JPH10306063A - Production of carbonic ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient process for producing carbonic ester in high selectivity in a homogeneous catalyst system with reduced corrosion caused by the reaction mixture, as the catalyst deterioration is inhibited. SOLUTION: This process for producing carbonic ester comprises the oxidative carbonylation step in which an alcohol is allowed to react with carbon monoxide and oxygen in the presence of metallic copper, metal compound or metal complex, a glycol ether of formula I: R1 O(CH(R2 )CH2 O)n R3 (R1 is a 1-6C alkyl group, R2 is a 1-2 alkyl group or H, R3 is a 1-6C alkyl group or H, n is an integer of 1-12) and a cyclic nitrogen compound, the discharge step in which the reaction mixture of liquid phase or liquid/vapor mixed phase is taken out of the reactor, the moisture removal step in which the moisture is separated and removed from the reaction mixture and the returning step in which the moisture-removed reaction mixture is allowed to return to the oxidative carbonylation tank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a carbonate ester. Carbonic esters such as dimethyl carbonate
In addition to being useful as a raw material for pharmaceuticals, agricultural chemicals, etc., it has recently attracted attention as an additive to gasoline (octane booster) or as a reagent replacing phosgene in the production of various carbonates used as raw materials for organic glass. .

[0002]

2. Description of the Related Art Hitherto, as a method for producing a carbonate ester, a method of reacting phosgene with an alcohol has been known, and has actually been industrialized. However,
This method has a problem that the device material is corroded by hydrochloric acid as a by-product and a problem that phosgene itself has extremely high toxicity. Therefore, a non-phosgene manufacturing technique that does not use phosgene has been required. In order to meet such demands, production of dimethyl carbonate by oxidative carbonylation of methanol using copper (I) chloride as a catalyst has been proposed, and this technique has already been known.

[0003] In the production of dimethyl carbonate by oxidative carbonylation of methanol using copper (I) chloride as a catalyst, equimolar water is produced at the same time as the production of dimethyl carbonate.

[0004] Since the produced water has the same reactivity as alcohols, the reaction of alcohols is inhibited by water, or the produced water reacts with a catalyst component such as copper to lose the catalyst. It was causing a problem of being active.

In order to solve such problems, Japanese Patent Application Laid-Open No. Hei 5-201930 discloses that unreacted raw materials (eg, alcohols), products (dimethyl carbonate), and water as a reaction by-product are supplied from a reactor. , Each of which is extracted in the gas phase, once cooled and agglomerated, passed through a membrane separator for water removal, dehydrated, and then returned to the reactor with high-concentration products and unreacted raw materials. Have been.

[0006] Such a system for extracting a gas phase from a reactor can be said to be an energy-efficient system. Nevertheless, the reason why gas phase extraction is required is that the catalyst system itself described in Japanese Patent Application Laid-Open No. 5-201930 is a slurry reaction insoluble in the reaction solution. In a slurry reaction system, it is difficult to perform dehydration directly from a reaction solution itself, through a separation membrane, or using a dehydrating agent, because of problems such as blockage of the separation membrane and blockage of piping.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a system in which the selectivity of carbonate ester is high under an efficient system.
It is an object of the present invention to provide a method for producing a carbonate ester in a homogeneous catalyst system which can suppress deterioration of the catalyst activity and also has low corrosiveness of a reaction solution.

[0008]

Means for Solving the Problems In order to solve the above problems, a method for producing a carbonate according to the present invention is described by using the following structural formula (I) with copper metal, a copper metal compound or a copper complex compound. Carbonylation reaction step in which alcohols are reacted with carbon monoxide and oxygen in the presence of glycol ethers and a cyclic nitrogen compound, and a reaction solution in a reaction vessel in which the carbonylation reaction is performed A reaction liquid extracting step of extracting in a phase or a gas-liquid mixed phase, and a water removing step of removing water in the extracted reaction liquid,
The reaction solution after the water is removed by the water removing step,
A step of returning to the reaction tank for performing the carbonyl oxidation reaction,
It is comprised so that it may have.

