Process for the preparation of a mixed dialkyl carbonate

Abstract

The invention relates to a process for the preparation of a mixed dialkyl carbonate of formula R1O(C=O)OR2, comprising reacting a dialkyl carbonate of formula R1O(C=O)OR1 and a dialkyl carbonate of formula R2O(C=O)OR2, wherein R1 and R2 are different alkyl groups, in the presence of a catalyst, wherein the catalyst comprises an aluminum phosphate and the aluminum phosphate is obtained by a process comprising: (a) mixing an aluminum containing salt with phosphoric acid in a molar ratio [Al] / [P] of from 0.1:1 to 20:1; (b) mixing a base with the mixture resulting from step (a), resulting in the formation of an aluminum phosphate precipitate; (c) optionally heating the precipitate containing mixture; and (d) recovering the precipitate.

Description

[0001] SP3176 PROCESS FOR THE PREPARATION OF A MIXED DIALKYL CARBONATE Field of the invention The present invention relates to a process for the 5 preparation of a mixed dialkyl carbonate. Background of the invention Mixed dialkyl carbonates are well-known and are of formula R1O(C=O)OR2, wherein R1 and R2 are different alkyl groups. An example of a mixed dialkyl carbonate is ethyl 10 methyl carbonate (EMC) which is of formula R1O(C=O)OR2wherein R1is methyl and R2is ethyl. EMC is known for its use as a solvent and as an organic synthesis intermediate. In specific, EMC has become an important solvent in electrolytes for lithium batteries in recent years. Due to the rapid 15 development of lithium batteries, the demand for ethyl methyl carbonate has also been expanding. Ethyl methyl carbonate may be produced by transesterification of dimethyl carbonate with ethanol. Further, ethyl methyl carbonate may be produced by 20 disproportionation (transesterification) of dimethyl carbonate with diethyl carbonate. Further, it is known to use aluminum phosphate as a catalyst in the latter disproportionation reaction. The article titled “Amorphous mesoporous aluminophosphate 25 as highly efficient heterogeneous catalysts for transesterification of diethyl carbonate with dimethyl carbonate” by Jinghui Shi et al. in Catalysis Communications, 12, 2011, pages 721-725, discloses the preparation of ethyl methyl carbonate (EMC) by reacting dimethyl carbonate (DMC) 30 and diethyl carbonate (DEC) in the presence of an aluminophosphate (AlPO) catalyst. According to above- article, the AlPO catalyst was prepared by dropping phosphoric acid into a mixed aqueous solution of aluminum nitrate and citric acid. After that, an aqueous ammonia solution was added dropwise until pH = 5.0, 5 followed by heating the mixture in air and calcining the resulting white solid. In above-mentioned article, it is disclosed that the mesoporous AlPO material, prepared using the citric acid route, can be used as a heterogeneous catalyst for EMC 10 production by the transesterification of DEC with DMC. The presence of abundant weak acid–base pairs on the surface of the mesoporous AlPO material is said to play a critical role on the activation of the reactants in the transesterification reaction. In said article, it is mentioned that using the 15 mesoporous AlPO catalyst in the batch experiment for preparation of EMC at 93 °C resulted in a 47.7% conversion of DEC (after 0.5 h reaction) and a selectivity to EMC of nearly 100%. In another article, titled “Amorphous magnesium 20 substituted mesoporous aluminophosphate: An acid-base sites synergistic catalysis for transesterification of diethyl carbonate and dimethyl carbonate in fixed-bed reactor” by Wang Hefang et al., in Microporous and Mesoporous Materials, 292, 2020, 109757, a mesoporous aluminophosphate (AlPO) 25 catalyst prepared using the citric acid route, was also used in the transesterification of DEC with DMC thereby producing EMC. However, in the latter catalyst part of the aluminum (Al) was replaced by magnesium (Mg) which is said to have significant influences on the acid-basic properties of the 30 catalyst. Above-mentioned article discloses DEC conversions up to 55.3% and selectivities to EMC up to 95.3%, and it shows that said activity and selectivity increase with the substitution of magnesium to mesoporous According to said article, the high catalytic activity of the Mg substituted AlPO catalyst was attributed to the synergistic catalysis of optimum amounts of strong basic and weak acid 5 sites. It is cumbersome to have to use citric acid in the preparation of an aluminophosphate catalyst or to incorporate magnesium in said catalyst, as disclosed in above-mentioned two articles. First of all, an additional chemical (i.e. 10 citric acid) has to be introduced, in addition to the phosphoric acid as mentioned above. Secondly, in the above- mentioned preparation method using citric acid, no precipitation of the aluminophosphate catalyst is achieved but the aqueous mixture first has to be heated in order to 15 evaporate the water and then recover a solid catalyst, which isolation method is highly energy-intensive. It is desired to be able to omit the use of citric acid and magnesium in such preparations of aluminophosphate catalysts. In addition, it is desired to maintain a high 20 activity and selectivity, or to even increase the activity and / or selectivity, of aluminophosphate catalysts in the preparation of mixed dialkyl carbonates from different dialkyl carbonates, such as in the preparation of ethyl methyl carbonate from dimethyl carbonate and diethyl 25 carbonate. Therefore, an object of the present invention is to provide a process for the preparation of a mixed dialkyl carbonate from different dialkyl carbonates using an aluminum phosphate as a