Note: Descriptions are shown in the official language in which they were submitted.
~L9S2S~3
VAPOR PHASE ADSORPTION PRCCESS FOR
CONCENTRATION OF ETHANOL FROM DILUTE
AQUEOUS MIXTURES THEREOF
Brief Summary of the Invention
Technical Field
_
This invention i5 directed in general to a
vapor phase adsorption process for selectively
adsorbing at least one organic molecular species
present in a minor amount from a dilute aqueous
mixturs using a hydrophobic adsorbent mass. ~he
hydrophobic adsorbent mass consists of a molecular
sieve material having greater selectivity for at
least one organic molecular species than for water.
More particularly, this invention is directed to a
vapor phase adsorption process or removing and
concentrating ethanol from water-ethanol mixtures
such as fermentation beer which contains typically
from about 8 to about 12 percent by weight ethanol
utilizing a molecular sieve material adsorbent such
as silica bonded F-silicalite or alumina-bonded
silicalite. As a viable alternative to the
preparation of ethanol from petroleum-bas~d
ethylene, the preparation o~ concentra~ed ethanol
from fermentation beer by the vapor phase adsorption
separation process oE the present invention is
especially important or supplementing world energy
and chemical needs.
Background Art
~thanol in dilute aqueous mixtures can be
pro~uced by fermentation processes utilizing a
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variety of agricultural and biomass raw materials
~uch as grains, molasses, sugar cane juice,
miscellaneous fruits, wood and the like. However,
the large propoxtion of industrial ethanol produced
in the world is made from petroleum-based ethylene.
In view of the limited petroleum resources
available, the production of ethanol from renewable
raw material resources by fermentation processes to
supplement the world energy and chemical needs is
understandably of major importance. It is
anticipated that in the near future a significant
amount of ethanol for fuel and chemicals will be
derived from fermentation processes.
In a conventional fermentation process,
yeast and other microorganisms convert sugars to
alcohol and carbon dioxide. Since sugar
concentrations in excess of about 16 weight percent
typic~lly inhibit the growth of yeast cells in the
initial stages of fermentation, dilution of the
s~arting sugar concentration with water is necessary
to properly control the sugar concentration and
permit the normal growth of yeast cells. The
diluted sugar concentrations result in lower ethanol
concentrations and hence high energy requirements
for distillation and purification of ethanol. It
has also been demonstrated that ethalnol
concentrations greater than about 10 weight percen~
in fermentation beer result in a phenomenon known as
"feedback inhibition" which inhibits further ethanol
production. The maximum ethanol concentration which
is typically attainable after about 36 hours of
conventional fermentation is usually about 8 to 12
weight percent. The major byproducts of the --
fermentation process in addition to carbon dioxide
.
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are dissolved and undissolved (distiller's dry
grain) solids, aldehydes, ketones and fusel oils.
The presence of ethanol in a minor amount in dilute
aqueous mixtures such as fermentation beer obtained
from the fermentation process requires large amounts
of heat energy to distill and purify the ethanol
therefrom.
Ethanol is conventionally recovered from
dilute aqueous mixtures such as fermentation beer by
traditional distillation processes. The
fermentation beer containing from about 8 to about
12 weight percent ethanol and byproducts is fed into
a still where ethanol is removed as overhead in a
concentration ranging from about 100- to about
l90-proof. The bo~toms from the still contain
dissolved and undissolved solids and the byproducts
are usually taken off as side draws. The
concentrated ethanol, nominally l90-proof, can be
further upgraded to nearly anhydrous l99-proof
ethanol needed for gasohol by azeotropic
distillation. However, as previously mentioned, the
conventional distillation process for recovering and
concentrating ethanol from dilute aqueous mixtures
such as fermentation beer is very energy intensive.
Large amounts of heat energy are required because
the major component of fermentation beer, i.e.,
water, is being heated to recover a minor component
of fermentation beer, i.e., ethanol. Also,
azeotropic distillation is an energy-intensive
operation. Energy consumptions from about 30,000 to
about 40,000 BTU per gallon of anhydrous ethanol are
not uncommon for typical distillation processes.
Since the cost of producing ethanol frcm
agricultural and biomass raw materials depends not
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;2S~
only on the fermentation of the raw materials but
also on the recovery and purification of ethanol
produced by the fermentation process, higher energy
consumptions during distillation and purification
result in higher ethanol-per-gallon cost and can
also contribute towards offsetting the energy
balance of ethanol production by fermentation
processes for fuel and chemical needs.
