A method and system for separating crude propylene oxide

Abstract

The present invention discloses a method and a separation system for separating crude propylene oxide. The crude propylene oxide contains propylene oxide, hydrocarbons, oxygen-containing compounds and high-boiling substances. The separation method includes: introducing the crude propylene oxide into a separation column I, and reducing the concentration of oxygen-containing compounds on the trays in the separation column I by means of side-stream withdrawal of materials from the separation column I. Among them, by side-stream withdrawal, the concentration of oxygen-containing compounds enriched in the column is reduced, and the concentration of oxygen-containing compounds enriched in the crude propylene oxide column is controlled at a relatively low level, avoiding problems such as blockage caused by aldehyde polymerization and corrosion of equipment by organic acids. It is applicable to the production process of preparing propylene oxide by the reaction of propylene and peroxide, and can achieve good technical effects.

Description

Technical Field

[0001] The present invention belongs to the separation method of crude propylene oxide, and particularly relates to a separation method and a separation system for crude propylene oxide. Background Art

[0002] Propylene oxide (PO) is the third largest propylene derivative after polypropylene and acrylonitrile, and is an important basic organic chemical synthesis raw material, mainly used for producing polyethers, propylene glycol, etc. It is also the main raw material for the fourth-generation detergent non-ionic surfactants, oilfield demulsifiers, pesticide emulsifiers, etc. Derivatives of propylene oxide are widely used in industries such as automobiles, construction, food, tobacco, medicine, and cosmetics. There are nearly a hundred downstream products produced, and it is an important raw material for fine chemical products.

[0003] The method of producing propylene oxide by epoxidizing propylene with cumene hydroperoxide (CHPPO) has the advantages of low investment, environmental friendliness, and no co-products, and has received more and more attention and research, and is expected to replace the chlorohydrin method with high three wastes and serious corrosion.

[0004] CN1307168C discloses a method for refining propylene oxide, which is a method for refining propylene oxide by subjecting a reaction solution containing propylene oxide and impurities such as water, hydrocarbons, and oxygen-containing organic compounds obtained by reacting cumene hydroperoxide with propylene to extractive distillation in an extractive distillation column using a hydrocarbon extractant having 7 to 20 carbons, characterized in that the concentration of propylene glycol in the extractant fed into the extractive distillation column is 20% by weight or less.

[0005] Through further research on the basis of the above invention, it is found that the boiling points of oxygen-containing compounds such as aldehydes, alcohols, organic acids, and water, which are by-products of the propylene epoxidation reaction, are between PO and heavier hydrocarbons such as ethylbenzene / cumene / 1,2-propanediol. When the reaction products enter the rectification column together for the separation of crude propylene oxide, the oxygen-containing compounds are easily enriched at local positions in the column. When the concentration reaches a certain level, adverse situations such as corrosion and blockage caused by the polymerization of aldehydes occur, seriously affecting the stable operation of the device. Summary of the Invention

[0006] In order to overcome the problems existing in the prior art, the present invention provides a separation method and a separation system for crude propylene oxide. Among them, by side-drawing, the concentration of oxygen-containing compounds enriched in the column is reduced, and the concentration of oxygen-containing compounds enriched in the crude propylene oxide column is controlled at a lower level, avoiding problems such as blockage caused by the polymerization of aldehydes and corrosion of equipment by organic acids. It is applicable to the production process of producing propylene oxide by reacting propylene with peroxide, and can achieve good technical effects.

[0007] One object of the present invention is to provide a method for separating crude propylene oxide, wherein the crude propylene oxide contains propylene oxide, hydrocarbons, oxygen-containing compounds and high-boiling substances, and the separation method includes: introducing the crude propylene oxide into a separation column I, and reducing the concentration of oxygen-containing compounds on the trays in the separation column I by means of side-stream withdrawal of materials from the separation column I.

[0008] Among them, the high-boiling substances refer to substances with a boiling point higher than 160 °C.

[0009] In a preferred embodiment, the oxygen-containing compounds include any one or more of aldehydes, ketones, organic acids, alcohols, esters, and water; and / or, the high-boiling substances include cumene and / or dipropylene glycol; and / or, the hydrocarbons include one or a combination of two or more of cumene, α,α-dimethylbenzyl alcohol, and 1,2-propanediol.

[0010] In a further preferred embodiment, the aldehyde is any one or more of formaldehyde, acetaldehyde, and propionaldehyde; and / or, the ketone is acetone; and / or, the organic acid is any one or more of formic acid, acetic acid, propionic acid, and benzoic acid; and / or, the alcohol is methanol and / or ethanol; and / or, the ester is methyl formate.

[0011] In a preferred embodiment, in the crude propylene oxide, based on mass concentration, the concentration of propylene oxide is 5-55%, the concentration of hydrocarbons is 0-90% (preferably not including 0), the concentration of oxygen-containing compounds is 0-20% (preferably not including 0), and the concentration of high-boiling substances is 0-10% (preferably not including 0).