R ₁ O (CH (R ₂ ) CH ₂ O) _n R ₃ Formula (I) (In the formula (I), R ₁ is an alkyl group having 1 to 6 carbon atoms, R ₂
Is an alkyl group or hydrogen having 1 to 2 carbon atoms, R ₃ is an alkyl group or hydrogen having 1 to 6 carbon atoms, and n is an integer of 1 to 12.) In a preferred embodiment, water in the reaction solution is removed. Is performed using a membrane system that selectively permeates water.

In a preferred embodiment, the membrane system for selectively permeating water is constituted by a membrane separation method of a pervaporation membrane method.

In a preferred embodiment, the cyclic nitrogen compound is constituted to be a pyridine.

In a preferred embodiment, the molar ratio of the cyclic nitrogen compound to 1 mol of copper atoms in the metal copper, the metal copper compound or the copper complex compound is in the range of 0.1 to 100.

In a preferred embodiment, the molar ratio of the glycol ether represented by the above structural formula (I) to 1 mol of copper atom in the metal copper, the metal copper compound or the copper complex compound is in the range of 1 to 20. It is configured as follows.

In the present invention, since a copper cyclic nitrogen compound complex (for example, a copper pyridine complex) is dissolved in glycol ethers, a homogeneous catalyst system can be realized. Then, the reaction liquid in the reaction tank is withdrawn as it is in a liquid state, and the water in the extracted reaction liquid is directly removed.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to FIG. FIG. 1 is a drawing showing a schematic flow of a process apparatus for carrying out the manufacturing method of the present invention.

The method for producing a carbonic acid ester according to the present invention is characterized in that, in a reaction vessel 10, an alcohol (e.g., a metal copper, a metal copper compound or a copper complex compound), a glycol ether and a cyclic nitrogen compound are added. In the example shown, methanol: MeOH) is converted to carbon monoxide (CO) and oxygen (O
₂ ). That is, in the presence of a homogeneous catalyst system containing copper, a carbonate is produced by oxidation and carbonylation of an alcohol. It is believed that the reaction mechanism is as follows.

2 (ROH) + 1/2 O ₂ + ₂ CuCl → 2 [CuORCl] +
H ₂ O (oxidation) 2 [CuORCl] + CO → (RO) ₂ CO + ₂ CuCl (carbonylation) Summarizing the above two equations, 2 (ROH) + CO + 1/2 O ₂ → (RO) ₂ CO + H ₂ O (oxidative carbonylation of alcohol).

The metal copper, metal copper compound or copper complex compound used in the present invention functions as a catalyst component. Examples of the metal copper compound include halides such as chloride, bromide and iodide (eg, CuCl, CuCl ₂ , CuB
r, CuBr ₂ , CuI); salts of inorganic acids such as nitric acid, carbonic acid, boric acid, phosphoric acid (for example, Cu (NO ₃ ) ₂ , Cu
CO ₃ .Cu (OH) ₂ .H ₂ O, CuB ₄ O ₇ , Cu
₃ (PO ₄ ) ₂ ); salts of organic acids such as formic acid, acetic acid, and oxalic acid (for example, Cu (HCOO) ₂ , Cu (CH ₃ CO
O) ₂ , Cu (C ₂ O ₄ )); oxides (eg, Cu ₂
O, CuO); hydroxides (for example, Cu (OH) ₂ ). Examples of the copper complex compound include a complex of the above metal copper compound and a coordinating compound. In this case, examples of the coordination compound used include amines such as trimethylamine; nitrogen-containing cyclic compounds such as pyridine; and organic phosphorus compounds such as triphenylphosphine. Among these, cuprous chloride (CuCl) or a complex thereof is particularly preferably used from the viewpoint of catalytic activity and selectivity (selectivity).

As the glycol ethers used in the present invention, those represented by the following structural formula (I) are used.

