Method and system for purifying and removing impurities from crude epoxypropane

Abstract

The invention provides a method and system for purifying and removing impurities from crude epoxypropane, and the method comprises the following steps: (1) an epoxidation reaction product after propylene recovery enters a crude epoxypropane recovery tower from the lower part and is purified in the crude epoxypropane recovery tower, a desalted water material is supplied to the side line of the crude epoxypropane recovery tower, and the crude epoxypropane recovery tower is separated from the crude epoxypropane recovery tower; a material rich in water-soluble impurities is extracted from the side line of the crude epoxypropane recovery tower, a crude epoxypropane tower top flow is obtained at the top of the crude epoxypropane tower, and a tower bottom flow is obtained at the bottom of the crude epoxypropane tower; and (2) the material rich in water-soluble impurities extracted from the measuring line of the crude epoxypropane recovery tower enters an extraction tower, an oil-phase material is separated from the tower top, and a waste water material rich in impurities is separated from the tower kettle. The method provided by the invention can effectively remove formaldehyde and organic acid in epoxypropane, and can be used in the industrial production process of epoxypropane separation.

Description

Technical Field

[0001] The invention relates to a method and system for purifying and removing impurities from crude propylene oxide. Background Art

[0002] Propylene oxide (PO) is the second largest propylene derivative after polypropylene and is an important basic organic chemical synthesis raw material. The industrial devices used to produce PO are mainly divided into three categories: chlorohydrin method (CHPO), hydrogen peroxide method (HPPO) and organic peroxide oxidation method, among which organic peroxide is produced by oxidation of isobutane, ethylbenzene or cumene.

[0003] When propylene is used as the raw material, in order to prevent the oxidant from penetrating the bed, which would lead to aggravated side reactions and safety risks, propylene is often used in excess, so the epoxidation product usually contains a large amount of unreacted propylene, PO, and solvent. Since there is a significant boiling point difference between propylene, PO, and solvent, the unreacted propylene can be recovered by distillation.

[0004] CN105330540A discloses a device for recovering refined propylene, which solves the problem of high energy consumption in the prior art by using a propylene recovery device composed of a high-pressure propylene recovery tower, a flash tank, a low-pressure propylene recovery tower and a depropanizer. By setting the temperature of the high-pressure and low-pressure tower bottoms below 120°C, PO thermal decomposition is better prevented.

[0005] CN101103010B circulates the unreacted propylene during the epoxidation reaction to the epoxidation reactor, which will lead to a significant increase in the pressure drop of the reactor bed, which is caused by aldehyde polymerization.

[0006] JP2005089405A discloses a method for stably producing propylene oxide by injecting water into the top of a propylene recovery tower, extracting aldehydes in propylene with the water, and removing them outside the system.

[0007] However, in the process of producing propylene oxide, due to the presence of oxidants, it is inevitable that oxygen-containing impurities and their derivatives will be generated, such as water, acid, alcohol, aldehyde, ketone and ester. Since some of the above impurities, such as water, methanol, methyl formate, etc., will form azeotropes with PO, it is difficult to separate them by conventional means. In addition, propylene oxide products have strict requirements on water, aldehydes, and isomers. Water will affect the hydroxyl value and foaming performance of the polymer, aldehydes will cause the product to emit odor and affect people's health, and isomers are end-capping agents for long polymer chains. Therefore, there are strict requirements on product purity in national standards and enterprise standards.

[0008] The national standard for the purity of high-quality propylene oxide is: propylene oxide ≥ 99.95%, water ≤ 0.02%, acetaldehyde + propionaldehyde ≤ 0.005%, acid ≤ 0.003%.

[0009] The quality purity requirements for high-quality propylene oxide in the enterprise standard are: propylene oxide ≥99.99%, water ≤0.003%, acetaldehyde + propionaldehyde ≤0.001%, acid ≤0.001%.

[0010] Crude PO and benzyl alcohol can be obtained by separating PO from high-boiling point components (solvent, benzyl alcohol, etc.). There are many public documents and patents on the refining of crude PO products to obtain high-purity PO.

[0011] CN104109137B discloses a method for purifying propylene oxide, which uses a combination of extractive distillation and liquid-liquid extraction to effectively remove water, methanol, acetaldehyde, and methyl formate impurities, and at the same time adds a water scrubber to recover propylene oxide and extractant in wastewater using the same extractant. The method has high extraction efficiency and can obtain a polymer-grade propylene oxide product with a purity exceeding 99.99wt%, and the propylene oxide recovery rate reaches 99.2-99.8%. However, it does not consider the impact of formaldehyde on the system.

