Pyrolysis Mechanism Of Tropical Agricultural Crop Waste And High-value Utilization Of Bio-char

Pineapple residue and banana pseudo-stem are typical biomass feedstock from tropical agricultural production.In this study,pyrolysis mechanism of them and high-value utilization of bio-char were explored.Pyrolysis process was explored based on waste biomass key components（cellulose,hemicellulose and lignin）.Pyrolysis characteristics of pineapple residue and banana pseudo-stem was conducted with thermogravimetric analysis.Both biomass samples decomposed rapidly at 150～400°C.At 650?℃,the pyrolysis of pineapple residue basically ended,and there was a significant mass loss peak for banana pseudo-stem.Kinetics of pyrolysis were compared by isoconversional method and multi-peak fitting method based on weight loss of biomass samples.With the increase of temperature,activation energy of pineapple residue gradually increased from 157 k J·mol^-1to 292k J·mol^-1,and that of banana pseudo-stem increased from 178 k J·mol^-1to 321 k J·mol^-1.As pyrolysis reaction proceeded,the energy required was higher for taking a start.Banana pseudo-stem was more difficult to thermally decompose than pineapple residue.Formation pathways and mechanism of pyrolysis products for tropical agricultural crops were developed.Evolved gas during pyrolysis was analyzed through Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry.The main evolved compounds were CH₄,CO₂,CO and various organic volatiles at 200～400℃.The amount of evolved gas was the largest at 320℃.The main carbon number of organic volatiles was C₄and C₅for pineapple residue,and that was C₂and C₃for banana pseudo-stem.In addition,physical and chemical properties of bio-chars were characterized by canning electron microscope,X-ray diffractometer,Fourier infrared analyzer and automatic physical adsorption analyzer.The biochar yield of banana pseudo-stem biochar was higher than that of pineapple residue,and aromatization degree of bio-char from banana pseudo-stem was lower than that of pineapple residue.With the increase of temperature,the specific surface areas of bio-char from pineapple residue and banana pseudo-stem gradually increased,and that of them were 329 m²·g^-1and 308 m²·g^-1at700℃,respectively.Bio-char was activated into porous carbon with KOH in different ratios of 1:1,1:3,and 1:5 in order to improve the utilization efficiency of pineapple residue and banana pseudo-stem.The porous carbon with high specific area(>1000 m²·g^-1)dominated by micropores was effectively formed through KOH activation.Among the porous carbons sourced from banana pseudo-stems,when mass ratio of bio-char to KOH was 1 to 3,the performance was the best with specific capacitance of 297 F·g^-1.The specific surface areas was 2313 m²·g^-1,of which micropores accounted for about 60.1%.Among the porous carbons sourced from pineapple residue,when mass ratio of bio-char to KOH was 1 to 5,the performance was the best with specific capacitance of 375 F·g^-1.The specific surface areas was 2378 m²·g^-1,of which micropores accounted for about 50.2%.Composite structure of olyaniline and porous carbon sourced from pineapple residue（PR/PANI composites）were prepared via in-site polymerization method in order to further obtain electrode material with excellent electrochemical performance.PR/PANI composites had high specific capacitance of 522 F·g^-1.It proved that pineapple residue and banana pseudo-stem were potential feedstock for electrochemical materials.