A Study on Triterpenoids in the Tertisry Wood Brown Coal from Nanning Basin by Means of Pyrolysis

Key words: 
• wood brown coal /
• pentacyclic triterpenoids /
• 8,14 -secohopane /
• pyrolysis /

Abstract: Pyrolysis was done by two methods, the Y series of experiments showed the process of comprehensive original organic matter evolved and the Z series showed the process of only kerogen evolved. The comprehensive original organic matter was composed of non-kerogen matter and kerogen, so based on the two series of experiments we can study deeply how triterpenoids are generated and how they change.From the result of pyrolysis, this paper showed the differences between the comprehensive original organtic matter generated from both non-kerogen matter and kerogen and from only kerogen, and approached geochemical significance of the triterpenoids.The comprehensive original organic matter generated much more pentacyclic triterpenoids than kerogen did, so most pentacyclic triterpenoids were yielded by the non-kerogen matter.In Z series, there were no 8, 14-secohopanes, it's clear that the kerogen didn't yield 8, 14secohopanes. In Y zeries, when the temperature was 400℃, the pentacyclic triterponoids disappeared but 8, 14-secohopanes remained and were abundant, so the pentacyclic triterpanoids changed into 8, 14-secohopanes in high temperature.Hopanes, hopenes and 8, 14-secohopanes are all able to indicate maturity. At 250℃ hopenes were very abundant, but at 300℃ they disappeared, so they can indicate immaturity.Biohopanes are instable, too, when it was 350℃ they disappeared, so they can indicate lowmaturity. Three hopanes parameters and two 8, 14-secohopane ones were calculated. With the rising of the temperature, the two parameters Ts/Tm and C₃₁αβ22S/22 (S+R) increased slowly in the beginning, but when the temperature exceeded 300℃, the parameters increased quickly;when it changed from 250℃ to 300℃, the parameter C₃₂αβ22S/22 (S+R) remained the same, but when it was higher than 300℃, it increased quickly ; the two 8, 14-secohopanes parameters C₂₇8β(H) /So (H) and C₂₈8β(H) /8α(H) decreased quickly when it was lower than 300℃, and decreased slowly when it was higher than 300℃. The five Parameters all varied greatly at 300℃, so they are nice maturity indexes.