Study On The Technology Of Producing Butadiene By Steam Cracking Naphthenic Hydrocarbons In Cracking Raw Materials

Butadiene is one of the most important light olefins.Its downstream derivatives are high value-added materials and intermediates.The demand for products is also increasing year by year.Due to the gradually lightening of the raw materials for steam cracking,resulting in a large gap in the production of butadiene,while the traditional naphtha cracking,the yield of butadiene is only about 5 wt%,so its output cannot meet the rising demand.However,the yield of butadiene obtained by steam cracking of heavier naphthenic materials is relatively high,so it is of great significance to explore the law of steam cracking conversion of cyclohexane to ease the domestic supply demand of butadiene.In order to obtain a higher yield of butadiene,this article first used cyclohexane as a raw material to investigate effects of cracking temperature,residence time,water-oil mass ratio on the yield of butadiene in a fixed bed reactor.research showed that under the conditions of cracking temperature of 775℃,water-oil mass ratio of 0.35 ～ 0.5,and residence time of 0.6s,the yield of butadiene could reach about 20 wt%.Based on this process condition,on the one hand,nitrogen was used instead of steam as the diluent,and it was found that steam was more suitable as a diluent for the cyclohexane cracking reaction;on the other hand,investigating the yield of butadiene from other naphthenic cracking raw materials cracking.It was found that both methylcyclohexane and ethylcyclohexane cracking could obtain a higher yield of butadiene,but the triene yield generated by cyclohexane cracking was significantly higher than the latter two.In order to solve the problem of carbon deposition in the cyclohexane steam cracking reaction,the effect of dimethyl disulfide inhibitor on the cracking performance was investigated by adding a coking inhibitor to the cyclohexane raw material.The experimental results showed that,with no dimethyl compared with the raw materials of disulfide inhibitors,the total yield of butadiene,ethylene and propylene added to the inhibitor group was more than 2%,and could significantly reduce the amount of coking and change the morphology of coke,making it easier to scorch.Finally,in order to obtain higher economic benefits and industrial application value,the mixed oil mixed with naphtha in different proportions of cyclohexane was used as the raw material,and the steam cracking reaction performance was investigated under the same cracking conditions.It was found that with the increase of cyclohexane incorporation ratio,the yield of butadiene continued to increase,but the degree of relative coking also gradually increased.When 50 wt% cyclohexane was mixed into naphtha,the yield of butadiene was high and the degree of coking was very small.Therefore,50 wt%cyclohexane mixed oil was selected as the cracking raw material to optimize the process conditions.The experimental results showed that increasing the cracking temperature,appropriately increasing the water-oil mass ratio and reducing the residence time were beneficial to the formation of butadiene and other lower olefins.Under the conditions of cracking temperature of 775℃,water-oil mass ratio of 0.4,and residence time of 0.5 s,a yield of butadiene of about 11.96 wt% could be obtained.