GLYCIDOL SYNTHESIS METHOD

Abstract

The invention relates to a method for obtaining glycidol in a semi-continuous or continuous manner by decarboxylating glycerol carbonate at reduced pressure, at a temperature less than or equal to 130 C. and in the presence of alkoxide catalysts of alkaline metals and alkaline earth metals, metal oxides, mixed metal oxides, metal stannates and mixed metal stannates, all of which optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2.

Claims

1. A method for producing glycidol by decarboxylating glycerol carbonate, which comprises the steps: a) Placing into contact, optionally in the presence of an organic solvent, glycerol carbonate with a catalyst selected from the group consisting of (C.sub.1-C.sub.n) alkoxides of alkaline metals and alkaline earth metals, metal oxides, mixed metal oxides, metal stannates, mixed metal stannates and mixtures thereof, wherein the catalyst is optionally supported via a support selected from the group consisting of SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2; and b) Carrying out the reaction at a temperature less than or equal to 130 C. at reduced pressure to continuously separate the glycidol formed by evaporation.

2. The method according to claim 1, wherein the catalysts are (C.sub.1-C.sub.n) alkoxides of alkaline metals and alkaline earth metals and are selected from the group consisting of sodium methoxide, potassium methoxide, sodium ethoxide and potassium ethoxide.

3. The method according to claim 1, wherein the catalysts are metal oxides and are selected from the group consisting of oxides of alkaline metals and alkaline earth metals and metals selected from zirconium, niobium, scandium, yttrium, lanthanum, zinc, cerium and tin, optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2.

4. The method according to claim 1, wherein the catalysts are mixed metal oxides and are selected from the group consisting of mixtures of two or more alkaline metal oxides and alkaline earth metals and metals selected from zirconium, niobium, scandium, yttrium, lanthanum, zinc, cerium and tin, optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2.

5. The method according to claim 1, wherein the catalysts are stannates and are selected from the group consisting of metal stannates and mixed metal stannates of alkaline metals and alkaline earth metals, optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2.

6. The method according to claim 5, wherein the metal stannates and mixed metal stannates of alkaline metals are from sodium and potassium.

7. The method according to claim 1, wherein the concentration of catalyst is comprised between 0.001% and 10%, in percentage by weight with respect to the glycerol carbonate.

8. The method according to claim 1, wherein the concentration of catalyst is comprised between 0.001% and 1%, in percentage by weight with respect to the glycerol carbonate.

9. The method according to claim 1, wherein the working pressure is less than or equal to 2 kPa.

10. The method according to claim 1, wherein the working pressure is less than or equal to 1 kPa.

11. The method according to claim 1, wherein the working pressure is comprised between 0.2 kPa and 1 kPa.

12. The method according to claim 1, wherein the temperature of the reaction is in the range of 100 to 130 C.

13. The method according to claim 1, which is carried out in a semi-continuous manner.

14. The method according to claim 1, which is carried out in a continuous manner.

15. The method according to claim 1, wherein the catalysts are metal oxides and are selected from the group consisting of oxides of alkaline metals and alkaline earth metals and metals selected from zirconium, niobium, scandium, yttrium, lanthanum, zinc, cerium and tin, optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2; and wherein the concentration of catalyst is comprised between 0.001% and 1%, in percentage by weight with respect to the glycerol carbonate.

16. The method according to claim 1, wherein the catalysts are metal oxides and are selected from the group consisting of oxides of alkaline metals and alkaline earth metals and metals selected from zirconium, niobium, scandium, yttrium, lanthanum, zinc, cerium and tin, optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2; wherein the concentration of catalyst is comprised between 0.001% and 1%, in percentage by weight with respect to the glycerol carbonate; and wherein the working pressure is less than or equal to 1 kPa.

17. The method according to claim 1, wherein the catalysts are metal oxides and are selected from the group consisting of oxides of alkaline metals and alkaline earth metals and metals selected from zirconium, niobium, scandium, yttrium, lanthanum, zinc, cerium and tin, optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2; wherein the concentration of catalyst is comprised between 0.001% and 1%, in percentage by weight with respect to the glycerol carbonate; wherein the working pressure is less than or equal to 1 kPa; and wherein the temperature of the reaction is in the range of 100 to 130 C.

18. The method according to claim 1, wherein the catalysts are metal oxides and are selected from the group consisting of oxides of alkaline metals and alkaline earth metals and metals selected from zirconium, niobium, scandium, yttrium, lanthanum, zinc, cerium and tin, optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2; wherein the concentration of catalyst is comprised between 0.001% and 1%, in percentage by weight with respect to the glycerol carbonate; wherein the working pressure is less than or equal to 1 kPa; wherein the temperature of the reaction is in the range of 100 to 130 C.; and which is carried out in a semi-continuous manner.

