Continuous method and system for preparing propylene carbonate from propylene and carbon dioxide

Abstract

The method for directly preparing propylene carbonate from propylene CO2 comprises the following steps: propylene, CO2, an oxide, a solvent and the like are conveyed into a fixed bed reactor according to a certain proportion for a reaction, a liquid feed is arranged at the bottom of the fixed bed reactor, and gas enters the fixed bed reactor in a bubbling form; wherein the temperature is 30-200 DEG C, and the pressure is 1-6 MPa. An epoxidation reaction is performed in a low-temperature section, and a cycloaddition reaction is performed in a high-temperature section. The epoxidation reaction catalyst is a molecular sieve, and the cycloaddition reaction catalyst is a metal oxide or a halogen-containing compound. According to the method disclosed by the invention, a continuous process for directly synthesizing the propylene carbonate through the CO2 sequential oxidative carboxylation reaction of the propylene is realized, the separation of an intermediate product epoxypropane is reduced, and the reaction energy consumption is effectively reduced. According to the method, the propylene carbonate also has relatively high selectivity and yield under the condition that the high utilization rate of the oxidant is ensured.

Description

Technical Field

[0001] This invention relates to the preparation of propylene carbonate from propylene and carbon dioxide, and more specifically, to a continuous method for preparing propylene carbonate from propylene and carbon dioxide. Background Technology

[0002] Propylene carbonate (PC) is a new generation of high-performance green solvent. It has the characteristics of strong polarity, low vapor pressure, excellent hydrolysis resistance and thermal stability. It has become the core raw material for high-end lithium battery electrolytes, biodegradable plastics and efficient CO2 capture systems. At the same time, its downstream products can be extended to produce high value-added products such as dimethyl carbonate and propylene glycol, forming a "zero carbon" closed-loop industrial chain.

[0003] Currently, the industrialization routes of propylene carbonate (C4H6O3) in my country are mainly divided into four categories: (1) Chloropropanol-phosgene cyclization method, in which phosgene is highly toxic and a large amount of hydrochloric acid is produced as a by-product, and environmental regulations have explicitly eliminated it; (2) Propylene glycol-DMC transesterification method, in which DMC raw material is expensive and the reaction is reversible, the single-pass conversion rate is low, and a large circulation volume is required, resulting in high energy consumption; (3) Urea-propylene glycol alcoholysis method, in which the reaction rate is slow, the catalyst is easily deactivated, and the by-product ammonia needs to be treated in addition to increase costs; (4) Propylene oxide-CO2 cycloaddition reaction has high atom economy and short reaction path, and is the most widely used method at present, but propylene oxide is flammable and explosive, transportation and storage costs are high, the product price fluctuates greatly with the raw material, and the reaction requires high pressure equipment, requiring the construction of new reaction equipment, and the product separation energy consumption is high.

[0004] Propylene liquid-phase epoxidation (HPPO) technology is mature. However, the methanol solvent in the HPPO process is prone to azeotropic reaction with propylene oxide (PO), making separation difficult and undoubtedly increasing separation energy consumption. For example, Chinese patent application CN109251193A discloses a method for preparing propylene carbonate, comprising: a) reacting propylene and an oxidant in the presence of a first catalyst to obtain a first reactant containing propylene oxide, wherein the first catalyst is a molecular sieve catalyst; b) reacting the propylene oxide in the first reactant obtained in step a with carbon dioxide in the presence of a second catalyst to obtain a second reactant containing propylene carbonate, wherein the second catalyst is at least partially a molecular sieve catalyst containing a structure-directing agent. In this patent application, the product after the reaction in step (a) needs to be purified to obtain propylene oxide, and then the purified propylene oxide reacts with carbon dioxide to obtain propylene carbonate. Summary of the Invention

[0005] One object of this invention is to provide a continuous reaction method for preparing propylene carbonate. In this method, the intermediate product from propylene oxidation does not require purification and is directly reacted with CO2 to synthesize propylene carbonate. This eliminates further intermediate steps, thus reducing energy consumption. Furthermore, since the initial feedstock is propylene, rather than propylene oxide, the hazards associated with the flammability, explosiveness, and transportation difficulties of propylene oxide are avoided.

[0006] This application discloses a continuous reaction method for preparing propylene carbonate, comprising: (1) Propylene, oxidant and solvent undergo epoxidation reaction under the catalysis of molecular sieve to obtain a mixture containing propylene oxide; (2) A mixture containing propylene oxide, CO2 and an additive are mixed and subjected to an addition reaction under the action of a catalyst to obtain propylene carbonate, wherein the additive includes one or more of straight-chain saturated monohydric alcohols, polyhydric alcohols and phenol and phenolic derivatives, and the catalyst is a metal oxide and / or a halogen-containing compound.

