Direct oxidation of propylene to produce propylene oxide and methanol to olefins combined production process

Abstract

The present invention relates to the technical field of propylene oxide production, and in particular to a combined production process of propylene oxide produced by direct oxidation of propylene and methanol to olefins. Hydrogen peroxide, propylene, and methanol solvents are introduced as reaction raw materials into an epoxidation reactor to contact an oxidation catalyst therein for reaction; the epoxidation reaction product is sequentially separated through a propylene recovery unit and a propylene oxide crude fractionation tower to obtain a methanol aqueous solution and crude propylene oxide; the crude propylene oxide is introduced into a propylene oxide refining tower to obtain a propylene oxide product with a purity greater than 99.9%; the methanol aqueous solution is passed through a methanol purification tower to obtain crude methanol; the crude methanol is passed through a clay processor to remove trace impurities, and all or part of the crude methanol is directly used as feed to an MTO reactor or an MTP reactor; the propylene product produced by the MTO reactor or the MTP reactor is refluxed to the epoxidation reactor.

Description

Technical Field

[0001] The present invention relates to the technical field of propylene oxide production, in particular to a combined production process of propylene oxide produced by direct oxidation of propylene and methanol to olefins. Background Art

[0002] Propylene oxide is the third-largest propylene derivative after polypropylene and acrylonitrile. It is an important basic organic chemical raw material, primarily used in the production of polyethers and propylene glycol. It is also a key raw material for fourth-generation detergent nonionic surfactants, oilfield demulsifiers, and pesticide emulsifiers. Propylene oxide derivatives are widely used in industries such as automotive, construction, food, tobacco, pharmaceuticals, and cosmetics. Nearly 100 downstream products have been produced, and it is a key raw material for fine chemical products. This demonstrates the crucial role of propylene oxide in the development of the national economy.

[0003] Currently, the main methods for producing propylene oxide in the world include the chlorohydrin method, the co-oxidation method (including the ethylbenzene co-oxidation method and the isobutane co-oxidation method), and the direct oxidation method with hydrogen peroxide. Among them, the chlorohydrin method is a mature and reliable process, but it has problems such as severe equipment corrosion, high water resource consumption, and large amounts of wastewater and waste residue discharged during the production process. The co-oxidation method has problems such as a long process, high investment, and the co-production of 2.2 to 2.5 tons of styrene or tert-butyl alcohol for every ton of propylene oxide produced, which restricts the source of raw materials and product sales. The new process for producing propylene oxide by directly oxidizing propylene with hydrogen peroxide over a titanium silicalite catalyst has mild reaction conditions, high product yield, no other by-products, and is basically pollution-free. It is an environmentally friendly clean production process and represents the development direction of propylene oxide production technology.

[0004] The direct epoxidation reaction of hydrogen peroxide and propylene generally uses a large amount of methanol as a solvent, dissolving the immiscible hydrogen peroxide and propylene in the same phase for reaction. The presence of the solvent methanol can improve the service life of the titanium silicate catalyst and the yield of the propylene oxide product. In the existing HPPO production process, the solvent methanol needs to be recycled back to the epoxidation reactor for reuse. In addition to the production of propylene oxide, the epoxidation reaction also produces a small amount of various trace impurities such as aldehydes, ketones, acids, ethers, and esters. Even though the solvent methanol undergoes a series of treatments to remove some impurities before recycling, some of these trace impurities are difficult to remove effectively and will continue to accumulate in the system as the methanol circulates. These accumulated impurities will continue to undergo other reactions in the epoxidation reactor and generate more new impurities, resulting in increasingly poor quality of the propylene oxide product and an increasing number of impurities in the recycled methanol. These large amounts of impurities also seriously affect the service life of the titanium silicate catalyst.

[0005] EP-A 1122248 discloses a method for processing a product stream from propylene epoxidation containing propylene, propylene oxide, methanol, and water. The method involves first separating the product stream into an overhead stream containing propylene, propylene oxide, and methanol and a bottoms product containing methanol and water in a pre-evaporator. The methanol in the bottoms product is recovered and recycled to the epoxidation reactor. Propylene oxide is obtained from the overhead product of an extractive distillation column, preferably using water as the extractant. The stream containing methanol and water obtained at the bottom of the extractive distillation column can be directly recycled to the epoxidation reactor. Although this method can effectively reduce propylene oxide losses, the activity and selectivity of the epoxidation catalyst decrease significantly over a short period of time, and a large amount of impurities accumulate during the methanol recycling process.

