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AB-1
AB-1MS
AB-5
AB-5MS
AB-PONA
AB Builtin - Guard
AB-CarboWax 20M
AB-INOWAX
AB-FFAP
AB-225
AB-35
AB-50+
AB-50+MS
AB-1301
AB-1701
AB-624
AB-PLOT Al2O3“KC”
AB-PLOT Al2O3“S”
AB-PLOT Al2O3“M”
AB-PLOT MoleSieve
AB-PLOT Q
Undeactivated Tubing
Deactivated Tubing
Customized columns
 
AichromBond AQ
AichromBond-SB
Aichrom Ion Exchange
Aichrom Chiral
Aichrom PAH
Aichrom Amino Acid
 
 
 PONA Analysis on AB-PONA Column
   Introduction

Gasoline, either naphtha, cracked or reformulated, contains large number of hydrocarbons including isomers. Because of complex compositions, the analysis of individual components is a challenging technique. ASTM D 5374 and D5374-92 give methods of detailed hydrocarbon analysis (DHA) for gasoline and other petrochemical applications. This specified DHA is done on high resolution capillary column, a 100% poly(dimethylsiloxane) column. Because of its specifically important role in DHA, this column is often called PONA column. Common PONA columns are either
0.20mm x 50m x 0.5um or 0.25mm x 100m x 0.5um.

Various software and methods have been developed for such PONA and DHA applications. There are two techniques for these applications. One is based on multi-dimensional GC, and other is based on high resolution chromatography. Both techniques use retention times of individual hydrocarbons to identify and quantify each composite separated. As the number of the composites of a gasoline can be as many as 500, the peak identification becomes very difficult and is very critical step for DHA. Often peak identification can be error. Intensive labor effort is then taken to manually correct errors in peak identification.

Among various software for ASTM D5134, a software called PONA developed by Beijing Chromtech Institute uses an algorithm of retention index to identify peaks. Because retention index is relatively insensitive to the variations from columns, instruments and methods, this software is able to automatically and correctly identify each peak with great confidence. Even though this algorithm improves accuracy of peak identification, it still requires minimum variations in column dimension, column retention time, column efficiency and column selectivity.

This application note describes a FCC gasoline application on an AB-PONA column. This AB-PONA column replicates the performances of HP-PONA column, an industrial fleet column, including column selectivity, column dimension and retention. Under the same instrumentation condition, the software PONA produces the same result as the one obtained from an HP-PONA column for this application.

   Experimental

2.1 Column
The column used is an AB-PONA column, 0.20mm x 50m x 0.5um, coated with AB-1 stationary phase, part number 0120-5005, obtained from Abel Industries, Inc., Newark, DE 19713, USA. The column temperature limits are -60C to 325/350C. Prior to each run, column was conditioned at 250C for 4hr.
2.2 Instrument condition
Instrumentation conditions are listed in Table I.

Table I the instrumentation conditions
Gas Chromatography

Agilent 6890 GC with ALS
Raw date acquisition
HP-Chemstation
Inlet
250c, s/s, split flow 140ml/min
Carrier
Nitrogen
Column head pressure
99kpa varied
Detector
FID, 300C
Oven
35C 10min, 0.5c/min to 60C, 2C/min to 180C, 10+min
Sample
A gasoline sample
Injection 1ul


2.3 Column retention time calibration

Constant pressure mode was used. Column head pressure was adjusted to have n-Pentane retention time around 9.75+-0.1min as holdup time prior to separation.

For a comparison, the analysis was repeated on an HP-PONA column at the same instrumentation condition.

 
   Software

3.1 DHA and PONA analysis
PONA software from Beijing Chromtech Institute, Beijing, China was used in a PC with OS Microsoft 95 or above. It uses the following formula (1) to calculate the retention index of all individual peaks.
RIi = ((RTi-Rtref_Cn)/(Rtref_Cn+1-Rtref_Cn)+ Cn)*100 (1)

RIi: Retention index of composite i
RTi: Retention time of composite i
Cn : Reference peak of carbon n
Cn+1: Reference peak of carbon n+1
Rtref_Cn :Retention time of reference peak Cn
Rtref_Cn+1:Retention time of reference peak Cn+1

