CN110201487B - Method for purifying and recycling high-purity high-yield methane-induced stable gas in ethylene process for preparing ethylene oxide - Google Patents
Method for purifying and recycling high-purity high-yield methane-induced stable gas in ethylene process for preparing ethylene oxide Download PDFInfo
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Abstract
The invention discloses a method for purifying and recycling high-purity high-yield methane-induced stable gas in ethylene-based epoxy ethane preparation, which comprises the following steps: (1) the natural gas enters a PSA system for dealkylation, decarbonization and dehydration to obtain methane product gas of non-adsorption phase gas, and the methane product gas is used as stable gas for preparing Ethylene Oxide (EO) by an ethylene method and enters a reactor for reaction; (2) obtaining adsorption phase gas from the step (1), and partially returning the adsorption phase gas to the ethylene oxide reaction circulating gas for reaction; (3) part of reaction circulating gas formed by the reaction returns to the ethylene oxide reactor, and part of reaction circulating gas enters a CO2 absorption tower for decarburization to form non-condensable gas and returns to the reactor; (4) enabling the top gas of the EO stripping tower to enter an EO reabsorption tower to form non-condensable gas, enabling the non-condensable gas to enter full-temperature-range pressure swing adsorption (FTrPSA) to recover ethylene, and enabling the outflow methane-rich tail gas to return to the step (1); part of the effluent ethylene-rich gas returns to the reaction recycle gas for recycling, and part of the effluent ethylene-rich gas is sent out to ethylene rectification for recycling and refining ethylene, and the ethylene is recycled as ethylene required by EO reaction.
Description
Technical Field
The invention relates to natural gas purification and comprehensive utilization in the fields of petrochemical industry and fine chemical industry, in particular to a high-purity high-yield methane-induced stable gas purification method for preparing ethylene oxide by an ethylene method.
Background
Ethylene Oxide (EO) and Ethylene Glycol (EG) at the downstream of the EO are used as main derivatives of ethylene and widely applied to the fields of surfactants, synthetic fibers and the like, wherein the key technology of ethylene oxide production selects an ethylene oxidation catalyst with good activity, high selectivity and long service life and corresponding operating conditions, and the use of a stabilizer (gas) in the reaction process is also accepted as an important technical link by process suppliers and manufacturers, which is related to the stability, safety and economy of an EO production device. Methane is widely used in the industry as a stabilizing gas in the process of producing EO by directly oxidizing ethylene. Compared with nitrogen stabilization, the method not only increases the stability and safety of the production process, but also has obvious economic benefit.
In the process of producing EO by directly oxidizing ethylene, methane is used as stabilizing, and the advantages of reducing the explosion range and improving the safety of the reaction are achieved. Because ethylene, oxygen and EO products which are used as raw materials for producing EO by directly oxidizing ethylene are flammable and explosive dangerous chemicals, the working concentration of the dangerous chemicals is diluted to be below the explosion limit of the dangerous chemicals in the air by adding methane stabilizing gas, for example, nitrogen is used as the stabilizing gas, the working concentration of ethylene is 20% (v), the working concentration of oxygen is 7%, the working concentration of ethylene is stabilized by methane, the working concentration of ethylene is 25%, and the working concentration of oxygen is 8%; secondly, remove more reaction heat, promoted the security and the stability of reactor operation. Because methane has larger heat capacity than nitrogen, the methane has good heat removal (heat transfer) medium for a large amount of heat released by the direct oxidation of ethylene, and has great effects on reducing local overheating or temperature runaway caused by the local overheating in the operation of the whole device, prolonging the service life of the catalyst, improving the selectivity of EO and stabilizing and safety the reaction; third, the stability of the reaction and EO selectivity are increased. Compared with nitrogen stabilization, methane is used as stabilizing gas, so that the working concentration of ethylene and oxygen in the feed gas is improved, the reaction rate is improved, the reaction can be carried out at a lower reaction temperature, the occurrence of side reactions is reduced, and the stability of the reaction and the selectivity of EO are improved. Meanwhile, the unit consumption of ethylene and oxygen is correspondingly reduced, and the economic benefit is increased; fourthly, further energy is saved. The reaction temperature and the circulating gas amount of methane under the same productivity condition are obviously reduced compared with nitrogen, so that the steam heating energy consumption and the circulating gas compression power consumption are reduced.
