Recycled polyacetal for the production of polyoxymethylene dialkyl ethers

Abstract

The present invention relates to a method for recycling polyacetal having 8 to 100,000 carbon atoms for obtaining a polyacetal of formula R-(OCH2) n A method for producing polyoxymethylene dialkyl ethers of the formula R-(OCH2) wherein R and R' independently represent a methyl group or an ethyl group and n is an integer greater than or equal to 1, the method comprising reacting an acid catalyst with a polyacetal having 8 to 100,000 carbon atoms, a k The step of reacting a mixture of a reactive polyoxymethylene dialkyl ether of ‑OR′ and an optional solvent, wherein k is an integer greater than or equal to 1.

Description

Technical Field

[0001] The present invention relates to a process for recycling polyacetal for producing polyoxymethylene dialkyl ethers, and to the use of these polyoxymethylene dialkyl ethers for preparing (meth)acrylic acid or esters, (meth)acrolein or neopentyl glycol. Background Art

[0002] Industrial production of polymer materials continues to increase. For example, market demand for polyoxymethylene (POM) polymers (also known as polyacetal or polyoxymethylene) has doubled over the past decade, leading to an increase in production capacity to 1.7 million tons per year in 2015. POM is widely used in a variety of commercial plastic products such as disposable lighter bodies, sports equipment, toys, pens, and also in complex engineering products, particularly in the automotive and electromechanical industries.

[0003] After the useful life of these products has ended, the products are discarded and become waste. In order to combat plastic pollution, methods of recycling this type of polymer are therefore needed.

[0004] Currently, POM can be reused in injection molding processes, but the implementation of these processes is limited by the degradation of the material and the release of formaldehyde, which is harmful to the environment and health. In addition, the chemical recycling of POM has not been widely studied, and few methods focusing on POM processing have been implemented.

[0005] For example, U.S. Patent Application No. 2014 / 0343302 describes the specialized processing of POMs into cyclic acetals, particularly trioxanes, in the presence of an aprotic solvent and a catalyst. The cyclic acetals can then be used to produce new POMs. However, the method described in this patent application is intended for use with POMs having a relatively small number of repeating units and is therefore unsuitable for POMs with greater length variation, which limits its application.

[0006] Therefore, there is a need for a POM recycling process that is applicable to all types of POM, especially those of large size, and that produces products other than cyclic acetals. Summary of the Invention

[0007] The present invention arises from the unexpected discovery of the inventors that polyacetals derived from plastic waste can be used to synthesize polyoxymethylene dialkyl ethers with minimal formaldehyde emission.

[0008] The present invention therefore relates to a method for recycling polyacetals containing 8 to 100 000 carbon atoms for the production of polyacetals of the formula R-(OCH2) n-OR', wherein R and R' independently represent a methyl group or an ethyl group and n is an integer greater than or equal to 1, the method comprising reacting an acid catalyst with a polyacetal containing 8 to 100,000 carbon atoms, a polyoxymethylene dialkyl ether of the formula R-(OCH2) k The step of reacting a mixture of a reactive polyoxymethylene dialkyl ether of -OR', wherein R and R' are as defined above and k is an integer greater than or equal to 1, and an optional solvent.

[0009] The present invention also relates to the formula R-(OCH2) k -OR' reactive polyoxymethylene dialkyl ethers for recycling polyacetals containing 8 to 100 000 carbon atoms to obtain polyacetals of the formula R-(OCH2) n -OR' produced polyoxymethylene dialkyl ether.

[0010] The present invention also relates to the use of the produced polyoxymethylene dialkyl ethers obtained by the recycling process according to the invention for the synthesis of (meth)acrylic acid or esters, (meth)acrolein or neopentyl glycol.

[0011] The present invention also relates to a process for synthesizing (meth)acrylic acid or ester or (meth)acrolein or neopentyl glycol, which comprises the step of reacting the produced polyoxymethylene dialkyl ether obtained by the recycling process according to the present invention. DETAILED DESCRIPTION

[0012] polyacetal

[0013] The process according to the present invention is a process for recycling polyacetal.

[0014] The term "polyacetal" means a homopolymer or copolymer based on formaldehyde. The polyacetal may be a mixture of homopolymers and / or copolymers based on formaldehyde.

[0015] For the purposes of the present invention, the term "homopolymer" means formaldehyde polymers, also known as polyoxymethylene (POM) or polyoxymethylene. Homopolymers are usually in the form of mixtures of homopolymers of different chain lengths.

[0016] For the purposes of the present invention, the term "copolymer" means a polymer of formaldehyde and one or more monomers other than formaldehyde. The copolymer is usually in the form of a mixture of copolymers of different chain lengths.

[0017] According to one embodiment, the polyacetal is a mixture of a homopolymer and a copolymer. Preferably, the mixture of a homopolymer and a copolymer comprises less than 20% by weight, preferably less than 15% by weight, less than 10% by weight, less than 9% by weight, less than 8% by weight, less than 7% by weight or less than 6% by weight, more preferably less than 5% by weight, less than 4% by weight, less than 3% by weight, less than 2% by weight or less than 1% by weight of copolymer, relative to the weight of the mixture of homopolymer and copolymer.

[0018] According to another embodiment, the polyacetal is a homopolymer.

[0019] The polyacetal may have a carbon number ranging from 8 to 100,000, 8 to 50,000, 8 to 10,000, or 8 to 100. Alternatively, the polyacetal may have a carbon number ranging from 100 to 100,000, 500 to 100,000, 1,000 to 100,000, 1,000 to 50,000, 3,000 to 50,000, or 3,000 to 10,000.

[0020] Polyacetal can be derived from various waste materials; it is then referred to as post-production or post-industrial polyacetal or post-consumer polyacetal. For example, polyacetal can be derived from waste products from the automotive, aviation, telecommunications, sports, leisure, electronics, electromechanical, etc. industries.

[0021] Polyacetals may also contain additives such as glass fibers, carbon fibers, carbon nanotubes, carbon black, pigments, etc. Polyacetals may also be contaminated with other polymers or pollutants, but in this case the waste to be recycled is selected such that these other polymers / pollutants are inert in the recycling process, i.e. they do not dissolve and / or react during the reaction.

[0022] Preferably, the polyacetal is ground to obtain polyacetal flakes of 0.05 to 2 cm. Preferably, the polyacetal flakes obtained after grinding are no more than 1.5 cm, 1 cm, 0.8 cm, 0.5 cm, 0.3 cm, 0.2 cm, 0.1 cm or 0.05 cm. Preferably, the ground polyacetal flakes are dried by any method known to those skilled in the art to remove any traces of residual water. For example, the polyacetal flakes can be dried under vacuum or under a nitrogen stream at a temperature preferably in the range of 20° C. to 100° C., more preferably 60° C. to 100° C., for a time preferably in the range of 2 to 30 hours, more preferably 5 to 60 hours. Alternatively, the polyacetal can be dried under a microwave stream for a period of less than 30 minutes, preferably less than 10 minutes.

[0023] Polyoxymethylene dialkyl ether

[0024] Polyoxymethylene dialkyl ethers are represented by the acronym POM for polyoxymethylene followed by one or more characters identifying the alkyl groups R and R' (POMX, where X = M for methyl, E for ethyl, or M / E for a mixture of methyl and ethyl) and an integer corresponding to the number of -(CH2O)- units in the polyoxymethylene dialkyl ether (POMX) produced. n ) is n, and in the case of reactive polyoxymethylene dialkyl ether (POMX k ) in the case of k).

