Note: Descriptions are shown in the official language in which they were submitted.
6 ~3~
"PROCESS FOR SEPARATING MONOTERPENES"
-
FIELD OF THE INVENTION
The field of art to which this invention pertains is the
solid bed adsorptive separatîon of terpenoids. More specifically,
the invention relates to a process for separating monoterpene alcohols
from a feed mixture comprising monoterpene alcohols, and monoterpene
S aldehydes and/or ketones by adsorptive separation using crystalline
aluminosilicate adsorbents.
BACKGROUND OF THE INVENTION
The use of crystalline aluminosilicates to perform hydro-
carbon separation is well known in the separation art. Examples of
such separations are disclosed ln U.S. Patents 2,985,589 and 3,201,491
wherein a type A zeolite is used to separate normal paraffins from
branched chain paraffins. the use of faujasites to separate olefinic
hydrocarbons from paraffinic hydrocarbons is descr~bed in U.S. Patents
3,265,750 and 3,510,423. These adsorbents allow a separation based on
the physical size differences in the molecules by allowing the smaller
or normal hydrocarbons to be passed into the cavities within the zeo-
litic adsorbent, while excluding the larger or branched chain molecules.
In addit~on to be;ng used in processes for separating hydro-
carbon types, adsorbents comprising type X or Y zeolites have also
been employed in processes to separate individual hydrocarbon isomers.
In the processes described, for example, in U.S. Patents 3,626,020 to
Neuzil, 3,663,638 to Neuzil, 3,665,046 to deRosset, 3,S68,266 to Chen
et al., 3,686,343 to~Bearden Jr. et al., 3,700,744 to Berger et al.,
3,734,974 to Neuzil, 3,894,109 to Rosback, 3,997,620 to Neuzil and
B426,274 to Hedge, ~articular zeoq~ ~ Yadso0~bel~76a're used to separate
the para~isomer of bialkyl substituted monocyclic aromatics from the
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,
., .
~;Z 6~73
other isomers, particularly paraxylene from other xylene isomers.
Turning specifically to the class of compounds of this
invention, terpenoids include the saturated or partially saturated
isomers of terpenes as well as derivatives such as alcohols, ketones,
. aldehydes, esters, etc. Terpenes are chiefly derived from essential
oils. The oxygenated terpenoid derivatives are particularly important
flavor and perfume materials. Most commonly used terpenes are
separated by fractional distillation. Howevers terpene compounds
are heat sensitive, th~s fractionation often requires energy inten-
sive vacuum distillation techniques to avoid degradation of compo-
nents.
Apart from fractionation, adsorptive separation techniques
have been used to isolate individual terpenes from essential oils
and other terpene containing feedstocks. U.S. Patent 2,760,993
teaches the use of activated clay, magnesia, charcoal and alumina
in conjunction with polar solvents to separate menthol from mint
oils. Preparation of a terpeneless essential oil by removal of
terpenes through distillation and adsorption onto neutral alumina
is taught in U.S. Patent 3,867,262.
Applicant has found that monoterpenoids can be separated
by adsorptive separation techniques using an X-type zeolite.
SUMMARY OF THE INVENTION
_
In brief summary the invention is in one embodiment a
process for separating an alcohol of a monoterpene from a feed
mixture containing alcohols, aldehydes and/or ketones of a mono-
terpene. The process comprises contacting, in liquid phase at
adsorption conditions, the feed with an X-type zeolite adsorbent
having sodium or potassium cations at cation exchange sites to
selectively adsorb the alcohol component of the feed mixture to
the substantial exclusion of the aldehyde and ketone components.
The unadsorbed portion of the feed or raffinate component is
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:~L2~13~ 73
removed from the adsorbent which is then contacted wi-th a desorbent
material at desorption conditions, thereby recovering the monoterpene
alcohol or extract component from the adsorben-t. In another embodiment
the alcohol containing adsorben-t is contacted with a hydrocarbon or
oxygenated hydrocarbon desorbent matérial.
Other embodiments o-f the present ;nvention encornpass
specific feed mixtures, desorbents, flow schemes and operating condi-
tions, all of which are hereinafter disclosed in the fol10wing dis-
cussion of each of the facets of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure~ 1 thru 3 are the chromatographic tracings
obtained from the pulse te3t~ of Examples I thru III,
respectively.
,.
