Method for producing polyoxymethylene dimethyl ether

Abstract

The present invention relates to a method for preparing polyoxymethylene dimethyl ether, comprising the following steps: 1 ) in a reactor R1 to obtain a product mixture; in a distillation unit D1, the product mixture is separated by distillation into OME 1 OME 2 , formaldehyde, methanol and water top flow and OME ≥3 - the bottom stream discharged from the distillation unit D1 is mixed with a stream containing methanol; - the mixture is treated in a reactive distillation unit RD2 to form a top stream containing methylal and an aqueous bottom stream; - the bottom stream discharged from the distillation unit D1 is introduced into a distillation unit D3 and the polyoxymethylene dimethyl ether is separated by distillation.

Description

Technical Field

[0001] The present disclosure relates to a method for preparing polyoxymethylene dimethyl ethers. Background Art

[0002] Synthetic energy carriers that are not produced based on crude oil or natural gas can reduce dependence on fossil energy and environmental pollution caused by the use of fossil energy. An example of such an energy carrier is polyoxymethylene dimethyl ethers (OMEs). Polyoxymethylene dimethyl ethers (OMEs) can be prepared from carbon dioxide and water and, if produced using renewable energy carriers, have the potential to close the carbon dioxide cycle when burned as fuel.

[0003] Furthermore, the use of polyoxymethylene dimethyl ethers as energy carriers offers other advantages. Polyoxymethylene dimethyl ethers have no carbon-carbon bonds and also have a high oxygen content. Polyoxymethylene dimethyl ethers burn without smoke and are therefore gentle on the internal combustion engine and downstream filter elements as well as the environment. Furthermore, smokeless combustion reduces nitrogen oxide emissions. 3-5 ) are of particular interest because of their diesel-like properties.

[0004] The reactants usually used to synthesize polyoxymethylene dimethyl ethers are a formaldehyde source (e.g., formaldehyde, trioxymethylene or polyoxymethylene) and a compound for methyl termination, such as methanol, methylal or dimethyl ether. If the reaction mixture contains methanol and water, they react with formaldehyde to form polyoxymethylene diol (MGD) according to the following reaction equations 1-4: n ; HO-(CH 2 O) n -H) and polyoxymethylene hemiacetal (HF n ; HO-(CH 2 O) n -CH 3 ). These reactions do not require a catalyst and reach chemical equilibrium very quickly. In addition, the chemical equilibrium is mainly on the product side, which means that monomeric formaldehyde (CH 2 O). According to the following reaction equation 5, methanol and HO—CH 2 O-CH 3 (HF 1 ) through acetalization to form methylal (H 3 CO-(CH 2 O) 1 -CH 3 ;OME 1 ), the presence of an acidic catalyst is required. According to the following reaction equation 7, by introducing additional CH 2O units to achieve chain growth. Methanol and polyoxymethylene hemiacetal HF n The further acetalization reaction between is carried out according to the following reaction equation 6. 2 O) 3 ) and methyl formate (HC(O)OCH 3 ) are shown by the following reaction equations 8 and 9.

[0005]

[0006]

[0007]

[0008]

[0009]

[0010]

[0011]

[0012]

[0013] 2CH 2 O → HCOOCH 3 9

[0014] Polyoxymethylene dimethyl ether H 3 CO-(CH 2 O) n -CH 3 (where n≥2(OME ≥2 ), especially n=3-5 (OME 3-5 An overview of known preparation methods of )) can be found in the following literature: for example, the publication of M. Ouda et al., React. Chem. Eng., 2017, 2, 50-59 pages. A distinction is made here between anhydrous and aqueous synthesis routes. Anhydrous synthesis routes show reduced formation of by-products, but the provision of reactants is energy intensive. The reactants provided for aqueous synthesis routes are less energy intensive, but by-products and water are also present in the reaction products.

[0015] For example, a reactant mixture containing methylal and trioxymethylene can be used as a starting point. The advantage of this synthesis scheme is that it produces polyoxymethylene dimethyl ethers in high yields and can be carried out essentially under anhydrous conditions, which reduces the amount of by-products. The disadvantage is that the preparation of anhydrous trioxymethylene is very energy-intensive and complicated, which adversely affects the energy efficiency and economic feasibility of the process.

[0016] US 2007 / 260094 A1 describes a process for preparing polyoxymethylene dimethyl ethers, in which methylal and trioxymethylene are fed into a reactor and reacted in the presence of an acidic catalyst, the amount of water introduced into the reaction mixture being less than 1% by weight.

[0017] The substantially anhydrous synthesis of polyoxymethylene dialkyl ethers can also be achieved by using trioxymethylene and a dialkyl ether (eg, dimethyl ether DME) as reactants.

[0018] DE 102005027690 A1 describes a method for preparing polyoxymethylene dialkyl ethers, wherein dialkyl ethers (dimethyl ether, methyl ethyl ether or diethyl ether) and trioxymethylene are fed into a reactor and reacted in the presence of an acidic catalyst, and the amount of water introduced into the reaction mixture by the dialkyl ether, trioxymethylene and / or the catalyst is less than 1% by weight. P. Haltenort et al., Catalysis Communications, 2018, 109, 80, describe the synthesis of polyoxymethylene dimethyl ethers from dimethyl ether (DME) and trioxymethylene using zeolites as acidic catalysts. Based on the reactants used, the maximum DME conversion is 13.9% by weight, OME 3-5 The maximum yield of 8.2 wt. % was 8.2 wt. %. The studies showed that the synthesis scheme starting from dimethyl ether and trioxymethylene resulted in relatively high reactor residence times.

[0019] It is also known that formaldehyde for the synthesis of polyoxymethylene dimethyl ethers is prepared by catalytic dehydrogenation of methanol, see, for example, M. Ouda, F. mantei et al., Reaction Chemistry and Engineering (React. Chem. Eng.), 2018, 129, 11164. This method can use an anhydrous reactant mixture, which means that only water formed during the synthesis process is present in the product mixture. However, the catalytic dehydrogenation of methanol is a complex chemical reaction, and its technical maturity is relatively low.

[0020] It is also known to use a reactant mixture comprising aqueous formaldehyde and methanol.

[0021] DE 102016222657 A1 describes a method for preparing polyoxymethylene dimethyl ethers, comprising the following steps:

[0022] (i) feeding formaldehyde, methanol and water into a reactor R and reacting to form a reaction mixture containing formaldehyde, water, methylene glycol, polyoxymethylene glycol, methanol, hemiformal, methylal and polyoxymethylene dimethyl ether;

[0023] (ii) the reaction mixture is fed to a reactive distillation column K1 and separated into polyoxymethylene glycol, methanol, hemiformal, methylal and polyoxymethylene dimethyl ether (OMET) having 2 to 3 oxymethylene units. 2-3 ) and polyoxymethylene dimethyl ether (OME ≥3 )'s high boiling point fraction F2.

[0024] Compared to anhydrous formaldehyde sources such as trioxymethylene, the preparation of aqueous formaldehyde solutions consumes less energy. However, when using reactants in an aqueous phase, there is a challenge to remove water from the product mixture as efficiently as possible. In addition, the presence of water leads to the formation of more by-products, which reduces the product yield.

[0025] The disadvantage of using methanol as a reactant is that the acetalization reaction between methanol and hemiacetal leads to the formation of additional water as a by-product (see above-mentioned reaction equations 5 and 6), and this reaction water also needs to be removed from the process. Due to the complex distillation behavior of the product mixture, water cannot be removed by standard distillation without removing some formaldehyde at the same time. As an alternative to distillation to remove water, other methods for removing water have therefore also been studied, such as adsorption, membrane-based separation methods or extraction. However, these methods pose further challenges to long-term operation. These alternative water removal methods are described, for example, in the following publications:

[0026] -N. Schmitz et al., Industrial & Engineering Chemistry Research, 2017, 56, 11519;

[0027] -N. Schmitz et al., Journal of Membrane Science, 2018, 564, 806;

[0028] -L. Wang et al., Journal of Chemical and Engineering Data (J. Chem. Eng. Data), 2018, 63, 3074;

[0029] -M. Shi et al., Can. J. Chem. Eng., 2018, 96, 968;

[0030] -D. Oestreich et al., Fuel, 2018, 214, 39;

[0031] -X. Li et al., Journal of Chemical and Engineering Data (J. Chem. Eng. Data), 2019, 64, 5548.