catalyst, which catalyst has a relatively high 30 activity and / or selectivity in said process, preferably an activity and / or selectivity which is improved as compared to that of the catalysts as prepared in accordance with above- mentioned two articles. Summary of the invention Surprisingly, it was found that the above object may be achieved by using in a process for the preparation of a mixed dialkyl carbonate from different dialkyl carbonates, an 5 aluminum phosphate as a catalyst, which aluminum phosphate is obtained by a process comprising: (a) mixing an aluminum containing salt with phosphoric acid in a molar ratio [Al] / [P] of from 0.1:1 to 20:1; (b) mixing a base with the mixture resulting from step 10 (a), resulting in the formation of an aluminum phosphate precipitate; (c) optionally heating the precipitate containing mixture; and (d) recovering the precipitate. 15 Accordingly, the present invention relates to a process for the preparation of a mixed dialkyl carbonate of formula R1O(C=O)OR2, comprising reacting a dialkyl carbonate of formula R1O(C=O)OR1and a dialkyl carbonate of formula R2O(C=O)OR2, wherein R1 and R2 are different alkyl groups, in 20 the presence of a catalyst, wherein the catalyst comprises an aluminum phosphate and the aluminum phosphate is obtained by a process comprising: (a) mixing an aluminum containing salt with phosphoric acid in a molar ratio [Al] / [P] of from 0.1:1 to 20:1; 25 (b) mixing a base with the mixture resulting from step (a), resulting in the formation of an aluminum phosphate precipitate; (c) optionally heating the precipitate containing mixture; and 30 (d) recovering the precipitate. The aluminum phosphate catalyst to be used in the process of the present invention may be prepared in the same way as disclosed in WO2019016126, which does not require the use of citric acid and / or magnesium is required in the two articles as mentioned above under “Background of the invention”. Said WO2019016126 discloses a process for the preparation of an alkanediol and a dialkyl carbonate 5 comprising reacting an alkylene carbonate and an alkanol in the presence of an aluminum phosphate catalyst. It does not disclose or suggest the use of the same catalyst in the preparation of a mixed dialkyl carbonate from different dialkyl carbonates. 10 As shown in the Examples hereinbelow, the aluminum phosphate catalyst as obtained in the above process shows a higher activity and selectivity in the preparation of a mixed dialkyl carbonate from different dialkyl carbonates, in specific in the preparation of ethyl methyl carbonate (EMC) 15 from dimethyl carbonate (DMC) and diethyl carbonate (DEC), than the aluminum phosphate catalysts as disclosed in the two articles as mentioned above under “Background of the invention”. Such different activity and selectivity imply that the catalysts as such are also different. 20 Further, the present invention relates to a process for preparing a battery electrolyte solution comprising combining a mixed dialkyl carbonate with one or more alkali metal salts, wherein the mixed dialkyl carbonate has been prepared by the above-mentioned process. 25 Brief description of the drawings Figure 1A shows CO2 desorption, as determined by CO2-TPD (“Temperature Programmed Desorption”), for aluminum phosphate catalysts, corresponding to Figure 7 in the above-mentioned article in Microporous and Mesoporous Materials, 292, 2020, 30 109757. Figure 1B shows CO2 desorption, as determined by CO2-TPD, for an aluminum phosphate catalyst as prepared under A) in the Examples hereinbelow in with the present invention. Figures 2A and 2B show the conversion of diethyl carbonate (DEC), in Figure 2A, and the yield of ethyl methyl 5 carbonate (EMC), in Figure 2B, versus the liquid hourly space velocity (LHSV) in the reaction of DEC with dimethyl carbonate (DMC) under B) in the Examples hereinbelow, when using the aluminum phosphate catalyst as prepared under A) in said Examples, in accordance with the present invention, as10 compared with the aluminum phosphate catalysts in the above- mentioned articles. Detailed description of the invention While the process of the present invention and the stream(s), catalyst or composition(s) used or produced in 15 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. 20 In the context of the present invention, in a case where a stream, catalyst or composition comprises two or more components, these components are to be selected in an overall amount not to exceed 100%. Further, where upper and lower limits are quoted for a 25 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. Within the present specification, “substantially no” means that no detectible amount of the component in question 30 is present in the catalyst or composition. In the process of the present invention, a mixed dialkyl carbonate is prepared from different dialkyl carbonates. That is to say, a mixed dialkyl carbonate of formula R1O(C=O)OR2, wherein R1 and R2 are different alkyl groups, is prepared by reacting a dialkyl carbonate of formula R1O(C=O)OR1 and a dialkyl carbonate of formula R2O(C=O)OR2, wherein R1 and R2 are different alkyl groups. In above-mentioned dialkyl carbonates of formulas R1O(C=O)OR2, R1O(C=O)OR1 and R2O(C=O)OR2, R1 and R2 are different alkyl groups. Preferably, R1 and R2 are C1-C4 alkyl groups, more preferably C1-C3 alkyl groups, most preferably C1-C2 alkyl groups. The C1-C4 alkyl groups comprise methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl and isobutyl groups. Most preferably, in the present invention, R1is methyl and R2is ethyl, in which case the mixed dialkyl carbonate is ethyl methyl carbonate (EMC), as