[0006] WO 02 / 02545 addresses the problem of methyl formate accumulation in the product propylene oxide. Although distillation can be used to remove some of the methyl formate from the circulating methanol, this only reduces the accumulation of impurities and cannot fundamentally solve the problem of decreased epoxidation catalyst activity.

[0007] CN1294125C discloses a method for reducing the impurity content of methanol by hydrogenating the solvent. Although this method can reduce the accumulation of impurities in the circulating methanol to a certain extent, it cannot fundamentally solve the problems of decreased catalyst activity and poor quality of the propylene oxide product caused by the methanol circulation. As can be seen from the examples, after the epoxidation process has been running for 500 hours, the conversion rate of hydrogen peroxide drops to 96%, and the acetaldehyde content in the propylene oxide product is as high as 700 ppm.

[0008] While existing methods for preparing and refining propylene oxide products typically achieve purity exceeding 99.5%, removing trace impurities such as methyl formate, acetaldehyde, propionaldehyde, and acetone from crude propylene oxide is difficult. Numerous patents, such as CN103172594B, US5106458, and CN100500659, have explored and reported methods for removing these impurities. While these methods can yield high-purity propylene oxide in a short period of time, they are complex processes and carry high operating costs.

[0009] In summary, the accumulation of large amounts of trace impurities in recycled methanol is a major cause of epoxidation catalyst deactivation. This detrimental effect is also reflected in a rapid decrease in propylene oxide selectivity, resulting in a high level of impurities in the propylene oxide product, making it difficult to meet product quality standards. The treatment of recycled methanol is difficult and costly, and the impurity content in wastewater also increases, making it increasingly difficult to handle. However, using fresh methanol as the feedstock for the epoxidation reaction can essentially completely resolve these issues, significantly extend the service life of the epoxidation catalyst, improve propylene oxide selectivity and product quality, and significantly reduce the impurity content in the solvent methanol. Summary of the Invention

[0010] To address the above-mentioned problems, the present invention provides a process for the combined production of propylene oxide and methanol to olefins by direct oxidation of propylene. Hydrogen peroxide, propylene, and methanol solvents are introduced as raw materials into an epoxidation reactor, where they contact an oxidation catalyst and react. The epoxidation product is separated sequentially through a propylene recovery unit and a crude propylene oxide fractionator to produce a methanol-water solution and crude propylene oxide. The crude propylene oxide enters a propylene oxide refining tower to produce a propylene oxide product with a purity greater than 99.9%. The methanol-water solution passes through a methanol purification tower to produce crude methanol. The crude methanol is then treated with a clay processor to remove trace impurities, and all or part of the crude methanol is directly used as feed to an MTO reactor or MTP reactor. The propylene product produced by the MTO reactor or MTP reactor is refluxed to the epoxidation reactor. Compared with the prior art, the present invention effectively integrates epoxidation technology with MTO / MTP technology, significantly extending the life of the propylene oxide catalyst, significantly reducing epoxidation reaction byproducts, simplifying the subsequent separation system, and achieving higher quality propylene oxide and methanol products.

[0011] The purpose of the present invention can be achieved by the following technical solutions:

[0012] The present invention provides a process for producing propylene oxide by direct oxidation of propylene and methanol to olefins, comprising the following steps:

[0013] (S1) an epoxidation reaction raw material enters an epoxidation reactor for an epoxidation reaction to obtain an epoxidation reaction product;

[0014] (S2) the epoxidation reaction product obtained in step (S1) enters a propylene recovery unit, wherein the propylene obtained is first circulated to the epoxidation reactor, and the methanol, water, and propylene oxide obtained further enter a propylene oxide crude fractionation tower, and finally the methanol-water solution obtained enters a methanol purification tower;

[0015] (S3) the methanol, water, and propylene oxide obtained in step (S2) are separated in a propylene oxide crude fractionation tower, crude propylene oxide containing trace amounts of methanol is obtained at the top of the tower, which is transferred to a propylene oxide refining tower, and the methanol-water solution obtained at the bottom of the tower enters a methanol purification tower;

[0016] (S4) The crude propylene oxide obtained in step (S3) is passed through a propylene oxide refining tower, whereby a propylene oxide product having a purity higher than 99.9% is obtained at the top of the tower and a methanol-water solution is obtained at the bottom of the tower, which is then sent to a wastewater treatment process;

[0017] (S5) After the methanol-water solution obtained in step (S2) and step (S3) enters a methanol purification tower, crude methanol is obtained at the top of the tower and wastewater is obtained at the bottom of the tower. The crude methanol is transferred to a clay processor, and the wastewater enters a wastewater treatment process;