[0032] Methylal is used as a solvent for the production of fragrances, resins or protective coatings. It is also tested as a fuel additive and as a synthetic fuel. The preparation of very essentially pure methylal is described, for example, in WO 2012 / 062822 A1. In this process, formaldehyde and methanol are reacted to give a product mixture containing methylal and water as well as unconverted methanol and formaldehyde. The product mixture is separated into three fractions in a reactive distillation unit. The fraction leaving the reactive distillation unit as a top stream is rich in methylal. The preparation of polyoxymethylene dimethyl ethers is not described. Summary of the invention

[0033] An object of the present disclosure is to prepare polyoxymethylene dimethyl ethers by an efficient and easily scalable process.

[0034] This object is achieved by two optional methods (“first independent embodiment” and “second independent embodiment”) according to the present disclosure described below.

[0035] According to a first independent embodiment of the present disclosure, the object is achieved by a method for preparing polyoxymethylene dimethyl ether, the method comprising the following steps:

[0036] - a stream S containing an aqueous formaldehyde source FA With methylal containing stream S OME1 Mix to obtain a reactant mixture M 反应物 (M Reactant ),

[0037] - Make the reactant mixture M 反应物 The reaction is carried out in reactor R1 to obtain a product mixture M R1 , the product mixture M R1 Containing formula H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ), H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 )) of polyoxymethylene dimethyl ether, as well as formaldehyde, methylal (OME 1 ), methanol and water,

[0038] - The product mixture M R1Introduced into the distillation unit D1, and the product mixture M R1 Distillation is separated into a first fraction and a second fraction, the first fraction containing methylal (OME 1 ), H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ), formaldehyde, methanol and water, and as the top flow KS D1 Leaving the distillation unit D1, the second fraction contains 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 )) of polyoxymethylene dimethyl ether and as underflow SS D1 Leaving distillation unit D1,

[0039] -The top stream KS D1 With methanol-containing stream S MeOH Mix to obtain a mixture M1,

[0040] - The mixture M1 is reacted in at least one reaction zone RZ of a reactive distillation unit RD2 in the presence of a catalyst, wherein H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) to give methylal (OME 1 ) and formaldehyde, formaldehyde and methanol react to obtain methylal (OME 1 ); and distilled into a first fraction and a second fraction, the first fraction containing methylal (OME 1 ) and as a top KS RD2 Leaving the reactive distillation unit RD2, the second fraction contains water and is taken as bottom stream SS RD2 Leaving the reactive distillation unit RD2,

[0041] - Set the bottom flow SS D1 Introduce distillation unit D3 and transfer bottom flow SS D1 The formula H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH2 O) n -CH 3 (where n≥6(OME ≥6 )) is distilled and separated into polyoxymethylene dimethyl ether, as the top stream KS D3 The fraction leaving the distillation unit D3 and as bottom stream SS D3 The fraction leaving the distillation unit.

[0042] Alternatively, according to a second independent embodiment, the object is achieved by a method for preparing polyoxymethylene dimethyl ether, the method comprising the following steps:

[0043] - a stream S containing an aqueous formaldehyde source FA With methylal containing stream S OME1 Mix to obtain a reactant mixture M 反应物 (M Reactant ),

[0044] - Make the reactant mixture M 反应物 The reaction is carried out in reactor R1 to obtain a product mixture M R1 , the product mixture M R1 Containing formula H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ), H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 )) of polyoxymethylene dimethyl ether, as well as formaldehyde, methylal (OME 1 ), methanol and water,

[0045] - The product mixture M R1 With methanol-containing stream S MeOH Mix to obtain a mixture M1,

[0046] - The mixture M1 is reacted in at least one reaction zone RZ of a reactive distillation unit RD1 in the presence of a catalyst, wherein H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) to give methylal (OME 1) and formaldehyde, formaldehyde and methanol react to obtain methylal (OME 1 ) and distilled into a first fraction and a second fraction, the first fraction containing water, methanol, formaldehyde, methylal (OME 1 ) and H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) and as a top KS RD1 Leaving the reactive distillation unit RD1, the second fraction contains the formula, H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 )) of polyoxymethylene dimethyl ether and as underflow SS RD1 Leaving the reactive distillation unit RD1,

[0047] -The top stream KS RD1 The distillation unit D2 is introduced and separated by distillation into a first fraction and a second fraction. The first fraction contains methylal and serves as the top stream KS D2 Leaving the distillation unit D2, the second fraction contains water and is taken as the bottom stream SS D2 Leaving distillation unit D2,

[0048] - Set the bottom flow SS RD1 Introduce distillation unit D3 and transfer bottom flow SS RD1 The formula H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 )) is distilled and separated into polyoxymethylene dimethyl ether, as the top stream KS D3 The fraction leaving the distillation unit D3 and as bottom stream SS D3 The fraction leaving the distillation unit.

[0049] As will be described in more detail below, the process according to the present disclosure enables efficient distillation of water and thus solves one of the main challenges of the process for preparing polyoxymethylene ethers.2 The formaldehyde formed during the reaction is present in the top flow KS in the form of methylal D1 (the first independent embodiment of the present disclosure) or the methanol present in the product mixture M R1 (a second independent embodiment of the present disclosure) wherein methanol, and passing a stream S containing methanol in an externally defined manner MeOH The added methanol is chemically bonded. Therefore, the removal of the methanol by the external methanol flow S can be regulated in a controlled manner (e.g., substantially completely removed). MeOH , undercurrent SS RD2 (the first independent embodiment of the present disclosure) or top stream KS RD1 and undercurrent SS D2 (The proportion of formaldehyde in the second independent embodiment of the present disclosure). No additional water removal unit is required.

[0050] The aqueous formaldehyde source used in the two independent embodiments of the present disclosure is preferably an aqueous formaldehyde solution, in particular a concentrated aqueous formaldehyde solution having a formaldehyde content of at least 70% by weight, more preferably at least 80% by weight, and even more preferably at least 90% by weight. Such aqueous formaldehyde solutions are commercially available or can be prepared by known methods, for example from a starting aqueous solution containing formaldehyde, which is passed through a concentrator unit (e.g. one or more thin-film evaporators) and thus converted into a concentrated aqueous formaldehyde solution. The preparation of concentrated aqueous formaldehyde solutions is described, for example, in WO 03 / 040075 A2, EP 1688168 A1, DE 10309289 A1 or DE 10309286 A1.

[0051] Therefore, the stream S containing formaldehyde and water FA Preferably it has a formaldehyde content of at least 70 wt%, more preferably at least 80 wt%, still more preferably at least 90 wt%, for example 70 to 97 wt%, more preferably 80 to 95 wt%, or 90 to 95 wt%.

[0052] As known to those skilled in the art, in aqueous formaldehyde solution, monomeric formaldehyde CH 2 O and its monomer hydrate methylene glycol (HO-(CH 2 O) 1 -H) and its oligomeric hydrates (also known as polyoxymethylene glycol (HO-(CH 2 O) n -H, where n≥2)) exist together. The formaldehyde content of the formaldehyde aqueous solution is related to the monomer formaldehyde CH 2 O, monomeric formaldehyde hydrate (i.e. methylene glycol (HO-(CH 2 O) 1 -H)) and paraformaldehyde hydrate (i.e., polyoxymethylene glycol (HO-(CH 2 O)n -H,n≥2))).

[0053] In the first and second embodiments of the method according to the present disclosure, the stream S containing formaldehyde and water FA With methylal (H 3 CO-(CH 2 O) 1 -CH 3 , also known as dimethoxymethane or OME 1 ) of the flow S OME1 Mix to obtain a reactant mixture M 反应物 As will be described in more detail below, the methylal-containing stream S OME1 Preferably, the top stream KS discharged from the reactive distillation unit RD2 (the first independent embodiment of the present disclosure) RD2 or the top stream KS discharged from the distillation unit D2 (the second independent embodiment of the present disclosure) D2 , which has been recycled for use with the aqueous formaldehyde source S FA Mixing. Different sources of methylal can be used to start the process according to the present disclosure. Preferably, the methylal-containing stream S OME1 The methylal stream may contain at least 70% by weight, more preferably at least 90% by weight of methylal. Optionally, the methylal stream may contain other components, such as methanol. However, methanol is not a OME1 The content in is preferably less than 10% by weight.

