Method for reacting silicone with hot or supercritical water

Abstract

The present invention relates to a method for reacting silicone with hot water or supercritical water at a temperature of 140° C. or higher to obtain a solid mixture containing silicon.

Description

[Technical Field]

[0001] The present invention relates to a method for reacting silicone with hot or supercritical water. [Background technology]

[0002] Silicone waste is currently incinerated. Because it has poor combustibility and forms dust that is difficult to incinerate, the combustion reaction requires strong airflow and high combustion chamber temperatures. The dust produced during this process is also a toxic by-product, ash, which requires costly and laborious disposal.

[0003] The use of hydrothermal water as a chemical reagent was investigated by Friedrich Bergius in 1913 as part of coal gasification, where it was identified as a key factor for natural carbonization. In hydrothermal regions, the dielectric constant of water is reduced to a level that allows the dissolution of nonpolar substances. High temperatures and pressures result in a complex network of reactions acting on lignocellulose, i.e., organic matter. Here, lignocellulose is decomposed and converted into carbon-rich materials through hydrolysis and solid-state reactions of C-O bonds and / or intramolecular rearrangement and elimination reactions of lignin. Depending on the temperature, solids, oils, or gases are obtained. In the field of biomass utilization, hydrothermal reactions have recently attracted considerable attention.

[0004] Kenichiro Itami, Koji Terakawa, Junichi Yoshida, and Koa Kajimoto discuss the cleavage of the Si-C bond of silane using supercritical water in "The Carbon-Silicon Bond Cleavage of Organosilicon Compounds in Supercritical Water" The Chemical Society of Japan Bull. Chem. Soc. Soc. Jpn., 77, 2071-2080 (2004). Summary of the Invention

[0005] The present invention provides a method for reacting silicone with hot water or supercritical water at a temperature of 140° C. or higher to obtain a silicon-containing solid mixture. DETAILED DESCRIPTION OF THE INVENTION

[0006] In the present invention, the water referred to as hot water is non-supercritical water at a temperature above 100°C, which exists in a liquid state as a result of a pressure equal to or greater than the vapor pressure at that temperature. Supercritical water is water at a temperature and pressure equal to or greater than its critical point (temperature 374.12°C and pressure 22.1 MPa).

[0007] Surprisingly, the hydrothermal reaction was successful in cleaving not only the Si-C bond but also the Si-O bond in silicones, converting the resulting intermediate into a precipitated silica-like solid, a process previously only known for cleaving Si-C bonds.

[0008] In the method of the present invention, liquid and solid silicones can be reacted in the liquid or supercritical phase. The reaction mixture of water and silicone / siloxane produces a hydrophobic, non-toxic solid mixture, which can then be safely disposed of or used as a filler due to its hydrophobic properties. This solid mixture can also be used to produce pure silicon (raw silicon / Rohsilicium), which means closing the material cycle: silicon → methylchlorosilane → siloxane → solid mixture → silicon. The carbon in the solid contributes to reducing the amount of coal required to produce pure silicon. This solid mixture can also be used as a filler in cement mixtures.

[0009] The term "silicone" encompasses oligomeric or polymeric organosiloxanes in which silicon atoms are linked through oxygen atoms, at least a portion of which bear one or more organic moieties, and compositions containing organosiloxanes.

[0010] The silicone preferably contains at most 1% by weight, more preferably at most 0.1% by weight, even more preferably at most 0.01% by weight of halogen, especially chlorine.

[0011] The composition containing the organosiloxane can contain, for example, fillers, catalysts, binders, and pigments, as well as the organosiloxane. Fillers include, for example, fumed and / or precipitated silica, chalk, and quartz.

[0012] The process of the present invention may be carried out in a batch or continuous mode.

[0013] The solid mixture obtained by the method of the present invention preferably contains 25 to 50 wt %, more preferably 30 to 45 wt %, and even more preferably 31 to 40 wt % silicon. The solid mixture preferably contains 0 to 65 wt %, more preferably 8 to 40 wt %, and even more preferably 15 to 35 wt % carbon.

[0014] In the present invention, the proportion of carbon and oxygen in the solid depends directly on the reaction temperature and the composition of the starting materials: the higher the temperature, the lower the carbon content and the higher the oxygen content.

[0015] In certain embodiments, a gas mixture is formed. The gas mixture preferably contains methane. Up to 400 g of methane can be produced per kg of silicone used. Preferably, 10 to 300 g of methane is produced per kg of silicone used.

[0016] In certain embodiments, the process of the present invention also produces a liquid phase. The liquid phase includes water, reaction by-products, and impurities introduced by the reactants. Depending on the operating regime, some or all of the liquid phase can be reused as a reactant, for example, to minimize the amount of wastewater.

[0017] In addition to methane, carbon monoxide, carbon dioxide, higher hydrocarbons, hydrogen, and water are produced in varying proportions. The composition of the gas mixture depends on pressure and temperature: the higher the pressure and temperature, the greater the proportion of methane in the gas mixture.

