Recycled MMA and its use in continuous polymerization process

Abstract

The invention relates to a novel method for preparing poly (alkyl (meth) acrylate). In the method, a polymer composition containing at least one poly (alkyl (meth) acrylate) is first thermally cracked to obtain at least one alkyl (meth) acrylate and at least one further alkyl ester. This mixture is then condensed and mixed with the stream of the poly (alkyl (meth) acrylate) production process. The poly (alkyl (meth) acrylate) is then obtained by polymerization.

Description

TECHNICAL FIELD

[0001] The present invention relates to a new process for the preparation of poly((alkyl) (meth) acrylate). In this process, a polymer composition comprising at least one poly((alkyl) (meth) acrylate) is first thermally cracked to obtain at least one (alkyl) (meth) acrylate and at least one other alkyl ester. This mixture is then condensed and mixed with a stream of a poly((alkyl) (meth) acrylate) preparation process. The poly((alkyl) (meth) acrylate) is then obtained by polymerization. BACKGROUND

[0002] (Alkyl) (meth) acrylates, especially methyl methacrylate (MMA), have a wide field of application.

[0003] MMA is particularly used for the preparation of polymethyl methacrylate (PMMA), which is distinguished by excellent optical properties, in particular high transparency and weather resistance (acrylic glass), as well as other physical properties. Its field of application includes glazing and facades in construction, lighting elements and vehicle tail lights in the automotive industry, aircraft windows, decorative elements, design elements or furniture elements, flat panel displays and displays, soundproof walls and illuminated advertising.

[0004] Production waste, so-called post-industrial waste, arises in the processing of PMMA. The post-industrial waste in particular includes offcuts and general waste arising in the production process and in the subsequent processing during and after extrusion or casting of PMMA molding compounds.

[0005] Products made from PMMA molding compounds, such as greenhouse glazing, sound barriers, aircraft glazing, splash-proof face screens or display screens, and colored molding compounds, such as for use in the automotive industry (e.g. light guides, tail lights and body parts), are usually disposed of by the user after use and, together with other types of plastic waste, are sent to landfills or are thermally disposed of and incinerated in power plants. Such old materials are often referred to as post-consumer waste. In addition, post-consumer waste, such as electrical waste and discarded devices, often also contains PMMA as a contaminant in addition to other plastics and additives in the sorting process. The proportion of MMA structural units in the PMMA polymers present in the waste varies and can be from 75% to more than 99%.

[0006] PMMA, both as post-industrial waste and as post-consumer waste, can in principle be depolymerized into its monomers and reused as so-called recycled MMA. Various depolymerization methods are described in the prior art, such as depolymerization in a metal bath, a rotary furnace, a fluidized bed reactor or an extruder.

[0007] For example, the documents DE 642 289 C, US 2,030,901, DE 3 146 194 A1, EP 3 635 043 and US 2,470,361 describe the thermal depolymerization of PMMA, in some cases followed by purification of the resulting monomer, for example by distillation.

[0008] The thermal catalytic depolymerization of PMMA and subsequent purification of the resulting monomer is described, for example, in US 2,858,255, DE 213 2716, WO 2019 / 003253, DE 197 29 065 and EP 2 895 576.

[0009] Also known is the depolymerization of PMMA in a fluidized bed, in some cases together with other polymers. This is described, for example, in US 5,663,420, WO 2000 / 017149 and US 8,304,573.

[0010] US 3,494,958 describes a method for the thermal depolymerization of PMMA. The resulting monomer can subsequently be purified by distillation. US 3,494,958 describes that this purification can be carried out, for example, analogously to the purification in the ACH process (C3 process).

[0011] The above-described methods generally have an insufficient monomer yield. Furthermore, the purity of the recycled alkyl (meth)acrylate achieved by the methods described in the prior art is insufficient to produce poly(alkyl (meth)acrylate) of sufficient quality. This is particularly true when the poly(methyl methacrylate) used in the depolymerization process contains a high proportion of additives, such as impact modifiers or pigments and / or other polymers.

[0012] The quality of the recycled alkyl (meth)acrylate, in particular recycled MMA (recycled MMA), is therefore significantly different from the quality of pure alkyl (meth)acrylate, in particular pure MMA obtained directly from the MMA production process. The MMA content in the recycled MMA generally does not meet the standard commercial specifications of 99.8% purity by weight of pure MMA. There are often several hundred ppm to several thousand ppm of interfering substances, which have a disadvantageous effect on the production of high-purity PMMA granules from the recycled MMA.

[0013] Depending on the post-industrial and / or post-consumer waste used to produce the recycled MMA, the recycled MMA also has an intolerable coloration and / or odor. The latter can come, for example, from sulfur-containing regulators and other additives that are released during the thermal depolymerization process and can be converted into odoriferous mercaptans.

[0014] It is therefore currently possible to use the recycled MMA from the depolymerization process directly as a raw material in the continuous PMMA polymerization.

[0015] Due to their low purity, recycled (meth)alkyl acrylates have only limited fields of application. In particular, they can only be used to produce poly((meth)alkyl acrylate) to a limited extent.

[0016] Popescu et al., "The characterization of recycled PMMA" (Characterization of recycled PMMA), Journal of Alloys and Compounds, Vol. 483, pp. 432-436 describes the physical properties of PMMA made from recycled MMA made by depolymerization of PMMA.

[0017] Kikuchi et al., "Design of recycling system for poly(methyl methacrylate) (PMMA). Part 1 : recycling scenario analysis" (Design of recycling system for poly(methyl methacrylate) (PMMA). Part 1 : recycling scenario analysis) Int. J. Life Cycle Assess (2014) 19:120-129 describes the depolymerization of PMMA and the purification of the recycled MMA obtained therefrom by distillation.

[0018] DE 10 2007 045 156 A1 describes a vented extruder for degassing of polymeric materials. The use of recycled MMA is not disclosed. SUMMARY

[0019] OBJECTIVE

[0020] There is therefore a need to provide an improved process for the production of poly((meth)alkyl acrylate) which does not have or only to a reduced extent has the disadvantages of the processes described in the prior art.

[0021] In addition, it is an object of the present application to use recycled (meth)alkyl acrylate having a lower purity compared to (meth)alkyl acrylate from the (meth)alkyl acrylate production process at least in a certain proportion for the production of poly((meth)alkyl acrylate) which meets the specifications. Interfering substances which are present should be effectively separable and removed in the poly((meth)alkyl acrylate) production process.

[0022] In particular, the process should have a lower emission of climate-affecting waste materials such as CO2.

[0023] SOLUTION

[0024] The object is achieved by a process for the preparation of poly(alkyl (meth)acrylate) comprising the following steps a) to h):

[0025] a) thermally cracking at least one polymer composition comprising at least one poly(alkyl (meth)acrylate), thereby obtaining a first gaseous stream comprising at least one alkyl (meth)acrylate and at least one other alkyl ester,

[0026] b) condensing the first gaseous stream obtained in step (a) to obtain a first liquid stream comprising the at least one alkyl (meth)acrylate and the at least one other alkyl ester,

[0027] c) mixing the first liquid stream obtained in step b) with an additional stream comprising at least one additional alkyl (meth)acrylate, wherein the additional stream is part of the process for the preparation of poly(alkyl (meth)acrylate), thereby obtaining a mixed stream comprising the first liquid stream and the additional stream,

[0028] e) partially polymerizing the mixed stream obtained in step c) to obtain a slurry comprising partially polymerized at least one alkyl (meth)acrylate, partially polymerized at least one additional alkyl (meth)acrylate and the at least one other alkyl ester,

[0029] f) polymerizing the slurry obtained in step e) in a vented extruder to obtain a polymer mixture comprising poly(alkyl (meth)acrylate),

[0030] g) degassing the slurry obtained in step e) and / or the polymer mixture obtained in step f) in a vented extruder to obtain a condensate stream comprising the at least one alkyl (meth)acrylate, the at least one additional alkyl (meth)acrylate, oligomers thereof and the at least one other alkyl ester,

[0031] h) separating the at least one other alkyl ester from the condensate stream obtained in step g) to obtain an alkyl (meth)acrylate stream comprising the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate.

[0032] The object is also achieved by a process for the preparation of poly(alkyl (meth)acrylate) comprising the following steps a) to h):

[0033] a) thermally cracking at least one polymer composition comprising at least one poly((alkyl) (meth)acrylate), to obtain a first gaseous stream comprising at least one (alkyl) (meth)acrylate and at least one other alkyl ester, wherein the at least one (alkyl) (meth)acrylate present in the first gaseous stream is selected from the group consisting of (meth)acrylic acid Ci- to C4-alkyl esters,

[0034] b) condensing the first gaseous stream obtained in step a) to obtain a first liquid stream comprising the at least one (alkyl) (meth)acrylate and the at least one other alkyl ester,

[0035] c) mixing the first liquid stream obtained in step b) with an additional stream comprising at least one additional (alkyl) (meth)acrylate, wherein the additional stream is part of a process for the preparation of poly((alkyl) (meth)acrylate), to obtain a mixed stream comprising the first liquid stream and the additional stream, wherein up to 50 wt.-% of the first liquid stream are mixed with the additional stream, based on the total weight of the resulting mixed stream,

[0036] e) partially polymerizing the mixed stream obtained in step c) to obtain a slurry comprising partially polymerized at least one (alkyl) (meth)acrylate, partially polymerized at least one additional (alkyl) (meth)acrylate and the at least one other alkyl ester,

[0037] f) polymerizing the slurry obtained in step e) in a vented extruder to obtain a polymer mixture comprising poly((alkyl) (meth)acrylate),

[0038] g) degassing the slurry obtained in step e) and / or the polymer mixture obtained in step f) in a vented extruder to obtain a condensate stream comprising the at least one (alkyl) (meth)acrylate, the at least one additional (alkyl) (meth)acrylate, oligomers thereof and the at least one other alkyl ester,

[0039] h) separating the at least one other alkyl ester from the condensate stream obtained in step g) to obtain an (alkyl) (meth)acrylate stream comprising the at least one (alkyl) (meth)acrylate and the at least one additional (alkyl) (meth)acrylate.

[0040] It has surprisingly been found that poly((alkyl) (meth)acrylate) with a purity of > 99% is obtained by the process of the present application.

[0041] The poly(alkyl (meth)acrylate)s produced by the process of the present application, in particular poly(methyl (meth)acrylate), have especially sufficient purity for producing pigmented poly(alkyl (meth)acrylate)s, in particular pigmented poly(methyl (meth)acrylate). In some cases, the poly(alkyl (meth)acrylate)s produced by the process of the present application, in particular poly(methyl (meth)acrylate), even have such a high level of purity that they are suitable for producing glass-clear poly(alkyl (meth)acrylate)s, in particular glass-clear poly(methyl (meth)acrylate). Furthermore, the poly(alkyl (meth)acrylate)s produced by the process of the present application also have a high transmission at 450 nm and a low yellowness value while at the same time having a sufficiently high Vicat softening temperature.

[0042] In particular, the process of the present application is surprisingly able to remove by-products, such as other alkyl esters, in a particularly efficient manner, so that they do not contaminate the poly(alkyl (meth)acrylate) produced, even if their standard boiling point temperature differs only slightly from the standard boiling point temperature of the alkyl (meth)acrylate, for example by + / - 1 K (Kelvin), preferably + / - 0.6 K. This is caused in particular by the process steps g) and h).

