EP3164210A1 - Novel supported anthraquinonic catalysts and uses of same for kraft cooking - Google Patents

Abstract

The present invention relates to a supported anthraquinonic catalyst obtainable by radical polymerization of a reaction mixture containing: - styrene; - at least one initiator generating free radicals; - at least one at least difunctional crosslinking agent; - at least one expanding agent; and - at least one anthraquinonic styrene monomer having Formula (I), wherein n is a whole number from 1 to 5.

Description

 NOVEL SUPPORTED ANTHRAQUINONIC CATALYSTS AND THEIR USES FOR KRAFT COOKING

The present invention relates to novel supported anthraquinone catalysts, processes for their preparation, and their uses, in particular for kraft cooking of wood chips.

The economic impact of the forest - wood - paper sector is important, particularly in France in the Aquitaine region. In this sector, the paper industry, and more precisely the industries producing cellulosic pulps, constitute a vital economic sector.

 The largest pulp production uses the kraft process as a cellulose extraction method. Based on the use of sodium hydroxide solution and sodium sulphide, the kraft process is today the universal process for the production of chemical pulp. This has many advantages such as a low level of residual lignin and good mechanical and physico-chemical properties of the fibers. This process is also self-sufficient in energy and allows a reduction in reagent consumption with regeneration of inorganic reagents.

 Despite these advantages, the kraft process has significant disadvantages: low yields (about 45%) because some hemicelluloses and cellulose is degraded; formation of volatile sulfur derivatives, responsible for olfactory nuisances ....

 Environmental constraints require the paper industry to move towards a cleaner and safer chemistry that remains competitive (depletion of forest resources, pollution harmful to humans and the environment). Sustainable development efforts have already been made, such as forest planting, paper and cardboard recycling, the use of biomass and the bio-refinery concept, process improvement, etc.

In particular, the use of anthraquinone in catalytic amount has proved to be very effective in improving soda and kraft cooking. It allows both to improve the yield of cellulosic pulp and to speed up delignification. Despite this efficacy, the non-regeneration of anthraquinone and its high cost are currently unfavorable for widespread industrial use. There is therefore a need for effective catalysts for cooking wood kraft, which can be recycled.

The present invention therefore aims to provide new anthraquinone catalysts especially for kraft cooking wood.

 The present invention also aims to provide new fully recyclable anthraquinone catalysts.

 The present invention also aims to provide effective anthraquinone catalysts for wood kraft cooking and to improve the efficiency of this process.

Thus, the present invention relates to a supported anthraquinone catalyst, comprising a polymeric support containing on the surface at least one anthraquinone unit, said supported anthraquinone catalyst being capable of being obtained by radical polymerization of a reaction mixture comprising:

 styrene;

 at least one initiator generating free radicals;

at least one at least one difunctional crosslinking agent selected from the group consisting of divinylbenzene, ethylene glycol dimethacrylate, di (ethylene glycol) dimethacrylate, compounds comprising an alkyl chain, interrupted by one or more groups; (CH ₂ ) _k O) _m with 2 <k <5, 1 <m <3, substituted in position a or ω by at least one acrylate, methacrylate, vinyl or styrenic function, and mixtures thereof;

 at least one porogenic agent; and

 at least one anthraquinone styrene monomer of formula (I)

in which n is an integer ranging from 1 to 5. The present invention also relates to a process for the preparation of a supported anthraquinone catalyst as defined above, by radical polymerization of a reaction mixture comprising:

 styrene;

 at least one initiator generating free radicals;

 at least one at least difunctional crosslinking agent as defined above;

 at least one porogenic agent; and

 at least one anthraquinone styrenic monomer of formula (I) as defined above.

Radical polymerization

 The anthraquinone catalyst according to the invention is obtained according to a process well known to those skilled in the art, radical polymerization. This process is carried out by growth and propagation of macroradicals. These macroradicals, with a very short life time, recombine irreversibly by coupling or disproportionation.

 Such a process consists of a chain polymerization which involves radicals as active species. It includes priming, propagation, termination and chain transfer reactions.

The first step of ^such a method consists in the generation of so-called primary radicals using a free radical initiator as defined below.

 According to one embodiment, the method used may be a so-called "controlled" or "living" radical polymerization process, which is also a process well known to those skilled in the art. Among these well-known methods of controlled radical polymerization, mention may be made, for example, of the RAFT (reversible addition-fragmentation chain transfer) or NMRP (nitroxide-controlled radical polymerization) methods.

According to one embodiment, the polymerization is carried out in a mold by simple heating. The reaction mixture is as defined above and comprises one or more monomers including a crosslinking agent, one or more porogens and an initiator. At the end of the polymerization, the catalyst is obtained in the form of a monolith which is purified with a more volatile solvent ^to remove the heavier blowing agents and reagents unreacted.

Monomers used to prepare the catalysts include styrene. According to one embodiment, the above-mentioned reaction mixture comprises from 10% to 30% by weight of styrene relative to the total weight of the reaction mixture. Preferably, the weight content of styrene in the reaction mixture is between 15% and 25%, and preferably between 20% and 25%.

ignitor

 As indicated above, the polymerization process is initiated by addition of a polymerization initiator (or initiator). These initiators are called "free radical initiators".

 Among these initiators, mention may be made of thermal initiators, redox or initiators for controlled radical polymerization.

 The thermal initiators are chosen from initiators that generate the radicals by thermal decomposition. Examples include organic peresters (t-butylperoxypivalate, t-amylperoxypivalate, t-butylperoxy-2-ethylhexanoate, etc.); organic compounds of the azo type, for example azobisamidinopropane hydrochloride, azobisisobutyronitrile, azobis (2,4-dimethylvaleronitrile, etc.); inorganic and organic peroxides, for example hydrogen peroxide, benzoyl peroxide and butyl peroxide.

 According to an advantageous embodiment of the invention, the initiator used is an organic peroxide or an organic compound of azo type. Such an initiator is preferably benzoyl peroxide or azobisisobutyronitrile (AIBN), and is preferably AIBN.

