Process for the continuous preparation of cyclic carbonates

Abstract

The present invention relates to a process for continuously producing a cyclic carbonate product by reacting an epoxide with carbon dioxide in the presence of a heterogeneous catalyst activated by an activating compound. The process is carried out in a first reactor, a second reactor, and a third reactor, each containing a slurry of the heterogeneous catalyst and the cyclic carbonate product present as a liquid. Carbon dioxide and an epoxide compound are continuously fed to the first reactor, the liquid cyclic carbonate is discharged, and unreacted carbon dioxide and epoxide are discharged as a first gaseous effluent stream to the second reactor, while substantially all of the heterogeneous catalyst remains in the first reactor. An activating compound is added to the third reactor. In the next step of the process, the third reactor becomes the second reactor, the second reactor becomes the first reactor, and the first reactor becomes the third reactor.

Description

[Technical field]

[0001] 1. A process for continuously preparing a cyclic carbonate product by reacting an epoxide compound with carbon dioxide in the presence of a heterogeneous catalyst activated by an activating compound, the process being carried out in at least a first reactor, a second reactor and a third reactor, each reactor containing the supported catalyst and a slurry of the cyclic carbonate product present as a liquid. [Background technology]

[0002] US2017197931 describes a process for preparing ethylene carbonate by reacting carbon dioxide with ethylene oxide in three fixed-bed adiabatic reactors in series at 8 MPa and reactor temperatures between 60 and 140° C. Bromo-ethanol is added with the feed to activate the catalyst.

[0003] EP 2257559 B1 describes a continuous process for the preparation of ethylene carbonate from ethylene oxide and carbon dioxide. The reaction is carried out in the presence of a dimeric aluminum salen complex supported on a modified SiO2 support as catalyst and nitrogen gas. The supported catalyst is present in a tubular reactor and the reactants are fed to the tubular reactor as a gaseous mixture of ethylene oxide, carbon dioxide and nitrogen. The temperature in the reactor is maintained at 60°C by a water bath and the pressure is atmospheric. The yield of ethylene carbonate was 80%.

[0004] For example, the advantage of the process of EP2257559B1 compared to the above-mentioned US2017197931 is that the reaction conditions can be close to ambient in terms of temperature and pressure. This results in a lower energy consumption of the process and less generation of by-products. However, the disadvantage of the continuous process described in EP2257559B1 is that the tubular reactor requires external cooling to avoid overheating as a result of the exothermic reaction to ethylene carbonate.

[0005] WO2019 / 125151 describes a method in which carbon dioxide and an epoxide compound react in a suspension of a liquid cyclic carbonate and a supported dimeric aluminum salen complex. According to this document, the liquid cyclic carbonate product acts as an efficient heat transfer medium to avoid overheating. In this method, the deactivated dimeric aluminum salen complex is reactivated by contacting the complex with a halide compound acting as an activating compound. Reactivation can be carried out by adding a halide compound to the deactivated dimeric aluminum salen complex in a separate step without adding extra carbon dioxide and epoxide compounds. The reaction can be carried out in a series of continuously stirred reactors, with the last reactor separating the cyclic carbonate product from the supported dimeric aluminum salen complex. The problem with this type of reactor configuration is that lower conversions are obtained and more reactor volume is required to achieve the desired production capacity. Additionally, operational problems such as clogging, plugging, pump failure, erosion, wear, breakage and leakage can occur with this type of reactor configuration. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent Application Publication No. 2017 / 197931 [Patent Document 2] European Patent No. 2257559 [Patent Document 3] International Publication No. 2019 / 125151 Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide a method that does not have the drawbacks described in the method of WO2019 / 125151. This is achieved in the following way: [Means for solving the problem]

[0008] 1. A process for continuously preparing a cyclic carbonate product by reacting an epoxide compound with carbon dioxide in the presence of a heterogeneous catalyst activated by an activating compound, comprising: The process is carried out in at least a first reactor, a second reactor, and a third reactor, each reactor containing the heterogeneous catalyst and a slurry of cyclic carbonate product present as a liquid; carbon dioxide and an epoxide compound are continuously fed to the first reactor, liquid cyclic carbonate is discharged as a first product stream, and unreacted carbon dioxide and epoxide are discharged as a first gaseous effluent stream, while substantially all of the heterogeneous catalyst remains in the first reactor, and the heterogeneous catalyst eventually becomes deactivated; a second reactor is continuously fed with the first gaseous effluent, liquid cyclic carbonate is discharged as a second product stream, and unreacted carbon dioxide and epoxide are discharged as a second gaseous effluent stream, while substantially all of the heterogeneous catalyst remains in the second reactor; adding an activating compound to the third reactor to activate the heterogeneous catalyst, thereby obtaining a reactor containing an activated heterogeneous catalyst; In the next step of the process, the third reactor becomes the second reactor, the second reactor becomes the first reactor and the first reactor becomes the third reactor, and the deactivated catalyst present in said reactor is activated.