[0025] In the present invention, a distinction is made between the terms "produced polyoxymethylene dialkyl ether" and "reactive polyoxymethylene dialkyl ether".

[0026] The produced polyoxymethylene dialkyl ether (or POMX n , wherein X=M when R and R' are methyl groups, X=E when R and R' are ethyl groups, or X=M / E when R and R' are a mixture of methyl and ethyl groups) is a polyoxymethylene dialkyl ether obtained by the polyoxymethylene recycling method according to the present invention.

[0027] Reactive polyoxymethylene dialkyl ether (or POMX k , wherein X=M when R and R' are methyl, X=E when R and R' are ethyl, or X=M / E when R and R' are a mixture of methyl and ethyl) is the polyoxymethylene dialkyl ether used as a reagent in the recycling process according to the present invention to obtain the produced polyoxymethylene dialkyl ether.

[0028] Produced polyoxymethylene dialkyl ether

[0029] The method according to the present invention provides a polyoxymethylene dialkyl ether produced from polyacetal, a reactive polyoxymethylene dialkyl ether and an acid catalyst. The produced polyoxymethylene dialkyl ether may especially comprise a polyoxymethylene dialkyl ether derived from the depolymerization of polyacetal and optionally a reactive polyoxymethylene dialkyl ether.

[0030] The polyoxymethylene dialkyl ether produced corresponds to the formula R-(OCH2) n -OR', wherein R and R' independently represent a methyl group or an ethyl group and n is an integer greater than or equal to 1.

[0031] The polyoxymethylene dialkyl ether produced can be recovered from the process according to the invention, in particular by a separation step, such as a distillation step. The recovery step allows the polyoxymethylene dialkyl ether produced to be separated from the remaining reaction mixture. The recovery step is described in detail below.

[0032] The polyoxymethylene dialkyl ether produced can be POMX with a specific n valuen or POMX with different values ​​of n n Preferably, the polyoxymethylene dialkyl ether produced is POMX n mixture.

[0033] By way of example, the following names are used for the polyoxymethylene dialkyl ethers produced:

[0034] - When the alkyl group is methyl, POMM n (polyoxymethylene dimethyl ether), and, for example, when n=1, POMM1, also known as methylal or dimethoxymethane (DMM);

[0035] -When the alkyl group is ethyl, POME n (polyoxymethylene diethyl ether), and for example when n=1, POME1, also known as diethoxymethane (ethylal, formaldehyde diethyl acetal); and

[0036] - When the alkyl group is a mixture of methyl and ethyl, POMM / E n (Polyoxymethylene methyl ethyl ether).

[0037] The method according to the invention makes it possible to obtain all grades of POMM simultaneously n 、POME n and POMM / E n , that is, from n = 1 to infinity. However, polyoxymethylene dialkyl ethers with a level n greater than 8 are difficult to detect and quantify by conventional analytical methods.

[0038] Preferably, the polyoxymethylene dialkyl ether produced has a number n ranging from 1 to 100, preferably from 1 to 50, 1 to 25 or 1 to 15, more preferably from 1 to 10, even more preferably from 1 to 8.

[0039] Preferably, the polyoxymethylene dialkyl ether produced contains less than 10% by weight of polyoxymethylene dialkyl ethers having a number n greater than 8, more preferably less than 9% by weight, less than 8% by weight, less than 7% by weight, less than 6% by weight, less than 5% by weight, less than 4% by weight, less than 3% by weight, less than 2% by weight of polyoxymethylene dialkyl ethers having a number n greater than 8, relative to the total weight of the polyoxymethylene dialkyl ethers produced.

[0040] The polyoxymethylene dialkyl ether produced may contain methylal and / or diethoxymethane which originates at least in part from the reactive polyoxymethylene dialkyl ether introduced together with the polyacetal at the beginning of the process. The methylal and / or diethoxymethane can advantageously be separated from the remainder of the polyoxymethylene dialkyl ether produced by an evaporation step (e.g., by distillation) and can optionally be recycled to the beginning of the process as reactive polyoxymethylene dialkyl ether by a recycling step. The evaporation and recycling steps are described below.

[0041] Preferably, the polyoxymethylene dialkyl ether produced is POMM 2-8 or POME 2-8 or POMM / E 2-8 mixture, i.e. containing POMM n or POME n or POMM / E n s, wherein n ranges from 2 to 8 (especially after the separation step from POMX1).

[0042] Preferably, the polyoxymethylene dialkyl ether produced is selected from the group consisting of: CH3-(OCH2)-OCH3, CH3-(OCH2)2-OCH3, CH3-(OCH2)3-OCH3, CH3-(OCH2)4-OCH3, CH3-(OCH2)5-OCH3, CH3-(OCH2)6-OCH3, CH3-(OCH2)7-OCH3, CH3-(OCH2)8-OCH3, C 2H5-(OCH2)-OC2H5, C2H5-(OCH2)2-OC2H5, C2H5-(OCH2)3-OC2H5, C2H5-(OCH2)4-OC2H5, C2H5-(OCH2)5-OC2H5, C2H5-(OCH2)6-OC2H5, C2H5-(OCH2)7-OC2H5, C2H5-(OCH2)8-OC2H5 and mixtures thereof.

[0043] Preferably, the polyoxymethylene dialkyl ether produced is POMM 2-8 , which is of the formula CH3-(OCH2) n -OCH3, wherein n = 2 to 8. Preferably, POMM 2-8 The composition is as follows:

[0044] [Table 1]

[0045] n 2 3 4 5 6 7 8 wt% 25-50 20-40 10-25 5-15 2-10 1-7 0-2

[0046] More specifically, POMM 2-8 The preferred composition of the compound is as follows:

[0047] [Table 2]

[0048] n 2 3 4 5 6 7 8 wt% 44 32 14 6 2.5 1 <1

[0049] According to one embodiment, the polyoxymethylene dialkyl ether produced is POMM 2-4 , which is of the formula CH3-(OCH2) n -OCH3, wherein n = 2 to 4. Preferably, POMM 2-4 The composition is as follows:

[0050] [Table 3]

[0051] n 2 3 4 wt% 50-70 15-35 5-15

[0052] According to one embodiment, the polyoxymethylene dialkyl ether produced is POMM 3-4 , which is of the formula CH3-(OCH2) n -OCH3 compounds, wherein n = 3 to 4. Preferably, POMM 3-4 The composition is as follows:

[0053] [Table 4]

[0054] n 3 4 wt% 50-70 30-50

[0055] According to one embodiment, the polyoxymethylene dialkyl ether produced is POMM 3-5 , which is of the formula CH3-(OCH2) n -OCH3, wherein n = 3 to 5. Preferably, POMM 3-5 The composition is as follows:

[0056] [Table 5]

[0057] n 3 4 5 wt% 40-60 20-40 10-30

[0058] According to one embodiment, the polyoxymethylene dialkyl ether produced is POME 2-4 , which is of the formula C2H5-(OCH2) n -OC2H5, wherein n=2 to 4.

