KR102138648B1 - A process for refining propylene oxide - Google Patents

Abstract

The present invention is (1) propylene, propylene oxide, a solution containing an organic solvent and water, and a first extraction agent, an aqueous solution of an organic solvent is sent to a first extraction-rectification column to perform separation, wherein the first extraction- The rectification conditions in the rectification column are that the propylene-rich column top product is obtained from the column top of the first extraction-rectification column, and the propylene oxide, organic solvent and water-rich column bottom product is the bottom column of the first extraction-rectification column. Characterized in that it is adjusted to obtain from; And (2) separating the column bottom product rich in propylene oxide, organic solvent and water obtained from the column bottom of the first extraction-rectification column to obtain a solution containing propylene oxide product and organic solvent and water. The present invention relates to a method for purifying propylene oxide. The method of the present invention has low energy consumption, simple technical process and high propylene oxide yield.

Description

Method for purifying propylene oxide {A PROCESS FOR REFINING PROPYLENE OXIDE}

The present invention relates to a method for purifying propylene oxide.

Currently, the process for producing propylene oxide mainly includes chlorohydrination, co-oxidation and direct-oxidation. Chlorohydrination and co-oxidation have disadvantages such as high cost and contamination. Direct-oxidation is a method of synthesizing propylene oxide by direct oxidation of propylene with a hydrogen dioxide solution in the presence of a Ti/Si molecular sieve catalyst. Direct-oxidation has advantages such as mild reaction conditions, simple technical processes, good product selectivity and environmentally friendly effects. Therefore, direct-oxidation of synthesizing propylene oxide by catalytic oxidation of propylene in the presence of a Ti/Si molecular sieve catalyst is considered to be a trend in propylene oxide synthesis technology.

In direct epoxidation of propylene and hydrogen dioxide solutions, large amounts of methanol are commonly used as solvents to dissolve excess propylene in the methanol solution and react with the hydrogen dioxide solution, thus higher hydrogen dioxide conversion and higher propylene oxide selectivity Can be guaranteed. However, in conditions to obtain high selectivity, a large amount of recycled solvent is also present in the reaction product. That is, the reaction product contains water, unreacted propylene, and a small amount of various kinds of impurities such as aldehyde, ether, alcohol, and ketone, as well as a large amount of organic solvent. Therefore, purification of propylene oxide becomes very difficult. Moreover, in rectification separation, propylene oxide can react with water and other hydroxyl-containing materials at higher temperatures to form impurities such as ethers, making purification of propylene oxide more difficult.

US5599955A discloses a method for the separation of direct epoxidation products. A mixture containing a large amount of solvent, unreacted propylene, propylene oxide, water and other impurities obtained from direct epoxidation can be separated and purified through a continuous distillation step. In the first distillation step, the reaction product is separated into a column top product containing propylene oxide, propylene and/or propane, and oxygen gas, and a column bottom product containing solvent, water and impurities. In order to obtain a lighter component column top product such as propylene and/or propane, and a column bottom product of crude propylene oxide, it is necessary that the column top product is further separated in a second distillation step.

US6024840A discloses a method for directly separating epoxidation products. The reaction product from the epoxidation reactor is first fed to a rectifying column, the column top pressure is 15-50 psi, the column bottom temperature is 80-110°C, the reflux ratio is 10-30:1, and the number of column plates is 20 -60. A mixture containing most impurities such as methanol, water and acetaldehyde is obtained from the bottom of the column, and a mixture containing propylene oxide, propylene and a small amount of methanol and acetaldehyde is obtained from the top of the column.

EP2168953A1 discloses an improved method for the separation of direct epoxidation products. The reaction product from the epoxidation reactor is fed to a rectifying column, a mixture of propylene oxide, propylene and a small amount of methanol is obtained from the top of the column, and a mixture of a large amount of methanol, water and impurities is obtained from the bottom of the column.

US2004/0192945A1 discloses a process for the separation of direct epoxidation products characterized in that unreacted propylene is absorbed directly by the reaction product through one-step rectification or recycled methanol and then returned to the reaction system. In the disclosed method, the epoxidation product from the main-reactor or post-reactor first passes through a propylene separation column, where propylene gas containing no propylene oxide is obtained from the top of the column, propylene oxide, methanol, water and other impurities A stream containing is obtained from the bottom of the column. Propylene gas containing a small amount of oxygen gas from the top of the column is absorbed by the bottom of the column or recycled methanol. After most of the propylene is absorbed, the remaining oxygen gas and a small amount of propylene are released. Operating parameters such as temperature, pressure and theoretical plate number for the propylene separation column are not disclosed, but the separation column operating pressure is less than 450 kPa, the column top temperature is about 0-15° C., and the column bottom temperature is 110-135° C. And theoretically it can be easily calculated that the number of plates is less than 20 from the column top stream to the composition of the column bottom stream. Furthermore, since the column bottom temperature in the propylene separation column is relatively high (110-135° C.), propylene oxide will form a large amount of by-products at higher temperatures, which will result in reduced propylene oxide yield.

In summary, in order to inhibit the reaction of propylene oxide and water or hydroxyl-containing materials at higher temperatures in the separation process of the direct epoxidation product, the conventional separation process substantially eliminates propylene oxide along the epoxidation reactor. 1 Adopt a separation method that discharges with propylene from the column top of the distillation column to reduce the residence time and operating temperature of propylene oxide in the column as much as possible to avoid side reactions between propylene oxide and alcohol/water and improve propylene oxide yield. However, since the column top stream in the first distillation column contains a large amount of propylene oxide and propylene and some solvent, it is necessary to separate the propylene from the propylene oxide and solvent through the propylene separation column. Furthermore, the propylene stream needs to be treated to remove the accompanying propylene oxide before it is compressed after it has been discharged and partially condensed from the column top of the propylene separation column. Therefore, it is necessary to mount a propylene oxide absorption column. This type of propylene oxide purification and separation process has a long process flow and requires many devices. Moreover, the condensation of the column top product requires a large amount of cooling water, so the energy consumption is relatively high. Further, in the method disclosed in US2004/0192945A1, propylene oxide is discharged from the bottom of the column, but the column bottom temperature of the propylene separation column is relatively high (110-135°C), resulting in reduced propylene oxide yield.

It is an object of the present invention to provide a method for purifying propylene oxide, which can effectively reduce propylene oxide yield loss in a purification process, and has a short process flow and low energy consumption.

The present invention

(1) propylene, propylene oxide, a solution containing an organic solvent and water, and a step of performing separation by sending an aqueous solution of an organic solvent as a first extraction agent to a first extraction-rectification column, in the first extraction-rectification column Rectification conditions are such that a propylene-rich column top product is obtained from the column top of the first extraction-rectification column and a propylene oxide, organic solvent and water-rich column bottom product is obtained from the column bottom of the first extraction-rectification column. Characterized by being adjusted; And

(2) separating the propylene oxide, organic solvent and water-rich column bottom product obtained from the column bottom of the first extraction-rectifying column to obtain a solution containing propylene oxide product and organic solvent and water.

It provides a method for purifying propylene oxide comprising a.

The present invention also

(0) sending propylene and hydrogen peroxide as a feedstock mixed and dissolved in an organic solvent to a reactor, and epoxidizing through at least one catalyst layer to produce a reaction product;

(1) a reaction product from the reactor outlet containing propylene, propylene oxide, an organic solvent and water, and an aqueous solution of an organic solvent as a first extractant is sent to a first extraction-rectification column to perform separation, wherein The rectification conditions in the first extraction-rectification column include: a propylene-rich column top product is obtained from the column top of the first extraction-rectification column, and a propylene oxide, organic solvent and water-rich column bottom product is the first extraction-rectification. Characterized by being adjusted to be obtained from the column bottom of the column; And

(2) separating the column bottom product rich in propylene oxide, organic solvent and water obtained from the bottom of the column of the first extraction-rectification column to obtain a solution containing propylene oxide product and organic solvent and water. It provides a method for producing and purifying propylene oxide.

In the present invention, during the purification of propylene oxide, in order to obtain a column bottom product rich in propylene oxide, organic solvent and water from the column bottom of the first extraction-rectification column, the column bottom temperature of the first extraction-rectification column is only 45. It only needs to be adjusted to -100°C. Thus, the method of the present invention avoids the reaction of propylene oxide with water or hydroxyl-containing materials at higher temperatures and reduces the loss of propylene oxide yield. Therefore, the method of the present invention has a simple technical process, effectively saves energy consumption, and is therefore very suitable for industrial use.

According to the present invention, there is provided a method for purifying propylene oxide, which can effectively reduce propylene oxide yield loss in a purification process, and has a short process flow and low energy consumption.

