Light Alkene Production By Oxidative Cracking Of Heavy Hydrocarbons

Light alkenes play a significant role in the petrochemical industry. They are commercially prepared by the traditional pyrolysis with the characteristics of high-energy consumption and high CO2 emission. Due to its strong endothermic nature, the further development in the pyrolysis is inhibited.The oxidative cracking of model compounds, such as hexane, cyclohexane, isooctane and decane, were investigated in this paper. Emphases were put on the co-production of light alkenes and CO by the gas phase oxidative cracking (GOC) of above hydrocarbons and the oxidative cracking of hexane with the addition of hydrogen over platinum based catalysts. The aim of this paper is to decrease the energy consumption, reduce CO2 emission and realize the high efficient utilization of carbon resource during the process for the production of light alkenes by the introduction of oxygen, hydrogen (or syngas) and to find out if there exists a relationship between the utilization of natural gas and the processing of heavy feed.It had been demonstrated by our experiments that higher conversion of hydrocarbons and yield of light alkenes could be obtained in the GOC of various hydrocarbons than those in the pyrolysis. The GOC process was also fit for the cycloalkanes, the ring cleavage of which was known to be hard in the pyrolysis process. Therefore, the GOC process could process naphthenes rich heavy feed. Apart from light alkenes, CO prevailed in the produced COX while the selectivity to CO2 was always below 1 %, so the efficient utilization of carbon resources in the GOC process is high. Based on the thermodynamic calculations, the GOC processcould proceed in an autothermic way, which would reduce greatly the discharging ofCO2 from the external burning of fuel. Due to the considerable CO in the products, the GOC process would be fit for offering raw materials to such process as hydroformylation, which demands for a mixture of light alkenes and CO instead of pure light alkenes.In the catalytic oxidative cracking of hexane with three typical catalysts, the selectivity to COX could not be low enough and the conversion of hexane and yield of light alkenes could not compete with those in the GOC process. With the platinum based catalysts, the selectivity to COX could be significantly depressed and the selectivity to light alkenes could be correspondingly enhanced in the oxidative cracking of hexane with the addition of hydrogen. However, the hydrogen produced in the reactions could not compensate for that added in the feed. Syngas (H2 / CO) could replace the pure hydrogen in the oxidative cracking of hexane with the addition of hydrogen, which not only acted as a hydrogen resource but also adjusted the ratio of light alkenes / H2 / CO in the products. The usage of syngas in the oxidative cracking of hexane enlightens a way to co-process natural gas and heavy feed.