RU2639872C2 - Method for purifying propylenoxide - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: method includes the following stages: (1) a solution containing a certain amount of propylene, propylenoxide, optional, propane, water and an organic solvent and an aqueous solution of organic solvent as the first extraction reagent comes into the first extraction distillation column, in which the separation is carried out. Rectification conditions in the first extractive distillation column are adjusted so that the enriched propylene product is the top fraction obtained from the top of the first extractive distillation column and a bottom product fraction, which is enriched with propylene oxide, an organic solvent and water, obtained from the bottom of the first extractive distillation column; (2) the product of the lower fraction, which is enriched with propylene oxide, an organic solvent and water and obtained from the bottom of the first extractive distillation column, is separated to obtain a propylenoxide product and a solution containing an organic solvent and water.EFFECT: method according to the present invention provides a low energy consumption, a simple process and a high yield of propylene oxide.23 cl, 3 dwg, 3 ex

Description

FIELD OF THE INVENTION

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

State of the art

The current process for the manufacture of propylene oxide mainly involves chlorohydrination, cooxidation and direct oxidation. Chlorohydrination and cooxidation have disadvantages, such as high cost and degree of contamination. Direct oxidation is a method of synthesizing propylene oxide by direct oxidation of propylene with a hydrogen peroxide solution in the presence of a Ti / Si molecular sieve as a catalyst. Direct oxidation has advantages such as mild reaction conditions, simplicity of the process, good selectivity to the product, and favorable environmental impact. Thus, it is believed that the direct oxidative synthesis of propylene oxide by catalytic oxidation of propylene in the presence of a molecular sieve of Ti / Si as a catalyst represents a trend in the technology of synthesis of propylene oxide.

In the case of direct epoxidation of propylene with a hydrogen peroxide solution, as a rule, a large amount of methanol is used as a solvent so as to dissolve the excess propylene in a methanol solution and react it with a hydrogen peroxide solution, and as a result, an increased degree of conversion of hydrogen peroxide and increased selectivity with respect to propylene oxide. However, according to the conditions for obtaining high selectivity, a large amount of reusable solvent is also present in the reaction product. In other words, the reaction product contains not only water, unreacted propylene and impurities that are present in a small amount and in a wide variety of species, such as aldehydes, ethers, alcohols and ketones, but also a large amount of organic solvent. Thus, purification of propylene oxide becomes very difficult. In addition, in the process of distillation separation, propylene oxide can react with water and other hydroxyl-containing substances at elevated temperatures, forming impurities such as ethers and, accordingly, purification of propylene oxide becomes more difficult.

US Pat. No. 5,599,955A describes a separation process for a direct epoxidation product. The mixture resulting from direct epoxidation, which contains a large amount of solvent, unreacted propylene, propylene oxide, water and other impurities, can be separated and purified using successive distillation steps. 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. It is necessary to carry out additional separation of the product of the upper fraction of the column in the second stage of distillation in order to obtain a product of the upper fraction of the column containing light components such as propylene and / or propane, and the product of the lower fraction of the column containing crude propylene oxide.

US patent US 6024840A describes a separation method for a direct epoxidation product. The reaction product from the epoxidation reactor first enters the distillation column, and the absolute pressure in the upper part of the column is from 15 to 50 psi (from 103.4 to 344.7 kPa), the temperature in the lower part of the column is from 80 to 110 ° C, the reflux coefficient is from 10 to 30: 1, and the number of columns in the column is from 20 to 60. A mixture containing methanol, water and a majority of impurities such as acetaldehyde is obtained from the bottom and a mixture containing propylene oxide, propylene and a small amount of methanol and tsetaldegida obtained from the column top.

EP 2168953A1 describes an improved separation process for a direct epoxidation product. The reaction product from the epoxidation reactor enters a distillation column in which a mixture containing propylene oxide, propylene and a small amount of methanol is obtained from the upper part, while a mixture containing a large amount of methanol, water and impurities is obtained from the lower part.

US patent application US 2004/0192945A1 describes a separation method for a direct epoxidation product, characterized in that the unreacted propylene is directly absorbed by the reaction product in a one-step distillation or recycle methanol and then sent back to the reaction system. In the described methods, the epoxidation product from the main reactor or additional reactor is first passed to a propylene separation column, where gaseous propylene not containing propylene oxide is obtained from the upper part, and a stream containing propylene oxide, methanol, water and other impurities is obtained from the lower part. Propylene gas containing a small amount of gaseous oxygen from the upper part is absorbed by the flow from the lower part or by recycle methanol. After the bulk of the propylene is absorbed, the remaining gaseous oxygen and a small amount of propylene are released. Although technological parameters are not described, such as temperature, pressure and the number of theoretical plates, propylene separation columns, it is easy to calculate, however, that the operating pressure of the separation column is not less than 450 kPa, the temperature in the upper part of the column is from about 0 to 15 ° C, the temperature at the bottom of the column is from 110 to 135 ° C, and the number of theoretical plates is at least 20, based on the composition of the stream from the top of the column and the stream from its bottom. In addition, since the temperature at the bottom of the propylene separation column is relatively high (from 110 to 135 ° C), and propylene oxide forms a large amount of by-products at elevated temperatures, and as a result, a reduced yield of propylene oxide is obtained.

To summarize the above, in order to inhibit the reaction of propylene oxide and water or hydroxyl-containing substances in a method of separating a direct epoxidation product, the previous separation methods mainly adopt a separation mode according to which propylene oxide leaves the upper part of the first distillation column of the next reactor together with propylene epoxidation so that the residence time of propylene oxide in the column and the operating temperature are reduced to a maximum but the extent possible in order to avoid side reactions between alcohols and propylene oxide / water to enhance the yield of propylene oxide. However, since the stream from the top of the first distillation column contains a large amount of propylene oxide and propylene and a small amount of solvent, it is therefore required to be passed through a column for separating propylene, in which the separation of propylene from propylene oxide and the solvent takes place.

In addition, the propylene stream, which, after exiting the top of the propylene separation column, partially condenses, still needs to be processed to separate the captured propylene oxide before compression. Thus, the installation of a column for the absorption of propylene oxide is necessary. A method for purifying and separating propylene oxide of this kind involves a long process flow and requires many devices. In addition, a large amount of chilled water is required to condense the product of the upper fraction of the column, and thus the energy consumption is relatively high. Moreover, although in the methods described in US patent application US 2004/0192945A1, propylene oxide exits from the lower part, the temperature in the lower part of the propylene separation column, however, is relatively high (from 110 to 135 ° C), and as a result This decreases the yield of propylene oxide.

SUMMARY OF THE INVENTION

The objective of the present invention is to provide a method for purifying propylene oxide, with which it is possible to effectively reduce losses and increase the yield of propylene oxide in the cleaning process, as well as to reduce the sequence of technological operations and reduce energy consumption.

The present invention provides a process for purifying propylene oxide, the process comprising the following steps:

(1) a solution containing propylene, propylene oxide, an organic solvent and water, and an aqueous solution of an organic solvent as a first extraction reagent enter the first extraction distillation column in which separation is carried out, and the distillation conditions in the first extraction distillation column are controlled so that the propylene-enriched product of the upper fraction of the column is obtained from the upper part of the first extraction distillation column, and the product of the lower fraction, cat ing enriched with propylene oxide, with an organic solvent and water, is obtained from the bottom of the first extractive distillation column; and

(2) the bottom product, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated to obtain a propylene oxide product and a solution containing an organic solvent and water.

The present invention also provides a process for the manufacture and purification of propylene oxide, the process comprising the following steps:

(0) hydrogen peroxide and propylene as starting materials are mixed and dissolved in an organic solvent, sent to the reactor and introduced into the epoxidation reaction using at least one catalytic layer to obtain a reaction product;

(1) the reaction product from the outlet of the reactor containing propylene, propylene oxide, an organic solvent and water, and an aqueous solution of an organic solvent as a first extraction reagent enter the first extraction distillation column in which separation is carried out, and the distillation conditions in the first extraction distillation column are regulated so that the propylene-enriched product of the upper fraction of the column is obtained from the top of the first extraction distillation column, and the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water, is obtained from the bottom of the first extraction distillation column; and

(2) the bottom product, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated to obtain a propylene oxide product and a solution containing an organic solvent and water.

According to the present invention, during the purification of propylene oxide, the temperature in the lower part of the column of the first extraction distillation column must be controlled exclusively in the range from 45 to 100 ° C to obtain a product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water, from the bottom of the first extraction distillation the columns. Thus, the method according to the present invention prevents the reaction of propylene oxide and water or hydroxyl-containing substances at elevated temperatures and reduces losses, increasing the yield of propylene oxide. Accordingly, the method according to the present invention provides the simplicity of the process and effectively reduces energy consumption, and, thus, it is very suitable for industrial applications.

