METHOD FOR PRODUCING END-SEALED LIQUID SILOXANES FROM SILICON WASTE

Description

[0001] The invention lies in the field of silicones, in particular it relates to a process for the production of end-sealed, liquid siloxanes such as alkoxysiloxanes, hydrogen siloxanes, chlorosiloxanes, polydimethylsiloxanes or vinylsiloxanes from silicone waste, in particular comprising silicone elastomers and / or silicone rubber, by their acid-catalyzed depolymerization in a solvent-free reaction system.

[0002] In connection with this invention, the designations M, D, T, and Q for organopolysiloxane building blocks are also used. For a reference to their meaning, see W. Noll, Chemie und Technologie der Silicones (Chemistry and Technology of Silicones), Verlag Chemie, Weinheim Bergstr., 1960, p. 2 ff.

[0003] Due to their unique material properties, silicone components meet specific requirements in the medical, pharmaceutical, and food industries. When processed correctly, they are completely physiologically inert. Silicone products are therefore found in food applications, medicine, and pharmaceuticals. Baby pacifiers and bottle nipples are made of silicone, as are diving masks. In technical industrial applications, silicone frequently appears as a material for seals or, in dynamic applications, for membranes. In the automotive sector, it is used for hoses, sheathing, and cable insulation.

[0004] Regarding its mechanical properties, silicone has a decisive advantage over other types of rubber: Silicone maintains relatively stable properties over a very wide temperature range, whereas the mechanical properties of many other materials deteriorate significantly in cold or hot conditions. For example, while an EPDM material may appear superior to a silicone compound in terms of its mechanical properties when viewed according to its technical data sheet (which specifies properties at room temperature), the opposite is true at high or low temperatures. Silicone's temperature resistance in air is approximately -80°C to 250°C. This property is frequently used for seals, as the very low compression set typical of silicone is particularly advantageous in this application.

[0005] Due to their excellent ozone, UV, and weather resistance, silicone compounds are frequently used in outdoor applications. Furthermore, silicone is highly flame-resistant and possesses both good electrical insulation and conductivity. Chemically, silicone is 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 exhibits very high gas permeability.

[0006] Besides 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 IIa medical devices) or long-term implants (for 30 days or more in Class IIb medical devices), where they fulfill critical functions in devices such as cardiac catheters, pacemakers, ventilators, neurostimulators, and defibrillators.

[0007] Silicone rubber intended for long-term implants is offered by only a very few manufacturers worldwide (e.g., NuSil Technology). The production of these compounds is subject to 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.

[0008] A key advantage of silicone is its biocompatibility, meaning it is well-tolerated by humans. The biocompatibility of a silicone compound is often demonstrated through USP Class VI classifications (USP stands for United States Pharmacopeia) or through testing according to the stricter (DIN EN) ISO 10993 standard. ISO 10993 is primarily used for testing medical devices intended for long-term or permanent implantation in the human body. For shorter-term applications, USP Class VI classification, or possibly a lower classification, is sufficient.

[0009] Furthermore, due to its ability to be used in a wide temperature range from approximately -80°C to approximately 250°C, silicone offers the possibility of steam sterilization (heating in an autoclave). Silicone products can thus be freed from living microorganisms, their resistant forms, viruses, etc. The excellent electrical insulating properties of silicone are also of particular importance in the medical field.

[0010] By varying the silicone rubbers used and the crosslinking methods, silicones can acquire special properties. For example, HTV silicone rubbers are flexible and resistant across a wide temperature range from -50°C to 200°C, and in some cases up to 300°C. They are found in seals in the automotive and food industries, in cable sheathing, and as damping material.

[0011] RTV silicone rubbers are valued primarily for their thermal conductivity and electrical insulation properties, which is why they are preferably used in the electrical and electronics sector.

[0012] Liquid silicone rubbers (also known as LSR) have a lower viscosity than HTV and RTV silicone rubbers. They can be injection-molded into a wide variety of shapes and processed into products such as silicone tubing. Because LSR silicones are always platinum-cured, products based on liquid silicones can be used in medical technology applications.

[0013] Thanks to its high stability within the human body, silicone thus provides very good protection for critical components and, due to the aforementioned properties, is also preferred for functional parts.

[0014] The fundamental difference between silicone rubber and other organic elastomers lies in the fact 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 being used primarily as a filler to achieve good properties.

[0015] Based on their state of matter and vulcanization temperatures, silicone rubbers can be divided into three groups: Silicone rubbers whose raw material is solid are referred to as HTV (high temperature vulcanizing) or HCR (high consistency rubber). They are typically vulcanized at high temperatures between 140°C and 200°C. Crosslinking occurs through peroxides or by addition reactions, with platinum compounds being used as catalysts.

[0016] Liquid silicone rubber, or LSR (Liquid Silicone Rubber), is a viscous raw material consisting of two components that are mixed immediately before processing. Curing occurs through an addition reaction at similar temperatures to HTV types, although the curing process is generally much faster.

[0017] Both silicone types can be colored. Finished elastomer articles made from HTV silicone and LSR silicone hardly differ in their properties.

[0018] The third group consists of so-called RTV silicones (room temperature vulcanizing). With these, cross-linking occurs at room temperature. They are often used as adhesives and / or sealants or in prototype manufacturing. They are available as both one-component and two-component systems.

[0019] While the performance characteristics derived from the exceptional chemical stability of silicones are advantageous for the service life of objects manufactured from them, their stability is a disadvantage when it comes to disposal at the end of their life cycle (end-of-life silicones or silicone waste). The terms silicone waste and end-of-life silicones are used synonymously within the meaning of this invention.

[0020] Laine et al., in ACS Omega 2019, 4, 3782-3789, describe the efforts undertaken to date to integrate silicones into the circular economy. In this article (page 3783, top left, lines 1 to 4), they state that the chemical recycling of silicones has focused on the depolymerization of silicone fluids and cross-linked silicone rubbers with the aim of obtaining monomers that can then be (re)polymerized, replacing new material. Assessing the relevant state of the art, the authors conclude that no technical solution for true recycling is currently available and state that a process would be attractive that allows for near-quantitative yields with low energy and cost input while almost completely preserving the original properties.A closed-loop process, in which the recycled silicone is even returned to its original application, would therefore be all the more attractive. Downcycling, particularly with silicone resins—that is, accepting the loss in value of recovered material resulting from its limited reuse in lower-quality products—is current industrial practice. Laine et al. focus on the production of a special copolymer of dodecaphenylsilsesquioxane and octamethylcyclotetrasiloxane in tetrahydrofuran by the action of tetrabutylammonium fluoride followed by thermal curing, and demonstrate that this material can also be broken down again by the action of tetrabutylammonium fluoride in THF.

