Process for producing cyclosiloxanes from silicone waste

Abstract

The invention relates to a process for producing at least one cyclosiloxane by catalysed depolymerisation of silicone waste, the process comprising or consisting of the steps of: (i) dissolving at least some of the silicone waste in at least one solvent containing or consisting of at least one aliphatic hydrocarbon (K) using at least one depolymerisation catalyst (D1); (ii) optionally deactivating the at least one depolymerisation catalyst (D1) and adding at least one additional depolymerisation catalyst (D2); (iii) distilling off the at least one cyclosiloxane from the mixture; characterised in that the at least one aliphatic hydrocarbon (K) comprises at least 16 carbon atoms.

Description

[0001] Process for the production of cyclosiloxanes from silicone waste

[0002] The invention lies in the field of production of cyclosiloxanes from silicone waste.

[0003] Silicones, also known as organosiloxanes, are materials containing alternating silicon and oxygen atoms, with various organic radicals bonded to the silicon. These compositions can be liquid, semi-solid, or solid depending on their molecular weight and degree of crosslinking.

[0004] Due to their special material characteristics, silicone parts meet specific requirements in medical, pharmaceutical, and food technology applications. When processed appropriately, they are completely physiologically inert. Silicone products can be found in food applications, medicine, and the pharmaceutical sector. Baby pacifiers and dummies are made from silicone, as are diving goggles. In technical industrial applications, silicone is often used as a material for seals or in dynamic applications for membranes. In the automotive sector, it is used for hoses, sheathing, and cable insulation.

[0005] When it comes to its mechanical properties, silicone has a key advantage over other types of rubber: they remain relatively stable over a very wide temperature range, whereas the mechanical properties of many other materials deteriorate significantly in cold or hot temperatures. For example, while an EPDM material may appear superior to a silicone compound in terms of its mechanical properties when viewed from the technical data sheet because the properties are specified at room temperature, the completely opposite picture emerges at high or low temperatures. Silicone's temperature resistance in air is approximately -80 °C to approx. 250 °C. This property is often used for seals, as this is where the very low compression set typical of silicone comes into play.

[0006] Due to their excellent ozone, UV, and weather resistance, silicone compounds are also frequently used in outdoor applications. Furthermore, silicone is highly flame-resistant and offers good electrical insulation and conductivity. Silicone is chemically resistant to substances such as vegetable and animal fats, hot water, and alcohol. Its resistance is limited to acids, alkalis, fuels, ketones, and water vapor. Silicone also has very high gas permeability.

[0007] In addition to industrial applications, silicone has been the preferred elastomer in the medical field for decades. Silicone components are also used as short-term implants (for less than 30 days in Class Ha medical devices) or long-term implants (for 30 days or more in Class Hb medical devices), fulfilling critical functions in devices such as cardiac catheters, pacemakers, ventilators, neurostimulators, and defibrillators.

[0008] Silicone rubber intended for long-term implants is offered by only a very few producers worldwide (e.g., NuSil Technology). The compounds are manufactured under strict regulations of the US Food and Drug Administration (FDA). Special attention must also be paid to purity during processing, and component production must take place in a cleanroom.

[0009] A key advantage of silicone is its biocompatibility, which means it is well tolerated by humans. The biocompatibility of a silicone compound is often demonstrated by USP Class VI classifications (USP stands for United States Pharmacopeia) or by tests according to the more stringent (DIN EN) ISO 10993 standard. (DIN EN) ISO 10993 is primarily used for testing medical devices that are implanted in the human body for long periods or permanently. For shorter applications, a USP Class VI classification or a lower classification is sufficient.

[0010] Furthermore, due to its ability to operate over a wide temperature range from approximately -80 °C to approximately 250 °C, silicone offers the potential for steam sterilization (heating in an autoclave). This allows silicone products to be freed from living microorganisms, their persistent forms, viruses, etc. Silicone's good electrical insulation properties are also particularly important in the medical field.

[0011] By varying the silicone rubbers used and the crosslinking methods, silicones can acquire special properties. HTV silicone rubbers, for example, are flexible and resistant over a wide temperature range from -50 °C to 200 °C, and sometimes up to 300 °C. They are used in seals in the automotive and food industries, in cable sheathing, or as damping materials.

[0012] RTV silicone rubbers are particularly valued for their thermal conductivity and electrical insulation properties, which is why they are primarily used in the electrical and electronics sectors.

[0013] Liquid silicone rubbers (also known as LSRs) have a lower viscosity than HTV and RTV silicone rubbers. They can be molded into a wide variety of shapes using injection molding, for example, into silicone tubing. Since LSR silicones are always platinum-cured, liquid silicone-based products can be used in medical technology. Thanks to its high stability within the human body, silicone provides excellent protection for critical components and, due to these properties, is also preferred for functional parts.

[0014] Basically, the difference between silicone rubber and other organic elastomers is that its main chains, which have an inorganic structure, do not consist of carbon compounds, but are formed from combinations of silicon and oxygen atoms, with pyrogenic silica or precipitated silica being used as filler for the targeted adjustment of mechanical properties such as Shore hardness, tensile strength and elasticity.

[0015] According to their aggregate states and their vulcanization temperatures, silicone rubbers can be divided into three groups:

[0016] HIV (high-temperature vulcanizing) or HCR (high-consistency rubber) refers to silicone rubbers whose raw material is solid. They are vulcanized at high temperatures, typically between 140 °C and 200 °C. Crosslinking occurs via peroxides or an addition reaction, with platinum compounds used as catalysts.

[0017] Liquid silicone rubber (LSR) is a viscous raw material consisting of two components that are mixed directly before processing. Curing occurs via an addition reaction at temperatures similar to those of HTV grades, although curing generally occurs much faster.

[0018] Both silicone types can be colored. Finished elastomer articles made of HTV silicone and LSR silicone have virtually no difference in their properties.

[0019] The third group are so-called RTV (room temperature vulcanizing) silicones. These silicones cure at room temperature. They are often used as adhesives and / or sealants, or in prototype production. They are available as both one- and two-component systems.

[0020] While the performance properties derived from the special chemical stability of silicones are advantageous for the service life of the articles manufactured from them, their stability during disposal at the end of their use (life cycle) is a burden. These silicones are also referred to as end-of-life silicones or simply as silicone waste. The terms silicone waste and end-of-life silicones are used synonymously for the purposes of this invention. A variety of processes for recycling silicones in general and vulcanized silicone rubber in particular are described in the literature. Acidic or basic catalysts are usually used for the depolymerization of silicones. The subsequent distillative separation of the cyclosiloxanes formed during depolymerization requires high temperatures. The state of the art usually describes processes at reaction temperatures >200 °C.At such high temperatures, distillates are typically obtained that are contaminated by decomposition products of fillers, dyes, adhesion promoters, vulcanization catalysts, moisture—possibly hidden in the form of silanol groups—and possibly process solvents. Further purification by filtration, extraction, phase separation, or additional distillation steps is necessary to obtain cyclosiloxanes with high purity. The removal of undesirable impurities or undesirable siloxane components typically requires further purification of the resulting cyclosiloxanes so that they can be universally used to produce new specialty silicones. Furthermore, not every type of silicone can usually be depolymerized using the same catalyst and the same process.While unfilled, low-viscosity silicones depolymerize relatively easily with strong acids or bases, making it possible to generate cyclosiloxanes by distillation, a completely different and differentiated picture emerges with filled silicones. The fillers and pigments present in silicone elastomers can inhibit the depolymerization catalysts used, either through purely physical adsorption of the depolymerization catalysts on the filler surface or through chemical reactions with the depolymerization catalysts. Furthermore, fillers can undergo more extensive crosslinking, agglomeration, or chemical modification during depolymerization, which can lead to a significant increase in viscosity and even gelling of the mixture.

[0021] In their review article "Degradation of silicone-based materials as a driving force for recyclability," Polym Int 2022; 71 : 521-531 (https: / / doi.org / 10.1002 / pi.6340), B. Rupasinghe and J.C. Furgal provide a general overview of the state of the art in the degradation of silicones by depolymerization and the associated challenges in silicone recycling. They conclude that there is still a need to make the catalytic processes underlying silicone recycling "greener." In particular, it is necessary for the processes to become more energy-efficient and, if possible, to use only environmentally friendly solvents or even to do without them entirely.

[0022] In their article "Full Circle Recycling of Polysiloxanes via Room-Temperature Fluoride-Catalyzed Depolymerization to Repolymerizable Cyclics," ACS Appl. Polym. Mater. 2021, 3, 4, 1828-1839 (https: / / doi.org / 10.1021 / acsapm.0c01406), the same authors describe a process for recycling polysiloxanes via fluoride-catalyzed depolymerization at room temperature to form repolymerizable cyclics. Different solvents were investigated for their suitability. The process was most efficient using tetrahydrofuran (THF) as the solvent. However, the boiling point of THF is lower than that of cyclosiloxanes, which complicates the distillative separation of the cyclosiloxanes from the reaction mixture.

