cyclohexane carbonitrile (C10A), 1,3,3-trimethyl-cyclohexane- carbonitrile (C10B), or 1,2,2,4-tetramethyl-cyclohexane carbonitrile (CUB) , in which the nitrile function is protected from chemical degradation. In such a nitrile solvent the hydrogenated quinone shows an improved solubility. Although some molecules of this kind are known, their market availability is currently only very limited and anyway too small to satisfy the needs of an industrial AO process.

Hence, there was still the need to provide polar solvents, in particular nitrile solvents, which ensure a sufficient or even improved solubility of the reduced (hydrogenated) quinone forms in the working solution, in order to increase the productivity of the AO process.

A further demand to polar solvents used in AO processes is that the polar solvents are less water extractable in order to reduce the content of total organic carbon (TOC) in final hydrogen peroxide solution, i.e. to provide a hydrogen peroxide solution having a sufficient purity.

Another problem of AO-processes known in the prior art is the formation of the undesired epoxide 2-ethyl-5,6,7,8-tetrahydro-8a,10a-epoxy-9,10- anthraquinone (ETEQ) during the oxidation of ETQH to obtain hydrogen peroxide. ETEQ does not participate significantly in the formation of hydrogen peroxide and reduces the amount of active ETQ, and thus the yield of hydrogen peroxide. The reasoning is the same for a process working with ATQ or BTQ instead of ETQ.

Consequently, the aim of the invention was to provide a nitrile solvent that is a suitable polar solvent for AO processes and by which the hydrogenated quinone of the working solution has a sufficient or even improved solubility in comparison to polar solvents usually used in AO processes, which facilitates the extraction of the produced hydrogen peroxide from the organic phase to the aqueous phase, and/or which minimize the formation rate of the epoxide 2-ethyl- 5,6,7, 8-tetrahydro-8a,10a-epoxy-9,10-anthraquinone (ETEQ), in order to produce a hydrogen peroxide solution in a sufficient quantity and which has an improved purity level, e.g. having a low total organic carbon (TOC) content.

SUMMARY OF THE INVENTION

The present invention relates to the use of a 1-alkyl-cyclohexane carbonitrile as polar solvent in a process for manufacturing an aqueous hydrogen peroxide solution using alkyl anthraquinones and/or tetrahydroalkylanthraquinones, in particular, to the use of the 1-alkyl- cyclohexane carbonitrile as polar solvent in a process for manufacturing an aqueous hydrogen peroxide solution comprising the following steps: - hydrogenating a working solution which comprises an alkylanthraquinone and/or a tetrahydroalkylantraquinone and a mixture of a non-polar organic solvent and a polar solvent;

- oxidizing the hydrogenated working solution to produce hydrogen peroxide; and

- isolating the hydrogen peroxide.

DETAILED DESCRIPTION OF THE INVENTION

Before the process of the invention will be described in detail, it is to be understood that this invention is not limited to specific process conditions described herein, since such conditions may, of course, vary.

It is also to be understood that the terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compound" means one compound or more than one compound.

The terms "containing", "contains" and "contained of as used herein are synonymous with "including", "includes" or " comprising", "comprises", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or process steps. It will be appreciated that the terms “containing”, “contains”, "comprising", "comprises" and "comprised of' as used herein comprise the terms "consisting of', "consists" and "consists of.

Throughout this application, the term "about" is used to indicate that a value includes the standard deviation of error for the device or method being employed to determine the value.

As used herein, the term “average” refers to number average unless indicated otherwise.

As used herein, the terms “% by weight”, “wt.- %”, “weight percentage”, or “percentage by weight” are used interchangeably. The same applies to the terms “% by volume”, “vol.- %”, “vol. percentage”, or “percentage by volume”, or “% by mol”, “mol- %”, “mol percentage”, or “percentage by mol”.

The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

All references cited in the present specification are hereby incorporated by reference in their entirety. In particular, the teachings of all references herein specifically referred to are incorporated by reference.

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

In the following passages, different alternatives, embodiments and variants of the invention are defined in more detail. Each alternative and embodiment so defined may be combined with any other alternative and embodiment, and this for each variant unless clearly indicated to the contrary or clearly incompatible when the value range of a same parameter is disjoined. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

Furthermore, the particular features, structures or characteristics described in present description may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and from different embodiments, as would be understood by those in the art.

