Investigation of olive pomace energy potential using thermal analysis, optimization and catalytic fast pyrolysis

In this study, olive pomace (OP) was characterized and used as biomass in fast pyrolysis and catalytic fast pyrolysis process to investigate its energy potential. The thermal behaviour of OP, coal and their mixtures were also studied using a Thermogravimetric (TG)-Fourier Transform Infrared Resonance (FTIR) integrated system. During the characterization of OP, preliminary analysis of pomace revealed a low moisture content of 4.23% making it very suitable for thermal conversion in energy use, a low ash content of 3.13% and high volatile substance content of 79.71%. The elemental analysis revealed that OP has 59.43% carbon, 8.97% hydrogen, 29.83% oxygen and a high heating value (HHV) of 27.68 MJ/kg. Cellulose, hemicellulose, and lignin content of OP were respectively 27.94%, 29.84% and 33.87%. During TGA/FTIR analysis, samples ranging from 20 to 30 mg were prepared at a carrier gas flow rate of 100 mL/min (nitrogen gas) and at different heating rates (10, 20, 30, 40 °C min-1) from room temperature to 950°C. The TGA/FTIR analysis results were modelled using the iso-conversion models of Flynn-Wall-Ozawa (FWO) and Kissenger-Akahira-Sunose (KAS) to determine kinetic and thermodynamic parameters. The fast pyrolysis of OP was conducted in a drop tube pyrolysis reactor. The effects of different pyrolysis parameters including nitrogen gas flow rate, feed-stock particle size and reaction temperature were studied to identify the optimum conditions for maximum biooil yield. The modelling and optimization of process parameters were achieved using efficient response surface methodology (RSM) with a central composite design (CCD). The maximum OP biooil yield of 58,13% (8,72 g) was obtained at 1.5 mm particle size, 490°C temperature and 400 mL min-1 carrier gas flow rate. During catalytic fast pyrolysis, zeolite Socony mobil-5 (ZSM-5), aluminium oxide (Al2O3), sodium carbonate (Na2CO3) and potassium carbonate (K2CO3) were used as catalysts at different reaction temperature of 425, 500, 575, 650 and 725 °C, 1,5 mm feed-stock particle size and 200mL min-1 carrier gas flow rate. The optimum reaction temperature for all four catalysts was 500°C and the highest biooil yield was 7,61g (50,73%) using Al2O3 as catalyst. The elemental and GC-MS analysis of catalytic fast pyrolysis biooil were carried out. The use of catalysts in this study aims to reduce oxygen content in biooil and increase biooil yield. Al2O3 had the lowest biooil oxygen content ranging between 12,53 and 5,73%. ZSM-5 had the highest biooil oxygen content ranging between 15,06 and 12,55%. The GC-MS analysis revealed that without the use of catalyst, pyrolysis oil from pomace contains mostly acids and small amounts of alcohol, aromatics, and ketones. The use of Al2O3, K2CO3, Na2CO3 and ZSM-5 catalysts has a major effect on biooil chemical compounds type and distribution. Carboxylic acid contents of biooil samples obtained from OP rapid pyrolysis decreased significantly with the application of catalysts. Aromatic content in biooil has increased significantly using catalysts and reached its highest (56,13%) for Al2O3. Low aromatic content can be observed when using Na2CO3as catalyst. Ketone and alcohol content in biooil has also increased using K2CO3, Na2CO3 and ZSM-5 as a catalyst. The same cannot be said for Al2O3.