Organopolysiloxane depolymerization

Abstract

The present invention relates to a process for preparing cyclic polysiloxane by reactive distillation of at least one organopolysiloxane in the presence of an alkaline salt catalyst selected from salts of K, Na, Rb or Cs, and a multidentate complexing agent.

Description

[0001] Depolymerization of organopolysiloxane

[0002] The present invention relates to cyclic organopolysiloxanes and more particularly to a process for preparing cyclic organopolysiloxanes by depolymerization of organopolysiloxanes in the presence of a catalytic system comprising an alkaline catalyst and a multidentate complexing agent.

[0003] Recycling industrial products and used silicone products is a current issue. Recycling silicone polymers could reduce gas emissions (CO, CO2) from the silicone industry by 75% and silicone waste by 65%.

[0004] One of the recycling routes considered is the depolymerization of organopolysiloxanes to produce cyclic organopolysiloxanes (or cyclosiloxane).

[0005] It is known, in particular from US5670689, the depolymerization of silanol-terminated polydimethylsiloxane (PDMS) in the presence of strong alkali hydroxide or quaternary hydroxide. The reaction is carried out at 140°C to lead to a 90% yield of a mixture of cyclic organopolysiloxanes. However, a high catalyst loading is required, in particular at least 2% by weight relative to the weight of PDMS-OH.

[0006] There is therefore an interest in providing an optimized process allowing the depolymerization of organopolysiloxane efficiently and making it possible to obtain a good yield of cyclic siloxanes, in particular D3 (hexamethylcyclotrisiloxane), D4 (octamethylcyclotetrasiloxane) and D5 (decamethylcyclopentasiloxane).

[0007] An objective of the present application is therefore to propose a process for depolymerizing organopolysiloxane efficiently and making it possible to obtain a good yield of cyclic organopolysiloxanes, in particular D3, D4 and D5.

[0008] Another objective of the present application is to provide a catalytic system for implementing this process.

[0009] Another objective of the present application is to propose a simple catalytic system allowing good reaction kinetics compatible with industrialization of the process.

[0010] Still other objectives will appear on reading the description of the invention which follows. These objectives are fulfilled by the present application which relates to a method for preparing cyclic organopolysiloxane OC by reactive distillation of at least one organopolysiloxane O in the presence of a catalyst of the alkali salt type chosen from salts of K, Na, Rb or Cs, and of a multidentate complexing agent.

[0011] The organopolysiloxane O of the invention may be any type of organopolysiloxane, in particular chosen from linear organopolysiloxanes, for example oils, or gums, or branched organopolysiloxanes.

[0012] The organopolysiloxane O may in particular be an oil or a gum, and preferably has a dynamic viscosity of between 50 and 600,000 mPa.s at 25°C or a consistency of between 200 and 2,000 expressed in tenths of millimeters at 25°C. All the viscosities referred to in the present disclosure correspond to a dynamic viscosity quantity at 25°C called “Newtonian”, that is to say the dynamic viscosity which is measured, in a manner known per se, with a Brookfield viscometer at a shear rate gradient sufficiently low so that the measured viscosity is independent of the rate gradient.

[0013] The term gum is used for organopolysiloxane compounds with viscosities typically greater than 600,000 mPa.s, which corresponds to a molecular weight greater than 260,000 g / mol.

[0014] The consistency or penetrability of a rubber is determined at 25°C using a PNR12 type penetrometer or equivalent model allowing a cylindrical head to be applied to the sample under standardized conditions.

[0015] These organopolysiloxanes O may comprise one or more functional units such as:

[0016] - OH ;

[0017] - H ;

[0018] - alkenyl in particular comprising from 2 to 6 carbon atoms, preferably vinyl;

[0019] - O-Alk with Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl;

[0020] - (O-Alk)x with Alk representing an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl, and x representing an integer between 2 and 200;

[0021] - amino group, in particular (Alk)-NH2 or (Alk)-NH-(Alk)-NH2, with Alk representing an alkyl comprising from 1 to 5 carbon atoms;

[0022] - cyclic amine for example -(CH2) z -O-piperidine in which z represents an integer from 1 to 5, preferably 3, and the piperidine may be substituted in particular by one or more alkyl groups comprising from 1 to 3 carbon atoms, preferably methyl, preferably the substituted piperidine is a group

[0023] Preferably, the organopolysiloxanes O may comprise one or more functional units such as H, OH, alkenyl (preferably vinyl), aryl, cyclic amine, as defined above.

[0024] The organopolysiloxanes O of the invention may be partially crosslinked.