The invention is further described using the drawings, which are part of the description herein. The drawings are used below to describe the present invention in conjunction with specific ways to implement the present invention, but do not limit the scope of the present invention in any way.
1 shows a flow chart for purifying propylene oxide in a preferred embodiment;
2 shows a flow chart for purifying propylene oxide in another preferred embodiment;
3 shows a flow chart for purifying propylene oxide in another preferred embodiment; here
T1: first extraction-rectification column
T2: Second rectification column
T3: Third rectification column
T4: fourth rectifying column;
T5: fifth rectifying column;
T6: Sixth rectification column.

Hereinafter, embodiments of the present invention will be described in detail. It should be understood that the described embodiments are only for the purpose of illustrating and describing the present invention, and do not limit the scope of the present invention in any way.

The present invention

(1) propylene, propylene oxide, a solution containing an organic solvent and water, and a step of performing separation by sending an aqueous solution of an organic solvent as a first extraction agent to a first extraction-rectification column, in the first extraction-rectification column Rectification conditions are such that a propylene-rich column top product is obtained from the column top of the first extraction-rectification column and a propylene oxide, organic solvent and water-rich column bottom product is obtained from the column bottom of the first extraction-rectification column. Characterized by being adjusted; And

(2) separating the propylene oxide, organic solvent and water-rich column bottom product obtained from the column bottom of the first extraction-rectifying column to obtain a solution containing propylene oxide product and organic solvent and water.

It provides a method for purifying propylene oxide comprising a.

The present invention also

(0) sending propylene and hydrogen peroxide as a feedstock mixed and dissolved in an organic solvent to a reactor, and epoxidizing through at least one catalyst layer to produce a reaction product;

(1) a reaction product from the reactor outlet containing propylene, propylene oxide, an organic solvent and water, and an aqueous solution of an organic solvent as a first extractant is sent to a first extraction-rectification column to perform separation, wherein The rectification conditions in the first extraction-rectification column include: a propylene-rich column top product is obtained from the column top of the first extraction-rectification column, and a propylene oxide, organic solvent and water-rich column bottom product is the first extraction-rectification. Characterized by being adjusted to be obtained from the column bottom of the column; And

(2) separating the column bottom product rich in propylene oxide, organic solvent and water obtained from the bottom of the column of the first extraction-rectification column to obtain a solution containing propylene oxide product and organic solvent and water. It provides a method for producing and purifying propylene oxide.

In the present invention, the hydrogen peroxide feedstock is used in the form of an aqueous solution containing 5-75% hydrogen peroxide, preferably a hydrogen peroxide product containing 20%-55% hydrogen peroxide produced by an anthraquinone process. The propylene feedstock may contain 0%-15% propane. The organic solvent is a solvent having a boiling point between the boiling point of propylene oxide and the boiling point of water, and includes an alcohol such as methanol, ethanol, or ter-butanol. Preferably, methanol is used as a solvent.

In the present invention, the reactor may be a fixed bed reactor or a slurry bed reactor. The catalyst may be a Ti/Si molecular sieve powder or a wet-bonded Ti/Si molecular sieve catalyst, and the Ti/Si molecular sieve is optionally modified. The catalyst can also be a mixture of modified Ti/Si molecular sieves and non-modified Ti/Si molecular sieves. Hydrogen peroxide and propylene as feedstocks are epoxidized under 10°C-80°C, preferably 25°C-55°C and 1.5 MPa-5.0 MPa. To improve the selectivity to propylene oxide, the organic solvent is preferably used in an amount in which 1 mole of hydrogen peroxide and 1-20 mole of solvent are mixed.

In the present invention, in order to reduce energy consumption and reduce cost, it is preferable that the first extractant is a solution containing organic solvent and water from step (2), partially or wholly.

In the present invention, when a solution containing an organic solvent and water is used as the first extractant, if there is an overplus, in order to further recover the organic solvent, the method of the present invention provides a solution containing the organic solvent and water. It is preferred to further comprise the step of rectifying separation in a fifth rectifying column to produce an organic solvent stream.

In the present invention, it is preferable that the solution containing propylene, propylene oxide, organic solvent and water is a product of propylene oxide production by direct propylene oxidation.

In the present invention, if the solution containing the propylene, propylene oxide, organic solvent and water is a product of the production of propylene oxide by direct propylene oxidation, the method of the present invention provides a method for producing propylene by direct propylene oxidation of the organic solvent stream. Partially or wholly recycled for use as an organic solvent for; And after compressing and removing at least one non-condensable gas such as oxygen and propane, the propylene-rich column top product obtained from the column top of the first extraction-rectification column is subjected to direct propylene oxidation of propylene oxide. It is preferred to further include the step of recycling for use as a reaction feedstock for production. Therefore, the organic solvent and propylene can be effectively used, and an energy saving purpose can be achieved.

In the present invention, the composition of the reaction product containing propylene, propylene oxide, organic solvent and water can be widely selected. In the present invention, the solution containing propylene, propylene oxide, organic solvent and water is 25-80 wt% organic solvent, 5-45 wt% water, 1-15 wt% propylene, 0-5 wt% It is preferred to include propane, 5-25wt% of propylene oxide and the remaining high-boiling organic material.

In the present invention, the object of the present invention can be achieved by the prior technical solution. In the present invention, in order to ensure that the propylene-rich column top product obtained from the column top of the first extraction-rectification column is well recovered and used, the first extraction-rectification conditions in the rectification column are the first extraction- The propylene-rich column top product obtained from the column top of the rectification column is adjusted to have a propylene oxide content of 1 wt% or less, preferably the rectification conditions in the first extraction-rectification column are the columns of the first extraction-rectification column It is preferred that the propylene-rich column top product obtained from the top is adjusted to have a methanol content of 20 wt% or less, preferably 10 wt% or less, more preferably 5 wt% or less.

In the present invention, the rectification conditions in the first extraction-rectification column are 95 wt% or more, preferably 98 wt% or more, more preferably 99 wt% or more of propylene in a solution containing propylene, propylene organoid, organic solvent and water. It is further preferred that the oxide is adjusted to be discharged as a column bottom product of the first extraction-rectification column.

In the present invention, the object of the present invention will be well achieved on the premise that the column bottom product rich in propylene oxide, organic solvent and water is obtained from the column bottom of the first extraction-rectification column. The composition of the aqueous solution of the organic solvent as the first extractant can be widely selected, and the specific composition of the aqueous solution of the organic solvent can be appropriately selected according to actual requirements. In the present invention, in order to further reduce the column bottom temperature of the first extraction-rectification column and to avoid side reactions of propylene oxide at higher temperatures and thus a decrease in yield, an aqueous solution of an organic solvent as the first extraction agent is 10-95. It is preferred to have an organic solvent content of wt%, preferably 40-80 wt%.

In the present invention, the object of the present invention will be well achieved on the premise that the column bottom product rich in propylene oxide, organic solvent and water is obtained from the column bottom of the first extraction-rectification column. The specific amount of the aqueous solution of the organic solvent as the first extractant may be appropriately selected according to actual requirements. In the present invention, in order to further reduce the column bottom temperature of the first extraction-rectification column and to avoid side reactions and yield reduction of propylene oxide at higher temperatures, the amount of aqueous solution of the organic solvent as the first extraction agent versus propylene, It is preferred that the ratio of the amount of the solution containing propylene oxide, organic solvent and water is 0.01-0.5:1, preferably 0.02-0.3:1, more preferably 0.03-0.2:1.

In the present invention, the object of the present invention can be achieved by the technical solutions described above, and the rectification conditions in the first extraction-rectification column can be widely selected and specifically adjusted according to actual requirements. In the present invention, under the conditions of the technical solution described above, the rectification conditions in the first extraction-rectification column generally have a column top pressure of standard atmospheric pressure to 0.5 MPaG, preferably 0.15-0.3 MPaG; Theoretically the number of column plates is 5-45, preferably 10-40; The column top temperature is 40-70°C, preferably 40-55°C; The column bottom temperature is 45-100°C, preferably 50-90°C.

In the present invention, there is no specific limitation on the separation process described in step (2), that is, as long as a solution containing propylene oxide product and organic solvent and water can be obtained by separation, the first extraction-rectification column The column bottom product rich in propylene oxide, organic solvent and water, which is obtained from the bottom of the column, is separated to obtain a solution containing the propylene oxide product and organic solvent and water.

However, in order to further reduce the energy consumption required for the process of the present invention, in a preferred embodiment of the present invention, in step (2) propylene oxide, organic solvent and water obtained from the bottom of the column of the first extraction-rectification column It is preferred that the separation of this rich column bottom product is performed by using the extraction-rectification separation. Specifically, the following steps are performed:

The propylene oxide obtained from the bottom of the column of the first extraction-rectification column, a column bottom product rich in organic solvent and water, and water as a second extractant are sent to a second rectification column to perform separation, and the propylene oxide product is Obtained from the top of the column of the second rectifying column, and a solution containing the organic solvent and water is obtained from the bottom of the column of the second rectifying column.