R ₁ O (CH (R ₂ ) CH ₂ O) _n R ₃ Formula (I) In the above formula (I), R ₁ has 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, more preferably Represents an alkyl group having 1 to ₂ carbon atoms, R ₂ represents an alkyl group having 1 to ₂ carbon atoms or hydrogen, preferably hydrogen or a methyl group, more preferably hydrogen, and R ₃ represents 1 to 6 carbon atoms (preferably Has 1 to 1 carbon atoms
4, more preferably represents an alkyl group having 1 to 2 carbon atoms or hydrogen, and n represents an integer of 1 to 12, preferably 1 to 6, more preferably 2 to 4. When the carbon number of R ₁ exceeds 6, there is a disadvantage that the solubility of the catalyst component is reduced. Further, when the number of carbon atoms of R ₂ exceeds 2, there is a disadvantage that the solubility of the catalyst component is also lowered. Also, R
_When the number of carbon atoms of ₃ exceeds 6, the disadvantage that the solubility of the catalyst component is lowered also occurs. On the other hand, when the value of n exceeds 12, the disadvantages of a decrease in the solubility of the catalyst component and an increase in the viscosity arise.

As described above, the glycol ethers used in the present invention are represented by the above structural formula (I), and typical compounds are oxidized with respect to 1 mol of methanol, ethanol, propanol and / or butanol. It is a glycol monoalkyl ether compound to which 2 to 12 moles of ethylene and / or propylene oxide are added. Another group of representative compounds are glycol dialkyl ether compounds in which the terminal OH group of the above glycol monoalkyl ether is substituted with a methyl group, an ethyl group, a propyl group or a butyl group. One or a mixture of two or more of these glycol ethers can be used.

Such glycol ethers are represented by C
Not only is the solubility of O and O ₂ high, but also the solubility of Cu-pyridine complexes and the like is high, and the precipitation of Cu compounds can be avoided. These glycol ethers can be easily synthesized by etherifying glycols and alcohols, but commercially available products can also be used. As a commercially available product, there is Hisolve manufactured by Toho Chemical Industry Co., Ltd. Glycol ethers are solvents widely used as gas absorbents and have excellent solubility for various gaseous substances. In addition, it is chemically inert, non-corrosive, does not form insolubles and precipitates; has high thermal stability, has no solvent deterioration;
It has features such as low solvent loss.

The cyclic nitrogen compound used in the present invention includes pyridine or pyridines having a substituent in the pyridine skeleton such as an alkyl group, an alkoxy group, or a halogen atom which does not inhibit the present reaction, for example, pyridine, 2-hydroxypyridine, 2-methylpyridine, 2-ethylpyridine, 2,4-
Dimethylpyridine, 2-methyl 4-hydroxypyridine,
2-hydroxy 4-methoxypyridine, 2-hydroxy 6-
Chloropyridine is mentioned. Further, a cyclic nitrogen compound such as phenanthroline, dipyridyl, imidazole and the like may be used. These form a complex compound with Cu as a catalyst and dissolve in the glycol ethers described above. Among these, it is particularly preferable to use pyridine, 2-hydroxypyridine, and 2-methylpyridine.

As the alcohol which is a reactant (raw material) of the present invention, a wide range of compounds having a hydroxyl group can be used. For example, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 1-butanol,
Pentanol, 1-hexanol, 1-octanol,
C1-C20 saturated or unsaturated aliphatic alcohols such as 1-decanol, 1-octadecanol, allyl alcohol, 2-buten-1-ol and 2-hexen-1-ol; cyclohexanol, cyclopentanol And alicyclic alcohols having 3 to 7 carbon atoms, such as benzyl alcohol and phenethyl alcohol. The alcohol used is not limited to a monohydric alcohol, but may be a dihydric alcohol such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, or propylene glycol, or a polyhydric alcohol such as glycerin.
Of these, methanol and ethanol are particularly preferably used from the viewpoint of the demand for reaction products.

Further, the carbon monoxide and oxygen used as the raw materials do not need to be high-purity gases, respectively, and may be diluted with an inert gas such as nitrogen, argon or carbon dioxide. In particular, under reaction conditions, it is preferable to perform dilution with an inert gas in order to prevent explosion due to oxygen. In that sense, air may be used instead of oxygen.

The composition of the reaction solution in the present invention contains metal copper, a metal copper compound or a copper complex compound as described above; a cyclic nitrogen compound; a glycol ether represented by the above structural formula (I); and an alcohol. It is composed. A conventional mixture of CuCl, pyridines and methanol is not suitable for the production of a carbonate ester since the Cu-pyridines complex precipitates out as a solid, but as shown in the present invention, a glycol ether having a predetermined structure is used. By adding it as a solvent, it is possible to produce a carbonate ester as a homogeneous catalyst system.

