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Topic: Sediment by extraction ASTM D 473-07  (Read 3577 times)

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Offline Andy932

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Sediment by extraction ASTM D 473-07
« on: April 27, 2017, 06:10:09 AM »
Hi guys perhaps this is a long shot. Can anyone help? Maybe someone has experience with this test?

I work in a Laboratory for an oil company in Manchester, England using various Wetchem/Physical tests (Titrations, Acid/Base numbers, XRF, Flash, Water KF etc..) I am generally very familiar with these tests and very rarely have problems but there is one I am totally new to. That is Sediment by extraction. I am extracting heavy fuel oils through a thimble using the solvent Toluene. The weight before and after test is calculated and reported in percentage terms. I have been following the ASTM method stated above.

The problem I am having is getting the weight of the thimble steady. I am calculating the sediment weight to 4 decimal places so the thimble weight before testing must be representative. After passing the hot Toluene through the thimble containing the HFO (13g) the end result thmble weight is lower than the initial thimble weight. Obviously this should not happen, it should always be greater than. The procedure is as follows

- Condition thimble in test apparatus with fresh Toluene for 1hr commencing the first point at which the Toluene fully passes through thimble
- After 1 hour has passed place thimble in Laboratory oven at 117c for 1 hour
- After 1 hour in oven has passed place thimble in beaker in desiccator for 1 hour
- After 1 hour in desiccator weigh
- Repeat above steps and note weight until consistent weight is achieved

The problem is getting the weight of the thimble consistent and achieving a positive weight after passing HFO through it.

In terms of the sample. It is agitated for homogeneity and then decanted into a beaker, measuring around 13.0g. The sample is then heated in the beaker above a hot place at 180c to evaporate any water in the sample. Water in the sample causes the test to fail whereas the HFO will pas back through the column before extraction is complete.

Any help will be much appreciated.

Andy

Offline Arkcon

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Re: Sediment by extraction ASTM D 473-07
« Reply #1 on: April 27, 2017, 06:23:55 AM »
You want get good results, until you have the initial thimble weight under control.  You have a through procedure for cleaning the thimble.  Are you following it carefully?  Something to try: condition the thimble, weigh, then recondition, and weigh again.  Do as many time as you can, 3 or 4 times.  What happens to the weight of a conditioned thimble?  Constant?  Fluctuating for the first two and then constant?

Meantime, reevaluate your balance.  Can you weigh the calibration weights, consistently, to 4 decimal places, while the thimble is conditioning?  How repeatable are those measurements?  You can gave us a table of your results.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline Andy932

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Re: Sediment by extraction ASTM D 473-07
« Reply #2 on: April 27, 2017, 06:59:55 AM »
Thanks for the quick reply.

Indeed the thimble has to weigh in consistently before the test can be accurately performed. What I will do;

I will run 3 or 4 times and see what I get again. I wasn't getting consistency with the conditioning before but I am now using double layered thimbles so will try with the new ones. In the ASTM method they use a thimble 'weighing not less than 15 g and not more than 17 g' whereas mine weighs circa 4g straight out of the box. I have also changed the desiccator humidity absorbents to see if it's a case they are not working properly (they hadn't changed colour)

In terms of the balance we don't calibrate balances, we aren't UKAS accredited so we're not obliged too. From experience I wouldn't expect any day to day deviation to be great enough to make a huge different in the result.

I was considering weighing the thimble straight out the oven and then use that weight before it has cooled. See if I can get consistency that way.

Offline Borek

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Re: Sediment by extraction ASTM D 473-07
« Reply #3 on: April 27, 2017, 09:00:15 AM »
I was considering weighing the thimble straight out the oven

Putting something hot on the balance is asking for troubles, if nothing else, just convection will make the reading fluctuate.
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Offline Corribus

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Re: Sediment by extraction ASTM D 473-07
« Reply #4 on: April 27, 2017, 03:47:53 PM »
In terms of the balance we don't calibrate balances, we aren't UKAS accredited so we're not obliged too. From experience I wouldn't expect any day to day deviation to be great enough to make a huge different in the result.
Assumptions are always better off checked. Anyway, just because you aren't required to calibrate balances doesn't mean you shouldn't do it. And in any case, I don't think Arckon was telling you to calibrate your balance - he was recommending that you use a standard mass to check and see whether your balance was reading a consistent result during the time scale of your experiment. If your standard mass changes the same way your thimble does, you know it's a problem with your balance. If your standard mass has a constant reading, you know it's something experimental and you can cross your balance off the list of possible problems.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

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