Petroleomics: another omics used outside of systems biology
What are the problems need to be tackled? Needless to say that one of them is the rapidly increasing cost of crude oil that is around $120 / barrel these days. Another vital one, directly connected to the cost, is the composition of the recoverable oil is constantly shifting to heavier molecules with more acidic character and higher sulfur content. “Presently, world oil reserves are being depleted three-times as fast as they are being discovered”.1 In other words, we are running low on “sweet” crudes, therefore, we need to explore production possibilities from fields that were not considered economically viable until now. A good example for this kind of projects is the Athabasca oil sands in Alberta, Canada that contains ~175 billion barrels of economically recoverable bitumen and heavy crude. A major handicap though, is that we don’t have a deep understanding on these types of extremely complex mixtures, and up until recently there were no ways to accurately analyze them either. Why would you need accurate characterization? Someone would ask. Well, it is pretty simple. As opposed to simple hydrocarbons on the low MW end that are considered as chemically relatively benign, the species in question can (will) largely contribute to catalyst poisoning, flocculation, solid deposition, instability and corrosion problems. These all are features that you want to avoid when designing petrochemical processes.
Mass spectroscopy to the rescue! Yes, the first step in solving the problem lays in mass spectrometry; more precisely a very sophisticated way of doing that was invented by Comisarow and Marshall in the mid-70s. It is called Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), and this method provides ultra-high resonance power (m/Δm50% = 50,000 – 1,000,000), thus differentiating molecules with very similar molecular masses (Δm ~ 0.0005 Da) is possible.2 The key is using a relatively high magnetic field during the measurement that efficiently separates the ions created by Electron Spray Ionization method (ESI). The whole process is most efficiently used for polar molecules containing heteroatoms where positive ions are generated by protonating (basic) analytes and negative ions are produced by deprotonating (acidic) analytes, and the fragmentation level is kept at minimum. Ok, so we’ve done the molecular analysis of organics in a complex mixture. The next step is to solve the results, namely, to perform a compositional sorting and structure-function analysis from the elemental composition and molecular mass distribution of the high-boiling point components of petroleum. For this it is well known now to apply graphical compositional images, such as the relative abundance vs. heteroatom class, relative abundance vs. double bond equivalent (DBE) and relative abundance vs. carbon atom number, subsequently. To help you out the DBE number is a measure of aromacity (DBE of CCHHNNOOSS = c – h/2 + n/2 +1), while the number of carbon atoms is a measure of the degree of alkylation in petrochemical sciences. For instance molecules characterized by the same heteroatom class can have different DBA and carbon atom numbers (e.g. C34H32N and C33H44N). Plotting DBE against the carbon number for a given heteroatom class is often found to be the most useful technique of all in applications, such as hydrotreatment processing, saturates vs. aromatics, heat exchanger deposits, distillates, etc. Another way of helping to understand the molecular-based behavior of complex oil mixtures is using the so called 3D van Krevelen plots, usually displayed in H/C vs. S/C, O/C or N/C depending on the heteroatom class.3
Although currently it is mainly used in close connection with petroleum the principles and analytical approaches of petroleomics described above can be utilized in other areas of energetics. It is only on us to connect the dots and start applying these rules elsewhere. Developing biofuels or other alternative energy sources based on environmental considerations might be the next big application area.
Can you name others?
References1) Johnson HR, Crawford PM, Bunger JW. Strategic significance of America’s oil shale resource volume I assessment of strategic issues. Office of Deputy Assistant Secretary for Petroleum Reserves. Office of Naval Petroleum and Oil Shale Reserves US Department of Energy Washington, DC, USA, March 2004. 2) Rodgers RP, Schaub TM, Marshall AG. Petroleomics: MS Returns to Its Roots. Analytical chemistry, 2005, 20A. 3) Marshall AG, Rodgers RP. Petroleomics: Chemistry of the underworld. PNAS, 105, 2008, 18090.