A method for preventing clogging of equipment during the separation of crude propylene oxide and applications thereof

Abstract

The application discloses a method for preventing the device from being blocked in the separation process of crude propylene oxide and application, the device comprises a light-removing tower and a heavy-removing tower connected in series, the overhead material of the light-removing tower is obtained by condensation and gas-liquid separation, and the overhead non-condensable gas and the overhead condensate of the light-removing tower are obtained, the tower kettle material of the light-removing tower enters the heavy-removing tower, and the propylene oxide product is obtained from the overhead of the heavy-removing tower; wherein, the overhead non-condensable gas of the light-removing tower is separated from the tower kettle material of the heavy-removing tower before the flare tank, and the protective gas is introduced into the overhead material of the light-removing tower and / or the overhead non-condensable gas of the light-removing tower and / or the flare tank before the flare tank. The application can better solve the problems in the prior art by means of dilution of the overhead gas, the overhead non-condensable gas, the protective gas supplementing into the flare tank before the flare tank, and flushing of the easily blocked parts by the condensate rich in propylene oxide, and the method and system can be used in the industrial production technology of propylene oxide.

Description

Technical Field

[0001] This invention relates to a method for preventing equipment blockage, and more particularly to a method and application for preventing equipment blockage during crude propylene oxide separation. Background Technology

[0002] The co-oxidation method for producing propylene oxide is significantly superior to the traditional chlorohydrin method in China in terms of environmental protection. This is mainly reflected in the following aspects: reliable process, stable product quality, high product purity, low acidity, low aldehyde value, and low moisture and ethylene oxide impurities.

[0003] In the propylene epoxidation reaction, in addition to the main reaction that produces the target products PO and DMBA, some side reactions that produce aldehydes and organic acids also occur. These side reactions mainly include:

[0004] (1) Propylene is oxidized to formaldehyde and acetaldehyde, and formaldehyde and acetaldehyde are further oxidized to formic acid and acetic acid;

[0005] In the epoxidation reactor, trace amounts of propylene are oxidized by CHP to formaldehyde and acetaldehyde, which are then further oxidized to formic acid and acetic acid, respectively. The production of formaldehyde and acetaldehyde affects propylene consumption and increases energy consumption in product refining. In addition to increasing propylene consumption, formic acid and acetic acid also cause equipment corrosion.

[0006] These impurities all need to be removed during the PO separation and purification process.

[0007]

[0008] (2) PO isomerization to propionaldehyde

[0009] In the reaction and separation units of the epoxidation reactor, trace amounts of PO are isomerized to propionaldehyde. Separating propionaldehyde from PO is difficult, and the presence of propionaldehyde increases energy consumption in subsequent product purification and affects product quality.

[0010]

[0011] The epoxidation reactor reaction product, after separating the light component (unreacted propylene) and heavy components (benzyl alcohol, cumene, etc.), yields crude propylene oxide containing impurities such as formaldehyde, acetaldehyde, propionaldehyde, acetone, water, methyl formate, and light hydrocarbons. According to existing technology, after removing light components from the crude propylene oxide, the top of the light component removal tower yields light hydrocarbons (C3-C5), formaldehyde, and acetaldehyde, while the bottom of the heavy component removal tower yields heavy components such as water, methanol, acetone, propionaldehyde, cumene, and / or ethylbenzene, as well as propylene glycol. It is known that the material collected from the top of the tower contains formaldehyde and acetaldehyde. Acetaldehyde undergoes polymerization under low temperature, room temperature, and acid catalysis, producing a small amount (≤5%) of the target product, tetraacetaldehyde, while also generating a large amount (≥90%) of the byproduct, triacetaldehyde. However, under specific catalyst and process conditions, the polymerization of acetaldehyde can be controlled to primarily produce tetraacetaldehyde. Metaldehyde exists as a stable solid at room temperature. It is a white, needle-like crystal that is flammable and is known as industrial solid alcohol.

[0012] The polymerization mechanism of acetaldehyde under acidic conditions is a cationic mechanism, as shown below:

[0013]

[0014] When the molecular chain of the reaction product has three or more oxygen atoms, the molecule itself can undergo intramolecular linkages to form metaldehyde, tetraacetaldehyde, pentaacetaldehyde, hexaacetaldehyde, etc. The number of polymers produced depends on various factors such as reaction temperature, reaction time, and the type of catalyst. When the temperature is above 0°C, the reaction almost completely produces metaldehyde, with a selectivity approaching 100%.

[0015] Furthermore, the polymerization of acetaldehyde is a strongly exothermic reaction, which will cause the system temperature to rise in an adiabatic and closed system. Since the boiling point of acetaldehyde is 20.8℃, this will cause the acetaldehyde to vaporize and the system pressure to increase.

[0016] As can be seen from the above, during the separation process of crude propylene oxide, formaldehyde and acetaldehyde are enriched and concentrated at the top of the light condensate removal tower, especially in the non-condensable gas pipeline and vent outlet, safety valve port, and the separatory tank before the flare. Aldehydes undergo acetal reaction and aldol condensation reaction to produce acetals such as polyacetaldehyde and β-hydroxy aldehyde, as well as further dehydration products such as alkenal. Acetals and other components are oligomers with poor flowability, which can clog pipelines and equipment. Acetaldehyde itself will undergo polymerization reaction, releasing a large amount of heat and even causing local overheating, which poses a safety risk. Summary of the Invention

[0017] The inventors discovered in their experimental research that the separation and purification process of crude propylene oxide mainly involves removing most of the light components such as formaldehyde, acetaldehyde, C3-C5 hydrocarbons, and methyl formate through a light component removal tower. Formaldehyde and acetaldehyde are mainly removed through non-condensable gas at the top of the tower. In order to reduce propylene oxide loss and lower the propylene oxide loss rate, formaldehyde and acetaldehyde will be enriched and concentrated, with a concentration exceeding 20 wt% or even as high as 60 wt%. They are very prone to undergo aldol condensation reaction and then dehydrate to generate larger molecular unsaturated aldehydes.