[0023] US 5,110,972 discloses numerous solvents for the production of cyclosiloxanes from silicone polymers. Specifically, a process for cracking high-molecular-weight silicone polymers is described, comprising the steps of dissolving the silicone polymer in an organic solution comprising an acid and heating the resulting mixture until the silicone polymer is substantially dissolved; adding a base; and distilling cyclosiloxanes from the solution. It is also described therein that the solvents should have a specific property profile. For example, they should be inexpensive and safe. They should be able to swell cured silicones. Furthermore, they should be easily separated from the cyclosiloxanes and solid byproducts.In this context, it is stated that the solvents should have a higher boiling point than tetrameric or pentameric cyclosiloxanes so that the solvents do not have to be distilled off. The solvents should also be as water-insoluble as possible so that water-soluble by-products and impurities can be removed by water extraction. Among other things, aliphatic hydrocarbons or oils are disclosed as solvents, but without specifying which aliphatic hydrocarbons or oils can be used to achieve the desired properties. Butyl Carbitol™ (also known as diethylene glycol monobutyl ether, butyl diglycol or (2-(2-butoxyethoxy)ethanol)) and Köppers' Methylnaphthalene Fraction™ (a hydrocarbon fraction containing predominantly alkylnaphthalenes) are described as particularly suitable solvents.However, it is described that the solvents used are transferred during the distillation of the cyclosiloxanes, contrary to what was intended, and are thus contained in the distillate. Experiments by the inventors have also shown that Butyl Carbitol™ is not generally suitable as a solvent, at least not because the silicone components used could not be dissolved (see non-inventive example 10 below). The possible applications therefore appear to be very limited. Furthermore, hydroxy-functional compounds such as Butyl Carbitol™ have the disadvantage that they can undergo undesirable side reactions, which can lead to gelling of the mixture. Köppers' Methylnaphthalene Fraction™, in turn, has the disadvantage of containing aromatic hydrocarbons. Aromatic hydrocarbons, especially polycyclic hydrocarbons, are increasingly classified as toxic to reproduction.They are also environmentally hazardous due to their long-term toxicity to aquatic organisms. Their use is therefore undesirable, not only because they pose a health risk to workers in industrial applications, but also because residual amounts remain in the recovered cyclosiloxanes and thus contaminate the resulting products with aromatic hydrocarbons. In this respect, US Pat. No. 5,110,972 addresses the most important questions in selecting a suitable solvent, but does not offer satisfactory solutions. Examples D and E, for example, disclose a two-phase distillate containing both water and solvent in addition to the cyclosiloxanes. The cyclosiloxane yield is calculated proportionally from the analysis of distillate and cold trap residue, without disclosing the exact composition of the two fractions.A processing and isolation of purified, largely anhydrous cyclosiloxane mixtures in a further process step is not disclosed, but would be necessary for the use of the cyclosiloxane mixtures for the production of new silicone products.

[0024] The object was therefore to provide a process for the production of cyclosiloxanes which has advantages over the prior art.

[0025] The specific objective is to develop a process for producing cyclosiloxanes from silicone waste that can be carried out at moderate temperatures, does not cause harmful emissions to air or water, and produces high-purity cyclosiloxane mixtures in a single step. These mixtures are ideally widely applicable for the production of organomodified siloxanes, silicone oils, silicone rubbers, or silicone elastomers, ideally without or with only minimal additional purification steps. Furthermore, the process should preferably be robust, not cause gelling or encrustation in the reactor, and be applicable to a wide variety of end-of-life silicones.

[0026] Surprisingly, it has been found that a special process for the preparation of cyclosiloxanes, in which at least one solvent is used which contains or consists of at least one aliphatic hydrocarbon (K) having at least 16 carbon atoms, as described in the claims, solves this problem.

[0027] A first subject of the invention is therefore a process for producing at least one cyclosiloxane by catalyzed depolymerization of silicone waste comprising the steps or consisting of the steps:

[0028] (i) dissolving at least part of the silicone waste in at least one solvent containing or consisting of at least one aliphatic hydrocarbon (K) using at least one depolymerization catalyst (D1),

[0029] (ii) optionally deactivating the at least one depolymerization catalyst (D1) and adding at least one further depolymerization catalyst (D2),

[0030] (iii) distilling off the at least one cyclosiloxane from the mixture, wherein the at least one aliphatic hydrocarbon (K) comprises at least 16 carbon atoms.

[0031] A further object of the invention is the use of at least one aliphatic hydrocarbon (K), as described above, as a solvent or as a solvent component in the production of at least one cyclosiloxane from silicone waste.

[0032] Yet another object of the invention is a composition obtained as distillate of the process according to the invention, characterized in that the mass fraction of the total of all cyclosiloxanes based on the total mass of the composition is at least 90%, preferably at least 92%, in particular at least 94%, and the mass fraction of the total of all aliphatic hydrocarbons (K) based on the total mass of the composition is at most 10%, preferably at most 8%, in particular at most 6%.

[0033] Yet another object of the invention is the use of the at least one cyclosiloxane prepared by the process according to the invention or the composition according to the invention for the production of organomodified siloxanes, silicone oils, silicone rubbers or silicone elastomers.

[0034] The invention also further relates to silicones, preferably selected from the group consisting of organomodified siloxanes, silicone oils, silicone rubbers or silicone elastomers, produced using the at least one cyclosiloxane produced by the process according to the invention or using the composition according to the invention.

[0035] Yet another object of the invention is the use of the correspondingly prepared silicones, preferably selected from organomodified siloxanes, as plastic additives, defoamers, foam stabilizers (e.g. polyurethane foam stabilizers), emulsifiers, demulsifiers, rheology additives, hydrophobizing agents, wetting agents, textile additives, paint additives, leveling additives, dispersing additives or as additives in polishes, cleaning agents and cosmetic preparations or for the production of silicone release coatings.

[0036] In connection with this invention, the M, D, T, and Q designations for organopolysiloxane building blocks are also used. For a reference on their meaning, see W. Noll, Chemie und Technologie der Silicone, Verlag Chemie, Weinheim Bergstr., 1960, p. 2 ff. Silicones are compounds that have D units with D = [R2SiO2 / 2], where R is an organic radical, preferably a hydrocarbon radical, especially a methyl radical.

[0037] Advantageous embodiments of the subject matter of the invention can be found in the claims, the examples, and the description. Furthermore, it is expressly pointed out that the disclosure of the subject matter of the present invention includes all combinations of individual features of the present or subsequent description of the invention and the patent claims. In particular, embodiments of one subject matter of the invention also apply mutatis mutandis to the embodiments of the other subject matter of the invention. As already explained above, the process according to the invention is a process for producing at least one cyclosiloxane by catalyzed depolymerization of silicone waste, comprising the steps or consisting of the steps:

[0038] (i) dissolving at least part of the silicone waste in at least one solvent containing or consisting of at least one aliphatic hydrocarbon (K) using at least one depolymerization catalyst (D1),

[0039] (ii) optionally deactivating the at least one depolymerization catalyst (D1) and adding at least one further depolymerization catalyst (D2),

[0040] (iii) distilling off the at least one cyclosiloxane from the mixture, characterized in that the at least one aliphatic hydrocarbon (K) comprises at least 16 carbon atoms.

[0041] The phrase "at least one" is synonymous with the phrase "one or more." The phrase "at least one cyclosiloxane" is therefore synonymous with the phrase "one or more cyclosiloxanes." The process thus enables the production of one or more cyclosiloxanes, i.e., one cyclosiloxane or a mixture of different cyclosiloxanes. Preferably, however, the product obtained is not a single cyclosiloxane, but rather several cyclosiloxanes. The process product therefore preferably contains or consists of a mixture of different cyclosiloxanes.

[0042] Therefore, a process for producing cyclosiloxanes from silicone waste by its catalyzed depolymerization is preferred, comprising the steps or consisting of the steps:

[0043] (i) dissolving at least part of the silicone waste in at least one solvent containing or consisting of at least one aliphatic hydrocarbon (K) using at least one depolymerization catalyst (D1),

[0044] (ii) optionally deactivating the at least one depolymerization catalyst (D1) and adding at least one further depolymerization catalyst (D2),

[0045] (iii) distilling off the cyclosiloxanes from the mixture, wherein the at least one aliphatic hydrocarbon (K) comprises at least 16 carbon atoms.

[0046] Steps (i), (ii) and (iii) are carried out in the specified order, i.e. in the order (i), (ii) and (iii), whereby step (ii) is optional and can be omitted. The process steps follow one another directly or indirectly. The process may comprise further upstream steps, intermediate steps or downstream steps, such as, for example, purification of the reactants, the intermediates and / or the end products and / or conversion of the end products to subsequent products. Purification of the end product, i.e. the cyclosiloxanes or the cyclosiloxane mixture, can be carried out, for example, by deodorization under vacuum or filtration with filter aid and requires that a technical purity of at least 90%, preferably at least 92%, in particular at least 94%, has already been achieved.Step (iii) can also be followed directly or indirectly by step (i), so that the process is run through once or several times, i.e. as a recirculation process. After the cyclosiloxanes have been distilled off from the mixture, silicone waste can, for example, be added again to the remaining distillation residue, as well as, if required, further solvent and / or, if required, one or more depolymerization catalysts (D1). If the process is carried out as a recirculation process, it is therefore advantageous if the solvent remains in the distillation residue and / or is returned to the distillation residue. If the process is carried out as a recirculation process, it is further advantageous if the optional step (ii) is omitted. The distillation residue can also be processed before reuse. It can be advantageous to separate solid components of the distillation residue (e.g.Fillers) from the liquid constituents of the distillation residue by separation processes familiar to the person skilled in the art and returning only the latter to the recycling process. It is also possible, in particular, to purify the solvent after step (iii) by washing out water-soluble constituents with water and then return it to the process. Although the process is preferably a discontinuous process, a continuous process is conceivable. In the discontinuous case, the reactor used can be, for example, a batch reactor; in the continuous case, a continuous stirred-tank reactor (CSTR reactor) or a tubular reactor or tubular flow reactor.

[0047] The process according to the invention enables the preparation of a cyclosiloxane or mixtures of different cyclosiloxanes of high purity. Cyclosiloxanes are known to those skilled in the art. These are siloxanes consisting exclusively of D units. Preferably, these are siloxanes of the formula D n with n > 3 with D = [R2SiO2 / 2], where R is an organic radical, preferably a hydrocarbon radical, in particular a methyl radical. The R radicals can be the same or different. However, the R radicals are preferably the same. Particularly preferably, all R radicals are methyl radicals. The commercially most important cyclosiloxanes and those preferred in the context of this invention are hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (De), tetradecamethylcycloheptasiloxane (D7), hexadecamethylcyclooctasiloxane (De).

[0048] The process according to the invention can be carried out on both liquid-viscous and partially or fully cured silicone waste.

