Chromatographic separations using a unique silica polymorph

Chromatographic separation of mixtures containing low molecular weight alcohols, ethylene glycol, phenol and water are made in the liquid and gas phase using as a column packing a unique crystalline silica polymorph, synthesized hydrothermally from a reaction system containing silica, water, an alkylonium base and fluoride anions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to the chromatographic separation of mixtures 
containing certain low molecular weight alcohols, ethylene glycol, phenol 
and water. This is accomplished by the use of a unique crystalline 
polymorph, hereinafter called "F-silicalite," as the fixed-bed or column 
packing. The properties of F-silicalite allow a sharp separation between 
components of a sample mixture, providing for good resolution of peaks on 
a chromatogram and quantitative analysis of the mixture. 
Chromatography is a process whereby different types of molecules are 
separated one from another. A sample mixture is introduced into a fluid 
phase or carrier stream which is then passed over a stationary phase or 
fixed bed. The fixed bed is of a composition that interacts with the 
components of the sample mixture in the carrier stream. Generally the 
fixed bed interacts differently or selectively with the individual 
components so that the components migrate at different rates through the 
fixed bed, thus achieving a separation. 
The carrier stream may be a gas or a liquid, in which case the method is 
termed either gas chromatography or liquid chromatography, respectively. 
In gas chromatography the gas phase may be contacted with a liquid 
surface. In this method, termed gas-liquid chromatography, the liquid 
surface may be in the form of a liquid on the surface of a solid support. 
In the operation of a typical chromatographic apparatus, the mixture to be 
analyzed is momentarily or intermittently injected into a carrier stream 
which is then passed through the fixed bed. Due to the separative 
properties of the composition of the fixed bed, components of the mixture 
are separated so that the relative concentrations of components of the 
mixture in the carrier stream vary with time as it emerges from the fixed 
bed. This variation in composition can be detected by measurement of an 
appropriate physical property, such as the index of refraction or the 
thermal conductivity. When the apparatus is provided with a recording 
means, such as a chart recorder, the variation is manifested in the form 
of peaks on a chart called a chromatogram, with each peak corresponding to 
a component in the mixture. FIGS. 1, 2, 4, 6-8, 10 and 11 show examples of 
such chromatograms. The retention time or the position of the maximum of a 
peak on the chromatogram is dependent on the migration time of the 
corresponding component through the fixed bed. Thus, by choosing a 
composition for the fixed bed of known properties and setting appropriate 
operating conditions, a person skilled in the art can identify components 
of a mixture by the positions of the peaks or retention times on the 
chromatogram. 
It is, therefore, desirable that the fixed bed have properties that allow 
for selective separation of components in a mixture in a manner that 
results in sharp, well-defined peaks. A composition may exhibit separative 
properties for a mixture but will be unsuitable for chromatographic 
applications if it separate components into broad, unresolvable peaks. By 
measuring areas under the peaks, for example by using an integrator, it is 
often possible to determine the relative concentrations of a component in 
various mixtures. If the peaks are too broad or overlap such that areas 
under individual peaks cannot be resolved this may not only lead to 
difficulty in identifying the components but also make it impossible to 
determine the relative concentrations. 
It is therefore desirable that the separative properties of the composition 
of the fixed bed be such that good separation and resolution of the peaks 
on a chromatogram be possible. 
Mixtures of compounds with similar properties are often difficult to 
separate under chromatographic conditions. These include, among others, 
isotopic mixtures and mixtures of chemically-related compounds such as 
organic compounds with the same functional group. 
One such class of mixtures are those polar compounds containing the --O--H 
or hydroxyl functional group. Included in this class are mixtures of 
alcohols, water and other compounds such as glycols and phenols. 
It is an object of the invention to provide a process for the separation of 
mixtures of this type. Specifically, an object of the invention is to 
provide for the separation of mixtures containing methanol, ethanol, 
1-propanol, 2-propanol, ethylene glycol, phenol and water. 
2. Prior Art 
As indicated above, the composition of the fixed bed must act selectively 
on the components of a mixture to effect a separation. One class of 
compounds that has been suggested for use as a fixed bed is zeolites. 
Zeolites are crystalline aluminosilicates having the general formula in 
terms of moles of oxides; 
EQU xM.sub.2/n O:Al.sub.2 O.sub.3 :ySiO.sub.2 :zH.sub.2 O, 
where M is an exchangeable cation, n is the valence of M and x, y and z are 
molar ratios of the corresponding oxide to Al.sub.2 O.sub.3. 
Zeolites act as molecular sieves. They can, therefore, be used for 
separations based on molecular size of a component molecule. The use of 
zeolites in chromatography, based on this property, is disclosed in U.S. 