[0021] Also highlighting the current state of the art in siloxane depolymerization towards recycling and reuse, and specifically focusing on the unique characteristics of the silicone copolymer chosen by Laine et al., JC Furgal and B. Rupasinghe, in their article "Full Circle Recycling of Polysiloxanes via Room-Temperature Fluoride-Catalyzed Depolymerization to Repolymerizable Cyclics," ACS Appl. Polymer Materials, March 10, 2021 (https: / / dx.doi.org / 10.2021 / asapm.0c011406), review the broad technical challenge of silicone recycling and apply the tetrabutylammonium fluoride catalysis described by Laine to commercial silicones. These depolymerizations consistently yield cyclic products (4-, 5-, and 6-membered rings).

[0022] EP 3744774 A1 also details how the experiments and work on recycling silicone waste described in the prior art yielded only unsatisfactory results. Since a technically feasible and attractive route for the material recycling of both silicone oils and solid silicones was lacking, this document proposes a process for recycling silicones by their chemical transformation into siloxanes and / or silanes containing acetoxy groups. This process involves subjecting the silicones to be recycled to heat treatment in digestion systems comprising acetic anhydride and / or acetoxysiloxane, as well as at least one Brønsted acid, preferably with the addition of acetic acid.

[0023] The unpublished European patent application with application number 20202477.4 describes an upcycling process for the production of acidic, end-equilibrated siloxanes with chain lengths greater than 3 silicon atoms, containing acetoxy groups, from end-of-life silicones, in particular comprising silicone adhesives and / or sealants and / or silicone rubber and / or silicone oil waste, by thermal digestion of the end-of-life silicones in an acidic reaction medium comprising acetic anhydride, acetic acid, and at least one other Brønsted acid with a pKa value < 4, wherein the digestion takes place in a reactor with a volume of at least 1 liter. The end-equilibrated siloxanes with chain lengths greater than 3 silicon atoms obtained in this way can be used directly as starting material for the synthesis of new high-quality silicone products, in particular for the production of surfactants.

[0024] As progressive as the teachings of the latter two publications are with regard to the increase or preservation of value of the recycled silicone material that can be achieved with them, the functionality obtained in the upcyclate or recyclate remains limited to the Si-acetoxy function and, as EP 3744774 A1 explains, additional synthesis steps are required, such as the conversion of the acetoxy function into an OH group or the conversion of the acetoxy function into an alkoxy group, in order to obtain further Si-bound functionalities.

[0025] In other words, in view of this state of the art, the universality of recycling processes can be improved to the extent that, starting from silicone waste, one can obtain end-capped siloxanes in just one step and with relatively low energy and cost input, in which the terminal silicon atom of the recyclate carries in particular the alkoxy function, the hydrogen function, the chlorine function, the methyl or the vinyl function.

[0026] Surprisingly, it has now been found that the production of end-capped siloxanes from silicone waste, preferably from silicone adhesives and / or sealants, as well as from silicone rubber, is successful through their acid-catalyzed depolymerization into alkoxysiloxanes, hydrogen siloxanes, chlorosiloxanes, polydimethylsiloxanes and / or vinylsiloxanes.

[0027] The invention relates to a process for producing end-capped liquid siloxanes with chain lengths greater than 3 silicon atoms from silicone waste, in particular comprising silicone elastomers and / or silicone rubbers, by their acid-catalyzed depolymerization in a solvent-free reaction system, which comprises at least one end-group MR<-providing compound, as well as at least one D-unit-providing compound, and at least one Brønsted acid.

[0028] In the context of this invention, the term "end-group MR< supplying compound" is understood to mean, in particular, an organosilicon compound having at least one silicon atom, which, when applying the process according to the invention, contributes one or two methyl groups and / or one or two chlorine atoms and / or one or two hydrogen atoms and / or one or two vinyl groups and / or one or two alkoxy groups, preferably one or two ethoxy groups and / or one or two methoxy groups, to terminal saturation, i.e., to the bonding saturation of the a- and w-positions of the desired end-sealed liquid siloxane."End-closed" within the meaning of this invention therefore means that the liquid siloxanes resulting according to the invention, with chain lengths > 3 silicon atoms, are substituted in their α,ω positions with methyl groups and / or chlorine atoms and / or hydrogen atoms and / or vinyl groups and / or alkoxy groups, in particular ethoxy groups and / or methoxy groups. Specifically excluded according to the invention are all chemical compounds providing acetoxy groups.

[0029] Liquid siloxanes are those that are liquid under standard conditions (T = 25°C, p = 1013 hPa).

[0030] According to the invention, the end-group MR<-providing compound comprises hexamethyldisiloxane, polydimethylsiloxanes, poly(methyl-hydrogen)siloxane, poly(methyl-hydrogen)polydimethylsiloxane copolymer, trimethylchlorosilane, dimethyldichlorosilane, dichlorotetramethyldisiloxane, α,ω-dichloropolydimethylsiloxane, monoa-ikoxytrimethylsilane, in particular monomethoxytrimethylsilane or monoethoxytrimethylsilane, dialkoxydimethylsilane, in particular dimethoxydimethylsilane or diethoxydimethylsilane, α,ω-dialkoxypolydimethylsiloxane, in particular α,ω-dimethoxypolydimethylsiloxane or α,ω-diethoxypolydimethylsiloxane, tetramethyldisiloxane, α,ω-dihydrogenpolydimethylsiloxane, divinyltetramethyldisiloxane or α,ω-Divinylpolydimethylsiloxanes, or mixtures of the aforementioned compounds.

[0031] According to a preferred embodiment of the invention, the D-unit-providing compound comprises in particular at least one cyclosiloxane selected from hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane and / or dodecamethylcylohexasiloxane and / or a siloxane containing D-groups, as referred to in the end-group MR<-providing compounds; in particular, the D-unit-providing compound is selected from one or more of the aforementioned compounds.