[0018] (S6) an adsorbent is provided in the clay processor, and the adsorbent adsorbs impurities in the crude methanol obtained in step (S5) to obtain treated methanol, and the treated methanol further enters the MTO reactor or the MTP reactor;

[0019] (S7) subjecting all or part of the treated methanol obtained in step (S6) to an MTO reaction in an MTO reactor, or subjecting all or part of the treated methanol to an MTP reaction in an MTP reactor to obtain an ethylene product and propylene, and refluxing the propylene to the epoxidation reactor;

[0020] When a portion of the treated methanol undergoes an MTO reaction in the MTO reactor, or a portion of the treated methanol undergoes an MTP reaction in the MTP reactor, another portion of the treated methanol is recycled to the epoxidation reactor;

[0021] Among them, the raw materials for the epoxidation reaction are hydrogen peroxide, methanol and propylene.

[0022] In one embodiment of the present invention, the epoxidation reactor is selected from one of a tubular fixed bed reactor, a trickle bed reactor or a plate exchange reactor.

[0023] In one embodiment of the present invention, the epoxidation reactor is a fixed bed reactor.

[0024] In one embodiment of the present invention, the epoxidation reactor is loaded with an oxidation catalyst;

[0025] The oxidation catalyst is a titanium silicon molecular sieve catalyst.

[0026] In one embodiment of the present invention, the propylene recovery unit comprises at least one distillation column;

[0027] The methanol-water solution recovered by the propylene recovery unit accounts for 60-80% of the total methanol-water solution at the outlet of the epoxidation reactor.

[0028] In one embodiment of the present invention, the methanol aqueous solution recovered at the bottom of the crude propylene oxide fraction tower accounts for 20%-30% of the total methanol aqueous solution at the outlet of the epoxidation reactor;

[0029] The purity of the propylene oxide recovered from the top of the crude propylene oxide fractionation tower is greater than 95%.

[0030] In one embodiment of the present invention, the methanol-water solution recovered by the propylene recovery unit and the propylene oxide crude fraction tower contains 75%-90% methanol, 5%-20% water, 0.2%-5% high boiling point impurities, 10ppm-100ppm hydrogen peroxide, 10ppm-50ppm aldehyde and ketone impurities and 1ppm-40ppm nitrogen-containing compounds.

[0031] In one embodiment of the present invention, the propylene oxide refining tower uses a sodium bisulfite aqueous solution as an extractant and a dealdehyde agent, and a propylene oxide product with a purity greater than 99.9% is obtained at the top of the tower.

[0032] In one embodiment of the present invention, the top components of the methanol purification tower include 90%-98% methanol, 2%-10% water, 10ppm-80ppm aldehyde and ketone impurities, and 1ppm-40ppm nitrogen-containing compounds.

[0033] In one embodiment of the present invention, the methanol-water solution at the bottom of the propylene oxide refining tower is recovered by steam stripping and combined with the top material of the methanol purification tower to enter the clay processor.

[0034] In one embodiment of the present invention, the clay processor is filled with clay, and the clay is acidic clay treated with sulfuric acid;

[0035] The acid clay comprises 60%-70% SiO2, 20%-30% Al2O3, 2%-5% Fe2O3 and 1%-5% MgO;

[0036] In the clay processor, the reaction temperature is 60-200℃ and the air velocity is 0.5-10h -1 .

[0037] In one embodiment of the present invention, the MTO reactor is selected from one of an axially fixed bed reactor, a radially fixed bed reactor or a fluidized bed reactor;

[0038] The MTP reactor is selected from one of an axially fixed bed reactor, a radially fixed bed reactor or a fluidized bed reactor.

[0039] In one embodiment of the present invention, the MTO reactor is filled with an MTO catalyst, and the MTO catalyst is selected from one of a SAPO-34 molecular sieve catalyst and a ZSM-5 molecular sieve catalyst;

[0040] The MTP reactor is filled with an MTP catalyst, which is selected from one of a SAPO-34 molecular sieve catalyst and a ZSM-5 molecular sieve catalyst.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The present invention relates to a combined production process of propylene oxide by direct oxidation of propylene and methanol to olefins, which uses fresh methanol or a small amount of recycled methanol as the solvent for the epoxidation reaction. This can avoid the problem of impurity accumulation caused by methanol recycling, greatly improve the service life of the titanium silicate catalyst and the selectivity of propylene oxide, and greatly reduce the impurity content of the obtained propylene oxide and methanol. Therefore, both the propylene oxide product purification process and the methanol purification process can be simplified.

