CN1534031A - A kind of catalytic distillation method of olefin direct epoxidation - Google Patents

Abstract

A catalytic distiling process for directly epoxidating olefine features that a tower which is vertically and sequentially divided into distilling segment, reaction segment and desorption segment is only used, and includes reacting between olefine, hydrogen peroxide, solvent and Ti-Si molecular sieve catalyst, condensing the excessive solvent and olefine and returning them back to reaction segment, and separating product from the substance discharged from tower bottom. Its advantages are high thermal efficiency and less energy consumption.

Description

A kind of catalytic distillation method of olefin direct epoxidation

Technical field

The invention relates to a method for epoxidizing olefins and hydrogen peroxide to generate organic epoxides with high selectivity under the catalysis of titanium-silicon molecular sieves.

Background technique

Typical bulk organic epoxides are ethylene oxide, propylene oxide and epichlorohydrin, which are basic organic chemical raw materials with a wide range of uses. For ethylene oxide, the current main production method is the process of direct epoxidation of ethylene and oxygen gas phase catalyzed by a silver catalyst with excellent performance. This process has advanced technology and economy, and the production process is basically pollution-free. For propylene oxide, the current production methods mainly include the chlorohydrin method and the co-oxidation method. Among them, the chlorohydrin method has high material consumption and energy consumption, serious equipment corrosion, and high cost for the treatment of three wastes; while the co-oxidation method has solved the corrosion and pollution problems. , but the process is more complicated, and the technical economy is often difficult to obtain good economic benefits due to the limitation of the use of co-products and market capacity. For epichlorohydrin, the current production methods mainly include the allyl chloride method and the allyl alcohol method. Since both of these two processes contain chloroalcoholization process, there are many by-products, high material consumption, high energy consumption, serious corrosion, and large investment in the treatment of three wastes. The technical economy of the process is very poor, and the pressure on environmental protection is high.

In order to solve the traditional process problem, in the late 1980s, US4833260 disclosed a method for direct epoxidation of olefins, which used titanium silicon molecular sieves as catalysts, directly epoxidized olefins with hydrogen peroxide, and selectively generated rings oxide. The reaction equation of this process is as follows (this reaction is an exothermic reaction, and Q represents heat):

Although the selectivity of this reaction is relatively high, due to the presence of strong polar compounds such as water or alcohol in the reaction system, the epoxides generated will partially undergo ring-opening reactions on the catalyst, reducing the selectivity of epoxides. For this reason, US4824976 and CN1319099A propose to process the catalyst with a suitable acid neutralizer before the reaction or in the reaction process, neutralize the acidic group that exists on the surface of the catalyst and play a catalytic role in the ring-opening of the epoxide, to achieve The purpose of inhibiting the ring-opening side reaction of epoxides. The alkaline substances mentioned in these patents can be water-soluble alkaline substances, such as alkalis such as sodium hydroxide, potassium hydroxide, ammonia water; aqueous solutions such as sodium carbonate, sodium bicarbonate and sodium hydrogen phosphate, and similar potassium and lithium salts Basic salts; basic carboxylic acid alkali metal and/or alkaline earth metal salts and alkali metal and/or alkaline earth metal alkoxides in aqueous solution; and tertiary amines or tertiary amine oxides, etc. Afterwards, US5646314 and US5675026 report again, and certain non-basic salt is neutral salt or acid salt such as lithium chloride, sodium sulfate, lithium nitrate, magnesium acetate and ammonium acetate can improve the epoxidation reaction of titanium silicon molecular sieve catalysis equally selective. However, the addition of these substances has an adverse effect on the post-treatment of the product, and some substances can even cause fouling and corrosion of equipment.