[0018] Formaldehyde undergoes an auto-oxidation reaction to produce methanol and formate:

[0019]

[0020] Formaldehyde undergoes an aldol condensation reaction to produce 2-hydroxyacetaldehyde, which can then undergo another aldol condensation reaction with formaldehyde.

[0021]

[0022] Formaldehyde and acetaldehyde undergo an aldol condensation reaction to produce trimethylolacetaldehyde, which then undergoes dehydration to produce acrolein.

[0023]

[0024]

[0025] Acetaldehyde undergoes an aldol condensation reaction to form β-hydroxybutyraldehyde, which still contains an α-hydrogen. Further condensation can occur with continued heating. Prolonged heating of the reactants can condense them into a resinous substance. During heating, β-hydroxybutyraldehyde also undergoes dehydration to form an α,β-unsaturated aldehyde, namely butenal.

[0026]

[0027] Meanwhile, both formaldehyde and acetaldehyde can react with methanol to form hemiacetals and acetals.

[0028]

[0029] Formaldehyde and acetaldehyde react to form paraformaldehyde, paraacetaldehyde, acetal, and other substances. These substances are highly viscous and have poor flowability, easily causing stagnation and clogging of equipment and pipelines. Acetaldehyde also forms metaldehyde and tetraacetaldehyde. The polymerization of acetaldehyde is a strongly exothermic reaction, which leads to a rise in system temperature in an adiabatic, closed system. Since acetaldehyde has a boiling point of 20.8℃ and propylene oxide has a boiling point of 34℃, this causes acetaldehyde and propylene oxide to vaporize, increasing the system pressure.

[0030]

[0031]

[0032] Therefore, in order to solve the technical problems existing in the prior art (the problem of formaldehyde and acetaldehyde enrichment and concentration during the crude propylene oxide separation and purification process causing aldol condensation reaction and acetal reaction to generate high-viscosity substances such as polyacetaldehyde and acetal that clog equipment, pipelines and valves such as light-light removal towers, heat exchangers, safety valves, containers and valves; and the problem of the storage container pressure increasing sharply due to the release of a large amount of heat during the reaction process, causing danger), the present invention provides a method and application for preventing blockage of the device during the crude propylene oxide separation process. The problem is effectively solved by diluting the device with protective gas (such as nitrogen) added to the top gas, top non-condensable gas and the liquid separator before the flare, and by flushing the easily blocked parts with propylene oxide-rich condensate. The method and system can be used in the industrial production technology of propylene oxide.

[0033] One objective of this invention is to provide a method for preventing blockage in a crude propylene oxide separation process, comprising: the apparatus including a light-weight removal tower and a heavy-weight removal tower connected in series; the top material of the light-weight removal tower is condensed and separated into a non-condensable gas and a condensate; the bottom material of the light-weight removal tower enters the heavy-weight removal tower, and propylene oxide product is obtained from the top of the heavy-weight removal tower; wherein the non-condensable gas at the top of the light-weight removal tower and part or all of the bottom material of the heavy-weight removal tower are sent to a pre-flare separator; and a protective gas (preferably nitrogen) is introduced into the top material of the light-weight removal tower and / or the non-condensable gas at the top of the light-weight removal tower and / or the pre-flare separator.

[0034] The function of the pre-flame separator is to remove condensate entrained in the venting gas, thereby reducing the amount of condensate in the venting main and preventing droplets from being carried to the flare head and forming fire rain. In this invention, when part of the bottom material of the de-burden tower goes to the pre-flame separator, it is discharged externally along with the bottom material.

[0035] In a preferred embodiment, the crude propylene oxide contains aldehydes, such as formaldehyde and / or acetaldehyde.

[0036] In a preferred embodiment, a condenser and a gas-liquid separator (preferably a reflux tank) are sequentially arranged at the top of the light-light removal tower, wherein the gas-liquid separator draws out the condensate and non-condensable gas at the top of the tower.

[0037] Taking the gas-liquid separation device as a reflux tank as an example, this invention dilutes the material at the top of the light-weight material removal tower and / or the non-condensable gas at the top of the tower and / or the liquid separator before the flare by adding a protective gas. The protective gas is added to the pipeline before the material at the top of the light-weight material removal tower enters the condenser. By reducing the partial pressure of propylene oxide in the gas phase, the content of propylene oxide emitted from the non-condensable gas is reduced, and the concentration of acetaldehyde is diluted, thus reducing propylene oxide loss. Since the gas phase (i.e., the non-condensable gas at the top of the tower) in the reflux tank contains highly concentrated formaldehyde and acetaldehyde, adding a protective gas (e.g., nitrogen) to the outlet of the non-condensable gas pipeline in the reflux tank can effectively dilute the aldehyde concentration, preventing the aldehydes from accumulating and polymerizing in the pipeline, releasing heat, and causing safety accidents due to pipeline blockage.

