Molecular sieve abstract
Molecularly adsorbed volatile liquid compounds are recovered from
molecular sieve adsorbent columns by directionally applying microwave
energy to the bed of the adsorbent to produce a mixed liquid-gas
effluent. The gas portion of the effluent generates pressure within
the bed to promote the discharge of the effluent from the column
bottoms. Preferably the discharged liquid-gas effluent is collected
in two to three separate fractions, the second or intermediate fraction
having a substantially higher concentration of the desorbed compound
than the first or third fractions. The desorption does not need
to be assisted by passing a carrier gas through the bed or by applying
reduced pressure to the outlet from the bed.
Molecular sieve claims
We claim:
1. The method of recovering a volatile liquid compound molecularly
adsorbed within porous granules of a molecular sieve adsorbent from
a dilute liquid solution thereof, said granules having a relatively
low dielectric loss compared to that of the adsorbed liquid and
being arranged in a bed contained in a column providing access port
means communicating respectively with the upper and lower portions
of the bed, said bed containing residual portions of the dilute
liquid solution, comprising desorbing said liquid compound with
the upper access port closed and the lower access port open so that
gas pressure can be maintained in the bed upper portion and desorbed
effluent can exit through the lower port, directionally applying
microwave energy so as to heat the adsorbed liquid in the bed upper
portions and to successive portions thereof, said bed at the start
of said microwave application being at a temperature at which the
adsorbed compound is in a liquid state, the amount of microwave
energy applied to said bed upper portion and said successive portions
thereof being sufficient to volatilize only part of the said desorbed
compound, expelling the desorbed compound from said granules in
a mixed liquid-gas form to provide an effluent, the gas portion
creating a pressure within said bed which pushes the expelled liquid
portion toward the lower port, and recovering the liquid-gas effluent
by removal through a lower port.
2. The method of claim 1 in which first and second portions of
the removed liquid-gas effluent are separately collected, the second
portion having a substantially higher concentration of the desorbed
compound than said first portion.
3. The method of claim 1 in which first, second, and third portions
of the removed liquid-gas effluent are separately collected, the
second portion having a substantially higher concentration of the
desorbed compound than the first and third portions.
4. The method of recovering a volatile liquid compound molecularly
adsorbed within porous granules of a molecular sieve adsorbent from
a dilute liquid solution thereof, said granules having a relatively
low dielectric loss compared to that of the adsorbed liquid and
being arranged in a bed contained in a column providing head space
above and collection space below the bed, upper access port means
communicating with said head space, and lower access port means
communicating with said collection space, said bed containing residual
portions of said dilute liquid solution, comprising, with the upper
port means closed and the lower port means open, directionally applying
microwave energy to the bed upper portion and to successive portions
thereof to selectively heat the adsorbed liquid compound within
said granules for desorption thereof, the amount of applied microwave
energy being sufficient to volatilize only part of the adsorbed
compound within said granules to expell a liquid-gas effluent, said
bed at the start of said microwave application being at a temperature
at which the adsorbed compound is in a liquid state, the gas portion
of the effluent creating a pressure in the bed upper portion pushing
the effluent toward the bed lower portion, removing the liquid-gas
effluent through a lower port, and separately collecting first and
second portions of the removed liquid-gas effluent, said second
portion having a substantially higher concentration of the desorbed
compound than said first portion.
5. The method of claim 4 in which first, second, and third portions
of the removed liquid gas effluent are separately collected, said
second portion having a substantially higher concentration of the
desorbed compound than said first and third portions.
6. The method of claim 4 in which said molecular sieve adsorbent
is an adsorbent capable of adsorbing ethanol and said adsorbed volatile
compound is ethanol.
7. The method of claim 4 in which said molecular sieve adsorbent
is capable of adsorbing water and said adsorbed volatile compound
is water.
8. The method of claim 4 in which first, second, and third portions
of the removed effluent are separately collected, such second portion
having a substantially higher concentration of the desorbed compound
than said first and third portions.
9. The method of claim 4 in which said molecular sieve adsorbent
is a silica polymorph.
10. The method of claim 4 in which said molecular sieve adsorbent
is zeolite.
11. The method of claim 4 in which said molecular sieve adsorbent
is a silica polymorph adsorbent capable of adsorbing ethanol and
said adsorbed volatile compound is ethanol which has been adsorbed
from a water solution thereof.
12. The method of claim 4 in which said molecular sieve adsorbent
is a zeolite adsorbent capable of adsorbing water and said adsorbed
volatile compound is water.