Description of drawings

The drawings are used to further clarify the present invention and form an integral part of the description of this application. These drawings, together with the following description of specific embodiments of the present invention, are used to explain the present invention, but they do not in any way limit the scope of the present invention.

FIG. 1 is a flow diagram of a propylene oxide purification process in a preferred embodiment;

FIG. 2 is a flow diagram of a propylene oxide purification process in a further preferred embodiment; and

FIG. 3 is a flow diagram of a propylene oxide purification process in a further preferred embodiment;

Where

T1 means a first extraction distillation column;

T2 means a second distillation column;

T3 means a third distillation column;

T4 means a fourth distillation column;

T5 means the fifth distillation column;

T6 means the sixth distillation column.

Specific Embodiments

Embodiments of the present invention will be described in detail below. It should be understood that the described embodiments are presented solely to illustrate and explain the present invention, and they do not in any way limit the scope of the present invention.

The present invention provides a process for purifying propylene oxide, the process comprising the following steps:

(1) a solution containing propylene, propylene oxide, an organic solvent and water, and an aqueous solution of an organic solvent as a first extraction reagent enter the first extraction distillation column in which separation is carried out, and the distillation conditions in the first extraction distillation column are controlled so that the propylene-enriched product of the upper fraction is obtained from the upper part of the first extraction distillation column, and the product of the lower fraction, which both aschen propylene oxide, an organic solvent and water, is obtained from the bottom of the first extractive distillation column; and

(2) the bottom product, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated to obtain a propylene oxide product and a solution containing an organic solvent and water.

The present invention also provides a process for the manufacture and purification of propylene oxide, the process comprising the following steps:

(0) hydrogen peroxide and propylene as starting materials are mixed and dissolved in an organic solvent, sent to the reactor and introduced into the epoxidation reaction using at least one catalytic layer to obtain a reaction product;

(1) the reaction product from the outlet of the reactor containing propylene, propylene oxide, an organic solvent and water, and an aqueous solution of an organic solvent as a first extraction reagent enter the first extraction distillation column in which separation is carried out, and the distillation conditions in the first extraction distillation column are regulated so that the propylene-enriched product of the upper fraction of the column is obtained from the top of the first extraction distillation column, and the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water, is obtained from the bottom of the first extraction distillation column; and

(2) the bottom product, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated to obtain a propylene oxide product and a solution containing an organic solvent and water.

According to the present invention, the hydrogen peroxide starting material is used in the form of an aqueous solution containing from 5% to 75% hydrogen peroxide, preferably a hydrogen peroxide product containing from 20% to 55% hydrogen peroxide manufactured by the anthraquinone method is used. Propylene starting material may contain from 0% to 15% propane. An organic solvent is a solvent having a boiling point between the boiling point of propylene oxide and the boiling point of water and comprising an alcohol such as methanol, ethanol or tert-butanol. The solvent used is preferably methanol.

According to the present invention, the reactor may be a fixed-bed reactor or a three-phase fluidized bed reactor. The catalyst may be a Ti / Si molecular sieve powder, or a supported Ti / Si molecular sieve, where the Ti / Si molecular sieve is optionally modified, can be used as a catalyst. The catalyst may also be a mixture of a modified Ti / Si molecular sieve and an unmodified Ti / Si molecular sieve. Hydrogen peroxide and propylene as starting materials are introduced into the epoxidation reaction at a temperature of from 10 ° C to 80 ° C, preferably from 25 ° C to 55 ° C and at a pressure of from 1.5 MPa to 5.0 MPa. In order to increase the selectivity for propylene oxide, the organic solvent is preferably used in such an amount that the mixture contains 1 mol of hydrogen peroxide and from 1 to 20 mol of solvent.

According to the present invention, in order to reduce energy consumption and lower costs, it is preferable when the first extraction reagent partially or completely is the solution obtained in stage (2) containing an organic solvent and water.

According to the present invention, when a solution containing an organic solvent and water is used as the first extraction reagent, if there is an excess to further regenerate the organic solvent, it is preferable that the method according to the present invention further includes a step in which the solution containing the organic solvent and water, subjected to distillation separation in a fifth distillation column to obtain a stream of organic solvent.

According to the present invention, it is preferable that the solution containing propylene, propylene oxide, an organic solvent and water is a product of the manufacture of propylene oxide by direct oxidation of propylene.

According to the present invention, when a solution containing propylene, propylene oxide, an organic solvent and water is a product of the production of propylene oxide by direct oxidation of propylene, it is preferable that the method according to the present invention further includes stages in which the stream of organic solvent is partially or completely returned and used in as an organic solvent for the manufacture of propylene oxide by direct oxidation of propylene; the propylene-enriched top fraction product obtained from the top of the first extraction distillation column, after compression and separation of at least one non-condensable gas such as oxygen and propane, is returned and used as a starting reaction material for the production of propylene oxide by direct oxidation of propylene. Thus, the organic solvent and propylene can be effectively used, and it becomes possible to achieve the goal of saving energy.

According to the present invention, the composition of the reaction product, which contains propylene, propylene oxide, an organic solvent and water, can be selected within a wide range. According to the present invention, it is preferable that the solution containing propylene, propylene oxide, an organic solvent and water contains from 25 to 80 wt.% Organic solvent, from 5 to 45 wt.% Water, from 1 to 15 wt.% Propylene, from 0 to 5 wt.% Propane, 5 to 25 wt.% Propylene oxide, and the remainder is a high boiling organic substance.

According to the present invention, the purpose of the present invention can be achieved using the technical solutions described above. According to the present invention, in order to properly receive and use the propylene-rich top fraction product obtained from the top of the first extraction distillation column, it is preferable that the distillation conditions in the first extraction distillation column be controlled so that the propylene-rich top fraction product obtained from the top of the first extraction distillation column, has a propylene oxide content of 1 wt.% sludge or less, preferably, the distillation conditions in the first extraction distillation column are controlled so that the propylene-enriched top fraction product obtained from the top of the first extraction distillation column has a methanol content of 20% by mass or less, preferably 10% by mass or less more preferably 5 wt.% or less.

According to the present invention, it is also preferable that the distillation conditions in the first extraction distillation column are controlled in such a way that 95 wt.% Or more, preferably 98 wt.% Or more, more preferably 99 wt.% Or more of propylene oxide in a solution containing propylene, propylene oxide, an organic solvent, and water are released as a product of the bottom fraction of the first extraction distillation column.

According to the present invention, the object of the present invention will be achieved appropriately provided that the bottom product, which is enriched in propylene oxide, an organic solvent and water, is obtained from the bottom of the first extraction distillation column. The composition of the aqueous solution of the organic solvent as the first extraction reagent can be widely selected, and the specific composition of the aqueous solution of the organic solvent can be appropriately selected depending on actual requirements. According to the present invention, in order to further reduce the temperature at the bottom of the column of the first extraction distillation column and to prevent the side reaction of propylene oxide at an elevated temperature and thus increase the yield, it is preferable that the aqueous solution of the organic solvent as the first extraction reagent has an organic solvent content, constituting from 10 to 95 wt.%, preferably from 40 to 80 wt.%.

According to the present invention, the object of the present invention will be achieved appropriately provided that the bottom product, which is enriched in propylene oxide, an organic solvent and water, is obtained from the bottom of the first extraction distillation column. The particular amount of an aqueous solution of an organic solvent used as the first extraction reagent can be appropriately selected depending on actual requirements. According to the present invention, in order to further reduce the temperature at the bottom of the column of the first extraction distillation column and to prevent a side reaction of propylene oxide at an elevated temperature and thus increase the yield, it is preferable that the ratio of the amount of the aqueous solution of the organic solvent used as the first extraction reagent and used the amount of a solution containing propylene, propylene oxide, an organic solvent and water is 0.01-0.5: 1, preferably 0.02-0.3: 1, more preferably 0.03-0.2: 1.

According to the present invention, the objective of the present invention can be achieved by using the technical solutions described above, and the distillation conditions in the first extraction distillation column can be selected within wide limits and can be adjusted in a certain way depending on actual requirements. According to the present invention, under the conditions of the preceding technical solutions, the distillation conditions in the first extraction distillation column typically include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, preferably from 0.15 to 0.3 MPa ; the number of theoretical plates of the column is from 5 to 45, preferably from 10 to 40; the temperature at the top of the column is from 40 to 70 ° C, preferably from 40 to 55 ° C; and the temperature at the bottom of the column is from 45 to 100 ° C, preferably from 50 to 90 ° C.

