RESUFTING FROM FERMENTATION.

The present invention refers to the use of a flexible, energy efficient method for separating into fractions a mix of fatty acids resulting from fermentation.

FIEED OF THE INVENTION

It is well known in the art to separate substances through means of determining their respective boiling points at certain pressures and to then separate them through means of a distillation column. It is however quite a challenge when multiple substances need to be separated from each other and furthermore if the mix of substances is not a constant over time. This is a problem that presents itself when fermenting organic waste into fatty acids.

The distribution of acids will vary over time, mostly due to the type of organic waste used in the fermentation process, but also the microbial composition which may vary over time. Fatty acids that can be produced as a mix of acids through fermentation are, C2 - CIO, but foremost C2 - C8 fatty acids. These acids can be both straight chain and branched acids, such as acetic acid, propionic acid, butyric acid, iso-butyric acid, pentanoic acid, iso-pentanoic acid, hexanoic acid, iso-hexanoic acid, heptanoic acid, iso-heptanoic acid, octanoic acid & iso- octanoic acid. There is a great need to be able to separate this mix of fatty acids, where the distribution between the fatty acids indeed will vary over time, in a flexible and energy efficient way.

SUMMARY OF THE INVENTION

Accordingly, with reference to accompanying figure, the invention refers to the use of a flexible, energy efficient method for separating into fractions a mix of fatty acids resulting from fermentation, said mix of fatty acids comprising at least three fatty acids selected from the group consisting of straight-chain or branched C2 - CIO fatty acids, but foremost C2 - C8 fatty acids. These acids can be both straight chain and branched acids, such as acetic acid, propionic acid, butyric acid, iso-butyric acid, pentanoic acid, iso-pentanoic acid, hexanoic acid, iso-hexanoic acid, heptanoic acid, iso-heptanoic acid, octanoic acid & iso-octanoic acid. The invention is characterized in that the mix of fatty acids, optionally after a pre-separation where acetic acid and possible water is removed from the stream, is fed into an inlet arrangement (10) of a dividing wall column (1), said dividing wall column (1) being provided with means for controlling temperature and pressure inside said dividing wall column (1). The dividing wall column (1) is further provided with a first outlet arrangement (11) at the top of the dividing wall column (1), a second outlet arrangement (12) at the middle of the dividing wall column (1) and a third outlet arrangement (13) at the bottom of the side wall column (1). At least the temperature and the pressure in the dividing wall column (1) is adjusted after analysis of the distribution of fatty acids in the mix of fatty acids prior to being fed into the inlet arrangement (10).

According to one embodiment of the invention, the inlet arrangement (10) comprises at least two inlets arranged at different heights, that the inlets are provided with guided inlet valves (10a, 10b etc), the guided inlet valves (10a, 10b etc) being selectively opened or closed depending of the result of the analysis of the fatty acid distribution.

The first and third outlet arrangement (11 and 13 respectively) are suitably provided with each one guided outlet valve (11a and 13a respectively), the guided outlet valves (11a and 13a respectively) regulating the flow depending of the result of the analysis of the fatty acid distribution. The first outlet arrangement (11) may advantageously comprise a reflux drum (1 lb) with a partial recirculation of the stream. The second outlet arrangement (12) suitably comprises at least two outlets arranged at different heights. The outlets are then each provided with guided outlet valves (12a, 12b etc), the guided outlet valves (12a, 12b etc) being selectively opened or closed and/or regulating the flow depending of the result of the analysis of the fatty acid distribution.

In accordance with an optional embodiment of the invention C2 acid is separated from the mix of fatty acids prior to feeding it into the dividing wall column (1). The C2 acid is then separated from the mix of fatty acids through means of a column 4 having an inlet 4a and an outlet 4b for remaining mix of fatty acids and an outlet (41) for C2 acid and possible water. The column (4) may be of a simpler design which is easy to control. The C2 acid stream may advantageously be fed back to the fermentation equipment.

In accordance with one specially advantageous embodiment of the invention the C2 and C3 acid and water is separated from the mix of fatty acids prior to feeding it into the dividing wall column (1), that the C2 and C3 acid is separated from the mix of fatty acids through means of a column (4) having an inlet (4a) and an outlet (4b) for remaining mix of fatty acids and an outlet (41) for C2 and C3 acid and water. It is known that C3 acid and water is difficult to separate from one another. Very large distilling columns and costly process will be needed in order to obtain higher purities. In fact the simplest way of separating C3 acid from water is by adding an alkali hydroxide such as sodium hydroxide whereby sodium propionate is formed. The latter is easily separated from water, but is no longer an acid. There is also a higher market value for the higher fatty acids such as C4 - CIO, whereby there is an amount of logic to allocate the C2 and C3 acids together with the water back to the fermentation equipment in order to build longer fatty acid chains.

In accordance with an advantageous embodiment of the invention one or more of; the guided inlet valves (10a, 10b etc), the guided outlet valves (11a, 12a, 12b etc and 13a respectively), the temperature in the dividing wall column (1) and the pressure in the dividing wall column (1) are guided by a control device (100).

The control device (100) is suitably provided with input data from at least one sensor (103), said sensor (103) determining the distribution between the different fatty acids in the mix of fatty acids.

