Page 394 - Multidimensional Chromatography

386 Multidimensional Chromatography

Figure 14.7 Typical chromatogram obtained by using the refinery analyser system shown in
Figure 14.6. Peak identification is as follows: 1, hydrogen; 2, C 6 , 3, propane; 4, acetylene;
5, propene; 6, hydrogen sulfide; 6, iso-butane; 8, propadiene; 9, n-butane, 10. iso-butene; 11,
1-butene; 12, trans-2-butene; 13, cis-2-butene; 14, 1,3-butadiene; 15, iso-pentane; 16, n-pen-
tane; 17, 1-pentene; 18, trans-2-pentene; 19, cis-2-pentene; 20, 2-methyl-2-butene; 21, carbon
dioxide; 22, ethene; 23, ethane; 24, oxygen argon, 25, nitrogen, 26, carbon monoxide.

The economic value of natural gas is primarily determined by the thermal energy
it contains, which is expressed in British thermal units (Btu) or calorific value (CV).
Other important physical properties comprise the liquid content, the burning charac-
teristics, the dew point and the compressibility. In order to enable the calculation of
these properties from its composition, a natural gas analysis should contain a
detailed determination of all of the individual components, even in the low-concen-
tration range.
Figure 14.8 shows a detailed schematic representation of a natural gas analysis
system, which fully complies with GPA standardization (8). This set-up utilizes
four packed columns in connection with a TCD and one capillary column in con-
nection with an FID. The contents of both sample loops, which are connected in
series, are used to perform two separate analyses, one on the capillary column and
one on the packed columns. The resulting chromatograms are depicted in Figure
14.9.
The packed column section contains a stripper pre-column (column 1), which
separates the C 6 fraction by back-flushing all compounds above n-pentane in one
peak. H 2 S, CO 2 ,C 2 ,O 2 ,N 2 and C 1 are trapped in columns 3 and 4, while C 3 –C 5
hydrocarbons elute from column 2 to the TCD. The remaining components are