According to the present invention, there is no particular limitation with respect to the separation process according to the present invention, which is described as step (2), i.e. the bottom product, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated to obtain a propylene oxide product and a solution containing an organic solvent and water, provided that the propylene oxide product and a solution containing an organic solvent and water can be obtained by separation. However, to further reduce the energy consumption required for the method according to the present invention, in a preferred embodiment of the present invention, the separation of the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is carried out in stage (2) by the use of extraction distillation separation. In particular, the following stage is carried out: the product of the lower fraction, which is enriched in propylene oxide, an organic solvent, and water and is obtained from the bottom of the first extraction distillation column, and water, as the second extraction reagent, is supplied to the second distillation column in order to carry out the separation, the propylene oxide product is obtained from the upper part of the second distillation column, and a solution containing an organic solvent and water is obtained from the lower part of the second distillation column.

According to the present invention, the object of the present invention can be achieved appropriately when the bottom product, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated according to the extraction distillation separation described above. According to the present invention, so that the resulting separated propylene oxide product can be recovered and used in an appropriate way, it is also preferable that the distillation separation conditions in the second distillation column are controlled so that the propylene oxide product obtained from the top of the second distillation column has a propylene oxide content constituting 98 wt.% or more.

According to the present invention, using the technical solutions described above, it is possible to appropriately separate the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the lower part of the first extraction distillation column. The distillation separation conditions in the second distillation column can be selected within wide limits, and they can be adjusted in a certain way depending on actual requirements. According to the present invention, it turns out that the conditions of distillation separation in the second distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 1.0 MPa, the number of theoretical plates of the column is from 20 to 50; the temperature at the top of the column is from 35 to 115 ° C, preferably from 40 to 70 ° C; and the temperature at the bottom of the column is from 75 to 110 ° C, preferably from 80 to 100 ° C.

According to the present invention, an aqueous solution of an organic solvent (such as an aqueous solution of methanol) is obtained from the bottom of the second distillation column. A portion of the resulting aqueous solution of the organic solvent can be returned to the top of the first extraction distillation column for use as the first extraction reagent of the first extraction distillation column; the remaining other part of the aqueous solution of the organic solvent is sent to the fifth distillation column, where it is subjected to distillation separation. An overhead product containing an organic solvent such as methanol (having an organic solvent content such as methanol of 95% by weight or more) obtained from the top of the fifth distillation column can be returned to the epoxidation reactor for use as an organic solvent in reactions epoxidation of propylene. The water stream (and this stream also contains a high boiling point organic substance) is obtained from the bottom of the fifth distillation column, and it can then be sent to a wastewater treatment plant to carry out further processing and recover the high boiling point organic matter.

Preferably, in the combination of the first extraction distillation column and the second extraction distillation column described above, a sixth distillation column may be present between the first extraction distillation column and the second distillation column, the stream from the bottom of the first extraction distillation column being the starting material for the sixth distillation column and the stream from the bottom of the sixth distillation column is the starting material for second extraction distillation column. According to this embodiment, the sixth distillation column is an ordinary distillation column, which is used to separate a small amount of propylene from the stream of the bottom of the first extraction distillation column and, thus, to further increase the purity of the final propylene oxide product. Technological conditions in the sixth distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, preferably from normal pressure to 0.3 MPa; the number of theoretical plates of the column is from 10 to 30, preferably from 15 to 25; the temperature at the top of the column is from 40 to 90 ° C, preferably from 40 to 80 ° C, and the temperature at the bottom of the column is from 70 to 100 ° C, preferably from 75 to 95 ° C. A propylene gas stream containing a small amount of propylene oxide and methanol is obtained from the top of the sixth distillation column and mixed with propylene gas obtained from the top of the first extraction distillation column for further processing. The propylene-free product of the lower fraction is obtained from the lower part of the sixth distillation column and sent to the second distillation column to effect separation.

In order to further reduce the energy consumption required for the method according to the present invention, according to a preferred embodiment of the present invention, the separation of the product of the bottom fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is carried out in step (2) by using a combination of ordinary distillation separation and extraction distillation separation. In particular, the following steps are carried out:

the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is subjected to distillation separation in a third distillation column, the crude propylene oxide containing an organic solvent is obtained from the upper part of the third distillation column, and a solution containing an organic solvent and water are obtained from the bottom of the third distillation column;

crude propylene oxide containing an organic solvent obtained from the upper part of the third distillation column, and water as a third extraction reagent is sent to the fourth distillation column to perform separation, the propylene oxide product is obtained from the upper part of the fourth distillation column, and a solution containing an organic solvent and water receive from the bottom of the fourth distillation column.

According to the present invention, when the product of the bottom fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated according to the combination of ordinary distillation separation and extraction distillation separation described above, the object of the present invention can be achieved appropriately. According to the present invention, in order to further reduce the energy consumption during separation, the conditions of the distillation separation in the third distillation column are preferably controlled so that the crude propylene oxide containing a solvent, such as methanol, obtained from the upper part of the third distillation column, has a propylene oxide content of 50 up to 99.5 wt.%, preferably from 60 to 80 wt.%.

According to the present invention, when the bottom product, which is enriched in propylene oxide, an organic solvent and water and is obtained from the bottom of the first extraction distillation column, is separated using the combination of ordinary distillation separation and extraction distillation separation described above, the object of the present invention can be achieved appropriately. According to the present invention, so that the resulting separated propylene oxide product can be properly recovered and reused, the distillation separation conditions in the fourth distillation column are preferably controlled so that the propylene oxide product obtained from the top of the fourth distillation column has a propylene oxide content of 99, 5 wt.% Or more.

According to the present invention, when the product of the bottom fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated according to the combination of ordinary distillation separation and extraction distillation separation described above, the object of the present invention can be achieved appropriately. The distillation separation conditions in the third distillation column and the distillation separation conditions in the fourth distillation column can be selected within wide limits, and they can be adjusted in a certain way depending on actual requirements. According to the present invention, under the conditions of the preceding technical solutions, it is preferable that the conditions of distillation separation in the third distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 0.8 MPa, preferably from normal pressure to 0.5 MPa; the number of theoretical plates of the column is from 10 to 60, preferably from 20 to 50; the temperature at the top of the column is from 40 to 95 ° C, preferably from 40 to 80 ° C, and the temperature at the bottom of the column is from 70 to 110 ° C, preferably from 75 to 100 ° C; The distillation separation conditions in the fourth distillation column include the following: the gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, preferably from normal pressure to 0.3 MPa, the number of theoretical plates of the column is from 10 to 60, preferably from 20 to 50, the temperature at the top of the column is from 40 to 95 ° C, preferably from 40 to 80 ° C, and the temperature at the bottom of the column is from 75 to 110 ° C, more preferably from 80 to 100 ° C.

According to the present invention, an aqueous solution of an organic solvent (such as an aqueous solution of methanol) is obtained from the bottom of the third distillation column. A portion of the resulting aqueous solution of the organic solvent can be returned to the top of the first extraction distillation column for use as the first extraction reagent of the first extraction distillation column; the remaining other part of the aqueous solution of the organic solvent is sent to the fifth distillation column, where it is subjected to distillation separation. An overhead product containing an organic solvent, such as methanol (having an organic solvent, such as methanol, comprising 95 wt.% Or more) obtained from the top of the fifth distillation column can be returned to the epoxidation reactor and used as an organic solvent for epoxidation propylene. The water stream (and this stream also contains a high boiling point organic substance) is obtained from the bottom of the fifth distillation column, and can then be sent to the wastewater treatment plant to carry out further processing and recover the high boiling point organic substance.

According to the present invention, an aqueous solution of an organic solvent (such as an aqueous solution of methanol) is obtained from the bottom of the fourth distillation column. A portion of the resulting aqueous solution of the organic solvent can be returned to the top of the first extraction distillation column for use as the first extraction reagent of the first extraction distillation column; the remaining other part of the aqueous solution of the organic solvent is sent to the fifth distillation column, where it is subjected to distillation separation. The top fraction product containing an organic solvent such as methanol (having an organic solvent content such as methanol of 95% by mass or more) obtained from the top of the fifth distillation column can be returned to the epoxidation reactor for use as an organic solvent in propylene epoxidation reactions. The water stream (and this stream also contains a high boiling point organic substance) is obtained from the bottom of the fifth distillation column, and it can then be sent to a wastewater treatment plant to carry out further processing and recover the high boiling point organic matter.