In the existing process flow for preparing EO by the direct ethylene oxidation method, it is worth noting that the oxidation reaction requires that the purity of the raw material gas and the fresh methane-stabilizing gas is higher, wherein the contents of the impurity components such as hydrocarbons with more than three carbon atoms, acetylene, hydrogen, moisture and the like in the methane-stabilizing gas must be strictly limited, because the impurity components generate a large amount of reaction heat with ethylene or oxygen under the action of the catalyst, the stability and the safety of the reaction are greatly influenced; secondly, the stabilization effect of methane is mostly realized in the reaction recycle gas, and the recycle gas contains more impurity components such as carbon dioxide (CO 2), water (H2O), inert gas argon (Ar) and trace sulfide, and the impurity components can be accumulated in the circulation process, so that the composition of the recycle gas is changed, the working concentration, the explosion limit and the catalyst use efficiency of flammable and explosive components such as ethylene and oxygen are influenced, and further the circulation proportion of the recycle gas needs to be continuously adjusted or the accumulation of the impurity components is avoided by increasing the discharge gas amount, so that the methane or the feed gas feeding amount needs to be further newly supplemented. More importantly, although the CO2 and H2O components play a certain stabilizing role in the ethylene oxide reaction, and further CO2 and H2O with certain concentrations in the circulating gas are allowed to exist, only 10-30% of the reaction gas is pumped out in the actual operation process to absorb the hot potassium carbonate aqueous solution to remove the CO2, the formed non-condensable gas is returned to the circulating gas again for recycling, and more water in the system is accumulated. Under the action of high temperature and high pressure and a catalyst, water can generate reforming reaction or water decomposition with methane, ethane or ethylene to generate hydrogen, carbon monoxide or CO2, and can also react with CO2, so that the occurrence probability of ethylene oxidation side reaction is increased, the stability and safety of the operation of the whole device are greatly reduced, and the energy consumption and the cost are further increased; thirdly, the methane stabilizing gas is required to be used in multiple sections such as a stripping tower for EO production, so that methane-rich noncondensable gas carrying more impurity components (including EO, CO2, EG, N2 and the like) is generated and is circularly accumulated in the whole EO process flow, more tail gas is required to be discharged in order to avoid accumulation of more impurity components in the system, the methane loss is larger, the newly supplemented methane is more, the EO production cost is higher, and the stability and the safety of the device are poorer.
At present, in an EO production process and device, a purification process of methane stabilizing gas is independent and isolated, and is not connected with other working sections in EO production, such as a circulating gas and a tail gas treatment device, so that more fresh methane stabilizing gas is required to be continuously supplemented, the waste of methane is more serious, the stability and the safety of the device become worse, and the energy consumption and the production cost are increased.
Disclosure of Invention
Aiming at the problems that in the EO production process and the device, the purification process of the methane stabilizing gas is independent and isolated, is not connected with other working sections in the EO production, such as a circulating gas and a tail gas treatment device, and further needs more fresh methane stabilizing gas to be continuously supplemented, the waste of methane is more serious, the stability and the safety of the device become worse, the energy consumption and the production cost are increased, and the like, the invention aims to provide a purification and reutilization method of the high-purity high-yield methane stabilizing gas in ethylene process ethylene oxide, which realizes the purposes of methane purification and recovery and reutilization as the stabilizing gas by coupling the natural gas purification of PSA decarbonization and dehydration, the EO reaction circulating gas drying and dehydration, the recovery of the methane-rich gas flowing out from each working section of EO, the FTrPSA recovery of tail gas and the like, and simultaneously minimizes the waste rate of methane, and the EO device is safer and more stable to operate and the economic benefit is improved.
Therefore, the technical scheme adopted by the invention is summarized as follows:
a method for purifying and recycling high-purity high-yield methane-induced stable gas in ethylene-based epoxy ethane production comprises the following steps:
(1) using commercial or industrial natural gas as raw material gas, directly or after adding/reducing pressure and heat exchange, entering a PSA system for removing hydrocarbon, decarbonizing and dehydrating with the operation temperature of 20-60 ℃ and the operation pressure of 1.0-3.0MPa, wherein the obtained non-adsorption phase gas is purified methane product gas, is used as stable gas in ethylene process ethylene oxide, is mixed with ethylene and oxygen and then enters an ethylene direct oxidation reactor for reaction, or/and part of the methane product gas is mixed with nitrogen and enters an ethylene oxide stripping tower, or/and enters a regeneration tower for absorbing carbon dioxide;
(2) the adsorption phase gas (namely desorption gas) obtained from the PSA system for hydrocarbon removal, decarbonization and dehydration is blown or pressurized, one part of the adsorption phase gas is directly returned to the ethylene oxide reaction circulating gas for reaction, and the other part of the adsorption phase gas is returned to the ethylene oxide stripping tower or enters a regeneration tower for absorbing carbon dioxide or directly enters a fuel gas pipe network as fuel gas;
(3) the reaction gas from the ethylene oxide reactor forms non-condensable gas rich in methane after passing through an ethylene oxide washing/absorption tower, the reaction circulating gas is formed after dehydration and drying are carried out through a drying system, one part of the reaction circulating gas is directly returned to a raw material ethylene, oxygen and methane mixer to be mixed and then returned to the ethylene oxide reactor for reaction, the other part of the reaction circulating gas enters a carbon dioxide absorption tower to be decarbonized, and the formed non-condensable gas rich in methane is directly returned to the raw material ethylene, oxygen and methane mixer to be mixed and then returned to the ethylene oxide reactor for reaction;
(4) the top gas from the ethylene oxide stripping tower enters an ethylene oxide reabsorption tower to form methane-rich noncondensable gas, the methane-rich noncondensable gas is compressed and then enters a full temperature range pressure swing adsorption (FTrPSA) system to recover ethylene, methane-rich tail gas flows out from a non-adsorption phase, one part of the methane-rich tail gas returns to the PSA system for hydrocarbon removal, decarburization and dehydration of the feed gas, the methane is further recovered for recycling, and the other part of the methane-rich tail gas enters a fuel gas pipe network as fuel gas for use; and (3) the ethylene-rich gas is discharged from the adsorption phase, one part of the ethylene-rich gas is returned to the EO reaction recycle gas to be recycled after pressurization, and the other part of the ethylene-rich gas is sent to ethylene rectification for further recovering and refining ethylene and is recycled as the ethylene raw material required by the EO reaction.