19. The method according to claim 1, wherein the catalysts are stannates and are selected from the group consisting of metal stannates and mixed metal stannates of alkaline metals and alkaline earth metals, optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2; wherein the metal stannates and mixed metal stannates of alkaline metals are from sodium and potassium; and wherein the concentration of catalyst is comprised between 0.001% and 1%, in percentage by weight with respect to the glycerol carbonate.

20. The method according to claim 1, wherein the catalysts are stannates and are selected from the group consisting of metal stannates and mixed metal stannates of alkaline metals and alkaline earth metals, optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2; wherein the metal stannates and mixed metal stannates of alkaline metals are from sodium and potassium; wherein the concentration of catalyst is comprised between 0.001% and 1%, in percentage by weight with respect to the glycerol carbonate; wherein the working pressure is less than or equal to 1 kPa; wherein the temperature of the reaction is in the range of 100 to 130 C.; and which is carried out in a semi-continuous manner.

Description

DESCRIPTION OF THE INVENTION

[0014] The inventors propose an industrially viable method for producing glycidol from glycerol carbonate which drastically reduces the energy consumption of the existing methods. This method has been achieved by means of the novel use of catalysts that are described below, which permit a working temperature less than or equal to 130 C.

[0015] Thus, the present invention relates to a method for producing glycidol by decarboxylation of glycerol carbonate which comprises the steps:

[0016] a) Placing into contact, optionally in the presence of an organic solvent, glycerol carbonate with a catalyst selected from the group consisting of (C.sub.1-C.sub.n) alkoxides of alkaline metals and alkaline earth metals, metal oxides, mixed metal oxides, metal stannates, mixed metal stannates and mixtures thereof, wherein the catalyst is optionally supported via a support selected from the group consisting of SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2; and

[0017] b) Carrying out the reaction at a temperature less than or equal to 130 C. at reduced pressure to continuously separate the glycidol formed by evaporation.

[0018] The optional solvent should have a boiling point such that it does not separate from the reaction medium by evaporation at the reduced working pressure and preferably does not have active hydrogens, that is to say hydrogens which can react with basic sites producing the formation of alkoxides which can initiate the ring-opening polymerization both of the starting glycerol carbonate and the glycidol formed with the consequent drastic reduction of the glycidol output. Non-limiting examples of solvents are polyethers with their protected OH terminal groups, for example forming ethers, such as for example polyethylene glycol 400, 600 or 2000 dimethyl ether or tetra methylene glycol dimethyl ether.

[0019] The reaction can be carried out both in a semi-continuous and continuous manner. In the first manner, the glycerol carbonate and the catalyst are introduced in the reactor and the glycidol is separated continuously by evaporation at reduced pressure. In the second method, the glycerol carbonate is continuously fed at a predetermined flowrate to the reactor in which the catalyst has been previously introduced and the glycidol is continuously separated by evaporation at reduced pressure.

[0020] In a particular embodiment, the catalysts are (C.sub.1-C.sub.n) alkoxides of alkaline metals and alkaline earth metals and are preferably selected from the group consisting of sodium methoxide, potassium methoxide, sodium ethoxide and potassium ethoxide. The term (C.sub.1-C.sub.n) alkoxide refers to the radical O(C.sub.1-C.sub.n) alkyl wherein the term alkyl refers to a saturated, linear or branched hydrocarbon chain which contains 1 to n atoms of carbon. The alkoxide group is saturated and contains only single bonds. The saturated (C.sub.1-C.sub.n) alkoxide can be substituted or unsubstituted as described in this description.

[0021] In another particular embodiment, the metal oxide catalysts are selected from the group consisting of oxides of alkaline metal and alkaline earth metals and metals selected from zirconium, niobium, scandium, yttrium, lanthanum, zinc, cerium and tin which can be used without support or supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2, that is to say, optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2.

[0022] In another particular embodiment, the catalysts are mixed metal oxides and are selected from the group consisting of mixtures of two or more alkaline metal oxides and alkaline earth metals and metals selected from zirconium, niobium, scandium, yttrium, lanthanum, zinc, cerium and tin which can be used without support or supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2.

[0023] In another particular embodiment, the catalysts are metal stannates and mixed metal stannates and are selected from the group consisting of metal stannates and mixed metal stannates of alkaline metals and alkaline earth metals, preferably of sodium and potassium. These catalysts are optionally supported via SiO.sub.2, -Al.sub.2O.sub.3, MgO and ZrO.sub.2. The metal stannate catalysts are obtained by calcination of the corresponding commercial stannates hydrated at temperatures greater than 200 C. The mixed metal stannate catalysts are obtained both by mechanically mixing the corresponding hydrated commercial stannates and calcinating at temperatures greater than 200 C. or dissolving the corresponding commercial stannates hydrated in water, evaporating the water, drying the residue and calcinating at temperatures greater than 200 C. The metal stannate and supported mixed metal stannate catalysts can, for example, be obtained by impregnating the support with an aqueous solution of the metal stannates to be deposited, drying the mixture and calcinating. The term stannate includes orthostannates and metastannates. Therefore, the invention relates to metal orthostannates and metastannates and to mixed metal orthostannates and metastannates.

