Process for the production of alkylene carbonate

Abstract

The invention relates to a continuous process for the production of an alkylene carbonate by the reaction of an alkylene oxide with carbon dioxide in the presence of a catalyst, in which process fresh carbon dioxide is fed to the process as part of a feed (i) comprising carbon dioxide and oxygen, in which feed (i) the oxygen concentration is greater than 0.01 mole%; fresh alkylene oxide is fed to the process as part of a feed (ii) comprising alkylene oxide; the molar ratio between carbon dioxide in the feed (i) and the alkylene oxide in the feed (ii) is greater than 1.02:1; (a) the alkylene oxide, carbon dioxide and the catalyst are continuously introduced into a reaction zone, from which a liquid product stream containing alkylene carbonate and catalyst and a gas stream comprising carbon dioxide and oxygen are withdrawn; (b) the alkylene carbonate and a stream containing catalyst are separated from the liquid product stream; (c) the alkylene carbonate, separated in step (b), is recovered as product.

Description

[0001] PROCESS FOR THE PRODUCTION OF ALKYLENE CARBONATE

[0002] Field of the invention

[0003] The present invention relates to a process for the production of alkylene carbonate.

[0004] Background of the invention

[0005] Processes for the production of alkylene carbonates are known. W02005003113 discloses a process in which carbon dioxide is contacted with an alkylene oxide in the presence of a suitable catalyst. The catalyst disclosed is a tetraalkyl phosphonium compound. W02005003113 discloses that the catalyst used has been recycled. US4434105 also discloses a process for the preparation of alkylene carbonates. Various catalysts are disclosed. US4434105 also describes that the catalyst after completion of the reaction may be reused.

[0006] In a continuous process, such as the continuous alkylene carbonate production process as disclosed in W02007096341 , the reaction product containing alkylene carbonate and catalyst may need to be subjected to a work-up treatment.

[0007] Such work-up treatment generally includes distillation, evaporation or crystallization to separate the alkylene carbonate product from the catalyst. According to W02007104730, it was found in a continuous alkylene carbonate production process using a phosphonium catalyst, that the activity of the catalyst decreases if the catalyst is being reused without taking appropriate steps to remove contaminants therefrom. Therefore, W02007104730 proposes that the used catalyst is purified before it is recycled.

[0008] The contaminants which are removed according to said W02007104730, are decomposition products of the phosphonium catalyst, such as phosphine oxides. By removing the latter contaminants, a build-up of these contaminants in the continuous process is avoided. In Example 1 of W02007104730, a catalyst solution comprising both propylene carbonate and used phosphonium catalyst (tetrabutyl phosphonium bromide; Bu4?Br) , also containing some tributyl phosphine oxide (i.e. Bu3P=O) , was subjected to distillation. Two consecutive distillations were needed to first remove the propylene carbonate and then to remove most of the tributyl phosphine oxide. The residue consisted mainly of the tetrabutyl phosphonium bromide.

[0009] The insertion of carbon dioxide into the oxirane moiety of alkylene oxides is a reversible reaction. That is to say, alkylene oxide may also be formed back from alkylene carbonate under release of carbon dioxide. It is expected that some contaminants which are formed during the production of alkylene carbonate and / or the work-up of the alkylene carbonate containing reaction mixture, may catalyze such back-reaction.

[0010] Further, in view of the above back-reaction, the work-up treatment may include a treatment with a sorption agent. According to W02009141361 , it was found that the back- reaction of alkylene carbonate into alkylene oxide and carbon dioxide may be prevented and the recovery of alkylene carbonate may be maximized accordingly, by carrying out, in a continuous alkylene carbonate production process using recycled catalyst, a treatment of alkylene carbonate and / or catalyst with a sorption agent comprising carbon.

[0011] Still further, various carbon dioxide containing streams may contain impurities such as oxygen (O2) . The oxygen concentration in these streams may be relatively high, e.g. greater than 0.01 mole%. If a relatively high amount of oxygen is present in the reaction mixture in the production of an alkylene carbonate from an alkylene oxide and carbon dioxide, the catalyst may be oxidized to some extent. For example, above-mentioned phosphonium catalyst may be oxidized into phosphine oxide. Generally, such contaminated carbon dioxide containing stream, containing a relatively high amount of oxygen, is purified in order to obtain a high- purity carbon dioxide for use as feed in said alkylene carbonate production process. However, removing such contaminants from carbon dioxide is cumbersome. Therefore, it is desired to omit such purification step and to be able to use such contaminated carbon dioxide directly as feed (starting material) in a process for the production of an alkylene carbonate from an alkylene oxide and carbon dioxide.