prepared by reacting diethyl carbonate (DEC) and dimethyl carbonate (DMC). Other suitable examples of mixed dialkyl carbonates that can be prepared in the present process, are isopropyl n- butyl carbonate, n-propyl n-butyl carbonate and ethyl n- propyl carbonate. The conditions in the present process may include a temperature of from 10 to 200 °C. Further, they may include a pressure of from 0.5 to 50 bara (5x104to 5x106N / m2). Preferably, said pressure ranges from 1 to 20 bar, more preferably 1.5 to 20 bar, most preferably 2 to 15 bar. Further, preferably said temperature ranges from ambient temperature to 200 °C, more preferably 20 to 200 °C, more preferably 30 to 200 °C, more preferably 40 to 170 °C, more preferably 50 to 140 °C, most preferably 60 to 120 °C. Further, the weight hourly space velocity (WHSV) in the present process may suitably range of from 0.5 to 50 kg / kgcat.hr (“kgcat” refers to the catalyst amount), more suitably 1 to 20 kg / kgcat.hr, more suitably 1 to 10 kg / kgcat.hr. Still further, the liquid hourly space velocity (LHSV) in the present process may suitably range of from 0.5 to 50 ml / gcat.hr (“gcat” refers the catalyst amount), more suitably 1 to 20 ml / gcat.hr, more suitably 1 to 10 ml / gcat.hr. Preferably, the present process is conducted in a co- current manner. A suitable way to operate the process of the 5 present invention is in a reactor with only liquids. A suitable reaction zone of this type is a pipe-type reaction zone wherein the reaction is conducted in a plug flow manner. For example, the present process may be carried out in one plug flow reactor or in a series of two or more plug flow 10 reactors. This will enable the reaction to approach equilibrium. Suitably, the pipe-type reactor is a fixed-bed reactor. A further possibility is to conduct the process of the present invention in a continuously stirred tank reactor 15 (CSTR). In the latter case the effluent from the CSTR is preferably subjected to a post-reaction in a plug flow reactor so that the reaction can approach equilibrium. The process of the present invention is preferably carried out continuously. 20 In the process of the present invention, the catalyst comprises an aluminum phosphate and the aluminum phosphate is obtained by a process comprising: (a) mixing an aluminum containing salt with phosphoric acid in a molar ratio [Al] / [P] of from 0.1:1 to 20:1; 25 (b) mixing a base with the mixture resulting from step (a), resulting in the formation of an aluminum phosphate precipitate; (c) optionally heating the precipitate containing mixture; and 30 (d) recovering the precipitate. In the present specification, aluminum phosphate may also be referred to as “AlPO”. The anhydrous form of aluminum phosphate or a hydrate of aluminum phosphate may be used in the present invention. examples of hydrates of aluminum phosphate are AlPO4·2H2O and AlPO4·1.5H2O. Preferably, the anhydrous form of aluminum phosphate is used in the present invention. 5 The catalyst comprising the aluminum phosphate is a heterogeneous catalyst. Further, preferably the aluminum phosphate in the present invention is amorphous. Preferably, more than 90%, more preferably more than 95%, most preferably more than 99% of the aluminum phosphate is amorphous. 10 Preferably, less than 10%, more preferably less than 5%, most preferably less than 1% of the aluminum phosphate is crystalline. Most preferably, the aluminum phosphate comprises substantially no crystalline structures. The aluminum phosphate used in the present process has a 15 molar (or atomic) ratio [Al] / [P] of from 0.1:1 to 20:1, suitably of from 0.5:1 to 10:1, more suitably of from 1:1 to 5:1, most suitably of from 1.5:1 to 3:1. Said molar ratio [Al] / [P] is at most 20:1, preferably at most 15:1, more preferably at most 10:1, more preferably at most 7:1, more 20 preferably at most 5:1, more preferably at most 4:1, more preferably at most 3:1, most preferably at most 2.5:1. Said molar ratio [Al] / [P] is at least 0.1:1, preferably at least 0.3:1, more preferably at least 0.5:1, more preferably at least 0.8:1, more preferably at least 1:1, more preferably at 25 least 1.3:1, most preferably at least 1.5:1. The aluminum phosphate used in the present invention may have a surface area (BET) which varies within a broad range, for example of from 20 to 400 m2 / g, suitably of from 50 to 300 m2 / g, most suitably of from 100 to 250 m2 / g. 30 Further, the aluminum phosphate used in the present invention may have a pore volume (as determined by mercury intrusion) which varies within a broad range, for example of from 0.30 to 0.95, preferably 0.50 to 0.95, more preferably 0.50 to 0.90, more preferably to 0.85, most preferably 0.60 to 0.75. Still further, surprisingly and advantageously, the aluminum phosphate used in the present invention, especially when prepared in a way as described below, may have a relatively high amount of super strong basic sites, as shown in the Examples hereinbelow. The relative amounts of weak basic sites, medium basic sites, strong basic sites and super strong basic sites may be determined by Temperature Programmed Desorption (TPD) of carbon dioxide (CO2). Upon increasing the basicity of these sites, the temperature at which CO2desorbs from these sites is likewise increased. For the aluminum phosphate used in the present invention, the relative amount of CO2 desorption at a temperature at or below 200 °C (herein referred to as “weak basic sites”), based on total CO2desorption and as determined by TPD, may be of from 10 to 50%, preferably 15 to 40%, more preferably 20 to 25%. Further, the relative amount of CO2desorption at a temperature