[0043] The additives and chain regulators which can be present in the polymer composition and the products obtained in the thermal cleavage of the polymer composition, such as mercaptans, can be removed simply and inexpensively by the process of the present application. For example, the poly(alkyl (meth)acrylate) obtained in the process of the present application contains at most 0.5% of by-products. Due to the process of the present application and the possible efficient removal of by-products therefrom, the poly(alkyl (meth)acrylate) produced according to the present application has no or only a very slight odor, despite the presence of mercaptans in the polymer composition.

[0044] The process of the present application and the poly(alkyl (meth)acrylate)s produced by the process of the present application also have a lower CO2 emission and thus a particularly low carbon footprint. This is achieved in particular as follows: The process of the present application also allows the use of polymer compositions having a relatively high proportion of additives and other impurities, and the raw material source is recyclable.

[0045] The process of the present application is therefore superior to currently known processes, as it meets the requirement of being able to be reused in a circular chain (circular economy) itself.

[0046] Furthermore, the by-products obtained in the depolymerization can be reused after their separation, thereby further reducing the carbon footprint and thus the global warming potential (GWP).

[0047] The process of the present application is explained in detail below.

[0048] In step a) of the process according to the application, at least one polymer composition is thermally cracked to obtain a first gas stream. The at least one polymer composition contains at least one poly(alkyl (meth)acrylate). The gas stream contains at least one alkyl (meth)acrylate and at least one other alkyl ester.

[0049] The expression "at least one polymer composition" in the present application means both exactly one polymer composition and a mixture of two or more polymer compositions. Preferred according to the application is a mixture of two or more polymer compositions.

[0050] The at least one polymer composition contains at least one poly(alkyl (meth)acrylate).

[0051] "at least one poly(alkyl (meth)acrylate)" in the present application means both exactly one poly(alkyl (meth)acrylate) and a mixture of two or more poly(alkyl (meth)acrylates). "Poly(alkyl (meth)acrylate)" in the present application means polymers and copolymers of alkyl (meth)acrylates.

[0052] Copolymers of alkyl (meth)acrylates are, for example, copolymers of alkyl (meth)acrylates with 1-alkenes, other alkyl (meth)acrylates, (meth)acrylic acid, styrene, polyesters, vinyl esters and / or polyurethane (meth)acrylates.

[0053] 1-alkenes which can be copolymerized with alkyl (meth)acrylates are known per se and are, for example, 1-hexene, 1-heptene, vinylcyclohexane, 3,3-dimethyl-1- propene, 3-methyl-1-diisobutene and 4-methylpent-1-ene.

[0054] The term "styrene" in the present application means not only styrene itself but also substituted styrenes, such as a-methylstyrene, a-ethylstyrene, vinyltoluene, p-methylstyrene, monochlorostyrene, dichlorostyrene and tribromostyrene.

[0055] Suitable polyesters are known per se and are preferably obtainable by polycondensation or ring-opening polymerization.

[0056] "polyurethane (meth)acrylates" in the present application mean (meth)acrylates which are connected to one another via urethane groups. They are obtainable by reaction of a hydroxyalkyl (meth)acrylate with a polyisocyanate and a polyalkylene oxide having at least two hydroxyl functional groups. Instead of a hydroxyalkyl (meth)acrylate, it is also possible to use an ester of (meth)acrylic acid with an oxiranen, such as, for example, oxirane or propylene oxide, or a corresponding oligomeric or polymeric oxirane. Suitable polyurethane (meth)acrylates are known per se.

[0057] The at least one polymer composition can for example be derived from production waste. In this case, the polymer composition is usually a so-called post-industrial waste, for example sprues, lumps formed at the start of extrusion, dust, chippings, polymer slurry from preliminary polymerization, edge sections, offcuts in the case of sheeting, rejects in the case of sheeting, film, blocks, semi-finished products, defective moldings or waste from injection molding.

[0058] It is also possible for the at least one polymer composition to come from so-called post-consumer waste. This usually involves waste from for example electrical waste and discarded devices, greenhouses, exhibition buildings, shop fitting materials or illuminated advertising.

[0059] The at least one polymer composition thus usually contains at least one further component. The at least one further component is for example selected from polymers other than poly(alkyl (meth)acrylate), pigments, dyes, fillers, auxiliaries, chain transfer agents, initiators, impact modifiers, mold release agents and UV additives.

[0060] It is thus also preferred that the process in which the polymer composition in step a) comprises at least one further component selected from polymers other than poly(alkyl (meth)acrylate), pigments, dyes, fillers, auxiliaries, chain transfer agents, initiators, impact modifiers, mold release agents and UV additives.

[0061] As polymers other than poly(alkyl (meth)acrylate) there can be considered in particular those which are generally usable as a blend with poly(alkyl (meth)acrylate). These include for example polyethylene, polyvinyl chloride, polystyrene, polyamides and biopolymers such as alpha-polysaccharides (starch), beta-polysaccharides (cellulose, chitin), lignin and polylactide.

[0062] Pigments are for example white, red, blue, green and / or yellow inorganic pigments. Particularly preferred are white inorganic pigments such as titanium dioxide.

[0063] Dyes are for example organic dyes known to the person skilled in the art.

[0064] Typical fillers are in particular mineral fillers. The mineral fillers are preferably selected from calcium carbonate, barium sulfate, quartz, quartz powder, precipitated silica, fumed silica, corundum, glass beads and cristobalite.

[0065] Typical auxiliaries are known per se and are for example selected from plasticizers, paraffins and / or inhibitors.

[0066] The plasticizers used are preferably esters, polyols, oils, low molecular weight polyethers or phthalates.

[0067] The paraffins which can be present in the polymer composition are known per se. For example, several paraffins with different melting points can be present in different concentrations.

[0068] Among the inhibitors, the compounds which are preferably present are substituted phenols, hydroquinone derivatives, phosphines and / or phosphites.

[0069] Chain transfer agents which can be considered are in particular compounds known for regulating the chain length in free-radical polymerization. Chain transfer agents generally include mercaptans, such as n-dodecyl mercaptan, and polyfunctional mercapto compounds, such as pentaerythritol tetra mercaptoacetate.

[0070] The initiators are likewise known per se and are selected, for example, from peroxides, azo compounds, persulfates and mixtures thereof.

[0071] The impact modifiers are known per se and are, for example, polymer particles which contain elastomers.

[0072] The mold release agents which can be considered include, inter alia, long-chain wax acids, such as stearic acid, palmitic acid or lauric acid, and monofunctional fatty or wax alcohols, such as diethylene glycol monopropyl ether.

[0073] The UV additives which can be considered include, inter alia, UV stabilizers. The UV stabilizers are preferably selected from benzophenone derivatives, benzotriazole derivatives, thioxanthone acid ester derivatives, piperidinol carboxylic acid ester derivatives and cinnamic acid ester derivatives.

[0074] The thermal cracking of the at least one polymer composition can be effected by methods known to the person skilled in the art.

[0075] The thermal cracking can be carried out in a reactor known to the person skilled in the art for thermal cracking. For example, the thermal cracking can be carried out in a pyrolysis reactor, in an extruder, in a rotary furnace, in fluidized-bed pyrolysis, in a metal bath and / or as dry distillation.

[0076] The polymer composition can be in solid or liquid form in the thermal cracking operation. If the polymer composition is in solid form, it can be in the form of a pure solid. It is likewise possible for the polymer composition to be present dispersed in a medium in solid form. The medium in which the polymer composition can be present dispersed can be, for example, a solid, such as quartz, metal chips or diatomaceous earth. It is likewise possible for the medium to be a gas, for example nitrogen, or a liquid, for example water or a hydrocarbon. It is possible for the medium to be liquid at room temperature but to be present as a gas under the conditions of the thermal cracking in step a).

[0077] For example, when the thermal cracking is carried out in an extruder, the polymer composition is in liquid (molten) form.

[0078] The polymer composition, especially when it is present in solid form, can be mechanically comminuted prior to the thermal cracking, for example to an average particle size distribution of below 6 mm (Qr, d50), preferably below 1.5 mm (Qr, d50), for example to a particle size distribution in the range of 0.1 mm (Qr, d50) to 6 mm (Qr, d50). The particle size distribution is preferably determined by laser diffraction measurement.

[0079] The temperature (T) in the thermal cracking in step a) is for example in the range of 240 °C to 800 °C, preferably in the range of 300 °C to 500 °C, more preferably in the range of 325 °C to 400 °C.

[0080] The pressure in the thermal cracking in step a) is for example in the range of 200 mbar to 1000 bar, preferably in the range of 400 mbar to 500 bar.

[0081] It is thus also preferred according to the present application that the process wherein the thermal cracking temperature in step a) is in the range of 240 °C to 800 °C and / or the thermal cracking pressure in step a) is in the range of 400 mbar to 500 bar.

[0082] The thermal cracking in step a) can be carried out in the presence of a catalyst. Catalysts suitable for the thermal cracking are known per se and are for example selected from the group consisting of molten metals, peroxides, potassium salts, for example potassium acetate, and alkali metal persulfates, for example monopersulfate potassium. Suitable molten metals are in particular lead and / or eutectic lead / tin mixtures.

[0083] If the thermal cracking in step a) is carried out in the presence of a catalyst, the cracking in step a) is also referred to as thermal catalytic cracking.

[0084] It is thus also preferred according to the present application that the process wherein the thermal cracking in step a) is a thermal catalytic cracking.

[0085] The thermal cracking in step a) operates the cracking of the poly((meth)alkyl acrylate). This cracking is also referred to as depolymerization. Depolymerization is known per se to the person skilled in the art. In depolymerization, the polymer is cracked into its monomer and oligomer units.

[0086] In the course of the thermal cracking in step a), the poly((meth)alkyl acrylate) is thus cracked into its monomer and oligomer units. As described above, the poly((meth)alkyl acrylate) is a polymer or copolymer of at least one (meth)alkyl acrylate. Thus, in the course of the thermal cracking, at least one (meth)alkyl acrylate is formed.

[0087] During the thermal cracking of the polymer composition, at least one further alkyl ester is additionally formed. "At least one further alkyl ester" in the present invention means both exactly one further alkyl ester and a mixture of two or more further alkyl esters. Preferred according to the present invention is a mixture of two or more further alkyl esters.

[0088] The first gas stream thus contains at least one alkyl (meth)acrylate and the at least one further alkyl ester formed in the thermal cracking operation.

[0089] As described above, the at least one alkyl (meth)acrylate is derived from a polyalkyl (meth)acrylate).

[0090] "Alkyl (meth)acrylate" in the present invention means both exactly one alkyl (meth)acrylate and a mixture of two or more alkyl (meth)acrylates. A mixture of two or more alkyl (meth)acrylates is preferred.

[0091] "(Meth)acrylic acid alkyl ester" in the present invention means an alkyl ester of (meth)acrylic acid having 1 to 18, preferably 1 to 12, especially preferably 1 to 4 carbon atoms in the alkyl group. The alkyl group can be linear, cyclic and / or branched. Furthermore, it can have aromatic groups. The alkyl group can additionally have heteroatoms within the alkyl group and / or be substituted by heteroatoms, such as is the case for hydroxypropyl (meth)acrylate and / or hydroxyethyl (meth)acrylate. For example, the alkyl (meth)acrylate of the present invention is selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, 1-methylethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isoamyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, allyl (meth)acrylate, polyethylene glycol (meth)acrylate, stearyl (meth)acrylate, benzyl (meth)acrylate, vinyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate and lauryl (meth)acrylate.