[0012] Therefore, an object of the present invention is to provide a continuous process for the production of an alkylene carbonate from an alkylene oxide and carbon dioxide using a catalyst, wherein contaminated carbon dioxide having a relatively high amount of oxygen may be used as feed (starting material) , without causing disadvantageous issues like above-mentioned oxidation of catalyst and wherein abovediscussed work-up treatments of the reaction product containing alkylene carbonate and catalyst may be avoided.

[0013] Summary of the invention

[0014] Surprisingly, it was found that the above object may be achieved by applying an excess of carbon dioxide in the fresh carbon dioxide feed over the alkylene oxide in the fresh alkylene oxide feed. In specific, the molar ratio between (I) carbon dioxide in the fresh carbon dioxide feed comprising carbon dioxide and oxygen, in which feed the oxygen concentration is greater than 0.01 mole%, and (II) the alkylene oxide in the fresh alkylene oxide feed is greater than 1.02:1.

[0015] Accordingly, the present invention relates to a continuous process for the production of an alkylene carbonate by the reaction of an alkylene oxide with carbon dioxide in the presence of a catalyst, in which process fresh carbon dioxide is fed to the process as part of a feed (i) comprising carbon dioxide and oxygen, in which feed (i) the oxygen concentration is greater than 0.01 mole%; fresh alkylene oxide is fed to the process as part of a feed (ii) comprising alkylene oxide; the molar ratio between carbon dioxide in the feed (i) and the alkylene oxide in the feed (ii) is greater than 1.02:1;

[0016] (a) the alkylene oxide, carbon dioxide and the catalyst are continuously introduced into a reaction zone, from which a liquid product stream containing alkylene carbonate and catalyst and a gas stream comprising carbon dioxide and oxygen are withdrawn;

[0017] (b) the alkylene carbonate and a stream containing catalyst are separated from the liquid product stream;

[0018] (c) the alkylene carbonate, separated in step (b) , is recovered as product.

[0019] Further, the present invention relates to a process for the preparation of an alkane diol and a dialkyl carbonate comprising reacting an alkylene carbonate with an alkanol in which the alkylene carbonate has been prepared by the above- mentioned process.

[0020] Further, the present invention relates to a process for preparing a battery electrolyte solution comprising combining an alkylene carbonate or a dialkyl carbonate with one or more alkali metal salts, wherein the alkylene carbonate has been prepared by the above-mentioned process and wherein the dialkyl carbonate has been prepared by the above-mentioned process .

[0021] Above-mentioned W02009141361 discloses that in the step of reacting carbon dioxide with the alkylene oxide, the molar ratio between carbon dioxide and alkylene oxide may be as low as 0.5:1. Further, as also disclosed in said W02009141361, in view of the reversibility of the reaction it is said to be preferred to ensure at least a slight excess of carbon dioxide, such as 1.0:1 to 10:1, more preferably from 1.01:1 to 2:1, most preferably from 1.01:1 to 1.2:1. However, the molar ratio between carbon dioxide and alkylene oxide as disclosed in W02009141361 only concerns such molar ratio in the reaction mixture in the reaction zone, not the molar ratio between (I) carbon dioxide in the fresh carbon dioxide feed and (II) the alkylene oxide in the fresh alkylene oxide feed before these fresh feeds are fed to the process. Furthermore, said W02009141361 does not disclose the use of contaminated carbon dioxide containing a relatively high oxygen concentration, as used in the process of the present invention. Neither does W02009141361 disclose, or even suggest, that such contaminated carbon dioxide may be used as fresh feed when applying a relatively high excess of carbon dioxide in such fresh carbon dioxide feed over the alkylene oxide in the fresh alkylene oxide feed as in the present process .

[0022] In the article by Ming-Ran Li et al. titled "Jet Loop Reactor-Intensified CO2 Utilization: An Efficient Strategy for the Synthesis of Ethylene Carbonate", in Ind. Eng. Chem. Res. , 2024, 63, pages 4257-4264, a process is disclosed wherein a jet loop reactor (JLR) is employed for the masstransfer intensification of liquid-gas phases in the production of ethylene carbonate (EC) from the cycloaddition of carbon dioxide (CO2) and ethylene oxide. In that process, a gas stream comprising carbon dioxide is withdrawn from the reactor and is then recycled completely into the reactor after combining the recycle carbon dioxide with fresh carbon dioxide. Said article does not disclose the use of contaminated carbon dioxide containing a relatively high oxygen concentration, as used in the process of the present invention .