Molecular sieve description
BACKGROUND AND PRIOR ART
U.S. Pat. No. 4277635 issued July 7 1981 describes a process
for recovering and concentrating ethanol from aqueous solutions
containing the ethanol at a lower concentration. For example, the
method can be employed, using single or multiple concentration stages,
as required, to produce a concentrated ethanol product of 80-95%
ethanol, or greater, from an aqueous fermentation beer containing
from 1-15% ethanol. The aqueous ethanol feed to be concentrated
is passed through a bed of a crystalline silica polymorph capable
of selectively adsorbing ethanol from aqueous solutions thereof.
Silicalite is indicated as a preferred adsorbent for this purpose.
The ethanol is selectively adsorbed in the molecular pore spaces
of the porous granules containing the molecular sieve adsorbent.
At the conclusion of the adsorption cycle, the disclosure of U.S.
Pat. No. 4277635 indicates that the bed should be drained to remove
excess feed which will be present in the void spaces between the
adsorbent granules as well as in the head space above the granular
bed. After drainage of the excess liquid, desorption of the ethanol
is obtained by passing a heated inert gas, such as carbon dioxide,
through the bed. As the passage of the heated gas continues, the
granules are heated and the ethanol is evolved as a gas, which is
carried out with the carbon dioxide. The ethanol is recovered from
the effluent gas by condensation to a liquid.
The ethanol desorption procedure described above has been found
to be relatively inefficient. The molecularly adsorbed ethanol is
contained within the pore spaces of the adsorbent granules, and
the granules are relatively poor conductors of heat. The heat from
the carrier gas, or other auxillary heating means if one is used,
therefore takes a considerable time to heat the interior portions
of the granules to temperatures at which the adsorbed ethanol is
vaporized. Further, the rate at which the ethanol is evolved from
the granules depends on the rate of diffusion through the capillary
passages of the granules, which is a rate limited process. A related
disadvantage of the desorption procedure using a heated carrier
gas is that the desorption is incomplete. The ethanol remaining
molecularly adsorbed within the granules therefore reduces the capacity
of the granules for the next adsorption cycle. This means in practice
that a larger amount of adsorbent must be used than the theoretical
minimum based on the adsorption capacity of the granules, and this
increases the cost of the recovery process. Also it has been found
that the carrier gas tends to remain within the pore spaces of the
granules, being difficult to remove therefrom, and that this residual
gas within the porous granules also reduces the capacity of the
granules on the next adsorption cycle.
SUMMARY OF INVENTION
This invention relates to the recovery of volatile liquid compounds
molecularly adsorbed within porous granules of a molecular sieve
adsorbent, the granules being arranged in a vertically-extending
bed contained in a column providing access port means communicating
respectively with the upper and lower portions of the bed. During
the experimental work which led to the present invention, it was
discovered that microwave heating of the absorbent bed adsorbed
volatile compound, and make it possible to produce a final product
of very high concentration. Because of the efficient use of the
adsorbent beds in the method of this invention, smaller size columns
and beds of lower construction and maintenance cost can be utilized
to produce a product of a desired high concentration.
THE DRAWINGS
The method of this invention is illustrated in preferred embodiments
in the accompanying drawings, in which:
FIG. 1 is a cross-sectional view of an apparatus which may be used
in practicing the method of this invention, including a molecular
sieve column having walls forming a wave guide, a microwave generator
for applying microwave energy to the top of the adsorbent bed within
the column, and valve-controlled inlets and outlets;
FIG. 2 is a diagrammatic cross-sectional view of a larger apparatus
which may be used in practicing the method of the invention, including
a large vertically-extending column containing the bed of molecular
sieve adsorbent, multiple vertically-spaced microwave generators
and wave guide applicators, and valve-controlled access ports;
FIG. 3 is a block diagram illustrating a mode of operation of the
apparatus of FIG. 1;
FIG. 4 is a curve representing the ethanol concentration of an
effluent obtained in the recovery of ethanol from a silicalite column
after passage of a dilute fermentation beer through the column;
FIG. 5 is a diagramatic representation of the apparatus of FIG.
1 illustrating the beginning of a desorption cycle;
FIG. 6 shows a typical curve of a desorption cycle, effluent concentration
being plotted against desorption time;
FIG. 7 is a diagramatic illustration similar to FIG. 5 representing
the middle of the first desorption cycle in which a product of intermediate
concentration is obtained; and
FIG. 8 is a curve showing effluent concentration plotted against
desorption time for a second desorption cycle to produce a highly
concentrated product.
