Preparation method of cyclic siloxane and cracking device
By using a series external circulation design of a batch-type and a self-cleaning scraped falling film pyrolyzer, combined with gradient heating and online decoking technology, the problems of low efficiency, low purity and coking blockage in traditional cyclic siloxane pyrolysis units are solved, achieving efficient and low-consumption preparation of cyclic siloxanes.
Patent Information
- Application Number
- CN202511779825.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-02-24
AI Technical Summary
Traditional cyclosiloxane cracking units suffer from problems such as low cracking efficiency, uneven temperature control, and equipment coking and blockage, leading to increased side reactions, low purity, high energy consumption, and impact on continuous production.
The design employs a series external circulation system combining a batch pyrolysis unit and a self-cleaning scraped-film falling film pyrolysis unit. This system utilizes gradient heating and online decoking technology to achieve deep pyrolysis through batch pyrolysis, while the self-cleaning scraped-film falling film pyrolysis unit increases the heat and mass transfer area. The external circulation system replenishes the catalyst, enabling rapid and efficient pyrolysis.
It improves the cracking efficiency and selectivity of cyclic siloxanes, reduces side reactions, lowers energy consumption, extends the continuous operation cycle of equipment, and enables the production of high-purity cyclic siloxanes.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of organosilicon cyclic pyrolysis, specifically a method for preparing cyclic siloxanes and a pyrolysis apparatus. Background Technology
[0002] Cyclosiloxanes are important chemical intermediates, which can be divided into methylcyclosiloxanes and methylphenylcyclosiloxanes. They are widely used in synthetic materials, new energy, electronic communications, rail transportation, and aerospace. Industrially, cyclosiloxanes are generally produced by high-temperature cracking of methyl hydrolysates (40%-50% methylcyclosiloxane, 50-60% hydroxyl-terminated linear methylpolysiloxane) or methylphenyl hydrolysates (40%-50% methylphenylcyclosiloxane, 50-60% hydroxyl-terminated linear methylphenylpolysiloxane). However, traditional cracking equipment has the following problems:
[0003] 1. Low pyrolysis efficiency: Pyrolysis reaction requires high temperature (usually >150-380℃). Traditional pyrolysis is in batch form, with small heat transfer area, which leads to limited heat transfer, low pyrolysis efficiency, long pyrolysis time in batch, easy to trigger side reactions, and short pyrolysis cycle. Generally, heat transfer can be improved by increasing the heating temperature (usually 180-480℃), but the side reactions are further enhanced and the pyrolysis cycle is further shortened.
[0004] 2. Uneven temperature control: Poor interface renewal and insufficient mixing in traditional pyrolysis reactors lead to uneven temperature distribution, limited mass transfer resulting in low pyrolysis efficiency, and prolonged local overheating leads to an increase in side reactions; during the pyrolysis process, over-pyrolysis is prone to occur, resulting in demethylation, phenyl reactions, disproportionation reactions, and low purity of the target product cyclosiloxane.
[0005] 3. Equipment coking and blockage: Under localized high temperatures and prolonged periods, reactants are prone to coking on the inner wall of the pyrolysis tube or the surface of the catalyst, requiring frequent shutdowns for cleaning and affecting continuous production. Summary of the Invention
[0006] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing cyclic siloxanes and a pyrolysis apparatus. The preparation method provided by the present invention has high pyrolysis efficiency, few side reactions, high selectivity, is not prone to coking, and has low energy consumption.
[0007] This invention provides a method for preparing cyclic siloxanes, comprising the following steps:
[0008] S1) The cyclic siloxane cracking feedstock is subjected to a batch cracking reaction under a catalyst to obtain gaseous products and liquid products from the cracking reactor.
[0009] S2) After external circulation heating, the liquid phase product obtained in step S1) is subjected to a self-cleaning scraped falling film tube pyrolysis reaction to obtain falling film tube pyrolysis gas phase product and falling film tube pyrolysis liquid phase product; when the liquid phase product of the pyrolysis vessel is subjected to external circulation heating, the cyclic siloxane pyrolysis feedstock and catalyst obtained in step S1) are added; the falling film tube pyrolysis liquid phase product is returned to step S1) as cyclic siloxane pyrolysis feedstock and step S1) is repeated.
[0010] The gaseous products from the pyrolysis vessel obtained in step S1) and the gaseous products from the falling film tube pyrolysis obtained in step S2) are subjected to cyclic siloxane distillation to obtain cyclic siloxanes.
[0011] The present invention provides a method for preparing cyclic siloxanes by cracking cyclic siloxane feedstock. Specifically, the cyclic siloxane cracking feedstock is a methyl hydrolysate or a methylphenyl hydrolysate; the methyl hydrolysate comprises 40 wt%~50 wt% of methylcyclosiloxane and 50 wt%~60 wt% of hydroxyl-terminated linear methylpolysiloxane; the methylphenyl hydrolysate comprises 40 wt%~50 wt% of methylphenylcyclosiloxane and 50 wt%~60 wt% of hydroxyl-terminated linear methylphenylpolysiloxane. The catalyst used in this invention is selected from one or more of KOH, NaOH, Li2CO3, and Na2CO3; the amount of the catalyst used is 0.4 wt%~5 wt% of the cyclic siloxane cracking feedstock in step S1).
