PRODUCTION D'ETHANOL A PARTIR DE SOLUTIONS FERMENTABLES DU SUCRE

PROCESS FOR PRODUCING ETHANOL FROM FERMENTABLE SUGAR SOLUTIONS

Abrégé anglais

Abstract:
For the formation of fermentable sugar solutions,
yeast is added to the sugar solution. The yeast solu-
tion formed is separated from the mixture formed and
introduced into the reaction chamber. After completion
of the fermentation process, the yeast is discharged
from the fermentation receptacle and at least partially
recycled for being mixed with the sugar solution after
having been combined with a nutrient solution. Before
separating the yeast solution; this solution can be
subjected to flocculation.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for producing ethanol from fermen-
table sugar solutions in which yeast is added to the sugar
solution prior to its introduction into a fermentation
receptacle, the yeast sludge is separated from the mixture
formed, the yeast sludge is introduced into the reaction
chamber and the yeast is discharged from the fermentation
receptacle after the fermentation process has been ton-
minated and is, after having been aerated and having been
supplied with a nutrient solution at least partially
recycled to the sugar solution prior to introduction into
the fermentation receptacle for producing the mixture.
2. A process as claimed in claim 1, in which the
mixture is subjected to a flocculation prior to separating
the yeast sludge.
3. A process as claimed in claim 2, in which the
solution separated from the yeast sludge prior to introduc-
ing same into the fermentation receptacle is added to the
flocculation together with polyelectrolytes.
4. A process as claimed in claim 2 or 3, in which
the flocculation is by flotation.
5. A process as claimed in claim 1, 2 or 3, in
which the nutrient solution comprises at least one of carbon
sources and nutrient salts.

Description

~Z~7739
The invention relates to a process for producing
ethanol from fermentable sugar solutions. Published EP-A-0 044
428 discloses for producing alcohol (ethanol) from starch or
starch-containing raw materials the production of a mash which is
obtained by comminution, thermal degradation and saccharification
of starch-containing raw materials. There is known a plurality
of sugar-containing raw materials from which sugar solutions can
directly be produced by extraction and it is already known to de-
grade such sugar solutions down to glucose and to subject the
mash thus obtained to fermentation. The fermentation process re-
quires, however, in dependence on the raw materials and, respec-
tively, the mash used differing conditions and a relatively long
reaction time for completing the fermentation. It is a drawback
of the known fermentation processes that the mashes and fer-
mentable substrates, respectively, show with proceeding fermenta-
tion varying concentrations in fermentable sugar as well as in
fermentation products which strongly influence with proceeding
fermentation the reaction speed or fermentation speed, respec-
tively. It is a further drawback that with the known processes
it is always only possible to produce a more or less pure alcohol
and this, as a rule, with an only low concentration.
The fermentable sugar solutions produced, as a rule, by
saccharification of starch-containing raw materials show a rela-
tively low concentration in sugar. With consideration of a morerapid fermentation it is advantageous to increase in these cases
the concentration in sugar by reducing the volume of the sub-
strate.
The invention provides a particularly simple process
which provides a directly fermentable substrate having a concen-
tration in sugar which is favourable for the subsequent fermenta-
tion step and which provides the possibility to do without thick-
ening apparatuses which are expensive with respect to construc-
tion and energy consumption. According to the invention the
yeast sludge is separated from the mixture formed, in that the
'J~
.. \ -- 1 --

1217739
yeast sludge is introduced into the reaction chamber and in that
the yeast is discharged from the fermentation receptacle after
the fermentation process has been terminated and is, after having
been aerated and having been supplied with a nutrient solution,
in particular with carbon sources and/or nutrient salts, at least
partially recycled to the sugar solution prior to introducing
same into the fermentation receptacle for the purpose of pro-
~ ~ - 2 -

~Z~7739
ducing the mash. In view of the addi.ti.on of yeast, the
yeast absorbs glucose from the su.gar solution after a
reaction time of approximately 10 minutes. By using said
yeast sludge enriched in gluco$e, the sugar contained in
the sugar solution is subjected to a particularly rapid
fermentation reaction and on account of the mild process
conditions it is not only possible to use most types of
commercially available yeasts for the purpose of achieving
a high fermentation efficiency but it is also possible to
circulate the yeast along a closed circuit and thus to
make the process less harmful to the environments~ For
this purpose and according to the invention, the yeast is
discharged from the fermentation receptacle aiter com-
pletion of the fermentati.on process and is, after having
been aerated and having been supplied with a nutrient
solution, in particular with carbon sources and/or nutrient
salts, at least partially recycled to the sugar solution
prior to introducing same into the fermentation receptacle
for the purpoce of producing the mash. Excessive yeast can
be separated and be used for other purposes.
In an advantageous manner, the yeast is, in particular
if l:he alcohol formed is continuously removed and for
example already removed during the fermentation by distil-
lation, never or only for a short ti.me interval subjected
to the influence of higher concentrations of fermentation
products, so that the biological material has a better
vitality. When working according t~ the inventlve process,

