SEPARATING COLUMN FOR GAS CHROMATOGRAPHY

-- 1 -- 63293-2404 i0 This invention relates to a method of fabricating a gas chromatography separating column from an elongated capillary tube, said column having a layer comprising a plurality of disunited particles of porous solid material disposed on an inner surface of the tube. The invention also relates to a column fabricated according to such a method. Such columns are applied in the chromatographic analysis of mixtures of paraffins, naphthenes and aromatics (PNA-analysis) and are, for example, used in reformer process analyzers, which provide information on feed and product changes for catalytic reformers.

Conventional analyzers used in gas chromatography, for example as described in the article "Better gasoline chromatography" by H. Boer and P. van Arkel in "Hydrocarbon Processing" February 1972, pages 80-84, comprise a packed column. However, the separation results of such conventional packed columns for higher fractions such as C11 and C12 are not accurate.

For higher fractions there is an increasing overlap between the naphthene and paraffin bands that prevents accurate measurement of their relative distribution.

Therefore, it is an object of the invention to provide a column which is capable to measure quantitatively the paraffin/ naphthene fractions with baseline or near-baseline separation throughout the entire sample.

It is another object of the invention to provide a column which can distinctly separate the isoparaffins and paraffins.

Therefore, the method of the present invention is characterized by the steps of: preparing a suspension comprising water and particles of finely divided 13X molecular sieve material (known per 63293-2404 i0 se) and settling the slurry thus obtained during a time interval of 30-120 minutes, filling an elongated capillary tube with the prepared suspension by pushing the suspension into the tube under a pressure of 27,5-82,5 kPa; and flowing an inert gas at 0.i-i ml/min through the tube for 2-5 hours to dry the tube thereby leaving a layer comprising a plurality of disunited particles of said solid material attached to the inner surface of the tube, the particle size in the column ranging from 0.4-12.0 m.

The gas chromatography separating column of the present invention is characterized by an elongated capillary tube; and a layer comprising a plurality of disunited particles of porous solid material disposed on the inner surface of said tube by filling said tube at a pressure of 27,5-82,5 kPa with a suspension comprising water and particles of finely divided 13X molecular sieve material (known per se) and obtained by settling the slurry during a time interval of 30-120 minutes, and flowing an inert gas at 0.i-i ml/min through said tube for 2-5 hours to dry said "tube thereby leaving a layer comprising a plurality of disunited particles of said solid material attached to the inner surface of said tube, the particle size in the column ranging from 0.4-12.0 m.

The layer of finely divided particles provides a high resolution, type separation of naphthenes, isoparaffins and paraffins boiling up to 255°C.

It is remarked that CH-A-386,732, CH-A-408,460 and US-A-3,514,925 disclose open tubular chromatography columns wherein a layer of particles is disposed on an inner surface thereof. However the specific column of the invention cannot be derived therefrom.

- 3 - I w4 )52 63293-2404 i0 The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which:

Figure 1 is a cross section through an elution chromatography separating column according to the present invention; Figure 2 is a chromatogram obtained with the column of the present invention; Figure 3 is a chromatogram obtained with the column of the present invention, and Figure 4 is a chromatogram obtained with a conventional packed column.

The method of the invention is carried out as follows:

A suspension of the solid particles in the liquid can be achieved by means of stirring or vibrating the slurry. Usually, a treatment of two to three minutes is sufficient if no additional comminution of the solid is desired. Before the slurry or suspension is pressed into the capillary tube it is advantageous to pass it through a pressure sieve in order to eliminate coarser agglomerates which could lead to cloggings in the capillary tube.

An advantageous method of separating the desired sized particles is to allow the larger particles to settle during a predetermined time interval in the range of 30-120 minutes. One half to two thirds of the upper portion of the slurry is then pipetted into a separate container. The finely ground solid particles are molecular sieve type 13X. The capillary is filled by means of a pressure vessel and an inert gas, such as nitrogen, helium, argon and so forth. The pressure to be used depends on the diameter and the length of the capillary and on the viscosity of the suspension; usually the pressure is between 4-12 psig. The capillary tube ç 1« 9o28 - 3a - 63293-2404 i0 should be cleansed from impurities by washing it thoroughly, such as by using 0.1-0.3 N HCl followed by water which is followed by acetone and finally water again, prior to filling. The purging of the tube is performed by flowing an inert gas, such as helium, through the tube to dry it thereby leaving a layer of material attached to the inner surface or wall of the tube. Usually a purge 0.i - 1 ml/min is maintained for approximately two to five hours to dry the tube. Next the columm is stabilized at 420-440°C for about twice as long as the drying period.

The following examples are presented to provide a more complete understanding of the invention. The specific techniques, conditions, materials, proportions and reported data set forth to illustrate the principles and practice of the invention are exemplary and should not be construed as limiting the scope of the invention.