The invention relates to a process for manufacturing an aqueous hydrogen peroxide solution comprising the following steps:

- hydrogenating a working solution which comprises an alkylanthraquinone and/or a tetrahydroalkylantraquinone and a mixture of a non-polar organic solvent and a polar solvent;

- oxidizing the hydrogenated working solution to produce hydrogen peroxide; and

- isolating the hydrogen peroxide, wherein the polar solvent is a 1-alkyl-cyclohexane carbonitrile.

Hence, the process according to the invention is an AO process. In the AO process of the invention, which is preferably a continuous process operated in loop, a working solution is used which is hence preferably circulated in a loop through the hydrogenation, oxidation and extraction steps.

The term "alkylanthraquinone" is intended to denote a 9, 10-anthraquinone substituted in position 1, 2 or 3 with at least one alkyl side chain of linear or branched aliphatic type comprising at least one carbon atom. Usually, these alkyl chains comprise less than 9 carbon atoms and, preferably, less than 6 carbon atoms. Examples of such alkylanthraquinones are ethylanthraquinones like 2- ethylanthraquinone (EQ), 2-isopropylanthraquinone, 2-sec- and 2-tert- butylanthraquinone (BQ), 1,3-, 2,3-, 1,4- and 2,7-dimethyl-anthraquinone, amylanthraquinones (AQ) like 2-sec-isoamylanthraquinone and 2-tert- amylanthraquinone and mixtures of these quinones.

The term "tetrahydroalkylanthraquinone" is intended to denote the tetrahydro-9, 10-anthraquinones corresponding to the 9, 10-alkylanthraquinones specified above. Hence, for EQ and AQ, they are respectively designated by ETQ and ATQ, their reduced forms (tetrahydroalkylanthrahydroquinones) being respectively ETQH and ATQH.

Preferably, an AQ or EQ or a mixture of both is used.

In order to ensure that the reduced (hydrogenated) quinone forms are sufficiently or even better solved by the polar solvent of the invention than the ones usually used in the prior art, the polar solvent according to the teaching of the invention is a 1-alkyl-cyclohexane carbonitrile, which has the following general formula (Formula I), wherein R is an alkyl-group:

I

According to the invention, it is preferred that the alkyl-group comprises at least 1 carbon atom, more preferably at least 2, 3, 4, 5, 6 or more carbon atoms. The alkyl-group usually contains at most 15 carbon atoms, often at most 13 carbon atoms, for instance at most 11 carbon atoms, preferably at most 9 or 7 carbon atoms. In a preferred embodiment, the number of carbon atoms of the alkyl group of the 1-alkyl-cyclohexane carbonitrile used in the process of the invention is between 1 and 15 or between 1 and 10 carbon atoms. Most preferred, the number of carbon atoms is between 1 and 7 carbon atoms.

The alkyl group of the 1-alkyl-cyclohexane carbonitrile can be linear, branched or a cyclo-alkyl group, like methyl-, ethyl-, propyl-, butyl-, pentyl-, hexyl-, cyclohexyl- cyclohexyl-ethyl, iso-propyl, iso-pentyl, methyl-butyl, methyl-pentyl, etc., and isomers thereof like for example l-(l-methyl-butyl)- cyclohexane carbonitrile or l-(2-methyl-butyl)-cyclohexane carbonitrile. According to the invention, the carbon of the alkyl group which is bonded to the carbon at the alpha position of the nitrile group can be a primary or a secondary carbon.

In particular it is preferred that the 1-alkyl-cyclohexane carbonitrile according to the invention is selected from the group consisting of I -w-butyl- cyclohexane carbonitrile (CUM), l-«-pentyl-cyclohexane-carbonitrile (C12C), I -/.s -pen ty I -cyclohexane carbonitrile (Cl 2D), and combinations thereof, as depicted below:

In a particular preferred embodiment the 1-alkyl-cycolhexane carbonitrile is CllM or C12D.

The 1-alkyl-cyclohexane carbonitrile used in the AO-process of the invention can be produced by any method known in the art.