[0012] In a further preferred embodiment, in the crude propylene oxide, based on mass concentration, the concentration of propylene oxide is 5-50%, the concentration of hydrocarbons is 10-85%, the concentration of oxygen-containing compounds is 0-15% (preferably not including 0), and the concentration of high-boiling substances is 0-8% (preferably not including 0).

[0013] For example, in the crude propylene oxide, based on mass concentration, the concentration of propylene oxide is 5%, 10%, 20%, 30%, 40%, or 50%, the concentration of hydrocarbons is 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or 80%, the concentration of oxygen-containing compounds is 1%, 2%, 5%, 8%, 10%, 12%, or 15%, and the concentration of high-boiling substances is 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%.

[0014] In a preferred embodiment, the crude propylene oxide is introduced into the separation column I. The light fraction I is drawn out from the upper part or the top of the separation column I, the heavy fraction I is drawn out from the lower part or the bottom of the separation column, and the material containing oxygenates is withdrawn from the side line of the separation column I.

[0015] In a further preferred embodiment, the light fraction I includes propylene oxide and optionally oxygenates; and / or, the heavy fraction I includes hydrocarbons, high-boiling substances and (a small amount of) propylene oxide; and / or, the material withdrawn from the side line includes oxygenates and propylene oxide.

[0016] In a still further preferred embodiment, in the light fraction I, the concentration of propylene oxide is 95% to 99% by mass concentration, and the concentration of oxygenates is 1% to 5%; and / or, in the heavy fraction I, the concentration of propylene oxide is 0% to 2%, and the total of hydrocarbons and high-boiling substances is 98% to 100%; in the material withdrawn from the side line, the concentration of propylene oxide is 97% to 99.5%, and the concentration of oxygenates is 0.5% to 3%.

[0017] For example, in the light fraction I, by mass concentration, the concentration of propylene oxide is 95%, 96%, 97%, 98% or 99%, and the concentration of oxygenates is 1%, 2%, 3%, 4% or 5%; and / or, in the heavy fraction I, the concentration of propylene oxide is 0%, 0.5%, 1%, 1.5% or 2%; in the material withdrawn from the side line, the concentration of propylene oxide is 97%, 97.5%, 98%, 98.5%, 99% or 99.5%, and the concentration of oxygenates is 0.5%, 1%, 1.5%, 2%, 2.5% or 3%.

[0018] In a preferred embodiment, the material withdrawn from the side line of the separation column I enters the separation column II.

[0019] In a further preferred embodiment, the light fraction II is drawn out from the upper part or the top of the separation column II, and the heavy fraction II is drawn out from the lower part or the bottom of the separation column II and (the heavy fraction II) is recycled back to the separation column I.

[0020] Among them, the side draw recycle is a combination. The logistics with a high concentration of oxygenates is drawn out from the side for treatment, and the logistics with a low concentration of oxygenates is returned. If there is no recycle, the purpose of reducing the concentration of oxygenates on the trays of the separation column I cannot be achieved.

[0021] In a still further preferred embodiment, by mass concentration, in the light fraction II, the concentration of propylene oxide is 96% to 99%, and the concentration of oxygenates is 1% to 4%; and / or, in the heavy fraction II, the concentration of epoxides is 98 to 99.9%, and the concentration of oxygenates is 0.1% to 2%.

[0022] For example, in the light fraction II, the concentration of propylene oxide is 96%, 97%, 98% or 99% by mass concentration, and the concentration of oxygen-containing compounds is 1%, 2%, 3% or 4%; and / or, in the heavy fraction II, the concentration of epoxide is 98%, 98.5%, 99%, 99.5% or 99.9%, and the concentration of oxygen-containing compounds is 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%.

[0023] In the present invention, the light fraction I drawn from the top or upper part of the separation column I is the target product I, and the light fraction II drawn from the top or upper part of the separation column II is the target product II. At the same time, the heavy fraction II with a higher concentration of propylene oxide is recycled back to the separation column I, which can further dilute the concentration of oxygen-containing compounds in the separation column I.

[0024] In a preferred implementation method, the method is carried out in the separation column I and the separation column II. The crude propylene oxide is introduced into the separation column I: the light fraction I is taken out from the upper part or the top of the separation column I, the heavy fraction I is taken out from the lower part or the bottom, and the side stream material is introduced into the separation column II; in the separation column II: the light fraction II is taken out from its upper part or the top, and the heavy fraction II is taken out from the lower part or the bottom, and the heavy fraction II is recycled back to the separation column I.

[0025] In a preferred implementation manner, the weight ratio of the side stream material taken out from the separation column I to the crude propylene oxide in the feed is 1:1000 to 1:50, preferably 1:500 to 1:100.

[0026] For example, the weight ratio of the side stream material taken out from the separation column I to the crude propylene oxide in the feed is 1:1000, 1:800, 1:600, 1:500, 1:400, 1:300, 1:200, 1:100, 1:80 or 1:50.