[0012] CN105555772A discloses a method for separating propylene oxide, which can effectively remove alcohol and aldehyde in crude PO by extractive distillation combined with water washing liquid-liquid extraction.

[0013] CN111655673A discloses a propylene oxide separation system and method, which can effectively remove impurities such as acetone, water, methanol, methyl formate, formaldehyde and its derivatives, 2-methylpentane, etc. by combining weight removal, extractive distillation and liquid-liquid extraction, and obtain a propylene oxide product with a purity exceeding 99.98wt%. However, the content of formaldehyde and its derivatives in the above crude PO is relatively low, below 80ppm. Summary of the invention

[0014] In order to overcome the problems existing in the prior art, the present invention provides a method for removing impurities in the process of propylene oxide purification. The researchers of the present invention found that in the process of crude PO production and benzyl alcohol purification, a large number of aldehyde derivatives in the form of hemiacetal and acetal will decompose, so that the total aldehyde (formaldehyde + acetaldehyde + propionaldehyde) content in the crude PO product exceeds 500ppm. Since aldehydes are easy to polycondense, the aldehyde content in crude PO is high, which is easy to cause scaling of pipelines, heat exchangers, and valves, which has a great impact on the downstream crude PO refining.

[0015] Therefore, the effective separation of aldehydes in the propylene oxide production process is very important for the propylene oxide production process. However, in the existing literature and patents, only the aldehyde removal methods in the recycled propylene and crude PO refining processes are mentioned, and there are no reports on the removal of aldehydes in the crude PO production and benzyl alcohol purification processes, especially formaldehyde.

[0016] In the process of propylene oxide production, the epoxidation reaction products inevitably generate aldehydes and alcohols, such as formaldehyde, acetaldehyde and propionaldehyde, and alcohols such as methanol and benzyl alcohol. The above hemiacetals or acetals will be decomposed by heat in the crude propylene oxide recovery tower. Formaldehyde has a low boiling point and is easily enriched in the crude PO at the top of the crude propylene oxide recovery tower, while alcohols with higher boiling points such as benzyl alcohol are concentrated in the bottom of the tower. Since formaldehyde is very easy to polymerize, the researchers found that when the molar content of hydroxyl groups in crude PO is lower than the molar content of formaldehyde, white polymers appear at a lower concentration of formaldehyde in crude PO (500-1000 ppm by weight), so it is necessary to control the formaldehyde content in crude PO.

[0017] To achieve the above-mentioned object, according to a first aspect of the present invention, the present invention provides a method for purifying crude propylene oxide and removing impurities, the method comprising:

[0018] (1) the epoxidation reaction product after propylene recovery enters a crude propylene oxide recovery tower from the bottom and is purified in the crude propylene oxide recovery tower, wherein a desalted water material is supplied to the side line of the crude propylene oxide recovery tower, and a material rich in water-soluble impurities is produced from the side line of the crude propylene oxide recovery tower, a crude propylene oxide tower top stream is obtained at the top of the crude propylene oxide tower, and a tower bottom stream is obtained at the bottom of the crude propylene oxide tower, wherein the injection point of the side line desalted water material is higher than the production point of the side line material rich in water-soluble impurities, and the number of theoretical plates between the two is N, and N≥2;

[0019] (2) the material rich in water-soluble impurities produced from the crude propylene oxide recovery tower side line enters the extraction tower, the oil phase material is separated from the tower top, and the wastewater material rich in impurities is separated from the tower bottom; the ratio k of the mass flow rate of the desalted water material stream 5 supplied from the side line to the mass flow rate of the epoxidation reaction product after propylene recovery satisfies the following relationship; in the formula, the epoxidation reaction product after propylene recovery is regarded as stream 1, and the crude propylene oxide tower top stream obtained from the tower top is regarded as stream 2;

[0020]

[0021] In the formula, by weight, is the concentration of formaldehyde in stream 1 (wt %); is the concentration of propylene oxide in stream 2 (wt %); is the concentration of formaldehyde in stream 2 (wt%); N is the number of theoretical plates between the injection point of the side desalted water of the crude propylene oxide recovery tower and the withdrawal point of the side material rich in water-soluble impurities.

[0022] According to a second aspect of the present invention, the present invention provides a system for purifying crude propylene oxide and removing impurities, the system comprising:

[0023] A crude propylene oxide recovery tower and an extraction tower connected in series along the material flow direction;

[0024] The crude propylene oxide recovery tower includes: a lower feed point for the epoxidation reaction product after propylene recovery, a side line desalted water material injection point, a line extraction point for materials rich in water-soluble impurities, a tower top extraction point for the crude propylene oxide tower top flow, and a tower bottom extraction point;

[0025] The extraction tower includes a feed point for materials rich in water-soluble impurities, a tower top withdrawal point and a tower bottom withdrawal point.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) According to the present invention, the content of aldehydes, especially formaldehyde, in crude PO is reduced to ≤300 ppm, thereby preventing the occurrence of aldehyde polymerization in the downstream crude PO refining process and improving the stability of the device operation;

[0028] (2) According to the present invention, the content of organic acid in crude PO is reduced to ≤10 ppm, thereby reducing the risk of system corrosion.

