CN108912071B - Preparation method of propylene oxide - Google Patents
Preparation method of propylene oxide Download PDFInfo
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- CN108912071B CN108912071B CN201810816776.9A CN201810816776A CN108912071B CN 108912071 B CN108912071 B CN 108912071B CN 201810816776 A CN201810816776 A CN 201810816776A CN 108912071 B CN108912071 B CN 108912071B
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D303/00—Compounds containing three-membered rings having one oxygen atom as the only ring hetero atom
- C07D303/02—Compounds containing oxirane rings
- C07D303/04—Compounds containing oxirane rings containing only hydrogen and carbon atoms in addition to the ring oxygen atoms
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D301/00—Preparation of oxiranes
- C07D301/02—Synthesis of the oxirane ring
- C07D301/03—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds
- C07D301/04—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds with air or molecular oxygen
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D301/00—Preparation of oxiranes
- C07D301/02—Synthesis of the oxirane ring
- C07D301/03—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds
- C07D301/19—Synthesis of the oxirane ring by oxidation of unsaturated compounds, or of mixtures of unsaturated and saturated compounds with organic hydroperoxides
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D301/00—Preparation of oxiranes
- C07D301/32—Separation; Purification
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Abstract
The invention discloses a preparation method of propylene oxide. Toluene, molecular oxygen and propylene are used as raw materials, and propylene oxide is prepared through a high-temperature reaction unit, a low-temperature reaction unit, a light component removal unit, a propylene removal unit, an epoxypropane refining unit and a benzene removal unit. The invention is an improvement on the basis of a method for preparing propylene oxide by toluene oxidation reaction and propylene epoxidation reaction. Compared with the prior art for preparing the propylene oxide, the method has the advantages of high toluene single-pass conversion rate, high reaction selectivity, high conversion rate, low energy consumption, short process flow and low operation cost.
Description
Technical Field
The invention relates to a preparation method of an organic matter, in particular to a preparation method of propylene oxide.
Background
Propylene Oxide (PO) is the third largest propylene derivative except polypropylene and acrylonitrile, is an important basic organic chemical raw material, is mainly used for producing polyether, propylene glycol and the like, and is also the main raw material of fourth-generation detergent nonionic surfactants, oil field demulsifiers, pesticide emulsifiers and the like. Derivatives of PO are widely used in the industries of automobiles, buildings, food, tobacco, medicines, cosmetics and the like. The current industrialized methods for producing propylene oxide include: chlorohydrin processes, co-oxidation processes, and direct oxidation processes. Chlorohydrin processPropylene and chlorine are used as raw materials, and the propylene oxide is obtained through chlorohydrination, saponification and refining processes, but a large amount of chlorine-containing wastewater is generated in the production process, so that the environment is polluted, and equipment is seriously corroded. The co-oxidation method is divided into an ethylbenzene hydroperoxide method (PO/SM method), an isobutane hydroperoxide method (PO/TBA method) and a hydrogen peroxide cumene method (CHP method) according to different raw materials, overcomes the defects of pollution, corrosion and the like of a chlorohydrin method, but has the disadvantages of long flow, large investment, more co-products and influence on the production of the propylene oxide to a certain extent due to more co-products. Direct oxidation of propylene with H2O2The process has the advantages of no co-production product, simple process, low investment cost, environmental protection and the defect of H2O2Is expensive and inconvenient to transport in large quantities, requires the construction of a high capacity H near the site of the propylene oxide plant2O2Provided is a device. In view of this, it is a consensus in the industry to develop research on the production process of propylene oxide and find a better preparation method.
Disclosure of Invention
The invention aims to provide a method for preparing propylene oxide by using toluene and propylene as raw materials and adopting an oxidation method, which overcomes the defects of the prior art.