[0059] Reactive polyoxymethylene dialkyl ether

[0060] The reactive polyoxymethylene dialkyl ether is contacted with polyacetal and an acid catalyst to obtain the produced polyoxymethylene dialkyl ether.

[0061] The reactive polyoxymethylene dialkyl ether according to the present invention corresponds to the formula R-(OCH2) k-OR', wherein R and R' independently represent methyl or ethyl and k is an integer greater than or equal to 1. Preferably, k is an integer ranging from 1 to 100, preferably from 1 to 50, 1 to 25 or 1 to 15, more preferably from 1 to 10, even more preferably from 1 to 8.

[0062] The reactive polyoxymethylene dialkyl ether may be POMX having a specific k value k or POMX with different k values k mixture.

[0063] Preferably, the reactive polyoxymethylene dialkyl ether comprises methylal and / or diethoxymethane.

[0064] According to a particular embodiment of the present invention, the reactive polyoxymethylene dialkyl ether comprises non-recycled methylal and / or diethoxymethane (also referred to as fresh methylal and / or diethoxymethane). For the purposes of the present invention, non-recycled compounds (or fresh compounds) are compounds that do not originate from a recycling step of the process.

[0065] Fresh methylal and / or diethoxymethane can be used, in particular, to initiate the process according to the invention. Once the process is running, the methylal and / or diethoxymethane can be separated from the produced polyoxymethylene dialkyl ether by an evaporation step (e.g., by distillation) and optionally recycled to the beginning of the process as reactive polyoxymethylene dialkyl ether by a recycling step. The evaporation and recycling steps are described below.

[0066] Thus, the reactive polyoxymethylene dialkyl ether may comprise recycled methylal and / or diethoxymethane.For the purposes of the present invention, recycled compounds are compounds originating from the recycling step of the process.

[0067] Preferably, the reactive polyoxymethylene dialkyl ether comprises recycled methylal and / or diethoxymethane as well as fresh methylal and / or diethoxymethane.

[0068] The reactive polyoxymethylene dialkyl ether may comprise one or more POMX having a k number greater than or equal to 2. k For example, the reactive polyoxymethylene dialkyl ether may comprise a compound selected from the group consisting of POMM2, POMM3, POMM4, POMM5, POMM6, POMM7, POMM8, higher grades of POMM, POME2, POME3, POME4, POME5, POME6, POME7, POME8, higher grades of POME, and mixtures thereof. These compounds may be fresh or recycled.

[0069] Preferably, the reactive polyoxymethylene dialkyl ether comprises methylal and / or diethoxymethane and one or more POMX having a k greater than or equal to 2. k .

[0070] In one embodiment of the present invention, the reactive polyoxymethylene dialkyl ether comprises only fresh methylal and / or diethoxymethane.

[0071] In one embodiment of the present invention, the reactive polyoxymethylene dialkyl ether comprises fresh methylal and / or diethoxymethane as well as recycled methylal and / or diethoxymethane.

[0072] In another embodiment of the present invention, the reactive polyoxymethylene dialkyl ether comprises fresh methylal and / or diethoxymethane, optionally recycled methylal and / or diethoxymethane and fresh or recycled POMX having a k number greater than or equal to 2. k mixture.

[0073] Preferably, the ratio of the mass of reactive polyoxymethylene dialkyl ether to the mass of polyacetal is at least 2:1, preferably at least 2.5:1, at least 3:1, at least 5:1, at least 6:1, at least 7:1, at least 8:1 or at least 9:1.

[0074] Preferably, the reactive polyoxymethylene dialkyl ether contains less than 5 wt%, preferably less than 4 wt%, less than 3 wt%, less than 2 wt% or less than 1 wt% of POMX having a k greater than 8. k , relative to POMX with k greater than or equal to 2 k The total weight of

[0075] Polyacetal recycling method

[0076] The process according to the invention comprises a step of reaction between an acid catalyst and a mixture comprising a polyacetal as defined above, a reactive polyoxymethylene dialkyl ether as defined above and optionally a solvent.

[0077] The presence of a solvent depends on the nature of the reactive polyoxymethylene dialkyl ether used. In practice, the reaction mixture must be at least partially liquid in order for the reaction to occur. For the purposes of the present invention, a liquid mixture means a mixture that can flow under its own weight at room temperature (20° C.). The reaction mixture may be a dispersion, i.e., a system containing solid flakes of polyacetal dispersed in a liquid phase. In practice, the polyacetal is usually in solid form and can be at least partially dissolved by the reactive polyoxymethylene dialkyl ether and the optional solvent. The solvent advantageously promotes the dissolution of the polyacetal. When only methylal and / or diethoxymethane are used as reactive polyoxymethylene dialkyl ethers, the presence of a solvent is not required.

[0078] Preferably, the solvent is selected to have a boiling point higher than the boiling point of the polyoxymethylene dialkyl ether produced that is desired to be obtained. Preferably, the solvent is selected to have a boiling point higher than the boiling point of the polyoxymethylene dialkyl ether produced with a number n=1 to 8. Preferably, the solvent has a boiling point higher than the boiling point of the polyoxymethylene dialkyl ether produced with the highest n value that is desired to be recovered. Other high-boiling-point POM can then be recycled to the beginning of the process together with the solvent via a recycling step. Preferably, the solvent has a boiling point greater than 120°C under partial vacuum (i.e., at about 10 mmHg), or a boiling point greater than 250°C corrected for atmospheric pressure.

[0079] The solvent may be selected from sulfolane, methylsulfolane, ethylsulfolane, diethylsulfolane, propylsulfolane, dipropylsulfolane, butylsulfolane, dibutylsulfolane, pentylsulfolane, dipentylsulfolane, hexylsulfolane, octylsulfolane, DMSO and mixtures thereof. Preferably, the solvent is sulfolane.

[0080] For example, under standard temperature and pressure conditions (25°C and atmospheric pressure), sulfolane has a boiling point of 285°C, methyl sulfone has a boiling point of 278°C, and DMSO has a boiling point of 189°C.

[0081] Preferably, the solvent is added in an amount ranging from 20% to 80% by mass, more preferably from 30% to 70% by mass, and even more preferably from 40% to 60% by mass, relative to the total mass of the mixture. Preferably, the amount of solvent in the mixture is about 50% by mass, relative to the total mass of the solvent + reactive polyoxymethylene dialkyl ether mixture.

[0082] Preferably, the mixture is dissolved at a temperature below 120°C, preferably from 20°C to 120°C, more preferably from 40°C to 110°C, preferably at a pressure ranging from atmospheric pressure to 10 bar.

[0083] The acid catalyst may be a homogeneous or heterogeneous catalyst. Preferably, the catalyst is a heterogeneous catalyst. The use of a heterogeneous catalyst advantageously facilitates its removal by filtration at the end of the reaction step.

[0084] As examples of catalysts suitable for use in the process according to the invention, mention may be made of acidic resins such as Amberlyst R and Lewatit R type resin, Lewis acid and For the purposes of this invention, an acidic resin is one that can supply H + Ionic macroporous polymeric cation exchange resins (e.g., styrene-divinylbenzene copolymers).

[0085] Preferably, the catalyst is selected from: acidic resins; organic or inorganic acids such as trifluoromethanesulfonic acid, perchloric acid, methanesulfonic acid, p-toluenesulfonic acid and sulfuric acid; Lewis acids such as BF3, AsF5; acidic mixed oxides such as WO3 / TiO2, phosphate alumina, tungsten alumina and zeolites; and mixtures thereof.

