Dear all,
I have finished my research about surface acidity on charcoal surface. As references, I cited some references about acid treatment effect on charcoal for metal ion adsorption in aqueous solution.
But, before determination of surface acidity, the problem occur when the charcoal (after carbonization) was activated by H2SO4(activator) in my research. I feel confuse to write the reaction between charcoal and H2SO4. As we know that when lignocellulosic matter was carbonized by high temperature, it could be oxidized as carboxylic acid.
Does carboxylic acid react with H2SO4? How the reaction?
For carboxylic acids (& dicarboxylic acids), it is well-known that in certain cases simple protonation occurs as the following equations show:
RCOOH + H2SO4 = RCOOH2+ + HSO4-
R(COOH)2 + 2H2SO4 = R(COOH2+)2 + 2HSO4-
Reactions of carboxylic acids are usually studied in Organic Chemistry III which means that they must be taught by experienced instructors who master the art of knowing the variables & the mechanisms involved to set the proper reaction conditions.
I think it is reasonable to propose that incomplete carbonizazion of lignin could generate a charcoal-like material still containing attached carboxylic acid groups. In as much as lignin contains about 0.7% of mineral components, it also seems reasonable to propose that these may be present as carboxylate metal salts. If this were the case, then treatment with sulphuric acid would convert these salts into the free acids, giving you a charcoal-like material with surface acidity due to the attached carboxylic acid groups. An alternative explanation might be that some of the sulphuric acid remains occluded in the charcoal pores and that this is responsible for the observed surface acidity.
Sulphuric acid can react with carboxylic acids giving carbocation with CO evolution (for aromatic carboxylic acids) Aliphatic acids undergoes this reaction under elevated temperature. At RT only protonation of carboxylic group occur. Please see the publication Article Reactions of Carboxylic Acids in Sulfuric Acid
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