- Pour silica gel into large neck, round, flat-bottomed flasks (~150-200 grams/flask)
- Place flasks in vacuum oven at 120°C for 24 hours at full vacuum (activation)
- Pour ~50 grams of activated silica gel in a 500 mL round bottomed flask already containing deasphalted crude from asphaltene precipitation of 10 grams of crude oil
- Add 200 mL of HPLC methylene chloride
- Shake the flask for at least 24 hours
- Rotavap until dry (looks like dirty sand), low vacuum and 50°C or higher vacuum with very low surface area contact with water
- Place in a vacuum oven at 50°C for 24 hours (full vacuum), watch the oven for the first 8 hours because the cold trap will probably plug
Column Setup
- Rinse column with methylene chloride and n-heptane or first solvent to be used
- Fill the column with 300 mL of n-heptane
- Add 30 grams of activated silica gel slowly with occasional tapping of the column to minimize trapped air in the silica and to prevent plug formation
- Drain 50 mL of n-heptane from the column to eliminate super-fine silica particles and to eliminate air trapped in the silica gel matrix
- Add the activated silica with adsorbed deasphalted crude (slowly and with tapping)
Column Operation
- Open the buret tip so that the column drains at 8-10 mL/min (fast drip). Use a 100 mL graduated cylinder to collect the eluted solvent. To prevent splashing place the graduated cylinder so that the solvent runs down the inside wall. When the 100 mL cylinder gets full, switch to another cylider without stopping the solvent flow. Empty the full cylinders into a round bottomed flask and label as E1 (extrography fraction 1).
- When the level of n-heptane approaches the top of the silica gel add more n-heptane in 100 mL increments
- When a pale yellow color gets to the bottom of the buret, switch to a new collection cylinder (now empty the full cylinders into a different round bottomed flask, labeled E2-4) and begin to add solvent #3 (68 % n-heptane/32 % toluene) the next time the solvent level approaches the top of the silica in the column.
- Continue to collect for E2-4 until the pale yellow color changes to dark orange and then gets significantly lighter in color (use ~ 500 mL solvent #3, may need 100 mL more in some cases).
- When the solvent level approaches the top of the silica gel add solvent #4 (40 % acetone/30 % toluene/30 % methylene chloride) in 100 mL increments (400 mL total, most of the color will come off the column in the first 100-200 mL)
- Switch collection cylinders when dark color reaches the bottom of the plug and from here on add to a round bottomed flask labeled E5.
- When the solvent level reaches the silica, continue to drain into the collection cylinder
- Force additional solvent out by applying pressure to the top of the column with nitrogen
- Allow the columns to dry for a little while, then turn the column over and empty the silica into a round bottomed flask. To aid in this, apply pressure through the buret tip with nitrogen.
Fraction Handling
- Rotavap E1, E2-4, and E5 until dry
- Transfer the samples to weighed, Qorpak, straight walled jars using methylene chloride
- Allow the samples to dry in a fume hood
- Add ~ 300 mL of pyridine to the silica gel from the column and let sit for ~ 20 minutes
- Using the large Buchner funnel and Whatman 934-AH glass microfiber filters, vacuum filtrate the silica gel. Wash the silica gel with pyridine until the filtrate is clear (this will take a couple hundred mL).
- Pour the filtrate and methylene chloride rinsings into a 1000 mL round bottom flask
- Rotavap this at 50°C and at a high vacuum (it takes a while).
- When the sample is dry, add a little methylene chloride to redissolve the material and pour it into a separatory funnel (pre-rinsed with methylene chloride) with a fritted glass disc on the bottom to eliminate any silica particles. Collect this material in the Qorpak jar labeled E5
Fraction Drying
- E1 and E2-4:
o Apply vacuum until gauge reads 20 or wherever the sample begins to bubble
o purge with nitrogen three times
o pull the vacuum down to 15, close the valve to the vacuum and turn the heat on (50°C)
o After several hours increase the vacuum, and eventually pull the maximum vacuum and keep the vacuum valve open
- E5:
o full vacuum after purging twice with nitrogen
o turn heat on to 70°C
- keep samples in oven for at least 24 hours
- weigh samples