[0023] Detailed description of the invention

[0024] The process of the present invention comprises multiple steps. In addition, said process may comprise one or more intermediate steps between consecutive steps. Further, said process may comprise one or more additional steps preceding the first step and / or following the last step. For example, in a case where said process comprises steps a) , b) and c) , said process may comprise one or more intermediate steps between steps a) and b) and between steps b) and c) . Further, said process may comprise one or more additional steps preceding step a) and / or following step c) .

[0025] While the process of the present invention and the stream(s) or composition ( s ) used or produced in said process are described in terms of "comprising", "containing" or "including" one or more various described steps and components, respectively, they can also "consist essentially of" or "consist of" said one or more various described steps and components, respectively.

[0026] In the context of the present invention, in a case where a stream or composition comprises two or more components, these components are to be selected in an overall amount not to exceed 100%.

[0027] Further, where upper and lower limits are quoted for a property then a range of values defined by a combination of any of the upper limits with any of the lower limits is also implied .

[0028] The process of the present invention is a continuous process for the production of an alkylene carbonate by the reaction of an alkylene oxide with carbon dioxide in the presence of a catalyst. In the present process, fresh carbon dioxide is fed to the process as part of a feed (i) comprising carbon dioxide and oxygen (herein also referred to as "fresh carbon dioxide feed") and fresh alkylene oxide is fed to the process as part of a feed (ii) comprising alkylene oxide (herein also referred to as "fresh alkylene oxide feed") . Within the present specification, "fresh carbon dioxide" and "fresh alkylene oxide" mean carbon dioxide and alkylene oxide, respectively, which has not been fed to the present process before. This is e.g. different from "recycle carbon dioxide" which has already been fed to the present process before and which is recycled to that process. The fresh carbon dioxide feed (i) does not comprise such recycle carbon dioxide. Neither does the fresh alkylene oxide feed (ii) comprise recycle alkylene oxide.

[0029] Advantageously, in the present invention, the oxygen concentration in the fresh carbon dioxide feed (i) is relatively high, namely greater than 0.01 mole%, and any preceding further purification is not needed to lower that oxygen concentration. Said oxygen concentration is on dry basis, thereby not considering any water that may be present in the fresh carbon dioxide feed (i) . Preferably, the oxygen concentration in feed (i) is of from greater than 0.01 to 2 mole%, more preferably of from 0.1 to 1.8 mole%, more preferably of from 0.2 to 1.5 mole%, more preferably of from 0.3 to 1 mole%, most preferably of from 0.3 to 0.8 mole%. The oxygen concentration in feed (i) is greater than 0.01 mole% and may be at least 0.1 mole% or at least 0.2 mole% or at least 0.3 mole% or at least 0.4 mole% or at least 0.6 mole% or at least 0.8 mole% or at least 1 mole%. Further, the oxygen concentration in feed (i) may be at most 3 mole% or at most 2.5 mole% or at most 2 mole% or at most 1.8 mole% or at most 1.5 mole% or at most 1.3 mole% or at most 1 mole% or at most 0.8 mole% or at most 0.6 mole% or at most 0.5 mole%. Further, it is required in the present invention that the molar ratio between carbon dioxide in the fresh carbon dioxide feed (i) and the alkylene oxide in the fresh alkylene oxide feed (ii) is greater than 1.02:1. In the present process, a molar excess of fresh carbon dioxide is fed to the present process as compared to the amount of fresh alkylene oxide fed to the present process. Preferably, said molar ratio is of from greater than 1.02:1 to 10:1, more preferably of from 1.05:1 to 5:1, preferably of from 1.1:1 to 2:1, most preferably of from 1.1:1 to 1.5:1. Said molar ratio is greater than 1.02:1 and may be at least 1.05:1 or at least 1.1:1 or at least 1.2:1 or at least 1.3:1 or at least 1.5:1 or at least 2:1. Further, said molar ratio may be at most 10:1 or at most 5:1 or at most 2:1 or at most 1.8:1 or at most 1.5:1. In the present invention, it is preferred that in case the fresh carbon dioxide feed (i) has an increased oxygen concentration, the above-mentioned molar ratio between carbon dioxide in the fresh carbon dioxide feed (i) and the alkylene oxide in the fresh alkylene oxide feed (ii) is also increased .

