# Study of Cocoa Pod Husks Thermal Decomposition
## 1 Introduction  
Ecuador is one of the biggest producers and exporters of cocoa, being the largest producer in America and ranking third worldwide. [1]. Locally, this industry generated 758 million of US dollars of income in 2021 due to the export of nearly 325,000 t of cocoa beans to forty different countries [2]. This implies a considerable amount of biomass residues generated during the process, mainly cocoa pod husk (CPH). These residues cannot be disposed of on the soil without any treatment because they may act as promoter to _Pltytophthora_ spp., the main cause of black pod rot [3]. Indeed, different studies have presented alternatives for using CPH residues such as anaerobic digestion [4], high value chemicals precursors [5; 6; 7], pectin extraction [8], and ash used as fertilizer [9; 10], among others. Thus, for example, CPH was studied as a source of renewable energy through anaerobic digestion, where it has been possible to recover 54% of the chemical oxygen demand of the waste in the form of methane, being able to produce 8341 MWh annually. Although there are some published studies on the liquid fraction obtained from the thermal degradation of CPH, they are scarce. For example, liquid smoke from CPH pyrolysis at 147 \({}^{\circ}\)C was characterized using GC/MS, having methanol, acetic acid and acetol as main components [11]. In addition, the composition of biooil from CPH pyrolysis at 500 \({}^{\circ}\)C was studied using Zr-Fe based catalyst to obtain useful chemicals such as acetone, 2-butanone, phenol and alkyl phenols [12]. More studies have been reported that convert biomass into biochar via thermochemical treatment as a sustainable way to benefit from such residues, thus helping the environment by reducing greenhouse gases emissions, mainly atmospheric carbon as CO\({}_{2}\). [PERSON] et al. [13] obtained biochar from CPH under different conditions (190-370 \({}^{\circ}\)C and 30-120 min), evaluating its thermochemical properties and metal content.  
Later, the same authors studied the surface area dependence on reaction temperature of CPH biochar obtained at 400-800 \({}^{\circ}\)C [14].  
In other related studies, substantial improvements have been observed in the application of CPH biochar for greenhouse-scale cultivation of cocoa crops in Indonesia. The results of this study reported an improvement in the morphology of the plants compared to the control, specifically in: size of the plants, the number of leaves, area of the leaves and the root weight. However, the improvement in production could not be verified due to the time it takes for the crop to reach the reproductive phase [15]. Additionally, applications have been proposed for the complete utilization of the CPH by digestion combined with slow pyrolysis, to take advantage of all the pyrolysis products (gas, liquids and carbon). Under this scheme high quality biochars can be produced O/C = 0.06-0.10, H/C = 0.46-0.48, and up to 57.6% of the energy can be recovered [16].  
In this work, the thermal decomposition of CPH has been studied from two points of view:  
1. Thermogravimetric analysis, including the proposal of a kinetic model that allows adjusting the experimental data. In this line, a new fitting strategy is proposed. Although this strategy has been applied to the CPH decomposition, it can be extrapolated to any other TG/DTG experimental data.
2. Identification of the main volatiles obtained under different pyrolysis conditions, which can guide the selection of the best operating parameters to maximize a compound or a certain type of compounds.  
The results presented here can be used as primary information for future applications of CPH.