CN112678774B - Method for recovering and recycling FTrPSA (fluorine-containing PSA) serving as tail gas of SiC-CVD (silicon carbide-chemical vapor deposition) chlorine-free epitaxial process by reacting ethylene with silane - Google Patents
Method for recovering and recycling FTrPSA (fluorine-containing PSA) serving as tail gas of SiC-CVD (silicon carbide-chemical vapor deposition) chlorine-free epitaxial process by reacting ethylene with silane Download PDFInfo
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Abstract
The invention discloses a method for recycling and recycling tail gas FTrPSA of a SiC-CVD chlorine-free epitaxial process by reacting ethylene with silane, which belongs to the technical field of semiconductor materials and environmental protection of semiconductor processes, and aims to solve the problems that the existing treatment method is high in energy consumption and high in cost, unsafe, and large in effective components cannot be effectively utilized and the emission also brings a greenhouse effect.
Description
Technical Field
The invention discloses a method for recovering and recycling FTrPSA (fluorine-doped silicon carbide) serving as tail gas of a SiC-CVD (chemical vapor deposition) chlorine-free epitaxial process by reacting ethylene with silane, belongs to the technical field of environmental protection of semiconductor materials and semiconductor manufacturing processes, and particularly relates to the technical field of tail gas treatment of the SiC-CVD epitaxial process.
Background
Silicon carbide (SiC) is used as a third generation semiconductor material, and has excellent characteristics of wide forbidden band, high temperature and high voltage resistance, high frequency and high power, radiation resistance and the like, so that the silicon carbide (SiC) is widely applied to power switches, frequency conversion and voltage transformation, power electronic components such as UPS and the like in fields of IT and electronic consumer products, automobiles, photovoltaic photoelectricity, nuclear reactors, aerospace and military with harsh system working conditions, and the like, wherein epitaxy is a key production step in which SiC materials are widely applied.
The SiC epitaxial process includes high temperature sublimation (PVT), chemical Vapor Deposition (CVD), liquid phase growth epitaxy (LPE), molecular Beam Epitaxy (MBE), electron cyclotron resonance plasma chemical vapor deposition (ECR-MPCVD), etc., but CVD processes having characteristics of low epitaxial growth temperature, large production lot, good uniformity of epitaxial film, and easy control of operation are commonly used in industry, in which silicon (Si) source and carbon (C) source (referred to as "reaction precursors") involved in the reaction are different and can be classified into SiC-CVD epitaxial processes of organosilicon compounds free of chlorine, and C/Si source simultaneously, and further, the composition of tail gas generated by different epitaxial processes is different, and the treatment method is different accordingly.
One of the conventional processes for chlorine-free epitaxy of SiC-CVD is currently in common use, and is silane (SiH 4 ) Is a Si source, ethylene (C) 2 H 4 ) Is a C source, in hydrogen (H) 2 ) Or argon (Ar) is carried by carrier gas and enters a CVD reaction chamber (furnace), and chemical vapor deposition reaction is carried out under certain temperature and pressure, and the generated epitaxial film is formed on a proper substrate or substrate (usually Si or SiC material), i.e. an epitaxial layer, is processed to obtain a qualified SiC epitaxial wafer, and contains a reaction product H in a gas phase 2 、CH 4 Light alkanes of two or more carbon atoms (C) containing ethane and higher hydrocarbons 2+ ) And a small amount of solid fine particles such as Si powder or Si clusters or C powder, and unreacted SiH 4 、C 2 H 4 Carrier gas H not participating in reaction 2 Or Ar, and trace or trace amounts of other impurities, such as carbon monoxide (CO), carbon dioxide (CO) 2 ) Etc. Commercially available H 2 As carrier gas, the epitaxy efficiency can be effectively improved. Because the tail gas contains toxic, harmful, inflammable and explosive silane, hydrogen, methane, ethylene and light hydrocarbon (C) 2 + ) The composition, and thus the method of treating the exhaust gas, is also relatively specific, especially with regard to safety issues.
The existing methods for treating the tail gas of the conventional SiC-CVD chlorine-free epitaxial process based on the reaction of ethylene and silane mainly comprise three methods, namely a dry adsorption method, a combustion method and a direct condensation method.
First, the dry adsorption can be one-time adsorption, and the adsorbents are silane, silicon cluster, ethylene and C 2+ Etc. non-adsorbates are predominantly H 2 、CH 4 A small amount of silane, C 2+ The components are tested to reach the standard and are directly discharged, wherein the adsorbent after adsorption saturation is replaced periodically; or Temperature Swing Adsorption (TSA) with on-line regeneration of adsorbent, adsorption at lower temperature, regeneration of adsorbent at higher temperature, and cyclic operation, wherein the saturated adsorbent is desorbed by using water vapor or inert nitrogen with higher temperature as regeneration carrier gas and flows out of the adsorption tower, and cooling or condensing to obtain silane and C 2+ And outputting the solution. The adsorption method only carries out purification treatment, is suitable for SiH in tail gas 4 Ethylene and C 2+ Low content of H in large amount 2 Almost completely wasted, and also has the emission of greenhouse gases, or the adsorption of light hydrocarbons C in exhaust gases 2+ The components exceed the standard and can reach the standard only by further catalytic combustion, thereby increasing the cost of tail gas treatment.
Second, the combustion method is to directly perform air oxidation treatment on the tail gas, because of H in the tail gas 2 、SiH 4 、CH 4 、C 2 H 4 C (C) 2+ All are very easy-to-burn components, and harmless H is formed after combustion 2 O、SiO 2 、CO 2 And the components are directly discharged after proper treatment. The combustion method is generally adopted in the industry due to the economical efficiency, and is mostly a miniaturized on-site treatment device, but air with the flow of several times of the tail gas is required to be introduced, so that the concentration of hydrogen, silane and the like which are extremely easy to explode in the air is ensured to be out of an explosion limit range, so that the consumption is higher, certain potential safety hazards exist, and meanwhile, a large amount of heat is generated by combustion and tiny particles are extremely easy to explode in the combustion process, a large amount of water is required to be sprayed in time, and secondary pollution emission or additional treatment is caused. In addition, a large amount of valuable H 2 、SiH 4 、C 2 H 4 、CH 4 The resources are not only not effectively utilized, but also the emission brings about a greenhouse effect. In addition, there is also an adsorption method as an auxiliary method for the combustion method, and when the combustion method fails to ignite or is stopped due to a safety hazard, the SiC-CVD process tail gas is automatically switched to the adsorption method device for treatment.
Thirdly, the direct condensation method is to cool the tail gas directly to below-60 to-30 ℃ to enable the silane and C to be 2 H 4 The components are liquefied into liquid, and the main component in the non-condensable gas is H 2 And CH (CH) 4 Carrying a small amount of SiH 4 、C 2 H 4 And the components are discharged or recovered after dry adsorption or combustion of non-condensable gas 2 And (5) treating the condensate again. However, due to non-condensable gas components, such as H, in the SiC-CVD chlorine-free epitaxy tail gas based on the reaction of ethylene with silane 2 、CH 4 The content is higher, a large amount of cold energy is wasted, the energy consumption is very high, and further the treatment cost is very high, so that the method is not generally adopted in industry.
Disclosure of Invention
The invention aims at: the method for recycling and recycling the tail gas of the SiC-CVD chlorine-free epitaxial process by reacting ethylene with silane is provided, so that the problems that the existing method for treating the tail gas of the SiC-CVD chlorine-free epitaxial process by reacting ethylene with silane is high in energy consumption, high in cost, unsafe, not capable of effectively utilizing a large amount of effective components and capable of bringing about greenhouse effect by emission are solved.