[0049] In a preferred embodiment of the invention, particularly in the case of fully cured silicone waste, its comminution into lumpy material is provided, which at the end of the comminution preferably has a maximum diameter of 5 cm, more preferably 1 to 10 mm, and particularly preferably 3 to 6 mm. According to the invention, the optional comminution of the material can preferably be carried out, for example, using a crusher, a shredder, a mill, a hammer mill, rollers or a kneading mill, or even cutting machines. Soft silicone waste can first be cold-embrittled by contact with, for example, liquid nitrogen or dry ice pellets. The resulting significantly reduced elasticity facilitates suitable comminution.

[0050] As will be apparent to the person skilled in the art, in order to achieve effective mixing, the process according to the invention is preferably carried out in reactors which have appropriate stirring elements, kneaders and / or shearing internals.

[0051] The process is not limited to a specific silicone waste. However, it is preferred that the silicone waste contains or consists of silicone elastomers and / or silicone rubbers. Silicone oils can also be used as silicone waste. Since silicone oils are already liquid, the proportion of the solvent to be used according to the invention, which comprises at least one aliphatic hydrocarbon (K), can be greatly reduced.

[0052] According to a preferred embodiment of the invention, the method according to the invention relates to a method for the recycling or upcycling of silicone waste, in particular silicone adhesive waste and / or silicone sealant waste and / or silicone rubber waste.

[0053] According to a particularly preferred embodiment of the invention, the method according to the invention is characterized in that the silicone waste comprises silicone adhesives and / or silicone sealants, preferably silicone adhesive and / or silicone sealant cartridges, in particular silicone adhesive and / or silicone sealant residues in and / or on polyolefin containers, preferably PE containers, preferably comprising HDPE and / or LDPE. Conventional silicone adhesive and / or silicone sealant cartridges comprise a silicone adhesive and / or silicone sealant compound in a polyolefin container, preferably a polyethylene container (PE container), which allows the silicone adhesive and / or silicone sealant compound to be dispensed. The container shell is usually made of HDPE (high-density polyethylene) and the semi-transparent container parts (plunger and dispensing tip) are usually made of LDPE (low-density polyethylene). HDPE and LDPE are known to those skilled in the art.HDPE has a high density between 0.94 g / cm. 3 and 0.97 g / cm 3 LDPE, on the other hand, has a lower density between 0.915 g / cm 3 and 0.935 g / cm 3 The process according to the invention thus also enables, in particular, the depolymerization of silicone waste, even if it contains, in addition to the silicone component, plastic residues that are not silicone-based, such as HDPE and LDPE.

[0054] If the silicone waste contains filler, it is released through the inventive reaction and dissolution of the silicone component. At the end of the inventive digestion, the small pieces of plastic residues that are not silicone-based can be separated from the filler-infused solvent, for example, using a coarse sieve. The solvent can then be separated from the solid, finely divided filler, for example, by allowing it to settle. According to the invention and without diminishing the teaching presented, further solutions can naturally be found for advantageously enhancing the basic process engineering operations discussed here, such as filtration or centrifugal separation of the filler from the solvent.

[0055] It is preferred that the silicone waste contains or consists of silicone elastomers and / or silicone rubbers which in turn contain filler. Filler-containing silicone elastomers or silicone rubbers are also referred to as filled silicone elastomers or silicone rubbers. The filler content is preferably 5 to 75 mass percent based on the total mass of the filled silicone elastomer or silicone rubber. The filler can be, for example, an organic or an inorganic filler. The filler is preferably selected from the group consisting of activated carbon, carbon black, graphite, carbon nanotubes, graphene, organic or inorganic dyes, silicas (e.g. precipitated silica or pyrogenic silica, which can each be hydrophilic or hydrophobic), chalk, metal oxides, metal hydroxides, metal oxide hydroxides, in particular aluminum oxide, aluminum hydroxide and aluminum oxide hydroxide, and inorganic pigments.The silicone elastomers and silicone rubbers may contain additional additives such as desiccants, adhesion promoters and catalysts and may also contain organic copolymer components.

[0056] The process according to the invention allows, after the separation of fillers and plastics that are not silicone-based, the upcycling of the removed silicone to cyclosiloxanes, which can be used for a variety of subsequent reactions.

[0057] The term "upcycling" in the context of this invention thus refers to the transformation of silicone waste into higher-value products. This results in a material upgrade. Based on the definition in I. Vollmer et al., Angew. Chem. Int. Ed. 2020, 59, pp. 15402-15423, the term "upcycling" in the context of this invention preferably refers to the transformation of silicone waste into chemicals that have a higher market value than monomers or pyrolysis oil.

[0058] Within the scope of the invention, the term "end-of-life silicones" or "silicone waste" encompasses all silicone-based or silicone-containing products, as well as products with silicone adhesions or silicone contamination, that have almost and / or completely reached their technical service life or durability, or that would otherwise be considered for disposal. Durability or service life refers to the period of time a material or object can be used without the replacement of core components or complete failure.Within the scope of the teaching, this also includes those silicone adhesives and silicone sealants (for example, in cartridges) whose shelf life or expiration date has almost been reached and / or exceeded (assessed according to the expected and / or already reached stage of curing), as well as, for example, more or less old sprue and / or stamping waste from silicone rubber production or also discarded electronic scrap containing silicone-sealed components / component assemblies. Within the scope of the teaching of the invention, the term "end-of-life silicones" or "silicone waste" also encompasses all silicone waste, including production waste, that does not meet the respective desired product specification, for example, injection-molded parts with deficiencies in mechanical properties, dimensions, or appearance.It includes, in particular, all silicones or silicone-containing parts, or parts with silicone adhesions or silicone contamination, that are otherwise intended for normal disposal and are therefore considered waste. It therefore also includes, for example, silicone adhesive cartridges and / or silicone sealant cartridges intended for disposal, in particular used silicone adhesive cartridges and / or silicone sealant cartridges in and on which silicone residues are still adhering or present. As already stated above, the terms "silicone waste" and "end-of-life silicones" are understood synonymously within the meaning of this invention.

[0059] The depolymerization of the silicone waste requires the use of one or more depolymerization catalysts. As described above, the process according to the invention uses at least one depolymerization catalyst (D1) and, optionally, at least one additional depolymerization catalyst (D2).

[0060] It is preferred that the at least one depolymerization catalyst (D1) and optionally the at least one depolymerization catalyst (D2) is selected from the group consisting of Bronsted acids, Lewis acids, Bronsted bases and Lewis bases.

[0061] It is preferred that Brønsted acids used as depolymerization catalyst (D1) or (D2) have a pKa of at most -1.30, preferably at most -2.90, in particular at most -4.90. Brønsted acids with a pKa of at most -1.30 are preferably selected from the group consisting of methanesulfonic acid and p-toluenesulfonic acid. Concentrated sulfuric acid is preferred as a Brønsted acid with a pKa of at most -2.90. Brønsted acids with a pKa of at most -4.90 are preferably selected from the group consisting of perfluoroalkanesulfonic acids (such as heptafluoropropanesulfonic acid, pentafluoroethanesulfonic acid, trifluoromethanesulfonic acid), perchloric acid, and chlorosulfonic acid. Perfluoroalkanesulfonic acids are particularly preferred. Trifluoromethanesulfonic acid is very particularly preferred. Sulfonic acid or perfluoroalkylsulfonic acid ion exchange resins are also preferred.

[0062] It is preferred that such Brønsted bases used as depolymerization catalyst (D1) or (D2) have a pKß value of at most 10, preferably at most 5, and in particular at most 0. It is preferred that the Brønsted bases are selected from the group consisting of alkali metal hydroxides, amines, quaternary ammonium hydroxides, quaternary phosphonium hydroxides, phosphonitrile chlorides, phosphazenes.

[0063] Preferred alkali metal hydroxides are sodium hydroxide and potassium hydroxide.

[0064] Preferred amines are low-volatility amines, in particular bicyclic diaza compounds (e.g. diazabicycloundecene (DBU), 1,4-diazabicyclo[2.2.2]octane (DABCO), guanidines (e.g. tetramethylguanidine), tertiary polyalkylamines (e.g. pentamethyldiethylenetriamine) and peralkylated polyalkyleneamines,

[0065] Preferred quaternary ammonium hydroxides are tetraalkylammonium hydroxides, in particular tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.

[0066] Preferred quaternary phosphonium hydroxides are tetraalkylphosphonium hydroxides, especially tetramethylphosphonium hydroxide tetraethylphosphonium hydroxide

[0067] Tetrapropylphosphonium hydroxide and tetrabutylphosphonium hydroxide.

[0068] The phosphonitrile chlorides can be linear or cyclic.

[0069] The phosphazenes can be halogen-containing or halogen-free. A preferred phosphazene is tert-butyliminotri(pyrrolidino)phosphorane.

[0070] The depolymerization catalysts (D1) and / or (D2) can also be selected from the group consisting of quaternary ammonium halides and quaternary phosphonium halides, preferably from the group consisting of tetraalkylammonium halides and tetraalkylphosphonium halides. The alkyl radicals can be selected independently of one another, i.e., they can be the same or different. Preferably, all alkyl radicals are the same.

[0071] The depolymerization catalysts (D1) and / or (D2) can therefore also be selected from the group consisting of tetraalkylammonium fluorides (e.g. tetramethylammonium fluoride, tetraethylammonium fluoride, tetrapropylammonium fluoride and tetrabutylammonium fluoride), tetraalkylphosphonium fluorides (e.g. tetramethylphosphonium fluoride,

[0072] Tetraethylphosphonium fluoride, tetrapropylphosphonium fluoride and tetrabutylphosphonium fluoride), tetraalkylammonium chlorides (e.g. tetramethylammonium chloride, tetraethylammonium chloride, tetrapropylammonium chloride and tetrabutylammonium chloride) and

[0073] Tetraalkylphosphonium chlorides (e.g. tetramethylphosphonium chloride,

[0074] Tetraethylphosphonium chloride, tetrapropylphosphonium chloride, and tetrabutylphosphonium chloride can be selected. A suitable tetraalkylphosphonium compound with various alkyl radicals is, for example, tributyloctylphosphonium chloride.