[0029] (3) According to the present invention, PO in the impurity material is effectively recovered, and the loss of PO is reduced.

[0030] The method of the invention can effectively remove formaldehyde and organic acid from propylene oxide, and can be used in the industrial production process of propylene oxide separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The flowchart of the system and method of the present invention is shown in FIG.

[0032] Description of Reference Numerals

[0033] A: Crude propylene oxide recovery tower; B: Extraction tower.

[0034] 1: Epoxidation reaction product after propylene recovery; 2: Crude propylene oxide tower top flow;

[0035] 3: side stream; 4: bottom stream of crude propylene oxide recovery tower;

[0036] 5: desalted water; 6: extracting oil phase from the top of the extraction tower;

[0037] 7: Fresh hydrocarbons; 8: Wastewater liquid. DETAILED DESCRIPTION

[0038] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0039] The present invention discloses a method for purifying crude propylene oxide and removing impurities, the method comprising:

[0040] (1) the epoxidation reaction product after propylene recovery enters a crude propylene oxide recovery tower from the bottom and is purified in the crude propylene oxide recovery tower, wherein a desalted water material is supplied to the side line of the crude propylene oxide recovery tower, and a material rich in water-soluble impurities is produced from the side line of the crude propylene oxide recovery tower, a crude propylene oxide tower top stream is obtained at the top of the crude propylene oxide tower, and a tower bottom stream is obtained at the bottom of the crude propylene oxide tower; wherein the injection point of the side line desalted water material is higher than the production point of the side line material rich in water-soluble impurities, and the number of theoretical plates between the two is N, and N≥2;

[0041] (2) the material rich in water-soluble impurities produced from the crude propylene oxide recovery tower side line enters the extraction tower, the oil phase material is separated from the tower top, and the wastewater material rich in impurities is separated from the tower bottom; the ratio k of the mass flow rate of the desalted water material stream 5 supplied from the side line to the mass flow rate of the epoxidation reaction product after propylene recovery satisfies the following relationship; in the formula, the epoxidation reaction product after propylene recovery is regarded as stream 1, and the crude propylene oxide tower top stream obtained from the tower top is regarded as stream 2;

[0042]

[0043] In the formula, by weight, is the concentration of formaldehyde in stream 1 (wt %); is the concentration of propylene oxide in stream 2 (wt %); is the concentration of formaldehyde in stream 2 (wt%); N is the theoretical plate number between the injection point of the side desalted water of the crude propylene oxide recovery tower and the withdrawal point of the side material rich in water-soluble impurities. This value is the minimum theoretical supply rate for achieving the formaldehyde removal effect according to the method of the present invention. The actual supply rate needs to be greater than the minimum theoretical supply rate. In this way, the formaldehyde can be effectively removed in the crude PO tower according to the method of the present invention.

[0044] The method of the present invention proposes for the first time to supply desalted water material to the side line of the crude propylene oxide tower, and at the same time control the injection point of the desalted water material of the side line to be higher than the extraction point of the material rich in water-soluble impurities of the side line, and the theoretical plate number between the two is N, N≥2; and preferably adopts the solvent hydrocarbon in the system as the extractant to recover PO. Compared with the prior art method, the present invention has the advantages of less PO loss, high dealdehyde efficiency and simple process.

[0045] In the present invention, propylene oxide in the side line is recovered in the extraction tower. The method of the present invention can effectively remove formaldehyde and organic acid from propylene oxide and can be used in the industrial production process of propylene oxide separation.

[0046] According to a preferred embodiment of the present invention, in step (1), the flow rate of desalted water is controlled so that the formaldehyde content of the crude propylene oxide tower top flow in step (1) is 0.01 to 300 wppm (weight), preferably 1 to 100 wppm (weight). This enables the downstream PO refining unit to operate stably for a long period of time.

[0047] According to a preferred embodiment of the present invention, the extraction point of the material rich in water-soluble impurities extracted from the side line in step (1) is higher than the feed point of the epoxidation reaction product, thereby achieving the effect of easy side line extraction of water-soluble impurities.

[0048] According to a preferred embodiment of the present invention, the injection point of the side line desalted water material is higher than the extraction point of the side line material rich in water-soluble impurities, and the theoretical plate number N between the two is 3-10. Thus, a high removal rate of water-soluble impurities can be achieved.

