WO2024227761A1 - Process for producing cyclosiloxanes from silicone waste - Google Patents

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

Process for the production of cyclosiloxanes from silicone waste

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

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 the molecular weight and degree of cross-linking.

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

In terms of its mechanical properties, silicone has a decisive advantage over other types of rubber: silicone's mechanical properties 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, if an EPDM material is superior to a silicone mixture in terms of its mechanical properties when looking at the technical data sheet because the properties are given at room temperature, the completely opposite picture emerges at high or low temperatures. Silicone's temperature resistance in air is around -80 °C to around 250 °C. This property is often used for seals, as this is where the very low compression set typical of silicone comes into play.

Due to their excellent ozone, UV and weather resistance, silicone mixtures are also often used in outdoor applications. Silicone is also very flame-retardant and has good electrical insulation and conductivity. Silicone is chemically resistant to plant and animal fats, hot water and alcohol, for example. Its resistance is limited to acids, alkalis, fuels and ketones, as well as water vapor. Silicone also has a very high gas permeability.

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 (for less than 30 days in Class Ha medical devices) or long-term implants (for 30 days or more in Medical devices of class Hb) and perform critical functions in devices such as cardiac catheters, pacemakers, ventilators, neurostimulators or defibrillators.

Silicone rubber, which is intended for use in long-term implants, is only offered by very few producers worldwide (e.g. NuSil Technology). The mixtures are manufactured under strict conditions of the U.S. Food and Drug Administration (FDA). Particular attention must also be paid to purity during processing and component production must take place in a clean room.

An important advantage of silicone is that it is biocompatible and therefore well tolerated by humans. The biocompatibility of a silicone mixture is often proven by USP Class VI classifications (USP stands for United States Pharmacopeia) or by tests according to the stricter (DIN EN) ISO 10993 guideline. (DIN EN) ISO 10993 is used primarily for testing medical devices that are implanted in the human body for a long time or permanently. For shorter applications, classification according to USP Class VI or possibly a lower classification is sufficient.

In addition, silicone offers the possibility of steam sterilization (heating in an autoclave) due to its ability to be used in a wide temperature range from around -80 °C to around 250 °C. Silicone products can thus be freed from living microorganisms, their permanent forms, viruses, etc. The good electrical insulation properties of silicone are also of particular importance in the medical field.

By varying the silicone rubbers used and the types of cross-linking, silicones can be given special properties. HTV silicone rubbers are flexible and resistant in a wide temperature range from -50 °C to 200 °C, sometimes up to 300 °C. They are found in seals in the automotive or food industry, in cable sheathing or as damping material.

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

Liquid silicones (also LSR, liquid silicone rubber) have a lower viscosity than HTV and RTV silicone rubbers. They can be molded into a wide variety of shapes using the injection molding process and processed into silicone hoses, for example. Since LSR silicones are always produced with platinum cross-linking, products based on liquid silicones can be used in medical technology areas. Thanks to its high stability within the human body, silicone provides very good protection for critical components and, due to these properties, is also preferred for functional parts.

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 fillers for the targeted adjustment of mechanical properties such as Shore hardness, tensile strength and elasticity.

According to their physical states and their vulcanization temperatures, silicone rubbers can be divided into three groups:

HIV (high temperature vulcanizing) or HCR (high consistency rubber) refers to silicone rubbers whose raw material is solid. They are vulcanized at high temperatures, usually between 140 °C and 200 °C. Crosslinking takes place using peroxides or an addition reaction, with platinum compounds being used as a catalyst.

Liquid silicone or LSR (Liquid Silicone Rubber) is a (viscous) liquid raw material and consists of two components that are mixed directly before processing. Crosslinking occurs through an addition reaction at temperatures similar to those of HTV types, although crosslinking generally occurs much faster.

Both types of silicone can be colored. Finished elastomer articles made of HTV silicone and LSR silicone hardly differ in their properties.

The third group are so-called RTV silicones (room temperature vulcanizing). With these, crosslinking takes place 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.

As advantageous as the performance properties derived from the special chemical stability of silicones are for the service life of the objects made from them, their stability is a burden when disposing of the silicones at the end of their use (life cycle). 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 large number 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 of >200 °C. At such high temperatures, distillates are usually obtained which are contaminated by decomposition products of the 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 further distillation steps are necessary to obtain cyclosiloxanes with high purity. The separation of undesirable impurities or undesirable siloxane components normally requires further purification of the cyclosiloxanes obtained so that they can be used universally to produce new specialty silicones. Furthermore, not every type of silicone can usually be depolymerized with 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 crosslink, agglomerate or be chemically modified during depolymerization, which can lead to a strong increase in viscosity and even gelling of the mixture.