[0007] The method for preparing propylene carbonate provided in this application uses propylene as a reaction raw material. By controlling the conditions of reaction step (2), propylene carbonate can be obtained in high yield without purifying the substances after reaction step (1). Furthermore, the product propylene carbonate is easily separated from impurities such as solvents used in the reaction process, and the step of purifying the intermediate product propylene oxide is eliminated, reducing the energy consumption of the separation process and achieving the goal of continuous production.

[0008] Compared with existing technologies, the method and system for the continuous reaction of propylene and CO2 to prepare propylene carbonate of the present invention have the following advantages: (1) This invention employs a continuous reaction process to directly generate propylene carbonate by connecting reactants such as propylene, oxidant, and CO2 in series. This ensures the utilization rate of the oxidant and that propylene carbonate exhibits high selectivity.

[0009] (2) This invention employs a sequential reaction, where the propylene oxide-containing mixture produced by the epoxidation reaction can undergo a cycloaddition reaction without separation and purification, converting it into propylene carbonate. This effectively avoids the energy-intensive process of separating propylene oxide from the solvent and reduces the dangers of transporting propylene oxide. It effectively reduces energy consumption and improves process safety.

[0010] (3) The unseparated alcohols / water in this invention are efficient hydrogen bond donors, which are beneficial for promoting the cycloaddition reaction and reducing the energy barrier required for the cycloaddition reaction. They are also efficient absorbers of CO2 and solvents for dissolving homogeneous catalysts, eliminating the need for expensive and specific ionic liquids to promote the contact between CO2 / catalyst and propylene oxide; the same effect can be achieved using cheaper catalysts. This invention effectively saves production costs and enhances the market competitiveness of the product. Especially with the help of phenol or diphenol additives, the addition of additives can strongly complex water and methanol molecules in the reaction system through hydrogen bonds, stabilizing the intermediate state of propylene oxide ring opening, thereby inhibiting the occurrence of side reactions and further improving the selectivity of propylene carbonate.

[0011] (4) Compared with the traditional two-step synthesis of propylene carbonate, this method significantly simplifies the process. It eliminates the need for complex separation, purification, storage and transportation, as well as re-separation and purification processes, requiring only one separation and purification step, effectively improving the overall economic efficiency of the process. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a reaction process for preparing propylene carbonate according to this application. Detailed Implementation

[0014] The method for preparing propylene carbonate by a continuous reaction according to the present invention is described in further detail below. The scope of protection of the present invention is not limited thereto, but is defined by the claims. Certain specific details disclosed provide a full understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments may be implemented using other materials, etc., without employing one or more of these specific details.

[0015] Unless the context otherwise requires, the terms “comprising” and “including” in the specification and claims shall be understood as open-ended and inclusive, meaning “including, but not limited to”.

[0016] The terms "implementation," "an implementation," "another implementation," or "certain implementations" used in this specification refer to specific features, structures, or characteristics described in relation to the implementation, which are included in at least one implementation. Therefore, "implementation," "an implementation," "another implementation," or "certain implementations" do not necessarily all refer to the same implementation. Furthermore, specific features, structures, or characteristics can be combined in any way within one or more implementations. Each feature disclosed in this specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0017] As described in the background section, methanol solvent in the propylene epoxidation process readily azeotropically with propylene oxide (PO), making separation difficult and undoubtedly increasing separation energy consumption. This application presents a continuous process coupling the liquid-phase epoxidation and cycloaddition reactions of propylene. By adding CO2 to the liquid-phase epoxidation reaction, propylene oxide is directly added to propylene carbonate in the presence of a solvent. This tandem reaction effectively avoids the energy consumption associated with propylene oxide separation, and the protic solvent, methanol, effectively promotes the cycloaddition reaction. This technical route saves on the separation energy consumption of the first-step epoxidation reaction and simplifies the purification and transportation of the raw material propylene oxide in the second-step cycloaddition reaction, effectively improving the overall economic efficiency of the process.

[0018] A method for preparing propylene carbonate by continuous reaction, comprising: (1) Propylene, oxidant, CO2 and solvent undergo epoxidation reaction at a certain temperature under the catalysis of molecular sieve to obtain a mixture containing propylene oxide; (2) A mixture containing propylene oxide is mixed with an additive and subjected to an addition reaction under the action of a cycloaddition catalyst to obtain propylene carbonate. The additive includes one or more of the following: straight-chain saturated monohydric alcohols, polyhydric alcohols, phenol and phenolic derivatives. The catalyst is a metal oxide and / or a halogen-containing compound.

