Since the invention of the diesel engine there has been biodiesel. Rudolf Diesel invented the engine in 1892, and at that time, was already crediting the engine with running off of plant oils. However, at that time there were limited concerns for the environment, and the price of petroleum based fuel was significantly cheaper than the cost of plant based oils; consequently, the usage of plant oil in the diesel engine was ignored. Presently, we live in a world that places far more importance on environmental concerns and the impacts of human action. Additionally, the availability of petroleum has become increasingly scarce and as a result has become far more expensive. ...view middle of the document...
The catalyst can be either an acid or base, however the acid catalyzed reactions often require heat to increase the reaction rate (Citation Missing). While the type of acid or base does not have to be specific, studies have shown that altering the catalyst can influence the rate at which the reaction reaches completion.
When the reaction does not go to completion there is the potential for unintended products. In a complete reaction each triglyceride will produce one glyceride and three FAMEs. However, if not all of the fatty acid chains are cleaved then the resulting products can have a mixture of monoglycerides, diglycerides, completely unreacted triglycerides, and left over alcohol; in addition to the desired products (Missing Citation). These partially reacted products have been shown to create complications in fuel systems and cause wear and tear of fuel lines and engine components (Missing Citation).
Since the ultimate goal of biodiesel production is use in diesel engines to decrease petroleum dependency, it is important to produce a biodiesel that is similar or better than traditional diesel in engine performance. It is also desirable to produce a fuel that will result in reduced pollutant emissions. While biodiesel has been shown to meet these requirements, it is important that the quality of the biodiesel be kept high to ensure those standards.
In order to meet these standards it is necessary to utilize methods to assess biodiesel quality. This can be done by chromatography, spectroscopy, or a combination of both. GC-MS, FTIR, UV-Vis, HPLC and NMR are all used to analyze biodiesel reactions and their products. The primary focus of this review will concentrate on NMR (nuclear magnetic resonance) spectroscopy, with additional focus on the relationship between high and low-field NMR applications as they relate to understanding biodiesel transesterification reactions and their products.
Theory of NMR:
NMR is a type of spectroscopy that probes nuclei to collect information about the quantity and relative configuration of the specific nuclei examined. The most common types of nuclei probed for the purposes of studying biodiesel are the 1H and 13C nuclei.
Radio waves are used to excite the nuclei and cause transitions in spin state that can be probed by the detector. However, in the absence of a magnetic field spin transitions are degenerate or equal in energy and therefor undetectable. Fortunately once in the presence of a magnetic field the energy levels for spin transitions are unequal or split, and the transition becomes detectable.
One of the key variables in the application of NMR spectroscopy is the strength of the magnet used to create the magnetic field, measured in Hertz (Hz). Stronger magnets generate a stronger magnetic field. This is important to the technique, because the stronger the magnetic field the larger the split in the energy levels becomes, which creates a higher energy transition. This...