[0075] The above-mentioned quaternary ammonium compounds and quaternary phosphonium compounds used as depolymerization catalysts (D1) and / or (D2) can be used in bulk or as an aqueous solution.

[0076] Numerous compounds can therefore be used as depolymerization catalysts (D1) and / or (D2). However, it is preferred that the at least one depolymerization catalyst (D1) and optionally the at least one depolymerization catalyst (D2) be selected from Brønsted acids, preferably trifluoromethanesulfonic acid, or Brønsted bases, preferably selected from the group consisting of alkali metal hydroxides, tetraalkylammonium hydroxides, tetraalkylphosphonium hydroxides, phosphazenes, and guanidines.

[0077] B. Rupasinghe and J.C. Furgal describe in the article “Full Circle Recycling of Polysiloxanes via Room-Temperature Fluoride-Catalyzed Depolymerization to Repolymerizable Cyclics,” ACS Appl. Polym. Mater. 2021, 3, 4, 1828-1839

[0078] (https: / / doi.org / 10.1021 / acsapm.0c01406) demonstrates the particular suitability of fluorides as depolymerization catalysts. However, fluorides have the major disadvantage that they can damage glass or enamel reactors under the reaction conditions (e.g., with the formation of SiF4). Amines or ammonium compounds, or their decomposition products, often have an unpleasant odor. Alkali metal hydroxides are often less suitable in the case of filled silicones due to possible side reactions with the filler. For these reasons, tetraalkylphosphonium hydroxides are particularly preferred as depolymerization catalysts (D1) and / or (D2).

[0079] It is preferred that in step (i) 0.05 to 10 parts by weight, preferably 0.1 to 3.0 parts by weight, in particular 0.2 to 1.5 parts by weight of the at least one depolymerization catalyst (D1) and optionally of the at least one depolymerization catalyst (D2) are used, based on 100 parts by weight of the silicone component of the silicone waste.

[0080] According to the invention, at least one solvent containing or consisting of at least one aliphatic hydrocarbon (K) is further used, wherein the at least one aliphatic hydrocarbon (K) comprises at least 16 carbon atoms.

[0081] Aliphatic hydrocarbons (K) are compounds composed only of carbon and hydrogen atoms and are non-aromatic. Aliphatic hydrocarbons (K) can be saturated or unsaturated, but saturated is preferred. This has the advantage that they are chemically inert under the reaction conditions. Aliphatic hydrocarbons (K) can be linear, branched, or cyclic, but they are preferably branched, since they then have a lower melting point than their linear structural isomers. Particularly preferred aliphatic hydrocarbons (K) are therefore saturated and branched, i.e., particularly preferred aliphatic hydrocarbons (K) are branched alkanes.

[0082] The at least one aliphatic hydrocarbon (K) has at least 16, preferably 16 to 60, in particular 16 to 50, carbon atoms. It is therefore also preferred that the at least one aliphatic hydrocarbon (K) is selected from branched alkanes, which preferably have 16 to 60, in particular 16 to 50, carbon atoms. The preferred saturated, branched, aliphatic hydrocarbons (K) (in short: branched alkanes) have the empirical formula C nH2n+2, where the index n is an integer greater than or equal to 16, preferably 16 to 60, in particular 16 to 50. The index n can therefore be, for example, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59 or 60, but it can also be higher. Particularly preferably, the aliphatic hydrocarbon (K) is a compound of the formula C16H34, the main component of tetrabutane.

[0083] It is preferred that the mass fraction of the total of all aliphatic hydrocarbons (K) in the solvent, based on the total mass of the solvent, is at least 99.0%, preferably at least 99.9%, in particular 100.0%.

[0084] It is further preferred that the evaporation loss of the at least one solvent and / or the at least one aliphatic hydrocarbon (K) determined according to ASTM D 972 (in particular ASTM D 972, 2022 edition) after 22 h at 107 °C is at most 0.8%, preferably at most 0.2%, in particular at most 0.15%, expressed as mass loss based on the initial weight.

[0085] It is further preferred that the Noack volatility of the at least one solvent and / or the at least one aliphatic hydrocarbon (K) determined according to ASTM D 5800 (preferably ASTM D 5800, 2021 edition) after 1 h at 250 °C is at most 45%, preferably at most 40%, in particular at most 10%, expressed as mass loss based on the initial weight.

[0086] It is also preferred that the Noack evaporation loss of the at least one solvent and / or the at least one aliphatic hydrocarbon (K), determined according to DIN 51581 (preferably according to DIN 51581-1:2011-09), after 1 h at 250°C is at most 45%, preferably at most 40%, in particular at most 10%, expressed as mass loss based on the initial weight. It is further preferred that the at least one solvent and / or the at least one hydrocarbon (K) is liquid at 25°C.

[0087] In order to enable easy mixing, it is preferred that the at least one solvent and / or the at least one hydrocarbon (K) has a kinematic viscosity of at most 1000 mm 2 / s, preferably not more than 500 mm 2 / s, in particular not more than 150 mm 2 / s at 20 °C, determined according to DIN EN ISO 3104 (preferably according to DIN EN ISO 3104:2021-01). The lower limit of the viscosity should be as low as possible. It is therefore also preferred that the at least one solvent and / or the at least one hydrocarbon have a kinematic viscosity of 1 to 1000 mm 2 / s, preferably from 5 to 500 mm 2 / s, especially from 10 to 150 mm 2 / s at 20 °C, determined according to DIN EN ISO 3104 (preferably according to DIN EN ISO 3104:2021-01).

[0088] It is also advantageous if the at least one solvent and / or the at least one hydrocarbon (K) has a boiling point or boiling range of at least 260 °C, preferably of at least 280 °C, in particular of at least 300 °C, at atmospheric pressure (1013.25 hPa).

[0089] It is preferred that the at least one solvent is selected from the group of mineral oil products, in particular from the group consisting of heating oil, diesel, paraffin oil, white oil (also in medical quality (Paraffinum liquidum)') and tetrabutane.

[0090] Suitable paraffin oils are commercially available, for example, from Shell under the names Shell Ondina X and Shell Risella X. They include numerous paraffin oils that exhibit the above-mentioned physicochemical parameters (evaporation loss, Noack volatility, viscosity, boiling point or boiling range) within the desired ranges, such as Shell Risella X 415 and Shell Risella X 430.

[0091] Another suitable paraffin oil is commercially available from Evonik under the name TEGOSOFT® IHD BASIC. It is a mixture of branched C16, C20, and C24 alkanes. The designation "Cx" stands, as is generally the case, for x carbon atoms. A Cx alkane is therefore an alkane with x carbon atoms.

[0092] Tetrabutane (also known as technical tetrabutane or tetrabutane (technical)) is a mixture of branched paraffins and its main component is hydrocarbons with 16 carbon atoms. Particularly preferred is a tetrabutane that contains a maximum of 2.0% hydrocarbons with fewer than 16 carbon atoms, at least 60.0% hydrocarbons with 16 carbon atoms, and a maximum of 40.0% hydrocarbons with more than 16 carbon atoms, each expressed as a mass fraction based on the total mass of the tetrabutane. Such a tetrabutane is commercially available, for example, from Evonik.

[0093] The amount of solvent used depends on the amount of silicone waste to be converted. It is preferred that the solvent partially, preferably predominantly, and especially completely surround the silicone waste.

[0094] Therefore, a process is preferred in which in step (i) 10 to 250 parts by weight, preferably 10 to 200 parts by weight, in particular 50 to 150 parts by weight of the at least one solvent are used, based on 100 parts by weight of the silicone waste.

[0095] Optionally, step (i) and / or step (ii) can be carried out with the addition of silicone oils or silicone additives, such as wetting agents, emulsifiers, defoamers, dispersants, hydrophobic agents, or waxes. These process additives are preferably polymeric. Process additives based on (organomodified) silicones or siloxanes, in particular, have the advantage of good system solubility.

[0096] It is preferred that the silicone additive is selected from the group consisting of hexamethyldisiloxane, polydimethylsiloxane, a,co-dialkoxypolydimethylsiloxane, in particular a,co-dimethoxypolydimethylsiloxane or a,co-diethoxypolydimethylsiloxane,

[0097] Divinyltetramethyldisiloxane or a,co-divinylpolydimethylsiloxane, a,co-dialkylpolydimethylsiloxane, in particular a,co-dimethylpolydimethylsiloxane or a,co-dioctylpolydimethylsiloxane, siloxanes functionalized with polyethers or glycols, in particular hydrolysis-stable polyethersiloxanes with (poly)ether radicals bonded to the siloxane via SiC bonds.

[0098] In summary, it is therefore preferred that in step (i) and / or step (ii) at least one silicone additive is additionally used, selected from the group consisting of hexamethyldisiloxane, polydimethylsiloxane, a,co-dialkoxypolydimethylsiloxane, in particular a,co-dimethoxypolydimethylsiloxane or a,co-diethoxypolydimethylsiloxane, divinyltetramethyldisiloxane or a,co-divinylpolydimethylsiloxane, a,co-dialkylpolydimethylsiloxane, in particular a,co-dimethylpolydimethylsiloxane or a,co-dioctylpolydimethylsiloxane, siloxanes functionalized with polyethers or glycols, in particular hydrolysis-stable polyethersiloxanes with (poly)ether radicals bonded to the siloxane via SiC bonds.

[0099] The use of silicone additives has the particular advantage that the cyclosiloxane yield can be improved.

[0100] It is preferred that step (i) is carried out at a temperature of 30°C to 180°C, preferably from 45°C to 160°C, in particular from 70°C to 130°C. It is further preferred that step (i) is carried out at atmospheric pressure (1013.25 hPa) ± 500 hPa, preferably ± 200 hPa, in particular ± 100 hPa. Step (i) can be carried out with passage or introduction of a protective gas. For inerting, drying, or deodorization, any vacuum down to 1 mbar can be used according to the pressure swing process. If step (i) is carried out at superatmospheric pressure, pressure-resistant equipment should be used. It is likewise preferred that step (i) is carried out over a period of 2 h to 12 h, preferably 3 h to 9 h, in particular 4 h to 8 h.