Pat. No. 3,626,666 to B. M. Drinkard and U.S. Pat. No. 3,699,182 to J. 
Cattanach. In these references, zeolites ZSM-5, ZSM-8 and calcium zeolite 
5A are used for separations of mixtures such as aromatic isomers, 
biphenyls and benzene with polysubstituted aromatic hydrocarbons. 
Some zeolites, principally those with a high silica-to-alumina ratio, 
exhibit hydrophobic/organophilic properties. These zeolites act 
selectively on the basis of polarity. An example of such an application is 
disclosed in U.S. Pat. No. 3,732,326 to N. Y. Chen wherein certain 
polar-selective zeolites having a high silica-to-alumina ratio, such as 
zeolite ZSM-5, are used in the separation of mixtures such as cyclohexane 
with methanol and benzene with butanol, using chromatographic techniques. 
SUMMARY OF THE INVENTION 
The objects of the invention are accomplished by the use of a unique silica 
polymorph as the fixed bed. This silica polymorph, denoted F-silicalite, 
is synthesized hydrothermally from a reaction system containing silica, 
water, an alkylonium base and fluoride anions. The composition and a 
process of manufacture are disclosed in U.S. Pat. No. 4,073,865 to E. M. 
Flanigen and R. L. Patton. 
To demonstrate the properties of F-silicalite as compared to similar 
compositions, tests were made under similar conditions using a zeolite, 
silicalite and F-silicalite as the fixed bed in a chromatographic 
apparatus. The zeolite used was one with a high silica-to-alumina ratio 
having properties similar to ZSM-5 where potassium is the exchangeable 
cation. The composition and a method of manufacture of ZSM-5 are disclosed 
in U.S. Pat. No. 3,702,886 to R. J. Argauer and G. R. Landolt. 
Silicalite, disclosed in U.S. Pat. No. 4,061,724 to R. W. Grose and E. M. 
Flanigen, is a crystalline silica polymorph with a crystal structure 
similar to a zeolite. Unlike a zeolite it does not contain structure 
alumina and therefore does not exhibit ion-exchange properties. It is 
hydrophobic and is suitable for separating organic materials from water. 
F-silicalite is a silica polymorph with properties quite similar to 
silicalite. It is distinguishable from silicalite by its X-ray diffraction 
pattern, water adsorption properties and infrared absorption spectrum. It 
also exhibits an exceptional degree of hydrophobicity. 
Using a solution of methanol, ethanol, 1-propanol and 2-propanol in water, 
tests were run using the above-referenced zeolite as the fixed bed in a 
liquid chromatographic apparatus. Water was used as a carrier fluid. The 
peaks of the chromatograph (FIG. 11) showed considerable broadening such 
that it was only possible to measure the peak corresponding to methanol 
meaningfully. 
Liquid chromatography tests using water as a carrier fluid were run using 
silicalite with a sample solution of methanol, ethanol, 1-propanol, 
2-propanol and water. The peaks on the chromatogram showed broadening such 
that only peaks corresponding to methanol and ethanol were recorded. 
Although zeolites of the ZSM-5 family and also silicalite exhibit 
hydrophobic properties, they did not exhibit suitable separatory 
properties for chromatographic separations of the above-mentioned 
alcohols. 
However, F-silicalite surprisingly proved to be a suitable composition for 
the chromatographic separation of alcohols. 
Use of F-silicalite to separate a solution of methanol, ethanol, 1-propanol 
and 2-propanol in water in tests like those above produced a chromatogram 
with separate and distinct peaks corresponding to the solution components. 
Heretofore there has not been in the art a suitable composition for 
separating solutions of the above mentioned low molecular weight alcohols 
in liquid chromatography. Use of F-silicalite, therefore, represents a 
major advantage over the prior art. It has been found to be equally useful 
in gas and liquid chromatography. F-silicalite also has been found 
suitable in chromatographic separation of solutions containing ethylene 
glycol and phenol, both of which are chemically related to alcohols. 
In accordance with the invention a process is provided for the 
chromatographic separation of mixtures of compounds having a hydroxyl 
functional group, said mixtures containing (a) two or more members of the 
group consisting of ethylene glycol, methanol, ethanol, 2-propanol, 
1-propanol and water or (b) phenol and water, which comprises passing said 
mixtures over a fixed bed of silicalite. 
The invention can alternately be described as providing a method of 
chromatographically separating fluid sample mixtures of the above 
composition, which comprises intermittently injecting a fluid sample 
mixture into a carrier fluid and passing said carrier fluid through a 
chromatographic separation column containing a fixed bed of F-silicalite.