According to one embodiment of the invention the control device (100) is advantageously provided with input data from post separation sensors selected from the group consisting of; a first outlet sensor (110), a second outlet sensor (120), a third outlet sensor (130) and a combination thereof, that the outlet sensor/s (110, 120, 130 respectively) is used for statistical process guiding by feeding sensory output from the sensor/s (110, 120, and 130 respectively) to the control device (100).

The three resulting streams from the dividing wall column when fed directly or indirectly (i.e. post separation of the C2 acid stream and advantageously also the C3 acid stream together with water) will indeed themselves contain a mix of acids, albeit a reduced number of acids in each of the three streams. Just as the distribution of acids in the fatty acid mix prior to separation varies, so does the need of purity or actual mix vary at a customer level. Some customers will require, say, a mix of hexanoic, heptanoic and octanoic acid. It will here be possible to adjust the settings of the dividing wall column to obtain such a desired mix of fatty acids from the third outlet arrangement. Another customer may at another time request high purity pentanoic acid, which will be possible to obtain through adjustment of the distillation parameters. The distribution i.e. number of fatty acids from the remaining outlet arrangements will of course be affected by the deliberate choice.

Accordingly a stream of fatty acids from the first outlet arrangement (11) is fed to a first holding tank (16) provided with a pump (16a) and a control valve (16b). The fatty acid stream from the second outlet arrangement (12) is fed to a second holding tank (15) provided with a pump (15a) and a control valve (15b) while stream of fatty acids from the a third outlet arrangement (13) is fed to a third holding tank (14) provided with a pump (14a) and a control valve (14b).

The fatty acids in the first, second and third holding tanks (14, 15 and 16 respectively) can then, depending on how the distillation parameters were set in the dividing wall column (1), be distilled further through two alternative routes in accordance to the present invention.

In accordance with a first embodiment the fatty acids in the first holding tank (14) is fed through an inlet (61) to a distillation unit (60) where the fatty acids can be separated through one or more outlets (62, 63). The fatty acids in the second holding tank (15) is fed through an inlet (71) to distillation unit (70) where the fatty acids can be separated through one or more outlets (72, 73). The fatty acids in the third holding tank (16) is fed through an inlet (81) to distillation unit (80) where the fatty acids can be separated through one or more outlets (82, 83).

It will of course be possible to utilise one and the same distillation unit (60 or 70 or 80) for separating the fatty acids in the first, second & third holding tanks (14, 15 and 16

respectively) one after the other. The distillation parameters will of course then need to be adjusted in accordance with the content in the holding tank and the desired separation.

In cases as described earlier, where distillation parameters in the dividing wall column (1) were set so that any of the three streams from the first, second or third outlet arrangement (11, 12 and 13 respectively) is constituted by only one fatty acid with acceptable purity, a further distillation will not be necessary for this fraction. Also in case were a certain mix of fatty acids is desired, further distillation can be omitted.

According to a second embodiment the dividing wall column (1) can due to its flexible design be used to further separate the fatty acids. Accordingly the fatty acids in the first, second and third holding tanks (14, 15 and 16 respectively) are one by one fed to a secondary holding tank (5) provided with a pump (51) and a control valve (51a) wherein the dividing wall column (1) is used for a second separation of fatty acids.

The secondary holding tank (5) is preferably provided with a holding tank sensor (103 ⁿ ), the holding tank sensor (103 ¹¹ ) providing data input to the control device (100) guiding the separation process.

The sensory inputs from the sensors selected from the group consisting of; tank sensor (103), input sensor (103 ¹ ), holding tank sensor (103 ¹¹ ), a first outlet sensor (110), a second outlet sensor (120), a third outlet sensor (130), at least one distillation temperature sensor (1 ^TI ), (l ^Tn ) etc, at least one distillation pressure sensor (l ^p ) and a combination thereof, is fed to the control device (100) for statistical process guiding. The control device (100), to be understood as a PLC, a computer or a similar programmable device, is intended to guide primarily the distillation process parameters such as temperature and pressure, but also inlet valves and outlet valves in order to provide an energy efficient separation of the mix of fatty acids, adapted to current mix and current desire of separation. Statistical process guiding is to be understood as a learning guiding system where guiding input is compared to actual output results and that the guiding system is gradually adjusting distillation parameters and possibly valve settings in accordance with pre-set algorithms in order to obtain the best possible results. Also here the actual distribution of fatty acids in the fatty acid mix fed into the dividing wall column is an important input affecting the end result.

The mix of fatty acids from the fermentation is suitably fed through an inlet (31) to a primary holding tank (3) provided with a pump (32) and a control valve (32a).

The primary holding tank (3) is suitably provided with a tank sensor (103), the tank sensor (103) providing data input to the control device (100) guiding the distillation process.

According to an alternative embodiment of the invention the inlet arrangement (10) after the primary holding tank (3) is provided with an input sensor (103 ¹ ), the input sensor (103 ¹ ) providing data input to the control device (100) guiding the separation process.

The pressure in the dividing wall column is suitably below 50 kPa, preferably in the range

10 - 30 kPa.