[0025] The organopolysiloxanes O of the invention may in particular be used organopolysiloxanes, having served for example as heat transfer fluid, which should be recycled, the process of the invention thus making it possible to generate cyclic organopolysiloxanes OC which can then be directly used in industrial processes, in particular in new polymerization processes. For example, the organopolysiloxanes O of the invention may be silicone oils, in particular terminated by trimethylsilyl, dimethylhydroxysilyl or dimethylvinylsilyl units, or silicone gels. In the case of the use of used organopolysiloxanes O, the organopolysiloxane may then contain other elements such as additives, pigments, etc. The inventors have shown that the presence of these other elements does not disrupt the depolymerization reaction and the formation of cyclic organopolysiloxanes OC.

[0026] According to one embodiment of the invention, the organopolysiloxane O of the invention comprises:

[0027] - at least 5 units, preferably at least 10 siloxyl units of formula R c SiO<4-c) / 2 in which

[0028] R, identical or different, represents

[0029] • an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl; • an aryl group comprising from 6 to 10 carbon atoms, preferably phenyl; and c = 0, 1, 2 or 3; and

[0030] - possibly one or more motifs of formula R 1 dR e SiO(4-de) / 2 in which:

[0031] R is as defined above

[0032] R 1 , identical or different, represents:

[0033] • an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl;

[0034] • a hydroxyl group (OH);

[0035] • a group (O-Alk) with Alk representing an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably OCH3 or OC2H5,

[0036] • a group (O-Alk) x with Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl, and x represents an integer between 2 and 200,

[0037] • an amino group chosen from (Alk)-NH2 or (Alk)-NH-(Alk)-NH2, with Alk representing an alkyl comprising from 1 to 5 carbon atoms;

[0038] • cyclic amine for example -(CH2) z-O-piperidine in which z represents an integer from 1 to 5, preferably 3, and the piperidine may be substituted in particular by one or more alkyl groups comprising from 1 to 3 carbon atoms, preferably methyl, preferably the substituted piperidine is a group

[0039] • a hydrogen; d=1, 2 or 3, preferably d=1 or 2, more preferably d=1; e=0, 1 or 2; and the sum d+e=1, 2 or 3.

[0040] It is understood in the above formulas that if more than one R group is present or if more than one R group 1 are present, they may be the same or different from each other. Preferably, in the above formulas R 1 , identical or different, represents:

[0041] • an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl;

[0042] • a hydroxyl group (OH);

[0043] • cyclic amine for example -(CH2) z-O-piperidine in which z represents an integer from 1 to 5, preferably 3, and the piperidine may be substituted in particular by one or more alkyl groups comprising from 1 to 3 carbon atoms, preferably methyl, preferably the substituted piperidine < r z NH r is a group;

[0044] • a hydrogen.

[0045] In the present invention:

[0046] - a siloxyl unit “M” represents a siloxyl unit of formula YsSiOi / 2,

[0047] - a siloxyl unit “D” represents a siloxyl unit of formula Y2SiO2 / 2,

[0048] - a siloxyl unit “T” represents a siloxyl unit of formula YSiOs / 2,

[0049] - a siloxyl unit “Q” represents a siloxyl unit of formula SiC>4 / 2, the symbols Y being R or R 1 .

[0050] The organopolysiloxane O may optionally comprise a small amount of T and Q units. Without wishing to be bound by any theory, the depolymerization process of the invention may be carried out on organopolysiloxanes O comprising long chains of successive D units. Preferably, the organopolysiloxane O according to the invention comprises less than 20%, preferably less than 10%, even more preferably less than 5% and even more preferably less than 2% of T or Q units as defined above relative to the number of total siloxyl units of the organopolysiloxane O. According to a preferred embodiment, the organopolysiloxane O of the invention is preferably chosen from the compounds of formula (I):

[0051] R 1 aR(3-a)SiO-(SiR2O) n -(SiR 1 RO) m -SiR 1 aR(3-a) (I) in which:

[0052] R, identical or different, represents:

[0053] • an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl;

[0054] • an aryl group comprising from 6 to 10 carbon atoms, preferably phenyl;

[0055] R 1 , identical or different, represents:

[0056] • an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl;

[0057] • a hydroxyl group (OH);

[0058] • a group (O-Alk) with Alk representing an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably OCH3 or OC2H5,

[0059] • a group (O-Alk) xwith Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl, and x represents an integer between 2 and 200,

[0060] • an amino group chosen from (Alk)-NH2 or (Alk)-NH-(Alk)-NH2, with Alk representing an alkyl comprising from 1 to 5 carbon atoms;

[0061] • cyclic amine for example -(CH2) z -O-piperidine in which z represents an integer from 1 to 5, preferably 3, and the piperidine may be substituted in particular by one or more alkyl groups comprising from 1 to 3 carbon atoms, preferably methyl, preferably the substituted piperidine is a group

[0062] • a hydrogen; a is an integer and represents 0, 1, 2 or 3, preferably 0, 1 or 2, more preferably 0 or 1; n represents an integer between 10 and 10,000, preferably between 10 and 5,000, preferably between 50 and 5,000, more preferably between 60 and 5,000, for example between 70 and 1,000; m represents an integer between 0 and 100, preferably between 0 and 50, more preferably between 0 and 30, preferably m=0.

