Effect of different pre-treatments and addition of plastic on the properties of bio-oil obtained by pyrolysis of greenhouse crop residue

Abstract

The bio-oil properties and yields during pyrolysis at 400, 500 and 600 °C of the residues from the cultivation of the pepper in greenhouse (Capsicum annuum L.) were studied. Different solid samples were investigated: the biomass fraction of the residue, the water-washed biomass sample, the cobalt-loaded biomass sample and three mixtures made with the biomass and plastic fractions of the residue. Results showed that temperature of pyrolysis has a moderate impact on the products’ yields and bio-oil properties for all solid samples. In general, the highest bio-oil yield was achieved operating at 600 °C while the higher char yield was reached at 400 °C. The pH of all the bio-oil samples was low, specially bio-oil from the cobalt-loaded biomass sample. Density, viscosity, cetane number, average boiling temperature, flashpoint, elemental analysis and ash content of the samples were analyzed and compared.The highest higher heating value was achieved for bio-oil (4218.6 kcal/kg) obtained from pyrolysis of the cobalt-loaded biomass sample. Infrared spectra and chromatography analysis revealed the presence of numerous compounds. Acetic acid is the main acid component of the bio-oil samples obtained from the biomass, the water-washed biomass and the cobalt-loaded biomass, although there are some differences in relative area. Other compounds such as ketones, phenolic or furans were also found. In bio-oils obtained from biomass and plastic mixtures, in general there was a decrease in the content of oxygenated compounds and acidic compounds, favoring the presence of non-oxygenated compounds. This work shows the feasibility of the obtaining of bio-oil from the greenhouse crop residue at the temperature range between 400 and 600 °C.