In the hydrogen peroxide epoxidation reaction system of olefins catalyzed by titanium-silicon molecular sieves, the catalyst titanium-silicon molecular sieves is a solid, and the olefins and hydrogen peroxide are dissolved in a solvent at the same time and contact the catalyst in liquid form to react. Due to the large heat release of the reaction, and the ineffective decomposition of hydrogen peroxide will intensify when the temperature exceeds 100°C, the reaction system has relatively high requirements on the reactor, and the reactor becomes the key equipment of the reaction process. EP0659473A1 discloses a trickle bed reaction process. The catalyst is filled in the trickle bed reactor in four sections in the form of large particles. There are gas risers and liquid collecting plates between the sections. The first three sections of the bed are mainly reaction Each section is equipped with an indirect cooler to take heat. Taking the epoxidation reaction of propylene as an example, under the reaction pressure above 1.25MPa, the reaction material flows downward from the top of the bed in the form of gas-liquid two-phase co-current and reacts, and the reaction mixture is collected in the main reaction section. The process of output, heat exchange, return and supplementary feeding, that is, after the reactants of each stage are cooled by an indirect cooler, part of it is recycled back to this stage, and the other part is mixed with fresh raw materials and enters the next stage. In order to increase the conversion rate of hydrogen peroxide, no fresh raw materials are added to the feed liquid entering the fourth stage, and the product and tail gas are extracted from the bottom of the bed. The structure of the reactor is complex, the operating pressure is high, and the temperature control depends on large-scale circulation of materials. After the reaction, the solvent needs to be evaporated and separated for recycling, so the energy consumption is very high.

CN1256273A discloses a continuous slurry circulation reaction process, which uses titanium-silicon molecular sieves with fine particles (the average particle diameter is 0.1-200nm) as a catalyst, and the catalyst is dispersed in the reaction feed liquid to flow in a slurry state, and simultaneously catalyzes propylene and Hydrogen peroxide is directly epoxidized to propylene oxide. The reactor is mainly composed of a tubular reaction section mainly for reaction, a tubular cooling section mainly for heat exchange and a gas-liquid separation section. The tube-and-tube reaction section and the cooling section are placed side by side, and the upper and lower ends are connected by U-shaped tubes to form a closed loop. The upper end of the tube-and-tube cooling section is connected to a gas-liquid separator. In order to ensure the full progress of the reaction, the length-to-diameter ratio of the tubes used in the reaction section is required to be 10:1 to 200:1, and distributors are installed on the ends of the tubes in the reaction section to promote the mixing of feed liquid and catalyst. According to the introduction of the patent, the process can realize the continuous epoxidation process of propylene and hydrogen peroxide, the reaction temperature is easy to control, the catalyst is easy to replace or regenerate, the molar ratio of propylene/hydrogen peroxide in the feed is low, and the operating pressure is low. However, the structure of the reaction device of this process is complicated, the energy consumption of solvent recovery is large, and a large amount of reaction heat has not been effectively utilized.

Contents of the invention

The purpose of this invention is to provide a kind of catalytic distillation method of olefin direct epoxidation, to overcome the shortcoming of above-mentioned prior art.

The method provided by the invention comprises:

The method provided by the invention is mainly carried out in a tower consisting of a reaction section, a distillation section and/or a stripping section. The distillation section is located above the reaction section, and the stripping section is located below the reaction section. The reaction section where the solvent enters the tower contacts and reacts with the titanium-silicon molecular sieve catalyst, the vaporized solvent returns to the reaction section, and the epoxide product is separated from the top of the tower or the bottom of the tower.

In the present invention, the reaction and separation are carried out in the same tower, and a large amount of reaction heat is directly used for evaporating and separating the remaining reactants and solvents. The utilization rate of the reaction heat is high, and no special heat extraction facilities are required, so the device structure is simple and the production process energy consumption is greatly reduced.

Detailed ways

The method provided by the invention is mainly carried out in a tower composed of a reaction section, a distillation section and/or a stripping section, wherein the distillation section is located above the reaction section, and the stripping section is located below the reaction section. The towers can be various types of packed towers, sieve tray towers, valve towers, spray towers, grid towers, etc. The reaction section, distillation section and stripping section can be combined with the same type of towers, or can be combined with Different types of towers are combined.

