Heating rate and ZSM-5 catalyst effects on date palm (Phoenix dactylifera L.) stones pyrolysis: Thermogravimetric analysis, production and characterization of syngases and bio-oils

In the present investigation, Date palm stones (DPS) were pyrolyzed under Nitrogen atmosphere in a laboratory scale fixed-bed reactor. Pyrolysis experiments were carried out at different heating rates (5 and 10.C/min), both in absence and presence of ZSM-5 catalyst (20 wt%). The effects of heating rate and ZSM-5 catalyst on DPS thermal behavior, pyrolysis products yields, syngases and bio-oils proprieties were investigated. TGA results showed that adding ZSM-5 revealed no significant impact on DPS thermal behavior. However, increasing the heating rate was followed by an increase in degradation peaks temperatures and maximum mass-loss rates (in absolute terms). These same effects were found when proceeding in presence of ZSM-5. Micro-GC results showed that the heating rate rise led to a thermal shift of pyrolytic gases (CO2, CO, C2H6, CH4 and H-2) release towards higher temperatures. However, the ZSM-5 addition had accelerated their release and enhanced their quality by essentially reducing CO2 contents by about 13%, for both heating rates. The produced syngases from DPS pyrolysis have proven good biofuels proprieties thanks to their important proportions of CH4 (17.19-21.74%) and H-2 (12.54-18.51%). DPS pyrolysis at a heating rate of 5 degrees C/min and in presence of ZSM-5 (20 wt%) can be defined as the optimum operational conditions that lead to maximum production of bio-oil (43.48%) with better quality. Under these conditions, DPS bio-oil presented the highest Carbon (73.58%) and Hydrogen (10.63%) contents and the lowest Oxygen (14.89%) and Nitrogen (0.9%) contents. Moreover, it had the highest HHV of 34.37 MJ/kg and the lowest viscosity of 8.54 mPa s, comparing to other bio-oils produced at 10 degrees C/min with and without ZSM-5 and to the bio-oil produced at 5 degrees C/min without ZSM-5. GC-MS analysis revealed that Dodecanoic acid and Oleic acid were the predominant components in DPS bio-oil with the respective percentages of 17.83 and 16.49%. This experimental investigation proved the potential use of date palm stones as renewable feedstocks for bio-oil production by pyrolysis. Furthermore, the low pyrolysis gradient (5.C/min) and the use of ZSM-5 catalyst have shown interesting results in enhancing the bio-oil quantity and quality.