Crude Oil Charactarisation

Discussions about GC and other "gas phase" separation techniques.

17 posts Page 1 of 2
Is there any method for crude oil analysis for components upto C35 and reporting the rest as C36+. Does it make sense to follow the simulated distillation method using the addition of internal standard C14-C17 and running the sample as spiked and nonspiked? Please help
bijish

You need to give us some idea of what you are trying to achieve. Crude oil analysis can be very complicated. Are you trying to identify all peaks or do you want to break down into groups.

Gasman
GasMan wrote:
bijish

You need to give us some idea of what you are trying to achieve. Crude oil analysis can be very complicated. Are you trying to identify all peaks or do you want to break down into groups.

Gasman


Thanks a lot for your reply. I would like to identify individual components upto Nonane. After nonane it will be reported as n-decane, decane isomers, n-undecane, undecane isomers etc upto n-C35 and C35 isomers. The remaining fraction is to be reported as C36+. Currently we are using a standard that contain most of the possible components in crude oil upto C25. This standard contains 3% Isooctane as internal standard. We are adding the same concentration of Internal standard to crude oil and inject into the GC. For components from C26 to C36 we are giving the same response factor as that of C25. Column used is HP-PONA 50 m x 0.2 x 0.5. It is not easy to get a baseline blank to subtract from the sample signal. Also after a number of injections peaks begin tailing.

Waiting for your feedback.

Bijish
Hello

"Column used is HP-PONA 50 m x 0.2 x 0.5. It is not easy to get a baseline blank to subtract from the sample signal. Also after a number of injections peaks begin tailing"

I would suggest to keep an eye on baking out procedure. It is 50m column and your sample is very complex so baking out needs to be long enough to remove everything from column.
Things like guard column (pre-column) and liner type can be considered as well.

Regards

Tomasz Kubowicz
I am not aware of a single method that will accomplish what you are trying to do. To me this would be a two injection process. You should look at the ASTM method D5134, which is how to get detailed information up to C9. You would need to backflush the C10+. The second injection would be something like the Simulated Distillation method D2887, and you could then use your Data Analysis software to group the compounds.

Gasman
It is a GC factoid that no column ever made could separate everything in crude oil below C7.

Peter
Peter Apps
There is ASTM D7900 which claims to be more accurate at the front end hydrocarbons, which might be worth looking at.
You probably need to do some sort of 2d GC or heart cutting.
GasMan wrote:
I am not aware of a single method that will accomplish what you are trying to do. To me this would be a two injection process. You should look at the ASTM method D5134, which is how to get detailed information up to C9. You would need to backflush the C10+. The second injection would be something like the Simulated Distillation method D2887, and you could then use your Data Analysis software to group the compounds.

Gasman


Thank you...Is it possible to convert the D2887 data from boiling point distribution to component composition?
bijish wrote:

Is it possible to convert the D2887 data from boiling point distribution to component composition?


No, this requires the use of GC methods with better separation.
GasMan wrote:
I am not aware of a single method that will accomplish what you are trying to do. To me this would be a two injection process. You should look at the ASTM method D5134, which is how to get detailed information up to C9. You would need to backflush the C10+. The second injection would be something like the Simulated Distillation method D2887, and you could then use your Data Analysis software to group the compounds.

Gasman


Could you please advise how to incorporate backflush on a capillary column in Agilent 7890A GC system..
I assume that you already have a capillary inlet and FID detector on your 7890A. You will also need an pressure source that can be controlled by the GC, a precolumn and a tee. The pre-column can be the same phase as your main column, but about 5 meters long. The pre-column in connected to your inlet and one leg of the tee. Your main column is connected to the tee and your detector. The remaining leg of the tee is connected to the pressure source.

You set up the pre-column as Column1, with the capillary inlet as the inlet to Column 1 and the outlet of Column1 is set to the pressure source. You should also set this column to be in ramped flow mode. Column2 is set up with the pressure source as the inlet and the detector as the outlet. Set this column to constant flow.

Set the flow of Column 2 to the flow that you require.

Set the flow of Column 1 to be 90% of Column 2 flow.

When you want to backflush, you set a negative flow for Column 1. The 7890A will then drop the pressure of the inlet so that it is less than the pressure set by the pressure source which will result in the flow in Column1 going backwards. If you are temperature programming, the pressures will compensate for changes in viscosity resulting in constant flows.

