Abstract
In this work, the cocoa pod husk (CPH) was converted into biochar products at higher carbonization temperatures (i.e., 400–800 °C). The pore and chemical properties of the resulting biochars and its post-leaching biochars by acid washing, including specific surface area, total pore volume, pore size distribution, true density, and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and Fourier Transform infrared spectroscopy (FTIR) were studied. Based on the pore properties, pyrolysis temperature at around 800 °C seemed to have the most profound impact on the pore development for producing biochar, where its Brunauer–Emmet–Teller (BET) surface area is 101 m2/g. More noticeably, more pores in the CPH-based biochar could be significantly created during the acid-washing, resulting in an increase of BET surface area from 101 to 342 m2/g. According to the data on the EDS and FTIR, the resulting biochars seemed to have oxygen-containing functional groups on the surface. Furthermore, the methylene blue (MB) adsorption performance of the optimal biochar product with maximal BET surface area was tested to fit its kinetics by the pseudo-second order model, showing a strong interaction between the biochar adsorbent and the cationic adsorbate.
Highlights
As the consumptions of cocoa bean and chocolate-related products became more and more widespread around the world, these significantly resulted in the spread of cultivation of cocoa (Theobroma cacao L.), including Central/South America, West Africa and Southeast Asia
The organic carbon in the cocoa pod husk (CPH)-BC-800 should be present in polycondensed aromatic structures, which are responsible for the stability of biochar when applied to the soils, and mitigated greenhouse gas (GHG like CH4 and CO2 ) emissions
In the literature [24,30,31], it has concluded that increasing carbonization temperature generally led to the variations on the chemical and physical properties of resulting biochar, including a decline of oxygen-containing or ion-exchange functional groups, an increase of specific surface area (SSA), and a higher content of nonvolatile elements
Summary
As the consumptions of cocoa bean and chocolate-related products (e.g., cakes, beverages and powders) became more and more widespread around the world, these significantly resulted in the spread of cultivation of cocoa (Theobroma cacao L.), including Central/South America, West Africa and Southeast Asia. 73% of production of cocoa beans in 2013/2014 based on the ratio of 3199 thousand tonnes (Africa) to 4373 thousand tonnes (world total). Côte d’Ivoire is the world’s leading exporter of cocoa beans, representing 39.9% of global net exports, followed by Ghana (20.5%) and Indonesia (8.6%). It involves removing ripe pods from the trees and opening them to extract the wet beans, further undergoing fermentation and drying processes before being bagged for export or delivery. Some cocoa-derived by-products will be generated during the post-harvesting period. It was reported that the ratio of CPH to cocoa beans may be up to 10 times by mass [4]. Over ten million tons of CPH could be generated every year [5]
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