[0030] Advantageously, the process of the present invention, wherein a relatively high excess of fresh carbon dioxide over fresh alkylene oxide is used, enables the use of contaminated carbon dioxide, in specific contaminated carbon dioxide containing a relatively high oxygen concentration as described above. Such contaminated carbon dioxide may originate from an ethylene oxide production plant or from a syngas production plant. Streams comprising carbon dioxide and oxygen as impurity, originating from such plants or other plants, may advantageously be used directly as fresh carbon dioxide feed in the present process without intermediate treatment to remove impurities like oxygen, and also without additional safety or operational risk. In the present process, the alkylene oxide to be reacted with carbon dioxide in the present process, is suitably a C2-4 alkylene oxide, preferably ethylene oxide and / or propylene oxide, or mixtures of such C2-4 alkylene oxides, most preferably ethylene oxide. Where ethylene oxide is used, the produced alkylene carbonate is ethylene carbonate. Where propylene oxide is used, the produced alkylene carbonate is propylene carbonate.

[0031] In step (a) of the present process, the alkylene oxide, carbon dioxide and the catalyst are continuously introduced into a reaction zone, from which a liquid product stream containing alkylene carbonate and catalyst and a gas stream comprising carbon dioxide and oxygen are withdrawn.

[0032] Preferably, at least part of above-mentioned liquid product stream containing alkylene carbonate and catalyst is recycled to the reaction zone, e.g. via above-mentioned liquid loop. Such recycle liquid product stream may be combined with the fresh alkylene oxide feed (ii) and / or with catalyst, and the resulting combined stream may then be fed to the present process, e.g. via above-mentioned liquid loop.

[0033] Further, preferably, at least part of above-mentioned gas stream comprising carbon dioxide and oxygen is recycled to the reaction zone, e.g. via above-mentioned gas loop. Such recycle gas stream may be combined with the fresh carbon dioxide feed (i) , and the resulting combined stream may then be fed to the present process, e.g. via above-mentioned gas loop. Generally, it is known to increase the conversion of carbon dioxide by recycling unconverted carbon dioxide to the reaction zone. However, because of the resulting increase in CO2 conversion, the relative amount of fresh carbon dioxide as fed to the process would then be reduced. This is different from the present process, wherein the molar ratio between carbon dioxide in the fresh carbon dioxide feed (i) and the alkylene oxide in the fresh alkylene oxide feed (ii) is kept relatively high, i.e. greater than 1.02:1.

[0034] Step (a) may be carried out in a reaction zone of any reactor. However, preferably, a jet loop reactor is employed. An example of a suitable jet loop reactor is disclosed in above-mentioned article by Ming-Ran Li et al. A jet loop reactor comprises a reactor or reactor vessel into which an ejector extends from the top of the reactor or reactor vessel, and a line (herein also referred to as "liquid loop") extending from the bottom of the reactor or reactor vessel to the ejector. Preferably, the ejector extends to below the surface of the liquid reaction mixture present at the bottom of the reactor or reactor vessel. The liquid loop in such jet loop reactor enables recycling part of the liquid product stream to the reaction zone of the same reactor. Further, the jet loop reactor may comprise a line (herein also referred to as "gas loop") extending from the top of the reactor or reactor vessel to the ejector. Said gas loop may contain a valve so as to enable closing and opening of the gas loop, in specific to enable recycling part of above-mentioned gas stream comprising carbon dioxide and oxygen to the reaction zone via said gas loop, wherein the non-recycled part of that stream may be either bled from the process or sent to a second reactor in series, such as below-mentioned plug-flow reactor. The ejector of the jet loop reactor may be a so- called "Venturi" ejector which is suitable for mixing liquid and gas streams and ejecting the resulting gas-liquid mixture into the reaction mixture inside the reactor or reactor vessel .