The technical scheme adopted by the invention is as follows:
the method for recovering and recycling the tail gas FTrPSA of the SiC-CVD chlorine-free epitaxial process by reacting ethylene with silane comprises the following steps:
step 1, pretreatment of raw gas, namely sequentially removing dust, particles, oil mist and partial high hydrocarbon impurities;
step 2, medium-temperature pressure swing adsorption concentration, namely directly or pressurizing raw gas from a pretreatment process to less than 1.0MPa, performing cold-heat exchange, and then entering a multi-tower pressure swing adsorption concentration process consisting of at least 4 towers, wherein at least one adsorption tower is in an adsorption step, the rest adsorption towers are in a desorption regeneration step, and the formed non-adsorption phase gas is an intermediate mixed gas;
Step 3, shallow-cooling pressure swing adsorption concentration, namely, performing precise filtration, compression and cold-heat exchange on intermediate mixed gas from a middle-temperature pressure swing adsorption concentration process, performing adsorption concentration on the intermediate mixed gas in the shallow-cooling pressure swing adsorption concentration process consisting of 4 or more adsorption towers, enabling methane hydrogen gas which flows out of the top of the adsorption tower to flow out of the hydrogen-enriched gas, performing adsorption purification on the intermediate mixed gas in the next process, desorbing and sucking the silane-enriched gas which flows out of the bottom of the adsorption tower, performing cold-heat exchange and pressurization, and returning the intermediate mixed gas to the subsequent process, namely shallow-cooling oil absorption;
step 4, performing adsorption purification, namely enabling methane hydrogen gas to enter an adsorption purification process consisting of 2 or 3 adsorption towers to form purified methane hydrogen gas, and entering the next process, namely performing pressure swing adsorption hydrogen extraction;
step 5, pressure swing adsorption hydrogen extraction, methane hydrogen purification, direct or cold-heat exchange to normal temperature, and multi-tower pressure swing adsorption hydrogen purification process comprising at least 4 towers, wherein the non-adsorption phase gas is ultra-high purity hydrogen with purity of 99.999-99.9999%, wherein CO and CO are obtained 2 The content of hydrocarbon is less than 0.1-1.0 ppm, and the content of hydrocarbon is less than 10ppm calculated by methane,Silane less than 0.1-1.0 ppm, and then the next procedure, hydrogen purification, is carried out;
Step 6, purifying the ultra-high purity hydrogen, namely purifying the ultra-high purity hydrogen at the operating temperature of 50-500 ℃ under normal pressure or under the pressure condition required by hydrogen used in the SiC-CVD process, removing trace impurities to obtain a final electronic grade hydrogen product, and cooling or reducing the temperature by heat exchange or reducing the pressure, or sending the final electronic grade hydrogen product into an electronic grade hydrogen product tank for storage, or directly returning the final electronic grade hydrogen product to the process requiring hydrogen in the SiC-CVD epitaxial process through a hydrogen product buffer tank;
step 7, shallow cold oil absorption, namely, silane-enriched desorption gas from a medium-temperature pressure swing adsorption concentration process enters the shallow cold oil absorption process from the bottom of an absorption tower after cold and heat exchange and compression, adopts a C4 liquid solvent with the temperature of 5-15 ℃ and the pressure of 2.5-3.5 MPa as an absorbent, sprays and absorbs the liquid from top to bottom, and flows out SiH containing SiH from the top of the absorption tower 4 And methane hydrogen non-condensable gas 1 enters the next process, namely middle-shallow cold rectification, ethylene-rich liquid flows out of the bottom of the absorption tower, enters the desorption tower, crude ethylene gas flows out of the top of the desorption tower, enters the subsequent process, namely ethylene refining, and C4 absorbent flows out of the bottom of the desorption tower and returns to the absorption tower for recycling;
step 8, middle and shallow cold rectification, namely, condensing a condensed fluid generated by condensation of the non-condensable gas 1 from a shallow cold oil absorption process, entering a middle and shallow cold rectification tower, introducing silane-rich gas flowing out of the top of the rectification tower into a next process, namely, silane purification, mixing ethylene-rich gas flowing out of the bottom of the rectification tower with crude ethylene gas from the shallow cold oil absorption process, introducing the mixture into a subsequent ethylene refining process, and returning the condensed non-condensable gas 2 to a shallow cold pressure swing adsorption concentration process, or returning the condensed fluid to a middle temperature pressure swing adsorption concentration process after cold-heat exchange, so as to further recover effective components;
Step 9, purifying silane, namely, feeding the silane-rich tower top gas from the middle-shallow cold rectifying tower into a pressure swing adsorption and silane purification system consisting of at least 2 adsorption towers, and directly or through SiH, wherein the silane product gas with the purity of more than or equal to 99.99% flows out from the adsorption tower top 4 The metal getter purifier is further purified and then is used as raw material gas for SiC-CVD epitaxial process, and the adsorption tower is vacuumized and decomposedThe desorption gas sucked and flowing out from the bottom of the adsorption tower is directly used as fuel gas or is subjected to pressurization and cold-heat exchange and then returned to a rectifying tower in the middle-shallow cold rectifying process to further recycle C 2 H 4 With SiH 4 ；
Step 10, refining ethylene, namely condensing crude ethylene gas from a shallow cold oil absorption process after decarburization treatment, mixing the crude ethylene gas with ethylene rich from a middle and shallow cold rectification process, feeding the mixture into an ethylene rectification tower for refining, discharging ethylene product gas from the top of the tower, and discharging C including ethane from the bottom of the tower 2+ The components are used as fuel gas or are externally conveyed.
Specific:
step 1, pretreatment of raw gas, wherein ethylene (C 2 H 4 ) As the main carbon (C) source, with Silane (SiH) 4 ) Chemical Vapor Deposition (CVD) of silicon (Si) source to produce a silicon carbide (SiC) epitaxial growth based off-gas in a chlorine-free process consisting essentially of hydrogen (H) 2 ) Methane (CH) 4 ) Silane (SiH) 4 ) Ethylene (C) 2 H 4 ) And trace amounts of carbon monoxide (CO), carbon dioxide (CO) 2 ) Containing ethane and light hydrocarbons (C) 2+ ) And silicon dioxide (SiO) 2 ) And carbon (C) fine particles, the pressure is normal pressure or low pressure, and the temperature is normal temperature; pretreating, namely, charging raw material gas to 0.2-0.3 MPa, feeding the raw material gas into a pretreatment unit consisting of a dust remover, a particle removal filter and a mist removal catcher, sequentially removing dust, particles, oil mist and partial high hydrocarbon impurities, and then entering the next working procedure, namely, medium-temperature pressure swing adsorption concentration;
step 2, medium temperature pressure swing adsorption concentration, namely directly or pressurizing raw gas from a pretreatment process to less than 1.0MPa, performing cold-heat exchange to 60-120 ℃, and then entering a multi-tower pressure swing adsorption concentration process consisting of at least 4 towers, wherein the operating pressure of the adsorption towers is 0.2-1.0 MPa, the operating temperature is 60-120 ℃, at least one adsorption tower is in an adsorption step, the rest adsorption towers are in a desorption regeneration step, the formed non-adsorption phase gas is an intermediate mixed gas, and the main component is H 2 、CH 4 With SiH 4 The next procedure, shallow cold pressure swing adsorption concentration, is carried out to form the suctionThe auxiliary phase gas is ethylene-rich gas, and enters a subsequent process, namely shallow cold oil absorption after being pressurized, wherein the adsorbent in the medium-temperature pressure swing adsorption concentration process adopts one or a combination of activated alumina, silica gel, activated carbon and molecular sieve and activated carbon or molecular sieve loaded with metal active components, and vacuum pumping regeneration is adopted during desorption;
Step 3, shallow cold pressure swing adsorption concentration, namely, performing precise filtration, compressing the intermediate mixed gas from the middle temperature pressure swing adsorption concentration step to 1.0-3.0 MPa, performing cold-heat exchange to-10 ℃, then entering the shallow cold pressure swing adsorption concentration step consisting of 4 or more adsorption towers, performing adsorption concentration at the operating temperature of-10 ℃ and the operating pressure of 1.0-3.0 MPa, enabling the methane hydrogen gas rich in hydrogen to flow out of the top of the adsorption tower, and performing the next step, namely, adsorption purification, to further purify and remove trace Silane (SiH) 4 ) Ethylene (C) 2 H 4 ) The silane-enriched desorption gas flowing out from the bottom of the adsorption tower is subjected to cold-heat exchange and pressurization and then returns to the subsequent process, namely shallow cold oil absorption, so as to further recover SiH 4 ；
