CS211743B1 - Polymeric sorbent with increased polarity for gas chromatography and method of its preparation - Google Patents

Abstract

The invention relates to a polymer sorbent with increased polarity for gas chromatography and a method of its preparation, which has significantly better properties than materials known to date. The essence of the sorbent according to the invention lies in the fact that it consists of a copolymer of glycidyl methacrylate and ethylene dimethacrylate containing 20 to 60 wt. % of the first component in a macroporous form with a measurable inner surface and in the shape of regular spherical particles, which was subjected to heating to a temperature of 250 to 300 °C for a period of less than 4 hours in an oxygen-free atmosphere

Description

The invention relates to a polymer sorbent with increased polarity for gas chromatography and a method of its preparation, which has significantly better properties than materials known to date.

Polymeric sorbents for gas chromatography have experienced maximum development during the period of the spread of macroporous crosslinked polymers. Unlike classical sorbents referred to as carriers, mainly inorganic porous substances, it is not necessary to treat polymeric sorbents before use by coating the surface with a so-called anchored phase, usually liquid. Their application is therefore mainly in the gas - solid mode (in contrast to the classical arrangement, where gas - liquid predominates).

The most well-known polymer sorbents for gas chromatography include, from a chemical point of view, very non-polar copolymers of styrene with divinylbenzene. Only some types are polymers of ethylene dimethacrylate. Among polar sorbents, porous polyphenylene oxide can also be included for concentrating gaseous components.

The degree of polarity is an important parameter describing the ability of a system to separate different groups of substances. In the case of gas chromatography, it is customary to use in the literature to express polarity the Rohrschneider constants (J. Chromatogr. 22. 6, 1966), i.e. 0.01 times the difference in the retention indices of benzene (x), ethanol (y), methyl ethyl ketone (z), nitromethane (u) and pyridine (s) on squalane (linear trimer of isoprene) as the anchored phase and on the tested anchored phase. Since this method is not completely correct for gas-solid chromatography, modified indices are used in the following text when graphitized carbon-based sorbents are used as the standard instead of squalane at 150°. Modified indices are marked with a comma.

As already mentioned, one of the most polar sorbents is polyethylene dimethacrylate characterized by the modified constants: x'= 1.30, y'= 2.90, z'= 2.21, u'= 3.44, Ts' not determined. Even subsequent modification of some polymer sorbents usually does not significantly increase the polarity. They are used mainly for the separation of non-polar substances,

Significant improvement can be achieved with sorbents based on hydroxyalkylacrylates or methacrylates (Czech Republic, a. o. 159 990), or their modifications, when the values are achieved: x' = 2.29, y' - 3.53, z' = 2.75, u' = 4.09, s' not determined. An increase in polarity can also be achieved by ternary copolymerization according to Czech Republic, a. o. 175 156.

Another significant increase is achieved by applying sorbents based on glycidyl esters of acrylic or raethacrylic acid copolymerized with alkylene dimethacrylate and acrylonitrile, respectively, according to Czechoslovak Patent No. A. 0. 188 619. The modified Rohrschneider constants of the best sample were:

x' = 3.62, y' = 4.64, z' = 4.43, u' = 7.00, s' = 5.97. These sorbents are characterized by relatively short retention times with good sorption properties documented by peak symmetry and linearity of the sorption isotherm.

According to the invention, it has been found that even these properties are not definitive and can be further significantly improved.

The essence of the polymer sorbent with increased polarity for gas chromatography according to the invention lies in the fact that it consists of copolymers of glycidyl methacrylate and ethylene dimethacrylate containing 20 to 60% by weight of the first component in a macroporous form with a measurable inner surface and in the shape of regular spherical particles, which has been subjected to heating to a temperature of 250 to 300 °C for a period of less than 4 hours in an oxygen-free atmosphere.

The essence of the method for preparing a polymer sorbent according to the invention consists in heating the copolymer of glycidyl methacrylate with ethylene dimethacrylate in a flow of inert gas to a temperature of 250 to 300 °C for 10 min to 4 h, and after cooling, it is extracted with a non-polar solvent selected from the group of benzene, toluene, xylene and a polar solvent selected from the group of alcohols or acetone and dried.

Heating macroporous copolymers of glycidyl methacrylate with ethylene dimethacrylate to temperatures of 250 to 300 °C in an inert oxygen-free atmosphere results in both a weight reduction due to the outflow of pyrolysis process products, which are formed by monomers and other substances, and a restructuring of the internal structure consisting of conformational changes of polymer chains. These can only be described indirectly, for example, by chromatographic data, since they take place at the molecular level. The exclusion of oxygen is necessary in particular to exclude oxidative degradation of the sorbent, its discoloration and loss of the desired properties. A properly prepared sorbent is white in color and still has the shape of strictly spherical, individual particles.

The processing itself is carried out in a tube, for example glass, metal, which can withstand temperatures up to 300 °C without changes. In order to be able to place the polymer in it, the lower part must be provided with a partition preventing the sorbent from escaping, but allowing gas flow. Suitable materials include sintered glass frits, metal screens, a roll of glass or metal wool, mineral wool, and others. Below this partition is an inlet for gas supply, usually represented by a narrowing of the tube to a diameter corresponding to the internal diameter of the hoses used. The upper part is also closed, for example, with a ground-glass stopper, a screw, etc., allowing gas discharge and temperature measurement inside the bed of the sorbent being processed. The entire cylinder should have the smallest possible diameter to avoid undesirable radial temperature gradients.