[0035] In step (a) of the present process, only one reactor may be used. However, it is also feasible to carry out the reaction of step (a) in two or more reactors. In such cases it may be advantageous to provide for the optimal amount of excess carbon dioxide in the reactors by removing or adding carbon dioxide between the reactors. The reactors are suitably conducted under plug flow conditions. It is preferred to have a back-mix reactor, e.g. a Continuously Stirred Tank Reactor (CSTR) , followed by a plug-flow reactor. Such a combination is known from e.g. US4314945. In particular, a jet loop reactor followed by a plug-flow reactor is preferred.

[0036] When using e.g. a CSTR or jet loop reactor in the present process, there will be a liquid reaction mixture at the bottom of the reactor and a gas cap inside the reactor above that liquid reaction mixture. In the liquid reaction mixture, the liquid is the continuous phase in which gas is dispersed, and in the gas cap the gas is the continuous phase. In step (a) of the present process, the liquid product stream containing alkylene carbonate and catalyst is withdrawn from the bottom of the reactor and the gas stream comprising carbon dioxide and oxygen is withdrawn from the top of the reactor. In the present process, the oxygen concentration in the gas cap, as well as the oxygen concentration in the liquid reaction mixture, may be of from 0.1 to 10 mole%, preferably 1 to 10 mole%, more preferably 2 to 8 mole%, more preferably 2 to 6 mole%, more preferably 2 to 5 mole%, most preferably 2 to 4 mole%. In the present invention, the oxygen concentration in the gas cap may advantageously be reduced by increasing the molar ratio between carbon dioxide in the fresh carbon dioxide feed (i) and the alkylene oxide in the fresh alkylene oxide feed (ii) . Furthermore, in the present invention, the molar ratio between carbon dioxide and the alkylene oxide in the liquid reaction mixture may be of from 1.0:1 to 10:1, more preferably 1.5:1 to 8:1, most preferably 2:1 to 5:1. In the present invention, wherein the oxygen concentration in the fresh carbon dioxide feed (i) is relatively high, i.e. greater than 0.01 mole%, the following disadvantages may advantageously be avoided by ensuring that the molar ratio between carbon dioxide in the fresh carbon dioxide feed (i) and the alkylene oxide in the fresh alkylene oxide feed (ii) is relatively high, i.e. greater than 1.02:1:

[0037] 1) A relatively high oxygen concentration in the gas cap above the reaction mixture in the reactor may cause a flammable mixture to be formed. Such situation is unsafe, especially since the contents of the reactor are hazardous.

[0038] 2) A relatively high oxygen concentration in the reaction mixture may degrade and deactivate (i.e. by oxidation) the catalyst to some extent, which catalyst is costly.

[0039] 3) In view of 1) and 2) above, such high oxygen concentration may limit the choice of suitable catalyst.

[0040] 4) A relatively high oxygen concentration in the reaction mixture may also cause unwanted side-reactions, causing a decrease of selectivity and yield.

[0041] In the present process, the reaction of the alkylene oxide with carbon dioxide is performed in the presence of a catalyst. The catalyst may be a phosphonium compound. Such catalysts are known, e.g. from US5153333, US2994705, US4434105, WO199957108, EP0776890, W02005003113 and W02007104730. Preferably, the catalyst is a phosphonium halide of formula (R) 4PX, in which X means halide and each R can be the same or different and can be selected from an alkyl, alkenyl, cyclic aliphatic or an aromatic group. The group R suitably contains from 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms. Most preferred are groups R being selected from methyl, ethyl, n-propyl, isopropyl, n- butyl, isobutyl, and t-butyl groups. Preferably, the halide ion is bromide or iodide. The most preferred phosphonium catalyst is tetra ( n-butyl ) phosphonium bromide.

[0042] In step (b) of the present process, the alkylene carbonate and a stream containing catalyst are separated from the liquid product stream withdrawn in step (a) . Optionally, in the present invention, the stream containing catalyst separated in step (b) is recycled to the reaction zone in step (a) . The catalyst, especially a phosphonium catalyst, may be recycled to the reaction zone in the presence of a solvent. This solvent may be an alcohol. Suitable alcohol solvents are alkylene diols, in particular ethanediol or propanediol. The use of ethanediol or propanediol has a further advantage when the alkylene carbonate is converted to alkylene glycol (alkanediol) , and the alkylene glycol is used as solvent for the catalyst. The optional catalyst containing recycle stream to step (a) suitably contains some alkylene carbonate. The alkylene carbonate ensures that the catalyst is in liquid form, which facilitates transportation. Further, it is envisaged that part of the optional catalyst containing recycle stream to step (a) is bled from the process. Catalyst may be recovered from such bleed stream.