UESCRI~TION OF THE INVENTION
lS Suitable feed mixtures are mixtures of:one or more mono-
terpenoid alcohols and it$ corresponding aldehyde or ketone. The term
terpenoids refers generally to the class of saturated, partial'ly saturated
or derivitized~terpenes. In turn, terpenes found in most living plants
are usually considered derivatives of isoprene. In most terpene compounds,
the isoprene units are arranged in head to tail fashion. Classification
of terpenes is done on the basis of isoprene units and degree or lack of
ring structure. Monoterpenes contain two isoprene units arranged in
either an open chain or ring structure.
The corresponding terpenoids of more well known monoterpenes
include c;tronellal, citranellol, geranial, geraniol, hydroxycitronellal,
and hydroxycitronellol. These chemicals have desirable fragrance prop-
erties and are most commonly used in perfumery.' While many of these
` chemicals are available in natural form, they may also be derived syn-
thetically. Derivation of perfume chemicals u5ually begins with beta-
pinene found in crude sulfate turp~ntine. Thermal'rearrangement ofbeta-pinene yields myracene whi'ch is an imporbant intermediate for
many fragrance compounds. Hydrochlorination of'myracene under appropriate
conditions followed by heating with sodium acetate will yield geraniol
and nerol acetates which after saponification and distillation will yield
,~ .
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;73
geraniol and nerol. Geraniol and nerol may be rearranged over a
copper catalyst to provide citronellol and, with further hydration,
hydroxycitronellol.
Aldehyde or ketone and alcohol mixtures of a monoterpene
are often obtained in the course of producing one component from
another. For instance, citronellal, which can be artificially
derived or obtained from the rectification of citronella oil, is
often reduced to produce citronellol thereby yielding a mixture
of the two. Another example is the synthesis of citral by the
oxidative dehydrogenation of the geometric isomers geraniol and
nerol to yield cis- and trans-citrals (neral and geranial) in mix-
ture with geraniol and nerol.
The aforementioned examples of monoterpenoid mixtures con-
taining aldehydes and alcohols is by no means exhaustive~ but only
serves to shaw possible sources of feed mixtures to which this
invention may be applied.
This invention provides an adsorptive separation method
for separating such alcohol/aldehyde and alcohol/ketone mixtures of
monoterpenes regardless of source. Thus suitable feed mixtures will
contain one or more cyclic or acyclic monoterpenoid alcohols and its
corresponding aldehyde and/or ketone. Hence a monoterpenoid may
contain a single alcohol and aldehyde combination such as hydroxy-
citronellol and hydroxycitronellal or mixtures of corresponding
monoterpenoids, for example, nerol-neral and geraniol-geranial.
The operability of the process disclosed herein incorporates
the discovery that alcohol monoterpenoids are preferentially adsorbed
from alcohol and monoterpenoid aldehyde and/or alcohol feed mixtures
by contact with an X faujasite having suitable cations. It was
further discovered that sodium or potassium cations provide the X
zeolite with the necessary adsorptive properties.
While the selectivity properties of an adsorbent are essen-
tial to the success of an adsorptive separation process, additional
properties are recognized as highly desirable, if not absolutely
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~Z~73
necessary, to the successful operation of a selective adsorption
process. In summary, these characteristics are: adsorptive capacity
for some volume of an extract component per volume of adsorbent; the
selective adsorption of an extract component with respect to a raf-
.~ ~;nate component and the desorben~ material; and, sufficiently fas~
rates of adsorption and desorption of the extract components to and
from the adsorbent.
Capacity of the adsorbent for ~dsorbing a specific volume
of one or more extract components largely determines the efficiency
of a process; the higher the adsorbent's capacity for an extract
component the better is the adsorbent. Increased capacity of a
particular adsor~ent makes it possible to reduce the amount of
adsorbent needed to separate the extract componen~ contained in a
particular quantity of feed mix~ure. A reduction in the amount sf
adsorbent required for a specific adsorptiue separation reduces the
cost of the separation process.
The second necessary adsorbent characteristic is thP ability
of the adsorbent ~to separate components of the feed; or, in other
words, that the adsorbent possesses adsorptive selectivity, (B) for
one component as compared to another component. Selectivity (B) is
expressed not only for one feed component as compared to another but
also between a feed mixture component and a desorbent material. The
selectivity, (B), as used throughout this specification is defined as
the ratio of the two components of the adsorbed phase over the ratio
of the same two components in the unadsorbed phase at equilibrium
conditions.
