A (1:3 by wt.) C-KOH quick-heated to 700 and then at 10 degrees C/hr. to 750 degrees C, kept so 30 min, cooled, neutralized with aq. 5% HCl, washed to pH similar to 5, and dried at 120 degrees C gave 46% of the final product. It removed best secondary oxidation and colorful and polar compds. from used frying rapeseed oil. But it raised the percentage of oxidates, presumably via oxidn. of triacylglycerols in the oil partly used up. The modified C reduced the proportion of satd. and raised the overall amt. of unsatd. acids. it appears applicable for com.-scale purification of frying oils.