The technical scheme adopted by the invention for solving the technical problem is that the preparation method of the propylene oxide comprises the following steps:
(1) high temperature reaction unit
Pretreating toluene, molecular oxygen and propylene, adding the pretreated toluene, molecular oxygen and propylene into a high-temperature reactor, and carrying out oxidation reaction and epoxidation reaction in the presence of an oxidation catalyst and an epoxidation catalyst to generate a high-temperature reaction liquid mainly containing propylene oxide, propylene, benzyl hydroperoxide, benzyl alcohol, benzaldehyde and toluene;
wherein, the molecular oxygen is one or more of air, pure oxygen, oxygen-enriched air or ozone, and preferably air;
wherein the temperature in the reaction process is 90-250 ℃, preferably 110-200 ℃; the pressure is 0.3-2.6 MPa, preferably 0.6-1.8 MPa; the molar ratio of molecular oxygen to propylene to toluene is (0.1-10): 0.01-2): 1, preferably (1-6): 0.05-1): 1; the retention time is 30-180 min;
wherein, the main reaction formula of the high-temperature reaction is (A) formula and (B) formula:
C6H5-CH3+O2→C6H5-CH2-OOH （A）
C6H5-CH2-OOH+CH3CH=CH2→C6H5-CH2-OH+CH3CH(O)CH2 （B）
(2) low temperature reaction unit
Under the low-temperature condition, in a low-temperature reactor, continuously carrying out epoxidation reaction on benzyl hydroperoxide and propylene in the high-temperature reaction liquid obtained in the step (1) under the condition of a catalyst, and simultaneously carrying out side reaction to generate low-temperature reaction liquid mainly containing propylene oxide, propylene, benzyl alcohol, benzaldehyde and toluene;
wherein the temperature of the low-temperature epoxidation reaction is 25-200 ℃, and preferably 35-100 ℃; the pressure is 0.1-5.0 MPa, preferably 0.1-2.5 MPa; the molar ratio of propene to benzylhydroperoxide (1-10) is 1, preferably (2-5) is 1; the retention time is 15-90 min;
wherein, the main reaction formula of the low-temperature reaction is the formula (B);
(3) light component removing unit
Performing light component removal treatment on the low-temperature reaction liquid obtained in the step (2) in a light component removal tower, obtaining a mixed solution mainly containing benzaldehyde, benzyl alcohol and toluene at the bottom of the tower, and obtaining a mixture of propylene and propylene oxide at the top of the tower;
the temperature of the top of the light component removal tower is-40-100 ℃, preferably 15-80 ℃; the temperature of the tower bottom is 25-121 ℃, and preferably 40-100 ℃; the pressure is 0.1-5.0 MPa, preferably 0.1-2.5 MPa;
(4) depropenization unit
Carrying out depropylene treatment on the mixture of propylene and epoxypropane obtained in the step (3) in a propylene separation tower to obtain propylene at the tower top, taking part of the propylene as reflux liquid of the propylene separation tower, collecting the rest propylene, or returning the rest propylene to the process as raw material to continuously participate in the reaction, and obtaining epoxypropane solution at the tower bottom;
the temperature of the top of the propylene separating tower is-40-100 ℃, preferably 25-60 ℃; the temperature of the tower bottom is 25-150 ℃, preferably 50-150 ℃; the pressure is 0.1-5.0 MPa, preferably 0.1-2.0 MPa;
(5) depropanizer unit
Purifying the epoxypropane solution obtained in the step (4) in an epoxypropane separation tower to obtain epoxypropane crude product at the tower top and water-containing and light-component impurities at the tower bottom, and carrying out biochemical treatment;
the temperature of the top of the epoxypropane separating tower is 0-100 ℃, preferably 25-80 ℃; the temperature of the tower bottom is 50-150 ℃, and 60-150 ℃ is preferred; the pressure is 0.1-5.0 MPa, preferably 0.1-2.0 MPa;
(6) propylene oxide refining unit
Refining the crude product of the epoxypropane obtained in the step (5) in an epoxypropane extraction rectifying tower to obtain an epoxypropane product at the top of the tower and impurities at the bottom of the tower;
the temperature of the top of the extraction and rectification tower is 0-100 ℃, and preferably 30-80 ℃; the temperature of the tower bottom is 50-150 ℃, and 60-110 ℃ is preferred; the pressure is 0.1-5.0 MPa, preferably 0.1-0.5 MPa; the extractant is one or more of C3-C10 hydrocarbon and process water, preferably process water;
(7) toluene removal unit
Pretreating the reaction liquid mainly containing benzaldehyde, benzyl alcohol and toluene obtained in the step (3), then performing debenzolization treatment in a toluene separation tower, obtaining a toluene derivative solution mainly containing benzaldehyde and benzyl alcohol at the bottom of the tower, obtaining toluene at the top of the tower, taking part of the toluene as a toluene tower reflux liquid, collecting the rest of the toluene, or recycling the rest of the toluene to the process as a raw material to continuously participate in the reaction;
the temperature of the top of the toluene separation tower is 100-180 ℃, and preferably 100-130 ℃; the temperature of the tower bottom is 120-250 ℃, preferably 130-200 ℃; the pressure is 0.1 to 5.0 MPaa, preferably 0.1 to 0.5 MPa.
