COPROCESSING OF PYROLYSIS OIL WITH VGO IN FCC UNIT TO PRODUCE LPG AND GASOLINE

Abstract

Lignocellulosic biomass-derived fast pyrolysis oil (FPO) has found applications within the petroleum refinery in recent years. This thesis investigates the possibility of upgrading FPO along with petroleum-derived fraction, vacuum gas oil (VGO), in fluid catalytic cracking (FCC) unit and look into the aspects of fast pyrolysis process integration in refinery context. The expelled Jatropha curcas seed cake (JCC) has been chosen as a biomass feedstock which is pyrolyzed in bubbling fluidized bed reactor at 530 °C temperature and atmospheric pressure. The char particles, which are not separable from pyrolysis gases or vapors by cyclone separator, are inherently collected along with FPO in large concentrations from nano-to-micro scale, which are highly dispersible and make FPO highly viscous to semi-solid. The char particles (> 200 nm) are separated by micro filtration (pore size: 0.2 μ) under vacuum line from FPO which helps in stabilization. The char free FPO is highly oxygenated (32 wt.%) and hence it has been hydrodeoxygenated over Pd/Al2O3 catalyst in a continuous stirred tank reactor at 300 °C temperature and 80 bar pressure to produce hydrodeoxygenated fast pyrolysis oil (HDO), which contains 10 wt.% of oxygen. The FPO is blended in proportions of 5, 10, 15, 17, and 20 with vacuum gas oil for catalytic cracking in advanced cracking evaluation (ACE-R) FCC unit. The FCC unit operating parameters like temperature and catalyst-to-oil ratios are optimized based on the higher yields of gasoline on catalytic cracking of pure VGO over equilibrium FCC catalyst. The results of co-processing of FPO with VGO indicated that the yields of gasoline and light cycle oil increased from 29 to 35 wt% and 14.8 to 20.4 wt.%, respectively, whereas the yields of dry gas and LPG decreased from 2.1 to 1.4 wt.% and 38.8 to 23.7 wt%, respectively, for an increase in the blending ratio from 5 to 20%. Moreover, the FCC product distribution pattern at iso-conversion of 66% is compared on co-processing of VGO, VGO with FPO and VGO with HDO. Further, the FPO and HDO are characterized by 1H, 13C, and 31P NMR techniques. From the NMR analysis it is observed that the liquid distillate from the co-processing of FPO with VGO contains more iso-paraffinic CH3 substructure components, whereas the liquid on co-processing HDO with VGO contains more paraffinic CH3 substructure. The 31P NMR analysis of crude FPO and iii HDO indicated that hydroxyl, carboxylic and methoxy groups are reduced during the hydrodeoxygenation of FPO. Furthermore, the co-processing studies have been extended to envisage the specific role of nature of aliphatic (acetic acid, acetol and glycolaldehyde) and aromatic (guaiacol) compounds, which helps in understanding the path of fast pyrolysis process integration with refinery units. From the experimental investigations on co-processing of C2-C3 carbonyls and VGO, it is observed that the presence of acetol increased the FCC conversion from 68 to 78 % with an increase in blending ratio. It is due to the increase in the yield of liquefied petroleum gas (LPG) from 21 to 47 wt.% and at the cost of decrease in yield of gasoline from 39 to 23 wt.% followed by light cycle oil (LCO) from 18 to 12 wt.% and heavy cycle oil (HCO) from 11 to 7 wt.%. The yield of LPG increases linearly with an increase in blending ratio. Further, the presence of acetol reduced the coke formation as compared to pure VGO catalytic cracking over FCC equilibrium catalyst at a constant C/O ratio of 5. While co-processing of glycolaldehyde dimer with vacuum gas oil, the FCC conversion increased from 69 to 75% with an increase in the blending ratio from 5 to 10 %; whereas beyond that the conversion decreased to 65 % for the blending ratio of 20 %. The dry gas and liquefied petroleum gas yield first increased from 1.8 to 2.4 wt.% and 35 to 43 wt.%, respectively with an increase in blending ratio from 5 to 10 %; and on further increase in blending ratio to 20 % the yields of dry gases and LPG decreased to 1.8 and 27 wt.%, respectively. Further, it was observed that the gasoline yield first decreased from 27 to 25 wt.%, and then increased to 32 wt.% with an increase in blending ratio. While the light cycle oil yield first decreased from 17 to 15 wt.% and then increased to 20 wt.%; whereas the yield of heavy cycle oil first decreased from 11 to 9 wt.%, and then increased to 13 wt.% with an increase in blending ratio from 5 to 10 wt.%. The yield of ethylene and propylene also followed the same trend with an increase in blending ratio of glycolaldehyde up to 10 wt.% blending, and there on the yields decreased with further increase in blending ratio. The increase in coke formation is observed beyond the blending ratio of 10% which is due to the increase in poly-aromatics formation. Similar results are found from the poly-aromatics analysis based on nuclear magnetic resonance (NMR) spectroscopy. Furthermore, the blended FCC feedstock and their liquid distillates were structurally characterized by means of average structural parameters like branchiness index, substitution iv index, average length of alkyl chains, and fraction of aromaticity per molecule by 1H, and gated decoupled 13C NMR techniques. Further, an attempt has been made to study the effect of catalyst-to-oil ratio (C/O) on the product distribution for the catalytic cracking of mixture of VGO with guaiacol and acetic acid. The simulated distillation (SIMDIST) based product analysis indicated that the presence of guaiacol increased the product selectivity of gasoline fraction; whereas the presence of acetic acid clearly increased the yield of light olefins, CO and CO2. The FCC conversion is higher on co-processing guaiacol followed by acetic acid with vacuum gas oil as compared to pure VGO catalytic cracking. An increase in coke and aromatics was observed in the following order: guaiacol +VGO feed > acetic acid +VGO feed > VGO. Higher yields of light olefins, CO and CO2 are observed while catalytic cracking of acetic acid +VGO feed with equilibrium FCC catalyst, subsequently light olefins have been reduced in case of guaiacol +VGO feed as compared to other feeds. The cracking patterns of liquid distillate have been further supported by FTIR analysis on cracking of acetic acid +VGO and guaiacol+ VGO feeds. It has been found that the carboxylic acid peaks (1650–1720 cm−1) were completely absent which indicated the complete conversion of acetic acid. However, the formation of phenol is observed in the liquid distillate on cracking of guaiacol+VGO feed. Therefore, it is preferable to separate the aromatic oxygenated compounds from pyrolysis oil before co-processing it with vacuum gas oil in refinery FCC unit by keeping in mind the limitations of total aromatics and the benzene percentages in gasoline. On catalytic cracking of glycerol by varying the temperature from 350 to 550 °C it is observed that a 100% conversion beyond 430°C and a maximum acetaldehyde yield of 53 wt.% is seen at 550 °C. The kinetic parameters were estimated with 4– (VGO, coke, gases and liquid distillate) and 5– (VGO, coke, dry gases, LPG and liquid distillate) lumps kinetic models for catalytic cracking of VGO and VGO with FPO. The experiments for VGO and VGO with FPO cracking have been carried out at different WHSV, varying from 6–24 h–1, a constant reaction temperature (530 OC) and catalyst–to–oil (C/O) ratio of 5. The deviation between the predicted and experimental products yields, for both 4– and 5– lumps models, is found to be less than 5%.