Process for preparing cyclic acetals which can be used as fuel components

Abstract

The present invention relates to a process for preparing cyclic acetals having general formula (I) wherein Y and Y, equal to or different from each other, are selected from H and a group OR, R being a linear or branched alkyl containing from 1 to 8 carbon atoms, comprising at least the following phases: (i) providing a reaction mixture comprising at least one vicinal diol having formula (II) ZCH.sub.2CHOHCH.sub.2OH wherein Z is selected from H and a group OR, R being a linear or branched alkyl containing from 1 to 8 carbon atoms, said mixture being substantially free of aldehydes having general formula R.sup.ICHO, wherein R.sup.I is a linear or branched alkyl containing from 1 to 6 carbon atoms, possibly substituted by an alkoxide group OR111, wherein R.sup.III is an alkyl containing from 1 to 4 carbon atoms; (ii) thermally treating said reaction mixture at a temperature within the range of 100 C.-300 C. in the presence of at least one acid catalyst, obtaining said compound having formula (I). The acetals having formula (I) can be used as fuel components. ##STR00001##

Claims

1. A process for preparing at least one compound having general formula (I): ##STR00004## wherein Y and Y, the same or different, are selected from the group consisting of H and a group OR, R being a linear or branched alkyl containing from 1 to 8 carbon atoms, comprising at least the following phases: (i) providing a reaction mixture comprising at least a vicinal diol having formula (II)
ZCH.sub.2CHOHCH.sub.2OH(II), wherein Z is selected from the group consisting of H and a group OR, R being a linear or branched alkyl containing from 1 to 8 carbon atoms, said mixture being substantially free of aldehydes having general formula R.sup.ICHO, wherein R.sup.I is a linear or branched alkyl containing from 1 to 6 carbon atoms, possibly substituted by an alkoxide group OR.sup.III, wherein R.sup.III is an alkyl containing from 1 to 4 carbon atoms; (ii) thermally treating said reaction mixture at a temperature within the range of 100 C.-300 C. in the presence of at least one acid catalyst, obtaining said compound having formula (I), and wherein the thermally treating is carried out while maintaining said reaction mixture in liquid phase.

2. The process according to claim 1, wherein said temperature is within the range of 150 C.-200 C.

3. The process according to claim 1, wherein said R is a linear or branched alkyl containing from 1 to 4 carbon atoms.

4. The process according to claim 1, wherein R is selected from the group consisting of ethyl, n-butyl, i-butyl, 3-methyl-1-butyl, 2-methyl-1-butyl and mixtures thereof.

5. The process according to claim 1, wherein said acid catalyst is selected from the group consisting of: ion-exchange acid resin, acid zeolite, silica-alumina and mixtures thereof.

6. The process according to claim 1, wherein said vicinal diol is obtained starting from glycerine.

7. The process according to claim 6, wherein said vicinal diol is 1,2-propanediol.

8. The process according to claim 7, further comprising obtaining said 1,2-propanediol by a catalytic hydrogenation process of glycerine with hydrogen.

9. The process according to claim 8, further comprising purifying by distillation said 1,2-propanediol obtained by means of said hydrogenation reaction before said thermal treatment.

10. The process according to claim 1, wherein said vicinal diol is obtained by means of an etherification process of glycerine with at least one alcohol.

11. The process according to claim 10, wherein said at least one alcohol is selected from the group consisting of: ethanol, n-butanol, i-butanol, 3-methyl-1-butanol, 2-methyl-1-butanol and mixtures thereof.

12. The process according to claim 6, wherein said glycerine is obtained from a trans-esterification reaction of triglycerides.

13. The process according to claim 1, wherein R.sup.I is a linear or branched alkyl containing from 1 to 6 carbon atoms that is substituted by an alkoxide group OR.sup.III, wherein R.sup.III is an alkyl containing from 1 to 4 carbon atoms.

14. The process according to claim 1, wherein R is ethyl or n-butyl or mixtures thereof.

15. The process according to claim 10, said at least one alcohol is ethanol, n-butanol or mixtures thereof.

Description

EXAMPLE 1

(A) Synthesis of 1,2-propanediol

(1) 20 cc of cupric chromite (Sigma-Aldrich) are charged into a fixed-bed reactor and the reactor is heated to 250 C. in hydrogen. An equimolar mixture of glycerine and hydrogen is then fed at a space velocity of 1 h.sup.1 and samples of the mixture are collected, which are analyzed by means of gaschromatography.

(2) The gaschromatographic analysis confirmed a substantially complete conversion of the glycerine, with a selectivity of about 97% to 1,2-propanediol, the complement to 100% consisting of propanol, ethylene glycol and methanol.

(3) The catalyst is stable under the reaction conditions for over 200 hours, as there is no variation in either the conversion or the selectivity towards the desired product during this period of time.

(4) The 1,2-propanediol obtained is separated from the reaction mixture by means of distillation.

(B) Synthesis of 2-ethyl-4-methyl-1,3-dioxolane

(5) 20 cc of acid resin Amberlyst 70 are charged into a fixed-bed reactor. After heating the reactor up to 180 C., 1,2-propanediol obtained according to Example 1 (A), is fed.

(6) The feeding is effected at a space velocity of 0.5 h.sup.1. The reaction mixture is kept in liquid phase, applying a counter-pressure of 7 bar to the reactor.

(7) Samples of the reaction mixture are collected during the reaction, and they are analyzed by means of gaschromatography.

(8) The conversion of 1,2-propanediol to 2-ethyl-4-methyl-1,3-dioxolane is substantially complete with a selectivity of about 96% to the desired product, the complement to 100% consisting of propionic aldehyde, from which the desired product is separated by distillation.

(9) The catalyst proves to be stable under the reaction conditions for over 300 hours, as there is no variation in either the conversion or the selectivity towards the desired product during this period of time.