Olefin, hydrogen peroxide and solvent enter the reaction section of the tower to contact with the titanium-silicon molecular sieve catalyst and react, the vaporized solvent returns to the reaction section, and the epoxide product is separated from the top or bottom of the tower.

The olefins are selected from alkenes, cycloalkenes, halogenated alkenes or meta-polyenes, preferably alkenes, cycloalkenes or halogenated alkenes with 3 to 18 carbon atoms, more preferably propene and chloropropene. They can be pure or contain substances that do not negatively affect the epoxidation reaction and product separation.

The hydrogen peroxide can be a pure product, but from a safety point of view, it is best to use an aqueous solution of hydrogen peroxide, and its concentration is 1% to 99%, preferably 20% to 60%.

In general, miscibility between olefins and aqueous hydrogen peroxide solution is not good. Therefore, in the prior art, solvents are added to the reaction system, such as methanol, ethanol, propanol, acetone, etc., to promote the mutual dissolution between olefins and hydrogen peroxide aqueous solution, so as to facilitate the contact with the solid catalyst for reaction. According to the method provided by the present invention, it is also necessary to select these solvents, but different from the prior art, these solvents also have an additional important function in addition to the dissolving function, that is, evaporation takes out the heat of reaction, which not only controls the reaction very conveniently temperature, and use the heat of reaction to separate the solvent from the reaction system. These solvents are selected from alcohols, ketones, acids, and esters, preferably alcohols with 1 to 8 carbon atoms and ketones with 3 to 8 carbon atoms, more preferably methanol, ethanol, propanol, butanol, acetone, and methyl ethyl ketone.

The titanium-silicon molecular sieve is a general term for a class of zeolites in which titanium atoms replace part of the silicon atoms in the molecular sieve lattice framework. Such materials are known in the prior art, such as titanium-containing zeolite, TS-1, which has an MFI topology similar to ZSM-5 aluminosilicate zeolite, and has a MEL topology similar to ZSM-11 aluminosilicate zeolite The titanium-containing zeolite, namely TS-2, and titanium-containing molecular sieves having a framework structure isomorphic to β zeolite, mordenite, ZSM-12, MCM-41 and ZSM-48, etc., preferably TS-1 and TS-2. The catalyst used in the present invention is directly processed from such molecular sieves, and can also be manufactured from these molecular sieves by means of loading or bonding. When the method of binding or supporting is used to make the catalyst, in order to avoid the non-selective decomposition of hydrogen peroxide or the ring-opening reaction of epoxide, the binder or carrier must be a non-acidic substance. Binders and carriers that can be used include titanium dioxide, silica, alumina, and silica-alumina, silica-titania, silica-magnesia composite oxides, etc., and some non-acidic clays Such as montmorillonite, kaolin, bentonite and sepiolite, among which the content of titanium silicon molecular sieve is preferably more than 5%, so as to ensure that the catalyst has sufficient activity. Catalysts can be packed in the tower in the form of various bundles, or scattered on the sieve plate in the sieve tray tower.

Theoretically, 1 mole of olefin needs to consume 1 mole of hydrogen peroxide for complete reaction. According to the method provided by the present invention, in order to improve the effective utilization rate of hydrogen peroxide, it is necessary to keep the excess of olefins in the reaction section of the tower. Therefore, the mol ratio of olefins and hydrogen peroxide in the feed should be 1～10:1, preferably 1.5～6: 1. Separation and recovery of unreacted olefins for reuse. The molar ratio of olefin to solvent in the reaction section of the tower can be selected from 1:3 to 1:20, preferably 1:5 to 1:15. In the above reaction conditions, the reaction temperature ranges from 40 to 100°C, preferably 55 to 80°C, the absolute reaction pressure is 0.1 to 3MPa, preferably 0.1 to 1.0MPa; the liquid hourly mass space velocity of the feed is 0.05 in terms of olefins ~10h ^-1 , preferably 0.1~8h ^-1 .