~Z~7~739
the yeast need only be ~enerated to an only low extent.
For separating the yeast sludge from the mash con-
taining the sugar solution, the mash can be sub~ected to
flotation, noting that the alrea~y initiated gas formation
can be made advantage of and tnat a flocculation can be
effected by adding polyelectrolytes. The flocculation, the
flotation and removal of yeast can be effected at fermen-
tation temperature (30 to ~5 C). ~ptionally, mixing of
the yeast with the,glucose solution is effected already '
at fermentation temperature. The floculation step can be
effected in an advantageous manner by adding the solution
separated from the yeast sludge prior to introducing same
into,the fermentation receptacle together with the poly-
electrolyt into this flocculationstep, noting that in
this manner the solution separated from the yeast sludge
and still containing sugar can at least partial~y be cir-
culated along a closed circuit. Circulation of the yeast
is, above all, made posslble on account of the short fer-
mentation time. For the purpose of regenerating the yeast,
the yeast extracted from the fermentation receptacle is
subjected to an aerobic treatment, noting that yeast may
be extracted in regular time intervals and can be used
for the production of animal feeding products.
In the following, the invention is further explained
cl e~c~oa~ y,'"g
~~~ 25 wlth reference to tlle~drawlng showing a pressure curve and
an embodiment. In the drawing, Figure ~ shows a pressure
curve for the fermentation process according to the

~217739
invention and Figure 2 SilOWS a simplified flow diagram
for the complete transformation of starch-containing raw
materials to alco~lol.
The amollnts givcn ~.r. the example of embodiment are
refel-red to 1 1 of sugar solution.
Glucose used = l82.8 g
yeast used = 1.47 kg sludge con-
taining about 4 % dry
solids
1~ reaction time = 10 min
polyelectrolyte used = 320 mg
( -1.75/kg_gl~ww~
reaction tlme = 10 min
flotatio~ time = 7.0 min
extracted sugar solution = 1.l0 1
discharged residual sugar = 52.9 g glucose
sugar subjected to fer-
mentation together with
yeast sludge = 1~9.~ g
~ T~le fermentation was e~fected in accordance with the
representation in the Figure of the drawing such that the
pressure was reduced to 35~ mbar immediately after starting
the ferment~tion. Approxlmatèly 45 minutes later the
pressure was further reduced to 260 mbar an~ the sugar
~5 content was determined after about 70 minutes. ~lhe lermen-
tation has been nearly completed during thls time interval
and distilLation of the alcohol formed can be observed

~Z17'739
-- 6
already during tnis time interval. A~out l80 minutes later
the pressure withln the reaction chamber was further step~
wisely reduced to complete distilla~ion an~ to complete
the yield in ethanol. Based on l 1 sugar soLution there
was obtained 0.34 1 disti]late containing 0.0/7 l ethanol,
i.e. 60.7 g ethar~ol. The yield ~ased on adsorbed sugar is
thus
60,7
_~ 7~ ____ = 0.915
129.9x0.511
Glucose could not be detected in the yeast sludge.
For performlng the whole process there results the
~ollowlng ti~e schedule:
Adsorption of glucose . . . . . . . . . . . 0.17 h
~occulation. . . . . . . . . . . . . . . . 0.02 h
flotation . . . . . . . . . . . . . . . . 0.12 h
fermentation ~ distillation . . . . . . . . 3.50 h
total process duratlon = 3.81 h
l'he solution circulated along a closed circuit and
having been separated from the yeast sludge prior to intro-
~0 duct1on into the reaction chamber has an average glucose
content of 3 to 5 % by weight.
The process stages for producing ethanol ~rom sugar-
containing raw materials is schematically shown in Fi~
gure 2. ~l'his flow diagram shows also the circulation
circuits proposed according to the invention for lmproving
the ut1lization of energy and tne ylela in glucose, re-
spectively.