1 q528 5o EXAMPLE 1 Fifteen metres of stainless steel capillary tube with an inner diameter of 0.5 millimetres were conditioned with 8 ml of 0.1 N HCl and washed with water which was followed by acetone and finally water again. Next, 2.14 g of finely divided 13X molecular sieve material were suspended in 50 ml of deionized H20 and stirred rapidly. The slurry was allowed to settle for mixlutes; then 10 ml of the slurry containing a I:I000 w.ratio 13X/H20 were pressed into the capillary tube at a pressure of 6 psig while venting the excess to waste at a rate of 5-7 drops per minute. After the tube had been filled, the gas pressure on the slurry was gradually decreased to obtain a purge of N2 at a rate of 0.5 ml/min which was maintained on the tube for two hours to dry it. The tube was then conditioned with a stream of He passing through the tube at a rate of 6 ml/min and at a temperature of 440 °C for five hours. The column produced in this way contains about 1 mg of 13X molecular sieve material, and the particle size in the column ranges frcm 0.4-12.0 microns.

EXAMPLE 2 Thirty-eight metres of a stainless steel capillary tube with an inner diameter of 0.38 millimetres were rinsed with 0.3 N HCl and washed with water which was followed by acetone and finally water. Then 5.75 g of finely ground 13X molecular sieve material were suspended in 250 ml H2 0 by stirring. The slurry was allowed to settle for 60 minutes. Then I0 ml of the slurry were separated and pressed into the capillary tube at a pressure of II psig., venting the excess to waste. After the tube had been filled in this manner, a purge of He at a rate of 0.2-0.3 ml/min for two hours was maintained on the tube. The tube was then conditioned with a stream of He passing through the tube at a rate of 4 ml/min and at a temperature of 440 °C for six hours.

The column produced in this way contains about I mg of 13X molecular sieve material, and the particle size in the column ranges from 0o4-12.0 microns.

J. d:9528 3o With reference now to Fig. I a cross section through a stainless steel capillary tube according to the present invention has been represented. A stainless steel tubing 2 has a layer 4 consisting of disunited, detached solid residue from a suspension of finely subdivided 13X molecular sieve material in H20 per Example 1 above. The important improved achieved by the present invention is demonstrated by Figs. 2 and 3 which illustrate the chromatograms obtained with columns prepared according to Examples I and 2 respectively. The horizontal axes in Figs. 2 and 3 represent time (in min). The reference numerals N and P represent naphthene peaks and paraffin peaks respectively.

The temperature program used with each of the columns to obtain the chromatograms in Figs. 2 and 3 was as follows: the column was maintained at an initial temperature of. i00 °C for five minutes; the temperature was then increased at a rate of I0.0 °C/rein until 150 °C was reached; the temperature was maintained at 150 °C for one minute; the temperature was then increased at a rate of 2.5 °C/min until 288 °C was reached; the temperature was then increased at a rate of 1.5 «C/min until 440 °C was reached; and the temperature was maintained at 440 °C for forty-two minutes. For purposes of conloarison, Fig. 4 illustrates a chromatogram obtained with a conventional 13X molecular sieve packed column which was one metre long and had an inside diameter of I. 27 millimetres and which was packed with 13X materia! having a size in the range of 60 to 80 mesh. The horizontal axis in Fig. 4 represents time (in rein). The paraffin peaks æd naphthene peaks have been represented by N and P respectively. The temperature program used with the packed 13X column to obtain the chromatogram in Fig. 4 was as follows: the column was maintained at an initial temperature of 178 °C for five minutes; the temperature was then increased at a rate of I0.0 °C/min until 198 °C was reached; the temperature was then increased at a rate of 4.0 °C/min until 330 °C was reached; the temperature was then increased at a rate of I. 5 °C/min until 1Z 9528 3.O 3.5 390 °C was reached; the temperature was then increased at a rate of 2.0 °C/min until 410 °C was reached; the temperature was then increased at a rate of 2.5 °C/min until 445 °C was reached; and the temperature was maintained at 445 °C for sixteen minutes.

From Fig. 4 it is apparent that the carbon number of separation on a packed column for paraffins/naphthenes is quantitative through C8 partially quantitative for C9 and useful for C10 . However, for CI1 and C12 saturates fractions there is increasing overlap between the naphthene and paraffin bands that prevents accurate measurement of their relative distribution. Clearing the results obtained with the column of the present invention as illustrated in Figs. 2 and 3, it is readily apparent that the column of the present invention distinctly separates the isoparaffins and paraffins. Moreover, quantitative measure of the paraffin/naphthene fractions is carried out with baseline or near-baseline separation throughout the entire sample. A number of individua! naphthenes and paraffins of interest can also be identified up to C8. The column of the present invention also provides good peak shape through C14 for better integration and quantitative measurement in the C9 + region. In addition, separation of the various hydrocarbon groups is generally carried out at a lower column temperature with the present invention, thus reducing the risk of oxidizing the sample as it is being separated.

Various modifications of the present invention will become apparent to those skilled in the art frown the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.

IZ_4 526 63293-2404 K 8868 CAN THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE