Bio-phenolic compounds production through fast pyrolysis: Demineralizing olive pomace pretreatments

Abstract

An original pathway to renewable production of phenol-rich bio-oil by fast pyrolysis of pretreated olive pomace (OP) was researched. However, inherent inorganic elements (especially alkali and alkaline earth metals) in biomass feedstocks largely modified the final bio-oil composition. To alter their catalytic activity in fast pyrolysis, different demineralisation processes (water, acid and alkali pretreatments) were employed. There was also an in-depth study of bio-oil phenolic compounds, analysing the oxygen-containing substituted groups linked to the benzene ring. From water leached samples, potassium was largely removed, enhancing the selective production of guaiacol (at room temperature) and syringol (at T = 90 ºC). Important differences were observed with HCl and HNO3 pretreatments regarding carboxylic acid and phenolic distribution. For pretreatment with NaOH, the sodium content in the sample was observed to increase to 83%. Thus, optimal phenolic selectivity (36.9%) was achieved for the alkali pretreated OP sample, where guaiacol (5.9%) and vinyl guaiacol (6.2%) yields increased and methyl guaiacol decreased. This study marks an efficient and clean pathway for converting agricultural waste into valuable phenolic enriched bio-oil. This could constitute a new way of obtaining these compounds by using renewable agriculture biomass.