[0049] According to a preferred embodiment of the present invention, the method further comprises: returning the oil phase material separated from the top of the extraction tower in step (2) to the crude propylene oxide recovery tower for separation, thereby achieving PO recovery and reducing PO loss.

[0050] According to a preferred embodiment of the present invention, preferably, the return point of the oil phase material obtained by separation at the top of the extraction tower in step (2) is higher than the injection point of the desalted water of the side line of the crude propylene oxide recovery tower, thereby achieving the effect of increasing the distribution ratio of formaldehyde in the water phase and the oil phase and increasing the formaldehyde removal rate.

[0051] In the present invention, there is no special requirement for the epoxidation reaction product after propylene is recovered. The epoxidation reaction product after propylene is separated from propylene in the prior art can be used as a purification raw material in the present invention. According to a preferred embodiment of the present invention, the epoxidation reaction product after propylene is recovered is obtained by recovering propylene from the reaction materials of the epoxidation reaction of organic hydroperoxide and propylene.

[0052] In the present invention, the composition of the epoxidation reaction product after propylene recovery is determined according to the specific reaction. According to a preferred embodiment of the present invention, preferably, the epoxidation reaction product after propylene recovery contains a mixed stream of propylene oxide, alcohol, acid, aldehyde, aldehyde derivative, water, benzyl alcohol and a solvent hydrocarbon corresponding to the organic hydroperoxide.

[0053] In the present invention, the type of the acid is determined according to the specific reaction. According to a preferred embodiment of the present invention, preferably, the acid is at least one of formic acid, acetic acid, propionic acid and butyric acid.

[0054] In the present invention, the type of the aldehyde is determined according to the specific reaction. According to a preferred embodiment of the present invention, preferably, the aldehyde is at least one of formaldehyde, acetaldehyde and propionaldehyde.

[0055] According to a preferred embodiment of the present invention, preferably, the aldehyde derivative includes at least one of hemiacetal and acetal; preferably at least one of formaldehyde, acetaldehyde and propionaldehyde.

[0056] In the present invention, the type of the alcohol is determined according to the specific reaction. According to a preferred embodiment of the present invention, preferably, the alcohol is methanol and / or propylene glycol.

[0057] According to a preferred embodiment of the present invention, preferably, the epoxidation reaction product after propylene recovery comes from a process for preparing propylene oxide by co-oxidation of cumene or ethylbenzene.

[0058] According to a preferred embodiment of the present invention, preferably, the epoxidation reaction product after propylene recovery contains: based on the total weight, a propylene oxide content of 5 to 40 weight %, a benzyl alcohol content of 5 to 60 weight %, a solvent hydrocarbon content corresponding to the organic hydroperoxide of 10 to 90 weight %, an acid content of 10 to 2000 ppm, a formaldehyde content and its derivatives content of 1 to 1000 ppm, and a water content of 1 to 1000 ppm.

[0059] In the present invention, the aldehyde derivatives include formaldehyde or at least one derivative of formaldehyde and acetaldehyde or propionaldehyde. The derivatives include at least one of hemiacetal and acetal.

[0060] In the present invention, the composition of the water-soluble impurities is determined according to the raw materials. According to a preferred embodiment of the present invention, preferably, the water-soluble impurities are at least one impurity selected from alcohol, acid, aldehyde, aldehyde derivatives, hydrocarbons, water or a combination thereof.

[0061] According to a preferred embodiment of the present invention, preferably, the water-soluble impurities are selected from one or more of formic acid, acetic acid, formaldehyde, acetaldehyde, methanol, propylene glycol and water.

[0062] According to a preferred embodiment of the present invention, preferably, the material rich in water-soluble impurities withdrawn from the side line in step (1) contains at least one impurity of alcohol, acid, aldehyde, aldehyde derivative, hydrocarbon, water or a combination thereof and contains 0.1 wt% to 50 wt% propylene oxide.

[0063] According to a preferred embodiment of the present invention, preferably, in step (2), the extractant of the extraction tower is a hydrocarbon.

[0064] According to a preferred embodiment of the present invention, preferably, the hydrocarbon is a solvent hydrocarbon used in a propylene oxide synthesis process; preferably, it is a hydrocarbon solvent in a process of co-oxidation of cumene or ethylbenzene to synthesize propylene oxide.

[0065] According to a preferred embodiment of the present invention, preferably, in step (2), the weight ratio of the flow rate of the fresh extractant hydrocarbon material to the flow rate of the material rich in water-soluble impurities produced from the crude propylene oxide recovery tower entering the extraction tower is greater than 0.6:1, preferably greater than 1:1, and more preferably 1.5-5:1. This enables effective extraction and recovery of PO.