[0032] The acid-catalyzed, solvent-free depolymerization according to the invention is preferably carried out in the temperature range of 30°C to 150°C, preferably in the temperature range of 45°C to 130°C and, in the case of the decomposition-labile α,ω-dihydrogenpolydimethylsiloxanes, particularly preferably in the temperature range of 35°C to 80°C.

[0033] Surprisingly for the person skilled in the art, the depolymerization of silicone waste to end-sealed siloxanes according to the invention proceeds quite rapidly under mild temperature conditions, which astonishingly enables synthetic access to the sensitive α,ω-dihydrogenpolydimethylsiloxanes without SiH loss in just one step (see example 3 according to the invention).

[0034] The method according to the invention is preferably carried out over a period of 1 hour to 10 hours, preferably from 2 hours to 8 hours, and particularly preferably from 3 to 6 hours.

[0035] The Brønstedt acid used according to the invention is preferably selected from protic acids with a pKa value of less than 1.30, such as preferably nitric acid, methanesulfonic acid and / or p-toluenesulfonic acid, preferably protic acids with a pKa value of less than 2.90, such as preferably concentrated sulfuric acid, particularly preferably protic acids with a pKa value of less than 4.90, such as preferably perfluoroalkanesulfonic acids like heptafluoropropanesulfonic acid, pentafluoroethanesulfonic acid, trifluoromethanesulfonic acid, perchloric acid and / or chlorosulfonic acid, wherein perfluoroalkanesulfonic acids are particularly preferred, and wherein trifluoromethanesulfonic acid is particularly preferred, and / or preferably sulfonic acid or perfluoroalkylsulfonic acid ion exchange resins.

[0036] The Brønstedt acid used according to the invention is preferably used in amounts of 0.05 to 3 percent by weight, preferably 0.1 to 1.0 percent by weight, and particularly preferably 0.2 to 0.8 percent by weight based on the total silicone content of the reaction system.

[0037] The inventive method can be carried out on both liquid-viscous and partially or completely cured silicone waste.

[0038] In a preferred embodiment of the invention, in the case of particularly fully cured silicone waste, the comminution into lumpy material is provided, which at the end of the comminution preferably has a diameter of 1 to 10 mm, in particular of 3 to 6 mm.

[0039] To achieve this target geometry, the silicone waste can advantageously first be cold-embrittled by contact with, for example, liquid nitrogen or dry ice pellets, i.e., significantly reduced in its elasticity, and then appropriately crushed.

[0040] According to the invention, the optional comminution of the cold-embrittled 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.

[0041] As is obvious to those skilled in the art, the inventive method for achieving effective mixing of the reaction system in acid-catalyzed, solvent-free depolymerization is preferably carried out in reactors that have appropriate stirring devices and / or shearing internals.

[0042] According to a preferred embodiment of the invention, the method relates to a process for the recycling or upcycling of silicone waste, in particular silicone adhesives and / or sealants, and silicone rubber waste. According to a further preferred embodiment of the invention, the silicones to be recycled have molar masses > 236 g / mol.

[0043] According to a particularly preferred embodiment of the invention, the process 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, and in particular silicone adhesive and / or silicone sealant residues in and / or on polyolefin containers, preferably PE containers, more 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 squeezed out, wherein the container shell is usually made of HDPE (high-density polyethylene) and the semi-transparent container parts (piston and dispensing tip) are usually made of LDPE (low-density polyethylene). HDPE and LDPE are familiar to experts.HDPE has a high density between 0.94 g / cm³ and 0.97 g / cm³; LDPE, on the other hand, has a lower density between 0.915 g / cm³ and 0.935 g / cm³.

[0044] The process according to the invention thus offers a further significant advantage: the essentially pure recycling of polyolefin, preferably polyethylene, in particular high-density polyethylene (HDPE), which is obtained from preferably used silicone adhesive and silicone sealant cartridges. More generally, it enables the recycling of silicone-contaminated polyolefin waste, preferably PE waste, by providing acidic alkoxysiloxanes, hydrogen siloxanes, chlorosiloxanes, polydimethylsiloxanes, and / or vinylsiloxanes with chain lengths greater than three silicon atoms, with essentially pure recovery of polyolefin, preferably polyethylene.

[0045] The significance and scale of the specific problem of silicone contamination in HDPE waste is highlighted, among other things, by a study from Ketenakkoord Kunststofkringloop en Afvalfonds Verpakkingen, "Kitkokers in een circulaire economie," by I. Gort and S. Haffmans, dated May 1, 2017 (available from Kennisinstituut Duurzaam Verpakken, Zuid Hollandlaan 7, 2596 AL The Hague, Netherlands, or on their website at https: / / kidv.nl / , specifically https: / / kidv.nl / media / rapporttages / kitkokers_in_een_circulaire_economy.pdf?1.1.2-rc.1), which illustrates the dramatic effects that even small amounts of silicone contamination can have on the reusability of recycled granules derived from waste. Thus, silicone components migrate even through the fine, 150-µm melt sieves of a granulate-producing extruder and thereby enter the re-granulate, ultimately causing production errors at the plastics processor who, for example, blow-extrudes plastic hoses.It has been observed that even a single silicone particle can cause surface defects and holes in the polymer, potentially rendering an entire production batch unusable. The contaminated HDPE is of inferior quality and can therefore only be used for non-critical applications.

[0046] These silicone-contaminated cartridge recyclates are currently only acceptable when processed into rough objects such as insulation walls, scaffolding planks, boundary posts, railway sleepers, and picnic tables, where the presence of silicone particles is less noticeable because a smooth surface is not necessarily expected. However, the study in question places no hope in the material recycling of the silicone component.

[0047] Silicone residue, especially from used and therefore partially emptied silicone sealant cartridges, adheres stubbornly to the surrounding cartridge wall, as well as to the plunger and nozzle, depending on the stage of the curing process. It is not easy, and certainly not completely, to remove it from the predominantly used HDPE. According to the study, all parts of a sealant cartridge are made of polyethylene, with the outer casing being HDPE and the semi-transparent parts (plunger and nozzle) often made of LDPE (low-density polyethylene).

[0048] According to the invention, it has now surprisingly been found that the fully cured silicone residues remaining in the cartridge can be completely removed from polyolefin, preferably HDPE and LDPE, by subjecting the preferably comminuted, e.g. cut into small pieces, sealant cartridge to a digestion in an acidic reaction medium comprising at least one end-group MR< supplying compound, as well as at least one D-unit supplying compound and at least one Brønsted acid.

