Measuring Moisture in N-Methyl-2-Pyrrolidone

Application Summary

Analysis Point Analyte Typ. Range Suitable Analyzer
H2O 0-10% OMA-300-InGaAs Process Analyzer


N-Methyl-2-Pyrrolidone (NMP) is commonly used in oil refineries as a solvent. According to Bushnell et al. (1976), NMP solvent is for extracting aromatic hydrocarbons from mixtures that contain aromatic and non-aromatic hydrocarbons. This is specifically useful in the purification process of lube oil, as undesirable aromatic content affects the viscosity of the oil. Other solvents, such as phenol and furfural, are also used for this purpose. However, NMP is considered superior because water does not form an azeotrope with NMP, as it does with phenol or furfural. This means that after the extraction is complete, the water can be separated from the NMP by simple distillation (Bushnell et al.,1976).

Unfortunately, NMP is highly hygroscopic. This is considered a disadvantage. Bushnell et al. (1976) clarify that while it is desirable to have some water content present in the NMP for the extraction process, characteristics like solvent power and solvent/oil miscibility of NMP do change as water is added to it. This is an important point to consider because the NMP used in the extraction process of hydrocarbons is recovered and re-used. Although the optimal water content in the NMP differs depending on the type of lube oil and its wax content, the typical water content is 2-4%, but never more than 10% by volume (Bushnell et al.,1976).

The OMA-300-InGaAs Process Analyzer provides a continuous measurement based on an infrared spectroscopy technique and has been field proven to be successful in measuring water content in the background NMP with a range of 0-10% by volume.

Absorbance Spectra of H2O

measuring moisture in NMP - spectrum

H2O Absorbance Spectrum: 1.08% H2O

OMA-300-InGaAs Process Analyzer

SIGMATM NIR Spectrophotometer

To analyze the chemical composition of the sample, the OMA performs infrared spectroscopy using an InGaAs (indium gallium arsenide) sensor. The system measures absorbance at 1350-1650nm, 1550-1850nm, & 1750-2150nm and quantifies the amount of light absorbed by the sample; the OMA plots this raw data to visualize a high-resolution absorbance spectrum.

SIGMA wavelength range

Three Wavelength Ranges: 1350-1650nm, 1550-1850nm, & 1750-2150nm

The OMA-300-InGaAs uses a long-life tungsten light source to transmit light through the sample fluid in the flow cell. The light is carried by fiber optic cables from the analyzer to the flow cell, where the chemical mixture of the sample has unique interactions with the light based on its current composition.

SIGMA wavelength range

Further Reading

Subject Type
OMA-300-InGaAs Process Analyzer Data sheet
Advantage of Collateral Data Technical note
Multi-Component Analysis Technical note