Pirólise da inflorescência do coqueiro para produção de fenóis de carvão

Abstract

The coconut crop has great economic relevance in Asia-Pacific and Brazil. Due to the high amount of fibers and waste generated, researchers have given special attention to adding value to these materials. Among them, some biomasses such as coconut inflorescence have been little researched. Using pyrolysis technology, coconut crop residues can be transformed into both liquid (bio-oil) and solid (biochar) fuels. In the case of biochar, it can also be used as an adsorbent. In this work, coconut inflorescence biomasses were pyrolyzed. Effects of pyrolysis temperature (290–710 °C) and heating rate (2–58 °C∙min-1 ) were evaluated. A rotatable central composite design was developed to identify interaction effects of these variables. Yield of products (biochar, gas and bio-oil) and concentration of phenol in bio-oil (Cphenol) were the response variables investigated. Response surface methodology was used to obtain optimal phenol concentration. Furthermore, the biomass and bio-oil were characterized by analysis of thermogravimetry, derived thermogravimetry and gas chromatography coupled to mass spectrometry. Temperature and heating rate showed significant effects on responses. A linear model was suitable for gas yield, while quadratic models were suitable for the other responses. A trade-off analysis between bio-oil yield and phenol concentration detected optimal values of 42.8% and 46.9 mg∙g-1 at 530 ºC and 10.0 ºC∙min-1 . Phenolic compounds accounted for 77.8% of the total bio-oil area based on the chromatography results. The biochar produced by inflorescence pyrolysis at 650 ºC and 10 ºC∙min-1 was chemically activated with K2CO3 and applied to remove methylene blue in aqueous solutions. The coal produced was characterized using point of zero charge, FTIR, TGA/DTG, XRD, BET, SEM and CHNS techniques. Experiments were carried out to evaluate the adsorption kinetics using adsorbate concentrations of 25 mg•L -1 , 50 mg•L -1 and 100 mgL-1 . Coconut inflorescence charcoal had a point zero charge of 7.8, while activated charcoal had a point of zero charge of 5.8. Functional groups such as methyl, methylene, alkyl, carbonyl and aromatic groups were observed in the FTIR. Thermogravimetric analysis revealed three zones of degradation related to the weight loss of hemicellulose, cellulose, lignin and other organic components. In X-ray diffraction, no cellulose peaks were observed in the coals, indicating conversion during pyrolysis. Surface area analysis showed that raw charcoal had a surface area of 113.0 m²•g -1 , while activated carbon had 515,3 m²•g -1 . CHNS analyzes were similar to coals from coconut fiber. The pseudo-second order model was the most suitable for kinetic data adjustments. The SIPS model better represented the isotherms in the equilibrium study, and the thermodynamic parameters indicated that the adsorption is endothermic and spontaneous in 30 ºC and 40 ºC, although it is non-spontaneous in 50 ºC and 60 ºC. Therefore, the activated carbon produced was a good alternative adsorptive material for the treatment of water contaminated with methylene blue.