In particular, according to the invention, the 1-alkyl-cyclohexane carbonitrile is produced by deprotonating cyclohexane carbonitrile at the alpha position of the nitrile function with the aid of freshly prepared lithium diisopropylamide (LDA). The thus obtained corresponding anion is then alkylated with an alkyl halide, preferably with an alkyl bromide or alkyl iodide to obtain the 1-alkyl-cyclohexane carbonitrile. The LDA is usually formed by treating a cooled (cooled to between -78 and 30 °C) mixture of tetrahydrofuran and diisopropylamine with /7-butyllithium. Instead of the freshly produced LDA in the production process for the 1 -alkyl-cycolhexane carbonitrile sodium amide can be used in order to facilitate the recycling of the amine. Suitable methods for producing the 1-alkyl-cyclohexane carbonitrile used in the AO process of the invention are described for example in the scientific publication of O. Gbadebo et al., Eur. J. Org. Chem, 2018, pages 7037-7045; C.H. Tilford et al., J. Am. Chem. Soc, 1949, 71, pages 1705-1709; or Tang et al. Chem. Sci, 2018, 9, pages 6374-6378.

According to the invention, the working solution of the AO process comprises at least 15 wt.-%, at least 25 wt.-%, preferably at least 30 wt.-%, more preferably at least 40 wt.-% of the above described 1-alkyl-cyclohexane carbonitrile, based on the total weight of the working solution.

In order to be able to also solubilize the quinone, the polarity of the solvent mixture is preferably not too high. Hence, there is preferably at least 30 wt.-% of non-polar solvent in the organic solvent mixture, and more preferably at least 40 wt. -%. Generally, there is not more than 80 wt.-% of this non-polar solvent, in the organic solvent mixture.

The non-polar solvent preferably is an aromatic solvent or a mixture of aromatic solvents. Aromatic solvents are for instance selected from benzene, toluene, xylene, tert-butylbenzene, trimethylbenzene, tetramethylbenzene, naphthalene, methylnaphthalene mixtures of polyalkylated benzenes, and mixtures thereof. The commercially available aromatic hydrocarbon solvent of type 150 from the Solvesso® series (or equivalent from other supplier) gives good results. S-150 (Solvesso®-! 50; CAS no. 64742-94-5) is known as an aromatic solvent of high aromatics which offer high solvency and controlled evaporation characteristics that make them excellent for use in many industrial applications and in particular as process fluids. The Solvesso® aromatic hydrocarbons are available in three boiling ranges with varying volatility, e.g. with a distillation range of 165-181 °C, of 182-207 °C or 232-295 °C. They may be obtained also naphthalene reduced or as ultra-low naphthalene grades. Solvesso® 150 (S-150) is characterized as follows: distillation range of 182-207 °C; flash point of 64 °C; aromatic content of greater than 99 % by wt; aniline point of 15 °C; density of 0.900 at 15 °C; and an evaporation rate (n-butyl acetate = 100) of 5.3. The hydrogenation reaction of the AO process according to the invention takes place in the presence of a catalyst (like for instance the one object of WO 2015/049327 in the name of the Applicant) and as for instance described in WO 2010/139728 also in the name of the applicant (the content of both references being incorporated by reference in the present application). Typically, the hydrogenation is conducted at a temperature of at least 45 °C and preferably up to 120 °C, more preferably up to 95 °C or even up to 80 °C only. Also typically, the hydrogenation is conducted at a pressure of from 0.2 to 5 bar. Hydrogen is typically fed into the vessel at a rate of from 650 to 750 normal m³ per ton of hydrogen peroxide to be produced.

The oxidation step of the AO process of the invention may take place in a conventional manner as known for AO processes. Typical oxidation reactors known for the anthraquinone cyclic process can be used for the oxidation. Bubble reactors, through which the oxy gen-containing gas and the working solution are passed co-currently or counter-currently, are frequently used. The bubble reactors can be free from internal devices or preferably contain internal devices in the form of packing or sieve plates. Oxidation can be performed at a temperature in the range from 30 to 70 °C, particularly at 40 to 60 °C. Oxidation is normally performed with an excess of oxygen, so that preferably over 90%, particularly over 95%, of the alkyl anthrahydroquinones contained in the working solution in hydroquinone form are converted to the quinone form.