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, only use environmentally friendly solvents or even do without solvents altogether.

The same authors describe 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) a process for recycling polysiloxanes via fluoride-catalyzed depolymerization at room temperature to repolymerizable cycles. Different solvents were investigated for their suitability. The process was most efficient with tetrahydrofuran (THF) as the solvent. The boiling point of THF is, however, lower than that of cyclosiloxanes, which makes the distillative separation of the cyclosiloxanes from the reaction mixture difficult.

US 5,110,972 discloses numerous solvents for the production of cyclosiloxanes from silicone polymers. Specifically, a process for cracking silicone polymers with a high molecular weight is described, the process 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 essentially dissolved; adding a base; and distilling off cyclosiloxanes from the solution. It is also already described there that the solvents should have a certain property profile. For example, they should be inexpensive and safe. They should be able to swell cured silicones. They should also be easy to separate from the cyclosiloxanes and solid by-products. In this context, it is described 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 insoluble in water as possible so that water-soluble by-products and impurities can be removed by water extraction. Aliphatic hydrocarbons or oils are disclosed as solvents, but without specifying which aliphatic hydrocarbons or oils can be used to achieve the properties desired above. Butyl Carbitol ™ (also referred to as diethylene glycol monobutyl ether, butyl diglycol or (2- (2-butoxyethoxy)ethanol) and Köppers' Methylnaphthalene Fraction ™ (a hydrocarbon fraction that predominantly contains 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 is desired, and are thus contained in the distillate. Experiments by the inventors have also shown that Butyl Carbitol ™ is at least not generally suitable as a solvent, since the silicone parts used could not be dissolved (see non-inventive example 10 below). The possible uses therefore appear to be very limited. In addition, 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 ™ has the disadvantage that it contains aromatic hydrocarbons. Aromatic hydrocarbons, especially polycyclic hydrocarbons, are increasingly classified as toxic to reproduction. They are also environmentally hazardous due to their toxicity to aquatic organisms with long-term effects. Their use is therefore undesirable, not only because they pose a health risk to employees in industrial use, but also because residual amounts remain in the cyclosiloxanes obtained and thus contaminate the subsequent products with aromatic hydrocarbons. In this respect, US 5,110,972 addresses the most important questions when selecting a suitable solvent, but does not offer any satisfactory solutions. Examples D and E reveal a two-phase distillate which contains both water and solvent in addition to the cyclosiloxanes. The cyclosiloxane yield is summed proportionally from the analysis of distillate and cold trap residue, without the exact composition of the two fractions is disclosed. A processing and isolation of purified, largely water-free cyclosiloxane mixtures in a further process step is not disclosed, but would be necessary for the use of the cyclosiloxane mixtures to produce new silicone products.

The object was therefore to provide a process for the preparation of cyclosiloxanes which has advantages over the prior art.

The particular task is to develop a process for producing cyclosiloxanes from silicone waste, which can be carried out at moderate temperatures, does not cause harmful emissions into the air or water and produces cyclosiloxane mixtures of high purity in one step, which can ideally be used widely for the production of organomodified siloxanes, silicone oils, silicone rubbers or silicone elastomers without or with only minimal further purification steps. Furthermore, the process should preferably be robust, not cause gelling or encrustation in the reactor and be applicable to a large number of different end-of-life silicones.

Surprisingly, it has been found that a special process for preparing 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.

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:

(i) dissolving at least a portion 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, wherein the at least one aliphatic hydrocarbon (K) comprises at least 16 carbon atoms.

Another 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.

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 all aliphatic hydrocarbons (K) based on the total mass of the composition is a maximum of 10%, preferably a maximum of 8%, in particular a maximum of 6%.

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 preparation of organomodified siloxanes, silicone oils, silicone rubbers or silicone elastomers.

Yet another subject matter of the invention are 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.

Yet another object of the invention is the use of the correspondingly produced 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, flow additives, dispersing additives or as additives in polishes, cleaning agents and cosmetic preparations or for the production of silicone release coatings.

In connection with this invention, use is also made of the M, D, T, Q designations for organopolysiloxane building units. For a reference to their meaning, see W. Noll, Chemistry and Technology of Silicones, 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, in particular a methyl radical.

Advantageous embodiments of the subject matter of the invention can be found in the claims, the examples and the description. In addition, 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 an subject matter according to the invention also apply mutatis mutandis to the embodiments of the other subject matters according to 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:

(i) dissolving at least a portion 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.

The wording “at least one” is synonymous with the wording “one or more”. The wording “at least one cyclosiloxane” is therefore synonymous with the wording “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, one does not obtain a single cyclosiloxane but rather several cyclosiloxanes. The process product therefore preferably contains or consists of a mixture of different cyclosiloxanes.

