Valorization, Comparison and Characterization of Coconuts Waste and Cactus in a Biorefinery Context Using NaClO2–C2H4O2 and Sequential NaClO2–C2H4O2/Autohydrolysis Pretreatment

Abstract

The search for new sources of lignocellulosic raw materials for the generation of energy and new compounds encourages the search for locations not well known and with a high potential for biomass availability as is the case of the Northeast Region of Brazil. Thus, the cactus (CAC), green coconut shell (GCS), mature coconut fibre and mature coconut shell were pretreated by NaClO 2-C 2 H 4 O 2 and sequential NaClO 2-C 2 H 4 O 2 /autohydrolysis aiming at the obtention of high added-value compounds in the liquid fraction and solid phase. The yield of the solid phase was between 61.42 and 90.97% and the reduction up to 91.63% of lignin in the materials pretreated by NaClO 2-C 2 H 4 O 2. After NaClO 2-C 2 H 4 O 2 /autohydrolysis pretreatment the obtained solids yield was between 43.57 and 52.08%, with a solubilization of the hemicellulose content up to 81.42%. For both pretreatments the cellulosic content remained almost unchanged. The pretreated solids were characterized by SEM, X-ray and crystallinity indexes showing significant modifications when submitted to pretreatments. These results were further confirmed by the enzymatic conversion yields of 81.68-90.03 and 86.97-90.36% of the LCMs pretreated by NaClO 2-C 2 H 4 O 2 and pretreated by NaClO 2-C 2 H 4 O 2 /autohydrolysis, respectively. The resulting liquors had a total phenolic compounds content between 0.20 and 3.05 g/L, lignin recovered up to 7.40 g/L (absence of sulphur) and xylooligosaccharides between 16.13 and 20.37 g/L. Thus, these pretreatments showed an efficient fractionation of LCMs, especially in the GCS, being an important requirement for the generation of products and byproducts in the context of the biorefinery.

Second-Generation Bioethanol from Coconut Husk

“…Another interesting pretreatment proposed by Gonçalves et al [ 30 ] for coconut husk is the use of oxidative conditions (NaClO 2 - C 2 H 4 O 2 ) for delignification and autohydrolysis for hemicellulose removal. The authors obtained a high sugar content after hydrolysis, a high delignification, and a reduction of hemicellulose as desired, but most lignin was conserved.…”

“…Gonçalves et al [ 30 ] used a two-step method to remove different components from the husk. First, they utilized oxidative conditions (NaClO 2 –C 2 H 4 O 2 ) to remove the lignin.…”

“…Up to now, all studies of the use of coconut husk for bioethanol production have been made in a small scale and only three studies mention the use of coconut husk as substrate for a biorefinery [ 30 , 32 , 33 ]. These works only discuss the possibility of using byproducts of ethanol production to obtain other substances but no tests to obtain other products have been reported.…”

“…Gonçalves et al [ 33 ] only suggested the use of sugars, acetic acid, phenolic compounds, and lignin found in the coconut hydrolysate to obtain different products using a biorefinery scheme with no further detail. Later, Gonçalves et al [ 30 ] proposed using their process to make ethanol from coconut husk to obtain also value-added products. They propose that the phenolic compounds obtained during pretreatment and autohydrolysis be used as food additives, since they are antioxidants, while lignin can be used to produce pharmaceutical and veterinarian bioactive compounds and thermoplastic polymers, as well as for energy production through gasification or pyrolysis.…”

El Tamaño De La Partícula De Bambú Angustifolia “Bambusoideae” Factor Determinante Del Porcentaje De Celulosa Extraido

“…O pré-tratamento da biomassa é fundamental em seu processo de transformação, uma vez que é responsável por facilitar a acessibilidade à biomassa lignocelulósica, ao quebrar as ligações complexas que envolvem os seus constituintes RAMBO et al, 2020),. NaClO 2(GONÇALVES et al, 2018), Ca(OH) 2(RABELO et al, 2011), dentre outros.…”