DETAILED DESCRIPTION OF THE INVENTION 
As indicated above, the process of the invention involves the use of 
F-silicalite in liquid and gas chromatography. F-silicalite for use in the 
process of the invention can be prepared by the process which comprises 
providing a reaction mixture having a pH below 11, preferably within the 
range of 7 to 11, more preferably 7.4 to 10, which in terms of moles of 
oxides contains from 150 to 1500 moles H.sub.2 O, from 13 to 50 moles 
SiO.sub.2, from 2 to 12 moles of fluoride ion and from 0 to 20 moles, 
preferably 0 to 6 moles, M.sub.2 O wherein M represents an alkali metal 
cation, each of the aforesaid reagents being present per mole of Q.sub.2 O 
wherein Q represents a quaternary cation having the formula (R.sub.4 X)+, 
in which each R represents hydrogen or an alkyl group containing from 2 to 
6 carbon atoms, and X represents phosphorous or nitrogen, heating the 
reaction mixture thus provided at a temperature of from 100.degree. to 
250.degree. C. until a crystalline hydrated precursor is formed, usually 
about 50 to 150 hours, isolating said crystalline precursor and calcining 
same at a temperature of from 400.degree. C. to 1000.degree. C. 
Further details of the synthesis of F-silicalite are found in the above 
cited U.S. Pat. No. 4,073,865 to E. M. Flanigen and R. L. Patton, which 
patent is incorporated into this specification by reference. 
In general a small crystal size of F-silicalite will result in less 
broadening of the peaks. However, too small a crystal size will cause an 
excessive pressure drop over the length of the fixed bed. In the examples 
below the crystal size was in the range of 20.times.20.times.150 microns. 
At this size the chromagraphic apparatus can be operated under low 
pressures at fairly high carrier flow rates. However any crystal size 
allowing normal operating conditions is suitable in the invention. 
It is preferred that the F-silicalite be as free from impurity as is 
possible. It is, therefore, recommended that it be acid-washed and 
calcined at about 600.degree. C. for at least two hours. 
The following examples illustrate the preferred embodiments of the 
invention. Shown are examples of liquid chromatography and gas 
chromatography. In all the examples the F-silicalite used was acid-washed 
and calcined at 600.degree. C. for 2 hours. The crystal size was about 
20.times.20.times.150 microns. In both the liquid and gas applications the 
pressure drop across the bed was near zero pounds per square inch. 
Examples 1-12 illustrate the process of the invention in liquid 
chromatography. In these examples, a liquid chromatograph apparatus 
typical in the art was used. The apparatus was a "Chromatronix 3500" 
liquid chromatograph with an L.D.C., Model 1107 refractometer as a 
detector (from Chromatronix, Inc.), peak retention times and peak areas 
were obtained with a Model 3373B integrator from Hewlett-Packard Retention 
time is defined as the time from sample injection to the occurrence of the 
maximum of the peak. The sample volume for each example was 1.0 microliter 
(ul.). The carrier fluid was water. In Examples 1 to 5 the column 
containing the fixed bed was 23 cm long and had an internal diameter of 
1.5 mm. The weight of the F-silicalite used in the fixed bed was 0.54 
grams. In Examples 6-12 a column 47 cm long, having an inside diameter of 
4.5 mm and containing 3.80 grams of of F-silicalite was used. 
EXAMPLE 1 
A sample solution composed of 1% methanol, 1% ethanol, 1% 1-propanol and 1% 
2-propanol in water was tested. The carrier flow rate was set at 2.0 
ml/min. FIG. 1 shows the chromatogram for this example. 
EXAMPLE 2 
A sample solution composed of 2% methanol and 0.5% ethanol in water was 
tested. The carrier flow rate was set at 0.8 ml/min. FIG. 2 shows the 
chromatogram for this example. 
FIGS. 1 and 2 show the peaks corresponding to the alcohol components to be 
distinct and sharp for each example. This good separation allows for 
quantitative analysis of alcohol solutions as illustrated by Examples 3 to 
5 below. 
EXAMPLES 3 TO 5 
Solutions of methanol, ethanol and 2-propanol were tested. The carrier flow 
rate was 2.0 ml/min for these examples. A summary of the results is shown 
in Table A. The peak areas are in arbitrary units related to the operating 
conditions of the chromatograph and chart recorder. 
TABLE A 
______________________________________ 
Retention Time 
Peak Area 
Component Vol. - % (min) (units) 
______________________________________ 
Example 3: 
Methanol 2.0 0.89 750.3 
Ethanol 2.0 1.99 2308. 
2-Propanol 
2.0 7.54 3017. 
Example 4: 
Methanol 1.0 0.86 375.1 
Ethanol 1.0 1.93 1162. 
2-Propanol 
1.0 7.82 1473. 
