Influence of the formaldehyde-to-phenol ratio in resin synthesis on the production of activated carbons from phenol-formaldehyde resins

Phenol-formaldehyde resins synthesized using different formaldehyde-to-phenol molar ratios (F/P ratios) were used as precursors for production of activated carbons from steam activation and KOH etching. The base-catalyzed method was employed in the synthesis with the F/P ratio ranging within 1-4. It was found that the resin yield decreased with the F/P ratio, while the fixed carbon content of the resins increased with the ratio. Solid-state ¹³C NMR analysis showed that increasing the F/P ratio resulted in an increased degree in aromatic ring substitution, which would lead to a promoted cross-linking upon heat treatment and thus to a higher carbon yield. The specific porosity of the carbons from steam activation was shown to decrease with the F/P ratio. The difference in the porosity has been ascribed to the different numbers of original pores embedded in the carbons prior to activation. The F/P ratio did not show obvious influence on the specific porosity development for carbon production using KOH etching. The yield for producing high-porosity carbons from KOH etching was higher than that from steam activation. For both of the activation methods, a F/P ratio of unity is recommended for creating high overall carbon porosity based on per unit mass of phenol used.