Method for Quantitative Analysis of Hydrogen in Porous Silica

Abstract

A method for quantitative analysis of hydrogen gas generated due to the decomposition of SiOH (silanol) in porous silica, which is a support of a metallocene catalyst is provided. The analysis enables the measurement of the content of hydrogen present in trace amounts in silica by employing an inert gas fusion-infrared absorption (IGFIA) method under specific pressure and temperature conditions.

Claims

1. A method for quantitative analysis of hydrogen in porous silica, comprising: (i) heating porous silica used in a production of metallocene polypropylene catalyst at 0.1 bar to 0.15 bar and at 550 C. to less than 700 C. for 60 seconds to 1.5 minutes to evaporate moisture, and then adsorbing the evaporated moisture on a moisture scrubber to remove the adsorbed moisture, and (ii) heating the porous silica from which moisture has been removed at 0.1 bar to 0.15 bar and at 1200 C. to 1300 C. for 60 seconds to 1.5 minutes to decompose a SiOH group, resulting in hydrogen gas, and then transferring the hydrogen gas to an infrared detector using a carrier gas to quantitatively analyze hydrogen using an inert gas fusion-infrared absorption (IGFIA) method.

2. The method according to claim 1, wherein (1) the heating is carried out at 0.102 bar to 0.104 bar and at 590 C. to 650 C. for 70 seconds to 1.2 minutes.

3. The method according to claim 1, wherein (1) the heating is carried out at 0.1 bar and at 600 C. to 610 C. for 90 seconds.

4. The method according to claim 1, wherein (ii) the heating is carried out at 0.102 bar to 0.104 bar and at 1230 C. to 1260 C. for 70 seconds to 1.2 minutes and wherein the carrier gas is helium (He) gas.

5. The method according to claim 1, wherein (ii) the heating is carried out at 0.1 bar and at 1250 C. for 90 seconds.

6. The method according to claim 1, wherein the porous silica has an average particle size of 30 m to 55 m and a BET surface area of 300 m.sup.2/g to 350 m.sup.2/g.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 shows the measurement of hydrogen content after removing moisture in the silica and decomposing SiOH according to one embodiment of the present invention.

[0017] FIG. 2 shows the hydrogen content in the silica analyzed according to Example 1 of the present invention.

[0018] FIG. 3 shows the hydrogen content in the silica analyzed according to Example 2 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described in more detail.

[0020] The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary meanings and should be construed as meaning and concept consistent with the technical idea of the present invention based on the principle that the inventor can properly define the concept of the term in order to explain its invention in the best way possible.

[0021] It is an object of the present invention to provide a method for quantitatively analyzing the content of hydrogen present in trace amounts in porous silica as a support used in the production of metallocene catalysts.

[0022] In order to achieve the object, in the method of the present invention, moisture in silica is removed and then a SiOH group is decomposed, resulting in hydrogen gas, and the hydrogen gas is transferred to an infrared detector (IR detector) using a carrier gas to analyze the content of hydrogen gas by an inert gas fusion-infrared absorption (IGFIA) method.

[0023] In one embodiment, the present invention provides a method for the quantitative analysis of hydrogen in porous silica, wherein the method comprises (i) heating porous silica used in the production of metallocene polypropylene catalyst at 0.1 to 0.15 bar and at 550 to less than 700 C., for example, 550 to 650 C. for 60 seconds to 1.5 minutes to evaporate moisture, and then adsorbing the evaporated moisture on a moisture scrubber to remove the adsorbed moisture, and (ii) heating the silica from which moisture has been removed at 0.1 to 0.15 bar and at 1200 to 1300 C. for 60 seconds to 1.5 minutes to decompose a SiOH group, resulting in hydrogen gas, and then transferring the hydrogen gas to an infrared detector using a helium (He) carrier gas to quantitatively analyze hydrogen using an inert gas fusion-infrared absorption (IGFIA) method.

[0024] In the present invention, the moisture scrubber absorbs moisture generated by heating of the porous silica sample and removes water vapor as shown in the following reaction scheme:

Mg(ClO.sub.4).sub.2(s)+3H.sub.2O(g).fwdarw.2HClO.sub.4.2H.sub.2O(s)+MgO(s)

[0025] The moisture scrubber may be made of Mg(ClO.sub.4).sub.2(s), for example and Mg(ClO.sub.4).sub.2(s) exists in a crystalline form before it absorbs moisture, but when it absorbs moisture it turns into a soft powder form.

[0026] The pressure, temperature, and time range defined in the heating step of (i) correspond to optimum conditions in which the moisture in the porous silica sample is evaporated and the evaporated water vapor is adsorbed on the moisture scrubber. If the pressure, temperature and time range are out of the above-defined range, the analysis accuracy of the hydrogen content in the silica sample may be degraded.

[0027] With respect to the temperature in the heating step of (i), the content of evaporated moisture was measured by heating the silica at the respective temperatures shown in the table below in an analytical environment of 0.1 bar. The measurement results are as follows:

TABLE-US-00001 Temperature ( C.) Moisture content (wt %) 700 0.02 850 14.5 1100 16.4 1250 63.7 1500 80.7 1750 84.5 1850 89.1 2100 98.9 2200 95.5 2300 95.5

[0028] As a result of measurement, moisture in the vapor form evaporated from silica was not measured below 700 C. Thus, below 700 C., all water vapor evaporated from the silica can be removed. However, at a temperature of 700 C. or higher, evaporated water vapor exists and some of the water vapor is decomposed into hydrogen and oxygen, so that the hydrogen content in the silica can not be accurately analyzed.

