ASTM D5443 for Paraffin, Naphthene, and Aromatic Hydrocarbon Type Analysis
ASTM D5443 Standard Test Method for Paraffin, Naphthene, and Aromatic Hydrocarbon Type Analysis in Petroleum Distillates Through 200°C by Multi-Dimensional Gas Chromatography
8. System Description
8.1 Commercial instruments are available that meet the specifications of this test method. One such system is based on pneumatic valves. Another system is based on rotary valves. Additional operating instructions are included in the operating and maintenance manuals for these instruments. The figures in this test method are applicable to these systems.
8.1.1 Fig. 1 and Fig. 2 illustrate typical instrument configurations that use different column valve switching techniques. This test method allows use of either configuration.
8.1.2 Figs. 3-13 illustrate the system flow configurations during the column test and sample analysis phases of this test method.
8.1.3 Table 3 and Table 4 list the conditions that apply during the column test and sample analysis phases for the instrument configuration in Fig. 1.
8.1.4 Table 5 and Table 6 list the conditions that apply during the column test and sample analysis phases for the instrument configuration in Fig. 2.
8.2 The polar column separates the sample into four fractions. The first three fractions are fore-flushed through the polar column and the last is back-flushed. Upon completion of each elution cycle, the flow through the column is stopped to maintain the relative position of non-eluted components within the column. For the purpose of simplicity, the three fore-flushes of the polar column will be called the "A", "B", and "C" cuts, respectively. The length of time associated with each cut will be called the "A", "B", and "C" times, respectively. These times are independent of each other and are a function of instrument configuration, column performance and carrier gas flow conditions.
9. Preparation of Apparatus
9.1 Place the gas chromatograph in service in accordance with the manufacturer's instructions. The initial settings listed in Table 3 and Table 4 have been found suitable for slider valve type instruments. The initial settings listed in Table 5 and Table 6 have been found suitable for rotary valve type instruments. Variances in column to column performance require that each flow setting and cut time be determined experimentally.
9.2 The carrier gas flow rates, A, B, and C times must be adjusted to produce acceptable analytical performance with the hydrocarbon test mixture in 7.6. These conditions are then recorded and must be used for sample analysis. The system is considered to meet the test method specifications if the hydrocarbon test mixture analysis absolute errors, as calculated in Sections 11 and 12, are equal to or less than the following: more or less 0.3 % per carbon number per hydrocarbon type (for example, C5 paraffins), and more or less 0.3 % per hydrocarbon class (for example, all paraffins).
9.3 Tuning Instrument Conditions with Hydrocarbon Test Mixture:
9.3.1 Configure the system initially as illustrated in Fig. 3. Use the conditions in Table 3 and Table 4 for slider valve type instruments or Table 5 and Table 6 for rotary valve type instruments.
9.3.2 Inject approximately 0.2 µL of the hydrocarbon test mixture and begin recording the signal from the detector. The sample injection marks the beginning of the A time. Allow paraffins and naphthenes with boiling points below 200°C to elute from the polar column. Retain aromatics, polynaphthenes, if present, and components boiling above 200°C on the polar column during the A time. If olefins are present in the first elution, they are hydrogenated by the platinum column. All eluting components are trapped on the molecular sieve column.
9.3.3 During the A time, a minimum of 80 % of the dodecane must elute from the polar column. The A time is too short or the A flow is too low if the dodecane elution is less than 80 %. The A time is too long or the A flow is too high if benzene or trans-decalin, or both, elute during the A time. Adjust the A time or A flow to meet these requirements.
9.3.4 At the end of the A time, change the configuration to that of Fig. 4. Place the polar column in stop flow and program the temperature of the molecular sieve column from 100 to 430°C, minimum, at the rate specified in either Table 3 or Table 5. Components will elute from the molecular sieve column as groups, by carbon number and group type. Within each carbon number group, naphthenes will elute first followed by paraffins. If the molecular sieve column contains a mixture of 13 X and five A types of molecular sieves, the group elution order will be first naphthenes as a group, followed by iso-paraffins as a group and then the normal paraffin, by carbon number.