at or above 500 °C (herein referred to as “super strong basic sites”), based on total CO2 desorption and as determined by TPD, may be of from 50 to 90%, preferably 60 to 85%, more preferably 75 to 80%. Still further, the relative amount of CO2desorption at a temperature between 200 and 500 °C, based on total CO2 desorption and as determined by TPD, may be of from 0 to 30% or 2 to 20% or 5 to 10%, or 0 to 10% or 0 to 5% or 0 to 2%, preferably 0%. The aluminum phosphate used in the present process may be provided in the form of a catalyst composition having any shape and any dimensions. For example, the catalyst may be shaped into a tablet form, which may have any shape, for example a cylindrical shape. Furthermore, the catalyst may be shaped in the form of an extrudate. A shaped catalyst composition comprising the phosphate may additionally comprise a residual amount (for example up to 2 wt.%) of any shaping aid (for example graphite) used when shaping. 5 In the present invention, synthesized aluminum phosphate is used. In specific, the aluminum phosphate is obtained by a process comprising: (a) mixing an aluminum containing salt with phosphoric acid in a molar ratio [Al] / [P] of from 0.1:1 to 20:1; 10 (b) mixing a base with the mixture resulting from step (a), resulting in the formation of an aluminum phosphate precipitate; (c) optionally heating the precipitate containing mixture; and 15 (d) recovering the precipitate. In the above-mentioned step (a), the aluminum containing salt may be any salt, for example aluminum nitrate. A hydrate of said salt may be used, for example Al(NO3)3·9H2O or Al(NO3)3·6H2O. Preferably, an aqueous solution containing said 20 salt is used. Further, preferably, an aqueous solution containing phosphoric acid is used. Said aluminum salt containing aqueous solution and said phosphoric acid containing aqueous solution may be mixed in said step (a). The molar ratio [Al] / [P] in the mixture resulting from said 25 step (a) is of from 0.1:1 to 20:1. The preferences for this ratio as described above in relation to the final aluminum phosphate also apply to this mixture obtained in said step (a). Further, the molar concentration (in mole / liter) of aluminum (Al3+) in the mixture resulting from said step (a) 30 may be of from 0.1 to 1.8 molar, and is preferably of from 0.2 to 1.3 molar, more preferably of from 0.2 to 0.9, more preferably of from 0.3 to 0.7, most preferably of from 0.3 to 0.6. Still further, the molar concentration (in mole / liter) of phosphate (PO43-) in the resulting from said step (a) may be of from 0.05 to 1.2 molar, and is preferably of from 0.1 to 0.8 molar, more preferably of from 0.1 to 0.6, more preferably of from 0.15 to 0.45, most preferably of from 5 0.15 to 0.35. It is preferred that in the above-mentioned step (a), no citric acid is used. Further, it is preferred that in step (a), no acid other than phosphoric acid is used. In the above-mentioned step (b), mixing a base with the 10 mixture resulting from step (a) initiates precipitation of aluminum phosphate. The base may be added to the mixture resulting from step (a), or the mixture resulting from step (a) may be added to the base, or both. Preferably, the base is added to the mixture resulting from step (a). Preferably, 15 an aqueous solution containing the base is used. Said base may be any base, for example ammonia. Preferably, the amount of base used in step (b) is sufficient to achieve a pH in the range of from 4 to 7, suitably of from 4.5 to 6.5, more suitably of from 5 to 6. 20 In the above-mentioned optional step (c), the aluminum phosphate precipitate containing mixture is heated, suitably at a temperature of from 20 to 100 °C, more suitably 20 to 95 °C, most suitably 70 to 95 °C. Said heating may be performed for a period of from 1 to 10 hours, suitably 1 to 5 hours, 25 more suitably 2 to 4 hours. This treatment in step (c) may be referred to as “ageing”. In the above-mentioned step (d), the aluminum phosphate precipitate is recovered. This may for example be done by filtering the precipitate containing mixture. The aluminum 30 phosphate (precipitate) may then be washed with water and subsequently dried, for example at a temperature of from 50 to 250 °C, suitably 70 to 150 °C. The aluminum phosphate precipitate recovered in step (d) may have a (volume-based) median pore diameter, before later calcining step and / or shaping step, which is in the range of 1 to 100 nanometers (nm), more suitably of from 5 to 80 nm, more suitably of from 10 to 60 nm, more suitably of from 15 to 45 nm. Said pore 5 diameter may be determined by a mercury (Hg) intrusion method. Further, the recovered aluminum phosphate may be subjected to a heat treatment at a temperature of from 200 to 1000 °C, suitably 400 to 800 °C, more suitably 500 to 700 °C. 10 Said heat treatment may be carried out in an inert gas atmosphere or in air, preferably in air. Said heating may be performed for a period of from 1 to 10 hours, suitably 1 to 5 hours, more suitably 2 to 4 hours. This heat treatment may be referred to as “calcining”. 