[0043] (2) The crude methanol can be effectively treated with trace amounts of aldehydes, ketones, and nitrogen-containing compounds by the clay processor. The indicators of the methanol output from the clay processor can fully meet the requirements of the MTO / MTP for raw methanol. The MTO reactor or MTP reactor supplies the produced propylene to the epoxidation reactor for epoxidation. The coupling of the two sets of equipment effectively solves the problems of recycled methanol quality and propylene raw material. For manufacturers who already have MTO / MTP and need to further increase industrial added value by extending the propylene industry chain, the solution of the present invention will be very suitable. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a flowchart of the process for producing propylene oxide by direct epoxidation of propylene in Comparative Example 1 of the present invention;

[0045] Figure 2 This is a flowchart of the process for producing propylene oxide by direct epoxidation of propylene in Comparative Example 2 of the present invention;

[0046] Figure 3 This is a flowchart of the process for producing propylene oxide through direct oxidation of propylene and methanol to olefins in Example 1 of the present invention;

[0047] Reference numerals in the figure: 1, epoxidation reaction feed; 2, epoxidation reaction product; 3, first product of propylene recovery unit; 4, second product of propylene recovery unit; 5, third product of propylene recovery unit; 6, bottom product of crude propylene oxide fractionator; 7, overhead product of crude propylene oxide fractionator; 8, bottom product of propylene oxide refining column; 9, overhead product of propylene oxide refining column; 10, overhead product of methanol purification column; 11, bottom product of methanol purification column; 12, product of clay processor; 13, reflux product of MTO reactor; 14, product of methanol hydrogenation unit;

[0048] 100 is the epoxidation reactor; 200 is the propylene recovery unit; 300 is the propylene oxide crude fraction tower; 400 is the propylene oxide refining tower; 500 is the methanol hydrogenation unit; 600 is the methanol purification tower; 700 is the clay processor; and 800 is the MTO reactor. DETAILED DESCRIPTION

[0049] The present invention provides a process for producing propylene oxide by direct oxidation of propylene and methanol to olefins, comprising the following steps:

[0050] (S1) an epoxidation reaction raw material enters an epoxidation reactor for an epoxidation reaction to obtain an epoxidation reaction product;

[0051] (S2) the epoxidation reaction product obtained in step (S1) enters a propylene recovery unit, wherein the propylene obtained is first circulated to the epoxidation reactor, and the methanol, water, and propylene oxide obtained further enter a propylene oxide crude fractionation tower, and finally the methanol-water solution obtained enters a methanol purification tower;

[0052] (S3) the methanol, water, and propylene oxide obtained in step (S2) are separated in a propylene oxide crude fractionation tower, crude propylene oxide containing trace amounts of methanol is obtained at the top of the tower, which is transferred to a propylene oxide refining tower, and the methanol-water solution obtained at the bottom of the tower enters a methanol purification tower;

[0053] (S4) The crude propylene oxide obtained in step (S3) is passed through a propylene oxide refining tower, whereby a propylene oxide product having a purity higher than 99.9% is obtained at the top of the tower and a methanol-water solution is obtained at the bottom of the tower, which is then sent to a wastewater treatment process;

[0054] (S5) After the methanol-water solution obtained in step (S2) and step (S3) enters a methanol purification tower, crude methanol is obtained at the top of the tower and wastewater is obtained at the bottom of the tower. The crude methanol is transferred to a clay processor, and the wastewater enters a wastewater treatment process;

[0055] (S6) an adsorbent is provided in the clay processor, and the adsorbent adsorbs impurities in the crude methanol obtained in step (S5) to obtain treated methanol, and the treated methanol further enters the MTO reactor or the MTP reactor;

[0056] (S7) subjecting all or part of the treated methanol obtained in step (S6) to an MTO reaction in an MTO reactor, or subjecting all or part of the treated methanol to an MTP reaction in an MTP reactor to obtain an ethylene product and propylene, and refluxing the propylene to the epoxidation reactor;

[0057] When a portion of the treated methanol undergoes an MTO reaction in the MTO reactor, or a portion of the treated methanol undergoes an MTP reaction in the MTP reactor, another portion of the treated methanol is recycled to the epoxidation reactor;

[0058] Among them, the raw materials for the epoxidation reaction are hydrogen peroxide, methanol and propylene.

[0059] In one embodiment of the present invention, the epoxidation reactor is selected from one of a tubular fixed bed reactor, a trickle bed reactor or a plate exchange reactor.

[0060] In one embodiment of the present invention, the epoxidation reactor is a fixed bed reactor.

