NO162519B - PROCEDURE FOR THE PREPARATION OF ALKYLENIC CARBONATE. - Google Patents

Description

The invention relates to a method for producing alkylene carbonates, as stated in the characterizing part of claim 1. Such reactions are well known.: Alkylene carbonates are useful as solvents or

as a source of the corresponding glycols.

Several methods are described for the single-step hydrogenation of alkylene oxides to glycols in the presence of a catalyst and carbon dioxide. Such methods are said to make it possible to reduce the amount of water used. Removal of excess water is a major expense in the conventional hydro-generation process. The carbon dioxide is not consumed in the process, but it has been proposed that the hydrogenation continues via alkylene carbonate as an intermediate product.

US patent 3,922,314 describes a method for the hydrogenation of ethylene oxide to ethylene glycol without the use of a catalyst but operates with an aqueous ethylene oxide solution containing at least 8% by weight of ethylene oxide and at least 0.1% by weight of carbon dioxide.

A catalyst process is described in British Patent 1,177,877 (or US Patent 3,629,343). Alkylene oxides are hydrogenated to glycols at temperatures of 80-220°C and pressures of 10-180 atm. in the presence of a halide catalyst. Preferred are alkali metal or quaternary ammonium halides, especially bromides and iodides. Alkali metal hydroxides, carbonates or bicarbonates were advantageous.

A similar method is described in US patent 4,160,116 where quaternary phosphonium halides, preferably iodides and bromides, were used to catalyze the hydrogenation of alkylene oxides in the presence of carbon dioxide. The temperature was 50-200°C and the pressure 3-50 kp/cm<2>.

Another such method is described in Japanese patent application 81-45426 in which molybdenum and/or tungsten compounds are combined with known catalysts such as alkali metal halides, quaternary ammonium or phosphonium salts, organic halides and organic amines. The reaction is carried out at 20-250°C and 0-30 kp/cm<2>manometer pressure.

The formation of alkylene carbonates, in contrast to the hydrogenation of alkylene oxides to glycols, takes place according to known techniques, without the presence of water. The catalysts and reaction conditions similar to those described above for the hydrogenation of alkylene oxides are useful.

In US patent 2,667,497, magnesium or calcium halides were used at 150-250 o C and 35-140 kp/cm^ 2 to prepare alkylene carbonates from the corresponding oxides.

US patent 2,766,258 describes the use of quaternary ammonium hydroxides, carbonates and bicarbonates to catalyze the reaction of alkylene oxides with carbon dioxide. The reaction was carried out at temperatures between 100-225°C and pressure of 21-350 kp/cm<2>.

The quaternary ammonium halides were used in US patent 2,773,070 at temperatures of 100-225°C and pressures greater than

2

21 kp/ra.

According to British Patent No. 1,485,925, an alkylene carbonate is prepared by reacting the corresponding alkylene oxide, at elevated pressure and temperature, with carbon dioxide in the presence of a protic compound and a nitrogenous base.

Three patents, US patent 2,994,705; 2,994,704; and 2,993,908 describe essentially the same conditions, 93-260°C and manometer pressure 8-212 kp/cm 2 , with organic phosphonium halides, organic sulfonium halides and urea hydrohalides as catalysts for the production of alkylene carbonates from the corresponding oxirane compound.

Hydrazine or a halide salt thereof was used to catalyze the reaction in US patent 3,535,341 at temperatures of 100-250°C. An anion exchange resin containing quaternary ammonium groups was described in US patent 4,233,221

as useful in vapor phase reaction.

Organic antimony halides were shown in Japanese Patent Application 80-122,776 to enable the formation of alkylene carbonates at room temperature to 120°C in an anhydrous mixture.

It has been found that the reaction of alkylene oxides to the corresponding carbonates can be carried out with known catalysts at lower temperatures than hitherto used and even in the presence of significant amounts of water. The hydrolysis of carbonates to glycols can be minimized and the main product is carbonate.

