Poor Yields of Elemental Sulfur extraction with Xylene from Encap™ Fast Acting™ Sulfur Plus AST™

Poor Yields of Elemental Sulfur extraction with Xylene from Encap™ Fast Acting™ Sulfur Plus AST™

Abstract: A procedure is presented for the extraction of elemental Sulfur from the Encap™ Fast Acting™ Sulfur Plus AST™ garden product. Sulfur yield was a disappointing 10% of the initial mass, approximately 25% of the amount expected. Suggestions for future work are included.

Background: A damaged bag of Encap™ Fast Acting™ Sulfur Plus AST™ was obtained containing 1.08kg of product. This was opened and dispensed into a Ziploc Bag for storage and the damaged packaging discarded. The material consists of roughly even proportions of dark brown pebbles and light-brown chocolate chip shaped pieces approximately 3 mm in diameter.

Source Material


The packaging indicates that the product contains 49.72% Sulfur, 54.25% Gypsum, and 5.6% other. This must be a remarkably effective fertilizer as it gives 110%. The author took great delight in this, and theorizes that the Encap marketing department may have had some involvement in this packaging design.

Package Label


The author assumed the following composition

• 40% Elemental Sulfur (S)
  
• 54% Gypsum (CaSO₄-2H₂O)
  
• 6% other including Bentonite Clay and Lignosulfonates
  

Procedure: 20 grams of product were placed in a 250ml beaker and 50mL of Klean-Strip Xylene added. This was covered with a round bottom flask to prevent excessive evaporation and heated to 60°C with an electric hot plate. The mixture was held at this temperature for 5 minutes with vigorous agitation by glass rod. The chocolate-chip shaped pieces were observed to break apart into a fine powder and the solvent became cloudy with particulates. The dark brown pebbles appeared unaffected. This was decanted through an unbleached coffee filter into a clean flask to cool. As the product cooled, many small crystals were observed setting out of the clear-yellow filtrate solution.

The wet source product was weighed and found to be heavier than expected, with an estimated yield under one gram. 50mL of additional Xylene was added, covered, and heated to 75°C for 5 minutes with glass-rod agitation. This was decanted through the filter into the beaker with the previous filtrate and placed on a shelf to recrystallize. A significant portion, possibly up to a half gram of the light-brown chocolate-chip shaped piece powder was captured in the filter.

After three days, the majority of the sulfur-bearing Xylene solvent was lost in a lab spill, but most of the sulfur crystals remained. The dry source material was weighed at 17g. The remaining Sulfur/Xylene mixture was heated to 100°C to evaporate the remaining Xylene. 2g of small yellow sulfur crystals were collected and placed in a vial labeled “Sulfur”. This product contains a very small number (2-3?) of brown fibers which are assumed to be from the filter.

Product


Discussion:
Those purchasing garden products as a source of elemental sulfur should avoid products with large percentages of Gypsum. The sulfur in Gypsum is not available for simple solvent extraction.

The author suspects that her coffee filters “shed” a small number of brown fibers. Search for new filter material is underway.

The theoretical yield of this procedure was 40% x 20 grams = 8 grams. The actual yield was 2 grams. Assuming that the portion lost with the spilled solvent would have been completely recovered, the yield could have been as much as 3 grams. This is between 1/4th and 1/3rd of the theoretical yield. This is disappointing.

Self-Criticism:
Use of a mechanical stirrer could improve the repeatability of the procedure.

Cats have no place in the lab, especially not knocking experiments off the damn shelf. Future in-progress experiments will be kept in a lidded plastic bin.

Future Work:
The author now has a quantity of reasonably pure Sulfur available, and will work up a solubility curve for Sulfur in Xylene as a function of temperature in the future. Examples of the specific procedure to follow would be appreciated.

The yield of this procedure was disappointing. The experiment will be repeated to determine if powdering and/or washing the source material prior to extraction increases the yield. Other variations could include increasing the solvent temperature or extraction time.

God these are a delight to read Keep on doing science, I love reading your posts!

Quote: Originally posted by ElizabethGreene

This must be a remarkably effective fertilizer as it gives 110%. [...] Those purchasing garden products as a source of elemental sulfur should avoid products with large percentages of Gypsum.

Quote: Originally posted by watson.fawkes

[...]I suspect the polyacrylamides (see "Active Ingredients") were as much responsible as the gypsum. They're used in various time-release products. I'm assuming here their purpose is to encapsulate, which would definitely make extraction harder. Look up the patents listed at the bottom to be sure. Grinding the material to powder should help recovery.

