Utilization of date palm stones for bio-oil and char production using flash and fast pyrolysis

Abstract

Flash and fast pyrolysis of date palm stones (Phoenix dactylifera L.) was carried out in two different well-swept fixed-bed reactors under a nitrogen atmosphere and the effect of pyrolysis temperature (400–700 °C) and retention time on the product yields and compositions was investigated. The results show that fast or flash pyrolysis of date palm stones yields more bio-oil than char or non-condensable gases, especially at moderate temperatures. A maximum bio-oil yield was obtained at a pyrolysis temperature of 500 °C as 40.4% and 38.3% via the flash and fast pyrolysis methods, respectively. The functional groups, morphology, surface areas, and the C, H, N, and O and ash, moisture, volatile matter, and fixed carbon content of the chars were examined using Fourier transform infrared spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, ultimate analysis devices, and proximate analysis, respectively. Chars with a maximum surface area were used for the adsorption of dyes from aqueous solutions and the adsorption capacity and the kinetics of the chars were determined. Bio-oil composition was investigated using gas chromatography/mass spectrometry and the content of C, H, N, and O was determined by ultimate analysis. The results show that the saturation adsorption capacities of char from flash pyrolysis are 100 and 70.9 mg/g for Methylene Blue and Acid Red 111, and that these values from fast pyrolysis are 105.2 and 97.1 mg/g for Methylene Blue and Acid Red 111, respectively. The bio-oils contain higher levels of oxygen than the chars. The heating values vary from 27.5 to 31.3 MJ/kg and from 24.9 to 28.2 MJ/kg for bio-oils and chars, respectively. In addition, the bio-oil products from the pyrolysis of date palm stones are predominantly fatty acids. The results indicate that the bio-oil products obtained by the pyrolysis of date palm stone may be used as fuel or for the production of chemicals, and the solid products used as fuel or adsorbents.