Relative selectivity is shown as Equation 1 below:
Equation 1
[vol. percent C/vol. percent D]
Selectivity = (B) = - - A
Cvol. percent Ctvol. percent D]U
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where C and D are two components of the feed represented in volume
percent and the subscripts A and U represent the adsorbed and unad-
sorbed phases respectively. The equ;libr;um cond;tions are deter~
mined when the feed passing over a bed of adsorbent does not change
co~position after contacting the bed of adsorbent. In other words,
there is no net transfer of material occurring between the unad-
sorbed and adsorbed phases.
Where selectivity of two components approaches 1.0 there
is no preferential adsorption of one component by the adsorbent with
respect to the other; they are both adsorbed (or non-adsorbed) to
about the same degree with respect to each other, As the (B) becomes
less than or greater than 1.0 there is a preferential adsorption by
the adsorbent for one component with respect to the other. When
comparing the selectivity by the adsorbent of one component C over
component D, a (B) larger than 1,0 indicates preferential adsorption
of component C within the adsorbent. A (B) less than 1.0 would in-
dicate that component D is preferentially adsorbed leaving an unad-
sorbed phase richer in component C and an adsorbed phase r;cher in
component D. While separation of an extract component from a raf-
finate component is theoretically possible when the selectivity ofthe adsorbent for the extract component with respect to the raffinate
component just exceeds a value of 1.0, it is preferred that such
selectivity have a value approaching or exceeding 2. Like relative
volatility, the higher the selectivity the eas;er the separation is
to perform. Higher selectivities permit a smaller amount of adsor-
bent to be used in the process. Ideally desorbent materials should
have a selectivity equal to about 1 or less than 1 with respect to
all extract components so that all of the extract components can be
extracted as a class and all raffinate components clearly rejected
into the raffinate stream.
The third important characteristic is the rate of exchange
or the relative rate of desorptlon of the extract component. Faster
rates of exchange reduce the amount of desorbent material needed to
remove the extract component and therefore permit a reduct;on in the
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operating cost of the process. With ~aster rates of eY.chanye, less
desorbent material has to be pumped through the process and separated
from the extract stream for reuse in the process.
The type X faujasites which compr;se the adsorbents of this
invention are known more generally as zeol;tes or crystalline alurnino-
silicates. Crystalline aluminosilicates or molecular sieves, as often
referred to by those skilled in the art, exhibit various mechanisms
for separating different molecules. ~he most basic action of these
materials is a sieving function in the separation of larger molecules
from smaller molecules. In the separation of aromatic hydrocarbons,
isomer separation ~s generally attributed to differences in electro-
chemical forces. With the larger and more complicated sugar molPcules,
the separation mechanism is theorized to consist of combined size
exclusion properties and electrostatic forces which as a result of
steric properties only exclude certain saccharide molecules ~rom
entering the sieve pores. Although no specif;c theory is adopted as
the basis of this invention, the preferential adsorption of the mono-
terpenoid alcohols ln this invention is attributed to d;fferences in
hydrophilicity and polarity caused by addltional or different functional
groups within the monoterpenoids.
The general structure and compos;t;on of the X type zeolite
used ;n this ;nvention is disclosed ;n U.S. Patents 2,883~244 and
3,120,007 which descr;be and deflne these mater;als.
Zeolites as ;nitially prepared or found
naturally are made up of alum;na and sil;con ox;des in a hydrated or
part;ally hydrated form which ;ncludes cat;ons at cat;on exchange
s;tes wh;ch serve to balance the electronegativity of the molecule.
As init;ally prepared, an X zeol;te will contain predom;nantly sod;um
cat;ons. It has been found that an X zeolite conta;ning sodium
cat;ons ;s an effect;ve adsorbent for this invention. However, ;t is
possible to replace these sod~um cat;ons w;th potass;um cations by
well-known ion exchange methods and still obta;n a h;ghly effective
adsorbent for use in th;s invention. Exchange of s~d;um cat;ons may
- .