15 Still further, the recovered aluminum phosphate may be shaped into any form, for example tablets, preferably after first milling and / or sieving. The mesh size used when sieving may be any, suitably of from 600 to 1800 µm, more suitably of from 1000 to 1400 µm. The sieved material having a size below 20 said mesh size may be used in such shaping. In case the aluminum phosphate is calcined, as described above, such calcination may be performed before and / or after such shaping, preferably after. The amount of catalyst used in the present process may 25 vary within wide ranges and should be sufficient to catalyze the desired reaction. Further, it is preferred that the catalyst used in the present process, comprising an aluminum phosphate as obtained in the above-described way, consists of said aluminum 30 phosphate. Further, it is preferred that said aluminum phosphate does not contain any elements other than aluminum, phosphorus and oxygen, such as e.g. citric acid and magnesium. Further, the present relates to a process for preparing a battery electrolyte solution comprising combining a mixed dialkyl carbonate with one or more alkali metal salts, wherein the mixed 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 mixed 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 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. Further, it is envisaged that the above-described aluminum phosphate is used as a catalyst in a process for the reverse reaction of converting the above-described mixed dialkyl carbonate of formula R1O(C=O)OR2into the above- described dialkyl carbonate of formula R1O(C=O)OR1 and dialkyl carbonate of formula R2O(C=O)OR2. It is preferred that in such process reactive distillation is applied in a reactive distillation column. The distillation column may contain trays with bubble caps, sieve trays, or Raschig rings. The skilled person will realize that several types of packings of catalyst and several tray configurations will be possible. Suitable columns have been described in, e.g., Ullmann’s Encyclopedia of Industrial Chemistry, 5thed. Vol. B4, pp 321 ff, 1992. In general, the dialkyl carbonate having a lower boiling point will flow upwardly and exit the reactive distillation column at the upper part and the dialkyl carbonate having a higher boiling point will flow downwardly and exit the reactive distillation column at the lower part. The invention is further by the following Examples. Examples A) Manufacture of aluminum phosphate (AlPO) catalyst 5 An aluminum phosphate (AlPO) catalyst was prepared as follows. 2 Moles of Al(NO3)3.9H2O was dissolved in 3 liters of deionized water. Under vigorous stirring, 1 liter of a solution which contained 1 mole of phosphoric acid was fed, 10 with a feed rate of 2.5 liters / hour, to the aluminum nitrate solution. The precipitation of aluminum phosphate was initiated by feeding aqueous ammonia (10 wt.%) under vigorous stirring, with a feed rate of 2.5 liters / hour, to the above- mentioned solution. The ammonia dosage was stopped when a pH 15 of 5.5 is reached. Then the whole batch was heated up to 90 °C. When said temperature of 90 °C was reached, said stirring was continued for a period of time of 2-3 hours. After said ageing step, the precipitate was filtered and the resulting filter cake was washed with water and then dried at 130 °C. 20 The surface area (BET) of said dried precipitate material was 220 m2 / g. Further, said aluminum phosphate precipitate material had a (volume-based) median pore diameter of 28 nanometers (nm), as determined by mercury (Hg) intrusion. Still further, said aluminum phosphate precipitate was 25 amorphous and comprised substantially no crystalline structures. Then said precipitate material was milled and sieved. Sieved material having sizes of from 150 to 600 µm was mixed with graphite, which is a tableting aid, and shaped into 3 mm 30 x 3 mm tablets of cylindrical shape. The prepared tablets were calcined at 600 °C in air for 3 hours. In the final AlPO molar / atomic ratio [Al] / [P] was 1.9:1. The surface area (BET) of the final catalyst was 159 m2 / g, and its pore volume was 0.66 cm3 / g. The AlPO catalyst manufactured in the above way in the 5 present Examples, wherein no citric acid and no magnesium are used as required in the following two articles [1] and [2] as mentioned above under “Background of the invention”, is different from the AlPO catalysts prepared according to said articles: Article Citric Magnesium? acid? [1] Catalysis Communications, 12, Yes No 2011, pages 721-725 [2] Microporous and Mesoporous Yes Yes Materials, 292, 2020, 109757 10 In manufacturing the AlPO catalysts from articles [1] and [2], citric acid is used. In specific, according to said articles, an amorphous mesoporous AlPO catalyst is prepared from Al(NO3)3 and H3PO4 with 1 mol equivalent of citric acid 15 as template. No sol-gel transition or precipitation occurs. The resulting solution is neutralized with aqueous ammonia and evaporated to isolate the AlPO catalyst as a white solid. On the contrary, the AlPO catalyst manufactured in the present Examples was prepared from Al(NO3)3 and H3PO4 in the 20 absence of citric acid as template, and the AlPO catalyst was then precipitated with aqueous ammonia via a sol-gel transition. Such precipitation is advantageous as less energy is required to recover the catalyst. Evaporation of water as applied in the citric acid route, requires a high energy 25 amount. On the contrary, the precipitated catalyst used in the present invention, can easily be recovered by less energy-intensive methods, such as filtration. Different properties of AlPO catalyst manufactured in the present Examples and the AlPO catalysts from articles [1] and [2] are mentioned in the table below: AlPO catalyst BET surface area Pore volume (m2 / g) (cm3 / g) Present Examples 159 0.66 [1]: AlPO 402 0.43 [2]: Mg0.1AlPO 436 0.49 [2]: Mg0.2AlPO 381 0.39 [2]: Mg0.3AlPO 346 0.38 As can be seen in the above table, the AlPO catalyst manufactured in the present Examples has a much lower surface area and a much higher pore volume than the AlPO catalysts from articles [1] and [2]. Furthermore, another difference with the AlPO catalysts from articles [1] and [2] concerns