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

(i) dissolving at least a portion 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 cyclosiloxanes from the mixture, wherein the at least one aliphatic hydrocarbon (K) comprises at least 16 carbon atoms.

Steps (i), (ii) and (iii) are carried out in the order given, 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 can have further upstream steps, intermediate steps or downstream steps, such as, for example, purification of the reactants, the intermediate products and/or the end products and/or conversion of the end products into 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 be omitted. step (i) can also be carried out again directly or indirectly, so that the process is carried out once or several times, i.e. as a circulation process. After the cyclosiloxanes have been distilled off from the mixture, silicone waste can, for example, be added again to the remaining distillation residue and, if required, further solvent and/or one or more depolymerization catalysts (D1). If the process is carried out as a circulation 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 circulation process, it is also 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 components of the distillation residue using separation processes familiar to those skilled in the art and to return only the latter to the circulation process. In particular, it is also possible to purify the solvent after step (iii) by washing out water-soluble components with water and to return it to the process. Although the process is preferably a discontinuous process, a continuous process is conceivable. In the discontinuous case, a batch reactor can be used as the reactor, for example, while in the continuous case a continuous stirred tank reactor (CSTR reactor) or a tubular reactor or tubular flow reactor can be used.

The process according to the invention enables the production of a cyclosiloxane or of mixtures of different cyclosiloxanes of high purity. Cyclosiloxanes are known to those skilled in the art. These are siloxanes which consist exclusively of D units. These are preferably 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. Preferably, however, the R radicals are 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).

The process according to the invention can be carried out on liquid-viscous as well as partially or completely cured silicone waste.

In a preferred embodiment of the invention, in the case of completely hardened silicone waste in particular, it is provided that it is crushed into lumpy material, which at the end of the crushing preferably has a maximum diameter of at most 5 cm, more preferably 1 to 10 mm, particularly preferably 3 to 6 mm. According to the invention, the optional crushing of the material can preferably be carried out, for example, with the aid of a crusher, a shredder, a mill, a hammer mill, with the aid of rollers or a kneading machine or also with the aid of cutting Machines. Soft silicone waste can first be cold embrittled by contact with liquid nitrogen or dry ice pellets, for example. The resulting significantly reduced elasticity facilitates appropriate shredding.

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.

The process is not restricted 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.

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

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 relates to silicone adhesive and/or silicone sealant cartridges, in particular relates to 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 enables the silicone adhesive and/or silicone sealant compound to be pressed out, the container shell usually being made of HDPE (high density polyethylene) and the semi-transparent container parts (piston and squeezing tip) usually being made of LDPE (low density polyethylene). HDPE and LDPE are known to those skilled in the art. HDPE has a high density of between 0.94 g/cm ³ and 0.97 g/cm ³ ; LDPE, on the other hand, has a lower density of between 0.915 g/cm ³ and 0.935 g/cm ³ . The process according to the invention therefore also enables 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.

If the silicone waste contains filler, this is released by 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 solvent containing the filler, for example using a coarse sieve, which can then be separated from the solid, finely divided filler, for example by allowing it to settle. According to the invention and without detracting from the teaching presented, further solutions can naturally be found for the advantageous embodiment of the basic process engineering operations addressed here, such as, for example, filtering or centrifugal separation of the filler from the solvent.

It is preferred that the silicone waste contains or consists of silicone elastomers and/or silicone rubbers which in turn contain filler. Silicone elastomers or silicone rubbers containing filler are also referred to as filled silicone elastomers or silicone rubbers. The filler content is preferably 5 to 75 percent by mass 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 can contain additional additives such as drying agents, adhesion promoters and catalysts and can also contain organic copolymer components.

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

The term "upcycling" in the sense of this invention therefore describes the transformation of silicone waste into higher-value products. This means that there is a material upgrading. Based on the definition in I. Vollmer et al., Angew. Chem. Int. Ed. 2020, 59, 1 5402-15423, the term "upcycling" in the sense of this invention therefore preferably describes the transformation of silicone waste into chemicals that have a higher market value than monomers or pyrolysis oil.

The term end-of-life silicones or silicone waste includes, within the scope of the teaching of the invention, all silicone-based or silicone-containing products as well as products with silicone adhesions or silicone contamination, which have almost and/or already completely reached their technical service life or durability or which would be intended for disposal for another reason. The durability or service life refers to the time that a material or an 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 durability or expiry date has almost been reached and/or exceeded (assessed according to the expected and/or already cured stage), as well as, for example, more or less old sprue and/or stamping waste from silicone rubber production or also discarded electronic scrap that contains silicone-sealed components/component groups. The term end-of-life silicones or silicone waste also includes, within the scope of the teaching according to the invention, all silicone waste, including production waste, that does not correspond to the respective desired product specification, for example injection-molded parts with deficiencies in mechanical properties, dimensions or appearance. It includes in particular all those 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 sticking or present. As already stated above, the terms “silicone waste” and “end-of-life silicones” are understood to be synonymous within the meaning of this invention.