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73
be essentially complete or partial wh;ch will y;eld a m;xture of sodium
and potassium cations. Typical ion exchange methods involve contacting
the ~eolite w;th an aqueous solut;on of the soluble salt of -the cation
to be placed on the s;eve and, after the des;red degree of exchange has
taken place, remov;ng the s;eve from the solut;on. The above procedure
or other ion exchange procedures may be used to replace sod;um cations
or remove unwanted cations from the zeolite adsorbent.
The adsorbent may be in the form of part;cles such as extru-
dates, aggregates, tablets, macrospheres or granules having a desired
particle range, preferably from about 16 to about 6~ mesh (Standard U.S.
Mesh). Less water content in the adsorbent is advantageous from the
standpoint of less water contaminat;on oF the product.
In addition to adsorbents, the complete functioning of an
adsorption separation process requires a desorbent to remove selectively
retained components from the adsorbent. A desorbent mater;al has been
defined as any substance capable of removing a selectively adsorbed feed
component from an adsorbent. For this invention, suitable desorbents
include alcohols, hydrocarbons and ketones. Out of this general class
of desorbents those having oxygen functional groups are preferred. Par-
ticularly effective desorbents which are most su;table for continuousadsorption processes consist of diethyl ketone, methyl ethyl ketone,
4-methyl-2-pentanone and l-butanol dissolved in hexane. Although general
classes and specific compounds have been mentioned, those skilled in the
art are aware of many criteria that govern the choice of a specific
desorbent material. Such factors include a sélectivity intermediate
between that of the extract and raffinate components, compatibility with
the feed mixturei and separability from the feed mixture. Separability
usually requires selection of desorbent material having a boiling point
substantially different from the feed components to permit subsequent
removal by simple fractionation. A substantially different boiling
point for the purpose of most adsorption processes means at least 5C
difference between the feed mixture components and the desorbent
materials. A more thorough discussion of desorbent criteria is contained
in U.S. Patent 4,423,279.
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The adsorpt;on-desorption operations may be carried out in a
dense fixed bed which is alternatively contacted with a feed mixture
and a desorbent material in which case the process will be only semi-
continuous. In another embodiment, generally referred to as 3 swing
- bed system, a set of two or more static beds of adsorbent may be
employed with appropriate valving so that a feed mixture can be passed
through one or more adsorbent beds of a set while a desorbent material
can be passed through one or more of the other beds in a set. The flow
of a feed mixture and a desorbent material may be ei~her up or down
through an adsorbent in such beds. Any of the conventional apparatus
employed in static bed fluid-solid contacting may be used.
Moving bed or simulated moving bed flow systems, however,
have a much greater separation efficiency than fixed bed systems and
are therefore preferred. In the moving bed or simulated moving bed
processes, the retention and displacement operations are continuously
taking place which allows both cont;nuous production of an extract and
a raff;nate stream and the continual use of feed and displacement fluid
streams. One preferred embod;ment of th;s process ut;lizes what is
known in the art as the simulated movlng bed countercurrent flow system.
In such a system, it is the progress;ve movement of mult;ple liquid
access points down a molecular sieve chamber that simulates ~he upward
movement of molecular sieve contained in the chamber. Reference can
also be made to D.B. Broughton's U.S. Patent 2,985,589, in which the
operating principles and sequence of such a flow system are described,
and to a paper entitled, "Continuous Adsorptive Process;ng -- A New
Separation Techn;que" by D.B Broughton presented at the 34th Annual
Meeting of the Society of Chemi~cal Engineers at Tokyo, Japan on
April 2, 1969, for
further explanat;on of the s;mulated moving bed countercurrent process
flow scheme.
Another embod;ment of a simulated moving bed flow system
suitable for use in the process of the present invent~on ls the co-
current high effic~ency simulated moving bed process disclosed in
_g_
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73
U.S. Patent 4,402l832 to Gerhold .
Wh~le th;s invention may be practlced ;n any type of flow
system, the manner of operation wlll affect desorbent selection.
Swing bed systems are less sensit;ve to desorbent selection so that
the process is likely to perform well with any material from the
aforementioned broad class of desorbents. However, in adsorptive
separation processes which are generally operated continuously at
substantially constant pressures and temperatures to ensure liquid
phase, the desorbent material relied upon must be selected more
judiciously. It is in the continuous separation processes where the
previously described class of preferred desorbents will offer the
greatest advantages.