The filled cylinder is placed in a tube furnace that allows heating to a temperature of about 500 °C using a resistance wire, microwave or other means. Before heating begins, an inert gas, such as nitrogen, argon, helium, is introduced into the tubes from below at a rate that prevents the column from rising and material from being lost to drift. The gas also acts as a temperature equalizing medium in the column. The escaping gas is then discharged to a device that eliminates volatile components, such as a furnace, a freeze-thaw separator or other device that eliminates environmental pollution.

After the time specified for modification has elapsed, the heating is switched off and the sorbent is allowed to cool with a constant gas flow. After reaching a temperature of approximately 20 to 50 °C, the product can be removed from the tube and subjected to extraction with an aromatic solvent and then with alcohol. Suitable solvents include benzene, toluene, ethanol, methanol. Extraction in a Soxhlet apparatus is most effective. After the solvent has been sucked off, the sorbent is dried either in air, observing safety rules, or under reduced pressure in an appropriate drying oven to constant weight. The sorbent thus obtained can then be directly used as a filling for gas chromatography columns.

The entire procedure is documented with the following examples.

Example

A macroporous copolymer of glycidyl methacrylate with ethylene dimethacrylate (60:40 wt.%), fraction 100 to 250 (um with a specific surface area (Sg) of 64 m2g ^- 1, characterized by polarity expressed by modified Rohrschneider constants x' 2.27, y' 3.86, z' 3.09, u' 4.87, s' 4.02, was filled into a glass tube with a diameter of 12 mm and a length of 200 mm provided with glass frit on one side. The tube was placed in a tube furnace and nitrogen was blown into it from below at a rate of 100 ml min ^-1 . The contents of the tube were heated to a temperature of 250 °C and left there for 60 minutes. Then it was removed, the sorbent was extracted with benzene and alcohol, dried and used as a filling for a gas chromatography column. The following were found constants: x'= 3.03, y'= 4.85, z'= 3.92, u'= 6.40.

Example 1 and 2

The sorbent was treated in the same way as in Example 1, except that the fraction 150 to 200 μm was heated to 260 °C for 2 hours. The resulting sorbent had the following constants: x'= 3.43, y'= 5.39, z = 4.26, u'= 7.15. The mixture of acetic acid esters was then separated on a column filled with this sorbent. Using a 100 cm x 0.3 cm column, a nitrogen flow rate of 25 ml min ^-1 and a temperature of 155 °C, the retention times (in brackets for the starting copolymer at 170 °C) were: methyl acetate 1.40 (1.50), ethyl acetate 1.9 (2.2), propyl acetate 3 (3.4), butyl acetate 4.8 (6.4), pentyl acetate 7.7 (11.4), hexyl acetate 11.7. On the same column, it was also possible to practically completely separate a mixture of 1-chlorobutane (boiling point 77.9 °C), ethyl acetate (bp 77.1) and methyl ethyl ketone (bp 79.6), while on polyethylene dimethacrylate all three substances appear as one peak and the separation factor on the starting sorbent is 0.80 and 0.65, respectively.

Example 3-8

A macroporous copolymer of glycidyl acrylate and ethylene dimethacrylate (45:65 wt. %) with a specific surface area (sg) of 109 m ² g ^_1 , fraction 150 to 180^um, was modified by heat treatment at different temperatures for different times. The table gives an overview of the results:

Example Modification X Rohrschneider constants Temperature °C Time, h y from at with 3 ⁺ - - 1 .44 2.66 2.23 3.48 2.67 4 250 1 1 .86 2.85 2.67 4.76 - 5 250 2 2.49 4.01 3.39 5.47 - 6 250 4 2.50 3.97 3.38 5.48 - 7 260 2 2.09 3.64 2.87 4.69 - 8 280 1 3.15 4.85 4.02 6.55 - ⁺ default copolymer Appendix 1 ad 9

The sorbent obtained according to Example 8 was filled into a 100 x 0.3 cm column and at a nitrogen flow rate of 25 ml min-1, the hydrocarbon mixture was separated, which can be characterized by retention times at a column temperature of 150 °C (in brackets, retention times for the starting copolymer at 175 °C), hexane 1.2 (1.5), heptane 2 (2.6), octane 3.1 (5.2), nona 5.4 (10), decane 9 (19.2), undecane 15.3 min.

Example 10

A copolymer of glycidyl methacrylate with ethylene dimethacrylate (20:80 wt. %) in a macroporous form with a specific surface area of 212 m ² g ^-1 , characterized by modified Rohrschneider constants: x' 1.05, y' 2.37, z' 1.89, u' 2.92, was heated for 30 min in a metal tube, equipped with a partition made of metal mesh with a mesh size of 50 /im, under which the gas supply was and closed with a cap with a drain tube and a thermometer well, to a temperature of 300 OC in a stream of argon. After cooling, it was extracted with toluene and methanol, dried and filled into a chromatographic column. The sorbent thus modified showed the constants: x'= 2.12, y'= 4.56; z'= 3.71, u'= 5.89.

Claims (2)

CLAIMS 1. Polymer sorbent with enhanced polarity for gas chromatography, characterized in that it consists of copolymers of glycidyl methacrylate and ethylenedimethacrylate containing 20 to 20 60 wt. a first component in a macroporous form having a measurable inner surface and in the form of regular spherical particles which has been heated to a temperature of 250 to 300 ° C for less than 4 hours in an oxygen-free atmosphere. 2. A process according to claim 1, wherein the copolymer of glycidyl methacrylate with ethylene dimethacrylate is heated in a stream of inert gas to 250-300 [deg.] C. for 10 min to 4 hours and extracted after cooling with a non-polar solvent selected from benzene. , toluene, xylene and a polar solvent selected from the group of alcohols or acetone, and dried.