[0049] In this process, the silicone residues detach completely from the carrier material, which is then obtained as an almost pure, silicone-free polyolefin, preferably HDPE or LDPE, by filtration and, if necessary, washing and drying.

[0050] The silicone released in this process is preferably transformed into an acidic alkoxysiloxane or hydrogen siloxane, chlorosiloxane, polydimethylsiloxane or vinylsiloxane with a chain length greater than 3 silicon atoms.

[0051] Thus, the method discovered according to the invention additionally opens up the technical possibility of obtaining, in addition to pure polyolefin, preferably HDPE, high-quality reactive siloxanes from inferior, problematic silicone waste in the sense of upcycling, which can be processed into valuable, surface-active additives.

[0052] End-of-life silicone sealant cartridges, with their silicone residues, can advantageously first be cold-embrittled by contact with, for example, liquid nitrogen or dry ice pellets, meaning their elasticity is significantly reduced, and then suitably crushed. The crushing of cold-embrittled silicone sealant cartridges can be carried out, for example, using a crusher, shredder, mill, hammer mill, rollers, kneading machine, or cutting machine. At the end of the crushing process, the small-sized, silicone-coated cartridge material preferably has edge lengths of 1 to 10 mm, particularly 3 to 6 mm. According to the invention, the crushed material can preferably be immediately subjected to acid-catalyzed depolymerization in a system comprising at least one end-group-providing compound, at least one D-unit-providing compound, and at least one Brønsted acid.

[0053] Less preferred, however, one can also, for example, in accordance with the teaching of WO 2008 / 097306 A1, subject the small-sized, silicone-containing cartridge material to a preliminary separation by introducing it into a liquid whose density lies between that of the silicone and the cartridge plastic, thus leading to a density separation of cartridge material and silicone components (corresponding to the formation of density-separated layers).

[0054] The limitations of this type of pre-separation are demonstrated, among other things, in the study by Ketenakkoord Kunststofkringloop en Afvalfonds Verpakkingen (see, pp. 22 and 34). For example, the separation efficiency in density separation decreases due to occluded air inclusions in the silicone, which cause buoyancy and result in more or less significant proportions of silicone ending up back in the plastic layer.

[0055] Preferably, the acid-catalyzed depolymerization is carried out in a reactor with a volume of at least one liter. Taking into account the aggressive nature of the reaction medium according to the invention, the reactor material is preferably selected from glass or ceramic, more preferably from metal, preferably high-alloy stainless steels, and particularly preferably from Hastelloy.

[0056] The reactor itself should – unless electrically heated – preferably have a heating jacket that allows coupling to a suitable heat transfer circuit (for example, based on heat transfer oil or superheated steam).

[0057] Preferably, the small-sized, silicone-coated cartridge material is moved in the acidic reaction medium by using an effective stirring device to ensure intensive contact and facilitate the removal of the silicone from HDPE / LDPE.

[0058] If the silicone sealant contains filler materials, these are also released by the acid-catalyzed depolymerizing reaction of the silicone with the HDPE or LDPE. At the end of the digestion process according to the invention, the small HDPE or LDPE particles can be separated from the liquid, end-sealed siloxane containing the filler material, for example, by filtering using a coarse sieve. The siloxane can then be separated from the solid, finely divided filler, for example, by allowing it to settle.

[0059] According to the invention and without diminishing the presented teaching, further solutions can naturally be found for the advantageous embodiment of the basic process engineering operations discussed here, such as filtration or centrifugal separation of the filler from the end-sealed, liquid siloxane.

[0060] Traces of silicone can be removed from the small HDPE or LDPE particles by suitable washing, for example by close contact with solvents, separation of these and subsequent drying of the pure polymer(s).

[0061] 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, which have almost and / or completely reached their technical lifespan or durability, or which would otherwise be destined for disposal. Durability or lifespan refers to the time a material or object can be used without the replacement of core components or complete failure.Within the scope of the invention, this also includes silicone adhesives and silicone sealants, for example in cartridges, whose expiration date is almost reached and / or has been 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 waste containing silicone-sealed components / component groups. Within the scope of the invention, the term "end-of-life silicones" or "silicone waste" also encompasses all silicone waste, including production waste. It particularly includes all those silicones or silicone-containing parts or parts with silicone adhesions or silicone contamination that are otherwise intended for ordinary disposal and are accordingly considered waste. It thus includes, for example,This also includes silicone adhesive and / or sealant cartridges intended for disposal, in particular used silicone adhesive and / or sealant cartridges in and on which silicone residues are still adhering or present. As stated above, the terms "silicone waste" and "end-of-life silicones" are to be understood synonymously within the meaning of this invention.

[0062] For the purposes of the present invention, the term "acidic depolymerization" encompasses the process of transforming the end-of-life silicones in the reaction system according to the invention, in particular into acidic alkoxysiloxanes, hydrogen siloxanes, chlorosiloxanes, polydimethylsiloxanes and / or vinylsiloxanes with chain lengths greater than 3 silicon atoms, preferably with the supply of thermal energy, more preferably comprising a corresponding heat treatment of the silicone waste at temperatures advantageously from 30°C to 150°C, preferably in the temperature range from 45°C to 130°C, and in the case of the decomposition-labile α,ω-dihydrogen polydimethylsiloxanes, particularly preferably in the temperature range from 35°C to 80°C.

[0063] Several prior art documents are dedicated to the de-siliconization of components, which are located in the field of electronic parts or discarded electronic waste (JP H04 318075 A and US 6.652.665 B1) or in synthetic fiber fabrics made of polyamide or polyester specifically for airbags (US 2010 / 0012623 A1 and EP 0950684 A2).

[0064] JP H04 318075 A teaches the removal of cured silicone resins from hard, insensitive substrates at room temperature, such as glass-epoxy and ceramic substrates, using a mixture consisting of aliphatic hydrocarbons, chlorinated aliphatic hydrocarbons and monocyclic aromatics, acetone, methyl ethyl ketone, cyclohexanone, acetic acid - n-butyl acetates or a mixture consisting of the aforementioned solvents or tetrahydrofuran with dodecylbenzenesulfonic acid, wherein the solvent content ranges from 40 to 90% by weight and the dodecylbenzenesulfonic acid content ranges from 60 to 10% by weight.