[0043] The amount of catalyst in the reactor or reaction zone in step (a) may conveniently be expressed in mole catalyst per mole alkylene oxide. Due to a lower amount of by-products, the carbonation is suitably carried out in the presence of at least 0.0001 mole of the catalyst per mole alkylene oxide. Preferably, the amount of catalyst present is such that it ranges from 0.0001 to 0.1 mole catalyst, more preferably from 0.001 to 0.05, and most preferably from 0.003 to 0.03 mole catalyst per mole alkylene oxide.

[0044] The reaction temperature in step (a) of the present process can be selected from a wide range. Suitably the temperature is selected from 30 to 300 °C. The advantage of relatively high temperature is the increase in reaction rate. However, if the reaction temperature is too high, side reactions may occur, or the undesired decomposition of the catalyst may be accelerated. Therefore, the temperature is suitably selected from 100 to 220 °C.

[0045] The skilled person will be able to adapt other reaction conditions as appropriate. The residence time of the alkylene oxide and the carbon dioxide in the reactor or reaction zone in step (a) of the present process can be selected without undue burden. The residence time can usually be varied between 5 min and 24 hours, preferably between 10 minutes and 10 hours. Conversion of alkylene oxide is suitably at least 95%, more preferably at least 98%. Dependent on the temperature and pressure the residence time may be adapted. The catalyst concentration may also vary between wide ranges. Suitable concentrations include from 1 to 25 wt . % , based on the total reaction mixture. Good results can be obtained with a catalyst concentration of 2 to 8 wt.%, based on the total reaction mixture.

[0046] The desired product alkylene carbonate may be recovered from the product mixture originating from step (a) in the following way. First of all, carbon dioxide and light components may be separated from the crude reactor effluent from said step (a) in one or more gas-liquid separators to form a bottom stream containing alkylene carbonate and catalyst. Said light components are compounds, other than carbon dioxide, which have a boiling point which is 185 °C or lower, more specifically 180 °C or lower. Examples of such light components in the crude effluent from the carbonation reactor may be unreacted alkylene oxide and any light contaminants formed during the carbonation reaction, such as acetone, propionaldehyde, allyl alcohol and acetaldehyde. Following the removal of said unreacted carbon dioxide and light components, alkylene carbonate and a stream containing catalyst are to be separated in accordance with step (b) of the present process. This may be achieved by sending the above-mentioned bottom stream containing alkylene carbonate and catalyst to a distillation column where it is distilled to form a first distillation overhead stream and a first distillation bottom stream. The first distillation overhead stream contains alkylene carbonate. The first distillation bottom stream contains catalyst and possibly some alkylene carbonate. The first distillation bottom stream may be partially or completely recycled to the reactor in accordance with optional step (d) of the present process.

[0047] In a situation where an alcohol is used as a solvent for the catalyst and such alcohol has a lower boiling point than the alkylene carbonate, as is the case when the alcohol used is propanediol and the alkylene carbonate is propylene carbonate or when the alcohol used is ethanediol and the alkylene carbonate is ethylene carbonate, the first distillation overhead stream contains said alcohol in addition to alkylene carbonate.

[0048] As to the way the distillation may be performed in order to separate catalyst from alkylene carbonate and any alcohol used as solvent for the catalyst, the skilled artisan can vary the temperature and number of trays without undue burden .

[0049] In accordance with step (c) of the present process, the alkylene carbonate separated in step (b) is recovered as product. This may be achieved as follows. The above-mentioned first distillation overhead stream may be distilled to form a second distillation overhead stream and a second distillation bottom stream. The second distillation bottom stream contains alkylene carbonate, i.e. the purified end product. In a situation where an alcohol is used a s a solvent for the catalyst and such alcohol ha s a lower boiling point than the alkylene carbonate , the distillation of the f irst distillation overhead stream should be carried out such that the second di stillation overhead stream contains said alcohol and the final alkylene carbonate product contains no or substantially no alcohol .

[0050] As to the way the distillation of the first distillation overhead stream may be performed in order to separate alkylene carbonate from any alcohol used as solvent for the catalyst , the s killed artisan can vary the temperature and number of trays without undue burden .

[0051] The alkylene carbonate that is produced in the present proces s can suitably be used for the production of an al kane diol and a dialkyl carbonate .