[0012] In step S1), this invention first performs a batch cracking reaction of the cyclic siloxane cracking feedstock under a catalyst to obtain gaseous and liquid products from the cracking vessel. Specifically, the cyclic siloxane cracking feedstock is subjected to a batch cracking reaction in a batch cracker to obtain gaseous and liquid products from the cracking vessel. This invention introduces the cyclic siloxane cracking feedstock into a batch cracker for batch cracking, resulting in a long residence time, providing deep cracking, and allowing for subsequent catalyst recycling. Inside the cracking vessel, through optimized stirring design, axial circulation and radial flow are enhanced, interface renewal within the vessel is strengthened, evaporation is enhanced, and the cracking catalyst is contained within.
[0013] This invention obtains the gaseous and liquid phase products from the pyrolysis reactor. The liquid phase product is then subjected to external circulation heating and followed by a self-cleaning scraped-plate falling film pyrolysis reaction to obtain the falling film pyrolysis gaseous and liquid phase products. In this invention, the gaseous product obtained from the top of the pyrolysis reactor can be further distilled to obtain cyclic siloxanes. The liquid phase product, containing catalyst and being the last unpyrolyted material in the reactor, can be used as an active substrate to restart pyrolysis in the self-cleaning scraped-plate falling film pyrolysis reactor. Specifically, in this invention, the liquid phase product obtained from the pyrolysis reactor is heated to the temperature of a self-cleaning scraped-plate falling film pyrolysis reaction via external circulation and then enters a self-cleaning scraped-plate falling film pyrolysis unit. In the self-cleaning scraped-plate falling film pyrolysis unit, the mixed liquid is evenly distributed to the inner wall of the unit by a distributor, forming a thin liquid film that flows downwards along the wall surface, creating a stable liquid film distribution system for the self-cleaning scraped-plate falling film pyrolysis reaction. After most of the cyclic siloxanes in the pyrolysis reaction liquid have cracked, falling film pyrolysis gas phase products and falling film pyrolysis liquid phase products are obtained. The falling film pyrolysis gas phase products can be further distilled to obtain cyclic siloxanes, and the falling film pyrolysis liquid phase products are the remaining un-cracked materials in the reactor. The self-cleaning scraped-plate falling film pyrolysis unit has a short pyrolysis residence time. The self-cleaning scraped-plate falling film pyrolysis design increases the heat and mass transfer area, and the internal scraper design provides good interface renewal, prevents pyrolysis gelation, and further enhances pyrolysis.
[0014] In this invention, when the liquid phase product of the pyrolysis reactor is subjected to external circulation heating, the cyclic siloxane pyrolysis feedstock and catalyst described in step S1) are added. Specifically, the obtained liquid phase product of the pyrolysis reactor and the added cyclic siloxane pyrolysis feedstock and catalyst are subjected to external circulation heating together, and then subjected to a self-cleaning scraped falling film pyrolysis reaction to obtain falling film pyrolysis gas phase product and falling film pyrolysis liquid phase product. In this invention, the liquid phase product of the pyrolysis reactor is pumped to the external circulation pipeline for external circulation heating via a circulation pump. After the external circulation pump, fresh cyclic siloxane pyrolysis feedstock and fresh pyrolysis catalyst can be added to restart pyrolysis in the self-cleaning scraped falling film pyrolysis reactor. This addition can be continuous or intermittent. The cyclic siloxane pyrolysis feedstock added in this invention is the same fresh feedstock as the cyclic siloxane pyrolysis feedstock described in step S1). Preferably, based on a cyclic siloxane production rate of 10 kg / h to 200 kg / h, the replenishment rate of the cyclic siloxane cracking feedstock of the present invention is 10 kg / h to 200 kg / h. The cyclic siloxane production rate of the present invention is preferably the same as the replenishment rate of the cyclic siloxane cracking feedstock. The amount of catalyst added in the present invention is 0.05 wt% to 0.5 wt% of the amount of cyclic siloxane cracking feedstock added, preferably 0.1 wt% to 0.5 wt%, more preferably 0.1 wt% to 0.3 wt%; the catalyst is the same as described above and will not be repeated.
[0015] When the cyclic siloxane cracking feedstock of the present invention is methyl hydrolysate, the batch cracking reaction is carried out at an absolute pressure of 5 kPa to 10 kPa and the temperature of the batch cracking reaction is 100℃ to 160℃; when the cyclic siloxane cracking feedstock is methylphenyl hydrolysate, the batch cracking reaction is carried out at an absolute pressure of 100 Pa to 1 kPa and the temperature of the batch cracking reaction is 290℃ to 350℃; the temperature of the self-cleaning scraper falling film tube cracking reaction is 5℃ to 25℃ higher than the temperature of the batch cracking reaction.