In the present invention, when the propylene oxide, organic solvent and water-rich column bottom product obtained from the column bottom of the first extraction-rectification column are separated according to the extraction-rectification separation described above, the object of the present invention is well achieved. Can. In the present invention, in order to enable the resulting separated propylene oxide product to be well recovered and used, the rectification separation conditions in the second rectification column are 98 wt% of the propylene oxide product obtained from the column top of the second rectification column. It is further preferable to have the above propylene oxide content.

In the present invention, according to the technical solution described above, the propylene oxide, organic solvent and water-rich column bottom product obtained from the column bottom of the first extraction-rectification column can be well separated. The rectifying separation conditions in the second rectifying column can be widely selected and can be particularly adjusted according to actual requirements. In the present invention, the rectifying separation conditions in the second rectifying column have a column top pressure of standard atmospheric pressure to 1.0 MPaG, and theoretically the number of column plates is 20-50; It is preferred that the column top temperature is 35-115°C, preferably 40-70°C, and the column bottom temperature is 75-110°C, preferably 80-100°C.

In the present invention, an aqueous solution of an organic solvent (such as an aqueous methanol solution) is obtained from the bottom of the column of the second rectifying column. A portion of the resulting aqueous solution of the organic solvent can be recycled to the top of the column of the first extraction-rectification column to be used as the first extractant of the first extraction-rectification column; The remaining portion of the aqueous solution of the organic solvent is sent to a fifth rectifying column and rectified. The epoxidation apparatus so that the column top product (with an organic solvent content (such as methanol) of 95 wt% or more) containing an organic solvent such as methanol obtained from the column top of the fifth rectifying column is used as an organic solvent for propylene epoxidation Can be recycled. A water stream (the stream also contains high-boiling organic material) is obtained from the bottom of the column of the fifth rectifying column and can be further sent to a sewage treatment plant for subsequent treatment for high-boiling organic material recovery.

Preferably, in the combination of the first extraction-rectification column and the second extraction-rectification column, a sixth rectification column may be present between the first extraction-rectification column and the second extraction-rectification column, and the first extraction The column bottom stream of the rectifying column is the feed to the sixth rectifying column, and the column bottom stream of the sixth rectifying column is the feed to the second extraction-rectifying column. In this embodiment, the sixth rectification column is a conventional rectification column used to remove a small amount of propylene from the column bottom stream of the first extraction-rectification column, thus further improving the purity of the final propylene oxide product. The operating condition in the sixth rectifying column is that the column top pressure is standard atmospheric pressure to 0.5 MPaG, preferably standard atmospheric pressure to 0.3 MPaG; Theoretically the number of column plates is 10-30, preferably 15-25; The column top temperature is 40-90°C, preferably 40-80°C; The column bottom temperature is 70-100°C, preferably 75-95°C. A gaseous propylene stream containing a small amount of propylene oxide and methanol is obtained from the column top of the sixth rectification column and mixed with propylene gas obtained from the column top of the first extraction-rectification column for further processing. The bottom product of the column that does not contain propylene is obtained from the bottom of the column of the first rectifying column and sent to the second rectifying column for separation.

In order to further reduce the energy consumption required by the process of the invention, in a preferred embodiment of the invention, in step (2) the propylene oxide, organic solvent and water obtained from the bottom of the column of the second extraction-rectification column are Separation of the rich column bottom product is performed using a conventional rectification separation and a combination of the above extraction-rectification separations. Specifically, the following steps are performed:

The propylene oxide, organic solvent and water-rich column bottom product obtained from the bottom of the column of the first extraction-rectification column are rectified and separated in a third rectification column, and the crude propylene oxide containing the organic solvent is removed from the third rectification column. Obtaining from the column top of the, and a solution containing an organic solvent and water from the column bottom of the third rectifying column; And

The crude propylene oxide containing the organic solvent obtained from the column top of the third rectifying column and water as a third extractant are sent to a fourth rectifying column for separation, and the propylene oxide product is top of the column of the fourth rectifying column. And obtaining a solution containing an organic solvent and water from the bottom of the column of the fourth rectifying column.

In the present invention, when the column bottom product rich in propylene oxide, organic solvent and water obtained from the column bottom of the first extraction-rectification column is separated according to the above-described combination of conventional rectification separation and the extraction-rectification separation, The object of the present invention can be achieved well. In the present invention, in order to further reduce the energy consumption in the separation, the crude propylene oxide containing a solvent such as methanol, preferably obtained by rectifying separation conditions in the third rectifying column from the column top of the third rectifying column is 50-. It is adjusted to have a propylene oxide content of 99.5 wt%, preferably 60-80 wt%.

In the present invention, in the present invention, the column bottom product rich in propylene oxide, organic solvent and water obtained from the column bottom of the first extraction-rectification column is subjected to the conventional rectification separation and the above-described combination of the extraction-rectification separation. When separated, the object of the present invention can be achieved well. In the present invention, in order to ensure that the resulting separated propylene oxide product can be recovered and reused well, the rectification separation conditions in the fourth rectification column are preferably 99.5 propylene oxide product obtained from the column top of the fourth rectification column. It is adjusted to have a propylene oxide of wt% or more.

In the present invention, in the present invention, the column bottom product rich in propylene oxide, organic solvent and water obtained from the column bottom of the first extraction-rectification column is subjected to the conventional rectification separation and the above-described combination of the extraction-rectification separation. When separated, the object of the present invention can be achieved well. The rectifying separation conditions in the third rectifying column and the rectifying separation conditions in the fourth rectifying column can be widely selected, and can be particularly adjusted according to actual requirements. In the present invention, under the conditions of the technical solution described above, the rectification separation conditions in the third rectification column have a column top pressure of standard air pressure to 0.8 MPaG, preferably standard air pressure to 0.5 MPaG; Theoretically the number of column plates is 10-60, preferably 20-50; The column top temperature is 40-95°C, preferably 40-80°C, and the column bottom temperature is 70-110°C, preferably 75-100°C; The rectifying separation condition in the fourth rectifying column is: the column top pressure is standard atmospheric pressure to 0.5 MPaG, preferably standard atmospheric pressure to 0.3 MPaG; Theoretically the number of column plates is 10-60, preferably 20-50; The column top temperature is 40-95°C, preferably 40-80°C; It is preferred that the column bottom temperature comprises 75-110°C, preferably 80-100°C.

In the present invention, an aqueous solution of an organic solvent (such as an aqueous methanol solution) is obtained from the column bottom of the third rectifying column. A portion of the resulting aqueous solution of organic solvent is recycled to the top of the column of the first extraction-rectification column to be used as the first extractant of the first extraction-rectification column; The remaining portion of the aqueous solution of the organic solvent is sent to a fifth rectifying column and rectified. The epoxidation apparatus so that the column top product containing organic solvent (such as organic solvent (such as methanol) content of 95 wt% or more) obtained from the column top of the fifth rectifying column is used as an organic solvent for propylene epoxidation Can be recycled. A water stream (the stream also contains high-boiling organic material) is obtained from the bottom of the column of the fifth rectifying column and can be further sent to a sewage treatment plant for subsequent treatment for high-boiling organic material recovery.

In the present invention, an aqueous solution of an organic solvent (such as an aqueous methanol solution) is obtained from the column bottom of the fourth rectifying column. A portion of the resulting aqueous solution of organic solvent is recycled to the top of the column of the first extraction-rectification column to be used as the first extractant of the first extraction-rectification column; The remaining portion of the aqueous solution of the organic solvent is sent to a fifth rectifying column and rectified. The epoxidation apparatus so that the column top product containing organic solvent (such as organic solvent (such as methanol) content of 95 wt% or more) obtained from the column top of the fifth rectifying column is used as an organic solvent for propylene epoxidation Can be recycled. A water stream (the stream also contains high-boiling organic material) is obtained from the bottom of the column of the fifth rectifying column and can be further sent to a sewage treatment plant for subsequent treatment for high-boiling organic material recovery.

Preferably, in the above combination of a first extraction-rectification column, a third conventional rectification column and a fourth extraction-rectification column, a sixth rectification column may be present between the first extraction-rectification column and the third conventional rectification column. And the column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third conventional rectification column. In this embodiment, the sixth rectification column is a conventional rectification column used to remove a small amount of propylene from the column bottom stream of the first extraction-rectification column, thus further improving the purity of the final propylene oxide product. The operating condition in the sixth rectifying column is that the column top pressure is standard atmospheric pressure to 0.5 MPaG, preferably standard atmospheric pressure to 0.3 MPaG; Theoretically the number of column plates is 10-30, preferably 15-25; The column top temperature is 40-90°C, preferably 40-80°C; The column bottom temperature is 70-100°C, preferably 75-95°C. A gaseous propylene stream containing a small amount of propylene oxide and methanol is obtained from the column top of the sixth rectification column and mixed with propylene gas obtained from the column top of the first extraction-rectification column for further processing. The bottom product of the column containing no propylene is obtained from the bottom of the column of the sixth rectifying column and sent to the third rectifying column for separation.