[0052] Accordingly, the present proces s also relates to a proces s for the preparation of an alkane diol and a dial kyl carbonate comprising reacting an alkylene carbonate with an alkanol over a transe sterification catalyst in which the alkylene carbonate ha s been prepared by the above-described alkylene carbonate production proces s and recovering the alkane diol and the dialkyl carbonate from the re sulting reaction mixture .

[0053] Further , accordingly, the present process also relates to a proces s for the preparation of an al kane diol and a dialkyl carbonate comprising : preparing an alkylene carbonate in accordance with the above-described al kylene carbonate production proces s ; and reacting the alkylene carbonate obtained in the preceding step with an al kanol over a transesterification catalyst and recovering the alkane diol and the dialkyl carbonate from the resulting reaction mixture . The alkanol used in above transesterification process is suitably a C1-4 alcohol. Preferably, the alkanol is methanol, ethanol or isopropanol. Said process may be performed in the presence of a heterogeneous transesterification catalyst.

[0054] The transesterification reaction in itself is known. In this context reference is made to US4691041, disclosing a process for the manufacture of ethylene glycol and dimethyl carbonate by the transesterification reaction over a heterogeneous catalyst system, in particular an ion exchange resin with tertiary amine, quaternary ammonium, sulphonic acid and carboxylic acid functional groups, alkali and alkaline earth silicates impregnated into silica and ammonium exchanged zeolites. US5359118 and US5231212 disclose a continuous process for preparing dialkyl carbonates over a range of catalysts, including alkali metal compounds, in particular alkali metal hydroxides or alcoholates, such as sodium hydroxide or methanolate, thallium compounds, nitrogen-containing bases such as trialkyl amines, phosphines, stibines, arsenines, sulphur or selenium compounds and tin, titanium or zirconium salts. According to W02005003113 the reaction of alkylene carbonate with an alkanol is conducted over heterogeneous catalysts, e.g. alumina .

[0055] Further, the present invention relates to a process for preparing a battery electrolyte solution comprising combining an alkylene carbonate or a dialkyl carbonate with one or more alkali metal salts, wherein the alkylene carbonate has been prepared by the above-described process and wherein the dialkyl carbonate has been prepared by the above-described process. Said combining may comprise blending. Said salts may be dissolved in the carbonate. Preferably, the alkylene carbonate or dialkyl carbonate is combined with the one or more alkali metal salts, one or more other carbonate compounds and optionally additives. Said one or more other carbonate compounds may comprise asymmetric dialkyl carbonates, including ethyl methyl carbonate, symmetric dialkyl carbonates, including diethyl carbonate and dimethyl carbonate, and alkylene carbonates, including ethylene carbonate. Further, said one or more alkali metal salts may comprise lithium salts and / or sodium salts.

[0056] The invention is further illustrated by the following Examples .

[0057] Examples

[0058] In the present Examples, the Upper Explosion Limit (UEL) was determined experimentally in a 16 liter spherical vessel with central ignition. In preparation, most of the screw connections in pipelines were replaced with soldered connections. Valves were replaced for suitable ones for operation with ethylene oxide (EO) . Before starting each test, the set-up was checked for its tightness. The test chamber was equipped with two high sampling frequency pressure transducers. Additionally, 3 vertical thermocouples were installed at different positions to ensure adequate temperature readings.

[0059] Tungsten fuse-wire (0 0.2 mm, 15 mm long) was used as the ignition source. Burning of the tungsten wire was initiated by connecting it to a 12 Volt battery. The supplied ignition energy was in the range of 10 to 140 Joule.

[0060] The experiments were conducted as follows: 1) The test chamber was cleaned and heated to the test temperature, equal to the reactor temperature of 150 °C; 2) Evacuation of test chamber (final vacuum pressure below 20 mbara) ; 3) Addition of gas mixture representative of the operation of the reactor with different molar CO2 / EO ratios, which lead to different oxygen concentrations; 4) Isolation of test chamber (closing inlet / outlet valves) ; 5) Ignition of the mixture and data acquisition .

[0061] The following data were recorded during each test: a) Static pressure inside test chamber (PS) ; b) High frequency, dynamic pressure inside test chamber - piezoelectric pressure sensors; channel 1 (Ch 1) on upper flange; channel 2 (Ch 2) on lower flange; c) Temperature inside test chamber - 3 thermocouples located vertically; d) Voltage and current during ignition.