The use of one or more depolymerization catalysts is necessary for the depolymerization of the silicone waste. As described above, at least one depolymerization catalyst (D1) and optionally additionally at least one depolymerization catalyst (D2) are used in the process according to the invention.

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 Brønsted acids, Lewis acids, Brønsted bases and Lewis bases.

It is preferred that Brønsted acids used as depolymerization catalyst (D1) or (D2) have a pKA value of at most -1.30, preferably at most -2.90, in particular at most -4.90. Brønsted acids with a pKA value 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 Brønsted acid with a pKA value of at most -2.90. Brønsted acids with a pKA value 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. Also preferred are sulfonic acid or perfluoroalkylsulfonic acid ion exchange resins.

It is preferred that such Brensted bases which are 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 Brannigan bases are selected from the group consisting of alkali metal hydroxides, amines, quaternary ammonium hydroxides, quaternary phosphonium hydroxides, phosphonitrile chlorides, phosphazenes.

Preferred alkali metal hydroxides are sodium hydroxide and potassium hydroxide.

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,

Preferred quaternary ammonium hydroxides are tetraalkylammonium hydroxides, especially tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.

Preferred quaternary phosphonium hydroxides are tetraalkylphosphonium hydroxides, especially tetramethylphosphonium hydroxide tetraethylphosphonium hydroxide

Tetrapropylphosphonium hydroxide and tetrabutylphosphonium hydroxide.

The phosphonitrile chlorides can be linear or cyclic.

The phosphazenes can be halogen-containing or halogen-free. A preferred phosphazene is tert-butylimino-tri(pyrrolidino)phosphorane.

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.

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,

tetraethylphosphonium fluoride, tetrapropylphosphonium fluoride and tetrabutylphosphonium fluoride), tetraalkylammonium chlorides (e.g. tetramethylammonium chloride, tetraethylammonium chloride, tetrapropylammonium chloride and tetrabutylammonium chloride) and

Tetraalkylphosphonium chlorides (e.g. tetramethylphosphonium chloride,

tetraethylphosphonium chloride, tetrapropylphosphonium chloride and tetrabutylphosphonium chloride), A suitable tetraalkylphosphonium compound with various alkyl radicals is, for example, tributyloctylphosphonium chloride.

The aforementioned 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.

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) is selected from Brønsted acids, preferably trifluoromethanesulfonic acid, or from Brønsted bases, preferably selected from the group consisting of alkali metal hydroxides, tetraalkylammonium hydroxides, tetraalkylphosphonium hydroxides, phosphazenes and guanidines.

B. Rupasinghe and J. C. Furgal describe in the article already cited in the introduction “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 particular suitability of fluorides as depolymerization catalysts. However, fluorides have the major disadvantage that they can damage reactors made of glass or enamel under the reaction conditions (e.g. with the formation of SiF4). Amines or ammonium compounds or their decomposition products, in turn, 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).

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 per 100 parts by weight of the silicone component of the silicone waste.

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.

Aliphatic hydrocarbons (K) are compounds that consist only of carbon and hydrogen atoms and are not aromatic. Aliphatic hydrocarbons (K) can be saturated or unsaturated, but it is preferred that aliphatic hydrocarbons (K) are saturated. This has the advantage that they are among the reaction conditions are chemically inert. The aliphatic hydrocarbons (K) can be linear or 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, ie particularly preferred aliphatic hydrocarbons (K) are branched alkanes.

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 _n H2n+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. The aliphatic hydrocarbon (K) is particularly preferably a compound of the formula C16H34, the main component of tetrabutane.

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%.

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.

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.

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.

In order to enable easy mixing, it is preferred that the at least solvent and/or the at least one hydrocarbon (K) has a kinematic viscosity of at most 1000 mm ² /s, preferably at most 500 mm ² /s, in particular at most 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 solvent and/or the at least one hydrocarbon has a kinematic viscosity of 1 to 1000 mm ² /s, preferably from 5 to 500 mm ² /s, in particular 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).

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 normal pressure (1013.25 hPa).

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.

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

Another suitable paraffin oil is commercially available from Evonik under the name TEGOSOFT® IHD BASIC. It is a mixture of branched Ci6, 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.

Tetrabutane (also known as technical tetrabutane or tetrabutane (technical)) is a mixture of branched paraffins and has hydrocarbons with 16 carbon atoms as its main component. Particularly preferred is a tetrabutane which has 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 given as a mass fraction based on the total mass. of tetrabutane. Such a tetrabutane is commercially available, for example, from the company Evonik.