According to the present invention, in the step (1) high temperature reaction unit, the high temperature reaction can be performed in one or more high temperature reactors, preferably in one high temperature reactor; if the number of the high-temperature reactors is two or more, the high-temperature reactors are connected in series or in parallel; the high-temperature reactor is a slurry bed reactor or a fixed bed reactor, preferably a slurry bed reactor;
in the step (2) low-temperature reaction unit, the low-temperature reaction can be carried out in one or more low-temperature reactors which are connected in series or in parallel, preferably in a plurality of low-temperature reactors connected in series; the low-temperature reactor is a slurry bed reactor or a fixed bed reactor, and preferably a fixed bed reactor;
the high-temperature reaction unit in the step (1) and the low-temperature reaction unit in the step (2) both need nitrogen protection;
in the high-temperature reaction unit in the step (1), the raw materials of toluene, molecular oxygen, propylene and protective gas nitrogen are required to be respectively pretreated until the pressure is 0.8-2.6 MPa and the temperature is 90-250 ℃ before being added into a high-temperature reactor;
in the step (7) benzene removal unit, the feed inlet of the extracting agent is arranged in the middle part of the tower or in the upper part of the tower, preferably in the upper part of the tower;
the pressure in the present invention is an absolute pressure unless otherwise specified. The reaction apparatus and equipment used, such as various towers, are conventional and have no special requirements.
The invention has the following beneficial effects:
(1) according to the invention, benzyl hydrogen peroxide obtained by oxidizing toluene is subjected to epoxidation reaction with propylene for the first time to generate propylene oxide, so that side reactions generated by self-decomposition of the benzyl hydrogen peroxide are effectively reduced;
(2) compared with the existing propylene oxide preparation method, the invention has the advantages that the toluene single-pass conversion rate is improved; the conversion rate of propylene is more than 99.0 percent, the selectivity of propylene oxide is improved, and the yield of propylene oxide is more than 95 percent; the purity of the propylene oxide is more than 99.5 percent;
the method has the characteristics of high toluene single-pass conversion rate, high reaction conversion rate, high selectivity, low production cost, high safety, low energy consumption, short process flow, low operation cost, low equipment investment, environmental friendliness and the like.
Drawings
FIG. 1 is a schematic process flow diagram of the present invention.
Detailed Description
The following examples serve to illustrate the invention. It should be emphasized that these examples are only intended to illustrate the present invention and should not be interpreted as limiting the scope of the present invention.
