Note: Descriptions are shown in the official language in which they were submitted.
113157~
1 The invention concerns a process for the continuous
preparation of alcohol, in particular ethanol, through fermenta-
tion in a fermenter.
Processes for production of alcohol through fermentation
are generally well known in the art. From G. R. Cysewski and Ch.
R. wilke, Biotechn. Bioeng. 19. 1125-1143 (1977) is also known a
process in which ethanol is removed during the fermentation from
the fermentor by means of vacuum, through which an increase in the
yield of alcohol is achieved through reduction in the inhibition
effect which occurs at higher concentrations.
In order to achieve the desired increase in productivity,
the process is carried out at a total pressure of 50 mm Hg. Such
low pressures, however, have the disadvantage, that they require
vacuum-tight, large fermenters. This places disproportionate de-
mands on the sealing systems and the container. Through applica-
tion of vacuum to the fermentor, the sterility required during the
continuous fermentation is no longer guaranteed, as at unsealed lo-
cations microorganisms can be introduced into the container.
It is therefore a goal of the invention to provide a
process which avoids the disadvantages discussed above and which
nonetheless reduces inhibition of the fermentation through increas-
ing alcohol concentration.
This object is achieved by the invention through a pro-
cess for continuous generation of ethanol through fermentation,
which is characterized by removal of a partial stream of the mash
from the fermenter during the fermentation in a continuous manner,
partial or total separation of ethanol from the mixture, and partial
reintroduction of the residual mixture into the fermenter.
~ he fermenter itself can thus be operated under normal
pressure or at slightly elevated or reduced pressures. Preferably,
" ~
1 `the pressure should lie within about 0.5 bar of atmospheric
pressure. m e culture substrate is continuously introduced into
the fermenter, and the fermenting occurs at constant temperature.
A partial stream of the mash from the fermenter is removed at a
particular location and after complete or partial removal of
alcohol is partially reintroduced into the reactor over a circu-
lating system. The amount withdrawn for the circulation is as a
rule a multiple of the amount of substrate which is introduced.
The amount of material effectively withdrawn, however, corresponds
to the amount of freshly added substrate, so that the contents of
the fermenter remains constant.
The removal of alcohol from the mash is carried out
external to the fermenter in a vacuum evaporator at temperatures
between about 18 and 45 C, preferably at the fermentation temper-
ature. m e vacuum is generated by means of a thermocompressor,
which concentrates and condenses the vapors; the heat liberated
thereby is again used for the evaporation. Simultaneously, the
thermocompressor generates the required vacuum.
The major portion of the carbon dioxide/carbon acid
generated in the process is removed directly from the fermenter.
The rest of the acids still contained in the mash are removed
before the thermocompressor.
The separation of yeast cells can follow immediately
after the fermenter, i.e., before separation of alcohol. m e
separation before the evaporator has the advantage, that the
evaporator is less quickly contaminated. A further advantage
is that the yeast cells can be immediately reintroduced into the
fermPnter at the same temperature thereby increasing the biomass
component. Simultaneously by this process the evaporator can be
operated at higher temperatures than the fermentation temperature.
113~71
1 This can be desirable, if one wishes optimally to coordinate the
thermal requirements of the evaporation with the compression
parameters in the use of thermocompression.
The yeast cells, however, can also be separated out
after the evaporator partially or completely and recirculated
into the fermenter. In both cases, it is necessary that a portion
of the substrate, in which after longer periods offermentation
poisons accumulate, be removed.
The invention may be better understood through the
schematic flow drawing. The single Figure illustrates a fermen-
ter container 1. This is provided with a stirrer 2, which is oper-
ated by use of an electromotor 3. In the dome of the fermenter 1
a mechanical foam separator 4 is arranged, which in turn is oper-
ated by an electromotor 5. m e foam separator 4 has a connector
6. In the upper portion of the fermenter 1, a conduit 7 is intro-
duced via a connector, at the end of which conduit a pump 8 is lo-
cated. At about the same height as conduit 7, but on the opposite
side, a conduit 9 is joined to a connector. A further connector
combines an air conduit 10 with the fermenter 1, w'nich feeds into
2~ an air separator 11. At the end of conduit 9 is a centrifuge 12,
with an input conduit 13 for the liquid phase and an output con-
duit 14 for the concentrated phase. From conduit 14, conduit 15
branches off. Between conduits 14 and 17 a pump 16 is installed.