[0054] Stream containing formaldehyde and water FA Preferably, outside the reactor R1, the methylal-containing stream M 反应物 Mix, then the reactant mixture M 反应物 Introduced into reactor R1. Alternatively, stream S FA and S OME1 It is also possible that they are mixed with one another only in the reactor R1.

[0055] In addition to formaldehyde, methylal and water, the reactant mixture M 反应物 It may also optionally contain other components, such as methanol or a number of general formula H 3 CO-(CH 2 O) n -CH 3 (where n≥6)(OME ≥6 ) of long-chain polyoxymethylene dimethyl ether. Long-chain polyoxymethylene dimethyl ether is used as bottom flow SS D3 It is discharged from the distillation unit D3 and recycled.

[0056] In the reactant mixture M 反应物The molar ratio of methylal to formaldehyde in the water-containing stream S is, for example, in the range of 0.3 to 2.0, more preferably in the range of 0.5 to 1.5. However, lower or higher methylal / formaldehyde molar ratios can also be selected. The preferred molar ratio depends on the formaldehyde- and water-containing stream S FA Formaldehyde content in methylal-containing streams OME1 The methylal content in

[0057] In the first and second embodiments of the method according to the present disclosure, the reactant mixture M 反应物 The reaction is carried out in reactor R1 to obtain a product mixture M R1 , which contains the formula H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ), H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 )) of polyoxymethylene dimethyl ether, as well as formaldehyde, methylal (OME 1 ), methanol and water. 1 ) to form polyoxymethylene dimethyl ether OME ≥2 Suitable conditions are known to those skilled in the art. The reaction is preferably carried out in the presence of an acidic catalyst. Solid catalysts or other liquid acids can be used. For example, the following catalysts can be cited: ion exchange resins with acidic groups (i.e., cation exchange resins), zeolites, aluminosilicates, aluminum oxides, transition metal oxides (which are optionally on a support material), graphene oxide, inorganic acids (e.g., sulfuric acid), organic acids (e.g., sulfonic acids), acidic ionic liquids, oxonium salts (e.g., trimethyloxonium salts). Reactor R1 is operated, for example, at a pressure of 1 bar to 10 bar and a temperature of 50° C. to 120° C. Reactor R1 is, for example, a fixed bed reactor. However, in the context of the present disclosure, other reactor types can also be used for reactant mixture M. 反应物 In addition to OME 2 OME 3-5 OME ≥6 , formaldehyde, OME 1 , methanol and water, the product mixture M R1 It may also optionally contain other components, such as a 2 O) n -CH3 (n≥1) hemiacetal, formula HO-(CH 2 O) n -H (n ≥ 1) diol, trioxymethylene and / or methyl formate.

[0058] According to a first independent embodiment of the process disclosed herein, in the distillation unit D1, the product mixture M R1 It is separated by distillation into a first fraction and a second fraction. The first fraction contains methylal (OME 1 ), H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ), formaldehyde, methanol and water, and as the top flow KS D1 Leaving the distillation unit D1, the second fraction contains 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 )) of polyoxymethylene dimethyl ether and as underflow SS D1 Leaving the distillation unit D1. The top stream KS may optionally be present D1 The other components in the formula are, for example, HO-(CH 2 O) n -CH 3 (n≥2) hemiacetal, formula HO-(CH 2 O) n -H(n≥1) diol, OME 3 , trioxymethylene and / or methyl formate. D1 Preferably without any OME ≥4 , preferably without any OME ≥3 The distillation unit D1 preferably contains no catalyst (in particular no acidic catalyst). The distillation unit D1 is preferably not a reactive distillation unit.

[0059] Therefore, the polyoxymethylene dimethyl ether OME 2 OME 3-5 and OME ≥6 The distillation unit D1 of the distillation separation makes OME 1-2 Discharged in top stream, OME ≥3The distillation unit D1 is discharged in the underflow. The person skilled in the art can determine suitable conditions for this by taking into account general expertise. The distillation unit D1 is, for example, a distillation column. The distillation unit generally comprises internal components for distillative separation, in particular trays, random packings or structured packings, as generally known to the person skilled in the art. The distillation unit D1 is operated, for example, at a pressure of 1 to 15 bar and a temperature of 60° C. to 250° C. If necessary, in order to promote the formation of formaldehyde, methanol, water, HO(CH 2 O) 1 -CH 3 (HF 1 ) and HO-(CH 2 O) 1 -H(MG 1 ), it may be advantageous to select a relatively long residence time in the distillation unit D1. Measures that can optionally be used to extend the residence time are known to the person skilled in the art. In this context, reference may be made, for example, to the measures described in paragraph

[0068] of DE 10 2016 222 657 A1. For example, the distillation unit D1 comprises a retention filler (e.g. as described in EP 1 074 296 A1) or a delay tray ( tray).

[0060] In a first independent embodiment of the process according to the present disclosure, the top stream KS discharged from the distillation unit D1 is D1 With methanol-containing stream S MeOH and mixing to obtain a mixture M1. Optionally, a stream S containing methanol MeOH It may also contain other ingredients (such as formaldehyde, water, OME 1 OME ≥2 or trioxymethylene). However, the methanol-containing stream S MeOH Preferably it contains at least 80% by weight of methanol, more preferably at least 90% by weight of methanol.

[0061] In a first independent embodiment of the process according to the present disclosure, the mixture M1 is reacted in at least one reaction zone RZ of a reactive distillation unit RD2 in the presence of a catalyst, wherein H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) to give methylal (OME 1 ) and formaldehyde, formaldehyde and methanol react to obtain methylal (OME 1 ); and distillation separation is achieved into a first fraction and a second fraction, the first fraction containing methylal (OME1 ) and as a top KS RD2 Leaving the reactive distillation unit RD2, the second fraction contains water and is taken as bottom stream SS RD2 Leaving the reactive distillation unit RD2.

[0062] The top stream KS discharged from the distillation unit D1 D1 With methanol-containing stream S MeOH The mixing is preferably carried out outside the reactive distillation unit RD2 and the resulting mixture M1 is then introduced into the reactive distillation unit RD2. However, in the context of the present disclosure, the top stream KS D1 and the methanol-containing stream S MeOH It is also possible that they are not mixed with one another until in the reactive distillation unit RD2.

[0063] The reactive distillation unit RD2 (e.g., reactive distillation column) used in the first independent embodiment of the process according to the present disclosure comprises one or more reaction zones RZ and one or more distillation separation zones. The reaction zone RZ contains one or more catalysts, in particular acidic catalysts (e.g., one or more acidic solid catalysts, such as ion exchange resins with acidic groups (i.e., cation exchange resins), zeolites, aluminosilicates, alumina, transition metal oxides (which are optionally on a support material) or graphene oxide) for OME 2 to produce methylal (OME 1 ) and formaldehyde (see above reaction equation 7), the reaction of formaldehyde and methanol also produces methylal (OME 1 ). The distillation separation zone comprises, for example, internals for distillation separation, in particular trays, random packings or structured packings, as generally known to the person skilled in the art. The catalyst can be fixed in the reaction zone RZ of the reactive distillation unit RD2 in a manner known to the person skilled in the art, for example as a random dump packing; in the form of a metal wire mesh body filled with catalyst or in the form of a catalyst shaped body mounted on a tray of the RZ reaction zone. If the reactive distillation unit RD2 comprises two or more reaction zones RZ, preferably there is a distillation separation zone between every two reaction zones RZ.

[0064] In the catalyst-containing reaction zone RZ of the reactive distillation unit RD2, a chemical reaction of the mixture M1 is carried out, wherein H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) to give methylal (OME 1 ) and formaldehyde, formaldehyde and methanol react to obtain methylal (OME 1). In addition, in the reactive distillation unit RD2, distillation separation is performed into a first fraction and a second fraction. The first fraction contains methylal (OME 1 ) and optionally methanol, and as top stream KS RD2 Leaving the reactive distillation unit RD2, the second fraction contains water and optionally excess methanol, unconverted formaldehyde, 2 O) n -CH 3 (n≥1) hemiacetal and / or HO-(CH 2 O) n -H (n ≥ 1) diol, and as the underflow SS RD2 Leaving the reactive distillation unit RD2.

[0065] The reactive distillation unit RD2 makes it possible to:

[0066] -Get the top KS RD2 , which contains mainly methylal and optionally a small amount of methanol and can therefore be recycled as a methylal source for use with an aqueous formaldehyde source S FA Mixed, and

[0067] - Via underflow SS RD2 To effectively remove water, the underflow SS RD2 Contains water and optionally an excess of methanol, unconverted formaldehyde, a 2 O) n -CH 3 (n≥1) hemiacetal and / or HO-(CH 2 O) n -H (n ≥ 1) diol.