Preferably, in the step (1), in the methane product gas, hydrocarbon components (C3 +) with three or more carbon atoms are less than or equal to 5-10 ppm, acetylene is less than or equal to 5ppm, hydrogen is less than or equal to 5-10 ppm, CO + CO2 is less than or equal to 5-10 ppm, sulfide is less than 1-10 ppm, and the dew point is less than-45 ℃.
Preferably, in the step (1), the PSA system for removing hydrocarbons, decarbonizing and dehydrating is pressure swing adsorption consisting of at least 4 or more adsorption towers connected in series or in parallel or in series and parallel, each adsorption tower is filled with one or more adsorbent combinations of activated alumina, silica gel, activated carbon and molecular sieves, the adsorption towers control and regulate the pressure change in the PSA adsorption and desorption cyclic operation process through a control system consisting of an adjusting valve or a program control valve arranged on a connecting pipeline, the pressure equalizing frequency is not more than 3 times, and the desorption process consists of forward/uniform pressure drop, reverse discharge, vacuum pumping/flushing, uniform pressure rising and final filling.
More preferably, the ratio of the amount of the non-adsorption phase gas (methane product gas) to the amount of the desorbed gas in the steps (1) and (2) can be realized by adjusting the timing of the adsorption and desorption cycle operations of the PSA system and controlling the combination of the regulating valve and the program control valve according to the ratio requirement of the ethylene oxide reaction cycle gas.
Preferably, the drying system in step (3) is a Temperature Swing Adsorption (TSA) system composed of two or three adsorption columns connected in series, one adsorption column in the two adsorption columns and one regeneration column, or, one-tower adsorption, one-tower hot blowing and one-tower cold blowing are carried out in three towers, each adsorption tower is filled with one or more adsorbent combinations of activated alumina, silica gel and molecular sieve, the adsorption temperature is 60-80 ℃, the regeneration temperature is 120-220 ℃, methane product gas is adopted, or from the methane-rich tail gas formed in step (4) after compression and ethylene recovery, or the desorbed gas from the step (2), or the methane product gas is cold blowing gas, and from the methane-rich tail gas formed after the compression and recovery of ethylene as described in step (4), or the desorption gas from the step (2) is hot blowing gas, and an inlet and outlet pipeline of each adsorption tower in the drying system is connected with a heater.
More preferably, the drying system in the step (3) is full-temperature-range pressure swing adsorption consisting of at least 4 adsorption towers which are connected in series or in parallel or in series and parallel, each adsorption tower is filled with one or more adsorbent combinations of activated alumina, silica gel and a molecular sieve, at least one adsorption tower is used for adsorption, the rest adsorption towers are used for desorption and regeneration, the adsorption pressure is the outlet pressure of reaction gas and is 0.3-1.5MPa, the adsorption and desorption regeneration temperatures are both 60-80 ℃, and the desorption steps are pressure equalizing, reverse releasing, evacuating/flushing, pressure equalizing and final charging. The desorption gas formed by the reverse discharge and the evacuation/flushing is directly or after being pressurized, or enters a stripping tower or a CO2 absorption tower for further recycling the methane.
More preferably, the drying system in the step (3) is separated by a pervaporation membrane composed of one or more stages of molecular sieve membranes, the condensate rich in water flows out of the permeation side, the condensate is mixed with the absorption liquid-carbonate solution in the CO2 absorption system in the EO production process, the mixture enters a CO2 absorption tower to remove CO2 in the condensate, the mixture rich in methane and ethylene flows out of the non-permeation side, one part of the mixture is recycled as EO reaction recycle gas, the other part of the mixture enters a carbon dioxide absorption tower to be decarbonized, the formed non-condensable gas rich in methane directly returns to a raw material ethylene, oxygen and methane mixer to return to an ethylene oxide reactor for reaction, the pervaporation pressure is 0.3-1.5MPa, and the pervaporation temperature is 60-80 ℃.
Preferably, the FTrPSA system in step (4) is pressure swing adsorption consisting of at least 4 adsorption towers connected in series or in parallel or in series and parallel, each adsorption tower is filled with one or more adsorbent combinations of activated alumina, silica gel, activated carbon, molecular sieves, and a control system consisting of an adjusting valve or a program control valve disposed on a connecting pipeline is used between the adsorption towers to control and adjust the pressure change during the PSA adsorption and desorption cycle operation, the pressure equalization frequency is not more than 3 times, and the desorption process consists of forward/uniform pressure drop, reverse discharge, vacuum pumping/flushing, uniform pressure rising and final filling; the adsorption pressure is 0.3-1.5MPa, and the adsorption and desorption temperatures are both 60-80 ℃.
