The Study Of Styrene Desulphurization Refining Technology

Styrene produced by the traditional methods are in short supply.There are approximately 4% to 6% of styrene in pyrolysis gasoline,which is by-product of ethylene plants based on the raw materials of light hydrocarbon,naphtha and diesel.With the larger size of plants and heavier quality of materials,the significant increase can be witnessed in the yield of pyrolysis gasoline,it’s promising to collect styrene from it.However,30 to 100 mg/kg of sulfur element can be detected in styrene produced in this way,which has negative effects on subsequent applications.The paper study the distributions and forms of sulfur element and optimize the processes of extractive distillation to reduce sulfur content of products.3,4-dimethylthiophene,which can be regarded as typical one,and thioether are both major sulfides in products,For pre-selection,the suitable entrainer was screened by UNIFAC model in term of selectivity.While selectivity of O-xylene to styrene follows the trends of SUL>NMP>DMSO,The selectivity of 3,4-DT to styrene follows the trends of NMP>DMA>γ-BL.Among these entrainers,NMP has an appropriate selectivity for both systems.Moreover,NMP was selected as a suitable entrainer.The separation process for the C8 mixture with NMP as an entrainer was simulated using the Aspen Plus software(version 8.4).The rigorous equilibrium stage model of the extractive distillation process was established by inputting the corresponding UNFAC model parameters into the process simulation software.The influence of the number of total stages,reflux ratio,mass ratio of S/F,feed stages,entrainer feed stage on the mass fraction of styrene and 3,4-DT in the product was researched in single-factor experiment,based on which best operating conditions of the extractive distillation process were determined combining with orthogonal test.While temperature:top(73.0℃),bottom(141.2℃),pressure:top(13.9 kPa),bottom(25.80 kPa),total stages(140),reflux ratio(3.5),mass ratio of S/F(12),feed satges(25),entrainer feed stages(6)were selected for extractive distillation column to ensure the product purity requirement.temperature:top(87.2℃),bottom(148.6℃),pressure:top(16.14 kPa),bottom(26.04 kPa),feed satges(10),reflux ratio(11)were selected for solvent recovery column.99.10wt% styrene can be obtained from the test device which running continuously for 150 hours,the sulfur content in the product is less than 10 ppm,the recovery of styrene remains approximately 80 percent.Thisprocess is feasible to collect styrene from pyrolysis gasoline and reduce sulfur content.