[0061] In one embodiment of the present invention, the epoxidation reactor is loaded with an oxidation catalyst;

[0062] The oxidation catalyst is a titanium silicon molecular sieve catalyst.

[0063] In one embodiment of the present invention, the propylene recovery unit comprises at least one distillation column;

[0064] The methanol-water solution recovered by the propylene recovery unit accounts for 60-80% of the total methanol-water solution at the outlet of the epoxidation reactor.

[0065] In one embodiment of the present invention, the methanol aqueous solution recovered at the bottom of the crude propylene oxide fraction tower accounts for 20%-30% of the total methanol aqueous solution at the outlet of the epoxidation reactor;

[0066] The purity of the propylene oxide recovered from the top of the crude propylene oxide fractionation tower is greater than 95%.

[0067] In one embodiment of the present invention, the methanol-water solution recovered by the propylene recovery unit and the propylene oxide crude fraction tower contains 75%-90% methanol, 5%-20% water, 0.2%-5% high boiling point impurities, 10ppm-100ppm hydrogen peroxide, 10ppm-50ppm aldehyde and ketone impurities and 1ppm-40ppm nitrogen-containing compounds.

[0068] In one embodiment of the present invention, the propylene oxide refining tower uses a sodium bisulfite aqueous solution as an extractant and a dealdehyde agent, and a propylene oxide product with a purity greater than 99.9% is obtained at the top of the tower.

[0069] In one embodiment of the present invention, the top components of the methanol purification tower include 90%-98% methanol, 2%-10% water, 10ppm-80ppm aldehyde and ketone impurities, and 1ppm-40ppm nitrogen-containing compounds.

[0070] In one embodiment of the present invention, the methanol-water solution at the bottom of the propylene oxide refining tower is recovered by steam stripping and combined with the top material of the methanol purification tower to enter the clay processor.

[0071] In one embodiment of the present invention, the clay processor is filled with clay, and the clay is acidic clay treated with sulfuric acid;

[0072] The acid clay comprises 60%-70% SiO2, 20%-30% Al2O3, 2%-5% Fe2O3 and 1%-5% MgO;

[0073] In the clay processor, the reaction temperature is 60-200℃ and the air velocity is 0.5-10h -1 .

[0074] In one embodiment of the present invention, the MTO reactor is selected from one of an axially fixed bed reactor, a radially fixed bed reactor or a fluidized bed reactor;

[0075] The MTP reactor is selected from one of an axially fixed bed reactor, a radially fixed bed reactor or a fluidized bed reactor.

[0076] In one embodiment of the present invention, the MTO reactor is filled with an MTO catalyst, and the MTO catalyst is selected from one of a SAPO-34 molecular sieve catalyst and a ZSM-5 molecular sieve catalyst;

[0077] The MTP reactor is filled with an MTP catalyst, which is selected from one of a SAPO-34 molecular sieve catalyst and a ZSM-5 molecular sieve catalyst.

[0078] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0079] In the present invention, the terms "first" and "second" are only used to distinguish in description and have no special meaning.

[0080] In the following comparative examples and examples, a titanium silicate molecular sieve catalyst was used as the epoxidation catalyst, a tubular fixed bed reactor was used as the reactor, and the hydrogen peroxide was a 50% aqueous solution obtained by the anthraquinone method.

[0081] Comparative Example 1

[0082] This comparative example provides a process for producing propylene oxide by direct epoxidation of propylene. Figure 1As shown, the epoxidation reaction raw material 1 includes 100 kg / h of hydrogen peroxide and 65 kg / h of fresh propylene, which respectively enter the epoxidation reactor 100 with the first product 3-propylene of the propylene recovery unit and the top product 10-crude methanol of the methanol purification tower. The epoxidation reactor 100 is a shell and tube reactor with a diameter of 1 m and a height of 10 m. The shell and tube reactor tube side adopts circulating cooling water for heat transfer. The epoxidation reaction product 2 includes methanol, propylene, propylene oxide, water and trace impurities. The epoxidation reaction product 2 enters the propylene recovery unit 200. The first product 3-propylene obtained from the propylene recovery unit is circulated to the epoxidation reactor 100. The second product 4-methanol, propylene oxide and water obtained from the propylene recovery unit enter the propylene oxide refining tower 400 to obtain The third product 5 of the propylene recovery unit - methanol aqueous solution enters the methanol purification tower 600; the propylene oxide refining tower 400 is an extractive distillation tower. The extractant in the extractive distillation tower uses water to extract and separate propylene oxide and methanol. The top product 9 - propylene oxide product is obtained at the top of the extractive distillation tower, and the bottom product 8 - methanol aqueous solution is obtained at the bottom of the tower. The methanol aqueous solution also enters the methanol purification tower 600. The methanol purification tower 600 purifies the inflowing methanol aqueous solution, and the top product 10 - crude methanol is obtained at the top of the tower. The crude methanol is recycled to the epoxidation reactor 100, and the bottom product 11 - wastewater is obtained at the bottom of the tower. The wastewater is biochemically treated after recovering major impurities such as propylene glycol and alcohol ether. After 800 hours of reaction in the epoxidation reactor 100, at a reaction temperature of 40° C., the hydrogen peroxide conversion rate dropped to 95%, the propylene oxide selectivity dropped to 90%, the methyl formate content in the propylene oxide product was 1%, the acetaldehyde + propionaldehyde content was 2%, and the methylal content was 1%. The purity of the crude methanol (recycled methanol in this comparative example) was only 95%, which contained a large amount of accumulated impurities, such as propionaldehyde, acetone, acetaldehyde, etc.

