METHOD FOR PRODUCING OXYMETHYLENE ETHER

Abstract

The invention relates to a method for production of oxymethylene ether of the general formula CH.sub.3O—(CH.sub.2O).sub.m—CH.sub.3 in a liquid phase process, wherein 1≤m≤10. In a catalytic reaction, molecular oxygen or an oxygen-containing oxidant and methanol, formaldehyde, and/or methyl formate are used as reactants in a solution and are converted by means of a vanadium-oxygen compound or a salt thereof as catalyst in the solution which vanadium-oxygen compound contains vanadium in the oxidation stage +IV or +V. The catalyst reduced during the catalytic reaction is restored to its starting state by oxidation by means of the molecular oxygen or the oxygen-containing oxidant.

Claims

1. A method for production of oxymethylene ether of the general formula CH.sub.3O—(CH.sub.2O).sub.m—CH.sub.3 in a liquid phase process, wherein 1≤m≤10, wherein in a catalytic reaction molecular oxygen or an oxygen-containing oxidant and methanol, formaldehyde, and/or methyl formate are used as reactants in a solution and are converted by means of a vanadium-oxygen compound or a salt thereof as catalyst in the solution, which vanadium-oxygen compound contains vanadium in the oxidation stage +IV or +V, wherein the catalyst reduced during the catalytic reaction is restored to its starting state by oxidation by means of the molecular oxygen or the oxygen-containing oxidant, wherein the catalyst is a polyoxometalate ion of the general formula [PMo.sub.xV.sub.yO.sub.40].sup.n−, wherein 6≤x≤11, 1≤y≤6 and x+y=12, [W.sub.xV.sub.yO.sub.19].sup.n−, wherein x+y=6, 3≤x≤5 and 1≤y≤3 or [P.sub.2W.sub.xV.sub.yO.sub.62].sup.n−, wherein x+y=18, 12≤x≤17 and 1≤y≤6, or is a VO.sup.2+-containing salt or a [VO.sub.3].sup.−-containing salt, wherein n, x and y are in each case an integer.

2. The method according to claim 1, wherein the oxymethylene ether produced in the catalytic reaction is separated from the solution, in particular by an extraction or by means of a separation method using a semi-permeable membrane.

3. The method according to claim 1, wherein exclusively the molecular oxygen or the oxygen-containing oxidant and methanol, formaldehyde and/or methyl formate are used as reactants in the catalytic reaction.

4. The method according to claim 1, wherein the VO.sup.2+-containing salt is VOSO.sub.4 and the [VO.sub.3].sup.−-containing salt is NH.sub.4VO.sub.3.

5. The method according to claim 1, wherein the molecular oxygen is contained in a gas mixture containing the molecular oxygen, in particular air, and the oxygen-containing oxidant is a peroxide, in particular H.sub.2O.sub.2, or N.sub.2O.

6. The method according to claim 1, wherein the oxidation by means of the molecular oxygen takes place at an oxygen pressure or an oxygen partial pressure in the range of 1 bar to 50 bar, in particular 1 bar to 30 bar, in particular 5 bar to 20 bar.

7. The method according to claim 1, wherein the catalytic reaction is carried out at a temperature of at most 150° C., in particular in a range of 70° C. to 150° C., in particular in a range of 70° C. to 90° C.

8. The method according to claim 1, wherein the solution contains less than 5% w/w water, in particular less than 1% w/w water.

9. The method according to claim 1, wherein the methanol, the formaldehyde and/or the methyl formate is/are also used in the catalytic reaction as, in particular sole, solvent or solvent mixture.

10. The method according to claim 1, wherein 1≤m≤6.

11. The method according to claim 1, wherein the oxymethylene ether is dimethoxymethane.

12. The method according to claim 11, wherein a further conversion of the dimethoxymethane caused by the catalyst is prevented by separating the dimethoxymethane and the catalyst from each other, in particular by extraction or by means of a separation method using a semi-permeable membrane.

13. The method according to claim 11, wherein the dimethoxymethane is separated from the solution by distillation, extraction or by means of a separation method using a semi-permeable membrane.