DETAILED DESCRIPTION
The desorption method of this invention can be used with most molecular
sieve adsorbents and with most liquids which are capable of molecularly
adsorbing. The preferred molecular sieve adsorbents are those having
a low dielectric loss compared to that of the adsorbed liquid. Two
important classes of such adsorbents are: (1) the hydrophobic crystalline
silica polymorph adsorbents, and (2) the hydrophilic crystalline
zeolite molecular sieve adsorbents. Silica polymorph adsorbents
are described in U.S. Pat. Nos. 4061724 and 4073965. A commercial
form of this kind of adsorbent is known by the generic name of "silicalite".
Silicalite adsorbents can be obtained from the Linde Division of
Union Carbide Corporation, Tarrytown, N.Y. They are produced as
described in U.S. Pat. No. 4061724. More recently, silicalite-type
adsorbents have been proposed which are silica analogues of the
silica-rich aluminosilicate zeolites. See Flanigen et al, "Silicalite
a New Hydrophobic Crystalline Silica Molecular Sieve", Nature,
271 512-516 (1978). The zeolite-type molecular sieve adsorbents
are crystalline aluminosilicate compounds. They are described in
U.S. Pat. Nos. 3702886 and 3709979 and also in Lee, H., "Applied
Aspects of Zeolite Adsorbents", in Molecular Sieves, 311-317
3rd Int. Molecular Sieve Conf., Zurich, Switzerland (September,
1973).
For use as adsorbents, such as in column adsorption processes,
the crystalline molecular sieve adsorbents are prepared in the form
of granules or pellets. Suitable binders may be used to hold together
the particles of the crystalline adsorbents. The resulting granular
adsorbents are highly porous, providing a multiplicity of capillary
passages which connect with the adsorption pore spaces of the silicalite
or other molecular sieve adsorbent. These granular molecular sieve
adsorbents have relatively low heat conductivity with respect to
the transfer of heat from the surfaces of the granules to the interiors
thereof. Further, the preferred class of molecular sieve adsorbents
and the granules formed therefrom are relatively poor absorbers
of microwave energy, that is, their dielectric loss factors are
low and consequently the power absorbed from applied microwave energy
is low. A liquid compound adsorbed within the molecular sieve granules
can thereby be heated sufficiently to vaporize and expell gas and
liquid while the granules remain at a much lower temperature. For
example, in connection with the development of this invention, it
has been estimated that the selective microwave heating of adsorbed
ethanol on silicalite is such that the ethanol is heated at a rate
over 3000 times greater than the silicalite. Similarly, water adsorbed
on a zeolite adsorbent will be heated at a rate several thousand
times faster than the zeolite. In general, therefore, the heating
of adsorbed liquids within molecular sieve granules will be greater
by several orders of magnitude than the adsorbent granules, the
heating of which is limited by their low capacity for absorbing
microwave energy and by the low rate of heat conduction through
the granules.
From what has already been said, it should be apparent that the
desorption method of this invention can be applied to a broad class
of volatile liquids adsorbed within molecular sieve adsorbent granules.
The molecular sieve compound forming the granules will be selected
in relation to the kind of liquid to be adsorbed, and with respect
to the relative dielectric loss factors, as discussed above. For
adsorption of small molecular size organic compounds from water,
such as ethanol from a fermentation beer, a silicalite-type adsorbent
can be used, while for adsorption of water from admixture with an
organic solvent, such as concentrated aqueous ethanol, a zeolite-type
adsorbent can be used. The desorption method of this invention is
therefore believed to be particularly useful in preparing highly
concentrated ethanol. A column of silicalite adsorbent can be used,
as described in U.S. Pat. No. 4277635 to prepare a concentrate
containing a small amount of water, such as 5% or less water. The
ethanol can then be further dehydrated in a zeolite column to prepare
the final substantially water-free ethanol. In commercial applications,
adsorption can be performed in single or multiple stages. For example,
the ethanol from the fermentation beer can be initially concentrated
to 50-60% ethanol, and thereafter concentrated in a second stage
also using a silicalite adsorbent column to a concentration of 80-95%.
Similarly, the further dehydration using a zeolite molecular sieve
column can be carried out in single or multiple stages with progressive
decrease in the water content of the ethanol.
