Solid residues from cocoa production chain: Assessment of thermochemical valorization routes

In the production of cocoa fruits, the main product (cocoa beans) represents only a small part of the total fruit weight, as the remaining 80–90 % is not used in chocolate production. These residual fractions are readily available, and the evaluation of their potential use as raw materials in diverse conversion processes is an important contribution to the search for more sustainable bioenergy sources without jeopardizing food security. The present study aims to discuss the characteristics of the main solid residues of the cocoa production chain, cocoa pod husks (CPH), and cocoa bean shells (CBS); to review the conversion routes that have been applied in the improvement of these residues; and to carry out mass and energy balances to evaluate their potential in energy generation and biofuels production through processes such as direct combustion, torrefaction, gasification, fast and slow pyrolysis, and hydrothermal carbonization. The compiled data from the processes reviewed indicate that the residual biomass derived from the cocoa production chain can be considered a suitable raw material for use in thermochemical conversion processes and generate high-quality energy carriers, such as biochar, hydrochar, bio-oil, and syngas. This review identified the lack of experimental studies of these residues in some conversion processes, such as gasification or fast pyrolysis, thus indicating the pathway for further studies. The selection of appropriate conversion technologies and adoption of effective waste management strategies can minimize the environmental impact of these residues while producing valuable products. This approach could generate additional income streams within the cocoa value chain.