Optimization and characterization of bio-oil and biochar production from date stone pyrolysis using Box–Behnken experimental design
H. Hammani, Mounir El Achaby, K. El harfi, M.A. El Mhammedi, A. Aboulkas
Abstract
In Morocco, large quantities of agricultural residues such as date stones are generated annually during the processing of date palm fruit. This waste is usually discarded although it can be used as an attractive energy source or can be converted into chemical products using thermochemical conversion processes. Among these processes, pyrolysis has attracted attention since it enables the production and chemical recovery. In this context, the use of date stones as a raw material for the production of bio-oil and biochar using a fixed-bed reactor is investigated. The pyrolysis process was performed by varying three parameters: temperature <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>400</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mo>-</mml:mo> </mml:mrow> <mml:mn>600</mml:mn> <mml:mspace width="3.33333pt"/> <mml:mtext>°</mml:mtext> <mml:mi mathvariant="normal">C</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> , heating rate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mo>-</mml:mo> </mml:mrow> <mml:mn>50</mml:mn> <mml:mspace width="3.33333pt"/> <mml:mtext>°</mml:mtext> <mml:mi mathvariant="normal">C</mml:mi> <mml:mo>·</mml:mo> <mml:msup> <mml:mi mathvariant="normal">min</mml:mi> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> , and particle size (0.5–1.5 mm). The modeling and optimization of the process parameters were conducted using the Box–Behnken experimental design. The maximum value of the desirability function was obtained at a pyrolysis temperature of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>500</mml:mn> <mml:mspace width="3.33333pt"/> <mml:mtext>°</mml:mtext> <mml:mi mathvariant="normal">C</mml:mi> </mml:mrow> </mml:math> , a heating rate of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>10</mml:mn> <mml:mspace width="3.33333pt"/> <mml:mtext>°</mml:mtext> <mml:mi mathvariant="normal">C</mml:mi> <mml:mo>/</mml:mo> <mml:mi mathvariant="normal">min</mml:mi> </mml:mrow> </mml:math> , and a particle size of 1.5 mm. Under these conditions, the bio-oil and biochar produced were successfully characterized using different analytical techniques including elemental analysis, chemical composition, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, gas chromatography–mass spectrometry, and scanning electron microscopy. The results show that the bio-oil can be used as a biofuel owing to its high content of aliphatic hydrocarbon compounds. The biochar having a high carbon content is a promising candidate for the production of activated carbon.