In general, therefore, the method of this invention can be used
for desorption of a volatile liquid compound molecularly adsorbed
within porous granules of a molecular sieve adsorbent. The granules
will be in a vertically-extending bed enclosed by a column, having
access ports in upper and lower portions thereof. The column will
have at least one access port in the upper portion thereof above
the top of the bed of adsorbent communicating with the head space
above the bed; and at least one access port in the bottom thereof
communicating with the collector space beneath the bed of adsorbent.
A screen or sieve plate is used to support the adsorbent bed while
permitting liquids or gases to pass therethrough. The columns may,
be formed of suitable corrosion-resistant metals such as stainless
steel. For the purpose of the present invention, a metal column
is desireable which will interiorly reflect the microwave energy
applied to the bed within the column. In one suitable apparatus
arrangement, as illustrated in FIG. 1 the column itself comprises
a wave guide for the microwave energy being an extension of a wave
guide connected to a microwave generator. Alternatively, as illustrated
in FIG. 2 microwave energy can be introduced through ports in the
side of the column, suitable microwave generators and wave guides
being connected to these ports, which can be sealed with a suitable
plastic such as Teflon, which allows microwave energy to pass through
with negligible absorption. If desired, a cylindrical wave guide
can be extended downwardly into the central portion of the adsorbent
bed. The cylindrical wave guide can be provided with a series of
slots for release of the microwave energy, the slots being sealed
by a suitable plastic such as Teflon.
As shown in FIG. 1 the molecular sieve column has a rectangular
cross-section, and is designed to form a wave guide. For example,
the column may be a section of a WR-340 wave guide. The column-wave
guide may be formed of stainless steel or other suitable metals
such as brass or aluminum. As shown, the bottom of the column is
closed by a downwardly inclined plate, which forms an underdrain
beneath a support screen. The inclination of the bottom assists
in collecting the liquid or liquid-gas mixture evolved by the desorption,
and also tends to reduce the reflection of the microwave energy
reaching the bottom wall of the column. The top of the column is
closed by a Teflon seal, which is in the form of a horizontally-extending
gasket sheet, which provides a gas and liquid seal at the top of
the column above the bed of molecular sieve adsorbent. Therefore,
there is an open head space above the top of the bed. Above the
Teflon seal, the wave guide extends upwardly and connects with a
microwave generator. The column and the extension will therefore
together provide a continuous wave guide, such as a wave guide of
the required design and cross-section corresponding to a standard
WR-340 wave guide.
The apparatus of FIG. 1 includes a bottom inlet controlled by a
valve V1 for introduction of the liquid for adsorption. In the adsorption
stage, a feed liquid, such as dilute aqueous ethanol, will pass
upwardly through the bed of adsorbent, such as a silicalite bed,
and will pass outwardly through the access port communicating with
the outlet conduit controlled by valve V2. The conduit connecting
with the underdrain at the bottom of the column is an extension
controlled by the valve V3 for removal of the effluent liquid and/or
gas during desorption. With the apparatus shown in FIG. 1 during
the adsorption stage, valves V1 and V2 will be open and valves V3
and V4 closed. The adsorption is preferably carried out in an upflow
mode, the liquid for adsorption entering through valve V1 and exiting
through valve V2. At the conclusion of the adsorption, the conduit
connecting through valve V3 can be used as a drain conduit, the
excess liquid for adsorption being drained from the bed as completely
as possible by gravity draining.
The desorption mode of operation of the apparatus of FIG. 1 is
illustrated in general in FIG. 3. The drained bed of molecular sieve
adsorbent will contain the volatile liquid compound in a molecularly
adsorbed form within the granules of the bed. The microwave generator
creates microwave energy which is directed downwardly onto the top
of the molecular sieve bed. The granules in the upper portion of
the bed are subjected to the microwave heating which partially vaporizes
the adsorbed liquid (viz. ethanol with a silicalite adsorbent or
water with a zeolite adsorbent). The volatilized liquid creates
gas pressure within the granules which expells gas and liquid from
the granules, and also creates gas pressure within the head space
above the bed. The expelled liquid therefore flows downwardly through
the bed into the underdrain, and a mixture of gas and liquid is
removed through the valve V3. As the zone of microwave heating moves
downwardly through the bed, the desorption process continues in
the same manner until the adsorbed liquid has been removed from
the entire bed. In this mode of operation, the bed at the start
of the desorption will be at a temperature at which the adsorbed
compound when separated from the granules would be entirely in a
liquid state. The amount of microwave energy applied to the bed
is sufficient to only partially vaporize the adsorbed compound.