After the oxidation, during the purification step, the hydrogen peroxide formed is separated from the working solution generally by means of an extraction step, for example using water, the hydrogen peroxide being recovered in the form of a crude aqueous hydrogen peroxide solution. The working solution leaving the extraction step is then recycled into the hydrogenation step in order to recommence the hydrogen peroxide production cycle, eventually after having been treated/regenerated.

In a preferred embodiment, after its extraction, the crude aqueous hydrogen peroxide solution is washed several times i.e., at least two times consecutively or even more times as required to reduce the content of impurities at a desired level, for example, the crude aqueous hydrogen peroxide solution is washed with an organic solvent, which is intended to reduce the content of impurities in the aqueous hydrogen peroxide solution as disclosed for example in GB 841323 A. This washing can consist, for example, in extracting impurities in the crude aqueous hydrogen peroxide solution by means of an organic solvent in apparatuses such as centrifugal extractors or liquid/liquid extraction columns, for example, operating counter-current wise. Liquid/liquid extraction columns are preferred. Among the liquid/liquid extraction columns, columns with random or structured packing (like Pall rings for instance) or perforated plates are preferred. The formers are especially preferred.

In a preferred embodiment, a chelating agent can be added to the washing solvent in order to reduce the content of given metals. For instance, an organophosphorus chelating agent can be added to the organic solvent as described in the above captioned patent application EP 3052439 in the name of the Applicant, the content of which is incorporated by reference in the present application.

The expression "crude aqueous hydrogen peroxide solution" is intended to denote the solutions obtained directly from a hydrogen peroxide synthesis step or from a hydrogen peroxide extraction step or from a storage unit. The crude aqueous hydrogen peroxide solution can have undergone one or more treatments to separate out impurities prior to the washing operation according to the process of the invention. It typically has a H2O2 concentration within the range of 30- 50% by weight.

By using the above described 1-alkyl-cyclohexane carbonitrile as polar solvent in the AO process of the invention, it is possible to achieve a solubility of the hydrogenated quinone of the working solution, which is sufficient, or comparable or even better than the one obtained by using sextate or diisobutylcarbinol (DBC), which are usually used as polar solvents in an AO process. The maximum solubility of a hydrogenated quinone (QH) in a solvent mixture is directly correlated with the productivity of the working solution. The higher is QH solubility, the higher will be theoretically quantity of hydrogen peroxide achievable per kg ofWS (productivity).

The degree of QH solubility can be indicated as test level (TL), which refers to the produced amount of H2O2 per kg working solution (g tLCh/kg of WS) at a specific temperature for a specific concentration of the polar solvent. According to the invention, it is preferred that at 70 °C and a polar solvent concentration in the working solution of 15 wt.-% the test level (TL) is at least 6.0, preferably at least 6.5 g FLCh/kg WS. In a further preferred embodiment, at 70 °C and a polar solvent concentration of 35 wt.-% TL is at least 10.0, preferably at least 11.0. In particular, the use of the 1-alkyl-cyclohexane carbonitrile of the invention as polar solvent in the AO process results into a better extraction of hydrogen peroxide from the organic phase to the aqueous phase in comparison to an AO process, wherein as polar solvent for example sextate, DBC or another known cyclohexane carbonitrile solvent, for example 2,2,6-trimethyl- cyclohexane carbonitrile (C10A), 1,3,3-trimethyl-cyclohexane-carbonitrile (C10B) or 1,2,2,4-tetramethyl-cyclohexane carbonitrile (CUB), is used. Indeed, the hydrogen peroxide concentration in organic phase is lower when using the 1- alkyl-cyclohexane carbonitrile instead of the other solvents. This effect can be indicated for example by the kb ratio of the solvent. The determination of the kb ratio according to the invention is described below in the examples. The kb ratio of the 1-alkyl-cyclohexane carbonitrile solvent is higher than of sextate, DBC, 2,2,6-trimethyl-cyclohexane carbonitrile (C10A), 1,3,3-trimethyl-cyclohexane- carbonitrile (Cl OB) or CUB. In particular, it is preferred that at a concentration of 30 wt.-% of the polar solvent in the mixture of polar solvent and non-polar solvent the kb ratio of 1-alkyl-cyclohexane-carbonitrile solvent is at least 200, at least 300, or at least 400.