 Among the initiators, mention may also be made of redox initiators, for which the production of radicals results from a redox reaction. Mention may in particular be made of redox initiator systems, such as those comprising oxidizing agents, such as binders (especially ammonium or alkali metal persulfates, etc.); chlorates and bromates (including inorganic or organic chlorates and / or bromates); reducing agents such as sulphites and bisulphites (including inorganic and / or organic sulphites or bisulfites); oxalic acid and ascorbic acid as well as mixtures of two or more of these compounds.

According to one embodiment, the above-mentioned reaction mixture comprises from 0.1% to 5% by weight of initiator relative to the total weight of the reaction mixture. Preferably, the content by weight of initiator in the reaction mixture is between 0.5% and 3%. Crosslinking agent

 As indicated above, the reaction medium also comprises at least one crosslinking agent.

 This crosslinking agent is an at least difunctional agent.

According to one embodiment, this crosslinking agent is a compound comprising an alkyl chain interrupted by one or more groups - ((CH ₂ ) _k O) _m with 2 <k <5, 1 <m <3, the (s) said group (s) being substituted in the α or ω position by at least one acrylate, methacrylate, vinyl or styrenic function.

 A crosslinking agent according to the invention comprises, for example, at least two functions, chosen in particular from the acrylate, methacrylate, vinyl and styrene functional groups.

 In particular, the crosslinking agent according to the invention comprises at least two vinyl functional groups or at least two (meth) acrylate functional groups.

 In one embodiment, the crosslinking agent is a crosslinking agent selected from the group consisting of divinylbenzene, ethylene glycol dimethacrylate, di (ethylene glycol) dimethacrylate, and mixtures thereof.

 Preferably, the crosslinking agent according to the invention is di (ethylene glycol) dimethacrylate.

 According to one embodiment, the aforementioned reaction mixture comprises from 10% to 30% by weight of crosslinking agent relative to the total weight of the reaction mixture. Preferably, the content by weight of crosslinking agent in the reaction mixture is between 12% and 25%, and preferably between 15% and 20%.

Porogenic agent

 The reaction mixture also comprises at least one porogenic agent, and preferably at least two porogenic agents.

 According to one embodiment, the blowing agent is chosen from compounds in which the catalyst is insoluble and in which the styrene-containing anthraquinone monomers of formula (I) are soluble at the temperature of the process of the invention.

The blowing agents do not react during the polymerization but participate in the formation of pores. They remain trapped in the pores, surrounded by the polymer mass until the end of the reaction. Their volume fraction is related to porosity. According to one embodiment, the boiling point of these compounds is higher than the polymerization temperature.

 According to one embodiment, the blowing agent is selected from the group consisting of toluene, long chain alcohols comprising at least 10 carbon atoms, and preferably from 10 to 20 carbon atoms, long chain alkanes comprising at least less than 10 carbon atoms, and preferably from 10 to 20 carbon atoms, oligomers of ethylene glycol and mixtures thereof.

The term "oligomer of ethylene glycol" refers in the context of the present invention to a compound consisting of at least two ethylene glycol units. Such a compound can be represented for example by the formula H- (OCH ₂ CH ₂ ) i -OH, i being an integer greater than or equal to 2, and preferably less than 4.

 Preferably, the anthraquinone supported catalyst according to the invention is obtained by the aforementioned method comprising the implementation of a mixture of at least two porogenic agents.

 According to one embodiment, the blowing agent is a mixture of at least two compounds selected from the group consisting of toluene, long-chain carbon alcohols comprising at least 10 carbon atoms, long-chain alkanes of at least 10 atoms of carbon and oligomers of ethylene glycol.

 According to one embodiment, the reaction mixture comprises dodecanol and / or toluene as a blowing agent. Preferably, the blowing agent is a mixture of dodecanol and toluene.

 According to one embodiment, the above-mentioned reaction mixture comprises from 10% to 60% by weight of porogenic agent (s) relative to the total weight of the reaction mixture. Preferably, the content by weight of agent (s) porogen (s) in the reaction mixture is between 30% and 60%, and preferably between 50% and 60%.

Monomer of formula (I)

 The reaction mixture according to the invention also comprises at least one monomer of formula (I) as defined above.

 This monomer is a monomer of the anthraquinone family.

 Preferably, in formula (I), n is 2.

According to one embodiment, the aforementioned reaction mixture comprises less than 10% by weight of anthraquinone styrene monomer of formula (I). Preferably, the content by weight of styrenic monomer anthraquinone of formula (I) in the reaction mixture is between 0.01% and 10%, and preferably between 5% and 10%.

 According to a preferred embodiment, the aforementioned reaction mixture comprises:

 from 10% to 30% by weight of styrene relative to the total weight of the reaction mixture;

 from 0.1% to 5% by weight of initiator, in particular of AIBN, relative to the total weight of the reaction mixture;

 from 10% to 30% by weight of crosslinking agent, in particular di (ethylene glycol) dimethacrylate, relative to the total weight of the reaction mixture;

 from 10% to 60% by weight of porogen (s), preferably a mixture of dodecanol and toluene, relative to the total weight of the reaction mixture; and

less than 10% by weight of anthraquinone styrenic monomer of formula (I), in particular in which n = 2.

Catalyst

 The catalysts according to the invention are supported catalysts which comprise a polymeric support containing on the surface at least one anthraquinone unit. This anthraquinone unit is derived from the aforementioned monomer of formula (I).

 These catalysts thus comprise a support of polymeric nature on which anthraquinone units are grafted.

 According to one embodiment, the anthraquinone catalysts supported according to the invention comprise from 5% to 20%, preferably from 8% to 1%, by weight of anthraquinone relative to the total weight of supported anthraquinone catalyst.

 The catalysts according to the invention are in particular in the form of monoliths.

 Monoliths are porous and solid materials formed in one piece. According to the invention, they are polymeric (organic) in nature.

 The catalysts according to the invention can also be designated as "macroporous rigid organic monoliths", or as monolithic anthraquinone catalysts or as monolithic catalysts.

The monolithic catalysts according to the invention are different from the catalysts usually used in emulsion, namely in the form of particles. The Catalysts according to the invention are not in the form of particles but of monoliths as indicated above.

