Enhancing aromatic hydrocarbon through catalytic pyrolysis on sequential pre-treatment of palm empty fruit bunch (PEFB) / Nur Nasulhah Kasim

Bio-oil produce from untreated biomass through pyrolysis consists of undesirable
oxygenated chemical compounds that contribute to the low quality of products.
Introduction of sequential pre-treatment on biomass prior to pyrolysis shows a
promising technique to enhance aromatic hydrocarbon in the bio-oil as an essential
precursor for the synthesis of additive fuel, plastisizer and formation of polymeric
compounds. In this study, the sequential pre-treatments of demineralization and
torrefaction palm empty fruit bunch (PEFB) successfully carried out using a fixed-bed
reactor in inert nitrogen gas at ambient pressure. The optimization on the pyrolysis
process conditions was done using response surface methodology (RSM) using a central
composite design (CCD) due to it was employed for the quadratic model that can
estimate the individual second-order effect. Then, ANOVA was used to analyse the
statistical parameters with the aid of RSM. HZSM-5 catalyst was used as a catalytic
cracking catalyst during catalytic pyrolysis and reaction mechanism between HZSM-5
and torrefied demineralized palm empty fruit bunch (TDPEFB) was proposed based on
the chemical compounds obtained in the bio-oil yield. Initially, demineralization was
performed on PEFB by sonicating 1% nitric acid for 10 min to reduce the alkali and
alkaline earth metals (AAEM). Torrefaction on the demineralized PEFB (DPEFB) was
carried out to eliminate the undesirable components such as carboxyl, moisture and
oxygen content using a fixed-bed reactor in inert nitrogen gas at 240 °C for 30 min. The
sequential pre-treatment of TDPEFB at 240 °C showed the positive results with
increased in carbon content to 49.34%, decreased in oxygen content at 44.78% and
acceptable in ash content of 1.87% as compared to untreated PEFB with the amount of
44.97%, 47.25% and 4.21%, respectively. This verifies that the sequential pre-treatment
enhance the characteristic of TDPEFB 240 prior to pyrolysis and catalytic pyrolysis
processes. Pyrolysis on TDPEFB 240 at optimum conditions with reaction temperature
of 490 °C (±15 °C) with heating rate of 85 °C·min−1 for 4.16 min showed a slight
increase in bio-oil yield up to 59.53% in comparison to 56.83% obtained from untreated
PEFB. This observation explained that by the removal of AAEM through
demineralization and reducing oxygen content through torrefaction in TDPEFB
promotes the primary reactions that increase the bio-oil yield. It seemed that
demineralization and torrefaction pre-treatment contribute to enhancement the quality
of bio-oil yield by retarding secondary reaction and eliminating oxygen content through
dehydration, dehydroxylation, decarbonylation and decarboxylation reactions. Further,
the optimal conditions on catalytic pyrolysis of TDPEFB 240 for the maximum bio-oil
yield of 59.20% were obtained at reaction temperature of 537 ℃ (±15 °C), holding time
of 4.55 min and catalyst loading of 10%. Based on the GC-MS analysis, sequential pretreatment
of TDPEFB 240 on catalytic pyrolysis in the presence of HZSM-5 zeolite
catalyst increased the formation of phenolic compounds (44.27%) and aromatic
hydrocarbon compounds (9.35%), whereas reduction in organic acids and oxygenated
compounds in the bio-oil were observed. From these results, catalytic pyrolysis of
TDPEFB 240 revealed that there is significant effect on the sequential pre-treatment
and HZSM-5 zeolite catalyst during the catalytic pyrolysis process. It can be described
through possible proposed reaction mechanism of cracking catalyst with TDPEFB 240
that involve hydrocarbon pool and phenolic pool mechanisms towards the formation of
aromatic hydrocarbon compounds based on the result from GC-MS analysis of bio-oil.