Furthermore, as mentioned above, it is state of the art that the epoxide 2- ethyl-5,6,7,8-tetrahydro-8a,10a-epoxy-9,10-anthraquinone (ETEQ) is an undesired by-product in the AO process obtained during the oxidation of 2-ethyl- 5,6,7, 8-tetrahydro-9,10-anthrahydroquinone. Consequently, it is desired to minimize its formation rate. As demonstrated in the examples, by using 1-alkyl- cyclohexane carbonitrile of the invention instead of for example DBC the ETEQ formation rate can be minimized. According to the invention it is preferred that the epoxide formation rate (g ETEQ/kg of total H2O2 produced) is less than 4.0, more preferred less than 3.8, even more preferred less than 3.5.

It has been further found out that due to the use of the 1-alkyl-cyclohexane carbonitrile solvent in the AO process of the invention, the TOC content in aqueous hydrogen peroxide is lower than the TOC content of an aqueous hydrogen peroxide by using sextate or DBC as polar solvents. In particular the TOC content of the aqueous hydrogen peroxide solution by using the 1-alkyl- cyclohexane carbonitrile of the invention as polar solvent in the AO process is lower than 400 ppm, lower than 300 ppm, lower than 200, lower than 100 ppm measured in a test mimicking the final stage of the water extraction of hydrogen peroxide from oxidized working solution of an AO process and described in the examples below. Hence, a higher purity level of the hydrogen peroxide solution can be obtained.

The 1-alkyl-cyclohexane carbonitrile solvent is suitable for the manufacture of hydrogen peroxide by the AO process wherein said process has a production capacity of hydrogen peroxide of up to 300 or 100 kilo tons per year (ktpa), i.e. the solvents are suitable for large scale AO-processes. Furthermore, the solvents are also suitable for small to medium scale AO-processes operating with a production capacity of hydrogen peroxide of up to 50 kilo tons per year (ktpa), and more preferably with a production capacity of hydrogen peroxide of up to 35 kilo tons per year (ktpa), and in particular with a production capacity of hydrogen peroxide of up to 20 kilo tons per year (ktpa). The dimension ktpa (kilo tons per annum) relates to metric tons.

A particular advantage of such scales AO process is that the hydrogen peroxide can be manufactured in a plant that may be located at any, even remote, industrial end user site and the solvents of the invention are therefore especially suitable. It is namely so that since the QH solubility and the kb ratio are more favourable with less amount of polar solvent, less emulsion is observed in the process and a purer H2O2 solution can be obtained (namely containing less TOC) and this for a longer period of time compared to when solvents known from prior art are used.

In a preferred sub-embodiment of the invention, the working solution is regenerated either continuously or intermittently, based on the results of a quality control, regeneration meaning conversion of certain degradants, like epoxy or anthrone derivatives, back into useful quinones. Here also, the 1-alkyl- cyclohexane carbonitrile of the invention is favourable because the amount of epoxide to be regenerated is reduced, the quality of the H2O2 solution can be maintained within the specifications namely in terms of TOC as mentioned above for a longer period of time.

The present invention is further illustrated by the following examples. It should be understood that the following examples are for illustration purposes only, and are not used to limit the present invention thereto.

EXAMPLES

Abbreviations AO: autooxidation

DBC: di-isobutylcarbinol

CUM: 1 -/7-butyl -cyclohexane carbonitrile

C12C: l-77-pentyl-cyclohexane carbonitrile

Cl 2D: l-zso-pentyl-cyclohexane carbonitrile

CUB: 1,2,2,4-tetramethyl-cyclohexane carbonitrile

C 10 A: 2, 2, 6-trimethy 1 -cy cl ohexane-carbonitril e

C10B: 1,3,3-trimethyl-cyclohexane-carbonitrile

LDA: lithium diisopropylamide

ETQ: 2-ethyl-5,6,7,8-tetrahydro-9,10-anthraquinone

ETEQ: 2-ethyl-5,6,7,8-tetrahydro-8a,10a-epoxy-9,10-anthraquinone

GC: Gas chromatography

NMR: Nuclear magnetic resonance

OP: organic phase r.t: room temperature

TOC: total organic carbon

WS: working solution

Production of the 1-alkyl-cvclohexane carbonitrile

The 1-alkyl-cy cohexane carbonitrile was produced according to the following equation:

wherein R was a w-butyl-. a w-pentyl- or a /.s -pentyl-group.