Step 4, adsorption purification, namely, methane hydrogen gas from the shallow-cooling pressure swing adsorption concentration process enters an adsorption purification process consisting of 2 or 3 adsorption towers, and is adsorbed at the operating temperature of-10-20 ℃ and the operating pressure of 1.0-3.0 MPa, so that a small amount of SiH in the methane hydrogen gas is further purified and removed 4 C (C) 2 H 4 Forming purified methane hydrogen gas, and entering the next process, namely, the pressure swing adsorption hydrogen extraction process;
step 5, pressure swing adsorption hydrogen extraction, namely, directly or after cold and heat exchange to normal temperature, introducing the purified methane hydrogen from an adsorption purification process into a multi-tower pressure swing adsorption hydrogen purification process consisting of at least 4 towers, wherein the operating pressure of the adsorption towers is 1.0-3.0 MPa, the operating temperature is-10-40 ℃, at least one adsorption tower is in an adsorption step, the rest adsorption towers are in a desorption regeneration step, and the formed non-adsorption phase gas is ultra-high purity hydrogen with the purity of 99.999-99.9999% (v/v), wherein the purity of CO and CO is greater than or equal to 99.999-99% (v/v) 2 The content of the catalyst is less than 0.1 to 1.0ppm, the content of hydrocarbon (calculated by methane) is less than 10ppm, and the content of silane is less than 0.1 to 1.0ppm, and the catalyst enters the next working procedureThe adsorbent in the pressure swing adsorption hydrogen extraction process adopts one or more of active alumina, silica gel, active carbon, aluminum silicate molecular sieve and carbon molecular sieve, flushing is adopted during desorption, or flushing and vacuumizing modes are adopted, the desorbed gas is methane-rich gas, and can be directly output as fuel gas, or enters low-temperature rectification to recover methane, so that the methane with the purity of more than or equal to 99.99% is prepared and returned to the SiC-CVD epitaxial process for recycling;
step 6, purifying the hydrogen, namely purifying the ultra-high purity hydrogen from a pressure swing adsorption hydrogen extraction process, or directly carrying out heat exchange after passing through an intermediate product storage tank, directly reducing the pressure to the pressure required by hydrogen for an SiC-CVD (chemical vapor deposition) epitaxial process at the temperature of 50-500 ℃ or through a reducing valve, entering a hydrogen purification process coupled by a metal getter or a palladium membrane-metal getter, purifying the hydrogen under the pressure condition that the operating temperature is 50-500 ℃ and the operating pressure is normal pressure or the pressure required by hydrogen in the SiC-CVD process, removing trace impurities to obtain a final electronic grade hydrogen product, wherein the purity reaches the product standard of the electronic grade hydrogen specified by the national and international semiconductor Society (SEMI), the purity of the hydrogen is more than or equal to 7-8N grade, and carrying out heat exchange cooling or depressurization, or sending the hydrogen into an electronic grade hydrogen product tank for storage, or directly returning the hydrogen product buffer tank to a working section required by the SiC-CVD epitaxial process, wherein the operating temperature of the hydrogen purification process is determined by the process of the metal getter or the palladium membrane, and the service life of the metal getter or the palladium membrane is at least longer than 2 years; the yield of the electronic grade hydrogen product obtained by the method is more than 75-85 percent;
Step 7, shallow cold oil absorption, namely, silane-enriched desorption gas from a medium-temperature pressure swing adsorption concentration process is subjected to cold-heat exchange to 5-15 ℃, compressed to 2.5-3.5 MPa, enters the shallow cold oil absorption process from the bottom of an absorption tower, adopts a C4 (n-butane, isobutane or mixed butane) liquid solvent with the temperature of 5-15 ℃ and the pressure of 2.5-3.5 MPa as an absorbent, sprays and absorbs from top to bottom, and flows out of the top of the absorption tower and contains SiH 4 And methane hydrogen non-condensable gas 1, then enters the next working procedure, namely middle-shallow cold rectification, further extracts silane, absorbs ethylene-rich liquid flowing out of the bottom of the tower, enters a desorption tower, and flows out of the top of the tower to obtain crude productEthylene gas enters the subsequent process, namely ethylene refining, flows out of the C4 absorbent from the bottom of the desorption tower, and returns to the absorption tower for recycling;
step 8, middle and shallow cold rectification, namely, enabling a non-condensable gas 1 from a shallow cold oil absorption process to enter a middle and shallow cold rectification tower with the operating temperature of-35 to-10 ℃ and the operating pressure of 2.0-2.5 MPa, enabling silane-rich gas flowing out of the top of the rectification tower to enter the next process, namely, silane purification, enabling ethylene-rich gas flowing out of the bottom of the rectification tower to be mixed with crude ethylene gas from the shallow cold oil absorption process to enter the subsequent ethylene refining process, enabling non-condensable gas 2 generated by condensation to return to the shallow cold pressure swing adsorption concentration process, or enabling the non-condensable gas 2 to return to the middle temperature pressure swing adsorption concentration process after cold heat exchange, and further recycling effective components;
Step 9, purifying silane, namely, introducing silane-enriched tower top gas from a middle-shallow cold rectifying tower into a pressure swing adsorption purification silane system which is formed by at least 2 or more adsorption towers with the operating temperature of 20-40 ℃ and the operating pressure of less than 1.0MPa after cold and heat exchange to 20-40 ℃ and depressurization to less than 1.0MPa, loading one or more combined adsorbents of diatomite, silica gel, active carbon and molecular sieve into the adsorption towers, and flowing Silane (SiH) with the purity of more than or equal to 99.99% out of the tower top 4 ) The yield of the product gas is more than or equal to 90-95 percent, and the product gas is directly or through SiH 4 After further purification by the metal getter purifier (purity is more than or equal to 99.999 percent), the purified metal getter purifier is used as a raw material gas required by the SiC-CVD epitaxial process for recycling, and the desorption gas flowing out of the bottom of the adsorption tower through vacuum pumping desorption by the adsorption tower is directly used as fuel gas or is returned to a rectifying tower in a middle-shallow cold rectifying process after pressurization and cold-heat exchange to further recycle C 2 H 4 With SiH 4 The corresponding yield reaches over 95-98 percent respectively;
step 10, refining ethylene, namely, condensing crude ethylene gas from a shallow cold oil absorption process after decarburization treatment, mixing the crude ethylene gas with ethylene rich from a middle and shallow cold rectification process, feeding the mixture into an ethylene rectification tower for refining, and discharging ethylene product gas from the top of the tower, wherein the purity is more than or equal to 99.99%, the yield is more than or equal to 90-95%, or returning the crude ethylene gas to a CVD process, and discharging the ethylene product gas from the bottom of the tower, wherein the crude ethylene gas comprises C including ethane 2+ The components are used as fuel gas or are externally conveyed.
In the technical proposal of the application, the method is based on the fact that a plurality of main components H are contained in CVD tail gas generated in the SiC-CVD chlorine-free epitaxial process based on the reaction of ethylene and silane 2 、SiH 4 、C 2 H 4 /CH 4 Various conventional separation methods including adsorption, rectification, absorption and the like are coupled to realize the recovery of H by SiC-CVD chlorine-free Cheng Weiqi Quan Wencheng pressure swing adsorption (FTrPSA) 2 、SiH 4 、C 2 H 4 CH (CH) 4 The waste gas is returned to the conventional SiC-CVD epitaxial process for recycling, so that the full-component recycling of the tail gas is realized, the tail gas emission is reduced, and the blank of the tail gas treatment technology of the SiC epitaxial process is filled; adopts the combination of medium temperature and shallow cold PSA concentration procedures, not only can effectively solve SiH 4 The change of the adsorption capacity caused by the change of the polarity along with the temperature can prevent the problem of difficult desorption caused by deep adsorption; meanwhile, the H in the adsorption tower is strictly controlled by adopting a replacement mode in the desorption process 2 /SiH 4 /CH 4 Avoiding the dangerous explosion of the inflammable and explosive components; by utilizing the difference of the operating temperatures of the working procedures and arranging a reasonable cold and heat exchange system, the cold and heat of the whole operating system is fully utilized; the pressure swing adsorption hydrogen extraction procedure fully utilizes a pressure swing mode to deeply purify and remove various trace impurity components from the feed gas containing hydrogen, thereby not only ensuring the feed gas feeding requirement of the hydrogen purification procedure, but also prolonging the service life of the adsorbent of the pressure swing adsorption purification procedure; the coupling of the non-condensable gas of shallow cold oil absorption and middle and shallow cold rectification, middle and shallow cold pressure swing adsorption concentration, adsorption purification and pressure swing adsorption hydrogen extraction processes leads the yield of the recovered effective components to be more than 70-80%, wherein the recovery rate of silane and ethylene is more than 90%.