[0019] Optional approach: A method for the continuous reaction preparation of propylene carbonate, comprising: (1) Propylene and oxidant undergo epoxidation reaction at a certain temperature under the catalysis of molecular sieve to obtain a mixture containing propylene oxide; (2) CO2 is introduced into a mixture containing propylene oxide and then mixed with an additive under the action of a catalyst to undergo an addition reaction to obtain propylene carbonate. The additive includes one or more of the following: straight-chain saturated monohydric alcohols, polyhydric alcohols, phenol and phenolic derivatives. The catalyst is a metal oxide and / or a halogen-containing compound.

[0020] The oxidizing agents include tert-butyl hydroperoxide, cyclohexyl hydroperoxide, cumene peroxide, and peroxide. At least one or more of ethylbenzene, hydrogen peroxide, peracetic acid, and perpropionic acid.

[0021] Preferably, the oxidant is hydrogen peroxide.

[0022] The solvent includes at least one or more of methanol, ethanol, acetonitrile, acetone and water.

[0023] Preferably, the solvent is methanol or acetonitrile.

[0024] The molecular sieves include one or a mixture of two or more of the following: titanium-silicon molecular sieves, silicon-aluminum molecular sieves, and heteroatom molecular sieves.

[0025] Preferably, the titanium-silicon molecular sieve includes at least one or more of TS-1, Ti-MWW, Ti-Beta, and Ti-MOR.

[0026] The preferred titanium-silicon molecular sieve is TS-1 titanium-silicon molecular sieve.

[0027] Alternatively, the straight-chain saturated monohydric alcohol may include at least one or more of ethanol, n-propanol, n-butanol, n-pentanol, and n-hexanol.

[0028] The polyols include at least one or more of ethylene glycol and polyethylene glycol.

[0029] In step (2), the mass ratio of the auxiliary agent to the mixture containing propylene oxide is less than 10%; Preferably, the mass ratio of the additive to the mixture containing propylene oxide is 0.05%-5%; More preferably, the mass ratio of the additive to the mixture containing propylene oxide is 0.05%-0.1%.

[0030] The mixture containing propylene oxide here refers to the mixture of all substances after the reaction in step (1), such as solvent, product and unreacted reactants; it can also be the total mass of all substances added at the beginning of the reaction (including the total mass of reactants and solvent).

[0031] The auxiliary agent is preferably selected from one or more of phenol and phenolic derivatives. Phenolic derivatives include o-diphenol, p-diphenol, or m-diphenol, etc.

[0032] Adding the additive effectively improves the selectivity of propylene carbonate; adding 0.1% can increase the selectivity by approximately 6-10%, significantly improving the overall yield of propylene carbonate. The additive also effectively suppresses the side reaction of propylene oxide and water to produce 1-2-propylene glycol. The additive strongly complexes water and methanol molecules in the reaction system through hydrogen bonds, weakening their attack on propylene oxide and stabilizing the ring-opening intermediate state of propylene oxide, thereby inhibiting the occurrence of side reactions.

[0033] The cycloaddition catalyst in step (2) includes homogeneous and heterogeneous catalysts. The homogeneous catalysts include ionic liquids, inorganic metal salts, and quaternary ammonium salt catalysts; the heterogeneous catalysts include metal oxides, supported catalysts, and functionalized molecular sieves, etc.

[0034] In some embodiments, the catalyst in step (2) is a halogenated compound, including one or more of metal halides, quaternary ammonium salts or functionalized ionic liquids.

[0035] Metal halides include potassium iodide and / or potassium bromide.

[0036] Alternatively, the catalyst may be a quaternary ammonium salt, including one or a mixture of two or more of tetrabutylammonium bromide, tetrabutylammonium iodide, and tetraethylammonium iodide.

[0037] Optionally, in step (2), the amount of catalyst added is 0.5-10% of the total mass of the mixed solvent system including propylene oxide.

[0038] The mixed solvent system, including propylene oxide, refers to the mixture of all substances after the reaction in step (1), such as solvent, product and unreacted reactants; it can also be the total mass of all substances added at the beginning of the reaction (including the total mass of reactants and solvent).

[0039] The mass of the mixed solvent here includes all components after the reaction in step (1), such as solvent, product, unreacted reactants, etc.

[0040] In some embodiments, the catalyst in step (2) is a metal oxide, including single metal oxides (such as zinc oxide, magnesium oxide, etc.) or composite metal oxides (such as hydrotalcite, etc.).

[0041] In step (2), the reaction temperature is controlled at 80-200℃.

[0042] In some embodiments, the reaction temperature in step (1) is 30-60°C.

[0043] The reaction solvent is an alcohol, such as methanol.

[0044] In step (1), the molar ratio of propylene to hydrogen peroxide is 1:(0.1-1). Alternatively, the molar ratio of propylene to hydrogen peroxide is 1:(0.3-1).

[0045] The molar ratio of propylene to CO2 is 1:(1-5).