Preferably, in the combination described above of the first extraction distillation column, the third ordinary distillation column and the fourth extraction distillation column, a sixth distillation column may be present between the first extraction distillation column and the third ordinary distillation column, the stream from the bottom of the first extraction distillation column being the starting material for the sixth distillation column, and flow from the bottom of the sixth re tifikatsionnoy column is the starting material for the third ordinary fractionator. According to this embodiment, the sixth distillation column is an ordinary distillation column that is used to separate a small amount of propylene from the stream from the bottom of the first extraction distillation column and thereby further increase the purity of the final propylene oxide product. Technological conditions in the sixth distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, preferably from normal pressure to 0.3 MPa; the number of theoretical plates of the column is from 10 to 30, preferably from 15 to 25; the temperature at the top of the column is from 40 to 90 ° C, preferably from 40 to 80 ° C, and the temperature at the bottom of the column is from 70 to 100 ° C, preferably from 75 to 95 ° C. A propylene gas stream containing a small amount of propylene oxide and methanol is obtained from the top of the sixth distillation column and mixed with propylene gas obtained from the top of the first extraction distillation column for further processing. The propylene-free product of the lower fraction is obtained from the lower part of the sixth distillation column and sent to the third distillation column to effect separation. According to the present invention, with regard to the distillation column into which the extraction reagent is directed to carry out the extraction distillation separation, the inlet position of the extraction reagent is not limited in a specific way, provided that the purpose of the extraction distillation can be achieved. In other words, as a rule, according to the prior art, the extraction reagent needs to be directed to a higher position, the inlet position of the stream to be separated, so that the extraction distillation separation can be carried out properly. For example, the extraction reagent can typically be directed to the top of the distillation column, while the stream to be separated can be directed to the middle of the distillation column. In this regard, there is no particular requirement according to the present invention. For example, in a first extraction distillation column according to the present invention, a reaction product containing propylene, propylene oxide, an organic solvent and water can be sent to the middle of the first extraction distillation column, and an aqueous solution of the organic solvent can be sent to the top of the first extraction distillation column. As for the other distillation columns into which the extraction reagent enters, such as, for example, a second distillation column and a fourth distillation column, the extraction reagent can be sent in a similar manner.

According to the present invention, the preferred inlet positions and the preferred number of theoretical column plates for each column are determined as follows, wherein the inlet position or column plate number for the inlet position is counted from the top of the column.

For the first extraction distillation column (T1), the number of theoretical plates of the column (n10) is from 5 to 45, for example, from 10 to 40; the inlet position for the shared stream is from the column plate [n10xn11] to the column plate [n10xn12]; and the inlet position for the extraction reagent is from the column plate [n10xn13] to the column plate [n10xn14].

For the second distillation column (T2), the number of theoretical plates of the column (n20) is from 20 to 50; the inlet position for the shared stream is from the column plate [n20xn21] to the column plate [n20xn22]; and the inlet position for the extraction reagent is from the column plate [n20xn23] to the column plate [n20xn24].

For the third distillation column (T3), the number of theoretical plates of the column (n30) is from 10 to 60, for example, from 20 to 50; and the inlet position for the shared stream is from the column plate [n30xn31] to the column plate [n30xn32].

For the fourth distillation column (T4), the number of theoretical plates of the column (n40) is from 10 to 60, for example, from 20 to 50; the inlet position for the shared stream is from the column plate [n40xn41] to the column plate [n40xn42]; and the inlet position for the extraction reagent is from the column plate [n40xn43] to the column plate [n40xn44].

For the sixth distillation column (T6), the number of theoretical plates of the column (n60) is from 10 to 30, for example, from 15 to 25; and the inlet position for the shared stream is from the column plate [n60xn61] to the column plate [n60xn62].

Description Column number i (T _i ) i one 2 3 four 6 The number of theoretical plates of the column n _i0 5-45 10-40 20-50 10-60 20-50 10-60 20-50 10-30 15-25 Inlet position for shared flow n _i1 0.06 0.3 0.05 0.1 0 n _i2 0.9 0.8 0.75 0.9 0.8 Inlet position for extraction reagent n _i3 0 0.1 - 0.05 - n _i4 0.5 0.5 - 0.5 -

Note. Square brackets indicate rounding up; for example, a column plate [7.5] means an eighth column plate.

According to the present invention, it is preferable that the first extraction reagent is an aqueous solution of an organic solvent. In addition to the organic solvent and water, the first extraction reagent may also contain a small amount (less than 5 wt.%, For example, less than 1 wt.%, Less than 0.1 wt.% Or less than 0.01 wt.%) Of impurities, such as propylene oxide , propylene, acetaldehyde, acetone, propylene glycol monomethyl ether. 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 an alcohol such as methanol, ethanol or tert-butanol. The solvent used is preferably methanol. Preferably, the aqueous solution of the organic solvent as the first extraction reagent has an organic solvent content of 10 to 95 wt.%, More preferably 40 to 80 wt.%.

According to the present invention, both the second extraction reagent and the third extraction reagent are water, including, but not limited to, desalinated water, distilled water, network, drinking water, city water, regenerated water and process water.

Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. According to preferred embodiments of the present invention, the solution containing propylene, propylene oxide, an organic solvent and water is a reaction product of the manufacture of propylene oxide by direct oxidation of propylene (hereinafter abbreviated as “epoxidation product”), and the organic solvent is methanol. According to one embodiment of the present invention, which is shown in FIG. 1, the method according to the present invention is as follows.

A mixture of hydrogen peroxide and propylene 107 as a starting material and methanol as a solvent are sent to an epoxidation reactor R1 and brought into contact with a Ti / Si molecular sieve as a catalyst to carry out epoxidation and to obtain a reaction product 101 containing propylene oxide. Reaction product 101 contains propylene oxide, methanol, propylene, optionally propane, water, residual hydrogen peroxide, and a small amount of by-products.

The epoxidation product 101 from the epoxidation reactor R1 is sent to the first extraction distillation column T1 from the middle of the first extraction distillation column T1. An aqueous methanol solution 106 as the first extraction reagent is sent to the first extraction distillation column T1 through the top of the first extraction distillation column T1. Extraction distillation separation is carried out in the first extraction distillation column T1 (wherein the distillation conditions in the first extraction distillation column T1 include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, preferably from 0.15 to 0.3 MPa; the number of theoretical plates of the column is from 5 to 45, preferably from 10 to 40; the temperature at the top of the column is from 40 to 70 ° C, preferably from 40 to 55 ° C; the temperature at the bottom of the column is from 45 to 100 ° C, preferably from 50 to 90 ° C; the mass ratio of the used amount of an aqueous solution of methanol 106 and the used amount of the reaction product 101 containing propylene, propylene oxide, an organic solvent and water is 0.01-0.5: 1, preferably 0.02-0.3: 1, more preferably 0.03-0.2: 1, and the aqueous methanol solution 106 has a methanol content of 10 to 95 wt.%). The propylene-enriched product of the upper fraction 102 is obtained from the upper part of the first extraction distillation column T1. The product of the bottom fraction 103, which is enriched in propylene oxide, methanol and water, is obtained from the bottom of the first extraction distillation column T1. The propylene-enriched product of the upper fraction of the column 102 has a propylene oxide content of 1 mass% or less, preferably 0.5 mass% or less, more preferably 0.1 mass% or less. The propylene-enriched product of the upper fraction of the column 102 after compression and separation of a non-condensable gas, such as oxygen gas and propane (not shown in the drawing), can be returned and used as starting reaction material 107 for the production of propylene oxide by direct oxidation of propylene.

The product of the bottom fraction 103, which is enriched in propylene oxide, methanol and water and is obtained from the bottom of the first extraction distillation column T1, is sent to the second distillation column T2 from the middle of the second distillation column T2. Water 108 as an extraction reagent is sent to the second distillation column T2 from the upper part of the second distillation column T2. Extraction distillation separation is carried out in the second distillation column T2 (the conditions of distillation separation in the second distillation column T2 include the following: gauge pressure in the upper part of the column is from normal pressure to 1.0 MPa, the number of theoretical plates of the column is from 20 to 50; the temperature in the upper part of the column is from 35 to 115 ° C, preferably from 40 to 70 ° C; and the temperature at the bottom of the column is from 75 to 110 ° C, preferably from 80 to 100 ° C), propylene oxide product UKT 104 (having a propylene oxide content of 98 mass% or more, preferably 99.5 mass% or more) is obtained from the top of the second distillation column T2. An aqueous solution of methanol 105 is obtained from the bottom of the second distillation column T2. A portion of the resulting aqueous methanol solution 105 can be returned to the top of the first extraction distillation column T1 and used as the first extraction reagent 106 of the first extraction distillation column.

The remaining other part of the aqueous methanol solution is sent to the fifth distillation column T5, where it is subjected to distillation separation. The methanol-containing product of the upper fraction 109 (having a methanol content of 95 mass% or more) obtained from the upper part of the fifth distillation column T5 can be returned to the epoxidation reactor and used as an organic solvent for the epoxidation of propylene. Water stream 110 (which stream also contains a high boiling point organic substance) is obtained from the bottom of the fifth distillation column T5 and can then be sent to a wastewater treatment plant to carry out further processing and recover the high boiling point organic substance. According to a further embodiment of the present invention, which is shown in FIG. 2, the method according to the present invention is as follows.

A mixture of 207 hydrogen peroxide and propylene as a starting material and methanol as a solvent are sent to an epoxidation reactor R1 and brought into contact with a Ti / Si molecular sieve as a catalyst to carry out epoxidation and obtain a reaction product 201 containing propylene oxide. Reaction product 201 contains propylene oxide, methanol, propylene, optionally propane, water, residual hydrogen peroxide, and a small amount of by-products.