[0083] Comparative Example 2

[0084] This comparative example provides a process for producing propylene oxide by direct epoxidation of propylene. Figure 2 As shown, Comparative Example 1 was repeated, except that the third product 5 of the propylene recovery unit, a methanol aqueous solution, and the bottom product 8 of the propylene oxide refining column, a methanol aqueous solution, were first introduced into a methanol hydrogenation unit 500 for impurity treatment, and then the methanol hydrogenation unit product 14 was further transferred to a methanol purification tower 600. In this case, the methanol hydrogenation unit 500 employed the method described in patent CN1294125C. Similarly, after 800 hours of reaction in the epoxidation reactor 100 at a reaction temperature of 40°C, the hydrogen peroxide conversion rate dropped to 97%, the propylene oxide selectivity dropped to 92%, and the propylene oxide product had a methyl formate content of 120 ppm, acetaldehyde + propionaldehyde contents of 900 ppm, and methylal contents of 100 ppm.

[0085] Example 1

[0086] This embodiment provides a process for producing propylene oxide by direct oxidation of propylene and methanol to olefins. Figure 3 As shown, the epoxidation reaction raw material 1 includes 100 kg / h of hydrogen peroxide and 300 kg / h of fresh methanol, which enter the epoxidation reactor 100 together with the first product 3-propylene of the propylene recovery unit and the reflux product 13-propylene of the MTO reactor, respectively. The obtained epoxidation reaction product 2 is separated by the propylene recovery unit 200, and the third product 5-methanol aqueous solution of the propylene recovery unit with a flow rate of 280 kg / h enters the methanol purification tower 600; the second product 4-methanol of the propylene recovery unit, propylene oxide and water enter the propylene oxide crude fraction tower 300 for separation, and the top of the tower is obtained with a purity of 9 The 7.5% crude propylene oxide overhead product 7, which contains trace amounts of methanol, then enters the propylene oxide refining tower 400 for refining. The propylene oxide refining tower 400 uses an aqueous sodium bisulfite solution as an extractant and a de-aldehyde agent to extract and separate propylene oxide and methanol. The propylene oxide refining tower overhead product 9, which is a propylene oxide product (with a purity greater than 99.9%), is obtained at the top of the tower. The propylene oxide refining tower bottom product 8, which is an aqueous solution containing a small amount of methanol, is obtained at the bottom of the tower. The aqueous solution containing a small amount of methanol is directly sent to the wastewater treatment process.