[0046] In step (1), under pressurized conditions, liquid propylene, hydrogen peroxide and methanol react at low temperature (30-60℃) under the action of a catalyst molecular sieve to produce propylene oxide.

[0047] In step (1), the oxidant is generally an aqueous solution or organic solution of the oxidant, with a mass fraction of 10-80%. For example, a 30% aqueous solution of hydrogen peroxide.

[0048] In step (1), the mass ratio of the oxidant to the solvent is 1:(10-60); preferably, the mass ratio of the oxidant to the solvent is 1:(10-50). Within this range, the oxidant (e.g., hydrogen peroxide) is more stable, and there are fewer byproducts after the reaction in step (1).

[0049] In the propylene oxidation process, the solvent methanol and the product propylene oxide are difficult to separate. The method provided in this application does not require purification of propylene oxide. Instead, all the epoxidation products are directly added to carbon dioxide in the presence of a catalyst and auxiliaries to prepare propylene carbonate. Furthermore, the propylene carbonate has high selectivity.

[0050] In some embodiments, the silicon-to-titanium ratio of the titanium-silicon molecular sieve is 20-200, and the preferred silicon-to-titanium ratio is 20-60.

[0051] The silicon-to-titanium ratio refers to the molar ratio of silicon to titanium.

[0052] Titanium silicate molecular sieves can be processed into strip shapes and spherical shapes.

[0053] Preferably, the formed strip catalyst is made by extruding TS-1 titanium silicon molecular sieve powder, neutral silica sol, and additives such as guar gum powder and water through an extruder.

[0054] Neutral silica sol and guar gum powder are used for molecular sieve powder molding, and the amount used can be selected according to the actual molding requirements.

[0055] In some embodiments, the titanium-silicon molecular sieve is treated in an aqueous solution of tetrapropylammonium hydroxide at a temperature of 100-200°C prior to the catalytic reaction.

[0056] The mass fraction of tetrapropylammonium hydroxide aqueous solution is 5-25%.

[0057] The titanium-silicon molecular sieve treated in a tetrapropylammonium hydroxide aqueous solution is then dried to remove moisture.

[0058] Titanium silicate molecular sieves treated with tetrapropylammonium hydroxide (TPA) aqueous solution can be directly applied to propylene oxidation reaction systems, or they can be extruded and molded before being applied to propylene oxidation reaction systems.

[0059] The catalyst can be modified and its performance improved by steam treatment of the catalyst in a high-temperature crystallization kettle with an aqueous solution of tetrapropylammonium hydroxide.

[0060] In the reaction system (including steps (1) and (2)), the reaction pressure is maintained at 1-6 MPa. Preferably, the reaction pressure is maintained at 2.5-3.5 MPa.

[0061] The raw material space velocity is 0.1-5 h⁻¹. -1 .

[0062] Propylene is fed through the liquid phase, while CO2 and equilibrium gas N2 are fed through the gas phase.

[0063] By employing the continuous synthesis process of propylene carbonate provided in this application, propylene, an oxidant (such as hydrogen peroxide (H2O2)), and CO2 are sequentially oxidized and carboxylated to synthesize propylene carbonate. Hydrogen peroxide exhibits high utilization and propylene carbonate demonstrates high selectivity. This application achieves the sequential generation of propylene carbonate by coupling the liquid-phase epoxidation reaction and cycloaddition reaction of propylene, avoiding the flammable and explosive hazards during the transportation of propylene oxide in the two-step process of existing technologies, and eliminating the step of separating and purifying the intermediate product propylene oxide. This significantly reduces energy consumption and improves the overall economic efficiency of the process.

[0064] The propylene CO2 continuous reaction technology for producing propylene carbonate presented in this application can be based on existing epoxidation reactors. As both are high-pressure reactions, only the reaction temperature and other conditions need to be changed to quickly establish a propylene carbonate production facility. This propylene CO2 continuous reaction technology can help companies quickly transform from producing intermediate products to producing high-end chemical products, thereby seizing a share of the high-end carbonate chemical market.

[0065] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0066] Reference Appendix Figure 1 A process flow diagram for the continuous preparation of propylene carbonate is provided, wherein the method for the continuous preparation of propylene carbonate includes: (1) The propylene in the first tank 1 is pressurized to become liquid propylene and is pumped into the first half of the reactor 6 by the first high-pressure liquid phase pump 2. The mixed solution of hydrogen peroxide and methanol in the second tank 3 is also pumped into the first half of the reactor 6 by the second high-pressure liquid phase pump 4. Carbon dioxide and nitrogen in the third tank 5 enter the first half of the reactor 6 through a gas flow meter.