[0038] After the material at the top of the light-weight removal tower is condensed and separated into gas and liquid in the reflux tank, the content of formaldehyde and acetaldehyde in the non-condensable gas is significantly increased compared to the material at the top. The non-condensable gas is diluted by adding protective gas from the outlet of the non-condensable gas pipeline in the reflux tank to ensure that the pipeline between the reflux tank and the flare-front separator does not become blocked. Since the distance between the reflux tank and the flare-front separator is generally designed to be far, when the temperature is below normal, especially in winter, the non-condensable gas at the top of the tower undergoes gas-liquid separation again in the pipeline and the flare-front separator. The protective gas and some formaldehyde and acetaldehyde enter the flare in the gas phase, while aldehyde polymers, acetals, and residual formaldehyde and acetaldehyde remain in the flare-front separator in the liquid phase, where they further undergo acetal and aldol condensation reactions, which pose a risk of overheating or even explosion. The viscosity of the medium increases, and the viscous substance blocks the bottom discharge valve.

[0039] In a preferred embodiment, the condensate at the top of the tower is divided into three parts: Part I, Part II, and Part III. Part I is collected externally, Part II is returned to the light-weight removal tower as reflux liquid, and Part III is used as cleaning liquid to the pre-flare separator and / or the easily clogged parts of the device (for flushing and removing blockages).

[0040] In a further preferred embodiment, the portion III is divided into multiple streams, which are independently sent to the pre-flare liquid separator and various easily clogged parts of the device.

[0041] The condensate at the top of the tower is rich in propylene oxide. Through extensive experimental research, the inventors discovered that propylene oxide has a good solubility for polyacetal and acetal, which can effectively eliminate clogging problems. Moreover, propylene oxide is an internal component of the system and is not introduced into the external medium. Therefore, flushing the easily clogged parts with propylene oxide-rich condensate is the most economical and reasonable choice.

[0042] In a further preferred embodiment, the easily clogged parts refer to the aldehyde-rich areas, especially the non-flowing media areas, including the vent, valves, pipes, safety valve ports, PT / PG pressure taps, etc., between the top of the light aldehyde removal tower and the liquid separator before the flare. The aforementioned easily clogged parts need to be cleaned.

[0043] In a further preferred embodiment, the easily clogged parts include the vent at the top of the light-weight material removal tower, the vent at the top of the light-weight material removal tower reflux tank (when the gas-liquid separator is a reflux tank), the pressure guide pipe of the local pressure gauge for the material at the top of the tower, the pressure guide pipe of the remote pressure gauge, the inlet of the safety valve at the top of the light-weight material removal tower, and the inlet of the safety valve at the top of the light-weight material removal tower reflux tank (when the gas-liquid separator is a reflux tank).

[0044] Under normal operating conditions, the fluid in these easily clogged areas is stagnant, forming dead zones where aldehydes tend to accumulate and polymerize, causing blockages. Using condensate from the top of the tower containing propylene oxide can effectively flush these areas and prevent blockages. If partial blockages have already occurred, the excellent solubility of propylene oxide in acetaldehyde polymers, acetals, and other substances can be utilized to continuously flush and dissolve them, alleviating or even completely eliminating the blockages. The flushing solution is returned to the light precipitator and reflux tank, thus being recycled without any loss of propylene oxide.

[0045] In addition, in the prior art, the heavy component in the de-heavy tower (containing some propylene oxide) was originally discharged as fuel for the incinerator. This invention changes it to the pre-flare separator, which utilizes the propylene oxide, propylene glycol, and cumene contained therein to dilute the concentration of aldehydes in the tank, dissolve aldehyde polymers, and acetals, thereby achieving waste utilization, reducing propylene oxide loss, and avoiding blockage of the pre-flare separator.

[0046] Preferably, at the initial stage of the start-up of the method, a stream of condensate from the top of the tower is first drawn to the pre-flame separator (preferably from the gas-liquid separation device, reflux tank) to dilute the aldehyde concentration in the tank. After the light removal tower and the heavy removal tower are running normally, the material in the bottom of the heavy removal tower is then controlled to enter the pre-flame separator.

[0047] In a preferred embodiment, the protective gas is introduced from the bottom of the pre-flare separator.

[0048] In a preferred embodiment, a portion III of the condensate at the top of the column enters the pre-flame separator from the upper part of the separator. Preferably, a portion III of the condensate at the top of the column enters the pre-flame separator together with or after mixing with part or all of the bottom material of the de-weighting column.

[0049] In a preferred embodiment, the crude propylene oxide contains aldehydes, such as formaldehyde and / or acetaldehyde.

[0050] In a further preferred embodiment, the content of aldehydes in the top material of the light-removal tower is not particularly limited, but is preferably, but not limited to, 5-50 wt%.

[0051] In a preferred embodiment, the top material of the light-light removal tower is mixed with the protective gas and then condensed to obtain a condensed mixture. The aldehyde content in the condensed mixture is controlled to be 10-50 wt%, for example, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%.

[0052] In a further preferred embodiment, the condensed mixture is subjected to gas-liquid separation to obtain a non-condensable gas at the top of the column. The non-condensable gas at the top of the column is mixed with a protective gas to obtain a diluted non-condensable gas at the top of the column. The content of aldehydes in the diluted non-condensable gas at the top of the column is controlled to be 10-40 wt%, preferably 15-30 wt%, for example, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%.