In particular, a 10 L double-jacketed batch reactor equipped with a bottom valve, a mechanical stirrer, a temperature probe and a condenser fitted with a nitrogen-inlet and a gas-outlet was purged with nitrogen (N2 flow for 16 hours) before being charged with diisopropylamine (202.39 g, 2.00 mol, 1.05 equiv.) and THF (3.8 L). A slight flow of nitrogen was maintained during the reaction. The resulting solution was cooled to -30 °C before adding a 2.5 M solution of n- butyllithium in hexane (800 mL, 2.00 mol, 1.05 equiv.) dropwise over 1 hour. The reaction mixture was next stirred at -30 °C for 1 hour before adding cyclohexane carbonitrile (207.95 g, 1.91 mol, 1.00 equiv.) dropwise over 30 minutes. The solution was then stirred at -30 °C for an additional 30 minutes before adding the alkyl bromide (2.10 mol, 1.10 equiv.) dropwise over 1 hour. The reaction mixture was next allowed to warm up to room temperature and was stirred overnight (18 hours). A 30 L double-jacketed batch reactor equipped with a bottom valve and a mechanical stirrer was next charged with water (4.5 L) and the reaction mixture was subsequently transferred with a pump from the 10 L reactor to the stirred 30 L reactor. Ethyl acetate (6.5 L) was next added and the resulting biphasic mixture was thoroughly stirred for 2 minutes. The layers were then separated and the organic layer was successively washed thrice with water (3x4.5 L), once with a saturated aqueous solution of NaHCCh (4.5 L) and once with brine (4.5 L). The organic layer was next dried over MgSC>4, filtered and concentrated under reduced pressure before being filtered to eliminate any residual solids. The crude reaction mixture was finally purified by vacuum distillation to afford the desired 1-alkyl-cyclohexanecarbonitrile as a colourless oil (CUM: Boiling point: 93 °C at 8.4 mbar; C12C: Boiling point: 116 °C at 10 mbar; C12D: Boiling point: 117 °C at 18 mbar). The yield for the produced 1- alkyl-cyclohexane-carbonitrile was estimated based on NMR on crude mixture and was equal to: 98% for Cl IM; 85% for C12C; and 98% for C12D.

To facilitate the recycling of amine, the use of sodium amide instead of lithium diisopropylamide was tested and gave similar yield as described in literature (C.H. Tilford et al., J. Am. Chem. Soc, 1949, 71, pages 1705- 1709).

AO Process

The AO process was carried out in a lab pilot. Therefore, the pilot was composed of a hydrogenation reactor with a slurry of palladium catalyst, an oxidation column and an extraction column. It was run with a closed loop of organic working solution composed initially by a mixture of alkylated anthraquinone (ethyl anthraquinone and ethyltetrahydroanthraquinone), Solvesso™ 150 and as polar solvent CUM, C12D, C12C, CUB, C10A, C10B, sextate or DBC. It was monitored periodically to evaluate the formation of the epoxide ETEQ with the total production of hydrogen peroxide.

Determination of QH solubility in working solutions

The determination of the QH solubility was performed on synthetic

EQ/ETQ working solutions. These quinones mixed in the tested solvents have been hydrogenated to a fixed level and cooled down successively to 4 different temperatures before the measurements (min 3 hours to stabilize the system between each measurement). The conditions applied for these tests were

EQ concentration 100g/kg

ETQ concentration 140 g/kg

Polar solvent variable (*)

Level of hydrogenation 10.8 NI H₂/kg WS (~ 116g of QH/kg of WS or a TL (Test Level) of 16.3g of ELCh/kg WS (= maximum theoretical value of TL if all QH is dissolved)

Temperature of hydrogenation 75 °C

The temperature of precipitation is indicated as temperature at which QH was measured. The QH solubility have been determined at 70 °C, 65, 60 and 55 °C. The theoretical values designated by the term "Test Level g H2O 2 kg WS) ” were calculated as follows:

1 mole (240g) ETQH (which actually is QH in the examples) per kg of WS will produce 1 mole (34g) of H2O2 per kg of WS.

