Impacts of cooking, pyrolysis and HTC pretreatments of noodles waste on evolution of products in activation

Abstract

Cooking and other thermal treatments like hydrothermal carbonization (HTC) and pyrolysis might impact the evolution of varied products in the activation of noodles. In this study, raw noodles were pretreated via cooking at 100 °C, pyrolysis at 500 °C and HTC at 260 °C, and subsequently activated with K2C2O4 at 800 °C. Correlation of the varied pretreatments with nature of the resulting activated carbon (AC), bio-oil and gases was paid particular attention. The results showed that cooking treatment enhanced the formation of mesopores in AC, but decreased overall yields of bio-oil and gases from 82.0 to 80.3 wt% during the activation. HTC pretreatment decreased the production of both AC and gases, but remarkably enhanced bio-oil formation. Pyrolysis increased aromatization degree of biochar and suppressed cracking reactions in activation, producing the highest overall yields of AC. However, pyrolysis and HTC destroyed sugars in noodles and reduced the occurrence of reactions for transformation of the functionalities like -OH, -C-H, C=O and C-O-C, which hindered development of pores. The highest specific surface area of AC from direct activation of raw noodles thus showed superior capability for the adsorption of tetracycline (TC) from aqueous solution. Life cycle analysis (LCA) indicated that HTC plus activation showed the least environmental impact, although the lowest yields and specific surface area of AC was obtained via this route. The results of this study will be interested to anyone working in the general field of bioenergy science and engineering.