Abstract
Olive stones are a by-product of the olive oil industry. In this work, the valorisation of olive stones through pyrolysis was attempted. Before pyrolysis, half of the samples were impregnated with sulphuric acid. Pyrolysis was carried out in a vertical tubular furnace with a ceramic support. The pyrolysis conditions assayed were: temperature between 400 and 600 °C, heating ramp between 5 and 20 °C∙min−1, and inert gas flow rate between 50 and 300 mL Ar∙min−1. Among them, temperature was the only parameter that influenced the pyrolysis product distribution. The most suitable temperature for obtaining biochar was 400 °C for both non-treated and pre-treated raw material, while for obtaining bio-oil, it was 600 °C for impregnated olive stones and 400 °C for the raw material. The impregnated olives stones led to bio-oils with much higher amounts of high-added-value products such as levoglucosenone and catechol. Finally, the biochars were impregnated with sulphuric acid and assayed as biocatalysts for the esterification of oleic acid with methanol in a stirred tank batch reactor at 60 °C for 30 min. Biochars from non-treated olive stones, which had lower specific surfaces, led to higher esterification yields (up to 96.2%).
Highlights
The agricultural exploitation of olive tree accounts for 11 × 106 ha in the world, most of them in Mediterranean countries, for example, Spain, Italy, Greece, Morocco, etc
In some olive oil companies, the olives are first de-stoned before entering the olive oil extraction system, in which the olives go through a decanter of two or three outlets to obtain olive oil and pomace, or olive oil, pomace
The results showed that acid pre-treatment resulted in 60% of biochar yield, compared to only about 31% of biochar yield without pre-treatment [28]
Summary
The agricultural exploitation of olive tree accounts for 11 × 106 ha in the world, most of them in Mediterranean countries, for example, Spain, Italy, Greece, Morocco, etc. 20 × 106 t [1] olives a year are produced worldwide. The main exploitation is the production of olive oil, which produces large amounts of by-products. Another main products of olives are table olives, known throughout the world as pickles and used as an ingredient in cooking. This work focuses mainly on olive stones (OS), which have an estimated production of 42,900 t/year in Spain [3]
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