¹H and ¹³C NMR NMR is typically obtained using deuterated NMR solvents to lock the field during acquisition. In some cases the use of these solvents is problematic as it prevents observation of solublized phases present in the sample. As an example we show here the NMR data obtained on a biodiesel production process. One of the major issues with the FAME product is the presence of glycerol in the product. NMR analysis is usually performed by dissolving the FAME in CDCl₃ in which glycerol is completely insoluble. Thus NMR analysis performed in this way does not allow analysis of residual glycerol content. However, if the FAME is run neat this issue does not arise.
Another analysis of enormous interest from the process control standpoint is the analysis of the glycerol/methanol phase. This phase contains considerable free fatty acids as well as the glycerol by product and excess methanol from the transesterification process. The three components are readily observed by ¹H and ¹³C NMR, and ²³Na can be used to observe NaOH content in the phase. Finally the shift and shape of the observed OH resonance can yield information on the pH of the glycerol phase. Typically this analysis is done in DMSO-d₆

Below are some examples of NMR obtained without a deuterated solvent:

Difference in aliphatic carbon distribution between FAME phase and Free Fatty Acids (FFA)

found in the glycerol – methanol phase.

1H NMR of aliphatic component found in the FAME phase as well as the FFA in the glycerol phase.

The 19.5 MHz Spintrack NMR analyzer was utilized to study a FAME biodiesel production reaction. The samples analyzed were: 

1) Used vegetable oil

2) Partially transesterified biodiesel product (bad biodiesel) 

3) High yield FAME biodiesel product 

4) Glycerin by-product from the process

CPMG T2 decays were generated and then that data was processed with a inverse laplace transformation to produce T2 distribution profiles.

NMR Experiment explanation is given below:

The CPMG data obtained on the four samples is shown below:

The T2 distribution profiles obtained by inverse Laplace transformation of the CPMG data are shown below:

Plainly TD-NMR can play a role in monitoring the biodiesel production process.

The 19.5 MHz Spintrack NMR analyzer was utilized to study a large series of  vacuum gas oils and FCC feeds for which PNA also has laboratory test data.

The analysis was performed on a SpinTrack 19.5 MHz TD-NMR spectrometer – CPMG T2 decays were generated and then that data was processed with a inverse laplace transformation to produce T2 distribution profiles. These T2 distribution profiles are currently being correlated to physical and chemical property data.

NMR Experiment explanation is given below:

The CPMG data obtained on the four samples is shown below:

The T2 distribution profiles obtained by inverse Laplace transformation of the CPMG data are shown below:

The correlation between T2 distribution and the metal content, viscosity, distillation range, density, asphaltene content are all being investigated at the current time.

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Below are examples of ¹³C NMR data obtained on biodiesel (FAME) and the vegetable oil precursor that it was made from by transesterification process involving microwave activation of the reaction between triglycerides and methanol in the presence of a caustic catalyst. Process NMR Associates is developing correlations between ¹³C NMR data and biodiesel properties stipulated in ASTM 6751.