There have been various attempts to develop
lower cost processes for recovering and
concentrating ethanol from fermentation beer. It
has been previously found that ethanol can be
recovered from dilute fermentation beers by a liquid
phase adsorption process utilizing certain adsorbent
materials such as activated carbons, ion exchange
resins and molecular sieves. TheSe adsorbent
materials can selectively adsorb either water from
aqueous ethanol or ethanol from dilute aqueous
solutions. In carrying out the liquid phase
adsorption processes, a fermentation beer is usually
pumped through a packed adsorbent bed wherein either
the liquid ethanol or water is adsorbed on the
adsorbent material. If ethanol is adsorbed on the
adsorbent material, ~he adsorbent material is
typically regenerated with a purge gas in which
concentrated ethanol is recovered therefrom. If
water is adsorbed on the adsorbent material, ethanol
is recoversd in the effluent from the adsorbent
material. However, such liquid phase adsorption
processes are usually not very efficient. The main
drawbacks of liquid phase adsorption processes are
poox ethanol recovery due to entrapment of part of
the dilute aqueous mixture, i.e., fermentation beer,
between and within particles of the adsorbent
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52S~3
material and lower ethanol product purity due to
residual water being retained in the ethanol
product. Another major and perhaps more critical
drawback is the distinct possibility that the solids
contained in the`liquid fermentation beer can plug
up voids in the packed adsorbent bed and cause
substantial mechanical problems~
The present invention consisting of a vapor
phase adsorption separation process provides a
practical and efficient low energy process for
recovering and concentrating at least one organic
molecular species such as ethanol from a dilute
aqueous mixture such as fermentation beer without
encountering any of the drawbacks associated with
liquid phase adsorption processes. According to the
present invention, a stripping gas enriched with
ethanol vapor and water vapor is passed through an
adsorbent material such as silicalite described in
U.S. Patent 4,0blj~24 or F-silicalite described in
~ U.S. Patent 4,073,865, both assigned to Union
Carbide Corporation. Ethanol in the vapor phase is
selectively adsorbed by the adsorbent material which
has a greater selectivity for ethanol than for
water. The adsorption of ethanol vapor is conducted
at a temperature and pressure which prevents the
capillary condensation of water in the adsorbent
material. The adsorbed ethanol is removed from the
adsorbent material by a non-sorbable heated purge
~as which is subsequently cooled to condense
ethanol. Essentially no liquid phase is present in
the ethanol adsorption step of the highly desirable
adsorption separation process of this invention.
Various liquid phase adsorption processes and the
drawbacks inheEent therewith are less desirable for
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concentrating ethanol from dilute aqueous mixtures
such as fermentation beer.
U.S. Patent 4,277,635 disclose~ a process
for concentrating ethanol from aqueous solutions
thereof, such as fermentation beer containing from 6
to 13~ by weight ethanol. The ethanol is remoYed
from the fermentation beer by liquid adsorption on a
molecular sieve material such as silicalite. The
patent states that residual fermentation beer
remaining in the adsorption column can be removed by
passing highly concentrated ethanol through the
adsorption column.
U.SO Patent 4,061,724 and U.S n Patent
4,073,865, both assigned to Vnion Carbide
Corporation, describe crystalline silica
compositions designated herein as silicalite and
F-silicalite respectively, which can ~e used as the
adsorbent mass in the pre~ent invention. These
patents describe the hydrophobic/organophilic
character of both silicalite and F-silicalite which
permits their use in selectively adsorbing organic
materials from water either in the liquid or vapor
phase.
U.SO Patent 3,732,326 relates to a method
of selectively sorbing a compound of generally low
polarity such as various hydrocarbons in admixture
with a compound of the same or greater polarity such
as water by passing the mixture over a crystalline
aluminosilicate having a silica/alumina mole ratio
of at least 35 such as mernbers of the amily of
ZSM-5 zeolites.
However, none of these references discloses
or suggests the vapor phase adsorption separation
process as claimed in the instant invention or
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removing and concentrating at least one organic
molecular species such as ethanol present in a minor
amount from a dilute aqueous mixture such as
fermentation beer utilizing a molecular sieve
material adsorbent.
Disclosure of Invention
The present invention is directed to an
adsorption separation process which comprises:
(a) vaporizing water and at least one
organic molecular species contained in a dilute
aqueous mixture by contacting the dilute aqueous
mixture with an essentially non-sorbable stripping
gas
(b) passing the stripping gas
enriched with water and at least one organic
molecular species into a fixed adsorption zone
containing a hydrophobic adsorbent mass consisting
essentially of a molecular sieve material having
selectivity for at least one organic molecular
species
(c) adsorbing at least one organic
molecular species into the adsorbent mass at a
temperature and pressure which prevents capillary
condensation of the water
(d) terminating the flow of stripping
gas enriched with water and at least one organic
molecular species into the adsorp~ion bed prior to
breakthrough of at least one organic molecular
species from the effluent end of said adsorption bed;
(e) removing at least one adsorbed
organic molecular species by heating the adsorbent
mass by passing an essentially non-sorbable hea~ed
purge gas through the adsorbent mass countercurrent
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to such enriched strippin~ gas, which purge gas can
be the same gas used for stripping the dilute
aqueous mixture in step (a);
If) condensing at least one organic
molecular species by cooling the purge gas enriched
with at leas~ one organic molecular species; and
(g) recovering at least one organic
molecular species in a concentrated form.
The present invention is also directed to
an adsorption separation process as described in
steps (a~ through (g~ above further comprising
cooling the adsorbent mass until the ~empera~ure is
essentially the same as at the beginning of step (b)
and repeating steps (a) through (g) until a
predetermined amount of at least one organic
molecular species is recovered in a concentrated
form from the dilute aqueous mixture.