It is contemplated that at least a portlon of the extract
output stream will pass into a separation means wherein at least a
portion of the desorbent material can be separated at separating
conditions to produce an extract product containing a reduced con-
centration of desorbent material. Preferably, but not necessary to
the operation of the process, at least a portion of the raffinate
output stream will also be passed to a separation means wherein at
least a portion of the desorbent material can be separated at sepa-
rating conditions to produce a desorbent stream which can be reused
in the process and a raffinate product containing a reduced concen-
tration of desorbent material. Typically the concentration oF
desorbent material in the extract product and the raffinate product
will be less than about 5 vol. % and more preferably less than about
1 vol. %. the separation means will typically be a fractionation
column, the design and operation of which is well known to the
separation art.
3~ Although both liquid and vapor phase operations can be
used in many adsorptive separation processes, liqu~d-phase operation
is necessary for this process because of the lower temperature and
the heat sensitiYity of the feed mixture components. In addition,
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i73
liquid phase operation lowers energy requirements and provides higher
yields of extract produ~t. Adsorption conditions will include a
temperature range of from about 20C to about 250C, with about 50C
to about 200C being more preferred, and a pressure sufficient to
ma1ntain liquid phase. Desorption conditions will include the same
range of temperatures and pressure as used for adsorption conditions.
The size of the units which can utilize the process of this
invention can vary anywhere from those of pilot-plant scale (see for
example U.S. Patent 3,706,812) to those of commercial scale and can
range in flow rates from as little as a few cc an hour up to many
thousands of gallons per hour.
In order to test various adsorbents and desorbent material
with a particular feed mixture to measure the adsorbent characteristics
of adsorptive capacity and selectivity and exchange rate, a dynamic
testing apparatus is employed. The apparatus consists of an adsorbent
chamber of approximately 70 cc volume having inlet and outlet portions
at opposite ends of the chamber. The chamber is contained within a
temperature control means and, in addition, pressure control equipment
is used to operate the chamber at a constant predetermined pressure.
Chromatographic analysis equipment can be attached to the outlet line
of the chamber and used to analyze "on-stream" the effluent stream
leaving the adsorbent chamber.
A pulse test, performed using this apparatus and the fol-
lowing general procedure, is used to determine selectivities and other
data for various adsorbent systems. The adsorbent is filled to equi-
librium with a particular desorbent by passing the desorbent material
through the adsorbent chamber. At a convenient time, a pulse of feed
containing known concentrations of a non-adsorbed paraffinic tracer
and the particular monoterpenoid feed mixture, all diluted in desorbent,
is injected for a duration of several minutes. Desorbent flow is re-
sumed, and the tracer and the feed isomers are eluted as in a liquid-
solid chromatographic operation. The effluent can be analyzed by
on-stream chromatographic equipment and traces of the envelopes of
~ '` '~ . ' ' . ~ ' '
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73
corresponding component peaks developed. Alternately, effluent samples
can be collected periodically and later analyzed separately by gas
chromatography.
From information derived from the chromatographic traces,
-ad~orbent performance can be rated in terms of capacity index for an
extract component, selectivity for one hydrocarbon with respect to
another, and the rate of desorption of an extract component by the
desorbent. The capacity index may be characterized by the distance
between the center of the peak envelope of the selectively adsorbed
component and the peak envelope of the tracer component or some other
known reference point. It is expressed in terms of the volume in
cubic centimeters of desorbent pumped during this time interval.
Selectivity, (B), for an extract component with respect to a raffinate
component may be characterized by the ratio of the distance between the
lS center of an extract component peak envelope and the tracer peak enve-
lope (or other reference point) to the corresponding distance between
the center of a raffinate component peak envelope and the tracer peak
envelope. The rate of exchange of an extract component with the de-
sorbent can generally be characterized by the width of the peak enve-
lopes at half intensity. The narrower the peak width the faster thedesorption rate. The desorption rate can also be characteri~ed by the
distance beween the center of the tracer peak envelope and the dis-
appearance of an extract component which has just been desorbed. This
distance is again the volume of desorbent pumped during this time inter-
val.
The following examples are presented for illustration purposesand more specifically are presented to illustrate the selectivity of the
adsorbents that make the process of the invention possible. Reference
to specific desorbent materials, feed mixtures and operating conditions
is not intended to unduly restrict or limit the claims of this invention.
-~2-
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EXAMPLE I
In this experiment a pulse test was performed to evaluate the
ability of the present invention to separate a monoterpene alcohol from
,its, corresponding aldehyde.