The epoxidation product 201 from the epoxidation reactor R1 is sent to the first extraction distillation column T1 from the middle of the first extraction distillation column T1. An aqueous solution of methanol 206 is sent to the first extraction distillation column T1 from the top of the first extraction distillation column T1. Extraction distillation separation is carried out in the first extraction distillation column T1 (wherein the distillation conditions in the first extraction distillation column T1 include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, preferably from 0.15 to 0.3 MPa; the number of theoretical plates of the column is from 5 to 45, preferably from 10 to 40; the temperature at the top of the column is from 40 to 70 ° C, preferably from 40 to 55 ° C; the temperature at the bottom of the column ranges from 45 to 100 ° C, preferably from 50 to 90 ° C; the mass ratio of the used amount of an aqueous solution of methanol 206 and the used amount of a solution 201 containing propylene, propylene oxide, an organic solvent and water is 0.01-0.5: 1 preferably 0.02-0.3: 1, more preferably 0.03-0.2: 1; and an aqueous solution of methanol 206 has a methanol content of 10 to 95% by weight). The propylene-enriched product of the upper fraction 202 is obtained from the upper part of the first extraction distillation column T1. The product of the bottom fraction 203, which is enriched in propylene oxide, methanol and water, is obtained from the bottom of the first extraction distillation column T1. The propylene-enriched product of the upper fraction of the column 202 has a propylene oxide content of 1 mass% or less, preferably 0.5 mass% or less, more preferably 0.1 mass% or less. The propylene-enriched product of the upper fraction of the column 202 after compression and separation of a non-condensable gas such as oxygen gas and propane (not shown in the drawing) can be returned and used as starting reaction material 207 for the production of propylene oxide by direct oxidation of propylene.

In order to further separate a small amount of propylene contained in the product of the bottom fraction 203 of the first extraction distillation column T1, and to reduce the content of propylene in the purified propylene oxide, the product of the bottom fraction 203, which is enriched in propylene oxide, methanol and water, is obtained from the bottom of the first extraction distillation column T1, sent to the sixth distillation column T6 from the top of the sixth distillation column T6. A small amount of propylene is separated in a sixth distillation column T6. The separation conditions in the sixth distillation column T6 include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, preferably from normal pressure to 0.3 MPa; the number of theoretical plates of the column is from 10 to 30, preferably from 15 to 25; the temperature at the top of the column is from 40 to 90 ° C, preferably from 40 to 80 ° C, and the temperature at the bottom of the column is from 70 to 100 ° C, preferably from 75 to 95 ° C. Propylene gas stream 211, containing a small amount of propylene oxide and methanol, is obtained from the top of the sixth distillation column T6 and mixed with propylene gas 202 obtained from the top of the first extraction distillation column T1 for further processing. The propylene-free product of the lower fraction 212 is obtained from the lower part of the sixth distillation column T6 and sent to the second distillation column T2 to carry out the separation.

The product of the lower fraction 212, which is enriched in propylene oxide, methanol and water and obtained from the sixth distillation column T6, is sent to the second distillation column T2 from the middle of the second distillation column T2. Water 208 as an extraction reagent is sent from the upper part of the second distillation column T2 to the second distillation column T2. Extraction distillation separation is carried out in the second distillation column T2 (the conditions of distillation separation in the second distillation column T2 include the following: gauge pressure in the upper part of the column is from normal pressure to 1.0 MPa, the number of theoretical plates of the column is from 20 to 50; the temperature in the upper part of the column is from 35 to 115 ° C, preferably from 40 to 70 ° C; and the temperature at the bottom of the column is from 75 to 110 ° C, preferably from 80 to 100 ° C). The propylene oxide product 204 (having a propylene oxide content of 98 wt.% Or more, preferably 99.5 wt.% Or more) is obtained from the top of the second distillation column T2. An aqueous methanol solution 205 is prepared from the bottom of the second T2 distillation column. Part of the resulting aqueous methanol solution 205 can be returned to the top of the first extraction distillation column T1 and used as the first extraction reagent 206 of the first extraction distillation column.

The remaining other part of the aqueous methanol solution 205 is sent to the fifth distillation column T5, where it is subjected to distillation separation. The methanol-containing product of the upper fraction 209 (having a methanol content of 95 mass% or more) obtained from the upper part of the fifth distillation column T5 can be returned to the epoxidation reactor and used as an organic solvent for the epoxidation of propylene. Water stream 210 (which stream also contains a high boiling point organic substance) is obtained from the bottom of the fifth distillation column T5 and can then be sent to a wastewater treatment plant to carry out further processing and recover the high boiling point organic substance.

According to a further embodiment of the present invention, which is shown in FIG. 3, the method according to the present invention is as follows.

A mixture of 307 hydrogen peroxide and propylene as a starting material and methanol as a solvent are sent to an epoxidation reactor R1 and brought into contact with a Ti / Si molecular sieve as a catalyst to carry out epoxidation to obtain a reaction product 301 containing propylene oxide. Reaction product 301 contains propylene oxide, methanol, propylene, optionally propane, water, residual hydrogen peroxide, and a small amount of by-products.

The epoxidation product 301 from the epoxidation reactor R1 is sent to the first extraction distillation column T1 from the middle of the first extraction distillation column T1. An aqueous solution of methanol 306 is sent to the first extraction distillation column T1 from the top of the first extraction distillation column T1. Extraction distillation separation is carried out in the first extraction distillation column T1 (wherein the distillation conditions in the first extraction distillation column T1 include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, preferably from 0.15 to 0.3 MPa; the number of theoretical plates of the column is from 5 to 45, preferably from 10 to 40; the temperature at the top of the column is from 40 to 70 ° C, preferably from 40 to 55 ° C; the temperature at the bottom of the column ranges from 45 to 100 ° C, preferably from 50 to 90 ° C; the mass ratio of the used amount of an aqueous solution of methanol 306 and the used amount of a solution 301 containing propylene, propylene oxide, an organic solvent and water is 0.01-0.5: 1 preferably 0.02-0.3: 1, more preferably 0.03-0.2: 1; and an aqueous solution of methanol 306 has a methanol content of 10 to 95% by weight). The propylene-enriched product of the upper fraction 302 is obtained from the top of the first extraction distillation column T1. The product of the bottom fraction 303, which is enriched in propylene oxide, methanol and water, is obtained from the bottom of the first extraction distillation column T1. The propylene-enriched product of the upper fraction of the column 302 has a propylene oxide content of 1 mass% or less, preferably 0.5 mass% or less, more preferably 0.1 mass% or less. Enriched with propylene, the product of the upper fraction of the column 302 after compression and separation of non-condensable gas can be returned and used as a starting reaction material for the production of propylene oxide by direct oxidation of propylene.

The product of the bottom fraction 303, which is enriched in propylene oxide, methanol and water and obtained from the bottom of the first extraction distillation column T1, is sent to the third distillation column T3 from the middle of the third distillation column T3. The distillation separation is carried out in the third distillation column T3 (the conditions of distillation separation in the third distillation column T3 include the following: gauge pressure in the upper part of the column is from normal pressure to 0.8 MPa, preferably from normal pressure to 0.5 MPa; the number of theoretical plates of the column is from 10 to 60, preferably from 20 to 50; the temperature at the top of the column is from 40 to 95 ° C, preferably from 40 to 80 ° C, and the temperature at the bottom of the column is from 70 to 110 ° C, preferably 75 to 100 ° C). The crude propylene oxide product of the upper fraction 304 containing a solvent, such as methanol (having a propylene oxide content of 50 to 90 wt.%, Preferably 60 to 80 wt.%), Is obtained from the top of the third distillation column T3. An aqueous methanol solution 305 is obtained from the bottom of the third T3 distillation column. Part of the resulting aqueous solution of methanol 305 can be returned to the top of the first extraction distillation column T1 and used as the first extraction reagent 306 of the first extraction distillation column T1. Another part of the aqueous methanol solution can be sent to the fifth distillation column T5 and subjected to distillation separation.

The crude propylene oxide product of the upper fraction 304 containing a solvent, such as methanol, is sent from the middle of the fourth distillation column T4 to the fourth distillation column T4. Water 308 as an extraction reagent is sent from the upper part of the fourth distillation column T4 to the fourth distillation column T4. Extraction distillation separation is carried out in the fourth distillation column T4 (gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, preferably from normal pressure to 0.3 MPa, the number of theoretical plates of the column is from 10 to 60, preferably from 20 to 50, the temperature at the top of the column is from 40 to 95 ° C, preferably from 40 to 80 ° C, and the temperature at the bottom of the column is from 75 to 110 ° C, preferably from 80 to 100 ° C). Propylene oxide product 309 (having a propylene oxide content of 99.5 mass% or more) is obtained from the top of the fourth distillation column T4. An aqueous solution of methanol 310 is obtained from the bottom of the fourth distillation column T4. Part of the resulting aqueous solution of methanol 310 can be returned to the top of the first extraction distillation column T1 and used as the first extraction reagent 306 of the first extraction distillation column T1. The other part can be sent to the fifth distillation column T5 together with a part of the aqueous methanol solution 305 obtained from the bottom of the third distillation column T3 in order to be subjected to distillation separation.