Embodiment 1 a method for preparing propylene oxide, comprising the steps of:
(1) high temperature reaction unit
Respectively pretreating toluene, air and propylene to the pressure of 1.4 MPa and the temperature of 110 ℃ before adding the toluene, the air and the propylene into a high-temperature reactor;
adding pretreated toluene, air and propylene into a high-temperature reactor filled with an oxidation catalyst and an epoxidation catalyst, wherein the molar ratio of oxygen, propylene and toluene in the air is 2:0.1:1, under the conditions of the temperature of 110 ℃ and the pressure of 1.3 MPa, under the action of the oxidation catalyst, the toluene and the oxygen in the air are subjected to oxidation reaction to generate benzyl hydrogen peroxide, the generated benzyl hydrogen peroxide and the propylene are subjected to epoxidation reaction under the action of the epoxidation catalyst to generate propylene oxide and benzyl alcohol, the reaction retention time is 45 min, high-temperature reaction liquid containing target products of the propylene oxide and the benzyl hydrogen peroxide is obtained, meanwhile, byproducts of the benzaldehyde and the benzyl alcohol are obtained, and the reaction liquid containing the target products of the propylene oxide and the benzyl hydrogen peroxide continuously enters a low-temperature reaction unit;
wherein the high-temperature reactor is a slurry bed reactor;
wherein the main reaction formulas of the high-temperature reaction are (A) formula and (B) formula:
C6H5-CH3+O2→C6H5-CH2-OOH （A）
C6H5-CH2-OOH+CH3CH=CH2→C6H5-CH2-OH+CH3CH(O)CH2 （B）
(2) low temperature reaction unit
In a low-temperature reactor, controlling the molar ratio of propylene to benzyl hydroperoxide to be 2.5:1, and controlling the temperature to be 40 ℃ and the pressure to be 1.8 MPa; under the action of an epoxidation catalyst, propylene and benzyl hydroperoxide are subjected to epoxidation reaction to generate propylene oxide and benzyl alcohol, side reaction is simultaneously carried out to generate benzaldehyde and benzyl alcohol, the reaction residence time is 30min, and low-temperature reaction liquid containing propylene oxide, propylene, benzyl alcohol, benzaldehyde and toluene is obtained;
wherein, the main reaction formula of the low-temperature reaction is the formula (B);
wherein, the low-temperature reactor is two fixed bed reactors connected in series;
(3) light component removing unit
Performing light component removal treatment on the low-temperature reaction liquid obtained in the low-temperature reaction unit in the step (2) in a light component removal tower, wherein the temperature at the top of the tower is 65 ℃, the temperature at the bottom of the tower is 85 ℃, and the operating pressure is 0.1 MPa; a mixed solution mainly containing benzaldehyde, benzyl alcohol and toluene is obtained at the bottom of the tower, and a mixture of propylene and propylene oxide is obtained at the top of the tower;
(4) depropenization unit
Carrying out depropylene treatment on the mixture of propylene and propylene oxide obtained in the light component removal unit in the step (3) in a propylene separation tower, wherein the temperature at the top of the tower is 35 ℃, the temperature at the bottom of the tower is 60 ℃, and the operating pressure is 0.1 MPa; obtaining propylene at the tower top, taking part of the propylene as reflux liquid of a propylene separation tower, collecting the rest propylene, and obtaining propylene oxide solution at the tower bottom;
(5) depropanizer unit
Purifying the epoxypropane solution obtained in the propylene removal unit in the step (4) in an epoxypropane separation tower, wherein the temperature at the top of the tower is 35 ℃, the temperature at the bottom of the tower is 75 ℃, and the operating pressure is 0.15 MPa; crude epoxypropane is obtained at the top of the tower, water-containing and light-component impurities are obtained at the bottom of the tower, and biochemical treatment is carried out;
(6) propylene oxide refining unit
Refining the crude epoxypropane obtained by the epoxypropane removing unit in the step (5) in an epoxypropane extraction rectifying tower, wherein the temperature of the top of the tower is 34 ℃, the temperature of the bottom of the tower is 95 ℃, the operating pressure is 0.15 MPa, and the extracting agent is process water; the epoxypropane product is obtained at the tower top, and the impurities are obtained at the tower bottom;
(7) toluene removal unit
After pretreatment, the reaction liquid mainly containing benzaldehyde, benzyl alcohol and toluene obtained from the light component removing unit in the step (3) is subjected to toluene removing treatment in a toluene separation tower, wherein the temperature at the top of the tower is 125 ℃, the temperature at the bottom of the tower is 165 ℃, and the operating pressure is 0.15 MPa; obtaining a mixed solution mainly containing benzaldehyde and benzyl alcohol at the bottom of the tower, obtaining toluene at the top of the tower, taking part of the toluene as a toluene tower reflux liquid, and collecting the residual toluene;
wherein the feed inlet of the extractant is arranged at the upper part of the tower;
in the embodiment, the high-temperature reaction unit in the step (1) and the low-temperature reaction unit in the step (2) both need nitrogen protection;
the pressure in the present example is an absolute pressure unless otherwise specified.