[0063] The presence of Si-H group in organopolysiloxane O can generate a release of dihydrogen. It may therefore be advantageous, in the device for implementing the method of the invention, in the case where the quantity of Si-H group is significant, to provide a device for managing the release of dihydrogen. To avoid the implementation of such a device, the quantity of Si-H group is preferably less than 20%, preferably less than 10%, preferably less than 5%, preferably less than 2% by weight relative to the total weight of organopolysiloxane O.

[0064] Particularly preferably, the organopolysiloxane O of the invention is a compound of formula (I) in which R 1 , identical or different, represents:

[0065] • an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl;

[0066] • a hydroxyl group (OH);

[0067] • cyclic amine for example -(CH2)z -O-piperidine in which z represents an integer from 1 to 5, preferably 3, and the piperidine may be substituted in particular by one or more alkyl groups comprising from 1 to 3 carbon atoms, preferably methyl, preferably the substituted piperidine

[0068] < z NH r is a group;

[0069] • a hydrogen.

[0070] Particularly preferably, the organopolysiloxane O of the invention is a compound of formula (I) in which R 1 , identical or different, represents CH3, vinyl, H or OH. Particularly preferably, the organopolysiloxane O of the invention is a compound of formula (I) in which

[0071] R, identical or different, represents CH3 or phenyl, preferably CH3;

[0072] R 1 , identical or different, represents:

[0073] • an alkenyl group comprising from 2 to 6 carbon atoms, preferably vinyl;

[0074] • a hydroxyl group (OH);

[0075] • cyclic amine for example -(CH2) z -O-piperidine in which z represents an integer from 1 to 5, preferably 3, and the piperidine may be substituted in particular by one or more alkyl groups comprising from 1 to 3 carbon atoms, preferably methyl, preferably the substituted piperidine is a group

[0076] • a hydrogen.

[0077] Particularly preferably, the organopolysiloxane O of the invention is a compound of formula (I) in which

[0078] R, identical or different, represents CH3 or phenyl, preferably CH3;

[0079] R 1 , identical or different, represents CH3, vinyl, H or OH.

[0080] Advantageously, the process of the invention can be carried out with organopolysiloxanes O having a dynamic viscosity of between 3 and 20,000,000 mPa.s, preferably between 3 and 6,000,000 mPa.s, for example between 3 and 1,000,000 mPa.s, at 25°C. Particularly advantageously, the process of the invention can be carried out with an organopolysiloxane O or a mixture of organopolysiloxanes O having a dynamic viscosity, of the organopolysiloxane O or the mixture of organopolysiloxanes O, of between 3 and 1,000,000 mPa.s, preferably between 100 and 60,000 mPa.s, at 25°C. It should therefore be understood that, advantageously, to facilitate the implementation of the process, in the context of organopolysiloxane mixtures that the organopolysiloxanes O may have variable viscosities to the extent that the viscosity of the mixture is as mentioned above. Furthermore, the process of the invention can be carried out in the presence of a solvent.The solvent must be chosen from solvents solubilizing organopolysiloxane O. The solvent may be an alcohol or n-paraffins. Preferably, the alcohol is chosen from fatty alcohols such as n-lauryl alcohol, n-myristyl alcohol, n-palmitic alcohol, n-stearyl alcohol, n-docosanol, or Guerbet alcohols such as 2-octyl 1-dodecanol, 2-decyl 1-tetradecanol. Preferably, the n-paraffins are chosen from the compounds C16H34, C Hss, C20H42, C22H46, or C24H5o- If a solvent is used in the process of the invention, the amount of solvent added is preferably between 5 and 50% by weight, preferably between 10 and 20% by weight, relative to the weight of organopolysiloxane O.Particularly advantageously, to facilitate the implementation of the process, the use of a solvent will allow the implementation of the process of the invention with more viscous organopolysiloxanes O, for example having a viscosity of between 1,000,000 and 20,000,000,000 mPa.s at 25°C so that the mixture (organopolysiloxane O + solvent) has a viscosity of between 3 and.

[0081] 1,000,000 mPa.s, preferably between 100 and 60,000 mPa.s at 25°C.

[0082] The alkali salt catalyst is an alkali metal salt comprising a metal M, the metal M being selected from K, Na, Rb or Cs, preferably K, Rb, Cs.