[0016] In some embodiments of the present invention, when the cyclic siloxane cracking feedstock is methyl hydrolysate, the temperature of the self-cleaning scraped falling film pyrolysis reaction is 110℃~165℃, preferably 110℃~120℃, and the temperature of the batch pyrolysis reaction is 100℃~160℃, preferably 100℃~110℃, and the batch pyrolysis reaction is carried out at an absolute pressure of 5 kPa~10 kPa, preferably 8 kPa~9 kPa; when the cyclic siloxane cracking feedstock is methylphenyl hydrolysate, the temperature of the self-cleaning scraped falling film pyrolysis reaction is 300℃~355℃, preferably 300℃~305℃, and the temperature of the batch pyrolysis reaction is 290℃~350℃, preferably 290℃~300℃, and the batch pyrolysis reaction is carried out at an absolute pressure of 100 Pa~1 kPa, preferably 800 Pa~900 Pa. The reaction is carried out at Pa; the temperature of the self-cleaning scraper falling film pyrolysis reaction is 5°C to 25°C higher than that of the batch pyrolysis reaction.
[0017] After obtaining the gas-phase product and liquid-phase product from the falling film tube pyrolysis, the present invention returns the liquid-phase product from the falling film tube pyrolysis as a feedstock for cyclic siloxane pyrolysis to step S1) and repeats step S1). This cycle of steps S1) and S2) is repeated approximately 1 to 2 hours. During the cycles of steps S1) and S2), the present invention employs a gradient heating design: the batch pyrolysis unit is used for low-temperature heating, the external circulation heating unit for medium-temperature heating, and the self-cleaning scraper falling film tube pyrolysis unit for high-temperature heating. Temperature gradient control is achieved by adjusting the power of each stage according to the material characteristics and residence time, avoiding prolonged local overheating and solving the problem of limited heat and mass transfer.
[0018] In this invention, when the liquid phase product of the pyrolysis reactor is subjected to external circulation heating, the material flow rate for external circulation heating is 5 t / h to 20 t / h, based on a cyclic siloxane production rate of 10 kg / h to 200 kg / h. In one embodiment of this invention, when the cyclic siloxane pyrolysis feedstock is methyl hydrolysate, the material flow rate for external circulation heating is 10 t / h to 20 t / h, based on a cyclic siloxane production rate of 100 kg / h to 200 kg / h. In another embodiment of this invention, when the cyclic siloxane pyrolysis feedstock is methylphenyl hydrolysate, the material flow rate for external circulation heating is 5 t / h to 10 t / h, based on a cyclic siloxane production rate of 10 kg / h to 100 kg / h. This invention achieves precise thermal compensation through circulation flow regulation, enabling gradient heating and solving the problem of excessive residence time and subsequent pyrolysis side reactions caused by local overheating in traditional processes (reducing side reactions by 40% to 80% compared to traditional batch pyrolysis).
[0019] In the cyclic process of steps S1) and S2), the gaseous products from the pyrolysis vessel obtained in step S1) and the gaseous products from the falling film pyrolysis vessel obtained in step S2) are subjected to cyclic siloxane distillation to obtain cyclic siloxanes. Specifically, the gaseous products from the pyrolysis vessel and the gaseous products from the falling film pyrolysis vessel are distilled into cyclic siloxanes in a distillation column. The top product of the distillation column is condensed to obtain cyclic siloxanes, and the bottom product of the distillation column is returned to step S2) to directly participate in the self-cleaning scraped falling film pyrolysis reaction.
[0020] The distillation described in this invention is carried out in a distillation column with a diameter of 300 mm to 600 mm and a height of 7000 mm to 10000 mm. When the cyclic siloxane cracking feedstock of this invention is methyl hydrolysate, the top temperature of the distillation column is 80℃ to 140℃, preferably 90℃ to 95℃, the top reflux ratio of the distillation column is 1 to 3, preferably 1.5 to 2, and the distillation is carried out at an absolute pressure of 5 kPa to 10 kPa. When the cyclic siloxane cracking feedstock of this invention is methylphenyl hydrolysate, the top temperature of the distillation column is 190℃ to 210℃, preferably 195℃ to 205℃, the top reflux ratio of the distillation column is 1 to 15, preferably 6 to 10, more preferably 6 to 9 or 9 to 10, and the distillation is carried out at an absolute pressure of 100 Pa to 1 kPa. The cracking products, cyclosiloxanes (containing cyclic, linear oligomers and trace impurities), enter the distillation column, which uses high-efficiency packing or tray structure and optimizes fluid distribution and pressure drop control (such as reducing tray resistance and optimizing gas-liquid distributors) to reduce energy consumption while ensuring separation efficiency.