[0092] In a further embodiment of the present invention, "(meth)acrylic acid alkyl ester" also means polyethylene glycol (meth)acrylate having a weight average molecular weight Mw in the range from 250 g / mol to 10 000 g / mol.

[0093] The term "(meth)acrylic acid" in the present invention includes acrylic acid and methacrylic acid. The term "(meth)acrylic acid ester" in the present invention includes acrylate and methacrylate.

[0094] “(Meth)acrylic acid alkyl ester” thus refers in the present invention both to a methyl acrylate and to an acrylic acid alkyl ester. Methyl acrylate is preferred according to the present invention. The at least one (meth)acrylic acid alkyl ester is for example a (meth)acrylic acid Ci-C4-alkyl ester. 18 - alkyl ester, preferably (meth)acrylic acid Ci-C4-alkyl ester, 12 - alkyl ester, preferably (meth)acrylic acid Ci-C4-alkyl ester,

[0095] It is thus also preferred that the at least one (meth)acrylic acid alkyl ester present in the first gas stream in step a) is selected from (meth)acrylic acid Ci- to C4-alkyl ester.

[0096] The at least one (meth)acrylic acid alkyl ester has a boiling temperature at standard pressure, for example, in the range of 50 °C to 300 °C, preferably in the range of 80 °C to 250 °C.

[0097] It is obvious that the at least one further alkyl ester is different from the at least one (meth)acrylic acid alkyl ester. The at least one further alkyl ester preferably does not comprise any (meth)acrylic acid ester units.

[0098] For example, the at least one further alkyl ester is selected from the group consisting of isobutyric acid Ci-C4-alkyl ester, propionic acid Ci-C4-alkyl ester, pivalic acid Ci-C4-alkyl ester and dicarboxylic acid diester.

[0099] Isobutyric acid Ci-C4-alkyl ester in the present invention refers to an alkyl ester of isobutyric acid having 1 to 4 carbon atoms in the alkyl group. The alkyl group can be linear or branched. It can additionally have heteroatoms within the alkyl group and / or be substituted by heteroatoms. Isobutyric acid Ci-C4-alkyl ester having heteroatoms within the alkyl group is for example 2-methoxyisobutyric acid methyl ester and 3-methoxyisobutyric acid methyl ester. Isobutyric acid Ci-C4-alkyl ester of the present invention is for example selected from the group consisting of isobutyric acid methyl ester, isobutyric acid ethyl ester, 2-methoxyisobutyric acid methyl ester and 3-methoxyisobutyric acid methyl ester.

[0100] Propionic acid Ci-C4-alkyl ester in the present invention refers to an alkyl ester of propionic acid having 1 to 4 carbon atoms in the alkyl group. The alkyl group can be linear or branched. It can additionally have heteroatoms within the alkyl group and / or be substituted by heteroatoms. Propionic acid Ci-C4-alkyl ester of the present invention is for example selected from the group consisting of propionic acid methyl ester and propionic acid ethyl ester.

[0101] C1-C4-alkyl formate in the present application means an alkyl ester of formic acid having 1 to 4 carbon atoms in the alkyl group. The alkyl group can be linear or branched. It can additionally have heteroatoms within the alkyl group and / or be substituted by heteroatoms. The C1-C4-alkyl formate of the present application is for example selected from the group consisting of methyl formate and ethyl formate.

[0102] Dicarboxylic acid diester in the present application means an alkyl ester of a dicarboxylic acid having 1 to 4 carbon atoms in the alkyl group. Dicarboxylic acid diester also means a carboxylic acid ester of a diol in which both hydroxyl groups have been esterified with a carboxylic acid. The dicarboxylic acid diester of the present application is for example selected from the group consisting of dimethyl malonate, dimethyl glutarate, dimethyl adipate and dimethyl pimelate.

[0103] The at least one further alkyl ester is preferably selected from the group consisting of methyl propionate, ethyl propionate, methyl isobutyrate, methyl pivalate, methyl 3-methoxyisobutyrate and a dicarboxylic acid diester.

[0104] It is thus also preferred that the at least one further alkyl ester is selected from the group consisting of methyl propionate, methyl isobutyrate, methyl pivalate, methyl 3-methoxyisobutyrate and a dicarboxylic acid diester.

[0105] The at least one further alkyl ester has for example a boiling temperature at standard pressure in the range of 50°C to 200°C, preferably in the range of 75°C to 150°C.

[0106] It is further preferred according to the present application that the boiling point of the at least one further alkyl ester at standard pressure differs from the boiling point of the at least one alkyl (meth)acrylate at standard pressure by -20°C to +20°C, preferably by -1°C to +1°C, more preferably by -0.6°C to +0.6°C.

[0107] As described above, the first gas stream is obtained by thermal cracking of the at least one polymer composition. The first gas stream thus typically contains at least one further component. It is obvious that the at least one further component is different from the at least one alkyl (meth)acrylate and the at least one further alkyl ester.

[0108] The at least one further component is for example formed by thermal cracking of the copolymer of the alkyl (meth)acrylate and / or by thermal cracking of the at least one further component optionally present in the at least one polymer composition. Furthermore, oligomers of the alkyl (meth)acrylate can also be formed in the thermal cracking; these are likewise encompassed in the term "at least one further component" in the present application.

[0109] For example, the at least one further component is selected from the group consisting of styrene, (meth)acrylic acid, sulfur-containing compounds, oligomers, dimers, Ci-C4-alkyl acids, di(meth)acrylate diesters, Ci-C4-alcohols, high-boiling aromatic compounds, aldehydes and ketones; preferably, the at least one further component is selected from the group consisting of styrene, (meth)acrylic acid, sulfur-containing compounds, oligomers and dimers.

[0110] It is thus also preferred that the process wherein the first gas stream comprises at least one further component selected from the group consisting of styrene, (meth)acrylic acid, sulfur-containing compounds, oligomers and dimers.

[0111] High-boiling aromatic compounds in the present invention refer to, for example, phenols, anilines, benzophenones, naphthalenes and / or pyridines, each of which can be substituted or unsubstituted.

[0112] For styrene as the at least one further component, the details and preferences already described above for styrene apply accordingly.

[0113] Sulfur-containing compounds are derived in particular from sulfur-containing chain transfer agents, in particular mercaptans, such as dodecyl mercaptan, and polyfunctional mercapto compounds, such as pentaerythritol tetrakismercaptoacetate, which can be present in the at least one polymer composition.

[0114] Oligomers in the present invention refer in particular to oligomers of the at least one (meth)acrylic alkyl ester, oligomers of (meth)acrylic acid and oligomers of mixtures thereof. The term "oligomers" includes not only higher oligomers, but also lower oligomers, such as, for example, trimers, tetramers and pentamers. In particular, the term "oligomers" includes molecules consisting of 3 to 10 units, wherein the units are obtainable from the at least one (meth)acrylic alkyl ester, (meth)acrylic acid or mixtures thereof.

[0115] Dimers in the present invention refer in particular to dimers of the at least one (meth)acrylic alkyl ester, dimers of (meth)acrylic acid and dimers of mixtures thereof.

[0116] Ci-C4-alkyl acids refer to aliphatic carboxylic acids having 1 to 4 carbon atoms. The Ci-C4-alkyl acids can be branched. For example, the Ci-C4-alkyl acids are selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid and isobutyric acid.

[0117] Di(meth)acrylate diesters refer not only to esters of (meth)acrylic acid with diols, but also to esters of (meth)acrylic acid with polyols, such as, for example, triols. For example, the di(meth)acrylate diesters are selected from the group consisting of ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,4-butanediol di(meth)acrylate and 1,3-butanediol di(meth)acrylate.

[0118] C1-C4 alcohols mean alcohols having 1 to 4 carbon atoms in the alkyl group. The alkyl group can be linear or branched. The alkyl group can likewise be substituted by heteroatoms. Examples of C1-C4 alcohols are methanol, ethanol, ethylene glycol, n-butanol and isobutanol.

[0119] Aldehydes are known per se to the person skilled in the art. For example, the aldehyde is selected from the group consisting of formaldehyde, acetaldehyde, methacrolein and propionaldehyde.

[0120] In the present application, ketones mean both monoketones, such as acetone, and diketones, such as diacetyl. The ketones of the present application are, for example, selected from the group consisting of diacetyl, acetone, acetylacetone and methylethylketone.

[0121] For example, the first gas stream obtained in the thermal cleavage operation contains 60 to 99 % by weight, preferably 80 to 98 % by weight, of the at least one alkyl (meth)acrylate, in each case based on the total weight of the first gas stream.

[0122] For example, the first gas stream obtained in the thermal cleavage operation contains 0.1 to 10 % by weight, preferably 0.5 to 5 % by weight, of the at least one further alkyl ester, in each case based on the total weight of the first gas stream.

[0123] For example, the first gas stream obtained in the thermal cleavage operation contains 0.1 to 30 % by weight, preferably 0.5 to 18 % by weight, of the at least one further component, in each case based on the total weight of the first gas stream.

[0124] In step b), the first gas stream obtained in step a) is condensed to obtain a first liquid stream. The first liquid stream contains the at least one alkyl (meth)acrylate and the at least one further alkyl ester.

[0125] The first liquid stream is also referred to as recycled poly(alkyl (meth)acrylate). If the poly(alkyl (meth)acrylate) contains poly(methyl methacrylate), the first liquid stream is also referred to as recycled poly(methyl methacrylate) or recycled PMMA.

[0126] The first gas stream can be condensed by methods known to the person skilled in the art; for example, the condensation can be carried out in a condenser.

[0127] For example, the first gas stream is condensed in step b) at a temperature in the range from -10 °C to 100 °C; preferably in the range from 0 °C to 90 °C, more preferably in the range from 20 °C to 80 °C.

[0128] The pressure in the condensation of the first gas stream in step b) is for example in the range of 0.1 bar to 1.1 bar, preferably in the range of 0.3 bar to 1 bar, particularly preferred in the range of 0.4 bar to 0.8 bar.

[0129] The first gas stream is preferably condensed by suction into a first gas stream which has been previously condensed and cooled, where the sucked-in first gas stream is subsequently condensed. A substream of the condensed first gas stream can then be separated off as a first liquid stream, and the first gas stream can be resucked into the condensed and cooled first gas stream.

[0130] In the condensation process, the first gas stream is changed from the gas phase into the liquid phase, while a first liquid stream is obtained.

[0131] Generally, the at least one (meth)alkyl acrylate ester present in the first liquid stream is the same at least one (meth)alkyl acrylate ester present in the first gas stream. Thus, for the at least one (meth)alkyl acrylate ester present in the first liquid stream, the details and preferences described above for the at least one (meth)alkyl acrylate ester present in the first gas stream apply accordingly.

[0132] Generally, the at least one further alkyl ester present in the first liquid stream is the same at least one further alkyl ester present in the first gas stream. Thus, for the at least one further alkyl ester present in the first liquid stream, the details and preferences described above for the at least one further alkyl ester present in the first gas stream apply accordingly.

[0133] The first liquid stream can additionally contain at least one further component which can be present in the first gas stream. For the at least one further component, the details and preferences described above apply accordingly.