[0053] In a further preferred embodiment, the non-condensable gas at the top of the dilution tower and part or all of the bottom material of the de-weighting tower enter the pre-flare separator, while protective gas is introduced into the pre-flare separator (blown in from the bottom). The content of aldehydes in the pre-flare separator is controlled to be 10-40 wt%, for example, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%.

[0054] The protective gas is introduced from the bottom of the liquid separator before the flare. Preferably, the protective gas is blown in through a gas distributor from the bottom of the liquid separator before the flare. This can enhance the disturbance and prevent formaldehyde and acetaldehyde from agglomerating and polymerizing.

[0055] In a preferred embodiment, alkali solution is added to part or all of the bottom material of the de-weighting tower before it enters the pre-flare separator.

[0056] In a further preferred embodiment, an alkaline solution is added to part or all of the bottom material of the deweighting tower to adjust the pH value of the bottom material to be close to neutral (preferably 6.5 to 7.5). This can reduce the occurrence of acetal and aldol condensation reactions in the separator before the flare.

[0057] Since the crude propylene oxide entering the refining / purification unit contains trace amounts of organic acids such as formic acid, acetic acid, and propionic acid, which promote acetal and aldol condensation reactions, an alkaline solution is added to part or all of the bottom material of the de-burden tower, i.e., the waste liquid containing propylene oxide, to adjust the pH value to near neutral. This can reduce the occurrence of acetal and aldol condensation reactions in the separatory tank before the flare.

[0058] In a further preferred embodiment, the alkaline solution is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, potassium carbonate solution, and sodium carbonate solution, preferably with a concentration of 5 to 40 wt%, more preferably 10 to 20 wt%, for example, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 30 wt%, or 40 wt%.

[0059] In a preferred embodiment, part or all of the bottom material of the de-weighting tower after pH adjustment with alkali solution enters the pre-flame separator from the top; preferably, a spray-type liquid distributor is used to enter the pre-flame separator from the top.

[0060] The bottom material (liquid rich in propylene oxide) of the de-burden tower is added to the top of the pre-flare separator and sprayed through a distributor to reduce the liquid content of the flare gas.

[0061] In a preferred embodiment, the light-light removal tower can be any light-light removal tower disclosed in the prior art, especially any light-light removal tower disclosed in the prior art for separating propylene oxide products. Preferably, but not limited to, the theoretical number of plates of the light-light removal tower is 30 to 100 (e.g., 30, 40, 50, 60, 70, 80, 90 or 100), preferably 50 to 90, and preferably fed in the middle.

[0062] In a further preferred embodiment, the conditions of the light-light removal tower can be any light-light removal tower conditions disclosed in the prior art, especially any light-light removal tower conditions disclosed in the prior art for separating propylene oxide products; preferably, but not limited to, the top operating temperature of the light-light removal tower is 30-80°C (e.g., 30°C, 40°C, 50°C, 60°C, 70°C or 80°C), preferably 40-80°C, and the top operating pressure is 0.05-1 MPaG (e.g., 0.05, 0.08, 0.1, 0.15, 0.2, 0.4, 0.6, 0.8, 1 MPaG), preferably 0.05-0.8 MPa.

[0063] In a preferred embodiment, the deweighting tower can be any deweighting tower disclosed in the prior art, especially any deweighting tower disclosed in the prior art for separating propylene oxide products. Preferably, but not limited to, the theoretical number of plates of the deweighting tower is 30 to 90 (e.g., 30, 40, 50, 60, 70, 80 or 90), preferably 40 to 70.

[0064] In a further preferred embodiment, the conditions of the deweighting tower can be any deweighting tower conditions disclosed in the prior art, especially any deweighting tower conditions disclosed in the prior art for separating propylene oxide products; preferably, but not limited to, the top operating temperature of the deweighting tower is 25-80°C (e.g., 25°C, 30°C, 40°C, 50°C, 60°C or 70°C), preferably 30-65°C, and the top operating pressure is 0.01-1 MPaG (e.g., 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.2, 0.4, 0.6, 0.8 or 1 MPaG), preferably 0.01-0.40 MPaG.

[0065] A second objective of this invention is to provide the application of the method described in one objective of this invention in the separation of crude propylene oxide.

[0066] The third objective of this invention is to provide a crude propylene oxide separation system, preferably used for the crude propylene oxide separation described in the second objective of this invention. The system includes a light-light removal tower, a heavy-light removal tower, and a pre-flare separator. A condenser and a gas-liquid separator (preferably a reflux tank) are sequentially arranged at the top of the light-light removal tower along the material flow direction. The gas-liquid separator and the bottom of the heavy-light removal tower are independently and / or together connected to the pre-flare separator via pipelines.

[0067] Vents, valves (e.g., safety valves), and pressure guide pipes are installed on the pipelines between the top of the light-weight removal tower, the gas-liquid separation device (preferably a reflux tank), and the liquid separator before the flare. Examples include vents at the top of the light-weight removal tower, vents at the reflux tank at the top of the light-weight removal tower, pressure guide pipes for the local pressure gauge of the material at the top of the tower, pressure guide pipes for the remote pressure gauge, inlet of the safety valve at the top of the light-weight removal tower, and inlet of the safety valve of the gas-liquid separation device at the top of the light-weight removal tower.

[0068] In a preferred embodiment, a crude propylene oxide inlet is provided in the middle of the light-light removal tower, and / or, the bottom of the light-light removal tower is connected to the middle of the heavy-light removal tower via a pipeline, and / or, a product outlet is provided at the top of the heavy-light removal tower.