[0083] Preferably, said alkali metal salt is chosen from silanolates, hydroxides, alkoxides and siliconates, preferably silanolates.

[0084] In the context of the present invention, when referring to the alkali metal salt, the following terms are understood to mean:

[0085] "silanolate" means a salt derived from a silanol group which is a functional group comprising at least one Si-OH group. Silanolates generally have a formula MOSi(R')s with M as defined above and R', identical or different, represents a linear or branched alkyl group comprising from 1 to 6 carbon atoms, or an alkenyl group comprising

[0086] 2 to 6 carbon atoms, preferably R', identical or different, represents methyl or vinyl.

[0087] "siliconate" a compound of formula M(OSi(R 3 )2) P -OSi(R 3 )2with M as defined above and R 3 represents an alkyl group comprising from 1 to 6 carbon atoms, preferably methyl, and p represents an integer between 1 and 20, preferably between 1 and 10.

[0088] “hydroxide” a group of formula MOH, with M as defined above.

[0089] “alkoxide” a compound of formula MOAlk, with M as defined above and Alk represents an alkyl, linear or branched, comprising from 1 to 22 carbon atoms, preferably from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms. Preferably, the alkaline catalyst of the invention is a catalyst of formula MX with

[0090] M is selected from K, Na, Rb, Cs, preferably K, Rb, Cs, preferably K; and

[0091] X is chosen from OSiR 4 2R 5 , OH, OAlk, with Alk representing an alkyl, linear or branched comprising from 1 to 22 carbon atoms, preferably from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, (OSi(R 3 )2) P -OSi(R 3 )2 with M as defined above and R 3 represents an alkyl group comprising from 1 to 6 carbon atoms, preferably methyl, and p represents an integer between 1 and 20, preferably between 1 and 10, R4 identical or different represents a linear or branched alkyl comprising from 1 to 6 carbon atoms, preferably methyl, R 5 represents a linear or branched alkyl comprising from 1 to 6 carbon atoms, preferably methyl, or a vinyl group, preferably X represents OSiMe3 (Me represents methyl), OSiMe2Vi (Vi represents vinyl), OH or O-tBu (tBu represents tert-butyl) OSi(Me)2-(OSi(Me)2) P -OSiMe3 with p as defined above.

[0092] Preferably, M is selected from K, Rb, Cs and X is selected from OSiMes, OSiMe2Vi (Vi represents vinyl), OH, OSi(Me)2-(OSi(Me)2) P -OSiMes p represents an integer between 1 and 20, preferably between 1 and 10, and O-tBu (tBu represents tert-butyl). Preferably the alkaline catalyst is KOSiMes.

[0093] For the purposes of the present application, the term "multidentate complexing agent" means a complexing agent of the alkali metal of the alkali salt catalyst, i.e. a complexing agent of K, Na, Rb or Cs, preferably a complexing agent of K, Rb or Cs.

[0094] Preferably, the multidentate complexing agents of the invention are chosen from crown ethers, cryptands which are diamine macroheterocycles and OH or OCH3 terminated polyethylene glycols (PEGs), preferably OCH3 terminated, preferably the polyethylene glycols are polyethylene glycol dimethyl ethers. Preferably, the PEGs are soluble in the reaction medium. Thus, and preferably, the PEGs have a low number-average molar mass (Mn), for example between 100 and 2000, preferably between 200 and 1000 g / mol. The number-average molar mass (Mn) can be measured by any technique known to those skilled in the art and for example by size exclusion chromatography (SEC).

[0095] Preferably, the crown ethers comprise from 2 to 8 oxygen atoms. Crown ethers are cyclic oligomers of ethylene oxide comprising as a repeating unit a (CH2-CH2-O) group, these crown ethers can be substituted or 2 carbon atoms of a (CH2-CH2-O) unit can be fused with a hydrocarbon ring, in particular cyclohexyl or phenyl.

[0096] Preferably, the multidentate complexing agents are chosen from:

[0097] The person skilled in the art knows, depending on the alkali metal, and in particular its size, the multidentate complexing agent that should be used.

[0098] The alkali salt is used in catalytic proportions, preferably in an amount of between 0.005 and 1.5% by weight relative to the weight of organopolysiloxane (O), preferably between 0.005 and 0.9%, more preferably between 0.01 and 0.8%.

[0099] Preferably, in the context of the present invention, the molar ratio of alkali salt / multidentate complexing agent is between 1 / 100 and 100 / 1, preferably between 1 / 50 and 50 / 1, preferably between 1 / 25 and 25 / 1, preferably between 1 / 10 and 10 / 1, preferably between 1 / 4 and 4 / 1, preferably between 1 / 2 and 2 / 1, preferably greater than or equal to 1, preferably between 1 and 2, for example the ratio is equal to 1.