The methanol-containing product of the upper fraction 311 (having a methanol content of 95 mass% or more) obtained from the upper part of the fifth distillation column T5 can be returned to the epoxidation reactor and used as an organic solvent. Water stream 312 (which stream also contains a high boiling point organic substance) is obtained from the bottom of the fifth distillation column T5 and can then be sent to a wastewater treatment plant to carry out further processing and recover the high boiling point organic substance. Using the method described above according to the third embodiment, which is the present invention, it is possible to significantly reduce the amount of water used as an extraction reagent, and it is also possible to effectively reduce operating costs.

Compared with the prior art, the distinguishing characteristics of the present invention include extraction distillation as a separation method carried out in the first column and the release of propylene oxide, methanol and water from the bottom. Under the conditions of the present invention, the pressure and temperature at the bottom of the column in the first extraction distillation column are low, so that the side reaction of propylene oxide at elevated temperature can be effectively inhibited, and the loss of propylene oxide yield can be reduced. Since the bulk of the propylene oxide leaves the lower part of the first extraction distillation column, almost no propylene oxide is contained in the gas-phase product from the upper part of the first extraction distillation column, and this product can go directly to the compressor for compression and then return to the propylene epoxidation system after separation of non-condensable gas. Thus, the separation procedure during the purification of propylene oxide is greatly simplified, and equipment investment and operating costs are reduced. The method according to the present invention has the following advantages: (1) low energy consumption: the temperature in the lower part of the column of the first extraction distillation column is only from 45 to 100 ° C, and the subsequent separation procedure is short-lived. Compared to the traditional propylene oxide purification method, the total energy consumption can be reduced by about 20% or more; (2) the simplicity of the process: the separation of propylene oxide can be carried out essentially using only two stages of extraction and rectification; (3) high propylene oxide yield: the operating pressure and temperature in the first extraction distillation column are low, and thus, propylene oxide side reactions can be effectively inhibited.

Example 1

This example was carried out according to the flowchart as shown in FIG. one.

32,000 kg of a Ti / Si molecular sieve as a 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 peroxide solution with a flow rate of 15721 kg / h and a purity of 50%, and methanol with a flow rate of 62547 kg / h were mixed and sent to reactor R1 from the bottom of the reactor. The molar ratio of propylene and hydrogen peroxide in the solution was 2.3, the hourly average feed rate of the hydrogen peroxide solution was 0.25 h ⁻¹ , and the molar ratio of methanol and hydrogen peroxide in the solution was 8.44. Propylene and a hydrogen peroxide solution were introduced into an epoxidation reaction to produce propylene oxide in a reactor. The temperature of the fixed bed reactor was 40 ° C, and the gauge pressure of the reaction mixture was 3.0 MPa.

T1

In the first extraction distillation column, the number of theoretical plates of the column was 40, the gauge pressure at the top of the column was 0.07 MPa, the temperature at the top of the column was 44.2 ° C, the temperature at the bottom of the column was 79 ° C, and the top of the first The extraction distillation column worked without reflux.

Source material T1

100653 kg / h of the reaction product from the epoxidation reactor (its composition contained 1.61 wt.% Methanol, 10.66 wt.% Propylene, 13.43 wt.% Water, 12.66 wt.% Propylene oxide, and the rest was by-product products such as acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and high boiling compounds; non-condensable gas such as propane and oxygen gas; and a small amount of unreacted hydrogen peroxide) were sent to the first extraction distillation column at the thirtieth theoretical plate columns (hereinafter, plates were counted from above).

Extraction reagent T1

20,000 kg / h of an aqueous solution of methanol containing impurities such as alcohols and ethers (methanol purity was 69.43%) and obtained from the stream leaving the bottom of the second distillation column, as the first extraction reagent, was sent to the first extraction distillation column at the first theoretical plate of the column.

Top fraction T1

12840 kg / h of propylene-enriched gas (its composition contained 83.56 wt.% Propylene, 12.35 wt.% Methanol, 1.26 wt.% Water, 1.76 wt.% Propane, 0.81 wt.% Gaseous oxygen and a small amount of impurities such as aldehydes and ketones) were obtained from the top of the first extraction distillation column. This gas from the top of the column, after being treated to separate non-condensable gas such as oxygen gas and propane, and then compressed by a compressor and condensation, could be returned to the epoxidation reactor and used as a starting reaction material for the production of propylene oxide by direct oxidation of propylene.

Lower fraction T1

107813 kg / h of flow was released from the bottom of the first extraction distillation column (its composition contained 68.93 wt.% Methanol, 17.80 wt.% Water, 11.82 wt.% Propylene oxide, and the rest was impurities, such as propylene , acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and compounds having a high boiling point).

T2

The number of theoretical plates of the column in the second distillation column was 45. The gauge pressure in the upper part of the column was 0.05 MPa, the temperature in the upper part of the column was 46.1 ° C, the temperature in the lower part of the column was 85 ° C, and the reflux coefficient was 7 .

Source material T2

The effluent from the bottom of the first extraction distillation column after injection to increase the pressure was directed to the second distillation column at the twenty-fifth theoretical plate of the column to carry out extraction distillation.

Extraction reagent T2

12000 kg / h of desalinated water as a second extraction reagent was sent to the second distillation column at the fifteenth theoretical plate of the column.

Top fraction T2

12780 kg / h of purified propylene oxide were obtained from the upper part of the second distillation column (the propylene oxide purity could reach 99.71 wt.%).

Lower fraction T2

107033 kg / h of the stream was discharged from the bottom of the second distillation column (its composition contained 69.43 wt.% Methanol, 29.14 wt.% Water, and the rest was impurities such as acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether and having high boiling point compounds).

Part of the effluent from the bottom of the second distillation column (20,000 kg / h) was cooled with a cooling device to 40 ° C and returned to the first extraction distillation column for use as a first extraction reagent.

The remaining part of the effluent from the bottom of the second distillation column (87033 kg / h) entered the fifth distillation column, where methanol was distilled.

The fifth distillation column was a traditional methanol distillation column, which could be operated in a single or double distillation mode, well known in the methanol recovery technique. The methanol obtained could be returned to the epoxidation reactor as a solvent.

When using the method according to the present invention, as described above, the propylene oxide purification system essentially required two distillation columns to obtain high purity propylene oxide.

Since the temperature at the bottom of the column of the first extraction distillation column was low, a side reaction of propylene oxide at an elevated temperature was effectively prevented, and an increased yield of propylene oxide was obtained. For reboilers of distillation columns in the first extraction distillation column and in the second distillation column, essentially low pressure steam was required as a heat source, and for the condensers in the upper part of the column, simple cooling with recirculated water rather than using chilled water was required. Thus, the capital and operating costs of the entire propylene oxide purification system were significantly reduced.

Example 2

This example was carried out according to the flowchart as shown in FIG. 2.

Epoxidation was carried out in the same manner as in example 1.

T1

In the first extraction distillation column, the number of theoretical plates of the column was 40, the gauge pressure at the top of the column was 0.07 MPa, the temperature at the top of the column was 44.2 ° C, the temperature at the bottom of the column was 79 ° C, and the top of the first The extraction distillation column worked without reflux.

Source material T1

100653 kg / h of the reaction product from the epoxidation reactor (its composition contained 61.61% by weight of methanol, 10.66% by weight of propylene, 13.43% by weight of water, 12.66% by weight of propylene oxide, and the rest were by-products products such as acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and high boiling compounds; non-condensable gas such as propane and oxygen gas; and a small amount of unreacted hydrogen peroxide) were sent to the first extraction distillation column at the thirtieth theoretical plate columns.

Extraction reagent T1

20,000 kg / h of an aqueous solution of methanol containing impurities such as alcohols and ethers (methanol purity was 69.5%) and obtained from the stream leaving the bottom of the second distillation column as the first extraction reagent was sent to the first extraction distillation the column at the first theoretical plate of the column.

Top fraction T1

12600 kg / h of propylene-enriched gas (its composition contained 84.7 wt.% Propylene, 11.4 wt.% Methanol, 1.1 wt.% Water, 1.8 wt.% Propane, 0.81 wt.% Gaseous oxygen and a small amount of impurities such as aldehydes and ketones) were obtained from the top of the first extraction distillation column. This gas from the top of the column, after being treated to separate non-condensable gas such as oxygen gas and propane, and then compressed by a compressor and condensation, could be returned to the epoxidation reactor and used as a starting reaction material for the production of propylene oxide by direct oxidation of propylene.

