Challenge of biodiesel production from sewage sludge catalyzed by KOH, KOH/activated carbon, and KOH/CaO

Abstract

The preparation reactions were catalyzed by base solid catalysts.

The preparation reactions were catalyzed by two loaded catalysts and KOH.

KOH/activated carbon was a better catalyst for biodiesel production.

The considerable compounds content, abundance, and low costs involved has led to the proposal to use sewage sludge as raw material for biodiesel production. The transesterification reaction is catalyzed using an acid catalyst instead of base catalysts because of the high free fatty acid concentration. However, the use of a base catalyst, particularly a solid base catalyst, has certain advantages, including faster reaction speed and easier separation. In this study, we utilize in situ transesterification by base catalyst (KOH, KOH/activated carbon (AC) and KOH/CaO) with sewage sludge as raw material. Many conditions have been tested to increase biodiesel yield through single-factor tests, including mass fraction and catalyst dosage. Preliminary experiments have optimized reaction time and temperature. However, the three catalysts did not work better than H₂SO₄, which had a maximum yield of 4.6% (dry sewage sludge base) considering the purity by KOH, KOH/CaO, and KOH/AC. The features of the catalyst were analyzed using XRD, BET and SEM. As to BET of KOH/AC and the good spiculate formation of KOH crystal appears to be essential to its function. As for KOH/CaO, the formation of K₂O and absorption points is likely essential.

Graphical abstract

Keywords

Biodiesel / Sewage sludge / Base catalyst / In situ transesterification

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Acknowledgements

The present study is supported by the Major Science and Technology Program for Water Pollution Control and Treatment (No. 2013ZX07314-001-006-01); Fundamental Research Funds for the Central Universities (No. 51308538); and the Research Funds of Renmin University of China (No. 15XNLD04).

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