[0069] In a preferred embodiment, the gas-liquid separation device is provided with a non-condensable gas outlet at the top of the tower and a condensate outlet at the top of the tower, wherein the non-condensable gas outlet at the top of the reflux tank and the bottom material outlet of the de-weighting tower are connected to the pre-flare separator via pipelines, either independently or together.

[0070] In a further preferred embodiment, protective gas feed lines are independently provided on the pipeline between the top of the light-light removal tower and the condenser, on the pipeline between the non-condensable gas outlet at the top of the gas-liquid separator and the pre-flare separator, and at the bottom of the pre-flare separator, for introducing protective gas (e.g., nitrogen).

[0071] In a further preferred embodiment, a gas distributor is provided at the bottom of the pre-flame separator. Preferably, the gas distributor is located above the protective gas inlet pipeline provided at the bottom of the pre-flame separator, and is used to bleed protective gas into the pre-flame separator from the bottom to agitate it.

[0072] In a preferred embodiment, the condensate outlet at the top of the gas-liquid separation device includes outlet I, outlet II, and outlet III. Outlet I is connected to an external sampling pipeline, outlet II is connected to the upper part of the light-weight removal tower via a pipeline, and outlet III is connected to the pre-flare separator and / or various easily clogged parts in the device via pipelines.

[0073] Preferably, outlet III is independently connected to the pre-flame separator and each easily clogged part of the device.

[0074] In a further preferred embodiment, the easily clogged parts include the vent, valve (e.g., safety valve), and pipeline between the top of the light-weight removal tower and the liquid separator in front of the flare; more preferably, the easily clogged parts include the vent at the top of the light-weight removal tower, the vent of the gas-liquid separation device at the top of the light-weight removal tower, the pressure guide pipe of the local pressure gauge at the top of the tower, the pressure guide pipe of the remote pressure gauge, the inlet of the safety valve at the top of the light-weight removal tower, and the inlet of the safety valve of the gas-liquid separation device at the top of the light-weight removal tower.

[0075] In a preferred embodiment, a liquid inlet is provided at the upper part of the pre-flame separator, and the liquid inlet is connected to both the outlet III of the reflux tank and the bottom of the deweighting tower; preferably, a nozzle-type liquid distributor is provided at the upper part of the pre-flame separator, which is connected to the liquid inlet of the pre-flame separator.

[0076] In a further preferred embodiment, an alkali feed pipe is provided on the pipeline between the bottom of the de-heavy tower and the pre-flame separator, for adding alkali before some or all of the bottom material of the de-heavy tower enters the pre-flame separator, so as to adjust the pH value of the bottom material of the de-heavy tower to near neutral.

[0077] In a preferred embodiment, the bottom of the deweight removal tower is optionally further provided with an external discharge pipeline.

[0078] The fourth objective of this invention is to provide a method for separating crude propylene oxide, which is carried out using the crude propylene oxide separation system described in the third objective of this invention.

[0079] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0080] Compared with the prior art, the present invention has the following beneficial effects: by (1) adding protective gas to dilute the material at the top of the light tower, the non-condensable gas at the top of the light tower, and the liquid separator before the flare, (2) using the condensate at the top of the light tower to flush the easily clogged parts, and (3) the protective gas is blown in from the bottom of the liquid separator before the flare to disturb, and (4) the bottom material of the heavy tower (waste liquid containing propylene oxide) enters the liquid separator before the flare, the technical solution can better solve the problem and can be used in the industrial production technology of propylene oxide. Attached Figure Description

[0081] Figure 1 A schematic diagram of the propylene oxide separation system of the present invention is shown;

[0082] Figure 2 The propylene oxide separation system used in Comparative Example 2 is shown (without top condensate flushing);

[0083] Figure 3 The propylene oxide separation system used in Comparative Example 3 is shown (without top condensate flushing and the bottom material of the de-weighting tower is discharged and incinerated);

[0084] Explanation of reference numerals in the attached figures:

[0085] C1 - Light weight removal tower, C2 - Heavy weight removal tower, D1 - Reflux tank, D2 - Flare pre-dispensing tank, E1 - Condenser, V1 - Light weight removal tower top vent valve, V2 - Reflux tank vent valve, PSV1 - Light weight removal tower top safety valve (double valve, not shown in the figure), PSV2 - Reflux tank safety valve (double valve, not shown in the figure).

[0086] 1-Crude propylene oxide stream, 2-Residue from the light-weight removal tower, 3-Residue from the top of the light-weight removal tower, 4-Protective gas (e.g., nitrogen), 7-Condensed mixture, 8-Non-condensable gas from the top of the tower, 9-Condensate from the top of the tower, 10-Washing liquid, 17-Reflux liquid, 18-Liquid phase extraction, 19-Mixed gas of non-condensable gas and protective gas from the top of the tower, 20-Non-condensable gas to the flare, 21-Liquid in the separator before the flare, 22-Propylene oxide product, 23-Residue from the bottom of the heavy-weight removal tower (heavy fractions such as acetone, propionaldehyde, propylene oxide, and cumene), 24-Alkali solution, 25-Mixed stream;