[0068] As described above, formaldehyde and methanol are reacted in the catalyst-containing reaction zone RZ of the reactive distillation unit RD2 to give methylal (OME 1 The molar ratio of formaldehyde to methanol in the mixture M1 can be used to control whether (i) the formaldehyde is mostly or even completely converted to OME 1 , and remaining unconverted methanol residues, or (ii) remaining unconverted formaldehyde residues. In variant (i), the underflow SS RD2 , preferably contains methanol and optionally relatively small amounts of formaldehyde in addition to water, while in variant (ii) the underflow SS RD2 , preferably contains, besides water, formaldehyde and optionally relatively small amounts of methanol.

[0069] In variant (i), the aqueous underflow SS RD2 Contains methanol, for example, in a proportion of ≥0 wt% to 80 wt%, more preferably ≥0 wt% to 30 wt%. RD2The total proportion of water and methanol is preferably greater than 95% by weight. 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) and / or methylal (OME 1 ) may also be present in the underflow SS in an optional proportion. RD2 These preferably amount to a proportion of less than 5% by weight, particularly preferably to a proportion of less than 1% by weight.

[0070] In variant (ii), the aqueous underflow SS RD2 Contains formaldehyde in a proportion of, for example, ≥ 0% to 60% by weight, more preferably 25% to 55% by weight. RD2 The total proportion of water and formaldehyde in the reaction mixture is preferably greater than 80% by weight, more preferably greater than 95% by weight. 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) and / or methylal (OME 1 ) may also be present in the underflow SS in an optional proportion. RD2 These preferably total to a proportion of less than 20% by weight (underflow SS RD2 Chinese OME 2 The proportion of OME is preferably less than 5% by weight. Particularly preferred is a proportion of less than 5% by weight (where OME 2 In the undercurrent SS RD2 The proportion in the aqueous underflow SS is preferably less than 2% by weight. RD2 Contains 25 wt % to 55 wt % formaldehyde, wherein the total proportion of water and formaldehyde in the underflow is greater than 95 wt %, and the underflow SS RD2 Chinese OME 2 The proportion is less than 2% by weight.

[0071] For H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) to give methylal (OME 1 ) and formaldehyde, and for the reaction of formaldehyde and methanol to obtain methylal (OME 1 ) are known to those skilled in the art. Acidic catalysts (e.g. one or more acidic solid catalysts, such as ion exchange resins with acidic groups (i.e. cation exchange resins), zeolites, aluminosilicates, aluminum oxides, transition metal oxides (optionally on a support material) or graphene oxide) are preferred.

[0072] The reactive distillation unit RD2 is operated, for example, at a pressure of 1 to 5 bar and a temperature of 40 to 140°C.

[0073] For example, the mixture M1 is introduced into the reactive distillation unit RD2 in a region above the reaction zone RZ containing the catalyst. Optionally, another reaction zone RZ containing the catalyst may be located above the region where the mixture M1 is introduced, and a mixture containing mainly (e.g. at least 80% by weight) formaldehyde, OME ≥2 or trioxymethylene or a mixture of at least two of these components. This is particularly useful for obtaining a top stream KS with a very low methanol content. RD2 Could be advantageous.

[0074] Optionally, in addition to the top stream KS RD2 and undercurrent SS RD2 In addition, at least one further side stream, for example a MeOH-rich side stream having a MeOH content of at least 70% by weight, can be withdrawn from the reactive distillation unit RD2. This side stream can be withdrawn, for example, from the reactive distillation unit RD2 between the reaction zone RZ and the underflow SS. RD2 The reaction distillation unit RD2 is discharged from the area between the discharge zones (i.e. the bottom of the reactive distillation unit RD2).

[0075] In a preferred embodiment, at least a portion of the top stream KS discharged from the reactive distillation unit RD2 is RD2 is recycled and used as methylal-containing stream S OME1 , which is mixed with a stream containing formaldehyde and water FA Mix to obtain a reactant mixture M 反应物 As mentioned above, the two streams are preferably mixed upstream of the reactor R1 and the resulting reactant mixture M is then 反应物 Alternatively, the two streams may not be mixed with one another until in the R1 reactor.

[0076] If the top stream KS discharged from the reactive distillation unit RD2 RD2 If methanol is still present in the top flow KS RD2 During its recycling it is advantageously passed through a distillation unit D4 in which the methanol is at least partially removed by distillation.

[0077] The top stream KS discharged from the reactive distillation unit RD2 RD2 During its circulation, it preferably passes through a mass flow distributor, in which the top flow KS RD2 By using a mass flow distributor, the reaction mixture M can be adjusted 反应物This in turn helps in the reaction mixture M 反应物 Establish a constant ratio of formaldehyde to methylal in the final product and adjust the long-chain polyoxymethylene dimethyl ether OME ≥3 The methylal separated in the mass flow distributor itself constitutes a potentially interesting starting material for other processes and can be stored until further use. Mass flow distributors that can divide the product stream into two or more substreams are known to those skilled in the art.

[0078] The bottom stream SS discharged from the distillation unit D1 in a first independent embodiment of the process according to the present disclosure is D1 Introduced into distillation unit D3. As mentioned above, the bottom flow SS D1 Contains H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 In the distillation unit D3, these polyoxymethylene dimethyl ethers are separated by distillation into the top stream KS D3 The fraction leaving the distillation unit D3 and as bottom stream SS D3 The conditions selected for the distillation separation in the distillation unit D3 can be adapted to the desired product spectrum. For example, the distillation unit D3 is operated so that the top stream KS discharged from the distillation unit D3 is D3 Contains H 3 CO-(CH 2 O) 3-5 -CH 3 , undercurrent SS D3 Containing formula H 3 CO-(CH 2 O) n -CH 3 (where n≥6). The distillation unit D3 comprises, for example, internals for separation by distillation, in particular trays, random packings or structured packings, as generally known to those skilled in the art. The distillation unit D3 is operated, for example, at a pressure of 0.05 bar to 3 bar and a temperature of 60° C. to 220° C. If the distillation unit is operated under reduced pressure (0.05 bar to less than 1.0 bar), it may be advantageous to use internals that result in low pressure gradients. The distillation unit D3 preferably does not contain a catalyst (in particular does not contain an acidic catalyst). The distillation unit D3 is preferably not a reactive distillation unit.

[0079] Optionally, the bottom stream SS discharged from the distillation unit D3 D3 At least a portion of the FA mix.

[0080] As described above, the bottom stream SS discharged from the reactive distillation unit RD2 RD2 In addition to water, formaldehyde may optionally be present (see variant (ii) above). Since formaldehyde is one of the reactants of the process according to the present disclosure, in this case, the underflow SS containing formaldehyde is RD2 It may be advantageous to recycle and introduce it into a concentrator unit FC, where a portion of the water is removed and the stream leaving the concentrator unit serves as stream S FA The effect of methylal on the OME1 Mix to obtain a reactant mixture M 反应物 Before being introduced into the concentrator unit FC, the recycled formaldehyde-containing underflow SS is preferably RD2 The formaldehyde-containing mixture M2 is mixed with a formaldehyde-containing starting material (e.g., an aqueous formaldehyde solution having a formaldehyde content of at least 30% by weight, more preferably at least 50% by weight) to obtain a formaldehyde-containing mixture M2. The formaldehyde-containing mixture M2 is introduced into a concentrator unit FC, and a portion of the water is removed in the concentrator unit FC to increase the formaldehyde concentration. A stream is discharged from the concentrator unit FC as a formaldehyde source S FA and with methylal-containing stream S OME1 Mix to obtain a reaction mixture M 反应物 .

[0081] Suitable elements of the concentrator unit are known to those skilled in the art. For example, the concentrator unit comprises one or more film evaporators. A film evaporator is, for example, a thin film evaporator, a spiral tube evaporator or a falling film evaporator. For suitable concentrator units for increasing the formaldehyde concentration in the aqueous formaldehyde solution, reference can be made to WO 03 / 040075 A2 and EP 1 688 168 A1.

[0082] In this series, there are three main process steps for selectively converting formaldehyde and methanol into long-chain OME: concentration of a formaldehyde source, reaction of formaldehyde with recycled methylal to form long-chain OME, and separation of the product mixture into a product stream containing long-chain OME, a product stream containing mainly water, and optionally a product stream containing mainly methylal.