Preferably, the feed gas comprises an offgas or tail gas containing hydrogen, silane, methane and light olefin as main components, which is produced in the rest of the semiconductor process using other olefins as carbon sources.
Preferably, in the pretreatment, in the working condition that the raw material gas is waste gas or tail gas containing other impurities including acid and Volatile Organic Compounds (VOCs) with higher concentration, besides a dust remover, a particle filter and an oil mist removing catcher, alkaline washing, a neutralization tower, a dryer and other impurities can be added to remove the acid and Volatile Organic Compounds (VOCs) impurity components with larger influence on the operation of the pressure swing adsorption concentration working procedure.
Preferably, in the middle temperature pressure swing adsorption concentration and adsorption tower desorption step, after the adsorption tower adsorption step is finished and before the pressure equalization step or the sequential discharge step is started, crude ethylene gas from the top of the desorption tower in the shallow cold oil absorption step, ethylene-rich gas from the bottom of the rectification tower in the middle and shallow cold rectification step, or ethylene product gas from ethylene refining is adopted for replacement, so that the concentration and the yield of ethylene in the process are improved.
Preferably, the raw material gas from pretreatment enters from the bottom of a first PSA adsorption tower (1-section PSA) serving as medium-temperature pressure swing adsorption concentration after being heated and pressurized, and the intermediate mixed gas of a non-adsorption phase flowing out of the top of the 1-section PSA enters from the bottom of a second PSA adsorption tower (2-section PSA) serving as shallow-cooling pressure swing adsorption after being subjected to cold-heat exchange, and the non-adsorption phase hydrogen-enriched methane-hydrogen gas flowing out of the top of the 2-section PSA enters into the next process, namely adsorption purification; the desorption gas from the PSA of the 1 section and the PSA of the 2 section enters a shallow cold oil absorption process after cold-heat exchange and pressurization, wherein part of the intermediate mixed gas or hydrogen-enriched methane hydrogen gas of the non-adsorption phase of the 1 section or the 2 section can be respectively used as the feed gas of the respective process to be complemented, and the concentration of ethylene or silane in the adsorption towers of the sections is regulated so as to improve the yield of the ethylene or the silane.
Preferably, the second PSA adsorption tower (2-stage PSA) as shallow-cold pressure swing adsorption concentration is added with a displacement step after the adsorption step and before the pressure equalization or sequential discharge step begins, and SiH is enriched by a rectifying tower from the middle-shallow cold rectifying process 4 Or SiH from silane purification step 4 The product gas is replaced to further promote SiH 4 In the present stepConcentration and yield.
Preferably, in the methane hydrogen gas feed gas from the shallow-cooling pressure swing adsorption concentration step, when the silane content exceeds 1%, ethanol or diethyl ether or low-carbon mixed alcohol ether is adopted as an absorbent to perform absorption purification instead of absorption purification, wherein the methane hydrogen gas from the shallow-cooling pressure swing adsorption concentration step is subjected to fine filtration and then pressurized to 2.0-3.0 MPa and enters an absorption tower through cold and heat exchange, purified methane hydrogen gas with the silane content less than 10ppm flows out of the top of the absorption tower and directly enters a pressure swing adsorption hydrogen extraction step, the absorption liquid flowing out of the bottom of the absorption tower enters the absorption tower to be desorbed, the operation conditions of the desorption are normal temperature and normal pressure, the desorbed silane-rich gas is mixed with non-condensable gas flowing out of the top of the absorption tower of the shallow-cooling oil absorption step after cold and heat exchange and pressurization, and then enters a middle-shallow-cooling rectification step with the operation temperature of-35 to-10 ℃ and the operation pressure of 1.0-2.5 MPa, and SiH is further recovered 4 。
Preferably, the middle-shallow cold rectifying process consists of two rectifying towers, the non-condensable gas 1 from the shallow cold oil absorbing process is condensed to produce condensed fluid, the condensed fluid enters the middle-shallow cold rectifying tower-1 with the operating temperature of minus 35 ℃ to minus 10 ℃ and the operating pressure of 2.0 MPa to 2.5MPa, and the non-condensable gas 3 of light components, mainly H, flows out from the top of the tower 2 、CH 4 Composition and trace SiH 4 Or the mixture is mixed with purified methane and hydrogen from the adsorption purification process through a cold heat exchanger to a temperature of 20-40 ℃ and then enters the pressure swing adsorption hydrogen extraction process to further recover H 2 Or/and CH 4 Or the mixture is mixed with the pretreated and purified raw material gas after being cooled to 5-20 ℃ by a cold heat exchanger and decompressed to less than 1MPa, and then the mixture enters a shallow-cooling pressure swing adsorption concentration process to further recover H 2 Or/and CH 4 ，H 2 or/CH (or) 4 The yield of the product gas is further improved, the heavy component fluid flowing out from the bottom of the rectifying tower-1 is fed into a middle-shallow cold rectifying tower-2 with the operating temperature of minus 35 to minus 10 ℃ and the operating pressure of 1.0 to 2.5MPa, the heavy component rich in ethylene flows out from the bottom of the middle-shallow cold rectifying tower-2, the heavy component rich in Silane (SiH) flows into an ethylene refining process, and the heavy component fluid flows out from the top of the middle-shallow cold rectifying tower-2 4 ) A kind of electronic deviceThe tower top gas is purified by a silane purification process or directly used as silane product gas (purity is more than 99.9 percent) or directly enters a silane metal getter to prepare SiH with purity more than or equal to 99.999 percent 4 The product gas is returned to the SiC-CVD epitaxial process for recycling, and the non-condensable gas 2 generated by condensation is returned to the medium-temperature pressure swing adsorption concentration process.
Preferably, the silane product gas obtained in the silane purification step has a purity of 99.99% or more, or is SiH-treated 4 The metal getter is prepared from hydrogenated metal pick (Zr) -vanadium (V) -iron (Fe) alloy, and is purified at 25-100 ℃ to obtain silane product with gas purity of 99.999% or more, wherein the silane product comprises oxygen (O) 2 ) Water (H) 2 O), carbon monoxide (CO), carbon dioxide (CO) 2 ) Total hydrocarbons, sulfides (H) 2 S) and siloxane are less than 0.01-0.1 ppm, and the service life of the metal getter is more than 1-2 years.
Preferably, the silane purification step is performed by using a distillation column top gas from a middle-shallow cold distillation step, wherein the distillation column top gas contains a small amount of C 2 H 4 、CO/CO 2 、O 2 、H 2 O contains a trace amount of Phosphane (PH) 3 ) Arsine (AsH) 3 ) Diborane (B) 2 H 6 ) And under the working condition of siloxane, the adsorption tower of the silane purification process is filled with one or more combined adsorbents of diatomite, silica gel, active carbon and molecular sieve, and also needs to be filled with the molecular sieve or active aluminum oxide (Al) loaded with metallic copper (Cu)/zinc (Zn) or copper oxide (CuO)/zinc oxide (ZnO) active components 2 O 3 ) The impurity removal depth of the adsorbent can reach the level of less than 50 to 100 ppb.
