Coffee husks characterization for the fast pyrolysis process

Abstract

The lignocellulosic biomass is a renewable alternative for fossil fuels. The extensive cultivation of coffee grounds in Brazil generates a large amount of residues, as coffee husks. The work aimed at performing the coffee husks characterization, investigating the viability for fast pyrolysis application. Coffee husks were dried, grinded in a knives mill and sieved using a mechanical sieving; different vibration frequencies and times were used to evaluate the effect of these variables in the size distribution. The true density was inferred for three distinct size ranges of the coffee husks, using a helium pycnometer. Proximate and ultimate analyses were performed. The analytical pyrolysis was realized at 550°C, using a micro pyrolyzer (CDS 5200), vapors was identified by a gas chromatograph and a mass spectrometer (GC-MS QP 2010 plus, Shimadzu). The influence of the particles irregular shape was evidenced in the results of size distribution. The values of true density were around 1.5 g/cm3. The smaller the particle size, the higher the true density of the sample. Coffee husks can be used to generate high added value compounds: 1,3 pentadiene, limonene and n-hexadecanoic acid. Considering the use of coffee husks bio-oil as a fuel, results indicated that the bio-oil will present high calorific value, important acidity and smaller increases in viscosity and molecular weight if compared to the bio-oil of other lignocellulosic materials.