More particularly, the present invention is
directed to an adsorption separation process which
comprises:
(a) vaporizing water and ethanol
contained in a fermentation beer by contacting the
fermentation beer with an essentially non-sorbable
stripping gas such as nitrogen, carbon dioxide
helium or argon;
(b) passing the stripping gas
enriched with water and ethanol into a fixed
adsorption zone containing a hydrophobic adsorbent
mass con~isting essentially of a silica-bonded
F-silicalite adsorbent or an alumina-bonded
silicalite adsorbent;
(c) adsorbing ethanol into the
adsorbent mass at a temperature and pressure which
prevents capillary condensation of the water7
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~d) terminating the flow of stripping
gas enriched with water and ethanol into the
adsorption bed prior to breakthrough of ethanol from
- the effluent end of the adsorption bed;
(e) removing ethanol by heating the
adsorbent mass by passing an essentially non-sorbable
heated purge gas such as nitrogen, carbon dioxide,
helium or argon ~hrough the adsorbent mass
countercurrent to such enriched stripping gas
(f) condensing ethanol by cooling the
purge gas enriched with ethanol;
~g) recovering ethanol in a
co~centrated form;
(h) cooling the adsorbent mass until
the temperature is essentially the same as at the
beginning of step (b); and
~i) repeating steps (a) through ~h)
until a predetermined amount of ethanol is recovered
from the fermentation beer.
Brief Description of Drawings
The present invention is further described
with reference to the accompanying drawings in which:
Fig. 1 is a schematic flowsheet of an
illustrative embodiment for carrying out the process
of this invention.
Fig. 2 illustrates an adsorption step
breakthrough profile of ethanol and water
concentrations in the effluent from the adsorption
column a~ 125F using alumina-bonded silicalite
adsoebent as determined by gas chromatographic
analysis.
Fig, 3 illustra~es a regeneration step
profile of ethanol and water concentrations in the
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nitrogen gas regeneration effluent at 200~ ~s
determined by gas chromatographic analysis.
Fig. 4 illustrates a profile of the
dependency of water and ethanol adsorption loadings
on their relative stauration (p/po) values at
adsorption temperatures ranging from about 75F to
about 150F and using alumina-bonded silicalite
adsorbent.
Fig. 5 illustrates an adsorption step
breakthrough profile of ethanol and water
concentrations in the effluent from the adsorption
column at 75F using silica-bonded F-silicalite
adsorbent as determined by gas chromatographic
analysis.
Detailed_Description
A dilute aqueous mixture such as
fermentation beer containing from about 8 to about
12 percent by weight ethanol can be stripped of
ethanol by any suitable stripping procedure. For
example, with reference to Fig. 1, a stripping gas
can be charged into the bottom of an external
packed-bed stripping column wherein fermentation
beer is flowing downward to give a stripping gas
enriched with ethanol vapor and some water vapor.
After ethanol and some water are stripped from the
fermentation beer, the enriched stripping gas is
removed f~om the top of the stripping column and
essentially ethanol-free fermentation beer is
removed from the bottom of the column. The
stripping column temperature and pressure are not
narrowly critical and can vary over a wide range.
The temperature in the stripping column can range
from about ambient to about 200F and the pressure
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in the stripping column can range from abut 15 psig
to about 200 psig. The flow of stripping gas is
dependent on the stripping col~mn temperature and
pressure and the liquid, i.e., fermentation beer,
feed rate. Alternatively, in the absence of an
external packed bed stripping column, a stripping
gas may be bubbled through the fermentation tanks or
holding tank ~o strip ethanol from the fermentation
beer.
The stripping gas used in the vaporizing
step (a) of this adsorption separation process can
be any vapor phase compound which does not
appreciably react with the dilute aqueous mixture,
e.g., fermented beer, constituents under the imposed
conditions~ Also, the stripping gas should not be
harmful to the adsorbent mass and should not be
appreciably adsorbed by the adsorbent mass. The
non-adsorbability of the stripping gas can be due
either to molecular size exclusion or to a weak
adsorptive attraction between it and the adsorbent
massO The preferred strippiny gas for use in the
adsorption ~eparation process of this invention is
selected from the group consisting of nitrogen,
carbon dioxide, helium and argon. The stripping gas
can also be the off-gases generated by the
fermentation process which can consist of
essentially carbon dioxide enriched with some
ethanol. For example, with reference to Fig. 1, the
off-gases from the battery of fermentation tanks may
be used as the stripping gas in the process of this
invention~ The stripping gas can be recycled for
further stripping in vaporizing step (a) described
above after passing through the adsorption bed
during adsorbing step ~c) also described above.
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~S~5~
The dilute aqueous mixture feedstock can be
any mixture of water and one or more organic
molecular species. Preferred feedstocks are those
obtained by ermentation processes, i.e.,
fermentation beers, utilizing a variety of
agricultural and biomass raw materials such as
grains, molasses, sugar cane juice, miscellaneous
fruits, wood and the like. P~rticularly preferred
dilute aqueous mixture feedstocks are mixtures of
water and one or more organic molecular species
containing from 2 to about 6 carbon atoms
inclusive. ~n especially preferred dilute aqueous
mixture feedstock is one in which the organic
molecular species is a primary alcohol containing
from 2 to about S carbon atoms inclusive, most
pre~erably ethanol and/or isopropanol. A
fermentation beer containing from about 8 to about
12 percent by weight ethanol is the most preferred
dilute aqueous mixture or use in the proc~ss of
this invention.