Lower fraction T1

From the bottom of the first extraction distillation column, 108053 kg / h of flow was released (its composition contained 68.93 wt.% Methanol, 17.80 wt.% Water, 11.82 wt.% Propylene oxide, 0.057 wt.% Propylene, and the rest was comprised impurities such as acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether and compounds having a high boiling point).

T6

The number of theoretical plates of the column in the sixth extraction distillation column was 10. The gauge pressure in the upper part of the column was 0.05 MPa, the temperature in the upper part of the column was 72.8 ° C, the temperature in the lower part of the column was 75.7 ° C, and the upper part of the sixth distillation column worked without reflux.

Source material T6

The outlet stream from the bottom of the first extraction distillation column after injection to increase the pressure was sent to the sixth distillation column at the first theoretical plate of the column to carry out ordinary distillation to separate a small amount of propylene contained in the effluent from the bottom of the first extraction distillation column.

Top fraction T6

3000 kg / h of propylene-containing gas stream (its composition contained 50.6 wt.% Methanol, 3 wt.% Propylene, 4.6 wt.% Water, 41.2 wt.% Propylene oxide, and the rest was non-condensable gas, such as propane) was obtained from the upper part of the sixth distillation column. This gas-phase flow from the upper part of the column could be further cooled by recirculating cooling water and then directed to the separation of the gas and liquid phases. The separated gas-phase product was mixed with gas from the top of the first extraction distillation column, and the separated liquid-phase product was sent together with the stream from the bottom of the first extraction distillation column to the sixth distillation column (not shown in the drawing).

Lower fraction T6

107912 kg / h of the stream was discharged from the bottom of the sixth distillation column (its composition contained 69.0 wt.% Methanol, 17.8 wt.% Water, 11.8 wt.% Propylene oxide, and the rest was impurities, such as acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and compounds having a high boiling point). This stream from the lower part was pumped to elevated pressure and then sent to a second distillation column to carry out extraction distillation.

T2

The number of theoretical plates of the column in the second distillation column was 45. The gauge pressure in the upper part of the column was 0.05 MPa, the temperature in the upper part of the column was 46.1 ° C, the temperature in the lower part of the column was 84.3 ° C, and the reflux coefficient was 7.

Source material T2

The outlet stream from the bottom of the sixth distillation column after injection to increase the pressure was sent to the second distillation column at the twenty-fifth theoretical plate of the column to carry out extraction distillation.

Extraction reagent T2

12000 kg / h of desalinated water as a second extraction reagent was sent to the second distillation column at the fifteenth theoretical plate of the column.

Top fraction T2

12710 kg / h of purified propylene oxide were obtained from the upper part of the second distillation column (purity of propylene oxide could reach 99.8 wt.%).

Lower fraction T2

From the bottom of the second distillation column, 107,202 kg / h of flow was released (its composition contained 69.5 wt.% Methanol, 29.1 wt.% Water, and the rest was impurities such as acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and having a high boiling point of the compound).

Part of the effluent from the bottom of the second distillation column (20,000 kg / h) was cooled with a cooling device to 40 ° C and returned to the first extraction distillation column for use as a first extraction reagent.

The remaining part of the effluent from the bottom of the second distillation column (87202 kg / h) entered the fifth distillation column, where methanol was distilled.

The fifth distillation column was a traditional methanol distillation column, which could be operated in a single or double distillation mode, well known in the methanol recovery technique. The methanol obtained could be returned to the epoxidation reactor as a solvent.

Compared to Example 1, Example 2 used an additional propylene separation column (sixth distillation column), which could further separate the propylene from the starting material and increase the purity of the final propylene oxide product.

Example 3

This example was carried out according to the flowchart as shown in FIG. 3.

Epoxidation was carried out in the same manner as in example 1.

T1

In the first extraction distillation column, the number of theoretical plates of the column was 40, gauge pressure at the top of the column was 0.07 MPa, the temperature at the top of the column was 44.2 ° C, the temperature at the bottom of the column was 75.3 ° C, and the top part of the first extraction distillation column worked without reflux.

Source material T1

100653 kg / h of the reaction product from the epoxidation reactor (its composition contained 61.61 wt.% Methanol, 10.66 wt.% Propylene, 13.43 wt.% Water, 12.66 wt.% Propylene oxide, and the rest were by-products products such as acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether and compounds having a high boiling point; non-condensable gas such as propane and oxygen gas; and a small amount of unreacted hydrogen peroxide) were sent to the first extraction distillation column at thirty fifth theoretical plate columns.

Extraction reagent T1

20,000 kg / h of an aqueous solution of methanol containing impurities such as alcohols and ethers (methanol purity was 80.14%) and obtained from the stream leaving the bottom of the third distillation column, as the first extraction reagent, was sent to the first extraction distillation column at the first theoretical plate of the column.

Top fraction T1

13500 kg / h of propylene-enriched gas (its composition contained 79.47 wt.% Propylene, 16.75 wt.% Methanol, 1.05 wt.% Water, 1.67 wt.% Propane, 0.77 wt.% Gaseous oxygen and a small amount of impurities such as aldehydes and ketones) were obtained from the top of the first extraction distillation column. This gas from the top of the column, after being treated to separate non-condensable gas such as oxygen gas and propane, and then compressed by a compressor and condensation, could be returned to the epoxidation reactor and used as a starting reaction material for the production of propylene oxide by direct oxidation of propylene.

Lower fraction T1

107,153 kg / h of the stream was discharged from the bottom of the first extraction distillation column (its composition contained 70.72 wt.% Methanol, 15.88 wt.% Water, 11.89 wt.% Propylene oxide, and the rest was impurities, such as acetaldehyde , acetone, propylene glycol, propylene glycol monomethyl ether, and compounds having a high boiling point).

The effluent from the bottom of the first extraction distillation column after injection to increase the pressure was directed to the third distillation column in order to pre-distill the propylene oxide.

T3

In the third distillation column, the number of theoretical plates of the column was 40. The gauge pressure at the top of the column was 0.05 MPa, the temperature at the top of the column was 42.1 ° C, the temperature at the bottom of the column was 81.7 ° C, and the reflux coefficient was 5.5.

Source material T3

The effluent from the bottom of the first extraction distillation column after injection to increase the pressure was directed to the third distillation column at the eighth theoretical plate of the column in order to pre-distill the propylene oxide.

Top fraction T3

13500 kg / h of crude propylene oxide (its composition contained 94.4 wt.% Propylene oxide, 5.4 wt.% Methanol, and the remaining mass was a small amount of impurities such as acetaldehyde and acetone) were obtained from the top of the third distillation column.

Lower fraction T3

From the bottom of the third distillation column, 93653 kg / h of flow was released (its composition contained 80.14 wt.% Methanol, 18.16 wt.% Water, and the rest was impurities such as acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and having a high boiling point of the compound).

Part of the effluent from the bottom of the third distillation column (20,000 kg / h) was cooled with a cooling device to 40 ° C and returned to the first extraction distillation column for use as a first extraction reagent.

The remaining part of the effluent from the bottom of the third distillation column (73653 kg / h) entered the fifth distillation column, where methanol was distilled.

The fifth distillation column was a traditional methanol distillation column, which could be operated in a single or double distillation mode, well known in the methanol recovery technique. The methanol obtained could be returned to the epoxidation reactor as a solvent.

T4

The number of theoretical plates of the column in the fourth distillation column was 42. The gauge pressure in the upper part of the column was 0.05 MPa, the temperature in the upper part of the column was 46.2 ° C, the temperature in the lower part of the column was 98.8 ° C, and the reflux coefficient was 2.

Source material T4

13500 kg / h of propylene oxide obtained from the upper part of the third distillation column, after injection, was added to increase the pressure to the fourth distillation column at the thirtieth theoretical plate of the column to carry out extraction distillation.

Extraction reagent T4

3000 kg / h of desalinated water as the third extraction reagent was sent to the second distillation column at the twentieth theoretical plate of the column.

Top fraction T4

12760 kg / h of purified propylene oxide (propylene oxide purity could reach 99.86 wt.%) Was obtained from the upper part of the fourth distillation column.

Lower fraction T4

From the bottom of the fourth distillation column, 3740 kg / h of flow was released (its composition contained 19.50 wt.% Methanol, 80.19 wt.% Water, and the rest was impurities such as acetaldehyde, acetone, propylene glycol, propylene glycol monomethyl ether, and having a high boiling point of the compound). This effluent from the bottom could also be sent to a fifth distillation column to separate methanol.

Compared to example 1, example 3 used an additional column for the crude propylene oxide (third distillation column), which reduced the load of extraction distillation for the fourth distillation column and increased the purity of the final propylene oxide product.