In the present invention, in a rectification column in which an extractant is supplied to perform extraction-rectification separation, the supply position of the extractant is not particularly limited on the premise that the extraction-rectification purpose can be achieved. That is, generally, according to the prior art, the extractant needs to be supplied at a position higher than the feed position of the stream to be separated so that extraction-rectification separation can be achieved well. For example, the extractant is generally fed to the top of the column of the rectifying column, while the stream to be separated can be fed to the middle portion of the rectifying column. In this regard, there are no special requirements in the present invention. For example, in the first extraction-rectification column of the present invention, the reaction product containing propylene, propylene oxide, organic solvent and water can be supplied to the middle portion of the first extraction-rectification column, and the aqueous solution of the organic solvent is It can be fed to the top of the column of the first extraction-rectification column. For other rectifying columns to which the extractant is supplied, for example, the second rectifying column and the fourth rectifying column, the extracting agent may be supplied in a similar manner.

In the present invention, the preferred feed position and the preferred theoretical column plate number of each column is as follows, wherein the number of columns for the feed position or feed position is calculated from the top of the column.

For the first extraction-rectification column (T1), the theoretical column plate number (n10) is 5-45, for example 10-40; The feed position for the stream to be separated is [n10 x n11] ^th column plate to [n10 x n12] ^th column plate; The feed location for the extractant is [n10 x n13] ^th column plate to [n10 x n14] ^th column plate.

For the second extraction-rectification column (T2), theoretically the number of column plates (n20) is 20-50; The feed position for the stream to be separated is [n20 x n21] ^th column plate to [n20 x n22] ^th column plate; The feed location for the extractant is [n20 x n23] ^th column plate to [n20 x n24] ^th column plate.

For the third extraction-rectification column (T3), the theoretical column plate number (n30) is 10-60, for example 20-50; The feed locations for the stream to be separated are [n30 x n31] ^th column plates to [n30 x n32] ^th column plates.

For the fourth extraction-rectification column (T4), the theoretical column plate number (n40) is 10-60, for example 20-50; The feed position for the stream to be separated is [n40 x n41] ^th column plate to [n40 x n42] ^th column plate; The feed location for the extractant is [n40 x n43] ^th column plate to [n40 x n14] ^th column plate.

For the sixth extraction-rectification column (T6), theoretically the number of column plates (n60) is 10-30, for example 15-25; The feed locations for the stream to be separated are [n60 x n61] ^th column plates to [n60 x n62] ^th column plates.

Explanation i ^th column (T _i ) i One 2 3 4 6 Theoretical column plate n _i0 5-45
10-40 20-50 10-60
20-50 10-60
20-50 10-30
15-25 Where to feed the separated stream n _i1 0.06 0.3 0.05 0.1 0 n _i2 0.9 0.8 0.75 0.9 0.8 Where to feed the extractant n _i3 0 0.1 - 0.05 - n _i4 0.5 0.5 - 0.5 -

Note: The symbol [] means "rounding up", eg [7.5] ^th column plate means 8 column plate.

In the present invention, it is preferable that the first extractant is an aqueous solution of an organic solvent. In addition to organic solvents and water, the first extractant also contains a small amount of (<5 wt%, e.g. <1 wt%, <0.1 wt%) such as propylene oxide, propylene, acetaldehyde, acetone, propylene glycol monomethyl ether. , Or <0.01 wt%).

Preferably, the organic solvent is a solvent having a boiling point between the boiling point of propylene oxide and the boiling point of water, including alcohol such as methanol, ethanol or tert-butanol. Preferably methanol is used as the solvent. Preferably, the aqueous solution of the organic solvent as the first extractant has an organic solvent content of 10-95 wt%, more preferably 40-80 wt%.

In the present invention, both the second extracting agent and the third extracting agent are water, including but not limited to demineralized water, distilled water, water, tap water, water and sewage, recycled water, and processed water.

Hereinafter, preferred embodiments of the present invention will be further described with reference to the accompanying drawings. In a preferred embodiment, the solution containing propylene, propylene oxide, organic solvent and water is the reaction product of propylene oxide production by direct propylene oxidation (hereinafter abbreviated to epoxidation product), and the organic solvent is methanol.

According to one embodiment of the present invention, as shown in FIG. 1, the process of the present invention is performed as follows.

A mixture 107 of hydrogen peroxide and propylene as a feedstock and methanol as a solvent enters the epoxy reactor (R1), and is contacted with a Ti/Si molecular sieve catalyst to effect epoxidation to produce a reaction product 101 containing propylene oxide. do. The reaction product 101 contains propylene oxide, methanol, propylene, optionally propane, water, residual hydrogen peroxide and a small amount of byproducts.

The epoxidation product 101 from the epoxy reactor R1 is sent to the first extraction-rectification column T1 from the middle portion of the first extraction-rectification column T1. As a first extractant, an aqueous methanol solution 106 is sent from the top of the first extraction-rectification column T1 to the first extraction-rectification column T1. Extraction-rectification separation is performed in the first extraction-rectification column (T1) (wherein the rectification conditions in the first extraction-rectification column (T1) have a column top pressure of standard atmospheric pressure to 0.5 MPaG, preferably 0.15-0.3) MPaG; theoretically the number of column plates is 5-45, preferably 10-45; column top temperature is 40-70°C, preferably 40-55°C; column bottom temperature is 45-100°C, preferably 50-90°C Phosphorus; the weight ratio of the amount of the aqueous solution of methanol 106 to the amount of the reaction product 101 containing propylene, propylene oxide, organic solvent and water is 0.01-0.5:1, preferably 0.02-0.3:1, more Preferably 0.03-0.2:1; aqueous methanol solution 106 has a methanol content of 10-95 wt%). A propylene-rich column top product 102 is obtained from the column top of the first extraction-rectification column (T1). A column bottom product 103 enriched in propylene oxide, methanol and water is obtained from the column bottom of the first extraction-rectification column (T1). The propylene-rich column top product 102 has a propylene oxide content of 1 wt% or less, preferably 0.5 wt% or less, more preferably 0.1 wt% or less. The propylene-rich column top product 102 is compressed and after removal of a non-condensable base such as oxygen gas and propane (not shown), the reaction feedstock for the production of propylene oxide by direct propylene oxidation (107) ) Can be recycled for use.

The column bottom product 103 enriched in propylene oxide, methanol and water, obtained from the column bottom of the first extraction-rectification column T1, is transferred from the middle portion of the second rectification column T2 to the second rectification column T2. Sent. As the extractant, water 108 is sent from the top of the column of the second rectifying column T2 to the second rectifying column T2. Extraction-rectification separation is performed in the second rectification column (T2) (in the rectification separation conditions in the second rectification column (T2), the column top pressure is standard atmospheric pressure to 1.0 MPaG, theoretically the number of column plates is 20-50), Column top temperature is 35-115°C, preferably 40-70°C; column bottom temperature is 75-110°C, preferably 80-100°C), propylene oxide product 104 (98 wt% or more, Preferably having a propylene oxide content of 99.5 wt% or more) is obtained from the column top of the second rectifying column (T2). An aqueous methanol solution 105 is obtained from the bottom of the column of the second rectifying column T2. A portion of the resulting aqueous methanol solution 105 may be recycled to the top of the column of the first extraction-rectification column T1 so that it is used as the first extraction agent 106 of the first extraction-rectification column.

The rest of the aqueous methanol solution is sent to a fifth rectifying column (T5) for rectification. The methanol-containing column top product 109 (having a methanol content of 95 wt% or more) obtained from the column top of the fifth rectifying column (T5) can be recycled to the epoxidation unit for use as an organic solvent for propylene epoxidation. . A water stream 110 (where the stream also contains a high-boiling organic material) is obtained from the bottom of the column of the fifth rectifying column T5 and is sent to a sewage treatment plant for subsequent treatment for high-boiling organic material recovery. Can be sent additionally.

According to another embodiment of the present invention, as shown in Figure 2, the method of the present invention is performed as follows.

A mixture of hydrogen peroxide and propylene as feedstock and methanol as solvent (207) enters the epoxy reactor (R1), and is contacted with a Ti/Si molecular sieve catalyst to effect epoxidation to produce a reaction product (201) containing propylene oxide. do. The reaction product 201 contains propylene oxide, methanol, propylene, optionally propane, water, residual hydrogen peroxide and a small amount of byproducts.