their basic sites, as determined by Temperature Programmed Desorption (TPD) of carbon dioxide (CO2) as shown in Figure 1. In Figure 1, “TCD” refers to the Thermal Conductivity Detector as used in the CO2-TPD analysis. Figure 1A is taken from Figure 7 in article [2]. The “AlPO” catalyst in Figure 1A is the one from article [1] without Mg, and the other 3 AlPO catalysts with Mg are from article [2]. Further, in Figure 1A, for each of these 4 AlPO catalysts, the lines BW, BM and BS represent the concentrations of weak, medium and strong basic sites, respectively, as calculated according to CO2-TPD. The 4thline is the total concentration of these basic sites (referred to in article [2] as “BTOTAL”). Upon increasing the basicity of these sites, the temperature at which CO2 desorbs from these sites is likewise increased. As can be seen from Figure 1A (see also Figure 7 and Table 3 in article [2]), the unmodified AlPO catalyst from article [1] contains mostly and medium basic sites. Partial replacement of the aluminium by magnesium, as in the modified AlPO catalyst from article [2], results in more medium and strong basic sites. Surprisingly, the AlPO catalyst manufactured in the present Examples also contains, in addition to weak basic sites, a high amount of super strong basic sites where CO2 desorption occurs at temperatures at or above 500 °C. In specific, as shown in Figure 1B, for the latter AlPO catalyst the relative amount of CO2 desorption at a temperature at or below 200 °C (weak basic sites) was only 21%, whereas the relative amount of CO2desorption at a temperature at or below 500 °C (super strong basic sites) was 79%. There was essentially no CO2 desorption between 200 and 500 °C. These super strong basic sites result in an AlPO catalyst having an advantageously higher activity and selectivity in the preparation of mixed dialkyl carbonates from different dialkyl carbonates, as is demonstrated below under B). B) Use of aluminum phosphate (AlPO) catalyst in the transesterification reaction of two dialkyl carbonates The aluminum phosphate (AlPO) catalyst prepared above under A) was used in the reaction of dimethyl carbonate (DMC) and diethyl carbonate (DEC), thereby producing ethyl methyl carbonate (EMC). Catalytic performance tests were carried out in a stainless-steel fixed bed reactor (outer diameter: 1 cm; length: 60 cm) placed in an electrically heated furnace. The reactor was loaded with AlPO catalyst, a 150-600 µm sieve fraction mentioned above under A), which catalyst was first diluted with inert ceramic material and then placed in the middle of the reactor. The feed to the reactor was a mixture of DEC and DMC with a molar ratio of 1:1 which was pumped through the reactor at a set flow rate of 14 ml / h. isothermal temperature was varied at 70, 90 and 105 °C. The composition of the liquid and gas flows from the reactor were measured by calibrated GC (gas chromatography). The conditions and results for these 5 experiments (Exp. 1a-1f) are summarized in the table below, wherein “LHSV” = liquid hourly space velocity (in ml / h / g of AlPO catalyst) and T = reactor temperature. Exp. AlPO Flow LHSV T DEC con- EMC yield (g) (ml / h) (ml / h / g) (°C) version (%) (%) 1a 2 14 7 70 47.8 47.4 1b 2 14 7 90 51.0 49.1 1c 2 14 7 105 51.5 47.5 1d 1 14 14 70 40.5 40.0 1e 1 14 14 90 49.7 48.9 1f 1 14 14 105 50.8 48.6 Since the reaction of DEC with DMC to EMC is equilibrium 10 limited (Keqis about 4), the theoretical DEC conversion to EMC at above-mentioned molar DEC:DMC feed ratio of 1:1 is limited to 50.3%, which at 100% selectivity results in a maximum EMC yield of 50.3%. As can be seen from Figures 2A and 2B, the activity and 15 selectivity of the AlPO catalyst manufactured in the present Examples in accordance with the present invention (referred to as “Shell AlPO” catalyst), is surprisingly and advantageously increased as compared to the AlPO catalysts from articles [1] and [2] mentioned above under A). The “AlPO 20 lit” catalyst corresponds with the AlPO catalyst from article [1], and the 3 “AlPO lit” catalysts which also contain magnesium (Mg) correspond with the AlPO catalysts from article [2]. The temperatures in Figures 2A and 2B refer to the reactor temperature. This increased AlPO activity is shown by an increased DEC conversion in Figure 2A. This increased DEC conversion is even shown at a reactor temperature of 90 °C which is lower than the reactor temperature of 100 °C as 5 applied in the preparation of the AlPO catalysts from articles [1] and [2]. Further, this increased AlPO catalyst selectivity is shown by an increased EMC yield in Figure 2B. EMC yield is the product of DEC conversion and selectivity to EMC. This 10 increased EMC yield is even shown at a reactor temperature of 105 °C which is higher than the reactor temperature of 100 °C as applied in the preparation of the AlPO catalysts from articles [1] and [2]. Thus, it appears from Figures 2A and 2B that with the 15 AlPO catalysts from articles [1] and [2] both the DEC conversion and the EMC yield decline with increasing LHSV, while in Exp. 1a-1f, which are in accordance with the present invention, surprisingly and advantageously both the DEC conversion and the EMC yield are higher, especially at a 20 relatively high LHSV (of ≥7) which is generally preferred in industrial practice. The above experiments were repeated (in Exp. 2a-5e) varying a wide range of reactor conditions. In Exp. 2a-5e, the feed to the reactor was a mixture of DEC and DMC with a 25 molar ratio of 3:1, whereas in Exp. 1a-1f this ratio was 1:1. The conditions and results for these experiments (Exp. 2a-5e) are summarized in the table below.