The stripping gas enriched with at least
one organic molecular species vapor, e~g., ethanol
vapor, and water vapor is passed into any suitable
fixed adsorption zone containing a hydrophobic
adsorbent mass consisting essentially of a molecular
sieve material. The particular species of molecular
sieve material employed in the present invention is
not a narrowly critical factor. In all event,
however, it should be capable of adsorbing from 5 to
i 30 50 times more organic molecular species, e.g.,
ethanol, than water under the process conditions of
temperature and pressure, and ~o subs~antially
exclude from adsorption essentially all of the other
constituents of the dilu~e aqueous mixture feedstock
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under those conditions. The preferred adsorbent
mass for use in the process of this invention
includes substantially hydrophobic molecular sieve
materials such as silica-bonded F-silicalite
described in U.S. Patent 4,073,865, alumina-bonded
silicalite described in U.S. Patent 4,061,724 and
Ultrahydrophobic Zeolite Y (U~P-Y) described in
copending Canadian Patent No. 1,131,195,
September 7, 1982. Other suitable memb~rs
of the high silica adsorbent group may also be used
in the process of this invention. With reference to
~ig. l, the stripping gas enriched with ethanol
vapor and water vapor is passed through ~he
adsorbent mass con~ained in the adsorption column,
ethanol is adsorbed by the adsorbent mass and the
stripping gas depleted of ethanol is removed from
the adsorption column. Certain organic byproducts
~uch as aldehydes and fusel oils may also be
adsorbed ln minor amounts into the adsorbent mass.
If the stripping gas is the o~f-gases generated by
the fermentation process which can consist of
~ essentially carbon dioxide enriched with ~ome
- ethanol as describea above, the adsorbent ma-~s can
further adsorb ethanol vapor which would be
naturally lost and vented as a byproduct ~rom ~he
fermentation process, and thereby improve the
overall e~ficiency o ethanol recovery from the
fermentation process.
The temperature and press;ure conditions for
the adsorption step must be ~elected to maintain the
~tripping gas enriched wlth at least one organic
201ecular specie~ vapor, e.g., ethanol vapor, and
water vapor in the vapor phase ~nd prevent capillary
condensation o~ the organic constituent, e.g.,
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,, _ , . . .
~52~
1~
ethanol, and water in the adsorption bedu Capillary
condensation contributes to poor ethanol recovery
due to entrapment of liquid water and ethanol
preventing further adsorption of ethanol vapor and
also lower ethanol product purity due to residual
water being retained in the adsorbent mass and hence
the regenerated ethanol product. It is preferred
that the stripping gas enriched with at least one
organic molecular species, e.g., ethanol, and water
passing into the adsorption bed and the adsorption
bed itself be at a temperature within the range of
from about ambient to abou 200F and at an
appropriate corresponding pressu~e within the range
of from about 1 atmosphere (absolute) up to about
lS 100 psia. It is preferred that steps (b) and (c) of
the adsorption separation process described above be
conducted at a tempera~ure of from about 25F to
about 50F higher than the temperature of vaporizing
step (a~ also described above in order to decrease
the relative saturation (p/po) of water in the
enriched stripping gas passing into and adsorbing
into, in part, the fixed adsorption bed containing
alumina-bonded silicalite adsorbent described in
U.S. Patent 4,061,724. Heating the enriched
stripping gas adjusts the relative saturation (p/po)
of ethanol and water 50 as to minimize the
coadsorption of water on the ethanol selective
adsorbent mass. This is more fully illustrated in
working Example 1 hereinbelow. The relative
saturation values (p/po) of water and ethanol and
the extent or amount of water and ethanol loadings
onto the adsorbent mass are different for various
adsorbent materials. For example, as illustrated in
working ~amp~e 2 hereinbelow, when using
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silica-bonded F-silcalite described in U.S. Patent
4,073,865 as the adsorbent mass, it is not necessary
to heat the enriched stripping gas to adjust the
relative saturation (p/po) of ethanol and water
because essentially no coadsorption of water occurs
on the silica-bonded F-silicalite adsorbent.
Accordingly, the stripping gas enriched with ethanol
and water may optionally be heated to adjust the
relative saturation (p/po) of water and ethanol
depending on the particular adsorbent mass utilized
in the process of this invention.
Immediately prior to or after the initial
breakthrough of the organic molecular species, e.g.,
ethanol, from the adsorption bed, regeneration of
the adsorbent mass with a heated non-sorbable purge
gas in commenced in a countercurrent direction with
respect to the directional flow of the enriched
stripping gas through the adsorption bed. Ethanol
is removed or desorbed from the adsorbent mass by
the heated non-sorbable purge gas. During the
countercurrent purge-desorption step, the
temperature of the non-sorbaable heated purge gas
entering the adsorption bed can range from about
100°F to about 700°F, and is preferably
from about 100°F ti abiyt 300°F higher than the
temperature of the enriched stripping gas stream
during the adsorption step. The countercurrent
purge-desorption step can be carried out in any
suitable manner, for example, either in a
conventional open-purge or closed loop manner.