[0066] According to a preferred embodiment of the present invention, preferably, in step (1), the operating conditions of the crude propylene oxide recovery tower include: an operating pressure of 0 to 1.0 MPag, and an operating temperature of 10 to 200°C.

[0067] According to a preferred embodiment of the present invention, preferably, in step (1), the operating conditions of the extraction tower include: an operating pressure of 0 to 1.0 MPag, and an operating temperature of 10 to 100°C.

[0068] The method of the present invention can achieve the purpose of the present invention, and there is no special requirement for the functional units of the purification system. According to the present invention, a system for purifying and removing impurities from crude propylene oxide is provided, which comprises: a crude propylene oxide recovery tower and an extraction tower connected in series along the material flow direction;

[0069] The crude propylene oxide recovery tower includes: a lower feed point for the epoxidation reaction product after propylene recovery, a side line desalted water material injection point, a line extraction point for materials rich in water-soluble impurities, a tower top extraction point for the crude propylene oxide tower top flow, and a tower bottom extraction point;

[0070] The extraction tower includes a feed point for materials rich in water-soluble impurities, a tower top withdrawal point and a tower bottom withdrawal point.

[0071] According to a preferred embodiment of the present invention, preferably, the side-line extraction point of the material rich in water-soluble impurities is higher than the lower feed point of the epoxidation reaction product, thereby achieving the effect of easy side-line extraction of water-soluble impurities.

[0072] According to a preferred embodiment of the present invention, the injection point of the side line desalted water material is higher than the extraction point of the side line material rich in water-soluble impurities, and the number of theoretical plates between the two is N, N≥2, preferably 3-10. This can achieve a high removal rate of water-soluble impurities.

[0073] According to a preferred embodiment of the present invention, preferably, the crude propylene oxide recovery tower comprises: a return point for the oil phase material separated from the top of the extraction tower.

[0074] According to a preferred embodiment of the present invention, it is more preferred that the return point of the oil phase material separated from the top of the extraction tower is higher than the injection point of the desalted water of the side line of the crude propylene oxide recovery tower, thereby achieving the effect of PO recovery and reducing PO loss.

[0075] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0076] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0077] In addition, the various embodiments of the present invention may be arbitrarily combined as long as they do not violate the concept of the present invention. The technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0078] The following examples are based on Figure 1 The process shown is carried out.

[0079] A system for purifying crude propylene oxide and removing impurities, comprising:

[0080] A crude propylene oxide recovery tower (A) and an extraction tower (B) connected in series along the material flow direction;

[0081] The crude propylene oxide recovery tower includes: a lower feed point for the epoxidation reaction product after propylene recovery, a side line desalted water material injection point, a line extraction point for materials rich in water-soluble impurities, a tower top extraction point for the crude propylene oxide tower top flow, and a tower bottom extraction point;

[0082] The extraction tower includes a feed point for materials rich in water-soluble impurities, a tower top withdrawal point and a tower bottom withdrawal point.

[0083] According to a preferred embodiment of the present invention, preferably, the line extraction point of the material rich in water-soluble impurities is higher than the lower feeding point of the epoxidation reaction product.

[0084] The propylene epoxidation product obtained by the epoxidation reaction of organic hydroperoxide with propylene after recovery: a mixed stream (1) containing propylene oxide, alcohol, acid, aldehyde, aldehyde derivative, water, benzyl alcohol and hydrocarbon corresponding to the organic hydroperoxide is introduced into a crude propylene oxide recovery tower (A) from the lower feed point and the additionally supplied desalted water (5) from the side desalted water material injection point, and a crude propylene oxide top stream (2) containing a small amount of impurities is obtained from the tower top extraction point and a tower bottom stream (4) is obtained from the tower bottom extraction point, and a crude propylene oxide containing alcohol, acid, aldehyde, aldehyde derivative, water, benzyl alcohol and hydrocarbon corresponding to the organic hydroperoxide is obtained from the side desalted water material injection point. At least one impurity of derivatives, hydrocarbons, water or a combination thereof and a side stream (3) containing 0.1wt% to 50wt% propylene oxide; the side stream (3) from the crude propylene oxide recovery tower is introduced into the extraction tower (B) from the feed point of the material rich in water-soluble impurities, and is contacted with the fresh hydrocarbon (7) of the extractant fed from the lower feed point for countercurrent extraction, and a tower top stream (extraction tower top extraction oil phase) (6) containing propylene oxide is obtained at the tower top extraction point and returned to the crude propylene oxide recovery tower, and a tower bottom wastewater stream (wastewater liquid) (8) containing acid, aldehyde, water and trace amounts of propylene oxide is extracted at the tower bottom extraction point.