Gasman
To add to backflush discussion: Agilent has a white paper describing how to set up a crude oil backflush "Prefractionator for Reliable Analysis of the Light Ends of Crude Oil and other
Petroleum Fractions", using their MMI inlet (hybrid split/splitless and PTV), an AUX EPC, and CFT (purged ultimate union) connector. It isn't exactly what you want, but in your case, the information in it may help inspire your method devloopment.

Good luck
GasMan wrote:
I assume that you already have a capillary inlet and FID detector on your 7890A. You will also need an pressure source that can be controlled by the GC, a precolumn and a tee. The pre-column can be the same phase as your main column, but about 5 meters long. The pre-column in connected to your inlet and one leg of the tee. Your main column is connected to the tee and your detector. The remaining leg of the tee is connected to the pressure source.

You set up the pre-column as Column1, with the capillary inlet as the inlet to Column 1 and the outlet of Column1 is set to the pressure source. You should also set this column to be in ramped flow mode. Column2 is set up with the pressure source as the inlet and the detector as the outlet. Set this column to constant flow.

Set the flow of Column 2 to the flow that you require.

Set the flow of Column 1 to be 90% of Column 2 flow.




When you want to backflush, you set a negative flow for Column 1. The 7890A will then drop the pressure of the inlet so that it is less than the pressure set by the pressure source which will result in the flow in Column1 going backwards. If you are temperature programming, the pressures will compensate for changes in viscosity resulting in constant flows.

Gasman
GasMan wrote:
I assume that you already have a capillary inlet and FID detector on your 7890A. You will also need an pressure source that can be controlled by the GC, a precolumn and a tee. The pre-column can be the same phase as your main column, but about 5 meters long. The pre-column in connected to your inlet and one leg of the tee. Your main column is connected to the tee and your detector. The remaining leg of the tee is connected to the pressure source.

You set up the pre-column as Column1, with the capillary inlet as the inlet to Column 1 and the outlet of Column1 is set to the pressure source. You should also set this column to be in ramped flow mode. Column2 is set up with the pressure source as the inlet and the detector as the outlet. Set this column to constant flow.

Set the flow of Column 2 to the flow that you require.

Set the flow of Column 1 to be 90% of Column 2 flow.

When you want to backflush, you set a negative flow for Column 1. The 7890A will then drop the pressure of the inlet so that it is less than the pressure set by the pressure source which will result in the flow in Column1 going backwards. If you are temperature programming, the pressures will compensate for changes in viscosity resulting in constant flows.

Gasman
GasMan wrote:
I assume that you already have a capillary inlet and FID detector on your 7890A. You will also need an pressure source that can be controlled by the GC, a precolumn and a tee. The pre-column can be the same phase as your main column, but about 5 meters long. The pre-column in connected to your inlet and one leg of the tee. Your main column is connected to the tee and your detector. The remaining leg of the tee is connected to the pressure source.

You set up the pre-column as Column1, with the capillary inlet as the inlet to Column 1 and the outlet of Column1 is set to the pressure source. You should also set this column to be in ramped flow mode. Column2 is set up with the pressure source as the inlet and the detector as the outlet. Set this column to constant flow.

Set the flow of Column 2 to the flow that you require.

Set the flow of Column 1 to be 90% of Column 2 flow.

When you want to backflush, you set a negative flow for Column 1. The 7890A will then drop the pressure of the inlet so that it is less than the pressure set by the pressure source which will result in the flow in Column1 going backwards. If you are temperature programming, the pressures will compensate for changes in viscosity resulting in constant flows.

Gasman


Thanks for ur great help!!! Is there any reason why normal components begin tailing initially compared to its isomers (in my chromatogram n-pentane starts tailing but isopentane not...
bijish,

Can I suggest you talk to someone like Separation Systems in Florida? They make an application that shoots neat crude on a PONA column to give you LSR up to C13 and then backflushes the balance of the crude. Then they marry that data to another run from another instrument that does C5 to C100 SimDis. Without a backflush, a 50 m PONA column will probably not elute C44 today any time (or even maybe tomorrow...)

Best regards,

AICMM
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