The development and application of chromatography and mass spectrometry techniques for the analysis of biodiesel and fuel related compounds

Abstract

As world crude oil supplies deplete, research has heightened into alternative fuels. One such fuel is biodiesel which is used in varying percentages with petrodiesel i.e.B5, where 5 represents the percentage of biodiesel present. Biodiesel is composed of varying fatty acid methyl esters (FAME) % and these percentages are dependent on feedstock origin. FAMEs in biodiesel are composed of varying chain length and degrees of unsaturation. FAMEs have a propensity to autooxidise which increases fuel viscosity and introduces new species into the fuel cycle. Chromatography and mass spectrometry have been applied to the analysis of rapeseed methyl ester (RME) and auto-oxidised RME. The benefits and disadvantages have been discussed, with each technique aiding the analysis. This research has demonstrated the complexity of RME auto-oxidation and the necessity of several techniques for analysis. Gas chromatography-mass spectrometry has provided information on small chain RME degradation products and FAMEs and supports auto-oxidation via homolytic ?-scission and Russell mechanism auto-oxidation pathways. However, it also suggests the presence of an epoxide auto-oxidation route. Positive ion ESI-MS techniques have demonstrated the presence of highly oxygenated species observed in auto-oxidised RME. Through the use of positive ion ESI-Fourier transform-ion cyclotron resonance MS suggested molecular formula have been detailed, with a [C18:1/C18:2/C18:3 + nO + Na]+ series reported. MS/MS has been used to identify the composition of a polymeric oxidation species and has been reported within. Throughout analysis C18:1, C18:2 and C18:3, the major FAMEs in RME have been observed to deplete, this is coincident with observations of new species and increased viscosity. This research describes detection and identification of auto-oxidation markers: C8:0, nonanal and methyl cis-9,10-epoxystearate. These auto-oxidation markers have been discussed and compared to C18:0 FAMEs, with a correlation observed. C18:0:methyl cis-9,10 epoxystearate has been suggested to be a useful comparison to identify extent of autooxidation. However, further studies are required in RME of known auto-oxidation age, followed by application of RME of unknown autooxidation age and other feedstocks. Also, investigated here is the use of electrochemistry coupled to a TOF-MS to investigate forced oxidation. Using electro chemistry positive ion ESI-MS, oxidation of RME has been shown to closely mimic auto-oxidation observed in natural auto-oxidation and forced oxidation studies. However, does not force oxidation through an epoxide route. Oxidation of RME using electrochemical techniques demonstrates a number of auto-oxidation products identified in natural and forced oxidation, further supporting the presence of autooxidation routes other than the epoxide route. Electrochemical oxidation was completed in minutes compared to forced oxidation (days) and natural auto-oxidation (years), potentially lending itself to be a quick screening technique for oxidation inhibitors. Chromatography and mass spectrometry techniques have also been applied to the analysis of samples of a polyisobutylene (PiB) type dispersant synthesis. The resulting samples and starting reagents were not suitable to be analysed via other techniques due to the insolubility of these PiB type compounds in MeOH, MeCN and DCM. This analysis was completed to investigate the presence of a vinylimidazole graft on a PiB succinimide. The aim of the synthesis was to produce a multiply vinylimidazole grafted PiB succinimide. Analysis completed using positive ion ESI-supercritical fluid chromatography-ultraviolet MS has demonstrated this is not the case. UV and MS data suggest the presence of a singly vinylimidazole grafted PiB succinimide. It also highlights the presence of a PiB succinimide and residual starting reagents.

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Identifiers

ORCID for G. John Langley: orcid.org/0000-0002-8323-7235

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