[0100] The method of the invention is carried out at a temperature between 50 and 200°C, preferably between 60 and 180°C, preferably between 120 and 160°C.

[0101] The method of the invention uses reactive distillation.

[0102] As is known to those skilled in the art, reactive distillation consists of the combination of separation by distillation and a reaction. The device implementing reactive distillation therefore combines a reactor and a distillation system. Reactive distillation, and the method of the invention, can be implemented continuously or discontinuously.

[0103] Batch reactive distillation combines the advantages of both reactive distillation and the batch process. The reaction mixture is charged into the reactor and the reaction products are distilled off gradually.

[0104] In the case of continuous implementation, the reagents are introduced continuously.

[0105] In one embodiment, the method of the invention, and the reactive distillation, is carried out continuously. Preferably, the temperature is between 50 and 200°C, preferably between 60 and 180°C, preferably between 120 and 160°C. Preferably, the pressure is between 0.01 and 50 mbar, preferably between 0.1 and 35 mbar, more preferably between 5 and 30 mbar.

[0106] A person skilled in the art will be able to adapt the pressure / temperature pair. For example, according to one embodiment the pressure is between 0.01 and 50 mbar for a temperature between 50 and 200°C, preferably the pressure is between 5 and 30 mbar for a temperature between 120 and 160°C.

[0107] In another embodiment, the method of the invention, and the reactive distillation, is carried out batchwise. Preferably, the temperature is between 50 and 200°C, preferably between 60 and 180°C, preferably between 120 and 160°C. Preferably, the pressure is between 0.01 and 50 mbar, preferably between 0.1 and 35 mbar, more preferably between 5 and 30 mbar.

[0108] In this embodiment, the reaction and heating begin at atmospheric pressure and then after 10 to 120 min, preferably 30 to 60 min after reaching the temperature, the reactive distillation begins at a pressure between 0.01 and 50 mbar, preferably between 0.1 and 35 mbar, more preferably between 5 and 30 mbar.

[0109] The method of the present invention can be carried out in the absence of solvent or in the presence of solvent, in particular of the alcohol type. Preferably, the alcohol is chosen from fatty alcohols such as n-lauryl alcohol, n-myristyl alcohol, n-palmitic alcohol, n-stearyl alcohol, n-docosanol, or Guerbet alcohols such as 2-octyl 1 -dodecanol, 2-decyl 1 -tetradecanol. The solvent may also be chosen from the group of n-paraffins such as the compounds C16H34, C Hss, C20H42, C22H46, C24H5o- If a solvent is used in the process of the invention, the amount of solvent added is preferably between 5 and 50% by weight, preferably between 10 and 20% by weight, relative to the weight of organopolysiloxane.

[0110] The cyclic organopolysiloxanes OC (or cyclic organopolysiloxanes) obtained by the method of the invention are preferably compounds D3, D4 or D5. Preferably, the cyclic organopolysiloxanes OC obtained are obtained in a mixture with more than 95% by weight of a mixture of compounds D3, D4 or D5, preferably from 95 to 99%, relative to the total weight of cyclic organopolysiloxanes OC produced.

[0111] Preferably, the majority compound obtained by the method of the invention is compound D4. Preferably, the method of the invention allows a yield of D4 of at least 80% by weight.

[0112] Compounds D3, D4 and D5 are preferably compounds of the following formulas:

[0113] As mentioned above, the starting organopolysiloxane O may comprise functions described by the group R 1described above. In these cases, at least one of the methyl groups of compounds D3, D4 and / or D5 may be substituted by at least one of the R 1 .

[0114] According to one embodiment in order to facilitate the recycling of compounds D3, D4 and D5, and their reuse in industrial processes, in particular polymerization, these compounds preferably comprise less than 10%, preferably less than 5%, preferably less than 2% and even more preferably less than 0.2% by weight of functions described by the group R 1 as described above relative to the total weight of compounds D3, D4 and D5.

[0115] The method of the invention preferably makes it possible to obtain a mass yield of cyclic organopolysiloxanes OC greater than 85%, preferably greater than 95% and possibly up to 99% by weight.

[0116] Optionally, compounds D3, D4 and D5 can be separated in particular by distillation, for example by distillation with numerous theoretical plates.

[0117] Particularly advantageously, the compounds D3, D4 and D5 obtained by the process of the invention can be directly used in other industrial processes to be polymerized and to manufacture new oils and gums. The present invention also relates to the use of a catalytic system comprising an alkali salt chosen from salts of K, Na, Rb or Cs, and a multidentate complexing agent, for the depolymerization of organopolysiloxanes O to produce cyclic organopolysiloxanes OC.

[0118] According to one embodiment, the alkali salt for the aforementioned use is as defined above.