[0101] It may be preferred that the process according to the invention comprises step (ii) and the at least one depolymerization catalyst (D1) a) is deactivated with at least one Brönsted base, provided that the at least one

[0102] Depolymerization catalyst (D1) is selected from Brönsted acids; or b) is deactivated with at least one Brönsted acid, provided that the at least one

[0103] Depolymerization catalyst (D1) is selected from Brönsted bases.

[0104] The Brønsted base or Brønsted acid used for deactivation by neutralization can be solid, liquid or gaseous.

[0105] If a gaseous base is chosen for deactivation, it is preferably ammonia. If a solid and / or liquid base is chosen for deactivation, it is preferably hydrogen carbonates and / or carbonates of alkali and / or alkaline earth metals, and / or an organic amine base in the form of a primary or secondary amine, and / or an acetate salt.

[0106] If desired, the salt precipitated during the optional neutralization can be removed preferably by filtration. If filled silicone waste is used, the released filler content can preferably be removed together with the precipitated salt.

[0107] According to a further preferred embodiment of the process according to the invention, the released filler content is first separated and then the filtrate thus obtained is neutralized by introducing a solid, liquid or gaseous base.

[0108] As is obvious to the expert, before processing unknown silicone waste, representative sampling is recommended, followed by test digestion on a laboratory and / or pilot plant scale to determine the current silicone content and the expected occurrence of silicone-free components. These include, among others, binders, plastics, and, in the case of electronic waste, metals, ceramics, etc.

[0109] It is preferred that step (ii) be carried out at a temperature of 0°C to 150°C, preferably from 20°C to 130°C, in particular from 30°C to 120°C. It is further preferred that step (ii) be carried out at atmospheric pressure (1013.25 hPa). It is also preferred that step (ii) be carried out over a period of at most 6 hours, preferably from 0.5 hours to 5 hours, in particular from 1 hour to 3 hours.

[0110] If the process according to the invention comprises step (ii), it is further preferred that the at least one depolymerization catalyst (D2) a) is selected from Brönsted bases, provided that the at least one depolymerization catalyst (D1) is selected from Brönsted acids, or b) is selected from Brönsted acids, provided that the at least one depolymerization catalyst (D1) is selected from Brönsted bases.

[0111] If the process according to the invention comprises step (ii), it is preferred that a Brønsted acid, preferably trifluoromethanesulfonic acid, is used as the depolymerization catalyst (D1) and a Brønsted base, preferably a tetraalkylphosphonium hydroxide and / or alkali metal hydroxide, in particular tetrabutyl hydroxide and / or potassium hydroxide, is used as the depolymerization catalyst (D2). The depolymerization catalyst (D1) is preferably deactivated in step (ii) with a carbonate, in particular anhydrous sodium carbonate.

[0112] From a process engineering perspective, it is advantageous if step (ii) of the process can be omitted. It may therefore also be preferred for the process according to the invention not to include step (ii).

[0113] If the process according to the invention does not comprise step (ii), it is preferred that a tetraalkylphosphonium hydroxide, in particular tetrabutyl hydroxide, is used as depolymerization catalyst (D1).

[0114] In step (i) and the optional step (ii) of the process, the silicone component of the silicone waste is depolymerized. In step (iii) of the process, one or more cyclosiloxanes are then distilled from the reaction mixture.

[0115] It is preferred that step (iii) is carried out at a temperature of 85°C to 180°C, preferably from 90°C to 130°C, in particular from 90°C to 120°C. It is further preferred that step (iii) is carried out at a pressure of at most 70 mbar, preferably from 1 to 40 mbar, in particular from 2 to 30 mbar. It is likewise preferred that step (iii) is carried out over a period of at most 24 hours, preferably from 1 hour to 22 hours, in particular from 2 hours to 20 hours. It is recommended to carry out the distillation under a protective gas, preferably with a light blanket of nitrogen. The temperature and pressure are adjusted so that constant distillation takes place without excessive foaming. If the distillation is slowed down, the temperature can be gradually increased and / or the vacuum gradually increased and, if appropriate, the yield can be increased by introducing nitrogen below the liquid level.If necessary, a pre-run of distillate is taken separately before the main fraction is collected.

[0116] It is preferred to carry out the process according to the invention in a reactor whose volume is preferably at least 1 liter, preferably at least 5 liters, in particular at least 10 liters. It is further preferred that the volume of the reactor be at most 500,000 liters, preferably 30,000 liters, in particular 15,000 liters.

[0117] It is further preferred to carry out the process according to the invention in a reactor with a water separator and at least one distillation column. The at least one column can be independent of one another and optionally unfilled or equipped with all conventional packings. The at least one column can be temperature-controlled entirely or zone-by-zone, from heating to cooling. It is further preferred that, in addition to the column, at least one further cooler with temperature control variably controlled by a cooling sole be used. It is further preferred that a reflux divider be used to recycle all or part of the distillate.

[0118] The term reactor is well known to those skilled in the art and therefore requires no special explanation. A reactor is usually, and preferably also within the meaning of this invention, a confined space, for example a stirred vessel (e.g., a stirred tank) or a tube (e.g., a flow tube as a flow reactor), in which chemical conversions can be carried out in a targeted manner. As those skilled in the art will know, these can be open or closed vessels in which the reactants are converted into the desired products or intermediates. The volume of reactors is specified by the manufacturer or can be determined by calibration. The reactor material can preferably be selected from suitable materials, such as advantageously glass or ceramic, preferably metal, in particular high-alloy stainless steels, particularly preferably Hastelloy. All of this is known to those skilled in the art.Suitable reactors preferably have devices that enable mixing of the reaction mass. Suitable stirring means are known to those skilled in the art and include, for example, dissolvers, propeller stirrers, anchor stirrers, beam stirrers, magnetic stirrers, beaker stirrers, jet mixers, or pitched-blade stirrers. The reactor itself - if not electrically heated - should preferably have a heating jacket that allows coupling to a suitable heat transfer circuit (for example, based on thermal oil or superheated steam). All known means can be used to heat or cool the reaction mass, such as double jackets, full-tube coils or half-tube coils, and all known coolants. With regard to the operating modes, a distinction can essentially be made between continuous and discontinuous operation.Continuous processes are preferably used for large product quantities, while batch processing is preferable for smaller product quantities. Experts know all this. Reactors, especially stirred tank reactors, are commercially available in a variety of forms, for example from Behälter KG Bremen GmbH & Co, Theodor-Barth-Str. 25, 28307 Bremen, Germany, or from Büchi AG, Gschwaderstrasse 12, 8610 Uster, Switzerland. Furthermore, reference is made to the book "Chemical Reactors: Fundamentals, Design and Simulation (German), April 19, 2017, by Jens Hagen; and also to the book "Handbook of Chemical Reactors, Fundamentals and Applications of Chemical Reaction Engineering," edited by Vladimir Reschetilowski, Publisher: Springer, Berlin; 1st ed. 2020." also to the book by Klaus Hertwig, Lothar Martens: Chemical Process Engineering: Calculation, Design and Operation of Chemical Reactors, Oldenbourg, Munich 2007.

[0119] As explained in more detail below, the process according to the invention enables the production of cyclosiloxanes with a low carbon footprint. It is preferred that the carbon footprint of the at least one cyclosiloxane produced according to the invention is less than 5, preferably less than 4.5, in particular less than 4 kg CO2 per kg of cyclosiloxane according to DIN EN ISO 14067 (in particular DIN EN ISO 14067:2019-02).

[0120] As explained in detail above, the choice of solvent is crucial for processes. The invention therefore further relates to the use of at least one aliphatic hydrocarbon (K), according to the above-described specifications, as a solvent or as a solvent component in the production of at least one cyclosiloxane, preferably cyclosiloxanes, from silicone waste.

[0121] As already explained above, the process according to the invention enables the production of individual cyclosiloxanes or cyclosiloxane mixtures of high purity.

[0122] A further subject of the invention is a composition obtained as a distillate of the process according to the invention, wherein the mass fraction of the total of all cyclosiloxanes based on the total mass of the composition is at least 90%, preferably at least 92%, in particular at least 94%, and the mass fraction of the total of all aliphatic hydrocarbons (K) based on the total mass of the composition is at most 10%, preferably at most 8%, in particular at most 6%.

[0123] It is further preferred that the mass fraction of water in the composition according to the invention is less than 0.3%, preferably less than 0.2%, in particular less than 0.1%, based on the total mass of the composition. Most preferably, the composition according to the invention is (essentially) anhydrous. Most preferably, the mass fraction of water in the composition according to the invention is therefore 0.0%, based on the total mass of the composition. It is preferred that the composition according to the invention comprises or consists of the following cyclosiloxanes:

[0124] Hexamethylcyclotrisiloxane (D3) in a mass fraction of 1% to 90%, preferably 1% to 30%, in particular 1% to 20%;

[0125] Octamethylcyclotetrasiloxane (D4) in a mass fraction of 1% to 90%, preferably 1% to 85%, in particular 1% to 80%;

[0126] Decamethylcyclopentasiloxane (D5) in a mass fraction of 1% to 90%, preferably 1% to 85%, in particular 1% to 70%;

[0127] Dodecamethylcyclohexasiloxane (De) in a mass fraction of 0% to 90%, preferably 1% to 15%, in particular 1% to 10%;

[0128] Tetradecamethylcycloheptasiloxane (D7) in a mass fraction of 0% to 10%, preferably from 0% to 5%, in particular from 0% to 2%. Hexadecamethylcyclooctasiloxane (De) in a mass fraction of 0% to 10%, preferably from 0% to 5%, in particular from 0% to 2%; in each case based on the total mass of all cyclosiloxanes.