[0029] The upper and lower limits of the pressure range of the heating step of (i) are set in consideration of the operating conditions of an apparatus used in the IGFIA method of the present invention, for example, ONH836 (LECO Corporation).

[0030] In addition, the upper and lower limits of the time range of the heating step of (i) are set in consideration of the time taken for moisture to sufficiently evaporate from the silica and to adsorb on the moisture scrubber.

[0031] In one embodiment, the heating step of (i) may be carried out at 0.102 to 0.104 bar and at 590 to 650 C. for 70 seconds to 1.2 minutes.

[0032] In other embodiment, the heating step of (i) may be carried out at 0.1 bar and at 600 to 610 C. for 90 seconds.

[0033] The pressure, temperature and time range defined in the heating step (ii) corresponds to the optimum conditions for decomposing SiOH in silica to generate hydrogen gas.

[0034] If the temperature range of the heating step of (ii) is out of the above range, the SiOH in the silica is not sufficiently decomposed.

[0035] In one embodiment, the heating step of (ii) may be carried out at 0.102 to 0.104 bar and at 1230 to 1260 C. for 70 seconds to 1.2 minutes.

[0036] In other embodiment, the heating step of (ii) may be carried out at 0.1 bar and at 1250 C. for 90 seconds.

[0037] In one embodiment, the porous silica has an average particle size of 25 to 60 m, for example 30 to 55 m and a BET surface area of 300 to 350 m.sup.2/g, for example 320 m.sup.2/g.

[0038] The IGFIA method used in the present invention is a method in which a small amount of a sample is placed in a graphite crucible in a furnace and burned at a high temperature under a stream of Ar or He as an inert carrier gas, for example by first heating at 600 C., then second heating to 1250 C., and the released gas is measured by infrared absorption. It is known to analyze H.sub.2 released by burning at high temperature and analyze the released H.sub.2 by an infrared detector.

[0039] In one embodiment, the hydrogen gas analyzer used in the IGFIA method of the present invention is not particularly limited as long as it is commonly used in the art, and may be, for example, ONH836 (LECO Corporation).

[0040] In one embodiment, the infrared detector used in the present invention is not particularly limited as long as it is commonly used in the art, and may be, for example, ONH836 (LECO Corporation).

[0041] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

EXAMPLES

[0042] 1. Preparation of Sample and Analysis of Hydrogen Content

[0043] (1) A silica sample A (Example 1) having an average particle size of 31 m and a silica sample B (Example 2) having an average particle size of 55 m (Grace, SYLOPOL948) were put into a Sn capsule (LECO Corporation, tin capsule, ID 5.0 mm, height 13 mm)/Ni basket (LECO, Ni basket, 1 g) in an amount of 0.01 g, respectively.

[0044] (2) A double graphite capsule (graphite crucible, LECO Corporation) was installed in a furnace (ONH836, LECO Corporation) and a Sn capsule/Ni basket containing the sample from (1) above was placed therein.

[0045] (3) Using He carrier gas, the sample from (2) above was heated at 600 C. and 0.1 bar for 90 seconds to evaporate moisture and the evaporated moisture was removed by adsorption on a moisture scrubber made of Mg(ClO.sub.4).sub.2 [heating step 1].

[0046] (4) Next, the sample from (3) above was decomposed by heating at 0.1 bar and at 1250 C. for 90 seconds, and the resulting hydrogen gas was measured using an ND-IR detector (heating step 2).

[0047] The results of measurement of hydrogen content after removing moisture in a silica sample and decomposing SiOH according to the present example are shown in FIG. 1.

[0048] 2. Analysis of Hydrogen Content

[0049] The results of hydrogen content analysis of the silica sample A having an average particle size of 31 m and the silica sample B having an average particle size of 55 m mentioned in 1. Preparation of sample and analysis of hydrogen content are shown in the table below. As the particle size increases, the relative surface area decreases. From this, the amount of OH adsorbed on the silica surface can be expected to be small. Relative standard deviation in the following table is data for determining the reproducibility of the analysis, so it is not related to the silica particle size.

TABLE-US-00002 Average particle Hydrogen content Relative standard size (m) (mg/kg) deviation (RSD %) Silica A 31 598 2.12 (Example 1) Silica B 55 445 5.71 (Example 2)

[0050] The analysis results of hydrogen content for the silica A (Example 1) and the silica B (Example 2) based on the above table are shown in FIGS. 2 and 3, respectively. As can be seen from the above table, according to the quantitative method of the present invention, it is possible to quantitatively analyze hydrogen present in a trace amount of 100 mg/kg to 1000 mg/kg in silica.

[0051] It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit or essential characteristics of the invention. Therefore, it should be understood that the above-described embodiments are illustrative in all aspects and not restrictive. In addition, the scope of the present invention is indicated by the following claims rather than the above detailed description.