In the present invention, the molar ratio of the cyclic nitrogen compound to 1 mol of copper atom in the metal copper, metal copper compound or copper complex compound as the catalyst is in the range of 0.1 to 100, preferably 0.5 to 100. It is set in the range of 50, more preferably in the range of 1-10. If this value is less than 0.1, there is a problem that the catalyst is not homogeneous, and if this value exceeds 100, there is a problem that the catalyst component is precipitated in the presence of alcohol.

The molar ratio of the glycol ether represented by the above structural formula (I) to 1 mol of copper atom in the metallic copper, the metallic copper compound or the complex compound of copper is in the range of 1 to 20, preferably 2 to 20. Range of 10, more preferably 3
-5 is set. If this value is less than 1, there is a disadvantage that the catalyst is not homogeneous, and if this value exceeds 20, there is a disadvantage that a sufficient reaction rate cannot be obtained due to a decrease in copper concentration.

Further, the molar ratio of alcohol to 1 mol of copper atom in metallic copper, metallic copper compound or copper complex compound is as follows:
The range is 3 to 50, preferably 4 to 40, and more preferably 5 to 30. If this value is less than 3, there arises a disadvantage that a sufficient reaction rate cannot be obtained, and if this value exceeds 50, there occurs a disadvantage that catalyst components are precipitated.

In the method for producing a carbonate according to the present invention, the reaction conditions are set as follows. That is, the reaction temperature is 30 to 180 ° C, preferably 50 to 1 ° C.
The temperature is set to 50 ° C., more preferably 80 to 140 ° C., and the carbon monoxide partial pressure (CO partial pressure) is 0.1 to 50 Kg / cm.
² , preferably 1 to 30 kg / cm ² , more preferably 1 to 25 kg / cm ² , and oxygen partial pressure (O ₂
Partial pressure), 0.001~10Kg / cm ^2, preferably, 0.005~5Kg / cm ^2, more preferably,
It is set to 0.01 to 3 Kg / cm ² . Reaction temperature 3
When the reaction temperature is lower than 0 ° C., there is a disadvantage that a sufficient reaction rate cannot be obtained. On the other hand, when the reaction temperature is higher than 180 ° C., there are disadvantages such as an increase in by-products and thermal decomposition of glycol ethers. . Further, when the CO partial pressure is less than 0.1 kg / cm ^2, there is a disadvantage that a sufficient reaction rate cannot be obtained. On the other hand, when the CO partial pressure exceeds 50 kg / cm ² , the pressure vessel (reactor)
The manufacturing cost is high, resulting in economic disadvantages. When the O ₂ partial pressure is less than 0.001 kg / cm ² ,
On the other hand, if the O ₂ partial pressure exceeds 10 kg / cm ² , there occurs a disadvantage that glycol ethers are oxidatively decomposed.

As shown in FIG. 1, a part of the reaction solution in the reaction tank 10 is withdrawn in a liquid phase or a gas-liquid mixed phase by a withdrawal line 7 (reaction solution withdrawing step). It is led.

In the water removing device 20, an operation for removing the water in the extracted reaction solution is performed (water removing step). The reaction liquid after the water removing operation is performed by the water removing device 20 passes through the circulation line 27 and is supplied to the reaction tank 10.
Is returned to. On the other hand, the water removed from the reaction solution is discharged through the discharge line 17 to the outside of the system.

A water removing device 2 used in the water removing step
A specification of 0 may use a membrane system that selectively permeates water. More specifically, a method based on a membrane separation method, for example, a vapor permeable membrane method or a pervaporation film method can be used, but a method based on a pervaporation film method is particularly preferable. As the pervaporation membrane, one that selectively separates water and a solvent and allows water to permeate to the permeation side as water vapor is used. Specifically, a polyvinyl alcohol-based composite film, a polyphosphazene film, a perfluorosulfonic acid film, an aromatic polyamide film,
An aromatic polyimide film, a silicon-based composite film, a polyacrylonitrile film, a polyacrylic acid / polyquaternary ammonium salt polyion complex (PIC) film, a quaternized chitosan, a polyparabanic acid film and the like are suitably used. Also,
Examples of the shape of the membrane include a flat membrane, a hollow fiber membrane, and a pleated membrane. In the pervaporation membrane method, a pressure difference is provided between the side where the reaction solution flows through the membrane and the side where water permeates and exits (the water permeation side is at a low pressure), and only water is vaporized based on this pressure difference. And exit through the membrane. Here, the gaseous water that has passed through the membrane is cooled and usually removed from the system in a liquid state. The operating conditions of the water removing device 20 may be appropriately set in consideration of the type of the membrane system to be used, the throughput, and the like.