[0085] In the following embodiments of the present invention:

[0086] The crude propylene oxide overhead stream (2) is stream 2;

[0087] The epoxidation reaction product after propylene recovery: a mixed stream (1) containing propylene oxide, alcohol, acid, aldehyde, aldehyde derivative, water, benzyl alcohol and a hydrocarbon corresponding to the organic hydroperoxide is stream 1;

[0088] The wastewater stream (wastewater liquid) (8) at the bottom of the extraction tower is stream 8;

[0089] The recovery rate of propylene oxide is calculated as follows: (mass flow rate of propylene oxide in stream 2 / mass flow rate of propylene oxide in stream 1)*100%;

[0090] The formaldehyde removal rate is calculated as follows: (mass flow rate of formaldehyde in stream 8 / mass flow rate of formaldehyde in stream 1)*100%.

[0091] [Example 1]

[0092] like Figure 1 As shown, in the feed stream (stream 1) of the crude propylene oxide recovery tower, by weight percentage, the content of propylene oxide is 18%, isopropylbenzene is 36%, dimethylbenzyl alcohol is 45%, the content of organic acid (calculated as formic acid) is 450ppm (0.045wt%), the content of formaldehyde is 250ppm (0.025wt%), the content of propylene glycol is 800ppm (0.08wt%), the content of water is 100ppm (0.01wt%), the content of acetaldehyde is 100ppm (0.01wt%), and others.

[0093] The top operating pressure of the crude propylene oxide recovery tower is 40 kPa (gauge pressure), the top operating temperature is 44°C, and the bottom operating temperature is 168°C.

[0094] The theoretical plate number between the side line desalted water injection point and the side line material extraction point is 3.

[0095] According to the formula Calculation shows that the weight ratio k (side desalted water supply rate) of the flow rate of the crude propylene oxide recovery tower side desalted water material (stream 5) to the feed process flow rate (stream 1) is ≥1.25%, and the actual desalted water supply rate is 1.86%.

[0096] The operating pressure at the top of the extraction tower is 50 kPa (gauge pressure), the operating temperature at the top is 40°C, the extractant is cumene, and the weight ratio of fresh hydrocarbon (cumene) material flow rate / side line material flow rate is 1.5:1.

[0097] The return point of the oil phase material separated from the top of the extraction tower in step (2) is higher than the injection point of the desalted water from the side line of the crude propylene oxide recovery tower.

[0098] Experimental results: In stream 2, the recovery rate of propylene oxide was 99.8%, the mass concentration was 99 wt%, formic acid was reduced to 5 ppm, formaldehyde was reduced to 100 ppm (0.01 wt%), and the formaldehyde removal rate was 92.9%.

[0099] [Example 2]

[0100] The same as [Example 1], except that, in the feed stream (stream 1) of the crude propylene oxide recovery tower, the content of propylene oxide, cumene, dimethylbenzyl alcohol, organic acid (as formic acid) content is 18%, formaldehyde content is 100 ppm (0.01wt%), propylene glycol is 800 ppm, water is 100 ppm, and others are contained in the feed stream (stream 1) of the crude propylene oxide recovery tower.

[0101] According to the formula Calculation shows that the weight ratio k (side desalted water supply rate) of the flow rate of the crude propylene oxide recovery tower side desalted water material (stream 5) to the feed process flow rate (stream 1) is ≥0.85%, and the actual desalted water supply rate is 1.46%.

[0102] Experimental results: In stream 2, the recovery rate of propylene oxide was 99.8%, the mass concentration was 99wt%, formic acid was reduced to 5ppm, formaldehyde was reduced to 50ppm, and the formaldehyde removal rate was 91.0%.

[0103] [Example 3]

[0104] The same as [Example 1], except that, in the feed stream (stream 1) of the crude propylene oxide recovery tower, the content of propylene oxide, cumene, dimethylbenzyl alcohol, organic acid (as formic acid) content is 18%, formaldehyde content is 450 ppm (0.045 wt%), propylene glycol is 800 ppm, water is 100 ppm, and others are contained in the feed stream (stream 1) of the crude propylene oxide recovery tower.

[0105] According to the formula Calculation shows that the weight ratio k (side desalted water supply rate) of the flow rate of the crude propylene oxide recovery tower side desalted water material (stream 5) to the feed process flow rate (stream 1) is ≥3.25%, and the actual desalted water supply rate is 3.86%.

[0106] Experimental results: In stream 2, the recovery rate of propylene oxide was 99.6%, the mass concentration was 99 wt%, formic acid was reduced to 5 ppm, formaldehyde was reduced to 100 ppm, and the formaldehyde removal rate was 96.4%.