[0009] Applicants have found that by practicing the process according to the invention, more efficient conversion of epoxide compounds to the desired cyclic carbonate products is possible, and further, since substantially all of the heterogeneous catalyst remains in the same reactor, there is no need to transfer, i.e., pump, a suspension containing the catalyst from one reactor to another.

[0010] In the first and second reactors, carbon dioxide is contacted with the epoxide compound in suspension in the liquid cyclic carbonate. Temperature and pressure conditions are selected such that the cyclic carbonate is in its liquid state. Temperature and pressure conditions are further selected such that the carbon dioxide and the epoxide are soluble in the liquid cyclic carbonate reaction medium. The temperature may be between 0 and 200°C, the pressure between 0 and 5.0 MPa (absolute), and the temperature is below the boiling point of the cyclic carbonate product at the selected pressure. At the high end of these temperature and pressure ranges, complex reactor vessels are required. Since favorable results in terms of selectivity and yield to the desired carbonate product can be achieved at lower temperatures and pressures, the temperature in the first and second reactors is between 20 and 150°C, more preferably between 40 and 120°C, and the absolute pressure is between 0.1 and 0.5 MPa, more preferably between 0.1 and 0.3 MPa. The pressure in the first reactor may be higher than the pressure in the second reactor. This is advantageous because no special means, such as a compressor or blower, need be present to create a flow of the first gaseous effluent to the second reactor.

[0011] In the process according to the invention, the first, second and third reactors change their relative operation modes after each step of the process. One step of the process involves operating the first and second reactors as described to prepare the cyclic carbonate product while the catalyst in the third reactor is regenerated. In the first reactor, a bulk operation is performed, in the second reactor, a finishing operation is performed, and in the third reactor, a regeneration operation is performed. Thus, one physical reactor can be the first, second and third reactor in different steps of the process. At the start of the next step, the third reactor, i.e. the reactor that has just been regenerated, becomes the second reactor, i.e. the finishing reactor, the second reactor becomes the first reactor, i.e. the bulk reactor, and the first reactor becomes the third reactor so that the deactivated catalyst is regenerated. This can be achieved by operating a series of sequence valves, so that the former third reactor is connected to the former second reactor, and these reactors operate as the first and second reactors according to the invention. The former first reactor containing the deactivated heterogeneous catalyst is disconnected from the supply conduits for carbon dioxide and epoxide compound and connected to the supply conduits for activating compound. The duration of one step can be between 1 and 30 days, preferably between 2 and 20 days. During such a period, the cyclic carbonate product can be continuously prepared in the first and second reactors. The addition of the activating compound to the third reactor to obtain the reactor containing the activated heterogeneous catalyst can be carried out in a shorter time.

[0012] Thus, the regeneration of the catalyst in the third reactor by adding an activating compound is carried out in a so-called off-line mode, in which no reactants such as carbon dioxide and epoxide or effluents from the first or second reactor are fed to the third reactor.

[0013] The process may be carried out in more than the three reactors described above, referred to as reactor trains. For example, multiple reactor trains may be operated in parallel according to the process of the present invention. The reactor effluents of these trains may be separated into products and activated compounds by a common separation method.

[0014] The reactor train may include an additional reactor, called the intermediate reactor. The intermediate reactor contains a heterogeneous catalyst and a slurry of cyclic carbonate product present as a liquid, as in the other reactors. The intermediate reactor is continuously fed with the gaseous effluent of the upstream reactor in the reactor train, the liquid cyclic carbonate is discharged as the intermediate reactor product stream, and the unreacted carbon dioxide and epoxide are discharged as the intermediate reactor gaseous effluent stream. Substantially all of the heterogeneous catalyst remains in the intermediate reactor. A train with more than three reactors includes a first reactor, a second reactor, and a third reactor according to the method of the present invention. The additional reactor operates in series with the first reactor and the second reactor, and the additional reactor is placed between the first reactor and the second reactor.

[0015] The reactor may be any reactor in which the reactants and catalyst in the liquid reaction mixture can be in intimate contact and to which the feedstock can be easily fed. The reactor, when used as the first and second reactor, is a continuously operated reactor. Such a reactor is continuously fed with carbon dioxide and epoxide compound and liquid cyclic carbonate is discharged. The rate at which gaseous carbon dioxide and gaseous or liquid epoxide are fed can agitate the liquid contents of the reactor so as to produce a substantially evenly distributed reaction mixture. A sparger nozzle can be used to add the gaseous compound to the reactor. Such agitation can also be achieved by using, for example, an ejector or mechanical agitation means such as, for example, an impeller. Such reactors are so-called bubble column slurry type reactors and mechanically agitated stirred tank reactors. In a preferred embodiment, the reactor is a continuously operated stirred reactor in which carbon dioxide and epoxide compound are continuously fed to the reactor and a portion of the cyclic carbonate product is continuously withdrawn as part of the liquid stream. The reactors in a reactor train are preferably of the same size and design. The reactors in a reactor train operated in parallel may vary from train to train.