Preferably, the full temperature range pressure swing adsorption (FTrPSA) system in the step (4) recovers ethylene, a shallow cold oil absorption system is adopted to replace the FTrPSA system to recover ethylene, the non-condensable gas rich in methane formed from the ethylene oxide reabsorption tower is compressed to 2.0-4.0MPa and is cooled to 10-20 ℃ through heat exchange, then the non-condensable gas enters an absorption tower using carbon four (containing n-butane or isobutane or mixed butane) as an absorbent, the non-condensable gas rich in methane flows out of the top of the absorption tower, and one part of the non-condensable gas returns to a PSA system of raw material gas for hydrocarbon removal, decarbonization and dehydration, and is further recovered with methane for recycling, and the other part of the non-condensable gas is used as fuel gas and enters; and (3) feeding the ethylene-rich absorption liquid flowing out of the bottom of the absorption tower into a desorption tower, and flowing out ethylene-rich gas from the top of the absorption tower, or directly recycling the ethylene-rich gas as EO reaction recycle gas, or externally sending the ethylene-rich gas to ethylene rectification for further recovering and refining ethylene, wherein the ethylene-rich gas is recycled as an ethylene raw material required by EO reaction, and the carbon-four absorption liquid flowing out of the bottom of the absorption tower is returned to the absorption tower for recycling.
Compared with the prior art, the technical scheme provided by the invention is as follows:
(1) coupling high-purity methane stabilizing gas obtained by purifying natural gas subjected to decarbonization and dehydration through PSA (pressure swing adsorption), with EO reaction circulating gas drying and dehydration, recovery of methane-rich gas flowing out of each workshop section of EO, FTrPSA (fluorine-doped PSA) recovery of tail gas and the like in the EO production process, so that the purposes of methane purification and recovery and reutilization as stabilizing gas are realized, meanwhile, the waste rate of the methane stabilizing gas is minimized, and the EO device is safer and more stable in operation and improves the economic benefit;
(2) the purification of the methane stabilizing gas obtained by decarbonization and dehydration of PSA can obtain high-purity methane, and the obtained desorption gas can be sent to the working procedures required in the EO production process, including directly returning to the EO reaction circulating gas to adjust the composition and the circulating quantity of the reaction circulating gas, so that the EO reaction is more stable and safer, and the methane in the desorption gas is recycled;
(3) the invention aims at the problems that in the prior EO production process, most of non-condensable gas of reaction mixed gas passing through an EO absorption tower is directly used as reaction circulating gas to introduce excessive moisture into a system, so that the circulating gas quantity is increased due to higher reaction temperature and increased side reaction, the supplement quantity of fresh ethylene, oxygen, methane and an inhibitor is increased, and the stability and safety operation of the system are greatly influenced, the non-condensable gas escaping from the EO absorption tower is dried, the load of the circulating gas is lightened, and simultaneously the temperature or pressure carried by the non-condensable gas is fully utilized, and temperature swing adsorption, or full temperature swing adsorption, or pervaporation membrane separation technology is selectively adopted for dehydration and drying;
(4) the invention can adjust the proportion of the circulation quantity of the dried EO reaction gas directly used as the circulating gas and the air input quantity of the CO2 absorption tower so as to ensure the proportion of the proper CO2 concentration in the circulating gas and the concentration of effective components such as methane, ethylene and the like and ensure that the EO reaction is carried out stably, safely and economically;
(5) the invention can simultaneously recycle ethylene and methane from the tail gas discharged by the CO2 absorption system, further reduces the supplement amount of stable gas caused by fresh ethylene and methane, further reduces the energy consumption and the unit consumption of ethylene and methane, and greatly improves the economic benefit of an EO device;
(6) the invention fully utilizes the methane-rich gas generated in each process in the EO production process, and also fully utilizes the energy carried by the material flow of each working section, including temperature and pressure, so that the energy consumption and the material consumption in the EO production process are both low.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and examples.
FIG. 1 is a process flow diagram of example 1 of the present invention;
FIG. 2 is a process flow diagram of example 4 of the present invention;
FIG. 3 is a process flow diagram of example 5 of the present invention;
FIG. 4 is a process flow diagram of example 6 of the present invention;
FIG. 5 is a process flow diagram of example 7 of the present invention.
Detailed Description
In order that those skilled in the art will better understand the present invention, the following examples will illustrate the invention in further detail.
