Process for separating mono-, di- and triglycerides

The separation of monoglycerides from diglycerides and triglycerides is performed by an adsorptive chromatographic process in liquid phase using sodium, magnesium, lithium or potassium-exchanged X zeolites or potassium or sodium-exchanged Y zeolite, or potassium-exchanged L zeolite as the adsorbent. A ketone or ketone/n-aliphatic hydrocarbon can be selected as the desorbent.

FIELD OF THE INVENTION 
The field of art to which this invention belongs is the solid bed 
adsorptive separation of glycerides. More specifically, the invention 
relates to a process for separating monoglycerides from di- and 
triglycerides by a process which employs Na, Mg, Li, or K-exchanged X, or 
Na or K-exchanged Y, or potassium-exchanged L zeolites. 
BACKGROUND OF THE INVENTION 
The separation of many classes of compounds by selective adsorption on 
molecular sieves or zeolites as well as other adsorbents is well known. 
For example, as disclosed in U.S. Pat. No. 4,048,205, methyl esters of 
fatty acids of various degrees of unsaturation may be separated from 
mixtures of esters of saturated and unsaturated fatty acids with X or Y 
zeolites exchanged with a selected cation. Further in U.S. Pat. No. 
4,353,838 it is disclosed that monoethanoid fatty acids may be separated 
from diethanoid fatty acids with crosslinked polystyrenes, e.g. 
"Amberlite". The refining of oils by admixing them with magnesium silicate 
to adsorb coloring matter and free fatty acids from glyceride oils is 
disclosed in U.S. Pat. No. 2,639,289. Subsequently, it has been suggested 
in U.S. Pat. No. 2,771,480 to use ion-exchange resins to adsorb the 
impurities found in glyceride oils. In an article by J. L. Lopez Ruiz et 
al., Grasas Y. Aceites 25 (5) pp. 280-84 (1974) the separation of 
monooleins from trioleins by adsorption on a Linde X zeolite 
(calcium-exchanged X type) was disclosed with desorption by ethyl alcohol. 
This has the disadvantage that ethyl alcohol can cause transesterification 
of the triglycerides to form mono- and diglycerides and fatty acid ethyl 
esters. 
The process of separating monoglycerides from di- and triglycerides 
described herein has many potential uses, for example, the purification of 
triglycerides, e.g. palm oil, by crystallization, is affected by the 
presence of monoglycerides. A process which separates monoglycerides from 
triglycerides can improve the purity and recovery of such 
crystallizations. Another application of our separation process results 
from the use of mono- and diglycerides as emulsifiers in large amounts in 
the food industry. These compounds are produced in ways, i.e., the 
reaction of glycerol with a fatty acid such as stearic acid, or with 
triglyceride mixtures such as tallow, which results in a mixture of 1- and 
2-monoglycerides, 1,2-diglycerides and 1,3-diglycerides. Separation of the 
components of the mixture is currently accomplished by molecular 
distillation, a process requiring high temperatures and high vacuum and 
which, nevertheless, results in low purities and yields. Applicant's 
discovery provides real benefits in terms of energy savings and product 
purity and recovery. 
Another important application of our separation process resides in the 
utility of the separated products, that is, pure monoglycerides and 
diglycerides, in the synthesis of triglycerides. Cocoa butter, for 
example, is a high value natural product consisting predominantly of a 
mixture of particular triglycerides where the 2-position of glycerol is 
esterified with an oleyl group and the 1- and 3-positions are esterified 
with either the palmitoyl or the stearyl group. When the 1- and 
3-positions are esterified with palmitoyl groups, the triglyceride is 
referred to as "POP". Likewise, when a stearyl group occupies both 1- and 
3-positions, the compound is called "SOS", and when 1- and 3-positions are 
filled by one palmitoyl and one stearyl group, the compound is referred to 
as "SOP". Cocoa butter is a predominant component in chocolate 
confections. It is believed that large quantities of these particular 
triglycerides could be synthesized and used as cocoa butter extenders. 
However, it is essential that the oleic acid moiety occurs at the 
2-position. This can be assured by using the 2 -oleyl-monoglyceride as 
precursor for such syntheses. A mixture of 2-monoglycerides and 
diglycerides can be obtained from the enzyme lipase, which is 
stereospecific and forms diglycerides and 2-monoglyceride from 
triglycerides. By reacting lipase with triglycerides containing the 
2-oleyl group and separating the resulting mono- and diglycerides a 
2-oleyl-monoglyceride could be produced. This separation can be achieved 
by the invention, whereby the extract will contain the desired 
2-monoglyceride. Alternatively, it is possible to synthesize the 
aforementioned triglycerides by using as precursors 1,3-diglycerides 
containing palmitoyl and stearyl groups and adding the oleyl group in the 
2 position, thereby affording triglycerides such as POP, SOP, and SOS. The 
process of the instant invention can be used to accomplish this by 
separation of glyceride mixtures which contain 1,3-diglycerides, obtaining 
the desired 1,3-diglycerides in the raffinate. 