In addition, higher temperatures previously used to produce glycols can be used to produce carbonates instead and, without producing large amounts of glycol, particularly higher glycols, provided that the molar ratio of carbon dioxide to alkylene oxide is maintained above about 1/1 and that the partial pressure of the carbon dioxide is above a previously selected value.

Alkylene oxides can be reacted with carbon dioxide to form alkylene carbonates in the presence of an effective amount of suitable catalysts at temperatures upwards of 20°C, especially above 90°C, preferably 90 to 170°C and in the presence of water, when the molar ratio of carbon dioxide to alkylene oxide is at least 1/1 and the partial pressure of the carbon dioxide is sufficient to provide the desired selectivity to alkylene carbonate. The pressure at which the reaction is carried out is in the range of approx. 10-200 kp/cm<2> manometer pressure, preferably manometer pressure 30 to 80 kp/cm 2. Suitable catalysts include one or more of the group consisting of quaternary organic ammonium and phosphonium halides, organic sulfonium halides and organic antimony halides, in particular methyltriphenylphosphonium iodide, tetraethylammonium bromide and tetraphenylantimony bromide . The corresponding carboxylates can also be used. The amount of catalyst used is generally up to approx. 0.10 mol per moles of alkylene oxide, preferably 0.001 to 0.02.

Contrary to what was previously expected, water can be present in significant amounts, even exceeding those used in previous hydrogenation processes, as the formation of large amounts of glycol and especially higher glycols is avoided by maintaining the molar ratio of carbon dioxide to alkylene oxide above 1/1 and that of carbon dioxide partial pressure is adjusted to provide the selectivity to the desired alkylene carbonate. Useful ratio of water to alkylene oxide is above approx. 0.01/1 and preferably from approx. 0.1/1 to approx. 4/1, most preferably from 0.1/1 to 2/1, although larger amounts of water are not excluded. Water addition also increases the rate of carbonate formation.

So far, alkylene oxides have been reacted with carbon dioxide for

to form alkylene carbonates at temperatures generally in the range 100-300°C, in particular approx. 150-225°C. Although this is not described in detail, it can be seen that the reaction was carried out without water. For example in US patent. 4,233,221, the reactants were dried by condensing water after compression so that the moisture level of the reactant gases was quite low, calculated to be about 0.2 mol%. Since carbonate hydrolysis was carried out at elevated temperatures and with catalysts as well useful for the direct hydrolysis of alkylene oxides to glycols, it seems possible that previously water was avoided if only carbonate was to be produced, otherwise hydrolysis to glycols could be expected.

It has now been found that reaction of alkylene oxides with carbon dioxides to form ethylene carbonate can be carried out in the presence of water. Alkylene carbonates can be produced with minimal losses by hydrolysis to glycols and especially higher glycols. Such a method can be applied to a stream combined of carbon dioxide, ethylene oxide and water obtained by extraction of ethylene oxide from a dilute aqueous solution with near-critical or super-critical carbon dioxide. The reaction can be carried out at lower temperatures than has hitherto been considered possible, i.e. above 20°C, and higher temperatures, i.e. above 90°C can be used without forming large amounts of glycols, especially higher glycols, provided that the molar ratio of carbon dioxide to alkylene oxide is retained over approx. 1/1 and that the partial pressure of the carbon dioxide is sufficient to provide the desired selectivity to the alkylene carbonate.

The reaction can be carried out in a large temperature range above approx. 20°C, especially above 90°C, and especially 90° to 170°C. Elevated temperature is preferred as the rate of alkylene carbonate formation is higher.

Total pressure is not a particularly critical variable in the reaction. Typically, it will be in the range of manometer pressure approx. 10-200 kp/cm<2>. However, the carbon dioxide partial pressure has been found to be very important.

The molar ratio of carbon dioxide to alkylene oxide must be at least approx. 1/1 and can vary from 1/1 to 100/1. Usually a ratio greater than 1/1 would be chosen, preferably 1/1 to 10/1. Where the method of the invention is associated with alkylene oxide extraction with near-critical or super-critical carbon dioxide, the ratio can be as high as 40/1-60/1.