A part of the reaction solution (including the catalyst) in the reaction tank 10 is sent to a purification step via an extraction line 12 in order to extract a carbonate product as a reaction product as a product. Products such as carbonate ester purified by a distillation column or the like in the purification step are taken out. On the other hand, the remaining raw material components (unreacted raw materials, catalyst liquid) separated in the purification step are passed through a recovery line 15 to a reaction tank. Returned to 10.

The amount of the reaction solution withdrawn from the extraction line 7 may be appropriately set in consideration of the capacity of the water removing device 20 to be used, the target amount of water removed, and the like.

The method for producing a carbonate according to the present invention described above with reference to FIG. 1 is a so-called continuous flow reaction in which alcohol, CO and O ₂ (and, if necessary, cyclic nitrogen Compound, glycol ethers), while the product is continuously withdrawn and recovered. The type of the reactor may be any type such as a stirring tank and a bubble column as long as a gas-liquid interface can be sufficiently obtained.

Needless to say, the method for producing a carbonate according to the present invention is not limited to such a continuous flow reaction.
A batch reaction, that is, a reaction system in which the above reaction solution composition is charged into a batch reactor and the above CO partial pressure and O ₂ partial pressure are further maintained while maintaining the above reaction temperature.

Further, in a method of sequentially performing an oxidation reaction and a carbonylation reaction by using two reaction tanks in series, a step of extracting a reaction solution from the oxidation reaction step and a step of removing water may be provided. Good.

[0039]

The present invention will be described below in more detail with reference to specific examples.

Example 1 Preparation of Charge Solution A 200 ml Erlenmeyer flask with a screw stopper was prepared.
11.7 g of pyridine was weighed therein, and 5.7 g of CuCl was gradually added while stirring the solution with a stirrer. Immediately after adding CuCl, triethylene glycol dimethyl ether (manufactured by Toho Chemical Industry Co., Ltd., HISOLVE MT
M) was added. The temperature was raised to about 50 ° C. and stirring was continued for a while. Then, when the solution became homogeneous, 171 g of methanol was added.

Dimethyl carbonate in continuous flow type reaction
Synthesis of (DMC) Next, using the experimental apparatus shown in FIG. 2, a synthesis experiment of dimethyl carbonate (DMC) was conducted by a continuous flow reaction. First, 200 ml of the reaction solution prepared as described above was charged into a 300 ml reactor 10 (autoclave: manufactured by Hastelloy C, withstand pressure of 50 kg / cm ² ) shown in FIG. After purging the inside of the reactor 10 with CO gas, the pressure was increased to 25 kg / cm ² with CO gas. Thereafter, the temperature was raised to 100 ° C. while stirring the solution at 1000 rpm. After the temperature reached the set temperature and the condition became stable, the supply of CO gas, O ₂ gas, methanol, and pyridine was started to start the reaction. The amount of CO gas supplied from line 1 is 1.25 mol /
hr, O ₂ gas supplied from line 2 is 0.1mol / hr
And From line 3, methanol containing 3.6% by weight of pyridine was supplied so that the liquid level of the flasher 30 became constant.

The extraction from the line 7a was performed in a gas-liquid mixed phase. The amount of liquid returned from the flasher 30 to the reactor 10 in the line 27 was 486 ml / hr.

The temperature of the flasher 30 is 90 to 110
° C, pressure is 3.5-4.0Kg / cm ² G at back pressure valve 40
Was controlled.

As a result, a mixture of water and methanol containing an average of 2 g of water per hour flowed out of the line 18 via the membrane separation device 20 and the vacuum pump 60. In addition, from line 32, dimethyl carbonate is
The liquid containing t% flowed out at an average of 169 ml / hr. In addition,
Reference numeral 50 in FIG. 2 denotes a back pressure valve, and reference numeral 70 denotes a recycle pump.