[0087] At the bottom of the crude propylene oxide fraction tower 300, 90 kg / h of 6-methanol aqueous solution as the bottom product of the crude propylene oxide fraction tower is obtained. The 6-methanol aqueous solution as the bottom product of the crude propylene oxide fraction tower and the third product 5-methanol aqueous solution from the propylene recovery unit are fed into the methanol purification tower 600. The mixed methanol aqueous solution contains 80% methanol, 16% water, 3% high-boiling impurities such as propylene glycol and 1-methoxy-2-propanol, 150 ppm of hydrogen peroxide, 40 ppm of propionaldehyde and acetone, 11 ppm of total nitrogen, and trace amounts of nitrogen brought in by the raw methanol. The amount of ethanol impurities; methanol and water and high-boiling point impurities are separated by a methanol purification tower 600, and a methanol purification tower top product 10-crude methanol with a purity of 99.5% is obtained at the top of the tower, and a methanol purification tower bottom product 11-wastewater containing trace water, aldehydes, ketones and nitrogen-containing compounds is obtained at the bottom of the tower. The wastewater is biochemically treated after recovering major impurities such as propylene glycol and alcohol ethers; the crude methanol enters a reactor filled with bleaching clay from the top of the bleaching clay processor 700 for impurity treatment. The inlet temperature of the bleaching clay processor 700 is 120°C and the methanol space velocity is 2h -1The nitrogen content of the clay processor product 12 obtained after treatment is 1.4ppm, and the aldehyde and ketone content is 10ppm. The clay processor product 12-treated methanol directly enters the MTO reactor 800 as a reaction raw material, wherein the MTO reactor 800 is a small fixed fluidized bed reactor, and the MTO reactor 800 is filled with SAPO-34 catalyst. The reaction temperature is 480°C, the reaction pressure is 0.25MPaG, and the reaction space velocity is 2h -1 By fine-tuning the reaction temperature, the ratio of the MTO reactor product - propylene / ethylene can be adjusted to 1.4, and the propylene output is 65 kg / h. The amount of propylene produced just matches the amount of propylene required for the epoxidation reaction. Then the reflux product 13-propylene of the MTO reactor is recycled to the epoxidation reactor 100 as a reaction raw material. Similarly, after 800 hours of reaction in the epoxidation reactor 100, at a reaction temperature of 40 ° C, the hydrogen peroxide conversion rate is still 99.2%, the propylene oxide selectivity is 97.5%, and the methyl formate content in the propylene oxide product is 40 ppm, the acetaldehyde + propionaldehyde content is 80 ppm, and the methylal content is 10 ppm. After the MTO reactor 800 uses the treated methanol treated by the above-mentioned device, by comparing the reaction performance of the catalyst after 40 hours, neither the product selectivity nor the catalyst service life is significantly affected. The effects of using two different methanols (fresh methanol and treated methanol) on the MTO catalyst are shown in Table 1.

[0088] Example 2

[0089] This embodiment provides a process for producing propylene oxide through direct oxidation of propylene and methanol to olefins. The MTO reactor 800 is replaced with an MTP reactor. 240 kg / h of treated methanol treated by the clay processor 700 is used in the MTP reactor as a reaction raw material. The remaining 60 kg / h of treated methanol is recycled to the epoxidation reactor 100. Other processes are the same as those in Example 1. The MTP reactor adopts an axial fixed-bed reactor. The treated methanol first enters a pre-reactor to be converted into dimethyl ether and water, and then enters the axial fixed-bed reactor together with water vapor and C4-C6 circulating hydrocarbons. The axial fixed-bed reactor is equipped with a ZSM-5 molecular sieve catalyst. The reaction temperature is 475°C, the reaction pressure is 0.13 MPaG, and the reaction space velocity is 1 h -1The MTP reactor product had a propylene / ethylene ratio of 5:1 and a propylene yield of 65 kg / h, precisely matching the propylene required for the epoxidation reaction. The reflux product from the MTP reactor was then recycled to the epoxidation reactor 100 as a starting material. Similarly, after 800 hours of reaction in the epoxidation reactor 100 at a reaction temperature of 40°C, the hydrogen peroxide conversion remained at 99.0%, the propylene oxide selectivity was 97.1%, and the propylene oxide product contained 47 ppm of methyl formate, 90 ppm of acetaldehyde and propionaldehyde, and 10 ppm of methylal. Comparison of the catalyst's performance after 200 hours of methanol treatment in the MTP reactor using the aforementioned device revealed no significant impact on either product selectivity or catalyst life. The effects of using two different methanol types (fresh methanol and treated methanol) on the MTP catalyst are shown in Table 1.

[0090] Table 1 Effects of different methanol as reaction raw materials on the results of MTO reaction or MTP reaction

[0091]