[0018] The preferred temperature in the process of the present invention is 160°C to 700°C, more preferably 200°C to 400°C, and even more preferably 250°C to 390°C. The preferred pressure in the process of the present invention is 10 to 400 bar, more preferably 20 to 320 bar, and even more preferably 50 to 280 bar, the lower limit of the pressure being the vapor pressure of the reaction mixture at the reaction temperature in each case. The preferred residence time in the process of the present invention is 1 minute to 24 hours, more preferably 5 minutes to 10 hours, and even more preferably 10 minutes to 1 hour.

[0019] In a preferred embodiment, the reaction mixture is depressurized to atmospheric pressure after completion of the reaction, and the resulting vapor is used for heat recovery and / or preheating of the reactants, resulting in significant heat recovery. [Example]

[0020] The following examples serve to further illustrate the invention described herein.

[0021] The following analytical methods and instruments are used for the characterization:

[0022] The elemental contents reported in the examples were measured using an energy dispersive X-ray spectrometer (EDX). EDX analysis was performed using a ZEISS Ultra 55 scanning electron microscope and an Oxford X-Max 80N energy dispersive X-ray spectrometer. Prior to analysis, the samples were vapor-coated with carbon to prevent charging phenomena using a Safematic Compact Coating Unit 010 / HV. The gas phase was analyzed using a mass spectrometer (ThermoStar™ GSD 320 T2, iridium cathode).

[0023] The following materials and equipment were used in carrying out the experiments in the examples.

[0024] The autoclave used in Example 1 consists of a cylindrical lower part (beaker) and a cover with several ports (e.g., for venting, temperature measurement, and pressure measurement). The volume of the autoclave is 594 mL. The autoclave is electrically heated. The stirrer used is a 5 cm diameter, four-blade pitched blade stirrer.

[0025] The silicone used in Example 1 was ELASTOSIL® LR 7665 from WACKER CHEMIE AG, Munich, which was fully cured according to the instructions. The water used was distilled.

[0026] In the following examples, unless otherwise specified, in each case, all amounts and percentages are by weight, all pressures are 0.10 MPa (abs.), and all temperatures are 20°C.

[0027] Example 1: An autoclave is charged with 30 g of finely chopped silicone (cubes with an edge length of 0.5 cm) and 150 mL of water and sealed. The autoclave is heated to 350 °C over 120 minutes and held at that temperature for 90 minutes. During the experiment, the pressure rises to 160 bar. The autoclave is cooled to room temperature over 12 hours. After cooling the reactor, samples are taken for gas analysis. The gas space of the autoclave is then purged with nitrogen and the autoclave is opened.

[0028] A clear liquid and a white or slightly gray solid are obtained. The liquid is removed and the solid is dried to give 21 g of solid.

[0029] Three experiments were performed, and the EDX analysis results of the solid mixtures are shown in Table 1. MV indicates the average value.

[0030] [Table 1]

[0031] Example 2: 1000 kg of solid silicone waste consisting of silicone rubber in a plastic container was crushed, including the container, into pieces 3 m in size. 3 The reaction is carried out in a stirred tank with 1500 kg of water at 350 °C and 160 bar for 2 hours. The two tanks are operated in parallel. One tank is preheated by heat recovery from cooling the other tank, and the remaining heat requirement is supplied externally. The reaction products are a solid / liquid mixture and a gas phase. The solid / liquid mixture is filtered, and the resulting solid has the composition shown in Table 1. According to current knowledge of hydrothermal carbonization, the added plastic container reacts to give a carbon-rich particulate solid. The liquid phase contains reaction by-products and, depending on the degree of contamination, can be used for further reaction of silicone waste. The gas phase contains not only water but also volatile by-products and may contain methane depending on the reaction regime and starting materials.

[0032] The solids are then passed on for beneficial use in Example 3.

[0033] Example 3: A beneficial use of the solids obtained in Examples 1 and 2 for the production of silicon metal.

[0034] The solids obtained in Examples 1 and 2 are pressed into pellets and serve as starting material for the production of pure silicon, where the silicon is reduced to pure silicon.

Claims

1. A method for obtaining a silicon-containing solid mixture by reacting silicone with hot or supercritical water at a temperature of 140°C or higher at a pressure of 160 bar or less, wherein the term "silicone" encompasses oligomeric or polymeric organosiloxanes in which silicon atoms are bonded via oxygen atoms and at least a portion of the silicon atoms bear one or more organic substituents, and compositions comprising organosiloxanes.

2. 10. The method of claim 1, wherein the silicone contains up to 1% by weight of a halogen.

3. 3. The method of claim 1, wherein the solid mixture comprises 25 to 50% by weight of silicon.

4. The method of any one of claims 1 to 3, wherein a methane-containing gas mixture is produced.

5. The method according to any one of claims 1 to 4, wherein the temperature is from 160°C to 700°C.

6. The method according to any one of claims 1 to 5, wherein the pressure is from 10 to 160 bar.

7. The method according to any one of claims 1 to 6, wherein the solid mixture produced is fed to the production of pure silicon.

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