Embodiment 2 a method for preparing propylene oxide, comprising the steps of:
(1) high temperature reaction unit
Respectively pretreating toluene, air and propylene to the pressure of 1.5 MPa and the temperature of 120 ℃ before adding the toluene, the air and the propylene into a high-temperature reactor;
adding pretreated toluene, air and propylene into a high-temperature reactor filled with an oxidation catalyst and an epoxidation catalyst, wherein the molar ratio of oxygen, propylene and toluene in the air is 3:0.2:1, under the conditions of the temperature of 120 ℃ and the pressure of 1.5 MPa, under the action of the oxidation catalyst, the toluene and the oxygen in the air are subjected to oxidation reaction to generate benzyl hydrogen peroxide, the generated benzyl hydrogen peroxide and the propylene are subjected to epoxidation reaction under the action of the epoxidation catalyst to generate propylene oxide and benzyl alcohol, the reaction retention time is 50 min, high-temperature reaction liquid containing target products of the propylene oxide and the benzyl hydrogen peroxide is obtained, meanwhile, byproducts of the benzaldehyde and the benzyl alcohol are obtained, and the reaction liquid containing the target products of the propylene oxide and the benzyl hydrogen peroxide continuously enters a low-temperature reaction unit;
wherein the high-temperature reactor is a slurry bed reactor;
wherein the main reaction formulas of the high-temperature reaction are (A) formula and (B) formula:
C6H5-CH3+O2→C6H5-CH2-OOH （A）
C6H5-CH2-OOH+CH3CH=CH2→C6H5-CH2-OH+CH3CH(O)CH2 （B）
(2) low temperature reaction unit
In a low-temperature reactor, controlling the molar ratio of propylene to benzyl hydroperoxide to be 3:1, wherein the temperature is 42 ℃ and the pressure is 1.9 MPa; under the action of an epoxidation catalyst, propylene and benzyl hydroperoxide are subjected to epoxidation reaction to generate propylene oxide and benzyl alcohol, side reaction is simultaneously carried out to generate benzaldehyde and benzyl alcohol, the reaction residence time is 35 min, and low-temperature reaction liquid containing propylene oxide, propylene, benzyl alcohol, benzaldehyde and toluene is obtained;
wherein, the main reaction formula of the low-temperature reaction is the formula (B);
wherein, the low-temperature reactor is two fixed bed reactors connected in series;
(3) light component removing unit
Performing light component removal treatment on the low-temperature reaction liquid obtained in the low-temperature reaction unit in the step (2) in a light component removal tower, wherein the temperature at the top of the tower is 67 ℃, the temperature at the bottom of the tower is 88 ℃, and the operating pressure is 0.1 MPa; a mixed solution mainly containing benzaldehyde, benzyl alcohol and toluene is obtained at the bottom of the tower, and a mixture of propylene and propylene oxide is obtained at the top of the tower;
(4) depropenization unit
Carrying out depropylene treatment on the mixture of propylene and propylene oxide obtained in the light component removal unit in the step (3) in a propylene separation tower, wherein the temperature at the top of the tower is 30 ℃, the temperature at the bottom of the tower is 65 ℃, and the operating pressure is 0.1 MPa; obtaining propylene at the top of the tower, taking part of the propylene as reflux liquid of a propylene separation tower, returning the rest propylene to the process as a raw material to continuously participate in the reaction, and obtaining a propylene oxide solution at the bottom of the tower;
(5) depropanizer unit
Purifying the epoxypropane solution obtained in the propylene removal unit in the step (4) in an epoxypropane separation tower, wherein the temperature at the top of the tower is 40 ℃, the temperature at the bottom of the tower is 80 ℃, and the operating pressure is 0.15 MPa; crude epoxypropane is obtained at the top of the tower, water-containing and light-component impurities are obtained at the bottom of the tower, and biochemical treatment is carried out;
(6) propylene oxide refining unit
Refining the crude epoxypropane obtained by the epoxypropane removing unit in the step (5) in an epoxypropane extraction rectifying tower, wherein the temperature of the top of the tower is 34 ℃, the temperature of the bottom of the tower is 95 ℃, the operating pressure is 0.15 MPa, and the extracting agent is process water; the epoxypropane product is obtained at the tower top, and the impurities are obtained at the tower bottom;
wherein, the feed inlet of the extractant is arranged at the upper part of the tower;
(7) toluene removal unit
After pretreatment, the reaction liquid mainly containing benzaldehyde, benzyl alcohol and toluene obtained from the light component removing unit in the step (3) is subjected to toluene removing treatment in a toluene separation tower, wherein the temperature at the top of the tower is 130 ℃, the temperature at the bottom of the tower is 200 ℃, and the operating pressure is 0.1-0.2 MPa; obtaining a mixed solution mainly containing benzaldehyde and benzyl alcohol at the bottom of the tower, obtaining toluene at the top of the tower, taking a part of the toluene as a toluene tower reflux liquid, and circulating the rest of the toluene to the process as a raw material to continuously participate in the reaction;
in the embodiment, the high-temperature reaction unit in the step (1) and the low-temperature reaction unit in the step (2) both need nitrogen protection;
the pressure in the present example is an absolute pressure unless otherwise specified.