Preferably, in the medium temperature pressure swing adsorption concentration, shallow cold pressure swing adsorption concentration, pressure swing adsorption hydrogen extraction and adsorption purification processes, under the operation condition that the adsorption pressure is more than or equal to 0.6MPa, the pressure change in the adsorption and desorption cycle operation process is controlled slowly and uniformly through a program control valve and a regulating valve on a pipeline connected between the adsorption towers, so that the airflow caused by overlarge pressure change of the system is prevented from scouring the adsorption tower bed layer and the pulverization of the adsorbent, and the operation of the process system is stable and safe.
Full temperature range pressure swing adsorption (English full name: full Temperature Range-Pressure Swing Adsorption; FTrPSA for short) is a method based on Pressure Swing Adsorption (PSA) and capable of being coupled with various separation technologies, and utilizes the differences of adsorption separation coefficients and physicochemical properties of different material components under different pressures and temperatures, and adopts cyclic operation that adsorption and desorption are easy to match and balance in the middle temperature and shallow cold pressure swing adsorption process to separate and purify the main effective component (H) 2 (purity of 99.9995% (v/v) or more) SiH 4 99.99% or more, and at the same time, ethylene (99.9% or more) or methane (99% or more) can be produced as a byproduct.
In summary, due to the adoption of the technical scheme, the beneficial effects of the invention are as follows:
1. in the invention, H can be recovered from the whole component of the tail gas of the SiC-CVD chlorine-free epitaxial process based on the reaction of ethylene and silane 2 、SiH 4 、C 2 H 4 CH (CH) 4 The waste gas is returned to the conventional SiC-CVD epitaxial process for recycling, so that the full-component recycling of the tail gas is realized, the tail gas emission is reduced, and the blank of the tail gas treatment technology of the SiC epitaxial process is filled;
2. by utilizing the physicochemical and relative separation coefficient characteristics of tail gas components in the middle temperature and shallow cooling temperature (-10-120 ℃) and middle-low pressure (0.2-3.0 MPa), the H of a non-adsorption phase is selectively separated and recovered at the same time 2 /CH 4 or/SiH 4 C of the adsorption phase 2 H 4 or/SiH 4 Avoiding SiH in adsorption cycle operation 4 Difficulties in the conversion of components as non-adsorbate components in the medium temperature range and adsorbate properties in the shallow cold range, and SiH 4 、C 2 H 4 Regeneration difficulties for deep adsorption of adsorbate components conventional temperature or pressure swing adsorption has difficulty in directly treating SiH 4 Inflammable and explosiveThe invention realizes the adsorption and regeneration cycle operation of a full-temperature-range pressure swing adsorption (FTrPSA) system in the middle-shallow cold temperature range (-35-20 ℃) based on the coupling of various adsorption and rectification/absorption separation technologies, and finally obtains electronic grade hydrogen, silane or ethylene products, thereby solving the problem that the traditional adsorption separation technology is difficult to recover H simultaneously 2 、SiH 4 、C 2 H 4 A technical bottleneck for reuse;
3. in realizing the full component (H) 2 、SiH 4 /C 2 H 4 Mainly) is recycled and reused, and SiC-CVD chlorine-free epitaxial process and sensitive oxygen-containing compound thereof, especially O, are not carried into the system 2 、H 2 O, CO, etc., so that the whole recycling process is stable, and the influence on the SiC epitaxial quality is reduced to zero degree;
4. the normal pressure or low pressure waste gas is purified, recycled and reused, and can be used for preparing hydrogen, silane and C according to the epitaxial process (electronic grade) of silicon carbide 2 H 4 The use condition adopts two treatment modes of pressurization or non-pressurization to obtain electronic grade hydrogen, silane and ethylene products which can be returned to the epitaxial process;
5. adopts the combination of medium temperature and shallow cold PSA concentration procedures, not only can effectively solve SiH 4 The change of the adsorption capacity caused by the change of the polarity along with the temperature can prevent the problem of difficult desorption caused by deep adsorption; meanwhile, the H in the adsorption tower is strictly controlled by adopting a replacement mode in the desorption process 2 /SiH 4 /CH 4 Avoiding the dangerous explosion of the inflammable and explosive components;
6. by utilizing the difference of the operating temperatures of the working procedures and arranging a reasonable cold and heat exchange system, the cold and heat of the whole operating system is fully utilized;
7. In the pressure swing adsorption hydrogen extraction process, a pressure swing mode is fully utilized, various trace or even trace impurity components are removed by deep purification of the feed gas containing hydrogen, the problem that new impurity components possibly formed by introducing hot nitrogen regeneration or a heat carrier into the hydrogen purification process and the recycling operation problem formed by difficult matching of adsorption and regeneration due to the fact that the trace or trace impurity components are removed by adopting traditional Temperature Swing Adsorption (TSA) are avoided, the feed gas feeding requirement of the hydrogen purification process is ensured, and the service life of the adsorbent of the pressure swing adsorption purification process is prolonged;
8. the coupling of the non-condensable gas of shallow cold oil absorption and middle and shallow cold rectification, middle and shallow cold pressure swing adsorption concentration, adsorption purification and pressure swing adsorption hydrogen extraction processes leads the yield of the recovered effective components to be more than 70-80%, wherein the recovery rate of silane and ethylene is more than 90%.
Drawings
FIG. 1 is a schematic flow chart of an embodiment 1 of the present invention;
FIG. 2 is a schematic flow chart of embodiment 2 of the present invention;
FIG. 3 is a schematic flow chart of embodiment 3 of the present invention;
FIG. 4 is a schematic flow chart of embodiment 4 of the present invention;
Fig. 5 is a schematic flow chart of embodiment 5 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Example 1
As shown in fig. 1, the method for recovering and recycling FTrPSA, which is the tail gas of the SiC-CVD chlorine-free epitaxy process by reacting ethylene with silane, comprises the following steps:
step 1, pretreatment of raw gas, wherein ethylene (C 2 H 4 ) As the main carbon (C) source, with Silane (SiH) 4 ) Chemical Vapor Deposition (CVD) of silicon (Si) source to produce a silicon carbide (SiC) epitaxial growth based off-gas in a chlorine-free process consisting essentially of hydrogen (H) 2 ) Methane (CH) 4 ) Silane (SiH) 4 ) Ethylene (C) 2 H 4 ) And trace amounts of carbon monoxide (CO), carbon dioxide (CO) 2 ) Containing ethane and light hydrocarbons (C) 2+ ) And silicon dioxide (SiO) 2 ) And carbon (C) fine particles, the pressure is normal pressure or low pressure, and the temperature is normal temperature; pretreating, namely, charging raw material gas to 0.2-0.3 MPa, feeding the raw material gas into a pretreatment unit consisting of a dust remover, a particle removal filter and a mist removal catcher, sequentially removing dust, particles, oil mist and partial high hydrocarbon impurities, and then entering the next working procedure, namely, medium-temperature pressure swing adsorption concentration;
Step 2, medium temperature pressure swing adsorption concentration, namely pressurizing raw material gas from a pretreatment process to 0.6-0.8 MPa, performing cold-heat exchange to 60-120 ℃, and then entering a multi-tower pressure swing adsorption concentration process consisting of 5 towers, wherein the operating pressure of the adsorption towers is 0.6-0.8 MPa, the operating temperature is 60-120 ℃, one adsorption tower is in an adsorption step, the other adsorption towers are in a desorption regeneration step, the formed non-adsorption phase gas is an intermediate mixed gas, and the main component is H 2 、CH 4 With SiH 4 The method comprises the steps of entering a shallow-cooling pressure swing adsorption concentration process, wherein the formed adsorption phase gas is ethylene-rich gas, and entering a shallow-cooling oil absorption process after being pressurized, wherein the adsorbent in the medium-temperature pressure swing adsorption concentration process adopts various combinations of activated alumina, silica gel, activated carbon and molecular sieve and activated carbon or molecular sieve loaded with metal active components, and vacuumizing is adopted for regeneration during desorption;