[0129] It is also preferred that the composition according to the invention comprises or consists of the following cyclosiloxanes:

[0130] Hexamethylcyclotrisiloxane (D3) in a mass fraction of 5% to 90%, preferably 5% to 30%, in particular 5% to 20%;

[0131] Octamethylcyclotetrasiloxane (D4) in a mass fraction of 1% to 90%, preferably 1% to 85%, in particular 1% to 80%;

[0132] Decamethylcyclopentasiloxane (D5) in a mass fraction of 1% to 90%, preferably 1% to 85%, in particular 1% to 70%;

[0133] Dodecamethylcyclohexasiloxane (De) in a mass fraction of 0% to 90%, preferably 1% to 15%, in particular 1% to 10%;

[0134] Tetradecamethylcycloheptasiloxane (D7) in a mass fraction of 0% to 10%, preferably from 0% to 5%, in particular from 0% to 2%. Hexadecamethylcyclooctasiloxane (Ds) in a mass fraction of 0% to 10%, preferably from 0% to 5%, in particular from 0% to 2%; in each case based on the total mass of all cyclosiloxanes.

[0135] The cyclosiloxanes or cyclosiloxane mixtures produced according to the process according to the invention are suitable for upcycling to produce silicone products.

[0136] A further subject of the invention is therefore the use of the at least one cyclosiloxane prepared by the process according to the invention or the composition according to the invention for the production of silicones, preferably selected from the group consisting of organomodified siloxanes, silicone oils, silicone rubbers and

[0137] Silicone elastomers. According to the study "Silicon - Chemistry Carbon Balance: An assessment of greenhouse gas emissions and reductions" (https: / / www.silicones.eu / wp-content / uploads / 2019 / 05 / SIL exec-summary en.pdf) by the Global Silicones Council, the production of silicones from silicon metal using conventional Müller-Rochow synthesis causes greenhouse gas emissions of approximately 6 kg of CO2 per kg of silicone (polydimethylsiloxane, PDMS). According to the DIN EN ISO 14067 standard for determining the CO2 footprint of products, the partial life cycle of a product can be considered, whose CO2 emissions relate only to the production of the product and not to its application. Compared to the classic Müller-Rochow synthesis, the process according to the invention is characterized by significantly lower process temperatures and the absence of chlorine or alkyl chlorides.The use of the at least one cyclosiloxane produced by the process according to the invention or the composition according to the invention enables a more sustainable production of specialty silicones, since less energy is required and the potential for emissions of HCl or alkyl chlorides is eliminated. Depending on the silicone waste used in each case with different contents of D units, the process according to the invention can be used to produce specialty silicones whose greenhouse gas emissions are less than 5, preferably less than 4 kg CO2 per kg of D units (where D = [R2SiO2 / 2] and R = methyl), wherein the silicones are preferably selected from the group consisting of organomodified siloxanes, silicone oils, silicone rubbers, and silicone elastomers.

[0138] These silicones produced in this way, preferably selected from the group consisting of organomodified siloxanes, silicone oils, silicone rubbers and silicone elastomers, demonstrate high quality and can be used without restriction in the usual areas of application.

[0139] The invention therefore also further relates to silicones, preferably selected from the group consisting of organomodified siloxanes, silicone oils, silicone rubbers or silicone elastomers, produced using the at least one cyclosiloxane produced by the process according to the invention or using the composition according to the invention.

[0140] A further subject of the invention is therefore the use of the correspondingly prepared silicones, preferably selected from organomodified siloxanes, as plastic additives, defoamers, foam stabilizers (e.g., polyurethane foam stabilizers), emulsifiers, demulsifiers, rheology additives, hydrophobing agents, wetting agents, textile additives, paint additives, flow control additives, dispersing additives, or as additives in polishes, cleaning agents, and cosmetic preparations, or for the production of silicone release coatings. Examples

[0141] The following examples serve solely to illustrate this invention to the person skilled in the art and do not represent any limitation of the claimed subject matter.

[0142] General methods:

[0143] Nuclear magnetic resonance spectroscopy (NMR spectroscopy):

[0144] The characterization of organosiloxanes can be achieved using the 1 Dog 29Si NMR spectroscopy. These methods, especially considering the multiplicity of couplings, are familiar to those skilled in the art.

[0145] Gas chromatography:

[0146] The gas chromatographic (GC) measurements were performed according to DIN 51405 (issue date January 2004). A gas chromatograph with an FID detector and a capillary column (HP1 from Agilent) was used. 200 mg of sample substance was dissolved in 10 ml of acetone, and dodecane (>99.8%) was used as an internal standard.

[0147] Unless otherwise stated, all percentages are to be understood as percentages by weight (mass fractions).

[0148] Raw materials:

[0149] Tetrabutane: Mixture of branched paraffins with Ci6 hydrocarbons as the main component (Evonik)

[0150] Shell Risella X 430: Paraffin oil with a kinematic viscosity of 44 mm 2 / s at

[0151] 40°C and an evaporation loss according to Noack of 1.8% at 250°C within 1 h

[0152] TEGOSOFT® IHD BASIC: Mixture of branched C16, C20 and C24 alkanes (Evonik)

[0153] TEGO® Antifoam MR 1015: defoamer (Evonik)

[0154] Silicone oil 5: Xiameter PMX-200 Silicone Fluid 5 cSt (Dow)

[0155] Silicone oil 10: Xiameter PMX-200 Silicone Fluid 10 cSt (Dow)

[0156] Photoinitiator TEGO® A18: Photoinitiator (Evonik)

[0157] Example 1 (according to the invention)

[0158] 309.7 g of a pasty, addition-curing LSR compound with approximately 50% SiO2 filler content are weighed into a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a pressure gauge, and a heater with an integrated thermocouple using a cartridge. After adding 309.7 g of tetrabutane as solvent, 14.1 g of hexamethyldisiloxane, and 0.65 g of trifluoromethanesulfonic acid, the mixture is slowly heated to 90 °C while stirring. A further 50 g of tetrabutane is added and the mixture is stirred at 90 °C for 6 h. After cooling to 60 °C, 3.3 g of sodium carbonate are added, and the mixture is stirred at 60 °C for 3 h. The filler is filtered off using a pressure filter press. In a distillation apparatus, 250 g of the filtrate are mixed with 5 g of finely ground potassium hydroxide and heated to 120 °C while stirring. 50 mg of TEGO® Antifoam MR 1015 are added, the pressure is gradually reduced to 25 mbar, and distillation is carried out for 2.5 hours. The total distillate yield is 83.2 g.The mixture is then distilled at 15 mbar for one hour and then at 10 mbar for a further 2.5 hours. 83.2 g of distillate are obtained. 1 Dog 29 Si-NMR analysis shows that the distillate contains 5.4% of the solvent used; 17.3% hexamethylcyclotrisiloxane (D3), 66.5% octamethylcyclotetrasiloxane (D4), and 10.8% decamethylcyclopentasiloxane (D5).

[0159] Example 2 (according to the invention)

[0160] 500 g of shredded silicone rubber waste (of various colors) are placed in a 2000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer, and a heating mantle with an integrated thermocouple. After adding 400 g of tetrabutane as solvent, 11.4 g of hexamethyldisiloxane, and 1.0 g of trifluoromethanesulfonic acid, the mixture is heated to 80 °C with stirring. After stirring for 1 h, the mixture is further heated to 100 °C. After stirring for 5.5 h at 100 °C, no solid silicone rubber particles are visible. After adding 2.6 g of anhydrous sodium carbonate, the mixture is stirred for a further hour at 100 °C. The reflux condenser is then replaced with a Vigreux column and distillation bridge, 5.1 g of tetramethylammonium hydroxide monohydrate is added, the mixture is stirred for 30 min at 100 °C, and the pressure is then reduced to 30 mbar to 20 mbar. The distillate foreshots are discarded and then distilled for a total of 11 h at 100 °C to 111 °C and 9 mbar to 7 mbar.128 g of distillate are obtained. 1 Dog 29 Si-NMR analysis shows that the distillate contains 1.1% of the solvent used; 17.3% hexamethylcyclotrisiloxane (D3), 74.2% octamethylcyclotetrasiloxane (D4) and 7.0%

[0161] Decamethylcyclopentasiloxane (D5). Example 3a (according to the invention)

[0162] 1376 g of variously colored, crushed silicone rubber particles (0.5–1 cm in diameter) are placed in a 4000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer, and a heating element with an integrated thermocouple. The mixture is heated to 40 °C with stirring along with 1376 g of TEGOSOFT® IHD BASIC as solvent and 89.3 g of a dioctylpolydimethylsiloxane with a molecular weight of 1100 g / mol. 2.9 g of trifluoromethanesulfonic acid are added, and the mixture is stirred for 4 h at 100 °C to 120 °C until all the rubber particles have dissolved. At 100 °C, 7.3 g of anhydrous sodium carbonate are added, and the mixture is stirred for 2 h.

[0163] Example 3b (according to the invention)

[0164] In a 2000 ml four-neck flask equipped with a stirrer, a Vigreux column and distillation bridge, a manifold, and a mantle heater with integrated thermocouple, 914 g of the reaction mixture from Example 5a are mixed with 4.7 g of tert-butyliminotri(pyrrolidino)phosphorane (>97%, Sigma Aldrich) at 80 °C while stirring and heated to 122 °C. 248 g of distillate are obtained at 122 °C and 8 mbar to 4 mbar.

[0165] Example 3c (according to the invention)

[0166] In a 2000 ml four-necked flask equipped with a stirrer, a Vigreux column and distillation bridge, a manometer, and a heating mantle with integrated thermocouple, 914 g of the reaction mixture from Example 5a are mixed with 4.7 g of tetramethylguanidine at 94°C while stirring and heated to 122°C. 96 g of distillate are obtained at 122°C and 4 mbar to 2 mbar.