The effluent removed from the bed will therefore comprise a liquid-gas
mixture. Only part of the recovered compound will therefore need
to be condensed to obtain the product in liquid form.
As indicated in FIG. 3 the molecular sieve column may have been
loaded using a liquid feed, or a recycled liquid, or a first stage
concentrate. It is the adsorbed volatile compound from these liquids
which is desorbed to form the liquid-gas effluent. This effluent
is passed to a condenser to obtain a recycled liquid, an intermediate
concentrate, or a final product. The collection of separate fractions
of the effluent will be further described below in relation to FIGS.
4-8. Next, however, it is desired to make reference to the apparatus
illustrated in FIG. 2 which represents an apparatus designed for
use with larger columns.
The microwave energy may be applied in various other ways which
also provide directional modes. One alternate design is shown in
FIG. 2. In another configuration, a cylindrical wave guide is extended
downwardly into the central portion of the adsorbent bed. The guide
can be provided with a series of slots sealed by Teflon for release
of the microwave energy in radial directions.
Referring now to the apparatus of FIG. 2 it consists of a large
vertically-extending column of circular cross-section, which may
be formed of stainless steel or other metal reflecting microwaves.
Within the column there is provided a vertically-extending bed of
the molecular sieve adsorbent. The bottom of the bed is supported
by a perforated plate above a conical space which functions as a
distributor for the introduction of liquid through the lower valve-controlled
access port, or as a collector for the effluent removed from the
bottom of the column through the same access port. The top of the
bed terminates below the top of the column to provide an open head
space which communicates with a valve-controlled access port. When
the adsorption is carried out in an upflow mode, the feed liquid
will enter through the lower access port and exit through the upper
access port. For the desorption cycle, the upper access port will
be closed and the lower access port open.
In the apparatus of FIG. 2 multiple independent microwave sources
are employed. As shown, these microwave sources are arranged in
vertically-spaced relation along opposite sides of the column. Each
source consists of an apparatus including a microwave generator
(MG), a wave guide (WG), and a tuner (T) interposed in wave guide.
The wave guides (WG) terminate in connections to the column interior
including openings or slots covered by Teflon seals to prevent escape
of liquid or gas while permitting microwaves to pass into the column
for irradiation of the adsorbent granules. The tuners (T) can be
used to maximize power transferred to the interior of the column
through the wave guides (WG). With the arrangement shown a cyclic
mode of operation can be used. At the beginning of the cycle, the
upper pair of sources (A) can be activated, applying the microwave
energy to the upper portion of the bed. After the upper portion
of the bed has been heated sufficiently to form the desorbed effluent,
the next lower pair of microwave sources (B) can be activated and
the upper sources (A) deactivated. The desorption will thereby proceed
progressively from the top toward the bottom of the column. Depending
on the height of the column and the bed, additional sources can
be provided. In the final stage of the desorption, the lowermost
source (C) will be activated with the other sources deactivated
to complete the desorption.
The operation of the apparatus of FIG. 2 in the desorption cycle
is therefore similar to the mode of operation described with respect
to the apparatus of FIG. 1. The microwave energy is directionally
applied so as to heat the adsorbed liquid in the upper portion of
the bed and to successive portions thereof. The bed at the start
of the microwave application is at a temperature at which the desorbed
compound would be in a liquid state. The amount of microwave energy
applied to the bed upper portion and the successive portions thereof
is sufficient to only partly volatilize the desorbed compound. This
permits the use of much less microwave energy than would be required
to fully convert the adsorbed compound to a gas. The effluent expelled
from the granules will be in a mixed liquid-gas form. The gas portion
of the effluent creates a pressure within the bed above the outlet
pressure (an "over pressure"), which pushes the expelled
liquid portion toward the lower access port. A pressure differential
is created from the head space to the outlet port. In embodiments
where vacuum is not applied to the outlet, the pressure in the head
space will be substantially above atmospheric. The liquid-gas effluent
is recovered by removal through this port.
OPERATIONAL EXAMPLES
FIG. 4 represents the kind of effluent that can be expected in
the first stage of desorption of ethanol when a dilute fermentation
beer has been applied to a silica polymorph adsorbent such as silicalite.
Even though the excess beer is drained from the column bed and,
if desired, the beer removal procedure of U.S. Pat. No. 4277635
is employed, there will still be residual beer adsorbed within the
column bed at the start of the ethanol desorption. The mixed liquid-gas
effluent may initially be evolved at a concentration corresponding
to that of the dilute beer, such as, 8-10% ethanol. As indicated
by the curve in FIG. 4 as the desorption continues, it will increase
sharply to a relatively high concentration level for an intermediate
period, and then will decline more gradually to a lower concentration.