[0107] [Example 4]

[0108] The same as [Example 1], except that the number of theoretical plates between the side line desalted water injection point and the side line material extraction point is 4.

[0109] According to the formula Calculation shows that the weight ratio k (side desalted water supply rate) of the flow rate of the crude propylene oxide recovery tower side desalted water material (stream 5) to the feed process flow rate (stream 1) is ≥0.25%, and the actual desalted water supply rate is 0.37%.

[0110] Experimental results: In stream 2, the recovery rate of propylene oxide was 99.9%, the mass concentration was 99 wt%, formic acid was reduced to 5 ppm, formaldehyde was reduced to 100 ppm, and the formaldehyde removal rate was 92.7%.

[0111] [Example 5]

[0112] Same as [Example 2], except that the number of theoretical plates between the side line desalted water injection point and the side line material extraction point is 2.

[0113] According to the formula Calculation shows that the weight ratio k (side desalted water supply rate) of the flow rate of the crude propylene oxide recovery tower side desalted water material (stream 5) to the feed process flow rate (stream 1) is ≥4.24%, and the actual desalted water supply rate is 7.29%.

[0114] Experimental results: In stream 2, the recovery rate of propylene oxide was 99.3%, the mass concentration was 99wt%, formic acid was reduced to 5ppm, formaldehyde was 50ppm, and the formaldehyde removal rate was 91.1%.

[0115] [Example 6]

[0116] Same as [Example 5], except that the weight ratio of fresh hydrocarbon (isopropylbenzene) material flow rate / side line material flow rate is 2:1.

[0117] According to the formula Calculation shows that the weight ratio k (side desalted water supply rate) of the flow rate of the crude propylene oxide recovery tower side desalted water material (stream 5) to the feed process flow rate (stream 1) is ≥4.24%, and the actual desalted water supply rate is 7.27%.

[0118] Experimental results: In stream 2, the recovery rate of propylene oxide was 99.8%, the mass concentration was 99wt%, formic acid was reduced to 5ppm, formaldehyde was reduced to 50ppm, and the formaldehyde removal rate was 90.9%.

[0119] [Comparative Example 1]

[0120] The difference from [Example 1] is that the actual desalted water supply rate is 1.20%.

[0121] Experimental results: In stream 2, the recovery rate of propylene oxide was 99.6%, the mass concentration was 99 wt%, formic acid was reduced to 5 ppm, the formaldehyde concentration was 457 ppm, and the formaldehyde removal rate was 67.2%.

[0122] [Comparative Example 2]

[0123] Same as [Example 1], except that the theoretical plate number between the side line desalted water injection point and the side line material extraction point is 1, the actual supply rate is consistent with the example, and the other conditions are the same.

[0124] Experimental results: In stream 2, the recovery rate of propylene oxide was 99.7%, the mass concentration was 99wt%, formic acid was reduced to 5ppm, the formaldehyde concentration was 912ppm, and the formaldehyde removal rate was 33.9%.

[0125] [Example 7]

[0126] Same as [Example 1], except that the weight ratio of fresh hydrocarbon (isopropylbenzene) material flow rate / side line material flow rate is 0.5:1.

[0127] Experimental results: In stream 2, the recovery rate of propylene oxide was 96.4%, the mass concentration was 99wt%, formic acid was reduced to 5ppm, the formaldehyde concentration was 100ppm, and the formaldehyde removal rate was 90.3%.

[0128] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for purifying crude propylene oxide and removing impurities, characterized in that: The method includes: (1) the epoxidation reaction product after propylene recovery enters a crude propylene oxide recovery tower from the bottom and is purified in the crude propylene oxide recovery tower, wherein a desalted water material is supplied to a side line of the crude propylene oxide recovery tower, and a material rich in water-soluble impurities is extracted from the side line of the crude propylene oxide recovery tower, a crude propylene oxide tower top stream is obtained at the top of the crude propylene oxide tower, and a tower bottom stream is obtained at the bottom of the crude propylene oxide tower; The injection point of the side-line desalted water material is higher than the extraction point of the side-line material rich in water-soluble impurities, and the number of theoretical plates between the two is N, N≥2; (2) the material rich in water-soluble impurities extracted from the crude propylene oxide recovery tower enters an extraction tower, an oil phase material is separated from the top of the tower, and a wastewater material rich in impurities is separated from the bottom of the tower; The ratio k of the mass flow rate of the desalted water material stream 5 supplied from the side line to the mass flow rate of the epoxidation reaction product after propylene recovery satisfies the following relationship: In the formula, the epoxidation reaction product after propylene recovery is stream 1, and the crude propylene oxide tower top stream obtained from the tower top is stream 2; In the formula, by weight, is the concentration of formaldehyde in stream 1 (wt %); is the concentration of propylene oxide in stream 2 (wt %); is the concentration of formaldehyde in stream 2 (wt%); N is the number of theoretical plates between the injection point of the side desalted water of the crude propylene oxide recovery tower and the withdrawal point of the side material rich in water-soluble impurities.