The epoxidation product 201 from the epoxy reactor R1 is sent to the first extraction-rectification column T1 from the middle portion of the first extraction-rectification column T1. The aqueous methanol solution 206 is sent to the first extraction-rectification column T1 from the column top of the first extraction-rectification column T1. Extraction-rectification separation is performed in the first extraction-rectification column (T1) (wherein the rectification conditions in the first extraction-rectification column (T1) have a column top pressure of standard atmospheric pressure to 0.5 MPaG, preferably 0.15-0.3) MPaG; theoretically the number of column plates is 5-45, preferably 10-40; column top temperature is 40-70°C, preferably 40-55°C; column bottom temperature is 45-100°C, preferably 50-90°C And the weight ratio of the amount of the aqueous solution of methanol 206 to the amount of the reaction product 201 containing propylene, propylene oxide, organic solvent and water is 0.01-0.5:1, preferably 0.02-0.3:1, more Preferably 0.03-0.2:1; aqueous methanol solution 206 has a methanol content of 10-95 wt%). A propylene-rich column top product 202 is obtained from the column top of the first extraction-rectification column T1. A column bottom product 203 rich in propylene oxide, methanol and water is obtained from the column bottom of the first extraction-rectification column (T1). The propylene-rich column top product 202 has a propylene oxide content of 1 wt% or less, preferably 0.5 wt% or less, more preferably 0.1 wt% or less. The propylene-rich column top product 202 is compressed and after removal of a non-condensable base such as oxygen gas and propane (not shown), a reaction feedstock (207) for the production of propylene oxide by direct propylene oxidation. ) Can be recycled for use.

In order to further remove the small amount of propylene contained in the column bottom product 203 of the first extraction-rectification column (T1) and to reduce the propylene content in the purified propylene oxide, the first extraction-rectification column (T1) The column bottom product 203 rich in propylene oxide, methanol and water, obtained from the column bottom, is sent to the sixth rectification column T6 from the column top of the sixth rectification column T6. A small amount of propylene is separated in the sixth rectifying column (T6). The separation condition in the sixth rectifying column (T6) is that the column top pressure is standard atmospheric pressure to 0.5 MPaG, preferably standard atmospheric pressure to 0.3 MPaG; Theoretically the number of column plates is 10-30, preferably 15-25; The column top temperature is 40-90°C, preferably 40-80°C; The column bottom temperature is 70-100°C, preferably 75-95°C. A gaseous propylene stream 211 containing a small amount of propylene oxide and methanol is obtained from the column top of the sixth rectification column (T6) and from the column top of the first extraction-rectification column (T1) for further processing. It is mixed with propylene gas (202). A column bottom product 212 that does not contain propylene is obtained from the column bottom of the sixth rectifying column T6, and is sent to the second rectifying column T2 for separation.

The column bottom product 212 rich in propylene oxide, methanol and water, obtained from the sixth rectifying column T6, is sent to the second rectifying column T2 from the middle portion of the second rectifying column T2. As an extractant, water 208 is sent from the top of the column of the second rectifying column T2 to the second rectifying column T2. Extraction-rectification separation is performed in the second rectification column (T2) (in the rectification separation conditions in the second rectification column (T2), the column top pressure is standard atmospheric pressure to 1.0 MPaG, theoretically the number of column plates is 20-50), Column top temperature is 35-115°C, preferably 40-70°C; column bottom temperature is 75-110°C, preferably 80-100°C), propylene oxide product 204 (98 wt% or more, Preferably having a propylene oxide content of 99.5 wt% or more) is obtained from the column top of the second rectifying column (T2). An aqueous methanol solution 205 is obtained from the bottom of the column of the second rectifying column (T2). A portion of the resulting aqueous methanol solution 205 may be recycled to the top of the column of the first extraction-rectification column T1 to be used as the first extraction agent 206 of the first extraction-rectification column.

The remaining portion of the aqueous methanol solution 205 is sent to the fifth rectifying column T5 to be rectified. The methanol-containing column top product 209 (having a methanol content of at least 95 wt%) obtained from the column top of the fifth rectifying column (T5) can be recycled to the epoxidation unit for use as an organic solvent for propylene epoxidation. . A water stream 210 (where the stream also contains high-boiling organic material) is obtained from the bottom of the column of the fifth rectifying column T5, and to a sewage treatment plant for subsequent treatment for high-boiling organic material recovery. Can be sent additionally.

According to another embodiment of the present invention, as shown in Figure 3, the method of the present invention is performed as follows.

A mixture 307 of hydrogen peroxide and propylene as a feedstock and methanol as a solvent enters the epoxy reactor (R1), and is contacted with a Ti/Si molecular sieve catalyst to effect epoxidation to produce a reaction product 301 containing propylene oxide. do. The reaction product 301 contains propylene oxide, methanol, propylene, optionally propane, water, residual hydrogen peroxide and a small amount of byproducts.

The epoxidation product 301 from the epoxy reactor R1 is sent to the first extraction-rectification column T1 from the middle portion of the first extraction-rectification column T1. The aqueous methanol solution 306 is sent to the first extraction-rectification column T1 from the column top of the first extraction-rectification column T1. Extraction-rectification separation is performed in the first extraction-rectification column (T1) (wherein the rectification conditions in the first extraction-rectification column (T1) have a column top pressure of standard atmospheric pressure to 0.5 MPaG, preferably 0.15-0.3) MPaG; theoretically the number of column plates is 5-45, preferably 10-40; column top temperature is 40-70°C, preferably 40-55°C; column bottom temperature is 45-100°C, preferably 50-90°C And the weight ratio of the amount of the aqueous solution of methanol 306 to the amount of the reaction product 301 containing propylene, propylene oxide, organic solvent and water is 0.01-0.5:1, preferably 0.02-0.3:1, more Preferably 0.03-0.2:1; aqueous methanol solution 306 has a methanol content of 10-95 wt%). A propylene-rich column top product 302 is obtained from the column top of the first extraction-rectification column T1. A column bottom product 303 rich in propylene oxide, methanol and water is obtained from the column bottom of the first extraction-rectification column (T1). The propylene-rich column top product 302 has a propylene oxide content of 1 wt% or less, preferably 0.5 wt% or less, more preferably 0.1 wt% or less. The propylene-rich column top product 302 is compressed and used as a reaction feedstock for the production of propylene oxide by direct propylene oxidation after removal of non-condensable bases such as oxygen gas and propane (not shown). It can be recycled as much as possible.

The column bottom product 303 rich in propylene oxide, methanol and water, obtained from the column bottom of the first extraction-rectification column T1, is transferred from the middle portion of the third rectification column T3 to the third rectification column T3. Sent. Rectification separation is performed in the third rectification column (T3) (the rectification separation conditions in the third rectification column (T3) have a column top pressure of standard atmospheric pressure to 0.8 MPaG, preferably standard atmospheric pressure to 0.5 MPaG; theoretical column Plate number is 10-60, preferably 20-50; column top temperature is 40-95°C, preferably 40-80°C; column bottom temperature is 70-110°C, preferably 75-100°C) . The crude propylene oxide column top product 304 containing a solvent such as methanol (with a propylene oxide content of 50-90 wt%, preferably 60-80 wt%) is obtained from the column top of the third rectifying column (T3). do. A methanol aqueous solution 305 is obtained from the bottom of the column of the third rectifying column (T3). A portion of the resulting aqueous methanol solution 305 may be recycled over the column of the first extraction-rectification column T1 to be used as the first extraction agent 306 of the first extraction-rectification column T1. The rest of the aqueous methanol solution can be sent to a fifth rectifying column (T5) to be rectified.

The crude propylene oxide column top product 304 containing a solvent such as methanol is sent to the fourth rectifying column T4 from the middle of the fourth rectifying column T4. As the extractant, water 308 is sent from the top of the fourth rectifying column T4 to the fourth rectifying column T4. Extraction-rectification separation is performed in the fourth rectification column (T4) (column top pressure is from standard atmospheric pressure to 0.5 MPaG, preferably from standard atmospheric pressure to 0.3 MPaG; theoretically the number of column plates is 10-60, preferably 20-50 ; Column top temperature is 40-95°C, preferably 40-80°C; column bottom temperature is 75-110°C, preferably 80-100°C). A propylene oxide product 309 (having a propylene oxide content of 99.5 wt% or more) is obtained from the column top of the fourth rectifying column (T4). A methanol aqueous solution 310 is obtained from the bottom of the column of the fourth rectifying column (T4). A portion of the resulting aqueous methanol solution 310 may be recycled to the top of the column of the first extraction-rectification column T1 to be used as the first extraction agent 306 of the first extraction-rectification column T1. The remaining portion can be sent to the fifth rectifying column (T5) together with a portion of the aqueous methanol solution (305) obtained from the bottom of the column of the third rectifying column (T3) to be rectified and separated.

The methanol-containing column top product 311 (having a methanol content of 95 wt% or more) obtained from the column top of the fifth rectifying column (T5) can be recycled to an epoxidation device for use as an organic solvent. A water stream 312 (the stream also contains high-boiling organic material) is obtained from the bottom of the column of the fifth rectifying column (T5), and for recovery of the high-boiling material to a sewage treatment plant for subsequent treatment. Can be sent additionally.