 The main characteristic of these monoliths is their porosity which persists even in the dry state. They consist of several grains (microspheres) aggregated in the form of clusters (aggregates of grains) and have pores whose size is highly dependent on the composition of the polymerization mixture (reaction mixture). "Pores" are irregular voids formed between and in clusters. They are interconnected and form channels that allow the monolith to be penetrated in its depth by solutes and solvents.

 The mechanical properties of these materials are related to the very strong crosslinking of their network.

 The catalysts obtained according to the invention are therefore porous materials consisting of pores of varying shapes and sizes. The pores are classified according to their size in three categories:

- micropores with pore diameters (d _p0 res) of less than 2 nm,

mesopores with _dp0 res between 2 nm and 50 nm,

macropores with _dp0 res greater than 50 nm.

 According to one embodiment, the catalyst of the invention is a mesoporous monolith.

 The porous structure of monoliths can be evaluated using several techniques among which:

 1) the nitrogen adsorption and desorption (BET) measurements which make it possible to determine the specific surface,

 2) mercury intrusion porosimetry (PIM) measurements that determine the pore size distribution,

 (3) scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) to visualize the morphology of monoliths,

4) reverse steric exclusion chromatography (ISEC) used to determine the porous structure by mathematical calculation from the elution times of a series of known molar mass standards through a monolithic column considered stationary phase. ISEC measurements show the porosity of wet monoliths while all other techniques characterize the porosity of the dry material and assume that their porosity does not change when they are in the presence of a liquid phase. Moreover, in the case of nitrogen adsorption and desorption measurements, the appearance of the adsorption isotherms gives indications on the type of porosity of the material: macro-, meso- or microporous.

 According to the invention, the average pore diameter of the catalysts in the dry state can vary from 5 nm to 10 nm as measured by the BET method (as detailed in the experimental section below) and from 50 nm to 300 nm as measured by mercury porosity (as detailed in the experimental section below).

 The monolithic catalysts according to the invention take the form of the polymerization reactor (tube or column), the latter may consist of different materials: glass, steel, silicone, synthetic polymers, ....

 Depending on the nature of the mold used to prepare these catalysts, they may have several geometric shapes, such as cylinders or balls. According to a preferred embodiment, the catalysts of the invention have a cylindrical shape.

 The diameter of the monoliths synthesized can be between 10 micrometers for example for chromatographic columns and 25 millimeters or even up to 200 millimeters for example for reaction media.

According to one embodiment, the supported anthraquinone catalyst has a specific surface area, determined by the BET method, greater than or equal to 20 m ² / g, and preferably between 20 and 200 m ² / g.

 The pore surface associated with that of the grains per unit mass represents the specific surface area of the porous material. The main contribution to the specific surface comes from micropores and then mesopores. The more micropores there are, the greater the specific surface area. Macropores have a negligible contribution to the specific surface but allow the liquid to circulate inside the monolith at a relatively low pressure. They are the ones that will support the hydraulic or electroosmotic flow in the monolith and allow convective mass transfer.

 The anthraquinone catalysts supported according to the invention have interesting mechanical properties. In particular, the Young's modulus of these catalysts can be between 100 MPa and 400 MPa.

 The Young's modulus characterizing the elastic behavior of the material was estimated by considering the monolith in rectangular form of width and height equal to 10 mm and length between supports of 35 mm.

The catalysts according to the invention also have the advantage of being able to be recycled, that is to say that they can be used at least once again after a first use, and this while retaining their catalytic properties. They can advantageously be reused several times after their first use. Preferably, they are recycled, that is to say reused, for at least 4, even 5 or even 6 times.

 This recyclability character is particularly advantageous especially with respect to conventional catalysts in the form of particles.

applications

 The present invention also relates to the use of the supported anthraquinone catalyst as defined above, for catalyzing the kraft or alkaline cooking of wood or lignocellulosic biomass.

 Alkaline cooking of wood (or soda process) is the simplest alkaline cooking method, in which the wood is treated with an aqueous solution of sodium hydroxide at a temperature between 150 ° C and 170 ° C. At the end of cooking, the black liquor containing dissolved organic and inorganic derivatives is concentrated by evaporation and burned. The residue obtained is the sodium carbonate which will be converted into sodium by caustification with calcium hydroxide. This process makes it possible to isolate the cellulose fibers after removal of a large part of the lignin and hemicelluloses.

 The kraft process, also known as the sulphate process, is a process in which sodium sulphate is used as a chemical in the regeneration of the cooking liquor. This process is used today in most paper mills which are easily recognizable thanks to the smell given by volatile sulfur compounds formed during cooking.

Typically, the wood chips are treated at a temperature of 160 ° C. to 180 ° C. (8-9 bar pressure) for 2 to 3 hours in a chemical reactor called digester in the presence of an aqueous solution of sodium hydroxide (NaOH) and sodium sulphide (Na ₂ S) called "white liquor".

 The liquor recovered at the end of cooking called "black liquor" contains mainly inorganic salts and organic compounds consisting of lignin and polysaccharides obtained by degradation but also small amounts of extractives. During this cooking, the lignin is dissolved releasing the cellulosic fibers.

The present invention also relates to a process for the preparation of a cellulosic pulp, comprising a kraft or alkaline cooking step of wood chips or of lignocellulosic biomass at a temperature of between 130.degree. 180 ° C for a period of 30 minutes to 120 minutes, in the presence of water, supported anthraquinone catalyst as defined above, and an aqueous solution of sodium hydroxide and / or sodium sulfide.

 The invention therefore also relates to the implementation of the sodium process or kraft process mentioned above with the catalyst according to the invention.

 This process consists in bringing wood chips or lignocellulosic biomass with water, said catalyst and an aqueous solution of sodium hydroxide and / or sodium sulphide (depending on the applied technology).

According to one embodiment, the content by weight of active alkali, namely the weight content of sodium hydroxide and sodium sulphide, expressed in equivalent grams of NaOH or Na ₂ O, is between 9% and 26% by weight. relative to the total weight of dry wood (wood chips or lignocellulosic biomass).