The method is characterized by what is stated in claim 1's characterizing part. Further features appear from requirements 2-4.

It is particularly important that water does not hydrolyze alkylene carbonates to glycols, especially higher glycols, under conditions found to be suitable for the process of the invention. It has now been found that glycol formation can be avoided by providing sufficient carbon dioxide. A person skilled in the art would not have predicted such a result because, with water present and especially at the higher temperatures used here, the state of the art states that water would hydrolyze the alkylene oxide to glycol. It was believed that when carbon dioxide was present, the reaction proceeded via the formation of alkylene carbonates as an intermediate compound. See e.g. US Patents 4,237,324 and 4,117,250 along with US Patent 3,629,343 to Levin, et al. The alkylene carbonate was apparently not observed in any significant amounts, as quantitative glycol yields were reported.

The amount of water that can be tolerated is somewhat related to

the other process conditions and the selectivity of the alkylene carbonate formed. Excess amounts of those useful for the direct hydrogenation of alkylene oxides to glycols have been demonstrated at lower temperatures, as will be seen in the following examples. At temperatures above approx. 90 oC, especially 9Q-170°C, water quantities up to a mole ratio of approx. 4/1 based on alkylene oxide, most preferably 0.1/1 to

2/1. The presence of water has a favorable effect on the rate of the carbonate reaction compared to what might be expected. This effect can be better expressed in comparison with certain catalysts, especially those in which the bond between the halide atom and the rest of the molecule is ionic, rather than covalent, as with the preferred quaternary phosphonium halides.

The catalysts which have been found useful in the process of the invention include many of those previously known. Many compounds which may be useful include one or more of the group consisting of organic quaternary ammonium or phosphonium halides, organic sulfonium halides, and organic antimony halides. The corresponding carboxylates can also be used. Examples of compounds that can be used are the following ammonium compounds, tetraethylammonium bromide and tetraethylammonium iodide. Specific phosphonium compounds include methyltriphenylphosphonium iodide and methyltriphenylphosphonium bromide. Sulfonium compounds may include trimethylsulfonium iodide and trimethylsulfonium bromide. Antimony compounds have been found to be quite effective when water is not present, but seem to be adversely affected when water is present. Typical compounds are tetraphenylantimony bromide and triphenylantimony chloride. Particularly preferred catalysts when water is present are methyltriphenylphosphonium iodide and tetraethylammonium bromide. Of the halides, bromides and iodides are preferred.

The amount of catalyst will be similar to that used in other methods, up to approx. 0.1 mol of catalyst per mol of alkylene oxide can be used, preferably 0.001-0.02 mol per moles, although larger or smaller amounts are not intended to be omitted.

While those skilled in the art have previously indicated that relatively high temperatures of 100°C or higher would be used either to form alkylene carbonates without water present or alkylene glycols when water was available to hydrolyze alkylene oxides, in the present process temperatures varying upwards from approx. . 20°C, preferably above 90°C, especially 90-170°C.

The reaction to form carbonates can be used in the presence

of significant amounts of water. At higher temperatures that are typical of the state of the art, glycols would be expected when water is present and this is actually the basis for several methods as previously described. As will be seen, even when operating at relatively high temperatures, it is possible to minimize hydrolysis and to form carbonates instead by controlling the molar ratio of carbon dioxide to alkylene oxide and the carbon dioxide partial pressure.

The first five examples that follow illustrate the formation of alkylene carbonates at temperatures below 90°C.

Example 1

o

It is operated below 90 C without the presence of water. The catalyst is introduced into a 130 cc bomb made by

"Parr Instrument Company".

Ethylene oxide and carbon dioxide are supplied at 78°C by immersing the bomb in a dry ice/acetone bath. The bomb is then closed and placed in a 36°C bath so that the internal temperature of the bomb is increased to 30°C and the reaction continues. Stirring takes place on a magnetically driven plate. After a suitable period of time, the bomb is removed from the bathroom and the contents analysed. The results of a number of such trials are shown in Table A below.