[0067] Propylene, oxidant, and CO2 are fed into the first half of the fixed-bed reactor in a molar ratio of 1:(0.1-1):(1-5). (2) The gas-liquid mixture is reacted in the first half of the fixed bed reactor at 30-60°C, and then enters the second half of the fixed bed reactor 7 at 80-200°C for reaction, with the overall pressure maintained at 1-6 MPa.

[0068] (3) The product is collected through condenser 8 and the product components are analyzed by gas chromatography.

[0069] Example 1 Preparation of TS-1 titanium-silicon molecular sieve catalyst 17.0 g of 25 wt% tetrapropylammonium hydroxide (TPAOH) was weighed and uniformly mixed with 21.0 g of deionized water, denoted as mixed solution A. Subsequently, 30.5 g of tetraethyl orthosilicate (TEOS) and 1.2 g of tetrabutyl titanate (TBOT) were weighed, uniformly mixed, and added to the previously prepared solution A, and stirred until homogeneous to obtain solution B. Solution B was ultrasonically treated for 5 min. After ultrasonic treatment, the solution was transferred to a crystallization vessel and crystallized at 170 °C for 24 h. After crystallization, a catalyst suspension was obtained, which was then centrifuged, and the solid was washed with deionized water until neutral. The catalyst was then dried in an oven at 80 °C for 12 h. After drying, it was removed and ground into a uniform powder. Finally, the powdered catalyst was calcined in a muffle furnace at 550 °C for 6 h to obtain TS-1 titanium-silicon molecular powder catalyst.

[0070] First, TS-1 titanium-silicon molecular powder was ground to below 60 mesh and added to a stainless steel crystallization kettle along with a 10wt% TPA aqueous solution. After modification at 170℃ for 24 h, the powder was removed, washed with deionized water, and dried in an 80℃ oven for 12 h to obtain dried titanium-silicon molecular sieves. A certain amount of guar gum powder and 30wt% silica sol were added to the dry molecular sieve, mixed thoroughly, and then dried in an oven at 80℃ for 12 h. The mass ratio of SiO2 to TS-1 in the silica sol was 1:4, and the mass of guar gum powder was 3% of the mass of TS-1. The thoroughly mixed material was then extruded into strands using an extruder. The formed catalyst was dried in an 80℃ oven for 12 h and then calcined at 550℃ for 6 h to obtain the extruded TS-1 molecular sieve catalyst.

[0071] Preparation of cycloaddition catalysts Tetrabutylammonium bromide, hexadecyltrimethylammonium bromide, and ammonia were added to 150 mL of an aqueous solution in a molar ratio of 1:2:2, with a bromine source concentration of 0.2 mol / L. After stirring, a homogeneous mixture was obtained. 2.8 g of tetraethyl orthosilicate was added to the mixture, and stirring was continued for 5 h to obtain a suspension. The suspension was centrifuged and washed with deionized water to obtain a white solid. The white solid was dried in an oven at 80 °C for 12 h to obtain a bromine-supported cycloaddition catalyst.

[0072] Example 2 In this embodiment, the titanium-silicon molecular sieve prepared in Example 1 is used as the epoxidation catalyst and the bromine-supported catalyst is used as the cycloaddition catalyst.

[0073] A methanol solution containing liquid propylene, 30% hydrogen peroxide, CO2, and balancing nitrogen gas was introduced into the first half of the fixed-bed reactor. The molar ratio of propylene, hydrogen peroxide, and CO2 was 3:1:3, and the pressure of the entire gas mixture was 3 MPa. 5 g of the strip-shaped TS-1 molecular sieve prepared in Example 1 was placed in the first half of the reactor. The mass hourly space velocities (WHSVs) of the liquid propylene, hydrogen peroxide, and methanol were 0.8 h⁻¹. -1 0.2h -1 2.5h -1 The reactant solution enters the first half of the reactor from bottom to top, where an epoxidation reaction is first carried out at 40°C. Then, all the reactants from the first half of the reactor enter the second half of the reactor for a cycloaddition reaction at 100°C. 5g of the bromine-supported catalyst prepared in Example 1 is placed in the second half of the reactor. The mixture discharged from the first half of the reactor enters the second half of the reactor and is continuously heated to the cycloaddition reaction temperature. The reaction products exiting the second half of the reactor enter a condenser for gas-liquid separation at -10°C, separating a mixed product containing propylene carbonate (mainly propylene carbonate, containing a small amount of unreacted propylene oxide and trace amounts of byproducts such as propylene glycol monomethyl ether and propylene glycol).

[0074] In the embodiments and comparative examples of this application, the gas phase components were analyzed by gas chromatography (propylene carbonate was basically undetectable), and the liquid phase products were collected, an internal standard (trimethylbenzene) was added, and then gas chromatography was performed.

