PYROLYSIS OF CHLOROPHYLL A AFTER PRELIMINARY HEATING AT A MODERATE TEMPERATURE - IMPLICATIONS FOR THE ORIGIN OF PRIST-1-ENE ON KEROGEN PYROLYSIS

Pyroprobe pyrolyses of chlorophyll a were performed to investigate the possible precursors and formation mechanisms of prist-1-ene often observed in the products of kerogen pyrolysis. Thermal maturation was simulated by preheating chlorophyll a for different times at 250-degrees-C. Phytadienes dominated the pyrolyzates from unheated or briefly preheated samples. Little prist-1-ene was produced from unheated chlorophyll a during pyrolysis at 400-degrees-C for 1 s, whereas a considerable yield was obtained after preheating. Pyrolysis at 470-degrees-C for 15 s produced prist-1-ene from both unheated and preheated chlorophyll a. The yield of prist-1-ene increased with the time of preheating, relative to the yield of phytadienes. Additional isoprenoid hydrocarbons (C9-C20) were formed from the fragmentation of chlorophyll a. Possible pyrolysis mechanisms to explain these results are presented.