Position-specific isotope analysis (PSIA) of propane can provide novel and valuable information to constrain the origin and history of natural gases. We conducted a systematic experimental study to determine the kinetics of propane pyrolysis, including bulk and position-specific carbon and hydrogen isotope fractionation of propane at 415 – 465 °C. As the dominant gaseous products, the yields of CH₄ and C₂H₆ increased with increasing C₃H₈ consumption. A significant amount of aromatic residues (C/H: ∼1) was generated, which was comparable to the yields of CH₄ and C₂H₆. Position-specific δ¹³C values of propane increased by up to 8.3 and 8.8‰ at the center and terminal positions respectively, while δ²H_center and δ²H_terminal increased by 110 and 131‰. An activation energy (E_a) of 69.9 (±29.1) kcal/mol and frequency factor (A) of 3.1 × 10¹⁵ (±7.9 × 10⁸) s⁻¹ were obtained based on a first-order reaction model. Using the average kinetic parameters from this study and previous studies on wet-gas cracking, propane cracking starts above 215 (±10.5) ^oC at a geological heating rate of 5 °C/m.y., corresponding to Easy R_o of 2.31%. An Arrhenius plot of kinetic isotope fractionation indicates both central C and H of propane show larger isotope fractionations compared with those at the terminal position in natural reservoirs. Position-specific (PS) isotopic fractionation factors (k*/k) at 215 °C were estimated as 0.983 and 0.987 for δ¹³C_center and δ¹³C_terminal, and 0.815 and 0.838 for δ²H_center and δ²H_terminal, respectively. PS isotopic compositions of natural propane in the ΔC_c-t - ΔH_c-t diagram may serve as a diagnostic indicator for the origins (kerogen vs. oil) and degradation (thermal cracking vs. biodegradation) of natural gases in sedimentary basins.

丙烷的位置特定同位素分析（PSIA）可提供新颖且有价值的信息，以限制天然气的起源和历史。我们进行了系统的实验研究，以确定丙烷热解的动力学，包括在415 – 465°C下丙烷的体积和位置特定的碳和氢同位素分馏。作为主要的气态产物，CH ₄和C ₂ H ₆的产率随C ₃ H ₈消耗量的增加而增加。产生了大量的芳族残基（C / H：〜1），与CH ₄和C ₂ H ₆的产率相当。位置特定δ ¹³丙烷的C值最多提高8.3和8.8‰分别在中心和末端位置，而δ ² ħ_中心和δ ² ħ_终端增加了110和131‰。基于一阶反应模型，获得了69.9（±29.1）kcal / mol的活化能（E _a）和3.1×10 ¹⁵（±7.9×10 ⁸）s ^-1的频率因子（A）。使用本研究和先前关于湿气裂解研究的平均动力学参数，丙烷裂解以高于5°C / my的地质升温速率在215（±10.5）^o C以上开始，对应于Easy R _o占2.31％。Arrhenius动力学同位素分馏图表明，丙烷的中心C和H均比天然油藏中的终端位置显示出更大的同位素分馏。位置特定的在215℃（PS）同位素分馏因子（K * / k）的估计为0.983和0.987为δ ¹³ C ^_中心和δ ¹³ Ç_终端，和0.815和0.838为δ ² ħ_中心和δ ² ħ_终端， 分别。ΔCc _-t -ΔHc _-t中天然丙烷的PS同位素组成 该图可作为沉积盆地中天然气的来源（干酪根与石油）和降解（热裂解与生物降解）的诊断指标。