2. The method according to claim 1, wherein: In step (1), the flow rate of desalted water is controlled so that the formaldehyde content of the crude propylene oxide tower top flow in step (1) is 0.01 to 300 wppm, preferably 1 to 100 wppm.

3. The method according to claim 1 or 2, wherein: The extraction point of the material rich in water-soluble impurities extracted from the side line in step (1) is higher than the feed point of the epoxidation reaction product; and / or N is 3-10; and / or The method further comprises: returning the oil phase material separated from the top of the extraction tower in step (2) to the crude propylene oxide recovery tower for separation; Preferably, the return point of the oil phase material separated from the top of the extraction tower in step (2) is higher than the injection point of the desalted water from the side line of the crude propylene oxide recovery tower.

4. The method according to any one of claims 1 to 3, wherein: The epoxidation product after propylene recovery comes from the process of preparing propylene oxide by co-oxidation of cumene or ethylbenzene; Preferably, the epoxidation reaction product after propylene recovery contains, based on the total weight, 5 to 40% by weight of propylene oxide, 5 to 60% by weight of benzyl alcohol, 10 to 90% by weight of the solvent hydrocarbon corresponding to the organic hydroperoxide, 10 to 2000 ppm of acid, 1 to 1000 ppm of formaldehyde and its derivatives, and 1 to 1000 ppm of water.

5. The method according to any one of claims 1 to 4, wherein: The water-soluble impurities are at least one impurity selected from alcohols, acids, aldehydes, aldehyde derivatives, hydrocarbons, water or combinations thereof; Preferably, the water-soluble impurities are selected from one or more of formic acid, acetic acid, formaldehyde, acetaldehyde, methanol, propylene glycol and water; Preferably, the material rich in water-soluble impurities withdrawn from the side line in step (1) contains at least one impurity of alcohol, acid, aldehyde, aldehyde derivative, hydrocarbon, water or a combination thereof and 0.1 wt% to 50 wt% propylene oxide.

6. The method according to any one of claims 1 to 5, wherein: In step (2), the extractant of the extraction tower is a hydrocarbon; preferably, the hydrocarbon is a solvent hydrocarbon used in the propylene oxide synthesis process; preferably, it is a hydrocarbon solvent in the process of co-oxidation of isopropylbenzene or ethylbenzene to synthesize propylene oxide.

7. The method according to any one of claims 1 to 6, wherein: In step (2), the weight ratio of the fresh extractant hydrocarbon material flow rate to the material rich in water-soluble impurities extracted from the crude propylene oxide recovery tower entering the extraction tower is greater than 0.6:1, preferably greater than 1:1, and more preferably 1.5-5:

1.

8. The method according to any one of claims 1 to 7, wherein: Step (1), the operating conditions of the crude propylene oxide recovery tower include: an operating pressure of 0 to 1.0 MPag, an operating temperature of 10 to 200° C.; and / or In step (2), the operating conditions of the extraction tower include: an operating pressure of 0 to 1.0 MPag and an operating temperature of 10 to 100°C.

9. A system for purifying crude propylene oxide and removing impurities, characterized in that: The system includes: A crude propylene oxide recovery tower and an extraction tower connected in series along the material flow direction; The crude propylene oxide recovery tower includes: a lower feed point for the epoxidation reaction product after propylene recovery, a side line desalted water material injection point, a line extraction point for materials rich in water-soluble impurities, a tower top extraction point for the crude propylene oxide tower top flow, and a tower bottom extraction point; The extraction tower includes a feed point for materials rich in water-soluble impurities, a tower top withdrawal point, and a tower bottom withdrawal point; The injection point of the side line desalted water material is higher than the extraction point of the side line material rich in water-soluble impurities, and the number of theoretical plates between the two is N, N≥2.

10. The system according to claim 9, wherein: The line extraction point of the material rich in water-soluble impurities is higher than the lower feed point of the epoxidation reaction product; and / or The injection point of the side line desalted water material is higher than the extraction point of the side line material rich in water-soluble impurities, and the theoretical plate number N between the two is 3-10; and / or Preferably, the crude propylene oxide recovery tower comprises: a return point for the oil phase material separated from the top of the extraction tower; More preferably, the return point of the oil phase material separated from the top of the extraction tower is higher than the injection point of the desalted water from the side line of the crude propylene oxide recovery tower.

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