Embodiment 3 a method for preparing propylene oxide, comprising the steps of:
(1) high temperature reaction unit
Respectively pretreating toluene, air and propylene to the pressure of 1.6MPa and the temperature of 180 ℃ before adding the toluene, the air and the propylene into a high-temperature reactor;
adding pretreated toluene, air and propylene into a high-temperature reactor filled with an oxidation catalyst and an epoxidation catalyst, wherein the molar ratio of oxygen, propylene and toluene in the air is 4:0.3:1, under the conditions of 180 ℃ and 1.5 MPa, under the action of the oxidation catalyst, the toluene and the oxygen in the air are subjected to oxidation reaction to generate benzyl hydrogen peroxide, the generated benzyl hydrogen peroxide and the propylene are subjected to epoxidation reaction under the action of the epoxidation catalyst to generate propylene oxide and benzyl alcohol, the reaction residence time is 60 min, so as to obtain high-temperature reaction liquid containing target products of the propylene oxide and the benzyl hydrogen peroxide, meanwhile, byproducts of the benzaldehyde and the benzyl alcohol are obtained, and the reaction liquid containing the target products of the propylene oxide and the benzyl hydrogen peroxide continuously enters a low-temperature reaction unit;
wherein the high-temperature reactor is a slurry bed reactor;
wherein the main reaction formulas of the high-temperature reaction are (A) formula and (B) formula:
C6H5-CH3+O2→C6H5-CH2-OOH （A）
C6H5-CH2-OOH+CH3CH=CH2→C6H5-CH2-OH+CH3CH(O)CH2 （B）
(2) low temperature reaction unit
Controlling the molar ratio of propylene to benzyl hydroperoxide to be 3.5:1 in a low-temperature reactor, wherein the temperature is 45 ℃ and the pressure is 2.3 MPa; under the action of an epoxidation catalyst, propylene and benzyl hydroperoxide are subjected to epoxidation reaction to generate propylene oxide and benzyl alcohol, side reaction is simultaneously carried out to generate benzaldehyde and benzyl alcohol, and the reaction residence time is 40 min, so that low-temperature reaction liquid containing propylene oxide, propylene, benzyl alcohol, benzaldehyde and toluene is obtained;
wherein, the main reaction formula of the low-temperature reaction is the formula (B);
wherein, the low-temperature reactor is two fixed bed reactors connected in series;
(3) light component removing unit
Performing light component removal treatment on the low-temperature reaction liquid obtained in the low-temperature reaction unit in the step (2) in a light component removal tower, wherein the temperature at the top of the tower is 60 ℃, the temperature at the bottom of the tower is 130 ℃, and the operating pressure is 2.3 MPa; a mixed solution mainly containing benzaldehyde, benzyl alcohol and toluene is obtained at the bottom of the tower, and a mixture of propylene and propylene oxide is obtained at the top of the tower;
(4) depropenization unit
Carrying out depropylene treatment on the mixture of propylene and propylene oxide obtained in the light component removal unit in the step (3) in a propylene separation tower, wherein the temperature at the top of the tower is 30 ℃, the temperature at the bottom of the tower is 110 ℃, and the operating pressure is 2.2 MPa; obtaining propylene at the tower top, taking part of the propylene as reflux liquid of a propylene separation tower, collecting the rest propylene, and obtaining propylene oxide solution at the tower bottom;
(5) depropanizer unit
Purifying the epoxypropane solution obtained in the propylene removal unit in the step (4) in an epoxypropane separation tower, wherein the temperature at the top of the tower is 60 ℃, the temperature at the bottom of the tower is 130 ℃, and the operating pressure is 2.0 MPa; crude epoxypropane is obtained at the top of the tower, water-containing and light-component impurities are obtained at the bottom of the tower, and biochemical treatment is carried out;
(6) propylene oxide refining unit