 According to one embodiment, the sulfide S, corresponding to the existing sulfur content defined as the ratio between sodium sulphide and active alkali, ranges from 25% to 35%.

 According to one embodiment, the dilution factor ranges from 3 to 4.5 (the dilution factor represents the ratio between the total amount of water (sum of the water contained in the wood plus the volume of white liquor) and the amount of dry wood).

 According to one embodiment, the content of anthraquinone catalyst according to the invention is less than 0.5% by weight relative to the weight of dry wood used.

 The use of the catalysts according to the invention is particularly advantageous in the context of the kraft process because the yields are improved compared to a kraft process with the anthraquinone catalysts according to the state of the art.

 In addition, these catalysts make it possible to use a lesser amount of reagents (sodium hydroxide and sodium sulphide) compared to the kraft processes with the anthraquinone catalysts according to the state of the art.

The present invention also relates to a process for preparing hydrogen peroxide, comprising a step of hydrogenation of the supported anthraquinone catalyst as defined above, followed by a step of oxidation with oxygen in the air. EXAMPLES

The reagents used are commercially available from Sigma-Aldrich.

Example 1 Preparation of an Anthraquinone Styrenic monomer of Formula (I)

 This example relates to the preparation of the monomer of the following formula:

 The synthesis of this monomer, hereinafter referred to as AQwittig, is carried out in four steps, according to the diagram below:

dation

The first step is a Diels-Alder reaction between myrcene and naphthoquinone which leads to the formation of 2- (4-methyl-pent-3-enyl) anthraquinone, 1A. This product was synthesized by the company "Resinic and Terpenic Derivatives". Myrcene and naphthoquinone are solubilized in toluene or a mixture of toluene and butanol. The solution is heated at 90 ° C until the reagents are consumed. The aromatization is carried out by following by adding 50% sodium or potassium hydroxide solution while maintaining the mixture at 70 ° C while bubbling oxygen. After evaporation of the solvents the 1A derivative is obtained with a yield greater than 90%.

 The synthesis protocol has been described by Cazeils (Synthesis of new paper-based cooking catalysts: study of their mechanisms of action, Thesis No. 3477, Bordeaux 1 University, 2007). The second stage of monomer synthesis is the epoxidation of the double bond of the anthraquinone side chain followed by an oxidative cleavage of the aldehyde epoxide (electrophilic opening of the epoxide). The last step is the Wittig reaction of the aldehyde with 4-vinylbenzyltriphenylphosphonium chloride in the presence of a phase transfer agent.

The second step is to synthesize 2- [2-3,3-dimethyl-oxiranyl) anthraquinone (1 B).

In a 1 liter three-necked flask equipped with a condenser, a dinitrogen inlet and a magnetized bar, the compound 1A in solution in CH ₂ Cl ₂ , meta-chloroperbenzoic acid (m-CPBA) and sodium hydrogencarbonate are introduced and stirred vigorously at room temperature (RT) for one hour under a nitrogen atmosphere. The organic phase is extracted with CH ₂ Cl ₂ , washed with an aqueous Na ₂ S ₂ 0 _{3 solution} until neutral, then dried over sodium sulphate, filtered and evaporated. Compound 1 B is obtained as a yellow solid (13.2 g, 43 mmol) with a yield of 94%. It is used without purification in the next step. The third step is to synthesize 3- (9,10-dioxo-9,10-dihydro-anthracen-2-yl) -propion-aldehyde (1 C).

Reagents M (g mol ^"1 ) m (g) or V (mL) n (mmol)

 1 B 306 6.9 g 22.55

Nal0 ₄ 214 14.5 g 67.76

 t-Bu-OH 300 mL

 HCOOH 25 mL

H ₂ 0 150 mL

In a one-liter one-liter flask equipped with a condenser and a magnetic bar, the compound 1B, sodium periodate, tert-butanol, formic acid and distilled water are introduced and stirred vigorously at room temperature. room temperature for 24 hours under a nitrogen atmosphere. The organic phase is extracted with ethyl acetate, washed with an aqueous solution of sodium carbonate until neutral, then dried over sodium sulfate, filtered and evaporated. Compound 1C is obtained as a pale yellow solid (5.55 g, 21.0 mmol) with a yield of 93%. It is used without purification in the next step.

The method further comprises an intermediate step of synthesizing 4-vinylbenzyltriphenylphosphonium chloride (1 E).

 1E

Reagents M (g mol- ¹ ) m (g) or V (ml) n (mmol) p-chloromethylstyrene 152 5 g 32.89

Ph ₃ P 262 8.62 g 32.89

Toluene 50 mL In a 100 ml 3-neck flask equipped with a condenser, a dinitrogen inlet and a magnetic bar, the p-chloromethylstyrene dissolved in toluene and triphenylphosphine are introduced and stirred vigorously under reflux of the solvent for 20 hours. . The white precipitate formed is filtered and dried under vacuum in the presence of P ₂ O ₅ . Compound 1 E is obtained in the form of a white solid (12.39 g, 29.93 mmol) with a yield of 91%. It is used without purification in the next step.

 The last step of the process is the synthesis of 2- [4- (4-vinyl-phenyl) -but-3-enyl] -anthraquinone (1 D).

Reagents M (g mol ^"1 ) m (g) or V (mL) n (mmol)

 1 C 264 0.2 g 0.757

 1 E 414 0.314 g 0.757

K ₂ C0 ₃ 138 0.157 g 1, 14

Bu ₄ N ⁺ HS0 ₄ Cat.

H ₂ 0 10 mL

CH ₂ Cl ₂ 10 mL

In a three-necked flask equipped with a condenser and a magnetic bar, the salt 1 E and an aqueous solution of potassium carbonate are introduced and stirred vigorously at room temperature for 3 hours. Then the compound 1C solubilized in dichloromethane and the phase transfer catalyst, Bu ₄ N ⁺ HSO ₄ ^" , are added, the reaction mixture is vigorously stirred at ambient temperature for 24 hours, The organic phase is extracted with CH ₂ Cl _{2 2} , washed with an aqueous solution of 3% hydrochloric acid until neutral, then dried over sodium sulphate, filtered and evaporated After purification by chromatography on a silica column (eluent CH ₂ Cl ₂ ), the compound 1 D is obtained pure (TLC) as a yellow solid (225 mg, 0.621 mmol) with a yield of 82%. Example 2 Preparation of a Supported Anthraquinone Catalyst

The general scheme of the polymerization reaction for the synthesis of the anthraquinone catalysts according to the invention (monoliths) is represented below. The monolithic supports are prepared in glass tubes of variable dimensions (diameter × height = 6 × 40 mm or 10 × 50 mm).