The testing apparatus was the above described pulse test
apparatus. For the pulse test, the column was filled with 70 cc of an
~ zeolite containing sodium cations at cation exchange sites and main-
tained at a temperature of 130C and a press'ure sufficient to maintain
liquid-phase operations. Gas chromatographic analysis equipment was
used to analyze periodically obtained effl'uent samples in order to
determine the composition of the effluent material at given time inter-
vals. The feed mixture employed for this test consists of 1.0 grams of
a crude commercial terpene m;xture containing approximately 15% hydroxy-
citronellal and 85% hydroxycitronellol, 0.2 grbms of tetradecane, and
1.3 grams of a desorbent material made up of 30 vol. % l-butanol and the
remainder hexane. The operations taking place in the test were as fol-
lows. The desorbent material was run continuously at a nominal liquid
hourly space velocity (LHSV) of 0.86 which amounted to a 1.00 cc per,
minute flow rate for the desorbent. At some convenient time interval
the desorbent was stopped and the feed mixture was run for a 2.6 minute
interval at a rate of 1.0 cc per minute. The desorbent stream was then
resumed at 0.86 LHSV and continued to pass into the adsorbent column
until all of the feed components had been eluted from the column as
determined by observing the chromatograph generated by the effluent
material leaving the adsorption column. The sequence of operations
usually takes about an h~ur. The 2.6 minute pulse of feed and subse-
quent desorption may be repeated in sequence as often as is desired.
The chromatograph tracing obtained is shown in Figure 1.
As demonstrated by its later appearance the alcohol compo-
nent was preferentially adsorbed. A clear separation between the
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hydroxycitronellol and hydroxycitronellal components is shown by the
pulse test data. Tailing of the hydroxycitronellal curve into the
later released hydroxycitronellol is a result of the large concen-
tration of the former component relative to the latter. From these
test results a selectivity of 1.64 was calculated which quantitatively
demonstrates the achievement of a satisfactory component separation.
EXAMPLE II
Another pulse test was run in substantially the same manner
as Example I except for the use of 70 cc of a potassium exchanged
X-type 7eolite in the column. The results of this test are shown in
Figure 2. As evident from Figure 2, the separation of the feed com-
ponents is more distinct than those obtained in Example I, which is
further supported by the calculation of a 2.5 selectivity for Example
II. In addition, the half width dimension for the hydroxycitronellal
peak was reduced thereby indicating faster rates of adsorption and
desorption.
EXAMPLE_III
Further testing with a potassium exchanged X zeolite was
performed using a commercial feed mixture containing aldehydes and
alcohols of two monoterpene hydrocarbons. In this example, a feed
mixture made up of 2.0 grams crude terpene mixture, 0.2 grams-tetra-
decane and 0.8 grams of a 50% methyl ethyl ketone-50% hexane desor-
bent. The terpene component contains approximately 58 vol. ~ geranial,
5 vol. % geraniol, 31 vol. % neral, and 6 vol. % nerol. Following a
procedure paralleling that of Example I, desorbent material was run
at a LHSV of 1.05, then the injection of 2.6 cc of feed at a rate of
1.23 cc/minute was accomplished, after which desorbent flow through
the column was continued. Graphical results of this test appear in
Figure 3. Again the curves show the later appearance of a mixed
14-
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~Z6~3~;73
alcohol stream peak. Displacement between the centers of the aldehyde
and alcohol curves is good, thereby confirming the ability to separate
a feed of mixed monoterpenoid alcohols and aldehydes. The separation
capability is further confirmed by the calculation of relative selec-
tivities for the various feed components as shown in Table 1.
Table 1
Component Pairs Selectivity
neral/geranial 1.0
neral/nerol 7.4
neral/geraniol 8.1
geranial/nerol 7.4
geraniol/geranial 8.1
nerol/geraniol 1.1
EXAMPLES IV - VII
In order to further evaluate the performance of various
adsorbents and desorbents in this process, a series of tests were
performed using a monoterpenoid mixture of geraniol, nerol, geranial,
and neral containing about 11% total alcohols. Conditions and
results for the tests are presented in Table 2.
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The selec~ivity data of Table 2 es~ablishes that a good
separation was ~chieved for all adsorbent-desorbent combinations
tested.
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