Example 5: 
Methanol 0.5 0.85 180.6 
Ethanol 0.5 1.93 550.2 
2-Propanol 
0.5 8.31 675.0 
______________________________________ 
FIG. 3 shows a plot of the component concentrations versus the peak area 
for each alcohol component. As shown in FIG. 3 the peak areas are linear 
in relation to the concentrations. This is very significant in that it 
allows quantitative analysis of solutions. Using a standard solution of 
known concentration in volume-percent, one can compute concentration of a 
component by the following relation; (concentration of 
sample)=(concentration of standard).times.(peak area of sample/peak area 
of standard). The concentration of the standard should be within the 
general range of that of the sample. The linear relationship may not be 
valid for all concentrations outside of the range of the above examples, 
so tests of standard solutions within a desired range should be made to 
ensure the relationship is still linear. 
EXAMPLE 6 
A sample solution containing ethylene glycol and methanol was tested. The 
carrier flow rate was set at 0.8 ml/min. As shown in FIG. 4 the retention 
times for methanol and ethylene glycol are similar. However, the peaks are 
sufficiently separate for useful analysis. As shown in FIG. 4, the 
retention time of ethylene glycol is less than methanol. Therefore, for 
solutions containing ethylene glycol, methanol, ethanol, 2-propanol, and 
1-propanol, the component peaks on the chromatogram will emerge in the 
above indicated order. 
EXAMPLES 7-12 
Solutions of ethylene glycol in water over a range of concentrations were 
tested. The carrier flow rate was 3.2 ml/min. for these examples. Table B 
shows a summary of these tests. 
TABLE B 
______________________________________ 
Concentration 
Peak Area 
Example No. (% by volume) 
(units) 
______________________________________ 
7 10 1610 
8 8 1295 
9 6 960.3 
10 4 642.5 
11 2 321.2 
12 1 158.6 
______________________________________ 
FIG. 5 is a plot showing a linear relationship between component peak area 
and concentration. In the same manner as explained above, this allows for 
quantitative analysis of ethylene glycol solutions. 
Examples 13 to 19 demonstrate embodiments of the invention using gas 
chromatography. A column 6 feet long and 1/4" in diameter was packed with 
approximately 15 grams of F-silicalite, incorporated into a gas 
chromatograph and baked for 2 hours at 300.degree. C. with a helium purge. 
The gas chromatograph was a "Varian" 1800 G.C. equipped with a thermal 
conductivity detector (from Varion Associates). Helium gas was used as a 
carrier. 
EXAMPLE 13 
A solutin of 95% ethanol and 5% water was tested. The helium flow rate was 
75 ml/min. The column temperature was 190.degree. C. and the detector 
temperature was 250.degree. C. The sample volumes were 5 .mu.l. In the 
chromatogram labeled FIG. 6 is shown a good separation of the ethanol and 
water peaks. 
EXAMPLE 14 
A solution consisting of 2-propanol, ethanol and water was tested. The 
helium flow was 75 ml/min. The column temperature was 190.degree. C. and 
the detector temperature was 250.degree. C. The sample volume was 5 .mu.l. 
As shown in the chromatogram in FIG. 7, the component peaks are distinct 
and well separated. 
EXAMPLES 15-18 
Samples of a commercial-grade ethylene glycol containing a trace of water 
were tested. The helium flow rate was 75 ml/min, the column temperature 
was 200.degree. C. and the detector temperature was 250.degree. C. The 
sample volumes are shown below in Table C. 
TABLE C 
______________________________________ 
Example No. Sample Volume, .mu.l 
______________________________________ 
15 5.0 
16 3.0 
17 2.0 
18 0.5 
______________________________________ 
FIG. 8 shows the resulting chromatograms superimposed. The ethylene glycol 
concentrations (by volume) in the carrier gas and the corresponding peak 
area were plotted in FIG. 9. Here is demonstrated the feasibility of 
quantitative analysis of ethylenee glycol solutions using gas 
chromatography in the same manner explained above for liquid 
chromatography. 
The small peak on the left of FIG. 8 corresponds to the trace of water 
(about 0.1%) present in the commercial ethylene glycol tested. These 
examples and also Examples 13 and 14 show how the process of the invention 
can be used to detect small amounts of water in solutions of alcohols and 
ethylene glycol. 
EXAMPLE 19 
This example demonstrates the chromatographic separation of phenol and 
water. The gas-chromatograph of Examples 13 to 18 was used except the 
column for the fixed bed was 47 cm long, had a diameter of 4.5 mm and 
contained 3.80 grams of F-silicalite. The helium flow was 75 ml/min. the 
column temperature was 250.degree. C. and the sample size was 5.0 .mu.l. A 
reagent-grade phenol containing a trace of water was tested; FIG. 10 shows 
a distinct and separated peak corresponding to the water. This shows the 
usefulness of the process of the invention in detecting water in phenol.