Analytical chemistry solutions to hazard evaluation of petroleum refining products

Abstract

Products of petroleum refining are substances that are both complex and variable. These substances are produced and distributed in high volumes; therefore, they are heavily scrutinized in terms of their potential hazards and risks. Because of inherent compositional complexity and variability, unique challenges exist in terms of their registration and evaluation. Continued dialogue between the industry and the decision-makers has revolved around the most appropriate approach to fill data gaps and ensure safe use of these substances. One of the challenging topics has been the extent of chemical compositional characterization of products of petroleum refining that may be necessary for substance identification and hazard evaluation. There are several novel analytical methods that can be used for comprehensive characterization of petroleum substances and identification of most abundant constituents. However, translation of the advances in analytical chemistry to regulatory decision-making has not been as evident. Therefore, the goal of this review is to bridge the divide between the science of chemical characterization of petroleum and the needs and expectations of the decision-makers. Collectively, mutual appreciation of the regulatory guidance and the realities of what information these new methods can deliver should facilitate the path forward in ensuring safety of the products of petroleum refining.

Figure 1.

A timeline of major developments in the fields of analytical chemistry and data analysis of petroleum UVCB, and the concomitant evolution of the regulatory frameworks for registration and hazard classification of these substances See abbreviations in the text.

Figure 2.

Literature review of the major analytical methods and their application for the analysis of petroleum substances. (A) A dendrogram of the major searches. The numbers indicate the quantity of publications for each search. See Supplemental Table 1 for information on the exact search terms and hyperlinks to the publications. (B) Cumulative histograms indicating the number of publications across time through December 2021. Colors correspond to the methods indicated in the inset.

Figure 3.

Example visualizations commonly used to represent hydrocarbon composition of petroleum substances analyzed using high resolution MS techniques. (A) A Kendrick mass defect (KMD) plot demonstrating repetitive patterns of CH₂-containing molecules in a petroleum sample. (B) A DBE vs carbon number plot indicating the relative proportions of molecules varying by their degree of aromaticity and carbon number in a sample. (C) van Krevelen plot display the degree of oxidation by plotting the H/C versus O/C ratio in a sample. (D) A stacked bar plot showing relative proportions of constituents from various chemical groups. (E) A plot of relative amounts of various hydrocarbon blocks in a sample.

Figure 4.

The use of various novel MS methods to address specific regulatory needs identified in this review. (A) Scholarly publications that were identified as relevant to each regulatory need/question (identified by colors). A total number of publications identified by a literature search is listed in the first circle (see Supplemental Table 2 for details). Upon examination of each study’s content, a number of publications were deemed not relevant (red circles); the remaining studies are shown in green circles. (B) The number of relevant publications as a function of the high-/ultra-high MS technique. Top left, a stacked bar graph indicating the number of publications as they pertain to each regulatory need/question in (A). Remaining stacked bar plots show the number of studies that used various separation (HPLC, GC, GC×GC or IMMS) or direct injection with each MS technique.