I have discovered combinations of zeolites and desorbents which separate 
the monoglycerides and diglycerides. The monoglycerides are adsorbed to 
the substantial exclusion of diglycerides and are concentrated in the 
extract. The diglycerides, therefore, are removed from the mixture of 
monoglycerides and diglycerides and are concentrated in the raffinate of 
the adsorptive separation apparatus. 
SUMMARY OF THIS INVENTION 
The present invention is a process for separating monoglycerides from a 
feed mixture comprising monoglycerides and at least one diglyceride and 
may additionally contain at least one triglyceride. The process comprises 
contacting the mixture at adsorption conditions with an adsorbent 
comprising an X type zeolite exchanged with potasssium, magnesium, lithium 
or sodium ion, or a Y type zeolite exchanged with potassium or sodium, or 
an L type zeolite exchanged with potassium. The monoglyceride is 
selectively adsorbed to the substantial exclusion of the diglycerides and 
triglycerides. Next, the monoglyceride is desorbed by a liquid ketone or a 
mixture of a ketone and paraffin desorbents. Diglycerides and 
triglycerides, if present, are removed before the monoglycerides and, 
together with part of the desorbent, constitute the raffinate. The 
desorbent may be selected from the ketones having up to 7 carbons, e.g., 
acetone, the pentanones, hexanones and heptanones. Specific examples of 
desorbent liquids useful in the process are acetone, methylethyl ketone, 
diethyl ketone, methylpropyl ketone, 2-hexanone, 2-heptanone, etc. and 
mixtures thereof with hexane. 
The steps of the process are: (a) maintaining net fluid flow through a 
column of the adsorbent in a single direction, which column contains at 
least three zones having separate operational functions occurring therein 
and being serially interconnected with the terminal zones of the column 
connected to provide a continuous connection of the zones; (b) maintaining 
an adsorption zone in the column, the zone defined by the adsorbent 
located between a feed input stream at an upstream boundary of the zone 
and a raffinate output stream at a downstream boundary of the zone; (c) 
maintaining a purification zone immediately upstream from the adsorption 
zone, the purification zone defined by the adsorbent located between an 
extract output stream at an upstream boundary of the purification zone and 
the feed input stream at a downstream boundary of the purification zone; 
(d) maintaining a desorption zone immediately upstream from the 
purification zone, the desorption zone defined by the adsorbent located 
between a desorbent input stream at an upstream boundary of the zone and 
the extract output stream at a downstream boundary of the zone; (e) 
passing the feed mixture into the adsorption zone at adsorption conditions 
to effect the selective adsorption of the monoglycerides by the adsorbent 
in the adsorption zone and withdrawing a raffinate output stream from the 
adsorption zone; (f) passing a desorbent material into the desorption zone 
at desorption conditions to effect the displacement of the monoglycerides 
from the adsorbent in the desorption zone; (g) withdrawing an extract 
output stream comprising monoglycerides and desorbent material from the 
desorption zone; (h) withdrawing a raffinate output stream comprising 
diglycerides from the desorption zone; (i) periodically advancing through 
the column of adsorbent in a downstream direction with respect to fluid 
flow in the adsorption zone, the feed input stream, raffinate output 
stream, desorbent input stream, and extract output stream to effect the 
shifting of zones through the adsorbent and the production of extract 
output and raffinate output streams. 
Other embodiments of our invention encompass details about feed mixtures, 
adsorbents, desorbent materials and operating conditions all of which are 
hereinafter disclosed in the following discussion of each of the facets of 
the present invention. 
DESCRIPTION OF THE INVENTION 
The following definitions of various terms used throughout this 
specification will be used in describing the operation, objects and 
advantages of the present invention. 
A "feed mixture" is a mixture containing one or more extract components and 
one or more raffinate components to be fed to an adsorbent of the process. 
The term "feed stream" indicates a stream of feed mixture which passes to 
an adsorbent used in the process. 