According to the third embodiment described above, the method of the present invention can significantly reduce the amount of water used as an extractant, and can effectively reduce the operation cost.

Compared to the prior art, the distinguishing feature of the present invention is that the extraction-rectification is the separation mode in the first column, and propylene, oxide, methanol and water are discharged from the bottom of the column. Under the conditions of the present invention, the pressure in the first extraction-rectification column and the column bottom temperature are low, so that side reactions of propylene oxide at higher temperatures can be effectively suppressed, and propylene oxide yield loss can be reduced. Since most of the propylene oxide is discharged from the bottom of the column of the first extraction-rectification column, the gaseous product from the top of the column of the first extraction-rectification column is substantially free of propylene oxide, is fed directly to the compressor and compressed, After removal of the non-condensable gas, it can be returned to the propylene epoxidation system. Therefore, the separation procedure during propylene oxide purification is greatly simplified, and the device investment and operation cost are reduced.

The method of the present invention has the following advantages: (1) Low energy consumption: the column bottom temperature of the first extraction-rectification column is only 45-100° C., and the subsequent separation procedure is short. Compared to a typical propylene oxide purification process, the total energy consumption can be reduced by about 20% dltkd. (2) Simple technical process: Separation of propylene oxide can be achieved in practically only two extraction-rectification steps. (3) High propylene oxide yield: The operating pressure and temperature in the first extraction-rectification column are low, so that side reactions of propylene oxide can be effectively suppressed.

Example One

This example was performed according to the process flow shown in FIG. 1.

32000 kg of Ti/Si molecular sieve catalyst was loaded into a fixed bed reactor (R1).

Fresh propylene with a flow rate of 22385 kg/h and a purity of 99.6%, a hydrogen dioxide solution with a flow rate of 15721 kg/h and a purity of 50%, and methanol having a flow rate of 62547 kg/h were mixed, and from the bottom of the reactor to the reactor (R1) Supplied. Propylene:hydrogen dioxide solution = 2.3 (molar ratio), the hourly space velocity of hydrogen dioxide is 0.25h ^-1 , methanol:hydrogen dioxide solution = 8.44 (molar ratio). The propylene and hydrogen dioxide solutions were epoxidized to produce propylene oxide in the reactor. The temperature of the fixed bed reactor was 40°C and the reaction pressure was 3.0 MPa (gauge).

T1

The first extraction-rectification column theoretically has a column plate number of 40, the column top pressure is 0.07 MPaG, the column top temperature is 44.2 °C, the column bottom temperature is 79 °C, and the column top of the first extraction-rectification column is without reflux. It worked.

T1 feedstock

Reaction products from the epoxidation reactor (61.61 wt% methanol, 10.66 wt% propylene, 13.43 wt% water, 12.66 wt% propylene oxide, acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and high proportions) Produced by-products such as point compounds; non-condensable gases such as propane and oxygen gas; and small amounts of unreacted hydrogen peroxide) 100653 kg/h was fed to the first extraction-rectification column in the 30th theoretical column plate (column Calculated from the top, the same below).

T1 extractant

First theoretical column in the first extraction-rectification column with 20000 kg/h of an aqueous methanol solution (methanol purity 69.43%) containing impurities such as alcohol and ether, derived from the exit column bottom stream of the second rectification column as the first extractant Plates were fed.

T1 upper

Propylene-rich gas (its composition was 83.56 wt% propylene, 12.35 wt% methanol, 1.26 wt% water, 1.76 wt% propane, 0.81 wt% oxygen gas and small amounts of impurities such as aldehyde and ketone) 12840 kg/h It was obtained from the column top of the extraction-rectification column. This column top gas is treated to remove non-condensable gases such as oxygen gas and propane, then compressed and condensed by a compressor, and then used as a reaction feedstock for the production of propylene oxide by direct propylene oxidation. It can be recycled to the ignition system.

T1 bottom

A stream of 107813 kg/h was withdrawn from the bottom of the column of the first extraction-rectification column (its composition was 68.93 wt% methanol, 17.80 wt% water, 11.82 wt% propylene oxide, and the rest was propylene, acetaldehyde, acetone, propylene glycol , Propylene glycol monomethyl ether, and high boiling point compounds).

T2

The second rectifying column theoretically had a column plate number of 45. The column top pressure was 0.05 MPaG, the column top temperature was 46.1°C, the column bottom temperature was 85°C, and the reflux ratio was 7.

T2 feedstock

After the discharged column bottom stream of the first extraction-rectification column was pumped at an increased pressure, extraction-rectification was performed by feeding the second rectification column from the 25th theoretical column plate.

T2 extractant

Demineralized water at 12000 kg/h was supplied to the second rectifying column as the second extractant from the 15th theoretical column plate.

T2 upper

Purified propylene oxide (propylene oxide purity could reach 99.71 wt%) 12780 kg/h was obtained from the column top of the second rectifying column.

T2 bottom

A stream of 107033 kg/h was discharged from the bottom of the column of the second rectifying column (69.43 wt% methanol, 29.14 wt% water, the rest acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and high boiling point compound) It was the same impurity).

A portion of the discharged column bottom stream of the second rectification column (20000 kg/h) was cooled to 40° C. by a cooler and returned to the first extraction-rectification column for use as a first extractant.

The remainder of the discharged column bottom stream of the second rectification column (87033 kg/h) entered the fifth rectification column and was methanol rectified. The fifth rectification column was a typical methanol rectification column capable of recovering methanol by operating in a single column mode or double-effect rectification well known in the art. The recovered methanol could be returned to the epoxidation apparatus as a solvent.

Using the method of the present invention as described above, the purification system for propylene oxide only required two rectification columns for high purity propylene oxide production. Since the lower column temperature of the first extraction-rectification column was lower, side reactions of propylene oxide at higher temperatures were avoided, and propylene oxide yield was improved. The rectification column reboilers of the first extraction-rectification column and the second rectification column only required low-pressure steam as a high-temperature source, and the upper condenser of the column required cooling by recirculating water rather than working with cooling water. Therefore, the investment cost and operation cost of the entire propylene oxide purification system have been significantly reduced.

Example 2

This example was performed according to the process flow shown in FIG. 2.

Epoxidation was performed in the same manner as in Example 1.

T1

The first extraction-rectification column theoretically has a column plate number of 40, the column top pressure is 0.07 MPaG, the column top temperature is 44.2 °C, the column bottom temperature is 79 °C, and the column top of the first extraction-rectification column is without reflux. It worked.

T1 feedstock

Reaction products from the epoxidation reactor (61.61 wt% methanol, 10.66 wt% propylene, 13.43 wt% water, 12.66 wt% propylene oxide, acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and high proportions of the rest) 100653 kg/h of the produced by-products such as point compounds; non-condensable gases such as propane and oxygen gas; and a small amount of unreacted hydrogen peroxide) were fed to the first extraction-rectification column in the 30th theoretical column plate.

T1 extractant

First theoretical column in the first extraction-rectification column with 20000 kg/h of an aqueous methanol solution (methanol purity 69.5%) containing impurities such as alcohol and ether, derived from the exit column bottom stream of the second rectification column as the first extractant Plates were fed.

T1 upper

Propylene-rich gas (its composition was 84.7 wt% propylene, 11.4 wt% methanol, 1.1 wt% water, 1.8 wt% propane, 0.81 wt% oxygen gas and small amounts of impurities such as aldehydes and ketones) 12600 kg/h first It was obtained from the column top of the extraction-rectification column. This column top gas is treated to remove non-condensable gases such as oxygen gas and propane, then compressed and condensed by a compressor, and then used as a reaction feedstock for the production of propylene oxide by direct propylene oxidation. It could be recycled to the fire apparatus.

T1 bottom

A stream of 108053 kg/h was discharged from the bottom of the column of the first extraction-rectification column (its composition was 68.93 wt% methanol, 17.80 wt% water, 11.82 wt% propylene oxide, 0.057 wt% propylene, and the rest was propylene, acetaldehyde , Impurities such as acetone, propylene glycol, propylene glycol monomethyl ether, and high-boiling compounds).

T6

The sixth rectifying column had a theoretical number of column plates of 10. The column top pressure was 0.05 MPaG, the column top temperature was 72.8°C, the column bottom temperature was 75.7°C, and the column top of the sixth rectifying column was operated without reflux.

T6 feedstock

The discharge of the first extraction-rectification column is performed by pumping the discharged column bottom stream of the first extraction-rectification column to the sixth rectification column in the first theoretical column plate after pumping at an increased pressure. The small amount of propylene contained in the column bottom stream was removed.