[0021] In some embodiments of the present invention, methyl hydrolysate is used as the feedstock for cyclic siloxane cracking. In step S1), the cyclic siloxane cracking feedstock is preheated to 100°C~110°C and then mixed with a catalyst before being fed into a batch cracker. The heating temperature of the batch cracker is controlled at 170°C~180°C, so that the material temperature of the cyclic siloxane cracking feedstock and catalyst is 100°C~110°C, and a batch cracking reaction is carried out to obtain gaseous and liquid phase products from the cracking vessel. In step S2), the liquid phase product from the cracking vessel is subjected to external circulation heating, while simultaneously replenishing the cyclic siloxane cracking feedstock and catalyst. The external circulation heating temperature is controlled at 170°C~180°C, so that the outlet temperature of the external circulation material is 110°C. The temperature is 170℃~180℃, and then the material enters the self-cleaning scraped-film falling film pyrolyzer. The heating temperature of the self-cleaning scraped-film falling film pyrolyzer is controlled at 170℃~180℃, so that the material temperature in the self-cleaning scraped-film falling film pyrolyzer is maintained at 110℃~100℃ to carry out the self-cleaning scraped-film falling film pyrolyzer reaction, and the self-cleaning scraped-film falling film pyrolyzer gas phase product and the self-cleaning scraped-film falling film pyrolyzer liquid phase product are obtained. The falling film pyrolyzer liquid phase product is returned to step S1) as the raw material for cyclic siloxane pyrolysis and step S1) is repeated. The pyrolysis reactor gas phase product obtained in step S1) and the self-cleaning scraped-film falling film pyrolyzer gas phase product obtained in step S2) are subjected to cyclic siloxane distillation to obtain cyclic siloxane.
[0022] In other embodiments of the present invention, methylphenyl hydrolysate is used as the feedstock for cyclic siloxane cracking. In step S1), the cyclic siloxane cracking feedstock is preheated to 180°C and then mixed with a catalyst before being fed into a batch cracker. The heating temperature of the batch cracker is controlled at 360°C to 370°C, so that the material temperature of the cyclic siloxane cracking feedstock and the catalyst is 290°C to 300°C, and the batch cracking reaction is carried out to obtain gaseous products and liquid products from the cracking vessel. In step S2), the liquid products from the cracking vessel are subjected to external circulation heating, while the cyclic siloxane cracking feedstock and the catalyst are replenished. The external circulation heating temperature is controlled at 390°C to 400°C, so that the outlet temperature of the external circulation material is 300°C. The material is heated to 305℃ and then enters a self-cleaning scraped-film falling film pyrolyzer. The heating temperature of the self-cleaning scraped-film falling film pyrolyzer is controlled at 450℃~460℃, so that the material temperature inside the self-cleaning scraped-film falling film pyrolyzer is maintained at 300℃~305℃ to carry out the self-cleaning scraped-film falling film pyrolyzer pyrolysis reaction, and the self-cleaning scraped-film falling film pyrolyzer gas phase product and self-cleaning scraped-film falling film pyrolyzer liquid phase product are obtained. The falling film pyrolysis liquid phase product is returned to step S1) as a raw material for cyclic siloxane pyrolysis and step S1) is repeated. The pyrolysis gas phase product obtained in step S1) and the falling film pyrolysis gas phase product obtained in step S2) are subjected to cyclic siloxane distillation to obtain cyclic siloxane.
[0023] In step S2) of this invention, the distillation of cyclic siloxanes also includes periodically performing ultrasonic-assisted coking; the frequency of the ultrasonic-assisted coking is 20 kHz to 40 kHz. In some embodiments of this invention, during the distillation of cyclic siloxanes in step S2), ultrasonic-assisted coking is performed simultaneously every 1 h to 5 h. An ultrasonic transducer is embedded in the inner wall of the pyrolysis tube, and the cavitation effect destroys the accumulated polymer, achieving online coking without stopping the operation.
[0024] The preparation method provided by this invention uses methyl hydrolysate or methylphenyl hydrolysate as raw materials, breaking the traditional static evaporation mode in a batch pyrolysis reactor. It achieves the production of high-purity cyclic compounds (purity ≥99%) through a pyrolysis-distillation coupling process. Specifically, it is based on the advantages and disadvantages of self-cleaning scraped-film falling film pyrolysis and batch pyrolysis (self-cleaning scraped-film falling film pyrolysis has a large heat transfer area, timely heat transfer, and high pyrolysis efficiency, but limited residence time; batch pyrolysis has poor heat transfer effect, but long residence time, which can further extend the time to pyrolyze the unpyrolyzed material in self-cleaning scraped-film falling film pyrolysis). It creatively combines the two and uses external circulation heating to make the unpyrolyzed material in the batch pyrolysis reaction serve as an active base material to restart the self-cleaning scraped-film falling film pyrolysis reaction with fresh material. This allows the cyclic siloxane pyrolysis raw material to circulate between the self-cleaning scraped-film falling film pyrolysis reaction and the batch pyrolysis reaction. The gaseous product generated in the cyclic process is further distilled to achieve the production of high-purity cyclic compounds (purity ≥99%).
