Measuring Benzene Precursors In Naphtha Splitter Bottoms

[RefineryMan79]

We are preparing to install a new Naphtha Splitter to reduce Benzene pre-cursors in the Reformer feed for MSAT II compliance. Our process engineers want me to install an online analyzer that measures the concentration of several Benzene precursors, namely Cyclohexane and Methylcyclopentane, in the splitter bottoms. I feel a process gas chromatograph could be unreliabe in seperating out similar sized molecules. Could I use another technology such as NIR (Near Infrared), NMR (Nuclear Magnetic Resonance), or a mass spectrometer? Is there another indicator that is easily measured to determine the perfomance of splitter?

 

[ash9144]

Cyclohexane bp=177F
Methyl cyclopentane bp=162F
Should be plenty of difference to determine by GC

 

[JLSeagull]

Check

http://www.restek.com/petro

I have a 16 page pdf named PCFL1195. I looked at the Restek separation in a figure labeled "Figure 5 Critical pairs of gasoline components resolved per ASTM specifications on an Rtx®-1PONA column."
Most component peaks were completely separated. 3 is close to 4, 8 close to 9, 11 close to 12, 19 close to 20.
1. ethanol
2. C5
3. tert-butanol
4. 2-methylbutene-2
5. 2,3-dimethylbutane
6. methyl tert-butyl ether (MTBE)
7. C6
8. 1-methylcyclopentene
9. benzene
10. cyclohexane
11. 3-ethylpentane
12. 1-tert-2-dimethylcyclopentane
13. C7
14. 2,2,3-trimethylpentane
15. 2,3,3-trimethylpentane
16. toluene
17. C8
18. ethylbenzene
19. p-xylene
20. 2,3-dimethylheptane
21. C9
22. 5-methylnonane
23. 1,2-methylethylbenzene
24. C10
25. C11 (undecane)
26. 1,2,3,5-tetramethylbenzene
27. naphthalene
28. C12 (dodecane)
29. 1-methylnaphthalene
30. C13 (tridecane)

Column: Rtx®-1PONA, 100m, 0.25mm ID, 0.5?m (cat.# 10195)
plus Rtx®-5PONA tuning column, 2.62m, 0.25mm ID,
1.0?m, connected via Press-Tight® connector
(cat.# 20446)
Sample: custom detailed hydrocarbon analysis
(DHA) mix, neat
Inj.: 0.01?L, split (split ratio 150:1), 4mm cup
inlet liner (cat.# 20709)
Inj. temp.: 200ºC
Carrier gas: helium, constant flow
Linear velocity: 28cm/sec. (2.3mL/min.)
Oven temp.: 5ºC (hold 15 min.) to 50ºC @ 5ºC/min. (hold
50 min.) to 200ºC @ 8ºC/min. (hold 10 min.)
Det.: FID @ 250ºC

 

[cloa]

I'd like to see them separate the identical 14 and 15. Obviously one solution to the OP's problem provided it doesn't care about stereography of the methylcyclopentane as lists on 1- form.

 

[JLSeagull]

I buy analyzers and do not select GC columns. On close inspection peak 14 stands alone and peaks 15 and 16 are not resolved. I will let the chemists determine how different 2,2,3- and 2,3,3- trimethylpentane are in boiling point or other properties. For some separations the GC folks use a mixture of boiling point and polar column packing. ;-)