T6 upper

Propylene-containing gas stream (its composition was 50.6 wt% methanol, 3 wt% propylene, 4.6 wt% water, 41.2 wt% propylene oxide, and the rest were non-condensable gases such as propane) 3000 kg/h sixth rectification column Was obtained from the top of the column. After further cooling the gaseous column upper stream with an internal circulation cooling water, gas-liquid separation was possible. The separated gas phase product was mixed with the column top gas of the first extraction-rectification column, and the separated liquid product was fed to the sixth rectification column together with the column bottom stream of the first extraction-rectification column (not shown). ).

T6 bottom

A stream of 107912 kg/h was withdrawn from the bottom of the column of the sixth rectifying column (its composition is 69.0 wt% methanol, 17.8 wt% water, 11.8 wt% propylene oxide, the rest is acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl Ether, and impurities such as high-boiling compounds). This column bottom stream was pumped to an increased pressure and then fed to a second rectification column to perform extraction-rectification.

T2

The second rectifying column theoretically had a column plate number of 45. The column top pressure was 0.05 MPaG, the column top temperature was 46.1°C, the column bottom temperature was 84.3°C, and the reflux ratio was 7.

T2 feedstock

After the discharged column bottom stream of the sixth rectification column was pumped at an increased pressure, extraction-rectification was performed by feeding the second rectification column from the 25th theoretical column plate.

T2 extractant

Demineralized water at 12000 kg/h was supplied to the second rectifying column as the second extractant from the 15th theoretical column plate.

T2 upper

12710 kg/h of purified propylene oxide (propylene oxide purity could reach 99.8 wt%) was obtained from the column top of the second rectifying column.

T2 bottom

A stream of 107202 kg/h was withdrawn from the bottom of the column of the second rectifying column (composition is 69.5 wt% methanol, 29.1 wt% water, the rest is acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and high boiling point compounds) It was the same impurity).

A portion of the discharged column bottom stream of the second rectification column (20000 kg/h) was cooled to 40° C. by a cooler and returned to the first extraction-rectification column for use as a first extractant.

The remainder of the discharged column bottom stream of the second rectification column (87202 kg/h) entered the fifth rectification column and was methanol rectified. The fifth rectification column was a typical methanol rectification column capable of recovering methanol by operating in single column mode or double-effect rectification well known in the art. The recovered methanol could be returned to the epoxidation apparatus as a solvent.

Compared to Example 1, one propylene separation column (sixth rectification column) was added in Example 2, which could further remove propylene in the feedstock and increase the purity of the final propylene oxide product.

Example 3

This example was performed according to the process flow shown in FIG. 1.

Epoxidation was performed in the same manner as in Example 1.

T1

The first extraction-rectification column theoretically has a column plate number of 40, the column top pressure is 0.07 MPaG, the column top temperature is 44.2 °C, the column bottom temperature is 75.3 °C, and the column top of the first extraction-rectification column is without reflux. It worked.

T1 feedstock

Reaction products from the epoxidation reactor (61.61 wt% methanol, 10.66 wt% propylene, 13.43 wt% water, 12.66 wt% propylene oxide, acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and high proportions of the rest) 100653 kg/h of the produced by-products such as point compounds; non-condensable gases such as propane and oxygen gas; and a small amount of unreacted hydrogen peroxide) were fed to the first extraction-rectification column in a 35th theoretical column plate.

T1 extractant

First theoretical column in the first extraction-rectification column with 20000 kg/h of aqueous methanol solution (methanol purity 80.14%) containing impurities such as alcohol and ether, derived from the exit column bottom stream of the third rectification column as the first extractant Plates were fed.

T1 upper

Propylene-rich gas (its composition was 79.47 wt% propylene, 16.75 wt% methanol, 1.05 wt% water, 1.67 wt% propane, 0.77 wt% oxygen gas and a small amount of impurities such as aldehydes and ketones) 13500 kg/h It was obtained from the column top of the extraction-rectification column. This column top gas is treated to remove non-condensable gases such as oxygen gas and propane, then compressed and condensed by a compressor, and then used as a reaction feedstock for the production of propylene oxide by direct propylene oxidation. It could be recycled to the fire apparatus.

T1 bottom

A stream of 107153 kg/h was withdrawn from the bottom of the column of the first extraction-rectification column (its composition was 70.72 wt% methanol, 15.88 wt% water, 11.89 wt% propylene oxide, and the rest was propylene, acetaldehyde, acetone, propylene glycol , Propylene glycol monomethyl ether, and high boiling point compounds).

The discharged column bottom stream of the first extraction-rectification column was pumped to an increased pressure, and then sent to a third rectification column to perform preliminary distillation of propylene oxide.

T3

The third rectifying column theoretically had a column plate number of 40. The column top pressure was 0.05 MPaG, the column top temperature was 42.1°C, the column bottom temperature was 81.7°C, and the reflux ratio was 5.5.

T3 feedstock

After the discharged column bottom stream of the first extraction-rectification column was pumped at increased pressure, it was fed to the third rectification column in the 8th theoretical column plate to perform preliminary distillation of propylene.

T3 upper

13500 kg/h of crude propylene oxide was obtained from the top of the column of the third rectification column (its composition was 94.4 wt% propylene oxide, 5.4 wt% methanol, and the rest were minor impurities such as acetaldehyde and acetone).

T3 bottom

A stream of 93653 kg/h was withdrawn from the bottom of the column of the third rectifying column (composition is 80.14 wt% methanol, 18.16 wt% water, the rest is acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and high boiling point compounds) It was the same impurity).

A portion of the discharged column bottom stream of the third rectification column (20000 kg/h) was cooled to 40° C. by a cooler and returned to the first extraction-rectification column for use as a first extractant.

The remainder of the discharged column bottom stream of the third rectification column (73653 kg/h) entered the fifth rectification column and was methanol rectified. The fifth rectification column was a typical methanol rectification column capable of recovering methanol by operating in single column mode or double-effect rectification well known in the art. The recovered methanol could be returned to the epoxidation apparatus as a solvent.

T4

The fourth rectifying column theoretically had a column plate number of 42. The column top pressure was 0.05 MPaG, the column top temperature was 46.2°C, the column bottom temperature was 98.8°C, and the reflux ratio was 2.

T4 feedstock

Extraction-rectification was performed by pumping 13500 kg/h of propylene oxide obtained from the column top of the third rectification column at an increased pressure and then feeding it to the fourth rectification column in the 30th theoretical column plate.

T4 extractant

As a third extractant, 3000 kg/h of demineralized water was supplied to the second rectifying column in the 20th theoretical column plate.

T4 upper

12760 kg/h of purified propylene oxide (propylene oxide purity could reach 99.86 wt%) was obtained from the column top of the fourth rectifying column.

T4 bottom

A stream of 3740 kg/h was withdrawn from the bottom of the column of the fourth rectifying column (19.50 wt% methanol, 80.19 wt% water, the rest acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and high boiling point compound) It was the same impurity). This discharged column bottom stream could also be sent to a fifth rectifying column to recover methanol.

Compared to Example 1, one crude propylene oxide column (third rectification column) was added to Example 3, which reduced the extraction-rectification loading of the fourth rectification column and increased the purity of the final propylene oxide product. .

While various embodiments of the invention have been illustrated and described, it will be apparent that the invention is not limited to these embodiments. Many modifications, variations, modifications, substitutions, and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the invention as set forth in the claims. In addition, it should be emphasized that in the various embodiments described above, technical features can be combined to form a new implementation, as long as the combined technical features do not contradict each other. In addition, as long as the combination is made without departing from the principles of the invention, the various embodiments described above can be randomly combined to form a new embodiment. These combined embodiments will also be apparent to those skilled in the art and are therefore within the scope of the invention.