The table below indicates the amounts of the reagents used for the synthesis of St-DVB-AQ monoliths with a diameter of 10 mm according to this example (monolith with divinylbenzene as crosslinking agent).

Reagents M (g mol ^"1 ) m (g) or V (ml) n (mmol) P (g / cm ³ )

AIBN 164 0.026 g 0.16 -

AQwittig 364 0.262 g 0.72 -

Styrene 172 0.96 mL 5.12 0.914

 DVB (Crosslinking Agent) 104 0.64 mL 5.58 0.909

 Dodecanol 186 2 mL 8.98 0.833

Toluene 92 0.4 mL 3.8 0.867 The reaction mixture composed of styrene, crosslinking agent (DVB, EGDMA or DEGMDA), toluene, dodecanol, AQwittig and AIBN (purified in ethanol at 50 ° C and recrystallized at 0 ° C) is introduced into a tube and sealed with a septum. Since the free space in the tube is too small relative to the volume of gas evolved by the initiator decomposition, it is necessary to add more volume by means of a balloon and a needle which pierces the septum. The reaction medium is homogenized under ultrasound at 50 ° C. (10 minutes) and degassed by sparging with nitrogen (10 minutes) in order to eliminate the oxygen which inhibits the polymerization. The medium is drawn under vacuum and then immersed in an oil bath heated at 70 ° C. for 24 hours. After polymerization, the monolith is carefully extracted from the contacted tube with liquid nitrogen and then washed with 700 mL of THF in soxhlet for about 8 hours to remove the porogens and unreacted monomers. After purification, it is dried under vacuum at 200 ° C for 12 hours. The synthesis yield is determined by an indirect method by UV-Visible spectrometry. The extraction solvent is concentrated to determine, by UV spectrometry, the unreacted AQwittig monomer in order to determine the AQ functionality of the monolith. The monolith is analyzed in UV, GC, SEM, BET and PIM.

AIBN is purified by crystallization in ethanol. After dissolving 5 g of AIBN in 50 mL of ethanol at 50 ° C, the solution is immediately filtered and the filtrate is cooled to 0 ° C. The AIBN crystallizes rapidly and the crystals obtained by filtration are dried under vacuum at room temperature and kept in a bottle protected from light.

The above detailed example relates to the preparation of monoliths from divinylbenzene as a crosslinking agent but has also been applied identically with EGDMA or DEGDMA crosslinking agents using the same amounts of reagents. number of moles.

Example 3 Dosage

As shown in Example 2, the extraction solvent is concentrated to determine, by UV spectrometry, unreacted AQwittig monomer to determine the anthraquinone (AQ) functionality of the monolith. The assay of grafted QA is performed by an indirect assay by evaluating the amount of unreacted QA. The AQwittig has a characteristic band at 327 nm which makes it possible to go back up after a calibration to the non-grafted concentration of AQ. The amount AQwittig grafted is the difference between the initial amount and the amount dosed.

UV-Vis spectrometry: Determination of the monomer AQwittig

 UV-Visible Assays are performed with Perkin Elmer Lambda Apparatus

18.

 The grafted anthraquinone is assayed by UV-Visible absorption in the following washing mixture: the THF solvent used for the purification of the monoliths, diluted in dichloromethane. After determining the absorbance at 327 nm of the solution, the amount of QA is determined based on pre-calibration with AQwittig solutions of known concentrations. The linearity of the calibration makes it possible to apply the Beer-Lambert law:

n A ₃₂₇ - ₃₂₇ pc · I i · r v- where I is the optical path length (the thickness of the quartz cuvette of 1 cm), ε ₃₂ 7 is the molar extinction coefficient at 327 nm and 20 ° C determined by linear regression from the calibration line (e ₃₂₇ of 57000 L mol ^"1 cm ^{" 1} ) and C is the concentration of AQwittig (in m M) (y = 0.57x + 0, 02).

 The Beer-Lambert law makes it possible to determine the equivalent concentration of AQwittig in the washing mixture.

The gravimetric efficiency (Y) in AQwittig is determined by making the ratio between the grafted mass and the mass introduced at the beginning. The grafted QA (T _AQ ) rate is determined after calculating the remaining mass (m _r ) of AQwittig according to the following equations:

_{TAQ iQQ (%)}

 mmonoliths ^ AQwittig

V ₌ ^m initial ~ ™ ^r - 100 (%)

 initial m

m _r = C · M · _AQwittig V _{mé | angel} (g) The results are shown in the table below: Grafted QA rate and AQwittig gravimetric efficiency incorporated in monoliths

St-DVB-AQ St-EGDMA-AQ St-DEGDMA-AQ

 A 0.521 0.819 0.689

 AQ exo 10.58% 8.77% 9.22%

 TAQ th 1 0.66% 8.81% 9.31%

 Y 99.3% 1 00% 99%

Grafted QA ( _TQA ) on monoliths is between 8 and 11% AQ per gram of monolith. The graft yield (Y) of grafted AQwittig, determined by UV, is greater than 99% in the case of the three types of monoliths.

Example 4 Catalyst Properties

1. Thermal stability of catalysts

 The thermal stability of the catalysts was tested by thermodynamic analysis (ATG).

 ATG was performed using a Shimadzu model TGA-50TA. About 10 mg of product is placed on a platinum boat and then heated to 500 ° C., with a gradient of 10 ° C./min, under a nitrogen or oxidizing (air) atmosphere.

This analysis has made it possible to demonstrate that the monolithic catalysts according to the invention are stable up to 300 ° C. and that they can therefore be used in cooking.