[0119] According to one embodiment, the multidentate complexing agent for the aforementioned use is as defined above.

[0120] Preferably, the multidentate complexing agents used for the depolymerization of organopolysiloxanes O are chosen from crown ethers, cryptands which are diamine macroheterocycles and polyethylene glycols (PEG) terminated OH or OCH3, preferably terminated OCH3, preferably the polyethylene glycols are polyethylene glycol dimethyl ether. Preferably, the PEGs are soluble in the reaction medium. Thus, and preferably, the PEGs have a low number-average molar mass (Mn), for example between 100 and 2000, preferably between 200 and 1000 g / mol.

[0121] Preferably, the crown ethers comprise from 2 to 8 oxygen atoms. Crown ethers are cyclic oligomers of ethylene oxide comprising as a repeating unit a (CH2-CH2-O) group, these crown ethers can be substituted or 2 carbon atoms of a (CH2-CH2-O) unit can be fused with a hydrocarbon ring, in particular cyclohexyl or phenyl.

[0122] Preferably, the multidentate complexing agents used for the depolymerization of organopolysiloxanes O are chosen from:

[0123] According to a preferred use, the alkali salt used for the depolymerization of organopolysiloxanes O is used in catalytic proportions, preferably in an amount of between 0.005 and 1.5% by weight relative to the weight of organopolysiloxane (O), preferably between 0.005 and 0.9%, more preferably between 0.01 and 0.8%.

[0124] Preferably, in the context of the aforementioned use, the molar ratio of alkali salt / multidentate complexing agent is between 1 / 100 and 100 / 1, preferably between 1 / 50 and 50 / 1, preferably between 1 / 25 and 25 / 1, preferably between 1 / 10 and 10 / 1, preferably between 1 / 4 and 4 / 1, preferably between 1 / 2 and 2 / 1, preferably greater than or equal to 1, preferably between 1 and 2, for example the ratio is equal to 1.

[0125] According to one embodiment, the aforementioned use is implemented by reactive distillation.

[0126] This application will now be described with the help of the following examples.

[0127] Organopolysiloxane 01: n = 70 viscosity 100 mPa.s

[0128] Organopolysiloxane 02 n=100 viscosity 350 mPa.s

[0129] Organopolysiloxane n=100 (used oil used as a heating bath for several years) viscosity 350 mPa.s

[0130] Organopolysiloxane 04: n=180 viscosity 1000 mPa.s

[0131] Organopolysiloxane 05:

[0132] Organopolysiloxane 06 : viscosity 450 mPa.s

[0133] Organopolysiloxane 07: viscosity 100 mPa.s

[0134] Organopolysiloxane 08: 50% weight of 07 + 50% weight of 01 the viscosity of the mixture is 100 mPa.s Organopolysiloxane 09: 50% weight of 01 + 50% weight of silicone gum of formula

[0135] , the viscosity of the mixture is less than 60,000 mPa.s

[0136] Organopolysiloxane 010: viscosity 250 mPa.s

[0137] Organopolysiloxane 01 1: 50% weight of 01 + 50% weight of PDMS with 5% Si-Ph unit compared to the total number of units and a viscosity of 60,000 mPa.s

[0138] Organopolysiloxane 012: 50% weight of 01 + 50% weight mixture of 2 organopolysiloxanes of type 05 but with a different number of units, one having a viscosity of 10,000 mPa.s and the other a viscosity of 60,000 mPas.s and a crosslinking catalyst

[0139] Organopolysiloxane 013: 50% by weight of 01 + 50% by weight of a mixture of 2 organopolysiloxanes of type 05 but with a different number of units, one having a viscosity of 10,000 mPa.s and the other a viscosity of 60,000 mPas.s and approximately 5% by weight of a silicone oil comprising Si-H units Organopolysiloxane 014: 01 + crosslinked silicone gel resulting from the crosslinking between 012 and 013 free of fillers

[0140] Alkali salt used in the examples

[0141] SA1: KOSiMe3

[0142] SA2: KOSiMe2Vi

[0143] SA3: KOH

[0144] SA4: KO-tBu

[0145] SA5: RbOSiMe3

[0146] SA6: CsOSiMe3 multidentate implemented in the Example 1: General protocol in discontinuous mode

[0147] In a flask (50 mL) topped with a Vigreux column, the organopolysiloxane, the alkali salt and the multidentate complexing agent are introduced and are heated at a temperature T for 30 minutes to 1 hour. Then the reaction mixture is distilled under reduced pressure for 20-25 minutes.

[0148] In the results mentioned in the example tables:

[0149] - the cyclosiloxane yield was determined by the mass ratio between the mass of the distilled products and the mass of the starting organosiloxane O;

[0150] - the D3 / D4 / D5 / other ratio was determined between the integrated intensity of the signals (D3 / D4 / D5 / other) in the 29Si-NMR spectrum, this ratio corresponds to a weight ratio.