Refining the crude epoxypropane obtained by the epoxypropane removing unit in the step (5) in an epoxypropane extraction rectifying tower, wherein the temperature of the top of the tower is 34 ℃, the temperature of the bottom of the tower is 95 ℃, the operating pressure is 0.15 MPa, and the extracting agent is process water; the epoxypropane product is obtained at the tower top, and the impurities are obtained at the tower bottom;
(7) toluene removal unit
After pretreatment, the reaction liquid mainly containing benzaldehyde, benzyl alcohol and toluene obtained from the light component removing unit in the step (3) is subjected to toluene removing treatment in a toluene separation tower, wherein the temperature at the top of the tower is 125 ℃, the temperature at the bottom of the tower is 170 ℃, and the operating pressure is 0.1-0.2 MPa; and obtaining a mixed solution mainly containing benzaldehyde and benzyl alcohol at the bottom of the tower, obtaining toluene at the top of the tower, taking a part of the toluene as a toluene tower reflux liquid, and circulating the rest of the toluene to the process as a raw material to continuously participate in the reaction.
Claims (10)
1. A method for preparing propylene oxide is characterized by comprising the following steps:
(1) high temperature reaction unit
Pretreating toluene, molecular oxygen and propylene, adding the pretreated toluene, molecular oxygen and propylene into a high-temperature reactor, and carrying out oxidation reaction and epoxidation reaction in the presence of an oxidation catalyst and an epoxidation catalyst to generate a high-temperature reaction liquid mainly containing propylene oxide, propylene, benzyl hydroperoxide, benzyl alcohol, benzaldehyde and toluene;
wherein the temperature in the high-temperature reaction process is 90-250 ℃, the pressure is 0.3-2.6 MPa, the molar ratio of molecular oxygen to propylene to toluene is 0.1-10: 0.01-2: 1, and the retention time is 30-180 min;
(2) low temperature reaction unit
Under the low-temperature condition, in a low-temperature reactor, continuously carrying out epoxidation reaction on benzyl hydroperoxide and propylene in the high-temperature reaction liquid obtained in the high-temperature reaction unit in the step (1) under the condition of an epoxidation catalyst, and simultaneously carrying out side reaction to generate low-temperature reaction liquid mainly containing epoxypropane, propylene, benzyl alcohol, benzaldehyde and toluene;
wherein the temperature of the low-temperature epoxidation reaction is 25-200 ℃, the pressure is 0.1-5.0 MPa, the molar ratio of propylene to benzyl hydroperoxide is 1-10:1, and the retention time is 15-90 min;
(3) light component removing unit
Performing light component removal treatment on the low-temperature reaction liquid obtained in the step (2) in a light component removal tower, obtaining a mixed solution mainly containing benzaldehyde, benzyl alcohol and toluene at the bottom of the tower, and obtaining a mixture of propylene and propylene oxide at the top of the tower;
wherein the temperature at the top of the light component removal tower is-40-100 ℃, the temperature at the bottom of the light component removal tower is 25-121 ℃, and the pressure is 0.1-5.0 MPa;
(4) depropenization unit
Carrying out depropylene treatment on the mixture of propylene and epoxypropane obtained in the step (3) in a propylene separation tower to obtain propylene at the tower top, taking part of the propylene as reflux liquid of the propylene separation tower, collecting the rest propylene, or returning the rest propylene to the process as raw material to continuously participate in the reaction, and obtaining epoxypropane solution at the tower bottom;
wherein the temperature of the top of the propylene separation tower is-40-100 ℃, the temperature of the bottom of the propylene separation tower is 25-150 ℃, and the pressure is 0.1-5.0 MPa;
(5) depropanizer unit
Purifying the epoxypropane solution obtained in the step (4) in an epoxypropane separation tower to obtain epoxypropane crude product at the tower top and water-containing and light-component impurities at the tower bottom, and carrying out biochemical treatment;
