Flue Gas Desulfurization Using Sorbent Synthesized from Lime (CaO) and Oil Palm Ash (OPA) Derived from Empty Fruit Bunches (EFB): Statistical Design Approach

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Abstract
The palm oil industry plays an important role in Malaysian economic development and in enhancing the economic welfare of the population. Despite obvious benefits of this industrial development, its activity contributes to environmental degradation. Oil palm ash (OPA), derived from the burning of empty fruit bunches (EFB), is one example of solid waste produced from the palm oil mill activities. In this study, the feasibility of using OPA derived from EFB was examined together with lime (CaO) as a sorbent for the dry-type flue gas desulfurization (FGD) process. Response surface methodology based on a three-variable central composite design (CCD) was used to determine the effect of hydration period (5–15 h), amount of OPA (5–12 g), and amount of CaO (2–6 g) on the activity of the sorbent. It was found that the model developed is adequate for predicting the desulfurization activity of sorbent within the range of the variables studied. The amount of OPA and CaO was found to be an important variable affecting the desulfurization activity, whereby a higher ratio of OPA to CaO led to a higher desulfurization activity of the sorbent. Based on a statistical method, the optimum sorbent preparation variables for obtaining sorbent with high desulfurization activity of 126.35 mg SO2 adsorbed/g Ca2+ can be synthesize using a hydration period of 6.52 h, 12 g OPA, 2 g CaO, 100 mL of water, and a hydration temperature of 100°C. Under those conditions, the experimental results were 121.27 and 119.90 mg SO2 adsorbed/g Ca2+, which are well matched with the theoretical value predicted by the regression model equation. The X-ray diffraction (XRD) analysis shows that more reactive species (due to the pozzolanic reaction between OPA and CaO to form complex compounds) were formed during the hydration process for sorbents with high desulfurization activity compare to sorbents with low desulfurization activity.