[0025] The present invention also provides a pyrolysis apparatus using any of the preparation methods described above, comprising a batch pyrolysis reaction unit, an external circulation unit, a self-cleaning scraped falling film pyrolysis reaction unit, and a distillation unit; wherein the batch pyrolysis reaction unit comprises a batch pyrolyzer, the batch pyrolyzer being provided with a heat medium inlet, a heat medium outlet, a top pyrolysis feedstock inlet, a top gas phase product outlet, and a bottom liquid phase product outlet;
[0026] The external circulation unit includes an external circulation pipeline, a circulation pump, and an external circulation heater. The external circulation pipeline has a raw material inlet, a catalyst inlet, an external circulation pipeline inlet, and an external circulation pipeline outlet. The circulation pump and the external circulation heater are sequentially arranged after the external circulation pipeline inlet and before the external circulation pipeline outlet.
[0027] The self-cleaning scraped-film falling film pyrolysis reaction unit includes a self-cleaning scraped-film falling film tubular pyrolysis unit. The self-cleaning scraped-film falling film tubular pyrolysis unit is provided with a heat medium inlet, a heat medium outlet, a top pyrolysis feedstock inlet, a top gas phase product outlet, and a bottom liquid phase product outlet. The self-cleaning scraped-film falling film tubular pyrolysis unit contains scrapers and has an external motor, which can clean the glue itself.
[0028] The distillation unit includes a distillation column, a top-collection condenser, a top-collection reflux pump, a vacuum tube, and a product collection pipe. The distillation column is provided with a top distillation product vapor phase outlet, a bottom distillation feed gas phase inlet, a bottom distillation liquid phase outlet, and a top-collection reflux inlet. The top-collection condenser is provided with a distillation product vapor phase inlet, a condensed product outlet, a refrigerant inlet, and a refrigerant outlet.
[0029] The heat transfer medium used in the pyrolysis device of the present invention is steam, heat transfer oil, molten salt, electric heating, etc., and the cold transfer medium used is circulating water, low temperature cold water, frozen brine, ethylene glycol aqueous solution, propylene glycol aqueous solution, etc.
[0030] In this invention, the batch-type pyrolysis reaction unit, the external circulation unit, and the self-cleaning scraped-plate falling film pyrolysis reaction unit are sequentially and cyclically connected. Specifically, the batch-type pyrolysis reaction unit is connected to the external circulation unit, the external circulation unit is connected to the self-cleaning scraped-plate falling film pyrolysis reaction unit, and the self-cleaning scraped-plate falling film pyrolysis reaction unit is connected to the batch-type pyrolysis reaction unit. More specifically, the bottom liquid phase product outlet of the batch-type pyrolysis reaction unit is connected to the external circulation pipeline inlet of the external circulation unit, the external circulation pipeline outlet of the external circulation unit is connected to the top inlet of the self-cleaning scraped-plate falling film pyrolysis reaction unit, and the bottom liquid phase product outlet of the self-cleaning scraped-plate falling film pyrolysis reaction unit is connected to the top inlet of the batch-type pyrolysis reaction unit.
[0031] The distillation unit of this invention is connected to the self-cleaning scraped-film falling film pyrolysis reaction unit and the batch pyrolysis reaction unit. Specifically, the top vapor phase product outlet of the self-cleaning scraped-film falling film pyrolysis reaction unit is connected to the distillation unit, and the top vapor phase product outlet of the batch pyrolysis reaction unit is connected to the bottom feed gas phase inlet of the distillation column of the distillation unit. In some embodiments of this invention, the top vapor phase product outlets of the self-cleaning scraped-film falling film pyrolysis reaction unit and the batch pyrolysis reaction unit are connected to the bottom feed gas phase inlet of the distillation column of the distillation unit via vapor phase pipelines.
[0032] This invention provides a method for preparing cyclic siloxanes and a pyrolysis apparatus. The method for preparing cyclic siloxanes provided by this invention has the following advantages compared with the prior art: (1) It adopts a series external circulation collaborative design of a self-cleaning scraped falling film tubular pyrolyzer and a batch pyrolyzer. The self-cleaning scraped falling film tubular pyrolyzer greatly increases the gas-liquid contact area. Combined with precise heating from an external heat source, it achieves rapid pyrolysis (main reaction: linear dimethylsiloxane oligomer pyrolysis to generate cyclic compounds). Then, the remaining unpyrolyzed material enters the batch pyrolyzer for deep pyrolysis. In the batch pyrolyzer, the axial circulation and radial flow are enhanced by optimizing the stirring design, which enhances the interface renewal and evaporation in the batch pyrolyzer; (2) The liquid phase is forced to circulate by an external circulation pump. Combined with the self-cleaning scraped falling film tubular pyrolyzer, a dynamic thin liquid film is formed, which significantly increases the heat exchange and evaporation area (30%-50% higher than the traditional batch pyrolysis). (3) Based on the pyrolysis characteristics such as material properties and residence time, the system maintains stable pyrolysis temperature by employing a gradient heating design with a self-cleaning scraped-film falling film pyrolysis reaction as the high-temperature section, a batch pyrolysis reaction as the low-temperature section, and external circulation heating as the medium-temperature section, as well as a thermal compensation design (such as dynamically adjusting the circulation flow rate or heating power). This reduces side reactions caused by local overheating and solves the problem of limited heat and mass transfer. In summary, this invention achieves a highly efficient, stable, low-consumption, and highly selective pyrolysis process through gradient heating, a self-cleaning scraped-film falling film pyrolysis unit, and a batch pyrolysis unit connected in series with external circulation, and innovative online decoking technology. It solves the problems of high energy consumption, poor selectivity, and coking blockage in traditional equipment, extends the continuous operation cycle, and has significant industrial application value. Attached Figure Description
[0033] Figure 1 This is a flowchart of the cracking apparatus and process flow diagram of the cyclic siloxane described in this invention. Detailed Implementation
[0034] This invention discloses a method for preparing cyclic siloxanes and a pyrolysis apparatus. Those skilled in the art can refer to this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to implement and apply the technology of this invention.
