Microwave Pyrolysis Process Potential of Waste Jatropha Curcas Seed Cake

Abstract

This chapter aims to express the potential of waste Jatropha curcas seed cake (JCSC) as an interesting option for energy generation. The results obtained by microwave pyrolysis (MWP) process, undoubtedly, indicate that the remaining organic liquid substances contained in JCSC, the solid residue obtained from the process, and the gaseous fraction are still a potential energy source that can be explored. The exploitation is particularly interesting in cases where an extensive production of this type of biomass waste exists and its transportation implies extensive paths and additional costs.

“Jatropha Curcas for Galapagos Islands” project is a current initiative aimed to reduce the requirements of fossil fuels for Galapagos Islands, which is framed under the “Zero fossil fuels for Galapagos Islands” national objective. The project is focused on gathering J. curcas fruit from living fences along the rural areas of the Province Manabí (Ecuador) to extract oil in small-scale facilities. The extracted oil is refined and transported to Galapagos Islands where it is used as biofuel for internal combustion engine generators to provide electricity to the islands. Although the by-products of extraction are currently not being exploited as an energy source, this possibility is seen as a remarkable choice for final disposition and energy generation improvement. In 2012, especially in this particular case, seed cake production was estimated to be 213 t/year as a result of its exponential growth since 2009.

Conventional pyrolysis presents some inconvenient situations, such as resistance to heat transfer, heat loss, and lack of fast heating. Taking into account that short operation/retention times are preferred in cases with growing demand, and low energy-intensive extraction technologies maximize the energy output of the primary energy source, MWP appears as a suitable option to be applied.

The available JCSC was assayed in a bench-scale MWP batch process that allows tar and chars formation and their separation for analysis. During the process, MWP operating conditions were programmed to reach 550 °C in 30 min from room temperature and maintain this condition for an additional 10 min. Also, JCSC was previously assayed to establish the content of volatile organic compounds with the purpose of estimating the organic liquid substances yield in case of a potential extraction. Liquid products (bio-oil) were analyzed through gas chromatography coupled with a mass-spectrometer detector (GC-MS) in order to determine the most representative compounds in a qualitative-basis. Their functional groups profile was obtained through a Fourier-Transform Infrared Spectroscopy (FTIR) assay. Bulk properties, such as density and calorific value, were obtained by applying existing standard methods suitable for diesel fuel. Analysis results were used to estimate its behavior as a liquid fuel by comparing the results with diesel-fuel quality standards and characteristics. In addition, calorific value, proximal and ultimate biomass analyses were developed for solid products in order to assess the suitability of a potential use as solid fuel.

The results show that the maximum content of potential liquid fuel substances is around 75 %, which leads to a conclusion that liquid fuel extraction by thermal methods is a suitable option to be evaluated regarding an augmentation of liquid fuel yield.