It has been found that water can be present without the formation of significant amounts of glycol, provided the temperature is sufficiently low. Surprisingly, it has been found that water has a beneficial effect on the selectivity of the carbonate with some catalysts, while with others the selectivity seems suppressed.

jfrEO = ethylene oxide

**~EC = ethylene carbonate

<*>a - trimethylsulfonium iodide

b = methyltriphenylphosphonium iodide

c = tetraphenylantimony bromide

d = triphenylantimony chloride

e - methyltrimethylphosphonium bromide

f = tetraethylammonium bromide

Example 2

The effect of water on catalysts

The procedure in Example 1 is followed except that different amounts of water are introduced into the "Parr bomb" with the following results.

Table B's data show that the presence of water does not seem to have any detectable effect on the entire conversion of ethylene oxide, the selectivity of the ethylene carbonate is reduced when catalyst "c" is used, while when the catalyst "b" is used, the selectivity of the ethylene carbonate is surprisingly improved. Catalyst "c" would be more suitable for a reaction system in which the amount of water present is not large. Note that the ratio of water to ethylene oxide is approx. 0.55/1 compared to the theoretical ratio 1/1 for the hydrolysis reaction. Catalyst "b" seems less effective when water is not present (see experiment 2), but its performance is increased when water is used. Note that this shown catalyst's ratio reaches almost 4/1 water/EO.

* c = tetraphenylantimony bromide

b = methyltriphenylphosphonium iodide

Although the method of the invention is particularly useful in connection with the formation of ethylene carbonate, it is more applicable to other oxirane compounds as will be seen from the following

the following example.

Example 3

Propylene carbonate formation

The catalyst and water (if used) are introduced into a 130 cc "Parr bomb". Propylene oxide and carbon dioxide are supplied with wood

-78°C by immersing the bomb in a dry-ice/acetone bath. The bomb is then closed and placed in a 36°C bath so that the internal temperature of the bomb is increased to 30°C and the reaction continues. After a suitable period of time, the bomb is removed from the bathroom and the contents analysed. The results of a number of such trials are shown in Table C below.

Example 4

Formation of 1, 2-butylene carbonate

The experimental procedure in Example 3 is followed with added 1,2-butylene oxide instead of propylene oxide. The results of a number of such trials are shown in Table D below.

Example 5

The catalyst along with E^O and solvents (when used) are introduced into a 300 cc electrically heated stainless steel autoclave equipped with iimpeller shaker manufactured by Auto-clave Engineers, Inc. Samples of ethylene oxide and carbon dioxide are fed at ^-78oC while the autoclave is immersed in a dry^ ice/ acetone bath. The autoclave is then closed and heated to the desired reaction temperature. After a suitable period of time, the autoclave is cooled and the contents analysed. The results of a number of such trials are shown in Table E below.

Table E

In- mil li- Max.

food moi pressure EO EC<****>Try Bath time kg/cm^ Conv. Seal. No. EO<*>CO? H20 THF<**>°C hours mmpressure%%

27 347 1590 346 1262 60 4 52.0 95.6 97.0 28 695 2794 695 - 60 6 104.8 95.8 90.5 29 1157 2113 583 - 50 6 57.7 98.2 95.5 30 349 1590 350 1263 70 27.5.

EO ethylene oxide

THF tetrahydrofuran

^ Each sample used 20 grams of methyltriphenylphosphonium iodide

<****>EC = ethylene carbonate

The following examples demonstrate that, contrary to the state of the art, it is possible to produce high alkylene carbonate yields over approx. 9 0°C in the presence of significant amounts of water and to suppress the formation of higher glycols.

Example 6

It is operated above 90°C with water present

A number of experiments were carried out at temperatures above 90°C with varying amounts of water present. Ethylene oxide, carbon dioxide, water, and methyltriphenylphosphonium iodide dissolved in ethylene carbonate were fed continuously to a one-liter, high-pressure, shaken, electrically heated autoclave. Both liquid products and unconverted steam were removed continuously from the autoclave and separated in an external steam-liquid separator. The mixing of both liquid and vapor streams was determined by gas chromatography and the conversion and selectivities were calculated. The results are given in Table F.