[0075] The final products in the liquid phase were quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0076] Example 3 The method for preparing propylene carbonate in this embodiment was carried out according to the method of Example 2. The difference was that, after the epoxidation reaction in the first half of the reactor, catechol was added after the mixture was discharged from the first half of the reactor and before it entered the second half of the reactor. The mass of catechol was 0.1 wt% of the initial total mass of the influent. It was dissolved in methanol and introduced through a side stream, with a methanol-to-catechol mass ratio of 100:1. The final liquid product was quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0077] Example 4 The method for preparing propylene carbonate in this embodiment is the same as that in Example 2, except that the cycloaddition catalyst is changed from a bromine-supported catalyst to tetrabutylammonium bromide, which is a homogeneous catalyst. After the mixture from the epoxidation reaction in the first half of the reactor is discharged from the first half of the reactor, and before entering the second half of the reactor, tetrabutylammonium bromide is added. The mass of tetrabutylammonium bromide is 8 wt% of the initial total mass of the influent. It is dissolved in methanol and then introduced into the reactor via a side stream. The mass ratio of methanol to tetrabutylammonium bromide is 2:1. The final liquid product is quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0078] Example 5 The method for preparing propylene carbonate in this embodiment is the same as in Example 4, except that catechol is added as an auxiliary agent. The method of introducing catechol and the amount added are the same as in Example 3. The final product in the liquid phase was quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0079] Example 6 The method for preparing propylene carbonate in this embodiment is the same as in Example 4, except that the cycloaddition catalyst was changed from tetrabutylammonium bromide to tetrabutylammonium iodide. The final product in the liquid phase was quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0080] Examples 7-11 The methods for preparing propylene carbonate in Examples 7-11 are the same as in Example 6, with the addition of catechol as an auxiliary agent. The catechol introduction method is the same as in Example 3. The amounts of catechol added in Examples 7-10 are 0.03 wt%, 0.05 wt%, 0.07 wt%, 0.10 wt%, and 0.12 wt%, respectively. The final liquid phase products were quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0081] Example 12 The difference between this embodiment 12 and other embodiments is that this embodiment uses an intermittent method to prepare propylene carbonate.

[0082] The steps and parameters for preparing propylene oxide are as described in Example 2. A methanol solution containing liquid propylene and 30% hydrogen peroxide is subjected to an oxidation reaction in the first half of a fixed-bed reactor under the action of TS-1 molecular sieve. The molar ratio of propylene to hydrogen peroxide is 3:1.

[0083] Unlike Example 2, 14.787 g of the product from the first step of the epoxidation reaction was directly subjected to the cycloaddition reaction without separation. This required high temperature to consume excess hydrogen peroxide, and the reaction catalyst was 0.568 g of tetrabutylammonium iodide. After exiting the microreactor, the reaction product entered a condenser for gas-liquid separation at -10°C. The separated liquid phase was the final product, propylene carbonate. The final liquid phase product was quantitatively analyzed and calculated using gas chromatography, as shown in Table 2.

[0084] Example 13 The difference between this embodiment 13 and other embodiments is that this embodiment uses an intermittent method to prepare propylene carbonate.

[0085] The steps and parameters for preparing propylene oxide are as described in Example 2. A methanol solution containing liquid propylene and 30% hydrogen peroxide is subjected to an oxidation reaction in the first half of a fixed-bed reactor under the action of TS-1 molecular sieve. The molar ratio of propylene to hydrogen peroxide is 3:1.

[0086] Unlike Example 2, 14.787 g of the product from the first step of the epoxidation reaction was directly subjected to the cycloaddition reaction without separation. This required high temperature to consume excess hydrogen peroxide. The reaction catalyst was 0.568 g of tetrabutylammonium iodide, and 0.014 g of catechol was added. After exiting the microreactor, the reaction product entered a condenser for gas-liquid separation at -10°C. The separated liquid phase was the final product, propylene carbonate. The final liquid phase product was quantitatively analyzed and calculated using gas chromatography, as shown in Table 2.

[0087] Comparative Example 1 This comparative example uses a one-pot method to synthesize propylene carbonate. This comparative example uses the method of Example 1 to prepare epoxidized solid-formed titanium-silicon molecular sieve catalyst. The difference is that the formed catalyst is ground into powder catalyst; and the bromine-supported catalyst for cycloaddition and 30% hydrogen peroxide and methanol solvent are used. All proportions are the same as in Example 2, and the reaction time is 1 hour.

[0088] The aforementioned titanium-silicon molecular sieve catalyst and bromine-supported catalyst were placed in a reactor. The temperature was raised to 100°C, and then 0.4 MPa of propylene and 1.5 MPa of CO2 were introduced into the reactor. The remaining pressure was supplemented with nitrogen to 3 MPa, and the reaction proceeded. After the reaction was completed, the temperature was lowered. The final products in the liquid phase were quantitatively analyzed and calculated using gas chromatography, as shown in Table 1.