Example 1
A method for purifying and recycling high-purity high-yield methane-induced stable gas in ethylene-based epoxy ethane production comprises the following steps:
(1) the commercial natural gas is used as a raw material, the components of the commercial natural gas are methane (CH 4) 94.18% (volume ratio, the same below), ethane (C2H 6) 3.50%, propane (C3H 8) 0.10%, butane (containing isobutane) 0.21%, carbon five carbon six alkane (C5 +) 0.14%, nitrogen (N2) 1.20%, carbon dioxide (CO 2) 0.67%, water dew point-17.8 ℃, hydrogen sulfide 0.76mg/m3, oxygen (O2) 0.1%, raw material gas pressure is 50KPa, temperature is normal temperature, flow is 2,500Nm3/H, the raw material gas is compressed to 2.3MPa by a compressor, and directly enters a PSA system for hydrocarbon and decarbonization dehydration with operation temperature of 30 ℃ and operation pressure of 2.3MPa, the system consists of 5 adsorption towers and corresponding pipelines, regulating valves and control valves, adsorbents filled in the adsorption towers are alumina, active carbon and molecular sieves, and form a composite adsorption tower, wherein 1 composite adsorption bed layer is formed all the time, after adsorption, carrying out pressure equalizing, reverse discharging, evacuating, pressure equalizing and raising twice, and finally filling twice to complete the preparation work before re-adsorption, namely, the operation mode of the PSA system is 5-tower 1-adsorption and 2-time pressure equalizing evacuation regeneration, the non-adsorption phase gas obtained from the system is purified methane product gas, the components of the non-adsorption phase gas are hydrocarbon components (C3 +) of three or more carbon atoms less than or equal to 5ppm, acetylene less than or equal to 2ppm, hydrogen less than or equal to 5ppm, CO + CO2 less than or equal to 10ppm, sulfide less than 1ppm, the dew point less than-74 ℃, the pressure of 2.2MPa, the temperature of 30 ℃, 90 percent of the non-adsorption phase gas serving as stable gas in ethylene-process ethylene oxide, mixing the stable gas with ethylene and oxygen, then entering an ethylene direct oxidation reactor for reaction, and mixing 10 percent of the methane product gas with low-pressure nitrogen gas after pressure reduction and entering an;
(2) the desorption gas which is obtained from a PSA system for hydrocarbon removal, decarburization and dehydration and is formed by reverse discharge and evacuation is about 400-430 Nm3/h, and through air blowing and pressurization, 40-50% of the desorption gas enters an EO reaction recycle gas compressor to be pressurized to the pressure 2.2MPa required by EO reaction and then directly returns to the ethylene oxide reaction recycle gas for reaction, the rest part of the desorption gas returns to an ethylene oxide stripping tower, the rest part of the desorption gas enters a regeneration tower for absorbing carbon dioxide, and a small amount of the desorption gas as fuel gas directly enters a fuel gas pipe network;
(3) the method comprises the steps of enabling reaction gas from an ethylene oxide reactor to pass through an ethylene oxide washing/absorbing tower to form non-condensable gas rich in methane, enabling the non-condensable gas to enter a drying system for dehydration and drying after heat exchange, enabling the drying system to be Temperature Swing Adsorption (TSA) consisting of two adsorption towers, enabling one of the two towers to be used for adsorption, enabling one of the two towers to be used for regeneration, enabling each adsorption tower to be filled with an adsorbent combination of active alumina, silica gel and a molecular sieve, enabling the adsorption temperature to be 60-80 ℃ and the regeneration temperature to be 160 ℃, enabling methane product gas to be used as regeneration gas, and heating the regeneration gas through a heater during heating. 80-90% of the dried reaction recycle gas is compressed to 2.2-2.3MPa by a recycle gas compressor, and is directly returned to the ethylene, oxygen and methane mixer to be mixed and then returned to the ethylene oxide reactor to react, 10-20% of the reaction recycle gas enters a carbon dioxide absorption tower to be decarbonized, and the formed non-condensable gas rich in methane is directly returned to the ethylene, oxygen and methane mixer to be mixed and then returned to the ethylene oxide reactor to react;
(4) the process comprises the steps that top gas from an ethylene oxide stripping tower enters an ethylene oxide reabsorption tower to form methane-rich non-condensable gas, the methane-rich non-condensable gas is compressed and then enters a full-temperature-range pressure swing adsorption (FTrPSA) system to recover ethylene, the FTrPSA system is formed by connecting 5 adsorption towers in series and in parallel to form pressure swing adsorption, each adsorption tower is filled with a plurality of adsorbent combinations of activated alumina, silica gel, activated carbon and molecular sieves, pressure change in the cyclic operation processes of PSA adsorption and desorption is controlled and adjusted through a control system consisting of an adjusting valve or a program control valve arranged on a connecting pipeline among the adsorption towers, the pressure equalizing frequency is 1 time, and the desorption process consists of replacement, pressure equalizing, reverse release, vacuumizing, pressure equalizing and final filling; the adsorption pressure is 0.8-1.0MPa, and the adsorption and desorption temperatures are both 60-80 ℃. The methane-rich tail gas and the replacement waste gas flow out from the non-adsorption phase, most of the methane-rich tail gas and the replacement waste gas return to a PSA system for the hydrocarbon removal, the decarburization and the dehydration of the feed gas, the methane is further recycled, and a small part of the methane is used as fuel gas and enters a fuel gas pipe network for use; the ethylene-rich gas is flowed out from the adsorption phase, the concentration of ethylene is 85-90%, most of ethylene is returned to EO reaction circulating gas, and is circularly used after being pressurized, the rest of ethylene is sent out to ethylene rectification for further recovering and refining ethylene, the purity is 99.99%, and the ethylene-rich gas can be circularly used as an ethylene raw material required by EO reaction or used as a monomer raw material of polyethylene.
