System Integration And Evaluation Of Residual Oil Deep Catalytic Cracking Process Coupled With CO₂ Recycling To Produce Polycarbonate

Nowadays,the environment problems caused by CO₂ emissions have attract worldwide attention.CO₂ emissions in oil refinery industry mainly comes from the catalytic cracking process,accounting for 25%.Some domestic refineries use residual oil as the raw material to produce propylene,butane,butene and other low carbon olefin through the deep catalytic cracking（DCC）.Taking the actual refinery（1.5 million tons of residual oil per year）as a reference,a system for the production of polycarbonate coupled with the CO₂ conversion by residual oil deep catalytic cracking process（DCC-P&CO₂-PPC）is proposed in this paper.The carbon dioxide in the flue gas emitted by the factory is used as raw material to produce high value-added polycarbonate（PPC）products.The novel DCC-P&CO₂-PPC process is established and verified by Aspen Plus,which includes residual oil deep catalytic cracking（DCC）unit,liquefied petroleum gas separation（LPG-SEP）unit,hydrogen peroxide propylene oxide（HPPO）unit and polycarbonate by one step synthesis with CO₂（CTP）unit.For the design of distillation column in LPG-SEP unit and HPPO unit,the initial value range of some given parameters（minimum reflux ratio,feed position,the number of plates in distillation column,distillate to feed ratio,etc.）are simply calculated,and then the optimal result of distillation column was obtained by strict calculation.The CO₂ capture material ZIF-DIA-3 prepared by our research group（adsorption capacity:5.83mmol/g,1 bar,55°C）,and the polymerization process of carbon dioxide and propylene oxide to polycarbonate was realized by using the synthesized IL-B catalyst（reaction temperature 60°C,2-4 bar,CO2 conversion rate 100%,PPC yield≥95%）are used in CTP unit.The influence of key system parameters,such as reflux ratio of the distillation columns of LPG-SEP unit and HPPO unit,feed position and propylene utilization ratio of LPG-SEP overall system energy consumption are investigated,and the process conditions and operating parameters of each unit are optimized.After the optimization of LPG-SEP unit,in order to improve the system’s oxidation utilization rate as much as possible,the propylene conversion ratio was 100%,and then the HPPO unit was optimized on this basis.The results show that the number of plates in the six distillation columns were 17,10,100,12,25 and 14,respectively.The reflux ratio of the six distillation columns is 0.98,28,6.3,0.2,10.2 and 0.35,respectively.The 11th,8th,46th,9th,9th and 7th plates were selected as feeding position of each distillation column.The purity of target product of each unit,CO₂ utilization rate of the system,energy consumption of unit product and other parameters achieve the optimal result:the purity of propylene of LPG-SEP unit is 99.38 vol.%;the purity of propylene oxide of HPPO unit is 99.26Vol.%;and the yield of PPC is 81689.72 kg/h.Meanwhile,the maximum of CO₂ utilization rate is 46.36%,the reducing of CO₂ emissions reaches 310400 t/y,and the maximum energy consumption per unit product value is 2402.0 CNY/MJ.The economic evaluation of DCC-P&CO₂-PPC system was carried out by analyzing the cost of PPC production（COP）,net present value（NPV）and internal rate of return（ROI）.The results showed that when the price of the residue oil and PPC are 5400 CNY/t and is 22000CNY/t,the COP,NPV and ROI are 16952.86 CNY/t,53.56×10⁸ CNY,and 196.96%,respectively.The results demonstrate the economic superiority of the system.The sensitivity analysis of COP,NPV and ROI shows that residue oil price has the greatest influence on COP,and PPC price has the greatest influence on NPV and ROI.Sensitivity analysis is conducted on COP,NPV and ROI and found that the residual oil price has the incredible impact on COP and PPC price has the greatest impact on NPV and ROI.Exergy economic analysis of the optimal system shows that the product exergy cost per unit of PPC is 384.7 CNY/GJ,only 14.8 CNY/GJ higher than that of propylene oxide,about 4.0%,but the average market price of PPC product was 47.3%higher than propylene oxide product.To sum up,this study provides a practical solution for the CO₂ capture,conversion and utilization in flue gas of refinery system and expanding the downstream industry chain of LPG.This program can realize low-carbon production and reuse of carbon resources in the system,and has guiding significance to improve the economic benefits of downstream products of the refinery,extend the downstream industry chain of petrochemicals and realizing low carbon petrochemical industry.