[0016] In the process of the present invention, substantially all of the heterogeneous catalyst remains in the reactor, while a portion of the liquid cyclic carbonate product is discharged from the reactor. Preferably, an amount of liquid cyclic carbonate product is discharged from the first and second reactors, as well as any intermediate reactor(s), which amount corresponds to the production of the cyclic carbonate product in the reactor, and the amount of suspension in the reactor remains substantially the same during this step. The liquid cyclic carbonate is separated from the heterogeneous catalyst with a filter. This filter can be located outside the reactor. Preferably, the filter is located inside the reactor. A vertically arranged cylindrical vessel is preferred. The preferred filter is a cross-flow filter. For the preferred supported dimeric salen aluminum complex as catalyst, it is a 10 μm filter, more preferably a 10 μm filter made up of so-called Johnson Screens® with Vee-Wire® filter elements. The filter can have the shape of a tube vertically arranged in the reactor, preferably in a vertically arranged cylindrical vessel. The filter may be equipped with a means to create a negative flow on the filter so as to remove any solids from the filter opening.

[0017] Suitably, a portion of the second gaseous effluent is recycled to the first reactor and a portion of the second gaseous effluent is removed from the process. Since the content of unreacted epoxide in the second gaseous effluent is minimized as a result of the reactor layout according to the process of the invention, the loss of epoxide by removal is also minimized.

[0018] The first and second product streams and any intermediate reactor product stream may still contain some epoxide compounds and some activated compounds. The epoxide compounds are appropriately separated from the product streams and returned to either the first reactor, the second reactor or any intermediate reactor. More preferably, the first and second product streams and any intermediate reactor product streams are contacted with carbon dioxide, resulting in a purified product stream and a loaded carbon dioxide stream containing the epoxide compounds. More preferably, the first and second product streams are combined in a combined stream, and the epoxides present in the combined product stream are removed by contacting the combined product stream with carbon dioxide, resulting in a purified product stream and a loaded carbon dioxide stream containing the epoxide compounds, and the loaded carbon dioxide stream is fed to the first reactor.

[0019] The purified product stream still contains some activator compound, carbon dioxide and epoxide compounds. The content of activator compound in this stream may vary over time. For example, at the beginning of the process, the content of activator compound may be high due to the fact that a freshly regenerated reactor is put into the stream. During the process, the content of activator compound gradually decreases. Suitably, in a distillation step (wherein the purified cyclic carbonate product is obtained as the bottom product of the distillation step), the cyclic carbonate product present in the purified product stream is separated from the activator compound present in the combined product stream. The activated compound obtained as the top product in this distillation can be further purified by separation of any entrained gases such as carbon dioxide and epoxide compounds. The activated compound obtained in the distillation step can be used to activate the deactivated catalyst in a third reactor. The activated compound is suitably added directly to the third reactor and / or stored. The stored activator compound can then be added to the third reactor at another time.

[0020] The applicant found that the distillation during the process is difficult to carry out due to flow and concentration fluctuations, and found that a more stable distillation can be carried out when the first and second product streams and / or the combined stream pass through a buffer vessel upstream of the distillation process. When the heterogeneous catalyst is the preferred supported dimeric salen aluminum complex and the activating compound is a halide compound, the amount of m of the dimeric salen aluminum complex present in the reactors in which the reaction to the cyclic carbonate product takes place, i.e., the first reactor and the second reactor, expressed in kmol, is 3 The volume of the buffer vessel(s) represented by is preferably 5 to 50 m 3 / kmol.