14. The method according to claim 1, wherein an oxymethylene ether of the general formula CH.sub.3O—(CH.sub.2O).sub.m—CH.sub.3 with m>1 is formed by further incubating the solution after formation of dimethoxymethane, in particular at an oxygen partial pressure below 1 bar and/or at a temperature below 70° C., until m has reached a selected value.

15. The method according to claim 14, wherein trioxane is added to the solution.

Description

[0028] FIG. 1 shows a reaction scheme of the conversion of methanol according to the invention.

1.SUP.st .EMBODIMENT

[0029] In a first embodiment, either 10 g methanol was used as solvent and reactant or substrate, respectively, or 1 mmol each of methyl formate (MF) or formaldehyde (FAl) was used as substrate in 10 g methanol as solvent. As catalyst, 0.1 mmol of polyoxometalate ion [PMo.sub.7V.sub.5O.sub.40].sup.8− (=HPA-5) was added. The resulting solution was stirred at 1000 rpm for 24 hours while being kept at a temperature of 90° C. and subjected to oxygen at an oxygen partial pressure of 20 bar. The results are summarized in the following table:

TABLE-US-00001 w.sub.H.sub.2.sub.O,pure substance/ w.sub.H.sub.2.sub.O,after/ Y.sub.CO.sub.2.sub./CO/ Substrate % w/w % w/w DME FAI MM DMM FA MF % Methanol (MeOH)    0.05 2.1 X — — X — — —/— Methyl formate (MF)    0.15 1.8 X — — X — X —/— Formaldehyde (FAl) >50 2.4 X — — X — — 0.6/—  w.sub.H.sub.2.sub.O,before = 0.5

[0030] The column w.sub.H.sub.2.sub.O, pure substance indicates the percentage by weight of water in the respective substrate. The column w.sub.H.sub.2.sub.O, after indicates the percentage by weight of water in the solution after the reaction. w.sub.H.sub.2.sub.O, before indicates, in the case of formaldehyde, the percentage by weight of water in the solution before the reaction. The presence of each reaction product was determined by nuclear magnetic resonance spectroscopy (NMR). If no reaction product was detected this was indicated by a “−”, otherwise by an “x”. The abbreviations have the following meanings: [0031] DME: Dimethyl ether [0032] FAI: Formaldehyde [0033] MM: Methoxymethanol [0034] DMM: Dimethoxymethane [0035] FA: Formic acid [0036] MF: Methyl formate

[0037] It can be seen from the table that by the use of methanol as starting material only the oxymethylene ether dimethoxymethane and the by-product dimethyl ether are formed with high selectivity and no CO.sub.2. Also, when formaldehyde or methyl formate is used, only the oxymethylene ether dimethoxymethane and the by-product dimethyl ether are formed. When methyl formate was used, some of the methyl formate used was still detectable in the batch after completion of the reaction.

2.SUP.nd .EMBODIMENT

[0038] For an alternative synthesis of OMEs with a chain length of 2 to 6, a molar ratio of trioxane to dimethoxymethane (methylal) of 0.33 and the catalyst in an amount of 1% w/w in relation to trioxane was used. The reactions were carried out in a glass flask at atmospheric pressure and a temperature of 25° C. Before the experiment, both the reaction vessel and the methylal were dried. After addition of the catalyst, the resulting solution was stirred at 800 rpm for 60 minutes. An analysis of the reaction products was performed by means of a gas chromatograph.

3.SUP.rd .EMBODIMENT

[0039] For another alternative synthesis of OMEs with a chain length of 2 to 6, a stainless steel reactor was used. This was filled with dimethoxymethane, trioxane and the catalyst. The molar ratio of dimethoxymethane to trioxane was varied between 2.5:1 and 1:2 and 2% w/w of catalyst was used in relation to the starting materials. The reaction temperature was set in a range of 70° C. to 130° C. The reaction time was selected in a range of 20 minutes to 120 minutes. A reaction pressure of 10 bar and a stirring speed of 300 rpm were set.

[0040] The 2.sup.nd and 3.sup.rd embodiments showed that starting from the dimethoxymethane formed in the method according to the invention, with the addition of trioxane, oxymethylene ethers with a chain length of 2 to 6, i.e. oxymethylene ethers in which 2≤m≤6 according to the general formula given above, can be obtained.