2. Mechanical stability of catalysts

The mechanical stability of the catalysts according to the invention was tested according to the test described below.

 Three-point bending: Mechanical stability of monoliths

The apparatus used is a MTS QTest25 Elite tensile machine with a maximum force of 25 kN. It makes it possible to calculate the Young's modulus using a TestWorks 4 software. The measurements were performed on cylindrical samples (radius 10 mm, height 40 mm) with an initial compression speed imposed at 1 mm / min. . The length between the supports is equal to 35 mm. 3. Morphology of monoliths

 The morphology of the monolithic catalysts can be analyzed according to various techniques described below.

Scanning electron microscopy (SEM)

 The internal structure of the monoliths was visualized with a scanning electron microscope type JOEL JMS-6700 Field Emission between 2-5 kV. The dry monoliths were first metallized with a layer of gold deposited for 20 seconds with a JOEL-JFC-1200 Fine Coater, to facilitate the evacuation of electrons to the surface.

Transmission electron microscopy (TEM)

 Transmission electron microscopy observations are performed on a MET 80 (MET) type apparatus (FEI) at 80 kV to observe the internal structure of the monoliths.

 Sample sections with a thickness of 50 and 75 nm are made on ultramicrotome ultracut E (Leica) using a diamond knife at a speed of 1 mm / sec floating on water. These sections are deposited on 600 mesh copper grids with fine hexagonal bars and are observed under a microscope.

In particular, SEM images have shown that monoliths are porous and homogeneous and that the presence of anthraquinone modifies the size of grains and intergranular voids.

Example 5 Porosity and Specific Surface of the Catalysts

 The methods used to measure these two parameters are described below.

1. Nitrogen adsorption porosimetry: Monolith porosity (BET) The specific surface area of monoliths was measured by nitrogen adsorption at 77K with a Micrometrics ASAP2100 device, assuming that the surface of a single nitrogen molecule is from 16.2 to. The samples are degassed and dried under vacuum at 120 ° C for 24 hours before each measurement. By monitoring the pressure, the number of adsorbed molecules is determined and an adsorption isotherm is obtained which makes it possible to calculate the specific surface using the BET model (Brunauer, Emmett, Teller) based on the analytical calculation of the isotherms of adsorption determined experimentally. This method measures the (multimolecular) adsorption and nitrogen desorption on the surface of the monolith during its cooling with liquid nitrogen and allows to deduce the porosity from the isotherms.

 For a given temperature, the relationship between the amount of adsorbed gas (mass or volume) and its pressure is called adsorption equilibrium isotherm. It expresses the thermodynamic equilibrium between the gas phase and the solid phase.

The shape of the adsorption isotherms gives indications on the characteristics of the material. In literature, six adsorption isotherm curves are described (Rouquerol, F. Llewellyn, P. Rouquerol, J. Luciani, L. Denoyel, R. Engineering Techniques 2003, P1050).

 - The type I isotherm is obtained for materials having only micropores that fill at pressures even lower than their diameter is lower.

 The type II adsorption isotherm is characteristic of a multimolecular adsorption and it is obtained with non-porous or macroporous adsorbents on the surface of which the adsorbed layer gradually thickens.

 - The type IV adsorption isotherm is obtained with mesoporous adsorbents in which a capillary condensation occurs. The desorption of the condensed nitrogen by capillarity in the mesopores is not reversible: a hysteresis of the desorption is generally observed with respect to the adsorption.

 The adsorption isotherms of type III and V are observed in the case of the adsorption of water vapor by a hydrophobic surface. They are much rarer for materials with weak adsorbent / adsorbable interactions.

 - The Type VI step adsorption isotherm was observed more recently in the case of adsorption by energetically homogeneous surfaces on which the adsorbed layers are formed one after the other.

The BET method makes it possible to determine in the dry state the total porosity of a monolith: micropores, mesopores and macropores. 2. Porosimetry by mercury intrusion: Porosity of monoliths (PIM)

Mercury intrusion porosimetry is used to characterize the pore size distribution and porosity of macroporous materials. The measurements are carried out on a Micrometrics AutoPore IV 9500 device on samples whose mass is between 0.4 and 1 g. The volume of non-wetting mercury (the contact angle of mercury, Q _Hg , is generally between 1 10 and 160 ° depending on the surfaces considered) penetrates into the pores of the sample (under vacuum) as a function of the applied pressure mercury.

 The diameter of the pore in which the mercury can penetrate is inversely proportional to the applied pressure: the smaller the pores, the greater the need for high pressure (Krajnc, P. Leber, N., Stefanec, D .; , S. Podgornik, A. Journal of Chromatography A 2005, 1065, (1), 69-73). The cylindrical pore model and the variation of the intrusion volume as a function of the pressure make it possible to calculate the average pore diameter.

 This technique makes it possible to measure only macropores that can not be compared with the BET method, which also measures small pores (Svec, F., Frechet, J.M.J. Chemistry of Materials 1995, 7, (4), 707-715).

3. Results

Influence of the presence of QA with different crosslinking agents on porosity

Agent

% AQ S _sp , m ² / g pores PI ¹⁾ , nm dpores BET ²⁾ , nm

 crosslinking

 DVB 0 21 265 -

DVB 10.5 134 1 18 5

EGDMA 0 1 13 ND 10

 EGDMA 8.8 153 46 6

 DEGDMA 0 130 46 5

 DEGDMA 9.2 97 ND 4

Conditions: M / P = 2/3 (volume ratio between monomers and pore-forming solvents); 1.5% AIBN; 24% St; 16% crosslinking agent; 50% Dod; 10% You; d _monollthe = 10 mm, 1) average pore diameter per PIM, 2) average pore diameter per BET The results obtained show that the presence of the AQwittig monomer in the St-DVB-AQ hydrophobic monoliths increases the specific surface area and decreases the pore diameter.

 In the case of more hydrophilic monoliths, based on EGDMA, the presence of anthraquinone causes an increase in the specific surface area but has no effect on the porosity.

The porosity of the DEGDMA-based monolith is not measurable by the PIM technique due to the absence of mercury penetration. This monolith does not exhibit macroporosity. According to the results obtained by PIM measurement for EGDMA or DVB-based monoliths, these two types of monoliths present macropores with, in addition, mesopores in the case of the EGDMA-based monolith.