[0027] Among them, if the extraction amount is higher than 1:50, it will cause too high a load on the separation column II, and the concentration of oxygen-containing compounds in the separation column I will not continuously decrease.

[0028] In a preferred implementation manner, the side stream extraction position of the separation column I is higher than the feed position of the separation column I (i.e., the feed position of the crude propylene oxide).

[0029] Among them, since the concentration of oxygen-containing compounds is relatively low below the feed position of the separation column I, side stream extraction at this position cannot achieve the purpose of removing oxygen-containing compounds. Therefore, the side stream extraction position needs to be higher than the feed position, and it is preferably taken from the tray with a lower concentration of cumene.

[0030] In a further preferred embodiment, the number of theoretical plates between the feed position and the side draw position of the separation column I accounts for 10-80%, preferably 20-70%, of the total number of theoretical plates of the separation column I.

[0031] For example, the number of theoretical plates between the feed position and the side draw position of the separation column I accounts for 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80% of the total number of theoretical plates of the separation column I.

[0032] In a preferred embodiment, the position where the heavy component II of the separation column II is recycled back to the separation column I is between the feed position and the side draw position of the separation column I.

[0033] Among them, since the recycled stream is a heavy component relative to the side stream, it should be recycled back to the separation column I below the side draw position; and if the recycling position is set below the feed position, the content of propylene oxide in the heavy component I at the bottom or lower part of the separation column I will be too high.

[0034] In a preferred embodiment, the side draw material of the separation column I enters the separation column II from the upper, middle or top of the separation column II.

[0035] Preferably, when a condenser is provided at the top of the separation column II, the side draw material of the separation column I enters the separation column II from the upper, middle or top of the separation column II; when no condenser is provided at the top of the separation column II, the side draw material of the separation column I enters the separation column II from the upper or top of the separation column II.

[0036] In a further preferred embodiment, counting from the top down of the number of plates of the separation column II, the side draw material of the separation column I enters the separation column II at the 0-30% plate of the separation column II, for example, enters from the first plate.

[0037] In the present invention, a stream containing oxygenated compounds such as propylene oxide, esters, aldehydes, water, and organic acids is drawn from the separation column I through a side draw to the separation column II. In the separation column II, propylene oxide is partially vaporized, and the oxygenated compounds are taken out of the separation column II from the upper or top of the separation column II by utilizing the difference in volatility between the oxygenated compounds and propylene oxide. A relatively pure propylene oxide is obtained at the lower part of the column or the bottom of the column and returned to the separation column I, which can further dilute the concentration of oxygenated compounds on the plates of the separation column I, achieving the purpose of reducing the enrichment amount of oxygenated compounds on the first separation plate. It should be noted that taking the CHPPO method as an example, since the concentration of oxygenated compounds below the feed position of the separation column I is relatively low, side drawing at this position cannot achieve the purpose of removing oxygenated compounds. Therefore, the side draw position needs to be higher than the feed position, and it is preferably drawn from the plate with a lower concentration of cumene.

[0038] In a preferred embodiment, the number of theoretical plates of the separation column I is 10 to 95, the operating pressure at the top of the column is 0.00 to 0.1 MPaG, the operating temperature at the top of the column is 20 to 80 °C, the operating temperature at the bottom of the column is 120 to 210 °C, and the reflux ratio is 0.1 to 10.

[0039] In a further preferred embodiment, the number of theoretical plates of the separation column I is 10 to 90, the operating pressure at the top of the column is 0 to 0.08 MPaG, the operating temperature at the top of the column is 20 to 70 °C, the operating temperature at the bottom of the column is 120 to 200 °C, and the reflux ratio is 1 to 5.

[0040] For example, the number of theoretical plates of the separation column I is 10, 20, 30, 40, 50, 60, 70, 80 or 90, the operating pressure at the top of the column is 0 MPaG, 0.01 MPaG, 0.02 MPaG, 0.03 MPaG, 0.04 MPaG, 0.05 MPaG, 0.06 MPaG, 0.07 MPaG or 0.08 MPaG, the operating temperature at the top of the column is 20 °C, 30 °C, 40 °C, 50 °C, 60 °C or 70 °C, the operating temperature at the bottom of the column is 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C or 200 °C, and the reflux ratio is 1, 2, 3, 4 or 5.

[0041] In a preferred embodiment, the number of theoretical plates of the separation column II is 5 to 50, the operating pressure at the top of the column is 0.00 to 0.1 MPaG, the operating temperature at the top of the column is 30 to 70 °C, and the operating temperature at the bottom of the column is 30 to 90 °C.

[0042] In a further preferred embodiment, the number of theoretical plates of the separation column II is 5 to 40, the operating pressure at the top of the column is 0.00 to 0.08 MPaG, the operating temperature at the top of the column is 30 to 65 °C, and the operating temperature at the bottom of the column is 30 to 80 °C.