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 in particular completely surrounds the silicone waste.

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.

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. In particular, process additives based on (organomodified) silicones or siloxanes have the advantage of good system solubility.

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,

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.

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.

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

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 Normal pressure (1013.25 hPa) ± 500 hPa, preferably ± 200 hPa, in particular ± 100 hPa. Step (i) can be carried out with passage or introduction of protective gas. For inerting, drying or deodorization, any vacuum up to 1 mbar can be used according to the pressure swing process. If step (i) is carried out at excess pressure, pressure-resistant equipment should be used. It is also 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.

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

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

Depolymerization catalyst (D1) is selected from Brönsted bases.

The Brönsted base or Brönsted acid used for deactivation by neutralization can be solid, liquid or gaseous.

If a gaseous base is chosen for deactivation, this is preferably ammonia. If a solid and/or liquid base is chosen for deactivation, this 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.

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

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

As the expert will understand, before processing unknown silicone waste, it is recommended to take representative samples and then test them on a laboratory and/or pilot plant scale in order to determine how high the current silicone content is and also what inevitable amount of silicone-free components can be expected. These include binding agents, plastics and, in the case of electronic waste, metals, ceramics, etc.

It is preferred that step (ii) is 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) is carried out at atmospheric pressure (1013.25 hPa). It is also preferred that step (ii) is carried out over a period of not more than 6 hours, preferably from 0.5 h to 5 h, in particular from 1 h to 3 h.

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.

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 deactivation of the depolymerization catalyst (D1) in step (ii) preferably takes place with a carbonate, in particular anhydrous sodium carbonate.

From a process engineering perspective, it is advantageous if step (ii) of the method can be omitted. It may therefore also be preferred that the method according to the invention does not comprise step (ii).

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).

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 off from the reaction mixture.

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 also 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 advisable to carry out the distillation under protective gas, preferably with a light blanket of nitrogen. The temperature and pressure are set 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 tightened and, if necessary, the yield can be increased by introducing nitrogen below the liquid level. If necessary, a preliminary distillate is taken separately before the main fraction is collected.

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 is at most 500,000 liters, preferably 30,000 liters, in particular 15,000 liters.

It is also 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 the usual packings. The at least one column can be temperature-controlled entirely or in zones, from heating to cooling. It is also preferred that, in addition to the column, at least one further cooler with temperature control that can be variably controlled by a cooling base is used. It is also preferred that a reflux divider is used in order to recirculate the distillate in whole or in part.

The term reactor is well known to those skilled in the art and therefore does not require any special explanation. A reactor is usually, and preferably in the sense of this invention, a delimited space, for example a stirred container (e.g. a stirred tank) or a tube (e.g. a flow tube as a flow reactor), in which chemical material conversions can be carried out in a targeted manner. As those skilled in the art will know, these can be open or closed containers 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 measuring volume. The reactor material can preferably be selected from suitable materials, such as advantageously glass or ceramic, preferably from metal, in particular high-alloy stainless steels, particularly preferably from Hastelloy. All of this is known to those skilled in the art. Suitable reactors preferably have devices that enable the reaction mass to be mixed. Suitable stirring means are known to the person skilled in the art and include, for example, dissolvers, propeller stirrers, anchor stirrers, beam stirrers, magnetic stirrers, cup stirrers, jet mixers or inclined blade stirrers. The reactor itself should - if not electrically heated - preferably have a heating jacket that allows coupling to a suitable heat transfer circuit (for example based on heat transfer oil or hot steam). All known means, such as double jackets, full-pipe coils or half-pipe coils and all known coolants, can be used to heat or cool the reaction mass. With regard to the operating modes, a distinction can essentially be made between continuous and discontinuous operation. Continuous processes can preferably be used for large product quantities, while batch processing is preferred for smaller product quantities. The person skilled in the art knows all this. Reactors, such as stirred tanks in particular, are in commercially available in many different ways, for example from Behälter KG Bremen GmbH & Co, Theodor-Barth-Str. 25, 28307 Bremen, Germany, or for example from Büchi AG, Gschwaderstrasse 12, 8610 Uster / Switzerland. In addition, reference is also made to the book "Chemical reactors: basics, design and simulation (German), April 19, 2017, by Jens Hagen"; also to the book "Handbook of chemical reactors, basics and applications of chemical reaction engineering, edited by Reschetilowski, Wladimir, Publisher: Springer, Berlin; 1st edition 2020"; also to the book by Klaus Hertwig, Lothar Martens: Chemical process engineering: calculation, design and operation of chemical reactors, Oldenbourg, Munich 2007.

