Charcoal from anaerobically digested dairy fiber for removal of hydrogen sulfide within biogas

Abstract

Anaerobically digested fibrous solid (AD fiber) is an abundant material that offers potential to produce value-added products such as biochar. The objective of this paper is to better understand how thermochemical processing conditions affect the capacity of biochars derived from AD fiber to adsorb H2S from biogas. AD fiber was pyrolyzed in an electric tube reactor at temperatures up to 600 °C and 60 min. The chars were employed for H2S scrubbing tests from a synthetic biogas. Results showed that the chars’ capacity for H2S removal is comparable to that of activated carbon. An additional step consisting of impregnation of the chars with Na2CO3 resulted in an improved capacity for H2S removal. To study the effect of ash, the AD fiber was also subjected to an alternative thermal treatment, hot water extraction (HWE), at 200 °C for 60 min. The resulting HWE material showed no removal of H2S from biogas, indicating that the ash and the environment employed for the thermal treatment of AD fiber play an important role in the char’s performance for H2S removal. Results also suggest that a portion of the S in the charcoal after the H2S sorption process exists as free or adsorbed S (i.e., not chemically bonded to the charcoal).