论文部分内容阅读
根据理论和实验资料,提出了一种新的烃气稳定碳同位素比值数学模拟方法。动力学模型采用了一系列平行的一级天然气生成反应,发生同位素交换的与未发生同位素交换的化学键相对裂解率用方程式表示为: k~*/k=(A_f~*/A_∫)exp(—△Ea/RT)式中R为气体常量,T为温度。利用量子化学计算估计不同简单分子均裂键裂解的熵(A_f~*/A_f)和焓(△Ea)条件。例如,我们获得短链正构烷烃(≤C_6)失去甲基官能团的平均△Ea为42.0 cal/mol,平均A_f~*/A_f为1.021。甲烷的生成存在明显差异,预测在200℃的沉积盆地条件下短链正构烷烃产生~(13)CH_4的速率比产生~(12)CH_4的速率慢2.4％,但在500℃的实验室加热条件下仅慢0.7％。就其它分子均裂纹裂解所进行的类似计算也显示了相似的结果(除少数例外),△Ea值介于0～60 cal/mol之间,A_f~*/A_f值介于1.00～1.04之间。大量数据处理结果揭示:(1)在△Ea值和化学键裂解能之间存在弱的波型曲线关系;(2)在△Ea值和A_f~*/A_f值之间存在明显的正相关性。 这些发现的重要意义在于可以采用适当的动力学模型阐明在恒温密闭系统条件下正十八烷生成甲烷的化学和同位素数据。根据特殊温度史,校正后的模型可以提供与油型干酪根和原油裂解有关的甲烷碳同位素组成、总甲烷生成量和甲烷产率间的定量关系。?
Based on the theoretical and experimental data, a new method for the mathematical simulation of hydrocarbon stable carbon isotope ratios is proposed. The kinetic model uses a series of parallel first-level natural gas generation reactions. The relative cleavage rate of chemical bonds with and without isotope exchange is expressed by the equation: k ~ * / k = (A_f ~ * / A_∫) exp - △ Ea / RT) where R is the gas constant and T is the temperature. Entropy (A_f ~ * / A_f) and enthalpy (△ Ea) conditions for the cleavage of different simple molecules were estimated using quantum chemistry calculations. For example, we obtained an average △ Ea of 42.0 cal / mol for the loss of methyl groups for short-chain n-alkanes (≤C_6) and an average A_f ~ * / A_f of 1.021. The formation of methane is obviously different. It is predicted that the production rate of ~ (13) CH_4 of short-chain normal paraffins is 2.4% slower than that of ~ (12) CH_4 generated in sedimentary basins at 200 ℃. However, Only 0.7% slower. Similar calculations for crack cracking by other molecules also show similar results (with a few exceptions), ΔEa values between 0 and 60 cal / mol and A_f * / A_f values between 1.00 and 1.04 . A large number of data processing results reveal that: (1) there is a weak curve between △ Ea and chemical bond cleavage energy; and (2) there is a significant positive correlation between ΔEa and A_f ~ * / A_f. The significance of these findings is that the appropriate kinetic models can be used to elucidate the chemical and isotopic data for the production of methane from n-octadecane under a closed temperature system. Based on the special temperature history, the calibrated model provides a quantitative relationship between the methane carbon isotope composition associated with kerogen and crude oil cracking, the total methane production and the methane production. ?