The solubility of n-decane in ethylene and its effect on the oligomerization of supercritical ethylene over heterogeneous catalysts

Abstract

We investigated the effect of coke solubility in supercritical ethylene on the ethylene oligomerization over nickel-based heterogeneous catalysts. The approach uses n-decane as a model compound for coke to simulate coke formed during the catalytic process. We report the solubility of n-decane in ethylene at 30, 50, and 75 oC and pressures ranging from 1 to 68 bar; conditions previously screened by our research group for ethylene oligomerization. We reproduced previous literature data on the solubility of n-decane in nitrogen to validate the flow system designed in the present work. The present study is the first to report the solubility of n-decane in ethylene under a broad range of conditions, including subcritical and supercritical conditions. We found that the ethylene – n-decane system deviates from ideality very quickly with increasing pressure. Beyond the ethylene critical point (P = 50.3 bar and T = 9.4 oC) the solubility (expressed in terms of mole fraction) of n-decane in ethylene at 30 oC reaches a maximum value of 3.0%; which is close to the value observed at 50 and 75 oC, under the same pressure. We used the solubility data to estimate the rate of coke dissolution and compared these values with kinetic data previously reported by our group under supercritical conditions. Analysis of coke dissolution rates in supercritical ethylene under different temperatures indicates that the transport of products from the catalyst surface to the bulk of supercritical ethylene controls the catalytic process at supercritical conditions. The approach used in the present work is novel because it accounts for the contribution of coke dissolution rates on the ethylene oligomerization over nickel-based solid catalysts..