step 3, shallow-cooling pressure swing adsorption concentration, namely, performing precision filtration, compressing intermediate mixed gas from the pressure swing adsorption concentration step to 2.0-3.0 MPa, performing cold-heat exchange to 5-10 ℃, then entering the shallow-cooling pressure swing adsorption concentration step consisting of 5 adsorption towers, performing adsorption concentration at the operating temperature of 5-10 ℃ and the operating pressure of 2.0-3.0 MPa, enabling methane hydrogen gas rich in hydrogen to flow out of the adsorption towers, entering an adsorption purification step, and further purifying and removing trace Silane (SiH) in the methane hydrogen gas 4 ) Ethylene (C) 2 H 4 ) The silane-enriched desorption gas flowing out from the bottom of the adsorption tower is returned to the shallow cold oil absorption process after cold-heat exchange and pressurization, and SiH is further recovered 4 ；
Step 4, adsorption purification, namely, methane hydrogen gas from the shallow-cooling pressure swing adsorption concentration process enters an adsorption net composed of 2 adsorption towersA chemical process, wherein the adsorption is carried out at the operating temperature of 5-10 ℃ and the operating pressure of 2.0-3.0 MPa, and a small amount of SiH is further purified and removed 4 C (C) 2 H 4 Forming purified methane hydrogen gas, and entering a pressure swing adsorption hydrogen extraction process;
step 5, pressure swing adsorption hydrogen extraction, namely purifying methane hydrogen from an adsorption purification process, performing cold-heat exchange to normal temperature, and then entering a multi-tower pressure swing adsorption hydrogen purification process consisting of 5 towers, wherein the operating pressure of the adsorption towers is 2.0-3.0 MPa, the operating temperature is 20-40 ℃, one adsorption tower is in an adsorption step, the other adsorption towers are in a desorption regeneration step, the formed non-adsorption phase gas is ultra-high purity hydrogen, the purity of the ultra-high purity hydrogen is greater than or equal to 99.999-99.9999% (v/v), and CO are contained in the multi-tower pressure swing adsorption hydrogen purification process 2 The content is less than 0.1-1.0 ppm, the hydrocarbon (calculated by methane) content is less than 10ppm, and the silane is less than 0.1-1.0 ppm, and the adsorbent enters a hydrogen purification process, and the adsorbent in the pressure swing adsorption hydrogen extraction process adopts various combinations of activated alumina, silica gel, activated carbon, aluminum silicate molecular sieve and carbon molecular sieve, and adopts a flushing and vacuumizing mode during desorption, so that desorption gas is methane-rich gas, and can be directly output as fuel gas;
Step 6, purifying hydrogen, namely, performing heat exchange to 400-450 ℃ on ultra-high purity hydrogen from a pressure swing adsorption hydrogen extraction process, then performing a hydrogen purification process consisting of a metal getter, purifying at the operating temperature of 400-450 ℃ and the operating pressure of 2.0-3.0 MPa to remove trace impurities, thereby obtaining a final electronic grade hydrogen product, wherein the purity of the final electronic grade hydrogen product reaches the product standard of electronic grade hydrogen specified by the national semiconductor institute (SEMI), the purity of the hydrogen is more than or equal to 7-8N, and the hydrogen is directly returned to a section requiring hydrogen in the SiC-CVD epitaxial process through heat exchange cooling and a hydrogen product buffer tank, wherein the service life of the metal getter is at least more than 2 years without regeneration, and the yield of the obtained electronic grade hydrogen product is more than 75-85%;
and 7, shallow cold oil absorption, namely performing silane-enriched desorption gas from a medium-temperature pressure swing adsorption concentration process, performing cold-heat exchange to 5-15 ℃, compressing to 2.5-3.5 MPa, and then performing shallow cold oil absorption from the bottom of the absorption tower, wherein the temperature is 5-15 ℃ and the pressure is 2.C4 (n-butane, isobutane or mixed butane) liquid solvent with pressure of 5-3.5 MPa is used as absorbent, and is sprayed and absorbed from top to bottom, siH is contained at the top of the absorption tower 4 And the non-condensable gas 1 of methane and hydrogen enters a middle-shallow cold rectifying process to further extract silane, the ethylene-rich liquid flows out of the bottom of the absorption tower, enters a desorption tower, the crude ethylene gas flows out of the top of the desorption tower, enters a post-ethylene refining process, and the C4 absorbent flows out of the bottom of the desorption tower and returns to the absorption tower for recycling;
step 8, middle and shallow cold rectification, namely, condensing a condensed fluid generated by condensing a non-condensable gas 1 from a shallow cold oil absorption process, entering a middle and shallow cold rectification tower with the operating temperature of-35 to-20 ℃ and the operating pressure of 2.0-2.5 MPa, enabling silane-enriched gas flowing out of the top of the rectification tower to enter a silane purification process, enabling ethylene-enriched gas flowing out of the bottom of the rectification tower to be mixed with crude ethylene gas from the shallow cold oil absorption process, enabling the mixture to enter an ethylene refining process, and returning the non-condensable gas 2 generated by condensing to the shallow cold pressure swing adsorption concentration process to further recover effective components;
step 9, purifying silane, namely, introducing silane-enriched tower top gas from a middle-shallow cold rectifying tower into a pressure swing adsorption purification silane system which is formed by 3 or more adsorption towers with the operating temperature of 20-40 ℃ and the operating pressure of less than 1.0MPa after cold and heat exchange to 20-40 ℃ and depressurization to less than 1.0MPa, wherein the adsorption towers are filled with adsorbents of various combinations of diatomite, silica gel, active carbon and molecular sieve, and the purity of Silane (SiH) with the purity of more than or equal to 99.99% flows out from the top of the adsorption tower 4 ) The yield of the product gas is more than or equal to 90 to 95 percent, and then SiH is carried out 4 After further purification by a metal getter purifier (purity is more than or equal to 99.999 percent), the purified metal getter purifier is used as raw material gas required by the SiC-CVD epitaxial process for recycling, and desorption gas which is desorbed by vacuumizing and flows out of the bottom of an adsorption tower is returned to a rectifying tower in a middle-shallow cold rectifying process after pressurization and cold-heat exchange to further recycle C 2 H 4 With SiH 4 The corresponding yield reaches over 95-98 percent respectively;
step 10, refining ethylene, namely condensing crude ethylene gas from a shallow cold oil absorption process after decarburization treatment, mixing the crude ethylene gas with ethylene rich from a middle and shallow cold rectification process, and feeding the mixture into ethylene rectificationRefining in a column, wherein the ethylene product gas flows out from the top of the column, the purity is more than or equal to 99.99%, the yield is more than or equal to 90-95%, and C including ethane flows out from the bottom of the column 2+ The component is used as fuel gas.
Example 2
As shown in fig. 2, in the adsorption column desorption step of the medium temperature pressure swing adsorption concentration step, after the adsorption column adsorption step is completed and before the pressure equalization or sequential discharge step is started, ethylene-rich gas from the bottom of the rectification column in the medium and shallow cold rectification step is adopted to improve the concentration and yield of ethylene in the process, as shown in example 1.
Example 3
As shown in fig. 3, based on example 1, the medium temperature pressure swing adsorption concentration and the shallow cold pressure swing adsorption concentration are combined into a process consisting of two sections of PSA, raw gas from pretreatment is heated and pressurized and enters from the bottom of a first PSA adsorption tower (1 section of PSA) serving as medium temperature pressure swing adsorption concentration, intermediate gas mixture of non-adsorption phase flowing out from the top of the 1 section of PSA enters from the bottom of a second PSA adsorption tower (2 sections of PSA) serving as shallow cold pressure swing adsorption after cold and heat exchange, and hydrogen-enriched methane-hydrogen gas of non-adsorption phase flowing out from the top of the 2 sections of PSA enters adsorption purification; the desorption gas from the PSA of the 1 section and the PSA of the 2 section enters a shallow cold oil absorption process after cold-heat exchange and pressurization, wherein part of the intermediate mixed gas or hydrogen-enriched methane hydrogen gas of the non-adsorption phase of the 1 section or the 2 section can be respectively used as the feed gas of the respective process to be complemented, and the concentration of ethylene or silane in the adsorption towers of the sections is regulated so as to improve the yield of the ethylene or the silane.