[0151] Example 2: Influence of temperature and pressure

[0152] The protocol of Example 1 is carried out with KOSiMes (SA1) as the alkali salt and a crown ether 18-6 (CM1). The reaction mixture is heated for 30 minutes before reactive distillation (temperature and pressure mentioned above).

[0153] The organopolysiloxane used is organopolysiloxane 01.

[0154] The results are grouped in Table 1 below.

[0155] [Table 1]

[0156] Other = (MesSi)20 + D6 These results show that the process of the invention allows the depolymerization and formation of cyclic organopolysiloxane with in particular a selectivity of the process for D4. Advantageously, the process of the invention requires a small quantity of catalyst.

[0157] Example 3: Influence of the anion X of the alkali salt

[0158] The protocol of Example 1 is carried out with KX as the alkali salt and a crown ether 18-6 (CM1). The reaction mixture is heated for 1 h before reactive distillation at a temperature of 140°C and a pressure of 10 mbar for 20-25 min.

[0159] Organopolysiloxane is 01.

[0160] The results are grouped in Table 2 below.

[0161] [Table 2]

[0162] These results show that the process of the invention can be implemented with different alkaline salts while notably maintaining selectivity in the production of D4.

[0163] Example 4: Influence of the multidentate complexing agent

[0164] The protocol of Example 1 is carried out with KOSiMes (SA1) as the alkali salt and a multidentate complexing agent. The reaction mixture is heated for 1 h before reactive distillation at a temperature of 140°C and a pressure of 10 mbar for 20-25 min.

[0165] Organopolysiloxane is 01.

[0166] The results are grouped in Table 3 below. [Table 3]

[0167] These results show that the process of the invention can be implemented with different complexing agents with good yields.

[0168] Example 5: Influence of organopolysiloxane

[0169] The protocol of Example 1 is carried out with KOSiMes (SA1) as the alkali salt and a crown ether 18-6 (CM1). The reaction mixture is heated for 1 h before reactive distillation, at a temperature of 140°C and a pressure of 10 mbar for 20-25 min.

[0170] The results are grouped in Table 4 below.

[0171] [Table 4]

[0172] Other = (MesIf)20 + D6

[0173] The results show that the process of the invention makes it possible to treat various organopolysiloxanes while allowing a good yield and good selectivity, particularly in D4. The examples also show that the process of the invention makes it possible to treat used silicone oils, gums and crosslinked silicone gels.

[0174] Example 6: Influence of the alkaline salt / multidentate complexing agent ratio

[0175] The protocol of Example 1 is implemented with different catalytic systems, at a temperature of 140°C. The reaction mixture is heated for 30 minutes before reactive distillation at a temperature of 140°C and a pressure of 10 mbar for 20-25 min.

[0176] Organopolysiloxane is 01.

[0177] The results are grouped in Table 5 below. [Table 5]

[0178] These results show that the catalytic system of the invention makes it possible to obtain a very high yield of cyclosiloxane.

[0179] Example 7: Example with an oil from a by-product of chlorosilane hydrolysis reaction

[0180] The protocol of Example 1 is implemented with different catalytic systems. The reaction mixture is heated to 150°C for 30 minutes before reactive distillation at a temperature of 150°C and a pressure of 5 mbar for 30 min.

[0181] Organopolysiloxane is an oil derived from chlorosilane hydrolysis reaction by-products comprising at least 95% of an organopolysiloxane comprising about 2% Si-H group, and other reaction products such as reaction product residues, catalyst, etc.

[0182] The results are grouped in Table 6 below. [Table 6]

[0183] These results show that the catalytic system of the invention allows the production of cyclosiloxane with oils from industrially generated by-products and therefore of complex composition.

Claims

DEMANDS 1. Method for preparing cyclic organopolysiloxane OC by reactive distillation of at least one organopolysiloxane O in the presence of an alkali salt catalyst chosen from salts of K, Na, Rb or Cs, and a multidentate complexant.

2. Method according to claim 1, wherein the organopolysiloxane O is selected from linear organopolysiloxanes, for example oils or gums, or branched organopolysiloxanes.