[0065] The teaching of US 6,652,665 B1 also aims at the removal of silicone deposits from electronic parts and uses quaternary ammonium fluorides in a hydroxyl-group-free, aprotic solvent as a washing solution for this purpose.

[0066] In US patent 2010 / 0012623 A1, Mignani refers to a delamination process for objects such as airbags, in which the silicone-coated substrate is separated from the silicone by dissolving or suspending it with an aqueous solution of an alkali or alkaline earth metal hydroxide in the presence of a phase transfer catalyst, optionally with heat treatment.

[0067] Also focusing on the utilization of polyamide, a valuable material specifically contained in airbag waste, EP 0950684 A2 deals with the processing of silicone resin-containing polyamide material by treating it with alkali hydroxide under heating, separating the solid material from the solution and neutralizing the solid material with phosphoric acid.

[0068] None of the aforementioned de-siliconizing processes, however, deals with the value-adding transformation of the silicone component to be removed, and in particular with the provision of high-quality end-sealed siloxanes that are suitable, for example, for the direct production of surfactants.

[0069] The method claimed according to the invention takes this circumstance into account and, in addition to the recovery of these silicone-bearing materials which are considered valuable, also allows the upcycling of the detached silicone preferably to a Brønsted acid alkoxysiloxane, hydrogen siloxane, chlorosiloxane, polydimethylsiloxane or vinylsiloxane with chain lengths greater than 3 silicon atoms, which can be used as reactive siloxanes for a variety of subsequent reactions.

[0070] In the context of this invention, the term "upcycling" thus denotes the transformation of silicone waste into higher-value products, resulting in a material upgrade; in accordance with the definition in I. Vollmer et al., Angew. Chem. Int. Ed. 2020, 59, 15402-15423, the term "upcycling" in the context of this invention preferably denotes the transformation of silicone waste into chemicals that have a higher market value than monomers or pyrolysis oil.

[0071] Since the digestion according to the invention takes place under moderate reaction conditions, for example, HDPE / LDPE recycled in this way does not suffer any loss of quality.

[0072] According to the invention, the acid-catalyzed depolymerization of the silicone waste is preferably carried out in the temperature range of 30 °C to 150 °C, preferably in the temperature range of 45 °C to 130 °C and - in the case of the decomposition-labile α,ω-dihydrogenpolydimethylsiloxanes - particularly preferably in the temperature range of 35 °C to 80 °C.

[0073] The digestion process according to the invention can advantageously be carried out at normal pressure (1013 hPa) or in pressure-resistant apparatus under overpressure. Preferably, the digestion process according to the invention is carried out at normal pressure.

[0074] According to the invention, the Brønstedt acid is preferably used in amounts of 0.1 to 1.5 mass percent, preferably in amounts of 0.15 to 1.0 mass percent, and particularly preferably in amounts of 0.2 to 0.8 mass percent based on the total silicon content of the reaction system.

[0075] The term reaction system refers to the entire mixture of substances that is subjected to the depolymerization according to the invention, i.e., comprising at least the silicone waste to be utilized, in particular comprising silicone elastomers and / or silicone rubbers, as well as at least one end-group MR< supplying compound, as well as at least one D-unit supplying compound and at least one Brønsted acid.

[0076] The process according to the invention is carried out without solvents. The use of solvents can, even in its slightest effect, lead to a reduction in the space-time yield of the end-sealed, liquid siloxanes such as alkoxysiloxanes, hydrogen siloxanes, chlorosiloxanes, polydimethylsiloxanes, and / or vinylsiloxanes, and may also necessitate the subsequent removal of the solvent. Furthermore, and depending on the specific chemical nature of the solvent, it could lead to a partial or complete inhibition of the depolymerization process according to the invention and / or to undesirable side reactions. Within the scope of the invention, "solvent-free reaction system" means that the proportion of solvent in the reaction system is less than 2% by weight, preferably less than 0.5% by weight, particularly preferably less than 0.1% by weight, and preferably less than 0.01% by weight.

[0077] According to the invention, solvents are understood to be organic solvents such as alkanes, cycloalkanes, aromatics, alkyl aromatics, ethers, esters, ketones, carboxylic acids, carboxylic anhydrides, carbonic acid esters, alcohols and / or water.

[0078] According to the invention, the term solvent does not include the end-group MR< supplying compound, the D-unit supplying compound, or the Brønsted acid to be used according to the invention.

[0079] Example 7, which is not according to the invention, illustrates the aforementioned aspect of inhibition, namely that no acid-catalyzed depolymerization of a cured silicone sealant takes place in a solvent-containing reaction system with isopropanol as the common solvent. The cured silicone sealant used is thus returned to the sealant virtually unchanged.

[0080] With regard to the Brønsted acid to be used according to the invention, it corresponds to a particularly preferred embodiment of the invention if, in the process according to the invention, protic acids with a pKa value of less than -1.30, such as preferably nitric acid, methanesulfonic acid and / or p-toluenesulfonic acid, preferably protic acids with a pKa value of less than -2.90, such as preferably concentrated sulfuric acid, particularly preferably protic acids with a pKa value of less than -4.90, such as preferably perfluoroalkanesulfonic acids like heptafluoropropanesulfonic acid, pentafluoroethanesulfonic acid, trifluoromethanesulfonic acid, perchloric acid and / or chlorosulfonic acid, are used, wherein perfluoroalkanesulfonic acids are particularly preferred, and trifluoromethanesulfonic acid is especially preferred, and / or wherein sulfonic acid or perfluoroalkylsulfonic acid ion exchange resins can preferably be used.

[0081] For the purposes of this invention, the term "silicone content" refers to the total mass of silicone in the reaction system.

[0082] The Brønsted acid chlorosiloxane produced according to the invention, due to its inherent acidic nature, requires no neutralization for further processing, particularly for the production of SiOC-linked derivatives such as SiOC-linked polyethersiloxanes. The Brønsted acid present in the chlorosiloxane from the process according to the invention does not generally interfere with further processing.

[0083] In contrast, if desired for further processing, the Brønsted acids alkoxysiloxanes, hydrogen siloxanes, polydimethylsiloxanes or vinylsiloxanes that can be produced according to the invention can optionally be neutralized by the introduction of a solid, liquid or gaseous base.

