Directed Generation Of Low Carbon Olefin Rich Gas From Volatiles From Poor Quality Heavy Oil Cracking

The trend of heavy and poor quality crude oil has intensified in recent years,and the increasingly scarce light cracking feedstock cannot meet the rapidly growing demand for low-carbon olefins such as ethylene and propylene,so the technology of catalytic cracking of heavy oil to produce more low-carbon olefins has become a research hotspot.Affected by the adaptation and matching requirements of catalyst structural properties and heavy oil macromolecules,the above mentioned technologies suffer from catalyst poisoning,low conversion and selectivity,and are in urgent need of further process optimization and development of more efficient catalysts.This paper focuses on the basic study of the process of targeted production of low carbon olefin rich process from volatiles of poor quality heavy oil cracking.The physical and chemical properties of the catalysts were characterized and analyzed,the structural properties of residue cracking oil were evaluated and determined,the weight loss properties,kinetic properties and product generation pattern of each component of residue cracking oil during the pyrolysis/catalytic cracking reaction were studied by TG-FTIR analyzer,and the distribution of residue thermal cracking products and reaction pathways were investigated.The catalytic cracking characteristics and product distribution of residual oil and gas were investigated,and the catalytic mechanism and reaction pathways were determined.The results of the study are as follows:（1）The structure of calcium aluminate contains more strong base sites and less weak and medium strong base sites;ZSM-5 has better crystallinity and significantly more B-acid than L-acid;the acid-base coupled catalysts have the advantages of both,and increasing the proportion of ZSM-5 can increase the specific surface area,reduce the pore size and pore volume,and increase the content of B-acid and L-acid.（2）Analysis of the group composition,elemental composition,functional group structure and molecular structure of the cracked oil shows that the order of the content of each chemical group is saturated fraction>aromatic fraction>resin fraction>asphaltene;the H/C ratio decreases with the weight of the fraction,the saturated fraction is mainly chain alkanes（63.20%）and cycloalkanes;the aromatic fraction mainly contains polycyclic aromatic hydrocarbons and alkyl substituted polycyclic aromatic hydrocarbons;the resin fraction is mainly thick cyclic aromatic hydrocarbons;the asphaltene is highly condensed thick cyclic The aromatic fraction mainly contains polycyclic aromatic hydrocarbons and alkyl-substituted polycyclic aromatic hydrocarbons.（3）As the fraction becomes heavier,the initial and termination cracking temperatures of the saturated,aromatic,resin fraction and asphaltene groups gradually increase,and the amount of residual carbon gradually increases and coking intensifies.The pyrolysis products of each chemical group were mainly methane,ethylene,C₂₊hydrocarbons,and light aromatics,with average reaction activation energies of 78.82 k J?mol^-1,103.46 k J?mol^-1,108.87 k J?mol^-1,110.56k J?mol^-1,and the main contributing components for the generation of low carbon olefins are the saturated and aromatic fractions.（4）The results of catalytic cracking of each chemical group showed that the introduction of catalysts effectively reduced the reaction activation energy and increased the cracking reaction rate,and the cracking products were CO,CO₂,CH₄,C₂H₄,C₂₊hydrocarbons and light aromatics.By analyzing the ratio of residue after catalytic cracking,it was found that CZ-1:5had the best catalytic activity for the four chemical groups,and the cracking was relatively complete with the least residue.（5）The residue pyrolysis products and catalytic cracking products of pyrolysis oil and gas are mainly low carbon olefins（14.97%）,C₅₊olefins,alkanes,diolefins,aromatics and a few oxygenated compounds,etc.The relative content of olefins increased under the action of calcium aluminate catalyst,but the relative content of low carbon olefins（23.72%）did not increase much;the relative content of low carbon olefins（35.62%）increased significantly under the action of ZSM-5 molecular sieve catalyst and was mainly propylene;among the acid-base coupled catalysts,CZ-1:5 had the best effect in catalytic residue pyrolysis oil and gas conversion,and the yield of low carbon olefins was the highest,which could reach 43.81%.