A by-pass 18 with the necessary vents not illustrated, is provided
to avoid the centrifuge. A pump 19 is installed between the con-
duits 13 and 20. The evaporator 21, which preferably is a falling
film evaporator, is associated with an input conduit 22 for the
heating medium and an output conduit 23, which latter is provided
with a pu~p 24. From the evap3rator head a vapor conduit 25 is
provided, and from the pot a conduit which leads either directly
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113~57~
1 ~back to fermenter 1 or to a centrifuge 27. From the centrifuge 27
runs a conduit 28 by pump 29 to the conduit 7. From conduit 28
branches a further conduit 30 in a canal system not illustrated.
The concentrate conduit 31 runs over a pump 32 and a conduit 33
back into fermenter 1. A thermocompressor 34 is connected with
conduit 25 and combined with a heat exchanger 36 by means of con-
duit 35. From heat exchanger 36 a product conduit 37 leads to a
rectifier column 38. The column 38 has an input conduit 39 for
the heating medium and an output conduit 40, which over pump 41
and conduit 42 is joined to conduit 22. A conduit 43 is provided
for the rectified alcohol and a conduit 44 for the residual hot
water.
In operation, the alcoholic fermentation mixture is in-
troduced into fermenter 1. By means of pump 8 and conduit 7, fresh
substrate is dosed into the fermenter. m e anaerobic mixture is
provided over time with very small amounts of air of about 0.1 -
0.2 vvm (volume of air per volume fermenter content per minute), via
conduit 10 and the air separator 11 to regenerate the yeast cells.
During the fermentation the stirrer 2 operates, by means of electro-
motor 3, to insure a constant mixing of the container content, as
the carbon acid gas generated in general is not sufficient for this
purpose. The carbon acids are continuously removed by gas exhaust
connector 6 of the mechanical foam separator 4, and can be carried
off for other uses. A partial stream is continuously removed from
the fermenter 1 by means of conduit 9 and as a rule freed of yeast
cells in centrifuge 12. The yeast cells are in the greater part
carried through conduit 14 by pump 16, conduit 17 and collector con-
duit 33 back into fermenter 1. A portion of the yeast, dependent
upon the concentration in fermenter 1, is removed by conduit 15 and
can be carried further to preparative treatments as feed yeasts.
-`` 1131571
1 A connector 9' is provided for complete emptying of the fermenter.
The mash freed of yeasts is carried from separator 12 by conduit
13 and pump 19, and conduit 20, into the evaporator 21. In the
evaporator, a vapor as azeotrope of alcohol and water is removed
under vacuum and conveyed by means of conduit 25 to the termocom-
pressor 34. The vapor is concentrated in known manner in thermo-
compressor 34. ~he heat generated in the concentration is trans-
ferred to the alcohol/water mixture in a heat exchanger 36, which
simultaneously serves as condenser, and a heat transfer medium,
for example water, is introduced. This circulates over conduit 22,
evaporator 21 and after transfer of the heat necessary for evapor-
ation of the azeotrope, over conduit 23 and pump 24 back to the
heat exchanger 36.
The mixture of alcohol and water is carried over conduit
37 to the rectifier column 38 from the heat exchanger. The heating
of the column 38 is carried out by means of heat transfer medium
from the heat exchanger 36 by conduit 39, and can be directly
returned to evaporator 21 over conduit 40, pump 41, conduit 42
and conduit 22. Through use of centrifuge 12, the residue from the
evaporator can be returned for the most part via conduit 7 to the
fermenter 1, and only a portion treated by canalization.
In a variant of the process, the centrifuge 12 is by-
passed by conduit 18. In this case, the mash together with the
yeasts is treated in evaporator 21. The residue of the evaporator
is led through centrifuge 27, a portion of the yeasts via conduit
28, and the pump 29, returned to the fermenter, and a portion dis-
charged via conduit 30. A part of the liquid phase as well is re-
turned to the fermenter via conduit 31, pump 32 and conduit 33, and
a portion fed into the canal system by means of conduit 45.
Without further analysis, the foregoing will so fully
reveal the gist of the present invention that others can, by ap-
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- ~13~571
1 plying current knowledge, readily adapt it for various applications
without omitting features that, from the standpoint of prior art,
fairly constitute essential characteristics of the generic or spec-
ific aspects of this invention.