[0134] According to the present application, it is preferred that the first gas stream is distilled after step a) and before step b). Thereby, a first top stream containing the at least one (meth)alkyl acrylate ester and the at least one further alkyl ester and a first bottom stream containing at least one component different from the at least one (meth)alkyl acrylate ester and the at least one further alkyl ester are obtained. In this embodiment, the first top stream obtained in the distillation process is then condensed in step b).

[0135] It is also preferred, therefore, that a method wherein the first gas stream is distilled after step a) and before step b), while obtaining a first top stream comprising the at least one (meth)alkyl acrylate and the at least one other alkyl ester and a first bottom stream comprising components different from the at least one (meth)alkyl acrylate and the at least one other alkyl ester, wherein the first top stream is condensed in step b).

[0136] The first gas stream can be condensed prior to distilling it after step a) and before step b). The method of condensing the first gas stream is known per se and is described, for example, hereinabove. Thus, in the present application, "distilling the first gas stream" refers not only to distilling the first gas stream in the gas phase, but in particular to distilling the first gas stream after it has been condensed.

[0137] The first gas stream can be distilled by methods known to the person skilled in the art and in reactors known to the person skilled in the art. For example, the first gas stream can be transferred to a distillation column and / or a rectification column and distilled therein. In the distillation of the first gas stream, components present in the first gas stream and having a boiling point higher than the at least one (meth)alkyl acrylate are obtained in the first bottom stream, while components present in the first gas stream and having a boiling point the same as or lower than the at least one (meth)alkyl acrylate are obtained in the first top stream.

[0138] The distillation can be carried out, for example, at a temperature in the range from 40 to 140 °C. Preferably, the bottom temperature in the distillation is in the range from 95 to 130 °C, more preferably in the range from 97 to 126 °C.

[0139] The distillation can be carried out, for example, at a pressure in the range from 10 to 250 mbar, preferably in the range from 15 to 150 mbar.

[0140] In the distillation of the first gas stream, a first top stream is obtained. The first top stream contains the at least one (meth)alkyl acrylate and the at least one other alkyl ester which were already present in the first gas stream.

[0141] The first top stream can additionally contain further components. In particular, the first top stream contains at least one further component present in the first gas stream which has a lower or exactly the same high boiling point than the at least one (meth)alkyl acrylate and the at least one other alkyl ester. Thus, the first top stream typically contains at least one further component selected from the group consisting of methyl propionate, ethyl propionate, methyl isobutyrate, methyl tert.-butyrate, methyl 3-methoxyisobutyrate and a diester of a dicarboxylic acid.

[0142] For example, the first top stream obtained in the distillation contains 60 wt.-% to < 99.8 wt.-%, preferably 85 wt.-% to 98 wt.-%, of the at least one (meth)alkyl acrylate, in each case based on the total weight of the first top stream.

[0143] For example, the first top stream obtained in the distillation contains 0.1 wt.-% to 10 wt.-%, preferably 0.5 wt.-% to 5 wt.-%, of the at least one further alkyl ester, in each case based on the total weight of the first top stream.

[0144] For example, the first top stream obtained in the distillation contains 0.1 wt.-% to 30 wt.-%, preferably 0.5 wt.-% to 14.5 wt.-%, of the at least one further component, in each case based on the total weight of the first top stream.

[0145] Furthermore, a first bottom stream is obtained. "Bottom stream" in the present application not only refers to a bottom product continuously withdrawn from the distillation, in particular from the reactor, but also to a bottom product which is retained in the reactor, for example in a batch mode of operation, as distillation residue and is only withdrawn from the reactor at a later point in time.

[0146] The first bottom stream contains at least one component which is different from the at least one (meth)alkyl acrylate and the at least one further alkyl ester. This component is typically at least one of the at least one further component present in the first gas stream. In particular, this at least one further component typically has a higher boiling temperature than the at least one (meth)alkyl acrylate present in the first gas stream and the at least one further alkyl ester present in the first gas stream. For example, this at least one further component is selected from the group consisting of sulfur-containing compounds, high-boiling aromatic compounds, oligomers and dimers. For the sulfur-containing compounds, high-boiling aromatic compounds, oligomers and dimers, the details and preferences described above for the sulfur-containing compounds, high-boiling aromatic compounds, oligomers and dimers present in the first gas stream apply accordingly.

[0147] The first bottom stream thus preferably contains sulfur-containing compounds, high-boiling aromatic compounds, oligomers and / or dimers.

[0148] In step c), the first liquid stream obtained in step b) is mixed with an additional stream to obtain a mixed stream. The additional stream contains at least one additional (meth)alkyl acrylate and is part of a process for the preparation of poly((meth)alkyl acrylate). The resulting mixed stream comprises the first liquid stream and the additional stream.

[0149] If the additional stream contains (methyl) methacrylate as additional (meth) acrylate alkyl ester and is part of a process for the preparation of poly((methyl) methacrylate), the additional stream is also referred to as pure (methyl) methacrylate or pure MMA.

[0150] It is apparent that the first liquid stream is different from the additional stream. For example, the first liquid stream contains in the range of 90 to < 99.8 wt.-% of the at least one (meth) acrylate alkyl ester, based on the total weight of the first liquid stream. For example, the additional stream contains at least 99.8 wt.-% of the at least one additional (meth) acrylate alkyl ester, based on the total weight of the additional stream. Preferably, the additional stream contains at least 99.8 wt.-% of (methyl) methacrylate, based on the total weight of the additional stream, and the additional stream is obtainable by a (methyl) methacrylate preparation process using Ci, C2, C3 and / or C4 feedstocks (methanol, ethylene, acetone, hydrogen cyanide, isobutene and / or methyl tert-butyl ether). These preparation processes are known per se to the person skilled in the art.

[0151] For example, at most 50 wt.-%, preferably at most 40 wt.-% of the first liquid stream is mixed with the additional stream, based on the total weight of the resulting mixed stream. For example, at least 1.5 wt.-%, preferably at least 5 wt.-% of the first liquid stream is mixed with the additional stream, based on the total weight of the resulting mixed stream.

[0152] It is also preferred therefore, wherein in step c) at most 50 wt.-% of the first liquid stream is mixed with the additional stream, based on the total weight of the resulting mixed stream.

[0153] For example, the first liquid stream contains in the range of 90 wt.-% to < 99.8 wt.-% of (meth) acrylate alkyl ester, preferably in the range of 94 wt.-% to 98 wt.-%, in each case based on the total weight of the first liquid stream, and 1.5 wt.-% to 25 wt.-%, preferably 9 wt.-% to 15 wt.-% of the first liquid stream is mixed with the additional stream, based on the total weight of the resulting mixed stream. This embodiment is preferred when optional step d) is not performed.

[0154] If optional step d) is performed in a preferred embodiment of the present application, the first liquid stream contains for example in the range of 90 wt.-% to < 99.8 wt.-% of (meth) acrylate alkyl ester, based on the total weight of the first liquid stream, and 1.5 wt.-% to 50 wt.-%, preferably 5 wt.-% to 20 wt.-% of the first liquid stream is mixed with the additional stream, based on the total weight of the resulting mixed stream.

[0155] It is also preferred, therefore, that the process is one in which the first liquid stream contains (meth)alkyl acrylate in the range of from 90 wt.% to < 99.8 wt.% based on the total weight of the first liquid stream and from 1.5 wt.% to 50 wt.% of the first liquid stream is mixed with the additional stream based on the total weight of the resulting mixed stream.

[0156] The additional stream mixed with the first liquid stream contains at least one additional (meth)alkyl acrylate. "At least one additional (meth)alkyl acrylate" means both exactly one additional (meth)alkyl acrylate and a mixture of two or more additional (meth)alkyl acrylates in the present application. Exactly one additional (meth)alkyl acrylate is preferred.

[0157] For the at least one additional (meth)alkyl acrylate present in the additional stream, the details and preferences described above for the at least one (meth)alkyl acrylate present in the first gas stream apply accordingly. Thus, the at least one additional (meth)alkyl acrylate is, for example, selected from (meth)alkyl acrylates having C1-C4-alkyl groups. The (meth)alkyl acrylate present in the additional stream is particularly preferably (meth)acrylic acid methyl ester.

[0158] The at least one (meth)alkyl acrylate present in the first liquid stream preferably comprises the same (meth)alkyl acrylate as the at least one additional (meth)alkyl acrylate comprised in the additional stream.

[0159] It is preferred according to the present application that at least 80 wt.%, preferably at least 90 wt.% of the at least one (meth)alkyl acrylate present in the first liquid stream is the same (meth)alkyl acrylate as the at least one additional (meth)alkyl acrylate present in the additional stream based on the total weight of the at least one (meth)alkyl acrylate present in the first liquid stream.

[0160] The additional stream is part of a process for preparing poly((alkyl) methacrylate). A "process for preparing poly((alkyl) methacrylate)" in the present invention refers to a process for preparing poly((alkyl) methacrylate) by polymerization of at least one (alkyl) methacrylate, optionally in the presence of monomers different from (alkyl) methacrylate. The polymerization can be, for example, a free radical polymerization or an anionic polymerization, preferably a free radical polymerization. Further preferably, the polymerization is a free radical polymerization in emulsion, solution or bulk, preferably in bulk. Particularly preferably, the polymerization is a free radical bulk polymerization, wherein the at least one (alkyl) methacrylate, optionally in the presence of monomers different from (alkyl) methacrylate, is first partially polymerized to obtain a slurry, which is then polymerized in a vented extruder to obtain a polymer mixture containing poly((alkyl) methacrylate).

[0161] The poly((alkyl) methacrylate) from the process for preparing poly((alkyl) methacrylate) can be the same or different from the poly((alkyl) methacrylate) present in the at least one polymer composition. For the poly((alkyl) methacrylate) from the process for preparing poly((alkyl) methacrylate), the details and preferences described above for the poly((alkyl) methacrylate) present in the at least one polymer composition apply accordingly.

[0162] The poly((alkyl) methacrylate) is thus preferably poly(methyl methacrylate).

[0163] It is thus also preferred that the process, wherein the poly((alkyl) methacrylate) present in the polymer mixture is poly(methyl methacrylate).

[0164] The additional stream is part of a process for preparing poly((alkyl) methacrylate). The additional stream can be, for example, a reaction stream directly from the preparation of the at least one additional (alkyl) methacrylate present in the additional stream. Further, it is possible and preferred according to the present invention that the additional stream is obtained in the process for preparing poly((alkyl) methacrylate). For example, the additional stream can be the second top stream described below and / or the condensate stream obtained in step g).

[0165] The first liquid stream can be mixed with the additional stream by methods known to the person skilled in the art. For example and preferably according to the present invention, the first liquid stream is fed into a device for preparing poly((alkyl) methacrylate) containing the additional stream. The resulting mixed stream is then preferably also present in the device for preparing poly((alkyl) methacrylate). The mixed stream is then preferably also part of the process for preparing poly((alkyl) methacrylate).

[0166] It is thus also preferred that the process wherein the mixed stream obtained in step c) is part of a process for the preparation of poly(alkyl (meth)acrylate).

[0167] The mixed stream comprises the first liquid stream and the additional stream. The mixed stream thus generally comprises the same components present in the first liquid stream and present in the additional stream. Thus, the mixed stream generally comprises the at least one alkyl (meth)acrylate, the at least one other alkyl ester, the at least one additional alkyl (meth)acrylate and, optionally, the at least one further component.