[0087] Crude propylene oxide stream 1 enters from the light component removal tower C1. Light component removal tower bottom material 2 enters the heavy component removal tower C2. The top of the heavy component removal tower contains the de-heavy propylene oxide product 22. The bottom material 23 of the heavy component removal tower consists of heavy components such as acetone, propionaldehyde, propylene oxide, and cumene. The bottom material 23 of the heavy component removal tower mixes with alkaline solution 24 to form a mixture stream 25. Mixture stream 25 is injected from the top of the separator D2 before the flare. The top material 3 of the light component removal tower mixes with protective gas 4 and is then condensed by condenser E1. After the non-condensable gas 8 and protective gas 4 are mixed in the reflux tank D1, they go to the pre-flare separator D2. One part of the condensate 9 at the top of the reflux tank D1 is reflux liquid 17, one part is liquid phase extract 18, and the rest is flushing liquid 10 (one part flushes the safety valve PSV2 at the top of the reflux tank of the light-duty removal tower, one part is used as the flushing liquid in the pre-flare separator D2 during the initial start-up, one part flushes the vent valve V1 at the top of the light-duty removal tower, one part flushes the safety valve at the top of PSV1-light-duty removal tower, and one part flushes the vent valve V2 of the reflux tank). Detailed Implementation

[0088] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0089] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0090] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0091] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0092]

Example 1

[0093] like Figure 1As shown, crude propylene oxide stream 1 enters from the light component removal tower C1, and the bottom material 2 from the light component removal tower enters the heavy component removal tower C2. The top of the heavy component removal tower contains the de-heavy propylene oxide product 22, and the bottom material 23 from the heavy component removal tower contains heavy components such as acetone, propionaldehyde, propylene oxide, and cumene. All the bottom material 23 from the heavy component removal tower is mixed with the alkaline solution 24 to form a mixture stream 25. The mixture stream 25 is sprayed from the top of the separator D2 before the flare. The top material 3 from the light component removal tower is mixed with the protective gas 4 and then passes through the condenser E1. The condensate goes to the reflux tank D1. The non-condensable gas 8 and nitrogen 4 at the top of the tower are mixed and then sent to the pre-flare separator D2. Of the condensate 9 at the top of the tower in the reflux tank D1, one is reflux liquid 17, one is liquid phase extract 18, and the rest is flushing liquid 10 (one flushes the safety valve PSV2 at the top of the reflux tank of the light-duty tower, one is used as flushing liquid for the pre-flare separator D2 during the initial start-up, one flushes the vent valve V1 at the top of the light-duty tower, one flushes the safety valve at the top of PSV1-light-duty tower, and one flushes the vent valve V2 of the reflux tank).

[0094] The light-weight removal tower has 65 theoretical plates, with an operating pressure of 0.15 MPaG at the top and an operating temperature of 58°C at the top. The heavy-weight removal tower has 50 theoretical plates, with an operating pressure of 0.05 MPaG at the top and an operating temperature of 46°C at the top.

[0095] The composition of each logistics item is shown in Table 1 below.

[0096] Table 1:

[0097] Logistics 1 Logistics 2 Logistics 4 Logistics 8 Logistics 22 Logistics 23 Nitrogen 0.00％ 0.00％ 100.00％ 14.44％ 0.00％ 0.00％ propylene 0.01％ 0.00％ 0.00％ 0.67％ 0.00％ 0.00％ propane 0.01％ 0.00％ 0.00％ 0.67％ 0.00％ 0.00％ formaldehyde 0.05％ 0.00％ 0.00％ 3.33％ 0.00％ 0.00％ Acetaldehyde 0.72％ 0.00％ 0.00％ 48.00％ 0.00％ 0.00％ Methyl formate 0.01％ 0.01％ 0.00％ 0.21％ 0.01％ 0.00％ PO 98.00％ 98.79％ 0.00％ 32.18％ 99.48％ 40.82％ propionaldehyde 0.03％ 0.03％ 0.00％ 0.00％ 0.00％ 2.57％ acetone 0.02％ 0.02％ 0.00％ 0.00％ 0.00％ 1.71％ 2-Methylpentane 0.04％ 0.04％ 0.00％ 0.00％ 0.02％ 1.41％ 4-Methylpentene 0.01％ 0.01％ 0.00％ 0.30％ 0.01％ 0.00％ 2-Methylpentene 0.01％ 0.01％ 0.00％ 0.00％ 0.01％ 0.02％ methanol 0.10％ 0.10％ 0.00％ 0.00％ 0.07％ 2.30％ water 0.97％ 0.98％ 0.00％ 0.21％ 0.40％ 49.29％ Formic acid 0.00％ 0.00％ 0.00％ 0.00％ 0.00％ 0.04％ Acetic acid 0.00％ 0.00％ 0.00％ 0.00％ 0.00％ 0.13％ Cumene 0.02％ 0.02％ 0.00％ 0.00％ 0.00％ 1.71％

[0098] PO recovery rate: 99.0%.

[0099] The top material of the light-weight removal tower is mixed with nitrogen and then condensed to obtain a condensed mixture. The aldehyde content in the condensed mixture 7 is controlled to be 40 wt%. By adding nitrogen, the formaldehyde and acetaldehyde content in the mixture 19 of non-condensable gas and protective gas at the top of the tower can be reduced to 20%. The non-condensable gas at the top of the dilution tower and the bottom material of the heavy-weight removal tower enter the pre-flare separator, while nitrogen is blown in from the bottom of the pre-flare separator to control the aldehyde content in the pre-flare separator to be 12 wt%. The pH value of the bottom material 23 of the heavy-weight removal tower is adjusted to 7.5. The method described in Example 1 can effectively prevent blockage of equipment, pipelines, valves, etc.

[0100]

Example 2

[0101] Same as [Example 1], except that the composition of the crude propylene oxide 1 feed and the amount of nitrogen added are different.

