Conversion of dairy sludge into biodiesel via Non-Catalytic transesterification

Abstract

Considering the current energy infrastructure utilizing renewable energy that is compatible with it will be advantageous. From the perspective of compatibility, the use of biodiesel is promising. Although practical implementation and commercialization of biodiesel have been prioritized, the valorization of dairy sludge into biodiesel via conventional conversion protocols (acid-/base-catalyzed (trans)esterification) has not yet been realized. Tolerance against free fatty acids (FFAs), saponified fatty acids (SFAs), and undefined impurities in acid-/base-catalyzed (trans)esterification are vulnerable. To overcome the technical inferiority of acid-/base-catalyzed (trans)esterification, this study adopted non-catalytic (trans)esterification, which can valorize dairy sludge into biodiesel with high efficiency in a reaction time of ≤ 1 min. The non-catalytic conversion platform used in this study is invulnerable to impurities, and its reaction kinetics are governed by the temperature. Biodiesel recovery by non-catalytic (trans)esterification ranged from 72 to 75.8 wt% of dairy sludge extracts at 380 ℃. One of the interesting findings is that biodiesel recoveries from non-catalytic (trans)esterification of dairy sludge extracts at ≥ 300 ℃ were nearly similar. This suggests that the yield of biodiesel was saturated at ≥ 300 ℃. From the perspective of the economic viability of biodiesel production, the direct conversion of dairy sludge into biodiesel without lipid extraction is desirable. Thus, non-catalytic (trans)esterification of the two dairy sludge samples was performed. Biodiesel recoveries from the two dairy sludge samples were 31.7 and 38.8 wt% at 380 ℃, respectively. This finding demonstrates the extraordinarily strong tolerance against impurities and technical superiority of the introduced biodiesel conversion platform.