An "extract component" is a type of compound or a compound that is more 
selectively adsorbed by the adsorbent while a "raffinate component" is a 
compound or type of compound that is less selectively adsorbed. In this 
process, monoglycerides are extract components and the diglycerides are 
raffinate components. The term "raffinate stream" or "raffinate output 
stream" means a stream through which a raffinate component is removed from 
an adsorbent. The composition of the raffinate stream can vary from 
essentially 100% desorbent material (hereinafter defined) to essentially 
100% raffinate components. The term "extract stream" or "extract output 
stream" shall mean a stream through which an extract material which has 
been desorbed by a desorbent material is removed from the adsorbent. The 
composition of the extract stream, likewise, can vary from essentially 
100% desorbent material to essentially 100% extract components. Although 
it is possible by the process of this invention to produce high-purity 
extract product (hereinafter defined) or a raffinate product (hereinafter 
defined) at high recoveries, it will be appreciated that an extract 
component is never completely adsorbed by the adsorbent, nor is a 
raffinate component completely nonadsorbed by the adsorbent. Therefore, 
small amounts of a raffinate component can appear in the extract stream, 
and likewise, small amounts of an extract component can appear in the 
raffinate stream. The extract and raffinate streams then are further 
distinguished from each other and from the feed mixture by the ratio of 
the concentrations of an extract component and a specific raffinate 
component, both appearing in the particular stream. For example, in one 
embodiment, the ratio of the concentration of the more selectively 
adsorbed monoglyceride to the concentration of less selectively adsorbed 
diglycerides will be highest in the extract stream, next highest in the 
feed mixture, and lowest in the raffinate stream. Likewise, the ratio of 
the less selectively adsorbed diglycerides to the more selectively 
adsorbed monoglycerides will be highest in the raffinate stream, next 
highest in the feed mixture, and the lowest in the extract stream. The 
term "desorbent material" shall mean generally a material capable of 
desorbing an extract component. The term "desorbent stream" or "desorbent 
input stream" indicates the stream through which desorbent material passes 
to the adsorbent. When the extract stream and the raffinate stream contain 
desorbent materials, at least a portion of the extract stream and 
preferably at least a portion of the raffinate stream from the adsorbent 
will be passed to separation means, typically fractionators, where at 
least a portion of the desorbent material will be separated at separation 
conditions to produce an extract product and a raffinate product. The 
terms "extract product" and "raffinate product" mean products produced by 
the process containing, respectively, an extract component and a raffinate 
component in higher concentrations than those found in the respective 
extract stream and the raffinate stream. The term "selective pore volume" 
of the adsorbent is defined as the volume of the adsorbent which 
selectively adsorbs extract components from a feed mixture. The term 
"nonselective void volume" of an adsorbent is the volume of an adsorbent 
which does not selectively retain an extract component from a feed 
mixture. This volume includes the cavities of the adsorbent which contain 
no adsorptive sites and the interstitial void spaces between adsorbent 
particles. The selective pore volume and the nonselective void volume are 
generally expressed in volumetric quantities and are of importance in 
determining the proper flow rates of fluid required to be passed into the 
process for efficient operations to take place for a given quantity of 
adsorbent. 
The term "desorbent material" as used herein shall mean any fluid substance 
capable of removing a selectively adsorbed feed component from the 
adsorbent. Generally, in a swing-bed system in which the selectively 
adsorbed feed component is removed from the adsorbent by a purge stream, 
desorbent material selection is not too critical and desorbent materials 
comprising gaseous hydrocarbons such as methane, ethane, etc., or other 
types of gases such as nitrogen or hydrogen may be used at elevated 
temperatures or reduced pressures or both to effectively purge the 
adsorbed feed component from the adsorbent. However, in adsorptive 
separation processes which employ zeolitic adsorbents and which are 
generally operated continuously at substantially constant pressures and 
temperatures to ensure liquid phase, the desorbent material relied upon 
must be judiciously selected to satisfy several criteria. First, the 
desorbent material must displace the extract components from the adsorbent 
with reasonable mass flow rates without itself being so strongly adsorbed 
as to unduly prevent the extract from displacing the desorbent material in 
a following adsorption cycle. Expressed in terms of the selectivity 
(hereinafter discussed in more detail), it is preferred that the adsorbent 
be more selective for the extract component with respect to a raffinate 
component than it is for the desorbent material with respect to a 
raffinate component. Secondly, desorbent materials must be compatible with 
the particular adsorbent and the particular feed mixture. More 
specifically, the desorbent must not react with either the adsorbent or 
any component of the feed material and must not reduce or destroy the 
critical selectivity of the adsorbent for the extract components with 
respect to the raffinate component. Desorbent materials to be used in the 
process of this invention should additionally be substances which are 
easily separable from the feed mixture that is passed into the process. 
After desorbing the extract components of the feed, both desorbent 
material and the extract components are typically removed in admixture 
from the adsorbent. Likewise, one or more raffinate components is 
typically withdrawn from the adsorbent in admixture with desorbent 
material and without a method of separating at least a portion of 
desorbent material, such as distillation, neither the purity of the 
extract product nor the purity of the raffinate product would be very 
high. It is, therefore, contemplated that any desorbent material used in 
this process will have a substantially different average boiling point 
than that of the feed mixture to allow separation of desorbent material 
from feed components in the extract and raffinate streams by simple 
fractionation thereby permitting reuse of desorbent material in the 
process. The term "substantially different" as used herein shall mean that 
the difference between the average boiling points between the desorbent 
material and the feed mixture shall be at least about 5.degree. C. The 
boiling range of the desorbent material may be higher or lower than that 
of the feed mixture. 
In the preferred isothermal, isobaric, liquid-phase operation of the 
process of this invention, ketones, e.g., methylethyl ketone, diethyl 
ketone, acetone and mixtures of a ketone and a paraffinic hydrocarbon, 
e.g. hexane, have been found to be effective desorbents. The desorbent may 
be dissolved in a suitable diluent, such as hexane, so as to modify the 
rate of desorption as desired. 