Retention time of reference peaks can be searched automatically based on empirical database

(2) Calculation of Octane Number
Two octane values defined by RON and MON are calculated as
i=N
RON = Cr + Fr‘ AiWi (2)
i=1

i=N
MON = Cm + Fm‘ BiWi (3)
i=1

Cr : given constant, RON
Fr : given correlation factor, ROM
Cm : given constant, MON
Fm : given correlation factor, MON
Ai : correlation coefficient of ith hydrocarbon, RON, listed in calibration table
Bi : correlation coefficient of ith hydrocarbon, MON, listed in calibration table
Wi : weight percentage of ith , measured by DHA
N : total number of peaks measured by DHA

(3) Calculation of Carbon/Hydrogen(C:H)ratio
i=N
C:H = ‘ (C:H)iWi (4)
i=1

(C:H)i : Carbon/Hydrogen of ith hydrocarbon
Wi :weight percentage of ith , measured by DHA
N : total number of peaks measured by DHA
(4) Calculation of Specific Gravity (D)
i=N
D = ‘ DiWi (5)
i=1

Di : Specific Gravity of ith hydrocarbon
Wi :weight percentage of ith , measured by DHA
N : total number of peaks measured by DHA

(5) Data Analysis:
Once the separation of each composite in a gasoline sample is completed, the raw data of DHA can be generated by HP Chemstation or similar data acquisition software. The raw data includes peak retention time, area and/or area percentage. The file format of the raw data file used in this PONA software is .D. After completion of the chromatography run, the PONA reads the raw data file, and automatically identify the reference peak from assigned one of three databases for three types of gasoline. Once the reference peaks are identified, the software can automatically calculate all physically and chemically values described in(1) to (4). The report file can be either printed or transfer to fit customized report generation.

 
   Result

Fig 1 shows the comparable chromatograms of a FCC gasoline sample on AB-PONA and HP-PONA columns. It is clearly that the AB-PONA exhibits a small retention time difference from the HP-PONA column, however, the peak elution order and relative peak height ratios are essentially same. Even with this retention time difference, the PONA software is able to identify all peaks in both chromatograms. The physical properties calculated are listed in table II

Table II Calculated physical properties
Column
AB-PONA
HP-PONA
Number of peaks identified by the software
300
301
Calculated RON
87.26
87.15
Calculated MON
78.18
78.07
C:H 7.33
7.34
Specific density 0.8064 0.8062

All other calculated values are listed in the table III.

Table III PONA analysis report of a FCC gasoline sample
PONA Columns AB HP AB HP
Types
Wt%
Wt%

V %
V %
P (Normal Paraffin)
3.29
3.28
3.68
3.67
I (Iso Paraffin)
25.81
25.69
28.37
28.20
O (Olefin)
9.14
9.40
10.08
10.40
N (Naphtha)
15.74
15.72
16.20
16.19
A (Aromatic) 46.02 45.91 41.67 41.54

Chromatograms of a FCC gasoline sample (0-20min.)"B-PONA Column (top) HP-PONA Column (bottom)
Chromatograms of a FCC gasoline sample (60-80min.)"B-PONA Column (top) HP-PONA Column (bottom)
Chromatograms of a FCC gasoline sample (20-40min.)"B-PONA Column (top) HP-PONA Column (bottom)
Chromatograms of a FCC gasoline sample (80-100min.)"B-PONA Column (top) HP-PONA Column (bottom)
Chromatograms of a FCC gasoline sample (40-60min.)"B-PONA Column (top) HP-PONA Column (bottom)
Chromatograms of a FCC gasoline sample (100-120min.)"B-PONA Column (top) HP-PONA Column (bottom)
 
   Conclusion
Based on the above results and same instrumentation conditions used, it can conclude that both AB-PONA and
HP-PONA are essential identical and able to work for PONA applications with the PONA software to produce almost identical result.
 
  Order Guild
Table IV lists the suggested parts for PONA application.
Table IV Suggested parts for PONA analysis
Item
Description P/N
1 PONA software 9901-PONA
2
AB-PONA 9902-PONA
3 Gasoline Sample 9903-PONA

 
  Other applications of AB-PONA column
  Separations of natural gas, pesticides, and VOC.