[0168] The first liquid stream can be mixed with the additional stream at any point in the process for the preparation of poly(alkyl (meth)acrylate). The first liquid stream is preferably mixed with the additional stream immediately upstream of or in the purification section of the process for the preparation of poly(alkyl (meth)acrylate) as described hereinafter. This is advantageous because it is then possible to perform at least partial separation of the at least one other alkyl ester in the purification section of the process for the preparation of poly(alkyl (meth)acrylate) in optional step d).

[0169] In optional step d), the at least one other alkyl ester is at least partially separated from the mixed stream obtained in step c) to obtain a purified mixed stream. The purified mixed stream contains the at least one alkyl (meth)acrylate, the at least one additional alkyl (meth)acrylate and a residue of the at least one other alkyl ester. In step e), the purified mixed stream obtained in step d) is then partially polymerized. Preferably, step d) is performed.

[0170] It is thus also preferred that the process wherein the method additionally comprises the following step d):

[0171] d) at least partially separating the at least one other alkyl ester from the mixed stream obtained in step c) to obtain a purified mixed stream comprising the at least one alkyl (meth)acrylate, the at least one additional alkyl (meth)acrylate and a residue of the at least one other alkyl ester,

[0172] wherein the purified mixed stream obtained in step d) is subsequently partially polymerized in step e).

[0173] The at least one other alkyl ester can be at least partially separated by any desired method. For example, the at least one other alkyl ester can be at least partially separated from the mixed stream obtained in step c) by distillation.

[0174] Preferably, the at least one other alkyl ester is at least partially separated in the purification section of the process for the preparation of poly(alkyl (meth)acrylate) as described hereinafter.

[0175] The purified mixed stream contains residues of the at least one further alkyl ester. The expression "residues of the at least one further alkyl ester" means in the present application from 0 to 8 % by weight, preferably from 0.1 to 3 % by weight, particularly preferably from 0.1 to 2 % by weight, in each case based on the total weight of the purified mixed stream, of the at least one further alkyl ester.

[0176] In step e) of the process according to the application, the mixed stream obtained in step c) is partially polymerized. A slurry containing partially polymerized at least one alkyl (meth)acrylate, partially polymerized at least one additional alkyl (meth)acrylate and residues of the at least one further alkyl ester is obtained here.

[0177] If the optional step d) is carried out, the purified mixed stream obtained in step d) is then partially polymerized in step e) of the process according to the application, to obtain a slurry containing partially polymerized at least one alkyl (meth)acrylate, partially polymerized at least one additional alkyl (meth)acrylate and residues of the at least one further alkyl ester.

[0178] "Partially polymerized" means in the present application that the total conversion of the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate is in the range of from 20 to 60 %, preferably in the range of from 35 to 50 %, based on the amount of the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate present in the mixed stream, preferably in the purified mixed stream. The total conversion of the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate is defined as the ratio of the total amount of the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate in the slurry obtained in step e) to the total amount of the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate in the mixed stream obtained in step c). The total amount of the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate is usually determined by GC analysis.

[0179] It is therefore also preferred that the process in which, in the partial polymerization in step e), the total conversion of the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate is in the range of from 20 to 60 %, based on the amount of the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate present in the purified mixed stream.

[0180] The partial polymerization in step e) can be carried out by methods known to the person skilled in the art. The partial polymerization is preferably carried out in the presence of at least one auxiliary.

[0181] The at least one auxiliary is also referred to as at least one additive.

[0182] It is therefore also preferred that the process wherein the partial polymerization in step e) is carried out in the presence of at least one auxiliary.

[0183] The at least one auxiliary can be supplied to the mixed stream at any point, for example in the reactor described hereinafter for the partial polymerization. Preferably, the at least one auxiliary is supplied to the mixed stream before the mixed stream is transferred to the reactor.

[0184] As at least one auxiliary it is suitable, for example, that the auxiliary known to the person skilled in the art which can initiate and / or influence the partial polymerization.

[0185] For example, the at least one auxiliary is selected from the group consisting of initiators, chain transfer agents and release agents.

[0186] It is therefore also preferred that the process wherein the at least one auxiliary is selected from the group consisting of initiators, chain transfer agents and release agents.

[0187] The details and preferences described above apply accordingly for this initiator, chain transfer agent and release agent.

[0188] The partial polymerization in step e) can be carried out, for example, by radical or anionic means. It is preferably carried out by radical means. Furthermore, the partial polymerization can be carried out in emulsion, solution or bulk. It is preferably carried out in bulk. Suitable reactors are reactors for the partial polymerization known to the person skilled in the art. For example, the partial polymerization can be carried out in a stirred tank reactor, preferably in a continuous stirred tank reactor.

[0189] For example, the temperature of the partial polymerization in step e) is in the range from 120 to 170 °C, preferably in the range from 130 to 160 °C.

[0190] For example, the partial polymerization is carried out at a pressure in the range from 1 to 5 bar (absolute) (bara), preferably in the range from 1.5 to 3 bar (absolute).

[0191] A slurry is obtained in the partial polymerization. The slurry contains the at least one partially polymerized alkyl (meth)acrylate, the at least one additional partially polymerized alkyl (meth)acrylate and the at least one further alkyl ester, and, when the optional step d) is carried out, the residue of the at least one further alkyl ester. Furthermore, the resulting slurry usually contains the at least one auxiliary for the partial polymerization, and / or reaction products thereof.

[0192] The expression "partially polymerized at least one (meth)alkyl acrylate" in the present invention means that part of the at least one (meth)alkyl acrylate is polymerized with itself and / or with the at least one additional (meth)alkyl acrylate, and that part of the at least one (meth)alkyl acrylate is present as monomer. The expression "partially polymerized at least one additional (meth)alkyl acrylate" in the present invention means that part of the at least one additional (meth)alkyl acrylate is polymerized with itself and / or with the at least one (meth)alkyl acrylate, and that part of the at least one additional (meth)alkyl acrylate is present as monomer.

[0193] In the polymerization of the at least one (meth)alkyl acrylate with itself and / or with the at least one additional (meth)alkyl acrylate, and in the polymerization of the at least one additional (meth)alkyl acrylate with itself and / or with the at least one (meth)alkyl acrylate, polymers of the at least one (meth)alkyl acrylate with itself and / or of the at least one additional (meth)alkyl acrylate, and polymers of the at least one additional (meth)alkyl acrylate with itself and / or of the at least one (meth)alkyl acrylate are formed. In addition, oligomers of the at least one (meth)alkyl acrylate, of the at least one additional (meth)alkyl acrylate, and mixtures thereof are formed.

[0194] "Oligomer" in this context means oligomers of the at least one (meth)alkyl acrylate, of the at least one additional (meth)alkyl acrylate, and mixtures thereof. The term "oligomer" includes not only higher oligomers, but also lower oligomers, such as dimers, trimers, tetramers, and pentamers. In particular, the term "oligomer" in this context includes molecules consisting of 2 to 10 units, wherein the units are obtainable from the at least one (meth)alkyl acrylate, the at least one additional (meth)alkyl acrylate, and mixtures thereof.

[0195] "Polymer" in this context means polymers of the at least one (meth)alkyl acrylate, of the at least one additional (meth)alkyl acrylate, and mixtures thereof. For example, polymers in this context comprise 1000 to 100 000 units, wherein the units are obtainable from the at least one (meth)alkyl acrylate, the at least one additional (meth)alkyl acrylate, and mixtures thereof.

[0196] In step f), the slurry obtained in step e) is polymerized in a vented extruder. This provides a polymer mixture containing poly((meth)alkyl acrylate).

[0197] The temperature in the vented extruder in step f) is for example in the range of 150 to 290°C, preferably in the range of 170 to 270°C.

[0198] The pressure in the degassing zone of the vented extruder in step f) is for example in the range of 0.1 bar (absolute) to 2 bar (absolute), preferably in the range of 0.15 bar (absolute) to 0.3 bar (absolute).

[0199] Suitable vented extruders are vented extruders known to the person skilled in the art. Suitable vented extruders are described for example in EP 2 212 091 A1 and WO 2009 / 040190 A1.

[0200] Generally, the slurry obtained in step e) is fed into the vented extruder via a material feed opening and then continues to advance therein, in the course of which the slurry polymerizes to obtain a polymer mixture. The slurry and the polymer mixture are thus conveyed along the vented extruder. At the extruder outlet, the resulting polymer mixture is discharged from the extruder. The extruder outlet is generally arranged at the end of the extruder opposite the material feed opening.

[0201] A polymer mixture is obtained in the polymerization in step f). This polymer mixture contains poly(alkyl (meth)acrylate). In addition, this polymer mixture can contain components of the slurry.

[0202] For the poly(alkyl (meth)acrylate) present in the polymer mixture, the details and preferences described above apply accordingly.

[0203] In step g) of the process of the present application, the slurry obtained in step e) and / or the polymer mixture obtained in step f) is degassed in a vented extruder, while obtaining a condensate stream. This condensate stream contains the at least one alkyl (meth)acrylate, the at least one additional alkyl (meth)acrylate, oligomers thereof and the at least one further alkyl ester.

[0204] The degassing in the vented extruder can be carried out by methods known to the person skilled in the art. The polymerization in step f) is preferably carried out simultaneously with the degassing in step g).

[0205] It is thus also preferred that the process in which steps f) and g) are carried out simultaneously.

[0206] In the present application, "degassing" means removing volatile constituents of the slurry and / or the polymer mixture, i.e. in particular the at least one alkyl (meth)acrylate, the at least one additional alkyl (meth)acrylate, oligomers thereof and the at least one further alkyl ester, from the slurry and / or the polymer mixture. These volatile constituents are obtained as a condensate stream.

[0207] The condensate stream contains, for example, in the range from 75 to 85 % by weight of the at least one (meth)alkyl acrylate and the total amount of the at least one additional (meth)alkyl acrylate, in the range from 0.1 to 5 % by weight of the at least one further alkyl ester and in the range from 10 to 20 % by weight of further constituents, in each case based on the total weight of the condensate stream. The further constituents include, for example, oligomers of the at least one (meth)alkyl acrylate and oligomers of the at least one additional (meth)alkyl acrylate.

[0208] The degassing in step g) can be carried out in a vented extruder known to the person skilled in the art. The degassing is preferably carried out in a vented extruder as described, for example, in EP 2 212 091 A1 and WO 2009 / 040190 A1.

[0209] It is preferred that the direction of removal of the condensate stream is essentially opposite to the direction of transport of the slurry and / or of the polymer mixture. The polymer mixture is thus transported out of the vented extruder in a direction opposite to the degassing.

[0210] It is thus also preferred that the method in which the degassing in step g) is carried out counter-current to the direction of transport of the polymer mixture obtained in step f).

[0211] Vented extruders of this type are described, for example, in EP 2 212 091 A1 and WO 2009 / 040190 A1.

[0212] It is further preferred that the degassing is carried out in at least two steps; for example, a first degassing operation is carried out in the front 1 / 3 of the vented extruder and a second degassing operation is carried out in the rear 1 / 3 of the vented extruder. The first degassing operation is preferably carried out at ambient pressure, while the second degassing operation is carried out at reduced pressure.

[0213] The condensate stream is usually obtained in gaseous form. It is possible and preferred according to the application that the condensate stream is condensed after step g) and before step h).

[0214] The degassed stream is thus usually first obtained and then condensed to give the condensate stream. If the degassing in the vented extruder is carried out in at least two steps, for example, a first degassed stream is obtained in the first degassing operation and a second degassed stream is obtained in the second degassing operation.