[0086] In one embodiment of the present invention, the polyacetal is at least partially dissolved with the reactive polyoxymethylene dialkyl ether and optionally a solvent in a first stage, and the mixture is then contacted with the acid catalyst.

[0087] In another embodiment of the present invention, the polyacetal is contacted with the acid catalyst and solvent in a first stage, and then the reactive polyoxymethylene dialkyl ether is added.

[0088] Preferably, in the case of a homogeneous catalyst, the catalyst is present in an amount ranging from 0.01 to 10 mol per kg of polyacetal, preferably from 0.02 to 5, more preferentially from 0.05 to 2 mol per kg of polyacetal.

[0089] Preferably, the reaction carried out in the presence of an acid catalyst is carried out at a temperature of below 120°C, preferably from 20°C to less than 120°C, more preferably from 40°C to 115°C or from 60 to 110°C and even more preferably from 80°C to 110°C, at a pressure in the range of 1 to 10 bar and preferably from 5 to 10 bar, to avoid boiling of the mixture.

[0090] The reaction can be carried out in batch mode or in continuous mode. In a batch configuration, the catalyst is preferably stirred together with the mixture, but it can also be placed in a basket that rotates in the reactor. In a continuous mode, the catalyst is preferably placed in a fixed bed or a fluidized bed. The mixture containing the polyacetal, the reactive polyoxymethylene dialkyl ether and the optional solvent flows through the catalyst bed from top to bottom or from bottom to top. Preferably, the liquid flows through the catalyst bed from bottom to top, and the catalyst grains (grains) remain fluid in the catalyst bed, but are not entrained.

[0091] Method according to the present invention can comprise filtering step.In one embodiment of the invention, before the reaction step with an acid catalyst, carry out the step of filtering the mixture, so as to block (retain) any pollutant, namely be present in the additive in the polyacetal and / or undissolved polyacetal sheet, mineral material filler such as glass or carbon fiber or other undissolved polymer.In another embodiment of the invention, before forming the mixture that comprises polyacetal and at least one reactive polyoxymethylene dialkyl ether and optional solvent, carry out filtering step.In this case, polyacetal is at least partially dissolved in a suitable solvent and carries out filtering step, so as to remove any pollutant, namely be present in the additive in the polyacetal, and / or undissolved polyacetal sheet, mineral material filler such as glass or carbon fiber or other undissolved polymer.Those skilled in the art will know which kind of solvent can dissolve polyacetal.As the example of suitable solvent, the solvent of above definition can be mentioned. In another embodiment of the invention, a filtration step is carried out after the mixture has been contacted with the catalyst and optionally neutralized, in order to remove solid particles, in particular any contaminants, i.e. additives present in the polyacetal, and / or undissolved polyacetal flakes, mineral material fillers such as glass or carbon fibers, other undissolved polymers and / or acidic or anionic resin particles.

[0092] The process according to the present invention may include a catalyst separation step. The optional catalyst separation step is performed after the reaction step. When the acid catalyst is dispersed in the reaction medium, the optional catalyst separation step can be performed by filtration or centrifugation. Alternatively, if the acid catalyst is contained in a basket, it is sufficient to remove the basket from the reactor. When the reaction is carried out in a continuous mode with an acid catalyst in a fixed bed, a separation step is not required because the catalyst remains trapped in the fixed bed.

[0093] The method according to the present invention may include a neutralization step. The optional neutralization step is carried out after the reaction step. The optional neutralization step can be carried out with an alkali to remove any traces of residual acid. Any alkali known to those skilled in the art can be used for this purpose. For example, aqueous sodium hydroxide solution, methanolic sodium hydroxide solution, sodium methoxide or potassium methoxide, a solution of sodium hydroxide in methylal, anhydrous sodium hydroxide, potassium hydroxide, lime, aqueous ammonia solution, triethylamine, diisopropylethylamine, melamine or anionic resins such as Ambersep 900OH resin can be used for this purpose. Preferably, the alkali is anhydrous.

[0094] After the reaction step, the reaction mixture contains all grades of polyoxymethylene dialkyl ethers, ie POMX wherein n=1 to infinity. n distribution.

[0095] The process according to the invention may comprise an evaporation step. The evaporation step allows the removal of all or part of the light compounds, in particular POMX where n=1 and possibly n=2 n . The light compounds are removed at the top of the evaporation unit. The evaporation step can be carried out with an evaporation unit selected from a rotary evaporator and / or a distillation column. The evaporation can be carried out in one step or in several successive steps. The evaporation step is a step of distillation preferably at atmospheric pressure or at a lower temperature under reduced pressure (for example at a temperature below 120° C., preferably below 110° C., at atmospheric pressure, or under reduced pressure (for example in the range of 0.4 to 0.6 atm)). Some or all of the light compounds removed during the evaporation step can be reintroduced into the reaction step as reactive polyoxymethylene dialkyl ether.

[0096] The method according to the invention may comprise a step of recovering the polyoxymethylene dialkyl ether produced. The recovery step allows the polyoxymethylene dialkyl ether produced, in particular POMX having a number n greater than or equal to 2 or 3, preferably wherein n=2 to 8, 2 to 5, 2 to 4, 3 to 5 or 3 to 4, to be recovered. n In particular, the recovery step allows the separation of the produced polyoxymethylene dialkyl ether from heavy compounds. The heavy compounds may be POMX n , wherein n is greater than the maximum n value of the polyoxymethylene dialkyl ether produced, in particular greater than 4, greater than 5, greater than 6, greater than 7, greater than 8 or greater than 10. The recovery step can be carried out in particular by distillation. The heavy compounds remain in the distillation tail fraction and the desired polyoxymethylene dialkyl ether produced is collected in the distillation head fraction. The distillation is preferably carried out under partial vacuum. The heating temperature is advantageously kept below 120° C. In fact, heating to above 120° C. can degrade the polyoxymethylene dialkyl ether produced. The vacuum level and the heating temperature are adjusted so as to distill out POMX of the target chain length. n The distillation can be carried out under partial vacuum at a pressure preferably in the range of 5 mbar to 60 mbar. The temperature-pressure pair corresponding to the desired polyoxymethylene dialkyl ether produced can be easily selected by a person skilled in the art. Some or all of the heavy compounds removed during the distillation step can be reintroduced into the reaction step as reactive polyoxymethylene dialkyl ether.

[0097] The process according to the invention may comprise a recycling step. The recycling step may in particular allow the reaction mixture to be recycled to the n-OR' is reintroduced into the reaction step. These compounds can be used as reactive polyoxymethylene dialkyl ethers. In particular, the recycling step makes it possible to reintroduce all or some of the light compounds removed in the evaporation step and / or all or some of the heavy compounds removed in the recovery step into the reaction step as reactive polyoxymethylene dialkyl ethers. Preferably, methylal (POMM1) and / or dimethoxymethane (POME1) recovered during the evaporation step are reintroduced into the reaction step as reactive polyoxymethylene dialkyl ethers. After the desired produced polyoxymethylene dialkyl ethers have been recovered, some or all of the heavy compounds, preferably POMX having a number n of less than 8 n It can also be reintroduced into the reaction step as a reactive polyoxymethylene dialkyl ether.