[0083] refer to Figure 1 An exemplary configuration of the first independent embodiment of the present disclosure is described in more detail.

[0084] The formaldehyde- and water-containing stream S is supplied via line 1 FA and the methylal-containing stream S supplied via line 9 OME1As will be described in more detail below, the methylal-containing stream S OME1 is the top flow KS which is discharged from the reactive distillation unit RD2 via line 7 and flows through the mass flow distributor T during its recirculation RD2 Optionally, stream S OME1 A small amount of methanol (<10 wt%) may be included. Optionally, long chain OME (e.g. OME ≥6 ), which serves as the underflow SS D3 , which is discharged from the distillation unit D3 via line 13, can be combined with the stream S FA and S OME1 mix.

[0085] By mixing the flow S FA and S OME1 (and optionally SS D3 ), obtain the reactant mixture M 反应物 , which is introduced into reactor R1, such as a fixed bed reactor, via pipeline 2. Formaldehyde and OME 1 In reactor R1, OME is obtained. 2 OME 3-5 and OME ≥6 The obtained product mixture M R1 Contains OME 2 OME 3-5 and OME ≥6 and OME 1 , formaldehyde, methanol and water.

[0086] Through pipeline 3, the product mixture M R1 The product mixture M is discharged from the reactor R1 and introduced into the distillation unit D1. R1 Distillation is separated into a first fraction and a second fraction, the first fraction containing methylal (OME 1 ), H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ), formaldehyde, methanol and water (and optionally OME 3 ) and through pipeline 4 as top flow KS D1 Leaving the distillation unit D1, the second fraction contains 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3(where n≥6(OME ≥6 )) and leaves the distillation unit D1 via line 11 as bottom stream SS D1 .

[0087] The top stream KS discharged from the distillation unit D1 via line 4 D1 and the methanol-containing stream S supplied via line 5 MeOH The resulting mixture M1 is introduced into the reactive distillation unit RD2 via line 6. The molar ratio of methanol to formaldehyde in the mixture M1 is selected so that the formaldehyde in the reactive distillation unit is completely converted into OME 1 , and an unconverted methanol residue remains.

[0088] The reactive distillation unit RD2 has a reaction zone containing a catalyst, wherein OME 2 (and optionally OME 3 , if the top stream KS discharged from the distillation unit D1 D1 Still contains a certain proportion of OME 3 ) to form methylal (OME 1 ) and formaldehyde, formaldehyde and methanol react to obtain methylal (OME 1 ). Furthermore, in the reactive distillation unit RD2, a distillative separation into a first fraction and a second fraction occurs, the first fraction containing methylal (and optionally methanol) and being supplied via line 7 as top stream KS RD2 Leaving the reactive distillation unit RD2, the second fraction contains mainly water and methanol, which is discharged via line 10 as underflow SS RD2 Leaving the reactive distillation unit RD2.

[0089] The top stream KS discharged from the reactive distillation unit RD2 via line 7 RD2 is recycled and used as methylal-containing stream S OME1 It works by connecting it to the flow S containing formaldehyde and water via pipe 9. FA (supplied via pipeline 1) to obtain a reactant mixture M 反应物 During its recycling process, the top flow KS RD2 Flows through mass flow distributor T, where top flow KS RD2 By using a mass flow distributor, the reactant mixture M can be adjusted 反应物 The methylal separated off in the mass flow distributor itself constitutes a potentially interesting raw material for other processes and can be stored for future use.

[0090] The underflow SS discharged from the distillation unit D1 via line 11 D1 Introduced into distillation unit D3. As mentioned above, the bottom flow SSD1 Contains OME 3-5 and OME ≥6 In the distillation unit D3, these polyoxymethylene dimethyl ethers are separated by distillation into OME 3-5 fraction and is passed through pipeline 12 as top flow KS D3 Leaving distillation unit D3; and containing OME ≥6 The fraction is passed through pipeline 13 as bottom flow SS D3 Leaving distillation unit D3. Optionally, bottom stream SS D3 Can be recycled and mixed with aqueous formaldehyde source S FA (Pipeline 1) Mixing.

[0091] refer to Figure 2 Further exemplary configurations of the first independent embodiment of the method according to the present disclosure are described in more detail. Figure 2 The process scheme shown is similar to Figure 1 The process schemes shown differ in that:

[0092] - In the mixture M1 (by applying the top flow KS D1 (Pipeline 4) and the methanol-containing stream S MeOH The molar ratio of methanol to formaldehyde is selected so that the methanol in the reactive distillation unit RD2 is largely converted into OME 1 , and the unconverted formaldehyde residue is used as the aqueous underflow SS RD2 The components are discharged from the reactive distillation unit RD2 via line 10.

[0093] -The underflow SS RD2 , containing, besides water, formaldehyde and optionally a small amount of methanol, is recycled and mixed with the aqueous formaldehyde solution supplied via line-2. The resulting mixture M2 is introduced via line-1 into a concentrator unit FC, which for example comprises one or more thin-film evaporators and removes a portion of the water via line 0, in order to increase the formaldehyde concentration. A stream is discharged from the concentrator unit FC via line 1 and serves as a formaldehyde source S FA .

[0094] about Figure 2 For all other features of the exemplary configuration of the first independent embodiment of the present disclosure shown, reference can be made to the above description of Figure 1 Description.

[0095] exist Figure 2 In one example of the process shown, reactor R1 is operated at 100°C and 10 bar. The acidic catalyst used is 46.

[0096] The reactant mixture M supplied to the reactor R1反应物 and the product mixture M obtained in reactor R1 R1 had the composition reported in Table 1 below.

[0097] Table 1: Reactant mixture M 反应物 The composition of the product mixture M obtained in the reactor R1 R1 Composition

[0098]

[0099] In the distillation unit D1, the top stream KS is separated by distillation. D1 and undercurrent SS D1 After that, the top stream KS D1 With methanol-containing stream S MeOH The mixture M1 is combined to obtain a mixture M1, and the mixture M1 is introduced into the reactive distillation unit RD2. The acidic catalyst used in the reactive distillation unit RD2 is 46. ​​The mixture M1 was introduced above the reaction zone containing the catalyst. During the distillation, a distillation temperature of 41° C. was established, which corresponds to OME 1 The boiling temperature of the azeotropic mixture of 1,2-dihydro-1,2-dimethyl-1,2-dihydro ...

[0100] Composition of the mixture M1 introduced into the reactive distillation unit RD2 and the top stream KS obtained in RD2 RD2 and undercurrent SS RD2 The composition of is reported in Table 2 below.

[0101] Table 2: Composition of the mixture M1 introduced into the reactive distillation unit RD2 and the top stream KS obtained in RD2 RD2 and undercurrent SS RD2 Composition

[0102]

[0103] Underflow SS basically consists of water and formaldehyde RD2 Can be recycled, thus becoming a starting source of aqueous formaldehyde S FA No additional water removal unit is required.

[0104] OME present in mixture M1 2 Basically complete reaction, so that the bottom flow SS RD2 And the top stream KS RD2 Basically free of OME 2 .

[0105] A second independent embodiment of the present disclosure will be described in more detail below.

[0106] As described above, in the first and second independent embodiments of the present disclosure, the reactant mixture M 反应物 First, the reaction is carried out in the reactor R1 to obtain the product mixture M R1 , which contains the formula H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ), H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 )) of polyoxymethylene dimethyl ether, as well as formaldehyde, methylal (OME 1 ), methanol and water.

[0107] In a second independent embodiment of the present disclosure, the product mixture M obtained in the reactor R1 R1 With methanol-containing stream S MeOH The resulting mixture M1 is reacted in at least one reaction zone RZ of a reactive distillation unit RD1 in the presence of a catalyst, wherein H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) to give methylal (OME 1 ) and formaldehyde, formaldehyde and methanol react to obtain methylal (OME 1 ) and distilled into a first fraction and a second fraction, the first fraction containing water, methanol, formaldehyde, methylal (OME 1 ) and H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) and as a top KS RD1 Leaving the reactive distillation unit RD1; the second fraction contains the formula H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH3 (where n≥6(OME ≥6 )) of polyoxymethylene dimethyl ether and as underflow SS RD1 Leaving the reactive distillation unit RD1.

