Chemical Education Today
Letters Solvent Swelling Demonstrations: Possible Extension to Other Types of Material I read with some interest the article by Campbell and Rupe in the July 2000 issue of J. Chem. Educ. (1), which describes experiments on the solvent-induced swelling of polymer slabs. As a chemist with a background in fuels and combustion, I found that the contents of this article had a considerable degree of contact with a long-standing interest of my own: the solvent-induced swelling of low-rank coals. I have published a good deal in this area over the last ten years (e.g. ref 2, the most recent in the series) and have often involved Honours students with the work. Low-rank coal means brown coal (lignite). In the USA, deposits of such are to be found in states including North Dakota and Texas. A safe, effective, and inexpensive demonstration of the swelling propensity of these is possible simply by placing about 1 g of the oven-dried coal, with particle sizes in the approximate range 1–3 mm, into a test tube and adding 5 cm3 of acetone. After an hour or less (preferably with gentle shaking) the coal sample will have swollen, perhaps by as much as 30%. This swelling can easily be measured by determining the height of coal with a ruler, before and after solvent addition. Alternatively, no doubt an overhead projector could be used to show the effect, as in the experiments described by Campbell and Rupe.
I find that in their interpretation of results these authors have invoked some of the ideas also used in interpreting coal swelling results, including the effect of the degree of crosslinkage. When demonstrated to tertiary students, the results of coal-swelling tests could be related to certain basic thermodynamic quantities including the solubility parameter of the solvent. Results for different low-rank coals are relevant to their respective suitabilities for processes such as solvent extraction of chemicals. In attempting such experiments, please note the following: 1. Use a low-rank coal. Higher-rank ones such as bituminous coals swell only very slightly if at all, probably because they are much less porous than low-rank coals. 2. While acetone has been suggested as a solvent methanol is also very effective, as is pyridine.
I will be happy to give informal advice. Literature Cited 1. Campbell, D. J.; Rupe, S. B. J. Chem. Educ. 2000, 77, 876–878. 2. Jones, J. C.; Hewitt, R. G.; Innes, R. A. Fuel 1997, 76, 575–577. J. C. Jones University of Aberdeen Department of Engineering, King’s College Aberdeen AB24 3UE, UK
[email protected] JChemEd.chem.wisc.edu • Vol. 78 No. 2 February 2001 • Journal of Chemical Education
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