Date of Award


Document Type


Degree Name

Master of Science (MS)


Chemical Engineering


The rheology of solvent refined lignite (SRL) melts was studied using a Brookfield rotational viscometer with a Thermosel system to enable high temperature measurements. The SRL samples were obtained from the Project Lignite process development unit at the University of North Dakota. The effects of temperature cycling, air exposure during heating and continuous shearing over extended periods of time on the viscosity of SRL melts were investigated to develop a suitable method for measuring the viscosities of these melts.

The viscometric data were analyzed for shear dependence and tested using Newtonian, Bingham plastic, and power law models. The Newtonian model was found to describe the behavior of deashed SRL. The behavior of undeashed SRL was described satisfactorily by both the Bingham plastic model and the power law model, although the latter gave a better fit. The power law parameters were correlated with temperature, ash content and melting point of undeashed SRL.

The effects of process variables on the apparent viscosity of undeashed SRL were investigated in detail, and empirical relations were developed in some cases. The process variables studied were conversion temperature, degree of conversion and solvent to coal ratio in the feed to the unit. Temperature was the only process variable found to correlate with the apparent viscosity of undeashed SRL.

The correlation of sample properties such as solvent content, ash concentration, melting point, solid density, molecular weight average with the apparent viscosity of deashed SRL was carried out. Solvent content and melting point of the sample were found to be linearly related to the apparent viscosity of undeashed SRL. Ash concentration and molecular weight average were found to relate to the apparent viscosity by a power greater than one. Density of undeashed SRL was found not to correlate with its apparent viscosity.

The relation between melting point of undeashed SRL and its apparent viscosity was subjected to further investigation. Multiple regression analysis was used to investigate the effect of solvent content, ash content, percent aromatics, percent ethers, percent nitrogen compounds and percent oxy acids on apparent viscosity. Of these, solvent content, percent aromatics and percent ethers were found to affect the apparent viscosity data significantly.