[0024] The catalysts formed by oxides and mixed oxides, supported or unsupported, can be produced by means of any of the methods known in the art. Thus, for example, they can be obtained by means of: mechanical mixing, wet impregnating of the oxide which acts as a support with solutions of precursor agents of the oxide to be deposited (non-limiting examples are nitrates, sulfates, chlorides, acetates, formates and oxalates of the corresponding metals) followed by drying and calcination; co-precipitation in basic medium of metal hydroxides from aqueous solutions of salts which contain the corresponding metals (non-limiting examples are nitrates, sulfates, chlorides, acetates, formates and oxalates of the corresponding metals) followed by drying and calcination; precipitation in basic medium of metal hydroxides over one of the oxides from aqueous solutions of salts which contain the corresponding metals (non-limiting examples are nitrates, sulfates, chlorides, acetates, formates and oxalates of the corresponding metals) followed by drying and calcination; and sol-gel methods. A large number of references concerning these and other reference methods can be found in the bibliography. See for example Handbook in Heterogeneous Catalysis, Ed. Ertl, Knzinger, Schth, Weitkamp, 2nd edition, vol 2, Wiley-VCH, 2008.

[0025] The concentration of catalyst, in percentage by weight with respect to the glycerol carbonate, can vary between 0.001% and 10%, but preferably is comprised between 0.001% and 1%, because higher concentrations in many cases lead to a reduction of the output. Without wishing to be bound in any way by theory, it is believed that the cause is due to the fact that high concentrations of catalyst drastically increase the ring-opening polymerization both of the starting glycerol carbonate and the glycidol formed, producing the formation of polyglycerols with the consequent reduction of the glycidol output.

[0026] The working temperature is less than or equal to 130 C. and in one particular embodiment is preferably between 100 C. and 130 C.

[0027] In one particular embodiment of the invention, the working pressure is less than or equal to 2 kPa, preferably less than or equal to 1 kPa and most preferably is comprised between 0.2 kPa and 1 kPa. When reduced pressure is mentioned in the present invention, it is understood as any pressure below atmospheric pressure.

[0028] The reaction time will depend both on the time it takes to completely convert the glycerol carbonate and the type of catalyst, the working pressure and the temperature. The reaction times according to the present invention are comprised between 30 mins and 7 hours, preferably 1 hour and 4 hours.

[0029] The invention is illustrated by means of the following examples which are provided exclusively in an illustrative manner and which do not intend to in any way limit the scope of the invention.

EXAMPLES

General Synthetic Method

[0030] All the reactions were carried out at reduced pressure in a 100 ml glass reactor, connected to a vacuum pump. The reactor was submerged in a bath placed on top of a heating plate to regulate the reaction temperature. A condenser was placed between the reactor and the pump, through whose liner a cooling liquid circulated at 10 C., connected to a collection container of the glycidol submerged in a cooling bath at 10 C. In a semi-continuous mode of operation, 0.065 moles of glycerol carbonate and the quantity of catalyst specified in each example were introduced into the reactor. The reaction was maintained with magnetic stirring at the reduced temperature and pressure selected during the reaction time desired to continuously separate by evaporation the glycidol formed. When the reaction finished, the vacuum was stopped and the glycidol accumulated in the condenser was weighed to calculate the output.

[0031] In the continuous mode of operation, the experimental system was the same with the exception that the glycerol carbonate was fed continuously to the reactor with a HPLC pump at a predetermined flowrate.

[0032] In the present specification, all the concentrations of catalyst are in % by weight relative to the quantity of glycerol carbonate.

Examples 1 to 5

Not Part of the Invention

[0033] Various experiments were carried out according to the semi-continuous mode of operation previously described, without catalyst and at different temperatures between 130 and 175 C. The results are given in Table 1. The examples 1 and 2 reveal that there is no reaction below 130 C., example 3 demonstrates that the reaction at 140 C. is virtually non-existent and examples 4 and 5 reveal that temperatures as high as 170 C. are necessary for obtaining outputs of industrial interest.

TABLE-US-00001 TABLE 1 Example T( C.) Pressure (kPa) Time (h) Y (%) 1 125 0.25 3 0 2 130 0.65 3 0 3 140 0.65 6 2 4 170 0.65 3 59 5 175 0.65 3 58 * Y: glycidol output

Example 6

Of the Invention

[0034] A reaction was carried out according to the semi-continuous mode of operation previously described using as a catalyst Cs.sub.2O supported via -Al.sub.2O.sub.3 with a content of Cs.sub.20 of 60% by weight, prepared by the method of wet impregnation and calcinated at 900 C. The concentration of catalyst was 0.65%, the reaction time 6 hours, the pressure 0.25 kPa and the temperature 120 C. The glycidol output was 65.5%.

