Urea dewaxing

FIGURE 9.6 Lattice arrangement of the hexagonal system of urea complex. 

Source K. A. Kobe and W. G. Domask, Extractive Crystallization—A New Separation Process. Part 1. Theoretical Basis, Petroleum Refiner 31(3) 106-113 (1952). With permission. 

FIGURE 9.7 Relative sizes of urea adduct and specific hydrocarbons. 

Source T. H. Rogers, J. S. Brown, R. Diekman, and G. D. Kems, Urea Dewaxing Gets More Emphasis, Petroleum Refiner 36(5) 217-220 (1957). With permission. 

FIGURE 9.8 Moles of urea versus carbon chain length for alkanes, alkenes, and other long-chain molecules. 

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Urea dewaxing, in which urea forms adducts with straight-chain paraffins that separated by filtration from the dewaxed oil. 

Urea dewaxing a continuous dewaxing process for producing low-pour-point oils, and using urea which forms a solid complex (adduct) with the straight-chain wax paraffins in the stock the complex is readily separated by filtration. 

Urea dewaxing, which had a brief period of success in the 1950s to 1960s and which removed normal paraffins using shape selective clath-rates. 

FIGURE 9.9 Gas chromatogram of paraffins obtained by urea dewaxing. 

Source J. Marechal and P. de Radzitzky, Some Aspects of Urea Dewaxing of Middle and Heavy Distillates, Journal of the Institute of Petroleum 46(434) 33 t5 (1960). 

FIGURE 9.13 Pour points of distillation fractions versus distillation midpoint before and after urea dewaxing. 

The foregoing shows that the commercial applications of urea dewaxing must lie with lighter waxy cuts because of its selectivity for n-paraffins and their location and distribution in waxy lube cuts. This is indeed the case and it has also been a significant limitation on the application of the technology. Lube refineries normally process a full slate of lubes for economic reasons and the urea technology s inability to handle this meant that its application has been confined to specific feeds. 

FIGURE 9.15 Schematic of urea dewaxing lube oil plant for Standard Oil in Whiting, Indiana. 

At the time of this writing, urea dewaxing has ceased to be a significant process in lube refining, overtaken by superior technologies. There is still interest in the chemistry, however, and it is conceivable that it may reemerge for other specific purposes. Papers on urea inclusion compounds regularly appear in the... 

Urea Dewaxing Results on Solvent Dewaxed Distillates... 

Feedstocks Dewaxed by the Edeleanu Urea Dewaxing Process... 

H. Franz, Urea Dewaxing Process Can Yield Normal Paraffins, Hydrocarbon Processing 44(9) 183-184 (1965). 

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