Example 6 Kraft Cooking in the Presence of the Catalysts of the Invention

The cooking is carried out using the rotary digester of Smurfit Kappa Cellulose Pine. The maritime pine peeling wood, in the form of chips, is sorted using sieves of different sizes to use fractions of diameter 7 mm and thickness 4 mm. The digester is an autoclave consisting of six shells, which are immersed in an oil bath. In order to determine the amount of wet wood required, the dryness is measured in an oven at 105 ° C for 24 hours on 200 g of damp wood. In each shell 450 g of wood chips (expressed in dry) are introduced including 180 g (40%) of thickness 4 mm and 270 g (60%) of diameter 7 mm. For each cooking, we have three control shells, without catalyst and three shells in the presence of catalyst.

The cooking conditions are different depending on the value of the targeted kappa index. The example was carried out for a targeted kappa index of 25. The white liquor is taken from the factory (industrial laundry). Active alkali (total amount of sodium hydroxide and sodium sulphide expressed in equivalent grams of NaOH or Na ₂ 0) and sulphidity (corresponding to the existing sulfur content defined as the ratio of sodium sulphide to active alkali ) are determined by a method of assaying the white liquor over two trials. The active alkali content used in cooking varies between 9-22% and the sulphidity between 25-30%. For all cooking we kept the same water content. The dilution factor of 3.5 represents the ratio between the total amount of water contained in a shell (the sum between the water of the wood, the volume of white liquor and the filler) and the quantity of dry wood.

The digester rotated without the shells is preheated to 80 ° C. At this temperature, shells filled with wood, liquor, water and in some cases with the catalyst are introduced. For example, for an alkali of 20%, in a control shell is introduced about 360 g wet wood thickness 4 mm, 520 g wet wood diameter 7 mm, 770 mL of white liquor active alkali of 1 16 g / Na ₂ 0 and 380 mL of water.

 At the end of cooking, the shells are cooled down by immersing them in cold water. In the case of shells with monoliths (catalysts), they are recovered and kept in the black liquor. For each shell, the chips are prewashed overnight, defibrated for 2 minutes, washed and dewatered; pulp is obtained at the end of this series of operations. The yield is calculated by weighing taking into account the dryness of the dough on 50 g.

 A quantity of 50 g of the recovered paste is diluted in 2.5 L of water and defibrated for 10 minutes. A sheet is made using the Noble Wood form with one liter of the diluted suspension. After drying the sheet on the Noble and Wood drier at 120 ° C to constant weight, the dry weight of the sheet is determined by weighing. This then makes it possible to calculate the volume necessary to take a gram of dough to measure the kappa index.

 To determine the kappa index of the dough which measures the degree of delignification of an unbleached dough, the following procedure was used. The kappa number is obtained by oxidation of the residual lignin in the presence of a precise volume of potassium permanganate brought into contact with the pulp for a determined time. In the presence of lignin, there is consumption of permanganate which must be between 20% and 60% of the initial quantity. The reaction is blocked by adding a solution of potassium iodide. The liberated iodine is then determined by a solution of sodium thiosulphate in an acid medium (ISO 302: 2004 standard, Pulps - Determination of Kappa number, 2nd edition, French Association of Standardization (AFNOR), 2004).

After reducing the total volume (paste + water) to 910 mL, 40 mL of KMnO ₄ 0.6 N and 50 mL of H ₂ S0 ₄ 8 N are added at the same time. The stopwatch is triggered at the end. for 2 minutes, using a thermometer, the temperature is measured C. The reaction is allowed to continue for up to 5 minutes and is then stopped by adding 20 ml of Kl (160 g / l). The released iodine is titrated by a solution of Na ₂ S ₂ 0 ₃ 0.6 N, in the presence of the fibers. A few drops of starch paste are added towards the end of the assay.

The volume V of Na ₂ S ₂ 0 ₃ necessary to decolorize the solution makes it possible to calculate the kappa number according to the relation:

Kappa index = (V - V _b | _anc ) x 6 x {1 + [(25 - C) x 0,013]}

where Vbianc corresponds to the volume of Na ₂ S ₂ 0 ₃ consumed using only water (without paste).

The table below lists all the results of control and monolithic cooking.

Water / Wood = 3.5 Quantity

 Active Alkali Sulphide Index Yield Maritime Pine = 450 g anthraquinone,%

% Na ₂ 0% kappa% t = 140 minutes (relative to dry wood)

 0 20 31 27 44.8

 0 21 31 25.2 43.5

 0 22 31 21, 3 40.9

 DVB

 0.2 16 31 37.3 46.9

 0.2 18 31 30.8 46.3

 0.2 20 31 22.5 43.9

 0 20 30 40, 1 50.1

 0 21 30 26.7 47.7

 0 22 30 23.7 46

 DVB

 0.2 16 30 47.4 51, 4

 0.2 18 30 34.6 49.9

 0.2 20 30 27.4 47.6

 0 20 27 36.6 45.1

 0 21 27 30.9 44.3

 0 22 27 20.8 43

 DVB

 0.2 16 27 44.2 46

 0.2 18 27 34, 1 45.1

 0.2 20 27 31, 2 43.7

 0 20 29 34.7 47

 0 21 29 26.5 45.3

 0 22 29 22.4 44.2

 DVB

 0.2 16 29 37.4 47.3

 0.2 18 29 32.4 46

 0.2 20 29 27.8 44.8

 0 20 31 29 44.8

 0 21 31 24.7 44

 0 22 31 23.6 43.8

 DEGDMA

 0.2 16 31 48.9 48.5

 0.2 18 31 32.6 46.6

0.2 20 31 25.4 45.4 0 18 28 36.6 46.2

 0 20 28 30.9 44.7

 0 22 28 20.8 45.2

 DEGDMA

 0.2 16 28 44.2 49.8

 0.2 18 28 34, 1 47.1

 0.2 20 28 31, 2 47

 0 18 29 40.6 48.6

 0 20 29 30.5 46.6

 0 22 29 25.2 45.1

 DEGDMA

 0.2 16 29 54.3 50.1

 0.2 18 29 37.9 47.1

 0.2 20 29 29.5 45.7

 0 18 26 35.6 46.8

 0 20 26 31, 3 44.7

 0 22 26 27 43.9

 DEGDMA

 0.4 16 26 42.4 47.9

 0.4 18 26 36.3 46.6

 0.4 20 26 27 45

This table of results makes it possible to observe the effectiveness of the catalysts of the invention in terms of yield. The above catalysts (DVB, EGDMA and DEDGMA) have the following characteristics:

St-DVB-AQ, St-EGDMA-AQ and St-DEGDMA-AQ monoliths have been found to be resistant under cooking conditions and do not degrade.

