Lignocellulose biomass has the potential to be transformed into biofuels and chemicals initially obtained from fossil-based materials. Although all biomass types can be thermally and biochemically converted into biofuels and chemicals, there is significant variation among types and compositions which makes challenging and less attractive to be efficiently converted into hydrocarbons. Fossil fuels depletion and environmental concern drive the search for an alternative energy source such as biomass which abundant and environment-friendly. Catalytic fast pyrolysis is a very promising technique for solid biomass conversion into high-value chemicals products such as aromatics and olefins in a single reactor and step. In this work, the first task was to characterize various biomass materials used in the study. Secondly, catalytic and non-catalytic pyrolysis of ten biomass species to produce aromatics and olefins were conducted in the fluidized bed reactor. The third undertaking was to investigate the effects of inherent mineral matters in the biomass on the catalytic production of aromatic and olefins. Finally, several techniques to improve the yields of aromatics hydrocarbons were proposed.
In the first task, ten biomass materials were selected for investigation in the thermogravimetric analyzer. The thermal characteristics and pyrolysis kinetics were investigated. In addition to proximate, ultimate analysis and chemical composition were evaluated. The results revealed changes in the pyrolysis characteristics with the rise in heating rates. Most notably, the shapes of thermograms were similar; however, the initial, maximum mass loss and final degradation temperatures shift to higher temperatures. The reaction processes are predominantly controlled by the first-order reaction and diffusion models at heating rates of 10°C/min and 20°C/min, while at elevated heating rates the reactions are partly controlled by diffusion and power law models. It was found that reaction the models best representing the pyrolysis kinetics of various biomass were having activation energies and pre-exponential factors were: 103.7 KJmol-1 and 108 sec-1 for bagasse, 98.5 KJmol-1 and 107sec-1 for rice straw, 93.99 KJmol-1 and 107 sec-1 for walnut, 99.68 KJmol-1 and 107 sec-1 for Pinewood, 108.23 KJmol-1 and 1013 sec-1 for bamboo, 122.56 KJmol-1 and 109 sec-1 for cypress, 130 KJmol-1 and 1010 sec-1 and 94.3 KJmol-1 and 107 sec-1 for poplar respectively. The activation energies and pre-exponential factors for the biomass components showed high reactivity based kinetics parameters at all the experimental conditions used in this work. However, lignin decomposed over a wider temperature range and has very small pre-exponential factors at all conditions.
Secondly, the catalytic and non-catalytic fast pyrolysis (CFP and non-CFP) conversion of the ten biomass species into olefins and aromatics compounds were conducted using a fluidized-bed reactor over HZSM-5 catalyst and sand as bed materials. The influence of biomass type and composition (cellulose, hemicellulose, and lignin) on the yield and selectivity of pyrolysis products was investigated. There was a great difference between CFP and non-CFP products yield. The highest aromatics carbon yield was only 1.34% (corncob) during non-CFP tests. While a remarkable improvement in aromatics carbon yields were 12.12 %, 12.52 %, and 12.58 % obtained from pinewood, corncob and poplar biomass during CFP tests, respectively. The dominant aromatic compound was benzene with selectivities of 49.6% (bagasse), 46.8% (rice straw), 48.0% (nutshell) and 50.78% (corncob). Moreover, the highest CFP olefins carbon yields were 10.19 % (pinewood), 10.69% (corncob) and 9.89 % (poplar), compared to highest non-CFP olefins carbon yields were low as 3.37% (bagasse), 2.85% (rice straw), and 2.82% (nutshell). While the higher carbon selectivities toward ethylene were 50.31 %, 59.46 %, 54.59 % and 51.67 % in pinewood, bamboo, indus, and poplar, respectively. The biomass feedstock rich in cellulose and hemicellulose content produce higher hydrocarbon yields than those with higher lignin content. Thus biomass composition can be used as markers for selecting biomass and predicting pyrolysis products distribution.
In the third endeavor, the catalytic fast pyrolysis (CFP) conversion of sugarcane bagasse (pretreated and untreated) over HZSM-5 zeolite catalyst were conducted in the fluidized-bed reactor. To compare the hydrocarbons yields and selectivities of pretreated and raw biomass materials in order to determine the effect of inorganic matter on the aromatics and olefins yields. The effects of reaction temperatures (RT) and sweeping gas flow rates (SGFR) on aromatics and olefins yields and selectivities were studied. The results showed a maximum aromatic yield of 12.41 % carbon was obtained during CFP of pretreated bagasse at an optimum gas flow rate of 2.5 Lmin-1 and temperature of 500 oC. While the highest olefin yield was 10.89 % carbon under the same CFP conditions. Benzene and ethylene were the dominant compounds in the aromatics and olefins respectively. The highest selectivity to benzene was 46.44 %, while that of ethylene was 45.45 % carbon. Slightly lower aromatic and olefin yields of 11.77 % and 9.9 %, respectively, were obtained from CFP of untreated biomass. In the last part, the yields of aromatics and olefins for the raw and treated bagasse were compared; and in addition to the yields and selectivities at optimum conditions were compared. The results suggest that inorganic matters have an inhibiting effect on hydrocarbons production and also caused catalyst deactivation by blocking the catalyst pores. It is evident that removal of inorganic matter would increase both liquid and hydrocarbon yields during CFP over HZSM-5. Hydrocarbon yields and selectivities were found not to depend only on temperature and sweeping gas flow rate, but also on the treatment process severity.
Lastly, the co-pyrolysis of bagasse(BG) and bio-plastic(BP) (chicken feather keratin) and their mixtures were conducted to produce aromatic hydrocarbons over an HZSM-5, USY, and dual catalysts layout. The effects of temperature, co-feeding ratios, feed-to-catalyst ratios and dual catalyst design on hydrocarbons yields and selectivities were investigated. The results showed general improvement in the aromatic hydrocarbons yields in all cases being studied. The aromatic hydrocarbons increase by 10 times when the temperature was changed from 400 – 700C. While the aromatics yields increase in the other cases were 1.5 times at co-feeding, 2.0 greater at feed/HZSM-5 ratio of 1:6, 1.21 higher at feed/USY ratio of 1:16, 0.7 times at HZSM-5/USY layout and 2.66 times at USY/HZSM-5 scenario. The selectivities towards benzene increase at higher ratios, while that of toluene showed an opposite trend. Xylenes selectivities were less sensitive to the changes in co-feeding ratios. The aromatic yields increase and then decrease with increasing feed-to-catalyst ratios for both catalysts. For HZSM-5 catalyst, the optimum aromatic yield was obtained at 1:6 feed-to-catalyst ratios, while that for USY catalyst was 1:16. Non-CFP of bagasse produced no aromatic hydrocarbons at all. While the HZSM-5 generated higher yields of aromatics. In contrast, the USY catalyst only produced toluene and xylenes and other hydrocarbons. The dual catalyst design (USY/HZSM-5) resulted in the highest aromatic hydrocarbons yields. The pyrolysis temperature is a significant parameter for hydrocarbons production. Co-feeding BG and BP enhance biomass conversion to aromatic compounds. For any type of a zeolite catalyst, there is an optimum feed-to-catalyst ratio that generates maximum hydrocarbons. Dual catalyst layout showed a new opportunity for efficient conversion of biomass materials into hydrocarbons