[0084] Preferably according to the invention, ammonia can be introduced as a gaseous base into the end-sealed siloxane to be optionally neutralized with Brønsted acid.

[0085] According to the invention, optionally usable solid and / or liquid bases may preferably comprise a hydrogen carbonate and / or carbonate of the alkali or alkaline earth metals, optionally also in the form of a hydrate, and / or an organic amine base in the form of a primary or secondary amine or an acetate salt, wherein the optional treatment of the siloxane with a solid and / or liquid and / or gaseous base is preferably carried out in the temperature range of 0°C to 140°C, more preferably from 20°C to 110°C, and most preferably between 30°C and 80°C.

[0086] The amount of base to be optionally introduced into the siloxane is preferably measured so that it corresponds at least to the acid equivalent present in the siloxane, preferably to 2 to 10 times that amount.

[0087] Any desired separation of the salt precipitated during the optional neutralization from the end-sealed siloxane can preferably be carried out by filtration. If filled silicone waste, in particular fully filled silicone elastomers and / or filled silicone rubbers, are converted into end-sealed siloxanes by the acid-catalyzed depolymerization according to the invention, the filler fraction released in this process can preferably be separated together with the precipitated salt.

[0088] According to a further embodiment of the method preferred according to the invention, the Brønsted acid end-sealed siloxane is first separated from the released filler fraction by filtration and the filtrate thus obtained is then neutralized by the introduction of a solid, liquid or gaseous base.

[0089] As is obvious to experts, before processing unknown silicone waste, it is recommended to conduct representative sampling followed by test digestion on a laboratory and / or pilot plant scale to determine the current silicone content and the expected amount of silicone-free components. These components include, among others, binders, plastics, and, for example, in the case of electronic waste, metals, ceramics, etc.

[0090] According to the invention, the reaction preferably takes place in a reactor whose volume is preferably at least 1 liter, but preferably at least 5 liters, in particular at least 10 liters, and preferably a maximum of 500,000 liters.

[0091] The term "reactor" is well known to those skilled in the art and therefore requires no further explanation. A reactor is usually, and preferably also in the context of this invention, defined as a confined space, for example, a stirred vessel (e.g., a stirred tank reactor) or a tube (e.g., a flow tube as a flow-through reactor), in which chemical transformations can be carried out in a controlled manner. As those skilled in the art 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 measuring the volume. The reactor material can preferably be selected from suitable materials, such as advantageously glass or ceramic, more preferably metal, in particular high-alloy stainless steels, and most preferably Hastelloy. All of this is known to those skilled in the art.Preferably, suitable reactors have devices that enable mixing of the reaction mass. Suitable stirring devices are known to those 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. All known means, such as double jackets, solid coils, or half-coils, can be used for heating or cooling the reaction mass. With regard to operating modes, a distinction can essentially be made between continuous and batch operation. Continuous processes are preferably used for large product quantities, while batch operation is preferred for smaller product quantities. All of this is known to those skilled in the art. Reactors, especially stirred tank reactors, are commercially available in a variety of ways, for example from Behälter KG Bremen GmbH & Co., Theodor-Barth-Str.25, 28307 Bremen, Germany, or, for example, at 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"; also to the book "Handbook of Chemical Reactors, Fundamentals and Applications of Chemical Reaction Engineering," edited by Vladimir Reschetilowski, published by Springer, Berlin; 1st edition 2020"; and also to the book by Klaus Hertwig and Lothar Martens: Chemical Process Engineering: Calculation, Design and Operation of Chemical Reactors, Oldenbourg, Munich 2007.

[0092] Another object of the present invention is end-sealed, acidic liquid siloxanes with chain lengths greater than 3 silicon atoms, preferably alkoxysiloxanes, hydrogen siloxanes, chlorosiloxanes, polydimethylsiloxanes and / or vinylsiloxanes, produced according to a process according to the invention as described above.

[0093] A further object of the present invention lies in the use of acidic siloxanes with chain lengths greater than 3 silicon atoms, preferably alkoxysiloxanes, hydrogen siloxanes or chlorosiloxanes, produced from silicone waste, particularly as described herein according to the invention, for the production of polyether siloxanes, especially for the production of polyurethane foam stabilizers, defoamers, paint, leveling and dispersing additives and / or dismulsifiers. Corresponding polyether siloxanes are obtainable, for example, by reacting hydrogen siloxanes with unsaturated polyetherols (for example, allyl polyethers) using noble metal catalysts (hydrosilylation) or also by reacting hydrogen siloxanes with polyetherols under catalytically induced hydrogen release (dehydrogenative SiOC coupling). Examples:

[0094] The following examples serve solely to illustrate this invention to those skilled in the art and do not constitute any limitation of the claimed method. The determination of water content according to the invention is generally carried out using the Karl Fischer method in accordance with DIN 51777, DGF E-III 10 and DGF C-III 13a. 29<Si NMR spectroscopy was used in all examples for reaction monitoring.

[0095] Within the scope of this invention, the 29< Si NMR samples are measured at a measurement frequency of 79.49 MHz in a Bruker Avance III spectrometer equipped with a 287430 probe head with a 10 mm slit width, dissolved in CDCI 3 at 22°C and against tetramethylsilane (TMS) as an external standard [δ( 29< Si) ​​= 0.0 ppm].

[0096] The gas chromatograms are recorded on an Agilent Technologies GC 7890B instrument equipped with an HP-1 column; 30m x 0.32mm ID x 0.25µm dF (Agilent Technologies No. 19091Z-413E) and hydrogen as the carrier gas with the following parameters: Detector: FID; 310°C Injector: Split; 290°C Mode: constant flow 2 mL / min Temperature program: 60°C with 8°C / min -150°C with 40°C / min - 300°C 10 min. Example 1 (according to the invention): Production of a polydimethylsiloxane from silicone sealant

[0097] 30 g of a silicone sealant strand (MEM® Universal Silicone (white)) applied to a polyethylene film and cured, are placed in a 500 ml four-necked round-bottom flask equipped with a KPG stirrer and attached reflux condenser, together with 70 g of decamethylcyclopentasiloxane and 12.5 g of hexamethyldisiloxane, while stirring slowly. Then, 0.69 g of concentrated sulfuric acid (0.6 wt% of the total mixture) is added and the mixture is heated to 120°C for 4 hours while continuing to stir. During the reaction, the lumpy components of the reaction matrix gradually liquefy, resulting in a slightly viscous liquid containing only fine solid particles. After filtration through a filter press (K 300 filter disc), a 29< Si NMR spectrum of the clear filtrate proves that a trimethylsilyl end-sealed polydimethylsiloxane has been formed. Example 2 (according to the invention): Production of an α-monochloropolydimethylsiloxane

[0098] 30 g of a silicone sealant strand applied and cured on a polyethylene film (Soudal Sanitary Shower & Bath, transparent) are placed in a 500 ml four-necked round-bottom flask equipped with a KPG stirrer and attached reflux condenser in the form of 3-4 mm irregular pieces, together with 60 g of decamethylcyclopentasiloxane and 10.0 g of trimethylchlorosilane under slow stirring, then mixed with 0.20 g of concentrated trifluoromethanesulfonic acid (0.2 wt% based on the total mixture) and heated to 50°C for 4 hours with continued stirring.