The prior art has recognized that certain characteristics of adsorbents are 
highly desirable, if not absolutely necessary, to the successful operation 
of a selective adsorption process. Among such 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 raffinate component and the desorbent material; and sufficiently fast 
rates of adsorption and desorption of the extract components to and from 
the adsorbent. 
Capacity of the adsorbent for adsorbing a specific volume of one or more 
extract components is, of course, a necessity; without such capacity. the 
adsorbent is useless for adsorptive separation. Furthermore, the higher 
the adsorbent's capacity for an extract component the better is the 
adsorbent. Increased capacity of a particular adsorbent makes it possible 
to reduce the amount of adsorbent needed to separate the extract component 
contained in a particular charge rate of feed mixture. A reduction in the 
amount of adsorbent required for a specific adsorptive separation reduces 
the cost of the separation process. It is important that the good initial 
capacity of the adsorbent be maintained during actual use in the 
separation process over some economically desirable life. 
The second necessary adsorbent characteristic is the ability of the 
adsorbent to separate components of the feed; or, in other words, that the 
adsorbent possess adsorptive selectivity, (B), for one component as 
compared to another component. Relative selectivity can be expressed not 
only for one feed component as compared to another but can also be 
expressed between any feed mixture component and the 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: 
##EQU1## 
where C and D are two components of the feed represented in volume percent 
and the subscripts A and U represent the adsorbed and unadsorbed phases, 
respectively. The equilibrium conditions are determined when the feed 
passing over a bed of adsorbent does not change composition after 
contacting the bed of adsorbent. In other words, there is no net transfer 
of material occurring between the unadsorbed 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 nonadsorbed) 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 indicate that component D is preferentially adsorbed 
leaving an unadsorbed phase richer in component C and an adsorbed phase 
richer in component D. While separation of an extract component from a 
raffinate component is theoretically possible when the selectivity of the 
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 easier the separation is to 
perform. Higher selectivities permit a smaller amount of adsorbent 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 of the extract 
component of the feed mixture material with the desorbent material or, in 
other words, the relative rate of desorption of the extract component. 
This characteristic relates directly to the amount of desorbent material 
that must be employed in the process to recover the extract component from 
the adsorbent; faster rates of exchange reduce the amount of desorbent 
material needed to remove the extract component and, therefore, permit a 
reduction in the operating cost of the process. With faster rates of 
exchange, less desorbent material has to be pumped through the process and 
separated from the extract stream for reuse in the process. 
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 following general 
procedure, is used to determine selectivities and other data for various 
adsorbent systems. The adsorbent is filled to equilibrium 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 nonadsorbed tracer (n-tetradecane for instance) and of 
the particular feed material all diluted in desorbent is injected for a 
duration of several minutes. Desorbent flow is resumed, and the tracer and 
the aromatic 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 corresponding component peaks 
developed. Alternately, effluent samples can be collected periodically and 
later analyzed separately by gas or liquid chromatography. 
From information derived from the chromatographic traces, adsorbent 
performance can be rated in terms of capacity index for an extract 
component, selectivity for one isomer with respect to the other, 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 isomer 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 center of an extract component peak envelope and the tracer 
peak envelope (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 
desorbent can generally be characterized by the width of the peak 
envelopes at half intensity. The narrower the peak width the faster the 
desorption rate. The desorption rate can also be characterized by the 
distance between the center of the tracer peak envelope and the 
disappearance of an extract component which has just been desorbed. This 
distance is again the volume of desorbent pumped during this time 
interval. 
The adsorbent to be used in the process of this invention comprises 
specific crystalline aluminosilicates. Crystalline aluminosilicates such 
as that encompassed by the present invention include crystalline 
aluminosilicate cage structures in which the alumina and silica tetrahedra 
are intimately connected in an open three-dimensional network. The 
tetrahedra are crosslinked by the sharing of oxygen atoms with spaces 
between the tetrahedra occupied by water molecules prior to partial or 
total dehydration of this zeolite. The dehydration of the zeolite results 
in crystals interlaced with cells having molecular dimensions. Thus, the 
crystalline aluminosilicates are often referred to as "molecular sieves" 
when the separation which they effect is dependent essentially upon 
differences between the sizes of the feed molecules as, for instance, when 
smaller normal paraffin molecules are separated from larger isoparaffin 
molecules by using a particular molecular sieve. In the process of this 
invention, however, the term "molecular sieves," although widely used, is 
not strictly suitable since the separation of specific glycerides is 
apparently dependent on differences in electrochemical attraction of the 
different isomers and the adsorbent rather than solely on physical size 
differences in the isomer molecules. 