[0102] The composition of each logistics item is shown in Table 2 below.

[0103] Table 2:

[0104]

[0105]

[0106] PO recovery rate: 99.2%.

[0107] The top material of the light-weight removal tower is mixed with nitrogen and then condensed to obtain a condensed mixture. The aldehyde content in the condensed mixture 7 is controlled to be 43 wt%. By adding nitrogen, the formaldehyde and acetaldehyde content in the mixture 19 of non-condensable gas and protective gas at the top of the tower can be reduced to 20%, and the probability of blockage in the mixture 19 is greatly reduced. The non-condensable gas at the top of the dilution tower and the bottom material of the heavy-weight removal tower enter the pre-flare separator, while nitrogen is blown in from the bottom of the pre-flare separator to control the aldehyde content in the pre-flare separator to be 13 wt%. The pH value of the bottom material 23 of the heavy-weight removal tower is adjusted to 7.2. The method described in Example 2 can effectively prevent blockage of equipment, pipelines, valves, etc.

[0108]

Example 3

[0109] Same as [Example 1], except that the composition of the crude propylene oxide 1 feed and the amount of nitrogen added are different.

[0110] The composition of each logistics item is shown in Table 3 below.

[0111] Table 3:

[0112]

[0113]

[0114] PO recovery rate: 99.0%.

[0115] The top material of the light-weight removal tower is mixed with nitrogen and then condensed to obtain a condensed mixture. The aldehyde content in the condensed mixture 7 is controlled at 40 wt%. By adding nitrogen, the formaldehyde and acetaldehyde content in the mixture 19 of non-condensable gas and protective gas at the top of the tower (54.31%) can be reduced to 20% of the mixture 19, significantly reducing the probability of blockage. The non-condensable gas at the top of the dilution tower and the bottom material of the heavy-weight removal tower enter the pre-flare separator, while nitrogen is blown in from the bottom of the pre-flare separator to control the aldehyde content in the pre-flare separator to 11 wt%. The pH of the bottom material 23 of the heavy-weight removal tower is adjusted to 7.1. The method described in Example 3 can effectively prevent blockage of equipment, pipelines, valves, etc.

[0116] Comparative Example 1

[0117] Similar to Example 1, but unlike Example 1, no nitrogen was added to any nitrogen pipelines. The PO recovery rate was 98.8%, the aldehyde concentration in the non-condensable gas 8 at the top of the tower reached 64.2%, and the aldehyde concentration in the mixed gas 19 and the separator D2 before the flare was even higher. Equipment, pipelines and valves were prone to blockage.

[0118] The composition of each logistics item is shown in Table 4 below.

[0119] Table 4:

[0120] Logistics 1 Logistics 2 Logistics 8 Logistics 22 Logistics 23 Nitrogen 0.00％ 0.00％ 0.00％ 0.00％ 0.00％ propylene 0.01％ 0.00％ 0.83％ 0.00％ 0.00％ propane 0.01％ 0.00％ 0.83％ 0.00％ 0.00％ formaldehyde 0.05％ 0.00％ 4.17％ 0.00％ 0.00％ Acetaldehyde 0.72％ 0.00％ 60.00％ 0.00％ 0.00％ Methyl formate 0.01％ 0.01％ 0.23％ 0.01％ 0.00％ PO 98.00％ 98.79％ 33.28％ 99.48％ 45.89％ propionaldehyde 0.03％ 0.03％ 0.00％ 0.00％ 2.34％ acetone 0.02％ 0.02％ 0.00％ 0.00％ 1.56％ 2-Methylpentane 0.04％ 0.04％ 0.00％ 0.02％ 1.51％ 4-Methylpentene 0.01％ 0.01％ 0.36％ 0.01％ 0.00％ 2-Methylpentene 0.01％ 0.01％ 0.00％ 0.01％ 0.02％ methanol 0.10％ 0.10％ 0.00％ 0.07％ 2.22％ water 0.97％ 0.98％ 0.30％ 0.40％ 44.74％ Formic acid 0.00％ 0.00％ 0.00％ 0.00％ 0.04％ Acetic acid 0.00％ 0.00％ 0.00％ 0.00％ 0.12％ Cumene 0.02％ 0.02％ 0.00％ 0.00％ 1.56％

[0121] Comparative Example 2

[0122] use Figure 2 The conditions for the heavy and light residue removal towers in the system shown are the same as in Example 1. The aldehyde concentration is higher in the separator D2 before the flare, making the equipment, pipes, and valves more prone to blockage.

[0123] Comparative Example 3

[0124] use Figure 3 The conditions for the heavy and light residue removal towers in the system shown are the same as in Example 1. The aldehyde concentration is higher in the separator D2 before the flare, making the equipment, pipes, and valves more prone to blockage.

[0125] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preventing the plugging of a device in the separation process of crude propylene oxide containing aldehyde substances, said device comprising a light-removing column and a heavy-removing column connected in series, the overhead material of said light-removing column being condensed and gas-liquid separated to obtain overhead non-condensable gas and overhead condensate, the column bottom material of said light-removing column entering said heavy-removing column, and propylene oxide product being obtained from the overhead of said heavy-removing column; wherein, The method comprises: introducing the non-condensable gas at the top of the light-removing column and part or all of the column bottom material of the heavy-removing column into a flare-preventing liquid tank before flare, and introducing a protective gas into the material at the top of the light-removing column and the non-condensable gas at the top of the light-removing column and the flare-preventing liquid tank; the column top condensate is divided into part I, part II and part III, wherein part I is discharged, part II is returned to the light-removing column as reflux liquid, and part III is sent to the flare-preventing liquid tank and the easily-clogged parts in the system as cleaning liquid.