[0098] When a solvent is used in the process, it generally remains at the bottom of the column and can be reused as solvent in the process according to the invention, possibly together with the higher-grade polyoxymethylene dialkyl ethers (especially with a number n greater than 8) it contains.

[0099] The produced polyoxymethylene dialkyl ethers obtained by the recycling process according to the invention can be used as starting material for the synthesis of other organic compounds, in particular (meth)acrylic acid or esters, (meth)acrolein or neopentyl glycol.

[0100] Therefore, the method according to the present invention may include the step of synthesizing (meth)acrylic acid or ester or (meth)acrolein or neopentyl glycol from the produced polyoxymethylene dialkyl ether.

[0101] The synthesis of (meth)acrylic acid or ester or (meth)acrolein or neopentyl glycol can be carried out under the conditions described below.

[0102] Use of polyoxymethylene dialkyl ethers produced by a recycling process

[0103] The produced polyoxymethylene dialkyl ethers obtained by the polyacetal recycling process according to the invention can be used as a substitute or additive for diesel fuel, as a substitute for methanol in fuel cells, and for the preservation of human or animal bodies and / or for embalming.

[0104] Furthermore, the polyoxymethylene dialkyl ethers produced by the polyacetal recycling method according to the present invention, especially POMM 2-8 、POME 2-8 or POMM / E 2-8 , optionally as a mixture with methylal and / or diethoxymethane, can be used as reagent or synthesis intermediate, in particular for the synthesis of (meth)acrylic acid or esters or (meth)acrolein or neopentyl glycol.

[0105] The synthesis of (meth)acrylic acid or ester or (meth)acrolein is preferably carried out by aldol condensation. Preferably, the synthesis of (meth)acrylic acid or ester or (meth)acrolein is carried out by reacting the produced polyoxymethylene dialkyl ether obtained by the polyacetal recycling process according to the present invention with a suitable carboxylic acid or ester or saturated aldehyde in the presence of a catalyst.

[0106] Preferably, the polyoxymethylene dialkyl ether produced is POMX n mixtures wherein the number n = 1 to 100, more preferably 1 to 50, 1 to 20 or 1 to 10 and even more preferably 1 to 8. Advantageously, the polyoxymethylene dialkyl ethers produced avoid the use of free formaldehyde, which simplifies the isolation of the produced (meth)acrylic acid or ester or (meth)acrolein.

[0107] Carboxylic acids and esters that can be used to synthesize (meth)acrylic acid or esters or (meth)acrolein are well known to those skilled in the art. Examples of carboxylic acids include propionic acid and acetic acid. Examples of esters include propionic esters such as methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, or methyl acetate. Examples of aldehydes include acetaldehyde and propionaldehyde.

[0108] The catalyst used for the synthesis of (meth)acrylic acid or esters or (meth)acrolein can be chosen from any acidic or basic catalyst known to those skilled in the art for reactions of this type. As examples of suitable catalysts, mention may be made of catalysts based on magnesium, calcium, aluminum, zirconium or thorium phosphoric acid and / or silicates, strontium hydroxyapatite, barium hydroxyapatite, silica doped with alkali metals or alkaline earth metals and / or zirconium, calcium hydroxyapatite and mixtures thereof.

[0109] Alcohols can also be added to the process for synthesizing (meth)acrylic acid or esters or (meth)acrolein. The alcohol can be used as a solvent for the reaction. Any alcohol known to those skilled in the art for this type of synthesis can be used. Examples of suitable alcohols include methanol, ethanol, propanol, isopropanol, isobutanol, tert-butanol, (phenyl)phenol, n-butanol, and chlorooctanol.

[0110] The synthesis of neopentyl glycol is preferably carried out by aldol condensation.Preferably, neopentyl glycol is synthesized by reacting the produced polyoxymethylene dialkyl ether obtained by the polyacetal recycling method according to the present invention with isobutyraldehyde.

[0111] Preferably, the polyoxymethylene dialkyl ether produced is POMX n mixtures wherein the number n=1 to 100, more preferably 1 to 50, 1 to 20 or 1 to 10 and even more preferably 1 to 8.

[0112] Preferably, the neopentyl glycol synthesis is catalyzed by a tertiary alkylamine compound.

[0113] Alcohols can also be added to the neopentyl glycol synthesis process. The alcohol can be used as a solvent for the reaction. Any alcohol known to those skilled in the art for this type of synthesis can be used. An example of a suitable alcohol that can be mentioned is methanol.

[0114] The invention is illustrated by means of the following non-limiting examples.

[0115] Example

[0116] Example 1: POMM 2-8 Production

[0117] 375 kg of post-production polyacetal homopolymer (previously ground into flakes no larger than 1 cm and dried under vacuum at 80° C. to remove any remaining traces of water) are added to 475 kg of fresh dimethoxymethane (POMM1) sold by Lambiotte (Belgium) in an autoclave at room temperature. 475 kg of POMM1 obtained from the distillation of the previous recycling step is also added to the autoclave cold (20° C.). The autoclave is then closed and heated to 100° C. The pressure in the autoclave is gradually increased and then stabilized at less than 6 bar as the temperature stabilizes. After about 30 minutes, the dissolved mixture is sent to the reactor and passed through a filter that blocks any contaminants and / or undissolved polymer.

[0118] In the reactor, the A bed of 15 Dry Acid Resin (DuPont) was placed on top of the grid. 15Dry resin (1325 kg) is first washed with methanol and then with dimethoxymethane in order to remove any remaining traces of water. The previously dissolved mixture is sent to the reactor in ascending flow mode. It is dispersed through the catalytic bed by a bottom distribution plate. When the reactor is used in ascending flow mode, the acidic resin beads move freely, but the linear velocity of the liquid is not enough to entrain any catalytic particles. The residence time of the liquid mixture in the reactor, that is, the ratio of the volume of resin (catalytic bed of resin) to the flow rate of the polyacetal solution in POMM1, is 1 hour. The temperature of the solution feeding the reactor is kept below 120°C and in particular at 115°C. The reactor is operated at a pressure of 10 bar to prevent any boiling of the reaction solution.

[0119] The reaction mixture is then sent to a distillation column. The pressure is reduced to atmospheric pressure and the temperature is lowered to 25°C. Concentrated sodium hydroxide solution is added to neutralize traces of acidic resin that have been entrained in the reaction mixture. The mixture is then sent to the distillation step.

[0120] The temperature at the top of the column was 42° C., and the temperature at the bottom was 80° C. At the top of the column, dimethoxymethane was obtained, condensed, and then returned to the dissolution autoclave (475 kg) for the next run. POMM 2-8+ A mixture is obtained at the bottom of the column. A mixture containing 331 kg of POMM2, 212 kg of POMM3, 130 kg of POMM4, 76 kg of POMM5, 44 kg of POMM6, 25 kg of POMM7, 14 kg of POMM8 and 16 kg of higher-grade POMM is obtained, as determined by chromatographic analysis.

[0121] Example 2: POMM 3-4 Production

[0122] 375 kg of post-production polyacetal homopolymer (previously ground into flakes not exceeding 0.5 cm and dried at 80° C. under vacuum) were added to 399 kg of fresh dimethoxymethane (POMM1) in an autoclave at room temperature.