In hydrated form, the crystalline aluminosilicates generally encompass 
those zeolites represented by the Formula below: 
EQU M.sub.2/n O:Al.sub.2 O.sub.3 :wSiO.sub.2 :yH.sub.2 O Formula 2 
where "M" is a cation which balances the electrovalence of the tetrahedra 
and is generally referred to as an exchangeable cationic site, "n" 
represents the valence of the cation, "w" represents the moles of 
SiO.sub.2, and "y" represents the moles of water. The generalized cation 
"M" may be monovalent, divalent or trivalent cations or mixtures thereof. 
The prior art has generally recognized that adsorbents comprising the type 
X and the type Y zeolites can be used in certain adsorptive separation 
processes. These zeolites are well known to the art. 
The type X structured zeolite in the hydrated or partially hydrated form 
can be represented in terms of mole oxides as shown in Formula 3 below: 
EQU (0.9.+-.0.2)M.sub.2/n O:Al.sub.2 O.sub.3 :(2.5.+-.0.5)SiO.sub.2 :yH.sub.2 O 
Formula 3 
where "M" represents at least one cation having a valence of not more than 
3, "n" represents the valence of "M", and "y" is a value up to about 9 
depending upon the identity of "M" and the degree of hydration of the 
crystal. As noted from Formula 3, the Si mole ratio is 2.5 0.5. The cation 
"M" may be one or more of a number of cations such as the hydrogen cation, 
the alkali metal cation, or the alkaline earth cations, or other selected 
cations, and is generally referred to as an exchangeable cationic site. As 
the type X zeolite is initially prepared, the cation "M" is usually 
predominately sodium and the zeolite is, therefore, referred to as a 
sodium-type X zeolite. Depending upon the purity of the reactants used to 
make the zeolite, other cations mentioned above may be present, however, 
as impurities. 
The type Y structured zeolite in the hydrated or partially hydrated form 
can be similarly represented in terms of mole oxides as in Formula 4 
below: 
EQU (0.9.+-.0.2)M.sub.2/n O:Al.sub.2 O.sub.3 :wSiO.sub.2 :yH.sub.2 O Formula 4 
where "M" is at least one cation having a valence not more than 3, "n" 
represents the valence of "M", "w" is a value greater than about 3 up to 
6, and "y" is a value up to about 9 depending upon the identity of "M", 
and the degree of hydration of the crystal. The SiO.sub.2 /Al.sub.2 
O.sub.3 mole ratio for type Y structured zeolites can thus be from about 3 
to about 6. Like the type X structured zeolite, the cation "M" may be one 
or more of a variety of cations but, as the type Y zeolite is initially 
prepared, the cation "M" is also usually predominately sodium. 
The L zeolite in the hydrated or partially hydrated form may be represented 
in terms of mole oxides as in Formula 5 below: 
EQU 0.9-1.3M.sub.2/n O:Al.sub.2 O.sub.3 :5.2-6.9SiO.sub.2 :yH.sub.2 O Formula 5 
where M designates at least one exchangeable cation as referred to above, n 
is the valence of M and y may be any value from 0 to about 9. It is 
preferred to synthesize the potassium form of the L type zeolite since the 
reactants to make this form are readily available and generally water 
soluble. Thus, the as-made form of the L zeolite is referred to as 
potassium-L, or K-L, zeolite. L-zeolite is characterized by planar 12-ring 
pores aligned to produce one-dimensional channels, linked to each other by 
small pore openings which will not admit water molecules. A minor 
two-dimensional pore system also exists, parallel to the aforesaid 
channels. 
The present invention is based on the discovery that the type Y zeolite 
with potassium or sodium cations at exchangeable cation sites is more 
selective for the monoglycerides than for the diglycerides, and that the 
type X zeolite having potassium, lithium, magnesium or sodium cations at 
exchangeable cationic sites and that the type L zeolite having potassium 
cations at the exchangeable sites is likewise more selective for the 
monoglycerides than the diglycerides. 
Typically, adsorbents used in separative processes contain the crystalline 
material dispersed in an amorphous binder material or inorganic matrix, 
having channels and cavities therein which enable liquid access to the 
crystalline material. Silica, alumina, or mixtures thereof are typical of 
such inorganic matrix materials. The binder aids in forming or 
agglomerating the crystalline particles which otherwise would comprise a 
fine powder. The adsorbent may thus be in the form of particles such as 
extrudates, aggregates, tablets, macrospheres or granules having a desired 
particle range, preferably from about 16 to about 60 mesh (Standard U.S. 
Mesh). Lower water content in the adsorbent is advantageous from the 
standpoint of having less water contamination of the product. 