[0021] Preferably, all or a portion of the epoxide obtained by distillation is recycled directly or indirectly to the first reactor. In this way, all or almost all of the epoxide is converted to the cyclic carbonate product. A portion of the epoxide obtained by distillation may be removed to avoid the accumulation of compounds boiling in the same range as the epoxide. These other compounds may have been present in any one of the feedstocks or may have been formed during the process. The heterogeneous catalyst may be any catalyst suitable for catalyzing the reaction of carbon dioxide and epoxide to cyclic carbonates and suitably activated by halide compounds. More particularly, heterogeneous catalysts include organic compounds containing one or more nucleophilic groups such as quaternary nitrogen halides. Examples of such catalysts are: Kohrt, C., Werner, T. Recyclable Bifunctional Polystyrene and Silica Gel-Supported Organocatalyst for the Coupling of CO2 with Epoxides. ChemSusChem 2015,8,2031-2034 Zakharova, M.V., Kleitz, F., Fontaine, F.-G. Carbon Dioxide Ovesolubility in Nanoconfined Liquids for the Synthesis of Cyclic Carbonates. ChemCatChem 2017, 9, 1886-1890, Kolle, J.M., Sayari, A. Substrate dependence on the fixation of CO2 to cyclic carbontes over reusable porous hybride solids. J CO2 Util. 2018, 26, 564-574, Liu, M., Liu, B., Liang, L., Wang, F., Shi, L., Sun, J. Design of bifunctional NH31-Zn / SBA-15 single-component heterogeneous catalyst for chemical fixation of carbon dioxide to cyclic carbonates. J.Mol.Catal.A Chem. 2016, 418-419, 78-85, and Lan D.-H., Chen, L., Au, C.-T., Yin, S.-F., One-pot synthesized multi-functional graphene oxide as a water-tolerant and efficient metal-free heterogeneous catalyst for cycloaddition reaction. Carbon 2015, 93, 22-31, DABCO-based ammonium salts as described in Hajipour,AR, Heidari,Y., Kozehgary,G. Silica grafted ammonium salts based on DABCO as heterogeneous catalysts for cyclic cabonate synthesis from carbon dioxide and epoxides. RSC Adv.2015,5,22373-22379, Bifunctional resorcinarenes salts, with ammonium-groups, as described in Jose,T., Canellas,S., Pericas,MA, Kleijn,AW, Polystyrene-supported bifunctional resorcinarenes as cheap, metal-free and recyclc catalyst for epoxide / CO2 coupling reactions, Greemn Chemistry 2017,19,5488, It is described in.