The reaction process that adopts the method for catalytic distillation to carry out olefin epoxidation can have following several specific embodiments, but the present invention is not limited thereto:

One of the implementation methods:

For the system of olefins with low boiling point and easy vaporization and the boiling point of the product is lower than the reaction temperature, the olefins can enter the tower from the lower end of the reaction section in one or more stages, and the oxidant hydrogen peroxide and solvent enter the tower from the upper end of the reaction section , After the olefin is vaporized, it mixes with the descending hydrogen peroxide and solvent during the rising process, contacts with the catalyst and reacts. At the same time, the heat released by the reaction vaporizes the solvent, removes the heat, and limits the temperature rise of the reaction section, thereby achieving the purpose of removing heat and controlling the temperature of the reaction section. The solvent is recycled in the reaction section through fractional distillation in the distillation section, and the unreacted olefin enters the condenser with the product epoxide to separate the product and then is recycled.

The second implementation mode:

For olefins with a relatively high boiling point but lower than the reaction temperature, the olefins, the oxidant hydrogen peroxide and the solvent are mixed together and enter the tower from the upper end of the reaction section to contact with the catalyst and react, and the heat released by the reaction vaporizes the solvent and removes the heat , keeping the temperature of the reaction section stable, so as to achieve the purpose of removing heat and controlling the temperature of the reaction section. The vaporized solvent and unreacted olefins enter the reaction section through fractionation and reflux in the distillation section for recycling, part of the solvent and products enter the stripping section, and the solvent is evaporated back to the reaction section for further use, and the products epoxide, water and possible by-products Extracted from the tower kettle.

The third implementation mode:

For olefins whose boiling point is higher than the reaction temperature, the olefins, the oxidant hydrogen peroxide and the solvent are mixed together and enter the tower from the upper end of the reaction section to contact with the catalyst and react. The heat released by the reaction vaporizes the solvent, removes the heat, and maintains The temperature of the reaction section is stable, so as to achieve the purpose of removing heat and controlling the temperature of the reaction section. The vaporized solvent enters the reaction section through fractional distillation and reflux for recycling in the distillation section, and the unreacted olefins that enter the stripping section along with the product epoxide are evaporated back to the reaction section in the stripping section to continue the reaction, and the product epoxide, water and possibly The generated by-products are extracted from the tower kettle.

The method provided by the invention is suitable for the direct epoxidation reaction of alkenes, halogenated olefins and other olefins, and is especially suitable for the direct epoxidation reaction of propylene or chloropropene and hydrogen peroxide.

The advantages of this process are as follows: (1) Direct epoxidation with hydrogen peroxide fundamentally solves the serious corrosion and pollution problems in the chlorohydrin process; (2) The epoxides generated by the reaction are removed from the reaction zone in time , effectively hindering the side reaction of the product, thereby improving the selectivity of epoxide; (3) using solvent evaporation to obtain heat, preventing the reaction section of the device from overheating, effectively preventing the thermal decomposition of hydrogen peroxide, and high hydrogen peroxide utilization; (4) Reaction and separation are coupled in one tower, the process is simple and investment is saved; (5) a large amount of reaction heat released in the epoxidation process is directly used for evaporation and separation of remaining reactants and solvents, and the utilization rate of reaction heat is high. There is no need for special heating facilities, so the device structure is simple, and the energy consumption in the production process is greatly reduced.

The following examples will further illustrate the method, but the method is not limited thereby.