The adsorbent may be employed in the form of a dense fixed bed which is 
alternately contacted with a feed mixture and a desorbent material in 
which case the process will be only semicontinuous. In another embodiment, 
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 is passed through 
one or more of the other beds in a set. The flow of a feed mixture and a 
desorbent material may be either up or down through an adsorbent in such 
beds. Any of the conventional apparatus employed in a 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 making place which 
allows both continuous production of an extract and a raffinate stream and 
the continual use of feed and displacement fluid streams. One preferred 
embodiment of this process utilizes what is known in the art as the 
simulated moving bed countercurrent flow system. In such a system, it is 
the progressive movement of multiple liquid access points down a molecular 
sieve chamber that simulates the upward movement of molecular sieve 
contained in the chamber. Reference can also be made to D. B. Broughton's 
U.S. Pat. No. No. 2,985,589, in which the operating principles and 
sequence of such a flow system are described, and to a paper entitled, 
"Continuous Adsorptive Processing--A New Separation Technique," by D. B. 
Broughton presented at the 34th Annual Meeting of the Society of Chemical 
Engineers at Tokyo, Japan on Apr. 2, 1969, both references incorporated 
herein by reference for further explanation of the simulated moving bed 
countercurrent process flow scheme. 
Another eabodiment of a simulated moving bed flow system suitable for use 
in the process of the present invention is the cocurrent high efficiency 
simulated moving bed process disclosed in U.S. Pat. No. 4,402,832 to 
Gerhold, incorporated by reference herein in its entirety. 
It is contemplated that at least a portion 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 concentration 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 separating conditions to produce a desorbent stream which can 
be reused in the process and a raffinate product containing a reduced 
concentration 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. 
Although both liquid and vapor phase operations can be used in many 
adsorptive separation processes, liquid-phase operation is preferred for 
this process because of the lower temperature requirements and because of 
the higher yields of an extract product that can be obtained with 
liquid-phase operation over those obtained with vapor-phase operation. 
Adsorption conditions will include a temperature range of from about 
20.degree. C. to about 250.degree. C. with about 100.degree. C. to about 
200.degree. C. being more preferred and a pressure sufficient to maintain 
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. Pat. 
No. 3,706,812) to those of commercial scale and can range in flow rates 
from as little as a few cc's an hour up to many thousands of gallons per 
hour. 
The following examples are presented for illustration purposes and more 
specifically are presented to illustrate the selectivity relationships 
that make the process of the invention possible. Reference to specific 
cations, desorbent materials, feed mixtures and operating conditions is 
not intended to unduly restrict the scope and spirit of the claims 
attached hereto.

EXAMPLE I 
In this experiment, the pulse test was performed to evaluate the ability of 
the present invention to separate monoglycerides from diglycerides. The 
adsorbent used was a potassium-exchanged X zeolite and can be prepared by 
mixing with 15 wt. % clay. Water is then added and the resulting mixture 
is extruded, calcined at about 400.degree. C., then ground to 20-50 mesh 
size. The adsorbent was redried at 350.degree. C. before it was utilized 
in the process in each test. It was noted that some adsorbents caused 
reactivity when exposed to the glyceride mixture, in particular 
transesterification reactions due to basicity of the adsorbent. It was 
found that this reactivity could be eliminated by deactivating the 
adsorbent with treatments which consumed this basicity, such as washing 
the adsorbent with aqueous solutions of sugars. Alternatively, material 
such as acid solutions or buffers could be used for adsorbent 
deactivation. For example, a commercially obtained potassium X faujasite 
was dried at 350.degree. C. and tested for reactivity in the 
above-described pulse test apparatus without treatment for deactivation. 
The desorbent used was methylethyl ketone (MEK) and the temperature was 
70.degree. C. The feed for this experiment was 2.6 cc of a solution 
containing 0.5 g pure glycerol monostearate and 2 cc MEK. 
The testing apparatus was the above-described pulse test apparatus. The 
results of the test are illustrated in FIG. 1a, which shows that in 
addition to glycerol monostearate, glycerol distearate was present in the 
column effluent, indicating transesterification was taking place in the 
column. 
A similar experiment was conducted, except that the adsorbent was 
deactivated by the following procedure: a 1200 cc column packed with the 
adsorbent was washed with an aqueous glucose solution containing 40% 
dissolved solids at a rate of about 140 cc hour until the base catalyzed 
conversion of glucose to fructose was nil. The adsorbent was then washed 
with water to remove any sugars, dried, and tested as in the above case. 
In this case analysis of the column effluent showed no production of 
glycerol distearate, FIG. 1b. 
The deactivated adsorbent so produced was used to evaluate the ability. of 
the present invention to separate monoglycerides from diglycerides. For 
this pulse test, the column was maintained at a temperature of 65.degree. 
