Reusable CFA250–PA–SO3H catalyst derived from coal ash a potential method for fuel synthesis

Abstract

The present study demonstrates a one-step preparation of a sulfonated coal–based solid acid catalyst (CFA₂₅₀–PA–SO₃H). The catalyst was derived from coal fly ash (CFA) by undergoing carbonization and sulfonation with concentrated 1,3–propanesulfonic acid. The reaction took place at a temperature of 120 °C for 3.5 h with a constant agitation speed of 100 rpm. The ratio of carbonized CFA₂₅₀–PA to 1,3–propanesulfonic acid was 3:8 wt/wt. As a result, the catalyst surface had a relatively high density of acidic –SO₃H sites attached. The mesoporous CFA₂₅₀–PA–SO₃H catalyst with an acid density of 9.336 mmol/g was synthesized by chemically treating CFA, a waste product of coal–burning power plants. Using phosphoric acid, the CFA was calcined at 250 °C and then sulfonated at 120 °C with 1, 3–propane sulfonic acid. The CFA₂₅₀–PA–SO₃H exhibited higher surface acidity and catalytic activity due to increased acidity and larger surface area (105 m²/g). The characteristics of the synthesized catalyst were determined using FT–IR spectroscopy, SEM images, TG analysis, X–ray photon spectroscopy (XPS), and N₂–adsorption and desorption isotherm, and the acidity was determined by titration. The mesoporous CFA₂₅₀–PA–SO₃H catalyst was then used to esterify oleic acid in a catalytic activity test. During the esterification reaction performed under optimal conditions (ratio of diethyl carbonate (4.36 g) to oleic acid (2.82 g), 3.5 wt.% catalyst concentration, 100 rpm agitation speed at 82 °C), the CFA₂₅₀–PA–SO₃H catalyst exhibited high activity (94.50% ethyl oleate for 2 h) and it stable for up to five cycles of recycling. In addition, this catalyst could be used to replace conventional environmentally hazardous homogeneous liquid acids through a solid acid–based catalytic process. This evaluation demonstrates that the technology is a very promising approach for developing low-cost and environmentally sustainable energy sources.