Claims (55)

(1) A solution containing propylene, propylene oxide, an organic solvent and water, and an aqueous solution of an organic solvent as a first extractant, is sent to a first extraction-rectification column to perform separation, wherein the organic solvent is used as a first extractant. The aqueous solution of has an organic solvent content of 10-95wt%, and the rectification conditions in the first extraction-rectification column are propylene-rich column top products obtained from the column top of the first extraction-rectification column, propylene oxide, organic Characterized in that the solvent- and water-rich column bottom product is adjusted to be obtained from the column bottom of the first extraction-rectification column; And
(2) separating the column bottom product rich in propylene oxide, organic solvent and water obtained from the bottom of the column of the first extraction-rectification column to obtain a solution containing propylene oxide product and organic solvent and water.
Method for purifying propylene oxide comprising a. According to claim 1,
The method according to claim 1, wherein the first extractant is a solution containing, in part or wholly, the organic solvent and water from step (2). According to claim 1,
The method further comprises rectifying and separating the solution containing the organic solvent and water in a fifth rectification column to produce an organic solvent stream. According to claim 2,
The method further comprises rectifying and separating the solution containing the organic solvent and water in a fifth rectification column to produce an organic solvent stream. According to claim 3,
The solution containing propylene, propylene oxide, organic solvent and water is a product of the production of propylene oxide by direct propylene oxidation,
The above method
Partially or wholly recycling the organic solvent stream to be used as an organic solvent for propylene production by direct propylene oxidation; And
Reaction feedstock for the production of propylene oxide by direct propylene oxidation after compressing and removing at least one non-condensable gas from the propylene-rich column top product obtained from the column top of the first extraction-rectification column Recycling to be used as
Method characterized in that it further comprises a. According to claim 4,
The solution containing propylene, propylene oxide, organic solvent and water is a product of the production of propylene oxide by direct propylene oxidation,
The above method
Partially or wholly recycling the organic solvent stream to be used as an organic solvent for propylene production by direct propylene oxidation; And
Reaction feedstock for the production of propylene oxide by direct propylene oxidation after compressing and removing at least one non-condensable gas from the propylene-rich column top product obtained from the column top of the first extraction-rectification column Recycling to be used as
Method characterized in that it further comprises a. The method according to any one of claims 1 to 6,
The solution containing propylene, propylene oxide, organic solvent and water is 25-80 wt% organic solvent, 5-45 wt% water, 1-15 wt% propylene, 0-5 wt% propane, 5- A method comprising 25 wt% propylene oxide and the rest of the high boiling organic material. The method according to any one of claims 1 to 6,
The rectification conditions in the first extraction-rectification column are characterized in that the propylene-rich column top product obtained from the column top of the first extraction-rectification column is adjusted to have a propylene oxide content of 1 wt% or less. The method according to any one of claims 1 to 6,
The method of claim 1, wherein the weight ratio of the amount of the aqueous solution of the organic solvent to the amount of the solution of the propylene, propylene oxide, organic solvent and water as the first extractant is 0.01-0.5:1. The method according to any one of claims 1 to 6,
The rectification conditions in the first extraction-rectification column, the column top pressure is standard atmospheric pressure to 0.5 MPaG, the theoretical number of column plates is 5-45, the column top temperature is 40-70°C, and the column bottom temperature is 45-100°C. Method comprising the. The method according to any one of claims 1 to 6,
The organic solvent is a method characterized in that the organic solvent for the production of propylene oxide by direct propylene oxidation. The method of claim 11,
The organic solvent is methanol. The method according to any one of claims 1 to 6,
The column bottom product rich in propylene oxide, organic solvent and water obtained from the column bottom of the first extraction-rectification column.
The propylene oxide obtained from the bottom of the column of the first extraction-rectification column, a column bottom product rich in organic solvent and water, and water as a second extractant are sent to a second rectification column to perform separation, and the propylene oxide product is Obtaining from a column top of a second rectifying column and a solution containing the organic solvent and water from a column bottom of the second rectifying column
Method characterized in that it is separated by a process comprising a. The method of claim 13,
The method of rectifying separation in the second rectifying column is characterized in that the propylene oxide product obtained from the column top of the second rectifying column is adjusted to have a propylene oxide content of 98 wt% or more. The method of claim 13,
In the second rectifying column, the rectifying separation conditions are: the column top pressure is standard atmospheric pressure to 1.0 MPaG, theoretically the number of column plates is 20-50, the column top temperature is 35-115°C, and the column bottom temperature is 75-110°C. Method comprising the one. The method of claim 14,
In the second rectifying column, the rectifying separation conditions are: the column top pressure is standard atmospheric pressure to 1.0 MPaG, theoretically the number of column plates is 20-50, the column top temperature is 35-115°C, and the column bottom temperature is 75-110°C. Method comprising the one. The method according to any one of claims 1 to 6,
The column bottom product rich in propylene oxide, organic solvent and water obtained from the column bottom of the first extraction-rectification column.
The propylene oxide, organic solvent and water-rich column bottom product obtained from the bottom of the column of the first extraction-rectification column are rectified and separated in a third rectification column, and the crude propylene oxide containing the organic solvent is removed from the third rectification column. Obtaining from the column top of the, and a solution containing an organic solvent and water from the column bottom of the third rectifying column; And
The crude propylene oxide containing the organic solvent obtained from the column top of the third rectifying column and water as a third extractant are sent to a fourth rectifying column for separation, and the propylene oxide product is top of the column of the fourth rectifying column. And a solution containing an organic solvent and water from the bottom of the column of the fourth rectifying column
Method characterized in that it is separated by a process comprising a. The method of claim 17,
The rectification separation condition in the third rectification column is characterized in that the crude propylene oxide containing an organic solvent obtained from the column top of the third rectification column is adjusted to have a propylene oxide content of 50-99.5 wt%. . The method of claim 18,
The rectification separation conditions in the third rectification column are characterized in that the crude propylene oxide containing the organic solvent obtained from the column top of the third rectification column is adjusted to have a propylene oxide content of 60-80 wt%. . The method of claim 17,
The rectification separation conditions in the fourth rectification column are characterized in that the propylene oxide product obtained from the column top of the fourth rectification column is adjusted to have a propylene oxide content of 99.5 wt% or more. The method of claim 18,
The rectification separation conditions in the fourth rectification column are characterized in that the propylene oxide product obtained from the column top of the fourth rectification column is adjusted to have a propylene oxide content of 99.5 wt% or more. The method of claim 19,
The rectification separation conditions in the fourth rectification column are characterized in that the propylene oxide product obtained from the column top of the fourth rectification column is adjusted to have a propylene oxide content of 99.5 wt% or more. The method of claim 17,
The rectifying separation conditions in the third rectifying column are: the column top pressure is standard atmospheric pressure to 0.8 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 70-110°C. That includes;
The rectification separation condition in the fourth rectification column is, the column top pressure is standard atmospheric pressure to 0.5 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 75-110°C. Method comprising the one. The method of claim 18,
The rectifying separation conditions in the third rectifying column are: the column top pressure is standard atmospheric pressure to 0.8 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 70-110°C. That includes;
The rectification separation condition in the fourth rectification column is, the column top pressure is standard atmospheric pressure to 0.5 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 75-110°C. Method comprising the one. The method of claim 19,
The rectifying separation conditions in the third rectifying column are: the column top pressure is standard atmospheric pressure to 0.8 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 70-110°C. That includes;
The rectification separation condition in the fourth rectification column is, the column top pressure is standard atmospheric pressure to 0.5 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 75-110°C. Method comprising the one. The method of claim 20,
The rectifying separation conditions in the third rectifying column are: the column top pressure is standard atmospheric pressure to 0.8 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 70-110°C. That includes;
The rectification separation condition in the fourth rectification column is, the column top pressure is standard atmospheric pressure to 0.5 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 75-110°C. Method comprising the one. The method of claim 21,
The rectifying separation conditions in the third rectifying column are: the column top pressure is standard atmospheric pressure to 0.8 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 70-110°C. That includes;
The rectification separation condition in the fourth rectification column is, the column top pressure is standard atmospheric pressure to 0.5 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 75-110°C. Method comprising the one. The method of claim 22,
The rectifying separation conditions in the third rectifying column are: the column top pressure is standard atmospheric pressure to 0.8 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 70-110°C. That includes;
The rectification separation condition in the fourth rectification column is, the column top pressure is standard atmospheric pressure to 0.5 MPaG, theoretically the number of column plates is 10-60, the column top temperature is 40-95°C, and the column bottom temperature is 75-110°C. Method comprising the one. The method of claim 13,
A sixth rectification column is present between the first extraction-rectification column and the second rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the second rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 13,
A sixth rectification column is present between the first extraction-rectification column and the second rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the second rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 14,
A sixth rectification column is present between the first extraction-rectification column and the second rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the second rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 14,
A sixth rectification column is present between the first extraction-rectification column and the second rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the second rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 15,
A sixth rectification column is present between the first extraction-rectification column and the second rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the second rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 15,
A sixth rectification column is present between the first extraction-rectification column and the second rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the second rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 16,
A sixth rectification column is present between the first extraction-rectification column and the second rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the second rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 16,
A sixth rectification column is present between the first extraction-rectification column and the second rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the second rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 17,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 17,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 18,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 18,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 19,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 19,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 23,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 23,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 24,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 24,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 25,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 25,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 26,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 26,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 27,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 27,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃. The method of claim 28,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.5 MPaG; Theoretically, the number of column plates is 10-30; The column top temperature is 40-90°C; Method comprising the column lower temperature is 70-100 ℃. The method of claim 28,
A sixth rectification column is present between the first extraction-rectification column and the third rectification column;
The column bottom stream of the first extraction-rectification column is the feed to the sixth rectification column, and the column bottom stream of the sixth rectification column is the feed to the third rectification column;
The operating conditions in the sixth rectifying column include a column top pressure of standard atmospheric pressure to 0.3 MPaG; Theoretically, the number of column plates is 15-25; The column top temperature is 40-80°C; Method comprising the column bottom temperature is 75-95 ℃.
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