Hydrates, Flow Assurance & Phase Equilibria Group, Institute of Petroleum Engineering, Heriot Watt University, Edinburgh, Scotland, EH14 4AS, UK.
Hydrates, Flow Assurance & Phase Equilibria Group, Institute of Petroleum Engineering, Heriot Watt University, Edinburgh, Scotland, EH14 4AS, UK.
J Chromatogr A. 2019 Apr 26;1591:138-146. doi: 10.1016/j.chroma.2019.01.035. Epub 2019 Jan 14.
The ultimate purpose of this research work is to get an insight into the incomplete elution of heavy n-alkanes which along with thermal cracking, is one of the two main factors questioning the reliability of High Temperature Gas Chromatography (HTGC) analysis of heavy oils. For this purpose, knowledge of how the Distribution Factors vary with temperature is an essential requirement in the GC modelling. This study provides an extension of the data set of distribution factors for n-alkanes up to nCH in a HT5 GC column over the temperature range 10 °C-430 °C, and introduces a method to determine the distribution coefficient of heavy n-alkanes by using two complimentary HTGC modes: i.) High-Efficiency mode, for efficient resolution with a long column operated at low flow rate with n-alkanes elution rate up to nC, and ii.) true SimDist mode, with a short column operated at high flow rate for inefficient resolution with n-alkanes elution rate up to nC. Furthermore, this study demonstrates the use of the in-house obtained distribution factors as the main input in the in-house GC model for the prediction of the retention times. Its validation has been carried out using distribution factors obtained at both constant flow rate and constant inlet pressure operating conditions, with an average relative error in the GC modelling at the same operating conditions of 4.4% for the former and 1.5% for the latter. This new extension of the data set of heavy n-alkanes distribution factors provides the basis for studying the partitioning and incomplete elution of heavy n-alkanes in HTGC analysis. Also, these new distribution factors can be used as input in GC modelling, to determine the optimum analytical conditions to improve the separation process and thus the HTGC practices.
本研究工作的最终目的是深入了解重质正构烷烃不完全洗脱的问题，这是质疑高温气相色谱（HTGC）分析重质油可靠性的两个主要因素之一。为此，了解分配系数随温度的变化规律是 GC 建模的基本要求。本研究扩展了在 HT5 色谱柱中温度范围为 10°C-430°C 时正构烷烃的分配系数数据集，直至 nCH，并引入了一种通过两种互补的 HTGC 模式来确定重质正构烷烃分配系数的方法：i）高效模式，在低流速下使用长柱进行高效分离，正构烷烃洗脱速率可达 nC，ii）真实 SimDist 模式，在高流速下使用短柱进行低效分离，正构烷烃洗脱速率可达 nC。此外，本研究还展示了使用自制的分配系数作为内建 GC 模型中预测保留时间的主要输入。通过在恒流速和恒入口压力操作条件下获得的分配系数对其进行了验证，在相同操作条件下，GC 建模的平均相对误差分别为 4.4%和 1.5%。该重质正构烷烃分配系数数据集的新扩展为研究 HTGC 分析中重质正构烷烃的分配和不完全洗脱提供了基础。此外，这些新的分配系数可作为 GC 建模的输入，以确定最佳分析条件，从而改进分离过程，进而改进 HTGC 实践。