From the above table it can be seen that even when operating at temperatures as high as 170°C that large yields of ethylene carbonate can be obtained, although the amount of water present appears to have a greater effect at 170°C than at 130° C. The fact is that the results in Tests 40 and 41 suggest that conditions may exist where glycol becomes the predominant product. The molar ratio of CC 2 /EO was greater than 1/1 for each experiment.

When the CC^/EO molar ratio is below 1/1, very different results are obtained, as will be seen from the following examples.

Example 7

Effect of C02/ EO ratio

The experimental procedures of Example 6 were repeated to duplicate Experiment 33, except that the pressure was 25 kp/cm 2 gauge pressure and the molar ratio of CC 2 /EO was changed from 2.0 to 0.5. Selectivities of 63.2% to ethylene carbonate (EC) and 36% to ethylene glycol (MEG) were obtained at a C02/EO ratio of 2, but selectivities of 58% to MEG and

41% to EC was obtained when the C02/E0 ratio was 0.5. Also

the formation of diethylene glycol (DEG) was significant at 1.4% selectivity when the C02/EO ratio was 0.5, while only 0.8% selectivity to DEG was detected in the products when the C02/EO ratio was 2. It is concluded that the molar ratio of C02/EO is an important factor if one wishes to produce alkylene carbonates instead of the corresponding glycol when an alkylene oxide is reacted with carbon dioxide in the presence of water. To achieve such results, the molar ratio of C02/EO should be above approx. 1. The most useful ratio is selected depending on the amount of water present and the operating temperature.

Example 8

Effect of C02 partial pressure

The importance of the partial pressure can be seen in the results from the experiments carried out according to the methods in Example 6, in which the absolute pressure and the partial pressure are varied.

You can see that if the partial pressure of the carbon dioxide is not kept sufficiently high, the reaction will produce significant amounts of glycol, which is not desirable if you want to produce ethylene carbonate instead. Accordingly, the temperature, the H 2 O/E 0 ratio and the CO 2 partial pressure will be adjusted to produce the desired selectivity of the carbonate. E.g. if the molar ratio of water to ethylene oxide in the feed was 1/1 and the reaction temperature was 130°C, then the partial pressure of the carbon dioxide would be kept at 65 kp/cm 2 or even higher to maximize the amounts of ethylene carbonate produced.

Example 9

Effect of H2 0/ EO ratio

In another series of experiments corresponding to the procedures in Example 6, the amount of water was varied with the following results:

Calculation of reaction rate constants indicates that increasing the conversion of ethylene oxide from 92% to 97.5% is equal to an increase in the reaction rate of approx. four times. Thus, unexpectedly, the addition of water to a dry feed significantly increases the reaction rate, while the reaction product is still predominantly ethylene carbonate.

Claims (4)

1. Process for the production of alkylene carbonate, particularly ethylene carbonate, by reacting the corresponding alkylene oxide with carbon dioxide in the presence of an effective amount, up to 0.1 mol per moles of alkylene oxide, of a catalyst and water, characterized in that the selectivity for alkylene carbonate is controlled and the formation of higher molecular weight glycols is suppressed by carrying out the reaction at a temperature above 20°C, preferably at 90-170°C, with a molar ratio between carbon dioxide and alkylene oxide of at least 1:1, preferably 1: 1 - 100:1, a molar ratio of water to alkylene oxide greater than 0.01:1, preferably 0.1:1 - 4:1, and with a partial pressure of the carbon dioxide sufficient to achieve the desired selectivity for alkylene carbonate , preferably exceeding the selectivity for alkylene glycol. 2. Process according to claim 1, characterized in that organic quaternary ammonium halides, organic quaternary phosphonium halides, organic sulfonium halides and organic antimony halides are used as catalyst. 3. Method according to claim 2, characterized in that an organic quaternary phosphonium halide is used as catalyst. 4. Method according to claim 2, characterized in that methyltriphenylphosphonium iodide is used as catalyst.