The grade of titanium-silicon molecular sieve catalyst used in the examples is HTS, produced by Hunan Jianchang Petrochemical Co., Ltd. The test was carried out in a glass tower with an inner diameter of 34mm. The catalyst was placed in the reaction section of the tower in layers in the form of bundled packages. The distillation section and the stripping section were all filled with φ3×6mm ceramic rings. The distance between the upper and lower feeding ports is 1000mm. The height of the reaction section, distillation section and stripping section is set according to the specific reaction. The tower body is wrapped with mineral wool electric heating blanket for heat preservation. The tower kettle is controlled by electric heating. Cool with tap water. The composition of the samples was analyzed by gas chromatography and the residual hydrogen peroxide was analyzed by iodometric method. The feed moles of hydrogen peroxide per unit time are represented by n ₀ , the remaining moles are represented by n _r , and the moles of epoxides are represented by n _E , then

Conversion rate of hydrogen peroxide=[(n ₀ -n _r )/n0]×100%

Selectivity of hydrogen peroxide epoxidation=[n _E /(n ₀ -n _r )]×100%

Example 1

This example is the direct epoxidation of propylene to propylene oxide.

The reaction raw materials are 27% industrial hydrogen peroxide, more than 99.9% polymer grade industrial propylene, and the solvent is analytically pure methanol. Hydrogen peroxide is fed into the reaction section of the tower from the upper feed port of the reaction section by a metering pump, and the propylene after decompression and steady flow is metered by a mass flow meter and then enters the tower from the lower feed port of the reaction section. The molar ratio is 2.5:1. After the device is started, methanol is first injected from the upper part of the reaction section. After the device is running smoothly, propylene and hydrogen peroxide are added, and methanol is added at the same time until the molar ratio of propylene to methanol in the reaction section is 1:8. The reaction conditions are as follows: the temperature of the reaction section is controlled at 60°C, the reaction pressure is 0.12MPa (absolute pressure), and the mass space velocity of propylene is 1.25h ^-1 . Propylene in the tower reacts with hydrogen peroxide while dissolving, the heat released by the reaction vaporizes the methanol and the generated propylene oxide, and enters the distillation section for fractionation along with the remaining propylene in the reaction, the methanol refluxes and then enters the reaction section, and the propylene oxide and propylene from The overhead distillation section enters the condenser, and the propylene oxide is initially condensed and separated, and the remaining gas is further cryogenically separated to separate the entrained propylene oxide and then evacuated. The water generated by the reaction and the water brought into the reaction system with hydrogen peroxide enter the tower kettle. Reaction result: the conversion rate of hydrogen peroxide is 99%, and the selectivity of hydrogen peroxide epoxidation is 95.5%.

Example 2

This example is the direct epoxidation of propylene to propylene oxide.

Reaction raw material and solvent are with embodiment 1. Propylene and hydrogen peroxide are fed in a molar ratio of 4:1, and the molar ratio of propylene to methanol in the reaction section is 1:12. The reaction conditions are: the temperature of the reaction section is controlled at 70°C, the reaction pressure is 0.2MPa (absolute pressure), and the mass space velocity of propylene is 3.5h ^-1 . Process operation method is the same as embodiment 1. Reaction result: the conversion rate of hydrogen peroxide is 100%, and the selectivity of hydrogen peroxide epoxidation is 97.3%.

Example 3

This embodiment is the direct epoxidation of allyl chloride to epichlorohydrin.

The reaction raw materials are all industrial products, wherein the purity of hydrogen peroxide is 50%, and the purity of chloropropene is 97.0%; the solvent is analytically pure methanol. After the device is opened, first allyl chloride and methanol are pumped into the tower with a molar ratio of 1:9. After the device is running smoothly, hydrogen peroxide is injected, and methanol and allyl chloride are replenished at the same time until the reaction section of allyl chloride and methanol The molar ratio is 1:9. Hydrogen peroxide and methanol are pumped into the tower from the upper inlet of the reaction section by a metering pump, and allyl chloride enters the tower from the lower inlet of the reaction section, and the molar ratio of allyl chloride to hydrogen peroxide in the reaction section is controlled to be 2:1. The reaction conditions are as follows: the temperature of the reaction section is controlled at 60° C., the reaction pressure is 0.15 MPa (absolute pressure), and the mass space velocity of allyl chloride is 4.5 h ⁻¹ . The heat released by the reaction of chloropropene and hydrogen peroxide vaporizes methanol and unreacted chloropropene, and enters the distillation section together. Methanol and chloropropene return to the reaction section to participate in the reaction again, and the remaining tail gas is emptied. Epichlorohydrin, water and part of methanol enter the stripping section, methanol is extracted and enters the reaction section, and epichlorohydrin and water enter the tower kettle. Reaction result: the conversion rate of hydrogen peroxide is 100%, and the selectivity of hydrogen peroxide epoxidation is 95.7%.