Example 7: Recycling Catalysts Example 7.1.

The monoliths are recovered completely and without loss during a first cooking and are tested again during a second cooking. Between two cooking, Monoliths are kept in black liquor and used without any purification steps. Black liquor keeps them in the same state of swelling and hydration at the end of cooking.

The results obtained are shown in the table below (same conditions as in Example 6).

This table of results makes it possible to observe the effectiveness of the catalysts according to the invention, once recycled.

Example 7.2. - Study of the evolution of Kappa index values according to the number of cooking by recycling the same monoliths

The Kappa index, which accounts for the residual lignin content on the fibers (the lower it is, the better the delignification has been), was measured on graded pasta. This classification consists of separating the fibers from the incuits. Measurement of the Kappa index is the measurement of the kappa index at the end of the process, eliminating incuits.

Table 1: Classified Kappa Index ([IK] _C ) according to the number of monolith recycling for active alkali of 22% compared to control cooks.

At a content by weight of active alkali of 22%, the effect on the Kappa number is preserved after 3 firings despite the sources of variation related to the process. No physical degradations of the monoliths were observed.

Table 2: Kappa index Classified according to the number of monoliths recycling for an active alkali of 26% compared to control cooks.

The first two bakes were made with a lot of wood different from the last three.

 In spite of this, for an active alkali content by weight of 26%, the effect on the Kappa number is preserved after five firings, in spite of the sources of variation related to the process. No physical degradations of the monoliths were observed.

All these results demonstrate the effectiveness of the monolithic catalysts according to the invention, even after several uses.

Claims

An anthraquinone supported catalyst in the form of a monolith, comprising a polymeric support containing at least one anthraquinone unit on the surface, said supported anthraquinone catalyst being obtainable by radical polymerization of a reaction mixture comprising:

 styrene;

 at least one initiator generating free radicals;

at least one at least one difunctional crosslinking agent selected from the group consisting of divinylbenzene, ethylene glycol dimethacrylate, di (ethylene glycol) dimethacrylate, compounds comprising an alkyl chain, interrupted by one or more groups; (CH ₂ ) _k O) _m with 2 <k <5, 1 <m <3, substituted in position a or ω by at least one acrylate, methacrylate, vinyl or styrenic function, and mixtures thereof;

 at least one porogenic agent; and

 at least one anthraquinone styrene monomer of formula (I)

 in which n is an integer ranging from 1 to 5.

The supported anthraquinone catalyst according to claim 1, wherein the blowing agent is selected from the group consisting of toluene, long chain alcohols having at least 10 carbon atoms, long chain alkanes having at least 10 carbon atoms oligomers of ethylene glycol and mixtures thereof.

The supported anthraquinone catalyst according to claim 1 or 2, wherein the blowing agent is a mixture of at least two compounds selected from the group consisting of toluene, long chain alcohols comprising at least 10 carbon atoms and alkanes long chain comprising at least 10 carbon atoms.

The supported anthraquinone catalyst according to any one of claims 1 to 3, wherein the blowing agent is a mixture of dodecanol and toluene.

A supported anthraquinone catalyst according to any one of claims 1 to 4, comprising from 5% to 20%, preferably from 8% to 1%, by weight of anthraquinone based on the total weight of supported anthraquinone catalyst.

The supported anthraquinone catalyst according to any one of claims 1 to 5, wherein the reaction mixture comprises:

 from 10% to 30% by weight of styrene relative to the total weight of the reaction mixture;

 from 0.1% to 5% by weight of initiator relative to the total weight of the reaction mixture;

 from 10% to 30% by weight of crosslinking agent relative to the total weight of the reaction mixture;

 from 10% to 60% by weight of pore-forming agent relative to the total weight of the reaction mixture; and

 less than 10% by weight of anthraquinone styrene monomer of formula (I).

7. supported anthraquinone catalyst according to any one of claims 1 to 6, whose specific surface area determined by the BET method is greater than or equal to 20 m ² / g, and preferably between 20 and 200 m ² / g.

The supported anthraquinone catalyst according to any one of claims 1 to 7, wherein the Young's modulus is between 100 MPa and 400 MPa.

9. Use of the supported anthraquinone catalyst according to any one of claims 1 to 8 for catalysing the kraft or alkaline cooking of wood.

A process for the preparation of a monolite supported anthraquinone catalyst according to any one of claims 1 to 8 by radical polymerization of a reaction mixture comprising:

 styrene;

 at least one initiator generating free radicals;

at least one at least one difunctional crosslinking agent selected from the group consisting of divinylbenzene, ethylene glycol dimethacrylate, di (ethylene glycol) dimethacrylate, compounds comprising an alkyl chain, interrupted by one or more groups; (CH ₂ ) _k O) _m with 2 <k <5, 1 <m <3, substituted in position a or ω by at least one acrylate, methacrylate, vinyl or styrenic function, and mixtures thereof;

 at least one porogenic agent; and

 at least one anthraquinone styrene monomer of formula (I)

in which n is an integer ranging from 1 to 5.

A process for preparing a cellulosic pulp, comprising a kraft or alkaline cooking step of wood chips or lignocellulosic biomass at a temperature of between 130 ° C. and 180 ° C. for a period of 30 minutes to 120 minutes, presence of water, supported anthraquinone catalyst according to any one of claims 1 to 8, and an aqueous solution of sodium hydroxide and / or sodium sulphide.