[0215] In step h), the at least one further alkyl ester is removed from the condensate stream obtained in step g) to give an (meth)alkyl acrylate stream. This (meth)alkyl acrylate stream contains the at least one (meth)alkyl acrylate and the at least one additional (meth)alkyl acrylate.

[0216] If in the preferred embodiment according to the present application the optional step d) is carried out, the residue of the at least one further alkyl ester is removed from the condensed material stream obtained in step g) in step h). Thus, the details and preferences described hereinafter for the at least one further alkyl ester apply accordingly to the residue of the at least one further alkyl ester.

[0217] The at least one further alkyl ester is typically removed in a purification section of the process for preparing poly(alkyl (meth)acrylate).

[0218] In the present application, the term "purification section" refers to a part of the process for preparing poly(alkyl (meth)acrylate) in which the condensed material stream is purified such that an alkyl (meth)acrylate stream is obtained. In particular, in the purification section the at least one further alkyl ester, and possibly oligomers present in the condensed material stream, are at least partially separated. The purification section typically comprises means for separating the components, such as a distillation column, a rectification column and / or a thin-film evaporator.

[0219] Processes for purifying condensed material streams, in particular for separating the at least one further alkyl ester from the condensed material stream, are known per se. For example, the at least one further alkyl ester can be removed by distillation. Preferably, the at least one further alkyl ester is separated in at least two steps.

[0220] For example, step h) comprises the following step h1):

[0221] h1) separating the condensed material stream into a second top stream comprising the at least one additional alkyl (meth)acrylate and the at least one further alkyl ester, and a second bottom stream comprising oligomers of the at least one alkyl (meth)acrylate and oligomers of the at least one additional alkyl (meth)acrylate.

[0222] The condensed material stream can be separated into the second top stream and the second bottom stream by methods known to the person skilled in the art. For example, by distillation and / or rectification and / or thin-film evaporation.

[0223] Preferably, the following step h2) is carried out after step h1):

[0224] h2) distilling the second top stream obtained in step h1) to obtain a third top stream comprising the at least one further alkyl ester, and a third bottom stream comprising the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate.

[0225] It is thus also preferred that the process wherein the separation in step h) comprises the following steps:

[0226] h1 ) separating the condensed material stream into a second overhead stream comprising the at least one (meth)acrylic acid alkyl ester, the at least one additional (meth)acrylic acid alkyl ester and the at least one further alkyl ester, and a second bottom stream comprising oligomers of the at least one (meth)acrylic acid alkyl ester and the at least one additional (meth)acrylic acid alkyl ester;

[0227] h2) distilling the second overhead stream obtained in step h1 ) to obtain a third overhead stream comprising the at least one further alkyl ester, and a third bottom stream comprising the at least one (meth)acrylic acid alkyl ester and the at least one additional (meth)acrylic acid alkyl ester.

[0228] Generally, the second overhead stream obtained in step h1 ) is continuously transferred to the distillation in step h2).

[0229] The third bottom stream obtained in step h2) comprises an (meth)acrylic acid alkyl ester stream.

[0230] The (meth)acrylic acid alkyl ester stream obtained in step h) and / or the third bottom stream obtained in step h2) can be at least partially recycled to at least one of steps c), e) and / or f).

[0231] It is thus also preferred that the process wherein the (meth)acrylic acid alkyl ester stream obtained in step h) is at least partially recycled to at least one of steps c), e) and / or f).

[0232] It is preferred according to the present application that in step c) the first liquid stream obtained in step b) is mixed with the condensed material stream prior to or during step h). In this case, the additional stream corresponds to the condensed material stream. This embodiment is particularly advantageous because step h) can subsequently comprise optional step d).

[0233] It is thus also preferred that the process wherein step h) comprises step d).

[0234] If step h) comprises step d), the at least one alkyl ester can be separated from the mixed stream together with the residue of the at least one alkyl ester separated from the condensed material stream.

[0235] The present application further provides a process for the preparation of poly((meth)acrylic acid alkyl ester) comprising the following steps c1 ) to h):

[0236] c1 ) mixing a first liquid stream comprising the at least one (meth)alkyl acrylate and the at least one further alkyl ester with an additional stream containing at least one additional (meth)alkyl acrylate, wherein the first liquid stream is obtainable by thermal cracking of at least one polymer composition, wherein the additional stream is part of a process for the preparation of poly((meth)alkyl acrylate), thereby obtaining a mixed stream comprising the first liquid stream and the additional stream,

[0237] e) partially polymerizing the mixed stream obtained in step c1 ) to obtain a slurry comprising partially polymerized at least one (meth)alkyl acrylate, partially polymerized at least one additional (meth)alkyl acrylate and the at least one further alkyl ester,

[0238] f) polymerizing the slurry obtained in step e) in a vented extruder to obtain a polymer mixture comprising poly((meth)alkyl acrylate),

[0239] g) degassing the slurry obtained in step e) and / or the polymer mixture obtained in step f) in a vented extruder to obtain a condensate stream comprising the at least one (meth)alkyl acrylate, the at least one additional (meth)alkyl acrylate, oligomers thereof and the at least one further alkyl ester,

[0240] h) separating the residue of the at least one further alkyl ester from the condensate stream obtained in step g) to obtain an (meth)alkyl acrylate stream comprising the at least one (meth)alkyl acrylate and the at least one additional (meth)alkyl acrylate.

[0241] In step c1 ) the first liquid stream is mixed with the additional stream. The first liquid stream is obtainable by thermal cracking of at least one polymer composition. The polymer composition is suitable with the details and preferences described above.

[0242] The first liquid stream is thus preferably obtainable by the following steps a) and b):

[0243] a) thermal cracking of at least one polymer composition comprising at least one poly((meth)alkyl acrylate) to obtain a first gaseous stream comprising at least one (meth)alkyl acrylate and at least one further alkyl ester,

[0244] b) condensing the first gaseous stream obtained in step (a) to obtain a first liquid stream comprising the at least one (meth)alkyl acrylate and the at least one further alkyl ester.

[0245] Steps a) and b) are suitable with the details and preferences described above, respectively.

[0246] The first liquid stream likewise corresponds to the details and preferences described above. Step c1 ) corresponds to the details and preferences described above for step c).

[0247] Steps e) to h) correspond to the details described above.

[0248] In a preferred embodiment, step d) described above is additionally carried out after step c1 ) and before step e). BRIEF DESCRIPTION OF DRAWINGS

[0249] Figure 1 : Process for the preparation of poly(alkyl (meth)acrylate) according to the prior art

[0250] Figure 2 : First embodiment of the process for the preparation of poly(alkyl (meth)acrylate) according to the invention

[0251] Figure 3 : Second embodiment of the process for the preparation of poly(alkyl (meth)acrylate) according to the invention

[0252] The invention is described in detail below with reference to the drawings, but the invention is not limited thereto.

[0253] Figure 1 A process for the preparation of poly(alkyl (meth)acrylate) according to the prior art is shown. An additional stream (A) comprising at least one additional alkyl (meth)acrylate is mixed with a third bottom stream (B) likewise comprising at least one additional alkyl (meth)acrylate to obtain a mixed stream (C1 ). The third bottom stream (B) can be obtained in the purification section 5 of the process as described below.

[0254] The mixed stream (C1 ) is mixed with an additive stream (D) and an atmospheric condensate (E) to obtain a second mixed stream (F1 ). This second mixed stream (F1 ) is transferred into a polymerization reactor 1. In there the second mixed stream (F1 ) is partially polymerized to obtain a slurry (G) comprising partially polymerized at least one additional alkyl (meth)acrylate. In addition, the slurry (G) also comprises at least one additional alkyl (meth)acrylate which has not yet been polymerized. The slurry (G) is then transferred into a vented extruder 2. In there the slurry (G) is further polymerized to obtain a degassed polymer mixture (J) comprising poly(alkyl (meth)acrylate).

[0255] In the vented extruder 2, the slurry (G) and / or the polymer mixture (J) is degassed to obtain a condensate stream. In Figure 1In the embodiment shown, the slurry (G) and / or polymer mixture (J) are first degassed under ambient pressure in a first region of the vented extruder 2 to obtain a first degassed stream (H). A further degassed step is performed under reduced pressure in a second region of the vented extruder 2 to obtain a second degassed stream (H').

[0256] The first degassed stream (H) is condensed in condenser (Kondensation) 4 to obtain standard pressure condensate (E), which is then at least partially mixed with the mixed stream (C1). A portion of the atmospheric pressure condensate (E) may also be mixed with the slurry (G). Figure 1 (Not shown in the image).

[0257] The second degassed stream (H') is also condensed in condenser 4. Vacuum degassed condensate (I) is obtained here. At least a portion of this is transferred to purification section 5. It is possible to mix a portion of the vacuum degassed condensate (I) with the atmospheric pressure condensate (E). Figure 1 (Not shown in the image). The vacuum degassed condensate (I) is purified in purification section 5. Purification section 5 may include, for example, a thin-film evaporator and a distillation column. In the thin-film evaporator, the vacuum degassed condensate (I) is partially evaporated to obtain a second top stream (not shown) and a second bottom stream (L). The second top stream is then transferred to the distillation column and subsequently to a third top stream (K) and a third bottom stream (B).

[0258] The polymer mixture (J) is processed in polymer processing 3 by known methods to obtain polymer pellets (M).

[0259] Figure 2 This illustrates a first embodiment of the method for preparing poly(alkyl methacrylate) according to the present invention. (Compared to...) Figure 1 The same reference numerals in the figures have the same meaning.

[0260] An additional stream (A) containing at least one additional alkyl methacrylate is mixed with a third bottom stream (B) containing at least one alkyl methacrylate and at least one additional alkyl methacrylate, and with a first liquid stream (N) containing at least one alkyl methacrylate and at least one other alkyl methacrylate to obtain a mixed stream (C).

[0261] The third bottom stream (B) can be obtained in the purification section 5 of this method as described below.

[0262] The mixture stream (C) is mixed with the additive stream (D) and the standard pressure condensate (E) to obtain a second mixed stream (F). This second mixed stream (F) is transferred into the polymerization reactor 1. Therein the second mixed stream (F) is partially polymerized to obtain a slurry (G) comprising partially polymerized at least one alkyl (meth)acrylate, partially polymerized at least one additional alkyl (meth)acrylate and the at least one further alkyl ester. The slurry (G) further comprises un-polymerized at least one alkyl (meth)acrylate and un-polymerized at least one additional alkyl (meth)acrylate. The slurry (G) is then transferred into the vented extruder 2. Therein the slurry (G) is further polymerized to obtain a degassed polymer mixture (J) comprising poly(alkyl (meth)acrylate).

[0263] In the vented extruder 2, the slurry (G) and / or the polymer mixture (J) is degassed as described above for Figure 1 the preparation of the poly(alkyl (meth)acrylate) and the obtained first degassed stream (H) and second degassed stream (H') are condensed in the condenser 4. The thus obtained vacuum degassed condensate (I) is purified as described for Figure 1 the preparation of the poly(alkyl (meth)acrylate) and the obtained third bottom stream (B) is recycled.

[0264] The polymer mixture (J) is processed in the polymer processing 3 by known methods to obtain polymer pellets (M).

[0265] Figure 3 A further embodiment of the process of the present application is shown. Figure 3 The same reference signs in Figure 2 the figures mean the same. Only the differences to the process according to Figure 2 the preparation of the poly(alkyl (meth)acrylate) are described in detail below.