Example 2
Based on example 1, as shown in fig. 1, industrial natural gas was used as a stabilizing gas in the ethylene process for preparing ethylene oxide, and the main components thereof were methane (CH 4) 97.15% (volume ratio, the same applies below), ethane (C2H 6) 0.50%, propane (C3H 8) 0.01%, butane (containing isobutane) 0.02%, carbon pentacarbon hexaalkane (C5 +) 0.014%, nitrogen (N2) 0.76%, carbon dioxide (CO 2) 1.4%, water dew point-17.8 ℃, hydrogen sulfide 0.26mg/m3, oxygen + argon (O2 + Ar) 0.006%, helium (He) 0.02%, feed gas pressure of 3.0MPa, temperature of room temperature, pressure required for EO reaction was the same as in example 1, pressure of natural gas raw material was adjusted by pressure adjustment valve, pressure was reduced to 2.3MPa, and then introduced into PSA system for decarbonization and dehydration, and the subsequent steps were the same as in example 1.
Example 3
Based on examples 1 and 2, as shown in fig. 1, the desorbed gas obtained from the PSA system of step (2) is blown and pressurized, 40 to 50% of the desorbed gas enters an EO reaction recycle gas compressor to be pressurized to a pressure of 2.2MPa required for EO reaction, and then directly returns to the ethylene oxide reaction recycle gas to react, and the rest of the desorbed gas enters a regeneration tower for carbon dioxide absorption, and a small amount of the desorbed gas is directly sent to a fuel gas pipe network, so that the load of a CO2 absorption system is increased, the circulation amount of a thermokalite absorbent is increased, and the displacement gas amount of the FTrPSA system is increased, the displacement gas is ethylene concentrated gas, and the concentration of ethylene is 85 to 90%.
Example 4
Based on example 1, as shown in fig. 2, the drying system in step (3) is a Temperature Swing Adsorption (TSA) composed of three adsorption towers connected in series, one adsorption tower in the three adsorption towers is used for adsorption, one hot blowing tower is used for hot blowing, one cold blowing tower is used for cold blowing, and the drying system is operated alternately, each adsorption tower is filled with a plurality of adsorbent combinations of activated alumina, silica gel and molecular sieve, the adsorption temperature is 60-80 ℃, the regeneration temperature is 160 ℃, the methane-rich tail gas generated after the compression and the ethylene recovery in step (4) is heated by a heater connected with an inlet and an outlet of the adsorption tower and then used as hot blowing gas to carry out hot blowing on the adsorption tower in heating regeneration, the generated regeneration waste gas directly enters a stripping tower after heat exchange, the methane product gas is cold blowing gas, and the generated cold blowing regeneration gas is mixed with the non-condensable gas absorbed by the CO2 in step (3) and is recycled as reaction cycle gas.
Example 5
Based on example 1, as shown in fig. 3, the drying system in step (3) is a full temperature range pressure swing adsorption (FTrPSA) composed of 5 adsorption towers connected in series, each adsorption tower is filled with a combination of multiple adsorbents, such as activated alumina, silica gel, and molecular sieve, one adsorption tower is used for adsorption, the other adsorption towers are used for desorption and regeneration, the pressure is equalized for the first time, the adsorption pressure is 1.2MPa of the outlet pressure of the reaction gas, the temperatures of adsorption and desorption regeneration are both 60-80 ℃, and the desorption steps are pressure equalization, reverse release, vacuum pumping, pressure equalization and final filling. And (4) reversely discharging and evacuating the formed desorption gas, directly blowing the desorption gas into a stripping tower, and further recovering methane for recycling.
Example 6
Based on example 1, as shown in fig. 4, the drying system in step (3) is separated by a pervaporation membrane composed of a primary molecular sieve membrane, part of water and condensate rich in water flow out of the permeation side, the condensate is mixed with an absorption liquid-carbonate solution in a CO2 absorption system in an EO production process, the mixture enters a CO2 absorption tower to remove CO2 therein, a part of methane-rich and ethylene mixed gas flowing out of the non-permeation side is recycled as EO reaction recycle gas, a part of the methane-rich and ethylene mixed gas enters a carbon dioxide absorption tower to be decarbonized, the formed methane-rich non-condensable gas is directly returned to a raw material ethylene, oxygen and methane mixer to be mixed and then returned to a vaporization ethylene oxide reactor to react, the pervaporation pressure is 1.2MPa, and the pervaporation temperature is 60 to 80 ℃.