[0035] Figure 1 The diagram below shows the cracking apparatus and process flow diagram of the cyclic siloxane described in this invention. This invention employs the following... Figure 1 The apparatus and process flow shown are used for the cracking of cyclic siloxanes. Figure 1In the diagram, E1 is the external circulation heater, R1 is the pyrolysis vessel, R2 is the self-cleaning scraper falling film pyrolysis unit, P1 is the circulation pump, T1 is the distillation column, E2 is the top-collection condenser, B is the vessel residue removed through the external circulation, VA is the vacuum, 1 and 25 are both cyclic siloxane feed lines, 24 is the catalyst feed line, 2, 4 and 5 are external circulation lines, 3 is the external circulation discharge line, 7 and 9 are liquid phase reflux pipes, 6, 8 and 10 are gas phase lines, 11 is the column top gas phase pipe, 12 and 13 are top-collection reflux pipes, 14 is the product C collection pipe, 15 is the vacuum pipe, and 16, 17, 18, 19, 20 and 21 are heat transfer pipes.
[0036] The present invention will be further described below with reference to the embodiments:
[0037] Examples 1-2: Preparation of methylcyclosiloxanes by pyrolysis:
[0038] 1. The raw material methyl hydrolysate (the product of hydrolysis of dimethyldichlorosilane, including 40%~50% methylcyclosiloxane and 50~60% hydroxyl-terminated linear methyl polysiloxane) is heated to 100~110℃ in a preheater;
[0039] 2. The heated raw material enters the pyrolysis reactor (2 m 3 The pyrolysis is carried out at 100℃~110℃, the pyrolysis vacuum is 5 kPa~10 kPa (absolute pressure), the starting material in the pyrolysis reactor is 0.8 tons~1 ton, and the amount of starting catalyst (KOH, NaOH, Li2CO3, Na2CO3) added is 0.4%~5%; the pyrolysis reactor is heated by steam, and the steam pressure is 0.8 MPa~2.0 MPa;
[0040] After the cracking begins, the external circulation is simultaneously activated to allow the cracked feedstock to enter the external circulation pipeline. The external circulation flow rate is 5 tons / h to 20 tons / h. Feedstock is then added at a rate of 100 kg / h to 200 kg / h and a temperature of 100℃ to 110℃. Catalyst is continuously fed at a rate of 0.05% to 0.3%. The external circulation heater is a steam heater with a steam pressure of 0.8 MPa to 2.0 MPa.
[0041] The feedstock from the pyrolysis reactor, the added fresh feedstock, and the added catalyst enter the self-cleaning scraped-plate falling film pyrolyzer via an external circulation pipeline for further pyrolysis. The self-cleaning scraped-plate falling film pyrolyzer has an area of 8 m². 2 ~10 m 2 The rotation speed is 30 rpm to 100 rpm; the self-cleaning scraper falling film pyrolyzer is steam heated, and the steam pressure is 0.8 MPa to 2.0 MPa.
[0042] 3. The raw material after cracking by the self-cleaning scraper falling film pyrolyzer enters the distillation column. The distillation column temperature is 80℃~140℃, the column diameter is 300 mm, the height is 10000 mm, and the packing is conventional packing. The top reflux ratio is 1~3, the vacuum is 5 kPa~10 kPa (absolute pressure), and the product is a mixture of D3, D4, and D5.
[0043] 4. In the distillation column distributor, ultrasonic cleaning (30 kHz) is activated every 2 hours of operation of the packing.
[0044] 5. After a pyrolysis cycle is completed, remove the residue from the pyrolysis vessel using the bottom circulation pump, and then proceed with the above steps to start the next cycle.
[0045] Examples 1 and 2 were both performed according to the above steps, and the specific parameters are shown in Table 1:
[0046] Table 1
[0047]
[0048] When by-products accumulate to a certain level in the system, the system is recycled until the cracking capacity decreases by 50% or the product purity fails to meet the requirements (>99%). At this point, the cracking system enters the dehydration phase. One cracking cycle is defined as the time from the start of feeding into the cracking system to the dehydration phase. The same applies below and will not be repeated here.
[0049] Comparative Examples 1-2
[0050] 1. The raw material methyl hydrolysate (the product of dimethyl dichlorosilane hydrolysis, including 40%~50% methylcyclosiloxane and 50~60% hydroxyl-terminated linear methyl polysiloxane) is preheated by a preheater.