[0043] For example, the number of theoretical plates of the separation column II is 5, 10, 15, 20, 25, 30, 35 or 40, the operating pressure at the top of the column is 0 MPaG, 0.01 MPaG, 0.02 MPaG, 0.03 MPaG, 0.04 MPaG, 0.05 MPaG, 0.06 MPaG, 0.07 MPaG or 0.08 MPaG, the operating temperature at the top of the column is 30 °C, 40 °C, 50 °C, 60 °C or 65 °C, and the operating temperature at the bottom of the column is 30 °C, 40 °C, 50 °C, 60 °C, 70 °C or 80 °C.

[0044] In a still further preferred embodiment, the difference between the top temperature and the bottom temperature of the separation column II is between 0.1 and 6 °C, preferably between 0.2 and 3 °C.

[0045] For example, the temperature difference between the top and bottom of the separation tower II is 0.1°C, 0.2°C, 0.5°C, 1°C, 2°C, 3°C, 4°C, 5°C or 6°C.

[0046] In the above technical solution, the separation tower II may not be equipped with a condenser and a reflux drum, and the overhead gas is directly led out, but it is equipped with a reboiler.

[0047] Therefore, by using the present invention, the concentration of oxygen-containing compounds in the crude propylene oxide tower is controlled at a relatively low level, avoiding problems such as blockage caused by aldehyde polymerization and corrosion of equipment by organic acids. It is applicable to the production process of preparing propylene oxide by the reaction of propylene and peroxide, and can achieve good technical effects.

[0048] A second object of the present invention is to provide a separation system for crude propylene oxide, preferably used for carrying out the separation method described in the first object of the present invention. Among them, the separation system includes a separation tower I and a separation tower II. A feed inlet I and a side draw outlet are provided on the separation tower I, and a feed inlet II is provided on the separation tower II. The side draw outlet is connected to the feed inlet II through a pipeline.

[0049] In a preferred embodiment, a light component outlet I and a heavy component outlet I are further provided on the separation tower I.

[0050] In a further preferred embodiment, the light component outlet I is provided at the upper part or the top of the separation tower I, and the heavy component outlet I is provided at the lower part or the bottom of the separation tower I.

[0051] In a preferred embodiment, the feed inlet I is provided in the middle and lower part of the separation tower I, and the side draw outlet is provided above the feed inlet I.

[0052] In a further preferred embodiment, the number of theoretical plates between the feed inlet I and the side draw outlet of the separation tower I accounts for 10-80% of the total number of theoretical plates of the separation tower I, preferably 20-70%.

[0053] In a preferred embodiment, the side draw outlet is provided below the light component outlet I.

[0054] In a preferred embodiment, the feed inlet I is provided above the heavy component outlet I.

[0055] In a preferred embodiment, a light component outlet II and a heavy component outlet II are further provided on the separation tower II.

[0056] In a further preferred embodiment, the light component outlet II is provided at the upper part or the top of the separation tower II, and the heavy component outlet II is provided at the lower part or the bottom of the separation tower II.

[0057] In a preferred embodiment, a recycle material inlet is provided on the separation column I.

[0058] In a further preferred embodiment, the recycle material inlet is connected to the bottoms outlet II of the separation column II through a pipeline.

[0059] In an even more preferred embodiment, on the separation column I, the recycle material inlet is arranged between the feed inlet I and the side draw outlet.

[0060] In a preferred embodiment, the separation column II may not be equipped with a condenser and a reflux drum, and the overhead gas is directly led out, but is equipped with a reboiler.

[0061] In a preferred embodiment, the number of theoretical plates of the separation column I is 10 - 95, the overhead operating pressure is 0.00 - 0.1 MPaG, the overhead operating temperature is 20 - 80 °C, the bottom operating temperature is 120 - 210 °C, and the reflux ratio is 0.1 - 10.

[0062] In a further preferred embodiment, the number of theoretical plates of the separation column I is 10 - 90, the overhead operating pressure is 0 - 0.08 MPaG, the overhead operating temperature is 20 - 70 °C, the bottom operating temperature is 120 - 200 °C, and the reflux ratio is 1 - 5.

[0063] For example, the number of theoretical plates of the separation column I is 10, 20, 30, 40, 50, 60, 70, 80 or 90, the overhead operating pressure is 0 MPaG, 0.01 MPaG, 0.02 MPaG, 0.03 MPaG, 0.04 MPaG, 0.05 MPaG, 0.06 MPaG, 0.07 MPaG or 0.08 MPaG, the overhead operating temperature is 20 °C, 30 °C, 40 °C, 50 °C, 60 °C or 70 °C, the bottom operating temperature is 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C or 200 °C, and the reflux ratio is 1, 2, 3, 4 or 5.

[0064] In a preferred embodiment, the number of theoretical plates of the separation column II is 5 - 50, the overhead operating pressure is 0.00 - 0.1 MPaG, the overhead operating temperature is 30 - 70 °C, and the bottom operating temperature is 30 - 90 °C.

[0065] In a further preferred embodiment, the number of theoretical plates of the separation column II is 5 - 40, the overhead operating pressure is 0.00 - 0.08 MPaG, the overhead operating temperature is 30 - 65 °C, and the bottom operating temperature is 30 - 80 °C.