[0099] During the reaction, the lumpy components of the reaction matrix gradually liquefy, resulting in a slightly viscous liquid containing only fine solid particles. After filtration through a filter press (K 300 filter disc), a 29<Si NMR spectrum of the clear filtrate confirms the formation of a mixed chloro-trimethylsilyl end-capped polydimethylsiloxane. Example 3 (according to the invention): Preparation of an α,ω-dihydrogen polydimethylsiloxane

[0100] 30 g of a silicone sealant strand applied and cured on a polyethylene film (Soudal Sanitary Shower & Bath, transparent) are placed in a 500 ml four-necked round-bottom flask equipped with a KPG stirrer and attached reflux condenser in the form of 3-4 mm irregular pieces, together with 40.0 g of decamethylcyclopentasiloxane and 30.0 g of an α,ω-dihydrogenpolydimethylsiloxane (SiH value: 3.06 mol SiH / kg determined by gas volumetry (decomposition of a weighed aliquot with sodium butoxide solution on a gas burette) corresponding to a mean chain length N = 9.3) under slow stirring and then mixed with 0.20 g of concentrated trifluoromethanesulfonic acid (0.2 wt% based on the total batch) and heated to 50°C for 2 hours with continued stirring.

[0101] During the reaction, the lumpy components of the reaction matrix gradually liquefy, resulting in a liquid with a hydrogen sulfide odor, now only containing fine solid particles. This liquid is then filtered using a filter press (K 300 filter disc). The corresponding < 29< µSi NMR spectrum of the resulting clear filtrate indicates the structure of an α,ω-dihydrogen polydimethylsiloxane with a mean chain length of approximately 28.7 µmol. A concurrent gas volumetric analysis of a weighed filtrate sample confirms that all the silicon hydroxide used is retained. Example 4 (according to the invention): Preparation of an α,ω-dichloropolydimethylsiloxane

[0102] 30 g of a silicone sealant strand applied and cured on a polyethylene film (Soudal Sanitary Shower & Bath, transparent) are placed in a 500 ml four-necked round-bottom flask equipped with a KPG stirrer and attached reflux condenser in the form of 3-4 mm irregular pieces, together with 40.0 g of decamethylcyclopentasiloxane and 30.0 g of an α,ω-dichloropolydimethylsiloxane (acidity: 4.32 mol / kg determined by acidimetric titration of an aliquot decomposed in H₂O / acetone) corresponding to a mean chain length N = 5.5) under slow stirring and then mixed with 0.60 g of concentrated sulfuric acid (0.6 wt% based on the total batch) and heated to 120°C for 4 hours with continued stirring.

[0103] During the course of the reaction, the lumpy components of the reaction matrix gradually liquefy, resulting in a liquid that is only permeated by fine solid particles. After filtration through a K 300 filter disc in a filter press, a clear filtrate is obtained, to which the corresponding 29< Si-NMR spectrum assigns the structure of an α,ω-dichloropolydimethylsiloxane with a mean chain length of N ca. 38.3. Example 5 (according to the invention): Preparation of an α,ω-diethoxypolydimethylsiloxane

[0104] 30 g of a silicone sealant strand applied and cured on a polyethylene film (Soudal Sanitary Shower & Bath, transparent) are placed in a 500 ml four-necked round-bottom flask equipped with a KPG stirrer and attached reflux condenser in the form of 3-4 mm irregular pieces, together with 70.0 g decamethylcyclopentasiloxane and 12.5 g diethoxydimethylsilane under slow stirring, then 0.69 g of concentrated sulfuric acid (0.6 wt% based on the total batch) is added and heated to 120°C for 4 hours with continued stirring.

[0105] During the course of the reaction, the lumpy components of the reaction matrix gradually liquefy, resulting in a liquid permeated with fine solid particles. After filtration through a K 300 filter disc in a filter press, a clear filtrate is obtained, the corresponding 29< Si-NMR spectrum of which confirms the structure of an α,ω-diethoxypolydimethylsiloxane with a mean chain length of N = ca. 20.7. Example 6 (according to the invention): Preparation of an α,ω-diethoxypolydimethylsiloxane

[0106] 30 g of a silicone sealant strand applied and cured on a polyethylene film (MEM ®< Universal Silicone (white)) are placed in a 500 ml four-necked round-bottom flask equipped with a KPG stirrer and attached reflux condenser in the form of 3-4 mm irregular pieces together with 70.0 g decamethylcyclopentasiloxane and 12.5 g diethoxydimethylsilane under slow stirring and then mixed with 0.69 g concentrated sulfuric acid (0.6 wt% based on the total batch) and heated to 120°C for 4 hours with continued stirring.

[0107] During the reaction, the lumpy components of the reaction matrix gradually liquefy, resulting in a liquid containing only fine solid particles. Filtration through a K 300 filter disc in a filter press yields a clear filtrate, the corresponding 29< µS NMR spectrum of which confirms the structure of an α,ω-diethoxypolydimethylsiloxane with a mean chain length of approximately 22.8 µS. Present at about 0.1 mol%, a very small signal is also observed at a chemical shift of approximately -67 ppm, indicating the presence of T-groups. Example 7 (not according to the invention): Attempt to synthesize an α,ω-dihydrogen polydimethylsiloxane

[0108] 30 g of a silicone sealant strand applied and cured on a polyethylene film (Hellweg Basic Silicone, transparent) are placed in a 500 ml four-necked round-bottom flask equipped with a KPG stirrer and attached reflux condenser in the form of 3-4 mm irregular pieces, together with 70.0 g isopropanol and 12.5 g of an α,ω-dihydrogen polydimethylsiloxane (SiH value: 3.06 mol SiH / kg determined by gas volumetry (decomposition of a weighed aliquot with sodium butoxide solution on a gas burette) corresponding to a mean chain length N = 9.3) under slow stirring and then mixed with 0.20 g of concentrated trifluoromethanesulfonic acid (0.2 wt% based on the total batch) and heated first for 2 hours at 22°C and then for 4 hours at 50°C with continued stirring.