Hence, the level in the examples equals: 34*QH/240.

Estimation of kb ratio from equilibration between aqueous hydrogen peroxide and organic solutions

An aqueous hydrogen peroxide solution (25 ml, 35 wt-%) and an organic solution (25 ml) prepared from Solvesso™ 150 and a polar solvent were stirred together in a flask for 30 minutes. After decantation and separation of phases by centrifugation, the hydrogen peroxide content was determined in organic phase using suitable analytical method and expressed in g per kg of phase. The hydrogen peroxide concentration in aqueous phase is equal before and after equilibration. The water concentration in aqueous phase (AP) and the total solvent concentration in organic phase (OP) both expressed in g per kg of phase were calculated by following formulas:

| H₂O | ^AP = 1000 - [H₂O₂]^AP

[Total solvent]^OP = 1000 - [H₂O₂]^OP

The kb ratio was calculated as:

[Total solvent]⁰¹* }

Formation rate of ETEO

The epoxide formation rate observed in AO process lab pilot was determined by measuring periodically (minimum 5 consecutive measurements spaced out in time at regular intervals) the concentration of ETEQ and hydrogen peroxide in the working solution obtained after oxidation. The concentration of ETEQ and H₂O₂ were measured respectively by high performance liquid chromatography and spectrophotometry using potassium titanium (IV) oxalate. The concentrations of these species were expressed in g of species per kg of working solution.

The total amount of H₂O₂ produced after one specified time (M^l) was obtained by following formula and expressed in kg :

M^t= F * ([H202]/1000) * At + M^t where F is the flow of working solution in kg per hour, [H₂O₂] is the concentration of H₂O₂ in working solution in g per kg, At is the elapsed time (expressed in hour) between time t and the time t-1 of the previous measurement and M^t is the total amount of H₂O₂ expressed in kg and produced at previous measurement at time t-1.

The total amount of H₂O₂ produced per kg of working solution after one specified time (M) is calculated by following formula and expressed in kg of total H₂O₂ produced per kg of working solution :

M = M^l/ m^ws where m^ws is the mass of working solution expressed in kg.

It was observed that the relationship between the ETEQ concentrations ([ETEQ]) and the total amounts of H₂O₂ (M) was linear with a slope corresponding to the epoxide formation rate expressed in g of ETEQ per kg of total H2O2 produced.

Determination of TOC content

The TOC content was measured in a test by mimicking the final stage of the water extraction of hydrogen peroxide from oxidized working solution of the AO process.

Therefore, a 50 ml penicillin flask equipped with a magnetic stir bar was charged with 20 g of aqueous hydrogen peroxide solution (45 wt.-%), 5 g of Solvesso™ 150 and 5 g of polar solvent. The resulting mixture was stirred for 10 minutes at 650 rpm and 60°C in the closed flask. The mixture was decanted at room temperature for 30 minutes. The tubing of the total organic carbon (TOC) analyser was introduced in the aqueous phase. The total carbon (TC) measurement was repeated three times and is equal to the TOC.

Results

1. QH solubility

In Figures 1 to 4 the QH solubilities by using CUM, C12C, C12D, sextate or DBC as polar solvent in the AO process at a temperature of 70 °C, 65 °C, 60 °C and 55 °C are depicted.

Based on curve it can be observed that the QH solubility of the solvents Cl IM and Cl 2D are slightly lower or similar or even better than sextate or DBC depending on the solvent concentration and temperature.

2. Kb ratio

In Table 1 and in Figures 5 and 6 the kb ratio by using Cl IM, C12D, sextate, DBC or C10A, C10B, Cl IB as polar solvent in the AO process are depicted.

As can be seen from the graphs, the kb ratio is higher when using Cl IM and C12D instead of sextate, DBC or C10A, C10B, Cl IB. It means that the extraction of hydrogen peroxide from organic phase to aqueous phase is better with Cl IM and Cl 2D. Indeed, hydrogen peroxide concentration in organic phase is lower when using Cl IM and Cl 2D instead of the two other solvents. Similar results as obtained by using Cl 2D are expected when using C12C which has also a non-sterically hindered pentyl group. They are observed for example with QH solubility.