With reference to the graph of FIG. 4 a first fraction F1 can be
collected having a concentration of from 8 to 50% ethanol, a second
fraction F2 with an ethanol concentration of 50 to 60%, and a third
fraction F3 having an ethanol concentration of from 10 to 50%. It
will be understood that these figures are not intended to be limiting
or in any way critical but are only given for purpose of illustration.
However, the curve of FIG. 2 is based on an actual experiment. The
fermentation beer had an ethanol concentration of about 8%, and
the intermediate produce obtained (F2) had a concentration in the
range of 50-60%. The grams of effluent recovered per minute of desorption
time are indicated on the lower axis of the graph. The apparatus
employed was similar to that shown in FIG. 1 the microwaves being
applied to the top of the bed and progressively heating the bed
in a downward direction. As can be seen from FIG. 4 the recovery
of the effluent was very rapid, collection of all three fractions
(F1 F2 and F3) being completed in 30 minutes.
FIGS. 5 to 8 represent further more generalized examples of the
desorption procedure just described with reference to FIG. 4. The
apparatus employed is similar to that of FIG. 1 as indicated by
the diagramatic illustrations of FIGS. 5 and 7. Looking first at
FIG. 5 the beginning of the first desorption cycle is illustrated.
The lower feed inlet valve and upper liquid outlet valve are closed.
The microwave energy is directed onto the top of the bed to provide
a heated zone within the uppermost portion of the bed. The heating
is controlled to produce a mixed liquid-gas effluent. The evolved
gas generates pressure within the upper portion of the bed and within
the head space. This gas pressure urges the liquid-gas effluent
downwardly through the bed into the underdrain for removal therefrom
through the open effluent valve. The removed effluent is passed
to a condenser. During the first portion of the desorption cycle,
the condensed effluent will be recycled to a first adsorption stage
because of its low ethanol concentration. This recycle may correspond
with the fraction F1 illustrated by the curve of FIG. 6 for the
first desorption cycle.
FIG. 7 illustrates the middle of the first desorption cycle in
which an intermediate product is produced. The arrangement of the
apparatus is the same as in FIG. 5. At this time, the heated zone
of the adsorbent bed in which the desorption is occurring has progressed
to an intermediate level in the bed, as shown in FIG. 7. The liquid-gas
effluent removed by the open effluent valve is for recovery of an
intermediate concentrate. With reference to FIG. 6 this fraction
may correspond to the fraction F2 which as indicated, would have
a concentration of the desired product of 50-60%. If desired, the
desorption can continue at a further recycle fraction (F3) collected.
The intermediate concentrate, such as the condensed fraction F2
is then subjected to another adsorption-desorption cycle, using
apparatus like that of FIG. 1.
It will be understood that the bed of adsorbent has been prepared
for the next adsorption cycle by completion of desorption so that
the bed has adequate adsorption capacity. After the completion of
the adsorption and the draining of the bed, or other special procedures
to remove dilute feed from the bed, desorption is carried out in
the same manner as described with reference to FIGS. 5 and 7 that
is, the microwave energy is applied to the top of the bed forming
a heated zone in which the desorption occurs, the zone moving progressively
down through the bed toward the bottom thereof. As shown in FIG.
8 a first fraction F1 can be collected having a concentration similar
to that of the intermediate product. This fraction can then be combined
with the fraction F2 of FIG. 6 to produce a combined liquid for
second stage adsorption and desorption. The intermediate fraction
F2 as indicated in FIG. 8 will contain the desired product in
a high concentration, such as 80-90%. If desired, a further fraction
F3 may be collected, which can be recycled with fresh fermentation
beer in the first stage adsorption.
From an inspection of the graphs of FIGS. 6 and 8 it will be apparent
that the fraction F1 is collected over the time from T.sub.0 to
T.sub.1 the fraction F2 is collected from the time T.sub.1 to T.sub.2
while the fraction F3 is collected during the time T.sub.2 to T.sub.3.
The specific times are not critical, but all fractions can be evolved
and collected in a short period of time, such as a total time of
30 to 60 minutes from T.sub.0 to T.sub.3. The separate fractions
are collected in relation to the desired concentrations of the product
fractions F2 and the recycle fractions F1 and F3. |