Regeneration of the adsorption bed can be
accomplished by using either conventional
thermal-swing or pressure-swing desorption. After
desorption of the organic molecular species, e.g.,
S2~
16
ethanol, from the adsorbent mass, the purge gas
enriched with ethanol is removed and the adsorbent
mass is cooled until the temperature is essentially
the same as at the beginning of the vaporizing step
(a) described aboveO The adsorbent mass can again
be used to adsorb an organic molecular species,
e.g., ethanol, in concentrated form from the dilute
aqueous mixture.
The purge gas utilized in the
countercurrent purge-desorption step is preferably
the same gas used for stripping the dilute agueous
mixture in vaporizing step (a) described above. The
purge gas can be any vapor phase compound which is
not harmful to the adsorbent mass and does not
appreciably react with any of the enriched stripping
gas constituents under the imposed conditions. The
purge gas is also essentially non-sorbable in the
adsorbent mass. The non adsorbability of the purge
gas can be due either to molecular size exclusion or
to weak adsorptive attraction between it and the
adsorption mass. The preferred purge gas for use in
the adsorption separation process of this invention
is selected from the group consisting of nitrogen,
carbon dioxide, helium and argon. The purge gas can
also be the off-gases generated by the fermentation
process which can consist of essentially carbon
dioxide enriched with some ethanol. For example,
with reference to Fig. 1, the off-gases from the
battery of fermentation tanks may be used as the
purge gas in the process of this invention. The
purge gas can be recycled for further desorption
after the organic molecular species and minor
amounts of water are condensed therefrom.
The purge gas enriched with ethanol and
some water can be dried by any suitable procedure
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\ ~9s~s~
17
such as by passing the gas through a dehydration
~olumn containing a bed of desiccant material such
as Type 3A zeoli~e to remove e~sentially all of the
: remaining water coadsorbed in the previous step.
~ha purge gas enriched wi~h ethanol is then cooled,
for example in a condenser/k~ock-out arangement, to
condense at least one organic molecular species,
e.g., ethanol, which is recovered in a concentrated
form. If the purge gas is the off-gases generated
by the fermentation process which can consist of
essentially c~rbon dioxide enriched with some
ethanol as desc~ibed above, additional ethanol vapor
can further be recovered in a concentrated form
which would be naturally lost and vented as a
byproduct from thefermentation p~ocess, and thereby
improve the overall efficiency of ethanol recovery
from the fermentation process. The concentration of
ethanol recovered from the process of this invention
is dependent on several factor~, prin~ipal amon~
which is the relative selectivity of the adsorbent
mass for ethanol. Ethanol is recovered from the
process of this invention in a concentraPed form,
for example, from about 180- to about 195-proo~. If
the purge gas enriched wi~h ethanol and some water
i~ dried before condensing, essentially 200-proof
ethanol product can be obtained. The 180- to
195-proof ethanol product ~an be further dehydrated
by azeotropic distillation or by t:he adsorptive heat
rise process described in Canadian Serial No.
401843.5, filed April 28, 1982 to obtain essentiallY
200-proof ethanol.
The proce~s o~ this invention is
illustrated by the following speciic embodiment
described wlth reference to Fig~ 1 of the drawings.
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58
18
~ith reference to the adsorption system
shown in Fig. 1, a fermentation beer containing
about 11 percent ethanol by volume is transferred
periodically from fermentation tanks 10 and 12 to
holding tank 14 though lines 16 and 18
respectively. The transfer of fermentation beer is
controlled by valves 20 and 22. The fermentation
beer is fed into the system at a rate of 5400
gallons per hour through line 24 and pump 26 and
thereafter through line 28 and heater 30 where the
temperature is raised to about 35 to 65C. The
fermentation beer enters the top of stripping column
34 from line 32. The strippiny column 34 is heated
to a temperature of 35C to 65C to enhance ethanol
stripping. Nitrogen, the stripping gas that will be
used in stripping ethanol from the fermentation
beer, enters the bottom side of stripping column 34
through line 36 essentially ethanol-free and at a
temperature to maintain the desired column
conditions. The nitrogen stripping gas is
introduced into the system through line 38. Line 38
also serves as the means to introduce make-up
nitrogen stripping gas into the operating system as
required~ The flow of stripping gas is dependent on
the column temperature and pressure and ranges from
100 to 1200 standard cubic feet per hour. An
optimization between compression and thermal energy
determines the exact column conditions. As the
fermentation beer flows downward in stripping column
34, the ethanol is stripped by the nitrogen and the
essentially ethanol-free fermentation beer is
removed from the bottom of stripping column 34
through line 40 and can be sent for recovery of
dissolved solids.