[0109] The granular components of the piston contents undergo no visible change during this treatment. After the entire mass has cooled, a piston contents is isolated in which a transparent, colorless liquid phase covers the visually unchanged silicone particles. Example 8 (according to the invention): Production of a polydimethylsiloxane from silicone sealant

[0110] 30 g of a silicone sealant strand (Hellweg Basic Silicone, transparent) applied and cured on a polyethylene film are placed in a 500 ml four-necked round-bottom flask equipped with a KPG stirrer and attached reflux condenser in the form of 3-4 mm irregular pieces, together with 70 g of decamethylcyclopentasiloxane and 12.5 g of hexamethyldisiloxane, while stirring slowly, and then 0.69 g of methanesulfonic acid (0.6 wt% based on the total batch) is added and heated to 120°C for 4 hours while continuing to stir.

[0111] During the reaction, the lumpy components of the reaction matrix gradually liquefy, resulting in a slightly viscous liquid containing only fine solid particles. After filtration through a filter press (K 300 filter disc), a 29<Si NMR spectrum of the clear filtrate confirms the formation of a trimethylsilyl end-capped polydimethylsiloxane.

Claims

1. Process for producing endcapped, liquid siloxanes having chain lengths of greater than 3 silicon atoms from silicone wastes, especially comprising silicone elastomers and / or silicone rubbers, by acid-catalysed depolymerization thereof in a solvent-free reaction system comprising (i) at least one compound providing end groups MR, (ii) at least one compound providing D units, and (iii) at least one Brønsted acid, wherein the compound providing end groups MR comprises hexamethyldisiloxane, polydimethylsiloxanes, poly(methylhydrogen)siloxane, poly(methylhydrogen)polydimethylsiloxane copolymer, trimethylchlorosilane, dimethyldichlorosilane, dichlorotetramethyldisiloxane, α,ω-dichloropolydimethylsiloxane, monoalkoxytrimethylsilane, in particular monomethoxytrimethylsilane or monoethoxytrimethylsilane, dialkoxydimethylsilane, in particular dimethoxydimethylsilane or diethoxydimethylsilane, α,ω-dialkoxypolydimethylsiloxanes, in particular α,ω-dimethoxypolydimethylsiloxanes or α,ω-diethoxypolydimethylsiloxanes, tetramethyldisiloxane, α,ω-dihydrogenpolydimethylsiloxanes, divinyltetramethyldisiloxane or α,ω-divinylpolydimethylsiloxanes or else mixtures of the abovementioned compounds.

2. Process according to Claim 1, wherein the compound providing D units comprises at least one cyclosiloxane selected from hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane and / or dodecamethylcylohexasiloxane and / or a siloxane containing D groups recited in Claim 2.

3. Process according to Claim 1 or 2, characterized in that the acid-catalysed, solvent-free depolymerization of the silicone wastes is carried out in a reactor having a volume of at least 5 litres, in particular at least 10 litres, and preferably not more than 500 000 litres.

4. Process according to at least one of Claims 1 to 3, characterized in that the acid-catalysed, solvent-free depolymerization of the silicone wastes is performed in the temperature range of 30°C to 150°C, preferably in the temperature range of 45°C to 130°C, wherein when using the compound providing end groups MR selected from tetramethyldisiloxane and / or α,ω-dihydrogenpolydimethylsiloxanes the acid-catalysed, solvent-free depolymerization is particularly preferably performed in the temperature range of 35°C to 80°C.

5. Process according to at least one of Claims 1 to 4, characterized in that the Brønsted acid is employed in amounts of 0.05 to 3 percent by weight, preferably of 0.1 to 1.0 percent by weight, particularly preferably of 0.2 to 0.8 percent by weight, based on the total silicone content of the reaction system.

6. Process according to at least one of Claims 1 to 5, characterized in that it employs as Brønsted acids • protic acids having a pKA of less than -1.30, such as preferably nitric acid, methanesulfonic acid and / or p-toluenesulfonic acid, • preferably protic acids having a pKA of less than - 2.90, such as preferably concentrated sulfuric acid, • particularly preferably protic acids having a pKA of less than -4.90, such as preferably perfluoroalkanesulfonic acids, such as heptafluoropropanesulfonic acid, pentafluoroethanesulfonic acid and / or trifluoromethanesulfonic acid, perchloric acid and / or chlorosulfonic acid, wherein especially perfluoroalkanesulfonic acids, most preferably trifluoromethanesulfonic acid, are preferred and / or preferably sulfonic acid- or perfluoroalkylsulfonic acid-acidified ion-exchange resins are employed.

7. Process according to at least one of Claims 1 to 6, characterized in that the acid-catalysed, solvent-free depolymerization of the silicone wastes is performed at standard pressure (1013 hPa) or positive pressure but particularly preferably at standard pressure.

8. Process according to at least one of Claims 1 to 7, characterized in that the silicone wastes comprise 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 polyethylene containers, preferably comprising HDPE and / or LDPE.

9. Process according to at least one of Claims 1 to 8, characterized in that the resulting endcapped, liquid siloxanes comprise alkoxysiloxanes, hydrogensiloxanes, chlorosiloxanes, polydimethylsiloxanes and / or vinylsiloxanes having chain lengths of greater than 3 silicon atoms.

10. Process according to at least one of Claims 1 to 9 utilizing silicone-contaminated polyolefin, preferably polyethylene, in particular silicone-contaminated polyethylene wastes, for providing acidic alkoxysiloxanes, hydrogensiloxanes, chlorosiloxanes, polydimethylsiloxanes and / or vinylsiloxanes having chain lengths of greater than 3 silicon atoms in the course of substantially single stream recovery of polyolefin, preferably polyethylene.