wherein the temperature of the top of the epoxypropane separation tower is 0-100 ℃, the temperature of the bottom of the epoxypropane separation tower is 50-150 ℃, and the pressure is 0.1-5.0 MPa;
(6) propylene oxide refining unit
Refining the crude product of the epoxypropane obtained in the step (5) in an epoxypropane extraction rectifying tower to obtain an epoxypropane product at the top of the tower and impurities at the bottom of the tower;
wherein the temperature of the top of the extraction and rectification tower is 0-100 ℃, the temperature of the bottom of the extraction and rectification tower is 50-150 ℃, and the pressure is 0.1-5.0 MPa; the extractant is one or more of C3-C10 hydrocarbon and process water;
(7) toluene removal unit
Pretreating the reaction liquid mainly containing benzaldehyde, benzyl alcohol and toluene obtained in the step (3), then performing debenzolization treatment in a toluene separation tower, obtaining a toluene derivative solution mainly containing benzaldehyde and benzyl alcohol at the bottom of the tower, obtaining toluene at the top of the tower, taking part of the toluene as a toluene tower reflux liquid, collecting the rest of the toluene, or recycling the rest of the toluene to the process as a raw material to continuously participate in the reaction;
wherein the temperature of the top of the toluene separation tower is 100-180 ℃, the temperature of the bottom of the toluene separation tower is 120-250 ℃, and the pressure is 0.1-5.0 MPa.
2. The method according to claim 1, wherein in the high-temperature reaction unit in the step (1), the molecular oxygen is air, the temperature in the high-temperature reaction process is 110-200 ℃, and the pressure is 0.6-1.8 MPa; the molar ratio of the molecular oxygen to the propylene to the toluene is 1-6: 0.05-1: 1.
3. The method according to claim 1, wherein nitrogen gas is required for both the step (1) high-temperature reaction unit and the step (2) low-temperature reaction unit; and (3) regulating the pH value of the reaction by adopting an alkaline additive.
4. The method according to claim 3, wherein in the high-temperature reaction unit in the step (1), the raw materials of toluene, molecular oxygen, propylene and protective gas nitrogen are respectively pretreated to a pressure of 0.8-2.6 MPa and a temperature of 90-250 ℃ before being added into the high-temperature reactor.
5. The method according to claim 1, wherein in the low-temperature reaction unit in the step (2), the temperature of the low-temperature epoxidation reaction is 35-100 ℃, the pressure is 0.1-2.5 MPa, and the molar ratio of the propylene to the benzylhydroperoxide is 2-5: 1.
6. The method according to claim 1, wherein in the light component removing unit in the step (3), the temperature at the top of the light component removing tower is 15-80 ℃, the temperature at the bottom of the light component removing tower is 40-100 ℃, and the pressure is 0.1-2.5 MPa.
7. The method according to claim 1, wherein in the depropylene removal unit in the step (4), the temperature at the top of the propylene separation column is 25 to 60 ℃, the temperature at the bottom of the propylene separation column is 50 to 150 ℃, and the pressure is 0.1 to 2.0 MPa.
8. The method according to claim 1, wherein in the propylene oxide removal unit in the step (5), the temperature at the top of the propylene oxide separation column is 25 to 80 ℃, the temperature at the bottom of the propylene oxide separation column is 60 to 150 ℃, and the pressure is 0.1 to 2.0 MPa.
9. The method according to claim 1, wherein in the propylene oxide refining unit in the step (6), the temperature at the top of the extractive distillation column is 30 to 80 ℃, the temperature at the bottom of the extractive distillation column is 60 to 110 ℃, and the pressure is 0.1 to 0.5 MPa.
10. The method according to claim 1, wherein in the step (7) of the benzene removing unit, the temperature of the top of the toluene separation column is 100 to 130 ℃, the temperature of the bottom of the toluene separation column is 130 to 200 ℃, and the pressure is 0.1 to 0.5 MPa.
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