3. A method according to claim 1 or 2, wherein the organopolysiloxanes O comprises - at least 5 motifs, preferably at least 10 siloxyl motifs of formula R c SiO<4-c) / 2 in which R, whether identical or different, represents - an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl; - an aryl group comprising 6 to 10 carbon atoms, preferably phenyl; and c = 0, 1, 2 or 3; and - possibly one or more formula R patterns 1 dReSiO<4-de) / 2 in which: R is as defined above R 1 , identical or different, represents: - an alkenyl group comprising 2 to 6 carbon atoms, preferably vinyl; - a hydroxyl group (OH); - an (O-Alk) group where Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably OCH3 or OC2H5, - a group (O-Alk) x with Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms carbon, preferably methyl, and x represents an integer between 2 and 200, - an amino group chosen from (Alk)-NH2 or (Alk)-NH-(Alk)-NH2, with Alk representing an alkyl comprising 1 to 5 carbon atoms; - cyclic amine for example -(CH2) z -O-piperidine in which z represents an integer from 1 to 5, preferably 3, and the piperidine may be substituted in particular by one or more alkyl groups comprising from 1 to 3 carbon atoms, preferably methyl, preferably the substituted piperidine is M ( z NH a group r; - a hydrogen; d=1, 2 or 3, preferably d=1 or 2, more preferably d=1; e=0, 1 or 2; and the sum d+e=1, 2 or 3.

4. Method according to any one of claims 1 to 3, wherein at least one oganopolysiloxane O corresponds to formula (I): R 1 aR(3-a)SiO-(SiR2O) n -(SiR 1 RO) m -SiR 1aR(3-a) (I) in which: R, whether identical or different, represents: - an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably methyl; - an aryl group comprising 6 to 10 carbon atoms, preferably phenyl; R 1 , identical or different, represents: - an alkenyl group comprising 2 to 6 carbon atoms, preferably vinyl; - a hydroxyl group (OH); - an (O-Alk) group where Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms, preferably OCH3 or OC2H5, - a group (O-Alk) xwith Alk represents an alkyl group comprising from 1 to 15 carbon atoms, preferably from 1 to 12 carbon atoms, preferably from 1 to 10 carbon atoms, preferably from 1 to 5 carbon atoms carbon, preferably methyl, and x represents an integer between 2 and 200, - an amino group chosen from (Alk)-NH2 or (Alk)-NH-(Alk)-NH2, with Alk representing an alkyl comprising 1 to 5 carbon atoms; - cyclic amine for example -(CH2) z -O-piperidine in which z represents an integer from 1 to 5, preferably 3, and the piperidine may be substituted in particular by one or more alkyl groups comprising from 1 to 3 carbon atoms, preferably methyl, preferably the substituted piperidine M < z NH r is a group; - a hydrogen; a is an integer and represents 0, 1, 2 or 3, preferably 0, 1 or 2, more preferably 0 or 1; n represents an integer between 10 and 10,000, preferably between 10 and 5,000, preferably between 50 and 5,000, more preferably between 60 and 5,000, for example between 70 and 1,000; m represents an integer between 0 and 100, preferably between 0 and 50, more preferably between 0 and 30, preferably m=0.

5. Method according to any one of claims 1 to 4, wherein the alkali salt is selected from alkali silanolates, alkali hydroxides, alkali alkoxides and alkali siliconates, preferably alkali silanolate.

6. Method according to any one of claims 1 to 5, wherein the alkali salt is a potassium salt, preferably KOSiMe3.

7. Method according to any one of claims 1 to 6, wherein the multidentate complexant is selected from crown ethers, cryptands which are diamine macroheterocycles and polyethylene glycols terminated OH or OCH3.

8. Method according to any one of claims 1 to 7, wherein the multidentate complexant is selected from crown ethers, and OCH3 terminated polyethylene glycols of weight molar mass between 100 and 2000, preferably between 200 and 1000 g / mol.

9. Method according to any one of claims 1 to 8 wherein reactive distillation is carried out at a temperature between 50 and 200°C, preferably between 60 and 180°C, preferably between 120 and 160°C.

10. Method according to any one of claims 1 to 9 wherein the amount of alkali salt used is between 0.005 and 1.5% by weight relative to the weight of organopolysiloxane (O), preferably between 0.005 and 0.9%, more preferably between 0.01 and 0.8%.

11. A method according to any one of claims 1 to 10, wherein a mixture of cyclic organopolysiloxane OC is obtained with more than 95% by weight of a mixture of compounds D3, D4, or D5 relative to the total weight of cyclic organopolysiloxanes OC produced 12. A method according to any one of claims 1 to 11, wherein the multidentate ligand is selected from:

13. Method according to any one of claims 1 to 12, characterized in that the mass yield of cyclic organopolysiloxane OC is greater than 85%.

14. Use of a catalytic system comprising an alkali salt, selected from salts of K, Na, Rb or Cs, and a multidentate complexing agent, for the depolymerization of organopolysiloxanes O to produce cyclic organopolysiloxanes OC.

15. Use according to claim 14, wherein the alkali salt is as defined in claim 5 or 6 and / or the multidentate complexing agent is as defined in any one of claims 7, 8 or 12.

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