Example 4
As shown in FIG. 4, in the embodiment 1, when the silane content is more than 1% in the methane-hydrogen gas feed gas from the shallow-cooling pressure swing adsorption concentration step, ethanol is used as an absorbent to perform absorption purification instead of absorption purification, wherein the methane-hydrogen gas from the shallow-cooling pressure swing adsorption concentration step is subjected to fine filtration and then is pressurized to 2.0-3.0 MPa and enters an absorption tower through cold-heat exchange to 5-10 ℃, and purified methane-hydrogen gas with the silane content less than 10ppm flows out from the top of the absorption tower and directly enters the pressure swing adsorption A hydrogen extraction step of desorbing the absorption liquid flowing out from the bottom of the absorption tower in a desorption tower under normal temperature and normal pressure (the desorbed ethanol absorbent is returned to the absorption tower for reuse) to desorb the silane-rich gas, mixing the silane-rich gas with the non-condensable gas flowing out from the top of the absorption tower in a shallow cold oil absorption step after cold heat exchange and pressurization, and then feeding the gas into a middle-shallow cold rectification step to further recover SiH 4 。
Example 5
As shown in FIG. 5, in the embodiment 1, the middle and shallow cold rectifying process consists of two rectifying towers, the non-condensable gas 1 from the shallow cold oil absorbing process is condensed to produce condensed fluid, and the condensed fluid enters the middle and shallow cold rectifying tower-1 with the operating temperature of-35 to-25 ℃ and the operating pressure of 2.0 to 2.5MPa, and the non-condensable gas 3 of light components, mainly H, flows out from the top of the tower 2 、CH 4 Composition and trace SiH 4 The mixture is mixed with the pretreated and purified raw material gas after being cooled to 5-20 ℃ and decompressed to less than 1MPa by a cold-heat exchanger and then enters a shallow-cooling pressure swing adsorption concentration process to further recycle H 2 Or/and CH 4 ，H 2 or/CH (or) 4 The yield of the product gas is further improved, the heavy component fluid flowing out from the bottom of the rectifying tower-1 is fed into a middle-shallow cold rectifying tower-2 with the operating temperature of minus 20 to minus 15 ℃ and the operating pressure of 1.5 to 2.5MPa, the heavy component rich in ethylene flows out from the bottom of the middle-shallow cold rectifying tower-2, the heavy component rich in Silane (SiH) flows into an ethylene refining process, and the heavy component fluid flows out from the top of the middle-shallow cold rectifying tower-2 4 ) The tower top gas of (2) enters a silane metal getter in a silane purification process to be purified to obtain SiH with the purity of more than or equal to 99.999 percent 4 The product gas is returned to the SiC-CVD epitaxial process for recycling, and the non-condensable gas 2 generated by condensation is returned to the medium-temperature pressure swing adsorption concentration process.
Example 6
In addition to the embodiment 1, the top gas of the rectifying tower from the middle and shallow cold rectifying step in the silane purifying step contains small amounts of C2H4, CO/CO2, O2 and H2O, and also contains trace amounts of phosphane (PH 3), arsine (AsH 3), diborane (B2H 6) and siloxane, and the adsorption tower in the silane purifying step is filled with various combined adsorbents of diatomite, silica gel, active carbon and molecular sieve, and also is filled with the molecular sieve or the active aluminum oxide (Al 2O 3) loaded with the active components of metallic copper (Cu)/zinc (Zn) or copper oxide (CuO)/zinc oxide (ZnO), so that the impurity removal depth can reach the level of less than 50-100 ppb.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (10)
1. The method for recovering and recycling the tail gas FTrPSA of the SiC-CVD chlorine-free epitaxial process by reacting ethylene with silane is characterized by comprising the following steps of: the method comprises the following steps:
step 1, pretreatment of raw gas, namely sequentially removing dust, particles, oil mist and partial high hydrocarbon impurities;
step 2, medium-temperature pressure swing adsorption concentration, namely directly or pressurizing raw gas from a pretreatment process to less than 1.0MPa, performing cold-heat exchange, and then entering a multi-tower pressure swing adsorption concentration process consisting of at least 4 towers, wherein at least one adsorption tower is in an adsorption step, the rest adsorption towers are in a desorption regeneration step, and the formed non-adsorption phase gas is an intermediate mixed gas;
step 3, shallow-cooling pressure swing adsorption concentration, namely, performing precise filtration, compression and cold-heat exchange on intermediate mixed gas from a middle-temperature pressure swing adsorption concentration process, performing adsorption concentration on the intermediate mixed gas in the shallow-cooling pressure swing adsorption concentration process consisting of 4 or more adsorption towers, enabling methane hydrogen gas which flows out of the top of the adsorption tower to flow out of the hydrogen-enriched gas, performing adsorption purification on the intermediate mixed gas in the next process, desorbing and sucking the silane-enriched gas which flows out of the bottom of the adsorption tower, performing cold-heat exchange and pressurization, and returning the intermediate mixed gas to the subsequent process, namely shallow-cooling oil absorption;
step 4, performing adsorption purification, namely enabling methane hydrogen gas to enter an adsorption purification process consisting of 2 or 3 adsorption towers to form purified methane hydrogen gas, and entering the next process, namely performing pressure swing adsorption hydrogen extraction;
Step 5, pressure swing adsorption hydrogen extraction, methane hydrogen purification, direct or cold-heat exchange to normal temperature, and multi-tower conversion consisting of at least 4 towersThe procedure of pressure adsorption and purification of hydrogen gas, the non-adsorption phase gas is ultra-high purity hydrogen gas with purity of more than or equal to 99.999-99.9999%, wherein, CO and CO 2 The content of hydrocarbon is less than 0.1-1.0 ppm, the content of silane is less than 10ppm and the content of silane is less than 0.1-1.0 ppm calculated by methane, and the process enters the next working procedure, namely hydrogen purification;
step 6, purifying the ultra-high purity hydrogen, namely purifying the ultra-high purity hydrogen at the operating temperature of 50-500 ℃ under normal pressure or under the pressure condition required by hydrogen used in the SiC-CVD process, removing trace impurities to obtain a final electronic grade hydrogen product, and cooling or reducing the temperature by heat exchange or reducing the pressure, or sending the final electronic grade hydrogen product into an electronic grade hydrogen product tank for storage, or directly returning the final electronic grade hydrogen product to the process requiring hydrogen in the SiC-CVD epitaxial process through a hydrogen product buffer tank;
step 7, shallow cold oil absorption, namely, silane-enriched desorption gas from a medium-temperature pressure swing adsorption concentration process enters the shallow cold oil absorption process from the bottom of an absorption tower after cold and heat exchange and compression, adopts a C4 liquid solvent with the temperature of 5-15 ℃ and the pressure of 2.5-3.5 MPa as an absorbent, sprays and absorbs the liquid from top to bottom, and flows out SiH containing SiH from the top of the absorption tower 4 And methane hydrogen non-condensable gas 1 enters the next process, namely middle-shallow cold rectification, ethylene-rich liquid flows out of the bottom of the absorption tower, enters the desorption tower, crude ethylene gas flows out of the top of the desorption tower, enters the subsequent process, namely ethylene refining, and C4 absorbent flows out of the bottom of the desorption tower and returns to the absorption tower for recycling;
step 8, middle and shallow cold rectification, namely, condensing a condensed fluid generated by condensation of the non-condensable gas 1 from a shallow cold oil absorption process, entering a middle and shallow cold rectification tower, introducing silane-rich gas flowing out of the top of the rectification tower into a next process, namely, silane purification, mixing ethylene-rich gas flowing out of the bottom of the rectification tower with crude ethylene gas from the shallow cold oil absorption process, introducing the mixture into a subsequent ethylene refining process, and returning the condensed non-condensable gas 2 to a shallow cold pressure swing adsorption concentration process, or returning the condensed fluid to a middle temperature pressure swing adsorption concentration process after cold-heat exchange, so as to further recover effective components;
step 9, purifying silane, namely, introducing silane-rich tower top gas from a middle-shallow cold rectifying tower into a pressure swing adsorption silane purifying system consisting of at least 2 or more adsorption towersThe silane product gas with purity of more than or equal to 99.99 percent flows out from the top of the adsorption tower and is directly or through SiH 4 The metal getter purifier is further purified and then used as raw material gas required by SiC-CVD epitaxial process for recycling, and the adsorption tower is subjected to vacuum desorption and desorption gas flowing out from the bottom of the adsorption tower, or directly used as fuel gas, or is subjected to pressurization and cold-heat exchange and then returned to a rectifying tower in a middle-shallow cold rectifying process for further recycling C 2 H 4 With SiH 4 ；
Step 10, refining ethylene, namely condensing crude ethylene gas from a shallow cold oil absorption process after decarburization treatment, mixing the crude ethylene gas with ethylene rich from a middle and shallow cold rectification process, feeding the mixture into an ethylene rectification tower for refining, discharging ethylene product gas from the top of the tower, and discharging C including ethane from the bottom of the tower 2+ The components are used as fuel gas or are externally conveyed.