Example 7
Based on example 1, as shown in fig. 5, the full temperature range pressure swing adsorption (FTrPSA) system in step (4) recovers ethylene, a shallow cold oil absorption system is used to replace the FTrPSA system to recover ethylene, the non-condensable gas rich in methane formed from the ethylene oxide reabsorber is compressed to 2.8MPa, heat exchange is performed to cool the non-condensable gas to 10 ℃, and the non-condensable gas enters an absorption tower using carbon four (containing n-butane or isobutane or mixed butane C4) solvent as an absorbent, the absorption tower is a packed tower, the absorption pressure is 2.8MPa, and the absorption temperature is 10 ℃. The non-condensable gas rich in methane flows out of the top of the absorption tower, 70-80% of the non-condensable gas returns to a PSA system for hydrocarbon removal, decarbonization and dehydration of feed gas, the methane is further recycled, and 20-30% of the non-condensable gas is fuel gas and enters a fuel gas pipe network for use; and (2) feeding the ethylene-rich absorption liquid flowing out of the bottom of the absorption tower into a desorption tower, flowing out an ethylene-rich gas from the top of the absorption tower, wherein the ethylene concentration is 92-94%, one part of the ethylene-rich gas is directly recycled as EO reaction recycle gas, one part of the ethylene-rich gas is sent to ethylene rectification for further recovery and refining of ethylene, the ethylene-rich gas is recycled as an ethylene raw material required by EO reaction, and the carbon-four absorption liquid flowing out of the bottom of the absorption tower is returned to the absorption tower.
The above description is only a preferred embodiment of the present invention, and not intended to limit the present invention, and the scope of the present invention is defined by the appended claims, and all changes that come within the meaning and range of equivalency of the specification are therefore intended to be embraced therein.
Claims (9)
1. A method for purifying and recycling high-purity high-yield methane-induced stable gas in ethylene-based epoxy ethane production is characterized by comprising the following steps:
(1) using commercial or industrial natural gas as raw material gas, pressurizing and heat exchanging, then entering a PSA system with the operation temperature of 20-60 ℃ and the operation pressure of 1.0-3.0MPa for removing hydrocarbon, decarbonizing and dehydrating, wherein the obtained non-adsorption phase gas is purified methane product gas, is used as stable gas in ethylene-to-ethylene oxide production, is mixed with ethylene and oxygen and then enters an ethylene direct oxidation reactor for reaction, or/and a part of methane product gas is mixed with nitrogen and enters an ethylene oxide stripping tower, or/and enters a regeneration tower for absorbing carbon dioxide;
(2) the adsorption phase gas obtained from the PSA system for hydrocarbon removal, decarburization and dehydration, namely desorption gas, is blown or pressurized, one part of the adsorption phase gas is directly returned to the ethylene oxide reaction circulating gas for reaction, and the other part of the adsorption phase gas is returned to the ethylene oxide stripping tower or enters a regeneration tower for absorbing carbon dioxide or directly enters a fuel gas pipe network as fuel gas;
(3) the reaction gas from the ethylene oxide reactor forms non-condensable gas rich in methane after passing through an ethylene oxide washing/absorption tower, the reaction circulating gas is formed after dehydration and drying are carried out through a drying system, one part of the reaction circulating gas is directly returned to a raw material ethylene, oxygen and methane mixer to be mixed and then returned to the ethylene oxide reactor for reaction, the other part of the reaction circulating gas enters a carbon dioxide absorption tower to be decarbonized, and the formed non-condensable gas rich in methane is directly returned to the raw material ethylene, oxygen and methane mixer to be mixed and then returned to the ethylene oxide reactor for reaction;
(4) the top gas from the ethylene oxide stripping tower enters an ethylene oxide reabsorption tower to form methane-rich noncondensable gas, the methane-rich noncondensable gas is compressed and then enters a full-temperature-range pressure swing adsorption (FTrPSA) system to recover ethylene, methane-rich tail gas flows out from a non-adsorption phase, and one part of the methane-rich tail gas returns to the PSA system for hydrocarbon removal, decarburization and dehydration of the feed gas to further recover methane for recycling, and the other part of the methane-rich tail gas enters a fuel gas pipe network as fuel gas for use; and (3) the ethylene-rich gas is discharged from the adsorption phase, one part of the ethylene-rich gas is returned to the EO reaction recycle gas to be recycled after pressurization, and the other part of the ethylene-rich gas is sent to ethylene rectification for further recovering and refining ethylene and is recycled as the ethylene raw material required by the EO reaction.
2. The method for purifying and recycling high-purity high-yield methane-induced stable gas in the process of preparing ethylene oxide by using ethylene according to claim 1, wherein in the step (1), hydrocarbon components of three or more carbon atoms in the methane product gas are less than or equal to 5-10 ppm, acetylene is less than or equal to 5ppm, hydrogen is less than or equal to 5-10 ppm, and CO + CO is added2Less than or equal to 5-10 ppm, less than 1-10 ppm of sulfide and less than-45 ℃ of dew point.
3. The high-purity high-yield methane-induced steady gas purification and recycling method for ethylene-process ethylene oxide according to claim 1, wherein in the step (1), the PSA system for hydrocarbon removal, decarbonization and dehydration is pressure swing adsorption consisting of 4 or more adsorption towers connected in series or in parallel or in series and in parallel, each adsorption tower is filled with one or more adsorbent combinations of activated alumina, silica gel, activated carbon and molecular sieve, the adsorption towers are controlled and adjusted for pressure change in the PSA adsorption and desorption cyclic operation process through a control system consisting of regulating valves or program control valves arranged on connecting pipelines, the pressure equalizing frequency is not more than 3 times, and the desorption process consists of forward/average pressure drop, reverse release, vacuumizing/flushing, pressure equalizing and final filling.