[0266] The first liquid stream (N) comprising the at least one alkyl (meth)acrylate and the at least one further alkyl ester is directly fed into the post-treatment section 5 and purified together with the vacuum degassed condensate (I), e.g. by means of a thin-film condenser and a rectification column, to obtain the third bottom stream (B) which is then mixed with the additional stream (A). In this embodiment, the first liquid stream (N) is thus mixed with the vacuum degassed condensate (I) which comprises inter alia the at least one additional alkyl (meth)acrylate and is part of the process for the preparation of the poly(alkyl (meth)acrylate) such that in this embodiment the vacuum degassed condensate (I) is the additional stream of step c) of the process according to the present application.

[0267] The third bottom stream (B) is then mixed with the additional stream (A) as described for Figure 2 the preparation of the poly(alkyl (meth)acrylate) to obtain a mixed stream. Figure 3 The other process steps in Figure 1those described in the detailed description.

[0268] List of reference signs

[0269] (A) additional stream

[0270] (B) third bottoms stream

[0271] (C) mixed stream

[0272] (C1) mixed stream

[0273] (D) additive stream

[0274] (E) atmospheric condensate

[0275] (F) second mixed stream

[0276] (F1) second mixed stream

[0277] (G) slurry

[0278] (H) first degassed stream

[0279] (H') second degassed stream

[0280] (I) vacuum degassed condensate

[0281] (J) degassed polymer mixture

[0282] (K) third overhead stream

[0283] (L) second bottoms stream

[0284] (M) polymer pellets

[0285] (N) first liquid stream

[0286] 1 polymerization reactor

[0287] 2 vented extruder

[0288] 3 polymer processing

[0289] 4 condenser

[0290] 5 purification section

[0291] The application is described in detail below with the help of examples, but is not limited thereto. DETAILED DESCRIPTION

[0292] EXAMPLE

[0293] Polymethyl methacrylate (PMMA) was prepared in a two-stage polymerization starting from various different monomer compositions

[0294] The additional stream is provided by a C3 production process for MMA. Table 1 shows the composition of the additional stream obtained.

[0295] Table 1

[0296] Stream Substance Concentration Unit (A) Methyl methacrylate (MMA) >99.98 wt.-% (A) Methyl acrylate 3 wt. ppm (A) Butanedione 1 wt. ppm (A) Dimerized MMA (DMMA) 2 wt. ppm (A) Methyl propionate 100 wt. ppm (A) Methyl isobutyrate 50 wt. ppm (A) Water 20 wt. ppm (A) Sum of unknown compounds 20 wt. ppm

[0297] Two different first liquid streams were obtained by depolymerizing poly(methyl methacrylate). The composition of the first liquid stream obtained in each case is given in Tables 2 and 3.

[0298] Table 2

[0299] Stream Substance Concentration Unit (N) MMA 97.9 wt.-% (N) Acetone 100 wt. ppm (N) Methanol 120 wt. ppm (N) Methyl acrylate 5000 wt. ppm (N) Methyl propionate 1000 wt. ppm (N) Methyl isobutyrate 5000 wt. ppm (N) Butanedione 50 wt. ppm (N) DMMA 2000 wt. ppm (N) Methyl pyruvate 15 wt. ppm (N) Total low boilers 8000 wt. ppm (N) Total high boilers 4900 wt. ppm

[0300] Table 3

[0301] Stream Substance Concentration Unit (N) MMA 91.2 wt.-% (N) Acetone 110 wt. ppm (N) Methanol 90 wt. ppm (N) Methyl acrylate 9820 wt. ppm (N) Methyl propionate 2000 wt. ppm (N) Methyl isobutyrate 4940 wt. ppm (N) Butanedione 26 wt. ppm (N) DMMA 9000 wt. ppm (N) Methyl pyruvate 15 wt. ppm (N) Total low boilers 11980 wt. ppm (N) Total high boilers 54800 wt. ppm

[0302] Measurement method:

[0303] The compositions reported in Tables 1, 2 and 3 were determined by gas chromatography (Agilent 88990, standard addition: isopropanol).

[0304] The quality and physical properties of the polymethyl methacrylate (PMMA) products prepared according to the examples were determined by the following methods: yellowing (D65 / 10°) was determined by photometric determination (Varian Cary 5000) according to DIN 6167 (1980; 01). Melt volumetric flow rate (MVR) was determined at 230°C with a 3.8 kg sample according to DIN EN ISO 1133 (2012; 03). Vicat softening temperature (VST) was determined according to DIN EN ISO 306 (2014; 03).

[0305] Comparative Example V1 : Preparation of PMMA starting from an additional stream

[0306] According to Figure 1 PMMA was prepared in the apparatus.

[0307] An additional feed stream (A) of 5000 kg / h according to Table 1 is continuously mixed with a third bottom feed stream (B) of 384 kg / h in a static mixer at 8°C. The third bottom feed stream (B) has an MMA concentration of 98.8% based on the total amount of the third bottom feed stream (B). The third bottom feed stream (B) is recycled from purification section 5, described below, and has a temperature of 10°C. Purification section 5 includes a thin-film evaporator coupled to a distillation column.

[0308] By mixing the additional feed stream (A) with the third bottom feed stream (B), a mixed feed stream (C1) comprising the additional feed stream (A) and the third bottom feed stream (B) is obtained. The mixed feed stream (C1) is then mixed with an additive feed stream (D) of 100 kg / h. The additive feed stream (D) contains palmitin as a release agent, high-boiling-point substances as additives, and polymerization modifiers such as dodecyl mercaptan dissolved in MMA. The MMA concentration is >90% by weight. Furthermore, an atmospheric pressure condensate (E) containing approximately 90% MMA and having a temperature of 5°C is added. The atmospheric pressure condensate (E) is obtained in a condenser 4 as described below.

[0309] The second mixed feed stream (F1), which reaches a total flow rate of 18,200 kg / h during the mixing process, is then heated to 150°C in a shell-and-tube heat exchanger and fed into a 10 m³ volumetric heat exchanger. 3 Partial polymerization was carried out in polymerization reactor 1. This was achieved by adding an initiator solution of 5 kg / h (…). Figure 1 (Not shown in the diagram) This leads to the second mixed stream (F1) being continuously polymerized at 150°C and slightly increased pressure, where approximately 45% conversion is established. The residence time is approximately 10 minutes.

[0310] The resulting slurry (G) is then preheated to approximately 210°C on the tube side in a shell-and-tube heat exchanger and fed into a vented extruder 2 at a feed rate of approximately 12,800 kg / h. The vented extruder operates with a temperature distribution pattern of 170°C to 270°C and undergoes degassing at two points. A first degassing process is performed in the first third of the vented extruder 2 under ambient pressure to obtain a first degassed feed stream (H); a second degassing process is performed under a vacuum of approximately 150 mbar (absolute) to obtain a second degassed feed stream (H').

[0311] The first degassed stream (H) obtained under standard pressure is condensed at 5°C and used as the standard pressure condensate (E). Approximately 5% of the standard pressure condensate (E) is mixed with the vacuum degassed condensate (I). Figure 1 (not shown in the image), and then it is fed into purification section 5.

[0312] A vacuum degassing condensate (I) of 509 kg / h is fed into purification section 5. This includes a DN500 thin-film evaporator coupled to a DN400 distillation column. This thin-film evaporator operates at 190 mbar (absolute) and 75°C and features a special scraper configuration (DVB type from SMS Buss). Spring-loaded PTFE scrapers are used, resulting in minimal friction and therefore minimal localized heating. The unit provides 4m... 2The shell side of the exchange area is heated with saturated steam at 1 bar (gauge pressure). A stabilizer mixture containing 2,4-dimethyl-6-tert-butylphenol (Topanol A) and 1,6-di-tert-butyl-4-methylphenol (Topanol O) dissolved in MMA is added to the vacuum degassed condensate (I) before the heat treatment. The concentration is approximately 200 ppm. Partial evaporation of the stabilized cold vacuum degassed condensate (I) yields a second top stream and a second bottom stream (L). The second bottom stream (L) at a rate of 98 kg / h is discharged from the method, still containing approximately 25% MMA. 0.5 Nm³ of steam is continuously supplied to the thin-film evaporator. 3 / h of air to support the action of the stabilizer mixture.

[0313] The resulting second top feed stream is then fed into a distillation column, which is centrally packed with 6m of structured packing (MP452Y type). The distillation column is operated at 180 mbar (absolute), 55°C at the bottom, and 29°C at the top. A vacuum is generated using a liquid ring vacuum pump, which operates with an additional feed stream (A) from the PMMA process as the working fluid. Figure 1 (Not shown in the image). Energy is introduced into the distillation column via a natural circulation evaporator heated with 1 bar (gauge pressure) saturated steam for a short residence time. Similarly, 0.5 Nm³ of steam is continuously supplied to the evaporator. 3 / h of air is supplied to support the stabilizer. Top condensation is carried out in two shell-and-tube heat exchangers operating with cooling water (20°C) and brine (2°C). At a reflux ratio of 0.95, a third top stream (K) is continuously drawn from the method at the top of the column. The third bottom stream (B) is mixed with the additional stream (A) as described above.

[0314] The degassed polymer mixture (J) obtained in the vented extruder 2 essentially contains PMMA. It is taken out as a continuous filament of planar material, cured in a water bath, and processed into polymer pellets (M) that are essentially composed of PMMA. The mass flow rate of the polymer pellets (M) is approximately 4975 kg / h.

[0315] The resulting polymer pellets (M) were then subjected to quality and physical properties as described above. The results are shown in Table 4.

[0316] Example B1 according to the application: Preparation of PMMA starting from a first liquid stream and an additional stream According to Figure 2 PMMA was prepared in the apparatus.

[0317] The preparation process is substantially similar to that described in Comparative Example V1. The same reference numerals in the accompanying drawings therefore have the same meaning. Thus, the changes in this method compared to that according to Comparative Example V1 are described below in essentially the same way.

[0318] The additional stream (A) of 5000 kg / h according to table 1 is continuously mixed in a static mixer with 640 kg / h of the first liquid stream (N) according to table 2 and 385 kg / h of the third bottoms stream (B) at 8°C to obtain a mixed stream (C). The third bottoms stream (B) has a concentration of MMA of 97.3% based on the total amount of the third bottoms stream (B). The third bottoms stream (B) is obtained by recycling as described in comparative example V1. The mixing ratio of the first liquid stream (N) to the additional stream (A) is given in table 4.

[0319] To the mixed stream (C) is supplied a stream of additive stream (D) and standard pressure condensate (E) which together amount to 14390 kg / h to obtain a second mixed stream (F) which together amount to approximately 20400 kg / h. The by-products present in the second mixed stream (F) are listed in table 4. The second mixed stream is then fed to the polymerization reactor 1 and further processed analogously to comparative example V1.

[0320] For the resulting polymer pellets (M) the quality and physical properties are determined as described above. The results can be found in table 4.

[0321] Example B2 according to the application: Preparation of PMMA starting from a first liquid stream and an additional stream In a device according to Figure 2 PMMA is prepared.

[0322] The preparation process is essentially carried out as described in example B1 according to the application. Therefore, the following essentially describes the changes compared to the process of example B1 according to the application.