[0123] 1799 kg of a light mixture of POMM1 (1060 kg) and POMM2 (739 kg) obtained from a previous run are also added, as well as 394 kg of a mixture of POMMs from a previous run containing 171 kg of POMM5, 98 kg of POMM6, 56 kg of POMM7, 31 kg of POMM8 and 37 kg of higher grade POMMs.

[0124] The autoclave is then closed and heated to 110° C. The pressure in the autoclave increases gradually and then stabilizes as the temperature. After about 45 minutes, the dissolved mixture is sent to the reactor and passed over a filter that retains any contaminants and / or undissolved polymer.

[0125] In the reactor of Example 1, A bed of 15 Dry Acid Resin was placed on top of the grid. During the first run, The 15Dry resin was first washed with methanol and then with dimethoxymethane to remove any remaining traces of water. In subsequent runs, if the resin was not contaminated with water, this washing was no longer necessary.

[0126] The previously dissolved mixture is fed to the reactor in ascending flow mode. It is dispersed through the catalytic bed by a bottom distribution plate. When the reactor is used in ascending flow mode, the acidic resin beads move freely, but the linear velocity of the liquid is insufficient to entrain any catalytic particles. The residence time of the liquid mixture in the reactor, i.e. the ratio of the volume of resin (catalytic bed of resin) to the flow rate of the polyacetal solution in POMM1, is 1 hour. The temperature of the solution feeding the reactor is kept below 120°C, in particular at 110°C. The reactor is operated at a pressure of 10 bar to prevent any boiling of the reaction solution.

[0127] The reaction mixture is then sent to a distillation column. The pressure is returned to atmospheric pressure. Triethylamine is injected into the solution to neutralize the fine catalytic particles ( Acidity caused by the presence of resin).

[0128] The temperature at the top of the column is 106° C. and the temperature at the bottom is 120° C. At the top of the column, a mixture of dimethoxymethane, POMM1 and POMM2 is obtained, condensed and returned to the dissolution autoclave (1799 kg of a light mixture of POMM1 (1060 kg) and POMM2 (739 kg)). 3+ A mixture of POMM3 and POMM4 is obtained at the bottom of the column. The bottom fraction is then sent to another distillation column operated under partial vacuum (60 mbar). The mixture of POMM3 and POMM4 is distilled and condensed; 763 kg of a mixture of POMM3 (474 ​​kg) and POMM4 (289 kg) is then obtained. A mixture of higher-grade POMMs is collected at the bottom of the column. 171 kg of POMM5, 98 kg of POMM6, 56 kg of POMM7, 31 kg of POMM8, and 37 kg of higher-grade POMMs are obtained and returned to the dissolution autoclave.

[0129] Example 3: POMM 3-5 Production

[0130] 375 kg of post-production polyacetal homopolymer (previously ground into pieces not exceeding 0.8 cm and dried at 70° C. under vacuum for 24 hours) are added to 364 kg of fresh dimethoxymethane in an autoclave at room temperature.

[0131] 1407 kg of a light mixture of POMM1 (829 kg) and POMM2 (578 kg) obtained from a previous run are also added, as well as 174 kg of a mixture of heavy POMMs from a previous run containing 77 kg of POMM6, 44 kg of POMM7, 24 kg of POMM8 and 29 kg of higher grade POMMs.

[0132] The autoclave is then closed and heated to 100° C. The pressure in the autoclave increases gradually and then stabilizes as the temperature. After about 60 minutes, the dissolved mixture is sent to the reactor and passed over a filter that retains any contaminants and / or undissolved polymer.

[0133] 1 kg of anhydrous methanesulfonic acid was injected into the reactor, which was a pressurized stirred reactor equipped with a condenser and operated at 100° C. The reaction lasted for 1 hour, then the temperature was reduced to 30° C. and maintained for 30 minutes, the pressure was returned to atmospheric pressure, and the injection 900OH anion resin was added to neutralize the acid catalyst. The reaction mixture was then filtered to remove solid particles and sent to a distillation column.

[0134] The temperature at the top of the column was 105° C. and the temperature at the bottom was 120° C. At the top of the column, a mixture of POMM1 and POMM2 was obtained, condensed and returned to the dissolution autoclave (POMM1 (829 kg) and POMM2 (578 kg)). 3+ A mixture of POMM3, POMM4, and POMM5 is obtained at the bottom of the column. The bottom fraction is then sent to another distillation column operated under partial vacuum (10 mbar) and at a temperature of 120°C at the bottom. The mixture of POMM3, POMM4, and POMM5 is distilled and condensed (371 kg of POMM3, 226 kg of POMM4, and 134 kg of POMM5). A mixture of higher-grade POMMs is collected at the bottom of the column. 77 kg of POMM6, 44 kg of POMM7, 24 kg of POMM8, and 29 kg of higher-grade POMMs are obtained and returned to the dissolution autoclave.

[0135] Example 4: POMM 2-4 Production

[0136] 100 kg of post-industrial polyacetal homopolymer (previously ground into pieces not exceeding 1 cm) were added to 183 kg of fresh dimethoxymethane in an autoclave at room temperature.

[0137] 380 kg of POMM1 from a previous run was also added, as well as 582 kg of sulfolane and 20 kg of POMM from a previous run. 5+ A mixture of a mixture of the POMM 5+ The mixture contains 12 kg of POMM5, 5 kg of POMM6, 2 kg of POMM7, and 1 kg of POMM8.

[0138] The autoclave is then closed and heated to 80° C. The pressure in the autoclave increases gradually and then stabilizes as the temperature. After about 80 minutes, the dissolved mixture is sent to the reactor and passed over a filter that retains any contaminants and / or undissolved polymer.

[0139] In the reactor, the A bed of 15Dry acidic resin was placed on top of the grid. During the first run, the Amberlyst resin was first washed with methanol and then with dimethoxymethane to remove any remaining traces of water. In subsequent runs, if the resin was not contaminated with water, this washing was no longer necessary.

[0140] The previously dissolved mixture is fed into the reactor in ascending flow mode (i.e., through the bottom of the reactor). It is dispersed through the catalytic bed by means of a bottom distribution plate. When the reactor is used in ascending flow mode, the acidic resin beads move freely, but the linear velocity of the liquid is insufficient to entrain any catalytic particles. The residence time of the liquid mixture in the reactor, i.e., the ratio of the volume of resin (catalytic bed of resin) to the flow rate of the polyacetal solution in POMM1 and solvent, is 30 min. The temperature of the solution feeding the reactor is maintained below 120°C, and in particular at 80°C. The reactor is operated at a pressure of 5 bar to avoid any boiling of the reaction mixture.

[0141] The reaction mixture is then sent to a distillation column. The pressure is returned to atmospheric pressure. Diisopropylethylamine is injected into the solution to neutralize the fine catalytic particles ( Acidity caused by the presence of resin).

[0142] The temperature at the top of the column was 45° C., and the temperature at the bottom was 80° C. At the top of the column, dimethoxymethane was obtained, condensed (380 kg), and then returned to the dissolution autoclave. POMM 2+ The mixture of POMM2, POMM3 and POMM4 is obtained at the bottom of the tower. The tower bottom fraction is then sent to the other distillation tower operated under partial vacuum (50mbar). The mixture of POMM2, POMM3 and POMM4 is distilled and condensed (177kg of POMM2, 76kg of POMM3 and 31kg of POMM4). The mixture of higher POMM is collected at the bottom of the tower. Obtain 12kg of POMM5, 5kg of POMM6, 2kg of POMM7, 1kg of POMM8 and 582kg of sulfolane and return to the dissolving autoclave.