[0066] For example, the number of theoretical plates of the separation column II is 5, 10, 15, 20, 25, 30, 35 or 40, the operating pressure at the top of the column is 0 MPaG, 0.01 MPaG, 0.02 MPaG, 0.03 MPaG, 0.04 MPaG, 0.05 MPaG, 0.06 MPaG, 0.07 MPaG or 0.08 MPaG, the operating temperature at the top of the column is 30°C, 40°C, 50°C, 60°C or 65°C, and the operating temperature at the bottom of the column is 30°C, 40°C, 50°C, 60°C, 70°C or 80°C.

[0067] In a further preferred embodiment, the difference between the temperature at the top and the temperature at the bottom of the separation column II is between 0.1 and 6°C, preferably between 0.2 and 3°C.

[0068] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. In the following text, in principle, the various technical solutions can be combined with each other to obtain new technical solutions, which should also be regarded as specifically disclosed herein.

[0069] Compared with the prior art, the present invention has the following beneficial effects: The present invention controls the enrichment concentration of oxygen-containing compounds in the crude propylene oxide column at a low level, avoiding problems such as blockage caused by aldehyde polymerization and corrosion of equipment by organic acids. It is applicable to the production process of preparing propylene oxide by the reaction of propylene with peroxide, and can achieve good technical effects. Description of the Drawings

[0070] Figure 1 A schematic diagram showing the separation system of the present invention is shown.

[0071] 1 - Crude propylene oxide, 2 - Light component I, 3 - Heavy component I, 4 - Side stream extraction material, 5 - Light component II, 6 - Heavy component II;

[0072] The reaction product of the epoxidation reaction of peroxide and propylene and the removal of propylene mainly includes propylene oxide, hydrocarbons, and oxygen-containing compounds such as aldehydes, esters, water, organic acids, and high-boiling substances, which is crude propylene oxide 1;

[0073] Crude propylene oxide 1 enters the separation column I. At the top of the column, light component I 2 mainly containing propylene oxide is obtained, and at the bottom of the column, heavy component I 3 containing hydrocarbons, high-boiling substances, and a small amount of propylene oxide is obtained. A side stream extraction material 4 containing propylene oxide and oxygen-containing compounds (including aldehydes, esters, water, organic acids, etc.) is extracted from the side line;

[0074] The side-draw stream 4 enters the separation column II, and the light fraction II 5 mainly containing propylene oxide and oxygen-containing compounds (including aldehydes, esters, water, etc.) is obtained at the top of the column; the heavy fraction II 6 containing propylene oxide is obtained at the bottom of the column and returned to the separation column I.

[0075] The separation column I is equipped with a reboiler, a condenser and their inlet and outlet streams. The separation column II is equipped with a reboiler and its inlet and outlet streams. The separation column II may not be equipped with a condenser and a reflux drum, and the overhead gas is directly led out. Those skilled in the art can easily understand its process and function, and will not be elaborated here.

[0076] Figure 2 Schematic diagram showing the comparative example.

[0077] In Figure 2 7 - fresh feed, I - separation column I.

[0078] When adopting the Figure 2 method shown:

[0079] The reaction product containing propylene oxide enters the separation column I. The reaction product mainly includes propylene oxide, hydrocarbons, oxygen-containing compounds, and high-boiling substances. The crude propylene oxide product is taken out at the top of the column, and the stream containing hydrocarbons, high-boiling substances and a small amount of propylene oxide is taken out at the bottom of the column. Detailed implementation mode

[0080] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only for further illustration of the present invention and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the content of the present invention still fall within the protection scope of the present invention.

[0081] In addition, it should be noted that the various specific technical features described in the following detailed implementation modes can be combined in any suitable way without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0082] In addition, any combination can be made between various different implementation modes of the present invention as long as it does not violate the idea of the present invention. The technical solutions formed thereby belong to a part of the original public content of this specification and also fall within the protection scope of the present invention.

[0083] If there is no special limitation on the raw materials used in the examples and comparative examples, they are all disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0084]

Example 1

[0085] As Figure 1As shown, in terms of weight percentage, the reaction product containing 0.1% acetaldehyde, 0.1% methyl formate, 14% propylene oxide, 0.2% water, 0.01% formic acid, 1% 1,2 - propanediol, 48.49% cumene, 33.1% α,α - dimethylbenzyl alcohol, 1% p - cymene, and 2% other components enters the 30th plate of Separation Column I. Separation Column I has a total of 40 plates (counting from the top of the column to the bottom as the 1st - 40th plate). The operating pressure at the top of the column is 0.04 MPaG, the operating temperature at the top of the column is 44 °C, the operating temperature at the bottom of the column is 181 °C, and the reflux ratio is 2.

[0086] In Separation Column I, the light fraction I contains 97.22% propylene oxide and 2.78% oxygen - containing compounds; the side - drawn material contains 98.12% propylene oxide and 1.88% oxygen - containing compounds; the heavy fraction I contains 0.02% propylene oxide, 99.97% (hydrocarbons + high - boiling substances), and 0.01% oxygen - containing compounds.