[0089] Comparative Example 2 This comparative example is the same as Comparative Example 1, except that the bromine-supported catalyst was replaced with tetrabutylammonium bromide. The final products in the liquid phase were quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0090] Comparative Example 3 In Comparative Example 3, the cycloaddition of pure propylene oxide with carbon dioxide in a solvent-free system was investigated. The steps and parameters for preparing propylene oxide in this comparative example are the same as in Example 2. A methanol solution containing liquid propylene and 30% hydrogen peroxide was reacted in the first half of the reactor under the action of TS-1 molecular sieves. The molar ratio of propylene to hydrogen peroxide was 3:1. The reactants were separated and purified to obtain pure propylene oxide. The purified propylene oxide was then fed back into the second half of the reactor according to the propylene oxide flow rate ratio, with other conditions the same as in Example 2. The final liquid phase products were quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0091] Comparative Example 4 In Comparative Example 4, the cycloaddition of pure propylene oxide with carbon dioxide in a solvent-free system was investigated. The steps and parameters for preparing propylene oxide in this comparative example are the same as in Example 4. A methanol solution containing liquid propylene and 30% hydrogen peroxide was reacted in the first half of the reactor under the action of TS-1 molecular sieves. The molar ratio of propylene to hydrogen peroxide was 3:1. The reactants were separated and purified to obtain pure propylene oxide. The purified propylene oxide was then fed back into the second half of the reactor according to the propylene oxide flow rate ratio, with other conditions the same as in Example 4. The final liquid product was quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0092] Comparative Example 5 In Comparative Example 5, the cycloaddition of pure propylene oxide with carbon dioxide in a solvent-free system was investigated. The steps and parameters for preparing propylene oxide in this comparative example are the same as in Example 5. A methanol solution containing liquid propylene and 30% hydrogen peroxide was reacted in the first half of the reactor under the action of TS-1 molecular sieves. The molar ratio of propylene to hydrogen peroxide was 3:1. The reactants were separated and purified to obtain pure propylene oxide. The purified propylene oxide was then fed back into the second half of the reactor according to the propylene oxide flow rate ratio, with other conditions the same as in Example 4. The final liquid phase products were quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0093] Comparative Example 6 In Comparative Example 6, the cycloaddition of pure propylene oxide with carbon dioxide in a solvent-free system was investigated. The steps and parameters for preparing propylene oxide in this comparative example are the same as in Example 6. A methanol solution containing liquid propylene and 30% hydrogen peroxide was reacted in the first half of the reactor under the action of TS-1 molecular sieves. The molar ratio of propylene to hydrogen peroxide was 3:1. The reactants were separated and purified to obtain pure propylene oxide. The purified propylene oxide was then fed back into the second half of the reactor according to the propylene oxide flow rate ratio, with other conditions the same as in Example 4. The final liquid phase products were quantitatively analyzed and calculated by gas chromatography, as shown in Table 1.

[0094] Comparative Example 7 In Comparative Example 7, the cycloaddition of pure propylene oxide with carbon dioxide in a solvent-free system was investigated. The steps and parameters for preparing propylene oxide are as described in Example 2. A methanol solution containing liquid propylene and 30% hydrogen peroxide is reacted in the first half of the reactor under the action of TS-1 molecular sieve. The molar ratio of propylene to hydrogen peroxide is 3:1. The reacted substances are separated and extracted to obtain pure propylene oxide. Purified propylene oxide (PO) and carbon dioxide were introduced into a microreactor. The reaction pressure was 3 MPa, the reaction temperature was 100 °C, and the reaction time was 1 h. The proportions were the same as those of the product after complete reaction in Example 2: PO mass 1.423 g, and the reaction catalyst mass tetrabutylammonium iodide 0.568 g. After exiting the microreactor, the reaction product entered a condenser for gas-liquid separation at -10 °C. The separated liquid phase was the final product, propylene carbonate. The final liquid phase product was quantitatively analyzed and calculated by gas chromatography, as shown in Table 2.

[0095] Comparative Example 8 Comparative Example 8 was prepared using the same method as Comparative Example 7, except that the cycloaddition reaction of propylene oxide (PO) and carbon dioxide in step (2) was carried out using 1-ethyl-3-methylimidazolium acetate as the catalyst. The final liquid phase products were quantitatively analyzed and calculated by gas chromatography, as shown in Table 2.

[0096]

[0097] Calculation formula Formula for calculating oxidant conversion rate: Oxidant conversion rate = (Total molar amount of oxidant - Molar amount of oxidant remaining in the product) / Total molar amount of oxidant Formula for calculating the effective utilization rate of oxidant: Effective utilization rate of oxidant = Sum of the total molar amounts of all products in the product / Molar amount added for oxidation Selectivity of propylene carbonate: molar amount of PC in the product / total molar amount of all products in the product.