4. The method for purifying and recycling the high-purity high-yield methane-induced stable gas in the ethylene-to-ethylene-process-produced epoxy ethane as claimed in claim 1, wherein the ratio of the gas amount of the non-adsorption phase to the gas amount of desorption phase in the steps (1) and (2) is realized by adjusting the time sequence of the adsorption and desorption cycle operation of the PSA system and controlling the combination of the regulating valve and the program control valve according to the ratio requirement of the ethylene oxide reaction cycle gas.
5. The method for purifying and recycling high-purity high-yield methane-induced steady gas in ethylene-based epoxy ethane production according to claim 1, wherein the drying system in step (3) is a Temperature Swing Adsorption (TSA) comprising two or three adsorption columns connected in series, one column of the two columns is used for adsorption, one column is used for regeneration, or one column of the three columns is used for adsorption, one column is used for hot blowing, and one column is used for cold blowing, each adsorption column is filled with one or more adsorbent combinations of activated alumina, silica gel and molecular sieve, the adsorption temperature is 60-80 ℃, the regeneration temperature is 120-220 ℃, methane product gas is used, or methane-rich tail gas is generated from step (4) after ethylene is compressed and recovered, or desorption gas is generated from step (2) as cold blowing gas and from step (4) after ethylene is compressed and recovered, and/or desorption gas generated from step (2) is hot blowing gas, and an inlet and outlet pipeline of each adsorption tower in the drying system is connected with a heater.
6. The method according to claim 1, wherein the drying system in step (3) is full-temperature pressure swing adsorption consisting of at least 4 adsorption towers connected in series or in parallel or in series and parallel, each adsorption tower is filled with one or more adsorbent combinations of activated alumina, silica gel and molecular sieve, at least one adsorption tower adsorbs the gas, the rest adsorption towers desorb and regenerate the gas at an adsorption pressure of 0.3-1.5MPa at a temperature of 60-80 ℃, the desorption steps are uniform pressure drop, reverse discharge, evacuation/flushing, uniform pressure rise and final flushing, and the desorbed gas formed by reverse discharge and evacuation/flushing directly or after pressurization enters a stripping tower or enters CO2And the absorption tower further recovers the methane for recycling.
7. The method as claimed in claim 1, wherein the drying system in step (3) is a pervaporation membrane separation system comprising one or more stages of molecular sieve membranes, and water-rich condensate is flowed from the permeate side to CO and EO production process2The absorption liquid in the absorption system is mixed with the carbonate solution to enter CO2The absorption tower removes CO in the gas2And a part of the methane-rich and ethylene mixed gas flowing out of the non-permeation side is recycled as EO reaction recycle gas, a part of the methane-rich and ethylene mixed gas enters a carbon dioxide absorption tower for decarburization, the formed methane-rich noncondensable gas directly returns to the raw material ethylene, oxygen and methane mixer to be mixed and then returns to the ethylene oxide reactor for reaction, the pervaporation pressure is 0.3-1.5MPa, and the pervaporation temperature is 60-80 ℃.
8. The method according to claim 1, wherein the FTrPSA system of step (4) is pressure swing adsorption consisting of 4 or more adsorption towers connected in series or in parallel or in series and parallel, each adsorption tower is filled with one or more adsorbent combinations of activated alumina, silica gel, activated carbon, molecular sieves, and a control system consisting of an adjusting valve or a programmed control valve disposed on a connecting pipeline controls and regulates pressure changes during PSA adsorption and desorption cycle operations, the number of pressure equalizations does not exceed 3, and the desorption process consists of forward/uniform pressure drop, reverse release, evacuation/flushing, uniform pressure rise, and final filling; the adsorption pressure is 0.3-1.5MPa, and the adsorption and desorption temperatures are both 60-80 ℃.
9. The method for purifying and recycling the high-purity high-yield methane-induced stable gas in the ethylene-to-ethylene-process-produced-ethylene oxide according to claim 1, wherein the full-temperature-range pressure swing adsorption FTrPSA system in the step (4) recovers ethylene, a shallow cold oil absorption system is used to replace the FTrPSA system to recover ethylene, the non-condensable gas rich in methane formed in the ethylene oxide reabsorption tower enters the absorption tower using the tetraalkyl carbon as an absorbent after being compressed to 2.0-4.0MPa and cooled to 10-20 ℃ through heat exchange, the non-condensable gas rich in methane flows out of the top of the absorption tower, one part of the non-condensable gas returns to the PSA system for hydrocarbon removal, decarbonization and dehydration of the feed gas, methane is further recovered for recycling, and the other part of the non-condensable gas enters a fuel gas pipe network as; and (3) feeding the ethylene-rich absorption liquid flowing out of the bottom of the absorption tower into a desorption tower, and flowing out ethylene-rich gas from the top of the desorption tower, or directly recycling the ethylene-rich gas as EO reaction recycle gas, or externally sending the ethylene-rich gas to ethylene rectification for further recovering and refining ethylene, wherein the ethylene-rich gas is recycled as an ethylene raw material required by EO reaction, and the carbon-four absorption liquid flowing out of the bottom of the absorption tower is returned to the absorption tower for recycling.
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