Table 1

3. Formation rate of ETEQ

Table 2 As can be seen from Table 2, Cl IM and C12D are beter than DBC and comparable with sextate. As indicted with respect to the kb ratio, similar results as obtained by using Cl 2D are expected when using C12C.

4. TOC measurement

Table 3

Based on the results of Table 3, it can be observed that the TOC value in aqueous hydrogen peroxide is quite lower with the 1-alkyl-cyclohexane carbonitrile solvent according to the invention than with the sextate or DBC or Cl OB which means that the 1-alkyl-cyclohexane carbonitriles are less soluble in aqueous hydrogen peroxide and hence allows reaching a higher purity level of hydrogen peroxide solution. As indicted with respect to the kb ratio, similar results as obtained by using Cl 2D are expected when using C12C.

Claims

C L A I M S

1. A process for manufacturing an aqueous hydrogen peroxide solution comprising the following steps:

- oxidizing the hydrogenated working solution to produce hydrogen peroxide; and

2. The process according to claim 1, wherein the process is a continuous process in which the working solution is circulated in a loop through the hydrogenation, oxidation and extraction step.

3. The process according to claim 1 or 2, wherein the alkyl anthraquinone is chosen from the group consisting of ethylanthraquinones like 2- ethylanthraquinone (EQ), 2-isopropylanthraquinone, 2-sec- and 2-tert- butylanthraquinone (BQ), 1,3-, 2,3-, 1,4- and 2,7-dimethyl-anthraquinone, amylanthraquinones (AQ) like 2-sec-isoamylanthraquinone and 2-tert- amylanthraquinone and mixtures of these quinones.

4. The process according to claim 3, wherein the quinone is EQ, BQ or AQ, preferably AQ or EQ.

5. The process according to any one of the preceding claims, wherein the alkyl group of the 1-alkyl-cyclohexane carbonitrile comprises from 1 to 15 carbon atoms.

6. The process according to claim 5, wherein the 1-alkyl-cyclohexane carbonitrile is selected from the group consisting of I -w-butyl -cyclohexane carbonitrile (CUM), l-w-pentyl-cyclohexane carbonitrile (C12C), 1 -Ao-pen tyl- cyclohexane carbonitrile (Cl 2D), and combinations thereof.

7. The process according to any one of the preceding claims, wherein the working solution comprises at least 15 wt.-% of the 1 -alkyl-cyclohexane carbonitrile, based on the total weight of the working solution.

8. The process according to any one of the preceding claims, wherein the non-polar organic solvent is an aromatic solvent or a mixture of aromatic solvents.

9. The process according to any one of the preceding claims, wherein the aqueous hydrogen peroxide solution has a total carbon organic (TOC) content of lower than 400 ppm, measured in the aqueous phase obtained in a test mimicking the final stage of the water extraction of hydrogen peroxide from oxidized working solution of the AO-process.

10. The process according to any one of the preceding claims, wherein at a concentration of 30 wt.-% of the 1 -alkyl-cyclohexane carbonitrile, based on the total weight of the mixture of the non-polar organic solvent and the 1 -alkyl- cyclohexane carbonitrile, the kb ratio of the 1 -alkyl-cyclohexane carbonitrile is at least 200.

11. The process according to any one of the preceding claims, wherein the epoxide formation rate is obtained as described in the specification and is below 4.0.

12. Use of a 1 -alkyl-cyclohexane carbonitrile as polar solvent in a process for manufacturing an aqueous hydrogen peroxide solution using alkyl anthraquinones and/or tetrahydroalkylanthraquinones.

13. The use of the 1 -alkyl-cyclohexane carbonitrile according to claim 12, wherein the alkyl group of the 1 -alkyl-cyclohexane carbonitrile comprises at least 3 carbon atoms, preferably the 1 -alkyl-cyclohexane carbonitrile is selected from the group consisting of l-w-butyl-cyclohexane carbonitrile (CUM), l -n- pentyl-cyclohexane carbonitrile (C12C), 1-Ao-pentyl-cyclohexane carbonitrile (Cl 2D), and combinations thereof.

14. The use of the 1-alkyl-cyclohexane carbonitrile according to claim 12 or 13, wherein the process for manufacturing an aqueous hydrogen peroxide solution is a process as defined in claims 1 to 11.