[0022] Imidazolium-based ionic liquids and salts as described in any one of the following papers: Xiao, L.-F., Li, F.-W., Peng, J.-J., Xia, C.-G. Immobilized ionic liquid / zinc chloride:Heterogeneous catalyst for synthesis of cyclic carbonates from carbon dioxide and epoxides. J.Mol.Catal.A Chem.2006,253,265-269, Han,L、Park,S.-W.、Park,D.-W. Silica grafted imidazolium-based ionic liquids: Efficient heterogeneous catalysts for chemical fixation of CO2 to a cyclic carbonate. Energy Environ.Sci.2009,2,1286-1292、 Sedeghzadeh,S.M. A heteropolyacid-base ionic liquid immobilized onto fibrous nano-silica as an efficient catalyst for the synthesis of cyclic carbonate from carbon dioxide and epoxides. Green Chem.2015,17,3059-3066、 Liu,M.、Lu,X.、Jiang,Y.、Sun, J.、Arai,M, Zwitterionic Imidazole-Urea Derivative Framework Bridged Mesoporous Hybrid Silica: A Highly Efficient Heterogeneous Nanocatalyst for Carbon Dioxide Conversion. ChemCatChem 2018,10,1860-1868、 Comes,A.、Collard,X.、Fusaro,L.、Atzori,L.、Cutrufello,M.G.、Aprile,C. Bi-functional heterogeneous catalysts for carbon dioxide conversion: Enhanced performances at low temperature. RSC Adv.2018,8,25342-25350、 Aprile,C.、Giacalone,F.、Agrigento,P.、Liotta,L.F.、Martens,J.A.,Pascarmona,P.P.、Gruttadauria,M. Multilayered Supported Ionic Liquids as Catalysts for Chemical Fixation of Carbon Dioxide:A High-Throughput Study in Supercritical Conditions. ChemSusChem 2011,4,1830-1837、 Agrigento P.、Al-Amsyar,S.M.、Soree,B.、Taherimehr,M.、Gruttadauria,M.、Aprile,C.、Pescarmona,P.P. Synthesis and high-throughput testing of multilayered supported ionic liquid catalysts for the conversion of CO2 and epoxides into cyclic carbonates. Catal.Sci.Technol.2014,4,1598-1607、 Calabrese,C.、Liotta,L.F.、Giacalone,F.、Gruttadauria,M.、Aprile,C. Supported Polyhedral Oligomeric Silsesquioxane-Based (POSS) Materials as Highly Active Organocatalysts for the Conversion of CO2. ChemCatChem 2019,11,560-567、 Lee,J.H.、Lee,A.S.、Lee,J.-C.、Hong,S.M.、Hwang,S.S.、Koo,C.M. Multifunctional Mesoporous Ionic Gels and Scaffolds Derived from Polyhedral Oligomeric Silsesquioxanes. ACS Appl.Mater.Interfaces 2017,9,3616-3623、 Akbari,Z.、Ghiaci,M. Heterogenization of a Green Homogeneous Catalyst: Synthesis and Characterization of Imidazolium Ionene / Br-Cl-@SiO2 as an Efficient Catalyst for the Cycloaddition of CO2 with Epoxides. Ind.Eng.Chem.Res.2017,56,9045-9053、 Su,Q.、Qi,Y.、Yao,X.、Cheng,W.、Dong,L.、Chen,S.、Zhang,S. Ionic Liquids tailored and confined by one-step assembly with mesoporous silica for boosting the catalytic conversion of O2 into cyclic carbonats. Green Chem.2018,20,3232-3241、 Han,L.、Li,H.、Choi,S.-J.、Park,M.-S.、Lee,S.-M.、Kim,Y.-J.、Park,D.-W. Ionic liquids grafted on carbon nanotubes as highly effiient heterogeneous catalysts for the synthesis of cyclic carbonates. Appl.Catal.A 2012,429-430,67-72、 Buaki-Sogo, M., Vivian, A., Bivona, L. A., Garcia, H., Gruttadauria, M., Aprile, C. Imidazolium functionalized carbon nanotubes for the synthesis of cyclic carbonates: Reducing the gap between homogeneous and heterogeneous Catalysis. Catal. Sci. Technol. 2016, 6, 8418 - 8427, Jayakumar, S., Li, H., Chen, J., Yang, Q. Cationi Zn-Porphyrin Polymer Coated onto CNTs as a Cooperative Catalyst for the Synthesis of Cyclic Carbonates. ACS Appl. Mater. Interfaces 2018, 10, 2546 - 2555, Xu, J., Xu, M., Wu, J., Wu, H., Zhang, W.-H., Li, Y.-X. Grapheneoxide immobilized with ionic liquids: Facile preparation and efficient Catalysis for solvent-free cycloaddition of CO2 to propylen carbonate. RSC Adv. 2015, 5, 72361 - 72368, and Calabrese, C., Liotta, L. F., Carbonell, E., Giacalone, F., Gruttadauria, M., Aprile, C. Imidazolium-Functionalized Carbon Nanohorns for the Conversion of Carbon Dioxide: Unprecedented Increase of Catalytic Activity after Recycling. ChemSusChem 2017, 10, 1202 - 1209, phosphonium salts described in Takahashi, T., Watahiki, T., Kitazume, S., Yasuda, H., Sakakura, T. Synergistic hybrid catalyst for cyclic carbonate synthesis: Remarkable acceleration caused by immobilization of homogeneous catalyst on silica. Chem. Commun. 2006, 1664-1666 and Sakai, T., Tsutsumi, Y., Ema, T. Highly active and robust organic-inorganic hybrid catalyst for the synthesis of cyclic carbonates from carbon dioxide and expoides. Green Chem. 2008, 10, 337-341; Motokura, K., Itagaki, S., Iwasawa, Y., Miyaji, A., Baba, T. Silica-supported aminopyridinium halides for catalytic transformations of epoxides to cyclic carbonates under atmospheric pressure of carbon dioxie. Pyridinium salts described in Green Chem. 2009, 11, 1876-1880. Porphyrin complexes described in Jayakumar, S., Li, H., Tao, L., Li, C., Liu, L., Chen, J., Yang, Q. Cationic Zn-Porphyrin Imbobilized in Mesoporou Silicas as Bifunctional Catalyst for CO2 Cycloaddition Reaction under Cocatalyst Free Conditions. ACS.Sustain.Chem.Eng.2018,6,9237-9245, and Saptal, VB, Sasaki, T., Harada, K., Nishio-Hamane, D., Bhanage, B M Hybrid Amine-Functionalized Graphene Oxide as a Robust Bifunctional Catalyst for Atmospheric Pressure Fixation of Carbon Dioxide using Cyclic Carbonates. Hybrid amine-functionalized graphene oxide as described in ChemSusChem 2016, 9, 644-650.

[0023] The preferred heterogeneous catalyst is a supported dimeric aluminum salen complex and the activating compound is a halide compound.

[0024] The supported dimeric aluminum salen complex may be any of the supported complexes disclosed in the previously mentioned EP 2 257 559 B1. Preferably, the complex is represented by the formula:

[0025] [ka] In the formula, S represents a solid support attached to the nitrogen atom via an alkylene bridging group, and the supported dimeric aluminum salen complex is activated by a halide compound. The alkylene bridging group can have between 1 and 5 carbon atoms. X 2 can be a C6 cyclic alkylene or benzylene. 2 is hydrogen. X 1 is preferably tert-butyl. In the above formula, Et represents any alkyl group, preferably having 1 to 10 carbon atoms. Preferably, Et is an ethyl group.