[0002] Exp. AlPO Flow LHSV T DEC con- EMC se- EMC (g) (ml / h) (ml / h / g) (°C) version lectivity yield (%) (%) (%) 2a 1 14 14 70 18.6 97.8 18.2 2b 1 14 14 80 24.1 97.1 23.4 2c 1 14 14 90 25.6 96.1 24.6 2d 1 14 14 100 25.4 95.7 24.3 2e 1 14 14 110 28.2 83.7 23.6 3a 1 7 7 70 24.5 97.1 23.8 3b 1 7 7 80 25.2 97.6 24.6 3c 1 7 7 90 25.8 94.6 24.4 3d 1 7 7 100 27.1 87.5 23.7 3e 1 7 7 110 28.8 77.1 22.2 4a 4 14 3.5 70 27.5 89.8 24.7 4b 4 14 3.5 80 28.4 86.6 24.6 4c 4 14 3.5 90 29.8 80.2 23.9 4d 4 14 3.5 100 31.3 72.2 22.6 4e 4 14 3.5 110 35.7 52.7 18.8 5a 3.5 7 2 70 27.5 89.8 24.7 5b 3.5 7 2 80 28.4 86.6 24.6 5c 3.5 7 2 90 29.8 80.2 23.9 5d 3.5 7 2 100 31.3 72.2 22.6 5e 3.5 7 2 110 35.7 52.7 18.8 Since the reaction of DEC with DMC to EMC is equilibrium limited (Keqis about 4), the theoretical DEC conversion to 5 EMC at above-mentioned molar DEC:DMC feed ratio of 3:1 is limited to 25.1%, which at 100% selectivity results in a maximum EMC yield of 25.1%. As can be seen from the above table (Exp. 2a-5e), both the reactor temperature and the LHSV have an impact on the DEC conversion and with selectivity decreasing at higher temperatures and at lower LHSV.