As will be 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 according to DIN EN ISO 14067 (in particular DIN EN ISO 14067:2019-02) is less than 5, preferably less than 4.5, in particular less than 4 kg CO2 per kg cyclosiloxane.

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

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

The invention further relates to 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%.

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. The composition according to the invention is very particularly preferably (substantially) water-free. The mass fraction of water in the composition according to the invention is therefore very particularly preferably 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:

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

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

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

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

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.

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

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

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

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

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

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.

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

A further subject matter 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 preparation of silicones, preferably selected from the group consisting of organomodified siloxanes, silicone oils, silicone rubbers and

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 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, the CO2 emissions of which only relate to the manufacture of the product and not to the use of the product. 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 not present. 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 D units (with D = [R ₂ SiO ₂ /2] and R = methyl), wherein the silicones are preferably selected from the group consisting of organomodified siloxanes, silicone oils, silicone rubbers and silicone elastomers.

These silicones produced in this way, preferably selected from the group consisting of organomodified siloxanes, silicone oils, silicone rubbers and silicone elastomers, show a high quality and can be used without restriction in the usual fields of application.

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.

A further subject matter of the invention is therefore also the use of the correspondingly produced silicones, preferably selected from organomodified siloxanes, as plastic additives, defoamers, foam stabilizers (eg polyurethane foam stabilizers), emulsifiers, demulsifiers, rheology additives, hydrophobizing agents, wetting agents, textile additives, paint additives, flow additives, dispersing additives or as additives in polishes, cleaning agents and cosmetic preparations or for the production of silicone release coatings. examples

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

General methods:

Nuclear magnetic resonance spectroscopy (NMR spectroscopy):

The characterization of organosiloxanes can be carried out using ¹ H and ²⁹ Si NMR spectroscopy. These methods, particularly taking into account the multiplicity of the couplings, are familiar to the person skilled in the art.

Gas chromatography:

The gas chromatographic measurements (GC measurements) were carried out in accordance with DIN 51405 (issue date January 2004). A gas chromatograph with FID detector and capillary column (HP1 from Agilent) is used. 200 mg of sample substance are dissolved in 10 ml acetone p.a. and dodecane (>99.8%) is used as an internal standard.

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

Raw materials:

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

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

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

TEGOSOFT® IHD BASIC: Mixture of branched Ci6-, C20- and C24-alkanes (Evonik)

TEGO® Antifoam MR 1015: defoamer (Evonik)

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

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

Photoinitiator TEGO® A18: Photoinitiator (Evonik)

Example 1 (according to the invention)

309.7 g of a pasty, addition-curing LSR compound with approx. 50% SiO2 filler content are weighed using a cartridge into a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer and a heating mantle with an integrated thermocouple. 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. After adding a further 50 g of tetrabutane, the mixture is stirred for 6 hours at 90 °C. After cooling to 60 °C, 3.3 g of sodium carbonate are added and stirred for 3 hours at 60 °C. 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 and the pressure is gradually reduced to 25 mbar and distilled for 2.5 hours. The total distillate yield is 83.2 g. The mixture is then distilled at 15 mbar for one hour and at 10 mbar for a further 2.5 hours. 83.2 g of distillate are obtained. According to ¹ H and ²⁹ Si NMR analysis, the distillate contains 5.4% of the solvent used; 17.3% hexamethylcyclotrisiloxane (D3), 66.5% octamethylcyclotetrasiloxane (D4) and 10.8% decamethylcyclopentasiloxane (D5).

Example 2 (according to the invention)

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 a solvent, 11.4 g of hexamethyldisiloxane and 1.0 g of trifluoromethanesulfonic acid, the mixture is first heated to 80 °C while stirring and, after stirring for 1 hour, further heated to 100 °C. After stirring for 5.5 hours 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. Then the reflux condenser is replaced by a Vigreux column and distillation bridge, 5.11 g of tetramethylammonium hydroxide monohydrate are added, stirred for 30 min at 100 °C and then the pressure is reduced to 30 mbar to 20 mbar. The distillate foreshots are disposed of and then distilled at 100 °C to 111 °C and 9 mbar to 7 mbar for a total of 11 h. 128 g of distillate are obtained. According to ¹ H and ²⁹ Si NMR analysis, the distillate contains 1.1% of the solvent used; 17.3% hexamethylcyclotrisiloxane (D3), 74.2% octamethylcyclotetrasiloxane (D4) and 7.0%

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

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

Example 3b (according to the invention)

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 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.

Example 3c (according to the invention)

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.