The specifications and operating conditions of the water removing device 20 were as follows.

[0046] <Operating Conditions of Moisture Removal Device 20> Liquid-side pressure: 3.5 to 3.9 Kg / cm ² G Permeation-side pressure: 0.01 Kg / cm ² G Temperature: 50 ° C. As shown in Table 1 below, A sample of the reaction solution was sampled, and the concentration of dimethyl carbonate (DMC) was measured by gas chromatography to determine the change over time in the CO-based selectivity S _CO .

The CO-based selectivity S _CO is defined as S _CO = DMC generation (mol) / CO consumption (mol) × 100.

As a comparative example, an experiment was conducted also in a reaction system without using the water removing device 20 (others are the same as those in the above-described embodiment).

The results are shown in Table 1 below.

[0050]

[Table 1] According to the experimental results shown in Table 1, in the method for producing a carbonate ester having the water removal step of the present invention, the selectivity of the CO-based selectivity S _CO was maintained at a high level over a long period of time, and the catalytic activity was low. It can be seen that the deterioration is suppressed.
Further, no corrosion was observed in the Hastelloy C reactor at the end of the test, and it was confirmed that the corrosion of the reaction solution was much lower than that of the conventional reaction system.

[0051]

The effects of the present invention are apparent from the above results. That is, the method for producing a carbonate according to the present invention comprises:
A homogeneous catalyst system is realized by dissolving a copper cyclic nitrogen compound complex (for example, a copper pyridine complex) in glycol ethers, and then withdrawing the reaction solution in the reaction vessel as a liquid, Is configured to directly remove water. Accordingly, an energy-efficient production process can be formed, and the selectivity of the carbonate ester is high, so that deterioration of the catalytic activity can be suppressed. In addition, the corrosiveness of the reaction solution is extremely low.

[Brief description of the drawings]

FIG. 1 is a drawing showing an example of a schematic flow of a process apparatus for performing a manufacturing method of the present invention.

FIG. 2 is a schematic flow chart of an experimental apparatus used in an example of the present invention.

[Explanation of symbols]

 10: reaction tank 20: water removal device

Claims (6)

[Claims] An alcohol is reacted with carbon monoxide and oxygen in the presence of copper metal, a copper metal compound or a copper complex compound, a glycol ether represented by the following structural formula (I), and a cyclic nitrogen compound. A carbonyl oxidation reaction step of reacting, a reaction liquid extracting step of extracting a reaction liquid in a reaction tank in which the carbonyl oxidation reaction is performed in a liquid phase or a gas-liquid mixed phase, and removing water in the extracted reaction liquid. A water removing step, and a reaction solution after water is removed by the water removing step.
A step of returning to the reaction tank for performing the carbonyl oxidation reaction,
A method for producing a carbonate ester comprising: R ₁ O (CH (R ₂ ) CH ₂ O) _n R ₃ Formula (I) (In the formula (I), R ₁ is an alkyl group having 1 to 6 carbon atoms, R ₂
Is an alkyl group or hydrogen having 1 to 2 carbon atoms, R ₃ is an alkyl group or hydrogen having 1 to 6 carbon atoms, and n is an integer of 1 to 12) 2. The method for producing a carbonate according to claim 1, wherein the water removal step of removing water in the reaction solution is performed using a membrane system that selectively transmits water. 3. The method for producing a carbonate ester according to claim 2, wherein the membrane system for selectively permeating water is a membrane separation method of a pervaporation membrane method. 4. The method for producing a carbonate according to claim 1, wherein the cyclic nitrogen compound is a pyridine. 5. The molar ratio of the cyclic nitrogen compound to 1 mol of copper atom of metallic copper, metallic copper compound or complex compound of copper is as follows:
The method for producing a carbonic acid ester according to any one of claims 1 to 4, which is in a range of 0.1 to 100. 6. The molar ratio of the glycol ether represented by the structural formula (I) to 1 mol of copper atom of the metal copper, the metal copper compound or the copper complex compound is in the range of 1 to 20. A method for producing a carbonate according to claim 5.