[0167] Example 4 (according to the invention)

[0168] In a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a pressure gauge, and a heating element with an integrated thermocouple, 300 g of shredded, colorless silicone tubing are placed. After adding 50 g of a trimethylsiloxy-terminated silicone oil with a viscosity of 10 mm 2 / s, 300 g TEGOSOFT® IHD BASIC as solvent and 8.8 g 40% aqueous tetrabutylphosphonium hydroxide solution, the mixture is stirred for 4 h at 110°C with initial foaming, with a further 75 g TEGOSOFT® IHD BASIC being added after 1 h. The reflux condenser is then replaced by a Vigreux column and distillation bridge, and water is removed at 110°C. 184 g of distillate is then obtained at 106°C to 108°C and 7 mbar to 6 mbar over 11 h. 1 Dog 29Si NMR analysis shows that the distillate contains 2.5% of the solvent used; 10.6% hexamethylcyclotrisiloxane (D3), 79% octamethylcyclotetrasiloxane (D4), and 5.9% decamethylcyclopentasiloxane (D5). Example 5 (according to the invention)

[0169] 318 g of a cyclosiloxane mixture with a purity of 97.7% prepared as in Example 4, 0.37 g of trifluoromethanesulfonic acid, and 60.24 g of a silicone acrylate prepared as in EP 0940422 B1, Example 1 are successively introduced into a 500 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer, and a heating mantle with an integrated thermocouple while stirring and the mixture is stirred at 100 °C for 10 h. After cooling to 70 °C, 2.65 g of anhydrous sodium carbonate are added, and the mixture is stirred at 70 °C for 3 h. After adding 1.5 g of filter aid, the mixture is filtered off using a filter press with an HS 2000 layer filter, and the yellow-brownish product is freed from volatile components using a thin-film evaporator at 130 °C and <1 mbar. A yellow-brownish silicone acrylate with a viscosity of 446 mPa s at 25 °C is obtained.

[0170] Example 6a (according to the invention)

[0171] In a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer, and a heating mantle with an integrated thermocouple, 380.3 g of a cyclosiloxane mixture with a purity of 97.7%, prepared according to Example 4, 54.9 g of hexamethyldisiloxane, and 123.5 g of poly(methylhydrogen)siloxane were placed with stirring. 0.56 g of trifluoromethanesulfonic acid was added, and the mixture was stirred at 40 °C for 2 h and then at room temperature for a further 14 h. Then, 8.4 g of sodium bicarbonate were added and the mixture was stirred at room temperature for 2 h. After filtration, a colorless, clear hydrogensiloxane with an SiH content of 3.4 mmol / g and a viscosity of 10.1 mPa s at room temperature was obtained.

[0172] Example 6b (according to the invention)

[0173] Now, 192.9 g of allyl glycidyl ether are placed in a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a pressure gauge, and a heating mantle with an integrated thermocouple. 3 ppm of platinum in the form of the Karstedt catalyst are added. After rendering the mixture inert and heating to 95 °C, 379.8 g of the hydrogen siloxane from Example 6a are added over half an hour, and the temperature is maintained at approximately 100 °C by counter-cooling. After stirring for 7 hours at 100 °C, the SiH content of the mixture, determined by gas volumetric analysis, is no longer measurable and corresponds to 100% reaction conversion. After distillation on a rotary evaporator at 135 °C and <0.1 mbar for 1 h, a clear, slightly brownish epoxy siloxane with an epoxy content of 4.05% epoxy oxygen is obtained. Example 6c (according to the invention)

[0174] Now, 44.39 g of acrylic acid, 5.04 g of concentrated acetic acid, and 68 mg of methylhydroquinone are placed in a 500 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer, and a heating mantle with an integrated thermocouple. 0.45 g of 50% aqueous chromium(III) acetate solution is added. The mixture is heated to 65 °C with stirring, and the epoxysiloxane from Example 6b is added over the course of 1 h. The temperature is continuously increased to 90 °C during the addition, and then stirred at 95 °C for 5 h. Upon cooling, 1 g of filter aid is stirred in, and the product is filtered through a pressure filter press with a KD 5 layer filter. A greenish-clear silicone acrylate with a viscosity of 469 mPa s at room temperature is obtained.

[0175] Example 7 (not according to the invention)

[0176] In a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer, and a heating element with an integrated thermocouple, 286 g of decamethylcyclopentasiloxane (D5), 13.9 g of hexamethyldisiloxane, and 30 g of silicone oil 10 are placed. 203 g of a pasty, addition-curing LSR compound with approximately 50% SiO2 filler content are added in four portions using a cartridge and heated to 90 °C with stirring. After adding 15 g of potassium methylate, the reaction mixture is gradually heated to 140 °C, and distillation is started at 890 mbar. After 1 h of distillation, the bottom product is gelled. 153 g of distillate were obtained, which was prepared according to 29 Si-NMR consists of 95.3% decamethylcyclopentasiloxane (D5).

[0177] Example 8 (not according to the invention)

[0178] In a 500 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer, and a heating mantle with an integrated thermocouple, 200 g of isononanol as solvent, 6.8 g of hexamethyldisiloxane, 0.63 g of trifluoromethanesulfonic acid, and 108 g of a pasty, addition-curing LSR compound with approximately 50% SiO2 filler are heated to 90 °C with stirring and stirred for 2 h. After adding 1.6 g of anhydrous sodium carbonate, the mixture is stirred at 60 °C for 2 h and then filtered through a coarse pleated filter. 250 g of the filtrate is heated to 100 °C with stirring, and 7.5 g of finely ground potassium hydroxide is added. After stirring at 100 °C for 30 min, a vacuum is applied and the temperature is increased. Distillation is carried out for 1.5 h at 115 °C to 150 °C and 715 mbar to 600 mbar. After 1.5 h of distillation, the bottoms are gelled. 152 g of distillate were obtained, which was 1 H-NMR shows that it consists mainly of isononanol. Example 9 (not according to the invention)

[0179] In a 500 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer, and a heating mantle with an integrated thermocouple, 22.6 g of silicone oil 5, 0.25 g of trifluoromethanesulfonic acid, and 105 g of a pasty, addition-curing LSR compound with approximately 50% SiO2 filler are heated to 100 °C with stirring. A further 22.6 g of silicone oil 5 and 105 g of pasty, addition-curing LSR compound are added, and stirring is continued. After adding 11.3 g of silicone oil 5, the mixture is stirred at 150 °C for 4 hours and again at 130 °C for 2 hours. After cooling to 60 °C, 0.9 g of anhydrous sodium carbonate is added, and the mixture is stirred for 2 hours. The mixture is filtered through a lacquer filter with a pore size of 125 pm. 127 g of the filtrate is heated to 190 °C with 2.5 g of concentrated sulfuric acid while stirring, and 2 mL to 3 mL of distillate is removed at room pressure. After cooling to 150 °C, another 2.5 g of concentrated sulfuric acid is added and heated to 190 °C.No more distillate is produced and the sump becomes highly viscous.

[0180] Example 10 (not according to the invention)

[0181] In a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer, and a heater with an integrated thermocouple, 300 g of shredded, colorless silicone tubing were placed. After adding 300 g of butyldiglycol (2-(2-butoxyethoxy)ethanol), 31.4 g of a dioctylpolydimethylsiloxane with a molecular weight of 1100 g / mol, and 8.3 g of 40% aqueous tetrabutylphosphonium hydroxide solution, the mixture was heated to 125 °C with stirring and stirred for 3 h. The silicone particles did not dissolve.

[0182] Example 11 (not according to the invention)

[0183] 650.2 g of shredded, colored silicone rubber waste are placed in a 2000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer, and a heating mantle with an integrated thermocouple. After adding 57.6 g of a dioctylpolydimethylsiloxane with a molecular weight of 1100 g / mol, 650.2 g of dodecane as solvent, and 1.4 g of trifluoromethanesulfonic acid, the mixture is stirred at 100°C for 6 h. After adding 3.5 g of anhydrous sodium carbonate, the mixture is stirred at 100°C for 1 h. The reflux condenser is then replaced with a Vigreux column and distillation bridge, 17.7 g of 40% aqueous tetrabutylphosphonium hydroxide solution is added, and the mixture is distilled at 85 °C to 100 °C, gradually reducing the pressure to 10 mbar. After 2.5 hours of distillation, the residue has dried out and can be separated from the rim of the flask as dark lumps. It weighs 432 g. 823 g of distillate are obtained. 1 Dog 29Si-NMR analysis shows that the distillate contains 67% of the solvent used, 2.6% hexamethylcyclotrisiloxane (D3), 21.5% octamethylcyclotetrasiloxane (D4), and 8% decamethylcyclopentasiloxane (D5). Example 12 (according to the invention)

[0184] In a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a pressure gauge, and a heater with an integrated thermocouple, 300 g of shredded, colored silicone rubber waste, 300 g of Shell Risella X 430, and 6 g of concentrated sulfuric acid (98%) are placed and stirred at 100 °C for 6 h. After adding 6.6 g of anhydrous sodium carbonate, the mixture is stirred at 70 °C for 2 h. The reflux condenser is then replaced with a Vigreux column and distillation head, and 7.5 g of 40% aqueous tetrabutylphosphonium hydroxide solution are added. The mixture is distilled at 105 °C to 130 °C at a gradually reduced pressure down to 9 mbar. 36 g of distillate are obtained in the first 30 min, then distillation stops and the viscosity of the bottom product increases.Another 7.5 g of 40% aqueous tetrabutylphosphonium hydroxide solution are added, and another 14.7 g of distillate are obtained before distillation stops again and the experiment is terminated. The distillate quantity is only 30% of theoretical and also consists of a water phase and a silicone phase. 1 Dog 29 Si-NMR analysis shows that the distillate contains 7.7% hexamethylcyclotrisiloxane (D3), 78.3% octamethylcyclotetrasiloxane (D4) and 12.2% decamethylcyclopentasiloxane (D5).

[0185] Application-technical testing:

[0186] Production of release coatings:

[0187] The performance testing of the silicone acrylates from inventive examples 5 and 6c was carried out in formulations for release coatings. Release coatings are known from the prior art, particularly as abhesive coatings on flat substrates, specifically for use in adhesive tapes or label laminates.

[0188] To prepare the formulations for release coatings, 98 g each of the silicone acrylates from Examples 5 and 6c and 2 g each of photoinitiator TEGO® A18 are thoroughly mixed (Examples A and B).