[0087] In Separation Column II, the light fraction II contains 97.82% propylene oxide; the recycled material contains 98.12% propylene oxide and 1.88% oxygen - containing compounds.

[0088] Separation Column I side - draws a product equal to 1% of the raw material mass flow rate from the 10th tray and sends it to the first plate of Separation Column II. Separation Column II has a total of 10 plates. The operating pressure at the top of the column is 0.04 MPaG, the operating temperature at the top of the column is 44 °C, the operating temperature at the bottom of the column is 45 °C, and the liquid phase drawn from the bottom of the column is returned to the 11th plate of Separation Column I.

[0089] The highest concentration of oxygen - containing compounds in Separation Column I is 0.6958% acetaldehyde, 0.6954% methyl formate, 1.3912% water, and 0.0533% formic acid.

[0090]

Example 2

[0091] Repeat the process of Example 1. The difference from Example 1 is that the product side - drawn from Separation Column I is 0.5% of the raw material mass flow rate.

[0092] In Separation Column I, the light fraction I contains 97.14% propylene oxide; the side - drawn material contains 98.05% propylene oxide and 1.95% oxygen - containing compounds; the heavy fraction I contains 0.56% propylene oxide, 99.42% (hydrocarbons + high - boiling substances), and 0.02% oxygen - containing compounds.

[0093] In Separation Column II, the light fraction II contains 97.75% propylene oxide and 2.25% oxygen - containing compounds; the recycled material contains 98.06% propylene oxide and 1.94% oxygen - containing compounds.

[0094] The highest concentrations of oxygenates in Separation Column I are 0.7176% acetaldehyde, 0.7102% methyl formate, 1.4369% water, and 0.0448% formic acid.

[0095]

Example 3

[0096] Repeat the process of Example 1. The difference from Example 1 is that the product taken from the side line of the 7th tray of Separation Column I goes to the first tray of Separation Column II, and the liquid phase at the bottom of Separation Column II is returned to the 8th tray of Separation Column I.

[0097] In Separation Column I, the light component I contains 97.22% propylene oxide and 2.78% oxygenates; the side-drawn material contains 98.09% propylene oxide and 0.0191% oxygenates; the heavy component I contains 0.03% propylene oxide and 99.97% (hydrocarbons + high-boiling substances).

[0098] In Separation Column II, the light component II contains 97.79% propylene oxide and 2.21% oxygenates; the recycled material contains 98.10% propylene oxide and 1.90% oxygenates.

[0099] The highest concentrations of oxygenates in Separation Column I are 0.6958% acetaldehyde, 0.6954% methyl formate, 1.3912% water, and 0.0530% formic acid.

[0100]

Example 4

[0101] Repeat the process of Example 1. The difference from Example 1 is that the operating pressure at the top of Separation Column I is 0 MPaG, the operating temperature at the top is 35 °C, and the operating temperature at the bottom of the column is 167 °C. The operating pressure at the top of Separation Column II is 0 MPaG, the operating temperature at the top is 34 °C, and the operating temperature at the bottom of the column is 35 °C.

[0102] In Separation Column I, the light component I contains 97.22% propylene oxide and 2.78% oxygenates; the side-drawn material contains 98.05% propylene oxide and 1.95% oxygenates; the heavy component I contains 0.03% propylene oxide and 99.97% (hydrocarbons + high-boiling substances).

[0103] In Separation Column II, the light component II contains 97.77% propylene oxide; the recycled material contains 98.06% propylene oxide and 1.94% oxygenates;.

[0104] The highest concentrations of oxygenates in Separation Column I are 0.6959% acetaldehyde, 0.6954% methyl formate, 1.3912% water, and 0.0529% formic acid.

[0105]

Example 5

[0106] Repeat the process of Example 1. Different from Example 1, the operating pressure at the top of Separation Column I is 0.1 MPaG, the operating temperature at the top is 55 °C, and the operating temperature at the bottom of the column is 196 °C. The operating pressure at the top of Separation Column II is 0.1 MPaG, the operating temperature at the top is 55 °C, and the operating temperature at the bottom of the column is 56 °C.

[0107] In Separation Column I, Light Component I contains 97.22% propylene oxide and 2.78% oxygen-containing compounds; the side-drawn material contains 98.17% propylene oxide and 1.83% oxygen-containing compounds; Heavy Component I contains 0.02% propylene oxide, 99.97% (hydrocarbons + high-boiling substances) and 0.01% oxygen-containing compounds.

[0108] In Separation Column II, Light Component II contains 97.85% propylene oxide and 2.15% oxygen-containing compounds; the recycle material contains 98.18% propylene oxide and 1.82% oxygen-containing compounds.

[0109] The maximum concentration of oxygen-containing compounds in Separation Column I is 0.6958% acetaldehyde, 0.6954% methyl formate, 1.3912% water, and 0.0647% formic acid.