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19
The nitrogen stripping gas enriched with
ethanol is removed from the top of stripping column
34 through line 42 and heater 44 and thereafter
through line 46 into the top of adsorption column
48. The nitrogen stripping gas enriched with
ethanol can be heated by heater 44 to adjust tbe
relative satura~ion ~p/po) thereof so as to minimize
the coadsorption of water on the ethanol selective
adsorbent mass~ The adsorption column 48 contains
an adsorbent mass of 1~8 inch diameter extrudates of
silica-bonded F-silicalite adsorbent within the
scope of U.S. Patent 4,073,865 which, under the
process conditions utilized herein, is capable of
adsorbing ethanol from the ethanol enriched nitrogen
stripping gas. As the nitrogen stripping gas
enriched with ethanol passes downward through the
adsorption mass contained in adsorption column 48,
the ethanol is adsorbed by the silica-bonded
F-silicalite adsorbent and the nitrogen stripping
gas depleted of ethanol is removed from adsorption
column 48 through line 50 and recycled back to the
stripping column 34 through blower 52 and line 36.
The nitrogen stripping gas depleted of ethanol is
recirculated to stripping column 34 utilizing a
compressor to make up the pressure drop through the
nitrogen stripping gas loop. When the adsorbent
mass is saturated with ethanol and ethanol begins to
break through into the effluent through line 50, the
adsorption column 48 is temporarily removed from
service and regenerated. A freshly regenerated
adsorption column replaces the ethanol satura~ed
adsorption column to continue the adsorption of
~ ethanol from the nitrogen s~ripping ga~ enriched
with ethanol.
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~s~s~
Regeneration of the ethanol saturated
adsorption column can be accomplished by a
thermal-swing m~thod. The selection of a particular
regeneration method depends on the relative energy
S efficiency of each method and the selectivity and
capacity of the adsorbent mass for ethanol. The
thermal-swing regeneration method is accomplished
using nitrogen as a purge gas which is introduced
into the system through line 54. Line 54 also
serves as the means to introduce make-up purge gas
into the operating system as required. The purge
gas is preferably the same as the stripping gas.
The nitrogen purge gas is forced at a pressure of 40
psia by blower 56 through valve 58 and heater 62
where its temperature is raised to 175C. The
nitrogen purge gas is forced through valve 58 when
valve 60 is closed and through valve 60 when valve
58 is closed. Valves 58 and 60 control the flow of
nitrogen purqe gas to heater 62 and thereby control
the sequence of heating or cooling adsorption column
48. The heated nitrogen purge gas passes through
line 64 into the bottom of adsorption column 48 in a
flow direction countercurrent to the direction of
flow of the stripping gas enriched with ethanol
thereinto. The action of the nitrogen purge gas
stream is to ~lush the void space between the
adsorbent pellets and to desorb the ethanol from the
adsorbent mass. The adsorbent mass is heated to a
temperature of 50C to 150C above the adsorption
temperature by means oE the heated nitrogen purge
gas during regeneration of adsorption column 48.
When essentially all of the ethanol is desorbed, the
adsorbent mass in adsorption column 48 is cooled
back to the adsorption conditions previously
D 1325a
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s~
21
establishedO The nitrogen purge gas enriched wi~h
e~hanol is removed from adsorption column 48 through
line 66 and is passed through cooler 68 where the
temperature is lowered to 5C and ethanol is
condensed and collected in knock-out ~0 at 180~ to
195-proof. The 180- to 195-proof ethanol is removed
~rom the system through line 72 and the nitrogen
purge ~as depleted with ethanol is passed from
knock-out 70 through line 74 and recycled back to
blower 5~ where the essentially ethanol-free
nitrogen purge gas can be ei~her heated or unheated
before entering adsorption column 4A by controlling
valves 58 and 60 as described previously. The 180-
to 195-proof ethanol product can be dehydrated with
azeotropic distillation or by the adsorptive heat
rise process described in Canadian Serial No.
40184~.5, file~ Anril 2~, 1982 to -obt~in essentiallv
200-proof ethanol.
Alternatively, the nitrogen purge gas
enriched with ethanol is removed from adsorption
column 48 through line 66 and is partially cooled in
cooler 76 before passing directly into the top of
dehydration column 78 containing a bed of desiccant
material consisting of Type 3A zeolite to remove
essentially all o~ the remaining water which was
coadsorbed in the previou~ step. The dry nitrogen
purge gas enriched with ethanol is removed from
dehydration column 78 through line 80 and is passed
through cooler 82 wherein the temperature is lowered
to 0C and ethanol is condensed andl collected in
knock~out B4 to recover essen~ially 200-proo~
ethanol plus other volatile organics such as
aldehydes and fusel oils which were also ~tripped
from the fermentation beer and coadsorbed by the
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adsorbent mass. The essentially 200-proof ethanol
is removed from the system through line 86 and the
nitrogen purge gas depleted with ethanol is passed
from knock-out 84 and recycled back into the
operational system as described aboveO
The dehydration column 78 can also be
regenerated using the thermal swing method in a
manner slmilar to regeneration of adsorption column
48 using nitrogen purge gas. Heated nitrogen purge
gas is passed through the desiccant material bed of
dehydration column 7~ to desorb water which is
removed from the operational system by a condenser
and knock-out arrangement described previously in
regard to removing ethanol from the systemO When
the bed of desic~ant material is saturated with
water and water begins to break through into the
effluent through line 80, the dehydration column 78
is temporarily removed from service and
regenerated. A freshly regenerated dehydration
column replaces the water saturated dehydra~ion
column to continue the adsorption of water from the
nitrogen stripping gas enriched with ethanol.