2. The method for recovering and recycling FTrPSA as defined in claim 1, wherein the tail gas of the SiC-CVD chlorine-free epitaxy process is prepared by reacting ethylene with silane, and the method is characterized in that: in the pretreatment, under the working condition that the raw material gas is waste gas or tail gas containing high concentration of impurities including acid and volatile organic compounds, except a dust remover, a particle filter and an oil mist removing catcher, an alkaline washing tower, a neutralizing tower or a dryer is additionally arranged to remove the impurity components of the acid and volatile organic compounds which have great influence on the operation of a pressure swing adsorption concentration process.
3. The method for recovering and recycling FTrPSA as defined in claim 1, wherein the tail gas of the SiC-CVD chlorine-free epitaxy process is prepared by reacting ethylene with silane, and the method is characterized in that: in the middle-temperature pressure swing adsorption concentration and adsorption tower desorption step, crude ethylene gas from the top of a desorption tower in a shallow cold oil absorption process or ethylene-rich gas from the bottom of a rectification tower in a middle-shallow cold rectification process or ethylene product gas from ethylene refining is adopted for replacement after the adsorption step of the adsorption tower and before the pressure equalization step or the sequential discharge step starts, so that the concentration and the yield of ethylene in the process are improved.
4. The method for recovering and recycling FTrPSA as defined in claim 1, wherein the tail gas of the SiC-CVD chlorine-free epitaxy process is prepared by reacting ethylene with silane, and the method is characterized in that: the medium temperature pressure swing adsorption concentration and shallow cold pressure swing adsorption concentration processes are combined into a process consisting of two sections of PSA, raw gas from pretreatment enters from the bottom of a first PSA adsorption tower serving as medium temperature pressure swing adsorption concentration after being heated and pressurized, intermediate mixed gas of a non-adsorption phase flowing out of the top of the 1 section of PSA tower enters from the bottom of a second PSA adsorption tower serving as shallow cold pressure swing adsorption after cold and heat exchange, and hydrogen-enriched methane hydrogen gas of the non-adsorption phase flowing out of the top of the 2 sections of PSA tower enters the next process, namely adsorption purification; the desorption gas from the PSA of the 1 section and the PSA of the 2 section enters a shallow cold oil absorption process after cold-heat exchange and pressurization, wherein part of the intermediate mixed gas or hydrogen-enriched methane hydrogen gas of the non-adsorption phase of the 1 section or the 2 section can be respectively used as the feed gas of the respective process to be complemented, and the concentration of ethylene or silane in the adsorption towers of the sections is regulated so as to improve the yield of the ethylene or the silane.
5. The method for recovering and recycling FTrPSA as defined in claim 4, wherein the tail gas of the SiC-CVD chlorine-free epitaxy process is prepared by reacting ethylene with silane, and the method is characterized by: the second PSA adsorption tower (2-section PSA) used as shallow-cold pressure swing adsorption concentration is added with a replacement step after the adsorption step is finished and before the pressure equalization or sequential discharge step is started, and a rectifying tower from a middle-shallow cold rectifying process is adopted to enrich SiH 4 Or SiH from silane purification step 4 The product gas is replaced.
6. The method for recovering and recycling FTrPSA as defined in claim 1, wherein the tail gas of the SiC-CVD chlorine-free epitaxy process is prepared by reacting ethylene with silane, and the method is characterized in that: the adsorption purification process comprises the steps of carrying out absorption purification by adopting an absorbent when the silane content in methane hydrogen gas feed gas from the shallow-cooling pressure swing adsorption concentration process exceeds 1%, and replacing adsorption purification, wherein the methane hydrogen gas from the shallow-cooling pressure swing adsorption concentration process is pressurized to 2.0-3.0 MPa after fine filtration and enters an absorption tower from the top of the absorption tower after cold and heat exchange to-10 DEG CPurified methane hydrogen gas with the silane content less than 10ppm directly enters a pressure swing adsorption hydrogen extraction process, absorption liquid flowing out of the bottom of an absorption tower enters a desorption tower for desorption, desorbed silane-rich gas is subjected to cold-heat exchange and pressurization and then is mixed with non-condensable gas flowing out of the top of the absorption tower in a shallow cold oil absorption process, and then enters a middle-shallow cold rectification process for further recovering SiH 4 。
7. The method for recovering and recycling FTrPSA as defined in claim 1, wherein the tail gas of the SiC-CVD chlorine-free epitaxy process is prepared by reacting ethylene with silane, and the method is characterized in that: the middle-shallow cold rectifying process consists of two rectifying towers, the non-condensable gas 1 from the shallow cold oil absorbing process is condensed to produce condensed fluid, the condensed fluid enters the middle-shallow cold rectifying tower-1, the non-condensable gas 3 of light components flows out from the top of the tower and enters the shallow cold removing pressure swing adsorption concentrating process to further recover H 2 Or/and CH 4 Heavy component fluid flowing out of the bottom of the rectifying tower-1 is fed into the middle-shallow cold rectifying tower-2, heavy component rich in ethylene flows out of the bottom of the rectifying tower-1, enters an ethylene refining process, and flows out of the top of the rectifying tower into a silane purifying process, or directly serves as silane product gas, or directly enters a silane metal getter for purification, so that SiH with the purity of more than or equal to 99.999% is obtained 4 The product gas is returned to the SiC-CVD epitaxial process for recycling, and the non-condensable gas 2 generated by condensation is returned to the medium-temperature pressure swing adsorption concentration process.
8. The method for recovering and recycling FTrPSA as defined in claim 1, wherein the tail gas of the SiC-CVD chlorine-free epitaxy process is prepared by reacting ethylene with silane, and the method is characterized in that: the purity of the silane product gas obtained in the silane purification process is more than or equal to 99.99 percent, or the silane product gas is subjected to SiH 4 The metal getter purifier is further purified and then recycled as a feed gas for the SiC-CVD epitaxial process.
9. The method for recovering and recycling FTrPSA as defined in claim 1, wherein the tail gas of the SiC-CVD chlorine-free epitaxy process is prepared by reacting ethylene with silane, and the method is characterized in that: the tower top gas of the rectifying tower from the middle and shallow cold rectifying process in the silane purifying process contains small amounts of C2H4, CO/CO2, O2 and H2O, and also contains trace amounts of phosphane, arsine, diborane and siloxane, and the adsorption tower in the silane purifying process is filled with one or more combined adsorbents of diatomite, silica gel, active carbon and molecular sieve, and also needs to be filled with the molecular sieve or the active aluminum oxide adsorbent loaded with metallic copper/zinc or copper oxide/zinc oxide active components.
10. The method for recovering and recycling FTrPSA as defined in claim 1, wherein the tail gas of the SiC-CVD chlorine-free epitaxy process is prepared by reacting ethylene with silane, and the method is characterized in that: the pressure change in the adsorption and desorption cycle operation process is realized by a program control valve and a regulating valve on a pipeline connected between the adsorption towers under the operation condition that the adsorption pressure is more than or equal to 0.6MPa in the middle temperature pressure swing adsorption concentration, shallow cold pressure swing adsorption concentration, pressure swing adsorption hydrogen extraction and adsorption purification processes.
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