C. and a pressure of 50 psig. Liquid chromatographic analysis equipment 
was used to analyze the column effluent stream in order to determine the 
composition of the effluent material at given time intervals. The feed 
mixture employed for each test comprised 2 cc pulses of a mixture 
containing 1.0 g of a glyceride mixture, 0.3 g n-tetradecane, which was 
used as a tracer, and 1.5 ml of methylethyl ketone (MEK). The glyceride 
mixture had approximately the following composition: 
______________________________________ 
monoglycerides: 
45.1% 
monopalmitate: 5.1% 
monostearate: 40% 
diglycerides: 51.5% 
dipalmitin: 1.9% 
1-palmitoyl-3-stearyl-glycerol: 8.4% 
2-palmitoyl-3-stearyl-glycerol: 5% 
1,3-distearyl glycerol: 24% 
1,2-distearyl glycerol: 12.2% 
triglycerides: 
2% 
stearic acid: 1.4% 
______________________________________ 
The operations taking place for each test were as follows. The desorbent 
material was run continuously at a nominal liquid hourly space velocity 
(LHSV) of 1.0. At some convenient time interval, a pulse of the feed 
mixture was introduced. The desorbent stream was then resumed at 1 LHSV 
and continued to pass into the adsorbent column until all of the feed 
components had been eluted from the column as determined by 
chromatographic analysis of the effluent material leaving the adsorption 
column. In most cases, the column effluent is analyzed for its mono- and 
diglyceride content; however, it was determined by complete analysis 
(Example X) that the triglycerides in the feed mixture are relatively 
unadsorbed and thus elute and are separated with the diglycerides, while 
the stearic acid in the feed mixture elutes with the monoglycerides. 
The results of the test of this Example are shown on the accompanying FIG. 
1c which comprises the chromatographic trace. 
It is clear from the test that the separation of monoglycerides from 
diglycerides is readily achieved by the process of the present invention. 
There is sufficient resolution between the monoglyceride curve and curves 
for the diglycerides for the separation. From equation 1, selectivities 
for the monoglycerides relative to the diglycerides approach infinity 
because the diglycerides have no significant retention volume. Note that 
all the different diglycerides of the mixture display such nonadsorptive 
behavior and are separated as a group, forming a raffinate product; 
likewise, all the monoglycerides of the mixture display similar adsorptive 
behavior and are extracted as a group, forming an extract product. Thus, 
analysis of the effluent for one monoglyceride, for example monostearate, 
and one diglyceride, for example distearate, serves to define the total 
monoglyceride and diglyceride elution from the adsorbent column. The 
monoglyceride retention volume was 4.5 cc. 
EXAMPLE II 
The pulse test of Example I was repeated for Y type molecular sieves. In 
this test, a type Y potassium-exchanged zeolite was used. he temperature 
was 120.degree. C. and the desorbent was 25 vol. % acetone in hexane. 
It is clear from FIG. 2, which yields a monoglyceride retention volume of 
5.2 cc, that the adsorbent of the present invention exhibits acceptable 
selectivity for the monoglycerides. 
EXAMPLE III 
The pulse test of Example II was repeated except that 100% acetone was used 
for the desorbent. The feed composition was as follows: 
______________________________________ 
0.3 g monoolein 99% 1-monooleyl glyceride 
1% 2-monooleyl glyceride 
0.3 g diolein 15% 1,2-dioleyl glyceride 
85% 1,3-dioleyl glyceride 
0.2 g n-C.sub.14 
2.1 cc diethyl ketone (DEK) 
______________________________________ 
The retention volume of the monooleins was 2.7 cc, as seen in FIG. 3. 
EXAMPLE IV 
The pulse test of Example I was repeated except that diethyl ketone was 
used for desorbent, Na-X was the adsorbent, and the temperature was 
120.degree. C. A monoglyceride retention volume of 2.5 cc was obtained, as 
seen in FIG. 4. 
EXAMPLE V 
The pulse test of Example I was repeated with the same feed, but with 100% 
acetone as desorbent and X type zeolite exchanged with potassium ions. The 
temperature of the test was 120.degree. C. A monoglyceride retention 
volume of 2.5 cc was obtained from the liquid chromatographic plot shown 
in FIG. 5. 
EXAMPLE VI 
The pulse test of Example I was repeated except that adsorbent was an X 
type zeolite exchanged with lithium and the temperature was 70.degree. C. 
It is clear from FIG. 6, which yields a monoglyceride retention volume of 
2.9 cc, that LiX adsorbent exhibits acceptable selectivity for 
monoglycerides. 
EXAMPLE VII 
The pulse test of Example III was repeated except that the Y type zeolite 
adsorbent was exchanged with sodium. Analysis of the test, shown in FIG. 
7, gives a monoglyceride retention volume of 2.1 cc. 
EXAMPLE VIII 
The experiment of Example I was repeated except that the adsorbent was a 
potassium-exchanged L type zeolite and the temperature was 120.degree. C. 
The test is illustrated in FIG. 8, from which a retention volume for the 
monoglycerides of 2.4 cc was calculated, indicating that 
potassium-exchanged L zeolite exhibits good selectivity for monoglycerides 
over diglycerides. 
EXAMPLE IX 
The experiment of Example VI was repeated except that the adsorbent was a 
magnesium-exchanged X zeolite. The test, shown in FIG. 9, indicates that 
the magnesium-exchanged X zeolite has adsorptive selectivity for 
monoglycerides, with a monoglyceride retention volume of 2.7 cc. 