[0051] 2. The heated raw materials and catalyst enter the cracking reactor (2 m). 3 The heating temperature and absolute vacuum pressure of the pyrolysis reactor are controlled to ensure that the material temperature in the pyrolysis reactor reaches the temperature required for the pyrolysis reaction.
[0052] 3. Start feeding fresh raw materials into the cracking reactor at a rate of 100 kg / h to 150 kg / h and a temperature of 100℃ to 110℃. The catalyst should be fed continuously at a rate of 0.05% to 0.3%.
[0053] 4. The raw material after cracking in the cracking vessel enters the distillation column. The distillation column has a diameter of 300 mm and a height of 10,000 mm, and is filled with conventional packing. The top reflux ratio and vacuum absolute pressure of the distillation column are controlled to carry out distillation. The product is cyclosiloxane, specifically a mixture of hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5).
[0054] The specific parameters are shown in Table 2:
[0055] Table 2
[0056]
[0057] Examples 3-4
[0058] Preparation of methylphenylcyclosiloxane by pyrolysis:
[0059] 1. The raw material, methylphenyl hydrolysate (the product after hydrolysis of methylphenyl dichlorosilane, including 40%~50% methylphenyl cyclosiloxane and 50%~60% hydroxyl-terminated linear methylphenyl polysiloxane), is heated to 170℃~180℃ in a preheater;
[0060] 2. The heated raw material enters the pyrolysis reactor (2 m 3 The material is heated to 290℃~300℃ for pyrolysis. The pyrolysis vacuum is 100 Pa-1 kPa (absolute pressure). The starting material in the pyrolysis reactor is 0.8 tons to 1 ton, and the starting catalyst (KOH, NaOH, Li2CO3, Na2CO3) is added at 0.4%~5%. The pyrolysis reactor is electrically heated, and the temperature of the electric heating block is 360℃~370℃.
[0061] After the cracking begins, the external circulation is simultaneously activated to allow the cracked feedstock to enter the external circulation pipeline. The external circulation flow rate is 5 tons / h to 10 tons / h. Fresh feedstock is then added at a rate of 30 kg / h to 100 kg / h and a feed temperature of 170℃ to 180℃. Catalyst is continuously fed at a rate of 0.05% to 0.3%. The external circulation preheater is electrically heated, with the electric heating block temperature at 390℃ to 400℃.
[0062] The feedstock after pyrolysis in the pyrolysis reactor, the added fresh feedstock, and the catalyst enter the falling film self-cleaning scraped-plate falling film tubular pyrolyzer via an external circulation pipeline for further pyrolysis. The self-cleaning scraped-plate falling film tubular pyrolyzer has an area of 8 m². 2 ~10 m 2 The rotation speed is 30 rpm to 100 rpm; the self-cleaning scraper falling film pyrolyzer is electrically heated, and the temperature of the electric heating block is 450℃ to 460℃.
[0063] 3. The raw material after cracking by the self-cleaning scraper falling film pyrolyzer enters the distillation column. The top temperature of the distillation column is 190℃~210℃, the column diameter is 300 mm, the height is 10000 mm, and the packing is conventional packing. The top reflux ratio is 1~15, the vacuum is 100 Pa~1kPa (absolute pressure), and the product is methylphenylcyclosiloxane.
[0064] 4. In the distillation column distributor, ultrasonic cleaning (30 kHz) is activated every 2 hours of operation of the packing.
[0065] 5. After a pyrolysis cycle is completed, remove the residue from the pyrolysis vessel using the bottom circulation pump, and then proceed with the above steps to start the next cycle.
[0066] Examples 3 and 4 were performed according to the above steps, and the specific parameters are shown in Table 3:
[0067] Table 3
[0068]
[0069] Comparative Examples 3-5
[0070] 1. The raw material methylphenyl hydrolysate (the product after hydrolysis of methylphenyl dichlorosilane, including 40%~50% methylphenyl cyclosiloxane and 50%~60% hydroxyl-terminated linear methylphenyl polysiloxane) is preheated by a preheater;
[0071] 2. The heated raw materials and catalyst enter the cracking reactor (2 m). 3 The heating temperature and absolute vacuum pressure of the pyrolysis reactor are controlled to ensure that the material temperature in the pyrolysis reactor reaches the temperature required for the pyrolysis reaction.
[0072] 3. Start feeding fresh raw materials into the cracking reactor at a rate of 20 kg / h to 100 kg / h and a temperature of 150℃ to 200℃. The catalyst should be fed continuously at a rate of 0.05% to 0.3%.
[0073] 4. The raw material after cracking in the cracking vessel enters the distillation column. The distillation column has a diameter of 300 mm and a height of 10,000 mm, and is filled with conventional packing. The top reflux ratio and vacuum absolute pressure of the distillation column are controlled to carry out distillation, and the product is methylphenylcyclosiloxane.