[0062] The tests were performed with two repetitions if ignition occurred and three repetitions if ignition did not occur.

[0063] The UEL values were determined with the following restrictions: i) Flammability (ignition) criterion: pressure rise during a test above 5% of the initial mixture pressure, as per EN1839; ii) UEL was determined as the highest oxygen concentration in the gas mixture composition for which there was no ignition in 3 repetitive tests; iii) Oxygen concentration step in a test mixture: 0.5 mole% O2.

[0064] The conclusion of the tests in the present Examples was that at conditions representative of operation of the reactor, the UEL is at 8 mole% O2 :

[0065]

[0066] (1) Experiments were carried out at 150 °C and 24.84 bara . At 8.0 mole% O2, the remaining composition was 2.0 mole% ethylene oxide, 7.6 mole% ethylene, 4.0 mole% methane and 77.7 mole% CO2. At 8.5 mole% O2, the remaining composition was 2.0 mole% ethylene oxide, 7.8 mole% ethylene, 4.2 mole% methane and 76.8 mole% CO2.

[0067] The relationship between (a) the oxygen concentration in the reactor and (b) the molar ratio between carbon dioxide in the fresh carbon dioxide feed (i) and ethylene oxide in the fresh ethylene oxide feed (ii) has been determined via simulation with a proprietary reactor model. Said relationship depends on the oxygen concentration in the fresh carbon dioxide feed (i) . The table below includes the results for two cases as an example, wherein the oxygen concentration in the fresh carbon dioxide feed was either 0.5 mole% or 1.3 mole% . This table shows that at 0.5 mole% of oxygen in the fresh carbon dioxide feed, the above-mentioned molar CO2 / EO ratio should be at least 1.08, whereas at 1.3 mole% of oxygen that ratio should be at least 1.18.

[0068]

Claims

C L A I M S1. A continuous process for the production of an alkylene carbonate by the reaction of an alkylene oxide with carbon dioxide in the presence of a catalyst, in which process fresh carbon dioxide is fed to the process as part of a feed (i) comprising carbon dioxide and oxygen, in which feed (i) the oxygen concentration is greater than 0.01 mole%; fresh alkylene oxide is fed to the process as part of a feed (ii) comprising alkylene oxide; the molar ratio between carbon dioxide in the feed (i) and the alkylene oxide in the feed (ii) is greater than 1.02:1;(a) the alkylene oxide, carbon dioxide and the catalyst are continuously introduced into a reaction zone, from which a liquid product stream containing alkylene carbonate and catalyst and a gas stream comprising carbon dioxide and oxygen are withdrawn;(b) the alkylene carbonate and a stream containing catalyst are separated from the liquid product stream;(c) the alkylene carbonate, separated in step (b) , is recovered as product.

2. The process according to claim 1, wherein the alkylene oxide is a C2-4 alkylene oxide.

3. The process according to claim 2, wherein the alkylene oxide is ethylene oxide.

4. The process according to any one of claims 1 to 3, wherein the oxygen concentration in the fresh carbon dioxide feed (i) is of from greater than 0.01 to 2 mole%.

5. The process according to claim 4, wherein the oxygen concentration in the fresh carbon dioxide feed (i) is of from0.1 to 1.8 mole% .

6. The process according to any one of claims 1 to 5, wherein at least part of the liquid product stream containing alkylene carbonate and catalyst is recycled to the reaction zone .

7. The process according to any one of claims 1 to 6, wherein at least part of the gas stream comprising carbon dioxide and oxygen is recycled to the reaction zone.

8. The process according to any one of claims 1 to 7, wherein the molar ratio between carbon dioxide in the fresh carbon dioxide feed (i) and the alkylene oxide in the fresh alkylene oxide feed (ii) is at least 1.05:1.

9. A process for the preparation of an alkane diol and a dialkyl carbonate comprising: preparing an alkylene carbonate in accordance with the process according to any one of claims 1 to 8; and reacting the alkylene carbonate obtained in the preceding step with an alkanol over a transesterification catalyst and recovering the alkane diol and the dialkyl carbonate from the resulting reaction mixture.

10. A process for preparing a battery electrolyte solution comprising combining an alkylene carbonate or a dialkyl carbonate with one or more alkali metal salts, wherein the alkylene carbonate has been prepared by the process according to any one of claims 1 to 8 and the dialkyl carbonate has been prepared by the process according to claim 9.

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