[0026] S represents a solid support. The catalyst complex can be attached to such a solid support by (a) covalent bonding, (b) steric entrapment, or (c) electrostatic bonding. For covalent bonding, the solid support S must contain or be derivatized to include reactive functional groups that can serve to covalently bond compounds to its surface. Such materials are well known in the art and include, by way of example, silicon dioxide supports, polyacrylamide supports, polystyrene supports, polyethylene glycol supports, and the like, that contain reactive Si-OH groups. Further examples are sol-gel materials. Silica can be modified to include 3-chloropropyloxy groups by treatment with (3-chloropropyl)triethoxysilane. Another example is Al-pillared clay, which can also be modified to include 3-chloropropyloxy groups by treatment with (3-chloropropyl)triethoxysilane. Solid supports for covalent attachment of particular interest in the present invention include siliceous MCM-41 and MCM-48, ITQ-2 and amorphous silica, SBA-15 and hexagonal mesoporous silica, which may be modified with 3-aminopropyl groups. Also of particular interest are sol-gels. Other conventional forms may also be used. For steric entrapment, the most suitable type of solid support is the zeolite, either natural or modified. The pore size must be small enough to entrap the catalyst, but large enough to allow reactants and products to enter and leave the catalyst. Suitable zeolites include zeolites X, Y and EMT, as well as zeolites X, Y and EMT partially decomposed to provide mesopores that allow easier transport of reactants and products. For electrostatic binding of the catalyst to the solid support, typical solid supports may include silica, Indian clay, Al-pillared clay, Al-MCM-41, K10, Laponite, Bentonite, and zinc-aluminum layered dihydroxide. Of these, silica and montmorillonite clays are of particular interest.Preferably, the support S is a particle selected from the group consisting of silica, alumina, titania, siliceous MCM-41 or siliceous MCM-48.

[0027] Preferably, the support S has the shape of a powder with dimensions small enough to create a high active catalytic surface per weight of support and large enough to be easily separated from the cyclic carbonate inside or outside the reactor. Preferably, the support powder particles have a particle size of more than 10 μm and less than 2000 μm for at least 90% by weight of the total particles. The particle size is measured by a Malvern® Mastersizer® 2000.

[0028] The supported catalyst complex as above is activated by a halide compound. The halide compound contains a halogen atom which may be Cl, Br or I, preferably Br. The quaternary nitrogen atom of the complex shown above is paired with a halide counterion. Possible activating compounds are described in EP2257559B1, which illustrates tetrabutylammonium bromide as a possible activating compound. Benzyl bromide is a preferred activating compound, since it can be separated from the preferred cyclic carbonate products such as propylene carbonate and ethylene carbonate by distillation.

[0029] An example of a preferred supported dimeric aluminum salen complex in which the complex is activated with benzyl bromide is shown below, where Et is ethyl, tBu is tert-butyl, and Osilica represents a silica support.

[0030] [ka]

[0031] In use, the Et group in the above formula may be exchanged with an organic group of a halide compound. For example, when benzyl bromide is used as the halide compound to activate the above supported dimeric aluminum salen complex, the Et group is exchanged with a benzyl group when the catalyst is reactivated.

[0032] An alternative to the above-mentioned supported dimeric aluminum salen complexes can be supported catalysts in which the aluminum salen complex moiety is bound to a support. By arranging these monomers close enough to each other, the same catalytic effect as the above-mentioned dimeric salen complexes can be achieved. Optionally, the supported monomeric aluminum salen complexes can be reacted with adjacent monomeric aluminum salen complexes to obtain supported dimeric aluminum salen complexes having two linking bridges to the support instead of one linking bridge as described above.

[0033] The epoxide product can be an epoxide as described in paragraphs 22-26 of EP 2257559B1 mentioned above. Preferably, the epoxide compound has 2-8 carbon atoms. Preferred epoxide compounds are ethylene oxide, propylene oxide, butylene oxide, pentene oxide, glycidol and styrene oxide. Cyclic carbonate products which can be produced from these preferred epoxides have the following general formula:

[0034] [ka] In the formula, R 1 is hydrogen or a group having 1 to 6 carbon atoms, preferably hydrogen, methyl, ethyl, propyl, hydroxymethyl and phenyl, R 2 is hydrogen. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 shows a flow scheme of the process according to the invention starting from propylene oxide and using a supported dimeric aluminum salen complex activated with benzyl bromide as catalyst. [Figure 2A] FIG. 2a shows a part of the scheme of the method of FIG. [Figure 2B] Figure 2b shows how the physical reactors (A), (B), and (C) are configured in the following process line-up. [Figure 2C]FIG. 2c shows how the physical reactors (A), (B), (C) are configured in a further process line-up. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The present invention is illustrated in Figure 1. Figure 1 shows a flow scheme of the process according to the present invention starting from propylene oxide and using a supported dimeric aluminum salen complex activated by benzyl bromide as a catalyst. Reactor (A) as the first reactor, reactor (B) as the second reactor, and reactor (C) as the third reactor are shown. All three reactors contain catalyst and a slurry of cyclic carbonate product. Reactor (A) is continuously fed with carbon dioxide via stream (2), stripper (G), and stream (15). In the stripper (G), the carbon dioxide gas contacts with the combined liquid product stream (13) to obtain a purified liquid product stream (14) and a loaded carbon dioxide stream (15) containing some propylene oxide compounds. This stream (15) is combined with fresh propylene oxide fed by (1) and a portion (8) of the unreacted carbon dioxide and propylene oxide from the reactor (B) as the second reactor, and the combined stream is fed to the reactor (A) in bulk operation (101) as the first reactor. In the reactor (A), liquid cyclic carbonate is formed by reaction of carbon dioxide with propylene oxide. During the process, a portion of the slurry is discharged as stream (4) to the filter (D), where the liquid cyclic carbonate is separated from the catalyst. The catalyst is returned to the reactor (A) by stream (5), and the catalyst-lean liquid cyclic carbonate is discharged from the reactor (A) as the first product stream (6). The unreacted carbon dioxide and propylene oxide are discharged as the first gaseous discharge stream (3) and are continuously fed to the second reactor (B) in the finishing operation (102).

[0037] During the step of this process in which liquid cyclic carbonate is formed in reactor (B) by reaction of carbon dioxide with propylene oxide, a portion of the slurry is discharged as stream (10) to filter (E), where it is separated from the catalyst. The catalyst is returned to reactor (B) via stream (11), and the catalyst-lean liquid cyclic carbonate is discharged from reactor (B) as second product stream (12). Unreacted carbon dioxide and propylene oxide are discharged as second gaseous discharge stream (7), a portion of which is recycled to the first reactor (A) and a portion of which is removed via stream (9).

[0038] The purified product streams (6) and (12) are collected in a buffer vessel (F), from which a combined product stream (13) is fed to a stripper (G). The purified liquid product stream (14) is fed to a distillation column (H) where the cyclic carbonate product present in the purified product stream is separated from benzyl bromide and other low boiling compounds. The benzyl bromide is fed to the reactor (C) via stream (17), optionally via a storage vessel (not shown). A purified cyclic carbonate product is obtained as the bottom product (16) of the distillation column (H).

[0039] In this process, the deactivated supported dimeric aluminum salen complex present in the third reactor, reactor (C), is activated by adding benzyl bromide via stream (17). Reactor (C) in FIG. 1 is in a regeneration operation (103).

[0040] A part of the scheme of the process of Figure 1 is shown in Figure 2a, Figure 2b shows how the physical reactors (A), (B) and (C) are configured in the line-up for the next step, and Figure 2c shows how the physical reactors (A), (B) and (C) are configured in the line-up for a further step.

[0041] The steps of the process of figures 1 and 2a end when the catalyst present in reactor (C) is reactivated and / or when the catalytic activity of the combined reactors (A) and (B) falls below an unacceptable level. The next step is started by switching the reactors, as shown in figure 2b, so that reactor (C) becomes the second reactor and reactor (B) becomes the first reactor, and reactor (A) is isolated from the process being carried out and regenerated as the third reactor in a regeneration operation (103). In this way, the deactivated catalyst in reactor (A) at the end of the previous step can be reactivated. This is repeated in a third step, in which reactors (A), (B) and (C) are arranged as shown in figure 2c. In a further step, the reactors are returned to the original arrangement of figure 2a. This sequence of steps is also shown in table 1 below. In this way, the catalyst present in reactors (A), (B) and (C) remains in the physical reaction vessel while the operations carried out by or in these reactors, i.e. bulk, work-up and regeneration, are changed after each step.

[0042] [Table 1]

[0043] The invention is illustrated by the following non-limiting examples. EXAMPLES

[0044] [Comparative example A] The operation of Comparative Example A shown in Figures 1-2 is compared with an operation having the sequence of steps shown in Table 2, in which the reactor in the bulk operation is used as the reactor in the finishing operation in the next step, and the reactor in the finishing operation is regenerated in this next step, with the cyclic carbonate production being equivalent to the operation as shown in Figures 1-2.

[0045] [Table 2]

[0046] In this comparison, experimentally obtained catalyst deactivation and catalyst lifetime characteristics were used. Catalyst deactivation is determined by the loss of activating compounds and occurs on the time scale of one process step, which can be between 2 and 20 days. Catalyst lifetime time is the point at which the catalyst after regeneration is unable to achieve the desired conversion, which is the illustrated process lineup. Catalyst lifetime is on the time scale of several months. A comparison with the process according to the invention is shown in Table 3.

[0047] [Comparative example B] The operation as shown in Figures 1-2 is compared with an operation using two reactors, each having twice the volume of reactor A and containing twice the amount of catalyst. In one reactor, cyclic carbonate is prepared while the other reactor is undergoing a regeneration operation. The calculations are based on a situation in which the same cyclic carbonate production is achieved as in the process of Figures 1 and 2.