Quote: Originally posted by Funkerman23

Pardon my asking but: was there any particular reason you chose xylene for the sulfur extractions? I know sulfur will dissolve in Carbon disulfide but ethanol & ether will dissolve it a little as well( CRC handbook is a nice reference but slightly soluble isn't to precise of a description) but digress.

No pardon required, I'm posting these here because I'm a complete chemistry noob and I lack a proper instructor to critique my work. I want people to ask questions and tell me when I'm doing something foolish.

Xylene is available at my local Home Depot. The choice was based on easy availability. My source of diethyl ether would be from truck starting fluid and these all seem to be mixtures containing hexane as well. Denatured alchohol has the same problem. It is a mixture of different substances introducing another component to the experiment.

I don't have a ready source for Carbon Disulfide and have not researched its synthesis. Do you have a procedure for it? I have Carbon and Sulfur now.

My local McKay's Used books has a 1989 copy of the CRC for $5.00. Is that new enough to have IUPAC names in it?

Quote: Originally posted by papaya

Couldn't you just distill sulfur from powder in a proper setup ?

Quote: Originally posted by ElizabethGreene

The boiling point is 445°C (Wikipedia, "Sulfur") though, and I would have to rig some sort of torch fired apparatus to reach that temperature. Would it spontaneously form Sulfur Dioxide with atmospheric Oxygen at that temperature?

Quote: Originally posted by woelen

A nice solvent for sulphur is toluene. I once did an experiment with that and quite some sulphur can be dissolved in hot toluene, while its solubility is low in cold toluene. [...] http://woelen.homescience.net/science/chem/exps/S+toluene/in... [...]

Quote: Originally posted by papaya

Couldn't you just distill sulfur from powder in a proper setup ?

Quote: Originally posted by ElizabethGreene

Addendum: The author has a free long-haired cat available named Blue. Smells slightly of Xylene, but appears undamaged. Note: Cat does not appear to care for author's attempts at paw cleaning. Note: Feline claws are an effective tool for placing small groups of holes in author.

I reattempted this today, with several notable changes.

1. The product was powdered in a dedicated lab blender prior to extraction. The powder was screened through fiberglass window screen and the larger material reground until it all passed through.
2. The solution was heated hotter, longer, and with mechanical agitation.
3. An Ice bath was used to expedite crystallization.
4. More source material was used in relation to solvent.
5. I "recycled" the Xylene, reducing the amount of Product lost in solution.

#5 requires some explanation.

The Xylene still had a strong yellow color even after chilling in the ice bath. I decanted the cold clear yellow solvent back into a beaker, added make-up solvent, and stir-bar and put it back on the heat. Then I added fresh source material. My working theory was that this solvent was saturated with the sulfur that would not recrystallize out, so any more that dissolved into it would come straight out in the end product. Theoretically this technique would allow one to trade time for better yield and reduced solvent use when crystallizing out a substance with a small difference in hot and cold solubility. There was a visible significant difference in yield between the first and subsequent rounds of extraction, indicating that this technique has some merit.

The final product is still drying, but I'm estimating the yield at ~45%. This is a notable improvement.

EDIT: Yield, 58grams, 37% of theoretical. Sodding pusspockets.


Lessons learned:

• If the solution in a flask is at 90c, the cool-to-the-touch neck of the flask will get "hot" when one starts pouring the solution out.
  
• Turn on the magnetic stirrer -before- adding the powder to the flask. or it will get buried and stuck.
  
• Any interruption in stirring (i.e. if the hot plate pops a circuit breaker) will allow insolubles to settle out. These insulate the bottom of the flask and can cause a significant temperature gradient between the bottom and top of the solution. I saw a difference of 20c and localized boiling at one point.
  
• I need to get a fire extinguisher for the lab. The current response plan of "scream" then "run" is insufficient.
  
• The hot Sulfur-Xylene clouded my plastic filter funnel. If I had it to do again I'd use the glass one for the hot filtration and the plastic one for adding the cold source material to the extraction flask.
  
• The blender works much better at dry grinding if it's less than 1/4th full.
  
• Get some spoons or scoops for the lab for transferring dry materials.
  
• Prolonged usage of the electric-skillet-turned-hot-plate at high temperatures causes it to smell. It came from goodwill so this could be old grease cooking off. Alternately it could be the teflon letting go and giving me cancer. The non-stick coating needs to come off for safety.
  
• A dust mask is required for safety when grinding, sifting, and transferring powdered materials.
  
• Need to add a weight to the magnetic stirrer to help reduce walk at high speeds.
  
• The cat appears to have learned a lesson, and remained a respectful distance away while watching the procedure.
  

Future Work:
I still have a pound and a half of source material, and am considering trying to distill it next.


[Edited on 30-7-2013 by ElizabethGreene]