[0323] The additional stream (A) of 5000 kg / h according to table 1 is continuously mixed in a static mixer with 160 kg / h of the first liquid stream (N) according to table 2 and 391 kg / h of the third bottoms stream (B) at 8°C to obtain a mixed stream (C). The third bottoms stream (B) has a concentration of MMA of 97.2% based on the total amount of the third bottoms stream (B). The third bottoms stream (B) is obtained by recycling as described in comparative example V1. The mixing ratio of the first liquid stream (N) to the additional stream (A) is given in table 4.

[0324] To the mixed stream (C) is supplied a stream of additive stream (D) and standard pressure condensate (E) which together amount to 13180 kg / h to obtain a second mixed stream (F) which together amount to approximately 18840 kg / h. The by-products present in the second mixed stream (F) are listed in table 4. The second mixed stream is then fed to the polymerization reactor 1 and further processed analogously to comparative example V1.

[0325] For the resulting polymer pellets (M) the quality and physical properties are determined as described above. The results can be found in table 4.

[0326] Example B3 according to the application: Preparation of PMMA starting from a purified first liquid stream and an additional stream

[0327] In the apparatus according to Figure 3 PMMA was produced.

[0328] The production process was essentially carried out as described in the production process of Comparative Example V1. Identical reference signs in the figures therefore have the same meaning. Thus, the following essentially describes the changes in the process compared to the process according to Comparative Example V1.

[0329] 5000 kg / h of the additional stream (A) according to Table 1 was continuously mixed in a static mixer at 8°C with 1575 kg / h of the third bottoms stream (B) while obtaining a mixed stream (C). The third bottoms stream (B) had a MMA concentration of 98.6%. The third bottoms stream (B) was obtained by recycling. In purification section 5, the first liquid stream (N) according to Table 2 was mixed into the vacuum degassing condensate (I) and both streams were purified together as described below while obtaining the third bottoms stream (B).

[0330] The stream of additive stream (D) and standard pressure condensate (E) which amounted to 15 570 kg / h was then mixed into the mixed stream (C) as described in Comparative Example V1 while obtaining a second mixed stream (F) which amounted to approximately 22 240 kg / h. The by-products present in the second mixed stream (F) are listed in Table 4. The second mixed stream (F) was then fed into the polymerization reactor 1 and further processed analogously to Comparative Example V1.

[0331] 532 kg / h of the vacuum degassing condensate (I) was mixed with the first liquid stream (N) according to Table 2 in purification section 5 and purified as described in Comparative Example V1. The reflux ratio of the rectification column was 1.5. The resulting third bottoms stream (B) was mixed with the additional stream (A) as described above.

[0332] For the resulting polymer pellets (M), the quality and physical properties were determined as described above. The results can be found in Table 4.

[0333] Example B4 according to the application: Preparation of PMMA starting from a purified first liquid stream and an additional stream

[0334] In the apparatus according to Figure 3 PMMA was produced.

[0335] The production process was essentially carried out as described in the production process of Comparative Example V1. Identical reference signs in the figures therefore have the same meaning. Thus, the following essentially describes the changes in the process compared to the process according to Comparative Example V1.

[0336] The additional stream (A) according to table 1 of 5000 kg / h is continuously mixed in a static mixer with 723 kg / h of a third bottoms stream (B) at 8°C to obtain a mixed stream (C). The third bottoms stream (B) has a MMA concentration of 97.3%. The third bottoms stream (B) is obtained by recycling. In purification section 5, the first liquid stream (N) according to table 3 is mixed to the vacuum degassed condensate (I) and both streams are purified as described below to obtain the third bottoms stream (B).

[0337] The stream of additive stream (D) and standard pressure condensate (E) which amounts to 13 580 kg / h is then mixed to the mixed stream (C) as described in comparative example V1 to obtain a second mixed stream (F) which amounts to approximately 19 400 kg / h. The by-products present in the second mixed stream (F) are listed in table 4. The second mixed stream (F) is then fed to the polymerization reactor 1 and further processed analogously to comparative example V1.

[0338] The vacuum degassed condensate (I) of 530 kg / h is mixed in purification section 5 with the first liquid stream (N) according to table 3 and purified as described in example B3 according to the invention.

[0339] For the resulting polymer pellets (M), the quality and physical properties are determined as described above. The results can be found in table 4.

[0340] Example B5 according to the application: Preparation of PMMA starting from a purified first liquid stream and an additional stream

[0341] PMMA is produced in a device according to Figure 3 Example B5 according to the application: Preparation of PMMA starting from a purified first liquid stream and an additional stream Figure 3 .

[0342] The production process is essentially carried out as described in example B3 according to the invention. Therefore, the following essentially describes the changes compared to the method of example B3 according to the invention.

[0343] The additional stream (A) according to table 1 of 5000 kg / h is continuously mixed in a static mixer with 2360 kg / h of a third bottoms stream (B) at 8°C to obtain a mixed stream (C). The third bottoms stream (B) has a MMA concentration of 96.4%. The third bottoms stream (B) is obtained by recycling. In purification section 5, the first liquid stream (N) according to table 3 is mixed to the vacuum degassed condensate (I) and both streams are purified as described below to obtain the third bottoms stream (B).

[0344] The additive stream (D) and the stream of the standard pressure condensate (E), which together amount to approximately 17 400 kg / h, are then mixed into the mixed stream (C) as described in Comparative Example V1, while obtaining a second mixed stream (F) which together amounts to approximately 24 860 kg / h. The by-products present in the second mixed stream (F) are listed in Table 4. The second mixed stream (F) is then fed into the polymerization reactor 1 and further processed analogously to Comparative Example V1.

[0345] The vacuum degassing condensate (I) of 535 kg / h is mixed with the first liquid stream (N) according to Table 3 in the purification section 5 and purified as described in Example B3 according to the application.

[0346] For the resulting polymer pellets (M), the quality and physical properties are determined as described above. The results can be found in Table 4.

[0347]

[0348]

[0349] From the results shown in Table 4 it can be seen that it is possible to produce PMMA from pure MMA combined with recycled MMA. The PMMA produced according to the application has a sufficient transmittance and a sufficiently low yellowness index for at least producing colored products. The melt volume flow rate is sufficient, while having a high Vicat softening temperature. It is thus possible to save resources and recycle MMA in equally good product quality by the process of the application.

[0350] When the recycled MMA used already has a high purity (Examples B1 and B3) and / or is purified together with a vacuum degassing condensate before mixing with pure MMA (Examples B3, B4 and B5), PMMA is obtained which can also be used as glass-like transparent PMMA. The latter case also allows using larger amounts of recycled MMA even if it has a lower purity.

Claims

1. A method for preparing poly(alkyl methacrylate), comprising the steps a) to h): a) Thermally pyrolyzing at least one polymer composition, said polymer composition comprising at least one poly((meth)acrylate), to obtain a first gas stream comprising at least one (meth)acrylate and at least one other alkyl ester, wherein the at least one (meth)acrylate present in the first gas stream is selected from C1- to C4-alkyl methacrylates. b) The first gaseous stream obtained in step a) is condensed to obtain a first liquid stream containing at least one (meth)acrylate alkyl ester and at least one other alkyl ester. c) The first liquid stream obtained in step b) is mixed with an additional stream containing at least one additional alkyl (meth)acrylate, wherein the additional stream is part of a poly(alkyl (meth)acrylate) preparation method, to obtain a mixed stream comprising the first liquid stream and the additional stream, wherein up to 50% by weight of the first liquid stream is mixed with the additional stream based on the total weight of the resulting mixed stream. e) Partially polymerize the mixture obtained in step c) to obtain a slurry comprising at least one partially polymerized (meth)acrylate, at least one partially polymerized additional (meth)acrylate, and said at least one other alkyl ester. f) Polymerize the slurry obtained in step e) in a vented extruder to obtain a polymer mixture containing poly(alkyl methacrylate). g) Degas the slurry obtained in step e) and / or the polymer mixture obtained in step f) in a degassing extruder to obtain a condensed feed stream comprising the at least one alkyl (meth)acrylate, the at least one additional alkyl (meth)acrylate, oligomers thereof, and the at least one other alkyl ester. h) Separate the at least one other alkyl ester from the condensate stream obtained in step g) to obtain a (meth)acrylate alkyl ester stream containing the at least one (meth)acrylate alkyl ester and the at least one additional (meth)acrylate alkyl ester.

2. The method according to claim 1, characterized in that... The method further includes the following step d): d) Obtaining a purified mixture stream by at least partially separating the at least one other alkyl ester from the mixture stream obtained in step c), comprising the at least one alkyl (meth)acrylate, the at least one additional alkyl (meth)acrylate, and residues of the at least one other alkyl ester. Then, the purified mixture obtained in step d) is partially polymerized in step e).

3. The method according to claim 1 or 2, characterized in that... The at least one other alkyl ester is selected from methyl propionate, methyl isobutyrate, methyl pentovalinate, methyl 3-methoxyisobutyrate, and dicarboxylic acid diesters.

4. The method according to any one of claims 1 to 3, characterized in that... The first gas stream contains at least one other component selected from styrene, (meth)acrylic acid, sulfur-containing compounds, oligomers, and dimers.

5. The method according to any one of claims 1 to 4, characterized in that... The first gas stream is distilled after step a) and before step b) to obtain a first top stream containing at least one (meth)acrylate alkyl ester and at least one other alkyl ester, and a first bottom stream containing at least one component different from the at least one (meth)acrylate alkyl ester and at least one other alkyl ester, wherein the first top stream is condensed in step b).

6. The method according to any one of claims 1 to 5, characterized in that... The first liquid stream contains alkyl (meth)acrylate in the range of 90% to <99.8% by weight based on the total weight of the first liquid stream, and 1.5% to 50% by weight of the first liquid stream is mixed with the additional stream based on the total weight of the resulting mixed stream.

7. The method according to claim 6, characterized in that... The at least one auxiliary agent is selected from initiators, chain transfer agents, and release agents.

8. The method according to any one of claims 1 to 7, characterized in that... In the partial polymerization in step e), the total conversion of the at least one alkyl (meth)acrylate and the at least one additional alkyl (meth)acrylate present in the purified mixed stream is in the range of 20% to 60%.

9. The method according to any one of claims 1 to 8, characterized in that... Steps f) and g) are performed simultaneously.

10. The method according to any one of claims 1 to 9, characterized in that... The degassing in step g) proceeds countercurrently to the conveying direction of the polymer mixture obtained in step f).

11. The method according to any one of claims 1 to 10, characterized in that... The poly(alkyl(meth)acrylate) present in the polymer mixture is poly(methyl(meth)acrylate).

12. The method according to any one of claims 1 to 11, characterized in that... Separation in step h) Includes the following steps: h1) The condensate stream is separated into a second top stream comprising the at least one alkyl (meth)acrylate, the at least one additional alkyl (meth)acrylate, and the at least one other alkyl ester, and a second bottom stream comprising oligomers of the at least one alkyl (meth)acrylate and oligomers of the at least one additional alkyl (meth)acrylate; h2) Distill the second top stream obtained in step h1) to obtain a third top stream containing the at least one other alkyl ester, and a third bottom stream containing the at least one (meth)acrylate alkyl ester and the at least one additional (meth)acrylate alkyl ester.

13. The method according to any one of claims 1 to 12, characterized in that... The alkyl methacrylate stream obtained in step h) is at least partially recycled to at least one of steps c), e) and / or f).

14. The method according to any one of claims 2 to 13, characterized in that... Step h) includes step d).

Images