[0048] [Table 3]

[0049] Table 3 shows that the sequence of Example A results in a shorter catalyst life and a greater loss of epoxide due to removal than when the process according to the invention is carried out. Comparative Example B shows that the point at which the catalyst after regeneration is unable to achieve a certain desired conversion (i.e., catalyst life time) is significantly shorter compared to the process according to the invention. The loss of epoxide is less. However, this does not offset the fact that the catalyst must be changed to a new catalyst more frequently when only one vessel is used compared to the process according to the invention.

Claims

1. 1. A process for continuously producing a cyclic carbonate product by reacting an epoxide compound with carbon dioxide in the presence of a heterogeneous catalyst activated by an activating compound, comprising: The heterogeneous catalyst comprises an organic compound containing one or more halogenated quaternary nitrogen groups; The active compound is a halide compound, The process is carried out in at least a first reactor, a second reactor, and a third reactor, each reactor containing a slurry of a heterogeneous catalyst and a cyclic carbonate product present as a liquid; carbon dioxide and an epoxide compound are continuously fed to the first reactor, liquid cyclic carbonate is discharged as a first product stream, unreacted carbon dioxide and epoxide are discharged as a first gaseous effluent stream, while substantially all of the heterogeneous catalyst remains in the first reactor, and the heterogeneous catalyst eventually becomes deactivated; said second reactor is continuously fed with the first gaseous effluent, liquid cyclic carbonate is discharged as a second product stream, unreacted carbon dioxide and epoxide are discharged as a second gaseous effluent stream, while substantially all of the heterogeneous catalyst remains in said second reactor; adding an activating compound to the third reactor to activate the heterogeneous catalyst, thereby obtaining a reactor containing an activated heterogeneous catalyst; In the next step of the process, the third reactor becomes the second reactor, the second reactor becomes the first reactor and the first reactor becomes the third reactor, and the deactivated catalyst present in said reactor is activated.

2. 2. The process of claim 1, wherein the temperature of the first and second reactors is between 20 and 150° C., the absolute pressure is between 0.1 and 0.5 MPa, and the temperature is below the boiling point of the cyclic carbonate product at the selected pressure.

3. 3. The method of claim 1 or 2, wherein the heterogeneous catalyst is a supported dimeric aluminum salen complex.

4. The supported dimeric aluminum salen complex has the following formula: 【Chemistry 1】 [wherein S represents a solid support bonded to a nitrogen atom by an alkylene group, the supported dimeric aluminum salen complex is activated by a halide compound, and X １ is tertiary butyl, and X ２ is hydrogen, and Et is an alkyl group having 1 to 10 carbon atoms.

5. The method according to claim 4, wherein the support S is composed of particles having an average diameter between 10 and 2000 μm.

6. The method of claim 5, wherein the support S is a particle selected from the group consisting of silica, alumina, titania, siliceous MCM-41 or siliceous MCM-48.

7. The method of claim 3 , wherein the halide compound is a benzyl halide.

8. The method of claim 7, wherein the benzyl halide is benzyl bromide.

9. The method of claim 1, wherein the duration of one step is between 1 and 30 days.

10. 2. The method of claim 1, wherein the first product stream and the second product stream are combined in a combined stream and epoxides present in the combined product stream are removed by contacting the combined product stream with carbon dioxide, resulting in a purified product stream and a loaded carbon dioxide stream comprising epoxide compounds, and the loaded carbon dioxide stream is fed to the first reactor.

11. 11. The method according to claim 10, wherein in a distillation step, the cyclic carbonate product present in the purified product stream is separated from the activated compound present in the combined product stream, and in the distillation step, a purified cyclic carbonate product is obtained as a bottom product of the distillation step.

12. 12. The process of claim 11, wherein the activating compound obtained in the distillation step is used to activate a deactivated catalyst in the third reactor.

13. 12. The method of claim 11, wherein the first product stream and the second product stream and / or the combined stream pass through a buffer vessel upstream of the distillation step.

14. The heterogeneous catalyst is a supported dimeric aluminum salen complex, the activating compound is a halide compound, and m is a ratio of m to the amount of dimeric aluminum salen complex expressed in kmol present in the first reactor and the second reactor. ３ The volume of the buffer vessel is 5 to 50 m ３ The method of claim 13, wherein the amount of the amine is 1 / kmol.

15. 2. The process of claim 1, wherein a portion of said second gaseous effluent is recycled to said first reactor and a portion of said second gaseous effluent is removed from the process.

16. The method of claim 1, wherein the epoxide compound has from 2 to 8 carbon atoms.

17. 17. The method of claim 16, wherein the epoxide compound is ethylene oxide, propylene oxide, butylene oxide, pentene oxide, glycidol or styrene oxide.

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