The combined effect of solar assisted torrefaction and pyrolysis on the production of valuable chemicals obtained from water hyacinth biomass

Abstract

In this study, both the torrefaction and pyrolysis of water hyacinth biomass samples were accomplished by using concentrated solar radiation. The first attempt was to prepare torrefied samples and then used those in the following pyrolysis process. The aim of preparing pretreated torrefied samples was to reduce moisture from the feedstock and make it perfect for the pyrolysis process besides improving product quality. Three different torrefied samples were prepared by pretreating at 200, 250, and 300℃. The pyrolysis operation was done by maintaining a reactor temperature of 440±10℃. Torrefaction severity had a greater influence on char yields. The char yield was found to be 27.4 wt.% for the non-torrefied sample (ST-Raw) while 42.3, 51.2, and 59.4 wt.% for torrefied samples of ST-200, ST-250, and ST-300 respectively. However, an increase in torrefaction temperature had negative consequences on bio-oil and syngas yields. The acidity of the bio-oils was greatly reduced with an increase in torrefaction temperature. The lowest acid content in ST-300 bio-oil sample was confirmed by the FTIR, and GC-MS analysis. This ensures that the torrefied bio-oils are more non-corrosive than non-torrefied bio-oils. The heating values of ST-300 bio-oils were found to be about 75% of diesel fuel. The char obtained in the pyrolysis process for all torrefied samples was of high quality and graded as peat or brown coal. Considering the characteristics of biomass, products, and method used in this study, solar pyrolysis is a promising technique to produce high-quality chemical intermediates. • The combined effect of solar torrefaction and pyrolysis on the products was investigated. • Torrefaction severity significantly increased char (27.4 to 59.4 wt.%) content. • Torrefaction severity improved the product's heating values. • Torrefaction reduced the acidity of bio-oils obtained in solar pyrolysis.