Claims

C L A M S 1. A process for the preparation of a mixed dialkyl carbonate of formula R1O(C=O)OR2, comprising reacting a dialkyl carbonate of formula R1O(C=O)OR1and a dialkyl carbonate of formula R2O(C=O)OR2, wherein R1 and R2 are different alkyl groups, in the presence of a catalyst, wherein the catalyst comprises an aluminum phosphate and the aluminum phosphate is obtained by a process comprising: (a) mixing an aluminum containing salt with phosphoric acid in a molar ratio [Al] / [P] of from 0.1:1 to 20:1; (b) mixing a base with the mixture resulting from step (a), resulting in the formation of an aluminum phosphate precipitate; (c) optionally heating the precipitate containing mixture; and (d) recovering the precipitate.

2. The process according to claim 1, wherein R1 and R2 are C1-C4 alkyl groups.

3. The process according to claim 2, wherein R1 is methyl and R2is ethyl.

4. The process according to any one of claims 1 to 3, wherein no citric acid is used in step (a) of the process for preparing the aluminum phosphate.

5. The process according to any one of claims 1 to 4, wherein the aluminum phosphate has a relative amount of carbon dioxide desorption at a temperature at or above 500 °C, based on total carbon dioxide desorption and asdetermined by Temperature Desorption, which is of from 50 to 90%.

6. The process according to any one of claims 1 to 5, 5 wherein more than 90% of the aluminum phosphate is amorphous.

7. The process according to any one of claims 1 to 6, wherein the aluminum phosphate has a molar (or atomic) ratio [Al] / [P] of from 0.5:1 to 10:

1. 10 8. The process according to any one of claims 1 to 7, wherein the aluminum phosphate has a surface area of from 20 to 400 m2 / g. 15 9. The process according to any one of claims 1 to 8, wherein the aluminum phosphate has a pore volume of from 0.30 to 0.

95.

10. A process for preparing a battery electrolyte solution 20 comprising combining a mixed dialkyl carbonate with one or more alkali metal salts, wherein the mixed dialkyl carbonate has been prepared by the process according to any one of claims 1 to 9.

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