EXAMPLE X 
This example illustrates the ability of our process, when operated in a 
preferred embodiment, which utilizes a continuous simulated moving bed 
countercurrent type of operation, and comprises a pilot plant scale 
testing apparatus known as a carousel unit described in detail in deRosset 
et al. U.S. Pat. No. 3,706,812, incorporated herein by reference. Briefly, 
the apparatus consists essentially of 24 serially connected adsorbent 
chambers having about 19.2 cc volume each. Total chamber volume of the 
apparatus is approximately 460 cc. The individual adsorbent chambers are 
serially connected to each other with relatively small diameter connecting 
piping and to a rotary type valve with other piping. The valve has inlet 
and outlet ports which direct the flow of feed and desorbent material to 
the chambers and extract and raffinate streams from the chambers. By 
manipulating the rotary valve and maintaining given pressure differentials 
and flow rates through the various lines passing into and out of the 
series of chambers, a simulated countercurrent flow is produced. The 
adsorbent remains stationary while fluid flows throughout the serially 
connected chambers in a manner which when viewed from any position within 
the adsorbent chambers is steady countercurrent flow. The moving of the 
rotary valve is done in a periodic shifting manner to allow a new 
operation to take place in the adsorbent beds located between the active 
inlet and outlet ports of the rotary valve. Attached to the rotary valve 
are input lines and output lines through which fluids to and from the 
process flow. The rotary valve contains a feed input line through which 
passes the feed mixture, and extract stream outlet line through which 
passes the desorbent material, i.e., methylethyl ketone, in admixture with 
iso-octane, monoglycerides and fatty acids, a desorbent material inlet 
line through which passes desorbent materials and a raffinate stream 
outlet line through which passes di- and triglycerides in admixture with 
desorbent material. Additionally, a flush material inlet line is used to 
admit flush material for the purpose of flushing feed components from 
lines which had previously contained feed material and which will 
subsequently contain the raffinate or extract stream. The flush material 
employed is iso-octane which then leaves the apparatus as part of the 
extract stream and raffinate stream. Additional apparatus details can be 
found in U.S. Pat. No. 3,706,812. In order to better understand the 
operations taking place within the apparatus reference can be made to D. 
B. Broughton, U.S. Pat. No. 2,985,589 and to D. B. Broughton et al., "The 
Separation of P-Xylene from C.sub.8 Hydrocarbon Mixtures by the Parex 
Process," presented at the Third Joint Annual Meeting, American Institute 
of Chemical Engineers and Puerto Rican Institute of Chemical Engineers, 
San Juan, Puerto Rico, May 17 through May 20, 1970. These references 
describe in detail the basic operations taking place in the testing 
apparatus used in this embodiment, and although said references are 
concerned with the separation of hydrocarbons, the testing apparatus 
itself is perfectly suited for purposes of this embodiment. 
The feed mixture to the apparatus was the glyceride mixture of Example I. 
The adsorbent used was a potassium-exchanged X faujasite, deactivated as 
in Example I. The desorbent was 25 volume % methylethyl ketone in 
iso-octane. 
The operating parameters of the carousel unit were as follows: 
1. A/F=2.6, where A is the selective pore volume of the adsorbent in cc and 
F is the feed rate tothe separation stage in cc/hr. The selective pore 
volume is that volume of the adsorbent which has the ability to 
selectively adsorb one component of a mixture over another. 
2. Process temperature=70.degree. C. 
3. Valve cycle time=90 min. 
A number of experiments, each of six hours duration, were conducted on the 
carousel unit. In these experiments it was observed that the free fatty 
acids were adsorbed along with the monoglycerides and so were separated 
with the extract, while the triglycerides were relatively unadsorbed like 
the diglycerides and so were separated with the raffinate. 
In these experiments the extract and raffinate streams were analyzed for 
their monoglyceride and fatty acid content, and di- and triglyceride 
content, respectively. The results of these experiments can be plotted as 
a curve of monoglyceride extract purity versus monoglyceride recovery and 
are illustrated in FIG. 10; the separation performance ranged from 
monoglyceride extract purity. of 88.1% at 97.5% recovery to 99+% purity at 
51.3% recovery on a fatty acid free basis. It was further discovered that 
the monoglyceride extracts were easily freed of fatty acid content by 
cooling the extracts to 0.degree. C., whereupon the monoglycerides 
precipitated and were filtered from the remaining mixture of desorbent and 
fatty acid. The raffinates, obtained under the conditions of high 
monoglyceride purity, were 97+% di- and triglycerides, with triglycerides 
constituting 10-12% of the raffinate glycerides. 
Thus, it is clear from the above that the use of a KX adsorbent enables the 
separation of monoglycerides from a glyceride mixture containing mono-, 
di- and triglycerides and free fatty acids. Since the effects of different 
operating conditions on the product purity and yield have not been 
completely investigated, the results of the above tests are not intended 
to represent the optimums that might be achieved.