[0108] The product mixture M discharged from the reactor R1 R1 With methanol-containing stream S MeOH The mixing is preferably carried out outside the reactive distillation unit RD1 and the resulting mixture M1 is then introduced into the reactive distillation unit RD1. However, in the context of the present disclosure, the product mixture M R1 and the methanol-containing stream S MeOH It is also possible that they are not mixed with one another until in the reactive distillation unit RD1.

[0109] Optionally, the methanol-containing stream S MeOH It may also contain other ingredients (such as formaldehyde, water, OME 1 OME ≥2 or trioxymethylene). However, the methanol-containing stream S MeOH Preferably it contains at least 80% by weight of methanol, more preferably at least 90% by weight of methanol.

[0110] The reactive distillation unit RD1 (e.g., reactive distillation column) used in the second independent embodiment of the process according to the present disclosure comprises one or more reaction zones RZ and one or more distillation separation zones. The reaction zone RZ contains one or more catalysts, in particular acidic catalysts (e.g., one or more acidic solid catalysts, such as ion exchange resins with acidic groups (i.e., cation exchange resins), zeolites, aluminosilicates, alumina, transition metal oxides (which are optionally on a support material) or graphene oxide) for OME 2 to produce methylal (OME 1 ) and formaldehyde (see above reaction equation 7), the reaction of formaldehyde and methanol also produces methylal (OME 1 ). The distillative separation zone comprises, for example, internals for distillative separation, in particular trays, random packings or structured packings, as generally known to the person skilled in the art. The catalyst can be fixed in the reaction zone RZ of the reactive distillation unit RD1 in a manner known to the person skilled in the art, for example as a random dump packing; in the form of a metal wire mesh body filled with catalyst or in the form of a catalyst shaped body mounted on a tray of the RZ reaction zone. If the reactive distillation unit RD1 comprises two or more reaction zones RZ, preferably there is a distillative separation zone between every two reaction zones RZ.

[0111] In the catalyst-containing reaction zone RZ of the reactive distillation unit RD1, a chemical reaction of the mixture M1 is carried out, wherein H 3 CO-(CH2 O) 2 -CH 3 (OME 2 ) to give methylal (OME 1 ) and formaldehyde, formaldehyde and methanol react to obtain methylal (OME 1 ). In addition, in the reactive distillation unit RD1, distillation separation is performed to form a first fraction and a second fraction. The first fraction contains water, methanol, formaldehyde, methylal (OME 1 ) and H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ), and optionally HO-(CH 2 O) n -CH 3 (n≥1) hemiacetal and / or HO-(CH 2 O) n -H (n ≥ 1) diols and as the top stream KS RD1 Leaving the reactive distillation unit RD1, the second fraction contains the formula H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 )) of polyoxymethylene dimethyl ether and as underflow SS RD1 Leaving the reactive distillation unit RD1.

[0112] By means of the reactive distillation unit RD1 and the distillation unit D2 downstream of the reactive distillation unit, the following objectives can be achieved (to be described in more detail below):

[0113] - A top stream KS can be discharged from the distillation unit D2 D2 , which contains mainly methylal and optionally a small amount of methanol and can therefore be recycled as a methylal source for use with an aqueous formaldehyde source S FA mix.

[0114] - Via underflow SS RD2 Water is effectively removed from the distillation unit D2.

[0115] For H 3 CO-(CH 2 O) 2 -CH 3 (OME 2) to give methylal (OME 1 ) and formaldehyde, and for the reaction of formaldehyde and methanol in the reaction zone RZ of the reactive distillation unit RD1 to obtain methylal (OME 1 ) are known to those skilled in the art. Acidic catalysts (e.g. one or more acidic solid catalysts, such as ion exchange resins with acidic groups (i.e. cation exchange resins), zeolites, aluminosilicates, aluminum oxides, transition metal oxides (optionally on a support material) or graphene oxide) are preferred.

[0116] The reactive distillation unit RD1 is operated, for example, at a pressure of 1 to 15 bar and a temperature of 60 to 250°C.

[0117] Preferably, the mixture M1 is introduced into the reactive distillation unit RD1 in a region below the reaction zone RZ containing the catalyst. If the reactive distillation unit RD1 comprises a plurality of reaction zones RZ, the mixture M1 is preferably introduced into the reactive distillation unit RD1 in a region below all reaction zones RZ present in RD1.

[0118] As described above, formaldehyde and methanol are reacted in the catalyst-containing reaction zone RZ of the reactive distillation unit RD1 to give methylal (OME 1 The molar ratio of formaldehyde to methanol in the mixture M1 can be used to control whether (i) the formaldehyde is mostly or even completely converted to OME 1 , and remaining unconverted methanol residues, or (ii) remaining unconverted formaldehyde residues.

[0119] As described above, the top stream KS discharged from the reactive distillation unit RD1 RD1 Contains water, methanol, formaldehyde, methylal (OME 1 ) and H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ). In variants (i) and (ii), the top stream KS RD1 Usually has a very low percentage of OME 2 , for example less than 5 wt %, more preferably less than 2 wt %. In variant (i), the top flow KS RD1 With a very low proportion of formaldehyde, for example less than 5% by weight. In variant (ii), the top stream KS RD1 There is a very low proportion of methanol, for example less than 5% by weight.

[0120] The top stream KS discharged from the reactive distillation unit RD1The distillation unit D2 is introduced and separated by distillation into a first fraction and a second fraction. The first fraction contains methylal and is used as the top stream KS D2 Leaving the distillation unit D2, the second fraction contains water and is taken as the bottom stream SS D2 Leaving distillation unit D2.

[0121] The distillation unit D2 is, for example, catalyst-free (in particular acidic catalyst-free). Alternatively, in the context of the present disclosure, the distillation unit D2 can also be a reactive distillation unit, which comprises one or more reaction zones RZ and one or more distillation separation zones. The reaction zone RZ contains one or more acidic catalysts (e.g. one or more acidic solid catalysts, such as ion exchange resins with acidic groups (i.e. cation exchange resins), zeolites, aluminosilicates, aluminum oxides, transition metal oxides (which are optionally on a support material) or graphene oxide).

[0122] The distillation unit D2 is operated, for example, at a pressure of 1 to 5 bar and a temperature of 40 to 140°C.

[0123] In the distillation unit D2, the distillation is separated into a first fraction and a second fraction. The first fraction contains methylal and is used as the top stream KS D2 Leaving the distillation unit D2, the second fraction contains water and is taken as the bottom stream SS D2 Leaving distillation unit D2.

[0124] Bottom stream SS D2 Chinese OME 2 The proportion is usually very low, for example less than 5% by weight, preferably less than 2% by weight, more preferably less than 1% by weight.

[0125] If the above-mentioned variant (i) is used (ie an excess of methanol, such that the top stream KS discharged from the reactive distillation unit RD1 RD1 With a very low proportion of formaldehyde), the underflow SS D2 Contains methanol in a proportion of, for example, ≥0 wt% to 80 wt%, more preferably ≥0 wt% to 30 wt%. D2 The total proportion of water and methanol is preferably greater than 95% by weight. D2 Optionally also contains formaldehyde, H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) and / or methylal (OME 1 ), these preferably account for a total proportion of less than 5% by weight, particularly preferably less than 1% by weight.

[0126] If the above-mentioned variant (ii) is used (ie the top stream KS discharged from the reactive distillation unit RD1 isRD1 The underflow SS D2 For example, it contains formaldehyde in the following proportions: ≥0 wt% to 60 wt%, more preferably 25 wt% to 55 wt%. D2 The total proportion of water and formaldehyde is preferably greater than 80% by weight, more preferably greater than 95% by weight. D2 Optionally, it also contains MeOH, H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) and / or methylal (OME 1 ), these preferably total proportion is less than 20 wt% (underflow SS D2 Chinese OME 2 The proportion of SS is preferably less than 5% by weight, particularly preferably less than 5% by weight (underflow SS D2 Chinese OME 2 The proportion is preferably less than 2% by weight). For example, the aqueous underflow SS D2 Contains 25 wt % to 55 wt % formaldehyde, wherein the total proportion of water and formaldehyde in the underflow is greater than 95 wt %, and the underflow SS D2 Chinese OME 2 The proportion is less than 2% by weight.

[0127] In a preferred embodiment, at least a portion of the top stream KS discharged from the distillation unit D2 D2 is recycled and used as methylal-containing stream S OME1 , which is mixed with a stream containing formaldehyde and water FA Mix to obtain a reactant mixture M 反应物 As mentioned above, the two streams are preferably mixed upstream of the reactor R1 and the resulting reactant mixture M is then 反应物 Alternatively, the two streams may not be mixed with one another until they are mixed in the R1 reactor.