9.3.5 Upon completion of the naphthene and paraffin elution, change the configuration to that of Fig. 5. Begin cooling the molecular sieve column to 100°C and switch the Tenax column into the A flow to receive the next cut from the polar column. Take the polar column out of stop flow. This marks the beginning of the B time.
9.3.6 During the B time, most, if not all, of the benzene and toluene, some of the C8 aromatics, decalin, naphthenes, and paraffins boiling above 200°C elute to the Tenax column. The B time is too short if all of the trans-decalin does not elute during the B time. The B time is too long if any of the o-Xylene or C9 aromatics elute during the B time. Adjust the B time to meet these requirements.
9.3.7 At the end of the B time, change the configuration to that of Fig. 6. Heat the Tenax column to 280°C and allow all trapped components to elute to the non-polar column. The aromatics and decalin elute from the non-polar column in boiling point order. Naphthenes and paraffins boiling above 200°C do not elute from the non-polar column at this time.
9.3.8 Four minutes and 30 s after the Tenax column begins to heat, change the configuration to that of Fig. 7 and back-flush the non-polar column. Cool the Tenax column to 60°C at this time. Continue the back-flush cycle for 5.5 min. Back-flush the naphthenes and paraffins boiling above 200°C from the non-polar column to the detector at this time.
9.3.9 At the end of this back-flush cycle, change the configuration to that of Fig. 8. This marks the beginning of the C time. The second cut of aromatics elute from the polar column to the Tenax trap. This elution contains some of the C8 aromatics, approximately one half of the C9 aromatics and a minor amount of C10 aromatics. Any remaining benzene and most, if not all, of the toluene that did not elute during the B time may elute at this time. Paraffins and naphthenes boiling above 200°C that did not totally elute during the B time may elute now.
9.3.10 The C time is too short if none of the o-Xylene elutes during the C time. The C time is too long if greater than 90 % of the o-Xylene elutes during the C time.
9.3.11 At the end of the C time, change the configuration to that of Fig. 9, place the polar column in stop flow. Heat the Tenax column to 280°C and allow all trapped components to elute to the non-polar column. The aromatics elute from the non-polar column in boiling point order.
9.3.12 Four minutes and 30 s after the Tenax trap begins to heat, change the configuration to that of Fig. 10 and back-flush the non-polar column. Cool the Tenax column to 60°C at this time. Continue this back-flush cycle for 5.5 min. Back-flush the naphthenes and paraffins boiling above 200°C from the non-polar column to the detector at this time.
9.3.13 At the end of this back-flush cycle, change the configuration to that of Fig. 11 and back-flush the polar column to the Tenax trap. This back-flush cycle lasts for approximately 10 min until all remaining components are back-flushed from the polar column to the Tenax column.
9.3.14 At the end of this back-flush cycle, change the configuration to that of Fig. 12. Heat the Tenax column to 280°C and allow all trapped components to elute to the non-polar column. The remaining aromatics with boiling points less than 200°C elute in boiling point order to the detector.
9.3.15 Approximately 6.5 min after the Tenax column begins to heat, change the configuration to that of Fig. 13 and back-flush the components boiling above 200°C from the non-polar column to the detector. Cool the Tenax column to 60°C and then stop the detector signal data collection.
9.4 Perform the steps outlined in Sections 11 and 12, below, to verify that the system is properly tuned. The system is considered to meet the test method specifications if the hydrocarbon test mixture analysis absolute errors are equal to or less than the following: more or less 0.3 % per carbon number per hydrocarbon type (for example, C5 paraffins), and more or less 0.3 % per hydrocarbon class (for example, all paraffins).
9.5 Record the actual times and temperatures and flows found necessary to meet the separation requirements as described in the various steps of 9.3. Use these parameters for all subsequent sample analyses.
