Desulfurization of jet fuel by pervaporation

This paper investigates pervaporation, a membrane separation process for the removal of sulfur-containing components from jet fuel. To this end, one type of commercial membrane from PolyAn GmbH was applied. The influence of the crucial reaction parameters of the pervaporation process, such as feed temperature, permeate pressure, and permeate temperature, on the characteristic pervaporation measures such as permeate flux and enrichment factor was tested experimentally. Fuels with different sulfur mass fractions were applied and the long-term stability of the membranes used was studied. Different spectroscopic methods were applied to investigate correlations between membrane performance and material properties of the membrane.It was found that an increased feed temperature had a positive effect on the permeate flux while it had a negative effect on the enrichment factor. At 100°C, the permeate flux amounted to 5.44kg/(hm2), while it was only 1.16kg/(hm2) at a feed temperature of 80°C. At a feed temperature of 80°C, the enrichment factor was 0.47, while it amounted to 0.64 at a feed temperature of 100°C. In the case of the permeate pressure, the trends were also antagonistic. Low permeate pressure enhanced the permeate flux but deteriorated the enrichment factor. At a value of 20mbar, the permeate flux amounted to 5.44kg/(hm2), while it was only 0.16kg/(hm2) at 100mbar. The enrichment factor was 0.64 at 20mbar and decreased to 0.35 at 100mbar. Different permeate temperatures and sulfur mass proportions had only a minor effect on the permeate flux and the enrichment factor. Experiments on the long-term stability of the membranes used showed that fortunately the pervaporation process could be run for more than 500h using membranes from PolyAn GmbH while still showing a measurable permeate flux and a remarkable reduction of the sulfur mass fraction in the permeate. However, a significant deactivation with time on stream was observed. The permeate flux continuously decreased from 3.5kg/(hm2) to 0.5kg/(hm2) after 532h of time on stream. The enrichment factor increased from 0.5 to 0.6. Long-term experiments with pretreated membranes revealed that interaction between the hydrocarbon matrix in kerosene Jet A-1 and the membrane material itself was not responsible for the observed degradation of performance.Spectroscopic investigations were used to show that the reduction of the permeate flux was probably caused by an irreversible inclusion of polar – mostly aromatic – molecules in the polymeric separation layer of the membrane. The probable influence of unknown additives on the permeate flux could not be proven but should be considered. No degradation of the membrane material itself was found.