[0092] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A process for producing propylene oxide by direct oxidation of propylene and methanol to olefins, characterized in that: The following steps are involved: (S1) an epoxidation reaction raw material enters an epoxidation reactor for an epoxidation reaction to obtain an epoxidation reaction product; (S2) the epoxidation reaction product obtained in step (S1) enters a propylene recovery unit, wherein the propylene obtained is first circulated to the epoxidation reactor, and the methanol, water, and propylene oxide obtained further enter a propylene oxide crude fractionation tower, and finally the methanol-water solution obtained enters a methanol purification tower; (S3) the methanol, water, and propylene oxide obtained in step (S2) are separated in a propylene oxide crude fractionation tower, crude propylene oxide containing trace amounts of methanol is obtained at the top of the tower, which is transferred to a propylene oxide refining tower, and the methanol-water solution obtained at the bottom of the tower enters a methanol purification tower; (S4) The crude propylene oxide obtained in step (S3) is passed through a propylene oxide refining tower to obtain a propylene oxide product at the top of the tower and a methanol aqueous solution at the bottom of the tower, and the methanol aqueous solution is sent to a wastewater treatment process; (S5) After the methanol-water solution obtained in step (S2) and step (S3) enters a methanol purification tower, crude methanol is obtained at the top of the tower and wastewater is obtained at the bottom of the tower. The crude methanol is transferred to a clay processor, and the wastewater enters a wastewater treatment process; (S6) an adsorbent is provided in the clay processor, and the adsorbent adsorbs impurities in the crude methanol obtained in step (S5) to obtain treated methanol, and the treated methanol further enters the MTO reactor or the MTP reactor; (S7) subjecting all or part of the treated methanol obtained in step (S6) to an MTO reaction in an MTO reactor, or subjecting all or part of the treated methanol to an MTP reaction in an MTP reactor to obtain an ethylene product and propylene, and refluxing the propylene to the epoxidation reactor; When a portion of the treated methanol undergoes an MTO reaction in the MTO reactor, or a portion of the treated methanol undergoes an MTP reaction in the MTP reactor, another portion of the treated methanol is recycled to the epoxidation reactor; Among them, the raw materials for the epoxidation reaction are hydrogen peroxide, methanol and propylene.

2. The process for producing propylene oxide by direct oxidation of propylene and methanol to olefins according to claim 1, characterized in that: The epoxidation reactor is filled with an oxidation catalyst; The oxidation catalyst is a titanium silicon molecular sieve catalyst.

3. The process for producing propylene oxide by direct oxidation of propylene and methanol to olefins according to claim 1, characterized in that: The propylene recovery unit includes at least one distillation column; The methanol-water solution recovered by the propylene recovery unit accounts for 60-80% of the total methanol-water solution at the outlet of the epoxidation reactor.

4. The process for producing propylene oxide by direct oxidation of propylene and methanol to olefins according to claim 1, characterized in that: The methanol aqueous solution recovered from the bottom of the crude propylene oxide fraction tower accounts for 20%-30% of the total methanol aqueous solution at the outlet of the epoxidation reactor; The purity of the propylene oxide recovered from the top of the crude propylene oxide fractionation tower is greater than 95%.

5. The process for producing propylene oxide by direct oxidation of propylene and methanol to olefins according to claim 1, characterized in that: The methanol-water solution recovered by the propylene recovery unit and the propylene oxide crude fraction tower contains 75%-90% methanol, 5%-20% water, 0.2%-5% high boiling point impurities, 10ppm-100ppm hydrogen peroxide, 10ppm-50ppm aldehyde and ketone impurities and 1ppm-40ppm nitrogen-containing compounds.

6. The process for producing propylene oxide by direct oxidation of propylene and methanol to olefins according to claim 1, characterized in that: The propylene oxide refining tower uses sodium bisulfite aqueous solution as the extractant and dealdehyde agent, and propylene oxide with a purity greater than 99.9% is obtained at the top of the tower.

7. The process for producing propylene oxide by direct oxidation of propylene and methanol to olefins according to claim 1, characterized in that: The top components of the methanol purification tower include 90%-98% methanol, 2%-10% water, 10ppm-80ppm aldehyde and ketone impurities and 1ppm-40ppm nitrogen-containing compounds.

8. The process for producing propylene oxide by direct oxidation of propylene and methanol to olefins according to claim 1, characterized in that: The methanol-water solution at the bottom of the propylene oxide refining tower is recovered by steam stripping and combined with the material at the top of the methanol purification tower to enter the clay processor.

9. The process for producing propylene oxide by direct oxidation of propylene and methanol to olefins according to claim 1, characterized in that: The clay processor is filled with clay, and the clay is acidic clay treated with sulfuric acid; The acid clay comprises 60%-70% SiO2, 20%-30% Al2O3, 2%-5% Fe2O3 and 1%-5% MgO; In the clay processor, the reaction temperature is 60-200℃ and the air velocity is 0.5-10h -1 .

10. The process for producing propylene oxide by direct oxidation of propylene and methanol to olefins according to claim 1, characterized in that: The MTO reactor is filled with an MTO catalyst, which is selected from one of a SAPO-34 molecular sieve catalyst and a ZSM-5 molecular sieve catalyst; The MTP reactor is filled with an MTP catalyst, which is selected from one of a SAPO-34 molecular sieve catalyst and a ZSM-5 molecular sieve catalyst.

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