Although this invention has been described
with respect to a number of details, it is not
intended that this invention should be limited
thereby. The examples which follow are intended
solely to illustrate the embodiments of this
invention which to date have been determined and are
not intended in any way to limit tbe scope of and
the intent of this invention.
As used in the examples appearing
hereinafter, the following designations, terms and
abbreviaions have the indicated meanings:
psig: pounds per s~uare inch gauge.
i
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i8
23
~: partial vapor pressure of ethanol
or water
po vapor pressure of pure ethanol or
pure water at a specified temperature.
relative saturation (p/po): refers to the
partial vapor pressure of ethanol or water in a
ratio relationship with the vapor pressure of pure
ethanol or pure water at a specified temperature.
loading~ refers to the amoun~ of ethanol
or water adsorbed into a specified amount of
adsorbent material and can be expressed by the
following formula:
Adsorbent ~oading = Wt- Adsorbate x lO0 ~ Wt%.
- Wt. Adsorbent
~xample 1
Into a laboratory saturator/bubbler device
was added a dilute aqueous mixture containing lO
percent by weight ethanol at ambient temperature and
20 psig. The saturator/bubbler device was attached
to an adsorption column constructed of l/2-inch
Schedule 40 stainless-steel plpe containing 65 grams
of alumina-bonded silicalite adsorbent within the
scope of U.S. Patent 4,061,724 and having a 16 x 40
mesh particle size. Nitrogen gas was used as the
stripping gas to vaporize ethanol from the dilute
a~ueous mixture. Nitrogen gas was buhbled into the
dilute aqueous mixture contained in the
saturator/bubbler device and effluent nitrogen gas
from the saturator/bubbler device was saturated with
both water and ethanol vapors. Gas chromatographic
analysis of this effluent nitrogen gas enriched with
water vapor and ethanol vapor showed about 0O6
percent by weight ethanol and about 0.8 percent by
weight water. The ef~luent nitrogen gas enriched
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i;25~il
2~
with water vapor and ethanol vapor was passed into
the adsorption column having a temperature of 125F
and at a rate of 3.6 standard cubic feet per hour.
The adsorption was allowed to continue until full
breakthrough occurred as indicated when the effluent
water and ethanol concentrations from the adsorption
column became equal to the corresponding
concentrations of water and ethanol in the enriched
nitrogen gas which entered the adsorption column.
The water and ethanol concentrations in the effluent
nitrogen gas from the adsorption column were also
determined by gas chromatographic analysis.
Following the adsorption step, the alumina-bonded
silicalite adsorbent contained in the adsorption
column was regenerated by the thermal swing method
at 200F using nitrogen gas which was passed through
the adsorption column at a rate of 3.7 standard
cubic feet per hour. The water and ethanol
concentrations in the nitrogen gas regeneration
effluent were determined by gas chromatographic
analysis.
Fig. 2 illustrates an adsorption step
breakthrough profile of ethanol and water
Goncentrations in the effluent from the adsorption
column at 125F as determined by gas chromatographic
analysis. As can be seen from Fig. 2, water i5 the
first component to break through into the adsorption
column effluent after about 1 hour o operation
followed by the more strongly adsorbed ethanol after
about 3 1/2 hours o operation. Essentially only
nitrogen gas is present in the adsorption column
effluent during the first hour of opera~ion.
Although the alumina-bonded silicalite adsorbent has
a higher capacity for ethanol, there is some water
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~5;~
.
adsorption capacity also. A small or nil water
adsorption capacity is desired to obtain higher
ethanol purity in the regeneration ~tep.
Fig. 3 illustrates a regeneration step
S profile of ethanol and water concentrations in the
nitrogen gas regeneration effluen~ as determined by
gas chromatographic analysis. As is readily
apparent from ~his profile, siqnificant ethanol
enrichment is obtained using nitrogen gas to purge
the adsorbed ethanol and some water from the
alumina-bonded silicalite adsorbent at a temperature
of 200F.
The temperature of the adsorption step was
varied and found to be an important process
parameSer due to the effect of temperature on the
relative saturation (p/ps) values of both water and
ethanol for the alumina-honded silicalite
adsorbent. As illustrated in Table A below, the
loading selectivity for ethanol increases with
increasing adsorption temperatures when utilizing
~he alumina-bonded silicalite adsorbent within the
scope of the U.S. Patent 4,061,724.
TABLE A
Ethanol/ Weight
Adsorption Water Percent
Temperature Ethanol Water Loading of Ethanol
(F~ Loading* Loading* Ratio ~Condensate)
, 75 7.05 ~.4~ l.g~ 61~2
lO0 6.19 3.3~ 1.88 65.3
125 5.35 2.13 2.51 71.5
150 4.7g 1.44 3.29 76.7
*The ethanol and water loading val~es are given in
grams per lO0 grams of adsorbent mass.
