METHOD FOR THE PURIFICATION OF FATTY ACID AKLYL ESTERS

Abstract

In a process for purifying fatty acid alkyl esters, particularly methyl and ethyl esters, by means of vacuum distillation in a distillation column, water or steam is introduced into the distillation column and, during distillation, brought into contact with the fatty acid alkyl esters in the gas phase. This results in a significant reduction in the sulphur content and in the acid number of the fatty acid alkyl ester.

Claims

1. A process for purifying fatty acid alkyl esters, comprising: distilling fatty acid alkyl esters by vacuum distillation in a distillation column; introducing water or steam into the distillation column; and, during distillation, contacting the fatty acid alkyl esters with the water or steam in the gas phase.

2. A process according to claim 1, wherein the water or steam is introduced in an amount of 0.5-10.0 kg/t of fatty acid alkyl ester into the distillation column.

3. A process according to claim 1, wherein a distillation residue is produced and a part is returned into the distillation column and the water or steam is supplied to the part of the distillation residue to be returned and introduced together with said part into the distillation column.

4. A process according to claim 1, wherein the water or steam is supplied to the fatty acid alkyl esters to be purified and introduced together with said esters into the distillation column.

5. A process according to claim 1, wherein the water or steam is fed directly into the distillation column.

6. A process according to claim 1, wherein highly volatile components including water are removed from the fatty acid alkyl esters prior to distillation.

7. A process according to claim 6, wherein highly volatile components including water are removed through flash evaporation.

8. A process according to claim 1, wherein the vacuum distillation is carried out at a pressure of <10 mbar, preferably <3 mbar.

9. A process according to claim 1, wherein the vacuum distillation is carried out at a temperature of 100-260° C.

10. A process according to claim 1, wherein the fatty acid alkyl esters comprise at least one of methyl fatty acid esters or ethyl fatty acid esters.

11. A process according to claim 1, wherein the water or steam is introduced in an amount of 2.0-5.0 kg/t of fatty acid alkyl ester into the distillation column.

12. A process according to claim 1, wherein the vacuum distillation is carried out at a pressure of <3 mbar.

13. A process according to claim 1, wherein the vacuum distillation is carried out at a temperature of 140-200° C.

Description

[0026] The invention is subsequently explained in greater detail by way of an example as well as the drawing.

[0027] FIG. 1 shows a graphical illustration of the sulphur reduction as a function of the amount of water added in a vacuum distillation according to an embodiment of the invention.

[0028] FIG. 2 shows a graphical illustration of the reduction of sulphur as well as of the acid number as a function of the amount of water added in a vacuum distillation according to an embodiment of the invention.

[0029] FIG. 3 shows a block diagram of an embodiment of the process according to the invention.

EXAMPLES

[0030] The effects of the introduction of water or steam into the distillation column in order to bring into contact the crude biodiesel in the gas phase with water or steam, respectively, during vacuum distillation were investigated.

[0031] Before the start of the study, the operational parameters such as mass balance, reflux rates, supply flows, etc. of the distillation column (rectification column) were determined. After setting constant conditions, samples of the starting product or the supply flow, respectively, and of the distillate were taken and analysed in regard to the sulphur content as well as the neutralization number thereof.

[0032] In the first step, the crude biodiesel 1 was freed from highly volatile substances 3 including water in a flash column 2 and subsequently fed into the distillation column 4. The mean supply rate from the flash column 2 to the distillation column 4 during the trials was 19.5 t/h. The pressure or the vacuum, respectively, at the top of the column was between 1.0 and 3.1 mbar. The mean distillation residue rate of the distillation system was kept at 5.4%. Due to the expected increase of the steam pressure in the distillation column there was set a higher sump temperature (184° C.-189° C.) in order to maintain a distillation residue rate as in normal operation (i.e., without addition of water/steam).

[0033] The energy necessary for distillation was supplied via a sump circulation flow. In this process, a part of the distillation residue 5 withdrawn from the column sump was heated in a heat exchanger 6. In the heat exchanger 6, water 7 was added as well and thereby supplied to the part of the distillation residue 5 to be returned into the column. The heated mixture 8 of distillation residue 5 and water 7 then was introduced into the distillation column 4, in which, during distillation, a close contact between water or steam, respectively, and the gaseous crude biodiesel 1 occurred.

[0034] The purified biodiesel 9 was withdrawn from the distillation column 4 and analysed. The highly volatile sulphur compounds as well as the water introduced into the column were removed by the vacuum system 10. The essential amount of the “washed-out” sulphur was withdrawn from the column sump along with the distillation residue 5 and then discharged from the sump circulation flow.

[0035] Table 1 shows the results for normal operation (experiment no° 9A) as well as for the introduction of various amounts of water into the distillation column.

TABLE-US-00001 TABLE 1 sulphur sulphur content content water addition (starting (after sulphur [kg H.sub.2O/t product) distillation) reduction exp. no.sup.o [kg/h] of ester] [ppm] [%]  9A 0 0 130 11 91.5 14 20 1.08 128 8 93.8 11 30 1.54 126 7 94.4  8 40 2.22 152 7 95.4  9 40 2.34 124 6 95.2 10 40 2.05 139 6 95.7

[0036] Table 2, apart from results for the sulphur content, indicates the results of the acid number analysis.

TABLE-US-00002 TABLE 2 water acid number acid number acid number addition (starting product) (after distillation) reduction exp. no.sup.o [kg/h] [mg KOH/g ester] [%]  9A 0 1.03 0.56 45.6 14 20 0.97 0.52 46.4 11 30 0.91 0.39 57.1 10 40 1.22 0.38 68.9

[0037] The results show that the introduction of water/steam into the distillation column will lead to a significant improvement. In spite of the required higher evaporation temperature in the column sump due to the higher system pressure, it was possible to notably reduce the sulphur content and, surprisingly, also the neutralization number of the biodiesel.