[0128] If the top stream KS discharged from the distillation unit D2 RD2 If methanol is still present in the top flow KS RD2 During its recycling it will advantageously be passed through a distillation unit D4 in which the methanol is at least partially removed by distillation.

[0129] The top stream KS discharged from the distillation unit D2 D2 During its circulation, it preferably passes through a mass flow distributor, in which the top flow KS D2 By using a mass flow distributor, the reaction mixture M can be adjusted 反应物This in turn helps in the reaction mixture M 反应物 Establish a constant ratio of formaldehyde to methylal in the final product and adjust the long-chain polyoxymethylene dimethyl ether OME ≥3 The methylal separated in the mass flow distributor itself constitutes a potentially interesting starting material for other processes and can be stored until further use. Mass flow distributors that can divide the product stream into two or more substreams are known to those skilled in the art.

[0130] In a second independent embodiment of the process according to the present disclosure, the bottom stream SS discharged from the reactive distillation unit RD1 is RD1 Introduced into distillation unit D3. As mentioned above, the bottom flow SS RD1 Contains H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 In the distillation unit D3, these polyoxymethylene dimethyl ethers are separated by distillation into the top stream KS D3 The fraction leaving the distillation unit D3 and as bottom stream SS D3 The conditions selected for the distillation separation in the distillation unit D3 can be adapted to the desired product spectrum. For example, the distillation unit D3 is operated so that the top stream KS discharged from the distillation unit D3 is D3 Contains H 3 CO-(CH 2 O) 3-5 -CH 3 , undercurrent SS D3 Containing formula H 3 CO-(CH 2 O) n -CH 3 (where n≥6). The distillation unit D3 comprises, for example, internals for separation by distillation, in particular trays, random packings or structured packings, as generally known to those skilled in the art. The distillation unit D3 is operated, for example, at a pressure of 0.05 bar to 3 bar and a temperature of 60° C. to 220° C. If the distillation unit is operated under reduced pressure (0.05 bar to less than 1.0 bar), it may be advantageous to use internals that generate a low pressure gradient. The distillation unit D3 preferably does not contain a catalyst (in particular does not contain an acidic catalyst). The distillation unit D3 is preferably not a reactive distillation unit.

[0131] As in the first independent embodiment, in the second independent embodiment of the present disclosure, the bottom stream SS discharged from the distillation unit D3 D3 At least a portion of the FA mix.

[0132] As mentioned above, the bottom stream SS discharged from the distillation unit D2 D2 In addition to water, formaldehyde may optionally be present (see variant (ii) above). Since formaldehyde is one of the reactants of the process according to the present disclosure, in this case, the underflow SS containing formaldehyde is D2 It may be advantageous to recycle and introduce it into a concentrator unit FC, where a portion of the water is removed and the stream leaving the concentrator unit serves as stream S FA The effect of methylal on the OME1 Mix to obtain a reactant mixture M 反应物 Before being introduced into the concentrator unit FC, the recycled formaldehyde-containing underflow SS is preferably RD2 The formaldehyde-containing mixture M2 is mixed with a formaldehyde-containing starting material (e.g., an aqueous formaldehyde solution having a formaldehyde content of at least 30% by weight, more preferably at least 50% by weight) to obtain a formaldehyde-containing mixture M2. The formaldehyde-containing mixture M2 is introduced into a concentrator unit FC, and a portion of the water is removed in the concentrator unit FC to increase the formaldehyde concentration. FA A stream is discharged from the concentrator unit FC and is mixed with the methylal-containing stream S OME1 Mix to obtain a reaction mixture M 反应物 .

[0133] refer to Figure 3 An exemplary configuration of a second independent embodiment of the present disclosure is described in more detail.

[0134] The aqueous formaldehyde solution supplied via line-2 and the underflow SS recycled from the distillation unit D2 D2 Mixed, Underflow SS D2 In addition to water, it also contains formaldehyde and optionally methanol. The resulting mixture M2 is introduced via line -1 into a concentrator unit FC, which comprises, for example, one or more thin-film evaporators, and removes a portion of the water via line 0, in order to increase the formaldehyde concentration. A stream is discharged from the concentrator unit FC via line 1 and serves as formaldehyde source S FA .

[0135] The formaldehyde source S is supplied via pipeline 1 FA and the methylal-containing stream S supplied via line 9 OME1 Mix. Stream S containing methylal OME1 It is the top stream KS D2, which has been discharged from the distillation unit D2 via line 7 and passes through the mass flow distributor T during its recycling. Optionally, the stream S OME1 A small amount of methanol (<10 wt%) may be contained. Optionally, OME (e.g. OME ≥6 ), which serves as the underflow SS D3 , which is discharged from the distillation unit D3 via line 13, can be combined with the stream S FA and S OME1 mix.

[0136] By mixing the flow S FA and S OME1 (and optionally SS D3 ), obtain the reactant mixture M 反应物 , which is introduced into reactor R1, such as a fixed bed reactor, via pipeline 2. Formaldehyde and OME 1 In reactor R1, OME is obtained. 2 OME 3-5 and OME ≥6 The obtained product mixture M R1 Contains OME 2 OME 3-5 and OME ≥6 and OME 1 , formaldehyde, methanol and water.

[0137] Through pipeline 3, the product mixture M R1 The stream S containing methanol is discharged from the reactor R1 and mixed with the stream S containing methanol supplied via the line 5. MeOH The mixture M1 is introduced into a reactive distillation unit RD1. The reactive distillation unit RD1 comprises a plurality of reaction zones and distillation separation zones, each reaction zone containing an acidic catalyst. The mixture M1 is introduced into the reactive distillation unit RD1 located below the reaction zone RZ containing the catalyst. The molar ratio of methanol to formaldehyde in the mixture M1 is selected so that the methanol in the reactive distillation unit RD1 is largely converted into OME 1 , so the top flow SS discharged from RD1 RD1 Has a relatively low proportion of methanol.

[0138] In the catalyst-containing reaction zone of the reactive distillation unit RD1, OME 2 The reaction yields methylal (OME 1 ) and formaldehyde, formaldehyde and methanol also react to give methylal (OME 1 ). In addition, in the reactive distillation unit RD1, distillation separation is performed into a first fraction and a second fraction. The first fraction contains water, methanol, formaldehyde, methylal (OME 1 ) and H 3 CO-(CH 2O) 2 -CH 3 (OME 2 ) and as a top KS RD1 Leaving the reactive distillation unit RD1, the second fraction contains the formula H 3 CO-(CH 2 O) 3-5 -CH 3 (OME 3-5 ) and H 3 CO-(CH 2 O) n -CH 3 (where n≥6(OME ≥6 )) of polyoxymethylene dimethyl ether and as underflow SS RD1 Leaving distillation unit D1.

[0139] The top flow KS discharged from RD1 is discharged through conduit 6. RD1 A catalyst-free distillation unit D2 is introduced. In this distillation unit D2, the distillation is separated into a first fraction and a second fraction, the first fraction containing methylal and serving as the top stream KS D2 Leaving the distillation unit D2, the second fraction contains water and formaldehyde and is taken as the bottom stream SS D2 Leaving distillation unit D2.

[0140] The top stream KS discharged from the distillation unit D2 via line 7 D2 is recycled and used as methylal-containing stream S OME1 It is mixed with the aqueous formaldehyde solution (supplied via pipeline-2) via pipeline 9. During its recycling, the top flow KS D2 Flows through mass flow distributor T, where top flow KS D2 By using a mass flow distributor, the reactant mixture M can be adjusted 反应物 The methylal separated off in the mass flow distributor itself constitutes a potentially interesting raw material for other processes and can be stored for future use.

[0141] The formaldehyde-containing underflow SS discharged from the distillation unit D2 via line 10 D2 The aqueous solution (which mainly consists of water and formaldehyde) is recycled and mixed with the formaldehyde starting aqueous solution supplied via pipeline-2.