[0110]

Example 6

[0111] As Figure 1 shown, a reaction product containing 0.1% acetaldehyde, 0.1% methyl formate, 14% propylene oxide, 0.2% water, 0.01% formic acid, 1% 1,2-propanediol, 48.49% cumene, 33.1% α,α-dimethylbenzyl alcohol, 1% diisopropylbenzene, and 2% other components by weight percentage enters the 60th plate of Separation Column I. Separation Column I has a total of 80 plates (numbered 1 - 80 from the top of the column to the bottom), the operating pressure at the top is 0.04 MPaG, the operating temperature at the top is 44 °C, the operating temperature at the bottom of the column is 181 °C, and the reflux ratio is 2.

[0112] In Separation Column I, Light Component I contains 97.22% propylene oxide and 2.78% oxygen-containing compounds; the side-drawn material contains 98.13% propylene oxide and 1.87% oxygen-containing compounds; Heavy Component I contains 0.02% propylene oxide, 99.97% (hydrocarbons + high-boiling substances) and 0.01% oxygen-containing compounds.

[0113] In Separation Column II, Light Component II contains 97.82% propylene oxide and 2.18% oxygen-containing compounds; the recycle material contains 98.13% propylene oxide and 1.87% oxygen-containing compounds.

[0114] The separation column I withdraws a product with a mass flow rate of 1% of the raw material from the side line of the 20th tray and sends it to the first tray of the separation column II. The separation column II has a total of 20 trays. The operating pressure at the top of the column is 0.04 MPaG, the operating temperature at the top of the column is 44 °C, the operating temperature at the bottom of the column is 45 °C, and the liquid phase withdrawn from the bottom of the column returns to the 22nd tray of the separation column I.

[0115] The highest concentration of oxygenated compounds in the separation column I is acetaldehyde 0.6959%, methyl formate 0.6956%, water 1.3912%, and formic acid 0.0535%.

[0116] In the present invention, the content of the light component I in some embodiments is the same because the change in conditions has a relatively small impact on the material at the top of the column.

[0117]

Comparative Example 1

[0118] As Figure 2 shown, in weight percentage, a reaction product containing acetaldehyde 0.1%, methyl formate 0.1%, propylene oxide 14%, water 0.2%, formic acid 0.01%, 1,2-propanediol 1%, cumene 48.49%, α,α-dimethylbenzyl alcohol 33.1%, diisopropylbenzene 1%, and other components 2% enters the 30th tray of the separation column I. The separation column I has a total of 40 trays. The operating pressure at the top of the column is 0.04 MPaG, the operating temperature at the top of the column is 44 °C, the operating temperature at the bottom of the column is 167 °C, and the reflux ratio is 2.

[0119] The highest concentration of oxygenated compounds in the separation column I is acetaldehyde 0.7395%, methyl formate 0.7212%, water 1.4860%, and formic acid 0.0453%.

[0120] It can be seen that the concentration of oxygenated compounds on the trays in this example is higher than that in the examples. The polymerization of aldehydes may cause blockage. Although the content of organic acids is slightly lower than that in the examples, due to the higher water content in this example, the corrosion is stronger, and adverse situations may occur in industrial production.

[0121] The present invention has been described in detail above in combination with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications, or improvements can be made to the technical solutions and their implementation manners of the present invention, and these all fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A method for separating crude propylene oxide, wherein, The crude propylene oxide contains propylene oxide, hydrocarbons, oxygen-containing compounds and high-boiling substances. The high-boiling substances refer to substances with a boiling point higher than 160 °C. In the crude propylene oxide, the concentration of propylene oxide is 5-55% by mass concentration, the concentration of hydrocarbons is 0-90%, the concentration of oxygen-containing compounds is 0-20%, and the concentration of high-boiling substances is 0-10%. The separation method includes: introducing the crude propylene oxide into Separation Tower I, and reducing the concentration of oxygen-containing compounds on the trays in Separation Tower I by way of side-stream withdrawal of materials from Separation Tower I; withdrawing light fraction I from the upper part or the top of Separation Tower I, withdrawing heavy fraction I from the lower part or the bottom of Separation Tower I, and introducing the side-stream withdrawn materials into Separation Tower II. The materials side-stream withdrawn from Separation Tower I enter Separation Tower II from the upper part or the middle part of Separation Tower II; the side-stream withdrawal position of Separation Tower I is higher than the feed position of Separation Tower I; in Separation Tower II: withdrawing light fraction II from its upper part or the top, and withdrawing heavy fraction II from the lower part or the bottom. The heavy fraction II is recycled back to Separation Tower I, and the position where the heavy fraction II of Separation Tower II is recycled back to Separation Tower I is between the feed position and the side-stream withdrawal position of Separation Tower I; the top operating temperature of Separation Tower II is 30-70 °C, the bottom operating temperature is 30-90 °C, and the difference between the top temperature and the bottom temperature of Separation Tower II is between 0.1 and 6 °C.