[0143] Example 5: POMM 3-4 Production

[0144] 100 kg of post-industrial polyacetal homopolymer (previously ground into flakes no larger than 0.1 cm and dried under vacuum at 80° C. for 8 hours) were added to 111 kg of fresh dimethoxymethane in an autoclave at room temperature. 768 kg of a light mixture of POMM1 (493 kg) and POMM2 (275 kg) obtained from a previous run were also added, as well as 750 kg of sulfolane and 61 kg of POMM obtained from a previous run. 5+ A mixture of a mixture of the POMM 5+ The mixture contains 33 kg of POMM5, 15 kg of POMM6, 7 kg of POMM7, 3 kg of POMM8 and 3 kg of higher grade POMM.

[0145] The autoclave is then closed and heated to 100°C. The pressure in the autoclave is gradually increased and then stabilized as the temperature. After about 50 minutes, the dissolved mixture is sent to the reactor and passed over a filter that retains any contaminants and / or undissolved polymer. In the reactor, A bed of 15 Dry Acid Resin was placed on top of the grid. During the first run, The 15Dry resin was washed first with methanol and then with dimethoxymethane to remove any remaining traces of water.

[0146] The previously dissolved mixture is fed into the reactor in an ascending flow mode (i.e., through the bottom of the reactor). It is dispersed through the catalyst bed by a bottom distribution plate. When the reactor is used in an ascending flow mode, the acidic resin beads move freely, but the linear velocity of the liquid is insufficient to entrain any catalytic particles. The residence time of the liquid mixture in the reactor, i.e., the ratio of the volume of resin (catalytic bed of resin) to the flow rate of the polyacetal solution in DMM and solvent, is 30 minutes. The temperature of the solution feeding the reactor is maintained below 120°C, specifically 105°C here. The reactor is operated at a pressure of 10 bar. The reaction mixture is then fed to a distillation column. The pressure is returned to atmospheric pressure.

[0147] The temperature at the top of the column was 105° C., and the temperature at the bottom was 120° C. At the top of the column, a mixture of dimethoxymethane (POMM1) and POMM2 was obtained, condensed (POMM1 (493 kg) and POMM2 (275 kg)), and returned to the dissolution autoclave. POMM 3+A mixture of POMM3 and sulfolane is obtained at the bottom of the column. The bottom fraction is then sent to another distillation column operated under partial vacuum (40 mbar). The mixture of POMM3 and POMM4 is distilled and condensed; 141 kg of POMM3 and 69 kg of POMM4 are collected as a mixture. A mixture of higher POMMs is collected at the bottom of the column. 61 kg of POMM4 is obtained. 5+ The mixture and 750 kg of sulfolane are returned to the dissolving autoclave, the POMM 5+ The mixture contains 33 kg of POMM5, 15 kg of POMM6, 7 kg of POMM7, 3 kg of POMM8 and 3 kg of higher grade POMM.

[0148] Example 6: POMM 3-5 Production

[0149] 90 g of polyacetal homopolymer (previously finely ground to a particle size not exceeding 0.05 cm and then dried overnight at 90° C. under a nitrogen stream) are added to 90 g of fresh dimethoxymethane in an autoclave at room temperature. 427 g of a light mixture of POMM1 (261 g) and POMM2 (166 g) from a previous run are added, as well as 546 g of sulfolane and 31 g of POMM obtained from a previous run. 6+ A mixture of the POMM 6+ Contains 15g of POMM6, 8g of POMM7, 4g of POMM8 and 4g of higher grade POMM.

[0150] The autoclave is then closed and heated to 110° C. The pressure in the autoclave increases gradually and then stabilizes as the temperature. After about 30 minutes, the dissolved mixture is sent to the reactor and passed over a filter that retains any contaminants and / or undissolved polymer.

[0151] 0.25 g of anhydrous methanesulfonic acid was injected into a pressurized stirred reactor equipped with a condenser and operated at 100°C. The reaction was continued for 1 hour, after which the temperature was lowered to 15°C and melamine was injected to neutralize the acid catalyst. The reaction mixture was then filtered to remove solid particles and passed to a distillation column. The pressure was returned to atmospheric pressure.

[0152] The temperature at the top of the column was 106° C., and the temperature at the bottom was 120° C. At the top of the column, 427 g of a light mixture of POMM1 (261 g) and POMM2 (166 g) were condensed and returned to the dissolution autoclave for subsequent runs. 3+A mixture of POMM3, POMM4, and POMM5 is obtained at the bottom of the column. The bottom fraction is then sent to another distillation column operated under partial vacuum (at 8 mbar). The mixture of POMM3, POMM4, and POMM5 is distilled and condensed at a high reflux rate; a mixture of 97 g of POMM3, 54 g of POMM4, and 29 g of POMM5 is collected. A mixture of higher-grade POMMs is collected at the bottom of the column. A mixture of 546 g of sulfolane and 31 g of POMM containing 15 g of POMM6, 8 g of POMM7, 4 g of POMM8, and 4 g of higher-grade POMM is collected and returned to the dissolution autoclave.

[0153] Example 7: POMM 2-8 Production

[0154] 150 kg of post-production polyacetal homopolymer (previously ground into pieces no larger than 1 cm and dried under vacuum at 80° C. to remove any remaining traces of water) is added to 475 kg of fresh dimethoxymethane (POMM1) sold by Lambiotte (Belgium) in an autoclave at room temperature. 832 kg of POMM1 and 101 kg of POMM2 obtained from the distillation of the previous recycling step are also added cold (20° C.) to the autoclave. The autoclave is then closed and heated to 100° C. The pressure in the autoclave is gradually increased and then stabilized at less than 6 bar as the temperature increases. After about 60 minutes, the dissolved mixture is sent to the reactor and passed through a filter that blocks any contaminants and / or undissolved polymer.

[0155] In the reactor, the A bed of 15 Dry Acid Resin (DuPont) was placed on top of the grid. 15Dry resin (1325 kg) is first washed with methanol and then with dimethoxymethane in order to remove any remaining traces of water. If the resin has already been washed in the previous step and if it is not contaminated with water, washing is not necessary. The previously dissolved mixture is sent to the reactor in ascending flow mode. It is dispersed through the catalytic bed by a bottom distribution plate. When the reactor is used in ascending flow mode, the acidic resin beads move freely, but the linear velocity of the liquid is not sufficient to entrain any catalytic particles. The residence time of the liquid mixture in the reactor, that is, the ratio of the volume of resin (catalytic bed of resin) to the flow rate of the polyacetal solution in the reactive POMM mixture, is 1 hour. The temperature of the solution feeding the reactor is kept below 120°C and in particular at 100°C. The reactor is operated at a pressure of 8 bar to prevent any boiling of the reaction solution.

[0156] The reaction mixture is then sent to a distillation column. The pressure is reduced to atmospheric pressure and the temperature is lowered to 25°C. Concentrated sodium hydroxide solution is added to neutralize traces of acidic resin that have been entrained in the reaction mixture. The mixture is then sent to the distillation step.

