COMPARISON OF LIQUID-PHASE AND GAS-PHASE PURE THERMAL-CRACKING OF N-HEXADECANE

Thermal cracking of n-hexadecane in the mild temperature (330-375 degr ees C) range has been investigated in liquid and gas phases. The kinet ic data of liquid-phase cracking are shown to be very similar to those of gas-phase cracking. However, the pattern and distribution of the p roducts are greatly phase dependent. In liquid-phase cracking, there i s an equimolar distribution of n-alkane and 1-alkene products in the C -3-C-13 range at low conversion; when the conversion is increased, mor e alkanes than alkenes are produced. To the contrary, more alkenes tha n alkanes are always determined in products from gas-phase cracking. L iquid-phase cracking gives a low selectivity of gas products and a hig h selectivity of addition compounds (C-18-C-30), whereas gas-phase cra cking produces a large amount of gas products and no addition compound s. The phase dependence of products can be interpreted in terms of a l ow concentration of hexadecane, under which B-scission occurs more pre ferentially than in liquid phase. Reaction mechanisms are suggested ba sed on the product analysis to account for cracking behaviors of liqui d-phase and gas-phase cracking.