Although various embodiments of the present invention have been illustrated and described above, it should be apparent that the present invention is not solely limited to these embodiments. Numerous modifications, changes, variations, substitutions and equivalents should be apparent to specialists in this field of technology, while not deviating from the idea and without going beyond the scope of the present invention, as described in the claims. In addition, it should be noted that the technical characteristics in the various embodiments described above can be combined with each other, forming a new embodiment, provided that the combined technical characteristics are not contradictory to each other. In addition, the various embodiments described above can be combined into random combinations to form a new embodiment, provided that this combination is carried out without deviating from the principles of the present invention. These resulting combinations of embodiments should also be apparent to those skilled in the art, and thus are within the scope of the present invention.

Claims (35)

1. The method of purification of propylene oxide, comprising the following stages: (1) a solution containing from 1 to 15 mass. % propylene, from 5 to 25 mass. % propylene oxide, from 25 to 80 mass. % organic solvent, from 0 to 5 mass. % propane and from 5 to 45 mass. % of water, in which the remaining mass is a high boiling point organic substance and an aqueous solution of an organic solvent as the first extraction reagent, are fed to the first extraction distillation column, in which separation is carried out, and the distillation conditions in the first extraction distillation column are regulated so that the propylene-enriched product of the upper fraction is obtained from the upper part of the first extraction distillation column, and the product of the lower the fraction, which is enriched with propylene oxide, an organic solvent and water, is obtained from the bottom of the first extraction distillation column; and (2) the bottom product, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated to obtain a propylene oxide product and a solution containing an organic solvent and water. 2. The method according to p. 1, and this method further includes a stage in which a solution containing an organic solvent and water is subjected to distillation separation in the fifth distillation column to obtain a stream of organic solvent. 3. The method according to claim 2, in which the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated by a method that includes the following steps: the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, and water, as a second extraction reagent, enters the second distillation column in order to separate ix, a propylene oxide product obtained from the top of the second distillation column and the solution containing an organic solvent and water, is obtained from the bottom of the second distillation column. 4. The method according to p. 2, in which the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated by a method that includes the following stages: the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the lower part of the first extraction distillation column, is subjected to distillation separation in a third distillation column; crude propylene oxide containing an organic solvent is obtained from the upper part of the third distillation column, a solution containing an organic solvent and water is obtained from the lower part of the third distillation column; crude propylene oxide containing an organic solvent obtained from the upper part of the third distillation column and water, as a third extraction reagent, enters the fourth distillation column to perform separation, the propylene oxide product is obtained from the upper part of the fourth distillation column, and a solution containing an organic solvent and water is obtained from the bottom of the fourth distillation column. 5. The method according to p. 1, in which the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated by a method that includes the following stages: the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, and water, as a second extraction reagent, enters the second distillation column in order to separate ix, a propylene oxide product obtained from the top of the second distillation column and the solution containing an organic solvent and water, is obtained from the bottom of the second distillation column. 6. The method according to p. 1, in which the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the bottom of the first extraction distillation column, is separated by a method that includes the following stages: the product of the lower fraction, which is enriched in propylene oxide, an organic solvent and water and obtained from the lower part of the first extraction distillation column, is subjected to distillation separation in a third distillation column; crude propylene oxide containing an organic solvent is obtained from the upper part of the third distillation column, a solution containing an organic solvent and water is obtained from the lower part of the third distillation column; crude propylene oxide containing an organic solvent obtained from the upper part of the third distillation column and water, as a third extraction reagent, enters the fourth distillation column to perform separation, the propylene oxide product is obtained from the upper part of the fourth distillation column, and a solution containing an organic solvent and water is obtained from the bottom of the fourth distillation column. 7. The method according to any one of paragraphs. 3-6, in which the sixth distillation column may be present between the first extraction distillation column and the second distillation column or third distillation column, moreover, the stream from the lower part of the first distillation column is the source material for the sixth distillation column, and the stream from the bottom of the sixth distillation column is the source material for the second distillation column or is the source material for the third distillation column; technological conditions in the sixth distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, preferably from normal pressure to 0.3 MPa; the number of theoretical plates of the column is from 10 to 30, more preferably from 15 to 25; the temperature at the top of the column is from 40 to 90 ° C, more preferably from 40 to 80 ° C and the temperature at the bottom of the column is from 70 to 100 ° C, more preferably from 75 to 95 ° C. 8. The method according to p. 1, in which the first extraction reagent partially or completely is a solution containing an organic solvent and water obtained in stage (2). 9. The method according to p. 2, in which the solution containing propylene, propylene oxide, an organic solvent and water, is a product of the manufacture of propylene oxide by direct oxidation of propylene, and this method further includes the following steps: the organic solvent stream is partially or completely returned and used as an organic solvent for the manufacture of propylene oxide by direct oxidation of propylene; and the upper fraction-enriched propylene product obtained from the top of the first extraction distillation column, after compression and separation of at least one non-condensable gas, is returned and used as a starting reaction material for the production of propylene oxide by direct oxidation of propylene. 10. The method according to any one of paragraphs. 1-6, 8-9, in which the conditions of the distillation in the first extraction distillation column are regulated so that the propylene-enriched product of the upper fraction obtained from the upper part of the first extraction distillation column has a propylene oxide content of 1 wt. % or less. 11. The method according to any one of paragraphs. 1-6, 8-9, in which an aqueous solution of an organic solvent as a first extraction reagent has an organic solvent content of from 10 to 95 wt. % 12. The method according to any one of paragraphs. 1-6, 8-9, in which the mass ratio of the used amount of an aqueous solution of an organic solvent as a first extraction reagent and the used amount of a solution containing propylene, propylene oxide, an organic solvent and water is from 0.01-0.5: 1. 13. The method according to any one of paragraphs. 1-6, 8-9, in which the conditions of distillation in the first extraction distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, the number of theoretical plates of the column is from 5 to 45, the temperature in the upper part the column is 40 to 70 ° C and the temperature at the bottom of the column is 45 to 100 ° C. 14. The method according to any one of paragraphs. 1-6, 8-9, in which the organic solvent is an organic solvent for the manufacture of propylene oxide by direct oxidation of propylene. 15. The method of claim 14, wherein the organic solvent is methanol. 16. The method according to p. 5, in which the conditions of the distillation separation in the second distillation column are controlled so that the propylene oxide product obtained from the upper part of the second distillation column has a propylene oxide content of 98 mass. % or more. 17. The method according to p. 5, in which the conditions of distillation separation in the second distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 1.0 MPa, the number of theoretical plates of the column is from 20 to 50, the temperature in the upper part the column is from 35 to 115 ° C and the temperature at the bottom of the column is from 75 to 110 ° C. 18. The method according to claim 6, in which the conditions of the distillation separation in the third distillation column are controlled so that the crude propylene oxide containing an organic solvent obtained from the upper part of the third distillation column has a propylene oxide content of from 50 to 99.5 wt. % 19. The method according to p. 18, in which the conditions of the distillation separation in the third distillation column are controlled so that the crude propylene oxide containing an organic solvent obtained from the upper part of the third distillation column has a propylene oxide content of from 60 to 80 wt. % 20. The method according to any one of paragraphs. 6, 18, 19, in which the conditions of the distillation separation in the fourth distillation column are controlled so that the propylene oxide product obtained from the upper part of the fourth distillation column has a propylene oxide content of 99.5 wt. % or more. 21. The method according to any one of paragraphs. 6, 18, 19, in which the conditions of distillation separation in the third distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 0.8 MPa, the number of theoretical plates of the column is from 10 to 60, the temperature in the upper part of the column is from 40 to 95 ° C and the temperature at the bottom of the column is from 70 to 110 ° C; The distillation separation conditions in the fourth distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, the number of theoretical plates of the column is from 10 to 60, the temperature in the upper part of the column is from 40 to 95 ° C and the temperature the bottom of the column is between 75 and 110 ° C. 22. The method according to p. 16, in which the conditions of distillation separation in the second distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 1.0 MPa, the number of theoretical plates of the column is from 20 to 50, the temperature in the upper part the column is from 35 to 115 ° C and the temperature at the bottom of the column is from 75 to 110 ° C. 23. The method according to p. 20, in which the conditions of distillation separation in the third distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 0.8 MPa, the number of theoretical plates of the column is from 10 to 60, the temperature in the upper part the column is from 40 to 95 ° C and the temperature at the bottom of the column is from 70 to 110 ° C; The distillation separation conditions in the fourth distillation column include the following: gauge pressure in the upper part of the column is from normal pressure to 0.5 MPa, the number of theoretical plates of the column is from 10 to 60, the temperature in the upper part of the column is from 40 to 95 ° C and the temperature the bottom of the column is between 75 and 110 ° C.

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