2. The method of claim 1, wherein, The crude epoxy propene contains formaldehyde and / or acetaldehyde.

3. The method of claim 1, wherein, The protective gas is introduced from the bottom of the flare-preventing liquid tank; and / or, Part III of the column top condensate enters the flare-preventing liquid tank from the upper part of the flare-preventing liquid tank.

4. The method of claim 3, wherein, Part III of the column top condensate enters the flare-preventing liquid tank together with or after mixing with part or all of the column bottom material of the heavy-removing column.

5. The method according to any one of claims 1 to 4, characterized in that, The material at the top of the light-removing column is mixed with the protective gas and then subjected to condensation treatment to obtain a condensed mixture, wherein the content of aldehyde substances in the condensed mixture is controlled to be 10-50 wt%.

6. The method of claim 5, wherein, The condensed mixture is subjected to gas-liquid separation to obtain non-condensable gas at the top, which is mixed with the protective gas to obtain diluted non-condensable gas at the top, wherein the content of aldehyde substances in the diluted non-condensable gas at the top is controlled to be 10-40 wt%.

7. The method of claim 6, wherein, The content of aldehyde substances in the diluted non-condensable gas at the top is controlled to be 15-30 wt%.

8. The method of claim 6, wherein, The diluted non-condensable gas at the top is introduced into the flare-preventing liquid tank together with part or all of the column bottom material of the heavy-removing column, and a protective gas is introduced into the flare-preventing liquid tank at the same time, wherein the content of aldehyde substances in the flare-preventing liquid tank is controlled to be 10-40 wt%.

9. The method of claim 5, wherein, The part or all of the column bottom material of the heavy-removing column is introduced into the flare-preventing liquid tank after being added with lye.

10. The method of claim 9, wherein, The lye is added to adjust the pH value of the part or all of the column bottom material to be close to neutral.

11. The method of claim 9, wherein, The part or all of the column bottom material of the heavy-removing column after being adjusted in pH value by the lye is introduced into the flare-preventing liquid tank from the upper part of the flare-preventing liquid tank.

12. The method of claim 11, wherein, The part or all of the column bottom material of the heavy-removing column after being adjusted in pH value by the lye is introduced into the flare-preventing liquid tank from the upper part of the flare-preventing liquid tank by using a spray head liquid distributor.

13. Use of the method of any one of claims 1-12 in the separation of crude epoxy propene.

14. A crude propylene oxide separation system, comprising a light-removing column, a heavy-removing column and a flare front knock-out drum, a condenser and a gas-liquid separation device are sequentially arranged at the top of the light-removing column in the direction of material flow, the gas-liquid separation device is connected with the column bottom of the heavy-removing column through a pipeline, and the flare front knock-out drum is connected with the gas-liquid separation device through a pipeline; a protective gas feeding pipeline is independently arranged on the pipeline between the top of the light-removing column and the condenser, on the pipeline between the non-condensable gas outlet at the top of the gas-liquid separation device and the flare front knock-out drum, and at the bottom of the flare front knock-out drum, for feeding protective gas; the condensate outlet at the top of the gas-liquid separation device comprises outlet I, outlet II and outlet III, wherein, Outlet I is connected with an external discharge pipeline, outlet II is connected with the upper part of the light-removing column through a pipeline, and outlet II is divided into multiple paths and connected with each easily-clogged part in the flare-preventing liquid tank and the system through a pipeline.

15. The crude propylene oxide separation system of claim 14, wherein, The gas-liquid separation device is a reflux tank.

16. The crude propylene oxide separation system of claim 14, wherein, A crude epoxy propene feeding port is arranged at the middle part of the light-removing column, the column bottom of the light-removing column is connected with the middle part of the heavy-removing column through a pipeline, and a product outlet is arranged at the top of the heavy-removing column.

17. The crude propylene oxide separation system of claim 14, wherein, A non-condensable gas outlet and a column top condensate outlet are arranged on the gas-liquid separation device, and the non-condensable gas outlet of the gas-liquid separation device is connected with the flare-preventing liquid tank through a pipeline.

18. The crude propylene oxide separation system of claim 14, wherein, A gas distributor is arranged at the bottom of the flare-preventing liquid tank.

19. The crude propylene oxide separation system of claim 18, wherein, The gas distributor is located above the protective gas feeding pipeline arranged at the bottom of the flare front knock-out drum, for the protective gas to be blown from the bottom of the flare front knock-out drum to be disturbed.

20. The crude propylene oxide separation system of any of claims 14-19, wherein, A liquid phase inlet is arranged at the upper part of the flare front knock-out drum, which is connected with the outlet III of the gas-liquid separation device and the kettle of the heavy component removal column.

21. The crude propylene oxide separation system of claim 20, wherein, A shower liquid distributor is arranged at the upper part of the flare front knock-out drum, which is connected with the liquid phase inlet of the flare front knock-out drum.

22. The crude propylene oxide separation system of claim 20, wherein, An alkali feeding pipeline is arranged on the pipeline between the kettle of the heavy component removal column and the flare front knock-out drum, for adding alkali before the partial or all kettle materials of the heavy component removal column enter the flare front knock-out drum.

23. A crude epoxy propylene separation method, which is performed by using the crude epoxy propylene separation system according to any one of claims 14-22.

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