[0157] The temperature at the top of the column was 42°C, and the temperature at the bottom was 80°C, and then the pressure was gradually reduced to continue distillation. At the top of the column, a portion of dimethoxymethane and POMM2 was obtained, condensed and returned to the dissolution autoclave (832 kg of POMM1 and 101 kg of POMM2) for the next run. 2-8+ A mixture is obtained at the bottom of the column. This mixture contains 179 kg of POMM2, 120 kg of POMM3, 49 kg of POMM4, 19 kg of POMM5, 7 kg of POMM6, 3 kg of POMM7, 1 kg of POMM8, and less than 1 kg of higher-grade POMM. The mass composition is thus 47% by weight of POMM2, 32% by weight of POMM3, 13% by weight of POMM4, 5% by weight of POMM5, 2% by weight of POMM6, 1% by weight of POMM7, 0.3% by weight of POMM8, and less than 1% by weight of higher-grade POMM.

Claims

1. Recycling of polyacetals containing 8 to 100,000 carbon atoms for the production of R-(OCH2) n -OR', wherein R and R' independently represent a methyl group or an ethyl group and n is an integer greater than or equal to 1, the method comprising reacting an acid catalyst with a polyacetal containing 8 to 100,000 carbon atoms, a polyoxymethylene dialkyl ether of the formula R-(OCH2) k a step of reacting a mixture of a reactive polyoxymethylene dialkyl ether of -OR' and an optional solvent, wherein R and R' are as defined above and k is an integer greater than or equal to 1, wherein the polyacetal is post-manufactured or post-industrial polyacetal or post-consumer polyacetal and the ratio of the mass of reactive polyoxymethylene dialkyl ether to the mass of polyacetal is at least 2:1, The acid catalyst is selected from the group consisting of: acidic resins; inorganic acids; Lewis acids; acidic mixed oxides; organic acids selected from trifluoromethanesulfonic acid, methanesulfonic acid, p-toluenesulfonic acid; and mixtures thereof. The reaction, which is carried out in the presence of an acid catalyst, is carried out at a temperature below 120° C. and a pressure in the range of 1 to 10 bar.

2. The method of claim 1, wherein the inorganic acid is selected from the group consisting of perchloric acid and sulfuric acid.

3. The method of claim 1, wherein the Lewis acid is selected from BF3, and AsF5.

4. The method of claim 1, wherein the acidic mixed oxide is selected from the group consisting of WO3 / TiO2, phosphate alumina, tungsten alumina and zeolites.

5. The method of claim 1, wherein the reaction is carried out at a temperature of 20°C to less than 120°C.

6. The process of claim 5, wherein the reaction is carried out at a temperature of 40°C to 115°C.

7. The process of claim 6, wherein the reaction is carried out at a temperature of 60°C to 110°C.

8. The process of claim 7, wherein the reaction is carried out at a temperature of 80 to 110°C.

9. The process of claim 1, wherein the reaction is carried out at a pressure of 5 to 10 bar.

10. The method of claim 1, further comprising the step of filtering the polyacetal and / or the mixture.

11. The process according to any one of claims 1 to 10, further comprising an evaporation step to remove the compound of formula R-(OCH2) n Some or all of the light compounds of -OR', wherein n=1 or 2.

12. The method according to any one of claims 1 to 10, further comprising a purification step of recovering the produced polyoxymethylene dialkyl ether.

13. The method of claim 12, wherein the recovery step allows the polyoxymethylene dialkyl ether produced to be combined with a polyoxymethylene dialkyl ether of the formula R-(OCH2) having an n greater than the maximum n value of the polyoxymethylene dialkyl ether produced. n -OR' heavy compounds separation.

14. The method of claim 12, wherein the recovering step is performed by distillation.

15. The process of any one of claims 1 to 10, further comprising a recycling step to convert the compound of formula R-(OCH2) having n greater than or equal to 1 into n A portion of the compound of -OR' is reintroduced into the reaction step as reactive polyoxymethylene dialkyl ether.

16. The method of claim 15, wherein the recycling step reintroduces all or some of the light compounds removed in the evaporation step and / or all or some of the heavy compounds removed in the recovery step into the reaction step as reactive polyoxymethylene dialkyl ether.

17. The method according to any one of claims 1 to 10, further comprising the step of synthesizing (meth)acrylic acid or ester or (meth)acrolein or neopentyl glycol from the produced polyoxymethylene dialkyl ether.

18. The method of any one of claims 1 to 10, wherein the reactive polyoxymethylene dialkyl ether comprises methylal and / or diethoxymethane.

19. The process according to any one of claims 1 to 10, wherein the reactive polyoxymethylene dialkyl ether comprises methylal and / or diethoxymethane and one or more compounds of the formula R-(OCH2) having a k number greater than or equal to 2 k -OR' compounds.

20. The process of any one of claims 1 to 10, wherein the polyoxymethylene dialkyl ether produced is selected from the group consisting of: CH3-(OCH2)-OCH3, CH3-(OCH2)2-OCH3, CH3-(OCH2)3-OCH3, CH3-(OCH2)4-OCH3, CH3-(OCH2)5-OCH3, CH3-(OCH2)6-OCH3, CH3-(OCH2)7-OCH3, CH3-(OCH 2)8-OCH3, C2H5-(OCH2)-OC2H5, C2H5-(OCH2)2-OC2H5, C2H5-(OCH2)3-OC2H5, C2H5-(OCH2)4-OC2H5, C2H5-(OCH2)5-OC2H5, C2H5-(OCH2)6-OC2H5, C2H5-(OCH2)7-OC2H5, C2H5-(OCH2)8-OC2H5 and mixtures thereof.

21. The process of any one of claims 1 to 10, wherein the polyoxymethylene dialkyl ether produced is: - wherein n = 2 to 8 of the formula CH3-(OCH2) n -OCH3 compounds, - wherein n = 2 to 4 of the formula CH3-(OCH2) n -OCH3 compounds, - wherein n = 3 to 4 of the formula CH3-(OCH2) n -OCH3 compounds, - wherein n = 3 to 5 of the formula CH3-(OCH2) n -OCH3 compounds, or - wherein n = 2 to 4 of the formula C2H5-(OCH2) n -OC2H5 mixture of compounds.

22. The method of any one of claims 1 to 10, wherein the polyacetal is a homopolymer.

23. The method of claim 1 , wherein the solvent is selected from the group consisting of sulfolane, methyl sulfolane, ethyl sulfolane, diethyl sulfolane, propyl sulfolane, dipropyl sulfolane, butyl sulfolane, dibutyl sulfolane, amyl sulfolane, dipentyl sulfolane, hexyl sulfolane, octyl sulfolane, DMSO, and mixtures thereof.

24. The process of claim 23, wherein the solvent is sulfolane.

25. The formula R-(OCH2) as defined in claim 1, 18 or 19 k -OR' is used for recycling polyacetal containing 8 to 100 000 carbon atoms into polyacetal of formula R-(OCH2) as defined in claim 1, 20 or 21 by a process as defined in any one of claims 1 to 24 n -OR' produced polyoxymethylene dialkyl ether.

26. A process for synthesizing (meth)acrylic acid or esters or (meth)acrolein or neopentyl glycol, comprising the step of reacting a produced polyoxymethylene dialkyl ether obtained by the recycling process according to one of claims 1 to 24.