Automatized Separation of Fractions from Petroleum Based on Spectrophotometric Signal Derivative Using Open-Source Hardware for the Determination of Ni and V Linked to Porphyrins

An automated method based on open-source hardware was created for the separation of porphyrins fractions from crude oil, an essential step for the quantification of V and Ni as metalloporphyrins. Preparative liquid chromatography was implemented with a reverse phase gradient from MeOH to toluene. The system allows three solvents and fractions changes by using quaternary valves connected to an Arduino microcontroller, programmed on the basis of the absorbance signal measured and its first derivative. Additionally, the method was applied to crude oils (Venezuelan National Institute of Standards and Technology (NIST) 8505 and from a marine reservoir). V and Ni were determined by inductively coupled plasma mass spectrometry (ICP-MS) and the V-porphyrin profile was determined by high performance liquid chromatography (HPLC)-ICP-MS. The concentrations of the metals grow in the last eluting toluene fractions, associated with asphaltenes. On the other hand, V-porphyrins in the first eluting MeOH fractions showed profiles of labile compounds, with a higher percentage in the Brazilian crude oil (4.9 mg L-1, corresponding to 18% of total V), in comparison to the one from the biodegraded NIST 8505 (59 mg L-1, corresponding to 7% of total V). The overall methodology has a good reproducibility and provides information on elements concentrations associated with porphyrin class compounds.

本研究开发了一种基于开源硬件的自动化方法，用于从原油中分离卟啉（porphyrins）组分，这是实现以金属卟啉（metalloporphyrins）形式存在的钒（V）与镍（Ni）定量分析的关键步骤。该方法采用制备型液相色谱（preparative liquid chromatography），以甲醇（MeOH）至甲苯（toluene）的反相梯度（reverse phase gradient）作为洗脱体系。系统通过连接至Arduino微控制器（Arduino microcontroller）的四通阀（quaternary valves）实现三种溶剂与组分的切换，切换逻辑基于实测吸光度信号及其一阶导数编写。此外，本方法已应用于两类原油样品：委内瑞拉国家标准与技术研究院（National Institute of Standards and Technology, NIST）8505标准参考物质，以及某海相储层原油。采用电感耦合等离子体质谱法（inductively coupled plasma mass spectrometry, ICP-MS）测定钒与镍的含量，通过高效液相色谱法-电感耦合等离子体质谱法（high performance liquid chromatography, HPLC-ICP-MS）分析卟啉钒的分布特征。实验结果表明，金属元素浓度在最后洗脱的甲苯组分中升高，该组分与沥青质（asphaltenes）相关。另一方面，首批洗脱的甲醇组分中的卟啉钒表现出易变化合物的分布特征，其在巴西原油中的浓度为4.9 mg·L⁻¹，占总钒的18%；相较而言，降解程度较高的NIST 8505样品中该组分浓度为59 mg·L⁻¹，仅占总钒的7%。整套方法具有良好的重现性，可提供与卟啉类化合物相关的金属元素浓度信息。