[0142] The bottom stream SS discharged from the reactive distillation unit RD1 via line 11 is RD1 Introduced into distillation unit D3. Underflow SS D1 Contains OME 3-5 and OME ≥6In the distillation unit D3, these polyoxymethylene dimethyl ethers are separated by distillation into OME 3-5 The fraction is passed through pipeline 12 as the top flow KS D3 Leaving distillation unit D3; and containing OME ≥6 The fraction is passed through pipeline 13 as bottom flow SS D3 Leaving distillation unit D3. Optionally, bottom stream SS D3 Can be recycled and mixed with aqueous formaldehyde source S FA (Pipeline 1) Mixing.

Claims

1. A method for preparing polyoxymethylene dimethyl ether, The following steps are involved: - a stream S containing an aqueous formaldehyde source FA With methylal containing stream S OME1 Mix to obtain a reactant mixture M 反应物 , - Make the reactant mixture M 反应物 The reaction is carried out in reactor R1 to obtain a product mixture M R1 , the product mixture M R1 Containing formula H 3 CO-(CH 2 O) 2 -CH 3 , H 3 CO-(CH 2 O) 3-5 -CH 3 and H 3 CO-(CH 2 O) n -CH 3 , polyoxymethylene dimethyl ether with n≥6, and formaldehyde, methylal, methanol and water, - the product mixture M R1 Introduced into the distillation unit D1, and the product mixture M R1 Distillation separation contains methylal, H 3 CO-(CH 2 O) 2 -CH 3 , formaldehyde, methanol and water, and as the top stream KS D1 Leaving the distillation unit D1, and containing the formula H 3 CO-(CH 2 O) 3-5 -CH 3 and H 3 CO-(CH 2 O) n -CH 3 and n ≥ 6 of the second fraction of the polyoxymethylene dimethyl ether, and as the bottom flow SS D1 Leaving the distillation unit D1, - The top stream KS D1 With methanol-containing stream S MeOH Mix to obtain a mixture M1, - The mixture M1 is reacted in at least one reaction zone RZ of a reactive distillation unit RD2 in the presence of a catalyst, wherein H 3 CO-(CH 2 O) 2 -CH 3 The reaction obtains methylal and formaldehyde, and formaldehyde and methanol react to obtain methylal; and distillation is carried out to separate the methylal (OME 1 ) and as a top stream KS RD2 The first fraction leaving the reactive distillation unit RD2 and containing water as bottom stream SS RD2 a second fraction leaving the reactive distillation unit RD2, and - The underflow SS D1 Introduce distillation unit D3, and the bottom flow SS D1 The formula H present in 3 CO-(CH 2 O) 3-5 -CH 3 and H 3 CO-(CH 2 O) n -CH 3 The polyoxymethylene dimethyl ether with n≥6 is separated by distillation to form KS as the top stream D3 The fraction leaving the distillation unit D3 and as bottom stream SS D3 The fraction leaving the distillation unit.

2. A method for preparing polyoxymethylene dimethyl ether, The following steps are involved: - a stream S containing an aqueous formaldehyde source FA With methylal containing stream S OME1 Mix to obtain a reactant mixture M 反应物 , - Make the reactant mixture M 反应物 The reaction is carried out in reactor R1 to obtain a product mixture M R1 , the product mixture M R1 Containing the formula H 3 CO-(CH 2 O) 2 -CH 3 , H 3 CO-(CH 2 O) 3-5 -CH 3 and H 3 CO-(CH 2 O) n -CH 3 Polyoxymethylene dimethyl ethers with n≥6, and formaldehyde, methylal, methanol and water, - the product mixture M R1 With methanol-containing stream S MeOH Mix to obtain a mixture M1, - The mixture M1 is reacted in at least one reaction zone RZ of a reactive distillation unit RD1 in the presence of a catalyst, wherein H 3 CO-(CH 2 O) 2 -CH 3 The reaction obtains methylal and formaldehyde, and formaldehyde and methanol react to obtain methylal; and distillation is performed to separate the methylal and methanol into water, methanol, formaldehyde, methylal and H 3 CO-(CH 2 O) 2 -CH 3 (OME 2 ) and as a top stream KS RD1 The first fraction leaving the reactive distillation unit RD1, and the fraction containing the formula H 3 CO-(CH 2 O) 3-5 -CH 3 and H 3 CO-(CH 2 O) n -CH 3 The polyoxymethylene dimethyl ether with n≥6 is used as the bottom flow SS RD1 the second fraction leaving the reactive distillation unit RD1, - The top stream KS RD1 Introduced into distillation unit D2, and separated by distillation into methylal and KS as top stream D2 The first fraction leaving the distillation unit D2 and containing water as bottom stream SS D2 a second fraction leaving said distillation unit D2, and - The underflow SS RD1 Introduce distillation unit D3, and the bottom flow SS RD1 The formula H 3 CO-(CH 2 O) 3-5 -CH 3 and H 3 CO-(CH 2 O) n -CH 3 The polyoxymethylene dimethyl ether with n≥6 is separated by distillation to form KS as the top stream D3 The fraction leaving the distillation unit D3 and as bottom stream SS D3 The fraction leaving the distillation unit.

3. The process according to claim 1 or 2, wherein the aqueous formaldehyde source is an aqueous formaldehyde solution having a formaldehyde content of at least 70% by weight.

4. The method according to claim 1 or 2, wherein the reactant mixture M is reacted in the presence of an acidic catalyst. 反应物 The reaction is carried out in the reactor R1.

5. The process according to claim 1 or 2, wherein the catalyst present in the reaction zone RZ of the reactive distillation unit RD1 or RD2 is an acidic catalyst.

6. The process according to claim 2, wherein the top stream KS discharged from the reactive distillation unit RD2 RD2 or the top stream KS discharged from the distillation unit D2 D2 At least a portion of the methylal is recycled and used as stream S containing methylal OME1 , which is combined with the formaldehyde and water-containing stream S FA Mix to obtain the reactant mixture M 反应物 .

7. The method according to claim 6, wherein the top flow KS RD2 or KS D2 During the recirculation process, it flows through a mass flow distributor in which the top flow KS RD2 or KS D2 part of which was diverted.

8. The process according to claim 2, wherein the bottom stream SS discharged from the reactive distillation unit RD2 RD2 or the bottom flow SS discharged from the distillation unit D2 D2 In addition to water, it also contains up to 80% by weight of methanol, wherein the underflow SS RD2 The total proportion of water and methanol is greater than 95% by weight.

9. The process according to claim 2, wherein the bottom stream SS discharged from the reactive distillation unit RD2 RD2 or the bottom flow SS discharged from the distillation unit D2 D2 In addition to water, it also contains formaldehyde in a proportion of up to 60% by weight, and the underflow SS RD2 The total proportion of water and formaldehyde is greater than 80% by weight.

10. The process according to claim 9, wherein the bottom stream SS discharged from the reactive distillation unit RD2 RD2 or the bottom flow SS discharged from the distillation unit D2 D2 Recirculated to the concentrator unit FC, where the underflow SS D2 and the underflow SS RD2 In the concentrating unit, a portion of the water is concentrated and removed, leaving the concentrator unit FC and used as stream S FA and with the methylal-containing stream S OME1 Mix to obtain the reactant mixture M 反应物 .

11. The process according to claim 10, wherein the recycled formaldehyde-containing underflow SS RD2 or SS D2 Before being introduced into the concentrator unit FC, it is mixed with a formaldehyde-containing starting material to obtain a formaldehyde-containing mixture M2, and the formaldehyde-containing mixture M2 is introduced into the concentrator unit FC.

12. The method according to claim 10 or 11, wherein the concentrator unit FC comprises at least one evaporator.

13. The process according to claim 1 or 2, wherein the top stream KS discharged from the distillation unit D3 D3 Contains H 3 CO-(CH 2 O) 3-5 -CH 3 , and the underflow SS D3 Containing the formula H 3 CO-(CH 2 O) n -CH 3 Polyoxymethylene dimethyl ether wherein n≥6.

14. The method according to claim 1 or 2, wherein the bottom flow SS D3 recirculates and with the flow S FA and / or the stream S OME1 mix.

15. The method according to claim 9, wherein the underflow SS RD2 The total proportion of water and formaldehyde is greater than 95% by weight.

16. The method according to claim 10, wherein the recycled formaldehyde-containing underflow SS RD2 or SS D2 Before being introduced into the concentrator unit FC, it is mixed with an aqueous solution containing formaldehyde to obtain a mixture M2 containing formaldehyde, and the mixture M2 containing formaldehyde is introduced into the concentrator unit FC.

17. The method according to claim 10 or 11, wherein the concentrator unit FC comprises at least one thin film evaporator.

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