[0035] This example and those below reveal how the use of one of the catalysts of the invention allows the reaction to be carried out at a temperature of 120 C., much lower than that of the known methods used at present for obtaining glycidol by decarboxylation of glycidol carbonate with an output which means that the process is industrially viable.

Example 7

Of the Invention

[0036] A reaction like in example 6 was carried out but with a concentration of catalyst of 0.60%, a reaction time of 5 hours and a temperature of 125 C. The glycidol output was 68.4%.

Example 8

Of the Invention

[0037] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst Cs.sub.2O supported via MgO with a content of Cs.sub.2O of 30% by weight, prepared by the method of wet impregnation and calcinated at 600 C. The concentration of catalyst was 0.2%, the reaction time 6.5 hours, the pressure 0.25 kPa and the temperature 130 C. The glycidol output was 70.5%.

Example 9

Of the Invention

[0038] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst Cs2O supported via MgO with a content of Cs.sub.2O of 30% by weight, prepared by the method of wet impregnation and calcinated at 600 C. The concentration of catalyst was 0.27%, the reaction time 4.5 hours, the pressure 0.25 kPa and the temperature 130 C. The glycidol output was 70.4%.

Example 10

Of the Invention

[0039] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst Cs.sub.2O obtained by calcinating cesium carbonate at 600 C. The concentration of catalyst was 0.2%, the reaction time 3 hours, the pressure 0.25 kPa and the temperature 130 C. The glycidol output was 67%.

Example 11

Of the Invention

[0040] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst CaO calcinated at 900 C. The concentration of catalyst was 0.16%, the reaction time 6 hours, the pressure 0.25 kPa and the temperature 130 C. The glycidol output was 67%.

Example 12

Of the Invention

[0041] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst Cs.sub.2O supported via ZrO.sub.2 with a content of CaO of 5% by weight, prepared by the method of wet impregnation and calcinated at 800 C. The concentration of catalyst was 0.5%, the reaction time 6 hours, the pressure 0.25 kPa and the temperature 130 C. The glycidol output was 53.4%.

Example 13

Of the Invention

[0042] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst Na.sub.2SnO.sub.3 obtained by calcinating the trihydrate at 350 C. The concentration of catalyst was 0.09%, the reaction time 6 hours, the pressure 0.25 kPa and the temperature 125 C. The glycidol output was 66%.

Example 14

Of the Invention

[0043] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst Na.sub.2SnO.sub.3 supported via -Al.sub.2O.sub.3 with a content of Na.sub.2SnO.sub.3 of 60% by weight, prepared by the method of wet impregnation and calcinated at 600 C. The concentration of catalyst was 0.47%, the reaction time 5 hours, the pressure 0.25 kPa and the temperature 125 C. The glycidol output was 69%.

Example 15

Of the Invention

[0044] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst K.sub.2O supported via MgO with a content of K.sub.2O of 30% by weight, prepared by the method of wet impregnation from KOH and calcinated at 600 C. The concentration of catalyst was 0.2%, the reaction time 6.5 hours, the pressure 0.25 kPa and the temperature 125 C. The glycidol output was 66%.

Example 16

Of the Invention

[0045] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst K.sub.2O supported via MgO with a content of K.sub.2O of 30% by weight, prepared by the method of wet impregnation from KOH and calcinated at 700 C. The concentration of catalyst was 0.43%, the reaction time 7 hours, the pressure 0.25 kPa and the temperature 125 C. and polyethylene glycol dimethyl ether was used with a molecular weight of 2000 in a proportion of 55.5% by weight with respect to the total of solvent and glycerol carbonate. The glycidol output was 74%.

Example 17

Of the Invention

[0046] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst MgO calcinated at 600 C. The concentration of catalyst was 0.46%, the reaction time 6 hours, the pressure 0.25 kPa and the temperature 130 C. The glycidol output was 56%.

Example 18

Of the Invention

[0047] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst sodium methoxide. The concentration of catalyst was 0.45%, the reaction time 2 hours, the pressure 0.20 kPa and the temperature 125 C. The glycidol output was 60.7%.

Example 19

Of the Invention

[0048] A reaction according to a semi-continuous mode of operation was carried out using as a catalyst a mechanically prepared mixture of Na.sub.2SnO.sub.3 and Sc2O3, with a content of Sc.sub.2O.sub.3 of 37% by weight and calcinated at 350 C. The concentration of catalyst was 1.5%, the reaction time 2 hours, the pressure 0.25 kPa and the temperature 125 C. The glycidol output was 59%.