Example 4

This embodiment is the direct epoxidation of allyl chloride to epichlorohydrin.

The reaction raw materials are all industrial products, wherein the purity of hydrogen peroxide is 27%, and the purity of chloropropene is 97.0%; the solvent is acetone of analytical grade. After the device is opened, first allyl chloride and acetone are pumped into the tower at a molar ratio of 1:10, and after the device is running smoothly, hydrogen peroxide is injected, and acetone and allyl chloride are replenished at the same time until the reaction stage of allyl chloride and acetone The molar ratio is 1:10, and the molar ratio of allyl chloride to hydrogen peroxide is 1.5:1. The reaction conditions are as follows: the temperature of the reaction section is controlled at 80° C., the reaction pressure is 0.2 MPa (absolute pressure), and the mass space velocity of allyl chloride is 2 h ⁻¹ . The heat released by the reaction of chloropropene and hydrogen peroxide vaporizes the solvent and unreacted chloropropene and enters the distillation section together, acetone and chloropropene return to the reaction section to participate in the reaction again, and the tail gas is emptied. Epichlorohydrin, water and part of acetone enter the stripping section, acetone is extracted and enter the reaction section, and epichlorohydrin and water enter the tower kettle. Reaction result: the conversion rate of hydrogen peroxide is 100%, and the selectivity of hydrogen peroxide epoxidation is 97.8%.

Claims (11)

1. A catalytic distillation method for direct epoxidation of olefins, characterized in that olefins, hydrogen peroxide and solvent enter the reaction section of the tower to contact and react with the titanium-silicon molecular sieve catalyst, and the vaporized solvent returns to the reaction section, and the epoxide product It can be separated from the top or bottom of the tower. 2, according to the method for claim 1, it is characterized in that described tower is made of reaction section, distillation section and/or stripping section, distillation section is positioned at the top of reaction section, stripping section is positioned at the below of reaction section, 3. A process according to claim 1, characterized in that said olefin is an alkene, a cyclic olefin, a halogenated olefin or a metapolyene. 4. The method according to claim 1 or 3, characterized in that said olefin is an alkene, a cycloolefin or a halogenated olefin containing 3 to 18 carbon atoms, more preferably propene and chloropropene. 5. A process according to claim 1 or 3, characterized in that said olefin is propylene, chloropropene. 6. The method according to claim 1, characterized in that said solvent is alcohol, ketone, acid, ester. 7. A process according to claim 1 or 6, characterized in that said solvent is an alcohol having 1 to 8 carbon atoms and a ketone having 3 to 8 carbon atoms. 8. The method according to claim 1, characterized in that the molar ratio of olefin to hydrogen peroxide is 1-10:1. 9. A process according to claim 1 or 8, characterized in that the molar ratio of olefin to hydrogen peroxide is 1.5-6:1. 10. The method according to claim 1, characterized in that the molar ratio of olefin to solvent in the reaction section is 1:3 to 1:20, the reaction temperature is 40 to 100°C, the absolute reaction pressure is 0.1 to 3 MPa, and the liquid time of the feed is The mass space velocity is 0.05~10h ^-1 in terms of olefins. 11. The method according to claim 1 or 10, characterized in that the molar ratio of olefin to solvent in the reaction section is 1:5 to 1:15, the reaction temperature is 55 to 80°C, the absolute reaction pressure is 0.1 to 1.0 MPa, and the feed The liquid hourly mass space velocity is 0.1~8h ^-1 in terms of olefins.