Example 4 (according to the invention)

300 g of shredded, colorless silicone tubing are placed in a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer and a heating mantle with integrated thermocouple. After adding 50 g of a trimethylsiloxy-terminated silicone oil with a viscosity of 10 mm ² /s, 300 g of TEGOSOFT® IHD BASIC as solvent and 8.8 g of 40% aqueous tetrabutylphosphonium hydroxide solution, the mixture is stirred for 4 h at 110°C with initial foaming, with a further 75 g of 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. Then, at 106 °C to 108 °C and 7 mbar to 6 mbar over 11 h, 184 g of distillate are obtained. According to ¹ H and ²⁹ Si NMR analysis, 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)

In a 500 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer and a heating mantle with integrated thermocouple, 318 g of a cyclosiloxane mixture with a purity of 97.7% prepared according to Example 4, 0.37 g of trifluoromethanesulfonic acid and 60.24 g of a silicone acrylate prepared according to EP 0940422 B1 Example 1 are introduced one after the other with stirring and stirred at 100 °C for 10 h. After cooling to 70 °C, 2.65 g of anhydrous sodium carbonate are added and 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 of 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.

Example 6a (according to the invention)

In a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer and a heating mantle with 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 are placed with stirring, 0.56 g of trifluoromethanesulfonic acid is added and the mixture is stirred at 40 °C for 2 hours and then stirred for a further 14 hours at room temperature. Then 8.4 g of sodium hydrogen carbonate is added and the mixture is stirred at room temperature for 2 hours. After filtration, a colorless, clear hydrogen siloxane with an SiH content of 3.4 mmol/g and a viscosity of 10.1 mPa s at room temperature was obtained.

Example 6b (according to the invention)

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 manometer and a heating mantle with an integrated thermocouple and mixed with 3 ppm of platinum in the form of the Karstedt catalyst. After inerting 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 kept at approx. 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)

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, and 0.45 g of 50% aqueous chromium(III) acetate solution are added. The mixture is heated to 65 °C while stirring and the epoxysiloxane from example 6b is added over the course of 1 h. The temperature was continuously increased to 90 °C during the addition and then stirred at 95 °C for 5 h. When 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.

Example 7 (not according to the invention)

286 g of decamethylcyclopentasiloxane (D5), 13.9 g of hexamethyldisiloxane and 30 g of silicone oil 10 are placed 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. 203 g of a pasty, addition-curing LSR compound with approx. 50% SiO2 filler content are added in four portions using a cartridge and heated to 90 °C while stirring. After adding 15 g of potassium methylate, the reaction mixture is heated step by step to 140 °C and distillation is started at 890 mbar. After 1 h of distillation, the bottoms are gelled. 153 g of distillate were obtained, which according to ²⁹ Si-NMR consists of 95.3% decamethylcyclopentasiloxane (D5).

Example 8 (not according to the invention)

In a 500 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer and a heating mantle with 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 approx. 50% SiO2 filler content are heated to 90 °C with stirring and stirred for 2 hours. After adding 1.6 g of anhydrous sodium carbonate, the mixture is stirred for 2 hours at 60 °C and filtered through a coarse pleated filter. 250 g of the filtrate are heated to 100 °C with stirring and 7.5 g of finely ground potassium hydroxide are added. After stirring for 30 minutes at 100 °C, a vacuum is applied and the temperature is increased. Distillation is carried out for 1.5 hours at 115 °C to 150 °C and 715 mbar to 600 mbar. After 1.5 hours of distillation, the bottom product is gelled. 152 g of distillate were obtained, which according to ¹ H-NMR consists mainly of isononanol. Example 9 (not according to the invention)

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 approx. 50% SiO2 filler content are heated to 100 °C with stirring. After adding a further 22.6 g of silicone oil 5 and 105 g of pasty, addition-curing LSR compound, stirring is continued. After adding 11.3 g of silicone oil 5, stirring is continued 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 stirring is continued for 2 hours. The mixture is filtered off using a lacquer filter with a pore size of 125 pm. 127 g of the filtrate are heated to 190 °C with 2.5 g of concentrated sulfuric acid while stirring, and 2 mL to 3 mL of distillate are 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.

Example 10 (not according to the invention)

300 g of shredded, colorless silicone tubing are placed in a 1000 mL four-necked glass flask equipped with a stirrer, a reflux condenser, a manometer and a heating mantle with integrated thermocouple. 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 is heated to 125 °C with stirring and stirred for 3 h. The silicone parts have not dissolved.