[0098]

[0099] Calculation formula Since propylene oxide was separated and purified, only the conversion rate and selectivity of the second step of propylene oxide to the target product propylene carbonate and by-products were calculated, while the by-products of the first step of epoxidation were ignored.

[0100] Byproducts: The total molar amount of all products other than PC / the molar amount of reactant PO. Selectivity of propylene carbonate: molar amount of PC in the product / molar amount of PO in the reactant It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for the continuous reaction preparation of propylene carbonate, comprising: (1) Propylene, oxidant, CO2 and solvent undergo epoxidation reaction at a certain temperature under the catalysis of molecular sieve to obtain a mixture containing propylene oxide; (2) A mixture containing propylene oxide is mixed with an additive and subjected to an addition reaction under the action of a cycloaddition catalyst to obtain propylene carbonate, wherein the additive includes one or more of the following: straight-chain saturated monohydric alcohols, polyhydric alcohols, phenol and phenolic derivatives, and the catalyst is a metal oxide and / or a halogen-containing compound. Preferably, the oxidant includes at least one or more of tert-butyl hydroperoxide, cyclohexyl hydroperoxide, cumene peroxide, ethylbenzene peroxide, hydrogen peroxide, peracetic acid, and peroxypropionic acid.

2. A method for the continuous reaction preparation of propylene carbonate, comprising: (1) Propylene, oxidant and solvent undergo epoxidation reaction at a certain temperature under the catalysis of molecular sieve to obtain a mixture containing propylene oxide; (2) CO2 is introduced into a mixture containing propylene oxide, and then mixed with an additive under the action of a catalyst to carry out an addition reaction to obtain propylene carbonate. The additive includes one or more of the following: straight-chain saturated monohydric alcohols, polyhydric alcohols, phenol and phenolic derivatives. The catalyst is a metal oxide and / or a halogen-containing compound. Preferably, the oxidant includes at least one or more of tert-butyl hydroperoxide, cyclohexyl hydroperoxide, cumene peroxide, ethylbenzene peroxide, hydrogen peroxide, peracetic acid, and peroxypropionic acid.

3. The method according to claim 1 or 2, characterized in that, The solvent includes at least one or more of methanol, ethanol, acetonitrile, acetone and water; Preferably, the mass ratio of the oxidant to the solvent is 1:(10-60). Preferably, the mass ratio of the oxidant to the solvent is 1:(10-50).

4. The method according to claim 1 or 2, characterized in that, In step (2), the auxiliary agent includes one or a mixture of two or more of the following: straight-chain saturated monohydric alcohols, polyhydric alcohols, phenol and phenolic derivatives; Preferably, the additive is o-diphenol, p-diphenol, or m-diphenol.

5. The method according to any one of claims 1-4, characterized in that, The mass ratio of the additive to the mixture containing propylene oxide is less than 10%; Preferably, the mass ratio of the additive to the mixture containing propylene oxide is 0.05%-5%; More preferably, the mass ratio of the additive to the mixture containing propylene oxide is 0.05%-0.1%.

6. The method according to any one of claims 1-5, characterized in that, The cycloaddition catalyst in step (2) includes homogeneous catalysts and heterogeneous catalysts, which are halogen-containing compounds, including one or more of metal halides, quaternary ammonium salts or functionalized ionic liquids; Preferably, the catalyst is a quaternary ammonium salt; More preferably, the quaternary ammonium salt is selected from one or more of tetrabutylammonium bromide, tetrabutylammonium iodide and tetraethylammonium iodide.

7. The method according to any one of claims 1-6, characterized in that, In step (2), the amount of catalyst added is 0.5-20% of the total mass of the mixed solvent system, including propylene oxide; Preferably, the amount of catalyst added is 5-10% of the total mass of the mixed solvent system, including propylene oxide.

8. The method according to any one of claims 1-7, characterized in that, In step (2), the cycloaddition reaction temperature is controlled at 80-200℃; In step (1), the reaction temperature is 30-60℃.

9. The method according to any one of claims 1-2, characterized in that, Molecular sieves include one or more of the following: titanium silicate molecular sieves, silica alumina molecular sieves, and heteroatom molecular sieves. Preferably, the catalyst is a titanium-silicon molecular sieve; Preferably, the silicon-to-titanium ratio of the titanium-silicon molecular sieve is 20-200; The preferred silicon-to-titanium ratio is 20-60.

10. The method according to any one of claims 1-9, characterized in that, The molecular sieve catalyst was treated in an aqueous solution of tetrapropylammonium hydroxide at a temperature of 100-200℃ before the catalytic reaction. The mass fraction of tetrapropylammonium hydroxide aqueous solution is 5-25%.

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