[0074] The specific parameters are shown in Table 4:
[0075] Table 4
[0076]
[0077] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for preparing a cyclic siloxane, characterized in that, Includes the following steps: S1) The cyclic siloxane cracking feedstock is subjected to a batch cracking reaction under a catalyst to obtain gaseous products and liquid products from the cracking reactor. S2) The liquid phase product obtained in step S1) is subjected to external circulation heating and then subjected to self-cleaning scraped falling film tube pyrolysis reaction to obtain falling film tube pyrolysis gas phase product and falling film tube pyrolysis liquid phase product. When the liquid phase product of the pyrolysis vessel is subjected to external circulation heating, the cyclic siloxane pyrolysis feedstock and catalyst described in step S1) are added. The falling film tubular pyrolysis liquid phase product is returned to step S1 as a cyclic siloxane pyrolysis feedstock and step S1 is repeated. The gaseous products from the pyrolysis vessel obtained in step S1) and the gaseous products from the falling film tube pyrolysis obtained in step S2) are subjected to cyclic siloxane distillation to obtain cyclic siloxanes.
2. The preparation method according to claim 1, characterized in that, In step S1), the cyclic siloxane cracking feedstock is methyl hydrolysate or methylphenyl hydrolysate; The methyl hydrolysate comprises 40 wt% to 50 wt% of methylcyclosiloxane and 50 wt% to 60 wt% of hydroxyl-terminated linear methylpolysiloxane; The methylphenyl hydrolysate comprises 40 wt% to 50 wt% of methylphenylcyclosiloxane and 50 wt% to 60 wt% of hydroxyl-terminated linear methylphenyl polysiloxane.
3. The preparation method according to claim 2, characterized in that, When the cyclic siloxane cracking feedstock is methyl hydrolysate, the temperature of the batch cracking reaction in step S1) is 100℃~160℃, the batch cracking reaction in step S1) is carried out at an absolute pressure of 5 kPa~10 kPa, and the temperature of the self-cleaning scraper falling film tube cracking reaction in step S2) is 110℃~165℃. When the cyclic siloxane cracking feedstock is methylphenyl hydrolysate, the temperature of the batch cracking reaction in step S1) is 290℃~350℃, the batch cracking reaction in step S2) is carried out at an absolute pressure of 100 Pa~1 kPa, and the temperature of the self-cleaning scraper falling film tube cracking reaction in step S2) is 300℃~355℃. The temperature of the self-cleaning scraper falling film pyrolysis reaction in step S2) is 5°C to 25°C higher than that of the batch pyrolysis reaction in step S1).
4. The preparation method according to claim 3, characterized in that, When the cyclic siloxane cracking feedstock is methyl hydrolysate, the temperature of the batch cracking reaction is 100℃~160℃, the batch cracking reaction is carried out at an absolute pressure of 5 kPa~10 kPa, and the temperature of the self-cleaning scraper falling film tube cracking reaction is 110℃~165℃. When the cyclic siloxane cracking feedstock is methylphenyl hydrolysate, the temperature of the batch cracking reaction is 290℃~350℃, the batch cracking reaction is carried out at an absolute pressure of 100 Pa~1 kPa, and the temperature of the self-cleaning scraper falling film tube cracking reaction is 300℃~355℃.
5. The preparation method according to claim 1, characterized in that, Based on a cyclic siloxane production rate of 10 kg / h to 200 kg / h, in step S2), the material flow rate of the external circulation heating is 5 t / h to 20 t / h.
6. The preparation method according to claim 1, characterized in that, Based on a cyclic siloxane production rate of 10 kg / h to 200 kg / h, in step S2), the replenishment rate of the cyclic siloxane cracking feedstock is 10 kg / h to 200 kg / h.
7. The preparation method according to claim 1, characterized in that, In step S2), the amount of catalyst added is 0.05 wt% to 0.5 wt% of the amount of cyclic siloxane cracking feedstock added.
8. The preparation method according to claim 1, characterized in that, When the cyclic siloxane cracking feedstock is methyl hydrolysate, the top temperature of the distillation column is 80℃~140℃, the top reflux ratio of the distillation column is 1~3, and the distillation is carried out at an absolute pressure of 5 kPa~10 kPa. When the cyclic siloxane cracking feedstock is methylphenyl hydrolysate, the temperature at the top of the distillation column is 190℃~210℃, the top reflux ratio of the distillation is 1~15, and the distillation is carried out at an absolute pressure of 100 Pa~1 kPa.
9. The preparation method according to claim 1, characterized in that, In step S2), during the distillation of cyclic siloxanes, ultrasonic-assisted coking is also performed periodically; the frequency of the ultrasonic-assisted coking is 20 kHz to 40 kHz.
10. A pyrolysis apparatus using the preparation method according to any one of claims 1 to 9, characterized in that, It includes a batch cracking reaction unit, an external circulation unit, a self-cleaning scraped falling film cracking reaction unit, and a distillation unit; The batch pyrolysis reaction unit, the external circulation unit, and the self-cleaning scraper falling film pyrolysis reaction unit are sequentially and cyclically connected. The distillation unit is connected to both the self-cleaning scraper falling film pyrolysis reaction unit and the batch pyrolysis reaction unit.