2. The separation method according to claim 1, wherein in the crude propylene oxide, the concentration of propylene oxide is 5-50% by mass concentration; and / or, the concentration of hydrocarbons is 10-85%.

3. The separation method according to claim 1, wherein in the crude propylene oxide, the concentration of oxygen-containing compounds is 0-15% by mass concentration; and / or, the concentration of high-boiling substances is 0-8%.

4. The separation method according to claim 1, characterized in that, The oxygen-containing compounds include any one or several of aldehydes, ketones, organic acids, alcohols, esters, and water; and / or, the high-boiling substances include cumene and / or dipropylene glycol; and / or, the hydrocarbons include one or a combination of two or more of cumene, α,α-dimethylbenzyl alcohol, and 1,2-propanediol.

5. The separation method according to claim 1, characterized in that, Withdraw the materials containing oxygen-containing compounds from the side-stream of Separation Tower I.

6. The separation method according to claim 1, wherein The weight ratio of the side-stream withdrawn materials of Separation Tower I to the crude propylene oxide in the feed is 1:1000-1:

50.

7. The separation method according to claim 1, characterized in that The weight ratio of the side-stream withdrawn materials of Separation Tower I to the crude propylene oxide in the feed is 1:500-1:

100.

8. The separation method according to claim 1, wherein the number of theoretical trays between the feed position and the side-stream withdrawal position of Separation Tower I accounts for 10-80% of the total number of theoretical trays of Separation Tower I.

9. The separation method according to claim 1, wherein the number of theoretical trays between the feed position and the side-stream withdrawal position of Separation Tower I accounts for 20-70% of the total number of theoretical trays of Separation Tower I.

10. The separation method according to claim 1, characterized in that, Calculated from the top to the bottom of the trays of Separation Tower II as 0-100%, the side-stream withdrawn materials of Separation Tower I enter Separation Tower II from 0-30% of Separation Tower II and excluding tray No.

0.

11. The separation method according to any one of claims 1 to 10, characterized in that the number of theoretical plates of the separation column I is 10 to 95, the top operating pressure is 0.00 to 0.1 MPaG, the top operating temperature is 20 to 80 °C, the bottom operating temperature is 120 to 210 °C, and the reflux ratio is 0.1 to 10; and / or, the number of theoretical plates of the separation column II is 5 to 50, the top operating pressure is 0.00 to 0.1 MPaG, the top operating temperature is 30 to 70 °C, and the bottom operating temperature is 30 to 90 °C.

12. The separation method according to claim 11, wherein The difference between the top temperature and the bottom temperature of the separation column II is between 0.2 and 3 °C.

13. A separation system for crude propylene oxide, which is used to carry out the separation method described in any one of claims 1 to 12, wherein, The separation system includes a separation column I and a separation column II. An inlet I and a side draw outlet are provided on the separation column I. An inlet II is provided on the separation column II. The side draw outlet is connected to the inlet II through a pipeline; a light component outlet I and a heavy component outlet I are further provided on the separation column I. The light component outlet I is provided at the upper part or the top of the separation column I, and the heavy component outlet I is provided at the lower part or the bottom of the separation column I; a light component outlet II and a heavy component outlet II are further provided on the separation column II. The light component outlet II is provided at the upper part or the top of the separation column II, and the heavy component outlet II is provided at the lower part or the bottom of the separation column II; a recycle material inlet is provided on the separation column I. The recycle material inlet is connected to the heavy component outlet II of the separation column II through a pipeline; the top operating temperature of the separation column II is 30 to 70 °C, the bottom operating temperature is 30 to 90 °C, and the difference between the top temperature and the bottom temperature of the separation column II is between 0.1 and 6 °C.

14. The separation system according to claim 13, characterized in that the inlet I is provided in the middle and lower part of the separation column I, and the side draw outlet is provided above the inlet I.

15. The separation system according to claim 14, wherein The number of theoretical plates between the inlet I and the side draw outlet of the separation column I accounts for 10 to 80% of the total number of theoretical plates of the separation column I.

16. The separation system according to claim 14, wherein The number of theoretical plates between the inlet I and the side draw outlet of the separation column I accounts for 20 to 70% of the total number of theoretical plates of the separation column I.

17. The separation system according to claim 13, characterized in that the side draw outlet is provided below the light component outlet I; and / or, the inlet I is provided above the heavy component outlet I; and / or, on the separation column I, the recycle material inlet is provided between the inlet I and the side draw outlet.

18. The separation system according to any one of claims 13 to 17, characterized in that the number of theoretical plates of the separation column I is 10 to 95, the top operating pressure is 0.00 to 0.1 MPaG, the top operating temperature is 20 to 80 °C, the bottom operating temperature is 120 to 210 °C, and the reflux ratio is 0.1 to 10; and / or, the number of theoretical plates of the separation column II is 5 to 50, the top operating pressure is 0.00 to 0.1 MPaG; and / or, The temperature difference between the top and the bottom of the separation tower II is between 0.2 and 3 °C.

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