,
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.
,~ .
26
Table A illustrates that although ethanol and water
loading decrease at elevated temperatures, the rate
of decrease of ethanol loading is not as great as
the rate of decrease of water loading and thus the
loading selectivity for ethanol increases with
increasing adsorption temperatures when utilizing
the alumina-bonded silicalite adsorbent. The
ethanol concentration in the alumina-bonded
silicalite adsorbent is dependent on adsorption
temperature and was found to increase from 61.2 to
76.7 weight percent for the increasing temperature
range from 75F to 150F re~pectively~ This
variation in ethanol product purity i5 due to the
dependence of both water and ethanol adsorption
loadings on the relative saturation (p/po) value of
water and ethanol at the adsorption temperature.
Increasing the adsorption temperature increases the
vapor pressure (po) of liquid ethanol or liquid
water and thus decreases the relative saturation
(p/po) value of ethanol or water, thereby increasing
the loading selectivity of ethanol for the
alumina-bonded silicalite adsorbent. This is
illustrated in Fig. 4.
Fig. 4 illustrates a profile of the
dependency of water and ethanol adsorption loadings
on their relative saturation (p/po) values at
adsorption temperatures ranging from about 75F to
about 150F and using alumina-bonded silicalite
adsorbent. It is noted that the water loading show~
a critical ~knee" at a relative saturation (p/po)
value of about 0.95. When using alumina-bonded
silicalite adsorbent in the process of this
invention, it is important to stay to the left of
this ~knee" or obtaining high ethanol concentration
product... For example, before passing nitrogen
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2S8
stripping gas enriched with ethanol and water into
the adsorption columnt the enriched stripping gas
can be heated to adjust the relative saturation
(p/po) of ethanol and water so as to minimize the
coadsorption of water on the ethanol selective
adsorbent mass. The relative saturation (p/po~
values of water and ethanol and the extent or amount
of water and ethanol loadings are different for
various adsorbent materials. It is therefose
necessary to optimize the trade-off be~ween ethanol
selectivity and ethanol loading.
Example 2
Into a laboratory saturator/bubbler device
was added a dilute aqueous mixture containing lO
percent by weight ethanol at ambient temperature and
20 psig. The saturator/bubbler device was at~ached
to an adsorption column ~onstructed of l/2-inch
Schedule 40 stainless-steel pipe containing 57 grams
of silica-bonded F-silicalite adsorbent within the
scope of U.S. Patent 4/073~865. The silica-bonded
F-silicalite adsorbent was in the form of l/B-inch
diameter extrudates. Helium gas was used as the
stripping gas to vaporize ethanol from the dilute
aqueous mixture. Helium gas was bubbled into the
dilute aqueous mixture contained in the
saturator/bubbler device and effluent helium gas
from the saturator/bubbler device was saturated with
both water and ethanol vapors. Gas chromatographic
3~ analysis of this effluent helium gas enriched with
water vapor and ethanol vapor showed about 0.65 mole
percent ethanol and about 1.6 mole percent water.
The effluent helium gas enriched with water vapor
and ethanol vapor was passed into the adsorption
D-132S8
;
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2~
column at a temperature of 75~F and at a rate of 3.5
standard cubic feet per hour. The adsorption was
allowed to continue until full breakthrough occurred
as indicated when the effluent water and ethanol
concentrations from the adsorption column became
equal to the corresponding concentrations of water
and ethanol in the enriched helium gas which entered
the adsorption column. The water and ethanol
concentrations in the effluent helium gas from the
adsorption column were also determined by gas
chromatographic analysis.
In a manner similar to Example 1, the
silica-bonded F-silicalite adsorbent contained in
the adsorption column can then be regenerated by the
thermal-swing method at 200F using helium gas which
is passed through the adsorption column at a rate of
about 3.6 standard cubic feet per hour. The water
and ethanol concentrations in the helium gas
regeneration effluent can be determined by gas
chromatographic analysis.
Fig. ~ illustrates an adsorption step
breakthrough profile of ethanol and water
concentrations in the effluent from the adsorption
column at 75F as determined by gas chromatographic
analysis. As can be seen from Fig. 5, it is
apparent that silica-bonded F-silicalite adsorbent
has very little water adsorption capacity as
evidenced by~the nearly instantaneous water
breakthrough. The relative adsorption capacity of
ethanol is much greater using silica-bonded
F-silicalite adsorbent rather than alumina-bonded
silicalite adsorbent in Example l. It is noted that
the relative satura~ion ~p/po) value of water is
nearly equal to unity at an adsorption temperature
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of 75F. However, even at a relative saturation
lP/P) value near unity for water, high ethanol
concentrations of up to 95 weight percent are
attainable using this silica-bonded F-silicalite
adsorbent. It is not necessary to heat the helium
stripping gas enriched with ethanol and water prior
to entering the adsorption column so as to adjust
the relative saturation ~p/po) of ethanol and water
because essentially no coadsorption of water occurs
on the silica-bonded F-silicalite adsorbent.
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