[0189] In addition, a release coating formulation is prepared in which 30 g of the component from Example 6c is mixed with 68 g of the component from Example 5 and 2 g of the photoinitiator TEGO® A18 (Example C).

[0190] The resulting coating compounds are applied to a flat substrate. In all application examples, this consists of a 50 cm wide, biaxially oriented polypropylene film (BOPP), which was subjected to corona pretreatment with a 1 kW generator prior to application of the coating compound. The coating compounds are applied using a 5-roll coating system from COATEMA® (Coating Machinery GmbH, Dormagen, Germany) with a basis weight of approximately 1 g / m². 2 applied and cured by exposure to UV light from a medium-pressure mercury vapor lamp from IST® Metz GmbH (Nürtingen, Germany), with 60 W / cm at a web speed of 100 m / min under a nitrogen atmosphere with a residual oxygen content of less than 50 ppm.

[0191] The coated samples are tested for rub-off, release value and residual adhesive strength.

[0192] Rub-off:

[0193] The adhesion of the cured coating to the substrate is tested by vigorously rubbing the coating with the thumb. If adhesion is inadequate, abrasion will form in the form of rubbery crumbs. Such crumbs should not form even with intensive rubbing. The test is conducted by a trained panel. The evaluation is categorized from 1 to 5, with 1 representing very good and 5 representing rather poor adhesion to the substrate.

[0194] Cut-off value:

[0195] The release effect against adhesive substances, in technical applications mostly in the form of adhesive tapes or labels, is expressed by the release value (TW), with a low release value indicating good release effect. The release value depends on the quality of the release coating, the adhesive itself, and the test conditions. To evaluate release coatings, therefore, identical adhesives and test conditions should be available. To determine the release values, adhesive tapes or label laminates are cut to a width of 2.5 cm and then their adhesive side is applied to the silicone coating to be tested. This test is carried out according to the FINAT Handbook 8th Edition, The Hague / NL, 2009 under the designation FTM 10, with the modification that storage takes place under pressure at 40 °C. The adhesive tape used is tesa® 7475 (trademark of Tesa SE, Germany, Hamburg).The values ​​given are the averages of five determinations and are expressed in [cN / 2.5 cm]. Systems with a release value below 10 cN / 2.5 cm are considered easy release and are generally suitable for many applications, such as label laminates.

[0196] Residual adhesive strength:

[0197] The residual adhesive strength (short-term residual adhesive strength: KUR) is determined according to the test specification from the FINAT Handbook 8th Edition, The Hague / NL, 2009, under the designation FTM 11. The test adhesive strip is exposed to silicone for one minute and the standard surface is an untreated BOPP surface. The adhesive tape used is tesa® 7475 (a trademark of Tesa SE, Hamburg, Germany). The residual adhesive strength is a measure of the crosslinking of the silicones. If non-polymerized and therefore migratable silicone components are present, increasingly lower residual adhesive strength values ​​are achieved with increasing proportions of such components. Values ​​above 80% are considered acceptable. The results of the rub-off test, the release values, and the short-term residual adhesive strengths (KUR) are shown in Table 1.

[0198] Table 1: Results of the application testing (rub-off in grades from 1 to 5; release values ​​(TW) in cN / 2.5 cm after 24 hours at 40°C storage; residual adhesive strength (KUR) in %).

[0199] The examples demonstrate good curing, as evidenced by the short-term residual adhesive strengths (SRT). The release values ​​also show an expected pattern of low and high release values, depending on the acrylate density and functionalization. A silicone component with a high acrylate density is necessary for good rub-off, so Example A shows only inadequate rub-off quality, while Examples B and C exhibit the opposite behavior.

Claims

Patent claims 1. A process for producing at least one cyclosiloxane by catalyzed depolymerization of silicone waste comprising the steps or consisting of the steps: (i) dissolving at least part of the silicone waste in at least one solvent containing or consisting of at least one aliphatic hydrocarbon (K) using at least one depolymerization catalyst (D1), (ii) optionally deactivating the at least one depolymerization catalyst (D1) and adding at least one further depolymerization catalyst (D2), (iii) distilling off the at least one cyclosiloxane from the mixture, characterized in that the at least one aliphatic hydrocarbon (K) comprises at least 16 carbon atoms.

2. Process according to claim 1, characterized in that the silicone waste contains or consists of silicone elastomers and / or silicone rubbers.

3. Process according to claim 1 or 2, characterized in that the at least one depolymerization catalyst (D1) and optionally the at least one depolymerization catalyst (D2) is selected from Bronsted acids, preferably trifluoromethanesulfonic acid, or from Bronsted bases, preferably selected from the group consisting of alkali metal hydroxides, tetraalkylammonium hydroxides, tetraalkylphosphonium hydroxides, phosphazenes and guanidines.

4. Process according to one of claims 1 to 3, characterized in that in step (i) 0.05 to 10 parts by weight, preferably 0.1 to 3.0 parts by weight, in particular 0.2 to 1.5 parts by weight of the at least one depolymerization catalyst (D1) and optionally of the at least one depolymerization catalyst (D2) are used, based on 100 parts by weight of the silicone component of the silicone waste.

5. Process according to one of claims 1 to 4, characterized in that the mass fraction of the total of all aliphatic hydrocarbons (K) in the solvent, based on the total mass of the solvent, is at least 99.0%, preferably at least 99.9%, in particular 100.0%.

6. Process according to one of claims 1 to 5, characterized in that the evaporation loss of the at least one solvent and / or of the at least one aliphatic hydrocarbon (K) determined according to ASTM D972 after 22 h at 107 °C is at most 0.8%, preferably at most 0.2%, in particular at most 0.15%, expressed as mass loss based on the initial weight; and / or the Noack volatility of the at least one solvent and / or of the at least one aliphatic hydrocarbon (K), determined according to ASTM D5800, after 1 h at 250 °C is at most 40%, preferably at most 20%, in particular at most 15%, given as mass loss based on the initial weight; and / or the Noack evaporation loss of the at least one solvent and / or of the at least one aliphatic hydrocarbon (K), determined according to DIN 51581, after 1 h at 250 °C is at most 40%, preferably at most 20%, in particular at most 15%, given as mass loss based on the initial weight.

7. The process according to any one of claims 1 to 6, characterized in that the at least one aliphatic hydrocarbon (K) is selected from branched alkanes, which preferably have 16 to 60, in particular 16 to 50, carbon atoms; and / or the at least one solvent is selected from the group consisting of heating oil, diesel, paraffin oil, white oil, and tetrabutane.

8. The method according to any one of claims 1 to 7, characterized in that in step (i) and / or (ii) at least one silicone additive is additionally used, selected from the group consisting of hexamethyldisiloxane, polydimethylsiloxane, a,co-dialkoxypolydimethylsiloxane, in particular a,co-dimethoxypolydimethylsiloxane or a,co-diethoxypolydimethylsiloxane, divinyltetramethyldisiloxane or a,co-divinylpolydimethylsiloxane, a,co-dialkylpolydimethylsiloxane, in particular a,co-dimethylpolydimethylsiloxane or a,co-dioctylpolydimethylsiloxane, siloxanes functionalized with polyethers or glycols, in particular hydrolysis-stable polyethersiloxanes with (poly)ether radicals bonded to the siloxane via SiC bonds.

9. The method according to any one of claims 1 to 8, characterized in that step (i) is carried out at a temperature of 30°C to 180°C, preferably from 45°C to 160°C, in particular from 70°C to 130°C; and / or at atmospheric pressure (1013.25 hPa) ± 500 hPa, preferably ± 200 hPa, in particular ± 100 hPa.

10. The process according to any one of claims 1 to 9, characterized in that it comprises step (ii) and the at least one depolymerization catalyst (D1) a) is deactivated with at least one Brønsted base, provided that the at least one depolymerization catalyst (D1) is selected from Brønsted acids; or b) is deactivated with at least one Brønsted acid, provided that the at least one depolymerization catalyst (D1) is selected from Brønsted bases.

11. The process according to any one of claims 1 to 10, characterized in that step (iii) is carried out at a temperature of 85°C to 180°C, preferably from 90°C to 130°C, in particular from 90°C to 120°C; and / or at a pressure of at most 70 mbar, preferably from 1 to 40 mbar, in particular from 2 to 30 mbar.

12. Process according to one of claims 1 to 11, characterized in that the carbon footprint of the at least one cyclosiloxane produced according to DIN EN ISO 14067 is less than 5, preferably less than 4.5, in particular less than 4 kg CO2 per kg cyclosiloxane.

13. Use of at least one aliphatic hydrocarbon (K) according to the specifications of one of the preceding claims as a solvent or as a solvent component in the production of at least one cyclosiloxane from silicone waste.

14. Composition obtained as distillate of the process according to one of claims 1 to 12, characterized in that the mass fraction of the total of all cyclosiloxanes based on the total mass of the composition is at least 90%, preferably at least 92%, in particular at least 94%, and the mass fraction of the total of all aliphatic hydrocarbons (K) based on the total mass of the composition is at most 10%, preferably at most 8%, in particular at most 6%.

15. Use of the at least one cyclosiloxane prepared by the process according to any one of claims 1 to 12 or of the composition according to claim 14 for the preparation of silicones, preferably selected from the group consisting of organomodified siloxanes, silicone oils, silicone rubbers or silicone elastomers.

16. Silicones, preferably selected from the group consisting of organomodified siloxanes, silicone oils, silicone rubbers or silicone elastomers, prepared using the at least one cyclosiloxane prepared by the process according to any one of claims 1 to 12 or using the composition according to claim 14.

17. Use of the silicones prepared according to claim 15 or the silicones according to claim 16, preferably selected from organomodified siloxanes, as plastics additives, defoamers, foam stabilizers, emulsifiers, demulsifiers, rheology additives, hydrophobizing agents, wetting agents, textile additives, paint additives, leveling additives, dispersing additives or as additives in polishes, cleaning agents and cosmetic preparations or for the production of silicone release coatings.

Images