Example 11 (not according to the invention)

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 for 6 h at 100°C. After adding 3.5 g of anhydrous sodium carbonate, the mixture is stirred for 1 h at 100°C. The reflux condenser is then replaced by a Vigreux column and distillation bridge, 17.7 g of 40% aqueous tetrabutylphosphonium hydroxide solution are added and the mixture is distilled at 85 °C to 100 °C and gradually reduced to a pressure of 10 mbar. After 2.5 hours of distillation, the sump has dried out, can be separated from the rim of the flask as dark lumps and weighs 432 g. 823 g of distillate are obtained. According to ¹ H and ²⁹ Si NMR analysis, 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)

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 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 and stirred for 6 hours at 100 °C. After adding 6.6 g of anhydrous sodium carbonate, stir for 2 hours at 70 °C. The reflux condenser is then replaced by a Vigreux column and distillation bridge 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 minutes, then the distillation stops and the viscosity of the sump increases. A further 7.5 g of 40% aqueous tetrabutylphosphonium hydroxide solution are added and another 14.7 g of distillate can be obtained before the distillation stops again and the experiment is aborted. The amount of distillate is only 30% of the theoretical amount and also consists of a water phase and a silicone phase. According to ¹ H and ²⁹ Si NMR analysis, the distillate contains 7.7% hexamethylcyclotrisiloxane (D3), 78.3% octamethylcyclotetrasiloxane (D4) and 12.2% decamethylcyclopentasiloxane (D5).

Application-technical testing:

Production of release coatings:

The application testing of the silicone acrylates from Examples 5 and 6c according to the invention is carried out in formulations for release coatings. Release coatings are known from the prior art, in particular as abhesive coatings on flat substrates and specifically for their use in adhesive tapes or label laminates.

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

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).

The coating masses produced in this way are applied to a flat carrier. In all application examples, this consists of a 50 cm wide, biaxially stretched polypropylene film (BOPP), which was subjected to corona pretreatment with a generator output of 1 kW before the coating mass was applied. The coating masses are applied using a 5-roll coating machine from COATEMA® (Coating Machinery GmbH, Dormagen, Germany) with a basis weight of approx. 1 g/m 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.

The samples coated in this way are tested for rub-off, release value and residual adhesive strength.

Rub-off:

The adhesion of the hardened coating to the carrier material is checked by rubbing the coating vigorously with the thumb. If there is insufficient adhesion, abrasion will form in the form of rubbery crumbs. Such crumbs should not form even with intensive rubbing. The test is carried out by a trained panel. The evaluation is categorized in ranges from 1 to 5, with 1 representing very good adhesion to the carrier material and 5 representing rather poor adhesion.

cut-off value:

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 describing a 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, the same adhesives and test conditions should therefore 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 in accordance with the FINAT Handbook 8th Edition, The Hague/NL, 2009 under the designation FTM 10, with the change 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 average of a five-fold determination and are given in the unit [cN / 2.5 cm]. Systems with a release value below 10 cN / 2.5 cm are considered easy release and are usually suitable for many applications such as label laminates.

residual adhesive strength:

The residual adhesive strength (short-term residual adhesive strength: KUR) is carried out according to the test specification from FINAT Handbook 8th Edition, The Hague/ NL, 2009 under the designation FTM 11, with the difference that the test adhesive strip is stored in silicone contact for one minute and the standard surface is an untreated BOPP surface. The adhesive tape used is tesa® 7475 (trademark of Tesa SE, Germany, Hamburg). The residual adhesive strength is a Measure of the cross-linking of the silicones. If non-polymerized and therefore migratable silicone components are present, the residual adhesive strength values achieved become increasingly lower as the proportion of such components increases. Values over 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.

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 %).

The examples show good curing, as can be seen from the short-term residual adhesive strengths (KUR). The release values also show an expected picture of low and high release values, depending on the acrylate density and functionalization. For a good rub-off, a silicone component with a high acrylate density is necessary, so example A only shows inadequate rub-off quality, while examples B and C show 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 a portion 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 per 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 the at least one aliphatic hydrocarbon (K) determined according to ASTM D972 after 22 hours 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 the at least one aliphatic hydrocarbon (K) determined according to ASTM D5800 after 1 hour 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 the at least one aliphatic hydrocarbon (K) determined according to DIN 51581 after 1 hour 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. Process according to 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. Process according to 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 is carried out at normal 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 Brönsted base, provided that the at least one depolymerization catalyst (D1) is selected from Brönsted acids; or b) is deactivated with at least one Brönsted acid, provided that the at least one depolymerization catalyst (D1) is selected from Brönsted bases. 11. Process according to 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 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 one of claims 1 to 12 or using the composition according to claim 14. 17. Use of the silicones produced according to claim 15 or the silicones according to claim 16, preferably selected from organomodified siloxanes, as plastic additives, defoamers, foam stabilizers, emulsifiers, demulsifiers, rheology additives, hydrophobizing agents, wetting agents, textile additives, paint additives, flow additives, dispersing additives or as additives in polishes, cleaning agents and cosmetic preparations or for the production of silicone release coatings.